POPULAR I/IANUALS IC-NRLF 003 Importing FOR FOREIGN PUBLICATIONS ON NATURAL HISTORY AND NATURAL SCIENCE. G. P. PUTNAM'S SONS are prepared to fill orders from the Trade, Libraries, &c., for English and French Works on Natural History and Science, and to take subscriptions for Periodicals treating of these subjects. They would invite special attention to the Publications of Mr. R. HARDWICKE and of Messrs. L. REEVE & Co., of London, any of which when not in stock will be promptly obtained. Complete Catalogues of Publications on the above sub- jects furnished on application. *The following are some of the more important of the Works of these Houses : PERIODICALS. HTHE POPULAR SCIENCE REVIEW. Edited by HENRY _L LAWSON, M.D. Containing able Articles from Representative Scientists on such subjects as Archaeology, Botany, Geology, Palaeontology, Chemistry, Mineralogy, Microscopy, Metallurgy, Mining, Physics, Photo- graphy, Zoology, Comparative Anatomy, and Medicine ; and putting the general reader au courant with the progress of Science at home and abroad during the quarter which has elapsed previous to publication. The Journal furnishes an amount of scientific information, in a popular and yet exact form, which cannot be found in any other English Periodical. Published Quarterly; price $5 a year ; $1.25 a number. Complete sets and back numbers supplied. II. THE MONTHLY MICROSCOPICAL JOURNAL. This Journal is devoted exclusively to the interests of Microscopical Science in the widest and most accurate sense of the term. It contains not only the proceedings of the Royal Microscopical Society, but also embraces communications from the leading Histologists of Great Britain, the Continent, and America, with a comprehensive resuini of the latest Foreign Inquiries, Critical Reviews and Short Notices of the more important works, Biblio- graphical Lists, and Descriptions of all new and improved forms of Microscopes and Microscopic Apparatus ; Correspondence on all matters of Histological Controversy ; and finally, a Department of " Notes and Queries," in which the student can put such questions as may elicit the special information he desires to obtain. Published Monthly ; price per yeaA^^o ; per number 75 cents. Com- plete sets, comprising an exhaustive Record of the progress of Microscopy, copiously illustrated, 7 vols., 8vo, cloth, $36. III. THE FLORAL MAGAZINE. New Series, enlarged to Royal 4to. Figures and Descriptions of Select New Flowers for the Garden, Stove, or Conservatory. By the Rev. H. H. DOMBRAIN. Monthly, with Four Colored Plates, $1.75 ; Annual Subscription, $21. IV. THE BOTANICAL MAGAZINE. Figures and Descriptions of New and Rare Plants of interest to the Botanical Student, and suitable for the Garden, Stove, or Greenhouse. By Dr. J. D. HOOKER, F.R.S. Monthly, with Six Colored Plates, $1.75 ; Annual Subscription, $21. FLORA. H^HE NATURAL HISTORY OF PLANTS. JL By H. BAILLON, President of the Linnaean Society of Paris, Professor of Medical Natural History and Director of the Botanical Garden of the Faculty of Medicine of Paris. Translated by MARCUS M. HARTOG, B. Sc. Lond., Scholar of Trinity College, Cambridge. Vols. I. and II., with 800 Wood Engravings, $12.50 each. T CONES PLANTARUM. _L Figures, with Brief Descriptive Characters and Remarks, of New and Rare Plants, selected from the Author's Herbarium. By Sir W. J. HOOKER, F.R.S. New Series, Vol. V. zoo Plates, $15.50. SELECT ORCHIDACEOUS PLANTS. By ROBERT WARNER, F.R.H.S. With Notes on Culture, by B. S. WILLIAMS. Folio, cloth gilt. Second Series, Parts I. to X., each, wit? 1 3 Colored Plates, $5.25. THE TOURIST'S FLORA; A Descriptive Catalogue of the Flowering Plants and Ferns of the British Islands, France, Germany, Switzerland, Italy, and the Italian Islands. By JOSEPH WOODS, F.L.S. Octavo, $9.00. BRITISH GRASSES ; An Introduction to the Sf&dy of the Grasses found in the British Isles. By M. PLUES. Crown SvoVrfc Colored Plates, drawn expressly for ihe Work by W. FITCH, and loo^Wrod Engravings, $5.25. FERNS. EVERY KNOWN FERN. Synopsis Filicum ; including Osmundacese, Schizgeacese, Marattiacese, and Ophioglossaceae, accompanied by Figures representing the essential characteristics of each Genus. By the late Sir W. J. HOOKER, K.H., and JOHN GILBERT BAKER, F.L.S., Assistant Curator of the Kew Gardens. Price $n plain ; colored by hand, $14. FERNS, BRITISH AND FOREIGN. Their History, Organography, Classification, Nomenclature, and Cul- ture, with Directions showing which are the best adapted for the Hothouse, Greenhouse, Open Air Fernery, or Wardian Case. With an Index of Genera, Species, and Synonyms. By JOHN SMITH, A.L.S., late Curator of the Royal Gardens, Kew. With 250 Wood Cuts. Crown 8vo, cloth, fully illustrated, price $3. Mr. Smith is acknowledged to be one of the first authorities on Perns, having been engaged nearly half a century in arranging them at Kew. GARDEN FERNS; Colored Figures and Descriptions, with Analysis of the Fructification and Venation, of a Selection of Exotic Ferns, adapted for cultivation in the Garden, Hothouse, and Conservatory. By Sir W. J. HOOKER, F.R.S. Royal 8vo, 64 Colored Plates, $21. INSECTS. HARVESTING ANTS AND TRAP-DOOR SPIDERS. Notes and Observations on their Habits and Dwellings. By J. T. MOGGRIDGE, F.L.S. Colored Plates, $5.25. BRITISH INSECTS. A Familiar Description of the Form, Structure, Habits, and Trans- formations of Insects. By E. F. STAVELEY, Author of " British Spiders." Crown 8vo, with 16 beautifully Colored Steel Plates and Numerous Wood Engravings, $7. 6 /A HALF-HOUKS WITH THE MICEOSCOPE. ~-^ ***: * PI. IX HALF- HOURS THE MICROSCOPE; BEING A POPULAR GUIDE TO THE USE OF THE MICROSCOPE AS MEANS OF AMUSEMENT AND INSTRUCTION. BY EDWIN LANKESTER, M.D. ILLUSTEATED FEOM NATUEE, BY TUFFEN WEST. .A. 3ST IE "W IE X> I T I O IsT. With Chapter on the Polwriscope by F. Kitton. NEW YORK : G. P. PUTNAM'S SONS, FOUETH AVENUE AND TWENTY-THIED STEEET. 1874. CONTENTS, CHAPTER J. PAGE A HA.LF-HOI7JI ON THE STRUCTURE OF THE MICROSCOPE 1 CHAPTER II. A HALF-HOUR WITH THE MICROSCOPE IN THE GARDEN 30 CHAPTER III. A HALF-HOUR WITH THE MICROSCOPE IN THE COUNTRY 47 CHAPTER IV. A HALF-HOUR WITH THE MICROSCOPE AT THE POND- SIDE $6 % CHAPTER Y. A HALF-HOUR WITH THE MISCROSCOPE AT THE SEA-SIDE 6? , CHAPTER VI. A IIALT-.HOUR WITH THE MICROSCOPE IN-DOORS 78 CHAPTER VII. A HAIF-HOUR WITH POLARIZED LIGHT APPENDIX. THE PREPARATION AND MOUNTING OF OLJECTS I 2 DESCRIPTION OF PLATES. In the examination of these Plates the observer is requested to remember that they are not all drawn to the same scale. Some objects, adapted for low powers, are only magnified a few times, whilst smaller objects are magnified many Jiundred times. All objects, of course, vary in apparent size, according to the powers with which they are examined. Descriptions of the objects will be found in the pages indicated. PLATE I. to face page 1. FIO. PAGE 1. Vegetable cells with, nucleus from apple 31 2. 'Cellular tissue from pith of elder 31 3. Stellate cell-tissue from rush 32 4. Flat tabular cell from surface of tongxie 91 5. Ciliated cell from windpipe of calf ?1 . Human blood corpuscles 91 7. Blood corpuscles from fowl 92 8. Blood corpuscle from frog 92 9. Blood corpuscle from sole , 92 10. Blood corpuscle from beetle 92 11. Filament of a species of Zygnema, a plant 60 a. Portion of a filament of the same, the cell- contents becoming changed into zoospores. &, Zoospore more highly magnified. X THE MICROSCOPE. FJO, PAGE 12. Filament of a species of OsciUatoria, a plant .... 60 a. Portion more highly magnified. ] 3. Pandorlna Morum, a plant 60 14. Volvox Globator, a plant 60 15. Englena viridis, a plant, showing various forms which it assumes 61 18o Amoeba, an infusory animalcule 69 a, b, c, show the various forms which thi-3 ani- malcule assumes 17. Actinoplirys Sol, the sun animalcule 62-60 18. Difflugia, an infusory animalcule 63 19. Arcella, an infusory animalcule , 63 20. Lagena, a species of Foraminifer 69 21. Polystomella crispa, a species of Foraminifer 69 22. Gldbigerina, a species of Foraminifer 69 23. Rosalina, from chalk, a Foraminifer 69 24. Living Rosalina, a Foraminifer C9 25. Texlilaria, a species of Foraminifer QQ PLATE II. to face page 32. 26. Uha in different stages of development , , ., gj a. Cells in single series. J. Commencement of lateral extension. c. Portion expanded. 27 Cosrnarium, a species of Desmid undergoing self- division. 28. Eaaslrum, a species cf Desmid 57 29. Closterium, a species of Desmid . t 57 a. Undergoing self-division. 0. D&midium, a species of Desmid v ... 57 DESCRIPTION OF PLATE3. xi FIG. PAGE 31. Pediastrum, a species of Desmid 57 32. Scencdcsmus, a species of Desmid , . . . . 57 S3. Surlrella nobilis, a species of Diatom 59 34. Pinnularia viridis, a species of Diatom 59 35. a. Navicula, a species of Diatom undergoing self- division &. Front view of the same. 36. Melosira varians, a species of Diatom 59 37. Melosira nummuloides undergoing self-division . ... 59 38. Coscinodiscus eccentricus, a species of Diatom 58 39. Paramecium Aurelia, an iufusory animalcule 64 40. Vorticella nebulifera, an infusory animalcule 63 41. Rotifer vulgaris, a wheel animalcule 65 42. Stomates on a portion of cuticle of hyacinth leaf .. 32 43. Sinuous walled cells and stomates from under sur- face of leaf of water-cress 32 44. Cuticle of wheat straw with stomates 33 45. Cuticle from petal of geranium (Pelargonium). ... 33 46. Cuticle from leaf of a species of aloe 33 47. Spiral vessel from leaf-stalk of garden rhubarb .... 35 48. Ditto unrolled 35 49. Annular vessel from wheat root 35 50. Dichotomous spiral vessels 35 51. Dotted duct from common radish * . . . 35 52. Scalariform tissue from fern root 35 53. Woody fibre from eider.. % ... 35 THE MICROSCOPE. PLATE III. to face page 40. FIG. PAGE 54. "Glandular" woody tissue 34 55. Transverse section of glandular woody tissue .... 3-1 56. Transverse section of oak 34 57. Long section of oak 34 58. Oblique section of oak 34 59. Section of cork , 35 60. Transverse section of coal 36 61. Longitudinal section of coal 36 62. Wheat starch 37 63. Oat starch 37 64. Potato starch 37 65. Tous-les-mois starch 37 66. Indian corn starch 38 67. Sago starch -. 37 68. Tapioca starch 37 69. Acicular raphides from garden hyacinth 38 70. Bundle of ditto from leaf of aloe contained in a cell 33 71. Compound raphides from stalk of garden rhubarb. . 39 72. Tabular prismatic raphides from outer coat of onion 39 73. Circular crystalline mass from a cactus 39 74. Simple vegetable hair from leaf of a common grass 40 75. Rudimentary hair from flower of pansy 40 76. Simple club-shaped hair, 40 77. Club-shaped hair from leaf of dock 41 78. Hair from throat of pansy 40 79. a. Hair formed of two cells from flower of white dead-nettle 41 79, 6. Many-jointed tapering hair with nuclei from common groundsel ..,-., ... 4] DESCRIPTION OF PLATES. xiii PTO, PAGE SO. Beaded hair of sow-thistle 41 81. Glandular hair from leaf of common tobacco 41 82. Hair from leaf of garden chrysanthemum 41 83. Rosette-shaped glandular hair from flower of verbena 41 84. Stellate hairs from the hollyhock (A Ithasa rosea).. 41 85. a. Stellate hair from leaf of lavender 41 85, 6. Hair from leaf of garden verbena, with warty surface 45 86. Hair from leaf of white poplar (Populus alba) .... 41 87. Ease of a hair on a mass of cellular tissue 41 88, a. A sting from common nettle 42 88, 6. Portion of a leaf of Valisneria 42 PLATE IV. to face page 48. 89. Palmclla cruenta gory dew 48 90. Yeast plant 48 91. Portions of vinegar plant 48 92. So-called cholera fungus obtained from the air. ... 48 93. Red rust of wheat 49 94. Puccinia yraminis mildew 49 95. Pent till him glaucum common mould 49 96. Boirytis from mouldy grape 49 , 97. Fungus from mouldy bread (Mucor Muccdo] .... 49 98. Fungus from human ear 49 99. Fungus from leaf of bramble (Phragmidium bul- I'osum) 49 100. Vine blight (Oldium Tuckeri) 50 101. Potato blight (Bolrylis infcslans) 50 102. a. Pea. blight (Erysiplie Pisi) 50 6. Asci and sporidia of pea blight CO 103. Fungus from a decayed Spanish nut 50 XIV THE MICROSCOPE, FIG. PAGE 104. Curious fungus from oil casks 50 105. Fungus of common ringworm (Achorion Schonlenii) 50 106. Fungus on stem of duckweed 50 a. Another within the cells. 107. a. Branched cells from stem of mushroom 51 I. Branched cells from rootlets of mushroom .... 51 C. Reproductive bodies borne ra fours on the gills of mushrooms 51 108. Section through a brilliant orange-coloured peziza 52 109. Section through the common yellow lichen of trees and walls 52 110. Leaf of Sphagnum bog moss 52 111. Sea weed Polyslphonia fastiyiata 67 a. Fruit-bearing organs. &. Spore. c. Portion of Bispore ; and d. Tetraspore. e. Antheridia. 112. Eeproductive organs of a moss, a species of Tortula 52 a. The calyptra. 6. The operculum. c. The peristome. d. The teeth. e. The spores. 113. Fructification on back of frond of male fern. ..... 53 114. Fructification on back of frond of common brakes 53 115. Capsules of Scolopendrium hartstongue. The sporules seen escaping 53 a. One of the latter more magnified 53 116. Fructification of Equisetum horsetail .......... 55 a. Shield-like disk of ditto, separated, surrounded by thecffl 55 DESCRIPTION OF PLATES. XV FIG. 116, 6. Spore, much magnified, with elastic filaments coiled closely round ...................... 55 c. Spore expanded .......................... 55 117, a. Fructification of Lycopodium club moss ...... 54 b. Sporules .................... . .... ....... 54 C. Sporules more highly magnified, PLATE V. to face page 56. 118. Delicate spiral cells from anthers of furze 44 119. Large well-developed spiral cells from anthers of hyacinth, with minute raphides in intercellular spaces 44 120. Irregular deposit in cells of anthers of white dead- nettle 44 121. Annular ducts from anthers of narcissus 44. 122. Stellate cells from anthers of crown imperial .... 44 123. Ovate pollen cells 44 124. Triangular pollen cells from hazel 44 125. Pollen cells of heath 44 126. Pollen cells of dandelion 44 127. Pollen cells of passion flower 45 128. Pollen cells of mallow 45 129. Eed poppy seed 46 130. Black mustard seed 46 131. Seed with deep and curved furrows 46 132. Great snapdragon seed * 46 133. Chickweed seed 41 134. Umbelliferous seed or fruit 46 135. Zygnema, conjugating 60- 136. Clostenum, conjugating 57 XV]' THE MICROSCOPE. FHJ. PAGE 137. Cosmarlum, conjugating .....,,* 57 138. Epiiheiiiia gibbet, conjugating 43 2 39. Melosira nummuloidcs, conjugating 59 110. Transverse section of common sponge 6} 141. Transverse section of common British sponge .... 63 a. Spicules of the same more magnified. Calcareous spicules of Grantia ciliufa. 68 142. Pin-like spiculum from Cliona, a boring sponge . . 69 143. Spiculum from Spongilla, a fresh-water sponge . . 69 144. Spiculum from unknown sponge 69 145. Spiculum from Tethea f>9 146. Common Hydra 70 a. Stinging organ from common Hydra 147. A species of Sertularia, a zoophyte 71 148. Campanularia Integra, a zoophyte 71 149. " Cup" of Campanularia volubilis, a zoophyte. ... 71 1 50. Spicula of Gorgonia verrucosa 71 151. Transverse section from base of spine of Echinus neglectus 72 152. Calcareous rosette from sucker of Echinus 72 153. Pedicellaria from Echinus 72 154. Pedicellaria from star-fish 72 PLATE VI. to face page 72. 155. Lepralia, a polyzoon 72 156. BoicerbanTcia densa, a polyzoon 73 157. Tobacco-pipe, or bird's-head processes of Notamia 73 a. Bird's-heau process. 158. Bugula avicularia 73 159. Bird 's-head process of Bugula Murrayana . 73 DESCRIPTION OF PLATES. XVU FIG. PAGE 160. Scrupularia swuposa, with bird's-head processes (avicularia) and sweeping bristles (vibracula). . 73 161. Snake-headed zoophyte Anyuinaria 73 162. Flustra foliacea sea mat 72 163. Plumatdla repens, a fresh-water polyzoon 74 164. Egg of Cristatella Muccdo, a fresh-water polyzoon 74 165. Transverse section of shell of Pinna, showing prismatic shell structure 74 166. Longitudinal section of shell of Pinna 75 167. Transverse section from oyster-shell 7 ft 168. Section of shell of Anomia, with tubular borings. . 75 169. Section of mother of pearl 75 170. Prawn-shell viewed as a transparent object 75 171. Teeth of whelk 73 172. Teeth of limpet 75 173. Teeth of periwinkle 73 174. Teeth of Limneus 75 175. Scale of sturgeon ganoid 7^ 176. Prickle from back of skate placoid 7 177. Borings by a minute parasite in a fossil fish-scale. . ^7 178. Scale of sole ctenoid * 179. Scale-, "whiting cycloid 77 a. CuL-^eous particles, magnified. 180. Scale of sprat cycloid 7V 181. Section of egg-shell 90 182. From soft egg. 183. Section of egg-shell of emu 90 PLATE VI I. to face page 80. 184. Human hair , . . , 78 a* Transverse section of human hair. XV111 THE MICROSCOPE. FIG. PAGE 185, a. Small mouse-hair......,,., , 79 6. Larger mouse-hair. c. Plain mouse-hair. d. Minute hair from ear of mouse. 136. Hair of long-eared bat 50 187. Transverse section of hair of peccary 80 183. Pith-like hair of musk-deer SO 1S9. Hair from tiger caterpillar . , So 190. a. Branched hairs from leg of garden spider (Epeira diadema) 81 b. Spine, with spiral flutings, from the same. C. Small brush-Lite hairs from an Australian spider. 191 . Hair from flabellum of crab 81 192. Portion of four of the barbs of a goose-quill 81 193. Portion of the same more magnified 81 194. Swan's-down 81 195. Head and mouth of a flea 82 196. Head and mouth of a bug 82 197. Mandible of humble bee Si 198. Head and mouth of louse 3 199. Head and mouth of gnat . . 83 200. Extremities of barbs of the sting of common bee. . 34 201. Head of honey bee 83 a. Piece of the tongue more magnified. 202. Mouth of blow-fly 84 203. Head and mouth of butterfly 84 204. One of the fangs of a spider, showing the poison- bag and duct 85 205. Foot of Empis, a species of fly 87 206. Foot of bee 87 207. Foot of spider 87 DESCRIPTION OF TLATES. FIG. 208. Head of common spider, showing eight simple eyes. a. Cornea of one of these more magnified 85 209. Skin of garden spider 85 210. Portion of compound eye of fly 83 211. Portions of the two wings of bee in flight 88 a. Nervule of wing. 212. Spiracle of fly 86 213. Spiracle of Dytiscus 86 214. Threads of garden spider (Epeira diadema) 86 Simple thread of the same. Thread of a concentric circle with viscous dots. PLATE VIII. to face page 88. 215. Fore leg of Gyrinus natator, whirligig beetle .... 87 216. Middle leg of the same 87 217. Hind leg of same 87 218. Fore leg of male Dytiscus 87 219. Middle leg of the same. 220. a. Gizzard of cockroach 89 6. Ditto, cut open. 221. a. Gizzard of cricket 89 &. Ditto, cut open. 222. Trachea from caterpillar 86 223. Proleg of caterpillar of common garden white butterfly, with the membranes in which the hooks are seated, expanded as in action 83 224. Part of leg of cockroach 225. Battledore scale from blue argus butterfly 88 226. Scale of ordinary shape from same 88 227. Scale from meadow-brown butterfly 88 228. Scaleofgnat .33 XX THE MICROSCOPE. PIG. PAGE 229. Scale reduced to a hair from clothes-moth 85 230. Hair-like scale from clothes-moth, with three prongs 89 231. Cartilage from mouse's ear 91 232. Transverse section of human bone 90 233. Striped muscular fibre from meat 92 234. a. Liber fibre of flay, natural state , . . . . 79 b. Ditto, broken across at short intervals 235. Wool from flannel 79 236. Silk ., 79 237. Cotton hair 79 238. Crystal of honey f;l> 239. Thick crystal of ordinary sugar same angles .... 39 240. Crystals of sugar from adulterated honey 40 241. Cuticle from berry of holly 35 242. Transverse section of whalebone 90 243. Transverse section of plum-stone 31 244. Transverse section of testa of seed of Guelder rose 13 245. Fruit of groundsel opaque 42 246. One hair of pappus of dandelion 42 247. Cottony hair of burdock 42 248. Portion of pappus of goats-beard 42 249. "Wood of young shoots of vine, the cells containing starch S3 250. Spiral fibres from testa of wild sage seed 35 PLATE IX. Frontispiece to face title-page. 1. lodo-sulphate of Quinine 2. Salicine 3. Aspartic Acid 4. Sulphate of Copper in Gelatine 5. Grey Hair (human) 6. Scales of Hyppophas rhainnoides VrWestimp. Robert Eandwicke ,1860 HALF-HOURS WITH THE MICROSCOPE, CHAPTER I . A HALF-HOUE ON THE STEUCTUEE OF THE MICEOSCOPE. THE Microscope is often regarded merely as a toy, capable of affording only a certain amount of amusement. However much this might have been the case when its manufacture was less perfectly understood, it is now an instrument of so much importance that scarcely any other can vie with it in the interest we attach to the discoveries made by its aid. By its means man increases the power of his vision, so that he thus gains a greater know- ledge of the nature of all objects by which he is surrounded. What eyes would be to the man who is born blind, the Microscope is to the man who sees only with his naked eye. It opens a new world to him, and thousands of objects whose form and shape, and even existence, he could only ima- gine, can now be observed with accuracy. Nor is this increase of knowledge without great advantages. Take for instance the study of plants and animals. Both are endowed with what we call life : they grow and perform certain living functions ; but as to the mode of their growth, and the way in which their functions were performed, little or nothing was known till the Microscope revealed their minute structure, and showed fe^\N v thei*- Carious parts were related to each other. The B 2 THE STRUCTURE OF Microscope has thus become a necessary instrument in the hands of the botanist, the physiologist, the zoologist, the anatomist, and the geologist. Let us. then, endeavour to understand how it is this little instrument has been of such great service in helping on the advancement of science. Its use depends entirely on its assisting the human eye to see to see more with its aid than it could possibly do without it. This it does by enabling the eye to be brought more closely in contact with an object than it otherwise could be. Just in proportion as we bring our eyes close to objects, do we see more of them. Thus, if we look at a printed bill from the opposite side of a street, we can see the larger letters only ; but if we go nearer we see the smaller letters, till at last we get to a point when we can see no more by getting closer. Now suppose there were letters printed on the bill so small that we could not see them with the naked eye, yet, by the aid of a lens a piece of convex glass we could bring our eyes nearer to the letters, and see them distinctly. It would depend entirely on the form of the lens, as to how close we could bring our eyes to the print, and see; but this great fact will be observed, that the nearer we can get our eyes to the print, the more we shall see. The most important part of a Microscope, then, consists of a lens, by means of which the eye can be brought nearer to any object, and is thus enabled to see more of it. Magnifying-glasses and Simple Microscopes consist mainly of this one element. In order, however, to enable the eye to get as close as possible to an object, it becomes convenient to use more than one lens in a glass through which we look. These lenses, for the sake of convenience, are fixed in a brass frame, and attached to the Simple Microscope ; when there are two lenses they THE MICROSCOPE. 3 are called doublets, and when three they are termed triplets. The magnify ing-glasses which are made to be held in the hand, frequently have two or three lenses, by which their power may be increased or decreased. Such instruments as these were the first which were employed by microscopic observers: and it is a proof of the essential nature of this part of the Microscope, that many of the greatest discoveries have been made with the Simple Mi- croscope. The nearer the glass or lens is brought to an object, so as to enable the eye to &ee, the more of its details will be observed. So that when we use a glass which enables us to see within one inch of an object, we see much more than if we could bring it within only an inch and a half or two inches. So on, till we come to distances so small as the eighth, sixteenth, or even twentieth of an inch. Although a great deal may be seen by a common hand-glass, such as may be purchased at an optician's for a few shillings, yet the hand is unsteady ; and if these glasses were made with a very short focus, it would be almost impossible to use them. Besides, it is very desirable, in examining objects, to have both hands free. On these accounts the glasses, which in such an arrangement are called object- glasses (see fig. 3), are attached to a stand, and placed in an arm, which moves up and down with rack- work. Tn this way, the distance of the object from the glass can be regulated with great nicety. Under- neath the glass, and attached to the same stand, is a little plate or framework, to hold objects, which are placed on a slide of glass. This is called the stage. (Fig. 1, G.) Sometimes rack-work is added to this stage, by which the objects can be moved upon it backwards and forwards, without being moved by the hand. Such an arrangement as this is B 2 4: THE STRUCTURE OF called a Simple Microscope. Of course many other things maybe added to it, to make it more conveni- ent for observation ; but these are its essential parts. But, although the Simple Microscope embraces the essential conditions of all Microscopes, and has, in the hands of competent observers, done so much for science, it is, nevertheless, going out of fashion, and giving way to the Compound Microscope. (Fig. 1, p. 5.) This instrument, as might be inferred from its name, is much more complicated than the Simple Microscope, but it is now constructed with so much accuracy, that it can be used with as great cer- tainty and ease as the Simple Microscope itself. In order to understand the mechanism of the Compound Microscope we must first of all study the principles on which it is constructed. If we take a common convex lens and place any small object on one side of it, so as to be in its focus, and then place on the other side a sheet of white paper, we shall find at a certain point that an enlarged picture of the object will be produced on the paper ; and this is the way in which pictures are formed by the camera of which the photographic artist avails himself for his portraits and sun-pictures. Now L we look at this picture with another lens of the same character but of somewhat less magnifying power, we shall obtain a second picture larger than the first, and this is the principle involved in the Compound Microscope. The superiority of this instrument over the Simple Microscope consists in an increase of magnifying power. There is, how- ever, a limit to the utility of this magnifying power ; for when objects are greatly magnified they become indistinct. This is seen in the Oxyhydrogen and Solar Microscopes, where the images are thrown, by means of highly magnifying lenses, on a white sheet; and, although made enormously large, their details THE MICROSCOPE. 5 are much less clear than when looked at by a lens magnifying much less. Another advantage of the Fig. 1 * Compound Microscope. Compound Microscope is the distance at which the eye is placed from the object, and the facility with * In this little work we have purposely abstained from mentioning either the names or the Microscopes of our principal makers, lest we should thereby seem to give a 6 THE STRUCTURE OF wLich the hands may be used for all purposes of manipulation. A brief description, aided by the accompanying illustration, will, it is hoped, suffice to make the beginner acquainted with the various parts of this important instrument. We have already mentioned that when powerful lenses are used in the examination of small objects the hand is not sufficiently steady to give a firm support to the lens employed, and this is equally true of the hand that holds the object. It is also essentially requisite to have both hands free, for the purpose of manipulation. Hence it becomes necessary to devise some mechanical means for the support of both the lens and the object. How these wants have been supplied by the enterprising skill and ingenuity of our opticians will be best seen as we describe the various parts of which the Compound Microscope consists. The most important part of the instrument is undoubtedly that which carries the various lenses or magnifying powers. These are contained in the interior of the tube or body, A, which is usually constructed of brass, and from 8 to 10 inches in length. At the upper end of the tube is the eye- piece, B, so named from its proximity to the eye of the observer. It consists of two plano-convex lenses, set in a short piece of tubing, with their flat surfaces turned towards the eye, and at a distance from each other of half their united focal lengths. The first of these lenses is the eye-glass, while that nearest the objective is termed the field lens. The use of the latter is to alter the course preference to any. The general excellence of these instru- ments is so well known and the names of their makers are so universal that the student will find no difficulty in provid- ing himself with an efficient instrument at a moderate cost. THE MICROSCOPE. of the light's rays in their passage to the eye, in such manner as to bring the image formed by the object-glass into a condition to be seen by the eye- glass. A stop also is placed between the two lenses in such a position that all the outer rays, which pro- duce the greatest amount of distortion, arising from spherical and chromatic aberration, are cut off. The short tube carrying the lenses (fig. 2) slides freely, but without looseness, into the upper end of the com- pound body, A, an arrangement which affords a ready and convenient method for changing the eye-pieoe. Compound Microscopes are generally fitted up with two eye-pieces, the one deep and the other shallow. The last has its lenses close together, and magnifies the most, whilst the other has them far- ther apart, and magnifies less. In the use of these eye-pieces, it should never be forgotten that the one which magnifies least is generally the most trust- worthy. Fig. 2. Eye-piece. At the opposite end of the tube A is the object- glass C. The use of this lens is to collect and bring to a point the rays of light that proceed from any object placed in its focus. At this point an enlarged image of the object will be formed in the focus of the eye-glass. We have only to look through the latter at the picture thus formed in order to obtain a second image larger than the first. And this is the way in which minute objects are made to appear so much larger than when seen by the unassisted eye. It will at once be seen how 8 THE STRUCTURE OP much of the utility of a Microscope depends on good object-glasses. Where they are faulty, the image they form is also faulty ; and when these faults in the first image are multiplied by the power of the eye-piece, they become like the faults of our friends when viewed through a similar medium of great magnitude. A good object-glass may be known by its giving a clear and well-defined view of any object we may wish to examine ; while a bad lens may be equally well known by the absence of these qualities. In short, a badly constructed objective is more apt to mislead than to guide the student, by the fictitious appearances it creates appearances that may be erroneously taken for realities, which have no exist- ence in the object itself. The object-glasses of our best opticians consist of several lenses arranged in pairs, set in a small brass tube. A screw at one end serves to attach them to the lower extremity of the compound body, A. (Fig. 3.) The body of the Microscope is supported by a stout metal arm, D, into the free end of which it screws. The opposite end of the arm is secured to the stem, E, by a screw, on which it moves Fig. 3. Object-Glass. a f on a P ivot B 7 this means the tube of the Microscope can be turned away from the stage an arrangement that gives this form of Microscope an advantage over those that are not so constructed. To the stem, J, which works up and down a hollow pillar by rack-work and pinion, is attached the stage, G. This, in its simplest form, consists of a thin flat plate of brass, for holding objects undergoing ex- THE MICROSCOPE. 9 animation. In the centre is a circular opening, for the passage of the light reflected upward by the mirror, H. There is also a sliding ledge, // against this the glass slide, on which the object is mounted, rests, when the Microscope is inclined from the perpendicular. In a stage of this kind the various parts of an object can only be brought under the eye by shifting the slide with the fingers. But in more expensive instruments the stage is usually con- structed of one or two sliding plates, to which motion is given by rackwork and pinion ; the whole being brought under the hand of the operator by two milled heads, a mechanical arrangement which enables him to move with ease and certainty the object he may wish to investigate. Underneath the stage is the diaphragm, K, a contrivance for limiting the amount of light supplied by the mirror, H. It consists of a thin, circular, flat plate of metal, turning on a pivot, and perforated with three or four cir- cular holes of varying diameter (fig. ^ 4), the Dia p hra gm. largest only being equal to the aperture in the stage. By turning the plate round, a succession of smaller openings is brought into the centre of the stage, and in one position of the diaphragm the light is totally excluded. By this small but useful contrivance the Microscopist can adjust the illumination of the mirror to suit the character of the object he may be investiga- ting. In some Microscopes the diaphragm is a fix- 10 THE STRUCTURE OF ture, but in the better class of instruments it is simply attached to the under part of the stage by a bayo- net catch, or by a sliding plate of me- tal (fig. 5), and can be readily removed pig. 5. Diaphragm, therefrom when it is desirable to employ other methods of illumi- nation. In working with the Microscope it is necessary to adopt some- artificial means for ensuring a larger supply of light than can be obtained from the natural diffused light of day, or from a lamp or candle. For this purpose the Microscope is fur- nished with a double mirror, H, having two reflect- ing surfaces, the one plane and the other convex. The latter is the one usually employed in the illu- mination of transparent objects ; the rays of light which are reflected from its concave surface are made to converge, and thus pass through the object in a condensed form to the eye. The plane mirror is used generally in conjunction with an achromatic condenser, when parallel rays only are required. The whole apparatus is attached to that portion of the hollow pillar continued beneath the stage, in such a manner that it can be moved freely up and down the stem that supports it. This motion enables the Microscopist to regulate the intensity of his light by increasing or decreasing the distance between the mirror and the stage ; while the peculiar way in which the mirror itself is suspended on two points of a crescent-shaped arm, turning on a pivot, gives an almost universal motion to the reflecting surfaces. The observer by this means can secure any degree of oblique illumination ha THE MICROSCOPE. 11 may require for the elucidation of the structure undergoing examination. We next come to the stand, which, though the most mechanical, is at the same time a very impor- tant part of the Compound Microscope. On the solidity and steadiness of this portion of the instru- ment depends in a great measure its utility. The form generally adhered to is that represented in our diagram (fig. 1, p. 5.) It consists of a tripod base, P, from which rise two flat upright pillars, 0. Between these, on the two hinge-joints shown at L, is sus- pended the whole of the apparatus already described : namely, the body carrying the lenses, the arm to which it is attached, the stage, and the mirror underneath it. By this contrivance the Microscope can be inclined at any angle between a vertical and horizontal position an advantage which can be duly appreciated by those who work with the instrument for two or three hours at a time. Close to the points of suspension are the milled heads, M ; these are connected with a pinion working in a rack cut in the stem, E. By turning the milled heads the tube is made to approach or recede from the stage until the proper focus of the object-glass is found. This is termed the coarse adjustment, and is gene- rally used for low powers, where delicate focussing is not required. But when high magnifying powers are used, that require a far greater degree of pre- cision, we have recourse to the fine adjustment, N, which consists of a screw acting on the end of a lever. The head of the screw by which motion ic communicated to the object-glass is divided into ten equal parts, and when caused to rotate through any of its divisions slightly raises or depresses the tube, carrying the objective with it. As the screw itself contains just 150 threads to an inch one revolution of its head will cause an alteration of the 150th 12 THE STRUCTURE OF of an inch in the distance of the lens from the object. When moved through only one of its divisions we obtain a result equal to the 1500th of an inch, and by causing it to rotate through half a division we secure a movement not exceeding the 3000th part of an inch in extent. Such nicety in the adjustment of the optical part of the Micro- scope may seem to the beginner unnecessary, but when he comes to work with high powers he will find that he needs the most delicate mechanical contrivances to enable him to secure the proper focus of a sensitive object-glass. But this is not the only use to which we can put the fine adjustment. The same process that serves to re- gulate the focus of a lens will also enable us to measure pretty accurately the thickness of an object or any of the small prominences or depressions found in its structure. By observing the number of divisions through which the head of the screw is made to pass while changing the focus of the object-glass from the bottom to the top of any small cavity or prominence we get a tolerable notion of its depth or height, &c. Connected with this apparatus is a special contrivance for protecting the object-glass to some extent from injury. It will sometimes happen, even with the most careful, when using high powers, that the lens is brought down with some force in contact with the glass cover that protects the object. This risk is not unfrequently incurred by admitting to one's study incautious friends, whose confidence is only equalled by their ignorance ; who although they may have never seen a Microscope before, will proceed to turn it up and down with a force sufficient to crack the lens. Such friends would have sufficient confidence in themselves to take the command of a man-of-war, even though it were the first time in their lives THE MICROSCOPE, 13 they Lad been on board a ship. Strict injunctions must be laid on all such not to approach the table until the instrument is quite ready for them to take a peep, coupled with a polite request that while doing so they will keep their hands behind them. A provision has been made which to some extent provides for such an emergency. The object-glass itself is screwed into a short tube, that fits accu- rately the lower end of the compound body and slides freely within it, being kept down in its place by a spiral spring, which presses upon it from behind. On the application . of a slight force or resistance to the object-glass the spring tube immediately yields, within certain limits, to the pressure, carrying with it the lens, which is thus often saved from destruction. Object-glasses of various degrees of magnifying power and excellence of workmanship are supplied with th-e Microscope, and may be purchased separately, according to the wants and resources of the student. It will be found that for all ordinary purposes the 1-inch and 1-inch objectives are the most useful powers. A substitute for the intermediate powers may be obtained by pulling out the draw-tube and using the higher eye-pieces. This method, though not so satisfactory in its results as the use of separate object-glasses, may be resorted to where a series of objectives are not within the reach of the observer. THE BINOCULAR MICROSCOPE. Since the invention of the Stereoscope attempts have been made to apply the Binocular principle in the construction of the Compound Micro- scope. After some failures this desideratum has been successfully achieved by Mr. F. H. "Wenham, a gentleman well known to microscopists by 14: THE STRUCTURE O the fertility of his resources and the ingenuity of his inventions in connection with the Microscope. It is to him that we are indebted for a Microscope that enables us to see objects in a natural manner, namely, with both eyes at once. Hitherto the ordinary single-tubed Microscope reduced the ob- server to the condition of a Cyclops. Although gifted with a pair of eyes he found it impossible to avail himself of this plurality of organs. He was condemned by the very nature of his Microscope to peer perpetually with a single eye through its solitary tube ; but thanks to- Mr. Wenham all this is changed. We have now the satisfaction of using a double-tubed Microscope that not only gives em- ployment to both eyes at once, but presents us with effects unknown and unattainable by the ordinary instrument. We no longer gaze at a flat surface, but a stereoscopic image stands out before us with a boldness and solidity perfectly marvellous to those who have only been accustomed to the ordinary single-tubed Microscope. " No one," says a writer in ' The Popular Science He view,' " can fail to be struck with the beautiful appearance of objects viewed under the Binocular Microscope. Its chief application is to such objects as require low powers, and can be seen by reflected light, when the wonderful relief and solidity of the bodies under observation astonish and delight even the adept. Foraminifera, always beautiful, have their beauties increased tenfold ; vegetable struc- tures, pollen, and a thousand other things, are seen in their true lights, and even diatoms, we may pre- dict, will receive elucidation, as to the vexed ques- tions of the convexity or concavity of their infinitely minute markings. The importance of the Binocular principle is especially apparent when applied to anatomical investigation. Prepared Microscopic TIIE MICROSCOPE. injections exhibit under the ordinary Microscope a mass of interlacing vessels, whose relation, being all on the same plane, it is not easy to make out with any degree of satisfaction. But placed under the Binocular they at once assume their relative position. Instead of a flat band of vessels, we now see layer above layer of tissue ; deeper vessels an- astomosing with those more superficial ; the larger vessels sending branches, some forward and some backward, and the whole injection assumes its natural appearance, instead of being only like a picture" Fortunately for the possessors of the ordinary Microscope, the Bin- ocular arrangement can be readily adapted to this instrument at a cost of a few- pounds. The addi- tional tube and prism does not interfere with the use of the instrument as a mon- ocular, the withdrawal of the prism instantly converts it into that form of instrument : this is necessary when high powers are used. The accompanying diagram (fig. 6) a section of the Bin- ocular will give * the reader a correct Fig. 6. Section of notion of the mecha- Binocular Microscope. 16 THE STRUCTUKE OF nism of the instrument. Let G represent the body of the ordinary Microscope and the secondary tube attached to the side of the former, which it will be seen has a portion of its surface cut away at the point of junction, F, as a means of commu- nication between them. The eye-pieces and draw- tubes are seen at D and E. The object-glass G is attached to the ordinary tube C in the usual way. Just above it is the small prism, A, mounted in a brass box, and so constructed as to slide into an opening in the tube at the back of the object-glass. By this arrangement it will be found that while one half of the light passes up the tube unobstructed the other half must first pass through the prism, where, after undergoing two re- flections (fig. 7), it es- capes in the direction of the additional tube B. The dotted lines in the diagram show the direction the light takes in its passage to the eyes. At H the rays are seen to cross each other. Those from the left side of the obj ect-glass traverse the . _ right tube, while those from Double-reflecting Prism. ^ rigbt ' side of the lens are projected up the left tube. In using the Binocular it must be remembered that the eyes of different individuals vary in their distance from each other. It will thus be seen that some contrivance is necessary to enable us to increase or decrease the distance between the eye- pieces to suit the requirements of all. This is accomplished by the two draw-tubes, D and E, which carry the eye-pieces. When drawn out, the THE MICROSCOPE. IT latter are made to diverge, and when pushed iu they converge. In this way any intermediate distance can be obtained to suit every kind of vision. "Where a Binocular Microscope is in daily use it will sometimes be necessary to withdraw the prism from the tube, to cleanse it from dust and other impurities gradually contracted by use. Whenever this may be necessary great care should be taken to employ no substance likely to scratch its highly polished surfaces; for on these being preserved intact in a great measure depends the efficiency of the in- strument. We know of nothing better adapted for removing impurities than a clean silk or cambric handkerchief, which, when not in use, should be kept in a closely-fitting drawer, to protect it from dust. There seems to be little doubt that this lately improved form of the Compound Microscope will eventually supersede all others. This opinion also seems to be entertained by the inventor himself, whose words we quote : " The numerous Microscopes that have been altered into Binoculars, in accordance with my last principle, and also the large quantity still in the course of manufacture, will, I think, justify me in making the assertion, without presumption, that henceforth no first-class Microscope will be con- sidered complete unless adapted with the Binocular arrangement." The Compound Microscope is now, undoubtedly, one of the most perfect instruments invented and used by man. In the case of all other instruments, the materials with which they are made and the defects of construction are drawbacks on their per- fect working ; but in the Compound Microscope we have an instrument working up to the theory of its construction. It does actually all that could c 18 THE STRUCTURE OF be expected from it, upon a correct theory of the principles upon which it is constructed. Neverthe- less, this instrument did not come perfect from its inventor's hands. Its principles were understood by the earlier microscopic observers in the seventeenth and eighteenth centuries, but there were certain drawbacks to its use, which were not overcome till the commencement of the second quarter of the present century. These drawbacks depended on the nature of the lenses used in its construction. The technical term for the defects alluded to are chromatic and spheri- cal aberration. Most persons are acquainted with the fact that, when light passes through irregular pieces of cut glass as the drops of a chandelier, a variety of colours is produced. These colours, when formed by a prism, produce a coloured image called the spectrum. Now, all pieces of glass with irregular surfaces produce, more or less, the colours of the spectrum when light passes through them j and this is the case with the lenses which are used as object-glasses for Microscopes. In glasses of defective construction, every object looked at through them is coloured by the agency of this property. The greater the number of lenses used in a Microscope, the greater, of course, is the liability to this colouring. This is chromatic aberration ; and the liability to it in the earlier- made Compound Microscopes was so great that it destroyed the value of the instrument for purposes of observation. Again, the rays of light, when passing through convex lenses, do not fall when they form a picture all on the same plane; and therefore, instead of forming the object as presented, pro- duce a picture of it that is bent and more or less distorted. This is spherical aberration, and a fault THE MICROSCOPE. 19 which was liable to be increased by the number of glasses, in the same way as chromatic aberration. This defect also is increased in Compound Micro- scopes ; and formerly, the two things operated so greatly to the prejudice of this instrument that it was seldom or never used. Gradually, however, means of improvement were discovered. These defects were rectified in tele- scopes; and at last a solution of all the difficulties that beset the path of the Microscope-maker was afforded by the discoveries of Mr. Joseph Jackson Lister, a gentleman engaged in business in London, who, in a paper published in the Philosophical Transactions for 1829, pointed out the way in which the Compound Microscope could be con- structed free from chromatic and spherical aberra- tion. This is done by such an arrangement of the lenses in the object-glass, that one lens corrects the defects of the other. Thus, in object-glasses of the highest power, as many as eight distinct lenses are combined. We have, first, a triplet, composed of two plano-convex lenses of crown-glass, with a plano-concave of flint-glass between them. Above this is placed a doublet, consisting of a double convex lens of crown, and a double concave one of flint-glass. At the back of this is a triplet, which consists of two double convex lenses of crown- glass, and a double concave one of flint placed be- tween them. Such are the combinations necessary to correct the defects of lenses when employed in Compound Microscopes. It is this instrument, then, which is most com- monly employed at the present day, and to which we are indebted for most of the recent progress in microscopic observation. In using the Microscope, a great variety of acces- sory apparatus may be employed to facilitate the c 2 20 THE STRUCTURE OF various objects which the observer has in vievr. As this is a book for beginners, w<; shall only mention a few of these. Microscopes are generally supplied with small slips of glass, three inches long and one inch wide. These are intended to place the objects on which are to be examined. They are cither used tempo- rarily or permanently with this object in view, Fig. 8. Forceps. and are called slides. When used temporarily, an object, such as a small insect, or part of an insect, Fig. 9. Bull's-eye Condenser. is placed upon the middle of it ; and it may be either placed immediately upon the stage at the THE MICROSCOPE, 21 proper distance from the object-glass, or a drop of water may be placed on the slide, and a piece of thinner glass placed over the object. This is the most convenient arrangement, as you may then tilt your Microscope without the slide or object falling off. Objects, when placed under the Microscope, are of t\vo kinds either transparent or opaque. When they are opaque, they may either be placed upon the slips of glass, or put between a small pair of forceps (tig. 8), which are fixed to the stage of the Microscope, and the light of a window or lamp allowed to fall upon them. This is not, however, sufficient, generally, to examine things with great accuracy ; and an instrument called a condenser (tig. 9) is provided for this purpose. It consists merely of a large lens, which is sometimes fixed to the stage, or has a separate stand. Its object is to allow a concentrated ray of light to be thrown on the opaque object whilst under the object-glass of the Microscope. This is called viewing objects by reflected light. Transparent objects, *>n the other hand, are viewed by transmitted light, reflected from the plane or concave surface of the mirror beneath the stage. The object of this mirror, which is called the re/lector, is to caUh the rays of light and con- centrate them on the object under the Microscope^ The rays of light thus pass through the object, and its parts are sesii much more clearly. Another convenient piece of apparatus is an animalcule cage. This consists of a little brass box, inverted, to the bottom of which is attached a piece of glass. Over this, again, is placed a lid or cover, with a glass top. The cover can be made to press on the glass beneath, and an object being placed between the two glasses, can be submitted 22 THE STRUCTURE OF to any amount of pressure thought necessary, (Fig. 10.) This is a very important instrument for examining minute Crustacea, animalcules, zoophytes, and other living and moving objects, especially when they live in water. Fig. 10. Animalcule Cage or Live Box. In the use of the cage and the slide, care must be taken not to break them by turning the object- glass down upon them. It is sometimes a difficult thing, when the object-glass has a focus of not more than a quarter or eighth of an inch, to adjust it to exactly the point at which the object is best seen, by means of the coarse handles on the rack- work. For this reason the Microscope has been provided with a fine adjustment, by which the object-glass is moved down on the object in a much slower and more gradual manner, and the destruction of an expensive objective glass is often thus prevented. The picture of the object brought to the eye in the Compound Microscope is always the wrong end upwards. That is, the picture is always the reverse in the Microscope to what it is with the naked eye. You need constantly to be aware of this, especially if you are going to dissect an object under the Microscope, as your right hand becomes left, and your left right. The observer, however, soon gets accustomed to this, and it creates no difficulty ulti- mately. But science constantly attends on the THE MICROSCOPE. 23 Microscope, and ministers to its slightest defects. A little instrument called an erector, composed of a lens which reverses the picture once more, is supplied by the optician, and can be had by those who practise the refinements of microscopic observation. It is a good plan to make drawings of all objects examined, or at any rate those which are new to the observer. A note-book should be kept for this purpose, and what cannot at once be identified by the object, may afterwards be so by the drawing. All persons, however, have not the gift of drawing, and for those who need assistance in this way, the camera lucida has been invented. This instrument is applied to the tube of the Microscope when placed at right angles with the stem, in such a way that a person looking into it sees the object directly under his eye, so that he may easily draw its form on a piece of paper placed un- derneath. (Fig. 11.) Some little practice is, however, necessary before the observer can obtain satisfac- tory results with this instrument. It is absolutely essential that the eye should be so placed that, while one part of the Fig. II. Camera Lucida. pupil receives the rays from the reflecting surface 24 THE C'i'AUCTURE OF of the prism, the other sees the paper below with the image clearly depicted upon it. Dr. Beale strongly recommends the neutral lens glass reflector in preference to the Wollaston camera lucida. It is also much less costly. (Fig. HA.) This consists of a short tube falling upon the eye-piece, with a piece of neutral lens glass placed at such an angle that, whilst the image of the object is reflected upwards, the paper below can be distinctly seen. (The price of this form of camera lucida is about four or five shillings.) Success in the use of the camera depends very Fig. HA. much on the arrangement of the light. If the image is too strongly illuminated, the paper will hardly be visible ; and, on the contrary, if the paper and pencil are too bright, the image is indistinct. A little practice will enable the observer to overcome both difficulties : this he will have attained when he can see the image and paper with equal distinctness. Another instrument which will be found of con- siderable service even to the beginner with the Microscope, is a micrometer' This is an instrument for measuring the size of objects observed. Exag- gerated notions about the smallness of objects arc very prevalent j and as it is almost impossible to say accurately how small an object is without some means of measuring, a Micrometer becomes essen- tial where accuracy is desired. This is effected by having some object of known size to compare with the object observed. The most convenient instru- ment of this kind is a glass slide, on which lines are drawn the hundredth and thousandth of an inch apart. If this slide, or stage micrometer as it is called, is placed on the stage,, the divisions may THE MICROSCOPE. Z.O be traced on the paper in the same way as the outline of an object : the dimensions of the latter can now be ascertained. Care must, however, be taken that the magnifying power is the same in both cases. Amongst the accessory apparatus are various arrangements for concentrating the light en the objects which are placed for examination under the Microscope. One of these combinations is called the achromatic condenser. This consists of a series of lenses, which are placed between the mirror and the stage, and which may consist of an ordinary object-glass. The stages of the larger kinds of Microscopes are fitted up with a screw or slide, by which the condenser can be fastened beneath and adjusted to the proper focus for throwing light on the object examined. The illumination of opaque objects by means of the bull's-eye condenser is sufficient when only the lowest powers are used ; but when any objective of less than inch-and-half focus is used this method of illumination is not satisfactory, and a form of reflector called a Lieberkiihn will be found to be a welcome addition to the Microscope. This instru- ment consists of a concave silvered speculum with a central aperture of the diameter of the front lens of the objective : a short tube is attached to the convex surface of the reflector, which slides over the object-glass. The action of the Lieberkiihn will be easily understood from the following diagram : a represents the objective with the LielerJcilhn in situ ; 6, the concave reflector j c, a stop for the purpose of preventing any direct light entering the objective (a small disk of black paper attached to the slide is generally sufficient) ; d, d, rays of light from the mirror ; e, e, reflected rays converging to a focus at f (the object). To obtain the full effect of this mode of illumination the mirror should THE STRUCTURE OF be placed a little out of the axis of the tube of the Microscope. By this method an oblique beam of light is thrown on the Lieberkuhn, and the light from it is reflected unequally upon the object ; thus producing the light and shade so necessary for the proper definition of an object. (The cost of a Lieberkuhn varies from 6s. to 15s. ; those for low powers costing more than those for the higher.) The details of many transparent objects are much more dis- tinctly seen when examined by light transmitted by the object only. This is called black ground illumination, and can be obtained in several ways. With a very low power the light can be reflected with sufficient obliquity if the mirror is thrown out of the axis ; but much better effects Fig. llB. Diagram illustrating are obtained when a the action of a Lieberkiihn." hemispherical lens a, omect-glasg ; o. a concave -.i 1111 silver 'reflector ; c, a black spot Wlth a cenlral black ("dark well") ; d, d, rays of light; stop, called a " spot e, e, the same reflected and lens," is placed be- brought to a focus at/. neath the object. The accompanying figure will explain its action : a is " spot lens " ; b, a brass tube in which it is mounted (this is fitted into a larger tube fitted to the short tube attached to the lower surface of the stage : by sliding this up or down, the proper distance from the object is obtained) ; c, THE MICROSCOPE. parallel lines from mirror ; d, the same rays made to rapidly converge by passing through the lens, and come to a focus at e j and if the focal length of the objective is greater than the distance between the object and the point e, the object will be illu- minated, and the field appear perfectly dark. Kg. lie. a, " Spot Lens," front view ; c, blackened concavity of ditto ; a', section of " Spot Lens " in its fitting, b ; c', central stop ; d d, parallel rays of light converging to a focus at e. Having said thus much with regard to apparatus, we will now give some directions for the use of the Microscope under ordinary circumstances. The Microscope may be either used by the light of the sun in the daytime, or at night by some form of artificial light. It is best used by daylight, as artificial light is likely to tire the eyes. Having determined to work by daylight, some spot should be selected near a window, out of the 28 THE STKUCTCRE OF direct light of the sun, in which to place a small, firm, steady table. On this the Microscope should be placed, and the object- 1 glass should be screwed on to the tube. The mirror should be then adjusted so as to throw a bright ray of light on to the object-glass. The eye-piece having been previously placed at the top of the tube, the Microscope is now ready to receive a transparent object. If the object to be examined is an animalcule, it may be con- veyed to the animalcule-cage by means of a glass tube, called a pipette or dipping- tube (fig. 12), which should be dipped into the water where the object is con- tained, with the finger covered over the upper orifice, so that no air can escape. By taking the finger off when the tube is in the water, the fluid will rush into the tube, and with it the object to be examined. The finger is again applied Fig. 12. Dipping Tubes, to the top of the tube, an 1 the fluid obtained conveyed to the animalcule-cage. Only such a quantity of the water should be allowed to fall out of the tube on to the cage as will enable the observer to put on the cover of the cage without pressing THE MICROSCOPE. 29 the fluid out at the sides of the cage. If the water is thus allowed to overflow, it runs over the glasses of the cage, and thus obscures vision. An object or objects having been thus placed in the cage, it is conveyed to the stage, and placed in such a position that the ray of light passing from the mirror to the object-glass may pass through it. This having been done, the observer must now place his eye over the eye-piece, and use the screw in the tube, and move the object- glass downwards until he gets a clear view, of objects moving in the water. This is called focussing. The glass may then be moved up or down, in order that the best view of the object may be obtained. When the object-glass is one of high power, the fine adjustment may be used for this purpose. When the proper focus is obtained, the object may be moved up or down, right or left, with the hand, or by the aid of the screws which are employed in the various forms of what are called mechanical stages. When objects not requiring the live-box or animalcule - cage are to observed, they may be transferred to the glass slide by aid of a thin slip of wood, or a porcupine-quill moistened at the end, or by a pair of small forceps. (Fig. 8.) Some transparent objects may be seen without any me- dium, but generally it, is best to place them 011 the slide with a drop or two of clean water, which may be placed on it with a dipping-tube. When water is used, it will generally be found best to cover the object with a small piece of thin glass. Small square pieces of thin glass are sold at all the opticians' shops for this purpose. The object is then placed under the object-glass as before. In order to render objects transparent, so that 30 THE STRUCTURE OF they may be viewed by transmitted light, very thin sections of them should be made. This may be effected by means of a very sharp scalpel, or a razor.. When objects are too small to be held in the hand to be cut, they may be placed between two pieces of cork, and a section of them made at the same time that the cork is cut through. Sometimes it is found desir- able to unravel an object under the Microscope. If this is the case, only a low power should be used, and the object may be placed on a glass slide, without any glass over, and two needles with small wooden * handles employed, ordinary sewing needles, with their eyes stuck in the handle of a hair pencil, will answer very well. (Fig. 14.) Even when dissection is not to be carried on under the Microscope, a pair of needles of this sort, for tearing minute structures in pieces, will be found very useful. *& 14< When opaque objects are Dissecting Needles. to ^ e examined, the light from the mirror may be shut off, and the aid of the bull's-eye condenser called in. The object being secured in the forceps attached to the stage (fig. 15), or laid upon a slide, the light is allowed to fall on it through the condenser. (Fig. 9.) The object-glass must be focussed in the same manner as for transparent objects, till the best distance is THE MICROSCOPE. secured for examining it. The petals of plants, the wings and other parts of insects, with many other objects, can only be examined in this way. Fig. 15. Stage Forceps. Even the beginner will find it useful to keep by him some little bottles, containing certain chemical re-agents. Thus, a solution of iodine is useful to apply to the tissues of plants, for the purpose of ascertaining the presence of starch. This solution may be made by adding five grains of iodine and five grains of iodide of potassium to an ounce of distilled water. It turns starch blue and cellulose brown. Cellulose is the substance that forms the walls of the cells in plants. Dilute sulphuric acid (1 to 3) is also useful as a re-agent ; if applied to cellulose previously stained with iodine, it imparts a blue or violet tint. Strong nitric acid turns albuminous matter a deep yellow; and when diluted (1 to 4) with water is used for separating the elementary tissues of vegetable substances either by boiling or maceration. The strong solution of potash (liquor potassse) can also be employed with advantage in softening and making clear opaque animal and vegetable substances. While using these powerful agents, great care should be taken to prevent the trans- parency of the object-glass becoming impaired by contact with them or by long exposure to their vapours. A HALF HOUR WITH THE CHAPTER II. A HALF-HOUR WITH THE MICROSCOPE IN THE GARDEN. AMOXGST the objects which can be examined by the Microscope, none are more easily obtained than plants. All who have a Microscope may not be fortunate enough to have a garden ; but plants are easily obtained, and even the Londoner has access to an unbounded store in Coven t Garden. We will, then, commence our microscopic studies with plants. On no department of nature has the Microscope thrown more light than on the struc- ture of plants ; and we will endeavour to study these in such a manner as to show the importance of the discoveries that have been made by the aid of this instrument. If we take, now, a portion of a plant, the thin section of an apple, or a portion of the coloured parts of a flower, or a section of a leaf, and place it, with a little water, on a glass slide under the Microscope, we shall see that these parts are com- posed of little roundish hollow bodies, sometimes pressed closely together, and sometimes loose, assuming very various shapes. These hollow bodies are called " cells," jand we shall find that all parts of plants are built tip of cells. Sometimes, however, they have so far lost their cellular shape that we cannot recognize it at all. Nevertheless, all the parts we see are formed out of cells. Cells tolerably round, and not pressed on each other, may be seen in most pulpy fruits. In fact, with a little care in making a thin section, and placing PLATE XL TuffeaWest sc adnat. London. Tbfcert Sardmcte, MICROSCOPE IN THE GARDEN. 33 it under the Microscope, the cellular structure of plants may be observed in all their soft parts. If, now, we take a thin section from an apple, or other soft fruit, or from a growing bud, or tuberous root, as the turnip, we shall find that many of the cells contain in their interior a " nucleus," or central spot, a representation of which is seen from the cells of an apple in figure 1 of the first plate. This nucleus is a* point of great import- ance in the history of the cell, for it has been found that the cell originates with it, and that all cells are either formed from a nucleus of this kind, or by the division of a thin membrane in the inte- rior of the cell, which represents the nucleus, and is called a " primordial utricle." When the cells of plants have thus originated, they either remain free or only slightly adherent to each other, or they press upon each other, assuming a variety of shapes ; they then form what is called a " tissue." When cells are equally pressed on all sides, they form twelve-sided figures, which, when cut through, present hexagonal spaces. This may be seen in the pith of most plants, more especially the common elder, which is seen at figure 2 of plate 1. Transverse slices of the stems of any kind of plant from the garden may be made by a razor, or sharp penknife, and will afford interesting objects for the Microscope. Cells, during their growth, assume a variety of shapes, and the tissues which they form are named accordingly. Two examples of such cells will be seen in figures 243 and 244 in plate 8, where the first represent cells from the hard shell of a plum stone, and the second the thin cells from the out- side of the seed of the guelder rose. 'Sometimes the cells are very much elongated, or they unite together to form an elongated tube ; the tissue thus formed is 34 A HALF HOUR AVITII THE called " vascular tissue ;" but where tlie cells retain their primitive form, it is called " cellular tissue." A very interesting form of the latter is the " stellate" tissue found in most water plants, and especially regularly developed in the common rush, a represen- tation of which is given in figure 3 plate 1. The object of this tissue is, evidently, to allow of the existence of a large quantity of air in the spaces between the cells j by which means the stem of the plant is lightened, and it is better adapted for growth in water. If the leaf of any plant is examined, it will be found that on the external surface there is a thin layer, called, after the thin external membrane in animals, the " epidermis." This layer is composed of very minute cells smaller than those in other parts of the plant, and when placed under the Microscope, presents a variety of forms of cellular tissue. The form of epidermal cells from various plants is seen in figure 42 and the following figures in plate 2. There is found in this layer a peculiar organ which exists on the outside of all parts of plants, and which demands attention. In the midst of the tissue, at very varying distances, are placed little openings, having a semilunar cell on each side. These openings are called " sto- mates," and can be well seen in the leaf of the hyacinth, which is shown in figure 42, where the cells of the epidermis are transparent ; but the little cells which form the stomate are filled with green colouring-matter. The stomates vary very much in size and in numbers. They are found in larger numbers on the lower than on the upper side of leaves. In the common water-cress they are very small, as seen in figure 43, plate 2, and the cells of the epidermis are sinuous. The sto- mates are found on all plants having an epidermis. MICROSCOPE IN THE GARDEN. 3g In figures 44 and 46 they are represented from the wheat and the aloe. In the latter plant the cells of the cuticle are very much thickened. They can also be seen on the cuticle of the fruit, as shown from the holly in figure 241, plate 8, and also on the organs and petals. These form a beautiful object under the Microscope. The petal of the common scarlet geranium (Pelargonium) affords a beautiful instance of the way in which the cells of plants become marked, by their pecu- liar method of growth. This is illustrated in the cells of the common red-flowered geranium at figure 45, in plate 2. The vascular tissue of plants is either plain or marked in its interior. If we examine the ribs of leaves, the green stems of plants, or a longitudinal section of wood, elongated fibres, lying side by side, are observed, as is seen in the case of the elder, at figure 53, plate 2. This is what is called "lig- neous" or "woody" tissue, and the greater part of the wood and solid parts of plants are com- posed of this tissue. Such tissue is seen upon the shoots of the young vine in figure 249, plate 8. The fibres mostly lie in bundles, and are divided from each other by cellular tissue. This latter, in the woody stems of trees, constitutes the "medullary rays," which are seen in transverse sections of stems, extending from the pith to the bark. The difference observable in the distribution of the woody fibres and the medullary rays renders the examination of transverse sections of the stems of plants a subject of much interest ; figure 54 and the following figures in plate 3, present the appearances of thin sections of various kinds of wood (figures 54, 55, 56, 57, plate 3). In the transverse sections of stems of most plants,, large open tubes are observed. This is seen in D 2 36 A HALF-HOUR WITH THE the case of the oak, figured at figure 55, plate 3. These are called " ducts," Such dacts may be well observed in the transverse section of the common radish, as seen at figure 51, plate 2, and in other roots. These ducts are often marked by pores, or dots, and are hence called u dotted ducts." These dots are the result of deposits in the interior of the tube of which the duct is formed, and a great variety of such markings are found in the interior of vascular tissue. One of the most common forms of marked vascular tissue is that which is called glandular woody tissue, of which a figure is given at 54, plate 3. This kind of tissue is found in all plants belonging to the cone-bearing, or fir tribe of plants. In order to discover it, recourse need not be had to the garden for growing plants, as every piece of furniture made of deal wood will afford a ready means of obtaining a specimen. All that is necessary to observe the little round disks with a black dot in the middle is to make a thin longitudinal section of a piece of deal, and place it under a half or quarter-inch object-glass, when they will be readily apparent. The application of a drop of water on the slide, or immersing them in Canada balsam, will bring out their structure better. If we take the leaf-stalk of a strawberry, or of garden rhubarb, and make a transverse section all round, nearly to the centre of the stalk, the lower part will at last break off, but be still held to the upper by very delicate threads. If we examine these threads, we shall find that they are fibres which have been left by the breaking of the vessel in which they were contained : such fibres are seen at figure 48, plate 2. These vessels are called " spiral vessels," and are found in the stems and leaves of many plants. They are seen rolled up aa MICROSCOPE IN THE GARDEN. 37 found in the garden rhubarb, at figure 47, plate 2. Sometimes these vessels are found branched, as in the common chickweed, which is seen at figure 50, plate 2. This arises from two spires coming in contact with each other, and adhering. Occasion- ally the spiral fibre breaks, or is absorbed at certain points, leaving only a circular portion in the form of a ring, as seen in a vessel from the root of wheat at figure 49, plate 2. Such vessels are called "annular," and may be observed in other roots besides those of growing wheat, as in the leaves of the garden rhubarb. A modification of this kind of tissue is seen in the stems and roots of ferns, in which the vessel assumes a many-sided form. This kind of tissue is called " scalariform," or ladder-like, and is seen in figure 52, plate 2. Sometimes the spiral fibre is free. This is repre- sented at figure 250, plate 8, from the testa of the seed of the wild sage. The bark as well as the wood of trees affords the same appearance under the Microscope. If a piece of the bark of any plant be examined by means of a very thin transparent section, and placed upon a slide, and put under an inch or a half-inch object- glass, the structure of the bark may be easily seen. On the outside of all is the cuticle, or epidermis, and under this lie two layers, composed, like the cuticle, of cellular tissue ; but the inner layer, before we come to the wood of the stem, is com- posed of woody tissue. The cellular layer, next the woody one, is often developed to a very great extent, and then constitutes what we know by the name of cork. The bark from which corks are made is obtained from an oak tree which grows in the Levant. If we make a very thin section of a cork, its cellular structure can be easily made out. The cells are almost cubical, and when submitted to the A HALF-HOUR WITH THE action of a little solution of caustic potash, they may frequently be seen to be slightly pitted. This is represented from cork in figure 59, plate 3. Many of the structures which are described above may be seen in common coal ; thus proving most satisfactorily that this substance has been formed from a decayed vegetation. A transverse and a longitudinal section of coal is shown at figures 60 and 61, plate 3. The examination of coal, how- ever, is by no means an easy task, and the hands and fingers may be made very black, and the Microscope very dirty, without any evident struc- ture being made out. Some kinds of coal are much better adapted for this purpose than others. Sections may be made by grinding, or coal may be submitted to the action of nitric acid till it is sufficiently soft to be cut. The amateur will not find it easy work to make sections of coal ; but should he wish to try, he may fasten a piece on to a slip of glass with Canada balsam, and when it has become firmly fixed, he may rub it down on a fine stone till it is sufficiently thin to allow its structure to be seen under the Microscope. Coal presents both vascular and cellular tissue. The vascular tissue is, for the most part, of the glandular woody kind ; thus leading to the inference that the greater portion of the vegetation that supplied the coal-beds belonged to the family of the firs. The external forms of the tissues of plants having been examined, we are now prepared to regard their contents. In the interior of the cells forming the roots and the growing parts of plants will be observed a number of minute grains, generally of a roundish form. If we make a thin slice of a potato, these granules may be very ob- viously seen, lying in the interior of the cells of which the potato is composed, as seen at figure 64, MICROSCOPE IN TI1E GARDEN. 39 plate 3. If we now take a drop of the solution of iodine, and apply it to these cells full of granular contents, we shall find that the granules assume a deep-blue colour. This is the proof that they are starch ; and as far as we at present know, no other substance but starch has the power of assuming this beautiful blue colour under the influence of iodine. We have thus a ready means at all times of distinguishing starch. The grains of starch are of various sizes and shapes. The starch of the flour of wheat has a round form, and varies in size ; that of the oat is characterized by the small granules of starch adhering together in globular shapes. When these globules are broken up, the grains appear very irregular. Grains of wheat starch and oat starch are seen in figures 62 and 63, plate 3. In the arrow-root called " Tous les Mois," the grains of starch are the largest known, and, like those of the potato, they look as if com- posed of a series of plates laid one upon the other, gradually becoming smaller to the top. This is seen at figure 65, plate 3. These lines do not, however, indicate a series of plates, but appear more like a series of contractions of a hollow vesicle or bag. This vesicular appearance of starch may be made apparent by gently heating it, after moistening, over a spirit-lamp on a glass slide, or by dropping on it a drop of strong sulphuric acid. This action of the starch-granule appears to be duo to the fact that the starch is converted into gum by the action of the heat on the sulphuric acid. Sago and tapioca are almost entirely composed of starch, and may be easily examined under the Microscope. Granules of sago are represented in figure 67, and those of tapioca at figure 68 ; they are readily distinguished by their size. The starch granules are insoluble in water, but they are easily diffused 4-0 A HALF -HOUR WITH THE through it ; so that by washing any vegetable tissue containing starch, with water, and pouring it oft' and allowing it to stand, the starch falls to the bottom. This may be done by bruising the vege- table tissue in a mortar, and then throwing it into cold water. The tissue falls to the bottom, and the starch is thus suspended in the water. In this way the various kinds of starches may be procured for microscopical examination. The granules of starch have frequently a little black irregular spot in their centre. In the starch of Indian corn it assumes the form of a cross, which is seen at figure 66, plate 3. Starch is a good object for the use of the polarizing apparatus, which can be applied to most compound Microscopes. The grains of starch, under the influence of polarized light, become coloured in a beautiful and peculiar manner, permitting of great variation, as in the case of all polarized objects. If we take a little of the white juice from the common dandelion, and put it under the Micro- scope, we shall often see, besides the globules of caoutchouc which make the juice milky, crystals of various forms. Such crystals are called by the botanist " raphides," signifying their needle-like form. They arise from the formation and accu- mulation of insoluble salts in the fluids of the plant. They are seen in various plants, and under very different circumstances. Beautiful needle-like crys- tals can be seen in the juice of the common hyacinth, represented at figure 69 ; the juice may be ob- tained by pressing. A question has been raised as to whether they are always formed in the cell. They are mostly found lying in the cell, as in the leaves of the common aloe, seen at figure 70, plate 3 : they may also be found in the tissues of the com- mon squill, and in the root of the iris. If a thin PLATE '6. itj^ MICROSCOPE IN THE GARDEN. 41 nection of the brown outer coat of the common onion is made, small prismatic crystals are observed. These are represented at figure 72, plate 3. Some- times several of these crystals unite together around a central mass, forming a stellate body. These bodies have been called " crystal glands," but they have no glandular properties. They may be seen in the root and leaf-stalk of common rhubarb, and may be easily observed in a bit of rhubarb from a spring tart. From such a source, the drawing was made at figure 71. These crystals are mostly formed of oxalate of lime. They are constantly found in plants producing oxalic acid. The gritty nature of rhubarb root arises from the presence of oxalate of lime. Sometimes the oxalate of lime assumes a round dish-like form. Such forms are seen in plants belonging to the cactus family. A circular crystalline mass, as seen in a common cactus, is represented at figure 73. Other substances, besides oxalate of lime, are found crystallized in the interior and on the surface of plants. Crystals of sulphate of lime have been found in the interior of cycadaceous plants. Car- bonate of lime is found in crystals on the surface of some species of Chara, or stonewort. There is a shrub not uncommon in gardens, known by the name of Deutzia scabra, on the under surface of the leaves of which there are beautiful stellate crystals of silica. The best way of seeing these is to put the leaf under the Microscope, and to examine it by the aid of reflected light. Sugar and honey assume a crystalline form, and may be known by the shape of their crystals. At figure 238, plate 8, a crystal of honey is repre- sented ; it is thinner and smaller than the crystal of cane sugar represented at figure 239. Honey is sometimes adulterated with sugar. Under these 42 A HALF-HOUR WITH THE circumstances the sugar crystal loses its definite outline, and assumes the form seen at figure 240. The external surface of the parts of all plants will afford a rich field of amusement and instruc- tion to the microscopic observer. The cuticle, or epidermis, of which we have before spoken, has a very varied structure, arid contains the little open- ings (stomates) before described. The cuticle, which, in a large number of cases, is smooth, becomes elevated in some instances, and forms a series of projections, which, according to their form, are called " papillae," " warts," " hairs," " glands," and " prickles." The papillae are slight elevations, con- sisting of one, two, or more cells ; the warts are larger and harder; whilst the hairs are long, the glands contain a secretion, and the prickles are hard and sharp. For examining the form and growth of these hairs, the flowers of the common pansy (heart's-ease) afford a good object. Some of the projections are merely papillae, as in the case of the kind of rudimentary hair represented in figure 75, plate 3 ; others are found longer, and more like hairs, as seen in figure 76 j whilst others are long, and, the sides of the hair having contracted, they assume the appearance of a knotted stick, as seen in the hair from the throat of the flower of the pansy, at figure 78. The family of grasses, wheat, barley, oats, and other forms, are favourable sub- jects for the examination of simple hairs, or hairs composed of a single elongated cell. At figure 74, a single hair is given from a common grass. All that is necessary to be done, in order to see these hairs, is to take any part of the plant where they are present, and to slice off a small portion with a sharp penknife or razor, and place it under the Microscope. They may be either examined dry, or a little water may be added, and a piece of thin MICROSCOPE IN THE GARDEN. 43 glass placed over them on the slide. Hairs are frequently formed of several cells. On the white dead-nettle the hairs are composed of two cells, as seen in figure 7 9 a. The nucleus, or cytoblast, is often seen in these, and is represented in figures 76, 77, and 79, plate 3. On the common groundsel hairs may be seen, composed of several cells, each cell containing a nucleus, as at figure 795. Hairs like a string of beads are found on the pimpernel and sow-thistle, which last will be found in figure 80, plate 3. Occasionally hairs become branched. Thus, on the leaf of the common chrysanthemum the hairs present the form of the letter T. This hair is represented at figure 82. On the under-surface of the leaves of the common hollyhock hairs are seen with several branches, giving them a stellated appearance, as seen at figure 84. The common lavender is covered with stellate hairs, as seen at figure S5a. These hairs may be examined as opaque or transparent objects, when immersed in a little glycerine. The hair of the tobacco plant presents a peculiar knobbed appearance. The presence of these hairs is a test of the purity of tobacco. It is shown in figure 81. The verbena has rosette -shaped hairs, as in figure 83. Sometimes hairs are covered over with little dots, which are supposed to be deposited after the growth of the cells of the hair. Such hairs may be seen in the common verbena, and are represented at figure 856. Hairs are sometimes loose and long, as in the white poplar, seen at figure 86. Occasionally an elevation, consisting of several cells, is formed at the base of a hair. These are shown in figure 87. When these cells contain a poisonous secretion, which is transmitted along the tube of the hair, the hair is called a glandular hair, or sting. Such are 44 A HALF-HOUR WITH THE the hairs of the common stinging-nettle, represented at figure SSa. The hairs constituting the down or " pappus " of compositous plants assume a variety of forms. The seed or fruit of the common groundsel has a beau- tiful crown, given at figure 245, in plate 8. The pappus of the dandelion appears notched, as seen at figure 246. The burdock has a cottony hair, while the goatsbeard is like a feather, both of which are represented respectively in figures 247 and 248. If a hair is examined in its growing state, with an object-glass of one quarter of an inch focus, a movement of the particles in its interior is often observed. This is easily seen in the hairs around the stamens of the common Spider wort (Trades- cantia Virginica). Such movements are very com- mon in the cells of water plants. One of those most commonly cultivated in aquavivaria at the present day, the Valisneria spiralis, affords the best example of this interesting phenomenon. In order to observe this movement, a growing leaf of the valisneria should be taken, and a longitudinal slice should be removed from its surface, by means of a sharp penknife or razor. The slice, or the sliced part left on the leaf, should now be put on a slide, a drop or two of water added, and covered with a thin piece of glass, when, after a little time, espe- cially in a warm room, the movement will be ob- served. This movement takes place in the little particles around the sides of the cells represented in figure 886, plate 3. It may also be seen in the leaves of the new water- weed (Anacharis alsinastrum), the frogbit, the rootlets of wheat, in the family of charas, and in the cells of many other water plants. In examining some species of Chara, the external bark, or rind, should be removed from MICHOSCOPE IX THE GARDEN. 45 the cells, or the movements will not be seen. This movement seems dependent on the internal proto- plasmic matter, or " primordial utricle," which is contained in many cells, and which, in these cases, is spread over the interior of the cell. It is, how- ever, capable of contraction, and when the plants are exposed to cold, the utricles contract and pre- vent the movement of the contents in the interior. It is, apparently, the extension of this substance beyond the walls of the cell which constitutes the little hairlike organs called " cilia," which are con- stantly moving, and by the aid of which the spores of some plants effect rapid movements. Such organs are found in the Pandorina Morum and Volvox globator, moveable plants represented at figures 13 and 14, plate 1. The effect of these cilia in producing the movements of plants is well seen in the Volvox globator, which, on account of its rapid movements, was at one time regarded as an animalcule, but it is now regarded as a plant. Cilia are, however, more frequently met with in the animal kingdom. They are seen in the drawing of Plumatella repens, at a, in figure 163 of plate 6. Amongst the parts of plants which can alone be investigated by the Microscope are the stamens. These organs are situated in the flower, between the petals and the pistil, and usually consist of a filament, or stalk, with a knob or anther at its top. If the anther is examined, it will usually be found to consist of two separate valves, or cases, in each of which is contained a quantity of powder, or dust, called " pollen." The walls of these valves are worth careful examination under the Microscope, on account of the beautifully-marked cellular tissue of which their inner walls consist. The cells of this tissue contain in their interior spiral fibres similar to those which have been described as present in 46 A HALF HOUR WITH THE certain forms of vascular tissue. In the anthers of the common furze the fibres are well marked, and are represented in figure 118, plate 5 ; in the common hyacinth they are larger, and frequently present, in their intercellular spaces, bundles of raphides, as seen at Figure 119. In the white dead-nettle the fibre is irregularly deposited, as at figure 120. In the anthers of the narcissus, given at figure 121, the cells are almost vascular in their structure, and present the same appearance as those described under the head of annular ducts. The reader should compare figure 121, plate 5, with figure 49, plate 2. In the crown imperial the fibres of the cells radiate from a central point in a stellate manner, as at figure 122. When the anther-cases have been examined, a little of the dust may be shaken on to a slide, and examined as an opaque or a transparent object. Each species of plant produces its own peculiar form of pollen. These little grains are actual cells. They are the cells of plants which in their position in the anther will not grow any further. They are destined to be carried into the pistil, where, meet- ing with other cells, they furnish a stimulus to their growth, and the embryo, or young plant, is pro- duced. The history cf the development of these cells, as well as of those in the interior of the pistil, is a very interesting one, and is one of those sub- jects of investigation which has been created by the aid of the Microscope. The pollen grains vary in size as well as form. They are frequently oval, as seen in figure 123, plate 5. In the hazel and many of the grasses they are triangular. Those from the hazel are represented at figure 124. In the heath they are tri-lobed, as at figure 125 ; in the dandelion, and many of the compositous order of plants, they are beautifully sculptured, as seen MICROSCOPE IN THE GARDEN. 47 at figure 126. IB the passion-flower, three rings are observed upon them, as though they had been formed with a turner's lathe figured at 127. In the common mallow, they are covered all over with little sharp-pointed projections, like a hand-grenade. These are represented at figure 128. The micro- scopic observer should make himself acquainted with the forms of pollen grains, as, on account of their small size and lightness, they are blown about in all directions, and may be found on very dif- ferent objects from those in which they have been produced. Some absurd mistakes have been com- mitted by confounding pollen grains with other forms of organic matter. Thus, pollen grains in bread were regarded as bodies connected with the production of cholera. The pistil, which is the central organ seated in the midst- of the stamens in the flower of plants, will afford a great variety of interesting points for examination with the Microscope. In the earliest stages of the growth of the pistil, thin sections of it may be made, and the position of the ovules observed. In the ovule will be found the embryo sac, a central cell, which, on being brought in contact with the pollen grain, grows into the seed. The seed contains the embryo, or young plant. In most plants this is sufficiently large to be seen by the naked eye ; but it may, nevertheless, be examined with advantage by a low microscopic power The seed is covered on the outside with a membrane, which is called the " testa." This membrane is often curiously marked, and the whole seed may be examined as an opaque object with the low powers of the Microscope. In order to do this, the light must be shut oft" from the mirror, and, the object being placed on the stage, a pencil of light should be thrown upon it by the aid of the 43 A nALF-nora WITH TEE bull's-eye condenser. If a seed of the red poppy be now examined, it will be found to have a uniform shape, and to be reticulated on its surface, as seen at figure 129, plate 5. The seed of the black mustard exhibits a surface apparently covered with a delicate network, seen at figure 130. Some seeds have deep and curved furrows on their sur- faces, such as exhibited in figure 131. The great snapdragon has a seed covered with irregular projecting ridges, having a granuled appearance, represented at figure 132. The seed of the chick- weed presents a series of blunt projections, as in figure 133. In the various forms of umbel- bearing plants, the seeds adhere to the fruit, and the fruit is commonly called the " seed." Such are caraway, coriander, dill, and anise seeds. The plants of this family are very common weeds in our gardens and fields, and may be easily procured for microscopic examination. Some of these fruits are covered over with little hooks, seen at figure 134, whilst others present variously -formed ridges and furrows, which are amongst the best means for distinguishing these plants the one from the other. PhAIE 4 London Robert MICROSCOPE IN THE COUNTRY. 49 CHAPTER III. A HALF-HOUR WITH THE MICROSCOPE IN THE COUNTRY. A COMPOUND Microscope is not easily conveyed and put up in the fields, but the produce of the roads and waysides may be easily brought to the Micro- scope at home. No one who has a Microscope should walk out into the country without supply- ing himself with a few small boxes, a hand- net, and three or four small bottles, in order to bring home objects for examination. The dry produce, which may be put into boxes, is of a different character from that which may be conveyed home in bottles. We shall, therefore, first direct attention to the minute forms of mosses, fungi, lichens, and ferns, which may be collected in boxes ; premising, however, that many members of these families may be found without going into the country to seek for them. The cheese in the pantry, and the decayed parts of fruits, and objects covered with mould, are good subjects for microscopic examination. Amongst the minuter plants and animals whose true nature can only be detected by the Microscope many are composed of a single cell, whilst others, like higher plants and animals, are formed by the union of a large number of cells. The greater proportion of the one -celled, or unicellular plants, as they are called, are found in water : but some are found on moist rocks, stones, and old walls. Amongst these there is one of exceedingly simple structure, called gory dew (Palmdla cruenta). This 50 A HALF-HOUB WITII THE plant appears as a red stain upon the surface of damp objects. If a little of this red matter is scraped off the object to which it is attached, and placed under the Microscope, it will be found to consist of a number of separate minute cells, as represented at figure 89, plate 4. This plant belongs to the same family as the red-snow plant, ard there are a number of forms of these minute organisms, which, on account of their rapid growth and red colour, have given rise to alarming appre- hensions, in former times, when their true nature was imperfectly understood. One of them attacks bread, and gives to it the appearance of having been dipped in blood. They also attack potatoes. Of the same simple structure, but not having a red colour, is the yeast-plant, or fungus, shown at figure 90, plate 4. This plant abounds in yeast, and may also be found in porter and ale. If vinegar is allowed to stand for some time, a minute plant is developed, called the vinegar- plant. In its earlier stages of growth it exhibits elongated cells, looking like broken pieces of thread, seen at figure 91. Threads more fully developed are often seen in decomposing fluids, and upon the surface of decomposing animal and vegetable substances ; such is the so-called cholera- fungus, which may be obtained by exposing damp slides to the air. They are shown at figure 92. Such plant-like threads can be collected from the air in clamp and unwholesome cellars and rooms, and were at one time supposed to be connected with the production of that fearful disease, the cholera. It has been rendered, however, exceed- ingly probable that all these appearances are but different forms of the fungus which produces common mould, and which is known by the name of Penicillium glaucum. This fungus is represented MICROSCOPE IN THE COUNTRY. 51 at figure 95. It may be found on the surface of preserves and jellies, and consists of a mass of fila- ments or threads serving as its base, from the surface of which individual filaments rise up, bear- ing a number of minute cells, which are the spores, or reproductive organs. These are seen at figure 96. Plants such as these, and belonging to the family of fungi, are found everywhere on the leaves of plants in the summer and autumn, forming irre- gular spots, of a yellow, red, or black colour. If such leaves are brought home and placed under the Microscope, they present a never-failing source of interest. The red appearance on the leaves of wheat, called the rust, is due to one of these fungi, seen at figure 93, plate 4. This appears to be an early stage of the fungus, which produces what is called mildew, and is represented at figure 94. These fungi are so common on the wheat-plant that their spores mingle with the seeds when ground into flour, and can be found, when care- fully sought for, in almost every piece of bread that is examined under the Microscope. Mouldy grapes, pears, apples, and other fruits, present fungi, having the same general form as that of common mould. Such a fungus is the Botrytis of mouldy grapes seen at figure 96. Mouldy bread also pre- sents a fungus of this kind. This species is called Mucor mucedo, and is represented at figure 97. Its spores are arranged in a globular form. A fungus not unlike the last has been described as growing in the human ear, and is figured at 98. The leaves of the common bramble present a fungus in which the spores are arranged on a more dense and elongated head. This is called Phragmidium bulbosum, and is represented at figure 99. The Outturn which attends the blight of the vine, seen E 2 52 A HALF-HOUR WITH THE at figure 100, and the Botrytis which accompanies the potato disease, figure 101, are other and in- teresting forms of these minute parasites. The common pea is subject to a blight which is ac- companied by a peculiar fungus, seen at figure 102a, which, when examined by a low power, presents a globular mass, surrounded by minute filaments. Under a high power the central ball is resolved into a series of little cases, containing in their interior the minute spores. These are seen at figure 1026. Seeds, as well as fruits, are liable to the attacks of fungi during their decay. Figure 103. Plate 4, represents a fungus found in a mould upon a common Spanish nut. This fungus looks like a red powder spread over the surface of the nut. A fungus has been described as attacking the oil- casks in the London docks : its fibres resemble threads of black silk. It is represented at figure 104. The spores are found scattered about the fibres. As we have already seen, fungi are found on the human body, and accompany certain forms of disease of the skin, more especially those of the head. In these cases the fungi insert them- selves into the follicle of the hair, and introduce themselves into its structure, so that it either falls off or becomes disorganized. The fungus of ring- worm, called Achorion Schonlenii, is given at figuie 105. If the seed of wheat is allowed to germinate in a damp place, the little rootlet which it sends down will be found covered over with a minute fungus. A fungus of some interest, on account of its unusual place of growth, may be found, in autumn, attached to the roots of the common duck-weed (Lemna minor), seen at figure 106 plate 4. In the same figure, at , is represented a fungus of a different kind, it is parasitic within the cells, and has a bead-liko MICROSCOPE IN THE COUNTRY. 53 appearance. It may be an earlier stage of the growth of the former. The microscopic structure of the higher forms of fungi is not without its interest. In the fungi a very elongated form of cellular tissue frequently occurs, and in the stem of the common mushroom it will be seen to be branched, as at figure 103. The looser portions of the fibres of the mushroom, which are found in the earth at the bottom of the stem, afford even a better illustration of this struc- ture, and is given at figure 107. The gills of the mushroom, when put under the Microscope, display a number of small projections surmounted with four round cells ; these are the spores arranged in fours, and which, on that account, are called tetra- S2)ores. They are seen at c, figure 107. In the woods, in winter time, fungi abound, and their parts may be examined under the Microscope with great interest. Amongst the winter beauties of the forest, none are more attractive than the various forms of peziza, or cup-moulds. If a section be made through one of the cups of these beautiful fungi, they will present the appearance drawn in figure 108, plate 4. A series of hollow elongated cases will be found lying between compressed elon- gated tissue. In these cases a series of rather oval minute cells will be found, which are the spores of the peziza. If these are magnified with a higher power, they will be seen to be covered over with minute spines, as seen at a. Amongst the objects which more especially attract the attention of observers in the country, in winter time, are the various forms of lichens, which grow parasitic upon the bark of trees. There is one of a yellow colour, which spreads on palings and the barks of trees, like dried pieces of yellow- paper. At the surface of the membranous scales of 54 A HALF-HOUR WITH THE which the plant is composed will be found deeper yellow spots. If one of these is cut through, and a thin section placed under the Microscope, it will be found to possess very similar organs to the peziza. A series of cases will be found, containing the minute spores by means of which the plant is reproduced. These cases, called asci, are figured at. 109. A walk across a damp uncultivated piece of ground will not fail to reveal some spots which are boggy, Here the bog-moss (Sphagnum} must be looked for, and when found, it may be regarded as a good illustration of the family of mosses, and portions preserved for microscopic examination. The leaves afford interesting examples of fibro-cellular tissue, as seen at figure 110; and this tissue may be examined from day to day, as affording an illus- tration of the process of development in vegetable tissue. Other forms of mosses may be found on banks, old walls, rocks, and crevices. The organs which produce the spores, or seeds, are well de- serving the attention of the microscopic observer. These represent the pistils in the higher plants. The organs which represent the stamens are also very interesting, but they are not so easily pro- cured. We therefore proceed to describe the spore-bearing organ. This may be easily seen with the naked eye, although its beauties cannot be brought fully out without the aid of the Micro- scope. The part which contains the spores is seated on a little stalk, and is called the " urn," and is represented in figure 112. Covering the urn, and fitting on to it like a nightcap, is the calyptra, marked a. On slipping off the calyptra, a conical body fitting into the urn is observed, and this is called the "operculum" (b). If the operculum is now lifted off t there is revealed, below, a series of MICROSCOPE IN THE COUNTRY. twisted hair-like threads (c), which are called the " peristome." These processes are held together by minute teeth (d). The spores (e) are found in the interior of the urn. All these parts are subject to great varieties in different kinds of mosses. .From the mosses we may pass on to the feins. Like the mosses, they have no regular flowers, and the parts which correspond to the urns of the mosses are the small brown scaly-looking bodies seated on the back of the fronds, or leaves. In the male fern the little brown bodies which contain the spores are round, as seen in figure 113, and in the common brakes they are placed on the edge of the fronds, as at figure 114. These organs, which are called " sori," may be easily seen as opaque objects, under the lower powers of the Microscope. In the common hart's-tongue, or scolopendrium, the sori are arranged in elongated bands. In this case the sori are covered with a membrane called an " indusium." On opening this, the sori are found lying close together. Each one of these sori is found to be made up of a number of cases called capsules, or " thecae," attached to a stalk by which they are fixed to the frond. This organ is seen at figure 115. These thecse are beautiful objects under the Microscope. Springing from the top of the stalk is a series of cells which surround the case, forming what is called the rt annulus." This ring possesses an elastic power ; so that when it breaks, the capsule is torn open, and the spores in the inside escape. The spores are covered over with little spines, as at a, in the same figure. The spores of ferns are often called seeds, but they are more like buds than seeds. If one of these spores is watched during its growth, it will be found that it grows into a little green membranous expansion, on the surface of which the two sets of organs 56 A HALF-HOUR WITH THE resembling the pollen grains and ovules of the higher plants are developed. The representatives of the pollen grains are little moving bodies, re- sembling animalcules, which pass over the surface of the membranous expansion till they reach the ovules, or true spores of the fern, which they fer- tilize, and the young plant then shoots forth. The ferns, of which so many species may be found in a walk in the country, or cultivated in a Ward's case in town, are worthy the minute attention of the possessor of a Microscope, on account of the great variety of forms which their organs of fructi- fication present. The club-mosses are found on boggy moors and open places, and present a variety in the forms of their fructification. The reproductive organs are formed out of a transformed branch, and are found lying at the base of scale-like bodies, resembling the scales which form the fruit of firs and pine- trees, as seen at figure 115, a. The spores of the club-mosses are of two kinds, large and small ; hence they are called " megaspores " and " micro- spores." The last are very minute, and when highly magnified, they present a reticulated ap- pearance. The spores are seen at b and c in figure 117. In the interior of these spores is a minute worm-like body, which acts the part of the pollen in higher plants. The megaspores are much larger. They represent the spores of ferns, and produce an expanded membrane, on which grow the true representatives of the ovules, which coming in contact with the microspores, new plants are produced. Another family of these flowerless plants, which has yielded highly interesting results to the micro- scopic observer is the group of horsetails. If these are gathered in the spring of the year, they will I London : Hbbert Ha.rcJmcke,1860 / , MICROSCOPE IN THE COUNTRY. 57 present two forms ; one showing the leaves and green parts of the fruit ; the other, the leaves changed into reproductive organs. These may be very easily examined as opaque objects under the Microscope. The spores are seated on round shield- like disks, represented in plate 4, at figure 116, a. When the spores are examined by a higher power, they present four spiral filaments, which are twisted round the body of the spore, and seen at b. If the spore is breathed upon whilst under the Microscope, the spiral filaments gradually relax their grasp, and they become expanded and attached to the spore only at one end, as represented at c. The cuticles of the Equisetums are strongly siliceous, and are very curious and interesting objects, and will repay the trouble taken in preparing them. This may be done by boiling a piece of the stem, in nitric acid and chlorate of potash, and, after washing the detached cuticle, transferring it to absolute alcohol, from thence to oil of cloves, and afterwards mounting in Canada balsam. The study of the flowerless plants is one of never-ceasing interest. Within the last few yeare much has been done by the aid of the Microscope to clear away the mystery which surrounded the functions performed by certain organs they possess. Much more, however, remains to be done ; and an interesting field is still open to the inquiries of the microscopist. We will now, however, take our Microscope to the pond-side, where we shall still find many plants to interest us, belonging to the lower, or flowerless groups together with animals, the companions of their aqaatic life, and the repre- sentatives of their simpler mode of existence. 58 A HALF-HOUR WITH THE CHAPTER IT. A HALF-HOUR WITH THE MICROSCOPE AT THE POND-SIDE. CISTERNS, ditches, ponds, and rivers, contain nume- rous objects to interest the microscopic observer. Some of these objects float on the surface of the water ; others are found swimming about in the midst of the water ; whilst the greater number are found at the bottom. In collecting objects from fresh water, little bottles may be used, and a common spoon or small net employed for collecting them. Where the objects are only few, large quantities of the water should be allowed to stand, and the whole poured off, with the exception of a table-spoonful or two, which may be then placed in a wine-glass. A little of the sediment may be taken up in a pipette or clipping-tube, and con- veyed to the animalcule-cage, and the cover having been put on, it may be placed under the Micro- scope. If the objects are moving about too rapidly, the cover may be pressed down till they are secured. They may be first sought out with a low power, and when it is wished to examine them more closely, a higher power may be put on. Of all the forms of microscopic plants which are found in fresh water, those belonging to the families of desmids and diatoms are most interest- ing. We have already spoken ot plants consisting of one cell, and these also consist of one cell ; but they have this peculiarity, that their cells are divided into two equal parts, each part having the same form as the other. The desmids are dis- MICROSCOPE AT THE POND-SIDE. 59 tinguished from the diatoms by their bright-green colour, and by their cells not depositing silex, or flinty matter, as is the case with the latter. The siliceous nature of the shells of diatoms is made apparent by their not being acted on by strong acids, as nitric and hydrochloric. The desmids sometimes abound in ditches and small pieces of standing water. Amongst other objects in a drop of water they are easily recog- nized by their beautiful bilateral forms and dark- green colour. One o-f the most charming of these is named Euastrum, and consists of two notched halves of a bright-green colour, with darker green spots. It is represented at figure 28, plate 2. The green matter is composed of a waxy substance, called chlorophyle, and is the same matter as that which produces the green colour of leaves. Some of the desmids assume a lunate form, and are named Closterium, a species of which is figured at 29, plate 2. There are various species of Clo- sterium, all of the same general form, and occa- sionally occurring in very great abundance. Some- times several of the cells are attached together, forming a long chain, as in the genus Desmidium, seen at figure 30, from which the family takes its name. These break up and go on growing. When they grow, the new cells are formed between the two halves of the parent cells. This is represented at figures 136 and 137, plate 5. In a genus called Scenedesmus, several cells are united, and the two last halves are furnished with horns, as seen at figure 32 ; at other times several cells unite, forming a globular mass, as in Pediastrum, represented at figure 31. In this case each cell presents two projections, forming objects of singular beauty. The diatoms are more numerous and widely 60 A HALF-HOUK WITH THE diffused than the desmids. The lattei are decom- posed, and their bodies perish when they die ; but from the fact that the diatoms deposit silex in their structure, they are almost imperishable. They are found in great abundance in the mud of rivers, ponds, and lakes. They are also present in those deposits of clay which once formed the bed of rivers and lakes, and which are now dry. In order to procure the diatoms from these deposits, ihe clay or earth should be well washed with pure water, and the deposit allowed to subside, and the water poured off. This may be repeated several times. The deposit is then to be washed with hydrochloric acid, and when the effervescence is over, the acid is poured off, and a fresh portion is added. This may be repeated several times, and when the hydrochloric acid ceases to act, nitric acid may be employed in the same manner. When no action occurs by its use cold, the deposit may be transferred to a watch-glass, and kept over a spirit-lamp, at a temperature of about 200, for three or four hours. The deposit must then be well washed with pure water, to remove all the acid. The deposit will be found now to consist almost entirely of diatoms. If anything else be found, it will be grains of sand. By casting the deposit into a small quantity of water, and allow- ing the heaviest particles alone to subside, these will be generally found to contain the sand and larger diatoms. By repeating this process suc- cessively, the deposits consist gradually of smaller and smaller diatoms, which may be examined with gradually higher powers, in proportion to their minuteness. Some are perfectly round, as in the case of the genus Coscinodiscus, a species of which is figured at 38, plate 2. It is marked beautifully over their surface ; others are triangular : some are MICROSCOPE AT THE POND-SIDE. 61 square, and attached together. The last form is seen in Melosira, species of which are figured at 36 and 37, plate 2, and 139, plate 5. The most common forms are those which are oval, or boat-shaped, and represented by species of Pin- nularia and Navicula in figures 34 and 35 a, in plate 2. Some of these are again larger at one end than the other, as in Surirella, figure 33. The markings upon the surface are very various. In some forms the markings are exceedingly minute : so small are they, that certain species of diatoms have been used as test objects, for testing the highest powers of the Microscope. Whilst living, the diatoms possess the power of moving about, and in some of them, as well as the desinids, a movement has been observed of the small particles in their interior. The diatoms are generally of a brownish or brownish-yellow colour, which seems to be due to a small quantity of iron in their composition. They are increased in the yame way as the desmids, by the production of new cells between the parent frustules. This process is seen in figure 3o, a and &, in plate 2. The continuance of the species in these organisms is secured by the process of conjugation and the sub- sequent formation of the spores. This process is exhibited in figures 13o and 136, plate 5. In some cases, however, the spore is found without the union of two cells, as in Melosira represented at figure 137, plate 5. Sometimes, attached to the bottom of a pond or river, or growing from immersed objects, or floating about in the water, will be found long green fila- ments. These are the fronds of confervse. All forms of these and they are very numerous will be found most beautiful objects for examination. They may be laid on a slip of glass in water, and A HALF-HOUR WITH THE covered over with a piece of thin glass ; or they may be placed in the animalcule-cage. They con- sist of a series of cells growing end to end, and their partition- walls can be easily seen. They are of a green colour, from the chlorophyle contained in their interior. In the case of the yoke-threads, the chlorophyle is frequently arranged in a spiral manner along the interior of the filament, as in the Zyynema represented at figure 11, plate 1. These yoke-threads may be often seen to unite with each other, and the contents of one cell are emptied into the other, forming the spore of the plant, as seen at figure 135, plate o. The cell contents some- times break up into smaller portions, called zoospores, which, when they escape from the cell in which they are contained, move about with great rapidity. This is seen in figure 11, plate 1, at a and b. The moving power of the lower plants is well seen in the division of these confervse, called Osdtiatorias, which are sometimes found in semi- putrid water. A species is figured at 12, plate 1. As they lie upon the glass slide they will be seen to move over each other in all directions : hence their name. Some of the spores formed by the confervse move about by the agency of little organs called cilia. These are extensions of the motile matter of the cell, and are found very commonly in the animal kingdom. Occasionally, a number of these ciliated spores are aggregated together, forming a rapidly- moving sphere. Of this the Pandorina Moruni affords a good example, seen at figure 13, plate 1, in which each spore possesses two cilia. But the most remarkable of this kind of moving plant is the Volvox globator, represented in figure 14 of the same plate. This beautiful moving plant was at one time thought to be an animalcule, but it is now MICROSCOPE AT THE POND-SIDE. 63 regarded as a true plant. It consists of a large number of spores, or cells, each having two cilia, and connected together by a delicate network of threads. In the interior of this moving sphere are seen smaller globular masses, of a dark-green colour, which are the young of the volvox, which have not yet developed the network, by means of which their spores are separated, and their ciliated ends pre- sented to the water, and by means of which their movements are effected. Another form which is now regarded as a loco- motive plant is the Euglena viridis, seen at figure 15, plate 1. It is often found in prodigious num- bers, giving to "water the appearance of green-pea soup. When placed under the Microscope, it fre- quently presents a red speck, or point, at one end, and an elongated tail at the other. The red spot has been regarded as an eye ; but if it is watched, it will be found the red colour will often extend from the red spot to the rest of the body ; and it is probable that the red colour is only a change in the condition of the chlorophyle contained in its interior. Amongst this class of plants it is not unfrequent for the chlorophyle to assume a red colour at certain stages of its growth. The transition from the filamentous to the mem- branous form of these plants is well seen in the species of Viva. These are found in both fresh and sea water. In the early stages of its growth, the ulva presents the filamentous form of a conferva, as seen at a, in figure 26, plate 2. Gradually the cells of the filament split up into two or three seams (b) j and this goes on till at last a broad flat membrane is produced (c). If the plants of our fresh waters are interesting, not less so are the animalcules ; for, just as we have one -celled plants so we have one-celled ani- 64 A HALF-HOUR WITH THE mals, and it was only by the aid of the Microscope that they were discovered and can be examined. Wherever the above plants are found, there will also be discovered animals to feed upon them. The animal is distinguished from the plant by its feed- ing on plants, whilst the latter feed on inorganic substances. There is considerable difficulty in at once dis- tinguishing between the lowest forms of animals and plants. Although the animal generally pos- sesses a mouth, and a stomach in which to digest its vegetable food, there are some forms of animal life so simple as not to possess either of these organs. In the sediment from ponds and rivers there will frequently be found small irregular masses of living, moving matter. If these are watched, they will be found to move about and change their form constantly. As they press them- selves slowly along, small portions of vegetable matter, or occasionally a diatom, mix, apparently, with their substance. Cells are produced in their interior, which bud off from the parent, and lead the same life. These creatures are called amsebas, and are represented in our first plate, figure 16. Although they have no mouth or stomach, they are referred to the animal kingdom. They appear to consist entirely of the formative matter found in the interior of all cells called moto planes or sarcode without any cell-wall. If we suppose an amoeba to assume the form of a disk, and to send forth tentacles, or minute elongated processes from all sides, v:e should have the sun animalcule (ActinopJirys Sol), which is represented at figure 17, plate 1. This curious creature has the power, apparently, of suddenly contracting its tentacles, and thus leaping about in the water. It can also contract its tentacles over particles of starch and MICROSCOPE AT THE POND -SIDE. 65 animalcules, and press them into the fleshy sub- stance in its centre. This is undoubtedly an animal, but it has no mouth or stomach. A large number of such forms present themselves under the Micro- scope. Some of them are covered with an external envelope, which they make artificially, by attaching small stones and other substances to their external surface, as in the case of the Difflugiae, seen at figure 18, plate 1 ; or they may form a regular case, or carapace, consisting of a hairy membrane, as in Arcella, represented at figure 19. We shall meet again with forms resembling these when wo take our Microscope to the sea- side. One of the most common animalcules met with in fresh water, and whose presence can easily be insured by steeping a few stalks of hay in a glass of water, is the bell-shaped animalcule. These animalcules, which are called Vorticetta, are of various sizes. Some are so large that their presence can easily be detected by the naked eye, whilst others require the highest powers of the Micro- scope. They are all distinguished by having a little cup-shaped body, which is placed upon a long stalk, figured at 40, in our second plate. The stalk has the peculiar power of contracting in a spiral manner, which the creature does when anything disturbs it in the slightest manner. In some species these stalks are branched, so that hundreds of these creatures are found on a single stem, forming an exceedingly beautiful object with the Microscope. The stalks of these compound vorticellse are con- tracted together, so that a large mass, expanding over the whole field of the Microscope, suddenly disappears, and, " like the baseless fabric of a vision, leave not a wrack behind." A little patience, however, and the fearful creatures will once more be seen to expand themselves in all their beauty. 66 A HALF-HOUR WITH THE The mouth of their little cup is surrounded by cilia, which are in constant movement j and when ex- amined minutely, they will be found to possess two apertures, through one of which currents of water pass into the body, and from the other pass out. Not unfrequently the cup breaks off its stalk. It then contracts its mouth, and proceeds to roll about free in the water. Many other curious changes in form and condition have been observed in these wonderful bell-shaped animalcules. If, now, we go to a very dirty pond indeed, into which cesspools are emptied, and dead dogs and cats are thrown, we shall find abundant employ- ment for our Microscope in the beautiful forms of animalcules which are placed by the Creator in these positions to clear away the dirt and filth, and prevent its destroying the life of higher animals. In such waters, amongst a host of minor forms, we are almost sure to meet with the magnificent Para- mcecium Aurelia, figured at 39, plate 2. He moves about the water a king amongst the smaller prey, on whom he feeds without ceasing. He is of an oblong form, covered all over with cilia, and very rapid and active in his movements, as able to dart backwards as forwards, and turning round with the greatest facility. In his inside several spots are observed. If a little indigo or carmine is intro- duced into the water in which he lives, these spots become coloured by his taking up these substances. From this, Ehrenberg concluded that these spots were stomachs, and as such spots are very common amongst these animalcules, he called them many- stomached (Polygastrica). There is, however, reason to doubt the correctness of this conclusion of the great microscopist, as, although these spots exist in the body, they are not necessarily stomachs. They are, in fact, empty spaces, or vacuoles in the MICEOSCOPE AT THE ?OND-SIDE, 67 interior of the little fleshy lump of which the ani- mal is composed. They are found in the vorticella, and in most of the true animalcules. All animalcules have been called infusory, be- cause they seem so abundant in many kinds of vegetable infusions. Ehrenberg divided them into Polygastric and RotifeTous. The last are also called wheel-animalcules, as, when looked at through the Microscope, they appear to be supplied with little wheels on the upper part of their body. The most common form of these creatures is the Rotifer vulgaris, represented at figure 41, plate 2. The branches or leaves of any of our common water- plants can scarcely be examined without some of those pretty little creatures being found nestling among them. The structure of these creatures is highly complicated, and the family to which it belongs is far removed from the poly gastric ani- malcules with which it is associated by Ehrenberg. On examination, the wheels will be found to consist of two extended lobes, the edges of which are covered with cilia. These cilia are in a con- stant state of movement, and produce the appear- ance of wheels moving on an axis. Between the wheels is the entrance to the mouth, which, in many species of wheel-animalcules, is furnished with a strong pair of jaws. This leads to an oesophagus, a stomach, and an intestinal tube. Two little spots on the neck seem to indicate the existence of eyes ; whilst a projecting organ, believed to be analogous to the antennae, or feelers of insects, is seen directly below them. The tail is finished off with a pair of little nippers, by which the creature has the power of attaching itself to objects. When moving, its whole body is extended, but it has the power of drawing itself up like a telescope in its case, and appearing almost round. P 2 68 A HALF-HOUR WITH THE The wheel-animalcules abound in our ponds and rivers, and sometimes occur in great numbers in the aquarium. The common wheel-animalcule, Rotifer vulgaris, is most frequently found in lead gutters and the drinking-fountains used for birds. If a little of the deposit which usually accumu- lates in the former is placed in a test-tube with water, and exposed to the light, in a short time the rotifers will be found swimming about in great numbers, and may be transferred to a live-box by means of a dipping-tube : if allowed to dry, they can be afterwards revived by adding a little water. Several of the wheel-animalcules are fixed, forming on the outside of their bodies a little case or tube in which they dwelh These forms are beautifully seen when illuminated by the spot lens. MICROSCOPE AT THE SEA-SIDF. 69 CHAPTER V. A HALF-HOUB WITH THE MICEOSCOPE AT THE SEA-SIDE. ON a visit to the sea-side, the Microscope is an essential instrument to all who would wish to study the wonders of the ocean. It is a curious fact, that the few grains of common salt in the gallon of sea-water seem to determine the exist- ence of thousands of plants and animals. We shall therefore find living in the sea-water, plants and animals belonging to the same families as those in fresh water, but belonging to entirely different species. The sea-weeds present strikingly different forms. Although many of them are microsopic, and belong to the families of Diatomacece and Confervacece, all the larger forms present interesting objects for examination in the structure of their fruit-bearing organs. No better subject for the latter purpose can be procured than the common bladder-wrack, which is so abundant on all our shores. If a frond of this fucus is examined, there will be found at certain parts a swollen mass, dotted over with round yellowish bodies. If one of these is taken and carefully pressed between two pieces of glass, it will present the spores surrounded with hairs of the most delicate and various structure. Some of the spores are divided into four parts, and on this account are called tetraspores. These are seen at d, figure 111, plate 4. The bladder-wrack is fre- quently covered with minute parasites ; one of the most common of these is Polysiphonia fastigialcl, 70 A HALF-HOUR WITH THE which is represented at figure 111, plate 4. As seen in the drawing, this little plant is branched, and the stems present a series of flattened cells. On the branches are placed the fruit-bearing organs, in the form of little capsules, seen at a. These capsules contain tetraspores (d). At the ends of the branches are organs of another kind, representing the stamens, and which are called antheridia. These are seen at e in the same figure. The sea-weeds present a great variety in the form of these organs, and may be easily preserved for investigation in small glasses of sea-water. The animal structures of the sea-water must now, however, claim our attention. Amongst the lowest form of animal life are the sponges. They are frequently cast on the shore with sea-weeds, and afford interesting objects for the Microscope. They are composed of animal matter, which lies upon a structure of horny, calcareous, or sili- ceous matter. The common sponge which is used for domestic purposes may be taken as a type of the whole group. If a thin section of the common sponge is made with a pair of sharp scissors and placed under a low power, it will be seen to be composed of a network of horny matter, repre- sented in figure 140, plate 5. If now we take one of the common forms from our own sea-shore, we shall find that the network is composed of sili- ceous spicules lying one over the other, as repre- sented in figure 141 of plate 5. If one of these spicules is examined (a) and compared with a spicule from another sponge, it will be found to differ in form and size ; and the species of sponges can actually be made out by the shape of their spicules. Some of our British sponges have cal- careous spicules. This is the case with Grantia ciliata. There is a little boring sponge, called MICROSCOPE AT THE SEA-SIDE. 71 Cliona, found in the shells of old oysters, which has its spicules pin-shaped, as seen at figure 142. The fresh-water sponge has very peculiar-shaped spicula, and is represented at figure 143. In some the siliceous bodies are round, with projections, as in Tetliea, seen in the drawing, figure 145. Sometimes the spicula assume a stellate form, and are even branched, as in the spicula of an unknown sponge given at figure 144. Amongst the lowest forms of animal life, none are more interesting to the microscopic observer than those belonging to the family of Foramini- fera (Hole-bearers). They are thus called on account of the minute holes which cover their shells. If we suppose a creature as simple in structure as the amoeba, or sun animalcule, of which we have previously spoken, and which are figured in 16 and 17, plate 1, with the power of forming a little calcareous shell, we should have a foramini- fer. Some of these shells have the form of a nautilus, and when first observed they were sup- posed to belong to this group of shell-fishes. In form they certainly resemble the higher forms of mollusca, as may be observed in figures 21 and 24, in plate 1. Sometimes, however, they are elon- gated or cone-shaped, as in figure 25. Other forms are seen in figures 20 and 22. They may often be found alive -at the sea-side, nestling in the roots of the gfgantic tayles which are so often thrown on the shore after a storm. If the roots of these plants (Laminarice) are washed, and the deposit examined carefully, the foraniinifera will be seen at the bottom of the vessel, and may be picked out one by one. When this is done, they will be found to have the power of protruding through the little holes in their shells their soft bodies, in the form of long tentacles, as seen at figure 24, in the ? 2 A HALF-HOUR WITH THE first plate. With these they seem to have the power of moving, as well as of taking up the matters by which they are nourished. The shells of these creatures are not so small but they may be seen with the naked eye, and they need only a low power to observe all their structure. They are found at great depths in the ocean, and have been brought up by the dredge from the deepest parts of the Atlantic. They are very abundant in some rocks, especially in the chalk : they may be ob- tained from the latter substance by rubbing a piece of chalk with a brush in water. The water must be first decanted from the coarser particles of chalk, and in subsequent deposits the foraminifera will be found. They may be obtained from dry sand in which they are contained, by throwing the sand into water, when the sand will si'nk and the foraminifera will swim on the surface, and may be skimmed off. They are best examined as opaque objects. The family of polyps will next command atten- tion. One of the most simple forms of this family is found in ponds and rivers, and is called the fresh-water polyp or hydra. It is figured at 146, plate 5. It may be easily observed, adhering to plants, with the naked eye, and needs only a low power with transmitted light to observe it accu- rately. Its body is cup-shaped, surmounted with eight long tentacles, which it has the power of re- tracting. It produces young ones by the process of budding, and the buds may be often seen protrud- ing from the side of their parents. It is very tenacious of life, and may be cut into several pieces, and each part will grow into a new hydra. These, with many other polyps and the jelly-fish, have their flesh filled with little hair-like bodies, which, from their property of stinging in some species, have PLATE 6. MICROSCOPE AT THE SEA-SIDE. 73 been called stinging hairs, as seen at a, figure 14G. If we suppose several of these hydras placed in little cups upon a common branch or stem, we should have a Sertularia, or such an animal as is represented at Figure 147, Plate 5. These polyps are very common on all our sea-shores j and the branches and cups are often cast up on the shore, and regarded by the uninstructed as sea-weeds. The branches and cups are called the polypidoms of the animal, and assume a great variety of forms. When the cups are fixed on ringed stalks, they constitute the genus Campanularia, seen at figure 148, plate 5. These cups are often objects of great beauty, as in those of Campanularia volubilis, figured in 149. It is the polypidom which consti- tutes the coral in the family of polyps, producing the masses of carbonate of lime which sometimes cover the bottom of the ocean and form reefs in the sea. In one family of polyps, known as sea-fans (Gforgoniai), which are calcareous, the fleshy mass covering the horny polypidom contains spicula of various forms, which are beautiful objects under the Microscope. These spicula are seen at figure 150, plate 5. The red coral of commerce is another interesting form of these polypidoms. In some families of these polyps, as in the campanularidse and the corynidse, the young, before they arrive at their mature stage, assume the forms of minute medusae or jelly-fishes. These are exceedingly beautiful objects for microscopic observation. Another family of animals common enough in the sea, are the star-fishes and sea-eggs (Echinoder- mata). Although not themselves microscopic, certain parts of their structure present very in- teresting objects for examination. If a section is made of one of the spines of the common echinus, or sea- egg, it presents under a low power a beau- 74 A HALF-HOUR WITH THE tifully radiated structure. This is seen at figure 151, plate 5. The suckers, also, of the same animal present little rosettes, surrounded by a very delicate hyaline disk, represented at figure 152. Upon the surfaces of both star-fishes and sea-eggs will be found little inoveable bodies which are called pedi- cettarice. In the sea-egg they pos&ess three moveable nipper-like limbs, whilst in the common star-fish they present only two. These are represented at figures 153 and 154, plate 5. A controversy has been raised on the question as to whether these bodies are parasitic animals, or part and parcel of the structure of the creature on which they are found. As they are so constantly present, they are undoubtedly parts of the animal on which they are found. The movements of the nippers are very active, and they frequently lay hold of objects which pass near them. As common on the shore as the polypidoms of the polyps, are the animal skeletons called, in some parts of the country, sea-mats (Flustra foliaceci). "When placed under a low power, and viewed by reflected light, the sea-mat is composed of little cavities or cells, seen at figure 162, plate 6. In each one of these is seated a creature of much more complicated organization than the polyps just ex- amined. It has, it is true, a ring of tentacles ; but if these are examined, the tentacles are found to be covered with cilia, as seen at a, in figure 163, plate 0. This family of creatures are called Polyzoa, or Eryozoa, and form a group of animals which are classed with the Mollusca, or shell-fish. Sometimes these creatures attach themselves to sea- weeds, oysters, stones, and other objects at the bottom of the sea, forming a kind of cellular membranous expansion. Such are the species of Lepralia, figured at 155. Sometimes the cells are elongated MICROSCOPE AT THE SEA-S1DF. 75 and elevated above the surface of the object on which they are placed, as in the case of Bowerbankia, seen at 156. A beautiful form of these creatures is the shepherd's-purse coral (Notamia bursarici), represented at figure 157. This creature belongs to a group of the polyzoa, remarkable for possess- ing little processes on the margins of their cells, in shape resembling the bowls of tobacco-pipes, birds' bills, and bristle-like organs. On examining them with the Microscope, they present a very compli- cated organization. The birds' bills possess two jaw-like processes, which open and shut like a bird's beak, and from this fact they have been called avicu- laria, or bird's-head processes (a). The tobacco-pipe form in Notamia is peculiar to that genus. In other species, as in Eugula, avicularia, seen in figure 158, these creatures possess not only the bird's-head process, but a second, consisting of a long bristle or seta, attached by a joint to a process below (a). These bodies are called vibracula, and the bristle-like extremity is kept constantly in action, and the form of avicularia is seen in Bugula Murrayana, at figure 159. Both processes are seen in Scrupularia scruposa, at figure 160. Few objects are more curious under the Microscope than these avicularia and vibracula in a state of action. Whilst the function of the vibracula, seen at a, figure 160, seems to be to sweep away objects that would interfere with the life of the animal in the cell, it has been suggested by some that the avicularia secure by their jaws the food necessary for its sustenance : it seems probable, however; that they serve the purpose of a protective police. Of the various forms which the cup itself assumes, none are more interesting than those of the snake- head zoophyte, shown at figure 161, plate 6, in which it assumes the form of a snake's head, with 76 A HALF-HOUR WITH THE the tentacula projecting like a many-parted tongue. The polyzoa are also inhabitants of the fresh water. Of these the most common form is the Plumatella repens, figured at 163. The eggs of a fresh-water species, Cristatella inuced