GIFT OF 
 PBQF. E. J. WIOKSOK 
 
 IOLOGV 
 LIBRARY 
 

 THE MICKOSCOPE. 
 
Tulli-n \Veht, ii(.-l. 
 
THE MICROSCOPE: 
 
 HISTORY, CONSTEUCTIONiNWD APPLICATION 
 
 A FAMILIAR INTRODUCTION yro THE paz OF THE INSTRUMENT. 
 
 Jv , A (/ 
 
 AND THE STUDYMDF MICROSCOPICAL SCIENCE. 
 
 BY JABEZ HOGG, F.LS., F.RM.S. 
 
 SECRETABV. ROYAL MICROSCOPICAL SOCIETY ; 
 
 MEMBER OF THE 
 
 EOYAL COLLBG1 OF SURGEONS OF dGLAND ; AL'THOR OF " ELZMEKTS OF KATL'HAL PHILOSOPHY, 
 " A MASUAL OF OPHTHXLMOSCOPIC 8CEOERT," XTC. 
 
 WITH UPWARDS OF FIVE HUNDRED ENGRA VINGS, AND 
 COLOURED ILLUSTRATIONS BY TUFFEX WEST. 
 
 LONDON : 
 
 GEORGE ROUTLEDGE AND SONS, 
 NEW YORK : 416, BROOME STREET. 
 
- OLOGY 
 UBRARY 
 
 LONDON : 
 
 PRINTED BY WOODFALL AND KINDER, 
 MILFORD LANE, STRAND, W.C. 
 
PKEFACE TO THE SIXTH EDITION. 
 
 N issuing the SIXTH Edition of this Work on 
 the MICROSCOPE, we may state that it has 
 been thoroughly revised and for the most part 
 re-written. Eight carefully and beautifully 
 executed Plates are added, which were drawn 
 by Tuffen West from natural objects, engraved 
 and printed by Edmund Evans in the first style of colour- 
 printing. 
 
 The Author cannot but express his grateful surprise at 
 the extraordinarily popular reception which his t>ook has 
 met with : a sale of fifty thousand is an unprecedented 
 event for a work of the kind. This circumstance is 
 extremely gratifying to him, because it affords reasonable 
 grounds for believing that his work has been useful, and 
 encourages renewed effort to make the volume still more 
 acceptable. It has been his endeavour to bring the 
 information contained in its pages up to the most recent 
 discoveries ; although, in a daily progressing field of 
 science, it is almost impossible to keep pace with the 
 advance of knowledge in all its ramifications. 
 
 The passing remarks the Author has seen occasion to 
 make upon the various objects that have fallen under his 
 notice are intended to serve, as would a finger-post or 
 
 256333 
 
n PREFACE. 
 
 guide in a country abounding in treasures. It was 
 impossible to have attempted a more detailed descrip- 
 tion than has been given in dealing with the vast expanse 
 of natural objects presented to his contemplation. If, 
 however, the notices have been sufficiently ample and 
 precise to assist the study of the reader, the Author will 
 have accomplished the most cherished object he had in 
 view in presenting the work to the public. 
 
 I, BEDFOKD SQUABS, 
 October, 1867. 
 
PREFACE TO THE FIEST EDITION. 
 
 HE Author of this Publication enured upon 
 his task with some hesitation and diffidence ; 
 hut the reasons which influenced him to 
 undertake it may be briefly told, and they 
 at once explain his motives, and plead his 
 justification, for the work which he now 
 ventures to submit to the indulgent con- 
 sideration of his readers. 
 
 It had been to him for some time a sub- 
 ject of regret, that one of the most useful 
 and fascinating studies that which belongs to the do- 
 main of microscopic observation should be, if not wholly 
 neglected, at best but coldly and indifferently appreciated 
 by the great mass of the general public ; and he formed 
 a strong opinion, that this apathy and inattention were 
 mainly attributable to the want of some concise, yet suffi- 
 ciently comprehensive, popular account of the Microscope, 
 both as regards the management and manipulation of the 
 instrument, and the varied wonders and hidden realms of 
 beauty that are disclosed and developed by its aid. He 
 saw around him valuable, erudite, and splendid volumes , 
 which, however, being chiefly designed for circulation 
 amongst a special class of readers, were necessarily pub- 
 
Vli PREFACE. 
 
 lished at a price that renders them practically unattainable 
 by the great bulk of the public. They are careful and 
 beautiful contributions to the objects of science, but they 
 cannot adequately bring the value and charm of micio- 
 scopic studies home, so to speak, to the firesides of the 
 people. Day after day, new and interesting discoveries, 
 and amplifications of truth already discerned, have been 
 made, but they have been either sacrificed in serials, or, 
 more usually, devoted to the pages of class publications ; 
 and thus this most important and attractive study has 
 Veen, in a great measure, the province of the' few only, 
 who have derived from it a rich store of enlightenment 
 and gratification : the many not having, however, parti- 
 cipated, to any great extent, in the instruction and enter- 
 tainment which always follow in the train of microscopical 
 studies. 1 
 
 The manifold uses and advantages of the Microscope 
 crowd upon us in such profusion, that we can only attempt 
 to enumerate them in the briefest and most rapid manner 
 in these prefatory pages. 
 
 It is not many years since this invaluable instrument 
 was regarded in the light of a costly toy ; it is now the 
 inseparable companion of the man of science. In the 
 medical world, its utility and necessity are fully appre- 
 ciated, even by those who formerly were slow to perceive 
 its benefits ; now, knowledge which could not be obtained 
 even by the minutest dissection is acquired readily by its 
 assistance, which has become as essential to the anatomist 
 and pathologist as are the scalpel and bedside observation. 
 The smallest portion of a diseased structure, placed under 
 a Microscope, will tell more in one minute to the ex- 
 perienced eye, than could be ascertained by long examina- 
 
 (1) At the time this work was written, scarcely a book of the kind had been 
 published at a price within the reach of the working classes. 
 
PREFACE. 12 
 
 lion of the mass of disease in the ordinary method. 
 Microscopic agency, in thus assisting the medical man, 
 contributes much to the alleviation of those multiplied 
 " ills which flesh is heir to." So fully impressed were the 
 Council of the Eoyal College of Surgeons with the import- 
 ance of the facts brought to light in a short space of time, 
 that, in 1841, they determined to establish a Professorship 
 of Histology, and to form a collection of preparations of 
 the elementary tissues of both animals and vegetables, 
 healthy and morbid, which should illustrate the value of 
 microscopical investigations in physiology and medical 
 science. From that time, histological anatomy deservedly 
 became an important branch of the education of the 
 medical student. 
 
 In the study of Vegetable Physiology, the Microscope 
 is an indispensable instrument ; it enables the student to 
 trace the earliest forms of vegetable life, and the functions 
 of the different tissues and vessels in plants. Valuable 
 assistance is derived from its agency in the detection of 
 adulterations. In the examination of flour, an article of 
 so much importance to all, the Microscope enables us 
 to judge of the size and shape of the starch-grains, their 
 markings, their isolation and agglomeration, and thus to 
 distinguish the starch-grains of one meal from those of 
 another. It detects these and other ingredients, invisible 
 to the naked eye, whether precipitated in atoms or aggre- 
 gated in crystals, which adulterate our food, our drink, 
 and our medicines. It discloses the lurking poison in 
 the minute crystallisations which its solutions precipitate. 
 " It tells the murderer that the blood which stains him is 
 that of his brother, and not of the other life which he 
 pretends to have taken ; and as a witness against the 
 criminal, it on one occasion appealed to the very sand on 
 which he trod at midnight." 
 
Xli PREFACE. 
 
 acknowledgments are likewise due to Mr. George Pearson, 
 for the great care he has bestowed upon the engravings 
 which illustrate these pages. 
 
 Finally, it- is the Author's hope that, by the instru- 
 mentality of this volume, he may possibly assist in bring- 
 ing the Microscope, and its most valuable and delightful 
 studies, before the general public in a more familiar, com- 
 pendious, and economical form than has hitherto been 
 attempted ; and that he may thus, in these days of a 
 diffused -taste for reading and the spread of cheap pub- 
 lications, supply further exercise for the intellectual 
 faculties, contribute to the additional amusement and 
 instruction of the family circle, and aid the student of 
 nature in investigating the wonderful and exquisite works 
 of the Almighty. If it shall be the good fortune of this 
 work, which is now confided with great diffidence to the 
 consideration of the public, to succeed in however slight a 
 degree, in furthering this design, the Author will feel 
 sincerely happy, and will be fully repaid for the attention, 
 time, and labour that he has expended. 
 
 LONDON, May, 1854. 
 
PAKT I 
 
 HISTORY OF THE INVENTION AND IMPROVEMENTS 
 OF THE MICROSCOPE. 
 
 CHAPTER I. 
 
 PAGE 
 HISTORY OF THE INVENTION AND IMPROVEMENTS OP THE 
 
 MICROSCOPE 1 
 
 CHAPTER II. 
 
 MECHANICAL AND OPTICAL PRINCIPLES INVOLVED IN THE 
 CONSTRUCTION OP THE MICROSCOPE LENSES MODE OP 
 ESTIMATING THEIR POWER MICROMETERS POLARISED 
 LIGHT CAMERA LUCIDA BINOCULAR INSTRUMENT 
 PHOTOGRAPHIC-DRAWING M1CROSPECTROSCOPY ACHRO- 
 MATIC LENSES MAGNIFYING POWER WOLLASTON'fl 
 DOUBLET CODDINGTON'S LENR SIMPLE AND COMPOUND 
 MICROSCOPES QUEKETT'S, ROSS'S, POWELL AND LEA- 
 LAND'S, BAKER'S, PILLISCHER'S, LADDS', MURRAY'S, HIGH- 
 LEY'S, COLLINS' s, AND OTHER MICROSCOPES ..... 15 
 
XIV CONTENTS. 
 
 CHAPTER III. 
 
 PAOI 
 
 PRELIMINARY DIRECTIONS ILLUMINATION ACCESSORY APPA- 
 RATUSACHROMATIC ILLUMINATOR GILLETT's, ROSS'S, 
 WEBSTER'S, AND OTHER CONDENSERS OBLIQUE ILLUMI- 
 NATION DOUBLE PRISM ILLUMINATION LIEBERKUHN 
 SIDE-REFLECTOR OBJECT-FINDERS SECTION CUTTERS 
 COLLECTING OBJECTS MODE OF INJECTING PREPARING 
 AND MOUNTING OBJECTS, ETC 159 
 
 PART II. 
 
 CHAPTER I. 
 
 VEGETABLE KINGDOM VITAL AND CHEMICAL CHARACTERISTICS 
 OF CELLS MICROSCOPIC FORMS OF VEGETABLE CELLS 
 FUNGI FUNGOID DISEASES ALG2E CONFERVJB DESMI- 
 DIACE2B MOSSES FERNS STRUCTURE OF PLANTS 
 ADULTERATION OF ARTICLES USED FOR FOOD PREPARA- 
 TION AND MOUNTING FOSSIL PLANTS . . 255 
 
 CHAPTER II. 
 
 PROTOZOA GREGARINJE RHIZOPODA POLYCYSTINA DIA- 
 TOM ACEJffi FOSSIL INFUSORIA SPONGES VORTICELLA 
 ACTINIZOA ROTIFERA POLYPIFERA ACALEPHA ECHI- 
 VODERMATA , . 
 
CONTENTS. X? 
 
 CHAPTER III. 
 
 PAGE 
 
 POLTZOA MOLLUSCA GASTEROPODA BRAG H IOPOD A CONCH I - 
 FERA CEPHALOPODA PTEROPODA TUNICATA CRUS- 
 TACEA ENTOMOSTRACA CIRRIPEDA ENTOZOA ANNU- 
 LOSA ANNELIDA 511 
 
 CHAPTER IV. 
 
 SUB-KINGDOM ARTICULATA INSECTA ARACHNIDA .... 579 
 
 CHAPTER V. 
 
 TBRTEBiATA PHYSIOLOGY HISTOLOGY BOUNDARY BE- 
 TWEEN THE TWO KINGDOMS CELL THEORY GROWTH OF 
 TISSUES SPECIAL TISSUES SKIN, NERVES, CARTILAGE, 
 TEETH, BONE, ETC 654 
 
 CHAPTER VI. 
 
 INORGANIC OR MINERAL KINGDOM FORMATION OF CRYSTALS 
 
 POLARISATION SPECTRUM ANALYSIS, ETC 728 
 
DESCRIPTION OF COLOURED PLATES. 
 PLATE L Page 255. 
 
 PROTOPHYTA. 
 
 Fig. 1. Pezizabicolor 2. Truffle 3. Sphseriaherbarum : o. piece of dead plant, with 
 8. herbarum natural size ; b. section of same, slightly magnified ; d, Ascus with 
 spores, and paraphyses more magnified 4. Peziza pygmsea 5. Proliferous 
 form of same 6. P. corpulasis; Ascus with spores and paraphyses, 
 merely given as a further illustration of structure in Peziza 7. Yeast, 
 good 8. Yeast, exhausted 9. Phyllactinia guttata 10. Yeast with fayus 
 spores and mycelium 11. Favus ferment, with torulae and bacteria-like 
 bodies 12. Puccinia-like-form in ditto, growing from saccharine solution 
 13. Aerozoa 14. Sporules, &c. from eczema produced by yeast 15. Volvox 
 globator 16. Amoeboid condition of portion of volvox 17. Pucciniabuxi 
 18. Ditto, more enlarged (17 to 20 illustrate Coniomycetes)19. JScidium 
 grossular ue, transverse section of leaf of currant affected by : a. spermo- 
 gones on upper surface ; b. perithecia with spores 20. Phragmidium bul- 
 bosum, development of 21. Pannelia parietina, trans, section through a 
 spermogone, showing green gonidia and spermatia escaping 22. ^cidium 
 berberidis, from leaf of berberry 23. Vaucheria sessilis 24. Stephano- 
 sphaera pluvialis : a. Full-grown example, germ-cells spindle-shaped, with 
 protoplasmic elongations, b. Besting-cell. c. division into four. d. Free 
 swimming ciliated young specimen, e. Amoeboid condition 25. a, b, c, d, e, 
 f and g, Development of Lichen gonidia 26. Pannelia stellaris (Lichen), 
 vertical section through apothecium, showing asci, spores, and paraphyses, 
 with gonidia and filamentous medulla, a. Sperm&tophore with spermatia 
 27. Moss gonidia a3mipg amoeboid form. 
 
 The intention of this plate has been, first to show illustrations of 
 various forms of Protophytes, as the lowest types of vegetable 
 structure ; (from 7 to 14), supposed modes of development or rudi- 
 mentary conditions ; and Confervoidese illustrated by Vaucheria in 
 the Siphonaceae, f. 23, Stephanosphaera 24, and Volvox 15, in the 
 Volvocineae ; and their remarkable amoeboid conditions illustrated 
 by 16, 24 e, and 27. The protean forms assumed in developmenl 
 by 7 to 14 ; 24 a to e ; 25 a to g t and 27. 
 
 PLATE II. Page 274. 
 
 PROTOPHYTA. ALG.E. 
 
 Fig. 27. Ceramium acanthonotum 28. Triploceras gracile 20. Cosmanura 
 radiatum-30. Micrasterias denticulata 31. Docidium pristidse 32. Calli- 
 thaiuniun plumula 33. Uiatomaceae, living : a. Licmophora splendida ; 
 b. Achnanthes longipes ; c. Grammatophora marina. These figures are in- 
 tended to show the general character of the endochrome and growth of 
 frustule 34. Callithamnion refractum 36, Jungermannia albicans. b. re- 
 presents elater and spores 36. Leaf with antheridia, or male elements, which 
 are represented more magnified at a to the left of the figure 37. Ceramium- 
 cchinotum 38. Pleurosigma angulatum, side view 39. Delesseria hypo- 
 glossum 40. Pleurosigma angulatum, front view, endochrome not repre- 
 sented 41. Ceramium fiabelligerum. 
 
 The intention of this plate is chiefly to show various forms of 
 Algse. The figures of Desmids, 28 to 33, illustrate the appearance 
 b 
 
XV111 DESCEIPTION OF COLOURED PLATES. 
 
 of the endochrome, and introduce some new forms, described "by 
 E. G. Lobb and W. Archer, Quar. Jour. Micro. Sci. vol. v. 1865, 
 p. 255 : and 38, 40 to illustrate diatom circulation. 
 
 PLATE III. Page 376. 
 
 PROTOZOA EHIZOPODA. 
 
 Figs. 43, 44, 45, 46, 47, 48, 49, 50, 51, 52. These figures are from diagrams by 
 Major Owen, to illustrate a paper given in Jour. Linn. Soc. vol. viii. p. 202. 
 They illustrate forms of living Polycystina, sketched from life by Major 
 Owen, and show the richly coloured appearance of the sarcode ; figs. 48 to 52 
 63. Monocystis lumbricorum, round form 54. Monocystis lumbricorum, 
 the usual elongated shape 55. Monocystis serpulae 56. Gregarina Sie- 
 boldii ; illustration of septate form, with reflexed hook-like processes 
 57. Monocystis lumbricorum, encysted 58. Monocystis lumbricorum, 
 more advanced and pseudo-naviceUae forming 59. Monocystis lumbricorum, 
 free pseudo-navicella of 60, 61. Monocystis lumbricorum, amoeboid forms 
 of 62. Cruciate sponge-spicule 63. Asteromma Humboldtii 64. Eozoon 
 Canadense, represents appearance of a portion of the natural size 65. Eo- 
 zoon Canadense, magnified, showing portions of cell-walls left uncoloured, 
 the animal sarcode inhabiting it coloured dark green as in nature, and 
 converted by fossilisation into a siliceous mineral : the narrow bands pass- 
 ing between these are processes (stolons) of the same substance 66. Acti- 
 nophiys Sol, budding 67. Euglena viridis ; a. contracted, 6. elongated form 
 68. Acineta tuberosa 69. fficistes longicornis (Davis). 70. Oxytricha 
 gibba (side view) 71. Oxytricha pellionella 72. Limnias (? n. sp.) 73. 
 Cyclidium glaucoma 74. Glaucoma scintillans 75 to 79, 80 to 85, illustrate 
 forms of Foraminifera found by Major Owen, living 75. Globigerina (Or- 
 bulina) acerosa, n. sp., broken open to show interior 76. Globigerina 
 (Orbulina) continens, n. sp. broken open to show interior 77. Globigerina 
 hirsuta 78. Globigerina (Orbulina) universa 79. Globigerina bulloides 
 80. Conochilus vorticella 81. Globigerina bulloides 82. Globigerina in- 
 flata, sinistral shell 83. Pulvinulina Micheliniana 84. Pulvinulina Canari- 
 ensis 85. P. Menardii. 
 
 The figures of recent Polycystina illustrate the surface-fauna of 
 mid-ocean ; the original drawings were made from living specimens, 
 as were those of the Foraminifera ; they well represent in their 
 natural state these elegant and interesting objects. 53 to 61 give 
 some idea of the state of our knowledge of forms and life-history 
 of the Gregarinse. Figures of Infusoria 67, 68, 70, 71, 73, 74 : 
 69, 72, new forms of Kotifera. 
 
 PLATE IV. Pagebll. 
 
 Fig. 86. Hartea elegans 87. Side view of Synapta spicula 88. Ophiocoma rosula 
 (very immature specimen), a. Claw hooks, fe. Palmate spicula. The develop- 
 ment of this creature has been described by G. Hodge, in Transactions of 
 Tyneside Naturalists' Field-Club 89. Spine of a star-fish, particularly 
 interesting as showing the reticular calcareous network obtaining in this 
 as in all other hard parts of the Echinodermata 90. Very minute Spa- 
 tangus, obtained from stomach of a bream : many of the spines are gone, 
 but the structure of the shell is intact and forms a beautiful object, interest- 
 ing in connexion with the source whence obtained 91 . Ophiocorna neglecta ; 
 wriggling or brittle Starfish. The plate does not admit of a figure on a 
 scale sufficient to show the full beauty of this object 92. Tubularia Du- 
 mortierii 93. Pedicellaria maudibulata from Uraster glacialis 94. Pedi- 
 
DESCRIPTION OF COLOURED PLATES. XIX 
 
 eeUaria forcepifonna, from the same 95. Cristatella mucedo, statoblast 
 96. Cristatella mucedo, statoblast, edge-view 97. Early stage of develop- 
 ment of same 98. Lophopus crystallinus 99. Plumatella repens and ova, 
 on a piece of submerged stem 100. Tsenia echinococcus 101. Hydatids in 
 human liver 102. Bilharzia haematobia 103. Amphistoma conicum 104. 
 Trichina spiralis from Hambro' pork 105. Trichina spiralis extracted 
 106, 107. Fasciolagigantea, after Cobbold. 
 
 PLATE V.Page 538. 
 
 MOLLTJSCA. 
 
 fig. 108. Velutina Isevigata, portion of lingual membrane 109. Velutina lvi- 
 gata, part of mandible 110. Hybocystis blennius, portion of palate 111. 
 Sepia officinalis, portion of palate 112. Aplysia hybrida, part of man- 
 dible 113. Loligo vulgaris, part of palate 114. Haliotis tuberculatus, part 
 of palate 115. Cistula catenata, part of palate 116. Patella radiata, part 
 of palate 117. Acmeoea vtrginea, part of palate 118. Cymba olla, part of 
 palate 119. Scapander ligniarius 120. Oncidoris bilamellata, part of 
 palate 121. Testacella Maugei, part of palate 122. Pleurobranchus plu- 
 mula, part of mandible 123. Turbo marmoratus, part of palate. 
 
 Figs. 108 to 123, Lingual membranes of Molluscs ; the drawings 
 made by Mrs. Maples from specimens in the late S. P. Wood- 
 ward's collection, now the property of F. E. Edwards, Esq. 
 
 Chosen without any special order, and simply as showing good 
 examples of the wonderful forms met with in the mouth-armature 
 of Gasteropod and Cephalopod Mollusca ; viewed by polarised light 
 and selenite stage. 
 
 PLATE Nl.Page 576. 
 
 INSECTA. 
 
 Fig. 124. Egg of Caradina Morpheus, Mottled Rustic Moth 125. Egg of Tortoise- 
 shell Butterfly, Vanessa Urtica 126. Egg of Common Footman, Lithosia 
 complanula 127. Egg of Shark Moth, Cucullia Umbratica 128. Maple- 
 aphis 129. Egg-shell of Acarus, empty 130. Egg of House-Fly 131. 
 Mouth of Tsetse-Fly, Qlossina morsitans 132. Vapourer Moth, Orgyia 
 antiqua : antenna of male 133. Vapourer Moth, antenna of female ; a. 
 branch more magnified to show rudimentary condition of the parts 
 134. Tortoise-shell Butterfly; head in profile, showing large compound 
 eye, one of the palpi, and spiral tongue 135. Tortoise-beetle, Cassida 
 viridis ; under surface of left fore-foot, to show the bifurcate tenent ap- 
 pendages, one of which is given at a. more magnified. This form of 
 appendage is characteristic of the family. See West on Feet of Insects, 
 Linn. Trans, vol. xxiii. tab. 43 136. Egg of Blue Argus Butterfly, 
 Polyoromatus Argus 137. Egg of Mottled Umber, Erannis Defolaria 
 138. Egg of Ennomos erosaria, Thorn-Moth 139. Egg of Aspilates Qilvaria, 
 Straw Belle 140. Blow-fly, Musca Vomitoria; left fore-foot, under- 
 surface, to show tenent hairs; o & more magnified; a from below, b 
 from the side 141. House-fly larva 142. Amara communis, left fore-foot, 
 under-surface, to show form of tenent appendages, of which one is given 
 more magnified at a. These, in the ground beetles, are met with only in 
 the males, and seem to be used for sexual purposes. The way in which 
 they are protected when not in use is shown by T. West 143. Ephydra 
 riparia : left fore-foot, under-surface. This fly is met with sometimes in 
 immense numbers on the water in salt-marshes ; it has no power of climb- 
 ing on glass, which is explained by the structure of the tenent hairs ; 
 the central tactile organ also is very peculiar, the whole acting as a float, 
 one to each foot, to enable the fly to rest on the surface of the water ; a. one 
 
XX DESCRIPTION OF COLOURED PLATES. 
 
 of the external hairs 144. Egg of Bot-Fly; the larva just escaping 145. 
 Egg of parasite of Pheasant 146. Egg of Scatophaga 147. Egg of parasite 
 of magpie 148. Egg of Jodisvernaria (Small Emerald Butterfly). 
 
 PLATE VII. Page 654. 
 
 VERTEBRATA. 
 
 Fig 149. Toe of mouse, integuments, bone of foot, and vessels 150. Tongue of 
 mouse, showing erectile papillae, muscular layer, <fec. 151. Brain of rat, 
 showing its vascular supply 152. Tongue of cat, showing fungi-form papillae, 
 with capillary loops passing into them, vessels, <fcc. ; perpendicular section 
 153. Kidney of cat, showing Malpighian turfts and arteries 154. Small 
 Intestine of rat, showing villi and layer of mucous membrane 155. Nose of 
 mouse, showing vascular supply to roots of whiskers 156. Vascular supply 
 to internal gill of tadpole, during one phase of its development 157. Sec- 
 tion through sclerotic and retina of cat's-eye, showing vascular supply of 
 choroid and other coats 158. Internal gill of tadpole, fully developed, exhi- 
 biting crests and vascular system, after Whitney. 
 
 This plate is designed to show the value of injected preparations 
 in the delineation of animal structures. By thus artificially re- 
 storing the blood and distending the tissue, a much better idea is 
 obtained of the relative condition of parts during life, while we 
 receive much assistance in the elucidation of complicated and deli- 
 neate membranes, the appearance of erectile tissues, papillae, &c. 
 
 PLATE VIII. To face Title. 
 
 POLARISCOPE OBJECTS. 
 
 Fig. 158. New Red Sandstone 159. Qtsartz 160. Granite 161. Sulph. Copper 
 162. Saliginine 163. Sulph. Iron and Cobalt, crystallized in the way 
 described by Thomas 164. Borax 165. Sulph. Nickel and Potash 166. 
 Kreatine 167. Starch granules 168. Aspartic Acid 169. Fibro-Cells, 
 Orchid. 170. Equisetum cuticle 171. Spicula Holothuria, Australia 172. 
 Spicula Holothuria, Port Essington 173. Deutzia Scabra ; upper and under 
 surface 174. Cat's tongue, process 175. Prawn shell, exuvia with crystals 
 of lime 176. Grayling scale 177. Scyllium caniculum scale 178. Rhi- 
 noceros horn, transverse section 179. Horse hoof 180. Dytiscus elytra 
 with crystals of lime. 
 
 This plate is especially intended to illustrate the beautiful and 
 gorgeous spectacle produced by polarised light on the various 
 objects here grouped together. It will be seen that all structures 
 belonging either to the animal, vegetable, or mineral kingdoms in 
 which the power of unequal or double refraction is suspected to be 
 present, are those which may be submitted to this mode of micro- 
 chemical investigation. 
 
 PLATE IX. Woodcut. -Page 498. 
 
 A3TEROIDEA-ECHINID.E CRUSTACEA, &c. 
 
THE MICEOSCOPE. 
 
 PAET I. 
 
 HISTORY OF THE INVENTION AND IMPROVEMENTS OF 
 THE MICROSCOPE. 
 
 CHAPTER I. 
 
 HISTORY OF TUE MICROSCOPE. 
 
 HE instrument known as the Mi- 
 croscope derives its name from 
 two Greek words, /xiKpbs, small, 
 and o-KOTreo), to view; that is, to 
 see or view such minute objects 
 as without its aid would be in- 
 visible. 
 
 The honour of the invention 
 is claimed by the Italians and the 
 Dutch; the name of the inventor, 
 however, is lost. Probably the- 
 discovery did not at first appear 
 sufficiently important to engage 
 the attention of those men who. 
 by their reputation in science, were able to establish at: 
 opinion of its merit, and to hand down the name of its 
 inventor to succeeding ages. 
 
 If we consider the microscope as an instrument con 
 sisting of one lens only, it is not at all improbable that ii 
 \vas known at a very early period, nay even in a degree t: 
 
2' v 'tosTbfct 01? THE MICROSCOPE. 
 
 the Greeks and Romans ; at any rate, it is tolerably certain 
 that spectacles were used as early as the thirteenth century. 
 Now as the glasses of these were made of different con- 
 vexities, and consequently of different magnifying powers, 
 it is natural to suppose that smaller and more convex 
 lenses were made, and applied to the examination of 
 minute objects. Many among the learned refuse to the 
 ancients a knowledge of magnifying lenses, and a fortiori 
 that of refracting telsscopes, since, according to them, the 
 Greeks and Romans had only very imperfect notions with 
 respect to the fabrication of glass. 
 
 From a passage in Aristophanes it is plain that globules 
 of glass were sold at the shops of the grocers of Athens, in 
 the time of that comic author. He speaks of them as 
 " burning spheres." 
 
 Pliny states that the immense theatre (it was capable of 
 containing eighty thousand persons) erected at Rome by 
 Scaurus, son-in-law of Sylla, was three stories in height, 
 and that the second of these stories was entirely inlaid 
 with a mosaic of glass. 
 
 Ptolemy, in his "Optics," has inserted a table of the 
 refractions which light experiences under different angles 
 of incidence, in passing from air into glass. The values 
 of these angles, which differ only in a slight degree from 
 those obtained in the present day by means of similar ex- 
 periments, prove that the glass of the ancients differed 
 very little from that manufactured in our own times. 
 
 There is in the French Cabinet of Medals a seal, said to 
 have belonged to Michael Augelo, the fabrication of which, 
 it is believed, ascends to a very remote epoch, and upon 
 which fifteen figures have been engraven in a circular 
 space of fourteen millimetres in diameter. These figures 
 are not all visible to the naked eye. 
 
 Cicero makes mention of an Iliad of Homer written 
 upon parchment, which was comprised in a nutshell. 
 
 Pliny relates that Myrmecides, a Milesian, executed in 
 ivory a square figure which a fly covered with its wings. 
 
 Unless it be maintained that the powers of vision of our 
 ancestors surpassed those of the most skilful modern 
 artists, these facts establish that the magnifying property 
 of lenses was known to the Greek? and Romans nearly 
 
HISTORY OF THE MICROSCOPE. 3 
 
 two thousand years ago. We may besides advance a step 
 .further, and borrow from Seneca a passage whence the 
 same truth will emerge in a manner still more direct and 
 decisive. In the " Natural Questions " we read : " How- 
 ever small and obscure the writing may be, it appears 
 larger and clearer when viewed through a globule of glass 
 filled with water." 
 
 Dutens has seen in the Museum of Portici ancient 
 lenses which had a focal length of only nine millimetres. 
 He actually possessed one of these lenses, but of a longe : 
 focus, which was extracted from the ruins of Hercu- 
 laneum. 
 
 At the meeting of the British Association, held at 
 Belfast in the year 1852, Sir David Brewster showed a 
 plate of rock-crystal worked into the form of a lens, which 
 was recently found among the ruins of Nineveh. Sir 
 David Brewster, so competent a j udge in a question of this 
 kind, maintained that this lens had been destined for 
 optical purposes, and that it never was an article of dress. 
 
 It is not difficult to fix the period when the microscope 
 first began to be generally known, and to be used for the 
 purpose of examining minute objects ; for though we are 
 ignorant of the name of the first inventor, we are acquainted 
 with the names of those who introduced it to public view. 
 Zacharias Jansens and his son are said to have made micro- 
 scopes before the year 1590 : about that time the ingenious 
 Cornelius Drebell brought one made by them with him 
 to England, and showed it to William Borrell and others. 
 It is possible this instrument of Drebell's was not strictly 
 what is now called a microscope, but was rather a kind 
 of microscopic telescope, something similar in principle 
 to that lately described by M. Aepinus in a letter to the 
 Academy of Sciences at St. Petersburg. It was formed of 
 a copper tube six feet long and one inch in diameter, 
 supported by three brass pillars in the shape of dolphins; 
 these were fixed to a base of ebony, on which the objects 
 to be viewed by the microscope were placed. Fontana, in 
 a work which he published in 1646, says that he had made 
 microscopes in the year 1618 : this may be perfectly true, 
 without derogating from the merit of the Jansens; for 
 we have many instance* in our own times of more than 
 B 2 
 
4 HISTORY OF THE MICROSCOPE. 
 
 one person having made the same invention nearly simul- 
 taneously, without any communication from one to the 
 uther. In 1685 Stelluti published a description of the 
 parts of a bee, which he had examined with a microscope. 
 
 The history of the microscope, like that of nations and 
 arts, has had its brilliant periods, in which it shone with 
 uncommon splendour, and was cultivated with extraordi- 
 nary ardour ; and these have been succeeded by intervals 
 marked with no discovery, and in which the science seemed 
 to fade away, or at least to lie dormant, till some favour- 
 able circumstance the discoveiy of a new object, or some 
 new improvement in the instruments of observation 
 awakened the attention of the curious, and reanimated 
 their researches. Thus, soon after the invention of the 
 microscope, the field it presented to observation was culti- 
 vated by men of the first rank in science, who enriched 
 almost every branch of natural history by the discoveries 
 they made by means of this instrument. 
 
 The Single, or Simple Microscope. We shall first speak of 
 the single microscope, that having been invented and used 
 long before the double or compound microscope. When 
 the lenses of the single microscope are very convex, and 
 consequently the magnifying power great, the field of view 
 is small ; and it is so difficult to adjust with accuracy their 
 focal distance, that it requires some practice to render the 
 use of them familiar. It was with an instrument of this 
 kind that Leeuwenhoek and Swammerdam, Lyonet and 
 Ellis, examined the invisible forms of nature, and by their 
 example stimulated others to the same pursuit. 
 
 About the year 1665, small glass globules began to be 
 occasionally applied to the single microscope, instead of 
 convex lenses ; and by these globules an immense magni- 
 fying power was obtained. Their invention has been 
 generally attributed to M. Hartsoeker ; though it appears 
 that we are really indebted to the celebrated Dr. Hooke 
 for this discoveiy, for he described the manner of making 
 them in the preface to his Micrographia Illustrata, pub- 
 lished in the year 1656. 
 
 Mr. Stephen Gray 1 having observed some irregular 
 particles within a glass globule, and finding that they 
 
 (1) Philosophical Transactions, 1696. 
 
HISTORY OP THE MICROSCOPE. O 
 
 appeared distinct and prodigiously magnified when held 
 close to his eye, concluded, that if he placed a globule of 
 water in which there were any particles more opaque than 
 the water near his eye, he should see those particles dis- 
 tinctly and highly magnified. The result of this idea far 
 exceeded his expectation. His method was, to take on a 
 pin a small portion of water which he knew contained 
 some minute animalcules ; this he laid on the end of a 
 small piece of brass wire, till there was formed somewhat 
 more than a hemisphere of water : on applying it then to 
 the eye, he found the animalcules enormously magnified ; 
 for those which were scarcely discernible with his glass 
 globules, with this appeared as large as ordinary-sized 
 peas. 
 
 Dr. Hooke thus describes the method of using this 
 water-microscope: " If you are desirous," .he says, "of 
 obtaining a microscope with one single refraction, and 
 consequently capable of procuring the greatest clearness 
 and brightness any one kind of microscope is susceptible 
 of, spread a little of the fluid you intend to examine on 
 a glass plate ; bring this under one of your globules, then 
 move it gently upwards till the fluid touches the globule, 
 to which it will soon adhere, and that so firmly as to bear 
 being moved a little backwards or forwards. By looking 
 through the globule, you will then have a perfect view of 
 the animalcules in the drop." 
 
 The construction of the single microscope is so simple, 
 that it is susceptible of but little improvement, and has 
 therefore undergone few alterations ; and these have been 
 ohiefly confined to the mode of mounting it, or to addi- 
 tions to its apparatus. The greatest improvement this 
 instrument has received was made by Lieberkuhn, 1 about 
 the year 1740 : it consists in placing the small lens in the 
 centre of a highly-polished concave speculum of silver, by 
 which means a strong light is reflected upon the upper 
 surface of an object, which is thus examined with great 
 ease and pleasure. Before this contrivance, it was almost 
 impossible to examine small opaque objects with any 
 degree of exactness ; for the dark side of the object being 
 next the eye, and also overshadowed by the proximity of 
 
 (J) Dr. Nathaniel Lieberkuhn of Berlin. 
 
HISTORY OF THE MICROSCOPE. 
 
 the instrument, its appearance was necessarily obscure and 
 indistinct. Lieberkuhn adapted a separate microscope to 
 every object : but all this labour was 
 not bestowed on trifling objects ; his 
 were generally the most curious ana- 
 tomical preparations, twelve of which, 
 with their microscopes, are deposited in 
 the Museum of the Royal College of 
 Surgeons. 
 
 Lieberkuhn's instrument, fig. 1, is 
 thus described by Professor Quekett : l a b 
 represents a piece of brass tube, about an 
 inch long and an inch in diameter, which 
 is provided with a cap at each extremity ; 
 the one at a carries a small double-convex 
 lens of half an inch in focal length, whilst 
 the one at b carries a condensing lens three- 
 quarters of an inch in diameter. 
 
 A vertical section of one of these instru- 
 ments is seen in fig. 2 : a represents the mag- 
 nifier, which is lodged in a cavity formed 
 partly by the cap a, and by the silver cup 
 or speculum L In front of the lens is the 
 speculum Z, which is a quarter of an inch 
 thick at its edge, and whose focus is about 
 half an inch ; in front of this again there is 
 a disk of metal c, three-eighths of an inch in 
 diameter, connected by a wire with the small 
 Fi e- ! knob d ; upon this disk the injected object 
 is fastened, and is covered over with some 
 kind of varnish which has dried of a hemispherical figure. 
 Between this knob and the inside and 
 outside of the tube there are two slips of 
 thin brass, which act as springs to keep 
 the wire and disk steady. When the 
 knob is moved, the injected object is 
 carried to or from the lens, so as to be in 
 its focus, and to be seen distinctly, whilst 
 the condensing lens b serves to concen- 
 trate the light on the speculum. To tha 
 
 tcvpe . 
 
 Micro- 
 
 (1) Practical Treatise on the Microscope, p. 16. 
 
HISTORY OP THE MICROSCOPE. 7 
 
 lower part of the tube a handle of ebony, about three 
 inches in length, is attached by a brass ferrule and two 
 screws. The use of this instrument is obvious : it is 
 held in the hand in such a position that the rays of light 
 from a lamp or white cloud may fall on the condenser 6, 
 by which they are concentrated on the speculum I ; this, 
 again, further condenses them on the object and the 
 disk c, which object, when so illuminated, can readily be 
 adjusted by the little knob d, so as to be in the focus of 
 the small magnifier at a. 
 
 We must not omit in this place some account of Leeu- 
 wenhoek's microscopes, which were rendered famous 
 throughout all Europe, on account of the numerous dis- 
 coveries he had made with them. At his death he be- 
 queathed a part of them to the Royal Society. 
 
 The microscopes he used were all single, and fitted up in 
 a convenient and simple manner : each consisted of a very 
 small double- con vex lens, let into a socket between two 
 plates riveted together, and pierced with a small hole ; the 
 object was placed on a silver point or needle, which, by 
 means of screws adapted for that purpose, might be turned 
 about, raised or depressed at pleasure, and thus be brought 
 nearer to, or be removed farther from the glass, as the eye 
 of the observer, the nature of the object, and the conve- 
 nient examination of its parts required. 
 
 Leeuwenhoek fixed his objects, if they were solid, to these 
 points with glue ; if they were fluid, he fitted them on a 
 little plate of talc, or thin-blown glass, which he afterwards 
 glued to the needle in the same manner as his other 
 objects. The glasses were all exceedingly clear, and of 
 different magnifying powers, proportioned to the nature of 
 the object and the parts designed to be examined. He 
 observed, in his letter to the Royal Society, that " from 
 upwards of forty years' experience, he had found the most 
 considerable discoveries were to be made with glasses of 
 moderate magnifying power, which exhibited the object 
 with the most perfect brightness and distinctness." Each 
 instrument was devoted to one or two objects ; hence he 
 had always some hundreds by him. 
 
 The three first compound microscopes that attract our 
 notice are those of Dr. Hooke, Eustachio Divini, and Philip 
 
HISTOHY OP THE MICROSCOPE. 
 
 Bonuani. Dr. Hooke gives us an account of his in the 
 preface to his Micrographia, published in the year 1667 : 
 it was about three inches in diameter, seven inches long, 
 and furnished with four draw-out tubes, by which it might 
 be lengthened as occasion required ; it had three glasses 
 a small object-glass, a middle glasi>, and a deep eye-glass. 
 Dr. Hooke used all the glasses when he wanted to take in 
 a considerable part of an object at once, as by the middle 
 glass a number of radiating pencils were conveyed to the 
 eye which would otherwise have been lost ; but when he 
 wanted to examine with accuracy the small parts of any 
 substance, he took out the middle glass, and only made 
 use of the eye and object lenses ; " for," he writes, " the 
 fewer the refractions are, the clearer and brighter the 
 object appears." 
 
 Dr. Hooke also gave us the first and most simple method 
 of finding how much any compound microscope magnifies 
 an object. He placed an accurate scale, divided into very 
 minute parts of an inch, on the stage of the microscope ; 
 adjusted the microscope till the divisions appeared distinct, 
 and then observed with the other eye how many divisions 
 of a rule similarly divided and laid on the stage were 
 included in one of the magnified divisions ; " for if one 
 division, as seen with one eye through the microscope, 
 extends to thirty divisions on the rule, which is seen by 
 the naked eye, it is evident that the diameter of the object 
 is increased or magnified thirty times." 
 
 An account of Eustachio Divini's microscope was read 
 at the Royal Society in 1668. It consisted of an object- 
 lens, a middle glass, and two eye-glasses, which were plano- 
 convex lenses, and were placed so that they touched each 
 other in the centre of their convex surfaces. The tube in 
 which the glasses were enclosed was as large as a man's 
 leg, and the eye-glasses as broad as the palm of the hand. 
 It had four several lengths : when shut up was 1 6 inches 
 long, and magnified the diameter of an object 41 times, 
 at the second length 90, at the third length 111, and at 
 the fourth length 143 times. It does not appear that 
 Divini varied the object-glasses. 
 
 Philip Bonnani published an account of his two micro- 
 scopes in 1698. Both were compound. The first was 
 
HISTORY OP THE MICROSCOPE. 9 
 
 similar to that which Mr. Martin published as new, in his 
 Mici-ographia Nova, in 1712. His second was like the 
 former, composed of three glasses, one for the eye, a 
 middle glass, and an object lens ; they were mounted in a 
 cylindrical tube, which was placed in a horizontal position; 
 behind the stage was a small tube with a convex lens at 
 each end ; beyond this was a lamp ; the whole capable of 
 various adjustments, and regulated by a pinion and rack. 
 The small tube was used to condense the light on to the 
 object. 
 
 A short time before this, Sir Isaac Newton having dis- 
 covered his celebrated theory of light and colours, was led 
 to improve the telescope, and apply his principles most 
 successfully to the construction of a compound reflecting 
 microscope. On the 6th of February, 1672, he communi- 
 cated to the Royal Society his " design of a microscope by 
 reflection." It consisted of a concave spherical speculum 
 of metal, and an eye-glass which magnified the reflected 
 image of any object placed between them in the conjugate 
 focus of the speculum. He also pointed out the proper 
 mode of illuminating objects by artificial light, as he 
 describes it, " of any convenient colour not too much 
 compounded," mono-chromatic. We find other two plans 
 of this kind; the first that of Dr. Robert Barker, and the 
 second that of Dr. Smith. In the latter there were two 
 reflecting mirrors, one concave, and the other convex : the 
 image was viewed by a lens. This microscope, though far 
 from being executed in the best manner, performed, says 
 Dr. Smith, very well, so that he did not doubt it would 
 have excelled others, had it been properly finished. 
 
 In 1738, Lieberkuhn's invention of the solar microscope 
 was communicated to the public. The vast magnifying 
 power obtained by this instrument, the colossal grandeur 
 with which it exhibited the " minutiae of nature." the plea- 
 sure which arose from being able to display the same object 
 to a number of observers at the same time, by affording a 
 new source of rational amusement, increased the number 
 of microscopic observers, who were further stimulated to 
 the same pursuits by Mr. Trembley's famous discovery of 
 the polype. The discovery of the wonderful properties of 
 this little animal, together with the works of Mr. Trembley, 
 
10 HISTORY OF THE MICROSCOPE. 
 
 Mr. Baker, and Mr. Adams, combined to spread the repu- 
 tation of the instrument. 
 
 In 1742, Mr. Henry Baker, F.R.S., published an ad- 
 mirable treatise on the microscope. He also read several 
 papers before the Royal Society on the subject of hia 
 microscopic discoveries. In the wood-cut (fig. 3) at the 
 end of this chapter we have represented an elegant scroll 
 " pocket microscope with a speculum," described by him 
 as a new invention. 
 
 In 1770, Dr. Hill published a treatise, in which he 
 endeavours by means of the microscope to explain the 
 construction of timber, and to show the number, the 
 nature, and office of its several parts, their various 
 arrangements and proportions in the different kinds ; and 
 he points out a way of judging, from the structure of 
 trees, the uses they will best serve in the affairs of life. 
 
 M. L. F. Delabarre published an account of his micro- 
 scope in 1777. It does not appear that it was superior in 
 any respect to those that were then made in England. It 
 was inferior to some; for those made by Mr. Adams, in 
 1771, possessed all the advantages of Delabarre's in a 
 higher degree, except that of changing the eye-glasses. 
 
 In 1774, Mr. George Adams, the son of the above, im- 
 proved his father's invention, and rendered it useful for 
 viewing opaque as well as transparent objects. This in- 
 strument, made and described by him, 1 continued in use 
 up to the time of the invention of the achromatic im- 
 provement, proposed and made in 1815 for Amici, who 
 subsequently gave so much time to the investigation of 
 polarised light, and the adaptation of a polarising apparatus 
 to the microscope. 
 
 In 1812, Dr. Wollaston proposed a doublet in which 
 the glasses were in contact, under the name of a " Periscopic 
 Microscope." And he says, "with this doublet I have 
 seen the finest striae and serratures on the scales of tho 
 lepisma and podura, and the scales on a gnat's wing." 
 
 In the year 1816, Frauenhofer, a celebrated optician of 
 Munich, constructed object-glasses for the microscope of a 
 single achromatic lens, in which the two glasses, although 
 in juxtaposition, were not cemented together: these glasses 
 
 (1) Microscopical Essays, 1787. 
 
HISTORY OF THE MICROSCOPE. 11 
 
 were very thick, and of long focus. Although such con- 
 siderable improvements had taken place in the making of 
 achromatic object-glasses since their first discovery by 
 Euler in 1776, we find, even at so late a period as 1821, 
 M. Biot writing, "that opticians regarded as impossible 
 the construction of a good achromatic microscope." Dr. 
 Wollaston also was of the same opinion, " that the com- 
 pound instrument would never rival the single." 
 
 In 1823, experiments were commenced in France by 
 M. Selligues, which were followed up by Frauenhofer in 
 Munich, by Amici in Modena, by M. Chevalier in Paris, 
 and by the late Dr. Goring and Mr. Tulley in London. To 
 M. Selligues we are indebted for the first plan of making 
 an object-glass composed of four achromatic compound 
 lenses, each consisting of two lenses. The focal length of 
 each object-glass was eighteen lines, its diameter six lines, 
 and its thickness in the centre six lines, the aperture only 
 one line. They could be used combined or separated. 
 
 A microscope constructed on this principle, by M. Che- 
 valier, was presented by M. Selligues to the Academic des 
 Sciences on the 5th of April, 1824. In the same year, and 
 without a knowledge of what had been done on the Con- 
 tinent, the late Mr. Tulley, at the suggestion of Dr. Goring, 
 constructed an achromatic object-glass for a compound 
 microscope of nine-tenths of an inch focal length, com- 
 posed of three lenses, and transmitting a pencil of 
 eighteen degrees ; this was the first that had been made in 
 England. 
 
 Sir David Brewster first pointed out in 1813, the value 
 of precious stones, the diamond, ruby, garnet, &c., for the 
 construction of microscopes. " The durability," he says, 
 " of lenses matfe of precious stones is one of their greatest 
 recommendations. Lenses of glass undergo decomposition, 
 and lose their polish in course of time. Mr. Baker found 
 the glass lenses of Leeuwenhoek utterly useless after they 
 became the property of the Royal Society. The glass 
 articles found in Nimroud were decomposed, while the 
 rock crystal lens was uninjured." Mr. Pritchard at one 
 time made two plano-convex lenses from a very perfect 
 diamond, one the twentieth of an inch focus, which was 
 
12 HISTORY OF THE MICROSCOPE. 
 
 purchased by the late Duke of Buckingham, and another 
 the thirtieth of an inch focus. 
 
 In March 1 8*25, M. Chevalier presented to the Society 
 for the Encouragement of the Sciences, an achromatic 
 lens of four lines focus, two lines in diameter, and one line 
 in thickness in the centre. This lens was greatly superior 
 to the one before noticed, which had been made by him 
 for M. Selligues. 
 
 In 1826, Professor Amici, of Modena, who from the 
 year 1815 to 1824 had abandoned his experiments on the 
 achromatic object-glass, was induced, after the report of 
 Fresnel to the Academy of Science, to resume them; and 
 in 1827 he brought to this country and to Paris a hori- 
 zontal microscope, in which the object-glass was composed 
 of three lenses superposed, each having a focus of six lines 
 and a large aperture. This microscope had also extra eye- 
 pieces, by which the magnifying power could be increased. 
 A microscope constructed on Amici's plan by Chevalier, 
 during the stay of that physician in Paris, was exhibited 
 at the Louvre, and a silver medal was awarded to its 
 maker. 1 
 
 " While these practical investigations were in progress," 
 says Mr. Ross, "the subject of achromatism engaged the 
 attention of some of the most profound mathematicians in 
 England. Sir John Herschel, Professors Airy and Barlow, 
 Mr. Coddington, and others, contributed largely to the 
 theoretical examination of the subject; and though the 
 results of their labours were not immediately applicable 
 to the microscope, they essentially promoted its im- 
 provement." 
 
 Mr. Jackson Lister, in 1829, succeeded in forming a 
 combination of lenses upon the theory propounded by 
 these gentlemen, and effected one of the greatest improve- 
 ments in the manufacture of object-glasses, by joining 
 together a plano-concave flint lens and a convex, by means 
 of a transparent cement, Canada balsam. This is desirable 
 
 (1) In 1855, when the Jury on Microscopes at the Paris Exposition were com- 
 paring the rival instruments, Professor Amici brought a compound achromatic 
 microscope, comparatively of small dimensions, which exhibited certain striae 
 in test objects better than any of the instruments under examination. This 
 superiority was produced by the introduction of a drop of water between th 
 object and the object-glass. 
 
HISTORY OF THE MICROSCOPE. 13 
 
 to be taken as a basis for the microscopic object-glass : it 
 diminishes very nearly half the loss of light from reflec- 
 tion, which is considerable at the numerous surfaces of a 
 combination ; the clearness of the field and brightness of 
 the picture is evidently increased by doing this; and it 
 prevents any dewiness or vegetation from forming on the 
 inner surfaces. Since this time, Mr. Ross has been con- 
 stantly employed in bringing the manufacture of object- 
 glasses to their greatest perfection, and at length they 
 have attained to their present improved manufacture. 
 Having applied Mr. Lister's principles with a degree of 
 success never anticipated, so perfect were the corrections 
 given to the achromatic object-glass, so completely were 
 the errors of sphericity and dispersion balanced or de- 
 stroyed, that the circumstance of covering the object 
 with a plate of the thinnest glass or talc disturbed the 
 corrections, if they had been adapted to an uncovered 
 object, and rendered an object-glass which was perfect 
 under one condition sensibly defective under the other. 
 Here was another and unexpected difficulty to be over- 
 come, but which was finally accomplished; for in a com- 
 munication made to the Society of Arts in 1837, Mr. Ross 
 stated, that by separating the anterior lens in the combi- 
 nation from the other two, he had been completely suc- 
 cessful. The construction of this object-glass will be 
 illustrated and explained in a future chapter. 
 
 The rapid improvement in the manufacture of the 
 achromatic compound microscope in this country has been 
 greatly furthered by the spirit of liberality evinced by Sir 
 David Brewster, the late Dr. Goring, Mr. R. H. Solly, 
 and Mr. Bowerbank. To the patronage of Dr. Goring 
 we owe the construction of the first triplet achromatic 
 object-glass, of the diamond lens, and of the improved 
 reflecting instrument of Amici by Cuthbert. 
 
 The achromatic microscopes now manufactured by our 
 London makers, Mr. Ross, Messrs. Powell and Lealand, 
 and Messrs. Smith and Beck, are unequalled in any part 
 of the world. This opinion is confirmed by the reports of 
 the juries on the Exhibition of Works of Industry of all 
 Nations, 1851; at that time the instruments exhibited by 
 Mr. Ross and Messrs. Smith and Beck, by far excelled 
 
14 
 
 HISTORY OF THE MICROSCOPE. 
 
 those of all other countries. Messrs. Powell and Lealand's 
 microscope, with object-glasses, was selected by the Royal 
 Society as the best against all competitors. See Juries' 
 Reports for much interesting matter on this subject; 
 article "Microscope," Penny Cyclopaedia, by Mr. Ross; 
 Practical Treatise on the Microscope, by Professor Quekett ; 
 Sir David Brewster's Treatise on the Microscope; Dujardin's 
 Observateur ; Maudl, Traite pratique du Microscope; Dr 
 Robin-, Du Microscope, &c. 
 
 Pig. $. Baker' i Scroll or Pocket Microscope, and the Modern Compound 
 Microtcope of W. Ladd't manufacture. 
 
CHAPTER II. 
 
 MECHANICAL AND OPTICAL PRINCIPLES INVOLVED IK THE CONSTBUOTIOIT 
 Of THE MICBOSCOPE LENSES MODE OF ESTIMATING THEIE POWER, 
 ETC. ACHBOMATIC LENSES MAGNIFYING FOWEB 
 WOLLASTON'8 DOUBLET CODDINGTON'S LENS BOSS'S 
 SIMPLE AND COMPOUND MICBOSCOPES MICBOMETEBS, 
 ETC. 
 
 N the construction of the modern mi- 
 croscope, optical and mechanical prin- 
 ciples of some importance are involved. 
 These principles we shall briefly ex- 
 plain, together with the more recent 
 improvements effected in the instru- 
 ment generally. 1 
 
 The microscope depends for its 
 utility and operation upon concave 
 and convex lenses, and the course of 
 the rays of light passing through them. 
 Lenses are usually denned as pieces of 
 glass, or other transparent substances, 
 having their two surfaces so formed 
 that the rays of light, in passing 
 through them, have their direction 
 changed, and are made to converge or diverge from their 
 original parallelism, or to become parallel after converging 
 or diverging. When a ray of light passes in an oblique 
 direction from one transparent medium to another of a 
 different density, the direction of the ray is changed both 
 on entering and leaving; this influence is the result of the 
 well-known law of refraction, that a ray of light passing 
 from a rare into a dense medium is refracted towards the 
 perpendicular, and vice versd. 
 
 (1) For a full explanation of the laws of optics, and their application to the 
 construction of lenses, the reader is referred to Dr. Bird and Mr. Brooke'* 
 " Manual of Natural Philosophy," Professor Potter's " Elementary Treatise on 
 Optics," Sir David Brewiter's "Optics," &c. 
 
16 
 
 CONSTRUCTION OF TIIE MICROSCOPE. 
 
 Dr. Arnott remarks : "But for this fact, which to many 
 persons might at first appear a subject of regret, as pre- 
 venting the distinct vision of objects through all trans- 
 parent media, light could have been of little utility to 
 man. There could have been neither lenses, as now ; nor 
 any optical instruments, as telescopes and microscopes, of 
 which lenses form a part ; nor even the eye itself." Rays 
 of light falling perpendicularly upon a surface of glass or 
 other transparent substance, pass through without being 
 beiit from the original line of their direction. Thus, if a 
 
 Fig. 4. 
 
 ray pass from Tc perpendicularly to the surface of the pieco 
 of glass at e (fig. 4), it will go on to h in the right line 
 k eo gh. But if the same ray be directed to the surface e 
 obliquely, as from a, instead of passing through in a direct 
 line to o in the direction aemb, it will be refracted to d, 
 in a direction approaching nearer to the perpendicular 
 line Jc h. The ray a e is termed the ray of incidence, or 
 the incident ray ; and the angle a e Jc which it makes with 
 the perpendicular k h is called the angle of incidence. 
 That part of the ray from e to d passing through the 
 transparent medium is called the ray of refraction, or the 
 refracted ray; and the angle deg which it make? with the 
 
CONSTRUCTION OF THE MICROSCOPE. 17 
 
 perpendicular is called the angle of refraction. The ray 
 projected from a to e and refracted to d, in passing out of 
 the transparent medium as at d, is as much bent from the 
 line of the refracted ray e d as that was from the line of 
 the original ray a e b ; the ray then passes from d to c, 
 parallel to the line of the original ray a e b. It follows, 
 then, that any ray passing through a transparent medium, 
 whose two surfaces, the one at which the ray enters, and 
 the one at which it passes out, are parallel planes, is first 
 refracted from its original course ; but in passing out is 
 bent into a line parallel to, and running in the same direc- 
 tion as the original line, the only difference being, that its 
 course at this stage is shifted a little to one side of that of 
 the original. If from the centre e a circle be described 
 with any radius, as d e, the arc a a measures the angle of 
 incidence a e k, and the arc g d the angle of refraction 
 g e d. A line a, k drawn from the point a perpendicular 
 to k h is called the sine of the angle of incidence; and the 
 line d g drawn from the point d perpendicular to k h is 
 called the sine of the angle of refraction. From the con- 
 clusions drawn from the principles of geometry, it has 
 been found, that in any particular transparent substance 
 the sine of the angle of incidence a k has always the same 
 ratio to the sine d g of the angle of refraction, no matter 
 what be the degree of obliquity with which the ray of inci- 
 dence a e is projected to the surface of the transparent 
 medium. If the ray of incidence passes from air obliquely 
 into water, the sine of incidence is to that of refraction as 
 4 to 3 ; if it passes from air into glass, the proportion is as 
 3 to 2 ; and if from air into diamond, it is as 5 to 2. 
 
 By the help of glasses of certain forms, we unite in the 
 same sensible point a great number of rays proceeding 
 from one point of an object ; and as each ray carries with 
 it the image of the point from whence it proceeded, and 
 all the rays united must form an image of the object from 
 whence they were emitted, this image is brighter in pro- 
 portion as there are more rays united, and more distinct 
 in proportion as the order in which they proceeded is 
 better preserved in their union. The point at which 
 parallel rays meet after converging through a lens is called 
 the principal focus, and its distance from the middle of 
 
18 
 
 CONSTRUCTION OF THE MICROSCOPE. 
 
 the lens the focal length. The radiant point and its image 
 after refraction are called conjugate foci. These foci vary 
 according to the distance of the radiant points. In every 
 lens the right line perpendicular to the two surfaces is 
 called the axis of the lens, and is seen in the annexed 
 flgure ; the point where the axis cuts the surface is called 
 the vertex of the lens. 
 
 Fig. 5 is intended to represent the different forms of 
 lenses in use ; a is a plane glass of equal thickness 
 
 throughout ; b, a meniscus, concave on one side, convex on 
 the other ; c, a double-concave ; d, a plano-concave ; e, a 
 double-convex ; /, a plano-convex. 
 
 The lenses employed in the construction of microscopes 
 are chiefly convex; concave lenses being only used to make 
 certain modifications in the course of the rays passing 
 through those of a convex form, whereby their perform- 
 ance is rendered more exact. In accordance with the laws 
 of refraction, when a pencil of parallel rays, passing 
 through the air, impinges upon a convex surface of glass, 
 the rays are made to converge - f for they will be bent 
 towards the centre of the circle, the radius being perpen- 
 dicular to each point of curvature. Parallel rays, falling 
 on a plano-convex lens, are brought to a focus at the dis- 
 tance of its diameter; and conversely, rays diverging from 
 that point are rendered parallel. Plano-convex lenses pos- 
 sess properties which render them valuable in the con- 
 etruct^m of microscopes. 
 
 Parallel rays, falling on a double-convex lens are brought 
 to a focus in the centre of its diameter ; conversely, rays 
 
CONSTRUCTION OF THE MICROSCOPE. 19 
 
 diverging from that point are rendered parallel. Hence 
 the focus of a double-convex lens will be at just half the 
 distance, or half the length, of the focus of a plano-convex 
 lens having the same curvature on one side. The distance 
 of the focus from the lens will depend as much on the 
 degree of curvature as upon the refracting power (called 
 the index of refraction) of the glass of which it may be 
 formed. A lens of crown-glass will have a longer focus 
 than a similar one of flint-glass ; since the latter has a 
 greater refracting power than the former. For all ordinary 
 practical purposes, we may consider the principal focus 
 as the focus for parallel rays is termed of a double-convex 
 lens to be at the distance of its radius, that is, in its centre 
 of curvature ; and that of a plano-convex lens to be at the 
 distance of twice its radius, that is, at the other end of the 
 diameter of its sphere of curvature. The converse of all 
 this occurs when divergent rays are made to fall on a 
 convex lens. Rays already converging are brought together 
 at a point nearer than the principal focus : whereas rays 
 diverging from a point within the principal focus are ren- 
 dered still more diverging, though in a diminished degree. 
 Rays diverging from points more distant than the prin- 
 cipal focus on either side, are brought to a focus beyond 
 it ; if the point of divergence be within the circle of curva- 
 ture, the focus of convergence will be beyond it ; and vice 
 versa. The same principles apply equally to a plano- 
 convex lens; allowance being made for the double distance 
 of its principal focus. They also apply to a lens whose 
 surfaces have different curvatures ; the principal focus of 
 such a lens is found by multiplying the radius of one 
 surface by the radius of the other, and dividing this pro- 
 duct by half the sum of the radii. 
 
 The refracting influence of concave lenses will be pre- 
 cisely the opposite of that of convex. Rays which fall 
 upon them in a parallel direction, will be made to diverge 
 as if from the principal focus, which is here called the 
 negative focus. This will be, for a plano-concave lens, at 
 the distance of the diameter of the sphere of curvature ; 
 and for a double-concave, in the centre of that sphere. If 
 a lens be convex on one side and concave on the other, 
 c 2 
 
20 CONSTRUCTION OP THE MICROSCOPE. 
 
 forming what is termed a meniscus, its effect will depend 
 upon the proportion between the two curvatures. 
 
 The rules by which the foci of all lenses may be found, 
 will be more advantageously studied in works on Optics. 
 
 As each ray carries with it the image of the object from 
 whence it proceeded, it follows, that if those rays, after 
 intersecting each other, and having formed an image at 
 their intersection, are again united by refraction or re- 
 flection, they will form a new image, and that repeatedly, 
 so long as their order is not disturbed. It follows, also, 
 that when the course of the luminous ray through several 
 lenses is under consideration, we may look on the image 
 first produced as an object in reference to the second lens, 
 and may consider the second image as produced by this 
 object, and so on successively. This is, indeed, a principle 
 involved in the adaptation of lenses to magnifying objects ; 
 and in fig. 6, it is seen that if the point of light be situated 
 
 Fig. 6. 
 
 above the line of the axis, the focus will then be below it, 
 and vice versd; but the surface of every luminous body may 
 be regarded as comprehending an infinite number of such 
 points, from all of which a pencil of light-rays proceeds, 
 and is refracted according to the general law ; so that 
 a perfect but inverted image or picture of the object is 
 formed upon any surface placed in the focus, and adapted 
 to receive the rays. If any object be placed at twice the 
 
CONSTRUCTION OF THE MICROSCOPE. 21 
 
 distance of the principal focus, the image being formed at 
 an equal distance on the other side of the lens, will be of 
 the same dimensions with the object, as in fig. 7 ; but if 
 
 the object be placed nearer to the lens, the image will be 
 farther from it, and of larger dimensions, as in fig. 8 ; and, 
 
 en the other hand, if the object be farther from the lens, 
 the image will be nearer to it, and smaller than itself. 
 But it is to be observed, that the larger the image is in 
 proportion to the object, the less bright it will be, because 
 the same amount of light has to be spread over a greater 
 surface ; whilst a smaller image will be much more 
 brilliant. 
 
 Aberration of Lenses. Although the image of an object 
 produced by the convex lens, fig. 8, appears at first view 
 to be an exact reproduction of the object, it is found, 
 when submitted to rigorous examination, to be more or less 
 confused and indistinct : which is augmented when viewed 
 in a microscope. This indistinctness and confusion arises 
 from two causes, one depending on form, and the other on 
 the material of the lens. That which depends on the 
 form of the lens we shall now proceed to explain. 
 
22 
 
 CONSTRUCTION OF THE MICROSCOPE. 
 
 In optical instruments the curvature of the lenses 
 employed is spherical, that being the only form which 
 can be given by grinding with the requisite degree of 
 truth. But convergent lenses, with spherical curvatures, 
 have the defect of not bringing all the rays of light which 
 pass through them to one and the same focus. Each 
 circle of rays from the axis of the lens to its circumference 
 has a different focus, as shown in fig. 9. The rays a a. 
 
 Fig. 9. 
 
 which pass through the lens near its circumference, it is 
 seen to be more refracted, or come to a focus at a shorter 
 distance behind it than the rays b b, which pass through 
 near its centre or axis, and are less refracted. The conse- 
 quence of this defect of lenses with spherical curvatures, 
 which is called spherical aberration, is that a well defined 
 image or picture is not formed by them, for when the 
 object is focused, for the circumferential rays, the picture 
 projected to the eye is rendered indistinct by a halo or 
 confot-ion produced by the central rays falling in a circle 
 of dissipation, before they have come to a focus. On the 
 other hand, when placed in the focus of the central rays, 
 the picture formed by them is rendered indistinct by the 
 halo produced by the circumferential rays, which have 
 already come to a focus and crossed, now fall in a state of 
 divergence, forming a circle of dissipation. The grosser 
 effects of this spherical aberration are corrected by cutting 
 off the passage of the rays a a, through the circumferences 
 of the lens, by means of a stop diaphragm, so that the 
 central rays, b b, only are concerned in the formation of 
 the picture. This defect is reduced to a minimum, by 
 
CONSTRUCTION OP THE MICROSCOPE. 23 
 
 using the meniscus form of lens, whin!* is the segment of 
 an ellipsoid instead of a sphere. 
 
 The ellipse and the hyperbola are curves of this kind, 
 in which the curvature diminishes from the central ray, or 
 axis, to the circumference b ; and mathematicians have 
 shown how spherical aberration may be entirely removed 
 by lenses whose sections are ellipses or hyperbolas. For 
 this curious discovery we are indebted to Descartes. 
 
 If a I, a V, for example, fig. 10, be part of an ellipse 
 
 Fig. 10. 
 
 whose greater axis is to the distance between its foci //as 
 the index of refraction is to unity, then parallel rays 
 r I', r" I incident upon the elliptical surface I' a I, will be 
 refracted by the single action of that surface into lines 
 which would meet exactly in the farther focus /, if there 
 were no second surface intervening between I a I' and/ 
 But as every useful lens must have two surfaces, we have 
 only to describe a circle I a I' round /as a centre, for the 
 second surface of the lens I ' I. 
 
 As all the rays refracted at the surface I a I' converge 
 accurately to/, and as the circular surface I a V is perpen- 
 dicular to every one of the refracted rays, all these rays 
 will go on to/ without suffering any refraction at the circular 
 surface. Hence it should follow, that a meniscus whose 
 convex surface is part of an ellipsoid, and whose convex 
 surface is part of any spherical surface whose centre is in 
 the farther focus, will have no appreciable spherical 
 aberration, and will refract parallel rays incident on ita 
 convex surface to the farther focus. 
 
SJ4 CONSTRUCTION OF THE MICROSCOPE. 
 
 In like manner, a concavo-convex lens, fig. \\,ll', whose 
 <y.>ncave surface I a I' is a circle described round the farther 
 
 Fig. 11. 
 
 locus of the ellipse, will cause parallel rays I I, I' I , to 
 diverge in directions I r, I' r", which, when continued back- 
 wards, will meet exactly in the focus/, which will be its 
 virtual focus. 
 
 If a plano-convex lens, fig. 12, has its convex surface 
 I a I' part of a hyperboloid, formed by the revolution of a 
 
 Fig. 12. 
 
 hyperbola whose greater axis is to the distance between 
 the foci as unity is to the index of refraction, then parallel 
 rays rl, r" I' failing perpendicularly on the plane surface, 
 will be refracted without aberration to the further focus 
 of the hyperboloid. The same property belongs to a 
 plano-concave lens having a similar hyperbolic surface, and 
 receiving parallel rays on its plane surface. 1 
 
 (1) It must be borne in mind, that in none of those lenses would the object 
 be correctly seen in focus, except at the one point known as the mathematical 
 or geometrica 1 axis of the lens. 
 
CONSTRUCTION OF THE MICROSCOPE. 25 
 
 When the convex side of a plano-convex lens is exposed 
 to parallel rays, the distance of the focus from the plane 
 side will be equal to twice the radius of its convex surface 
 diminished by two-thirds of the thickness of the lens ; 
 but when the plane is exposed to parallel rays, the distance 
 of the focus from the convex side will be equal to twice 
 the radius. 
 
 A meniscus with spherical surfaces, fig. 13, has the 
 property of refracting all converging rays to its focus, if 
 
 its first surface be convex, provided the distance of the 
 point of convergence or divergence from the centre of the 
 first surface is to the radius of the first surface as the index 
 of refraction is to unity. Thus, if m I I' n be a meni- 
 scus, and r I, / V rays converging to the point e, whose 
 distance e c from the centre of the first surface I a I' of the 
 meniscus is to the radius ca, or c I, as the index of refrac- 
 tion is to unity, that is as 1*500 to 1 in glass; then if/ is 
 the focus of the first surface, describe, with any radius less 
 than fa,B, circle m a' n for the second surface of the lens. 
 Xow it will be found by projection, that the rays r I, r I', 
 whether near the axis a e or remote from it, will be re- 
 fracted accurately to the focus/; and as all these rays fall 
 perpendicularly on the second surface m n, they will still 
 pass on, without refraction, to the focus/. In like man- 
 ner, it is obvious that rays /,/', diverging from / will 
 
26 CONSTRUCTION OF THE MICROSCOPE. 
 
 be refracted into r l,r' I', which diverge accurately from 
 the virtual focus. 1 
 
 Spherical aberration is not so much connected with the 
 focal length of the lens as depending on the relative con- 
 vexity of its surfaces, and is much reduced by observing 
 a certain ratio between the radii of its anterior and pos- 
 terior surfaces; thus the spherical aberration of a lens, 
 the radius of one surface of which is six or seven times 
 greater than that of the other, as in fig. 14, is very much 
 
 Fig. M. 
 
 less when its more convex surface is turned forward to 
 receive parallel rays, than when its less convex surface is 
 turned forwards. 
 
 This is still better effected, or even got rid of altogether, 
 by using combinations of lenses, so disposed that their 
 opposite aberrations shall correct each other, whilst mag- 
 nifying power is gained. For it is seen that, as the aber- 
 ration of a concave lens is just the opposite of that of a 
 convex lens, the aberration of a convex lens 
 placed in its most favourable position may be 
 corrected by a concave lens of much less 
 power in its most favourable position. This 
 is the principle of a combination proposed by 
 Sir John F. W. Herschel, fig. 15, an " aplanatic 
 doublet," consisting of a double-convex lens 
 and a meniscus; a doublet of this kind is 
 found extremely useful and available for micro- 
 scopic purposes : it affords a large field, like 
 the Coddington lens. 
 
 Chromatic aberration. Another and serious difficulty 
 arises, in the unequal refrangibility of the different 
 
 (1) Brewster's "Treatise on Optics." 
 
 Fig. 15. 
 
CONSTRUCTION OP THE MICROSCOPE. 
 
 27 
 
 coloured rays which together make up white light, so that 
 they are not all brought to the same focus, even by a lens 
 free from spherical aberration. It is, indeed, this differ- 
 ence in their refrangibility which causes their complete 
 separation by the prism into a spectrum. 
 
 The correction of chromatic with spherical aberration is 
 effected in a most ingenious manner, by combining a con- 
 vex lens made of crown-glass, and a concave lens of flint- 
 glass. If we examine closely the image projected on the 
 table of a camera obscura provided with a common lens, 
 we see that it is bordered with the colours of the rainbow , 
 or if we look through a common magnifying-glass at the 
 letters on the title-page of a book, we see them slightly 
 coloured at their edges in the same manner. The cause 
 of this iridescent border is that the primitive rays red, 
 yellow, and blue, of which a colourless ray of light is com- 
 posed, are not all equally refrangible. Hence they are 
 not all brought to one point or focus, but the blue rays 
 being the most refrangible, come to a focus nearer the lens 
 than the yellow ones, which are less refrangible, and the 
 yellow rays than the red, which are the least refrangible. 
 Thus, in fig. 16, chromatic aberration proves still more 
 
 SLUE 
 YELLOW 
 
 RED 
 
 RED 
 
 YELLOW 
 
 BLUE 
 
 Fig. 16. 
 
 detrimental to the distinct definition of images formed by 
 a lens, than spherical aberration. This arises more from 
 the size of the circles of dissipation, than from the iri- 
 descent border, and it may still exist, although the spherical 
 aberration of the lens be altogether corrected. Chromatic 
 aberration is, as before stated, corrected by combining, in 
 the construction of lenses, two media of opposite form, and 
 differing from each other in the proportion in which they 
 
28 CONSTRUCTION OF THE MICROSCOPE. 
 
 respectively refract and disperse the rays of light ; so that 
 the one medium may, by equal and contrary dispersion, 
 neutralize the dispersion caused by the other, without, at 
 the same time, wholly neutralizing its refraction. Remark- 
 able enough, the media found the most valuable for such 
 a purpose should be the combination of pieces of crown 
 and flint glass, of crown-glass whose index of refraction is 
 1*519, and dispersive power 0'036, and of flint-glass whose 
 index of refraction is 1-589, and dispersive power 0-0393. 
 The focal length of the convex crown-glass lens must be 
 4J inches, and that of the concave flint-glass lens 7| 
 inches, the combined focal length of which is 10 inches. 
 The following tig. 17 will serve us to explain how rays 
 of light are brought to a single focus, free from colour. 
 
 Tig. 17. 
 
 In this diagram, L L is a convex lens of crown-glass, and 
 1 1 a concave one of flint-glass. A convex lens will refract 
 a ray of light (s) falling at F on it exactly in the same 
 manner as the prism ABC, whose faces touch the two 
 surfaces of the lens at the points where the ray enters, and 
 quits. The ray s F, thus refracted by the lens L L, or 
 prism ABC, would have formed a spectrum (P T) on a 
 screen or wall, had there been no other lens, the violet ray 
 (F v) crossing the axis of the lens at v, and going to the 
 upper end (P) of the spectrum ; and the red ray (F R) 
 going to the lower end (T). But, as the flint-glass lens (1 1} 
 or the prism A a c, which receives the rays F v, F R, at the 
 same points, is interposed, these rays will be united at/, 
 and form a small circle of white light, the ray (s F) being 
 now refracted without colour from its primitive direction 
 
CONSTRUCTION OP THE MICROSCOPE. 
 
 29 
 
 (s FI) into the new direction (P/). In like manner, the 
 corresponding ray (s F') will be refracted to^ and a white 
 and colourless image there formed by the two lenses. 
 
 The Magnifying Power of Lenses. To assist us in gain- 
 ing a clearer notion of the mode in which a single lens 
 serves to magnify minute objects, it is necessary to take a 
 passing glance at the ordinary phenomena of vision. The 
 human eye is so constituted, that it can only have distinct- 
 vision when the rays falling upon it are parallel or slightly 
 divergent ; because the retina, on which the image im- 
 pinges, requires the intervention of the crystalline lens to 
 bring the rays to an accurate focus upon its surface. The 
 limit of distinct vision is generally estimated at from six 
 to ten inches; objects viewed nearer, to most persons, 
 become indistinct, although they may be larger. The 
 apparent size of an object 
 is, indeed, the angle it sub- 
 
 tends to the 
 
 eye, 
 
 or the 
 
 angle formed by two lines 
 drawn from the centre of 
 the eye to the extremity of 
 the object. This will be 
 understood upon reference 
 to fig. 18. The lines drawn 
 from the eye to A and R form 
 an angle, which, when the 
 distance is small, is nearly 
 twice as great as the angle 
 from the eye to o w, formed by lines drawn at twice the 
 distance. The arrow at A R will therefore appear nearly 
 twice as long as o w, being seen under twice the angle; 
 and in the same proportion for .any greater or less differ- 
 ence in distance. This, then, is called the angle of vision^ 
 or the visual angle. Now the utility of a convex lens 
 interposed between a near object and the eye consists in 
 its reducing the divergence of the rays forming the several 
 pencils issuing from it ; so that they enter the eye in a 
 state of moderate divergence, as if they had issued from 
 an object beyond the nearest limit of distinct vision ; and 
 a well-defined image is consequently formed upon the 
 retina. In fig. 19, a double-convex lens is placed before 
 
30 
 
 CONSTRUCTION OF THE MICROSCOPE. 
 
 the eye, near which is a small arrow, to represent the 
 object under examination ; and the cones drawn from it 
 
 Fig. 19. 
 
 are portions of the rays of light diverging from those 
 points and falling upon the lens. These rays, if permitted 
 to fall at once upon the pupil, would be too divergent to 
 allow of their being brought to a focus upon the retina by 
 the dioptric media of the eye. But being first passed 
 through the lens, they are bent into nearly parallel lines, 
 or into lines diverging from some points within the limits 
 of distinct vision. Thus altered, the eye receives them 
 precisely as if they had emanated directly from a larger 
 arrow placed at ten inches from the eye. The difference 
 between the real and the imaginary arrow is called the 
 magnifying power of the lens. The object, when thus 
 seen, appears to be magnified nearly in the proportion 
 which the focal distance of the lens bears to the distance 
 of the object when viewed by the unassisted eye ; and is 
 entirely owing to the object being distinctly viewed so 
 much nearer to the eye than it could be without the lens. l 
 With these preliminary remarks as to the medium by 
 which microscopic power is obtained, we shall proceed to 
 apply them to the construction of a perfect instrument, 
 
 The Microscope. A microscope, as we have before ex- 
 plained, may be either a single, or simple^ or a compound 
 
 (1) " The Mapnifyjng Power of Short Spaces " has been most ably elucidated by 
 John Gorham, Esq. M.R.C.S. See Journal of Microscopical Society, October. 
 
CONSTRUCTION OP THE MICROSCOPE. 31 
 
 instrument. The simple microscope may consist of one, 
 as seen in fig. 19, or of two or three lenses; but these 
 latter are so arranged as to have the effect only of a single 
 lens. In the compound microscope, not less than two- 
 lenses must be employed : one to form an inverted image 
 of the object, which, being the nearest to the object, is 
 called the object-glass; and the other to magnify this 
 image, and from being next the eye of the observer, called 
 the eye-glass. Both these may be formed out of a com- 
 bination of lenses, as will be hereafter seen. 
 
 We have hitherto considered a lens only in reference to 
 its enlargement of the object, or the increase of the angle 
 under which the object is seen. A further and equally 
 important consideration is that of the number of rays or 
 quantity of light by which every point of the object is 
 rendered visible ; and much may be accomplished, as we 
 have before pointed out, by the combination of two or 
 more lenses instead of one, thus reducing the angles of 
 incidence and refraction. The first satisfactory arrange- 
 ment for this purpose was the invention of the celebrated 
 Dr. Wollaston. His doublet (fig. 20) consisted of two 
 plano-convex lenses having their focal lengths in the pro- 
 portion of one to three, or nearly so, and placed at a 
 distance which can be ascertained best by actual expe- 
 riment. Their plane sides are placed towards the object, 
 and the lens of shortest focal length next the object. 
 
 It appears that Dr. Wollaston was led to this invention 
 by considering that the achromatic Huyghenian eye- 
 piece, which will be presently described, would, if reversed, 
 possess similar good properties as a simple microscope. 
 But it will be evident, when the eye-piece is understood, 
 that the circumstances which render it achromatic are 
 very imperfectly applicable to the simple microscope, and 
 that the doublet, withe ut a nice adjustment of the stop, 
 would be valueless. Dr. Wollaston makes no allusion to 
 a stop, nor is it certain that he contemplated its intro- 
 duction ; although his illness, which terminated fatally 
 soon after the presentation of his paper to the Royal 
 Society, may account for the omission. 
 
 The nature of the corrections which take place in the 
 doublet is explained in the annexed diagram, where I o V is 
 
32 CONSTRUCTION OF THE MICROSCOPE. 
 
 the object, p a portion of the cornea of the eye, and d 
 the stop, or limiting aperture. 
 
 Fig. 20. 
 
 Now it will be observed that each of the pencils of light 
 from the extremities 1 1 1 of the object is rendered exccntri- 
 cal by the stop ; consequently, each passes through the two 
 lenses on opposite sides of their common axis op; thus 
 <3ach becomes affected by opposite errors, which to some ex- 
 tent balance and correct each other. To take the pencil I, 
 for instance, which enters the eye at r 6, r b : it is bent to 
 the right at the first lens, and to the left at the second ; 
 and as each bending alters the direction of the blue rays 
 more than the red, and moreover as the blue rays fail 
 
CONSTRUCTION OP THE MICROSCOPE. 33 
 
 nearer the margin of the second lens, where the refraction 
 being more powerful than near the centre, compensates in 
 some degree for the greater focal length of the second 
 lens, the blue rays will emerge very nearly parallel, and 
 of consequence coloirless to the eye. At the same time, 
 the spherical aberration has been diminished by the 
 circumstance that the side of the pencil which passes 
 one lens nearest the axis passes the other nearest the 
 margin. 
 
 This explanation applies only to the pencils near the 
 extremities of the object. The central pencils, it is obvious, 
 would pass both lenses symmetrically, the same portions 
 of light occupying nearly the same relative places on both 
 lenses. The blue light would enter the second lens nearei 
 to its axis than the red ; and being thus less refracted than 
 the red by the second lens, a small amount of compensa- 
 tion would take place, quite different in principle, and 
 inferior in degree, to that which is produced in the excen- 
 trical pencils. In the intermediate spaces the corrections 
 are still more imperfect and uncertain ; and this explains 
 the cause of the aberrations which must of necessity exist 
 even in the best-made doublet. It is. however, infinitely 
 superior to a single lens, and will transmit a pencil of an 
 angle of from 35 to 50 without any very sensible errors. 
 It exhibits, therefore, many of the usual test-objects in a 
 very beautiful manner. 
 
 The next step in the improvement of the simple micro- 
 scope bears more relation to the eye-piece ; this was 
 effected by Mr. Holland : it consists in substituting two 
 lenses for the first in the doublet, and retaining the stop 
 between them and the third. The first bending being 
 thus effected by two lenses instead of one, is accompanied 
 by smaller aberrations, which are, therefore, more com- 
 pletely balanced or corrected at the second bending, in the 
 opposite direction, by the third lens. 
 
 Hand Magnifiers. Before we proceed further, it will 
 be as well to bestow a passing notice on the simple hand 
 magnifier, so often employed by microscopists in the pre- 
 liminary examinations of objects. 
 
 A very good form of lens was proposed by Dr. Wollaston, 
 and called by him the Periscopic lens : which consisted of 
 
,$4 CONSTRUCTION OF THE MICROSCOPE. 
 
 two hemispherical lenses cemented together by their plane 
 foces, having a stop between them to limit the aperture. 
 A similar "proposal was made by Sir David Brewster in 
 1820, who, however, executed the project in a better man- 
 ner, by cutting a groove in a whole sphere, and filling the 
 groove with opaque matter. His lens, which is better 
 known as the Coddingtou lens, 1 is shown at fig. 21 : it 
 gives a large field of view, which is equally good in all 
 directions, as it is evident that the pencils a b and b a pass 
 
 FL-. 22 
 
 Fig. 21. 
 
 through under precisely the same circumstances. Its 
 spherical form has the further advantage of rendering the 
 position in which it is held of comparatively little conse- 
 quence. It is therefore very convenient as a hand magni- 
 fier ; but its definition is, of course, not so good as that of 
 a well-made doublet or achromatic lens. It is generally 
 set in a folding case, as represented in the figure, and so 
 contrived that it is admirably adapted for the waistcoat- 
 pocket; which, together with the small holder, fig. 22, for 
 
 (1) The late Mr. Coddington, of Cambridge, who had a high opinion of the 
 value of this lens, had one of these grooved spheres executed by Mr. Carey, 
 who gave it the name of the Coddington Lens, supposing that it was invented 
 by the person who employed him, whereas Mr. Coddington never laid clain; to 
 it, and the circumstance of his having one made was not until nine years after 
 it was described by Sir David Brewster in the " Edinburgh Journal." 
 
CONSTRUCTION OF THE MICROSCOPE. 
 
 securing small objects and holding them during 
 
 tion, are all that is required for afield instrument 
 
 a day's ramble. This useful little holder maybe purclwwaiE 
 
 in a case at Mr. Weedon's, 41, Hart-street, Blcomsbroy. 
 
 The Stanhope lens is similarly constructed, although outr 
 
 so good and convenient as the former, and is but ^eidoK 
 
 to be purchased properly made. 
 
 When the magnifying power of a lens is considerable, 
 or when its focal length is short, and its .-proper disfcaafle 
 from the object equally short, it then becomes. neeesnqy 
 to be placed at a proper distance with great precision.; it 
 cannot therefore be held with sufficient accuracy nft 
 steadiness by the unassisted hand, but mast be mouaiaft 
 in a frame, having a rack or screw to. move it to wards ar 
 from another frame or stage which holds the object. & 
 is then called a microscope; and it is furnished, acoeci- 
 ing to circumstances, with lenses and mirrors to 
 and reflect the light upon the object, with other 
 nienoes. 
 
 Fig. 23. Rott's Simple Microscope. 
 
 The best of the kind was that contrived by Mr. 
 
 represented in fig. 23 \ and consists of a circular font % 
 
 from which rises a short tubular stem d, into wkiA 
 
 D2 
 
36 CONSTRUCTION OF THE MICEOSCOPE. 
 
 aides another short tube c, carrying at its top a joint /; 
 to this joint is fixed a square tube a, through which a rod 
 & slides; this rod has at one end another but smaller 
 joint g, to which is attached a collar h, for receiving the 
 lens i. By means of the joint at/, the square rod can be 
 moved up or down, so as to bring the lens close to the 
 object; and by the rod sliding through the square tube a, 
 the distance between the stand and the lens may be either 
 increased or diminished : the joint g, at the end of the 
 rod, is for the purpose of allowing the lens to be brought 
 either horizontally or at an angle to the subject to be 
 investigated. By means of the sliding arm the distance 
 between the table and the jointed arm can be increased 
 or diminished. This microscope is provided with lenses 
 of one-inch and half-inch focal length, and is thereby 
 most useful for the examination and dissection of objects. 
 It is readily unscrewed and taken to pieces, and may be 
 packed in a small case for the pocket. 
 
 Another highly-useful and more complete simple micro- 
 scope was contrived by Mr. W. Valentine, and made for 
 him by Mr. Ross in 1831. It is thus described by the 
 latter gentleman, and is represented in fig. 24. It is sup- 
 ported on a firm tripod, made of bell-metal, the feet of 
 which, a a a. are mad to close up for the purpose of pack- 
 ing it in a box. The firm pillar b rises from the tripod, 
 and carries the stage e\ this is further strengthened by the 
 two supports rr. From the pillar a triangular bar d, and 
 a triangular tube c, is moved up and down by a screw, 
 having fifty threads in the inch, and turned by a large 
 milled head v, which is situated at the base of the pillar : 
 'this is the fine adjustment. The small triangular bar d 
 its moved up and down within the triangular tube c, by 
 turning the milled head t, forming the coarse adjustment : 
 this bar carries the leris-holder mnop. The stage e con- 
 sists of three plates ; the lowest one is firmly attached to 
 the pillar, and upon this the other two work. The upper 
 one carries a small elevated stage g, on which the objects 
 are placed; this stage is mounted on a tube/, and has a 
 spring clip h, for holding, if necessary, the objects under 
 examination. By means of two screws placed diagonally, 
 ne of which is seen at *, this elevated stage can be moved 
 
CONSTRUCTION OP THE MICROSCOPE. 
 
 in two directions, at right angles to one another; andtfams 
 different parts of objects can be brought successively into 
 
 Fig. ^.^Valentine's Microscope. 
 
 the field of view. The arm n p, for carrying the lenses, 
 is attached to the triangular bar d by a conical pin, on 
 which it is made to turn horizontally, and the arm itself 
 can be lengthened or shortened by means of the rack and 
 pinion m o ; hence the lens q can be applied to every part 
 of an object without moving the stage. 
 
 The mirror I is fitted into the largest of the three legs, 
 and consists of a concave and plane glass reflector. To 
 the under side of the stage is fitted a Wollaston's condenser 
 1c ; and the lens is made to slide up and down by means 
 of two small handles projecting from the cell in which the 
 lens is set. Two small tubes i, with either a condensing 
 lens for opaque objects, or a pair of forceps, may be 
 attached to this side of the stage. The magnifiers are 
 
CONSTRUCTION OP THE MICROSCOPE. 
 
 simple lenses or doublets; or it could be easily con* 
 rasted into a compound microscope by inserting a com- 
 d body, supported on a bent arm, in the place of the 
 - carrying the single lenses. 
 
 An arrangement devised by the late Mr. Quekett, for a 
 microscope, represented in fig. 25, is one of value 
 
 Simple Microscope. 
 
 and convenience. The instrument is made by Mr. Ladd 
 rf Beck Street, and is furnished by him with three mag- 
 aiSers, namely, an inch, and half-inch, ordinary lenses, 
 aacf a quarter-inch Coddington ; these will be found to be 
 ffa powers most useful for the purposes to which this 
 affltniment is specially adapted. The lenses, mirror, con- 
 dtaer, vertical stem, &c., all fit into hollows cut for their 
 MMpticna:on the under side of the stage, and are then 
 cowered and kept in place by the side flaps : so that, when 
 Befced together, and the flaps kept secure by an. India 
 BBbberjbaiid, the instrument is very conveniently portable. 
 Wfr size and firmness of the stage afford great, facilities 
 for dissection, and other scientific investigations. 
 
 "EttEJCoMPouND MICROSCOPE. The compound microscope 
 awy, as before stated, consist of only two lenses, while a 
 aple microscope has been shown to contain sometimes 
 flfcse. In the triplet for the simple microscope, however, 
 ^rwa* explained that the object of the first two lenses was/ 
 
CONSTRUCTION OP THE MICROSCOPE. 39 
 
 to do what might have been accomplished, though not BO 
 well, by one ; and the third merely effected certain modi- 
 fications in the light before it en- 
 tered the eye. But in the com- 
 pound microscope the two lenses 
 have totally different functions : the 
 first receives the rays from the ob- 
 ject, and bringing them to new foci, 
 forms an image, which the second 
 lens treats as an original object, and 
 magnifies it just as the siugle mi- 
 croscope magnified the object itself. 
 Fig. 26 shows the earliest form of 
 the compound microscope, with the 
 magnified, image of a fly, as given 
 by Adams, which he describes as 
 consisting of an object-glass, ln> a 
 field glass de, and an eye-glass, /#; 
 the object, b' d, being placed a little 
 further from the lens than. its prin- 
 cipal focal distance, the pencil of 
 rays from which converge to a focus, 
 and form an inverted image of the 
 object at p q, which image is viewed 
 by the eye placed at a through 
 the eye-glass f g. The rays remain 
 parallel after passing out until they 
 reach the eye, when they will con- 
 verge by the refractive powers of 
 this organ, and be collected on the 
 retina. But the image differs from 
 the real object in a very essential 
 particular. The light being emitted 
 from the object in every direc- 
 tion, renders it visible to an eye 
 placed in any position ; but the points of the image formed 
 by a lens emitting no more than a small conical body of 
 rays, which it receives from the glass, can be visible only 
 to the eye situate within its range. Thus the pencil of 
 rays emanating from the object at d, unless converged by 
 the field-lens to/, would cross each other, and diverge 
 
 Fig 26. 
 
40 CONSTRUCTION OF THE MICROSCOPE. 
 
 towards h, and therefore would never arrive at the lens/<jr, 
 without the interposition of the plano-convex lens at de, 
 placed at a smaller distance from the object ; and by this 
 means the pencil d n, which would have proceeded to h, 
 is refracted or bent towards the lens/<7, having a radial 
 point at p q. The object is magnified upon two accounts : 
 first, because if we view the image with the naked eye, it 
 would appear as much longer than the object as the image 
 is really longer than it, or as the distance/ b is greater 
 than the distance from the real object to/' ; and secondly, 
 because this picture is again magnified by the eye-glass. 
 The compound microscope, then, consists of an object-lens, 
 I n, by which the image is formed, enlarged, and inverted ; 
 an amplifying lens, d e, by which the field of view is en- 
 larged, and is consequently called the field-glass ; and an 
 eye-glass or lens/#, by which the eye is permitted to ap- 
 proach very near, and consequently enabled to view the 
 image under a large angle of apparent magnitude. The 
 two, when combined, are termed the eye-piece. 
 
 Mr. Lister's investigations in the year 1829, made for 
 the purpose of improving and correcting the imperfections 
 of the object-glasses of the compound microscope, led to 
 the most important results. Mr. Ross also presented to 
 the Society of Arts, in 1837, a paper on the subject, this 
 was published in the 51st volume of their Transactions: 
 he thus writes : 
 
 "In the course of a practical investigation, with the 
 view of constructing a combination of lenses for the object- 
 glass of a compound microscope which should be free from 
 the effects of aberration, both for central and oblique 
 pencils of great angle, I obtained the greatest possible 
 distance between the object and object-glass ; for in 
 object-glasses of short focal length, their closeness to the 
 object has been an obstacle in many cases to the use of 
 high magnifying powers, and is a constant source of 
 inconvenience. 
 
 " In the improved combination the diameter is only suf- 
 ficient to admit the proper pencil ; the convex lenses are 
 wrought to an edge, and the concave have only sufficient 
 thickness to support their figure : consequently the com- 
 bination is the thinnest possible, and it follows that there 
 
CONSTRUCTION OF THE MICROSCOPE. 41 
 
 will be the greatest distance between the object and the 
 object-glass. The focal length is -^ of an inch, having an 
 angular aperture of 60, with a distance of -^ of an inch, 
 and a magnifying power of 970 times linear, with perfect 
 definition on the most difficult Podura scales. I have 
 made object-glasses % of an inch focal length ; but as the 
 angular aperture cannot be advantageously increased if 
 the greatest distance between the object and object-glass is 
 preserved, their use will be very limited. 
 
 " The quality of the definition produced by an achro- 
 matic compound microscope will depend upon the accuracy 
 with which the aberrations, both chromatic and spherical, 
 are balanced, together with the general perfection of the 
 workmanship. Now in Woiiaston's doublets and Holland s 
 triplets there are no means of producing a balance of the 
 aberrations, as they are composed of convex lenses only ; 
 therefore the best thing that can be done is to make the 
 aberrations a minimum. The remaining positive aberra- 
 tion in these forms produces its peculiar effect upon 
 objects (particularly the detail of the thin transparent 
 class), which may lead to misapprehension of their true 
 structure ; but with the achromatic object-glass, where 
 the aberrations are correctly balanced, the most minute 
 parts of an object are accurately displayed, so that a satis- 
 factory judgment of their character maybe formed. When 
 an object has its aberrations balanced for viewing an 
 opaque object, and it is required to examine that object 
 by transmitted light, the correction will remain ; but if it 
 is necessary to immerse the object in a fluid, or to cover it 
 with glass, an aberration arises from these circumstances 
 which will disturb the previous correction, and conse- 
 quently deteriorate the definition; and this defect will be 
 more obvious from the increase of distance between the 
 object and object-glass. 
 
 " If an object-glass is constructed as represented in 
 fig. 27, where the posterior combination p and the middle 
 m have together an excess of negative aberration, and if 
 this be corrected by the anterior combination a having an 
 excess of positive aberration, then this latter combination 
 can be made to act more or less powerfully upon p and TW, 
 by making it approach to or recede from them ; for when 
 
a! 
 
 42 CONSTRICTION OF THE MICROSCOPE. 
 
 the three act in close contact, the distance of the object 
 from, the object-glass is greatest, and consequently the 
 rays from the object are diverging 
 from a point at a greater distance 
 than when the combinations are 
 separated; and as a lens bends 
 the rays more, or acts with greater 
 effect, the more distant the object 
 is from which the rays diverge, the 
 effect of the anterior combination 
 a upon the other two, p and m, 
 will vary with its distance from 
 thence. 
 
 " When, therefore, the correction 
 of the whole is effected for an 
 opaque object, with a certain dis- 
 tance between the anterior and middle combination, if they 
 are then put in contact, the distance between the object 
 and. object-glass will be increased ; consequently, the ante- 
 rior combination will act more powerfully, and the whole 
 will have an excess of positive aberration. Now the effect 
 of the aberration produced by a piece of flat and parallel 
 glass being of the negative character, it is obvious that the 
 above considerations suggest the means of correction, by 
 moving the lenses nearer together, till the positive aberra- 
 tion thereby produced balances the negative aberration 
 caused by the medium. 
 
 " The preceding refers only to the spherical aberration ; 
 but the effect of the chromatic is also seen when an object 
 is covered with a piece of glass : for in the course of my 
 experiments I observed that it produced a chromatic 
 thickening of. the outline of the Podura and other delicate 
 scales ; and if diverging rays near the axis and at the 
 margin are projected through a piece of flat parallel glass, 
 with the various indices of refraction for the different 
 colours, it will be seen that each ray will emerge, sepa- 
 rated, into a beam consisting of the component colours of 
 the ray, and that eaoh beam is widely different in form. 
 This difference, being magnified by the power of the 
 microscope, readily accounts for the chromatic thickening 
 of the outline just mentioned. Therefore, to obtain the 
 
CONSTRUCTION OP THE MICROSCOPE. 
 
 43 
 
 finest definition of extremely delicate and minute objects, 
 they should be viewed without a covering : if it be 
 desirable to immerse them in a fhrid, they should be 
 covered with the thinnest possible film of talc, as, from the 
 character of the chromatic aberration, it will be seen that 
 varying the distances of the combinations will not sensibly 
 affect the correction ; though object-lenses may be made 
 to include a grven fluid, or solid medium, in their correc- 
 tion for colour. 
 
 " The mechanism for applying these principles to the 
 correction of an object-glass under the various circum- 
 stances, is represented in fig. 28, 
 where the anterior lens is set in 
 the end of a tube a, which slides 
 on the cylinder 6, containing the 
 remainder of the combination ; 
 the tube a, holding the lens nearest 
 the object, may then be moved 
 upon the cylinder 6, for the pur- 
 pose of varying the distance, ac- 
 cording to the thickness of the 
 glass covering the object/ by 
 turning the screwed ring c, or 
 more simply by sliding the one on 
 the other, and clamping them to- 
 gether- when adjusted. An apei> 
 ture is made in the tube a, within 
 which is seen a mark engraved on 
 the cylinder-; and on the edge of which are two marks, a 
 longer and a shorter, engraved upon the tube. When the 
 mark on the cylinder coincides with the longer mark on 
 the tube, the adjustment is perfect for an uncovered 
 object; and when the coincidence is with the short mark, 
 the proper distance is obtained to balance the aberrations 
 produced by glass the hundredth of an inch thick, and 
 such glass can be readily supplied. This adjustment should 
 be tested experimentally by-moving the milled edge, so as 
 to separate or close together the combinations, and then 
 bringing the object "to distinct vision by the screw adjust- 
 ment of the microscope. In this process the milled edge 
 of the object-glass will be employed to adjust for character 
 
 Fig. 28, 
 
44 
 
 CONSTRUCTION OP THE MICROSCOPE. 
 
 of definition, and the fine screw movement of the micro- 
 scope for correct focus. 
 
 " It is hardly necessary to observe, that the necessity 
 for this correction is wholly independent of any particular 
 construction of the object-glass, as in all cases where the 
 object-glass is corrected for an object uncovered, any 
 covering of glass will create a different value of aberra- 
 tion to the first lens, which previously balanced the aber- 
 ration resulting from the rest of the lenses ; and as this 
 disturbance is effected at the first refraction, it is inde- 
 pendent of the other part of the combination. The visibi- 
 lity of the effect depends on the distance of the object from 
 the object-glass, the angle of the pencil transmitted, the 
 focal length of the combination, the thickness of the glass 
 covering the object, and the general perfection of the cor- 
 rections of chromatism and the oblique pencils. 
 
 " With this adjusting object-glass, therefore, we can 
 have the requisites of the greatest possible distance 
 between the object and object-glass, an intense and 
 sharply-defined image throughout the field, from the 
 large pencil transmitted, and the accurate correction of 
 the aberrations; also, by the adjustment, the means of 
 preserving. that correction under all the varied circum- 
 stances in which it may be necessary to place an object for 
 the purpose of observation." 
 
 Angle of Aperture. The definition of an object-glass 
 much depends upon the in- 
 creased "angle of aperture." 
 The angle of aperture is that 
 angle, which the most ex- 
 treme rays that are capable 
 of being transmitted through 
 the object-glass make at the 
 point of focus : b a 6, in 
 figs. 29 and 30, is the angle 
 of aperture ; but it will be 
 seen that the angle of aper- 
 ture is much greater in fig. 
 29 than in fig. 30, which re- 
 presents an uncorrected lens; 
 consequently, a much larger quantity of light is trans- 
 
CONSTRUCTION OF THE MICROSCOPE. 45 
 
 Jiitted by the former than by the latter, when any 
 object is subjected to examination. In order to see an 
 object distinctly with an uncorrected lens, it is ne- 
 cessary to diminish the aperture so much, by the aid of 
 stops, as to interfere with the transmission of the amount 
 of light required to see the object perfectly. The greatest 
 aiijgle of aperture of which a given lens is capable, will be 
 found by determining the greatest obliquity with which it 
 is possible for rays to fall upon the object-glass, so as to be 
 refracted to the eye-glass. Dr. Goring and Mr. Pritchard 
 contrived an instrument for ascertaining this, for any 
 given object-glass ; which instrument is fully described in 
 Dr. Lardner's useful little work on the microscope. 
 
 A very perfect instrument for measuring the angle of 
 aperture, designed by Mr. Gillett, consists of two micro- 
 scopes, the optical axes of which may be adjusted to 
 coincidence. One of these is attached horizontally to the 
 traversing arm of a horizontal graduated circle, and is 
 adjusted so that the point of a needle, made to coincide 
 with the axis of motion of the movable arm, may be in 
 focus and in the centre of the field of view. The other 
 microscope, to which the object-glass to be examined is 
 attached, is fixed, and so adjusted that the point of the 
 same needle may be in focus in the centre of its field. The 
 eye-piece of the latter is then removed, and a cap with a 
 very small aperture is substituted, close to which a lamp 
 is placed. It is evident that the rays transmitted by the 
 aperture will pursue the same course in reaching the point 
 of the needle as the visual rays from that point to the 
 eye, but in a contrary direction ; and being transmitted 
 through the movable microscope, the eye will perceive an 
 image of the bright spot of light throughout that angular 
 space that represents the true aperture of the object-glass 
 examined. The applications of this instrument in the 
 construction of object-glasses are too numerous to be here 
 detailed: amongst the most obvious of which may be 
 mentioned the ready means it presents of determining the 
 nature, and measuring the amount of aberration in any 
 given optical combination. 
 
 There is yet another source of inaccuracy which is more 
 mechanical than optical. All the lenses composing the 
 
CONSTRUCTION OF THE MICROSCOPE. 
 
 microscope require to be set in their respective tubes, sc 
 that their several axes shall be directed in the same 
 straight line with the greatest mathematical precision. 
 This is what is called centering the lenses, and it is a 
 process which, in the case of microscopes, demands 
 great skill on the part of .the manufacturer. The slightest 
 deviation from true centering would 
 cause the images produced by the 
 lenses to be laterally displaced, one 
 being thrown more or less to the right, 
 and the other to the left, or one up- 
 wards and the other downwards ; and 
 even though the aberrations should be 
 perfectly effaced, the superposition of 
 such displaced images would effectually 
 destroy the efficiency of the instru- 
 ment. It should also be so accurate, 
 that the optical axis of the instrument 
 should not be in the least altered by 
 movement in a vertical direction ; so 
 that, if an object be brought into 
 the centre of the field with a low 
 power, and a higher power be then 
 substituted, it should be found in 
 the centre of its field, notwithstanding 
 the great alteration in focus. 
 
 Fig. 31 represents the body of one 
 of Mr. Ross's compound microscopes 
 with the triple object-glass, where o is 
 an object; and above it is seen the 
 triple achromatic object-glass, in con- 
 nection with the eye-piece e e, ff the 
 plano-convex lens ; e e being the eye- 
 glass, and // the field-glass, and be- 
 tween them, at Ib, a dark spot or dia- 
 phragm. The course of the light is 
 shown by three rays drawn from the 
 centre, and three from each end of the 
 object o; these rays, if not prevented by the lens //, or 
 the diaphragm at b b, would form an image at a a; but as 
 they meet with the lens / f in their passage, they are 
 
CONSTRUCTION OF THE .MICROSCOPE. 47 
 
 converged by it and meet at b b, where the diaphragm is 
 placed to intercept all the light except that required for 
 the formation of a perfect image j the image at 6 6 .is 
 further magnified by the lens e e, as if it were an original 
 object. The triple achromatic combination constructed 
 on Mr. Lister's improved plan, although capable of trans- 
 mitting large angular pencils, and corrected as to its own 
 errors of spherical and chromatic aberration, would, in 
 some instances, be less effective without an eye-piece of 
 peculiar construction. 
 
 The eye-piece, which up to this time is considered to be 
 the best to employ with achromatic object-glasses, to the 
 performance of which it is desired to give the greatest 
 possible effect, is described by Mr. Cornelius Varley, in the 
 fifty -first volume of the Transactions of the Society of Arts. 
 The eye-piece in question was invented by Huyghens for 
 telescopes, with no other view than that of diminishing the 
 spherical aberration by producing the refractions at two 
 glasses instead of one, and of increasing the field of view. 
 It consists of two plano-convex lenses, with their plane 
 sides towards the eye, and placed at a distance apart equal 
 to half the sum of their focal lengths, with a stop or 
 diaphragm placed midway between the lenses. Huyghens 
 was not aware of the value of his eye-piece ; it was 
 reserved for Boscovich to point out that he had, by this 
 important arrangement, accidentally corrected a great part 
 of the chromatic aberration. Let %. 32 represent the 
 Huyghenian eye-piece of a microscope, // being the field- 
 glass, and e e the eye-glass, and I m n the two extreme 
 ra}'s of each of the three pencils emanating from the 
 centre and ends of the object, of which, but for the field- 
 glass, a series of coloured images would be formed from r r 
 to b b ; those near r r being red, those near b b blue, and 
 the intermediate ones green, yellow, and so on, corres- 
 ponding with the colours of the prismatic spectrum. This 
 order of colours is the reverse of that of the common com- 
 pound microscope, in which the single objectrglass projects 
 the red image beyond the blue. 
 
 The effect just described, of projecting the blue image 
 beyond the red, is purposely produced for reasons presently 
 to >e given, and is called <?ver correcting the object-glass 
 
48 
 
 CONSTRUCTION OF THE MICROSCOPE. 
 
 &s to colour. It is to be observed also, that the images 
 6 b and r r are curved in the wrong direction to be dis- 
 tinctly seen by a convex eye-lens, and this is a further 
 defect of the compound microscope of two lenses. But 
 
 the field-glass, at the same time that it bends the rays and 
 converges them to foci at b' b f and r r, also reverses the 
 curvature of the images as there shown, and gives them 
 the form best adapted for distinct vision by the eye-glass e e. 
 The field- glass has at the same time brought the blue and 
 red images closer together, so that they are adapted to 
 
CONSTRUCTION OP THE MICROSCOPE. 48 
 
 uucoloured through the eye-glass. To render this 
 important point more intelligible, let it be supposed that 
 the object-glass had not been over-corrected, that it had 
 been perfectly achromatic; the rays would then have 
 become coloured as soon as they had passed the field-glass; 
 the blue rays, to take the central pencil, for example, 
 would converge at 6", and the red rays at r, which is just 
 the reverse of what the eye-lens requires ; for as its blue 
 focus is also shorter than its red, it would demand rather 
 that the blue image should be at r", and the red at &". 
 This effect we have shown to be produced by the over- 
 correction of the object-glass, which protrudes the blue 
 foci b b as much beyond the red foci r r as the sum <jf 
 the distances between the red and the blue foci of the 
 field-lens and eye-lens ; so that the separation b r is 
 exactly taken up in passing through those two lenses, and 
 the whole of the colours coincide as to focal distance- as 
 soon as the rays have passed the eye-lens. But while they 
 coincide as to distance, they differ in another respect, 
 the blue images are rendered smaller than the red by the 
 superior refractive power of the field-glass upon the blue 
 rays. In tracing the pencil I, for instance, it will be 
 noticed that, after passing the field-glass, two sets of lines 
 are drawn, one whole and one dotted, the former repre- 
 senting the red, and the latter the blue rays. This is the 
 accidental effect in the Huyghenian eye-piece pointed out 
 by Boscovich. The separation into colours of the field- 
 glass is like the over-correction of the object-glass, it 
 leads to a subsequent complete correction. For if the 
 differently coloured rays were kept together till they 
 reached the eye-glass, they would then become coloured, 
 and present coloured images to the eye ; but fortunately, 
 and most beautifully, the separation effected by the field- 
 glass causes the blue rays to fall so much nearer the centre 
 of the eye-glass, where, owing to the spherical figure, the 
 refractive power is less than at the margin, that that 
 spherical error of the eye-lens constitutes a nearly perfect 
 balance to the chromatic dispersion of the field-lens, 
 and the blue and red rays I' and V emerge sensibly 
 parallel, presenting, in consequence, the perfect defini- 
 tion of a single point to the eye. The same reasoning 
 
CONSTRUCTION OF THE MICROSCOPE. 
 
 Fig. 33. 
 
 ia true of the intermediate colours and of the other 
 pencils. The eye-glass e e not only brings together the 
 images 6' &', r r, but it likewise has the most important 
 effect of rendering them flat, thus at once correcting both 
 the chromatic and spherical aberration. 
 
 The Huyghenian eye -piece, which we have described, ia 
 the best for merely optical purposes ; but when it is- 
 required to measure the magnified image, 
 we use the eye-piece invented by Mr. 
 Ramsden, and called by him the micrometer 
 eye-piece. The arrangement may be readily- 
 understood upon reference to fig. 33. The. 
 field-glass has now its plane face turned 
 towards the object ; the rays from the ob- 
 ject are made to converge immediately in. 
 front of the field-glass ; and here is placed a plane-glass, 
 on which are engraved divisions of l-100th of an inch or 
 
 less. The markings of these 
 divisions come into focus, 
 therefore, at the same time 
 as the image of the object, 
 and both are distinctly seen 
 together. The glass with its 
 divisions is shown in fig. 34, 
 on which, at A, are seen some 
 magnified grains of starch. 
 Thus the measure of the 
 magnified image is given by 
 mere inspection ; and the 
 value of such measurements, 
 
 Fig. 34. 
 
 in reference to the real object, when once obtained, is con- 
 stant for the same object-glass. 
 
 It is affirmed by Mr. Ross, that if the achromatic prin- 
 ciple were applied to the construction of eye-pieces, the 
 latter is the form with which the greatest perfection would 
 be obtained. That such an adaptation might be produc- 
 tive of valuable results, appears from Mr. Brooke's state- 
 ment, that he has employed as an eye-piece, a triplet 
 objective of one inch focus, the definition obtained by it 
 being superior to that afforded by the ordinary Huyghe- 
 nian eye-piece. Some of the lowest French achromatic 
 
CONSTRUCTION OF THE MICROSCOPE. 51 
 
 object-glasses answer extremely well for this purpose ; and 
 as the sets are usually made removable, the front pair can 
 be readily separated for the experiment. 
 
 Mr. Lister places on the stage of his microscope a 
 divided scale, the value of which is known ; and viewing 
 the scale as the microscopic object, observes how many of 
 the divisions on the scale attached to the eye-piece corre- 
 spond with one of those in the magnified image. If, for 
 instance, ten of those in the eye-piece correspond with one 
 of those in the image, and if the divisions are known to be 
 equal, then the image is ten times larger than the object, 
 and the dimensions of the object are ten times less than 
 indicated by the micrometer. If the divisions on the 
 micrometer and on the magnified scale are not equal, it 
 becomes a mere rule-of-three sum ; but in general this 
 trouble is taken by the maker of the instrument, who 
 furnishes a table showing the value of each division of the 
 micrometer for every object-glass with which it may be 
 used. 
 
 Mr. Jackson invented the simple and cheap form of 
 micrometer, represented in fig. 35, which he described 
 in the Microscopical Society's Transactions, 1840. It 
 consists of a slip of glass placed in the focus of the eye- 
 glass, with the divisions sufficiently fine to have the value 
 of the ten-thousandth of an inch with the quarter-inch 
 object-glass, and the twenty-thousandth with the eighth ; 
 at the same time the half, or even the quarter of a 
 division may be estimated, thus affording the means of 
 attaining all the accuracy that is really available. It 
 may therefore entirely supersede the more complicated 
 and expensive screw-micrometer, being much handier 
 to use, and not liable to derangement in inexperienced 
 hands. 
 
 The positive eye-piece gives the best view of the micro- 
 meter, the negative of the object. The former is quite 
 free from distortion, even to the edges of the field; but 
 the object is slightly coloured. The latter is free from 
 colour, but is slightly distorted at the edges. In the 
 centre of the field, however, to the extent of half its 
 diameter, there is no perceptible distortion ; and the 
 clearness of the definition gives a precision to the measure- 
 E 2 
 
52 CONSTRUCTION OF THE MICROSCOPE. 
 
 ment which is very satisfactory. For this reason M.r. 
 Jackson gives it the preference. 
 
 Fig. 35. Mr. Jackson's Micrometer eye-piece. 
 
 Short bold lines are ruled on a piece of glass, a, fig. 35; 
 and to facilitate counting, the fifth is drawn longer, and 
 the tenth still longer, as in the common rule. Very finely 
 levigated plumbago is rubbed into the lines, to render 
 them visible ; and they are covered with a piece of thin 
 glass, cemented by Canada balsam, to secure the plumbago 
 from being wiped out. The slip of glass thus prepared is 
 placed in a thin brass frame, so that it may slide freely ; 
 and is acted on at one end by a pushing-screw, and at the 
 other by a slight spring. 
 
 Slips are cut in the negative eye-piece on each side, b, 
 so that the brass frame may be pressed across the field in 
 the focus of the eye-glass, as at m; the cell of which 
 should have a longer screw than usual, to admit of adjust- 
 
CONSTRUCTION OF THE MICROSCOPE. 53 
 
 inent for different eyes. The brass frame is retained in its 
 place by a spring -within the tube of the eye-piece ; and 
 in using it the object is brought to the centre of the field 
 by the stage movements ; and the coincidence between 
 one side of it and one of the long lines is made with great 
 accuracy by means of the small pushing-screw that moves 
 the slip of glass. The divisions are then read off as easily 
 as the inches and tenths on a common rule. The operation, 
 indeed, is nothing more than the laying a rule across the 
 body to be measured; and it matters not whether the 
 object be transparent or opaque, mounted or not mounted, 
 if its edges can be distinctly seen, its diameter can be 
 taken. 
 
 Previously, however, to using the micrometer, the value 
 of the divisions should be ascertained with each object- 
 glass ; the mode of doing which is best performed as 
 follows : 
 
 " Lay a slip of ruled glass en the stage ; and having 
 turned the eye-piece so that the lines on the two glasses 
 are parallel, read off the number of divisions in the eye- 
 piece which cover one on the stage. Eepeat this process 
 with different portions of the stage-micrometer, and if 
 there be any difference, take the mean. Suppose the 
 hundredth of an inch on the stage requires eighteen divi- 
 sions in the eye-piece to cover it ; it is quite plain that an 
 inch would require eighteen hundred, and an object which 
 occupied nine of these divisions would measure the two- 
 hundredth of an inch. This is the common mode of 
 expressing microscopical measurements ; but I am of 
 opinion that a decimal notation would be preferable, if 
 universally adopted. 
 
 " Take the instance supposed, and let the microscope be 
 furnished with a draw-tube, marked on the side with 
 inches and tenths. By drawing this out a short distance, 
 the image of the stage micrometer may be expanded until 
 one division is covered by twenty in the eye-piece. These 
 will then have the value of two-thousandths of an inch, 
 and the object which before measured nine will then mea- 
 sure ten ; which, divided by 2,000, gives the decimal 
 fraction -005. 
 
 " Enter in a table the length to which the tube is drawn 
 
54 CONSTRUCTION OF THE MICROSCOPE. 
 
 out, and the number of divisions on the eye-piece micro- 
 meter equivalent to an inch on the stage ; and any 
 measurements afterwards taken with that micrometer and 
 object-glass may, by a short process of mental arithmetic, 
 be reduced to the decimal parts of an inch, if not actually 
 observed in them. 
 
 " In ascertaining the value of the micrometer with a 
 deep object-glass, the hundredth of an inch on the stage 
 will occupy too much of the field ; the two-hundredth or 
 five-hundredth should then be used., and the number of 
 divisions corresponding to that quantity be multiplied by 
 two hundred or five hundred, as the case may be. 
 
 " The micrometer should not be fitted into too deep an 
 eye-piece, for it is essential to preserve clear definition. 
 TH middle eye-piece is for most purposes the best, pro 
 vided the object-glass be of the first quality ; otherwise, 
 t^se the eye-piece of lowest power. The lens above the 
 micrometer should not be of shorter focus than three- 
 quarters of an inch, even with the best object-glasses; and 
 the slit cut in the tube can be closed at any time by a 
 small sliding bar, as at Z, fig. 35." 
 
 We subjoin the following comparative micrometrical 
 measures given by Dr. Hannover, as a reference-table. 
 
 Millemetre. 
 
 Paris lines. 
 
 Vienna lines. 
 
 Rhenish lines. 
 
 English inch. 
 
 1 
 
 0-443296 
 
 0-1555550 
 
 0-458813 
 
 0-0393708 
 
 2-255829 
 
 1 
 
 1 027643 
 
 1-035003 
 
 0-0888138 
 
 2-195149 
 
 0-973101 
 
 1 
 
 1T071625 
 
 0-0864248 
 
 2-179538 
 
 0-."6618l 
 
 0-992888 
 
 1 
 
 0-0858101 
 
 25-39954 
 
 11-25952 
 
 11-57076 
 
 11-65364 
 
 1 
 
 The wonderful tracing on glass executed by M. Nobert, 
 of Earth, in Prussia, deserves attention. The plan adopted 
 by him is, to trace on glass ten separate bands at equal 
 distances from each other, each band being composed of 
 parallel lines of some fraction of a Prussian inch apart ; in 
 some they are l-1000th, and in others only 1 -4000th of a 
 Prussian inch separated. The distance of these parallel 
 lines forms part of a geometric series : 
 
CONSTRUCTION OF THE MICROSCOPE. 
 
 0-001000 lines. 
 0-000857 ., 
 0-000735 ] 
 0-000630 
 0-000540 
 
 0-000463 lines. 
 0-000397 
 0-000340 
 0-000292 
 0-000225 
 
 To see these lines at all, it is requisite to use a micro- 
 scope with a magnifying power of 100 diameters; the 
 bands containing the fewest number of lines will then be 
 visible. To distinguish the finer lines, it will be necessary 
 to use a magnifying power of 300, and then the lines which 
 are only 1-4 7 00th of an inch (Prussian) apart will be 
 seen perfectly traced. Of all the tests yet found for 
 object-glasses of high power, these would seem the most 
 valuable. These tracings have tended to confirm the 
 undulating theoiy of light, the different colours of the 
 spectrum being exhibited in the ruled spaces according to 
 the separation of the lines ; and in those cases where the 
 distances between the lines are smaller than the length of 
 the violet-coloured waves, no colour is perceived ; and it 
 .is stated, that if inequalities amounting to -000002 line 
 occur in some of the systems, stripes of another colour 
 would appear in them. 
 
 Achromatic object-glasses for microscopes are of Tftrious 
 foci, differing from.2 inches to l-50th of an inch. 
 
 Magnifying Power of Mr. Ross's Object-Glasses 
 various Eye-Pieces. 
 
 v GLASSES, 
 
 OBJECT GLASSES. 
 
 EYE-PIECES. 
 
 2-inch. 
 
 1-inch. 
 
 i-inch. 
 
 i-inch. 
 
 J-inch. 
 
 T Vch. 
 
 A 
 
 20 
 
 60 
 
 100 
 
 220 
 
 420 
 
 600 
 
 B 
 
 30 
 
 80 
 
 130 
 
 350 
 
 670 
 
 8?0 
 
 C 
 
 40 
 
 100 
 
 180 
 
 500 
 
 900 
 
 1200 
 
 Value of each 
 
 
 
 
 
 
 
 space in the Mi- 
 crometer eye- 
 
 *o 
 
 ih 
 
 1000 
 
 430* 
 
 W*o 
 
 1*1*0 
 
 glass, with the 
 various object- 
 
 0025 
 
 001031 
 
 0005263 
 
 0002325 
 
 0001111 
 
 000074 
 
 glasses. 
 
 
 
 
 
 
 
CONSTRUCTION OF THE MICROSCOPE. 
 
 Magnifying Power of Messrs. Powell and Zealand's 
 A clii -omatic Object- Glasses. 
 
 ?- I 
 
 
 
 Object 
 
 Glasses. 
 
 Angular 
 Aperture. 
 
 Magnifying Power with tlie various 
 Eye-Pieces. 
 
 Price. m 
 
 
 
 No. 1. 
 
 No. 2. 
 
 No. 3. 
 
 No. 4. 
 
 No. 5. 
 
 
 Inches. 
 
 Deg. 
 
 
 
 
 
 
 t. 
 
 2 
 
 14 
 
 25 
 
 37 
 
 SO 
 
 100 
 
 150 
 
 2 15 
 
 I 
 
 28 
 
 50 
 
 74 
 
 100 
 
 200 
 
 300 
 
 3 
 
 4 
 
 70 
 
 100 
 
 148 
 
 200 
 
 400 
 
 GOO 
 
 5 
 
 I 
 
 95 
 
 200 
 
 296 
 
 '100 
 
 800 
 
 1200 
 
 5 5 
 
 i 
 
 125 
 
 400 
 
 592 
 
 800 
 
 160G 
 
 2400 
 
 8 8 
 
 i 
 
 145 
 
 GOO 
 
 888 
 
 1200 
 
 2400 
 
 3600 
 
 10 10 
 
 \ * 
 
 175 
 
 800 
 
 1184 
 
 1GOO 
 
 3200 
 
 4800 
 
 1C 16 
 
 Schmidt's goniometer positive eye-piece, for measuring 
 the angles of crystals, is so arranged as to be easily rotated 
 within a large and accurately graduated circle. In the 
 focus of the eye-piece a single cobweb is drawn across, and 
 to the upper part is attached a vernier. The crystals 
 being placed in the field of the microscope, and care being 
 taken that they lie perfectly flat, the vernier is brought to 
 zero, and then the whole apparatus turned until the line 
 is parallel with one face of the crystal ; the frame-work 
 bearing the cobweb, with the vernier, is now rotated until 
 the cobweb becomes parallel with the next face of the 
 crystal, and the number of degrees which it has traversed 
 may then be accurately read off. 
 
 To the most complete instruments a set of eye-pieces, 
 consisting of not less than three, is usually made. These 
 differ in power ; the longest is always the lowest power, 
 and is marked A. Its angular aperture, which determines 
 the size of the field of view, is generally less than that of 
 the others (if constructed on the Huygheneau plan), being 
 Emited by the diameter of the body. It is usually about 
 20 degrees. The next eye-piece, or middle power, marked 
 B, and the deepest, c, have more than 30 degrees of angular 
 aperture. 
 
 For viewing thin sections of recent or fossil woods, 
 coal, the fructification of ferns and mosses ; fossil-shells, 
 seeds, small insects, or parts of larger ones ; molluscs or 
 
DEFINING AND PENETRATING POWER. 57 
 
 the circulation in the frog, &c., the eye-piece A is best 
 adapted. 
 
 For examining the details of any of the above objects, 
 ;j> ^ill be advisable to substitute the eye-piece B, which 
 also should ; be used in the observation of crystals when 
 illuminated by polarised light, the pollen of flowers, minute 
 dissection of insects, the vascular and cellular tissues of 
 plants, the Haversian canals and lacunae of bone, and the 
 serrated laminae of the crystalline lens in the eyes of birds 
 and fishes. 
 
 The eye-piece c is of use when it is requisite to investi- 
 gate the intimate structure of delicate tissues \ and also in 
 observations upon fossil infusoria, volvox, scales from 
 moths' wings, raphides, &c. The employment of this eye- 
 piece, when a higher power is required, obviates the neces- 
 sity of using a deeper object-glass, which always occasions 
 a fresh arrangement of the illumination and focus. It 
 must be borne in mind, that the more powerful the eye- 
 piece, the more apparent will the imperfections of the 
 object-glass become ; hence less confidence should be 
 placed in the observations made under a powerful eye- 
 piece than when a similar degree of amplification is 
 obtained with a shallow one and a deeper object-glass. 
 
 The degree of perfection in the construction of the 
 optical part of a microscope is judged of by the distinct- 
 ness and comfort with which it exhibits certain objects, 
 the details of which can only be made visible by combi- 
 nations of lenses of high magnifying power, and a near 
 approach to correctness. Such are termed by the micro- 
 scopist test-objects. Mr. C. Brooke, F.R.S., whose labours 
 have been devoted to the correction of errors which have 
 crept into this part of philosophical research, says: In 
 order to arrive at any satisfactory conclusions regarding 
 the action of any transparent medium on light, it is neces- 
 sary to form some definite conceptions regarding the ex- 
 ternal form and internal structure of the medium. This 
 observation appears to apply in full force to microscopic 
 test-objects; and for the purposes of the present inquiry, 
 it will suffice to limit our observations to the structure of 
 two well-known test-objects, the scales of Podura plumbea, 
 and the siliceous loricse, or valves of the genus Pleurosigma, 
 
58 CONSTRUCTION OF "THE MICROSCOPE. 
 
 freed from organic matter : the former of these is com- 
 monly adopted as the test of the defining power of an 
 achromatic object-glass, and the several species of the 
 latter as the tests of the penetrating or separating power, 
 as it has been termed. The defining power depends only 
 on the due correction of chromatic and spherical aberra- 
 tions, so that the image of any point of an object formed 
 on the retina may not overlap and confuse the images of 
 adjacent points. This correction is never theoretically 
 perfect, since there will always be residual terms in the 
 general expression for the aberration, whatever practicable 
 number of surfaces we may introduce as arbitrary con- 
 stants; but it is practically perfect when the residual 
 error is a quantity less than that which the eye can appre- 
 ciate. The separation of the markings of the Pleurosig- 
 mata and other analogous objects is found to depend on 
 good denning power associated with large angle of 
 aperture. 
 
 The Podura scale appears to be a compound structure, 
 'consisting of a very delicate transparent lamina or mem- 
 brane, covered with an imbricated arrangement of epi- 
 thelial plates, the length of which is six or eight times 
 their breadth, somewhat resembling the tiles on a roof, or 
 the long pile of some kinds of plush. This structure may 
 be readily shown by putting a live Podura into a small 
 test- tube, and inverting it on a glass-slide; the insert 
 should then be allowed for some time to leap and run 
 about in the confined space. By this means the scales 
 will be freely deposited on the glass; and being subse- 
 quently trodden on by 'the insect, several will be found 
 from which the epithelial plates have been partially rubbed 
 off, and at the margin of the undisturbed portion the form 
 and position of the plates may be readily recognised. 
 This structure appears to be rendered most evident by 
 mounting the scales thus obtained in Canada balsam, and 
 illuminating them by means of Wenham's parabolic re- 
 'flector. The structure may also be very clearly recognised 
 When the scale is seen as an opaque object under a Ross's 
 (specially adjusted Tor uncovered objects), illuminated 
 
 a combination of the parabola and a flat Lieberkuhn. 
 under-side of the scate thus appears as a smooth 
 
DEFINING AND PENETRATING POWER. 59 
 
 glistening surface, with very slight markings, correspond- 
 ing, probably, to the points of insertion of the plates on 
 the contrary side. The minuteness and close proximity 
 of the epithelial plates will readily account for their being 
 a good test of definition, while their prominence renders 
 them independent of the separating power due to large 
 angle of aperture. 
 
 The structure of the second class of test-objects above 
 mentioned differs entirely from that above described; it 
 will suffice for the present purpose to notice the valves of 
 three species only of the genus Pleurosigma; which, as 
 arranged in the order of easy visibility, are, P. formosum, 
 P. hippocampus, P. angulatum. These appear to consist 
 of a lamina of homogeneous transparent silex, studded 
 with rounded knobs of protuberances, which, in P. formosum 
 and P. angulatum, are arranged like a tier of round shot- 
 in a triangular pile, and in hippocampus like a similar tier 
 in a quadrangular pile, as has frequently been described ; 
 and the visibility of these projections is probably propro- 
 tional to their convexity. The " dots " have by some been 
 supposed to be depressions; this, however, is clearly not 
 the case, as fracture is invariably observed to take place 
 between the rows of dots, and not through them, as would 
 naturally occur if the dots were depressions, and conse- 
 quently the substance is thinner there than elsewhere. 
 
 This, in fact, is always observed to take place in the 
 siliceous loricae of some of the border tribes that occupy a 
 sort of neutral, and yet not undisputed, ground between 
 the confines of the animal and vegetable kingdoms; as, 
 for example, the Isthmia, which possesses a reticulated 
 structure, with depressions between the meshes, somewhat 
 analogous to that which would result from pasting together 
 bobbin-net and tissue-paper. The valves of P. angulatum, 
 and similar other objects, have been by some writers sup- 
 posed to be made up of two substances possessing different 
 degrees of refractive power; but this hypothesis is purely gra- 
 tuitous, since the observed phenomena will naturally result 
 from a series of rounded or lenticular protuberances of one 
 homogeneous substance. Moreover, if the centres of the 
 markings were centres of greatest density, if, in fact, the 
 structure were at all analogous to that of the crystalline 
 
00 CONSTRUCTION OP THE MICROSCOPE. 
 
 lens, it is difficult to conceive why the oblique rays only 
 should be visibly affected. When P. hippocampus or P. for- 
 mosum is illuminated by a Gillett's condenser, with a cen- 
 tral stop placed under the lenses, and viewed by a quarter- 
 inch object-glass of 70 aperture, both being accurately 
 adjusted, we may observe in succession, as the object-glass 
 approaches the object, first a series of well-defined bright 
 dots ; secondly, a series of dark dots replacing these ; and 
 thirdly, the latter are again replaced by bright dots, not, 
 however, as well defined, as the first series. A similar 
 succession of bright and dark points may be observed in 
 the centre of the markings of some species of Coscinodiscus 
 from Bermuda. 
 
 These appearances would result if a thin plate of glass 
 were studded with minute, equal, and equidistant plano- 
 convex lenses, the foci of which would necessarily lie in 
 the same plane. If the focal surface, or plane of vision, of 
 the object-glass be made to coincide with this plane, a 
 series of bright points would result from the accumulation 
 of the light falling on each lens. If the plane of vision be 
 next made to coincide with the surfaces of the lenses, these 
 points would appear dark, in consequence of the rays being 
 refracted towards points now out of focus. Lastly, if the 
 plane of vision be made to coincide with the plane beneath 
 the lenses that contain their several foci, so that each lens 
 may be, as it were, combined with the object-glass, then a 
 second series of bright points will result from the accumu- 
 lation of the rays transmitted at those points. Moreover, 
 as all rays capable of entering the object-glass are concerned 
 in the formation of the second series of bright focal points, 
 whereas the first series are formed by the rays of a conical 
 shell of light only, it is evident that the circle of least 
 confusion must be much less, and therefore the bright 
 points better defined in the first than in the last series. 
 
 If the supposed lenses were of small convexity, it is 
 evident that the course of the more oblique rays only 
 would be sensibly influenced ; hence probably the structure 
 of P. anaulatum is recognised only by object-glasses of 
 large angular apertures, which are capable of admitting 
 very oblique rays, 
 
 It does not appear to be desirable that objects should be 
 
MECHANICAL ARRANGEMENTS. 61 
 
 illuminated by an entire, or, as it may be termed, a solid 
 cone of light of much larger angle than that of the object- 
 glass. The extinction of an object by excess of illumina- 
 tion may be well illustrated by viewing with a one-inch 
 object-glass the Isthmia, illuminated by Gillett's condenser. 
 When this is in focus, and its full aperture open, the 
 markings above described are wholly invisible; but as the 
 aperture is successively diminished by the revolving dia- 
 phragm, the object becomes more and more distinct, and 
 is perfectly defined when the aperture of the illuminating 
 pencil is reduced to about 20. The same point may be 
 attained, although with much sacrifice of definition, by 
 gradually depressing the condenser, so that the rays may 
 diverge before they reach the object; and it may be 
 remarked, generally, that the definition of objects is 
 always most perfect when an illuminating pencil of suit- 
 able form is accurately adjusted to focus, that is, so that 
 the source of light and the plane of vision may be conju- 
 gate foci of the illuminator. If a condenser of 120 
 aperture, or upwards, be used as an illuminator, the mark- 
 ings of Diatomacese will be scarcely distinguishable with 
 the best object-glass, the glare of the central rays over- 
 powering the structure of those that are more oblique. 
 
 There are indeed almost as many methods employed 
 for bringing out the markings on test-objects, as there are 
 skilled and efficient microscopists, each one preferring his 
 own, simply because he has been at great pains in work- 
 ing it out with the utmost nicety. The late Professor 
 Quekett, in his treatise on the microscope, recommends 
 " oblique light with the mirror and lamp, removing all 
 appliances under the stage ; then, after much patience and 
 perseverance, Grammatophora suhtilissima and the Amician 
 test may be resolved." Another plan is to use the flat 
 mirror, the achromatic condenser, and a paraffin lamp, day- 
 light not being so easily managed, or even so good for the 
 -|th or higher objectives. 
 
 Mr. Lobb's method is seen in Fig. 36 : "The microscope 
 is placed in the horizontal position, and a small camphine 
 lamp so adjusted that its reservoir may be close against 
 the end of the rack-tube ; having the A eye-piece, the 
 one-inch objective, and the achromatic condensor of 170 
 
62 
 
 THE MICROSCOPE. 
 
 aperture, place "No. I aperture of the wheel of dia- 
 phragms in the field, then, looking through the eye-piece, 
 centre the aperture accurately; then bring No. 11 aper- 
 ture in the field, and again centre the lamp flame, and be 
 careful that it corresponds with the axis of the pupil of 
 the eye. 
 
 " Should we wish to examine hairs, scales, or morbid 
 structures, use No. 3, 4, or 5 apertures of the wheel of 
 diaphragms without a stop, the Jth, i^th, i^th, o^th, or 
 objectr-glasses, and the A, B, or C eye-piece as 
 
 /ig. 36. Powell and Lealand's Microscope arranged for LolVs illumination. 
 A. Secondary Stage carrying Achromatic Condenser. 
 
 thought proper ; now bring the object into focus, and by 
 racking up the condenser for the best light, very clear 
 and satisfactory definition will be obtained. Nothing 
 more is required when examining these objects than the 
 selection of the most suitable aperture, and focussing the 
 condenser for the illumination which defiles the best; too 
 much and too little light being equally bad. 
 
 " If we wish to examine objects such as Plnirosigma 
 
SEMINATION OF TEST-OBJECTS. 63 
 
 foiinosum, P. quadratum, P. angulatum, and their allies, 
 bring No. 11 aperture in the field, rack up the con- 
 denser until the field is very bright, then put on No. 1 
 stop, and rack up the condenser until the stop disappears : 
 if the desired effect be not obtained, try No. 2 stop ; the 
 condenser will then require to be racked up stiil higher, 
 and the dots will come out easily. To examine Navicula 
 cuspidatum, A T . rhomboides, Pleurosigma fasciola, Pluero- 
 ttigma macrum, &c., still use No. 11 aperture, and stop 
 No. 2, which will require a slight alteration in position 
 only, when the checks will appear distinctly. 
 
 " For the Amician test use the slots instead of No. 2 
 ctop ; and for very difficult lines, such as those of the 
 Acus, the condenser must be so arranged (when focussed 
 up till the field becomes exceedingly bright) that a shades 
 is thrown on the object from the left hand, and No. 1 
 and No. 2 stop used, so as to darken a little the right 
 hand side of the field. The |-th and ^th object-glasses 
 are generally found the best suited for the Acus with the 
 B eye-piece ; in fact, the B eye-piece is mostly to be pre- 
 ferred with high powers." 
 
 In short, the whole requires perfect centering as well 
 as careful illumination, and the condenser used must 
 have a wide aperture : we have found Collins's answer 
 exceedingly well, and with it we have brought out the 
 markings on the P. fasciola, JV. Acus, &c. 
 
 When employing high powers for viewing test, or 
 indeed any objects, only that part which is exactly in 
 focus can be perfectly seen at one time ; and even a very 
 slight turn of the fine adjustment, or " slow motion," often 
 causes a totally different set of appearances to present 
 themselves. It is desirable during our examination to 
 keep the finger on the slow motion, and thus bring into 
 view different parts or thicknesses of an object, so that in 
 the most careful manner layers or sets of vessels may be 
 seen and continuously traced. A clearer idea of the 
 nature of a doubtful structure is in this way obtained, 
 while we are in the act, as it were, of changing the focus. 
 "When different structural features present themselves on 
 different planes, it is often a most difficult task to deter- 
 mine which of them is the nearer. This may be regarded 
 
64 THE MICROSCOPE. 
 
 as a result inherent in our mode of viewing objects by 
 transmitted light ; nevertheless . it is often productive of 
 serious embarrassment when we are dealing with the 
 almost inappreciable markings on the siliceous diatoms, &c. 
 The following general rule is given by Mr. Wenham 
 (Quart. Journ. Micros. Scien. 1854, p. 138) for securing 
 the most efficient performance of an object-glass with any 
 ordinary object : " Select any dark speck or opaque por- 
 tion of the object, and bring the outline into perfect 
 focus ) then lay the finger on the milled head of the fine 
 adjustment, and move it briskly backwards and forwards 
 in both directions from the first position. Observe the 
 expansion of the dark outline of the object, both when 
 within and when without the focus. If the greater ex- 
 pansion, or coma, be when the object is without the focus, 
 or farther from the objective, the lenses must be placed 
 farther asunder, or towards the mark ' uncovered.' If 
 the greater coma be when the object is within the focus, 
 or nearer to the objective, the lenses must be brought 
 closer together, or towards the mark * covered.' When 
 the object-glass is in proper adjustment, the expansion of 
 the outline is exactly the same both within and without 
 the focus. A different indication, however, is afforded by 
 such test-objects as present (like the Podura-scale, the 
 Diatoms, &c.) a set of distinct dots or other markings. 
 For if the dots have a tendency to run into lines when the 
 object is without the focus, the glasses must be brought 
 closer together ; on the contrary, if the lines appear when 
 the object is within the focal point, the glasses must be 
 further separated." Mr. Wenham remarks upon the dif- 
 ficulty of accurately making this adjustment even in the 
 best made objectives. 
 
 Mr. E. Beck, in a paper contributed to the proceedings 
 of the Eoyal Microscopical Society, directs particular 
 attention to avoidance of errors of interpretation. Viewing 
 objects by transmitted light, he observes, is a method 
 peculiar to the microscopist ; it is, however, one to which 
 our vision, applied in the ordinary way, is so much un- 
 accustomed, that in many instances it not only conveys 
 imperfect notions of an object, but produces appearances 
 \ hich bear little or no resemblance to the true stnirturo 
 
ERRORS OP INTERPRETATION. 
 
 65 
 
 of the object. An instance of this is furnished in an 
 examination of the scales of Lepisma saccharina. 
 
 " Upon the more abundant scales the most prominent 
 markings appear as a series of double lines, which run 
 parallel and at considerable intervals from end to end of 
 the scale, whilst other lines, generally much fainter, 
 radiate from the quill, and take the same direction as the 
 outline of the scale when near the fixed or quill end ; 
 but there is, in addition, an interrupted appearance at the 
 sides of the scale which is very different from the mere 
 union, or ' cross-hatchings,' of the two sets of lines." 
 (Fig. 37, Nos. 1 and 2, the upper portions.) 
 
 Fig. 37. Portions of Scales of Lepisma, after Beck. 
 
 The scales themselves are formed of some truly trans- 
 parent substance, for water instantly and almost entirely 
 obliterates their markings, but they reappear unaltered as 
 the moisture leaves them ; therefore the fact of their being 
 visible at all, under any circumstances, is due to the refrac- 
 tion of light by superficial irregularities, and the following 
 experiment establishes this fact, whilst it determines nt 
 time the structure of each side of the scale, a 
 
66 THE MICROSCOPE. 
 
 matter which it is impossible to do from the appearance of 
 the markings in their unaltered state : 
 
 " Eemove some of the scales by pressing a clean and dry 
 slide against the body of the insect, and cover them with 
 a piece of thin glass, which may be prevented from moving 
 by a little paste at each corner. No. 3 may then be taken 
 as an exaggerated section of the various parts. AB is the 
 glass slide, with a scale, (7, closely adherent to it, and D 
 the thin glass cover. If a very small drop of water be 
 placed at the edge of the thin glass, it will run under by 
 capillary attraction ; but when it reaches the scale, (7, it 
 will run first between it and the glass slide A B, because 
 the attraction there will be greater, and consequently the 
 markings on that side of the scale which is in contact with 
 the slide will be obliterated, while those on the other side 
 will, for some time at least, remain unaltered : when such 
 is the case, the strongly marked vertical lines disappear, 
 and the radiating ones become continuous. (See No. 1, 
 the lower left hand portion.) To try the same experiment 
 with the other, or inner surface of the scales, it is only 
 requisite to transfer them, by pressing the first piece of 
 glass, by which they were taken from the insect, upon 
 another piece, and then the same process as before may be 
 repeated with the scales that have adhered to the second 
 slide ; the radiating lines will now disappear, and the ver- 
 tical ones become continuous. (See No. 2, left portion.) 
 These results, therefore, show that the interrupted appear- 
 ance is produced by two sets of uninterrupted lines on 
 different surfaces, the lines in each instance being caused 
 by corrugations or folds on the external surfaces of the 
 scales. Nos. 1 and 2 are parts of a camera lucida drawing 
 of a scale which happened to have the opposite surfaces 
 obliterated in different parts. No. 4 shows parts of a 
 small scale in a dry and natural state ; at the upper part 
 the interrupted appearance is not much unlike that seen 
 at the sides of the larger scales, but lower down, where 
 lines of equal strength cross nearly at right angles, the 
 lines are entirely lost in a seriee of dots, and exactly the 
 same appearance is shown in No. 5 to be produced by two 
 scales at a part where they overlie each other, altnough 
 each one separately shows only parallel vertical lines." 
 
ERRORS OF INTERPRETATION. 67 
 
 Another very characteristic fallacy resulting from con- 
 figuration is furnished in the supposed tubular structure 
 of human hair. When we view this object by transmitted 
 light, it presents the appearance of a darkish flattened 
 band down the centre ; this, however, is entirely due to 
 the convergence of the rays of light produced by the 
 convexity of the surface of the hair. That it is a solid 
 structure is proved by making a transverse section of the 
 hair-shaft, when it is seen filled up with medullary sub- 
 stance, with the centre somewhat darker than the other 
 part. It is, in fact, a spiral outgrowth of epithelial scales, 
 overlapping each other like tiles on a house-top, and this 
 gives a striated appearance to the surface. A cylindrical 
 thread of glass in balsam appears as a flattened, band-like 
 streak, of little brilliancy. Another instance of fallacy 
 arising from diversity in the refractive power of the in- 
 ternal parts of an object, is furnished by the mistakes for- 
 merly made with regard to the true character of the lacunae 
 and canaliculi of bone-structure, which were long mis- 
 taken for solid corpuscles, with radiating opaque filaments 
 proceeding from a dense centre ; we now know them to 
 be minute chambers, with diverging passages, excavated in 
 the solid osseous substance. That such is truly the case, 
 is shown by the effects of Canada balsam : as this infil- 
 trates the osseous substance, and fills up the excavations, 
 it quite obliterates the bone corpuscles. 
 
 The molecular movements of finely divided particles, 
 seen in nearly all cases when certain objects are first 
 suspended in water, or other fluids, is often a source of 
 embarrassment to beginners. If a minute portion of 
 indigo or carmine be rubbed up with a little water, and 
 a drop placed on a glass slide under the microscope, it will 
 at once exhibit this peculiar perpetual motion appearance. 
 This movement was first observed in the granular particles 
 seen among the pollen grains of plants, known as fovilla, 
 which are set free when the pollen is crushed. Important 
 vital endowments were formerly attributed to these par- 
 ticles, but Dr. Robert Brown showed such granules were 
 common enough both in organic and inorganic substances, 
 and therefore they were in noway particularly "indicative 
 of life." We must especially notice another point which 
 f2 
 
68 THE MICROSCOPE. 
 
 is a common cause of annoyance, as well as a source of 
 embarrassment, to the microscopist, the disturbance pro- 
 duced by the passage of light through transparent bodies ; 
 this greatly impairs the sharpness of outline, and is caused 
 by what is called the inflection or diffraction of light. 
 
 If a divergent pencil of light fall upon any opaque 
 object placed between the light and a screen, it is evident 
 that a shadow will be cast upon the screen : from our 
 previous observation that light always moves in straight 
 lines, we should expect to find that the image would be 
 clear, sharp, and well-defined ; but we know from experi- 
 ment that this is not so, and that there will be no exact 
 margin between the strongly illuminated part outside, and 
 that part of the screen which is covered by the object, but 
 there will be more or less of a shading off at the edges of 
 the image. 
 
 From this it is inferred that the rays of light which 
 pass the edges of the opaque object do not proceed in the 
 same straight lines in which they would have proceeded if 
 the object had not been present. This effect is called in- 
 flection or diffraction, and is a consequence of the general 
 property of undulation. When any system of waves meets 
 with an obstacle, subsidiary systems of undulation will be 
 formed round the extremities of the obstacle, and will be 
 propagated from those points independently of, and simul- 
 taneously with, the original system of waves. And for a 
 certain space around the lines in which the rays, grazing 
 the edge of the opaque body, would have proceeded, the 
 two systems of undulation will intersect and produce the 
 phenomena of interference. 
 
 If the opaque body be very small, and the distance 
 from the luminous point very large in proportion, the two 
 pencils formed by inflection will intersect, and all the 
 phenomena of interference will ensue. Thus, if the light 
 be homogeneous, a bright line of light will be formed 
 under the centre of the opaque object, outside of which 
 will be dark lines, and then bright and dark lines alter- 
 nately. If the light be compound solar light, a series of 
 coloured fringes will be formed. The following is a very 
 good illustration of how errors of interpretation may 
 easily arise. If a small sphere formed of any opaque sub- 
 
DIFFRACTION SHADOW. 69 
 
 stance be suspended in a dark room, and a pencil of homo- 
 geneous light be allowed to fall upon it, so that its shadow 
 may be received on a screen, it will be found that a bright 
 spot will appear in the middle of the shadow, outside of 
 which will be a dark circle, and beyond this a bright 
 circle, and so on, the circles corresponding successively 
 to the interference of the rays, by which their brilliancy 
 is either doubled or extinguished ; the colour of the bright 
 circles corresponds to that of the light. If common com- 
 pound light be used, the central spot will be white, and 
 will be surrounded by a series of coloured fringes. 
 
 No rule can be laid down for the avoidance of errors 
 such as we have been dwelling upon, but the practised 
 microscopist will, however, in time learn, almost as it were 
 instinctively, to overcome the difficulties of diffraction, as 
 well as those due to oblique illumination at certain angles, 
 particularly in that which results in the production of a 
 double image or overlying shadow, which we have seen 
 nearly as strongly marked as the real image. This kind 
 of shadow is sometimes called the "diffraction spectrum" 
 although it must be evident to anyone who will be at the 
 trouble to study the subject, that it is due to a different 
 cause. It cannot be denied that errors of interpretation 
 are not unfrequently due, as Mr. Brooke has shown, to 
 the increasing desire there is to produce object-glasses with 
 large angles of aperture. Mr. Brooke observes : " The 
 superiority in resolving power possessed by objectives of 
 large angular aperture is obtained at the expense of other 
 advantages." And Messrs. Sullivant and Wormley, in their 
 paper on " Nobert's Test-Plate and the Striae of Diatoms," 
 American Journal of Science, 1861, are convinced "that 
 when the resolving power of an objective is near its limit, 
 4 spectral ' or spurious lines are to be seen, and these are 
 only to be distinguished from the true by a practised eye.' 
 Hence they think " that the mere exhibition of lines is 
 not always conclusive evidence of their ultimate resolu- 
 tion." * For the same reason we have not the amount 
 of confidence in the higher powers that some observers 
 seem to have ; we know, indeed, with every increase in 
 this direction, how liable we are to encounter unforeseen 
 errors and exaggerations, and we still prefer the tn or 
 
70 THE MICROSCOPE. 
 
 J-inch of Ross, because we know its precise working and 
 defining power, and that most of the great achievements and 
 discoveries of the microscope have been made with powers 
 in no way superior to the last-mentioned J objective. The 
 many important contributions to microscopy by Owen, 
 Carpenter, Quekett, Ralfs, &c. have been made with 
 powers of limited capacity. 
 
 MECHANICAL ARRANGEMENTS. 
 
 Having explained the more important optical principles 
 of the achromatic compound microscope, it remains for 
 us to notice the mechanical and accessory arrangements 
 for giving these principles their full effect. In few philo- 
 sophical instruments is theoretical perfection so nearly 
 reached as in the microscope : in it the highest optical 
 skill is combined with the most consummate mechanical 
 contrivance, and the mechanism of the instrument is of 
 much more importance than might be imagined by those 
 who have not studied the subject. In the first place, steadi- 
 ness, or freedom from vibrations not equally communicated 
 to the object under examination, and to the object-glass or 
 lenses by which it is viewed, is a point of the utmost im- 
 portance. The various improvements which of late years 
 have combined to make the microscope the superior instru- 
 ment it is, may be classed under eight heads : 
 
 1. The circular rack, which is placed immediately under 
 the stage, and which is capable of carrying it round, in 
 some instruments, the entire revolution of a circle, is a 
 very convenient movement for altering the angle at A?hich 
 an object is viewed, without putting it out of field or focus; 
 it may also be used as a goniometer, for measuring crystals. 
 
 2. The clamping arc, peculiar to Eoss's microscopes, fixes 
 the microscope at any inclination, even after the suspension 
 joint has become supple by long use. 
 
 3. The advantage of the sub-stage for holding and ad- 
 justing, by universal motions, all the illuminating and 
 polarising apparatus placed beneath the object, can hardly 
 be overrated. 
 
 4. The dark-ground illuminator is an excellent contri- 
 vance by which a bright light is apparently thrown on 
 semi-opaque objects, though really coming benoath them, 
 
OPTICAL IMPROVEMENTS. 71 
 
 but so obliquely, that none of it enters the object-glass 
 but that which is interrupted by the object. 
 
 5. Mr. Brooke's double nose-piece, or Baker's treble, is 
 a useful piece of mechanism attached to the end of the 
 microscope body, by which two or three object-glasses 
 can be screwed on to it at once, and rapidly changed. 
 
 6. The double arm to the mirror allows it to be ex- 
 tended so as to cast a very oblique light on objects, as 
 well as to be raised near them without any preparatory 
 movement. 
 
 7. The separation of the outer and inner lenses of object- 
 glasses is an arrangement by which the greatest possible 
 flatness of field and penetration are secured. 
 
 8. The great and manifold advantages of the binocular 
 arrangement are very obvious ; objects stand out with 
 stereoscopic effect, and the ease to the eyes of the observer 
 is very great. When high powers are required, the prism 
 can be drawn aside, and the microscope used as a mon- 
 ocular instrument. 
 
 As regards recent optical improvements, Mr. Ross (the 
 elder), as we have already explained (page 40), was the 
 first to notice that however perfect the correction of an 
 object-glass might be, " the circumstance of covering the 
 object with a piece of the thinnest glass or talc, disturbed 
 the corrections if they had been adapted to an uncovered 
 object, and rendered an object-glass which was perfect 
 under one condition, seriously defective under the other." 
 To remedy this defect, he devised the well-known contri- 
 vance called the adjustment of object-glasses, by which 
 they are rendered equally correct for covered or uncovered 
 objects 
 
 The following diagrams (fig. 38) of the different object- 
 glasses will help to explain the complex structure, and 
 consequent costliness, of an achromatic combination. The 
 double-convex and plano-convex lenses are of crown glass, 
 and the piano- and double-concave, and meniscus lenses, 
 of flint glass. 
 
 It will be seen, therefore, that each of the object-glasses 
 from the J to the ^V, is made up of as many as eight dis- 
 tinct lenses, the back combination being a triplet composed 
 of two double-convex lenses o'f crown, with a double- 
 
72 
 
 THE MICROSCv-PK 
 
 concave lens of flint glass between them, the intermediate 
 combination being a doublet composed of a double-convex 
 lens of crown glass with a double-concave of flint, glass ; 
 and the front combination being another triplet composed 
 of two plano-convex lenses of crown, and a plano-concave 
 lens of flint glass between them. This will also explain 
 the composition of the shallower object-glasses ; the dis- 
 tance between the different combinations throughout all 
 the objectives, and their size, depending on the amount of 
 magnifying power required. It may be briefly stated that 
 the principal qualities to be looked for in an object-glass 
 
 Fig. 38. Forms of Object-glasses. 
 
 A, Double-convex lens ; B, Plano-concave ; C, Bi-convex ana plano-concave, 
 united : shown in their various combinations, as at D, form the 3-in. 2-iu. or 
 l^-in. ; at E, 1-in. and f-in. ; and at F, the |-in. ^ -in. J-in. and ^-in. ob- 
 jectives. 
 
 are, 1st, Resolution, or the power of showing clearly minuU 
 details, which is chiefly effected by increase of light ad- 
 mitted through the objective, by what is termed angular 
 aperture; 2d, Penetration, or that power which enables 
 the observer to see deep into the structure of objects with- 
 out any alteration of focus ; 3d, Definition, or the capa- 
 bilities of an objective for showing the various details of 
 an object, especially its boundaries, with the most perfect 
 and exquisite sharpness ; 4th, Flatness of field, or marginal 
 and central definition, which, denotes the exact capability 
 
OPTICAL IMPROVEMENTS. 73 
 
 of the objective to show the peripheral or marginal por- 
 tions of the field with the same sharpness as the central 1 
 
 A considerable accession of available power has been 
 effected by both Foreign and English manufacturers since 
 the appearance of the third edition of our book, 1859. In 
 those by continental makers, this has been achieved by 
 the intervention of a third medium between the external 
 surface of the objective, and the covering glass of the 
 object. We may particularize those of M. Hartnack 
 Oberhauser's successor, as being most conspicuous ; but 
 the objective, which is said to be superior to all yet manu- 
 factured, is the -fath of an inch of Powell and Lealand, 
 who, some time before, produced good objectives of ^th 
 and s^th of an inch focus. In these object-glasses, exces- 
 sive angular aperture has been judiciously sacrificed to a 
 more comprehensive and practical utility. It should be 
 stated, however, that the priority of construction of an 
 effective ^th objective is due to Mr. Wenham, to whom 
 the microscope was largely indebted before he made this 
 glass in 1856. It was constructed on a principle differing 
 from that usually adopted in the high powers, in having a 
 single front lens. A single anterior lens transmits more 
 light, gives clearer definition, with any required extent of 
 aperture ; from its simplicity, it is comparatively freer 
 from errors of workmanship, and the chromatic and 
 spherical aberrations can be more perfectly corrected. 
 Mr. Wenham says, "that such object-glasses will chal- 
 lenge comparison with the best made and more expensive 
 forms." 
 
 Dr. Beale's account of the performance of the ^&th is, 
 that it is even better than the ^th inch. Plenty of light 
 for illuminating the objects to be examined is obtained by 
 the use of a condenser provided with a thin cap, having an 
 opening of not more than ^yth inch in diameter. The 
 objects should be covered with the thinnest glass, or with 
 mica, and then there is room to focus to the lower surface 
 of very thin specimens, which can alone be examined by 
 such high powers. Particular attention is drawn to these 
 very high powers, because the statements recently made in 
 
 (1) See an excellent paper by J. Plumer, Esq. "On the Choice of a Micro- 
 Scope." Micros. Jmtm. vol. UL p. 153. 
 
74 THE MICROSCOPE. 
 
 favour of the spontaneous generation theory, may pro- 
 bably be studied with some advantage. Not only are the 
 minuter atoms too small to be studied by the T ^th or i^th, 
 but particles too transparent to be observed by the ^tli 
 are, according to Dr. Beale, distinctly demonstrated by 
 the ^jjth ; he observes, " I feel sure that further careful 
 study, by the aid of these high powers, of the develop- 
 ment and increase of some of the lowest organisms, and 
 the movements which have been seen to occur in certain 
 forms of living matter (amoeba, white blood-corpuscles, 
 young epithelial cells, &e.), will lead to most valuable 
 results, bearing upon the much debated question of vital 
 actions. 
 
 " The most delicate constituent of the nerve-fibres of 
 the plexus in the summit of the papilla (see Phil. 2 J rans 
 for 1864) can be readily traced by the aid of this power. 
 The finest nerve-fibres thus rendered visible, are so thin, 
 that in a drawing they would be represented by fine 
 single lines. Near the summit of the papilla there is a 
 very intricate interlacement of nerve-fibres, which, although 
 scarcely brought out by the ^g-th, is very clearly demon- 
 strated by this power. In this object, the separation of 
 the fibres, as they ramify in various places, one behind 
 anothei > is remarkable, and the flat appearance of tbe 
 specimen as seen by the aVth gives place to that of con- 
 siderable depth of tissue and perspective. Tbe finest 
 nerve-fibres, ramifying in the cornea of the eye, and in 
 certain forms of connective tissue, are beautifully brought 
 out ; and their relation to the delicate processes from the 
 connective-tissue corpuscles can be more satisfactorily 
 demonstrated than by the ^th. The advantage of the 
 g\jth in such investigations seems mainly due to its re- 
 markable power of penetration." 
 
 The one great drawback to the use of this objective, 
 and a very serious one to most microscopists, is its costli- 
 ness. The price of this power alone is almost more than 
 many can afford to give for a complete instrument. 
 
 In flatness of field, and in perfection of definition, both 
 at the centre and margin of the field of view, few objec- 
 tives have equalled the recent T Vth of Mr. Eoss, who 
 appears to have inherited his late lather's Avell-known skill 
 
PENETRATING POWER. 75 
 
 in all that appertains to the microscope. Mr. .Baker has 
 also made considerable advances in the same direction: 
 his objectives have been made with a greater angle of 
 aperture than formerly, and with more penetration. Much 
 misconception, however, exists with regard to the available 
 angle of aperture for optical requirements ; it will be as 
 well to remark that an admirable method of determining 
 this was proposed by Professor Govin, of Turin, which 
 consists in placing the microscope perpendicularly to any 
 plane dark non-reflecting surface (as a table covered with 
 a green cloth), and having converted the instrument into 
 a telescope, by placing above the eye-piece a suitable com- 
 bination of two lenses (such as the Examining- Glass of 
 Mr. Ross), and then examining and marking the greatest 
 lateral distance on either side at which a clear image of 
 some distinct object, such as a narrow strip of white card- 
 board or paper, laid on the table can be perceived. " Half 
 the distance between these two points, divided by the ver- 
 tical distance of the focal point of the objective from the 
 surface of the table, will, by reference to a table of natural 
 tangents, give half the required angle of aperture. This 
 will, in many cases, be found to be considerably less than 
 what may be termed the angle of admission of diffused 
 light. To illustrate this, supposing the focal point to be 
 at a distance of O'Ol inch from the surface of the objective, 
 a reference to a table of natural tangents will show that an 
 angular aperture of 17 will necessitate a linear aperture of 
 0'22 inch : an aperture of 170 will require O28 inch, and 
 one of 174, of 0'38 inch, in order to admit the extreme 
 rays, which, for objectives of ^th inch focus, is manifestly 
 impossible." 
 
 In regard to angle of aperture, it may be stated once 
 and for all, that large angle of aperture is necessarily 
 incompatible with that far more generally useful quality 
 of penetration. Penetrating power J is synonymous with 
 
 (1) Penetrating Power. " The origin of this tenn will be found in the Phil. 
 Trans, for 1SOO, in an article by Sir Wm. HerecLel, entitled ' On tlie Power of 
 Penetration into space possessed by Telescopes.' In that article, we are told 
 that when, owing to the darkness, a distant church steeple was invisible, a certain 
 telescope described, clearly showed the time upon the clock. This, adds Sir 
 William, was not owing to magnifying power alone, for the steeple could not be 
 discerned by the naked eye. Ana he has shown in the same article, that the 
 
76 THE MICROSCOPE. 
 
 depth of focus, that is, extreme distance of two planes, the 
 points of which are at the same time sufficiently in focus 
 for the purpose of distinct vision. This distance will 
 manifestly increase as the angle of aperture diminishes, 
 just as in a landscape camera the fore and back grounds 
 can be brought into sensible focus simultaneously only by 
 the use of a small diaphragm, which greatly diminishes 
 the angular aperture of the incident peneils. But, at the 
 same time, it must be borne in mind, that illumination, 
 cceteris paribus, increases or diminishes with angle of 
 aperture, and the best working glass will be that in which 
 a compromise is effected between these two conflicting 
 requisites. 
 
 We entirely agree with Mr. Brooke, that "for all practical 
 purposes, except developing the markings of diatoms, an 
 objective of moderate aperture will be found most available. 
 It may reasonably be doubted whether the development of 
 the dottings of difficult diatoms is not an object rather of 
 curiosity than of utility, and whether it is worth the labour 
 that has been bestowed upon the production of glasses for 
 that especial purpose ; the labour of construction being 
 immensely augmented by the difficulty of duly balancing 
 the aberrations of the more oblique pencils. So much is 
 this the case, that in the best constructed objectives of the 
 
 words 'penetrating power' have a definite meaning, and that the amount of 
 this power possessed by a telescope, can be obtained by calciilation. And of 
 course, this must also be true of a microscope. This power, says Mr. Ryland, 
 in a very interesting paper, must not be confused with angular aperture, which 
 has reference to the objective alone ; neither has it any connexion with either 
 definition or thickness of field. In a word, as magnifying power expresses the 
 angle subtended by an object or image at the eye of the observer, so penetrative 
 power is the measure of the angle subtended by the eye at the object, or the 
 equivalent of that angle in the case of telescopic or microscopic vision. The 
 one is the measure of size, the other of brightness. The latter, however, must 
 not be confused with ' illumination.' The one power is neither less important 
 nor less essential to distinct vision than the other. There required little mag- 
 nifying power, and there was no illumination, in the case of the church steeple, 
 still the hour could be read on the dial." 
 
 The third power, the visual power of microscopes, is one which has rarely 
 been recognised as distinct. 
 
 For an object to be magnified 100 times, that is &oen at 100th part of the 
 distance, it is necessary not only that the angle subtended by it at the eye the 
 magnifying power but also the angle subtended by the eye at the object the 
 penetrating power shall be increased one hundred-fold. When this is the case, 
 the visual power will be 100 also. 
 
 If we approach an object bodily, these angles naturally increase in the same 
 
 Eroportion, but it is not so where optical instruments are employed. R. G. 
 ylaad " On the Optical Powers of the Microscope." Micros. Jour. Science, 
 voL vii. p. 27. 
 
MAGNIFYING POWER. 77 
 
 largest angles, the visual effect is sensibly impaired when 
 the rays are transmitted through any other thickness of 
 covering-glass than that for which they have been specially 
 corrected." 
 
 The value of penetrating power is especially felt when 
 the binocular arrangement is employed, since the assistance 
 which it is able to give in the estimation of the solid 
 forms of objects, is altogether neutralized by the employ- 
 ment cf objectives of such wide angular aperture as not to 
 show any part of the object, save what is precisely in 
 focus; and, therefore, there cannot be a doubt of the supe- 
 rior value of objectives of a moderate angle of aperture 
 for ordinary working purposes. 
 
 " Successful observation, with very high power, is 
 mainly dependent upon illumination. Indeed, by ordinary 
 means, it is not possible to obtain a light sufficiently in- 
 tense to illustrate an object magnified 3,000 diameters. 
 I have tried various plans, and have come to the conclu- 
 sion, that the most satisfactory results are obtained by the 
 use of Reiner's eye-piece as a condenser. By this means I 
 ^an obtain a light sufficient for a magnifying power of 
 10,000 linear. 
 
 " My method of increasing the size of the image, with- 
 out altering the object-glass, is as follows : 
 
 " Supposing the limits of magnifying power of the 
 object-glass to have been reached, I then increase the 
 distance between it and the eye-piece, by lengthening the 
 body by the aid of a draw-tube. The ^th objective 
 being applied when the tube is increased in length, so 
 that from the lowest glass of the object-glass to the eye- 
 glass of eye-piece, the distance measures 24 inches, the 
 magnifying power corresponds to upwards of 10,000 dia- 
 meters, 20 inches about 6,000, 15 inches about 2,600, 11 
 inches about 1,800. 
 
 " If there is any reflection from the interior of the tube 
 which renders the image indistinct, let the tube be lined 
 with black velvet ; of course the practical utility of in- 
 creasing the magnifying power entirely depends upon the 
 character of the specimen, and the preparations best. 
 suited for examination by very high powers must be im- 
 mersed in the strongest glycerine that can be procured. 
 
78 THE MICROSCOPE. 
 
 In this way, I have been able to see points which I have 
 failed to bring out in any other way." 1 
 
 Magnifying power, as we have already explained, has to 
 do with size only, and only expresses the magnitude of the 
 angle subtended by the enlarged image, at the eye, as com- 
 pared with that subtended by the object itself under the 
 circumstances of ordinary standard vision; namely, at a 
 distance of ten inches from the eye. 
 
 The Kelner eye-piece, while it increases the magnifica- 
 tion, detracts from the definition ; on this account, it is 
 only used when desirous to show the whole of an object 
 at once, as an insect, or in viewing the series of rings 
 formed by different crystals with polarized light. This 
 differs from the ordinary Huyghenian eye-piece in having 
 a double-convex field-glass, and an achromatic meniscus 
 eye-glass. 
 
 COMPOUND MICROSCOPES. 
 
 It should be understood that the descriptions we are 
 about to give of Compound Microscopes cannot embrace 
 that of every manufacturer. Want of space forbids this, 
 and therefore we particularly wish to disclaim any inten- 
 tion of instituting invidious comparisons ; our desire is 
 solely that of giving, as concisely as possible, a description 
 of those instruments that have more immediately fallen 
 under our notice, or have been the companions of our 
 microscopical pursuits. At the head of our list stands 
 
 Ross's microscope, an instrument of which the aim is 
 not simplicity, but perfection not the production of the 
 best effect compatible with limited means, but the attain- 
 ment of everything that the microscope can accomplish, 
 without regard to cost or complexity. Without any un- 
 due preference, the first place may fairly be assigned to 
 this large Compound Microscope of Mr. Eoss, as the one 
 which was earliest brought (in all essential features, at 
 least) to its present form. The general plan of Mr. Ross's 
 microscope will be seen to be essentially that which has 
 been adopted in a simpler form by many other makers ; 
 but it is carried out with the greatest attention to solidity 
 
 (1) Beale, " How to Work with the Microscope.- 
 
BOSS S MICROSCOPE. 
 
 79 
 
 of construction, in those parts especially which are most 
 liable to tremor, and to the due balancing of the weight 
 of the different parts upon the horizontal axis. The 
 " coarse " adjustment is made by the large milled-head 
 
 Fig. 39. Ross's No. la Large Microscope, with Binocular arrangement and 
 
 Object-glass. Scale $. 
 B. Sub-stage of ditto, with new Achromatic Condenser. Scale J. 
 
 situated just behind the summit of the uprights, which 
 turns a pinion working into a rack cut on the back of a 
 very strong flattened stem, that carries the transverse arm 
 at ita summit A second inilled-head (which is here coil- 
 
80 THE MICROSCOPE. 
 
 cealed by the stage-fittings) is attached to the other end of 
 the axis of the pinion (as in fig. 39), so as to be worked 
 with the left hand. The "fine" adjustment is effected by 
 the milled-head on the transverse arm, just behind the base 
 of the "body." This acts upon the "nose" ur tube pro- 
 jecting below the arm, wherein the objectives are screwed. 
 The other milled-head seen at the summit of the stem 
 serves to secure the transverse arm to this, and may be 
 tightened or slackened at pleasure, so as to regulate the 
 traversing movement of the arm. This movement is only 
 allowed to take place in one direction; namely, towards 
 the right side, being checked in the opposite by a " stop," 
 which secures the coincidence of the axis of the body with 
 the centre of the stage, and with the axis of the illu- 
 minating apparatus beneath it. It is in the movements 
 of the stage that the greatest contrivance is shown. These 
 are three ; namely, a traversing movement from side to 
 side, a traversing movement from before backwards, and 
 a rotatory movement. The traversing movements, which 
 allow the platform carrying the object to be shifted about 
 an inch in each direction, are effected by the two milled- 
 heads situated at the right of the stage; and these are 
 placed side by side, in such a position that one may be 
 conveniently acted on by the fore-finger, and the other by 
 the middle-finger, the thumb being readily passed from one 
 to the other. The traversing portion of the stage carries 
 the platform whereon the object is laid, which has a ledge 
 at the back for it to rest against ; and this platform has 
 a sliding movement of its own from before backwards, by 
 which the object is first brought near to the axis of the 
 microscope, its perfect adjustment being then obtained 
 by traversing movements. To this platform, and to the 
 traversing slides which carry it, a rotatory movement is 
 imparted by a milled-head placed underneath the stage 
 on the left-hand side ; for this milled-head turns a pinion 
 which works against the circular rack (seen in the figure), 
 whereby the whole apparatus above is carried round about 
 two-thirds of a revolution, without in the least disturbing 
 the place of the object, or removing it from the field of 
 the microscope. This rotatory movement is useful for twc 
 purposes first, in the examination of very delicate objects 
 
POWELL AND LEALAND*S MICROSCOPE. 81 
 
 by oblique light, in order that, without disturbing the 
 illuminating apparatus, the effect of the light and shadow 
 may be seen in every direction, whereby important addi- 
 tional information is often gained ; and, secondly, in the 
 examination of objects under polarized light a class of 
 appearances being produced by the rotation of the object 
 between the prisms, which is not developed by the rota- 
 tion of either of the prisms themselves. The graduation, 
 of the circular rack, moreover, enables it to be used as 
 a goniometer. In the improved form of this instrument 
 here represented, the whole stage-apparatus is made so 
 thin, and the opening beneath so large, as to permit the 
 employment of light of extreme obliquity ; and to enable 
 the mirror to afford this, it is mounted upon an extending 
 arm, the socket of which slides upon a cylindrical stem. 
 Below the stage, and in front of the stem that carries the 
 mirror, is a dovetail sliding-bar, which is moved up and 
 down by the milled-head shown at its side. This sliding- 
 bar carries what is termed by Mr. Eoss the "secondary 
 stage " (shown separately at B), which consists of a cylin- 
 drical tube for the reception of the achromatic condenser, 
 the polarizing prisms and other fittings as in Messrs. Powell 
 and Lealand's arrangement; it is here shown as fitted with 
 a condenser specially devised by Mr. T. Koss for the illu- 
 mination of a large field under low magnifying powers. 
 To this secondary stage, also, a rotatory motion is com- 
 municated by the turning of a milled-head ; and a tra- 
 versing movement of limited extent is likewise given to 
 it by means of two screws, one on the front and the other 
 on the left-hand side of the frame which carries it, in order 
 that its axis may be brought into perfect coincidence with 
 the axis of the " body." 
 
 The mechanical movements and general finish of the 
 instrument is all that can be desired by the practised 
 observer, and tends towards that saving of time and 
 labour as essential in microscopical pursuits as in other 
 branches of science. Although our description is confined 
 to Mr. Ross's h'rst-class microscope, other instruments 
 without the accessory arrangements described may be had 
 equally well made and suited to the means of the student, 
 ranging in prices from 121. 12*. upwards. 
 
 Q 
 
82 THE MICROSCOPE. 
 
 The general plan of Powell and Lealand's Compound 
 Microscope is represented in fig. 40. The tripod-stand 
 gives a firm support to the trunnions that carry the tube 
 to which the stage is attached, and from which a triangular 
 stem is raised by the rack-and-pinion movement set in 
 
 Fig. 40. Powell and Lm.iand's Mirrnscope, with Amid prism arranged 
 for oblique illumination. 
 
 action by the double-milled head, whereby the coarse ad- 
 justment of the focus is obtained. To the upper part of 
 the triangular bar a broad arm is fixed, bearing the com- 
 pound body ; this arm is hollow, and contains the mechanism 
 for the fine adjustment, which is effected by turning the 
 email milled-head. The arm is connected with the tri- 
 angular bar by a strong conical pin, on which it turns, so 
 that the compound body may be moved aside from the 
 stage when necessary ; by a mechanical arrangement it 
 
LADD'S MICROSCOPE. 83 
 
 stops when central. The stage is of an entirely new con- 
 struction, having vertical, horizontal, and circular move- 
 ments, and graduated for the purpose of registering objects 
 so as to be found at pleasure; and in order to do this 
 effectually a clamping piece is provided against which the 
 object slide rests, and the circular motion of the stage is 
 stopped. It is an exceedingly effectual method of finding 
 a favourite object The stage is remarkably strong, and 
 at the same time so thin, that the utmost obliquity of 
 illumination is attainable, the under portion being entirely 
 turned out : it has a dove-tailed sliding bar moveable 
 by rack and pinion; into this bar slides the under stage, 
 having vertical and horizontal motions for centering, and 
 also a circular motion ; into the stage are affixed the 
 various appliances for underneath illumination, removed 
 in our woodcut. Their achromatic condenser is of 170 
 aperture, with nine openings and five central stops. The 
 openings and stops having independent movements, the 
 manipulator can regulate these at will, which is admitted 
 to be an improvement. There is an especial appliance 
 provided for the use of a set of dark- wells, with or with- 
 out the condenser. The mirror is attached to a quadrant 
 of brass and two arms, in order to obtain greater obliquity 
 of illumination ; the whole fits into a short piece of tube 
 made to slide either up or down the long tube attached 
 to the bottom of the stage by which the mirror is con- 
 nected with the other part of the stand ; the reflectors 
 are both plane and concave, as in other instruments. 
 
 Powell and Lealand have another pattern, somewhat 
 resembling the instrument just described, but larger and 
 more massive in its general arrangements. The construc- 
 tion of the stage and sub- stage differ entirely : both of 
 these rest on a large solid brass ring, firmly attached to 
 the stem of the instrument. The upper side of this ring 
 bears a sort of carriage that supports the stage, and to 
 this carriage a rotatory motion is given by a milled-head, 
 the amount of the movement which may be carried through 
 an entire revolution being exactly measured by the gradua- 
 tion of a circle of gun-metal, which is borne on the upper 
 surface of the ring. The rotatory action of the stage being 
 thus effected beneath the traversing movement, the center- 
 o2 
 
84 THE MICROSCOPE. 
 
 ing of an object brought into the axis of the microscope 
 is not disturbed by it ; and the workmanship is so accurate 
 that the stage may be driven through its whole revolution 
 without throwing out of the field an object viewed with 
 the j^-th objective. The stage withal is made thin enough 
 to admit of the most oblique light being thrown on the 
 object, such as that obtained by the use of the Amici 
 prism, as shown arranged in the preceding figure. The 
 sub-stage is also provided with rotatory, rectangular, and 
 vertical movements, and is made in such a manner as to 
 admit of the simultaneous use of the polarising prism and 
 of the achromatic condenser. This instrument combines 
 remarkable steadiness with great solidity, and is so well 
 balanced on its horizontal axis that it requires no clamping 
 in whatever position it may be placed. 
 
 Cheaper instruments are furnished by Powell and Lea- 
 land, such as a student's microscope, with |-inch stage 
 movement, coarse and fine adjustments to body, plane and 
 concave mirrors, revolving diaphragm, Lister's dark-wells, 
 and two eye-pieces, for the price of SI. 
 
 An improved form of microscope (fig. 41) is manu- 
 factured by Mr. Ladd, of Beak Street, Eegent Street; 
 having a stand so simple and light in its construction as 
 to render it very portable and useful. It is fitted with a 
 magnetic stage, which facilitates the moving of the objects 
 when placed on it by the unaided fingers; a point of some 
 importance to such microscopists as desire to retain and 
 cultivate delicacy of touch in preference to that growing 
 dependence upon mechanical movements. The main 
 features of this form of microscope are, that the bear- 
 ings for the compound body, stage, and sub-stage are all 
 fitted, while connected together into the dovetailed brass 
 bar running from top to bottom of the instrument. The 
 magnet is attached to the under part of the stage, and a 
 gilt iron bar, ledge, or keeper, serves for an object-rest. 
 The sub-stage is constructed of three thin plates having 
 rectangular movements, the top one having a tube attached, 
 into which is fitted the Polariscope, spotted lens, &c., the 
 focussing of which is by a rack placed below. The mirror, 
 being provided with a double-jointed arm, can be used 
 with any amount of obliquity. The stand forms a tripod 
 
BAKER'S MICROSCOPE. 85 
 
 strengthened by cross bars ; the beanty of the chain move- 
 ment (with which all Mr. Ladd's microscopes are furnished 
 is made apparent by a simple and effective fine adjustmeL 
 
 Pig. 41. Ladd s Student* Microgcope. 
 
 attached to the milled head, thus making the one adjust- 
 ment subsidiary to both purposes. The general appearance 
 of the instrument is one of elegance, stability, lightness, 
 and compactness. 
 
 Mr. Baker (Holborn) has kept pace with our leading 
 manufacturers, and his first-class microscopes fairly entitle 
 him to take his place among the makers of superior in- 
 struments. One of his best forms, shown in fig. 42, 
 combines good workmanship with remarkable solidity and 
 completeness in all its details. 
 
 In this instrument, two uprights are strengthened by 
 two internal buttresses mounted on a solid tripod. At 
 the upper part, and between the uprights, is an axis upon 
 which the whole of the upper part of the instrument 
 turns, so as to enable it to take a horizontal, vertical, or 
 
86 
 
 THE MICROSCOPE. 
 
 any intermediate position such, for instance, as that 
 shown in the drawing. This moveable part is fixed to 
 the axis near the centre of gravity, and consists of the 
 stage and the arm screwed into the square bar which 
 
 Fig. 42. Baker's Ao. 1 'uuin^ouna Altcrusco^e. 
 
 carries the tube or body, with object-glass screwed into 
 its place. The upper or table-stage has rectangular rack- 
 and- pinion movements, working one inch in each direction. 
 A circular and sliding motion is also given to the top plate. 
 
BAKERS STUDENT'S. 
 
 87 
 
 The square bar, together with the arm and microscope- 
 tube, is moved by the larger milled-heads, and a more 
 
 Fig. 43. Baker' $ No. 2 Compound ificroicope. 
 
 delicate adjustment of this optical part is effected by the 
 smaller milled-head seen behind the body. This milled- 
 head is graduated, affording a means of measuring the 
 
88 
 
 THE MICROSCOPE. 
 
 thickness of an object or the thin covering-glass. The 
 other milled-head fixes the arm to the square bar. Below 
 the table-stage is the secondary or sub-stage, into which is 
 fitted the diaphragm, polariscope, achromatic condenser, 
 and other illuminating apparatus. It is supplied with 
 centering screws, circular and focussing rack-work, giving 
 perfect and accurate adjustments. Sliding upon the lower 
 end of the instrument is a large double mirror, with 
 double-jointed arm, and above this a full-size Amici prism 
 for oblique illumination. The microscope is furnished with 
 a draw-tube, divided into tenths of an inch, and is thus 
 rendered as perfect as is necessary for all purposes. 
 
 Fig. 43 represents Mr. Baker's smaller Compound 
 Microscope, differing in some respects from that just 
 
 Fig. 44. Baker's Educational Afimwcope. 
 
BAKER'S BINOCULAR. 
 
 89 
 
 described. It is not fitted with sub-stage, but such an 
 appliance may be readily attached, dovetailed grooves being 
 left for the purpose. The motions to stage and body, and 
 general finish, are similar to those of the best instruments, 
 and it is altogether such a microscope as can be well re- 
 commended for medical or other purposes where a good 
 stand is required, and to which it is intended that further 
 additions shall be hereafter made. 
 
 A smaller compound achromatic microscope, called the 
 " Educational," fig. 44, is made by Mr. Baker. This is 
 peculiarly adapted for students, and is supplied in a neat 
 mahogany case, with the necessary apparatus and excellent 
 object-glasses, for the small price of 41. 4s. If with iron 
 stand and in portable case, 31. 3s. 
 
 Mr. Baker, in his binocular instrument, fig. 46, has 
 succeeded in reducing some of the difficulties to a mini- 
 mum. The setting of the prism, with its necessary stops, 
 is so contrived that it is contained 
 in one piece or fitting, so that 
 when the monocular body is re- 
 quired to be used, this piece can 
 be removed, and an uninterrupted 
 field obtained, the light enter- 
 ing the tube at the utmost obli- 
 quity for high powers. At fig. 45, 
 the body and nose-piece is seen de- 
 tached. It has this advantage, 
 that the prism remains in perma- 
 nent adjustment when the brass 
 nose-piece B is screwed home. 
 
 Another feature in connexion 
 with the use of the binocular, 
 and not the least important, is 
 that of illumination ; we have 
 been much pleased with the sim- 
 
 pie arrangement of a cheap con- 
 denser by the Same optician. It 
 
 consist? of two plano-convex lenses, the lower one being 
 hemispherical ; the upper lens (of a Bomewhat smaller 
 diameter) is placed just within its focus ; the two are 
 fitted into a sliding-tube which admits of easy adjustment 
 
 A. Bodies detached Jrom Stand. 
 * Hose-piece containing Pria*. 
 
90 
 
 THE MICROSCOPE. 
 
 This condenser has the property of throwing a soft 
 white-cloud with low powers, adding greatly to the defini- 
 tion and stereoscopic effect of the binocular ; it is moreover 
 useful in giving a full, clear field with the higher powers. 
 
 Fig. 46. Baker's Student's Binocular Microscope. 
 
 We can also refer with some confidence to the Student's 
 Binocular Microscope produced by Mr. Baker; it pos- 
 sesses remarkable excellence for the small sum charged 
 for it. This instrument is rather larger than the Educa- 
 tional by the same maker, and is fitted with sliding-stage. 
 It has the usual coarse and fine movements, and is supplied 
 
PILLISCHER'S MICROSCOPE. 91 
 
 with a double mirror and one pair of eye-pkces, the latter 
 having rack and pinion adjustment. It is seen in fig. 46, 
 and sold as there represented for 6/. a less sum than is 
 charged for altering the larger microscopes. 
 
 Fig. i7.-FiUi$chr'i No. 1 Binocular Microtoopt. 
 
92 THE MICROSCOPE. 
 
 Mr. Pillischer (New Bond Street) is favourably known 
 for the excellency of his instruments. His No. 1 Micro- 
 scope (fig. 47) is of good workmanship, and somewhat 
 novel in design. It is constructed on a plan which may 
 be described as intermediate between that of Smith and 
 Beck and Ross's well-known pattern, and in point of 
 finish is quite equal to the microscopes of the first- 
 mentioned manufacturers. The bent form given to the 
 arm carrying the body gives increased strength and soli- 
 dity to the instrument, although it is doubtful whether 
 it adds to its steadiness when placed in the horizontal 
 position. The straight body rests for a great part of its 
 length upon a straight bar of solid brass, ploughed into 
 a groove for the reception of the rack which is attached 
 to the body, the groove being of such a form that the rack 
 is held firmly while it glides smoothly through it. This 
 is so firm, and gives such a steady uniform motion, as 
 almost to render the fine adjustment unnecessary. The 
 fine adjustment screw is removed from the usual position 
 and placed in front of the body, just above and in front 
 of the Wenham prism. The binocular bodies are inclined 
 at a smaller angle to one another than in most makers, 
 which, with the range of motion given to the eye-pieces 
 by the rack and pinion, enables observers whose eyes 
 differ greatly in separation to use the instrument with 
 equal facility. The prism is so well set that it illuminates 
 both fields with equal intensity. The stage is provided 
 with rectangular traversing movements to the extent of 
 an inch and a quarter in each direction. The niilled-heads 
 which effect these are placed on the same axis, instead of 
 side by side, one of them the vertical one being re- 
 peated on the left of the stage, so that the movements 
 may be communicated either by the right hand alone or 
 by both hands acting in concert. The stage-plate has the 
 ordinary vertical and rotatory motions, but to a much 
 greater extent than usual ; and the platform which carries 
 the object is provided with a spring clip to secure the 
 object when the stage is placed in the vertical position. 
 A regularly fitted sub-stage with centering screws is made 
 in the usual way to carry an achromatic condenser, dia- 
 phragm, polarising, and other apparatus in short, no 
 
PILLISCHER'S STUDENT'S. 93 
 
 instrument can be better adapted than this to all the 
 ordinary wants of the pathologist or skilled microscopist. 
 The object-glasses furnished with this instrument are 
 thoroughly good working powers-. 
 
 Fiy. 43. Pillischei's larger Students Microscope. 
 
 Fig. 48 is a compound microscope, made by Mr. Pilli- 
 scher for the use of students. In every respect it is 
 a compact, handy instrument, and well finished in its 
 mechanical details. The body is furnished with a draw- 
 tube, by which its length can be increased about six 
 
94 THE MICROSCOPE. 
 
 inches ; coarse and fine adjustments ; moveable mecha- 
 nical stage as in the larger instrument ; two eye-pieces ; 
 superior objectives of 1 inch and ^-inch focus, of 15 and 
 80 angular aperture ; condenser, polarising apparatus and 
 selenite, parabolic reflector, diaphragm, &c., packed in a 
 mahogany case, for the price of 151. 1 5s. This instru- 
 ment takes its place among the best of its class. 
 
 Fig. 49. PMischer's 5i. Prize Medal Microscope. 
 
 The instrument fig. 49 Mr. Pillischer designates his 
 51. Prize Medal Microscope, is an excellent student's in- 
 strument, simple and novel in its construction, and well 
 adapted to almost any description of work. The body is 
 furnished with a draw- tube and fine adjustment ; the arm 
 which supports this derives additional steadiness from the 
 square solid form given to the box in which the rack and 
 pinion move. A convenient and simple lever-stage, with 
 a double joint, enables the right hand to move the object 
 
OOLLINS'S BINOCULAR. 95 
 
 in any direction with great facility. This can be readily 
 detached when it is desired to clear the stage for a frog- 
 plate, &c. The instrument is furnished with a dividing 
 set of powers, working with a tolerably flat-field ; dia- 
 phragm, condenser for opaque objects, live box, &c. The 
 whole packs in a neat case, measuring only 8x6 inches ; 
 forming one of the most portable microscopes for the use 
 of the student we have seen. 
 
 The Binocular manufactured by Mr. Collins (Great Titch- 
 field Street, Portland Place), is constructed on the model 
 suggested by Dr. Harley, and contains all the recent im- 
 provements for combining rapidity of application with 
 simplicity in manipulation. Indeed, so far as the saving 
 of time is concerned, we scarcely know how a change for 
 the better could be devised. The whole of the appliances 
 of the instrument, prism, polariscope, stage condenser, 
 objectives of both high and low powers, &c. are attached 
 to the microscope itself and that, too, in such a manner 
 as to enable the observer to place them in exact position 
 without the turn of a single screw or a moment's delay. 
 
 Collins's Binocular, represented in fig. 50, is fitted into 
 the bottom of a mahogany box, which forms at the same 
 time the stand ; round it a groove is run to receive the 
 lip of a glass shade. The instrument itself is made of 
 polished brass, and is eighteen inches high. The eye- 
 pieces are supplied with shades (a a) to protect the eyes. 
 
 At the end of the transverse arm (/) is the box which 
 contains both Wenham's binocular prism and the analyser 
 of the polariscope ; and by merely drawing it a little out, 
 or pushing it further in, the instrument can be instantly 
 changed from a binocular to a monocular, and still further 
 to a polarising microscope. 
 
 Immediately beneath (/) are the two objectives, a 
 quarter and an inch ; so that, in order to change the 
 power, all that is necessary is to slide them backwards or 
 forwards. Moreover, these are fitted with the universal 
 screw, so that either of them may be detached, as in an 
 ordinary instrument, and a quarter, or one-eighth, or other 
 power put in its place, at the option of the observer. The 
 instrument is fitted with a coarse and fine adjustment, and 
 lias the additional advantage of a magnetic stage, in the 
 
96 
 
 THE MICROSCOPE. 
 
 cross-bar (A) of which is a groove, in order that the ob- 
 server may enjoy the luxury of applying a MaltwoooYs 
 finder, as in larger instruments possessing moveable stages. 
 
 Fig. bQ.Collins's Binocular Microscope. 
 
 Beneath the stage is seen the polariser (p), fitted into the 
 circular diaphragm. The double mirror (m) possesses a 
 triple joint, so that it can be applied obliquely in ail 
 directions. 
 
 Collins's Student five-guinea Binocular Microscope con- 
 sists of two eye-pieces, rack adjustment, top-sliding stage, 
 wheel of diaphragms, concave mirrors with adjustments 
 axes for inclining to any angle, tweezers and glass plate, 
 1 in. and J in. achromatic objectives, C series. Packed 
 
COLLINS'S STUDENT'S. ft 7 
 
 in polished mahogany cabinet complete (fig. 51) s a* ex- 
 ceedingly cheap instrument. 
 
 Fig 51. ColUntff Student's Binocular Microtoopt. 
 
 Collins'* Lawson Binocular Dissecting Microscope. 
 This instrument is intended to supply a want, often felt 
 in anatomical and botanical investigations, when only a 
 moderate magnifying power is required. 
 
 In consequence of using both eyes it can be worked with 
 for a length of time with great comfort. A large range of 
 field is obtained, and plenty of room for working. It 
 consists of a neat oblong French-polished mahogany box, 
 measuring, when closed, 6 in. by 4 in., fig. 52. The top 
 and front let down by hinges, and on the inside of them 
 are fitted the scissors, needles, and knives necessary for 
 dissecting. The two sides draw out about six inches, 
 and are hollowed out so as to serve as rests for the hands. 
 The magnification is obtained by two lenses mounted in 
 the eye-pieces, as represented in the diagram, and may te 
 adjusted to the focus by a sliding bar. These show the 
 object beautifully in relief. Beneath is a gutta-percha 
 trough or stage, to pin the object down to, which can be 
 
98 
 
 THE MICROSCOPE. 
 
 filled with water if required. Under this is the mirror 
 for transparent illumination, and the light from it is passed 
 through a circle of glass in the centre cf the trough. The 
 
 Fig. 52. Lawson's Dissecting Microscope. 
 
 instrument is admirably adapted for the wants of students 
 in the preparation and dissection of microscopic objects, 
 and also answers well for botanical investigations. 
 
 A cheap form of Dissect- 
 ing Microscope, represented 
 in the annexed woodcut 
 ffig. 53), has been con- 
 structed by Mr. Baker. 
 The instrument consists of 
 a solid circular foot of brass, 
 from the border of which 
 arises a firm pillar support- 
 ing the stage which is of 
 ample dimensions and a 
 firm horizontal bar, into 
 which the lenses are 
 screwed. The latter is ele- 
 vated and depressed by a 
 rack and pinion movement, 
 Pig. 53.- Baker's Disstaing Microscope, the milled-head being situate 
 
HIGHLEY'S MICROSCOPE. 
 
 99 
 
 at a level a little below that of the stage. In the centre 
 of the foot is placed the mirror, which moves in an arc 
 of brass ; that, in its turn, works upon a pivot in the foot 
 of the instrument. This handy microscope, with three 
 powers and mahogany case, is sold at thirty-five shillings. 
 
 Fig. Si.Highley's Professional Microscope. 
 
 Highley's Professional Microscope, shown in fig. 54, is 
 a useful and well-made instrument, mounted on a tripod, 
 with coarse and fine adjustment, mechanical stage, &c. 
 The mode in which the body is supported is very good 
 in principle, and the milled-heads for the coarse adjust- 
 ment are in a position which is easily reached by the left- 
 hand when the elbow is resting on the table, whilst the 
 right-hand finds the milled-heads of the traversing stage, 
 &c. It is arranged for a secondary stage, and all the 
 necessary apparatus to make a complete instrument. Al- 
 though the tripod is a very good form for a microscope, 
 it requires all the solidity and metal of a Powell and 
 Lealand, or it will not remain (without clamping) perfectly 
 steady and well balanced when placed in the horizontal 
 
 H2 
 
100 THE MICROSCOPE. 
 
 position. The new form of tripod by this manufacturer 
 is, however, well constructed, and, in our opinion, possesses 
 advantages both in weight and steadiness. 
 
 Fig. 55.Hghley'8 Complete Students Microscope. 
 
 Highley's Complete Microscope, of which the general 
 plan is shown in the accompanying fig. 55, may be classed 
 among the cheapest form of instruments manufactured for 
 the use of the student. The stand is made in the tripod 
 form, and the coarse adjustment given by the usual rack 
 and pinion motion, whilst the fine adjustment, or lo^ 
 motion, is given by a milled-head acting on the ob- 
 jective. The roominess, ffctness, and thinness of the stag? 
 
especially adapt it for the examination of anatomical and 
 pathological specimens. The usual diaphragm-plate admits 
 the application of illuminating apparatus, such as the 
 Webster condenser, polarising prism, &c. The cost of 
 the instrument, fitted with two good ordinary object- 
 lasses of 1 inch and inch focus, is 61. 16s. Qd. 
 
 
 Fig. 56. Hov/tStudenfs Microscope. 
 
 Mr. How (Foster Lane) is the manufacturer of the im- 
 posing-looking instrument fig. 56. It is of fair workman 
 
ship, suitable for all ordinary investigations, well deserving 
 a place among cheap microscopes for the student. The 
 stand is of brass, firm and well finished; the body is 
 fitted with coarse and fine adjustments for focussing ; and 
 a draw-tube for increasing the magnifying power of the 
 eye-piece. The stage has an arrangement, simple but 
 novel in construction, by which a near approach to a 
 universal movement is obtained. The moveable, or upper 
 plate, is held to the fixed lower plate with springs, and, 
 although offering a convenient resistance, allows of a 
 smoothness of motion quite remarkable. It resembles 
 the magnetic stage, but is far more reliable, and can be 
 moved upwards, downwards, laterally, or in a slanting direc- 
 tion, thus enabling the microscopist to follow living objects 
 with great facility, superseding to some extent the more 
 expensive mechanical stage. A dividing set of object- 
 glasses is supplied with the B eye-piece, thus giving a 
 range of power varying from 40 to about 200 diameters. 
 His powers are of English workmanship, but differ from 
 the higher-priced objectives in having smaller angular 
 apertures, which is, perhaps, a legitimate mode of lessening 
 the cost. The instrument being made with the universal 
 screw, other objectives of a better class can be added at 
 any time. There is also a condenser mounted on a brass 
 stand for the illumination of opaque objects. The whole 
 is fitted in a mahogany case, with drawer for objects, and 
 sold at 51. 5s. 
 
 Murray and Heath's (Jermyn Street) Student's Micro- 
 scope (fig. 57) is a good solid form of instrument with a 
 bent tripod-stand. The great object of furnishing a stand 
 at a low price which shall be capable, if desired, of being 
 adapted to the use of the higher objectives, and fitted for 
 the addition of all accessory apparatus, has been very 
 satisfactorily carried out and obtained in this microscope. 
 The stand is remarkably firm, and, being bronzed over, is 
 well adapted for daily use in the class-room or laboratory. 
 The adjustment is effected by a chain-movement, which 
 gives sufficient delicacy for powers up to the J inch. The 
 stage is perfectly flat, and the slide-rest moves smoothly 
 and freely over it. If the instrument is intended for use 
 in the laboratory, a glass stage is made to replace the brass 
 
MURRAY AND HEATH'S MICROSCOPE. 103 
 
 one. The objectives furnished with this microscope are a 
 i inch of 75 angular aperture, and a 1 inch of 15, both 
 of excellent quality. A binocular body, with fine adjust- 
 
 Fig. 57. Murray and Heath's 51. 5s. Students Microscope. 
 
 ment, is added for a small additional sum, and the instru- 
 ment then becomes all the student can desire. 
 
 Murray and Heath's Class Microscope, represented in 
 fig. 58, is especially intended for the use of teachers in 
 the demonstration of objects to a class of students. It is 
 but too well known to those who are engaged in teaching 
 how liable the objects exhibited, and sometimes even the 
 object-glass itself, are to be injured in the hands of those 
 
104 THE MICROSCOPE. 
 
 unaccustomed to use the microscope. In order to avoid 
 this risk, Messrs. Murray and Heath have constructed au 
 instrument intended to combine an ordinary with a de- 
 monstrating or class microscope. It consists of the usuai 
 microscope body (A), which can be inclined at any angle, 
 with a mirror (c) on a ball-and-socket joint ; and a stage- 
 plate with universal movement. When about to be used a* 
 a class microscope, the slide is placed in a shallow box 
 into which it is locked by means of a key. The same 
 key locks this box firmly on the stage-plate. When the 
 object has been found, this latter can be secured firmly 
 on the stage in the same manner. After focussing, the 
 
 Fig. 58. Murray and Heath's Class Microscope. 
 
 body is also locked in its place with the same key, which 
 is seen at D, the final adjustment being made with the 
 eye-piece. The body is then placed in the horizontal posi- 
 tion, and fastened with a screw. The instrument can now 
 be passed round a class-room without possibility of injury 
 either to object or object-glass. The illumination is ob- 
 tained either by directing the instrument towards the 
 window, or by means of a small lamp (B), similar to that 
 employed by Dr. Beale, and which can be so adjusted as 
 to be used either for opaque or transparent objects. 
 
 This instrument appears to be particularly well adapted 
 to the purposes for which it is intended, and, at the same 
 time, if without the contrivance for locking, to be a useful 
 portable form for general, professional, or sea-side pur- 
 poses. 
 
BEALE'S CLASS MICROSCOPE. 105 
 
 It should be added, that a novel and efficient form of 
 achromatic condenser is supplied with the instrument; 
 a series of small stops of various sizes are made to drop 
 into a minute hole drilled in the centre of the anterior 
 plano-convex k-ns, which convert it into a spot-glass, or 
 dark-ground illuminator. The whole is packed in a 
 mahogany case, and sold for 51. 5s. 
 
 Fig. 59. .Beak's Clinical Microscope. 
 
 Dr. Beale devised an exceedingly simple and con- 
 venient form of microscope, for the purposes of clinical 
 instruction and of class demonstration (fig. 59). Over the 
 body of the microscope, which is of small dimensions, a 
 tube is fitted with a bell-shaped mouth at the end. This 
 tube slides freely over the body, but is capable of being 
 fixed at will by means of a clamping-screw. The slide con- 
 taining the object is placed across the bell-mouth, and held 
 there by a spring pressing against the back of it, and is 
 thus maintained perpendicularly to the axis of the instru- 
 ment. When the focus is adjusted the clamping-screw is 
 fixed, and the fine adjustment necessary for the differ- 
 ences of vision in different individuals is effected by 
 drawing out or pressing in the eye-piece. The object and 
 object-glass are thus protected from mutual injury, an 
 accident of by no means unfrequent occurrence in careless 
 or unpractised hands. In this form the instrument is 
 adapted to the clinical examination of secretions, &c. and 
 must be directed by the hand towards day or artificial 
 light. For demonstration to a class, this instrument ia 
 attached horizontally to a small wooden stand by means 
 of a clamp, supported by two legs. To the stand a small 
 
106 THE MICROSCOPE. 
 
 oil-lamp is likewise attached ; and a stem proceeding from 
 the lower edge of the bell-mouth carries any desired form 
 of condensing or illuminating apparatus. This stand is 
 capable of being freely handed round a large class without 
 the focus becoming at all deranged, even when a very deep 
 objective is employed. This instrument is manufactured 
 by Mr. S. Highley. 1 
 
 Fig. 60. Warington's Universal Microscope. 
 
 While alluding to cheap microscopes, we would men- 
 tion Warington's Travelling Microscope, made by Salmon, 
 100, Fenchurch Street. It has a simple, firm, wooden 
 stand, whereby the cost is greatly diminished ; and an 
 arrangement of its parts which enables it to be used for 
 
 (1) A very simple instrument, contrived by Mr. T. C. Archer for the purpose 
 or being used either as a lecture-room or as an ordinary table microscope, is 
 manufactured by Messrs. Parkes of Birmingham, and sold, with a set of achro- 
 matic powers, for 2J. 5*. in case complete 
 
SEA-SIDE MICROSCOPES. 
 
 107 
 
 viewing objects in aquaria, and under other circumstances 
 where any ordinary form of instrument could not be made 
 available. It is altogether a useful student's microscope, 
 having the recommendation of folding up into a small com- 
 pass, and not liable to much injury either from chemical 
 or marine investigations. For 31. this microscope is furnished 
 
 Fig. (51. ll~aringto)t's Microscope packed. 
 
 complete, with one eye-piece, quite sufficient for all ordi- 
 nary investigations. 
 
 Fig. 60 is a representation of Warington's microscope, 
 as it appears when put together, and ready for use ; and 
 fig. 61 fo* packing in a small wood case. The draw-tube 
 itself is the coarse adjustment; whilst a finer is secured by 
 a well-made union-joint, into which the object-glass is made 
 to screw. "With an additional arm for the reception of a 
 single lens, it can be converted into a dissecting microscope. 
 
 Fig. 62. Murray and Heath' s Sea-side Pocket Micro* A*pe. 
 
108 
 
 THE MICROSCOPE. 
 
 Fig. 62 represents a small portable instrument by Murray 
 and Heath, designated " The Sea-side Pocket Microscope," 
 the chief recommendation of which is its simplicity of 
 construction and its small compact form ; the whole packs 
 into a case six inches long, and may be carried without 
 incumbrance in the pocket of the field-naturalist. 
 
 The body of the instrument is seen at c, supported on 
 a tripod, which is removed and folded up at B. If desired, 
 it can be used in the upright position, as at A, when a 
 pair of short legs placed near the mirror must be turned 
 down, and forms a tolerably steady support to the body. 
 The adjustment is made by sliding the body through the 
 outer tube, which carries a triple combination of achromatic 
 objectives. A live-box, &c. is added ; and, when packed 
 in a morocco case, is sold for 21. 5s. 
 
 Fig 63. Baker's TravelUS* Microscope. 
 
 An instrument somewhat similar in appearance to the 
 foregoing, but differing so materially in detail as almost to 
 
BAKER'S TRAVELLER'S MICROSCOPE. 109 
 
 claim to "be a new invention (fig. 63), has been introduced 
 by Baker, and not inappropriately called "The Travel- 
 ler's Microscope," from its obvious capabilities. The aim 
 has been to combine steadiness with extreme portability. 
 The compound body is permanently affixed to the fore-leg 
 of the tripod-stand ; the two other legs are supported on 
 capstan-bar joints, which can be tightened at pleasure, or 
 folded up parallel with the former when not in use. The 
 difficulty of using high powers with an instrument the 
 body of which slides in cloth is well known ; the tube 
 becomes tarnished by continued use, and a firm adjust- 
 ment, which shall be easy of access, is almost indispen- 
 sable. To obtain an approximate focus, the inner tube is 
 drawn out until the combined length of the tubes is eight 
 inches; the body is then returned to its "jacket," and 
 placed at a proper distance from the stage to suit the 
 object-glass employed. The fine adjustment is effected by 
 means of a tangent-screw (fifty threads to the inch) placed 
 conveniently behind the body, and worked by a milled- 
 head acting on a spring contained in the upright which 
 supports the body. 
 
 This part of the instrument is very satisfactory ; it is 
 steady and works efficiently. A mechanical stage is not 
 generally applied, but can be if required. Sufficient 
 movement is obtained by a plain stage, with two springs 
 to hold the live-box or glass slip. 
 
 This microscope is carried in a leathern case 10 inches 
 by 3, seen in the woodcut (similar to that made for deer- 
 stalking telescopes), and fitted with object-glass, eye-piece, 
 live-box, &c. ; the weight of the whole not exceeding two 
 pounds in weight, and it therefore especially recommends 
 itself to the field-naturalist. 
 
 The whole merit of this invention is due to Mr. Moginie, 
 of Mr. Baker's establishment, Holborn, who has devoted 
 much time and thoughtfulness towards bringing it to its 
 present state of perfection. 
 
 Highley's Pocket Microscope (fig. 64), for botanical or 
 field uses, consists of a short tube furnished with a sliding 
 eye-tube, fitting into an outer tube. The coarse adjustment 
 is made by sliding the body through the outer tube, which 
 carries the object ; the fine adjustment by sliding the eye- 
 
110 THE MICROSCOPE. 
 
 tube in or out. The object, if transparent, is illuminated 
 either by holding up the microscope towards a white cloud, 
 or other source of light, or by directing it towards a mirror 
 laid upon the table at such an angle as to reflect the light. 
 
 Fig. Gl.Higliley's Pocket Microscope. 
 
 If opaque, it is allowed to receive direct light through an 
 aperture in the outer tube. The extreme simplicity and 
 portability of the instrument which is only six inches 
 long constitutes its chief recommendation. 
 
 Norman's (178, City Eoad) Universal Educational 
 Microscope consists of a well-finished stand with tripod 
 foot and two uprights, with axis for giving inclination to 
 the optical part. The body has quick and slow motions, 
 one Huyghenian eye-piece, three achromatic object-glasses, 
 viz. a i-inch dividing into J and 1 inch, all of fair de- 
 fining power and English made. The stage has a large 
 slid ing-piece, and a revolving wheel of diaphragms \ the 
 mirror has sliding and oblique motions for the better illu- 
 mination of the object under examination. The following 
 apparatus is also supplied with the instrument : a stand 
 condenser with adjustment, stage and hand forceps, live- 
 box or animalculae cage, a frog-plate for viewing the circu- 
 lation of the blood in the web of a frog's foot ; also three 
 good objects to test the different object-glasses, one hol- 
 lowed and two plain slips, some thin glass. The whole is 
 packed in a mahogany or walnut cabinet, with a drawer 
 for objects, lock and key, and sold for the small price of 
 3J. 5. 
 
 24 first-class objects, suited for the object-glasses, are 
 supplied with this instrument for II. Is. 
 
 Mr. E. Wheeler's (Holloway) well-made instruments de- 
 serve commendation and notice; they are carefully finished 
 and quite up to the modern standard. The full assorted 
 sets of objects which Mr. Wheeler supplies in a very neat 
 
SIMPLE MICROSCOPES. Ill 
 
 book-folding case, the names on which can be read off at 
 a glance, are particularly well selected. Many of the cases 
 are so arranged as to form complete sets of certain classes 
 of specimens admirably suited for educational purposes, and 
 also for the elucidation of general and particular principles ; 
 as, for instance, the various parts of an insect, to show 
 peculiarities of structure for the illustration of entomo- 
 logical lectures, the same for botanical, anatomical, &c. 
 Many of our drawings have been made from Mr. Wheeler's 
 excellent specimens. 
 
 Mr. Piper, of the Old Change Microscopical Society, 
 devised a convenient, cheap, and portable object-case. It 
 is a compact oblong paste-board box, made to contain six, 
 twelve, or twenty-four shallow trays, with six or twelve 
 divisions just the size of the ordinary glass slides. The 
 objects lie flat in these trays, which pack one above the 
 other. For handiness, neat packing, facility of finding 
 and reading off names of objects, this case cannot be 
 surpassed. It is but right to add, that it is adapted to 
 the use of those whose aim is the economically useful 
 cabinet for storing and classifying objects. This " uni- 
 versal" object-case is sold by Baker, Holborn. 
 
 Several forms of simple microscopes have been devised 
 for field use under various designations, such as " Diatom 
 Finders," &c. One of the most useful little instruments 
 of the class is that described by Mr. J. N. Tomkins, in 
 the Trans. Micros. Soc. vol. vii. p. 57, 1859. Another 
 was invented by Dr. VV. Gairdner of Edinburgh, and made 
 by Mr. Bryson of that city, neatly packed in a case for the 
 waistcoat-pocket. Want of space will not permit us to 
 enter further into this department, nor can we go into 
 a critical examination of the productions of numerous 
 well-known makers of microscopes ; as, for instance, the 
 Educational Microscopes of Messrs. Smith and Beck, of 
 Cheapside; Mr. Browning, 111, Minories ; Mr. Matthews 
 of Portugal Street ; Mr. Dancer of Manchester ; Messrs. 
 Abraham of Liverpool ; Mr. King of Bristol, &c. all of 
 whom have obtained a deservedly high reputation for 
 their convenient forms of educational and other well- 
 manufactured instruments. 
 
112 THE MICROSCOPE. 
 
 APPLICATION OP BINOCULARITY TO THE MICROSCOPE. 
 
 The application of this principle to microscopic pur- 
 poses seems to have been tried as early as 1677, by a 
 French philosopher, le Pere Cherubin, of Orleans, a Capu- 
 chin friar. The following is an extract from the description 
 given by him of his instrument : " Some years ago I 
 resolved to effect what I had long before premeditated, to 
 make a microscope to see the smallest objects with the 
 two eyes conjointly; and this project has succeeded even 
 beyond my expectation, with advantages above the single 
 instrument so extraordinary and so surprising, that every 
 intelligent person to whom I have shown the effect, has 
 assured me that inquiring philosophers will be highly 
 pleased with the communication." 
 
 This communication long slumbered and was forgotten, 
 and nothing more was heard of the subject until Professor 
 Wheatstone's very surprising invention of the stereoscope, 
 which he evidently expected to apply to the microscope, 
 for he applied to both Ross and Powell to make him 
 a binocular microscope. But this was not done ; and 
 during the year 1853 a notice appeared in Silliman's 
 American Journal of a binocular instrument constructed 
 by Professor Riddel of America, who contrived a binocular 
 microscope in 1851, with the view " of rendering both eyes 
 serviceable in microscopic observations." "Behind the ob- 
 jective/' he says, " and as near thereto as possible, the light 
 is equally divided and bent at right angles, and made to 
 travel in opposite directions, by means of two rectangular 
 prisms, which are in contact by their edges somewhat 
 ground away, the reflected rays are received, at a proper 
 distance for binocular vision, upon two other rectangular 
 prisms, and again bent at right angles, being thus either 
 completely inverted for an inverted microscope, or restored 
 to their tirst direction for the direct microscope." M. 
 Nachet also constructed a binocular microscope, upon the 
 same principle as his double microscope, with the tubes 
 placed vertically and 2J inches distant. This had many 
 disadvantages and inconveniences, which Mr. F. H. Wenham 
 ingeniously succeeded in modifying and improving. 
 
THE BINOCULAR MICROSCOPE. 113 
 
 In describing his improvements, he observes : " That in 
 obtaining binocularity with the compound achromatic mi- 
 croscope, in its complete acting state, there are far greater 
 practical difficulties to contend against, and which it is 
 highly important to overcome, in order to correct some of 
 the false appearances arising from what is considered the 
 very perfection of the instrument. 
 
 " All the object-glasses, from the one-inch upwards, are 
 possessed of considerable angular aperture ; consequently, 
 images of the object are obtained from a different point of 
 view, with the two opposite extremes of the margin of the 
 cone of rays; and the resulting effect is, that there are a 
 number of dissimilar perspectives of the object all blended 
 together upon the single retina at once. For this reason, 
 if the object has any considerable bulk, we shall have a 
 more accurate notion of its form by reducing the aperture 
 of the object-glass. 
 
 " Select any object lying in an inclined position, and 
 place it in the centre of the field of view of the micro- 
 scope; then, with a card held close to the object-glass, 
 stop off alternately the right or left hand portion of the 
 front lens : it will be seen that during each alternate 
 change certain parts of the object will alter in their rela- 
 tive position. 
 
 " To illustrate this, fig. 5 #, 6 
 are enlarged drawings of a portion 
 of the egg of the common bed-bug 
 (Cimex lecticularis), theoperculum 
 which covers the orifice having 
 been forced off at the time the 
 young was hatched. The figures 
 exactly represent the two positions 
 that the inclined orifice will oc- 
 Fig - e5 - cupy when the right and left hand 
 
 portions of the object-glass are stopped off. It was illumi- 
 nated as an opaque object, and drawn under a two-thirds 
 object-glass of about 28 of aperture. If this experiment 
 is repeated, by holding the card over the eye-piece, and 
 stopping off alternately the right and left half of the 
 ultimate emergent pencil, exactly the same changes and 
 appearances will be observed in the object under view. 
 
 1 
 
114 
 
 THE MICROSCOPE 
 
 The two different images just produced are sucL as are 
 required for obtaining stereoscopic vision. It is therefore 
 evident that if, instead of bringing them confusedly toge- 
 ther into one eye, we can separate them so as to bring fig. 
 96 a b into the left and right eye, in the combined effect 
 of the two projections, we shall obtain all that is necessary 
 to enable us to form a correct judgment of the solidity 
 and distances of the various parts of the object. 
 
 " Diagram 3, fig. 66, represents the methods that I have 
 contrived for obtaining the effect of bringing the two eves 
 
 Fig. 66. 
 
 sufficiently close to each other to enable them both to see 
 through the same eye-piece together, a a a are rays con- 
 verging from the field lens of the eye-piece ; after passing 
 the eye-lens b, if not intercepted, they would come to a 
 focus at c ; but they are arrested by the inclined surfaces, 
 d d, of two solid glass prisms. From the refraction of the 
 under incident surface of the prisms, the focus of the eye- 
 piece becomes elongated, and falls within the substance of 
 the glass at e. The rays then diverge, and after being 
 reflected by the second inclined surface /, emerge from the 
 upper side of the prism, when their course is rendered 
 still more divergent, as shown by the figure. The reflecting 
 angle that I have given to the prisms is 47. I also find 
 it is requisite to grind away the contact edges of the 
 prisms, as represented, as it prevents the extreme margins 
 
THE B1NOCDLAB MICROSCOPE. 115 
 
 of the reflecting surfaces from coming into operation 3 
 which can seldom be made very perfect. 
 
 " The definition with these prisms is good ; but they 
 are liable to objection on account of the extremely small 
 portion of the field of view that they take in, and which 
 arises from the distance that the eyes are of necessity 
 placed beyond the focus of the eye-piece, where, the rays 
 being divergent, the pupil of the eye is incapable of taking 
 them all in ; also there is great nicety required in the 
 length of the prisms, which must differ for nearly every 
 different observer." 
 
 The great disadvantages of the first arrangement of the 
 binocular microscope were the expensive alterations 
 required in their adaptation : to most persons, the view 
 that it gave of the object was pseudoscopic, and not that 
 of solidity and roundness ; and the two bodies being 
 united at a fixed angle of convergence, the distance be- 
 tween their axes could not be adapted to the varying 
 distances between the eyes of different individuals. At 
 length, these, as well as other defects, have been com- 
 pletely overcome by the improvements the instrument 
 has recently received at the hands of the inventor; and 
 we have no hesitation in saying that Wenham's prism is 
 the most valuable addition the microscope has received 
 since the perfection of the object-glasses. The adaptation 
 does not at all interfere with the use of the instrument 
 as a monocular microscope, and such additions as the 
 microspectroscope can be as easily used with it as in the 
 old form ; it also affords a ready comparison between 
 the object as seen singly, and by natural double vision, 
 and thus may be obtained an ever ready test, or sight 
 analysis of the structure under examination. Besides, 
 the relief afforded to the eyes is, to our sensation, 
 something quite marvellous, and we believe, therefore, 
 much less risk is run of doing injury to vision. Objects 
 become easily distinguishable, more especially all opaque 
 or semi-opaque ones ; and for the more transparent ones 
 all that is required is to use care in their illumination 
 diffuse the light by placing a piece of ordinary tracing or 
 tissue paper, or ground glass, between the light and the 
 object ; or even polarised light for peculiar substances will 
 i2 
 
116 THE MICROSCOPE. 
 
 enable us to bring them out in greater perfection and 
 beauty. Another advantage gained by the last improvement 
 is, that the ordinary single-bodied microscope can be con- 
 verted into a binocular instrument by simply fixing an- 
 other tube at the proper anglo, and adding a small prism 
 mounted in a brass box. The latter is made to slide into 
 the lower part of the body immediately over the objective. 
 By its aid the rays of light proceeding from the object 
 are reflected in two directions, which, by means of the 
 double body, are conveyed to both eyes, and thereby a 
 stereoscopic view of the object under observation is ob- 
 tained. The most important point to be observed, when 
 using the binocular, is that each eye has a clear view of 
 the object. This is readily ascertained by closing the eyes 
 alternately without moving the head away from the in- 
 strument, when, if it be found that the two images do not 
 quite coincide, it must be corrected by racking out or in 
 the draw-tubes, which should form a part of the bodies 
 of all binoculars. If both fields be not equally illuminated, 
 the object is not rendered stereoscopic. 
 
 Mr. Wenham's most important improvement consists in 
 splitting up and dividing the pencil of rays proceeding from 
 the objective by the interposition of a prism of the form 
 shown in fig. 67. This is so placed in the body or tube 
 of the microscope (fig. 68, a) as only to interrupt one-half 
 (a c) of the pencil, the other half (a b) going on con- 
 tinuously to the field-glass, eye-piece, of the principal 
 body. The interrupted half of the pencil, on its entrance 
 into the prism, is subjected to very slight refraction, since 
 its axial ray is perpendicular to the surface it meets. 
 Within the prism it is subjected to two reflections at 
 b and c, which send it forth again obliquely on the line 
 b towards the eye-piece of the secondary body, to the left- 
 hand side of the figure; and since at its emergence its 
 axial ray is again perpendicular to the surface of the glass, 
 it suffers no more refraction on passing out of the prism 
 than on entering it. By this arrangement, the image re- 
 ceived by the right eye is formed by the rays which have 
 passed through the left half of the objective ; whilst the 
 image received by the left eye is formed by the rays which 
 have passed through the right half, and which have been 
 
WENHAM 8 BINOCULAR. 
 
 117 
 
 subjective to two reflections within the prism, passing 
 through only two surfaces of glass. The prism is held 
 by the ends only on the sides of a small brass drawer, 
 so that all the four polished surfaces are accessible, and 
 should slide in so far that its edge may just reach the 
 
 Fig.7. 
 
 Fig. 68. 
 
 central line of the objective, and oe drawn back against 
 a stop, so as to clear the aperture of the same. In this 
 case the straight tube acts as a single microscope. 
 
 " Both the transmitting and reflecting surfaces of the 
 prism should be accessible, for the purpose of wiping off 
 particles of dust or mildew particles of any kind ad- 
 hering to the prism will prevent total reflection at the 
 point of contact. If the prism is well made and polished, 
 and of the smallest size possible for admitting the pencil, 
 the difference between the direct and reflected image is 
 scarcely appreciable. 
 
 " The binocular constructed as we have described performs 
 satisfactorily up to the th inch; but for powers above 
 
118 THE MICROSCOPE. 
 
 this a special arrangement is needed for the prism, which 
 must be set close behind the lens of the Jth or 
 t^th inch, in order to obtain an entire field of view in 
 each eye. This it is found to accomplish perfectly when 
 placed in that position ; but still, for very delicate test- 
 objects, requiring the utmost extent of aperture for their 
 definition, it will not resolve them as clearly as with a 
 single body, from the fact that the aperture is divided 
 and half only effective in each eye. This difficulty has 
 at length been nearly overcome by Messrs. Powell and 
 Lealand, by means of an inclined disc of glass with 
 parallel sides, the partial reflection from the under surface 
 of which is again reflected into the second eye, by means 
 of a rectangular prism. As the disc is made thinner, so 
 do the images approximate and the distance between them 
 diminish. Therefore, if the glass is made as thin as pos- 
 sible, and a very slight angle given to the two sides, it 
 may be so arranged that both images are ultimately com- 
 bined at the eye-piece. There would be no difficulty in 
 working the glass to a mean thickness of -g^th of an 
 inch. In this form the angle between the sides would be 
 so exceedingly small that * the chromatic effect, considered 
 as a prism, would be inappreciable in the direct eye-tube. 1 
 " A strong light should be avoided for the illumination 
 of objects observed with the binocular microscope, as 
 direct rays tend to destroy the stereoscopic effect. The 
 illuminator that has been found to give an excellent effect 
 consists of three plano-convex lenses, so combined as to 
 give a very large area of light, as well as great intensity. 
 The final emergent pencil should have, if possible, an 
 angular aperture of 170. Just above the top lens should 
 be placed a sliding-cap, the crown of which is covered 
 with a diffusing film. For this, the best material is the 
 beautiful snow-white powder obtained from turning glass 
 with a diamond turning-tool This may be obtained from 
 the opticians, and should be well washed to free it from 
 the larger particles. A thin film of this impalpable 
 powder should be compressed between two discs of thin 
 glass, and fixed in the top of the sliding-cap, which is to 
 be raised or lowered till the most intense light is obtained 
 
 (1) Quarterly Journal of Microscopital Science, vol. i. 1861, and vol. vi. 1866. 
 
SPECTRO-MICROSCOPY. 119 
 
 on the film. This illuminator is employed in the position 
 of the achromatic condenser, and a disc of slightly coloured 
 neutral tint-glass placed below the bottom lens increases 
 the purity of the light, and gives greater distinctness to 
 objects. The effect of this diffusing film is sometimes 
 enhanced by condensing light down on the object from 
 above as well as from below." 
 
 An important improvement has been effected in Nachet's 
 binocular by Professor Smith, of Kenyon College, U.S. 
 It consists in the adaptation of Nachet's set of prisms for 
 use as eye-pieces, with any monocular instrument. The 
 prisms being mounted in a light material, vulcanite, are 
 made to fit into the microscope body and take the place 
 of the ordinary eye-piece. The image transmitted by the 
 objective is brought to a focus on the face of the first 
 equilateral triangular prism by the intervention of an 
 erector eye-piece placed beneath it. The second set of 
 prisms are by a rack-and-pinion movement adjusted to 
 suit any visual angle; while the illumination of both 
 fields is quite perfect, even with high powers. 
 
 SPECTRO-MICROSCOPY. 
 
 The application of the spectroscope to the microscope is 
 one of the most beautiful additions the instrument has lately 
 received. The honour of the invention appears to belong 
 to H. C. Sorby, F.RS., whose first experiments were made 
 with a simple triangular prism, arranged and fixed below 
 the stage, so that a minute spectrum of any transparent 
 object might be readily examined, when placed in position 
 immediately before the slit. Shortly after the publication 
 of Mr. Sorby's paper, Mr. Huggins proposed to adapt a 
 direct vision spectroscope to the eye-piece, and so enable 
 us to view the spectra of opaque as well as transparent 
 objects. The exact form of prism finally adopted, and 
 now in general use, is that known as the Sorby-JBrowning 
 Spectroscope. 
 
 The first spectroscope made by Mr. Browning (Minories) 
 is represented in tig. 69. A prism is placed at P, which is 
 enclosed in a box, so as to give a black field, by excluding 
 
120 
 
 THE MICROSCOPE. 
 
 extraneous light. The rays of light, after passing between 
 the knife-edges at K, are rendered parallel by means of 
 the lens at L. Then passing through the prism and con- 
 denser (c), they reach the object at o. The light is placed 
 at w, and if it be proposed to examine a liquid, it can be 
 placed in a small tube (T), closed at one end ; or a trans- 
 parent object may be placed on the stage in the usual 
 
 Fig. 69. Sectional view oj tlw Browning Spectroscope. 
 
 manner. By the addition of a small telescope, instead of 
 a condenser, this contrivance can be applied to a micro- 
 scope in place of the eye-piece, and it can then be used for 
 the examination of opaque objects. 
 
 The great objection to this form is its limited range, 
 and the constant shifting of parts it requires for finding 
 and focussing the object, and the awkward position of the 
 microscope, whether it be used under the stage or as an 
 eye-piece. 
 
 Fig. 70. The Browning Hugging Micro-spectroscope. 
 
 The apparatus used by Mr. Huggins (fig. 70) was a star 
 
8PECTRO-MICROSCOPY. 121 
 
 spectroscope, of which the collimative-tube was inserted 
 in the body of the microscope, instead of an eye-piece. 
 AVith this apparatus he has succeeded in obtaining a 
 spectrum showing the absorption-bands from a mere frag- 
 ment of single blood-disc, when mounted as a transparent 
 object. In fig. 70, K represents the knife-edges, c the tube 
 containing the collimating-lens, P the prisms, T the teles- 
 cope, and M the micrometer ; the object is placed on the 
 stages at o, and must be illuminated from below if trans- 
 parent, or, if opaque, from above by any kind of con- 
 denser. 
 
 Mr. Sorby suggested that a prism might be made of 
 dense flint-glass, of such a form that it could be used in 
 two different positions, and that in one it should give 
 twee the dispersion that it would in the other, but that 
 the angle made by the incident and emergent rays should 
 be the same in both positions. 
 
 Fig. 71. Fig. 72. 
 
 Figs. 71 and 72 represent prisms of the kind made by 
 Mr. Browning, used in two different positions, i and I' 
 being the same angle as I and i'. 
 
 For most absorption-bands, particularly if faint, the 
 prism would be used in the first position, in which it 
 gives the least dispersion ; but when greater dispersion 
 is required, so as to\separate some particular lines more 
 widely, or to show the spectra of the metals, or Fraun- 
 hofer's lines in the solar spectrum, then the prism must 
 be used as in fig. 72. This answers well for liquids or 
 transparent objects, but it is, of course, not applicable to 
 opaque objects. 
 
122 
 
 THE MICROSCOPE. 
 
 To combine both purposes, some form of direct vision- 
 prisms which can be applied to the body of the micro- 
 scope is required. Fig. 73 represents the arrangement of 
 direct vision-prisms, invented by A. Herschel. The line 
 B R' shows the path of a ray of light through the prisms, 
 where it would be seen that the emergent ray R' is parallel 
 and coincident with the incident ray R. 
 
 Fig. 73. 
 
 Fig. 74. 
 
 Another very compact combination is shown in fig. 74. 
 Any number of these prisms (p P P) may be used, accord- 
 ing to the amount of dispersion required. They are 
 mounted in a similar way to a Nicols' prism, and are 
 applied directly over the eye-piece of the microscope. 
 The slit s s is placed in the focus of the first glass (F) if 
 a negative, or below the second glass if a positive eye- 
 piece be employed. One edge of the slit is moveable, 
 and, in using the instrument, the slit is first opened wide, 
 so that a clear view of the object is obtained. The part 
 of the object of which the spectrum is to be examined 
 is then made to coincide with the fixed edge of the slit, 
 and the moveable edge is screwed up, until a brilliant 
 coloured spectrum is produced. The absorption-bands 
 will then be readily found by slightly altering the focus. 
 This contrivance answers perfectly for opaque objocta 
 
SPECTRO-MTCRO&COPY. 123 
 
 without any preparation ; and, when desirable, the same 
 prism can be placed below the stage, and a micrometer 
 used in the eye-piece of the microscope, thus avoiding a 
 multiplication of apparatus. 
 
 The latest improvement is that shown in fig. 75, also 
 effected by Mr. Browning, who deserves great credit for 
 the skill displayed in the invention and construction of 
 this new and elegant micro-spectroscope. 
 
 Fig. 75. The Sorby-Brovrning Micro-spectroscope, 
 
 The prism is contained in a small tube, which can be 
 removed at pleasure. Below the prism is an achromatic 
 eye-piece, having an adjustable slit between the two 
 lenses, the upper lens being furnished with a screw 
 motion to focus the slit. A side slit, capable of adjust- 
 ment, admits, when required, a second beam of light from 
 any object whose spectrum it is desired to compare with 
 that of the object placed on the stage of the microscope. 
 This second beam of light strikes against a very small 
 prism, suitably placed inside the apparatus, and is reflected 
 up through the compound prism, forming a spectrum in 
 the same field with that obtained from the object on the 
 stage. 
 
 A is a brass tube, carrying the compound direct vision 
 prism. B, a milled head, with screw motion to adjust the 
 focus of the achromatic eye lens, c, milled head, with 
 screw motion to open or shut the slit vertically. Another 
 
124 THE MICROSCOPE. 
 
 screw at right angles to c, but which from its position 
 could not be shown in the cut, regulates the slit hori- 
 zontally. This screw has a larger head, and when once 
 recognised cannot be mistaken for the other. D D is an appa- 
 ratus for holding a small tube, that the spectrum given 
 by its contents may be compared with that from an object 
 on the stage. E is a square-headed screw, opening and shut- 
 ting a slit to admit the quantity of light required to form 
 the second spectrum. A light entering the round hole 
 near E, strikes against the right-angled prism, which we 
 have mentioned as being placed inside the apparatus, and 
 is reflected up through the slit belonging to the compound 
 prism. If any incandescent object be placed in a suitable 
 position with reference to the round hole, its spectrum 
 will be obtained. F shows the position of the field lens of 
 the eye-piece. G is a tube made to fit the microscope to 
 which the instrument is applied. To use this instrument 
 insert G, like an eye-piece in the microscope tube, taking 
 care that the slit at the top of the eye-piece is in the same 
 direction as the slit below the prism. Screw on to the 
 microscope the object-glass required, and place the object 
 whose spectrum is to be viewed on the stage. Illuminate 
 with the stage mirror if it be transparent; with mirror,, 
 Lieberkiihn, and dark well, by side reflector, or bull's-eye 
 condenser if opaque. Remove A, and open the slit by 
 means of the milled-head, not shown in cut, but which is 
 at right angles to D D. When the slit is sufficiently open 
 the rest of the apparatus acts like an ordinary eye-piece, 
 and any object can be focussed in the usual way. Having 
 focussed the object, replace A, and gradually close the slit 
 till a good spectrum is obtained. The spectrum will be 
 much improved by throwing the object a little out of 
 focus. 
 
 Every part of the spectrum differs a little from adjacent 
 parts in refrangibility, and delicate bands or lines can only 
 be brought out by accurately focussing that particular part 
 of the spectrum. This can be done by the milled head B. 
 Disappointment will occur in any attempt at delicate in- 
 vestigation if this direction be not carefully attended to. 
 
 At Ba small mirror is attached, which is omitted in the 
 diagram to prevent confusion. It is like the mirror belov 
 
8PECTRO MICKOSCoPr. 1 25 
 
 the stage of a microscope, and is mounted in a similar 
 manner. By means of this mirror light may be reflected 
 into the eye-piece, and in this way two spectra may be 
 procured from one lamp. 
 
 For observing the spectra of liquids in cells or tubes 
 of considerable diameter, say not less than ^jth of an 
 inch, powers from 2 inch to 1 inch will be the most 
 suitable, and of course low powers only can be used to 
 investigate the spectra of opaque objects ; but when the 
 spectra of very minute objects are to be viewed, powers of 
 from half an inch to one-twentieth, or even higher, may 
 be employed. 
 
 Blood, madder, aniline red, permanganate of potash, in 
 crystals or solution, are convenient substances to begin 
 experiments with. Solutions when made too strong pro- 
 duce dark clouds instead of absorption bands. Professor 
 Church has recently pointed out that zircon, an almost 
 colourless stone, gives well-defined absorption-bands. 
 
 Mr. Sorby says of the correct performance of a spectrum 
 adaptation, " The best tests are, first, that the absorption- 
 bands in blood can be seen when they are very faint ; 
 second, to well divide the bands in permanganate of 
 potash; and, third, to see distinctly the very tine line 
 given in the red by a solution of chloride of cobalt dis- 
 solved in a concentrated cold solution of chloride of calcium : 
 there is a line so fine that it looks like a Fraunhofer's 
 line. An instrument that shows all these well is all that 
 can be desired. 
 
 " The objects most easily obtained, and which furnish 
 us with the greatest variety of spectra, are coloured 
 crystals, coloured solutions, and coloured glasses. The 
 spectrum microscope enables us to examine the spectra of 
 very minute crystals, of very small quantities of material 
 in solution, and of small blow-pipe beads. As previously 
 named, the thickness of the object makes a very great 
 difference in the spectrum. For example, an extremely 
 thin crystal of ferricyanide of potassium cuts off all the 
 blue rays, and leaves merely red, orange, yellow, and more 
 or less green ; but on increasing the thickness, tho green 
 and yellow disappear ; and when very much thicker, little 
 else but a bright red light is transmitted. In all such 
 
126 THE MICROSCOPE. 
 
 cases, the apparent magnitude of the effect of an increase 
 in thickness is far greater when the object is thin than 
 when thick, and past a certain thickness the change is 
 comparatively very slight. If only small crystals can be 
 obtained, it is well to mount a number of different thick- 
 nesses ; but when it is possible to obtain crystals of suf- 
 ficient size, it is far better to make them into wedge- 
 shaped objects, since then the effect of gradual change in 
 thickness can easily be observed. Different kinds of 
 crystals require different treatment, but, as a general rule, 
 I find that it is best to grind them on moderately soft 
 Water-of-Ayr stone with a small quantity of water, which 
 soon becomes a saturated solution, and then to polish 
 them with a little rouge spread on paper laid over a flat 
 surface ; or else, in some cases, to dissolve off a thin layer 
 by carefully rubbing the crystal on moist blotting-paper 
 until the scratches are removed. Then, whenever it is 
 admissible, I mount the crystal on a glass, and also cover 
 it with a piece of thin glass with Canada balsam. Strongly 
 coloured solutions may be examined in test-tubes, or may 
 be kept sealed up in small bottles made out of glass tubes, 
 the light then examined being that which passes through 
 the centre of the tube from side to side. (Most of these 
 solutions require the addition of a little gum Arabic to 
 make them keep.) Such tubes may be laid on the ordinary 
 stage, or laid on the stage attached to the eye-piece. 
 Smaller quantities may be examined in cells cut out of 
 thick glass tubes, one side being fixed on the ordinary 
 glass with Canada balsam, like a microscopic object, and 
 the other covered with thin glass, which readily holds on 
 by capillary attraction, or may be cemented fast with gold 
 size or Canada balsam, if it be desirable to keep it as a 
 permanent object. Such tubes may be made of any length 
 that may be required for very slightly-coloured solutions. 
 Cells made out of spirit thermometer tubes, so as to be 
 about ^th of an inch in diameter, and an inch long, 
 are very suitable for the examination of very small quan- 
 tities ; but where plenty of material can be obtained, it 
 is far better to use cells cut out of strong tubes, having 
 an interior diameter of about |ths of an inch, cut wedge- 
 shape, so that the thickness of the solution may be }th 
 
8PECTRO-MICR08COPT. 127 
 
 of an inch, or more, on one side, and not above - 4 ^jth on 
 the other ; and then the effect of different thicknesses can 
 easily be ascertained. 
 
 " Fortunately, the various modifications of the colouring 
 matter of blood yield such well-marked and characteristic 
 spectra, that there are few subjects to which the spectrum- 
 microscope can be applied with greater advantage than the 
 detection of blood-stains, even when perfectly dry. For 
 this purpose condensed light may be used, provided a 
 sufficiently bright light be thrown on the object by means 
 of a parabolic reflector or bull's-eye condenser. A speck 
 of blood on white paper shows the spectrum very well, 
 provided it be fresh, and the colour be neither too dark 
 nor too light, and the thickness of the colouring matter 
 neither too great nor too little. A mere atom, invisible to 
 the naked eye, which would not weigh above the ioo&oooth 
 of a grain, is then sufficient to show the characteristic 
 absorption-bands. They are, however, far better seen in 
 solution. About T&ffth of a grain of liquid blood, in a cell 
 of ^th of an inch in diameter, and an inch long, gives 
 a spectrum as well marked as could be desired. In 
 exhibiting the instrument to a number of persons at a 
 meeting, I have found that no object is more convenient, 
 or excites more attention, than one in which a number of 
 cells are fixed in a line, side by side, containing a solution 
 of various red-colouring matters. In one I mount blood, 
 which gives two well-marked absorption-bands in the 
 green ; in another magenta, which gives only one distinct 
 band in the green ; and in another I place the juice of 
 some red-coloured fruit, which shows no well-defined 
 absorption-band. Keeping a larger cell containing blood 
 on the stage attached to the eye-piece, these three objects 
 can be passed one after another in front of the object-glass, 
 and the total difference between the spectrum of blood and 
 that of either fruit-juice or magenta, and the perfect iden- 
 tity of the spectra when both are blood, can be seen at 
 a glance. By holding coloured glasses, which cut off the 
 red, but allow the green rays to pass, we can readily show 
 how the presence of any foreign colouring-matter, which 
 entirely alters the general colour, might not in any degree 
 disguise the characteristic part of the spectrum ; and by 
 
128 
 
 THE MICROSCOPE. 
 
 changing the cell held on the eye-piece for a tube con- 
 taining an ammoniacal solution of cochineal, it is easy to 
 t-how that, though it yields a spectrum with two absorp- 
 tion-bands, more like those due to blood than I have seen 
 in any other substance, they differ so much in relation, 
 size, and position, that ther<> is no chance of their being 
 confounded when compared together side by side.'' 1 
 
 We have been usually taught that the red-blood corpuscles consisted of two 
 substances, haematin and globulin; bat later researches lead to the belief 
 that they consist of one crystalline substance, termed globulin or hccmnto-globu- 
 lin. A solution of this substance, as well as of certain products of its decora- 
 position, produces the absorption-bands referred to. Hoppe was the first to 
 demonstrate this fact : he found that a very dilute solution of blood was suffi- 
 cient for the purpose. Professor Stokes proved that this colouring-matter is 
 
 capable of existing in two 
 states of oxidation, and that 
 _p a very different spectrum 
 is produced according as 
 the substance, which ht: 
 has termed cruorine, is in 
 a more or less oxidised 
 condition. 2 Proto -sulphate 
 of iron, or proto-chloride 
 of tin, causes the reduction 
 of the colouring-matter, 
 and, by exposure to air, 
 oxygen is absorbed, and 
 the solution again exhibits 
 the spectrum character- 
 istic of the more oxidised 
 state. The different sub- 
 stances obtained from 
 blood colouring - matter 
 produce different bands. 
 Thus, hcematin gives rise 
 to a band in the red spec- 
 trum ; hcemato - globulin 
 produces two bands, the 
 second twice the breadth 
 of the first in the yellow 
 portion of the spectrum 
 between the lines D and E, 
 No, 1. The absorption- 
 bands differ according to 
 the strength of the solu- 
 tion employed, and the 
 medium in which the blood- 
 alt is dissolved ; but an 
 exceedingly minute pro- 
 portion dissolved in water 
 is sufficient to bring out 
 very distinct bands. 
 
 No. 1. Arterial Blood, Scarlet Cruorine. 
 
 No. 2. Venous Blood, Purple Cruorine. 
 
 Xo. 3. Blood treated with Acetic Acid. 
 
 II 
 
 No. 4. Solution of Hir-matin. 
 
 ABSORPTION-BANDS, AFTER STORES. 
 
 (1) Popular Science Review, January, 1866. 
 
 (2) Professor Stokes, " On the Reduction and Oxidation of the Colouring- 
 matter of the Blood" (Proceed. Royal Soc. vol. xiii. p. 355). The oxidising 
 solution is made as follows : To a solution of proto-sulphate of iron, enough 
 tartaric acid is added to prevent precipitation by alkalies. A small quantity of 
 this solution, made slightly alkaline by ammonia or carbonate of soda, is to be 
 added to the weak solution of blood in water. 
 
THE CAMERA LUCIDA. 
 
 129 
 
 THE CAMERA LUCIDA. 
 
 The Camera Lucida, fig. 79, invented by Dr. Wollaston, 
 in 1807, is a valuable addition to the microscopy 
 for making drawings of structures, or for obtaining, 
 with a micrometer, measurements of objects. It consists 
 
 Fig. 79. 
 
 of a four-sided prism of glass, set in a brass frame or 
 as represented in the figure annexed ; and by means of m 
 short tube it is slipped over the front part of either of the 
 eye-pieces, its cap having been previously removed. 
 Mr. Ross attaches the prism, by two short supports, to 
 a circular piece of brass at the end of the tube ; on this it 
 can be slightly rotated, whilst the prism itself can also be 
 turned up or down, by means of two screws with milled 
 
ISO THE MICROSCOPE. 
 
 heads. So arranged, the camera may be adapted to the 
 eye-piece, the microscope having been previously placed 
 in a horizontal position ; if the light be then reflected up 
 through the compound body, an eye placed over the 
 square hole in the frame of the prism, will see the image of 
 any object on the stage upon a sheet of white paper 
 placed on the table immediately below it. But should it 
 happen that the whole of the field of view is not well 
 illuminated, then, either by revolving the circular plate or 
 turning the prism upon the screws, the desired object will 
 be effected. The chief difficulty in the use of this instru- 
 ment is for the artist to be able to see, at one and the 
 same time, the pencil and the image. To facilitate this in 
 some measure, the one or two lenses below the prism will 
 cause the rays from the paper and pencil to diverge at the 
 same angle as those received from the prism, whereby 
 both object and pencil may be seen with the same degree 
 of distinctness. 
 
 The following is the method for employing the Camera 
 Lucida with the microscope. The first step to be taken, 
 after the object about to be drawn has been properly 
 illuminated, adjusted, and brought into the centre of the 
 field of view, is to place the compound body of the micro- 
 scope in a horizontal position, and to fix it there. The 
 cap of the eye-piece having been removed, the camera is 
 to be slid on in its stead : if the prism be properly 
 adjusted, a circle of white light, with the object within it, 
 will be seen on a piece of white paper placed on the table 
 immediately under the camera, when the eye of the 
 observer is placed over the uncovered edge of the prism, 
 and its axis directed towards the paper on the table. 
 Should, however, the field of view be only in part illumi- 
 nated, the prism must either be turned round on the eye- 
 piece, or revolved on its axis, by the screws affixed to its 
 frame-work, until the entire field is illuminated. The 
 next step is to procure a hard, sharp-pointed pencil, which, 
 in order to be well seen, may be blackened with ink round 
 the point ; the observer is then to bring his eye so near 
 the edge of the prism that he may be able to see on the 
 paper, at one and the same time, the pencil-point and the 
 image of the object. When he has accomplished this, the 
 
THE CAMERA LUCID A. 131 
 
 pencil may be moved along the outline of the image, so 
 as to trace it on the paper. However easy this may 
 appear in description, it will be found very difficult in 
 practice ; and the observer must not be foiled in his first 
 attempts, but must persevere until he accomplishes his 
 purpose. Sometimes he will find that he can see the 
 pencil-point, and all at once it disappears : this happens 
 from the movement of the axis of the eye. The plan then 
 is to keep the pencil upon the paper, and to move about 
 the eye until the pencil is again seen, when the eye is to 
 be kept steadfastly fixed on the same position until the 
 entire outline is traced. It will be found the best plan for 
 the beginner to employ at first an inch object-glass, and 
 some object, such as a piece of moss, that has a well- 
 defined outline, and to make many tracings, and examine 
 how nearly they agree with each other ; and when he has 
 succeeded to his liking, he may then take a more compli- 
 cated subject. If the operation is conducted by lamp- 
 light, it will be found very advantageous not to illuminate 
 the object too much, but rather to illuminate the paper 
 on which the sketch is to be made, either by means of the 
 lamp with the condensing lens, or a small taper placed 
 near it. When the object is so complicated that too much 
 time would be required for it to be completed at one 
 sitting, the paper should be fixed to the table by a weight, 
 or on a board by drawing-pins. An excellent plan to 
 tdopt is to fix the microscope on a piece of deal about two 
 feet in length and one foot in breadth, and to pin the 
 paper to the same ; there will then be no risk of the shift- 
 ing of the paper, as, when the wood is moved, both micro- 
 scope and paper will move with it. In all sketches made 
 by the camera, certain things must be borne in mind; the 
 eye, when once applied to it, should be kept steadily fixed 
 in one position ; and if the sketches are to be reserved for 
 comparison with others, the distance between the paper 
 and the camera should be always the same. A short rule 
 or a piece of wood may be placed between the paper and 
 the under-surface either of the compound body or the arm 
 supporting it, in order to regulate the distance, as the size 
 of the drawing made by the camera will depend upon the 
 distance between it and the paper. It is aleo very desirable, 
 
 E2 
 
132 THE MICROSCOPE. 
 
 before the camera is removed, to make a tracing in some 
 part of the paper of two or more of the divisions of the 
 stage micrometer, in order that they may form a guide to 
 the measurement of all parts of the object. Some persons 
 cover the whole of the drawing over with squares, to facili- 
 tate, not only the measurement, but in order that a larger 
 or smaller drawing may be made from it than that given 
 by the camera. It must be recollected, that an accurate 
 outline is the only thing the camera will give : the finishing 
 of the picture must depend entirely upon the skill of the 
 artist himself. 
 
 ON THE POLARISATION OP LIGHT AS APPLIED TO THE 
 MICROSCOPE. 
 
 Common light moves in two planes at right angles to 
 each other, polarised light moves only in one plane. 
 Common light may be turned into polarised light either 
 by transmission or reflection ; in the first instance, one of 
 the planes of common light is got rid of by reflection, in 
 the other, by absorption. Huyghens was among the first 
 to notice that a ray of light has not the same properties 
 in every part of its circumference, and he compared it to 
 a magnet or a collection of magnets ; and supposed that 
 the minute particles of which it was said to be composed 
 had different poles, which, when acted on in certain ways, 
 arranged themselves in particular positions ; and thence 
 the term polarisation, a term having neither reference to 
 cause nor effect. It is to Malus, however, who, in 1808, 
 discovered polarisation by reflection, that we are indebted 
 for the series of splendid phenomena which have since that 
 period been developed ; phenomena of such surpassing 
 beauty as far to exceed all ordinary objects presented 
 to our eyes under the microscope. It has been truly 
 observed by Sir David Brewster, that " the application of 
 the principles of double refraction to the examination of 
 structures is of the highest value. The chemist may per- 
 form the most dexterous analysis ; the crystallographer 
 may examine crystals by the nicest determination of their 
 forms and cleavage : the anatomist or botanist may use 
 the dissecting knife and microscope with the most exqui- 
 site skill; but there are still structures in the mineral, 
 
POLARISED LIGHT. 
 
 133 
 
 vegetable, and animal kingdoms, which defy all such modes 
 of examination, and which will yield only to the magical 
 anafysis of polarised light. A body which is quite trans- 
 parent to the eye, and which might be judged as mono- 
 tonous in structure as it is in aspect, will yet exhibit, 
 under polarised light, the most exquisite organisation, and 
 will display the result of new laws of combination which 
 the imagination even could scarcely have conceived. In 
 evidence of the utility of this agent in exploring mineral, 
 vegetable, and animal structures, the extraordinary organi- 
 sation of Apophyllite and Analcime may be referred to ; 
 also the symmetrical and figurate depositions of siliceous 
 crystals in the epidermis of equisetaceous plants, and the 
 wonderful variations of density in the crystalline lenses of 
 the eyes of animals. 
 
 Oo 
 
 Fig. 80. 
 
 If we transmit a beam of the sun's light through a cir- 
 cular aperture into a darkened room, and if we reflect it 
 from any crystallised or uncrystallised body, or transmit 
 it through a thin plate of either of them, it will be reflcted 
 and transmitted in the very same manner, and with the 
 same intensity, whether the surface of the body is held 
 above or below the beam, or on the right side or left, pro- 
 vided that in all cases it falls upon the surface in the same 
 manner; or, what amounts to the same thing, the beam of 
 solar light has the same properties on all its sides; and 
 this is true, whether it is white light as directly emitted 
 from the sun, or from a candle or any burning or self- 
 luminous body; and all such light is called common light. 
 A section of such a beam of light will be a circle, like a b 
 c d, fig. 80 ; and we shall distinguish the section of a beam 
 
134 THE MICROSCOPE. 
 
 of common light by a circle with two diameters a b, c d, at 
 right angles to each other. 
 
 If we now allow the same beam of light to fall upon a 
 rhomb of Iceland spar, and examine the two circular 
 beams, o E e, formed by double refraction, we shall find, 
 1st, that the beams o E e have different properties on 
 different sides, so that each of them differs in this respect 
 from the beam of common light. 
 
 2d. That the beam o differs from E e in nothing ex- 
 cepting that the former has the same properties at the 
 sides a b' that the latter has at the sides c and d' ; or in 
 general that the diameters of the beam, at the extremities 
 of which the beam has similar properties, are at right 
 angles to each other, as a' b' and c' d' for example. 
 
 Thesa two beams, o, E e, are therefore said to be 
 polarised, or to be beams of polarised light, because they 
 have sides or poles of different properties and planes passing 
 through the lines a b, c d ; or a b' } c' d', are said to be the 
 planes of polarisation of each beam, because they have the 
 same property, and one which no other plane passing 
 through the beam possesses. 
 
 Now it is a curious fact, that if we cause the two 
 polarised beams o, E e to be united into one, or if we 
 produce them by a thin plate of Iceland spar, which is not 
 capable of separating them, we obtain a beam which has 
 exactly the same properties as the beam abed of common 
 light. Hence we infer that a beam of common light, a b 
 c d, consists of two beams of polarised light, w r hose plane 
 of polarisation, or whose diameters of similar properties, 
 are at right angles to one another. If o be laid above 
 E e, it will produce a figure like abed; and we shall 
 therefore represent polarised light by such figures. If we 
 were to place o above E e } so that the planes of polarisa- 
 tion a' b 1 and c d' coincide, then we should have a beam of 
 polarised light twice as luminous as either o or E e, and 
 possessing exactly the same properties; for the lines of 
 similar property in the one beam coincide with the lines of 
 similar property in the other. Hence it follows that there 
 are three ways of converting a beam of common light, a b 
 c d, into a beam or beams of polarised light. 
 
 1st. We may separate the beam of common light, abed, 
 
POLARISED LIGUT. 135 
 
 component parts o and E e. 2d. We may turn round 
 the planes of polarisation, abed, til! they coincide or are 
 parallel to each other. 3d. We may absorb or stop one of 
 the beams, and leave the other, which will consequently 
 be in a state of polarisation." 1 
 
 The first of these methods of producing polarised light 
 is that in which we employ a doubly refracting crystal, 
 and was first discovered to exist in a transparent mineral 
 substance called Iceland spar, calcareous spar, or carbonate 
 of lime. This substance is admirably adapted for exhibit- 
 ing this phenomenon, and is the one generally used by 
 microscopists. Iceland spar is composed of fifty-six parts 
 of lime and forty- four parts of carbonic acid ; it is found 
 in various shapes in almost all 
 countries; but whether found in 
 crystals or in masses, we can always 
 cleave it or split it into shapes re- 
 presented by fig. 81, which is called 
 a rhomb of Iceland spar, a solid 
 bounded by six equal and similar 
 rhomboidal surfaces, whose sides 
 are parallel, and whose angles b a c, Fig. si. 
 
 a c d, are 101 55' and 78 b'. The 
 
 line a x, called the axis of the rhomb, or of the crystal, is 
 equally inclined to each of the six faces at an angle of 
 45 23.' It is very transparent, and generally colourless. Its 
 natural faces when it is split are commonly even and per- 
 fectly polished ; but when they are not so, we may, by a 
 new clevage, replace the imperfect face by a better one, 
 or we may grind and polish an imperfect face. 
 
 It is found that in all bodies where there seems to be 
 an irregularity of structure, as salts, crystallised minerals, 
 fec., on light passing through them, it is divided into two 
 distinct pencils. If we take a crystal of Iceland spar, and 
 look at a black line or dot on a sheet of paper, there will 
 appear to be two lines or dots ; and on turning the spar 
 round, these objects will seem to turn round also; and 
 twice in the revolution they will fall upon each other, 
 which occurs when the two positions of the spar are exactly 
 opposite, that is, when turned one-half from the position 
 
 (1) Brewster's " Optics " 
 
THE MICROSCOPE. 
 
 iv&ere it is first observed. In the accompanying diagram, 
 Sgi 82, the line appears double, as a b and c d, or the dot, 
 
 Fig. 82. 
 
 as e and /. Or allow a ray of light, g h, to fall thus on the 
 crystal, it will in its passage through be separated into two 
 rays, hf, he; and on coming to the opposite surface of the 
 crystal, they will pass out at ef in the direction of i k, 
 parallel to g h. The plane I m n o is designated the prin- 
 cipal section of the crystal, and the line drawn from the 
 solid angle I to the angle o is where the axis of the crystal 
 is contained ; it is also the optic axis of the mineral. Now 
 when a ray of light passes along this axis, it is undivided, 
 and there is only one image; but in all other directions 
 there are two. 
 
 If two crystals of Iceland spar be used, the only differ- 
 ence will be, that the objects seem farther apart, from the 
 increased thickness. But if two crystals be placed with 
 tfeeir principal sections at right angles to each other, the 
 ordinary ray refracted in the first will be the extraordinary 
 aa the second, and so on vice versd. At the intermediate 
 position of the two crystals there is a subdivision of each 
 ray, and therefore four images are seen ; when the crystals 
 are at an angle of 45 to each other, then the images are 
 U seen of equal intensity. 
 
 Mr. Nicol first succeeded in making rhombs of Iceland 
 spar into single-image prisms, by dividing one into two 
 equal portions. His mode of proceeding is thus described 
 in the Edinburgh Philosophical Journal (vol. vi. p. 83) : 
 
POLARISED LIGHT. 137 
 
 "A rhomb of Iceland spar of one-fourth of an inch in 
 length, and about four-eighths of an inch in breadth and 
 thickness, is divided into two equal portions in a plane, 
 passing through the acute lateral angle, and nearly touching 
 the obtuse solid angle. The sectional plane of each of 
 these halves must be carefully polished, and the portions 
 cemented firmly with Canada balsam, so as to form a 
 rhomb similar to what it was before its division; by this 
 management the ordinary and extraordinary rays are so 
 separated that only one of them is transmitted : the cause 
 of this great divergence of the rays is considered to be 
 owing to the action of the Canada balsam, the refractive 
 index of which (1-549) is that between the ordinary 
 (1-6543) and the extraordinary (1'4833) refraction of 
 calcareous spar, and which will change the direction of 
 both rays in an opposite manner before they enter the 
 posterior half of the combination." The direction of rays 
 
 Fig. 83. 
 
 passing through such a prism is indicated by the arrow, 
 fig. 83, and the combination is shown mounted, one for 
 
 Fig. 84. 
 
 Fig. 85. 
 
 use under the stage of the microscope, fig. 84, termed the 
 polarizer; another, fig. 85, screwed on to and above the 
 
1S8 
 
 THE MICROSCOPE. 
 
 object-glasses, is called the analyser. The definition is 
 better if the analyser be placed at top of the A eye-piece, 
 and it is more easily rotated than the polariser. 
 
 Method of using the polarising JPrism, fig. 84. After 
 having adapted it to slide into a groove on the under-surface 
 of the stage, it is held in its place by turning the small 
 milled-head screw at one end : the other prism, fig. 85, is 
 screwed on above the object-glasses, and made to pass into 
 the body of the microscope itself. The light having been 
 reflected through them by the uijrror, it becomes necessary 
 to make the axes of the two prisms coincide ; this is done 
 by regulating the milled-head screw, until by revolving the 
 polarising prism, the field of view is entirely darkened twice 
 during one revolution. This should be 
 ascertained, and carefully corrected by 
 the maker and adapter of the apparatus. 
 If very minute salts or crystals are to be 
 viewed, it is preferable to place the ana- 
 lyser above the eye-piece; it will then 
 require to be mounted as in fig. 86. Thus 
 the polariscope consists of two parts ; one 
 for polarising, the other for analysing 
 or testing the light, There is no essen- 
 tial difference between the two parts, 
 except what convenience or economy may 
 lead us to adopt ; and either part, there- 
 fore, may be used as polariser or analyser ; 
 but whichever we use as the polariser, the 
 other becomes the analyser. 
 The tourmaline, a precious stone of a neutral or bluish 
 tint, forms an excellent analyser; it should be cut about 
 o*0th of an inch thick, and parallel to its axis. The great 
 objection to it is, that the transmitted polarised beam is 
 more or less coloured. The best tourmaline to choose is 
 the one that stops the most light when its axis is at right 
 angles to that of the polariser, and yet admits the most 
 when in the same plane. It is necessary to choose the 
 stme as perfect as possible, the size is of no importance 
 when used with the microscope. 
 
 In the illumination of objects by polarised light, when 
 under view with high powers, for the purpose of obtaining 
 
 Fig. 86. 
 
POLARISED LIGHT. 139 
 
 the maximum effect, it is also requisite that the angle of 
 aperture of the polariser should be the same as the object- 
 glass, each ray of which should be directly opposed by a 
 ray of polarised light. The Polarising Condenser is merely 
 an ordinary achromatic condenser of large aperture, close 
 under the bottom lens of which is placed a plate of tour- 
 maline, used in combination with a superposed film of 
 selenite or not, as required . The effect of this arrangement 
 on some objects is very remarkable, bringing out strongly 
 colours which are almost invisible by the usual mode. 
 
 The production of colour by polarised light has been 
 thus most clearly and comprehensively explained by Mr. 
 Woodward, in his " Introduction to the Study of Polarised 
 Light." 1 
 
 , 
 
 Fig. 87 A. 
 
 abed represent the rectangular vibrations by which 
 a ray of common light is supposed tb be propagated. 
 
 c, a plate of tourmaline, called in this situation the 
 polariser, and so turned that a b may vibrate in the plane 
 of its crystallographical axis. 
 
 (1) Mr. Woodward constructed a very available form of polariscope for most 
 purposes ; the instrument is described in Element* of Natural Philosophy, by 
 Jabez Hogg. 
 
140 THE MICROSCOPE. 
 
 f t light polarised by e, by stopping the vibrations c d, 
 and transmitting those of a b. 
 
 g, a piece of selenite of such a thickness as to produce 
 red light, and its complementary colour green. 
 
 k, the polarised light / bifurcated, or divided into ordi- 
 nary and extraordinary rays, and thus said to be de- 
 polarised by the double refractor g, and forming two planes 
 of polarised light, o and e, vibrating at right angles to 
 each other. 
 
 i, a second plate of tourmaline, here called the analyser, 
 with its axis in the same direction as that of e, through 
 which the several systems of waves of the ordinary and 
 extraordinary rays h, not being inclined at a greater 
 angle to the axis of the analyser than that of 45 degrees, 
 are transmitted and brought together under conditions 
 that may produce interferences. 
 
 &, the waves R o and R e, for red light of the ordinary 
 and extraordinary systems meeting in the same state of 
 vibration, occasioned by a difference of an even number 
 of half undulations, and thus forming a wave of doubled 
 intensity for red light. 
 
 I m, the waves Y o and Y e and B o and B e for yellow and 
 blue of the ordinary and extraordinary systems respec- 
 tively meeting together, with a difference of an odd 
 number of half undulations, and thus neutralising each 
 other by interferences. 
 
 n, red light, the result of the coincidence of the waves 
 for red light, and the neutralisation by interferences of 
 those for yellow and blue respectively. 
 
 A, fig. 87 B, depolarised light, as fig. 87 A. 
 
 i, the analyser turned one quarter of a circle, its axis 
 being at right angles to that of i in fig. 87 A. 
 
 k t the waves R o ne, for red light of the ordinary and 
 extraordinary systems meeting together with a difference 
 of an odd number of half undulations, and thus neutral- 
 ising each other by interference. 
 
 I m, the waves Y o Y e and BO Be, for yellow and blue of 
 the two systems severally meeting together in the same 
 state of vibration, occasioned by the difference of an even 
 number of half undulations, and forming by their coin- 
 cidences waves of doubled intensity for yellow and blue 
 light. 
 
POLAUISED LIGHT. 141 
 
 n, green light, the result of the coincidences of the 
 waves for yellow and blue light respectively, and the 
 neutralisation by interference of those for red light. 
 
 By substituting Nicol's prisms for the two plates of 
 tourmaline, and by the addition of the object-glass and 
 eye -piece, the diagrams would then represent the passage 
 of polarised light through a microscope. 
 
 For showing objects by polarised light under the micro- 
 scope that are not in themselves doubly refractive, put 
 upon the stage a film of selenite, which exhibits, under 
 ordinary circumstances, the red ray in one position of the 
 polarising prism, and the green ray in another, using a 
 double-image prism over the eye-piece ; each arc will 
 assume one of these complementary colours, whilst the 
 centre of the field will remain colourless. Into this field 
 introduce any microscopic object which in the usual 
 arrangement of the polariscope undergoes no change in 
 colour, when it will immediately display the most brilliant 
 effects. Sections of wood, feathers, algae, and scales, are 
 among the objects best suited for this kind of exhibition. 
 The power suited for the purpose is a two-inch object- 
 glass, the intensity of colour, as well as the separating 
 power of the prism, being impaired under much higher 
 amplification ; although in some few instances, such as in 
 viewing animalcules, the one-inch object-glass is perhaps 
 to be preferred. 
 
 Selenite is the native crystallised hydrated sulphate of 
 lime. A beautiful fibrous variety called satin gypsum is 
 found in Derbyshire. It is found also at Shotover Hill, 
 near Oxford, where the labourers call it quarry-glass. Very 
 large crystals of it are found at Montmartre, near Paris. 
 The form of the crystal most frequently met with is that 
 of an oblique rectangular prism, with ten rhomboidal 
 faces, two of which are much larger than the rest. It is 
 usually slit into thin laminae parallel to these large 
 lateral faces; the film having a thickness of from one- 
 twentieth to the one-sixtieth of an inch. In the two rec- 
 tangular directions they allow perpendicular rays of pola- 
 rised light to traverse them unchanged ; these directions 
 are called the neutral axes. In two other directions, 
 however, which form respectively angles of 45 with the 
 
2 THE MICROSCOPE. 
 
 neutral axes, these films have the property of double 
 refraction. These directions are known as the depolarising 
 axes. 
 
 The thickness of the film of selenite determines the 
 particular tint. If, therefore, we use a film of irregular 
 thickness, different colours are presented by the different 
 thicknesses. These facts admit of very curious and beau- 
 tiful illustration, when used under the object placed on the 
 stage of the microscope. The films employed should be 
 mounted between two glasses for protection. Some persons 
 employ a large film mounted in this way between plates of 
 glass, with a raised edge, to act as a stage for supporting 
 the object, it is then called the " selenite stage." The best 
 film for the microscope is that which gives blue, and its 
 complementary colour yellow. Mr. Darker has constructed 
 a very neat stage of brass for this purpose, producing a 
 mixture of all the colours by superimposing three films, 
 one on the other; by a slight variation in their positions, 
 produced by means of an endless-screw motion, all the 
 colours of the spectrum are shown. When objects are 
 thus exhibited, we must bear in mind that all the negative 
 tints, as we term them, are diminished, and all the 
 positive ones increased; the effect of this plate is to mask 
 the true character of the phenomena. Polarised structures 
 should therefore never be drawn and coloured under such 
 conditions. 
 
 Dr. Herapath, of Bristol, described a salt of quinine, 
 which is remarkable for its polarising properties. The salt 
 was first accidentally observed by Mr. Phelps, a pupil of 
 Dr. Herapath' s, in a bottle which contained a solution of 
 disulphate of quinine: the salt is formed by dissolving 
 disulphate of quinine in concentrated acetic acid, then 
 warming the solution, and dropping into it carefully, and 
 by small quantities at a time, a spirituous solution of 
 iodine. On placing this mixture aside for some hours, 
 brilliant plates of the new salt will be formed. The crystals 
 of this salt, when examined by reflected light, have a 
 brilliant emerald-green colour, with almost a metallic 
 lustre; they appear like portions of the elytrse of cantha- 
 rides, and are also very similar to murexide in appearance. 
 When examined by transmitted light, they scarcely possess 
 
1OLARISED LIGHT. 143 
 
 any colour, there is only a slightly olive-green tinge ; but 
 if two crystals, crossing at right angles, be examined, the 
 spot \vhere they intersect appears perfectly black, even if 
 the crystals are not one five-hundredth of an inch in thick- 
 ness. * If the light be in the slightest degree polarised as 
 by reflection from a cloud, or by the blue sky, or from the 
 glass surface of the mirror of the microscope placed at the 
 polarising angle 56 45' these little prisms immediately 
 assume complementary colours: one appears green, and 
 the other pink, and the part at which they cross is a 
 chocolate or deep chestnut-brown, instead of black. As 
 the result of a series of very elaborate experiments, Dr. 
 Herapath finds that this salt possesses the properties cf 
 tourmaline in a very exalted degree, as well as of a plate 
 of selenite ; so that it combines the properties of polarising 
 a ray and of depolarising it. Dr. Herapath has succeeded 
 in making artificial tourmalines large enough to surmount 
 the eye-piece of the microscope; so that all experiments 
 with those crystals upon polarised light may be made 
 without the tourmaline or Nicol's prism. The brilliancy 
 of the colours is much more intense with the artificial 
 crystal than when employing the natural tourmaline. As 
 an analyser above the eye-piece, it offers some advantages 
 over the Nicol's prism in the same position, as it gives a 
 perfectly uniform tint of colour over a much more exten- 
 sive field than can be had with the prism. 1 As these 
 crystals are liable to be injured by damp, and thus lose 
 their polarising property, when out of use they should he 
 kept in a dark dry place. 
 
 " The following experiments, if carefully performed, will 
 illustrate the most striking phenomena of double refraction, 
 and form a useful introduction to the practical application 
 of this principle. 
 
 (1) Dr. Herapath has given a later and better process for the manufacture of 
 these artificial tourmalines in the Quarterly Journal of Microscopical Science for 
 January, 1854. "These beautiful rosette crystals are best made as follows : 
 Take a moderately strong solution of Cinchonidine in Herapath's test-fluid (as 
 already described). A little of this is dropped on the centre of a slide and laid 
 down for a time, until the first crystals are observed to be formed near the 
 margin. The slide should now be placed upon the stage of the microscope, and 
 the progress of formation of the crystals closely watched. When these are seen 
 to be large enough, and it is deemed necessary to stop their further development, 
 the slide must be quickly transferred to the palm of the hand, the warmth ol 
 whkh will be found sufficient to stop further crystallization." 
 
144 THE MICROSCOPE. 
 
 "A plate of brass, fig. 88, three inches by one, perforated 
 with a series of holes from about one-sixteenth to one- 
 
 Fig. 88. Red is represented by perpendicular lines ; Green by oblique. 
 
 fourth of an inch in diameter; the size of the smallest 
 should be in accordance with the power of the object-glass, 
 and the separating power of the double refraction. 
 
 " Experiment 1. Place the brass plate so that the smallest 
 hole shall be in the centre of the stage of the instrument; 
 employ a low power (1^ or 2 inch) object-glass, and adjust 
 the focus as for an ordinary microscopic object; place the 
 double image prism over the eye-piece, and there will 
 appear two distinct images; then, by revolving the prism, 
 these will describe a circle, the circumference of which 
 cuts the centre of the field of view ; the one is called the 
 ordinary, the other the extraordinary ray. By passing the 
 slide along, that the larger orifices may appear in the field, 
 the images will not be completely separated, but will 
 overlap, as represented in the figure. 
 
 " Experiment 2. Screw the Nicol's prism into its place 
 under the stage, still retaining the double image prism 
 over the eye-piece ; then, by examining the object, there 
 will appear in some positions two, but in others only one 
 image; and it will be observed, that at 90 from the latter 
 position this ray will be cut off, and that which was first 
 observed will become visible; at 180, or one-half the 
 circle, an alternate change will take place; at 270, another 
 change; and at 360, or the completion of the circle, the 
 original appearance. 
 
 " Before proceeding to the next experiment, it will be as 
 well to observe the position of the Nicol's prism, which 
 should be adjusted with its angles parallel to the square 
 parts of the stage. In order to secure the greatest 
 brilliancy in the experiment, the proper relative position 
 of the selenite may be determined by noticing the natural 
 
POLARISED LIGHT. 145 
 
 flaws in the film, which will be observed to run parallel 
 with each other; these flaws should be adjusted at about 
 46 from the square parts of the stage, to obtain the 
 greatest amount of depolarisation. 
 
 "Experiment 3. If we now take the plate of seleuite thus 
 prepared, and place it under the piece of brass on the 
 stage, we shall see, instead of the alternate black and 
 white images, two coloured images composed of the con- 
 stituents of white light, which will alternately change by 
 revolving the eye-piece at every quarter of the circle ; then, 
 by passing along the brass, the images will overlap ; and 
 at the point at which they do so, white light will be pro- 
 duced. If, by accident, the prism be placed at an angle of 
 45 from the square part of the stage, no particular colour 
 will be perceived; and it will then illustrate the phenomena 
 of the neutral axis of the selenite, because when placed in 
 that relative position no depolarisation takes place. The 
 phenomena of polarised light may be further illustrated 
 by the addition of a second double image prism, and a 
 film of selenite adapted between the two. The systems 
 of coloured rings in crystals cut perpendicularly to tho 
 principal axis of the crystal are best seen by employing the 
 lowest object-glass." 
 
 To show the phenomena of the rings round the optic 
 axes of the crystals, Mr. Lobb adopts the following plan, 
 which is by far the best, and the rings are exhibited in the 
 greatest perfection : 
 
 1. The B eye-piece without a diaphragm, and the lenses 
 so adjusted that the field-lens may be brought nearer to, 
 or farther from the eye-lens as occasion may require ; thus 
 giving different powers, and different fields, and when 
 adjusted for the largest field it will be full 15 inches, and 
 take in the widest separation of the axis of the aragonite. 
 
 2. A crystal stage to receive the crystals, and to be 
 placed over the eye-piece, so constructed as to receive a 
 tourmaline, and that to turn round. 
 
 3. A tourmaline of a blue tint. 
 
 4. A large Nicol's prism as a polariser. 
 
 5. A common t.vo-inch lens, not achromatic; which 
 must be set in a brass tube long enough when screwed into 
 
 L 
 
146 THE MICROSCOPE. 
 
 the microscope to reach the polariser, that all extraneous 
 light may be excluded. 
 
 The concave mirror should be used with a bull's-eye 
 condenser by lamplight. The condenser may be dispensed 
 with by daylight. The above apparatus is furnished by 
 Messrs. Powell and Lealand. 
 
 The crystals best adapted to show the phenomena of 
 rings round the optic axes, are : 
 
 Quartz. A uniaxial crystal, one system of rings, no 
 entire cross of black, only the ends of it, the centre being 
 coloured, and as the tourmaline is revolved, the colour 
 gradually changing into all the colours of the spectrum, 
 one colour only displayed at once. 
 
 Quartz. Cut so as to exhibit right-handed polarisation. 
 
 Quartz. Cut so as to exhibit left-handed polarisation ; 
 
 that is, the one shows the same phenomena when the 
 
 tourmaline is turned to the right, as the other does when 
 
 turned to the left. 
 
 Quartz. -Cut so as to exhibit straight lines. 
 Calc Spar. A uniaxial crystal, one system of rings, and 
 a black cross, which changes into a white cro^s on revolving 
 the tourmaline, and the colours of the rings into their 
 complementary colours, 
 
 Topaz. A biaxial crystal, although it has two axes, only 
 exhibits one system of rings with one fringe, owing to the 
 wide separation of the axes. The fringe and colours 
 change on revolving the tourmaline ; this is the case in all 
 the crystals. 
 
 Borax. A biaxial crystal; the colours more intense 
 than in topaz, but the rings not so complete, only one 
 set of rings taken in, from the same cause as topaz. 
 
 Rochelle Salt. A biaxial crystal; the colours more 
 widely spread. Very beautiful. Only one set of rings 
 taken in. 
 
 Carbonate of Lead. A biaxial crystal, axes not much 
 separated, both systems of rings exhibited, far more widely ' 
 spread than those of nitre. 
 
 Aragonite. A biaxial crystal, axes widely separated j but 
 both systems of rings exhibited, and decidedly the best 
 crystal for displaying the phenomena of biaxial crystals. 
 The field-lens of the eye-piece requires to be brought as 
 
POLARISED LIGHT. 14f 
 
 close as possible to the eye-lens, to see properly the pheno- 
 mena in quartz and aragonite ; it must be placed at an 
 intermediate distance for viewing topaz, borax, RocheUe 
 salt, and carbonate of lead; it must be drawn out to Ha 
 full extent to view nitre and calc spar. 
 
 The powers of the micro-polariscope cannot be better 
 displayed than in the exhibition of the foregoing pheno- 
 mena; there is nothing more beautiful, and few studies 
 more interesting and enlarging to the mind than that of 
 light, whether common or polarised, which must be entered 
 upon if the phenomena are to be understood. 
 
 The crystal eye-piece, with an artificial tourmaline as an 
 analyser, will be found very useful for polariscope objecta 
 generally; there is some spherical aberration, but the 
 largeness of the field far more than compensates for the 
 same; it does best for those objects that require the two- 
 inch object glass. 
 
 Mr. Darker of Lambeth, Messrs. Elliott of the Strand, 
 Messrs. Home and Co., Newgate St., and M. Soliel of 
 Paris, supply properly cut crystals. 
 
 It was long believed that all crystals had only one axis 
 of double refraction; but Brewster found that the great 
 body of crystals, which are either formed by art, or which 
 occur in the mineral kingdom, have two axes of double re- 
 fraction, or rather axes around which the double refractioa 
 takes place; in the axes themselves there is no double 
 refraction. 
 
 Nitre crystallises in six-sided prisms with angles of about 
 120. It has two axes of double refraction, along which 
 a ray of light is not divided into two. These axes are each 
 inclined about 21 to the axes of the prism, and 5 to each 
 other. If, therefore, we cut off a piece from a prism of 
 nitre with a knife driven by a smart blow of a hamme^ 
 and polish the two surfaces perpendicular to the axes of 
 the prism, so as to leave the thickness of the sixth or 
 eighth of an inch, and then transmit a ray of polarised 
 light along the axes of the prism, we shall see the double 
 system of rings shown in figs. 89 and 90. 
 
 When the line connecting the two axes of the crystal a 
 inclined 45 to the plane of primitive polarisation, a cross 
 is seen as at fig. 89, on revolving the nitre, it gradually 
 
 L2 
 
148 THE MICROSCOPE. 
 
 assumes the form of the two hyperbolic curves, fig. 90. But 
 if the tourmaline be revolved, the black crossed lines will 
 
 Fig. 90. 
 
 be replaced by white spaces, and the red rings by green, 
 the yellow by indigo, and so on. These systems of rings 
 have, generally speaking, the same colours as those of 
 thin plates, or as those of a system of rings round one 
 axis. The orders of the colours commence at the centres 
 of each system; but at a certain distance, which corre- 
 sponds to the sixth ring, the rings, instead of returning 
 and encircling each pole, encircle the two poles as an 
 ellipse does its two foci. When we diminish or increase 
 the thickness of the plate of nitre, the rings are diminished 
 or increased accordingly. 
 
 Small specimens of salts may also be crystallised and 
 mounted in Canada balsam for viewing under the stage of 
 the microscope ; by arresting the crystallisation at certain 
 stages, a greater variety of forms and colours will be 
 obtained : we may enumerate salicine, asparagine, acetate 
 of copper, phospho-borate of soda, sugar, carbonate of 
 lime, chlorate of potassa, oxalic acid, and all the oxalates 
 found in urine, with the other salts from the same fluid, a 
 few of which are shown at fig. 91. 
 
 Dr. W. B. Herapath contributed an interesting addi- 
 tion to the uses of polarised light, by applying it to discover 
 the salts of alkaloids, quinine, &c. in the urine of patients. 
 
POLARISED LIGHT. 
 
 He says : " It has long been a favourite subject of inquiry 
 with the professional man to trace the course of remedies 
 
 (V 
 
 . Urinary Salts. 
 
 a, Uric acid; b, Oxidate of lime, octahedral crystals of; c, Oxalate of lime 
 allowed to dry, forming a black cube; d, Oxalate of lime, as it occasionally 
 appears, termed the dumb-bell crystal. 
 
 in the system of the patient under his care, and to know 
 what has become of the various substances which he might 
 have administered during the treatment of the disease. 
 
 " Having been struck with the facility of application, 
 and the extreme delicacy of the reaction of polarised light, 
 when going through the series of experiments upon the 
 sulphate of iodo-quinine, I determined upon attempting 
 to bring this method practically into use for the detection 
 of minute quantities of quinine in organic fluids; and after 
 more or less success by different methods of experimenting, 
 I have at length discovered a process by which it is possible 
 to obtain demonstrative evidence of the presence of quinine, 
 even if in quantities not exceeding the one-millionth part 
 of a grain; in fact, in quantities so exceedingly minute, that 
 all other methods would fail in recognising its existence. 
 Take for test fluid a mixture of three drachms of pure 
 acetic acid, with one fluid-drachm of rectified spirits-of- 
 wine, to which add six drops of diluted sulphuric acid 
 
 " One drop of this test-fluid placed on a glass-slide, 
 and the merest atom of the alkaloid added, in a short time 
 
150 
 
 THE MICROSCOPE. 
 
 eolution will take place ; then, upon the tip of a very fine 
 glass-rod let an extremely minute drop of the alcoholic 
 solution of iodine be added. The first effect is the produc- 
 tion of the yellow or cinnamon-coloured compound of iodine 
 and quinine, which forms as a small circular spot ; the 
 alcohol separates in little drops, which by a sort of repul- 
 sive movement, drive the fluid away ; after a time, the acid 
 liquid again flows over the spot, and the polarising crystals 
 of sulphate of iodo-quinine are slowly produced in beautiful 
 rosettes. This succeeds best without the aid of heat. 
 
 " To render these crystals evident, it merely remains to 
 bring the glass-slide upon the field of the microscope, with 
 the selenite stage and single tourmaline, or Nicol's prism, 
 "beneath it ; instantly the crystals assume the two comple- 
 mentary colours of the stage ; red and green, supposing 
 that the pink stage is employed, or blue and yellow, pro- 
 Tided the blue selenite is made use of. All those crystals 
 at right angles to the plane of the tourmaline, producing 
 
 .-In tliis figure heraldic lim-s are adopted to denote colour. The 
 lotted parts indicate yellow, the straight lines red, the horizontal lines blue, 
 a the diagonal, -or oblique lines, green. The arrows show the plane of the 
 tourmaline, a, blue stage ; ft, red stage of selenite employed. 
 
 tL&t tint which an analysing-plate of tourmaline would 
 produce when at right angles to the polarising-plate ; 
 
POLARISED LIGHT. 
 
 151 
 
 whilst those at 90 to these educe the complementary tint, 
 as the analysing-plate would also have done if revolved 
 through an arc of 90. 
 
 "This test is so ready of application, and so delicate, 
 that it must become the test, par excellence, for quinine : 
 fig. 92, a and 6. Not only do these peculiar crystals act 
 in the way just related, but they may be easily proved to 
 possess the whole of the optical properties of that remark- 
 able salt of quinine, the sulphate of iodo-quinine. 
 
 " To test for quinidine, it is merely necessary to allow 
 the drop of acid solution to evaporate to dryness upon the 
 slide, and to examine the crystalline mass by two tourma- 
 lines, crossed at right angles, and without the stage. 
 Immediately little circular discs of white, with a well- 
 defined black cross very vividly shown, start into existence, 
 should quinidine be present even in very minute traces. 
 These crystals are represented in fig. 93. 
 
 Fig. 93. 
 
 " If we employ the selenite stage in the examination of 
 this object, we obtain one of the most gorgeous appear- 
 ances in the whole domain of the polarising-microscope : 
 the black cross at once disappears, and is replaced by one 
 which consists of two colours, being divided into a cross 
 
152 
 
 THE MICROSCOPE. 
 
 Pig. 94. Snow Cryitali. 
 
SNOW CRYSTALS. 153 
 
 having a red and green fringe, whilst the four intermediate 
 sectors are of a gorgeous orange-yellow. These appear- 
 ances alter upon the revolution of the analysing- plate of 
 tourmaline ; when the blue stage is employed, the cross 
 will assume a blue or yellow tint, according to the position 
 of the aualysing-plate. These phenomena are analogous 
 to those exhibited by certain circular crystals of boracic 
 acid, and to those circular discs of salicine (prepared by 
 fusion) ; the difference being, that the salts of quinidine 
 have more intense depolarising powers than either of the 
 other substances ; besides which, the mode of preparation 
 effectually excludes these from consideration. Quinine 
 prepared in the same manner as quinidine has a very 
 different mode of crystallisation ; but it occasionally pre- 
 sents circular corneous plates, also exhibiting the black 
 cross and white sectors, but not with one-tenth part of the 
 brilliancy, which of course enables us readily to discrimi- 
 nate the two." 
 
 Ice doubly refracts, while water singly refracts. Ice 
 takes the rhomboidic form ; and snow in its crystalline 
 form may be regarded as the skeleton crystals of this 
 system. A sheet of clear ice, of about one inch thick, and 
 slowly formed in still weather, will show the circular rings 
 and cross if viewed by polarised light. 
 
 It is probable that the conditions of snow formation are 
 more complex than might be imagined, familiar as we are 
 with the conditions relating to the crystallisation of water 
 on the earth's surface. Dr. Smallwood, of Isle Jesus, 
 Canada East, has traced an apparent connection between 
 the form of the compound varieties of snow crystals and 
 the electrical condition of the atmosphere, whether nega- 
 tive or positive ; and is instituting experiments for his 
 better information on the subject. 
 
 A great variety of animal, vegetable, and other sub- 
 stances possess a doubly refracting or depolarising struc- 
 ture, as : a quill cut and laid out flat on glass ; the cornea 
 of a sheep's eye ; skin, hair, a thin section of a finger-nail ; 
 sections of bone, teeth, horn, silk, cotton, whalebone'; 
 stems of plants containing silica or flint ; barley, wheat, <kc. 
 The larger-grained starches foi*m splendid objects ; tons- 
 les-mois, being the largest, may be taken as a type of all 
 
51 THE MICROSCOPE. 
 
 the others. It presents a black cross, the arms of which 
 meet at the hilum. On rotating the analyser, the 
 
 black cross disappears, and 
 at 90 is replaced by a white 
 cross ; another, but much 
 fainter black cross being per- 
 ceived between the arms of 
 the white cross. Hitherto, 
 however, no colour is percep- 
 tible. But if a thin plate of 
 selenite be interposed between 
 the starch-grains and the po- 
 
 Poiat; Starch, seen under polarised ,. , ij-j j 
 
 ii g ht. lanser, most splendid and 
 
 delicate colours appear. All 
 
 the colours change by revolving the analyser, and become 
 complementary at every quadrant of the circle. West and 
 East India arrow-root, sago, tapioca, and many othei 
 starch-grains, present a similar appearance ; but in pro- 
 portion as the grains are smaller, so are their markings 
 and colourings less distinct. 
 
 " The application of this modification of light to the 
 illumination of very minute structures has not yet been 
 fully carried out ; but still there is no test of differences 
 in density between any two or more parts of the same 
 substance that can at all approach it in delicacy. All 
 structures, therefore, belonging either to the animal, vege- 
 table, or mineral kingdom, in which the power of unequal 
 or double refraction is suspected to be present, are those 
 that should especially be investigated by polarized light. 
 Some of the most delicate of the elementary tissues of 
 animal, such as the tubes of nerves, the ultimate fibrillse 
 of muscles, &c., are amongst the most striking subjects that 
 may be studied with advantage under this method of illu- 
 mination. Every structure that the microscopist is 
 investigating should be examined by this light, as well 
 as by that either transmitted or reflected. Objects 
 mounted in Canada balsam, that are far too delicate to 
 exhibit any structure under transmitted, will often be 
 well seen under polarised light ; its uses, therefore, are 
 manifold."i 
 
 (1) Quekett's Practical Treatise on the Use of the Mitroscope. 
 
APPLICATION 01-' rilOTOGR.miY. 15-1) 
 
 A fine effect may be obtained by using Furze's spotted 
 lens, with a Herapathite polariser; see Mic. Soc. Trans. 
 2d series, vol. iii. p. 63. 
 
 APPLICATION OF PHOTOGRAPHY TO THE MICROSCOPE. 
 
 At the time this book was projected, it was thought that 
 if the objects so beautifully exhibited under the microscope 
 could be drawn by light on the page of the book, or on 
 the wood-blocks, so that the engraver might work directly 
 from the drawings thus made, truthfulness would be in- 
 sured, and we should present to the reader a valuable 
 record of microscopic research never before seen or 
 attempted. But in this we were doomed to disappoint- 
 ment by the existence of a patent, which presented ob- 
 stacles too great to be surmounted ; and the idea was 
 abandoned, with the exception of a few drawings then 
 prepared, and ready to hand : the patent restrictions having 
 been since removed, we have embodied them in our pages. 
 The eye and feet of fly, antenna of moth, paddles of whirli- 
 gig, with a few others, were first taken on a film of collo- 
 dion, then floated off the glass on to the surface of a block 
 of wood, the wood having been previously and lightly 
 inked with printer's ink or amber-varnish, and the film 
 gently rubbed or smoothed down to an even surface, at 
 the same time carefully pressing out all bubbles of air or 
 fluid. 
 
 For the purposes of photography the only necessary 
 addition to the ordinary microscope is that of a dark 
 chamber ; it should indeed form a camera obscura, having 
 at one end an aperture for the insertion of the eye-piece 
 end of the microscopic tube, and at the other a groove for 
 carrying the crown-glass for focussing. This dark chamber 
 must not exceed eighteen inches in length ; for if longer, 
 the pencil of light transmitted by the object-glass is dif- 
 fused over too large a surface, and a faint and unsatis- 
 factory picture results therefrom. Another advantage is, 
 that pictures at this distance are in size very nearly equal 
 to the object seen in the microscope. In some instances, 
 oetter pictures are produced by taking away the eye-pieoe 
 
1-3G THE MICROSCOPE. 
 
 of the microscope altogether. The time of producing the 
 picture varies from five to twenty seconds, with the strength 
 of the daylight. A camphine lamp, light Caunel coal-gas, 
 or the lime-light, will enable a good manipulator to pro- 
 duce pictures nearly equal to those produced by sun-light. 
 Collodion offers the best medium, as a strong negative can 
 be made to produce any number of printed positives. 
 
 The light is transmitted from the mirror through the 
 object and lenses, and brought to a focus on the ground- 
 glass, or prepared surface of collodion, in the usual manner. 
 Care must be taken not to use the burning focus of the 
 lenses. The gas microscope may be used to make an 
 enlarged copy of an object, it is only necessary to pin up 
 against the screen a piece of prepared calotype paper to 
 receive the reflected image. Mr. Wenham gives direc- 
 tions for improving " microscopic photography " in the 
 Quarterly Journal of Microscopical Science for January, 
 1855. In this paper he has shown how to insure quick 
 and accurate focussing ; or, in other words, the making of 
 the actinic and visual foci of the objective coincident. The 
 simplest and cheapest way of producing coincidence is to 
 screw a biconvex lens into the place of the back-stop of 
 the object-glass, which thus acts as part of its optical com- 
 bination. An ordinary spectacle lens, carefully centred 
 and turned down to the required size, answers the purpose 
 exceedingly well. 
 
 An excellent method has been proposed and adopted by 
 Mr. Wenham, for exhibiting the form of certain very 
 minute markings upon objects. A negative photographic 
 impression of the object is first taken on collodion, in the 
 ordinary way, with the highest power of the microscope 
 that can be used. After this has been properly fixed, it is 
 placed in the sliding frame of an ordinary camera, and the 
 frame end of the latter adjusted into an opening cut in 
 the shutter of a perfectly dark room. Parallel rays of 
 sunlight are then thrown through the picture by means 
 of a flat piece of looking-glass fixed outside the shutter at 
 such an angle as to catch and reflect the rays through the 
 camera. A screen standing in the room, opposite the lens 
 of the camera, will now receive an image, exactly as from 
 a magic lantern, and the size of the image will be propor- 
 
APPLICATION OP PHOTOGRAPHY. 157 
 
 tionate to the distance. On this screen is placed a sheet 
 of photogenic paper intended to receive the magnified 
 picture. We ought to add, however, that it requires con- 
 siderable practice to avoid the distortion and error of 
 definition occasioned by a want of coincidence in the 
 chemical and visual foci. Imperfections are much in- 
 creased when the highest powers of the microscope are 
 employed ; false notions of structure are also given, 
 which is the case in Mr. Wenham's photograph of P. An- 
 gulatum. 
 
 Mr. S. Highley has a mode of adapting an object-glass to 
 the ordinary camera, for the purpose of taking microscopic 
 objects on collodion and other surfaces, fig. 96; a sec- 
 tional view of his arrangement is here given, which is 
 
 Fig. 96. Highlit Camera. 
 
 very compact, steady, and ever ready for immediate use. 
 The tube A screws into the flange of a camera which has 
 a range of twenty-four inches; the front of this tube is 
 closed, and into it screws the object-glass B. Over A slides 
 another tube c; this is closed by a plate, D, which extends 
 beyond the upper and lower circumference of c, and carries 
 a small tube, E, on which the mirror F is adjusted. To the 
 upper part of D the fine adjustment G is attached ; this 
 consists of a spring-wire coil acting on an inner tube, to 
 which the stage-plate H is fixed, and is regulated by a gra- 
 duated head, K, acting on a fine screw, likewise attached to 
 
158 THE MICROSCOPE. 
 
 the stage-plate, after the manner of Oberhauser's micro- 
 scopes. An index L is affixed opposite the graduated head 
 K. The stage and clamp slides vertically on H ; and by 
 sliding this up or down, and the glass object-slide hori- 
 zontally, the requisite amount of movement is obtained to 
 bring the object into the field. The object being brought 
 into view, the image is roughly adjusted on the focussing- 
 glass by sliding c on A j the focussing is completed by aid 
 of the fine adjustments G K, and allowance then made for 
 the amount of non-coincidence between the chemical and 
 visual foci of the object-glass. The difference in each glass 
 employed should be ascertained by experiment in the first 
 instance, and then noted. By employing a finely-ground 
 focussing-glass greased with oil, this arrangement forms an 
 agreeable method of viewing microscopical objects with 
 both eyes, and is less fatiguing. As a very large field is 
 presented to the observer, this arrangement might be 
 advantageously employed for class demonstration. 
 
 Fig. 97.IIigfiley's Photo-micrographic Arrangement. 
 
 This arrangement combines the most recent improve- 
 ments of Dr. Maddox, and consists of a lens-carrier with, 
 ordinary adjustments; stage with gymbal motions so as 
 to bring any object parallel to the surface of the object- 
 glass ; bright ground illuminator, graduating diaphragm ; 
 and a speculum reflector for giving the light from a 
 MTi"lc surface. 
 
CHAPTER TIL 
 
 PTStlMETART DIRECTIONS ILLUMINATION ACCESSORV APPARATUS 
 GILLETT'S, ROSS'S, WEBSTER'S, AND OTHER CONDFNSERS - OBLIQUH 
 ILLUMINATION-DOUBLE PRISM ILLUMINATION THE LIEBERKUHN SIDB 
 REFLECTOR GAS-LAMPS OBJECT FINDERS COLLECTING STICKS AKI- 
 MALCULE CAGES SECTIOIT CUTTEP.S PREPAKING AND MOUTHING OB- 
 JECT8, ETC. 
 
 AVING selected an apartment 
 with a northern aspect, and, if 
 possible, with only one window, 
 and that not overshadowed by 
 trees or buildings : in such a 
 room, on a firm, steady table, 
 keep your instruments and ap- 
 paratus open, and at all times 
 ready for observation. A large 
 bell-glass will be found most 
 convenient for keeping dust from 
 the microscope when set up for 
 use. In winter it will be proper 
 to slightly warm the instrument 
 before it is used, otherwise the 
 perspiration from the eye will 
 condense on the eye-glass, and 
 greatly impede vision. When 
 you clean the eye-glasses, do not remove more than one at 
 a time, and replace it before you touch another ; by so 
 doing you will preserve the component glasses in their 
 proper places : recollect that if intermingled they are 
 useless. Keep a piece of well-dusted and very dry 
 chamois leather, slightly impregnated with the finest 
 tripoli or rotten-stone powder, in a small box, to wipe 
 the glasses. 
 
160 THE MICROSCOPE. 
 
 When you look through the instrument, be sure to 
 place your eye quite close to the eye-piece, otherwise the 
 whole field of view will not be visible ; and observe, more- 
 over, if you see a round disc of light, at least when the 
 object is not on the slider-holder : if you do not, it is a 
 sign that something is wrong; perhaps the body is not 
 placed directly before the stage aperture, or may not be 
 properly directed towards the light. Use the smallest 
 amount of light possible, if you work for any length of 
 time. Choose a steady light, with a shade to protect the 
 eyes, one of the old-fashioned fan-shades will be found 
 useful for this purpose : use the eyes alternately. Sit in a 
 comfortable position, and bring the instrument to the 
 proper angle, which will prevent congestion of the eyes ; 
 this is indicated if the microscopist is annoyed with little 
 moving objects apparently floating before them : if the 
 eye-lashes are reflected from the eye-glass, you are looking 
 upon the eye-glass instead of through it. Take care that 
 the mirror is properly arranged. 
 
 The following are Sir David Brewster's excellent direc- 
 tions for viewing objects : 
 
 " First. Protect the eye from all surrounding light, let- 
 ting only the rays which proceed from the illuminated 
 centre of the object fall upon il 
 
 " Secondly. Delicate observations should not be made 
 when the fluid which lubricates the cornea is in a viscid 
 state, or there is any irritation or inflammation about any 
 part of the eye. 
 
 " Thirdly. The best position for microscopic observations 
 is with the microscope bent to such an angle with the 
 body, that the head may always remain in a natural and 
 easy attitude ; consequently, the worst position would be 
 that which compels us to look downwards vertically. 
 
 " Fourthly. If we lie horizontally on the back, parallel 
 markings and lines on objects will be seen more perfectly 
 when their direction is vertical, or in a contrary direction 
 to that in which the lubricating fluid descends over the 
 cornea of the eye. 
 
 " Fifthly. Only a portion of the object should be viewed 
 at one time, and every other part excluded. The light 
 which illuminates that part should be admitted through a 
 
ILLUMINATING THE OBJECTS. 161 
 
 email diaphragm ; at night, from the concentrated light of 
 a sperm-oil or gas lamp, having a faint blue -tinted chim- 
 ney-glass, to correct the yellow colour which predominates 
 in all our artificial illumination. If in the day-time, close 
 a, portion of the window-shutters. 
 
 " Sixthly. In all cases when high powers are used, the 
 intensity of the illumination should be increased by optical 
 contrivances below the object and stage : this is generally 
 effected by using achromatic condensers beneath the stage. 
 The apparatus for illumination should be as perfect as the 
 magnifying power." 
 
 If these directions are strictly followed, no injury to the 
 eyes from using a microscope need be feared. 
 
 Mr. Ross very properly remarks, that the manner in 
 which an object is lighted is second in importance only to 
 the excellence of the glass through which it is seen. When 
 investigating any new or unknown specimen, it should be 
 viewed in turns by every description of light, direct and 
 oblique, as a transparent object and as an opaque object, 
 with strong and with faint light, with large angular pencils 
 thrown in all possible directions. Every change will pro- 
 bably develope some new fact in reference to the structure 
 of the object, which should itself be varied in the mode of 
 mounting in every possible way. 
 
 It should be seen both wet and dry, and immersed in 
 fluids of various qualities and densities ; such as water, 
 alcohol, oil, and Canada balsam ; the last having a refrac- 
 tive power nearly equal to that of glass. 
 
 If the object be a delicate vegetable tissue, it will be, in 
 some respects, rendered more visible by gently heating 01 
 scorching before a clear fire, between two plates of glass. 
 In this way the spiral vessels of asparagus and other 
 similar vegetables will be beautifully displayed. Dyeing 
 the objects in tincture of iodine, or some one of the dye- 
 woods, will, in some cases, answer the purpose better. 
 
 But the principal question in regard to illumination is 
 the magnitude of the illuminating pencil, particularly in 
 reference to transparent objects. Generally speaking, the 
 illuminating pencil should be not quite so large as can 
 be received by the lens : any light beyond this produces 
 indistinctness and glare. The superfluous l ; ght from the 
 
162 THE MICROSCOPE. 
 
 mirror may be cut off by a screen, having various-sized 
 apertures placed below the stage. 
 
 The Diaphragm, fig. 98, is the instrument used for 
 effecting this purpose. It consists of two plates of brass, 
 one of which is perforated with four or five holes of dif- 
 
 Fig- 98. The Diaphragm. 
 
 ferent sizes ; this plate is of a circular figure, and is made 
 to revolve upon another plate by a central pin or axis ; 
 this last plate is also provided with a hole as large as the 
 largest in the diaphragm-plate, and corresponds in situa- 
 tion to the axis of the compound body. To ascertain 
 when either of the holes in the diaphragm-plate is in the 
 centre, a bent spring is fitted into the second plate, and 
 rubs against the edge of the diaphragm-plate, which is 
 provided with notches. The space between the smallest 
 and largest is great enough to use for the purpose of shut- 
 ting off all the light from the mirror. 
 
 GILLETT'S ILLUMINATOR, OR CONDENSER. The advan- 
 tages of employing an achromatic condenser were first 
 pointed out by Dujardin, since which time an object-glass 
 has been frequently but inconveniently employed; and 
 more recently achromatic illuminators have been con- 
 structed by most of our instrument makers. Some years 
 since, Mr. Gillett was led by observation to appreciate the 
 importance of controlling not merely the quantity of light 
 which may be effected by a diaphragm placed anywhere 
 between the source of light and the object, but the angle 
 of aperture of the illuminating pencil, which can be effected 
 only by a diaphragm placed immediately behind the 
 achromatic illuminating combination. Such a diaphragm 
 is represented in fig. 99, manufactured by Mr. Ross : it 
 consists of an achromatic illuminating lens c, which is 
 
GILLETT'S ILLUMINATOR. 163 
 
 about equal to an object-glass of one-quarter of an inch 
 focal length, having an angular aperture of 80. This 
 lens is placed on the top of a brass tube, intersecting 
 
 Fig. 99Gillelt's Condenser. 
 
 which, at an angle of about 25, is a circular rotating 
 brass plate a b, provided with a conical diaphragm, having 
 a series of circular apertures of different sizes h y, each of 
 which in succession, as the diaphragm is rotated, propor- 
 tionally limits the light transmitted through the illumi- 
 nating lens. The circular plate in which the conical dia- 
 phragm is fixed is provided with a spring and catch <?/, 
 the latter indicating when an aperture is central with the 
 illuminating lens, also the number of the aperture as 
 marked on the graduated circular plate. Three of these 
 apertures have central discs, for circularly oblique illumi- 
 nation, allowing only the passage of a hollow cone of light 
 to illuminate the object. The illuminator above described 
 is placed in the secondary stage i t, which is situated below 
 the general stage of the microscope, and consists of a 
 cylindrical tube having a rotatory motion, also a rect- 
 angular adjustment, which is effected by means of two 
 screws I m, one in front, and the other on the left side of 
 its frame. This tube receives and supports all the various 
 
164 THE MICROSCOPE. 
 
 illuminating and polarising apparatus, or other auxiliaries 
 which are placed underneath the object. The tube and its 
 frame are affixed to a dovetailed sliding bar /j, which can 
 be easily moved up or down, or taken off for conveniently 
 attaching the various apparatus. This sliding bar fits into 
 a second sliding bar, which, by means of a rnilled-head 
 screw, moving a rack and pinion, regulates the distance of 
 the apparatus from the stage. 
 
 Directions for Use by Day or Lamplight. In the adjust- 
 ment of the compound body of the microscope with the 
 illuminator above described, two important results are to 
 be sought first, their centricity, and secondly, the fittest 
 condensation of the light to be employed. With regard to 
 the first, place the illuminator in the cylindrical tube, and 
 press upwards the sliding bar in its place, until checked 
 by the stop ; move the microscope body either vertically 
 or inclined for convenient use ; and with the rack and 
 pinion which regulates the sliding bar, bring the illu- 
 minating lens to a level with the upper surface of the 
 object-stage ; then move the arm which holds the micro- 
 scope body to the right, until it meets the stop, whereby 
 its central position is attained j adjust the reflecting mirror 
 so as to throw light up the illuminator, and place upon 
 the mirror a piece of clean white paper to obtain a uniform 
 disc of light. Then put on the low eye-piece, and a low 
 power (the half-inch), as more convenient for the mere 
 adjustment of the instrument ; place a transparent object 
 on the stage, adjust the microscope-tube, until vision is 
 obtained of the object ; then remove the object, and take 
 off the cap of the eye-piece, and in its place fix on the eye- 
 glass called the "centering eye-glass," described below, 
 which will be found greatly to facilitate the adjustment 
 now under consideration, namely, the centering of the 
 compound body of the microscope with the illuminating 
 apparatus of whatever description. 1 The centering-glass, 
 being thus affixed to the top of the eye-piece, is then to 
 
 (1) This centering-glass consists of a tubular cap containing two plano-convex 
 lenses, which are applied and adjusted so that the image of the aperture in the 
 object-glass, and the images of the apertures at the lenses arid in the diaphragms 
 contained in the tube which holds the illuminating combination, may all be in 
 focus at the same time, as with the same adjustment they may be brought suffi- 
 ciently near in focus to recognise their centricity. 
 
GILLETT'S ILLUMINATOH. 165 
 
 be adjusted by its sli ding-tube (without disturbing the 
 microscope-tube) until the images of the diaphragms in 
 the object-glass and centering lens are distinctly seen. 
 The illuminator should now be moved by means of the 
 left-hand screw on the secondary stage, while looking 
 through the microscope, to enable the observer to recog- 
 nise the diaphragm belonging to the illuminator, and by 
 means of the two adjusting screws, to place this diaphragm 
 central with the others ; thus, the first condition, that of 
 centricity, will be accomplished. Kemove the white paper 
 from the mirror, and also the centering-glass, and replace 
 the cap on the eye-piece, also the object on the stage, of 
 which distinct vision should then be obtained by the rack 
 and pinion, or fine screw adjustment, should it have 
 become deranged. 
 
 The second process is to ascertain that the fittest con- 
 centration of light is obtained. For this purpose the 
 mirror should now be so inclined that the image of some 
 intercepting distant object, such as a house-top, or chim- 
 ney, tree, window-frame, or (if lamp-light be employed) 
 the lamp's flame may be brought into the field of view ; 
 these, though not distinctly seen, may be recognised by 
 partially darkening or otherwise occupying the field ; then 
 distinct vision of such object must be obtained by means 
 of the rack and pinion moving the secondary stage to and 
 from the object. Excepting the case of the lamp's flame, 
 the above objects are considered as the representatives of 
 the source of light ; for when daylight is employed as, for 
 example, a white cloud its motion prevents the image 
 being easily produced : then it is convenient to employ a 
 distant object, such as the above, the difference of the 
 focal length of the illuminating lens for such an object, 
 and for the white cloud, being almost insensible. This, 
 last adjustment being effected by the movement of the 
 secondary stage alone, the microscope tube remaining un- 
 disturbed, also the object on the object-stage uninterrupted 
 in focus, the source of the illuminating light and the 
 object to be examined will both be distinctly seen at the 
 same time. These adjustments, whether for daylight or 
 lamplight, being completed, the mirror may be turned se- 
 as wholly to reflect the light either of the sky or of the 
 
166 THE 3JICROSOOPE. 
 
 lamp; and the eye-piece and object-glass suitable for 
 examining the object may be employed, and the focus 
 adjusted accordingly. The conical diaphragm with its 
 various apertures may now be rotated, until that quality 
 of illumination is obtained which gives a cool, distinct, 
 and definite view of the object. Upon changing the 
 object-glass, the centering eye-glass should always be 
 employed to ascertain that the centricity of the illumi- 
 nating condenser and microscope body has not been 
 deranged. 
 
 It has been stated that the image of a white cloud oppo- 
 site the sun is the best for illuminating transparent objects 
 when viewed by transmitted light. Mr. Gillett has success- 
 fully imitated this natural surface by an apparatus consist- 
 ing of a large parabolic reflector, with a small camphine 
 lamp on an adjustable stand, having its flame nearly in 
 the focus; also of two other reflectors of hyperbolic figure, 
 which are employed according to the object-glasses used on 
 the microscope. The parabolic mirror and one of these are 
 attached opposite to each other on the bent arm by which 
 they are supported, having their axes coincident, and the 
 enamel disc placed between them. The small hyperbolic 
 reflector receives the light reflected from the large paro- 
 bolic reflector, and concentrates the rays on the small 
 enamel disc. The surface of this disc is roughened, so that 
 the forms of all the incident pencils are broken up, and 
 the effect of a white cloud produced. 
 
 Several important modifications and valuable improve- 
 ments in condensers have been introduced by makers, and, 
 therefore, deserve especial notice. Two things should be 
 required of achromatic condensers intended for general use 
 and for research : I^irst, that the optical combination em- 
 ployed should be adapted to a considerable range of power 
 say, from an inch, or |ds upwards to the highest ; and, 
 secondly, that they should be capable of working with a 
 large aperture through the ordinary glass slides. When 
 low powers are employed, a pleasantly lit field can be 
 obtained by using a condenser a little out of focus, so that 
 the rays cross before reaching the object ; but a condenser 
 for general use should send a sufficient quantity, and no 
 more, of oblique rays, when in focus, through an object 
 
BOSS'S CONDENSER. 167 
 
 seen with very moderate magnification, and should be 
 capable of giving a dark-ground illumination with a J 
 inch or f ds object glass. 
 
 In Mr. Ross's ^ths condenser, represented at A, 
 fig. 39, these desiderata are well provided for. The 
 optical combination is exactly the same as in his large 
 angled j^ths objectives, and the front lens has a diameter 
 o th of an inch. In all good condensers the diaphragm 
 should be brought close to the lower lens ; that is the 
 case with this instrument, which is provided with two 
 revolving wheels of diaphragms. The upper one is pierced 
 with eight circular apertures ; one of which is filled in 
 with a polarizing slice of tourmaline ; another is made 
 with a little rim, so as to receive any experimental stops 
 the microscopist may wish to try. Omitting this last- 
 mentioned stop, we have seven others, marked respec- 
 tively 109, 95, 82, 70, 59, 49, and 40. These stops 
 allow the lenses to work with the angles of aperture 
 named. In the wheel of diaphragms, below them, is 
 arranged another set of stops, for combination with the 
 preceding. 
 
 A single slot stop keeps out the central rays, and 
 allows a radial beam, including its proportion of marginal 
 rays, to illuminate the object '. This can be used with the 
 larger of the open stops. The two-slot stop gives passages 
 to two such pencils of light, one at right angles to the 
 other, a plan very effective with certain diatoms and other 
 objects. The three-slot stop allows the transmission of 
 three pencils, equidistant from each other. This gives the 
 three readings of the P. angulatum. The arrangement 
 for working the diaphragms in the condenser is very con- 
 venient, and the whole apparatus rotates with the sub-stage. 
 The lenses are also capable of adjustment to suit different 
 thicknesses of glass. 
 
 The proportion which, from the size of the front lens, 
 the marginal and central rays bear to each other, is such 
 that, when the stop allowing 40 of aperture is employed, 
 the two sets of lines, on Pleurosigma hippocampus and P. 
 angulatum, are distinctly shown with a one-fifth objective 
 and an A eye-piece. A slight change in the position of 
 the flat mirror makes this stop work excellently with the 
 
168 THE MICROSCOPE. 
 
 Podura scale. Thus, this arrangement enables an experi- 
 menter viewing a new object to see surface markings, and 
 to obtain penetration with one and *the same stop ; an. 
 important gain in original investigation. The slot stops 
 have been found very useful in investigating unknown 
 objects, as well as in displaying those that are known; 
 and with the whole aperture and the two-slot stop, many 
 diatoms with double sets of lines are well brought out. 
 The microscopist will find that from 40 to 59 angle of 
 aperture will, in many cases, give the best results, when a 
 J or objective is employed. 
 
 An excellent condenser of very large angular aperture 
 is made by Messrs. Powell and Lealand, in which every 
 requisite modification of the illuminating pencil may be 
 produced by two revolving discs, one containing apertures 
 of various sizes, and the other various diaphragms for 
 excluding the central portion, or for admitting only 
 angular portions, of the pencil of light. These discs are 
 placed immediately below the posterior lens of the illumi- 
 nator. This method of modifying the illuminating pencil 
 was first applied in Gillett's condenser, as constructed 
 by Mr. Ross. The improved hemispherical condenser 
 lately introduced by the Rev. J. B. Reade, answers 
 its purpose remarkably well. The plane surface of the 
 hemisphere is placed upwards, and is covered by a dia- 
 phragm in which are marginal apertures, capable of adjust- 
 ment either to an interval of 90 with each other, when 
 the arrangement of the dots to be developed is quad- 
 rangular, as in P. rhomboides, or P. hippocampus, or to 
 one of 60 and 120, when they are arranged in equilateral 
 triangles, as in P. angulatum, &c. An ingenious plan of 
 illuminating minute objects, mounted in Canada balsam, 
 by reflected light, has been devised by Mr. Wenhamt: 
 this consists of a small truncated glass paraboloid, which 
 is temporarily attached to the under side of the slide 
 containing the object, by a little gum, oil, or fluid Canada 
 balsam. The rays internally reflected from the convex 
 surface of the paraboloid, impinge very obliquely on the 
 under-surface of the slide, are transmitted in consequence 
 of the fluid-uniting medium, and then internally reflected 
 from the upper surface of the covering glass on to the 
 
COLLINS'S CONDENSER. 169 
 
 object. Very minute variations of surface contour may 
 by these means "be rendered evident. 
 
 Collins's Webster's Universal Achromatic Condenser 
 (fig. 100), a superior mechanical contrivance, is provided 
 with a diaphragm which so gradually shuts off all excess 
 of light, that any amount of illumination can be admitted 
 
 Fig. 100. Collins?* Webster's Universal Condenser. Shutter Diaphragm seen separately 
 
 with the greatest nicety. This valuable addition to the 
 microscope can be fitted to any instrument with or without 
 a sub-stage arrangement. Its chief advantages are that, 
 while its performing qualities take rank with much more 
 expensive forms, it is moderately cheap, and is at once an 
 achromatic condenser, parabolic illuminator, and graduating 
 diaphragm, with polariser added. By means of a lever, the 
 central aperture can be gradually closed, without losing 
 sight of 'the object, and at the same time the alteration is 
 effected with a great amount of delicacy. Provided an 
 object-glass has sufficient "resolving power," its capa- 
 bilities are greatly increased by this condenser, in bringing 
 out the markings on the difficult test-objects; when in 
 connexion with the Polariscope, a great increase of light 
 is obtained so much so that, by using a polarising prism 
 with the "spot lens stop" the object appears brilliantly 
 illumined on a dark ground, with fine coloured effects. 
 When high powers are used in connexion with the polari- 
 scope, the advantage derived by such an addition to the 
 ordinary mode of illumination will be at once apparent to 
 every microscopist. 
 
170 THE MICROSCOPE. 
 
 Professor Smith, of Kenyon College, America, invented 
 a condenser for the illumination of opaque objects under 
 high powers. It has been felt that it would be of im- 
 mense advantage to the physiologist if he could illuminate 
 small bodies, such as blood-globules, and view them as 
 opaque objects with the Jth or j^th ; hitherto there have 
 been great difficulties in the way of accomplishing this, 
 but Professor Smith has hit upon a contrivance which 
 promises to be useful. 
 
 In this instrument a pencil of light is admitted above 
 the objective and thrown down through it on to the object, 
 by means of a small silver mirror placed on one side, and 
 cutting off a portion of the aperture. Powell and Lealand 
 devised what they considered to be an improvement, and 
 substituted for the small silver mirror, to which Professor 
 Smith gave a preference, a flat piece of glass placed at an 
 angle of 45 across the tube, interposed like an adapter 
 between the objective and the microscope body. A pencil 
 of light entering by a side aperture striking against this 
 flat glass is partly reflected down through the objective 
 and on to the object, the magnified image of which is 
 viewed through the glass. If the flat glass be ground so 
 as to have parallel surfaces, no great amount of error can 
 be detected. 
 
 Smith and Beck place a disc of thin covering glass, at 
 an angle of about 45, in the optic axis of the microscope 
 body, close behind the setting of the object-glass in a special 
 adapter, leaving a suitable aperture for admitting light from 
 a lamp, rays from which are reflected downwards upon the 
 object. The object-glass is thus made its own achromatic 
 condenser. 
 
 But the idea of employing the object-glass as its own 
 condenser was suggested by Mr. Hewitt five years ago, 
 and then Mr. Wenham was induced to give the plan a 
 trial. A concave speculum was fitted at an angle into the 
 body of the microscope, having a central hole sufficiently 
 large to admit the full pencil from the objective, through 
 the back of which the rays from a lamp (the light from 
 which was admitted through a hole in the side of the 
 body) were reflected downwards. The object was strongly 
 illuminated, but there was so much glare from the internal 
 
OBLIQUE ILLUMINATION. 171 
 
 fittings, and a reflection from the back of the object- 
 glass-lenses, that an unfavourable opinion was formed of 
 its practicability. It has since been demonstrated that 
 the light was too intense ; and the most useful, the central 
 portion of rays, were wanting. A simple disc of thin 
 glass and its partial reflection meets these objections. If 
 such a disc be used with a little care, it is found to be 
 quite as accurate as the other plan, and the natural surface 
 of the glass is a better reflector than any artificial one. It 
 has, however, the disadvantage of extreme fragility. By 
 making the object-glass its own condenser, and examining 
 diatoms as opaque objects under high powers, we may 
 now hope to solve the much vexed question as to the true 
 nature of their markings. Mr. Browning has employed 
 the apparatus in a form much more nearly resembling that 
 of the original inventor, only substituting a small glass 
 reflecting-prism for the metallic reflector. Some advan- 
 tages are gained by the adoption of this latter arrangement. 
 Such modes of illumination bid fair to correct many errors 
 of interpretation resulting from an exclusive use of trans 
 parent illumination. 
 
 Oblique Illumination is of the greatest importance in 
 the demonstration of structure, especially that of test- 
 objects ; and much greater obliquity is often required 
 than can be obtained by throwing the mirror out of the 
 axis of the microscope. Various methods are described ih 
 the "Transactions" of the Microscopical Society of London, 
 for almost every microscopist has devoted some attention 
 to the subject in his attempts to resolve the more diffi- 
 cult lined or dotted objects, as diatoms ; therefore, to 
 give a full description of all is quite uncalled for, if 
 not impossible, in our pages ; it is nevertheless most 
 advisable, in doubtful cases, to have recourse to every 
 method which shall present the object under a different 
 aspect. One of the earliest methods devised for obtaining 
 oblique light, was the eccentric prism of Nachet, which 
 occupied the place of the present achromatic condenser, 
 and, like it, received its light from the mirror ; by simply 
 turning it in its socket, oblique rays were thrown upon the 
 object from every side. This had, however, defects which 
 Mr. Soliitt proposed to remedy, by employing an achro- 
 
172 THE MICROSCOPE. 
 
 matic condenser of a very long focus and large aperture, 
 mounted in such a way as to enable its axis to be inclined 
 to that of the microscope through a wide angular range ; 
 a condenser of this construction, he says, is also suitable 
 for all ordinary purposes. 1 A combination of the reflect- 
 ing and refracting powers of a prism is much preferred by 
 some ; such, for instance, as that known as Amici's prism, 
 which causes the rays to be reflected by a plane surface, 
 and made to converge by a lenticular one, so that the 
 prism answers the double purpose of mirror and condenser 
 at the same time. "Abraham's Achromatic Lenticular 
 Prism " is an excellent substitute for the achromatic con- 
 denser, and answers the double purpose of mirror and con 
 denser. This prism, represented half-size in fig. 101, is made 
 
 Fig. 101. Abraham's Achromatic Lenticular Prism. Half-size. 
 
 up of two kinds of glass, set in a frame of brass ; the part 
 employed as the reflector (A) is of flint glass, hollowed out at 
 its upper surface, and into this is accurately fitted a double 
 convex lens of crown glass (B), so contrived as to have a 
 focus of about four inches. By the tube (G), the prism can 
 be applied to the ordinary support of the mirror ; and by 
 means of the flat semicircle (D), and a joint in the connect- 
 ing piece (F), it can be turned in every possible direction, 
 the semicircle sliding through a spring clip at E. By this 
 
 (1) Quart. Journal Micros. Science, vol. iii p. 87. 
 
OBLIQUE ILLUMINATION. 173 
 
 instrument, achromatic condensed light may be thrown 
 upoa any object on the stage. The prism has the usual 
 swinging motion, accomplished by the frame turning on 
 two screws, one of which is seen at c, at the end of the 
 semicircle. 
 
 A thin stage is of importance when a very oblique 
 pencil is used, and, to a certain extent, the larger its lower 
 aperture, the more oblique will be the rays we are enabled 
 to transmit to the object. For this reason the thin stage 
 introduced by such makers as Powell and Lealand, is in 
 every way an improvement on the thicker stage of the 
 older instruments. A revolving stage also possesses ad- 
 vantages : it enables the observer to keep the object in 
 the centre of the field of view, and while its various parts 
 are thus presented in succession to rays of greater or less 
 obliquity, an insight into the structure is often afforded 
 which could not otherwise have been obtained. " Thus, 
 suppose that an object be marked by longitudinal stria3, 
 too faint to be seen by ordinary direct light, the oblique 
 light most useful for bringing them into view will be that 
 proceeding in either of the directions c and D ; that which 
 falls upon it in the directions A and B 
 tending to obscure the striae rather than 
 to disclose them. But if the stria3 should 
 be due to furrows or prominences which 
 have one side inclined and the other side 
 abrupt, they will not be brought into 
 view indifferently by light from c, or 
 from D, but will be shown best by that 
 which makes the strongest shadow; 
 hence, if there be a projecting ridge, 
 with an abrupt side looking towards c, it will be best seen 
 by light from D ; whilst, if there be a furrow with a steep 
 bank on the side of c, it will be by light from that side that 
 it will be best displayed. But it is not at all unfrequent 
 for the longitudinal striae to be crossed by others ; and 
 these transverse striae will usually be best seen by the light 
 that is least favourable for the longitudinal, so that, in 
 order to bring them into distinct view, either the illumi- 
 nating pencil or the object must be moved a quarter 
 round." 
 
174 THE MICKOSCOPE. 
 
 For those who desire to obtain a very oblique illumi- 
 nating pencil, with objectives of lower powers, bui^. large 
 angular aperture, and with an inexpensive arrangement, 
 the Hemispherical Condenser (Kettledrum) of the Eev. 
 J. B. Eeade will be found serviceable. 1 This gentleman 
 now, however, uses a double hemispherical condenser for 
 the examination of the most difficult tests ; and the great 
 obliquity of the illuminating pencils gives every facility 
 for dealing with the close fine lines of the Amician test 
 and the Macrum. Diaphragms of tinfoil are placed 
 between the two hemispheres. By looking down the 
 body of the microscope when the eye-piece is removed, 
 and examining the dimensions of the little discs of light, 
 it is seen at a glance whether one or other of the aper- 
 tures require to be more or less deeply cut. In the one 
 case, the little lappet of tinfoil can be so doubled as to 
 shorten the aperture, and, in the other, it may be cut 
 deeper and thrown further back. To obtain these very 
 slight but not unimportant variations, and in a moment, 
 is an advantage which observers will readily recognise. 
 Mr. Eeade also uses more durable diaphragms of thin 
 brass, and, by -a new arrangement, the precise amount of 
 light is obtained at once. A fixed diaphragm, with aper- 
 tures at right angles to each other, and cut nearly to the 
 centre, is placed on the lower hemisphere ; and another 
 diaphragm, of which the outline is a right angle upon a 
 semicircle, is placed in a slit of the tube between the 
 condensers, so that the vertex of the right angle divides 
 the space between the long V apertures of the lower 
 diaphragm. When pushed home, it nearly shuts up these 
 apertures of the fixed diaphragm ; but by gently drawing 
 it out, and moving it a little sideways, if necessary, we 
 can obtain, with the utmost nicety, just that length of 
 either aperture which the test-lines under examination 
 require. 
 
 The very perfection of oblique illumination for resolving 
 the markings on test-objects, is the double prism made 
 use of by Mr. J. Newton Tomkins. The method of employ- 
 ing the two prisms we give in our friend's words : 
 
 (1) Rev. J. B. Reade, F.R.S. on a New Hemispherical Condenser. Trans. 
 Micros. Soc. 1861, p. 59, and vol. vii. page 3, 1867. 
 
SOLLITT'S ILLUMINATION. 
 
 175 
 
 " My first attempts at oblique prism-illumination were 
 made, many years ago, with Abraham's (of Liverpool) 
 Achromatic Lenticular Prism; the high character given 
 of the performance of this instrument by the late Professor 
 Quekett and by Mr. Sollitt, of Hull, led me to believe 
 that it would entirely supersede the necessity of using a 
 condenser during the examination of the highest class 
 test-objects. In my hands, however, it failed to do this ; 
 the pencil of light transmitted proved to be too diffused, 
 and the shadows too faint to enable me to bring out the 
 markings of single-lined tests satisfactorily. I subjoin Mr. 
 Sollitt's directions for using this prism, as communicated 
 
 Fig. 102. Sollitt's Single-Prism Illumination. 
 
 to Mr. Abraham : ' When I require the prism for defi- 
 nition and direct light, I use it in place of the mirror 
 under the stage ; but when required for oblique light, that 
 is, for illuminating lined objects, or for black-ground 
 illumination, I use it on a separate stand, as shown in 
 fig. 102, the object being illuminated by the very oblique 
 ray, c B. Let A B be a supposed ray of direct light, coin- 
 cident with the axis of the microscope, then so long as the 
 angle c B A is less than half the angle of aperture of the 
 object lenses, the field will remain illuminated by oblique 
 light, and, the lined objects (if placed in their proper 
 position) will be brought out in the most beautiful manner. 
 I place the prism about five inches in front of the object, 
 and by this method, with my widest apertures, I bring 
 
176 THE MICROSCOPE. 
 
 out the lines on Navicula Angulata, Ceratoneis Fasciola, 
 Amician Test, Grammatophom Subtilissima, and even on 
 the Navicula Acus, with the greatest ease. In viewing 
 these delicate objects, the lines must be at right angles 
 with the direction of the light. If the angle c B A be 
 greater than half the angle of aperture of the object lenses, 
 then you have the object beautifully illuminated on a 
 black ground ; and when the light is properly managed, 
 the result is very superior to that obtained by the parabolic 
 reflector the objects on the black-ground appear as though 
 they were in full sunlight, bringing out the fine markings 
 on delicate tissues most satisfactorily.' 
 
 "My next trial was made with a small rectangular 
 achromatic prism with a focus of two inches and a half 
 not of four or five inches, as in Mr. Sollitt's case fur- 
 nished by Messrs. Powell and Lealand ; and I then found 
 it easy to resolve the markings of all test objects which 
 were disposed at right angles with the source of illumina- 
 tion. With a view of resolving the crossed-lines of P. 
 Formosum, AT. Angulata, and the like, I employed the 
 usual microscope mirror, so disposed by means of a double- 
 jointed arm that the light from the lamp might be reflected 
 as nearly as possible at right angles with the second set of 
 lines, but met with but moderate success, since the double 
 reflection, due to the primary reflection from the silvered 
 surface of the mirror, and the secondary reflection from 
 the glass of '-the mirror itself, caused a haze that militated 
 materially against true definition of the markings which 
 characterise such delicate tests as N. Rhomboides, P. Ma- 
 crum, &c. 
 
 " The next step was to substitute for the mirror a second 
 lamp and a second prism, also. mounted on a separate stand, 
 with rack-work adjustment, and provided with a universal- 
 joint arm. The success of this plan was undoubted ; I 
 was now enabled to resolve the crossed lines of N. Rkom- 
 boides (the Amician Test of the London, although, per- 
 haps, not of the American microscopists) with a sharpness 
 which was hitherto unattainable ; and even the difficult 
 object P. Hacwm came out in well-defined squares. The 
 advantage of the universal-joint fitted to the second prism 
 consists in the fact that the diagonal lines of such tests as 
 
DOUBLE PRISM ILLUMINATION. 
 
 177 
 
 P. Eigidum may be brought out with ease by simply 
 inclining the prism to the angle necessary to cause the 
 shadows of this series of lines to fall directly opposite ta 
 the source of light. 
 
 '* The method of using this combination will be readily 
 understood by referring to fig. 103. 
 
 "The microscope (A) is placed at the usual angle of 
 inclination ; a valve say, of N. jRhombaides is selected 
 which lies vertically on the stage ; the front lamp (c) is 
 adjusted so that the centre of the flame shall be eleven 
 inches above the table, and ten inches from the object ; 
 an object glass of moderate angle, such as a Ross's old 
 J inch, with 60 of aperture, will be found convenient 
 for this first step in the process j the front prism (D), with 
 its convex surface turned towards the lamp (c), is placed 
 1J 2 inches from the stage, and so adjusted that the 
 pencil of transmitted light shall fall with the utmost 
 obliquity on the object ; now (referring to the former 
 fig. 102), the angle c B A being about 40, or greater than 
 
 Fig. 103. Mr. Newton Tomkinf Double Prism Illumination. 
 
 half the angle of aperture of the lens, the valve under 
 examination will be brightly illuminated on a black- 
 
178 THE MICROSCOPE. 
 
 ground. An Jth, T Vth, or a y 5 th, is then substituted for 
 the J inch lens ; and since the angle of aperture of either 
 of these lenses exceeds 140, the whole field will be illu- 
 minated with a very oblique pencil of light. By careful 
 manipulation of the prism, and the closest attention to the 
 due adjustment of the object-glass itself, the transverse 
 markings on the valve (which are by far the most difficult 
 to resolve) should now come out with great clearness. 
 
 "The reason for using the J inch lens in the first 
 instance, is to find, by ' Maltwood,' or otherwise, the 
 particular object desired, and to determine the exact 
 position of lamp and prism ; by commencing to work with 
 the T^th or ^th these would be impracticable. The light 
 of the lamp is now to be shut off, and a side prism* (B) 
 inclined parallel to the plane of the stage-plate, and 
 brought as near to the under-side of the object as the 
 form of the fixed stage will admit, placed in position. 
 The light of a second lamp (E) is then caused, as before, 
 to fall very obliquely on the object, and the longitudinal 
 markings will be readily shown. On restoring the light 
 of the front lamp (c), and paying particular attention that 
 neither light shall be in excess, the valve will be brought 
 out in squares, with a sharpness and a delicacy of tracing 
 which I venture to assert will bear comparison with the 
 best results obtained by use of the expensive modern 
 oondenser. I would by no means undervalue the advan- 
 tages to be derived from the employment of the condensers 
 now furnished by our eminent makers ; but, seeing that 
 these are manifestly articles of luxury, I incline to the 
 opinion, that to those microscopists who are economically 
 disposed, and already possess one rectangular prism, the 
 trifling addition of a second prism and a second lamp will 
 enable them to do good service to the cause of resolving 
 many difficult test-objects hitherto insurmountable, amongst 
 which I would place in the foremost rank Amphipleura 
 pellucida (N. Acus), the markings on which I do not 
 yet despair of seeing ' crossed ' by some enthusiastic 
 observer." 
 
 We have witnessed with surprise the ease with which 
 difficult markings are brought out by this mode of illumi- 
 nation. 
 
THE PARABOLIC REFLECTOR. 
 
 179 
 
 'fhe Parabolic Reflector. -Mr. F. H. Wenham (Micros. 
 Trans. 1851) proposed a parabolic illuminator, for the pur- 
 pose of obtaining perfect definition under nigh powers. 
 Those who have experimented on the subject, may have ob- 
 served that there is something in the nature of oblique light 
 reflected from a metallic surface particularly favourable for 
 the purpose of bringing out minute markings, which may, 
 in some measure, be attributed to the circumstance of light 
 so reflected being purely achromatic. In order to render 
 this property available, Mr. Wenham contrived a very in- 
 genious metallic reflector, by which the condensation of 
 lateral light may be effected. 1 
 
 Fig. 104. Wenham's Parabolic Reflector. 
 
 " The apparatus is shown in section in fig. 104 ; a a is 
 a parabolic reflector, of a tenth of an inch focus, with a 
 
 (1) Mr. Shadbolt contrived a modification of Wenham's Reflector, and called 
 it a " Sphero-Annular Condenser;" which consists of a ring of glass whose 
 surface was so shaped as to present a prismatic section, the inclination of the 
 outer side being such as to produce a total reflection of the rays impinging on 
 it, and to direct these through the inner side of the ring, so as to fall at a very 
 oblique angle upon the object from every azimuth of the circle. A combination 
 of both methods is adopted in the parabolic illuminator now very generally 
 used. This consists of a paraboloid of glass resembling a cast of the interior 
 of Wenham's Parabolic Speculum, but reflecting the rays which fall upon the 
 turface of the glass like Shadbolt's Annular Condenset 
 N2 
 
180 THE MICROSCOPE. 
 
 polished silver surface, having the apex so far cut away as 
 to bring the focal point at such a distance above the top 
 of the apparatus (which is closed with a screw-cap when, 
 not in use) as may allow the rays to pass through the 
 thickest glass commonly used for mounting objects upon 
 before coming to a focus. 
 
 " At the base of the parabola is placed a disc of thin 
 glass b 6, in the centre of which is cemented a dark well r 
 with a flange equal in diameter to the aperture at the top 
 of the reflector, for the purpose of preventing the direct 
 rays from the source of light passing through the 
 apparatus. 
 
 "The reflector is moved to and from the object by 
 means of the rack and pinion c, and has similar adjust- 
 ments for centering, and is fixed under the stage of the 
 microscope in the same way as the ordinary achromatic 
 condenser: in addition, there is a revolving diaphragm d, 
 made to slide on the bottom tube of the apparatus ; it has- 
 two apertures e e, placed diametrically, for the purpose of 
 obtaining two pencils of oblique light in opposite direc- 
 tions. The effects of the chromatic and spherical aber- 
 rations, in the shape of fog and colour about the objects, 
 caused by the glass slides upon which they are mounted, 
 frequently require compensation; for as the parabola has 
 the property of throwing parallel rays uncoloured to a 
 point, when used alone, it is most suitable for objects 
 without glass underneath. 
 
 " By the addition of a meniscus, this compensation is 
 obtained, and also greater purity and intensity of illumina- 
 tion is procured ; and as the silver reflector is now closed 
 with glass, it is hermetically sealed, and permanently pro- 
 tected from dust and damp, and will therefore retain its 
 polish. The light most suitable for this method of illumi- 
 nation is lamp or candle light, the rays of which must in 
 all cases be rendered parallel by means of a large plano- 
 convex lens, or condenser; the light may then be used 
 direct, or reflected from the plane mirror. The object 
 having been adjusted, the illuminator is moved to and fro 
 till the best effect is produced. For the purpose of viewing 
 some objects, such as naviculse, the circular diaphragm 
 should be slid on the extremity of the apparatus, and 
 
THE LIEBBRKiiHN. 
 
 181 
 
 revolved till the two pencils of light are thrown most 
 suitably across the object." 
 
 The Lieberkuhn. The -concave speculum termed a 
 " Lieberkiihn," from its celebrated inventor, was formerly 
 much in use as a reflector, but is now almost abandoned, 
 or rather replaced by other and better contrivances. The 
 Lieberkuhn is generally attached to the object-glass, in 
 the manner represented at fig. 105, where a exhibits tin 
 lower part of the compound body, 6, the object-glass, ova ' 
 which is slid a tube and the 
 Lieberkuhn, c, attached to it ; 
 the rays of light reflected from 
 the mirror are brought to a focus 
 upon an object d, placed between 
 it and the mirror. The object 
 may either be mounted on a slip 
 of glass, or else held in the for- 
 ceps, / ; and when too small to 
 fill up the entire field of view, 
 or when transparent, it is neces- 
 sary to place behind it the dark 
 well, e. 
 
 Each Lieberkuhn being 
 mounted on a short piece of Fig - 105< 
 
 tube, can be slid up and down ion the outside of the 
 object-glass, so that the maximum of illumination may be 
 readily obtained. In the higher powers the end of the 
 object-glass is turned small enough to pass through the 
 aperture in the centre of the Lieberkiihn ; but in the 
 lower powers, where a great amount of reflecting surface 
 would be lost on account of the large size of the glasses 
 employed if this plan were adopted, the aperture in the 
 centre of the Lieberkuhn is made to admit as many rays 
 as will fill the field of view, and no more. 
 
 As the flood of light thrown back by the Lieberkuhn is 
 sometimes so great as to obliterate much of the beauty and 
 delicacy of structure of certain objects, it was proposed by 
 Mr. Bridgeman, of Norwich, to cover up a portion of its 
 reflecting surface by gumming a piece of dull-black paper 
 over one half of the reflector ; then, by rotating the 
 Lieberkuhn upon the object-glass, any proportion of oblique 
 
182 THE MICROSCOPE. 
 
 light may be thrown upon the object, and in any particular 
 direction. In this way points of structure have been 
 brought out which were lost under the full illumination of 
 the Lieberldihn. Mr. Beck sought to effect an improve- 
 ment upon the proposal of Mr. Bridgeman, and, by 
 employing the segment of a Lieberkiihn, produced what he 
 terms a "Parabolic reflector." This is made to slide in the 
 ordinary way over the object-glass, and admits of being 
 turned in any direction towards the source of light. The 
 parabolic reflector can also be employed with high powers. 
 Mr. Sorby discovered, while experimenting with a reflector 
 of the kind, the value of studying the peculiarities of 
 objects under every kind of illumination ; for, on viewing 
 specimens of iron and steel with this reflector, he found 
 that, owing to the obliquity of illumination, the more 
 brilliantly polished parts reflected the light beyond the 
 aperture of the objective, and he could not therefore 
 distinguish them from those parts which merely absorbed 
 the light. To throw the illumination more perpendicularly 
 upon the specimen, he was obliged to place a small flat 
 mirror immediately in front of the objective, and cover half 
 its aperture, and at the same time stop-off, by means of a 
 semi-cylindrical tube, the light from the parabolic reflector, 
 By such an arrangement, Mr. Sorby found it produce the 
 reverse appearances of the former mode of illumination, 
 and it proved to be a valuable aid in ascertaining the true 
 condition of the object. Mr. Baker has produced a cheaper 
 and simpler form of this parabolic reflector, which answers 
 its purpose remarkably well, giving increased facilities for 
 the illumination of opaque objects with the microscope 
 get in that direction most convenient for working. The 
 brilliancy of the illumination is very much increased by 
 placing a condensing-lens before the light, or by employing 
 the Bockett lamp. It is, however, only just to Mr. Ross 
 that we should add, that this " parabolic reflector " is 
 but a slight modification of his Side-reflector, contrived 
 several years ago, for the purpose of superseding th 
 Lieberkiihn. 
 
 The BulVs-eye Condenser. All opaque objects require to 
 be illuminated by rays which, being thrown upon their sur- 
 face, shall be reflected back into the microscope. The same 
 
JBULI/-6-EYE CONDENSER. 
 
 183 
 
 mode of viewing objects is often applied to semi-opaque, 
 or even some transparent ones, to demonstrate peculiarities 
 of structure. A condensing lens is used for converging 
 rays from a lamp upon the 
 mirror ; or for reducing the 
 diverging rays of the lamp 
 to parallelism, for use either 
 with the parabolic illumi- 
 nator, or Ross's side-reflector. 
 A plano-convex lens (fig. 
 106), of about three inches 
 focal length, is the form ge- 
 nerally adopted ; it is borne 
 upon a swivel-joint, which 
 allows of its being turned 
 in any direction, and placed 
 at any angle; the tube is 
 double, and thus admits of 
 being lengthened or short- 
 ened. When used by day- 
 light, its plane side should 
 be turned towards the ob- 
 ject, and the same position 
 should be given when used 
 for converging the rays from 
 a lamp ; but w r hen used 
 with the parabolic or side- 
 reflector, the plane side 
 must be turned towards the 
 lamp. Sometimes a smaller, 
 
 double convex lens is made use of in addition ; this is 
 then often fixed into the stage of the microscope. 
 
 In fig. 107 the bull's-eye lens, c, slides up and down 
 a brass rod, screwed into a solid foot ; and made to con- 
 centrate the light upon the object from the table gas- 
 lamp, d. Air. Brooke's method of viewing opaque objects 
 under the highest powers of the microscope (the & and ^ 
 inch object-glass) is effected by two reflections. The rays 
 from a lamp rendered parallel by a condensing lens are 
 received on an elliptic reflector, the end of which is cut 
 off a little beyond the focus; the rays of light converging 
 
 Fig. 1C6. The Condensing Lens. 
 
184 
 
 THE MICROSCOPE. 
 
 from this surface are reflected down on the object by a 
 plane mirror attached to the object-glass, and on a level 
 
 Fig. 107. Condenser and Table Gas-lamp. 
 
 with the outer surface. By such means the structure of 
 the scale of the Podura, and the different characters of its 
 inner and outer surfaces, are rendered distinctly visible. 
 
 Lamps. It is of the utmost importance, both on account 
 of the injury often done to the eyes, as well as for the per- 
 fection of illumination when artificial light is employed, that 
 its quality should be of the whitest and purest kind. The 
 most useful and economical lamp is Collins' Bockett lamp ; 
 it consists of a good paraffin lamp, reflector, and a 2 
 condenser, mounted together on a brass-rod stand, which 
 admits of being raised from 9 to 16 inches. The pale -blue 
 chimney supplied with it gives whiteness to the flame, 
 and for all the requirements of the microscopist it is de- 
 
MICROSCOPE LAMPS. 
 
 186 
 
 Fig. 108. Collins' Bockctt Lamp. 
 
 cidedly the most convenient lamp we have seen. Those 
 
 Fig. IW.Highley's Gcu-lamp, with Steam-tofh attached. 
 
186 
 
 THE MICROSCOPE. 
 
 among us who have gas at command will, no doubt, give 
 it the preference on account of its convenience, and 
 freedom from all kind of trouble. An excellent form of 
 gas-lamp is Highley's (fig. 109). 
 
 The mono-chromatic gas-lamp, fig. 110, is very useful and 
 most economical. Gas, as a source of light, presents great 
 advantages over oil and spirit, on account of cleanliness, 
 being ever ready for use, and affording a perfect control 
 over the flame ; but when the ordinary gas-iamps are used 
 
 Fig. 110. Gas-lamp arranged for itse. 
 
 for the purpose of illuminating the field of the micro 
 scope, a yellow glaring light is given, alike injurious to 
 the eye and the definition of the object under examina- 
 tion. To correct these evils, this lamp was arranged, which 
 
FINDERS AND INDICATORS. 187 
 
 is also otherwise useful to the microscopist. It consists 
 of a stage A, supported by a tube and socket, sliding on 
 an upright rod rising from the stand. This carries an 
 argand burner B ; a metal cone c rises to the level of the 
 burner, and is about one-eighth of an inch from its outer 
 margin. 
 
 This arrangement gives a bright cylindrical flame. The 
 bottom of the stage A is covered with wire-gauze, to cut 
 off irregular currents of air, and thus secures a steady 
 flame. Over the burner is placed a Leblond's blue glass 
 chimney D. This corrects the colour of the flame to a 
 certain extent ; but it is still further rectified by a disc of 
 bluish-black neutral-tint glass E, fitted in a tube F, attached 
 obliquely to the shield G. G is a half- cylinder of metal, 
 which serves to shield the eyes from all extraneous light, 
 but may be rotated on the stage A by aid of the ivory 
 knot H, when the full light from the flame is desired. A 
 metallic reflector I, fixed on its supports, so as to be 
 parallel to E, concentrates the light. By the combination 
 of the two glasses D and E, the yellow rays of the flame 
 are absorbed, and the arrangement affords a soft white 
 light, which may be still further improved by receiving 
 the rays on a concave mirror, backed with plaster-of-Paris 
 L ; and where a very strong light is required, a condensing 
 lens should be interposed, as shown in the cut, between 
 the lamp and the mirror of the microscope. By removing 
 the shield G, and bringing the shade M over the burner, it 
 may be used as a reading-lamp. A retort ring N supports 
 a water-bath o, or a wrought- iron plate P, 6 inches by 2J 
 inches, both used in mounting objects. The stop-cock Q 
 gives the means of regulating the flame. The screw R 
 clamps the lamp-head at any height desired. The lamp 
 may be attached to any gas-supply by vulcanised India- 
 rubber tubing. 
 
 Finders and Indicators. A finder, as applied to the 
 microscope, is the means of registering the position of any 
 particular object in a slide : as, for instance, some particu- 
 larly good specimen of a diatom, so that it may be referred 
 to at a future time. The subject has been fully discussed 
 in the pages of the Quarterly Journal of Microscopical 
 Science. The traversing stage admits of such finders as 
 
188 THE MICROSCOPE. 
 
 those of Mr. Okeden, Mr. Tyrrell, Mr. Amyot, &c., 
 being used. The first named (Mr. Okeden's) finder 
 consists of two graduated scales, one of them vertical, 
 attached to the fixed stage-plate, and the other horizontal, 
 attached to an arm carried by the intermediate plate ; the 
 first of these scales enables the observer to " set " the 
 vertically-sliding plate to any determinate position in 
 
 Fig. lll.Amyot's Object Finder. 
 
 relation to the fixed plate, while the second gives him the 
 like power of setting the horizontally-sliding plate by the 
 intermediate. The finder the author has been in the 
 habit of using for some years is a very ingenious and 
 effective instrument described by Mr. Amyot. It consists 
 of a box-wood plate, with a circular hole ^-ths of an inch 
 in diameter cut out of its centre, into which a disc of 
 ivory, pierced in the exact centre with a very fine needle, 
 fits ; this disc can be readily removed by seizing a little 
 brass peg, attached to it, with the forceps. The box-wood 
 is ruled with two axes, vertical and horizontal, which are 
 graduated to 50ths or lOOths of an inch. The diagram 
 (fig. Ill) represents the finder with bone centre-piece in 
 situ. The dotted ring shows the rabbet on which the 
 centre-piece rests ; a, brass pin attached to centre-piece ; 
 b, b, two brass pins for steadying the instrument against the 
 
OBJECT FI3IDER8. 189 
 
 left side of the microscope stage. The scales may be ruled 
 in brass or bronze and inlaid, and horizontal lines might 
 be ruled on the surface of the stage as a guide for placing 
 the slide. This form of instrument possesses the advantage 
 of not requiring the common object slides to be ruled, or 
 in any way prepared. 
 
 It is thus used : 1st. Put the finder on the stage and 
 find the central needle hole with the microscope. 2d. Ee- 
 move the centre-piece with a small pair of forceps. 
 3d. Place the slide on the wood, taking care that the stage 
 screws be not used to move the object after the finder has 
 once been centred. 
 
 The position of any object then occupying the centre of 
 the field will be shown by the sides and ends of the slide 
 on the scales of the finder, and can be registered at sight. 
 To find the object again : Find the centre hole, remove 
 the disk as before, then place the slide according to the 
 letter and number marked upon it, when the object sought 
 will occupy the centre of the field. 
 
 For those microscopists whose instruments are without 
 a traversing stage " Maltwood's finder " will be found an 
 efficient substitute for the one just described. This consists 
 of a glass slide, 3x1^ inches, on which is photographed a 
 scale occupying a square inch ; this is divided by horizontal 
 and vertical lines into 2,500 squares, each of which con- 
 tains two numbers marking its "latitude," or place in 
 the vertical series, and its "longitude," or place in the 
 horizontal series. The scale is in each instance an exact 
 distance from the bottom and left-hand end of the glass 
 slide ; and the slide when in use should rest upon the 
 ledge of the stage of the microscope, and be made to abut 
 against a stop, a simple pin, about an inch and a half from 
 the centre of the stage. To use this finder, the object- 
 slide must be placed under the microscope with the same 
 care as the finder ; and when some especial object, whose 
 place it is desired to record, has been brought into the 
 field of view, the object-slide being removed, the finder 
 laid down in its place, the numbers of the square then in 
 the field of view are to be read off and recorded. This 
 should also be recorded upon tht object-slide ; and at any 
 future tune, when it is wished to refer to the same object, 
 
190 THE MICEOSCOPE. 
 
 the process will have to be reversed, by first finding this 
 particular square on the finder, and then replacing it by 
 the object-slide. 
 
 A simple form of finder, suggested by Mr. TV. K. Bridge- 
 man, of Norwich, and sold by Baker, Holborn, is, from 
 its ingenuity and comparative accuracy, worthy of notice. 
 
 Fig. 112. Sridgeman's Finder. 
 
 This finder (fig. 112) consists of a curved pin of steel, 
 which is attached to the stand by means of a circular 
 fitting of brass. It is so contrived that when the mechanical 
 stage is brought into the rectangular position, and an 
 object laid thereon, it can be pressed down upon the slide. 
 If the latter be covered with paper, the point of the pin 
 leaves a slight puncture : all that is necessary, when we 
 wish to examine the object in future, is to move the stage 
 till the puncture on the slide comes under the point of 
 the finder. 
 
 Forceps. For holding minute objects, such as parts of 
 plants or insects, to be examined either as transparent or 
 opaque objects, the most useful is represented by fig.113, 
 
 Fig.113. 
 
 and consists of a piece of steel wire, about three inches 
 long, which slides through a small tube, connected to a 
 stout pin by means of a cradle-joint ; to one end of the 
 wire is attached a pair'of blades, fitting closely together 
 by their own elasticity, but which, fur the reception of any 
 
DIPPING TUBES. 
 
 191 
 
 object, may be separated by pressing the two projecting 
 studs ; to the opposite end of the wire is adapted a small 
 brass cup, filled with cork, into which pins, passed through 
 discs of cork, card-board, or other material, having objects 
 mounted on them, may be stuck. 
 
 Dipping-tubes are tubes of glass, fig. 114, about nine inches 
 in length, open at both ends, and from one-eighth to one- 
 
 Fig. 114. Dipping Tubes. 
 
 Fig. 115. 
 
 fourth of an inch in diameter. The ends must be nicely 
 rounded off in the flame of a blow-pipe; some of them may 
 be made perfectly straight, while others should be drawn out 
 to a fine point, and made of either of the shapes a, 6, c, d, e. 
 The method of using them is as follows : Supposing the 
 animalcules are contained in a phial or glass jar (fig. 115), 
 and having observed where they are most numerous, 
 either \7ith the naked eye, or with a pocket-magnifier, 
 
192 THE MICROSCOPE. 
 
 cither of the glass-tubes, having one end previously closed 
 by the thumb or fore-finger, wetted for the purpose, is 
 introduced into the phial in the manner represented by 
 the figure : this prevents the water from entering the 
 tube ; and when the end is near to the object which it is 
 wished to obtain, the finger is to be quickly removed and 
 as quickly replaced. The moment the finger is taken off, 
 the atmospheric pressure will force the water, *nd with it, 
 in all probability, the desired objects, up the tube. When 
 the finger has been replaced, the tube containing the fluid 
 should be withdrawn from the phial ; and as the tube is 
 almost certain to contain much more fluid than is requisite, 
 the entire quantity must be dropped into a watch-glass, 
 and the particular insect can be caught by putting the 
 tube over it, when a small quantity of fluid is sure to run 
 up by capillary attraction. This small quantity is to be 
 placed upon a glass-slide for examination. It is necessary 
 to add a small quantity of vegetable matter to animalcules, 
 if we wish to keep them alive for many days ; and as 
 many species are found on confervas and duck-weed, some 
 instrument is required to take small portions of such plants 
 
 Fig. 116. 
 
 out of the jar in which they are growing. For this pur- 
 pose it will be necessary to make use of the forceps, 
 fig. 116, made of brass; the points are a little curved, to 
 keep them accurately together, and the blades are provided 
 with a hole and a steadying-pin. This instrument is also 
 useful for picking up any minute object. 
 
 Fig. 117, at B, is represented a convenient, cheap, and 
 portable " Collecting-bottle and Stick;" simply an ordinary 
 walking-cane divided by a screw, or socket-joint j into two 
 parts for the convenience of packing, and terminated by a 
 brass ring, which is either a fixture or made to screw on 
 and off This ring is adapted to receive the male-screw of 
 the well-known wide-mouthed bottle, used by perfumers 
 
COLLECTING BOTTLE AND NET. 
 
 193 
 
 and chemists for pomade ; this is exactly adapted 
 to fit into tho screw of the brass ring. The facilities 
 
 Fig. 117. 
 
 A. Trough for showing circulation in fish-tail. 
 
 B. Collecting bottle and stick. 
 
 J 
 
 afforded by such an arrangement are obvious enough ; 
 broken bottles can be readily replaced at a small cost, 
 and each bottle when filled corked up and replaced by 
 another. A small fine-gauze net and a hook is made to 
 screw into the same stock ; the whole packs into a very 
 small compass. 
 
 Fig. 118. Collecting Net. 
 
 Collecting Animalcules. For collecting fresh water or 
 marine animals, the small net, made similar to a landing- 
 net, fig. 118, will be found useful : this should be securely 
 fastened to the brass ring a, and fitted firmly into the 
 socket b ; when not in use, the socket may be carried in 
 the pocket ; and the net, by contracting the diameter of 
 the ring (which th'e construction admits of) may be carried 
 inside the hat. 
 
 For collecting desmids, diatoms, and other small crea- 
 tures, Mr. Williamson has a cheap and simple contrivance 
 for converting the end of a walking-stick or umbrella into 
 what he terms a "collecting-stick/' In fig. 119, a repre- 
 
 
 
194 
 
 THE MICROSCOPE. 
 
 aents a piece of whalebone, about 18 inches long, bent 
 
 lound the end of the stick or umbrella, , and made fast 
 in that position by one or two rings, 
 c, of gutta-percha, india-rubber, or 
 of brass, d. A small wide-mouthed 
 bottle, having a rim which will 
 prevent its falling through, is 
 now inserted in the loop thus 
 formed, and is held tightly there 
 by the ends of the whalebone 
 being drawn further through the 
 ring, and thus diminishing the 
 size of the loop. The bottle thus 
 I fixed may be used for dipping out 
 the animalcules. "Whalebone can 
 be moulded to any form by plac- 
 ing it for a short time near the 
 fire. 
 
 Fig. 120 is a box containing 
 six bottles for holding the speci- 
 mens when caught. These bottles 
 should be filled up to the cork 
 with water when and where col- 
 lected, and care must be taken 
 not to mix the specimens from 
 one brook with those from another, 
 
 otherwise serious damage may take place, and on reaching 
 
 home we may find the greater part of our stock either 
 
 dead or dying. Always separate 
 
 the various species as speedily 
 
 as possible. This can be done 
 
 easily, by emptying each bottle 
 
 in its turn into a soup-plate ; 
 
 then with the feather of a pen 
 
 first lift out the smaller ones, 
 
 and with the quill-end cut like 
 
 a scoop lift out the larger, 
 
 classifying and allotting each 
 
 to its separate bottle. 
 
 Live-Box. Mr. Varley im- Fig. 120. 
 
 proved the form of this instrument by making a channel 
 
 Fig. 119. 
 
ANIMALCULE-CAGE. 195 
 
 all round the object-plate, so that the fluid and animalcules 
 in it were retained at the top of the object-plate by capil- 
 lary attraction. The cover is made in the usual way to 
 slide up and down over the object-plate. The plate of 
 brass to which the tube supporting the tablet and cover 
 is attached, is of a circular form, slightly flattened on its 
 two opposite sides for convenience of package. The in- 
 
 Fig. 121. Varleifs Aiiimakule-cage. 
 
 strament is seen in elevation and in section in fig. 121 
 A, B, in both figures, is a flat plate of brass to which the 
 short tube carrying the object-plate or tablet is fixed; 
 d, the piece of brass into which the tablet c is fastened ; 
 b, the. tubular part of the cover, into the rim of which 
 the thin plate of glass a is cemented. 
 
 Compressorium. The purpose of this instrument is to 
 apply a gradual pressure to objects whose structure can 
 only be made out when they are pressed or thinned out 
 by extension. The general plan of the compressorium is 
 shown in fig 122 
 
 Ross's Compressorium consists of a stout plate of brass 
 A, about three inches long, having in its centre a piece of 
 glass like the bottom of a live-box. This piece of glass 
 is set in a frame B, which slides in and out so that it can 
 be removed for the convenience of preparing any object 
 upon it, under water if desirable. The upper moveable 
 part D is attached to a screw-motion at (7; and at one end 
 of the brass-plate A, which forms the bed of the instru- 
 ment, is an upright piece of brass (7, grooved so as to 
 o2 
 
196 
 
 THE MICROSCOPE. 
 
 receive a vertical plate, to which a downward motion is 
 given by a single fine screw, surrounded by a spiral spring,, 
 which elevates the plate as soon as the screw-pressure is 
 removed. The vertical plate carries an arm at right angles 
 to its own plane, terminating in a square frame Z>, capable 
 of receiving very thin, or somewhat thicker glass. The 
 arm has likewise a horizontal motion, so that the upper 
 
 Fig. 122. Boss's Compressorium. 
 
 plate D can be turned completely off the lower one B. 
 Should the thin upper glass be broken, it can be instantly 
 replaced, as no cement is required ; it is merely needful to 
 remove the fragments and slip a fresh glass in. It often 
 happens that on account of the trouble attendant upon 
 the use of all ordinary Compressorium s, the microscopist 
 simply uses a slide and a piece of covering-glass ; but if 
 he wishes an exact means of regulating the pressure, 
 some such Compressorium as "Ross's should always be 
 employed. 
 
CHARA AND POLYPE TROUGHS. 197 
 
 Smith and Beck's trough, for chara and polypes, a sec- 
 tional view of which is shown at fig. 123, is made of three 
 pieces of glass, the bottom being a thick strip, 
 and the front a of thinner glass than the back 
 6 ; the whole is cemented together with Jeffery's 
 marine-glue. The method adopted for confining 
 objects near to the front glass varies according 
 to circumstances. One of the most convenient 
 plans is to place in the trough a piece of glass 
 that will stand across it diagonally, as at c ; then 
 if the object be heavier than water, it will sink, 
 until stopped by this plate of glass. At other 
 times, when used to view chara, the diagonal 
 plate may be made to press it close to the front 
 by means of thin strips of glass, a wedge of glass 
 or cork, or even a folded spring. When using 
 the trough, it is necessary that the microscope ^s- 1 -^ 
 should be in a position nearly horizontal. 
 
 Mr. Walker's trough for exhibiting the circulation of 
 the -blood in a fish's tail, &c. (fig. 117 A) consists of a piece 
 of plate-glass about 6 inches long, and 2 inches wide ; 
 upon this, three other pieces of plate-glass, about J 
 inch wide, are cemented with marine-glue. Three pieces 
 of strong covering glass, about a J inch wide, are 
 also cemented on to the plate, and a piece of mode- 
 rately strong covering glass on to the top of these thin 
 slips ; a piece of plate-glass is then cemented to the top 
 of the thin glass, abutting on the ends of the slips ; the 
 whole forming an open trough, terminating in a thin cell, 
 which is closed at all parts, except where it communicates 
 with the bottom of the trough. 
 
 The fish, wrapped in a little wet linen, is placed in the 
 trough, and the tail is thrust flat into the thin cell ; a 
 small quantity of water is placed in the large trough, and 
 the fish kept in its place by one or two elastic bands or 
 strips of thin sheet-lead passed round the glass and over 
 the body of the fish. 
 
 The advantages of this arrangement are : 1st. The 
 fish cannot throw up its tail and splash the object-glass 
 with water. 2d. In consequence of the tail being kept 
 flat in the cell, the view is perfect, and there is little risk 
 
198 THE MICROSCOPE. 
 
 of the object getting out of focus. 3d. If the tail be not 
 pushed too far into the cell, the vessels at its root are not 
 compressed, and the circulation goes on very freely. 
 4th. The fish may be kept on the stage of the microscope 
 for two or three hours without injury. Mr. Macaulay has 
 suggested, as an improvement, that the three sides of the 
 cell should be made of a single strip of plate-glass, bent to 
 the shape represented in our wood-cut. 
 
 Growing-cells. Considerable attention has been given 
 to various forms of growing-cells for maintaining a con- 
 tinuous supply of fresh water to objects under constant 
 observation, fur the purpose of sustaining vital growth for 
 a long period. The employment of such cells is strongly 
 commended to microscopists, as there is yet much to 
 be discovered concerning the metamorphoses which somo 
 of the lower microscopic forms of plant and animal life 
 pass through $ a patient investigation will probably show 
 that many which are now classed as distinct species 
 are merely different phases of the same type, w T hich alter- 
 nate in a higher or lower scale of development accord- 
 ing to the varied conditions of temperature and nutrition 
 under which they are grown. 
 
 Professor Smith, of Kenyon College, furnished us with 
 what he has called a growing slide, or trough. It con- 
 sists of two pieces of thinnish glass cemented together; 
 in one corner of the upper cover a small hole is bored, 
 and through this a fresh supply of water is introduced 
 without in any way disturbing the desmid, or living object 
 under inspection. Mr. Beck has contrived an improved 
 form of cell ; but, whilst the first-mentioned may be con- 
 structed for a few pence, the latter cannot be had for a 
 less price than ten shillings. 
 
 Dissecting Knives, &c. Knives and needles of various 
 kinds and sizes are required for microscopic dissection ; the 
 best for the purpose are represented in tigs. 124, 125, and 
 126, being, in fact, the very delicately made knives used 
 by surgeons in operations upon the eye. Dissecting needles 
 may be either straight or curved. They may be fixed, or 
 made to take in and out of their handles. The most con- 
 venient are shown in fig. 125; those made of Palladium 
 by Mr. Weedon, Hart Street, are very much the best. 
 
DISSECTING KNIVES. 
 
 199 
 
 Fig. 124. 
 
 Pig.lK 
 
 Fig.lJ6. 
 
 The mode of using a pair of needles in breaking up 
 tissues into very small pieces is represented in fig. 127. 
 
 Fig. 127. Ttasing-out Membrane. 
 
 With a pair of the small needles held firmly between the 
 fore-finger and thumb, the structure must be teased out ; 
 
200 
 
 THE MICROSCOPE. 
 
 an operation which requires care and perseverance, as most 
 of the animal tissues are very difficult of separation. All 
 substances should be carefully separated from dust and 
 other impurities which renders their structure indistinct 
 or confusing. With very delicate membranes, and with 
 those of the nervous system of the smaller animals, in- 
 sects, &c., it becomes necessary that the investigation 
 should be carried on under water, or in fluid of some sort, 
 in a glass cell, and having a strong light thrown down 
 upon it by the aid of the condensing lens, as represented 
 in fig. 128. A certain amount of change of structure must 
 be expected and allowed for ; as nearly all membranes 
 imbibe some portion of the fluid. Delicate structures are 
 often advantageously wetted with dilute solutions of sugar 
 or common salt, to prevent the changes from endosmosis, 
 which result from the use of pure water. The contents of 
 bodies are frequently rendered more distinct by the addi- 
 
 Fig. 128. Dissecting under water. 
 
 tion of re-agents. If the object be a portion of an in- 
 jected animal, it is better to pin it out on a leaded-cork, 
 
VALENTIN'S KNIFE. 
 
 201 
 
 covered "with white wax, and then immerse it in the water- 
 trough ; the more delicate the structure, the sooner after 
 death should it be examined, especially animal tissues. 
 With some vegetable structures, the dissection should be 
 carried on under water. The sepa- 
 ration of the woody and vascular 
 tissues, and the spiral vessels, is best 
 effected by maceration and tearing 
 with fine needles. 
 
 Valentin's Knife. For making fine 
 sections of large substances, or those, 
 soft in structure, such as the liver, 
 spleen, kidney, &c., the double-bladed 
 knife, the invention of Professor 
 Valentin, may be used with advan- 
 tage. An improved construction of 
 this knife, by the late Mr. John 
 Quekett, is represented in fig. 129. 1 
 It consists of two blades, one of 
 which is prolonged by a flat piece of 
 steel to form a handle, and having 
 two pieces of wood riveted to it, for 
 the purpose of its being held more 
 steadily ; to this blade another one 
 is attached by a screw ; this last is 
 also lengthened by a shorter piece of 
 steel, and both it and the preceding 
 have slots cut out in them exactly 
 opposite to each other, up and down 
 which slot a rivet with two heads is 
 made to slide, for the purpose either 
 of allowing the blades to be widely 
 separated or brought so closely to- 
 gether as to touch. One head of this 
 rivet, being smaller than the hole in 
 the end of the slot, can be drawn Fi s- 129 - 
 
 through it ; so that the blade seen in the front of the figure 
 may be turned away from the other in order to be sharpened, 
 
 (1) Another fcim of this instrument is constructed by Mf. Matthews, the 
 blades being made with a convex instead of a straight edge, -their distances from 
 each other being regulated by a milled-head screw, and their separation for 
 cleaning being more readily accomplished. 
 
J02 
 
 THE MICROSCOPE. 
 
 or allow of the section made by it being taKen away from 
 between the blades. The blades are so constructed that 
 their opposed surfaces are either flat or very slightly concave, 
 that they may fit accurately to each other, which is effected 
 more completely by a steadying pin, seen at the base of tho 
 front blade. When the instrument is required to be used, 
 the thickness of the section about to be made will depend 
 upon the distance the blades are apart ; and this is regu- 
 lated by sliding up and down the rivet, as the blades, by 
 their own elasticity, will always spring open and keep the 
 rivet in place ; a cut is then to be made by it, as with 
 an ordinary knife, and the part cut will be found between 
 the blades, from which it may be separated either by open- 
 ing them as wide as possible by the rivet, or by turning 
 them apart in the manner before described, and floating 
 the section out in water. 
 
 Dissecting Scissors. In addition to the forceps and 
 knives, scissors will be necessary for the purposes of dissec- 
 tion : of these the most useful are shown in fig. 1 30. They 
 
 Fig. 130. Dissecting Scissors. 
 
 are made both straight and curved ; of the first kind, two 
 pairs will be required, one having the extremities broad, 
 and the other sharp-pointed ; if large dissections be under- 
 taken, a still stronger pair, with the extremities broad, 
 and made rough like a file, will be necessary. In dis- 
 secting under the microscope, the curved-pointed pair 
 shown at / are the most convenient. In all of these 
 instruments the points should fit accurately together : 
 sometimes those that are very sharp are apt to cross ; this 
 
SMITH|S SECTION INSTRUMENT. 
 
 203 
 
 may in a great measure be prevented by having the 
 branches wide at the base where they are riveted. Tha 
 points can be sharpened on a hone, and a magnifier em- 
 ployed to examine if they fit closely together. 
 
 Section-cutting Instruments. There are a numerous class 
 of substances much too hard to admit of beinsj cut either 
 by scissors or a Valentin's knife, more especially if we re- 
 quire very thin and perfect sections. As most important 
 information is to be gained respecting the structure of 
 various substances, such as stems and roots of plants, 
 horns, hoofs, cartilages, and other firm parts of animals, 
 by cutting very thin sections for mounting as transparent 
 objects, it would be quite impossible for the microscopist 
 to get on without a section-cutting instrument. Among 
 the many mechanical contrivances which have been de- 
 vised for the purpose, the ingenious little machine in- 
 vented by Mr. James Smith 1 will be found to do its work 
 with neatness and precision. 
 
 Vertical or top view. Side view. 
 
 Fig. 131. Smith's Section Instrument. 
 
 Smith's Section Instrument (fig. 131) consists of an outer 
 tube A, A, the upper part of which screws into the lower, 
 and has at the top a flat circular plate E, E, which 
 forms the cutting-table. ..Firmly fixed to the lower part 
 of the tube A, and extending throughout its whole length, 
 is the inner tube B, B, which forms, with the moveable 
 bar D, a holding for the specimen to be cut, while, at the 
 same time, it supports the upper part of the tube A, A, and 
 gives it greater firmness in screwing up and down. The 
 
 (1) " On a Section Instrument, by James Smith." (Micros. Soc. Tran*. 
 roL viii. page 1, 1860.) 
 
204 THE MICROSCOPE. 
 
 bar D moving backwards and forwards in the tube by 
 lueans of the screws c, c, serves, in conjunction with tlw 
 points F, IT,- to fix the specimen to be cut, which is effected 
 as follows : 
 
 The cutting surface E, E, being slightly screwed up, as 
 shown in the drawing,"' and the bar D being drawn back 
 a sufficient distance, the specimen to be cut is placed in 
 the instrument, and firmly fixed by turning the screws 
 c, c ; it is then cut level with the surface by a proper 
 knife or chisel, and the table being screwed down one or 
 more divisions (as shown in the left-hand diagram), a 
 section is cut, and if found of sufficient thinness, a number 
 may be cut by continuing to turn the table down a similar 
 number of divisions, until it will screw no further, when 
 the table must be again screwed up, and the specimen 
 loosened and raised if more sections be required. The 
 principal points of the instrument are : 
 
 1st. Its portability the tube being about two and a 
 half inches long by one inch in diameter. 2d. The 
 specimen to be cut is fixed once for all, and the cutting- 
 surface screwed down to it, a feature that will render it 
 peculiarly applicable to the cutting of soft substances. 
 3d. The ease with which a number of sections may be 
 cut without disturbing the specimen when once properly 
 fixed, while the size of the tube, and the facility with 
 which it can be adapted to objects of various diameters, 
 enable the operator to get sections of stems of plants, &c. 
 whole. In cutting sections of hard woods, which require 
 considerable purchase, the instrument may be placed in a 
 semicircular opening in the edge of the working-table, so 
 that the flat plate or cutting-surface may rest upon it, and 
 the strain thrown on the table. When used for cutting 
 soft substances, it can be held in the hand. 
 
 Fig. 130 represents Mr. Gibbon's " Section-cutting Ma- 
 chine." It consists of a stout brass frame, A /*, having 
 an opening in the top plate, for a tube B, half an inch in 
 diameter, and in depth one and a half inches. In this 
 tube a loose piston, c, works freely, and is steadied by the 
 filot seen in it. To a female screw D, motion is given by 
 the toothed wheel ; and the teeth of which, B , answer 
 the triple purposes of thumb-milling, ratchet-stop, and 
 
SECTION CUTTING. 
 
 205 
 
 graduation. This is screwed to a block of wood, r, having 
 a rabbet cut in for the purpose of securing it to the table. 
 
 Fig. 13-2. Gibbon's Section Cutting Jfocfcfee. 
 
 The machine is self-regulating, and is capable of being 
 worked as rapidly as the skill of the operator may dictate. 
 Sections of woods, when cut from hard woods containing 
 gum, resin, &c., should be soaked in essential oil, alcohol, 
 or ether, before they are mounted as transparent objects. 
 A razor may be fixed to the bench for the purpose of 
 cutting these fine sections, or a fine plane will answer very 
 well. The instrument used by Mr. Topping, fig. 133, con- 
 sists of a b, a flat piece of mahogany, seven inches long 
 and four wide, to the under surface of which is attached, 
 at right angles, a piece g of same size as a b. d is a flat 
 plate of brass, four inches long and three wide, screwed to 
 the upper surface of a b ; to the middle of this plate is 
 attached a tube of the same metal e i, three inches long 
 and half an inch in diameter, and provided at its lower 
 end with a screw f, working in a nut, and having a disk k 
 exactly adapted to the bore of the tube ; this disk is con- 
 nected with the upper end of the screw, and is moved up 
 or down by it c is another screw connected with a curved 
 piece of brass h, which is capable of being carried to the 
 opposite side of the tube by it. The piece of wood about 
 
206 
 
 THE MICROSCOPE. 
 
 to be cut is put into the tube e, and is raised or depressed 
 by the screw/; whilst, before cutting, the curved piece of 
 
 Fig. 133. Topping's Section Cutting Machine. 
 
 metal h should be firmly pressed against it by the screw c. 
 This instrument, if fastened to the edge of a bench or 
 table, is always ready for use. The knife employed may 
 be one constructed for the purpose ; or a razor ground flat 
 on one side. 
 
 Method of making Sections. If the wood be green, it 
 should be cut to the required length, and be immersed for 
 a few days in strong alcohol, to get rid of all resinous 
 matters. When this is accomplished, it may be soaked in 
 water for a week or ten days; it will then be ready for 
 cutting. If the wood be dry, it should be first soaked in 
 water and afterwards immersed in spirit, and before cutting 
 placed in water again, as in the case of the green wood. 
 The wood, if too large, should be cut so as to fit tightly 
 into the square hole, and be driven into it by a wooden 
 mallet; if, on the contrary, it be round, and at the same 
 time too small for the hole, wedges of deal or other soft 
 wood may be employed to fix it firmly : these will have 
 the advantage of affording support, and if necessary, may 
 be cut with the specimen, from which they may afterwards 
 be easily separated. The process of cutting consists in 
 raising the wood by the micrometer screw, so that the 
 
SECTION-CUTTING. 
 
 207 
 
 Ihinnjst possible slice may be taken off by the knife; after 
 a few thick slices have been removed to make the surface 
 level, a small quantity of water or spirit may be placed 
 upon it; the screw is then to be turned one or more 
 divisions, and the knife passed over the wood until a slice 
 is removed; this, if well wetted, will not curl up, but will 
 adhere to the knife, from which it may be removed by 
 pressing blotting-paper upon it, or by sliding it off upon 
 a piece of glass by means of a wetted finger. The plan 
 generally adopted is to have a vessel of water by the side of 
 the machine, and to place every section in it : those that 
 are thin can then be easily separated from the thick by 
 their floating more readily in the water; and all that are 
 good, and not immediately wanted, may be put away in 
 bottles with spirit and water, and preserved for future 
 examination. If the entire structure of any exogenous 
 wood is required to be examined, the sections must be 
 made in at least three different ways; these may be 
 termed the transverse, the longitudinal, and the oblique, 
 or, as they are sometimes called, the horizontal, ver- 
 tical, and tangental : each of these will exhibit different 
 
 Fig. 134. Section* of Wood. 
 
 appearances, as may be seen upon reference to fig. 134 : 
 b is a vertical section through the pith of a coniferous 
 plant : this exhibits the medullary rays, which are known 
 
208 THE MICROSCOPE. 
 
 to the cabinet-maker as the silver grain; and at e is a 
 magnified view of a part of the same : the woody fibres 
 are seen with their dots I, and the horizontal lines Ic indi- 
 cating the medullary rays cut lengthwise ; whilst at c is a 
 tangental section, and /a portion of the same magnified: 
 the openings of the medullary rays m m, and the woody 
 fibres with vertical slices of the dots, are seen. Very 
 instructive preparations may be made by cutting oblique 
 sections of the stem, especially when large vessels are 
 present, as then the internal structure of the walls of some 
 of them may oftentimes be examined. The diagram above 
 given refers only to sections of a pine ; all exogenous stems, 
 however, will exhibit three different appearances, according 
 to the direction in which the cut is made ; but in order to 
 arrive at a true understanding of the arrangement of the 
 woody and vascular bundles in eudogens, horizontal and 
 vertical sections only will be required. Many specimens 
 of wood that are very hard and brittle may be much 
 softened by boiling in water ; and as the cutting-machine 
 will answer for other structures besides wood, it should 
 be stated, that all horny tissues will also be softened by 
 boiling, and can then be cut very readily. 
 
 Preparation of Hard Tissues. All sections of recent and 
 greasy bones should be soaked in ether for some time, and 
 afterwards dried in the air, before they are fit for the saw, 
 file, and hone ; by dissolving out the grease, the lacunae 
 and canaliculi show up very much better. When it is 
 wished to examine the bone-cells of fossil bone, chippings 
 only are required; these may be procured by striking the 
 bone with the sharp edge of a small mineralogical-hammer: 
 carefully select the thinnest of the chips, and mount them 
 at once, without grinding, in Canada balsam. If desirable 
 to compare bone structures, it must be borne in mind that 
 the specimens for comparison should be cut in one and the 
 same direction ; as the bone-cells, on which we rely for our 
 determination, are always longest in the direction of the 
 shaft of the bone, it follows that if one section were trans- 
 verse, and the other longitudinal, there must be a vast 
 difference in the measurement of the bone-cells, in conse- 
 quence of their long diameter being seen in the one case, 
 
SECTIONS OF TEETH. 
 
 209 
 
 and their short diameter in the other. In all doubtful 
 cases, the better plan is to examine a number of fragments, 
 both transverse and longitudinal, taken from the same 
 bone, and to form an opinion from the shape of bone-cell 
 which most commonly prevails. 
 
 The Teeth. The best mode of examining teeth is by 
 making fine sections. Specimens should be taken, both 
 from young and old teeth, to note 
 the changes. A longitudinal or 
 transverse slice should be first 
 taken off; a circular saw, fitted to 
 the lathe, fig. 135, cuts sections 
 very quickly then rub down, first 
 by the aid of the corundum-wheel, 
 which should also be fitted to 
 the head-stock of the lathe, then 
 finish them off between two 
 pieces of water-of-Ayr stone, and 
 finally clean and polish between 
 plates of glass, or on a polishing 
 strap with putty powder. The 
 section requires to be washed in 
 ether, to remove all dirt and im- 
 purities ; when well polished and 
 dried, it may be preserved under 
 thin glass, and cemented down 
 with gold-size or varnish. 
 
 Such polished sections are preferable to many others 
 which, on account of their irregular surface, require to be 
 covered with fluids, as Canada-balsam, turpentine, <fec., in 
 order to fit them for examination with high powers. It 
 almost always happens, that some portion of these fluids 
 enters the dentine, which then becomes indistinct, and 
 almost invisible in its ramifications. 
 
 Two sections made perpendicularly to one another 
 through the middle of the crown and fang of a tooth, 
 from before backwards, and from right to left, are suffi- 
 cient to exhibit the more important features of the teeth ; 
 but sections ought also to be prepared, showing the surface 
 of the pulp cavity and that of the enamel ; and likewise 
 various oblique and transverse sections through the dentina 
 
 Fig. 135 -Small Lathe for 
 polishing. 
 
210 THE MICROSCOPE. 
 
 in the fangs, to exhibit the anastomoses of their branches. 
 The dental cartilage is easily shown by maceration in 
 hydrochloric-acid, a process which requires a longer or 
 shorter time, according to the concentration of the acid. 
 It is very instructive also to macerate thin sections in 
 acid, and to examine them upon a slip of glass, at 
 intervals, until they entirely break up. The enamel 
 prisms are readily isolated in developing enamel in this 
 way, and the transverse lines readily seen when the section 
 is moistened with hydrochloric acid. The early develop- 
 ment may be studied in embryos of two, three, or four 
 months with the simple microscope ; and in transverse 
 sections of parts hardened in spirits of wine. The pulp of 
 mature teeth is obtained by breaking them in a vice, and 
 the nerves can be made out without difficulty on the addi- 
 tion of a dilute solution of caustic soda. 
 
 To cut through the enamel of the tooth, it will be 
 necessary to lessen the friction, by dropping water upon 
 the saw as it is made to revolve. The section is after- 
 wards very quickly ground down by holding it against 
 the flat side of the corundum- wheel. 1 A small handle, 
 mounted with shell-lac, to fix the section in, forms a ready 
 holder : polish, as before directed, between two pieces of 
 the water-of-Ayr stone, or on a hone of Turkey-stone kept 
 wet with water. As the flatness of the polished surface is 
 a matter of the first importance, that of the stones them- 
 selves should be tested from time to time ; and whenever 
 they are found to have been rubbed down on one part 
 more than another, they should be flattened on a paving 
 stone with fine sand, or on a lead plate with emery. When 
 this has been sufficiently accomplished, the section is to be 
 secured, with Canada balsam, to a slip of thick well- 
 annealed glass, in the following manner : Some Canada 
 balsam, previously rendered somewhat stiff by evaporation 
 of part of its turpentine, is to be melted on the glass-slip, 
 so as to form a thick drop, covering a space somewhat 
 larger than the size of the section, and it should then be 
 set aside to cool ; during which process, the bubbles that 
 may have formed in it will usually burst. When cold, its 
 
 (1) Corundum is a species of emery composition ; alumina, red oxide of iron t 
 and lime ; it is much used by dentists a* a polishing material. 
 
PREPARING SECTIONS. 21] 
 
 hardness should be tested with the edge of the thumb 
 nail, for it should be -with difficulty indented by pressure, 
 and yet should not be so resinous as to be brittle. If it 
 be too soft, as indicated by its too ready yielding to the 
 thumb-nail, it should be boiled a little more ; if too hard, 
 which will be shown by its chipping, it should be re-melted 
 and diluted with more fluid balsam, and then set aside to 
 cool as before. When of the right consistence, the section 
 should be laid upon its surface, with the polished side 
 downwards; the slip of glass is next to be gradually 
 warmed until the balsam is softened, care being taken to 
 avoid the formation of bubbles, and the section is then to 
 be gently pressed down upon the liquefied balsam in a sort 
 of wave towards the side, and an equable pressure being 
 finally made over the whole. When the section has been 
 thus secured to the glass, it may be readily reduced in 
 thickness by grinding. When the thinness of the section 
 is such as to cause the water to spread around it between 
 the glass and the stone, an excess of thickness on either 
 side may often be detected by noticing the smaller distance 
 to which the liquid extends. In proportion as the section 
 attached to the glass is ground away, the superfluous 
 balsam which may have exuded around it will be brought 
 into contact with the stone ; and this should be removed 
 with a knife, care being taken that a margin be still left 
 round the edge of the section. As the section approaches 
 the degree of thinness which is most suitable for the 
 display of its organization, great care must be taken that 
 the grinding process is not carried too far ; and frequent 
 recourse should be had to the microscope to examine it. 
 The final polish must be given upon a leathern strap, or 
 upon the surface of a board covered with buff-leather, 
 sprinkled with putty-powder and water, until all marks 
 and scratches have been rubbed out of the section. 
 
 In mounting sections of bone, or teeth, it is important 
 to avoid the penetration of the Canada balsam into the 
 interior of the lacunae and canaliculi; since, when these 
 are filled by it, they become almost invisible. The benefit 
 which is derived from covering the surfaces of the 
 specimen with Canada balsam, may be obtained, without 
 the injury resulting from the penetration of the balsam 
 
 p2 
 
THE MICROSCOPE. 
 
 into its interior, by adopting the following method: 
 A small quantity of balsam, proportioned to the size of 
 the specimen, is to be spread upon a slip of glass, and to 
 be rendered stifier by boiling, until it becomes nearly 
 solid when cold ; the same is to be done to the thin glass 
 cover ; next, the specimen being placed on the balsamed 
 surface, and being overlaid by the balsamed cover, such a 
 degree of warmth is to be applied as will suffice to liquefy 
 the balsam, without causing it to flow freely ; and the 
 glass cover is then to be quickly pressed down, and the 
 slide to be rapidly cooled, so as to give as little time as 
 possible for the penetration of the liquefied balsam. 
 
 Circular Disc. For the purpose of cutting glass covers 
 or making shallow cells with japanners' gold-size for mount- 
 ing objects, 1 fig. 136 will be found useful; it is made 
 
 Fig. 130. Circular Disc Machine. 
 
 of two circular wheels of wood, these being let into a 
 solid block of wood, and secured there by central screws. 
 A handle of wood is fixed into the upper part of one, for 
 the purpose of turning it round, the motion being com- 
 municated to the other by an endless band of catgut 
 running in the grooved edge of each. On the upper sur- 
 face of the wheel, under the right hand, are fixed, by 
 means of screws, two strips of brass, which serve as springs 
 
 (1) Mr. Shadbolt's little turn-table, invented for the same purpose, is in every 
 way superior to this, and is now in very general use. 
 
GLASS CELL CUTTING. 213 
 
 for securing the glass slip; a camel's-hair pencil, previously 
 dipped in japanners' gold-size, is then taken between the 
 finger and thumb, and held as represented in the woodcut, 
 when the wheel is put in motion, and a perfect circle is 
 rapidly formed ; the cell is then removed and put aside to 
 dry. In the same way, by securing a sheet of thin glass 
 under the brass springs, and substituting for the pencil 
 a cutting diamond, a circular cover may be readily cut 
 out. A cutting diamond is not only useful to the micro- 
 scopist for the above purpose, but also for writing the 
 names of mounted objects on the ends of the glass slides. 
 A glazier's diamond for cutting glass slides is both conve- 
 nient and economical : the mode of using it may be acquired 
 in any glazier's shop. 
 
 Cutting glass ceils. Mr. H. H. Brown has also con- 
 trived a brass plate for cutting out the centres of pieces of 
 thin glass, to form very shallow cells. It consists of a thin 
 plate of brass, perforated with holes corresponding to the 
 diameter of the cell required, and counter-sunk to a suit- 
 able thickness. To use it, it must be heated, and a little 
 sealing-wax or shellac melted into the counter-sunk parts ; 
 on this, while hot, the disc of thin glass is to be firmly 
 pressed. "When cold, the centres may be easily removed 
 with a common rat's-tail file, the edges being afterwards 
 smoothed over by a fine watch-maker's file. The plate 
 must once more be heated and the glass rings removed, 
 and finally be cleansed from adhesive wax by a little ether. 
 Mr. Brooke has long made use of a small brass press for 
 the purpose of cutting out thin circles of glass and con- 
 verting the same into shallow cells. 
 
 Cells for mounting objects may be made of vulcanite 
 by slicing-tubing made of this material. Glycerine does 
 not act upon it. Mr. Henry Lee uses cells cut from tubes 
 of cardboard; these he finds very useful for mounting dry 
 and opaque objects. Both have the great advantage of 
 cheapness the former are sold for about 3d. a dozen and 
 the latter Is. a gross. Mr. Suffolk devised a cheap tin-cell, 
 which must partially supersede the more expensive glass- 
 cell; it appears to answer equally well for fluid or dry 
 mounting. The metallic rings for making these cells 
 are manufactured in various sizes and thicknesses by 
 
214 THE MICROSCOPE. 
 
 Collins, of Great Titchfield Street, and sold at 3d. per 
 
 Dr. Guy brought under the notice of microscopists, a 
 plan for preserving metallic sublimations, crystals, &c. in 
 small round, or oval tubes, hermetically sealed at both 
 ends. This plan may be made available for the display of 
 insects, parts of flowers, as stamens, pollen, &c. See his 
 paper in the Micros. Journal, New Series, vol. ii p. 77. 
 
 Fig. 337, full size. Spring-clip for mounting. 
 
 Dr. Maddox describes a Wire Spring-clip for mounting 
 purposes, Micros. Soc. Trans. 1865, p. 84. To make the 
 clip, take a straight piece of brass wire four and three- 
 quarter inches in length, turn one end at six-eighths of an 
 inch with a pair of wire-pliers at right angles ; this second 
 portion, at half an inch, again bend at right angles in the 
 same plane ; now, at three-quarters of an inch, turn the 
 wire over on itself, leaving at the bend space sufficient to 
 admit a thick slide. At one inch and five-eighths twist 
 the wire completely on itself, and bring the now short 
 ends at right angles to the longest part ; file this end quite 
 Hat. Give the first portion of the wire a slight curvature, 
 so that the point and bend may act as a stiff spring 
 Against the under surface of the slide when applied. This, 
 although a very simple and inexpensive^ clip to make, has 
 been very much improved upon, as will be admitted by 
 those who have used the little handy spring-clip shown 
 full size in fig. 137. The Universal Clip, as it deserves to 
 be called, may be purchased for Is. 6d. per doz. of Baker, 
 Holborn, so that objects of great delicacy can be mounted 
 and left to dry and harden for any necessary length of 
 time. The little nipple which is seen to press upon the 
 glass cover in fig. 138, is made of a piece of cork or thick 
 leather. The clip simply requires pinching together be- 
 tween the thumb and finger; as soon as it is released tha 
 
MOUNTING OBJECTS. 215 
 
 little cork nipple comes down with considerable force upon 
 the glass cover. In mounting algae, &c. with a gelatine 
 medium, the specimen should 
 be placed on the glass slide 
 with a small quantity of water, 
 and when properly arranged, 
 the thin glass cover must be 
 carefully put on, and a suffi- 
 cient quantity of gelatine me- 
 dium placed by its side ; gentle 
 heat should be applied to drive 
 out the water, when the gela- 
 tine flows under to take its place ; then put the object 
 aside to dry and harden. 
 
 General Directions for the Preparation and Mounting 
 of Objects, The objects exhibited by the microscope are 
 either opaque or transparent. The former, in the majority 
 of instances, require little or no preparation beyond placing 
 them in such a position as to show their external surface 
 by reflected or condensed light, and covering with thin glass to 
 exclude dust. Those objects, however, which it is intended 
 to examine by transmitted light require, in most cases, to 
 be prepared previously to mounting them, in whatevei 
 vehicle may be found most suitable for exhibiting theii 
 structure. The medium most used for mounting trans 
 parent objects is Canada balsam. The pure balsam is, 
 however, too thick for use, and it requires to be diluted 
 with spirit of turpentine to render it sufficiently fluid to 
 permeate the structure to be exhibited. As a general rule, 
 it should be just fluid enough to drop readily from the 
 point of a needle. Those who desire to avoid the trouble 
 of mixing their own mounting medium, can procure it 
 ready for use from any of the microscope makers. There 
 are some few objects whose structure is so transparent 
 that they must be mounted diy. Scales from the wings 
 of butterflies and moths, of the podura and lepisma sac- 
 charina, and some of the diatomacese are of this class. All 
 that is necessary in preparing objects for dry mounting, 
 is to take care that they are free from extraneous matter, 
 and to fix them permanently in that position in which 
 their structure will show to the best advantage. Care 
 
216 THE MICROSCOPE. 
 
 should be taken to have no draught of air through the 
 room while handling very delicate objects ; many a beauti- 
 ful object has been wafted from under the hand of th& 
 microscopist in this way, sometimes, even by his own 
 breath. 
 
 The preparation of very minute objects which require 
 particular chemical treatment before mounting, will be 
 more fully described hereafter. To this class belong the 
 diatomaceae, whose delicate structure forms one of the most 
 beautiful objects which can be exhibited. In mounting 
 entemological specimens, the first thing, of course, is the 
 dissection of the insect. This is best accomplished by 
 the aid of Collins's Dissecting Microscope, a pair of small 
 brass forceps, and very finely-pointed scissors ; the parts 
 to be prepared and mounted should first be carefully 
 detached from the insect with the scissors, then immersed 
 in a solution of caustic alkali (Liquor Potassae) for a few 
 days, to soften and dissolve out the fat and soft parts : the 
 length of time it is necessary to immerse them can only be 
 ascertained by experience, but, as a general rule, the objects 
 assume a certain amount of transparency when they have 
 been long enough in the alkali ; when this is ascertained 
 to be the case, the object is to be placed in a flat receptacle 
 (a shallow pomatum pot is as good a thing as can be used), 
 and put to soak for two or three hours in soft or distilled 
 water. It is then to be placed between two slips of glass, 
 and gently pressed till the softer parts, &c. are removed. 
 These will frequently adhere to the edge of the object ; it 
 will, therefore, be necessary to wash the latter carefully 
 in water to get rid of the superfluous matter, a process 
 which will be much aided by delicate touches of a camel's- 
 hair brush. Place the object now and then under the 
 microscope to see that all extraneous matter is removed, 
 and when this is accomplished take the specimen up care- 
 fully with the camel's-hair brush, and lay it on a piece of 
 very smooth paper (thick ivory note is very good for 
 the purpose), arrange it, if necessary, to its natural appear- 
 ance with the brush and a finely-pointed needle, place a 
 second piece of paper over it, and press it flat between 
 two slips of glass, and compress it by one of the American. 
 clips which may be bought for a few pence per dozen. 
 
PREPARING AND MOUNTING. 217 
 
 When thoroughly dry (which it will probably be in about 
 twenty-four hours, if in a warm room), separate the 
 glasses, and gently unfold the paper ; then, with a little 
 careful manipulation, the object may be readily detached, 
 and should be at once placed in a little spirit of turpentine, 
 where it should remain for a few days till it is rendered 
 transparent and fit for mounting. The time during which 
 it should remain in this liquid will depend on the struc- 
 ture ; some objects, such as wings of flies, will be quickly 
 permeated, while horny and dense objects require an 
 immersion of a fortnight or even longer. A pomatum pot 
 with a concave bottom and well-fitting lid will be found 
 to answer admirably for the soaking process, and it is 
 well, in preparing several specimens at a time, to have two 
 pots, one for large and medium, the other for very small 
 objects, or the smaller ones will be found often to adhere 
 to the larger. 
 
 The glasses on which objects are mounted are usually 
 slips of flatted crown or sheet glass cut to a size of three 
 inches by one, and ground at the edges. The mode ot 
 mounting the object is as follows : Having chosen a glass 
 slide, clean and polish it with a piece of chamois leather, 
 ascertain the centre of the slide by means of a piece of 
 paper or card of exactly the same she as itself, and in 
 which a hole has been cut exactly in the centre, 
 place the piece of paper under the slide, and, having 
 removed the object to be mounted from the turpentine in 
 
 Fig. 139. Showing the mode of placing Glass Cover on th Object. 
 
 which it has been soaked, lay it on the slide on the spot 
 corresponding to the hole in the card underneath ; then 
 tain up a small quantity of the prepared Canada balsam 
 on the point of a large needle or pointed pen-knife, and 
 
218 THE MICROSCOPE. 
 
 drop it immediately over the object, slightly warm tlio 
 under part of the slide over a spirit-lamp to diffuse the 
 balsam and cause it thoroughly to penetrate the object, 
 and immediately cover the latter with one of the small 
 circles of thin glass, sold by opticians for the purpose. 
 In laying the glass cover on the object, care should bo 
 taken to bring the edge of the circle down first, and let 
 the other fall slowly on the object (see fig. 139), to prevent 
 the formation of bubbles from the sudden displacement of 
 the air. It requires some little practice to keep the object 
 in the centre of the circle. 
 
 Sometimes, notwithstanding all the care of the operator, 
 bubbles will appear. These may generally be got rid of 
 by gently warming the under part of the slide over the 
 spirit-lamp, when the bubbles will usually leave the 
 object, and travel towards the edge of the circle. In most 
 cases they will entirely disappear as the balsam becomes 
 firmer and drier. If it be desired to dry the balsam 
 quickly, the slide may be placed in some warm situation 
 where the heat does not much exceed 100, and it must 
 be maintained in a perfectly horizontal position, to prevent 
 displacement, until the balsam has become dry. When 
 this has been ascertained to be the case, the superfluous 
 balsam which surrounds the edge of the circle may be 
 scraped off by the point of a penknife; and when the 
 major part has been removed in this way, the remainder 
 may be got rid of, and the edges of balsam rendered smooth 
 by rubbing gently with an old silk handkerchief moistened 
 with spirit of turpentine. The edge of the circle of balsam 
 will probably appear white and dull, but it may be rendered 
 transparent by gently warming the under part of the slide 
 over a spirit-lamp, and again placing the object in a warm 
 room till the balsam has a second time become hard and 
 dry ; after which the name of the object should be written 
 with a small writing diamond at one end of the slide. 
 Some microscopists prefer to cover the slide with orna- 
 mental paper, which may be procured very cheaply. 
 
 In covering the slides with paper, their edges need not 
 be ground, but may be rubbed with a fine file, which will 
 prevent the sharp glass from damaging the paper cover, 
 and cutting the fingers of the operator. The foregoing is 
 
PREPARING AND MOUNTING. 219 
 
 the method by which objects are mounted in balsam ; 
 there are, however, some specimens, the mounting of 
 which, in balsam, would render them almost invisible, in 
 which case if not suitable for dry-mounting they should 
 be placed in fluid in cells, the size and depth of which 
 must be regulated by the proportions of the object. If 
 it be the scale of a fish, or the pollen of a flower, a very 
 shallow cell will suffice, and it may be formed of " Bruns- 
 wick black" in the manner already described. When the 
 cell is quite dry, take the object (which should have been 
 some time previously soaked in the fluid in which it is to 
 be mounted to dispel the air from its substance), place it in 
 the middle of the circle, fill the space quite full of the 
 mounting fluid, and cover it with a glass circle ; place the 
 tdge, down first, and bring the whole surface of the circle 
 very gradually upon the cell as pointed out in the former 
 case. Some of the fluid will immediately escape under the 
 edge ; this may be absorbed by a piece of filtering paper. 
 Should too much escape, a bubble will make its appearance 
 in the cell \ in this case the process must be repeated. 
 When this has been performed successfully, secure the glass 
 circle in its place with a small spring-clip ; then take a 
 camel's-hair brush, charged with varnish, and carry it 
 round, and slightly over the edge of the cover. Allow the 
 first layer to dry before another is added, and continue to 
 add more gradually until the cell is made perfectly air-tight. 
 Glass or metal cells must be employed for those objects 
 whose bulk renders the method just described inadmissible. 
 Glass-cells may be fastened to the glass-slide either by 
 Canada balsam, by Jefferey's marine glue, or Brunswick 
 black ; the latter will be rendered very durable by mixing 
 it with a small quantity of India-rubber varnish (made by 
 dissolving small strips of caoutchouc in gas-tar). The pro- 
 cess of mounting in glass-cells is similar to that employed 
 in making varnish-cells, except that a somewhat larger 
 quantity of cementing medium is required on account of 
 the greater weight of the cell. Objects mounted in this 
 way should always be kept in the horizontal position, and 
 a little fresh varnish applied now and then, if the cement 
 show any tendency to crack. 
 
 In mounting objects in balsam, great care should be 
 
220 THE MICROSCOPE. 
 
 taken to have the specimens quite dry before soaking them 
 in turpentine. Objects mounted in cells, on the contrary 
 should have become perfectly saturated with the mounting 
 fluid before being finally secured. 
 
 It is preferable to mount and preserve specimens of animal 
 tissues in shallow cells, to avoid undue pressure on the 
 preparation. Cells intended to contain preparations im- 
 mersed in fluid must be made of a substance impervious 
 to the fluid used; on the whole, the 
 most useful are those made with 
 circles of thin glass, cemented to 
 the glass-slide with marine glue, 
 such as we have here represented 
 (fig. 140). The surface of the glass 
 ""' f r should te sli S htl J roughened before 
 
 applying the cement. 
 Different modes of mounting may be employed with 
 advantage, to show different structures ; entomological 
 specimens, such as legs, wings, spiracles, trachea;, ovi- 
 positors, stings, tongues, palates, corneae, &c. show best 
 in balsam : the trachea of the house-cricket, however., 
 should be mounted dry. Sections of bone show best; 
 when mounted dry, or in a cell with fluid. Scales of 
 butterflies, moths, &c. should be mounted dry. Other 
 objects, as sections of wood 'and stones of fruit, exhibit 
 their structure best in a cell with fluid. 
 
 There are some objects much more difficult to prepare 
 than others, and which tax the patience of the beginner 
 in a manner which can hardly be imagined by any one 
 who has never made the attempt. The structure of many 
 creatures is so delicate, as to require the very greatest care to 
 prevent mutilation, and consequent spoliation of the spe- 
 cimen. The beginner, therefore, must not be discouraged 
 by a few failures in commencing, but should persevere 
 in his attempts, and constant practice will soon teach him 
 the best way of managing intricate and difficult objects. 
 The room in which he operates should be free from dust, 
 smoke, and intrusion, and everything used should be kept 
 scrupulously clean, since a very small speck of dirt, which 
 may be almost invisible by the naked eye, will assume 
 unpleasant proportions under the microscope, and not only 
 
JPREPARING AND MOUNTING. 221 
 
 mar the beauty, but possibly interrupt a clear view of a 
 very splendid and delicate object. Then, again, if the 
 microscopist prefers to cut and grind his own glass slips, 
 he should be very careful that there are no sand-specks or 
 air-bubbles in the centre of the slide, or of the glass- 
 cover : many a good object has been spoiled from neglect 
 of this precaution. A good light by which to work is 
 also highly important. In using the ordinary microscope, 
 the microscopist should keep both eyes open, the practice of 
 closing the eye not in use being injurious to the sight 
 of both. The beginner who is about to purchase a micro- 
 scope, will do well to procure a binocular, the price of 
 which has been reduced so much as to bring it within 
 the reach of those of even moderate means. 
 
 The preservation of objects is a matter of much im- 
 portance. They ought to be kept in a cool and dry 
 place. Sections of bone, the pollen of plants, and the 
 scales of the podura and butterflies, become spoiled if 
 kept in a damp atmosphere. Objects Amounted dry should 
 be carefully protected from, dust, which will find its way 
 into crevices and corners where one might hardly suppose 
 it could possibly enter. 
 
 Some opaque objects require dry mounting; others 
 show best in fluid ; the eiytra of some beetles are mag- 
 nificent objects when mounted in balsam. Cells punched 
 out of thick mill-board, or turned in some hard wood, or 
 Mr. Suffolk's metal-rings, are much lighter and more con- 
 venient than glass for such objects, and also for those 
 mounted dry. In mounting objects in fluid, the glass-cover 
 should come nearly, but not quite, to the edge of the cell ; 
 a slight margin must be left for the cement, which ought 
 to project slightly over the edge of the cover, in order to 
 unite it securely to the cell. In cells, however, that con- 
 tain balsam, there is no necessity for cement, and the 
 appearance of the slide will be improved by choosing a 
 cover of exactly the same size as the cell. 
 
 There are some objects which require considerable dex- 
 terity and patience to prepare them for mounting. The 
 petal of the pelargonium is one of these. It is necessary 
 to split it in order to show its structure to perfection. 
 This is effected by dividing the base of the petal with a 
 
222 THE MICROSCOPE. 
 
 sharp penkcife, and then, with two small pairs of forceps, 
 tearing asunder the two parts; the upper surface, which 
 is the part to be mounted, must then be dried and placed 
 for a short time in spirit of turpentine, previously to 
 being mounted in balsam. If well prepared, the colour 
 of the petal will be almost as fresh as in its natural state. 
 
 In mounting diatomaceog, to show them as nearly as 
 possible in their natural condition, they should be first 
 well washed in distilled water and mounted in a medium 
 composed of one part of spirits of wine to seven parts of 
 distilled water. The siliceous coverings of the diatoms, 
 however, which show such beautiful forms under the 
 higher powers of the microscope, require considerable 
 preparation. The guano, or infusorial earth containing 
 them, should first be washed several times in water till 
 the water is colourless, allowing sufficient time for pre- 
 cipitation between each washing. The deposit must then 
 be put into nitro-hydrochloric acid (equal parts of nitric 
 and hydrochloric acids). A violent effervescence takes 
 place, and when this has subsided, the whole should be 
 subjected to heat, nearly but not quite up to the boiling- 
 point, for six or eight hours. The acid must now be care- 
 fully poured off, and the precipitate washed in a large 
 quantity of water, allowing some three or four hours 
 between each washing, for the subsidence of some of the 
 lighter forms; the sediment must be examined under 
 the microscope with an inch object-glass, and the siliceous 
 valves of the diatoms picked out with a coarse hair or 
 bristle. 
 
 When it is desired to exhibit one of the larger forms, 
 it can be placed separately in the middle of a glass-slide, 
 and mounted in Canada balsam ; or when it is wished to 
 mount several forms at once, the fluid containing the 
 skeletons should be gently shaken, and a drop spread over 
 the centre of a slide, the glass being held over a spirit- 
 lamp till the fluid has all evaporated, when the object may 
 be either dry-covered or mounted in balsam in the usual 
 way, according as its structure may require the one or the 
 other treatment. Diatoms may be kept in distilled water 
 in a small corked phial for any length of time. 
 
 For vegetable preparations, distilled water in which 
 
GLYCERINE JELLY. 223 
 
 camphor has been kept is a good mounting medium ; some 
 preporers, however, add spirits of wine in the proportion 
 of one draehm to eleven drachms of water ; others add to 
 these saltpetre, two grains to the ounce of fluid. The 
 mounting-fluid should be prepared and allowed to settle, 
 when the major part can be poured off clear a much 
 better mode than filtering, as particles of the paper are 
 apt to get mixed with the liquid. 
 
 F. M. Bimmington's Glycerine Jelly has become an 
 established preparation, and one found to possess many 
 advantages over Canada balsam, and some other media 
 used for the same purpose, in the facility with which 
 objects can be mounted, and efficiently preserved, and the 
 transparency it gives to many animal and vegetable struc- 
 tures. Its antiseptic powers are sufficient to prevent 
 changes in any object immersed in it, if not too bulky. 
 It is especially adapted for mounting alga3, fungi, vegetable 
 and animal tissues, urinary deposits (as casts, epithelium, 
 crystals), also anatomical specimens, starch granules, des- 
 midiacese, diatomacea3, &c. Objects to be mounted in this 
 medium only require to be soaked in weak alcohol for a 
 time, greater or less, as may be necessary, for the purpose 
 of dissolving out any soluble matter, or for driving out 
 air entangled in the cellular meshes. When it is thought 
 that this has been accomplished, the object is laid on a 
 slide and freed from superfluous moisture, the slide gently 
 warmed, and a quantity of the jelly, deemed sufficient for 
 the purpose, laid by the side of it, and made to touch it. 
 It will thus be immersed ; the cover, previously warmed, is 
 to be laid upon it, and gently pressed. The slide may now 
 be laid aside and finished by running it round with varnish. 
 
 The jelly should be liquefied by holding the bottle at 
 some distance above a lamp, or by dipping it into hot 
 water. No more than what is necessary need be liquefied, 
 and it should never be made hot. 
 
 For certain delicate organisms, as the desmidiaceae and 
 diatomaceae, whose plasma may be affected by too dense 
 a medium, the jelly may be diluted one-quarter or one- 
 third with camphor-water. 
 
 For mounting pathological or injected preparations, the 
 following medium will be found to answer very well : 
 
224 THE MICROSCOPE. 
 
 Bichloride of mercury, one grain ; chloride of sodium, 
 ninety grains; distilled water, one pint: set aside, and, when 
 perfectly clear, decant and preserve in a stoppered bottle. 
 All preparations used in mounting, and objects themselves, 
 should be carefully preserved from dust. Balsam should 
 be kept in a wide-mouthed bottle, over which a small 
 tumbler or cupping-glass must be inverted. It is ad- 
 visable to avoid the use of a cork, as it will be broken 
 in attempting to withdraw it, and portions will not only 
 adhere to the neck of the bottle, but are apt to get into 
 the balsam. Objects, and parts of objects, already prepared 
 and dry, may be kept neatly folded up in ivory-paper, as 
 it is not well to have too many objects in the turpentine 
 at the same time, in order to avoid confusion. Glass- 
 slides which are soiled with balsam can be cleaned with 
 turpentine and a piece of rag the glass circles will require 
 to be soaked in turpentine to get rid of any balsam they 
 may happen to contract. When a greasy appearance is 
 present, it may be removed by a piece of rag moistened 
 with rectified spirit. Some remove it by rubbing the 
 glass with caustic alkali ; but as this liquid acts on flint- 
 glass, and sometimes makes it partially opaque or milky, 
 its use should be entirely discarded a weak solution of 
 ammonia, or cyanide of potassium, answers the purpose best. 
 In order to demonstrate the internal structure of animal 
 tissues under very high magnifying powers, Dr. Beale l says 
 the specimen must be placed in a viscid medium, and sub- 
 jected to considerable pressure to make it sufficiently thin. 
 Price's glycerine, having a specific gravity of 1,240, and 
 a strong syrup, are the best adapted for preserving all soft 
 tissues. In practice, the specimen is first immersed in a 
 solution of weak glycerine or syrup, and the density ol 
 the fluid is gradually increased. In this way, and in the 
 course of -two or three days, the softest and most delicate 
 tissues swell out, and become more transparent; but no 
 chemical change is produced in the specimens. The one 
 thing to be observed is, that the strength of these fluids 
 should be increased very gradually until the whole of the 
 tissues are thoroughly penetrated and saturated by the 
 strongest that can be obtained. Cerebral tissues, delicate 
 
 (1) Beale, " How to Work with the Microscope." 
 
STAINING ANIMAL TISSUES. 225 
 
 n rvous textures, like the retina, may be permeated \rj 
 the strongest glycerine, and, when fully saturated with i 
 dissected with a<degree of minuteness unattainable in any 
 other way. " The smallest animalcules, entozoa, polyp^ 
 molluscs, insects, Crustacea, fungi, algae, and the delicate 
 parts of vegetable tissues, are equally well preserved by 
 it." All the various colouring-solutions, as carmine, aniline, 
 &c., should be always prepared for use with glycerine or 
 syrup as a basis. 
 
 The staining or colouring fluid employed by Dr. Beaie 
 is made as follows : Carmine, 10 grains ; strong liquid 
 ammonia, J drachm ; Price's glycerine, 2 ounces ; dis- 
 tilled water, 2 ounces j alcohol, J ounce. The carmine 
 is Hx> be placed in a test-tube, and the ammonia added to 
 it. Upon applying the gentle heat of a spirit-lamp, it is 
 dissolved. Boil it up for a few seconds, and allow it to 
 cool before adding the glycerine and rest of the ingredients. 
 Lastly, pass it through a filter, or allow it to stand by and 
 decant off the clear solution. The solution should neither 
 be too alkaline, nor perfectly neutral ; if the former, the 
 colouring becomes too intense, and thus much of the soft 
 or imperfectly formed tissue is destroyed; and, if the 
 latter, the uniform staining of tissue and germinal matter 
 equally mars the result. The permeating power of the 
 solution may be increased by the addition of a little more 
 water and alcohol. 
 
 After the specimen has been properly stained, it should 
 be washed in a solution, consisting of strong glycerine two 
 parts, water one part ; and then transferred to the following 
 acid fluid : Strong glycerine, one ounce ; strong acetic acid, 
 five drops; where it must remain three or four days to 
 regain the volume it occupied when fresh. To mount 
 specimens so prepared, take a small portion and spread it 
 out on the glass-slide ; add a drop of fresh glycerine, and 
 cover with thin glass ; warm it gently, and press it down 
 with a needle-point. 
 
 Examine the specimen with a quarter power, and, if a 
 good deal of granular matter appears to be mixed in with 
 it, remove the glass cover, and wash it by adding drop 
 after drop of the glycerine and acid solution. The slide 
 tliould be inclined, and, at the same time, gently warmed 
 
 Q 
 
22(5 THE MICROSCOPE. 
 
 over the lamp. When a few drops of pure glycerine have 
 been allowed to flow over it, the thin glass cover must be 
 re-applied and pressed tightly down. If the preparation 
 looks clear under an eighth or twelfth, the glass cover may 
 be cemented on, and the specimen left to dry. The success 
 of Dr. Beale's process, it appears, much depends upon the 
 care and patience with which each stage of the soaking, 
 washing, warming, and pressure is carried out. Each point 
 of structural difference is gradually brought out by sub- 
 jecting the specimen to a little firmer pressure, or by 
 soaking it in a little fresh glycerine in a watch-glass, and 
 then applying gentle heat. By the aid of needles, and 
 a little careful manipulation, tissues may be laid out per- 
 fectly smooth and flat. 
 
 A word about making and preparing Transparent In- 
 jections. The great desideratum of a transparent injecting 
 fluid is, that it shall not, by the action of osmosis, dye the 
 tissue meant to be injected. This at once bars the use of 
 soluble colours, and necessitates the use of insoluble colour- 
 ing matter in an exceedingly fine state of subdivision. 
 The following composition is stated to succeed admirably, 
 showing vessels of soWth of an inch diameter, with a 
 clear outline even under a th objective, without a grain 
 of extravasation of the colouring matter: Take 180 grains 
 best carmine ; J fluid ounce of ammonia, common strength, 
 sp. gr. 0'92 ; 3 to 4 ounces distilled water. Put these 
 ingredients into a small flask, and allow them to digest 
 without heat for 24 or 36 hours, or until the carmine 
 ; tS dissolved. Then take a Winchester quart-bottle, and 
 mark upon it the line to which 16 ounces of water 
 extend. The coloured solution must then be filtered 
 into the bottle, and pure water must be added until 
 the whole is equal to 16 ounces. Next dissolve 600 
 grains of potash-alum in about 10 fluid ounces of water, 
 and add to this, under constant boiling, a solution of 
 carbonate of soda, until a slight permanent precipitate 
 is produced. Filter and add water up to 16 fluid ounces. 
 Boil, and add this solution, while boiling, to the cold 
 ammoniacal solution of carmine in the Winchester quart, 
 and shake vigorously for a few minutes. A drop now 
 placed upon white filter-paper should show no coloured 
 
MOUNTING POLYZOA. 227 
 
 ring; if it do, the whole must be rejected. Supposing 
 the precipitation to be complete, or nearly so, shake 
 vigorously for half an hour, and allow to stand till quite 
 cold ; the shaking must then Toe renewed, and the bottle 
 filled up with cold water. After allowing the precipitate 
 to settle for a day, draw off the clear supernatant fluid 
 with a syphon. Repeat the washing until the clear fluid 
 gives no precipitate with chloride of barium. So much 
 water must be left with the fluid that at last it may 
 measure 40 fluid ounces. For the injection-fluid, take 24 
 ounces of the above coloured fluid, and 3 ounces of good 
 gelatine; allow these to remain together all night, then 
 dissolve by the aid of a water-bath, and strain through 
 fine muslin. On injecting, the ordinary precautions for a 
 gelatine injection are alone necessary. 
 
 Mounting Polyzoa. Mr. Morris, of Bath, has succeeded 
 in obtaining beautiful specimens of polyzoa and hydroid 
 zoophytes, with expanded tentacles, by adding spirit of 
 wine, drop by drop, to the salt-water cell in which they 
 have been confined. The polypidoms should be thus 
 treated as soon as possible after capture. 
 
 A plan of mounting objects in a mixture of balsam and 
 chloroform is described by Mr. Win. Henry Heys in the 
 Microscopical Journal thus : Take a quantity of the oldest 
 balsam procurable, and place it in an open glass cup, and 
 mix with it as much chloroform as will make the whole 
 quite fluid, so that a very small quantity will drop from 
 the lip of the containing vessel. Then put this prepared 
 balsam into long thin half-ounce vials, and cork and set 
 them aside for at least a month. The advantage of having 
 it ready-made is, that there is no waste, and none of the 
 usual and troublesome preparation required for putting up 
 objects in Canada balsam; and if it has stood for some 
 time, it loses the yellow tinge which is observable in most 
 samples when first mixed, and, moreover, air-bubbles escape 
 more readily. 
 
 Mr. Goadby's fluids are cheap and most effectual for 
 preserving and mounting animal structures in. The fol- 
 lowing are his formula : 
 
 Take for No. 1 solution, bay salt, 4 oz. ; alum, 2 oz. ; 
 corrosive sublimate, 2 grains ; boiling water, 1 quart : mix. 
 
228 THE MICROSCOPE. 
 
 For No. 2 solution, bay salt, 4 oz. ; alum, 2 oz. ; corrosive 
 sublimate, 4 grs. ; boiling- water, 2 quarts : mix. 
 
 The No. 1 is too strong for most purposes, and should 
 only be employed where great astringency is needed to 
 give form and support to very delicate structures. No. 2 
 is best adapted for permanent preparation ; but neither 
 should be used in the preservation of animals containing 
 carbonate of lime (all the mollusca), as the alum becomes 
 decomposed, sulphate of lime is precipitated, and the pre- 
 paration spoiled. For such use the following : 
 
 Bay salt, 8 oz.; corrosive sublimate, 2 grs.; water y 
 1 quart : mix. 
 
 The corrosive sublimate is Used to prevent the growth 
 of vegetation in the fluid ; but as this salt possesses the 
 property of coagulating albumen, these solutions cannot be 
 used in the preservation of ova, or when it is desired to 
 maintain the transparency of certain tissues, such as the 
 cellular tissue, the white corpuscles of the blood, &c. 
 
 Mr. Goadby's method of making marine-glue for cement- 
 ing cells is as follows : dissolve separately equal parts of 
 shell-lac and India-rubber in coal or mineral naphtha, and 
 afterwards mix the solutions carefully by the application 
 of heat. It may be rendered thinner by the addition of 
 more naphtha, and is always readily dissolved by naphtha, 
 ether, or solution of potash, when it becomes hard or dry 
 in our stock-pots. 
 
 Preparation and Preservation of Algce, &c. Mr. Ralfs 
 gives excellent directions for making preparations of algse 
 for microscopic investigations : " The fluid found to 
 answer best is mac5 in the following way : to sixteen 
 parts of distilled water add one part of rectified spirits 
 of wine, and a few drops of creosote, sufficient to saturate 
 it ; stir in a small quantity of prepared chalk, and then 
 filter; with this fluid mix an equal measure of camphor- 
 water (water saturated with camphor) ; and before using, 
 strain off through a piece of fine linen. 
 
 " This fluid I do not find to alter the appearance of 
 the endochrome of algse more than distilled water alone 
 does after some time ; there is certainly less probability of 
 confervoid filaments making their appearance in the pre- 
 parations ; and there would seem to be nothing tc prevent 
 
PRESERVATION OF ALGLB. 229 
 
 such a growth from taking place, when the object is 
 mounted in water only, provided a germ of one of these 
 minute plants happen to be present, as well as a small 
 quantity of free carbonic acid. 
 
 " My method of making cells in which to mount pre- 
 parations of algae is as follows : some objects require very 
 shallow, and others somewhat deeper cells. The former 
 may be made with a mixture of japanners' gold-size and 
 litharge, to which (if a dark colour is preferred) a small 
 quantity of lamp-black can be added. These materials 
 should be rubbed up together with a painter's muller, and 
 the mixture laid on the slips of glass with a camel-hair 
 pencil as expeditiously as possible, since it quickly becomes 
 hard ; so that it is expedient to make but a small quantity 
 at a time. For the deeper cells marine-glue answers ex- 
 tremely well, provided it is not too soft. It must be 
 melted and dropped upon the slip of glass : then flattened, 
 whilst warm, with a piece of wet glass, and what is super- 
 fluous cut away with a knife, so as to leave only the walls 
 of the cell ; these, if they have become loosened, may be 
 made firm again by warming the under surface of the slip 
 of glass. The surface of the cells must be made quite flat ; 
 which can be easily done by rubbing them upon a wet 
 piece of smooth marble, covered with the finest emery- 
 powder. 
 
 " When about to mount a preparation, a very thin 
 layer of gold-size must be put upon the wall of the cell, 
 as well as on the edge of the piece of thin glass which is 
 to cover it ; before this is quite dry, the fluid with the 
 ibject is to be put into the cell, and the cover of thin glass 
 slowly laid upon it, beginning at one end ; gentle pressure 
 must then be used to squeeze out the superfluous fluid ; 
 and, after carefully wiping the slide dry, a thin coat of 
 gold-size should be applied round the edge of the cell, and 
 a second coat so soon as the first is dry ; a thin coat or 
 two of black sealing-wax varnish may then be put on with 
 advantage, in order to prevent effectually the admission 
 of air into the cell, or the escape of fluid out of it. 
 
 " I would remark, that the gold-size employed should 
 be of the consistance of treacle ; when purchased, it is 
 usually too fluid, and should be exposed for some time in 
 
230 THE MICROSCOPE. 
 
 an open vessel ; a process which renders it fit for use. In 
 mounting the Desmidaceoe, great attention is necessary to 
 exclude air-bubbles, which cannot l>e avoided unless the 
 fluid completely fills the cells j and also not to use too 
 much fluid, as in this case the smaller species will often be 
 washed away on the escape of the superfluous portion. As 
 the cells cannot be sealed whilst any moisture remains on 
 their edge, it should be removed by blotting-paper, in 
 preference to any other mode. A thin description of glass 
 is manufactured expressly for the purpose of covering 
 specimens when mounted. 
 
 " The rare species of Desmidacece are frequently scattered 
 amongst decayed vegetable matter, so that it is difficult to 
 procure good specimens for mounting. In such cases, a 
 small portion of the mass should be mixed with a little of 
 the creosote fluid, and stirred briskly with a needle. 
 After this has been done, the Desmidacece will sink to the 
 bottom, when the refuse should be carefully removed. 
 Successive portions having been thus treated, specimens 
 will at length be procured sufficiently free from foreign 
 matter. Even in ordinary circumstances, if a small extra 
 quantity of fluid be placed in the cell, and the slide gently 
 inclined, most of the dirt may be removed by a needle 
 before the cell is closed ; which process will materially 
 increase the beauty of the preparation. 
 
 " If the cells are insufficiently baked, the japan occa- 
 sionally peels off the glass after the specimen has been 
 mounted for some time. To obviate this inconvenience, 
 Mr. Jenner previously heats the cell, with much caution, 
 over a rushlight, until the japan becomes of a dark colour, 
 and vapour ceases to arise from it. When gold-size is used 
 for closing the cell, the intrusion of some of it frequently 
 destroys valuable specimens, whatever care may be taken. 
 Mr. Jenner has therefore relinquished it, and now employs 
 a varnish made of coarsely comminuted purified shell-lac 
 or translucent sealing-wax, to which is added rectified 
 spirits of wine, in sufficient quantity to cover it. This 
 varnish will be ready for use in about twelve hours : when 
 it is too thick, a little more spirit should be added. Mr. 
 Jeuner applies three coats of this varnish, and about a week 
 afterwards a fourth, composed of japan varnish or gold- 
 
INJECTING ANIMAL BODIES. 231 
 
 size. 1 To preserve the brush in a fit state, it should 
 always be cleaned with spirits of wine whenever it has 
 been used." 
 
 Mr. Topping's fluid for mounting consists of one ounce 
 of rectified spirits to five ounces of distilled water j this he 
 thinks superior to any other combination. To preserve 
 delicate colours, however, he prefers to use a solution of 
 acetate of alumina, one ounce of the acetate to four ounces 
 of distilled water : of other solutions he says, that they 
 tend to destroy the colouring matter of delicate objects, 
 and ultimately spoil them by rendering them opaque. 
 
 Injtcting Animal Bodies. For minute injections, the 
 most essential instrument is a proper syringe. This is 
 usually made of brass, of such a size 
 that the top of the thumb may press on 
 the button at the top of the piston-rod 
 when drawn out, while the body is sup- 
 ported between the two fingers. Fig. 
 141 represents the syringe : a is a cylin- 
 drical brass body, with a screw at the 
 top for the purpose of firmly screwing 
 down the cover 6, after the piston c is 
 introduced into it ; this is rendered 
 air-tight with leather; the bottom of 
 the syringe d also unscrews for the con- 
 venience of cleaning ; e is a stop-cock, 
 on the end of which another stop-cock 
 / fits accurately ; and on the end of 
 this either of the small pipes g, which 
 are of different sizes, may be fixed. The 
 transverse wires across the pipes are in- 
 tended to secure them more tightly to the 
 vessels, into which they may be inserted with thread, so 
 that they may not slip out. In addition to the syringe, 
 a large tin vessel, to contain hot water, with two or three 
 smaller ones fixed in it, for the injections, will be found 
 useful. 
 
 To prepare the material for injecting : Take of the 
 finest and most transparent glue one pound, break it into 
 small pieces, put it into an earthen pot, and pour on it 
 
 (1) " Coachmaker's Black" is an excellent Tarnish. 
 
 Fig. 141. 
 
30* THE MIOROBOOFB. 
 
 f&ree pints of cold w j ater ; let it stand twenty-four hours, 
 .tiering it now and then with a stick; then set it over 
 A slow fire for half an hour, or until all the pieces are per- 
 fcetly dissolved ; skim off the froth from the surface, and 
 a&Tain through a flannel for use. Isinglass and cuttings of 
 parchment make an excellent size, and are preferable for 
 Tfiary particular injections. If gelatine be employed it must 
 be- soaked for some hours in cold water before it is warmed. 
 About an ounce of gelatine to a pint of water will be suf- 
 ieiently strong, but in very hot weather it is necessary to 
 add a little more gelatine. It must be soaked in part of 
 the cold water until it swells up and becomes soft, when the 
 jest of the water, made hot, is to be added. Good gelatine 
 for injecting purposes may be obtained for two shillings a 
 pound. 
 
 The size thus prepared may be coloured with any of the 
 following : 
 
 For Red. To a pint of size, add 2 oz. of Chinese vermilion. 
 ,, Yellow. ,, ,, 2i oz. of chrome-yellow. 
 
 White. ,, ,, 3|oz. of flake-white. 
 
 Blue. ,, ,, 6 oz. of fine blue smalts. 
 
 It is necessary to remember, that whatever colouring 
 matter is employed must be very finely levigated before it is 
 mixed with the injection. This is a matter of great im- 
 portance: for a small lump or mass of colour, dirt, &c. 
 will clog the minute vessels, so that the injection will not 
 pass into them, and the object will be defeated. The mix- 
 ture of size and colour should be frequently stirred, or the 
 colouring matter will sink to the bottom. Respecting the 
 choice of a proper subject for injecting, it may be remarked, 
 that the injection will usually go furthest in young subjects ; 
 and the more the fluids have been exhausted during life, 
 the greater will be the success of the injection. 
 
 To prepare the subject, the principal points to be aimed 
 at are, to dissolve the fluids, empty the vessels of them, 
 relax the solids, and prevent the injection from coagulating 
 too soon. For this purpose it is necessary to place the 
 animal, or part to be injected, in warm water, as hot as 
 the operator's hand will bear. This should be kept at 
 nearly the same temperature for some time by occasionally 
 adding hot water. The length of time required is in pro- 
 portion to the size of the part and the amount of ita 
 
INJECTING ANIMAL BODIES. 233 
 
 rigidity. Ruysch (from whom the art of injecting baa 
 been called the Ruyschian art) recommends a previous 
 maceration for a day or two iii cold water. 
 
 The size must always be kept hot with the aid of warm 
 water ; for if a naked fire be used, there is danger of 
 burning it. The size may be placed in a vessel which can 
 be heated by standing it in a common tin saucepan of hot 
 water. A convenient form of apparatus for melting the 
 size, and afterwards keeping it at- a proper temperature, is 
 
 Fig. 14J. Melting Vessel. 
 
 shown in fig. 142. It consists merely of a water-bath, in 
 which the cans containing the injecting fluid can be kept 
 hot, and their contents protected from dust by means of 
 their covers. A small apparatus of this kind could be 
 made by any tin-worker, and fitted over a gas jet to stand 
 on the table. 
 
 The operator should be provided with several pairs of 
 strong forceps, for seizing the vessel or stopping the escape 
 
 Fig. 148. 
 
 of injection. A small needle, fig. 143, will be found useful 
 for passing the thread round the vessel into which the 
 
234 THE MICROSCOPE. 
 
 injecting pipe is to be inserted. Where the vessels are 
 large, a needle commonly known as an aneurism needle 
 answers the purpose very well. The thickness of thread 
 must vary according to the size of the vessel. The silk 
 used by surgeons will be found the best adapted for the 
 purpose, and not too thin, or it may cut through the 
 vessel. 
 
 When the size and the subject have both been properly 
 prepared, have the injection as hot as the fingers can well 
 bear. One of the pipes g, fig. 141, must then be placed in 
 the largest artery of the part, and made secure by tying. 
 Put the stop-cock / into the open end of the pipe e, and 
 it is then ready to receive the injection from successive 
 applications to the syringe a, leaving sufiicient space only 
 for the piston c. The injection should be thrown in by a 
 very steady and gentle pressure on the end of the piston- 
 rod. The resistance of the vessels, when nearly full, is often 
 considerable; but it must not be overcome by violent 
 pressure with the syringe. When as much injection is 
 passed as may be thought advisable, the preparation may 
 be left (with the stop-cock closed in the pipe) for twenty- 
 four hours, when more material may be thrown in. 
 
 As the method of injecting the minute capillaries with 
 coloured size is often attended with doubtful success, 
 various other plans have been proposed. Ruysch's method, 
 according to Rigerius, was to employ melted tallow coloured 
 with vermilion, to which in the summer a little white wax 
 was added. Monro recommended coloured oil of turpen- 
 tine for the small vessels ; after the use of which, he threw 
 in the common coarse injection. This is made of tallow 
 and red lead, well mixed and heated before it is used. 
 The cold paint injection succeeds well if thrown carefully 
 into the minute arteries; but its tendency to become 
 brown by age is an objection to its use. 
 
 Professor Breschet frequently employed with success milk, 
 isinglass, the alcoholic solution of gum-lac, spirit varnish, 
 and spirit of turpentine ; but he highly recommends the 
 colouring matter extracted from Campeachy, Fernambone, 
 or Sandal woods. He says : " The colouring matter of 
 Campeachy wood easily dissolves in water and in alcohol : 
 it is so penetrating that it becomes rapidly spread through 
 
INJECTING ANIMAL BODIES. 235 
 
 the vascular net-works. The sole inconvenience of this 
 kind of injection is, that it cannot be made to distend any 
 except most delicate vessels, and that its ready penetra- 
 tion does not admit of distinguishing between arteries, 
 veins, and lymphatics." He also recommends a solution 
 of caoutchouc. 
 
 Another process, which may be termed the chemical 
 process, was published in the Comptes Itendus, 1841, as 
 the invention of M. Doyers. According to this, an aqueous 
 solution of bichromate of potass, 1,048 grains to two pints 
 of water, is thrown into the vessels; and after a short 
 time, in the same manner and in the same vessels, an 
 aqueous solution of acetate of lead, 2,000 grains to a pint 
 of water, is injected. This is an excellent method, as the 
 material is quite fluid, and the precipitation of the chromate 
 of lead which takes place in the vessels themselves gives a 
 fine sulphur-yellow colour. Mr. Topping prepares many 
 fine injections in this way. 
 
 Mr. Goadby has improved upon the process last named 
 by uniting to the chemical solutions a portion of gelatine, 
 as follows: 
 
 Saturated solution of bichromate of potash, 8 fluid 
 ounces; water, 8 ounces; gelatine, 2 ounces. 
 
 Saturated solution of acetate of lead, 8 fluid ounces; 
 water, 8 ounces; gelatine, 2 ounces. 
 
 The majority of preparations thus injected require to be 
 dried and mounted in Canada balsam. Each preparation, 
 when placed on a slip of glass, will necessarily possess 
 more or less of the coloured infiltrated gelatine, (by this is 
 meant the gelatine coloured by the blood, which, together 
 with the acetate of potash resulting from the chemical 
 decomposition, may have transuded through the coats of 
 the vessel,) which, when dry, forms, together with the 
 different shades of the chromate of lead, beautiful objects, 
 possessing depth and richness of colour. The gelatine also 
 separates and defines the different layers of vessels: the 
 arteries are always readily distinguishable by the purity 
 and brightness of the chromate of lead within them, while 
 the veins are detected by the altered colour imparted by 
 the blood. 
 
 Those preparations which require to be kept wet can be 
 
236 THE MICROSCOPE. 
 
 preserved perfectly in Mr. Goadby's No. 2 fluid, specific 
 gravity 1*100; the No. 1 fluid destroys them. 
 
 " I would recommend that the slips of glass employed 
 for the dry preparation be instantly inscribed with the 
 name of the preparation, written with a diamond ; for, 
 when dry, it is difficult to recognise one preparation from 
 the other, until the operator's eye be educated to the 
 effects of this chemi co-gelatinous injection. Where so 
 much wet abounds, gummed paper is apt to come off. 
 When dry, it is sufficient, for the purpose of brief exami- 
 nation by the microscope, to wet the surface of a prepara- 
 tion with, clean oil of turpentine ; immediately after 
 examination, it should be put away carefully in a box, to 
 keep it from the dust, until it can be mounted in Canada 
 balsam. 
 
 " The bichromate of potash is greatly superior in colour 
 to the chromate, which yields too pale a yellow; and sub- 
 sequent experience has proved that the acetate of potash 
 frequently effects its liberation by destruction of the 
 capillaries, and this even long after the preparations have 
 been mounted in Canada balsam; perhaps this may be 
 owing to some chemical action of the acetate of potash 
 upon them. I would suggest the substitution of the 
 nitrate for the acetate of lead, as we should then have, in 
 the liberated nitrate of potash, a valuable auxiliary in the 
 process of preservation. Although highly desirable, as 
 the demonstrator of the capillaries of normal tissues, I do 
 not think this kind of injection fitted for morbid prepara- 
 tions ; the infiltrated gelatine producing appearances of a 
 puzzling kind, and calculated to mislead the pathologist. 
 In preparing portions of dried well-injected skin for 
 examination by the microscope, I have tried the effect of 
 dilute nitric acid as a corroder with very good results. 
 But, probably, liquor potassa would have answered this 
 purpose better. 
 
 " When size-injection is to be employed, coloured either 
 with vermilion or the chromate of lead, the animal should 
 be previously prepared by bleeding, to empty the vessels ; 
 for if they be filled with coagulated blood, it is quite im- 
 possible to transmit even size, to say nothing of the colour- 
 ing matter. Hence the difficulty of procuring gcod 
 
TRANSPARENT INJECTIONS. 287 
 
 injections of the human subject. But with the chemico- 
 gelatinous injections no such preparation is necessary ; and 
 success should always be certain, for the potash liquefies 
 the blood, while constant and long-continued pressure by 
 the syringe drives it through the parietes of the vessel 
 into the cellular tissue." 
 
 Transparent Injections. " Much more strongly," writes 
 Dr. Beale, "can I recommend to you the use of transparent 
 fluids for making injections. It is true, that these are not 
 likely to be so much admired by general observers as 
 opaque injections. Indeed, it is not easy to find any 
 object which will rival in beauty many tissues that iiave 
 been freely injected with vermilion or chromate of luad : 
 although it must be confessed that from such preparations 
 we learn but little save the general arrangement of the 
 capillary vessels of the part, their capacity, and the mag- 
 nitude of the meshes of the network Of the relations 
 which these vessels bear to the elementary structures 
 which give to the texture under examination its peculiar 
 properties, such preparations tell us nothing. Opaque 
 injections are for the most part only adapted for examina- 
 tion with low powers, while the tissues to which the vessels 
 are distributed can only be seen with the help of very high 
 magnifying powers. Transparent injections, on the other 
 hand, though they fail to excite the wonder of the un- 
 initiated, show us not only the general arrangement of 
 the capillary network, but the precise relation which 
 each little tube bears to the tissue with which it is in 
 contact. 
 
 " In order to make injected preparations for examination 
 by transmitted light, several different substances may be 
 used as injecting fluids. 
 
 " Injection with Plain Size. A tissue which has been in 
 jected with plain size, when cold is of a good consistence 
 for obtaining thin sections, and many important points 
 may be learned from a specimen prepared in this manner 
 which would not be detected by other modes of prepara- 
 tion. A mixture of equal parts of gelatine and glycerine 
 is, however, much to be preferred for this purpose, and 
 the specimen thus prepared is sure to keep well. 
 
 " Colouring Matters for Transparent Injections. The chief 
 
238 THE MICROSCOPE. 
 
 colouring matters used for making transparent injections 
 are carmine and Prussian blue. The former is prepared 
 by adding a little solution of ammonia (liquor ammoniae) 
 to the carmine, and diluting the mixture until the proper 
 colour is obtained, or it may be diluted with size. 
 
 " The Prussian Blue consists of an insoluble precipitate, 
 so minutely divided, that it appears like a solution to the 
 eye. The particles of freshly prepared Prussian blue are 
 very much smaller than those of any of the colouring 
 matters employed for making opaque injections. 
 
 "Advantages of Employing Prussian Blue. I have lately 
 been employing Prussian blue very much, and according 
 to my experience it possesses advantages over every other 
 colouring matter. It is inexpensive, may be injected 
 cold, the preparation does not require to be warmed, 
 no size is required it penetrates the capillaries without 
 the necessity of applying much force, it does not run out 
 when a section is made for examination, neither do any 
 particles which may escape from the larger vessels divided 
 in making the section, adhere to it and thus render the 
 section obscure, a structure may be well injected with it 
 in the course of a few minutes. Specimens prepared in 
 this manner may be preserved in any of the ordinary pre- 
 servative solutions, or may be dried and mounted in Canada 
 balsam, (but I give the preference to glycerine, or glycerine 
 jelly,) and they may be examined with the highest magni- 
 fying powers. After having tried very many methods of 
 making this preparation I have found the following one to 
 succeed best. 
 
 " Composition of the Prussian Blue Fluid for Making 
 Transparent Injections : 
 
 Glycerine . . . 1 oz. 
 
 Wood, naphtha, or pyroacetic spirit . . . 1| drachms. 
 
 Spirits of wine 1 oz. 
 
 Ferrocyanide of potassium 12 grs. 
 
 Tincture of sesquichloride of iron ... 1 drachm. 
 Water 4 ozs. 
 
 " The ferrocyauide of potassium is to be dissolved in one 
 ounce of the water, and the tincture of sesquichloride of 
 iron added to another ounce. These solutions should be 
 mixed together very gradually, and well shaken in a bottle. 
 
INJECTING TISSUES, 2S9 
 
 The iron being added to the solution of the ferrocyanide of 
 potassium. When thoroughly mixed, these solutions should 
 produce a dark blue mixture, in which no precipitate or 
 flocculi are observable. Next, the naphtha is to be mixed 
 with the spirit, and the glycerine and the remaining two 
 ounces of the water added. This colourless fluid is, lastly, 
 to be slowly mixed with the Prussian blue, the whole being 
 well shaken in a large bottle during the admixture. The 
 tincture of sesquichloride of iron is recommended because 
 it can always be obtained of uniform strength. It is 
 generally called the muriated tincture of iron, and may 
 always be purchased of druggists. 
 
 " Permit me, then, most earnestly to recommend all who 
 are fond of injecting, to employ transparent injections, and 
 to endeavour, by trying various transparent colouring 
 matters, to discover several which may be employed for 
 the purpose ; for I feel sure that by the use of carefully 
 prepared transparent injections, many new points in the 
 anatomy of tissues will be made out. 
 
 " Of Injecting Different Systems of Vessels with Different 
 Colours. It is often desirable to inject different systems 
 of vessels distributed to a part with different colours, in 
 order to ascertain the arrangement of each set of vessels 
 and their relation to each other. A portion of the gall- 
 bladder in which the veins have been injected with white 
 lead, and the arteries with vermilion forms a beautiful 
 preparation. Each artery, even to its smallest branches, 
 is seen to be accompanied by two small veins, one lying 
 on either side of it. 
 
 " In this injection of the liver, four sets of tubes have 
 been injected as follows : The artery with vermilion, the 
 portal vein with white lead, the duct with Prussian blue, 
 and the hepatic vein with lake. There are many opaque 
 colouring matters which may be employed for double 
 injections, but I am acquainted with very few transparent 
 ones, the employment of which affords very satisfactory 
 results. 
 
 "Mercurial Injections are not much used for micro- 
 scopical purposes, although mercury was much employed 
 formerly for injecting lymphatic vessels and the ducts of 
 glandular organs. The pressure of the column of mercury 
 
2-10 THE MICROSCOPB. 
 
 supersedes the necessity of any other kind of force for 
 driving it into the vessels. The mercurial injecting 
 apparatus consists of a glass tube, about half an inch in 
 diameter and twelve inches in length, to one end of which 
 has been fitted a steel screw to which a steel injecting pipe 
 may be attached. The pipes and stopcocks must be made 
 of steel, for otherwise they would be destroyed by the 
 action of the mercury. 
 
 " Injecting the Lower Animals. The vessels of fishes are 
 exceedingly tender, and require great caution in filling 
 them. It is often difficult or quite impossible to tie the 
 pipe in the vessel of a fish, and it will generally be found 
 a much easier process to cut off the tail of the fish, and 
 put the pipe into the divided vessel which lies imme- 
 diately beneath the spinal column. In this simple manner 
 beautiful injections of fish may be made. 
 
 "Mollusca. (Slug, snail, oyster, &c.) The tenuity of the 
 vessels of the mollusca often renders it impossible to tie 
 the pipe in the usual manner. The capillaries are, how- 
 ever, usually very large, so that the injection runs very 
 readily. In different parts of the bodies of these animals 
 are numerous lacunae or spaces, which communicate 
 directly with the vessels. Now, if an opening be made 
 through the integument of the muscular foot of the 
 animal, a pipe may be inserted, and thus the vessels may 
 be injected from these lacunae with comparative facility. 
 
 "Insects. Injections of insects may be made by forcing 
 the injection into the general abdominal cavity, when it 
 passes into the dorsal vessel and is afterwards distributed 
 to the system. The superfluous injection is then washed 
 away, and such parts of the body as may be required, 
 removed for examination. 
 
 " Of the Practical Operation of Injecting. I propose now 
 to inject a frog and the eye of an ox, in order that you 
 may see the several steps of the process. We must bear 
 in mind that a successful injection cannot be made until 
 the muscular rigidity which comes on shortly after death, 
 and which affects the muscular fibres of the arteries as 
 well as those of the muscles themselves, has passed off. 
 In some few instances in which the fluid does not neces- 
 sarily pass through arterial trunks before it reaches the 
 
INJECTING TISSUES. 241 
 
 capillaries (as in the liver), the injection may be effected 
 satisfactorily immediately after the death of the animal. 
 
 " The steps of the process are very similar in making the 
 opaque injections, except that when size is employed, the 
 specimen must be placed in warm water until warm 
 through, otherwise the size will solidify in the smaller 
 vessels, and the further flow of the injecting fluid will be 
 prevented. Soaking for many hours is sometimes neces- 
 sary for warming a large preparation thoroughly, and it is 
 desirable to change the water frequently. The size must 
 also be kept warm, strained immediately before use, and 
 well stirred up each time the syringe is filled. 
 
 " In the first place, the following instruments must be 
 conveniently arranged : 
 
 " The syringe thoroughly clean and in working order, 
 with pipes, stopcock, and corks. 
 
 " One or two scalpels. 
 
 " Two or three pair of sharp scissors. 
 
 ''Dissecting forceps. 
 
 " Bull's-nose forceps, for stopping up any vessel through 
 which the injection may escape accidentally. 
 
 " Curved needle, threaded with silk or thread, the thick- 
 ness of the latter depending upon the size of the vessel to 
 be tied. 
 
 " Wash-bottle. Injecting fluid in a small vessel. 
 
 " I will commence with the frog. An incision is made 
 through the skin, and the sternum divided in the middle 
 line with a pair of strong scissors ; the two sides may 
 easily be separated, and the heart is exposed. Next the 
 sac in which the heart is contained (pericardium) is opened 
 with scissors and the fleshy part of the heart seized with 
 the forceps ; a small opening is made near its lower part, 
 and a considerable quantity of blood escapes from the 
 wound this is washed away carefully by the wash-bottle. 
 Into the opening the tip of the heart being still held 
 firmly by the forceps, a pipe is inserted and directed 
 upwards towards the base of the heart to the point where 
 the artery is seen to be connected with the muscular sub- 
 stance. Before I insert the pipe, however, I draw up 
 a little of the injecting fluid so as to fill it, for if this were 
 not done, when I began to inject, the air contained in the 
 
242 THE MICROSCOPE. 
 
 pipe \vould necessarily be forced into the vessels, and the 
 injection would fail. 
 
 " The point of the pipe can with very little trouble be 
 made to enter the artery. The needle with the thread is 
 next carried round the vessel and the thread seized with 
 forceps, the needle unthreaded and withdrawn, or one end 
 of the thread may be held firmly, while the needle is with- 
 drawn over it in the opposite direction. The thread is 
 now tied over the vessel, so as to include the tip of the 
 pipe only, for if the pipe be tied too far up, there is greater 
 danger of its point passing through the delicate coats of 
 the vessel. 
 
 " The nozzle of the syringe, which has been well washed 
 in warm water, is now plunged beneath the surface of the 
 fluid, the piston moved up and down two or three times, 
 so as to force out the air completely, and the syringe 
 filled with fluid. It is then connected with the pipe, which 
 is firmly held by the finger and thumb of the left hand, 
 with a screwing movement, a little of the injection being 
 first forced into the wide part of the pipe so as to prevent 
 the possibility of any air being included. 
 
 " The pipe and syringe being still held with the left hand, 
 the piston is slowly and gently forced down with a slightly 
 screwing movement with the right, care being taken not 
 to distend the vessel so as to endanger rupture of its 
 coats. The handle of the syringe is to be kept uppermost, 
 and the syringe should never be completely emptied, in 
 case of a little air remaining, which would thus be 
 forced into the vessels. The injection is now observed 
 running into the smaller vessels in different parts of the 
 organism. 
 
 " I will now proceed to inject the ox-eye in the same 
 manner. The pipe is inserted into this branch of artery 
 close to the nerve. Two minutes will probably be suffi- 
 cient to ensure a complete injection. In making an 
 injection of the eye, if the globe becomes very much 
 distended by the entrance of the injecting fluid, an opening 
 may be made in the cornea to allow the escape of the 
 aqueous fluid which will leave room for the entrance of 
 the injection, and permit the complete distension of the 
 vessels. 
 
INJECTING TISSUES. 243 
 
 " We will now examine these injections. A portion of 
 the intestine of the frog may be removed with scissors, 
 opened, and the mucous surface washed with the aid of 
 the wash-bottle. It may be allowed to soak in glycerine 
 for a short time, and then examined. 
 
 " This portion of the delicate choroidal membrane which 
 has been carefully removed in the same manner shows the 
 vessels perfectly injected, and in this preparation of the 
 ciliary processes you will not fail to observe that all the 
 capillary vessels are fully distended with fluid, although 
 the injection was made so quickly. 
 
 " Of Injecting the Ducts of Glands. The modes of inject- 
 ing which we ha v$ just .considered, although applicable to 
 the injection of vessels, are not adapted for injecting the 
 ducts and glandular, structure of glands ; for as these 
 ducts usually contain a certain quantity of the secretion, 
 and are always lined with epithelium, it follows that when 
 we attempt to force , fluid into the duct, the epithelium 
 and secretion must be driven towards the secreting struc- 
 ture of the gland, which is thus effectually plugged up 
 with a colourless material, and there is no possibility of 
 making out the arrangement of the parts. In such a case 
 it is obviously useless to introduce an injecting fluid, for 
 the greatest force which could be employed would be insuf- 
 ficient to drive the contents through the basement mem- 
 brane, and the only possible result of the attempt would 
 be rupture of the thin walls of the secreting structure and 
 extravasation of the contents. As I have before mentioned, 
 partial success has been obtained by employing mercury, 
 but the preparations thus made are not adapted for micro- 
 scopical observation. 
 
 " After death the minute ducts of the liver always contain 
 a little bile. No force which can be employed is sufficient 
 to force this bile through the basement membrane, for it 
 will not permeate it in this direction. When any attempt 
 is made to inject the ducts, the epithelium and mucus, in 
 their interior, and the bile, form an insurmountable barrier 
 to the onward course of the injection. Hence it was ob- 
 viously necessary to remove the bile from the ducts before 
 one could hope to make a successful injection. It occurred 
 to me, that any accumulation of fluid in the smallest 
 
 B2 
 
H4 THE MICROSCOPE. 
 
 "branches of the portal vein or in the capillaries, must ne- 
 cessarily compress the ducts and the secreting structure of 
 the liver which fill up the intervals between them. The 
 result of such a pressure would be to drive the bile towards 
 the large ducts and to promote its escape. Tepid water 
 iras, therefore, injected into the portal vein. The liver 
 became greatly distended, and bile with much ductal 
 epithelium flowed by drops from the divided extremity of 
 the duct. The bile soon became thinner, owing to its 
 dilution with water, which permeated the intervening mem- 
 brane, and entered the ducts. These long, narrow, highly- 
 tortuous channels were thus effectually washed out from 
 the point where they commenced as tubes not more than 
 l-300th of an inch in diameter, to their termination in the 
 common duct, and much of the thick layer of epithelium 
 lining their interior was washed out at the same time. 
 The water was removed by placing the liver in cloths with 
 sponges under pressure for twenty-four hours or longer. 
 All the vessels and the duct were then perfectly empty 
 and in a very favourable state for receiving injection. The 
 duct was first injected with a coloured material. Freshly 
 precipitated chromate of lead, white lead, vermilion, or 
 other colouring matter may be used, but for many reasons 
 to which I have alluded, the Prussian blue injection is the 
 one best adapted for this purpose. It is the only material 
 which furnishes good results when the injected prepara- 
 tions are required to be submitted to high magnifying 
 powers. Preparations injected in this manner should be 
 examined as transparent objects." l 
 
 Of Preparing Portions of Injected Preparations for Mi- 
 woscopical Examination. When thin tissues, such as the 
 mucous membrane of the intestines or other parts, have 
 been injected, it is necessary to lay them perfectly flat, 
 smd wash the mucus and epithelium from the free sur- 
 face, either by forcing a current of water from the wash- 
 bottle, or by placing them in water and brushing the 
 surface gently with a camel's hair brush. Pieces of a 
 convenient size may then be removed and mounted in 
 a solution of naphtha and creosote, in dilute alcohol, in 
 
 { Dr. L. Beale, "On the Anatomy of the Liver of Man and Vertebrate 
 
CHEMICAL RE-AGENTS. 24$ 
 
 glycerine, or in gelatine and glycerine. The most ini 
 portant points in any such injections are shown if the 
 preparation be dried and mounted in Canada balsam. The 
 specimen must, in the first place, be well washed and 
 floated upon a glass slide "with a considerable quantity of 
 water, which must be allowed to flow off the slide very 
 gradually. The specimen may then be allowed to dry 
 under a glass shade, in order that it may be protected 
 from dust. The drying should be effected at the ordinary 
 temperature of the air, but it is much expedited if * 
 shallow basin filled with sulphuric acid be placed with it 
 under a bell-jar." 
 
 Chemical Re-agents. The following chemical re-agents 
 and preservative fluids are recommended for microscopic 
 uses: 1 
 
 1. Alcohol, principally for the removal of air from, 
 sections of wood and other preparations ; also as a solvent 
 for certain colouring matters. 
 
 2. jther, chiefly as a solvent for resins, fatty and other 
 essential oils, <fec. ; also useful for the removal of air. 
 
 3. Solution of Caustic Potass, as a solvent for fatty 
 matters; also of use occasionally in consequence of ite 
 action upon the rest of the cell-contents and thickening 
 layers. This solution acts best upon being heated. 
 
 4. Solution of Iodine (iodine one grain, iodide of potas- 
 sium three grains, distilled water one ounce) for the 
 coloration of the cell-membrane and of the cell-contents. 
 
 5. Concentrated Sulphuric Acid, employed chiefly in the 
 examination of pollen and spores. 
 
 6. Diluted Sulphuric Acid (three parts acid, one part 
 water), for the coloration of cells previously immersed hi 
 the iodine solution. The preparation is first moistened 
 with the iodine solution, which is afterwards removed wrfcfe 
 a hair pencil, and a drop of sulphuric acid added by means 
 of a glass rod ; the preparation is then immediately covered 
 with a piece of glass. The action of the sulphuric acid 
 and iodine, as well as that of the iodised chloride of zinc 
 solution, is not always uniform throughout the whote 
 
 (1) A set of 12 test-bottles, packed in a small box, is supplied by Mr. 
 Matthews of Portugal Street, Lincoln's Inn Fields, the price of which is oly c 
 few shillings. 
 
THE MICROSCOPE. 
 
 surface of the preparation. The colour is more intense 
 where the mixture is more concentrated; it frequently 
 happens that many spots remain uncoloured. The colour 
 changes after some time, the blue being frequently changed 
 into red after twenty-four hours. 
 
 7. A Solution of Chloride of Zinc, Iodine, and Iodide of 
 Potassium. A drop of this compound solution, added to 
 a preparation placed in a little water, produces the same 
 colour as iodine and sulphuric acid. This solution, which 
 was first proposed and employed by Professor Schultz, is 
 more convenient in its application than iodine and sulphuric 
 acid, and performs nearly the same services, while it does 
 not, like the sulphuric acid, destroy the tissues to which it 
 is applied. It is prepared by dissolving zinc in hydro- 
 chloric acid ; the solution is then saturated with iodide of 
 potassium : more iodine is to be added if necessary, and 
 the solution diluted with water. 
 
 8. Nitric Acid, or what is better, chlorate of potass and 
 nitric acid, as an agent to effect the isolation of cells. The 
 mode of employing this agent, also discovered by Professor 
 Schultz, is as follows : 
 
 The object, a thin section of wood, for instance, is intro- 
 duced, with an equal bulk of chloride, or chlorate of potass, 
 into a long and moderately wide tube, and as much nitric 
 acid as will at least cover the whole. 
 
 The tube is then warmed over a spirit-lamp ; a copious 
 evolution of gas takes place, upon which the tube is re- 
 moved from the flame, and the action of the oxidising agent 
 allowed to continue for two or three minutes. The con- 
 tents of the tube are then poured into a watch glass with 
 water, from which the slightly cohering particles are col- 
 lected and placed in a tube, and again boiled in alcohol as 
 long as any colour is communicated. 
 
 They are again boiled in a little water. The cells may 
 now be isolated under the simple microscope by means of 
 needles. The boiling with nitric acid and chlorate of 
 potass should never be carried on in the same room with 
 the microscope, the glasses of which may suffer injury 
 from the vapours. The same remark applies to all chemical 
 Tapours. 
 
 Thin sections of vegetable tissue are warmed for half a 
 
CHEMICAL RE-AGENTS. 
 
 minute, or a minute, in a watch-glass : boiling is here un- 
 necessary. The section is taken out, and treated with 
 water in another watch-glass. 
 
 9. Oil of Lemons, or any other essential oil, a drop of 
 which will be found of value in the investigation of pollen 
 and spores. 
 
 Lastly may be enumerated a pretty strong solution of 
 Carbonate of Soda and also of Acetic Acid; which latter, 
 however, is more especially useful in the investigation of 
 animal tissues. 
 
 To the above may be added a test for protein compounds. 
 This test is composed of sugar and sulphuric acid, and is 
 thus employed: A thin section or portion of the tissue to 
 be examined is placed in a drop of simple syrup, this is 
 ihen removed by means of a hair pencil, and a drop of the 
 diluted sulphuric acid added ; the red colour usually does 
 not appear until after the lapse of about ten minutes. 
 
 In making thin sections of tissues, it is recommended 
 that, in those objects the consistence of which differs in 
 different parts, the section should be carried from the 
 harder into the softer portion; also, in making a thin 
 section of a very minute yielding substance, to enclose it 
 between two pieces of cork, and to slice the whole together. 
 It is also useful sometimes to saturate the object with 
 mucilage, which is to be allowed to dry slowly; in this 
 way very delicate tissues may be sliced, or otherwise 
 divided without injury, and with great facility. 
 
 Some of the above re-agents must be used with caution, as 
 it is not unusual for them to assume crystalline forms while 
 under the microscope. Without a knowledge of this fact, and 
 a perfect recognition of crystalline forms, errors in micro- 
 chemical research must occur. For example, if a drop of 
 liquor potassse be allowed to evaporate on a slip of glass, 
 crystals appear, chiefly of six-sided tables, precisely like 
 cystine ; when in quantity, they are often crowded together 
 as the cystine plates are, and sometimes exhibit a similar 
 nucleus-like body in their centres. This peculiarity of 
 crystallization does not arise from the presence of impurities; 
 perfectly pure potash often exhibits the same phenomenon. 
 
 The form of the crystals of acetate of potash varies 
 according to the strength of the acid out of which it 
 
248 THE MICROSCOPE. 
 
 crystallizes, and if formed out of strong acid, very much 
 resembles that of the crystals of uric acid ; when mixed 
 up with other forms, long dagger-like or lancet-shaped 
 crystals are seen, which might well deceive. 
 
 We may also notice in this place what Majendie pointed 
 out, that in certain albuminous mixtures, iodine loses the 
 property of colouring starch blue. This difficulty must be 
 got rid of before iodine can be said to be an infallible test 
 in micro-chemistry. 
 
 Collecting Objects. Mr. G. Shadbolt contributes the fol- 
 lowing useful hints for collecting objects for microscopical 
 examination : 
 
 " Rivers, brooks, springs, fountains, ponds, marshes, 
 bogs, and rocks by the sea-side, are all localities that may 
 be expected to be productive; some being more prolific 
 than others, and the species obtained differing, of course, 
 in general, to a certain extent, according to the habitat. 
 On considering the nature of some of the places indicated, 
 it will be apparent that, in order to spend a day in col- 
 lecting with any comfort, it will be necessary to make 
 some provision for keeping the feet dry, for which a pair 
 of India-rubber goloshes will answer, or better still, a pair 
 of waterproof fishing-boots; but without one or other the 
 work is by no means pleasant. 
 
 " A dozen or two of small bottles made of glass-tubing, 
 about half an inch in diameter, and without necks, and 
 from one to two inches in length, are the most convenient 
 depositories for the specimens, if intended ultimately foi 
 mounting; and it is advisable also to take two or three 
 wide-mouthed bottles of a largersize, holding from one to 
 two fluid-ounces, an old iron spoon, a tin box, some pieces 
 of linen or calico, two or three inches square, a piece of 
 string, a slip or two of glass, with the edges ground, such 
 as are used for mounting objects; and lastly, a good and 
 pretty powerful hand-magnifier. Two Coddingtoii lenses, 
 mounted in one frame of about half an inch, and one-tenth 
 of an inch in focal power, are specially convenient. 
 
 " Swanscombe Salt-marsh will be found well worth a 
 visit; and it can be reached by steam-boat or railway 
 from London-bridge to Northfleet. On quitting the rail- 
 way station, make towards the almshouses on the top of 
 
COLLECTING OBJECTS. 249 
 
 the hill ; and arriving at the road, turn to the left, descend 
 the hill, and cross a sort of bridge over a somewhat insig- 
 nificant stream. Continue along the main-road a little 
 farther, to a point where it begins to ascend again, and 
 diverges to the left towards the railway; here quit it, 
 taking your course along an obscure road, nearly in a 
 direct line with the main one ; passing a windmill on the 
 right hand, and continuing until you arrive at another 
 still more obscure road, turning off to the right; which 
 road appears as if made of the mud dredged from the 
 bottom of the river, and partially hardened. This is 
 Swanscombe Salt-marsh; and the road just described 
 leads towards Broad Ness Beacon. On either side is a 
 sort of ditch ; one containing salt or very brackish water, 
 the other filled with a sort of black mud, about the con- 
 sistence of cream, the surface being in parts of a slaty 
 grey, with little patches here and there of a most brilliant 
 brown colour, glistening in the sunshine, and presenting a 
 striking contrast to the sombre shade. By carefully in- 
 sinuating the end of one of the slips of glass under this 
 brilliant brown substance, and raising it gently, it can be 
 examined with the Coddiugton; and it will probably be 
 found to consist of myriads of specimens of Pleurosigma 
 (navicula of Ehrenberg) anyidatum, or balticum, or some 
 other species of this genus. The iron spoon is now useful, 
 as by its aid the brown stratum, with little or no mud, can 
 be skimmed off and bottled for future examination. On 
 the surface of the water in the other ditch may be noticed 
 a floating mass of a dark olive colour, which to the touch 
 feels not unlike a lump of the curd of milk, and consists 
 of Cyclotella menighiniana, and a surirella or two em- 
 bedded in a mass of Spirulina hittchinsia; and another 
 mass of floating weed, which feels harsh to the touch, pro- 
 ceeding from a quantity of a synedra, closely investing a 
 filamentous alga; and elsewhere Melotira nummuloides 
 (gallionella of Ehrenberg). 
 
 " lu a trench by the sea-wall, as it is termed, is a mass 
 of brown matter of a shade somewhat different to any 
 hitherto observed, adhering to some 'of the parts of the 
 trench, being partially submerged, and having a some- 
 what tremulous motion on agitating the water. This is a 
 
260 THE MICROSCOPE. 
 
 species of Schizonema; and it consists of a quantity ol 
 gelatinous hollow filaments filled with an immense number 
 of bright-brown shuttle-shaped bodies, like very minute 
 naviculce. 
 
 " It is not necessary to be particular about collecting 
 the specimen free from mud, as the filaments are so tougb 
 that the mud can be readily washed away by shaking the 
 whole violently in a bottle of water, and pouring off the 
 mud, without at all injuring the specimen. The Amphi- 
 porium alatum communicates a somewhat frothy appear- 
 ance to the otherwise clear water, and to get any quantity 
 of this requires a little management ; but by skimming 
 the surface with the spoon, and using one of the largei 
 bottles, an abundance may readily be obtained. Betweer 
 the sea-wall and the river the marsh is intersected in every 
 direction with a number of meandering creeks, being ir 
 some places eight to ten feet deep, though in others quite 
 shallow ; but it is exceedingly difficult to make one's waj 
 amongst them, and I have never found them so prolific 
 any where, on the few occasions of my visiting the place, 
 as in the parts more away from the influence of the tide. 
 It will be observed, that the brilliant brown colour, of s 
 deep but bright cinnamon tint, is one of the best indica- 
 tions of the presence of diatomacece ; and though this is bj 
 no means universal, the variation is most frequently de- 
 pendent upon the presence of something which qualifies 
 the tint. The peculiarity of the colour is due to the 
 endochrome contained in the frustule ; and this must ic 
 general be got rid of before the beautiful and delicate 
 marking can be made out. But it is highly advantageous 
 and instructive to view them in a living state ; and this 
 should be done as soon as possible after reaching home 
 with all specimens procured from salt-water localities, as 
 they rapidly putrefy in confinement, and emit a mosl 
 disgusting odour, not unlike that arising from a box oi 
 inferior congreve-matches. 
 
 " Washing in fresh water, and then immersing in creo- 
 sote water, preserves many of the species in a very natural- 
 looking manner; but they are killed by the fresh water. 
 and the endochrome becomes much condensed in the 
 Pleurosigmata and some other species. The addition ol 
 
COLLECTING OBJECTS. 251 
 
 spirits quite spoils the appearance of the frustules, as it 
 dissolves the endochrome. 
 
 " There is another salt-marsh a little farther down the 
 same railway, at Higham, which it would be well to 
 explore. The most favourable months for procuring dia- 
 tomacece, are April, May, September, and October; but 
 some species are found in perfection as early as February, 
 and many as late as November, and a few at all times of 
 the year. There is a piece of boggy ground near Keston, 
 beyond Bromley, in Kent, where the river Bavensbourne 
 takes its rise, where many interesting species of desmi- 
 ddcece and other fresh- water algse may be procured. From 
 Bromley, walk on towards Keston, passing near Hayes 
 Common and Bromley Common on the right. Continue 
 for about another half-mile along the road, and then turn 
 to the right hand; pass the reservoirs, and approach an 
 open space where there is a bog of about a quarter of a 
 mile in extent ; and tending towards the right, make your 
 way amongst heaths, ferns, mosses, and the beautiful 
 Drosera rotimdifolia (sun-dew), to the lower part of the 
 little stream rippling through a sort of narrow trench in 
 the Sphagnum, &c. By working your way up the stream, 
 you avoid the inconvenience which would otherwise be 
 experienced of the water being rendered turbid, in con- 
 sequence of having to tread in the boggy ground. In the 
 centre of the little stream may be observed something of a 
 pale pea-green colour flickering about in the current, 
 which, on your attempting to grasp, most likely eludes 
 you, and slips through the fingers, from being of a gelatin- 
 ous nature. It consists of a hyaline substance, with a 
 comparatively small quantity of a bright green endo- 
 chrome, disposed in little branches, and this is the Dra- 
 parnaldia glomerata. Another object is a mass of green 
 filaments, rather harsh to the touch, and very slippery. 
 When viewed with a lens of moderate power, each filament 
 is seen to be surrounded with several bands of green dots, 
 looking like a ribbon twisted spirally, and may be recog- 
 nised as a species of Zygnema. In various parts there 
 are other Zygnemaceoe, as spirogyra, mougeotia, mesocarpus, 
 and many more. 
 
 " Keeping up the stream, and occasionally diverging a 
 
252 THE MICROSCOPE. 
 
 little on either side of it, amongst the miniature Days ai 
 pools formed by the sphagnum, on looking straight dov 
 into the water we shall probably see at the bottom a litt 
 mass of jelly of a bright green, studded with numeroi 
 brilliant bubbles of oxygen-gas. This is the gener 
 appearance of most of the desmidacece, as Micrasteria 
 Euastrum, Closterium, Cosmarium, &c. The spoon is aL 
 a handy tool in this case, though, by practice, the fingi 
 will do nearly as well ; the chief difficulty arises whe 
 the specimen is brought to the surface of the water, it IK 
 being easy to get it out without losing a considerable po 
 tion of it. Little pools in the bog, made by the footstej 
 of cattle, are particularly good spots to find desmidiec 
 many species being in a very contracted space. The moi 
 prolific bog is at Tunbridge Wells, near a house known i 
 Fisher's Castle, not far from Hurst Wood. There is also 
 good one at Eslier, at a spot called West-End. It mui 
 not be imagined that nothing can be obtained in th 
 department of botany without going some distance froi 
 town j but assuredly only commoner and fewer species ca 
 be met with nearer home. At the West India Docks ai 
 Synedra fasciculata, Gomphonema curvata, Diatoma elongc 
 turn, Diatoma mdgare, Surirella ovata, &c. ; and at th 
 same place a few objects, not of the botanical class, i 
 Spongilla fluviatilis, Cordyloplwra lacustris, Alcyondh 
 stagnorum, &c., are obtainable in abundance in the autumi 
 In the ornamental water in St. James's Park may be foun< 
 Gocconema lanceolatum, and other species of this genu 
 Gomphonema cristatum, &c. Epping Forest, about th 
 neighbourhood of Leytonstone, Snaresbrook, Wanstea< 
 and Woodford Bridge, are also capital localities for th 
 filamentous algse, especially the last-named, where Nitell 
 trcmslucens and Char a vulgaris abound." x 
 
 On the north side of the Serpentine, Hyde Park, esp( 
 cially near the bridge, may be found : 
 
 Cymbella maculata. 
 Gomphonema cristatum. 
 Scenedesmus quadricauda. 
 
 ,, obliquus. 
 
 Ankistrodesmus falcatus. 
 Pediastrum Heptactys. 
 Cocconema lanceolatum. 
 Amphora ovalis. 
 
 Cocconeis placentula. 
 Uvella liyalina. 
 Gallionella nummuloides. 
 Euastrum elegans. 
 Pixidula operculata. 
 Cladophora glomerata and Sphsn 
 plea crispa, with many ottw 
 
 (1) "Quarterly Journal of Microscopical Science.' 
 
LIST OF OBJECTS. 
 
 253 
 
 Mr. Wheeler, of Tollington Eoad, Holloway, K, has 
 furnished us with the following list of 100 interesting 
 and popular objects, in book-case complete : 
 
 Pleurosigma angulata, 
 strigosa. 
 
 fonnosum. 
 Scales of Podura. 
 
 i, Lepisma. 
 Hair of Indian bat. 
 ,, mouse. 
 ,, Larva of Dermestes. 
 
 Triceratium from Thames mud. 
 Arachaoidiscus. 
 
 w os. infusoria from Guano. 
 Fos. infusoria, Barbadoes. 
 
 ,, Upper Bann, Ireland 
 
 Island of Mull. 
 ,, Tuscany. 
 
 Infusoria from Thames mud. 
 Spicules of Gor^onia. 
 
 sponge. 
 
 ,, fresh water. 
 
 Gemmules of sponge. 
 
 Section of shell Pinna. 
 .. crab. 
 
 Haliotis. 
 
 ,, spine of Echinus. 
 
 Cidaris. 
 
 Xanthidia in flint. 
 Moss agate. 
 Limestone. 
 
 Fossil tooth of shark 
 
 fish. 
 
 Fossil bone of whale. 
 reptile. 
 
 elk. 
 
 Fossil wood (Exogen). 
 (Endogen). 
 Sections of coal. 
 Simple cellular tissue. 
 Stellate tissue. 
 Fibro-cellular tissue. 
 Spiral vessels. 
 Hairs from leaf of Deutzia. 
 Seeds of a fern. 
 Sections of fir. 
 
 oak. 
 ,, mahogany. 
 
 clematis. 
 Petal of geranium. 
 
 Leaf insect. 
 
 Flea. 
 
 Parasite of peacock. 
 
 Skin of caterpillar. 
 
 Wing of a butterfly. 
 
 Scales of ditto. 
 roboscis of blow-fly. 
 Stomach of ditto. 
 Foot of ditto. 
 Spiracles of Dytiscus. 
 Foot of Ophion. 
 Proboscis of moth. 
 
 Tran. sects, of human hairs. 
 
 ,, hairs of elephant. 
 
 ,, whalebone. 
 
 Feather of bird. 
 Trans, sects, of human bone. 
 
 bone of bird. 
 
 fish. 
 
 ,, reptile. 
 
 Blood of bird. 
 fish. 
 
 reptile. 
 ,, human. 
 
 Opaque : 
 Gold dust. 
 Fossil shells. 
 Pollens. 
 Fern spores. 
 Needle antimony. 
 Avanturine. 
 
 Polariscope : 
 Selenite. 
 Starch. 
 
 Hairs from leaf. 
 Kmbryo oysters. 
 Rhinoceros horn. 
 Hoof of horse. 
 Agate. 
 Sandstone. 
 
 Sulphate of Cadmium. 
 Salicine. 
 Tartaric acid. 
 Carbonate of lime. 
 
 Anatomical : 
 Section of cartilage, showing ttt 
 
 formation of the bone-cells. 
 Muscle of mammalia. 
 reptile. 
 bird, 
 fish. 
 
 Injections of: 
 Human lung. 
 ,, intestine. 
 ,, skin. 
 ,, kidney. 
 ,, stomach. 
 muscle. 
 ,, section of finger. 
 
254 
 
 THE MICROSCOPE. 
 
 Mr. Collins has introduced a very complete Mounting- 
 Case, which will prove useful to microscopists, especially 
 so to those who devote a good deal of attention to the 
 preparation of specimens. A place is here found for 
 everything : the little box contains : Shadbolt's turn- 
 table, brass table, spirit-lamp, pipettes, spring clips, 
 wooden clips, tweezers, tin cells, balsam, marine glue, 
 asphalte, turps, gold size, thin glass covers, glass slips, and 
 five extra bottles. The price of this neat and convenient 
 case is 30s. Another box, more particularly adapted for 
 anatomical purposes, includes a neat injecting apparatus. 
 
 Fig. 143. Collins' Mounting Cabinet. 
 
 A modification of Dr. Beale's neutral-tint glass for 
 drawing is made by Mr. Collins, who supplies three glasses 
 of different shades, which drop into a dovetail, so that 
 they can be more easily cleaned and efficiently adapted 
 to the power used ; with his more complete instruments a 
 prism is also supplied. 
 

 Tun.-!. \Ve>,t .l.-l 
 
 I'drnimd Kvans. 
 
 I'LATK 1. 
 
PART II. 
 
 THE VEGETABLE KINGDOM VITAL CHARACTERISTICS OF CELLS THE PEO- 
 TOCOCCUS PLUVIALIS OSCILLATOR!^ FUNGI ALG^E DESMIDACE, 
 MOSSES FEKNS STRUCTURE OF PLAXTS STARCH ADULTERATION OF 
 ARTICLES USED FOR FOOD PREPARATION OF VEGETABLE STRUCTURES, 
 KTC. 
 
 1XCE the introduction of the achro- 
 H matic microscope, we have obtained 
 nearly the whole of the valuable 
 information we possess of the mi- 
 nute structure of plants. Indeed 
 in no department of nature has 
 microscopic investigation been more 
 fertile of results than in that of 
 the vegetable kingdom. The hum- 
 blest tribes of plants have had 
 for microscopists an attraction, 
 unequalled by that of any other 
 
 ( 1 J3L K* '\FL department of nature, from the 
 
 jMKJ&uk time of our countryman Robert 
 V^Kfts^nB Brown, down to the present day. 
 Although Brown had observed and 
 recorded certain facts in the phy- 
 siology of vegetable life, it was 
 Professor ^chleiden's labours that 
 brought to light the great truth, 
 "that the life-history of the individual cell is the first 
 important and indispensable basis whereon to found a 
 true physiology of the life-history of plants, as well as 
 that of the higher orders of creation." The first problem 
 
256 THE MICROSCOPE. 
 
 which, this observer set himself to solve, was, How is the 
 cell originated ? It is not here desirable to go deeply into 
 this most interesting inquiry; the object proposed is to 
 give a slight sketch of the formative processes of plant 
 life, chiefly in its relation to the earliest, or cell condition. 
 
 Almost every day brings forth a new discovery by 
 which old land-marks established with a view to the separa- 
 tion, arrangement, and classification of the vegetable and 
 animal kingdoms become unsettled ; the lowest forms of 
 life, vegetable and animal, approach so near to each other, 
 that we cannot with certainty always discriminate them, 
 and say where the one ends and the other begins. The 
 boundary assigned to the vegetable kingdom is, perhaps, 
 too limited, and our definition of a vegetable organism 
 requires to be enlarged : of this any one who will be at 
 the trouble to study the microscopic forms of life must 
 feel perfectly convinced. At the present day, the only 
 generally applicable rule that can be applied to distinguish 
 animals from vegetables is the dependence of the animal 
 for nutriment upon organic compounds already formed, 
 which it takes into the interior of its body; this at 
 once distinguishes it from the plant, which only possesses 
 the power of obtaining its alimentary matter, by absorp- 
 tion, from the inorganic elements by which it is surrounded. 
 Although there appear to be certain exceptions to this 
 rule, yet it almost universally prevails. 
 
 Kiitzing maintains, that every organic being is con- 
 stituted of vegetable and animal elements, and according 
 as the one or the other prevails, the being becomes an 
 animal or a vegetable : in the first stages of the develop- 
 ment of superior beings, and permanently in those of 
 inferior rank, the two elements are equally balanced. " If 
 nature," writes Humboldt, " had endowed us with micro- 
 scopic powers of sight, and if the integuments of plants 
 were transparent, the vegetable kingdom would by no 
 means present that aspect of immobility and repose under 
 which it appears to our senses." And so with regard to 
 the instruments of motion in the higher classes of crea- 
 tion, the muscles of animals very soon disappear as we 
 descend in the scale to the simplest forms of life ; never- 
 theless, we cannot deny animality to those minute crea- 
 
CHARACTERISTICS OF CELLS. 257 
 
 tures as the Amoeba in which we are quite unable 
 to distinguish either muscles or any other distinct organs. 
 Hence there is always some danger of believing that to be 
 simple which in reality only seems to be so, and which 
 the minuteness or transparency of organization may only 
 conceal from our limited power of vision. 
 
 Plants and animals, if seen at the earliest stage of 
 existence, present themselves to our eyes as an aggregation 
 of transparent cells. Everything prior to the appearance 
 of the cell may, in the actual state of our microscopical 
 knowledge, be considered as not fully and certainly demon- 
 strated ; and therefore it is incumbent upon us to take our 
 starting-point from the simple cell, which is the same, in re- 
 spect to its principal characters, in animals and vegetables. 
 The external coating of a cell is nearly or quite solid and 
 transparent, and with no indication of structure; while 
 in its interior is found a liquid or solid substance, with a 
 nucleus either adhering to its wall or within its cavity. 
 A nucleolus can sometimes be demonstrated within the 
 nucleus ; and (a state common to all living cells) an in- 
 cessant mutual interchange of materials is going on between 
 the fluid contents and matter external to the cell, by 
 a process termed osmose, or diffusion, which causes a per- 
 petual variation in its relative condition. Chemical reagents 
 give a manifestly different result in the animal and vege- 
 table cell, hence we may conclude that there is an important 
 difference in their chemical composition. The vegetable 
 cell has an extremely fine delicate membrane lining the 
 inner wall, to perceive which we must have recourse 
 to reagents, and then we find the apparently simple cell- 
 wall made up of two layer?, each differing in composition 
 and properties. The inner layer has received the name of 
 primordial utricle, and ; ts composition has been shown 
 to be albuminous ; agreeing in this respect with the form- 
 ative substance of animal tissues. The external layer is 
 regarded as the cell- wall, although it takes iio part, essen- 
 tially, in the formation of the cell ; it is composed of celln- 
 lin, a material allied to the cellulose of vegetable tissues. 
 The contents are more or less coloured : the internal 
 colouring substance is termed endochrome ; when green il 
 is called chlorophyll. 
 
 a 
 
258 THE MICROSCOPE. 
 
 The successive changes in the cell contents furnish 
 other very important characteristics, such as the dis- 
 appearance and re-absorption of the nucleus ; this occurs 
 in every cell at some period of its existence j in the cells 
 of the higher plants, the inner membrane, or primordial 
 utricle, entirely disappears. The Algge, and some few 
 unicellular plants, form an exception to the rule. In the 
 animal, the enlargement of the cell-wall takes place in a 
 uniform manner, whereas in the plant this is effected by 
 a deposition of successive layers on its inner surface, in the 
 shape of continuous rings, spiral bands, or other inter- 
 mediate forms. Then the wall not only increases in size, 
 but appears to possess a power of separating and appro- 
 priating certain substances, as lime, silica, lignine, &c., 
 which form the so-called cuticle. In animals as well as 
 in plants, new cells are formed within the old cells ; but 
 in the former, this process of a new formation begins in 
 the extracellular fluid, while in the latter it is mostly 
 endogenous. Multiplication of vegetable cells is effected 
 by three different modes : 1st, Many nuclei appear in the 
 maternal cell floating together with granular matter; 
 around each collects a minute vesicle, this gradually 
 increasing fills the maternal cell, which is eventually 
 absorbed. 2d, The internal substance of the cell divides 
 into two or more portions, each being furnished with a 
 nucleus. 3d, In the third mode of multiplication, the 
 wall itself of the maternal cell becomes gradually con- 
 stricted, and divides into two portions.* 
 
 * "In most cells, especially when young, a minute, rounded, colourless 
 body may be seen, either in the middle or on one side, called the nucleus. This is 
 very distinct in a cell of the pulp of an apple : and within this nucleus is often 
 to be seen another smaller body, frequently appearing as a mere dot, called the 
 nucleolus. 
 
 " The nucleus Is imbedded in a soft substance, which fills up the entire cell ; 
 this is the protoplasm (protos, first, plasma, formative substance). As it is very 
 transparent, it is readily overlooked ; but it may usually be shown distinctly 
 by adding a little glycerine to the edge of the cover with a glass rod, when it 
 contracts and separates from the cell-walls. The protoplasm in some cells is 
 semi-solid, and of uniform consistence, while in others it is liquid in the centre, 
 the outer portion being somewhat firmer, and immediately in contact with the 
 cell-wall. In the latter case it forms an inner cell to the cell-wall, and is called 
 the primordial utricle. The terms ' protoplasm ' and ' primordial utricle ' are 
 however used by some authors synonymously. 
 
 " The protoplasm is the essential portion of the cell, and it forms or secretes 
 the cell-wall upon its outer surface in the process of formation of the cell, con- 
 sidered as a whole. It is also of different chemical composition, from the cell 
 wall being allied in this respect to animal matter." GriffUht. 
 
CELL-DEVELOPMENT. 259 
 
 Taking for our examination the more simple organisms 
 among vegetables, we shall find numbers which present, in 
 their earliest as well as in their permanent state, the cell 
 in its simplest condition, and its reproduction a bare re- 
 petition of the same thing. Unicellular plants, then, in 
 the strictest sense, are represented only by those in which 
 the whole cycle of life is completely shut up in the one. 
 cell ; the first reconstruction or division being at once the 
 commencement of a new cycle, in which, consequently, 
 the whole vegetative life is run through in the same cell 
 where the propagation also appears. 
 
 Fig. 144. Cell Development. (Protococcus pluvialis. ) 
 
 Protococcus pluvialis, Kiitzing. HcBmatococcus pluvialis, Flotow. CJtiamido- 
 oocctw versat ilis, A Braun. CMamidococcus pluvialis. Flotow and Braun. 
 
 A, division of a simple cell into two, each primordial vesicle having developed a 
 cellulin envelope around itself; B, Zoospores, after their escape from the 
 cells ; o, division of an encysted cell into segments ; D, division of another 
 cell, with vibratile filaments projecting from cell- wall ; E, an encysted cell ; 
 r, division of an encysted cell into four, with vibratile filaments projecting ; 
 o, division of a young cell into two. 
 
 The most widely distributed of these single-cell plants 
 is the Palmoglceo, macrococca, of Kiitzing, which spreads 
 itself as a green slime over damp stones, walls, &c. If a 
 small portion be scraped off and placed on a slip of glass, 
 and examined with a half or quarter-inch power, it will bo 
 seen to consist of a number of ovoid cells, having a trans- 
 parent structureless envelope, nearly filled by a granular 
 matter of a greenish colour. At certain periods this mass 
 divides into two parts, and ultimately the coll becomes two. 
 Sometimes the cells are united end to end, just as we see 
 
260 THE MICROSCOPE. 
 
 them united in the actively-growing yeast plant ; but in 
 this case the growth is accelerated, apparently, by cold and 
 damp. Another plant belonging to the same species, the 
 Protococcus pluvialis, is found in every pool of water, the 
 spores of which must be always floating in the air, since 
 it appears after every shower of rain. 
 
 Unicellular plants occur in the series of Fungi and 
 Algce, which have many and very varied correspondence in 
 morphological respects. The unicellular Algae that is to 
 say, Algae, the contents of which, containing already 
 organized particles, are inclosed in a single, semifluid 
 envelope, and this again in a cell-membrane, often 
 consisting of several layers of different kinds ; and many, 
 moreover, possess the power of dividing into several 
 secondary cells, for the most part equivalent to the primary 
 cell. To this species of unicellular plant belongs Protococcus 
 pluvialis. That this is the case is clearly seen in the still 
 form of this plant, which is most distinctly characterised 
 by its cell-membrane, a more or less thick though always 
 colourless envelope. It never, however, secretes true 
 thickening layers on the surface. Although this cell- 
 membrane exhibits all the optical characters of one com- 
 posed of cellulose, it is impossible to demonstrate the 
 presence of that principle by means of iodine and sulphuric 
 acid ; it is not coloured by those reagents even after the 
 contents of the cell have been expressed. 
 
 The contents vary much in consistence, colour, solid 
 and fluid constituents ; the red and green portions oi 
 which appear to be of equal physiological importance 
 The green colour is removed by ether, on the evaporation 
 of which solvent there remain green as well as colourless 
 drops. Dilute sulphuric acid at first renders the colour 
 paler; but its prolonged action produces a bright green 
 hue, which gradually becomes more and more intense, and 
 often almost a blue-green. Hydrochloric acid has a simi- 
 lar effect ; a tinge of brown is produced by nitric acid. 
 Carbonate of potash scarcely affects the green colour ; it 
 is gradually but totally destroyed by caustic potash, the 
 contents at the same time swelling and becoming 
 transparent. 
 
 The change of colour from green to red in Euglena 
 
UNICELLULAR PLANTS. 2G1 
 
 appears to be a process very nearly allied to that which 
 takes place in Protococcus, if it be not identical with it. 
 The red substance of Prot. pluvialis is not always of an 
 oily aspect; it only becomes so in more advanced age. 
 And according to Colm's researches, this oily material 13 
 much more generally distributed than has been supposed, 
 among the lower Algae; occurring in many true brown 
 spores, such as of (Edogonium, Spirogyra, Vaucheria, &c. 
 
 When still or motile cells of Protococcus are brought in 
 contact with a very weak solution of iodine, they become 
 internally, in most parts, of an intense violet or blue colour. 
 With respect to the solid constituents of the Protococcus 
 cell contents, they may be distinguished into chlorophyll 
 vesicles, colourless or green particles, amylaceous granules, 
 and nucleus. The motile form of Protococcus consists, 
 as it were, of two cells, one within the other, both of which, 
 however, differ essentially from the common vegetable cell : 
 the external having a true cell- membrane and fluid con- 
 tents ; the other, or internal one, with denser, muco-gela- 
 tinous coloured contents, but without a true cell-wall. 
 Cohn called the external transparent vesicle the " enve- 
 loping " cell," and the internal coloured one the " primor- 
 dial cell" The term, "primordial sac, or utricle," can 
 only be applied to its peripheral layer, and not to that 
 together with the contents. 
 
 The form of Protococcus (fig. 144) presents a perfect 
 analogy between the primordial cell and the nucleus of 
 the common plant-cell The filaments which proceed 
 from the central mass to the peripheric cell-wall, are 
 tubular, giving passage to the red molecules from the 
 central mass. These filaments, however, which proceed 
 from the outer wall of the primordial cell towards the 
 inner surface of the enveloping cell, correspond morpho- 
 logically to the so-termed mucous filaments by which the 
 cytoblasts are commonly retained in the centre of their 
 cells. That they also correspond chemically with these, 
 is proved by the fact that they are rendered more distinct 
 by iodine, and that they can be made to retract by means 
 of reagents ; and in fact they exhibit, in the course 
 of development, peculiarities which characterise them as 
 consisting of protoplasm. 
 
262 THE MICROSCOPE. 
 
 The existence of delicate threads passing from the 
 central mass to the enveloping cells, and the appearance 
 occasionally of little particles having molecular motion, 
 serve to show that the contents of the enveloping cell are 
 less of a gelatinous consistence, than of a fluid nature. 
 And the continuity of the primordial cell- -wall with the 
 filaments proves it is surrounded only with a layer of 
 protoplasm, and is not inclosed in a dense membrane 
 of cellulose. The most distinctive characteristic of the 
 primordial cell, and what appears to constitute its most 
 essential importance in the life of the cell in general, but 
 particularly in that of the zoospore, consists in its being 
 the contractile element of the vegetable organism that, 
 is to say, that from an intrinsic activity it possesses the 
 faculty of altering its figure, without any corresponding 
 change in volume. 
 
 The Protococcus pluvialis has true motile organs, 
 namely, two long vibratile cilia arising from the primordial 
 cell (fig. 1 44, B, a), which, passing through two openings in 
 the enveloping cell, move about in the water. These organs, 
 during the life of the cell, move so rapidly, that it is 
 then difficult to perceive them ; they are only recognisable 
 by the currents they produce in the water. But when 
 the motion is slackened they are evident enough. They 
 are also rendered very distinct by iodine. They are always 
 placed upon the extreme point of the conical elongation, 
 on the anterior end of the primordial cell, and in such a 
 manner as to appear to be immediate continuations of its 
 substance ; and as that process itself consists of protoplasm, 
 it is evident that the cilia must be regarded also as com- 
 posed of the same substance. They resemble, in some 
 respects, the so-called proboscis of certain Infusoria, such 
 as Euglena and Monads, and do not differ very materially 
 from the non- vibratile, retractile filaments of Acineta and 
 Actinophrys. 
 
 It is only that portion of the vibratile filaments beyond 
 the enveloping cell that exhibits any motion, the portion 
 within the outer cell being always motionless, and in that 
 part of their course the filaments appear to be surrounded 
 with a sheath. This seems to be the case, not only from 
 the greater thickness at that part, but also from the cir- 
 
UNICELLULAR PLANTS. 263 
 
 cumstance that when, passing from the cell form into the 
 still condition, the cilia disappear, the Y-shaped, or forked 
 internal portions remain visible. And it is then, also, that 
 the openings through the enveloping cell- wall become, for 
 the first time, visible. 
 
 Perhaps the most remarkable of all the numerous 
 aspects presented by Protococcus pluvialis, is the form of 
 naked zoospores named by Flotow Hcematococcus porphyro- 
 cephalus. These are extraordinarily minute globules, con- 
 sisting of a green, red, and colourless substance in unequal 
 proportions. The colourless protoplasm in them, as in all 
 primordial cells, constitutes the outermost delicate boun- 
 dary; the red substance is for the most part collected 
 towards the anterior end in minute spherules ; the granular 
 green substance occupies more the under part, while the 
 middle is usually colourless. 
 
 Propagation depends upon a division of the cell 
 contents particularly of the colourless or coloured proto- 
 plasm, or of the primordial sac. This body, without any 
 demonstrable influence of a nucleus, is capable of sub- 
 dividing into a determinate number of portions. Each of 
 these acquires a globular figure, and in the next place 
 surrounds itself with an envelope of protoplasm, and then 
 represents a visible organism, which after the reabsorption 
 of the parent cell-membrane, is capable of existence as an 
 independent reproductive individual. Besides these, which 
 are the most usual modes of propagation viz. tbat of the 
 still-cells into two, and of the motile into four, secondary 
 cells there are a number of others which may be con- 
 sidered as irregular, and in which forms are produced 
 which do not re-enter the usual cycle until they have 
 gone through a series of generations. Sometimes, under 
 certain circumstances, the cell-contents of the still form 
 separate into eight or more portions, which become naked 
 zoospores of small size (fig. 144 B.) It is not quite 
 clear what becomes of this form of motile zoospores, but 
 there seems reason for believing that they occasionally 
 develop an enveloping cyst, and thus become encysted 
 coospores, and at other times secrete a cellulin tissue, 
 and become still-cells ; but most of them probably perish 
 without any further change. They would thus correspond 
 
261 THE MICROSCOPE. 
 
 with the smaller motile spores observed by Thuret and 
 A, Braun in other Algae (the Fucoid, &c.), associated with 
 the larger germinating spores, themselves deprived of the 
 germinative faculty. 
 
 It appears that both longitudinal and transverse division 
 of the primordial cell may take place ; but that the 
 vibratile cilia of the parent cell retain almost to the last 
 moment their function and their motion after the primor- 
 dial cell inclosed by it has long been detached as a whole, 
 and become transformed into the independent secondary 
 cells (fig. 144, G). 
 
 The most striking of the vital phenomena presented by 
 this organism is that of periodicity. Certain forms for 
 instance, encysted zoospores, of a certain colour, appear in 
 a given infusion, at first exclusively, then they gradually 
 diminish, become more and more rare, and finally dis- 
 appear altogether. After some time their number again 
 increases, and reaches as before to an incredible extent ; 
 and this proceeding may be repeated several times. 
 Thus, a glass which at one time presented only still 
 forms, contained at another nothing but motile ones. The 
 same thing may be observed with respect to segmen- 
 tation. If a number of motile cells be transferred 
 from a larger glass into a small vessel, it will be found, 
 after the lapse of a few hours, that most of them have 
 subsided to the bottom, and in the course of the day they 
 will all be observed to be on the point of subdivision. On 
 the following morning the divisional generation will have 
 become free ; on the next, the bottom of the vessel 
 will be found covered with a new generation of self- 
 dividing colls, which again proceed to the formation of a 
 new generation, and so on. This regularity, however, is 
 not always observed. The influence of every change in 
 the external conditions of life upon the propagation is 
 very remarkable. It is only necessary to pour water 
 from a smaller into a larger and shallower vessel, or one^of 
 a different kind, to at once induce the commencement of 
 segmentation in numerous cells. The same thing occurs 
 in other Algae ; thus the Vaucheria almost always develop 
 zoospores, at whatever time of year they may be brought 
 from their natural habitat into a room. Light is conducive 
 
FRESH-WATKR ALG.E. 263 
 
 to the manifestation of vital action in the motile zoospores, 
 and they always seek it, collecting themselves at the 
 surface of the water, and at the edges of the vessel. 
 
 But in the act of propagation, on the contrary, and when 
 about to pass into the still condition, the motile Pro- 
 tococcus cell seems to shun the light ; at all events it 
 chen seeks the bottom of the vessel, or that part of the 
 drop of water in which it may be placed, furthest from 
 the light. Too strong sunlight, as when it is concentrated 
 by a lens, at once kills the zoospores. A temperature of 
 undue elevation is injurious to the development of the 
 more vigorous vital activity, that is to say, for the forma- 
 tion of the zoospores ; whilst a more moderate warmth, 
 particularly that of the vernal sun, is singularly favour- 
 able to it. Frost destroys the motile, but not the still 
 zoospores.* 
 
 Stephanosplicera pluvialis is another variety of fresh- 
 water alga3, first observed by Cohn. It consists of a 
 hyaline globe, containing eight green primordial cells, 
 arranged in a circle (see Plate 1, No. 24 </). The globe 
 rotates, somewhat in the same manner as the volvox, by 
 the aid of projecting cilise, two of which are seen to proceed 
 from each cell and pierce the transparent envelope. Every 
 cell divides first into two, then four, and lastly eight 
 young cells, each of which divides into a great number of 
 microgonidia, and are seen to have a motion within the 
 globe, and ultimately escape from it. Under certain cir- 
 cumstances each of the eight cells is observed to move 
 about in the interior of the mother-cell ; eventually they 
 escape, lose their cilia, form a thicker membrane as at 6, 
 for a time become motionless, and sink to the bottom of 
 the vessel. If the vessel be permitted to become thoroughly 
 dry, and again water is poured into it, motile Stephano- 
 sphaera reappear : from which circumstances it is probable 
 that the green globes are the resting spores of the plant. 
 When in its condition of greatest activity its division into 
 eight is perfected during the night, and early in the 
 morning the young family escapes from the cell, soon to 
 pass through similar changes. It is calculated that in 
 
 On the " Natural History of Protococcus pluvialis," by F. Cohn, translated 
 Oy Q. Busk. F.R.S. for the Ray Society 
 
266 THE MICROSCOPE. 
 
 eight days, under favourable circumstances, 16.777,216 
 families may be formed from one resting-cell of Stephano- 
 sphsera. In certain of the cells, and at particular periods, 
 the remarkable amaboid bodies (Tlate 1, No. 24 c), have 
 been noticed. There is a marked difference between 
 Stephanosphaera and Chlamydococcus, " for, while in the 
 latter the individual portions of a primordial cell separate 
 entirely from one another, each developing its own enve- 
 loping membrane, and ultimately escaping as a unicellular 
 individual ; in the former, on the other hand, the eight 
 portions remain for a time united as a family." * 
 
 The simplest forms of vegetable life are met with in the 
 Confervoids, which are as interesting as they are in- 
 structive to the microscopist. The confervas consist of 
 unbranched filaments composed of cylindrical cells, placed 
 end to end ; their reproductive process is carried on by 
 zoospores produced from the cell contents. The fresh- 
 water genera are principally of a yellowish green colour ; 
 sometimes presenting a striated appearance, which* has 
 given rise to a supposition that their filaments are spiral. 
 They are indeed plentifully distributed both in fresh and 
 salt-water. 
 
 Oscillator iacece. The study of the structure of the Oscil- 
 latorice is particularly interesting, from the fact that we 
 may not unreasonably expect to find in it a key to the 
 singular motion from which they received their generic 
 name, and which now, for more than a century, lias 
 formed an object of curiosity and interest to the micro- 
 scopist, without having received, as yet, a satisfactory 
 explanation. 
 
 The following different tissues are observable in the true 
 Oscillatorlce : 1, An outer inclosing sheath ; 2, A special 
 cell-membrane, with its contents ; and 3, The axis, or pith, 
 of the filament. 
 
 " The filaments of certain species are inclosed in sheaths 
 or continuous tubes, never showing any cross-markings 
 corresponding to the striae of the filament ; they are clearly 
 composed of a kind of cellulose, although they remain 
 unaffected by iodine- In other species, these tubes are 
 
 * See an interesting paper by F. Currey, F.R.S. Journal of Microscopico' 
 Science, vol. vi. 1858, p. 131 : also by Mr. Win. Archer, vol. v. 1865, p. 116 
 
OONFERVOID Al&JR. 
 
 267 
 
 absent, or have not yet been observed; when present, 
 Aey will be found projecting on one or both sides of 
 
 Fig. 145. Conferrce. 
 
 I, Volvox globator. 2, A section of volvpx, showing the ciliated margin of the 
 cell. 8, A portion more highly magnified, to show the young rolvocina, with 
 their nuclei and thread-like attachments. 4, Spirogyra, near which are spores 
 in different stages of development. 5, Conferva floccosa. 6, Stigeoclonium 
 protensum, jointed filaments and single zoospores. 7, Staurocarpus gradlis, 
 conjugating filaments and spores. 
 
 the filament, being somewhat longer than the latter. 
 Filaments inclosed in sheaths never, or but slightly, ex- 
 hibit their peculiar motion, although they may be seen 
 sliding in them, backwards and forwards, or leaving them 
 altogether. 
 
 The filaments themselves have been supposed to consist 
 wholly of protoplasm ; this view, however, is scarcely 
 correct, since the protoplasm is enclosed in a cell-mem- 
 brane. The cellulin coat always shows cross-markings 
 corresponding to the striae when such are observable 
 
263 
 
 THE MICROSCOPE. 
 
 in thft filament, and which divide it into distinct joints 
 or cells. 
 
 The presence of this cell-membrane may be best de- 
 monstrated by breaking up the filaments, either by moving 
 the thin glass cover, or by cutting through a mass of them 
 in all directions with a fine dissecting knife. On now 
 examining the slide, in most in- 
 stances many detached empty 
 pieces of this cell-membrane, with 
 its striae, will be found, as well 
 as filaments partly deprived of 
 the protoplasm, showing in those 
 places the empty, striated cel- 
 lulin coat. On the application 
 of iodine all these appearances 
 become unmistakably evident ; 
 the greater portions of the fila- 
 ment turning brown or red, while 
 the empty cells, with their striae, 
 remain either unaffected, or at 
 
 Fig. 146. MesogUarermicularis most present a slight yellowish 
 
 tint > as is frequently the case 
 with cellulose when old. 
 
 With regard to the contents of the cell, the protoplasm 
 (or endochrome) is coloured in the Oscillator ice, and is de- 
 posited within it in the form of circular bands or rings 
 around the axis of the cylindrical filament ; iodine turns 
 them brown or red, and syrup and dilute sulphuric acid 
 produce a beautiful rose colour. As to their mode of pro- 
 pagation, nothing positive is known. If kept for some 
 time they gradually lose their green colour those exposed 
 to the sun, much sooner than others less exposed ; the 
 stratum eventually becoming brown, sinks to the bottom 
 of the vessel, and presents a granular layer, embodying 
 great numbers of filaments in all stages of decay.* 
 
 The movements 01 the O&ciUatorice are indeed very sin- 
 gular, so much so that it is in vain to attempt to explain 
 them as altogether dependent on physical causes, and 
 equally so to show that they are due to a sarcode or animal 
 
 * Dr. F. d'Alquen, "On the Structure of the Oscillatorise," Journal cj 
 Microscopical Science, voL iv. p. '245. 1856. 
 
MARINE ALGJE. 
 
 269 
 
 membrane. Their motion is not less lively than that of 
 the Bacterice, which Dujardin and Ehrenberg placed among 
 infusional animalcules. To observe the movements of the 
 filaments, the very uppermost surface ought to be brought 
 into focus, leaving the margins rather undefined, bearing in 
 mind that the filament is not a flat but a cylindrical body. 
 Certainly, with regard to its movement, or the mechanism 
 by which it is effected, nothing positive is known. 
 
 The Bacillaria paradoxa is by far the most interesting 
 specimen of the genus ; the movements of which are very 
 remarkable, and so little understood that it is rightly 
 called paradoxical. 
 
 The Marine Confervoid Algje present a general appear- 
 Aiice which might at first sight be mistaken for plants 
 very much higher in the scale of organization. In the 
 Ulvaceas, the frond has no longer the form of a filament, 
 but assumes that of a membranous expansion of the cell. 
 These cells, in which zoospores are found, have an in. 
 creased quantity of green protoplasm 
 accumulated towards one point of the 
 cell-wall; and the zoospores are ob- 
 served to converge with their apices 
 towards the same point. In. some 
 genera, which seem to be closely re- 
 lated in form and structure to the 
 Bryopsidece, we notice this important 
 difference, that the zoospores are de- 
 veloped in an organ specially destined 
 to this purpose, which presents pecu- 
 liarities of form, distinguishing it from 
 every other part of the branching 
 tubular frond. In the genus Derbesia, 
 distinct spore cases are seen, a young 
 branch of which, when destined to be- 
 come a sporecase, instead of elongating 
 indefinitely, begins, after having arrived 
 at a certain length, to swell out into 
 an ovoid vesicle, in the cavity of which a rapid accumu- 
 lation of protoplasma takes place. This is then separated 
 from the rest of the plant, and becomes an opaque mass, 
 surrounded by a distinct membrane. After a time a 
 
 Fig. 147. Sphacelarta 
 cirrhosa, with spores 
 borne at the sides of tlie 
 branchlets. 
 
270 THE MICROSCOPE. 
 
 division of the mass takes place, and a number of pyriform 
 zoospores, each of which is furnished with a crown of cilise, 
 are set free. 
 
 In many families of the olive-coloured Algae, reproduc- 
 tion by zoospores is the general rule ; they differ, however, 
 in the arrangement of their cilia. These organs, which 
 are always two in number, are usually of unequal length, 
 and emanate not from the beak, but from a reddish- 
 coloured point in its neighbourhood. The shortest is 
 directed backwards, and seems to serve during the motion 
 of the spoje as a rudder. The longest, directed forwards, is 
 closely applied to the colourless beak. Ectocarpus is one 
 of the simplest forms of olive-coloured Algae, consisting 
 of branching filaments, the extremity of any of which is 
 liable to become converted into a sporangium, by the ab- 
 sorption of the septa of the terminal cells. The zoospores 
 are arranged in regular horizontal layers. In many genera 
 a peculiarity exists, the signification of which is not yet 
 completely understood namely, that of a double fructifi- 
 cation. The ovoidal sporangia contain numerous zoospores. 
 In the genus Cutleria (fig. 150), there is seen another feature 
 of interest : the appearance of two kinds of organs, which 
 seem to be opposed to each other as regards their repro- 
 ductive functions. The sporangia not only differ from 
 those of other genera, but the frond consists of olive- 
 coloured irregularly-divided flabelli, on each side of which 
 tufts (sori) consisting of the reproductive organs, inter- 
 mixed with hair-like bodies, are scattered. The zoospores 
 are divided by transverse partitions into four cavities, each 
 of which is again bisected by a longitudinal median 
 septum. When first thrown oft' they are in appearance so 
 much like the spores of Puccinia, that they may be mis- 
 taken for them ; they are, however, about three times larger 
 than those of the other olive- coloured algae. 
 
 The fruit of most olive-green Sea-weeds is enclosed 
 in spherical cavities under the epidermis of the frond, 
 termed conceptacles, and may be either male or female. 
 The zoids are bottle- shaped, each possessing a pair of cilia ; 
 the transparent vesicle in which they are contained is 
 itself inclosed in a second of similar form, and we have 
 no certain evidence of the function performed by the 
 
MARINE ALG2E. 
 
 271 
 
 antheridia. In monoecious and dioecious Fuci, the female 
 conceptacles are distinguished from the male by their olive 
 colour. The spores are developed in each in the interior of 
 a perispore, which is borne on a pedicle emanating from the 
 inner wall of the conceptacle. They rupture the perispore 
 at the apex ; at first the spore appears simple, but soon after 
 a series of changes take 
 place, consisting in a 
 splitting of the endo- 
 chrorne into six or eight 
 masses, which become 
 spheroidal sporules. A 
 budding-out occurs in a 
 few hours' time, and ulti- 
 mately elongates into a 
 cylindrical tube. The 
 Vaucherice present a dou- 
 ble mode of reproduction, 
 and their fronds consist 
 of branched tubes, much 
 resembling in general 
 character that of the 
 Bryopsidece, from which 
 indeed they differ only in respect of the arrangement of 
 their contents, chlorophyll. In that most remarkable 
 plant Saprolegnia ferox, which is structually so closely 
 allied to Vaucherice, though separated from them by the 
 absence of green colouring matter, we find a correspond- 
 ing analogy in the processes of its development. In the 
 process of the formation of its zoospores, we have an 
 intermediate step between that of the Algae and a class of 
 plants usually placed among Fungi. Cohn has shown us 
 that Pilobolus is structually more closely allied to the 
 former class than to that of the latter. Pilobolus has 
 a somewhat remarkable ephemeral existence ; the spore 
 germinates about mid-day, the plant grows till evening, 
 re-opens during the night, and in the morning the spore-case 
 bursts and the whole disappears, leaving behind scarcely 
 a trace of its former existence. 
 
 Red Sea-weeds, Floridece, present great varieties of struc- 
 ture, although comparatively little is known of their re- 
 
 Fig. 148. Development of Viva. 
 
 A, isolated cells of spores. B and c, clus- 
 tering of the same. D, cells in the fila- 
 mentous stage. 
 
272 
 
 THE MICROSCOPE. 
 
 productive processes ; it will, however, be sufficient for our 
 purpose to notice the three leading forms. The first form, 
 to which the term polyspore has been applied, is that of 
 a gelatinous or membranous pericarp or conceptacle, in 
 which an indefinite number of sporidia are contained. 
 This organ may be either at the summit or base of a 
 branch, or it may be concealed in or below the cortical 
 layer of the stem. In some cases a number of sporidiuni- 
 bearing filaments emanate from a kind of membrane 
 at the base of a spheroidal cellular perisporangium, by 
 the rupture of which the sporidia formed from the 
 endochrome of the filaments make their escape. Other 
 changes have been observed ; however, they all agree in 
 one particular, namely, that the sporidium is developed 
 in the interior of a cell, the wall of which forms its 
 perispore, and the internal protoplasmic membrane en- 
 dochrome, the sporidium itself, for 
 the escape of which the perispore rup- 
 tures at its apex. 
 
 The second form is more simple, 
 and consists of a globular or ovoid 
 cell, containing a central granular 
 mass, which ultimately divides into 
 four quadrate- shaped spores, which 
 when at maturity escape by rupture 
 of the cell-wall. This organ, called 
 a tetraspore, takes its origin in the 
 cortical layer. The tetraspores are 
 arranged either in an isolated manner 
 along the branches, or in numbers to- 
 gether ; in some instances the branches 
 which contain them are so modified in 
 form that they look like special or- 
 gans, and have been called stichidia ; 
 as, for example, in Dasya (fig. 149). 
 Of the third kind of reproluctive or- 
 gan a difference of opinion exists as to 
 s. agm the signification of their antheridia ; 
 although always produced in precisely 
 the same situations as the tetraspores and polyspores, 
 they are "agglomerations of little colourless cells, either 
 
 and two rows of 
 diameters. 
 
MARINE ALG.E. 
 
 273 
 
 united in a bunch as in GrifitJisia, or enclosed in a trans- 
 parent cylinder, as in Polysiphonia, or covering a kind of ex- 
 panded disc of peculiar form, as in Laurenda" According 
 to competent observers, these cellules contain spermatozoids. 
 Nageli describes the spermatozoid as a spiral fibre, which, as 
 it escapes, lengthens itself in the form of a screw. Thuret 
 does not coincide in this view; on the contrary, he says 
 that the contents are granular, and offer no trace of a 
 spiral filament, but are expelled from the cells by a slow 
 motion. The antheridia appear in their most simple form 
 in Callithamnion, being reduced to a mass of cells com- 
 posed of numerous little bunches which are sessile on the 
 bifurcations of the terminal branches. Are not these spiral 
 filaments closely allied to Oscillatoriacece ? The spores are 
 simpler structures than the tetraspores, and mostly occupy 
 a more important posi- 
 tion. They are not scat- 
 tered through the frond, 
 but grouped in definite 
 masses, and generally 
 enclosed in a special 
 
 capsule or conceptacle, 
 
 which may be mistaken 
 
 for a tetraspore case. 
 
 The simplest form of 
 
 the spore fruit consists 
 
 of spherical masses of 
 
 spores attached to the 
 
 wall of the Irond, or 
 
 imbedded in its sub- 
 
 etance. without a prope v 
 
 conceptacle ; such a fruit 
 
 13 called a favellidium, 
 
 and occurs in llaly- 
 
 menia ; the same name 
 
 is applied to the fruits 
 
 ot similar structures not 
 
 perfectly immersed,, as 
 
 those of Gigartina, Gelidium, &c., where they form tuber- 
 cular swellings on the lobes. In some, the tubercles pre- 
 sent a pore at the summit, through which the spores find 
 
 Fig. 150. Cutleria dichotoma. Section of <n 
 lucinia of a frond, showing the stalked eight 
 chambered oosporangts prmoing on tuft* 
 with intercalated hairs Magnified 50 dia- 
 meters. 
 
274 THE MICROSCOPE. 
 
 exit; when such a fruit is wholly external, as in Cera- 
 mium (see Plate II. Nos. 27 and 37) and Callithamnion, 
 it is called a favella. The characteristic of Delesseria, 
 No. 39, the coccidium, either occurs on lateral branches, or 
 is sessile on the face of the frond, and consists of a case 
 of angular spores attached to a central wall. The cera- 
 midium is the most complete form of the conceptacular 
 fruit : this is enclosed in an yvate case, with an apical 
 spore, containing a tuft of pear-shaped spores arising from 
 the base of the cavity. 
 
 The general external appearance of the Eed Sea- weeds 
 is very varied. They are exquisite objects for the Micro- 
 scope ; we have figured several interesting varieties in 
 Plate II., each showing peculiarities of fructification. Their 
 beautiful leaf-like fronds are either simple, lobed, or 
 curiously pinnate or feathered. The Floridese of warmer 
 climates exhibit most elegantly formed reticulated fronds, 
 as may be seen on reference to the late Dr. Harvey's last 
 great work, " Phycologia Australica." 
 
 In the plant which results from the germination of the 
 aggregate zoospores of Vaucheria, a genus of Siphonaceae 
 (Plate I. fig. 23), Kaisten has observed that on those 
 filaments which come in contact with the atmosphere, 
 are formed organs of a peculiar structure, which have 
 the appearance of nipple or egg-shaped buddings-out 
 of the cell-wall, distributed in pairs along the whole 
 course of the older filaments ; one elongates and curves 
 round to meet its fellow, which is seen to swell out 
 into a globular form; finally conjugation takes place, 
 preceded, however, by the conversion of the green con- 
 tents of the tubular organ into oil globules. If the fila- 
 ments be gathered at a favourable period, and cultivated 
 in a vessel of water well exposed to the light, the blind 
 ends, or ramifications of the filaments, are found densely 
 filled with green contents, appearing to be almost black ; 
 if these ends be watched early in the morning, a remark- 
 able series of changes is seen to occur in them when 
 about to produce gonidia, and, ultimately, they escape 
 in a peculiar way from the filament. The admirable essays 
 of Unger, Nageli, and Pringsheim on the process of theii 
 reproduction might be consulted with advantage. 
 
DKSMIDIACE.*:, DIATOMACE.E, ALG.K. 
 
VOLVOX GLOBATOR. 
 
 275 
 
 A fresh-water alga of singular beauty and interest to 
 the microscopist is the Volvox globator. This little cell 
 eo well known to the older observers as the globe- 
 animalcule, or revolving-cell, is represented in fig. 145, 
 Nos. 1, 2, 3, and Plate I. No. 15. These revolving globular 
 bodies were for a very long time classed with the lower 
 forms of animal life, and there remained for the micro- 
 chemical investigator of the present time to settle the per- 
 plexing question, and assign to them a place among plants. 
 .Leeuwenhbek first perceived the motion of what he 
 termed globes, "not more than the 30th of an inch in 
 
 diameter, rolling through 
 water; and judged them to 
 be animated." These globes 
 are s.tudded with innumerable 
 minute green spots, each of 
 which is seen to be a perfect 
 cell, about the 3,500th part of 
 an inch in size, with a nucleus 
 and two active cilia attached. 
 The whole are bound together 
 by threads forming a beautiful 
 net- work. Within the globe 
 busy active nature is at work 
 carefully providing a continu- 
 ance of the species; and from 
 six to twenty little bright- 
 green spheres have been found 
 enclosed in the larger trans- 
 parent case. As each Mttle 
 cell arrives at maturity, the 
 parent cell enlarges, and 
 
 i. roivox, just before the young burst ultimately bursts asunder, 
 : Bunching tprth its offsprii^ 
 4, to seek an independent exi > 
 ^nce. Both older and 
 younger spheres possess openings through which the water 
 freely flows, affording food and air to the wonderfully 
 constructed little being. 
 
 Dr. Carpenter believes, "The Volvocinece, whose vegetable 
 nature has been made known to us by observation of cer- 
 T 2 
 
 Fig. 151. 
 
 3, Doddium davutum. 
 
276 THE MICROSCOPE. 
 
 tain stages in the history of their lives, are but the motile 
 forms (Zoospores) of some other plants, whose relation to 
 them is at present unknown." Professor Williamson, 
 having carefully examined the Volvox globator, says : 
 " That the increase of its internal cells is carried on in a 
 manner precisely analogous to that of the algse; that 
 between the outer integument and the primordial cell- wall 
 of each cell, a hyaline membrane is secreted, causing the 
 outer integument to expand; and as the primordial cell- 
 wall is attached to it at various points, it causes the inter- 
 nal colouring- matter, or endochrome, to assume a stellate 
 form (see Plate I. No. 15), the points of one cell being in 
 contact with those of the neighbouring cell, these points 
 forming at a subsequent period the lines of communication 
 between the green spots generally seen within the full- 
 grown Volvox." Cilia can be distinctly seen on the outer 
 edge of the adult Volvox ; by compressing and rupturing 
 one, they may even be counted. Professor Busk has been 
 able to satisfy himself, by the addition of the chemical 
 test iodine, of the presence of a very minute quantity of 
 starch in the interior of the Volvox, which he considers 
 as conclusive of their vegetable character. A singular 
 provision is made in the structure of the gem mules, con- 
 sisting of a slender elastic filament, by which each is at- 
 tached to the parent cell- wall : at times it appears to thrust 
 itself out, as if in search of food ; it is then seen quickly to 
 recover its former nestling-place by contracting the tether. 
 It is impossible not to recognize the great similarity 
 between the structure of Volvox, and that of the motile 
 cell of Protococcus pluvialis. The influence of re-agents 
 will sometimes cause the connecting processes of the young 
 cells as in Protococcus, to be drawn back into the central 
 mass, and the connecting threads are sometimes seen as 
 double lines, which seem like tubular prolongations of a 
 consistent membrane. At other times they appear to be con- 
 nected by star-like prolongations to the parent cell, Plate I. 
 No. 15, presenting an almost identical appearance with 
 Pediastrum pertusum. Mr. Busk says that the body 
 designated by Ehrenberg Splwerosira volvox is an ordinary 
 volvox in a different phase of development; its only 
 marked feature of dissimilarity being that a large proper- 
 
VOLVOCINEJ5. 277 
 
 tion of the green cells, instead of being single, are very 
 commonly double or quadruple ; and the groups of ciliated 
 cells thus produced, form by their aggregation discoid 
 bodies, each furnished with a single cilium. These clusters 
 separate themselves from the primary sphere, and swim 
 forth freely under the forms which have been designated 
 Uvella and Syncrypta by Ehrenberg. According to Mr. 
 Carter, however, Splwerosira is the male or spermatic 
 form of Volvox ylobator. Dr. Braxton Hicks believes that 
 he has seen the young volvox pass into an amaboid state ; 
 he observes : "Towards the end of autumn the endochrome 
 mass of the volvox increases to nearly double its ordinary 
 size, but instead of undergoing the usual subdivision, so 
 as to produce a macro-gonidiurn, it loses its colour and 
 regularity of form, and becomes an irregular mass of 
 colourless protoplasum, containing a number of brownish 
 granules." (Plate I. No. 16.) 
 
 The final change and ultimate destination of these 
 curious amoeboid bodies have not as yet been made out ; 
 but from Dr. Hick's previous observation, made on similar 
 bodies developed from the protoplasmic contents of the 
 cells of the roots of mosses, " which in the course of two 
 hours become changed into ciliated bodies," he thinks it 
 very probable that this is designedly the way in which 
 these fragile structures are enabled to retain life, and to 
 resist all the varied external conditions, such as damp, 
 dry ness, and rapid alternations of heat and cold. 1 
 
 (1) We have had volvox under the microscope for several months, towards the 
 end of summer and throughout the autumn, and made more than a hundred 
 examinations, without having once seen the remarkable change described by 
 Dr. Hicks in the Quarterly Jour. Micros. Science, voL viiL p. 96, 1862. Never- 
 theless, as Mr. Archer observes : "If this reasoning be correct, then contrac- 
 tility, amoeboid contractility for I can find no more comprehensive and expressive 
 single aljective must be accepted as an inherent quality or characteristic, 
 occasionally more t,r less vividly evinced, of the vegetable cell-contents, and 
 this in common with the animal; in other words, that the nature of the proto- 
 plasm in each is similar, as has indeed, as is well known, been urged befoie on 
 grounds not so strong ; thus reserving Siebold's doctrine, tha' this very con- 
 tractility formed the strongest distinction between animals and plants, as he 
 assumed it to be present in the former and absent in the latter of the two 
 kingdoms of the organic world. Therefore, an organism whose known structural 
 affinities, and whose mode of growth and of ultimate fructification point it out 
 as truly a plant, but of which, fiowever, certain cells may for a time assume a 
 contractile, even a locomotive, quasi-rhizopodous state,inust not by any means 
 on thia latter account alone be assumed as even temporarily belonging to the 
 animal kingdom, or as tending towards a mutation of its vegetable nature. 
 And from this it of course follows that an organism whose structural affinities 
 and reproduction are unknown, but which may possibly present an actively 
 
278 THE MICROSCOPE. 
 
 Desmidiacece. A remarkably beautiful family of confer- 
 void algae, the most distinctive characteristics of the species 
 being their bilateral symmetry. Each frustule is, however, 
 a perfect unicellular plant, with a homogeneous structureless 
 membrane, enclosing a cellular skeleton filled with chloro- 
 phyll. Four modes of reproduction have been observed in 
 the desmids, and many points still remain to be cleared 
 up. Braun remarks of the products of conjugation, " that 
 they do not pass, like the swarming-cells of the Palmellacece 
 and the reproductive cells of the Diatomacese, directly and 
 by uninterrupted growth into the primary generation of 
 the new vegetative series, but persist for a long time in a 
 condition of rest, during which, excepting as regards im- 
 perceptible internal processes, they remain wholly un- 
 changed. To distinguish these from the germ- cell (gonidia) 
 I shall call them seed-cells (spores). Certain early condi- 
 tions observed in Closterium and Euastrum, namely, families 
 of unusually small individuals, enclosed in transparent, 
 colourless vesicles, render it even probable that in certain 
 genera of this family a number of individuals are produced 
 from one spore, by a formation of transitory generations 
 occurring already within the spore." * 
 
 contractile, even locomotive power, need not on this latter account be assumed 
 as therefore necessarily an animal. In the former category fall the Volvocinacea? 
 and Rhisidium ; in the latter category Eiiglena and its allies, the so-called 
 Astasiaean Infusoria, suggest themselves ; and these must of course wait until 
 their reproduction and history are better known before we can feel satisfied as 
 to their true position ; yet it seems highly probable that these will presently, if 
 they do not even now, take their place amongst admitted plants. 
 
 " Several writers have, indeed, from time to time, put forward the (now, I 
 think, generally accepted) view that the protoplasm of the vegatable and the 
 sarcode of the animal cell are identical in nature ; and, in seeking for analogies 
 as regards contractility in the vegetable protoplasm as compared with the 
 animal, and as demonstrative thereof, special attention has been directed to 
 several of the now familiar phenomena displayed by certain vegetable cells. 
 Such are the vibratory movements of ciliae, and drawing in of these, the circula- 
 tory movements of the cell contents, as in the hairs of the Tradescantia, &c., the 
 contractile vacuole in Gonium, Volvox, <fec., and so forth. But while these are, 
 I think, unquestionably to a considerable, but more limited extent, manifesta- 
 tions of the same phenomenon, it seems to me that none of these cases present 
 so exact an analogy, strongly as they may indicate it, with the rhizopodous con- 
 tractility as do the amoeboid bodies of Stephanosphara, of Volvox, of the 
 Moss-radicles, and of llhisidium. The amoeboid bodies of Stephanosphaera seem 
 to display this rhizopodous contractility in greatly the most marked or ex- 
 aggerated degree, as their vigorous and energetic power of locomotion indicate : 
 in them, and indeed in those of Volvox, the Moss, and Rhisidium, the pseudo- 
 podal processes and their mode of protrusion and withdrawal, the flow of the 
 granules, and the locomotion of the whole body, were in all respects analogous 
 to the similar phenomena evinced by a true amoeba." Wm. Archer, Quarterly 
 Journ. Micros. Science, vol. v. p. 185. 
 
 (1) " The Phenomenon of Rejuvenescence in Nature." 
 
DKSMIDIACEJB. 279 
 
 Reproduction both by conjugation and subdivision 
 variously modified, is common to all the families of 
 Desmidiacese ; and in the Zygnemaceae, which have a 
 close relation to them, the phenomena of conjugation are 
 very well known. In Staurocarpus we have those re- 
 markable quadrate spores formed in the cross branch, 
 produced by conjugation. In Spirogyra the union of two 
 cells belonging to the opposite filaments takes place by the 
 expansion of one side of each, so as to form a papilla or 
 short rounded-off tube (see fig. 145). The ends of the two 
 projections then come into contact, become slightly flattened, 
 then pressed together, and finally united. The double wall 
 formed by their union dissolves, or is broken through, so 
 that a free passage is established between the two cells. 
 Upon this, the whole of the chlorophyll, previously 
 arranged round the inside of each of tl.e cells, becomes a 
 confused mass, which soon forms itself either in the cavity 
 of one of them, or in the connecting canal, into a globular 
 or oval spore invested with the colourless cellulose mem- 
 brane shown in one of our drawings of Penium (Fig. 155). 
 In Closterium conjugation takes place in a somewhat 
 similar manner, represented at No. 25, although it is 
 quite clear that if the formation of germs by conjugation 
 were the only provision for the reproduction of a species, 
 all must disappear, inasmuch as the conjugation and 
 consequent destruction of a pair of Closteria for the 
 formation of one new plant will ultimately destroy the 
 species. 1 Another mode, however, that of subdivision, 
 appears to be designed as an effectual safeguard against 
 such a possible extinction. Mr. Lobb has observed this 
 process take place in Micrasterias denticulate, (Plate II. 
 tig. 30), in the course of three hours and a half. The small 
 hyaline hemisphere, put forth in the first instance from each 
 frustule, enlarges with the flowing in of the endochrome ; it 
 then undergoes progressive subdivision at its edges, first 
 into three lobes, then into five, then into seven, then into 
 thirteen, and finally at the time of its separation, acquires 
 the characteristic notched outline of its type, being only 
 distinguishable from the older half by its smaller size. 2 
 
 (1) In certain species of Closterium the act of conjugation gives origin to two 
 sporangia. (2) E. G. Lobb, Trant. Micro*. Soc. N.8. vol. L, 1861. 
 
THE MICROSCOPE 
 
 280 
 
 Desmidiacece. The once disputed question relating to 
 the vegetable nature of these cells received much valuable 
 elucidation from Mr. Ralfs, who gave to the world the 
 
 Fig. 152. 
 
 1, Ettattrum oblongum. 2, Micra<terias rotata. 3, Desmidium quadrangulatum. 
 4, Didymoprium Grevillii. 
 
 results of his laborious researches in his excellent work on 
 The British Desmidiece, published in 1848; and the con- 
 clusions arrived at by this painstaking author have been 
 generally accepted by men of science. The interest which 
 has so long attached to this topic will warrant us in 
 devoting some space to its consideration ; and we avail our- 
 selves for that purpose of Mr. Ralfs' labours, with a 
 recommendation to those of our readers who would 
 wish to familiarise themselves more completely with this 
 peculiar species, to consult the pages of the book above 
 referred to. 
 
 Desmidiacece are grass-green in colour, surrounded by a 
 transparent structureless membrane, a few only having 
 their integuments coloured ; they are all inhabitants of 
 fresh water. Their most obvious peculiarities are the 
 beauty and variety of their forms and their external mark- 
 ings and appendages ; but their most distinctive character 
 is their evident division into two or more segments. Each 
 cell or joint in the Desmidiacece generally consist of two 
 symmetrical valves or segments ; and the suture or line of 
 junction is in general well marked. The multiplication of 
 the cells by repeated transverse division is full of interest, 
 
DESMIDIACEJB. 
 
 281 
 
 both on account of the remarkable manner in which it 
 takes place, and because it unfolds the nature of the pro- 
 cess in other families, and furnishes a valuable addition to 
 our knowledge of their structure and physiology. 
 
 Pig. 153. 
 
 5, Micrcwteria*, sporangium of. 6, Didymoprium Borreri. 7, Cosmarium Ralftii. 
 8, Staurattrum hirsutum. 
 
 The compressed and deeply-constricted cells of Euastrum 
 offer most favourable opportunities for ascertaining the 
 manner of their division ; for although the frond is really 
 a single cell, yet this cell in all its stages appears like two, 
 the segments being always distinct, even from the com- 
 mencement. As the connecting portion is so small, and 
 necessarily produces the new segments, which cannot arise 
 from a broader base than its opening, these are at first 
 very minute ; though they rapidly increase in size. The 
 segments are separated by the elongation of the connecting 
 tube, which is converted into two roundish hyaline lobules. 
 These lobules increase in size, acquire colour, and gradually 
 put on the appearance of the old portions. Of course, aa 
 they increase, the original segments are pushed further 
 asunder, and at length are disconnected, each taking with 
 it a new segment to supply the place of that from which 
 it has separated. 
 
 It is curious to trace the progressive development of 
 tl e new portions. At first they are devoid of colour, and 
 
282 
 
 THE MICROSCOPE. 
 
 have much the appearance of condensed gelatine ; but as 
 they increase in size, the internal fluid acquires a green 
 tint, which is at first very faint, but soon becomes darker ; 
 
 Fig. 154. 
 
 7, Sphcerozosma vertebratum. 8, 9, Xanthidive. 10, X. armatum. 11, Cosmo-- 
 rium crenatum. 13, 17, Sporangia of Cosmarium. 14, X. fasiculatum. 19, 
 Arthrodesmus convergens. 15, Staurastrumtumidum. 16, Staurastrumdttitatum. 
 
 at length it assumes a granular state. At the same time 
 the new segments increase in size, and obtain their normal 
 figure ; the covering in some species shows the presence 
 of puncta or granules. In Xanthidium and Staurastrum 
 the spines and processes make their appearance last, 
 beginning as mere tubercles, and then lengthening until 
 they attain their perfect form and size, armed with seta3 ; 
 but complete separation frequently occurs before the whole 
 process is completed. This singular process is repeated 
 again and again, so that the older segments are united 
 successively, as it were, with many generations. When 
 the cells approach maturity, molecular movements may 
 be at times noticed in their contents, precisely similar to 
 what has been described by Agardh and others as occurring 
 in Confervce. This movement has been aptly termed a 
 swarming. All the Desmidiacece are semi-gelatinous. In 
 some the mucus is condensed into a distinct and well-defined 
 
DESM1DIACEJE. 
 
 283 
 
 hyaline sheath or covering, as in Didymoprium Gremllii 
 and Staurastrum tumidum ; in others it is more attenu- 
 ated, and the fact that it forms a covering is discerned 
 
 Fig. 155. 
 
 21. Peiit-.im. 24, Pediastrum biradiatum. 25, Clostvrium, showing conjugation 
 or sell-tli vision. 27, Penium Jenneri. 28, Aptogonum dtsmidium. 29, Pedias- 
 trum jiccticum. 30, Ankistrodesmus falcatus. 33, Conjugation of Penium 
 mnr^aritaceuin,. 34. SpircUemia. 35, Closterium. 
 
 only by its preventing the contact of the coloured cells. 
 In general its quantity is merely sufficient to hold the 
 fronds together in a kind of filmy cloud, which is dispersed 
 by the slightest touch. When they are left exposed by 
 the evaporation of the water, this mucus becomes denser, 
 and is apparently secreted in larger quantities, to protect 
 them from the effects of drought. Meyen states, " that the 
 large and small granules contain starch, and were some- 
 times even entirely composed of it ; " and " in the month 
 of May he observed many specimens of Closterium in 
 which the whole interior was granulated; these grains gave 
 with iodine the beautiful blue colour, indicative of the 
 presence of starch." 1 
 
 (1) The test for starch can be easily applied, and so remove any doubt that 
 may exist. It is only necessary to bear in mind that unless granular matter 
 
284 THE MICROSCOPE. 
 
 " Did we trust solely to the eye, we should indeed be 
 very liable to pronounce these variable and beautiful forms 
 as belonging to animals rather than vegetables. All 
 favours this supposition. Their symmetrical division into 
 parts ; the exquisite disc-form, finely cut and toothed 
 Micrasterias ; the lobed Euastrum; the Cosmarium, glit- 
 tering as it were with gems ; the Xanthidium, armed with 
 spines ; the scimitar-shaped Closterium, embellished with 
 striae ; the Desmidium, resembling a tape- worm ; aud the 
 strangely insect-like Staurastrum, sometimes furnished 
 with arms, as if for the purpose of seizing its prey ; all 
 these characteristics appear to a superficial observer to 
 belong rather to the lowest forms of animal, than vege- 
 table life." Another indication Dr. Bailey adduced, by 
 rendering apparent their power of motion ; taking a por- 
 tion of mud covered with Closteria, and placing it in 
 water exposed to light ; after a time, it will be seen that 
 if the Closteria are buried in the mud, they work their 
 way to the surface, and cover it with a green stratum : 
 this is no doubt owing to the stimulus light exerts upon 
 all matter, although at first appearing very like a volun- 
 tary effort. Another is atforded by their retiring beneath 
 the surface when the poc. ". dry up. Mr. Ralfs states that 
 he has taken advantage of this circumstance to obtain 
 specimens less mingled with foreign matter than they 
 would otherwise have been. 
 
 During the summmer of 1854 the Rev. Lord S. G. 
 Osborne drew our attention to the economy of an interest- 
 ing specimen of this family, the Closterium Lunula; after 
 many careful investigations he came to the conclusion 
 that the membrane of the endochrome, both on its inner 
 and outer surface, is ciliated. 
 
 In the Closterium Lunula, we have ascertained that the 
 best view of its circulation is obtained by the use of 
 strong daylight, or sunlight transmitted through coloured 
 glass, or such a combination of tinted glass as thnt 
 
 be seen in the interior of the coll, stm-ii cannot be present. A small quantity of 
 diluted tincture of iodine may be appiie.!, removing the free iodine by the aid of 
 heat, occasionally adding a li tie water to facilitate its removal. Tim also will 
 assist in the removal of the brownish slain which at first obscures the charac- 
 teristic purple tint; and then, by applying the highest power of the microscope, 
 the peculiar colour of the purple iodide of starch will in general be perceived. 
 
DESM1DIAC. 
 
 285 
 
 proposed by Mr. Rainey, and adapted to a l-4th achro- 
 matic condenser ; with which must be used a l-8th ob- 
 ject-glass. The Gillett's condenser, or parabolic reflector, 
 will do equally well it used with a 1-Sth objective. In 
 diagram A, tig. 156, a specimen of the 0. Lunula, as seen 
 
 Fig. 156. Clotteria Lunula. 
 
 with the above arrangement of microscopic power, and a 
 deep eye-piece, the cilia are in full action along the edge of 
 the membrane which encloses the endochrome ; and also, 
 but not so distinctly, along the inside of the edges of the 
 frond itself. Their action is precisely the same as that 
 in the branchiae of the mussel : there is the same wavy 
 motion; and as the water dries up between the glasses 
 in which the specimen is enclosed, the circulation becomes 
 fainter, and the cilia are seen with more distinctness. 
 
 In diagram A, a line is drawn at 6 to a small oval mark; 
 these exist at intervals, and more or less in number over 
 the surface of the endochrome itself, beneath the mem- 
 brane which invests it. These seem to be attached by 
 email pedicles, and are usually seen in motion on the spot 
 to which they are thus fastened ; from time to time they 
 
^00 THE MICROSCOPE. 
 
 break away, and are carried by the circulation of the fluid, 
 which works all over the endochrome, to the chambers at 
 the extremities \ there they join a crowd of similar bodies, 
 each in action within those chambers, when the specimen 
 is a healthy one. 
 
 The circulation, when made out over the centre of the 
 frond, for instance at a. is in appearance of a wholly 
 different nature from that seen at the edges. In the 
 latter, the matter circulated is in globules, passing each 
 other, in distinct lines, in opposite directions ; in the cir- 
 culation as seen at a, the streams are broad, tortuous, of 
 far greater body, and passing with much less rapidity. To 
 see the centre circulation, use a Gillett's illuminator and 
 the l-8th power ; work the fine adjustment so as to bring 
 the centre of the frond into focus, then almost lose it by 
 raising the objective ; after this, with great care, work the 
 milled head till the dark body of the endochrome is made 
 out ; a hair's-breadth more adjustment gives this circula- 
 tion with the utmost distinctness, if it is a good specimen. 
 It will be clearly seen, by the same means, at all the 
 points where the spaces are put ; and from them may be 
 traced, with care, down to both extremities. 
 
 The endochrome itself is evidently so constructed as to 
 admit of contraction and expansion in every direction. At 
 times the edges are in semi-lunar curves, leaving uninter- 
 rupted clear spaces visible between the green matter and 
 the investing membrane ; at other times, the endochrome 
 is seen with a straight margin, but so contracted as to 
 leave a well-defined transparent space along its whole edge, 
 between itself and the exterior case. It is interesting to 
 keep changing the focus, that at one moment we may see 
 the globular circulation between the outer and inner case, 
 and again the mere sluggish movement between the inner 
 case and the endochrome. 
 
 At B is given an enlarged sketch of one extremity of 
 a C. Lunuia. The arrows within the chamber pointing to 
 b, denote the direction of a very strong current of fluid, 
 which can be detected, and occasionally traced, most dis- 
 tinctly ; it is acted upon by cilia at the edges of the 
 chamber, but its chief force appears to come from some 
 impulse given from the very centre of the endochrome. 
 
DESMIDIACEA 287 
 
 The fluid is here acting in positive jets, that is, with an 
 almost arterial action ; and according to the strength with 
 which it is acting at the time, the loose floating bodies are 
 propelled to a greater or less distance from the end of the 
 endochrome ; the fluid thus impelled from a centre, and 
 kept in activity by the lateral cilia, causes strong eddies, 
 which give a twisting motion to the free bodies. The 
 line a, in this diagram, denotes the outline of the mem- 
 brane which encloses the endochrome ; on both sides of 
 this cilia may be detected. The circulation exterior to it 
 passes and repasses it in opposite directions, in three or 
 four distinct courses of globules ; these, when they arrive 
 at c, seem to encounter the fluid jetted through an 
 aperture at the apex of the chamber ; which disperses them 
 so much, that they appear to be driven, for the most part, 
 back again on the precise course by which they had 
 arrived. Some, however, do enter the chamber ; occasion- 
 ally, but very rarely, one of the loose bodies may be seen 
 to escape from within, and get into the outer current, it is 
 then carried about until it becomes adherent to the side of 
 the frond. 
 
 With regard to the propagation of the C. Lunula, we 
 have never seen anything like conjugation; but we have 
 repeatedly seen what the reverend gentleman has so well 
 described increase by self-division. 
 
 Observe the diagram D ; but for the moment suppose 
 the two halves of the frond, represented as separate, 
 to just overlap each other. Having watched for some 
 time, the one half may be seen to remain passive ; the 
 other has a motion from side to side, as if moving on an 
 axis at the point of juncture : the separation then becomes 
 more and more evident, the motion more active, until at 
 last with a jerk one segment leaves the other, and they 
 are seen as drawn. It will be observed, that in each 
 segment the endochrome has already a waist ; but there 
 is only one chamber, which is the one belonging to the 
 one extremity of the original entire frond. The globular 
 circulation, for some hours previous to subdivision, and for 
 some few hours afterwards, runs quite round the obtuse 
 end of the endochrome a, by almost imperceptible 
 degrees; from the end of the endochrome symptoms of 
 
288 THE MICROSCOPE. 
 
 an elongation of the membranous sac appear, giving a 
 semi-lunar sort of chamber ; this, as the eudochrome 
 elongates, becomes more denned, until it has the form and 
 outline of the chamber at the perfect extremity. The 
 obtuse end 6 of the frond is at the same time elongat- 
 ing and contracting; these processes go on ; in about five 
 hours from the division of the one segment from the other, 
 the appearance of each half is that of a nearly perfect 
 specimen, the chamber at the new end is complete, the 
 globular circulation exterior to it becomes affected by the cir- 
 culation from within the said chamber; and, in a few hours 
 more, some of the free bodies descend, become exposed to, 
 and tossed about in the eddies of the chamber, and the 
 frond, under a l-6th power, shows itself in all its beau- 
 tiful construction. E is a diagram of one end of a C. didij- 
 motocum, in which the same process was noticed. 
 
 The Euasti"um Didelta is well worthy 
 
 of attention, as well as many other species, 
 
 the Xanthidium Penium, Docidium, <kc. 
 The Arthrodesmus Incus has a very 
 
 beautiful hyaline membrane stretching 
 ^ from point to point, cut at the edges, 
 
 something like the Micrasterias. This is 
 represented at fig. 157. 
 
 The Mode of Finding and Taking Desmidiacece. As 
 the difficulty of obtaining specimens is very great, it will 
 materially assist the efforts of the microscopist to know 
 the method adopted by Mr. Ralfs, Mr. Jenner, and Mr. 
 Thwaites. " In the water the filamentous species resemble 
 the Zygnemata ; but their green colour is generally paler 
 and more opaque. When they are much diffused in the 
 water, take a piece of linen, about the size of a pocket 
 handkerchief, lay it on the ground in the form of a bag, 
 and then, by the aid of a tin box, scoop up the water 
 and strain it through the bag, repeating the process as 
 often as may be required. The larger species, Euastrum, 
 Micrqsterias, Closterium, &c., are generally situated at the 
 bottom of the pool, either spread out as a thin gelatinous 
 stratum, or collected into finger-like tufts. If the finger 
 be gently passed beneath them, they will rise to the sur- 
 face in little masses, and with care may be removed and 
 
DESMIDIACELB. 289 
 
 straiiied through the linen as above described. At first 
 nothing appears on the linen except a mere stain or a little 
 dirt ; but by repeated fillings-up and strainings a consi- 
 derable quantity will be obtained. If not very gelatinous, 
 the water passes freely through the linen, from which the 
 specimen can be scraped with a knife, and transferred to a 
 smaller piec-e ; but in many species the fluid at length 
 does not admit of being strained off without the employ- 
 ment of such force as would cause the fronds also to pass 
 through, and in this case it should be poured into bottles 
 until they are quite full. But many species of Stawas- 
 trum, Pediastrum, <fec., usually form a greenish or dirty 
 cloud upon the stems and leaves of the filiform aquatic 
 plants; and to collect them requires more care than is 
 necessary in the former instances. In this state the 
 slightest touch will break up the whole mass, and disperse 
 it through the water : for securing them, let the hand be 
 passed very gently into the water and beneath the cloud, 
 the palm upwards and the fingers apart, so that the leaves 
 or stem of the inverted plant may lie between them, and 
 as near the palm as possible ; then close the fingers, and 
 keeping the hand in the same position, but concave, draw 
 it cautiously towards the surface ; when, if the plant has 
 been allowed to slip easily and equably through the fingers, 
 the Desmidiacece, in this way brushed off, will be found 
 lying in the palm. The greatest difficulty is in withdraw- 
 ing the hand from the surface of the water, and probably 
 but little will be retained at first ; practice, however, will 
 soon render the operation easy and successful. The con- 
 tents of the hand should be at once transferred either to a 
 bottle, or, in case much water has been taken up, into the 
 box, which must be close at hand ; and when this is full, 
 it can be emptied on the linen as before. But in this case 
 the linen should be pressed gently, and a portion only of 
 the water expelled, the remainder being poured into the 
 bottle, and the process repeated as often as necessary." 
 
 When carried home, the bottles will apparently contain 
 only foul water ; but if it remain undisturbed for a few 
 hours, the Desmidiacece will sink to the bottom, and most 
 of the water may then be poured off. If a little filtered 
 rain- water be added occasionally, to replace what has been 
 u 
 
290 THE MICROSCOPE. 
 
 drawn off, and the bottle be exposed to the light of the sun, 
 the Dewnidiacece will remain unaltered for a long time. 
 
 fungi.-^-This interesting class of cellular flowerless 
 plants are chiefly microscopic, many requiring a high magni- 
 fying power to determine their peculiarities of structure. 
 They abound in damp places, among decaying and decayed 
 vegetable and animal matters, everywhere, and in almost 
 every place. The structure of all Fungi exhibits a well de- 
 nned separation into two parts, a mycelium (thallus) jointed 
 and branched, forming a kind of cottony filamentous mass, 
 and a reproductive spore or fruit, which, although exceed- 
 ingly minute, differs somewhat in appearance under the 
 microscope. The "spawn" used for planting mushroom 
 beds is composed of mycelium, and may be readily obtained 
 for examination (fig. 188,. No. 19). The dust- like powder 
 of any of the moulds or mildew when sprinkled on a slip 
 of glass and kept under a bell glass over water, will soon 
 throw out filaments and spores in all directions. 
 
 De Bary's observations show that resting-spores are not 
 peculiar to the algse ; for he found them in two genera ot 
 fungi, and Tulasne ascertained their production in Perono- 
 sporce, many of which are parasitic, as P. parasitica, a 
 species found on the cabbage and turnip leaf, as well as 
 on the shepherd's-purse, Capsella bursapastoris. For the 
 growth of P. infestans, the potato mould, the exclusion 
 of light seems to be needful, and it is easy to conceive 
 how the spores, washed down to the tuber during heavy 
 rains, throw out germinating threads, which easily pene- 
 trate the thick cuticle of the potato, and quickly produce a 
 murrain. 
 
 The Rev. M. J. Berkeley, our English authority on 
 Fungi, says : " The genus Cystopus comprises those para- 
 sitic fungi amongst the Uredines which are remarkable for 
 their white spores. Till the resting-spores of the different 
 species were ascertained, it was almost impossible to find 
 good distinctive characters : one species at least, Cystopus 
 candidus, is to be found everywhere on the common 
 shepherd's-purse, and often accompanied by Peronospora 
 parasitica. It is also frequent on the cruciferse : the aero- 
 spores, or gonidia, which spring from the swollen threads 
 of the mycelium, form necklaces, as in oidium, the joints 
 
PARASITIC FUNGI. 291 
 
 of which give rise to zoospores, as first observed "by Pre- 
 vost, in 1807. Like those of Peronospora, they move 
 about in water by means of two lash-like appendages, and 
 there germinate. When resting on the leaves of a plant, 
 they make their way by means of a germinating thread 
 into its subjacent tissues, and throw out little suckers. 
 The branched mycelium gives off sporangia and antheridia, 
 exactly as in Peronospora ; when ripe, the sporangia are 
 strongly warted. They fall, doubtless, with the leaves to 
 the ground, where they remain till a fitting season arrives 
 for their development. The provision made for the rapid 
 development of these parasites and for the preservation of 
 their species is truly marvellous, and sufficiently accounts 
 for the difficulty of extermination and their apparently 
 sudden dispersion, especially in wet weather." 
 
 De Bary's observations on the germination of Uromyces 
 appendicidatus are interesting, inasmuch as they show that 
 the sporidia produce a mycelium, from which springs in 
 succession 1st, spermogonia; 2dly, peridia, producing 
 chains of orange-coloured fruit, or, in other words, an 
 jEcidium ; and 3dly, the original fruit of Uromyces, ac- 
 companied by the more simple fruit commonly called 
 uredo, and now called Mrafo-stylospores. The germination 
 of the fruit produced by the peridia, as well as that of 
 the wrafo-stylospores, produces, according to De Bary, 
 1st, Ure Jo-sty lospores, and 2d, the original Uromyces- 
 spores. Thus we see the Uromyces-spores passing through 
 the generations of promyceliurn, sporidia, and mycelium 
 the latter producing successively the two different products, 
 spermogonia and aecidia, and ultimately the original fruit 
 of Uromyces, accompanied by the Uredo. The spermatia, 
 or contents of the spermogonia, never germinate ; but we 
 find the fruit of the aecidia, and also of the Uredo, repro- 
 ducing first the Uredo itself, and subsequently the original 
 fruit of Uromyces. Other interesting points, noticed bv 
 the same author, are, " that not only has each species of 
 parasite a certain special nutrient plant, but that in certain 
 Uredines with multiple fruit and alternate generations 
 each sort of reproductive organ buries its germ in a dif- 
 lerent nutrient plant ; and that the vegetation of the para- 
 site is the cause of the disease." 
 u2 
 
292 THE MICROSCOPE. 
 
 De Bary has also earned out a series of experiments 
 which go far to satisfy him that the sporidia of Puccinia 
 qraminis germinate on the leaves of Herberts, and that the 
 ^Ecidium of the Berberis (Plate I. No. 22) is a stage in the 
 cycle of development of Puccinia. Thus, whilst in most 
 Uredines the entire development is carried out upon one 
 and the same nutrient plant, the alternate generations in 
 Puccinia graminis require a change of host. This is a 
 state of things well understood now in the animal kingdom 
 in the Tseniae and Trematoda, but Puccinia graminis is, 
 we believe, the first of the parasitic fungi in which it has 
 been particularly ascertained. Another point of interest 
 is a confirmation of the supposed injurious effect of the 
 proximity of Berberis to corn, which has been denied. 
 De Bary further shows that Mucor mucedo (the common 
 mould) has three, if not four, different forms of fruit ; and 
 that the mould called Thamnidium by Link, or Ascophora 
 elegans by Corda, and the mould described by Berkeley as 
 Botrytis Jonesii, and made into a new genus by Fresenius, 
 under the name of Chcetocladium, are only varieties of the 
 fruit of Mucor mucedo. Also that yeast, Achyla, Sapro- 
 legnia, and Entomophthora or Empusa, are identically the 
 same as Mucor mucedo, consequently that a large reduction 
 is needed in the genera of the mucorini. 
 
 The main interest, however, of De Bary's paper on the 
 fructification of the Ascomycetes, consists in observations 
 on Erysiphe Cichoracearum, &c., in which the author 
 traces the origin of the peritheciuin, from its earliest state 
 up to the formation of the single ascus and spores. He 
 notices two cells as being always present and visible from 
 the earliest period, one of which he conjectures may be 
 the female, and the other the antheridium or male organ. 
 He says that the cell, by the division of which the ascus 
 and its coating are formed, only develops itself when it 
 has been in contact with the antheridium ; and he con- 
 siders it very probable that impregration is effected by 
 such contact, and that the perithecium of Erysiphe (ex- 
 cepting the outer wall) is the product of such impreg 
 nation. 
 
 De Bary's paper on parasitic fungi was, it appears, 
 undertaken with a view to contribute to the solution of 
 
PARASITIC FUNGI. 293 
 
 the question as to their origin ; and he concludes that 
 endophytes are not produced from the metamorphosed 
 substance of diseased plants, but that they originate from 
 germs which penetrate healthy plants and develop a 
 mycelium. In the course of his investigations he notices 
 the occurrence in the genus Cystopus of organs similar to 
 those long since discovered by Tulasne in Peronospora, 
 which have been called Oogonia. He observes that rami- 
 fications perform the functions of antheridia, or male 
 organs ; and he proceeds to describe the production by the 
 oospores (or impregnated contents of the oogonia) of active 
 zoos pores, similar to those produced by the ordinary spores 
 of Cystoptts. Dr. De Bary states that these zoospores, after 
 remaining active for three or four hours, lose their cilia and 
 power of motion, assume a cellulose covering, and ger- 
 minate. He adds that the germ-filaments enter readily 
 by the stomates and leaves of the nutrient plant, but that 
 those filaments only become developed which enter the 
 stomates of cotyledons. In Peronospora the development 
 of the antheridia, oogonia, and oospores is said by De Bary 
 to be the same as ia Cystopus ; and he gives particulars of 
 the mode of germination of the conidia, and remarks on 
 the growth of the parasite, which will be more profitably 
 studied in the paper itself. 
 
 Parasitic fungi, vegetable blights as they are commonly 
 called, have of late years become objects of earnest atten- 
 tion, on account both of the enormous damage done to our 
 growing crops, and also of the many curious facts in their 
 history which have been brought to light. Corn-blights 
 consist chiefly of mildew, Puccinia, smut, bunt, rust, or 
 red-robin, Uredo. Oidium is a common mildew ; Bo- 
 trytis another; sEcidium forms a kind of rust infecting 
 pear-trees, the peridia of which form a very pretty object 
 for the microscope. (Plate I. No. 22, JEcidium Berberidis.) 
 In the full-grown condition they appear as little cups filled 
 with reddish-brown powder (spores), and may be detected in 
 their earliest stages by the deformities they produce in the 
 structure of the plants infested, or by pale or' reddish spots 
 on the green surface, arising from the presence of the 
 fungus beneath. They are common on the coltsfoot, the 
 berberry, gooseberry, buckthorn, nettle, &c. Plate I. No. 19, 
 
294 THE MIOBOSCGPB. 
 
 .represents a vertical section of a leaf of black-currant, in- 
 fested with JEcidium grossularice ; its sperm ogonia are 
 seen on the surface, and the perithecia below. The family 
 Sphceriacei (No. 3, Plate I.), common enough on most 
 herbaceous stems, first seem to be little black spots, a; 
 when examined more closely are found to resemble little 
 brownish bottles, b, filled with rolls of spores. Other in- 
 structive specimens are 
 
 Cystopus candidus (Uredo olim), Crucifer White-rust; 
 conidia equal, globose ; membrane equal, ochraceous ; 
 oospores sub-globose, epispore yellowish-brown, with irre- 
 gular obtuse warts : warts solid. On shepherd's purse, 
 cabbage, and other Cruciferae : receptacle consisting of 
 thick branched threads ; conidia concatenate, at length 
 separating ; oospores deeply seated on the mycelium. 
 Phyllactinia guttata (Olim Erysiphe). Plate I. No. 9. 
 Hazel Blight ; amphigenous ; mycelium web-like, often 
 evanescent; conceptacles large, scattered, hemispherical, 
 at length depressed; appendages hyaline, rigid, simple; 
 sporangia 4-20, containing 2-4 spores. On leaves of haw- 
 thorn, hazel, ash, elm, &c. Aregma '(Phragniidium) bul- 
 bosum. Plate I. No. 20. Bramble Brand; hypogynous, 
 with a dull red stain on the upper surface; spores in 
 large tufts, 4-septate, terminal joint apiculate; peduncles 
 incrassated, and bulbous at the base. Puccinia variabilis, 
 Variable Brand ; sori amphigenous, minute, roundish, sur- 
 rounded by the ruptured epidermis, nearly black ; spores 
 variable, obtuse, cells often subdivided ; peduncle very 
 short. On leaves of dandelion. Puccinia buxi, Box Brand. 
 Plate I. No. 17. Sori sub-rotund, convex, and scattered; 
 spores brown, oblong, rather strongly constricted, lower 
 cell slightly attenuated ; peduncle very long. On both 
 surfaces of box leaves : spores uniseptate, supported on a 
 distinct peduncle. Plate I. No. 18. Trichobasis (Uredo 
 olim) senecionis, Groundsel- rust ; spots obliterated ; sori 
 solitary or regularly crowded ; sub-rotund and oval, on the 
 under surface, surrounded by the ruptured epidermis; 
 spores sub-globose, orange. On various species of groundsel : 
 spores free ; attached at first to a short peduncle, which 
 at length falls away. 
 
 It appears that at particular periods of the year the 
 
PARASITIC FUNGI. 
 
 295 
 
 atmosphere is, so to speak, more fully charged with the 
 various spores of fungi than it is at others. The spores of 
 the moulds aspergillus, penicillium, and pucdnia are per- 
 haps the most widely distributed bodies, and towards the 
 end of the hot weather, or about autumn time, they are 
 very abundant Among those who have taken them at this 
 period of the year, we must ever associate the name of the 
 Rev. Lord Godolphin Osborne, who first experimented in 
 this direction during the cholera visitation of 1854. He 
 exposed prepared slips of glass, slightly moistened with 
 glycerine, over cesspools, gully-holes, &c., near the dwell- 
 ings of those where the disease appeared, and caught 
 what he termed aerozoa chiefly minute germs and spores 
 of fungi A drawing made from one of these glasses 
 (Plate I. No. 13), exhibits spores almost identical with 
 those found on the human skin, &c. 
 
 From the year 1854 to the present time we have amused 
 ourselves by catching these floating atoms, and, so far as 
 we can judge, they are found eveiy where, and in and on 
 every conceivable thing, if we only look close enough for 
 them. Even the open mouth is an excellent trap ; of 
 this there is ample evidence, since we find on the delicate 
 membrane lining the mouth of the sucking, crying infant, 
 and on the Diphtheritic sore throat of the adult, the de- 
 structive plant Oidium albicans. The human or animal 
 stomach is invaded, and in a certain deranged condition we 
 find the Sarcina ventriculi, with its remarkable-looking 
 quaternate spores, its torulae, &c., seriously interfering with 
 the functions of this organ. 1 Torula dia-betica is another 
 of these destructive products found in the human bladder. 
 
 Fig. 158. Sarcina ventriculi. 
 
 (1) What part do tne fungi, or bacteria, play in the production of that fearful 
 scourge of the human race, cancer? is a question not ^infrequently asked sine* 
 
296 THE MICROSCOPE. 
 
 It is now more than a quarter of a century since Pro 
 fessor Owen first pointed out the vegetable nature of a 
 diseased growth found in the lungs of a Flamingo he 
 was dissecting. Soon after, Bassi discovered the vege- 
 table character of a disease which caused great devas- 
 tation among silkworms ; and, about the same time. 
 Schbnlein, of Berlin, was led to the detection of certain 
 cryptogamic vegetable formations in connexion with skin 
 diseases. 
 
 The Favus fungus is perhaps best known from its 
 having been the first to attract the attention of Schonlein. 
 It is commonly called cupped ringworm, or honeycomb 
 scall, but it is very rarely seen in this metropolis. The 
 crust is of a dingy yellow colour, and almost entirely 
 composed of the Achorion, mixed with epithelial scales 
 and broken hairs. When the fungus once establishes 
 itself, so fearful are its ravages, that in a very short space 
 of time the whole of the cutaneous surface, with the ex- 
 ception of the palms of the hands and soles of the feet, 
 becomes covered with it. As the spores penetrate the 
 hair-follicles they destroy the sheaths of the hairs, which 
 shrivel up and lose their colouring matter, and then break 
 off, leaving the surface bald. 
 
 Upon comparing the fermentation of the achorion 
 fungus with that of good healthy yeast, it will be seen to 
 be almost identical. In the first place, it is as actively 
 
 in the first edition of this book % (1854) we expressed a belief in "the fungoid 
 origin of cancer." Subsequent examinations of diseased structure more or less 
 tend to confirm this view ; it appears that in this disease we have superadded to 
 a fungoid growth " degraded germinal matter" which, by its entrance into the 
 circulation, produces a ferment and blood poisoning. The circular animal cell 
 degenerates, is converted into the ovoid or elongated vegetable cell, and ulti- 
 mately the structure, or some organ it may be, is changed into that remarkable- 
 looking caudate body, the typical cancer cell. This in some respects bears the 
 most perfect resemblance to certain spores of fungi, and to the yeast torulse. 
 As might be expected, its form is modified and its character more or less 
 changed by the peculiar kind of nourishment and condensed tissue in which it 
 is deposited and grows ; its powers of growth are, so to speak, perverted and 
 degraded, and then, as we see in other instances, it soon obtains a power of in- 
 definite multiplication, nnd destroys, not only the vitality of the organ, but the 
 individual. M. Davaii>e believes he has traced splenic disease in sheep to the 
 entrance into the blood oi bacterium-like bodies, and fungi; a zymotic disease 
 is caused by the ferment, and by the rapid growth of the fungi the life of the 
 animal is quickly sacrificed to the destroyer. 
 
 To mount specimens of fungi, separate them, and add a drop or two of spirit: 
 when this has evaporated, add a drop of glycerine solution, or balsam dissolved 
 in chloroform, and put on a glnss cover. If the balsam renders the asci too 
 transparent, use gelatine : no cells are required. 
 
YEAST DEVELOPMENT. 297 
 
 carried on by the former as by the latter. There is, how- 
 ever, just a slight difference in the size of the spores or 
 cells (Plate I. Nos. 7, 8, 11), those from yeast being the 
 larger and more clearly spherical, with a greater number 
 of reproductive spores, that is, cells with a single, clear, 
 nucleated cell in their interior, while others are filled 
 with a darker granular matter, having only a slight ten- 
 dency to coalesce or become filamentous; those from 
 achorion are for the most part ovoid, and very prone to 
 coalesce and produce elongated cells or torulae. With re- 
 ference to the slight difference in size, we must look upon 
 this as a matter of very little importance ; for to the pre- 
 sence of light in the one case, and its almost total exclu- 
 sion in the other, this difference, no doubt, is almost en- 
 tirely due. It would be more trustworthy if comparisons 
 of this kind could be made at the same stage of develop- 
 ment ; for be it remembered that yeast obtained from a 
 brewery is in a more favourable state, inasmuch as it is 
 stopped at a certain stage of growth or development, and 
 then set to begin its fermentation over again in fresh sup- 
 plies of a new pabulum, which give increased health and 
 vigour to the plant ; while, on the other hand, the 
 achorion, or Favus fungus, is obtained and used in an ex- 
 hausted state from an already ill-nourished or starved-out 
 soil. Neither can we attach much importance to differ- 
 ences in size and form of the spores, for even this occurs 
 in yeast ferment ; and although the ovoid is most fre- 
 quently seen in achorion, it is equally common to yeast 
 when exhausted. This is strikingly exhibited in Plate 
 I. Xo. 8, a drawing made from a drop of exhausted yeast 
 taken from porter ; here we have oval and elongated cells 
 with torulae. To ensure success in these and similar ex- 
 periments, the fungus or yeast should be left floating on 
 the surface of liquids ; the process is either carried on very 
 slowly, or is entirely arrested by submersion. 
 
 Turpiu and others, in their experiments on yeast, noticed 
 that the cells become oval and bud out in about an hour after 
 being added to the wort (Hg. 159) ; but this change depends 
 as much upon temperature and density of the solution as 
 upon the quality of the yeast. It is a well-ascertained 
 fact that when yeast is added to distillery warn, which is 
 
298 THE MICROSCOPE. 
 
 worked at a higher temperature than brewers' wort, fer- 
 mentation commences earlier, and the yeast-cell grows to a 
 much larger size. It is, indeed, forced in this way much 
 as a plant in a hothouse is, and then obtains to greater 
 perfection in a shorter time. It will, however, be seen 
 that it sooner becomes exhausted ; and now, if we take a 
 portion of this yeast and add it to barley wort, and at the 
 same time keep it in a temperature of from 60 to 65 
 Fahr., it ferments languidly, and small yeast-cells are the 
 product. If the yeast is allowed to stand in a warm 
 place for a few days, it partially recovers its activity, but 
 never quite. With such a yeast there is always a good 
 deal of torulse mixed up with the degenerated cells, and 
 sometimes a filamentous mass, which falls to the bottom of 
 the vessel ; from this stage it readily passes to that of 
 must and mildew, and then becomes a wasteful feeder or 
 destroyer. 
 
 With yeast already in a state of exhaustion, we have 
 seen a crop of fungus produced in the head of a strumous 
 boy, seven years of age, who was much out of health, and 
 had suffered from eczema of the eyelids, with impetigo. 
 On placing portions of the broken hairs on a glass slip, 
 and moistening with a drop of liquor potassa?, spores and 
 torulae were seen in abundance ; represented in Plate I. 
 No. 14. 
 
 In another experiment we took portions of penicillium 
 and aspergillus moulds, and added these to sweetwort, 
 and stood them by in a warm room. On the second 
 day afterwards in one of the solutions, and the third in 
 the other, fermentation had fairly set in ; the surface of 
 the solution was covered with a film, which proved to be 
 well-developed ovoid spores, filled with smaller granular 
 spores (conidia) : Plate I. No. 8. On the sixth day the 
 cells changed in form and were more spherical. Again 
 removing these to another supply of fresh wort, the results 
 obtained were quite characteristic of exhausted yeast 
 ferment. 
 
 Extreme simplicity of structure characterises all mould* 
 or mildews. Their reproductive organs are somewhat 
 more complex, and both in penicillium and aspergillus the 
 mycelium terminates in a club-shaped head, bearing upon 
 
YEAST PLANT. 
 
 299 
 
 it smaller filaments with small bead-like bodies upon the 
 apex, piled one upon the other, or, more properly speak- 
 ing, strung together ; these, again, are surmounted by 
 larger spores of a discoid shape filled with granular 
 matter, and others which are quite empty. Those of the 
 aspergillus are apparently without granular matter or 
 nuclei, and are more highly refractive. The puccinia are 
 club-shaped, the very rapid growth of the spores and 
 spawn of which appears to exert a specific and peculiarly 
 exhaustive action over the tissues of the plant on which it 
 feeds. Plate I. No. 12, represents a portion of the mould 
 taken from a saccharine solution. 
 
 The yeast plant, in its most perfect condition, is chiefly 
 made up of globular vesicles, measuring, when fully 
 grown, about the ffgbffth of an inch in diameter. The 
 older cells are filled with granular or nucleated matter ; 
 the nucleus rapidly increases, and nearly fills up the parent 
 cell, which then becomes ovoid, and ultimately the young 
 cell buds out and is separated from the parent. Some- 
 
 
 
 Fig. 159. A diagrammatic representation oftJie development of the Yeast Plo.nt. 
 No. 1, Fresh Yeast; No. 2, one hour after adding it to wort; No 3, three 
 hours ; No. 4, eight hours ; No. 5, third day, after which jointed filaments 
 are produced. 
 
 times other and smaller ceils are formed within the young 
 one before it leaves the parent globule. This process goes 
 
300 
 
 THE MICROSCOPE. 
 
 on most rapidly until the supply of food becomes ex- 
 hausted ; the vesicles, it would appear, derive their 
 nourishment by the process of osmose, sucking in, as it 
 were, certain portions of the organic fluid and chemically 
 decomposing it, appropriating a part of its nitrogen and 
 throwing off the carbonic acid. If, however, it be placed 
 
 Fig. 160. Fungoid growths. 
 
 1, Section from a Tomata, showing sporangiae growing from cuticle. 2, A por- 
 tion of same, detached, to show the mode of budding out from the upper part 
 of a branch. 3, Vertical and lateral views of spores with oospores turned out. 
 6, 7, and 8, Different stages of growth of Mycoderma cerevisice. 9, Torula 
 diabetica. 
 
 in any adverse condition, it becomes surrounded by layers 
 of condensed material, resulting from the death of the 
 
MOULDS, ETC. 
 
 301 
 
 germinal matter ; ultimately a mere trace of life remains, 
 which, taking the form of an impalpable powder, is free to 
 be driven hither and thither with every breath of air. 
 
 From those facts we may conclude that it matters little 
 whether we take yeast, achorion, or penicillium spores; 
 the resultant is the same, and depends much more on the 
 food or nourishment supplied, whether the pabulum con- 
 tains more or less of a saccharine, albuminous, or nitro- 
 genous material, lactic acid, &c., together with light and 
 temperature ; whether we have a mould (green or blue), 
 an achorion, or yeast fungus produced. Diversity of form 
 in the cells, as well as quality and quantity of their 
 material contents, are certainly due to, and in a manner 
 regulated and controlled by that beautiful law of diffusion, 
 wliich admits, separates, sifts, and refines the coarser from 
 
 Fig. 161. Fungi. (Magnified 200 diameters.) 
 
 1, Brachycladium ptnicttlatum., growing on the stem of a plant. 2, AspergiUvs 
 glaucus, growing on cheese, &c. 3, Botrytis ; the common form of mould on 
 decaying vegetable substances. 4, Sphceria, fungi caught < ver a sewer (foul 
 air). 5, Fungi growing on a pumpkin. 6, Fungi caught in the air at the 
 time of the cholera visitation, 1854. 
 
 the finer, the lighter from the denser particles, through 
 the porous structure of the cell-wall. 
 
302 THE MICROSCOPE. 
 
 We cannot conclude this brief notice of the fungi with- 
 out adding a few words upon that curious group of subter- 
 ranean plants, which instead of producing their spores at 
 the summit of a basidium, or extremity of a simple filament, 
 produces them in the interior of a vesicle or pouch, called 
 a theca or ascus. Of this species the best known example 
 is the truffle (Tuber cibarium). 
 
 It is, perhaps, not very generally known that the 
 curiously formed, irregular mass, so much esteemed for its 
 delicious taste, and sought after as a luxury, the truffle, is 
 in truth a species of mushroom ; more properly speaking, a 
 subterranean puff-ball, or fungus. Its existence, entirely 
 removed from the action of light, is an anomaly even 
 among plants of the fungus kind ; for light, although not 
 in a large degree necessary to the fungus, is almost 
 always indispensable to its full development. It would, 
 therefore, be most difficult to discover, if it were not for 
 a peculiar and penetrating odour, which dogs are taught 
 to recognise ; and by the aid of these useful animals its 
 presence is detected hidden beneath the soil. 
 
 Tulasne and others have pointed out that these fungi 
 present two essentially different types. In the one, Hy- 
 menogastrece, the internal fleshy mass presents a number of 
 irregular cavities, lined by a membrane analogous to that 
 which clothes the gills of the Agaric, and the superficial 
 cells produce at their free extremities three or four spores, 
 or seeds, which become detached, and eventually fill up 
 the cavities. The other type, Elaphemycce, Tuberacece, 
 comprising those of the truffle kind, and as may be sur- 
 mised by the scientific name assigned to them Tuber 
 nbarinm, are plants characterised from the underground 
 root presenting a fleshy mass, the outer surface of which 
 constitutes the common envelope, peridium, while the 
 numerous narrow sinuous cavities are lined and in part 
 filled up by filamentous tissue, mingled with cells of a 
 peculiar form, and terminating in spores. 
 
 A section from the fleshy-looking mass cut very thin 
 (Plate I. No. 2), and viewed under a power of 250 
 diameters, is found to be chiefly composed of cellular 
 substance, the interspaces of which are filled up by 
 jointed filaments, homologous to th<? mycelium or spawn 
 
TRUFFLES. 303 
 
 of other fungi, in the mushroom as an example, it is the 
 mushroom spawn, while the t eins, the reproductive 
 parts, contain in their cellular tiss'.e minute ovoid capsules, 
 with two or more globular yellowish seeds ; this curious 
 structure having all the parts of nutrition and reproduction 
 enclosed internally, instead of externally, as in other fungi. 
 
 Truffles are produced in this way : the mycelium quickly 
 decays and allows the fungoid body to grow on in an 
 isolated condition. About September the ground becomes 
 covered with numerous white cylindrical articulated fila- 
 ments, not visible singly to the unassisted eye, but by 
 their immense numbers and rapid growth readily seen, 
 and found traversing the soil in every direction. These 
 white flaxen threads are continuous with other flocculent 
 filaments of the same nature. In the young truffles the 
 external layer is gradually consolidated, and in a short 
 time the destruction of the flocculent filaments are com- 
 plete and lost in the young plant, which is soon isolated 
 in the soil, and then the outer or cortical coat hardens, 
 and ultimately has the appearance of a small nut. Thus, 
 like other fungi, truffles are reproduced by spores, which 
 give origin to filamentous mycelium and seed-vessels, the 
 source of numerous offspring. Groups of spores are pretty 
 objects ; their stellate appearance reminds one of the 
 Xanthidiae ; the mass of the full-grown plant at particular 
 seasons is almost wholly made up of these bodies, which 
 are of a yellowish-brown colour. 
 
 In these plants we have a double system of laminated 
 filaments ; one set arising from the cortical tissue absorb- 
 ing the surrounding moisture and serving to transmit this 
 to the cells in which the spores are formed, being there- 
 fore the organs of nutrition ; the others white and opaque, 
 terminating externally also, but conveying air to all parts 
 of the body, and bringing the whole into contact with 
 sporigeuous cells. 
 
 The spores are developed freely in the vesicular cells 
 destined to produce them. They are limited in number 
 in each vesicle; less than two is never seen in one vesicle; 
 the hexagonal basket-work arrangement of each seed ap- 
 pears to close with a lid, and ten or twelve short spinea 
 project out from every point. 
 
30-1 THE MICROSCOPE. 
 
 Beneath the external dark-coloured reticulated mem- 
 brane is a second integument, smooth and transparent, 
 easily separated by maceration, although it resists the 
 action of chemical agents, and is not coloured by iodine. 
 The simple cavity of the internal spore is filled with 
 minute granular particles and fatty globules, suspended 
 in a fluid probably albuminous, as well as the various 
 chemical salts found by Kiegel, and upon which its peculiar 
 flavour depends. 
 
 "Two new British fungi" are figured and described by 
 the Eev. M. J. Berkeley, in vol. xxv. p. 43 1 ? Linneaii 
 Soc. Trans. Peziza pygmaea, Plate I. No. 4, is a remark- 
 ably interesting specimen of a genus which presents much 
 variety in form. The description given of it is, " that it is 
 about \ inch high, the stem- often splitting or branching 
 out into several divisions, each of which is terminated by 
 a minute cup, giving the plant the appearance of a Ditiola, 
 or a Tympanis. Each cup produces other smaller cups on 
 its surface ; the branched and young cups resemble the 
 genus Solenia : in a specimen found at Wimbledon, the 
 mass of secondary cups gave the plant almost the ap- 
 pearance of a small Gyromitra" The proliferous form, is 
 shown at Plate I. No. 5. The colour of the- mature plant 
 is a bright apricot, whitish and tormentose at the base of 
 the stem. Found in swampy places, rotten gorse, &c. at 
 Ascot, Wimbledon, &c. Peziza belongs to the Ascomycetous 
 fungi ; the genus contains numerous species, and many of 
 them are brightly coloured, as in the very pretty P. bicolor, 
 Plate I. No. 1. Tulasne says that some of them have a 
 secondary fructification, consisting of stylospores. They 
 are mostly found growing on trunks of trees, dead 
 wood, &c. 
 
 We now pass to the examination of Lichens ; in these 
 plants, as in the Fungi, the germination of the spore 
 consists in the emission of a hollow filament from some 
 part of its surface. This filament, which is simply an 
 extension of the spore-membrane, branches repeatedly, 
 and spreads over the surface on which the spore has beec 
 sown j at the same time it divides by numerous septa 
 \vhich occur at irregular intervals. By the intertwining 
 of the resultant ramifications, a stroma is formed, to which 
 
LICHENS. 305 
 
 the term hypothallus is applied, and which constitutes the 
 vegetative system of the future lichen. So far the develop- 
 ment is the same as that of the fungi ; but at a longer or 
 shorter period after the formation of the hypothallus, wo 
 may observe upon its surface a whitish layer of spheroidal 
 cellules, intimately united with each other as well as with 
 the filaments from which they take their origin. This 
 layer is the groundwork for a second formation of globular 
 cells, and these are only to be distinguished from the 
 first by the chlorophyll which they contain. They are 
 called gonidia, and are peculiar to Lichens. Such is the 
 formation of the most simply organized of the class, as the 
 Verrucarice, the receptacles (apothecia) of which closely 
 resemble those of a SpJiceria, and are found upon the sur- 
 face of the hypothallus. In the more complicated foliaceous 
 Lichens, as Pai-melia, the mature tballus is made up of two 
 kinds of tissues, the medullary and the cortical The cor- 
 ticular portion forms the layers, an inferior and superior, 
 and consists of thick-walled cells, closely adherent to 
 each other ; from the surface of the inferior layer are given 
 off numerous root-like appendages, on either side of which, 
 or rather embedded in its cortical substance, are the gonidia, 
 which form a green tissue. Of the spore-like organs, 
 spermatia and stylospores, there are three varieties, to 
 which the terms apothecia, spermogonia, and pyenides 
 have been applied. The most common form of the apo- 
 thecium is that of the disc, which may bo plane, convex, 
 or cup-shaped. This form is that which characterises the 
 Gymnocarpous Lichens. In the A ngiocarpece the organ is 
 closed upwards, its superior surface becoming internal, so 
 as to form a conceptacle like that of the Pyrenomy- 
 cetes; the form, however, of which is subject to much 
 variation. 
 
 The reproductive organs of Lichens, as in Fungi, are of 
 five kinds . 1, Sporules, which are formed by the con- 
 struction and subsequent separation of the extremity of a 
 simple cylindrical filament ; 2, Spermatia with their sup- 
 porting pedicles; 3, Stylospores with their styles; 4, 
 Thecse or asci ; 5, Basidia with their basidiospores. As 
 regards the complexity of their form and structure they 
 may be taken in the order in which they are here placed ; 
 1 
 
306 THE MICROSCOPE. 
 
 but, of the last-mentioned, it should be stated that they are 
 almost solely found in Fungi, which have really no other 
 reproductive organ. The spores present many points of dif- 
 ference, both in number and character, in different genera 
 and species, and for this reason are most interesting micro- 
 scopic objects. We would direct the reader's attention to 
 an interesting and valuable paper, from the pen of Dr. 
 Lauder Lindsay, in the Linnean Soc. Trans., vol. xxv. 
 p. 493, " On the Lichens of New Zealand" (the country 
 par excellence of certain Lichens). The paper is very 
 beautifully illustrated, showing chiefly the minute or 
 microscopic anatomy of the reproductive organs of the 
 species examined, especially the character of their spores 
 and spermatia. 
 
 A vertical section of Parmelia stdlata is given in 
 Plate I. No. 26 : it belongs to an extensive genus of 
 Gymnocarpous open-fruited Lichens, found growing upon 
 trees, palings, stones, walls, &c. The emission of the ripe 
 spores of the Lichens is a curious process, and not unlike 
 that which is seen to take place in some of the Fungi, as 
 in Pezizce, Sphcerice, &c. If a portion of the thallus be 
 moistened and placed in a common phial, with the apothecia 
 turned toward one side, in a few hours the opposite sur- 
 face of the glass will be found covered with patches of 
 spores, easily perceptible by their colour ; or if placed on 
 a moistened surface, and one of the usual glass slips laid 
 over it, the latter will be covered in a short time. As to 
 the powers of dissemination of these lowly organized 
 plants, Dr. Hicks's observations lead to the conclusion 
 that the gonidia of Lichens have greater powers in this 
 direction than has been generally supposed. He found 
 by placing a clean sheet of glass in the open air during a 
 fall of snow, and receiving the melting water in a tube or 
 bottle, that he obtained large quantities of what has been 
 looked upon as a " unicellular plant, commonly called 
 * Chlorococcus,' the cells of which may remain in a dor- 
 mant condition for a long time during cold weather, 
 but upon the return of warmth and moisture they begin 
 to increase by a process of subdivision, into two, four, 
 or eight portions, which soon assume a rounded form and 
 burst the parent cell- wall open; these secondary cells 
 
LICHENS. 307 
 
 soon begin to divide and subdivide again, and t'nis process 
 may go on without much variation even for years. The 
 phenomena described may also be watched by taking a 
 portion of the bark of a tree on which the Chlorococcus 
 has been deposited, and placing it under a glass to keep it 
 in a moderately moist atmosphere ; the only difference 
 being a change in colour, which is caused by the growth of 
 the fibres, as may be seen on microscopical examination. 
 And this," Dr. Hicks says, " is an instructive point, be- 
 cause it will be found that the colour varies notably accord- 
 ing to the Lichen prevalent in its neighbourhood." J He 
 thinks there can be no doubt that what has been 
 called Chlorococcus, is nothing more than the gonidia of 
 some Lichen ; and that under suitable conditions, chiefly 
 drought and warmth, the gonidium often throws out from 
 its external envelope, a small fibre, which, adhering and 
 branching, ultimately encases it and forms a " soridium." 
 ' The soridia also remain dormant for a very long time, 
 and do not develop into thalli unless in a favourable 
 situation ; in some cases it may be for years. It will be 
 easily perceived that the soridium contains all the elements 
 of a thallus in miniature ; in fact, a thallus does frequently 
 arise from one alone, yet, generally, the fibres of neigh 
 bouring soridia interlace, and thus a thallus is matured 
 more rapidly. This is one of the causes of the variation 
 of appearance, so common in many species of Lichens, and 
 is more readily seen towards the centre of the parent 
 thallus. When the gonidia remain attached to the parent 
 thallus, the circumstances are, of course, generally very 
 favourable, and then they develop into secondary thalli, 
 attached more or less to the older one, which, in many 
 instances, decays beneath them. This process being con- 
 tinued year after year, gives an apparent thickness and 
 spongy appearance to the Lichen, and is the principal 
 cause of the various modifications in the external aspect 
 of the Lichens which caused them formerly to be mis- 
 classified." 2 
 
 (1) "For instance, -where the yellow Pannelia is found, the Chlorococcus will 
 assume a yellow tinge in its soridial stage. Viewed by transmitted ligl it, they 
 are also opaque balls, with irregular outline." 
 
 (2) " Contributions to the Knowledge of the Development of the Gonidia of 
 Lichens." By J. Braxton Hicks, M.D. &c., Quarterly Journal of Microscopical 
 Science, voL viii. 860, p. 239.) 
 
 x 2 
 
ouS 
 
 THE MICROSCOPE. 
 
 The little group of Hepaticoe or Liverworts, which is 
 intermediate between Lichens and Mosses, presents nume- 
 rous objects of interest for the microscupist. These 
 plants are produced by dust-like grains called spores, and 
 minute cellular nodules called yemmcG or buds. The 
 gemmae of Marchantia polymorphia are produced in 
 elegant membranous cups, with a toothed margin growing 
 on the upper surface of the frond, especially in very damp 
 court yards between the stones, or near running water, 
 where its lobed fronds are found covering extensive 
 surfaces of moist soil. At the period of fructification, 
 these fronds send up stalks, which carry at their summit 
 round shield-like or radiating discs. Besides which, it 
 generally bears upon its surface a number of little open 
 basket-shaped " conceptacles " which are borne upon the 
 surface of the frond ; as in fig. 162, and may be found 
 
 in nil stages of develop- 
 ment When mature 
 it contains a number of 
 little green round or ob- 
 long discs, each com- 
 posed of two or more 
 layers of cells; the wall 
 is surmounted by a glis- 
 tening fringe of teetii, 
 whose edges are them- 
 selves regularly fringed 
 with minute outgrowths. 
 The cup seems to bo 
 formed by a develop- 
 ment of the superior 
 
 epidermis, which is raised up and finally bursts and 
 spreads out, laying bare the seeds. The development of 
 this structure presents much analogy to that of the sori of 
 Ferns. 
 
 Muscacece, Mosses, are an interesting form of vegetable 
 life, Linnaeus called them servi, servants, or workmen, 
 as they seem to labour to produce vegetation in newly- 
 formed countries, where soil is not yet formed. They also 
 fill and consolidate bogs, and form rich mould for the 
 growth of larger plants, which they protect from the 
 
 Fig. \62, Geinwiparous Conceptacle of Mar- 
 chantia p i> I y morphia, expanding and rising 
 from the surface of a frond. 
 
MOSSES. 
 
 309 
 
 winter's cold. The common, or Wall Screw-moss, fig. 
 163, growing almost every where on old walls and other 
 brick-work, if examined closely, will be found to have 
 springing from its base numerous very slender stems, each 
 
 Fig. 163. Screw Moss. 
 
 of wh.eh terminates in a dark brown case, which encloses 
 its fruit. If a patch of the moss is gathered when in 
 this state, and the green part of the base is put into water, 
 the threads of the fringe will uncoil and disentangle them- 
 selves in a most curious and beautiful manner ; from 
 this circumstance the plant takes its popular name of 
 Screw-moss. The leaf usually consists of either a single or 
 a double layer of cells, having flattened sides, by which 
 they aahere one to anotner. The 
 leaf-cells of the Sphagnum bog- 
 moss, rig. 179, exhibit a very curi- 
 ous departure from the ordinary 
 type ; for instead of being small and 
 polygonal, they are large and elon- 
 gated, and contain spiral fibres 
 loosely coiled in their interior. Mr. 
 Huxley pointed out, that the young 
 leaf does not differ from the older, 
 and that both are evolved by a 
 gradual process of "differentiation" 
 Mosses, like liverworts, possess 
 both antheridiaand pistillida, which 
 are engaged in the process of fmc- 
 tification. The fertilized cell be- 
 comes gradually developed into a conical body elevated 
 
 'iff. 164. Ifotith nf Cnpxtitf 
 Fanaria, showing f'erittoitH 
 
310 THE MICROSCOPE. 
 
 upon a foot stalk ; and this at length tears across the 
 walls of the flask-shaped body, carrying the higher 
 part upwards as a calyptra or hood upon its summit, 
 whib the lower part remains to form a kind of collar 
 round the base. These spoi e-capsules are closed on their 
 summit by opercula or lids, and their mouths when 
 laid open are surrounded by a beautiful toothed fringe, 
 termed the peristome. This fringe is shown in fig. 164 
 in mouth of capsule of Funaria, with its peristome 
 in situ. The fringes of teeth are variously constructed, 
 and are of great service in discrimi- 
 nating the genera. In N ecltera anti- 
 pyretica, fig 165, the peristome is 
 double, the inner being composed of 
 teeth united by cross bars, forming 
 a very pretty trellis. The seed spores 
 are contained in the upper part of 
 the capsule, where they are clus- 
 tered round a central pillar, which 
 Fig. 165. Double Peristome of is termed the columella : and at the 
 
 Neckera Antipyretica. ,. ,1 . . 
 
 time of maturity, the interior of the 
 capsule is almost entirely occupied by spores. 
 
 It may here be mentioned, that all mosses and lichens 
 are more easily detached from the rocks and walls on 
 which they grow in frosty weather than at any other 
 
 season, and consequently 
 they are best studied in 
 winter. One of the com- 
 monest, Scale-moss, fig. 
 166 (Jungermannia bideu- 
 tata), grows in patches, 
 in moist, shady situa- 
 tions, near the roots of 
 trees; see Plate II. Nos. 
 
 vessels are little oval bodies, which if gathered when 
 unexpanded, and brought into a warm room, burst 
 under the eye with violence the moment a drop of 
 water is applied to them, the valves of the vessel taking 
 the shape of a cross, and the seeds distending in a cloud 
 of brown dust. If this dust be examined with the 
 
EQUISETACEJE. 
 
 31) 
 
 microscope, a number of curious little chains, looking 
 something like the spring of a watch, will be found 
 among it, their use being to scatter the seeds ; and if the 
 seed-vessel be examined while in 
 the act of bursting, these little 
 springs will be found twisting 
 and writhing about like a nest 
 of serpents. The undulating 
 Hair-moss (Polytrichum undu- 
 latum), fig. 167, is found on 
 moist shady banks, and in 
 woods and thickets. The seed- 
 vessel has a curious shaggy cap ; 
 but in its construction it is very 
 similar to that of the Screw- 
 moss, except that the fringe 
 around its opening is not twisted. 
 
 Equi&etacece. The history of 
 the development of the Equise- 
 taceae (horse-tails) corresponds in 
 some respects with that of Ferns. 
 The spore-case of this solitary 
 genus is a most interesting object 
 under the microscope ; they have 
 apparently only one coat, for the 
 outer coat splits up into four 
 thread-like processes (elaters), 
 clubbed at their free ends. 
 While the spore remains on the Flg 
 sporange, these fibres are rolled round the spore, as seen 
 in fig. 170, o; but by gently shaking the fruit spike, the 
 spores are discharged, the coiled fibres immediately unroll, 
 as at F, their elasticity causing them to spring about in a 
 most curious manner. In a few minutes this motion appa- 
 rently ceases, but if breathed upon they again unroll and 
 dart about with wonderful elasticity. 
 
 Ferns. In the Ferns we have an intermediate state, 
 somewhat between mosses and flowering plants; this 
 world not apply to the reproductive apparatus, which is 
 formed upon the same type as that of Mosses ; and, 
 furthermore, it is to be observed, that Ferns do not form 
 
312 
 
 THE MICROSCOPE. 
 
 buds like other plants, but that their leaves, or fronds as 
 they are properly called, when they first appear, are rolled 
 up in a circinate form, and gradually unfold, as in fig. 1 68. 
 
 Fig. 168. Male Fern. A portion of leat with sori. 
 
 Ferns have no visible flowers; and their seeds are produced 
 in clusters, called sori, on the backs of the leaves. Each 
 sorus contains numerous thecse, and each theca encloses 
 almost innumerable sporanges, with spores or seeds. 
 There are numerous kinds of ferns, all remarkable for some 
 interesting peculiarity ; but it is their spores which are 
 chiefly sought for by the microscopist. 
 
 The first account of the true mode of development of 
 Ferns from their spores was published in 1844, by Nageli, 
 in a memoir entitled Moving Spiral Filaments (spermatic 
 filaments) in Ferns, wherein he announced the existence of 
 the bodies now called antheridia; but, mistaking the 
 archegonia for modified forms of the antheridia, he was 
 led away from a minute investigation of them. If lie had 
 followed the development of the prothallia further, he 
 would have detected the relations of the nascent embryo, 
 which would probably have put him on the right track. 
 As it was, the remarkable discovery of the moving spiral 
 filaments occupied all his attention, and caused him to fall 
 
FERNS. 
 
 31S 
 
 into an error in certain important respects ; for example, 
 he has represented what is undoubtedly an archcgonium 
 filled with cellules, sperm-ctlls, which, he states, " emerged 
 from it as from the antheridia." This description is not 
 quite correct. 
 
 The reproduction of ferns had, until within the last few 
 years, been a vexed question among botanists. The riddle 
 was at length solved by the labours of Count Suminski, 
 who discovered that it is in the structures developed from 
 the spores in germination that the pistillidia and antheridia 
 of ferns are to be sought. The nature of the phenomena 
 by which the propagation of ferns is effected, is as follows. 
 In all the different species of ferns, the spores are contained 
 in brown dots, on lines collected on the under surfaces, or 
 along the edges of the fronds. Each of the spore-cases 
 is surrounded by an elastic 
 ring, which when the time 
 arrives for the spores to be 
 set free, makes an effort 
 to straighten itself, and in 
 so doing causes the spore- 
 case to which it is attached 
 to split open, and the spore 
 dust to be dispersed. Very 
 soon after these spores 
 
 have begun to germinate, 
 
 a flat plate-like expansion, ,,. 
 
 ,*?. Fig. 169. Sorus of Depana prnhfera. 
 
 somewhat resembling a 
 
 heart in form, shows itself. This expansion gradually 
 thickens, the tube from which it had sprung withering 
 away. So far, observes Mr. Henfrey, there is nothing very 
 remarkable in the development of these plants from their 
 spores, but the succeeding phenomena are exceedingly 
 curious. The main particulars are thus described by him : 
 " At an early period of the expanding growth of the leaf- 
 like product of the spore, termed the prothallium or 
 germ-frond, a number of little cellular bodies are found 
 projecting from the lower surface, which, if placed in 
 water when ripe, burst and discharge a quantity of micro- 
 scopic filaments, curled like a corkscrew, and furnished 
 with vibrating hair-like appendages, by the motion of 
 
314 THE MICROSCOPE. 
 
 which they are rapidly propelled through the water. The 
 cellular bodies from which these are discharged are termed 
 the antheridia of the ferns, and are in their physiological 
 .nature the representatives of the pollen of the flowering 
 plants. At a somewhat later period other cellular bodies 
 of larger size and more complex structure are found in 
 small numbers about the central part of the lower surface 
 of the prothallium on the thickened portion, situated 
 between the notch and the part where the radical filaments 
 arise. These, the pistillidia or archegonia of the ferns, are 
 analogous to the ovules or nascent seeds of flowering 
 plants, and contain, like them, a germinal vesicle, which 
 becomes fertilized through the agency of the spiral fila- 
 ments mentioned above, and is then gradually developed 
 into an embryo plant possessing a terminal bud. This 
 bud begins at once to unfold and push out leaves with a 
 circinate vernation, which are of a very simple form at 
 first, and rise up to view beneath the prothallium, coming 
 out at the notch ; single fibrous roots are at the same 
 time sent down into the earth, the delicate expanded pro- 
 thallium withers away, and the foundation of the perfect 
 fern plant is laid. As the bud unfolds new leaves, the 
 root stock gradually acquires size and strength, and the 
 leaves become larger and more developed ; but it is a long 
 time before they assume the complete form characteristic 
 of the species." 
 
 These observations on Ferns have acquired vastly- 
 increased interest from the subsequent investigations of 
 Hoffnieister, Mettenius, and Sunrinski, on the allied Cryp- 
 togams, and, above all, from Hoffmeister's observations on 
 the processes occurring in the impregnation of the Coni- 
 fers. Not only have these investigations given us a satis- 
 factory interpretation of the archegonia and antheridia of 
 the Mosses and Liverworts, but they have made known 
 and co-ordinated the existence of analogous phenomena 
 in the Equisetacece, Lycopodiacece, and Rhizocdrpece, and 
 shown, moreover, that the bodies described by Mr. Brown 
 in the Conifers, under the name of ' corpuscles." are 
 analogous to the archegonia of the Cryptogams ; so that a 
 link is hereby formed between these groups and the higher 
 flowering plants. 
 
CHARA. 315 
 
 The fruits, cr sori, of Ferns afford a very beautiful 
 variety of objects for the microscopist, and they possess an 
 advantage in requiring little or no preparation nothing 
 more being necessary than that of taking a portion of a 
 frond, place it on a glass-slip under the microscope, and 
 throwing a condensed light upon it by the aid of the side 
 reflector. Even germination may be watched by simply 
 employing gentle heat and moisture. Take, as Hoff- 
 meister directs, a frond of a Fern whose fructification is 
 mature, lay it upon a piece of glass covered with fine 
 paper, and place the spore-bearing surface downwards 
 upon this ; in the course of a day or two this paper will 
 be found to be covered with a fine brownish dust, which 
 consists of the liberated spores. These must be carefully 
 collected, and spread out upon the surface of a smooth 
 fragment of porous sandstone, and then placed in a saucer, 
 the bottom of which is before covered with water ; a glass 
 tumbler being inverted over it to ensure the requisite supply 
 of moisture, and prevent rapid evaporization. Some of the 
 protliallia soon germinate; if the cup be kept only slightly 
 moist for some time, and then suddenly watered, a large 
 number of antheridia and archegonia quickly open, and in a 
 few hours the surface of the larger prothallia will be covered 
 with moving antherozoids. If sections of these be made, 
 that is, the canals laid open, with a power of 200 or 300 
 diameters we may occasionally see antherozoids in motion 
 
 CHARACE.E. Chara vulgaris is the plant in which the 
 important fact of vegetable circulation was discovered ; 
 Fig. 170, No. 1, is a portion of the plant of the natural 
 size. Every knot or joint may produce roots ; but it is 
 somewhat remarkable, that they always proceed from the 
 upper surface of the knot, and then turn downwards ; so 
 that it is not peculiar that the first roots also should rise 
 upwards with the plant, come out of the base of the 
 branch, and then turn downwards. 
 
 Mr. Varley noticed : " The ripe globules spontaneously 
 open ; the filaments expand and separate into clusters.'* 
 " These tube-like filaments are divided into numerous 
 compartments, in which are produced the most extra- 
 ordinary objects ever observed of vegetable origin, Fig. 
 170 A. At first they are seen agitating and moving in their 
 
316 
 
 THE MICROSCOPE. 
 
 cells, where they are coiled up in their confined spaces, 
 every cell holding one. They gradually escape from their 
 
 Fig. 170. 
 
 1, Branch of Chara vulgarit. 2, Magnified view : the arrows indicate the courM 
 taken by the granules in the tubes. 3, A limb of ditto, with buds at joints. 
 4, Portion of a leaf of Vallisneria spiralis, with cells and granules. 
 
CHARA. 317 
 
 cells, and the whole field soou appears filled with life. 
 They are generally spirals of two or three coils, and 
 never become straight, though their agitated motion alters 
 their shape in some degree. At their foremost end is a 
 filament so fine as only to be seen by its motion, which is 
 very rapid and vibratory, running along it in waves : and 
 of a globule be forcibly opened before it is ripe, the fila- 
 ments will give little or no indication of life." 
 
 They swim about freely for a time, but gradually getting 
 slower and slower ; in about an hour they become quite 
 motionless. Unger described these moving filaments in 
 tipltagnum (bog- moss) as Infusoria, under the name of 
 
 Fig. ll\.Ar,theridia of Chura fragilii, 4c. 
 
 A, Portion of filament dividing into Phytozoa, " anlheroidt." B, A valve, with 
 its group of antheridial filaments, composed of a series of cells, within each of 
 which an anther zoi<i is formed, c, The escape of the mature antlierozoidi is 
 shown. D, Antheridium, or globule, developed at the base of nucule. E, Nu- 
 cule enlarged, and globule laid open by the separation of its valves. F. Spores 
 and elaters of jui*etum. o, Spores surrounded by elaters of Equitetum. 
 
 Spirillum ; and consequently they have been the cause of 
 much controversy. Schleiden, very properly denying their 
 animal nature, says : " They are nothing more than fibre 
 
318 THE MICROSCOPE. 
 
 in an early stage of development." The Characeoe are all 
 aquatic plants of filamentous structure. Some authors 
 have divided the species into two genera, Nitella (simple 
 tubes) and Char a (cortical tubes). The circulation in 
 the ordinary tubes or cells consists in the movement 
 of the gelatinous protoplasmic sac, seen, as one mass, slowly 
 passing up one side, across the ends, and down the 
 opposite side, not perpendicularly, but in an oblique or 
 spiral course, as indicated in the figure. The CJiaraccce 
 multiply by gemmae, produced at the articulations of 
 their stems. 
 
 Mr. 11. J. Carter, in a paper of great interest, published 
 January, 1857, on the "Development of the Root-cell and 
 its Nucleus, in Chara Verticillata," describes a structureless 
 cell-wall, and a protoplasm composed of many organs. 
 " This," he says, " is surrounded by a cell, the ' proto- 
 plasmic sac,' which is divided into a fixed and rotatory 
 portion ; these again respectively enclose the nucleus 
 ' granules,' and axial fluid ; while small portions of irre- 
 gular shaped granular bodies are common to both. If 
 we take the simple root- cell about the eighteenth hour 
 after germination, when it will be about half-an-inch long, 
 and 1 -600th of an inch broad, and place it in water between 
 two slips of glass for microscopic observation, under a 
 magnifying power of about four hundred diameters, we 
 shall find, if the circulation be active and the cell -wall 
 strong and healthy, that the nucleus, which is globular, 
 gradually becomes somewhat flattened, having several 
 hyaline vacuoles of different sizes ; the change goes on 
 gradually until it appears of more elongated form, growing 
 fainter on its outline, and then entirely disappears, leaving 
 a white space corresponding to its capsule or cell-wall, 
 with a faint remnant of some structure on the centre. 
 Subsequently, this space becomes filled up with the fixed 
 protoplasm, and after an hour or two the nucleus re- 
 appears a little behind its former situation, but now 
 reduced in size, and with its nucleolus double, instead of 
 single as before ; each nucleolus being about one-fourth 
 part as large as the old nucleolus, and hardly perceptible. 
 Meanwhile a faint septum is seen obliquely extending 
 across the fixed protoplasm, a little beyond the nucleus ; 
 
DEVELOPMENT OP CHARA. 319 
 
 and if iodine be applied at this time, the division is seen 
 to be confined to the protoplasm, as the latter, from crn- 
 traction, withdraws itself from each side of the line 
 where the septum appeared, ard leaves a free space which 
 is bounded laterally by an uninterrupted continuation of 
 the protoplasmic sac. In this way changes go on until its 
 shape is altered and it becomes converted into a bunch 
 of rootlets. Thus the new cells are never entirely with- 
 out a nucleus, which would appear to exert some influ- 
 ence upon their development, for as soon as the only two 
 new cells which the root-cell gives off are formed, the old 
 nucleus becomes effete. 
 
 " Now as to the office of the nucleus, nothing more is 
 revealed to us in the development of the roots of Chara, 
 than that, so long as new cells are to be budded forth, 
 the nucleus continues in active operation, but when this 
 ceases it becomes effete ; while the rotation of the pro- 
 toplasm and subsequent enlargement of the cell, <fcc., 
 which are much better exemplified in the plant-stem than 
 in the root-cell, go on after the nucleus ceases to exist. 
 Hence the development of the root-cells of Chara affords us 
 nothing positive respecting the functions of this organ ; 
 and therefore, if we wish to assign to it any uses in par- 
 ticular, they must be derived from analogy with some 
 organism in which there is a similar nucleus whose office is 
 known. If for this purpose we may be allowed to 
 compare the nucleus of Chara with that of the rhizo- 
 podous cell, which inhabits its protoplasm, we shali 
 find the two identical in elementary composition ; that 
 is, both consist at first of a ' nuclear utricle,' respec- 
 tively enclosing a structureless homogeneous nucleolus ; 
 the latter, too, in both, is endowed with a low degree of 
 movement. 
 
 " After this, however, the nucleolus of the Rhizopod cell 
 becomes granular and opaque ; and when, under circum- 
 stances favourable for propagation, a new cell-wall is 
 formed around the nuclear utricle, or this may be an 
 enlargement of the nuclear utricle itself, I do not know 
 which ; the granular substance of the uucleolus becomes 
 circumscribed, and shows that it is surrounded by a sphe- 
 rical, capsular cell ; the granules enlarge, separate, pass 
 
320 THE MICROSCOPE. 
 
 through the spherical capsule into the cavity of the 
 nuclear utricle ; a mass of protoplasm makes its appearance, 
 and this divides up into monads, or, as I first called them, 
 ' gonidia.' J 
 
 "The movement of the rotating protoplasm in the 
 Characece is also very slow ; for, when it is viewed in the 
 long iuteriiodes of Nitella with a very low power, or even 
 with the naked eye, it seems hardly to move faster than 
 the foot of a Gasteropod ; still there is no positive evidence 
 that it moves round the cell after the manner of the latter, 
 although it would appear to possess the power of move- 
 ment per sc. Hence the question remains undecided, viz. 
 whether it moves round the cell hy itself, or by the aid of 
 cilia disposed on the inner surface of the protoplasmic sac, 
 in like manner to those which appear to exist in the 
 abdominal cavity of Vaginicola crystallma, and which have 
 been seen in Closterium lunula." 2 
 
 The stems and arms of Chara are tubular, and entirely 
 covered with smaller tubes, the circulation can mostly be 
 observed in these, as shown at Fig. 170. Any ordinary cut- 
 ting to obtain sections would squeeze the tube flat, and spoil 
 it and the lining ; it is, therefore, better to avoid this, by 
 laying the Chara on smooth wood, just covered with 
 water; then, with a sharp knife, make suddenly a num- 
 ber of quick cuts across it, and so obtain the various 
 sections required. Wet a slip of glass, and turn the wood 
 over so as just to touch the water, and the sections 
 will fall from the wood on to the glass, ready for the 
 microscope. 
 
 " The Chara tribe is most abundant in still waters or 
 ponds that never become quite dry ; if found in running 
 water, it is mostly met with out of the current, in holes or 
 side bays, where the stream has little effect, and never on 
 any prominence exposed to the current. If the Chara 
 could bear a current, its fruit would mostly be carried on 
 and be deposited in whorls ; but it sends out from its 
 variouo joints very long roots into the water, and these 
 would by agitation be destroyed, and then the plant 
 
 <1) Ann. and Mag. Nat. Hint. vol. xvii. 1856. 
 
 (2) In Plate I. No. 27, is represented the Mossgronida, assuming the amoeboid 
 foru as described by Dr. Ilicus in the Linnean Trans. 1862. 
 
CHARA. 321 
 
 decays; for although it may grow long before roots are 
 formed, yet when they are produced their destruction 
 involves the death of the plant. In order, therefore, to 
 preserve Chara, every care must be taken to imitate the 
 stillness of the water by never shaking or suddenly turning 
 the vessel. It is also important that the Char a should be 
 disturbed as little as possible ; and if requisite, it must 
 be done in the most gentle manner, as, for instance, in 
 cutting off a specimen, or causing it to descend in order 
 to keep the summit of the plant below the surface of the 
 water. 
 
 Similar care is requisite for Vallisneria ; but the warmest 
 and most equal temperature is better suited to this plant. 
 It should be planted in the middle of the jar in about 
 two inches deep of mould, which has been closely 
 pressed ; over this place two or three handfuls of leaves, 
 then gently fill the jar with water. When the water- 
 requires to be changed, a small portion is sufficient to 
 change at a time. It appears to thrive in proportion to 
 the frequency of the changing of the water, taking care 
 that the water added rather increases the temperature 
 than lowers it. 
 
 The natural habitat of the Frog-bit, another water- 
 plant of great interest, is on the surface of ponds and 
 ditches; in the autumn its seeds fall, and become buried 
 in the mud at the bottom during the winter; in the 
 spring these plants rise to the surface, produce flowers, 
 and grow to their full size during summer. Chara may be 
 found in many places around London, the Isle of Dogs 
 and in ditches near the Thames bank. 
 
 Anacharis alsinastrum. This remarkable plant is so 
 unlike any other water-plant, that it may be at once 
 recognised by its leaves growing in threes round a slender 
 stringy stem. The watermen on the river have already 
 named it " Water-thyme," from a faint general resemblance 
 which it bears to that plant. In 1851 the Anacharis 
 was noticed by Mr. Marshall and others in the river 
 at Ely, but not in great quantities. Next year it had 
 increased so much, that the river might be said to be full 
 of it. 
 
 The colour of the plant is deep green ; the leaves are 
 
322 THE MICROSCOPE. 
 
 nearly half an inch long, by an eighth wide, egg-shaped at 
 the point, and beset with minute teeth, which cause them to 
 cling. The stems are very brittle, so that whenever the 
 plant is disturbed, fragments are broken off. Its powers 
 of increase are prodigious, as every fragment is capable of 
 becoming an independent plant, producing roots and 
 stems, and extending itself indefinitely in every direction. 
 Most of our water-plants require, in order to their increase, 
 to be rooted in the bottom or sides of the river or drain 
 in which they are found; but this is independent altogether 
 of that condition, and actually grows as it travels slowly 
 down the stream after being cut. The specific gravity of 
 it is so nearly that of water, that it is more disposed to sink 
 than float. A small branch of the plant is represented, 
 with a Hydra attached to it, in a subsequent chapter. 
 
 Mr. Lawson pointed out the particular cells in which 
 the current or circulation will be most readily seen 
 viz. the elongated cells around the margin of the leaf 
 and those of the midrib. On examining the leaf with 
 polarised light, these cells, and these alone, are found to 
 contain a large proportion of silica, and present a very 
 interesting appearance. A bright band of light encircles 
 the leaf, and traverses its centre. In fact, the leaf is set, 
 as it were, in a framework of silica. By boiling the leaf 
 for a short time in equal parts of nitric acid and water, 
 a portion of the vegetable tissue is destroyed, and the 
 silica rendered more distinct, without changing the form 
 of the leaf. 1 
 
 It is necessary to make a thin section or strip from the 
 leaf of Vallisneria, for the purpose of exhibiting the circu- 
 lation in the cells, as shown in fig. 170, No. 4. Among the 
 cells granules, a few of a more transparent character than 
 the rest, may be seen, having a nucleolus within. 
 
 The phenomenon of cell rotation is seen in other plants 
 besides those growing in water. The leaf of the common 
 plantain or dock, Plantago, furnishes a good example ; the 
 movement being seen both in the cells of the plant, and 
 hairs of the cuticle torn from the midribs. The Spider- 
 wort will be noticed further on. 
 
 (1) See also a paper in Vol. IV. Microscopical Journal of Science, on the Ci 
 eulation in the Leaf of Anacharis, by Jlr F H. Wenharo 
 
STRUCTURE OF PLANTS. 323 
 
 Structure of Plants. The development of cells in plants 
 takes place in all cases in essentially the same way, 
 but the form of the result is subject to a number of im- 
 portant modifications. Most elementary works on Botany 
 enter so fully into this interesting question, that it is quite 
 unnecessary to do more than refer very briefly to the 
 more important structural peculiarities of plants. Cell' 
 division, as we have seen, is the universal formative pro- 
 cess by which vegetative growth is effected, and free-cell- 
 formation occurs only in the production of cells connected 
 with reproduction. In the lower classes of plants, espe- 
 cially in aquatic genera, we can observe the process of cell- 
 division in all its details ; but in the higher, knowledge 
 of this kind is only accessible by dissection. 
 
 As long as the cell retains its primordial utricle, it is 
 capable of producing new cells, and organized forms of 
 assimilated matter, like starch, chlorophyll, &c. in its con- 
 tents. This is the case in all nascent tissues, but it ceases 
 to be so at various periods in different parts of the vege- 
 table organization. In all woody tissues, in all pitted and 
 spiral-fibrous cells it disappears early ; the secondary de- 
 posits of the ligneous character being formed apparently 
 from the watery cell-sap. In herbaceous organs, such as 
 leaves, in the cells of the cellular plants generally, the 
 primordial utricle remains. "This explains why the 
 power to form adventitious buds exists not only in the 
 cambrium layer of the higher plants, but, under certain 
 conditions, even in the leaves, and why germination or 
 propagation by little cellular bulbels, or isolated cells 
 detached from the vegetative organs, is so common among 
 the cellular plants, and in the Mosses and Liverworts, 
 where parenchyrnatous tissues so greatly predominate." 
 (Henfrey.) 
 
 The tissues of plants, properly so called, consist of col- 
 lections of cells of uniform character, permanently combined 
 together by more or less complete union of their outer sur- 
 faces. Tissues are of many kinds, according to the form 
 of the cells, the character of the cell-membrane, and the 
 manner in which the cells are connected together. The 
 milk-vessels found in connexion with certain cells appear 
 to be formed out of the intercellular passages, and not by 
 
 T2 
 
THE MICROSCOPE. 
 
 fusion o celis ; hence they do not constitute a true cellular 
 tissue. 
 
 Vascular tissue is formed by the fusion of perpendicular 
 rows of cells ; by the absorption of their contiguous walls 
 they become converted into continuous tubes of more or 
 less considerable length. Then we have a combination of 
 tissues destined for particular purposes in the economy of 
 the plant, divided into three primary systems the Cellular, 
 the Fibro-vascular, and Cortical. The 1st, Cellular, forms 
 the great mass of the living structure of plants ; and it is- 
 in this system that the vital processes of vegetation are 
 chiefly carried on. The 2d, Fibro-vascular, forms all the 
 woody structures, which in all cases are composed of a 
 quantity of conjoined portions of cellular and vascular 
 tissue arranged in a peculiar manner ; differing in their 
 modes of growth in different classes of plants, and which 
 in consequence present considerable differences in the 
 structure of their mature steins. The 3d, Cortical, also 
 termed the epidermal, exists in the form of a simple flat 
 layer of cells united firmly together by their sides, and 
 forming a continuous coat over the surface of a plant. 
 Such a layer clothes all the organs of plants above the 
 Mosses, and, as stems grow older, the epidermal layer 
 gives place to the bark or rind. Stomata are orifices 
 between the meeting angles of the epidermal cells ; most 
 abundant usually on the lower surface of leaves, often 
 wanting on the upper surface. On the leaves of aquatic 
 plants they are only found on the upper surface, and are 
 absent where the leaf touches the water. 
 
 Hairs and scales of all kind depend on the development 
 of the epidermal cells. Simple hairs are merely single 
 epidermal cells produced in a tubular filament, and when 
 cell-multiplication occurs in them they present a number 
 of joints ; see hairs of nettle, fig. 188, No. 2. Thorns, such 
 as those of the rose, are aborted branches, in which the 
 cells become thickened by woody secondary deposits. In 
 leathery or hard leaves, and in the thick tough leaves of 
 succulent plants, such as the aloes, the secondary layers 
 acquire great thickness. The aerial roots of the Orchi- 
 dacea3 exhibit a curious structure, the growing extremities 
 being clothed by a whitish cellular tissue composed of several 
 
FORMATION OF WOODY FIBRE. 325 
 
 layers of cells with a delicate spiral fibrous deposit on 
 their walls. This layer forms a kind of coat over the real 
 epidermis of the root, and is known by the name of the 
 Velamen radicum. The young shoots of Dicotyledonous 
 trees and shrubs are clothed with epidermis-like herbaceous 
 plants ; but, before the close of the past season of growth, 
 in most cases the green colour gives place to brown, which 
 is owing to the formation of a layer of cork from the outer 
 layers of cortical parenchyma. Cork is composed of 
 tubular thin-walled cells containing only air ; and some- 
 times these intercellular passages occupy a considerable 
 space, and communicate in all directions, forming a system 
 of air-spaces in the tissue. In addition there is the secre- 
 tory system, consisting of glands, simple and compound, 
 milk-vessels, and canals filled with resins, oils, &c. 
 
 Much of the physiological histor} r of plant life has yet 
 to be made out : the mode in which the circulation and 
 the formation of wood are carried on is by no means a 
 settled question. Mr. Herbert Spencer observes i 1 "That 
 the supposition that certain vessels and strings of partially 
 united cells, lined with spiral, annular, reticulated, or 
 other frameworks, are carriers of the plant juices, is 
 objected to on the ground that they often contain air; 
 as the pressure of air arrests the movements of blood 
 through arteries and veins, its presence on the ducts of 
 stems and patioles is assumed to unfit them as channels 
 for sap. On the other hand, that these structures have 
 a respiratory office, as some have thought, is certainly 
 not more tenable, since the presence of air in them 
 negatives the belief that their function is to distribute 
 liquid. The presence of liquid in them equally nega- 
 tives the belief that their function is to distribute air. 
 K"or can any better defence be made for the hypothesis 
 which I find propounded, that these parts serve 'to 
 give strength to the parenchyma.' In the absence of any 
 feasible alternative, the hypothesis that these vessels are 
 distributors of sap claims reconsideration." To obtain data 
 for an opinion on this vexed question, Mr. Spencer insti- 
 tuted a series of experiments on the absorption of dyes by 
 plants. His first experiments were failures, and it was only 
 
 0) LinneanSoc. Trans, vol. xxv. pajrs 405. 
 
326 THE MICROSCOPE. 
 
 after trying experiments with leaves of different ages and 
 different characters, and with undeveloped axes, as well as 
 with axes of special kinds, that it became manifest that 
 the appearances presented by ordinary stems, when thus 
 tested, are in a great degree misleading. " If an adult shoot 
 of a tree or shrub be cut off, and have its lower end placed 
 in an alumed decoction of logwood, or a dilute solution 
 of magenta, 1 the dye will, in the course of a few hours, 
 ascend to a distance, varying according to the rate of eva- 
 poration from the leaves. On making longitudinal 
 sections of the part traversed by it, the dye is found to 
 have penetrated extensive tracts of the woody tissue ; and, 
 on making transverse sections, the openings of the ducts 
 appear as empty spaces in the midst of a deeply-coloured 
 prosenchyma. It would thus seem that the liquid is carried 
 up the denser parts of the vascular bundles, neglecting the 
 cambium layer, the central pith, and the spiral vessels of 
 the medullary sheath." This, however, is found to be only 
 partially true. " There are indications that while the layer 
 of pitted cells next the cambium has served as a channel 
 for part of the liquid, the rest has ascended the pitted 
 ducts, and oozed out of these into the prosenchyma around. 
 This is seen, if, instead of allowing the dye time for oozing 
 through the prosenchyraa, the end of the shoot be just 
 dipped into the dye and taken out again, we find that, 
 although it has become diffused to some distance round 
 the ducts, it has left tracts of wood between the ducts 
 mentioned. Again, if we use one dye after another, a 
 shoot that has absorbed magenta for an hour and then 
 placed for five minutes in the logwood decoction, transverse 
 sections taken at a short distance from the end of the shoot, 
 show the mouths of the ducts surrounded by dark stains 
 in the midst of the much wider red stains. The behaviour 
 of these corresponds perfectly with the expectation that a 
 liquid will ascend capillary tubes in preference to simple 
 cellular tissue, or tissue not differentiated into continuous 
 
 (1) "These two dyes have affinities for different components of the tissues, and 
 may be advantageously used in different cases. Magenta is rapidly taken up by 
 woody matter and secondary deposits, while logwood colours the cell-membranes, 
 and takes but reluctantly to the substances seized by magenta. By trying both 
 of them on the same structure, we may guard ourselves against any error arising 
 from relative combination." 
 
STRUCTURE OP PLANTS. 
 
 327 
 
 canals. Experiments with leaves bring out parallel facts ; 
 and this, then, is confirmed, that in ordinary stems the 
 staining of the wood by an ascending coloured liquid is 
 due, not to the passage of the coloured liquid up the sub- 
 
 Fig. 172. Termination of Vascular Syttem (after Spencer). 
 
 1. Absorbent organ from the leaf of Euphorbia, nerilfolia. The cluster of 
 fibrous cells forming one of the terminations of the vascular system is here 
 embedded in a solid parenchyma. 
 
 2. A structure of analogous kind from the leaf of Ficus elastica. Here the 
 expanded terminations of the vessels are embedded in the network paren- 
 chyma, the cells of which unite to form envelopes for them. 
 
 3. End view of an absorbent organ from the root of a turnip. It is taken 
 from the outermost layer of vessels. Its funnel-shaped interior is drawn as it 
 presents itself when looked at from the outside of this kyer, its narrow end 
 being directed towards the centre of the turnip. 
 
 4. Shows on a larger scale one of these absorbents from the leaf of Panax 
 Lessonii. In this figure is clearly seen the way in which the cells of the net- 
 work parenchyma unite into a closely-fitting case for the spiral cells. 
 
 5. A less-developed absorbent, showing its approximate connexion with a 
 duct. In their simplest forms, these structures consist of only two fenestratcd 
 cells, with tneir ends bent round so as to meet. Such types occur in the cen- 
 
328 THE MICROSCOPE. 
 
 tral miss of the turnip, where the vascular system is relatively imperfect 
 Besides the comparatively regular forms of these absorbents, there are forms 
 composed of amorphous masses of f enestrated cells. It should be added that 
 both the regular and irregular kinds are very variable in their numbers : in 
 some turnips they are abundant, and in others scarcely to be found. Possibly 
 their presence depends on the age of the turnip. 
 
 6. Represents a much more massive absorbent from the same leaf, the sur- 
 rounding tissues being omitted. 
 
 7. Similarly represents, without its sheath, an absorbent from the leaf of 
 Clusia flava. 
 
 8. A longitudinal section through the axis of another such organ, showing its 
 annuli of reticulated cells when cut through. The cellular tissue which fills 
 the interior is supposed to be removed. 
 
 stance of the wood, but to the permeability of its ducts 
 and such of its pitted cells as are united into regular 
 canals ; and the facts showing this at the same time in- 
 dicate with tolerable clearness the process by which wood 
 is formed, for what in these cases is seen to take place 
 with dye may be fairly presumed to take place with sap." 
 
 Taking it, then, as a fact that the vessels and ducts are 
 the channels through which the sap is distributed, the 
 varying permeability of their walls, and consequent for- 
 mation of wood, is due to the exposure of the plant 
 to intermittent mechanical strains, actual or potential, or 
 both, in this way. "If a trunk, a bough, shoot, or a 
 petule is bent by a gust of wind, the substance of its 
 convex side is subject to longitudinal tension, the substance 
 of its concave side being at the same time compressed. 
 This is the primary mechanical effect. The secondary is 
 when the tissues of the convex side are stretched, they 
 also produce lateral compression of them. In short, that 
 " the formation of wood is due to intermittent transverse 
 strains, such as are produced in the aerial parts of upright 
 plants by the action of the wind." Thus the subject is 
 most ingeniously worked out, and the results of many 
 very interesting and instructive experiments are recorded 
 by the author of the paper. 
 
 "In the course of experiments on the absorption of 
 dyes by leaves, it happened that, in making sections 
 parallel to the plane of a leaf, with the view of separating 
 its middle layer, containing the vessels, I came upon some 
 structures that were new to me. These structures, where 
 they are present, form the terminations of the vascular 
 system. They are masses of irregular and imperfectly 
 united fibrous cells, such as those out of v.'hich vessels 
 
STRUCTURE OP PLANTS. 329 
 
 are developed ; and they are sometimes slender, sometimes 
 bulky usually, however, being more or less club-shaped. 
 In transverse sections of leaves, their distinctive characters 
 are not shown ; they are taken for the smaller veins. It 
 is only by carefully slicing away the surface of a leaf, 
 until we come down to that part which contains them, 
 that we get any idea of their nature. Fig. 172, No. 1, repre- 
 sents a specimen taken from a leaf of Euphorbia neriifolia. 
 Occupying one of the interspaces of the ultimate venous 
 network, it consists of a spirally-lined duct or set of 
 ducts, which connects with the neighbouring vein a 
 cluster of half-reticulated, half-scalariform cells. These 
 cells have projections, many of them tapering, which insert 
 themselves into the adjacent intercellular spaces, thus 
 producing an extensive surface of contact between the 
 organ and the embedding tissues. A further trait is, that 
 the ensheathing prosenchyma is either but little developed 
 or wholly absent ; and consequently this expanded vascular 
 structure, especially at its end, comes immediately in con- 
 tact with the tissues concerned in assimilation. The leaf 
 of Euphorbia neriifolia is a very fleshy one ; and in it 
 these organs are distributed through a compact, though 
 watery, cellular mass. But in any leaf, of the ordinary 
 type, which possesses them, they lie in the network of 
 parenchyma, composing its lower layer ; and wherever they 
 occur in this layer its cells unite to enclose them. This 
 arrangement is shown in No. 2, representing a sample 
 from the Caoutchouc-leaf as seen with the upper part of 
 its envelope removed ; and it is shown still more clearly 
 in a sample from the leaf of Panax Lessonii, No. 4. 
 Nos. 6 and 7 represent, without their sheaths, other such 
 organs from the leaves of Panax Lt&sonii and Clusia 
 Jlava. Some relation seems to exist between their forms 
 and the thicknesses of the layers in which they lie. 
 Certain very thick leaves, such as those of Clusia Jlava, 
 have them less abundantly distributed than is usual, but 
 more massive. When the parenchyma is developed not 
 to so great an extreme, though still largely, as in the 
 leaves of Holly, Aucuba, Camellia, they are not so bulky ; 
 and in thinner leaves, like those of Privet, Elder, &c., 
 they become longer and less conspicuously club-shaped. 
 
330 THE MICROSCOPE. 
 
 " Some adaptations to their respective positions seem 
 implied by these modifications ; and we may naturally 
 expect that in many thin leaves these free ends, becoming 
 still narrower, lose the distinctive and suggestive characters 
 possessed by those shown in the drawings. Eelations of 
 this kind are not regular, however. In various other 
 genera, members of which I have examined, as Rims, 
 Viburnum, Griselinia, Brexia, Botryodendron, Pereslcia, 
 the variations in the bulk and form of these structures are 
 not directly determined by the spaces which the leaves 
 allow; obviously there are other modifying causes. It 
 should be added that while these expanded free extre- 
 mities graduate into tapering free extremities, not differing 
 from ordinary vessels, they also pass insensibly into the 
 ordinary inosculations. Occasionally, along with numerous 
 free endings, there occur loops ; and from such loops there 
 are transitions to the ultimate meshes of the veins. 
 
 " These organs are by no means common to all leaves. 
 In many that afford ample spaces for them they are not to 
 be found. So far as I have observed, they are absent from 
 the thick leaves of plants which form very little wood. 
 In Sempervivum, in Echeveria, in Bryopliyllum they do not 
 appear to exist ; and I have been unable to discern them 
 in Kalanchoe rotundifolia, in Kleinia ante-euphorbium, and 
 ficoides, in the several species of Crassula, and in other suc- 
 culent plants. It may be added that they are not absolutely 
 confined to leaves, but occur in stems that have assumed 
 the functions of leaves. At least I have found,, in the 
 green parenchyma of Opuntia, organs that are analogous, 
 though much more rudely and irregularly formed. In 
 other parts, too, that have usurped the leaf-function, they 
 occur, as in the phyllodes of the Australian acacias. 
 These have them abundantly developed ; and it is interest- 
 ing to observe that here, where the two vertically-placed 
 surfaces of the flattened-out petiole are equally adapted to 
 the assimilative function, there exist two layers of these 
 expanded vascular terminations, one applied to the inner 
 surface of each layer of parenchyma. 
 
 "Considering the structures and positions of these organs, 
 as well as the natures of the plants possessing them, may 
 we not form a shrewd suspicion respecting their function 1 
 
STRUCTURE OF PLANTS. 331 
 
 I& it not probable that they facilitate absorption of the juices 
 carried back from the leaf for the nutrition of the stem 
 and roots ? They are admirably adapted for performing 
 this office. Their component fibrous cells, having angles 
 insinuated between the cells of the parenchyma, are shaped 
 .just as they should be for taking up its contents, and the 
 absence of sheathing tissue between them and the paren- 
 chyma facilitates the passage of the elaborated liquids. 
 Moreover, there is the fact that they are allied to organs 
 which obviously have absorbent functions. I am indebted 
 to Dr. Hooker for pointing out the figures of two such 
 organs in the Icones Anatomicoe of Link. One of them 
 is from the end of a dicotyledonous root-fibre, and the other 
 is from the pro thai lus of a young fern. In each case a 
 cluster of fibrous cells, seated at a place from which liquid 
 has to be drawn, is connected by vessels with the parts to 
 which liquid has been carried. I have met with another 
 such organ, more elaborately constructed, evidently adapted 
 to the same office, in the common turnip-root. As shown by 
 the end view and longitudinal section in Nos. 3, 5, and 8, 
 this organ consists of rings of fenestrated cells, arranged 
 with varying degrees of regularity into a funnel, ordinarily 
 having its apex directed towards the central mass of the 
 turnip, with which it has, in some cases at least, a traceable 
 connexion by a canal. Presenting as it does an external 
 porous surface terminating one of the bramches of the vas- 
 cular system, each of these organs is well fitted for taking 
 up with rapidity the nutriment laid by in the turnip-root, 
 and used by the plant when it sends up its flower-stalk. 
 The cotyledons of young beans furnish other examples 
 of such structures, exactly in the places where, if they be 
 absorbents, we may expect to find them. Amid the 
 branchings and inosculations of the vascular layer running 
 through the mass of nutriment deposited in each coty- , 
 ledon, there are found conspicuous free terminations that 
 are club-shaped, and which prove to be composed, like 
 those in leaves, of irregularly-formed and clustered fibrous 
 cells, some of them diverging from the plane of the vascular 
 layer, dipping down into the mass of starch and albumen 
 which the young plant has to utilize, and which these 
 structures can have no other function but to take up." 
 
332 
 
 THE MICROSCOPE. 
 
 To return to cell- development j we found the cell chang- 
 ing in its outward form, the transparent membranous cell 
 wall becoming thickened, and spontaneous fissure taking 
 place; and thus is formed a series of connected cells 
 variously modified and arranged, according to the conditions 
 under which they are developed and the functions which, 
 they are destined to exercise. The typical form, as we have 
 
 Fig. 173. a, elementary cells ; b, branched cellular tissue. 
 
 before observed, of the vegetable cell .is spheroidal ; but 
 when developed under pressure within walls, or denser 
 tissues, it takes other shapes ; 
 as the oblong, lobed, square, 
 prismatical, cylindrical, fusi- 
 form, muriform, stellate, fila- 
 mentous, &c. : and is then 
 termed Parenchyma, and the 
 cells woven together are called 
 cellular tissue. In pulpy fruits 
 the cells may be easily separated 
 one from the other : a thin trans- 
 verse section of a strawberry is 
 represented at fig. 188, No. 15 : 
 within the cells are smaller 
 cells, commonly known as the 
 pulp. Fig. 173, a, is the ele- 
 mentary form of oval cells or 
 vesicles > P as ^g on to the for- 
 mation of branched cellular 
 
 ,. 7 T> 111 
 
 tissue, o. Remarkable speci- 
 mens of the filamentous tissue may be seen in fig. 188, 
 No. 1 9, the circular elongated cells from the Mushroom ; 
 only another and more closely connected growth of inuce- 
 dinous fungi, commonly called mushroom spawn. 
 
 nai shape of ceils. 2, A vertical 
 
 section of elongated cell. 
 
CELLULAR TISSUES. 
 
 333 
 
 Fig. Vlf. Stellate tissue, from stem 
 of a Rush. 
 
 Fig. 175, in thfe stellate tissue cut from the stem of a 
 rush, we have the forma- 
 tive network dividing into 
 ducts for the purpose of 
 giving strength and light- 
 ness to the stem of the plant. 
 These ducts may undergo 
 other transformations; the 
 cell itself become gra- 
 dually changed into a 
 spiral continuous tube or 
 duct, as seen in fig. 198 ; 
 these are sometimes formed by the breaking down of the 
 partitions ; in the centre of which we may have a com- 
 pound spiral duct, resembling portions of tracheae from 
 the silkworm. 
 
 Another important change occurs in the original cell, 
 it is that of its conversion into woody fibre. Common 
 woody fibre (Pleurenchyma) 
 has its sides free from de- 
 finite markings. In the 
 coniferous plants, the tubes 
 are furnished with circular 
 discs ; these discs are 
 thought to be contrivances 
 to enable the tubules of 
 
 the WOodv tissues tO dis- Fig. 176. A section of stem of Clematis, 
 ,, '. with pores, Inijhly magnified, to show 
 
 charge their contents from ihe n ne W hi C h pa**es round them. 
 oue to the other, or into the 
 
 cellular spaces. Plants having aromatic secretions are 
 furnished with glands ; these form a series of interesting 
 objects, and such as the sage-leaf should be mounted as 
 opaque specimens. A large central gland is seen in a section 
 of a leaf from Ficus elastica, India-rubber-tree, fig. 177, No. 2. 
 Professor Quekett observes, " The nature of the pores, or 
 discs, in conifers, has long been a subject for controversy; 
 it is now certain that the bordered pores are not peculiar to 
 one fibre, but are formed between two contiguous to each 
 other, and always exist in greatest numbers on those sides 
 of the woody fibres parallel to the medullary rays. They 
 are hollow ; their shape biconvex ; and in their centre is 
 
334 
 
 THE MICROSCOPE. 
 
 a small circular or oval spot, fig. 176 : the latter may 
 occur singly, or be crossed by another at right angles, 
 
 Fig. m. 
 
 1, Vertical section of root of Alder, with outer wall. 2, A vertical section of a 
 leaf of the India-rubber tree, exhibiting a central gland. 
 
 which gives the appearance of a cross, as in fig. 204, Nos. 3, 
 4, a vertical section of fossil wood, remarkable for having 
 three or four rows of woody tissue occupied by large pores 
 without central markings." 
 
 We now pass to the milk, lacticiferous ducts or tissue, 
 
 the proper vessels of the old 
 writers. These ducts con- 
 vey a peculiar fluid, some- 
 times called latex, usually 
 turbid, and coloured red, 
 white, or yellow ; often, 
 however, colourless. It is 
 supposed they carry latex 
 to all the newly-formed 
 organs, which are nourished 
 
 ^* ^ The fluid be comes 
 
 darker after being mounted for specimens to be viewed 
 under the microscope. This tissue is remarkable from its 
 resemblance to the earliest aggregation of cells, the yeast- 
 plant and therefore has some claim to being considered 
 the stage of development preceding that of the return- 
 
 7B. -Lacticiferous tissue. 
 
CELLULAR TISSUES. 
 
 335 
 
 lated ducts seen in fig. 178. In a section from tho 
 India-rubber-tree, fig. 177, No. 2, a network of these lac- 
 tiferous tubes will be found filled with a brownish or 
 
 Fig. 179. 
 
 !, A portion of the leaf of Sphagnum, showing ducts, vascular tissue, and spiral 
 fibre in the interior of its cells. 2, Porous cells, from the testa of Gourd- 
 seed, communicating -with each other, and resembling ducts. 
 
 granular matter ; that in fig. 178 is an enlarged view of 
 this tissue from the wood of an exogen, taken near the 
 root. 
 
 I, Reticulated ducts. 
 
 Fig. 180. 
 2, A vertical section of Fern-root. 
 
 In many plants external to the cuticle, there exists a 
 very delicate transparent pellicle, without any decided 
 traces of organisation, though occasionally somewhat gra- 
 nular in appearance, and marked by lines that seem to 
 be impressions of the junction of the cells in contact with 
 each other. In nearly all plants, the* cuticle is perforat 
 
336 THE MICROSCOPE. 
 
 by minute openings termed Stomata, which are bordered by 
 cells of a peculiar form, distinct from those of the cuticle. 
 In Iris germanica, fig. 181, each surface has nearly 12,000 
 
 1, Portion of a vertical section of the Leaf of the Iris: a, a, elongated cells of 
 the epidermis; b, stomaia cut through longitudinally; c, c, cells of the 
 parenchyma; d, d, colourless tissue of the interior of the leaf. 2, Portion of 
 leaf of Iris germanica, torn from its surface; a, elongated cells of the cuticle; 
 b, cells of the stomata; c, cells of the parenchyma; d, impressions on the epi- 
 dermic cells ; e, lacunae in the parenchyma. 
 
 stomata in every square inch ; and in Yucca each surface 
 has about 40,000. 
 
 The structure of the leaf of the common Iris shows 
 a central portion, formed by thick- walled colourless tissue, 
 very different from ordinary leaf-cells or from woody fibre. 
 
 Fig. 182. A portion of the efidermi$ of the Sugar-cane, showing the two kinds oj. 
 cells of which ii is composed. (Magnified 200 diameters.) 
 
CSLLULAR TISSUE. 337 
 
 Variously-cut sections of leaves should be made, and slices 
 taken parallel to the surfaces at different distances, for the 
 purpose of microscopic examination. 
 
 Among the cell-contents of some plants, are beautiful 
 crystals called Raphides : the term is derived from pac^is, 
 a needle, from the resemblance of the crystal to a needle. 
 They are composed of the phosphate and oxalate of lime ; 
 there is a difference of opinion as to their use in the 
 -economy of the plant. 
 
 Mr. Gulliver has insisted upon the value of Eaphides 
 as characteristic points in many families of plants. 
 
 He observes that doubts as to the value of raphides as 
 natural characters and as to their importance in the vege- 
 table economy at all will be entertained by those who do 
 not clearly distinguish between raphides and sphseraphides. 
 Schleiden asserts that the '"needle-formed crystals, in 
 bundles of from twenty to thirty in a cell, are present in 
 almost all plants," and " that inorganic crystals are rarely 
 met with in cells in a full state of vitality." 
 
 He further states that so really practical is the presence 
 or absence of raphides, that by noticing them he has been 
 able to pick out pots of seedling Onagraceae, which had 
 been accidentally mixed with pots of other seedlings of 
 the same age, and at that period of growth when no 
 botanical character before in use would have been so 
 readily sufficient for the diagnosis. 
 
 If we examine a portion of the layers of an onion, fig. 
 183, No. 1, or a thin section of the stem or root of the 
 garden rhubarb, fig. 183, No. 4, we shall find many cells 
 in which, either bundles of needle-shaped crystals, or 
 masses of a stellate form occur, not strictly raphides. 
 
 Raphides were first noticed by Malpighi in Opuntia. 
 and subsequently described by Jurine and Raspail. 
 According to the latter observer, the needle-shape or 
 acicular are composed of phosphate, and the stellate of 
 oxalate of lime. There are others having lime as a basis, 
 in combination with tartaric, malic, or citric acid. These 
 are easily destroyed by acetic acid, and are also very soluble 
 in many of the fluids employed in the conservation of ob- 
 jects; some of them are as large as the l-40th of an inch, 
 others are as small as the l-1000th. They occur in all 
 z 
 
538 THE MICROSCOPE. 
 
 parts of the plant ; in the stem, bark, leaves, stipules, 
 petals, fruit, root, and even in the pollen, with some 
 exceptions. They are always situated in the interior 
 of cells, and not, as stated by Raspail and others, in the 
 
 Fig. 183. 
 
 1, A section from the outer layer of the bulb of an Onion, showing crystals of 
 carbonate of lime. 3, Cells of the Pear, showing Sclerogen, or gritty tissue. 
 4, Cells of garden Rhubarb, filled with raphides. 5, Cells from same, filled 
 with starch-grains. 
 
 intercellular passages. 1 Some of the containing cells be- 
 come much elongated ; but still the cell- wall can be readily 
 traced. In some species of Aloe, as, for instance, Aloe 
 verrucosa, with the naked eye we are able to discern small 
 silky filaments: when magnified, they are found to be 
 bundles of the acicular form of raphides, which no doubt 
 act the part of a stay or prop to the internal soft pulp. 
 
 In portions of the cuticle of the medicinal squill 
 Scilla maritima several large cells may be observed, full 
 of bundles of needle-shaped crystal. These cells, however, 
 do not lie in the same plane as the smaller ones belonging 
 to the cuticle. In the cuticle of an onion every cell is oc- 
 cupied either by an octahedral or a prismatic crystal of 
 oxalate of lime : in some specimens the octahedral form 
 predominates ; but in others from the same plant the 
 
 (1) "As an exception, many years ago they were discovered in the interior of 
 the spiral vessels in the stem of the grape-vine ; but with some botanists this 
 <rould not he considered as an exceptional case, the vessels being regarded as 
 elongated cells." Quekett. 
 
CRYSTALS IN PLANTS. 
 
 339 
 
 crystals will be principally prismatic, and are arranged aa 
 if they were beginning to assume a stellate form. Some 
 plants, as many of the cactus 
 tribe, are made up almost 
 entirely of raphides. In 
 some instances every cell of 
 the cuticle contains a stel- 
 late mass of crystals ; in 
 others the whole interior is 
 full of them, rendering the 
 plant so exceedingly brittle, 
 that the least touch will 
 occasion a fracture; so much 
 so, that some specimens of 
 Cactus senilis, said to be a 
 thousand years old, which 
 were sent a few years since 
 to Kew from South America, 
 were obliged to be packed 
 
 -.I 11 .1 Fig. 184 Siliceous cuticle from under 
 
 in COtton, With all the Care surface of leaf of Deutzia scabra. 
 
 of the most delicate jewel- 
 lery, to preserve them during transport. 
 
 Raphides, of peculiar figure, are common in the bark of 
 many trees. In the Hiccory 
 (Cari/a alba) may be ob- 
 served masses of flattened 
 prisms having both extre- 
 mities pointed. In vertical 
 sections from the stem of 
 Elceagnus angustifolia, nu- 
 merous raphides of large size 
 are embedded in the pith. 
 Raphides are also found in 
 the bark of the apple-tree, 
 and in the testa of the seeds 
 of the elm ; every cell con- 
 tains two or more very 
 minute crystals. 
 
 In figs. 184 and 185 we 
 have other representations y^ 
 of the crystalline structure 
 
 z 2 
 
 185. Siliceout cuticle of Orau 
 (Pharus cristattu), 
 
340 
 
 THE MICROSCOPE. 
 
 of plants, in sections taken from grass, and the leaf of 
 Deutzia scabra. This insoluble material is called silica, 
 and is abundantly distributed throughout certain orders 
 of plants, leaving a skeleton after the soft vegetable 
 matters have been destroyed : masses of it, having the 
 appearance of irregularly-formed blackened glass, will 
 always be found after the burning of hay or straw ; which 
 is caused by the fusion of the silica contained in tbe 
 cuticle combining with the potash in the vegetable tissue, 
 thus forming a silicate of potash (glass). To display this 
 siliceous structure, it is necessary to cut very thin slices 
 from the cuticle, and mount them in fluid or Canada 
 balsam. 
 
 In the Grammacece, especially the canes ; in the Equi- 
 setum hyemale, or Dutch rush ; in the husk of the rice, 
 
 wheat, and other grains, 
 silica is abundantly found. 
 In the Pharus cristatus, 
 an exotic grass, fig. 185, 
 we have beautifully-ar- 
 ranged masses of silica with 
 raphides. The leaves of 
 Deutzia, fig. 184 are re- 
 markable for their stel- 
 late hairs developed from 
 the cuticle, of both their 
 upper and under surfaces ; 
 
 c^fyrg H^ 
 ^^ - : 1| g -| 
 
 . .::> ^ '.s| 
 
 -,:'SM;ci' 
 
 ,-^3^' .- ^s 
 
 Fig. 
 
 CL Portion of the husk of Wheat, 
 showing siliceous crystals. 
 
 forming most interesting 
 and attractive objects when 
 examined under the micro- 
 scope with polarised light. 
 See Plate VIII. No. 173. 
 
 Silica is found in all Ru- 
 biacece; both in the stem 
 and leaves, and if present in sufficient thickness, depolarises 
 light. This is especially the case in the prickles, which 
 all these plants have on the margin of the leaves and the 
 angles of the stem. One of the order Compositce, a plant 
 popularly known as the "sneezewort," (Archillce ptarmica) 
 has a large amount of silica in the hairs found on the 
 double serratures of its leaves j commonly said to be the 
 
CELL-CONTENTS. STARCH. 
 
 341 
 
 cause of its errhine properties when powdered and used as 
 snuff. It is in the underlying or true epidermis, that the 
 silica occurs. This membrane is permeable by fluids, not 
 by means of pores, but by endosmotic force. 
 
 " The most generally-distributed and conspicuous of the 
 cell-contents is Starch; at 
 the same time it is one of 
 ^reat value and interest, per- 
 forming a similar office in 
 the economy of plants as that 
 of fat in animals. It occurs 
 in all plants at some period of 
 their existence, and is the 
 chief and great mark of dis- 
 tinction between the vege- 
 table and animal kingdoms. 
 Its presence is detected by 
 testing with a solution of 
 iodine, which changes it to 
 a characteristic blue or violet 
 colour. 1 Being insoluble in 
 
 cold water, it can be readily Fig. 137. section of a cane : with ceii- 
 washed away and separated 
 from other matters contained 
 in the cellular parts of full-grown plants. It is often 
 found in small granular masses in the interior of cells, 
 shown in fig. 183 from the garden-rhubarb. Starch-grains 
 are variable in size; the tous-les-mois, fig. 188, No. 5, are 
 very large ; in the potato, No. 14, they are smaller ; and 
 in rice, No. 6, they are very small indeed. Nearly all pre- 
 sent the appearance of concentric irregular circles ; and most 
 of the granules have a circular spot, termed the hilum, 
 around which a large number of curved lines arrange them- 
 selves: better seen under polarised light. Plate YIII.No. 167. 
 Leeuwenhoek, to whom we are indebted for the earliest 
 notice of starch-granules, enters with considerable minute- 
 ness into a description of those of several plants such as 
 wheat, barley, rye, oats, peas, beans, kidney-beans, buck- 
 wheat, maize, and rice ; and veiy carefully describes 
 experiments made by him in order to investigate the 
 structure of starch-granules. Dr. Keissek regards the 
 
 (1) This is not a test for starch when combined with albuminous matters. 
 
342 THE MICROSCOPE. 
 
 granule as a perfect cell, from the phenomena presented 
 during its decay or dissolution, when left for some time in 
 water. Schleiden and others, after examining its expan- 
 sion and alteration under the influence of heat and of 
 sulphuric acid, considered it to be a solid homogeneous 
 structure. 
 
 Professor Busk agrees with M. Martin in believing the 
 primary form of the starch-granule to be " a spherical or 
 ovate vesicle, the appearance of which under the micro- 
 scope, when submitted to the action of strong sulphuric 
 acid, conveys the idea of an unfolding of plaits or rugse, 
 which have, as it were, been tucked in towards the centre 
 of the starch-grain." 1 The mode of applying the concen- 
 trated sulphuric acid is thus described by Mr. Busk : " A 
 small quantity of the starch to be examined is placed 
 upon a slip of glass, and covered with five or six drops of 
 water, in which it is well stirred about ; then with the 
 point of a slender glass-rod the smallest possible quantity 
 of solution of iodine is applied, which requires to be 
 quickly and well mixed with the starch and water; as 
 much of the latter as will must be allowed to drain off, 
 leaving the moistened starch behind, or a portion of it 
 may be removed by an inclination of the glass, before it is 
 covered with a piece of thin glass. The object must be 
 placed on the field of the microscope, and the ^-inch 
 object-glass brought to a focus close to the upper edge of 
 the thin glass. With a slender glass-rod a small drop of 
 strong sulphuric acid must be carefully placed immediately 
 upon, or rather above the edge of the cover, great care 
 being necessary to prevent its running over. The acid 
 quickly insinuates itself between the glasses, and its course 
 may be traced by the rapid change in the appearance of 
 the starch-granules as it comes in contact with them. 
 The course of the acid is to be followed by moving the 
 object gently upwards ; and when, from its diffusion, the 
 re-agent begins to act slowly, the peculiar changes in the 
 starch- granules can be more readily witnessed. In pressing 
 or moving the glasses, the starch disc becomes torn, and 
 is then distinctly seen, especially in those coloured blue, to 
 
 (1) Professor G. Busk, F.R.S., on the Structure of the Starch-granule; Quar- 
 terly Journal of Microscopical Science, April, 1853. 
 
CELL-CONTENTS STARCH. 
 
 343 
 
 consist of two layers, an upper and a lower one ; and the 
 collapsed vesicular bodies of an extremely fine but strong 
 and elastic membrane." Mr. Busk believes the hilum 
 to be a central opening into the interior of the ovate 
 vesicle. 
 
 15 
 
 1, Nucleated Cells. 2, Stinging-nettle Hairs, Urtica Dioica. 3, Ciliated spores 
 of Conferva. 4, Starch grains, broken by the application of heat. 5, Starch 
 from Tous-les-mois. 6. Starch from Rice. 7, Starch from Sago. 8, Imita- 
 tion Sago-starch. 9, Wheat-starch. 10, Rhubarb-starch, in isolated 
 cells. 11, Maize-starch. 12, Oat-starch. 13, Barley-starch. 14, Potato- 
 starch. 15, Section of Strawberry, cells ovoid, containing granular matter. 
 16, Section of Potato, with starch destroyed by fungoid disease. 17, Potato, 
 with nearly all starch-grains absent. 18, Section of Potato, cells filled with 
 healthy starch. (These starches are grouped for comparison.) 19, Mushroom 
 spawn, elongated cells. 
 
 Nitric acid communicates to wheat-starch a fine orange- 
 yellow colour ; and recently-prepared tincture of guaiacum 
 gives a blue colour to the starch of good wheat-flour. 
 
344 THE MICROSCOPE. 
 
 Pure wheat-flour is almost entirely dissolved in a strong 
 solution of potash, containing twelve per cent, of the alkali ; 
 but mineral substances used for the purpose of adultera- 
 tion remain undissolved. 
 
 Wheat-flour is frequently adulterated with various sub- 
 stances ; and in the detection of these adulterations, the 
 microscope, together with a slight knowledge of the action 
 of chemical re-agents, lends important assistance. It 
 enables us to judge of the size, shape, and markings on the 
 starch grains, and thereby to distinguish the granules of 
 
 J. 189. Wheat-Flour Starch-granules, with a small portion of its cellulose 
 (Magnified 420 diameters.) 
 
 one meal from that of another. In some cases the micro- 
 scopic examination is aided by an application of a solu- 
 tion of potash. Thus we may readily detect the mixture 
 of wheat-flour with either potato-starch, meal of the 
 pea or bean, by the addition of a little water to a small 
 quantity of the flour, then, by adding a few drops of 
 a solution of potash (made of the strength one part liquid 
 potash to three parts of water), the granules of the potato- 
 
ADULTERATION OP WHEAT-FLOUR. 345 
 
 starch will immediately swell up, and acquire three or four 
 times their natural size ; while those of the wheat-starch 
 are scarcely affected by it ; if adulterated with pea or bean 
 meal, the hexagonal tissue of the seed is at the same time 
 rendered very obvious under the microscope. Polarised 
 light will be of use as an additional aid ; wheat-starch 
 presents a faint black cross proceeding from the central 
 hilum, whereas the starch of the oat shows nothing of 
 the kind. 
 
 Fig. 190. Potato Starch-yranules, sold under Ike name of British Arrow-root, 
 used to adulterate flour and bread. (Magnified 240 diameters.) 
 
 The diseases of wheat and corn are readily detected 
 under the microscope ; some of which will be seen to be 
 produced by a parasitic fungus, and by an animalcule re- 
 presented in another place : all are more or less dangerous 
 when mixed with articles of food. 
 
 Adulteration of bread with boiled and maslied potatoes, 
 next to that by alum, is, perhaps, the one which is most 
 commonly resorted to. The great objection to the use of 
 potatoes in bread, is, that they are made to take the place 
 
346 THB MICROSCOPE. 
 
 of an article very much more nutritious. This adulteration, 
 can be instantly detected by means of the microscope. 
 The cells which contain the starch- corpuscles are, in the 
 potato, very large, fig. 190 ; in the raw potato they are 
 adherent to each other, and form a reticulated structure, 
 in the meshes of which the well-defined starch- granules 
 are clearly seen ; in the boiled potato, however, the cells 
 separate readily from each other, each forming a distinct 
 article : the starch-corpuscles are less distinct and of an 
 altered form. 
 
 Fig. 191. Adulterated Cocoa, sold under the name of Homoeopathic Cocca. 
 (After Hassall.) 
 
 aaa, granules and cells of cocoa; bbb, granules of Canna-starch, or Tous-les- 
 mois; c, granules of Tapioca-starch. 
 
 Adulteration with alum and "stuff." This adulteration 
 is practised with a twofold object : first to render flour of 
 a bad colour and inferior quality white and equal, in 
 appearance only, to flour of superior quality ; and secondly 
 to enable the flour to retain a larger proportion of water, 
 
ADULTERATION OF POOD. 347 
 
 by which the loaf is made to weigh heavier. By dissolving 
 out the alum in water and then re-crystallising it under 
 the microscope, this adulteration is readily detected. 
 
 Before leaving the subject of starch, allusion may be 
 made to the prevalent and destructive epidemic amongst 
 potatoes, which is a disease of the tuber, not of the haulm 
 or leaves. " Examined in an early stage, such potatoes 
 are found to be composed of cells of the usual size ; but 
 they contain little or no starch : this will be seen upon 
 reference to Nos. 16 and 17, fig. 188. Hence it may be 
 
 Fig. 192. Structure and Character of genuine Ground Coffee. (After Hassall.) 
 
 inferred, that the natural nutriment of the plant being 
 deficient, the haulm dies, the cells of the tuber soon turn 
 black and decompose; and ftmgi developed as in most 
 other decaying vegetable substances. 
 
 "This will undoubtedly explain the most prominent 
 symptom of the potato-disease, the tendency to decom- 
 position ; and is a point in which the microscope confirms 
 the result of chemical experiment : for it has been found 
 
348 
 
 THE MICROSCOPE. 
 
 that the diseased potatoes contain a larger proportion of 
 water than those that are healthy. A want of organizing 
 power is evidently the cause of this deficiency of starch ; 
 but we fear the microscope will never tell us in what the 
 want of this organising force consists." 1 
 
 The adulteration of articles of food and drink has long 
 been a matter of uneasy interest, and of strong, though 
 vague, misgiving. Accum's Death in the Pot, between 
 thirty and forty years ago, awoke attention to the subject; 
 which has since been more or less accurately explored by 
 
 Fig. 193. Sample of Coffee, adulterated with both Chicory and Roasted 
 Wheat. (After Hassall.) 
 
 m a a, small fragments of coffee ; b b b, portions of chicory ; c c c, starch-granules 
 of wheat. 
 
 Mitchell, Normandy, Chevalier, Jules Gamier, and Harel; 
 and has at length derived a singularly lucid exposi- 
 tion from Dr. Hassall's researches, whose report of these 
 inquiries fills between 600 and 700 closely printed pages 
 
 (1) Professor Quekett's Histology of Vegetables. We would refer the reader 
 to a curious work on Fungi, by Arimini, an Italian botanist, 1759. 
 
ADULTERATION OF FOOD. 
 
 34D 
 
 of a large octavo, replete with details of the fraudulent 
 contaminations commonly practised by the people's pur- 
 veyors, at the people's expense of health and pocket. 1 
 
 " In nearly all articles," said Dr. Hassall, before a com- 
 mittee appointed by the House of Commons to inquire 
 into these adulterations, " whether food, drink, or drugs, 
 my opinion is that adulteration prevails. And many of 
 the substances employed in the adulterating process were 
 not only injurious to health, but even poisonous." The 
 microscope was the effective instrument in the work of 
 
 Fig. 1M. Tea adulterated with foreign leaves. (After Hassall.) 
 
 a, upper surface of leaf; b, lower surface, showing cells; c, chloropht.il cells; 
 d, elongated cells found on the upper surface of the leaf in the course of the 
 veins ; e, spiral vessel ; /, cell of turmeri: ; g, fragment of Prussian blue ; A 
 particles of white powder, probably China clay. 
 
 detection. Less than five years ago, it would, we are told, 
 have been impossible to. detect the presence of chicory in 
 coffee : in fact, the opinion of three distinguished chemists 
 was actually quoted in the House of Commons to that effect; 
 
 (1) Food and Us Adulterations; comprising the Reports of the Analytical Sani- 
 tary Commission of the Lancet, for the years 1851 to 1854 inclusive. By Arthur 
 Hill Hassall, M.D. 
 
350 
 
 THE MICROSCOPE. 
 
 whereas by the use of the microscope the differences of 
 structure in these two substances, as in many other cases, 
 can be promptly discerned. Out of thirty-four samples of 
 coffee purchased, chicory was discovered in thirty-one ; 
 chicory itself being also adulterated with all manner of 
 compounds. There is no falling back either upon tea or 
 chocolate ; for these seem rather worse used than coffee. 
 Tea is adulterated, not only here, but still more in China ; 
 while as to chocolate, the processes employed in corrupting 
 the manufacture are described as " diabolical." " It 4 ~ 
 
 Fig. 195. 
 
 1, Radiating cells from the outer shell of the Ivory Nut. 2, Section of a Nut, 
 showing cells with small radiating pores. 
 
 often mixed with brick-dust to the amount of ten per 
 cent., ochre twelve per cent., and peroxide of iron twenty- 
 two per cent., and animal fats of the worst description. In 
 this country, cocoa is sold under the names of flake, rock, 
 granulated, soluble, dietetic, homoeopathic cocoa, &c., fig. 
 191. Such names are evidently employed to disguise the 
 fact that they are compounded of sugar, starch, and other 
 substances. 
 
 To return to the subject more immediately before us 
 Some of the plants belonging to the Orchideos Com- 
 melinece particularly Tradescantia virginica (Spiderwort), 
 portions of the epidermis, and the jointed hairs of 
 the filament, form interesting microscopic objects. The 
 surface of the latter is marked with extremely fine longi- 
 tudinal parallel equidistant lines or striae, whose intervals 
 are equal, from about TSWTJ- to 20000 of an ^ ncn - * fc 
 might therefore in some cases be used as a micrometer or 
 test object. The nucleus of the joint or cell is very dis- 
 tinct as well as regular in form ; and by gentle pressure 
 
CIRCULATION OP SAP IN PLANTS. 351 
 
 is easily separated entire from the joint. It then appears 
 to be exactly round, nearly lenticular, and its granular 
 matter is either held together by a coagulated pulp not 
 visibly granular, or, which may be considered equally pro- 
 bable, by an enveloping membrane. The analogy of this 
 nucleus to that existing in the various stages of develop- 
 ment of the colls in which the grains of pollen are formed 
 in the same species, is sufficiently obvious. 
 
 In the joint of the same, when immersed in water, 
 being at the same time freed from air, and consequently 
 made more transparent, a circulation of very minute 
 granular matter is visible. This requires at least a J power 
 to show it well. The motion of the granular fluid is 
 seldom in one uniform circle, but in several apparently 
 independent currents : and these again, though often 
 exactly longitudinal, and consequently in the direction of 
 the striae of the membrane, are not unfrequently observed 
 forming various angles with these striae. The smallest of 
 the currents appear to consist of a single series of granules. 
 The course of these currents seems often in some degree 
 affected by the nucleus, towards or from which many of 
 them occasionally tend or appear to proceed. They can 
 hardly, however, be said to be impeded by the nucleus, 
 for they are occasionally observed passing between its 
 surface and that of the cell ; a proof that this body does 
 not adhere to both sides of the cavity, and also that the 
 number and various directions of the currents cannot be 
 owing to partial obstructions arising from the unequal 
 compression of the cell. 
 
 Flower-buds. "In the very early stage of the flower- 
 bud, while the anthera are yet colourless, their loculi 
 are filled with minute lenticular grains, having a trans- 
 parent flat limb, with a slightly convex and minutely 
 granular semi-opaque disc. This disc is the nucleus of 
 the cell, which probably loses its membrane or limb, and, 
 gradually enlarging, forms in the next stage a grain also 
 lenticular, and which is marked either with only one 
 transparent line dividing it into two equal parts, or with 
 two lines crossing at right angles, and dividing it into four 
 equal parts. In each of the quadratures a small nucleus 
 is visible ; and, even where one transparent line is only dis- 
 
352 THE MICROSCOPE. 
 
 tinguishable, two nuclei may frequently be found in each 
 semicircular division. These nuclei may be readily ex- 
 tracted from the containing grain by pressure, and after 
 separation retain their original form. In the next stage, 
 the greater number of grains consist of the semicircular 
 divisions, naturally separated, but now containing only 
 one nucleus, which has gradually increased in size. In 
 the succeeding stage the grain apparently consists of the 
 nucleus of the former stage, but considerably enlarged, 
 and having an oval form, and a somewhat granular surface. 
 This oval grain, continuing to increase in size, and in the 
 thickening of its membrane, acquires a pale yellow colour; 
 and is now the perfect grain pollen." 
 
 In the whole tribe of Orchidese an abundance of raphides 
 may be found in almost every part of the cellular tissue. 
 The crystals are usually cylindrical in form, and so arranged 
 as to disguise their true character, often causing them to 
 be overlooked : by making use of a dark-ground illumina- 
 tor, or polarised light, this is not likely to occur. The 
 cause of the disease known as " spot " in Orchids, of 
 which several kinds have been noticed by cultivators, has 
 been traced by Mr. Berkeley, in one instance, to the oc- 
 currence of a minute parasitic fungus, belonging to the 
 genus Leptothyrium. A description of the disease, with 
 illustrations, giving the general appearance of the diseased 
 leaves, and a magnified figure of the parasite, appears in 
 the 1st part of the new series of the Journal of the Horti- 
 cultural Society. 
 
 Tlie Colouring matter of Flowers. M. F. Hildebrands, 
 having carefully investigated the colouring matters of 
 flowers, has arrived at the following conclusion respecting 
 them, and their distribution in the tissue of the several 
 organs. 
 
 1. That the colour of flowers is in constant connexion 
 with the cell contents, never with the walls of cells. 
 
 2. Blue, violet, rose, and (if there be no yellow in the 
 flower) deep red are due, with little exception, to a cell- 
 fluid of corresponding colour. 
 
 3. Yellow, orange, and green, are usually associated 
 with solid, granular, or vesicular substances in the 
 cells. 
 
WOODY TISSUE. 
 
 353 
 
 4. Brown or gray, and in many cases bright red and 
 orange (apparently uniform to the naked eye), are found 
 to be compounded of other colours, as yellow, green, or 
 orange with violet, or green and red; bright red and orange 
 in like manner of blue-red with yellow or orange. 
 
 5. Black, excepting in the bean, is due to a very deeply- 
 coloured cell-fluid. 
 
 6. All the cells of an organ are rarely uniformly 
 coloured. 
 
 7. The colour usually resides in one or in a few of the 
 outer layers of cells. 
 
 8. The coloured cells are but exceptionally covered by 
 a layer of uncoloured ones. 
 
 9. Combinations of colour are occasioned by diversely- 
 coloured matters in the same or in adjacent cells. 
 
 The Woody tissue of plants is not without its interest, 
 it consists of elongated transparent tubes of considerable 
 strength : some are almost entirely made up of this 
 tissue. It is by far the most useful, and supplies 
 material for our linen, cordage, paper, and many 
 other important articles in every 
 branch of art. This tissue, re- 
 markable for its toughness, is 
 termed fibre, the outer membrane 
 of which is usually structureless. 
 In Flax and Hemp, iii which the 
 fibres are of great length, there 
 are traces of transverse markings, 
 and tubercles at short intervals. 
 In the rough condition, in which 
 it is imported into this country, 
 the fibres have been separated, to 
 a certain extent, by a process 
 termed hackling. It is once 
 more subjected to a repetition of 
 hackling, maceration, and bleach- *. 
 ing, before it can be reduced to the 
 white silky condition required by the spinner and weaver, 
 when it has the appearance of structureless tubes, fig. 197 B. 
 China-grass, New Zealand flax, and some other plants, pro- 
 duce a similar material, but are not so strong, in conse* 
 
 Jgjfc,* FibrM 
 
354 
 
 THE MICROSCOPE. 
 
 quence of the outer membrane containing more lignine. 
 It is important to the manufacturer that he should be 
 able to determine the true character of some of the textures 
 of articles of clothing, and this he may readily do with the 
 microscope. In linen we find each component thread made 
 up of the longitudinal, rounded, unmarked fibres of flax ; but 
 if cotton has been mixed, we recognise a flattened, more or 
 less twisted band, as in fig. 1966, having a very striking 
 resemblance to hair, which, in 
 reality, it is ; since, in the condi- 
 tion of elongated cells, it lines the 
 inner surface of the pod. These, 
 again, should be contrasted with 
 the filaments of silk, fig. 196 A, and 
 also of wool, fig. 197 A. The latter 
 may be at once recognised by the 
 zigzag transverse markings on its 
 fibres. The surface of wool is 
 covered with these furrowed and 
 twisted fine cross lines, of which 
 there are from 2,000 to 4,000 in 
 an inch. On this structure de- 
 pends its felting property. In 
 ** ments of e r?ax. B> a " judging of fleeces, attention should 
 be paid to the fineness and elasti- 
 city of the fibre, the furrowed and scaly surface, as shown 
 by the microscope, the quantity of fibre in a given surface, 
 the purity of the fleece, upon which depend the success of 
 the scouring and subsequent operations. 
 
 In the mummy-cloths of the Egyptians, flax only was 
 used, whereas the Peruvians used cotton alone. By recent 
 improvements introduced into the manufacturing pro- 
 cesses, flax has been reduced to the fineness and texture of 
 silk, and made to resemble other materials. 
 
 Silk is secreted from a pair of long tubes ending in 
 a pore of the under-lip of the silkworm. Each thread is 
 made of two filaments coming from these, and they are 
 glued together by a secretion from a small gland near. 
 The quality of the silk depends on the character and 
 difference of the two secretions. 
 
 All woody fibre is made up of elongated cells, generally 
 
 Fig. 197. 
 
VASCULAR TISSUE. 355 
 
 more or less pointed at both extremities, and having their 
 walls strengthened by internal deposits. Occasionally, 
 however, the fibre is short, as in the Clematis, Elder, &c. ; 
 it is marked with pores or dots, from a deficiency of the 
 internal deposits at these points. 
 Vascular tissue consists of 
 cells, more or less elongated, 
 joined end to end, or over- 
 lapping each other, in which 
 either a spiral fibre, or a mo- 
 dification of the same, has 
 been deposited ; hence, if the 
 spiral be perfect, it is called 
 a true spiral vessel ; if inter- 
 rupted, or the fibre breaks up 
 into rings, it is termed annu- 
 lar; if the rings are connected 
 together by branching fibres, 
 so that a network is pro- 
 duced, the vessel is called 
 reticulated; if the vertical 
 fibres are short, and equidis- 
 tant, the vessel is said to be 
 scalariform, from its resemblance to a ladder. Spiral 
 vessels have been also termed trachecs, from their resem- 
 blance to the air-tubes of insects, as in fig. 198. 
 
 Under thie head other membranaceous tubes are included, 
 in which the arrangement of the fibre has been consider- 
 ably modified in its deposition. Elongated tubes or ducts, 
 with porous walls, come under the head of vascular tissue; 
 they somewhat differ from the spiral varieties, inasmuch 
 as they cannot be unrolled without breaking. It is a 
 curious fact, that mostly the spiral coils from right to 
 left ; and it has been suggested that the direction of the 
 fibre may determine that in which the plant coils round 
 an upright pole. The Hop has left-handed spirals, and is 
 a left-handed climber, which would therefore appear to 
 support this theory. The nature of the fibre, and the 
 development of the tissue, have been frequently the subject 
 of dispute between botanists. 
 The late Mr. Edwin Quekett gave much attention to this 
 
 A A3 
 
 Kg. 108. Simple and compound 
 spiral vessels. 
 
356 
 
 THE MICROSCOPE. 
 
 subject ; and published an excellent paper in the Micro- 
 scopical Society's Transactions) 1840, which contains the 
 results of his observations. 
 
 1 Fig. 199. 
 
 1, Interior cast of the siliceous portion of spiral tubes of the Opuntia. 2, Vertical 
 section of Elm, showing spiral fibre. 
 
 In order to watch the development of the membranous 
 tubes of plants, no better example can be chosen than the 
 
 Fig. 200. 
 
 A transverse section of Taxus baccata (Yew), showing the woody fibre. 
 2, Vertical section of the Yew, exhibiting pores and spiral fibres. 
 
VASCULAR TISSUE. 357 
 
 young flower-stalk of the long-leek (Allium porrum), in 
 the state in which this vegetable is usually sent to market; 
 it is then most frequently found to be about an inch or 
 
 Pig. 201. 
 
 1, Portion ol transverse section of stem of Cedar, showing pith, wood, and bark. 
 2, Portion of transverse section of stem of Clematis, showing medullary rays. 
 
 more in length, and from a quarter to half an inch in 
 diameter. This membrane occurs very low down amidst the 
 sheathing bases of the leaves; and from having to lengthen 
 to two or three feet, and containing large vessels, it forms 
 a very fit subject for ascertaining the early appearances of 
 the vascular tissue. 
 
 To examine the development of vessels, it is necessary 
 to be very careful in making dissections of the recent 
 plant ; and it will be found useful to macerate the specimen 
 for a time in boiling water, which will render the tissues 
 more easily separable. When the examination is directed 
 in search of the larger vessels, it will be found that at this 
 early stage they present merely the form of very elongated 
 cells, arranged in distinct lines; amongst which some 
 vessels, especially the annular, will be found matured,, 
 even before the cytoblasts have disappeared from the cells 
 of the surrounding tissue. 
 
 As development proceeds, the vessels rapidly increase 
 in length, tiU they arrive at perfection. No increase in 
 diameter is perceptible after their first formation. At 
 this period, in the living plant the young vessels appear 
 full of fluid, which is apparently, as remarked by Schleiden r 
 of a thick character, and which he has designated vege- 
 table jelly ; by boiling which, or by the addition of alcohol, 
 the contents, or at least the albuminous portion, becomes 
 coagulated. From this circumstance, every cell appears 
 
358 
 
 THE MICKOSCOPE. 
 
 SHIP 
 
 to enclose another in a shrivelled condition ; this state is 
 
 sometimes so far extended, that a thick granular cord is 
 
 all that can be seen of the contents. 
 
 "The period of growth at which the laying down of 
 
 fibre commences, determines the distance between the 
 several coils; for instance, when it is 
 first formed, the coils are quite close, 
 scarcely any perceptible trace of mem- 
 brane existing between them. In the 
 annular vessel, the development of 
 the cell and the adherence of the 
 granules to each other are conducted 
 in the same manner ; the deposit 
 showing a tendency towards the spiral 
 direction, by the presence of a spire 
 connecting two rings, or by a ring 
 being developed in the middle of a 
 spiral fibre. The annular vessel is 
 the first observed in the youngest 
 parts of plants, and when found alone 
 
 Fig.202.-^ section from indicates a low degree of organisation; 
 the stem of a coniferous as shown by its occurrence in SpJidr 
 gnum, Equisetum, and Lycopodium, 
 
 the zones of annual w hich plants, in the ascending scale of 
 
 growth, annual rings. *. . *? 
 
 vegetation, are almost the first that 
 possess vascular tissue. 
 
 " It will be found that spiral fibre occurring with rings 
 marks a higher step in the scale of organising power; the 
 true spiral more so; and the reticulated and dotted mark 
 the highest ; this being the order in which these several 
 vessels are placed in herbaceous exogens proceeding from 
 within outwards, the differences of structure of the several 
 vessels being indices of the vital energy of the plant at 
 the several periods of its development. In those vessels 
 in which the annular or spiral character of the fibre is 
 departed from, some curious modifications of the above 
 process are to be observed, as in the reticulated vessels 
 met with in the common balsam (Eahamlna hortensis). 
 The primary formation of fibre in these vessels : s marked 
 by the tendency of the granules to take a spiral course, 
 when it happens that some one of the granules becomes 
 
VASCULAB TISSUE. 359 
 
 enlarged by the deposition of new matter around it. This 
 becomes a point originating another fibre or branch, which 
 becomes developed by the successive attraction of granules 
 into bead-like strings, taking a contrary direction to the 
 original fibre, forming a cross-bar, or ramifying, thereby 
 causing the appearance by which the vessel is recognised. 
 
 "In the exogenic vessel, the development of fibre proceeds 
 in the same manner as in the last example ; but the vessels 
 will be seen to be dotted with a central mark, usually of a 
 red colour, which, when viewed under high power, may be 
 thought to resemble a minute garnet set in the centre of 
 each dot. This red colour is owing to the dot being 
 somewhat hollowed or cupped, and the centre only thin 
 membrane. These vessels are best seen in the young 
 shoots of the Willow. In the endogenic vessel the con- 
 necting branches are given off beneath each other, so that 
 the dots, which are rounded, are arranged in longitudinal 
 rows ; but in the acrogenic, or scalariform, in which the 
 vessels are generally angular, and present distinct facets, 
 the branches come off in the same line, corresponding 
 generally to the angles of the vessel; the spaces left 
 between are linear instead of round." 
 
 Mr. E. Quekett affirms, in opposition to the views enter- 
 tained by Mirbel, Richard, and Bischoff, "that the dots 
 left in these several vessels are not holes, neither do they 
 consist of broken-up fibre, but are the membranous tubes, 
 unsupported by internal deposit ; and on account of the 
 extreme tenuity of the tissue, and the minute space between 
 the fibres, the light in its transmission becomes decomposed, 
 and appears of a greenish-red hue. The structure of the 
 dot is best seen by examining the broken edge of any such 
 vessels, when it will be found that the fracture has been 
 caused by the vessel giving way from one dot to another, 
 so that the torn edge of the membrane can be observed in. 
 each dot." 
 
 PREPARATION OP VEGETABLE TISSUES. 
 
 The proper mode of preparing and preserving vegetable 
 tissues is a matter of some importance to the microscopist; 
 we therefore propose to add a few general directions for 
 the student's guidance. 
 
360 THE MICROSCOPE. 
 
 Vegetable tissues are best prepared for the microscope 
 by making thin sections, either by maceration, by tearing be- 
 tween the thumb and the blade of a knife, or by dissection, 
 
 The spiral and other vessels of plants require to be 
 dissected out under a simple magnifying-glass. Take, for 
 instance, a piece of asparagus, and separate with the 
 needle-points the vessels, which require to be finished 
 under a magnifying-glass, in a single drop of distilled 
 water. When properly done, keep in spirits of wine and 
 irater until mounted. 
 
 Vascular tissue requires both maceration and dissection 
 for its separation. The cuticle or external covering of 
 plants- is a highly interesting structure ; it is best seen in the 
 pelargonium, oleander, &c. ; and may be mounted dry or 
 in Canada balsam. 
 
 Cellular tissue is best seen in fine sections from the pith 
 of elder, pulp of peach, pear, &c. The petals of flowers 
 are mostly composed of cellular tissue, and their brilliant 
 colours arise from the fluid contained within the cells. In 
 the petal of the anagallis, or scarlet chickweed, the spiral 
 vessels diverging from the base, and the singular cellules 
 which fringe the edge, are very interesting. The petal of 
 the geranium is one of the most beautiful objects for 
 microscopic examination. The usual way of preparing it 
 is by immersing the leaf in sulphuric ether for a few 
 seconds, allowing the fluid to evaporate, and then putting 
 it up dry. Dr. Inman of Liverpool suggests the following 
 method : " First peel off the epidermis from the petal, which 
 may be readily done by making an incision through it at 
 the end of the leaf, and then tearing it forwards by the 
 forceps. This is then arranged on a slip of glass, and 
 allowed to dry ; when dry, it adheres to the glass. Place 
 on it a little Canada balsam diluted with turpentine, and 
 boil it for an instant over the spirit-lamp ; this blisters it, 
 but does not remove the colour ; then cover it with a thin 
 slip of glass, to preserve it. Many cells will be found 
 showing the mamilla very distinctly, and the hairs sur- 
 rounding its base, each being slightly curved and pointed 
 towards the apex of the mamilla. It is these hairs and the 
 mamilla which give the velvety appearance to the petal." 
 
 Fibro- cellular tissue is found readily in Sphagnum or 
 
PREPARATION OF TISSUES. 361 
 
 bog-moss, and in the elegant creeper Cobcea tcandens. In 
 some orchidaceous plants the leaves are almost entirely 
 composed of it. A modification of this form of tissue is 
 found in the testa of some seeds, as in those of Sctlvia, 
 Collomia grandiflora, <fec. 
 
 The curious and interesting sporules of ferns, when 
 ripe, burst, and are dispersed to a distance ; so that they 
 should be gathered before they come to maturity, and 
 mounted as opaque objects. The development of ferns 
 may be observed by placing the seeds in moistened flannel, 
 and keeping them at a warm temperature. At first a 
 single cellule is produced, then a second ; after this the 
 first divides into two, and then others follow ; by which a 
 lateral increase takes place. 
 
 Pollen-grains from most flowers are very interesting 
 objects; the darker kinds show best when mounted in 
 dark cells, and viewed as opaque ; objects more trans- 
 
 Fig. 80S. Pollen grain* and seed*. 
 
 A, Seed of Clove-pink. B, Poppy seed, c. Pollen of Passion flower (Pamjlora 
 ccErnlea). D, Pollen of Cobcea scandent. 
 
 parent should be mounted in fluid, to show internal 
 structure. The prettiest and most delicate forms are found 
 in Amarantacece, Cucurbitacece, Malvaceae, and Passiflorece ; 
 others are furnished from the Convolvulus, Geranium, 
 Campanula, Hollyhock, and some other plants. The 
 curious peculiarities of a few are shown in fig. 203. 
 
362 
 
 THE MICROSCOPE. 
 
 Many of the smaller kinds of seeds will reward the 
 microscopist ; use only a low power ; that of Caryo- 
 phyllum (clove-pink), is regularly covered with curiously- 
 jagged divisions; every one of which has a small bright, 
 black hemispherical knob in its middle, represented in 
 fig. 160, A. 
 
 The seeds of the carrot are remarkably formed, 
 having some resemblance to a star-fish, with its long 
 radiating processes. The seeds of umbelliferous plants 
 have peculiar receptacles for essential oil, in their coats, 
 termed mttce ; various points of interest may be noted 
 as occurring in the testae, envelopes of seeds, such as 
 the fibre-cells of Cobcea, and the stellate cells of the 
 Star-anise. 
 
 All plants are provided with hairs; and a few, like 
 insects, with hairs of a defensive character. Those in 
 the Urtica dioica, commonly called the Sting ing -nettle, are 
 elongated hairs, developed from the cuticle, usually of a 
 conical figure, and containing an irritating fluid ; in some 
 of them a circulation is visible : when examined under the 
 microscope, with a power of 100 diameters, they present 
 the appearance seen at fig. 188, No. 2. At No. 3, same 
 figure, are represented a few interesting ciliated spores 
 from Confervce. 
 
 The circulation of the fluid-contents of vegetable cells 
 may be examined at the same time with the Chlorophyll 
 globules, by selecting for the purpose the transparent 
 water-plants Chara, Nitella, Anacharis, and Vallisneria, 
 or the hairs of Groundsel and Tradescantia. The circula- 
 tion of the sap in plants growing in water is termed by 
 botanists Cyclosis. 
 
 Fossil plants. We detect in some of the primordial 
 fossils a noticeable likeness to families familiar to tho 
 modern algseologist. The cord-like plant, Chorda filium, 
 known as ' dead men's ropes,' from its proving fatal at 
 times to the too adventurous swimmer who gets entangled 
 in its thick wreaths, had a Lower Silurian representative, 
 known to the palaeontologist as the Palceochorda, or 
 ancient chorda, which existed, apparently, in two species, 
 a larger and a smaller. The still better known Ghondrus 
 crispus, the Irish moss, or Carrageen moss, has, likewise, 
 
FOSSIL PLANTS. 
 
 363 
 
 The fucoids, or 
 
 its apparent, though more distant representative, in Chon- 
 dritis, a Lower Silurian alga, of which there seems to 
 exist at least three species, 
 weeds, appear to have also 
 their representatives in such 
 plants as Fucoides gracilis, 
 of the Lower Silurians of 
 the Malverns ; in short, the 
 Thallogens of the first ages 
 of vegetable life, seem to 
 have resembled, in the group, 
 and in at least their more 
 prominent features, the A Igce. 
 of the existing time. And 
 with the first indications of 
 land we pass direct from the 
 Thallogens to the Acrogens, 
 from the sea- weeds to the 
 fern -allies. The Lycopo- 
 diaceoe, or club-mosses, bear 
 in the axils of their leaves 
 minute circular cases, which 
 form the receptacles of their 
 spore-like seeds. And when, 
 high in the Upper Silurian 
 system, and just when pre- 
 paring to quit it for the 
 Lower Old Red Sandstone, 
 we detect our earliest ter- 
 restrial organisms, we find that they are composed exclu- 
 sively of those little spore-receptacles. 
 
 " The existing plants whence we derive our analogies in 
 dealing with the vegetation of this early period, contribute 
 but little, if at all, to the support of animal life. The 
 ferns and their allies remain untouched by the grazing 
 animals. Our native club-mosses, though once used in 
 medicine, are positively deleterious; horsetails (Kquise- 
 tacece), though harmless, so abound in silex, which wrap 
 them round with a cuticle of stone, that they are rarely 
 cropped by cattle ; while the thickets of fern which cover 
 our hill and dell, and seem so temptingly rich and green 
 
 Fig. 204. 
 
 , Woody fibre from the root of the 
 Elder, exhibiting small pores. 2, 
 Woody fibre of fossil ood, showing 
 large pores. 3, Woody fibre of tossil 
 wood, bordered with pores and spiral 
 fibres. 4, Fossil wood taken from coal. 
 
364 
 
 THE MICROSCOPE. 
 
 in their season, scarce support the existence of a single 
 creature, and remain untouched, in stem and leaf, from 
 their first appearance in spring, until they droop and 
 wither under the frosts of early winter. 
 
 " It is not until we enter into the earlier Tertiaries that 
 we succeed in detecting a true dicotyledonous tree ; on such 
 an amount of observation is this order determined, that 
 when Dr. John Wilson, the Parsee Missionary, submitted 
 to me specimens of fossil woods which he had picked up 
 in the Egyptian Desert, in order that, if possible, I might 
 determine their age, I told him that if they exhibited the 
 coniferous structure, they might belong to any geologic 
 period from the times of the Lower Old Red Sandstone 
 downwards; but if they manifested in their tissue the 
 dicotyledonous character, they could not be older than the 
 times of the Tertiary. On submitting them in thin slices 
 to the microscope, they were found to exhibit the peculiar 
 dicotyledonous structure as strongly as the oak or chest- 
 nut. And Lieutenant Newbold's researches in the deposit 
 in which they occur has since demonstrated, on strati- 
 graphical evidence, that it belongs to the comparatively 
 modern formations of the Tertiary. 
 
 " The flora of the coal measures was the richest and most 
 luxuriant, in at least individual productions, with which 
 the fossil botanist has formed any acquaintance. Never 
 before or since did our planet bear so rank a vegetation as 
 that of which the numerous coal seams and inflammable 
 shales of the carboniferous period form but a portion of 
 the remains, the portion spared, in the first instance, by 
 dissipation and decay, and in the second by the denuding 
 agencies. Almost all our coal, the stored-up fuel of a 
 world, forms but a comparatively small part of the pro- 
 duce of this wonderful flora. Yet, with all this singularly 
 profuse vegetation of the coal measures, it was a flora un- 
 fitted, apparently, for the support of either graminiveroua 
 bird or herbivorous quadruped. Nor does the flora of the 
 Oolite seem to have been in the least suited for the pur- 
 poses of the shepherd or herdsman. Not until we enter 
 on the Tertiary periods do we find floras amid which man 
 might have profitably laboured : nay, there are whole orders 
 and families of plants, of the very first importance to man, 
 
FOSSIL PLANTS. 365 
 
 which do not appear until late in even the Tertiary ages. 
 The true grasses scarce appear in the fossil state at all. 
 For the first time, amid the remains of a flora that seems 
 to have had its few flowers, the Oolitic ages, do we 
 detect, in a few broken fragments of the wings of butter- 
 flies, decided traces of the flower-sucking insects. Not, 
 however, until we enter into the great Tertiary division do 
 these become numerous. The first bee makes its appear- 
 ance in the amber of the Eocene, locked up hermetically 
 in its gem-like tomb, an embalmed corpse in a crystal 
 coffin, along with fragments of flower-bearing herbs and 
 trees. Her tomb remains to testify to the gradual fitting 
 up of our earth as a place of habitation for a creature 
 destined to seek delight for the mind and eye, as certainly 
 as for the proper senses, and in especial marks the intro- 
 duction of the stately forest trees, and the arrival of the 
 delicious flowers." l 
 
 " Sweet flowers ! what living eye hath viewed 
 Their myriads ? endlessly renewed ; 
 Wherever strikes the sun's glad ray, 
 Where'er the subtile waters stray, 
 Wherever sportive zephyrs bend 
 Their course, or genial showers descend. ' 
 
 (1) Hugh Miller's Testimony of the Rock*. 
 
CHAPTEE II. 
 
 DIVISION OF ANIMAL KINGDOM. 
 
 PBOTOZOA GBEGARINjE KHIZOPODA PCXLYCYSTINA DIATOMACE^E FOSStt 
 INFUSORIA, SPONGIC^, HYDROZOA, VOBTICELIuK, 
 AOTIffOZOA, BOTLFER^E, POLYZOA. &C. 
 
 'INGE our very limited space forbade 
 more than a cursory glance at 
 the many and varied points of 
 beauty and arrangement dis- 
 played in every part of the vege- 
 table kingdom; so in the pre- 
 sent division is it necessary 
 to be equally brief in noticing 
 the wonders displayed by the 
 help of the microscope, in the 
 world of animal life. In the 
 course of remarks made upon 
 the early condition of vegetable 
 life, we drew attention to the difficulties presented in all 
 attempts to mark out the boundary line between vege- 
 tables and animals, and to define where the one ends, 
 and the other begins. 
 
 Upon reviewing the different characters by which 
 it has been attempted to distinguish the special subjects 
 of the botanist and zoologist, we find that animals and 
 plants are not two natural divisions, but are specialised 
 members of one and the same group of organised beings. 
 When a certain number of characters concur in the same 
 organism, its title to be regarded as a "plant," or an 
 1 ' animal," may be readily recognised ; but there are very 
 numerous living beings, especially those that retain the 
 
DIVISION OP ANIMAL KINGDOM. 367 
 
 form of nucleated cells, which manifest the common or- 
 ganic characters, but are without the true distinctive 
 superadditions of either kingdom. 
 
 The animal kingdom is conveniently arranged under the 
 following primary groups, sub-kingdoms, or departments : 
 PBOTOZOA, CCEJLENTERATA, ANNULOSA, MOLLUSCA, and 
 VEBTEBRATA. These are again divided into classes, classes 
 into orders, orders into families, families into genera, and 
 genera into species. In the first-named department, the 
 Protozoa, is included a vast number of creatures of the 
 simplest organisation, classified as follows: 1. Gregarinidae, 
 2. Rhizopoda, 3. Polycystina, 4. Thalassicollidse, 5. Spongidse, 
 6. Infusoria. It is not unusual to place Rhizopoda and 
 its typical form, Amoeba, in the front rank; and as the 
 presence of a mouth characterises the Infusoria, the re- 
 maining part of the Protozoa are frequently designated by 
 a collective name, Astomata. 
 
 The first-named, Gregariniclce } form a group of the very 
 simplest structural character, and any one of them, setting 
 minor modifications aside, may be said to consist of a sac, 
 composed of a more or less structureless membrane, con- 
 taining a soft semi-fluid substance, in the midst of which 
 is a circular vacuole or vesicle, having in its centre a more 
 solid particle or nucleus. Professor Huxley appends to 
 this description the obvious, but highly important re- 
 flection, that its statements are all true concerning the ova 
 of any of the animals much higher in the scale. 1 The 
 Gregarinidae inhabit the bodies of other animals, and they 
 multiply by becoming encysted, and dividing into a multi- 
 tude of minute objects, called pseudo-navicellce, from their 
 resemblance in shape to the ship-like diatoms (namculce). 
 When a young pseudo-navicella escapes, it behaves some- 
 what like an amoeba, and, if it chance to get swallowed 
 by an appropriate host, it grows into the parent form. 
 The whole life-history of these creatures is not known, as 
 they have not been traced into the exhibition of sexual 
 properties ; and it is therefore possible that their position 
 in the scale may not be exactly defined. 
 
 In the course of the numerous investigations made of 
 the flesh of animals dying during the year 1866 from the 
 cattle-plague, it was noticed that large quantities of pecu- 
 liar bodies infested the muscular structures, more especially 
 
 (1) Huxley's "Lectures on the Elements of Comparative Anatomy." 
 
368 THE MICROSCOPE. 
 
 that of the heart, and it was supposed that these had 
 some share in the production of the disease ; but upon 
 making further investigations this has been found not to 
 be so, and since the same bodies are known to be gene- 
 rally distributed throughout the ultimate fibres of animals 
 dying from other diseases, the only interest that can 
 attach to the discovery is, that it promises to add some 
 valuable facts to our knowledge of the remarkable group 
 of Protozoa, the Gregarince. The Gregarines observed 
 in the flesh of oxen, and described by Dr. Beale, 
 have elongated spindle-shaped sacs, containing granular 
 reniform bodies arranged horizontally, and apparently 
 capable of multiplying by division. The investing 
 sac is covered with minute, motionless, hair-like bodies. 
 No nucleus is present in the sac ; but the reniform 
 granular masses are stated by Dr. Cobbold to possess 
 nucleolL The structure thus presented is not far removed, 
 from that of many Gregarince, particularly of the larger 
 individuals occurring in the earthworm, though the hair- 
 like processes sometimes observable on these are con- 
 sidered as extraneous by Dr. Leiberkiihn. The compacted 
 reniform masses may be considered as the results of a pro- 
 cess of segmentation, similar to that by which the pseudo- 
 naviculae are formed. The bodies thus described are by 
 no means peculiar to diseased cattle; they are met 
 with in the healthy muscles of the ox, sheep, pig, deer, 
 rat, mouse, mole, and perhaps other animals. Gregarince, 
 in various stages, are represented in Plate III. figs. 53, 
 54, 55, and 56. Miescher, in 1843, described such bodies, 
 taken from the muscles of a mouse, and a very good 
 account of them, obtained from the muscles of a pig, is 
 given by Mr. Rainey, in the " Philosophical Transactions," 
 for 1857, though he erroneously regarded them as the 
 young stage of cestoid entozoa. They have been described 
 under a variety of titles, such as worm-nodules, egg-sacs, 
 eggs of the fluke, young measles, " corpuscles produced by 
 muscular degeneration" &c. When considered in con- 
 nexion with the minute cysts described by Gabler, Virchow, 
 and Dressier, from the human liver, they have an especial 
 interest; and the observations of Lindemann on the psoro- 
 spermial sacs obtained from the hair of a peasant at 
 
GREGARINA OP EARTHWORM. 369 
 
 Nischney-Novgorod, and in the kidneys of a patient who 
 died from Bright's disease, bear very strongly on the nature 
 of these bodies. The people of Novgorod are believed to 
 get these parasites from washing in water in which Grega- 
 rinoe abound. 1 The most interesting inquiry which is 
 placed before us by these various facts is whether, as 
 Professor Leuckart has observed, "the psorospermiae " 
 (and we may add the " spurious entozoa " of cattle, and 
 even many so-called Gregarinae) are to be considered as 
 the result of a special animal development, or whether 
 they are the final products of pathological metamor- 
 phosis. 
 
 It appears, from the reseaches of M. Claparede and 
 others, that some of the unilocular forms do present very 
 curious, elongated, and active forms, which, from their 
 movements and general appearance, might be mistaken for 
 nematodes. Dr. Joseph Leidy has, in the " Transactions 
 of the Philadelphia Society, 1853," denied the fact that 
 the Gregarince are unicellular animals, on the following 
 grounds : In the examinations of some new species of 
 Gregarince which he has described, and also in the 
 G. Blotharum of Siehold, he discovered that the membrane 
 enclosing the granular mass of the posterior sac was 
 double. He observes : " Within the parietal tunic of the 
 posterior sac is a second membrane, which is transparent, 
 colourless, and marked by a most beautiful set of exceed- 
 ingly regular parallel longitudinal lines." 
 
 M. Leiberkiihn contributed a very elaborate paper 
 on the Gregarina of the earthworm. He does not express 
 any very decided opinion upon the two questions which 
 have been discussed by Leidy and Bruch, but devotes the 
 principal part of his memoir to the development and re- 
 production of the Gregarinse. With regard to the develop- 
 ment of Gregarinae into a filaria-like worm, which Bruch 
 thought probable, M. Leiberkiihn says but little, but, 
 nevertheless, has proved beyond doubt that the nematodes 
 
 (1) Many vague and improbable statements appeared at one time on a sup- 
 posed discovery of Gregarinae in the human hair. Upon a more careful exami- 
 nation being made by competent persons, the foreign body proved to be a well- 
 known vegetable fnngus, often found associated with a disease, or dirty 
 neglected stat t of the skin. It is very well known that Gregarines are neve* 
 found on free jr exposed surfaces. 
 
 B B 
 
370 THE MICROSCOPE. 
 
 of the earthworm are developed from eggs, whence they 
 emerge, not as Gregarinse, but as true nematodes. The 
 transformation of two Gregarinae, after a process of encysta 
 tion, into navicula-like bodies, has been fully described by 
 Bruch ; but Leiberkiihn has more carefully illustrated the 
 changes that go on, and has endeavoured to trace the ex- 
 istence of the pseudo-naviculas after they have been 
 expelled from the cyst. In the perivisceral cavity of the 
 earthworm he found large numbers of small corpuscles, 
 /exhibiting amoeba-like movements, and likewise pseudo- 
 : naviculse, containing granules, formed from encysted Gre- 
 garine. He imagines that these latter bodies burst, and 
 that their contained granules develope into the amceoiform 
 bodies which subsequently become Gregarinse. M. Lei- 
 berkiihn shortly afterwards published another paper,* in 
 which he adopts the same view, that the amcebiform 
 corpuscles of the blood of fish are Gregarines. But few 
 physiologists will feel disposed to agree with him, in 
 considering these bodies as parasites. 
 
 Mr. E. Eay Lankester has contributed a valuable 
 and exhaustive paper on this subject; 1 he observes: "I 
 .have made careful examination of more than a hundred 
 worms, for the purpose of studying these questions, but 
 have succeeded in arriving at no other conclusion than 
 that certain forms of these may be the products of encysted 
 Gregarinse. The G. Lumbrici is one of those forms which 
 are unilocular, and are met with most frequently among 
 Annelids. It consists of a transparent contractile sac 
 {which has not hitherto been demonstrated to be formed 
 by more than a single membrane), enclosing the charac- 
 teristic granules and vesicle. The vesicle is not always very 
 distinct, and is sometimes altogether absent ; occasionally 
 it contains no granules, sometimes several, one of which 
 is generally nucleated. In some of these cysts a number 
 of nucleated cells may be seen, developing together from 
 the enclosed Gregarina, which gradually become fused 
 together and broken up, until the entire mass is converted 
 into these nucleated bodies, which are then evident in 
 different stages of development, assuming the form of a 
 
 (1) E. Ray Lankester, " On the Gregarinidse found in the common Earth- 
 worm." Micros. Trans, vol. iii. p. 83. 
 
PROTOZOA. GBEQABINJE. 371 
 
 double cone, like that presented by some species of 
 Diatomaceae, whence their name pseudo-naviculae. At 
 length the cyst contains nothing but pseudo-naviculae, 
 sometimes enclosing granules, which gradually disappear, 
 and finally the cyst bursts. Ency station seems to take 
 place much more rarely among the bilocular forms of 
 Gregarinse than in the unilocidar species found in the 
 earthworm and other Annelids." 
 
 In the Gregarince the food is taken in indiscriminately 
 at every point of the surface of the body by imbibition. 
 The food most likely is in the fluid state. In Spongilla, 
 also, this is probably the case. But it is generally agreed 
 that in Amoeba, Actinophrys, and agastric Infusoria, only 
 solid alimentary particles are taken as food. The simplest 
 animal is indeed far more complex than is implied in the 
 word unicellular, and it can be clearly proved that there 
 are few points in common between a simple cell and a so- 
 called unicellular protozoon. The system of contractile 
 vesicles and dependent sinuses, so general in the least 
 organized protozoon, is unknown in the history of cells. 
 Fluid absoption by the surface is the normal method of 
 feeding in these low types of animal life. This absorptive 
 faculty is an inherent property of the substance of which 
 they are composed. It attracts certain aliments, as gela- 
 tine attracts water. Tissue, distinguished by the same 
 character, prevails throughout the entire class of the Pro- 
 tozoa. Although the Gregarinoe mostly inhabit the intes- 
 tines of invertebrate animals, they are often found in the 
 alimentary canal of the Vm-tebrata. In this class they 
 appear to be represented, however, by very closely allied 
 organisms, the Psorospermice. Miiller gave this last- 
 mentioned name to some very singular minute bodies he 
 discovered within sacs upon the skin and gills, and in the 
 internal organs, of many fishes. These animals are gene- 
 rally of a cylindrical or somewhat elliptical form, although 
 sometimes a sort of head appears to be produced by the 
 constriction of the anterior extremity of the body, and 
 this head-like portion is occasionally furnished with a 
 curious soft process and lobes. They are very sluggish in 
 their movements, although a few possess true cilia. Their 
 curious mode of development, with other points in the 
 BB 2 
 
372 
 
 THE MICROSCOPE. 
 
 history of these minute parasites, are well worthy of 
 investigation. 
 
 The Rhizopoda appear as creatures of a low type of 
 organization, and are considered, with the former, to hold 
 a medium state between animals and vegetables. Almost 
 all of tbem live in water ; it would be a fruitless search 
 to look for distinct internal organs, as the small bladder- 
 looking spaces enclosed within their substance, believe^ 
 by Ehrenberg to be stomachs, present only the appear- 
 ance of transparent gelatinous cells, or rather moving 
 spaces, within the sarcode envelope, and may be regarded 
 as the earliest dawn of a circulatory system. 
 
 The term Rhizopoda is derived from the Greek, antf 
 
 Fig. 205. Simple Rhizopods. 
 
 A, Difflugia proteiformis. B, Difflugia oblonga. - c, D, Arcella acuminata ant? 
 dentata. 
 
 means " root-footed," the body is composed entirely of 
 gelatinous matter, sarcode, motion being effected by the 
 extension of portions of the substance into processes, 
 which, as in fig. 205, is seen to partake of various forms. 
 
 Lobosa. In the deposit formed at the bottom of fresh- 
 water ponds, we may often meet with a singular minute 
 gelatinous body, which constantly changes its form even 
 tinder our eyes ; and moves about by means of finger-like 
 processes, called pseudopodia, which it appears to have the 
 power of shooting out from any part of its substance. 
 
PROTOZOA. AMCEBA. 
 
 373 
 
 This shapeless mass is well known to microscopic observers 
 under the name of the Proteus (Amoeba dijftuens, fig. 206), 
 which, from the continual changes of shape it presents, is 
 
 Fig. 206. Amoeba difflvens, or Proteus, in different forms. 
 
 honoured with the name of a fabled god, who could be 
 either animal, vegetable, or mineral in his nature. This 
 curious animal presents us with the essential characters of 
 the large class Rhizopoda in their simplest form. It ap- 
 pears to be of an exceedingly voracious disposition, seizing 
 upon any minute aquatic animals or plants that may come 
 in its way, and appropriating them to the nutrition of its 
 own gelatinous body. The mode in which this tender 
 and apparently helpless creature effects this object is very 
 remarkable. The gelatinous matter of which it is com- 
 posed is capable, as we have seen, of extension in every 
 direction ; accordingly, when the Amoeba meets with any- 
 thing that it regards as suitable for its support, the sub- 
 stance of the creature, as it were, grows round the object 
 until it is completely enclosed within its body. The sub- 
 stances swallowed (if such a term be admissible) by this 
 hungry mass of jelly are often so large, that the creature 
 itself only seems to form a sort of gelatinous coat enclosing 
 its prey. 
 
 Professor Ecker believes in an exact similarity of con- 
 tractile substance between that of the lower animal forms, 
 such as the Rhizopoda, and that observed in the Hydra. 
 He says : " The properties of this substance, in its simplest 
 form, are seen in the Amoeba, the body of which, as is 
 known, consists of a perfectly transparent albumen-like 
 homogeneous substance, in which nothing but a few 
 granules are imbedded, and which presents no trace of 
 
374 THE MICROSCOPE. 
 
 farther organization. This substance is in the highest 
 degree extensible and contractile ; and from the main mass 
 are given out, now in one part and now in another, per- 
 fectly transparent rounded processes, which glide over the 
 glass like oil, and are then again merged in a central mass. 
 There is no external membrane. In the body of the 
 Amoeba there occur, besides the granules, clear spaces with 
 fluid contents, which are sometimes unchangeable in 
 form, and sometimes exhibit rhythmical contractions." 
 
 Belonging to the family is the very curious Acineta of 
 Ehrenberg, Actinophrys sol, " sun-animalcule." This 
 creature consists of a jelly-like contractile substance, or 
 sarcode, with tentacular filaments radiating from the 
 central mass, in such a manner as to have suggested the 
 name for the species. It abounds in pools where Desmi- 
 diacece are found in many parts around London ; they 
 are ravenous feeders, not only upon the -Desmidiacece, but 
 also upon all kinds of minute spores and animalcules. 
 (Plate III. fig. 66.) It was on examining some beautiful 
 Desmidiacece that my attention was arrested by the 
 curious appearance of two or three very small Actinophrys 
 floating very lightly upon the surface of the water, in the 
 form of a ball, with their delicate tentacular filaments 
 perfectly erect all over their bodies ; in fact, they seemed 
 to be floating upon these delicate filaments. 1 
 
 The most beautiful forms of the Rhizopoda are found 
 among those possessing a calcareous covering, as the 
 Polythalamia, Eosalina, Faujasina, &c. ; their systematic 
 arrangement is founded upon their shells, which exhibit 
 a very great diversity in form. Out of these forms, it 
 would appear that the labours of various naturalists in the 
 last hundred years have made us acquainted with nearly 
 2,000 recent and fossil Foraminifera ; and although the 
 observations of Dr. Carpenter 2 tend to show the pro- 
 bability that very many of these supposed species are 
 merely varieties, still the number is sufficiently great 
 to prove the importance and interesting nature of the 
 inquiry. 
 
 (1) Weston, Journ. Micros. Science, vol. iv. New series, p. 110; Clapa- 
 rede, Ann. Nat. His. Second series, vol. xv. p. 211. 
 
 (2) Carpenter's "Introduction to the Study of the Foraminifera," published 
 by the Ray Soc. 1862. 
 
FORAMINIFERA. 375 
 
 Dr. Schultze acknowledges the difficulties attending the 
 study of the Rhizopoda, and insists, very properly, upon 
 the necessity of viewing them in all positions, and under 
 different modes of illumination and of preparation, in 
 order to arrive at a due conception of their astonishing 
 conformation. When the shells of Foraminifera are dis- 
 solved in dilute acid, an organic basis is always left after 
 the removal of the calcareous matter, accurately retaining 
 the form of the shell with all its openings and pores. 
 The earthy constituent is mainly carbonate of lime \ but 
 Dr. Schultze has satisfied himself of the presence of a 
 minute amount of phosphate of lime in the shells of 
 recent Orbiculina adunca from the Antilles and of Poly- 
 stomdla strigilata from the Adriatic. 
 
 Fig. 207. 
 
 1, Separated prisum From outer layer of Pinna shell. ^.-Skeletons of Forami- 
 nifera from limestone. 3, Recent shell of Polystomella crlspa; viewed with 
 dark-ground illuminator. 
 
 The solitary Rhizopoda, furnished with a horny shell or 
 capsule, forming a case for the animal, is nearly the only 
 representative of the Arcellidce. In the Arcella, from 
 which the family derives its name, the shell is somewhat 
 of a bell-shape, with a very large round opening. In 
 
376 THE MICROSCOPE. 
 
 Englypha it is of an oval or flask-like form, with the 
 opening at the smaller end, and the shell appears as 
 . though formed of a sort of mosaic of small horny pieces. 
 In Dijftugia, Fig. 205, A B, the shell is often globular. 
 Rhizopods which never develop more than one chamber 
 or loculus are classed as Monothalamia. 1 
 
 The Polythalamia, or Multilocular Rhizopods, in their 
 earliest state, are unilocular ; but, as the animal increases, 
 successive chambers are added in a definite pattern for 
 ^ach family of the order. They all inhabit the sea, and 
 frequently occur in such great numbers, that the fine 
 calcareous sand which constitutes the sea-shore in many 
 places consists almost entirely of their microscopic coats. 
 At former periods of the earth's history, they existed in 
 even greater profusion than at present ; and their fragile 
 shells form the principal constituent of several very 
 important geological formations. Thus the chalk appears 
 to consist almost entirely of the shells of these animals, 
 either in a perfect state, or worn and broken by the action 
 of the waves ; they occur again in great quantities in the 
 rnarly and sandy strata of the Tertiary epoch. 
 
 In the Stichostegidae the chambers are placed end to 
 end in a row, so as form a straight or but slightly curved 
 shell. In the second family, the Enallostegidce, the 
 chambers are arranged alternately in two or three parallel 
 lines ; and as the construction of the shell is always 
 commenced with a single small chamber, the whole neces- 
 sarily acquires a more or less pyramidal form. The third 
 family, the Helicostegidce, presents us with some of the most 
 beautiful forms that it is possible to meet with in shells. 
 They commence by a small central chamber ; and each of 
 the subsequent chambers, which are arranged in a spiral 
 form so as to give the entire shell much the aspect of a 
 minute flattened snail, is larger than the one preceding it. 
 It is in this family that we find the nearest approach, in 
 external form, to the large chambered shells of the cepha- 
 lopodous mollusca, of which the Nautilus pompilius is an 
 example. The fourth family, the Entomostegidce, stand in the 
 same relation to the preceding as the Enallostegidce to the 
 
 (1) Dijfcugia and Ancella form a connecting link between the naked forma, 
 Amttba t Actinophrys, &c. and the shell-bearing Rhizopods, Lagena ttriata, <tc. 
 
IrKKUAKlMDA, I'oLYC YSTKN A, FoKA.M I M> KltA ; KoilFKRA, ETC. 
 
 PLATE 111. 
 
FORAMINIFERA. 
 
 377 
 
 Stichostegidce ; that is to say, the chambers are also arranged 
 in a spiral form, but in a double series. A fifth family 
 includes those shells in which the chambers are arranged 
 round a common perpendicular axis in such a manner that 
 each chamber occupies the entire length of the shell. The 
 orifices of the chambers are placed alternately at each end 
 of the shell, and are furnished with a curious tooth-like 
 process. The Miliola serve as an example of this family. 
 Every handful of sea-sand, every shaking of a dried sponge, 
 and the contents of the stomachs of most Lamellibranch 
 molluscs, oyster and mussel, are pretty sure to exhibit a 
 considerable admixture of these minute calcareous, or 
 occasionally silicious, Foraminifera. 
 
 It is considered that the fossil shells, termed Nuin- 
 mulites, found in great quantities in the chalk and lower 
 tertiary strata, are also to be regarded as members of this 
 class ; in a fossilized state, whole mountains consist almost 
 entirely of their shells. The late Professor Quekett had an 
 opportunity of examining a few living specimens, which, he 
 says, " are composed of a sarcode element, built up into a 
 series of chambers with calcareous material." 
 
 The great Pyramid of Egypt, covering eleven acres of 
 ground, is based on blocks of limestone consisting of 
 Foraminifera, Nummulites, or stone coin, and other fossil 
 animalcules. Nummulites vary in size from a very minute 
 object to that of a crown-piece, and many appear like a 
 snake coiled up in a round form. A chain of moun- 
 tains in the United States, 300 feet high, seems wholly 
 formed of one kind of these fossil-shells. The crystalline 
 marble of the Pyrenees, and the limestone ranges at 
 the head of the Adriatic gulf, are composed of small 
 Nummulites. Vast deposits of Foraminifera have been 
 traced in Egypt and the Holy Land, on the shores of 
 the Red Sea, Arabia, and Hindostan, and, in fact, may be 
 said to spread over thousands of square miles from the 
 Pyrenees to the Himalayas. 
 
 The fossilized Foraminifera in the Poorbaudar lime- 
 stone, although occasionally reaching the twenty-fifth, do 
 not average more than the hundredth part of an inch in 
 diameter ; so that more than a million of them msy be 
 computed to exist in a cubic inch of the stone. They may 
 
378 THE MICROSCOPE. 
 
 be separated into two divisions those in which the cells 
 are large, the regularity of their arrangement visible, and 
 their bond of union consisting of a single constructed por- 
 tion between each; and those in which the cells are 
 minute, not averaging more than the 900th part of an 
 inch in diameter, the regularity of their arrangement not 
 distinctly seen, and their bond of union consisting of many 
 thread-like filaments. To ascertain the mineral composi- 
 tion of the amber-coloured particles or casts, after having 
 found that it was mostly carbonate of lime with which 
 they were surrounded, they were placed for a few mo- 
 ments in the reducing flame of a blow-pipe, and it was 
 observed that on subsequently exposing them to the influ- 
 ence of a magnet, they were all attracted by it. Hence, in 
 a rough way, this rock may be said to be composed of 
 carbonate of lime and oxide of iron. 
 
 By far the greater number of Foraminifera are marine. 
 They are found in most seas, and in those of the tropics 
 they increase both in size and variety, forming extensive 
 deposits. 
 
 During the Canadian Geological Survey large masses 
 of what appeared to be a fossil organism, the Eozoon 
 Canadense, were discovered in rocks situated near the 
 base of the Laurentian series of North America. Dr. 
 Dawson, of Montreal, referred these remains to an animal 
 of the foraminiferal type ; and specimens were sent by 
 Sir W. Logan to Dr. Carpenter, requesting him to subject 
 them to a careful examination. As far back as 1858 Sir 
 W. Logan had suspected the existence of organic remains 
 in specimens from the Grand Calumet limestone, on the 
 Ottawa river, but a microscopic examination of one of 
 these specimens was not successful. Similar forms being 
 seen by Sir William in blocks from the Grenville bed of 
 the Laurentian limestone were in their turn tried, and 
 ultimately revealed their true structure to Dr. Dawson 
 and Dr. Sterry Hunt. 
 
 The masses ot which these fossils consist are composed 
 of layers of serpentine alternating with calc spar. It 
 was found by these observers that the calcareous layers 
 represented the original shell ; and the siliceous layers 
 the flesh, or sarcode, of the once living creature. These 
 
EOZOON CANADENSE. 379 
 
 results were arrived at through comparison of the appear- 
 ance presented by the Eozoon with the microscopic struc- 
 ture which Dr. Carpenter had previously shown to 
 characterise certain members of the foraminifera. The 
 Eozoon not only exceeded other known foraminifera in 
 size, to an extent that might have easily led observers 
 astray, but, from its apparently very irregular mode of 
 growth, its general external form afforded no help in its 
 identification, and it was only by careful examination of 
 its minute structure that its true character could be 
 ascertained. Dr. Carpenter says : " The minute struc- 
 ture of Eozoon may be determined by the microscopic 
 examination either of thin transparent sections, or of 
 portions which have been subjected to the action of 
 dilute acids, so as to remove the calcareous shell, leaving 
 only the internal casts, or models, in silex, of the chambers 
 and other cavities, originally occupied by the substance of 
 one animal/* 
 
 Dr. Carpenter found the preservation of minute struc- 
 ture so complete that he was able to detect " delicate 
 pseudopodial threads, wnich were put forth through pores 
 in the shell wall, of less than I0 ^ 00 th of an inch in 
 diameter " (see Plate III. figs. 64, 65) and in a paper 
 read at the meeting of the Geological Society he stated 
 that he had detected Eozoon in a specimen of ophicalcite 
 from Cesha Lipa in Bohemia, in a specimen of gneiss from 
 near Moldau, and in a specimen of serpentine limestone 
 sent to Sir C. Lyell by Dr. Giimbel, of Bavaria, all these 
 being parts of the great formation of "fundamental" 
 gneiss, which is considered by Sir Roderick Murchison 
 as the equivalent of the Laurentian rocks of Canada. 
 There can be little doubt that a rich field of research is 
 now opened to those who will undertake the examination 
 of rocks of various ages, which present the appearance 
 of analogous structure ; as it is, the microscope has been 
 the means of demonstrating the existence of animal life 
 at a very ancient geological date ; and, in the words of 
 Sir W. Logan, " we are carried back to a period so far 
 remote that the appearance of the so-called Primordial 
 Fauna may be considered a comparatively modern event." 
 
 Eecent Foraminifera present symmetrical shells, of 
 
380 
 
 THE MICROSCOPE. 
 
 minute size for the most part, and consisting, as we 
 have already seen, either of one, two, or more con- 
 nected chambers. A jelly-like mass, or " sarcode," occu- 
 pies the chambers and their connecting passages ; and, 
 protruding itself both from the external aperture of 
 
 Fig. 203. 
 
 1, Section of Faujasina,: a a, radiating interseptal canals; 6, their internal 
 bifurcations ; c, a transverse branch ; d, tubular wall of the chambers. 2, 
 Rosalina ornata, with its pseudopodia protruded. 
 
 the last chamber, and in many cases from the sometimes 
 numerous perforations in the shell-walls, extends itself not 
 only over the surface of the shell, but also into radiating 
 contractile threads or pseudopodia, and into gemmule-like 
 masses, which latter become coated over with calcareous 
 matter, and thus form additional segments of the animal. 1 
 " Foraminifera, indeed, are to be compared with the 
 other lowest orders of animals and of plants in the study 
 of their specific relations. In these several low forms of 
 creatures we have comparatively few species, but ex- 
 tremely numerous individuals, with an enormous range of 
 
 (1) Among the more important works on Foraminifera, reference may be 
 made to D'Orbigny's Foraminifkres fussiles du Bassin Tertiaire de Vienna 
 (Autrihe); Schultze, Ueber den Organismus der Polythalamien, 1854; Car- 
 penter's and Williamson's Researches on the Foraminifera, Phil. Trans. 1856. 
 Also an excellent paper by Mr. W. R. Parker, in the Annals of Nat-ural History, 
 April, 1857. Specimens of Foraminifera may be obtained for examination from 
 the shaking of dried Sponges; but if required alive they must be dredged for, or 
 picked off the fronds of living seaweeds, over the surface of which they are 
 seen to move by the aid of a lens. 
 
FORAMINIFERA. 
 
 381 
 
 variety. In the higher orders of plants and animals the 
 specific forms are more definite, there being a more com- 
 plex organization, harmonizing with the special habits of 
 each creature ; and the individuals of each species are less 
 
 Fig. 209. Foraminifera taken in Deep-tea Soundings. (Atlantic.) 
 
 numerous than is the case in the Protozoans and Proto- 
 phytes." 
 
 These lowly organized Foraminifera, having great 
 simplicity of structure, more easily adapt themselves to 
 varying external conditions than the more complex and 
 specialized higher animals. 
 
382 
 
 THE MICROSCOPE. 
 
 ID the deep-sea soundings, portions of many beau- 
 tiful Diatoms, figured and described by Professor "W". 
 Smith, in gatherings from the Bay of Biscay, near Biar- 
 ritz, are Melosira cribrosa, marine, orbicular, cellulate, 
 
 Fig. 210. Foraminif&ra taken in Deep-sea Soundings. (Atlantic.) 
 
 cellules, all equal and hexagonal. He writes : " In De- 
 cember, 1853, I received isolated frustules of this species, 
 collected on the coast of Normandy, under the above 
 name, from M. de Brebisson ; and I have since detected 
 the same in a gathering from the Black Sea. In no case 
 have I seen the frustules in a recent state, and do not know 
 
FORAMINIFERA. 383 
 
 whether they ever form a lengthened filament. As this is 
 the only circumstance that would justify their separation 
 from Coscinodiscus, to which the separated valve would 
 otherwise seem to belong (Synop. British Diatomacece, 
 vol. i. p. 22), their position in Melosira must rest upon the 
 authority of my accurate correspondent." 
 
 In figs. 209 and 210 are represented many of the beau- 
 tiful forms brought up with soundings made in 1856, for 
 the purpose of ascertaining the depth of the Atlantic, 
 prior to the laying down of the electric telegraph wire 
 from England to America; these specimens were taken 
 from a depth of 2,070 fathoms. 
 
 Major S. R J. Owen, while dredging the surface of 
 mid-ocean Indian and Atlantic oceans found attached to 
 his nets a few interesting forms of Ehizopods, belonging to 
 the two genera Globigerina and Pulvinulina, which always 
 make their appearance on the surface of the ocean after 
 sunset. 1 
 
 "Many of the forms," writes this observer, "have 
 hitherto been claimed by the geologist, but I have found 
 them enjoying life in this their true home, the siliceous 
 shells filled with coloured sarcode, and sometimes this 
 sarcode in a state of distension somewhat similar to that 
 found projecting from the Foraminifera, but not in such 
 slender threads. There are no objects in nature more 
 brilliant in their colouring or more exquisitely delicate in 
 their forms and structure. Some are of but one colour, 
 crimson, yellow, or blue ; sometimes two colours are found 
 on the same individual, but always separate, and rarely if 
 ever mixed to form green or purple. In a globular 
 species, whose shell is made up of the most delicate fret- 
 work, the brilliant colours of the sarcode shine through the 
 little perforations very prettily. In two specimens of the 
 triangular and square forms (Plate III. figs. 44, 45, and 
 46), the respective tints of yellow and crimson are vivid 
 and delicately shaded. In one the pink lines are concen- 
 tric ; while another is of a stellate form (fig. 43), the 
 points and uncoloured parts being bright clear crystal, 
 while a beautiful crimson ring surrounds the central por- 
 
 (1) Journ. Linn. Soc. vol. viii. p. 202 ; voL ix. p. 147, 1866, and January. 
 
384 THE MICROSCOPE. 
 
 tion. One globular species appears like a specimen of the 
 Chinese ball-cutting one sphere within another j but it 
 is of a marked and distinct kind. 
 
 "The shells of some of the globular forms of these 
 Polycystina, whose conjugation I believe I have witnessed, 
 are composed of a fine fretwork, with one or more large 
 circular holes ; and I suspect the junction to take place 
 by the union of two such apertures. That the figures of 
 these shells become elongated, lose their globular form 
 after death, and present a disturbed surface is seen in 
 some of the figures represented near the bottom part of 
 Plate III." Major Owen proposes to make Orbulina a 
 subgenus of GloUgerina. The internal chambers of the 
 former are in form remarkably like those of the latter, 
 and like them also they present themselves with varying 
 surfaces, some free from, while others are covered with, 
 spines. Those without internal chambers have been 
 known as Orbulina universa, fig. 78, Plate III. while 
 figs. 75 and 76, although members of the same family, 
 have been separated ; but he wishes to see all united under 
 the name of " Globigerina universa" 
 
 The minute siliceous shells of Polycystina present won- 
 derful beauty and variety of form ; all are more or less 
 perforated, and often prolonged into spines or other pro- 
 jections, through which the sarcode body extends itself 
 into pseudopodial prolongations resembling those of Acti- 
 nophrys. When seen besporting themselves in all their 
 living splendour, their brilliancy of colouring, says Major 
 Owen, "renders them objects of unusual attraction." We 
 have endeavoured to give some idea of the colour of the 
 living forms in Plate III. Nos. 43 to 52. The same ob- 
 server believes that they wish to avoid the light, " as they 
 are rarely found on the surface of the sea in the day time ; 
 it is after sunset, and during the first part of the night 
 especially, that they make their appearance." 
 
 The Polycystina appear to have most affinity with the 
 foraminifera. Thirty four genera and about two hundred 
 and ninety species have been described. They are most 
 abundant in the fossil state ; and are very plentiful in the 
 rocks of Bermuda, in the tripoli of Hichmond, Virginia, in 
 the marls of Sicily, and other places. Their minute shells 
 
SPONGES. 385 
 
 form beautiful microscopic objects for the binocular ; they 
 must be mounted dry, and viewed either with the dark 
 ground illuminator, or by condensed light. 
 
 8PONGIAD.E. SPONGES. 
 
 The term Porifera, or Canal-bearing Zoophyte, was 
 applied by Professor Grant to designate the remarkable 
 class of organized beings known as sponges, which are met 
 with in every sea, growing in great abundance on the 
 surface of rocks. 
 
 Ellis, in the course of his investigations, was astounded 
 by discovering that sponges possessed a system of pores 
 and vessels, through which sea-water passed, with all the 
 appearance of the regular circulation of fluids in animal 
 bodies, and for the seeming purpose of conveying ani- 
 malcules to the animals for food. 
 
 The description given of sponges by Dr. Johnston is, 
 that they are " organized bodies growing in a variety of 
 forms, permanently rooted, unmoving and irritable, fleshy, 
 fibro-reticular, or irregularly cellular ; elastic and bibulous, 
 composed of a tibro-corneous axis or skeleton, often inter- 
 woven with siliceous or calcareous spicula, and containing 
 an organic gelatine in the interstices and interior canals ; 
 and are reproduced by gelatinous granules called gem- 
 mules, which are generated in the interior, but in no 
 special organ. All are aquatic, and with few exceptions 
 marine." l Our author continues : " Mr. John Hogg, in a 
 letter to me dated June 25, states that the green colour 
 of the fresh-water sponge (Spongilla fluviatilis) depends 
 upon the action of light, as he has proved by experi- 
 ments which showed that pale-coloured specimens became 
 green when they were exposed for a few days to the 
 light and full rays of the sun ; while, on the contrary, 
 green specimens were blanched by being made to grow 
 in darkness or shade." 
 
 The living sponge, when highly magnified, exhibits a 
 reticulated structure, permeated by pores, which united 
 into cells or tubes, ramify through the mass in every 
 direction, and terminate in larger openings. In most 
 
 (1) See Dr. Johnston's History of British Sponges, atd Mr. Bowerbank's revi- 
 sion of the class, in the publications of the Kay Socieay. 
 C C 
 
38G 
 
 THE MICROSCOPE. 
 
 sponges the tissue is strengthened and supported by 
 spines, spicula, of various forms ; and which, in some 
 species, are siliceous, and in others calcareous. The 
 minute pores, through which the water is imbibed, have 
 a fine transverse gelatinous network and projecting spicula, 
 for the purpose of excluding large animals cr noxious par- 
 ticles ; water incessantly enters into these pores, traverses 
 the cells or tubes, and is finally ejected from the larger 
 
 Fig. 211. 
 
 1, A portion of Sponge, Halichondria simulans, showing siliceous spicula 
 imbedded in the sarcode matrix. 2, Spicula divested of its matrix. 
 
 vents. But the pores of the sponge have not the power of 
 contracting and expanding, as Ellis supposed ; the water 
 is attracted to these openings by the action of instruments 
 of a very extraordinary nature (cilia), by which currents 
 are produced in the fluid, and propelled in the direction 
 required by the economy of the animal. 
 
 Mr. Bowerbank, in a paper on the "Structure and 
 Vitality of Spongiadce" states that sponges consist princi- 
 pally of sarcode, strengthened sometimes by a siliceous or 
 calcareous skeleton, having remarkable reparative and 
 digestive powers, and consequently a most tenacious 
 vitality ; so much so, that having cut a living sponge into 
 three segments, and reversed the position of the centre 
 piece, after the lapse of a moderate interval, a complete 
 junction of the parts became effected, so as to render the 
 previous separation indistinguishable. 
 
 Professor Grant's careful and laborious researches, have 
 finally classed sponges in the animal series of the creation. 
 
TS 
 
 11 
 
 ili: 
 
 jS-SiS 1 
 
 Ort g - 
 
 - B i 2 i 
 
 a "gfi 
 Ml 1 ? 
 
 Ilil 
 
 ti 
 
 i 
 
388 THE MICROSCOPE. 
 
 He ascertained that the water was perpetually sucked into 
 the substance of the sponge, through the minute pores that 
 cover its surface, and again expelled through the larger 
 orifices. His own account is so very interesting, that we 
 cannot resist giving, in his own words, the results arrived 
 at in these investigations : " Having placed a portion of 
 live sponge (Sponyia coalita, fig. 1, No. 213) in a watch- 
 
 1. Pponyia ccidlitn. 2, Spnngia panicea. 
 
 glass with some sea-water, I beheld for the first time the 
 splendid spectacle of this living fountain, better repre- 
 sented in No. 2, vomiting forth from a circular cavity an 
 impetuous torrent of liquid matter, and hurling along in 
 rapid succession opaque masses, which it strewed every- 
 where around. The beauty and novelty of such a scene 
 in the animal kingdom long arrested my attention ; but 
 after twenty-five minutes of constant observation, I was 
 obliged to withdraw my eye from fatigue, without having 
 seen the torrent for one instant change its direction, or 
 diminish the rapidity of its course. In observing another 
 species (Spongia panicea), I placed two entire portions of 
 this together in a glass of sea-water, with their orifices 
 opposite to each other at the distance of two inches ; they 
 appeared to the naked eye like two living batteries, and 
 soon covered each other with the materials they ejected. 
 T placed one ~.f them in a shallow vessel, and just covered 
 
SPONGES. 389 
 
 its surface and highest orifice with water. On strewing 
 some powdered chalk on the surface of the water, the 
 currents were visible to a great distance ; and on placing 
 some pieces of cork or of dry paper over the apertures, I 
 could perceive them moving, by the force of the currents, 
 at the distance of ten feet from the table on which the 
 specimen rested." 
 
 Dr. JST. Lieberkiihn, in his valuable contributions to 
 the History of the Development of tJie Spongillce, observes 
 that with regard to the skeleton of S. fluviatilis, the 
 spicules are not united at the base by a siliceous material, 
 as stated by Meyen, but by a substance destructible by 
 heat. The spicules are usually arranged in aggregate 
 bundles, which meet point to point at an obtuse angle, and 
 project slightly above the surface of the sponge. Minute 
 portions of the gelatinous substance exhibit under the 
 microscope amceba-like movements, respecting which it is 
 unknown whether they are vital phenomena, as supposed 
 by Dujardin, or referable to a process of decomposition. 1 
 
 The living spoitgilla; are often seated, not immediately 
 upon the wood, stone, &c. upon which they may be 
 growing, but separated from it by a peculiar dark-brown 
 substance often several inches thick. This mass is com- 
 posed chiefly of the remains of the dead sponge, empty 
 gemmule-cases with their amphidiscs, various forms of 
 siliceous spicules, &c. ; and occasionally there may be 
 
 (1) The motile phenomena hitherto observed in sponges are connected with 
 larger or smaller portions of the external integument, and of the exhalent 
 tubules, or with isolated cells. When the exhalent tubules of Spongilla con- 
 tract, their walls become shortened and thickened, and the prev.ously smooth 
 surface uneven, from the presence of the spherical contracted cells, whose 
 outlines at the same time are rendered very distinct, whilst they were before 
 invisible, or at most here and there perceptible. Other motile phenomena are 
 witnessed when a Spongilla with external membrane and exhalent canals is 
 produced from a cut-off portion. The fragment thus cut off may be so thin as 
 to consist of only a single layer of reticular parenchymatous fibres. The inter- 
 stitial rounded, oval, or irregular spaces, under these circumstances, become for 
 the most part closed, owing to the gradual increase in breadth of the trape- 
 culse, or cavities may be left when their membranes are stretched over them 
 only from the upper and under sides of the trabeculse, which enclose a space 
 between them, and may become portions of the outer membrane with exhalent 
 canals. It cannot be determined with certainty to what extent this change of 
 form is connected with any multiplication of cells. Lastly, movements in the 
 individual cells have been noticed, the globular cells becoming stellate, and the 
 stellate ones globular in turn, but without any locomotion. This phenomenon 
 occurs, not only in the cells of the uninjured substance, but also in those which 
 have been detached. N. Leiberkiihn, "On the Motile Phenomena in Sponges," 
 Micros. Journ. voL iv. 1864, p. 189, and Journ. Micros Science, voL v. 1857, p. 
 212, "On the Development of the Spongillae." 
 
390 
 
 THE MICROSCOPE. 
 
 found in it gemn.ules still retaining their brown coloul 
 and contents capable of development. 
 
 Pig. 214. Geodia Barretti (Bowerbank). 
 
 A section at right angles to the surface, exhibiting the radial disposition of the 
 fasciculi of the skeleton, and a portion of the dermal crust of the sponge, 
 magnified 50 diameters, a, intermarninal cavities ; 6, the basal diaphragms ol 
 the intermarginal cavities : c, imbedded ovaria forming the dermal crust ol 
 the sponge ; d, the large patentoternate spicula, the heads of which form the 
 areas, for the valvular bases of the intermarginal cavities ; e, recurvo-ternate 
 defensive and aggressive spicuia within the summits of the intercellular 
 spaces of the sponge ; /, portions of the interstitial membranes of the 
 sponge, crowded with minute stellate spicula : g, portions of the secondary 
 system of external defensive spicula (1) 
 
 The usual contents of the gemmules have been described 
 by Meyen (Muller's Archiv. 1839, p. 83). In many in- 
 
 (1) See Bowerbank's Monograph of the, British Spotyjiadce, Ray Soc. p. 10P. 
 
SPONGES. 391 
 
 stances Lieberkuhn found that the globular arrangement 
 no longer existed, the globules being replaced by granules 
 exhibiting an active molecular motion. That the gem- 
 mules are formed from agglomerations of sponge-cells may 
 be readily proved in the branched sponge containing 
 smooth gemmules. Lieberkiihn notices four kinds of 
 gemmules characterised respectively by their cases or 
 shells. 
 
 1. Those with smooth cases. 
 
 2. Those with stellate amphidiscs. 
 
 3. Those with amphidiscs, in which the discoid ex- 
 tremities are entire, and not stellate. 
 
 4. Gemmules whose case, instead of amphidiscs, is fur- 
 nished with minute, usually slightly curved siliceous 
 spicules. 
 
 It would appear, therefore, that the " globules " of 
 Meyen are nothing more than altered sponge-cells. The 
 autumn is the most favourable season for observing the 
 process of their formation. 
 
 In the journal of the Bombay branch of the Royal 
 Asiatic Society for 1849, Surgeon H. J. Carter gives a very 
 accurate account of fresh-water sponges found in the 
 water tanks of Bombay. Of five species that he disco- 
 vered, one was the Spongilla friabilis, the others he named 
 Sp. cinerea, Sp. alba, Sp. Meyeni, Sp. plumosa. 
 
 Spongilla cinerea is stated to present on its surface a 
 dark rusty, copper colour, lighter towards the interior, and 
 purplish under water. It throws up no processes, but 
 extends horizontally in circular patches, over surfaces two 
 or three feet in circumference, or accumulates on small 
 objects ; and is seldom more than half an inch in thick- 
 ness. It is found on the sides of fresh -water tanks, on 
 rocks, stones, or gravel. The ova are spheroidal, about 
 l-63d of an inch in diameter, presenting rough points ex- 
 ternally. Spicula of two kinds, large and small ; large 
 spicula, slightly curved, smooth, pointed at both ends, 
 about l-67th of an inch in length ; small spicula, slightly 
 curved, thickly spiniferous, about 1 -380th of an inch in 
 length. 
 
 Spongilla friabilis. Growing in circumscribed masses, 
 on lixed bodies, or enveloping floating objects ; seldom 
 
392 
 
 THE MICROSCOPE. 
 
 attaining more than two inches in thickness. From the 
 other sponges it is distinguished by the smooth spicula 
 which surround its seed-like bodies, and the matted 
 structure. 
 
 Spongilla alba. Its texture is coarse and open ; struc- 
 ture reticulated. The investing membrane abounds in 
 minute spicula; has seed-like spheroidal bodies about 
 l-30th of an inch in diameter, with rough points exter- 
 nally. The large spicula are slightly curved, smooth, 
 pointed at each end, about l-54th of an inch in length ; 
 the small spicula are slightly curved, thickly spiniferous, 
 or pointed at both ends; the former, pertaining to the 
 seed-like bodies, are about l-200th of an inch in length ; 
 the latter, pertaining to the investing membrane, are more 
 slender, and a little less in length; these last numerous 
 small spiniferous spicula when dry present a white-lace 
 appearance, from which Mr. Carter gives them the name 
 of alba. 
 
 Spongilla meyeni is massive, having large lobes, mam- 
 millary eminences, or pyramidal, compressed, obtuse, or 
 sharp-pointed projections, of an inch or more in height ; 
 also low wavy ridges. Its seed-like bodies are spheroidal, 
 about 1-4 7th of an inch in diameter, studded with little 
 toothed discs. 
 
 Mr. Carter enters very minutely into the structure of 
 " fresh- water sponge, which " he believes " is composed 
 of a fleshy mass, supported on a fibrous, reticulated, horny 
 skeleton. The fleshy mass containing a great number 
 of seed-like bodies in all stages of development, and 
 the horny skeleton permeated throughout with siliceous 
 spicula. When the fleshy mass is examined by the aid of 
 the microscope, it is found to be composed of a number of 
 cells, imbedded in and held together by an intercellular 
 substance. 
 
 " In the development of the sponge-cell of Spongilla, a 
 set of large granules make their appearance at a very early 
 period, and increase in number < and size until they form 
 a remarkable feature. At this time they are about 
 1-1 0,000th of an inch in diameter, of an elliptical shape, 
 and of a light amber colour by transmitted light ; they 
 are the colour bearing granules or cells, and give the 
 
SPONGES. 393 
 
 colour of chlorophyll to this organism when it becomes 
 green. The transparent intercellular substance of Spon- 
 gilla has a polymorphism equally great with the fully 
 developed cells. This, however, can only be satisfactorily 
 seen when the new sponge is growing out from the seed- 
 like body, at which time it spreads itself over the glass in 
 a transparent film, charged with contracting vesicles of dif- 
 ferent sizes, and in various degrees of dilatation and con- 
 traction. How this substance is produced so early, it is 
 difficult to conceive, since it seems to come into existence 
 independently of the development of the sponge-ovules, 
 which are seen imbedded in it, and there undergoing 
 their transformation into sponge-cells. The spicula, too, 
 are developed synchronously with the advancing trans- 
 parent border, from little glairy globules about the size of 
 the largest ovules, which send out a linear process on 
 each side, and thus gradually grow into their ultimate 
 forms. The only way of accounting for the early appear- 
 ance of this intercellular-substance is to consider that it is 
 a development from some remnants of the original proto- 
 plasm ; and perhaps possesses also the power of producing 
 new sponge-cells, as we see the protoplasm in Vorticella 
 and the roots of Chara producing new buds, independently 
 of the cell-nucleus. 
 
 " The cells of the investing membrane are characterised 
 by their uniformly granular composition and colourless 
 appearance. They are nucleated, possess the contracting 
 vesicle singly or in plurality, and are spread over the 
 membrane in such numbers, that it seems to be almost 
 entirely composed of them ; while they are of such 
 extreme thinness, and drawn out into such long digitated 
 forms, that they present a foliated arrangement, not unlike 
 a compressed layer of multifidous leaves, ever moving and 
 changing their shapes. The apertures are circular or 
 elliptical holes in the investing membrane in the cells. 
 Through these apertures the particles of food are admitted 
 into the cavity of the investing membrane. The Paren- 
 chyma consists oi a mass of gelatinous substance, in which 
 are embedded the smooth spicules and ovi-bearing cells, 
 and through which pass the afferent and efferent canals. 
 Tne ovi-bearing cells do not curst and allow their con- 
 
394 THE MICROSCOPE. 
 
 tents to become indiscriminately scattered through the 
 gelatinous mass in which they are imbedded, but each 
 becomes developed separately in the following way : the 
 ovules and granules of the ovi-bearing cells subside into a 
 granular mass by the former losing their denned shape 
 and passing into small mono-ciliated and unciliated sponge 
 cells ; this mass then becomes spread over the interior 
 surface of the ovi-bearing cell, leaving a cavity in the 
 centre, into which the cilia of the monociliated sponge- 
 cells dip and keep up an undulating motion ; meanwhile, 
 an aperture becomes developed in one part of the cell 
 which communicates with the adjoining afferent canal, and 
 thus the ovi-bearing cell passes into an ampullaceous 
 spherical sac. The cilia may now be seen undulating in 
 the interior ; and if the Spongilla be fed with carmine, this 
 colouring matter will not only be observed to be entirely 
 confined to the ampullaceous sacs, but when the Spongilla 
 is torn to pieces and placed under a microscope, particles 
 of the carmine will be found in the interior of the mono- 
 ciliated and unciliated sponge cells, proving that of such 
 cells the ampullaceous sac is partly composed. This sac 
 then must be regarded as the animal of Spongilla^ as 
 much as the Polype- cell is regarded as the animal of the 
 Polype, and the whole mass of Spongilla as analogous to 
 a Polypidom. 
 
 " The united efforts of all the ciliated sponge-cells in 
 the ampullaceous sac are quite sufficient to produce a con- 
 siderable current, and thus catch the particles of food as 
 they pass through the afferent canals. Thus we find 
 Spongilla composed of a number of stomachal sacs im- 
 bedded in a gelatinous substance permeated with spicules 
 for its support, and an apparatus for bringing them food, as 
 well as one for conveying away the refuse, while the nourish- 
 ment abstracted by the process of digestion common to 
 Rhizopodous cells (e. g. Amoeba), no doubt passes through the 
 intercellular gelatinous substance into the general develop- 
 ment of the mass ; and if right in comparing the ampul- 
 laceous sacs to the stomachal cavities of the simplest 
 polypes, are we not further justified in drawing a resem- 
 blance between the ciliated sponge-cells and those which 
 line the stomach of Cordylophora, of Otostoma, and many 
 
DEVELOPMENT OF SPONGES. 395 
 
 of Ehrenberg's Allotreta, together with those in the stomach 
 of the Rotifera and Plan aria t 
 
 "The 'swarm-spore,' described by M. N. Ueberkiihn, 
 appears to be a ciliated form of the seed-like body, and 
 the same as the ' gemnmle ' described by Grant ; but this 
 I have not yet been able to see. The formation of the 
 seed-like body, however, now that we know the struc- 
 ture of the ampullaceous sacs, seems very intelligible, 
 for we have only to conceive an enlargement of the small 
 sponge-cells lining the interior, with the addition of 
 ovules to them respectively, and the spicnle-bearing 
 sponge-cells of the cortical substance supplying the 
 spii-ular crust to the exterior, to have a globular capsule 
 thus composed, with a hilum precisely like the seed-like 
 body a conjecture which seems to derive support from 
 the fact, that in some instances, when Spongilla is begin- 
 mng to experience the want of nourishment, these sacs, 
 small as they are, assume a defined, rigid, spherical form, 
 from their pellicle becoming hardened and encrusted with 
 extremely minute spicules." * 
 
 Clionce. Not the least wonderful circumstance con- 
 nected with the history of sponges, is the power possessed 
 by certain species of boring into substances, the hardness 
 of which might be considered as a sufficient protection 
 against such apparently contemptible foes. Shells (both 
 living and dead), coral, and even solid rocks, are attacked 
 by these humble destroyers, gradually broken up, and, no 
 doubt, finally reduced to such a state as to render sub- 
 stances which would otherwise remain dead and useless in 
 the economy of nature available for the supply of the 
 necessities of other living creatures. 
 
 These boring sponges constitute the genus Cliona of 
 Dr. Grant. They are branched in their form, or consist of 
 lobes united by delicate stems ; they all bury themselves 
 in shells or other calcareous objects, preserving their com- 
 munication with the water by means of perforations in the 
 outer wall of the shell. Tho mechanism by which a crea- 
 ture of so low a type of organisation contrives to produce 
 such remarkable effects is still doubtful, from the great 
 difficulties which lie in the way of coming to any satis- 
 
 (1! Ann. of Nat. Ifitt., July, 18*7. 
 
39G 
 
 THE MICROSCOPE. 
 
 factory conclusions upon the habits of an animal that 
 works so completely in the dark as the Cl-iona celata it 
 will probably long remain so. Mr. Hancock, to whom we 
 are indebted for a valuable memoir upon the boring 
 sponges, published in the Annals and Magazine of Natural 
 History, attributes their excavating power to the presence 
 of a multitude of minute siliceous crystalline particles 
 adhering to the surface of the sponge ; these he supposes 
 to be set in motion by some means analogous to ciliary 
 action. In whatever way this action may be produced, 
 however, there can be no doubt that these sponges are 
 constantly and silently effecting the disintegration of sub- 
 marine calcareous bodies the shelly coverings, it may be, 
 of animals far higher in organisation than they ; nay, in 
 many instances they prove themselves formidable enemies 
 even to living mollusca, by boring completely through the 
 shell. In this case the animal whose domicile is so unce- 
 remoniously invaded, has no alternative but to raise a wall 
 of new shelly matter between himself and his unwelcome 
 guest and in this manner generally succeeds at last in 
 barring him out. 
 
 Skeletons of Sponges. The skeletons of sponges, which 
 give shape and substance to the mass of sarcode that con- 
 stitutes the living animal, is best made out by cutting thin 
 slices of sponge submitted to firm compression, and view- 
 ing these slices mounted upon a dark ground, or backed up 
 with black paper. 
 
 The skeletons of sponges are composed principally of 
 two materials, the one animal, the other mineral ; the first 
 of a fibrous horny nature, the second either siliceous or 
 calcareous. The fibrous portion consist of a network of 
 smooth, and more or less cylindrical, threads of a light- 
 yellow colour, and, with few exceptions, always solid ; 
 they frequently aiiastamose, and vary considerably in size ; 
 when developed to a great extent, needle-shaped siliceous 
 bodies termed spicula (little spines) are formed in their in- 
 terior; in a few cases only one of these spicula is met 
 with, but most commonly they occur in bundles. In some 
 sponges, as those belonging to the genus Halichondria, the 
 same horny kind of material is present in greater or less 
 abundance ; but its fibrous structure has become obscure : 
 
SPONGES. 397 
 
 the fibres, however, in these cases are represented ly sili- 
 ceous needle-shaped spicula, and the horny matter serves 
 the important office of binding them firmly together, as 
 
 Fig. 215. 
 
 1. Tmnsverse section of a branch of Myriapore. 2, A section of the stem of 
 
 Virgularia mirabilis. 3, A spiculum from the outer surfn<>e of a Sea-pen. 4, 
 
 Spicula from crust of Isis hippurln. 5, Spicula from G .ninna elongata. 6, 
 Spicula from Alcyonium. 7, Spicula from Gorgoni-j, vmbra.cu.lum. 
 
 shown in fig. 213, No. 1. There are, however, some re- 
 markable exceptions to this rule, one, DictyocJialix pumi- 
 ccus, described by Mr. S. Stutchbury, in which the fibrous 
 skeleton is composed of threads of silex quite as trans- 
 parent as glass ; another, the Hyalonema, Glass-rope. 
 
 The mineral portion, as before stated, consists of spicula 
 composed either of silica or carbonate of lime ; the first 
 kind is the most common and likewise most variable in 
 shape, and presents every gradation in form, from the 
 acuate or needle-shaped to that of a star. The calcareous 
 spicula, on the contrary, are more simple in their form, 
 
THE MICROSCOPE. 
 
 being principally acicular, but not unfrequently branched 
 or even tri- or quad-radiate : the two kinds, the sili- 
 ceous and calcareous, according to Dr. Johnston, not 
 having hitherto been detected co existent in any native 
 sponges. 
 
 The spicula exhibit a more or less distinct trace of a 
 central cavity or canal, the extremities of which are closed, 
 or hermetically sealed ; in their natural situation they are 
 invested by an animal membrane, sarcode, which is not 
 confined to their external surface ; but in many of the 
 large kinds, as pointed out by Mr. Bowerbank, its presence 
 may be detected in their central cavity, by exposing them 
 for a short time to a red heat, when the animal matter 
 will become carbonised, and appear as a black line in their 
 interior. 
 
 Many authors have described the spicula as being crys- 
 talline, and of an angular figure, and have considered them 
 analogous to the r aphides in plants ; but it requires no 
 great magnifying power to prove that they are always 
 round, and, according to their size, are made up of one or 
 more concentric layers, as shown in fig. 212, No. 2. The 
 spicula occupy certain definite situations in sponges ; 
 some are peculiar to the crust, others to the sarcode, 
 others to the margins of the large canals, others to the 
 fibrous network of the skeleton, and others belong exclu- 
 sively to the gemmules. Thus, for instance, in Pachyma- 
 tisma Johnstonia, according to Mr. Bowerbank, the spicules 
 of the crust are simple, minute, and fusiform, having their 
 surfaces irregularly tuberculated, and their terminations 
 very obtuse ; whilst those of the sarcode are of a stellate 
 form, the rays varying in number from three to ten or 
 twelve. 
 
 Silica, however, may be found in one or more species of 
 sponge of the genus Dysidea, not only in the form of 
 spicula, but as grains of sand of irregular shape and size, 
 evidently of extraneous origin, but so firmly surrounded 
 by horny matter as to form, with a few short and slightly- 
 curved spicula, the fibrous skeleton of the animal. In these 
 sponges the spicula are of large size, and are disposed in 
 lines parallel with the masses of sand. 
 
 Most of the sponges of the earlier geological periods had 
 
SPONGES. 399 
 
 tubular fibres ; but in all existing species, with one or two 
 exceptions, they are solid. These tubular fibres are very 
 commonly filled with portions of iron, which accounts for 
 the colour of many of the remains in flint. 
 
 The Moss-agates, found among the pebbles at Brighton 
 and elsewhere, are flints containing the fossilised remains of 
 sponges. The coloured fibres seen in the GVeew-jaspers of 
 the East are of the same character. There is reason to 
 believe that most flints were originally sponges ; those 
 from chalk even retain their original form. Eecent 
 sponges from the Sussex coast present forms precisely 
 similar to some chalk flints, but it is from sections made 
 sufficiently thin to be transparent, for examination under 
 the microscope, that we learn their true nature and 
 origin. 
 
 Every horny sponge, whilst living, is invested with a 
 coating of jelly-like substance, which can only be preserved 
 by placing the sponge in spirit and water immediately 
 after its removal from its place of growth. Spicula are 
 not exclusively confined to the body of sponges, but occa- 
 sionally form the skeleton of the gemmules, and are situated 
 either on the external or internal surface of these bodies. 
 A good example of the former kind occurs in the common 
 fresh-water sponge (Spongilla jluviatilis), represented in 
 fig. 216, No. 1, and No. 3. The spicula are very minute 
 in size, and are disposed in lines radiating from the 
 centre to the circumference, the markings on the outer 
 surface of the gemmules being the ends of spicula. In all 
 the young gemmules the spicula project from the outer 
 margin as so many spines ; but in process of growth the 
 spines become more and more blunt, until at last they 
 appear as so many angular tubercles. Turkey sponge 
 (Spongia ojficinalis) is brought from the Mediterranean, 
 has a horny network skeleton rather fine in the fibres, 
 solid, small in size, and light in colour. In some larger 
 specimens there is a single large fibre, or a bundle of 
 smaller ones. In Ualichondria simulans the skeleton is a 
 framework of siliceous needle shaped spicula, arranged in 
 bundles kept together by a thick coat of horny matter. 
 Other species of Halichondria have siliceous spicula 
 pointed at both extrerr.ities acerate (fig. 212, No 2) ; 
 
400 THE MICROSCOPE. 
 
 while the spicula of some are round at one end, and 
 pointed at the other acuate ; some have spicula round at 
 one end, the former being dilated into a knob spinulate.' 
 
 Fig. 216. 
 
 1 Gemmnle of SpongiUa fluviatilis, enclosed in spicula. 2, Birotulate spicula, 
 ' from Flnviatilis. 3, Geinmules of SpongiUa fluviatilis, after having been im- 
 mersed in acid, to show coating of birotulate spicula. 
 
 Among the genus Grantia, Geodia, and Levant sponge, 
 are found spicula of a large size, radiating in three direc- 
 tions triradiate. In the Levant specimen, a central 
 communicating cavity can be distinctly seen. Some 
 Smyrna sponges, and species of Geodia, have four rays 
 quadriradiate. Some spicula in P. Johmtonia and Geodia 
 have as many as ten rays multiradiate. In some species 
 of Tethya and Geodia the spicula consist of a central sphe- 
 rical body, from which short conical spines proceed- 
 stellate spicula. (Fig. 212, Nos. 4 and 5.) Spicula 
 having both extremities bent alike bicurvate have been 
 obtained from Trieste sponge. Some South Sea sponges 
 have spicula twice bent, and have extremities like the 
 flukes of an anchor bicurvate anchorate ; sometimes the 
 flukes have three pointed ends. (Fig. 212, No. 6.) The 
 gemmules in fresh-water sponges are generally found in 
 the oldest portions near the base, and each one is protected 
 by a framework of bundles of acerate spicula of the flesh, 
 as shown in fig. 212, No. 9 ; but in many marine species, 
 Geodia and Pachymatisma, they are principally confined to 
 the crust. In the fresh- water sponges, the amount of 
 animal matter in the gemmules is considerable; but in 
 
BPICULA FROM SPONGES. 401 
 
 Pachymatisma, Geodia, and many other marine species, a 
 very small quantity only is ever to be found, the substance 
 of each gemmule being almost entirely composed of 
 minute siliceous spicula ; if they be viewed when taken 
 fresh from the sponge, and also after removing the animal 
 matter by boiling in acid, a slight increase in trans- 
 parency is the only perceptible difference of appearance 
 noticed. 
 
 HYALONEMA, " GLASS-ROPE" SPONGE. A bundle of from 
 200 to 300 threads of transparent silica, glistening with a 
 satiny lustre like the most brilliant spun glass; each 
 thread is about eighteen inches long, in the middle the 
 thickness of a knitting needle, and gradually tapering 
 towards either end to a fine point ; the whole bundle 
 coiled like a strand of rope into a lengthened spiral, the 
 threads of the middle and lower portions remaining com- 
 pactly coiled by a permanent twist of the individual 
 threads; the upper portions of the coil frayed out, so 
 that the glassy threads stand separate from each other. 
 The spicules on the outside of the coil stretch its entire 
 length, each taking about two and a half turns of the 
 spiral. One of these long needles is about one-third of a 
 line in diameter in the centre, gradually tapering towards 
 either end. The spirally twisted portion of the needle 
 occupies rather more than the middle half of its entire 
 length. In the lower portion of the coil, which is em- 
 bedded in the sponge, the spicule becomes straight, and 
 tapers down to an extreme tenuity, ultimately becoming 
 so tine that it is scarcely possible to trace it to its termi- 
 nation. 
 
 "Many spicules of the awl-shaped and simple cross 
 types, especially short spicules, are met with within the 
 siliceous coil to its very centre, and, in cases where the 
 coil has been brought home without the sponge, such 
 needles can be shaken out from the interstices of the 
 threads. The spicules of Hyalonema are marked in their 
 character, and all the forms are found in all specimens of 
 the sponge imbedding the characteristic bundle of enor- 
 mous spicules ; so that there can be no reasonable doubt 
 ot the specific identity of the sponge in all cases. 
 
 <k WiUiin the round apertures on the surfoce of the 
 
 D D 
 
402 THE MICROSCOPE. 
 
 sponge there is usually a brownish orange-coloured mem- 
 brane, which Schultze found presented the marked cha- 
 racters of a minute parasitic polyp, probably alcyonarian, 
 which inhabited the oscula and their passages during the 
 life of the sponge. 
 
 "The glassy wisp of Hyalonema is certainly very re- 
 markable, but it is not entirely without analogy, Hyalo- 
 nema seems to represent the extreme form of a little group 
 of sponges, including, with probably a few other forms, 
 Euplertella (A Icyonellum) speciosa (Quoi and Gaimard), and 
 E. cucumer (Owen). The last-named is an oval sponge 
 with siliceous spicules, in form and character somewhat 
 like the spicules of Hyalonema. From one end of the 
 sponge a tuft of long siliceous threads, resembling in 
 structure those of the Japan sponge, twine round a stone 
 or other foreign body. Dr. Bowerbank isolated one of 
 the spines of Euplectella, three inches long." See Intel- 
 lectual Observer, March, 1867. 
 
 INFUSORIA. 
 
 The term Infusoria is applied to a certain class of 
 animals because they were first discovered in water where 
 vegetable matter was decomposing, the infusion was con- 
 sidered necessary for their production. Now, however, it 
 is an established fact, that they are in a healthier state of 
 existence when taken from pure streams and clear ponds 
 than from putrid and stagnant waters. A little bundle of 
 hay, or sage leaves, left for about ten days in a mug con- 
 taining some pure rain-water, caught before entering a 
 butt, produces the common wheel-animalcules, which are 
 found adhering to the sides of the mug near to the surface 
 of the water. The only use of the vegetable matter seems 
 to be to facilitate in some way the development of the ova 
 of animalcules which find their way into the water. It 
 was at one time thought an indispensable condition that 
 air be admitted to the infusion : but even this element is 
 not absolutely needed in the case of infusorial life ; and 
 the appearance of living organisms at all under the circum- 
 stances, has been regarded as important evidence in favour 
 of the doctrine of spontaneous generation. 
 
INFUSORIA. 403 
 
 The astronomer turns his telescope from the earth, and 
 ranges over the vast vault of heaven, to detect and delineate 
 the beautiful objects of his pursuit. The naturalist turns 
 his microscope to the earth, and in a drop of water finds a 
 wondrous world of animated beings, more numerous than 
 the stars of the milky way ; and these he classifies into 
 genera and families, and catalogues in his history of the 
 invisible world. 
 
 The Infusoria are a mighty family, as they frequently, 
 in countless myriads, cover leagues of the ocean, and give 
 to it a beautiful tinge from their vivid hue. They are 
 discovered in all climes, have been found alive sixty feet 
 below the surface of the earth, and in the mud brought up 
 from a depth of sixteen hundred feet of the ocean. They 
 exist at the poles and the equator, in the fluids of the 
 animal body, and plants, and in the most powerful acids. 
 A brotherhood will be found in a little transparent shell, 
 to which a drop of water is a world ; and within these are 
 sometimes other communities, performing all the functions 
 granted them by their Creator, and eagerly pursuing the 
 chase of others less than themselves. 
 
 The forms of the Infusoria are endless ; some changing 
 their shape at pleasure, others resembling globes, eels, 
 trumpets, serpents, boats, stars, pitchers, wheels, flasks, 
 cups, funnels, fans, and fruits. 
 
 The multiplication of the species is effected in some by 
 spontaneous division or fissuration, in others by gemma- 
 tion or budding, as well as a true sexual process. The 
 first step in the process by which infusorial animals are 
 eliminated, is the formation of globular corpuscles or cells, 
 which, by their aggregation in some cases, and individual 
 evolutions in others, give birth to organisms which sub- 
 sequently appear. 
 
 The Infusoria have no night in their existence ; they 
 issue into life in a state of activity, and continue the 
 duration of their being in one ceaseless state of motion ; 
 their term is short, they have no time for rest, and there- 
 fore have but one day, which ends only with their death 
 and decomposition. Nevertheless, they appear to love 
 that which promotes life, the light of heaven ; but 
 others, born in the bowels of the earth, and who never 
 
404 THE MICROSCOPE. 
 
 partook of the blessing, like the ignorant among man- 
 kind, have their own contracted round of unenlightened 
 joys, perform their mechanical duties, and expire hidden 
 an i unknown. 
 
 On examining the structure of infusorial animalcules, 
 some are found to have a soft yielding skin, so elastic aa 
 to stretch when food or other circumstances render it 
 necessary, returning again to its previous condition as the 
 cause of distension ceases ; these are designated iltoricated, 
 which signifies shell-less. Others are termed loricated, 
 from being covered with a shell, which is beautifully 
 transparent, and flexible like horn. When the delicate 
 and soft substance in which the functions of life perform 
 their allotted duties perishes, the coat that protected it 
 from injury during its hours of existence remains as a 
 token of the past labours of nature ; this covering con- 
 sists mostly of siliceous material or of lime united with 
 oxide of iron, destructible in some instances either by 
 chemical agents or by fire. 
 
 Some of these minute beings have apportioned to them 
 setce, or bristles ; these stiff hairs, attached to the surface 
 of their bodies, do not rotate, but are movable, and appear 
 to be a means for the support of their bodies, as aids in 
 climbing over obstacles that present themselves, or as 
 feelers. Others are possessed of unci, or hooks, projecting 
 from the under part of the body, which are capable of 
 motion ; and by their means the animalcule can attach 
 itself to anything that lies in its way. Some, again, 
 have styles, which are a kind of thick bristle, jointed 
 at the base, possessing a movement, but not rotary ; they 
 are in the shape of a cone, large at their base, and delicate at 
 their summit. Many, also,- can extend and withdraw their 
 bodies at pleasure, in a similar manner to the snail or 
 leech. 
 
 One of the most interesting and important organs pos- 
 sessed by infusorial animalcules is scientifically known by 
 the term cilium, which is the Latin word for eyelash, the 
 plural being cilia. Its appearance is that of a minute 
 delicate hair. 
 
 The cilium is not only useful in the act of progression, 
 but also as an assistance in procuring food ; the two duties 
 
INFUSORIA CILIA. 405 
 
 being performed at the same time, the motion of the 
 organs that propels it forward causing a current to set 
 towards the mouth, which carries with it the prey on 
 which the animal feeds. From the cilia being found in 
 the ^ills of the young tadpole, the oyster, and mussel, it 
 would appear that they are serviceable as organs of respi- 
 ration, by imbibing oxygen, and emitting the carbonic acid 
 generated in the blood during its circulation through the 
 body; they are also believed to be the medium of taste 
 and touch. It is not only at the mouth, but over the 
 whole body that cilia are discovered ; and it is now satis- 
 factorily shown that cilia exist also in the internal organs 
 of man and other vertebrated animals; and are agents 
 by which many of the most important functions of the 
 animal economy are performed. They vary in size from 
 the 1000th to the 10,000th of an inch in length. These 
 minute organs would often be invisible, were it not from 
 the water being coloured when placed under a microscope ; 
 then the little currents made by the action of the cilia are 
 easily perceived; and when the water is evaporated, the 
 delicate tracing of their formation may be observed on the 
 glass. They are differently placed, and vary in quantity 
 in the numerous species of Infusoria. In some they are 
 in rows the whole length of the body, in others on the 
 base ; many have them over the whole of the body ; some- 
 times they fringe the mouth, form bands around projec- 
 tions on the body ; and many have but two projecting 
 from the mouth, as long as the body of the creature. 
 Ehrenberg says they are fixed at their base by the bulb 
 moving in a socket, in a similar manner to a man's out- 
 stretched arm; and by their moving round in a circle, 
 they form a cone, of which the apex is the bulb. Poison, 
 galvanism applied to the animal, even death, will not im- 
 mediately stop the motion of the cilia ; they continue 
 moving some hours afterwards, even longer than nervous 
 or muscular action can be sustained, until the fluids dry 
 up, and they stiffen. 
 
 Very little is known of the muscular attachment of cilia 
 in Infusoria ; but the motive power must be derived from 
 muscular structure in all. Now in the wheel-animalcules 
 the cilia are in circular rows ; and each revolves around 
 
406 THE MICROSCOPE. 
 
 its bulb, giving a singular appearance, seeming to move 
 together like a wheel upon its axle, whence their name 
 Rotifer ; in a few of these muscles can be traced. The 
 cilia must not be mistaken by the young microscopist for 
 the stiff hairs and bristles found on some, and serving, as 
 before stated, for the purpose of locomotion in crawling or 
 climbing. 
 
 If the roof of the mouth of a living frog be scraped 
 with the end of a scalpel, and the detached mucous mem- 
 brane placed on a glass slide, and examined with a power 
 of 300 diameters, the ciliated epithelium-cells will be well 
 seen. When a number of these are collected together, the 
 movement is effected with apparent regularity; but in 
 detached scales it is often so violent, that the scale itself is 
 whirled about in a similar manner to an animalcule pro- 
 vided with a locomotive apparatus of the same description, 
 and has frequently been mistaken for such. The animals 
 commonly employed for the examination of the cilia are 
 the oyster and the mussel; but the latter are generally 
 preferred. 
 
 To exhibit the movement to the best advantage, the 
 following method must be adopted : open carefully 
 the shells of one of those molluscs, spilling as little as 
 possible of the contained fluid; then with a pair of fine 
 scissors remove a portion of one of the gills (branchiae) ; 
 lay this on a slide, or the tablet of an animalcule cage, and 
 add to it a drop or two of the fluid from the shell ; by 
 means of the needle-points separate the filaments one from 
 the other, cover it lightly with a thin piece of glass, and 
 it is ready for examination. The cilia may then be seen 
 in several rows beating and lashing the water, and pro- 
 ducing an infinity of currents in it. If fresh water instead 
 of that from the shell be added, the movement will speedily 
 stop ; hence the necessity of the caution of preserving the 
 liquid contained in the shell. To observe the action of any 
 one of the cilia, and its form and structure, some hours 
 should be allowed to elapse after the preparation of the 
 filaments as above given, their movements then will have 
 become sluggish. If a power of 400 diameters be used, 
 and that part of the cilia attached to the epithelium scale 
 narefully watched, each one will be found to revolve a 
 
INFUSORIA. 407 
 
 quarter of a circle, whereby a *' feathering movement M is 
 effected, and a current in one direction constantly pro- 
 duced. In the higher animals, the action of the cilia can 
 oaly be observed a very short time after death. In a polypus 
 of the nose, when situated at the upper and back part of 
 the Schueiderian membrane, the cilia may be beautifully 
 seen in rapid action some few hours after its removal ; but 
 hi the respiratory and other tracts, where ciliated epi- 
 thelium is found, it would be almost impossible ever to 
 see it in action, unless the body were opened immediately 
 after death. In some animals it may be seen in the in- 
 terior of the kidney, as first made known by Professor 
 Bowman in the expanding extremity of the small tube 
 surrounding the network of blood-vessels forming the so- 
 called Malpighian body. In order to exhibit the ciliary 
 action, the kidney should have a very thin slice cut from 
 it; and this is to be moistened with the serum of the 
 blood of the same animal. The vascular and secreting 
 portions of the organ may then be seen with a power of 
 250 diameters, and also the cilia in the expanded extremity 
 of each tube, as it passes over to surround the vessels; the 
 epithelium of the tubes themselves is of the spheroidal or 
 glandular character. 
 
 The infusorial and invisible atoms of life have various 
 periods allotted to them for the enjoyments of existence ; 
 some accomplish their destiny in a few hours, others in a 
 few weeks. The watchful devotee in this branch of science 
 has traced an animalcule through a course of existence 
 extending to the old age of twenty-three days. The vital 
 spark flies instantaneously in general ; but in those of a 
 higher organisation there is a spasmodic convulsion, as if the 
 delicate and intricate machinery rendered life so exquisite, 
 that the parting with the " heavenly flame " \vas reluctant 
 and painful. The most surprising circumstance attendant 
 on the nature of some of the Infusoria is that of apparent 
 death. When the water or mud in which they have sported 
 in the fulness of buoyant health becomes dried up, they lie 
 an inanimate speck of matter; but after months, nay, years, 
 a drop of water being applied, their bodies will be resusci- 
 tated, and in a short time their frames become active with 
 life. Leeuweuhoek kept some in a hard and dry condition. 
 
408 THE MICROSCOPE. 
 
 and restored them to life after a sleep of more than 
 twenty-one months. Professor Owen saw an animalcule 
 that had been entombed in a grave of dry sand four years 
 reborn to all the activity of life. Spallanzani tried the 
 experiment of alternate life and death, and accomplished 
 it in some instances on the same object fifteen times , after 
 which nature was exhausted, and refused further aid in 
 this miraculous care of those minute objects of her won- 
 derful works. 
 
 Naturalists consider the phosphoric light of the marine 
 animalcule to be the effect of vital action. The sparks 
 are intermittent like the fire-fly ; they measure from the 
 12,000th to the 100th of an inch in size. Captain Scoresby 
 found that the broad expanse of waters at Greenland was 
 nearly all discoloured by animalcules, and computed that 
 of some species one hundred and fifty millions would find 
 ample room in a tumbler of water. The phosphorescence 
 of the sea is eloquently portrayed by Darwin, in his 
 Voyage of the Beagle. Mr. Gosse thus describes the 
 luminous appearances presented by a closer inspection of 
 these minute animalcules : " Some weeks afterwards I had 
 an opportunity of becoming acquainted with the minute 
 animals, to which a great portion of the luminousness of 
 the sea is attributed. One of my large glass vases of sea- 
 water I had observed to become suddenly at night, when 
 tapped with the finger, studded with minute but brilliant 
 sparks at various points on the surface of the water. I set 
 the jar in the window, and was not long in discovering, 
 without the aid of a lens, a goodly number of the tiny 
 jelly-like globules of Noctiluca miliaris swimming about 
 in various directions. They swam with an even gliding 
 motion, much resembling that of the Volvox globator of 
 our fresh-water pools. They congregated in little groups, 
 and a shake of the vessel sent them darting down from 
 the surface. It was not easy to keep them in view when 
 seen, owing rather to their extreme delicacy and colourless 
 transparency than to their minuteness. They were, in 
 fact, distinctly appreciable by the naked eye, measuring 
 from l-50th to l-30th of an inch in diameter." Nocti- 
 luca miliaris belongs to the highest class of the Protozoa, 
 and with a power of about 200 diameters they are seen 
 
INFUSORIA. 409 
 
 of various forms and stages of growth, represented in 
 fig. 217. 1 
 
 Ehrenberg included in his family of Infusoria, Rhizop- 
 oda, Unicellular, and other Algae, embryonic forms, and 
 Rotifers. Most naturalists, however, now admit that the 
 
 Fig. 217. Noctiluca miliaris. 
 
 organization of the Rotiferse is of a far higher nature than 
 had been suspected by Ehrenberg ; and some assert that 
 their proper place in the classification of animals is the 
 annulose sub-kingdom ; the true nature of many of the In- 
 fusoria is still a disputed question. In outward form they 
 may be said to vary almost indefinitely ; but anatomically 
 their bodies should be regarded as consisting of three dis- 
 tinct structures. The cuticle or integument (" pellicula " of 
 Carter), on which are borne the cilia and other locomotive 
 apparatus ; the cortical layer or parenchyma of the body 
 (" diaphane " of Carter) ; and the chyme mass, occupying 
 the abdominal cavity, or interior of the body (sarcode or 
 " abdominal mucus " of Carter), within which the par- 
 ticles of food rotate. The term "ventral" is usually ap- 
 plied to that side of the body on which the mouth is 
 placed. 
 
 In the well-known Paramcecium we have the true and 
 most widely distributed type of the Infusoria. The 
 general structural character of this minute animal is 
 common to the species; indeed, its structural features may 
 be accepted as a fair definition of the whole group. The 
 Paramcecium is surrounded on its external covering by 
 cilia, which are constantly in action, and enable it to move 
 about in its watery element in a most remarkably active 
 manner. At one point the body appears to be slightly 
 
 (1) See Gosse's Naturalist's Rambles: Huxley, Micro. Journal, 1855 
 
410 THE MICROSCOPE. 
 
 constricted, and here is a slit seen which opens into a little 
 funnel-shaped cavity, leading to the gullet and stomach. 
 The outer or cortical layer is composed of a denser ma- 
 terial, which indicates a differentiation into cellular layers, 
 whild the internal substance is evidently composed oi 
 sarcode which exhibits, at two points in particular, the 
 power of contracting and dilating : a process available both 
 for the expulsion of digested food, and for aeration of the 
 circulatory system. The whole systemic arrangement 
 should be regarded as the very simplest form of respiratory 
 and secretory mechanism. The several circular trans- 
 parent bodies seen in the interior of these animals led 
 Ehrenberg to denominate the group " Polygastrica " (many 
 stomached). The remarkable powers of multiplication by 
 fission and germination, as well as by a true sexual process, 
 which these creatures exhibit, have attracted the attention 
 of all observers; within the last few years, Miiller, 
 Balbiani, Stein, and others, have shown that the sexual 
 organs of such animals as Paramcecium are those bodies 
 which have hitherto been simply regarded as the 
 " nucleus," and " nucleolus ; " and ultimately it was seen 
 that the Infusoria have a life history as wonderful as that 
 of the higher classes of animals. Although Ehrenberg 
 was the first to call attention to the importance of the 
 " nucleus " in the reproductive process, it is to the observa- 
 tions of Balbiani that we are indebted for an explanation of 
 its importance in the generative function : his investiga- 
 tions also derive additional interest from the very complete 
 manner in which they have been carried out. As an in- 
 stance, he states that in his examinations of Paramcecium 
 aurelice, he could not look upon them as conclusive until 
 he had succeeded in extracting uninjured some of the egcrs 
 from the parent body, and had subjected them to the 
 action of the surrounding water, when he saw each egg 
 resolve itself into two portions, the smaller being enclosed 
 within the larger ; then by employing re-agents, acetic acid 
 and iodine, he produced the changes more rapidly ; and in 
 this way again and again obtained abundant proofs of the 
 truth of each observation. So much then for Dr. Bal- 
 biani's researches on the phenomena of reproduction 
 among the Infusoria, which have added much valuable 
 
INFUSORIA. 
 
 411 
 
 information to our former meagre knowledge of these in- 
 teresting forms of organic life. 
 
 Some Infusoria undergo a process of encystation before 
 reproduction by fissure ; that is, they become coated with 
 a secretion of gelatinous matter, which gradually hardens 
 so as to enclose the body in a "cyst." According to 
 Stein, the process of encystation is sometimes followed by 
 a remarkable succession of phenomena, such as have been 
 observed to occur in the case of Vorticella microstoma. 
 An old Vorticella loses or retracts its cilia, becomes en- 
 cysted, and finally drops off its stalk. The cyst may either 
 burst and discharge its contents, or become wholly 
 changed into an Acineta-form body. The latter may sub- 
 sequently develop a foot-stalk, assume the appearance of 
 a Podophyra, or even that of the Acimta tuberosa, 
 Plate III. No. 68. In either case, the band-like nucleus 
 becomes transformed into a peculiar ovate body, somewhat, 
 like No?. 71 or 73, the narrow end of which is provided 
 with a circlet of vibratile cilia, and a mouth leading into 
 an internal cavity, with a contractile vesicle in its interior, 
 Relations, somewhat similar 
 to those which connect 
 Vorticella and Acineta, have 
 been stated to exist between 
 other families, as Aspidisca 
 or Trichoda, and Oxytricha, 
 Plate III. No. 71. 
 
 MONADIDJE. Monads. 
 These are amongst the 
 smallest atoms of matter 
 possessing the mysterious 
 principle of life, discernible 
 by the highest magnifying 
 power of the microscope. 
 Minute, however, as they 
 are, no one can say that they 
 do not derive their suste- 
 nance by preying on animals j Fi&rio spirilla, _, _-, , 
 
 1 +-U r, thPTv^ol VPS toto ; near which an enlarged view ol 
 
 even less than themselves, ^^ shown, 
 as larger ones of the same 
 species do upon them. 
 
412 THE MICEOSCOrS. 
 
 Monads vary in their colours, some are red, green, or 
 yellow, others nearly colourless. In shape they are round 
 or oval (5 and 6, fig. 226), and possessed of immense 
 activity, having one or more cilia devoted to the purpose 
 of locomotion. Monads have been claimed by the bota- 
 nist, and accordingly placed among the Volvocinece, confer- 
 void Algce. Ehrenberg described them as Infusoria. He 
 says : " All true Infusoria even the smallest monads, are 
 organised animal bodies." 
 
 VIBRIO. Vibriones. In this family Ehrenberg wrongly 
 includes the well-known eels in paste and vinegar. 
 
 Vibrio spirilla, Trembling animalcules, when motionless 
 are seen as very minute bodies ; but when exerting the 
 powers of locomotion they take a spiral form, like the 
 threads of a fine screw, and by undulations wind them- 
 selves through the water with rapidity. Each apparent 
 hair is a collection of animals bound together by a pliant 
 band ; thus, as they are individually so small, little is 
 known of their structure. Still they form very interesting 
 objects to view ; their very minuteness claiming attention, 
 while their activity and motions excite surprise. The 
 species are numerous, as represented in fig. 218. They are 
 almost invariably the first organisms found in decaying 
 acetous and putrefying organic matters. When treated 
 with iodine and then sulphuric acid, their jointed structure 
 is rendered visible to the higest powers of the microscope, 
 but not otherwise. 
 
 ASTASI.EA. Astasia, signifying without a station, in con- 
 tradistinction to those living in groups, is the term given 
 to a kind of crimson-coloured animalcule, the 350th of an 
 inch in length, that exist in enormous numbers, and give 
 the waters in which they live the appearance of their 
 bodies. Ehrenberg describes several varieties of them. 
 
 The family Euglenas of Dujardin in many particulars 
 corresponds with that of the Astasice of Ehrenberg ; while 
 Mr. Carter would refer Euglence to the vegetable and 
 Astasice to the animal kingdom. "The power, however, 
 to vary the figure can be no adequate character, for this is 
 partaken by the gonidia of various algae; the tapering, 
 hairlike prolongation, the existence of one, two, or more 
 ciliary filaments, and the red speck, are also the well- 
 
INFUSORIA. 413 
 
 known characteristics of some zoospores." The individuals 
 are all free, and furnished with a hairlike appendage ; ova 
 are perceptible in Astasia hcematodes, and probably exist in 
 other species. From their varying colour, their apparent 
 changes of form, and the rapidity of their motions, they 
 are most interesting objects under the microscope. The 
 immense number in which these Infusoria are sometimes 
 developed in a few days, and the blood-red colour they 
 impart, have frequently been the cause of alarm and 
 anxiety to persons residing in the vicinity of ponds which 
 have become coloured by their swarming. Ehrenberg de- 
 scribes a species of Euglena, E. sanguined, and he con- 
 jectures that the miracle in Egypt, recorded by Moses, of 
 turning the water into blood, might have been effected by 
 the agency of these creatures. Very lately, Mr. Shep- 
 pard l met with another specimen, probably belonging 
 to this family, adhering to the submerged stones in a 
 clear spring, between Ashford and Maidstone. His 
 specimens were taken home in a piece of glazed paper, 
 and upon opening them he found the paper " stained 
 with hues of red, blue, and purple;" and the whole "re- 
 sembling clots of red jelly, or recently coagulated blood." 
 Upon placing a small quantity on a glass side for viewing 
 under the Microscope, " the colour appeared to be opaque- 
 red, looking like a small quantity of vermilion mixed with 
 the water ; but when held up to the light the red disap- 
 peared, and a pale transparent blue took its place." 
 
 Believing this colour to depend upon the presence of 
 albumen mixed with the animal organisms, Mr. Sheppard 
 placed a small quantity of the jelly-like substance in con- 
 tact with some white of egg diluted with water ; and " soon 
 the whole became converted into magenta dye," the 
 solution exhibiting the same colouring properties, namely, 
 that of reflecting from its surface all the red and yellow 
 rays, and transmitting the blue and violet." Mr. Brown- 
 ing, upon submitting specimens to the micro-spectroscope, 
 found that it gave a very marked baud in the red-ray. The 
 whole spectrum is, indeed, very remarkable, and, writes 
 
 0) "An example of the production of a coloured fluid possessing remarkable 
 qualities by the action of monads (or some other oiicroscopic organism) upon 
 organized substances." By J. B. Sheppaid, M.R.C.S. Trans. Microt.Soc. July, 
 JSC7, p. 64. 
 
414 THE MICROSCOPE. 
 
 Mr. Sorby, "it is the only blue solution in class C (of 
 which blood is the type) that gives this particular spec- 
 trum." The fluid emits a most pungent and disagreeable 
 odour when the bottle in which it is kept is uncorked. 
 
 The common form of the Euglence is represented in 
 Plate III. No. 67, a contracted, b elongated. Oxytricha 
 are larger and the body more elongated ; their movements 
 are more impulsive, alternately creeping, running, and 
 climbing. In all the species digestive vacuoles are evi- 
 dent ; and they multiply by self-division, as well as ova. 
 Ehrenberg counted ten cilia anteriorly, and four or five 
 setae posteriorly. The species is found both in fresh and 
 brackish water. Plate III. No. 70, represents a side view 
 of 0. gibba, No. 71, 0. Pelliondla. In. the genus Glau- 
 coma, Nos. 73 and 74, Ehrenberg saw "indications of an 
 alimentary canal." Dujardin places Glaucoma among 
 Paramsecia ; the body is oval and covered with cilia ; 
 mouth large, with vibratory valves ; increase takes place 
 by self-division. A re- examination of all the enumerated 
 species of Infusoria is quite necessary before we can come 
 to any safe conclusion as to their true affinities, especially 
 as many appear to be only larval forms of life. 
 
 " The question of how far individuals belonging to the 
 same species may vary is one more intimately connected 
 with that department of Zoology which treats of the dis- 
 tribution of animals than their development. For it can 
 be readily shown that animals are capable of becoming 
 modified to an indefinite extent by the physical conditions 
 under which they are placed, and, indeed, that one species 
 may be, so to speak, made to pass into that of another ; so 
 that many of the apparently dissimilar animal forms found 
 on the earth may be more correctly viewed as varietiss of 
 the same species, the differences between them being due 
 to the external agencies to which each has respectively 
 been subjected." 
 
 The remarkable manner in which the Infusoria make 
 their appearance in fluids, and the seeming inexplicable 
 phases in their existence, led some early observers to start 
 a " spontaneous generation " theory of life ; but the re- 
 searches of M. Pasteur and others have completely exploded 
 this view of the formation of living organisms. The order 
 
INFUSORIA. 415 
 
 in which these minute creatures appear in vegetable in- 
 fusions has been made the subject of careful inquiry. Mr. 
 Samuelson, whose researches on this point were carried on 
 in conjunction with Dr. Balbiani of Paris, and confirmed 
 by him, tells us that when a carefully prepared infusion of 
 vegetable matter in distilled water is exposed to the air, 
 the Protozoa which first appear in it are Amcebce : these in 
 a few days disappear, and are succeded by ciliated infusoria, 
 such as Kolpoda, Gydidium glaucoma, and sometimes Vor- 
 ticella, and these in their turn by what we have looked 
 upon as higher forms, Oxytrichum, JSuplotes, Kerona, &c. 
 Mr. Samuelson thinks that Monads are but the larval con- 
 dition of the ciliated infusoria, and he noticed the constant 
 occurrence of Monads belonging to the species Gircomonas 
 fusiformis, or acuminata of Dujardin, &c., in pure distilled 
 water after a certain exposure to the air, and this without 
 the previous admixture of vegetable matter of any kind in 
 the water. The same results were obtained upon shaking 
 rags, from various and distant parts of the world, over the 
 distilled water; in all cases in about three weeks he 
 invariably obtained forms of ciliated infusoria. " The fusi- 
 form body of the Circomonas bears a long whip-like cilium 
 at its anterior end, and a short seta at its caudal extremity : 
 this finally drops off, and when exposed to excessive heat 
 and light, the animal is transformed into an Amoeba" 
 
 Mr. Samuelson's results do not very materially differ 
 from our own, save in one or two particulars. The suc- 
 cession of generations do not take quite the same course, 
 and the animal and vegetable bodies generally appear 
 simultaneously, or so soon after each other that it is at 
 times difficult to decide the priority of appearance ; but 
 our experiments have been chiefly confined to collections 
 of rain and distilled water, witJiout the addition of vege- 
 table matter of any kind. We are, however, quite agreed 
 as to the very extensive distribution of these infusorial 
 germs, and their great tenacity of life. With regard to the 
 supposed purity of rain-water, at no time can it be taken 
 without the numerous matters floating in the air being 
 brought down with it ; and, consequently, witliin a few hours 
 after it is caught, Protococcus pluvialis, Amoeba, and Circo- 
 moncj may always be found in vast numbers. It is somewhat 
 
416 
 
 THE MICROSCOPE. 
 
 remarkable that the purest snow-water, caught in a 
 glass vessel, and allowed to remain well corked, will, in 
 the course of two or three weeks, be found to contain 
 Amoeba and Circomonas, but it rarely presents other forms 
 of animal life ; the vegetable matter then completes its 
 growth very slowly, gradually passes to Conferva?, and for a 
 time no other change is seen to take place ; so that it is 
 painfully apparent that the atmosphere in which we live and 
 move and have our being is something more than a mixture 
 of gases, as apparently determined by chemical analysis. 
 
 Fig. 219. 
 
 1, Achnanthidvum, coarotatum. 2, A. liweare. 3, Tryblionella gracillii. 4, 
 Amphitetras antediluviana. 5, 6, and 7, Orthosira spinosa. Front view, with 
 globular and oval forms. (Fossil Infusoria from Springfield, Barbadoes.) 
 
 Ehrenberg's " Poly gastric Infusoria" have indeed under- 
 gone a complete revision : some have been degraded to the 
 vegetable kingdom, as the Desmidiacece, Volvocinece, &c., 
 whilst others have been advanced a step higher in the 
 animal series ; none having received so much attention from 
 microscopists, or excited so much controversy, as the Desmi- 
 diacece and Diatomacece. The first of these we have already 
 disposed of in our remarks on the vegetable kingdom, 
 where we must be content to leave them for the present ; 
 
DIATOMACELE. 417 
 
 not so the DiatumcuecK, which offer many interesting stvuc- 
 tural characteristics of sufficient importance to warrant our 
 keeping them in the animal division. They are most 
 striking objects under the microscope, from the very pecu- 
 liar beauty and variety of their forms, and from their 
 bilateral symmetry, external markings, and indestructible 
 siliceous skeletons ; so that we believe they would be more 
 correctly placed in a median, or Molluscian sub-kingdom. 
 Appearing everywhere with the first-born of life, and 
 wherever matter is found in a condition fit for their deve- 
 1 >pment and nourishment, these marvellous indestructible 
 creatures have been preserved and brought down to us, in 
 forms unchanged, from the remotest periods of our globe's 
 history ; and supplying, as they do to the microscopist, 
 some of the most valuable test-objects, the Gyrosigma, 
 Grammatop/iora, Fragilaria, Ripidophora, Pleurosigma 
 angulatum, with many others, it cannot be a matter of 
 surprise that considerable attention should have been di- 
 rected to them, and an earnest inquiry instituted into their 
 nature and structure. 
 
 "Comparing," says Kiitzing, "the arguments which 
 seem to indicate the vegetable nature of Diatomacece with 
 those which favour their animal nature, we are of neces- 
 sity led to the latter opinion. If we suppose them to be 
 plants, we must admit every frustule, every Navicida to be 
 a cell. We must suppose this cell with walls penetrated 
 by silica, developed within another cell of a different 
 nature, at least in every case where there is a distinct 
 peduncle, or investing tube. In this siliceous wall we 
 must recognise a complication certainly unequalled in the 
 vegetable kingdom. It would still remain to be proved 
 that the eminently nitrogenous internal substance corre- 
 sponded with the generic substance, and that the oil 
 globules could take the place of starch. The multipli- 
 cation would be a simple cellular reduplication ; but it 
 would remain to be proved that it takes place, as in other 
 vegetable cells, either by the formation of two distinct 
 primitive utricles, or by the introttection or constriction of 
 the wall itself. Finally, there would still remain un 
 explained the external motions and the internal changes ; 
 and we must prove the accumulated observations on the 
 
 B ff 
 
418 
 
 THE MICROSCOPE. 
 
 exterior organs of motion to be false, by a cleare r line of 
 argument than has hitherto been adopted by those who 
 are opposed to this view. But again, admitting their 
 animal nature, much would remain to be investigated, 
 both in their organic structure and their vital functions ; 
 excepting this, so far as we know, we have only one diffi- 
 culty to overcome, that of the probably ternary non- 
 azotised composition of the external gelatinous substance 
 of the peduncles and investing tubes. But as the presence 
 of nitrogen is not a positive character of animal nature, 
 
 Fig. 220. 
 
 1, Cymbella Ehreribergii. 2, Side view of the same, slhowmg an arrangement of 
 the sarcode and pseudopodia. 3, Pleurosigmata lanceolatum. 4, Lateral view 
 of a portion of the same. 5, 6, and 7, Piunularia. 8, Diatoma vulgar e. 9, 
 Nitzschia varvula. 
 
 so the absence of it is not a proof of vegetable. And, in 
 order that the objection should really have some weight, 
 it would be well to demonstrate that this substance is 
 isomeric with starch. For then, supposing all the argu- 
 ments in favour of the animal nature of Diatomacece were 
 proved by new and more circumstantial observations, this 
 peculiarity, if it deserve the name of objection, might still 
 be regarded as an important discovery. We should then 
 have in the animal, as well as in the vegetable kingdom, a 
 ternary substance similar to that forming the bases of the 
 vegetable tissue." 
 
DIATOMACE^. 
 
 Diatomacefe, brittleworts, siliceous Bacillaria, are organ- 
 isms composed of two symmetrical plates or valves, narrow 
 or wand-like, navicular as a miniature boat or "little 
 ship ; " hence their name, Navicula. A rectangular or 
 prismatic figure is, however, the typical form of this 
 family, and the angles of junction of the valves a?e as a 
 rule, acute. Deeply notched frastules, such as we see in 
 the Desmids, Micrasterias denticulata, Docidium pristidce, 
 Plate II. Nos. 30 and 31, do not occur, and the produc- 
 tion of spines and tubercks is rare among the Diatoms. 
 Each individual Diatom is enclosed by a soft organic 
 matter (sarcode); the internal portion is yellowish or 
 orange-brown in colour. In the discoid forms two por- 
 tions are commonly distinguishable, viz. the disc and 
 margin or rim, and these present different markings, with 
 an occasional central prominence, called an umbo or boss. 
 Great variety of outline may prevail in a genus, so much 
 so, that no accurate definition can be safely 
 laid down : thus in the genera Navicula, 
 Pinnularia, the frustules are in one aspect 
 boat-shaped, and in another oblong with 
 truncated ends, prismatic. Mr. Brightwell 
 thus describes and explains the transitions 
 of form produced by a change in position 
 of the fruotules of the genus Triceratium. 1 
 " The normal view of the frustule may be 
 represented by a vertical section of a tri- 
 angular prism. If the frustule be placed 
 upon one of its flat sides, we look down 
 upon its ridge and obtain a front view of 
 its two other sloping sides. If it be placed 
 upon one of its ridges, we have a front 
 view of one of its flat sides, generally 
 broader than long, and of its smooth or 
 transparent suture or 
 brane. If the frustule be progressing 
 towards self- division, it is then often considerably longer 
 than broad, and when nearly matured for separation, pre- 
 sents the appearance of a double frustule." So with re- 
 
 ,. Pig. 221. GompTio- 
 
 Connecting mem- nena dvngatum. 
 and capitatum. 
 
 1) Journ. Micros. Soc. roL L p. 248. 
 2 
 
420 THE MICROSCOPE. 
 
 gard to the beautilul Surirella constricta, the side view is 
 io longer bacillar, bat the breadth of the valve is very 
 considerable, and when about to undergo subdivision it 
 becomes square^shaped. The distinctive character, how- 
 ever, of this genus, in addition to the presence of canaliculi, 
 is derived from the longitudinal line down the centre of 
 each valve, and the prolongation of the margins into 
 " alas." The sudden change in appearance presented t<? 
 the eye as the frustule is seen to roll over, is very remark- 
 able. As a rule, therefore, we must examine all specimens 
 in every aspect, to accomplish which very shallow cells 
 should be selected, say of l-100th of an inch deep, and 
 covered with glass l-250th of an inch thick. A good 
 penetrating objective must be used, and careful illumina- 
 tion obtained. The examination of living specimens 
 should be conducted during very bright weather, the 
 mirror directed towards a white cloud, or even sunlight : 
 with coloured glasses to protect the eyes from injury. 
 The Diatomacese are perhaps more widely distributed than 
 any other class of infusorial life ; they inhabit fresh, salt, 
 and brackish water ; many grow attached to other bodies 
 by a stalk (Plate II. No. 33), Licmophora and Achnanthes; 
 while others, as the Pleurosigma, No. 40, swim about 
 perfectly free in the water. 
 
 There are a considerable number of Diatomaceee which, 
 while in the young state, are enclosed in a muco-gelatinous 
 sheath ; while others are attached by a stipes or stalk to 
 Algae. Ehrenberg recognised a tribe of compound Dia- 
 toms, with a double lorica, and introduced them into his 
 great family of Bacillaria, under the name of Lacernata or 
 Navicula. Silex enters largely into the composition of 
 their valves, but, being in combination with organic sub- 
 stances, it does not depolarize light. In several genera 
 silex is very deficient, and the wall of the frustule of 
 great delicacy. Mr. Brightwellj speaking of the lorica or 
 siliceous covering of the Triceratium, states " that the 
 valves are resolvable into several distinct layers of silex, 
 dividing like thin divisions of talc, and frequently of such 
 exquisite delicacy as to be difficult of detection." Nageli 
 speaks of a mucilaginous pellicle on the inside of ths 
 organic layer as a sort of third tunic ; and, as Meneghini 
 
DIATOMACEJ5. 
 
 421 
 
 truly observes, " An organic membrane ought to exist, for 
 '.he silica could not become solid except by crystallizing or 
 iepositing itself on some pre-existing substance." The 
 surface of the frustules is generally very beautifully 
 sculptured, and the markings assume the appearance of 
 dots (puncta), stripes (striae), ribs (costae), pinnules 
 (pinnae), of furrows and fine lines ; longitudinal, trans- 
 verse, and radiating bands ; canals or canaliculi ; and of 
 cells or areolae ; whilst all present striking varieties and 
 modifications in their form, character, and degree of deve- 
 lopment. Again, the fine lines or striae of many frustules 
 are resolvable into rows of minute dots, such as occur in 
 rieurosigma. &c. 
 
 The nature of the markings on the Diatom valves is one 
 of considerable in- 
 terest, and has ex- 
 cited much atten- 
 tion, and attempts 
 have been made to 
 produce them arti- 
 ficially. On the ad- 
 dition of sulphuric 
 acid to a mixture of 
 powdered fluor spar 
 and sand, an imme- 
 diate evolution of 
 fluoride of silicon 
 takes place, as is 
 shown by the white 
 fumes. This white- 
 ness is due to the 
 presence of minute 
 particles of silex 
 arising out of the 
 decomposition of the 
 fluoride by the mois- 
 ture contained in the 
 atmosphere \ and il ' 
 a solid body be ex- 
 posed to these vapours, a portion of the silex will be 
 deposited on it, in the form of a fine white powder, con- 
 
 attenvatum. 2, PUurosigma an 
 gulatum, magnified 250 diameters. 3 . Pleura- 
 sigma Spencerii, magnified 350 diameters. 
 
422 THE MICROSCOPE. 
 
 sisting of thin walled vesicles filled with air. If some of 
 the deposit be crushed between two pieces of glass, and 
 examined with a power of about 300 diameters, a marking 
 will be perceived on the outer or convex surface of many of 
 these vesicles, similar to that of many Diatomacese, such 
 as Pleurosigma.) Coscinodiscus, &c. Rounded elevations, 
 more or less hexagonal at the base, and more or less 
 regularly arranged, cover the surface of the siliceous 
 pellicle, and not infrequently this kind of marking is so 
 regular as to give the fragments exactly the appearance of 
 portions of diatomaeeous valves. 
 
 This remarkable circumstance attracted the attention of 
 Professor Max Schultze, who devoted a great deal of time 
 to the investigation of the subject, and has recorded in a 
 voluminous paper 1 the results of his observations. He 
 says, " The appearances presented under the microscope by 
 the siliceous pellicles were such as to suggest that they 
 were due possibly to crystallisation. The minute eleva- 
 tions on the surface, when viewed on the side, often appear 
 sharply acuminate, so as readily to convey the impression 
 that they are formed by minute crystals of silex ; and this 
 impression is strengthened at first sight by their sharply 
 denned hexagonal basis, when viewed vertically. The 
 circumstance, again, that these elevations are sometimes 
 rounded at the summit and circular at the base, might be 
 attributed to the accidental interference of free hydrofluo- 
 silicic acid, &c. But experiments to eleminate the action 
 of this agent showed that it had nothing to do with the 
 variety of appearance in the elevations. 
 
 " Most of the species of the diatomacese are characterised 
 by the presence on their outer surface of certain differences 
 of relief, referable either to elevations or to depressions 
 disposed in rows. The opinions of microscopists with re- 
 spect to the nature of this marking are divided. Whilst 
 in the larger forms, and those distinguished by their coarser 
 dots, the appearance is manifestly due to the existence of 
 thinner spots in the valve, we can not so easily explain the 
 cause of the striation or punctation in Pleurosigma 
 angulatum and similar finely-marked forms. In these it 
 
 (1) " Verhandl. d. Natur Hist. Vereins der Preussisch. Rhbinland, tu West- 
 pfc.il." Jahr rx. p. 1. Micros. Jour. Science, vol. iii. p. 120. 
 
DIATOMACELfi. 423 
 
 often seeins as if the appearance were due to pyramidal 
 elevations, with hexagonal bases, standing in regular rows, 
 exactly like those observed in the siliceous vesicles above 
 mentioned. 
 
 " In any case, it seemed likely, since the marking just 
 noticed is essentially alike in many different species of 
 diatoms, that its ultimate causes were to be sought, less, 
 perhaps, in any organic formative process, than in the 
 deposition of silex under the same laws as those by which 
 its deposition in the other case is regulated. Were this ulti- 
 mate cause shown to be crystallisation the question would 
 be solved. But that the secretion of amorphous silex in 
 diatoms, as in these pellicles, is undeniable, on account of 
 their specific gravity being about 2*2, the specific gravity 
 of crystallised silex being 2 -6." 
 
 But further investigation rendered the correctness of 
 this assumption (that the markings are due to crystallisa- 
 tion) doubtful in the highest degree, and it soon became 
 quite certain that neither in the artificial siliceous pellicles 
 nor in the diatom valves are the peculiar forms essentially 
 due to a crystalline structure. 
 
 Mr. Charles Stodder, of Boston, says, " I have reasons 
 for thinking that neither party has the true explanation 
 of the structure. My opinion is that the exterior of the 
 shell is smooth, or nearly so, and that the borders of the 
 hexagons, or other shaped areola?, and costae of the Cos- 
 tate forms, are internal projections from the outer plate, 
 as on the under side of the leaf of the Victoria Regia, in- 
 tended to give strength to the cell with the smallest 
 quantity of material. This will explain the trace of the 
 hexagons seen on the inner plate of HeUopelta, as only 
 the projecting wall of the areola? would come in contact 
 with the inner plate. Dr. Griffiths reasoned that the 
 areolae were depressions, because they were the thinnest 
 parts of the shell ; the facts are correct, but the inference 
 may not be, as there is another explanation of the pheno- 
 mena." See directions for the illumination of test-objects, 
 page 174. 
 
 Movements of Diatoms. The researches of Professor 
 Max Schultze, of Bonn, published 1865, appear to throw 
 some light on the vexed question of the movements of the 
 
424 THE MICROSCOPE. 
 
 Diatomacece. This author is of opinion that a sarcode 
 substance envelopes the external surface of the diatom, 
 and its movement is due to this agent exclusively. He 
 prefers the P. angulatum, Plate II. JSo. 38, lor examination 
 to the larger P. balticum, because the transverse markings 
 on its frustule do not impede to so great an extent the 
 observation of what is going on within. When you have 
 a living specimen of P. angulatum under the microscope, 
 it always has its broad side turned to view, with one long 
 curved "raphe" uppermost, and the other in contact with 
 the glass on which it is placed ; at the central part is seen 
 the thickened " umbilicus," Plate 2, No. 40. Within the 
 siliceous frustule is the yellow colouring matter, or "endo- 
 chrome," which fills the cavity more or less completely, 
 and is arranged in two longitudinal masses, to the right 
 and lei't of the raphe. In the broader part of the IVus- 
 tule these bands of endochrome describe one or two com- 
 plicated windings. It is only possible in those specimens 
 in which the bands are narrow properly to trace their 
 foldings, and ascertain that only two exist, since an 
 examination of frustules richer in endochrome has led to 
 the impression that there are three or four of these bands. 
 " The next objects which strike the eye on examining 
 a living Pleurosigma are highly refractive oil-globules. 
 These are four in number ; one pair near either end of the 
 the Diatom. They are not, however, all in the same place, 
 one globule of each pair being nearer the observer than 
 the other ; their relative position is best seen when a view 
 of the narrow side of the frustule can be obtained, so that 
 one raphe is to the left and the other to the right. The 
 blue-black colour, which is assumed by these globules 
 after the Diatom has been treated with hyperosrnic acid, 
 demonstrates that they consist of oleaginous matter. The 
 middle of the cavity of the frustule is occupied by a 
 colourless finely granular mass, whose position in the body 
 is not so clearly seen in the flat view as in the side view. 
 Besides the central mass, the conical cavities at either end 
 of the siliceous shell are seen to be filled with a similar 
 granular substance, and two linear extensions from each of 
 the three masses are developed, closely underlying that 
 part of the shell which is beneath the raphse; so that 
 
DIATOMACKM. 425 
 
 in the side view they appear attached to the right and left 
 edges of the interior of the frustule. This colourless 
 granular substance carries in its centre, near the middle 
 part of the Diatom, an imperfectly developed nucleus 
 which it is not very easy to see, but may be easily de- 
 monstrated by the application of acid. The colourless 
 substance is what, in other Diatoms, Schultze shows to be 
 Protoplasm, or vegetable sarcode, and which contains 
 numerous small refractive particles. On adding a drop of 
 hyperosmic acid, these are coloured blue-black, and prove 
 to be iat. It is, however, exceedingly difficult to deter- 
 mine the exact limitations of the protoplasm, on ac- 
 count of the highly refractive character of the siliceous 
 shell, and the obstruction presented by the bands of 
 endochrome. 
 
 After a short distance, the protoplasm reappears, and 
 is contracted into a considerable mass within the conical 
 terminations of the frustule. Schultze observed in this 
 part of the protoplasm a rapid molecular movement such 
 as is known to occur in the Closterium, and further, a 
 current of the granules of the protoplasm along the raphe. 
 Pleurosigma angidatum " crawls" as do all Diatoms pos- 
 sessing a raphe, along this line of suture. To crawl along, 
 it must have a tixed support. He believes free swimming 
 movements are never to be observed in this or in any 
 other Diatom. Accordingly, Schultze invariably found 
 that the raphe is in contact with either the glass slip or 
 the glass cover, between which the Diatom is placed, or is 
 in apposition with some foreign body of considerable size. 
 Schultze repeated the experiments of Siebold, and ob- 
 served, as he and also Wenham had done long before, 
 that particles of foreign matter stick to the raphe as 
 though it were covered with some glutinous material, 
 and are carried slowly along by the action of a current. 
 This he observed in many Diatomacese, and found in- 
 variably that foreign particles adhered only to the raphe, 
 or what corresponded to it. " There is obviously," says 
 Schultze, " but one explanation ; it is clear that there must 
 be a band of protoplasm lying along the raphe, which 
 causes the particles of colouring matter to adhere, and 
 gives rise to a gliding movement For there is but one phe- 
 
426 THE MICROSCOPE. 
 
 nomenon which can be compared with the gliding motion 
 of foreign bodies on the Diatomacese, and that is, the 
 taking up and casting off of particles by the pseudopodia 
 of the rhizopoda, as observed, for instance, on placing a 
 living Gromia or Miliolina in still water along with 
 powdered carmine. The nature of the adhesion and of 
 the motion is in both cases the same in all respects. And 
 since, with Diatoms as unicellular organisms, protoplasm 
 forms the principal part of the cell body (in many cases 
 two distinctly moving protoplasms), everything suggests 
 that the external movements are referable to the move- 
 ments of this protoplasm." It is quite evident to those 
 who have studied the movements of the Diatoms that 
 they are surrounded by a sarcode structure far more deli- 
 cate in its character than that of the Amoeba. Six years 
 before Schultze's observations were published, the fact 
 appeared in a third edition of this work, page 307 ; therein 
 it is stated that "The act of progression rather favours 
 the notion of contractile tentacular filaments, pseudo- 
 podia, as the organs of locomotion and prehension. The 
 hyaline or sarcode covering is of so transparant a nature 
 that as yet no microscopic power has enabled us to assign 
 its precise boundary and attachments. 1 Some observers 
 would deny a membranaceous (hyaline) covering of any 
 kind to Diatoms, which we have certainly seen." Pro- 
 fessor Smith, of America, has satisfactorily traced a sar- 
 code covering in Pinnularia. The denning power, pene- 
 tration of the objective, and mode of illumination, is 
 everything in such investigations. 
 
 It was in 1841 Messrs. Harrison and Sollitt, of Hull, 
 discovered the beautiful longitudinal and transverse strice 
 (groovings) on the Pleurosigma hippocampus. A curved 
 graceful line runs done the shell, in the centre of which is 
 an expanded oval opening. Near to the central opening 
 
 (1) Referring to the strength and vigour of the movements of the Diato- 
 macese, Dr. Donkin (Quart. Jour. Mic. Sci. vol. VI. new series, p. 26), observed 
 a species Bacillaria cursoria, discovered by himself, push away "A. arenaria, 
 & species at least six times their own size ; " and Mr. Barkas states that he has 
 seen them " push away particles of foreign matter, and that with the greatest 
 apparent ease, at least one hundred times larger than all the frustules com- 
 bined ; and what is more remarkable still, is that they not only push the accu- 
 mulated particles away when they are in their direct line of motion, but, if 
 they merely touch them in passing, they drag them after them as though they 
 were literally hold by some magnetic attraction, or strong cement." 
 
DlATOMACEjE. 
 
 427 
 
 the dots elongate cross ways, presenting the appearance of 
 email short bands. The Pleurosigma angulatum (fig. 223), 
 was first discovered in the Huraber ; the lines upon its 
 surface resemble the most elegant tracery, which are 
 resolvable into raised minute dots. The markings are 
 seen to be longitudinal, transverse, and oblique. 
 
 In the vicinity of Hull many very interesting varieties 
 of Diatomacece have been found, the beauty of the varied 
 forms of which are such as to delight the microscopist ; 
 
 Fig. 223. 
 
 1, Pleurotigma angulatum. 2, Portion of the same, magnified 1200 diameters. 
 3, Portion of P. formosum, magnified 5500 diameters. 
 
 at the same time some of them are highly useful, as form- 
 ing that class of test objects which are best calculated above 
 all others for determining the excellence and powers of 
 object-glasses. It has been shown by Mr. Sollitt that 
 the markings on some of the shells are so fine as to range 
 between the 30,000th and 130,000th of an inch; the 
 Pleurosigma strigilis having the strongest markings, and 
 the Pleurosigma acus the finest. 
 
 As to the value of the Diatomacece as test-objects, it is 
 generally admitted, and since Mr. J. D. Sollitt first pro- 
 posed the use of their shells for this purpose, we append 
 his measurements of the lines : 
 
 Atnphipleura Pellucida, or Acus, 130,000 in the inch, cross lines. 
 
 Sigmoidea, 70,000 in the inch. 
 Navicula Rhomboides, 111,000 in the inch, cross line* 
 
428 THE MICROSCOPE. 
 
 Plaurosigma Fasciola, fine shell, 86,000 in the inch, cross lines. 
 ,, strong shell, 64,000 in the inch, cross linos. 
 
 Strigosum, 72,000 in the inch, diagonal lines. 
 
 Angulatum, 51,000 in the inch, diagonal lines. 
 Quadratuni, 50,000 in the inch, diagonal lines. 
 
 fcpencerii, 50,000 in the inch, cross lines. 
 
 Attenuatum, 42,000 in the inch, cross lines. 
 
 ,, Balticum, 40,000 in the inch, cross lines. 
 
 Formosum, 32,000 in the inch, diagonal lines. 
 
 Strigilis, 30,000 in the inch, cross lines. 
 
 Mr. Norman, of Hull, has favoured us with the follow- 
 ing : 
 
 HINTS FOR COLLECTING DIATOMACEJ3. 
 
 These minute forms are found in all waters, but the 
 most interesting species are those found in salt water, 
 especially shallow lagoons, salt water marshes, estuaries of 
 rivers, pools left by the tide, &c. 
 
 Their presence in any quantity is always shown by the 
 colour they impart to the aquatic plants and sea-weeds 
 they are found attached to, and it' found on the mud, 
 which is very frequently the case, they impart to it also a 
 yellowish brown colour approaching to black brown, if in 
 great numbers. This brownish pellicle, if carefully re- 
 moved with a spoon (without disturbing the mud) will be 
 found very pure. Capital gatherings of Diatomaceae 
 might be obtained by carefully scraping the brown coloured 
 layer from mooring posts, and piles of wharfs and jetties. 
 
 In clear running ditches the plants and stones have 
 often long streamers of yellowish brown slimy matter 
 attached to them, which is generally entirely Diato- 
 maceous. 
 
 When found in large quantities on the mud the layer 
 is often covered with bead-like bubbles of oxygen. This 
 often detaches them from the bottom and buoys them to 
 the surface, where they form a dense brown scum, which 
 is blown to leeward in large quantities, and presents the 
 general appearance of dark-coloured yeast. In this form 
 it may be collected in abundance, often quite free from 
 particles of sand and other impurities. Good and rare 
 species have been obtained from the stomachs of oysters, 
 scallops, and other shell-fish inhabiting deep water. The 
 sea-cucumbers (Holothuridae) found so frequently in 
 southern latitudes contain many species. These animals 
 
DIATOMACE.E. 429 
 
 might be simply dried and preserved just as found, and 
 the contents of the stomach afterwards obtained by 
 dissection. 
 
 Noctilucae, which are the cause of phosphorescence in 
 the sea, are Diatom feeders, and might be caught in large 
 quantities in a fine gauze towing-net, and preserved. The 
 Ascidians found attached to oyster shells and stones from 
 leep water have yielded excellent gatherings. The Salpse 
 often noticed in warm latitudes floating on the surface of 
 the sea, and assuming chain and other like forms, should 
 be bottled up for examination. These Salpee are well 
 known Diatom feeders* Deep-sea soundings ought to be 
 preserved, especially from great depths, and are often 
 exclusively Diatomaceous. Sea-weed from rocks ought to 
 be preserved, especially the smaller species, and if covered 
 with a brown furriness, so much the better. Very rare 
 species have been found in immense quantities in the 
 ARCTIC and ANTARCTIC regions, by melting the "pancakz 
 ice" often found d.scoloured by these minute beings. The 
 sea is often observed to be covered by brownish patches. 
 The discoloured water (or " spawn" as it is called) should 
 be collected, filtered through cotton wool, and the 
 brown residue preserved. When a fine impalpable dust 
 is observed to be falling at sea, it ought to be collected 
 from the folded sails and other places where it lodges. 
 This may yield DiatomaceiP., which from the method of 
 collecting would be highly interesting to examine. The 
 roots of the various species of Mangrove (RhLzaphora), 
 which form impenetrable barriers along the salt water 
 rivers and estuaries in the tropical parts of Africa, 
 Australia, the Eastern Archipelago, &c., are found fre- 
 quently covered with a brown mucous slime very rich in 
 Diatoniacese. When the Diatomacese are collected from 
 any of the above-mentioned sources, they may be at once 
 transferred to small bottles, or the deposit may be partially 
 dried and wrapped up in pieces of paper or tinfoil. 
 When placed in bottles, a few drops of spirits added will 
 keep them nice and sweet. In all cases it is essential to 
 keep the gatherings separate and distinct, and that the 
 locality whence obtained be written on each package. 
 
 The collector will probably find that, notwithstanding 
 
430 THE MICROSCOPE. 
 
 every care, his specimens are mixed with much foreign 
 matter, in the form of minute particles of mud or sand, 
 which impair their value, and interfere with observation, 
 especially with the higher powers of his instrument. 
 These substances the student may remove in various 
 ways : by repeated washings in pure water, and at the 
 same time, profiting by the various specific gravities of the 
 Diatoms and the intermixed substances, to secure their 
 separation ; but, more particularly, by availing himself of 
 the tendency which the Diatomacece generally have to 
 make their way towards the light. This affords an easy 
 mode of separating and procuring them in a tolerably clean 
 state ; all that is necessary being to place the gathering 
 which contains them in a shallow vessel, and leave them 
 undisturbed for a sufficient length of time in the sunlight, 
 and then carefully remove them from the surface of the 
 mud or water. The simplest method of preserving the 
 specimens, and the one most generally useful to the scien- 
 tific observer, is simply to dry them upon small portions of 
 talc, which can at any time be placed under the micro- 
 scope, and examined without further preparation; and 
 this mode possesses one great advantage, that is, that the 
 specimens can be submitted without further preparation to 
 a heat sufficient to remove all the cell-contents and softer 
 parts, leaving the siliceous epiderm in a transparent 
 state. 
 
 ON CLEANING DIATOMACEOUS DEPOSITS. "The fir^t 
 point to be ascertained is the nature of the material which 
 binds the mass together. In the generality of deposits, 
 this seems to be aluminous or earthy matter, often mixed 
 with some siliceous material which renders the action of 
 acids of little avail. When the bulk of the deposit is 
 clayey matter, the best plan is to place the lumps broken 
 quite small into a vessel and pour on a few ounces of hot 
 water, rendered thoroughly alkaline with common washing 
 soda. This plan frequently answers, causing the lumps to 
 swell, gradually separating into layers, and finally falling 
 asunder into a pulpy mass. The strong soda ley must 
 now be removed by repeated washing, and afterwards 
 boiling in a flask with pure nitric acid ; the whole must 
 afterwards be transferred to a large stoppered vessel and 
 
FOSSIL INFUSORIA. 431 
 
 violently shaken, in order to break up the minute frag- 
 ments of dirt, and set free the siliceous Diatoms. After 
 shaking, allow the vessel to stand for half an hour or 
 more according to the size and density of the valves : the 
 Diatoms having subdivided, the dirty water is drawn off 
 by a syphon, and fresh water added, and the shaking re- 
 peated. The whole secret depends upon getting rid of 
 the impurities by this violent shaking and washing ; when 
 quite free from all impurities the material may be trans- 
 ferred to a test tube, washed in distilled water, and finally 
 mounted." l 
 
 Fossil Infusoria. Startling and almost incredible as the 
 assertion may appear to some, it is none the less a fact, 
 established beyond all question by the aid of the micro- 
 scope, that some of our most gigantic mountain-ranges, 
 such as the mighty Andes, towering into space 25,250 feet 
 above the level of the sea, their base occupying so vast an 
 area of land ; as also our massive limestone rocks, the sand 
 that covers our boundless deserts, and the soil of many of 
 our wide-extended plains ; are principally composed of 
 portions of invisible animalcules. And, as Dr. Buckland 
 truly observes : " The remains of such minute animals 
 have added much more to the mass of materials which 
 compose the exterior crust of the globe than the bones of 
 elephants, hippopotami, and whales." 
 
 The stratum of slate, fourteen feet thick, found at Bilin, 
 in Austria, was the first that was discovered to consist almost 
 entirely of minute flinty shells. A cubic inch does not 
 weigh quite half an ounce ; and in this bulk it is estimated 
 there are not less than forty thousand millions of indi- 
 vidual organic remains ! This slate, as well as the Tripoli, 
 found in Africa, is ground to a powder, and sold for 
 polishing. The similarity of the formation of each is 
 proved by the microscope ; and their properties being the 
 same, in commerce they both pass under the name of 
 Tripoli : one merchant alone in Berlin disposes annually of 
 many hundred tons weight. The thickness of a single shell 
 is about the sixth of a human hair, and its weight the hun- 
 
 (1) Q. Norman, Esq. Micros. Journ. vol. iv. p. 238. For other methods of 
 cleaning and preparing Diatoms, see Smith's Synopsis of the British Diato- 
 macece; also Quar. Journ. Micros. Sciem.*, voL vii. p. 107, and vol. i. N. & 181, 
 p. 143. 
 
432 
 
 THE MICROSCOPE. 
 
 dred-and-eighty-seven-millionth part of a grain. The 
 well-known Turkey stone, so much used for the purpose of 
 sharpening razors and tools ; the Rotten-stone of com- 
 merce, a polishing material ; and the pavement of the 
 quadrangle of the Royal Exchange, are all composed of 
 infusorial remains. 
 
 Fig. 224. 
 
 1, Shell of ArachnohUsrus. 2, Acti>>ocyclus (Bermuda). 3. Cocc'neis (Algoa B.iyj. 
 4, Cuscinodiscus( Bermuda.) 5, tslhmia enervis. 6. Zygocerm, rhombus. 
 
 The bei'gh-mehl, mountain-meal, in Norway and Lapland, 
 has been found thirty feet in thickness ; in Saxony, twenty- 
 eight feet thick ; and it has also been discovered in Tus- 
 cany, Bohemia, Africa, Asia, the South Sea Islands, and 
 South America ; of this, almost the entire mass is com- 
 posed of flinty skeletons of Diatomacece. That in Tuscany 
 and Bohemia resembles pure magnesia, and consists 
 entirely of a shell called campilodiscus, about the 200th 
 of an inch in size. 
 
FOSSIL INFUSORIA. l33 
 
 Darwiu, writing of Patagonia, says : " Here along the 
 coast, for hundreds of miles, we have our great tertiary for- 
 mation, including many tertiary shells, all apparently 
 extinct. The most common shell is a massive gigantic 
 oyster, sometimes a foot or more in diameter. The beds 
 composing this formation are covered by others of a 
 peculiar soft white stone, including much gypsum, and 
 resembling chalk ; but really of the nature of pumice- 
 stone. It is highly remarkable, from its being composed, 
 to at least one-tenth of its bulk, of Infusoria; and Pro- 
 fessor Ehrenberg has already recognized in it thirty 
 marine forms. This bed, which extends for five hundred 
 miles along the coast, and probably runs to a considerably 
 greater distance, is more than eight hundred feet in thick- 
 ness at Port St. Julian.'* Ehrenberg discovered in the 
 rock of the volcanic island of Ascension many siliceous 
 shells of fresh- water Infusoria; and the same indefatigable 
 investigator found that the immense oceans of sandy 
 deserts in Africa were in great part composed of the shells 
 of animalcules. The mighty Deltas, and other deposits of 
 rivers, are also found to be filled with the remains of this 
 vast family of minute organization. At Richmond in 
 Virginia, United States, there is a flinty marl many miles 
 in extent, and from twelve to twenty-five feet in thickness, 
 almost wholly composed of the shells of marine animal- 
 cules ; for in the slightest particles of it they are discover' 
 able. On these myriads of skeletons are built the towns 
 of Richmond and Petersburg. - The species in these earths 
 are chiefly Naviculce; but the most attractive, from the 
 beauty of its form, is the Coscinodiscus, or sieve like disc, 
 found alike near Cuxhaven, at the mouth of the Elbe, in 
 the Baltic, near Wismar, in the guano, and the stomachs 
 of our oysters, scallops, and other shell-fish. Another 
 large deposit is found at Andover, Connecticut ; and 
 Ehreuberg states "that similar beds occur by the river 
 Amazon, and in great extent from Virginia to Labrador." 
 The chalk and flints of our sea- coasts are found to be 
 principally shells and animal remains. Ehrenberg com- 
 putes, that in a cubic inch of chalk there are the remains 
 of a million distinct organic beings. The Paris basin, one 
 hundred and eighty miles long, and averaging ninety in 
 F * 
 
434 THE MICROSCOPE. 
 
 breadth, abounds in Infusoria and other siliceous remains, 
 Ehrenberg, on examining the immense deposit of mud 
 at the harbour of Wismar, Mecklenburg-Schwerin, found 
 one-tenth to consist of the shells of Infusoria ; giving a 
 mass of animal remains amounting to 22,885 cubic feet 
 in bulk, and weighing forty tons, as the quantity annually 
 deposited there. How vast, how utterly incomprehen- 
 sible, then, must be the number of once living beings, 
 whose remains have in the lapse of time accumulated ! 
 In the frigid regions of the North Pole no less than sixty- 
 eight species of the fossil Infusoria have been found. 
 The guano of the island of Ichaboe abounds with fossil 
 Infusoria, which must have first entered the stomachs of 
 fish, then those of the sea- fowl, and became ultimately 
 deposited on the islands, incrustating its surface ; whence 
 they are transported, after the lapse of centuries, to aid 
 the fruition of the earth, for the benefit of the present race 
 of civilized man. The hazy and injurious atmosphere met 
 with off Cape Verd Islands, and hundreds of miles distant 
 from the coast of Africa, is caused entirely by a brown 
 dust, which upon being examined microscopically by 
 Ehrenberg, was found chiefly to consist of the flinty shells 
 of Infusoria, and the siliceous tissue of plants : of these 
 Infusoria, sixty- four proved to belong to fresh- watei 
 species, and two were denizens of the ocean. From the 
 direction of the periodical winds, this dust is reasonably 
 supposed to be the finer portions of the sands of the desert 
 of the interior of Africa. 
 
 The deposit of the beneficent Nile, that fertilises so 
 large a tract of country, has undergone the keen scientific 
 scrutiny of Ehrenberg ; and he found the nutritive prin- 
 ciple to consist of fossil Infusoria. So profusely were they 
 diffused, that he could not detect the smallest particle of 
 the deposit that did not contain the remains of one or 
 more of the extensive but diminutive family that once 
 revelled in all the enjoyment of animal existence. It is 
 very remarkable that at Holderness, in digging out a sub- 
 merged forest on the coast, numbers of fresh-water fossil 
 DiatomacecB have been discovered, although the sea flows 
 over the place at every tide. 
 
 Mode of Preparing Fossil Infusoria. Before entering 
 
PREPAKATION OF FOSSIL INFUSORIA. 435 
 
 on further details of the fossil Infusoria, we would first 
 Btate how they may be prepared for microscopic examina- 
 tion. A great many of the infusorial earths may be 
 mounted as objects without any previous washing or pre- 
 paration ; some, such as chalk, however, must be repeat- 
 edly washed, to deprive the Infusoria of all impurities ; 
 whilst others, by far the most numerous class, require 
 either to be digested for a long time, or even boiled in 
 strong nitric or hydro-chloric acid, for the same purpose. 
 Place a small portion of the earth to be prepared in a test- 
 tube, or other convenient vessel, capable of bearing the 
 heat of a lamp ; then pour upon it enough diluted hydro- 
 chloric acid to about half fill the tube. Brisk effervescence 
 will now take place, which may be assisted by the applica- 
 tion of a small amount of heat, either from a sand-bath or 
 from a lamp : as soon as the action of the acid has ceased, 
 another supply may be added, and the same continued 
 until no further effect is produced. Strong nitric acid 
 should now be substituted for the hydro-chloric, when a 
 further effervescence will take place, which may be greatly 
 aided by heat ; after two or three fresh supplies of this 
 acid, distilled water may be employed to neutralise all the 
 remains of the acid in the tube ; and this repeated until 
 the water comes away perfectly clear, and without any 
 trace of acidity. The residuum of the earth, which con- 
 sists of silica, will contain all the infusorial forms ; and 
 some of this may be taken up by a dipping-tube, laid on 
 a slide, and examined in the usual manner. Should per- 
 fect specimens of the Coscinodiscus, Gallionella, or Navi- 
 cula be present, they may be mounted in Canada balsam ; 
 if not, the slide may be wiped clean, and another portion 
 of the sediment taken, and dealt with in the same way, 
 which, if good, after being dried, may be mounted in Canada 
 balsam. 
 
 Dr. Redfern adopts an excellent mode of isolating Navi- 
 culce and other test-objects. He says : u Having found 
 the methods ordinarily employed very tedious, and fre- 
 quently destructive of the specimens, I adopted the follow- 
 ing plan. Select a fine hair which has been split at its 
 free extremity into from three to five or six parts, and 
 having fixed it in a common needle-holder by passing it 
 f p-2 
 
436 THE MICROSCOPE. 
 
 through a slit in a piece of cork, use it as a forceps under 
 a two-thirds of an inch objective, with an erecting eye- 
 piece. When the split extremity of the hair touches the 
 glass-slide, its parts separate from each other to an amount 
 proportionate to the pressure, and on beii g brought up to 
 the object, are easily made to seize it, when it can be 
 transferred as a single specimen to another slide without 
 injury. The object is most easily seized when pushed to 
 the edge of the fluid on the slide. Hairs split at the ex- 
 tremity may always be found in a shaving-brush which has 
 been in use for some time. Those should be selected which 
 have thin split portions so closely in contact that they 
 appear single until touched at their ends. I have also 
 found entire hairs very useful, when set in needle-holders, 
 in a similar manner ; any amount of flexibility being given 
 to them by regulating the length of the part of the hair 
 in use." Professor Smith, of Kenyon, U.S. contrived a 
 very ingenious "Mechanical finger " for picking up and 
 arranging diatoms and other minute objects. 
 
 Professor J. W. Bailey, of New York, has enriched the 
 Museum of the College of Surgeons with several valuable 
 specimens of the skeletons of Infusoria; among them is a 
 fresh-water Badllaria, named Meridian circulare, which 
 Professor Quekett, in the Historical Catalogue, describes 
 as " consisting of a series of wedge-shaped bivalve siliceous 
 loricse, arranged in spiral coils ; when perfect, and in cer- 
 tain positions, they resemble circles ; each lorica is articu- 
 lated by two lateral surfaces." It is asserted that they 
 creep about when free from the stalk-plate. (Fig. 2.25, No. 
 1 6.) Cocconema lanceolata have two lanceolate flinty cases 
 that taper towards their ends, one of which is attached to 
 a little foot. Each lorica has a line marked in its centre, 
 and transverse rows of dots on both sides : Ehrenberg says 
 there are twenty-six rows in the one-hundredth of a line. 
 (Fig, 225, No. 14.) Adinanthes Longipes have at the 
 margins two coarse convex pieces roughly dotted, and two 
 inner pieces firmly grooved ; the inside seems filled with 
 green matter. At one corner they are affixed to a jointed 
 pedicle, which in many specimens contains green granules. 
 In a specimen of a fossil E^},notia, found in some Bermuda 
 earth, the flinty case is i'i four parts; it is of a half- 
 
FOSSIL INFUSORIA. 437 
 
 lanceolate shape, and a little indented on both margins ; 
 two of them have curved rows of dots, and the other two 
 are partly grooved with finer rows. Ehrenberg says they 
 have four openings, all on one side (fig. 225, No. 13), 
 
 Fig. 225. 
 
 7, Campiioditcu* clypeus. 8, Biddnlphia. 9, Gallinnelia tnlcatn. 10, Trice- 
 r-tium, found in Thames mud. 11, Gomi>honemn gemitiatum, with their ^Ik- 
 like attachments. 12, D ' ctyocha fibula. 13, Eunolia. 14, Cocconema. 15, Fra~ 
 gilaria pectinaiit. 16, Meridian circulars. 17, Diatomafl'>ccnlosum. 
 
 presenting a row of dots varying very much in number ; 
 minute striae in some cases extend from each dot towards 
 the middle of the lorica ; and on the circumference there 
 are two of these dots. The spirals and the individual 
 lorica are very fragile, and therefore easily separated from 
 each other. Of a glistening whiteness is the ribbon-liko 
 flinty case of Fra/jilaria pectiiialis, which consists of 
 many bivalve segments : on the articulating surface there 
 are small grooves, represented in fig. 225, No. 15. A sin- 
 
438 THE MICROSCOPE. 
 
 gular class of objects are Diatoma flocculosum, being rather 
 oblong-looking, and joined 'to each other at opposite cor- 
 ners : they are sometimes grooved on each side. (Fig. 225, 
 No. 17.) The "Swollen Eunotia" is generally about 
 from the llth to the 200th of an. inch in length: a 
 groove, widest in the centre, and tapering off to the ends, 
 passes along its centre on both sides ; it has curved lines 
 proceeding from it. So wonderfully close are these lines 
 or ribs, that as many as eight of them have been 
 counted in the space of the 1 200th of an inch. They are 
 usually found when alive adhering to a branch of some 
 weed that forms the green coating over stagnant waters. 
 They propagate by self-division ; a slight line running 
 down the centre marks where the separation will occur, 
 on each becoming perfectly developed as a distinct crea- 
 ture ; and thus they grow, and separate, filling the earth 
 with their flinty shells. 
 
 Gallionella sulcata is found in many parts of North 
 America ; it somewhat resembles the cylindrical box for 
 spices, which was at one time so common among good 
 housewives; scientifically, it is described as consisting of 
 chains of cylindrical bivalve loricse, having their outer 
 surfaces marked or furrowed with longitudinal strise ; short 
 joints may occasionally be seen, having their ends upper- 
 most, the depth of the furrows being shown on the margin ; 
 within the margin is a thin transparent rim having ra- 
 diating strise. Sometimes as many as forty will be found 
 joined together. (Fig. 225, No. 9.) The Gallionella received 
 its designation from a celebrated French naturalist named 
 Gaillon, it is often termed the Box-chain Animalcule, and 
 when the flinty case is seen lying on its face, it much re- 
 sembles a coin. These living infusoria are found in almost 
 all waters, and are stated to be so rapid in their growth, 
 that one hundred and forty millions will by self-division 
 be produced in twenty-four hours. A species named the 
 Striped Gallionella was discovered by Dr. Mautell near 
 London ; the same species is also found in the ocean. 
 Sometimes the chains are three inches long; their size is 
 from the 14th to the 400th part of an inch. 
 
 Professor Quekett, in the catalogue we have referred to, 
 describes an ' earth from Bohemia, particularly rich in 
 
FOS3IL INFUSORIA. 439 
 
 fossil specimens of Navicula viridis, which consists of four 
 prismatic loricae, two ventral and two lateral ; the former 
 having round, the latter truncate extremities ; and both 
 provided with two rows of transverse markings and dots, 
 longer and more marked on the ventral than on the lateral 
 surfaces. The specimens having their ventral surfaces 
 uppermost, exhibit a longitudinal marking in the centre, 
 with a slight dilatation or knob at each extremity ; this 
 marking is interrupted in the middle of the lorica, and a 
 diamond-shaped spot is left ; if one of the lateral loricae be 
 examined, two of the same spots will be seen, one on each 
 side ; they are of triangular figure, and appear to be thicker 
 parts of the shell, described as holes by Ehrenberg." Four 
 smaller triangular spots may be observed in the same 
 lorica. one being situated at each corner ; these also have 
 been considered as openings by Ehrenberg : their length 
 varies considerably; some exceed the 100th, whilst others 
 are even smaller than the 1000th of an inch. lathmia ener- 
 vis (fig. 224, No. o) is usually found attached to sea-weed ; it 
 is in three parts; and of a trapezoid shape, the centre part 
 appears like a band passing over, and is bounded by broad 
 straight lines : its outer surface is covered with a network 
 of rounded reticulations, arranged in parallel lines. Among 
 the most remarkable is Amplutttras antediluviana ; this 
 is of a cubical or box-like figure, and consists of three 
 portions, the one in the centre bein^ in the form of a band, 
 as shown at fig. 225, No. 8, and the two lateral ones having 
 four slightly projecting angles, with an opening into each. 
 When viewed in detached pieces, the central one is like 
 a box. and the two lateral portions resemble the cover and 
 bottom. The former may be readily known, as consisting 
 merely of a square frame-work with striated sides ; but 
 both the latter are marked with radiating reticulations. 
 When recent, they are found in zigzag chains, from their 
 cohering only by alternate angles. In some instances, as 
 in Biddulphia, and Isthmia, two young specimens may be 
 found within an old one. Cocconeis is marked with eight 
 or ten lines proceeding from the inner margin to the 
 centre ; between which are dotted furrows, with the earlier 
 spot in the centre of each. (Fig. 224, No. 3.) 
 
 Camp Hod iscus clyptut is oval, and curved in opposite 
 
440 THE MICROSCOPE, 
 
 ways at the long and short diameters. On the margin 
 there are two series of dots, sometimes joined ; and on the 
 oval centre there are also dots about the margin, while the 
 middle is nearly plain. (Fig. 225, No. 7.) Actinocyclus has 
 a round bivalve flinty case, with numerous cells formed by 
 radiating partitions; very often every alternate cell only 
 is on the same plane. The specimen in the Museum of 
 the College of Surgeons is exquisite in its markings ; it 
 was found in some Bermuda earth, and has a beautifully- 
 raised margin, and a five-rayed star in the centre ; the 
 number of cells is ten, five being on one plane and five on 
 another. One set has the usual hexagonal reticulations 
 crossed with diagonal lines, the other has the same lines, 
 with a much smaller series of triangular reticulations, so 
 disposed that they appear to form with each other parts 
 of very small circles. One valve from this specimen is 
 represented in fig. 224, No. 2. 
 
 As well as the beautiful shell of the Coscinodiscus, found 
 both in a fossil and recent state, there is one of exquisite 
 elegance and richness, of the genus Arachnoidiscus, so 
 named from the resemblance of the markings of the shell 
 to the slender fibres of a spider's web. (Fig. 224, No. 1.) This 
 is found in the guano of Ichaboe, and also in earth from 
 the United States, as well as among sea- weed from Japan, 
 and the Cape of Good Hope. Mr. Shadbolt believes : 
 ' These shells are not, strictly speaking, bivalves, although 
 capable of being separated into two corresponding por- 
 tions ; but are more properly multivalves, each shell con- 
 sisting of two discoid portions, and two annular valves 
 exactly similar respectively to one another." (See Micro- 
 scojncal Society's Transactions, for an excellent paper on, 
 these shells by Mr. Shadbolt.) 
 
 Artists who design for art -manufacturers might derive 
 many useful hints from the revelations of the microscope, 
 as evidenced in the arrangement of the shell last noticed, 
 and in that of the genus Coscinodiscus; a very handsome ob- 
 ject, the shells of which are marked with a network of cells 
 in a hexagonal form, arranged in radiating lines or circles, 
 and varying from 1 -200th to 1 -800th of an inch in diameter. 
 A specimen found in Bermuda earth has on one of its valves 
 two parallel rows of oval cells that form a kind of cross ; 
 
XANTHIDIA. 441 
 
 which gradually enlarge from the centre to the margin \ 
 the angles of the cross are filled up with hexagonal cells 
 as previously noticed. (Fig. 224. No. 4.) 
 
 The unskilled manipulator may for some time endeavour 
 to adjust a slide, having a piece of glass exposed not larger 
 in size than a pea, on which he is informed an invisible 
 object worthy his attention is fixed, before he is rewarded 
 by a sight of Triceratium faiiis, extracted from the mud of 
 the too-muddy Thames. The hexagonal markings, cells, 
 are beautiful, and at each corner there is i curved pro- 
 jecting horn or foot. (Fig. 225, No. 10.) In Bermuda earth 
 there is a small species found, which has its three margins 
 curved ; and also a curious species, which resembles the 
 triradiate spiculum of a sponge. 
 
 It is remarkable how, in these minute and obscure 
 organisms, we find ourselves met by the same difficulties 
 concerning any positive laws governing the formation 
 of generic types, as in larger and more complex forms of 
 animal and vegetable life. It appears as if we could 
 carry our real knowledge little beyond that of species ; and 
 when we attempt to define kinds and groups, we are en- 
 countered on every side by forms, which set at nought our 
 definitions. 
 
 Man even uses infusorial remains as food ; for the berg- 
 mehl, or mountain-meal found in Swedish Lapland, and 
 which, in periods of scarcity, the poor are driven to mix 
 with their flour, is principally composed of the flinty shells 
 of the GallioneUa sulcata, Navicula viridis, and Gompho- 
 nema geminatum Dr. Trail, on analysing it, found it 
 to consist of 22 per cent of organic matter, 72 of silica, 
 5 -85 of alumina, and (H5 of oxide of iron. This would 
 seem to be the same substance described by M. Laribe the 
 missionary, and put to a similar use in China : " This 
 earth," he says, "is only used in seasons of extreme 
 dearth." 
 
 XANTHIDIA. In conjunction with the skeletons of the 
 former species it will be as well to offer a few remarks upon 
 animals long classed with Infusoria, and but rarely found 
 except in the fossil state. There is every reason to believe 
 that the Xanthidia, double-bar animalcules, are sporangia 
 of De&nidioctce. In proof of this it can be shown that 
 
442 THE MICROSCOPE. 
 
 their skeletons are composed of a horny substance, and not 
 of silica, as was once supposed. 
 
 The name Xanthidia is derived from a Greek word sig- 
 nifying yellow, that being their prevailing hue. They are 
 found plenteously in a fossil state, imbedded in flint as 
 many as twenty being detected in a piece the twelfth of 
 an inch in diameter * in fact, it is rare to find a gun-flint 
 without them. When living they may be described as 
 having a round transparent shell, from which proceed 
 spikes varying in size and shape. One kind, found by Dr. 
 Bailey in the United States, was of an oval form, the 288th 
 of an inch in length ; and another species circular, found 
 by the late Dr. Mantell, at Clapham : both were of a 
 beautiful green colour. Specimens of Branched Xntlti- 
 diurn, found in flint by Dr. Mantell. were from the 300th 
 to the 500th of an inch in diameter. Mr. Ealfs pays: 
 " That the orbicular s pi nous bodies so frequent in flint, 
 are fossil sporangia of Desmidiacece, cannot, I think, be 
 doubted, when they are compared with figures of the 
 more recent forms. Indeed, the late Dr. G. Mantell, who, 
 in his Medals of Creation, without any misgiving, had 
 adopted Ehrenberg's ideas concerning them, changed his 
 opinion ; and in his last work regards them as having been 
 reproductive bodies, although he is still uncertain whether 
 they are of vegetal)] e origin." 
 
 The fossil forms vary as much as recent Sporangia, in 
 being smooth, bristly, or furnished with spines, some 
 are simple, and others branched at the extremity Some- 
 times, a membrane may be traced, even more distinctly 
 than in recent specimens, either covering the spines, or 
 entangled with them. Writers have described the fossil 
 forms as having been siliceous in the living state ; but 
 Mr. Williamson informs us that he possesses specimens 
 which exhibit bent spine? and torn margins ; and this 
 wholly contradicts the idea that they were siliceous be- 
 fore they were embedded in the flint. In the present 
 state of our knowledge, it would be somewhat premature 
 to identify the fossil with recent species ; it is better, 
 therefore, at least for the present, to retain the names 
 bestowed on the former by those observers who have de- 
 scribed them. 
 
XANTHIDIA. 443 
 
 Near to Sydden Spoint, and the Round Down Cliff, ou 
 the Dover beach, Mr. H. Deane cut out a piece of pyrites 
 with the adherent chalk, which, ou examination, " exposed 
 to view bodies similar to, if not identical with, Xan- 
 thidia in flints ; he clearly recognised X. spinosum, ramo- 
 sum, tubiferum, simplex, tubiferum recumum, malleofei-um, 
 and pyjcidiculum, together with casts of Polythalamia, and 
 other bodies frequently found in flints. In shape they are 
 somewhat flattened spheres, the greater part of them 
 having a remarkable resemblance to gemmules of sponge, 
 with a circular opening in the centre of one of the 
 flattened sides. The arms or spines of all appear to be 
 perfectly closed at the ends, even including those which 
 have been considered in the flint, specimens decidedly 
 tubiferous ; showing that if the arms are tubes, they could 
 afford no egress to a ciliated apparatus similar to those 
 existing among Zoophytes. On submitting them to pres- 
 sure in water between two pieces of glass, they were torn 
 asuiider laterally, like a horny or tough cartilaginous sub- 
 stance ; and the arms in immediate contact with the glass 
 were bent. Some specimens, put up after several weeks* 
 maceration in water, were so flaccid, that, as the water in 
 which they were .suspended evaporated away, the spines or 
 arms fell inclined to the glass. These circumstances alone 
 seem clearly to disprove the idea of their being purely 
 siliceous. The casts of the Polythalamia, portions of 
 minute crustaceans, &c. appeared also to be, like the Xan- 
 thidia, some modification Oi organic matter : and in the case 
 of the Polythalamia, the bouie* are so perfectly preserved, 
 that in some the lining membranes of the shells are readily 
 distinguishable." 
 
 Mr. Wilkinson, who examined recent XantJiidia found in 
 the Thames mud, and slime, on piles and stones at Green- 
 hithe. said that, in his opinion, they are not siliceous, 
 but of a horny nature, simnar to the wiry sponges, which 
 Mr. Bowerbank describes as being very difficult to destroy 
 without the action of lire. He also met with a peculiarity 
 in a X. spinosum, which he has never seen in any other 
 species ; it was in a piece of a irun-flint. There appeared, 
 as it were, a groove or division round the circum- 
 ference, similar to that formed by two cups when placed 
 
444 THE MICROSCOPE. 
 
 on each other, so as to make their rims or upper edges 
 meet. 
 
 The other fossil Infusoria, found most abundantly in the 
 chalk and flint of England, are the Rotalia, or wheel- shaped, 
 and the Textularia or woven-work animalcules; the latter 
 having the appearance of a cluster of eggs in a pyramidical 
 form, the largest being at the base, and lessening toward 
 the apex. 
 
 We must here bring to a close this short notice of 
 some of the marvellous creations in the invisible world , 
 every glimpse inspiring awe, from the immensity, variety, 
 beauty, and minuteness of its organised habitants. Immen- 
 sity, in its common impression on the mind, hardly conveys 
 the idea of the myriads upon myriads of Infusoria that 
 have lived and died to produce the tripoli, the opal, the 
 flints, the bog-iron, the ochres, and limestones of the world. 
 Professor Owen beautifully explains the uses of this vast 
 amount of animalcule life: "Consider their incredible 
 numbers, their universal distribution, their insatiable 
 voracity ; and that it is the particles of decaying vegetable 
 and animal bodies which they are appointed to devour 
 and assimilate. Surely we must, in some degree, be in- 
 debted to these ever-active, invisible scavengers, for the 
 salubrity of the atmosphere and the purity of water. Nor 
 is this all ; they perform a still more important office in 
 preventing the gradual diminution of the present amount 
 of organised matter upon the earth. For when this matter 
 is dissolved or suspended in water, in that state of com- 
 minution and decay which immediately precedes its final 
 decomposition into the elementary gases, and its con- 
 sequent return from the organic to the inorganic world, 
 these wakeful members of nature's invisible police are 
 everywhere ready to arrest the fugitive organised particles, 
 and turn them back into the ascending stream of animal 
 life. Having converted the dead and decomposing par- 
 ticles into their own living tissues, they themselves become 
 the food of larger Infusoria, and of numerous other small 
 animals, which in their turn are devoured by larger ani- 
 mals ; -and thus a food, fit for the nourishment of the 
 highest organised beings, is brought back, by a short route, 
 from the extremity of the realms of organised matter. 
 
VORTICELLnXffi. 4J5 
 
 These invisible animalcules may be compared, in the great 
 organic world, to the minute capillaries in the microcosm 
 of the animal body ; receiving organic matter in its state 
 of minutest subdivision, and when in full career to escape 
 from the organic system, turning it back, by a new route, 
 towards the central and highest point of that system." 
 
 Such, then, seem to be some of the purposes for which 
 are created the wonderful invisible myriads of infusorial 
 animalcules. In the words of Holy Writ : " All these 
 things live and remain for ever for all uses ; and they are 
 all obedient. All things are double one against another ; 
 and He hath made nothing imperfect. One thing estab- 
 lisheth the good of another ; and who shall be filled with 
 beholding His glory ? " 
 
 VORTICELLID^;. We now come to a family, which includes 
 some of the most beautiful of living infusorial animalcules, 
 and in which we meet with phenomena more curious than 
 any yet witnessed, and perhaps as wonderful as any that 
 will be presented to our notice, in the natural history of 
 the higher classes of animals. The family of Voriicellidce, 
 bell-animalcules, are characterised by the possession of a 
 fringe of rather long cilia, surrounding the anterior ex- 
 tremity, which can be exerted and drawn in at the pleasure 
 of the creatures. Some are furnished with a horny case 
 for the protection of their delicate bedies, -whilst others 
 are quite naked. 
 
 The genus Vorticella, from which the name given to 
 the family is derived, consists of little creatures placed at 
 the top of a long flexible stalk, the other extremity of 
 which is attached to some object, such as the stem or leaves 
 of an aquatic plant. This stem, slender as it is, is never- 
 theless a hollow tube, through the entire length of which 
 runs a muscular thread of still more minute diameter. 
 When in activity, and secure from danger, the little Vw- 
 ticella stretches its stalk to the utmost, whilst its fringe of 
 cilia is constantly drawing to its mouth any luckless 
 animalcule that may come within the influence of the 
 vortex it creates ; but at the least alarm the cilia vanish, 
 and the stalk, with the rapidity of lightning, draws itself 
 up into a little spiral coil. But the Vorticella is not 
 wholly condemned to pass a sort of vegetable existence, 
 
446 
 
 THE MICROSCOPE. 
 
 rooted, as it were, to a single spot by its slender stalk ; its 
 Creator has foreseen the probable arrival of a period in its 
 existence when the power of locomotion would become 
 
 Fig. 226. 
 
 1, 2, 3, Hydras in various stages of development. 4, A group of Stentor poly- 
 morphiLS, many-shaped Stentor. 5, Englena-. 6, Monads. 
 
 necessary, and this necessity is provided for in a manner 
 calculated to excite our highest admiration. At the lower 
 extremity of the body of the animal, at the point of its 
 junction with the stalk, a new fringe of cilia is deve- 
 loped ; and when this is fully formed, the Vorticella quits 
 its stalk, and casts itself freely upon its world of waters. 
 The development of this locomotive fringe of cilia, and 
 the subsequent acquisition of the power of swimming by 
 the Vorticella, is generally connected with the propagation 
 of the species, which, in this and some of the allied genera, 
 presents a series of most curious and complicated phe- 
 nomena. 
 
VOiiTlCELLIDJi. 447 
 
 The Vorticella possess means of propagation which is 
 denied to other Infusoria, with the exception of a few, 
 although we meet with the same in other forms of animal 
 life. The mode of reproduction referred to is called 
 gemmation; it consists in the production of a sort of 
 bud, which gradually acquires the form and structure 
 of the perfect animal. In the Vorticellce, these buds, 
 when mature, quit the parent stem after developing a 
 circlet of cilia at the lower extremity, and fix themselves 
 in a new habitation in exactly the same manner as those 
 individuals produced by the fissuration of the bell. 
 
 At an earlier or later period of their existence, the 
 Vorticellce withdraw the discs surrounded by cilia which 
 forms the anterior portion of their bodies, and con- 
 tracting themselves into a ball, secrete a gelatinous cover- 
 ing, which gradually solidifies, and forms a sort of capsule, 
 within which the animal is completely inclosed. By this 
 process the little animal is said to become encysted; and 
 at this point of its history it is seen to be more compli- 
 cated. Sometimes its further progress commences by the 
 breaking up of the nucleus into a number of minute oval 
 discs, which swim about in the thin gelatinous mass inti 
 which the substance of a parent has become dissolved. 
 The body of the parent animal, inclosed within the cyst, 
 now becomes apparently divided into separate little sacs 
 or bags, some of which gradually acquire a considerable 
 increase in size, and at length break through the walls of 
 the cyst. After a time one of these projections of the 
 internal substance bursts at the apex ; and through the 
 opening thus formed the gelatinous contents of the cyst, 
 enclosed embryos, are suddenly shot out into the water, 
 there to become diffused, giving rise to new generations. 
 From the name Acineta given to them by Ehrenberg, who 
 described them as a new genus, they are denominated 
 Acineta-forms. 
 
 But the final object of this singular metamorphosis 
 still remains to be described. The nucleus, which at the 
 change of the encysted animalcule into the Acineta-form 
 was still distinctly observable, becomes entirely and alto- 
 gether converted into an active young Vorticella, acquiring 
 an ovate form, with a circlet of cilia round its narrower 
 
448 THE MICROSCOPE. 
 
 extremity, and presenting at the opposite end a distinct 
 mouth. Within this young animal, whilst still inclosed in 
 the body of its parent, we see a distinct nucleus, and the 
 usual contractile space of the full-grown creature. When 
 mature, the offspring tears its way through the membranes 
 inclosing the Acineta, which, however, immediately close 
 again. The latter continues protruding and retracting it? 
 filaments, and soon produces in its interior a new nucleus, 
 which in its turn becomes metamorphosed into a young 
 Vorticella. 
 
 The same faculty of enclosing themselves in a cyst is 
 said to be made use of by the Vor- 
 ticella, as a means of self-preservation 
 if the water in which they have been 
 living dries up. When the animal is 
 thus encased, the mud at the bottom 
 of the pool may be baked quite hard 
 in the sun without doing it the least 
 injury ; and in this state the creatures 
 are often taken up by the wind with 
 the dust which it raises from the sur- 
 face of the parched ground, and borne 
 
 *[8 fco g reat distance s, *o as to cause 
 their appearance in most unexpected 
 loocalities (they are frequently found in roof gutters), where 
 the first shower of rain calls them back to active life. 
 
 Conochilus vorticella, 1 belonging to the family ^cistina, 
 Plate III. No. 80, is one of the most remarkable and in- 
 teresting Rotifers met with. It is found in compound 
 groups of a whitish globular form in shallow ponds about 
 London. On Hampstead Heath a good supply is often 
 obtained throughout the summer months. The group 
 consists of from twenty to thirty, or more, animals, of about 
 twice the size of the full-grown volvox, and, like the 
 latter, can be readily seen actively rolling about when the 
 collecting-bottle is held up to the light. The colony is 
 attached to a centre disc, resembling a wheel with its 
 naves and spokes. The foot-stalk is three or four times 
 the length of the body, and has a somewhat spiral form, 
 which it contracts at pleasure, drawing the body down in 
 an instant close to the axis, although it does not appear to 
 
KOTJFFJLE. 449 
 
 have the power of retracting itself perfectly within the 
 hyaline memhrane. The hyaline membrane is at certain 
 periods of the year so very translucent that it cannot be 
 made out ; later in the season it is found studded with para- 
 sitic desmids, when its gelatinous form is readily seen. The 
 body is ovoid or cup-shaped, and the mouth is surrounded 
 by long cilia, which are always in rapid motion. When 
 the animal becomes alarmed it instantly retracts, and then 
 has the appearance of a small round ball On the frontal 
 plane four thickish conical erect papillas are placed, each fur- 
 nished with one or more spines or setee ; very near their 
 base, rather behind, and between the division of the 
 ciliary band, are the very minute visual organs. The 
 jaws, it is said, are furnished with teeth, but these we 
 have not been able to make out, chiefly owing to their 
 disposition to break up in a short time after being placed 
 in confinement. The stomach is oval, and two ovoid 
 bodies are observed near the termination of the oasophagus ; 
 below these the ova-sack encloses a single ovum of a dark 
 colour. The ovum is surrounded by spinous processes, or 
 cilia, and when first thrown off it lodges for a time in the 
 hyaline membrane ; but, when set free, moves slowly 
 about. A few minutes after being placed in the glass-cell 
 the colony become uneasy, break themselves off one after 
 the other, and swim away to die. They were formerly 
 classed among Volvocineoe, but bear no resemblance to 
 them, except in their roll through the water; and are 
 more properly placed among the Rotifers. 
 
 Acineta tuberosa, Plato ILL No. 68. The researches of 
 Stein are said to prove that the several members of this 
 family are simply a developmental phase of Vorticellina; 
 this view, however, is controverted by Lachmann, Cla- 
 parede, and others who have witnessed the reproduction of 
 Acinetce from parent forms. A. tuberosa has a triangular- 
 shaped body and three obtuse tubercles or horns, each 
 furnished with tentacula. Many other forms of this 
 genus are well known ; but, notwithstanding the diversity 
 in construction, Stein declares their tubular ramified pro- 
 cesses to be morphologically and physiologically identical 
 with ordinary tentacula. Vaginicola crystalline* he puts 
 forward as one of the best illustrations to be obtained of 
 
 GO 
 
450 THE MICBOSCOPE. 
 
 the conversion of an encysted Vorticellina into an Acineta. 
 He also considers Actinophrys Sol and Podophrya jixa, 
 (Ehr.) to be the acinetiform representatives of Vorticella 
 microstoma. 
 
 Stentors, Trichodina, and a few others are included by 
 some authors in the Vorticellina. Stentors (fig. 226, No. 4) 
 are exclusively found in fresh water, between or upon 
 water plants in still running waters. Some are colourless, 
 others green, black, or clear blue. " It is," says M. Du- 
 jardin, " in the Stentors where we can view the several 
 supposed internal organs isolately, and that new observa- 
 tions will make known their real nature." 
 
 Rotiferce comprise animals which were placed by 
 Ehrenberg in nine genera ; named Ptygura, JEcistes, Cono- 
 chilus, Megalotiocha, Lacinularia, Tubicolaria, Limnias? 
 Melicerta, and Cephalosiphon. As, however, each of these 
 genera contain but a single species, Mr. Gosse proposes to 
 reduce the nine to two ; thus, Ptygura, jflcistes, Tubico- 
 laria, Limnias, Melicerta, and Cephalosiphon, as they seem 
 to be only so many species of one genus, might constitute 
 one, and Megalotrocha, Lacinularia, and Conochilus, an- 
 other. Mr. Gosse also wishes to construct a family to be 
 called Melicertodce; in this he would include two genera, 
 Melicerta and Megalotrocha, degrading some of the present 
 genera to form species of Melicerta, and others, to constitute 
 three species of Megalotrocha. Each group will be readily 
 distinguished the former by the circumstance that the 
 individuals are solitary ; in the latter they are, in adult 
 life, aggregated in a common envelope spherical masses, 
 composed of many animals radiating from a central point. 
 These compound masses are either free or fixed. In the 
 genus Melicerta, or tube-dwellers proper, the front or 
 upper part of the body is capable of being turned in 
 upon itself, concealed with purse-like folds, and of being 
 expanded, at the will of the animal, into a disc form, which 
 is usually much wider than the diameter of the body ; 
 this again is either flat or in the form of a shallow funnel. 
 Its outline will form either a simple circle, as in M. pty- 
 gura and M. cecistes, two circles united at one point, as in 
 Limnias (Plate III. JS"o. 72), or four sinuous lobes, more or 
 less developed, as in M. cephalosiphon t M. tubicvlaria, and 
 
ROTIFERS. 451 
 
 2f. ringetis, in each of which there is, according to Pro- 
 fessor Huxley, a double edge to the disc, of which the 
 subordinate one is placed on the under-side, and a little 
 within the line of the principle one. The former is fringed 
 with minute cilia, whose vibratile waves form well-marked 
 movements, which run evenly along the margin. The 
 eggs are usually laid within the case. 
 
 To the genus Melicerta Mr. H. Davis 1 adds one, if not 
 two, new species, which he has named, provisionally, M. 
 longicomis and M. intermedias. The two peculiarities of 
 these new forms are the remarkable length of the antennae, 
 and the construction of tube-dwellings for the purpose of 
 concealing themselves and their eggs. (Plate III. No. 
 69.) jEcistes longicomis : each animal lives in a separate 
 semi-transparent cylindrical sheath (urceolus), into which 
 it entirely withdraws on the approach of danger. The foot- 
 stalk is long, and firmly attached to the bottom of the tube. 
 Two or three ova are concealed in the lower part of the urce- 
 olus. The trochal disc is large, and completely surrounded 
 by a ciliary wreath. The antennae, two, are very long, well 
 placed below the disc, and terminating in a small brush of 
 setse. The tube, Mr. Davis believes, is built up in the same 
 way as that of Melicerta. 
 
 Mr. Slack describes, in the "Intellectual Observer," 
 a tubicolous Rotifer, discovered in the stems of the Ana- 
 charis, which shows an affinity with ^Ecistes, Limnias. and 
 Melicerta, but differs in some points, especially in the an- 
 tennae; this, named by Mr. Gosse Cephalosiphon, displays 
 a single antenna of extraordinary length and versatile 
 power. Like Melicerta and Limnias, it shows no visible 
 construction below the disc, whereas in jEcistes this is a 
 conspicuous feature. 
 
 " The animal inhabits a case slightly trumpet-shaped, 
 generally of greater length and slenderness compared with 
 those of its allies, standing erect on the pond-weed. It is 
 irregular and floccose in outline, very opaque, and of a 
 deep umber brown by transmitted light, but of a much 
 lighter hue by reflected light. It is composed, doubtless, 
 of an excretion from the skin as the foundation layer, 
 
 (1) "On two new species of the genus JScistes ," by Henry Davis, F.P.M.S. 
 Micros. Soc. Trans. April 18C7. 
 
452 THE MICROSCOPE. 
 
 thickened and rendered opaque by the addition of the 
 dark material, which I conjecture to be the faecal pellets 
 sucessively discharged in process of growth. Contrary to 
 the rule in the allied genera, the petaloid disc is made to 
 open by the bending forward of the head towards the 
 ventral aspect, and its widest margin is the dorsal one. 
 Immediately behind the disc are two minute lateral horn- 
 like points, which project from the head, and curve to- 
 wards each other. These are sometimes visible both in a 
 frontal and a lateral view, and with the disc closed or 
 open ; but at other times the closest scrutiny fails in dis- 
 cerning them. Behind these, in the median line, there 
 is an organ which is never concealed : it is the single 
 antenna, which stands up perpendicularly from the occiput 
 to a great height (being almost half as long as the body, 
 exclusive of the foot), and generally arches over the front, 
 but is capable of vigorous and sudden movements to and 
 fro, and from side to side. It is evidently tubular through- 
 out ; either a simple tube with thick walls, or else, if the 
 walls are thin, furnished with a slender piston which runs 
 through its length. 
 
 " The Cephalosiphon is very lively and active in its 
 motions. It is very ready to protrude from its case, and 
 not at all prone to retire upon ordinary alarms, such as a 
 jar upon the instrument, that would send the Floscularia 
 or the Steplianoceros into its retreat in an instant. It is 
 very curious to see it protruding : the long antenna is first 
 thrust out, and jerked to and fro as a feeler, exploring the 
 surrounding water for safety. The entire height of an 
 average specimen, in its ordinary state of extension, is 
 l-33d of an inch ; of which the foot is l-50th, the body 
 1 -200th, and the antennae 1 -400th of an inch. 
 
 The rotating or wheel-animalcules occupy the most 
 conspicuous place among infusorial animals. They re- 
 quire water for their development, although they are 
 indwellers occasionally of the cells of mosses and damp 
 weeds. They do not possess many stomachs, but cue, 
 and generally have teeth and jaws to supply its wants. 
 They can elongate and contract their bodies, and seme 
 species have their extremity prolonged to a tail, or rather 
 a foot, or a forked process, by means of which they 
 
ROTIFERS. 
 
 453 
 
 fix themselves to extraneous substances ; while the cilia 
 is in rapid motion, this prevents the anterior portion of 
 the body being drawn in by the force of the rotatory 
 
 v/ 
 
 Fig. 228. 
 
 1, The common Wheel-Animalcule, Rotifer vulgaris, -with its cilia or rotaton 
 6, protruded : e, its horn ; d, oesophagus ; e, gut ; /, outer case ; y, eggs. 2, Tho 
 same in a contracted state, and at rest: at <jis seen the development of the 
 young. 3, Pitcher-shaped Brachionus: a, its jaws; b, shell; c, cilia, or rota- 
 tors: d. tail. 4. Bakers Brachionut : a, the jaws and teeth; d, the shell; c, 
 the cilia ; c, the stomach. 
 
 action. They multiply by eggs ; a few have been seen to 
 bring forth their young alive. In the atmosphere the eggs 
 have been discovered whirling along by the force of the 
 wind to some resting-place, where, when circumstances 
 admit, they spring into active life, and fulfil their appointed 
 destiny. The eggs are of an oval form, and some ten, 
 twenty, or thirty may be seen in an animal, of a brown- 
 colour, others are of a delicate pink and deep golden yel- 
 ICTT. In those ^>f a light colour, the young are sometime* 
 
454 THE MICROSCOPE. 
 
 seen with their cilia in active vibration. Ehrenberg 
 accurately described the upper part of a common wheel-ani- 
 malcule, with the cilia, jaws, teeth, eyes, &c., as seen under 
 a magnifying power of 200 diameters, and represented in 
 fig. 228, No. 1. The small arrows indicate the direction of 
 the currents produced by the cilia b, turning on their base. 
 At the will of the animal a change is made in the direction 
 in which the wheels appear to revolve, these it has the 
 power of withdrawing, with the quickness of thought ; a 
 cluster of hairs appears at the extremity, that do not 
 revolve, and certainly differ from the cilia : as they are 
 usually protruded when the creature is moving from place 
 to place, their function has been imagined to be that of 
 feelers. 
 
 The red spots, very generally believed to be the eyes of 
 the Rotiferce, are mostly of a bright red colour ; and the 
 number and arrangement of these organs vary. In some 
 species there have been discovered as many as eight, often 
 placed on either side of the head, in a row, circle, 
 or cluster, and in some they take a triangular shape. 
 The Rotiferce delight in the sunshine; and when the 
 bright luminary is hidden behind clouds, the animals 
 sink to the bottom of the water, and there remain. 
 When the water of their haunts is becoming much evapo- 
 rated, they rise to the top, and give a bright-red tint to 
 it; but when caught and placed in ajar, their beautiful 
 colour fades in a few days. Locomotion is performed by 
 swimming, the rotatory action of the crowns of cilia im- 
 pelling it forward; in other instances it bends its body, 
 then moves its tail up towards the head, with the two 
 processes that serve as feet near the tail ; it then jerks its 
 head to a further distance, again draws up its tail, and so 
 proceeds on its journey. Another peculiarity is that 
 of drawing in the head and tail until nearly globular, 
 and remaining in this condition fixed by the sucker; at 
 other times they become a complete ball, and are rolled 
 about by every agitation of the water. 
 
 The body of the wheel-animalcule is of a whitish colour ; 
 its form is indicated in the engraving. The tube for 
 respiration appears to allow of water passing to the inside. 
 On the food being drawn by the currents to the cup part 
 
ROTIFERS. 
 
 455 
 
 of the wheels, it passes through a funnel as it were to the 
 inouth, which is situated rather lower down, and where 
 the food is crushed by teeth placed on the plates of the 
 jaw, with a hammer- like action ; from this point it passes 
 through the alimentary canal for the sustenance of the 
 animal. 
 
 BRACHION^EA. Ehrenberg's genus Brachionus, " Spine- 
 bearing animalcules," belonging to the Rotiferce, are truly 
 interesting, from their very perfect and complex orga- 
 nisation. Some are entirely enclosed in a horny covering, 
 others only partially covered. Their structure, so beau- 
 tiful and symmetrical, has always made them favourites 
 with those who delight in microscopical studies. Bra- 
 chionus striatu*, "Striped shell animalcule" (No. 3, fig. 
 228), of an elegant, jug-like form, has the transparent 
 coat or carapace, striated and scalloped out at the upper 
 part ; through which the citron- 
 coloured inhabitant protrudes itself. 
 Two hornlike processes are appended 
 to its under-side. As occasions re- 
 quire, it sinks firmly and securely 
 within its crystal home, which is suffi- 
 ciently transparent to permit a view 
 of its organisation. Its progress is 
 effected by means of ciliary processes. 
 Brachionus Pala, or Anurce Cerm- 
 cornis, "Bent horn animalcule," is 
 possessed of double rotatory organs, 
 and four long processes, which project 
 above the external coat. It measures 
 the90thpart of an inch. Brachionus 
 Ovalis, " Egg-shaped brachionus," is 
 remarkable for the strength ^ of its 
 transparent coat, which is beyond 
 that of other horny creatures. Its 
 projecting tail, as well as head, is at 
 pleasure withdrawn into its very 
 strong case. Brachionus Dentatus, 
 " Toothed brachionus." This active, 
 bright pink-eyed little creature, the 90th part of an inch 
 iu size, is apparently enclosed in a two-valved shell, having 
 
 Fig. 229. 
 Brachionus Ovalis, closed. 
 
456 THE MICROSCOPE. 
 
 each 2nd indented so as to form two pair of teeth. Mr. 
 Pritchard says : " In addition to the rotatory organs 
 for supplying it with food, 1 have observed it attached 
 to a stem of confervas, and abrading it with its teeth 
 fixed in the bulbous oesophagus, which, during the opera- 
 tion, oscillates quickly; the rotatory cilia at the same 
 time move rapidly, which makes it highly probable that 
 they perform some office connected with the organs of 
 respiration, as their motion seems altogether unnecessary 
 while the creature is feeding in this manner." Brachionus 
 Bakeri, "Baker's brachionus," (fig. 228, No. 4), is a curious 
 and beautifully-formed animal. At the points of a half- 
 circle are situated the rotatory organs and cilia, between 
 which rise some long spines, each side of the shell pro- 
 ceeding to a point in the lower part, while a square seems- 
 taken out of its body, forming thus two spines ; from the 
 central part of the body projects a long tail. The eggs are 
 sometimes attached to these spines, and in other instances- 
 are seen in the ovisac. 
 
 Notommata Aurita, the " Eared notommata." The ana- 
 tomy of this animal, a genus of Rotiferce, family Hyda- 
 tincea, has been most lucidly explained and illustrated by 
 Mr. P. H. Gosse, in the Microscopical Society's Transactions. 
 
 Mr. Gosse states, that his specimens were found in a jar 
 of water obtained in the autumn from a pond near Wal- 
 thamstow, the jar having stood in his study-window 
 through the winter; and from a swarm in the succeeding 
 February he selected one the 70th of an inch in length 
 when extended, but its contractions and elongations 
 rendered its size variable. 
 
 " Its form, viewed dorsally, is somewhat cylindrical, but 
 it frequently becomes pyriform by the repletion of the. 
 abdominal viscera. Viewed laterally, the back is arched 
 gibbous posteriorly, with the head somewhat obliquely 
 truncate, the belly nearly straight. The posterior ex- 
 tremity is produced into a retractile foot, terminating in 
 two pointed toes ; this, both in function and structure, is 
 certainly analogous to a limb, and must not be mistaken 
 for the tail, which is a minute projection higher up the. 
 body. When not swimming or rotating, the head assumes 
 a rounded outline, displaying through the transparent 
 
ROTIFERS. 457 
 
 integument an oval mark on each side, within which a 
 tremulous motion is perceived ; but at the pleasure of the 
 animal a semi-globular lobe is suddenly projected from 
 each of these spots by evolution of the integument. 
 These projections have suggested the trivial name of 
 aurita. Each lobe is crowned with a wheel of cilia, the 
 rapid rotation of whose waves forms the principal source 
 of swift progression in swimming. The protrusions of 
 these lobes are evidently eversions of the skin, ordinarily 
 concealed in two lateral cavities. They may be protruded 
 by pressure, and are then seen to be covered with long 
 but firm and close-set cilia, which are bent backward, and 
 move more languidly, as death approaches. The whole- 
 front is also fringed with short vibratile cilia, which extend 
 all along the face, as far as the constriction of the neck. 
 The whole body is clear and nearly colourless ; but its- 
 transparency is much hindered by the net-work of dim 
 lines and corrugations that are everywhere seen, particu- 
 larly all about the head." 
 
 Mr. Gosse, throwing a little carmine into the water, saw the 
 jaws working slightly, the points opening a little way, and 
 then closing; the rods of the hammers were drawn tcwards- 
 the bottom for opening, and upwards for closing. A little 
 mass of pigment was soon accumulated beneath the tips 
 of the jaws, which spread itself over a rounded surface, 
 but did not pass farther; nor did an atom at this time go- 
 into the stomach. 
 
 After entering into further minute details of the little 
 animal, he observes: "They possess organs that many 
 others do not, and want some that others possess. They 
 prove that the minuteness of the animals of this clasa 
 does not prevent them from having an organisation most 
 elaborate and complex, and therefore it justifies the belief 
 that the Rotiferce should occupy a place in the scale of 
 animal life much higher than that which has been commonly 
 assigned to them." 
 
 Like most of the class, this Notommata is predatory. 
 Mr. Gosse once saw one eagerly nibbling at the contracted 
 body of a sluggish Rotifer vulgaris; the mouth was drawn 
 obliquely forward, and the jaws were protruded to the food, 
 so as to touch it. It did not appear, however, to do the 
 
458 THE MICROSCOPE. 
 
 rotifer much damage. It appeared chiefly to feed on 
 monads. 
 
 FLOSCULARijEA. The Stephanoceros, " Crowned animal- 
 cule." This beautiful little creature is about the 36th 
 of an inch in length ; and is enclosed in a transparent 
 cylindrical flexible case, ovei which it protrudes five long 
 arms in a graceful manner, which, touching at their points, 
 give a form from which it derives its name. These 
 arms are furnished with several rows of short cilia, and 
 retain the prey brought within their grasp until it can be 
 swallowed. The case is attached to the animal on the 
 part we may term the shoulders ; so that when it shrinks 
 down in its transparent home, the case is drawn inwards. 
 To the bottom of its home it is secured by an elongation 
 of the body; and this part, as well as the body, contracts 
 instantly on the approach of danger, the arms coming 
 close together are also withdrawn. Its mouth differs 
 a little from the common wheel-animalcule ; it has two 
 distinct sets of teeth, with which it tears and crushes its 
 food. The eggs of the Stephanoceros, after leaving the ani- 
 mal's body, remain in their crystal-like shell until hatched ; 
 and Dr. Mantell from close observation found, that about 
 eighty hours elapsed before their organs were all developed 
 and fitted for use. 
 
 Limnias Ceratophylli, " Water-nymph," is of this family, 
 being about the 20th of an inch in size, and is enclosed in 
 a white transparent cylindrical case, one-half the length of 
 the animal ; which, being glutinous, becomes of a brownish 
 colour, from the adhesion of extraneous matter. Its rota- 
 tory apparatus is divided into two lobes, possessing vibra- 
 ting cilia, as well as a singular projecting angular chin. In 
 the rows of little eggs in the body of the parent, may 
 clearly be distinguished most of the young organs in a 
 Btate of activity. From its fondness for hornwort, it is 
 often called by the name of that plant. (Plate III. No. 72.) 
 
 Floscularia Ornata, " Elegant floscularia," is a beautiful 
 type of the family, and has its rotatory organs divided 
 into several parts ; when it contracts itself into a small 
 compass, its transparent covering becomes wrinkled. This 
 creature is an interesting object, as its internal structure 
 can be seen through the translucent sheath that constitutes 
 
KOTIFERJS. 459 
 
 its dwelling. The little beings are very rapacious, although 
 but the 108th part of an inch in size. Floscularia Pro- 
 boscidea, " Horned floscularia," has six lobes, fringed with 
 cilia shorter than in the preceding species. Its name is de- 
 rived from a peculiar kind of horn or proboscis, also having 
 cilia placed in the centre of the lobes. The eggs cast off 
 by the parent enclosed in a sheath, are very pretty objects 
 for microscopic observation. In fact, the tinted case, the 
 light ethereal frame of the tiny animal, the variously 
 coloured food, <fec., in the stomach, combine in rendering it 
 singularly interesting. 
 
 Melicerta Ringens, "Beaded melicerta." Of all the Me- 
 licerta, or " Honey floscularia," this is the most beautiful. 
 Its crystalline body is first enclosed in a pellucid covering, 
 wider at the top than the bottom, of a dark yellow or 
 reddish-brown colour, which gradually becomes encrusted 
 with zones of a variety of shapes, glued together by some 
 peculiar exudation that hardens in water : it is these little 
 pellets, appearing as rows of beads, give the name to 
 the animal. Mr. Gosse furnishes an excellent account of 
 the " architectural instincts of Melicerta, ringens" which is 
 not only truly surprising, but full of interest. He writes : 
 " This is an animalcule so minute as to be with difficulty 
 appreciable by the naked eye, inhabiting a tube composed of 
 pellets, which it forms and lays one by one. It is a mason 
 who not only builds up his mansion brick by brick, but 
 makes his bricks as he goes on, from substances which he 
 collects around him, shaping them in a mould which he 
 carries upon his body. 
 
 " The animal, as it slowly protrudes itself from its inge- 
 niously-formed mansion, appears a complicated mass of 
 transparent flesh, involved in many folds, displaying at 
 one side a pair of hooked spines, and at the other two 
 slender, short blunt processes projecting horizontally. As 
 it exposes itself more and more, suddenly two large rounded 
 discs are expanded, around which, at the same instant, 
 a wreath of cilia is seen performing its surprising motions. 
 Often the animal contents itself with this degree of ex- 
 posure ; but sometimes it protrudes farther, and displays 
 two other smaller leaflets opposite to the former, but in 
 the same plane, margined with cilia in like manner. The 
 
460 THE MICROSCOPE 
 
 appearance is not unlike that of a flower of four unequal 
 petals; from which circumstance Linnseus gave it the 
 name ringens, by which it is still known." 
 
 Below the large petals on the ventral aspect, and just 
 above the level of the projecting respiratory tubes, is a 
 small circular disc or aperture, within the margin of which 
 a rapid rotation goes on. This little organ, which seems 
 to have hitherto escaped observation, Mr. Gosse can com- 
 pare to nothing so well as to one of those little circular 
 ventilators which we sometimes see in one of the upper 
 panes of a kitchen- window, running round and round, for 
 the cure of smoky chimneys. The gizzard, or muscular 
 bulb of the gullet, is always very distinct, and its structure 
 is readily demonstrated. It consists of two sub-hemisphe- 
 rical portions, or jaws, each of which is crossed by three 
 developed teeth, which are succeeded by three or four 
 parallel lines, as if new teeth might grow from thence. 
 The teeth are straight, slender, swelling towards their 
 extremity, and pointed. These armed hemispheres work 
 on each other, and on a V-shaped or tabuliform apparatus 
 beneath, common to most of the Rotifers, but in this genus 
 very small. 
 
 The pellets composing the case are very regular in form 
 and position : in a fine specimen, about the 1-2 8th of an 
 inch in length when fully expanded, of which the tube was 
 the 1-3 6th of an inch, Mr. Gosse counted about fifteen 
 longitudinal rows of pellets at one view, which might 
 give about thirty-two or thirty-four rows in all. 
 
 In November, 1850, Mr. Gosse found a fine specimen 
 attached to a submerged moss from a pond at Hackney; 
 this he saw engaged in building its case, and at the same 
 time discovered the use of the curious little rotatory organ 
 on the neck. When fully expanded, the head is bent back 
 at nearly a right angle to the body, so that the disc is 
 placed nearly perpendicularly, instead of horizontally; the 
 larger petals, which are the frontal ones, being above the 
 smaller pair. Now, below the large petals (that is, on the 
 ventral side) there is a projecting angular chin, which is 
 ciliated ; and immediately below this is the little organ in 
 question. It appears to form a small hemispherical cup, 
 and is capable of some degree of projection, as if on a short 
 
BOTIFERfi. 461 
 
 pedicle. On mixing carmine with the water, the course of 
 the ciliary current is readily traced, and forms a fine 
 spectacle. The particles are hurled round the margin of 
 the disc, until they pass off in front through the great 
 sinus, between the larger petals. If the pigment be abun- 
 dant, the cloudy torrent for the most part rushes off, and 
 prevents our seeing what takes place ; but if the atoms be 
 few, we see them swiftly glide along the facial surface, fol- 
 lowing the irregularities of outline with beautiful precision, 
 dash round the projecting chin like a fleet of boats doubling 
 a bold headland, and lodge themselves, one after another, 
 in the little cup-like receptacle beneath. Mr. Gosse, be- 
 lieving that the pellets of the case might be prepared in 
 the cup-like receptacle, watched the animal, and presently 
 had the satisfaction of seeing it bend its head forward, as 
 anticipated, and after a second or two raise it again ; the 
 little cup having in the meantime lost its contents. It 
 immediately began to fill again ; and when it was full, and 
 the contents were consolidated by rotation, aided probably 
 by the admixture of a salivary secretion, it was again bent 
 down to the margin of the case, and emptied of its pellet. 
 This process he saw repeated many times in succession, 
 until a goodly array of dark-red pellets were laid upon the 
 yellowish-brown ones, but very irregularly. After a certain 
 number were deposited in one part, the animal would 
 suddenly turn itself round in its case, and deposit some 
 in another part. It took from two and a half to three and 
 a half minutes to make and deposit a pellet. , 
 
 Melicerta may be found in clear ponds, niill-ponds, and 
 other places through which a current of water gently 
 flows. It a portion of water-weed be brought home and 
 placed in a small glass zoophyte-trough, and carefully exa- 
 mined with a magnifying power of about fifty diameters, 
 a fe*v delicate looking projections of a reddish brown 
 colour will probably be seen adhering to the plant ; these 
 are the tubular cases of melicerta, which, after a short 
 period of rest, will throw out little animals of one-twelfth 
 of an inch in length. 1 
 
 (1) For further information, see Gosae, Trans. Micros. Soc. voL iii 1852, 
 p. 58 ; Slack's Marvels of Pond Life, 1861 ; and Pritchard's History of Infusoria. 
 4th Edition, 186L 
 
462 
 
 THE MICROSCOPE. 
 
 POLYPIFERA. The chief characteristic of this vast race 
 of animals is, that their mouths are surrounded by 
 radiating tentacula, arranged some- 
 what like the ray of a flower; and hence 
 the term Zoophyte. So plant-like, 
 indeed, are their forms, that the early 
 observers regarded them as vegetating 
 stones, and invented many theories to 
 explain their growth. 
 
 They belong to a sub-kingdom 
 termed Coelenterata, now divided and 
 subdivided by Professor Huxley into 
 the following : 
 
 Septa, *c., x 5 or 6. Septa, &c., x 4. 
 
 Simple soft-bodied. 
 
 1. ACTINIDJE. 1. BEROID2E. 
 
 Actinea, Minyas. Cydippe, Cesium. 
 
 Compound Skeleton spicular, 
 
 2. ZOANTHID.ZE. 2. ALCYONIDJS. 
 
 Zoanthus. Alcyonium. 
 
 Compound Skeleton sclerobasic. 
 3. ANTIPATHIDJE. 3. GORGONIDA. 
 
 Antipathes. Gorgon-ia, Isis, 
 
 Corallium. 
 
 Compound and Simple Steleton thecal continuoua 
 
 4. PERFORATA. 
 
 Porites, Madrepora. 
 
 5. TABULATA. 
 Millepora, Seriatopora. 
 
 6. APOROSA. 
 Cyathina, Oculina. 
 Astrcea, Fungia. 
 
 4. TUBIPORID.S:. 
 Tubipora* 
 5. RUGOSA. 
 Stauria, Cyuthanoniit. 
 Cyathophyllum. 
 Cystiphyllum. 
 
 Opposed to all our common ideas 
 of animal life is this singular portion 
 of creation. If we cut a limb off a tree, 
 or sever that of an animal, these parts 
 will wither and decompose, by passing 
 into other forms of matter. Cut a tree 
 across its middle, and its natural symmetry is irrepa- 
 rably disfigured j slit it down its centre, aud it is de- 
 stroyed : all animals so treated suffer instant death, with 
 the exception of the polype tribe ; for they will put forth 
 new limbs, form a new head or tail, and if slit, become 
 two separate perfect creatures. 
 
 Fig. 230. Asteroid 
 Zoophytes. 
 
FOLYPIFERA. 463 
 
 The seas which wash our shores swarm with beautiful 
 forms of minute Polypes, having nearly the same organisa- 
 tion as the Hydra, but which are protected by an external 
 horny integument. This peculiar covering sends forth 
 shoots or buds, which are developed into new polypes, thus 
 producing a compound animal; but the exercise of this 
 gemmiparous faculty is prevented by a horny defence 
 from effecting any other change than that of adding to the 
 general size, and to the number of tentacles, prehensile 
 fingers, and digestive sacs ; yet the pattern according to 
 which new polypes, and branches of polypes, are developed, 
 is fixed and determinate in each species, and there conse- 
 quently results a particular form of the whole compound 
 animal, by which the species can be readily recognized. 
 
 Cordylophora, a fresh water group of zoophytes, has 
 been made the subject of an admirable memoir by Pro- 
 fessor Allman. (See Phil. Trans. 1853, "On the 
 Anatomy and Physiology of Cordylophora.") In the inte- 
 resting and pretty group, Corynidce, the tentacles are 
 not arranged in a single transverse series, as in Hydra, 
 but are usually scattered more or less irregularly over 
 the surface of the polype while in Tubularia there are 
 two transverse rows of tentacles, an upper shorter, and 
 a lower longer. The reproductive organs, which in Hydra 
 are extremely simple, attain, in many of the Corynidce and 
 Tubulariadce, to the condition of zooids, sometimes be- 
 coming detached, and swimming about freely before dis- 
 charging their products. These free zooids have always 
 the form of a bell or disc, from whose centre a pyriform 
 or oval body either a closed sac or an open-mouthed 
 polype is suspended; and they have been regarded as 
 distinct animals, and grouped together with other forms of 
 Hydrozoa, under the head of Medusas. The bell possesses 
 considerable contractility, and at each contraction the 
 water which fills its cavity is forced out, and the bell itself 
 is thereby propelled in the opposite direction. In Titbit* 
 laria a more completely medusiform body is developed, 
 but is never detached. 
 
 In the Scrtulariadcc, the numerous digestive zooids, or 
 polypes, developed from the original germ, remain always 
 attached ; but their most remarkable feature is the posses- 
 
464 THE MICROS30PE. 
 
 eion of a " cell," surrounding the base of each polype, and 
 usually capable of receiving it when retracted. The de- 
 velopment of this cell at once distinguishes it from the 
 not altogether dissimilar group, the Diphydce and Physo- 
 phoridce. In some Sertulariadce (Sertularia dynamena), 
 the margins of the cells are converted into membranous 
 valves; and in the genus Plumularia, we find special 
 organs of offence. 
 
 The Diphydce are among the most remarkable and 
 beautiful inhabitants of the ocean, to whose warmer 
 regions, they, like the Physophoridce, are principally con- 
 fined. They are free swimmers in the adult state, and 
 probably, at all times of their existence ; but while actively 
 locomotive by means of the contractions of the natatorial 
 organs with which they are provided, they possess no 
 special supporting apparatus, or " float," such as that de- 
 veloped in the Physophoridce. The tentacle of the Diphydce 
 is a long filiform process of the peduncle, capable of great 
 elongation and contraction ; the terminal filament of 
 which is closely beset with minute thread-cells, so that the 
 whole must constitute a very efficient weapon of offence. 
 Three genera of the Physophoridce are particularly worthy 
 of notice : the Physalia, whose air-vesicle may attain the 
 length of eight or nine inches, while its formidable ten- 
 tacles hang down for as many feet, inflicting instantaneous 
 death upon the smaller animals, and giving rise to no small 
 amount of pain and irritation, even in man ; and the 
 Velella and Porpita, in which the texture of the air-vesicle 
 is so exceedingly firm, as to give it the appearance of an 
 internal shell, while its cavity is subdivided into numerous 
 chambers. Originally, however, the " shell " of the Velella 
 is a perfectly simple air-vesicle, like that of any other 
 Physophorid. In the very peculiar genus Lucernaria, 
 lovely " Lamp-polype," with little knobbed tentacles we 
 have a Hydrozoon, in which the polype occupies the centre 
 of an expanded disc, the two presenting essentially the same 
 structure and relations as in the Medusiform zooids of 
 other divisions. In fact, a Lucernaria is in all essential 
 respects comparable to an Aurelia, or other Medusa fixed 
 by the middle of the upper surface of its disc. 
 
 Mr. Huxley prefers the term Lucernariadce to that of 
 
POLYPJFERA. 465 
 
 Medusas; and he does so " from the fact that the Medusidos 
 of authors consists of two groups, the Naked-eyed (Gym- 
 nophthalmata) and the Covered-eyed (Stegnnophthalmata). 
 Some of which, the Aurelia, is but a derivative zooid form 
 of an animal, essentially resembling Lucernaria; while so 
 far as regards the Naked-eyed Medusae, we have no evidence 
 that any genus except jEginopsis, is other than the repro- 
 ductive zooid of one of the Hydrides or Sertulariadce. It 
 seems better, therefore, to avoid the term Medusae, as the 
 denomination of an ascertained group, reserving it merely 
 to denote the medusiform creatures of whose origin we 
 are ignorant, but whose structure entitles them to a pro- 
 visional place among the Lucernariadce. As our know- 
 ledge increases, we shall be able to arrange those Medusae 
 which are the zooids of Hydridce, Sertulariadce, Diphydce, 
 or Physophoridce, under their respective groups, while the 
 rest will form the sub-sections of the Lucernariadce; the 
 first consisting of such forms as Aurelia and RhizostomOf 
 zooids developed by fission from fixed Lucernariadce; the 
 second consisting of such forms as jEginopsis, free Lucer- 
 nariadce, developed at once from the ovum, without any 
 fixed state." 
 
 The Actinozoa are those Ccelenterata in which the 
 stomach is a sac suspended within and entirely distinct 
 from the body, from whose parietes it is separated by 
 a portion of the general cavity of the body, which may- 
 receive the special denomination of " peri visceral cavity. '' 
 The stomach communicates freely by an inferior aperture 
 with the general cavity. A rough conception of the rela- 
 tions between the Actinozoa and the Hydrozoa may be 
 obtained by supposing the walls of the natatorial disc of a> 
 Lucernaria to become united with those of its central 
 polype; it would then become, to all intents and purposes, 
 an Actizozoon. As the Hydra is the type of the Hydro- 
 zoa, so the " Sea-anemone*' (A ;tinia) is considered to be the 
 type of the Actinozoa. As in the Hydrozia, the body of 
 the Actinia is essentially composed of two layers, a super- 
 ficial layer, composed of polygonal cells, frequently de- 
 tached and renewed again, beneath which lies a granular 
 layer ; whilst in the deep dermal layer two sets of mus- 
 cular fibres are found, -a superficial circular, and a 
 H H 
 
466 THE MICROSCOPE. 
 
 longitudinal set : both are flattened, and exhibit no trans- 
 verse striation. In some Actiniae, such as A. mesembryan- 
 themum, bright blue sacs are placed at the edges of the oral 
 
 Fig. 231. Hydra, with tentacles displayed and magnified, adhering to a ttctfk of 
 
 Anacharis alsinaMrum. 
 
 disc, while in A. gemmacea, A. sessilis, &c. clear spots are 
 scattered over the integument, which have been regarded 
 as apertures or tubercles ; M. Hollard, however, states, that 
 these are imperforate Ampullae, possessing a kind of bila- 
 biate mouth, surrounded by a sphincter- like arrangement of 
 muscular fibres. Any foreign body introduced into these 
 ampullae is seized and forcibly held ; or if the finger be 
 placed within reach, it gives the sensation of a very fine 
 rasp passing over it. The margins of the radiate tentacles 
 of the young animal are surrounded by cilia ; the gastric 
 epithelium is likewise ciliated, and doubtless secretes a 
 powerfully solvent fluid. The majority of the Actiniae 
 are oviparous, the young being developed from ova within, 
 and evacuated by the mouth : they are also capable of 
 multiplication by budding, and occasionally by fission. 
 while their power of restoring themselves after muti 
 
POLYPIFEBA. 467 
 
 lation appears to be as great as that possessed by the 
 Hydra. 1 
 
 The great majority of the Actinozoa exhibit a structure 
 closely corresponding with that of the Actimince ; but from 
 the manner in which they grow up into compound masses 
 of associated Zooids, produced by gemmation or by fission, 
 they stand in nearly the same relation to Actinia, as the 
 compound Hydrozoa to Hydra. 
 
 Sir John Dayell believes that Actinice conquer their prey 
 by mere strength ; this is doubtless the case, as from 
 experience we find nothing like a stinging property be- 
 longing to the tentacles ; nor are there any poison vesicles 
 attached thereunto. The tentacles appear to be armed 
 with rows of spines, which give a clinging and slight 
 rasping sensation when the finger is thrust against them ; 
 and by the same means they are able to obtain a firm 
 hold of any smaller animal that falls within their reach. 
 Animals with a hard case or shell seem to escape from 
 their clutches without having sustained the smallest in- 
 jury. The same remarks apply to the Hydra; they have 
 neither the power to sting or benumb their prey, as 
 asserted by many authorities. It has been said that 
 certain minute organs found in polypes, and variously 
 styled thread capsules, filiferous capsules, or urticating 
 cells, are stinging organs. This thread Agassiz likens te 
 a lasso thrown by the polype to secure its prey. Mr. 
 Lewes writes : " On a survey of the places where these 
 'urticating cells' are present, I stumbled upon an unlucky 
 fact, and one likely to excite our suspicion. They are 
 present in a few jelly-fish which urticate, in Actinice which 
 urticate, and in all polypes, which, if they do not urticate, 
 
 (l)The Author's aquarium affords at this time (1856) a curious illustration of 
 increase both by budding and fissuration, in a beautiful A. dianthus. In the first 
 case an offset was seen to protrude ; it resembled a small bud near the foot; this 
 increased until it attained to a perfect animal of a considerable size, when it be- 
 came detached. In another, the animal, after having remained for several weeks 
 firmly adherent'to the side of the glass, with a part of its disc out of the water, by a 
 great effort tore itself away, leaving six small pieces behind, attached to the glass. 
 For some days these pieces served only to mark so many spots, but in about a 
 week rudimentary tentacles were observed to be sprouting out from each piece, 
 which went on rapidly increasing, and ultimately six perfect animals resulted 
 therefrom. The repair of the marginal portion of the disc of the parent animal 
 was completed in a few days, and it suffered no injury whatever from its self- 
 mutilation. This furnishes a proof, if one were wanting, of the hydrozoid cha- 
 racter of this class of animals. 
 
 H H 2 
 
468 THE MICROSCOPE. 
 
 are popularly supposed to do so, and at any rate possess 
 some peculiar power of adhesion. In all these cases, organ 
 and function may be said to go together ; but the cells are 
 also present in the majority of jelly-fish which do not 
 urticate, in Solids which do not urticate, and in Planarice 
 which do not urticate. Here, then, we have the organ 
 without any corresponding function; urticating cells, 
 but no urtication. It thus appears that animals having 
 the cells, have none of the power attributed to the 
 cells ; and that even in those animals which have the 
 power, it is only present in the tentacles, where the cells 
 are much less abundant than in parts not manifesting the 
 power ; the conclusion, therefore, presses on us, that the 
 power does not depend upon these cells. When at rest, 
 and in an ordinary natural state, the animal is never seen 
 to dart out these threads, nor upon capturing his prey ; it 
 is only when some force is used to dislodge him from some 
 spot to which he has securely attached himself, that he 
 presses or squeezes out these threads ; more for the pur- 
 pose of compressing himself into a closer and smaller 
 mass, to add to the difficulty of detaching him. 
 
 "Actinice do not effect their preparation of nutriment by 
 chemical means ; that is, they do not, in the strict sense of 
 the term, digest, but simply derive nourishment by mecha- 
 nical pressure, exerted upon any particle of food that they 
 may draw into their stomachs. This has been proved by 
 experiments made after the manner of Reaumur. A small 
 piece of meat having been put into a quill, and allowed to 
 remain in the stomach of the Actinia sufficiently long, and 
 then withdrawn, no solvent fluid is found to have acted 
 upon it. When placed under the microscope the muscle 
 fibres are not at all disintegrated, and the stride are as 
 perfect as before the experiment, with the exception of a 
 pulpiness and loss of colour, as in any ordinary mechanical 
 maceration. 
 
 " Light has been thrown upon the reproductive system 
 of the Actinice by M. Jules Haime, in the Annales des 
 Sciences Naturelles, 1854, 4 ieme seYie, torn. i. ; which con- 
 tains accurate and detailed descriptions and plates of the 
 disposition of ova and spermatozoa in the Actinice. To 
 find the ovaries it is only necessary to take a live animal, 
 
POLYWFERA. 469 
 
 and with a rapid, but not deep incision, lay open the 
 envelope from the outside ; a series of convoluted bands 
 will bulge through the opening, but if these are quickly 
 brushed aside, certain lobular or grape-like masses will be 
 perceived, darker in colour, and almost entirely hidden by 
 these bands, but growing from the wall of the envelope. 
 They do not appear to have a fixed locality, as they may 
 be found near the base, about the centre, or close to the 
 disc ; it is, therefore, sometimes necessary to make three 
 or four incisions before detecting them; once seen, they 
 will be easily distinguished from the convoluted bands, 
 although very difficult to remove them without removing 
 some of the bands." 
 
 The manner in which the aggregation of zooids, consti- 
 tuting a compound coral, is developed from the primarily 
 solitary Actinozoic embryo, exercises an all-important 
 influence upon the form of the Corallum. Sometimes, as 
 in most Turbinolidce, neither gemmation nor fission ever 
 take place. In the Oculinidce, gemmation alone occurs, 
 and in these and other Actinozoa, the development of buds 
 takes place either from the base or from the sides of a 
 corallite, or from the coenosarc. Certain of the extinct 
 Rugosa, however, exhibit calicular gemmation, the buds 
 being developed from the oral disc or cup, which can 
 hardly have retained any active vitality. The massive 
 coralla of some Cyatliophyllidce, thus standing like inverted 
 pyramids, all the buds supported upon the narrow surface 
 of the primary zooid, have a very singular and striking 
 aspect. The Ueroidce appear at first to differ very widely 
 from the type of structure which prevails among the 
 other Actinozoa, but a close examination of any of their 
 forms suffices to demonstrate the justice of the conclusion 
 advocated by Frey and Leuckart, as to their essential 
 identity with Actinia. The Cydippe, which abounds upon 
 our own coasts, affords, from its small size and extreme 
 transparency, an excellent subject for the student of e- 
 roidce. It is impossible here to enter into the varieties 
 of form presented by the Beroidce, and which chiefly arise 
 from the development of lateral lobes, a process which is 
 earned to so great a length in Cesium that the body 
 becomes ribbon-like. The fieroidce and the Actinidcs 
 
470 THE MICROSCOPE. 
 
 inhabit the shallower and even deeper parts of all seas ; 
 Alcyonidce and Gorgonidce are found at considerable 
 depths ; Gorallium and Gorgonia abound both in cold 
 and -warm latitudes. The Perforata and Tabulata almost 
 exclusively haunt the shallower parts of warm seas, but 
 the Turbinolidce extend into very cold regions. The whole 
 group of the Rugosa is now extinct, only one genus, 
 Holocystis, having survived even the palaeozoic period. Not 
 only heat, but light, and probably rapid and effectual 
 aeration, are essential conditions for the activity of the 
 reef-building Actinozoa. Different species of corals exhibit 
 great differences as to the rapidity of growth, and the 
 depth at which they nourish best ; and no one must be 
 taken as evidence for another in these respects. Certain 
 species of Perforata, MadrepoMae, and Poritidce, appear 
 to be at once the fastest growers, and those which delight 
 in the shallowest waters. The Astrceidce among the 
 Aporosa, and Seriatopora among the Tabulata, live at 
 greater depths, and are probably slower of increase. The 
 most careful accounts of the structure of corals extant, are 
 from the pens of M. M. Milne Edwards and Haime, pub- 
 lished at various times in the Annales des Sciences Natu- 
 relles, in the Memoires du Museum, and in the publicatione 
 of the Palseontographical Society ; and by Mr. Darwin, 
 whose beautiful work on Coral Reefs will amply repay 
 perusal. 
 
 With these brief introductory observations, the principal 
 part of which have been derived from Professor Huxley's 
 lectures, we proceed to direct the reader's attention tc 
 some of the more interesting generic forms. 
 
 HYDRA, FRESH-WATER POLYPE. In polypes of this 
 family the body generally consists of a homogeneous 
 aggregation of vesicular granules, held together by a sort 
 of glairy intercellular substance, and capable of greal 
 extension and contraction; so that the creature can at 
 pleasure assume a great variety of forms, extending its 
 body and tentacles until the latter become so fine as to be 
 almost invisible, and again retracting itself until it acquires 
 the appearance of a small gelatinous mass. The tentacles 
 which surround the anterior extremity are irregular in 
 number; they are capable of extension to a very great 
 
HYDRA. 471 
 
 length when seeking for prey ; and on coining in contact 
 with any object floating through the water, they imme- 
 diately twine round it, and convey it to the mouth. In 
 some genera the tentacles appear to be tubular, the inter- 
 nal cavity being continuous with that of the stomach. 
 The mouth is situated in the centre of the circle of ten- 
 tacles, and leads directly into a simple digestive cavity. 
 
 Hydros, are found in ponds and rivulets, adhering to the 
 leaves of aquatic plants, or twigs and sticks that have 
 fallen into the water. When stretched out, they resemble 
 pieces of hair, from a quarter to three-quarters of an inch 
 in length. Some are of a light-green colour, and others 
 brown or yellow; that is, the five varieties found in 
 England. It received its name from its several long arms 
 being supposed to resemble the fifty-headed water-serpent 
 called Hydra, which was destroyed by Hercules in the 
 lake of Lerna, as we are informed in fabulous history. 
 Leeuwenhoek, in 1703, first drew attention to the Hydra; 
 and in 1739, M. Trembley from the Hague, more accu- 
 rately described its habits. 
 
 Polypes are not vegetarians ; M. Trembley fed Hydrce 
 on minced fish, beef, mutton, and veal; they are voracious 
 and active in seizing worms and larvse much larger than 
 themselves, which they devour with avidity. They care- 
 fully and adroitly bring their food towards their mouth ; 
 and when near, pounce upon it with eagerness. To make 
 up for the want of teeth, the mouth enlarges to receive 
 the food brought to it by the arms that have twined around 
 the sacrifice. The red worm that tinges the mud of the 
 Thames appears to be the dainty dish they like best to 
 have set before them. Dr. Mantell saw the lasso of a 
 polype thrown over two worms at the same time; yet 
 they could not escape, and lost all power of motion. 
 
 Dr. Johnston states : " Sometimes it happens that two 
 polypes will seize upon the same worm, when a struggle for 
 the prey ensues, in which the strongest gains, of course, 
 the victory ; or each polype begins quietly to swallow his 
 portion, and continues to gulp down his half, until the 
 mouths of the pair near, and come at length into actual 
 contact. The rest that now ensues, appears to prove that 
 they are sensible of their untoward position, from which 
 
472 THE MICROSCOPE. 
 
 t&ey are frequently liberated by the opportune break of 
 the \vorrn, when each obtains his share ; but should the 
 prey prove too tough, woe to the unready! the more 
 resolute dilates the mouth to the requisite extent, ana 
 deliberately swallows his opponent ; sometimes partially, 
 so as, however, to compel the discharge of the bait ; while 
 at other times the entire polype is engulfed ! But a polype 
 IB no fitting food for a polype, and his capacity of endurance 
 saves him from this living tomb ; for, after a time, when 
 the worm is sucked out of him, the sufferer is disgorged 
 with no other loss than his dinner." 
 
 The organ of prehension, which is called the hasta, con- 
 sists of a sac opening at the surface of the tentacle, within 
 which, at the lower portion, is placed a saucer- shaped 
 vesicle, supporting a minute ovate body, which again bears 
 a sharp calcareous piece called the sagitta, arrow. This 
 can be pushed out at the pleasure of the animal, serving 
 to roughen the surface of the tentacle, and afford a much 
 firmer hold of its living prey. The polype increases 
 rapidly: a portion of the body swells, a young one puts 
 forth its head from the part, its arms begin to grow, it 
 then is industrious in catching food ; its body, communi- 
 cating with that of its parent and participating in the 
 fears and actions of its progenitor, is finally cast off to 
 wander the world of waters. Sometimes, ere yet free from 
 parental attachment, it has two generations on its own 
 body. Four or five offspring are thus produced weekly. 
 But the most extraordinary circumstance in respect to this 
 creature is thus described by M. Trembley : " If one of 
 them be cut in two, the fore part, which contains the head 
 and mouth and arms, lengthens itself, creeps, and eats on 
 the same day. The tail part forms a head and mouth at 
 the wounded end, and shoots forth arms more or less 
 speedily, as the heat is favourable. If the polype be cut 
 the long way through the head, stomach, and body, each 
 part is half a pipe, with half a head, half a mouth, and 
 some of the arms at one of its ends. The edges of these 
 lialf pipes gradually round themselves and unite, beginning 
 at the tail end ; and the half mouth and half stomach of 
 each becomes complete. A polype has been cut lengthways 
 at seven in the morning, and in eight hours afterwardi 
 
TUBULARIAD.E. 473 
 
 each part has devoured a worm as long as itself." Still 
 more wonderful is the fact, that if turned inside out, 
 the parts at once accommodate themselves to their new 
 condition, and carry on all their functions as before 
 the accident. Indeed, this animal seems so peculiarly 
 endowed with the germs of vitality in every part of its 
 body, that it may be cut into ten pieces, and everyone 
 will" become a new, perfect, living animal. This seems 
 bordering on the vegetable kingdom, in which it is 
 common to propagate by means of slips from the mature 
 shrub. 
 
 The best known of the British species are Hydra vul- 
 garis, Common polype, H. viridis, Green polype, H. Fusca, 
 Brown polype, H. verrucosa, and H. lutea. 
 
 Every reflecting person who reads even the slight 
 sketch we have given of this polype must be struck \vitl 
 astonishment at a creature so primitive in structure, pos- 
 sessing the actions, sensations, and powers of higher 
 organised beings. The stomach is but one simple Struc- 
 tureless membrane or cell, the external surface-cells form- 
 ing a kind of double skin, the inside a mere wall of cells 
 running crosswise, possessed of a velvet-like surface, and 
 red or brown coloured grains held together by a glutinous 
 substance. This singular formation, with some of the 
 functions of animal life, has led to many learned surmises 
 and discussions tending to the most important results in 
 the science of physiology. 
 
 TUBULARIAD"^. The Tubular or Vaginated Polypes are 
 of an arborescent appearance ; the animals live near the 
 ends of branches, and are found attached to stones, sea- 
 weeds, and shells. 1 The Tubularia indivisa, " Individed 
 tubes," are found on shells, with a living head resembling 
 a fine scarlet cluster of blossoms. Ellis says, " they seem 
 part of an oat-straw with the joints cut off." At the summit 
 protrudes the scarlet-coloured polypes, well furnished with 
 tentacula, and connected with a pinkish fluid that fills tha 
 tubes. It was in these that Dr. Roget discovered the 
 singular peculiarity of a circulation, similar to that seen. 
 in many plants. He says, " In a specimen of the Tubu- 
 
 (1) These pro frronped with Hydroida, and at the head of the family stand 
 Van Beneclcn'a Hydractinia ; and Gaertner's Coryne. 
 
474 THE MICROSCOPE. 
 
 laria indivisa, when magnified one hundred times, a 
 current of particles was seen within the tubular stem of 
 the polype, strikingly resembling, in steadiness and 
 continuity of its stream, the vegetable circulation in 
 the chara. Its general course was parallel to the slightly 
 spiral lines of irregular spots on the surface of the tube, 
 ascending on the one side, and descending on the other ; 
 each of the opposite currents occupying one-half of the 
 circumference of the cylindric cavity. At the knots, or 
 contracted parts of the tube, slight eddies were noticed 
 in the currents j and at each, end of the tube the par- 
 ticles were seen to turn round, and pass over to the other 
 side. 
 
 " The particles carried by it present an analogy to those 
 of the blood in the higher animals of one side, and of the 
 sap of vegetables on the other. Some of them appear to be 
 derived from the digested food, and others from the 
 melting down of parts absorbed ; but it would be highly 
 interesting to ascertain distinctly how they are produced, 
 and what is the office they perform, as well as the true 
 character of their remarkable activity and seemingly 
 spontaneous motions ; for the hypothesis of their indi- 
 vidual vitality is too startling to be adopted without good 
 evidence." 
 
 Respecting the singular property of the head dropping 
 off, Tubularia indivisa, Sir J. G. Dalyell observes, " The 
 head is deciduous, falling in general soon after recovery 
 from the sea. It is regenerated at intervals of from ten 
 days to several weeks, but with the number of external 
 organs successively diminishing, though the stem is always 
 elongated. It seems to rise within this tubular stem front 
 below, and to be dependent on the presence of the internal 
 tenacious matter with which the tube is occupied. A head 
 springs from the remaining stem, cut off very near the 
 root ; and a redundance of heads may be obtained from 
 artificial sections. Thus, twenty-two heads were produced 
 through the course of 150 days from three sections of a 
 single stem." 
 
 Included in this family are the T. ramous, T. ramea, the 
 "branched pipe-coralline, with its dark brown stem termi- 
 nating in clusters of red and yellow polyps ; and the 
 
TUB ULAKIAD^E. 
 
 475 
 
 Hermia Glandulosa of Dr. Johnston, who says " I found 
 the name in Shakspeare : 
 
 What wicked and dissembling glass of mine, 
 Made me compare with Hermia's sphery eyne ?' " 
 
 The fancy that the glands which surround the heads 
 were the guardians of the animal, its " sphery eyne," sug- 
 gested the name here adopted. 
 These polypes are adherent by 
 a tubular fibre, and creep along 
 the surface of the object on which 
 they grow ; they are seldom 
 an inch in height, irregularly 
 branched; the stem filiform, 
 tubular, horny, sub-pellucid, 
 wrinkled, and sometimes ringed 
 at intervals, especially at the 
 origin of the branches, each of 
 which is terminated with an 
 oval or club-shaped head of a 
 reddish colour, and armed with 
 short scattered tentacula,tipped 
 with a globular apex. The ends 
 of the branches are not perfo- 
 rated, but completely covered 
 with a continuation of the horny 
 sheath of the stem. The animal 
 can bend its armed hands at 
 will, or give to any separate ten- 
 taculum a distinct motion and 
 direction ; but all its move- 
 ments are very slow. 
 
 The beautiful little Coryne Coryne. "2, A tubercle detached, 
 
 stauridia, "Slender coryne," "* ""tfUfied 200 diameters, 
 (fig. 232, No. 1), is thus described by Mr. Gosse : " It ww 
 found by me adhering to the footstalk of a Rhodymenia, 
 about which it creeps in the form of a white thread ; by 
 placing both beneath the microscope, this thread appeared 
 cylindrical and tubular, perfectly transparent, without 
 wrinkles, but permeated by a central core, apparently cel- 
 lular in texture, and hollow ; within which a rather slow 
 
 Fig. 232. 
 Coryne Stauridia, Slender 
 
476 THE MICROSCOPE. 
 
 circulation of globules, few in number, and remote, is per- 
 ceived. It sends off numerous branches ; the terminal 
 head of which is oblong, cylindrical, rounded at the end. 
 At the extreme point are fixed four tentacula of the usual 
 form, long, slender, and furnished with globular heads ; 
 one of which is shown at No. 2, detached, and more highly 
 magnified. It is much infested with parasites : a vorticella 
 grows on it, and a sort of vibrio ; the latter in immense 
 numbers, forming aggregated clusters here and there ; 
 the individuals adhering to each other, and projecting in 
 bristling points in every direction. These animalcules 
 vary in length ; some being as long as l-80th of an inch, 
 with a diameter of l-7000th of an inch. They are straight, 
 equal in thickness throughout, and marked with distinct 
 transverse lines j they bend themselves about with consi- 
 derable activity, and frequently adhere to the polype by 
 one extremity, while the remainder projects freely." 
 
 Some of this family attain a considerable size ; the 
 Corymorpha nutans, one of the most beautiful of the 
 group, attains a length of four inches and a half. Of 
 the beauty of its appearance, Forbes, who discovered it in 
 the British seas, speaks in the following terms : " When 
 placed in a vessel of sea- water, it presented the appearance 
 of a beautiful flower. Its head gracefully nodded (whence 
 the appropriate specific appellation given it by Sars), bend- 
 ing the upper part of its stem. It waved its long tentacula 
 to and fro at pleasure, but seemed to have no power of 
 contracting them. It could not be regarded as by any 
 means an apathetic animal, and its beauty excited the 
 admiration of all who saw it." The general colour of the 
 creature is a delicate pink, with longitudinal lines of 
 brownish or red dots. The tentacles are very numerous 
 and long, and of a white colour ; and the ovaries, which 
 are situated immediately above the circle of tentacles, 
 are orange. Most of the Tubulariadce inhabit the sea ; 
 one species, the CordylopJiora lacustris, is found in the 
 dock of the Grand Canal, Dublin, in water which is per- 
 fectly fresh. 
 
 SERTULARIAD.E. This interesting and beautiful family 
 of pclypes derive their name from their plant-like appear- 
 ance, and are readily attainable on our own sea-shores. 
 
8ERTULARIAD.E. 477 
 
 Linnaeus made a large genus of them ; but Lamarck con- 
 siderably reduced his classification. There are seventeen 
 British species, which Dr. Fleming proposes to divide into 
 two groups, \vith stems simple or compound. 
 
 The tentacles of Sertularia 
 are abundantly supplied with 
 cilia ; the cells are pitcher- 
 shaped, arranged alternately, 
 or in pairs obliquely, not 
 exactly opposite, on the stem 
 and branches of the poly- 
 pidom, which is horny. La- 
 mouroux classed with this 
 family Thoa; of which there 
 have been several kinds found 
 iu Great Britain. The name 
 is supposed to be derived from 
 the Greek word for sharp; 
 but we think, with Dr. John- 
 ston, that it more probably Fig> 33._si C kie-Coraiiine. %*- 
 is a mis-spelling of Thoe, one tario, Poiypuiom of. 
 
 of the Nereids, nymphs of the sea. They are generally 
 of a brown and yellow colour, branched, and from an inch 
 and a half to six inches in height. 
 
 Sertularia pumila. This is parasitic, and spreads its 
 brown-coloured shoots over various fuci and sea-shells; 
 but rarely attains more than half an inch in height. 
 Stewart says : " This species, and probably many others, 
 in some particular states of the atmosphere, emits a phos- 
 phorescent light in the dark. If a leaf of the fucus 
 serratus, with Sertularia upon it, receives a smart stroke 
 in the dark, the whole is most beautifully illuminated 1 , 
 every denticle seeming to be on fire." 
 
 On the south-eastern coast of England the most common 
 kind found is the Sertularia setacea, or operculata, Seahair- 
 Coralline : it reaches from six inches and upwards in 
 height, and grows in tufts, like bunches of hair. The 
 stem and branches seem composed of separate pieces, 
 fitting accurately into each other, and terminate in a 
 star-like head, from which radiate the tentacles. Mr. 
 Lister was observing a living specimen, when a little 
 
THE MICROSCOPE. 
 
 globular animalcule swam rapidly by one of the expanded 
 polypes; the latter immediately contracted, seized the 
 globule, and brought it to the mouth or central opening 
 by its tentacula ; these gradually opened again, with 
 
 the exception of one, which 
 remained folded, with its ex- 
 tremity on the animalcule. 
 The mouth instantly seemed 
 filled with cilia, which, closing 
 over the prey, was carried 
 slowly down its stomach ; 
 here it was imperfectly seen, 
 and soon disappeared. 
 
 Appertaining to this family 
 are Dr. Fleming's Thuiarea, 
 so named by him from their 
 resemblance to a cedar-tree; 
 some kinds look more like a 
 knobbed thornstick with a 
 bottle-clearer at the top ; 
 others resemble a fir-tree. 
 Antennularia are so called 
 from their resemblance to a 
 lobster's antenna. They are 
 plentiful on the north-eastern 
 coast of England and the 
 coast of Ireland, brown in 
 colour, and covered with 
 i, piumuiaria pinnata, Feather polype- hair-like little branches; and 
 
 2, Doris tubercttlata, Sea slug. ag t he hairy process IS COn- 
 
 tinued up its jointed stem, it is sometimes denominated 
 Sea-beard. Dr. Hassall's Coppinia is another very interest- 
 ing species. 
 
 The Piumuiaria, so named from their shoots and 
 offsets being plumose, are an extensive and beautiful 
 family. Professor Grant thus describes the Piumuiaria 
 falcata : " The Sickle Coralline is common in the deeper 
 parts of the Frith of Forth ; its vesicles are very numerous, 
 and its ova are in full maturity at the beginning of May. 
 The ova are large, of a light-brown colour, semi-opaque, 
 nearly spherical, composed of minute transparent granules, 
 
 Fig. 234. 
 
BERTULARIAD2B. 479 
 
 ciliated on the surface, and distinctly irritable. There 
 are only two ova in each vesicle ; so that they do not 
 require any external capsules, like those of the Campanu- 
 laria, to allow them sufficient space to come to maturity. 
 On placing an entire vesicle, with its two ova, under the 
 microscope, we perceive through the transparent sides the 
 cilia vibrating on the surface of the contained ova, and the 
 currents produced in the fluid within by their motion. 
 When we open the vesicles with two needles, in a drop of 
 sea- water, the ova glide to and fro through the water, at 
 first slowly, but afterwards more quickly, and their cilia 
 propel them with the same part always forward. They 
 are highly irritable, and frequently contract their bodies 
 so as to exhibit those singular changes of form spoken of 
 by Cavolini. These contractions are particularly observed 
 when they come in contact with a hair, a filament of 
 conferva, a grain of sand, or any minute object ; and they 
 are likewise frequent and remarkable at the time when 
 the ovum is busied in attaching its body permanently to 
 the surface of the glass. After fixing themselves, they 
 become flat and circular, and the more opaque parts of 
 the ova assume a radiated appearance ; so that they now 
 appear, even to the naked eye, like so many minute grey- 
 coloured stars, having the interstices between the rays 
 filled with a colourless transparent matter, which seems to 
 harden into horn. The grey matter swells in the centre, 
 where the rays meet, and rises perpendicularly upwards 
 surrounded by the transparent horny matter, so as to form 
 the trunk of the future zoophyte. The rays first formed 
 are obviously the fleshy central substance of the roots ; 
 and the portion of that substance which grows perpen- 
 dicularly upwards, forms the fleshy central part of the 
 stem. As early as I could observe the stem, it was open 
 at the top ; and when it bifurcated to form two branches, 
 both were open at their extremities ; but the fleshy central 
 matter had nowhere developed itself as yet into the form 
 of a polype. Polypes, therefore, are not the first formed of 
 this zoophyte, but appear long after the formation of tho 
 root and stem, as the leaves and flowers of a plant." 
 
 Attached tofucus and shells in abundance on the southern 
 coast of England, may be found the Plumularia cristata. It 
 
480 THE MICROSCOPE. 
 
 is affixed by a horny, branching, interlacing, tubular fibre 
 to the object on which it grows. At different parts there 
 are plumose shoots, usually about an inch in height. The 
 cells are of a yellow colour, set in the stalk, of a bell- 
 shape, and are compared to the flower of the lily of the 
 valley ; the rim is cut into eight equal teeth ; the polype 
 minute and delicate, tentacles ten and annulate, with a 
 mouth infundibuliform in shape. 
 
 " Each plume," says Mr. Lister, in reference to a speci- 
 men of this species, " might comprise from 400 to 500 
 polypes ;" " and a specimen," writes Dr. Johnston, " of no 
 unusual size, before me, has twelve plumes, with certainly 
 not fewer cells on each than the larger number mentioned : 
 thus giving 6000 polypes as the tenantry of a single poly- 
 pidom ! Now, many such specimens, all united too by a 
 common fibre, and all the offshoots of one common parent, 
 are often located on one sea- weed, the site then of a popu- 
 lation which nor London nor Pekin can rival." 
 
 Plumularia pinnata, " Feather polyp," (represented mag- 
 nified in fig. 234, No. 1,) is as remarkable for the ele- 
 gance of its form, as its likeness to the feather of a pen. 
 It serves not among the denizens of the deep the same 
 purpose as its earthly prototype j nature writes her 
 works in hieroglyphics formed by the objects themselves. 
 It is plumous, and the cells in a close row, cup-like, 
 and supported on the under side by a lengthened spinous 
 process. 
 
 An interest pervades the valuable work of Dr. Johnston, 
 arising from the circumstance that the plates and wood- 
 cuts which adorn the volume are, with few exceptions, 
 engraved from drawings made for it by Mrs. Johnston, 
 who also engraved several of them ; and the Doctor states, 
 he could not have undertaken the history without such 
 assistance. From this devotion too, and understanding of 
 the subject, it was natural, when an opportunity presented 
 itself, to write in the catalogue of Zoophytes a lasting 
 memorial of his " colleague :" and thus is written the 
 graceful compliment of the beautiful Plumularia Catha- 
 rina : " Catharine's Feather," whose stem is plumous, pinnse 
 opposite, bent inwards; cells distant, campanulate, with 
 an even margin ; vesicles scattered, pear-shaped, sm ooth. 
 
SERTULARIADJE. 481 
 
 Found iii old shells, corallines, <fcc., iii deep water; in 
 Frith of Forth and in Berwick Bay, by Dr. Coldstream. 
 
 The sub-families, Campanularia and Laomedea, are also 
 frequently found on our shores ; they possess a simple 
 circle of cilia on their feelers or arms, with pitcher- 
 shaped cells on stalks that branch, twist, or climb on an 
 axis. 
 
 Campanularia volubilis, " Twining polype," is the com- 
 monest of the family : it is parasitical, and infests the an- 
 tennae of crabs ; its stem is filiform, and at the end of 
 its slender branches are situated the cells containing the 
 polypes. The polype itself is slender when protruded, 
 somewhat like Plumularia pinnata, and becomes dilated 
 at the base into a sort of foot which spreads over the dia- 
 phragm ; widening again at the top, where it fills the 
 mouth of the cell, and gives origin to about twenty slender 
 tentacula, set in two or three series. From the central 
 space, which is surrounded by tentacles, a large fleshy 
 mouth protrudes, somewhat funnel-shaped, with lips, en- 
 dowed with the power of protrusion and contraction; 
 these appear to be very sensitive. Mr. Gosse found the 
 species in great abundance round Small-mouth Caves. 
 
 The Campanularia gelatinosa and its beautiful bell- 
 shaped cells, out of which the animals protrude, giving the 
 semblance of a green flower on a delicate pink stalk. It 
 is indeed an interesting object, and currents may be 
 seen in its tubes. Dr. Johnston says, " On Saturday, May 
 29th, 1837, a specimen of Campanularia gelatinosa was 
 procured from the shore ; and after having ascertained 
 that the polypes were active and entire, it was placed 
 in a saucer of sea- water. Here it remained undisturbed 
 until Monday afternoon, when all the polypes had dis- 
 appeared. Some cells were empty, or nearly so ; others 
 were half-filled with the wasted body of the polype, 
 which had lost, however, every vestige of their tentacula. 
 The water had become putrid, and the specimen wag 
 therefore removed to another vessel with pure water, and 
 again set aside. On examining it on the Thursday, June 
 1st, the cells were evidently filling again, although no 
 tentacula were visibly protruded ; but on the afternoon of 
 Friday, June 2d, every cell had its polype, complete, aad 
 
 1 1 
 
482 THE MICROSCOPE. 
 
 displayed in the greatest perfection. Had these singular 
 facts been known to Linnaeus, how eagerly and effectively 
 would he have impressed them into the support of his 
 favourite theory ! Like the flowers of the field, the heads, 
 or ' flores,' of these polypidoms expand their petaloid 
 arms, which after a time fall, like blighted blossoms off a 
 tree ; they do become ' old in their youth,' and, rendered 
 hebetous and unfit for duty or ornament by age or acci- 
 dent, the common trunk throws them off, and supplies its 
 wants by ever-young and vigorous growths. The pheno- 
 mena are of those which justly challenge admiration, and 
 excuse a sober scepticism, so alien are they to all we are 
 accustomed to observe in more familiar organisms. Faithful 
 observation renders the fact undeniable ; but besides that, 
 a reflection on the history of the Hydra might almost 
 have led us to anticipate such events in the life of these 
 Zoophytes. ' Verily, for mine own part/ observes Baker, 
 'the more I look into Nature's works, the sooner am 
 I induced to believe of her even those things that seein 
 incredible.' " 
 
 ACTINIAD^:. All persons accustomed to wander by the 
 sea-shore must have admired the livid green, dark little 
 jelly-masses adhering to the rocks, called Actinia, from a 
 Greek word signifying a ray, and left in some little pool 
 by the ebbing tide, living as they do principally within 
 high and low water mark, and expanding their broad sur- 
 faces and fringing feelers to the finger of inquisitive youth, 
 so often thrust into the centre, to feel the effect of the 
 suction and rasping, as the poor animal draws itself up in 
 the form of a little fleshy hillock. 
 
 Some few years ago it might have been necessary to 
 explain what we meant by an Actinia, or " Sea-anemone '* 
 thanks to the universal distribution of aquaria, this 
 beautiful class of animals is no longer unfamiliar to the 
 world. Nevertheless, much as people read, and hear, and 
 write, and observe in the matter, we do not hesitate to say 
 that the natural arrangement of these animals is as little 
 known in the world of naturalists, as their very existence 
 was a short time ago to the world at large. A familiar 
 instance of this position may be given in a few words. 
 Dr. Johnston (Hist. Urit. Zooph.) describes three distinct 
 
ACTIXIADJ!. 
 
 483 
 
 Actinia;, under the names of A. troglodytes (the Cave- 
 dweller), A. viduata, and A. Anguicoma (the Snaky- 
 locked). Mr. Gosse, in his Devonshire Coast, makes A. 
 viduata synonymous -with A. anguicoma ; and gives a 
 drawing and a description of an anemone which he calls 
 anguicoma, and which closely resembles undoubted 
 specimens of Johnston's A. troglodytes. Many objections 
 might be taken to Mr. Gosse's description of species, which 
 he makes out from the number of their tentacles, although 
 found in company with each other, and, as he justly re- 
 marks, are of " the same size and form." 
 
 Of the voracity of the actinia many remarkable state- 
 ments have been made known; it may nevertheless be 
 kept in the aquarium for many months, if supplied with 
 
 1 Actinia rubra Sea marigold, near which is one shown retracted. 2, Actinia 
 bellis, Daisy sea-auemone (side view). 
 
 water containing particles of organic matter. Although 
 the several structures of actinia admit of being resolved 
 into two foundation membranes, an ectoderm and an en- 
 doderm, yet each of these, more especially the former, 
 manifests a tendency to differentiate into secondary layers, 
 so that several apparently distinct tissues are recognisable 
 in the body of the fully-formed animal. Both membranes 
 havo their free surfaces more or less covered with cilia 
 
484 THE MICROSCOPE. 
 
 and the margin of the disc is furnished with a series of 
 white or bright blue specks, which some observers believe 
 to be rudimentary organs of vision ; but the3 r are rather 
 to be regarded as sac-shaped prolongations of the outer 
 layer. A transverse section of the 
 body of the actinia exhibits two 
 concentric tubes, the outer being 
 constituted by the body-wall, and 
 the inner by the digestive sac. 
 The wide space which intervenes 
 between these tubes is divided by 
 a number of radiating partitions, or 
 "mesenteries," arriving at definite 
 intervals from the inner surface of 
 Fig. 236.-Actinia uiiis, seen the body wall. To the face of the 
 from above with its crown of mesenteries are attached the repro- 
 
 tentacles fully expanded. , . i i 
 
 ductive organs, which occur sa 
 
 thickened bands of a reddish tint, at certain periods 
 filled with ova. The animal has the power of effecting 
 considerable alterations of form, as well as of locomo- 
 tion ; although if well supplied with food it attaches 
 itself so firmly as not to be removed without laceration 
 of its base. 
 
 Allied to the family Actinias are those laminated, in- 
 verted pyramidal looking bodies, Fungia, commonly called 
 "Sea-mushrooms," often found in great variety. The 
 colour of the polypidom is white, of a flattened round 
 shape, made up of thin plates or scales, embedded in a 
 translucent jelly-like substance, and within which is a 
 large polype ; the foot-stalk, by means of which the 
 animal is attached to the rock whereon it lives, is of a 
 calcareous nature. Ellis says : "The more elevated folds 
 or plaits have borders like the denticulated edge of 
 needlework-lace. These are covered with innumerable 
 oblong vesicles, formed of a gelatinous substance, which 
 appear alive under water, and may be observed to move 
 like an insect. I have observed these radiating folds of 
 the animal, which secrete the lamella, and which shrink 
 between them when the animal contracts itself on being 
 disturbed. They are constantly moving in tremulous un- 
 dulations ; but the vesicles appeared to me to be air- 
 
ACTINIA. 
 
 485 
 
 Teasels placed along the edges of the folds, and the vesi- 
 cles disappeared when the animal was touched." 
 
 Fig. 237 
 
 1. Fungia agariciformis. 2, Alcyonium, Cydonium Mulleri. 3, 
 
 polypes protruding and tentacles expanded, others closed. 4, Zoantharit^ 
 viewed from above. 5, Madrepore, Abrotanoidc. 6, Madrepore, cell slightly 
 magnified, showing internal structure. 7, Corattidce; Corah 8, Coral, polypes 
 protruding from the cells. 9, Gorgonia nobttis, polypes expanded. 10, Tubi- 
 pora musica. 11, a tube of same, with polype expanded, and one cut longi- 
 tudinally to show internal structure. 12, Scrtularia, polypes protruded ; and 
 others withdrawn into polypidoms. 
 
486 THE MICROSCOPE. 
 
 MADREPORID.E. Madrepores, Mother- pores, "treo- 
 corals," differ from other corals in not having a small 
 skeleton, but one inducted by numbers of small cells for 
 the residence of the living animal : these are very visible 
 in the Madrepore muricata, when the polype is dead and 
 decomposed; but most distinct in the Oculina ramea, as 
 they are situated at the apparently broken stumps that 
 branch from the trunk of the skeleton (fig. 237, No. 5). 
 Every branch is seen to be covered with multitudes of 
 small pits or dots, scarcely visible to the unassisted vision ; 
 but, when viewed under the microscope, are found to be 
 cells of the most beautiful construction, remarkable alike 
 for their mathematical regularity and the exquisite fineness 
 of the materials employed in their composition. A mag- 
 nified drawing of a cell is given at No. 6. The living 
 polypes are exquisite objects for a low power ; their vary- 
 ing colours adding to the richness of the hues covering the 
 bed of the ocean. 
 
 ASTEROIDE^J. A group of Zoophytes received the name 
 of Asteroida from the polypes presenting the form of a 
 star. The fleshy mass is supported by hard calcareous 
 spicula ; some having thick branching processes, perform- 
 ing the part of the skeleton in the human frame. This 
 central internal support is usually denominated the axis. 
 The fleshy mass, or covering, is possessed of sensation, and 
 is ramified by vascular tubes and canals for the sustenance 
 of the animal, and carrying on its vital functions. In- 
 cluded in this genera are Gorgoniadce, Pennatulidce, Alcy- 
 onidce, Isidce, and Tubiporidas. 
 
 The term coral, or coralium, is restricted to the hard 
 structures deposited in the tissues or by the tissues of the 
 Actinozoa. The whole of this class, however, which are 
 thought to possess a framework called a " coral," are not 
 coralligenous. The Ctenophora, and several species, as the 
 soft-bodied non-adherent Zoantharia, deposit no coralium. 
 There are two kinds of such structure, one called the 
 " sclerobasic " coralium, a true tegumentary excretion, 
 formed by the successive growths from the outer surface of 
 the ocderon ; and another, the " sclerodermic " coralium, 
 deposited within the tissues of the animal. Two prin- 
 cipal modifications of form distinguish the sclerobasis : in 
 
A8TEROIDE.fi. 487 
 
 some it constitutes a free axis, virgate or primately divided 
 and varying in thickness ; in others it is attached, simple 
 or branched, and plant-like, as in Gorgonidce, from which 
 circumstance the name of " Sea-shrubs " has been applied 
 to them. In the Gorgonia we have, in addition to the 
 basal corallum, a deposition of tissue secretions, sclero- 
 derinic spicules appear within the substance of the in- 
 vesting membrane, and when the animal is dried, and the 
 soft parts washed away, a thin layer of calcareous spicules 
 is seen adhering to the horny sclerobasis. M. Valen- 
 ciennes made out five kinds of spicules, or sclerites, which 
 he severally designates capitate, fusiform, massive, stellate, 
 and squanious. These spicules form interesting objects 
 for the microscope, mounted dry or in balsam. "The 
 parts of a typical coralite are these : first, an outer wall, or 
 * theca,' somewhat cylindrical in form, terminating distally 
 in a cup-like excavation, or ' calice,' and having its central 
 axis traversed by a columella. The space between this 
 and the theca is divided into loculi, or chambers, by a 
 number of radiating vertical partitions, the septa. These 
 do not, in certain instances, quite reach the columella, but 
 are broken up into upright pillars or pali, arranged in one, 
 two, or more circular rows termed * coronets ; ' all of 
 which are best brought into view by transverse section." 
 Longitudinal division of a corallite shows certain modifi- 
 cations and changes in the partitions, or dissepiments ; and 
 the septa are seen to be covered with " styliform or echi- 
 nulate processes," which meet to form " synapticula3 or 
 transverse props, extending across the loculi like the bars 
 of a grate." Nevertheless, there is no difficulty in recog- 
 nising the close resemblance that sucn an organism pre- 
 sents to the typical Actinia, and they have accordingly 
 been classed with the Actinozoa. 
 
 The Gorgonidob are permanently fixed, as are many other 
 corallitic actinozoa, and multiply by continuous gemma- 
 tion. As to their muscular system, most of them appear 
 to be well endowed in this particular. Fennatulidce pos- 
 sess so much muscular contractibility, that Mr. Darwin 
 relates, that on the south coast of America he observed 
 " a Sea-pen which, on being touched, forcibly drew back 
 into the sand some inches of its compound, polypi-covered 
 
488 THE MICROSCOPE. 
 
 mass." The muscular fibre, however, is wanting in those 
 distinct transverse striae, so fully developed in the muscle 
 of the higher orders of animals. 
 
 The ova of the compound Actinias are of a rounded 
 form, often brilliantly coloured, and their embryos, by a 
 series of gradual changes, finally assume the appearance 
 and condition of the parent. Milne Edwards, to whom 
 we are indebted for most of our knowledge of the repro- 
 ductive processes of aotinozoa, insists on the necessity of 
 distinguishing between that of gemmation and fissura- 
 tion, the polype-bud at first being no more than a pro- 
 tuberance from the parent "enclosing a caecal diverticulum 
 of the somatic cavity." Both simple and composite Fun- 
 gidce occur, and multiply by lateral gemmation. 
 
 The Gorgonidce differ from all other Alcyonaria in 
 having an erect branching caenosarc so firmly rooted that 
 they are reputed to rival oaks in size ; but it is doubtful 
 whether they ever attain to a height of more than five or 
 six feet. 
 
 Pennatulidce. This family derives its name from 
 penna, a quill, and the spicula closely resemble a pen, one 
 of which is represented in fig. 239, No. 1. The polypes 
 are fleshy white, provided with eight rather long retractile 
 tentacula, beautifully ciliated on the inner aspect with two 
 series of short processes, and strengthened moreover with 
 crystalline spicula, there being a row of these up the 
 stalk : the series of smaller processes are ciliated. The 
 mouth, in the centre of the tentacula, is somewhat 
 angular, and bounded by a white ligament, a process from 
 which encircles the base of each tentaculum, and thus 
 seems to issue from an aperture. The ova lie between the 
 membraneous part of the pinnae ; they are globular, of a 
 yellowish colour, and by a little pressure can be made to 
 pass through the mouth. 
 
 Dr. Grant writes : "A more singular and beautiful 
 spectacle could scarcely be conceived than that of a deep 
 purple Pennatula phosphorea, with all its delicate trans- 
 parent polypes expanded and emitting their usual brilliant 
 phosphorescent light, sailing through the still and dark 
 abyss, by the regular and synchronous pulsations of the 
 minute fringed arms of ,the polypes." The power of 
 
TUBIPORID-E. 489 
 
 locomotion is doubted by other writers, and the pale blue 
 light is said only to be emitted when under the influence 
 of some degree of irritation. 
 
 Alcyonaria. Actinozoa, in which each polype is fur- 
 nished with eight primately fringed tentacles. Corallum 
 sclerobasic or spicular. 
 
 Alcyonium digitatum, " Fingered Alcyonium " (Fig. 
 237, No. 2). The French call it Main de Her, "sea- 
 hand," the Germans Diebshand, "thief's hand." Some- 
 times they are very small ; but when larger are named by 
 the fishermen Cows -paps, and Dead Heris Hands. The 
 mass, at first repulsive, when placed in sea-water gradually 
 expands into delicately pellucid polypes, with crowns of 
 beautiful tentacula. The cells occupied by the polypes are 
 placed at the terminations of canals which run through 
 the polypidom, and which, by their union with each 
 other, serve to maintain a communication between the in- 
 dividual polypes constituting the mass. The rest of the 
 polypidom is made up of a transparent gelatinous sub- 
 stance, containing calcareous spicula, and pervaded by 
 numerous small fibres, which form a sort of irregular net- 
 work. Alcyonidce aifc always attached to submarine 
 bodies. The species already mentioned is exceedingly 
 common round our coasts ; so much so that, as Dr. John- 
 ston says, " scarce a shell or stone can be dredged from 
 the deep that does not serve as a support to one or more 
 specimens." 
 
 The ova, as Professor Grant remarks, placed under the 
 microscope, and viewed by transmitted light, appear as 
 opaque spheres surrounded by a thin transparent margin, 
 which increase in thickness as the ova begin to grow, 
 and such of the ova as lie in contact unite and grow as 
 one ovum. A rapid current in the water immediately 
 around each ovum, drawing along with it all the loose 
 particles and floating animalcules, is distinctly seen moving 
 with an equal velocity as in other ciliated ova ; and a 
 zone of very minute vibrating cilia is quite perceptible, 
 surrounding the transparent margin of all the ova. 
 
 TUBIPORID.E. To this family belongs the handsome 
 Tubiporamusica, "Organ-pipe Coral" (fig. 237, No. 10), the 
 polypidom of which is composed of parallel tubes, united by 
 
490 THE MICROSCOPE. 
 
 lateral plates, or transverse partitions, placed at regular dis- 
 tances; in this manner large masses, consisting of a congeries 
 of pipes or tubes, are formed. When the animals are 
 alive, each tube contains a polype of a beautiful bright- 
 green colour, and the upper part of the surface is covered 
 with a gelatinous mass, formed by a confluence of the 
 polypes. This species occurs in great abundance on the 
 coasts of New South Wales, of the Eed Sea, and of the 
 Molucca Islands, varying in colour from a bright red to a 
 deep orange. It grows in large hemispherical masses, from 
 one to two feet in circumstance, which first appear as 
 small specks adhering to a shell or rock ; as they increase, 
 the tubes resemble a group of diverging rays, and at length 
 other tubes are produced on the transverse plates, thus 
 filling up the intervals, and constituting one uniform 
 tubular mass \ the surface being covered with a green 
 fleshy substance beset with stellate polypes. 
 
 Mr. Dana, who devoted much time to the examination 
 of the corals of the Pacific, thus writes of their diversities 
 of form and character : " Trees of coral are well known ; 
 and, although not emulating in size the oaks of our forests 
 for they do not exceed six or eight feet in height they 
 are gracefully branched, and the whole surface blooms with 
 coral polypes in place of leaves and flowers. Shrubbery, 
 turfts of rushes, beds of pinks, and feathery mosses, are 
 most exactly imitated. Many species spread out in broad 
 leaves or folia, and resemble some large-leaved plant just 
 unfolding ; when alive, the surface of each leaf is covered 
 with polype flowers. The cactus, the lichen, clinging to 
 the rock, and the fungus in all its varieties, have their 
 numerous representatives. Besides these forms imitating 
 vegetation, there are gracefully-modelled vases, some of 
 which are three or four feet in diameter, made up of a 
 network of branches and branchlets and sprigs of flowers. 
 There are also solid coral hemispheres like domes among 
 the vases and shrubbery, occasionally ten or even twenty 
 feet in diameter, whose symmetrical surface is gorgeously 
 decked with polype-stars of purple and emerald green." 
 
 Nothing can be more impressive than the manner in 
 which these diminutive creatures carry out their stupen- 
 dous undertakings, which we denominate instinct, intelli- 
 
AC A LI: MM:. 491 
 
 gence, or design. Commencing betimes from a depth of a 
 thousand or fifteen hundred feet, they work upwards in a 
 perpendicular direction ; and on arriving at the surface 
 form a crescent, presenting the back of the arch in that 
 direction from which the storms and winds generally pro- 
 ceed : by which means the wall protects the busy millions 
 at work beneath and within. These breakwaters will re- 
 sist more powerful seas than if formed of granite ; rising 
 as they do in a mighty expanse of water, exposed to the 
 utmost powers of the heavy and tumultuous billows that 
 eternally lash against them. 
 
 As we glance at the map of the world, and think of the 
 profusion of fragrant vegetation and delicious food almost 
 spontaneously produced on the lovely sunny islands of the 
 broad Pacific, how startling does it seem, when we are 
 told that these islands, bearing on their bosoms gardens of 
 Eden, are entirely formed by the slow-growing corals, 
 which, rising up in beautiful and delicate forms, displace 
 the mighty ocean, defy its gigantic strength, and display a 
 shelly bosom to the expanse of day ! The vegetation of 
 the sea, cast on its surface, undergoes a chemical change ; 
 the deposit from rains aids in filling up the little gaping 
 catacomb, the fowls of the air and the ocean find a resting 
 place, and assist in clothing the rocks ; mosses carpet the 
 surface, seed brought by birds, plants carried by the 
 oceanic currents, animalcules floating in the atmosphere, 
 live, propagate, and die, and are succeeded, by the assist- 
 ance their remains bestow, by more advanced vegetable and 
 animal life : and thus generation after generation exist and 
 perish, until at length the coral island becomes a paradise 
 filled with the choicest exotics, the most beautiful birds 
 and delicious fruits, among which man may indolently 
 revel to the utmost desire of his heart. 
 
 ACALEPHJE. In great variety of form and colour, 
 swimming freely about the waters of the ocean, are found 
 in abundance th beautiful Acalephce. Some of them 
 have a remarkable stinging property, from which circum- 
 stance they derive their name of Sea-nettles ; others, from 
 their gelatinous nature, are known as Sea-jelly, or Jelly- 
 fish. 
 
 These interesting animals were first arranged in three 
 
492 THE MICROSCOPE. 
 
 orders : A. stabiles (fixed), A. liber ce (free), and A. Jiydro- 
 staticce (hydrostatic). Cuvier classed them in two orders : 
 A. simplices and A. hydrostaticcv. They 
 are now, however, divided differently, 
 and arranged in groups according to the 
 peculiar mode by which they effect their 
 locomotion. A very interesting point of 
 connexion between this class and the 
 preceding is the interchange of form. 
 Some of the Zoophyta, as the Tubula- 
 riadce and the Campanulariadce, give 
 birth to a progeny which are in every 
 respect Naked-eyed Medusae; while, on 
 the other hand, the young of the Medusae 
 are in their earlier stages stationary 
 
 The Medusae spread on the surface of the water a beau- 
 ful jelly-like mass, in form resembling an umbrella ; and, 
 by a continual contraction and opening out of this, they 
 swim freely about (Plate IX. c, d, e, h). They are all 
 more or less 1 phosphorescent. The Iteroe, one of the family 
 Ctenophora, propel themselves with active ciliated arms. 
 The Physalidoe have an organ common to fishes, swim- 
 ming bladders, by filling or emptying which they rise or 
 sink, and move along in their watery home. 
 
 The Medusoid family, Lucernaridce, has, from a mis- 
 taken view of its organization, been referred to the class 
 Actinozoa : Milne-Edwards has, however, placed it in a 
 sub-class, under the name of Podactinaria. In the 
 Lucernaridce the body is cup-shaped, about an inch in 
 height, terminating in a short foot-stalk. Round the 
 distal margin of the cup arise a number of short tentacles, 
 which are disposed in eight or nine turfts ; in Carduella 
 they form one continuous series. Their free extremities 
 appear sucker-like, and the whole organism is semi-trans- 
 parent, of a gelatinous consistence, and variously coloured. 
 The cup, viewed from above, presents in its centre a four- 
 lobed mouth, which is seen to form the free extremity of 
 a distinct polypite, occupying the axis of the entire 
 hydrosoma. Its gastric region exhibits a number of 
 tubular filaments, arranged in vertical rows dipping into 
 
LUCERNAKID^E. 493 
 
 the digestive cavity. The space between the polypite-wall 
 and the inner surface of the cup is equally divided. A 
 circular sinus has its course beneath the insertion of the 
 tentacles. By means of a band of muscular fibres which 
 transverse its margin, and another set which radiate 
 towards the polypite, the distal extremity of the cup can 
 be folded or drawn inwards. It has been observed to 
 detach itself, and swim in an inverted position by the 
 slowly repeated movements of its cup-like umbrella, thus 
 resembling Pelagia, a more active and permanently free 
 member of the same order. 
 
 Three families of the beautiful Lucernaridse, all of 
 which are at once distinguishable by their umbrella, may 
 be denned as follows : 
 
 Family 1, Lucernaridae. Reproductive elements de- 
 veloped in the primitive hydrosoma, without the inter- 
 vention of free zooids. Umbrella with short marginal 
 tentacles and a proximal hydrorhiza. Polypite single. 
 Family 2, Pelagidae. Reproductive elements developed in 
 a free umbrella, which either constitutes the primitative 
 hydrosoma, or is produced by fission from an attached 
 Lucernaroid. Umbrella with marginal tentacles. Poly- 
 pite single. Family 3, Rhizostomidae. Reproductive ele- 
 ments developed in free zooids produced by fission from 
 attached Lucernaroids. Umbrella without marginal ten- 
 tacles. Polypites numerous, modified, forming with the 
 genitalia a dendriform mass depending from the umbrella. 
 
 For a further description of this interesting species see 
 Professor Miiller's paper, Journal of Microscopical Science, 
 vol. iii. p. 265 ; or, Professor Greene's Manual of the 
 Coelenterata. 
 
 The flat circular horny disc forming the skeleton of 
 Propita gigantea, to the naked eye exhibits both radiating 
 and concentric markings ; and, when examined with a 
 power of 40 diameters, its upper surface is found, to be 
 furrowed, and two rows of small projecting spines occui 
 upon the ridges between the furrows, the ridges being the 
 radiating fibres above noticed. The under-surface, or that 
 to which the greater portion of the soft parts of the 
 animal are attached, is more deeply furrowed ; and pliose 
 or folds of the mantle fit accurately into the furrows, from 
 
494 THE MICROSCOPE. 
 
 which, they can easily be removed by the application of a 
 gentle force. The concentric markings have in all cases 
 small scalloped edges ; they occur at certain regular inter- 
 vals, and are so many indications of the lines of growth. 
 In the centre there is a circular depression ; and between 
 its circumference and that of the first concentric marking 
 there are eight flattened radii. If the under-surface be 
 examined with a power of 100 linear, the ridges will all 
 be found to have small jointed tubular processes like hairs 
 projecting from them. In no part of this horny tissue is 
 there a trace of a cellular or a reticular structure. 
 
 Wonderfully beautiful as are these creatures in form and 
 colour, the amount of solid matter contained in their 
 tissues is incredibly small. The greater part of their sub- 
 stance appears to consist of a fluid, differing little, if at 
 all, from the sea-water in which the animal swims ; and 
 when this is drained away, so extreme is the tenuity of 
 the membranes which contained it, that the dried residue 
 of a jelly-fish, weighing two pounds, which was exa- 
 mined by Professor Owen, weighed only thirty grains. 
 The transparency of the tissues render the whole of the 
 Acalepkce delightful objects for the microscope. 1 
 
 The Echiiiodermata belong to the division Annuloida, the 
 most familiar of examples of which are star-fishes and 
 sea-urchins. The labours of that distinguished comparative 
 anatomist and physiologist of Berlin, Johannes Miiller, 
 have made us better acquainted with the structure and 
 development of these remarkable animals than with those 
 of most classes of the animal kingdom. The series of feet 
 which protrude along certain fixed lines from the body of 
 an Echinoderm have received the name of " ambulacra ; " 
 and hence, says Mr. Huxley, " we may distinguish their 
 system of vessels as the ambulacral vascular system. The 
 existence of an ambulacral vascular system has as yet been 
 demonstrated only in the following orders : Echinidea, 
 Ophiuridea, Crinoidea, Asteridea, and ffolothuridea, with 
 which the fossil Cystidea and Blastoidea are inseparably 
 connected. I therefore limit the Echinodermata to the 
 
 (1) See an excellent paper in the Transaction of the Microscopical Society, 
 " On the Anatomy of Two Species of Naked-eyed Medusae," by G. Busk, Esq. ; 
 also Professor Forbes' works on this family. 
 
ASTER1DEA. 496 
 
 very natural group formed by these orders. A more or 
 less complete calcareous skeleton is always developed 
 within the Echinoderms, resembling that of the Actinozoa, 
 not only in this respect, but also in consisting of detached 
 spicula. In this form the skeleton remains in the Holo- 
 thuridea, but in the other Echinoderms, the spicula coalesce 
 into networks, which may become consolidated into dense 
 plates by additional deposits. It is by the different shape 
 and arrangement of these plates that the diversity ex- 
 hibited by the skeletons of different Echinodemata is 
 produced." 
 
 Asteridea. Star-fishes have been divided according to 
 the mode of locomotion into Spinigrades, moving by 
 means of spines ; Cirrhigrades, by suckers ; and Pinni- 
 grades, by fins or pinnae. Of the last-named division we 
 have only one British genus, Comatula. At the very 
 extremity of each ray is an organ like an eye, having 
 spinous appendages, which are termed the eyelids. It is 
 doubtful, however, whether these parts have really any 
 visual endowment ; no proof of their possessing the 
 faculty of sight has ever been advanced, and, from what 
 we know of the nature of this sense generally in the 
 lowest forms of animal life, we should be disposed to con- 
 sider that the organs in question must serve some other as 
 yet unknown purpose. 
 
 The species Ophiura and Ophiocoma, Plate IV. Nos. 88 
 and 91, may be easily recognised by the great length and 
 tenuity of their rays, and their excessive fragility. The 
 whole surface, both of disc and rays, is covered by scales, 
 which are so closely approximated as to give an almost 
 perfectly smooth surface. These scales are arranged in 
 definite and often in very beautiful patterns, and in some 
 species the primary scales are edged cr encircle! by series 
 of circular bosses or tubercles, giving a reticulated appear- 
 ance to the disc and rays. Ophicoma rosida has its spines 
 tipped with curious anchor-shaped processes, which are 
 supposed to facilitate the motion of the creature. In 
 Ophiura they are very short, and not apparent without 
 careful inspection ; while in Ophiocoma they are so long 
 as to give quite a bristly, sinous appearance to the animal, 
 being sometimes, in fact, very much longer than the 
 
496 THE MICROSCOPE. 
 
 breadth of the rays. A striking species is the Palmipes 
 membranaceus, the " Bird's-foot Sea-star," which is almost 
 as thin as parchment, and might, as Professor Forbes says, 
 be readily mistaken for the torn-off skin of some bulkier 
 species. Its surface is covered with a number of raised 
 tubercles, and very closely-set fasciculi of short and sharp 
 spines. Asterias aurantiaca and Luidia fragilissima 
 present a surface-structure very different from any of the 
 species previously noticed, their tuberculated epidermis 
 being so closely set with upright spines as to be almost 
 wholly invisible. These spines are arranged in a radiated 
 or rosette-shaped manner, and have a roughened surface. 
 A portion of the ray of Luidia forms a microscopic object 
 of exquisite beauty. A single spine is given in Plate IY. 
 No. 89. 
 
 The cirrhigrade star-fishes are furnished with certain 
 curious appendages, the use of which is at present very 
 imperfectly understood. These are the " pedicellariae " and 
 " madreporiform tubercle" The latter is a rounded, 
 cushion-like eminence of considerable size, situated on the 
 disc, mostly very much out of the centre. It is irregularly 
 fissured in a radiate manner, and is not at all unlike the 
 animal from which it derives its name. Various conjec- 
 tures have, 'been made as to the use of this tubercle. 
 Forbes looks upon it as being merely the analogue of the 
 stalk which exists in the young condition of the crinoid 
 star-fishes. The pedicellari<x (Plate IV. Nos. 93 and 94) 
 are pincer-like organs irregularly scattered over the surface 
 of the animal, and which have distinct characters in the 
 different species. They were supposed to be parasitic 
 creatures, but are now generally admitted to be true epider- 
 mic appendages. They are in a constantly active motion 
 during the life of the star-fish, and grasp firmly anything 
 which is brought between their blades. Their nearest 
 analogues are the birds'-head processes which occur in 
 certain zoophytes. The Pedicellarice of Echinus are pn- 
 tially covered with ciliated epithelium : they are also 
 placed upon a stalk, the lower portion of which encloses 
 a calcareous nucleus, whilst the other portions are soft, and 
 spirally retractile. 
 
 The Feather-star (Comatula rosacea) is perhaps the most 
 
ASTERIDEA. 497 
 
 interesting of the British star-fishes, and quite unique in 
 the gracefulness of its form and the exquisite beauty of its 
 colouring ; its life- history is not only remarkable, but it 
 possesses the additional interest of being the only living 
 representative in our seas of the group of organisms so 
 familiar to us in the fossil state as Encrinites. The deli- 
 cate structure of this species renders it impossible to ex- 
 hibit it satisfactorily in a dry or mounted state. The cen- 
 tral cup-shaped body gives off five rays, which divide so 
 near the base as to appear like ten. These are furnished 
 throughout their length with membranaceous pinnae. 
 Tubularia Dumortierii, Plate IV. JSTo. 92, appears rather 
 to belong to Comatula than Tubularia. A description of 
 this interesting polype will be found in Johnston's Brit. 
 Zoophytes, p. 53. 
 
 Professor Wyville Thompson, in a paper on " Sea- 
 Lilies " (see Intellectual Observer, August, 1864), says: 
 " Comatula rosacea, the most common British species, is 
 found abundantly in Lamlash Bay, in Arran and Strang- 
 ford Loughs, in Dulkey Sound, in Kirkwall Bay, and 
 generally distributed in deep water all round the British 
 and Irish coasts. In general structure it resembles very 
 closely the head of Neocrinus decorus ; it has, however, no 
 stem, but in the position of the stem, and forming the 
 base of the cup, there is a hemispherical plate covered 
 with rows of cirrhi, exactly like the stem-cirrhi on the 
 stalked forms. When at rest it holds on to a stone or 
 weed, and spreads out its beautiful feathery crimson 
 arms, like the petals of a flower. At other times it swims 
 rapidly through the water by graceful impulses of its arms. 
 In spring, the hundreds of ovaries dotted over its pinnules 
 are turgid with eggs, and if at this time it is captured, and 
 placed with some sea-weed in a tank, bunches of bright 
 orange-coloured eggs hang in clusters around, giving the 
 delicate pinnatic arms the appearance of the fronds of 
 some wonderfully graceful fern in rich fructification. 
 
 " The phases passed through by the young before they 
 come to resemble their parents in form and mode of life 
 are of extraordinary beauty, and most instructive in deter- 
 mining the true zoological relation which the free crinoida 
 bear to their fixed ancestors. At first a minute, almost 
 K K 
 
498 
 
 THE MICROSCOPE. 
 
 invisible, pale yellow germ escapes from the egg ; this, if 
 placed under the microscope the first day after its birth, 
 has a very definite form, but not the least like a star-fish. 
 Four bands of long vibratile cilia guard the body at dif- 
 ferent points, and by their motion the little animal whirls 
 about in the water. About the end of the second day two 
 rows of five each of delicate calcareous trellised plates may 
 be seen, making a kind of five-sided basket. A dark mass 
 now collects within the trellised basket, and the rings are 
 united together by little bundles of rods, till they form 
 what looks like a joined pillar supporting the basket. 
 Gradually the plates enlarge and distort the outer wall ; 
 and the stem-like series of joints lengthen, stretching out 
 the narrow end with it. The old mouth disappears, tha 
 gelatinous wall settles round the little living skeleton, a 
 round sucker appears, and the animal fixes itself upright 
 to a sea- weed or a stone at the bottom of the tank. Five 
 leaf-like valves, each supported by one of the upper tier of 
 plates, now open on the top of the wider extremity, and 
 the little creature looks when these valves are open much 
 like a microscopic wine-glass, and when closed like a 
 tulip bud." 
 
 Echinidce? Sea-urchins are found in abundance upon 
 our sea-shores, lurking among the rocks, where they entrap 
 their prey. Their spines and suckers are used as feet, or 
 as a mode of progression, even to the climbing of rocks, in 
 order to feed upon corallines and zoophytes : they march 
 along with ease where apparently no footing could be found, 
 or dig holes with their spines to bury themselves in the 
 sand, to escape pursuers, or hide from observation. The 
 
 (1) Description of Plate 9 : 
 
 ASTEROIDS. 
 
 a, Astrophyton scutatum. 
 n, Ophiocoma rosula. 
 
 NCDIBRANCHIATA GASTROPODA. 
 
 1), Doris pinnatifida back and 
 side view. 
 
 ACALKPH/E. 
 
 c, JEquorea Forbesina. 
 
 d, Medusa Bud. 
 
 e, Thaumantias corynetet. 
 *, Cydippe pyleus. 
 
 ECHINOIDEJE. 
 
 /, Echinus (A Young Sea-urchin). 
 g, Echinus sphara. 
 
 TUNICATA. 
 
 i, Ascidias. 
 
 k, Botryllus violaceus, on a Fucus. 
 
 CRUSTACEA. 
 
 I, Corystes cossivelaunus. 
 m, Eurynome aspera. 
 o, Pagurus Prideaurii. 
 p, Ebalia Permantii. 
 
PLATE IX. Asteroidea, Echinidea, Crustacea, c, 
 KK2 
 
ECHINIDEA. 501 
 
 Echinodermata, 1 sea-urchins, or sea-eggs, derive their name 
 from these curious spinous processes. 
 
 In most Echinidea all the feet are expanded into sucker 
 discs, at their extremities, and are here strengthened by a 
 calcareous plate or plates ; but in the Echino-cidaris and 
 some others, the feet of the oral portion of the ambulacra 
 only have this structure, while those of the apical portion 
 are pectinated, flattened, and gill-like. Miiller distinguishes 
 four kinds of feet in the Spatangoidca, simple locomotive 
 feet, without any sucking disc ; locomotive feet, provided 
 with terminal suckers, and containing a skeleton ; tactile 
 feet, whose expanded extremity is papillose ; and gill-like 
 feet, triangular, flattened, with more or less pectinated 
 lamellae. 
 
 In the Clypeastrodea the pebaloid portions of the am- 
 bulacra possess branchial feet, interspersed with delicate 
 Icccmotive sucker feet, provided with a calcareous 
 skeleton. In the Ophiuridea and Crinoidea the feet are 
 tentaculiforin ; and there are no vesicles at the bases of 
 the feet, while in the Asteridea they are well developed, but 
 simpler than those of the Echinidea. The madreporic canal 
 is, in the Asteridea, strengthened by a remarkable cal- 
 careous framework, which has given rise to the notion 
 that it is filled with sand, and to the name " sand-canal," 
 which has been applied to it. The canal terminates in 
 the madreporic tubercle, which is always placed inter- 
 radially on the antambulacral surface of the star-iish. 
 
 In some, Holothuridea, the feet are scattered over the 
 whole ambulacral region, as well in the inter-ambulacra 
 .is in the ambulacra. In others, Psolus, the feet are de- 
 veloped only from three of the five ambulacra ; while in 
 the Synapta and Chirodatce there is only a circlet around 
 the mouth. 
 
 Many star-fishes, and Synapta among the Holothuridea, 
 have the curious habit of breaking themselves up into 
 fragments when taken ; Miiller has pointed out the very 
 curious fact, that in Synapta, at any rate, this act may be 
 prevented by cutting through the oral nervous circle. The 
 nervous circle in the Echinus surrounds the oesophagus near 
 the mouth, and is enclosed by the alveoli, between which the 
 
 (1) Derived from echinot, seine, and derma, akin. 
 
502 TTIE MICKOSCOPE. 
 
 ambulacra! nerves pass to reach it. In the Asteridea, the 
 circle lies at the extreme limit of the soft membrane, which 
 surrounds the mouth, and may be readily exposed by cut- 
 ting away the hard inter-ambulacral oral lips. In the 
 Holothuridea it lies immediately beneath the perisoma of 
 the oral disc. The only known organs of sense in the 
 Echinodermata are the pigmented " eye-spots," developed 
 in connexion with the ends of the ambulacral nerves, and 
 on the oral nervous circle in many Holothuridea. 
 
 The great majority of the Echinodermata commence 
 their existence as free-swimming larveo covered with cilia, 
 but a great difference exists in their further course, accord- 
 ing as they belong to the Asteridea, the Holothimdea, and 
 the Crinoidea on the one hand, or to the Echinidea and 
 Opliiuridea on the other. Of the development of the 
 Crinoidea, we know very little, beyond the observations of 
 Mr. Thompson, that the larva of the Comatula is provided 
 with several transverse bands of cilia, almost like that of 
 a Holothuria, and that the development of the Echinoderm 
 commences while the larva is still free. At a later period, 
 the young Comatula is seated upon a long, jointed stem, so 
 as to resemble a Pentacrinm ; and it becomes detached 
 from this stem, in assuming its adult condition. 
 
 Mr. Huxley, after mature examination of this class of 
 animals, says, " he can see no reason for retaining them 
 amongst the Radiata of Cuvicr, but. on the other hand, 
 thinks them properly placed among the Annuloida." 
 
 The skeleton of the Ecliinoderms generally consists of an 
 assemblage of plates, or joints, of calcareous matter. The 
 minute structure of which presents a reticulated character, 
 and the solid parts are usually composed of a series of 
 super-imposed lamina) or scales. The openings, or areola?, 
 in one layer being always placed over the solid cell-walls 
 of the layer beneath it, the spines are situated on the ex- 
 ternal surface of the shell ; they are generally of a conical 
 figure, and are articulated with the tubercles by a ball- 
 and-socket joint. When a thin transverse section of one of 
 these spines is examined with the naked eye, it appears to 
 be made up of a series of concentric layers, varying 
 considerably in number; not, however, with the size of 
 the spine, but with the distance from the base at which 
 
ECHINIDEA. 603 
 
 the section was made : when a section taken from the 
 middle of the spine is examined with a power of fifty 
 diameters, it will be seen that the centre is occupied by a 
 reticulated structure ; around the margin of this may be 
 observed a series of small 
 structureless spots, ar- 
 ranged at equal distances 
 apart (Fig. 240, No. 1) : 
 these are the ribs or pil- 
 lars, and indicate the 
 external surface of the 
 first layer deposited ; pass- 
 ing towards the margin, 
 other rows of larger pil- 
 lars may be seen, giving 
 it a beautiful indented 
 appearance ; all the other 
 parts of the section are 
 occupied by the usual 
 reticulated tissue. In the 
 greater number of spines 
 the sections of the pillars 
 present no structure, in 
 others they exhibit a 
 series of concentric rings 
 of successive growth, 
 which strongly remind 
 us of the medullary rays 
 of plants ; occasionally 
 they are traversed by 
 reticulated structures, as 
 represented in Fig. 246, 
 No. 1 . When a vertical 
 section of a spine is ex- 
 amined, it is found to 
 be composed of cones 
 placed one over the other, 
 the outer margin of each 
 cone being formed by the series of pillars. In the genus 
 Echinus the number of cones is considerable, while in that 
 of Claris there are seldom more than one or two; so that 
 
 Fig. 239. 
 
 Pnlypidom of Pennatula phospjwrea. 2, 
 Synapta Chirodota. 3, Anchor-shaped 
 spiculum and plate from skin of Sy~ 
 iuipta. 
 
504 THE MICROSCOPE. 
 
 from these species transverse sections may be made, having 
 no concentric rings, and in which only the external row of 
 pillars can be seen. 
 
 " The skeleton of the Echinodermata contains very little 
 organic matter. When it is submitted to the action of 
 very dilute acid, to dissolve out the calcareous matter, the 
 residuum is very small in amount. When obtained, it is 
 found to possess the reticular structure of the calcareous 
 shell (Fig. 240, No. 1) ; the meshes or areoleo being bounded 
 
 Fig. 240. 
 
 1, Section of spine of Echinus, exhibiting reticulated structure, the calcareous 
 portion haying been dissolved out by acid. 2, Transverse .section of shell 
 of the Pinna ingens. 3, Horizontal section of shell of Tercbralulala rubicunda, 
 showing its radiating perforations. 
 
 by a substance in which a fibious appearance, intermingled 
 with granules, may be discerned under a sufficiently high 
 magnifying power, as originally pointed out by Professor 
 Valentine. This tissue bears a close resemblance to the 
 areolar tissue of higher animals ; and the shell may pro- 
 bably be considered as formed, not by the consolidation of 
 the cells of the epidermis, as in the MolliLsca, but by the 
 calcification of the fibro-areolar tissue of the true skin. 
 
BCHINIDEA. 505 
 
 This calcification of areolar or simply fibrous tissue, ny the 
 deposit of mineral substance, not in the meshes of areolse, 
 but in intimate union with the organic basis, is a condition 
 of much interest to the physiologist ; for it presents us 
 with an example, even in this low grade of the animal 
 kingdom, of a process which seems to have an important 
 share in the formation and growth of bone, namely, in 
 the progressive calcification of the fibrous tissue of the 
 periosteum membrane covering the bone." l 
 
 From their peculiarity of structure they may be said to 
 be almost imperishable. Their shells exist abundantly in 
 all our chalky cliffs, innumerable specimens of which may 
 be obtained, exhibiting the same wondrous forms and 
 characters as those which now frequent our shores. 
 
 The Crinoidea, " Sea-lilies," so called from the resem- 
 blance which many of them present to the lily, were ex- 
 ceedingly abundant in former ages of the world ; and their 
 remains often form the great bulk of large masses of rock, 
 fig. 241. These animals were all supported upon a long 
 stalk, at the extremity of which they floated in the waters 
 of those ancient seas, spreading their long arms in every 
 direction in search of the small animals which constituted 
 their food. Each of the arms, again, was feathered with 
 a double series of similarly jointed appendages ; so that 
 the number of separate calcareous pieces forming the 
 skeleton of one of these animals was most enormous. It 
 has been calculated that one species, the Pentacrinus 
 briareus, must have been composed of at least 150,000 
 joints; and "as each joint," according to Dr. Carpenter, 
 " was furnished with at least two bundles of muscular 
 fibre, one for its contraction, the other for its extension, 
 we have 300,000 such in the body of a single Penta- 
 crinus on amount of muscular apparatus far exceeding 
 any that has been elsewhere observed in the animal 
 creation." A furrow runs along the inside of the arms, 
 which is covered with a continuation of the skin of the 
 disc; and from this the ambulacra are protruded, as in 
 other Echinodermata. 
 
 In the family of Ophiuridea, so called from the resem- 
 blance of their arms to a serpent's tail, (Gr. ophis, a snake, 
 
 (1) Dr. Carpenter, Cyclopaedia of Anatomy and Phytiokyy- 
 
600 
 
 THE MICROSCOPE. 
 
 oura, a tail) ; the body forms a roundish or somewhat 
 pentagonal disc, furnished with five long simple arms, 
 which have no furrow for the protrusion of the ambulacra. 
 Ophiuridea are exceedingly plentiful in all 
 our seas, and their remains occur in all 
 the more recent marine strata of the 
 earth's crust. They are more commtonly 
 called Sand Stars, or Brittle Stars. 
 
 "However much the faunas of the 
 various geologic periods may have differed 
 from each other, or from the fauna which 
 now exists, in their aspect and character, 
 they were all, if I may so speak, equally 
 underlaid by the great leading ideas which 
 still constitute the master types of animal 
 life. And these leading ideas are four in 
 number. First, there is the star-like type' 
 of life, life embodied in a form that, as 
 in the corals, the sea anemones, the sea 
 urchins, and the star fishes, radiates out- 
 wards from a centre ; second, there is 
 the articulated type of life, life embodied 
 in a form composed, as in the worms, 
 crustaceans, and insects, of a series of 
 rings united by their edges, but more or 
 less moveable on each other ; third, there 
 is the bilateral or molluscan type of life, 
 Fig. 241. Encrinus, life embodied in a form in which 
 there is a duality of corresponding parts, 
 ranged, as in the cuttle fishes, the claws, and the snails, 
 on the sides of a central axis or plane ; and fourth there is 
 the vertebrate type of life life embodied in a form in 
 which au internal skeleton is built up into two cavities 
 placed the one over the other, the upper for the reception 
 of the nervous centres, central and spinal, the lower for 
 the lodgment of the respiratory, circulatory, and digestive 
 organs. Such have been the four central ideas of the 
 faunas of every succeeding generation, except perhaps the 
 earliest of all, that of the Lower Silurian System, in which, 
 so far as is yet known, only three of the number existed, 
 the radiated, articulated, and molluscan ideas or types. 
 
ECHIXIDEA. 
 
 That Omnipotent Creator, infinite in His resources who, 
 in at least the details of His workings, seems never yet to 
 have repeated Himself, but, as Lyell well expresses it, 
 breaks, when the parents of a species have been moulded, 
 the dye in which they were cast, manifests Himself, in 
 these four great ideas, as the unchanging and unchangeable 
 
 Fig. 242. Holalhuridea, Sea-cucumbers. 
 
 One. They serve to bind together the present with the 
 past, and determine the unity of the authorship of a wonder- 
 
508 THE MICROSCOPE. 
 
 fully complicated design, executed on a groundwork broad 
 as time, and whose scope and bearing are deep as 
 eternity." l 
 
 The Synaptidce are characterised by a total absence of 
 ambulacra, the motions of the animals being assisted by 
 peculiar anchor-like processes which project from the skin, 
 and roughen the surface of the animal. The spiculmn re- 
 presented in fig. 239 is serrated on the convex edge, and, 
 Dr. Herepath says, apparently belongs to S. Galliermii, 
 but that the drawing of the animal near it is singularly 
 inaccurate, although taken from Professor Forbes' work ; 
 and that the oral tentacles are imaginary developments of 
 S. digitata. See Herepath, " On the Genus Synapta," 
 Quar. Journ. Micros. Science, 1865, p. 1. The spicules 
 are beautiful objects for polarised light. (Plate IV. No. 
 87, shows a side view of one set in the skin.) 
 
 Holothuridea, " Sea-cucumbers." In this family the 
 body acquires a slug-like form. The radiate structure is 
 in fact scarcely recognisable in these animals, except in 
 the arrangement of the tentacles which surround the 
 mouth. The body is always more or less elongated, with 
 the mouth at one end and the anal opening at the other ; 
 the calcareous deposit in the skin is reduced to scattered 
 granules; and in one family the ambulacra are entirely 
 wanting. 
 
 The integument consists of a number of minute reticu- 
 lated plates, set closely on the substance of the skin. The 
 forms of the plates are various, as well as the spicula set 
 in them. The Australian seas furnish many varieties : 
 Plate VIII. Nos. 171 and 172, are representations of 
 plates and spicula under polarised light. Objects of this 
 class are also well suited for black-ground illumination. 
 
 The structure of the spines and other solid parts of the 
 skeleton of Echinodermata can only be displayed by 
 making thin sections, in the way described for cutting 
 bone, at page 209. Their peculiar texture requires that 
 certain precautions should be taken to prevent the section 
 from breaking whilst being reduced to a desirable thin- 
 ness, and to prevent the interspaces of the network froDi 
 being clogged by the particles abraded in the reducing 
 
 (1) Miller's Testimony of tTie Rocks. 
 
PRESERVATION OP THE POLTPIDOMS OP ZOOPHYTES. 509 
 
 process. In mounting the specimens, liquid balsam must 
 be employed, and only a very gentle heat should be ap- 
 plied ; and if, after it has been mounted, the section 
 should be found too thick, it will be easy to remove the 
 glass cover and reduce it further, care being taken to 
 harden the balsam, as directed in preparing bone sections. 
 
 PRESERVATION OF THE POLYPIDOMS OP ZOOPHYTES. 
 
 The following excellent and simple plan for preserving 
 zoophytes as fluid preparations; so as to retain the polypes 
 and their tentacular arms in situ, was adopted by the late 
 Dr. Golding Bird. For this purpose a lively specimen 
 should be chosen, and then plunged into cold pure water ; l 
 the polypes are killed almost immediately, and their ten- 
 tacles often do not retract : proper-sized specimens should 
 then be selected, and preserved in weak alcohol. Little 
 phials about two inches long should be procured, made 
 from thin flat glass tubes, so as to be half an inch wide, 
 and about a quarter of an inch, or even less, from back to 
 front. The specimens should be fixed to a thin platinum, 
 wire, and then placed in one of these phials (previously 
 filled with weak spirits), so as to reach half-way down. 
 "When several are thus arranged, they should be put on a 
 glass cylinder, and removed to the air-pump. On pump- 
 ing out the air, a copious ebullition of bubbles" will take 
 place ; and many of the tentacles previously concealed 
 will emerge from their cells. After being left in vacuo 
 for a few hours, the bottles should be filled up, closely 
 corked, and tied over, like anatomical preparations in 
 general. For all examinations with a one or two-inch 
 object-glass, these bottles are most excellent, and afford 
 cheap and useful substitutes for the more expensive and 
 difficultly-managed cells. In this manner, specimens of 
 the genera Membraniporce, Akyonidce, and Crisiadce, &c., 
 exhibit their structure most beautifully. 
 
 A few dozen of these little bottles hardly occupy any 
 room, and would form a useful accompaniment to the 
 microscopist by the sea-side. Any one visiting the caverns 
 
 (1) A small quantity of gin thrown into distilled water answers the purpose 
 better than pure water, and specimens maybe put up ia the same. The animals 
 ore nearly always preserved in their po'ypidoms by using this fluid to kill them. 
 
510 THE MICROSCOPE. 
 
 in St. Catherine's Island at Tenby, might reap a harvest 
 which would afford amusement and instruction for many 
 weeks. These caverns are so rich in zoophytes and 
 sponges, that they are literally roofed with the Laomedece, 
 Grantice, and their allies ; whilst the elegant Tubularice 
 afford an ornament to the shallow pools on the floor ; and 
 the walls are wreathed with the pink, yellow, green, and 
 purple Actiniae. 
 
 When these objects are examined by polarised light, 
 most interesting results are produced. For this purpose, 
 let a piece of selenite be placed on the stage of the micro- 
 scope, and the polarising prisms arranged so that the ray 
 transmitted is absorbed by the analyser. If a specimen of 
 Sertularia operculata be placed on the selenite stage, and 
 examined with a two-inch object-glass, the central stem is 
 shown to be a continuous tube, assuming a pink tint 
 throughout its whole extent. The cells appear violet in 
 colour ; their pointed orifices are seen much more distinctly 
 than when viewed with common light The vesicles are 
 paler than the rest of the object ; and their lids, which so 
 remarkably resemble the operculum of the theca of a 
 inoss, are beautifully distinct, being of an orange-yellowish 
 colour. This zoophyte is often covered with minute 
 bivalve shells, distinguished by the naked eye from the 
 vesicles only by their circular form ; and these, when pre- 
 sent, add much to the beauty of the specimen, presenting 
 a striated structure, and becoming illuminated with most 
 beautiful colours. 
 
ECHINODERMATA, IT YDKO/.OA, PoLYZOA, IlELMINTIIOIDA. 
 
 I'LATK IV. 
 
CHAPTER IIL 
 
 VOLTZOA MOLLTTSCA GASTEROPODA BRACHIOPODA CONCHIFBRA - 
 OKPHAXOPODA PTEROPODA TUNICATA CRUSTACEA ENTOMOSTBACA- 
 ANNULOSA CIBBIPEDA ENTOZOA ANNELIDA. 
 
 HE term Mollusc, derived from mollis, 
 soft, is one which at once indicates a 
 chief structural characteristic of the 
 class of animals about to occupy our atten- 
 tion. The body of most of the molluscous 
 sub-kingdom is soft and fleshy ; and all except 
 the Tunicata and a few Pteropoda are covered 
 or protected by a hard calcareous shell. The 
 shell is of two kinds ; first of an epidermal 
 character, being formed upon the surface of a 
 filmy cloak-like organ called a mantle, an- 
 swering to the true skin of othei animals; 
 and next of a dermal character, being con- 
 cealed within the substance of the mantle, 
 and frequently moulded into a great diversity 
 of forms, and coloured with various tints. 
 
 The molluscs belonging to the class Gaste- 
 ropoda have become a large and important 
 section of the animal series, presenting very 
 many objects of great interest for the micro- 
 scopist. Of the large family of molluscs, the 
 only species which bears any resemblance in structure to 
 the Polyzoa, which now form a portion of the molluscous 
 division, is the Urachiopoda, and this is confined to a re- 
 semblance in internal structure. 
 
512 
 
 THE MICROSCOPE. 
 
 The Polyzoa were placed by Dr. Johnston under 
 the head Ascidioida ; in the generality of works they are 
 named Bryozoa, and the individual, Bryozoon; derived 
 from the Greek words fipvov, sea- 
 moss ; owi/, animal. (Fig. 243.) 
 The Polyzoa are all compound as- 
 sociated animals, whence their 
 name ; but when a polyzoon egg is 
 hatched, as in the case of Pluma- 
 tclla, it commences life as an iso- 
 lated being, and by subsequent 
 growth, resembling budding, mul- 
 tiplies into a colony. All are most 
 bountifully supplied with cilia, and 
 the play of these is most energetic, 
 for the purpose of securing an 
 abundant supply of food, and ap- 
 parently without exertion on the 
 part of the creature itself. From 
 this most marked characteristic, 
 Dr. Farre was induced to give them 
 the name of Ciliobrachiata. But 
 it has at length been determined to 
 transfer the Polyzoa, F lustra, Le- 
 pralia, Anguinaria spatulata^ &c. 
 to the sub-molluscan kingdom 3 
 
 Polyzoa are generally fouii/1 tlvlag 
 together in great numbers, resem- 
 bling in this respect some of the Actinozoa, and are 
 protected by membranaceous corerings or polypidoi'.^. 
 Protrusion and retraction are performed by two setrf ,>' 
 muscles, one acting on the body of the animal, the oth* 1 
 
 (1) Mr.-Gosse, in his Manual of Marine Zoology, adopts the idea, now p?*tty 
 general, that the Polyzoa belong to the Molluscous division, in spite of their 
 external resemblances to Polypes, and he places them among Molluscs. In this, 
 perhaps, he has thought more of systematic views on classification than of the 
 student's convenience. It seems to us quite clear that, without adopting De 
 Blainville's principle of classifying animals according to their envelope as the 
 best principle of scientific classification, we should adopt it in works of refer- 
 ence like the present, since the external characters are necessarily those most 
 immediately recognised by the student ; and in the case of the Polyzoa, they are 
 BO remarkably similar in external characteristics to the hydroicl polypes, that 
 they were always classed with them, until the profounder investigations of Van 
 Benedeu, Allman, and others, revealed the resemblances betv -en the internal 
 thoracterifltiea of the Polyxou cud thoco of Molluscs. 
 
 * 
 
 *ai 'structure ; another 
 
 animal withdrawn into its 
 
POLYZOA. 513 
 
 upon its cell. The oral extremity is surrounded by a circle 
 of long tubular tentacles covered with cilia ; at each of these 
 feelers or arms there is an aperture, the one at the base 
 communicating with a canal that passes round the edge of 
 the oral aperture or mouth. The food passes down a long 
 gullet, that contracts during the process of swallowing. At 
 the end of this is an orifice that opens into what appears 
 to be a gizzard, having two bodies opposite to each other, 
 with a rough surface, as if for the comminution of food, 
 moved by muscular fibres. Those of the species without 
 this gizzard have a digestive stomach that secretes a 
 coloured fluid. From the upper part of the stomach near 
 the entrance from the gizzard arises an intestine, having 
 a narrow opening surrounded by cilia that proceeds 
 upwards, ending in an orifice near to the tentacles, from 
 which the refuse food is ejected. 
 
 Their cells are of various shapes, and from one, a family 
 of millions come, budding forth from its sides; and 
 though the living matter disappears, the catacombs exist 
 for the foundation of their families, branching out and 
 enduring for ages. 
 
 Bryozoon Bowerbankia received its name from Dr. Arthur 
 Farre, in honour of the well-known microscopist, Mr. 
 Bowerbank. A magnified representation of the animal is 
 seen in fig. 243. " When fully expanded, it is about one- 
 twelfth of an inch in length. In its retracted state, it is 
 completely enclosed in a delicate horny cell, sufficiently 
 transparent to admit of the whole structure of the con- 
 tained animal being seen through its walls. The cells are 
 connected together by a cylindrical creeping stem, upon 
 which they are thickly set, sessile, ascending from its 
 sides and upper surface. The animal, when completely 
 expanded, is seen to possess ten arms of about one-third 
 the length of the whole body ; each arm being thickly 
 ciliated on either side, and armed at the back by about 
 a dozen fine hair-like processes, which project at nearly 
 right angles from the tentacles, remaining motionless, 
 while the cilia are in constant and active vibration." 
 
 Notamia, Back-cell, so named from the cells being exactly 
 opposite, and united back to back with a thick partition, 
 and having a joint above and below each pair. In some 
 
 L L 
 
514 
 
 THE MICROSCOPE. 
 
 species of the Flwtrce the interior of the cell is protected 
 by a lid which bears some appearance to the head and 
 beak of a bird, and hence it is termed the bird's-head 
 process. This has been made the subject of investigation 
 by many naturalists. George Busk, Esq., F.R.S., 1 con- 
 tributed to the Transactions of the Microscopical Society, 
 1849, an admirable paper on the Notamia bursaria, 
 "Shepherd's-purse Coralline," (represented in fig. 244, 
 Nos. 1 and 3), which adds to our knowledge of this 
 curious process. He says : " This most beautiful pearl- 
 
 . 244. 
 
 i, Notarr.ia turtaria, Shepherd's -purse Coralline. 2, Anguinaria spatulata, 
 Snake Coralline, growing with the Campanularia Integra. 3, The Shepherd's 
 purse Animalcule withdrawn into its cup, and the internal organism 
 shown greatly magnified. 
 
 coloured coralline adheres by small tubes to fuel, from 
 whence it changes into flat cells; each single cell, like 
 
 (1) Mr. Busk has added to the description here given of this bird's-head 
 process in the Quarterly Journal of Microicopical Science, for January 1854. 
 
POLTZOA. 515 
 
 the bracket of a shelf, broad at top and narrow at the 
 bottom : these are placed back to back in pairs, one above 
 another, on an extremely slender tube that seems to 
 run through the middle of the branches of the whole 
 coralline. The cells are open at top. Some of them have 
 black spots in them ; and from the top of many of them 
 a figure seems to issue out like a short tobacco-pipe, the 
 small end of which seems to be inserted in the tube that 
 passes through the middle of the whole. The cells in pairs 
 are thought by some to have the appearance of the small 
 I ods of the plant " Shepherd's Purse," by others the shape 
 ut the seed-vessel of the Veronica, Speedwell. 
 
 ' The polypidom of this bryozoon, like those of most of 
 ils congeners, may be said to consist of a radical portion, 
 by which it is affixed to the objects upon which it grows, 
 and of a celliferous portion or branches, upon which the 
 polypes themselves are lodged. The radical portion in the 
 present species consists of a central discoid body of a 
 nearly circular form, and of branches radiating from the 
 periphery of the disc, which thence exhibits something of 
 the aspect of the body of an ophiura. The radical tubes 
 or branches springing from the margin of the disc are 
 usually five or six in number, and they are given off at 
 pretty regular distances apart ; but besides these radical 
 tubes, one or more celliferous branches are not unfrequently 
 seen to arise immediately from the upper surface of the 
 discoid portion. 
 
 " The central disc, and the radical tubes arising from it, 
 exhibit a similar structure, and are formed of a thick, firm, 
 apparently horny envelope, containing a coarse granular 
 matter, of a yellowish-white colour, and which in some 
 portions of the tubes assumes the form of distinct irregu- 
 larly-globular masses, of nearly uniform size. The central 
 disc is subdivided into distinct compartments by septa of 
 considerable thickness, and each radiating branch arises 
 from one of these distinct compartments; so that there 
 appears to be no communication between one radical 
 branch and another. The radical branches give off at 
 irregular distances secondary branches, which ultimately 
 become celliferous. Each of these secondary branches, 
 however, arises from a distinct compartment, as it were, of 
 
 LL2 
 
516 THE MICROSCOPE. 
 
 the tube from which it springs. This compartment is 
 formed, like those of the central disc, by a thick septum, 
 which shuts off the origin of the secondary branch from 
 the main cavity of the primary one." 
 
 The larger, or polypiferous cells, Mr. Busk proposes to 
 term cells, and the smaller tobacco-pipe-shaped organs 
 cups; the latter being usually above the f ' rmer through- 
 out the polypidom, " excepting immediately below each 
 fork, where the cup is invariably absent above one of the 
 cells of the pair from between which the fork springs. 
 The polype-cells are several times larger than the cups, 
 and their walls are much thinner ; in fact, sufficiently 
 transparent to allow of the contents of the cell being 
 pretty well seen, without any preparation, even during the 
 life of the animal. In shape they are inversely conical, 
 and the outer and upper angle is usually produced into a 
 prominent, sharp point. From the internal and upper 
 angle arises the tubular prolongation going to form the 
 next cell or cup, as the case may be, in succession. They 
 are entirely closed at the top, contrary to what is stated 
 by previous observers ; and, as has been shown, there is no 
 connexion whatever between the cell and the cup placed 
 immediately above and behind it. The aperture of the cell 
 is on the anterior face, and towards the upper margin ; it 
 is of a crescentic form, and placed obliquely, as it were, 
 across the upper and internal angle of the cell, with the 
 convexity of the curve directed upwards and inwards. The 
 lips of the aperture are strengthened by thin bands of 
 horny material ; and, under favourable circumstances, 
 indications of short muscular fibres, for the purpose of 
 opening or closing the aperture, may be seen." 
 
 The shell, which Mr. Busk believes to be entire at the 
 bottom, though closed only by a very delicate membrane, 
 contains an ascidoid polype of the usual typical form of 
 that class. " It has ten tentacles, and no gizzard. Two 
 sets of muscular fibres at least may be distinguished as 
 appertaining to the polype. The most important of these 
 are the retractor muscles, which, arising from the bottom 
 of the cell, in the form of long, somewhat flattened, 
 transversely striped, isolated fibres, about the one ten- 
 thousandth of an inch in width, are inserted, some of them 
 
CELLEPORIDJE. 517 
 
 at the base of the tentacles, and others lower down the 
 body of the polype." 
 
 When we consider the minuteness of the delicate little 
 sprig which is the natural size of this polype, we cannot 
 but wonder at the triumphs of the microscope in giving 
 such precise details as Mr. Busk relates of the Notamia 
 bursaria. Its beautiful and perfect organisation, the care- 
 ful provision for the safety and engagements of this 
 minute being, make us awe-stricken at the power of Divine 
 intelligence. 
 
 The Halodactylus, better known as Alcyonidium, is re- 
 markable among the marine forms of Polyzoa, for the large 
 size of its tentacular crowns; these when expanded are 
 distinctly visible to the unassisted eye, and present a spec- 
 tacle of great beauty when viewed with the binocular 
 microscope. Its polyzoary has a spongy aspect very much 
 resembling that of the Alcyonian zoophyte : when how- 
 ever the animals are expanded, they are at once seen to be 
 widely different, as the plumose turfts which then issue 
 from the surface of Halodactylus give it the appearance of 
 a beautiful downy film. The opacity of its polyzoary 
 renders it unsuited for the examination of anything more 
 than the tentacular crown. 
 
 Lepralia, " Sea-scurf," from the Greek for marine 
 leprosy, is the name given to this family of the Celle- 
 poridce by Dr. Johnston. 
 
 Lepralia nitida, found attached to shells, is thus 
 described : " Crust spreading circularly, closely adherent, 
 rather thin, greyish white, calcareous ; cells contiguous, 
 in radiating rows, large, subalternate, ovate, ventricose, 
 silvery, the walls fissured with six or seven cross slits 
 which are on the mesial line ; aperture subquadrangular, 
 depressed, terminal ; anterior to it there is often found a 
 globular, pearly, smooth, oviferous operculum, with a round 
 even aperture. The remarkable structure of the cells 
 renders this one of the most interesting species under the 
 microscope. There is sometimes an appearance of a spine 
 on each side of the lower angle of the mouth, which is 
 merely the commencement of the walls of the next cell.** 
 
 L. coccinea, L. variolosa, L. ciliata, L. t>~ispinosa, and 
 L. immersa, are the other British species. 
 
518 THE MICROSCOPE. 
 
 The family Cellularia, little-cells, have a curious and 
 wonderful provision of nature for their protection, an 
 operculum, a lid or cover over the apertures of each cell. 
 Cellularia ciliata is parasitical, branching, calcareous, 
 white and tufted ; grows about half an inch in height, and 
 the oblique aperture is armed on the outer edge with four 
 or five long hollow spines. The operculum is pearly, and 
 near the base there is that singular appendage, described 
 as the birds-head process. Its beauty and transparency 
 render it a favourite object with microscopists. 
 
 The Cellularia (uowBugula) avicularia are very accurately 
 described by Mr. Gosse, from his own observations upon 
 specimens secured on the Devonshire coast, during a resi- 
 dence there. He says : " Well does it deserve the name of 
 BircCs-head Coralline, given to it by the illustrious Ellis ; 
 for it presents those curious appendages that resemble vul- 
 tures' heads in great perfection. All my specimens were 
 most thickly studded witli them ; not a cell without its 
 bird's head, and all see-sawing, and snapping, and opening 
 their jaws with the most amusing activity ; and what was 
 marvellous, equally so in one specimen from whose cells 
 all the polypes had died away, as in those in which they 
 were still protruding their lovely bells of tentacles. The 
 stem ascends perpendicularly from a slender base, which is 
 attached to the rock, or to the cells of a Lepralia growing 
 from the rock. The central part of the spine is most ex- 
 panded, the diminution above and below being pretty 
 regular ; during life, the usual colour is a pale buff, but 
 the cells become nearly white in death. When examined 
 microscopically it is, however, that the curious organisa- 
 tion of this zoophyte is discovered, especially when in full 
 health and vigour, with all the beautiful polypes protruded 
 and expanded to the utmost, on the watch for prey. It 
 seems to me as poor a thing to strain one's eyes at a 
 microscope over a dead and dry polypidom, as it does to 
 examine a shrivelled and blackened flower out of a her- 
 barium ; though I know well that both are often indispen- 
 sable for the making out of technical characters. But if 
 you want to get an insight into the structure and functions 
 of these minute animals, or if you would be charmed 
 with the perception of beauty, or delighted with new 
 
CUISIAI'.K. 511) 
 
 and singular adaptations of meuis to an end, or if you 
 desire to see vitality under its most unusual, and yet most 
 interesting phases, or if you would have emotions of 
 adoring wonder excited, and the tribute of praise elicited 
 to that mighty Creator who made all things for His own 
 glory, then take such a zoophyte as this, fresh from the 
 clear tide-pool, take him without inflicting injury ; there- 
 fore detach with care a minute portion of the surface-rock, 
 and drop your prisoner, with every organ in full activity, 
 into a najTow glass cell with parallel sides, filled with clear 
 sea-water, and put the whole on the stage of the micro- 
 scope, with a power of not more than 100 linear, at least, 
 for the first examination. I greatly mistake if you will 
 not confess that the intellectual treat obtained is well 
 worth ay, ten times more than worth all your trouble." 
 
 CRISIAD.E, signifying a separation; applied to a parasi- 
 tical family. Crisia cornuta, " Goat's-horn Coralline " of Ellis, 
 having cells linked in a single series : the same remark ap- 
 plies to C. chelata, " Bull's-horn Coralline ;" the latter look 
 like a number of shoes fitting close to the ancle, joined by 
 the toe-part to the heel of others. Ellis says : " This beau- 
 tiful coralline is one of the smallest we meet with. It rises 
 from tubuli growing upon fuci, and passes from thence into 
 sickle-shaped branches, consisting of single rows of cells, 
 looking when magnified like bull's horns inverted, each one 
 arising out of the top of the other. The upper branches take 
 their rise from the fore-part of the entrance of a cell, where 
 we may observe a stiff, short hair, which seems to be the 
 beginning of a branch. The opening of each cell, which 
 is in the front of its upper part, is surrounded by a thin 
 circular rim ; and the substance of the cells appears to 
 consist of a fine transparent shell or coral-like substance." 
 
 Crisia eburnsa, " Tufted-ivory Coralline," attains the 
 height of an inch, and displays its beautiful white, bushy 
 tufts, with often a dash of light-red intermingled. Its cells 
 are loosely aggregated and cylindrical, with bent tubular 
 orifices free ; while the Crisia aculeata have cells closely 
 aggregated, cylindrical, nearly straight, with long slender 
 spines springing from the margin of every cell, giving it a 
 delicate and pretty appearance. 
 
 EucRATiAD-fi. We select from this family a spec : raen of 
 
520 THE MICROSCOPE. 
 
 great interest, the Anguinaria, from the Latin anguis, a 
 snake. This, and also Notamia, belong to the class Polyzoa. 
 An account of the Anguinaria spatulata, " Snake-head 
 Coralline/' appeared in the Transactions of the Microscopical 
 Society, by Mr. Busk, who corrects the errors of other ob- 
 servers. The polype is parasitical upon fuci, and is not un- 
 frequently associated with other kinds on the same plants, 
 as in tig. 244, No. 2, on Campanularia. The A. spatulata 
 "as a whole, consists, like all its congeners, of two distinct 
 portions, one usually termed the radical, and another which 
 constitutes the proper polype cells. In the present instance, 
 the arrangement of these parts is in some respects 
 very peculiar and curious ; but it will be found upon 
 strict examination to accord accurately with the uni- 
 versal type." 
 
 " In the radical tubes, and on the dorsal or upper surface 
 of the dilated extremity of the polype-cell, represented 
 at No. 2, this earthy matter is deposited in the form of 
 minute angular or rounded particles, presenting faint 
 traces of a linear arrangement ; but in the main body 
 of the polype-cell, or the upright portion, the calcareous 
 material is arranged in beautifully regular rings, giving 
 that part of the zoophyte a peculiarly elegant appear- 
 ance under the microscope. This calcareous ingredient 
 is sufficiently abundant to render the contents of the 
 radical tubes and polype-cells indistinct ; and to obtain 
 a satisfactory view of these parts it is necessary to remove 
 the earthy matter by some weak acid. When this is 
 done, it will be found that the contents of the radical 
 portion are coarsely granular, and the wall rather thicker 
 than those of the proper polype-cell. The latter contains 
 an ascidian polype, which has about twelve tentacles, and 
 no gizzard." The polype, as far as Mr. Busk has observed, 
 is always lodged in the upright portion of the cell ; but 
 the long retractor muscular fibres arise near the com- 
 mencement of the horizontal portion of the cell, from its 
 upper wall, and nearly at one point. 
 
 The expanded portion of the cell, besides the special 
 muscles of the aperture, contains other muscular fibres, in 
 all respects resembling those described by Dr. Farre, as 
 conducing to the extrusion of the polype in Bowerbankia t 
 
SSCHARID.E. 
 
 521 
 
 and which are also very distinct in the Notamia ; but 
 which, in the present instance, would seem to have for 
 their chief function the drawing-up or corrugation of the 
 membraneous portion of the polype-cell. These muscular 
 fibres have a distinct central nucleus or thicker portion, as 
 is the case in the analogous muscles in some other polypes. 
 
 ESCHARID^E. This interesting family justly deserves the 
 great attention many naturalists have bestowed upon it. 
 Linnaeus named it Flustra, from the 
 Saxon word flustran, to weave ; it is 
 commonly called a Seamat, and re- 
 sembles fine network spread over 
 stones, rocks, shells, and marine plants. 
 This network, when submitted to the 
 powers of the microscope, is found to 
 be a cluster of cells, in each of which 
 dwells an animal, that protrudes its 
 feelers when searching for food, and 
 sinks into its little home when tired, 
 or alarmed by approaching danger. 
 
 Dr. Grant estimates that a single 
 Flustra has as many as four hundred 
 millions of cilia on these restless ten- 
 tacles. The tentacula vary from ten to 
 twelve ; the general organization con- 
 sists of a gullet, a gizzard, a stomach, 
 and intestines, the body itself being quite transparent. 
 When collected together in clusters they take the form of 
 a delicate minute tree, having cells in all parts, and of 
 various colours. Larnouroux says : " When the animal 
 has acquired its full growth, it protrudes from the opening 
 of its cell a small globular body, which it fixes near the 
 aperture, and, as it increases in size, soon assumes the form 
 of a new cell; it is yet closed, but through the trans- 
 parent membrane that covers its surface the motions of 
 a polype may be detected ; the habitation at length 
 bursts, and the tentacles protrude ; eddies are pro- 
 duced in the water, and conduct to the polype the 
 atoms necessary for its subsistence. The aperture of 
 the cells is formed by a semicircular lid, convex ex- 
 ternally and concave internally, which folds down when 
 
 lype; the animal is 
 represented out of its 
 polypidom. 
 
522 THE MiJROSCOPE 
 
 the polype is about to advance firm the cell. The opening 
 of this lid in the F. truncata, where it is very long, appears 
 through the microscope like the opening of a snake's jaws ; 
 and the organs by which this motion is effected are not 
 perceptible. The lids of the cells open and shut in the 
 Flustrce without the slightest perceptible synchronous 
 motion of the polypes." 
 
 In the formation of their stony skeletons, the animals 
 appear to take a most insignificant part ; they are princi- 
 pally secreted by the integuments or membranes with^wbich 
 they are invested, in like manner as the bones and nails in 
 man are secreted by tissues designed for that purpose, and 
 acting slowly and imperceptibly. From an analysis of the 
 stony corals, it appears that their composition is very 
 analogous to that of shells. The porcellaneous shells, as 
 Jie cowry, are composed of animal gluten and carbonate 
 of lime, and resemble, in their mode of formation, the 
 enamel of the teeth; whereas the pearly shells, as the 
 oyster, are formed of carbonate of lime and a gelatinous or 
 cartilaginous substance, the earthy matter being secreted 
 and deposited in the interstices of a cellular tissue, as in 
 bones. In like manner, some corals yield gelatine upon 
 the removal of the lime, while others afford a substance in 
 every respect resembling the membranous structure ob- 
 tained by an analysis of the nacreous (pearly) shells. 
 A recent elaborate analysis of between thirty and forty 
 species of corals, by an eminent American chemist (Mr. J3. 
 Silliman), has shown, contrary to expectation, that they 
 contain a much larger proportion of fluorine than of 
 phosphoric acid. 
 
 FLustra foliacea, the broad-leaved Horn-wrack of Ellis, 
 is about four inches high, and of a brown colour. The cells 
 are small, in alternating rows ; and sometimes covered by 
 a lid opening downwards. Hook says : " For curiosity and 
 beauty, I have not, among all the plants or vegetables 
 I have yet observed, seen any one comparable to this 
 sea-weed." Flustra truncata is abundant in deep water, 
 and grows to a height of about four inches ; it is of a 
 delicate yellow colour, and bushy. This is the narrow- 
 leaved Horn-wrack of Ellis ; for it must not be forgotten 
 that the older writers regarded the whole genera as plants. 
 
E8CIiARlD.fi. 523 
 
 Flustra chartacea. Ellis states : " The cells of this sea 
 mat are of an oblong square figure, swelling out a little in 
 the middle of each side. The openings of the cells are 
 .defended by a helmet-like figure; from hence the polype- 
 shaped suckers extend themselves. This sea-mat is of a 
 slender and delicate texture, like a semi-transparent paper, 
 of a very light straw-colour. It was first found on the 
 coast of Sussex, adhering to a shell. I have since met, on 
 the same coast, about Hastings, in the year 1765, with 
 several specimens whose tops are digitated, and others that 
 were very irregularly divided." 
 
 The Flustra carbasea grow out in a leaf-like manner, 
 gradually widening to the end : they are found on shells of 
 a yellowish-brown colour ; on one of the sides the cells are 
 both large and smooth. The animals have about twenty- 
 two arms or feelers, which, says Dr. Grant, after a most 
 careful examination of these polypes, 4i are nearly a third 
 of the length of the body; and there appear to be about 
 fifty cilia on each side of a tentacle, making 2200 cilia 
 on each polype. In this species there are more than 
 eighteen cells in a square line, or 1800 in a square inch of 
 surface ; and the branches of an ordinary specimen pre- 
 sent about ten square inches of surface ; so that a common 
 specimen of the F. carbasea presents more than 18,000 
 polypes, 396,000 tentacles, and 39,600,000 cilia. 
 
 " They are very irritable, and frequently observed to 
 contract the circular margin of their broad extremity, 
 and to stop suddenly in their course when swimming ; 
 they swim with a gentle gliding motion, often appear 
 stationary, revolving rapidly round their long axis, with 
 their broad end uppermost, and they bound straight for- 
 ward, or in circles, without any other apparent object than 
 to keep themselves afloat till they find themselves in a 
 favourable situation for fixing and assuming the perfect 
 state. The transformation of the ova, from that moving, 
 irritable, free condition of animalcules, to that of the fixed 
 and almost inert zoophytes, exhibits a new metamorphosis 
 in the animal kingdom not less remarkable than that of 
 many reptiles from their first aquatic condition, or that of 
 insects from their larva state." 
 
 Flustra avicularis. This is another ot the little beauties 
 
524 THE MICROSCOPE 
 
 of the deep, found usually on old shells, an inch in height, 
 spreading itself fan-like, and of an ashy colour, deeply 
 divided in a dichotomous manner into narrow, thin, plane 
 segments, truncate at the end, formed of four or live series 
 of oblong cells, capped with a hollow, globose, pearly, oper- 
 culum seated between the spines, of which there is one on 
 either side of the circular aperture. The opercula are so 
 numerous, that they give to the upper surface the appear- 
 ance of being thickly strewn with orient pearls ; the under- 
 surface is even and longitudinally striated, the number of 
 striae corresponding to the number of rows in which the 
 cells are disposed. Dr. Johnston describes, amongst many 
 other British species, F. membranacea, " a gauze-like incrus- 
 tation on the frond of the sea-weed, spreading irregularly 
 to the extent of several square inches." 
 
 Dr. Perceval Wright discovered on the western coast of 
 Ireland a new genus of Alcyonidce, which he named after 
 the well-known naturalist Mr. Harte, Hartea elegans, Plate 
 IV. No. 86. This polype is solitary, the body cylindrical, 
 and fixed by its base to the rock ; it has eight ciliated 
 tentacles, which are knobbed at their base and most freely 
 displayed. It is a very beautiful polyzoon of a clear white 
 colour, and when fully expanded stands three-quarters of 
 an inch high. 1 
 
 The fresh-water Polyzoa are peculiarly interesting ob- 
 jects for microscopic observation, from the very beautiful 
 manner in which they display their ciliated tentacula, set 
 upon a crescentic, horseshoe-shaped " lophopore." The 
 arrangement of the latter appendage has been the cause of 
 separating the fresh-water Polyzoa, from their marine 
 allies, into a sub-class ; the former being named llippocrepn 
 (horseshoe-like), and the latter Infundibulata (funnel- 
 like). 2 The most striking form among the Hippocrepa is 
 the Cri&tatella Mucedo a wandering Polyzoon, capable of 
 moving freely through the water. It may be met with 
 during a great part of the summer in our ponds and streams, 
 amidst the stems and leaves of aquatic plants (Plate IV. 
 
 (1) On a new genus of Alcyonidce,. By Dr. E. Perceval Wright. Micros. 
 Journ. Science, vol. v. p. 213 1865. 
 
 2) The reader is referred to a valuable treatise on the structure and olassifi- 
 rtation of this group by Professor Allnian, Monograph of the British Fresh- 
 voter Polyzoa, published by the Ray Society, 1857. 
 
POLYZOA. 525 
 
 No. 97). It is always regarded as one of the most exqui- 
 site specimens of the class Polyzoa ; should there be 
 any difficulty in finding the animal itself, the eggs, met 
 with late in the summer or autumn, should be care- 
 fully stored in an aquarium without fish. The eggs or 
 " statoblasts," No. 95, are small, dark, circular bodies, 
 about the size of a pin's head, surrounded by a series of 
 minute hooked spines ; the animal conceals them among 
 tangled masses of decayed grasses and confervas. Polyzoa 
 are known to live upon Desmids and Algae ; and to keep 
 them alive the tank must be freely supplied with such 
 kinds of food. Cristatella Mucedo is rarely found in the 
 same spot a second day, it wanders about apparently in 
 search of food ; it is, therefore, provided with a contractile 
 disc or foot, and by means of this it creeps about not far 
 from the surface of the water, for it delights to display its 
 beautiful crests of tantacula (about eight in number), in the 
 broad light of day or sunlight ; in this respect Cristatella also 
 differs from most Polyzoa. Below the external margin is 
 a series of tubular chambers visible through the translucent 
 membrane ; and the csenaecium or common dermal system 
 is of a light yellow colour, often concealing several dark, 
 brownish-looking eggs. 
 
 Lophopus crystallinus is a finer Polyzoon than the former, 
 and displays beautiful plumes of transparent tentacles 
 arranged in a double horseshoe-shaped series. They at 
 times abound in slow running streams, adhering to the 
 stems of water-plants. "When first removed from the water 
 they resemble masses of the ova of one of the water snails, 
 and have often been mistaken for them. On putting one 
 of those jelly-like masses into a glass trough with some of 
 the clear water from the stream, delicate tubes will be 
 cautiously protruded, and then the beautiful fringes of cilia 
 are soon brought into play. The organization of L. Crys- 
 tallinus is simple, although it is provided with organs 
 of digestion, circulation, respiration, and generation. A 
 nervous 1 and muscular system are also tolerably well 
 
 (1) It has been demonstrated by Fritz Miiller that the Polyzoa possess a ner- 
 vous system : " The nervous system of each branch consisting of 1st, a consi- 
 derable sized ganglion situated at its origin ; 2d, of a nervous trunk running the 
 entire length of the branch, at the upper part of which it subdivides into 
 branches, going to the ganglia of the internodes arising at this part ; and 3d, of 
 
526 THE MICROSCOPE. 
 
 developed. It increases both by budding and by ova, 
 both of which conditions are shown in Plate IY. No. 98. 
 The ova are generally seen enclosed in the transparent 
 case of the parent. In Lophopus and most other fresh- 
 water genera, such as Cmstatella, Plumatella, and A Icyo- 
 nella, the neural margin of the lophopore is extended into 
 two triangular arms, giving it the appearance of a deep 
 crescent. 
 
 Alcyonella is a genus of fresh-water polyzoa, found 
 usually about the autumnal period of the year in the 
 several Docks at the East end of London, adhering to 
 floating pieces of timber. It assumes the form of an 
 irregular sponge-like mass, with an aggregation of meni- 
 branaceous tube-like openings covering the surface. 
 From these openings, the polypes are seen to project, the 
 mouths of which are encircled with a single series of 
 filiform ciliated tentacles, which keep the surrounding 
 water in active motion. The polypidom seen in water 
 has the appearance of a blackish-green sponge. 
 
 Trembley gave an interesting account of the family of 
 Alcyonella ; and Mr. J. Newton Tomkins favours us with 
 the following observations on the development of the 
 Alcyonella stagnorum (fluwatella) : 
 
 "The ova now under examination (J-inch obj. A. eye- 
 piece 100 liii. diam., "Wollaston's condenser), are the 
 products of some healthy specimens of Alcyonella stag- 
 norum given me by Mr. Lloyd, and sketched in full 
 activity in September 1856. Soon after this period 
 their movements decreased in energy, numerous ova were 
 detached, which floated to the surface of the water of 
 the jar in which they were confined, and in the course 
 of a very few weeks no trace remained of the parent 
 animals, except a spongy mass of an almost gelatinous 
 character, which still exists, though devoid of definite 
 form, and appears composed of a mass of broken and 
 disorganized cells. 
 
 " In November, with a view of preserving the water in 
 a normal condition, I introduced a sprig of Anacha'ris 
 
 a rich nervous plexus resting on the trunk, and connecting the g_anglia just 
 mentioned, as well as the basal ganglia of the individual polypides." For 
 farther account, see paper in the Micros. Journ. voL i. New Scries, p. 330. 
 
POLYZOA. 527 
 
 Alsinastrum, and finding it grew freely, but soon covered 
 with a filamentous confervoid growth, threw in two small 
 water-snails, which are there still. About January last, 
 the ova, which till then had floated on the surface of the 
 water, began to sink and attach themselves to the leaves of 
 the Anacharis and elsewhere. Latterly, they have all 
 subsided to the bottom of the jar, where they lie in com- 
 pany with a quantity of decayed vegetable matter, spawn 
 of the Limnceus, &c. They are of a light-brown colour, 
 ovoid in shape, longest diameter -0089, shortest diameter 
 0172. The outer rim seems built up of cells of oblong 
 shape, but necessarily ill-defined, owing to their being ob- 
 served by light transmitted through two surfaces; the 
 inner or central portion also cellular, but from the con- 
 vexity of the object, more easy to determine as to its true 
 nature, formed of larger hexagonal- shaped cells. Seen by 
 higher power (J-in. obj. A. eye-piece 220 lin. diam.), 
 these central cells, besides being unmistakably hexagonal 
 in form, have each a distinct dark nucleus in the centre : 
 this, however, may be an optical fallacy, due to their 
 peculiar position on a curved surface. No movement yet 
 visible, April 25, 1857." 
 
 Plumatella Repents, Plate IV. No. 99, so named from its 
 feather-like crown of tentacles, is a well-known fresh-water 
 Polyzoon, found in ponds and rivulets attached to aquatic 
 plants, generally choosing the under-surface for the pur- 
 pose of avoiding the strong light. It is a very elegant 
 variety, rather timid, withdrawing on the least disturbance 
 of the water, and not again venturing to display its beau- 
 tiful plume until all is once more perfectly quiet. Pro- 
 fessor Allman says of it: " Except in the condition of 
 the dermal system the structure of Plumatella differs in 
 no essential point from that of Alcyonella. This system, 
 however, in the coalescence of the tubes into a common 
 mass in Alcyonella, while they remain totally distinct in 
 Plumatella, presents us with a difference of sufficient im- 
 portance to justify the placing the two forms in separate 
 generic groups. The number of known species are twelve, 
 of which nine are British. The ca3nsecium consists of a 
 linear-branched series of tubula. cells of membrano- 
 corneous consistence, which is terminated by the orifice 
 
528 
 
 THE MICROSCOPE 
 
 destined for the egress of the polypides. The tentacula 
 are about sixty in number, long, and ciliated on either 
 side. The statoblasts are ovoid, of a dark- brown colour 
 without marginal spines, and contained within the poly- 
 
 Fig. 247. 
 
 1, Portion of a transverse section of the spine of an Echinus. 2, Crystals of 
 carbonate of Lime, from the surface of shell of Oyster. 3, Horizontal section 
 of shell of Haliotis splendens, with stellate pigment in the interior. 4, 
 Portion of shell of a Crab, showing granules beneath the articular layer. 5, 
 Another portion of the same shell, showing its hexagonal structure. 
 
 pidoni, through the transparent walls of which they can be 
 readily seen. It occurs in greatest perfection during the 
 
SHELL OP MOLLUSCA 529 
 
 summer and towards autumn, often obtaining to a consi- 
 derable size." Most of the species may be found in the 
 ponds around London, and few objects are capable of 
 affording greater pleasure than these Polyzoa when examined 
 in a living state under a moderate power, and with a dark- 
 ground illuminator. The withdrawal of the Polyzoa 
 from the Radiate sub-kingdom, and their location among 
 Mollusca, was a step in the right direction ; while the 
 important division of the molluscan sub-kingdom by 
 Milne-Edwards into primary sections of the Mollusca and 
 Molluscoida, the latter including the Tunicata and the 
 Polyzoa, is all that can be desired in the systematic 
 location of the Polyzoa. 
 
 Shell of Mollusca. The simplest form of shell occurs in 
 the rudimentary oval plate of the common Slug, Limax 
 rufus ; it is imbedded in the shield situated at the back 
 and near the head of the animal 
 
 When a molluscous or conchiferous shell is composed of 
 a single piece, it is then termed univalve ; when of two 
 pieces, 'bivalve. The bivalve Mollusca exhibit no trace of 
 any distinct head ; whilst in the univalve this part of the 
 body is well-marked, and usually furnished with special 
 organs of sense (tentacles, eyes, nerves, &c.). 
 
 The older naturalists recognised a group of multi- 
 valve shells, or shells composed of several valves, the 
 majority of which belonged to the Cirrhopod order of 
 Crustacea, and were regarded as Mollusca by earlier ob- 
 servers. The PlvoladeS) however, which in other respects 
 are true bivalve Mollusca, are furnished with a pair of 
 accessory plates in the neighbourhood of the hinge ; 
 whilst the Chitons, a small but sin- 
 gular group of Molluscs nearly 
 allied to the univalve limpets, have 
 an oval shell composed of eight 
 movable plates, which gives them a 
 great resemblance to enormous 
 woodlice ; and they have been re- 
 garded as forming a sort of transi- 
 tion towards the articulated divi- Fig. 248.-^piy*ia, sea- 
 sion. Those Mollusca not furnished 
 
 with a shell, or having only a small calcareous plate ca- 
 ll M 
 
530 THE MICROSCOPE. 
 
 closed within the mantle, are called Nudibranchtata : an 
 example of this family is seen in fig. 248, Aplysia ; but it is 
 remarkable that most of them are provided with a small 
 shell when they lirst quit the egg. In the shell-bearing 
 or Testaceous Mollusca, this embryonic shell, which often 
 differs greatly in shape and texture from the shell of the 
 mature animal, is, however, a commencement of the latter ; 
 additions being constantly made to the free edge by the 
 secretion of calcareous matter at the margin of the mantle. 
 The delicate membranaceous part of the mantle, which 
 lines the internal portion of the shell inhabited by the 
 animal, has also the power of secreting a thin layer of 
 shelly matter upon its inner surface. This is frequently of 
 a pearly lustre ; and in many bivalves a new layer of this 
 substance is deposited at the time when the size of the 
 shell is increased by additions to its margins, for it must 
 be observed that the formation of new shell is not con- 
 stantly going on, but appears to be subject to periodical 
 interruptions, as indicated by lines on the surface of the 
 shell ; which are called lines of growth. In many cases, 
 the margin of the mantle, instead of being even, presents 
 lobes of tubercles ; these produce corresponding irregula- 
 rities, ribs, tubercles, or spines, on the surface of the 
 shell 
 
 Dr. Bowerbank says, " Shell is developed from cells 
 that in process of growth have become hardened by the 
 deposition of calcareous matter in the interior." This 
 earthy matter consists principally of carbonate of lime, 
 deposited in a crystalline state ; and in certain shell, as in 
 that of the common Oyster (fig. 247, No. 2), from the 
 animal-cell not having sufficiently controlled the mode of 
 deposition of the earth particles, they have assumed the 
 form of perfect rhomboidal crystals. 
 
 The shell of the genus Pinna, " Wing-shells," is com- 
 posed of a series of hexagonal cells filled with transparent 
 calcareous matter, seen in fig. 240, No. 2, the outer layer 
 of which can be split up into prisms, like so many basaltic 
 columns ; as at No. 1. 
 
 Organs of sense are possessed by so^ne of this class in an 
 advanced state of development. I", the Scallop (Pecten), 
 for example, eyes occur in great numbers, placed among 
 
MOLLLSCA. 53] 
 
 the tentacles on the borders of the mantle. In other 
 genera, the eyes are differently placed, in Pinna on the 
 fore part of the mantle, and around the siphon-orifices in 
 Pholcuf and Solen. In the Cockle (Cardium) the short 
 siphons are surrounded with an extraordinary number of 
 tentacles, capable of protrusion, each of which bears a 
 pretty little eye; these are beautiful objects under the 
 microscope. Cockles are able to perform vigorous leaps by 
 means of a well developed foot, which they possess ; in 
 other species the foot is grooved ; and being associated 
 with a gland which has the power of secreting a gluti- 
 nous substance, the latter is drawn out into slender 
 threads, with a sucker-like or flattened extremity, by 
 which they attach themselves to rocks. The grooved foot 
 is then withdrawn, and the thread hardens into an elastic 
 sort of cord, called a byssus. It is by an aggregation of 
 these threads that the common Mussel moors itself 
 securely. The hinge of the shell is formed of variously 
 shaped dentations ; those under the beak are called car- 
 dinal teeth ; those on either side are lateral teeth. 
 
 The Pholadidce are a series of animals remarkable for 
 their destructive boring propensities. The Teredo, ship- 
 worm, is well known for the damage it does to the 
 bottoms of ships, especially in the tropical seas. Others 
 of this family give a preference to sandstone, and even the 
 most compact marble has been found bored through by 
 them. 
 
 Mr. J. Robertson says : " Having, while residing here 
 (Brighton), opportunities of studying the Pholas dactylus, 
 I have endeavoured during the last six months to discover 
 how this mollusc makes its hole or crypt in the chalk, by 
 a chemical solvent? by absorption? by ciliary currents? 
 or by rotatory motions ? My observations, dissections, and 
 experiments set at rest controversy in my mind. Between 
 twenty and thirty of these creatures have been at work in 
 lumps of chalk in sea water in a finger glass and a pan, at 
 my window, for the last three months. The Pholas dac- 
 tylus makes its hole by grating the chalk with its rasp-like 
 valves, licking it up when pulverized with its foot, forcing 
 it up through its principal or branchial siphon, and 
 squirting it out in oblong nodules. The crypt protects the 
 M it 2 
 
532 THE MICROSCOPE. 
 
 Pholas from Confervce, which, when they get at it, grow 
 not merely outside, but even within the lips of the 
 valves, preventing the action of the siphons. In the foot 
 there is a gelatinous spring, or style, which when taken 
 out has great elasticity, and which seems the mainspring 
 of the motion of the Pholas dactylus" 
 
 Tunicate, The most remarkable group of animals be- 
 longing to this order are the Asddians. The cell of the 
 Polyzoon is represented in the Ascidian by a test or tunic 
 from which they derive their name of a membraneous or 
 cartilaginous consistence, and often including calcareous 
 spicules, having two orifices, within which is another 
 envelope, distinguished as the mantle. Few microscopic 
 spectacles are more interesting than the sight of the circu- 
 lation along this network of muslin- like fabric, and that 
 of , the ciliary movement by which the circulating fluid is 
 kept moving. In the transparent species, such as Clave- 
 lina and Peropftora, this movement is seen to great advan- 
 tage. The animals are found very commonly adhering to 
 the broad fronds of fud, or on pieces of shell, near low 
 water-mark. They thrive in tanks, and multiply both b) 
 fissuration and budding. Two species are figured in Plate 
 IX. i and k, Botryllus violaceus belonging to the family 
 Didemnians, the zooids of which are often arranged in the 
 beautiful stellate clusters seen in the plate. 1 
 
 Pteropoda. The most prominent character of this class 
 is the possession of two broad muscular fins, one on either 
 side of the neck, somewhat resembling the expanded 
 wings of a butterfly, whence Cuvier gave them the name 
 of Pteropoda, "wing-footed." In Clio, the anatomy of 
 which has been carefully investigated, there is a very 
 curious apparatus developed for seizing its prey. On each 
 side of the mouth are three fleshy warts, covered with 
 minute red specks. Under the microscope, these specks, 
 numbering about three thousand on each tentacle, are seen 
 to be transparent cylinders, each containing in its cavity 
 twenty stalked discs, and forming so many adhesive 
 suckers. 
 
 (1) For information respecting the Compound Ascidians, see the admirable 
 monograph of Milne-Edwards, Art. Tunicata in the Cyclop. Anatomy and Phy- 
 tiology, Huxley in Phil. Trans, for 1851, or Journ. Micros. Soc. voL iv. 1S56 
 l*o Prof. Allman, same journal, voL vii. 1859. 
 
MOLLUSC A. 533 
 
 The Oyster is the type of the tribe Ostracea, all of 
 which are Acephalus, that is, animals without a distinct 
 head. The gills, or breathing apparatus, form what is 
 commonly called the beard of the oyster. The creature 
 is attached by strong muscles to its shell. The mouth of 
 the oyster is a mere opening in the body, without jaws or 
 teeth ; its food consists of nourishing substances suspended 
 in the water, and which are drawn into the shell when it 
 is open by means of cilia. Oysters attach one of their 
 valves to rocky ground, or some fixed substance, by a mu- 
 cilaginous liquid, which soon becomes as hard as the shell 
 itself. They spawn some time in May ; and their growth 
 is so rapid, that in three days after the deposition of the 
 spawn, the shell of the young oyster is nearly a quarter of 
 an inch broad ; in three months it is larger than a shil- 
 ling. The spawn is a very interesting object for micro- 
 scopic examination, especially with polarised light. The 
 young fry is represented in fig. 254 ; some with cilia pro- 
 truded 
 
 In the stomach of the Oyster, and in the alimentary 
 canal, myriads of living Paramcecium and other Infusoria 
 are found swimming in great activity ; swarnis of a con- 
 glomerate and ciliated living organism, somewhat resem- 
 bling the Volvox globator, and so extremely delicate in 
 their structure that they require a good objective to define 
 them. 
 
 Pearls are usually met with in the Meleagrina Marga- 
 ritifera, " Pearl Oyster," which, however, does not belong 
 to the family Ostracea. They are likewise found in the 
 Mussel known as Mya Margaritifera t and an inferior kind 
 in many Mussels of the rivers of Great Britain ; and, at 
 one time, the pearl-fishery of Ireland was justly cele- 
 brated. Naturalists somewhat differ in their opinions as 
 to the mode in which pearls are formed. Some think that 
 they are produced by particles of sand getting into the 
 stomach ; the animal, to prevent the roughness of these 
 particles from injuring its delicate structure, covers them 
 over with a secretion from a gland, and, by continual ad- 
 ditions, they gradually increase in size. Mussels, in which 
 artificial pearls were said to have been formed by tht, 
 Chinese, have frequently found their way to this country. 
 
534 
 
 THE MICROSCOPE. 
 
 It is now, however, very generally admitted to be a dis- 
 eased condition. Pearls are matured on a nucleus, con- 
 sisting of the same matter as that from which the new 
 layers of shell proceed at the edge of the Mussel or 
 Oyster. The finest kinds are formed in the body of the 
 animal, or originate in the pearly-looking part of the shell. 
 It is from the size, roundness, and brilliancy of pearls 
 that their value is estimated. 
 
 The microscope discloses a difference in the structure of 
 pearls : those having a prismatic cellular structure have a 
 brown horny nucleus, surrounded by small imperfectly- 
 
 Pig. 249. 
 
 I, A transverse section of a Pearl from Oyster, showing its prismatic structure. 
 2, A transverse section of another Pearl, showing its central cellular struc- 
 ture, with outside rings of true pearly matter. (Magnified 50 diameters.) 
 
 formed prismatic cells ; there is also a ring of horny 
 matter, followed by other prisms, and so on, as represented 
 
MOLLUSCA. 
 
 535 
 
 in fig. 249 ; and all transverse sections of pearls from 
 Oysters show the same successive rings of growth or 
 deposit. 
 
 In a segment of a transverse section of a small purple 
 pearl from a species of Mytilm (fig. 250), all trace of 
 prismatic structure has disappeared, and only a series of 
 tine curved or radiating lines is seen. This pearl consists 
 of a "beautiful purple-coloured series of concentric laminae ; 
 many of which have a series of concentric zones, and are 
 of & yellow tint. The most beautiful sections for micro- 
 scopic examination are obtained from Scotch pearls. 
 
 Brachiopoda, " Lamp-shells," or, as the name literally 
 
 Fi. 250. 
 
 1, A transverse section of a small Pearl- from a species of Mytilus. 2, Hori- 
 zontal section of same Pearl magnified 250 diameters, to show prismatic 
 structure and transverse striae. 
 
 signifies, arm-footed, is intended to express a most re- 
 markable characteristic of these animals, the presence of a 
 pair of arms, often of great length, rolled up in a spiral 
 form, and believed by Cuvier to replace the foot in other 
 bivalves. Professor Owen has shown that these organs 
 are tubes closed at each end, and contain a fluid, which by 
 
536 THE MICROSCOPE. 
 
 the contraction of the circular muscular fibres of which 
 the walls of the tube are composed, is propelled from the 
 base to the extremity, thereby unrolling, as he believes, 
 the spiral coils. One side of each arm is fringed with a 
 vast number of long filaments : these are ciliated. The 
 shell is opened by a peculiar process, which has given to 
 the Terebratula the name of Coach-spring Shell. In the 
 shell there are minute openings surrounded by a series of 
 radiating lines : these at first appear like dark oval spots ; 
 but in a vertical section they are seen to be perforations or 
 tubes running obliquely from the inner to the outer surface 
 of the shell, and having a series of radiating lines on the 
 edge, as in fig. 240, No. 3. The outer layer has been re- 
 moved, to show a radiating structure around the perfora- 
 tions. Dr. Carpenter fully describes Terebratula in the 
 Philosophical Magazine, 1854. 
 
 Not less curious than beautiful is the internal layer of 
 many kinds of bivalves, which present an iridescent 
 lustre, the whole surface being varied with a series of 
 grooved lines running nearly parallel to each other. The 
 well-known gorgeously coloured univalve, the Ear-shell, 
 Haliotus splendens, has been ascertained to consist of 
 numerous plates, resembling tortoise-shell, forming a series 
 of hexagonal cells, in the centre of which the stellate 
 pigment is deposited" (fig. 246, No. 3), alternating with 
 thin layers of pearl, or nacre; and this exhibits, when 
 highly magnified, a series of irregular undulating folds, re- 
 presented in the upper portion of the section. The iride- 
 scent lines are often extremely pleasing ; and if a piece be 
 submitted to the action of diluted hydrochloric acid, until 
 the calcareous portion of the nacreous layers are dissolved 
 out, the plates of animal matter fall apart, each one carry- 
 ing with it the membraneous residuum of the layer of 
 nacre that belonged to its inner surface. But the nacre 
 and membrane covering some of these horny plates remain 
 undisturbed j and their folded or plaited surfaces, although 
 divested of calcareous matter, exhibit iridescent hues of 
 the most gorgeous description. If the membrane be 
 spread out with a needle, and the plates unfolded to a 
 considerable extent, the iridescence is no longer seen; a 
 fact which clearly demonstrates that the beautiful colours 
 
GASTEROPODA. 537 
 
 presented "by the nacreous portions of shells, commonly 
 called mother-of-pearl, are produced solely by the disposi- 
 tion of single membraneous layers in folds or plaits, lying 
 more or less obliquely to the general surface. 
 
 In the Chitonidce, Coat of mail Shells, the shell consists 
 of eight transverse plates, imbedded in the mantle ; in the 
 Limpets, the ordinary form is that of a cone. The 
 arrangement of the teeth is somewhat remarkable. 
 
 The majority of Gasteropoda are furnished with a 
 shell, denominated spirivalve. The cause of this spiral 
 arrangement is said to be owing to the shape of the body 
 of the animal inhabiting the shell, which, as it grows, 
 enlarges its shell principally in one direction ; thus, of 
 course, making it form a spire, modified in shape according 
 to the degree in which each successive turn surpasses in 
 bulk that which preceded it. It would rather appear that 
 this is principally owing to the ciliary motion imparted to 
 the early stage of the embryo ; the first deposit of calca- 
 reous matter forming the axis, the tube continues to rotate 
 upon its axial pillar or columella, as it is called ; and by 
 reason of some other peculiar vital tendency, the shell is 
 gradually deposited in a series of cells ; thus enlarging its 
 conical form, and winding obliquely from right to left. 
 Every turn around the axis is termed a whorl; and when 
 the columella is hollow, it is said to be umbilicated. In 
 the spiri valve-shelled Gasteropoda, we find a difference in 
 structure between that part of the mantle which enve- 
 lopes the viscera, and which is always concealed within 
 the cavity of the shell, and the portion placed around its 
 aperture. 
 
 The mouths of most Gasteropoda consist of a strong 
 muscular cavity, and a crescentic-shaped tooth-bearing 
 membrane, armed with sharp points, and separated by 
 semi-circular cutting spaces, admirably adapted for the 
 division of the food upon which they feed. Most of them 
 are beautiful objects for the microscope. 
 
 Professor Huxley very properly objects to the use of the 
 commonly accepted term tongue for the tooth-bearing 
 membrane of the mollusca, and more appropriately desig- 
 nates it " the odontophore." 
 
 " The odontophore consists essentially of a cartilaginous 
 
538 THE MICROSCOPE. 
 
 strap, which "bears a long series of transversely-disposed 
 teeth. The ends of the strap are connected with muscles 
 attached to the upper and lower surface of the hinder ex- 
 tremities of the cartilaginous cushions ; and these muscles, 
 by their alternate contractions, cause the toothed strap to 
 work backwards and forwards over the end of the pulley 
 formed by its anterior end. The strap consequently acts 
 
 2 
 
 Fig. 251. 
 
 1, Palate of Buccinum undatum, r.r.mmon Whelk, seen under polarised light. 
 2, Palate of Doris tuberculata, Sea-slug. 
 
 after the fashion of a chain- saw (rather of a rasp,) upon 
 any substance to which it is applied, and the resulting 
 wear and tear of its anterior teeth are made good by the 
 incessant development of new teeth in the secreting sac in 
 which the hinder end of the strap is lodged. Besides the 
 chain-saw-like motion of the strap, the odontophore may 
 be capable of a licking or scraping action as a whole." 1 
 
 In the constant growth of the band we observe the 
 development of new teeth. In some the teeth on the 
 extreme part of the band differ much, both in size and 
 form, from those in the median line : so much, that if at 
 any time one portion be separated from the other and 
 then examined, it might be supposed to belong to another 
 species. 
 
 Since the investigations of Professor Loven, of Stock- 
 holm, into the lingual dentition of the glossophorous Mol- 
 lusca, various observers have studied the subject with 
 great advantage to our knowledge of the affinities of those 
 animals. Although the patterns or types of the lingual 
 membranes are, on the whole, remarkably constant, yet 
 
 (1) Elements of Comparative Anatomy, p. 36. 
 
TONGUES, ETC., OF GASTEUOPODS. 
 108 , .k i'* no 
 
 
 
 \\.F.MapleH.aU. nat. del. 
 
 PLATE V. 
 
 Kdmiuul Kvaii>. 
 
3A8TEROPODA. .539 
 
 their systematic value is not uniform ; and therefore tha 
 attempts to remodel the arrangement of the Gasteropoda 
 by their peculiarities of dentition have not become so com- 
 plete a success as was at first expected. Some, how- 
 ever, hold a different opinion ; and Dr. J. E. Gray writes : 
 " One result of the study of these papers (Loven's, On 
 the Tongues of Mollusca) and the examination of the 
 tongues of several molluscs has been to establish more 
 firmly the theory which I have long entertained, that no 
 species of gasteropodus molluscous animal can be properly 
 placed in the system unless we are enabled to examine the 
 animal, the shell, the operculum, and the structure of its 
 tongue ; and as none of these parts but the shell can be 
 examined in the fossil species, their position in the various 
 genera must be always attended with more or less uncer- 
 tainty." 1 
 
 Dr. Troschel has laboured much in this field of investi- 
 gation, and in his valuable work on the subject attempts a 
 classification of the principal types by their lingual den- 
 tition. The union under one formula of so many creatures 
 widely differing in anatomy, habits, and shell structure, 
 clearly indicates that, if the lingual ribbon contains 
 generic characters, they have not yet been ascertained. At 
 the same time, it does present differences which may offer 
 collateral evidence in cases otherwise difficult of discrimi- 
 nation. It does not help us to separate carnivorous from 
 phytophagus animals ; but it seems possible to make use 
 of it as a mark between species ; for, in all, there is a dis- 
 tinct difference between the tongues even of the most 
 closely allied. Thus, amongst other changes, it has been 
 found necessary to remove the Proserpinadae from the 
 neighbourhood of the Cyclophoridce, to which they were 
 formerly supposed to be nearly related, and to place them 
 in a more natural position near the Neritidce. That these 
 investigations are of value is also shown by the light 
 which has been shed on the true position of Aporrhais, 
 supposed by so great a naturalist as Forbes to be akin to 
 the Cerithiidce, but which is shown by its dentition to 
 belong to the Strombidce? 
 
 (1) Annalt of Nat. Hist. Ser. ii. vol. x. p. 413. 
 
 (2) See a paper on the subject in the Trans. Linn. Soc. 1367. 
 
540 THE MICROSCOPE. 
 
 The relations of the freshwater operculata are as varied 
 as those of the land. Ampullaria seems to find its nearest 
 marine relative in Natica, an opinion which seems con- 
 firmed by the form of the shell. A West Indian species 
 found on the trees of the forests of those islands, and placed 
 by Lamarch in the ffelicina, would rather appear to belong 
 to Neritina. The several peculiarities of their teeth, espe- 
 cially that of H. nemoralis, with its numerous uncini, its 
 sub-opaque trapezoid laterals, which seem heretofore to 
 have been overlooked, confirm the belief in its close rela- 
 tionship to Neritina. The horny mandibles of the Mol- 
 lusca may be deserving of some attention with a view to 
 the elucidation of their affinities. In Cyclotus translucidus 
 the mandible is divided into two portions by a median 
 articulation, and it is covered with fine denticulations 
 in regular rows, somewhat like that of Velutwa, Plate V. 
 No. 109. In most of the inoperculata, the mandible is 
 horse-shoe-shaped, and striate or corrugate. In Ampul- 
 laria, the same organ is beak-shaped, like the upper man- 
 dible of Octopus or Loligo. 
 
 " The lingual band, we should premise, has been, for con- 
 venience of description, divided into longitudinal areas, 
 which are crossed by many rows of teeth. There are 
 five, distinguishable by the different characters of the teeth 
 they bear ; but the characteristics are not always present. 
 The teeth are consequently named median, lateral, and 
 uncini, although the latter are not necessarily more hooked 
 than the others. The areas bearing the uncini have been 
 called pleurae. Since each row is a repetition of all the 
 rest, the system of teeth admits of easy representation by 
 a numerical formula, in which, when the uncini are very 
 numerous, they are indicated by the sign oc (infinity), and 
 the others by the proper figure. Thus, oo 5 1 5 oc , 
 which represents the system in the genus Trochus, signifies 
 that each row consists of one median, flanked on both 
 sides by five lateral teeth, and these again by a large 
 number of uncini. When only three areas are found, the 
 outer ones are to be considered as the pleura 1 , inasmuch as 
 there is frequently a manifest division in the membrane 
 between them and the lateral areas." 
 
 Most of the Cephalopod molluscs are provided with 
 
TEETH OP GASTEROPODA. 541 
 
 strong, well developed teeth ; they are all animal feeders. 
 Loven describes those of the cuttle-fish (Sepia ojficinalis, 
 Plate V. No. Ill), as like Pteropoda, formula of teeth, 
 3*1 '3. The Sepia is also furnished with a retractile 
 proboscis, and a prehensile spiny collar, apparently for the 
 purpose of holding its prey while the teeth are employed 
 in drilling or abrading it. In the Squid (Loligo, No. 113), 
 the medians, broad at the base, approach the tricuspid form 
 with a prolonged acute central cusp ; while the uncini are 
 much prolonged and slightly curved. The lingual band 
 increases in breadth towards the hinder part, in some in- 
 stances to twice the diameter of the anterior. The band, 
 when mounted dry, forms a fine object for the black- 
 ground illuminator, or side reflector. The lingual band of 
 Octopus tuberculatus differs slightly with Sepia. 
 
 The Nudibranchiata have become more attractive since 
 the publication of the valuable and beautifully-illustrated 
 monograph of Messrs. Alder and Hancock. The nudi- 
 branchs are without a shelly covering, slug-like in their 
 appearance, and most voracious feeders, greedily devouring 
 zoophytes, sponges, &c. (Plate IX. 6.) They possess the 
 remarkable property of restoring lost parts ; their powers 
 of endurance are great, so that they may be kept alive for 
 some time in a small glass jar of sea-water. While keep- 
 ing a specimen of the Piplida in confinement, the Eev. 
 Mr. Lowe noticed on several occasions a display of a bril- 
 liant phosphorescence. Many of the genus Dorididoe and 
 Eolidida are infested with parasitic Entromostraca, which 
 either live freely on the surface, under the skin, or adhere 
 to the branchiae of the animals. Oncidoris bilamellata (the 
 Sea-lemon) belongs to the Dorididae ; its mouth is provided 
 with a narrow band of strong hooked teeth (Plate Y. No. 
 1 20), which in some species are serrated ; all are provided 
 with mandibles, consisting of two horny plates uniting 
 near the fore part. The median row of teeth are small and 
 inconspicuous; the band is represented by the formula 
 2 1 2. A portion of the mandible of Aplysia hybrida 
 (the Sea-hare) is shown in Plate V. No. 112. 
 
 Patella radiata (the Rock-limpet). The band of this 
 mollusc, No. 116, may be readily distinguished from the 
 common limpet of our coasts ; the remarkably long ribbon- 
 
542 THE MICROSCOPE. 
 
 like membrane, which lies folded up in the abdominal 
 cavity, is furnished with numerous rows of strong, nearly 
 opaque, dark brown tricuspid teeth. The teeth of Acmcea 
 (No. 117) are differently arranged ; their formula is 3 1 3. 
 Chitonidce are said to be near relatives of the Patellidce ; the 
 mouths of all are furnished with mandibles. 
 
 Testacella maugei, belonging to the Pulmonifera, is slug- 
 like in its appearance, and, curiously enough, is subter- 
 ranean in its habits, chiefly feeding on earth-worms. During 
 winter and in dry weather it forms a kind of cocoon, 
 and thus completely encloses itself in an opaque white 
 mantle, which effectually protects it from atmospheric 
 influences. Its lingual membrane is large, and covered 
 with about fifty rows of divergent teeth, which gradually 
 diminish in size towards the median row ; each tooth is 
 barbed and pointed, broader towards the base, and fur- 
 nished with an articulating nipple set in the basement 
 membrane. A few rows are represented slightly mag- 
 nified, Plate V. No. 121. Their formula is 1 0. 
 
 Gymba olla (the Boat-shell) belongs to the species 
 Velutinidse, formula, 1 * 0, or 1 1 1. The lingual band, 
 No. 118, is narrow and ribbon- like in its appearance, with 
 numerous trident-shaped teeth set on a strong muscular 
 membrane. The end of the strap and its connexion with 
 the muscles at the hinder extremity of the cartilaginous 
 cushion is shown in the drawing. The blueish appearance 
 seen in the Plate is due to a selenite film and polarised 
 light. Scapander ligniarius (the Boatman shell). The 
 band (Plate V. No. 119), is narrow, but the teeth are bold 
 and of extraordinary size ; their formula is 1 1. This 
 mollusc is said to be without eyes. Pleurobranchus plu- 
 mula belongs to the same family ; its teeth are simple, re- 
 curved, and convex, and arranged in numerous divergent 
 rows ; the medians of which are largest. The mandible 
 (Plate Y. No. 122), presents an exceedingly pretty tesse- 
 lated appearance, and the numerous divergent rows have 
 tricuspided denticulations. Velutina loevigata (the Velvety 
 shell), formula 3 1 3. The teeth (Plate V. No. 108) are 
 small and fine ; medians recurved, with a series of deli- 
 cate denticulations on either side of the central cusp, 
 which is much prolonged : 1st laterals, denticulate, with 
 
GASTEROIODA. 543 
 
 outer cusp prolonged j 2d and 3d laterals, simple curved 
 or hooked-shaped. The mandible, No. 109, divided 
 in the centre, forms two plates of divergent denticu- 
 lations. 
 
 Halioti* tuberculatus (the Ear-shell), is a well-known 
 beautiful shell much used for ornamental purposes. The 
 lingual band, Plate Y. No. 114, is well developed. The 
 medians are flattened out, recurved obtuse teeth ; 1st 
 laterals, trapezoidal or beam-like ; uncini numerous, about 
 sixty, denticulate, the few first pairs are prolonged into 
 strong pointed cusps. Turbo marmoratus (the Top-shell). 
 After the outer layer of shell is removed, it presents a 
 delicate pearly appearance. The lingual band, No. 123, 
 closely resembles Trochus ; it is long and narrow, the 
 median teeth are broadest, with five recurved laterals, and 
 numerous rows of uncini, slender and hooked. A single 
 row only is represented in the plate. Cyclotus translu- 
 cidus, a family of operculate land-shells, belongs to the 
 Cyclostomatulce. The teeth shown at No. 110, formula 
 3 1 3, are arranged in slightly divergent rows on a narrow 
 band ; they are more or less subquadrate, recurved, with 
 their central cusps prolonged. Cistula catenata, one of 
 the family Cyclophoridte ; its band, No. 115, formula 
 2 1 2, shows teeth resembling those of Liltorina, and 
 should certainly be separated from Cydophoridae. It 
 would also seem that the teeth of Cyclostomatidce point to 
 a near alliance with the Trochidce; but this question can 
 only be determined by an examination of several species, 
 when it may, perhaps, be decided to give them rank as a 
 sub-order. They are numerous enough ; the West Indian 
 islands alone furnish us with 200 species. 
 
 Professor William Thompson, in his paper " On the 
 Dentition of British Pulmonifera," Ann. Nat. His. voL 
 vii. 1851, pointed out that the length of the lingual band, 
 and number of rows of teeth borne on it, vary greatly in 
 different species. The rows, however, being closely set 
 are usually very numerous ; but it is among the Pul- 
 monifera we meet with the most astonishing instances 
 of large numbers of teeth. Limax maximum possesses 
 26,800, distributed through 180 rows of 160 each; the 
 individual teeth measuring only one 10,000th of an inch. 
 
544 THE MICROSCOPE. 
 
 Helix pomatia has 21,000, and its comparatively dwarfed 
 congener, H. obvoluta, no less than 15,000. When it is 
 remembered that these estimates refer to series of forms, 
 curiously carved and sculptured, the total area sustaining 
 them not measuring in most of the molluscs half an inch in 
 length, we must be filled with admiration at the marvellous 
 creative power bestowed upon the organization of these 
 lowly-creeping creatures. 
 
 The Preparation of Teeth of Mollusca. The method of 
 preparing the lingual membranes of Mollusca is as fol- 
 lows : The animal having been taken from its shell, pin 
 down the muscular foot to a piece of cork, pour water upon 
 it, and let the water be changed as often as it becomes 
 turbid. Then with a dissecting microscope and a good 
 bull's eye condenser cut open and expose to view the floor 
 of the mouth; pin back the cut edges throughout its 
 whole length, and work out the dental band with knife 
 and forceps. When the band is detached place it in a 
 watch-glass, and again clean it well by repeated washings 
 and a camel's hair brush : then place it in weak spirit and 
 water, where it must remain for a few days before mount- 
 ing. If the membrane is dense and fatty it must be soaked 
 for a time in liquor potassce, and when removed carefully 
 washed. The best fluids for mounting are glycerine, weak 
 spirit and water, Eimmington's glycerine-jelly, or Goadby's 
 solution. Canada balsam renders them so very pellucid 
 that the finer teeth are completely lost in it. 
 
 Thread-cells. These curious appendages, so commonly 
 met with in the Actinozoa, and in the tentacles surround- 
 ing the mouth of the Medusae, are also seen in some 
 species of Mollusca. 
 
 These prehensile threads, now generally termed " urti- 
 cating organs," were discovered in 1835, in the Hydra, by 
 Corda and by Ehrenberg. About the same time they were 
 found by R. Wagner in the Actiniae, who at first regarded 
 them as zoosperms. Subsequently, however, he recog- 
 nised their identity with similar organs in the Medusae, 
 and gave them the name of urticating organs. Since then 
 numerous observations have shown that these organs exist 
 in the entire class of polypes ; in that of the Hydra, 
 Medusae, as well as in the Synaptae, many Turbellariae, 
 
OVA OP MOLLUSCA, 545 
 
 some -Annelids, and lastly among the Mollusca, the 
 Eolidae in particular. 
 
 Max Schultze has divided these organs into two cate- 
 gories ; one including those of a rod-like form, or the 
 bacillar, which are found pretty generally in the Turbel- 
 lariae ; and the other containing the urticating capsules 
 armed with a long filament. But the researches of other 
 observers, including Dr. Bergh, have shown that this dis- 
 tinction is unimportant. 
 
 Dr. Bergh has devoted much attention to the urticating 
 filaments or cnida of the Mollusca, which are far less well 
 known than those of the Caelenterata. The existence of 
 sacs with cnida that is to say, the existence of true 
 urticating batteries is then at the present day a well- 
 established fact as regards the typical forms of the Eolidae, 
 i.e. in the genera Eolidida, Montagna, Facelina. 
 
 In every case the urticating batteries are planted at the 
 extremities of the papillae above the hepatic lobe. The 
 sac opens to the exterior by a minute pore situated at the 
 summit. Its walls are muscular, a circular layer of fibres 
 being the most considerable element The interior is filled 
 with urticating cells, together with cysts full of closely- 
 packed filaments and free filaments. The genus Pleuro- 
 phyllidium, according to Dr. Bergh, is the only mollusc 
 besides the Eolidae in which cnida are met with, and it is 
 to be remarked that in their anatomical conformation these 
 animals appear to approach very closely to the Eolidae. 
 
 The use of these cnida is still involved in doubt. Mr. 
 Lewes, however, has shown that they do not serve to 
 paralyse the animals upon which Actiniae feed. 
 
 Ova of Mollusca. It is interesting to watch the develop- 
 ment of the spawn of the Mollusca under a low magnifying 
 power. The ova of the Limnanu is usually found adhering 
 to the surfaces of stones, pieces of weed, or other matters in 
 the water ; they are always contained in a long ribbon- 
 like delicate ova-sac of a curious and beautiful form. 
 The mass of eggs deposited by the Doris resembles a frill 
 of lace of great beauty. In Aplysia the spawn resem- 
 ble-s long strings of vermicelli, of varying tints through- 
 
 (1) On Urticating Filaments in the Mollusca, by Dr. Bergh. Journ. Micros. Sei. 
 ToL ii. p. 274. 1862. 
 
 N N 
 
546 
 
 THE MICROSCOPE. 
 
 out the different parts of the thread. The Limnceus stag- 
 nalis deposits small sacs, containing from fifty to sixty 
 
 Fig. 252. Limncea stagnalis. 
 
 ova; one of which is represented at a, fig. 252. When 
 examined soon after they are deposited, the vesicles appear 
 to be filled with a perfectly clear fluid; at the end of 
 twenty-four hours a very minute yellow spot, the nucleus, 
 or germ, may be seen near the side of the cell-wall. In 
 about forty- eight hours afterwards, this small germ has a 
 smaller central spot rather deeper in colour, which is the 
 nucleolus. On the fourth day the nucleus has changed its 
 position, and is enlarged to double the size : a magnified 
 view is given at b ; upon viewing it more closely, a trans- 
 verse fissure or depression is seen ; this on the eighth day 
 most distinctly divides the small mass into the shell and 
 soft part of the future animal, c. It is then detached from 
 the side of the cell, and moves with a rotatory motion 
 around the cell-interior; the direction of this motion is 
 from the right to the left, and is always increased when 
 the sunlight falls upon it. The increase is gradual up to 
 the sixteenth day, when the spiral axis can now be made 
 out as at d; it presents a striking difference in appearance 
 to the soft parts. On the eighteenth day, these changes 
 are more distinctly visible, and the ova crowd down to the 
 mouth of the ova-sac ; by using a higher magnifying power, 
 a minute black speck, the future eye, is seen protruded 
 
GASTEROPODA. 547 
 
 with the tentacles, at e. Upon closely observing it, a 
 fringe of cilia is noticed in motion near the edge of the 
 shell. It is now apparent that the rotatory motion first 
 observed must have been in a great measure due to this ; 
 and the current kept up in the fluid contents of the cell 
 by the ciliary fringes. For days after the young animal 
 has escaped from the egg, this ciliary motion is carried 
 on. not alone by the fringe surrounding the mouth, but 
 by cilia entirely surrounding the tentacles themselves, 
 which whips up the supply of nourish- 
 ment, and at the same time the proper 
 aeration of the blood is effected. Whilst 
 in the ova, it probably is by this motion 
 that the cell-contents are converted into 
 tissues and shell. From the twenty-sixth 
 to the twenty-eighth day, it appears 
 actively engaged near the side of the 
 egg, using all its force to break through 
 the cell- wall, which at length it succeeds 
 in doing; leaving the shell in the ova- 
 sac, and immediately attaching itself to 
 the side of the glass-vase, to recommence 
 its ciliary play, and appears in the ad- 
 vanced stage represented at / It is still 
 some months before it grows to the 
 perfect form represented at fig. 253, 
 where the animal is drawn with its sucker-like foot adhering 
 closely to the side of the glass-vase. One of these snails 
 may deposit from two to three of these ova-sacs a week ; 
 producing, in the course of six weeks or two months, from 
 900 to 1,000 young, thus supplying food for fish. 
 
 The shell itself is deposited in minute cells, which take 
 up a circular position around the axis ; on its under-surface 
 a hyaline membrane is secreted. The integument expands, 
 and at various points an internal colouring-matter or pig- 
 ment is deposited. The increase of the membrane goes 
 on until the expanded foot is formed, the outer edge of 
 which is rounded off and turned over by condensed tissue 
 in the form of a twisted wire ; this encloses a net-work of 
 small vessels filled with a fluid in constant and rapid 
 motion. The course of the blood or fluid, as it passes 
 
 NN2 
 
 Pig. 253.r- 
 
 tlagnalis. 
 
548 THE MICROSCOPE. 
 
 from the heart, may be traced through the larger branches 
 to the respiratory organs, consisting of branchial-fringes 
 placed above the mouth; the blood may also be seen 
 returning through other vessels. The heart, a strong mus- 
 cular apparatus, is pear-shaped, and enclosed within a 
 pericardium or enveloping membrane, which is extremely 
 thin and pellucid. Affixed to the sides of the heart are mus- 
 cular bands of considerable strength, the action of which 
 appears very like the alternate to-and-fro motion occasioned 
 by drawing out bands of India-rubber, and which, although 
 so minute, must be analogous to the muscular cords of the 
 mammal heart ; it beats or contracts at the rate of about 
 sixty times a minute ; and is placed rather far back in the 
 body, towards the axis of the shell. The nervous system 
 is made up of ganglia, or nervous centres, and distributed 
 throughout the various portions of the body. 
 
 The singular arrangement of the eye cannot be omitted ; 
 it appears at an early stage of life to be within the tentacle, 
 and consequently capable of being retracted into it. In the 
 adult animal, the eye is situated at the base of the tentacle ; 
 and although it can be protruded at pleasure for a short 
 distance, it seems to depend much upon the tentacle for 
 protection as a coverlid it invariably draws down the ten- 
 tacle over the eye when that organ needs protection. The 
 eye itself is pyriform, somewhat resembling the round 
 figure of the human eye-ball, with its optic-nerve attached. 
 In colour it is very dark, having a central pupillary-open- 
 ing for the admission of light. The tentacle, which is cylin- 
 drical in the young animal, becomes flat and triangular in 
 shape in the adult. The young animal is for some time 
 without teeth ; consequently, it does not very early betake 
 itself to a vegetable sustenance : in place of teeth it has 
 two rows of cilia, as before stated, which drop off when the 
 teeth are fully formed. The lingual band bearing the 
 teeth, or the " tongue," as it is termed, consists of several 
 rows of cutting spines, pointed with silica. 
 
 It is a fact of some interest, physiologically, to know 
 that if the young animal is kept in fresh water alone, 
 without vegetable matter of any kind, it retains its cilia, 
 but arrest of development follows, and it acquires no 
 gastric teeth, and never attains perfection in form or size t 
 
GASTEROPODA. 549 
 
 If, at the same time, it is confined within a narrow cell, or 
 space, it grows only to such a size as will enable it to move 
 about freely ; thus it is made to adapt itself to the neces- 
 sities of a restricted state of existence. Some young 
 animals in a narrow glass-cell, at the end of six months, 
 were alive and well, and the cilia retained around the 
 tentacles in constant activity ; whilst other animals of the 
 same brood and age, placed in a situation favourable to 
 growth, attained their full size, and produced young, which 
 grew in three weeks to the size of their elder relations. 
 
 Should any injury occur to the shell, or a portion of it 
 become broken off, the calcareous deposit is quickly resumed, 
 in order to replace the lost part ; the cells being apparently 
 only half the size of those originally deposited. This 
 may be thought to afford some proof of the statement 
 made by Professor Paget, " that, as a rule, the reparative 
 power in each perfect species, whether it be higher or 
 lower in the scale, is in an inverse proportion to the 
 amount of change through which it has passed in its 
 development from the embryonic to the perfect state. 
 And the deduction to be made from them is, that the 
 powers for development from the embryo are identical 
 with those exercised for the restoration from injuries ; in 
 other words, that the powers are the same by which per- 
 fection is first achieved, and by which, when lost, it is 
 recovered. Indeed, it would almost seem as if the species 
 that have the least means of escape or defence from 
 mutilation were those on which the most ample power of 
 repair has been bestowed, an admirable instance, if it be 
 only generally true, of the beneficence that has prepared 
 for the welfare of even the least of the living world, with 
 as much care as if they were the sole objects of the Divine 
 regard." 
 
 The* primordial cell-wall of the cell does not appear to 
 enter into the formative process of the embryo the cell- 
 contents alone nourishing the vital blastema of the nucleus. 
 A gradual cycle of progressive development once set up, 
 goes on, until the animal is sufficiently matured to break 
 through the cell-wall and escape from the ova-sac. At 
 the same time, it may be inferred, that all this is in some 
 measure aided by the process of endosmose ; and that cer- 
 
550 THE MICROSCOPE. 
 
 tain gases or fluids are drawn into the interior, and thus aid 
 in the supply of nourishment for the growth of the animal. 
 The cell- wall appears to bear the same relation to the 
 future perfect animal that the egg-shell of the chick does 
 to it ; it is, in fact, hut an external covering to a certain 
 amount of gaseous and fluid matter, used for placing the 
 germ of life in a more favourable state for development, 
 assisted, as it is, by an increase of temperature, usually 
 the resultant of a chemical action, set up or once begun 
 in an organism and a medium. " The ovum destined to 
 become a new creature originates from a cell, enclosing 
 gemmules, from which its tissues are formed, and nutriment 
 is assimilated, and which eventually enables the animal to 
 successively renew its organs, through a series of 'meta- 
 morphoses that give it permanent conditions, not only 
 different, but even directly contrary to those which it had 
 primitively." 
 
 Cephalopoda. Molluscous animals without a foot, or 
 a distinct head, and covered with fleshy arms, bearing 
 sucker-like discs. The Cuttles and Squids form the prin- 
 cipal groups of this class, only a few species of which are 
 found on our shores. These molluscs are the nearest 
 approach of all invertebrate animals to the vertebrate 
 forms ; and their organs of sense appear to be highly de- 
 veloped. 1 Cuttle-fish bone, cut in thin sections, or broken 
 into small fragments, are interesting microscopic objects: 
 the peculiarities of structure are best seen when small 
 pieces are detached with a sharp knife. In the living 
 state these creatures have the power of suddenly changing 
 the colour of their skins. 
 
 Structure of Shell. We may exhibit the structure of 
 shell by using an acid solvent in the following manner. 
 If a sufficient quantity of hydrochloric acid, considerably 
 diluted with water (say one part acid to twenty-four of 
 water), be poured upon a shell contained in a glass vessel, 
 it will soon exhibit a soft floating substance, consisting of 
 innumerable membranes, which retain the figure of the 
 shell, and afford a beautiful and popular object for thi 
 
 (1) In the Cephalopoda -we have the first' indication of a true internal 
 skeleton, in the form of a broad flattened cartilage which protects the central 
 (optic) ganglia of the nervous system. 
 
STRUCTURE OF SHELL. 551 
 
 microscope. In analysing shells of a finer texture than 
 such as are generally submitted to the test of experiment, 
 the greatest circumspection is necessary. So much so, 
 that M. Herissant, whose attention was particularly devoted 
 to the subject, after placing a porcelain shell in spirits of 
 wine, added, from day to day, for the space of two months, 
 a single drop of spirits of nitre, lest the air, generated or 
 let loose by the action of the hydrochloric acid on the 
 earthy substance, should tear the net-work of the fine 
 membranaeeous structure. This gradual operation was 
 attended with complete success, and a delicate and beauti- 
 fully reticulated film, resembling a spider's web in texture, 
 rewarded the patience of the operator ; the organization of 
 which film, from its extreme fineness, he was not, however, 
 able to delineate. In shells of peculiar delicacy, even five 
 or six months are sometimes necessary for their complete 
 development ; but in others of a coarser texture the process 
 is soon completed. Sections of shells are usually mounted 
 in Canada balsam, or in shallow cells with glycerine. 
 
 Mr. George Rainey pointed out the remarkable fact 
 that many of the appearances presented by the shell or 
 hard structures of animals, and which had been usually 
 referred to cell-development, are really produced by the 
 physical laws which govern the aggregation of certain crys- 
 tallizable salts when exposed to the action of vegetable and 
 animal substances in a state of solution. Mr. Rainey gives 
 a process for obtaining artificially a crystalline substance 
 which closely resembles shell in its chemical structure. 
 
 " The chemical substances to be employed in the pro- 
 duction of the artificial calculi are, a soluble compound of 
 lime, and carbonate of potash or soda, dissolved in separate 
 portions of water; and some viscid vegetable or animal 
 substance, such as gum or albumen, mixed with each of 
 these solutions. The mechanical conditions required to 
 act in conjunction with the chemical means are, the pre- 
 sence of such a quantity of the viscid material in each 
 solution as will be sufficient to make the two solutions, 
 when mixed together, of about the same density as that of 
 the nascent carbonate of lime, and a state ef perfect rest 
 of the fluid in which the decomposition is going on, so 
 that the newly-formed compound may be interfered with 
 
552 THE MICROSCOPE. 
 
 as little as possible in its subsidence to the sides and 
 bottom of the vessel. This will require two or three 
 weeks, or longer, according to the size and completeness 
 of the calculi. But I have not found that they increase- 
 at all after six weeks." 
 
 Mr. Eainey shows 1 the analogy or identity of his arti- 
 ficially formed crystals with those found in natural pro- 
 ducts both in animals and vegetables, chiefly confining 
 himself to the structure and formation of shells and bone, 
 pigmental and other cells, and the structure and develop- 
 ment of the crystalline lenses, which he contends are all 
 formed upon precisely the same physical principles as the 
 artificial crystals. Take, for instance, the calculi found in 
 the body : these cannot be distinguished from the crystals 
 of artifically formed carbonate of lime. Again, the shell 
 of the crustaceans ; the resemblance between these and the 
 artificial products is, in some respects, more complete than 
 in that of calculi. All the appearances in shells can 
 be best observed by merely cleaning them in water, and 
 examining them in glycerine, grinding being unnecessary 
 and injurious. Polarised light is indispensable ; as in the 
 young hermit-crab, at the part where the calcareous and 
 membranous portions of the shell are continuous, the cir- 
 cular forms of globular carbonate are so delicate that no 
 evidence whatever of its presence can be detected under 
 powerful lenses, and with the best illumination, until 
 polarised light is brought to bear upon the specimen. To 
 obtain the most satisfactory results in the investigation of 
 the process of calcification of animal tissues, it is indis- 
 pensably necessary that the parts examined should be in 
 the earliest stages of the process, and before the calcifying 
 membrane is entirely covered with the globular coalescing 
 deposit. The usual plan of examining shells in thin 
 vertical sections is entirely useless, unless it be simply to 
 see the number and arrangement of their layers ; the part 
 of the section in such specimens, in which the calcifying 
 process ought to be best seen, being entirely ground off. 
 This part, being the softest, can only be preserved in 
 the process of grinding by extreme care, and by keep- 
 
 (1) Q. Rainey, "On the Mode of Formation of Shells, Bone, &c. byaproctu of 
 Molecular Coalescence." 1858. 
 
STRUCTURE OP SHELL. 553 
 
 ing the lower edge of the section always thicker than the 
 upper. 
 
 Dr. Carpenter describes the shell of the Crab and Lobster 
 as being composed of three layers, viz. the epidermis or 
 cuticle, the rete-mucosum or pigment, and the corium. 
 The epidermis is of a horny nature, being generally more 
 or less brown in colour, and under the highest magnifying 
 powers presenting no trace of structure (fig. 247, No. 2) ; 
 it invests all the outer parts of the shell, and has in many 
 instances large cylindrical or feather-like hairs developed 
 from certain portions of its surface. The rete-mucosum, 
 or pigment cells, consist of either a series of hexagonal 
 cells, forming a distinct stratum, or of pigmental matter 
 diffused throughout a certain thickness of the calcareous 
 layer. (Fig. 247, No. 5.) In the Crab and Lobster it is 
 very thin, but in the Crayfish it occupies in some parts 
 more than one-third of the entire thickness of the shell ; 
 when examined by the microscope, this portion appears to 
 be composed of a large number of very thin laminae, which 
 are indicated by fine lines taking the same direction on 
 the surface of the shell, the number of lines being the 
 greatest in the oldest specimens ; these layers, even in the 
 Crayfish, are covered by a thin stratum of very minute 
 hexagonal cells, without any trace of cell matter in their 
 interior. The corium is the thickest layer of the three, 
 being the one on which the strength of the shell depends, 
 in consequence of the calcareous material deposited in it. 
 (Fig. 247, No. 4.) When a vertical section of the shell of 
 the Crab is examined, it is found to be traversed by parallel 
 tubes, resembling those in the dentine of the human tooth ; 
 these tubes extend from the inner to the outer surface of the 
 shell, and are occasionally covered by wavy lines, probably 
 those of growth, shown in a portion of No. 3, fig. 247. If 
 a horizontal section of the same shell be made, so that the 
 tubes be divided at right angles to their length, the sur- 
 face will clearly exhibit their open ends, surrounded by 
 calcareous matter. In Shrimps and very small Crabs, the. 
 deposition of the calcareous matter takes place in concen- 
 tric rings like those of agate ; and occasionally small cen- 
 tres of ossification, somewhat like Pinna, with radiating 
 strise, are met with in the Shrimp. If the calcareous 
 
554 
 
 THE MICEOSCOPB, 
 
 portion of the shell be steeped in hydrochloric acid, a 
 distinct animal structure or basis is left behind, and the 
 characters of the part will be very accurately preserved. 
 The calcareous matter, like that of bone, generally pre- 
 sents a more or less granular appearance, as at No. 4, and 
 so angular in figure as to resemble certain forms of rhom- 
 boidal crystals : No. 2 is a section from the outer brown 
 shell of the Oyster. The beauty of all such structures is 
 much increased if viewed with polarised light on the 
 selenite stage. 1 
 
 Crustacea. The skeletons of Crustacea are external to 
 the soft parts ; in a great number of species the shell is 
 thin and membranous, in others it is of a horny material, 
 thickened with calcareous matter, having a distinct series 
 of pigment cells of a stellate 
 figure, all supplying beautiful 
 objects for microscopic examina- 
 tion and polarised light. The 
 Astacus, Crayfish, may be taken 
 as the type of that large and 
 important group of Crustacea to 
 which the term Podophthalma, 
 Stalk-eyed, is applied. 2 
 
 Cirrhopoda or Oirripedia, 
 when mature, attach themselves 
 to rocks and other objects. The 
 Barnacle (fig. 254) and Acorn- 
 shell are the best known exam- 
 ples of this order; they gene- 
 Fig. 254. rally select floating objects to 
 
 Young fiy of the Oyster, a dwell Upon ', and bottoms of 
 
 d ships have been covered by them 
 of Barnacles. to such an extent as even to 
 
 impede their progress through the water. The soft bodies 
 of these animals are enclosed in a case composed of five 
 calcareous plates j from this circumstance they were 
 grouped with the multivalve shells of the older, concholo- 
 
 (1) See Prof. Huxley's article on the "Tegumentary Organs," Cyclop. Anat. 
 and Physio, vol. v. p. 487. 
 
 (2) Some valuable information will be found on the minute structure of shells 
 in Prof. Williamson's paper, "On some Histological Features in the Shells of 
 the Crustacea," Journ. Micros. Scien. vol. viii. p. 35, 1860. 
 
ENTOMOSTRACA. 555 
 
 gists. Their limbs are converted into tufts of jointed 
 cirri, and protrude through an opening in the mantle 
 which lines the interior of the shell. The cirri, twelve 
 in number, are covered with cilia, which, when the animal 
 is alive, are in continual motion. The intestinal canal is 
 complete, and the nervous system exhibits the usual 
 series of ganglia, characteristic of the articulate type. 
 The head is marked only by the position of the mouth, 
 and is armed with a pair of jaws, if we may so term 
 the shells. 
 
 BalanidcBy " Sea-acorns," a sessile species, whose curious 
 little habitations may constantly be met with upon the 
 rocks of the sea-shore, and not unfrequently upon many 
 species of marine shells. The shell forms a short tube, 
 and is usually composed of six segments securely united 
 together. The lower part of the tube is firmly fixed to the 
 object on which the Balanus has taken up its abode ; whilst 
 the superior orifice is closed by a movable roof, composed 
 of from two to four valves, between which the little tenant 
 of this curious domicile protrudes his delicate cirri in search 
 of nourishment. In the young state the Balanidce freely 
 swim about, and somewhat resemble the following group, 
 Entomostraca. 
 
 Entomostraca, or Water-fleas, undergo a series of remark- 
 able changes from the moment of their escape from the 
 egg to the attainment of their fully matured form. And 
 it is of the highest interest to remark that, in obedience 
 to a law which, if not universal, is at any rate widely pre- 
 valent in the animal kingdom, these temporary or larval 
 forms are themselves closely analogous to the prefect forms 
 of groups still lower in the scale of existence, so that many 
 of them in their early forms were formerly, before their 
 life-history was known, either classed as distinct species, or 
 placed in a position very far from that which they are now 
 seen to occupy. The embryo of the Shore-crab (Carcinm 
 mcenas) before, and for a short time after, its liberation 
 from the ovum, presents both in size and general outline 
 a strong resemblance to Entomostraca. In this transi- 
 tion stage it was assigned to a distinct genus under the 
 name of Zoea ; and having undergone a still further trans- 
 formation was called Megalopa. In this latter stage it 
 
556 
 
 THE MICROSCOPE. 
 
 puts on somewhat the appearance of the Lobster crab 
 (Galathea), and after another step attains its true crab- 
 form, being the highest development of which it is capable. 
 These changes are not produced gradually, but by a suc- 
 cession of " moults," the animal becoming at times sluggish, 
 casting its hard covering, and reappearing in a new guise. 
 The after growth of a crustacean is carried on by the system 
 of moulting ; the hard calcareous case of the animal pre- 
 venting its growth in any other mode. And as in the 
 higher orders of Crustacea, so also amongst the Entomos- 
 traca, transformations of this kind constantly take place. 
 Cyclops quadricornis, when first born, is totally unlike its 
 parents, being of an ovoid shape, having only two shoit 
 antenna and two pairs of feet ; in three moults the 
 animal reaches its perfect form, with its two pairs of an- 
 tennae, five pairs of feet, and body divided into several 
 distinct rings or segments. 
 
 The animals comprising the order Ostracoda are generally 
 of very minute size ; the body, 
 which strongly resembles that 
 of the Copepoda, is always 
 enclosed in a little bivalve 
 shell, the feet and antenna 
 being protruded between the 
 lower edges of the valves. 
 These little shells so closely 
 resemble those of minute 
 bivalve Mollusca, that those 
 of some of the larger species 
 have actually been described 
 by conchologists as the cover- 
 ing of animals belonging to 
 that class. The antennaj are 
 often curiously branched ; and 
 the hinder extremity is usu- 
 ally prolonged into a sort of 
 tail, which is seen in constant 
 action when the animal is in 
 motion. In Cypridina, the 
 body is entirely enclosed by 
 a shell, of which the genus Gypris (fig. 255) is an example ; 
 
 Fig. 255. 
 
ENTOMOSTRACA. 557 
 
 and in Daphnia, " Water-fleas," the head is protruded be- 
 yond the shell. In Polyphemidce the head is large, and 
 almost entirely occupied by an enormous eye, giving the 
 creatures a most singular appearance; the Monoculw is 
 a well-known example of this group. Another family, 
 not provided with a shell or carapace, called Branchio- 
 poda, from the name of the typical genus, Branchiopus 
 stagnalis (fig. 255), is often found after heavy rains in 
 cart-ruts and other small pools. 
 
 Daphnia pulex is found commonly in fresh water, and 
 is scarcely inferior to its marine relative, Talitrus locusta, 
 in agility. The Corophium longicome, remarkable for its 
 long antennae, is not less so for its singular habits. It 
 is found at Eochelle, where it burrows in the sand, and 
 wages constant war with all other marine creatures of 
 moderate size that come in its way. 
 
 Dr. Baird has followed up the successive generations in 
 Daphnia pulex ; so far as the fourth change in the Daphnia 
 born from the ordinary ova, and so far as the third in those 
 born from the ephippial eggs. These ephippia, or " winter 
 eggs," require a few words of explanation. They are, in fact, 
 eggs covered with envelopes of more than usual hardness 
 and thickness, being enabled to withstand an excess of 
 cold, which would surely prove fatal to the parent. This 
 observer found, upon examining ponds which had been 
 filled up again by the rain after remaining two months 
 dry, numerous specimens of the Cyclops quadricomis in 
 all stages of growth. Dr. Baird, in his " Natural History 
 of British Entomostraca," 1850, tells us that they have 
 many enemies. 
 
 " The larva of the Corethra plumicomis y known to micro- 
 scopical observers as the skeleton larva, is exceedingly rapa- 
 cious of the Daphnia. Pritchard tells us they are the choice 
 food of a species of Nais ; and Dr. Parnell states that the 
 Lochlevin trout owes its superior sweetness and richness of 
 flavour to its food, which consists of small shell-fish and En- 
 tomostraca." These animals abound both in fresh and salt 
 water. A rtemice are formed exclusively in salt water, in salt 
 marshes, and in water highly charged with salt. " Myriads 
 of these Entomostraca are to be found in the salterns at 
 Lymington, in the open tanks or reservoirs where the brine 
 
558 THE MICROSCOPE. 
 
 is deposited previous to boiling. A pint of the fluid 
 contains about a quarter of a pound of salt, and this con- 
 centrated solution destroys most other marine animals." 
 During the fine days in summer Artemice may be observed 
 in immense numbers near the surface of the water, and, as 
 they are frequently of a lively red colour, the water appears 
 tinged with the same hue. 1 There is nothing more elegant 
 than the form of this little animal. Its movements are 
 peculiar. It swims almost always on its back, and by means 
 of its tail it runs in all directions, its feet being in constant 
 motion. They are both oviparous and ovoviviparous, accord- 
 ing to the season of the year. At certain periods they only 
 lay eggs, while during the hot summer months they pro- 
 duce their young alive. In about fifteen days the eggs are 
 expelled in numbers varying from 50 to 150. As is the 
 case with many of the Entomostraca, the young present a 
 very different appearance from the adult animals ; and 
 they are so exactly like the young of Chirocephalus, that with 
 difficulty they can be distinguished the one from the other. 
 The ova of other species are furnished with thick cap- 
 sules, and imbedded in a dark opaque substance, presenting 
 a minutely cellular appearance, and occupying the inter- 
 space between the body of the animal and the back of the 
 shell. This is called the ephippium. 2 The shell is often 
 beautifully transparent, sometimes spotted with pigment : 
 it consists of a substance known as chitine, impregnated 
 with a variable amount of carbonate of lime, which pro- 
 duces a copious effervescence on the addition of a small 
 quantity of acid, and when boiled it turns red, like the 
 lobster. Their shells vary in structure. Sometimes they 
 consist of two valves united at the back, and resembling 
 
 (1) It is a curious fact that salt-water when highly concentrated frequently 
 assumes a red colour, and that this should have been attributed to the presence 
 of the Artemia, salina, as in the case of fresh-water noticed elsewhere found 
 coloured red by a species of Paramcecium, The cause of this red colour, which 
 was well known to take place in the salt marshes and reservoirs of salt-water 
 at Montpellier, was made the subject of a very grave discussion in France. 
 Some maintained that the colour was caused by the presence of Artemice, while 
 others declared that it arose from vegetable matter, either Hcematococcus or 
 frotococcus. M. Joly, came to the conclusion, after many careful examinations, 
 that the red colour depends upon the presence of myriads of monads, and that 
 the Artemice living upon these partook of the same red hue, and thus the water 
 appeared to be of the same colour. 
 
 (2) See paper on " Reproduction in DapJmia" by Sir John Lubbock, Philoa, 
 Trans. 1857, p. 79. 
 
ANNULOSA. 559 
 
 the bivalve shell of a mussel ; others are simply folded at 
 the back, so as to appeal* like a bivalve, but are really 
 not so ; or they consist of a number of rings or seg- 
 ments. The body of the Cypris presents a reticulated 
 appearance, resembling that of cell structure. All the 
 Entomostraca are best preserved in a solution of chloride 
 of calcium. 
 
 ANNULOSA. Articulata. The animals composing the 
 sub-kingdom Articulata are characterised by having the 
 body enclosed in a tunic, or integument, consisting of a 
 series of rings, segments, or joints, " articulated " together 
 by a flexible membrane. 
 
 The Anmdosa are divided, by Professor Huxley, into 
 two principal groups, the Arttiropoda and the Annuloida. 
 TheArthropoda, comprising Insecla, Myriapoda, Crustacea, 
 and Arachnida, possess a definitely segmented body; the 
 segments being provided with appendages, the anterior of 
 which are so modified as to subserve the functions of sen- 
 sation and manducation. They have almost always a heart, 
 communicating with the general cavity of the body, for 
 propelling the true corpusculated blood which that cavity 
 contains. The nervous system consists of a longer or a 
 shorter chain of ganglia. 
 
 Nothing can be more variable than the characters of the 
 body, the appendages, and the nervous system among the 
 rest of the Annulosa, which are included under the Annu- 
 loida; nevertheless, there are two features in which they 
 all agree ; firstly, they possess a remarkable system of 
 vessels, either ciliated, or deprived of cilia, and containing 
 a fluid very different from the true blood which fills the 
 general cavity of the body or perivisceral space ; secondly, 
 in no annuloid animal has any true heart been hitherto 
 discovered. Contractile vessels belonging to the system 
 just referred to abound, but no organ comparable in struc- 
 ture to the heart of other animals has yet been found in 
 any of the A nnuloida. 
 
 The Annuloida, as thus defined and limited, fall into 
 two parallel series ; in one of which, for the most part, 
 dioecious forms predominate, as the Annelida, while of 
 the latter, the Trematoda may be regarded as the typical 
 example ; on the other hand, the Echinoderniata and 
 
560 THE MICROSCOPE. 
 
 Rotifera, the Tceniadce and the Nematoidea, may be con- 
 sidered as the most aberrant groups of their respective 
 series. 
 
 Under the head Annelida, Mr. Huxley includes the 
 errant and tubicular Annelids of Cuvier, and the Gephyrea 
 of De Quatrefages; he thinks that the Terricola the 
 Earthworms and Naides should be separated from the 
 Scoledce of Milne Edwards, and brought into the same 
 group. So far as external structure is concerned, the 
 genus Polynoe is, perhaps, the best fitted to serve as the 
 type to which other Annelida may be referred : the com- 
 monest form of the genus being the P. squamata. 1 The 
 best developed branchiae among the Annelids are possessed 
 by the Amphinomidce, the Unnicidce, the Terebellidce, and 
 the Serpulidce. The branchia3 in the three former families 
 are ciliated, branched plumes or tufts attached to the 
 dorsal surface of more or fewer of the segments. In the 
 last they are exclusively attached to the anterior segments 
 of the body, and present the form of two large plumes, 
 each consisting of a principal stem, with many lateral 
 branches; this stem is itself supported on a kind of 
 cartilaginous skeleton. 
 
 The teeth in a great number of the Annelida are very 
 curious and distinctive. In the Polynoe there are four, 
 planted in the muscular wall of the proboscis. In the 
 Nereis there are two powerful teeth working horizontally, 
 besides minute accessory denticles. In Syllis there is a 
 circle of sharp teeth', surrounding a triangular median 
 tooth. In Glycera there are a pair of teeth ; but the most 
 complex arrangement of teeth is that presented by the 
 EnnicidcB. The tubicular Annelids possess neither pro- 
 boscis nor teeth. 
 
 Many Annelids pass through a larval condition, in 
 which the body exhibits mere indications of segments, 
 and the appendages are entirely absent; locomotive 
 function being performed by a circlet of cilia, disposed 
 around the anterior part of the body. There is a large 
 group of very remarkable organisms, observes Mr. Huxley, 
 the minute " wheel animalcules," Rotifera, whose whole 
 
 (1) Consult a valuable paper on this genus in M tiller's Archiv. 1857. Also 
 Huxley's "Elements of Comparative Anatomy." 
 
ANNULOSA. 561 
 
 organization demonstrates, not merely their annulose 
 nature, but their position among the Annuloida, and 
 which exhibit precisely the same indistinct segmentation, 
 the same general absence of appendages, and whose means 
 of locomotion are in like manner confined to one or two 
 ciliated circlets at the anterior part of the body. The 
 connexion between the Annelida and the Rotifera is 
 further illustrated by such remarkable forms as the 
 Poly ophthalmia of De Quatrefages, a true Annelid, which, 
 nevertheless, possesses on each side of the head a ciliated 
 lobe, capable of being voluntarily protruded and retracted, 
 and presenting a close resemblance to the trochal disc of a 
 Botifer. Hydatina senta has been so well and accurately 
 described by Dr. Cohn, 1 and others, that it may be taken 
 as the typical form of the Rotifera. The trochal disc in 
 the species, undergoes great changes of form. In Hydatina, 
 it is circular, and its margin is skirted by two distinct con- 
 tinuous bands of cilia, the one immediately in front of, the 
 other behind the mouth. In Brachionus the ciliated circlet 
 fringing the edges of the trochal disc is horseshoe-shaped, 
 but the circlet is produced into three lobes or processes, 
 which stand out perpendicularly to the surface of the 
 trochal disc. In Stephanoceros it fringes the edges of a 
 number of tentaculiform processes, into which the trochal 
 disc is produced, so as to give the whole animal somewhat 
 the appearance of a Polyzoon. 
 
 The Turbellaria, a group of serpent-like worms, for 
 the most part the inhabitants of fresh and salt waters, a 
 few only being found in damp siuations on land, are 
 characterised by the ciliation of the entire surface of the 
 body. In their internal organisation they approximate in 
 many respects to the Trematoda, while in others they 
 exhibit a certain affinity with the other great group of 
 parasitic Annuloida, the Nematoidea. Polycelis Icevigatus, 
 one of the Dendrocoda so well described by De Quatrefages 
 in his Monograph on the Marine Planarice, may be most 
 advantageously selected as a type of the group. The 
 NemertidoB have engaged the attention of the same learned 
 authority, the ova of which undergo a remarkable kind of 
 
 (1) Utber die Fortflawzung der Radtrlhiere, Von Dr. F. Cohn, in Breslao, 
 1859. 
 
 O O 
 
562 THE MICROSCOPE. 
 
 metamorphosis. The embryo has at first a ciliated non- 
 contractile, oval body, exhibiting no structure but a semi- 
 lunar superficial cleft, provided with raised edges. After 
 a time, a small actively-contractile, vermiform creature, 
 resembling the parent, escapes from the interior of the 
 larval form, which it leaves behind like a cast skin. The 
 semilunar cleft becomes the mouth of the imago, and is 
 only part of the larva carried away. The Gordiacei 1 best 
 enable us to connect the Turbellaria with the very puzzling 
 group Nematoidea, and the structure of several species 
 belonging to the two genera which compose the group 
 Mermis and Gordius, have recently been made the subject 
 of two elaborate monographs by Meissner. 2 
 
 The Gordiacei are excessively elongated, thread-like 
 worms, plentiful enough in Thames mud, and, as Von 
 Siebold discovered, partake both of the free habit of the 
 Nemertidce, and of the parasitic nature of the Nematoidea. 
 The young Mermis, for instance, is parasitic upon insects, 
 inhabiting the peri visceral cavity of the larva or of the 
 imago. 
 
 The Nemertidce seem to differ from their close allies the 
 Turbellaria, in possessing a vascular system distinct from 
 and added to the water-vessels. In the Hirudinidce, Leeches 
 and Earthworms, a system of vessels homologonous with 
 the pseud-heemal system exists, and, in addition a series 
 of more or less coiled tubules lie in the perivisceral cavity, 
 and open, by pores, on the ventral surface of the body. 
 These organs have been regarded sometimes as secretory, 
 sometimes as respiratory apparatus; but all that we 
 know about them in reality is that they are tubular, and 
 are more or less richly ciliated within, and that, in some 
 cases (Nais, Lumbricus), they present at their internal ex- 
 tremities a ciliated aperture, whereby they freely com- 
 municate with the perivisceral cavity. 
 
 There remains, however, yet another system of vessels 
 in the Annuloida the ambulacral vessels of the Echino- 
 dermata. These are frequently termed " water- vessels," 
 and, indeed, if we regard the structure with reference to 
 
 (1) Huxley, General Natural History. 
 
 (2) Beitrdge zur Anatomic und Physiologic von Mermis Albicaus, v. Zeitschrift 
 fur Wiss, Zoologie, Bd. v 1854 ; and Beitrdge zurAnat. f Physiol. des Gordiacen, 
 Ibid. Bd. vii, 1855. 
 
ANNULOSA. 563 
 
 their peculiar functions, they singularly resemble true 
 water-vessels ; they open by an external pore, and are 
 ciliated internally ; they unite around the gullet, as do the 
 water- vessels in some Trematoda, and are eventually shut 
 off from such communication; the ambulacral vessels of 
 the HolothuridoB undergo precisely this change, and thus 
 they facilitate our comprehension of a transition from the 
 water-vessels of the Trematoda to the pseud-hsemal vessels 
 of the Annelida. We may take it as an established fact 
 that, whatever the functions of this varied vascular system 
 and its contents in different classes of the Annuloida, 
 they have nothing to do with the blood or true blood 
 vessels. The latter are entirely absent in all the Annu- 
 loida at present known, the blood (improperly called 
 " chyle-aqueous fluid ") being simply contained in the peri- 
 visceral cavity and its processes. The development of 
 the Nematoidea appears to take place without metamor- 
 phosis ; the embryo assuming within the egg a form nearly 
 resembling that of the adult. Encysted asexual nematoid 
 worms are frequently found in various parts of the body 
 of fishes; and the remarkable Trichina spiralis is the 
 asexual state of a nematoid worm, encysted within the 
 substance of the muscles of man. Zooid development is 
 only known to occur in one nematoid, the Filaria Medi- 
 nensis, Guinea-worm. Mr. Busk's careful observations 
 have long since placed this fact beyond a doubt. 
 
 The Tceniadce and the Acanthocephala, like the Trema- 
 toda, entirely parasitic in their habits, differ from them in 
 the total absence of mouth or digestive cavity. The 
 Taniada, Tapeworms, are ribbon-like creatures, usually 
 divided throughout the greater part of their length into 
 segments, whose usual habitation is the intestinal cavity 
 of vertebrate animals ; and apparently of a carnivorous 
 vertebrate, in fact, though capable of existence elsewhere, 
 it is there alone that they are able to attain their complete 
 development. The anterior extremity of a taenoid worm 
 is usually called the head, and bears the organ by which 
 the animal attaches itself to the mucous membrane of the 
 creature which it infests. These organs are either suckers 
 or hooks, or both conjoined. In Tcenia, four suckers are 
 combined with a circlet of hooks, disposed around a median 
 o o 2 
 
664 THE MICROSCOPE. 
 
 terminal prominence. The embryo passes tt rough, a 
 similar course of development to the Trematoda ; viz. 
 four forms or changes : but the embryo itself is very 
 peculiar, consisting of an oval non-ciliated mass, provided 
 upon one face with six hooks, three upon each side of the 
 middle line. The Tceniadce are found in many other 
 situations besides the alimentary canal : the eye, the brain, 
 the muscular tissues, the liver, &c. ; the following cystic 
 worms are included in this genera, Cysticercus Anthoce- 
 phalus, Ccenurus, and T. Echinococcus. Plate IV. No. 100, 
 this figure shows an entire and full-grown Tcenia with 
 rostellum and suckers, and then three succeeding segments, 
 the last of which contains the ova, &c. The water-vascular 
 system is represented coloured with carmine. This para- 
 site infests the human body more frequently than other 
 varieties. This accuratelv-drawn figure is copied from 
 Cobbold. 
 
 Von Siebold, Leuckart, and others, have shown, by many 
 interesting experiments, such as feeding puppies with Cys- 
 ticercus pisiformis, that in the course of a few weeks these 
 entozoa are transformed into fully formed Tcenia serrata , 
 again, rabbits fed with the embryo of the Tcenia, the 
 embryo bore their way, by means of hooks, through the 
 walls of the intestine, until they reach some blood-vessel : 
 by the current of blood they are carried into the liver, 
 and here Leuckart has traced their further development. 
 The embryos grow to the 1-1 6th of an inch in length, and 
 become elongated, so as almost to resemble an Ascarid in 
 form ; they then make their way to the surface of the liver, 
 and pass out into the peritoneal cavity. 
 
 In like manner, Cysticercus fasciolaris is rapidly developed 
 within the liver of white mice ; Cysticercus celluloses seen 
 in the muscles of the pig fed with the Tcenia solium, pro- 
 duces the diseased state of pork familiarly known as 
 " measly pork." If a lamb is the subject of the feeding 
 experiment with Tcenia serrata, the final transformation 
 will be very different ; within a fortnight, symptoms of 'a 
 disease known as " staggers" are manifested, and in the 
 course of a few weeks, the Ccenurus cerebralis will be found 
 transformed and developed within the brain. Von Siebold 
 pointed out the bearing of this fact upon the important 
 
TREMATODA. 565 
 
 practical problem of the prevention of " staggers." Others 
 of the same family of parasites are quite as remarkable, in 
 giving a preference to the alimentary canal of fishes. The 
 Echinorliynchus is developed in the canal of the Flounder, 
 Tricenophorus nodulus in the liver of the Salmon, attain- 
 ing a more perfect development in the alimentary canal of 
 the Perch and Pike. Another, found in the Stickleback, 
 becomes changed in the intestines of water birds, which 
 devour these fish ; and thus, by careful and repeated 
 observations with the microscope, the connexion existing 
 between the Cystic and Cestoid Entozoa have been most 
 satisfactorily established. 
 
 The Fluke belongs to the order Trematoda, which 
 signifies that they are internal parasites, suctorial worms, 
 or helminths ; they are all usually visible to the naked 
 eye, although a few of the smallest scarcely exceed l-100th 
 of an inch in length ; many are larger, and the species best 
 known, Fasciola hepatica, attains to an inch or more in 
 length. The Fluke shown in Plate IV. No. 103, is cone- 
 shaped : it is the Amphistome conicum of Kudolphi. This 
 parasite is common in oxen, sheep, and deer, and it has also 
 been found in the Dorcas antelope. It almost invariably 
 takes up its abode in the first stomach, or rumen, attaching 
 itself to the walls of the interior. 1 In the full-grown state 
 it never exceeds half an inch in length ; in our plate it is 
 represented magnified. On closer inspection it will be seen 
 that the animal is furnished with two pores or suckers, one 
 at either extremity of the body, the lower being by far the 
 larger of the two. By means of the latter the Amphistome 
 anchors itself to the papillated folds of the paunch, or first 
 stomach, as this organ is improperly called. 
 
 In the figure the oral sucker at the anterior end, or head, 
 leads into a narrow tube, forming the throat or oesophagus, 
 and this speedily divides, or rather widens out, into a pair 
 of capacious canals. These cavities are correctly regarded 
 
 (1) The larval condition of AmphiAomaw. all probability lives in or upon the 
 body of snails. This we infer from the circumstance that the larvae, cercarice, 
 of a closely allied species, the Amphistomasubclavatum, which is known to infest 
 the alimentary canal of frogs and newts, have been also found on the surface of 
 the body of the Planorbis by ourselves, whilst Van Beneden discovered the 
 larvae in a species of Cyclas. The cercarice, larvae, are taken, it is supposed, by 
 the cattle while drinking. They then attach themselves to the walls of th 
 t tomach, where they soon complete their further stages of development. 
 
566 THE MICROSCOPE. 
 
 as together constituting the stomach ; but they are coecal, 
 that is, closed below, having no other outlet than the 
 entrance above mentioned. The water-vascular system, 
 artificially coloured in the plate, or rather the vessels thus 
 named, bear a very striking resemblance to that of arteries 
 or veins ; and the centrally-placed pouch, shown in the 
 figure, might very easily be taken to represent the heart. 
 This large cavity gives origin to two primary trunks, which 
 pass forward along the inner sides of the digestive caeca ; in 
 their passage they send off secondary branches, which divide 
 and sub-divide until we arrive at a series of minute capil- 
 lary ramifications ; the latter, according to Blanchard, 
 terminating in small oval-shaped sacs or lacunas. 
 
 " It should be further observed, that the surface of the 
 Amphistome, though quite smooth to the naked eye, is 
 clothed with a series of minute tubercles, which may be 
 readily brought into view under a half-inch object glass. 
 Beneath the cuticle we find a layer of cellules forming the 
 true skin ; and beneath this, again, there are two, if not 
 three, layers of muscular fibre ; an anterior longitudinal 
 series and an inner circular set being readily distinguish- 
 able. The substance of the body is traversed by bands of 
 cellular parenchyma or connective tissue, which here and 
 there form thickened sheaths for the support of the various 
 delicate organs above described." The reproductive organs 
 of flukes possess the greatest amount of interest both from 
 an anatomical and physiological point of view. They are 
 produced from eggs, which are found in large numbers in 
 the ova-sac; varying in size from l-150th to l-250th of 
 an inch. 
 
 ""The large fluke (Fasciola hepatica) is not only of 
 frequent occurrence in all varieties of grazing cattle, but 
 has likewise been found in the horse, the ass, and also in 
 the hare and rabbit, and in some other animals. Its occur- 
 rence in man has been recorded by more than than one 
 observer ; the oral sucker forming the mouth leads to the 
 short oesophagus, which very soon divides into two primary 
 stomachal or intestinal trunks, which latter in their turn 
 give off branshes and branchlets ; the whole together form- 
 ing that beautiful dendritic system of vessels which has 
 often been compared to plant-venation. This remarkably- 
 
TREMATODA. 567 
 
 formed digestive apparatus is accurately represented in 
 Plate IV. Nos. 106 and 107, Fasciola gigantea of Cobbold, 
 which should be contrasted with the somewhat similarly 
 racemose character of the water- vascular system. Let it be 
 expresely noted, however, that in the digestive system the 
 majority of the tubes branch out in a direction obliquely 
 downwards, whereas those of the vascular system slope 
 obliquely upwards. A further comparison of the dis- 
 position of these two systems of structure, with the 
 same systems figured and described as characteristic of 
 the Amphistome, will at once serve to demonstrate the 
 important differences which subsist between the several 
 members of the two genera, if we turn to the con- 
 sideration of the habits of Fasciola hepatica, which, 
 in so far as they relate to the excitation of the liver 
 disease in sheep, acquire the highest practical import- 
 ance. Intelligent cattle-breeders, agriculturists, and veteri- 
 narians have all along observed that the rot, as this 
 disease is commonly called, is particularly prevalent after 
 long-continued wet weather, and more especially so if 
 there have been a succession of wet seasons ; and from this 
 circumstance they have very naturally inferred that the 
 humidity of the atmosphere, coupled with a moist condi- 
 tion of the soil, forms the sole cause of the malady. Co- 
 ordinating with these facts, it has likewise been noticed that 
 the flocks grazing in low pastures and marshy districts are 
 much more liable to the invasion of this endemic disease 
 than are those pasturing on higher and drier grounds ; a 
 noteworthy exception occurring in the case of those flocks 
 feeding in the salt-water marshes of our eastern shores." * 
 Plate IV. No. 106, Fasciola gigantea: the anterior surface 
 is exposed to display oral and ventral suckers, and the 
 dendriform digestive apparatus injected with ultramarine ; 
 JSTo. 107, shows the dorsal aspect of the specimen and 
 the multiramose character of the water-vascular system, 
 the vessels injected with vermilion. 
 
 One of the most remarkable of the Trematode helminths 
 is BUharna hcematobra of Cobbold ; Distomia hcematobium 
 of some other authors. Plate IV. !Nb. 102. This genus 
 
 (1) Entozoa: An Introduction to the Study of Helminthology. By T. Spencer 
 Cobbold, M.D. F.R.S. 1866. P. 143. 
 
{568 THE MICROSCOPE. 
 
 of fluke, discovered by Dr. Bilharz in the human portal 
 system of blood vessels, gives rise to a very serious state of 
 disease among the people of Egypt. So common is the 
 occurrence of this worm, that this physician expressed his 
 belief that half the grown-up people are infested with it. 
 Griesinger conjectures that the young of the parasite exists 
 in the waters of the Nile, and in the fishes which abound 
 therein. Dr. Cobbold thinks " it more probable that the 
 larvse, in the form of cercariee, redia3, and sporocysts, will 
 be found in certain gasteropod moliusca proper to the 
 locality." The anatomy of this fluke is fully described in 
 Kuchenmeister's able work on Parasites, by Leuckart, and 
 by Cobbold. The eggs and embryos of Bilharzia are 
 peculiar in possessing the power of altering their forms in 
 both stages of life ; and it is more than probable that the 
 embryo form has been mistaken for some extraordinary 
 form of ciliated infusorial animalcule, their movements 
 being most quick and lively. We cannot fail to notice 
 the curious leech-like form of the male animal, and, re- 
 markable enough, he is generally found carrying the female 
 about. The whip-like appendage seen in the figure is a 
 portion of the body of the female. The disease produced 
 by them is said to be more virulent in the summer months, 
 which is probably owing to the prevalence of the cercarian 
 Iarva3 at the spring time of the year. 
 
 Trichina spiralis. This, the smallest of the helminths, 
 measures only the l-20th of an inch. The female is a little 
 larger ; it was discovered by Professor Owen in a portion 
 of the human muscle sent to him from St. Bartholomew's 
 Hospital, 1834. The young animal presents the form of 
 a spirally- coiled worm in the interior of a minute oval- 
 shaped cyst (Plate IV. No. 104), a very small speck 
 scarcely visible to the naked eye. In the muscle it resem- 
 bles a little particle of millet seed, more or less calcareous 
 in its composition. The history of the development of 
 Trichinae in the human muscle is briefly that in a few 
 hours after the ingestion of diseased flesh, Trichince, dis- 
 engaged from the muscle, are found free in the stomach : 
 they pass thence into the duodenum, and afterwards 
 advance still further into the small intestine, where they 
 become, developed. From the third or fourth day, ova or 
 
TRICHINA SPIRALIS. 569 
 
 spermatic cells are found, the sexes in the mean while be- 
 coming distinctly marked. Shortly afterwards the ova are 
 impregnated, and young living entozoa are developed within 
 the bodies of the female. The young have been noticed 
 (by Virchow) under the form of minute Filarice, more 
 especially in the serous cavities, in the mesenteric glands, 
 &c. Continuing their migrations, they penetrate as 
 far as the interior of the primitive muscular fasciculi, 
 where they may be found as early even as three days 
 after ingestion, in considerable numbers, and so far deve- 
 loped that the young entozoa have almost attained a size 
 equal to that of the full-grown Trichinae. They pro- 
 gressively advance into the interior of the muscular fasci- 
 culi, where they are often seen several in a file one after 
 the other. Behind them the muscular tissue becomes 
 atrophied, and around them an irritation is set up, and 
 from the commencement of the third week they are found 
 ancysted. The sarcolemma is now thickened, and the 
 contents of the muscular fibres exhibit indications of a 
 more active cell-growth ; the cyst is the product of a sort 
 of inflammatory irritation. 
 
 Professor Virchow draws the following conclusions : 
 " 1. The ingestion of pig's-flesh, fresh or badly dressed, 
 containing Trichince, is attended with the greatest danger, 
 and may prove the proximate cause of death. 2. The 
 Trichinae maintain their living properties in decomposed 
 flesh ; they resist immersion in water for weeks together, 
 and when encysted may, without injury to their vitality, 
 be plunged in a sufficiently dilute solution of chromic acid 
 for at least ten days. 3. On the contrary, they perish and 
 are deprived of all noxious influence in ham which has 
 been well smoked, kept a sufficient length of time, and 
 then well boiled before it is consumed." 
 
 The Echinococcus found in cysts, chiefly in the human 
 liver, is represented in Plate IV. No. 101. A large col- 
 lection was taken from the liver of a boy who died in 
 Charing-cross Hospital from accidental rupture of the 
 liver. The cysts containing these parasites are always 
 situated in cavities in the interior of the body. These 
 cavities may be situated in any part of the tissues or organs 
 of the body, but are more frequently found in the solid 
 
570 
 
 THE MICROSCOPE. 
 
 viscera, and especially in diseased livers. Fig. 256 repre- 
 sents the microscopical appearance of the contents of a cyst. 
 
 . Fig. 256. Cystic Disease of Liver. (Human). 
 
 a, Cyst with an echinococcus enclosed. &, Detached hooklets from the head of 
 Echinococcus, magnified 250 diameters, c, Crystals found in the cyst, choles- 
 terine. d, Cylindrical epithelium, some enclosed in structureless globules. 
 e. Puro-mucus, and fat corpuscles. 
 
 Mr. Busk, who has examined several of these cysts, 
 says : "When a large hydatid cyst, for instance, in the 
 liver of the sheep, very shortly after the death of the 
 animal, is carefully opened by a very small puncture, so. as 
 to prevent at first the too rapid exit of the fluid, and con- 
 sequent collapse of the sac, its internal surface will be 
 found covered with minute granulations resembling grains 
 of sand. These bodies are not equally distributed over 
 the cyst, but are more thickly situated in some parts than 
 in others. They are detached with the greatest facility, 
 and on the slightest motion of the cyst, and are rarely 
 found adherent after a few days' delay. When detached, 
 they subside rapidly in the fluid, and consequently will 
 then be usually found collected in the lowest part of the 
 cyst, and frequently entangled in fragments of the inner 
 thin membrane. When some of these granulations are 
 placed between glass under the microscope, and viewed 
 with a power of 250 diameters, upon pressure being em- 
 ployed it will be seen, after rupture of the delicate enve- 
 loping membrane, that the Echinococci composing the gra- 
 nulations are all attached to a common central mass by 
 short pedicles ; which, as well as the central mass, appear 
 to be composed of a substance more coarsely granular by 
 
571 
 
 far than that of which the laminae of the cyst are formed. 
 This granular matter is prolonged beyond the mass of 
 Echinococci into a short pedicle, common to the whole, and 
 by which the granulation is attached to the interior of the 
 hydatid cyst, as represented in No. 101. In specimens 
 preserved in spirits, Echinococci of all imaginable forms and 
 appearances are to be met with, differences owing to de- 
 composition or to mechanical injury ; and in many cases 
 no traces of them can be found except the booklets or 
 spines, -which, like the fossil remains of animals in 
 geology, remain as certain indications of their source, and 
 not unfrequently afford the only proof we can obtain of 
 the true nature of the hydatid." 1 
 
 The Echinorhynchi, or Acantho cephali, constitute a 
 group of entozoa, with respect to whose development and 
 life-history we are indebted to Prof. Leuckart of Giessen. 
 Most observers, and in particular Von Beneden and G. 
 Wagner, have been disposed to assign to the Echinorhynci 
 a simple metamorphosis, hardly perhaps more remarkable 
 than that which has been shown to take place in some 
 other of the Nematode worms. The latter observer goes 
 so far even as to believe that the organization of the per- 
 fect animal may be discerned in the embryo. Leuckart 
 instituted, in 1861, a series of experiments with the ova 
 of Echinorhynchm Proteus, which is found parasitic upon 
 the Gammarus Pulex. The ova " of E. Proteus resemble 
 in form and structure those of the allied species. They 
 are of a fusiform shape, surrounded with two mem- 
 branes, an external, of a more albuminous nature, and an 
 internal, chitinous one. When the eggs have reached the 
 intestine, the outer of these membranes is lost, being in 
 fact digested; whilst the inner envelope remains until 
 ruptured by the embryo." 2 
 
 Anguillulce are very small eel-like worms, of which one 
 species, 3 Anguillula fluviatilis, is found in rain-water 
 amongst Confervas and Desmidiacece, in wet moss and 
 moist earth, and sometimes in the alimentary canal of the 
 
 1) Microscopical Society's Transactions. 1st Seriee. 
 
 (2) Prof. Leuckart "On Echinorhynchus." Journ. Micro. Soc. voL iii. p. 57. 1863. 
 
 (3) For the fullest information of marine, land, and fresh-water species, con- 
 It Dr. Bastian's "Monograph on the Anguillulida." Lin. Soc. Trans. voL 
 
 xxv. p. 75. The "Anguillula Aceti." Popular Science Review, January, 1863. 
 
572 THE MICROSCOPE. 
 
 Limneus, the frog, fish, &c. ; another species is met with 
 in the ears of wheat affected with a blight termed the 
 " cockle ;" another, the A. glutinis, is found in sour paste; 
 and another, A. aceti, in stale, bad vinegar. If grains 
 of the affected wheat are soaked in water for an hour 
 or two before they are cut open, the eels will be seen in 
 a state of activity when placed under the microscope. 
 The paste-eel makes its appearance spontaneously in the 
 midst of paste that is turning sour ; but the best means of 
 securing a supply for any occasion, consists in allowing 
 any portion of a mass of paste in which they show them- 
 selves, to dry up, and then lay it by for stock; if at any 
 time a portion of this is introduced into a little fresh 
 made paste, and the whole kept warm and moist for a few 
 days, it will be found to swarm with these curious little 
 worms. A small portion of paste spread over one face of 
 a Coddington lens is a ready way of showing them. 
 
 Planarice: a genus of the order Turbellaria. Some of the 
 species are very common in pools, and resemble minute 
 leeches; their motion is continuous and gliding, and they 
 are always found crawling over the surfaces of aquatic 
 plants and animals, both in fresh and salt water. The 
 body has the flattened sole-like shape of the Trematode 
 JEJntozoa; the mouth is surrounded by a circular sucker, 
 this is applied to the surface of the plant from which the 
 animal draws its nourishment. The mouth is also fur- 
 nished with a long funnel-shaped proboscis, and this, even 
 when detached from the body, continues to swallow any- 
 thing presented to it. 
 
 "In imitation of the name bestowed on the trunk of 
 the elephant, the extensile organ serving to imbibe the 
 nutriment of many of the smaller animals is called a pro- 
 boscis, whether it simply unfolds from the root, protrudes 
 from a sheath, or unwinds from a regular series of volu- 
 tions. But in none is the designation equally strict and 
 appropriate as in the Planarice. There it is absolutely the 
 organ of the elephant in miniature, with this exception, 
 that it is neither annulated nor composed of segments. 
 It is of surprising length, being little, if any, shorter when 
 fully extended than the whole animal. It seems of greater 
 consistency, harder, and tougher than the rest of the body 
 
573 
 
 BO as to admit insertion into decaying vegetables, and 
 waen stretched to the utmost the root becomes an apex of 
 the slenderest cone." 1 
 
 Planarice multiply by eggs, and by spontaneous fissura- 
 tion, in a transverse direction, each segment becoming a 
 perfect animal. Professor Agassiz believes that the infu- 
 sorial animals, Paramcecium and Kolpoda, are nothing else 
 than Planarian larvce. 
 
 Hirudinidce, the Leech tribe, are usually believed tc 
 form a link between the Annelida on the one hand, and 
 the Trematoda on the other; but their affinities are closer 
 connected with the latter than the former. Totally deprived 
 of the characteristic setae of the Annelida, and exhibiting 
 no sectional divisions, they are provided -with suckers so 
 constantly possessed by the Trematoda, and present no 
 small resemblance] to them in their reproductive organs. 
 On the other hand, in the arrangement of their nervous 
 system and in their vascular system, the Hirudinidce 
 resemble the Annelida. The head in most of these animals 
 is distinctly marked, and furnished with eyes, tentacles, 
 mouth, and teeth, and in some instances with auditory 
 vesicles, containing otolithes. The nervous system con- 
 sists of a series of ganglia running along the ventral 
 portion of the animal, and communicating with a central 
 mass of brain. 
 
 The medicinal leech puts forth strong claims to our 
 attention, on the ground of the services which it renders 
 to mankind. The whole of the family live by sucking the 
 blood of other animals ; and, for this purpose, the mouth 
 of the leech is furnished with an apparatus of horny teeth, 
 by which they bite through the skin. In the common 
 leech, three of these teeth exist, arranged in a triangular, 
 or rather triradiate form, a structure which accounts for 
 the peculiar appearance of leech-bites in the human skin. 
 The most interesting part of the anatomy of the leech to 
 microscopists is the structure of the mouth (fig. 257). 
 "This piece of mechanism," says Professor Rymer Jones, 
 " is a dilatable orifice, which would seem at first sight to 
 be but a simple hole. It is not so ; for we find that just 
 
 (1) Sir John Dalyell's Obiervationt on tome interesting Phenomena exhibited 
 ty teveral Speciet of Planarice. 1814. 
 
574 THE MICROSCOPE. 
 
 within the margin of this hole three beautiful little semi- 
 circular saws are situated, arranged so that their edges 
 meet in the centre. It is by means 
 of these saws that the leech makes 
 the incisions whence blood is to be 
 procured, an operation which is per- 
 formed in the following manner : 
 No sooner is the sucker firmly fixed 
 to the skin, than the mouth becomes 
 slightly everted, and the edges of 
 the saws are thus made to press 
 upon the tense skin j a sawing 
 movement being at the same time 
 given to each, whereby it is made 
 
 Fig. M7.-3fo.tt of Lee*. gradually ^ pierce ^ surfaC6j ^ 
 
 cut its way to the small blood-vessels beneath. Nothing 
 could be more admirably adapted to secure the end in viSw 
 than the shape of the wound thus inflicted, the lips of which 
 must necessarily be drawn asunder by the very contrac- 
 tility of the skin itself ; and that the enormous sacculated 
 stomach, which fills nearly the whole body of the leech, 
 was designed to contain its greedily devoured meal, there 
 can be no reasonable question. The leech, in its native 
 element, could hardly hope for a supply of hot blood 
 as food ; and, on the other hand, its habits are most 
 abstemious, and it may be kept alive and healthy for 
 years, with no other apparent nourishment than what is 
 derived from pure water frequently changed ; even when 
 at large, minute aquatic insects and their larvae form its 
 usual diet." 
 
 In Clepsinidce, the body is of a leech-like form, but very 
 much narrowed in front, and the mouth is furnished with 
 a protrusile proboscis. These animals live in fresh water, 
 where they may often be seen creeping upon aquatic 
 plants. They prey upon water-snails. 
 
 TuHcola. The worms belonging to this series of 
 branchiferous Annelida are all marine, and distinguished 
 by their invariable habit of forming a tube or case, 
 within which the soft parts of the animal can be en- 
 tirely retracted. This tube is usually attached to stones 
 or other submarine bodies. It is often composed of various 
 
ANNELIDA. 575 
 
 foreign materials, such as sand, small stones, and the 
 debris of shells, lined internally with a smooth coating of 
 hardened mucus ; in others it is of a leathery or horny 
 consistency ; and in some it is composed, like the shells of 
 Mollusca, of calcareous matter secreted by the animal. 
 The Tubicolce generally live in societies, winding their 
 tubes into a mass which often attains a considerable size : 
 a few are solitary in their habits. They retain their posi- 
 tion in their habitations by means of appendages very 
 similar to those of free worms, with tufts of bristles and 
 spines ; the latter, in the tubicular Annelids, are usually 
 hooked ; so that, by applying them to the walls of its 
 domicile, the animal is enabled to oppose a considerable 
 resistance to any effort to draw it out of its case. In the 
 best known family of the order (Sabellidce), the branchiae 
 are placed on the head, where they form a circle of 
 plumes or a tuft of branched organs. The Serpulce form 
 irregularly twisted calcareous tubes, and often grow 
 together in large masses, when they secure themselves to 
 shells and similar objects ; other species, Terebella, which 
 build their cases of sand and 
 stones, appear to prefer a 
 life of solitude. The curious 
 little spiral shells seen upon 
 the fronds of sea-weeds, are 
 formed by an animal be- 
 longing to the family Spi- 
 rorbis. 
 
 If the animals be placed 
 in a vessel of sea-water, a 
 very pleasing spectacle will 
 soon be witnessed. The mouth 
 of the tube is first seen to 
 open, by the raising of an 
 exquisitely-constructed door, 
 and then the creature cauti- 
 ously protrudes the anterior Hg . ^_ 
 part ot its body, spreading caicareout tube. 
 
 out at the same time two beautiful fan-like expansions, of a 
 rich purple, or scarlet colour, which float elegantly in the sur- 
 rounding water, and serve as branchial or breathing organs. 
 
576 THE MICROSCOPE. 
 
 The Serpula, if withdrawn from its calcareous tube (%. 
 260), is found to have the lower part of the body com- 
 posed of a series of flattened rings, and entirely destitute 
 of limbs or other appendages. Its food is brought to its 
 mouth by currents created by the cilia on the branchial 
 tufts. 
 
 Some of the Annelids are without tubes or cells of any 
 sort, and simply bury their bodies in the sand about the 
 tidal mark. The Arenicola, lob-worm, is a well-known 
 specimen of the class ; its body is so transparent tfrat the 
 circulating fluids can be distinctly seen under a moderate 
 magnifying power. Two kinds of fluids flow through the 
 vessels, one nearly colourless, the other red ; the vessels 
 through which the latter circulate are looked upon as 
 blood-vessels. A few also have not only no tubes but are 
 free and active swimmers. Drs. Carpenter and Claparede, 
 during a sojourn at Lamlash Bay, Arran, met with an 
 interesting member of this class of Annelids, the Tomopteris 
 onisciformis. It possesses a remarkable pair of "frontal 
 horns," projecting laterally from the most anterior part of 
 head, as well as pair of greatly elongated appendages, 
 designated by those observers as " the second antennce" in 
 contradistinction to another and a shorter pair of appen- 
 dages situated just in advance of them, the first pair 
 being characteristic of the larval, and the second of the 
 adult state of the annelid. 
 
 " The head also bears on its dorsal surface a pair of 
 ciliated epaulettes, which extend over the edges of the 
 bilobed nervous ganglion. These, at a certain stage of 
 development, are fringed with long cilia both at their 
 margins and their base ; but as the cilia are only occa- 
 sionally to be seen in activity, they may escape the atten- 
 tion of the observer. Cilia are likewise distinguishable on 
 certain parts of that innermost layer of the general integu- 
 ment which forms the external boundary of the peri- 
 visceral space, and by their agency a special movement is 
 imparted to the corpuscles of the fluid contained in the 
 cavity." 
 
 The development of the caudal prolongation is peculiar, 
 and this as well as other points of interest are given 
 in the Lin. Soc. Trans, vols. xxii. and xxiii. pp. 335 
 
I NBI i at EGGS, rrc. 
 
 K'Jinu-i.l Kv:m 
 
 I.AIK VI 
 
ANGUILLULJ! 577 
 
 and 59. Dr. Carpenter believes that this creature "is 
 a degraded form of the annelidan type its nearest affi- 
 nities being (as already pointed out by Drs. Leuckart 
 and Pagenstecher) the chaetopod or setigerous Annelids. 
 Every part of the characteristic organization of the type 
 is here reduced to the extreme of simplicity. The alimen- 
 tary canal passes in a straight line from one extremity of 
 the body to the other, without either sacculations or glan- 
 dular appendages. The nutritive fluid which transudes 
 through its walls, and which finds its way into the peri- 
 visceral cavity, is distributed throughout the body solely 
 by means of extensions of that cavity, through which it is 
 propelled in part by the agency of cilia that clothe its walls. 
 This fluid is obviously the homologue of the blood of higher 
 animals, that we cannot but regard the existence of the type 
 of structure before us (the wonderful transparency of the 
 body not permitting the slightest doubt as to the absence 
 of anything resembling a dorsal vessel) as affording a 
 further confirmation of the view of the so-called circulat- 
 ing apparatus of the higher Annelida, which regards their 
 perivisceral cavity and its extensions as representing the 
 proper sanguiferous system, and which looks upon the 
 system of vessels containing coloured fluid as a special 
 arrangement having reference rather to the respiratory 
 functions. 1 The extreme tenuity of the walls of the body 
 and its appendages renders it unnecessary that any special 
 provision should be made for the aeration of the nutritive 
 fluid ; and we accordingly find neither branchiae nor any 
 trace of what is commonly described as the sanguiferous 
 system in Annelida. The centres of the nervous system 
 would seem to consist solely of the cephalic ganglia the 
 absence of the ordinary longitudinal series being apparently 
 related to the very incomplete segmentation of the body, 
 and constituting a link of affinity to the Turbellarian 
 Worms. The ocelli present a condition of extreme sim- 
 plicity, yet the duplication of the corneale in each of them 
 marks that tendency to repetition which so peculiarly 
 distinguishes the Articulate type. It is, however, the 
 extreme simpl'city of its generative apparatus that con- 
 
 (1) See Prof. Huxley's Lectures in Medical Times and Gazette. July 12 and 26, 
 1856. 
 
 P P 
 
578 THE MICROSCOPE. 
 
 stitutes one of the chief points of interest in the organiza- 
 tion of Tomopteris" 
 
 Not solely in this class, but in that of the Annelida 
 generally, does much interest attach to the developmental 
 period. Most of them come forth from the egg in a con- 
 dition so closely resembling the cililated gemmules of 
 polypes, that competent observers have been known to 
 mistake them for animals of a lower class ; fortunately a 
 few hours' careful watching is sufficient to dispel the 
 illusory belief, and the embryonic globular shapeless 
 mass is seen soon to change its form ; segmentation takes 
 place, and the various internal organs become more and 
 more developed ; eye spots appear, and the young animal 
 assumes the likeness of its parent. 
 
 The Actinotrocha, even in the adult state, in many parti- 
 culars resembles the "bipinnarian larva of the star-fish." 
 Its long body is surmounted by a head, or mouth, around 
 which is placed a number of ciliated ventacula : they are 
 not only employed for feeding purposes, but also for 
 enabling it to swim about ; and in this particular, accord- 
 ing to Dr. A. Schneider and other competent authorities, 
 it is quite remarkable. 1 Dr. Carpenter tells us that he 
 has captured these free-swimming Annelids among other 
 marine animals by the careful use of the " stick-net." 
 
 (1} See Ann. Nat. Hist. vol. ix. 1862, p. 486. 
 
CHAPTER IV. 
 
 BtTB-KIXODOM ABTIOTLATA. INSECTA. ARACHKIDA, 
 
 MONG the numerous objects 
 which engage the attention 
 of the microscopist, the in- 
 sect tribes in general are far 
 from being the least 
 interesting ; their 
 curious and won- 
 derful economy is a subject 
 well deserving especial in- 
 vestigation. Earth, air, and 
 water, teem with the 
 various tribes of insects, 
 many of which are invisible to the unassisted eye, but 
 presenting, when viewed with the microscope, the most 
 beautiful mechanism in their frame- work, the most perfect 
 regularity in their laws of being, and exhibiting the same 
 wondrous adaptation of parts to the creature's wants, 
 which, throughout creation, furnishes traces of the love 
 and wisdom that so strongly mark the works of God. 1 
 
 " I cannot," says the learned Swammerdam, " after an 
 attentive examination of the nature and structure of both 
 the least and largest of the great family of nature, but 
 allow the less an equal, perhaps a superior degree of 
 dignity. Whoever duly considers the conduct and instinct 
 of the one with the manners and actions of the other, 
 must acknowledge all are under the direction and control 
 of a superior and supreme Intelligence ; which, as in the 
 
 (1) We commend to the reader the excellent Introduction to Entomology, by 
 Kirby and Spence. Longmans. Art. "Insecta," Otlop. Ant. and Physio. 
 
 pp2 
 
580 THE MICROSCOPE. 
 
 largest it extends beyond the limits of our comprehension, 
 escapes our researches in the smallest. If, while we dis- 
 sect with care the larger animals, we are filled with wonder 
 at the elegant disposition of their limbs, the inimitable 
 order of their muscles, and the regular direction of their 
 veins, arteries, and nerves, to what a height is our astonish- 
 ment raised when we discover all these parts arranged in 
 the least of- them in the same regular manner ! How is 
 it possible but that we must stand amazed, when we reHect 
 that those little animals, whose bodies are smaller than the 
 point of the dissecting knife, have muscles, veins, arteries, 
 and every other part common to large animals ! Crea- 
 tures so very diminutive that our hands are not delicate 
 enough to manage, nor our eyes sufficiently acute to see 
 them." 
 
 The Articulate sub-kingdom, Insecta, is divided and 
 sub-divided into orders, families, genera, species, as for 
 example : 
 
 Lepidoptera ; typical form, Butterfly, Moth. 
 
 Dipteria; 1 typical form, Fly, Gnat, &c. 
 
 Aptera ; typical form, Flea, Louse, Springtail. 
 
 Coleoptera; typical form, Beetle, Water Beetle, &c. 
 
 Orthoptera ; typical form, Locust, Grasshopper. 
 
 Neuroptera ; typical form, Dragon-fly, May-fly. 
 
 Hymenoptera ; typical form, Bee, Wasp, Ant. 
 
 Homoptera; typical form, Plant-louse (Aphis\ Lan- 
 tern-fly. 
 
 Hemiptera typical form, Water-scorpion, Water-boat- 
 man. 
 
 Araclmida ; typical form, Spider, Scorpion, &c. The 
 Acarina belong to this genus, family A carea, well known 
 as "Mites" and "Ticks." 
 
 Insects are characterised by a simple breathing ap- 
 paratus ; by the division of the body into distinct regions 
 or segments ; when three, the middle one, the thorax, 
 bears three pairs of jointed legs, and usually two pairs 
 of wings ; and by the possession of a single pair of jointed 
 
 (1) Comprised within the order Diptera, or two-winged flies, are several 
 genera having no wings, the apterous and suctorial Pulex, and the apterous and 
 pupiparous Kpiaboscidce : among the latter, we have the winged Uippobosoc, or 
 horse fly, and some others. 
 
DfSBCTA. 581 
 
 The metamorphoses which all undergo, before 
 they arrive at the perfect state and are able to fulfil all 
 the ends of their existence, are more curious and striking 
 than in any other department of nature ; and in the 
 greater number of species the same individual differs so 
 materially at the several periods of life, both in its in- 
 ternal and external conformation, in its habits, locality, 
 and kind of food, that it becomes one of the most inter- 
 esting investigations of the physiologist to ascertain the 
 manner in which these changes are effected, to trace the 
 successive steps by which that despised and almost un- 
 noticed larva that but a few days before lay grovelling in 
 the earth, with an internal organization fitted only for 
 the reception and assimilation of the crudest vegetable 
 matter, has had the whole of its external form so com- 
 pletely changed, as now to have become an object of 
 admiration and delight, and able to "spurn the dull 
 earth," and wing its way into the wide expanse of air, 
 with internal parts adapted only for the reception of the 
 purest and most concentrated aliment, which is now ren- 
 dered absolutely necessary for its support, and the reno- 
 vation increased energies demand. 
 
 The greater number of insects undergo a complete series 
 of changes. They are for the most part oviparous, and 
 their eggs assume a variety of forms, colour, &c. as 
 will be seen in Plate VI. On first leaving the egg, they 
 assume a more or less worm-like appearance, known as 
 larva, maggot, or caterpillar. The next stage is that of 
 the nympha, pupa, or chrysalis , this is succeeded by that 
 of the perfect insect or iniago. In some insects the 
 changes are incomplete; the body, legs, and antennae 
 are nearly similar, but wings are wanting. In others the 
 pupa continues active, is of a large size, and acquireg 
 rudimentary wings ; and some are without material altera- 
 tion of structure, the change consisting in what is termed 
 " jedysis," a casting off, or moulting only. 
 
 The heads of insects present many points of interest; 
 Plate VI. No. 134, shows the head of the Tortoise butter- 
 fly in profile, with large compound eye, palpi, and spiral 
 tongue. No. 131 is a portion of the head with lancets, 
 &c. of the Glossina morsitan*, Tsetse-fly of Africa. In 
 
582 
 
 THE MICROSCOPE. 
 
 the mouths and tongues of insects, the most admirable art 
 and wisdom are displayed ; and their diversity of form is 
 almost as great as the variety of species. The mouth is 
 usually placed in the fore part of the head, extending 
 somewhat downwards. Many have the mouth armed with 
 strong jaws, or mandibles, provided with muscles of great 
 
 *tg. 25d.Under-surface of a Wasp's tongue, Feelers, c. (Within the circle the 
 same is seen life-size.) 
 
 power, with which they bruise and tear their food, answer- 
 ing to the teeth of the higher animals ; and in their 
 various shapes and modifications serving as knives, scissors, 
 augers, files, saws, trowels, pincers, or other tools, accord- 
 ing to the requirements of each insect. 
 
 The tongue is generally a compact instrument, used 
 principally to extract the juices on which the insect feeds, 
 varying greatly in its length in the different species. It ia 
 capable of being extended or contracted at the insect's 
 
INSECTA. 583 
 
 pleasure ; sometimes it is dexterously rolled up in a taper and 
 spiral form, as in the Butterfly ; tubular and fleshy, as in the 
 Wasp. In fig. 259, the under lip of the Wasp is represented 
 with its brush on either side ; above which are two jointed 
 feelers (palpi labiales), the use of which is probably for the 
 purpose of making an examination of the food before it is 
 
 Fig. 260. Eye of Fly (magnified 150 diameter*.) 
 
 taken into the mouth, or that of cleaning the tongue. Near 
 these feelers the antennae or horns are placed, as curious in 
 form as they are delicate in structure. The antennae of the 
 male generally differ from those of the female : some writers 
 believe these are organs of smell or hearing ; others that 
 they are solely intended to add to the perfection of touch 
 or feeling, increasing their sensibility to the least motion 
 or disturbance. Apart from their use, they are the most 
 interesting and distinguishing characteristics of insects, 
 and appear to be often employed for the purpose of ex- 
 amining every object they alight upon. 
 
584 
 
 THE MICROSCOPE. 
 
 The structure of the eye is in all creatures a most 
 admirable piece of mechanism, in none more so than in 
 those of the insect tribe. The eyes differ in each species ; 
 varying in number, situation, 
 figure, simplicity of con- 
 struction, and in colour. Fig. 
 260 represents a portion of 
 the eye of the common Fly, 
 drawn by the light of the sun 
 upon a prepared photographic 
 surface of wood ready for the 
 engraver. Fig. 261 repre- 
 sents a side view of the eye 
 when thrown down, showing Fig 201. 
 
 the compound nature of the organ, with its series of 
 cylindrical tubes ; better seen in fig. 262. 
 
 " On examining the head of an insect, we find a couple 
 of protuberances, more or less prominent, and situated 
 symmetrically one on each side. Their outline at the base 
 is for the most part oval, elliptical, circular, or truncated ; 
 while their curved surfaces are spherical, spheroidal, or 
 pyriform. These horny, round, and naked parts seem to 
 be the corner of the eyes of insects ; at least, they aje 
 with propriety so termed, from the analogy they bear to 
 those transparent tunics in the higher classes of animals. 
 They differ, however, from these ; for, when viewed by the 
 microscope, they display a large number of hexagonal 
 facets, which constitute the medium for the admission of 
 light to as many simple eyes. Under an ordinary lens, 
 and by reflected light, the entire surface of one cornea 
 presents a beautiful reticulation, like very fine wire gauze, 
 with a minute papilla, or at least a slight elevation, in the 
 centre of each mesh. These are resolved, however, by the 
 aid of a compound microscope, and with a power of from 
 80 to 100 diameters, into an almost incredible number 
 (when compared with the space they occupy) of minute, 
 regular, geometrical hexagons, well defined, and capable of 
 being computed with tolerable ease, their exceeding minute- 
 ness being taken into consideration. When viewed in this 
 way, the entire surface bears a resemblance to that which 
 might easily and artificially be produced by straining a 
 
INSECTS' EYES. 
 
 585 
 
 portion of Brussels lace with hexagonal meshes over a 
 small hemisphere of ground glass. That this gives a toler- 
 ably fair idea of thtf intricate carving on the exterior may 
 be further shown from the fact, that delicate and beautiful 
 pasts in collodion can be procured from the surface, by 
 giving it three or four coats with a camel-hair pencil. 
 When dry it peels off in thin flakes, upon which the 
 impressions are left so distinct, that their hexagonal form 
 can be discovered with a Coddington lens. This experi- 
 ment will be found useful in examining the configuration 
 of the facets of the hard and unyielding eyes of many o* 
 the Coleoptera, in which the reticulations become either 
 distorted by corrugation, or broken by the pressure re- 
 quired to flatten them. It will be observed also, that by 
 tine method perfect casts can be obtained without any dis- 
 section whatever ; and 
 that these art if da I 
 exuvice for such thi-y 
 really are become 
 available for micro- 
 scopic investigations, 
 obviating the necessity 
 for a more lengthened 
 or laborious prepara- 
 tion. The dissection 
 of the cornea of an 
 insect's eye is by no 
 
 mP!in P3cv T havp 
 ,Aby. Ild\ e 
 
 USed generally a small 
 c ' .,, 
 
 pair Ot Scissors, With 
 
 well - adjusted and 
 pointed extremities, and a camel-hair pencil, having a por 
 tion of the hairs cut off at the end, which is thereby flat- 
 tened. The extremity of the cedar handle should be cut 
 to a fine point, so that the brush may be the more easily 
 revolved between the finger and thumb ; and the coloured 
 pigment on the interior may be scrubbed off by this 
 simple process. A brush thus prepared, and slightly 
 moistened, forms by far the best forceps for manipulating 
 these objects preparatory to mounting ; as, if only touched 
 with any hard-pointed substance, they will often spring 
 from the table and be lost. 
 
 B 
 
 Fi s- 20 ' 2 - 
 
 > is a section O f the eye of Melolontha rulgmi*, 
 Cockchafer. B, a portion more highly niag- 
 nified, showing the facets of the cornea, and 
 its transparent pjramids, surrounded with 
 pigment. At A they meet, and form the optic 
 
 nerve - 
 
586 
 
 THE MICROSCOPE. 
 
 "Each hexagon forms the slightly horny case of an 
 eye. 1 Their margins of separation are often thickly set 
 with hair, as in the Bee ; in other instances naked, as in 
 the Dragon-fly, House-fly, &c. The number of these lenses 
 has been calculated by various authors, and their multi- 
 tude, cannot fail to excite astonish- 
 ment. Hooke counted 7,000 in the 
 /^xjlj^. eye of a House-fly ; Leeuwenhoek 
 //tfSliSii^ more than 12,000 in that of a 
 Dragon-fly ; and Geoifry cites a 
 calculation, according to which 
 there are 34,650 of such facets in 
 the eye of a Butterfly." 2 
 
 The trunk is situated between 
 the head and the abdomen ; the legs 
 and wings are inserted into it. The 
 thorax is the upper part of the 
 trunk ; the sides and back of which 
 are usually armed with points or 
 hairs. The abdomen forms the 
 posterior part of the body, and is 
 Fig. 263 . Breathing - aper- generally made up of rings or seg- 
 ^e^^Sciiiestheobl merits, by means of which the 
 ject about the natural size.) insect lengthens or shortens itself. 
 Running along the sides of the abdomen are the spiracles, 
 or breathing apertures, fig. 263, communicating directly 
 with the internal respiratory organs. Pure air being thus 
 freely admitted to every part, and the circulating fluids 
 
 (1) "Each of the eyelets, or 'ocelli,' which aggregated constitute the com- 
 pound eye of a Bee, is itself a perfect instrument of vision, consisting of two 
 remarkably formed lenses, namely, an outer corneal' lens and an inner or 
 ' conical' lens. The 'corneal' lens is a hexahedral or six-sided prism, and it is 
 the assemblage of these prisms that forms what is called the ' cornea' of the 
 compound eye. This ' cornea ' may easily be peeled off', and if the whole or a 
 portion be placed under the microscope, it will be seen that each corneal lens is 
 not a simple lens but a double convex compound one, composed of two plano- 
 convex lenses of different densities or refracting powers, joined together by their 
 plane surfaces. The effect of this arrangement is, that if there should be any 
 aberration of the rays of light during their passage through one portion of the 
 lens, it is rectified in its transit through the other. It appears questionable 
 whether the norml shape of these lenses is hexagonal, or whether this form is 
 not rather a necessity of growth, &c., that is, that they are normally round, but 
 assume the hexagonal shape during the process of development in consequence 
 of their agglomeration." J. Samuelson and B. Hicks, ''On the Eye of the 
 Bee," Juurn. Micros. Soc vol. i. p. 51. 
 
 (2) " Remarks on the Cornea of the Eye in Insects," by John Gorham, 
 11.U.C.S. Journ. Micros. Science, p. 76, 1853. 
 
INSECTS' FEET. 
 
 587 
 
 kept exposed to the vivifying influence cf the atmosphere, 
 
 the necessity for more complicated and cumbersome 
 
 breathing organs is at once obviated ; and the whole body 
 
 is at the same time rendered lighter. The spiracles are 
 
 usually nine or ten in num- 
 
 ber, and consist of a horny 
 
 ring, of an oval form. The 
 
 air-tubes are exquisitely 
 
 composed of two thin 
 
 membranes, between which 
 
 a delicate elastic thread or 
 
 spiral fibre, is interposed, 
 
 forming a cylindrical pipe, 
 
 and keeping the tube always 
 
 in a distended condition ; 
 
 thus wonderfully preserving 
 
 the sides from collapse or 
 
 pressure in their passage 
 
 through the air, which 
 
 Otherwise might Occasion 
 
 tf ,. v,. c\n i 
 
 SUnOCatlon. lg. JO 4: re- 
 
 presents the beautiful me- 
 chanism of a portion of the tracheae of Hydropilus, 
 showing the peculiar arrangement of the spiral tubes, 
 which give it elasticity and strength. 
 
 The legs of insects are extremely curious and interest- 
 ing ; each leg consists of several horny cylinders, connected 
 by joints and ligaments, inclosing within them sets of 
 powerful muscles, whereby their movements are effected. 
 
 Feet of Flies, <kc. " The tarsus, or foot of the Fly, con- 
 sists of a deeply bifid, membranous structure, pulvillus ; 
 anterior to the attachment of this part to the fifth tarsal 
 joint, or the upper surface, are seated two claws, or * tarsal 
 ungues,' which are freely movable in every direction. 
 These ungues differ greatly in their outline, size, and rela- 
 tive development to the tarsi, and to the bodies of the 
 insects possessing them, and in their covering ; most are 
 naked over their entire surface, having however a hex- 
 agonal network at their bases, which indicates a rudimen- 
 tary condition of minute scale-like hairs, such as are common 
 on some part of the integument of all insects. Flexor and 
 
 S- 264. Magnified portions of the 
 trachea of the ffydrophilus, show- 
 ing spiral tubes and, their arrange- 
 
 ment - 
 
588 
 
 THE MICROSCOPE. 
 
 extensor muscles are attached to both ungues and the 
 flaps ; the flaps, corrugated or arranged on the ridge and 
 furrow plan, are in some cases perfectly smooth on 
 their superior surface, in others this surface is covered 
 with minute scale-like hairs. The thickness of the flaps 
 on the Blow-fly does not exceed the 1 -2000th of an inch 
 at the margin ; thence they increase in thickness towards 
 the point of attachment. Projecting from their inferior 
 surface are the organs which have been termed ' hairs,' 
 1 hair-like appendages/ ' trumpet-shaped hairs,' &c. That 
 
 these are the immediate 
 agents in holding is now 
 admitted by most obser- 
 vers, and it will be con- 
 venient to term them 
 '"tenent" hairs,' in allu- 
 sion to their office. Plate 
 VI. No. 140, the under 
 surface of left forefoot of 
 Musca Vomit-aria, is shown 
 with tenent-kairs ; a and b 
 are more magnified hairs, 
 a from below, b from the 
 side. 'No. 142 is the left 
 forefoot of Amara commu- 
 nis, showing under surface 
 
 object natural size.) dages, one of which is seen 
 
 more magnified at a. Nc. 143, under surface of left forefoot, 
 Ephydra riparia. This fly is met with sometimes in im- 
 mense numbers on the water in salt marshes ; it has no 
 power of climbing on glass, which is explained by the 
 structure of the tenent-hairs : the central tactile organ is 
 also very peculiar, the whole acting as a float, one to each 
 foot, to enable the fly to rest on the surface of the water ; a 
 is one of the external hairs. No. 135, under surface of left 
 1 'ivloot of Cassida viridis (Tortoise-beetle), showing the 
 bifurcate tenent appendages, one of which is given at a 
 inor< magn fled. These, in the ground-beetles, are met 
 with only in the males, and are used for sexual purposes,. 
 The delicacy of the structure of these hairs in the fly, the 
 
INSECTS' HAIRS. 589 
 
 bend near their extremity, in each of which supervenes an 
 elastic membranous expansion, and from which a very 
 minute quantity of a clear, transparent fluid is emitted 
 when the tiy is actively moving, explains its capacity for 
 clinging to polished surfaces. It simply remains to add 
 that the tubular nature of the shaft of the tenent-hairs on 
 the foot cf this insect has been surmised, although its 
 minute size and homogeneity hardly admits of actual con- 
 firmation. At the root of the pulvillus, or its under sur- 
 face, is a process, which in some instances is short and 
 thick, in others long and curved, and tapering to its ex- 
 tremity (ScatopJiaga), setose (JSmpis), plumose (Hippobos- 
 cidce), or, in one remarkable example (Ephydra\ so closely 
 resembling in its appearance the very rudimentary pul- 
 villus with which it is associated. Just at the base of the 
 fifth tarsal joint, on its under surface, there is present, in 
 Eristalis, a pair of short, very slightly curved hairs, which 
 point almost directly downwards. It became desirable to 
 endeavour to ascertain how far the structure of these 
 tenent-hairs agrees with that of true hairs, on which some 
 valuable critical observations were made last year by Dr. 
 Hicks. 1 
 
 " Tenent-hairs are usually present in some modification 
 or other, that it is really difficult to name a beetle which 
 has not some form of them ; the only one I yet know that 
 seems to me really to possess nothing of the kind is a 
 species of Helops, which lives on sandy heaths ; I suppose 
 the dense cushion of hairs on the tarsi here to be for the 
 protection, simply, of the joints to which they are attached. 
 I have detected them on the tarsal joints of species of 
 Ephydra, and on the first basal tarsal joint of the Drone 
 of the Hive-bee. A very rudimentary form of tenent-hairs 
 is present on the under surface of some of the Tree-bugs 
 (Ptntatomidce), which have in addition a large, deeply-cleft 
 organ at the extremity of the tarsus, which appears to be 
 a true sucker. 
 
 " When walking on a rough surface, the foot represents 
 that of a Coleopterous insect without any tenent appen- 
 dages. The ungiies are always attached to the last joint of 
 
 (1) Sec Trans. Linn. 3oc. vol. xxiii p. 143. 
 
590 THE MICROSCOPE. 
 
 an insect's tarsus. They are not attached to the fifth tarsal 
 joint of a Dipterous insect ; neither are they attached to 
 the fifth tarsal joint of a Hymenopterous insect, but to the 
 terminal sucker, which again, in this great order, is a 
 sixth tarsal joint, membranous, flexible, elastic in the 
 highest degree, retractile to almost its fullest extent within 
 the fifth tarsal joint a joint modified to an extraordinary 
 degree for special purposes. 
 
 " The plantula of Lucanus, with its pair of minute claws, 
 at once occurred as a case strictly in point. The ungues 
 are hairs modified for special purposes ; and they have the 
 structure of true hairs. The sustentacula of Epcira, the 
 analogous structures on the entire under surface of the 
 last tarsal joints in Pholcus, the condition of the parts in 
 the hind limbs of Notonecta, in both its mature and earlier 
 conditions, as well as in /Sarcoptes, Fsoroptes, and some 
 other Acari, all contribute to the proof of this fact. The 
 various orders of insects have, for the most part, each their 
 own type of foot. Thus there is the Coleopterous type, the 
 Hymenopterous type, the Dipterous type, the Homop- 
 terous type, &c. ; and so very distinctive, that in critical 
 instances they will sometimes serve at once to show 
 to which order an insect should be referred. Thus, 
 amongst all the Diptera, I have as yet met with but one 
 subdivision which presents an exception to the structure 
 described. This exception is furnished by the Tipulidce, 
 which have the Hymenopterous foot. With hardly an 
 exception, then, I believe the form of foot described will 
 be found universal amongst the Diptera. and will be found 
 amongst the members of this order alone. It may be 
 desirable to add a few words on the best plan of conduct- 
 ing observations on these parts. Their action should be 
 studied in Lvdng insects under the influence of chloroform, 
 careful notes taken of appearances, and accurate drawings 
 made. It is of the greatest advantage to preserve carefully 
 all the parts examined : for this purpose Deane's medium 
 or glycerine jelly suits very well; some of the delicate 
 preparations, however, can only be kept satisfactorily in a 
 solution of chloride of zinc. The old plan of soaking in 
 caustic potash, crushing, washing, putting into spirits of 
 wine (or pressing and drying first), and then into turpen- 
 
INSECTS TONGUES. 
 
 591 
 
 tine, and lastly into Canada balsam, is perfectly useless, 
 except in rare instances where points connected with the 
 structure of the integument have to be made out Of 
 course, the parts should be viewed from above, from below, 
 and in profile, in order to gain exact ideas of their rela- 
 tions. The binocular microscope, however, promises to 
 diminish vastly the difficulties which had until recently 
 to be encountered, as by its use the parts may be clearly 
 viewed just as they are, without preparation of any kind." 1 
 
 Fig. 266. 
 
 1, Foot and leg of OpMen. 2, Foot and leg of Flesh-fly. 3, Foot and leg of 
 Drone-fly. (The small circles inclose objects about natural size.) 
 
 Fig. 267 represents the tongue and piercing apparatus 
 of the Drone-fly. This remarkable compound structure, 
 together with the admirable form and exquisite beauty of 
 the apparatus, must strike the mind with wonder and 
 delight, and lead the observer to reflect on the weakness 
 and impotence of all human mechanism, when compared 
 with the skill and inimitable finish displayed in the object 
 before us. The harder structures which surround it have 
 
 (1) Tuffen West, Trans. Linn. Soc. voL juriii. p. 383. 
 
502 
 
 THE MICROSCOPE. 
 
 Pig. 267. Tongue and Piercing Apparatus of Drone-fly. 
 
INSECTS' TONGUES. 59 3 
 
 been removed for the purpose of bringing the several parts 
 into view, and which consist of two ptilpi, or feelers, 
 covered with short hairs, and united to the head by a se' 
 of muscles ; these feelers appear to be in frequent requisi 
 tion for guarding the other organs from external injury. 
 The two lancets seen above them are formed somewhat like 
 a cutlass, or the dissecting knife of the anatomist, and are 
 purposely intended for making a deep and sharp cut, also 
 for cutting vertically with a sweeping stroke. The other 
 and larger cutting instrument appears to be intended to 
 enlarge the wound, if necessary ; or it may be for the 
 purpose of irritating and exciting the part around, thereby 
 increasing the flow of blood to the part, being jagged or 
 toothed at the extremity. The larger apparatus, with its 
 three peculiar prongs, or teeth, is tubular, to permit of the 
 blood passing through it and thence to the stomach; this 
 is inclosed in a case which entirely covers it. The spongy 
 tongue itself projects some distance beyond this apparatus, 
 and is composed of a beautiful network of soft muscular 
 spiral fibres, forming a series of absorbent tubes; and these 
 are moved by powerful muscles and ligaments, the retrac- 
 tile character of which may be seen in the drawing of the 
 proboscis of the Fly, fig. 268 : by the aid of two booklets 
 placed in each side, he is enabled to draw in and dart 
 out the tongue with wonderful rapidity. Another set of 
 muscles is seen at the root of the whole apparatus. 
 
 " In the organization of the mouth of various insects we 
 have a modification of form, to adapt them to a different 
 mode of use ; as in the Muscidce, or common House-flies. 
 When the food is easily accessible, and almost entirely 
 liquid, the parts of the mouth are soft and fleshy, and 
 simply adapted to form a sucking tube, which in a state of 
 rest is closely folded up in a deep fissure, on the under 
 surface of the head. The proboscis at its base appears to 
 be formed by the union of the lacinia above and the labium 
 below, the latter forming the chief portion of the organ, 
 which is tenanted by d lated muscular lips. In the Tabanu* 
 these are exceedingly large and broad, and are widely ex- 
 panded, to encompass the wound made by the insect with 
 its lancet-shaped mandibles in the skin of the animal it 
 attacks. On their outer surface they are fleshy and 
 QQ 
 
594 THE MICROSCOPE. 
 
 muscular, to lit them to be employed as prehensile organs; 
 while on their inner they are more soft and delicate, but 
 thickly covered with rows of very minute stiff hairs, 
 directed a little backwards, and arranged closely together. 
 There are very many rows of these hairs on each of the 
 lips ; and from their being arranged in a similar direction, 
 they are easily employed by the insect in scraping or tear- 
 ing delicate surfaces. It is by means of this curious 
 structure that the busy House-fly often occasions much 
 mischief to the covers of our books, by scraping off the 
 white of egg and sugar varnish used to give them the 
 polish, leaving traces of its depredations in the soiled and 
 spotted appearance which it occasions on them. It is by 
 means of these also that it teases us in the heat of summer, 
 when it alights on the hand or face, to sip the perspiration 
 as it exudes from and is condensed upon the skin. The 
 fluid ascends the proboscis, partly by a sucking action, 
 assisted by the muscles of the lips themselves, which are 
 of a spiral form, arranged around a highly elastic, ten- 
 dinous, and ligamentous structure, with other retractile 
 additions for rapidity and facility of motion." l 
 
 The beautiful form of the spiral structure of the tongue 
 should be viewed under a magnifying power of 250 dia- 
 meters, or a quarter-inch object-glass. 
 
 These insects are of great service in the economy of 
 nature, their province being the consumption of decaying 
 animal matter, which is found about in quantities so small 
 as to be imperceptible to most people, and is not removable 
 by ordinary means, even in the best-kept apartments, during 
 hot weather. It was asserted by Linnaeus, that three flies 
 would consume a dead horse as quickly as a lion. This 
 was, of course, said with reference to the offspring of 
 such three flies ; and it is possible the assertion may be 
 correct, since the young begin to eat as soon as they are 
 born. A single Blow-fly has been known to produce twenty 
 thousand living Iarva3 (one of which is represented in Plate 
 VI. No. 141), and in twenty-four hours each has increased 
 its own weight above two hundred times ; in five days it 
 attains to its full size. When the larvae are of full size, 
 
 (1) Mr. G. Newport, Cyclopccdia of Anatomy and Physiology. 
 
IXSECTA 
 
 595 
 
 they change into the pupa state, and remain in that state 
 a few days ; they then become flies, soon produce thou- 
 
 Flg. 288. Proboscis of House-fly. Drawn from a preparation by Topping. (The 
 
 small circle incloses the same about natural size.) 
 
 QQ 2 
 
596 THE MICROSCOPE. 
 
 sands of eggs, larvae, and flies, and this is repeated again 
 and again until the whole brood is destroyed by winter's 
 cold. 1 
 
 The " Tsetse" fly of tropical Africa (Glossina morsitans] : 
 the mouth, proboscis, and piercing apparatus of one, viewed 
 from the under-side, is represented in Plate VI. No. 131. 
 The biting apparatus consists of four parts, of which two 
 are lateral setose palpi ; if a horny case for the protection 
 of the proboscis and its contained style can be so called. 
 The palpi, although arising from two roots, when joined 
 together and accurately embracing the proboscis, as they 
 will do when the fly is at rest, appear as one only ; but 
 when the insect is in the act of piercing or sucking, they 
 divide, and are thrown directly upwards. The palpi are 
 furnished on the outer, or convex sides, with long and 
 sharply pointed, dark-brown setae or hairs ; while the 
 inner or concave sides which are brought in contact with 
 the proboscis are perfectly smooth and fleshy. Three cir- 
 cular openings seem to indicate the tubular character of 
 what in the common fly is a fleshy, expanded, and highly- 
 developed muscular proboscis : in the Glossina it is a 
 straight, horny-looking, red-coloured bristle, the apex of 
 which is slightly dilated and rounded, and apparently 
 barbed, while it expands a little towards the base, and 
 there dilates into a large-sized fleshy bag, or muscular sac, 
 filled with a red-coloured fluid. The proboscis is grooved 
 on the under-side for the purpose of receiving a slender 
 glassy style, acutely pointed, and equal to it in length. 
 The style, nicely adapted to the groove, and taking its 
 rise from the poison gland, is the penetrating instrument. 
 A series of long and thin muscular bands embrace this 
 gland, and their tendinous insertions are so arranged as to 
 bring considerable force to bear upon its contents. Phy- 
 siological science has made us familiar with the fact, that 
 
 (1) Dead flies may be constantly observed, about autumn, surrounded by a 
 Bort of halo, which, upon examination, is found to consist of the spores of a 
 fungus. The abdomen is much distended, and the rings composing it are 
 separated from each other, the intervals being occupied by white prominent 
 xones, constituted of a fungoid growth proceeding from the interior of the 
 body. Further examination will show that the whole of the contents or the 
 body of the fly have been consumed by the parasitic growth, and that nothing 
 remains but an empty shell, lined with a thin felt-like layer composed of the 
 interlaced mycelia of the innumerable fungi. See Dr. F.-Cohn's observations 
 upon the parasite in vol. v. p. 154, Journ. Micros. Sci. 1857. 
 
WINGS OF INSECTS. 597 
 
 all fluid poisons are enormously increased in their power 
 for good or for evil, when injected beneath the skin ; this 
 knowledge prepares us to understand how it is that a drop 
 from the poison gland of that wonderful little fly is suffi- 
 ciently potent and virulent to destroy a large animal in 
 a few minutes. Dr. Livingstone tells us that on one 
 occasion he lost forty-three oxen in as many minutes, 
 " when not more than a score of the ' Tsetse ' flies could 
 be seen." The tongue is neither large nor well developed, 
 but this is in a measure balanced by the mouth and lips ; 
 the latter are muscular, and capable of affording great 
 assistance while the fly is in the act of sucking the blood 
 of its victim. The wings are long and powerful ; the legs 
 strong and muscular ; the feet provided with the usual 
 appendages, terminating in a pair of strong claws of a 
 rather large size. 
 
 The wings of insects exhibit variety in form and struc- 
 ture, as well as beauty of colouring ; the art with which 
 they are connected to the body, the curious manner in 
 which some are folded up, the tine articulations provided 
 for this purpose, with the various ramilications by which 
 the nourishing fluids are circulated and the wings strength- 
 ened, all afford a fund of rational investigation highly 
 entertaining, and exhibiting, when examined under the 
 microscope, beautiful and wonderful design in their forma- 
 tion. Take the Libellulidce (Dragon-flies) as an example, 
 whose wings, with their horny framework, are as elegant, 
 delicate, and as transparent as gauze; often ornamented 
 with coloured spots, which, at different inclinations of the 
 sun's rays, show all the tints of the rainbow. One species 
 (Calepttryx virgo) will be seen sailing for hours over a piece 
 of water, all the while chasing, capturing, and devouring 
 the numerous insects that cross its course ; at another time 
 driving away competitors, or making its escape from an 
 enemy, without ever seeming tired or inclined to alight. 
 
 In tine weather, female Dragon flies are seen to deposit 
 their eggs upon the water, making a strange noise, as 
 though they were heating the water; the cluster of eggs 
 looks like a floating bunch of sumi! grapes. The Lirvse, 
 when hatched, live in the water; and it is scarcely pos- 
 sible to fancy more strange looking creatures. They are 
 
598 THE MICROSCOPE. 
 
 short and comparatively thick, with movements heavy and 
 clumsy, and after shedding their skins become pupse : still 
 continuing to live in the water. The pupse differ from 
 the larvae principally in having four small scales on their 
 sides ; these conceal their future wings. While the Dragon- 
 fly continues in its aquatic state, both as larva and pupa, 
 it devours all the insects it can entrap ; and as it only 
 moves slowly, it is furnished with a very curious apparatus 
 near its head, which it projects at pleasure, and uses as 
 a trap. This apparatus consists of a pair of very large, 
 jointed, movable jaws, which the insect keeps closely 
 folded over its head, like a large mask, till it sees its 
 prey; when it does, it creeps softly along till it is suffi- 
 ciently near ; it then darts out those long, arm-like jaws, 
 and suddenly seizing its prey, conveys it to its moiith. 
 When the Dragon-fly is about to emerge from its pupa- 
 case, it places itself on the brink of the pond, or on the 
 leaf of some water-plant sufficiently strong to bear its 
 weight, and there divests itself of its pupa-case. When the 
 perfect insect first appears, it has two very small wings ; 
 these gradually increase, and in a short time two other 
 wings appear. As soon as the wings are fully expanded, 
 and have attained their beautiful gauze-like texture, the 
 Dragon-fly begins to dart about, and then commences its 
 work of destruction. 
 
 Equally rapid, exactly steered, and unwearied in its 
 flight is the Gnat. The wings of a Gnat have been calcu- 
 lated, during its flight, to vibrate 3,000 times in a minute ; 
 these wonderful wings are covered on surface and edge 
 with a fine down or hair. The alternations of bright sun- 
 shine and rain, so commonly seen in March, are extremely 
 favourable to the appearance of Gnats. The first that 
 appear are called Winter Midges (Trichocera hyemaiis). As 
 the spring advances, these Midges are succeeded by others 
 somewhat different ; and as the weather becomes warmer, 
 the true Gnats appear. The sting of the Gnat (Culex 
 pipiens) is well known ; although the insects themselves, 
 so very rapid in their movements, are so much dreaded 
 that very few people care to examine the delicacy and 
 elegance of their forms. The sting is very curiously con- 
 trived (see fig. 269), and inclosed in a sheath, folds up 
 
STINGS OF INSECTS. 
 
 599 
 
 after one or more of the six lancets have pierced the flesh ; 
 it will inflict a severe though minute wound, the pain of 
 which is increased by an acrid liquid injected into it 
 through a curiously-formed proboscis ; this latter is covered 
 over with feathers or scales. A magnified view of one of 
 these feathers is seen at No. 3. Another scale from a 
 
 1. Head of CvJex pipieiu, Female Gnat, detached from the body. 2, Wing. 
 .3, A Scale from the Proboscis. 4, Proboscis and Lancets. The reticulation 
 on each aide of the head showg the space occupied by the eyes. The feather 
 or scale from proboscis IK magnified 250 diameters 
 
600 THE MICROSCOPS. 
 
 Gnat's wing is magnified 500 diameters, fig. 273, No. 7. 
 The proboscis is protected on either side by antennae, or 
 feelers. 
 
 The metamorphosis of the larva of Corethra plumi- 
 cornis, one of the Gnat tribe, has been carefully in- 
 vestigated by Professor Eymer Jones, F.RS. 1 This 
 competent observer brings out many points of interest ; 
 one in particular deserves notice, namely, the use of 
 the four remarkable-looking jet-black bodies situated 
 in the body of the larva, two of which are placed in 
 the thoracic region, and two near the centre of the pos- 
 terior half of the body. These have hitherto puzzled all 
 observers, but at length receive elucidation at the hands of 
 Professor Jones, who had the good fortune to witness the 
 metamorphosis. In form these bodies are more or less 
 kidney-shaped, and to all appearance completely isolated 
 in the body. Upon crushing the insect beneath the com- 
 pressorum, they are found to be filled with air, and by their 
 means the creature is enabled to rise and sink at pleasure. 
 They are composed of a series of small vesicles, each of 
 which has several coats : of these the outermost, when feebly 
 magnified, seems of a uniform hue of black, but under a 
 higher power is seen to be made up of many pigment cells, 
 so as to give the organ a reticulated appearance ; and it is 
 only when this black pigment has been removed, togethei 
 with a dull opaque membrane whereon the black patches 
 rest, that the real air-sac is displayed. When thus denuded, 
 the true walls of the air-sac appear to be composed of 
 a dense membrane, possessing great refractive power, the 
 effect of which upon transmitted light is extraordinary. 
 When highly magnified, it is found to be entirely com- 
 posed of numerous coils of a delicate fib re,., similar to that 
 which maintains the permeability of the tracheae of ordi- 
 nary insects, arranged in several superimposed layers, and 
 having the appearance of being closed in on all sides. It is 
 not until the larva thus constituted has arrived at its full 
 size that the appearances described become complicated by 
 intermixture with organs belonging to the pupa condition 
 of the insect. At this period, however, the rudiments of 
 
 (1) See Tram. Micros. Foe. Oct. 1867, " On the Structure and Metamorphosis 
 of the larva of Corethra pluinioornis. " 
 
IXSECTA. 601 
 
 future limbs begin to show themselves under the form of 
 transparent vesicles, which, as they enlarge, crowd the 
 thoracic region of the body. The change from the larva 
 to the pupa condition involves phenomena of the most 
 startling character. The air- sacs, situated both in the 
 thoracic region and in the hinder portion, burst and 
 unfold themselves into an elaborate tracheal system, and 
 a pair of ear-shaped tubes, of which not the slightest trace 
 could hitherto be discerned, make their appearance upon 
 the dorsal aspect of the thorax ; two long tracheae seem to 
 be thus simultaneously produced, occupying the two sides 
 of the body, and constituting the main trunks, from which 
 large branches are given off to supply, in front, the head, 
 the eyes, and the nascent limbs; while posteriorly they 
 spread over the now conspicuous ovaries, and terminate by 
 ramifying largely through the thin lamellae that constitute 
 the caudal appendages. In individuals subjected to micro- 
 scopic examination within a very brief period after their 
 assumption of the pupa state, the places originally filled 
 by the air-sacs of the larva are found to be occupied by 
 the lateral remnants of their external coats, clearly indi- 
 cated by ragged membranes, covered with patches of black 
 pigment, in the immediate vicinity of which numerous 
 air-bubbles are met with, extravasating, as it were, into 
 the cellular tissue. 
 
 The family Phryganeidce, the larvae of which are aquatic, 
 present almost as little resemblance to the imago as those 
 of some metabolous insects. They are long, softish grubs, 
 furnished with six feet, and with a horny head armed with 
 jaws, generally fitted for biting vegetable matters, although 
 some appear to be carnivorous. To protect their soft 
 bodies, which constitute a very favourite food with fishes, 
 the larvae are always inclosed in cases formed of bits of 
 straw and sticks, pebbles, and even small shells. The 
 materials of these curious cases are united by means of 
 fine silken threads, spun like those of the caterpillars of 
 the Lepidoptera, from a spinnaret situated on the labium. 
 In increasing the size of its case to suit its growth, the 
 larva is said to add to the anterior part only, cutting off a 
 portion of the opposite extremity. When in motion, tho 
 larva pushes its head and the three thoracic seginente, 
 
602 THE MICROSCOPE. 
 
 which are of a harder consistence than the rest of the 
 body, out of its case ; and as the latter is but little, if at 
 all, heavier than the water, the creature easily drags it 
 along behind, thus keeping its abdomen always sheltered. 
 It adheres stoutly to the inside of its dwelling by means of 
 a pair of articulated caudal appendages, generally assisted 
 by three tubercles on the first abdominal segment. Before 
 changing to the pupa state, the larva fixes his case to some 
 object in the water, and then closes up the two extremities 
 with a silken grating, through which the water necessary 
 for the respiration of the pupa readily passes. The pupa 
 is furnished with a large pair of hooked jaws, by means of 
 which, when about to assume the perfect state, it bites 
 through the grating of its prison, and thus sets itself free 
 in the water. In this form the pupce of some species 
 ewini freely through the water by means of their long hind 
 legs, or creep about plants with the other four ; frequently 
 rising to the surface of the water, they there undergo their 
 final change, using their deserted skin as a sort of raft, 
 from which to rise into the air ; others climb to the surface 
 of aquatic plants for the same purpose. 
 
 The perfect insect (Phryganea grandis) has four wings, 
 with branched nervures, the anterior pair of which, clothed 
 with hairs, are more frequently used than the posterior. 
 The organs of the mouth, except the palpi, are rudimen- 
 tary, and apparently quite unfit for use. The head is fur- 
 nished with a pair of large eyes, and with three ocelli ; 
 the antennae are generally very long. Some species are so 
 exactly like Moths, that they have often been supposed to 
 belong to the Lepidopterous order ; in point of fact, these 
 insects may be considered to form a connecting link 
 between the Neuro2)tera and the Lepidoptera. The females 
 have been seen to descend to the depth of a foot or more 
 in the water, to deposit their eggs. 
 
 Eggs of Insects, Plate VI. No. 124, &c. In form, 
 colour, and variety of design, the eggs of insects are more 
 surprisingly varied than those of the feathered tribes ; 
 but as from their smallness they escape observation, our 
 acquaintance with their structure and peculiarities is neces- 
 sarily limited and imperfect. Although the eggs of the 
 animal series differ much in their external characteristics, 
 
EGGS OF INSECTS. 603 
 
 they closely resemble each other while yet a part of the 
 ovarian ova, and prior to their detachment from the ovary. 
 At one period of their formation all eggs consist of three 
 similar parts : 1st. The internal nucleated cell, or ger- 
 minal vesicle, with its macula ; 2d. The vitellus, or yolk- 
 substance ; and 3d. The vesicular envelope, or vitelline 
 membrane. The germinal vesicle being the first produced 
 may be regarded as the ovigerm ; then comes the yolk- 
 substance, which gradually envelopes it, or is deposited 
 around it ; and the vitelline membrane, the latest formed, 
 incloses the whole. The chemical constituents of the egg 
 contents are albumen, fatty matters, and a proportion of a 
 substance precipitable by water. The production of the 
 chorion, or shell membrane, does not take place till the 
 ovum has attained nearly the full size, and it then appears 
 to proceed, in part at least, from the consolidation over the 
 whole surface of one or more layers of an albuminous fluid 
 secreted from the wall of the oviduct. The observations 
 of H. Meyer have shown that a part of the outer mem- 
 brane is derived from a conversion into it of the inner 
 cellular or epithelial lining membrane of the oviduct, at 
 the place where it is in closest contact with the surface of 
 the ovum. Dr. Allen Thompson therefore thinks that 
 " many of the varieties in the appearance and structure of 
 the external covering of eggs may probably depend on the 
 different modes of development of these cells." 
 
 The embryo cell is so directly connected with the 
 germinal vesicle that at a certain period it disappears alto- 
 gether, and is absorbed into the germinal yolk, or rather 
 becomes the nucleus of the embryo, when a greater degree 
 of compactness is observed in the yolk, and all that remains 
 of th-3 germinal vesicle is one or more highly refracting 
 fat globules and albuminoid bodies. Towards the end of 
 the period of incubation, the head of the young cater- 
 pillar, according to Meissner, lies towards the dot or 
 opening in the lid, which he terms the micropyle? from its 
 resemblance to a small gate, or opening through which the 
 worm emerges forth. From a number of careful observa- 
 
 (1) The term micropyle (a little gate) haa heretofore only been ud in its re 
 tAtion with the vegetable kingdom : it is used to denote the opening or foramen 
 towards which the radicle is always pointed. 
 
604 THE MICROSCOPE. 
 
 tions made on the silkworm, we have not been able to 
 satisfy ourselves of the correctness of these particulars : 
 in every case, indeed, the young worm makes its way out 
 from a point generally below this spot. Leuckart, how- 
 ever, expresses his belief in this micropyle, and says, " It 
 becomes at a later period converted into a funnel, which is 
 connected directly with the mouth of the embryo, and 
 serves to convey nourishment from without to it." We, 
 on the contrary, look upon it as an involuted portion of 
 membrane, indicating the spot where the formative pro- 
 cess of the outer membrane terminated, or where at a still 
 earlier stage, and while the ova was yet in the ova-sac, the 
 spermatozoa passed in to fecundate the yolk mass. 
 
 The germinal vesicle is very large and well marked, 
 while the egg is yet in the ova-sac of the insect. By pre- 
 paring sections, after Dr. Hallifax's method, 1 we find that 
 the germinal vesicle in the bee's egg is not situated imme- 
 diately near or even below the so-called micropyle, but 
 rather more to the side of the egg ; just in the position 
 which the head of the embryo is subsequently found to 
 occupy when it arrives at maturity. 
 
 The egg membrane, or envelope, of all the Lepidop- 
 tera, is composed of three separate and distinct layers : 
 an external slightly raised coat, tough and hard in its 
 character, a middle one of united cells, and a fine trans- 
 parent vitelline lining membrane, perfectly smooth and 
 homogenous in structure, imparting solidity, and giving a 
 fine iridescent hue to the surface, such as most of us admire 
 in old glass exhumed from the ruins of Pompeii. The 
 germinal vesicle is of a proportionately large size for the 
 egg, and its macula is at first single, then multiple. In 
 the silk-worm's egg the outer membrane is comprised of 
 an inner reticulated membrane of ?*ow-nucleated cells, and 
 in the outer layer the cells are arranged in an irregular 
 circular form, also non-nucleated, with minute interstitial 
 setae or hairs projecting outward. 
 
 The outer surface of the egg-shell of Coccus Persicce is 
 
 (1) Dr. Hallifax adopts the method of killing the insect with chloroform : he 
 then immerses it in a bath of hot wax, in which it is allowed to remain until the 
 wax becomes cold and hard ; now with a sharp knife a section is easily made in 
 the required direction without in the least disturbing any of the fragile parts, 
 or internal organs. 
 
[v.rK.rnoxs, FTC. 
 
 ' 
 
 ^:; . 
 
 Pf-ATK VII. 
 
EGOS OP INSECTS. 605 
 
 covered by minute rings, of which the ends somewhat over- 
 lap. These rings are thought to be identical in their 
 character with the whitish substance which exudes through 
 pores on the under-side of the" body ; and it is more than 
 probable that these layers of rings and their arrangement 
 account for the beautiful prismatic hues which they pre- 
 sent when viewed as opaque objects under the microscope, 
 and by the aid of the side-condenser. This white sub- 
 stance, it should be observed, becomes a part of the intimate 
 structure of the egg-shell, and is in nowise affected by 
 either strong spirit or dilute acids. Sir John Lubbock 1 
 states that in the greenish eggs of Phryganea, " the colour 
 is due to the yolk-globules themselves. In Coccus, how- 
 ever, this is not so ; the yolk-globules are slightly yellow, 
 and the green hue of the egg is owing to the green granules, 
 which are only minute oil globules. When, however, the 
 egg arrives at maturity, and the upper chamber has been 
 removed by absorption, these green granules will be found 
 to be replaced by dark-green globules, regular in size, and 
 about 1 -8000th of an inch in diameter, and which appear 
 to be in no way the same in the yolk of Phryganea eggs." 
 Another curious fact has been noticed, which partially 
 bears on the question of colour : the production of parasite 
 bodies within the eggs of some insects. In the Coccus, for 
 instance, parasitic cells of a green colour occur, " shaped 
 like a string of sausages, in length about the 1 -2000th of 
 an inch by about the I -7000th in breadth." 
 
 The eggs of Moths and Butterflies present many varying 
 tints of colour ; in speaking of this quality we do not re- 
 strict the term solely to those prismatic changes to which 
 allusion is so often made, and which are liable to constant 
 mutations according to the accident of the rays of light 
 thrown upon them ; but we more particularly refer to the 
 several natural transitions of colour, the prevailing tints 
 of which are yellow, white, grey, and a light-brown. In 
 some eggs the yellow, white, and grey are delicately blended, 
 and when viewed with a magnifying power of about fifty 
 diameters, and by the aid of a side-reflector (parabolic- 
 reflector), present many beautiful combinations. The 
 Diost delicate opalescent or rather iridescent tints appear 
 
 (1) Phil. Trant. 1859, p. 34L 
 
606 THE MICROSCOPE. 
 
 on others, of wl icli the eggs of the feathered tribes 
 furnish no example. The egg of the Mottled Umber 
 Moth (Erannis defolaria), Plate VI. No. 137, is in every 
 particular very beautiful. It is ovoid, with regular 
 hexagonal reticulations, and at each corner studded with 
 a raised knob or button ; the space within the hexagon is 
 finely punctated, and the play of colours is exquisitely 
 delicate. In this egg no micropyle can be seen. The 
 egg of the Thorn Moth (Ennomos erosaria), Plate VI. 
 No. 138, is of an elongated brick-looking form, one end of 
 which is slightly tapered off, while the other in which 
 the lid is placed is flattened and surrounded by a beauti- 
 fully white- beaded border, having for its centre a slightly 
 raised reticulated micropyle. The empty egg-shell gives 
 a fine opalescent play of colours, while that containing the 
 young worm appears of a brownish-yellow. 
 
 The egg of the Straw-belle Moth (Aspilates gtivaria), 
 Plate VI. No. 139, is delicately tinted, somewhat long 
 and narrow, with sides slightly flattened or rounded off, 
 and irregularly serrated. The top is convex, and the base 
 a little indented, in which are seen the lid and micropyle. 
 The young worm, however, usually makes its way through 
 the upper convex side : the indentation represented in the 
 drawing shows the place of exit. 
 
 An example of those eggs possessing a good deal of 
 natural colour is presented in that of the Common Puss 
 Moth (C. Vinula), a large spheroidal- shaped egg, having, 
 under the microscope, the appearance of a fine ripe 
 orange ; the micropyle exactly corresponds to the depres- 
 sion left in this fruit by the removal of the stalk ; the sur- 
 face is finely reticulated, and the natural colour a deep 
 orange. 
 
 The egg of the Mottled Rustic Moth (Caradina 
 Morpheus), No. 124, is subconical, and equally divided 
 throughout by a series of ribs, which terminate in a well- 
 marked geometrically-formed lid. The Tortoise-shell 
 Butterfly (Vanessa urtica), No. 125, presents us with a 
 delicate ovoid egg, divided into segments, the ribs of 
 which turn in towards the micropyle. The Common 
 Footman (Lithosia campanula), No. 126, produces a per- 
 fectly globular egg covered with fine reticulations, and of 
 
TONGUES OF INSECTS. 607 
 
 a delicate buff colour. The egg of the Shark Moth (Cu- 
 cullia umbratiea), No. 127, is subconical in form, with 
 ribs and cross-bars passing up from a flattened base to the 
 summit, and turning over to form the lid. No. 136, the 
 Egg of Blue Argus Butterfly (Poiyvmmatu* Argus). That 
 of ^he Small Emerald Moth (Jodin Vernai-ia), No. 1 34, is 
 an egg of singular form and beauty, an oval, flattened on 
 both sides, of silvery iridescence, and covered throughout 
 with minute reticulations and dots. It is particularly 
 translucent, so much so that the yellow-brown worm is 
 readily seen curled up within. The lid or micropyle is 
 not detected until the caterpillar eats its way out of the 
 shell. It should be stated that the whole series of eggs 
 in the plate are considerably over-coloured, and conse- 
 quently lose much of their beautiful transparency. The 
 eggs of Flies and Parasites also present much variety in 
 form, colour, and construction. Many of their eggs are 
 provided with a veritable lid, which opens up with a hinge- 
 like articulation. The cover is shown in Plate YL No. 
 144, Egg of Bot-fly, from which the larva is seen just 
 escaping ; No. 146, Egg of Scatophaga ; No. 147, Egg of 
 Parasite of Magpie. 1 
 
 Moths and Butterflies supply the microscopist with 
 some of the most beautiful objects for examination. What 
 can be more wonderful in its adaptation than the antenna 
 of the Moth, represented in fig. 271, No. 1, with a thin, 
 finger-like extremity almost supplying the insect with a 
 perfect and useful hand, moved throughout its extent by 
 a muscular apparatus of the most exquisite construction ! 
 The tongue of Butterfly, No. 2, is evidently made for the 
 purpose of dipping into the interior of flowers and extracting 
 the juices ; this is furnished with a spiral band of muscle : 
 an enlarged view of a portion is given at No. 3. See also 
 Plate VI. Nos. 132 and 133, Antennae of Vapour Moth. 
 
 The inconceivably delicate structure of the maxillaB or 
 tongues (for there are two) of the Butterfly, rolled up like 
 the trunk of an elephant, and capable, like it, of every 
 variety of movement, has been carefully examined and 
 described by Mr. Newport. " Each maxilla is convex on 
 
 (1) A paper on the Eggs of Insects, giving many other form* wffl be found in 
 the Intellectual Obterver, Oct 1867. 
 
60S 
 
 THE MICROSCOPE. 
 
 Fig. 271. 
 
 1, The .Antenna of the Silkworm-moth. 2, Tongue of a Butterfly. 3 A portion 
 f -n Tongue h'ghty magnified, showing its muscular fibrs. 4 The Tnn-ln-n- 
 
 what nelr'th , na^afaSf SakWOm ' (The 8maU Ch ' CleS enCl ' Se each some: 
 
IN8ECTA. COO 
 
 its outer surface, but concave on its inner; so that when 
 the two are approximated, they form a tube by their union, 
 through which fluids may be drawn into the mouth. The 
 inner or concave surface, which forms the tube, is lined 
 with a very smooth membrane, and extends throughout 
 the whole length of the organ: but that each maxilla is 
 hollow in its interior, forming a tube ' in itself/ as is 
 generally described, is a mistake; which has doubtless 
 arisen from the existence of large tracheae, or breathing- 
 tubes, in. the interior of each portion of the proboscis. In 
 some species, the extremity of each maxilla is studded 
 externally with a great number of minute papillae, or 
 fringes as in the Vanessa atalanta in which they are 
 little elongated barrel-shaped bodies, terminated by smaller 
 papillae at their extremities." Mr. Newport supposes that 
 the way in which the insect is enabled to purnp up the 
 fluid nourishment into its mouth is this : " On alighting on 
 a flower, the insect makes a powerful expiratory effort, by 
 which the air is expelled from the interior air-tubes, and 
 from those with which they are connected in the head and 
 body ; and at the moment of applying its proboscis to the 
 food, it makes an iuspiratory effort, by which the central 
 canal in the proboscis is dilated, and the food ascends it at 
 the same instant to supply the vacuum produced; and 
 thus it passes into the mouth and stomach : the constant 
 ascent of the fluid being assisted by the action of the 
 muscles of the proboscis, which continues during the whole 
 time that the insect is feeding. By this combined agency 
 of the acts of respiration and the muscles of the proboscis, 
 we are also enabled to understand the manner in which 
 the Humming-bird sphynx extracts in an instant the honey 
 from a flower while hovering over it, without alighting; 
 and which it certainly would be unable to do, were the 
 ascent of the fluid entirely dependent upon the action of 
 the muscles of the organ." 1 
 
 The wings of Moths and Butterflies are covered with 
 scales or feathers, carefully overlapping each other, as tiles 
 are made to cover the tops of houses. The iridescent variety 
 of colouring on their wings arises from a peculiar wavy 
 arrangement of the scales. Figs. 272 and 273 are magni- 
 
 (1) Cyclop. Anat. Pkytiol., article "Insecta." 
 R R 
 
610 
 
 THE MICROSCOPE. 
 
 fied representations of a few of them. No. 1 is a scale of 
 the M^rpho menelaus, taken from the side of the wing, of a 
 
 Fig. 272. Scaletfrom Butterflies' and Moths' wings. (Magnified 200 diaiteters.) 
 
 1, Scale of Morpho Menelaus. Z, Large Scale of Polyommatus Aryiolus, azure 
 blue. 3, Hipparchia Janira Argiolus. 4, Pontia Brassica. 5, Podura 
 Plumbea. C, Small Scale of Azure Blue. 
 
 pale-blue colour : it measures about 1-1 20th of an inch in 
 length, and exhibits a series of longitudinal stripes or lines, 
 between which are disposed cross-lines or striae, giving it 
 the appearance of brick-work. The microscope should be 
 enabled to make out these markings with the spaces 
 between them clear and distinct, as shown in fig. 27 3 9 
 No. la. 
 
 Polyommatus argiolus, Azure-blue, Nos. 2 and 6, are 
 large and small scales taken from the under-side of the 
 wing of this beautiful blue butterfly; the small scale is 
 covered with a series of spots, and exhibits both longitu- 
 
IK8ECTA. Gil 
 
 dinal and transverse striae, which should be clearly defined, 
 *nd the spots separated : this is a good test of the defining 
 power of a quarter-inch object-glass. 
 
 No. 3, Hipparchia janira, Common Meadow Brown 
 Butterfly scale : on this we see a number of brown spots 
 of irregular shape and longitudinal striae. 
 
 No. 4, Pontia brassica, Cabbage-butterfly, affords an 
 excellent criterion of the penetration and definition of a 
 microscope: it is provided at its free extremity with a 
 brush-like appendage. With a high power, the longitu- 
 dinal markings appear like rows of little beads. Cheva- 
 lier's test-object is the scale of the Pontia brassica, the 
 granules of which must be rendered distinct. Mohl and 
 Schacht use Hipparchia janira as a test for penetration, 
 with a moderate angular aperture and oblique illumina- 
 tion. Amici's test-object is Navicufa Rhomboides, the dis- 
 play of the lines forming the test ; this is a very good test 
 for angular aperture. 
 
 Fig.273. Portion* of Scales, magnified 500 diametert. 
 
 la, Portion of Scale of Morpho Menelaus. 5a, Portion of Large Scale of Podura 
 Plumbea. 7, Scale from the Wing of Gnat ; its two layers are here represented. 
 8, Portion of a Large Scale of Lepitma Saccharina. 
 
 The Tinea vestianella, Clothes-moth, possesses very deli- 
 cate and unique scales ; two of these are imperfectly 
 represented near the Acarus taken from one of these moths, 
 C41. The feathers from the under-side of the 
 
612 THE MICROSCOPE. 
 
 wiug are the best, requiring some management of illumi- 
 nation to bring out the lines sharp and clear. 
 
 The common Clothes-moth generally lays its eggs on 
 the woollen or fur articles it is bent upon destroying ; the 
 larva begins to eat immediately it is hatched ; then with 
 the hairs or wool it first gnaws off, it forms a case or 
 tube, under the protection of which it devours the sub- 
 stance of the article on which it fixes its abode. This 
 tube is of parchment-like consistence, and quite white; 
 is cylindrical in its shape, and furnished at both ends with 
 a kind of flap, which the insect raises at pleasure, and 
 crawls out, ; or it projects the front part of its body with 
 its fore-feet through the opening, just enough to enable 
 it to creep about without removing the rest of its body from 
 the tube, which it draws after it. There are several kinds 
 of Clothes-moths, the caterpillars of many bury them- 
 selves in the article on wnich they feed, 
 ; - instead of making the tube before-men- 
 tioned. The moths also differ very much 
 in appearance ; the commonest is of a light 
 buff colour ; one species, Tinea tapetzella, 
 fig. 274, is nearly black, with the larger 
 wings white tipped, or pale grey. 
 Mr. Topping, the well known preparer of microscopic 
 objects, generally furnishes three kinds of test-objects, which 
 he covers with the thinnest glass, in order that object- 
 glasses of the highest powers may be used in their exami- 
 nation. The following are arranged in their order of 
 value as test-objects : 
 
 Amician test. 
 N. v. Rhomboides. 
 Grammatophora subtilisimfc. 
 Pleurosigma fasciola. 
 
 cuspidata. 
 
 angulatum. 
 
 strigosum. 
 
 prolongation. 
 
 Spencerii. 
 
 Balticum. 
 hippocampus. 
 
 strigilis. 
 
 formosum. 
 
 SCALES. 
 
 Meadow Brown. 
 Pontia Brassica. 
 Azure Blue. 
 From Gnat's Wing. 
 Tinea Vestianella. 
 Amathusia Horsefieldii. 
 Morpho' Menelaus. 
 Podura plumbea. 
 Lepisma saccharina. 
 
 HAIRS. 
 Indian Bat. 
 
 ,, Mouse. 
 
 Mole. 
 Larva of Dermestes. 
 
 Mr. J . T. Norman, of City Road, preparer of specimens for the microscope, 
 furnished our Eggs of Insects. 
 
INSECTA. 613 
 
 In a genus Coccina (Dorthesia), several species of which 
 are found in this country, the female although apterous 
 and active in all stages is completely covered with a 
 snow-white secretion, which gives it more the appearance 
 of a little plaster-cast than anything else. 
 
 In another tribe, the Phytophthiria, both sexes are 
 either wingless or furnished with four distinctly veined 
 wings. The rostrum springs apparently from the breast ; 
 the tarsi are two-jointed, and furnished with two claws. 
 The most familiar species of this tribe are the Aphides, 
 Plant-lice, which have ever been regarded with consider- 
 able interest by the naturalist. Their bodies are flask- 
 shaped, and furnished with six feet, a pair of antennae, 
 and very generally with a pair of short tubes close to the 
 extremity of the abdomen, from which a clear sweet 
 secretion exudes. Both sexes are at one period winged, 
 at another wingless ; and individuals of the same species 
 are often winged and apterous at different periods of the 
 year. Perhaps the most remarkable phenomena in the 
 history of generation was first observed in the Aphis, and 
 to which great significance has been given by Professor 
 Owen, under the name Parthenogenesis or virgin-procre- 
 ation. This mode of generation is not confined to insect- 
 life, the same has been observed in the fialpce among 
 mollusca, the Distomata among entozoa, each parent giving 
 birth to an embryo different to itself; and this embryo 
 living as an independent animal, gives birth, without inter- 
 course, to another and to a successive series, until at length 
 a progeny is formed bearing the likeness of the first parent. 
 In the Aphis the ova are deposited by the parent insect, 
 and in due time produce larval wingless Aphides. Each 
 virgin Aphis of this brood will produce other similar 
 broods without intercourse; this will go on to the 
 eleventh generation, the last generation being winged, and 
 male and female : these have intercourse, and then com- 
 mence the same series of phenomena over again. 
 
 The Maple-aphis, better known as the Leaf Insect 
 <Plate VI. JSTo. 128), averages about the one-fiftieth of 
 an inch in length, and, although long sold and exhibited 
 under the name of the "Leaf Insect," nothing was 
 known of its origin and history, with the exception of 
 
14 THE MICROSCOPE. 
 
 what the Eev. J. Thornton stated in 1852, to whom 
 we owe its discovery on the leaves of the maple ; he, 
 believing it to be a species of Aphides, called it Phyl- 
 lopJwrus testudinatus. Subsequently it attracted the 
 attention of the Dutch naturalist Van der Hoeven, 
 who regarded it as the larval form of an undetermined 
 species of Aphis, and named it Periphyllus. It has more 
 recently engaged the attention of Dr. Balbiani and M. 
 Siguoret, whose united investigations are given in the 
 " Comptes Eendus " of June 17, 1867. They have posi- 
 tively ascertained that it is the larva of Aphis aceris ; a 
 brown species is also met with during a great part of the 
 year upon the young shoots of the maple. At the same 
 time a curious fact was made out, constituting a new and 
 remarkable peculiarity in the development of this group 
 of insects, already presenting so many curious phenomena 
 in connexion with their reproduction. It really appears 
 that the female produces two kinds of young one normal, 
 the other abnormal; the first are alone capable of con- 
 tinuing the course of their development, and capable of 
 reproducing the species ; whilst the latter retain their 
 original form, which is never changed throughout their 
 existence. They increase so little in size, that it appears 
 almost doubtful whether they eat ; the mouth is so very 
 rudimentary that this surmise in some measure gains sup- 
 port from the circumstance ; they undergo no change of 
 skin, never acquire wings like the reproductive insect, 
 and their antennae always retain the five joints which 
 are peculiar to all young Aphides before the first moult. 
 Neither are they all of the same colour, some being of a 
 bright green, as represented in our Plate, while others are 
 of a darker, or brownish-green, colour. The brown-green 
 embryos differ from the adult female only in those cha- 
 racters analogous to all other species ; and that chiefly 
 with regard to the hairs, which are long and simple. In 
 the green embryos, in the place of hairs, the body is sur- 
 rounded with scaly, transparent lamellae, more or less 
 oblong in shape, each of which is traversed by divergent 
 ramifying nervures. These lamellae not only occupy the 
 body, but also the anterior part of the head, the first joint 
 of the antennae, and the outer edge of the tibiae of the- 
 
APHIDES. 615 
 
 two anterior pair of legs. The dorsal surface in these 
 insects is covered with a mosaic of hexagonal plates, very 
 closely resembling the plates of the carapace of the tor- 
 toise. In this particular our artist has certainly fallen 
 into an error. Another peculiarity is that the body is 
 much flattened out, and looks so much like a scale on the 
 surface of the leaf, that it requires considerable practice, 
 as well as quickness of sight, to detect the young Maple- 
 aphis. One of the lamellae is seen highly magnified at c, 
 and a tenent-hair at b. The antennae taper off towards the 
 apex, are serrate on both edges, and terminate in fine 
 setae, one of which is shown at a. ' Below the insertions 
 of the antennae, brilliant scarlet- coloured compound eyes 
 are placed, which receive their nervous supply from the 
 central ganglion. 
 
 Aphides live upon plants, the juices of which they 
 suck, and, when they occur in great numbers, cause con- 
 siderable damage to vegetation ; a fact well known to 
 the gardener and farmer. Many plants are liable to be 
 attacked by swarms of these insects, which cause the 
 leaves to curl up : they grow sickly, and their produce is 
 greatly reduced. One striking instance is presented in the 
 devastation caused by the Hop-fly (Aphis humuli). 
 
 The Aphrophora bifasciata, common Frog-hopper, has 
 the antennae placed between the eyes, and the scutellum 
 visible that is to say, not covered by a process of the 
 prothorax. The eyes, never more than two in number, 
 are sometimes wanting. These little creatures are always 
 furnished with long hind legs, which enable them to per- 
 form most extraordinary 
 leaping feats. The best- 
 known British species, be- 
 cause so very abundant in 
 gardens, is the Cuckoo-spit, 
 Froth-fly, fig. 275. The 
 names Cuckoo-spit and 
 
 Froth-fly both allude tO the Fig ^5.-Ap7irophora pum*ria, 
 
 peculiar habit of the insect, , Cuckoo-spit. 
 
 While in the larva State, of > The frothy substance, b, The pupa. 
 
 enveloping itself in a kind of frothy secretion, somewhat 
 resembling saliva ; and this, indeed, was at one tiiuo sup- 
 
616 THE MICROSCOPE. 
 
 posed to be the saliva of the cuckoo, being found 011 the 
 young shoots of plants just about the time the cuckoo is 
 heard in the woods. 
 
 The Hymenoptera are distinguished from other insects 
 with membranous wings by the presence of an ovipositor 
 of peculiar construction at the extremity of the abdomen 
 of the females, which serves for placing the eggs in the 
 required position ; and in the males of some (Bees, Wasps, 
 &c.) constitutes a most formidable offensive weapon. As 
 the structure of this organ, which is rarely absent, is 
 essentially the same throughout the order, the form of its 
 component parts being merely modified to suit the exigencies 
 of the different insects, a short description of its structure 
 will not be considered out of place. The ovipositor, 
 borer, or sting, generally consists of five pieces : a pair of 
 horny supports (fig. 279) forming a sheath for the borer 
 or ovipositor, being jointed at the point where they issue 
 from the ca.vity of the last abdominal segment, and the 
 last joint is usually as long as the borer itself. The latter 
 consists of three bristles, of which the superior is grooved 
 along its lower surface, for the reception of a pair of finer 
 styles, and these are barbed at the point. The three 
 pieces, when fitted together, form a narrow tube, through 
 which the eggs pass to their destination, the poisonous 
 fluid also, which renders the sting of the Bee so painful, 
 is forced down the same into the wound. In the Saw-fly, 
 a part of this organ remains rudimentary, in other respects 
 it does not very much differ. 
 
 The larvae of most Hymenoptera are footless grubs, 
 furnished with a soft head, and exhibiting but little, if 
 any. advance upon those of Diptera (Plate VI. No. 141). 
 In the Saw-fly, however, the larva, instead of being, as 
 above described, a mere footless maggot, presents the 
 closest resemblance to the caterpillar of the Lepidoptera ; 
 it is provided with a distinct head, with six thoracic legs, 
 and in most cases, from twelve to sixteen pro-legs are 
 appended to the abdominal segments. 
 
 The Saw-fly, fig. 276, most destructive to the goose- 
 berry-bush, is remarkable for the way in which the female 
 provides for the safety of her eggs. This fly has a flat 
 yellow body, and four transparent wings, the outer two of 
 
OVIPOSITORS OF INSECTS. 
 
 C17 
 
 which have brown edges. The female lays her eggs on 
 the under-side of the leaf, along the projecting veins; 
 these are firmly attached, and cannot be removed without 
 
 Fig. -276. The Caterpillar and Saw-fly of Gooseberry tree. 
 
 crushing. The instrument which the little insect uses for 
 the purpose of cutting the leaf is the most remarkable 
 piece of perfect mechanism imaginable ; securely lodged, 
 
 Fi. 277. Saws of Saw-fly. (The small circle incloses the same nearly the 
 natural size.) 
 
 when not in use, in a long narrow slit beneath the abdomen, 
 and protected" by two horny plates, which at first appear 
 io consist of a single piece ; but upon closer inspection 
 
CIS THE MICROSCOPE. 
 
 four plates are seen to enter into their construction: 
 namely, two saws, placed side by side, as in fig. 277 ; 
 and two supports, somewhat like the saws in shape. A 
 deep groove runs along the thicker edge of the latter, 
 which is so arranged that the saws glide backwards and 
 forwards, without a possibility of running out of the 
 groove. When the cut is made, the four are drawn 
 together; and through a central canal, which is now 
 formed by combining the whole, an egg is protruded 
 into the fissure made by the saws in the leaf. The cutting 
 edges of the saws are provided with about eighteen or 
 twenty teeth : these have sharp points of extreme delicacy, 
 and together make a serrated edge of the exact form 
 given to the finest and best-made surgical saws. In the 
 summer-time the proceedings of this little insect can be 
 watched, and the method of using this curious instrument 
 seen, by the aid of a hand magnifier ; they are not easily 
 alarmed when busy at their work. 
 
 Many other insects are provided with instruments for 
 boring into the bark or solid wood itself. The Cynip bores 
 a hole into the side of the oak-apple, 
 for the purpose of depositing her egg. 
 The larva when hatched finds a com- 
 fortable lodging, and a good supply of 
 food ; when full grown, it eats its way 
 out of the nut, and, dropping to the 
 ground, it assumes the form of the per- 
 fect fly. The most important of this 
 family is the Cynip gallce tinctorice, 
 
 Fig. 27S.-FemaleEglan- fig. 278, which IS the Cause of the gall- 
 fine Gall-fly and lana. nu ^ a nu ^ mos ^ extensively employed 
 
 in the manufacture of ink and for dyeing purposes. 
 
 Some of the Wasp tribe, so very peculiar in their habits, 
 are active agents in the economy of nature. The solitary 
 Mason-wasps curiously construct nests in the form of 
 cells, for the purpose of carefully rearing their young. 
 The social-wasps, like bees, live in communities, and 
 have nearly the same divisions of labour and regulations 
 for the good government of the colony. ^ The struc- 
 ture and mechanical contrivance of the wasp's sting can 
 only be seen under the microscope. The sting consists of 
 
STINGS OP INSECTS. 
 
 619 
 
 tw) barbed darts, which will penetrate the flesh deeply, 
 and, from a peculiar arrangement of their serrated edges, 
 their immediate withdrawal is prevented ; by the great 
 muscular effort required for this purpose, a small sac or 
 
 Fig. 279. 
 
 1, Btlng of Wasp. 2, Sting of Bee (The small circles show each nearly th. 
 
 full size.) 
 
620 THE MICROSCOPE. 
 
 "bag near the root is pressed upon, and its irritating con 
 tents squeezed out into the wound. After the fluid is 
 injected, the wasp has the power of contracting the 
 barbed points, and then it withdraws the sting from its 
 victim. In fig. 279 the sting of the wasp is shown, with 
 its attachments and muscular arrangement ; and it will be 
 seen that the sting is most wonderfully adapted to become 
 an instrument of a very effective and dangerous character. 
 The palpi near it are placed there for the purpose of 
 cleaning or wiping it ; at all events, this appears to be one 
 of the uses they are put to. 
 
 The proboscis or trunk of the Honey-bee next demands 
 attention ; this is used, with its curious accessories, to 
 collect the honey while roving about from flower to 
 flower. The proboscis itself (fig. 280) is very curiously 
 divided ; the divisions are elegant and regular, beset with 
 triangular hairs, which, beiLg numerous, appear at first 
 sight as a number of different articulations. The two 
 outside lancets are spear-shaped, of a membranaceous or 
 horny substance, set on one side with short hairs, and 
 having their interior hollow \ at the base of each is a 
 hinge-articulation, which permits of considerable motion 
 in several directions, and is evidently used by the busy 
 insect for the purpose of opening the internal parts of 
 flowers, and thus facilitating the introduction of its pro- 
 boscis. The two shorter feelers are closely connected to 
 the proboscis, and terminate in three-jointed articulations. 
 Swarnrnerdam. thought these were used as fingers in 
 assisting the removal of obstructions ; but it is more pro- 
 bable that they are made use of by the insect for storing, 
 and removing the bee-bread to and from the pocket- 
 receptacles in the legs. The lower part of the proboscis 
 is so formed that it can be considerably enlarged at its 
 base, and thus made to contain a larger quantity of the 
 collected juice of flowers ; at the same time, it is in this 
 cavity that the nectar is transformed into pure honey by 
 some peculiar chemical process. The proboscis tapers on 7 
 to a little nipple-like extremity, and at its base will be 
 seen two shorter and stronger mandibles, which serve the 
 little insects in the construction of their cells, and from 
 between which is protruded a long and narrow tongue 
 
TONGUE OF BEE. 
 
 621 
 
 or lance ; the whole is most ingeniously connected to the 
 head by a horny sheath, and a series of muscles and 
 ligaments. The proboscis, being cylindrical, extracts the 
 juice of the flower in a somewhat similar way to that of 
 the butterfly : when loaded with honey, the insect's next 
 
 1, Honey-hoe's tongue. 2, Leg, showing pocket for carrying the Bee-bread. 
 (The small circles show the objects about the natural size!) 
 
622 THE MICROSCOPE. 
 
 care is to fill the very ingenious pockets situated in its 
 hind legs (one of which is shown at No. 2) with bee-bread ; 
 when these little pockets are filled with as much pollen 
 as the bee can conveniently carry, it flies back to the hive 
 with its valuable load, where it is speedily assisted to 
 unload by its fellow- workers ; the pollen is at once 
 kneaded and packed closely in the cells provided for its 
 preservation. The quantity of this collected in one day 
 by a single hive during favourable weather is said to be 
 at least a pound ; this chiefly constitutes the food of the 
 working-bees in the hive. The wax is another secretion 
 exuding through the skin of the insect ; it is found in 
 little pouches in the under-part of the body, but is not 
 collected and brought home ready for use, as has been 
 generally supposed. The waxen walls of the cells are, 
 when completed, strengthened by a varnish, called pro- 
 polis, collected from the buds of the poplar and other 
 trees, and besmeared over by the aid of the wonderful 
 apparatus represented in the engraving. If a bee is 
 attentively observed as it settles down upon a flower, 
 the activity and promptitude with which it uses the 
 apparatus is truly surprising ; it lengthens the tongue, 
 applies it to the bottom of the petals, then shortens it, 
 bending and turning it in all possible directions, for the 
 purpose of exploring the interior, and removing the pollen. 
 In the words of Brook : 
 
 " The dainty suckle and the fragrant thyme, 
 By chemical reduction they sublime ; 
 Their sweets with bland attempering suction strain, 
 And curious through their neat alembics drain ; 
 Imbib'd recluse, the pure secretions glide, 
 And vital warmth concocts th' ambrosial tide." 
 
 The leading characteristic of the vast order Coleoptera, 
 Beetles, consists in the leathery or horny texture of the 
 anterioij wings (elytra), which serve as sheaths for the 
 posterior wings in repose, and generally meet in a straight 
 line down the back. 
 
 The elytra present us with wing-cases of many Curculios, 
 Diamond beetles, the most brilliant of opaque objects. 
 Some are improved by being mounted in Canada balsam, 
 whilst others are more or less injured by it : a trial of a 
 small portion, by first touching it with turpentine, decides 
 
INSECTA 623 
 
 this point. Oblique or side illumination shows the play 
 of colours on the scale to the greatest advantage. 
 
 To the genus Ptinus belongs a small beetle known as 
 the Death-watch, fig. 281. This and the species Anobium 
 are found in our houses, doing much in- 
 jury whilst in the larval state. The eggs 
 are often deposited near some crack in a 
 piece of furniture, or on the binding of an 
 old book. As the larvae are hatched, they 
 begin to eat their way into any furniture 
 on which they may have been deposited ; 
 and, having attained a sufficient depth, Fifr 2gl 
 
 they undergo transformation, and return, The Death-watch, 
 by other passages, as perfect beetles. In Atropus, magnified, 
 furniture attacked by them, small round holes, about 
 the size of the head of a pin, may be seen, and to these 
 holes the term worm-eaten has been applied ; and the 
 noise, made by the insect striking its head against the 
 wood, has given rise to the name of Death-watch. The 
 larva is called a Book-worm when it attacks books ; old 
 books and those seldom used, are often found bored 
 through by it. Kirby and Spence mention, that in one 
 case twenty-seven folio volumes were eaten through, in a 
 straight line, by this insect. The beetle is very small, and 
 almost black. The head is particularly small ; and from 
 the prominence of the thorax, looks as 
 if it were covered with a hood. The 
 Anobium puniceum, fig. 282, attacks 
 dried objects of natural history, and all 
 kinds of bread and biscuits, particularly 
 sailors' biscuits, in which maggots fre- 
 quently abound. In collections of in- 
 sects, it first consumes the interior; 
 when the larva assails birds, it is gene- 
 rally the feet that it devours first ; and 
 in plants, the stem or woody part. The Fi g- ^.-AncHunp^ 
 
 i 11 i . . ii 3 niceum, magnified. 
 
 larva is a small white maggot, the body 
 .of which is wrinkled, and consists of several segments 
 covered with fine hairs ; its jaws are strong and horny, 
 and of a dark brown. The body is white, and so trans- 
 parent, that the internal organs of the insect can te seen 
 
624 THE MICROSCOPE. 
 
 through it. The "beetle itself is of a reddish-brown 
 
 colour, covered with fine hairs. 
 
 The Bacon -beetle (Dermestes lardarius) is another of 
 
 the destructive beetle family. The larva of this beetle is 
 particularly partial to the skin 
 of any animal that may fall in 
 its way; consequently it de- 
 stroys stuffed animals and birds 
 in collections of natural his- 
 tory, whenever it can gain ac- 
 cess to them. It attacks hams 
 and bacon for the skin's sake ; 
 Fig. 283. Dermestes lardarius. and, being a very glutton, ex- 
 
 Larva, pupa, and imago. 
 
 This larva is long and slender, its body nearly round, and 
 is divided into thirteen segments, of a blackish-brown in 
 the middle, and white at the edge ; the whole being fur- 
 nished with bristle-shaped reddish-brown hairs. 
 
 The Dermestidce belong to the family of Necrophagous 
 beetles, six genera of which have been found in Great 
 Britain. The D. lardarius is black about the head and 
 tail, with an ash-grey band across the back, having three 
 black spots on each wing-case. Sometimes this band takes 
 a yellowish tinge, and then the hairs, which are here dis- 
 posed in tufts, are likewise of a yellowish-grey colour. 
 The beetle is most destructive in spring. The larvae, like 
 those of the clothes moths, are but seldom seen, being 
 careful to conceal themselves in the bodies they attack, 
 and their presence can only be guessed at by finding 
 occasionally their cast-off skins, which they change several 
 times during their larvae state. Specimens of hair put 
 up by the mounters and labelled " Hair of Dermestes," 
 do not belong to the species at all. These hairs, long 
 favourite objects with microscopists, and placed by them 
 among test-objects, may, it is believed, be those found in. 
 tufts at the extremity of the body of Anthrenus muse- 
 orum. Westwood says that the larvae of these beetle* 
 are furnished with tufts of hairs, which are " individually 
 formed of a series of minute conical pieces placed in suc- 
 cession, the base being very slender, and the extremity 
 a large oblong knot, placed on a slender footstalk." This 
 
FOOT OF WATER-LEETLE. 
 
 025 
 
 description comes very near to that of the hair in question. 
 It is also suggested that the larvae of another genus, that 
 of Tiresius serra, furnish these hairs ; but, however that 
 may be, it is quite clear that the hairs called " Dermestes " 
 (fig. 307) are not -obtained from the -Bacon-beetle. 
 
 In the Gyrinus, Whirligig, we have a combination of 
 contrivances to facilitate the creature's movements in the 
 element in which it lives. The hind legs are converted 
 into a pair of oars of remarkable efficiency, the point ot 
 
 Fig. 284. 
 1, Leg ot Gyrinus, Whirligig, with paddle expanded. 2, With paddle closed up. 
 
 their connexion with the body being adapted with great 
 precision to ensure the most effectual application of the 
 propelling power ; as it strikes out behind in the act of 
 swimming, a membranous expansion of a portion of the 
 legs enables the insect to move about with great rapidity ; 
 upon the legs being drawn back again towards the body, 
 
 the membrane closes 
 
 up, 
 
 and thus offers but a small 
 
 resistance to the water (fig. 284). The eyes are not the 
 least curious part of the merry little creature ; while one 
 
 s s 
 
626 THE MICROSCOPE. 
 
 portion of them, that fitted for seeing in the air, is fixed 
 on the upper part of the head, the lower portion, for 
 seeing under the water, is placed at the lowest part, a 
 thin division separating the two. 
 
 Sir John Lubbock-, writing of aquatic insects, says : l 
 "Though most of the great orders are represented, no 
 aquatic Hymenoptera or Orthoptera had till now (1864) 
 been discovered. Great, therefore, was my astonishment, 
 when I saw a small Hymenopterous insect, evidently quite 
 at its ease, and actually swimming by means of its wings. 
 At first I could hardly believe my sight ; but having found 
 several specimens, and shown them to some of my friends, 
 there can be no doubt about the fact. Moreover, the same 
 insect was again observed, within a week, by another ento- 
 mologist, Mr. Duchess, of Stepney. It is a curious coinci- 
 dence that, after remaining so long unnoticed, this little 
 insect should thus be found almost simultaneously by two 
 independent observers. Mr. "Walker at first considered 
 the insect to be Polynema fuscipes, but though allied to 
 that species, it is not identical with it. So completely 
 aquatic is it in its habits that it can remain immersed for 
 at least twelve hours ; but it nevertheless requires to come 
 to the surface at certain intervals to renew the air in its 
 tracheae. It is uncertain whether P. natans can also use 
 its wings in flight. They are at any rate not easily incited 
 to do so. It is a very minute species, and well fitted for 
 microscopical observation, the female measuring 0'38 of an 
 inch, and the male 042." 
 
 Dytiscus marginalis, derived from dutes, a diver. Larva 
 narrow, body composed of twelve segments, including 
 head, which is large and strong, bearing antennae, and 
 armed with two powerful jaws. Several varieties of this 
 beetle are met with in fresh and still waters. The larvae 
 feed upon other aquatic larvae, such as the Gnat, Dragon- 
 fly, &c. The suckers on the legs, the feet, &c. are very 
 interesting objects, and should be mounted for viewing 
 both as transparent and opaque objects. 
 
 To the Orthoptera belong Locustina, Gryllina, and Ache- 
 tina, all herbivorous insects. The first is represented by our 
 well-known Grasshopper (Gryllus viridissimus), the secon d, 
 
 (1) Journ. Micros. Soc. vol. iv. p 339. 1864. 
 
SPRING-TAILS. 627 
 
 the Gryuina, appear to frequent trees and shrubs more 
 than the other tribes, the members of which generally 
 l^eep among herbage ; and, in accordance with this habit, 
 many of the exotic species have wing-cases which present 
 the most perfect resemblance to leaves both in colour and 
 venation. Of the Achetina, the common Cricket (Acheta 
 domestica), fig. 285, the noisy little denizen of the kitchen* 
 hearth, is the best example. These insects have the 
 antennae slender and tapering, and often considerably 
 .onger than the body. They agree with the Gryllina in 
 the structure of their singing apparatus ; but the wings, 
 instead of being arranged in the form of a high-pitched 
 ?oof, are laid flat upon the back. Some of them possess 
 ocelli, whilst others are destitute of those organs. The 
 wiogs are very long, and folded up in such a manner as 
 to project beyond the wing-cases in the form of a pair of 
 tapering tails ; the abdomen is also furnished, in both 
 sexes, with a pair of pilose, bristle-shaped, caudal appen- 
 dages : in the female these form a long slender ovipositor, 
 the two filaments being placed side by side, and somewhat 
 thickened at the tip. The tarsi are three-jointed. The 
 horny covering and muscular apparalus under the wing- 
 cases of the Cricket 
 are very curious, and 
 will repay microscopi- 
 cal examination. The 
 
 Cricket has tWO wings, Fig- 286. The Cricket. 
 
 covered by elytra or wing-cases of a dry membranous consis- 
 tency, near the base of which is a horny ridge having trans- 
 verse furrows, exactly resembling a rasp or file ; this it rubs 
 against its body with a very brisk motion, and produces 
 the well-known merry chirp ; the intensity of which is 
 increased by a hollow space, called the tympanum, acting 
 as a sounding-board. The gastric teeth are numerous. 
 
 In Thysanura there is a remarkable diversity of struc- 
 ture ; they undergo no metamorphosis, and have no wings. 
 This order contains two families, Spring-tails, Poduridce, 
 and Lepismence. In the former, the caudal appendage 
 has the form of a forked tail (Podura, fig. 286), which is 
 bent under the body when not in use ; by its sudden ex- 
 tension the insect causes itself to spring to a very great 
 s s 2 
 
623 THE MICROSCOPE. 
 
 distance, in comparison with its size. The body is 
 covered with numerous minute scales, mostly of a beau- 
 tiful silvery or pearly lustre, and curiously striated. 
 
 Podura plumbea, Lead-colour Spring-tails, are generally 
 found in damp places, leaping about like fleas. They 
 
 prefer a moist atmosphere, 
 some take to the surface 
 of the water in secluded 
 places ; their food seems 
 to be vegetable matter of 
 any kind in a stage of 
 
 Fig. 286. Podura plunibea. (In the small decay; the little active 
 
 circle the iusect appears life-size.) creatures are seen to leap 
 about if a stone in a damp situation in the garden is 
 turned up, or if a dark, damp corner of the cellar, about 
 the beer-barrel, is searched; or if we peep among the 
 roots of the ferns in the fern-case. Poduridae, varying in 
 form, colour, &c. are produced from eggs, undergo no 
 metamorphosis, are not parasitic, have from twelve to 
 sixteen simple eyes ; are furnished with strong mandibles, 
 and a broad, curious- looking snout, and a rather long 
 body, terminating in a bifid tail, which by alternately ex- 
 panding and contracting, enables them to leap great dis- 
 tances. The antennae are very long, and covered with 
 scales and fine hairs. To obtain the scales from the body 
 without damage which is certain to occur if the Podura 
 is touched by the fingers take a small test-tube and 
 quickly place it over the insect, when it instantly springs 
 up and clings to the side of the tube; insert a thin glass- 
 cover beneath, and close up the open end. One drop of 
 chloroform carefully administered instantly kills the in- 
 sect ; in a very short time this evaporates and leaves the 
 tube quite dry. By gently shaking the tube a number of 
 scales will drop off and adhere to the thin glass cover ; 
 remove this, and make it secure to the ordinary glass-slip. 
 
 Mr. E. Eeck says, "that the best scales are obtained 
 from insects found in comparatively dry places." Mr. 
 S. J. Mclntire, in an interesting paper on the Podura, 1 
 confirms this statement, but believes that the " test-scale " 
 figured by Mr. Beck belongs to a distinct species. The 
 
 (1) Science Gossip, March, 1867. 
 
SCALES OF LEPISMA. 629 
 
 markings on the scale are better seen when an achromatic 
 condenser is employed with a good objective. Under a 
 power of 500 diameters, the surface appears to be covered 
 with extremely delicate longitudinal and wavy lines. The 
 smaller scales are much more difficult to resolve than the 
 larger, and these form a good test of the defining power 
 of a l-8th or l-12th object-glass. jXo. 5 a, fig. 274~ is a 
 portion of a large scale. Fig. 273, No. 5, the longitudinal 
 markings are shown under a lower power. " But the 
 transverse striae on the scale of the speckled Podura are 
 rendered more distinct when the central rays are stopped 
 out Any error in the correction of the lenses, whether 
 in the manufacture or in the adjustment of the thin 
 covering glass, is immediately detected by the peculiar 
 appearance which these markings present." 
 
 Lepisma sacc/tarina has a spindle-shaped body covered 
 with silvery scales, the sides of the abdomen being fur- 
 nished with a series of appendages or false feet, with 
 long-jointed bristle-like organs at their extremities. The 
 head is concealed under a pro-thorax ; the eyes are usually 
 compound, and generally occupy the greater part of the 
 head. The antennae are very long, and composed of 
 numerous joints ; the maxillary palpi, which are from five 
 to seven jointed, are very conspicuous. These insects are 
 also inhabitants, of moist places. The Lepisma saccharina 
 is commonly found about houses, in sash-frame?, old sugar- 
 casks, &c. ; from the latter circumstance it derives its 
 name. The scales (fig. 273, !N"o. 8) have long been 
 favourite objects, and much used for testing the power of 
 penetration and definition of object-glasses. The scales 
 should be mounted under thin glass covers ; oblique light 
 shows some portions of the scale to advantage : other 
 parts are rendered more distinct when the central rays of 
 the achromatic condenser are stopped out. 
 
 The metamorphosis is complete in the Suctoria, or 
 Siphonaptera, a wingless family the larva, pupa, and 
 imago of which are .very distinct in their appearances 
 the well-known Flea is the best example of this small 
 group. By many authors these insects have been arranged 
 with the Diptera : this is most decidedly incorrect, since, 
 they differ in many particulars. The external covering of 
 
630 
 
 THE MICROSCOPE. 
 
 the Flea (fig. 287) is a horny case, divided into distinct 
 segments ; those upon the thorax being always disunited. 
 Although apterous, the Flea has the rudiments of four 
 
 Fig. 287 
 
 1. Female Flea. 2 Male Flea. (The small circles enclose fleas the actual or 
 life size.) 
 
THE FLEA. 631 
 
 wings, in the form of horny plates on "both sides of the 
 thoracic segments. Its mouth consists of a pair of sword- 
 shaped mandibles, finely -serrated ; these, with a sharp, 
 penetrating needle-like organ, constitute the formidable 
 weapons with which it pierces through the skin. 
 
 The neck is long, the body covered over with scales, the 
 edges of which are set with short spikes or hairs ; from its 
 head project a pair of antennae, feelers or horns, a pro- 
 boscis, which forms a sheath to the pair of lance-shaped 
 weapons. On each side of the head a large compound eye 
 is placed. It has six many-jointed powerful legs, termi- 
 nating in two -hooked claws ; a pair of long hind legs are 
 kept folded up when the insect is at rest, which in the 
 act of jumping it suddenly straightens out, at the same 
 time exhausting all its muscular force in the effort. The 
 female Flea, fig. 287, lays a great number of eggs, sticking 
 them together with a glutinous secretion ; the Flea infest- 
 ing the dog or cat glues its eggs fast to the roots of the 
 hairs ; in four days' time the eggs are hatched, and a small 
 white larva or grub is seen crawling about, and feeding 
 most actively. No. 4 (fig. 289) is a magnified view of one, 
 covered with short hairs, doubtless for the purpose of 
 preventing its dislodgment. After remaining in this 
 state about nine or ten days, it assumes the pupa form ; 
 this it retains four days ; and in nine days more it be- 
 comes a perfect Flea. The head of the Flea found in the 
 cat (No. 3, fig. 289) somewhat differs in form from that 
 of the species infesting the human being. Its jaws are 
 furnished with more formidable-looking mandibles, and 
 from between the first and second joints behind the head 
 short strong spines project. 
 
 Arachnida. The animals forming the class Arachnida 
 include spiders and their allies, most of which are looked 
 upon with disgust and aversion by the generality of man- 
 kind. Arachnida are divided into two orders, Trachearia 
 and Pulinonaria. The first includes the Acaridce or 
 Mites, in which we find tracheae, as in insects, but no 
 distinct vascular apparatus : in the second, spiders and 
 scorpions are included, and these have a pulmonary cavity, 
 and a well-developed circulatory system. The above are 
 distinguished from Podoptfialmia or Arthropoda by their 
 
632 THE MICROSCOPE. 
 
 aerial respiration, their possession of four pairs of legs 
 attached to an anterior division of the body, and the total 
 absence of antennae. The body is also covered with a 
 softish skin, which sometimes attains a horny consistency, 
 but nothing more. In the higher forms, the body is 
 divided into two parts, the anterior of which, as in Crus- 
 tacea, consists of a thoracic segment, amalgamated with 
 the head, and forming together a whole called the cephalo- 
 thorax. In the highest classes the division of the thorax 
 into separate segments becomes apparent; the anterior 
 segment is, however, amalgamated with the head. The 
 structure of the abdomen varies greatly. In some cases 
 it forms a soft round mass, without any traces of seg- 
 mentation ' } whilst in others, as scorpions, it is continued 
 into a long flexible jointed tail. 
 
 Acarea, an order of animals not strictly belonging to 
 insects, but rather to Arachnida, Spiders, Scorpions, &c. 
 The general description of the class is that the head 
 is united with the thorax, forming a cephalo-thorax ; no 
 antenna?, simple eyes, body presenting transverse striaB or 
 furrows between the second and third pair of legs, which 
 are eight in number, terminated by an acetabulum and 
 claws. These animals are commonly called mites, and 
 the best known species is that found in cheese, tliQAcarus 
 domesticus. Most of the species are oviparous and vivi- 
 parous, their eggs are very numerous. The spider enve- 
 lopes its eggs in a beautiful silken cocoon. Scorpions 
 produce their young alive, and it is deserving of notice 
 that in this family the embryo is developed in the ovum 
 while it still remains in the ovary. The existence of a 
 micropyle has not yet been made out in the ova of Arach- 
 nida. For the sake of convenience we have included 
 Parasites in this part of our work, and in Plate VI. Nos. 
 144 to 147 are representations of their eggs, from some of 
 which the larvas are just emerging. 
 
 The Malophagus, or Sheep-tick, fig. 288, is apterous, 
 and seems to be a connecting link between acarina and 
 insects proper. The Sarcoptes scabiei produces the itch in 
 the human being : it is also found to be the cause of mange 
 in the dog. In one pustule on a dog suffering from this 
 disease, as many as thirty parasites have been found. 
 
THE SHEEP-TICK. 
 
 633 
 
 The Louse (fig. 290, No. 1). Whenever wretchedness, 
 disease, and hunger seize upon mankind, this horrid 
 parasite seldom fails to appear in the train of such 
 calamities, and to increase in proportion as neglect of 
 
 l*i e '. i:SS. MalvpUarjus ovinus, Sheep-tick. (The small circle encloses one 
 of life size.) 
 
 personal cleanliness engenders loathsome disease. When 
 examined under the microscope, our disgust of it is in no 
 ,way diminished. In the head may he distinguished two 
 large eyes, and near to them are the two antennas ; the 
 front of the head is long, and somewhat tapering off to 
 form a snout, which serves as a sheath to the proboscis 
 and the instrument of torture with which it pierces the 
 flesh and draws the blood. To the fore part of its body 
 six legs arc affixed, having each five joints, terminated 
 by two unequal hooks ; these, with other portions, are 
 covered with short hairs. Around the outer margin of 
 
34 
 
 THE MICROSCOPE. 
 
 the body may be seen small circular dots, the breathing 
 apertures, with which all the class are freely provided, 
 rendering them very tenacious of life, and difficult to kill. 
 There is another louse, rather differing in its characteristics 
 
 Fig. 289. 
 
 1, Bog's parasite. 2, Rat Acarus. 3, Head of Cat-Flea. 4, Larva, or; grub ol 
 Flea, (The life size of each is given in the small circles.) 
 
ACA1UNA. 
 
 C35 
 
 Fig. 290. Porwite*. Acariva. 
 
 1. Louse. Human ; magnified 50 diameters. 2, Acarut dometticus, Choese- 
 ilite^ under surface. 3, Acanu Scabiti, Itch-Insect; magnified 850 dia- 
 meters. 4, Entozoon folliculorum, Grub from the human skin In various 
 twees of existence, from the egg upwards : magnified 350 diameters. (The 
 email circles near represent the objects about the natural size.) 
 
036 THE MICROSCOPE. 
 
 from this, found upon the body of the very poor and dirty t 
 known as the body or crab-louse. Leeuwenhoek carried his 
 researches on the habits of these insects further than most 
 investigators, even allowing his zeal to overcome his disgust 
 for such creatures as the louse. In describing its mode of 
 taking food, &c., he observes : " In my experiments, 
 although I had at one time several on my hand drawing 
 blood, yet I very rarely felt any pain from their punctures ; 
 which is not to be wondered at, when we consider the 
 excessive slenderness of the piercer ; for, upon comparing 
 this with a hair taken from the back of my hand, I judged, 
 from the most accurate computation I could form by the 
 microscope, that the hair was 700 times larger than this 
 incredibly slender piercer, which consequently by its 
 punctures must excite little or no pain, unless it happens 
 to touch a nerve. Hence I have been induced to think 
 that the pain or uneasiness those persons suffer who are 
 infested by these creatures, is not so much produced from 
 the piercer as from a real sting, which the male louse 
 carries in the hinder part of his body, and uses as a 
 weapon of defence." He found, from experiments made 
 to ascertain the possible increase of these pests, that from 
 two females he obtained in eight weeks the almost in- 
 credible number of 10,000 eggs. 
 
 The Itch-insect, Acarus scabiei (fig. 290, No. 3, magni- 
 fied 350 diameters). Dr. Bononio was among the first to 
 detect the parasitic character of the disease known as the 
 itch. On turning out one of the pustules, or little blad- 
 ders, from between the fingers, with the points of very 
 fine needles, under the microscope, a minute animal was 
 discovered, very nimble in its motion, covered with short 
 hairs, having a short head, a pair of strong mandibles or 
 cutting jaws, and eight legs, terminating in remarkable 
 appendages, each provided with a sucker and setae. 
 
 It has no eyes ; but when disturbed it quickly draws in 
 its head and feet, and then somewhat resembles the tor- 
 toise in appearance, its march is precisely that of the tor- 
 toise. It usually lays sixteen eggs, which are carefully 
 deposited in furrows under the skin, and ranged in pairs j 
 these hatch in about ten days. 
 
 To find the itch-insect, the operator must examine care- 
 
ACARUS DOMESTICUS. 637 
 
 fully the parts surrounding each pustule, he will then seo 
 a rod line or spot communicating with it ; this part, and 
 not the pustule, must be probed with a fine-pointed instru- 
 ment ; the operator must not be disappointed by repeated 
 failures. Dr. Bourguignon bestowed much time in 
 studying the habits of this troublesome parasite. To 
 arrive at a knowledge of its haunts he arranged his mi- 
 croscope so as to enable him to observe it under the skin 
 of the diseased person. The rays of light from a lamp or 
 candle must be carefully brought to a brilliant focus by 
 means of the condensing or bull's-eye lens upon the 
 chosen point of observation ; a Leiberkiihn should also be 
 attached to the object-glass. 
 
 No. 4, fig. 290, Demodex folliculorum, is another re- 
 markable parasite found beneath the skin of man : it is 
 sometimes obtained from a spot where the sebaceous folli- 
 cles, or fat glands, are abundant ; such as the forehead, the 
 side of the nose, and the angles between the nose and 
 lip ; if the part where a little black spot or a pustule is 
 seen be squeezed rather hard, the oily matter there accu- 
 mulated will be forced out in a globular form ; if this be 
 laid on a glass slide, and a small quantity of oil added to 
 it, to cause the separation of the harder portions, the 
 parasite in all probability will float out ; after the addition 
 of more oil, it can then be taken away from the oily 
 matter by means of a fine-pointed sable pencil-brush, and 
 transferred to a clean slide ; when dry it should be im- 
 mersed in Canada balsam, covered over with thin glass, 
 and mounted in the usual way. 
 
 The Cheese-mite, Acarm domesticus (fig. 290, No. 2), 
 has a peculiar elongation of its snout, forming strong, 
 cutting, dart-shaped mandibles, which it has the power of 
 advancing separately or together. The powder of old and 
 dry cheese almost entirely consists of mites and their eggs, 
 which are hatched in about eight days ; if deprived of 
 food, they have been seen to kill and eat each other. 
 Acari infest almost the whole of our dried articles of 
 food. A c. passularum has two very long buccal bristles ; it 
 lives upon dried figs, and other saccharine fruits. Ac. de- 
 stntctor has long black hairs ; it feeds upon the contents 
 of entomological cabinets, espncially butterflies ; Ac. pru- 
 
638 
 
 THE MICROSCOPE. 
 
 norum is found on dried plums, &c. ; Ac. favor um finds 
 its food in old honeycombs ; Acarus sacchari (fig. 291) is 
 commonly present in the more impure kinds of sugar. 
 The discovery of the general prevalence of this acarus 
 rests, we believe, with Dr. Hassall. 
 
 The Sugar acarus approaches somewhat, in its organisa- 
 tion and habits, Acarus domesticus ; it attains to a size so 
 considerable, that it is plainly visible to the unaided sight. 
 
 Fig. 291. 
 Ova and young of the Acarus sacchari, Sugar-Insect, after Hassall. 
 
 When present in sugar, it may always be detected by the 
 following proceeding : two or three drachms or teaspoonfuls 
 of sugar should be dissolved in a large wine-glass of tepid 
 water, and the solution allowed to remain at rest for an 
 hour or so ; at the end of that time the acari will be 
 found, some on the surface of the liquid, some adhering to 
 the sides of the glass, and others at the bottom, mixed up 
 with the copious and dark sediment, formed of fragments 
 of cane, woody fibre, grit, dirt, and starch-granules, which 
 usually subside on the solution of even a small quantity of 
 sugar in hot water. The Acarus sacchari, when first 
 hatched, is scarcely visible ; as it grows it becomes elon- 
 gated and cylindrical, until it is about twice as long as 
 
ACARINA PARASITES. 
 
 639 
 
 broad; after a time the legs and proboscis begin to protrude. 
 The body is partially 
 covered by seta}, and the 
 feet terminate in hooks. 
 These stages of the de- 
 velopment of the acarus 
 areexhibitedin.fig.291. 
 
 The A cants farinas, 
 Flour-mite. This is of 
 occasional occurrence in 
 flour, but is never pre- 
 sent unless it has be- 
 come damaged. Any 
 flour, therefore, contain- 
 ing the animal in ques- 
 tion is in a state unfit 
 for consumption. We 
 believe that it is found 
 more frequently in the 
 flour of the Leguminosas 
 than that of the Gra- 
 minece. 
 
 This acarus differs con- 
 siderably in structure 
 from the Sugar-mite, 
 particularly so in its 
 pennate setae. 
 
 Dr. Burnett esta- ** ^2.-^ 
 blished to his satisfac- 
 tion the following facts : 
 " 1. That though there 
 are single species of pa- 
 rasites peculiar to parti- 
 cular animals, there are 
 others which are found 
 on different species of 
 the same genus; as is 
 the case in the para- 
 sites living on birds of 
 the genus Lanu > (gulls), ^ Hippobosca u^ nis . 2 , Nirmiima * 
 
 and the diurnal birds OI and female, parasites infesting Swallows. 
 
640 
 
 THE MICROSCOPE. 
 
 prey. 2. The parasites of the human body confine them- 
 selves strictly to particular regions ; when they are found 
 
 Fig. 294. 
 
 1, Parasite of Turkey. 2, Acarus of common Fowl, under surface. 3, Parasite 
 of Pheasant. (The small circle encloses each about life size.) 
 
 elsewhere, it is the result of accident. Thus, the Pediculi 
 capitis live in the head ; P. vestimenti, upon the surface of 
 the body; the P. tabescentium, on the bodies of those dying 
 of marasmus ; and the P. inguinalis, about the groins, arm- 
 
ACABINA PARASITES. 
 
 641 
 
 pits, mouth, and eyes." From an examination of the 
 structure of these parasites, Dr. Burnett is of opinion that 
 
 
 
 Fig. 295. 
 
 1, Acarus of Beetle. 2, Acarus of Fly. 3, Acarus of Clothes-Moth. (The 
 circles enclose each about life size.) 
 
 they should be placed in an order by themselves, closely 
 allied to Insecta ; the mandibulate parasites occupying the 
 highest, and the haustellate the lowest, position in the 
 order : thus confirming to some extent the observations 
 made by Mr. Denny. 
 
 There is a remarkable species of acarus described by 
 T T 
 
642 THE MICROSCOPE. 
 
 Dr. Eobins, found spinning a white silken web on the base 
 of the sparrow's thigh, or on the fore-part of its body ; on 
 raising this delicate web, you perceive that it is filled with 
 minute eggs, from, which the young issue, being in due 
 time hatched by the warmth of the body it is destined to 
 
 annoy. In fig. 296 are 
 seen some eggs of a 
 parasite infesting the 
 hornbill ; they are 
 glued to the feathers 
 near the head of the 
 bird ; the Iarva3 are 
 ready to leave the egg 
 in two days. Another, 
 curiously enough, se- 
 lects the pultnonic ori- 
 fice of the snail : when 
 
 Fig. 296.-ZonE of the Parasite of Hornbill. the an i ma l Dilates this 
 
 orifice, for the purpose of allowing the air to penetrate its 
 respiratory cavity, the female acarus slips through the open- 
 ing, and lays her eggs in the folds of the mucous membrane, 
 where they are gradually developed. The young, upon 
 issuing forth from the eggs, select some portion of the 
 snail's body upon which to feed and perfect their growth. 
 
 Ixodidce are furnished with a powerful rostrum, armed 
 with recurvate spines, with which they pierce the skin of 
 the unfortunate animal upon whose blood they live. So 
 firmly do these anchor-like organs retain their hold, that if 
 the parasite is pulled away it usually carries a portion of 
 the skin of its victim with it. These creatures live upon 
 a great variety of animals. The dog is very liable to their 
 attacks, and many species fix themselves exclusively upon 
 serpents and other reptiles. Glyciphagus cursor is found 
 in the feathers of the owl, and in the cavities of the bones 
 of skeletons. Gamasidce are furnished with a sucking 
 apparatus very similar to that of Ixodidce, usually attaching 
 themselves to the bodies of beetles; the common Dung- 
 beetle (Geotroupes) is often found with its lower surface 
 nearly covered with them. 
 
 There are other families leading a more active Ufa, 
 being furnished with eyes. One family, Hydrachnidce, 
 
ACARINA PARASITES. 
 
 643 
 
 Water-mites, inhabit the water, where they swim about 
 with considerable rapidity by means of their fringed legs. 
 
 Pig. 207. 
 
 1, Parasite of Eagle. 2, Parasite of V&ture. 3, Parasite of Pigeon. (Tfte 
 circles juclose each about life size). 
 
 In their young state, they attach themselves parasitically 
 to aquatic animals ; they then possess only six legs, and 
 pass through a quiescent or pupa state before acquiring 
 the fourth pair. Orbitadce, unlike other Acarea, live 
 upon vegetable matter, principally damp leaves and moss ; 
 
 TT2 
 
644 THE MICROSCOPE 
 
 they have a mouth adapted for biting such food, and are 
 covered with a hard and very brittle skin. The Bdellidce 
 live among damp moss, have the body divided apparently 
 into two parts by a constriction, and the rostrum and 
 palpi very long ; whilst Trombidiidce, of which the little 
 scarlet mite so often seen in gardens is an example, have 
 their palpi converted into little raptorial organs. 
 
 Another family of parasites are commonly met with in 
 the bodies of fishes, attaching themselves to the branchiae, 
 to the soft skin under the fins, or to the eyes, much to 
 the annoyance of the unfortunate victim. Some of these 
 found on fresh-water fish are sufficiently transparent to 
 show the circulation of their fluids most interesting 
 objects for the microscope. 
 
 The "Water-snail, Limnoeus^ is tormented by a larva of 
 the family Amphistoma, which attaches itself by a series 
 of hooklets and bristles to various parts of the body and 
 mantle ; under a low magnifying power, when congre- 
 gated together, they appear somewhat like tufts of threads. 1 
 
 ARACHNIDA, Spiders. Epeira diadema is the best 
 known of the British species of Garden Spiders: it 
 is readily recognised by the beautiful little gem-like 
 marks' on its body and legs. Spiders abound on every 
 shrub ; and if we consider that the Spider is destitute of 
 a distinct head, without antennae, one-half of its body 
 attached to the other by a very slender connexion, and so 
 soft as not to bear the least pressure, -its limbs so slightly 
 attached to its body that they fall off at a very slight 
 touch, it appears ill-adapted either to escape the many 
 dangers which threaten it on all sides or to supply itself 
 with food ; and the economy of such an animal is deserving 
 of the microsccpist's attention. 
 
 The several important organs peculiar to the Spider 
 tribe are represented in fig. 299. Of these, No. 1 show 
 the spinning apparatus; four only are the spinnarets, or 
 organs by which their silky threads are emitted. Their 
 structure is very remarkable ; the surface of each spinnaret 
 is pierced by an infinite number of minute holes, shown 
 
 (1) The earliest known account of the parasite tribes is given in Redi's 
 Treatise de Generations -Insectorum ; see also H. Denny's Monographia 
 rorum Britannia. 1842. 
 
AllACHNIDA. 
 
 645 
 
 in No. 2, from each of which there escapes as many little 
 drops of a liquid as there are holes, -which, .drying the 
 moment they come in contact with the air, immediately 
 form so many delicate threads. Immediately after the 
 filaments have passed through the pores, they unite first 
 together, and then with those of the next, to form one 
 common thread ; so that the thread of the spider is com- 
 
 V 
 
 Fig. 298. Epeira diadema, Diadem Spider. 
 
 posed of a large number of minute filaments, perhaps 
 many thousands, of such extreme tenuity that the eye can- 
 not detect them until they are twisted together into the 
 working thread. In the two pairs of spinnarets a different 
 anatomical structure can be detected; the pair above, 
 which are a little the longest, show a multitude of small 
 perforations, the edges of which do not project, and which 
 therefore refcemble a sieve. The shorter pair have pro- 
 jecting tubes independent of the perforations which exist 
 
646 
 
 THE MICROSCOPE. 
 
 in those above. The tubes are hollow, and perforated at 
 their extremities ; and it is supposed that the agglutinating 
 threads issue from these tubes, while those emitted from 
 the perforations do not possess that property. It will be 
 seen, by throwing a little dust on a circular Spider's web, 
 that it adheres to the threads which are spirally disposed, 
 but not to those that radiate from the centre to the cir 
 cumference; the latter are also the stronger of the set. 
 
 Pig. 299. 
 
 1, Spinnarets of Spider. 2, Extreme end of one of the upper pair of sphma- 
 rets. 3, End of under pair of spinnarets. 4, Foot of Spider. 5, Side view 
 of eye. 6, The arrangement of the four pairs of eyes. 
 
 The rapidity with which these webs are constructed is 
 as astonishing as is the accuracy with which the webs 
 are formed. There are many different kinds of Spiders ; 
 but nearly all of them envelop their eggs in a covering of 
 silk, forming a round ball, which the Spider takes care to 
 hang up in some sheltered place till the spring. The 
 mode in which the ball is formed is very curious : the 
 mother Spider uses her own body as a guage to measure 
 her work, in the same way as a bird uses its body to 
 guage the size and form of its nest. The Spider first 
 spreads a thin coating of silk as a foundation, taking care 
 to have this circular by turning its body round during the 
 In the same manner it spins a raised border 
 
ABACHNIDA. 647 
 
 round this till it takes the form of a cup ; it is at this 
 stage of the work that it begins to lay its eggs in the cup, 
 and not content to fill it up to the brim, it also piles up 
 a large round heap, as high as the cup is deep. Here, 
 then, is a cup full of eggs, the under half covered and pro- 
 tected by the silken sides of the cup, but the upper still 
 bare and exposed to the air and the cold. She now seta 
 to work to cover these also : the process is similar to the pre- 
 ceding, that is, she weaves a thick web of silk all round 
 them, and, instead of a cup-shaped nest, like some birds, 
 the whole partakes of the form of a ball much larger than 
 the body of the Spider. 
 
 The feet of the Spider, one of which is represented at 
 JSTo. 4, are curiously constructed. Each foot, when mag- 
 nified, is seen to be armed with strong horny claws, with 
 serrations on the under-surface. By this arrangement the 
 Spider is enabled to regulate the issue of its rope from the 
 spinnarets. Some have, in addition, a remarkable comb- 
 like claw, for the purpose of separating certain threads 
 which enter into the composition of their delicate webs. 
 
 One of the most remarkable members of the family, the 
 Argyroneta aquatica, Diving Spider, weaves itself a curious 
 little bell-shaped globule, which it takes with it to the 
 bottom of the water, whither it retires to devour its prey. 
 Notwithstanding its aquatic habits, this, like the rest of 
 its order, is fitted only for aerial respiration ; it therefore 
 fills its miniature balloon with air, which it carries down 
 with it entangled amongst the hairs of its body. This 
 closely resembles the earliest diving-bells. 
 
 Mr. Quekett recommended the following as a simple 
 method of obtaining a perfect system of tracheal tubes 
 from the larvae of insects : A small opening having been 
 made in the body, it is to be placed in strong acetic acid, 
 which softens or decomposes all the viscera : the trachea 
 must then be well washed with a syringe, and removed 
 from the body, by cutting away the connexions of the 
 main trunks with the spiracles, by means of fine-pointed 
 scissors. For mounting, they should be floated on to the 
 glass-slide, and laid out in the position best adapted for 
 displaying them. If we wish to mount them in Canada 
 balsam, they should be allowed to dry upon the slide, 
 
648 THE MICROSCOPE. 
 
 "but their natural appearance is best preserved by mount- 
 ing in weak spirit and water, or Goadby's solution, using a 
 very shallow cell, to avoid pressure. The spiracles should 
 be dissected out with a fine knife and scissors. 
 
 Mr. Hepworttis Mode of Preparing and Mounting In- 
 sects. He destroys life with sulphuric ether, then washes 
 the insects thoroughly in two or three waters in a wide- 
 necked bottle; he afterwards immerses them in caustic 
 potash or Brandish's solution, and allows them to remain 
 in it from one day to several weeks or months, according 
 to the opacity of the insect ; with a camel-hair pencil he 
 then presses the contents of the abdomen and other soft 
 parts dissolved by the potash out in a saucer of clean 
 water, holding the head and thorax with one brush, and 
 gently pressing the other with a rolling motion against the 
 body from the head to the extremities. The potash must 
 afterwards be completely washed out, or crystals may 
 form. The insects must then be dried, the more delicate 
 specimens being spread out or floated on to glass-slides,, 
 covered with thin glass and tied down with thread. 
 When dry, they must be immersed in rectified spirits of tur- 
 pentine, and placed under an air-pump. When sufficiently 
 saturated they are ready for mounting in Canada balsam ; 
 but they may be retained for months in the turpentine 
 without injury. Before mounting, as much turpentine as 
 possible must be drained and cleaned off the slide ; but 
 the thin glass must not be removed, or air would be re- 
 admitted. Balsam thinned with chloroform is then to be 
 dropped on the slide so as to touch the cover, and it will 
 be drawn under by capillary attraction. After pressing 
 down the cover, the slide may be left to dry and to be 
 finished off. If quicker drying be required, the slide 
 must be warmed over a spirit-lamp, but not made too hot, 
 as boiling disarranges the object. Vapours of turpentine 
 or chloroform may cause a few bubbles, but these dis- 
 appear when condensed by cooling. 1 
 
 TRANSFORMATION OF INSECTS. 
 
 The metamorphoses of the insect race offer some of 
 the most curious and wonderful of nature's phenomena for 
 
 (1) Journ. Micros. Soc. vol. i. p. 73. 
 
TRANSFORMATION OF INSECTS. 649 
 
 contemplation. " We see," says an old author, " some of 
 these creatures crawl for a time as helpless worms upon 
 the earth, like ourselves ; they then retire into a covering, 
 which answers the end of a coffin or a sepulchre, wherein 
 they are invisibly transformed, and come forth in glorious 
 array, with wings and painted plumes, more like the inha- 
 bitants of the heavens than such worms as they were in 
 their former state. The transformation is so striking and 
 pleasant an emblem of the present, intermediate, and 
 glorified state of man, that people of the most remote 
 antiquity, when they buried their dead, embalmed and 
 enclosed them in an artificial covering, so figured and 
 painted as to resemble the caterpillar in the intermediate- 
 state ; and as Joseph was the first we read of that was 
 embalmed in Egypt, where this custom prevailed, it was 
 probably of Hebrew origin." 
 
 Faint and imperfect symbol though it be, yet it may, 
 perchance, offer a glimpse of the metamorphosis awaiting 
 our own frail bodies. Between the highest and lowest 
 degree of corporeal and spiritual perfection, that there are 
 many intermediate degrees, the result of which is one 
 universal chain of being, no one can for a moment gain- 
 gay. Thus the angel Raphael is made to say, in Milton's- 
 Paradise Lost, 
 
 1 What surmounts the reach 
 
 Of human sense, I shall delineate so, 
 
 By likening spiritual to corporeal forms, 
 
 As may express them best : though what if earth 
 
 Be 'but the shadow of heaven, and things therein 
 
 Each to other like, more than on earth is thought 1 " 
 
 The great class of insects, which furnishes four- fifths of 
 the existing species of the animal kingdom, has two chief 
 divisions. In the one, the Ametabola, we have an imper- 
 fect, in the other, the Metabola, a perfect metamorphosis ;. 
 that is, in the former there is no quiescent pupa state, and 
 the metamorphosis is accompanied by no striking change 
 of form ; in the latter, there is an inactive pupa that takes 
 no nourishment, and so great a change of form, that only 
 by watching the progress of the metamorphosis can we 
 recognise the pupa and the imago as belonging to the 
 same animal 
 
 The degree of metamorphosis is, however, very different 
 
650 THE MICROSCOPE. 
 
 in different groups of insects. In its most complete form, 
 as exemplified in the Butterflies, Moths, Beetles, and many 
 other insects, the metamorphosis takes place in three very 
 distinct stages. In the first, which is called the larva state, 
 the insect has the form of a grub, sometimes furnished 
 with feet, sometimes destitute of those organs. Different 
 forms of insects in this state are popularly known as Cater- 
 pillars, Grubs, and Maggots. During this period of its 
 existence, the whole business of the insect is eating, which 
 it usually does most voraciously, changing its skin repeat- 
 edly, to allow for the rapid increase in its bulk ; and after 
 remaining in this form for a certain time, which varies 
 greatly in different species, it passes to the second period 
 of its existence, in which it is denominated a pupa. In 
 this condition the insect is perfectly quiescent, neithei 
 eating nor moving. It is sometimes completely enclosed 
 in a horny case, in which the position of the limbs of the 
 future insect is indicated by ridges and prominences: 
 sometimes covered with a case of a softer consistence, 
 which fits closely round the limbs, as well as the body, 
 thus leaving the former a certain amount of freedom. 
 Pupoe of this description are sometimes enclosed within 
 the dried larva skin, which thus forms a horny case for the 
 protection of its tender and helpless inmate. After lying 
 in this manner, with scarcely a sign of life, for a longer 01 
 shorter period, the insect, arrived at maturity, bursts from 
 its prison in the full enjoyment of all its faculties. It is 
 then said to be in the imago or perfect state. This meta- 
 morphosis is one of the most remarkable phenomena in 
 the history of insects, and was long regarded as perhaps 
 the most marvellous thing in nature ; although recent 
 researches have shown that the history of many of the 
 lower animals presents us with circumstances equally iJ 
 not more wonderful, nevertheless the metamorphosis of the 
 higher insects is a phenomenon which cannot fail to arrest 
 our attention. To see the same animal appearing first as 
 a soft worm-like creature, crawling slowly along, and de- 
 vouring everything that comes in its way, and then, aftei 
 an intermediate period of death-like repose, emerging from 
 its quiescent state, furnished with wings, adorned with 
 brilliant colours, and confined in its choice cf food to the 
 
TRANSFORMATION OP INSECTS. 651 
 
 most delicate fluids of the vegetable kingdom, is a spec- 
 tacle that must be regarded with the highest interest; 
 especially when we remember that these dissimilar crea- 
 tures are all composed of the same elements, and that the 
 principal organs of the adult animal were in a manner 
 shadowed out in all its previous stages. 
 
 Nor is the singularity of their natural history the only 
 claim that these insects have upon our attention. Lowly 
 as they seem in point of organization, there are few 
 animals that exceed them in commercial importance. To 
 give an instance gr two ; the finest red dyes known to our 
 manufacturers are derived from insects. The Lecanium 
 ilicis, an inhabitant of the Ilex, Evergreen-oak, growing in 
 countries near the Mediterranean, was employed for this 
 purpose by the ancient Greeks and Romans, as it is still 
 by the Arabs ; and, until the introduction of the Mexican 
 cochineal, another species, the Coccus polonicus, living 
 on the roots of the Sderanthus perennis in Central Europe, 
 was much used for the same purpose. The Mexican cochi- 
 neal, which has driven all other kinds out of the market, is 
 one of the species Coccinia; this pretty insect was long 
 regarded as a parasite upon the Cactus opuntia, Prickly- 
 pear a plant common in Central America. The com- 
 mercial importance of this insect is shown by a single fact : 
 in 1850, no less than 2,514,512 Ibs. of cochineal were im- 
 ported into Great Britain alone (value about 7s. per Ib.) ; 
 and as about 70,000 insects are required to weigh a 
 pound, we may form some idea of the almost countless 
 numbers annually destroyed. For many years the culti- 
 vation, or rather feeding, of cochineal was entirely confined 
 to Mexico ; but the insect has lately been introduced into 
 Spain, and the French possessions in Africa, with every 
 prospect of success. A fourth species, of great import- 
 ance, is the Lac insect, Coccus lacca, an inhabitant of the 
 East Indies, where it feeds upon the Banian-tree, Ficus 
 religiosa, and other trees. It is to this insect we are 
 indebted, not only for the dye-stuffs known as lac-dye 
 and lac-lake, of which upwards of 18,000 cwts. were 
 imported in 1850, but also for the well-known sub- 
 substance called shell-lac, so much used in the preparation 
 of sealing-wax and varnishes. It is somewhat remark- 
 
652 THE MICROSCOPE. 
 
 able that only the female insects yield a good colouring 
 matter. 
 
 Of all the secretions peculiar to insects, silk may well 
 he regarded as the most valuable, since it has become as 
 much an essential to the purposes of mankind as to the 
 economy of its producers. The fluid, before it comes in 
 contact with the air, is viscous and transparent in the young 
 larva, but thick and opaque in the more mature. It is found, 
 by chemical analysis, to be chiefly composed of Bombic 
 acid, a gummy matter, a portion of a substance resembling 
 wax, and a little colouring matter. Silk may be placed in 
 boiling water without undergoing any change ; the strongest 
 acids are required to dissolve it; and it has never yet been 
 imitated artificially. More than 500,000 human beings 
 derive their sole support from the culture and manufacture 
 of silk ; and the importance of the Silkworm to Great 
 Britain alone is represented by the large sum of 16,500,0002, 
 annually. Then we have large sums of money changing 
 hands from the labours of the useful little Bee , tons' 
 weight of honey and wax are yearly consumed ; England 
 pays more than 50,0001. for foreign honey and wax, in 
 addition to her own valuable produce. A great variety oi 
 scents, which from their agreeable odours are much used in 
 perfumery, are manufactured from insects. The Spanish 
 My is an indispensable article in the treatment of certain 
 forms of disease ; and that invaluable agent, Chloroform, 
 was first made from formic acid ; an acid discovered in the 
 Formic ant, and from which it has derived its name. 
 Then there are Gall-nuts, produced by a small fly, for which 
 a substitute could not be found in dyeing and ink-making 
 
 " Much more extensive and important than any of the 
 foregoing, but, as less palpable, even more disregarded, are 
 the general uses of insect existence. Disease, engendered 
 of corruption in substances animal and vegetable, would 
 defy all the precautions of man, unless these were aided 
 by scavenger- insects, those myriads of flies and carrion 
 beetles, whose perpetual labours, even in our tempered 
 climate but infinitely more so in warmer regions are 
 essentially important to cleanliness and health. 
 
 " A use of this nature, and one performed perhaps to an 
 extent we little think of is the purification of standing 
 
TRANSFORMATION OP INSECTS. 
 
 653 
 
 waters by the innumerable insects which usually inhabit 
 them. We have witnessed ample proof of the efficacy in 
 this respect of Gnat larvae, when keeping them to observe 
 their transformations. Water swarming with these ' lives 
 of buoyancy ' has been perfectly sweet at the end of ten 
 days; while that from the same pond, containing only 
 vegetable matter, has become speedily offensive. 
 
 " We have already pointed out the utility of insects in 
 affording ever-new subjects of interesting inquiry. And 
 let those who will look scorn upon our pursuit ; but few 
 are more adapted to improve the mind. In its minute 
 details, it is well calculated to give habits of observation 
 and of accurate perception ; while, as a whole, the study 
 of this department of nature, so intimately linked with 
 others above and below it has no common tendency to lift 
 our thoughts to the great Creative Source of Being, to 
 Him who has not designed the minutest part of the 
 minutest object without reference to some use connected 
 with the whole." 
 
 The shapely limb anJ Jubricated joint 
 Within the small dimensions of a point, 
 Muscle and nerve miraculously spun, 
 His mighty work, who speaks, and it is done ; 
 The invisible in things scarce seen revealed, 
 To whom an atom is an ample field." 
 
CHAPTEK Y. 
 
 VERTEBRATA. 
 
 PHYSIOLOGY HISTOLOGY BOUNDARY BETWEEN THE TWO KINGDOMS CELL 
 DEVELOPMENT GROWTH OF TISSUES SKIN, CARTILAGE, TEETH, 
 BONE. ETC. 
 
 HE most complicated state in which 
 matter exists, is where, under 
 the influence of life, it forms 
 bodies with a curious internal 
 structure of tubes and cavities, 
 in which fluids are moving and 
 producing incessant internal 
 changes. These are called orga- 
 nised bodies, because of the 
 various organs which they contain, and 
 they form two remarkable classes ; those 
 of the lowest class are for the most part 
 fixed to the soil, and are recognised as 
 vegetables, the structure of these we have 
 already considered; those of the higher 
 order are endowed with power of locomo- 
 tion, and are called animals. Some of the peculiarities 
 and minute structure of the invertebrate animals have 
 already been made the subject of investigation, and we 
 now propose to extend our observations to the vertebrate. 
 The study of the Science of Life, or the building up of 
 the living structure, is termed Physiology, or Biology ; l 
 and that part of it more particularly relating to the minute 
 structure of the organs of animals has been termed 
 Histology. 11 
 
 (1) From /?>?, life, and Xo-yor, discourse & discourse on life ; a nore expres- 
 sive term than physiology. 
 
 (2) From lo-ror, a tissue, or web, and \<wcr, a discourse. 
 
ANIMALS AND VEGETABLES. 655 
 
 Physiology has for its object the scientific co-ordination 
 of the phenomena and laws of life ; yet, writes Mr. Lewes, 
 " the attempts to define what we are to understand by Life, 
 have hitherto proved almost if not quite valueless." In 
 our previous investigations, we must have seen the value 
 and advantage of " studying Life in its simpler forms, 
 if Life is to be understood in its more complex ; and 
 no sooner do we comprehend the fact that the lower 
 animals present to us the more important phenomena of 
 Life under simpler forms and conditions, than we at once 
 recognise the study as indispensable." 
 
 It was Ehrenberg who first asserted that there was an 
 absolute boundary between animals and plants ; finding 
 even, as he fancied he did, in the smallest of the former, 
 the Infusoria, which had previously been regarded as 
 mere unorganised masses of mucus, the same systems of 
 organs as those by which the most highly-developed animal 
 is characterised, that is to say, distinct nutritive, motile, 
 vascular, sexual, and sensitive systems. Siebold called 
 the existence of these organs in question, regarding the 
 organisation of the Infusoria as a homogeneous paren- 
 chyma, in which he recognised only a nucleus, and in one 
 division a mouth and oesophagus. Nevertheless he asserted 
 that plants and animals were essentially distinct, and that 
 there was no transition from one to the other, the nature 
 of the plant being always immotile and rigid, whilst the 
 animal possessed the faculty of contracting and expanding 
 its body. This contractility is, in his opinion, alone to be 
 taken as the characteristic feature. It is not, however, the 
 animal organisation itself which is contractile, but only a 
 single tissue in it ; all the rest, skin, bones, and connective 
 tissue, are as rigid or passive as the vegetable membrane, 
 or, at most, only elastic ; in the higher animals the muscles 
 only are contractile, and in those of the lowest classes, viz. 
 the Infusoria, the entire body. 
 
 Whence Ecker assumed the existence of a special con- 
 tractile substance, which sometimes occurs in a formed 
 state, as a contractile cell or as muscular substance, some- 
 times amorphous, as in the bodies of the Infusoria, Bliizo- 
 poda, and Hydrozoa. Kdlliker confirmed this view, and 
 carried it out, particularly in the case of the Infusoria, 
 
656 THE MICROSCOPE. 
 
 which he at one time declared to be unicellular animals 
 with a contractile cell-membrane and contents. The con- 
 tractile substance is characterised by the following attri- 
 butes : it is homogeneous, or finely granular, transparent, 
 of the consistence of albumen, gelatiniform, soft, more 
 refracti re than water, but less so than oil ; insoluble in 
 water, but gradually decomposed; destroyed by caustic 
 potash ; coagulated and contracted by carbonate of potash, 
 as well as by alcohol and nitric acid ; having the power of 
 forming aqueous cavities, which originate either by the 
 separation of the water contained in it, or by its reception 
 from without ; owing to which the remainder becomes 
 denser and more granular, and lastly, it represents the 
 appearance, in water, of contractile drops, which move like 
 an Amoeba. All these properties had already been observed 
 by Dujardin, in a substance of which the Infusoria and 
 Bhizopoda are principally composed, and which he termed 
 *' sarcode ; " the aqueous spaces or hollows he named 
 " vacuoles," regarding them as .the most characteristic 
 features of the substance ; these spaces had been errone- 
 ously regarded by Ehrenberg as stomachs. All these 
 properties, however, are possessed by a substance in the 
 plant-cell, which must be regarded as the prime seat of 
 almost all vital activity, but especially of all the motile 
 phenomena in its interior the protoplasm. Not only do 
 its optical, chemical, and physical relations coincide with 
 those of the "sarcode," or contractile substance, but it 
 also possesses the faculty of forming " vacuoles " at all 
 times, and even externally to the cell ; a property, it is 
 true, which has for the most part been hitherto overlooked 
 or misinterpreted. These clear, aqueous spaces, the so- 
 termed vesicular contents, are present in all young 
 cells, and play a considerable part in cell division, and the 
 sap-currents ; they are in all respects analogous to the 
 vacuoles of the sarcode. 1 
 
 (1) Mr. Huxley has satisfied himself that in all the animal tissues the so- 
 called nucleus (endoplast) is the homologue of the primordial utricle, with 
 nucleus and contents (endoplast) of the plant, the otlu-r liistological elements 
 being invariably modifications of the periplastic substance. Upon this view we 
 find that all the discrepancies which had appeared to exist between the animal 
 and vegetable structure disappear : and it becomes easy to trace the absolute 
 identity of plan in the two, the differences between them being produced merely 
 by the nature and form of the deposits in, or modifications of, the periplastic 
 
HISTOLOGY. 657 
 
 In organised beings, the way in which nature works out 
 her most secret processes is by far too minute for observa- 
 tion by unassisted vision ; even with the aid of the improved 
 microscope, comparatively a very small portion has, up to 
 this time, been revealed to us. To point out in detail the 
 discoveries made through the employment of this instru- 
 ment, as regards physiology, would be to give a history of 
 modern biological science ; for there is no department in 
 this study which is not more or less grounded upon the 
 facts and teachings of the microscope. 
 
 To the casual observer, the brain and nerves appear tx> 
 be composed of fibres. The microscope, however, reveals 
 to us, as was first pointed out by Ehrenberg, that these 
 supposed fibres do not exist, or rather, that they all consist 
 of numerous tubes, the walls of which are distinct, and 
 contain a fluid which may be seen to flow from their broken 
 extremities on pressure. In looking at a muscle, it appears 
 to be made up of fine longitudinal fibres only. The micro- 
 scope tells us that each of these supposed fine fibres is com- 
 posed of numerous smaller ones, and that these are crossed 
 by lines which have received the name of transverse striae ; 
 that muscular contraction, the cause of motion in animals, 
 is produced by the relaxation or approximation of these 
 transverse striae. 
 
 The microscope has shown us that a distinct network of' 
 vessels lies between the arteries and veins, partaking of 
 the properties of neither, and possessed of others peculiar 
 to themselves. These have been denominated intermediary 
 vessels by Berres, and, serving to connect the arterial with 
 the venous system, are commonly known as capillaries. 
 
 On regarding with the naked eye the different glands 
 in which the secretions are formed, how complex they 
 appear, how various in conformation ! The microscope- 
 teaches us that they are all formed on one type ; that the 
 
 substance. In both plants and animals there is but one histological element 
 the endoplast which does nothing but grow and vegetatively repeat itself; 
 the other element the periplastic substance being the subject of all the che- 
 mical and morphological metamorphoses in consequence of which specific 
 tissues arise. The differences between the two kingdoms are mainly, first, 
 That in the plant the endoplast grows, and the primordial utricle attains a 
 large comparative size, while in the animal the endoplast remains small, the 
 principal bulk of its tissues being formed by the periplastic substance; and 
 secondly, In the nature of the chemical changes which take place in the peri? 
 plastic substance in each case. 
 
 U U 
 
658 THE MICROSCOPE. 
 
 ultimate element of every gland is a simple sacculated 
 membrane, to which the blood-vessels have access; and 
 that all glands are formed from a greater or less number, 
 or different arrangement only of the primary structure. 
 
 Our notions respecting the skin were vague until the 
 microscope discovered its real anatomy, and showed us 
 the existence and relations of the papillae, of the sudorific 
 organs and their ducts, the inhalent muscular apparatus, 
 and so on. All our knowledge of epidermic structures, 
 such as hair, horn, feather, &c., the real structure of 
 cartilage, bone, tooth, tendon, cellular tissue, and, in a 
 word, of all the solid textures, has been revealed to us by 
 the same agency ; so that it may be truly said, that all our 
 real knowledge of structural anatomy, and all our acquaint- 
 ance with the true composition of every organ in the body, 
 have been arrived at by means of the microscope, and 
 could never have been known without it. 
 
 In addition to this, and what is of greater importance, 
 after having studied the healthy structure of the body, 
 most beneficial aid is afforded in the investigation of 
 changes produced by disease. We may cite one notable 
 example. Dr. Andrew Clarke, after having carefully 
 studied the appearances of sputa from patients under his 
 care, says, " that the microscopical inspection of expecto- 
 ration affords, at a very early period of consumption, defi- 
 nite information, not otherwise attainable, regarding the 
 nature of the malady; and at all times must furnish 
 valuable aid in forming a prognosis regarding the cause of 
 the complaint." The expectoration generally shows pus, 
 cells, lung tissue, blood corpuscles, and granular material, 
 mixed with, at times, a small amount of fat corpuscles. 
 
 The space allotted to this division of our subject enables 
 us to give only a short and imperfect sketch of a few of 
 the fundamental tissues of the animal body. First, enu- 
 merating merely the elementary substances recognised by 
 chemistry as entering into the formative processes, we shall 
 proceed to inquire into that most interesting and wonderful 
 starting-point of life, the cell ; admitted to be, and indeed 
 demonstrable as, the common centre alike of animal and 
 vegetable organisms. 
 
HISTOLOGY. 
 
 659 
 
 THE HUMAN B)DY, ITS PHYSIOLOGICAL COMPOSITION HO) 
 CHARACTER. 
 
 The elementary substances found in the human body are 
 oxygen, hydrogen, carbon, nitrogen, phosphorus, sulphur, 
 chlorine, fluorine, iron, manganese, titanium, and calcium. 
 Silenium is found in the hair, and fluorine in combination 
 
 Fig. 300. Diagram thawing variout fonru of development in Animal Cells. 
 
 1, Shows a newly formed cell. 2, Subdivision of the nucleut. 3, The nncleut 
 changes its situation, and at 4, subdivides and disappears. 5, The walls of 
 the cell increase in thickness. 6, the cell becomes branched, or ttellate. 7, 
 Two cells are seen to coalesce. 8, They have coalesced and run into each 
 other. 9, Again they take another form and become multilocular. 10, 11, 12, 
 Cells sprouting out to form membrane and vessels. 14, Development of 
 complicated cells, which, at 13, have coalesced to form tissue. 
 
 with lime forms the enamel of the teeth, iron is the 
 chief colouring-matter of the blood, the black pigment of 
 the choroid of the eye, and the skin of the negro, 
 u u 2 
 
660 THE MICROSCOPE. 
 
 Cells. All animal and vegetable structures, tlie micro- 
 scope has revealed to us, are developed from cells or their 
 nuclei ; and the materials for building up animal structures 
 are furnished from the yolk and the blood. 
 
 The animal nucleated cell, fig. 300, is more or less of a 
 globular form ; within the delicate cell- wall a granular 
 matter is inclosed suspended in a fluid; the wall being 
 somewhat darker than the rest. There are usually one or 
 two spherical masses termed nuclei ; these enclose central 
 dots, termed the nucleoli. The size of a cell may be 
 l-300th part of an inch in diameter, some are larger, some 
 smaller ; the nucleus may be 1,3000th of an inch in dia- 
 meter ; the nucleolus 1-1 0,0 00th of an inch in diameter, 
 more or less. 
 
 Of the Cell. Dr. Beale's views of the cell are so ori- 
 ginal, and his theory of its development so carefully 
 studied and worked out, that we shall attempt, in as few 
 words as possible, to place them before our readers. The 
 cell has always been considered, and is still so, by many 
 good authorities, to consist, as just stated, of certain defi- 
 nite parts, viz. cell-wall, cell-contents, and nucleus ; to each 
 of which various different functions have been assigned. 
 Many affirm that the vital force is resident in the nucleus 
 alone, while others attribute to the cell- wall, or even to the 
 inter-cellular substance, the power of producing chemical 
 and other changes. Dr. Beale considers this view to be 
 entirely erroneous, and states that every cell or " anatomi- 
 cal elementary part" consists of matter in two different 
 states or stages of existence matter which lives (germinal 
 matter), and matter which is formed (formed material), 
 and which has ceased to manifest purely vital phenomena ; 
 all living entities, from the smallest living particle to the 
 most complex cell, consist of matter in these two states, 
 the relative proportions of which differ at different periods 
 of the life of the cell, and vary with the different con- 
 ditions under which it may be placed. If a tissue be 
 examined before development has proceeded to any great 
 extent, masses of germinal matter will be found almost 
 continuous with each other, without any appearance of the 
 cells from which all tissues are said to be originally formed. 
 
CELL FORMATION. 661 
 
 As growth proceeds, these masses become separated, and 
 the small processes or tubes which connected them are 
 drawn out, as it were, and become thinner and thinner ; 
 so that, for instance, in the formation of stellate tissue, so 
 far from the rays having been shot out by unequal growth 
 from special points of the original cell-wall, they have 
 been continuous from the very first. 
 
 Of tlie Structure and Formation of the simple Cell Muce- 
 dines. The mucedines, commonly called mildews, are 
 among the simplest living things known, and are therefore 
 well adapted for observation. If the membranous invest- 
 ment of a fully developed spore taken from one of these 
 fungi be ruptured, innumerable minute particles, some not 
 more than 1-100, 000th of an inch in diameter, are set free : 
 these constitute the living growing matter, in contradis- 
 tinction to the envelope or outer part of the cells. " Ger- 
 minal matter " may always be readily distinguished from 
 formed material by its capability of becoming dyed by an 
 alkaline solution of carmine, while the latter remains 
 perfectly colourless. Directly such a minute living par- 
 ticle comes into contact with air or water, a thin layer 
 upon its outer part becomes changed into a soft, passive, 
 transparent homogeneous substance (cell- wall), exhibiting 
 a membranous character, which protects the matter within. 
 Nutrient matter passes through this into the interior, and 
 there becomes changed into living matter ; so that growth 
 takes place, not by additions to the outside, but by the 
 introduction of new matter into the interior. If pabulum 
 be abundant, and the external conditions (temperature, 
 moisture, &c.) favourable, it readily passes through the 
 thin external membrane, and the living matter rapidly 
 increases. But if the external conditions be unfavourable, 
 less pabulum transudes, and the living matter within dies, 
 layer after layer, until the envelope becomes very much 
 thickened, with a proportionate decrease in the size of the 
 living matter. If all this living matter die, and only 
 formed material remain, no increase can take place ; but if 
 the smallest particle remain alive, any amount of living 
 matter, and afterwards of tissue or formed material, may 
 be produced. The position of the germinal matter in the 
 cell varies with the direction in which the pabulum reaches 
 
662 THE MICROSCOPE. 
 
 it \ thus in the columnar epithelial cells covering the villi 
 of the intestines, in which the pabulum flows from the 
 free surface towards the attached extremity, the germinal 
 mass is found near the centre or near the free edge of the 
 cells j but in the mucus-forming cells from the mouth and 
 fauces, in which the pabulum flows in the opposite direc- 
 tion, the germinal mass is found to be placed quite at the 
 attached end of the cells, where it has consequently easier 
 access to the pabulum, upon which its growth and secretive 
 power depends. 
 
 Cell-wall and Cell-contents. In the mucus cells above 
 mentioned, and in many other cells, two kinds of formed 
 material are produced from the original germinal matter ; 
 these are spoken of as the cell-wall, and the peculiar 
 matter found inclosed in it, the cell-contents. For instance, 
 in the starch-containing cell of the potato, the cell-wall is 
 formed around and invests the germinal matter, while the 
 starch is deposited as small insoluble particles in the very 
 substance of the germinal matter. So that by the death 
 of particles on the surface of the cell-wall the cellulose 
 cell-wall is produced, while by the death of some of the 
 particles further inwards, and therefore under different 
 conditions, starch is formed. This outer part of the ger- 
 minal matter, which eventually lies between the starch 
 grains on the inside and the cell wall on the outside, is 
 known as the "primordial utricle" of the vegetable cell. 
 Fat-cells or adipose vesicles are formed in precisely the 
 same way ; fat may, moreover, be deposited amongst the 
 germinal matter of other cells, such as the cartilage or 
 nerve cell. 
 
 Of the so-called Intercellular Substance. In cartilage, 
 tendon, and some other tissues there is no line of sepa- 
 ration between the portions of formed material which 
 belong to each respective mass of germinal matter ; and 
 hence it has been supposed that these tissues were deve- 
 loped in a different way to the epithelial structures. A 
 "cell," or elementary part of adult cartilage or tendon, 
 merely differs from the epithelial cells, spoken of above, 
 in not having a distinct margin around its own particular 
 formed material, and if a line were drawn midway between 
 the various germinal masses, it would roughly mark out 
 
CELL FORMATION. 663 
 
 the point to which the formed material corresponding to 
 each extended ; and each cell would then be exactly 
 analogous to the mucous-forming cells. In all of these cells, 
 of mucous membrane, tendon, cartilage, muscle, &c., there 
 is no abrupt demarcation between the germinal matter and 
 the formed material, but the one passes gradually into the 
 other. All living cells consist of matter in these two 
 different states ; the one being an active condition, vital ; 
 the other merely passive, in which no vital actions are 
 exhibited : upon matter in this first state, all growth, 
 multiplication, conversion, all life depends ; while in the 
 second condition, matter may exhibit many very peculiar 
 properties, but it does not grow or multiply, or convert or 
 form ; in short, it does not live, though it may increase hy 
 new matter heing superadded to it. 
 
 Of the Nucleus and Nucleolus. A mass of germinal 
 matter, besides increasing in quantity, may divide into 
 several, and thus cell-multiplication may occur ; and in all 
 cases it is to he observed that this multiplication is not 
 due to a " growing-in," or constriction of the cell-wall or 
 formed material, but entirely to changes occurring in the 
 germinal matter. In many cases a smaller spherical mass 
 may he observed in the centre of the germinal mass, 
 which often divides before the parent mass itself does; 
 but it is by no means a necessary part of the process, for 
 division as often takes place where no such bodies are to 
 be seen; and it frequently happens that these small 
 bodies may make their appearance only after the division 
 of the original mass. And again, within these, other still 
 smaller ones are sometimes produced. The former are 
 termed nuclei, tbe latter nucleoli. These are to be regarded 
 as but new living centres appearing in centres already pre- 
 existing, and may perhaps mark the commencement of a 
 set of changes ditiering in some minor particulars from 
 the first that have occurred. But although both nuclei 
 and nucleoli are germinal or living matter, they are not 
 undergoing conversion into formed material. Nuclei do 
 not always exhibit their vital powers, but under certain 
 circumstances they may do so, and then they exhibit the 
 characters of ordinary germinal matter ; they absorb pabu- 
 lum and increase in size, and the original germinal matter 
 
64 THE MICROSCOPE. 
 
 becomes changed into formed material, while fresh nuclei 
 .and nucleoli are developed. And so far from nuclei being 
 formed first, and the other elements of the cell deposited 
 around them, they always make their appearance in the 
 substance of pre-existing matter, and have neither a 
 -different constitution to ordinary germinal matter, nor 
 perform any special function. 
 
 Of the Increase of Cells. Several distinct modes of cell- 
 multiplication have been described, but in all cases the 
 germinal matter divides, and is the only material actively 
 concerned in the process ; which may, however, take place 
 in different ways. 
 
 1. The parent mass may simply divide into two equal 
 parts, apparently in obedience to a tendency of the por- 
 tions to move away from each other as soon as the original 
 mass has reached a certain size. 
 
 2. The parent mass may divide in three, four, or more 
 equal portions. 
 
 3. From every part of the parent mass protrusions may 
 occur, each of which, when detached, absorbs nutrient 
 matter, and soon attains the same size as its parent. 
 During these processes of increase and multiplication, the 
 formed material is perfectly passive, and when a septum 
 or partition exists, it does not result from a " gro wing-in" 
 of this dead structure, but is produced by the conversion 
 of part of the germinal matter into a thin layer of formed 
 material. 
 
 Of tlie Changes of the Cell in Disease. If the conditions 
 under which cells ordinarily live be modified beyond a 
 certain extent, a morbid change may result. For instance, 
 if cells, which normally grow slowly, be supplied with an 
 excess of nutrient pabulum, they grow that is, convert 
 certain of the constituents of the pabulum that come into 
 contact with them into matter like themselves at an 
 increased rate. In this way the inflammatory product 
 pus results. " The abnormal pus-corpuscle may be pro- 
 duced from the germinal or living matter of a normal 
 epithelial cell, tlie germinal matter of which has been supplied 
 with pabulum much more freely than in the normal state" 
 In cells in which the access of nutrient pabulum is more 
 restricted tlian in the abnormal state, as in normal cells 
 
CELL FORMATION. 865 
 
 passing from the embryonic to the adult state, the outer 
 part of the germinal matter undergoes conversion into 
 formed material, which increases as the supply of pabulum 
 becomes reduced. 
 
 Dr. Beale, in short, considers that "all formed matter 
 results from changes in the germinal matter, and that the 
 action of the cell really consists in a change from the living 
 to the lifeless state of the matter of which it is composed ; 
 and that the products formed by the cell do not depend 
 upon any metabolic action exerted by the cell-wall or 
 nucleus upon the pabulum, nor are they simply separated 
 from, or deposited by, the blood." And he looks upon 
 the "living cell" as a minute body, consisting partly of 
 living matter influenced by vital force, and partly of life- 
 less matter resulting from the death of the first, in which 
 chemical and physical changes occur, which may be 
 modified by the influence of surrounding substances and 
 external forces. 
 
 In pursuing the subject of cell development, we shall 
 proceed by the aid of our old lights in this intricate path 
 of physiological science. And it is only right that we 
 should add, that the views we have endeavoured to place 
 fairly before our readers have not been unhesitatingly 
 accepted, but, on the contrary, those of the German school 
 are greatly preferred by many physiologists. 
 
 Change of Cells into Tissues. This may take place by 
 a joining together or coalescence of cells in a rudimentary 
 state. Cells may meet, and at the point of contact coalesce 
 and run into each other, thus forming a tube ; indeed, 
 in this manner minute tubular structures are formed. 
 Another mode is : cells aggregate into a mass, and at the 
 point of contact run into each other, thus producing a 
 multilocular cavity ; No. 9, fig. 300. Glandular struc- 
 tures are formed in this way. Membrane is formed of a 
 deposit from the cytoblastema ; before the cell-membrane 
 is formed, the substance from the cytoblastema coalesces 
 with those particles close at hand, thus forming a delicate 
 film-like membrane. This membrane Professor T. Wharton 
 Jones calls endosmotic, retentive membrane. We have- 
 the cells coalescing to form a filament or fibre. The nucleus, 
 may disappear, or form another structure j and where 
 
666 THE MICKOSCOPF. 
 
 regeneration of tissue is proceeding, there is found a 
 larger number of granules. 
 
 According to some histologists, cells may be formed in 
 cytoblastema independent of any pre-existing cells ; this 
 is cited as an instance of that mysterious agency desig- 
 nated spontaneous generation. There are cells which, so 
 far as we know, after full development, undergo no further 
 metamorphosis ; such as those of the epithelium, the blood 
 corpuscles, &c. 
 
 As an instance where previously-existing cells exert an 
 influence on those about to be formed, we may adduce a 
 fractured bone, between the ends of which osseous matter 
 is deposited. We infer from this, that the substance of the 
 bone determines, as it were, the formation of other cells, 
 first into cartilage, and then into bone. Generally, how- 
 ever, where a part has to be repaired, it does not seem to 
 determine the generation of a texture similar to itself 
 for example, muscle and skin. We have an exception to the 
 last observation in the case of nerves, which if cut across, 
 a substance is formed between the ends which transmits 
 the nervous influence, but the ends must not be separated 
 to any great distance, or this will not occur. The 
 same remark applies to bone. There may be a single 
 layer of cells so arranged side by side, and presenting 
 a columnar or basaltic form ; this arrangement is seen 
 in the cells of the intestinal tract, fig. 303 a. Another 
 change of cell is this : they shoot out processes from 
 certain parts of them, as seen in fig. 300, Nos. 10, 11; 
 this kind of formation occurs on the inner surface of 
 the sclerotic coat of the eye. The cylindrical form of cell 
 is found with delicate processes shooting out from the 
 broad end ; these are called ciliated, fig. 303 d, and the 
 cilia having a vibratile motion urge on the secretions of 
 the part in a particular direction. 
 
 In some cases the walls of the cell increase in thickness 
 (fig. 300, No. 5). Under the microscope, some cells 
 appear to be composed of concentric laminae. In plants 
 this is the common mode of increase in the thickness of 
 the cell, but the deposit does not take place entirely 
 around, but only here and there, so that vacant spaces 
 are left which form canals, and may become branched : 
 
CELI^GROWTH. 667 
 
 these canals are named pore-canals (fig. 300, No. 6). 
 They do not perforate the outer layers ; consequently the 
 blind ends seen through the outer membrane, and which 
 were supposed to be apertures, are nothing of the kind. 
 Henle believes he has found canals in cells in animals 
 similar to those in vegetables in the cartilage of the 
 epiglottis, for instance. In other instances, cells may 
 be aggregated, like a bunch of raisins, and the parts 
 in contact with each other disappear, so constituting 
 a multilocular cavity : examples of this are seen in 
 the racemose glands (fig. 300, No. 9). Schwann 
 conjectures another mode of coalescence. From cells 
 formed as usual, processes sprout out; but this change 
 takes place at the expense of the cell-membrane itself, 
 and when it has gone on to some extent, we have 
 the appearance of a net-work formed (fig. 300, No. 
 11, and 12). Capillary vessels are formed in this way. 
 Cells, we thus perceive, coalesce to form tissues, when 
 they have not attained their full growth as such ; or when 
 they have been fully formed they become flattened, and 
 assume the solid form. Deposits of matter may take 
 place from the cytoblastema with similar adjoining sub- 
 stance, constituting a delicate membrane, with here and 
 there nuclei, as in the capsule of the lens, the membrane 
 of the aqueous humour of the eye, or sheath of the primi- 
 tive fasciculus of muscle ; or the cells may coalesce in the 
 linear series, to form fibre. 
 
 Development of Complicated Cells. Here the nucleated 
 cell is surrounded by a deposit, and that again surrounded 
 so as to constitute a membrane ; so that the nucleated cell 
 may be looked upon as the nucleus to the cell so formed 
 (fig. 300, Nos. 13 and 14). Sometimes the nucleus under- 
 goes important changes in the development of tissues, as 
 well as the cell itself. In some cases, where the cells have 
 joined in the linear series, the nucleus becomes oval, elon- 
 gated, so that the nucleus of one cell tends to meet the 
 nucleus of another cell; they subsequently coalesce, and 
 thus fibre is said to be formed. 
 
 Action of Celh. The subsequent changes of the cell 
 depend in a great degree on endosmosis, or diffusion. The 
 nature of the membrane is a necessary condition, for it 
 
668 
 
 THE MICROSCOPE. 
 
 determines the way in which the stream should pass ; and 
 we find in general that the current is from the rarer to the 
 denser fluid. If we immerse a porous tube half filled with 
 a strong solution of common salt in a jar of water, we notice 
 that the level of the fluid inside the tube rapidly rises 
 above the outside, while the water becomes slightly salt 
 to the taste. It is not a constant circumstance that the 
 stream is from the rarer to the denser fluid ; with alcohol 
 and water, for instance, the stream is from the latter to 
 the former. Mineral substances, even pipeclay and chalk, 
 permit of endosrnosis in a low degree. In glands, the cells, 
 being filled with their peculiar fluid, are conveyed to the 
 wall of the intercellular passage, and through this the 
 secretion arrives at the surface of the body. 
 
 The Epithelium. If we cut very thin slices from the 
 superficial portions of the skin, we can raise from it a 
 delicate membrane ; or, what is better, by using chemical 
 or mechanical irritation, we obtain what is ordinarily 
 called a blister ; to it we give the name of epidermis. The 
 microscope has shown this to be a tissue of high and 
 remarkable organisation ; being, in point of fact, an aggre- 
 gation of cells, differing, in different 
 situations, in regard to form, colour, 
 and composition. These laminated ele- 
 
 ; '-V ; ^ .".. mentary cells, found on the surfaces, 
 .CfinlUP have generally nuclei. The form of 
 the nucleus is rounded or oval, and is 
 the 1 -3000th to l-5000th of an inch 
 in diameter. Each nucleus has two or 
 three nucleoli, with outlines more or 
 less irregular. The epithelium cells 
 may be divided into three kinds : the 
 1st is termed the tesselated or pave- 
 ment ; 2d, the columnar or basaltic ; 
 3d, the ciliated or vibratile epithelium. 
 of the s ome ma k e a 4^ combining the tesse- 
 lated and the columnar : this may be 
 considered as transition epithelium, and is found only in 
 certain mucous passages. These various cells are repre- 
 sented in fig. 303, a, 6, c, and d. 
 
 rig. m.A 
 
EPITHELIAL CELLS. 
 
 GCtt 
 
 Tesselated epithe- 
 lium is the simplest 
 form, and, as its name 
 implies, resembles flags 
 of pavement, over- 
 lapping each other 
 at their edges. They 
 assume, more or less, 
 the polygonal form, 
 and their size varies in 
 the different mem- 
 branes. The cells of the 
 pericardium, or cover- 
 ing membrane of the Fig. 302. 
 
 heart, are much smaller 1, Simple isolated cells containing reproductive 
 , ', , granules. 2, Mucous membrane of stomach, 
 
 tnan those OI tne COVer- showing nucleated cells. 3, One of the 
 
 ing membrane of the ^^SSSSSf^SffSAASf- 
 
 lungs, &c. On some 
 surfaces we have many 
 layers in the skin, for 
 instance ; if a verti- 
 cal section of such 
 be made, and viewed 
 under the microscope, 
 it will be seen to be 
 composed of number- 
 _ess layers, shown in 
 fig. 304. The skin 
 taken from the sole 
 of the foot, in con- 
 sequence of the con- 
 tinued pressure there 
 
 (1) a is a diagram of a portion of the involuted mucous membrane, showing 
 the continuation of its elements in the follicles and villi, with a nerve entering 
 its submncous tissue. The upper surface of one \illus is seen covered with 
 cylindrical epithelium ; the other is denuded, and with the dark line of base- 
 ment membrane only running round it : b, pavement epithelium scales, sepa- 
 rated and magnified 200 diameters ; in the centre of each is a nucleus, with a 
 smaller spot in its interior, called the nvcleoli. c, pavement epithelium scales, 
 from the mucous membrane of the bronchial or air tubes of the lung ; d 
 represents another form of epithelium, termed the vibratilc or ciliated : the 
 nuclei are visible, with cilia at their upper or free surfaces, magnified 250 
 diameters. 
 
670 THE MICROSCOPE. 
 
 experienced, presents a distinctly stratified appearance. 
 These layers of cells are held together by intercellular 
 substance, which exists in quantities ; if the epithelium 
 be taken from these membranes it is more easily seen, be- 
 cause the cells are not so closely aggregated together as in 
 the skin ; therefore a piece of epithelium from the mouth 
 is recommended for display under the microscope, and by 
 the addition of a drop of the solution of iodine the cells are 
 much better seen. The cells from serous and mucous mem- 
 branes are acted upon by acetic acid, and dissolved if the 
 acid be of considerable strength : but if the acid be weaker, 
 the cells swell up. Cells are not affected by alcohol, ether, 
 ammonia, or its salts; but they are dissolved by caustic 
 potash, which also dissolves the intercellular substance. 
 
 Columnar or Cylindrical Epithelium, Fig. 303, a. The 
 nucleus is generally better seen than in the former kind of 
 cells, although formed from them. If we examine a portion 
 sideways, it resembles those at d, the upper part being 
 broader, and the nucleus being midway between the two 
 extremities. When the cells of the cylindrical epithelium 
 are closely aggregated together, they become compressed 
 into the prismatic form ; when they are less so, the rounded 
 shape prevails. Consequently, when we take a bird's-eye 
 view of them, from above or below, they appear like the 
 pavement epithelium, at c, and thus error might creep! in ; 
 but we must become fully satisfied by examining them 
 sideways, and with various reagents. Their chemical com- 
 position is the same, and the cells dissolve in strong acetic 
 acid. As examples of the situations in which this form of 
 epithelium is found, we may instance the intestinal tract 
 along the ducts of the glands, as the liver, &c. 
 
 In no situations do we find these two kinds of epithe- 
 lium terminating abruptly the one in the other ; but there 
 is a gradual change of the one kind into that of the 
 adjoining; for example, where the tesselated epithelium 
 is gradually supplanted by the cylindrical, as it passes from 
 jhe oesophagus to line the interior of the stomach ; it is 
 then termed transition epithelium. 
 
 Ciliated Kpithelium^ig. 303, d. The cells do not differ 
 materially from those of the cylindrical ; the great distinc- 
 tion between he two is, that in the former there are no 
 
CILIATED EPITHELIUM. 671 
 
 cilia attached to the broad end. Examples of the situations 
 in which these are found are, investing membrane of the 
 respiratory passages, upper part of the pharynx, larynx, 
 bronchi, and the lateral ventricles of the brain, &c. 
 
 Epithelium is found to grow from the surface of the 
 cutis outwards in most places it is constantly growing 
 outwards, and as continually being thrown off from the 
 surface : it must at the same time be remembered, that 
 though the epithelium is in close contact with the cutis, 
 or true skin, it is not a deposit from it, but derives only 
 its materials of formation and nourishment from it 
 
 The epidermis is destitute of sensibility, yet it invests 
 very sensitive parts : it is not vascular, but invests very 
 vascular parts. Its exfoliation takes place regularly, as 
 may be exampled in reptiles and the Batrachia, who throw 
 off their skin : the moulting of birds is analogous. In the 
 early periods of life in the human subject, exfoliation takes 
 place from the surface of the skin ; from the mouth the 
 morsel of food is always mixed with detached cells. In 
 the process of digestion the same thing occurs in fact, it 
 is only when the epithelium cells are thrown off that the 
 gastric juice is secreted by the tubes of the stomach. 
 
 Cilia. The most remarkable circumstance in connexion 
 with cells is the movement of their cilia. There are three 
 ways in which the cilia ordinarily move the rotatory, the 
 ondulatory, and the wavy, like a field of wheat set in 
 motion by a steady breeze. No satisfactory explanation 
 has been given of the cause of this vibratile motion. The 
 current produced by them is from within outwards, in most 
 places ; in the respiratory passages, on the contrary, it is 
 from without inwards. In the Frog's mouth, it takes the 
 same course. The ciliary motion may be seen in the kidney 
 of the Frog or Newt ; the cilia in the latter continue in 
 active motion for some minutes after the animal is dead. 
 Make a very thin section of the kidney with a sharp knife, 
 and take care to disturb the structure as little as possible ; 
 then moisten it with a little of the serum of the animal, 
 place it in a glass cell, and cover with thin glass and a 
 magnifying power of 250 diameters. 
 
 Pigment. Pigment granules are found in greater or 
 less quantities in the skin and bodies of white and dark 
 
672 
 
 THE MICROSCOPE. 
 
 Fig. 304. Pigment cells 
 from the eye. 
 
 races. In the eye there is pigment, and it affords a good 
 example of nucleated cells, in which are contained the 
 pigment particles, fig. 304. These are placed there for an 
 optical purpose, that of absorbing 
 the rays of light. In the peculiar 
 colouration found in the eyes of some 
 animals, called Tapetum lucidum, the 
 colour is not owing to the pigment 
 particles, but to the interference of 
 the light : it is reflected from it, as- 
 in mother-of-pearl, coloured feathers, 
 scales of fishes, &c. The colour of 
 the skin is owing to the granular 
 contents of the pigment cells ; these 
 are like ordinary elementary gra- 
 nules, with the addition of colour ; 
 and this latter may be removed by 
 the action of chlorine. 
 
 The Nails are appendages to the 
 epidermis, and present a mould of 
 the cutis beneath; from the cutis 
 the materials are furnished for the 
 formation and growth of the nail. 
 Like the epidermis, the nail is- 
 stratified, the markings are parallel 
 to the surface, and the appearance 
 is produced by the coalescence of the 
 cells and their lying over each other. 
 See Plate VII., No. 149, toe of mouse. 
 The stratified arrangement when a 
 section is examined by polarised 
 light, presents the appearance seen 
 in the processes of the cat's tongue, 
 Plate VIII. No. 174. 
 
 Hairs. The form and structure 
 of hairs differ much ; some are cy- 
 lindrical, others flattened. A hair 
 is divided into a body or shaft, and 
 a root which is in the skin (fig. 
 305.) The shaft is again divided 
 into two parts : the external is 
 termed the cortical portion, and the internal the medul- 
 
 Fig. 305. A single Hair, 
 seen near its bulb. 
 
HAIRS, SECTIONS OF. 
 
 673 
 
 lary portion ; the latter does not usually exist in the whole 
 length of the shaft. The cortical part consists of fibres, 
 
 Fig. 306. 
 
 1, Transverse section of human hair, showing the cylinder of medullary sub- 
 stance. 2 Longitudinal section, showing the fibrous character of the same 
 pigment or colouring matter, and serrated edges. 
 
 arranged parallel to each other: besides these there are, 
 on the exterior, minute epithelial scales, which are ar- 
 ranged like the tiles on a house, producing the appearance 
 of transverse markings. The fibres gradually expand out, 
 
 ..-. 
 
 Hair from the Indian Bat, magnified 500 diameters. 2, Hair sr.ppoMd to 
 belong to (Deivustes?) Anthrenus, magnified 250 diameters. 3, Hair from th 
 Mouse, raagniticu 250 diameters. 
 
674 THE MICROSCOPE. 
 
 * 
 
 forming a wall to the bulb enclosed in its capsule. The 
 development of a hair commences at the bottom of the 
 follicle, and by the aggregation of successive cytoblasts, 
 or new cells, are gradually protruded from the follicle, both 
 by the elongation of its constituent cells, and by the addition 
 of new layers of these to its base ; the apex and shaft of 
 hair being formed before the bulb, just as the crown of a 
 tooth is before its fang. The cytoblasts are round and 
 loose at the base of the hair, but are more compressed and 
 elongated in the shaft; and by this rectilinear arrange- 
 ment the hair assumes a fibrous appearance. Of sixteen 
 species of the Bat tribe, the hairs of which were examined 
 by the late Professor Quekett, all were analogous in struc- 
 ture ; and the diversity of surfaces which these hairs pre- 
 sent are in reality owing to the development of scales 
 on their exterior. By submitting hairs to a scraping pro- 
 cess, these minute scale- like bodies, tolerably constant as 
 regards their size and figure, can be procured; so that 
 Bats' hair may be said to consist of a shaft invested with 
 scales, which are developed to a greater or less degree, and 
 varying in their mode of arrangement in the different 
 species of the animal ; that part of the hair nearest the 
 bulb is nearly free from scales, but as we proceed toward 
 the apex the scaly character becomes evident. Many of 
 the scales are not unlike those procured from the wings 
 of butterflies, but, being very much smaller, exhibit no 
 trace of striae on their surfaces ; those taken from dark- 
 coloured hairs have colouring- matter deposited on them in 
 small patches. In some cases they appear to terminate in 
 a pointed process ; in others the free margin is serrated. By 
 
 scraping, many of them will 
 be detached separately ; but in 
 some few cases, as many as 
 four or five will be found joined 
 together : in the larger hairs, 
 the cellular structure of the 
 interior, as well as the fibrous 
 Fig. 303. Transversesectionof Hair character of the shaft, are 
 of Pccari, showing its fibrous better seen after the scales 
 
 have been removed. 
 The hair owes the greater part of its colour to pigment- 
 
SKIN, GLANDS OP. 
 
 675 
 
 Fig. 309. Pigment Cells from 
 the skin. 
 
 cells: as these decay, and become gradually divested of 
 their colouring-matter, they appear whitened, or " turn 
 grey." These hexagonal cells also give colour to the skin 
 of the negro, and are situated immediately beneath the 
 transparent coat. A small por- 
 tion is shown in fig. 309, the 
 vacant space denoting the situa- 
 tion of a lost hair. 
 
 Certain parts of the skin and 
 mucous membranes are espe- 
 cially supplied with papillae, 
 which serve as organs of touch ; 
 throughout the greater part of 
 the skin there are papillae more 
 or less sensitive, but only at 
 the extremities of the fingers, 
 lips, and in a few other situa- 
 tions, are these highly dev 
 loped, as in fig. 310. Papillae 
 are either filiform or tubiform, 
 and have entering into them nerves and blood-vessels ; 
 the former supplying the sensibility of the skin, and termi- 
 nating in loops, as shown in fig. 310. Papillae injected are 
 shown in Plate VII. No. 150, tongue of mouse ; villi from 
 small intestine of rat, No. 154. 
 
 The skin is the seat of two 
 processes in particular ; one of 
 which is destined to free the 
 blood from a large quantity 
 of fluid, and the other to 
 draw off a considerable 
 amount of solid matter. 
 To effect these processes we 
 meet with two distinct classes 
 of glar.dulse in its substance : 
 the sudoriferous, or sweat 
 glands ; and the sebaceous, 
 or oil glands. They are both 
 formed, however, upon the Fame simple plan, and can 
 frequently be distinguished only by the nature of their 
 iecreted product. The oil-glands of the skin an 
 x x 2 
 
 Fig. 310. A section of skin from tlit 
 finger, showing the vascular net- 
 work of papUlce, at the surface of 
 the cutis. 
 
676 
 
 THE MICROSCOPE. 
 
 similar in structure to the perspiratory ducts, being com- 
 posed of thrpo layers derived respectively from the scarf- 
 skin, which lines their interior ; 
 ^he sensitive skin, which is the 
 medium of distribution for the 
 vessels and nerves ; and the 
 'orium, with its fibres, giving 
 'hem strength and support. 
 Like the sudoriferous ducts, they 
 are in some situations spiral ; 
 
 Fig.311. Capillary network and dis-\)\}t this is not a constant fea- 
 
 tribution of papillae over the tongue. , _p ,-\ ,1 
 
 ture ; more irequently they pass 
 
 directly to their destination ; they are also larger, as 
 shown in fig. 312, proceeding from the oil or fat vesicle 
 
 situated at its 
 lower extremity. 
 Oil - glands are 
 freely distributed 
 to some parts, 
 whilst in others 
 they are entirely 
 absent : in a few 
 situations they are 
 worthy of parti- 
 cular notice, as in 
 the eyelids, where 
 they possess great elegance of distribution and form, and 
 open by minute pores along the edges of the lids ; in the 
 ear-passages, where they produce that amber-coloured 
 substance known as the wax of the ears ; and in the scalp, 
 where they resemble small clusters of grapes, and open in 
 pairs into the sheath of the hair, supplying it with a 
 pomade of Nature's own preparing. 
 
 Internal parts of the body. We shall now have under 
 consideration cells of a much higher order than any before 
 referred to ; the cell found floating in the animal fluids is 
 known as the blood-cell, and requires a vascular system of 
 its own for distribution over the whole animal body. 
 The red blood cells, or corpuscles, have a circular form, 
 somewhat flattened ; their size is about l-3,200th of an 
 inch in diameter. It is well known that the blood-cor- 
 
 Fig. 312. Distribution of the tactile nerves at the 
 extremity of the fingers, as seen in a thin perpen- 
 dicular section of the skin. 
 
SECTION OF SKIN. 
 
 677 
 
 puscles, when floating in their own serum, or after having 
 been treated with acetic acid or water, appear to he fur- 
 nished with perfectly plain coverings, composed of a simple, 
 homogeneous membrane, without distinction of parts. But, 
 when the blood is treated with a solution of magenta (nitrate 
 of rosanilin) or with a dilute solution of tannin, the cor- 
 puscles present changes which seem irreconcileable with 
 such a proposition. Dr. W. Roberts, of Manchester, com- 
 municated an account of his observations on this subject to 
 
 Fig. 313. A vertical section of the Human Skin, showing the sweat-glands, sur- 
 rounded by fat-globules, the ducts passing upwards through the epithelial 
 layer to the epidermis or external cuticle, magnified 250 diameters. 
 
 the Royal Society (Proc. Roy. Soc. voL xiL p. 481), in 
 which he shows that nearly every disc possessed a parietal 
 macula, capable of being stained by a dye. It was com- 
 monly of a lenticular shape, but sometimes square, and as 
 a rule very minute, not covering more than l-20th or l-30th 
 of the circumference. Moreover, in the blood of many of 
 
678 THE MICROSCOPE. 
 
 the lower animals a similar tinted particle appeared when 
 the corpuscles were treated with magenta. The conclusion 
 to be drawn from this and other observations noted by 
 Dr. Roberts, is that a duplication at one. or at most at 
 two points only, is indicated by direct proof ; but certain 
 appearances occasionally observed ivour the notion of a 
 complete duplication. 
 
 The wall of the cell is a transparent structureless mem- 
 brane, and is of greater thickness than we find the analogous 
 membrane of cells to be generally. The red corpuscles of 
 birds, reptiles, &c. possess a distinct nucleus ; but, on 
 examining those of the human subject and other Mam- 
 malia, no distinct nucleus can be made out. By applying 
 dilute acetic acid, the red corpuscle becomes bleached, and 
 its walls distended, but no nucleus appears. If a red cor- 
 puscle from the Frog be treated in the same manner, we 
 see a nucleus, and the red colouring matter is drawn out 
 by exosmosis. Water causes the corpuscle to swell up, 
 and the colouring- matter disappears, but its real nature is 
 masked ; upon employing a drop of solution of iodine, the 
 wall is coloured or tinged, and made distinct. The cells 
 themselves have a tendency to undergo spontaneously 
 certain changes, one of the most common is a wrinkling up 
 of the walls, with a surface somewhat like that of a mul- 
 berry ; this may also be produced by mechanical pressure, 
 the addition of oil, &c. 
 
 There is another set of corpuscles, slightly larger than 
 the red set ; these are termed colourless corpuscles, which, 
 when distended by the action o, f water, are seen as nucleated 
 cells, whose diameter is about the 1-2, 500th of an inch, 
 and a double contour of the walls is observed ; sometimes 
 there is a slight tinge of colour to be seen in the nucleus. 
 There is a third kind of corpuscles in the blood, more 
 numerous than those above referred to, but of about the 
 same diameter ; when distended, they are seen to be cells 
 filled with granular matter ; sometimes a clear spot is 
 noticed on one side ; very dilute acetic acid being applied, 
 the granules are dissolved out, and a clear central nucleus 
 remains, if the acid be used stronger, an appearance is 
 seen as if there were several nuclei aggregated together. 
 This latter appearance was considered to be the natural 
 
BLOOD CELLS. 
 
 679 
 
 state of the nucleus, the particles of which were either 
 tending to unite with one another, or there was a sepa- 
 ration of the nucleus into several smaller portions. 
 Wharton Jones, however, says there is no subdivision of 
 the nucleus. 
 
 If we examine a drop of blood under the microscope , 
 
 . Fig. 314. 
 
 1, A portion of the web of a Frog's foot, spread out and slightly magnified to 
 show the distribution of the blood-vessels. 2, A portion magnified 250 dia- 
 meters, showing the ovoid form of the blood-discs in the vessel, beueath 
 which a layer of hexagonal nucleated epithelium-cells appear. 3, Human 
 blood discs, as they appear when fresh drawn (magnified 250 dijuneters). 
 
 the corpuscles aggregate themselves together like rolls of 
 coins, fig. 314, No. 3, presenting a kind of network so 
 long as they remain suspended in their liquor sanguinit. 
 After the lapse of a few minutes, the fibrin, from its elasti- 
 city, contracts more and more, and a yellow fluid, called 
 serum, is pressed out, or, in other words, the components 
 of the liquor sanguinis, with exception of the fibrin, and 
 only a shrunken, jelly-like mass remains. 
 
 The blood-corpuscles of the lower animals Mr. Gulliver 
 has especially studied. In the blood-corpuscles of birds, 
 
680 THE MICROSCOPE. 
 
 and animals below them, there are nuclei ; but the cells, 
 instead of being circular, as in the human subject, are 
 elliptical, and larger. The corpuscles in Mammalia in 
 general are like those of man in form and size, being a 
 little larger or smaller. The most marked exception is in 
 the blood of the Musk-deer, in which the corpuscles are 
 of extreme smallness, about the 1-12, 000th of an inch in 
 diameter. The Elephant has the largest, which are about 
 1- 2,000th of an inch in diameter. The Goat, of all common 
 animals, has very small corpuscles ; but they are, withal, 
 twice as large as those of the Musk-deer. Another excep- 
 tion in regard to form is in the Camel tribe, where they 
 are oval, and resemble those of the oviparous Vertebrata, 
 as the Frog, shown in fig. 314, No. 2. In the Meno- 
 branchus lateralis, they are of a much larger size than in 
 any animal, being the 1-3 50th of an inch ; in the Proteus, 
 the l-400th of an inch in the longest diameter ; in the 
 Salamander, or Water-newt, l-600th; in the Frog, l-900th; 
 Lizards, l-l,400th ; in Birds, l-l,700th ; and in Man, the 
 1-3, 200th of an inch. Of Fishes, the cartilaginous have 
 the largest corpuscles ; in the Gold-fish, they are about the 
 1-1, 700th of an inch in their longest diameter. 
 
 The large size of the blood-discs in reptiles, especially" in 
 the Batrachia, has been of great service to the physiologist, 
 by enabling him to ascertain many particulars regarding 
 their structure which could not have been otherwise deter- 
 mined with certainty. The value of the spectroscope in 
 the chemical examination of the blood has been already 
 pointed out in our remarks on the application of this 
 instrument to the microscope. See page 119. 
 
 An interestingsubject to Physiologists has been noticed 
 the production from the blood, under certain conditions, 
 of red albuminous crystals, which, although formed from 
 animal matter, and sometimes, in all probability, during 
 life, have the same regular forms as inorganic crystals. 
 Virchow was the first who paid particular attention to 
 their actual nature, and proved them to differ from saline 
 or earthy crystals. If we add water to a drop of blood 
 spread out under the object-glass of the microscope, as the 
 drop is beginning to dry up, the edges of the heaps of blood- 
 corpuscles are seen to undergo a sudden change : a few 
 
BLOOD-CRYSTALS. 681 
 
 corpuscles disappear, others have dark thick edges, become 
 angular and elongated, and are extended into small well- 
 defined rodlets. In this manner an enormous quantity of 
 crystals are formed, which are too small to enable us to 
 determine their shape ; they rapidly move lengthways, the 
 entire field of vision being gradually covered by a dense 
 network of acicular crystal^, crossing one another in every 
 direction, with other crystals presenting a rhomboid form. 
 
 Dr. Garrod discovered, that by a slow evaporation of 
 portions of the serum of blood taken from patients labour- 
 ing under gout, he could obtain strings of crystals of uric 
 add. His mode of procedure is to pour a little serum 
 into a watch glass, and add a few drops of acetic acid ; 
 in this mixture place a few very fine filaments of silk or 
 tow, and stand it by for twenty-four hours under a glass- 
 shade. Upon removing the glass and submitting the 
 filaments to microscopical examination, they are found 
 studded with minute crystals. 
 
 A peculiar fatty matter was discovered by Virchow in the 
 tissues of the human body and in certain nerves which he 
 termed My din. In the liver it exists in large quantities, 
 and much is found in the yolk of the egg. It is colour- 
 less, glistening, semi-fluid, prone to form drops, and capable 
 of being drawn out into long threads, which curve and 
 twist into very peculiar forms. The masses often exhibit 
 double contours, or many lines are observed equi-dislant 
 from one another and vary- 
 ing in thickness. Choles- 
 terin is a component of all 
 forms of nyelin ; Beneke 
 has, in fact, shown that it 
 is a mechanical mixture of 
 diolesterin and etiolate of 
 lipyl. No. 1, fig. 314, 
 
 the foot Of the Frog, when ^ zib.-nend of Long-tared 
 
 stretched out, shows the (Piecotus Auritu*.) 
 
 distribution of the blood-vessels in the web : the two 
 sets of vessels the arteries and veins are very readily 
 made out when kept steadily on the stage of the micro- 
 scope ; the rhythm and valvular action of the latter may 
 be observed, although they are much better seen in the ear 
 
682 
 
 THE MICROSCOPE. 
 
 or wing of the Long-eared Bat, as Professor Wharton Jones 
 pointed out. 
 
 To view the circulation of blood in the Frog's foot, the 
 older micros sopists, Baker, Adams, and others, were in the 
 habit of tying the frog to a frame of brass ; at the present 
 time the entire body of the animal, with the exception 
 of the foot about to be examined, is secured in a black 
 silk bag, and this is fastened to a plate, termed the frog- 
 plate, shown at a a a in fig. 316. The bag provided should 
 
 Fig. 316. 
 
 be from three to four inches in length, and two and a half 
 inches broad, shown at b b, having a piece of tape, c c, 
 sewn to each side, about midway between the mouth and 
 the bottom ; and the mouth itself capable of being closed 
 by a drawing-in string, d d. Into this bag the frog is 
 placed, and only the leg which is about to be examined 
 kept outside ; the string d d must then be drawn suf- 
 ficiently tight around the small part of the lag to prevent 
 the foot from being pulled into the bag, but not to stop 
 the circulation ; three short pieces of thread, ///, are now 
 passed around the three principal toes; and the bag with 
 the frog must be fastened to the plate a a by means of the 
 tapes c c. When this is accomplished, the threads /// 
 are passed either through some of the holes in the edge 
 of the plate, three of which are shown at g g g, in order 
 to keep the web open ; or, what answers better, in a series 
 
TADPOLE, CIRCULATION IN. 683 
 
 of pegs of the shape represented by h, each having a slit 
 extending more than half-way down it ; the threads are 
 wound round these two or three times, and then the end 
 is secured by putting it into the slit i. The plate is now 
 ready to be adapted to the stage of the microscope : the 
 square hole upon which the foot must be placed is brought 
 over the aperture in the stage through which the light 
 passes to the object-glass, so that the web may be strongly 
 illuminated by the mirror. 
 
 The circulation of the Tadpole is best seen by placing 
 the creature on its back, when we immediately observe 
 the beating heart, a bulbous-looking cavity, formed of the 
 most delicate, transparent tissues, through which are seen 
 the globules of the blood, perpetually, but alternately, en- 
 tering by one orifice and leaving it by another. The heart 
 is enclosed within an envelope or pericardium ; and this 
 is, perhaps, the most delicate and certainly the most 
 elegant thing in the creature's organism. Its extreme 
 fineness makes it often elude the eye under the single 
 microscope, but under the binocular its form is distinctly 
 revealed. Passing along the course of the great blood- 
 vessels to the right and left of the heart, the eye is 
 arrested by a large oval body, of a more complicated 
 structure. This is the inner gill, which, in the tadpole, is 
 formed of delicate, transparent tissue, traversed by arteries, 
 and presenting a crimson network of blood-vessels. 
 
 The Tadpole is hatched with respiratory and circulatory 
 organs resembling those of the fish. It lives in, and 
 breathes oxygen from the air contained in, the water, 
 and during the early period of its existence respires ex 
 clusively by gills. 
 
 It will be remembered that in nearly all fish the heart 
 has but two cavities, an auricle and ventricle ; that the 
 blood of the latter is returned by the veins to the auricle, 
 passes into the ventricle, is then transmitted to the gills, 
 where, being exposed to the air contained in the water, it 
 becomes deprived of carbonic acid, aerated, and rendered 
 fit for recirculation through the system. In the reptile we 
 find a modification of plan. The heart has three cavities, 
 two auricles and one ventricle ; by this contrivance there 
 is a perpetual mixture in the heart of the impure car- 
 
684 THE MICROSCOPE. 
 
 bonized blood which has already circulated through the 
 body, and flows into the ventricle from the right auricle, 
 with the pure aerated blood returned from the lungs, and 
 which also flows at the same instant into the ventricle 
 from the left auricle. Thus the habitual circulation of 
 this " cold-blooded " mixture is the cause of the low tone 
 of vitality that distinguishes reptiles. 
 
 For the purpose of observation the tadpole must, of 
 course, be selected during the period in which the skin 
 is perfectly transparent. The first examinations reveal 
 plainly enough the appearances already described of the 
 form and situation of the heart, and the three great arte- 
 rial trunks proceeding (right and left) from it. Many ob- 
 servations are required to arrive at the true anatomical 
 arrange merit of these vessels. First, they are closely 
 connected with the corresponding gill. The upper one 
 (the cephalic) runs along the upper edge of the gill,, and 
 gives off, in its course, a branch which ascends to the 
 mouth, which, with its accompanying vein, is termed the 
 labial artery and vein. The cephalic artery continues its 
 course around the gill, until it suddenly curves upwards 
 and backwards, and reaches the upper surface of the head, 
 where it dips between the eye and the brain, towards 
 which it is evidently travelling. 
 
 It would be a mistake to suppose that you can make 
 this out distinctly, in the average of tadpoles taken, 
 without some preparation. The great obstacle is the large 
 coil of intestines, usually distended with dark-coloured 
 food. This must be got rid of by making your tadpoles 
 live on plain water for some days. Plate VII. No. 15li, 
 exhibits the view of the vessels obtained under the in- 
 fluence of low diet, and we are now enabled to trace the 
 course of the three large arteries. The third trunk, 
 traversing the lung, is seen to emerge from the lower 
 edge and descend into the abdomen to form the great 
 abdominal aorta. A small black-looking starved little 
 tadpole shows the heart beating and the blood circulating, 
 but the latter is quite colourless, not a single red globule 
 visible anywhere. The globules chase one another away 
 like globules ot water, the heart is a colourless globe, the 
 gills two transparent ovals, and the bowels a colourless, 
 
TADPOLE, CIRCULATION IX, 685 
 
 transparent coiL Through the empty coil the artery is seen 
 on each side descending from the gills, converging to the 
 spine, meeting its fellow, and with it uniting to form the 
 abdominal aorta, the large central vessel coloured red in 
 the figure. After the aorta has supplied the abdominal 
 viscera, a prolongation, or caudal artery is seen descend- 
 ing to the tail, the all-important organ of locomotion in 
 the tadpole. This artery, entering the root of the tail, is 
 imbedded deeply in the flesh, whence it emerges, and then 
 continues its course, closely accompanied by the vein, to 
 within a short distance of the tail's extremity, where, 
 being reduced to a state of extreme fineness, it terminates 
 in a capillary loop, which is composed of the end of the 
 artery and the beginning of the vein. The artery, in its 
 course, gives off branches continually to supply the neigh- 
 bouring tissue. We may often observe that the blood 
 current in the tail, even in the main artery or vein, is 
 sluggish or even still. This occurs independently of 
 the heart, which may continue to beat as usual ; it 
 happens, because the circulation in the tail depends very 
 much on the motion of the organ. When this is sus- 
 pended (as in confining the tadpole under the microscope), 
 the blood moves sluggishly, or stops, till the tail regains 
 its freedom and motion, when the activity of the current 
 is restored. This fact is thus alluded to by Dr. 
 Grant : " It is the restless activity of the worm and of 
 the insect that makes every fibre of their body, as it were, 
 a heart to propel their blood and circulate their fluids, 
 while the slow-creeping snail that feeds upon the turf has 
 a heart as complicated as that of the red-blooded, verte- 
 brated fish, that bounds with such velocity through the 
 deep. It is because the fish is muscular and active in 
 every point that it requires no more heart than a snail to 
 keep up the necessary movements of its blood." 
 
 Having traced the arterial system, which conveys the 
 blood from the heart to the extremities, we will now note 
 its return by the veins back again to the heart. 
 
 The caudal vein runs near to the artery during the greater 
 part of its course, with its stream, of course, towards the 
 heart. This stream is sxvollen by perpetual tributaries from 
 vessels so numerous that their loops form a network which 
 
686 THE MICROSCOPE. 
 
 covers the entire surface of the tail. As the vein approaches 
 the root of the tail it lies superficially to the artery, and 
 diverges from it at the point of entering the abdomen. 
 Here it approaches the kidneys, sends off branches to 
 them, while the main trunk continues its course on- 
 ward ; and, passing upwards behind a coil of intestine, it 
 approaches the liver, and runs in a curved course along the 
 margin of that organ. This blood is seen to enter the 
 vena cava by numerous fine channels, which converge 
 towards the great vein as it passes in close proximity to 
 the organ. Beyond the liver the vena cava continues its 
 course upwards and inwards to its termination in the sinus 
 venosus or rudimentary auricle of the heart. This ter- 
 mination is the junction of not less than six distinct venous 
 trunks, incessantly pouring their blood into the heart. 
 The circulation in the fringed lips forms a most compli- 
 cated network of vessels, out of which proceeds a vein 
 corresponding to the artery already traced. This descends 
 in a direct course till it joins the principal vein of the 
 head, which corresponds to our own jugular. 
 
 Thus we have traced the blood through its main chan- 
 nels, and completed the circle of its course. 
 
 The blood is driven by the heart into each inner gill 
 through three large blood-vessels, which arise directly from 
 the truncus arteriosus, and may be called the afferent vessels 
 of the gill (See enlarged view of gill, Plate VII. No. 156). 
 
 It will be seen that " each internal gill or entire 
 branchial organ consists of cartilaginous arches (Xo. 156), 
 with a piece of additional framework of a solidly tri- 
 angular form, stretching beyond the arches, and composed 
 of semi-transparent, gelatinous-looking material. These 
 parts, forming the framework of the organ, support upon 
 their upper surface the three rows of crests with their 
 vascular network, and the main arterial and venous trunks 
 which lie parallel with and between them. The three 
 systemic arteries arising, right and left, from the truncus 
 arteriosus, enter each gill on its cardiac side, and then 
 follow the course of the crests, lying in close proximity to 
 them. The upper of these branchial arteries runs alone 
 on the outside of the upper crest, and another branch 
 leaving the trunk and passing into the network of the 
 
TADPOLE, CIRCULATION IN. 687 
 
 crest, whence a returning vessel may be traced carrying 
 back the blood across the branchial artery, and to a vessel 
 lying close to and taking the same course as the artery 
 itself. Carrying the eye along the latter vessel we find, 
 at a short distance from the first of these crest branches, a 
 second, which leaves the main trunk and enters the crest, 
 when a corresponding returning vessel conveys the blood 
 across the arterial trunk into the vessel lying beside it, as 
 in the former instance. A succession of these branches 
 (each taking a similar course) may be traced from one end 
 of the crest to the other. But it is now to be observed 
 that the trunk from which these arterial branches spring 
 diminishes in size as it proceeds in its course (like the gill 
 artery in fishes), while the vessel running parallel to it and 
 receiving the stream as it returns from the crest enlarges in 
 the same degree. Thus, the artery or afferent vessel which 
 brings the blood to the gill is large at its entrance, but 
 gradually diminishes and dwindles to a point at the op- 
 posite end of the crest ; while the venous or efferent vessel, 
 beginning as a mere radical, gradually enlarges, and thus 
 becomes the trunk that conveys the blood out of the gill 
 to its ultimate destination. Calling this vessel the upper 
 branchial vein as long as it remains in contact with the 
 gill, we subsequently change its name when it leaves the 
 gill and winds upwards for distribution to the head, and 
 then designate it the cephalic artery. The middle branchial 
 artery and vein proceed in like manner in connexion with 
 the middle crest, and the lower artery and vein in connexion 
 with the lower crest. The middle and lower venous trunks, 
 having reached the extremity of the crests, curve down- 
 wards and inwards, and then leave the gill. The former 
 trunk, converging towards the spine, meets its fellow, and 
 with it forms the ventral aorta. The latter gives origin to 
 the pulmonary artery, and supplies also the integuments 
 of the neck. Curious and beautiful is the final stage of 
 the metamorphosis, when the waning tadpole and incipient 
 frog coexist, and are actually seen together in the same 
 subject. The dwindling gills and the shrinking tail the 
 last remnants of the tadpole form are yet seen, in com- 
 pany with the coloured, spotted skin, the newly-formed 
 and slender legs, the flat head, the wide and toothless 
 
688 THE MICROSCOPE. 
 
 mouth, and the crouching attitude of the all but perfect 
 reptile. 
 
 " By the process now described, the three systemic 
 arteries become continuous with the corresponding efferent 
 trunks that convey the blood for distribution through the 
 body, while, simultaneously, the vital fluid is being 
 abstracted from the special trunks belonging to the gill 
 and its vascular crests. These, with the gill structure 
 connected with and dependent upon them, being thus 
 deprived of their blood, shrink, become absorbed, and 
 disappear. Such appears to be the beautifully simple 
 mechanism by which the transition in the type of the 
 respiratory function from fish to reptile is accomplished. 
 If we take a tadpole a few days old, when the outer gills 
 are fully developed, and immerse it for another few days 
 in a weak solution of chromic acid (Mr. Archer's method), 
 we may, by placing the tadpole under a dissecting micro- 
 scope, and with the aid of a needle and camel-hair brush, 
 then remove the integuments, disclose the tufts of the 
 inner gills, and by carefully getting rid of a prominent roll 
 of intestine that occupies the upper part of the abdomen, 
 succeed in revealing the incipient lungs. These are situated 
 behind the gut and close to the spine, and appear as a pair 
 of minute tubular sacs, united at their upper and open 
 extremities. The chromic acid renders the tissues friable, 
 so that they can be readily peeled away." 
 
 That we may see how the circulation is carried on during 
 life in the gills, the outer covering must be carefully raised, 
 or even stripped off. This can be accomplished by put- 
 ting the Tadpole under the influence of chloroform a 
 drop of the fluid is sufficient for the purpose. 1 
 
 The blood-vessels of mammals are divided with refer- 
 ence to their structure into arteries, capillaries, and veins ; 
 yet these three divisions are by no means broadly separated 
 from each other, inasmuch as the capillaries are continued 
 into the veins just as imperceptibly as they arise from the 
 arteries. But with reference to their structure, while the 
 capillaries possess only a single coat without any special 
 structure, the larger vessels present, with but few excep- 
 
 (1) We refer the reader to Mr. W. U. Whitney's highly interesting and valuahl* 
 paper in the Trans. Micros. 6'oc. for 1861 and 1867. 
 
CAPILLARY CIRCULATION. 689 
 
 tions, three layers, which are designated as the inner coat, 
 or tunica in tima ; the middle coat or circular fibrous coat, 
 tunica media; and an outer coat, tunica externa or nd- 
 venttiia. The first is the thinnest coat, and consists of a 
 cellular layer, the epithelium ; generally, also of an elastic 
 coat, with the fibres disposed in a longitudinal direction. 
 The second, middle coat, is a thicker layer, and the principal 
 seat of the muscular fibres of the vessels ; .in the veins, 
 however, it contains numerous longitudinal fibres, and in 
 the largest vessels more or less elastic elements and con- 
 nective tissue. The third coat has its fibres again arranged 
 for the most part longitudinally, and it is as thick as, or even 
 thicker than, the middle coat, and consists of connective 
 and elastic tissues. This coat, the tunica adventitia of 
 large arteries, contains muscular fibres in animals, but none 
 iu man. According to J. Lister (Quart. Joum. Micros. 
 Men. 1857, p. 8), the smallest arteries of the frog's web 
 show contractile fibre-cells, which measure from the 1-1 00th 
 to l-200thof an inch, and run in a spiral direction, making 
 one and a half up to two and a half turns round the inner 
 coat of the vessel, and such fibre-cells in a single layer 
 constitute the only muscular elements of the vessel. 
 
 The blood-vessels of the eye are extremely numerous, 
 and present different conditions in the several parts. In 
 the choroid coat, they are arranged in a most beautiful 
 stellate manner, and the capillary network of the inner- 
 most layer of the choroid coat, when injected, forms an 
 attractive object. A vertical section of the eye of a cat, 
 showing its several vascular and nervous coats, is given in 
 Plate VII. No. 157. 
 
 The circulation in the foot of the Frog and the tail 
 of the Newt is, for the most |>art, the capillary circula- 
 tion. The ramifications of the minute arteries form a 
 continuous network, from which the small branches of 
 the veins take their rise. The point at which the arteries 
 terminate and the minute veins commence, cannot be 
 exactly defined ; the transition is gradual ; but the inter- 
 mediate network is so far peculiar, that the small vessels 
 which compose it maintain nearly the same size through- 
 out ; they do not diminish in diameter in one direction, 
 hke arteries and veins; hence the term capillary, from 
 
 Y Y 
 
690 
 
 THE MICROSCOPE. 
 
 capillus, a hair. (Fig. 317.) The size of the capillaries 
 is proportioned in all animals to that of the blood-cor- 
 puscles ; thus, amongst the ReptUia, where the blood-cor- 
 puscles, are the largest, the capillaries are also the largest : 
 
 but it does not follow that they 
 
 should be always of the same 
 size in all the tissues of one 
 and the same animal ; for if 
 we examine and carefully mea- 
 sure in the human subject 
 their sizes in different tissues, 
 we shall find that they vary 
 greatly even in individual tis- 
 sues, and, at a rough estimate, 
 examples may occur as large as 
 a thousandth, whilst others are 
 as small as the four or five- 
 thousandth of an inch. They 
 should be measured, if possible, 
 in their natural state ; when in- 
 sltghtly 
 
 Fig. 317. A network of capillaries 
 conveying blood to the lungs. 
 
 jected, their size is 
 increased; but, when dried, they 
 diminish so considerably that in some specimens vessels 
 imperfectly filled with injection have been known to shrink 
 from the three to the twenty -thousandth of an inch. 
 
 Fig. 318. 
 
 1, Blood-vessels of the Eye ; back view of the Ms and ciliary processes. 
 of the membrana pupillaris, from the eye of a Kitten. 3, Fibres or t 
 
 2, Vessel 
 
 ibres or tubes from 
 
 the lens of the Ox. (A sectional view of a Cat's eye is given in Plate VII. 
 No. 157.) 
 
CAPILLARIES. 
 
 691 
 
 Capillaries are, with very few exceptions, always sup- 
 ported by an areolar network, which serves not only as an 
 investment to them, but connects them intimately with 
 the tissues they are destined to supply. A possibility 
 arises, in first examinations, of mistaking or confounding 
 capillaries with nerves, 
 especially if the part 
 under observation should 
 have been left for some 
 time in strong preserving 
 or alkaline solutions. 
 
 A weak solution of 
 caustic soda, and also 
 another of acetic acid, are 
 both of use ; the first is 
 available for the purpose 
 of tracing nerves ; the 
 latter in making out 
 vessels, structure of pa- 
 pillae, unstriped muscle, 
 <fec., inasmuch as it renders 
 their nucleimore obvious ^ 319 _ m ^^ a flne ^^ of 
 
 while SOda thickens and air-tubetfor supplying the lungs with air. 
 
 makes them less so. It is very useful sometimes to use 
 these re-agents alternately ; the rule is, to apply them to the 
 object while under 
 the microscope, so as 
 to watch their gra- 
 dual operation. 
 
 It is not in the 
 blood alone that cells 
 float in a fluid ; the 
 chyle and lymph are 
 colourless corpuscles 
 flowing along their 
 especially - adapted 
 tubes and ducts, and 
 carrying the nutritive 
 particles gathered 
 
 from the food to the ^8- 320.-^ capillary of blood-vessels distributed 
 i i j i f to the fat tittue. Better seen in some of the in 
 
 blood-Vessels, for the jected specimens, Plate VII. 
 
692 
 
 THE MICROSCOPE. 
 
 reparation of the framework, or growth that incessantly 
 goes on in the animal body. 
 
 Classification of the Animal Tissues. Professor Schwann 
 classifies the fundamental tissues of the human body as 
 follows : and it will be seen that more than half are 
 made up of cellular tissue or simple membrane. 
 
 1. Simple membrane : employed alone \ 
 in the formation of compound > 
 membranes J 
 
 2. Fibrous tissues 
 
 3. Cellular tissues ........ 
 
 4. Sclerous, calcareous, or hard tissues | 
 
 5. Compound membranes: composed^ 
 
 of simple membrane and a layer of / 
 cells of various forms (ephithelium > 
 or epidermis), or of areola or con- \ 
 nective tissue and epithelium . . J 
 
 6. Compound tissues ; a, those com- \ 
 
 posed of tubes of homogenous (_ 
 membrane, containing a peculiar i 
 substance ......... ) 
 
 &, those composed of white fibrous \ 
 tissues and cartilage ..... j 
 
 Examples : Walls of cells, capsule of 
 
 lens of the eye, sarcolemma of 
 
 muscle, &c. 
 Examples : White and yellow fibrous 
 
 tissue, areola tissue, elastic tissue, 
 
 &c. 
 Examples : Cartilage, fat, pigment, 
 
 grey nervous matter, <fcc. 
 Examples : Rudimentary skeleton of 
 
 invertebrata, bone, teeth, &c. 
 
 Examples : Mucous membrane, skin, 
 true or secreting glands, serous and 
 synovial membranes. 
 
 Examples : Muscle, nerve. 
 Example : Fibro-cartilage. 
 
 Cellular or Formative Membrane. Areolar or connective 
 tissue is generally distributed throughout the body, and 
 
 various forms of this tissue are 
 found ; it is seen uniting to- 
 gether component parts, filling 
 up interstices between them, 
 and affording a support to the 
 blood-vessels and nerves, be- 
 fore they are distributed to the 
 various organs. This tissue is 
 soft, clear, smooth, and ex- 
 tremely minute, being the 
 1-1 2,000th of an inch in dia- 
 meter, sometimes less. The 
 fibre is usually found united 
 together in bundles ; if 
 
 Fig. 321. Fibrous tissue, lining the in- these be acted UDOn by dilute 
 terior of the eggshell, the lime having , -j ii_ 11 
 
 been previously removed b y immersion acetlC acid, they SWeil lip, 
 
 in dilute hydrochloric add. become transparent, and the 
 
 appearance of fibrous structure is no longer seen, although 
 
FIBROUS TISSUE. 
 
 6U3 
 
 some fibres that were not previously observed may become 
 more distinct. The first kind does not refract the light 
 strongly; the second kind does, showing some chemical 
 difference in their composition. 
 
 Cellular tissue, if dried, becomes a yellowish, brittle, 
 transparent mass ; but regains its former state if placed in 
 water. The fibres have a remarkable arrangement and 
 disposition. They are often deposited in a spiral manner ; 
 at other times they are regularly undulating. In fibres 
 taken from some parts of the body, we find a fasciculus 
 wound round in a spiral form. As a consequence, when 
 acetic acid is applied, we perceive projections of swollen 
 cellular tissue, and the depressions, from not having been 
 acted on, have a constricted appearance. The fibrous tissue 
 lining the eggshell, fig. 321, is the simplest form in which 
 it is found. 
 
 Fat is generally found in the cellular tissue ; it is not 
 secreted from it, but is contained in its proper cells, and 
 termed adipose tissue ; the elementary cells of which are 
 from the 1 -300th to the 1- 600th of an inch in diameter 
 (fig. 322). The cell- wall is very delicate and transparent ; 
 sometimes there are one or two nuclei enclosed. 
 dissolves out the fat-cells from 
 the tissues. Acetic acid acts 
 upon the cell-wall, and causes 
 the contents to pass from within 
 outwards. 
 
 Fibrous tissue, elastic and 
 non-elastic, is usually divided 
 into white and yellow fibrous 
 tissue. The yellow is elastic, 
 and of great strength, consisting 
 of bundles of fibres which are 
 highly elastic. (Fig. 324, No. 2.) 
 The white (fig. 324, No. 1), 
 though non-elastic, is of great 
 
 cfvoTirrlTi and nf a fihinincr 8- s?2 - cdls f rom tdipote tissue, 
 
 strength, ana t a smmng, ^. /a() magnifled 10 o diameters, 
 silvery appearance. 
 
 These two kinds of fibrous tissue differ from each other 
 in many respects, but chiefly in their ultimate structure, 
 their physical properties, and their colour : both are largely 
 
604 
 
 THE MICROSCOPE. 
 
 employed in those parts subservient to the organs of loco- 
 motion. 
 
 The white fibrous tissue is (when perfectly cleared of 
 the areolar) of a silvery lustre, and composed of bundles 
 of fibres running, for the most part, in a parallel direc- 
 tion ; but if there be more than one 
 plane of fibres they cross or inter- 
 lace with each other. In some 
 specimens it is very difficult to 
 make out the fibres distinctly, 
 except with oblique light ; from 
 this circumstance it would appear 
 that this tissue is composed of 
 /contents of a longitudinally striated membrane, 
 
 single fat-cell, separated and which is often found Split Up into 
 magnified 250 diameters. 
 
 principally employed in the formation of ligaments and 
 tendons a purpose for which it is admirably fitted on 
 account of its inelasticity: it also enters into the formation 
 
 1 2 
 
 Fig. 824. 
 
 1, White fibrous or non-elastic tissue. 2, Yellow fibrous or elastic tissue 
 taken near a ligament. 
 
 of fibrous membranes, viz. the pericardium, dura matin', 
 periosteum, perichondrium, sclerotic coat of the eye, and 
 
MUSCULAR FIBRE. 
 
 695 
 
 ,. 
 
 Fig. 825. White fibrous tissue from the 
 identic coat of f/te eye. 
 
 all the fasciae. It is sparingly supplied with capillaries 
 and nerves : the former always run in the areolar tissue, 
 connecting the bundles of fibres together ; in the gene- 
 rality of the fibrous tissues, the capillaries are not well 
 seen, except in that of the dura mater and periosteum ; 
 in other parts it must he injected to show them. 
 
 The yellow fibrous tissue 
 is highly elastic ; it consists 
 of bundles of fibres covered 
 with, and connected together 
 by, areolar tissue : the fibres 
 are of a yellow colour, some 
 round, others flattened ; 
 they are not always paral- 
 lel, but frequently bifurcate 
 and anastomose with neigh- 
 bouring fibres. It is always 
 difficult to separate the fibres 
 from each other ; and when 
 separated, the elasticity of 
 each individual fibre is shown 
 
 by its tendency to curl up at the end. The fibres in the 
 human subject vary in diameter from the 1 -5,000th to 
 1-1 0,000th of an inch. Acetic acid of Ordinary strength 
 does not act on yellow fibrous tissue; nor for a very 
 long time after maceration in water or spirit does its 
 elasticity diminish. Very long boiling extracts from it a 
 minute quantity of a substance nearly allied to gelatine ; 
 neither nuclei nor a trace of a cell can be seen in it after 
 the addition of acetic acid : both are readily seen when 
 white fibrous element is treated with this acid. 
 
 Muscular Fibre. There are three different kinds of 
 muscular fibre found in the animal body : 1st, in the 
 muscle of the skeleton ; 2d, in the muscle of the heart ; 
 and 3d, in the stomach, intestine, &c. The functions of 
 muscular fibre may be referred to two kinds voluntary 
 and involuntary. The muscles endowed with voluntary 
 power are those of the skeleton ; the involuntary are those 
 of the heart, stomach, intestine, &c. 
 
 Muscular fibre is held together by a very delicate tubular 
 sheath, nearly resembling simple structureless membrane. 
 
COG 
 
 THE MICROSCOPE. 
 
 This cannot always be discerned ; but when the two ends 
 are drawn asunder it will be perceived to rise up in 
 wrinkles, or the fragments of the torn muscle will be 
 seen to be connected by the untorn membrane, as at 
 fig. 326. This membrane is termed Myolemma. It is best 
 seen when a piece of muscle is subjected to the action of 
 
 fluids, as diluted acetic or 
 citric acid, or the fluid alka- 
 lies ; which occasion it to swell 
 and become easy of separa- 
 tion. It has no share in the 
 contraction of the muscle itself, 
 which is made up of a series 
 of bundles of highly elastic 
 fibres : portions of a separated 
 
 Fig 326. Muscularfibrebroken across, 
 the fragments connected by the untorn 
 structureless membrane, myolemma. 
 (Magnified 100 diameters.) 
 
 bundle are shown at fig. 327, 
 and the ultimate structure of 
 a fibre, under a magnifying power of 600 diameters, at 
 fig. 328, No. 1. 
 
 Dr. Hyde Salter pointed out, that in the tongue the 
 muscles pass directly into the bundles of the suhmucous 
 
 connective tissue, which 
 serve as their tendons. Such 
 a transition is shown in fig. 
 328, No. 2 ; the tendon, the 
 lower part of which may be 
 seen passing insensibly into 
 the striped muscle, the glan- 
 dular sarcous elements of 
 the latter appearing, as it 
 were, to be deposited in the 
 substance of the tendon (just 
 as calcareous particles are 
 deposited in bone), at first leaving the tissue about the 
 walls of the cavities of the eiidoplasts, and that in some 
 other directions, unaltered. The.se portions, which would 
 have represented the elastic element in ordinary connective 
 tissue, disappear in the centre of the muscular bundle, and 
 the endoplasts are immediately surrounded by muscle ; 
 just as, in many specimens of bone (see figs, of bone), the 
 lacunae have no distinguishable walls. On ihe other hand 
 
 Fiy. 327. Muscular fibre, broken up 
 Into irregular and distinct bands; 
 a few blood globules are distributed 
 about. (Magnified 200 diameters). 
 
MUSCULAR FIBRE. 697 
 
 at the surface of the bundle the representative of the 
 elastic element remains, and often becomes as much de- 
 veloped as its sarcolemnia. There is no question here of 
 muscle resulting from the contents of fused cells. It 
 is obviously and readily seen to be but a metamorphosis 
 of the periplastic substance, in all respects comparable 
 to that which occurs in ossification, or in the develop- 
 ment of tendon. In this case, we might expect that, as 
 there is an areolar form of connective tissue, so 
 
 Fig. 328. 
 
 , Muscular fibre, and zfascicnhts of a muscle taken from a young Pig. (Mag- 
 -ified 600 diameters ) 2, Muscular fibre from the tongue >! Lamb, showing 
 Continuity of the upper portion, with connective tissue of the lower portion 
 3, Branched mus-le, ending in stellate connective cells, from the upper lip o1 
 the Kat. 
 
 we find some similar arrangement of muscle ; such may, 
 indeed, be seen very beautifully in the termination of the 
 branched muscles, as they are called. In lig. 328, No. 3, 
 the termination of a muscular fibre from the lip of a Eat, 
 is shown : and the stellate "cells" of areolated connective 
 tissue are seen passing into the divided extremities of 
 the muscular bundle, becoming gradually striated as they 
 do so. In the muscle it is obvious enough, that what- 
 ever homology there may be between the stellate "cells" 
 and the muscular bundles with which they are con- 
 tinuous, there is no functional analogy, the stellate bodies 
 having no contractile faculty. The nervous tubule is 
 developed in essentially the same manner as a muscular 
 fasciculus, the only difference being, that fatty matters 
 take the place of syntonin. Now it commonly happens 
 that the nerve-tubule terminates in stellate bodies (fig. 
 330) of a precisely similar nature ; these are supposed to 
 
G98 
 
 THE MICROSCOPE. 
 
 possess important nervous functions ; and are now known 
 as " ganglionic cells." 
 
 The muscular fibre, known as the non-striated, or invo- 
 luntary, consists of a series of tubes presenting a flattened 
 appearance, without the transverse striae so characteristic 
 of the former : elongated nuclei immediately appear upon 
 the application of a little dilute acetic acid. Professor 
 Wharton Jones first demonstrated this structure in his 
 lectures at Charing Cross Hospital, about 1843 : he was 
 led to infer, from appearances in very young fibre, that 
 the striped muscular fibre is originally composed of 
 similar elements to the unstriped, or plain muscular tissue, 
 which, in the process of deve- 
 lopment, becomes enclosed in a 
 sarcolemma (simple membrane) 
 common to many of them ; the 
 fibres then split into smaller 
 fibres (fibrillce). Thus account- 
 ing for the nuclei of striped 
 muscular fibre ; which, accord- 
 ing to his views, are " the per- 
 sistent nuclei of the primitive 
 muscular-fibre cells." 
 
 The rion-striated fibre is beau- 
 tifully seen in connexion with 
 the skin surrounding the hairs 
 of the head, a few fibres of 
 which are separately shown in 
 fig. 329. Professor Kolliker ori- 
 ginally described these muscles 
 of the skin, of which there appear 
 Pig. 329. A portion of the invoiun- to be one or two in connexion 
 
 fury muscular fibre surrounding ,-, i_ i r n- i 
 
 the hair. with each hair-follicle, arising 
 
 from the more superficial parts 
 
 of the outer skin, then passing down to the root of the hair, 
 close behind the fat-gland, and there embracing it. It is 
 indeed most remarkable that skin, when covered with 
 hair, should alone be provided with these muscular 
 fibres ; the effect of the contraction of which must be 
 to thrust up the hair- follicles and depress the inter- 
 mediate portions of skin, and thus produce that peculiar 
 
NERVOUS STRUCTURE. 
 
 699 
 
 and before unaccountable state of the surface known as 
 goose-skin. 
 
 Nerves. The nervous system consists of 
 brain, spinal marrow, and nerves. There 
 are two sets of nerves in the body ; in the 
 one set the nerves are white, firm, shining, 
 more or less rounded, with transverse mark- 
 ings ; in the other, they are softer, not so 
 consistent, of a reddish grey colour, and 
 generally flat. 
 
 Under the microscope, nerves are seen to 
 be composed of minute fibres or tubules, full 
 of nervous matter, arranged in bundles, Fig. a.,o. -A 
 and connected by an intervening fibro-cel- 
 lular tissue, through which capillaries ramify. 
 A layer of the same, or of a more delicate, 
 transparent, structureless tissue surrounds 
 the whole nerve, forming a sheath. The 
 slight pressure of the thin glass, when 
 placed on the nerve-tibre, causes nearly the 
 whole of the contents to flow out in the 
 form of a granular material ; it therefore 
 becomes necessary to exercise considerable 
 care in breaking up structures to view these 
 tubules, which should be immersed in a 
 very weak solution of spirit and water. 
 
 On Microscopical Examination of Nerve* It would 
 
 scarcely be necessary to insist on the great importance of 
 removing and examining the 
 nervous centres as soon as 
 possible after death, were it 
 not that the practice is too 
 often neglected. Great cau- 
 tion also should be exercised 
 to avoid injuring the parts, so 
 that when hardened, perfect 
 or entire sections of them may 
 be obtained for examination in muscles. 
 
 under the microscope. After they have been carefully 
 examined externally, by the assistance of a lens, if neces- 
 sary, incisions should be made, not at random, but in a 
 
 processes issuing 
 out, which at a 
 is filled with a 
 corpuscle con- 
 taining black 
 pigment, above 
 this are corpus- 
 cles with nuclei 
 and their nu- 
 cleoli ; at 6 is a 
 corpuscle en- 
 closing within 
 its sheath gra- 
 nular matter : 
 this is taken 
 from the root of 
 a spinal nerve. 
 
VOO THE MICROSCOPE. 
 
 regular manner through them ; and wherever there is 
 reason to suspoct the existence of disease, small portions 
 should be removed, and examined while perfectly fresh 
 under high magnifying powers. The nature of the lesion 
 having been thus ascertained, the morbid parts, with 
 some of the surrounding healthy tissue, should be re- 
 moved, and after being divided, if necessary, into smaller 
 portions, should be macerated in a weak solution of chromic 
 acil. It is very important to cut and subdivide the 
 parts, when necessary, in such a manner, that their rela- 
 tion to the rest may be recognised after they have become 
 hardened for the purpose of making sections. Thus, 
 unless the locality of the lesion require a different course, 
 one incision may be made through the crura cerebri, 
 immediately in front of the small or motor roof of the 
 trifacial nerves, and a third through the base of the 
 anterior pyramids, immediately below the attachment of 
 the sixth pair of cerebral nerves. With regard to the 
 spinal cord, if it be cut up into small portions and 
 hardened in chromic acid, it will be found better to divide 
 it in three places : 1st, through the middle of the cervical 
 enlargements ; 2d, through the middle of the dorsal 
 region ; and 3rd, through the middle of the lumbar 
 enlargement. 
 
 If, however, the lesion be suspected to exist at another 
 point, the cord must be divided there; as it is highly 
 important that the nature of any morbid portion that 
 may be found should be examined under the microscope 
 in a perfectly fresh state ; for the nerve-fibres undergo a 
 considerable and very deceptive alteration by the action 
 of chromic acid. But it is no less important, and indeed is 
 absolutely necessary for an exact and complete investiga- 
 tion, that entire portions of the cord, in the locality of the 
 lesion, be hardened in chromic acid, so that thin, but 
 perfect sections may be made for examination under the 
 microscope. 
 
 " The strength of the chromic acid solution.should differ 
 for different parts of the cerebro-spinal centres. For the 
 convolutions of the cerebral hemispheres and cerebellum, 
 the proportions should be one of the crystallised acid to 
 about four hundred of water, while for the pons varolii, 
 
SECTIONS OF SPINAL CORD 701 
 
 medulla oblongata, and spinal cord, the strength of the 
 solution may be in the proportion of one of the acid to 
 about three or even two hundred of water. It is best, 
 however, to begin with the weaker solution and increase 
 its strength at the end of some hours. If the cerebral 
 and cerebellar hemispheres be hardened in a solution of 
 greater strength, they become friable and unfit for making 
 perfect sections." 1 
 
 Method of Preparing Sections of the Spinal Cord. Bj 
 a peculiar method of preparation, Mr. Lockhart Clarku 
 obtains beautiful sections showing the arrangement of the 
 nerve-fibres and vesicles in the spinal cord and other 
 parts of the nervous system. The results are recorded in 
 the Philosophical Transactions for 1851, Part 2. The 
 cord it appears is first hardened in acetic acid and alcohol, 
 when excessively thin sections may be readily obtained 
 with a sharp knife. These are then soaked in pure spirit, 
 which permeates the texture in every part, and drives out 
 the acetic acid, and afterwards transferred to turpentine 
 which expels the spirit, and lastly the sections are 
 mounted in Canada balsam. By this plan the tissues of 
 the embryos of mammalian animals can also be rendered so 
 transparent that the smallest ossific points can be seen in 
 the temporary cartilages. To render the specimen more 
 transparent immerse it in alcohol to which a few drops 
 of a solution of soda have been added, and allow it to 
 remain quietly for a few days. When sufficiently acted 
 on, remove it, and preserve permanently in weak spirit. The 
 principle of the action of the fluid may be explained 
 thus : alcohol alone tends to coagulate albuminous textures 
 and render them opaque, at the same time that it hardens 
 them. The alkali, on the other hand, renders the tissues 
 soft and transparent, and if time were allowed, would 
 cause their complete solution. These two fluids in con- 
 junction harden the texture and at the time make it clear 
 and transparent. Many soft tissues may thus be hardened 
 sufficiently to enable us to cut very thin sections. 
 
 Nerves may be examined in thin sections of the skin 
 after the addition of acetic acid and a solution of soda. 
 Gerber boils the skin until it becomes quite transparent, 
 
 (1) Lockhart Clarke on the Microscopical Examination of iVerre*. 
 
702 THE MICROSCOPE. 
 
 then allows it to remain a few hours in turpentine, or 
 until the nerves are seen to be white and shining, when 
 they are ready for cutting into perpendicular sections with 
 the double (Valentine's) knife. 
 
 It is proposed to employ chloride of gold to stain the 
 tissues of the body. Tissues soaked in a weak solution 
 of from one to two per cent, of this salt in distilled water, 
 and afterwards exposed to light, are found to exhibit 
 certain parts, as nerve-fibres, connective tissue, corpuscles, 
 and cells generally, stained of violet-red colour, while 
 other parts, as intercellular substance, &c. are left un- 
 touched. The soaking must be continued until the tissue 
 assumes a straw-yellow colour, then taken out of the solu- 
 tion and placed in dilute acetic acid of one to two per 
 cent. The colour will be seen to gradually develop itself, 
 and Kolliker and Cohnheim, who have tried it, say that 
 nerve-fibre, &c. are exceedingly well shown in this way. 
 
 Consolidated Tissues. Such tissues are formed by a 
 chemical combination with the albumen and gelatine of 
 the fibre ; this in cartilaginous 
 formations is termed chondrine, 
 the cells of which become con- 
 solidated by calcareous deposits, 
 and a gradual transition results 
 therefrom. Cartilage is the 
 firmest structure next to bone 
 met with ; it is very elastic, 
 and, as an intercellular sub- 
 stance, is generally divided into 
 two kinds. Between the ribs 
 we find this substance presenting 
 a uniform bluish appearance, 
 Fig. 332 . Cartiiarje from ear of and slightly granular : this is 
 
 or white cartilae. The 
 
 posed layers. other form of intercellular sub- 
 
 stance is developed in fibrous substances ; and it is in 
 this peculiarly-formed felt-work that cells with nuclei are 
 found. This is known as yellow, fibrous, or spongy car- 
 tilage, the yellow colour depending on the mode of fibrous 
 arrangement of the intercellular substance : it is found in 
 the ears, and other parts. 
 
CARTILAGE. 
 
 703 
 
 Cartilage forms the entire skeleton in some kinds of 
 fishes, the Skate, Lamprey, &c. ; and it is nourished with- 
 
 Fig. 333. 
 
 1, Cartilage from Rabbit's ear, showing latye cells embfd<!ed in a fibrous 
 matrix. 2, Cartilage from Human ribs, with celia in groups:, each having a 
 granular nucleus. (Magnified 200 diameters.) 
 
 out coming into direct contact with the blood-vessels, 
 therefore it is said to be non-vascular ; nourishment is 
 derived by imbition from ihesurround- 
 ing blood-vessels. When examined 
 microscopically, the simplest form of 
 cartilage is seen to resemble in a 
 striking manner the cellular tissue of 
 vegetables ; it consists of an aggre- 
 gation of cells of a spherical or oval 
 form, capable in some cases of being 
 separated from each other, and every 
 cell having a nucleus, with a nucleolus 
 in its interior. In figs. 332, 333, and 
 334, we have varieties of this structure. 
 In the more highly organized scale 
 of animals, a strong fibrous capsule, 
 or sheath, surrounds the cartilage- 
 cells ; some of the fibres dip in amongst 
 the cells, and bind them firmly 
 together. In those inhabitants of the 
 water, the Eay and Shark, the entire skeleton being car- 
 tilaginous, the cell is imbedded in a matrix, which ma v 
 
 Fig. 334. Cartilage from 
 the Cuttle-Jish, showing 
 stellate form of cells. 
 
704 THE MICROSCOPE. 
 
 be strictly termed inter cellular. Cells are frequently or 
 entirely isolated, as in the section from the ear of a Mouse 
 (fig. 332), they then rarely become converted into bone. 
 In the highest animals it is generally invested by a fine 
 
 1 Fig. 835. 
 
 1, Cartilage from the head of Skate, with clusters of nucleated cells ami 
 nucleoli inrlosed. 2, Cartilage from the Frog, with cells having nucleoli, 
 magnified 200 diameters. 
 
 and delicate membrane, termed perichondrium, which brings 
 the blood-vessels in close contact with the cartilage ; and, 
 when in actual contact with the extremities of bones, is 
 covered by a vascular membrane having a large number of 
 vessels terminating in it, for the purpose of supplying u 
 lubricating fluid to the end of the bones: this, ihe synovia! 
 membrane, is a very beautiful structure when injected and 
 viewed under a 1-inch power. 
 
 In the earliest stages of existence, the entire framework 
 or a very large proportion is composed of cartilage, which, 
 by a gradual addition of earthy matter, becomes consoli- 
 dated into bone. The mode of development, and the 
 change from one to the other, is represented in the section 
 (fig. 336) ; it will there be seen that the calcareous matter 
 is deposited in nearly straight lines, which stretch from 
 the ossified surface into the substance of the matrix of 
 the cartilage, the amount of calcareous matter in which 
 gradually diminishes as we recede from the ossified part. 
 If the deposit has taken place to any great extent, the 
 
TEETH. 
 
 calcareous matter becomes crowded and consolidated ; as 
 the process advances, the bone thickens, and a series .of 
 grooves, of a stellate form as in the annexed cut (fig. 337, 
 No. 2), are found upon its sur- 
 face, which become gradually 
 converted into canals for the 
 passage of blood-vessels. 
 
 In certain forms of disease, 
 many of the soft parts of the 
 human body are converted into 
 cartilaginous and bony masses, 
 which have received the name 
 of Enchondroma (figs. 338 and 
 339). The microscopical cha- 
 racteristics of this change have 
 been described by the author 
 in the Transactions of the Patho- 
 logical Society of London, vol. iv. 
 
 Teeth. It is desirable to be- 
 come acquainted with the struc- 
 ture of teeth under the micro- 
 scope ; they are highly interest- 
 ing to the physiologist, and im- 
 portant guides to the naturalist 
 in the classification of animals. 
 Professor Owen has said, " If 
 the microscope is essential to 
 the full and true interpretation 
 of the vegetable remains of a 
 former world, it is not less in- 
 dispensable to the investigator 
 of the fossilised parts of animals. 
 It has sometimes happened that 
 a few scattered teeth have been 
 the only indications of animal 
 life throughout an extensive stratum; and when these 
 teeth happened not to be characterised by any well-marked 
 peculiarity of external form, there remained no other 
 test by which their nature could be ascertained than that 
 of the microscopic examination of their intimate tissue. 
 By the microscope alone could the existence of Keuper- 
 
 z z 
 
 Fig. 336. A vertical section oj 
 cartilage, with clusters of cells 
 arranged in columns previous to 
 conversion into tone, which is 
 seen consolidated at the upper 
 surface. The greater opacity of 
 this portion is owing to the in- 
 crease of osseous fibres, the 
 opacity of the cell contents, 
 and the multiplication of oil- 
 globules; the dark intercel- 
 lular spaces become occupied 
 by vessels. 
 
706 THE MICROSCOPE. 
 
 reptiles in the Lower sandstones of the New red system, 
 
 Fig. 337. 
 
 1, Section of the tendo-Achillis as it joins the oscalcis : showing tho *Mi*+* 
 ceUs i of tendon gradually coalescing to form the round or waf ceUs of the 
 cartilage 2, A small transverse section of enchondroma, showing the eradua! 
 
 in Warwickshire, have been placed beyond a doubt. By 
 
 the microscope, the 
 supposed monarch 
 of theSaurian tribes 
 the so-called Ba- 
 silosaurus has 
 been deposed, and 
 removed from the 
 head of the Eepti- 
 lian to the bottom 
 of the Mammalian 
 division. The mi- 
 croscope has de- 
 graded the Sauro- 
 cephalus from the 
 class of reptiles to 
 that of fishes. It 
 has settled the 
 doubts entertained 
 by some of the 
 highest authorities 
 in palaeontology as 
 to the true affinities 
 
 icrt* n A "e~ m*v*fc<JCO O, gt- 
 ge, and is seen converted into bone 
 
 A iL ~"""6" "*"* * 
 
 at the upper portion. 
 
 of the gigantic Me- 
 gatherium ; and by 
 
TEETH. 
 
 707 
 
 'demonstrating the identity of its dental structure with 
 that of the Sloth, has yielded us an unerring indication of 
 the true nature of its food." 
 
 The teeth of Man and of most of the higher animals 
 are composed of three different 
 substances, Dentine (known as 
 ivory in the tusk of the elephant), 
 Enamel, and Cemenlum, or crusta 
 petrosa: These are variously dis- 
 posed, according to the purposes 
 which the tooth is to serve : in 
 Man the whole crown of the 
 tooth is covered with enamel, 
 shown in the darker marginal Fig zz9.-po 
 part of fig. 340 ; its root or fang 
 is covered with cementum, 
 whilst the substance or body of the tooth is composed of 
 dentine. 
 
 In the human subject, two sets of teeth are developed, 
 the milk and permanent : the first are formed from one 
 
 Fig 340 Sections of Human Molar Tooth (magnified 50 diameters) 
 1, Vertical Section. 2, Horizontal Section. 
 
 set of bulbs, which in time shrink, and let the teeth fall 
 out the permanent set is then produced from new bulbn, 
 
708 
 
 THE MICROSCOPE. 
 
 situated by the side of the old ones. Blandin was the first 
 to point out that the teeth are developed in the mucous 
 membrane, in a similar way to hair and nails. Other ob- 
 servers have been led to the same conclusion ; and, more 
 lately, Professor Goodsir demonstrated that the teeth are 
 first formed in grooves of the mucous membrane, and sub- 
 sequently converted into closed sacs by a process of involu- 
 tion, and that their final adhesion to the jaw is a com- 
 paratively late part of the process. It is now generally 
 conceded that teeth belong to the muco-dermoid, and not 
 
 Pig. 341. 
 
 .1, "A section of a cusp of the posterior molar, upper jaw of a Child, The inner 
 outline represents it before the addition of acetic acid the outer after- 
 wards, when Nasmyth's membrane g is seen raised up in folds ; /, the enamel 
 organ ; e, the dentine. The central portion is tilled up with pulp. 2. Edge 
 of the pulp of a molar cusp, showing the first rudiment of the. dentine, com- 
 mencing in a perfectly transparent layer between the nuclei of the pulp and 
 the membrana preformativa. 3, Nasmyth's membrane detached from the 
 subjacent enamel by acetic acid. 3, The stellate-cells of the enamel-organ. 
 5, Tooth of the Frog, acted on by dilute hydrochloric acid, so as to dissolve 
 out the enamel and free Nasmyth's membrane. The structure of the dentine 
 e is rendered indistinct. At the base, Nasmyth's membrane is continued over 
 the bony substance at z, in which the nuclei of the lacunae are visible. (After 
 Huxley.) 6. Decalcified tooth-structure; a, the dentine; &, enamel organ; 
 c, enamel ; d, Nasmyth s membrane. 
 
 to the periosteal, series of tissues ; that, instead of standing 
 in close relation to the endo-skeleton, they are part of the 
 dermal or exo-skeleton ; their true anologues being the 
 hair, and some other epidermic appendages. Professor 
 Huxley has proved that, although teeth are developed in 
 
TEETH. 
 
 709 
 
 two ways, these are mere varieties of the same mode in 
 the animal kingdom. In the first, which may be typified 
 by the Mackerel and the Frog, the pulp is never free, but 
 from the first is inclosed within the capsule, seeming to 
 sink down as fast as it grows. In the other, the pulp pro- 
 jects freely at one period above the surface of the mucous 
 membrane, becoming subsequently included within a cap- 
 sule formed by the involution of the latter ; this occurs 
 in the human subject. The Skate offers a sort of inter- 
 mediate stage. 
 
 The enamel forms a continuous layer, and invests the 
 crown of the tooth; it is thickest upon the masticating 
 surface, and decreases towards the neck, where it usually 
 terminates. The external surface of the enamel appear 
 
 Fig. 342. Tooth Structure. 
 
 1, Longitudinal section of superior canine tooth, exhibiting general arrange- 
 ment, and contour markings, slightly magnified. 2 and 3, Portions from same 
 highly magnified, showing the relative position of lone-cells, cementum at 
 2, dentine fibres, and commencement of enamel at 3. 4, Dentine fibres 
 decalcified. 5, Nasmyth's membrane separated and the calcareous matter 
 dissolved out with dilute acid. 6, Cells of the pulp lying between it and the 
 ivory. 7, A transverse section of enamel, showing the sheaths of fibres, 
 contents removed, and magnified 300 diameters. 
 
 smooth, but is always marked by delicate elevations and 
 transverse ridges, and covered by a fine membrane (Na- 
 smyth's membrane), containing calcareous matter : this 
 membrane is separable after the action of hydrochloric acid; 
 it then appears like a network of areolar tissue, shown in 
 fig. 342, No. 6 ; which is Huxley's " calcified membrana 
 
710 THE MICROSCOPE 
 
 preformativa" of the whole pulp. Nasmyth says : "In all 
 cases where this covering has been removed by means of 
 acid, it has, of course, the appearance of a simple mem- 
 brane, in consequence of the earthly deposit having been 
 dissolved out, and the animal tissue only remaining. The 
 structure and appearance of the covering detached in this 
 manner from the enamel is the same in every respect as 
 that observed in the capsule of the unextruded tooth, and 
 consisting, like it, of two layers, fibrous externally, and 
 having on its external surface the peculiar reticulated 
 appearance common to both." 
 
 " On examining carefully fine sections of several teeth 
 under the microscope, I perceived here also," observes 
 ISTasmyth, " that the structure in question was continuous 
 with the crusta petrosa of the fang of the tooth." 
 
 The enamel has a fibrous bluish aspect, is very brittle, 
 and much harder than the other dentinal structures ; it 
 is, indeed, so hard, that it strikes fire with steel ; if an 
 attempt be made to cut it without the application of water 
 to keep it cooled down, it burns with an ammoniacal 
 odour, such as we perceive when horse-hoof is burnt. It is 
 composed of prisms, about l-5,000th of an inch in breadth, 
 more or less wavy, and transversely striped. Two kinds of 
 bands or stripes are seen traversing enamel, the direction 
 of one of which nearly coincides with that of the dentine 
 fibres ; the other set of stripes indicate the laminated struc- 
 ture of enamel. Under polarised light, a third set become 
 visible, arising from the variable inclination of the axes 
 of the fibres to the plane of polarisation. The enamel 
 is often traversed by cracks or fissures, mostly running 
 parallel with one set of the fibres : these are sometimes 
 described as canals ; but as they resemble splits, and are 
 seldom seen in young teeth, it is more likely that they 
 are caused by the nature of the food and drink, which is 
 taken into the mouth at temperatures varying many de- 
 grees ; we also trace the commencement of disease from 
 a fissure in the enamel. "When a section of the enamel 
 is cut obliquely, it has somewhat of a hexagonal or six- 
 sided appearance. The dentine consists of a transparent 
 basement membrane, with alternating layers of cal- 
 careous matter, traversed by very fine branching tubuli, 
 
TEETH. 711 
 
 which commence at the pulp cavity, and pass up to the 
 enamel. 
 
 Czermak discovered that the curious appearances of 
 globular conglomerate formations in the substance of 
 dentine depend on its mode of calcification and the 
 presence of earthy material ; and he attributes the contour 
 lines to the same cause. Contour markings vary in in- 
 tensity and number; they are most abundant in the root, 
 and most marked in the crown. Vertical sections exhibit 
 them the best; as fig. 342, JS"o. 1. In preparing a specimen, 
 first make the section accurately, 
 then decalcify it by submersion in 
 dilute muriatic acid ; then dry it 
 and mount in Canada balsam with 
 continued heat, so as to allow the 
 specimen to soak in the fluid resin 
 for some time before it cools. It is 
 the white opacity at the extremity 
 
 of the contour markings which Fig. 343. Transverse, section of 
 . -, f Tooth of Pristis, showing ori- 
 
 gives the appearance of rings on aces of medullary canals, with 
 
 tVip tnnfh -fancy systems of radiating fibres 
 
 tne room rang. * . } analogoU3 to the 
 
 " The tOOth-SUbstance appears, Haversian canals in true 
 
 says Czermark, " on its inner sur- b Be - 
 face, not as a symmetrical whole, but consisting of balls 
 of various diameter, which are fused together into a 
 mass with one another in different degrees, and on which 
 the dentinal tubes in contact with the germ cavity are 
 terminated. By reflected light, back-ground illumination, 
 one perceives this stalactite-like condition of the inner 
 surface of the tooth-substance very distinctly, by means of 
 the varied illumination of the globular elevations, and by 
 the shadows which they cast. Here one has evidently to 
 do with a stage of development of the tooth-substance; 
 for the older the tooth is, the less striking in general are 
 these conditions, and the more even is the surface of the 
 wall of the germ-cavity. In very old teeth considerable 
 unevenness again makes its appearance; these, however, 
 are not globular, but have a cicatrised, distorted appear- 
 ance. It is best to make the preparation from a tooth of 
 which the root is not perfectly completed. With such 
 preparations, one is readily convinced that the ground- 
 
712 THE MICROSCOPE. 
 
 substance of the last-formed layer of the tooth-substance 
 appears, at least partly, in the form of balls, which are 
 fused one among another, and with the balls of the penul- 
 timate layers ; and one also perceives that in general their 
 diameter becomes less and less, somewhat in the form of a 
 point, towards the periphery of the tooth-substance. To 
 obtain specimens, procure a tooth of which the fang is 
 half-grown; then introduce the point of a penknife into its 
 open extremity, and scraping the inner surface, detach 
 small portions, which exhibit the globules admirably." l 
 
 The cementum is the 
 cortical layer of osseous tis- 
 sue, forming an outer coat- 
 ing to the fangs, which it 
 sometimes cements toge- 
 ther. It commences as a 
 very thin layer at the part 
 
 Fig. ^.-Transverse section of Tooth oj ^ Q the enamel CeaSGS, 
 Myliobates, Eagle-ray, viewed es an and increases in thickness 
 
 So q us e sttctur^ sh w its radiatlas towards the ends of the 
 
 fangs. Its internal surface 
 
 is intimately united with the dentine^ and in many teeth 
 it would appear as if the earliest determined arrangement 
 of the fibres of the dentine started from the canaliculi, as 
 they radiate from the lacunae in the cement. The inter- 
 lacunar layer is often striated, and exhibits a laminated 
 structure : sometimes it appears as if Haversian canals 
 were running in a perpendicular direction to the pulp 
 cavity. The canaliculi frequently run out into numerous 
 branches, connecting one with another, and anastomising 
 with the ends of the dentine fibres. The thick layers of 
 cement which occur in old teeth show immense quantities 
 of aggregated lacunae of an irregular and elongated form. 
 Professor Owen believes that by age the pulp ceases to pro- 
 duce or nourish the dentine, which then becomes converted 
 into osteo-dentinz, and thereby the layer of crusta is so 
 much increased as often to fill up the pulp cavity of the 
 tooth. Professor Simonds assures us that this is not the case 
 in the Herbivora. For instance, in the horse, the oblitera- 
 
 (1) Czermak: translated by James A. Salter, M.B., Quarterly Journal of 
 Microscopical Science, July, 1823. 
 
BONE. 
 
 713 
 
 tion of the cavity is gradually effected by an increased 
 formation of dentine ; and this is not supplanted by an 
 abnormal or diseased growth, as would be the case were 
 the pulp to become ossified, but as the pulp diminishes, 
 so is the supply of nutriment to the tooth lessened, and at 
 length entirely cut off from the interior. " To provide for 
 the vitality of the tooth under 
 these circumstances, the crusta 
 increases in quantity on the 
 fang, at the expense of the per- 
 fectly-formed dentine, which is 
 lying in immediate contact with 
 its inner surface. Through the 
 medium of the canals in the 
 crusta, which open on its 
 borders, the tooth now draws 
 its nourishment from the blood- 
 vessels of the socket ; and thus 
 it continues, long after the obli- 
 teration of its pulp cavity, to 
 serve all the purposes as a part 
 of the living organism." 1 
 
 Bone. The elements of bone 
 are lamella and small cor- 
 puscles ; the latter are possibly 
 merely spaces between the for- 
 mer, in which is deposited the 
 earthy substance. The lamellae 
 have for their basis a cartila- 
 ginous substance combined 
 with earthy matter, or salts. 
 These salts are chemically com- 
 bined with the organic basis. Acids dissolve only the 
 earthy salts, and leave the organic basis of the same 
 form as the bone itself. The lamellop. are homoge- 
 neous throughout, like the intercellular substance of car- 
 tilage, but chemically different, being resolved by boiling 
 in water into colla, whereas cartilage is resolved into 
 chondrine. 
 
 Fig. 345. A transverse section of the 
 human clavicle, or collar-bone, mag- 
 nified 95 diameters ; which ex- 
 hibits the Haversian canals, the 
 concentric laminae, and the con- 
 centric arrangement of bone-cell* 
 around them. Some of the Ha- 
 versian canals are white, others 
 black ; the latter are filled with 
 a deposit of opaque matter, used 
 in the grinding and polishing the 
 section. When viewed under a 
 lower power, they appear to be 
 only a series of small black dots, 
 as shown in fig. 346. 
 
 (1) Profesaor Simonds, on the "Structure and Development of Teeth o* 
 
714 
 
 THE MICROSCOPE. 
 
 Professor Quekett's paper in an early number of the 
 Micros. Soc. Trans, gave an 
 excellent account of the " In- 
 timate structure of Bone." To 
 this paper we are indebted 
 for the following microscopical 
 investigation of bone : 
 
 Bone consists of a hard and 
 soft part ; the hard is com- 
 posed of carbonate, phosphate, 
 and fluate of lime, and of car- 
 bonate and phosphate of mag- 
 nesia, deposited in a cartila- 
 ginous or other matrix; whilst 
 the soft consists of that matrix, 
 and of the periosteum which 
 invests the outer surface of 
 the bone, and of the medullary 
 membrane which lines its in- 
 terior or medullary cavity, and 
 is continued into the minutest 
 pores. If we take for exami- 
 nation a long bone of one of 
 the extremities of the human 
 subject, or of any mammalian 
 animal, we shall find that the 
 bony substance, or shaft, is 
 slightly porous, or rather oc- 
 cupied, both on its external 
 and internal surfaces, by a 
 series of very minute canals, 
 which, from their having been 
 first described by our coun- 
 tryman Clopton Havers, are 
 
 thlS the 
 
 of small Wocfc dots. 
 
 Fig. W.-A transverse section of tJ* , 
 
 Hummus, or fore-arm lone, of a sian canals, and serve lor the 
 hffifc^Ha'M; canal*; transmission of blood-vessels 
 with a slight tendency to a con- into the interior of the bone. 
 
 centric arrangement of bone-cells T /> ^-i 
 
 around them The bone-ceils are If now a thin transverse sec- 
 
 f 
 
 and be examined by the micro- 
 
BOXE STRUCTURE. 
 
 715 
 
 
 scope with a power of 200 linear, we shall see the Haversian 
 canals very plainly, and around them a series of concentric 
 bony laminae, from three to ten or twelve in number. If 
 the section should consist of the entire circle of the shaft, 
 we shall notice, besides the concentric laminas round the 
 Haversian canals, two other series of laminae, the one 
 around the outer margin of the section, the other round 
 the inner or medullary cavity. 
 Between the laminae is situ- 
 ated a concentric arrangement 
 of spider-like looking bodies, 
 which have, by different au- 
 thors, received the name of 
 osseous corpuscles, lacunae, or 
 bone -cells, according as to 
 whether they were ascertained 
 to be solid or hollow : these 
 bone- cells have little tubes or 
 canals radiating from them, 
 which are termed canaliculi. 
 The average length of the 
 lacunae, or bone-cells, in the 
 human subject is the l-2,000th 
 of an inch ; they are of an 
 oval figure, and somewhat flat- 
 tened on their opposite sur- 
 faces, and are usually about 
 one-third greater in thickness 
 than they are in breadth; hence, as will be presently 
 shown, it becomes necessary to know in what direction 
 a specimen is cut, in order to judge of their comparative 
 size. The older anatomists supposed them, from their 
 opacity, to be little solid masses of bone ; but if the sec- 
 tion be treated with spirits of turpentine coloured with 
 alkanet-rcot, or if it has been soaked in very liquid 
 Canada balsam for any great length of time, it can 
 then be unequivocally demonstrated that both these sub- 
 stances will gain entrance into the bone-cells through the 
 canaliculi. The bone cells, when viewed by transmitted 
 light, for the most part appear perfectly opaque ; and they 
 will appear the more opaque the nearer the section of 
 
 
 
 Fig. 348. A transverse section 'of the 
 jremur, or leg-bone of an Ostrich 
 (magnified 95 diameters). When 
 contrasted with the preceding 
 figure, it will be noticed that the 
 Haversian canals are much smaller 
 and more numerous, and many of 
 them run in a transverse direction. 
 
71<J 
 
 THE MICROSCOPE. 
 
 them approaches to a transverse one : for when the cells 
 are cut through their shorter diameter, they are often of 
 such a depth that the rays of light interfere with each 
 other in their passage through them, and darkness results ; 
 whereas if the section be made in the long diameter of the 
 cells, they will appear transparent. When viewed as an 
 opaque object, with a dark ground at the back and con- 
 densed light, the bone-cells and canaliculi will appear quite 
 white, and the intercellular substance, which was trans- 
 parent when viewed by transmitted light, is now perfectly 
 
 dark. The soft part consists 
 of the periosteum, which in- 
 vest the outer, and of the 
 medullary membrane, which 
 invests the inner surface, lines 
 the Haversian canals, and is 
 continued from them, through 
 the canaliculi, into the interior 
 of the bone-cells ; and of the 
 cartilaginous or other matrix, 
 which forms the investment 
 of the minute ossific granules. 
 The earthy matter of the bone 
 may be readily shown by 
 macerating the section for a 
 Fig. 349. .4 horizontal section of the short time in a dilute solution 
 
 lower Jaw-bone of a Conger eel, /> , , - rp, . , 
 
 which exhibits a single plane of 01 caustic potash. The animal 
 bone-cells arranged in parallel lines, matter may be procured by 
 There are no Haversian canals pre- . ,., J , ., " . .>. 
 
 sent ; and when this specimen is USing dilute hydrochloric acid 
 contrasted with that of fig. 347, j^ofprj/l n f pmiatip r>nfn<s>i 
 it will be noticed that the canali- mste aOl 01 Caustic potash , 
 
 cuii given off from each of the when all the earthy matter 
 
 bone-cells of this fish are very few J AV i* MI 
 
 in number in comparison with IS removed the Section Will 
 
 that of the reptile. exhibit nearly the same form 
 
 as when the earthy constituent was present ; and if then 
 viewed microscopically, it will be noticed that all the 
 parts characterising the section previous to its maceration 
 in the acid will be still visible, but not so distinct as 
 when both constitutents were in combination. When, 
 however, the animal matter is removed, the bone will not 
 exhibit the cells and the canaliculi, but is opaque and 
 very brittle, and nothing but the Haversian canals and a 
 
BONE STRUCTURE. 
 
 717 
 
 granular structure can be seen. 
 The parts which a transverse 
 or a longitudinal section of a 
 long bone of a mammalian 
 animal exhibits, will be the 
 Haversian canals, the con- 
 centric bony laminae, the bone- 
 cells and their canaliculi; 
 even these, except the bony 
 lamina, may be seen in all 
 mammalian bones (fig. 345). 
 Whether long or otherwise, 
 they are, nevertheless, so dif- 
 ferently arranged in the flat 
 bones, such as those of the 
 
 i -I! j ,-i . i Fig. 350. A portion 
 
 skull, and in the irregular */ a siren (siren 
 bones, as the vertebrae, as to 
 require notice. Those of the 
 head are composed of two thin 
 layers of compact texture; 
 enclosed between which is 
 another layer of variable thick- 
 ness, of a cellular or cancel- 
 lated structure. The two outer 
 layers are called tables the 
 one being the outer, the other 
 the inner table ; and the middle 
 or cancellated layer is termed 
 the diploe : in this last the 
 principal blood-vessels ramify. 
 The outer table of the skull 
 is less dense than the inner ; 
 the latter, from its brittle- 
 ness, is termed by anatomists 
 
 the vitreous table. When 
 
 a vertical section of a bone Flg ^_ A ^ ^ 
 
 of the skull IS made SO as taken from the exterior of the shaft 
 +rk iT^lml thp. tlirpp Iflvpro of the Humerus of a Pterodactyl* ; 
 
 to include tne tnree layers this exhibit3 th6 elongated bone- 
 above mentioned, bone-Cells cells characteristic of the order 
 
 may be seen in all ; but each Reptaia ' 
 
 of the three layers differ in structure : the middle or can- 
 
 which are larger in this animal than 
 
718 
 
 THE MICROSCOPE, 
 
 collated structure will be found to resemble the cancellated 
 structure in the long bones viz. thin plates of bone, with 
 one layer of bone-cells without Haversian canals ; the outer 
 layer will exhibit Haversian canals of large size, with bone- 
 cells of large size, and a slightly laminated arrangement ; 
 but the inner or vitreous layer resembles the densest bdhe, 
 as the outer part of the shaft of a long bone, for instance, 
 and will exhibit both smaller Haversian canals and more 
 numerous bone-cells of ordinary shape around them. 
 
 A transverse section of the long bone of a bird, when 
 contrasted with that of a mammal, exhibits the following- 
 peculiarities : the Haversian 
 canals are more abundant, 
 much smaller, and often run 
 in a direction at right angles 
 to that of the shaft, by which 
 JR means the concentric laminated 
 arrangement is in some cases 
 lost ; the direction of the canals 
 follows the curve of the bone ; 
 the bone-cells also are much 
 smaller and more numerous ; 
 but the number of canaliculi 
 given off from each of the cells 
 is less than from those of mam- 
 mals, fig. 348 : the average 
 length of a bone-cell of the 
 
 Fig. B52.-A horizontal section of a Ostnch IS l-2,000th of an inch, 
 scale, or flattened spine, from the the breadth 1-6, 000th. 
 
 In the StptiKa, the bones 
 
 ing with them. This specimen ae, Or SOlld ; but the Specific 
 shows, besides these wavy tubes, rrravitv i<3 nnf n o-raof *a fKaf 
 numerous bone-cells, whose cana- g ravi py 1S not so g reat as tnat 
 
 licuii communicate with the tubes, of birds or mammals. The 
 
 as in many specimens of dentine. ^ boneg Q mogt of ^ 
 
 Chelonian reptiles are solid, but the long bones of the 
 extremities are either hollow or cancellated; the ribs of 
 the Serpent tribe are hollow, the medullary cavity per- 
 forming the office of an Haversian canal ; the bone-cells 
 are accordingly arranged in concentric circles around the 
 canal. The vertebras of these animals are solid ; and the 
 
BONE STRUCTURE. 719 
 
 bone, like that of some of the birds, is remarkable for ik 
 density and its whiteness. When a transverse section is 
 taken from one of the long bones, and contrasted with 
 that of a mammal or bird, we shall notice at once the 
 difference which the reptile presents : there are very few, 
 if any, Haversian canals, and these of large size ; and at 
 one view, in the section, fig. 347, we shall find the canals 
 and the bone-cells arranged both vertically and longi- 
 tudinally : the bone-cells are most remarkable for the 
 great size to which they attain ; in the Turtle they are 
 1-3 7 5th of an inch in length, the canaliculi are extremely 
 numerous, and are of a size proportionate to that of the 
 bone-cell. 
 
 In fishes we have a greater variation in^the minute 
 structure of the skeleton than in either of the three classes 
 already noticed. Of all the varieties of structure in the 
 bones of fishes, by far the greater number exhibit nothing 
 more than a series of ramifying tubes, like those of teeth ; 
 others exhibit Haversian canals, with numerous fine tubes 
 or canaliculi, like ivory tubes, connected with them ; a few 
 consist of Haversian canals, with fine tubes and bone- 
 cells, fig. 349; and a rare form, found only as yet in the 
 sword of the Swordfish (Ittiopkorus), exhibits Haversian 
 canals and a concentric laminated arrangement of the 
 bone, but no bone-cells. The Haversian canals, when 
 they are present, are of large size, and very numerous, and 
 then the bone-cells are, generally speaking, either absent 
 or but few in number; their place being occupied by 
 tubes or canaliculi, which are often of a very large size. 
 The bone-cells are remarkable for their graduate figure, 
 and the canaliculi which are derived from them are few in 
 number; they are seen to anastomose freely with the 
 canaliculi given off" from neighbouring cells; and if the 
 specimen under examination is a thin layer of bone, such 
 as the scale of an osseous fish, from the cells lying nearly 
 all in one plane, the anastomoses of the canalicali are 
 seen beautifully distinct. In the hard scales of many of 
 the osseous fishes, such as the Lepidosteus and Calicthys, 
 and in the spines of the Siluridce, the bone-cells are 
 beautifully seen ; in the true bony scales comprising the 
 exo-skeleton of the cartilaginous fishes, the bone-cells are 
 
720 THE MICROSCOPE. 
 
 to be seen in great numbers. In the spines of some of the 
 Ray family may be noticed a peculiar structure : the Haver- 
 sian canals are large and very numerous, and communi- 
 cating with each canal are an infinite number of wavy 
 tubes, which are connected with the canals in the same 
 manner as the dentinal tubes of the teeth are connected 
 with the pulp-cavity ; and if such a specimen were placed 
 by the side of a section of the tooth of some of the Shark 
 tribe, the discrimination of one from the other would be 
 no easy matter. In the spine of a Ray, fig. 352, the 
 analogy between bone and the ivory of the teeth is made 
 more evident ; for in this fish we have tubes, like those of 
 ivory, anastomosing with the canaliculi of bone-cells. 
 
 Now, if we proceed at once to the application of the 
 facts which have been laid down, and make a fragment of 
 bone of an extinct animal the subject of investigation; 
 we first find that the bone-cells in Mammalia are tolerably 
 uniform in size ; and if we take 1 -2,000th of an inch as a 
 standard, the bone-cells of birds will fall below that 
 standard; but the bone-cells of reptiles are very much 
 larger than either of the two preceding; and those of 
 fishes are so entirely different from all three, both in size 
 and shape, that they are not for a moment to be mistaken 
 for one or the other ; so that the determination of a minute 
 yet characteristic fragment of fishes' bone is a task easily 
 performed. If the portion of bone should not exhibit 
 bone-cells, but present either one or other of the characters 
 mentioned in a preceding paragraph, the task of discrimi- 
 nation will be as easy as when the bone-cells exist. We 
 have now the mammal, the bird, and the reptile to deal 
 with ; in consequence of the very great size of the cells 
 and their canaliculi in the reptile, a portion of bone of one 
 of these animals can readily be distinguished from that of 
 a bird or a mammal ; the only difficulty lies between these 
 two last : but, notwithstanding that on a cursory glance 
 the bone of a bird appears very like that of a mammal, 
 there are certain points in their minute structure in which 
 they differ ; and one of these points is in the difference ir 
 size of their bone-cells. To determine accurately, there- 
 fore, between the two, we must, if the section be a trans- 
 verse one, also note the comparative sizes of the Haversian 
 
FISH SCALES. 
 
 721 
 
 canals, and the tortuosity of their course ; for the diameter 
 of the canal bears a certain proportion to the size of the 
 bone-cells, and after some little practice the eye will 
 readily detect the difference. 
 
 A curious modification of horn is presented in the ap- 
 pendage borne by the Ehinoceros u-pon its snout, which 
 in many points resembles a bundle of hairs. When a 
 transverse section is made and viewed by polarised light, 
 each cylinder is seen to have 
 a cross diverging from a cen- 
 tral spot; the lights and 
 shadows of this cross are 
 replaced by bands of con- 
 trasted complementary co- 
 lours, if the selenite plate is 
 interposed (fig. 353). See 
 Plate VIII No. 178. ^ 
 bone is almost identical in light 
 structure, and is similarly affected by polarised light 
 
 A knowledge of the form and structure of scales of 
 fishes (fig. 354), like that of 
 teeth, has been "shown by 
 M. Agassiz to afford an uner- 
 ring indication of the particu- 
 lar class to which the fish may 
 belong : in the examination 
 of fossil remains, the appli- 
 cation of this knowledge has 
 been attended with extraor- 
 dinary results. As a class of 
 objects for the microscope, the 
 scales of fishes are exceedingly 
 curious and beautiful, especially 
 when mounted in fluid or 
 Canada balsam, and viewed by 
 polarised light Many are seen 
 best as opaque objects, and are 
 then mounted dry between 
 glasses. M. Agassiz divides the scales into four orders,, 
 which he names Placoid, Ganoid, Ctenoid, and Cycloid^ 
 in the first two the scales are more or less coated with 
 3 A 
 
 *** S! *.-Scaic of Sol*. 
 
722 THE MICROSCOPE. 
 
 enamel, in the others they are of a horny nature. To the 
 Placoid order belong the Skates, Dog-fish, Bay, and Sharks ; 
 cartilaginous fishes, having skins covered with small prickly 
 or flattened spines. To the Ganoid belong the Sturgeon, 
 Lepidosteus, Hassar-fish, and Polypterus ; fishes of this 
 order are more generally found in a fossil state, and the 
 scales are of a bony character. To the Ctenoid belong the 
 Pike, Perch, Pope, Basse, Weaver-fish, &c. ; their scales 
 are notched like the teeth of a cornb. To the Cycloid 
 belong the Salmon, Herring, Eel, Carp, Blenny, and the 
 majority of our edible fishes ; their scales are circular and 
 laminated. The scales of the Eel tribe are of an oval 
 figure, and are among the most remarkable that can be 
 selected for microscopic examination. To procure them, a 
 sharp knife must be passed beneath the epidermal layer, 
 and a portion of it raised, in a similar manner as directed 
 for tearing off the cuticle from plants : after a few trials 
 some will be detached. They are of an oval figure, rather 
 softer than the scales of other fishes, and in some parts of 
 the skin do not form a continuous layer. When the skin 
 has been stripped off, previous to the fish being cooked, 
 the scales can be obtained from the under surface, with a 
 knife or pair of forceps. The scales of the viviparous 
 Blenny are of a circular figure, situated under the epider- 
 mal layer ; they were described by Mr. Yarrell as mucous 
 glands, from their figure and small number. The surface 
 of the skin of this fish, when fresh, appears to be covered 
 with follicles ; if, however, a portion be scraped off, it will 
 be found to be a mass of delicate circular scales. A piece 
 of the skin, when dried, exhibits the scales to great 
 advantage, and, like those of the Eel, are beautiful objects 
 for polarised light. The prismatic colours exhibited by 
 fish are said to be due to the presence of fatty matter in 
 the skin; but the beautiful metallic tints displayed by 
 so many of them are rather due to the numerous micro- 
 scopic plates, or scales, distributed over its surface. 
 
 Having thus brought our brief examination of a few of 
 the more important structures of the animal economy to 
 a close, it only remains for us to express a hope that it 
 will be found to smooth the way, or in some degree assist 
 the investigations of the student to a better and more 
 
ERRORS OF INTERPRETATION. 723 
 
 general survey of the whole fabric. Such a survey will 
 not be unattended with its difficulties and disappoint- 
 ments, but it will bring its own reward for any amount 
 of labour bestowed. To the medical student, desirous 
 of obtaining further information in his especial depart- 
 ment of microscopy, we recommend Dr. Beale's book 
 on " The Microscope, and its Application to Clinical 
 Medicine." 1 
 
 The importance of becoming thoroughly familiar with 
 the structural and microscopical characters of any par- 
 ticular organ in a healthy condition, cannot be too strongly 
 urged upon the attention of the student ; as to a want of 
 this knowledge must be attributed many erroneous de- 
 scriptions of morbid appearances. All who wish to use 
 the microscope successfully, with reference to the exami- 
 nation of organs in a diseased state, will do well to 
 acquaint themselves with minute anatomy generally, not 
 only of the human subject, but of the lower animals ; 
 without such knowledge it will be found impossible to 
 study pathology, or prosecute pathological inquiries with 
 any degree of success. 
 
 A large amount of wrong observation has been recorded 
 on cells and cellular structures : since Schwann announced 
 his "cell theory," almost everything round has been 
 regarded as a cell ; any single body within this, or where 
 there are several, the largest, has been regarded as a 
 nucleus, and any spot within the nucleus has been viewed 
 as a nucleolus. Whereas many of the so-called cells are 
 homogeneous spheres ; many of the nuclei are vacuoles, 
 and so forth. 
 
 Such errors are natural, at first inevitable ; they can be 
 corrected only by practice, by testing observations in other 
 ways, especially by chemical re-agents, and by comparison 
 with the observations of others. " The marvel is not that 
 the microscope should suggest false views do not our 
 eyes play us that trick? but that it should reveal so 
 many astounding facts as it really does ; and the one con- 
 
 (1) The Cyclopcedia of Anatomy and Physiology will be found a most valuable 
 book of reference for the student in all matters relating to physiology and 
 minute anatomy. Numerous valuable papers are distributed throughout the 
 Trans, of the Royal Micros. Soc. : Huxley's Lectures on Comparative Anatomy ; 
 Owen's Lectures on Comparative Anatomy ; Carpenter's Physiology, edited by H, 
 Power, and Kolliker's Manual of Human Microscopic Anatomy. 
 
 3 A2 
 
724 THE MICROSCOPE. 
 
 solatory reflection which accompanies the difficult task of 
 microscopic investigation is the unanimity which now 
 reigns among observers on so vast a "body of observations. 
 If we read in physiological works of the yolk cells and 
 coloured oil globules of the yolk, and the beautiful 
 function of assimilation which has been attributed to 
 them, they exist but in the imagination of the authors 
 who have regarded the one as cells simply because they 
 are round, and the other as consisting of fat because they 
 are highly refractive, such errors of interpretation do- 
 not discredit it any more than the mis-interpretations, 
 which have helped to make Ehrenberg's name at once 
 famous and suspicious, alter the facts which he saw, and 
 could not rightly interpret. In truth, the eye is only 
 a preliminary instrument in science. "What we see has to 
 be interpreted ; and, as it is very difficult to confine our- 
 selves to pure observation unmixed by hypothetical inter- 
 pretation, we need many collateral confirmations." 
 
 The principal physical characters to be regarded in micro- 
 ecopic examinations may be summed up as follows : 
 
 1. Shape. Accurate observation of the shape of bodies 
 is very necessary, as many are distinguished by this phy- 
 sical property. Thus the human blood-globules present 
 a round biconcave disc, and are in this respect different 
 from the oval corpuscles of birds, reptiles, and fishes. 
 The distinction between round and globular is very requi- 
 site. Human blood corpuscles are round and flat; but 
 they become globular on the addition of water. Minute 
 structures seen under the microscope may also be likened 
 to the shape of well-known objects, such as that of a pear, 
 balloon, kidney, heart, &c. 
 
 2. Colour. The colour of structures varies greatly, and 
 often differs under the microscope from what was pre- 
 viously conceived regarding them. Thus the coloured 
 corpuscles of the blood, though commonly called red, are, 
 in fact, yellow. Many objects present different colours, 
 according to the mode of illumination ; that is, as the light 
 is reflected from or transmitted through their substance, as 
 in the case of certain scales of insects, feathers of birds, &c. 
 Colour is often produced, modified, or lost, by re-agents ; 
 AS when iodine comes in contact with starch-granules, when 
 
ANIMAL STRUCTURES MODE OP INVESTIGATING. 725 
 
 nitric acid is added to chlorophyle, or chlorine-water to the 
 pigment-cells of the choroid, and so on. 
 
 3. Edge or Border. This may present peculiarities 
 worthy of notice. Thus, it may be dark and abrupt on the 
 field of the microscope ; so fine as to be scarcely visible ; 
 or it may be smooth, irregular, serrated, beaded, &c. 
 
 4. Size. The size of the minute bodies, fibres, or tubes, 
 which are found in the various textures of animals, can 
 only be determined with exactitude by actual measure- 
 ment. It will be observed, for the most part, that these 
 minute structures vary in diameter ; so that when their 
 medium size cannot be determined, the variations in size 
 from the smaller to the larger should be stated. Human 
 blood-globules in a state of health have a pretty general 
 medium size, and these may consequently be taken as a 
 standard with advantage, and bodies described as being two, 
 three, or more times larger than this structure ; or all may 
 be measured with a micrometer, as explained at page 51. 
 
 5. Transparency. This physical property varies greatly 
 in the ultimate elements of numerous textures. Some 
 corpuscles are quite diaphanous ; others are more or less 
 opaque. The opacity may depend upon corrugation or 
 irregularities on the external surface, or upon contents of 
 different kinds. Some bodies are so opaque as to prevent 
 the transmission of the rays of light ; in this case they 
 look black when seen by transmitted light, though white 
 if viewed by reflected light ; others, such as fatty particles 
 and oil-globules, refract the rays of light strongly, and 
 present a peculiarly luminous appearance. 
 
 6. Surface. Many textures, especially laminated ones, 
 present a different structure on the surface from that 
 which exists below. If, then, in the demonstration, these 
 have not been separated, the focal point must be changed 
 by means of the fine adjustment. In this way the capil- 
 laries in the web of the Frog's foot may be seen to be 
 covered with an epidermic layer, and the cuticle of certain 
 minute -Fungi or Infusoria to possess peculiar markings. 
 Not unfrequentiy, the fracture of such structures enables 
 us, on examining the broken edge, to distinguish the dif- 
 ference in structure between the surface and the deeper 
 layers of the tissue under examination. 
 
726 THE MICROSCOPE. 
 
 7. Contents. The contents of those structures which 
 consist of envelopes, as cells, or of various kinds of tubes, 
 are very important. These may consist of included cells or 
 nuclei, granules of different kinds, pigment matter, or 
 crystals : a fair illustration of the changes effected by dis- 
 ease is given in fig. 256, from a cyst in a diseased liver : 
 occasionally their contents present definite moving cur- 
 rents, as in the cells of some vegetables ; or trembling 
 rotatory molecular movements, as in the ordinary globules 
 of saliva in the mouth. 
 
 8. Effects of Re-agents. These are most important in 
 determining the structure and chemical composition of 
 numerous tissues. Thus water generally causes cell-for- 
 mations to swell out from endosmosis ; while syrup, gum- 
 water, and concentrated saline solutions, cause them to 
 collapse from exosmosis. Acetic acid possesses the valu- 
 able property of dissolving coagulated albumen, and in 
 consequence renders the whole class of albuminous tissues 
 more transparent. Thus it operates on cell-walls, causing 
 them either to dissolve, or become so thin as to display 
 their contents more clearly. Ether, on the other hand, 
 and the alkalies, operate on fatty compounds, causing their 
 solution and disappearance. The mineral acids dissolve 
 most of the mineral constituents that are met with ; so 
 that in this way we are enabled to tell with tolerable cer- 
 tainty, at all events, the group of chemical compounds to 
 which any particular structure may be referred. 
 
 Many, if not all, animal structures require examination 
 in several ways before an accurate idea of their general 
 structure can be obtained. It is of much importance 
 to examine a body by reflected light, transmitted light, 
 and by polarised light ; when immersed in water, or in a 
 highly refracting fluid, such as glycerine, oil, turpentine, 
 and Canada-balsam ; with a cover and without a cover, 
 with the application of distilled water and of chemical 
 re-agents. The most scrupulous cleanliness must always 
 be observed in microscopical examinations ; many errors 
 have arisen in consequence of a want of sufficient care not 
 having been taken to prevent the admixture of various 
 accidental substances. The better way of avoiding errors 
 from this cause is to become familiar with the characters 
 
ANIMAL STRUCTURES MODE OF INVESTIGATING. 727 
 
 of common substances which are likely to be mixed up 
 with preparations, as the following: oil globules, air 
 bubbles, portions of worsted, cotton, and linen, silk and 
 wool fibres, hairs from plants, vegetable tissues, human 
 hair, portions of feathers, and the starches wheat and 
 potato starch from bread crumbs. In taking fluids from 
 bottles and vessels, the possibility of mixing small portions 
 of their contents must be avoided ; the pipette should be 
 washed immediately after it has been used. Another 
 fallacy arises from the great transparency of some struc- 
 tures ; a membrane may appear perfectly clear and trans- 
 parent when in reality it is covered with a delicate layer 
 of epithelium, which only becomes visible after the appli- 
 cation of some chemical re-agent ; on the other hand, by 
 the action of re-agents, a fibrous appearance is produced. 
 Acetic acid, when added to many preparations, frequently 
 produces a swelling of the tissue, which looks like base- 
 ment membrane, but which in reality has been formed by 
 the action of the acid. The mechanical pressure of the 
 thin glass, if pressed down tightly, alters structures very 
 much; the appearance of the blood discs are, at times, 
 much distorted in this way, and lead to false conclusions 1 
 and erroneous descriptions. 
 
 Should it be desirable to make an examination of the 
 vital fluid, blood, the smallest drop, caused by the prick of 
 a fine needle, may be placed on a strip of glass, and waved 
 backwards and forwards, that the blood may dry as quickly 
 as possible ; in this way the corpuscles or blood-discs 
 retain their form ; and if the preservation of the specimen 
 is wished, a thin glass cover carefully placed over it, asd. 
 cemented down, in the way directed at page 217. 
 
 To the advanced observer, the examination of the mucous 
 membrane will afford some instruction. Should the speci- 
 men be small, it will be better to pin it to a piece of cork; 
 then well wash it by means of a small syringe. If the 
 investing epithelium is required for examination, a por- 
 tion can be detached from the surface by a knife ; when 
 placed on a glass slide, add a drop of iodine solution, then 
 view it with a J-inch power. Villi and papilla? are best 
 made out in injected specimens, as will be seen on reference 
 to Plate VII. 
 
CHAPTER VI. 
 
 THE MINERAL KINGDOM. 
 UfOBGANIC MATTEB FORMATION OF CRYSTALS POLABISATIOW, BTO. 
 
 our meagre search through organic nature 
 we met with an endless variety of beautiful 
 and instructive materials for the employment 
 of the microscope. If we now turn our atten- 
 tion to the inorganic or mineral kingdom we 
 shall find a vast storehouse filled with objects 
 of unsurpassed interest to the microscopist. 
 In the examination of the many beautiful 
 forms presented to us in the phenomena of crystallisation, 
 and the study of the varied chemical combinations, the 
 student will discover a never-ending source of useful occu- 
 pation. 
 
 We are as yet in great ignorance of the manner in 
 which the majority of crystals belonging to the mineral 
 kingdom are formed : we know, however, that very few can 
 be reproduced by the chemist. But, although ignorant of 
 the means whereby the great majority of crystals have 
 been formed in the vast laboratory of nature, we can 
 crystallise an immense number of substances, watch their 
 numerous intricate modes of formation, and that in the 
 smallest appreciable quantities, when aided by the micro- 
 scope. Among natural crystals those employed in the 
 formation of rocks open up a wide field to our view. The 
 varieties of granites present us with the earliest crystal- 
 lised condition of the earth's crust as it cooled down, the 
 structure of which is beautifully exhibited under polarised 
 light. Plate VIII. No. 160, is a section of a 
 
FORMATION OP CRYSTALS. 
 
 729 
 
 shown on a red selenite ground. Crystallisation under a 
 somewhat different condition and combination is seen in 
 the New Red Sandstone, No. 158. 
 
 The prismatic rings of another crystalline substance, 
 Quartz, represented in No. 159, possess great interest. 
 Again, that of Arragonite, Tremolite, and Carbonate of 
 Lime. The latter is frequently seen in combination with 
 animal structure, and is then productive of many re- 
 markable changes and modifications, such as we have 
 represented in Plate VIII. Nos. 171, 172, 175, and 180, 
 all of which should be prepared for examination with as 
 well as without the polariscope. 
 
 The formation of artificial crystal may be readily 
 effected, and the process watched, under the microscope, by 
 simply placing a drop of a saturated solution of any salt 
 upon a previously warmed slip of glass. The following 
 list of salts and other substances form a beautiful series 
 of objects for polarised light : 
 
 Alum. 
 Asparagine. 
 
 Aspartic Acid. Plate VIII. No. 168. 
 Bitartrate of Ammonia. 
 Boracic Acid. 
 
 Borax. Plate VIII. No. 164. 
 Carbonate of Lime. 
 Soda. 
 
 Chlorate of Potash. 
 Chloride of Barium. 
 Cobalt. 
 Copper and Ammonia. 
 
 Sodium. 
 Cholesterine. 
 Chromate of Potash. 
 Cinchonine. 
 Cinchonidine. 
 Citric Acid. 
 Hippuric Acid. 
 Iodide of Mercury. 
 
 Potassium. 
 
 ,, Quinine, 
 lodo-disulphate of Quinine. 
 Murexide. 
 Nitrate of Bismuth. 
 
 Barytes. 
 Brucine. 
 
 ,, Strontian. 
 Uranium. 
 Ozalate of Ammonia. 
 Chromium. 
 
 Chromium and Potash. 
 Lime. 
 8od. 
 
 Oxalic Acid. 
 
 Oxalurate of Ammonia. 
 
 Permanganate of Potash. 
 
 Phosphate of Lead and Soda. 
 
 Platino-cyanide of Magnesia. 
 
 Plumose Quinidine. 
 
 Prussiate of Potash, red and yellow. 
 
 Quinidine. 
 
 Santonine. 
 
 Salicine. 
 
 Salignine. Plate VRL No. 162. 
 
 Sulphate of Cadmium. 
 
 Copper. 
 
 Copper and Potash. 
 Sulphate of Iron. 
 
 Iron, Cobalt, and Nickel 
 
 Magnesia. 
 
 Nickel and Potash. 
 
 Soda. 
 
 Zinc. 
 Sugar.' 
 
 Tartaric Acid. 
 Thionurate of Ammonia. 
 Triple Phosphate. 
 Urate of Ammonia. 
 
 Soda. 
 
 Urea, and all the urinary deposit*. 
 Uric Acid. 
 
 MINERALS. 
 
 Agates, various. 
 Asbestiform Serpentine* 
 Avauturine. 
 Carbonate of Lime. 
 Carrara Marble. 
 
730 
 
 THE MICROSCOPE. 
 
 Indurated Sandstone, Howth. 
 
 Indurated Sandstone, Bromsgrove. 
 
 Gibraltar rock. 
 
 Granite, various localities. No. 160. 
 
 Hornblend Schist. 
 
 Labrador Spar. 
 
 Norway Rock. 
 
 Quartz Rock, various. No. 159. 
 
 ,, in Bog Iron Ore. 
 
 Quartzite, Mont Blanc. 
 Sandstone, Plate VIII. No. 158. 
 Satin Spar. 
 
 Selenites, various colours. 
 Tin Ore, with Tourmalin. 
 
 VEGETABLE SUBSTANCES. 
 
 CUTICLE of Leaf of Correa Cardinalis, 
 Dentzia scabra. 
 
 PL VIII. No. 173. 
 Elseagnus. 
 
 ,, Onosma taurica. 
 
 Equisetum. No. 174. 
 
 Fibro cells from orchid. No. 169. 
 Oncidium bicallosum. 
 
 Scalariform vessels from Fern. 
 
 ScyUium. No. 177. 
 
 SILICIOUS CUTICLES. Various. 
 
 Starch. Various. No. 167. 
 
 Very interesting results will be obtained by combining 
 two or more chemical salts. Mr. Davies 1 succeeded in 
 forming numerous beautiful double salts in the following 
 manner. To a nearly saturated solution of the sulphate 
 of copper and sulphate of magnesia add a drop, on the 
 glass-slide, and dry quickly. To effect this, heat the 
 slide so as to fuse the salts in its water of crystallisation, 
 and there remains an amorphous film on the hot glass. 
 Put the slide aside and allow it to cool slowly ; it will 
 gradually absorb a certain amount of moisture from, the 
 air, and begin to throw out crystals. If now placed 
 under the microscope, numerous points will be seen to 
 start out here and there. The starting points may be 
 produced at pleasure by touching the film with a fine 
 needle point, so as to admit of a slight amount of moisture 
 being absorbed by the mass of salt. Development is at 
 once suspended by applying gentle heat; cover the 
 specimen with balsam and thin glass. The balsam should 
 completely cover the edges of the thin glass circle, other- 
 wise moisture will probably insinuate itself, and destroy 
 the form of the crystals. 
 
 Mr. Thomas succeeded in crystallising " the salts of 
 the magnetic metals " at very high temperatures, which 
 gave interesting results, and produced curious forms of 
 crystals. Plate VIII. No. 163 are representations of 
 crystals of sulphate of iron and cobalt, No. 165, of nickel 
 and potash, obtained in the following manner : To form 
 the sulphate of iron crystal, add to a concentrated solution 
 of iron a small quantity of sugar, to prevent oxidation. 
 Put a drop of the solution on a glass slide, and drive out the 
 
 (1) Quart. Jonrn. Micros. Scieti., vol. ii. p. 128. 1862. 
 
SUBLIMATION OF ALKALOIDS. 73 i 
 
 water of crystallisation as quickly as possible, by the 
 aid of a spirit lamp ; then with a Bunseu's burner bring 
 the plate to a high temperature. Immediately a remark- 
 able change is seen to take place in the form of the crystal, 
 and if properly managed the " foliation " represented in 
 the plate will be fairly exhibited. The slide must not be 
 allowed to cool down too rapidly or the crystals will 
 probably absorb moisture from the atmosphere, and in so 
 doing the crystals alter their forms. Immerse them in 
 balsam, and cover in the usual way before quite cold. 
 
 Sublimation of Alkaloids. Dr. Guy a few years ago 
 directed the attention of microscopists to the fact that the 
 crystalline shape of bodies belonging to the inorganic 
 world might lead to their detection. Subsequently, Dr, 
 A. Helwig, of Mayence, took the matter up, and showed 
 that the plan was applicable not only to inorganic but also 
 to organic substances, and especially to the poisonous alka- 
 loids. By improving on Dr. A. Hel wig's process, and 
 substituting a bit of porcelain, Dr. Guy has been able to 
 watch the process more minutely, and to regulate it more 
 exactly. He has by this means been able to obtain 
 characteristic crusts composed of crystals of strychnine 
 weighing not more than l-3,000th or 1 -5,000th of a grain. 
 Morphia gives equally characteristic results. For the 
 examination of these, Dr. Guy recommends the use of a 
 binocular microscope with an inch object-glass. But it is 
 not to crystalline forms alone that one need trust; the 
 whole behaviour of a substance as it melts and is converted 
 into vapour is eminently characteristic, and when once 
 deposited on the microscopical slide, under the object- 
 glass, the application of re-agents may give still more satis- 
 factory results. The re-agents, however, which are here to 
 be applied are not of the kind ordinarily employed. Colour- 
 tests under the microscope are, comparatively speaking, 
 useless : those that give rise to peculiar crystalline forms 
 are rather to be sought after. For instance, the crystals 
 produced by the action of carbazotic acid on morphia are 
 by themselves almost perfectly characteristic. These ex- 
 periments should not, however, be undertaken for medico- 
 legal purposes by one unskilled in their conduct, for the 
 effects of the re-agents themselves might be mistaken by 
 
732 THE MICROSCOPE. 
 
 the uninitiated for the result of their action on the sub- 
 stances under examination. 
 
 Dr. Guy's 1 method of procedure is as follows : " Pro- 
 vide small crucibles, covers, slabs, or fragments of white 
 porcelain ; a few microscopic cell-glasses, with a thickness 
 of about one-eighth of an inch and a diameter of circle of 
 about two-thirds of an inch : and discs of window-glass 
 about the size of a shilling. Place the porcelain slab on 
 the ring of a retort-holder or other convenient support ; 
 then the glass cell ; and upon the porcelain in the centre 
 of the cell a minute portion of the alkaloid or other white 
 powder, or crystal reduced to powder ; then pass the clean 
 glass dish through the flame of the spirit-lamp till the 
 moisture is driven off, and adjust it with the forceps over 
 the glass ring ; now apply the flame of the spirit-lamp to 
 the porcelain, underneath the powder or crystal, and con- 
 tinue the heat till the powder undergoes its characteristic 
 change and gives off vapour. Watch the deposit of this 
 vapour on the glass dish, and remove the spirit-lamp, 
 either directly or after a short interval, as experience may 
 determine. 
 
 " The white surface of porcelain being visible through 
 the glass disc, as through a window, the behaviour of 
 the substance under examination is easy to observe. It 
 may be driven off without undergoing change or leaving 
 residue, and the disc may be covered with crystals, as 
 happens with arsenious acid, or with an amorphous 
 sublimate, as happens with calomel ; it may coalesce, 
 throw out long silky crystals, to be gradually transferred 
 as crystals to the glass disc, as is the case with corrosive 
 sublimate; and it may melt, with or without previous 
 change of colour, retain or shift its place, deposit carbon 
 more or less abundantly, and yield a sublimate of detached 
 crystals (veratrine), twigs (solanine), tufts (meconine), 
 branching patterns (strychnine, morphine, cryptopia, &c.), 
 watered patterns with or without crystalloids (several alka- 
 loids and glucosides), the melting and deposition of carbon 
 being a common property of the alkaloids and of some 
 analogous active principles. 
 
 (1) Dr. W. A. Guy, P.B.S. &c. on the "Sublimation of the Alkaloids." 
 Pharmaceutical Journal, June and August, 1867. Micros. Jour. Dec. 1867 
 
SUBLIMATION OP ALKALOIDS. 733 
 
 "The principal precaution to be observed in the 
 application of heat is, that it should be moderate and 
 gradual. It is best to act on the assumption that the 
 substance under examination may be one of a considerable 
 group of bodies, some of which sublime at very moderate 
 temperatures. The spirit-lamp should, therefore, be placed 
 at first three or four inches below the slab of porcelain, so 
 that the point of its flame may not touch it ; and if, under 
 this low temperature, the disc of glass is not dimmed, the 
 lamp should be raised by degrees till the mist makes its 
 appearance. Then, as a general rule, the lamp should be 
 withdrawn, the disc removed, and a new one put in its 
 place. It may be well to state that, as the disc has been 
 passed through the flame to drive off moisture, and has in 
 this way been heated, the flame of the spirit lamp should 
 not be allowed to play on the porcelain slab after the mist 
 has appeared on the disc, at least not for any length of 
 time ; for, if this precaution be neglected, it may happen 
 with the alkaloids as with arsenious acid or corrosive sub- 
 limate, that the mist does not form at all, or that it is 
 driven off as soon as it is deposited. Perhaps, too, it may 
 not be quite unnecessary to recommend that each disc of 
 glass, as it is removed, should be placed with the subli- 
 mate upwards against a glass slide or fragment of porcelain ; 
 and that in this position (sublimate upwards) it should be 
 retained. If this very simple precaution be overlooked, it 
 is quite possible that we may mistake one surface for th<3 
 other, and find ourselves applying our re-agents to the 
 wrong one. The chief precaution relating to the ex- 
 amination and disposal of the sublimates consists in 
 measures for preserving their identity during the examina- 
 tion to which we may have to subject them. This is best 
 done by writing the names and that of the reagents on 
 discs of paper, and placing paper and disk together in 
 sunken grooves or circular spaces. 
 
 " As a precaution omitted by an experimenter so prac- 
 tised as Dr. Helwig is very likely to be overlooked by 
 others, it is well to insist upon and to prescribe as the 
 first step to be taken with a crystalline solution which wo 
 are about to use as a test, the determination of its proper 
 crystalline form or forms as evaporated on a flat surface of 
 
734 THE MICROSCOPE. 
 
 glass. Another mistake, arising out of a similar want of 
 caution, may consist in confounding the effect of some 
 saline re-agent with that of the water which holds it in 
 solution. 
 
 " Now these remarks have a direct practical bearing on 
 the selection of tests. A preference ought to be given to 
 re-agents which leave no residue of their own : to distilled 
 water, to alcohol, ether, chloroform, benzole, and fusel oil ; 
 and to acetic acid and the dilute mineral acids. Then 
 those salts should be preferred of which the solutions 
 yield dry residues of one or two definite forms, not such as 
 put on many different shapes, are deliquescent themselves, 
 and are likely to leave moist and unstable compounds. 
 Nor is the strength of the solution a matter of little or no 
 importance ', for it should be borne in mind that the sub- 
 limates to which we apply them contain very minute frac- 
 tions of a grain; and that a very strong solution, after 
 acting on this minute quantity, would leave a coarse 
 deposit of its own, both over the general surface and at 
 the margin of the spot, which, blending with the reaction, 
 would obscure and confuse it. As a general rule, there- 
 fore, solutions of a moderate strength are to be preferred, 
 'Mich as 1 grain of carbazotic acid to 250 of water, and 1 
 grain of bichromate of potash to 100, the same of the red 
 prussiate of potash, and of the nitro-prusside of sodium." 
 
 Other than the alkaloids and volatile metallic poisons 
 were found to yield sublimates when heated, as urea, 
 uric acid, hippuric acid, alloxan, uramile, &c.; but these 
 results scarcely prepared one to expect a sublimate from a 
 blood-stain. Yet, on separating the fibres of a small spot 
 of a cotton texture stained with blood about twenty-five 
 years since, and submitting a section of the fibre an eighth 
 of an inch long to heat, a figured pattern of the colour of 
 blood was obtained, such as might be caused by a solution 
 of blood in some thin oily liquid : this figured pattern was 
 surrounded by a colourless border, having bright figured 
 patterns such as those which mark the less characteristic 
 portions of crystalline sublimates. Dr. Guy, on repeating 
 his experiments, found the results constant ; and on con- 
 ducting them with care, and under the guidance of micro- 
 scopic examinations, two sublimates were uniformly ob- 
 
SPECTRUM ANALYSTS. 735 
 
 tained, the first colourless and apparently crystalline, the 
 second, under a high temperature, of the colour of the 
 blood-stain from which it was procured, and of the figured 
 pattern mentioned. 
 
 Mr. Sorby's attention has been directed to obtain a defi- 
 nite method of qualitative analysis of "animal and vegetable 
 colouring matters," and of animal substances generally, by 
 means of the spectrum microscope. He has also so com- 
 bined the spectroscope with the binocular microscope as 
 to make it available for the purpose of distinguishing 
 minute portions of coloured minerals in thin sections of 
 rocks and meteorites. He employs an ordinary large 
 binocular microscope, with an object-glass of about three- 
 inches focal length, corrected for looking through glass an 
 inch thick ; the lenses being at the top, and as far as pos- 
 sible from the slit. This objective is placed at the focus, 
 and between it and the lenses, at a distance of about half 
 an inch from them, is a compound prism, composed of a 
 rectangular prism of flint-glass and two of crown-glass, of 
 about 61, one at each end. This arrangement gives direct 
 vision and a spectrum of a suitable size for these inquiries, 
 since a wide dispersion often produces indistinctness of 
 the absorption bands. That we may have the opportunity 
 of comparing two spectra side by side, a small rectangular 
 prism is fixed over half the slit, and with the acute angle 
 parallel to it and passing beyond it 1 
 
 " This gives an admirable result, the only defect being 
 that, when the spectra are in focus, their line of junction 
 is some distance within it ; and therefore to correct this 
 employ a cylindrical lens of about two feet focal length, 
 with its axis in the line of the slit, which can easily be 
 fixed at such a distance between the slit and the prisms 
 as to bring the spectra and their line of contact to the 
 same focus. In front of the slit, close to the small rectan- 
 gular prism, is a stop with a circular opening, to shut out 
 lateral light, and a small achromatic lens of about half 
 an inch focal length, which gives a better field, and 
 counteracts the effect of the concave surface of the liquid 
 in the tubes used in the experiments, if they are not 
 
 (1) Mr. Sorby's prisms and their arrangement have been entrusted to Mr. 
 Browning's skilful hands, who Ls prepared to adapt them to any microscope. 
 
736 THE MICROSCOPE, 
 
 quite full. These are cut from barometer-tubes, having 
 an internal diameter of about one-seventh of an inch, and 
 an external diameter of about three-sevenths of an inch. 
 They are made half an inch long, ground flat at each end, 
 and fixed with Canada balsam on slips of glass two inches 
 long and about six-tenths of an inch wide, so that the 
 centre of the tube is about one-fourth of an inch from 
 one edge. By this arrangement the liquid may be 
 examined through the length of the tube by laying the 
 slip of glass flat on the stage of the microscope, or through 
 the side of the tube, by placing the slip vertical and the 
 tube horizontal. Cells of this size can be turned upside 
 down and deposits removed without any liquid being 
 lost ; and the upper surface of the liquid is sufficiently 
 flat, even when inclined at a considerable angle. If 
 requisite, small bits of thin glass can be laid on the top, 
 which are held on by capillary attraction, or fastened 
 on with gold-size, if it be desirable to keep the solution 
 for a longer time. When the depth of colour is too great 
 in the line of the length of the cell, we can at once see 
 what would be the effect of about one-fourth of the colour 
 by turning it sideways ; and thus we can save much time, 
 and quickly ascertain what strength of solution would 
 give the best result. Very frequently an excellent 
 spectrum is obtained in one direction with one reagent, 
 and in the other with another, without further trouble. 
 
 " The scale of measurement consists of two small JSTicoPs 
 prisms, and an intermediate plate of quartz. If white 
 light, passing through two such prisms, without the plate 
 of quartz, be examined with the spectrum-microscope, it 
 of urse gives an ordinary continuous spectrum ; but if 
 we place between the prisms a thick plate of quartz or 
 self aite, with its axis at 45 to the plane of polarisation, 
 th< tfgh no difference can be seen in the light with the 
 naksd eye, the spectrum is entirely changed. The light is 
 still white, but it is made up of alternate black and 
 coloured bands, evenly distributed over the whole spec- 
 trum. The number of these depends on the thickness of 
 the depolarising plate, so that we may have, if we please, 
 almost innumerable fine black lines, or fewer broader 
 bands, black in the centre and shaded off at each side. 
 
SPECTRUM ANALYSIS. 737 
 
 These facts are of course easily explained by the inter- 
 ference of waves. It would be impossible to have a mope 
 convenient or suitable scale for measuring the spectra of 
 coloured solids and liquids. If we use a micrometer in 
 the eyepiece, an alteration in the width of the slit modifies 
 the readings, and the least movement of the apparatus 
 may lead to error, whereas this scale is not open to either 
 objection. Besides this, the unequal dispersion of the 
 spectrum makes the blue end too broad, so that a given 
 width, as measured with a micrometer in the eyepiece, 
 is not of the same optical value as the same width in 
 the red. The divisions in the interference- spectrum 
 bear, on the contrary, the same relation to the length, 
 of the waves of light in all parts of the spectrum, and 
 no want of adjustment in the instrument alters their 
 position. As will be seen from the diagram (fig. 355), 
 the unequal dispersion makes the distance between the 
 bands in the blue about twice as great as in the 
 red. The perfection of a spectrum would be one in 
 which they were all at equal intervals ; but possibly 
 no such uniform dispersion could be produced. By 
 having a direct-vision prism, composed of one of flint- 
 glass of 60, and two of crown-glass of suitable angle, we 
 can place it over the eyepiece, and can diminish the 
 dispersion at the blue end, or increase that at the red end, 
 by turning it in one position or the other, and thus see 
 either end to the greatest advantage. 
 
 " Since the number of divisions depends on the thick- 
 ness of the interference-plate, it became necessary to decide 
 what number should be adopted. Ten it was thought 
 would be most suitable ; but, on trying, it appeared to be 
 too few for practical work. Twenty is too many, since it 
 then becomes extremely difficult to count them. Twelve 
 is as many as can be easily counted ; it is a number easily 
 remembered, gives sufficient accuracy, and has a variety of 
 other advantages. With twelve divisions the sodium-line 
 P comes very accurately at 3 ; and thus, by adjusting the 
 plate so that a bright sodium-light is hid in the centre of 
 the band, when the Nicol's prisms are crossed, it is accu- 
 rately at 3J, when they are arranged parallel, so as to give 
 a wider field. The general character of the scale will 
 Si 
 
738 THE MICROSCOPE. 
 
 be best understood from the following figure, in which 
 the bands are numbered, and given below the principal 
 Fraunhofer lines. The centre of the bands is black, and 
 
 0123456 78 9 10 11 12 
 
 < ' IIIHltlUlll < ? 
 
 Fig. 355. A BCD m b F o 
 
 they are shaded off gradually at each side, so that the 
 shaded part is about equal to the intermediate bright 
 spaces. Taking, then, the centres of the black bauds as 
 1, 2, 3, &c., the centres of the spaces are 1J, 2J, 3| y &c., 
 the lower edges of each f , If, &c., and the upper 1J, 2J, 
 &c., we can easily divide these quarters into eighths by 
 the eye ; and this is as near as is required in the sub- 
 ject before us, and corresponds as nearly as possible to 
 1-1 00th part of the whole spectrum, visible under ordinary 
 circumstances by gaslight and daylight. Absorption-bands 
 at the red end are best seen by lamplight, and those at the 
 blue end by daylight. 
 
 On this scale the position of some of the principal lines 
 of the solar spectrum is about as follows : 
 
 A f B 1J C 2| D 3i 
 
 E 5^ b 6^ F 7 G 10$ 
 
 At first plates of selenite, which are easily prepared, 
 were used, because they can be split to nearly the re- 
 quisite thickness with parallel faces ; but its depolarising 
 power varies so much with the temperature, that even 
 the ordinary atmospheric changes alter the position of the 
 bands. However, quartz cut parallel to the principal 
 axis of the crystal is so slightly affected in this manner 
 as not to be open to this objection, but is prepared with 
 far greater difficulty. The sides should be perfectly 
 parallel, the thickness about '043 inch, and gradually 
 polished down with rouge until the sodium-line is seen in 
 its proper place. This must be done carefully, since a 
 difference of 1-1 0,000th inch in thickness would make it 
 decidedly incorrect. 
 
 The two Nicol's prisms and the intervening plate are 
 mounted in a tube, and attached to a piece of brass in such 
 
SPECTRUM ANALYSIS. 739 
 
 a manner that the centre of the aperture exactly corre- 
 sponds to the centre of any of the cells used in the experi- 
 ments, which are all made to correspond in such a manner 
 that any of them, or this apparatus, may be placed on the 
 stage and be in the proper place without further adjust- 
 ment, which, of course, saves much time and trouble. 1 
 
 In the preparation of vegetable colouring matters foi 
 the spectroscope, care must be taken to employ a small 
 quantity of spirits of wine ; filter the solution, and 
 evaporate it at once to dryness at a very gentle heat, 
 otherwise if we attempt to keep the colouring matters in 
 a fluid state they quickly decompose. It is necessary to 
 employ various reagents in developing characteristic spectra. 
 The most valuable reagent is sulphite of soda, which 
 admits of the division of colours into groups. Of the 
 mode of applying reagents, ample directions are given. 
 
 Mr. Sorby's qualitative analysis is just the kind of thing 
 to employ in detecting adulterations in many substances met 
 with in commerce, as well as in inquiries where very small 
 quantities of material are at command. By this method 
 we might be able in a few minutes to form a very satisfac- 
 tory opinion, or at least one that might meet all practical 
 requirements, and narrow the inquiry to a surprising 
 extent ; if this can be said even now, surely further re- 
 search cannot fail to make it most useful in cases where 
 ordinary chemical analysis would be of little or no use ; 
 for in this way we may be able to detect the presence 
 of chlorophyll in some of the lower animal forms; as 
 the amoeba, hydra, &c., or, on the other hand, the red 
 colouring matter of the blood, cruorine, in worms, molluscs, 
 and insects. A number of colouring matters can be 
 obtained, by using ether, from sponges, polyzoa, and the 
 crustaceans; these, if examined in this way, may give 
 unexpected results. 
 
 For further information on this interesting subject we 
 must refer the reader to Mr. Sorby's paper " On a Definite 
 Method of Qualitative Analysis of Vegetable and Animal 
 Colouring Matter by means of the Spectrum Microscope," 
 published in the Proc. Roy. Soc. No. 92, 1867. 
 
 (1) See a paper by Dr. Gladstone, on the Spectra of Solutions of Salt* 
 Quart. Journ. Chem. Soc. vol. xi. p. 36. 
 
 3 B 2 
 
740 THE MICROSCOPE. 
 
 It would be a vain attempt were we to try to convey 
 to our readers any idea of the great discoveries which have 
 "been made by the microscope, or of the important pur- 
 poses to which it has been applied. Second only to the 
 telescope, though in many respects superior to it, the 
 microscope transcends all other instruments in the scientific 
 value as well as in the social interest of its results. While 
 the human eye, the telescope and microscope combined, 
 enables us to enjoy and examine the scenery around us, to 
 study the forms of life with which we are more imme- 
 diately connected, it fails to transport us into the depth of 
 space, to throw into relief the planets and the stars, and 
 to indicate the forms and arrangements in the worlds of 
 life and motion, which distance diminishes and conceals. 
 To these mysterious abodes, so long unrevealed, the tele- 
 scope has at last conveyed us. It has shown us those 
 worlds and systems, of which our own earth and our own 
 system are the types ; but it fails to enlighten us respecting 
 the nature and constitution of the celestial bodies, and the 
 forms of life for which they are created. 
 
 In its downward scrutiny, as well as in its upward 
 aspirations, the human eye has equally failed. In the 
 general view which it commands of animal, vegetable, and 
 mineral structures, it cannot reach those delicate organisa- 
 tions on which life depends, or those structures of inor- 
 ganic matter from which its origin and composition can be 
 derived. Into these mysterious regions, where the philo- 
 sopher has been groping his way, the microscope now 
 conducts him. The dark abodes of unseen life are lighted 
 up for his contemplation, organizations of transcendent 
 beauty appeal to his wonder new aspects of life, new 
 forms of being, new laws of reproduction, new functions 
 in exercise, reward the genius of the theoretical and 
 practical optician, and the skill and toil of the naturalist. 
 "With wonders like these all nature is pregnant : the earth, 
 the ocean, and the air times past and times present, now 
 surrender their secrets to the microscope. 
 
 What we know at present, even of things the most near 
 and familiar to us, is so little in comparison of what we 
 know not, that there remains an illimitable scope for our 
 inquiries and discoveries ; and every step we take serves to 
 
CONCLUSION. 
 
 741 
 
 enlarge our capacities, and give us still more noble and 
 just ideas of the power, wisdom, and goodness of God. 
 This marvellous universe is so full of wonders, so teems 
 with objects of latent beauty, that perhaps eternity alone 
 will open up and develop sufficient opportunities to enable 
 us to survey and admire and appreciate them alL 
 
 " And Eves the man, whose universal eye 
 Has swept at once th' unbounded scheme of things, 
 Mark'd their dependence so, and firm accord, 
 As with unfaltering accent to conclude 
 That this availeth nought ? Has any seen 
 The mighty chain of beings, lessening down 
 From infinite perfection to the brink 
 Of dreary nothing, desolate abyss I 
 From which astonish'd thought, recoiling, turns? 
 Till then, alone let zealous praise ascend. 
 And hymns of holy wonder, to that Power, 
 Whose wisdom shines as lovely on our minds 
 As on our smiling eyes his servant sun." THOKSOV 
 
APPENDIX. 
 
 AN increasing demand for good, useful, and moderately 
 priced instruments fit for students and others, naturally 
 enough has had the effect of inducing makers to vie with 
 each other in their endeavours to give a better class micro- 
 scope for a small sum. Among those manufacturers who have 
 effected much for the microscope, not only in the way of 
 improvements, but in its production at a moderate cost, 
 we should have mentioned Messrs. K. and I. Beck. 
 Their Popular Microscope will be readily understood on 
 reference to fig. 357. 
 
 The body, A (in the illustration shown as binocular), 
 is carried by a strong arm, B ; and this is attached to a 
 square bar, c, which may be moved up or down by a 
 rack- work and pinion in the lower part of the stand, where 
 the stage, D, and the mirror, E, are attached. 
 
 The base, P, is triangular; and it is connected with the 
 parts of the instrument already described by a broad stay, 
 G, which moves on centres at the top and bottom, so as to 
 allow the end of the tube, H, to fit by its projecting pin 
 into various holes along the medial line of the base. 
 With this arrangement, if the body of the microscope be 
 required in a more or less inclined position as in the figure, 
 four holes are provided near the extremity of the base for 
 the pin of the tube to fit into. A hole near the stout pin, L, 
 is used when a vertical position is wanted ; while to obtain 
 the horizontal position, the pin of the tube is placed in a 
 hole in the stud, K, the inner surface of the stay, o, resting 
 at the same time on the top of the stout pin, L. This form of 
 construction is entirely new, and has the following advan- 
 tages : it is strong, firm, and yet light ; the instrument 
 cannot alter from any particular inclination it is put into, 
 
744 APPENDIX. 
 
 which is not unfrequently the case when the ordinary 
 
 Fig. 357. Beck's Popular Microscope. 
 
 joint works loose ; and in every position the heavier part 
 
APPENDIX. 
 
 of the stand is brought over the centre of the 
 ensure an equality of balance. 
 
 745 
 
 to 
 
 F g. 358. -Beefs Studcnfs Microtcope. 
 
746 APPENDIX. 
 
 To adjust the focus of the object-glass, turn the 
 milled heads o for a quick movement, or the milled head 
 P for a slow one. 
 
 The stage, D, is circular, and upon it fits a plate, T; 
 this again carries the object-holder, u, which is provided 
 with a ledge, v, and a light spring, w ; it is held on the 
 plate T by a spring underneath, so that it can be moved 
 about easily and smoothly by one or by both hands. The 
 small spring, w, is fastened to the object-holder by a 
 milled head, which will unscrew ; so that the position of 
 the spring may be altered to give more or less pressure 
 upon the edge of the object, or it may be removed alto- 
 gether, if necessary. 
 
 When a stage with only a flat surface is required, the 
 object-holder, u, may be removed by unscrewing, from the 
 under side of the plate T, two small milled heads which 
 connect a circular spring with the object-holder; or, by 
 removing the plain stage altogether, an extra simple flat 
 plate may be substituted. 
 
 Beneath the stage there is a cylindrical fitting for the 
 reception of a diaphragm, or for any additional apparatus 
 that may be required in that position. 
 
 The mirror, E, besides swinging in a rotating semicircle, 
 will slide up or down the tube, H, or it will turn on either 
 side for oblique illumination. 
 
 Their Educational and Student's Microscopes, and larger 
 instruments are well known, and therefore need no 
 particular mention. 
 
 CROUCH S CHEAP BINOCULAR MICROSCOPE. 
 
 The instrument (fig. 359) manufactured by Mr. H. Crouch, 
 London Wall, possesses many important advantages as a 
 cheap microscope. First it combines perfect optical per- 
 formance with good workmanship in the construction of 
 the stand. It is well balanced, and stands firmly in any 
 position. The polariscope can be used (the analyser 
 being adapted to binocular) with the 2-inch. The 
 stage is of a new construction, giving universal move- 
 ments of 1^ inch in extent. The condenser is on a separate 
 
APPENDIX. 747 
 
 stand, and the accessory apparatus can be adapted at any 
 time, without returning the instrument to the maker's 
 hands. 
 
 Fig. 359. Crone*'! Microscope. Scale J. 
 
 The latest improvement effected in this cheap instru- 
 ment is the adaptation of a concentric rotating stage, a 
 most convenient and useful addition. This stage (fig. 360) 
 is an adaptation of Nachet's principle, and consists of : A, 
 a lower plate or stage attached to stand in the ordinary 
 manner, with fitting beneath (F) to receive the accessory 
 illuminating apparatus. B is an upper plate rotating con- 
 
748 
 
 APPENDIX. 
 
 centrically with optic axis of microscope, c a plate of 
 polished glass let in and secured to upper surface of B. 
 D D, a v spring attached to outer edge of the plate B and 
 rotating with it, having at the outer extremities projecting 
 "ivory" points d d. E the object-carrier, consisting of 
 another plate of polished glass, mounted in brass frame, 
 
 Fig. 360. Crouch's Concentric Stage. Scale |. 
 
 having an attachment for holding the object. The plate 
 E projecting slightly on the lower surface from the brass 
 frame is kept in contact with the circular plate c (also 
 slightly projecting above B), the two glass surfaces being 
 in contact, and kept so by the pressure of the "ivory 
 points" dd; thus securing a beautifully smooth and 
 delicate though firm adjustment, which admits of 
 an object being found with extreme facility under the 
 highest powers. It is particularly adapted for the ex- 
 amination of objects in fluid of any kind, the adjustments 
 not being subject to oxidation; any minute object may 
 very readily be found, and the slightest change in the 
 field is easily effected ; there is no slipping back or recoil. 
 
APPENDIX. 
 
 749 
 
 The whole stage may also be concentrically rotated; 
 this is most essential in the examination of the markings 
 on certain test objects ; and, what is very important, there 
 is no danger of the apparatus getting out of order. For 
 histological work, and for the teacher who wishes to 
 demonstrate any peculiar feature of an object, it is 
 
 Pig. 361. Browning's Students Microscope. 
 
 certain to prove exceedingly useful The stage can be 
 added to any instrument. 
 
 BROWNING'S COMPLETE MICROSCOPE. 
 
 Mr. Browning's Student's Complete Microscope differs 
 from the educational instruments of other makers, possessing 
 
750 
 
 APPENDIX. 
 
 mechanical motions to the stage. It has a handsome brass 
 stand, large body, with coarse and fine adjustments, and 
 drawer tube to eye-piece, and separate 1-inch and J-inch 
 objectives of very superior quality, of moderate angular 
 aperture, cut to the Microscopic Society's gauge. 
 
 The stage is arranged to receive the polariscope, and the 
 whole instrument is so made that additional apparatus may 
 at any time be added to it, at pleasure. The performance 
 of the objectives is unusually good ; the instrument is well 
 
 Pig. 362. Ladd's Microscope. 
 
APPENDIX. 751 
 
 made, and remarkably cheap at the price, 6 6*. ; we very 
 cordially recommend it for general use. 
 
 Mr. Ladd has lately effected improvements in the 
 manufacture of his instruments in mechanical details, 
 and in obtaining a perfect centre of gravity. In his best 
 instrument, such as that represented in fig. 362, he has 
 taken great care to obtain a perfect balance in any position, 
 even when placed on its horizontal axis ; no instrument 
 can be better adapted than this to all the wants of the 
 microscopist, and which is one combining many of the 
 advantages of the more expensive forms. 
 
 Nachet and Hartnack of Paris, and Merz of Munich, 
 hold an almost equal rank as makers of first-class micro- 
 scopes, and in point of excellence of workmanship 
 fairly rival those of English makers. Hartnaek's latest 
 improvement consists in an exquisitely-fitted concentric 
 stage, which works with marvellous neatness and pre- 
 cision. Nachet has also effected considerable improve- 
 ments in his circular stage, as well as in the arrangement 
 of his binocular form of body; for fuller particulars of 
 which we must refer the reader to the Monthly Micro- 
 scopical Journal. 
 
 IMMERSION OBJECTIVES. 
 
 Messrs. Hartnack and Merz and others have likewise added 
 greatly to their well-earned reputations by the construction 
 of immersion objectives of a very superior order. We have 
 had especial opportunities of comparing the respective 
 merits of Hartnack's -f$ and -^, Merz's ^, and Noberts's 
 -^, of which we can speak in the highest terms of praise. 
 All work through ordinary thick glass covers with 
 great facility, and are therefore adapted either for the 
 examination of pathological specimens or for the most 
 delicately-lined test-objects. The low price at which they 
 are sold is no unimportant consideration to the student in 
 microscopical science ; the -^ of either Hartnack or Merz 
 can be purchased for about 6 6s., while their other powers 
 are equally cheap. Amici nearly fifty years ago demon- 
 strated the value of the immersion system : and Soemmering, 
 writing of one of Amici's microscopes, observes : " Its 
 magnifying power, and the admirable precision and clear- 
 ness with which the object is seen, seems astonishing." 
 
752 APPENDIX. 
 
 It is not difficult to see that Amici's method of connecting 
 the objective with the cover-glass by a film of water must 
 necessarily very much diminish the reflection which usually 
 takes place in the incidence of oblique light when the 
 ordinary or dry objective is employed. The limiting angle 
 of refraction of water being about 48 degrees, it follows 
 that whatever is the degree of obliquity in the incident 
 light falling on the object, the immersion lens never has 
 to deal with rays of greater obliquity than 48 degrees. 
 To this, as well as the greater number of parallel rays 
 brought to a focus, and the increased angle of aperture, 
 is due the greater clearness and precision of the image 
 obtained. 
 
 "The advantages," writes Mr, J. Mayall, 1 "mainly 
 claimed for the immersion objectives are : greater work- 
 ing distance between the object and the objective, increase 
 of light, superior definition and clearness in the optical 
 image, which image is obtained by much simpler illumi- 
 nating apparatus, and with less manipulative skill than 
 that considered indispensable in using high-power dry 
 objectives." 
 
 We are pleased to add that Messrs. Powell and Lealand 
 are turning their attention to the construction of objectives 
 on the immersion system. This cannot however be effected 
 by making the front lens moveable, so that the objective 
 may be used either wet or dry. 
 
 (1) Tht Monthly Microscopical Journal, 1869, p. 82. 
 
INDEX. 
 
 ABERRATION, CHROMATIC, 26. 
 
 of lenses, 21. 
 
 spherical, 26. 
 
 Abraham's reflecting prism, 172. 
 Absorption bands, 1S8. 
 Acalephse, 491. 
 Acarina,632. 
 Acanis beetle, 455. 
 
 cloth moth, 641. 
 
 domesticus, 637. 
 
 of dog, 634. 
 
 farinse, 639. 
 
 of fly, 641. 
 
 of fowl, 640. 
 
 of rat, 634. 
 
 sacchari, 638. 
 
 scabiei, 635. 
 
 of swallow, 639. 
 
 Achetina, 627. 
 Achnanthes Longipes, 420. 
 Achorion, 296. 
 Achromatic condenser, 166. 
 
 corrections, 40. 
 
 illuminator, 167. 
 
 object-glasses, 42. 
 
 Acineta-form infusoria, 40x. 
 
 vorticella, 447. 
 
 Acineta tuberosa, 411, 449. 
 Actinia actinozoa, 465. 
 
 rubra, 483. 
 
 bellis,484. 
 
 Actiniforum zoophytes, 485. 
 
 Actinophrys sol, 374. 
 
 Actinotrocha, 578. 
 
 Actinozoa, 485. 
 
 Adams' microscope, 10. 
 
 Adipose tissue, 693. 
 
 Adulteration of food, 345. 
 
 ^cistes, 451. 
 
 ^cidium, 293. 
 
 Agates, 399. 
 
 Alcyonella stagnorum, 526. 
 
 Alcyenidae,489, 524. 
 
 Alcjonium digitatum, 489. 
 
 polypidoms, preparation of, 509. 
 
 Algae, 'development of, 269. 
 Alkaloids, sublimation of; 73L 
 Amici's microscopes, 12. 
 
 prisms, 82. 
 
 Amphistome conicum, 565. 
 Amphitetras, 416. 
 
 Amoeba, 373. 
 
 Amoeboid state of volvox, 277. 
 Anacharis alsinastrum, 32L 
 Analysis, spectrum, 735. 
 Angle of aperture, 44. 
 
 of incidence, 16. 
 
 of refraction, 17. 
 
 mode of measuring, 45. 
 
 Anguillulse, 571. 
 Anguinaria spatulata, 520. 
 Animalcule, sun, 374. 
 Animalcules, 402. 
 
 cage, Varley's, 195. 
 
 collecting, 193. 
 
 history of, 4C3. 
 
 infusorial, 414. 
 
 AniniAl cell, 659. 
 
 action of cilia In, 671. 
 
 bodies, injecting, 231. 
 
 cells, change into tissues, 665. 
 
 cellular membrane, 692. 
 
 connective tissue, 662. 
 
 elementary substance, 659. 
 
 epithelium, 668. 
 
 fibrous tissue, 694. 
 
 kingdom, division of, 366. 
 
 life, 655. 
 
 structure, 66L 
 
 structure, mode of investigating, 
 
 724. 
 
 tissues classified, 692. 
 
 tissue consolidated, 702. 
 
 tissues, staining, 225. 
 
 Annelida, 575. 
 
 Annulosa, 559. 
 
 Anobium, 633. 
 
 Antennae of insects, 607. 
 
 Amyot's finder, 188. 
 
 Aphides, 613. 
 
 Aphrophora bifasciata, 615. 
 
 Aplanatic doublet iens; Mi 
 
 Aplysia, 529. 
 
 Aquatic box, 194. 
 
 Arachnida, 631, 644. 
 
 Arachnoidiscus, 432. 
 
 Archer on amoeboid bodies, 277. 
 
 Arcella acuminata, 372. 
 
 Arenicola, 576. 
 
 Aristophanes, microscope known to, J, 
 
 Artemise, 557. 
 
 Artieulata. 579. 
 
 Asci of lichens, 305, 
 
 3c 
 
754 
 
 INDEX. 
 
 Aspergillus, 001. 
 Astasia, 412. 
 Asteroidea, 495. 
 Atropus, 623. 
 Atlantic soundings, 382. 
 
 BAKER on the microscope, 10. 
 Baker's microscopes, 86. 
 
 brachionus, 456. 
 
 Baccillaria paradoxa, 269. 
 
 Bacterium, 412. 
 
 Baird, Dr., on entomostraca, 557. 
 
 Balanidse, 555. 
 
 Balbiani, Dr., on paramaecium, 410. 
 
 Barnacle, 554. 
 
 De Bary on fungi, 291. 
 
 Bat, head of, 681. 
 
 Beale, Dr. on cell development, 659. 
 
 on a new object glass, 73. 
 
 on magnifying power, 77. 
 
 on glycerine for preserving objects, 
 
 224. 
 
 on method of staining tissues, 225. 
 
 on injecting, 237. 
 
 Beck, Mr. R, on errors of interpreta- 
 tion, 64. 
 Bee's tongue, leg, &c., 612. 
 
 eye, 586: 
 
 Beetles, 623. 
 
 bacon, 624. 
 
 diamond, 622. 
 
 tortoise, 588. 
 
 water, 625. 
 
 Bell-animalcule, 445. 
 
 Berg-mehl, 432. 
 
 Bergh, Dr., on urticating organs, 545. 
 
 on podura scales, 628. 
 
 Berkeley on two new British fungi, 304. 
 
 on fungi, 290. 
 
 Beroe, 492. 
 
 Bichromate of potash injection, 236. 
 
 Biddulphia, 437. 
 
 Bilharzia hsematobra, 567. 
 
 Binocular microscope, 117. 
 
 Bird's-head coralline, 518. 
 
 Blood-corpuscles, 678. 
 
 crystallization of, 680, 
 
 disc, size of, 680. 
 
 spectrum, 128. 
 
 vessels, structure of, 688. 
 
 Blow-fly, 590. 
 Beckett's lamp, 185. 
 Bone, 714. 
 
 cutting sections of, 208. 
 
 eel, 716. 
 
 fishes, 719. 
 
 human, 713. 
 
 ostrich, 7*15. 
 
 reptiles, 714. 
 
 sting ray, 718. 
 
 Bonnani's microscope, 8. 
 
 Botrytis, 301. 
 
 Bot-fly, egg of, 607. 
 
 ^ourgingnon, Dr., on acarus scabiei, 
 
 Bowerbank on sponges, 386. 
 
 Bowerbankia, 512. 
 
 Brachionus, 455. 
 
 Brachiopoda, 535. 
 
 Brewster, Sir David, on viewing ob- 
 jects, 160. 
 
 Nineveh lens, 3. 
 
 on double refractory crystals, 147. 
 
 Bridgeman's reflector, 181. 
 
 finder, 190. 
 
 Brightwell on navicula, 419, 
 
 Brooke, Mr., on opaque objects, 183. 
 
 on test objects, 57. 
 
 Browning's spectro-microscope, 120. 
 
 oblique illuminator, 171. 
 
 Bryozoa Bowerbankia, 512. 
 
 Buccinum undatum, palate, 538. 
 
 Burnett, Dr., on parasites, 639. 
 
 Busk, Mr., on anguinaria spatulata, 
 520. 
 
 on starch granules, 342. 
 
 on echinococci, 570. 
 
 volvox, 276. 
 
 Butterflies, eggs of, 605. 
 
 tongues of, 607. 
 
 CALEPTERYX VIRGO, 597. 
 Calcification of animal tissues, 552. 
 Callithamuion, 273. 
 Camera-lucida, 129. 
 Campanularia volubilis, 481. 
 
 gelatinosa, 481. 
 
 Campilodiscus clypeus, 439. 
 Cancer-cell, 296. 
 Cane, section of, 341. 
 Capillaries, 689. 
 
 in fat, 691. 
 
 Carbonate of lime in shell, 528. 
 Carpenter, Dr., on volvocinese, 275 
 
 on diatomacese shell, 553. 
 
 on tomopteris, 576. 
 
 on eozoon, 379. 
 
 Cartilage, 702. 
 
 from ear of mouse, 702. 
 
 rabbit's ear, 703. 
 
 Carter, Mr., on chara development, 31$ 
 
 on spongilla, 391. 
 
 Cassida viridis, 588. 
 Cedar, stem of, 357. 
 Cell formation, 659. 
 
 action of, 667. 
 
 animal, 660. 
 
 changes, 258, 661. 
 
 changes in disease, 664. 
 
 contents, 662. 
 
 development, 239, 059. 
 
 nucleus, 663. 
 
 pigment, 671. 
 
 Cells, complicated, 667. 
 
 for desmids, 230. 
 
 for mounting, 213. 
 
 growing, 198. 
 
 motile, 261. 
 
 Suffolk's, 221. 
 
 vegetable, 257 
 
INDEX. 
 
 756 
 
 Cellularia, 518. 
 
 avicularia, 518. 
 
 Cellular tissue of plants, 323. 
 
 in animals, 662. 
 
 Cements, 219. 
 
 Cephalopod, tongue of, 540. 
 Cephalopoda, 550. 
 Cephalosiphon, 451. 
 Characese, 315. 
 
 antheridia of, 317. 
 
 development, 318. 
 
 Cheese-mite, 637. 
 
 Chemical re-agents, 245. 
 
 China-grass, 353. 
 
 Chitonidre, 537. 
 
 Chloride of gold, 701. 
 
 Chloroform and balsam nurture for 
 
 mounting, 227. 
 Cilia, 404, 671. 
 
 movement of, mode of exhibiting, 
 
 406. 
 
 Ciliated epithelium, 670. 
 Cimex lecticularis, egg of, 113. 
 Circulation of blood in frog, to view, 
 
 682. 
 
 Cirrhopoda, 554. 
 Clarke, J/ockhart, on the preparation of 
 
 spinal cord, 761. 
 Clematis, section of, 333, 357. 
 Clepsinidae, 574. 
 Clionse, 395. 
 Clip for mounting, 214. 
 Closterium lunula, 285. 
 Clothes moth, 612. 
 Clypeastrodea, 601. 
 Coal, structure of, 363. 
 Cobbold, Dr., on helminths, 5C7. 
 Cocconema, 437. 
 Coccus persicse, 604. 
 
 egg of, 605. 
 
 Cochineal insect, its value, 651. 
 Cocoa, adulteration of, 346. 
 Ccelenterata, 462. 
 Coddington's lens, 34. 
 Coffee, structure of, 347. 
 Conn on stephanosphaera, 265. 
 Coleoptera, 622. 
 Collecting objects, 248. 
 
 animalcules, 248. 
 
 bottle, 192. 
 
 net, 193. 
 
 stick, Mr. Williamson's, 193. 
 
 Collins' mounting case, 254. 
 
 microscope, 95. 
 
 Collodion for multiplying objects, 585. 
 Comatula, 496. 
 Compressorium, 195. 
 Condensers, Gillett's, 163. 
 
 Powell and Lealand's, 169. 
 
 Collins's, 169. 
 
 Ross's, 167. 
 
 J. B. Reade's, 174. 
 
 buL's-eye, 182. 
 
 Confervoideae, 267. 
 Conjugation in desmids, 79. 
 
 Conochilus, 448. 
 Consolidated tissues, 701 
 Coral reefs, 491. 
 Corals, 490. 
 Cordylophora, 463. 
 Corethra plumicornis larva, 600. 
 Corn-blights, 293. 
 Corymorpha nutans, 476. 
 Coryne-stauridia, 475. 
 Coscinodiscus, 440. 
 Cosmarium, 282. 
 Crabshell, 528. 
 Crayfish, 553. 
 
 shell of, 553. 
 
 Cricket, 627. 
 Crinoidea, 505. 
 Crisiadse, 519. 
 Cristatella mucedo, 524. 
 Crustacea, 554. 
 Crystals, formation of, 729. 
 
 of snow, 153. 
 
 quinine, 151. 
 
 urinary salts, 149. 
 
 mode of showing optical axis. 145. 
 
 Cuckoo-spit, 615. 
 Culex, head of, 599. 
 Cutleria dichotoma, 273. 
 Cutting sections, 203. 
 
 glass cells, 213. 
 
 Cuttlefish-bone, 546. 
 
 Cyclops, 556. 
 
 Cymba olla, tongue of, 542. 
 
 Cymbella Ehrenbergii, 418. 
 
 Cynips gallae, 618. 
 
 Cypridse, 556. 
 
 Cystic disease of liver, 570. 
 
 Cysticercus fasciolaris, 564. 
 
 pisiformis, 564 
 
 Czennak on tooth substance, 711. 
 
 DALYELL, SiRJ.G.,on tubularidse, 474. 
 
 on actiniae, 467. 
 
 Dana, Prof., on corals, 490. 
 
 Daphnia pulex, 557. 
 
 Darkens selenite stage, 142. 
 
 Darwin on infusoria, 433. 
 
 Dasfa Kiitzingiana, 272. 
 
 Davis on a new rotifer, 451. 
 
 Death-watch beetle, 623. 
 
 Deep-sea soundings, 381. 
 
 Delabarre's microscope, 10. 
 
 Delessaria, 274. 
 
 Demodcx folliculorum, 637. 
 
 Dentine, 707. 
 
 Deparia prolifera, 313. 
 
 Dermestes lardarius, 624. 
 
 Dermestidae, 624. 
 
 Designing from microscopic forms, 440 
 
 Desmidiaceae, 278. 
 
 finding and preserving, 288. 
 
 Deutzia scabia, 339. 
 Diamond beetle, scales of, 628. 
 Diaphragm, description of, 163. 
 Diatomacese, 416. 
 Kutzing on, 417. 
 
756 
 
 INDEX. 
 
 Diatomacea, on collecting, 428. 
 
 Diatoms, movements of, 423. 
 
 Difflugia, 372. 
 
 Diffraction of light, 68. 
 
 Diphydse, 464. 
 
 Dipping tubes, 191. 
 
 Directions for keeping instrument, 159. 
 
 for mounting and preparing ob- 
 
 jects, 215. 
 Disc, circular, 212. 
 Dissecting knives and needles, 198. 
 
 - microscopes, 98. 
 
 under water, 200. 
 
 - scissors, 202. 
 Distoma, 567. 
 Divini's microscope, 7. 
 
 Doris tuberculata, palate of, 538. 
 Dragon-fly, 597. 
 Drone-fly, 591. 
 Dytiscus marginalis, 626. 
 
 - sucker from leg of, 588. 
 
 ECHINID.S:, 498. 
 Echinococci, 569. 
 Echinodermata, 494. 
 Echinorhynchus, 571. 
 Ecker, on protozoa, 373. 
 Eel, scales of, 722. 
 Eggs of insects, 602. 
 
 - of gasteropoda, 545. 
 
 Egyptian cloth, 354. 
 Ehre 
 
 nberg's brachionus, 455. 
 on boundary between plants and 
 -> animals, 655. 
 Elder-root, section of, 363. 
 Elm, section of, 356. 
 Enamel, 709. 
 Enchondroma, 704. 
 Encrinus, 506. 
 Entomostraca, 555. 
 Entozoa, 565. - 
 Eozoon canadense, 378. 
 Epeira diadem, 645. 
 Epithelium, tesselated, 668. 
 
 - columnar, 670. 
 Equisetacese, 311. 
 Equisetum, section of, 332. 
 Errors of interpretation, 65, 723. 
 Escharidae, 521. 
 
 - foliacea, 522. 
 Euastrum, 280. 
 Eucratiadae, 519. 
 Euglena, 412. 
 Eunotia, 437. 
 Euphorbia neriifolia, 329. 
 Etiplectella, 402. 
 Eye-glass, 81. 
 
 Eye, human, vessels in, 689. 
 
 - pigment, 672. 
 
 - section of cat's, 689. 
 Eye-piece, the, 47. 
 
 - Huyghenian, 47. 
 
 - Ramsden, 50. 
 
 - micrometer, Jackson's.52. 
 
 - Kelner, 78. 
 
 Eyes of insects, 584. 
 
 FASCIOLA HEPATICA, 56C 
 Fat cells, 694. 
 Favus fungus, 296. 
 Feather-star, 496. 
 Feet of insects, 587. 
 Ferns, 811. 
 
 section of root, 335. 
 
 Fibre, muscular, 695. 
 
 in the tongue, 697. 
 
 involuntary, 698. 
 
 Fibrous tissue, 693. : , ,, 
 
 white and yellow 691 " ,."' 
 
 Finders, 187. ' 
 
 Amyot's, 188, 
 
 Maltwood's, 189. 
 
 Fishes' scales, 721. 
 Flatness of field, 72. 
 Flax, 353. 
 Flea, 630. 
 
 cat's, 634. 
 
 larva of, 634. 
 
 Flora of coal measure, 364. 
 
 Florideae, 271. 
 
 Flower buds, 351. 
 
 Flowers, colouring matter of, 35X. 
 
 Flukes. 565. 
 
 Floscuiaria ornata, 458. 
 
 Floscularise, 453. 
 
 Flustrse, 521. 
 
 avicularis, 523. 
 
 chartacea, 523. 
 
 foliacea, 522. 
 
 Fly, foot and leg of, 587, 591 
 
 tongue, 595. 
 
 fungoid disease of, 596. 
 
 Tsetse, of Africa, 596. 
 
 Follicles of pig's stomach, 669 
 Foraminifera, 375. 
 
 skeletons of, 381, 
 
 fangasina, section of, 380. 
 
 fossil, 377. 
 
 Forceps for holding objects, 190. 
 Fossil infusoria, 431. 
 
 mode of preparing, 434. 
 
 Fossil plants, 362. 
 Fraunhofer's glasses, 10. 
 
 lines, 738. 
 
 Frog-plate, 632. 
 
 bit, 321. 
 
 circulation, 679. 
 
 hopper, 615. 
 
 Fungi, 290. 
 
 Berkeley on, 290. 
 
 De Bary on, 291. 
 
 floating, 295. 
 
 Fungiae, 484. 
 Fungoid growths, 296. 
 Furze's spotted lens, 155 
 Fragillaria pectinalis, 437. 
 Funaria, capsule of, 309. 
 
 GALL-FLY, 618. 
 Gallionella sulcata, 438. 
 
INDEX. 
 
 757 
 
 Garrod's, Dr. , crystals in blood, 681. 
 Gas-lamp. 185. 
 Gasteropoda, 537. 
 
 linsrual bands of, 538. 
 
 Gemmules of sponges, 400. 
 Geodia Barretti, 390. 
 Qibbons's section-cutter, 205. 
 Gillett's illuminator, 163. 
 
 measuring angle of aperture, mode 
 
 of, 45. 
 
 Gill of tadpole, circulation in, 686. 
 Glass-rope sponge, 401. 
 Glaucoma, 414. 
 
 Globigerina, 384. : '-_ 
 
 Glossina morsitans, 596. 
 Glycerine for mounting, 224. 
 
 Rimmington's, 223. 
 
 Gnat, description of, 598. 
 Goadby's fluid, 227. 
 
 process of injecting, 235. 
 
 Gomphonema, 419. 
 Goniometer, Schmidt's, 56. 
 Gordiacea, 562. 
 Gorgonidse, 487. 
 
 spiculae from, 487. 
 
 Gorham, T. on eyes of insects, 584. 
 Goring, Dr., achromatic object-glassw, 
 
 13. 
 Gosse on notommata, 456. 
 
 on cellularia, 518. 
 
 on coryne stauridia, 475. 
 
 on meficerta ringens, 459. 
 
 Gourd seed, section of, 335. 
 
 Graminacese, 340. 
 
 Grant, Dr., on flustra, 521. 
 
 on alcyonidse, 489. 
 
 on plumularia, 478. 
 
 on sponges, 386. 
 
 Grass, cuticle of, 339. 
 
 Gray, Dr., on mollusca, 539. 
 
 Gregarinida, 367. 
 
 Gregarina of earth-worm, 270. " . 
 
 Growing cell, 198. 
 
 Guinea-worm, 563. 
 
 Gulliver on raphides, 337. 
 
 on blood discs, 679. 
 
 Guy, Dr., on sublimation, 731. 
 Gyrinus, paddle of, 625. 
 
 HAIK, HUMAN, 672. 
 
 bat, Indian, 673. 
 
 gregarines in, 369. 
 
 moss, 311. . 
 
 mouse, 673. 
 
 pecari, 674. 
 
 Haliotus splendens, 536. 
 
 tuberculatus, tongue of, 543. 
 
 Hallifar, Dr., on preparing insects, 604. 
 
 Hand magnifiers, 33. 
 
 Hard tissues, preparation of, 208. 
 
 Hartea elegans, 524. 
 
 Hassall, Dr., on the adulteration of 
 
 food, 349. 
 
 Henfrey, Prof., on ferns, 313. 
 Hemp, 353. 
 
 Hepaticae, SOS. 
 
 Hepworth, Mr., on mounting insects 
 
 tH8 
 Herapath's, Dr., polarising crystal, 142. 
 
 iodo-quinine, 149. 
 
 on polarisation as a test, 148. 
 
 Hermia glandulosa, 475. 
 
 Herschel's aplanatic doublet lens, 26. 
 
 , A., spectroscope, 122. 
 
 Hey*s mounting fluid, 227. 
 
 Hicks, Dr. B., on amoeboid bodies, 227. 
 
 on lichens, gonida of, 306. 
 
 Highley's gas-lamp, 185. 
 
 microscopes, 99. 
 
 photographic camera, 157. 
 
 Hill's microscope, 10. 
 Hipparchia janira, 611. 
 Hirudinidae, 573. 
 Holland's eye-piece, 33. 
 Holothuridse, 508. 
 
 drawing of, life-size, 507. - 
 
 Honey-bee, 620. 
 
 Hooke's microscope, 7. 
 
 How's microscope, 101. 
 
 Horn, rhinoceros, 721. 
 
 Human body, composition of, 659. 
 
 Huxley, T. H. on animal tissues, 655 
 
 on echinidae, 494. 
 
 on tongue of mollusca, 538. 
 
 on actinozoa, 468. 
 
 on rotifera, 560. 
 
 on tooth development, 70S. 
 
 Huyghenian eye-piece, 47. 
 Hyalonema, 401. 
 Hydatids, 570. 
 Hydra, 446, 466, 470. 
 Hydrachnidae, 642. 
 Hydractinia, 473. 
 Hydrophilus, trachea of, 587. 
 Hyrnenoptera, 616. 
 aquatic, 626. 
 
 ICELAND SPAR, 135. 
 Improvements in microscope, 10. 
 India-rubber tree, 329. 
 
 section of leaf, 334. 
 
 Indicators, 187. 
 Infusoria, 402. 
 - cilia, 405. 
 
 fossil, 431. 
 
 history of, 403. 
 
 Infusorial animalcules, 402. 
 
 Pasteur's researches on, 414, V 
 
 Injecting, mode of, 231. 
 
 lower animals, 244. 
 
 mercurial, 239. 
 
 steps of the process, 241. 
 
 the ducts and glands, 243. 
 
 Injected preparations, to mount, 244. 
 Injections, transparent, 226. 
 
 coloured, 232. 
 
 Insects, 579. 
 
 commercial importance of, 651. 
 
 dissection of, by Swamnierdam, 
 
 679. 
 
753 
 
 INDEX. 
 
 Insects' eggs, 602. 
 
 eyes, 584. 
 
 feet, 587. 
 
 hairs, tenent, 589. 
 
 itch, 635. 
 
 injecting, 240. 
 
 ovipositors, 616. 
 
 preparing and mounting, 590, 648. 
 
 proboscis, 599. 
 
 spiracles, 586. 
 
 stings, 619. 
 
 tongues, 582, 607. 
 
 transformations of, 648. 
 
 wings of, 597. 
 
 Interpretation, errors of, 67. 
 Intercellular substance, 662. 
 lodo-quinine, 151. 
 Iris-leaf, 336. 
 Isthmia enervis, 432. 
 Ivory nut, section of, 350. 
 Ixodidse, 642. 
 
 JACKSON'S micrometer, 51. 
 
 Jelly-fish, 491. 
 
 Johnstone, Dr., on sponges, 385. 
 
 on hydra, 471. 
 
 on campanularia, 481. 
 
 Jones, Wharton, on non-striated mus- 
 cular fibre, 698. 
 
 Rvmer, on the coretha pluini 
 
 cornis, 600. 
 Jungennannia bidentata, 310. 
 
 KETTLEDRUM condenser, 174. 
 Kelner eye-piece, 78. 
 Knives for dissecting, 119. 
 Kolliker on the muscles of the skin, 
 
 698. 
 Kutzing on vegetables and animals, 
 
 256. 
 on diatomacese, 417. 
 
 LADDS'S microscopes, 84. 
 Lamps, 184. 
 Lamp-shells, 535. 
 
 Lankester, E. R., on gregarina of earth- 
 worm, 370. 
 
 Lathe for polishing, 209. 
 Leaf-insect, 613. 
 r/eech, medicinal, 573. 
 Leeuwenhoek's microscope, 6. 
 Lenses, achromatic, 28. 
 
 chromatic, aberration of, 26. 
 
 Coddington, 34. 
 
 concavo-convex, 19. 
 
 condensing, 183. 
 
 correction of, 28. 
 
 curvature of, 22. 
 
 double convex, 18. 
 
 forms of, 18. 
 
 magnifying power of, 29. 
 
 meniscus, 25. 
 
 -* tracing rays through, 17. 
 
 Lenses, periscopic, 33. 
 plano-convex, 24. 
 
 - refraction of light through, 16. 
 
 spherical aberration of, 26. 
 
 Stanhope, 35. 
 
 Lepidoptera, eggs of, 605. 
 
 tongue of, 608. 
 
 wing-scales of, 609. 
 
 Lepisma, 529. 
 
 scale of, as a test, 611. 
 
 Lepralia nitida, 517. 
 
 Leuchart on echinorhynchus, 571. 
 
 Lewes on actinise, 4G7. 
 
 on life, 655. 
 
 thread cells, 467. 
 
 Libellulidae, wings of, 597. 
 
 Lichens, 304. 
 
 Lieberkuhn, Dr. N., on gregarina, 369 
 
 microscope, 5. 
 
 on spongilla, 389. 
 
 Life, animal, 655. 
 Light, diffraction of, 68, 
 
 polarisation of, 132. 
 
 Limax rufus, 529. 
 Limnsea stagnalis, 545. 
 Limnias ceratophylli, 458. 
 Lister's lenses, 13. 
 
 achromatic corrections, 40. 
 
 List of objects, Wheeler's, 253. 
 
 Live-box, 194. 
 
 Liver, diseased, 567. 
 
 Liverworts, 308. 
 
 Lobb, Mr., on polarising crystals, 145 
 
 on the illumination of test objects, 
 
 61. 
 
 micrasterias, 279. 
 
 Lob-worm, 576. 
 
 Loligo, palate of, 541. 
 
 Lophopus crystal] um, 525. 
 
 Loven on mollusca, 538. 
 
 Louse, 633. 
 
 Lubbock, Sir J., on the eggs of insects, 
 
 605. 
 
 on aquatic insects, 626. 
 
 Lucernaridse, 493. 
 Luidia fragilissima, 496. 
 Lung, capillaries of, 690. 
 Lymphatic, vessels of, 669. 
 
 MADREPORID^E, 486. 
 
 Maddox, Dr., wire clip, 214. 
 
 Magnifiers, hand, 33. 
 
 Magnifying power of single lenses, J9 
 
 of object-glasses, Ross's, 55. 
 
 Powell's, 56. 
 
 Maltwood's finder, 189. 
 Maple-aphis, 613. 
 Marchantia polymorplria, 308. 
 Mechanical arrangements, 70. 
 Medusap, 492. 
 
 Meissner on the micropyle, 60S. 
 Melicerta ringens, 459. 
 Melolantha, eye of, 585. 
 Melting vessel, 233. 
 Mercurial injections, 239. 
 
INDEX. 
 
 750 
 
 Mesoglia vermicularis, 268. 
 Micrometers, 51. 
 Microscope, Baker on the, 10. 
 
 Baker's binocular, 89. 
 
 compound, 88 
 
 dissecting, 98. 
 
 student's, 88. 
 
 traveller's, 108. 
 
 Bonnani's, 8. 
 
 B re water's diamond, 11. 
 
 Collins's binocular, 95. 
 
 dissecting, 98. 
 
 student's, 97. 
 
 compound, 38. 
 
 Frauenhofer, lenses for, 10. 
 
 G. Adams's, 10. 
 
 compound, 39. 
 
 E. Divini's compound, 8. 
 
 Goring's compound, 7. 
 
 Highley's clinical, 105. 
 
 pocket, 110. 
 
 professional, 99. 
 
 student's, 100. 
 
 Hooke's compound, 7. 
 
 water, 5. 
 
 How's student's, 101. 
 
 Huvghenian eye-piece o^ 
 
 LaddVs, 84. 
 
 Lieberkuhn's, 5. 
 
 Lister's, improvements in, 43. 
 
 Murray and Heath's, 103. 
 
 class, 104. 
 
 pocket, 107. 
 
 Newton's 
 
 Norman's, 100. 
 
 Pillischer"s binocular, 9L 
 
 prize, 94. 
 
 student's, 93. 
 
 Powell and Lealand's, 82. 
 
 arranged for test objects, 62. 
 
 Quekett's dissecting, 38. 
 
 Ross's, combination of object- 
 glasses, 43. 
 
 compound, 79. 
 
 simple, 35. 
 
 8. Gray's globule, 4. 
 
 simple, 5, 30, 
 
 simple, for dissections, 98. 
 
 Valentine's simple, 36. 
 
 Warrington's, 106. 
 
 binocular, 112. 
 
 Wheeler's, 110. 
 
 Wollaston's doublet, 31. 
 
 periscopic, 16. 
 
 Microspectroscopy, 119. 
 
 Micrasterias, 280. 
 
 Miller, Hugh, on fossil plants, 364. 
 
 Mineral kingdom, 728. 
 
 Mite, cheese, 637. 
 
 flour, 639. 
 
 Molecular movements, 67. 
 Mollusca, 511. 
 
 injecting, 240. 
 
 tongues of, 539. 
 
 Monads, 411. 
 
 Morpho Menelaus, scale of, Oil. 
 
 Moss-agates, 399. 
 
 Mosses, 309. 
 
 Moths and butterflies, 607. 
 
 Motile organs in cells, 262. 
 
 Mottled umber moth, 606. 
 
 Mounting and preparing, 215. 
 
 spring clip for, 214. 
 
 injections, 244. 
 
 case, Collin's, 254. 
 
 Movements of diatoms, 423. 
 
 Mucidines, development of, 661. 
 
 Mucor mucedo, 292. 
 
 Mucous membrane, 669. 
 
 Murray and Heath's microscopes, 103. 
 
 Muscular fibre, 695. 
 
 Mushroom spawn, 343. 
 
 Mussel, 531. 
 
 Myelin, 681. 
 
 Myolemma, 696. 
 
 Mytilus, 535. 
 
 NAILS, the, 672. 
 Navicufce, 419. 
 Neckera antipyretica, 310. 
 Nematoidea, 563. 
 Nemertidse, 562. 
 Nerves, 699. 
 
 perfection of sections, 701. 
 
 stellate corpuscle, 699. 
 
 Newport on moths' tongues, 607. 
 
 Nicd's prism, 136. 
 
 Nitella, 320. 
 
 Noberf g ruled micrometer lines, 54. 
 
 Noctiluca miliaris, 409. 
 
 Norman on collecting diatoms, 428. 
 
 Norman's microscope, 100. 
 
 Notommata aurita, 456. 
 
 Nudibranchiata, 530. 
 
 tongues of, 541. 
 
 Nummulites, 377. 
 
 OBJECT-OLA 8SE8, forms of, 72. 
 
 Ross's, 55. 
 
 Objects, Shadbolt on collecting, 248. 
 
 directions for viewing, 160. 
 
 mounting and preserving, 215. 
 
 Oblique illumination, 171. 
 
 J. N. Tomkins's double prism, i T4. 
 
 Oidinm, 293. 
 
 Opuntia, 356. 
 
 Onion, section of, 338. 
 
 Ophiocoma, 495. 
 
 Ophiura, 495. 
 
 Orchidese, 350. 
 
 Orthoptera, 626. 
 
 Osborne, Lord S. G., ou fungi, 293. 
 
 on closterium lunula, 284. 
 
 Oscillatoriae, 266. 
 
 Ostracoda, 556. 
 
 Ova mollusca, 545. 
 
 Owen, Major, on foraminifera, 388. 
 
 Professor, on animalcule life, 444 
 
 on microscopic investigation, 705 
 
 Oxytricha, 414. 
 
760 
 
 INDEX. 
 
 -- eggs 
 - of fo 
 
 Oyster, 533. 
 
 - fry. 554. 
 
 - pearl, 533. 
 
 PALATES OF MOLLUSCA, 539. - 
 Panax Lessonii, 329. 
 Papilliseofskin, 675. 
 Parabolic reflectors, 179. 
 Paramsecium, 409. 
 Parasites, 612. 
 
 - of dog, 634.^ 
 of eagle, 643 
 
 of, 607. 
 of fowl, 640. , 
 
 - of hornbill, 642. 
 
 - human, 633. 
 
 - of pheasant, 640. 
 
 - of pigeon, 643. 
 
 - of sheep, 633. 
 
 - of swallow, 639. 
 
 - of turkey, 640. 
 
 - of vulture, 643. 
 Parasitic fungi, 293. 
 Parmelia, 305. 
 
 - stellata, 306. 
 Patella, tongue of, 541. 
 Pear cells, 338. 
 
 Pearl oyster, 533. 
 
 Pearls, artificial, 533. 
 
 Pedicellarise of starfish, 496. '" J 
 
 Pediculi, 636. 
 
 Penetrating power of object-glasses, 75. 
 
 Penium, 283. 
 
 Pennatulidse, 488. 
 
 - phosphorea, 488. 
 Peziza,304. i^^&fev 
 Peronosporse, 290. - .-,...;, T : -.v 
 Pholas dactylus, 531. 
 Photography applied' to microscope, 
 
 155. 
 
 Phryganea, eggs of, 605. 
 Phryganeidae, 601. 
 Phyllactinia, 294. 
 Pigment cells from skin, 675. 
 Pillischer's microscope, 91. 
 Pinna, 530. 
 Planarise, 562. 
 Plants and animals, 257. ' 
 
 annular vessels, 358. 
 
 - cellular tissue of, 323. 
 < - circulation in, 320. 
 
 x crystals in, 337. / V 
 
 - fossil, 362. 
 
 - hairs of, 324. 
 
 - lactiferous tissue of, 334. 
 
 - lice, 613. 
 
 pollen grains, 361. 
 
 - pollen and seeds from, 361. 
 
 - - preparation of tissues, 359. 
 
 - raphides in, 337, 
 
 - cutting sections of, 205. 
 
 silicia in, 340. 
 
 - silicious cuticle of, 339. 
 
 - starch in, 341. 
 
 - starch of potato, 345. 
 
 Plants and animals, starch, wheat 
 flour, 344. 
 
 stellate tissue, 333. 
 
 structure of, 323. 
 
 unicellular, 260. 
 
 vascular system of, 327. 
 
 vascular tissue of, 324. 
 
 vital characteristics, 257. 
 
 woody tissue, 353. f 
 
 Phosphorescence, marine, 408. ; 
 Pleurobranchus, mandible of, 542. : 
 Pleurosigma, 421. 
 
 as a test object, 59. 
 
 Plumatella repens, 527. 
 Plumularia, 478. 
 
 pinnata, 480. 
 
 Podura plumbia, 628. 
 
 scale, as a test, 610. 
 
 Polarisation of light, 132, 729. 
 Polarised light, objects for, 729. 
 Polariser, 137. 
 Polyzoa, 512. 
 
 mounting, 227. 
 
 fresh-water, 524. 
 
 Polycystina, 384. 
 Polygastrica of Ehrenberg, 416. 
 Polyommatus argiolus, 610. 
 Polypifera, 462. 
 Polythalamia, 376. ' 
 Pontia brassica, 611. 
 Potato mould, 290. 
 
 starches, 343. 
 
 Powell and Lealand's microscopes, 8i 
 Powell's condenser, 168. 
 Preparation of insects, 648. 
 Preparing sections of bone, 209. 
 
 tongues of mollusca, 544. 
 
 vegetable tissues, 359. 
 
 Prism for binocular, 117. 
 
 for micro-spectroscope, 121. 
 
 polarising, method of using, 138. 
 
 Sollitt's, 175. 
 
 Propita gigantea, 493. 
 
 Protoco'ccus'pluvialis, 259. 
 
 Protozoa, 363. 
 
 Prussian blue for injections, 238. 
 
 Pteropoda, 532. 
 
 Puccinia, 292. 
 
 buxi, 294. 
 
 Pumpkin fungi, 301. 
 
 QUEKETT on the vascular tissue of 
 plants, 358. 
 
 on polarised light, 154. 
 
 on fossil infusoria, 438. 
 
 on the structure of bone, 714. 
 
 dissecting microscope, 38. 
 
 on resolving test objects, 61. 
 
 Quinine, its detection, 149. 
 Quinidine, test for, 151. 
 crystals of, 151. 
 
 RAINEY, on artificial shell, 551. 
 on desmidiacese, 288. 
 
INDEX. 
 
 '61 
 
 Haifa, Mr., on preservation of algse, 228. 
 
 Raphides in plants, 337. 
 
 Beade's, Rev. J. B., hemispherical 
 
 condenser, 174. 
 Re-agents, effects of, 726. 
 Redfern on separating naviculse, 435. 
 Red seaweeds, 271. 
 Reflector, parabolic, 179, 182. 
 
 Shadbolt's, Mr., 179. 
 
 side, 182. 
 
 Rhinoceros horn, 721. 
 
 Rhizopoda, 372. 
 
 Rhubarb cells, with raphides and 
 
 starch, 388. 
 
 spiral vessels, 355. 
 
 Ringworm, 296. 
 
 Roberts, Dr., on blood cell, 677. 
 Robertson, J., on pholas, 531. 
 Ross's compressorum, 195. 
 
 microscopes, 78 
 
 object-glasses, 74. 
 
 Rotifer, 452. 
 Rush, stem of, 333 
 
 SALTEB, DK. HYDE, on muscle, 496. 
 Salts, urinary, 149. 
 Samuelson, J., on infusoria, 415. 
 Sandstone, 729. 
 Sarcina ventriculi, 295. 
 Sarcode, 656. 
 Saw-fly, 616. 
 Scales of fish, 721. 
 
 of lepidoptera, 609. 
 
 of podura, 628, 
 
 Scapander, tongue of, 542. 
 Schultze, Dr., on rhizopoda, 875. 
 
 on the diatom valve, 422. 
 
 Schwann's classification of tissues, 692. 
 Scissors, dissecting, 202. 
 Sea-cucumbers, 508. 
 
 lilies, 497, 505. 
 
 jelly-fish, 491. 
 
 slug, 529. 
 
 soundings, 383. 
 
 urchins, 498. 
 
 Sections of tissues, 247. 
 Section-cutting machines, 203. 
 Selenite, 14L 
 Sepia, palate of, 541. 
 Serpula, 575. 
 Sertulariadse, 476. 
 
 pumila, 477. 
 
 setacea, 477. 
 
 Shadbolt, Mr., on collecting, 248. 
 
 Sheep-tick, 633. 
 
 Shell, structure of, 546. 
 
 artificial formation of, 551 
 
 8h<>pi<ard,J.B.,oncoloured monads, 413. 
 
 Silk, 3-54. 
 
 Silkworm moth, antenna of, 60S. 
 
 Silkworm's breathing aperture, 586. 
 
 Siiigl- microscope, 4. 
 
 Skin, capillaries of, 675. 
 
 fungoid diseases o 296. 
 
 nerves of, 616. 
 
 Skin, section of, 677. 
 
 Slack, H. J., on a new rotifer, 451. 
 
 Smith and Beck's troughs, 197. 
 
 oblique illuminator, 170. 
 
 Smith's, Prof., condenser, 170. 
 
 growing slide, 198. 
 
 mechanical finger, 436. 
 
 Mr. J., section-cutter, 203. 
 
 Snow, crystals of, 152. 
 Sollitton diatoms as test objects, 427. 
 Sollitt's prism illumination, 175. 
 Sorby's standard interference spec- 
 trum, 738. 
 
 spectroscope, 123. 
 
 Son of ferns, 315. 
 Sphacelaria cirrhosa, 269. 
 Spectro-microscopy, 119. 
 
 Speculum, Lieberkuhn's, 181. 
 Spencer, Herbert, on the formation of 
 
 fibre in plants, 825. 
 Sphagnum, 809. 
 Sphseriacei, 294. 
 Sphaerosira volvox, 276. 
 Spiders, 644. 
 
 diving, 647. 
 
 Spiderwort, 350. 
 Sponges, 885. 
 
 motile phenomena In, 
 
 skeletons of, 396. 
 
 spicula from, 387, 890. 
 
 Spongia coalita, 388. 
 
 geodia, 390. 
 
 Spongilla cinera, 39L 
 -alba, 392. 
 
 development of, 389 ; , 
 
 gemmules of, 400. 
 
 Spring clips, 214. 
 Starches, 843. 
 
 in plants, 342. 
 
 potato, polarised, 154. v] 
 
 tests for, 283. 
 
 Star-fishes, 495. . 
 
 Staurastrum, 282. 
 
 Stellate tissue from a rush, 383. 
 
 Stentors, 450. 
 
 Stephanoceros, 458. 
 
 Stephanosphaera pluvialis, 265. 
 
 Stichostegida?, 276. 
 
 Stinging-nettle hairs, 324. 
 
 Stokes's, Prof, absorption bands, 128. 
 
 Stomach, mucous membrane of, 669, 
 
 Structure of shell, 529. 
 
 Suctoria, 629. 
 
 Sugar insect, 638. 
 
 cane, section of, 336. 
 
 Surirella constricta, 420. 
 Swammerdam's dissection of insect*, 
 
 579. 
 
 Synapta chirodota, 503. 
 Synaptidse, 508. 
 
 TADPOLE, circulation of, 683. 
 
 gill of, 686. 
 
 TseniadiP, 563. 
 
762 
 
 INDEX. 
 
 Tapeworms, 563. 
 
 Tea, adulterated, 349. 
 
 Teeth, preparing sections of, 209. 
 
 of mollusca, how to prepare, 544. 
 
 sections, mounting of, 211. 
 
 Terebratula, 536. 
 
 Teredo, 531. 
 
 Test objects, 57, 61, 65. 
 
 Testacella, tongue of, 542. 
 
 Thomas, Mr., on crystallization, 730. 
 
 Thompson on mollusca tongues, 543. 
 
 Prof. W., on sea-lilies, 497. 
 
 Thread cells, 544. 
 
 in actiniae, 467. 
 
 in mollusca, 544. 
 
 Thuiarea, 478. 
 Thysanura, 627. 
 Tinea vestianella, 611. 
 Tissue, woody, 353. 
 
 animal, 6. 
 
 Tissues, consolidated animal, 702. 
 
 elastic and non-elastic, 694. 
 
 Tomato, diseased, 300. 
 
 Tomkins, Mr. J. N. on alcyonella, 526. 
 
 double prism illumination, 174. 
 
 Tomopteris onisciformis, 576. 
 Tooth, section of, 707. 
 
 structure, 709. 
 
 ofprestis, 711. 
 
 of eagle-ray, 712. 
 
 Topping's test objects, 612. 
 
 section-cutter, 206. 
 
 Torula cerevisia, 300. 
 
 diabetica, 295. 
 
 Tourmaline, 138. 
 
 artificial, 143. 
 
 Tradescantia, circulation in, 350. 
 
 Transformation, insect, 648. 
 
 Transparent injections, 226. 
 
 Trematoda, 563. 
 
 Trembley on hydra, 471. 
 
 Triceratium, 419. 
 
 Trichobasis, 294. 
 
 Crichocera hyemalis, 598. 
 
 frichoda, 411. 
 
 Trichina spiralis, 568. 
 
 Trochell, Dr., on mollusca, 539. 
 
 Troughs for exhibiting circulation, 197 
 
 Truffles, 302. 
 
 Tsetse-fly of Africa, 596. 
 
 Tubercibarium, 302. 
 
 Tubicola, 574. 
 
 Tubiporidse, 489. 
 
 Tubularidae, 473. 
 
 Tubularia Dumortierii, 497. 
 
 Tunicata, 532. 
 
 Turbellaria, 561. 
 
 Turbo mannoratus, tongue of, 543. 
 
 ULV^L development, 271. 
 Uredo, 291. 
 Urinary salts, 149. 
 Uromyces, 291. 
 
 Urticating organs in actinse, 467 
 in mollusca, 544. 
 
 VALENTINE'S knife, 201. 
 
 Vallisneria, 321. 
 
 Varley's animalculse cage, 195. 
 
 on chara, 315. 
 
 Vaucheria, 274. 
 Vegetable structure, 323. 
 
 cell, 255. 
 
 - cellular tissue, 360. 
 
 kingdom, 255. 
 
 division between animal and, 
 
 256. 
 
 preparation of, 359. 
 
 preparation of tissues, 359 
 
 starch, 341. 
 
 vascular tissue, 324. 
 
 Velutina, palate of, 540. 
 
 Vertebrata, 654. 
 
 Vibrio spirilla, 412. 
 
 Viewing objects, directions for, 160 
 
 Virchow on trichina, 569. 
 
 Volvox globator, 275. 
 
 Vorticellidse, 445. 
 
 WALKER'S trough for fish, 197. 
 Warington's microscope, 106. 
 Wasp, 618. 
 
 tongue of, 582. 
 
 Water-beetle, 625. 
 
 Water-microscope, 5. 
 
 Water-mites, 643. 
 
 Wenham on photography applied to 
 
 microscopic drawing, 156. 
 
 on the binocular microscope, 112. 
 
 on object-glasses, 64. 
 
 on a parabolic reflector, 179. 
 
 West, Tuflfen, on feet of flies, 588. 
 Wheat, portion of husk of, 340. 
 
 flour, adulterations of, 344. 
 
 Wheeler's microscopes and cabinets, 
 
 110. 
 
 list of objects, 253. 
 
 Whelk, palate of, 537. 
 
 Whirligig, 625. 
 
 Whitney, W.U., on the tadpole, 683. 
 
 Williamson's collecting stick, 193. 
 
 Wing-shell, 530. 
 
 Wollaston's lenses, 36. 
 
 Wood, cutting sections of, 206. 
 
 Woodward, Mr., on polarised light, 139. 
 
 Wool, 354. 
 
 Wright, Dr., on alcyonida, 524. 
 
 XANTHIDI^J, 282, 441. 
 
 YEAST-PLANT, 299. 
 Yew, section of, 356. 
 
 ZOOPHYTES, canal-bearing, 385. 
 
 a fresh-water group, 463. 
 
 preservation of polypidoms of, 508. 
 
 skeletons of, 490. 
 
 Zygoceros rhombus, 432 
 
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