THE LIBRARY 
 
 OF 
 
 THE UNIVERSITY 
 OF CALIFORNIA 
 
 PRESENTED BY 
 
 PROF. CHARLES A. KOFOID AND 
 MRS. PRUDENCE W. KOFOID 
 
TEXT-BOOK 
 
 OF 
 
 VEGETABLE AND ANIMAL 
 
 PHYSIOLOGY. | 
 
 DESIGNED FOR THE USE OF 
 
 SCHOOLS, SEMINARIES, AND COLLEGES IN THE UNITED STATES. 
 
 
 
 BT 
 
 HENRY aOADBY, M. D., 
 
 PROFESSOR OF VEGETABLE AND ANIMAL PHYSIOLOGY AND ENTOMOLOGY, IN THE STATE AGRI- 
 CULTURAL COLLEGE OF MICHIGAN; FELLOW OF THE LINNJSAN SOCIETY OF LONDON; 
 CORRESPONDING MEMBER OF THE ALBANY (N. Y.) INSTITUTE ; HONORARY 
 MEMBER OF THE LITERARY AND HISTORICAL SOCIETY OF QUEBEC; 
 AND FORMERLY DISSECTOR OF MINUTE ANATOMY TO THE 
 ROYA.I. COLLEGE OF SURGEONS OF ENGLAND. 
 
 (BmbeUtefcefr foitfr wpfoar&s of Jfour gunbr^ anb Jfiftg Illustration*. 
 
 NEW YORK: 
 D. APPLETON AND COMPANY, 
 
 346 & 348 BROADWAY. 
 
 1858. 
 
ENTKBID according to Act of Congress, in the year 1868, by 
 
 D. APPLETON & CO., 
 
 In the Clerk's Office of the District Court of the United States for the 
 Southern District of New York. 
 
TO 
 
 MES. JOHN GEEGOEY, 
 
 MILWAUKIE, WISCONSIN. 
 
 My DEAE LIZZIE: 
 
 I do not know any one to whom the following pages will prove 
 more attractive than to yourself. 
 
 Cradled, as you literally were in the midst of Microscopes ; surrounded 
 by, and throughout your early life accustomed to examine preparations of 
 all sizes and kinds, and frequently to hear descriptions of them in the 
 public lecture room, this volume, with its illustrations, must needs possess 
 greater charms for you than for most readers. 
 
 You will be constantly reminded, when gazing on the pictorial repre- 
 sentations of well-remembered preparations, of the many delightful hours 
 we have spent together in days that are past, enraptured with the sur- 
 passing beauty of the originals ! 
 
 But, under any circumstances, as a record of the labors of my life, I 
 cannot but think it will ever be acceptable to you ; moreover, I venture 
 to hope it will be found of some value in your family, by contributing to 
 the education of your own children. 
 
 It is a subject of deep regret to me, that I have been deprived of your 
 judicious, keen criticism ; but, with all its faults, I dedicate this book to 
 you, as the least testimonial I can offer of a Father's fond affection. 
 
 That you may long enjoy every earthly blessing, is the sincere and 
 heartfelt wish of, 
 
 My Dear Child, 
 
 THE AUTHOR. 
 
PREFACE. 
 
 THE Author having been appointed to the Chairs of Vege- 
 table and Animal Physiology and Entomology, in the State 
 Agricultural College of Michigan, has felt the want of a suita- 
 ble text-book, for the use of his students, and not being aware 
 of any existing work on the plan he considers essential for the 
 acquisition of these subjects, he has prepared the accompany- 
 ing volume to aid him in his labors, and to fulfil a request, 
 previously made to him by the Superintendent of Public 
 Instruction of the State of Michigan, the Hon. Ira Mayhew, 
 to write such a work. 
 
 The " Botanies " hitherto published, are insufficient as 
 physiologies ; and the Animal physiologies, as yet prepared 
 " for the use of Schools," are simply epitomized treatises on 
 Human anatomy, and are generally too technical and obscure 
 to be available for the purposes of popular instruction. 
 
 This latter subject, a distasteful one, even to Medical 
 Students, who rarely learn it, must necessarily prove a severe 
 tax to the youth of both sexes, who throng the public and 
 private schools of the country, whilst many of the illustrations 
 supposed to be necessary to these books, are, to say the least 
 of them, most uninviting. 
 
 The attempt to teach only Human Physiology, like a 
 similar proceeding in regard to anatomy, can only end in 
 failure: whereas, if the origin (so to speak) of the organic 
 structures in the animal kingdom, be sought for and steadily 
 pursued through all the classes, showing their gradual com- 
 plication, and the necessity for the addition of accessory 
 organs, till they reach their utmost development and cul- 
 
PREFACE. 
 
 minate in man, the study may (possibly) be rendered an 
 agreeable and interesting one, and be fruitful in profitable 
 
 results. 
 
 Throughout the accompanying pages, this principle has 
 been kept steadily in view, and it has been deemed of more 
 importance to impart solid and thorough instruction on the 
 few subjects discussed, rather than embrace the whole field 
 of physiology, and, for want of space, foil to do justice to any 
 
 part of it. 
 
 The development of the nutrimental organs, and of the 
 brain and nervous system, have been considered as of pri- 
 mary importance, and to the consideration of these topics 
 much space and great care have been devoted. The latter 
 subject has always been most difficult to understand, and the 
 attempt has been made by the Author, to popularize this 
 very abstruse subject; with what success remains to be 
 seen. 
 
 In proof that the views above-enunciated are supported 
 by high authority, the opinions of the distinguished Haller, 
 and the late Baron Cuvier, are quoted; moreover, the 
 Authors of the best and most reliable treatise on human 
 physiology Todd and Bowman have adopted, and given 
 expression to the same opinion. 
 
 u A knowledge of human anatomy alone, is not sufficient to 
 enable us to form accurate views of the functions of the vari- 
 ous organs." Before an exact knowledge can be formed of 
 the functions of most parts of living bodies, Haller says, that 
 " the construction of the same part must be examined and 
 compared in man, in various quadrupeds, in birds, in fishes, 
 and even in insects." 
 
 Cuvier has compared the examination of the comparative 
 anatomy of an organ in its gradation from its most complex 
 to its simplest state, to an experiment which consists in re- 
 moving successive portions of the organ, with a view to 
 determine its most essential and important part. In the ani- 
 mal series we see this experiment performed by the hand of 
 nature, without those disturbances which mechanical violence 
 must inevitably produce. Thus we learn that one portion 
 of the nervous system, in those animals in which it has a defi- 
 
PREFACE. Vii 
 
 nite arrangement, is pre-eminently associated with the mental 
 principle, and is connected with, and presides over, the other 
 parts. 
 
 The brain is always situated at the anterior or cephalic 
 extremity of the animal, and with it are invariably connected 
 the organs of the senses, the inlets to perception. We soon 
 find that the brain exhibits a subdivision into distinct parts ; 
 and of the relative importance of these parts, and their con- 
 nection with the organs of sense, and with the intellectual 
 functions, we derive the most important information, from 
 the study of comparative anatomy. 
 
 In place of " questions," the Author has preferred to give 
 an analysis of the paragraphs, which will render it equally 
 compulsory with the Teachers and the students, to make 
 themselves acquainted with the book; moreover, it forms 
 an analytical index of the contents of the lessons, of much 
 value. 
 
 Instead of appending a glossary of technical terms, neces- 
 sarily used, the translation of difficult, or uncommon words 
 has been given, simultaneously with the use of them, and to 
 this rule, it is hoped, there are but few exceptions. 
 
 It is presumed that the beauty of the wood engravings, 
 that so plentifully adorn this work, is so apparent, that little 
 requires to be said in their praise ; the Author feels, however, 
 desirous of expressing his deep obligations, and tendering his 
 best thanks to the accomplished artist who produced them, 
 Mr. H. E. Downer, of this City. As the work of a young 
 man only nineteen years of age, they are extraordinary ; whilst 
 the incessant labor necessary to their production, and the 
 untiring energy and zeal displayed by him, are worthy of the 
 utmost commendation. It may be a matter of observation 
 and remark, that the style of all the engravings is peculiar. 
 Nearly thirty years ago, the Author had a series of 400 
 diagrams, for public lectures, prepared on this principle 
 white figures, on a dead-black ground. They consisted of 
 subjects kindred to the illustrations of this book, and, from 
 their distinctness, elicited universal approbation. 
 
 He has always (subsequently) thought that the same plan 
 would prove most effective for wood-engravings of the same 
 
Vlll PREFACE. 
 
 tissues and structures, and this opinion induced him to make 
 the experiment : how far it is successful, he leaves others to 
 determine. He ventures to presume that, in the delineation 
 of nerves, there can be no doubt, as they are always eminently 
 white ; and such is their extreme delicacy in the lower ani- 
 mals, that justice could not be done to them by the adoption 
 of any other method. 
 
 In the list of engravings, the word " Original " very fre- 
 quently occurs ; it is not intended to imply that such illustra- 
 tions have not been published before, but simply to indicate 
 that the drawings have been made from preparations dissected 
 by the Author, and to be found, either in the Museum of the 
 Koyal College of Surgeons, or forming a portion of his pri- 
 vate collection. He is quite aware, however, that a great 
 proportion of them are not only original, but unique, and 
 have not been published before. 
 
 Finally, should the perusal of this book impart to its 
 readers only a tithe of the pleasure the Author has had in its 
 production, they and he will be alike repaid. 
 
 DHTBOIT, MICHIGAN, February, 1858. 
 
ANALYSIS OF THE LESSONS/ 
 
 PART I. 
 
 VEGETABLE TISSUES* 
 
 LESSON I. INTRODUCTION, p. 1. 
 
 1. Physiology explained. 2. It has become a modern science. 3. Yalue of 
 the Microscope. 4. Histology, its origin. 5. Its relation to Physiology. 6. 
 Direct application. 7. A knowledge of the ultimate structure of tissues insisted 
 on. 8. The study of Physiology a work of time. 9. Analysis of the lowest 
 plants. 10. The properties of a cell. 11. Subject continued. 12. TheVolvox 
 globator. 13. Their habitat. 14. Their locomotion. 15. More accurately de- 
 scribed. 16. Method of seeing these organs. 17. The name given to them. 
 
 LESSON II. INTRODUCTION, CONTINUED, r ... p. 4. 
 
 18. The nature of the large green masses. 19. How they escape. 20. The 
 higher and lower plants compared. 21. Analysis of a forest tree. 22. Exam- 
 ination of the root. 23. Fluid of the spongioles. 24. Production of latex. 25. 
 Exhalation, and aeration. 26. Assimilation explained. 27. Nutrition described. 
 28. Secretion explained. 29. The transitory life of cells. 30. Absorbent cells 
 always changing. 31. Absorption in plants and animals compared. 32. The 
 transitory duration of cells, exemplified. 33. Fall of the leaf: what causes it. 
 34. Secreting cells, equally transitory. 35. Function of cells. 
 
 LESSON HI. INTRODUCTION, CONCLUDED, p. 7. 
 
 36. Reproduction denned. 37. The germ considered. 38. The elements of 
 animals and plants alike. 39. The embryo condition of both the same. 40. 
 Identity of the lowest animals and plants. 41. The irritability of animalcules 
 exhibited. 42. Its cessation. 43. Their digestive cavities. 44. Ehrenberg's 
 opinions on this subject. 45. These opinions refuted. 46. The Enchelis pupa. 
 47. Their vibratile cilia. 48. Their mode of development. 49. Maturity, and 
 
 * The numbers refer to the paragraphs. 
 
X ANALYSIS OF THE LESSONS. 
 
 its consequences. 50. Distribution of the germ cells. 61. Identity of this pro- 
 cess of development in plants. 52. Development of the "Frog's spittle." 53. 
 The first stage. 54. The second stage. 55. The third stage spontaneous di- 
 vision. 56. Termination of the process. 57. Similarity of the ultimate struc- 
 ture of the tissues of plants and animals. 58. Tissues peculiar to animals. 59. 
 Cellular characteristics of certain animal tissues. 
 
 LESSON" IV. ON THE STRUCTURE OF VEGETABLE TISSUES. STARCH, . p. 11. 
 
 60. Simplicity of their structure. 61. Cellulose. 62. Its characters. 63. 
 Its chemical characters. 64. The tissues of the higher plants. 65. Their 
 union. CELLULAR TISSUE 66. The formation of this tissue. 67. The size of 
 cells. 68. The union of cells. 69. Formation of tubes. 70. Cellular plants. 
 71. The structure of pith. 72. Porosity of cells. 73. Porous cells. 74. Cells 
 possess contents. 75. Sometimes a nucleus. 76. Sometimes formed for special 
 contents. 77. Starch. 78. Where found. 79. Structure of Potato. 80. Of 
 a corpuscle of starch. 81. The lines not always found. 82. The largest cor- 
 puscle of starch. 83. The Indian Corn starch. 84. Wheat starch.' 85. Rice 
 starch. 86. The use of Starch to the plant. 
 
 LESSON V. THE SUBJECT OP STARCH CONCLUDED. GUMS AND SUGAR, . p. 16. 
 
 87. Analysis of starch found in a given quantity of Potatoes. 88. Its vari- 
 ations. 89. The structures containing Starch. 90. Starch a constituent of poi- 
 sonous plants. 91. Wheat starch and gluten in situ. 92. The same in moun- 
 tain rice. 93. A chemical test for starch. 94. Its mode of action. 95. The 
 method of converting starch into dextrine. 96. Gum, where found. 97. The 
 different kind of gums. 98. Gum Arabic. 99. Combined with Cerracine. 
 100. Mucilage. 101. Cerracine described. 102. Pectine : its characters. 103. 
 Sugar : its varieties. 104. Cane sugar. 105. Mannite. 
 
 LESSON VI. OILS, WAX, CHLOROPHYLLE, RESINOUS PRODUCTS, CAOUT- 
 CHOUC, p. 18. 
 
 106. Vegetable Oils : their affinities. 107. Where met with. 108. They are 
 fixed, or essential. 109. The composition of fat oils. 110. Castor Oil. 111. 
 Essential oils : where found. 112. Oil and oil cells of the Almond. 113. Same 
 in the Cocoanut. 114. WAX: where found. 115. Bees supposed to secrete wax. 
 116. Where and when they obtain it. 117. They collect it in a pure state. 
 118. How they work it. 119. The Bee is really laden. 120. Ear Wax. 121. 
 CHLOROPHYLLE : what it is. 122. Resinous products. 123. More fully described. 
 124. CAOUTCHOUC : where found. 125. Gutta Percha : where procured. 126. 
 The lactiferous vessels of plants. 127. The properties of the milky juice. 
 
 LESSON VII. RAPHIDES, p. 21. 
 
 128. What they are ; the name translated. 129. They are sometimes stel- 
 late. 130. Where found. 131. Oxalic acid in plants. 132. How neutralized. 
 133. And rendered wholesome. 134. Raphides of the Onion. 135. Their shape. 
 136. Plurality of crystals in cells. 137. Raphides in Pie-plant. 138. The quan- 
 
ANALYSIS OF THE LESSONS. XI 
 
 tity in English as compared with Turkey Khubarb. 139. Stellate crystals, where 
 found. 140. Other acids found in plants. 141. Phosphate of Lime. 142. The 
 number of raphides found in a given space. 143. Their number in the Cacti. 
 144. Bark of trees contains them. 145. And the testa of certain seeds. 
 
 LESSON VIII. SCLEROGEN, OR LlGNINE, p. 24. 
 
 146. Definition of the name. 147. Sclerogen of Nut Ivory. 148. Originally 
 soft. 149. Demonstration of it. 150. Gritty tissue. 161. A Pear demon- 
 strated. 152. Probable intention of this structure. 153. Demonstration of this 
 tissue, repeated. 154. Sclerogen in testa of Nut Ivory. 165. The Sclerogen of 
 fruit stones described. 156. The Cherry stone demonstrated. 157. The Cocoa- 
 nut shell. 158. Importance of wood and bass-cells. 159. Bass-cells described. 
 160. The uses to which they are applied. 161. Flax, Hemp, &c., where pro- 
 cured. 162. Other plants described. 163. Tenacity of woody fibre, tabulated. 
 164. The fibre preserved in Chinese rice paper. 165. Necessity of examining 
 Flax, microscopically. 166. How to proceed. 167. What will be seen. 168. 
 The outer membrane. 169. Length of tubes. 170. Cotton not woody fibre. 
 
 LESSON IX. VASCULAR TISSUE, p. 28. 
 
 171. Action of the roots of a plant. 172. Effects of the motion of the sap. 
 173. Formation of vascular tissue. 174. Vascular tissue in Monocotyledonous 
 plants. 175. In Dicotyledonous plants. 176. Development of wood. 177. 
 Value of the spiral fibre. 178. Vascular tissue under the microscope. 179. The 
 several forms of vessels. 180. The original form of spiral vessels. 181. Disin- 
 tegration of spiral vessels. 182. The process of decay. 183. Absorption does 
 not cease. 184. The mode in which an annulus divides. 185. Formation of 
 " old vessels." 186. The shape of vessels. 187. Scalariform vessels. 
 
 LESSON X. POROUS AND DOTTED DUCTS, p. 32. 
 
 188. Description of ducts. 189. Distinction between spiral vessels and ducts. 
 190. The trees they are peculiar to. 191. A description of the cells. 192. 
 Dotted ducts of the Pines, described. 193. Value of their characters. 194. 
 Shape of the dotted or porous vessels. 195. The perforations of old dotted 
 ducts. 196. They are often jointed. 197. Where found : their appearance. 
 198. Porous ducts of the Locust tree. 199. Same in the Apple tree. 200. And 
 in the Bass-wood. 201. Description of it. 
 
 LESSON XI. SILICA, p. 34. 
 
 202. Its importance to the plant. 203. Necessity for Carbonate of lime. 
 204. How it is compounded. 205. Silica exists in plants as pure flint. 206. How 
 it is obtained. 207. Grasses contain silica in large quantity. 208. The method 
 of digesting it. 209. Silica succumbs to alkalies. 210. The silicates formed by 
 the Chemist. 211. Properties of the natural silicates. 212. This subject con- 
 tinued. 213. The probable process of silicification of plants and animals. 214. 
 Continued. 215. Artificial fossilization, or silicification. 
 
X li ANALYSIS OF THE LESSONS. 
 
 LESSON Xn. SILICA, CONTINUED, P- 36. 
 
 216. Silica abounds in the lowest plants. 217. The loricaB of the Diatoms. 
 218. The Arachmoidiscus. 219. Recent and fossil Diatomaceae. 220. Silica in 
 the grasses. 221. How it is that straw grows erect. 222. How to demonstrate 
 its structure. 223. Defence of the grasses : husk of Rye. 224. Husks, and 
 pale of grasses : effects of brown bread. 225. Demonstration of this state 
 ment. 226. By means of the microscope. 227. The action of silica on the 
 organs of nutrition. 228. The Berg-mehl. 229. Its microscopical character. 
 
 LESSON Xm. SILICA, CONCLUDED, , , p. 38. 
 
 230. Silica from the husk of the Oat. 231. From the husk of the Rice. 
 232. Flint in the Horse tails. 233. The flint a cast of the cuticle. 234. Struc- 
 ture of the Stomata. 235. The uses of Dutch rush. 236. The bullrushes. 
 237. Silica not confined to the grasses. 238. The Deutzia scabra. 239. The 
 structure of the upper cuticle. 240. The under cuticle. 241. Use of the leaves 
 of Deutzia. 242. Large amount of silica in the canes. 243. The like in reeds. 
 244. The formation of vegetable sap. 245. Mutual decomposition of some oi 
 the elements. 246. The silicic acid of Chara translucens, and allied species. 
 
 LESSON XIV. HAIRS, p. 41. 
 
 247. Composition of hairs. 248. Variety of their form. 249. How consti- 
 tuted. 250. Where found. 251. They are sometimes very extensively de- 
 veloped. 252. Hairs of the Cowitch. 253. Of Venus' Fly-trap. 254. Hairs 
 of Cotton. 255. The division of hairs. 256. Glandular hairs. 257. Stalked 
 hairs. 258. Hairs are sometimes ducts. 259. Hair of the nettle. 260. How 
 to avoid being stung by it. 261. Hair of Chinese sundew. 
 
 LESSON XV. CUTICLE, p. 44. 
 
 262. Resemblance between the cuticle of plants and animals. 263. Mode of 
 its formation in plants. 264. Its texture. 265. Position of the stomata. 266. 
 Opening and closing of the stomata : on what this action depends. 267. The 
 number of stomata. 268. Number in different plants tabulated. 269. Leaves 
 upon which stomata are not found. 270. Stomata of Ruscus aculeatus. 271. 
 Of the Ivy. 272. Of the White Lily. 
 
 LESSON XVI. LEAVES, . . . ; ,,.'... V p. 46. 
 
 273. Nature of leaves: their varieties. 274. AERIAL LEAVES description 
 of them. 275. Vascular system of the leaf. 276. How distributed. 277. The 
 Parenchyma. 278. How formed. 279. The upper cells of the Parenchyma. 
 280. Examination of a Melon leaf. 281. Of the leaf of the Balsam. 282. The 
 green color of leaves. 283. The dark color of the Negro skin : how caused. 
 284. The same law governs the color of the leaf of a plant and the human 
 skin. 285. The vascular system of a leaf. 
 
 LESSON XVII OP THE STEMS OF TREES, p. 48. 
 
 286. Their anatomical character. 287. Of what the stems are composed. 
 
ANALYSIS OP THE LESSONS. Xlli 
 
 288. Description continued. 289. Differences in the mode of arrangement, and 
 consequent division of plants : character of Endogens. 290. Character of 
 Exogens. 291. And of Acrogens. 292. Resume. 293. Other distinctions. 294. 
 Recapitulation. 295. Exogens most numerous. 296. The Acrogen described. 
 297. Tree Ferns, the best example. 298. Transverse section of Tree Fern de- 
 scribed. 
 
 LESSON XVIII. THE ENDOGENOUS STEM, p. 61. 
 
 299. Its characters defined. 300. Endogens belong to hot climates. 301. 
 The Endogenous stem exemplified. 302. The early condition of it. 303. The 
 cellular tissue. 304. The dotted vessels. 305. Exempt from parasitic plants. 
 306. The soft wood is internal. 307. The rapidity of their growth. 308. Vas- 
 cular bundles of the Bamboo. 
 
 LESSON XIX. THE EXOGENOUS STEM, p. 52. 
 
 309. Originally cellular. 310. Development of other tissues. 311. Com- 
 pleted structure. 312. The second year's growth. 313. The Cambium cells. 
 314. The medullary sheath. 315. The second year's growth more fully ex- 
 plained. 316.- Changes in the permanent woody stem. 317. Order in which 
 the tissues are produced. 318. Tissues of the second year. 319. The third 
 year's growth. 320. The subject continued. 321. The characters of the tissues 
 given separately. The Wood. 322. How the layers of wood are formed. 323. 
 They consist of woody fibres. 324. Hardness of the wood in old trees. 325. 
 The heart-wood is colored in some trees. 326. Proportions of heart-wood and 
 albumen differ. 327. Durability of wood. 
 
 LESSON XX. THE REMAINING TISSUES, . : . ;'.'' .' V;. : r v -. . . p. 55. 
 
 The Medullary rays. 328. Their structure. 329. Their position. 330. Their 
 size varies. The Cambium layer. 331. Where situated. 332. Its composition. 
 333. What can be done in the spring. The Bark. 334. Its development. 335. 
 The inner bark. 336. The fibres of Bass-wood. 337. Separation of the fibres. 
 338. Immunity from decay of woody fibre. 339. The importance of woody 
 fibre : known to the ancient Egyptians. 340. They employed it in the manu- 
 facture of linen. 341. An ancient mummy exhumed by Belzoni. 342. A still 
 older one at Rome. 343. These facts known to microscopists. 344. Ancient 
 Peruvian mummy cloth. 345. Economic value of woody fibre. 346. Our obli- 
 gations to this tissue. 
 
 PART II. 
 
 ANIMAL TISSUES. 
 
 LESSON XXL THE ORIGINAL COMPOUNDS OP THE ANIMAL BODY, . . p. 59. 
 
 347. Composition and uses of the parts of an Egg. 348. Albumen : what 
 
 becomes of it. 349. Its changes not confined to embryonic, or young condition 
 
 of life. 350, Gelatine : what becomes of it. 351. Non-gelatinous tissues. 
 
Xiv ANALYSIS OF THE LESSONS. 
 
 352. Chemical composition of Albumen. 353. Its change into fibrine. 354. 
 Chemical composition of fibrine. 355. Solubility of fibrine. 356. Resemblance 
 of albumen and fibrine. 357. Proteine : its composition. 358. Under what 
 circumstances albumen coagulates. Tendency of fibrine to form tissues : Tu- 
 mors. 359. Conversion of albumen into fibrine. 260. Where it appears. 361. 
 In the blood : its proportion. 362. Coagulable lymph : how formed. 363. Ex- 
 udation : how formed. 364. Latex of plants compared with blood. 365. Fib- 
 rillation of fibrine. 366. Tissues formed by it. 367. Membrana putaminis. 
 368. Utility of fibrillated fibrine. 
 
 LESSON XXII. OF CELLS, MEMBRANES, AND FIBRES, p. 63. 
 
 369. Animal cell : its history : comparison of cellulose and cellular tissue. 
 370. Composition of animal cells. 371. Contents of animal cells. 372. Nu- 
 cleoli. 373. Multiplication of cells. 374. Cartilage. 375. Cellular areolar 
 tissue : its structure : demonstration of it. 376. White and yellow fibrous tis- 
 sue. 877. Where found. 378. Demonstration of white fibrous tissue. 379. 
 Demonstration of yellow fibrous tissue. 380. Ligamentum nuchae : illustrated. 
 
 LESSON XXLTI. SIMPLE CELLS FLOATING IN ANIMAL FLUIDS, ... p. 66. 
 
 381. Human blood: circulation in Frog's foot. 382. Red corpuscles: their 
 form. 383. Their elasticity. 384. Their size. 385. Does the human blood 
 corpuscle contain a nucleus? 886. Membrane of corpuscle : effect of water : 
 effect of syrup. 387. Measurement. 388. Effect of inflammation : rouleau. 
 889. Frog's blood : illustration : its fibrillation. 390. Fibrillation and illustra- 
 tion of blood : Locust. 391. Probability of a nucleus in human blood: exami- 
 nation of blood taken by Mosquitos, illustrated. 392. Shape and comparative 
 size of blood corpuscles in animals, illustrated. 393. Colorless- corpuscle, illus- 
 trated. 394. Formation of colorless corpuscles. 395. Their change into red 
 corpuscles. 896. Their power to repair injuries. 
 
 LESSON XXTV. CELLS DEVELOPED UPON FREE SURFACES OF THE BODY, p. 71. 
 
 397. Epidermis. 398. Structure of epidermis : ablutions. 399. Sponge 
 bath : temperature of room. 400. Effects of cold chill. 401. Effect of cold 
 water on young children. 402. Necessity of warm clothing for females. 403. 
 Corsets advocated. 404. Shoulder straps to be used to remove weight of 
 clothing from the hips. 405. To produce reaction in young children. 406. 
 Improper time to take a bath. 407. Another form of bath. 408. Friction re- 
 commended. 409. Many ducts in epidermis : of what kind. 410. Intention of 
 their production. 41 1. Effects of the removal of epidermis : secretions of its cells. 
 
 LESSON XXV. THE NAILS, V^t ff /. p. 74. 
 
 412. Composition of nail. 413. Matrix of the nail : its structure and com- 
 position, illustrated. 414. Malpighian layer : its structure, illustration. 415. 
 Structure of horny layer, illustrated. 416. Vascularity of matrix of the nail, 
 illustrated. 417. Operation for removal of nail : why it does or does not grow 
 again. 418. How operation should be performed. 419. Horny hoofs of cattle : 
 their vascularity. 
 
ANALYSIS OF THE LESSONS. XV 
 
 LESSON XXVI. HAIR, p. 77 
 
 420. Structure of Hair : the Jjiyers of which it consists. 421. The cortical 
 substance. 422. The medullary substance. 423. Difference between feathers and 
 hair. 424. Vascularity of feathers. 425. Structure of a feather illustrated and 
 explained. 426. Cuticle of human hair : its composition. 427. How attached. 
 428. Shaft of a hair. 429. Epidermic scales removable : illustration. 430. 
 Action of Caustic Potash and Soda on cortical substance : pigment granules : 
 air. 431. Scales of the root of hair, illustrated. 432. Structure of medulla : 
 action of caustic soda upon it : air contained in it : illustrated. 433. Air de- 
 monstrated in the shaft of human eye-brow, illustrated. 434. Transverse sec- 
 tions of human hair described and illustrated. 435. Elasticity of hair : absorp- 
 tion of moisture. 436. Chemical composition of hair. 437. Structure of Wool : 
 Browne's comparison of a. Negro's hair and wool : his statements examined. 
 438. These opinions refuted. 439. Hair of Negro, illustrated : Hair of Indian, 
 illustrated. 440. Hair of beard. 441. Why the hair of the Indian and Negro 
 should be stronger and coarser than hair of a white man. 
 
 LESSON XXVII. HAIR, CONCLUDED, p. 83 
 
 442. Importance of a knowledge of the structure of Hair. 443. Vascularity 
 of follicle of feline animals. 444. The structure of transverse sections of vi- 
 .brissae : Tiger and Cat. 445. Importance of vibrissae to the feline animals. 
 446. Their use. 447. An experiment. 448. Value of transverse sections of 
 hair. 449. Vibrissae, Rat and Raccoon ; air in the medulla. 450. Pachyder- 
 matous (thick-skinned) animals : plurality of medullary canals : hair of the Ele- 
 phant's tail, illustrated. 451. Hair of the Elephant's proboscis and Hog's bristle 
 compared. 452. Structure of whalebone : hair from the mane of the Horse an 
 exception to the pachydermatous rule. 453. Hair of the Turkey. 454. Hair 
 of the Ruminantia : cellular structure of the Stag's hair explained and illustrated : 
 Wapeti Deer. 455. Ooat's hair : comparison. 456. Hair of Ornithorhyncus 
 paradoxus : its peculiarity explained. 457. Quill of the Porcupine described 
 and illustrated : its affinity to hair. 458. Quill of English Hedgehog described 
 and figured. 459. Quill of the American Porcupine : the difference of structure 
 explained. 460. Imbrications on the hairs of animals. 461. Hair of the Seal 
 described and illustrated. 462. Mouse hair, its peculiarities : hair of Phasco- 
 gale pennicillata. 463. Hair of Indian Bat. 464. Remarkable hair of Aphro- 
 dita hispida. 465. Curious hair of Dermestes lardarius. 466. Hairs of the 
 larva described. 
 
 LESSON XXVIII. EPITHELIUM. SEROUS AND SYNOVIAL MEMBRANES, . p. 93. 
 
 467. Epidermis and Epithelium compared. 468. Where found. 469. Form 
 of cells. 470. Tessellated or pavement epitheh'um. 471. Nucleus in cells. 
 472. Cylinder epithelium. 473. How to see the cylindrical cells. 474. Cylinder 
 epithelium : where found. 475. Ciliated epithelium : where found. 476. Action 
 of epithelium : its continuance after death. 477. This phenomenon not confined 
 to man. 478. Ciliated epithelium of the Frog : how seen. 479. Ciliated epi- 
 thelium, from the drum of human ear. 480. Epithelium, like epidermis, ex- 
 
xv i ANALYSIS OF THE LESSONS. 
 
 foliatca 4S1 Epithelium on serous membranes. 482. Two nuclei found iri 
 one cell. SEROUS AND SYNOVIAL MEMBRANES.-483. Their structure. 484. 
 Closed sacs : their contents. 485. Where found. 486. Serous membranes 
 invest abdominal viscera. 487. Synovial membrane: its description: where 
 found. 488. Burs mucosffi. 
 
 LESSON XXIX. ORGANS or NUTRITION, p. 97. 
 
 489. Examination of stagnant water by the microscope : its revelations. 
 490. Plurality of digestive sacs. 491. Probably this description is erroneous. 
 492. Characters of the Rotifera. 493. Arrangement of their vibratile organs. 
 494. Remarkable tenacity of life. 495. Habitat of ENTOZOA. 496. Description 
 of them. 497. The Acephalocyst. 498. Description of it. 499. Two species 
 of them : mode of multiplication. 600. The Ccenurus cerebralis. 501. The 
 "gid," or mad-staggers in animals: what produces it. 502. Description of 
 Coanurus. 603. Hydatids have no sex. 604. Echinococcus hominis : descrip- 
 tion of it. 505. Cysticercus celluloBa. 506. Where found. 607. Tania solium, 
 or Tape-worm, described. 508. Distoma : two species of them. 509. Distoma 
 kepaticum, described. 610. J)istoma lanceolatum, described. 611. Parasites of 
 the Pig, enumerated. 
 
 LESSON XXX. ORGANS OF NUTRITION, CONTINUED. POLYPI, ... p. 103. 
 
 612. General description of them. 513. Marine Polypes. 514. Freshwater 
 Polypes enumerated and described. 515. Habits of the Hydrse. 516. Their 
 simplicity of structure. 617. Mode of reproduction by budding (gemmation), 
 and cutting them. 618. Marine Polypes. 519. Corallium rubrum. 520. What 
 becomes of the nutriment. 521. Nutritive organs of C. rubrum described. 
 
 LESSON XXXI. ORGANS OF NUTRITION IN ACALEPHA, p. 106. 
 
 522. General description of the Acalepha. 523. Perorfs description of them. 
 524. Our present information of them. 625. Rhizostoma Cuvieri, described. 
 526. Cetonia aurita, described. 
 
 LESSON XXXII. ORGANS OF NUTRITION IN THE ECHINODERMATA, . . p. 109. 
 
 627. The characters which distinguish them. 528. Their digestive apparatus. 
 529. Nutrimental organs of Asterias. 530. Ccecal apparatus. 631. Echinida 
 explained and described. 532. Description of the teeth : salivary follicles. 533. 
 Cavity of the " lantern of Aristotle," Pharynx, (Esophagus, &c. 534. The heart 
 described. HOLOTHURIA. 535. Description of them. 536. The mouth : tenta- 
 cula. 637. Their teeth. 538. The oesophagus and stomach of H. elegans. 539. 
 The branchiae (gills). 540. Spontaneous rupture of the integument in Holothuria. 
 641. Caused by great muscular irritability. 542. The tendinous chords. 543. 
 Cucumaria frondosa. 544. The sexes distinct: the ova. 545. Great fertility 
 of Holothuria : the ovarium. 546. The respiratory organs described. 547. 
 Intestines terminate in the cloaca. SIPUNCULUS. 548. Rough Syrinx, or Tube- 
 worm. 649. Description of it. 
 
ANALYSIS OF THE LESSONS. XV11 
 
 LESSON XXXIII. ORGANS OF NUTRITION IN THE ANNELLATA, . . . p. 118. 
 
 550. Name of the class : how obtained. 551. Peculiarity of the class. 
 552. Respiratory organs most attractive. 553. Mode of action of these organs. 
 554. Their nutrimental organs. 555. Nutrimental organs of Aphrodita aculeata. 
 556. Mouth of the Leech. 557. Its oesophagus and stomach described. 558. 
 Army surgeons avail themselves of a peculiarity of the nutrimental canal. 559. 
 The common mode of treating leeches condemned. 560. A better plan pro- 
 posed : blood-sucking propensity in leeches- a curious phenomenon. 561. 
 Arenicola piscatorum^ its blood : respiratory tufts. 562. Its nutrimental organs. 
 563. Circulation of the blood. 
 
 LESSON XXXIY. ORGANS OP NUTRITION IN THE EPIZOA, .... p. 122. 
 
 564. The class described. 565. Mode of attachment of the Lernoea. 566. 
 The mouth and alimentary canal. 567. The nervous system : heart and circu- 
 lation of the blood. 568. The Ovaria described. 569. Disparity in size of the 
 sexes : the male illustrated. 
 
 LESSON XXXY. ORGANS OF NUTRITION IN THE CIRRIPEDIA, . . . p. 123. 
 
 570. Many of them parasitic : Tubicinella. 571. Meaning of their name. 
 572. Superior protection of the visceral mass. 573. The common Barnacle de- 
 scribed. 574. The sessile Cirripeds. 575. The structure of a Lepad explained : 
 their branchiae. 
 
 LESSON XXXYI. ORGANS OF NUTRITION IN THE CRUSTACEA, . . . p. 125. 
 
 576. General description of the class. 577. Their breathing organs. 578. 
 Their skeleton described. 579. The power of locomotion of the Lobster. 580. 
 The mouth : position of the gills. 581. Mouth, oesophagus and stomach de- 
 scribed. 582. Their gastric teeth. 583. The alimentary canal. 584. Aorta 
 and pulmonary vein : nervous system. 585. The venous sinuses. 686. They 
 occupy the place of veins : extent of these sinuses. 587. Casting their claws 
 (Lobsters) explained. 588. Difficulty of demonstrating these sinuses. 
 
 LESSON XXXVII. ORGANS OF NUTRITION IN INSECTS, p. 128. 
 
 589. General description of the nutrimental canal in animals. 590. Modi- 
 fications to which it is liable. 591. Its structure in Insects. 592. Length of 
 their intestines. 693. The several parts into which they are divisible. 594. The 
 salivary glands. 595. The parts described not always present. 596. The bile 
 vessels. 597. The pharynx. 598. The oesophagus. 499. Mode of separation 
 from the stomach. 600. The pumping stomach. 601. More fully explained. 
 602. The proventriculus. 603. The stomach. 604. The duodenum. 605. The 
 ileum. 606. The colon. 607. The coecum. 608. The biliary vessels. 609. The 
 salivary glands. 610. Principles of classification. 611. The Linnean system. 
 
 LESSON XXXVIII. NUTRITION IN INSECTS, CONTINUED, p. 132. 
 
 612. The Linnaean system exemplified. 613. The structure of the mouth in 
 
ANALYSIS OF THE LESSONS. 
 
 Insects. 614. The Coleopterous order. 615. Comparative length of the ali- 
 mentary canal. 616. Nutrimental organs of Cicindela campestris. 617. The 
 mouth in the Hemipterous order described. 618. Nutrimental organs of 
 Cimex lectularius. 619. The Cockroaches: nutrimental organs of Blatta Ameri- 
 cana described. 620. Description of Pancreatic follicles, peculiar to these in- 
 sects. 621. Their salivary glands illustrated. 
 
 LESSON XXXIX. NUTRITION IN INSECTS, CONTINUED, p. 138. 
 
 622. The Linnsean order of Hemiptera discussed. 623. The Orthopterous 
 order. 624. Nutrimental organs in the Cricket. 626. Salivary glands in Locusta 
 viridissima. 626. The Proventriculus (gizzard) of Gryllotalpa (Mole Cricket). 
 627. Intestinal glands. 628. Ileum of Acheta domestica. 629. Parallelism be- 
 tween vegetable feeding insects and the ruminant quadrupeds. 630. Organs 
 necessary to digest this kind of food. 631. Mouth in the Lepidoptera. 632. 
 Mode of using it. 633. Structure of the under jaws. 634. Structure of the 
 JSsophagus. 635. Alimentary canal of the Cabbage Butterfly. 636. Descrip- 
 tion of it. 
 
 LESSON XL. NUTRITION IN INSECTS, CONTINUED, p. 141. 
 
 637. Nutrimental organs in the Larva : peculiarity in the development of the 
 salivary glands. Structure of the alimentary canal. 638. True salivary glands 
 described. 639. Silk vessels. 640. The change from a Caterpillar to a Chrysalis. 
 641. The formation of silk for the Cocoon. 642. The alimentary canal de- 
 scribed : its several parts. 643. Description of the minute structure of the liver. 
 
 LESSON XTJ. NUTRITION IN INSECTS, CONTINUED, p. 144 
 
 644. Neuropterous insects described. 645. The Dragon flies: their great 
 importance. 646. The Agrions. 647. As larvae, pupae, imago, their habits 
 remain unchanged. 648. Mouth of a Dragon fly. 649. Use of the palpi. 650. 
 Use of the peculiar under lip. 651. THE HYMENOPTERA. The Bees: their 
 mouth. 652. Their nutrimental organs. 653. The pumping stomach. 654. 
 Action of the true stomach. 655. Function of the crop. 656. Structure of 
 the stomach and the bile ducts. 
 
 LESSON XLII. NUTRITION IN INSECTS, CONCLUDED, p. 147. 
 
 657. Form of the mouth in the DIPTERA. 658. Its peculiar form in the pre- 
 daceous diptera. 659. Also in the phytivorous species (vegetable feeders). 
 660. Mouth of ffelophilus tenax. 661. Use of the rugous, fleshy lips. 662. 
 Great development of the pumping stomach. 663. The salivary glands. 664. 
 Position and connections of the oesophagus. 665. Action of the pumping 
 stomach explained. 666. The alimentary canal described. 667. The Apterous 
 insects. 668. Comparison of the nutrimental organs in Insects, and in other 
 animals. 669. Analogy in the digestive sacs of L. viridissima and the Rumi- 
 nants. 670. Resume. 
 
 LESSON XLIH. ORGANS OP NUTRITION IN ARACHNIDA, p. 151. 
 
 671. Characteristics of the class. 672. Minute and parasitic Arachnidans. 
 
ANALYSIS OF THE LESSONS. xix 
 
 673. Demodex folliculorum. 674. Description of its mouth. 675. Nutrimental 
 organs not yet found. 676. The itch : what causes it. 677. The Acarus scabicei. 
 678. Its mouth described. 679. The Spiders. 680. Nutrimental organs of the 
 domestic Spider. 681. Easy mode of finding the class of any articulate animal. 
 682. Characters of the Myriopods. 
 
 LESSON XLIV. ORGANS OP NUTRITION IN THE TUNICATE MOLLUSCA, . p. 155. 
 
 683. Nutrition predominates in the Mollusca. 684. Tunicata and other Mol- 
 luscs are headless. 685. The cause of their name. 686. The Brachiopods. 
 687. The Lamellibranchiata. 688. The Pteropoda. 689. The Gasteropoda. 
 690. The Cephalopoda. 691. Tunicata: how found: their tunic described. 
 692. Lining of the tunic : Cynthia pupa described. 693. The nutritive organs. 
 694. They are devoid of teeth, jaws, and salivary glands : possess a liver. 695. 
 Development of ovaria and oviducts. 696. The Pyrosoma described. 697. De- 
 scription continued. 
 
 LESSON XLV. NUTRITION IN THE BRACHIOPODA, p. 157. 
 
 698. The orders of the class enumerated. 699. Alimentary tube in Tere- 
 bratula; the arms described. 700. The nutrimental organs described. 701. 
 The same subject continued. 
 
 LESSON XLYI. NUTRITION IN THE LAMELLIBRANCHIATA, AND IN THE 
 
 PTEROPODA, p. 160. 
 
 702. Organs of nutrition in the Oyster : its ovarium. 703. Development of 
 locomotive organs in Molluscous animals. 704. Form and position of them in 
 the Pteropods. 705. Some of them are provided with a shell. 706. Their size : 
 where found : they constitute the food of the Whale. 707. Hyalaea described. 
 708. Its nutrimental organs. 
 
 LESSON XLVII. NUTRITION IN THE GASTEROPODS, AND IN THE CEPHA- 
 
 LOPODS, p. 162. 
 
 709. Position of the respiratory organs in certain Gasteropods. 710. Eolis 
 Inca. 711. Necessity for a higher grade of the nutrimental function. 712. Form 
 of the mouth in Aplysia faciata. 713. Its organs of nutrition. 714. The same 
 continued. 715. Number of gastric cavities : development of teeth. 716. The 
 teeth of Buccinum undatum: the tongue of the Limpet. 717. General de- 
 scription of the CEPHALOPODS. 718. The tongue and salivary glands. 719. 
 Alimentary canal described. 720. Description continued. 721. Description 
 concluded. 722. Apparently defenceless. 723. Desirable food for other ani- 
 mals. 724. The wisdom and beneficence of God displayed: their passive means 
 of defence. 725. Situation of the ink-bag. 726. "Indian Ink" and "Sepia," 
 how made. 727. Ink obtained from fossil Cuttle-fishes. 728. Their internal 
 skeleton. 729. Varied shape of the bone. 730. Its great lightness in Sepia 
 officinalis. 731. Microscopical exhibition of it. 732. The " blushing " of Cuttle- 
 fishes. 
 
XX 
 
 ANALYSIS OF THE LESSONS. 
 
 LESSON XL VIII. NUTRITION IN FISHES AND REPTILES, p. 167. 
 
 733. The habits of Fishes. 734. Their accessory glands. 735. The ali- 
 mentary canal. 736. Alimentary canal of the Herring described. REPTILES. 
 737. Their habits. 738. The Frog's tongue. 739. They are carnivorous and 
 predaceous. 740. The subject continued. 741. Their sense of hearing and 
 sight. 742. Method of seizing their prey. 743. It must be done quickly. 744. 
 Harmlessness of Frogs. 745. The Frog's teeth : pulps injected. 746. Alimen- 
 tary apparatus described. 747. The stomach injected. 748. The duodenum. 
 749. The ileum. 750. Batrachians not amphibious. 751. The true amphibia 
 described. 752. The Menobranchus described. 753. Its internal structure. 754. 
 The Menopoma : its stomach. 755. The gradual development of the stomach. 
 756. Stomach of the Snapping Turtle. 
 
 LESSON XLIX. NUTRITION IN BIRDS, p. 173. 
 
 767. Adaptation of the nutrimental apparatus. 758. Comparison of the 
 several forms of the bill in Birds. 759. The same subject continued. 760. 
 Continued and concluded. 76L The nutrimental canal of the Fowl described. 
 762. Continued. 763. The muscles of the gizzard: their action. 764. Ne- 
 cessity of flint for Canary birds. 765. The subject continued. 766. The re- 
 mainder of the alimentary canal described. Same in the Crow. 
 
 LESSON L. NUTRITION IN THE MAMMALIA, p. 177. 
 
 767. Great variety of the digestive organs in this class. 768. The develop- 
 ment of organs of sense accessory to nutrition. 769. The Rodentia, stomach 
 of the Rat. 770. The same examined internally : injected, and microscopically 
 examined. 771. The Rat, omnivorous. 772. The mode in which they are sup- 
 posed to digest their food. 773. Musk-rat and other Rodents, vegetable feeders. 
 774. Especial form of nutrimental organs necessary for grass. 775. The Ru- 
 minants possess four stomachs. 776. Their natural gregarious habits. 777. 
 Their domestic habits. 778. Mode of feeding : what becomes of the food. 
 779. The subject continued. 780. Action of the second stomach. 781. The 
 subject continued. 782. Process of insalivation, or " chewing the cud." 
 
 LESSON LI. NUTRITION IN MAMMALIA, CONTINUED, p. 180. 
 
 783. The third stomach hi the ruminant described. 784. The fourth and last 
 stomach; its function. 785. Peculiar addition to the second stomach in Camels 
 and Dromedaries. 786. Comparative length of the intestinal canal. 787. Its 
 structure. 788. "Peyer's glands "in the small intestines. 789. Structure of 
 the large intestine. 790. The teeth in the Carnivorous animals. 791. Structure 
 of the tongue in the higher animals. 792. Peculiar structure of the tongue in 
 the feline animals : use they make of it. 793. Subject continued. 794. The 
 like. 795. The Cat's tongue : its effects. 
 
 LESSON LIL NUTRITION IN MAMMALIA, CONCLUDED, p. 182. 
 
 796. The filiform papillae, where situate : the fungiform and circumvallate 
 papilla: other filiform papillae. 797. Structure of the stomach; Villi of 
 
ANALYSIS OF THE LESSONS. Xxi 
 
 the small intestines : Cat, Lion. 798. The intestinal glandular system. 799. 
 The solitary glands. 800. The same in the Lion. 801. Structure of the tongue 
 in Dogs. 802. Filiform and circumvallate papillae of the Dog. 803. Mucous 
 membrane of the stomach : Dog. 804. Separation of stomach from duodenum. 
 805. Duodenum of a Dog. 806. Jejunum and Ileum. 807. The colon. 808. 
 Certain accessory organs considered. 
 
 LESSON LIU THE STRUCTURE OP THE TEETH, p. 188. 
 
 809. Introduction. 810. Ultimate structure of the human gums considered. 
 811. THE TEETH. Sclerogenous tissue. 812. The tissues composing human 
 teeth, and those of the higher mammalia : the mode of their arrangement. 
 813. The structure of Enamel. 814. Its brittleness. 815. Its prismatic struc- 
 ture. 816. The method of separating the prisms described. 817. Connection 
 of the prisms to each other. 818. The facets of the prisms. 819. The same 
 demonstrated: their number. 820. The prisms separated. 821. Method by 
 which the dentinal tubuli (ivory) are connected to the enamel. 822. The junc- 
 tion of dentine with crusta petrosa. 
 
 LESSON LIV. THE STRUCTURE OP THE TEETH, CONTINUED, .... p. 192. 
 
 823. Probable formation of the prisms of enamel. 824. Appearance of the 
 dentine ; it forms a case in which the pulp is enclosed : aperture for the trans- 
 mission of vessels and nerves. 825. Description of dentine. 826. Direction 
 of the tubuli. 827. Illustration described. 828. The Crusta Petrosa described. 
 829. Its bone cells. 830. The canaliculi. 831. Ossification of the pulp cavity. 
 832. Examination of the tubular character of the dentinal canals. 833. A fur- 
 ther description of them. 
 
 LESSON LV. THE STRUCTURE OF THE TEETH, CONTINUED, ^_. . . p. 194. 
 
 834. Structure of the teeth in Dogs : molar tooth described. 835. The 
 molar of a Cat. 836. Canine tooth of a Horse. 837. Tusk of a Hog : longi- 
 tudinal section. 838. Transverse section of it. 839. Teeth of the Herbivorous 
 quadruped. 840. Peculiar arrangement of their tissues : necessity for it. 841. 
 This arrangement may be seen in the crown of a molar tooth. 842. Action of 
 flint upon teeth. 843. The systems of enamel hi the upper and under jaw. 
 844. Arrangement in the upper jaw demonstrated. 845. The tissues shown on 
 the same plane in a Sheep's molar tooth. 
 
 LESSON LVI. THE STRUCTURE OP THE TEETH, CONTINUED, .... p. 198. 
 
 846. Structure of the teeth in the Rodentia. 847. Effect of a broken tooth 
 of a Rat, or a Rabbit. 848. They are broken artificially for Museum purposes. 
 849. Structure seen in a longitudinal section of a Rabbit's incisor. 850. The 
 same in transverse section. 851. Structure of the molar teeth in the Rabbit. 
 852. Demonstration of it. 853. Molar of the Musk-rat : demonstration. 
 
 LESSON LVII. THE STRUCTURE OP THE TEETH, CONCLUDED, .... p. 200. 
 854. The degradation of teeth : loss of tissue. 855. Structure of the teeth in 
 
ANALYSIS OF THE LESSONS. 
 
 Reptiles. 856. Vaso-dcntinc in the Pristis and Myliobatis. 857. Peculiarity and 
 demonstration of the Pristis. 858. The vaso-dentine best seen in longitudinal 
 section. 859. Ramified tubuli shown in transverse section. 860. Osteo-dentine 
 shown in the fossil tooth of a Shark. 861. The canals described : osteo-dentina 
 in the tooth of the Muscalonge. 
 
 LESSON LVIIL THE SALIVARY GLANDS, p. 203. 
 
 862. Salivary glands in the human subject enumerated. 863. The parotid. 
 864. The submaxillary glands. 865. The sublingual glands. 866. Their struc- 
 ture. 867. Structure of the lobules. 868. The ducts : the general application 
 of description. 869. These glands found in Reptiles, but divided. 870. Func- 
 tion of these glands. 871. Nature of their secretion. 872. Analogical infer- 
 ence in regard to their secretion respectively. 873. Necessity of masticating 
 the food. 874. The three properties of saliva. 875. The effect of saliva on 
 grass in a Cow's stomach. 876. These effects demonstrated by experiment. 
 877. Experiment made on a Caterpillar. 878. Can the stomach destroy the 
 living principle in organic matter ? 879. This property belongs exclusively to the 
 saliva. 
 
 LESSON LIX. THE SALIVARY GLANDS, CONCLUDED, p. 205. 
 
 880. Pain of a Mosquito bite. 881. What produces it ? 882. Why is the 
 bite of a Rattlesnake poisonous ? 883. If a Man be bitten by a Dog, &c., why 
 should he have hydrophobia? 884. These questions answered. 885. Saliva 
 harmless or fatal according to the method of its exhibition. 886. If a Mosquito 
 were larger, probable effects of its bite. 887. Pain inflicted by other Insects : 
 how caused. 888. Division of the salivary glands in the Reptiles significant. 
 889. Glands in the Boa Constrictor. 890. How he insalivates his food. 891. 
 Bite of a mad Dog not always fatal : bite of a sound Dog may be fatal. 892. 
 Distinct property in the glands respectively. 893. The phenomena of the dog's 
 accounted for. 894. This opinion supported. 895. The aid of Chemistry in- 
 voked : the teachings of comparative Anatomy important. 896. The third func- 
 tion of salivary glands explained. 897. Life destroying character of these glands 
 in Insects. 898. Why should Insects possess three pairs of these glands ? 899. 
 Salivary glands in Nepa. 900. Difficulties of the question. 901. These glands 
 misnamed by butchers. 902. The true sweetbread. 
 
 LESSON LX. THE PROPERTIES OP THE GASTRIC JUICE AND Mucus, p. 208. 
 903. The saliva moistens dry food. 904. Gastric juice and mucus neces- 
 sary to healthy digestion. 905. Water dilutes the gastric juice and impairs its 
 function. 906. Its effect upon the capillary circulation. 907. Water contain- 
 ing much lime is unfit to drink. 908. Such water should be boiled : the reason 
 why. 909. Where the mucus tubes maybe found. 910. The capillaries in 
 connection with them. 911. Gastric' glands: where found: their function. 
 912. These glands less definite in Man than in other animals. 913. Glands from 
 the pylorus of a Dog. 914. The like from a total Calf. 
 
ANALYSIS OF THE LESSONS. XX111 
 
 LESSON LXI. NUTRITION IN MAN, p. 210. 
 
 915. The order in which the digestive organs are used, and the function that 
 each performs. 916. The action of the teeth. 917. Process of insalivation. 
 918. Action of the tongue. 919. Structure of the human tongue : function of 
 the tongue in animals. 920. The oesophagus. 921. Action of its muscles. 
 922. Form of the stomach. 923. Its muscular coats. 924. The cardiac and 
 pyloric orifices explained. 925. Chemical influences and muscular action on the 
 food. 926. The action of heat upon the food. 927. Action of the pyloric valve. 
 
 LESSON LXIL NUTRITION IN MAN, CONTINUED, p. 213. 
 
 928. Formation of chyle: organs necessary. 929. Characteristics of the 
 chyle. 930. Where the chyle goes to, and for what purpose. 931. Peculiarity 
 of the villous coat of the human stomach. 932. The Duodenum : Brunner's 
 glands. 933. Position and description of these glands. 934. Villi of the Duo- 
 denum. 935. Mucus crypts, or follicles of Leiberkuhn. 936. The Jejunum: 
 mucus crypts described. 937. Villi of the small intestine contain lacteals. 
 
 LESSON LXIII. NUTRITION IN MAN, CONTINUED, p. 215. 
 
 938. Precise relation of human lacteals to the villi unknown. 939. They ex- 
 ceed the capillaries in size. 940. How does the chyle get into the lacteals? 
 941. Some original observations on this subject recorded. 942. The human 
 ileum : its glands. 943. These glands described. 944. Description continued. 
 945. Contents of these glands. 946. Their liability to disease : typhoid Peyerian 
 glands. 947. Mucous membrane of human large intestine. 948. Solitary glands. 
 949. General form of the nutrimental organs. 
 
 LESSON LXIV. NUTRITION IN MAN, CONTINUED, v 1 , -T> . ,- . . p. 218. 
 
 . 950. Resume: Animalcules. 951. The Rotifera. 952. The Entozoa. 953. 
 The Polypi. 954. The Acalepha. 955. The Echinodermata. 956. The higher 
 orders of Echinoderms. 957. The Annellides. 958. The Epizoa. 959. The 
 Cirripeds. 960. The Crustacea. 961. The Insects. 962. Their accessory or- 
 gans. 963. The Arachnida. 964. The Mollusca generally. 965. The Tunicata. 
 966. The Cephalopods. 967. The Fishes. 968. The Reptiles. 969. The Birds. 
 970. The Mammalia. 
 
 LESSON LXV. NUTRITION IN MAN, CONCLUDED, p. 220 
 
 971. The human intestinal tract a wonderful piece of mechanism : rules for 
 a healthy stomach. 972. Imprudence in eating and drinking. 973. The mus- 
 cular coat of the stomach and all the digestive organs require repose. 974. The 
 most nutritious meats indicated and proved by experiments on the stomach of 
 Martin. 975. A form of bread that is injurious, especially to children. 976. 
 What takes place if alum be used. 977. The use of saleratus condemned. 
 978. Hot biscuits objectionable. 979. Desirability of good home-made bread. 
 980. Unripe fruits should be avoided. 981. The husks of green corn pernicious. 
 982. Conclusion. 
 
ANALYSIS OF THE LESSONS. 
 
 LESSONLXVI. ON MUSCULAR FIBRE, ..f.V V r , p. 223. 
 
 983. What is its condition in the lower animals: in Mollusca. 984. The 
 kinds of fibre in Insects and Crustacea. 985. To what organic structures the 
 striped and non-striped fibre belongs. 986. Fossil muscular fibre, from the Bel- 
 emnite. 987. The subject continued. 988. The integument also fossil. 989. 
 The striped fibre prevalent in the Articulata. 990. Its structure in Insects. 
 991. Demonstration in Blatta Americana. 992. The like in lulus. 993. Muscle 
 in the higher animals seen by unassisted vision. 994. Analyzed by dissection 
 what appears. 995. Structure of an ultimate fibre. 
 
 LESSON LXVIL MUSCULAR FIBRE, CONTINUED, p. 225. 
 
 996. The fibre consists of longitudinal and transverse lines. 99*7. Uncertain 
 in what direction a muscle will split. 998. The myolemma. 999. A distinct 
 tissue: how to show it. 1000. The myolemma not perforated. 1001. Muscular 
 tissue non-vascular. 1002. Yet the substance of muscle is extremely vascular. 
 
 1003. The fibres of animal life abundantly supplied with nerves : their situation. 
 
 1004. Description of them. 1005. Ultimate structure of striped muscle. 1006. 
 How to prepare it. 1007. "What object-glass is necessary to show it. 1008. 
 Appearance of the fibrilte. 1009. The sarcous element. 1010. A twelfth ob- 
 ject-glass desirable. 1011. Built up of cells a double line should be seen. 1012. 
 The sarcolemma. 1013. Resume. 
 
 LESSON LXVIIL COMPOUND TUBULAR TISSUES. MUSCULAR FIBRE, 
 
 CONCLUDED, p. 227. 
 
 1014. Muscular fibre compared with fresh-water algaa. 1015. Demonstration. 
 1016. Characteristics of the algae. 1017. The sporangia. 1018. Mode of prop- 
 agation. 1919. The Callithalmia Baileii. 1020. A bud of it. 1021. Marine 
 alga, from Barbadoes. 1022. Alga from Lake Michigan. 1023. Its cells de- 
 scribed. 1024. Comparison with muscular fibre. 1025. The (apparently) vege- 
 table origin of muscular fibre. 1026. Ultimate element of a muscle. 1027. 
 Analogy with vegetable cells. 1028. Probable generative power of the sarcous 
 element 1029. Muscle in thin transverse section. 1030. Muscle of organic 
 life. 1031. Description. 1032. Size of these fibres. 1033. Arrangement of 
 them. 1034. The fibres of the heart. 1035. The characteristics of the non- 
 striped fibre. 1936. Reagents necessary to show nuclei. 1037. The true struc- 
 ture of muscular fibre discovered by Mr. Wm. Bowman. 
 
 LESSON LXIX. COMPOUND TUBULAR TISSUES, CONTINUED. THE NER- 
 
 TOUS SYSTEM, p. 232. 
 
 1038. The correction of the classification of animals, by Cuvier. 1039. 
 His dissections of nervous systems. 1040. His adoption of external characters 
 for the three lowest classes. 1041. The divisions of the animal kingdom accord- 
 ing to this author. 1042. Animals of the first class. 1043. The molluscous ani- 
 mals. 1044. The Articulata. 1045. The Radiata. 1046. Dr. Grant's system. 
 1047. Dr. Grant's, compared with Cuvier's system. 1048. Reason for the new 
 name proposed for the first class. 1049. The like for the second and third 
 classes. 1050. So for the fourth. 1051. Owen, as opposed to Grant. 1052. 
 The Vertebrata. 1053. Owen's name for it. 1054. The like for Mollusca. 
 
ANALYSIS OP THE LESSONS. XXV 
 
 1055. And Articulata. 1056. The Radiate Class. 1057. He endorses Tiede- 
 mann. 1058. But divides the class. 1059. The lower animals exhibit the 
 effects of a nervous system. 1060. It is presumed to exist. 
 
 LESSON LXX. NERVOUS SYSTEM, CONTINUED, p. 234. 
 
 1061. The three first classes, well defined by Owen; the last, doubtful. 
 1062. Hunter's preparation of Asterias papposa. 1063. Tiedemann's Echino- 
 dermata. 1064. His description of the vascular system, quoted. 1065. Iden- 
 tity of the vascular and nervous systems. 1066. Causes that may have led to 
 error. 106*7. The necessities of a nervous system. 1068. Does a nervous sys- 
 tem exist without a ganglion? 1069. A ganglion described. 1070. How to 
 define a nerve, or ganglion. 1071. Plants exercise their functions without a 
 nervous system. 1072. Inquiries to commence with the Articulata. 
 
 LESSON LXXI. NERVOUS SYSTEM IN THE ARTICULATA. ENTOZTOA 
 
 ANNELLIDA, p. 236. 
 
 1073. Nervous system imperfectly developed in the Entozoa. 1074. Its 
 condition in Strongylus gigas. 1075. And in the Ascarides. 1076. The ANNEL- 
 LIDES present a marked advance. 1077. Their organs of sense. 1078. A 
 higher type of development attained. 1079. How it commences. 1080. Ner- 
 vous system in the Leech. 1081. Description continued. 1082. And con- 
 cluded. 1083. Nervous system in the Earth-worm. 1084. The like in the 
 Nereis. 1085. Ganglia in Eunice gigantea. 
 
 LESSON LXXII. NERVOUS SYSTEM OP CIRRIPEDIA AND MYRIOPODA, . p. 239. 
 
 1086. The nervous system simple in the Cirripeds. 1087. Its condition de- 
 scribed in Lepas vitrea. 1088. The MYRIOPODS described. 1089. The condi- 
 tion of their nervous system. 1090. The brain of lulus described. 1091. De- 
 scription continued. 1092. Continued. 1093. Continued. 1094. Concluded. 
 1095. Nervous system in Pdydesmus maculata. 1096. Continued. 1097. -The 
 same in Scolopendra. 1098. Nervous system in this class, contains the leading 
 divisions of the higher animals. 1099. Demonstration. 1100. Sympathetic 
 
 LESSON LXXIII. NERVOUS SYSTEM IN CRUSTACEA, p. 242. 
 
 1101. The nervous system possesses great scope of development in this 
 class. 1102. General description of the brain. 1103. The Ganglia of the Ce- 
 phalo-thorax. 1104. Nervous system of the Sand-hopper. 1105. Description 
 of it. 1106. Nervous system of the Cymothoa. 1107. Nervous system in the 
 Lobster and Cray-fish. 1108. Nervous system most concentrated in the Crabs. 
 Description. 1109. Description concluded. 
 
 LESSON LXXIV. NERVOUS SYSTEM IN INSECTS, p. 244. 
 
 1110. The nervous system in insects. 1111. Its condition in larvae. 1112. 
 Nervous system of Cossus ligniperda. Analogue of the brain and spinal chord. 
 1113. Description of nervous system. 1114. Description continued. 1115. 
 
ANALYSIS OF THE LESSONS. 
 
 Continued. 1116. Concluded. 1117. The motor nerves first described by 
 Lyonnet. 1118. Limulus polyphemus described ; its agreement with insects. 
 
 LESSON LXXV. NERVOUS SYSTEM OF INSECTS, CONTINUED, .... p. 247. 
 1119. Segmented condition of the lower Articulata. 1 1 20. Analysis of these 
 segments. 1121. Position of the ganglia relatively to the segments. 1122. The 
 brain of a Caterpillar described. 1123. The recurrent (sympathetic) nerve. 
 1124. Method of connecting the divided brain. 1125. Necessity for the pecu- 
 liar position of each portion of the brain. 1126. Character of the nerves aris- 
 ing from the inferior portion of the brain. 1127. First thoracic ganglion. 
 1128. Second and third thoracic ganglions. 1129. The position of the arteries, 
 misnamed respiratory nerves, described. 1130. The caudal ganglia. 1131. 
 Other reference to the brain of this caterpillar. 1132. Condition of the ganglia 
 in the larval state of insects. 1133. Their condition in the perfect insect. 
 1184. Description of the nervous system in Blatta Americana. 
 
 LESSON LXXVI. NERVOUS SYSTEM IN ARACHNIDA, p. 251. 
 
 1135. The class described its position. 1136. In these animals the ner- 
 vous system is concentrated ; the heart and respiratory organs better de- 
 veloped. 1137. No metamorphosis. 1138. The cephalo-thorax. 1139. Num- 
 ber of their legs. 1140. Number of legs in Crustacea. 1141. Majority air 
 breathing. 1142. The Mites. 1143. The Demodex folliculorum. 1144. The 
 itch, and the mange what causes them. 1145. The Acarus scabicei. 1146. 
 Nature of the itch who are affected by it. 1147. Nervous system in the 
 Mites, not known; the nervous system in Scorpions. 1148. Description of it. 
 1149. The same in Spiders. 
 
 LESSON LXXVIL NERVOUS SYSTEM IN THE MOLLUSCA, p. 253. 
 
 1150. Differs from the Articulata. 1151. Nervous system unsymmetrical. 
 1152. Its condition in Articulata. 1153. The like in Mollusca. 1154. Its ad- 
 vance of development in Insects. 1155. Comparison with Mollusca. 1156. 
 Why so called. 1157. Many of them headless. 1168. THE TUNICATA its 
 nervous system. 1159. The Salpae. 1160. General description. 1161. Salpa 
 polycratica. Its nervous system. 1162. Is the Salpa a perfect animal ? 
 
 LESSON LXXYIII. NERVOUS SYSTEM IN THE BRACHIOPODA, ... p. 256. 
 
 1163. Brachiopods: definition. 1164. Terebratula Australis described. 
 1165. Its habits. 1166. The mantle. 1167. The respiratory apparatus. 1168. 
 Respiration : how performed. 1169. The arms. 1170. Continued. 1171. The 
 alimentary canal. 1172. The vascular system. 1173. The nervous system. 
 1174. The muscles. 1175. The pedicle. 1176. Remarks. 
 
 LESSON LXXIX. -NERVOUS SYSTEM OF THE LAMELLIBRANCHIATA, . . p. 259. 
 
 1177. Nature of the shell of the Brachiopods. 1178. The like in the Lamel- 
 libranchiata. 1179. Their nervous system. 1180. The branchial ganglion. 
 1181. The nervous system in Mytilus edulis described. 1182. The ganglionic 
 centres. 1183. Their mode of connection. 1184. The cephalic ganglions. 
 
ANALYSIS OF THE LESSONS. XXV11 
 
 1185. The respiratory ganglions. 1186. The pallial nerves. 1187. The post- 
 pallial nerves. 1188. Remarks. 
 
 LESSON LXXX. NERVOUS SYSTEM IN THE GASTEROPODA, p. 263 
 
 1189. The word explained. 1190. Their sexes. 1191. Their muscular sys- 
 tem. 1192. Aggregation of the nervous system. 1193. The principal centres 
 of the nervous system. 1194. The nervous system of Bulla lignaria. 1195. In 
 the Carinaria Mediterranea. 1196. Greatest accumulation of cerebral nervous 
 matter in Buccinum and ffarpa. 1197. Nervous system of Harpa elongata. 
 1198. Remarks. 
 
 LESSON LXXXI. NERVOUS SYSTEM IN PTEROPODA AND CEPHALOPODA, p. 266. 
 
 1199. Origin of the name. 1200. General particulars of the class. 1201. 
 Their nervous system. 1202. Nervous system of Clio borealis. 1203. The CE- 
 PHALOPODS the nearest to the Yertebrata. 1204. The nervous system of Nauti- 
 lus pompilius. 
 
 LESSON LXXXIL NERVOUS SYSTEM IN THE FISHES, p. 268. 
 
 1205. Preliminary remarks. 1206. The nervous system in the long worm- 
 like .Fishes. 1207. Analogous to the highest Vertebrata. 1208. The brain does 
 not fill the cavity of the cranium. 1209. The spinal chord nearly equal in its 
 development. 1210. Its condition in Rays and Flying-fishes. 
 
 LESSON LXXXIII. NERVOUS SYSTEM IN FISHES, CONCLUDED, ... p. 270. 
 
 1211. Ganglionic enlargements of the spinal chord in the Trigla cucullus. 
 1212. Demonstration of them. 1213. The posterior extremity of the spinal 
 chord sometimes enlarged. 1214. Three pairs of rounded lobes in the brain of 
 the Conger Eel. 1215. Description of them. 1216. The optic lobes. 1217. 
 The cerebral hemispheres. 1218. The olfactory tubercles. 1219. Size of the 
 optic lobes in Trigla lyra. 1220. Development of the optic lobes. 1221. The 
 medullary walls. 1222. Comparison of the optic lobes of Fishes with human 
 optic lobes. 
 
 LESSON LXXXIY. NERVOUS SYSTEM IN REPTILES, p. 271. 
 
 1223. Preliminary observations. 1224. Continued: concluded. 1225. Ner- 
 vous system of the Tadpole : description continued. 1226. Description con- 
 cluded. 1227. Development of nervous system in the higher amphibia com- 
 pared with the human embryo. 1228. Nervous system of adult Frog, and its 
 developing condition. 1229. The Reptile brain, and the brain of Fishes, con- 
 trasted. 
 
 LESSON LXXXY. NERVOUS SYSTEM IN THE BIRDS, p. 273. 
 
 1230. Condition of the brain in the class. 1231. The Cerebellum. 1232. 
 The optic ganglia. 1233. The Cerebral hemispheres. 1234. The connection 
 of Birds and Reptiles in the Old World. 1235. The brain of the Chick, after 
 
ANALYSIS OP THE LESSONS. 
 
 two days of incubation. 1236. The brain of the adult Stork described. 1237. 
 Description continued. 1238. Concluded. 1239. The brain of the Buzzard. 
 1240. Concluding remarks. 
 
 LESSON LXXXVL NERVOUS SYSTEM IN MAMMALIA AND MAN, ... p. 276. 
 
 1241. Condition of the nervous system in the lowest animals. 1242. Its 
 progressive development. 1243. Its condition in the lowest articulata. 1244. 
 Nervous system in the Leech. 1245. The brain increases in size, proportion- 
 ably with the increase of organs of special sense. 1246. The nervous system in 
 the bivalve-mollusca considered. 1247. Their brain examined. 1248. Higher 
 condition of the brain in the Testaceous mollusca. 1249. Transition to the 
 Fishes. 1250. The higher Fishes and the amphibious Keptiles considered. 
 1251. Ascent to the Mammalia. 1252. The function of commissures. 1253. 
 Analysis of the brain in the lower animals. 1254. Development of the Cerebro- 
 spinal axis of man. 1255. Continued. 1256. Subject continued. 1257. De- 
 monstrated. 1258. The demonstration continued. 1259. And concluded: 
 commentary. 
 
 LESSON LXXXVII. NERVOUS SYSTEM OF MAMMALIA AND MAN, 
 
 CONTINUED, p. 281. 
 
 1260. Comparative size of the human spinal chord. 1261. The medulla 
 oblongata. 1262. The microscopical characteristics of nerve. 1263. The struc- 
 ture of a nerve. 1264. The " nerve fibres." 1265. Their composition. .1266. 
 The white substance. 1267. It easily dissolves. 1268. The axis-cylinder. 
 1269. Demonstration of it and the white substance. 1270. Axis-cylinder con- 
 taining white substance. 1271. Tubes of the median nerve (human) demon- 
 strated. 1272. The sympathetic nerve described. 1273. And demonstrated. 
 1274. The structure of ganglions. 1275. Ganglion corpuscles not confined to 
 ganglia. 1276. Structure of nervous matter in the animal kingdom. 1277. 
 Ganglion of the Cockroach. 
 
 LESSON LXXXVni. NERVOUS SYSTEM IN MAMMALIA AND MAN, 
 
 CONCLUDED, p. 285. 
 
 1278. Vascularity of nerves. 1279. Nerves accompany arteries and veins. 
 1280. Character of the blood-vessels of nerves. 1281. Demonstration of them. 
 1282. Nerve from human pericardium. 1283. Blood-vessels of ganglions de- 
 monstrated. 1284. Their peculiarity. 1285. Concluding remarks. 
 
 LESSON LXXXIX. ORGANS OP SPECIAL SENSE THE EYE, .... p. 287. 
 
 1286. Introduction. 1287. The eye an optical instrument: demonstration. 
 1288. Requirements of a visual organ. 1289. Proof of the statement offered. 
 1290. Animals destitute of vision, who seek or shun the light. 1291. The 
 effect of light upon plants. 1292. Red spots in animals described as eyes. 
 1293. Their real nature. 1294. Fallacy of this doctrine. 1295. It is doubtful if 
 the Radiata possess eyes. 1296. But they exist in Articulata in Epizoa gen- 
 erally : in Cirripeds not at all. 
 
ANALYSIS OF THE LESSONS. XXIX 
 
 LESSON XC. THE EYE IN THE ANNELLATA, CRUSTACEA, MYRIAPODS, 
 
 AND INSECTS, p. 289. 
 
 1297. Eyes always found in the Annellata. 1298. The number of them hi 
 the medicinal Leech. 1299. In the higher forms of worms reduced to two. 
 1300. In the higher forms of CRUSTACEA the eyes are pedunculated. 1301. Plan 
 of their construction. 1302. The eyes of the MYRIAPODS described. 1303. The 
 eyes of INSECTS. 1304. The compound eye. 1305. Eyes for short vision. 
 1306. Eyes adapted for longer vision. 1307. Bees have Telescopic vision. 
 1308. Description of it. 1309. Disagreement of authors in regard to the struc- 
 ture of the eye in Insects. 1310. Structure according to Straus-Durckheim. 
 1311. The opinions of Marcel de Serres. 1312. Miiller's opinions. 1313. He 
 discovered a crystalline lens. 1314. The conical lenses according to Straus and 
 Miiller. 1315. Demonstration. of these views. 
 
 LESSON XCL THE EYE IN INSECTS, CONTINUED, p. 291. 
 
 1316. The subject not exhausted by Miiller. 1317. Another account. 1318. 
 The conical bodies. 1319. Their color. 1320. They are supposed to represent 
 the vitreous humor. 1321. Their figure. 1322. Disposition of the optic fila- 
 ments. 1323. The filaments possess an axis-cylinder. 1324. The cones in a 
 Caterpillar. 1325. The method of connecting the eyes with the brain demon- 
 strated. 1326. The inferior portion of the brain in Blatta Americana. 1327. 
 The fatty layer in Musca carnaria. 1328. The action of this form of eye. 1329. 
 Necessity for this form of visual organ. 1330. Enumeration of the facetted 
 eye. 1331. The hairs, or eye-lashes. 1332. Bees possess them: for why. 
 1333. The Telescopic eye. 1334. Its structure described. 
 
 LESSON XCIL THE EYE IN INSECTS, CONCLUDED, p. 295. 
 
 1335. The connection of the optic nerves of the single eyes demonstrated. 
 1336. Structure of the transparent cornea. 1337. Method of connection with 
 the lenses. 1338. Probability of an aqueous humor. 1339. Mechanical figure 
 of the facetted eye : the reason for it. 1340. The variation in shape of them. 
 1341. Demonstration. 1342. Structure of the cornea in Prionus longimanus. 
 1343. The membrane lining the cornea. 1344. Description of it. 1345. The 
 cornea after removing the membrane. 1346. Description of it. 1347. The 
 prismatic, or lenticular bodies. 1348. There are double-convex lenses in addi- 
 tion. 1349. The great substance of the cornea. 1350. Straus and Muller agree 
 in the depth of the cornea. 1351. Wherein they differ. 1352. Resume". 1353. 
 Concluding demonstration. 
 
 LESSON XCIII. THE EYE IN ARACHNIDA, MOLLUSCA, AND FISHES, . . p. 299. 
 1354. The largest eyes in this class are met with in the Scorpions. 1355. Their 
 structure described. 1356. No visual organs in the slow-moving Mollusca. 
 1357. The eyes in the Gasteropods. 1358. They are placed on tubercles. 1369. 
 Demonstration of Cyprea tigris. 1360. The like in Carinaria Mediterranea. 
 1361. The eyes of Mollusca approximate Fishes. 1362. The number of eyes in 
 the Vertebrata. 1363. The eyes of Fishes. 1364. Their crystalline lens. 1365. 
 The Fishes in which the visual organs are of least size. 
 
XXX ANALYSIS OF THE LESSONS. 
 
 LESSON XCIV. ORGANS OF VISION IN THE HIGHER ANIMALS, . . . p. 301. 
 1366. The eyes in the higher animals more complicated. 1367. Enumera- 
 tion of the tissues composing them. 1368. The sclerotica. 1369. The choroid. 
 1370. Its composition. 1371. Thetapetum. 1372. The iris. 1373. The ciliary 
 processes. 1374. The retina. 1375. The zonula ciliaris. 1376. The humors 
 of the eye. 1377. The anterior chamber. 1378. The posterior chamber. 
 1379. The crystalline humor. 1380. The vitreous humor. 1381. The sclerotic 
 coat 1382. The transparent cornea. 1383. Summary. 
 
 LESSON XCV. THE EYES IN REPTILES, BIRDS, AND MAMMALIA, . . p. 304. 
 
 1384. Introduction. 1385. The sclerotic in Crocodiles, Tortoises, and Tur- 
 tles. 1386. The eye of Emys Europoea described. 1387. The choroid of the 
 Snapping Turtle. 1388. The posterior portion of it. 1389. Description of its 
 vessels. 1390. The ciliary processes. 1391. The pupil of BIRDS. 1392. They 
 possess a nictitating membrane. 1393. Size of the eyes in the Ruminantia and 
 other mammals. 1394. Affinities of visual organs. 1395. The eye in the Cetacea. 
 1396. The eye in the Ruminant. 1397. Peculiarities of structure. 1398. Func- 
 tion of the ciliary processes in general. 1399. Their function in the Ruminant. 
 
 LESSON XCVI. THE EYES IN MAMMALIA, CONTINUED, AND IN MAN, . p. 307. 
 
 1400. Ciliary processes in the Feline animals. 1401. In the Cat. 1402. The 
 venae vorticosae of the Dog. 1403. The human eye. 1404. The eye-balls. 
 1406. Demonstration. 1406. How the ciliary processes may be seen. 1407. 
 Further demonstration. 1408. The arteria centralis retina. 1409. The forma- 
 tion of the crystalline lens. 1410. The anterior capsule of the lens. 1411. 
 Sometimes called " membrana pupillaris." 1412. The posterior capsule. 1413. 
 Demonstration of it. 1414. The vessels become absorbed. 1415. The tarsal 
 cartilages. 1416. The Meibomian glands. 1417. Nature of their secretion. 
 1418. Conclusion. 
 
LIST OF ILLUSTRATIONS. 
 
 NO. PAGE 
 
 1. Volvox globator, Original, . . ., *, $ 
 
 2. Do. do., burst, . . . .. ' .. .do. . . . . 4 
 
 3. Enchelis pupa, ...... do. ,;., . . ;.$&&+*>:. 8 
 
 4. Enchelis showing constriction, . . . do. ...; , ( , . 8 
 
 5. Enchelis further advanced, . . . ' do. . . ., . 8 
 
 6. Enchelis dividing, do. ... . 9 
 
 7. Zygnema, first stage, . . . % . do. .... 10 
 
 8. Zygnema, second stage, , . . . do 10 
 
 9. Zygnema, third stage, . . . -^ . do. . . . .10 
 
 10. Single cell, Pineapple, do. .... 12 
 
 11. Cells of Cucumber, ..... do. .... 12 
 
 12. Polyhedral cells, Authors,* ... 12 
 
 13. Pith of Elder, ...... Original, .... 13 
 
 14. Pith of Elder, . .-;..'>..-"!..,,? . Authors, .... 13 
 
 15. Section of Cherry, Original, . . . .13 
 
 16. Section of Potato, do 14 
 
 17. Corpuscle, Potato starch, .... do. . _. . . 14 
 
 18. Corpuscle of Tous les mois, .... do 14 
 
 19. Corpuscle of Indian Corn, ... do. .... 15 
 
 20. Corpuscle of Wheat, do. w . . 15 
 
 21. Corpuscle of Eice, .<; . do. .-;.*; t .'>- ; . 15 
 
 22. Section of grain of Wheat, . . +> ,'^i,4ou .*. :. 16 
 
 23. Section of grain of Mountain Eice, . . do. . . '. . 16 
 
 24. Section of Almond, . . . . * do. . ; . . . . 19 
 
 25. Section of Cocoanut, . . . . ^ * . do. . . \ . 19 
 
 26. Lactiferous vessels, . . . . Authors, .... 20 
 
 27. Eaphides of Onion, Original, . .- . : \. . 22 
 
 28. Eaphides of Ehubarb, do. .... . 22 
 
 29. Eaphides of Beet root, .... Authors,. .'/, . 22 
 
 30. Melon Cactus, do. . . .. t . . 22 
 
 81. Encephalatus pungens, .... do. r ,;;*-, . . 22 
 
 32. Squilla maritima . . . ,.. : .. ;r - : . do 23 
 
 33. Cells of Eumex, .... T' do. .. . . .23 
 
 34. Cells of Maple leaf, showing Eaphides, . Original, .... 23 
 
 35. Testa of the Elm, with Eaphides, . . do. .... 24 
 
 * By "Authors" is meant that all who have written on this subject have used the same 
 figure, and when good, they have been preferred to copying a preparation, simply to save time. 
 
LIST OF ILLUSTRATIONS. 
 
 HO PA01! 
 
 36. Nut Ivory, Original, 25 
 
 37. Gritty tissue of Pear, how formed, do. 25 
 
 38. Gritty tissue of Pear, highly magnified, do. 25 
 
 89. Testa of Nut Ivory, sclerogen of, do. 25 
 
 40. Section of Cherry stone, sclerogen of, do. 26 
 
 41. Section of shell of Cocoanut, showing sclerogen, ... do. 26 
 
 42. Flax Plant, Authors, 27 
 
 43. Hemp Plant, do. 27 
 
 44. New Zealand Flax, , do. 27 
 
 45. Yucca gloriosa, do. 27 
 
 46. Fibres of Flax displaying elementary structure, . . . Original, 28 
 
 47. Spiral vessels in their full integrity, do. 29 
 
 48. Spiral vessels becoming annular, do. 30 
 
 49. Annular vessels fully developed, do. 30 
 
 50. Annular rings, do. 31 
 
 61. Scalariform vessels, Authors, 31 
 
 52. Old vessel, Original, 31 
 
 58. Scalariform vessels from a transverse section of a Fern, . . do. 31 
 
 54. Dotted duct of Fir, T' < .' do. 32 
 
 55. Dotted duct of Pine, .,. ; ;.'i . do. 32 
 
 56. Dotted duct of Pinus Strobus, - " ! Authors, 32 
 
 57. Dotted duct of Araucaria, ^ . : *< do. 32 
 
 58. Duct from fossil wood, k ; . Original, 33 
 
 59. Porous tissue, Authors, 33 
 
 60. Dotted vessel, . 1 Vl- J * : *" do. 33 
 
 61. Porous duct, Locust tree, Original, 34 
 
 62. Porous vessel, Apple, do. 34 
 
 68. Porous duct, Bass-wood, do. 34 
 
 64. Arachnoidiscus Ehrenbergii, from Peruvian guano, ... do. 36 
 
 65. Silica of Rye, do. 37 
 
 66. Campilodiscus clupeus, from the Bergmehl, . . . * ; **'* do. 39 
 
 67. Silica of the Oat, . & do. 39 
 
 68. Silica of the Wheat, ;-: ^ ^l ? - do. 39 
 
 69. Silica of the Rice, uv - -i-' . do. 39 
 
 70. Silica of Equisetum hyemale, > i~ do. 39 
 
 71. Upper cuticle, Deutzia scabra (stellate crystals), v < ''** do. 40 
 
 72. Under cuticle, " " " " '. -v ^r do. 41 
 78. Hair of Cowitch, showing spines, "-,-'-, do. 42 
 
 74. Venus' Fly-trap showing the like, . . . . . . Authors, 42 
 
 75. Fibres of Cotton, showing ultimate structure of, . . . . Original, 43 
 
 76. Hairs of plants, ^b =#.-./ Authors, 48 
 
 77. Hair of Nettle, with poison gland, . . . . ife;*^. do. 43 
 
 78. Hair of Chinese Sundew, do. 43 
 
 79. Cuticle of Ruscus aculeatus, Original, 45 
 
 80. Cuticle of Ivy, . . -o '' do. 45 
 
 81. Cuticle of White Lily ,. T , do. 45 
 
 82. Section of Melon leaf, showing its structure do. 46 
 
 88. Section of Balsam, do. 47 
 
 84. Cherry leaf, to show venation, Authors, 48 
 
 85. Tree Fern, .... i ...... do. 50 
 
 86. Section of Fern, showing its structure, , , ... do. 50 
 
 87. Monocotoledonous stem, do. 51 
 
 88. Exogenous stem, *.-...... do. 53 
 
LIST OF ILLUSTRATIONS. 
 
 XXX1U 
 
 NO. 
 
 PAGE 
 
 Authors, 54 
 Original, 62 
 do. 64 
 do. 65 
 do. 65 
 do. 65 
 do. 65 
 do. 66 
 do. 67 
 do. 68 
 do. 68 
 do. 68 
 do. 68 
 do. 69 
 do. 69 
 do. 70 
 do. 70 
 do. 70 
 do. 70 
 do. 70 
 do. 72 
 Kolliker, 75 
 do. 75 
 Original, 75 
 do. 76 
 do. 77 
 do. 78 
 do. 78 
 do. 78 
 do. 79 
 do. 79 
 do. 80 
 do. 80 
 do. 80 
 do. 81 
 do. 81 
 do. 81 
 do. 82 
 do. 82 
 do. 82 
 do. 83 
 do. 83 
 do. 84 
 do. 84 
 do. 85 
 do. 85 
 do. 86 
 do. 86 
 do. 86 
 do. 86 
 do. 87 
 do. . 87 
 do. 87 
 
 90. Membrana putaminis (lining membrane of egg shell), . . 
 91. Cephalic cartilage, Tadpole, 
 92. White fibrous tissue alone, ....... . . 
 93. White and yellow fibrous tissue combined, .... 
 94. Yellow fibrous tissue alone, . 
 
 
 96. Transverse section of Ligamentum nuchse, 
 97. Human blood corpuscles, 
 98. Frog's blood, 
 99. Fibrillation of Frog's blood, 
 100. Fibrillated blood of Locust, 
 101. Blood fibrillating in the corpuscles, Frog, . . 
 102. Corpuscles of human blood from the crop and stomach of Mosquito, 
 103. " " " 
 104. Blood corpuscles, Fowl, 
 
 106. Blood corpuscles, Musk Deer, . . . . 
 107. Blood corpuscles, Mouse, 
 108. Colorless corpuscles, Human, 
 109. Human epidermis, . . 
 110. Transverse section through the body and bed of a Nail, 
 111. Transverse section through the body of a Nail, 
 112. Nail plates separated, 
 113. Vascularity of matrix of Nail, 
 114. Striations of cortical substance of Human Hair, . . 
 115. Feather of a Rook, medulla injected, 
 116 Feather of a Bird, 
 
 117. Barbules, and barbulinse of the feather of a Bird, . 
 118. External surface of Human Hair, . . . .... , ., t .,;._. 
 
 120. Plates from the cortical substance of the shaft, . . >......,.:;,.- 
 121. Scales from the root, . . ,'....., .... "*,* -.-vjexj*** 
 122. White Hair from the head, 
 123. Hair of Human eyebrow, . . . . . 
 124. Transverse section of Human Hair, 
 125. Another view, 
 126. Wool, 
 
 127. Transverse section of Hair, full-blooded Negro, 
 128. Another section, . 
 129. Transverse section of Hair from the Menomonee Indian, 
 130. Hair from the beard, white man, 
 131. Transverse section, Tiger's whisker, 
 132. Transverse section, Cat's whisker, 
 133. Transverse section of Vibrissa, (whisker of) Eat, . 
 134. Transverse section of Vibrissa, (whisker of) Raccoon, 
 135. Transverse section of Hair from Elephant's proboscis, . 
 136. Transverse section of a Hog's bristle, . . . 
 
 138. Transverse section of Hair from Elephant's tail, 
 139. Transverse section of Whalebone, . . . 
 
 141. Transverse section of Hair from Horse's mane, 
 
LIST OF ILLUSTRATIONS. 
 
 NO. PAGB 
 
 142. Transverse section of Hair from Turkey's beard, . . Original, 87 
 
 143. Hair of Stag, longitudinal, do. 
 
 144. Hair of Wapeti Deer, longitudinal, . . . .--*-< do. 
 
 145. Hair of Goat, longitudinal, . . . . do. 
 
 146. Hair of Ornithorhyncus paradoxus, .... -i-'* do. 
 
 147. Structure of the narrow portion magnified, .... do. 89 
 
 148. Structure of the enlarged portion, do. 
 
 149. Transverse section, Porcupine's quill, do. 
 
 150. Transverse section, quill of English Hedgehog, ... do. 90 
 
 151. Longitudinal section, quill of English Hegehog, ... do. 90 
 
 152. Transverse section, quill of the American Porcupine, . . do. 90 
 
 153. Hair of Seal, longitudinal, P-p do. 
 
 154. Mouse hair, longitudinal, M do. 91 
 
 155. Shaft and bulb of the hair, Phascogale penicillata, . .a i -j * do. 91 
 
 156. Succeeding portion, do. 
 
 157. Greatest enlargement of the same hair, do. 91 
 
 158. Hair of Indian Bat, **i do. 91 
 
 159. Hair of Aphrodita hispida, latfNjj**- * do. 92 
 
 160. Hair of larva of Dermestes lardarius, . . . . *4*<;; do. 92 
 
 161. Hair of larva of Dermestes lardarius enlarged, 500 diameters, . do. 92 
 
 162. Pavement epithelium, ........ do. 94 
 
 163. Ciliated epithelium, do. 95 
 
 164. Ciliated epithelium from the Frog's mouth, .... do. 96 
 
 165. Monas termo, nutrimental organs of .... Ehrenberg, 97 
 
 166. Alimentary canal, Vorticella citrina, do. 98 
 
 167. Alimentary canal, Stentor polymorphous, i*V . .>* :,^i., ^ *, ... do. 98 
 
 168. Rotifer vulgaris, .:^. ,;, . . Authors, 98 
 
 169. Notomate clavulata . . ... . . . ,& t , w do. 99 
 
 170. The Acephalocyst, . . -:, ; Wu^vi -; '.v<*;n-.v. .-*. do. 99 
 
 171. Coenurus cerebralis, . iu~.~ i j.> f- . Original, 100 
 
 172. Echinococcus hominis, . .... .... .... - do. 101 
 
 178. Cysticercus cellulosa, . .--^-* '-'. J ........ . ^ . . Authors, 101 
 
 174. Head of Cysticercus cellulosa magnified, .... Original, 101 
 
 175. Distoma hepaticum, ,,i ,u. *~. . do. 102 
 
 176. Distoma lanceolatum, . . . ..... Hunterian Museum, 102 
 
 177. Hydra fusca, from the fresh waters, . . -_,,.. . . Authors, 103 
 
 178. Hydra viridis, from the fresh waters, . . . . '^IK do. 104 
 
 179. Corallium rubrum (red coral), . . . . Original, 105 
 
 180. Polype of Corallium rubrum magnified, .-: /*:.; . i . Milne Edwards, 105 
 
 181. Rhizostoma Cuvieri, or jelly fish, . . . . Hunterian Museum, 107 
 
 182. Vertical section of Rhizostoma Cuvieri injected, . do. 107 
 188. Cetonia aurita, another jelly fish, . . . ,4.;...-jJ . do. 109 
 
 184. Cetonia aurita lying on its back, . ..i,^/- *' wv; i . . Original, 109 
 
 185. Echinus, with and without spines, . ,^4. *./-.,, . . Authors, 109 
 
 186. Nutrimental organs, Asterias rubens, . -,-:!. i. . Tiedemann, 110 
 
 187. Nutrimental organs, Echinus, . . . . i,u,.; . . Sharpey, 111 
 
 188. Lantern of Aristotle, . . .^^ .....,^j.i ^. . : -^4; *,,. . Forbes, 111 
 
 189. Two teeth of Echinus, . . ..... ._ .^ ^ Original' 111 
 
 190. Cucumaria frondosa (perfect animal), . . . . do. ' 112 
 
 191. Holothuria elegans Hunterian Museum, 113 
 
 192. Ovarium, Cucumaria frondosa, . . .,,.,*' . . . Original, 115 
 198. Ovarium, Cucumaria frondosa, tubes of, enlarged, . . . do. 115 
 194. Respiratory organg of Cucumaria frondosa, . do. 116 
 
LIST OF ILLUSTRATIONS. 
 
 XXXV 
 
 NO. 
 
 195. 
 
 196. 
 
 197. 
 
 198. 
 
 199. 
 
 200. 
 
 201. 
 
 202. 
 
 203. 
 
 204. 
 
 205. 
 
 206. 
 
 207. 
 
 208. 
 
 209. 
 
 210. 
 
 211. 
 
 212. 
 
 213. 
 
 214. 
 
 215. 
 
 216. 
 
 217. 
 
 218. 
 
 219. 
 
 220. 
 
 221. 
 
 222. 
 
 223. 
 
 224. 
 
 225. 
 
 226. 
 
 227. 
 
 228. 
 
 229. 
 
 230. 
 
 231. 
 
 232. 
 
 233. 
 
 234. 
 
 235. 
 
 236. 
 
 237. 
 
 238. 
 
 239. 
 
 240. 
 
 241. 
 
 242. 
 
 245. 
 246. 
 247. 
 
 Sipunculus, or rough Syrinx, Original, 
 
 PAGE 
 
 117 
 
 Nutrimental canal of Sipunculus, do. 117 
 
 Muscular coat, Sipinuculus, ....... do. 118 
 
 Serpula contortuplicata, do. 119 
 
 Nutrimental organs, Aphrodita aculeata, do. 119 
 
 Mouth of Leech, do. 120 
 
 One jaw of mouth of Leech, do. 120 
 
 Alimentary canal of Leech, do. 120 
 
 Arenicola piscatorium (fisherman's worm), . . Hunterian Museum, 121 
 
 Actheres percarum, parasitic on the Perch, .... Nordmann. 122 
 
 Male of Actheres percarum, do. 123 
 
 Nutrimental organs, Lepas vitrea, . . . . Original, 124 
 
 Stomach of Lobster (external surface), do. 126 
 
 Stomach of Lobster opened to show gastric teeth, . . do. 126 
 
 Longitudinal section of Lobster, do. 127 
 
 Coleopterous wings (Beetles), do. 132 
 
 Hemipterous wings (Tree Bugs), do. 132 
 
 Lepidopterous wings (Butterflies), do. 132 
 
 Neuropterous wings (Dragon Flies), do. 132 
 
 Hymenopterous wings (Bees, Wasps), do. 132 
 
 Dipterous wings (House Flies, &c.) ...... do. 133 
 
 Upper portion of mouth, Cicindela hybrida, .... do. 133 
 
 Lower portion of Cicindela hybrida, do. 133 
 
 Alimentary canal, Cicindela campestris, .... do. 134 
 
 Crop of Dyticus marginalis, . . .... . . do. 134 
 
 Upper part of mouth, Tree Bug, . ..... . do. 135 
 
 The rostrum of Tree Bug, do. 135 
 
 Alimentary canal, Cimex lectularius, do. 135 
 
 Alimentary canal, Blatta Americana, ..... do. 136 
 
 Lateral view of gastric teeth of Blatta Americana, . . do. 137 
 
 Lateral view seen in situ, .. #. ...-.. ,v . . do. 137 
 
 Pavement epithelium of membrane below gastric teeth, . do. 137 
 
 Salivary glands, Blatta Americana, do. 137 
 
 Alimentary canal, Locusta viridissima, do. 138 
 
 Proventriculus of Gryllotalpa, do. 139 
 
 One row of teeth more highly magnified, .... do. 139 
 
 Ileum, Acheta domestica, . do. 140 
 
 More highly magnified view of the intestinal glands of Ileum, do. 140 
 
 Mouth of Butterfly (Cynthia cardui), do. 140 
 
 Alimentary canal (Pontia Brassica), ...... do. 141 
 
 Nutrimental organs, Cossus ligniperda, do. 142 
 
 Spinneret of Cossus ligniperda, . . ... . . do. 143 
 
 Highly magnified view of liver of Caterpillar, .... do. 143 
 
 Upper part of mouth of Libellula, . . ..... do. 144 
 
 Lower portion of mouth of Libellula, do. 145 
 
 Mouth of Hymenoptera, ........ do. 145 
 
 Nutrimental organs, Apis mellifica, do. 146 
 
 Upper portion of mouth, Helophilus tenax, .... do. 147 
 
 Under lip of Helophilus tenax, do. 147 
 
 Nutrimental organs, Musca camaria, ..... do. 148 
 
 Demodex folliculorum, ........ Authors, 151 
 
 Demodex from the scalp, ....... do. 151 
 
 Demodex, magnified, do. 151 
 
LIST OF ILLUSTRATIONS. 
 
 KO. PAGE 
 
 248. Acarus scabkei, Original, 152 
 
 249. Upper jaws of Spider, do. 153 
 
 250. Under jaws of Spider, do. 153 
 
 251. Nutrimental organs of the Spider, do. 154 
 
 252. Muscular coat, Cynthia pupa, Hunterian Museum, 155 
 
 258. Organs of nutrition, Cynthia pupa, do. 156 
 
 254. Pyrosoma gigantium, do. 157 
 
 255A. Lingula, natural size, Original, 158 
 
 255. Nutrimental organs in situ, Terebratula Australis, . . do. 158 
 
 256. A side view of Terebratula Australis, do. 159 
 
 257. Alimentary canal of Terebratula Australis, front view, . do. 159 
 
 258. Back view of alimentary canal, Terebratula Australis,. . . do. 160 
 
 259. The arms of Terebratula, do. 160 
 
 260. Nutrimental organs, Oyster, do. 161 
 
 261. Hyalaea, do. 162 
 
 262. Nutrimental organs of Hyalaea, - / v do. 162 
 
 263. Eolis Inca, Authors, 163 
 
 264. Nutrimental organs, Aplysia faciata, Original, 163 
 
 265. Tongue, Buccinum undatum, -i^ do. 164 
 
 1 266. Nutrimental organs, Nautilus, Hunterian Museum, 165 
 
 267. Bone of Cuttle-fish magnified, Original, 167 
 
 268. Nutrimental organs, Herring, Hunterian Museum, 168 
 
 269. Palate of Frog, injected, Original, 169 
 
 270. Mucous membrane of stomach of Frog, do. 170 
 
 271. Duodenum of Frog, .V> do. 170 
 
 272. Ileum of Frog, H , . do. 171 
 
 273. Duodenum of Toad, . . . . . . . V *:. ;, do. 171 
 
 274. Large intestine, Frog, .;-. v... do. 171 
 
 275. Stomach of Menobranchus, . . * .--. : ; ^f ''. t . :'. v .-,-. . -.^ do. 172 
 
 276. Ileum of Menobranchus, . . ^ . * . . . . do. 172 
 
 277. Stomach of Menopoma, do. 172 
 
 278. Stomach of Snapping Turtle, .'-.,, . % **'<*; . . do. 172 
 
 279. Alimentary canal of Fowl, Authors, 174 
 
 280. Duodenum of Fowl, injected, Original, 175 
 
 281. Gizzard (external aspect) Crow, . . . . . . f toii\ do. 176 
 
 282. Gizzard cut open, ; . . . do. 176 
 
 283. Stomach of Rat, -. : do. 177 
 
 284. Mucous membrane of stomach of Musk-rat, . . ata**jt do. 178 
 
 285. Stomachs, Herbivorous quadruped, ,- ; > ; ' . . : .' do. 179 
 
 286. Peyerian glands injected, Calf, '#. -^ -,- do. 181 
 
 287. Colon, Calf, injected, . . .*'. . : v .'.;.-: do. 181 
 
 288. Cat's tongue, * '.f . ) . do. 183 
 
 289. Mucous membrane, Cat's stomach, ..=, ...,i :;.-...>.-,*, - .. do. 183 
 
 290. Ileum, Cat, / do. 183 
 
 291. Ileum, Lion, . . . . . ,i',t ;;,'., . . do. 184 
 
 292. Glandulae agmenatae, Lion, . . . . . , .,v ; -^ . do. 184 
 
 293. Solitary glands, colon, Lion, , . . '*++ : ^ \ .* ;'. . .-, ., . -., do. 185 
 
 294. Section of solitary gland, Lion, . . .... do. 185 
 
 295. Colon of the Cat, do. 185 
 
 296. Vessels of the sub-papillary layer, Lion, ....*. do! 185 
 
 297. Filiform papillae, injected, tongue, Dog, ...,_. . do. 186 
 
 298. Circumvallate papillae, tongue, Dog, . ..... do. 186 
 
 299. Mucous membrane, stomach of Dog, .... do. 186 
 
LIST OF ELLUSTEATIONS. XXXV11 
 
 NO. PAGE 
 
 300. Junction of stomach and duodenum of Dog, .... Original, 186 
 
 301. Duodenum of Dog, . , . -. do. 187 
 
 302. Colon of Dog, . .. . . . . do. 187 
 
 303. Papillae of the gum, Human, . ...... . . do. 188 
 
 304. Facets of enamel, Human, do. 190 
 
 305. Prisms of enamel, Human, do. 190 
 
 306. Junction of dentine and enamel, Human Canine tooth, . . do. 190 
 
 307. Connection with enamel of Molar tooth, .... do. 191 
 
 308. Connection with cementum, do. 191 
 
 309. Transverse section of enamel, ........ do. 192 
 
 310. Longitudinal section of Canine tooth, Human, .... do. 193 
 
 311. Transverse section of dentinal tubuli, . ...... . do. 194 
 
 312. A more crowded view, do. 194 
 
 313. Molar tooth, Dog, . ... .. ..'.".. . . . do. 194 
 
 314. Molar tooth, Cat, .,,,;;.; . . do. 195 
 
 315. Transverse section, Canine tooth of Horse, .... do. 195 
 
 316. Do. do. do., ....... . do. 195 
 
 317. Do. do. do., .... do. 195 
 
 318. Longitudinal section, Hog's tusk, do. 196 
 
 319. Transverse section, Hog's tusk, do. 196 
 
 320. Molar tooth of Cow, do. 197 
 
 321. Section of Molar tooth, Sheep, ...... do. 197 
 
 322. Longitudinal section of incisor, Rabbit, do. 199 
 
 323. Transverse section of incisor, Rabbit, . do. 199 
 
 324. Transverse section of Molar tooth, Rabbit, .... do. 199 
 
 325. Transverse section of Molar tooth, Musk-rat, ... do. 200 
 
 326. Longitudinal section of tooth, Pristis, do. 201 
 
 327. Longitudinal section of tooth, Myliobatis, .... do. 201 
 
 328. Transverse section of tooth, Myliobatis, . . . .,.<m?.;.. do. 202 
 
 329. Longitudinal section of tooth of Shark, Fossil, .. ..; , . ... do. 202 
 
 330. Transverse section of Maskanonge* (Muskalonge), ... do. 202 
 
 331. Poison fang of a Serpent, __ do. 206 
 
 332. Gastric glands of a Dog, *f*u.) i-fi Authors, 210 
 
 333. Gastric glands of a Calf, . ... Original, 210 
 
 334. Human tongue, do. 211 
 
 335. External form, Human stomach, Authors, 212 
 
 336. Mucous membrane of Human stomach, injected, . . . Original, 213 
 
 337. Brunner's glands, do. 214 
 
 338. Mucous membrane of Duodenum, ...... do. 214 
 
 339. Mucous membrane of Jejunum, Human, .... do. 214 
 
 340. Peyer's patch, Human, Authors, 216 
 
 341. Typhoid Peyerian glands, . < do. 216 
 
 342. Colon, Human, . do. 217 
 
 343. Jejunum, Monkey, . ......... I. . . . do. 217 
 
 344. Colon, Monkey, . .. ., ., .. ., . . . . do. 217 
 
 345. Fossil muscular fibre, , do. 224 
 
 346. The same, . do. 224 
 
 347. Another illustration do. 224 
 
 348. Muscular fibre, Blatta Americana, do. 225 
 
 349. Muscular fibre, lulus, . . ...... do. 225 
 
 350. Transverse cleavage of muscular fibre, Human, . . . Bowman, 226 
 
 B51. Vascularity of muscle, . Original, 226 
 
 352. Distribution of nerves to muscle, . . Authors, 227 
 
xxxviii 
 
 LIST OF ILLUSTRATIONS. 
 
 NO. 
 
 858. 
 854. 
 855. 
 856. 
 857. 
 858. 
 859. 
 860. 
 861. 
 862. 
 863. 
 864. 
 865. 
 866. 
 867. 
 868. 
 869. 
 870. 
 871. 
 872. 
 878. 
 874. 
 875. 
 876. 
 877. 
 878. 
 879. 
 380. 
 881. 
 882. 
 883. 
 884. 
 885. 
 886. 
 887. 
 888. 
 889. 
 890. 
 891. 
 892. 
 393. 
 894. 
 895. 
 396. 
 897. 
 398. 
 899. 
 400. 
 401. 
 402. 
 403. 
 404. 
 405. 
 
 Muscle torn to show fibrilhe, . *>".--';'>. . . Bowman, 
 Structure of ultimate fibril, . . . . - Original, 
 
 Parasitic fresh-water Alga 
 Callithalmia Baileii 
 Alga, from Barbadoes, . 
 Alga, from Lake Michigan, . 
 Transverse section of muscular fibre, 
 Organic muscular fibre 
 
 do. 
 do. 
 do. 
 do. 
 do. 
 do. 
 
 Original, 
 do. 
 do. 
 do. 
 do. 
 do. 
 
 Nervous system, Asterias rubens, . . . .'~# "' . . Tiedemann 
 
 Nervous system, Leech, ' 
 
 Nervous system, Lepas, . . '^t- . uyj . 
 
 Brain of lulus, . . .:;*. 
 
 Portion of Nervous system, Polydesmus, 
 
 Nervous system, Talitrus, 
 
 Nervous system, Cymothoa, 
 
 Nervous system, Lobster, . do. 
 
 Nervous system, Crab, do. 
 
 Nervous system, Caterpillar, do. 
 
 Brain of Caterpillar, highly magnified, . . . . Ji 
 Nervous system in situ, Blatta Americana, --i-- >* I f rv.i -< -* 
 Nervous system, Spider, . . - . . . *' .'' 
 
 Salpa Poly cratica, ; "> ^ .^IWiWM^I 
 
 Nervous system of Salpa Polycratica, . . . . i : .*.L 
 
 Dorsal mantle of Terebratula Australis, . . - .- :>. <. 
 Nervous system of Terebratula Australis, . . . .- ^--M 
 Nervous system of Mytilus edulis, . . '< -< i" -.:;>*v 
 
 Nervous system of Bulla lignaria, . . . - * ; ;.* <- 
 Nervous system of Carinaria Mediterranea, -'V-J to & .': ;* w 
 
 Nervous system of Harpa elongata, . . -. *. vv;. ?*..--. 
 
 Nervous system of Clio borealis, . . ^V-^ !v i-'^*. W ^ 
 
 Nervous system of Pearly Nautilus, ~v.it. . -> ^.^ -- .;., i . 
 
 Nervous system of Trigla lyra, . . . 
 
 Nervous system of Conger Eel, . . 
 
 Nervous system of Tadpole, fourth day, . . : J> L fa &-. 
 
 Nervous system of Tadpole, sixth day, . - . . . . r w> j 
 
 Nervous system of adult Frog, . . ..>..-8W;H .*::- -'L f .. . 
 
 Brain of the Turtle, . , ., .:.,;: .,.; ;,U '.=** . . f 
 
 Brain of the Chick, . . . . . . . . . . . ; - , , 
 
 Brain of the Stork, . . .. . .,4-^:^1^^*^ 
 
 Brain of the Buzzard, . .,^.^11 &'.. ., . :, ^^^/., f ;, 
 
 Brain of the Human Embryo, ,r;.i4ii;li .:Ici; 
 
 Brain of the Human Embryo, side view, . .,*L-ii$iv. atti . ,;> 
 Brain of the Human Embryo, sectional view, . . . . ^m 
 
 Cerebro-spinal axis, Man, . . . .. . .. -i..,;\ 4 
 
 Axis cylinder, of nerve, . . . . . . . , 14 
 
 White substance of Schwann, . . . . . .]'. . 
 
 Axis cylinder, containing white substance, . . . . 
 
 White substance covering the termination of axis cylinder, 
 Median nerve, Human, . . .. ^ : 
 
 Sympathetic nerve, Human, ,v, . 
 
 Section of sympathetic ganglion, 
 
 Ganglion corpuscles from the gray substance of the spinal chord, 
 Portion of nerve, Blatta Americana,. , ,:&;... o 
 
 PAGE 
 227 
 227 
 229 
 229 
 229 
 230 
 231 
 232 
 235 
 237 
 239 
 240 
 241 
 243 
 243 
 243 
 244 
 
 do. 
 
 249 
 
 do. 
 
 250 
 
 do. 
 
 253 
 
 do. 
 
 255 
 
 do. 
 
 255 
 
 do. 
 
 257 
 
 do.- 
 
 259 
 
 do. 
 
 261 
 
 do. 
 
 264 
 
 do. 
 
 264 
 
 do. 
 
 265 
 
 do. 
 
 267 
 
 Owen. 
 
 267 
 
 Authors, 
 
 270 
 
 do. 
 
 270 
 
 do. 
 
 272 
 
 do. 
 
 272 
 
 do. 
 
 273 
 
 do. 
 
 273 
 
 do. 
 
 274 
 
 do. 
 
 275 
 
 do. 
 
 275 
 
 do. 
 
 279 
 
 do. 
 
 279 
 
 do. 
 
 279 
 
 Original, 
 
 282 
 
 do. 
 
 283 
 
 do. 
 
 283 
 
 do. 
 
 283 
 
 do. 
 
 283 
 
 do. 
 
 283 
 
 do. 
 
 283 
 
 do. 
 
 284 
 
 do. 
 
 284 
 
 do. 
 
 284 
 
' LIST OF ILLUSTEATIONS. 
 
 XXXIX 
 
 NO. 
 
 PAGE 
 
 406. Portion of caudal ganglion of Blatta Americana, 
 
 Original, 284 
 
 407. Neurilemma of nerve, injected, 
 
 do. 285 
 
 408. Portion of human pericardium, 
 
 do. 286 
 
 409. Vascularity of sympathetic ganglion, . ...... 
 
 do. 286 
 
 410. Transparent cornea, Lobster, 
 
 do. 289 
 
 411. Insect Eye, according to Straus, ...... Durckheim 291 
 
 
 Miiller, 291 
 
 413. Cornea, Musca carnaria ; lenses in situ, .... 
 
 Original, 292 
 
 414. Posterior membrane of Caterpillar, with lenses in situ, . . 
 
 do. 292 
 
 415. Conical lenses, Musca carnaria, 
 
 do. 292 
 
 
 do. 292 
 
 
 do. 293 
 
 418. Fat lobules, Musca carnaria, . . . , .. ., , . . .v 
 
 do. 293 
 
 419. Brain, Mantis religiosa, 
 
 do. 295 
 
 
 do. 296 
 
 421. Transparent cornea, towards the edge, Musca carnaria, - * - - 
 
 do. 296 
 
 422. Transparent cornea, at the edge, Musca carnaria, . . 
 
 do. 296 
 
 423. Posterior layer of the transparent cornea, Prionus longimanus, 
 
 do. 297 
 
 424. Prismatic lenses in situ, Prionus longimanus, . . ... 
 
 do. 297 
 
 425. Section of the eye, Prionus longimanus, .... 
 
 do. 298 
 
 426. Cyprea Tigris (Leopard cowry), . . . 
 
 Authors, 300 
 
 427. Fibres of crystalline lens, Codfish, 
 
 Original, 301 
 
 428. Conjunctiva injected, Human, ....... 
 
 do. 302 
 
 429. Fibres of the crystalline lens, Human, 
 
 do. 303 
 
 430. Fibres of the crystalline lens, Ox, 
 
 do. 303 
 
 431. Bony plates of the eye in Reptiles and Birds, 
 
 Authors, 305 
 
 432. Eye of the Tortoise, 
 
 do. 305 
 
 433. Choroid coat of the eye, Snapping Turtle, . . . . 
 
 Original, 305 
 
 434. Ciliary processes of the same, . . 
 
 do. 305 
 
 435. Ciliary processes, Ox, 
 
 do. 306 
 
 436. Ciliary processes, Cat, 
 
 do. 307 
 
 437. Venae vorticosae, Dog, 
 
 do. 307 
 
 438. Longitudinal section of the Human Eye, 
 
 Authors, 308 
 
 439. Ciliary processes, Human, 
 
 do. 310 
 
 440. Ciliary processes, injected and magnified, 
 
 Original, 31 
 
 441. Vessels of the arteria centralis retina, injected, Human, 
 
 do. 311 
 
 442. Anterior capsule of the lens, Human, . . . f 
 
 do. 311 
 
 
 do. 311 
 
 444. Meibomian glands, in situ, 
 
 do. 312 
 
 
 do. 313 
 
PART I. 
 VEGETABLE PHYSIOLOGY. 
 
 LESSON I. 
 
 INTRODUCTION. 
 
 1. Physiology, or the science which teaches the functions of all 
 the different parts or organs of animals and plants ; or the offices 
 which they perform in the economy of the individual ; or, in other 
 words, the science of life, is daily esteemed of greater importance. 
 
 2. Physiology, as now understood, has become quite a modern 
 science, and one that owes its great advancement and chief excel- 
 lence to the Microscope alone. 
 
 3. Without its invaluable aid, our notions and opinions would be 
 as crude, unsatisfactory, and erroneous, as were those of our fore- 
 fathers. Before its mighty presence every fragment of a tissue is 
 bound to succumb ; it has no preconceived theory to support ; it is 
 called upon to do but one thing to assist us in our researches, and 
 nobly it does it ! it tells the truth, whereby the laws of physiologi- 
 cal science are rendered as certain as a problem in Mathematics. 
 
 4. The Microscope has originated a new science Histology 
 from two Greek words, which signify a " discourse on tissues ; " now 
 what is a tissue ? Webster's definition is as follows : " in anato- 
 my, texture or organization of parts. The peculiar, intimate struc- 
 ture of a part is called its tissue. A part of a fibrous structure is 
 called a fibrous tissue. The organs of the body are made up of 
 simpler elements, some generally diffused through the body, and 
 others peculiar to particular organs. These simpler structures are 
 called the tissues of the body ; as, the cellular tissue, the mucous 
 tissue, &c." 
 
 1 
 
2 VEGETABLE PHYSIOLOGY. [LESSON 1. 
 
 5. Since the invention and constitution of Histology, as a sci- 
 ence, Physiology has made enormous strides. 
 
 6. A knowledge of the intimate structure of the tissues, as well 
 of vegetables as of animals, has been of the greatest value to the 
 physiologist. Had the important theory of development by cells 
 not been discovered by Schawn and Schleiden in plants, the like 
 processes had remained unknown as the true principle of develop- 
 ment of the inferior animals, of the development of the Ovum in 
 the higher mammalia, and as the plan by which the human family is 
 continued. 
 
 7. There can be no accurate knowledge of Physiology, save that 
 which is based upon an intimate acquaintance with the ultimate mi- 
 croscopical structure of all tissues; this cannot be learned from 
 books, at the present time, simply because no sufficiently illustrated 
 and voluminous work on this subject has yet been published ; under 
 the best circumstances, it appears to be most desirable to learn by the 
 actual examination of the structures themselves. 
 
 8. It is quite true that it requires a lifetime to acquire the skill 
 to prepare such illustrations, but the devotion necessary to become 
 accomplished as a physiologist, is certainly not greater than the re- 
 quirements of Chemistry, Botany, or any other science, or greater 
 than is necessary to qualify a man for the legal or other learned pro- 
 fessions. 
 
 9. The simple cellular plants offer illustrations of the lowest or- 
 ganized forms we are acquainted with. In them we find that a sin- 
 gle cell constitutes the entire plant. 
 
 10. This cell is produced from its germ, assimilates nutriment, 
 converts a portion of it into the substance of its own cell-wall, se- 
 cretes a nucleus within its cavity, and ultimately produces a repro- 
 ductive germ, that is to continue the race. 
 
 11. "When its own term of life is completed, it bursts, and liber- 
 ates the reproductive germs contained in its interior, and sets them 
 free, each being capable of going through the like series of opera- 
 tions ; or the cell wall is absorbed, thus freeing the germ. 
 
 12. These facts are illustrated by the accompanying figures of 
 Volvox globatoT) described by Professor Ehrenberg, as an animal, 
 but which has long been known as a simple fresh water alga. A 
 perfect figure of this beautiful organism is shown at Fig. 1. 
 
 13. The Volvoces are only to be found in stagnant pools of clear, 
 pellucid water ; placed under the field of a Microscope, they present 
 a very charming sight. In form a perfect sphere, the membrane con- 
 
LESSON 1.] INTRODUCTION. 3 
 
 stituting the outer wall, or integument, as transparent as glass, its 
 surface covered with minute green dots (5), with several spheres of 
 variable size, and much darker green contained within it (a), con- 
 tribute to form an object of unequalled F 
 beauty ! 
 
 14. Neither is this all ; those per- 
 sons who see it for the first time, will 
 be surprised to find that it (a plant) is 
 locomotive. 
 
 15. It will constantly be seen roll- 
 ing to and fro, with a remarkably 
 steady, equable motion; no obstacle 
 retards it nothing accelerates its 
 speed : frequently it occurs that two of 
 
 them are seen approaching each other 
 
 Volvox globator. 
 
 in opposite directions ; collision appears 
 
 to be imminent, but just at the instant of anticipated conflict, one 
 turns off to the right, and the other to the left, and each pursues 
 its way. 
 
 16. The locomotive organs are not easily seen, even by the Mi- 
 croscope two essentials are necessary ; firstly, an excellent fourth 
 achromatic object glass,* and, secondly, careful and judicious man- 
 agement of the light. These conditions being established, a number 
 
 * Certain expressions have been used in this work which require explanation; thus, in 
 speaking of the magnifying power employed, "a fourth," or "an eighth " object glass is men- 
 tioned. 
 
 An Achromatic object glass, if of French construction, consists of three plano-convex 
 lenses; if English, of three pairs (six) of lenses. The focal length of such combinations, 
 always short, may yet be of variable length, while the magnifying power may be the same, 
 therefore focal length forms no indication of magnifying power. 
 
 For the perfect demonstration of the latter, it is usual to use the achromatic combination 
 as a single lens, and test its exact capabilities by comparison with a single plano-convex 
 lens, and then to name the former by the focal length of the single lens, with which it 
 agrees. 
 
 An "inch " achromatic means that the glass is equivalent to a plano-convex lens with an 
 inch focus in other words, that it magnifies exactly ten diameters: a "fourth," or an 
 " eighth," mean that they are equal to plano-convex lenses, of one-fourth or one-eighth of an 
 inch focus, or 40 or 80 diameters. 
 
 In the Compound Microscope, there are two additional modes of obtaining an enlarged 
 image, beyond the use of the object glass ; these are, the length of the tube of the compound 
 body, and the eye-piece. The legitimate way to obtain power is by the object glass, as, 
 although the other two plans may greatly enlarge the image, they are powerless to show 
 structures that the object glass fails to develop. 
 
 The great number of diameters pompously claime ^ oy some authors, depends entirely 
 upon the length of tube and depth of eye-piece both of them objectionable (frequently falla- 
 cious) modes of obtaining magnifying power. The best and fairest way is to state the value 
 of the object glass employed. 
 
4 VEGETABLE PHYSIOLOGY. [LESSON 2. 
 
 of delicate, hairlike processes, in constant vibration, will be seen 
 against the light, surrounding the outer margin of the globe (c) ; 
 once clearly seen, they will readily be discovered, arising from the 
 minute dots which cover the external surface (b). By their incessant 
 vibratile action, the rolling motion results, for which these plants are 
 remarkable. 
 
 17. These organs are called cilia, from the Latin word cilium, an 
 eye-lash, which they are supposed most nearly to resemble ; and, from 
 their action, vibratile cilia. These plants are large enough to be 
 seen, when held against the light, by good, unassisted vision. 
 
 LESSON II. 
 
 INTRODUCTION, CONTINUED. 
 
 18. Not only are the perfect forms, or parent plants, seen in 
 incessant motion, but the large green masses (a), so conspicuous 
 in the interior, are also in constant rotation, until, when they have 
 become mature, they desire to effect their liberation and commence 
 an independent existence ; at this period they will be seen to have 
 FlQ 2 numerous small, immature germs in 
 
 their interior, also in motion. 
 
 19. The mode by which they es- 
 cape is by the rupture of the parent 
 cell (Fig. 2) ; here a decided break in 
 the cell-wall is seen, and one of the 
 germs, covered with vibratile cilia, has 
 just effected its liberation, to be speed- 
 ily followed by the remainder. 
 
 20. The higher forms of vegetable 
 life are only distinguishable from the 
 lower forms by the multiplication of 
 
 voivoxgiobator, burst. similar cells, so that by the concur- 
 
 rent labors of all, a more complete and lasting effect may be pro- 
 duced. 
 
 21. The analysis of even the mighty monarch of the forest, shows 
 that all the soft and growing parts are composed of similar cells ; their 
 function is to absorb and prepare the nutriment, which is afterwards 
 
LESSON 2.] INTRODUCTION. 5 
 
 to be applied to the extension of the solid internal skeleton of the 
 trunk and branches. 
 
 22. At the extremities of the roots of all the more perfect plants, 
 we find a set of soft cells, making up those succulent bodies which 
 are known as the spongioles ; these are specially destined to perform 
 the absorption of nutritious fluid. 
 
 23. This fluid, being conveyed by the vessels of the stem and 
 branches to the leaves, is here subjected to the action of the cells 
 which make up the parenchyma (pulp) of these organs. 
 
 24. The crude, watery, ascending sap, is thus converted, by a va- 
 riety of chemical and vital operations, into the thick, glutinous 
 latex / which, like the blood of animals, contains the materials for 
 the production of new tissue, and also the elements of the various 
 secretions. 
 
 25. This process of conversion includes the exhalation of super- 
 fluous liquid, and also that interchange of gaseous ingredients between 
 the sap and the air, which may be termed aeration ; but it involves, 
 besides these obvious chemical alterations, a new arrangement of the 
 particles of the sap, by which a variety of new products are generat- 
 ed, some of them possessing a tendency to pass into the form of solid 
 organized tissue, by a process of coagulation, when withdrawn from 
 the living vessels. To this peculiar converting process, which is such 
 an important step towards the production of perfect living tissue from 
 the crude aliments, the term Assimilation is applied. 
 
 26. ASSIMILATION, therefore, is the peculiar process by which for- 
 eign substance is converted into the likeness of the individual. Thus 
 the food assimilated by a plant, becomes identical with itself ; and 
 on the same principle, Man, in common with other animals, assimi- 
 lates or converts his and their food. As the elaborated sap descends 
 in its proper vessels through the stem, it yields up to the growing 
 parts the nutrient materials they respectively require. These grow- 
 ing parts may be the ordinary tissues, of which the chief part of the 
 fabric is composed, and which are destined to a comparative perma- 
 nency of duration ; and in the growth and extension of these, the 
 process of Nutrition is commonly regarded as consisting. 
 
 27. By NUTRITION is meant the food which promotes the growth 
 of plants, and promotes the growth and repairs the waste in animals. 
 On the other hand, certain groups of cells have for their office the 
 separation of peculiar products from the sap, such as oil (fixed or 
 essential), starch, resin, &c., which they store up against the time 
 when they may be demanded : these cells are said to perform the act 
 of Secretion. 
 
6 VEGETABLE PHYSIOLOGY. [LESSON 2. 
 
 28. SECRETION, in plants, consists in the process of separating 
 from the sap materials differing from itself. This function is dele- 
 gated to cells, in the Vegetable Kingdom, but the allied function in 
 the Animal Kingdom is performed by glands. In them resides the 
 power of secerning or secreting from the blood, substances entirely 
 different from it, or any of its constituents, as bile, saliva, mu- 
 cus, &c. 
 
 29. It is very important to remark in regard to all the cells thus 
 actively concerned in the Vegetative functions in plants, by which 
 the development and extension of the permanent fabric is provided 
 for, that they have but a very transitory life as individuals. 
 
 30. The Absorbent cells at the extremities of the rootlets are 
 continually being renewed ; some of the old ones dying and decaying 
 away, whilst others are converted into the solid texture of the root, 
 and thus contribute to its progressive elongation. 
 
 31. In the process of ABSORPTION, another broad distinction 
 occurs between Plants and Animals. In the former kingdom, this, 
 like all other vegetative functions, is performed by cells ; but in the 
 Animal Kingdom the imbibition, or absorption, is performed by 
 special vessels, as the lacteals (laCta, milk,) and lymphatics. 
 
 32. Of the transitory duration of the Assimilating cells, we have 
 an obvious proof in the fall of the leaf; which takes place at inter- 
 vals, to be followed by the production of a new set of cells, having 
 similar functions. 
 
 33. The fall of the leaf results merely from the death and decay 
 of its tissue ; as is evident from the fact, that, for some time pre- 
 viously, its regular functions cease, and that, instead of appropriating 
 carbon from the atmosphere, there is a liberation of carbonic acid (a 
 result of their decomposition) in large amount. Thus, the process 
 takes place in evergreens equally with deciduous (falling off) plants ; 
 the only difference being, that the leaves in the latter are all cast off 
 and renewed together, whilst in the former they are continually being 
 shed and replaced, a few at a time. 
 
 34. The Secreting cells have usually a like transitory duration ; 
 being destined to give up their contents by the rupture or liquefac- 
 tion of their walls, whenever called upon to do so, by the demand 
 set up in the growing parts of their neighborhood, for the peculiar 
 products they have set apart. 
 
 35. Not only are the proper organic functions of all Plants thus 
 dependent upon the agency of cells, but their Reproduction is so 
 likewise. 
 
LESSON 3.] INTRODUCTION. V 
 
 LESSON III. 
 INTRODUCTION CONCLUDED. 
 
 36. REPRODUCTION, to renew that which has been destroyed. 
 Trees are reproduced by new shoots from the roots, or from cuttings 
 or slips. Some animals, as the Lobster, Crab, &c., possess the power 
 of reproducing, or generating lost parts. In the lowest tribes of the 
 Cryptogamia, where each cell is an independent individual, every 
 one has the power of preparing within itself the reproductive germs, 
 from which new generations may arise. 
 
 37. The GERM is the origin, or first principle ; that from which 
 any thing springs. In botany it is the ovary or seed-bud of a plant, 
 the rudiment of fruit yet in embryo. In the higher plants we find a 
 complex apparatus superadded for the purpose of aiding the early 
 development of these germs, by supplying them with nutriment pre- 
 viously elaborated by the parent; yet still this operation is of a 
 purely accessory kind, and the essential part of the process remains 
 the same. 
 
 38. Now we shall find that although the fabric of Animals 
 appears to be formed on a plan entirely different from that of Plants, 
 and although the objects to be attained are so dissimilar, there is 
 much greater accordance amongst their elementary parts, than might 
 have been anticipated. 
 
 39. The starting point of both is the same ; for the embryo of 
 the Animal, up to a certain grade of its development, consists, like 
 that of a Plant, of nothing else than an aggregation of cells. 
 
 40. The lowest class of animals, the Microscopical Animalcula, 
 or the invisible inhabitants of stagnant water, appear to be identical 
 with the simple cellular plants, already referred to ( Volvox globaior). 
 The bodies of these creatures are singularly elastic, and remarkable 
 for their transparency. The whole of this class (animalcules) are 
 locomotive in a high degree, and by the means of similar organs 
 vibratile cilia. Unlike the uniform progression of the plant, these 
 creatures exhibit the most astonishing irritability. 
 
 41. Whilst swimming along at a rapid rate of speed, pursuing 
 their prey, a portion of vegetable matter or some extraneous sub- 
 stance will arrest their career ; suddenly, they throw out the water 
 with which their interior was distended, and instantly contract to such 
 a speck as to become perfectly invisible. 
 
8 VEGETABLE PHYSIOLOGY. [LESSON 3. 
 
 42. Every thing remaining still and quiet, they re-fill their 
 bodies with water, the vibratile organs again appear, motion is re- 
 sumed, and off they go. 
 
 43. During the time they remain passive, which often occurs, 
 they can be examined with great ease ; it will then appear that their 
 body contains a variable number of distinct globular particles, to 
 which Ehrenberg ascribes the function of gastric cavities or 
 stomachs. 
 
 44. According to the same authority, many of these creatures 
 possess not less than three hundred of these cells, or stomachs. 
 
 45. Now, the probability is, judging especially from the analogy 
 furnished by the vegetable kingdom, that these spots are only nuclei, 
 or immature germ spots, waiting the period for their full develop- 
 ment, and the mode by which these creatures propagate, appears to 
 confirm this opinion. 
 
 46. The Enchelis pupa, a beautiful flask-shaped animalcule, is 
 one of those animals that should greatly assist our inquiries. When 
 fully extended, and active, the creature presents a row of vibratile 
 cilia (a Fig. 3), surrounding the oral (mouth) aperture (5), whilst the 
 spots, or nutrimental sacs of Ehrenberg, are referred to at c. 
 
 FIG. 3. FIG. 4. FIG. 5. 
 
 Enchelis pupa. Enchelis showing constriction. The same, further advanced. . 
 
 If a specimen be followed by the stage adjustments of the mi- 
 croscope, a slight notch or constriction will appear (Fig. 4, a) sur- 
 rounding its body as if a fine thread were tied around it. 
 
 47. This constriction will rapidly increase (Fig. 5), and by 
 this time a series of vibratile organs will be developed at the 
 other extremity of the body. The incessant vibration of the cilia 
 causes a vortex in the water, by means of which particles of matter, 
 as well smaller animalcules, as extraneous substances, are driven to 
 the creature's mouth : if proper food, it is immediately swallowed ; 
 but if it consist of deleterious matter, the mouth is instantly closed, 
 
LESSON 3.] INTRODUCTION. 9 
 
 the cilia are either quiet, or entirely disappear, and the animal most 
 frequently rushes from the spot. 
 
 48. At the time that cilia appear at each extremity of the body 
 (Fig. 5), two mouths are formed, and the animal 
 
 pursues its prey, and receives food at both. But 
 still the constriction continues to advance, until the 
 body is nearly cut in twain the two portions being 
 joined by the merest pedicle (Fig. 6) ; presently this 
 becomes absorbed, and the two bodies, thus evolved 
 by spontaneous scission, swim off in contrary direc- 
 tions, never again to meet in this world ! 
 
 49. Each half of the body, thus divided, is 
 
 equally young, and rapidly attains maturity, which Development of the 
 is no sooner accomplished, than the same process is 
 repeated, and this continues without intermission in the Enchelis (and 
 allied animals), throughout the summer and autumnal months, until, 
 at the approach of winter, other modes of continuance of the species 
 are resorted to. 
 
 50. Throughout these changes, however, it will be seen, that a 
 fair distribution is made of the germ cells (if such they be) ; one 
 half of the divided body may have a few more of them than the 
 other, but they visibly increase in both immediately, and continue so 
 to do till the time arrives for self- division. 
 
 51. A mode of reproduction in the lower plants, is identical, in 
 every respect, to the spontaneous division of the body in the lower 
 animals. 
 
 52. A species of Conferva, commonly called " Frog's spittle," 
 and erroneously supposed to be the ova of that animal, has been 
 watched, and carefully traced through corresponding developments. 
 
 53. When the plant is first collected, it may consist of a long 
 chain of distinct cells (Fig. 7), each having a septum, or parti- 
 tion, at either extremity which separates it from the cell above, 
 and below (a, b) ; in the centre is a mass of endochrome (internal 
 green), or chlorophylle (green of a leaf), possessing a number of nu- 
 cleated spots (c). 
 
 54. In a few days the cell would be seen to elongate considerably 
 (Fig. 8), and the mass of endochrome diffuse itself confusedly, with- 
 in the cell, till eventually it assumes the form of a beautiful double 
 spiral coil (a), the nuclei being greatly decreased in size. 
 
 55. Presently, another phase presents itself; the cell becomes 
 still more elongated, and narrower (Fig. 9), the mass of endochrome 
 
10 
 
 VEGETABLE PHYSIOLOGY. [LESSON 3. 
 
 suddenly contracts in bulk, and seeks the centre of the cell, then it 
 spontaneously divides (a, a), at the same time a delicate line is run, 
 as it were, across the cell dividing it into two immediately beneath 
 the divided endochrome (b). 
 
 56. Subsequently, the divided endochrome seeks the centre of 
 each cell, the spiral coil is broken up, and the entire mass assumes 
 
 FIG. 8. FIG. 9. 
 
 Zygnema (Frog's spittle) in the Development of Zygnema, Spontaneous division (third 
 first stage. progressing (second stage). stage). 
 
 the solid cylindrical form which characterized the first figure of this 
 series ; the cells become well formed, and grow correspondingly with 
 the increased size of the endochrome, and especially of its nuclei 
 the whole cell, in fact, is preparing to go through the like series of 
 consecutive changes, in which it originated. 
 
 57. Again, as regards the vegetative type of the original con- 
 stitution of animal tissues, we find among the lowest tribes of 
 animals, as well as among certain of the highest tribes that retain 
 many embryonic peculiarities, even in the adult condition, a great 
 proportion of the complete fabric to be possessed of a distinct vege- 
 tative origin. In most of the higher animals, however, a large pro- 
 portion of the structure consists of tissues in which no distinct trace 
 of a cellular origin appears to be apparent ; and it has been only 
 since improved methods of observation have been brought to bear 
 upon their analysis, and more especially since they have been exam- 
 ined not only in their complete state, but in the course of their de- 
 velopment, that they have been reduced to the same category with 
 the tissues of plants, and of the lower animals. 
 
LESSON 4.] STRUCTURE OP VEGETABLE TISSUES. 11 
 
 58. Other tissues, which are peculiar to animals, cannot be re- 
 ferred to the same origin ; but these will be found to have a grade 
 of organization even lower than that of simple isolated cells, and to 
 be referrible to the solidification of the plastic or organizable fluid 
 prepared by the assimilating cells, and set free by their rupture. 
 
 59. We shall find, however, that (as in plants) all the tissues 
 most actively concerned in the vital operations, retain their original 
 cellular form ; and it will be easy to refer to distinct groups of cells 
 in the bodies of animals, not merely for the performance of the func- 
 tions of Absorption, Assimilation, Respiration, Secretion, and Re- 
 production, which are common to them with plants, but also those of 
 Muscular contraction, and Nervous action, which they alone per- 
 form. 
 
 LESSOR IV. 
 
 ON THE STRUCTURE OF VEGETABLE TISSUES. 
 
 60. All the tissues of plants are remarkable for their simplicity 
 of structure, as compared with the tissues of animals. 
 
 61. In their earliest and simplest condition, plants are found to 
 consist of a series of minute vesicles, composed of a membrane called 
 cellulose. 
 
 62. It is also known as simple membrane, and possesses char- 
 acteristics which distinguish it from all other tissues, that is to say ; 
 it is elastic, transparent, easily permeable by fluids, and structureless. 
 
 63. It constitutes the basis of all vegetable tissues, and it is uni- 
 versally present. With regard to its chemical characters it appears 
 to be closely allied to starch ; treated with sulphuric acid, it turns 
 yellow ; when, if subjected to the action of tincture of iodine, a beau- 
 tiful purple color results, indicating the iodide of starch. 
 
 64. As the higher plants advance in growth, they are found to 
 consist of two kinds of tissue cellular and vascular, and these are 
 variously modified to form the elementary organs. 
 
 65. By their union, the elementary tissues form the compound 
 organs, by which the several functions of plants are carried on. 
 
 CELLULAR TISSUE. 
 
 66. By the conjunction of a series of minute vesicles, utricles, 
 or cells, this tissue is formed. They appear to be perfectly spherical 
 
12 VEGETABLE PHYSIOLOGY. [LESSON 4. 
 
 when first developed, but the elasticity of the membrane composing 
 their cell-wall, readily yields to the pressure of surrounding like 
 cells, by which they assume an egg-shape or elongated form (Fig. 
 10); they are often angular (Fig. 11), or even polyhedral (many 
 sides) (Fig. 12). 
 
 FIG. 10. FIG. 11. FIG. 12. 
 
 Single cell of Pineapple. Cells of Cucumber. Polyhedral cells. 
 
 67. Again, the size of cells is found to be as variable as their 
 figure, in different plants, and in different parts of the same plant. 
 
 Dr. Hook counted more than a thousand in a line, an inch long, 
 in Cork ! 
 
 68. Notwithstanding each cell originally consists of a separate 
 membrane, the walls of contiguous cells may become united in the 
 progress of growth. 
 
 69. When cells are united at their extremities, it frequently hap- 
 pens that the walls, which form the point of junction) become ab- 
 sorbed, and thus a tube is formed. 
 
 70. The simplest kinds of plants, as Sea-weeds, are called cellu- 
 lares, being entirely composed of cellular tissue ; so too the pulpy 
 parts of fruits and vegetables, and it is the great object of Horticul- 
 ture to extend, as far as possible, the production of this tissue. 
 
 71. The pith of trees and plants is cellular ; and such is the 
 structure of cotton and rice-paper. 
 
 72. Cells generally transmit fluids through the parietes of the 
 cell-wall, to which rule some mosses and other plants offer exception ; 
 in them, minute apertures, or holes, are found in the cells in a sin- 
 gle cell of a Euphorbiaceous plant, as many as forty-five openings 
 have been counted. 
 
 73. Another form of cell is known as tne porous cell, in which 
 the membrane has been thickened at certain parts, leaving thin round 
 spots, which, viewed by transmitted light,* appear like holes (see Fig. 
 
 * There are two modes of illuminating objects seen by the microscope ; one is, to throw 
 light upon the object this is called direct light. The other plan consists in throwing light 
 through a transparent object this is called transmitted light. 
 
LESSON 4.] STRUCTUKE OP VEGETABLE TISSUES. 
 
 13 
 
 Pith of Elder, porous cells. 
 
 13), of which the accompanying figure of FIG. is. 
 
 the pith of Elder affords a good example. 
 Authors have figured this tissue as if com- 
 posed of many sides (polyhedral), but this 
 appears to have arisen from the section being 
 too thick; the tissue is a singularly transpa- 
 rent one, and if three or four layers of cells 
 be present, the outlines of the cell walls run 
 together in such manner as to create great 
 confusion ; this is shown in Fig. 14 ; but if the section do not in- 
 clude more than two layers (Fig. 13), it will be seen that one layer 
 is simply aside of the other. 
 
 74. But to return to Cells ; we have seen that the envelopes, or 
 outer walls of these, are composed of Cellulose ; generally, they are 
 found to possess contents of some kind. The Cellulose itself is 
 composed of sugar, gum, or vegetable jelly, which offers another form 
 of its chemistry, and while all plants are made up of similar cells, the 
 chief difference amongst them consists in the different form of the cells. 
 
 75. It frequently happens that only a nucleus is found ; this 
 differs materially in size and color ; thus in the fruit of a ripe Cherry 
 (Fig. 15), we have a series of cells widely differing in size, each con- 
 
 FIG. 14 
 
 FIG. 15. 
 
 Pith of Elder, according to authors. 
 
 Transverse section of a Cherry. 
 
 taining a large, fleshy, brownish-colored nucleus (a), the size of which 
 approximates to the dimensions of the cell containing it. Its surface 
 is seen to be covered with a series of minute spots, of greater inten- 
 sity of color the nucleoli, or smaller nuclei. 
 
 76. Other cells are formed for the reception of special contents, 
 which, as will be hereafter seen, are extremely various. 
 
 77. At the head of this list, however, fecula, or starch, in rela- 
 tion to human necessities, is most conspicuous; almost two-thirds 
 of the human family being nourished exclusively upon Starch, 
 
14 
 
 VEGETABLE PHYSIOLOGY. 
 
 LESSON 4. 
 
 78. This very valuable product constitutes an important ele- 
 ment of all the cereal (edible, as wheat, etc.) grains ; it forms the 
 nutritive principle of the leguminous plants (Peas, Beans], and is 
 more or less actively distributed throughout the vegetable kingdom. 
 It occurs in every plant, and it is found in every part ; it will only 
 pay the cost of separation, however, when found in the root, tubers, 
 seeds, fruits, and (more easily, as in the Sago Palm) the pith. 
 
 FIG. 17. 
 FIG. 16. 
 
 Corpuscle of Potato Starch, 
 magnified. 
 
 FIG. 18. 
 
 Section of Potato, showing 
 the starch in situ. 
 
 Corpuscle of Tous les mois, 
 magnified. 
 
 79. The Potato (Fig. 16) is found to consist of cells of variable 
 size, formed of cellulose, and filled with corpuscles of starch these, 
 too, vary remarkably, some being very large, others minute, and the 
 remainder of intermediate size, so that every cell may be quite full. 
 
 80. Examined by the Microscope, a corpuscle of starch (Fig. 17) 
 is a very interesting and beautiful object; each corpuscle possesses 
 somewhere, but its situation is uncertain, a circular spot called the 
 hilum; this is (erroneously) supposed to be its point of attachment 
 to the cell- wall. Around the hilum, a number of extremely delicate, 
 transparent, concentric rings are seen. 
 
 81. The observer will, however, sometimes look for these charac- 
 teristics in vain not a single corpuscle of the veritable tissue is 
 found to display them ! The secret is that the hilum and concentric 
 lines are placed only on one side, and the other side chances to be 
 uppermost. 
 
 82. The largest known corpuscles of starch in the vegetable 
 kingdom are found in Canna cocdnea, or Tous les mois (Fig. 18), a 
 plant extensively cultivated in the South of France; the peculiar 
 French name signifies " every month," and is given to the plant from 
 the circumstance of its flowering monthly ; here the hilum and con- 
 centric lines are distinctly seen. 
 
LESSON 4.] 
 
 GUMS AND SUGARS. 
 
 15 
 
 83. There are no two forms or species of starch precisely alike, 
 and the points of difference, although frequently minute, become 
 characteristic; thus it will be seen that the starch of Indian corn 
 (Fig. 19) differs materially from the forms yet presented. 
 
 84. The starch of Wheat (Fig. 20) offers another variety ; here 
 the corpuscle is nearly round, the hilum always in the centre, and 
 only one ring surrounding it. 
 
 85. We have examined the largest form of starch (Tous les mois) ; 
 we will now consider the smallest, Rice. The starch of this plant 
 (Fig. 21) is remarkable no less for the great irregularity of its form 
 than for its minuteness. The question has yet to be determined 
 whether or not starch be more or less nutritive in proportion to its 
 
 FIG 19. 
 
 FIG. 
 
 FIG. 21. 
 
 Corpuscles of Wheat 
 Starch. 
 
 Corpuscles of Rico 
 Starch. 
 
 Corpuscles of Indian Corn, 
 magnified. 
 
 size ; should it eventually be settled in the affirmative, Tous les mois 
 will undoubtedly take the first rank in the category, and Rice the 
 last; the Potato, and the contents of the leguminosse (peas, beans), 
 together with the Cereal grains, will then hold an intermediate place. 
 The Tous les mois is such a valuable form of starch, that it is much 
 to be regretted its cultivation has not been attempted in this country. 
 
 Now that we have a " Model Farm " in our midst, it is to be 
 hoped the attempt to raise it will be speedily made, and the results 
 made known, for the good of the community. There appears to be 
 no sufficient reason why the experiment should not be eminently suc- 
 cessful. 
 
 86. Starch is laid up by the plants forming it, as a store of nour- 
 ishment upon which they can draw for their subsistence in a season 
 of need ; hence, the quantity yielded differs in the same plant at dif- 
 ferent periods of its growth. Thus, starch abounds h>the potato 
 towards the latter part of the season, but it decreases in Spring, be- 
 cause of the germination of the tubers, which at such a time re- 
 quire to appropriate it. 
 
16 VEGETABLE PHYSIOLOGY. [LESSON 5. 
 
 LESSON Y. 
 
 THE SUBJECT OF STAKCH CONCLUDED. GUMS AND SUGARS. 
 
 87. It was found by experiment that 240 Ibs. of potatoes left in 
 the ground, contained of starch : 
 
 In August. 23 to 25 Ibs. 
 
 " September 82 " 88 " 
 
 " October 82 " 40 * 
 
 " November 38 " 46 " 
 
 " April 88 " 28 " 
 
 " May 28 " 20 " 
 
 88. The quantity of starch remained the same during the dor- 
 mant state in Winter, but decreased as soon as the plant began to 
 grow, and to require a supply of nutriment. 
 
 89. Starch exists in roots, stems, the receptacles of flowers, and 
 in pulpy fruits. The stem of the sago palm, the receptacle of the 
 artichoke, and the pulp of the apple, are situations in which starch is 
 found. 
 
 90. Instances are not wanting in which starch, used for human 
 food, is found associated with the deadliest poison ; thus in Jatropha 
 manihot, a euphorbiaceous plant, the Indians, while engaged in ob- 
 taining the tapioca of commerce, or cassava-meal, dip their arrow- 
 heads in the fluid that exudes, to the intent that they may be thereby 
 poisoned. A more fatal poison is not known than the deadly milk of 
 this euphorbiacean ! 
 
 91. Amongst the Cereals none are more valued for nutrient qual- 
 
 FIG. 22. FIG. 23. 
 
 Section of a grain of wheat Oryzopsis asperifolia, or Mountain Bice. 
 
 ity than wheat; this appears to arise from another element abun- 
 dantly found associated with starch in this grain, viz., glfiten. A por- 
 .tion of a grain of wheat, highly magnified (Fig. 22), displays the 
 pericarp (a), -showing a number of vessels cut through; the epis- 
 
LESSON 5.] GUMS AND SUGARS. 17 
 
 perm (b), an intermediate layer (c), the gluten cells (d), and the starch 
 cells (e). 
 
 92. It is well known that rice contains very little nutriment, 
 yet a wild species, found abundantly in "Wisconsin, and known as 
 mountain rice, appears to offer an exception to this rule. In a highly 
 magnified view of a section of Oryzopsis asperifolia, or mountain 
 rice (Fig. 23), we see the pericarp (a), of great substance, and filled 
 (apparently) with bordered pores. To this succeeds (b) the episperm, 
 followed by an intermediate layer (c), and beneath this layer the 
 
 -gluten cells (d), as in the Triticum (wheat). Lastly, we find the 
 cells (e) containing the minute corpuscles of starch. 
 
 93. In addition to the microscopical test for starch (hilum and 
 concentric rings), there is a simple chemical test of much impor- 
 tance, i. e., the Tincture of Iodine ; this re-agent has been briefly al- 
 luded to above 
 
 94. If a tissue suspected to contain starch be treated with a mi- 
 nute quantity (the less the better) of this fluid, and starch be present, 
 a beautiful purple color is the immediate result ; by this simple pro- 
 cess a new combination is formed the iodide of starch. Tincture 
 of iodine fails to produce a similar effect upon any other known veg- 
 etable tissue, and hence it may be regarded as an unfailing test of the 
 presence of Fecula. 
 
 95. By the action of malt, or of sulphuric acid, or by long boil- 
 ing in water, a gummy matter is produced from starch called dextrin, 
 or soluble starch. This material is now abundantly used as a cheap 
 and efficacious form of gum for envelopes, postage stamps, &c. By 
 many authors it is supposed that dextrin is formed of the substance 
 contained in the interior of the corpuscles ; at all events, the forma- 
 tion of dextrin is one of the first steps in the conversion of starch 
 into sugar. 
 
 96. GUM is a substance abundantly produced in the vegetable 
 kingdom. It is found in many seeds, exudes from the stems and 
 twigs of numerous trees, and is contained in the juices of others from 
 which it does not exude. 
 
 97. The different kinds of gum have been divided into those 
 which are soluble in cold water (gum arabic and mucilage), and those 
 which only swell up into a gelatinous matter (tragacanth, cerasine, 
 and pectine.) 
 
 98. Grum arabic, or gum Senegal, is produced by various species 
 of acacia, chiefly natives of Arabia ; hence its scientific name, gum 
 acacia, or, on the other hand, its common name of gum arabic. 
 
 2 
 
18 VEGETABLE PHYSIOLOGY. LESSON 6. 
 
 From the bark of these trees it exudes as a thick juice, which subse- 
 quently concretes into tears. 
 
 99. Gum arabic is combined with cerasine, in the gum of the 
 cherry and plum. 
 
 100. Mucilage is found in many of the mallow tribe, as marsh 
 mallow, and in linseed. 
 
 101. CERASINE is that part of the gum of the cherry (cerasus), 
 plum, and almond trees which is insoluble in cold water. 
 
 102. PECTINB is a substance procured from pulpy fruits, as the 
 pear and apple ; it forms a jelly with water, and when dried resem- 
 bles gum, or isinglass. 
 
 103. SUGAR is a substance which exists in many plants : they have 
 been divided into those which undergo vinous fermentation, as cane, 
 and grape sugar, and those which are not fermentesible, as mannite. 
 
 104. Cane sugar comes from the sugar-cane (Saccharum officina- 
 rum), beet-root (Beta vulgaris), sugar-maple (Acer saccharinum) , 
 Chinese sugar-cane (Sorghum sativum), and many other plants. 
 
 105. MANNITE is the chief ingredient of manna, which exudes 
 from the Ornus europcBa and Ornus rotundifolia ; it is exported from 
 Sicily and Calabria, under the name of flake manna. It is also 
 found in mushrooms, celery, and many species of sea- weeds. 
 
 LESSON VI. 
 
 OILS, WAX, CHLOEOPHYLLE, RESINOUS PRODUCTS, CAOUTCHOUC. 
 
 106. Oil abounds to a great extent in the vegetable kingdom, 
 and cells appear to be formed for its special reception ; it seems to 
 hold the same relation to the vegetable that fat holds to the animal 
 kingdom. 
 
 107. This substance is chiefly met with in the seeds of plants ; it 
 is highly nutritious (to the plant), and appears to nourish the em- 
 bryo, until organs are developed capable of obtaining sustenance from 
 other sources. 
 
 108. The oils found in plants are either fixed or essential. The 
 former are found (drying oil) in linseed ; fat oils from the olive 
 (Olea europcea), and solid, as lard, in the palm. 
 
 109. The fat oils contain a large quantity of stearine, and are 
 hence used as a substitute for animal fat in the composition of can- 
 
LESSON 6.] OILS, WAX, CHLOEOPHYLLE, ETC. 
 
 19 
 
 dies, and for greasing the wheels of locomotives and cars on railroads, 
 especially in Europe. 
 
 110. The valuable properties of castor oil, obtained from the 
 seeds of Ricinus communis, as a medicine, are well known. 
 
 111. THE ESSENTIAL OILS occur in the stem, leaves, flowers and 
 fruit of many odoriferous plants, and are procured by distillation 
 with water ; they are called essences, and contain the concentrated 
 odor of the plant. The most conspicuous of these are the oils of 
 cinnamon, otto or attar of roses, of peppermint, caraway, cloves, &c. 
 
 112. Amongst the seeds of plants used for human food, or nuts 
 as they are called, the almond claims attention. If a thin section of 
 it be made, and submitted to the microscope, a number of cells (Fig. 
 24) filled with a concrete oil will be seen. The masses into which it 
 resolves itself are of a variable size ; there is some difficulty in mak- 
 ing these preparations and preserving them, as the oil frequently 
 quits the cells, and follows the knife ; moreover, the great density of 
 the preserving fluid, causes the oil to flow out of the cells, and fuse 
 
 FIG. 25. 
 
 FIG. 24. 
 
 Section of Almond, showing 
 oil in situ. 
 
 Section of Cocoa-nut. 
 
 into large patches on the outside of the tissue ; cells thus emptied 
 are shown in the figure. 
 
 113. The cells of the Cocoa-nut also contain ^, concrete oil (Fig. 
 25), which", obtained by pressure, possesses much value as an oil for 
 lamps, and a material in the composition of candles. 
 
 114. WAX is another peculiar fatty substance, sometimes found 
 in the stem and fruit of plants. It is procured from several species 
 of Palms, the candle-berry Myrtle (Myrica cerifera, and Myrica 
 cordifolid] ; it is also found on the external surface of fruits, forming 
 the bloom of grapes, plums, &c., and on the leaves of many plants. 
 
 115. It is a popular opinion that the honey-bee forms, secretes, or 
 
VEGETABLE PHYSIOLOGY. 
 
 [LESSON 6. 
 
 deposits, the wax required to build its cells ; this, however, is a mis- 
 take, wax being solely a vegetable product, and neither the bee, nor 
 any other animal, is capable of secreting it. 
 
 116. During the active season of the year, when this material is 
 most needed, the bees seek those plants which their instinct tells them 
 supply the wax. 
 
 117. They possess the power of collecting it in a state of great 
 purity free from the extraneous materials with which it is more or 
 less combined. 
 
 118. With their jaws, they fashion it into thin scales, and place 
 them between the plates of the abdomen for safety, to be conveyed to 
 the hive for use. 
 
 119. Well may this singularly industrious little creature be called 
 laden ; with its stomach filled with nectar to be converted into honey, 
 its abdominal rings lined with cakes of wax, and the hollow spaces or 
 baskets of its thighs, and the hairs of its body filled, or covered with 
 grains of pollen for bee-bread. 
 
 120. The secretion of the ceruminous glands (ear-wax) of animals, 
 differs altogether from vegetable wax. 
 
 121. CHLOROPHYLLE, or the green coloring matter of leaves, is 
 allied to wax, being soluble in ether and alcohol, but insoluble in 
 water. 
 
 122. RESINOUS PRODUCTS. The milky and colored juices of plants 
 frequently contain resins mixed with volatile oils, in the form of 
 balsams. 
 
 123. These are either fluid or solid; 
 the former may be illustrated by the Bal- 
 sam of Tolu, Balsam of Copaiva, Carpathian 
 Balsam, Strasburg Turpentine, Canada Bal- 
 sam, and many others. The solid forms 
 may be illustrated by common resin. Bur- 
 gundy pitch, Mastic, Sandarach, Elami, 
 G-uaiacum, Dragon's blood, and others. 
 
 124. CAOUTCHOUC (India-rubber) is ana- 
 logous to essential oils ; it is found associated 
 with them and resinous matters, in the milky 
 juice of plants. It is procured from various 
 species of Ficus, as Ficus elastica, &c., by 
 wounding the plants. 
 
 Lactiferous vessels. 125. A kind of Caoutchouc, called gutta 
 
 percha, imported from Singapore, and Borneo, is procured from ISO- 
 
 FIG. 26. 
 
LESSON 7.] BAPHIDES. 21 
 
 nandra Gutta ; the chief difference between this gum and India-rubber 
 appears to be, that the milky juice that yields it (the latter) contains a 
 greater amount of starch. 
 
 126. The milky juice, above referred to, is contained in a system 
 of distinct vessels (Fig. 26), called lactiferous (lacta, milk) ducts; 
 this structure may be easily seen in the India-rubber tree (Ficus 
 elastica). Dandelion, Lettuce, Celandine, and the various species of 
 Ficus and Euphorbia. 
 
 127. Some of these milky juices are bland, as in the Cow-tree 
 (Oalactodendron utile] ; others are narcotic, as in the Poppy and 
 Lettuce ; others purgative, as Gamboge ; others diuretic, as Dandelion 
 (Taraxacum). 
 
 LESSOR YII. 
 
 EAPHIDES. 
 
 128. In addition to the various forms of cell contents already 
 enumerated mineral matter, having either lime as its basis, or silica 
 (flint), is abundantly found. Where flinty matter obtains, it fre- 
 quently assumes an acicular or needle-like shape hence called 
 JRaphides, from the Greek raphis, a needle. 
 
 129. The needle shape is not, by any means, universal ; they are 
 as frequently found of a Stellate (star) form, and not unfrequently as 
 single crystals, having an octohedral (eight sides), rectangular (right 
 angled), or prismatic (in form of a prism) form. 
 
 130. No part of the plant appears to be free from them ; they are 
 found in the stem, bark, leaves, stipules, sepals, fruit, root, spiral-ves- 
 sels, and even in the pollen. 
 
 131. Some plants are known to secrete Oxalic acid, which is a 
 fatal poison to man, and many other animals. 
 
 132. To counteract the effect of this vicious material, and neu- 
 tralize it, such plants (Onion, Pie-plant or fihubarb), feed greedily 
 upon Carbonate of lime. This earth has great affinity for the 
 oxygen of Oxalic acid ; they seek each other, combine, and in the form 
 of crystals of varying figure, the new compound is deposited in cells 
 as the Oxalate of lime a perfectly innocuous combination. 
 
 133. By this simple and beautiful arrangement, delicious and 
 nutritious vegetables are redeemed to the use of man, which, other- 
 wise, would prove speedily fatal to him. 
 
22 
 
 VEGETABLE PHYSIOLOGY. 
 
 [LESSON 7. 
 
 134. If the thin, transparent, and dried outer layer of a 
 FIQ 2T ripe onion be submitted to the mi- 
 
 croscope, a beautiful assemblage of 
 crystals of this newly formed miner- 
 al will be seen in the cells respec- 
 tively (Fig. 27). 
 
 135. These are sometimes octa- 
 gonal ; frequently prismatic. 
 
 136. When the lime has been suf- 
 ficiently abundant, and the fruit is 
 well developed, and of large size, 
 it is usual to find more than one 
 crystal in a cell; whenever this oc- 
 curs, they always form crosses, sometimes composed of two, fre- 
 quently of a plurality of crystals. 
 
 137. The root of the Pie-plant (Ehubarb) con- 
 tains a vast number of stellate crystals of oxalate of 
 lime. (Fig. 28.) 
 
 138. The common English rhubarb, so abun- 
 dantly cultivated in our Gardens, and offering such a 
 delicious, and highly nutritive material for pies and 
 tarts, in advance of all other fruits, contains a far less 
 amount of this mineral than the Turkey Rhubarb, so 
 valuable as a medicine. In the latter, it exists to so 
 
 FIG. 31. 
 
 Raphides ; Onion containing prismatic crys- 
 tals of Oxalate fluid. 
 
 FIG. 23. 
 
 Eaphides, Rhubarb. 
 
 FIG. 29. 
 
 Melon Cactus, the cells of Encephalatus pungens, containing starch and 
 
 which contain raphides. raphidian cells. 
 
LESSON 7.] 
 
 RAPHIDES. 
 
 23 
 
 great extent, that the only test for this root, as compared with the 
 English, which is frequently substituted for it, is to chew a small 
 piece of it, when if it be found particularly gritty (occasioned by the 
 crystals of oxalate of lime), its identity is assured. 
 
 139. Crystals of oxalate of lime, of the stellate form, are also 
 found in the Beet-root (Fig. 29), the melon cactus (Fig. 30), and (to- 
 gether with starch) in a Cycadaceous plant (Encephalartus pungens) 
 (Fig. 31). The bulb of the Squill plant (Squilla maritima) (Fig. 32) 
 contains raphides. 
 
 140. Oxalic is not the only acid found combined with lime to 
 
 FIG. 
 
 FIG. 33. 
 
 Squilla maritima. 
 
 Cells of Kumex, containing raphides. 
 
 form raphides in the plant ; on the contrary, phosphoric, malic, sul- 
 phuric, and carbonic acids, all contribute to the varied forms of these 
 crystals. 
 
 141. Phosphate of lime generally produces acicular crystals (a), 
 FIG. 34. as seen in the cells of Rumex 
 
 (Rhubarb) (Fig. 33) ; the leaf of 
 the maple also affords similar crys- 
 tals (Fig. 34). 
 
 142. So wonderfully abundant 
 are raphides in certain plants, that 
 
 Cells of Maple leaf, containing raphides. the kte p rof> Bailey (of Weflt 
 
 Point) computed in a square inch of Locust-bark, the thickness of 
 writing paper, more than a million and a half of these crystals ! 
 
 143. Certain species of the Cactus tribe of plants contain such 
 an inordinate quantity of raphides that they appear to be almost en- 
 tirely made up of them ; sometimes every cell of the cuticle contains 
 stellate crystals, whereby these plants are rendered exceedingly brit- 
 
24 
 
 VEGETABLE PHYSIOLOGY. 
 
 [LESSON 8. 
 
 tie, so much so, that the least touch will produce 
 a fracture. 
 
 144. The bark of trees is a source fruitful in 
 raphides ; they are abundantly found not only 
 in the Locust (as we have seen), but in the 
 Hickory, Apple, Pear, &c. 
 
 145. It has been remarked that the testa 
 (shell) of many seeds contain them, and a 
 figure is given (Fig. 35) of the testa of the seed 
 
 raphides. 
 
 LESSON VIII. 
 
 SCLEROGEN, OR LIGNINE. 
 
 146. This word comes from the Greek skleros, hard, and is ap- 
 plied to certain depositions found in the interior of cells. It is also 
 called Lignine, or woody fibre ; it is supposed to be a modified form 
 of cellulose. 
 
 147. The albumen of the fruit of a Palm (Phytelephas macro 
 carpa], hardened by this peculiar deposition, forms not only a most 
 beautiful object for the microscope, but it has become an important 
 article of commerce ; handles for canes and umbrellas are turned out 
 of this valuable substance, known as the nut, or vegetable Ivory ; 
 pipe bowls, and a variety of articles are fashioned out of it. 
 
 148. For a few months after it is gathered, it remains so soft 
 that it DC ay be easily cut in thin sections with a penknife, but expo- 
 sure to the atmosphere inspissates it, and it becomes so remarkably 
 hard that it can be turned, and highly polished in a lathe, with great 
 
 149. A thin section, examined by the microscope, presents a 
 charming appearance (Fig. 36). The cells are all distinctly visible, 
 each one containing in its centre a vesicle composed of sclerogen, or 
 lignine ; from this vesicle a series of tubes radiate to the inner mar- 
 gin of the cell- wall but they never pass through it to an adjoining 
 cell. In the nut ivory, the tubes are of unusual size, and have a 
 knobbed termination. 
 
 150. Those persons who eat pears and quinces, will have observed 
 that as they approach the seeds, in the centre of these fruits, their 
 
LESSON 8.] SCLEROGEN, OR LIGNINE. 25 
 
 teeth come in contact with a number of minute, hard particles in the 
 pulp cells ; they try to crush them with their teeth, but find them 
 much too dense. These constitute what is called the gritty tissue. 
 
 151. A thin slice of a pear examined by the microscope (Fig. 37), 
 shows that this tissue is made up of a variable number of distinct 
 particles (a), which form a mass, of uncertain size, amidst the pulp 
 cells (b). 
 
 FIG. 36. FIG. 37. 
 
 Nut Ivory. Gritty tissue of the Pear. 
 
 152. There can be no doubt that the intention of surrounding the 
 seeds with this peculiar tissue is, to afford them a certain degree of 
 protection ; and it appears to foreshadow the more perfect develop- 
 ment of a superior tissue designed for the same purpose (protection), 
 met with in the cherry, plum, peach, and other fruit stones. 
 
 153. Some of the elements of the gritty tissue, of increased size, 
 are shown in the accompanying figure (Fig. 38) ; in common with 
 
 FIG. 38. FIG 39. 
 
 Sclerogenous elements of gritty tissue, magnified Testa of Nut Ivory. 
 
 300 diameters. 
 
 other like tissues, there is a central vesicle, associated with radiating 
 tubes. 
 
 154. The testa, or husk, of the Nut Ivory (Fig. 39), presents a 
 very fine view of the arrangement of the sclerogen ; it is only neces- 
 
VEGETABLE PHYSIOLOGY. 
 
 [LESSON 8. 
 
 sary to grind it down thin enough to transmit light easily, and mount 
 it in fluid as a preparation. 
 
 155. Thin sections of the Peach, Cherry, and Plum stones, show 
 structures not very dissimilar ; these, together with the Hazel-nut, 
 Walnut (English), and Cocoa-nut, so much resemble the ultimate 
 structure of bone, as frequently to be mistaken for it ; there is only 
 one broad character that separates them in bone, the tubes con- 
 nected with the central vesicles (here called canaliculi, or little 
 tubes) freely anastomose (or join) throughout the tissue, whereas in 
 vegetable similar structures, the tubes are confined within the limits 
 of the cell- wall. 
 
 156. The Cherry-stone (Fig. 40) and the Peach-stone, very 
 much resemble each other; in both the like general arrangement 
 
 occurs. 
 
 157. But the culminating point of beauty of these tissues, appears 
 to be the Cocoa-nut, seen in transverse section (Fig. 41). The cells 
 
 FIG. 40. 
 
 FIG. 41. 
 
 Section of Cherry-stone. 
 
 and their internal vesicles are of 
 greatly increased size, as compared 
 with similar structures, and the 
 connecting tubes correspondingly numerous and delicate. 
 
 Transverse section of shell of 
 Cocoa-nut. 
 
 WOODY FIBRE. 
 
 158. Of all the forms of cells, the wood and bass-cells are most 
 important in the domestic economy of mankind. 
 
 159. The " bass-cells " are the longest of all ; their walls are gen- 
 erally very thick, and mostly much bent, but rarely marked with pores 
 or spiral fibres ; only in the silk plant (Asclepias Syriaca), the Olean- 
 der, and allied plants, is a spiral striation of the walls observed. 
 
 160. The materials used for ropes, cordage, linen, certain Indian 
 muslins, mummy cloth, and mats, consist of the woody fibre of plants, 
 from which the more delicate tissues have been removed by long-con- 
 tinued maceration in water. 
 
LESSON 8.] 
 
 SCLEROGEN, OR LIGNINE. 
 
 FIG. 42. 
 
 FIG. 43. 
 
 Linum usitatissimum, or Flax plant. 
 
 Cannabis sativa, or Hemp plant. 
 
 161. Flax (or lint) is thus procured from the bark of Linum 
 usitatissimum (Fig. 42), hemp, from Cannabis sativa (Fig. 43), New 
 
 FIG. 44. 
 
 FIG. 45. 
 
 Phormium tenax. New Zealand flax. 
 
 Zealand flax from Phormium tenax 
 (Fig. 44), and bass (or bast) from the 
 common Lime, or Linden tree. 
 
 162. Fibres are also procured for 
 manufacturing purposes from the Pine- 
 apple plant (Ananassa sativa}, from 
 
 Yucca gloriosa (Fig. 45), from Boehmeria nivea, which yields the 
 Chinese grass-fibre, from most of the plants belonging to the mallow 
 and nettle tribes, and from some of the leguminous plants. 
 
 163. The tenacity of different kinds of woody fibre, as^ contrasted 
 with silk, is given by De Candolle, thus : 
 
 Yucca gloriosa. 
 
28 VEGETABLE PHYSIOLOGY. [LESSON 9. 
 
 Silk supported a weight of 84 H>s. 
 
 New Zealand Flax 23 4 ' 5 
 
 Common Hemp 16 1-8 
 
 Common Flax 11 3-4 
 
 If the maceration of the fibre be carried on to much extent, a pulp is 
 formed from which paper is manufactured. 
 
 164. In ordinary paper the vegetable structure is entirely de- 
 stroyed, but in the Chinese rice-paper, which is not prepared by 
 maceration, and hi the paper of Japan, made from the mulberry, it 
 is preserved. 
 
 165. The structure of flax, so largely employed in the manufac- 
 ture of linen, is peculiar ; and to guard ourselves against those manu- 
 facturers who employ (frequently) a large percentage of cotton, to be 
 used in manufactures hereafter to be warranted " all linen," it is 
 worth the while to examine it. 
 
 166. If a linen thread be scraped with the thumb-nail to separate 
 
 it into its primitive elements, or ultimate fibres, and 
 placed under the microscope, an appearance will be 
 presented like Fig. 46. 
 
 167. It will now be seen that we have a series of 
 (apparently) solid, cylindrical, many-jointed fibres 
 the joints not very dissimilar to those of a bamboo 
 cane ; really, however, they are tubes, so nearly 
 filled with solid contents that it is by no means easy 
 to satisfy oneself of the fact. 
 
 168. The outer membrane of the tube is struc- 
 tureless, although, occasionally, delicate transverse 
 markings may be seen. 
 
 169. These tubes are of great length, and usually pointed at both 
 ends ; they are also remarkable for their toughness. 
 
 170. Cotton is not woody fibre, but simply the hair of the plant 
 producing it, and will be described under the proper head. 
 
 LESSON IX. 
 
 VASCULAE TISSUE. 
 
 171. The roots of a plant absorb a continued influx of nutrient 
 matter, whjch circulates through it, while the superfluous water is 
 evaporated by the stomata (breathing mouths). 
 
LESSON 9.] VASCULAR TISSUE. 29 
 
 172. This movement of the sap alters the form of the cells 
 through which it passes, and elongates them. 
 
 173. The walls of most of these elongated cells become thickened, 
 they have a tendency to aggregate, and thus is formed, in the midst 
 of the cellular tissue, bundles of elongated cells, or vessels, called 
 vascular bundles, which to the naked eye look like dense fibres 
 running through the tissue of the plant. 
 
 174. In one great division of plants (Monocotyledons], to which 
 the Grasses, Lilies, Palms, &c., belong, the development of these 
 vascular bundles stops short at a certain stage, and they undergo no 
 further alteration. 
 
 175. In another class, on the contrary (Dicotyledons), to which 
 belong our forest trees, kitchen vegetables, and many others, there is 
 a continuous development of cells on the outer side of each vascular 
 bundle, which become in turn vascular bundle cells, and so unceas- 
 ingly increase the thickness of the bundles. 
 
 176. As a consequence, they gradually close up together into a 
 firm tissue, or into that form we call wood. 
 
 177. In relation to human wants, these vascular bundles become 
 important on account of the chief portion of their contents (the spiral 
 fibre) constituting wood, and woody fibre, or bass. 
 
 178. Examined by the microscope, vascular tissue, in its original 
 development, presents itself as a spirally wound coil of woody fibre, 
 within a cell, of cellulose (Fig. 47). PIG 
 
 179. A vascular bundle, microscopically 
 examined, displays vessels in several distinct 
 forms ; some like Fig. 47, others becoming an- 
 nular ; annular vessels perfectly formed ; scal- 
 ariform (scala, a ladder) vessels ; and old ves- 
 sels either emptied of their contents, or filled 
 with woody fibre. 
 
 180. There appears to be great probabil- 
 ity for believing that spiral vessels are always 
 formed originally like Fig. 47 ; having sub- 
 served the purpose for which they were de- 
 veloped, they begin to degenerate ; this process 
 is, however, a slow one, and no great impedi- 
 ment appears to accrue for some time to the 
 transmission of the sap not until the ligneous Spiral vessels - 
 elements are entirely removed, or the old vessels be filled with them. 
 
VEGETABLE PHYSIOLOGY. 
 
 [LESSON 9. 
 
 FIG. 48. 
 
 FIG. 49. 
 
 Vessel becoming annular. 
 
 To substantiate these opinions, the following series of illustrations, 
 drawn from existing preparations, are offered. 
 
 181. The first stage of the process of disintegration appears to be 
 a concentration of the spiral element into a filament of greatly in- 
 creased robustness (Fig. 48) ; the newly formed spiral then throws 
 
 itself into a loose and irreg- 
 ular coil within the cell, the 
 parietes (sides) of the latter 
 becoming at this period par- 
 ticularly distinct; the ter- 
 minations of the filament ex- 
 hibit a tendency to form 
 rings, which having done, by 
 a process of absorption, they 
 are cut off, and separated by 
 an interval of space. This 
 process continues till the en- 
 tire tube contains only a se- 
 ries of rings, more or less 
 widely separated (Fig. 49), 
 now called annula, from anellus, a little ring. 
 
 182. The process of gradual decadence (decay) does not stop 
 here. It is very easy, by long continued maceration in water, to 
 separate these rings from the tubular envelope, for they, being com- 
 posed of woody fibre, can resist the action of water, to which the 
 tubes of cellulose must speedily succumb. These rings, thus obtained, 
 are shown at Fig. 50. In this view of them it will be seen that they 
 are not round, but compressed rings, with a variable number of 
 angles. 
 
 183. It is easy to understand that the process of absorption, al- 
 ready in operation to produce a series of rings out of a continuous 
 spiral thread, does not necessarily cease, and such appears to be 
 the fact. 
 
 184. One of the rings (A), has been divided into eight portions, 
 to show the like separation which occurs in nature ; absorption and 
 concentration having firstly formed the irregular filament, and second- 
 ly divided it into a series of distinct rings, still continues, by divid- 
 ing the rings respectively, all of them remaining in situ (situation, 
 place), and removing a portion of each divided fragment rounding 
 its extremities till a scalariform vessel (Fig. 51) results. 
 
LESSON 9.] 
 
 VASCULAK TISSUE. 
 
 31 
 
 185. From this point the absorptive process continues, until every 
 particle of ligneous matter is removed from the tube, which is now 
 
 FIG. 51. 
 
 FIG. 50. 
 
 Annular rings. 
 
 FIG. 52. 
 
 Scalariform v 
 
 Old vessel. 
 
 called an old vessel (Fig. 52) ; this either continues permanently 
 empty, or becomes filled with a bundle of woody fibre. 
 
 186. Spiral vessels are nearly round, F IG . 53. 
 annular vessels are more or less com- 
 pressed tubes, but scalariform vessels 
 
 preserve a beautifully symmetrical figure, 
 while an old vessel returns to the origi- 
 nal rounded form. 
 
 187. The figure of the scalariform^ 
 as compared with the annular, vessel, 
 seems to arise from the fact of the annu- 
 lar rings being broken up, and the tube 
 of cellulose readily yielding, between the 
 ligneous particles, to the pressure which 
 
 Uniformly Surrounds it. A beautiful Scalariform vessels, from stem of fern. 
 
 view of Scalariform vessels, from the stem of a Fern, is given in 
 Fig. 53, in which it will be seen that they form groups, of variable 
 size, in the midst of the cellular tissue. There cannot be a finer ex- 
 hibition of these vessels, than a transverse section of the stem of a 
 fern discloses. 
 
32 
 
 VEGETABLE PHYSIOLOGY. 
 
 [LESSON 10. 
 
 LESSON X. 
 
 POROUS AND DOTTED DUCTS. 
 
 188. In addition to the spiral, and other vessels already de- 
 scribed, tubes or canals are also found in plants ; these are called 
 duds, and give to woods their various degrees of porosity. 
 
 189. Spiral vessels can be easily unrolled ducts possess no such 
 capability, and hence the word duct is limited to such vessels as can- 
 not be unwound. 
 
 FIG. 54. 190. Dotted ducts are peculiar to firs, pines, and cone- 
 bearing trees; they consist of spindle-shaped, or fusiform 
 cells (Fig. 54), bearing a variable number, according to spe- 
 cies, of saucer-shaped discs, each having a small circle in the 
 centre. 
 
 191. These peculiar markings are formed by concave de- 
 pressions on the outside of the walls of contiguous tubes, 
 which are closely applied to each other, forming lenticular 
 (shaped like a lens) cavities between the vessels, like two 
 watch-glasses in close apposition ; when seen by transmitted 
 light they appear like discs. 
 
 192. This structure is common to, and characteristic of 
 duct"f the * ne cone-bearing trees ; the number of discs, or ducts, in a 
 
 Fir * given cell is found to differ in the several species, thus the 
 pine (Fig. 55) has only a single row in each cell ; the pinus strobus 
 (Weymouth pine, Fig. 56) has two rows of discs, arranged on the 
 same plane; whilst Araucaria has two and three rows (Fig. 57), ar- 
 ranged alternately. 
 
 FIG. 55. 
 
 FIG. 56. 
 
 FIG. 57 
 
 Dotted ducts of 
 the Pine. 
 
 Ducts of Pinus 
 Strobus. 
 
 Ducts, Araucaria. 
 
 193. These characters are so constant that, by the number of 
 discs in a cell, together with the mode of their arrangement, Fossil 
 
LESSON 10.] POEOUS AND DOTTED DUCTS. 
 
 Coniferous woods have been easily arranged in species ; a figure of 
 fossil wood, from a cone-bearing tree, is presented (Fig. 58). In this 
 illustration the cell is filled with four rows of alternate ducts. The 
 small spot in the centre of each concave disc, is supposed to be all 
 that remains of a series of vessels formerly (during the development 
 of the plant) existing in that situation. 
 
 FIG. 59. 
 
 FIG. 58. 
 
 Single duct, from Fossil wood. 
 (Much magnified.) 
 
 194. The vessels constituting the porous, dotted, or 
 pitted vascular tissue, are continuous tubes of large 
 size, and usually present broad or oblique extremities ; 
 but sometimes the terminations are pointed (Fig. 59). 
 Their dotted, or pitted, appearance is supposed to de- 
 pend on the mode in which the encrusting matter is 
 formed inside. In place of being deposited equally 
 over the whole surface of the membrane, as in ordinary 
 woody fibre, it leaves rounded uncovered spots at vari- 
 ous intervals, and these, when viewed by transmitted tlssue - 
 light, appear from their thinness to be perforations or holes. 
 
 195. In old dotted ducts it frequently happens, that the thin 
 membrane of the dots, or pits, has become absorbed, 
 
 and actual perforations taken place. 
 
 196. Dotted vessels often present a jointed Appear- 
 ance, such as is shown in Fig. 60 ; in such cases, they are 
 seen to be formed of dotted cells placed end to end, so 
 as to form continuous cylindrical tubes. 
 
 197. Dotted ducts are abundantly found in the wood 
 of trees, and they constitute the large rounded openings 
 seen in transverse sections of the stems of oak, pop- 
 lar, willow, &c. They also abound in the Bamboo, and 
 in other plants of rapid growth. 
 
 r r & Dotted vessels. 
 
 198. Porous ducts are very numerous in the Locust 
 
 tree, and are of great beauty (Fig. 61) ; it will be seen that the lower 
 3 
 
 Porous 
 
 FIG. 60. 
 
34 
 
 VEGETABLE PHYSIOLOGY. 
 
 [LESSON 11. 
 
 part of one duct, and the upper portion of another is shown together 
 with two perfect cells : the pores are bordered pores. 
 
 199. In the apple tree another form of porous vessel is found ; 
 a porous vessel with very minute pores placed in the interstices of a 
 double spiral, suddenly bulges out into an inordinately large cell, 
 destitute of pores, and having a number of lines, or bars, running 
 irregularly across it (Fig. 62) ; it does not appear that there is any 
 membrane between these bars, or lines, to connect them. 
 FIG. 61. 
 
 FIG. 62. 
 
 FIG. 63. 
 
 Porous duct, Locust Porous vessel, Apple. Porous duct, Basswood. 
 
 200. But the most beautiful ducts or vessels of this kind, are 
 found in the Basswood; here, they exist in great number and of 
 considerable length, having a uniform diameter for the greater part 
 of their course ; the ends are pointed. 
 
 201. They consist of a singularly beautiful double-spiral thread 
 (Fig. 63), in the meshes of which one, and sometimes two ducts are seen. 
 The whole of this structure is confined in a tube of cellulose, which, 
 under the microscope, presents a very glistening appearance. 
 
 LESSON XI. 
 
 SILICA. 
 
 202. This mineral, so abundantly found in all kinds of soils, uni- 
 versally throughout the surface of the Globe, is of the greatest conse- 
 quence to the vegetable kingdom. 
 
 203. We have already seen that certain vegetables have a para- 
 mount necessity for the Carbonate of lime ; with its assistance, as an 
 article of food, they nourish, and luxuriate without it, they perish. 
 
 204. The carbonate of lime rarely exists in its pure, original state, 
 
LESSON 11.] SILICA. 35 
 
 but is usually associated with an acid, sometimes oxalic, at other 
 times phosphoric, or carbonic acid. 
 
 205. Silica, on the contrary, is found in large quantity in vegeta- 
 ble tissues in all its integrity as pure flint. 
 
 206. There can be no doubt that the roots obtain this mineral 
 from the earth ; elaborate, or digest it, and reproduce it in a new and 
 characteristic form. 
 
 207. Each of the grasses, for example, affords a large supply of 
 this mineral ; but the/orw and arrangement of it is always peculiar, 
 and such as can only be found in that particular species, in which 
 such form, however, is constant. It may excite our wonder and sur- 
 prise to learn how it is possible for the roots of a plant to decompose, 
 that they may feed upon such an intractable substance as flint ! 
 
 208. Yet the process is a very simple and natural one : in addi- 
 tion to flinty materials, the earth contains large supplies of alkalies 
 potash and soda. 
 
 209. Silica, that resists the action of the most powerful acids, 
 succumbs to alkalies. By union with these elements, the flint is 
 dissolved to a fluid state, and forms the silicate of potash, or of soda, 
 as the case may be. 
 
 210. The Chemist can form artificial silicates : by a process of 
 manipulation of one kind, he forms a silicate soluble in water ; by 
 another process he makes an insoluble silicate. 
 
 211. By their effects it would appear that the silicates formed by 
 nature, are (originally) soluble / that they are so much reduced by 
 the addition of water as to become easy of access to the roots of the 
 plants which absorb them ; at the same time it is possible that the 
 superabundance of the alkaline materials, may render an insoluble sili- 
 cate sufficiently fluid to be appropriated by the roots. 
 
 212. Under any circumstances it is quite certain that the silica 
 found in plants after they have elaborated it, is always perfectly 
 insoluble. If, however, it be formed as a soluble silicate, then it 
 becomes insoluble in the tissues of the plant due, doubtless, to the 
 vital energies of the organism. 
 
 213. The mode by which the tissues of plants and animals become 
 silicifled, or fossilized, is a very simple one : they lie beneath the sur- 
 face of the earth, in and surrounded by the silicates of potash, or soda ; 
 these materials are gradually absorbed by the tissues, which, whether 
 wood or bone, are easily accessible to the transmission of fluids. 
 
 214. By slow and insensible degrees, through a long series of 
 years, the character of the original tissues gradually changes, the 
 
36 VEGETABLE PHYSIOLOGY. [LESSON 12. 
 
 fluid silica taking their place. None of the structures found fossilized 
 have a tendency to decomposition, and, from the moment they begin 
 to absorb liquid flint, this process is rendered impossible : they can 
 afford, therefore, to wait the development of time, and whenever the 
 circumstances are favorable, the aqueous particles are removed by 
 evaporation, and the solid silica alone remains. 
 
 215. This process is so remarkably slow in nature, that the soft 
 parts of animals are very rarely found fossil ; but they, in common 
 with bones and woods, may be easily converted into flint, artificially 
 and the softer the tissue (brain) the quicker and more certain the 
 experiment. 
 
 LESSON XII. 
 
 SILICA, (CONTINUED.) 
 
 216. Silica obtains to the greatest extent in the lowest forms of 
 vegetable life. A large class of minute (microscopical) organisms, 
 originally classed by Ehrenberg with the animal kingdom, are now 
 known to be vegetable, and from their possessing a double external 
 covering, like the bivalve (bis, two) shells, they are called Diatomacce 
 (two-atoms). 
 
 217. The loricae (shells) of the organic structures included under 
 this head are formed entirely of pure flint, the pattern (so to speak) 
 being always remarkable, peculiar, and limited to species. 
 
 218. The Arachnoidiscus (Spider's web disc), found in Peruvian 
 Guano (Fig. 64), is a very beautiful 
 
 example ; the specimen has been sub- 
 ject to long continued boiling in 
 strong nitric acid a usual method of 
 procuring these forms for microscopical 
 purposes to free them from the ex- 
 traneous materials with which they 
 were surrounded ; the exact, nay, 
 mathematical precision with which it 
 is divided, renders it a very remark- 
 able illustration. 
 
 219. Kindred forms are so abun- 
 dant, both recent, in all the fresh- Arachnoidiscus Ehrenbergii. 
 
 water pools, and fossil, constituting by far the greater part of the 
 
LESSON 12.] SILICA. 37 
 
 Earth's surface, that the temptation to figure and describe them is 
 very great ; belonging to the vegetable kingdom, too, such a proceed- 
 ing would be quite justifiable in this place but it would transcend the 
 limits of the present work. 
 
 220. The grasses, which include all the Cereal grains, Canes, 
 Horse-tails, &c., are conspicuous for the large amount of silica which 
 enters into their composition. Who has not marvelled at the singu- 
 larly erect position of a stalk of wheat, or rye, or barley, each support- 
 ing a heavy ear of grain at its summit ? 
 
 221. And yet how few persons have enquired how it is, and why, 
 that a slender stalk can grow so tall, and maintain, even against ad- 
 verse elements, its perpendicular, erect form. 
 
 222. If a piece of straw of wheat, or any other cereal, be boiled 
 in strong nitric acid, well washed in clean water, and examined by 
 the Microscope, the secret will be developed ; it will then be seen that 
 it is defended from the root to the summit with a coat of pure, beau- 
 tifully transparent silica, composed of millions of minute particles, 
 all nicely jointed or fitted to each other. 
 
 223. Upon this principle all the grasses are defended by a skele- 
 ton (as it were) composed of flint. The silica of the husk (chaff) of 
 the rye, is shown at Fig. 65 ; it consists of a number of long bars 
 
 Fio 65 (6), connected with smaller oval bodies (a) 
 
 these are the casts in flint of the stomata, or 
 breathing mouths. 
 
 224. The husks of all the cereals, together 
 with the hairs (palese), are also entirely cov- 
 ered with flinty matter, and those persons who 
 indulge to much extent in the use of oat-cake, 
 or brown bread, are liable to large concretions 
 of flinty matter (that no stomach can possibly 
 digest) forming in the intestinal canal, which 
 must necessarily (sooner or later) prove fatal. 
 
 225. In the Museum of the Royal College 
 
 of Surgeons, England, several such masses may be seen, all the result 
 of post-mortem examinations. 
 
 226. The Microscope has satisfactorily determined, long ago, that 
 some of these concreted masses are composed of silica of the oat, and 
 others of the silica of wheat, obtained from the intestines of the in- 
 veterate eaters of brown bread, or oat-cake. 
 
 227. There is a popular prejudice in favor of this description of 
 food, and used occasionally, and in moderation, it is well founded. 
 
38 VEGETABLE PHYSIOLOGY. [LESSON 13. 
 
 There can be no doubt that the minute particles of flint, liberated by 
 the digestion of the food, will have a tendency to slightly irritate the 
 mucous membrane of the stomach and bowels, thereby increasing the 
 circulation of the blood, and waking up (as it were) the dormant en- 
 ergies of the muscular coat of these tissues. But this increased ac- 
 tivity is intended to expel or digest the foreign enemy, the flint, and 
 when repeated attempts of this kind end only in failure, the stomach 
 and intestinal canal relapse into a state of increased torpor, and leave 
 the obnoxious substance to pass, or not, as it may ; these are the cir- 
 cumstances which originate concretions. 
 
 228. In the Kingdom of Saxony there is a mountain range 
 of many miles extent, composed of a white, pulverulent earth, 
 called by the inhabitants Berg-mehl, Mountain-meal. In seasons of 
 scarcity, the people are wont to mix this Berg-mehl with equal parts 
 of flour to make their bread, and assert that it is not unwholesome. 
 During a short period in the Summer months, this practice is found 
 in most seasons to prevail, without bad results. 
 
 229. Examined by the Microscope, the Mountain-meal is found 
 to consist principally of a number of minute fossil diatoms, but chiefly 
 of a form limited (almost) to this formation Campilodiscus clupeus 
 (Fig. 66). All that remains of this fossil is the flinty lorica (shell), 
 with its minute, sharp processes, which are likely to occasion the 
 same amount of irritation as that resulting from the flint of the 
 wheat, or oat. 
 
 LESSON XIII. 
 
 SILICA (CONCLUDED). 
 
 230. The silicious particles of the Oat (Fig. 67) resemble those 
 of the Rye, except that they are smaller in size ; in the Wheat (Fig. 
 68) they are not smaller; the same elements will be found in all these 
 illustrations, that is to say, the lengthened bar and the connecting 
 rounded piece a cast in flint of the breathing mouth. Moreover, 
 the bars have all serrated (toothed, like a saw) edges, by means of 
 which they lock into each other to form a continuous tissue, just as 
 the bones of the human skull interlock at the sutures. 
 
 231. The flint obtained from the husk of the Rice, differs some- 
 what from the preceding illustrations (Fig. 69). Here we find that 
 the bars are shorter and broader, the serratures finer and more uni- 
 
LESSON 13.] 
 
 SILICA. 
 
 31) 
 
 form in size ; the stomata are apparent as nucleated spots in a tortu- 
 ous line, which occupies the central portion of each bar. 
 
 232. The various species of Horse-tails (Equisetum) are remarl a- 
 ble for the large amount of flint found in their cuticular covering. 
 
 FIG. 67. 
 
 Campilodiscus clupens, from 
 the JSerg-inehl. 
 
 Silica of the Out. 
 
 FIG. 68. 
 
 
 Silica of the Wheat. 
 
 One species (E. hyemale), or Dutch rush, or scouring rush, presents a 
 flinty layer, which forms a fine object under the Microscope (Fig. 70). 
 
 233. The flint in this plant appears to be an accurate cast of the 
 tissue (cuticle) with which it is in contact ; every cell, and the nucleus 
 of every cell, is faithfully represented. 
 
 234. In addition to this structure of the cells, the stomata are 
 
 FIG. 69. 
 
 FIG. 70. 
 
 Silica of Eice. Equisetuiu Hyemale. 
 
 well represented, and, as will be seen by reference to the Fig. (a, a), 
 they are double the one internal, the other external. The internal 
 breathing-mouths are the large circles, with irregular openings; 
 through these openings, and through the transparent sides of the cir- 
 cles, the external stomata may be seen. These consist of a pair of 
 lips, which open in the direction of the long axis of the plant, and, 
 
40 VEGETABLE PHYSIOLOGY. [LESSON 13. 
 
 provided with coarse serratures on their internal margins, their ends 
 are attenuated (reduced, made thin) and accuminated (pointed). 
 
 235. The Dutch rush used to be employed extensively by cabi- 
 netmakers, to smooth their work, preparatory to polishing it, but 
 since the introduction of glass or sand paper, of various degrees of 
 fineness, it has fallen into disuse with these artisans ; it is still great- 
 ly employed, however, by plaster-of-paris figure makers, to file down 
 the seams left by the junction of the several parts of their piece- 
 moulds, and for this purpose it is invaluable. 
 
 236. The Bull-rushes, and all the plants of this order, also con- 
 tain large quantities of silica. 
 
 237. Silica, however, is not by any means restricted to the 
 Grasses; it enters into the composition of a vast number of plants, 
 in some of them associated with the cells of the bark in others with 
 the cells of the cuticles of the leaves. 
 
 238. In the latter situation it is found in a very common garden 
 shrub, which has no vulgar name, the Deutzia scabra ; on the upper 
 cuticle may be seen a series of large, exquisitely beautiful stellate 
 crystals of flint, of (comparatively) large size(Fig 71). 
 
 Fm. 71. 
 
 Upper cuticle, Deutzia scabra. 
 
 239. On the upper cuticle, the stars are composed of from 3 to 
 f) radii, four and five rays, however, being the most abundant. 
 
 240. The under cuticle has a much more dense number of smaller 
 stars, placed nearer together, and the rays of which amount to from 
 10 to 13 (Fig. 72). 
 
LESSON 14.] HAIES. 41 
 
 241. In this country, it appears that the domestics have dis- 
 covered the economic value of Deutzia, as they employ the leaves 
 with which to rub up and brighten their tin-wares a function they 
 must be very capable of per- FIQ 
 
 forming. 
 
 242. The quantity of Sil- 
 ica contained in the Canes, 
 especially the bamboo, is very 
 great ; in the latter it is fre- 
 quently found in the form of 
 a solid layer, between the 
 
 joints, Called Tabasheer." Under cuticle, D. scabra. 
 
 243. Reeds, from the large 
 
 quantity of Silica they contain, are said, during hurricanes in warm 
 climates, to have actually caused conflagrations, by striking against 
 each other, and producing flame by friction. 
 
 244. Silicate of potash in a vegetable sap may be mixed with ox- 
 alic acid, by which oxalate of potash and silicic acid will be pro- 
 duced, and thus the silica may be deposited in cells by this process 
 of double decomposition. 
 
 245. When these chemical compounds meet, they mutually de- 
 compose each other in this wise : Oxygen has more affinity for potash 
 than for the acid with which it has combined to form oxalic acid ; 
 it therefore quits the acid, which is set free, and joins the potash to 
 form a new compound oxalate of potash. Then the silica has more 
 affinity for the acid liberated by the oxygen than for potash ; it com- 
 bines with it, therefore, and forms silicic acid, and thus new com- 
 pounds result. 
 
 246. Chara translucens possesses a covering of silicic acid, which 
 could only have been formed in the manner indicated ; C. vulgaris 
 has a covering composed of silicic acid and carbonate of lime, while 
 Chara hispida has a covering of carbonate of lime alone. 
 
 LESSON XIV. 
 
 HAIES. 
 
 247. Hairs are composed of one or more transparent delicate 
 cells, proceeding from the epidermis, and covered with the cuticle. 
 
 248. Their form is very various ; some are erect, others oblique, 
 or they may lie parallel to the surface, as in the mullein. 
 
42 VEGETABLE PHYSIOLOGY. [LESSON 14. 
 
 249. Sometimes they are composed of a single cell, which is sim- 
 ple and undivided, or forked, or branched ; at other times they are 
 composed of many cells, either placed end to end, or united together 
 laterally, and gradually forming a cone, as in compound hairs. 
 
 250. Hairs occur on various parts of plants ; as the stem, leaves, 
 flowers, seed-vessels and seeds, and even in the interior of vessels. 
 
 251. Hairs are developed occasionally to a great extent on plants 
 exposed to elevated temperatures, as well as on those growing on 
 lofty mountains. Different parts of plants are transformed into 
 hairs, as may be seen in the flowering stalks of Ehus Cotinus, and in 
 the calyx of Composites. 
 
 FIG. 73. FIG. 74. 
 
 Macuna pruriens, or Oowitch. Dioncea muscipula, or Venus' Fly-trap. 
 
 252. On the pod of the Cowitch (Macuna pruriens), hairs are 
 produced with projections on their surface, which cause great irrita- 
 tion when applied to the skin (Fig. 73). 
 
 253. In Venus' Fly-trap (Dionwa muscipula), stiff hairs exist on 
 the blades of the leaf (Fig. 74), which, when touched, cause them to 
 close (a), thereby impaling the fly. 
 
 254. Cotton is simply the hair surrounding the seeds of Gossipi- 
 um herbaceum ; as they dry, they collapse into a flat band with 
 rather rounded borders, and ultimately become twisted (Fig. 75) ; by 
 these characters, the fibre of cotton can be readily distinguished un- 
 der the microscope from all other tissues, and when associated with 
 flax, can be identified, and counted with great precision. 
 
 255. The hairs most frequently met with in plants are called 
 lymphatic, from their not being connected with any particular secre- 
 tion. Those, on the other hand, which have secreting cells at their 
 base, or apex, are called glandular hairs. 
 
LESSON 14.] 
 
 HAIRS. 
 
 43 
 
 256. Glands are collections of cells forming secretions ; they are 
 either stalked or not stalked. The former are glandular hairs, hav- 
 ing the secreting cells at the apex. 
 
 FIG. 75. FIG. 76. 
 
 Fibres of cotton (Gossipium herbaceum). 
 
 Hairs of plants. 
 
 FIG. 78. 
 
 257. These stalked hairs are either composed of a single cell, with 
 a dilatation at the apex (Fig. 76, A), or of several cells united to- 
 
 Fig. 77. gether, the upper one being the secreting organ (Fig. 
 76, B). In place of a single terminating secreting 
 cell, there are occasionally two (Fig. 76, C), or more (D). 
 
 258. Hairs sometimes serve as ducts through which 
 the secretion Of glands is discharged ; these are glandu- 
 lar hairs, with the secreting cells at the base. Such 
 hairs are found in the ommon nettle (Fig. 77), in 
 Loasa, or Chili nettle, and in Malpighia, and are usu- 
 ally called stings. 
 
 259. In the Nettle (Urtica dioi- 
 ca), they consist of a single conical 
 cell, dilated at its base (see Fig.), 
 and closed at first at the apex by a 
 small globular button placed ob- 
 liquely (a). This button breaks off 
 on the slightest touch, when the 
 
 Hah^uS^i snar P extremity of the hair enters 
 oica (nettle), the skin, and pours into the wound 
 the irritating fluid which has been pressed out 
 from the elastic epidermal cells at the base. 
 
 260. When a nettle is grasped with violence, 
 the sting is fractured, and hence no injury is done Hair, Drosera rotundifo- 
 to the skin. 
 
44 VEGETABLE PHYSIOLOGY. [LESSON 15. 
 
 261. The globular apex of glandular hairs sometimes forms a 
 viscid secretion, as in the Chinese Sundew (Drosera rotundifolia). 
 The hairs of this plant, by means of its peculiar secretion, are 
 enabled to detain insects which chance to alight on them (Fig. 78). 
 
 LESSON XV. 
 
 CUTICLE. 
 
 262. This tissue in plants corresponds remarkably with the kin- 
 dred tissue in animals, especially in man. In both it is non-vascular, 
 transparent, more or less thick, and abundantly supplied with hair, 
 as we have just seen. 
 
 263. In plants, it is usually formed by a layer or layers of com- 
 pressed cells, which assume a flattened shape, and have their walls 
 bounded by straight or by flexuous lines. Every leaf presents a cu- 
 ticle on the upper and on the under surface, each composed entirely 
 of cells, but in many plants dissimilar in the two cuticles. 
 
 264. The cuticle is sometimes thin and soft, at other times dense 
 and hard. In the former case it may easily be detached from the 
 subjacent cells ; in the latter, the cells become thickened by deposits, 
 and sometimes the layers are so produced as to leave uncovered 
 spots, which communicate with the interior of the cell by canals pass- 
 ing through the thickened layers. 
 
 265. In terrestrial plants the breathing mouths (stomata) are 
 placed, generally, wholly on the under cuticle, but some plants have 
 in addition a few scattered organs of this description on the upper 
 cuticle. The object of placing these important organs on the under 
 surface of the leaf, is to protect them from the rain, which would in- 
 terfere with the due performance of their function if it fell upon the 
 surface to which they were attached. 
 
 266. Stomata open or close, according to the state of moisture or 
 dryness in the atmosphere. By examining under the microscope, 
 thin strips of cuticle in a moist and dry state, it will be seen that in 
 the former case the lips are distended ; they assume a crescentic or 
 arched form, and leave a marked opening between them ; while in 
 the latter, they approach each other, and close the orifice. 
 
 267. The number of stomata varies from a, few hundreds to many 
 thousands on a surface of one inch square. 
 
LESSON 15.] 
 
 CUTICLE. 
 
 45 
 
 268. This fact will be best illustrated by reference to the follow- 
 ing table : 
 
 STOMATA IN ONE INCH SQUARE. 
 
 Upper side. Under side. 
 
 Mistletoe 200 200 
 
 Tradescantia 2,000 2,000 
 
 Rheum Palmatum 1,000 40,000 
 
 Crinum amabile 20,000 20,000 
 
 Aloe 25,000 20,000 
 
 Clove-pink 38,500 38,500 
 
 Yucca 40,000 40,000 
 
 Mezereon None 4,000 
 
 Poeony None 13,000 
 
 Vine None 13,600 
 
 Holly None 63,600 
 
 Cherry-laurel None 90,000 
 
 Lilac Few 160,000 
 
 269. Stomata are not usually found on leaves always submerged ; 
 but in floating leaves they are restricted to the upper surface ; neither 
 
 FIG. 79. 
 
 FIG. 81. 
 
 Cuticle, Ivy. 
 Cuticle, Euscus aculeatus. 
 
 are they ever found on the upper surface of leaves which have a dense 
 shining cuticle. 
 
 270. In Euscus aculeatus 
 (Butcher's broom, Fig. 79), 
 the cells of the cuticle are 
 very symmetrical, and the 
 stomata (a, a) well seen. 
 
 271. The under cuticle of 
 the Ivy (Fig. 80), is distin- 
 guished by the* wavy lines, 
 which constitute the outer 
 walls of the cuticular cells; 
 
 the stomata in this plant (a) Cuticle, White niy. 
 
 are well marked, and of large size. 
 
 272. In the White Lily (Fig. 81), the cells of the cuticle, and 
 
46 VEGETABLE PHYSIOLOGY. [LESSON 16. 
 
 the stomata, are both unusually large, and present a very beautiful 
 view of this important structure. 
 
 LESSOJST XYI. 
 
 LEAVES. 
 
 273. Leaves are expansions of the bark, developed in a sym- 
 metrical manner, as lateral appendages of the stem, and having a 
 connection with the internal part of the ascending axis. They 
 gradually expand in various ways, acquire vascular tissue, and ulti- 
 mately assume their permanent form and position on the axis. They 
 may be divided into aerial and submerged leaves, the former being 
 produced in the air, and the latter under water. 
 
 274. Aerial leaves. These leaves consist of vascular tissue in 
 the form of veins, ribs, or nerves, of cellular tissue or parenchyma 
 filling up the interstices between the veins, and of a cuticular 
 covering. 
 
 275. The vascular system of the leaf is continuous with the 
 stem, those vessels which occupy the internal part of the stem be- 
 coming superior, or placed on the upper surface, in the leaf; while 
 the more external are placed on the lower surface. The vascular 
 
 FIG ^ system is well displayed 
 
 in what are called skele- 
 ton leaves, in which the 
 cellular part has been 
 removed, and the fibro- 
 vascular left. 
 
 276. The vascular 
 system of the leaf is dis- 
 tributed through the cel- 
 lular tissue in the form 
 of simple, or branched 
 veins. 
 
 277. The parenchy- 
 ma (para, beside or 
 
 Section, melon leaf. , , 
 
 between ; chyma, any 
 
 thing spread out, a tissue) of the leaf is the cellular tissue surround- 
 ing the vessels, and enclosed within the upper and under cuticles. 
 
LESSON 16.] LEAVES. 47 
 
 278. It is formed of two distinct series of cells, each containing 
 chlorophylle, or green colored granules, but differing in their form 
 and arrangement. This is best seen by making a vertical section of 
 a leaf and examining it by the microscope. One of these layers is 
 connected with the upper surface, and consists of compact oblong 
 cells placed endwise (Fig. 82, a) ; the other, connected with the lower 
 side, consists of loosely aggregated cells, having numerous cavities 
 between them (5), and, when these cells have an elongated form, 
 their long diameter is always parallel with the cuticle. 
 
 279. The cells on the upper side are usually placed close to each 
 other, without any space between them, except in cases where sto- 
 mata occur (e). 
 
 280. The figure (82) represents a section of a melon leaf, per- 
 pendicular to the surface. The upper cuticle is marked c; it shows 
 hairs (d) on its surface, and two openings of stomata (e). Below the 
 upper cuticle are layers of oblong cells (a), with two spaces between 
 them (/), communicating with stomata. The lower cuticle (g) } also 
 exhibits hairs and stomata; and above it are layers of loose cells (5), 
 with numerous lacimse (openings, h). The vascular bundles running 
 through the parenchyma are marked i. 
 
 281. In a vertical section of a leaf of the common garden Balsam 
 (Balsamina hortensis. Fig. 83), we see 
 
 the upper cuticle at a ; in the section 
 from which the drawing was made, al- 
 though only one layer of cells thick, 
 there are two, and three layers of the 
 upper and under cuticle. A double 
 series of compact, oblong cells, beneath 
 the upper cuticle are shown at 6, the 
 smaller cells, belonging to the central, 
 and under portion of the leaf, c ; be- 
 tween this layer are two spiral vessels, 
 d; the under cuticle, containing nu- 
 merous stomata, e. 
 
 282. The green color of leaves is 
 wholly due to the chlorophylle (chloros, 
 green; phyUum, a leaf) contained in 
 
 the oblong and other shaped cells; in this respect these cells bear 
 very close analogy to the color-producing or pigment (paint] cells 
 of the human family, and other animals. 
 
 283. The dark color of the skin of a negro, or of an Indian, is 
 
48 
 
 VEGETABLE PHYSIOLOGY. 
 
 [LESSON 17. 
 
 FiG.St 
 
 solely due to the secretion of color-cells, or pigment, in a certain 
 layer of the skin ; the human hair, and the hair 
 of animals, depends for its color on a like se- 
 cretion within the cells of the pith and cortical 
 substance ; and the black, or choroid coat of the 
 eye, in man and animals, is solely composed of 
 minute cells, filled with infinitesimal particles 
 of a black paint. 
 
 284. It is interesting to observe that the 
 same law is in operation to give color to the 
 leaf of a tree, and the skin, and other parts of 
 a man. 
 
 285. It only remains to show the vascular 
 system of a leaf, and for this purpose the leaf 
 of a cherry tree is selected. Here the stalk 
 (petiole) ends in a single mid-rib (Fig. 84, a, a) ; 
 this gives oft primary veins (&), which subdi- 
 vide into secondary veins (c), curving within 
 the margin. 
 
 Clierry leaf. 
 
 LESSON XVII. 
 
 OF THE STEMS OF TEEES. 
 
 286. The anatomical character of the stems of trees must now be 
 considered. This structure consists of the elementary tissues, vari- 
 ously combined, and arranged in different ways. 
 
 287. In some plants the part which represents the stem is entire- 
 ly composed of cells, which take the form of very narrow filaments ; 
 they are either simple or branched, as in some of the fungi and con- 
 fervse, or they form an expanded thallus, or frond (a term applied to 
 the stem of certain plants, where the stalk and leaves are so inti- 
 mately blended that they cannot be separated). In well formed, 
 conspicuous stems, cellular and vascular tissue are both present. 
 
 288. Such stems always have as the basis of their structure a 
 dense cellular parenchyma, in the midst of which is usually found 
 fibro-vascular bundles, or fasciculi of woody fibres, with ducts of va- 
 rious kinds, and generally associated with spiral vessels. 
 
 289. It is in the mode of arrangement of these bundles, that the 
 
LESSON 17.] STEMS OF TREES. 49 
 
 important difference exists between the plants called Endogenous 
 and Exogenous; for in the former, the bundles are dispersed 
 throughout the whole diameter of the plant, without any particular 
 plan, the intervals being filled by cellular tissue. 
 
 290. In the latter they are arranged side by side, so that a hol- 
 low cylinder of wood is formed, which includes within it the pith, 
 whilst itself is enclosed in another (outer) layer the bark. 
 
 291. But there is yet another and lower form of vegetable life 
 Acrogens ; in these the bundles of vessels are simultaneously pro- 
 duced, and the additions to the stem take place at the summit, by 
 the union of the bases of the leaves tree-ferns afford an example. 
 
 292. Thus we have, 
 
 Acrogens (from akros, summit; genncein, to produce), or sum- 
 mit growers. 
 
 Endogens (from endon, within), or inside growers. 
 
 Exogens (exo, outward), or outside growers. 
 
 298. But other and important distinctions still further define 
 these three orders of plants, even in their earliest state. Thus, 
 Acrogens have a cellular embryo, which has no cotyledon (Greek for 
 seed-lobe) ; or, in other words, has no leafy appendages to the young 
 plant ; they are called therefore Acotyledonous (a, without). Endo- 
 gens have an embryo with one cotyledon, and when sprouting send 
 up a single seed-leaf; these therefore are called Monocotyledonous 
 (monos, one). Exogens possess two such seed-lobes, or cotyledons, 
 and are called Dicotyledonous (dis, two). 
 
 294. Consequently, Acrogens are Acotyledonous. 
 
 Endogens are Monocotyledonous. 
 Exogens are Dycotyledonous. 
 
 295. In all parts of the globe, Exogens are by far the most nu- 
 merous of the Vegetable Kingdom ; the forest trees of the World 
 are Exogens, although in warm climates they are found associated 
 alike with Endogens and Acrogens, which, in such climates, are 
 more abundant, and attain greater size, than in more temperate 
 regions. 
 
 296. In its external aspect the Acrogenous stem greatly re- 
 sembles the Endogens / it is unbranched, usually of small, nearly 
 uniform diameter, and produces leaves at its summit (Fig. 85). 
 
 297. The Tree Ferns, which furnish the best example of this 
 kind of stem, are met with only in hot climates. 
 
 In India, they present a stem from six inches to eight inches in 
 diameter, and attain a height of from fifty to sixty feet. 
 4 
 
50 
 
 VEGETABLE PHYSIOLOGY. 
 
 [LESSON 17. 
 
 FIG. 85. 
 
 The foliage, consisting of leaves 
 ten or twelve feet in length, is always 
 produced at the summit ; and, as the 
 stem continues to grow, the leaves 
 make an impression on it which be- 
 comes permanent, and adds greatly to 
 its external beauty. 
 
 For the reason above given, this 
 stem may be known at a glance ; but, 
 if a doubt exist, it will be immediately 
 removed by examining its internal 
 structure, as seen in transverse sec- 
 tion. 
 
 FIG. 86. 
 
 Tree Fern. 
 
 Section of Tree fern, transverse. 
 
 298. A transverse section of an 
 acrogenous stem (Fig. 86), shows a 
 circle of vascular tissue composed of 
 masses (a), of various forms and 
 sizes, situated near the circumfer- 
 ence; the centre (b) being either 
 hollow or formed of cellular tissue. On the outside of the vas- 
 cular circle, cells exist (c), covered by an epidermal layer (e), 
 often of hard and dense consistence, originally formed by the bases 
 of the leaves, which remain for a long time attached to the stem. 
 The vascular masses (a) are bordered by dark-colored woody fibres 
 (f) ; the pale-colored vessels, generally scalariform, which occupy 
 the centres of the vascular masses, are shown at g. The vascular 
 system is of greater density than the rest of the tissue, and is usually 
 distinguished by the dark color of the layer which surrounds the 
 paler vessels. 
 
LESSON 18.] THE ENDOGENOUS STEM. 51 
 
 LESSOJST XYIII. 
 
 THE ENDOGENOUS STEM. 
 
 299. Endogenous stems have no separable bark; no distinct con- 
 centric circles ; the vascular circles are progressive and definite, the 
 solidity diminishing from the circumference to the centre ; no dis- 
 tinct pith ; no medullary sheath nor medullary rays ; the cellular 
 tissue being interposed between the vascular bundles. 
 
 300. For the full development of the Endogen we must seek hot 
 climates, there it is that its peculiar mode of growth is seen in per- 
 fection. The palms and screw pines offer the best examples; the 
 former have simple, unbranched, cylindrical stems, attaining to a 
 great height, and covered by a large mass of remarkable foliage. 
 
 301. The peculiar structure of this order of plants, will be best 
 seen by reference to the accompanying figures; the first (Fig. 87, A), 
 
 Fio. 87. 
 
 Monocotyledonous stem. 
 
 is a transverse, and the second (B), a longitudinal section of the 
 same stem ; the letters in both refer to the like structures. 
 
 302. In its early state the Endogenous stem consists entirely of 
 cellular tissue ; but as it increases in age, vascular bundles are pro- 
 duced, and these consist of woody fibre, spiral, dotted, and lactiferous 
 vessels. 
 
 303. The cellular tissue (a, a, a, a) is here seen distributed 
 
52 VEGETABLE PHYSIOLOGY. [LESSON 19. 
 
 throughout the section ; from the outer layer of it, which represents 
 the bark in the Exogen, to the internal portion which, in the same 
 order, would be the pith it is, in fact, only interrupted by the vas- 
 cular bundles. 
 
 304. The dotted vessels are seen at &, b, b, b ; c, c, c, c, are the 
 woody fibres, and d, d, d, d, the spiral vessels. 
 
 305. From the peculiar mode of growth of the Endogenous stems 
 they have perfect immunity from the effects resulting to Exogenous 
 stems, of the parasitic plants which cling to, and climb around them. 
 
 306. In the Endogenous stem the soft part is internal, whereby 
 the outer portion, from its greater density, is enabled to resist the 
 pressure of the climber; but in the Exogenous stem the soft wood is 
 external, and consequently yields to the least pressure, and climbing 
 plants, therefore, make deep and permanent indentations in the 
 latter. 
 
 307. Some Endogenous stems grow with such rapidity, that the 
 sudden increase of the outer part occasions a rupture of the central 
 cells, and by this means the hollow in the stems of grasses is pro- 
 duced. 
 
 308. The vascular bundles, in the Bamboo, cross the stem, and 
 form a series of partitions which divide the cane, and give it a jointed 
 appearance ; between these partitions, however, the central cells have 
 been ruptured, in the manner above alluded to. 
 
 LESSON XIX. 
 
 THE EXOGENOUS STEM. 
 
 309. Like the Endogenous, the Exogenous stem in its earliest 
 condition is wholly cellular. 
 
 310. By degrees, and as the plant increases in age, the cellular 
 tissue begins to be traversed by vascular bundles, which soon di- 
 vide the stem into two marked portions ; one of these forming the 
 central pith, or medulla ; and the other forming the cortical bark, 
 covered with epidermis. The connection between these two portions 
 (pith and bark) is maintained by lines of cellular tissue, called me- 
 dullary rays, which are interposed between the vascular bundles. 
 
 311. The complete structure of mature exogenous stems, which 
 
LESSON 19.] 
 
 THE EXOGENOUS STEM. 
 
 53 
 
 die down annually, consists of a central cellular pith, a circle of vas- 
 cular bundles in the form of wedge-shaped masses, an external bark, 
 with its integumentary covering, and rays connecting the pith to the 
 bark. 
 
 312. In stems which are not annual, the growth of the second 
 year consists of a new formation of vascular bundles outside the pre- 
 viously formed layer, between it and the bark. 
 
 313. Between the pith and bark also, there are annually formed 
 a layer of active, formative cells, called cambium cells, which are 
 concerned in the development of new woody fibres. In illustration a 
 transverse section of the maple 
 
 (Fig. 88, A) is shown, at the com- 
 mencement of its second year's 
 growth ; a longitudinal section of 
 the same plant (B) is combined 
 with the former, and the letters of 
 reference apply to the like tissue, 
 in both sections. 
 
 314. The layer of spiral vessels 
 which surround the pith, and con- 
 stitute what is called the medulla- 
 ry sheath, are seen at a ; the me- 
 dullary rays pass through this 
 layer, at different points, to the 
 bark ; at b are the porous or pitted 
 vessels, presenting (in A) large 
 
 rounded openings ; c, c, fibres formed of fusiform tubes, the letter to 
 the right hand marking the fibres forming the wood of the stem, and 
 the letter to the left, those which form the cortical fibres of the inner 
 bark ; d, cambium cells, between the wood and bark ; e, e, cortical 
 cells, often of a greenish color, forming a cellular layer of bark ; /, 
 outer cellular layer of bark, composed of cubical colorless cells, often 
 of a corky nature, and hence called suberous ; this cortical layer is 
 covered by the general integument, or epidermis. 
 
 315. Thus, at the commencement of the second year's growth, 
 there is a distinct formation of cambium cells, by the action of which 
 a new layer of wood and a new layer of fibrous bark is formed, and 
 these cambium cells, being in connection with the medullary rays, 
 keep up the connection between the medullary and cortical cells. 
 
 316. It is exceedingly interesting and instructive to notice the 
 changes that take place in the permanent woody stem of the exoge- 
 
 Exogenous wood. Maple. 
 
54 
 
 VEGETABLE PHYSIOLOGY. 
 
 [LESSON 19. 
 
 nous plant, after three years' growth ; this is shown in Fig. 89. The 
 yearly growth of the woody fibre is marked by the figures 1, 2, 3, 
 and the same letters apply to like tissues in both figures, A being the 
 transverse and B the longitudinal section. The pith, a, a, consisting 
 of hexagonal cellular tissue, 5, b, >, pitted or dotted vessels, and c, c, 
 c, woody fibres of successive bark ; d, d, spiral vessels of the medullary 
 sheath ; e, e, layer of cambium cells, between wood and bark ; /, /, 
 inner fibrous layer of bark , g, g, cellular envelope, forming middle 
 layer of bark ; A, A, outer corky layer of bark ; i, i, medullary ray 
 which, in the transverse section (A) is seen running without interrup- 
 tion from the pith to the bark ; but in the logitudmal section (B) it 
 
 FIG. 
 
 Exogenous, or Dicotyledonous wood. 
 
 is mutilated, owing to the slight flexure which usually occurs, and 
 which generally prevents us from tracing the ray in an undivided 
 straight line, when the stem is cut longitudinally. 
 
 317. Thus it will be found that the tissues have been produced in 
 the following order : first year the pith, surrounded by spiral vessels, 
 or medullary sheath, outside of which are the pitted vessels and 
 fibrous tissue of the first year's growth. 
 
 318. In the second year, the pitted vessels succeed to the woody 
 fibrous tissue of the first year, and these vessels are followed by the 
 deposition of woody fibre, forming the second annual layer. 
 
 319. The third year commences with the formation of pitted ves- 
 
LESSON 20.] THE REMAINING TISSUES. 55 
 
 sels, succeeded by woody fibre, as before ; but now the bark must be 
 formed : it has existed already twice before ; but, when no longer re- 
 quired as such, its structure has become transformed into the woody 
 fibrous tissue in many Exogens, however, its elements remain 
 permanently. 
 
 320. To the woody fibres, cambium cells succeed, then, the inner 
 fibrous layer of the bark; next, the cellular envelope, , which forms 
 the middle layer of the bark; and, lastly, the outer corky layer, cov- 
 ered with epidermis. 
 
 321. It is only necessary, now, to describe briefly the characteris- 
 tics of these tissues severally, by way of recapitulation, and first- 
 ly of 
 
 322. The ivood. The layers of wood are formed outside the me- 
 dullary sheath, or the vascular zone which surrounds the pith. 
 
 S23. They consist of woody fibres, mixed with dotted ducts, oc- 
 casionally mixed with annular, reticulated, and spiral vessels. In the 
 young state the tubes of the woody tissue are pervious, but by de- 
 grees they fill up by the deposit of lignine within them. 
 
 324. In old, exogenous trees, the central wood is hard and dura- 
 ble, Constituting the Heart-ivood, while the external layer is soft, and 
 forms the Albernum or Sap-wood. 
 
 325. The ligneous matter forming the heart-wood of some trees, 
 acquires color ; thus it is black in the Ebony, brown in the Black 
 Walnut, yellow in the Barberry and Judas-tree, purple in the Red 
 Cedar, and green in the Guaiac tree. 
 
 326. The proportions between the heart-wood and alburnum dif- 
 fer greatly in different trees ; those, however, in which the hard wood 
 predominates are best suited for building, and better adapted to with- 
 stand the attacks of insects, or the wet or dry rot. 
 
 327. The durability of wood depends on the nature of the lignine, 
 and this greatly varies in different trees. 
 
 LESSON XX. 
 
 THE EEMAINING TISSUES. 
 
 328. The Medullary Bays. These consist of flattened, cellular 
 tissue, having the appearance of bricks in a wall ; in the young stem 
 
56 VEGETABLE PHYSIOLOGY. [LESSON 20. 
 
 these rays are large, but in the more advanced woody stem, they ap- 
 pear as lines only. This tissue constitutes the " silver grain " of ma- 
 ple, and other trees, when cut in the direction from the pith to the 
 bark. 
 
 329. They do not proceed in a continuous line, however, from the 
 top to the bottom of the tree, but pass through the woody fibres in 
 such a way as to be interrupted in their course. 
 
 330. The medullary rays in some plants (Clematis) are large and 
 broad, while the woody wedges are comparatively small ; in most exo- 
 genous plants these rays are complete, but in the Cork-oak, and 
 others, they only extend partially through the stem. 
 
 331. Cambium Layer. This layer is found between the wood 
 and the bark, and has been originally connected with both. 
 
 332. It is composed of a layer of nucleated cells, formed in a 
 mucilaginous fluid called Cambium, and they are concerned in the 
 formation of the woody tubes of the inner bark, and in the addi- 
 tions made to the cells of the medullary rays. 
 
 333. In the Spring of the year, during the flow of the sap, these 
 cells are actively engaged in the process of growth, at which time the 
 bark may be easily separated from the wood. 
 
 334. The Bark. Originally this tissue is composed of uniform 
 cellular tissue, resembling that of the central part of the stem ; trans- 
 formations take place, however, in the progress of growth, by which 
 fusiform (spindle shaped) tubes are formed in the inner portion of 
 the bark next to the woody circle. 
 
 335. This portion is called the inner bark ; it consists of woody 
 fibre, and some lactiferous vessels ; it is the fibrous part of the bark, 
 and is frequently called Bass, or Bast tissue. 
 
 336. These fibres are long and tenacious, and are employed ex- 
 tensively for economic purposes.; those of the Lime-tree, Hemp, 
 Nettle, and Daphne canndbina, are employed for different articles 
 of useful manufacture. 
 
 337. Sometimes the fibres separate, so as to form meshes, as in 
 the Lace-bark tree ; at other times they form a continuous layer, as 
 in the Horse-chestnut. 
 
 338. The most remarkable fact in connection with woody fibre, 
 is its immunity from decay ; worn to rags, in an apparent state of 
 thorough disintegration as linen, it is doomed again to meet our gaze 
 in a new form as paper. 
 
 339. The value and importance of woody fibre, as applied to do- 
 mestic manufactures, cannot be overrated, and appears to have been 
 
LESSON 20.] THE EEMAINING TISSUES. 57 
 
 known at a very early period of the world's history ; thus we find 
 that the ancient Egyptians were as well acquainted with the value 
 and importance of flax, as employed in the construction of linen, as 
 we are. 
 
 340. They used it expressly for this purpose, to the exclusion of 
 every other vegetable tissue ; the mummy-cloth, in which the bodies 
 of the dead were enrolled, and of which such amazing quantities were 
 used, no less for the mummified remains of cats, the Ibis, bullocks' 
 heads, &o., than for the needs of poor humanity, was composed en- 
 tirely of flax. If the deceased person chanced to be a King, or a 
 Priestess (probably, also, any very distinguished person), a layer of 
 beautifully "fine linen " was placed next to the body. 
 
 341. Belzoni, the celebrated Egyptian traveller, brought to Eng- 
 land, and placed in the British Museum, the Sarcophagus, containing 
 the body of a King, exhumed from the tomb of the ancient Kings of 
 Thebes. The Sarcophagus was in the last stage of decay, but the 
 vegetable papyrus, which recorded the rank of the deceased, and the 
 date of his demise, together with the several layers of mummy cloth, 
 were as perfect as though made yesterday ! And yet this body had 
 lain in the tomb upwards of five thousand years ! 
 
 342. But a still older mummy may be seen in the Muesum of the 
 Vatican at Rome ; the individual is admitted to have lived contem- 
 poraneously with the Patriarch Abraham yet the mummy cloth is 
 by no means decayed ! 
 
 343. These facts are well known to persons possessing Micro- 
 scopes, and curious in such matters, who have had no difficulty in pro- 
 curing specimens for examination.* We have seen that the layer 
 placed next to the body was of fine texture, and free from bitumen ; 
 the layer which succeeded this was somewhat coarser, and imbued 
 with bitumen (mineral pitch) slightly. Of the remaining layers, 
 each one was coarser than that which preceded it, till the outer layer 
 was remarkably coarse, strong, and close in texture. The bitumen 
 increased with the coarseness of the cloth, so that the outer layers 
 were perfectly saturated with it. 
 
 344. If the Egyptians constructed their mummy cloth of flax, 
 the ancient Peruvians, who also embalmed their dead, invariably em- 
 ployed cotton for this purpose, and the only mode of discriminating 
 between Peruvian and Egyptian mummy cloth, is by submitting them 
 to the Microscope. 
 
 * The author has many such examples in his possession, ranging from 2,000 to 5,000 
 years old. 
 
58 VEGETABLE PHYSIOLOGY. [LESSON 20. 
 
 345. The woody fibre of flax and hemp is chiefly employed by us 
 for economic purposes ; in the Philippine Islands the fibre from the 
 leaves of a plain tain is used; in Mexico the leaves of some wild 
 species of pine-apple furnish a similar substance ; an endless variety 
 of plants are used for cordage, for almost every country applies its 
 own plants to this purpose. 
 
 346. Our obligations to woody fibre are infinite ; without its aid 
 we might forego the luxury of a shirt to our back, sails and cordage 
 for our ships, or a door-mat upon which to clean our shoes ; without 
 its assistance this book could not have had existence, for the paper 
 upon which it is printed, and the wood upon which the engravings 
 have been made, are woody fibre. 
 
PART II. 
 
 ANIMAL PHYSIOLOGY. 
 
 LESSOR XXI. 
 
 THE OKIGINAL COMPOUNDS OF THE ANIMAL BODY. 
 
 347. THE egg of an viperous (egg-laying) animal, is found to 
 consist of two parts the yelk, and the white, as it is called. The 
 yelk is incapable of forming a tissue, and is destined to be entirely 
 converted, by the process of incubation, into cells. The white is 
 known to chemists by another name, that of albumen, and this is 
 found to be the most universal and important constituent of organ- 
 ized beings. 
 
 348. Albumen, through the aid of a series of chemical and vital 
 processes, becomes nerve, muscle, tendon, ligament, membrane, 
 areolar tissue, horny substance, feathers, the animal portion of 
 bone, $c. 
 
 349. These remarkable changes are not confined to the embryo, 
 or the young condition of an animal, for, on the contrary, they are 
 constantly taking place through all the phases of adult life. By the 
 wonderful chemistry of digestion, all substances of similar compo- 
 sition are reduced to albumen, which forms an essential part of the 
 fluids absorbed for the nourishment of the tissues. 
 
 350. When Gelatine (calves-foot jelly) is consumed as food, there 
 is little doubt that it becomes associated with the general circulation, 
 but the doctrine of Chemical affinity appears to prevail in the organ- 
 ization of tissues like joins like so that on this principle the 
 gelatine goes to where it belongs to the gelatinous tissues the 
 bones and teeth. 
 
60 ANIMAL PHYSIOLOGY. [LESSON 21. 
 
 351. Nerves, muscles, ligaments, tendons, are not gelatinous ; 
 this element forms no part of their structure, and consequently the 
 capillaries belonging to these tissues respectively, refuse to recognize 
 its presence, and pass it on. 
 
 352. Albumen exists in a soluble state in animal fluids ; it may 
 be easily dissolved in water, when it forms a glairy, colorless, and 
 almost tasteless fluid. In this state, however, it is always found 
 combined with a minute quantity of free Soda ; hence it is supposed 
 that pure Albumen is insoluble in water, and requires the assistance of 
 an alkali. Whether in its soluble or insoluble state, albumen always 
 contains a small portion of sulphur, which blackens silver ; for this 
 reason a silver spoon is made black at the breakfast table, when eggs 
 are present, and to avoid this contingency many persons prefer to use 
 a bone, or ivory spoon, with eggs. 
 
 353. Albumen shows no disposition to become organized, or to 
 form tissues ; but after its introduction into the body of a living 
 animal, it changes into another compound, having new and peculiar 
 properties, called Fibrine. 
 
 354. According to the analysis of Dumas, the ultimate compo- 
 sition of Fibrine, and Albumen, shows that the former contains less 
 Carbon, and more Nitrogen, than the latter ; the chemical compo- 
 sition of these elements does not appear to be of much account, as 
 the transformation of Albumen into Fibrine is much more a vital 
 than a chemical process. 
 
 355. Like Albumen, Fibrine may exist in a soluble, or in a co- 
 agulated state ; but it is only found soluble in living animal fluids, 
 as the Chyle, Lymph, and Blood. When withdrawn from the blood- 
 vessels, the Blood soon coagulates, as do also the Chyle and Lymph ; 
 this coagulation is due to a change in the condition of the Fibrine, 
 the particles of which have a tendency to aggregation in a definite 
 and peculiar manner. This process is called fibrillation, which 
 seems to be allied to crystallization. 
 
 356. A single fact will suffice to show the close chemical relation 
 subsisting between Albumen and Fibrine, that from both of these (no 
 less than from many vegetable substances used for food) a similar 
 substance may be obtained by a simple process. 
 
 357. If boiled Albumen be dissolved in a weak solution of caus- 
 tic alkali, and the liquid be neutralized by an acid, a precipitate falls 
 down in grayish white flocks ; this being collected and washed, is 
 gelatinous, of a grayish color, and semi-transparent ; and when dried, 
 it is yellowish, hard, easily pulverized, tasteless, insoluble in water 
 
LESSON 21.] COMPOUNDS OF THE ANIMAL BODY. 61 
 
 and alcohol, and decomposes by heat without fusing : this substance 
 has been called Proteine, from an idea that it is the first and funda- 
 mental principle of which Albumen, Fibrine, &c., are but modifica- 
 tions. It contains the same proportions of Carbon, Hydrogen, Oxy- 
 gen, and Nitrogen, as Albumen and Fibrine ; but it is destitute of 
 Sulphur and Phosphorus; Liebig, however, doubts the latter as- 
 sertion. 
 
 358. Albumen shows no tendency to coagulate, except by the aid 
 of chemical influences, and its coagulum is devoid of structure. 
 Fibrine exhibits a constant tendency to form solid tissues, and it 
 appears only to be kept in check by the operation of influences not 
 understood. It is highly probable that the production of tumors, 
 and morbid growths, in the interior of the body, no less than upon 
 its external surface, owe their origin to the persevering tendency of 
 Fibrine to form tissues ; exhibited at a period when the law (what- 
 ever it may be) that should govern it, is in abeyance. Certain it is 
 that a great number of adventitious (accidental, extrinsic) growths 
 when microscopically examined, consist only of fibrillated fibrine. 
 
 359. The conversion of Albumen into Fibrine may be regarded 
 as the first great step in the process of nutrition ; the mode by 
 which the varied materials used for food, are made to form a part of 
 the tissues of the living body. 
 
 360. Fibrine first makes its appearance in the Chyle the fluid 
 found in the Lacteals (lacta, milk) ; Chyle is the immediate product 
 of digestion, and will be more fully explained hereafter. 
 
 361. The proportion of Fibrine in the blood, as indicated by the 
 firmness of its coagulum, is much greater than that contained in the 
 Chyle, and in certain conditions of the blood, resulting from disease, 
 the proportion of fibrine is increased to twice, thrice, or even four 
 times its usual amount. 
 
 362. In the process by which injuries to parts are repaired, there 
 is an exudation of fibrine ; this is said to form plastic, or coagulable 
 lymph. 
 
 363. In exudation, the liquor sanguinis (fluid portion of the 
 blood) is alone poured out, and this fluid holds the fibrine in solu- 
 tion ; the solid portion (red corpuscles) takes no share in this process 
 of reparation. 
 
 364. When describing the latex in plants, a comparison was in- 
 stituted between its properties and the properties of the blood in ani- 
 mals, particularly in relation to its ability to form tissues by a process 
 of coagulation. 
 
62 ANIMAL PHYSIOLOGY. [LESSON 21. 
 
 It was to this particular principle of exudation of the plastic 
 lymph, whereby a new tissue may be formed without the agency of 
 development by cells, that the comparison was intended to apply. 
 
 365. Examined by the microscope, it will be seen that the usual 
 mode by which tissues are constructed out of fibrine, consists in a 
 tissue of densely matted fibres, which cross each other in every pos- 
 sible direction ; this can be well seen in the Crassamentum, or clot 
 (the solid, colored portion) of human blood, or of the blood of any 
 other animal. The clot should be hardened by boiling, and thin 
 slices of it made with a sharp razor ; the fibres (fibrillated) of fibrine 
 will be clearly seen, and in their meshes, or interstices, the red cor- 
 puscles. The arrangement, however, of the fibrine is still better seen 
 in the Bufy coat, or fluid portion of the blood which arises above 
 the surface of the clot. 
 
 366. This mode of tissue forming is not limited to the process of 
 repair ; there are certain distinct tissues in the Animal Kingdom, 
 always, and alone formed on this principle. 
 
 If the Hen's egg be boiled moderately hard, the white will dis- 
 play a tough, semi-transparent membrane in which it is enclosed, and 
 which separates it from the shell : it is called Membrana putaminis. 
 
 367. If this membrane be macerated in water for a few days, it 
 may then be separated into layers many of which will be found to 
 enter into its composition ; examine one layer by the microscope, 
 
 and an appearance will present itself like 
 Fig. 90. Now drop a piece of the shell 
 into Acetic Acid, which will quickly re- 
 move the Carbonate of lime, with which 
 the animal membrane has been consoli- 
 dated ; examine this membrane with the 
 microscope, and it will then appear that 
 the animal basis of the egg shell is a sim- 
 
 ^^^^^^*^^ pie matted tissue of fibrillated fibrine, 
 Membrana putaminis. 
 
 ofiering its meshes as receptacles for the 
 deposition of the mineral matter. 
 
 Here, then, is an animal membrane destitute of blood-vessels, 
 and wholly formed by the consolidation of Fibrinous elements. 
 
 368. Wounds that are said to heal (in surgical language) by " the 
 first intention," are really knit together by the plasticity of the co- 
 agulable lymph, as the liquor sanguinis of the blood is called ; in 
 other words, lymph is thrown out from each lip of the wound, and 
 extending across to, and joining the other lip, the lymph fibrillates 
 
LESSON 22.] CELLS, MEMBRANE, AND FIBEE. 63 
 
 (forms fibres), by which process the lips (say a cut finger) are brought 
 together, and permanently laced by the newly formed fibres. In 
 this operation lymph is thrown out in excess, and the portion of it 
 that cannot be used, dries up, by exposure to the atmosphere, and is 
 invariably of a yellowish color never red thereby showing the 
 absence of the red corpuscles in this process. 
 
 LESSON XXII. 
 
 OF CELLS, MEMBEANE, AND FIBEE. 
 
 369. The history of the vegetable cell has already been given ; 
 the history of the animal cell is in every respect precisely similar. 
 So perfectly identical is the cellular tissue of a plant, and an animal 
 cellular tissue, that the microscope fails to detect a point of differ- 
 ence ; when, too, we consider the number of diverse animal tissues 
 having a cell-structure for their basis, this fact is not a little remark- 
 able. 
 
 Still, there are important differences between them, which the 
 Chemist can detect, although the microscope in this respect is 
 powerless. 
 
 370. We have seen that the cell-wall of a plant is composed of 
 cellulose / the animal cell- wall is equally transparent, and possesses 
 all the other microscopical characteristics, but it is chemically differ- 
 ent ; every animal cell-wall is solely composed of an animal element, 
 namely, Proteine. 
 
 371. Great difference exists in the contents of animal cells ; thus 
 the cells which float in the Chyle, the Lymph, and the Blood, the 
 latter devoid of color, have no single nucleus, but a variable number 
 of scattered particles in the nature of nucleoli (little nuclei), each of 
 which obtains an independent existence by the bursting or absorption 
 of the cell- wall : here, again, is a vegetable parallelism. 
 
 372. The liberated nucleoli float in the fluid, till they, in their 
 turn, mature into perfect cells. 
 
 In animal, as in vegetable cells, the nucleus appears to be the 
 all-important portion of it; the membrane appears to have little 
 else to do than simply containing and isolating it. 
 
 373. In many animal tissues the multiplication of the cells can 
 
04 ANIMAL PHYSIOLOGY. [LESSON 22. 
 
 be distinctly traced to the spontaneous division of the nucleus, as in 
 plants. 
 
 374. A good example of this fact is met with in the develop- 
 
 ment of Cartilage ; if we examine young 
 Cartilage (or the Cartilage of young 
 animals), where the tissue is in a state 
 of active formation, groups of cells will 
 be found, the nucleus sometimes entire, 
 sometimes just divided, and other ex- 
 amples in which division and subdivision 
 (into four parts) have taken place (Fig. 
 91) ; the primary cells (a) contain an 
 entire nucleus; the secondary cells (b) 
 
 -- " show the division into four nucleoli, 
 while the remainder of the cells sim- 
 ply demonstrate division. 
 
 SIMPLE FIBROUS TISSUES. 
 
 375. All animals possess a very large amount of what has been 
 improperly called Cellular tissue ; this term is now restricted, how- 
 ever, to those tissues which are found to consist of a congeries of 
 cells, and the word Areolar has been proposed (and adopted) in place 
 of Cellular tissue. 
 
 Examined by the microscope this tissue is found to consist of a 
 net-work of minute fibres and bands, interwoven in every possible 
 directipn, leaving innumerable interspaces communicating with each 
 other. When a butcher kills a calf, he makes a small hole in the 
 skin, applies his mouth, and blows into it ; by this means he distends 
 the whole body, because he has inflated the areolar tissue. If the 
 human body, the body of a dog, or of any other animal, be allowed to 
 remain in the water after death, gas is generated as the result of in- 
 cipient decomposition ; it fills the meshes of the areolar tissue, and 
 distends the body enormously ; as a consequence of its great buoy- 
 ancy it is enabled to float on the surface of the water. 
 
 376. The fibres which enter into the composition of Areolar tis- 
 sue, designate two other distinct tissues, i. e., the white fibrous and 
 the yellow fibrous tissues,' both of these have an independent exist- 
 ence, however, in other parts of the body. 
 
 377. Thus the white fibrous tissue exists alone in Ligaments, 
 Tendons, Fibrous Membranes, &c., where it presents precisely the 
 
LESSON 22.] CELLS, MEMBKANE, AND FIBRE. 
 
 65 
 
 same characters as when it is found associated with the yellow ele- 
 ment to form areolar tissue. 
 
 The yellow fibrous tissue exists separately in the middle coat 
 of the arteries, the Chordae vocales (vocal cords), the Ligamentum 
 
 FIG. 93. 
 
 FIG. 92. 
 
 White Fibrous Tissue. 
 
 White and Yellow Fibrous Tissues. 
 
 nuchae (or suspensory ligament, which supports the head), of quad- 
 rupeds. 
 
 378. The white, called also the inelastic fibrous tissue, consists 
 of bands (Fig. 92) which run parallel with each other, and form a 
 series of wavy lines ; they appear to be composed of a number of 
 
 Fig. 95. 
 
 FIG. 94. 
 
 Yellow Fibrous Tissue. Ligamentum nuchae. Ox. 
 
 component fibres ; it is not so, however, since no manipulation can 
 succeed in separating them. Areolar tissue from many parts of the 
 5 
 
66 ANIMAL PHYSIOLOGY. [LESSON 23. 
 
 body is found to be composed of the two elements ; that is to say, 
 of the white and yellow fibrous tissues. If the areolar, or cellular 
 tissue, beneath the pectoralis major muscle (large muscle of the 
 chest) be examined, microscopically, these elements will be seen as 
 clearly as in the subjoined figure (Fig. 93) obtained from this situa- 
 tion ; a shows the white and b the yellow fibrous tissue. 
 
 FIG % 379. The yellow, or elastic fibre, exists as 
 
 long, branched filaments, with a dark border, 
 and always curling when not put on the stretch 
 (Fig. 94). 
 
 380. This tissue is seen in great perfection 
 in the strong Ligamentum nuchoe of the Ox 
 (Fig. 95), and its tendency to curl at the ends is 
 well marked ; a transverse section of the same 
 tissue is shown at Fig. 96. 
 
 LESSON XXIII. 
 
 SIMPLE CELLS, FLOATING IN ANIMAL FLUID. 
 
 381. If the human blood be examined by the Microscope, or, 
 still better, the circulation of the blood in the web of the Frog's foot, 
 a great number of distinct bodies, or cells, will be seen floating in an 
 invisible fluid. The cells are the red corpuscles, characteristic of the 
 blood in all the red-blooded animals ; the fluid in which they float is 
 the liquor sanguinis. 
 
 382. The red corpuscles have been called " globules " an im- 
 proper name because untrue. Their figure differs in various animals, 
 but they are not globular in any. In man, and the mammalia, they 
 are flattened discs, slightly concave on both sides ; in all the Ovipa- 
 rous (egg-bearing) vertebrata, they are oval, and of much greater size 
 than in the mammals, or man. 
 
 383. That the corpuscles are very elastic is proved by the alter- 
 ation of figure which they undergo in passing through narrow capil- 
 lary blood-vessels, particularly when passing the bent, or rounded 
 part of the vessel ; as soon as they have more room, they instantly 
 recover their original figure. 
 
 384. The size of the corpuscles not only greatly differs in various 
 animals, but even in the same individual some being met with as 
 
LESSON 23.] CELLS FLOATING IN ANIMAL FLUID. 67 
 
 much as a third larger or smaller than the average. The size of 
 the animal offers no criterion for the size of the blood corpuscle, al- 
 though it is true that they are largest in the elephant of all the mam- 
 malia, he being, at the same time, the largest mammal ; but the pigmy 
 mouse tribe (Fig. 107) possesses corpuscles many times larger than 
 those of the musk deer (Moschus Javanicus). 
 
 385. Much controversy has existed amongst microscopists as to 
 whether the human blood discs contain a nucleus or not. Reasoning 
 from analogy they ought to possess a nucleus, and many observers 
 have a firm conviction that they can plainly detect it. In all the 
 Ovipara it certainly exists, and can be rendered apparent by dissolv- 
 ing the external envelope and setting the nucleus free. A represen- 
 tation of the corpuscles of human blood is given (Fig. 97); the 
 preparation from which the drawing was made 9T 
 
 is dry, and it can be placed in focus, so as to 
 show a very distinct, red colored nucleus (a). 
 Those who deny the presence of a nucleus, at- 
 tribute the effect of color to refraction. 
 
 386. The membrane which forms the cell- 
 wall of the corpuscle is readily permeable by 
 fluids, and under their influence its form is 
 
 easily altered ; treated with water, the liquid Human Blood Cor P U8cles - 
 readily passes into the cell ; firstly the disc becomes flat, then double 
 convex, so that all trace of the nucleated spot is lost ; afterwards it 
 becomes globular, and in the end it bursts the contents (whatever 
 they may be) escaping. But if treated with a thick syrup, or albu- 
 men in solution, their contents will pass out, and the cell-wall assume 
 a shrivelled appearance ; the first effect of this treatment is to increase 
 the concavity, and render the central spot more conspicuous. 
 
 387. It has been stated that the size of the human red corpuscle 
 varies, and according to accurate measurements it appears to range 
 from the l-4,000th to the l-2,800th of an inch ; probably the aver- 
 age is about the l-3,200th. 
 
 388. When inflammatory action exists, the red corpuscles have a 
 great tendency to aggregate and form rouleau (b, Fig. 97); this 
 condition is so certain that frequently when fingers have been pricked 
 to show the blood obtained, to a party of assembled guests, one of 
 them has thus demonstrated the presence of slight inflammatory 
 action. 
 
 389. From a series of experiments made upon the frog's blood, 
 the corpuscles of which are shown in Fig. 98, it appears that the nu- 
 
68 
 
 ANIMAL PHYSIOLOGY. 
 
 [LESSON 23. 
 
 FIG. 98. 
 
 cleus consists wholly of Fibrine; the blood of a 
 frog was placed upon a slip of glass, and slightly 
 diluted with water ; in due time the cell membrane 
 dissolved, and liberated the nuclei. These main- 
 tained their integrity for a time, but in the end be- 
 gan, insensibly, to dissolve. They firstly became 
 completely spherical, and shortly afterwards, the 
 sphere simultaneously diminishing, and the water 
 evaporating, a number of radii suddenly shot out 
 from all that remained of the nuclei, and this process continued un- 
 til the water had completely evaporated. The dried preparation be- 
 ing examined, disclosed fibrillation of fibrine emanating from the 
 nuclei respectively; but the water being insufficient to complete 
 their entire resolution, portions of the majority of the nuclei re- 
 mained, and are still permanent (Fig. 99). This experiment was re- 
 
 Corpuscles of Blood, 
 Frog. 
 
 FIG. 99. 
 
 FIG. 100. 
 
 Fibrillation of Fibrine, Blood of Frog. 
 
 Fibrillated Blood of Locust 
 
 FIG. 101. 
 
 peated several times, with the like uniform results, and six prepara- 
 tions exist to confirm these facts. In every instance the cell-wall ap- 
 peared to dissolve entirely, and exhibited no tendency to fibrillate ; 
 moreover, the fibres of fibrine are, in every instance, distinctly seen 
 emanating from all that remains of the nuclei 
 
 390. The same experiment was made on the blood of a locust, 
 with precisely the like results (Fig. 
 100). Here some of the blood cor- 
 puscles are (comparatively) large (a) y 
 while others are minute (b) ; fat or oil 
 globules are also seen at c. So great 
 is the disposition for blood to fibrillate 
 when drawn from the body, that the 
 
 Blood Fibrillating Frog. nuclei of ^ fr()g , g ^^ yery ^ 
 
 quently throws out fibres of fibrine, within the cell-wall, as illustrated 
 
LESSON 23.] CELLS FLOATING IN ANIMAL FLUID. 69 
 
 in Fig. 101. This illustration has been magnified with an 
 eighth object glass, to give greater size and distinctness to the figure. 
 The nuclei (a) will be clearly seen within the cells, and the fibres 
 of fibrine range from four to seven in number ; in every instance they 
 can be seen to be pulled out, as it were, from the nuclei. This has 
 been seen before by Prof. Owen, but misinterpreted (if the above 
 facts be true) ; the Professor believed that the lines indicated a puck- 
 ering of the cell-wall. 
 
 391. If these observations can be depended on, and they require 
 confirmation by another experimenter, there seems to be great 
 reason to believe that the human corpuscle contains a nucleus, and 
 that its element is chiefly fibrine. That the fibres of fibrine, in the 
 experiments alluded to, really arose from the nuclei, and not from 
 the colorless corpuscles, is rendered certain by the fact that all that 
 remains of them retains the red color distinctly ; the nuclei, as will 
 be seen by reference to the figure, are of all sizes some moderately 
 large, others quite minute. 
 
 About an hour after a mosquito ha'd made a meal, it was killed, 
 and the human blood contained in its crop and stomach examined by 
 the microscope. The nuclei (real or apparent) had disappeared, 
 leaving only a faint ring (Fig. 102) to mark its place. 
 
 Another mosquito was FI<J m 
 
 killed three or four hours after 
 a meal; in this instance, nei- 
 ther nuclei nor rings could be 
 discovered (Fig. 103) ; but in 
 both instances the corpuscles 
 retained their full s i Z e_ a ppa- H ^ mbloodw ^ cle8 ' from8tomMhofMos< l uito - 
 rently uninjured by the action of the digestive process. These ex- 
 periments were repeated several times, with the same uniform results, 
 and the preparations exist to confirm the accuracy of the experiments. 
 
 The inference appears to be that the human blood corpuscle does 
 contain a nucleus ; that its structure differs from that of the cell- 
 wall, and that it is far more accessible to the action of the saliva and 
 the gastric juice than the latter, which remains intact long after the 
 former has disappeared. 
 
 392. The shape of the human blood corpuscle is discoidal ; so too 
 in the mammalia ; in the birds, reptiles, and fishes, it attains much 
 greater size, and is more or less oval or oblong in shape, as may be 
 seen in the blood of the common fowl (Fig. 104). It has been said 
 that the ostrich possesses the largest red corpuscle of all the warm- 
 
70 
 
 ANIMAL PHYSIOLOGY. 
 
 LESSON 23. 
 
 FIG. 104. 
 
 Blood corpuscles, Fowl. 
 
 FIG. 105. 
 
 blooded animals ; but the subjoined figure of the ostrich blood (Fig. 
 105), accurately copied from the preparation, 
 and carefully drawn to scale, tends to disprove 
 this assertion, as the corpuscles of the fowl, 
 both preparations being examined by a fourth 
 object glass, are certainly larger. 
 
 If the ostrich has borne the reputation of 
 possessing the largest, there can be no doubt 
 that the beautiful little Musk Deer possesses 
 the smallest blood corpuscles of all the warm- 
 blooded animals. 
 
 Magnified by a fourth object glass, they are 
 but infinitesimal specks (Fig. 106) ; for com- 
 parison, the blood of the mouse is shown (Fig. 107). 
 
 393. In addition to the red corpuscle, all the vertebrate animals 
 possess also a colorless corpuscle (Fig. 108), which is uniformly 
 round, and possesses a variable number of granular bodies, or 
 nucleoli. 
 
 These bodies may be seen (in the frog's foot) in the same vessels 
 with the red corpuscles; they are very sluggish, apparently possess- 
 
 Blood corpuscles, Ostrich. 
 
 FIG. 106. 
 
 FIG. 107. 
 
 FIG. 108. 
 
 Blood corpuscles, Musk Deer. Blood corpuscles, Mouse. Colorless corpuscles, human. 
 
 ing greater specific gravity than the red corpuscles ; they cling to 
 the sides of the vessels, and only move when struck against by the 
 red corpuscles. Occasionally it happens that a red corpuscle strikes 
 a colorless one up into the general current of the circulation, where 
 it circulates for a longer period than usual ; but as soon as the im- 
 petus of the blow begins to fail, it drops out (apparently by its own 
 weight), and once more clings to the sides of the vessel. 
 
 394. The origin of the colorless corpuscle appears to be the fol- 
 lowing : the liquor sanguinis receives constant fresh accessions of 
 albumen and fibrine, the result of the digestion of the food. This 
 has a tendency to alter the specific gravity of that fluid (liq. san- 
 guinis) : if this were to take place, and the density of the fluid be- 
 come too great, the blood corpuscles (red) would scarcely be able to 
 move ; but if, on the other hand, it became too light, the red corpus- 
 
LESSON 24.] CELLS UPON FREE SURFACES OF THE BODY. 71 
 
 cles would flow at a rapid rate, and simulate fever. These conditions 
 of the blood really occur under the influence of disease ; in a state 
 of health it appears to be imperative that the liquor sanguinis main- 
 tain a certain specific gravity, but still the weighty elements pour in ! 
 "What is now to be done ? 
 
 To relieve this state of things it seems probable that the excess 
 of albumen and fibrine is rolled up, in the solid form, to get it out 
 of the way, and thus the specific gravity of the fluid is maintained. 
 
 395. The observations, particularly of Mr. Paget, lead to the 
 conclusion that these colorless corpuscles gradually change into the 
 red corpuscles, and if this theory be correct, the whole phenomena 
 of their development is remarkably simple and beautiful. Firstly, 
 the colorless corpuscle, formed out of the excess of the materials 
 held in solution in the liquor sanguinis, takes on the solid form, 
 in which it is no longer soluble ; and secondly, the series of gradual 
 changes by which it becomes transformed, with new characteristics, 
 into the red corpuscle. Mr. Paget's observations regarding the 
 origin of the red corpuscle, confirm the experiments on the frog's 
 blood, in regard to the fibrinous character of the nucleus, and offer an 
 additional reason for believing that this body should and does exist 
 in human blood. 
 
 396. The colorless corpuscles appear to possess great power to 
 repair injuries. If the web of the frog's foot be artificially inflamed 
 under the microscope, the colorless corpuscles will be seen to rush in 
 considerable quantity from all adjacent parts, to the seat of injury, 
 and there they remain till the disease disappear. 
 
 If a boil, or other inflamed surface in the human subject, be 
 pricked with a needle, and the fluid thus procured be examined with 
 a microscope, it will appear to be almost composed of the colorless 
 corpuscles, thus demonstrating their activity to cure disease. 
 
 LESSON XXIY. 
 
 CELLS DEVELOPED UPON FREE SURFACES OF THE BODY. 
 
 397. A great difference exists between the cells forming the ex- 
 ternal surface of the body, Epidermis (epi, upon; derma, skin), 
 or the cellular covering of the external surface ; and the Epithelium, 
 or the cellular covering of the internal mucous membrane. 
 
72 ANIMAL PHYSIOLOGY. [LESSON 24. 
 
 FIG. 109. 398. The Epidermis consists of several layers, pro- 
 
 duced by and forming the external surface of the cuti- 
 cle ; the external one being a series of horny, trans- 
 parent, flattened, scale-like cells (Fig. 109), the lower 
 layers of this tissue possess the true cellular character. 
 Scales of human The outer layers are continually being exfoliated, or 
 thrown off, and are as constantly being reproduced 
 below. The preservation of a healthy skin demands the removal of 
 the entire epidermic layer, by frequent ablution, always accompanied 
 by the liberal use of that valuable detergent soap. 
 
 399. For the strict purposes of health, neither a plunge nor 
 shower bath is necessary the latter is even obnoxious to some tem- 
 peraments : the most comfortable and healthful form of bath is at 
 the same time the most facile a sponge bath expedition in its use 
 being the most important element. 
 
 The bath itself should never exceed five minutes ; the rubbing 
 dry (the most essential part of the process) occupying another five 
 minutes or more an amount of time that every one can afford at the 
 beginning of the day. This bath should be taken immediately on 
 rising in the morning, as at such time reaction is greater and quicker 
 than at any other period of the twenty-four hours. 
 
 It is very necessary to attend to the temperature of the water, 
 and of the room in which the bath is taken. During hot summer 
 weather, water may be used at the ordinary temperature of the at- 
 mosphere, the room indicating not less than 70 Fahrenheit. But at a 
 less external heat than 70 the water should be warm, or at least tepid. 
 
 400- A sudden cold chill on the surface of the body is prejudicial 
 to health ; it checks the circulation of the blood to the external sur- 
 face, interferes with the secretions, and particularly arrests the excre- 
 ting power of the skin. 
 
 401. It is a popular belief with mothers, that washing young 
 children daily, in cold water, makes them hardy. This is a grave 
 mistake ; the feeble circulation of a child requires the aid and assist- 
 ance of warmth warm water and warm clothing. The greatest 
 medical man who ever lived John Hunter recommended three 
 rules for the management of children, and they express the substance 
 of a volume ; he says, " give them plenty of milk, plenty of sleep, 
 and plenty of flannel." 
 
 402. In this changeable climate, children and females are too 
 thinly clad, and the great mortality amongst females is mainly due to 
 this cause ; they are so much exposed to external influences that they 
 
LESSON 24.] CELLS UPON FREE SURFACES OF THE BODY. 73 
 
 are unable to maintain a sufficient degree of vital heat, hence, all 
 their functions are indifferently performed; they sicken and die. 
 Many females, of all ages, and even in the depth of winter, cover the 
 upper part of the body with but two garments, whilst the hips are 
 covered with an excess of clothing. Now it happens that the chest 
 and body, which are unclothed, contain all the important organs of 
 life, and special care should be taken to preserve them. 
 
 403. European women, remarkable for their robust health, all 
 wear corsets, the substance of which, in addition to other appliances 
 (stay-bones), gives alike great support and warmth to the body. More- 
 over, they greatly improve the figure, and render the set and fit of a 
 dress perfect. It seems a pity that because a few silly, thoughtless 
 girls would persist in destroying themselves by tight lacing, that such 
 a very useful and necessary garment should be discarded. The prac- 
 tice of wearing so many clothes upon the hips is highly reprehensible, 
 as it originates disease of a serious and distressful character. 
 
 404. If it be deemed essential to protect the lower portion of the 
 body with such a great accumulation of dress, each garment ought to 
 be suspended from the shoulders by means of straps, unless a corset 
 be worn ; but if a corset be not employed, it would be preferable, 
 on the score of health, to provide each article with a body ; in either 
 case the weight would be removed from the hips. 
 
 405. After bathing a child and wiping its body quite dry, fric- 
 tion all over the surface, and especially of the limbs and down the 
 spine, with the palm of the hand, in the nature of good, brisk, quick 
 rubbing, should be practised till the surface be red indicative of 
 reaction ; after this envelope the body in flannel. 
 
 406. For adults to bathe after a meal, or after fatiguing exercise, 
 is eminently dangerous. Three fatal cases were recorded by the New 
 York papers, all occurring within a year, from this sole cause ; the 
 first was the death of an American lady of refinement and position, 
 from taking a bath soon after dinner ; of Sergeant Hume, while alone 
 in a warm bath, and of Lorenzo Shepherd, of New York, under pre- 
 cisely similar circumstances. 
 
 407. Those persons who do not happen to possess a sponge, may re- 
 sort to the following plan with great advantage : as soon as you get out 
 of bed in the morning, wash your hands, face, and neck ; then, in the 
 same basin of water, put your feet at once for about half a minute, 
 rubbing them briskly at the time ; then, with the towel that has been 
 dampened by wiping the face, feet, &c., rub your whole body well 
 (without the addition of more water), fast, and hard, mouth shut, and 
 the breast projecting. Allow five minutes for this operation. 
 
74 ANIMAL PHYSIOLOGY. [LESSON 25. 
 
 408. There is yet another plan, superior in some of its effects to all 
 that has preceded it ; at night, when you go to bed, and whenever you 
 get out of bed during the night, spend from two to five minutes rub- 
 bing your whole body and limbs with your hands, as far as you can 
 reach in every direction ; let it be done briskly, quickly, and hard. 
 By this practice the softness and mobility of the skin will be pre- 
 served, which too frequent washings has a tendency to destroy. 
 
 409. The cuticle has neither nerves nor blood-vessels, but it is 
 abundantly pierced by the evacuating ducts of the sebaceous (fatty) 
 and sudoriferous (sweat) glands, and also by the shafts of the hairs. 
 
 410. It appears to be developed for the sole purpose of protect- 
 ing the layer beneath it the true skin. 
 
 411. If the cuticle be accidentally removed, the true skin suf- 
 fers acute pain from exposure to the air, and change of temperature. 
 In addition to the cells of the epidermis whose function it is to secrete 
 horn, there are other cells secreting only pigment (paint) ; in the white 
 races of mankind these cells are easily distinguished, but they are 
 most apparent in the colored races. There appears to be great 
 relation subsisting between the development of pigment cells in man, 
 and exposure to light, that is to say, the greater the light, the more the 
 color. It is under circumstances of intense heat and light, that the 
 negro, the red Indian, and all the varieties of the colored races of 
 mankind, are produced and nourish. In this respect the analogy 
 with plants is no less perfect than admirable. 
 
 LESSON XXY. 
 
 THE NAILS. 
 
 412. May be regarded as an altered, transformed, or modified 
 epidermis ; they consist of two layers a soft mucous and the horny 
 layer, or true nail. 
 
 413. The bed, or matrix of the nail, corresponds with it accu- 
 rately in size and form. If the nail be removed by maceration, its 
 anterior (front) and middle portions are divested of epidermis, and 
 become uncovered ; the lateral portions, or edges, and the posterior 
 portion (back part) are invested by a part of the cutis. This will be 
 best understood by consulting the accompanying figure (Fig. 110), 
 which gives a view of a transverse section of a nail, made through 
 the body and bed of it. The bed of the nail (with black ridges) is 
 
LESSON 25.] 
 
 THE NAILS. 
 
 shown at a, the corium and lateral parts at , the stratum, first de- 
 scribed by Malpighi, and called by his name, with white ridges, at c 
 horny layer, on the wall of the nail, e; horny layer, or proper nail 
 substance, f with short notches upon its under surface, d. 
 
 FIG. 110. 
 
 Transverse section, through the body and bed of the Nail. 
 
 414. The Malpighian layer of the nail, like that of the epider- 
 mis, consists wholly of nucleated cells, and agrees in all essential 
 points with it, except that the deep portion contains a series of large 
 perpendicular cells. In the negro, the Malpighian layer of the nail is 
 black, and its cells even appear to contain dark brown nuclei, as well 
 as yellowish brown ones in dark Europeans. An enlarged view of a 
 transverse section through the body of the nail (Fig. Ill), will better 
 explain these facts. A, represents the cutis (true skin) of the bed of 
 the nail ; B, Malpighian layer ; C, horny layer, or proper nail sub- 
 stance ; a, layers of the bed of the nail ; 5, white ridges of the 
 Malpighian layer; c, ridges of the horny 
 layer of the nail ; d, deepest perpendicular 
 cells of the Malpighian layer; e, its upper 
 series of flat cells ; /", nuclei of the horny 
 layer. 
 
 415. The structure of the horny layer 
 can only be ascertained by the aid of re- 
 agents ; thus, boiled in dilute caustic soda, 
 it appears in the form of beautifully definite 
 
 FIG. 112. 
 
 FIG. 111. 
 
 Transverse section through the 
 body of a Nail. 
 
 Nail plates from the surface, boiled 
 in Caustic Soda. 
 
 nucleated cells (Fig. 112); the distended membrane of the cells is 
 shown at a, and the nuclei at b. 
 
76 ANIMAL PHYSIOLOGY. LESSON 25. 
 
 416. The vascularity of the bed, or matrix of the nail, is an ob- 
 ject of great interest; these vessels differ entirely in their form, ar- 
 rangement and size, from the capillaries of the cutis vera (true skin), 
 as may be seen by reference to Fig. 113. The capillaries of this tis- 
 sue are remarkable for their extreme fineness and parallelism ; their 
 function appears to be to secrete the horny layer, which forms the 
 true substance of the nail. The vessels of the cutis vera (true skin) 
 everywhere surround the vessels of the matrix, the terminal looped 
 capillaries of the papillae of the skin being distinctly visible. 
 
 417. In that horribly severe and excruciating operation of what 
 
 is called minor surgery (!), the removal of 
 a nail because its edges grow inwards, and 
 produce great pain, associated with con- 
 stant irritation, the unfortunate patient 
 frequently desires to know " if the nail 
 will grow again." The answer to this 
 anxious question is generally very vague, 
 " sometimes it does, and sometimes it does 
 not." A little practical physiology would 
 enable the operator to give a positive an- 
 swer " It shall either grow again, or not, 
 at your pleasure." If the peculiar stra. 
 raiL turn of vessels just examined be included 
 in the operation, the nail can never grow again, as the vessels which 
 produce it are gone, and there is no power in the human subject (or 
 higher mammals) to reproduce lost parts : they, therefore, once re- 
 moved, can never be replaced, and their function is gone. 
 
 418. It appears to be bad surgery, however, to remove an entire 
 nail for the fault of its edges ; they alone should be removed, care 
 being taken to include these particular vessels, with the offending 
 portion of the nail. 
 
 419. The horny hoofs of horses, sheep, oxen, pigs, &c., are all 
 formed by a similar layer of vessels, which, when minutely injected 
 and well displayed, form objects of exceeding beauty, particularly 
 the vascular lamellae of the Horse's hoof, which is intended to act as 
 a series of beautifully elastic springs. Notwithstanding the exquisite 
 sensibility of this especial vascular layer, the terminal loops of the 
 nerves have hitherto escaped detection. 
 
LESSON 26.] HAIE. 77 
 
 LESSO1ST XXYI. 
 
 HAIR. 
 
 420. Hair, in its origin, is an epidermic tissue, and is formed out 
 of cells ; but by the time it has acquired its full development, it has 
 become so completely modified that all trace of its origin is lost, and 
 can only be reclaimed by the judicious application of re-agents. The 
 hair originates within a follicle (a little bag), which is formed by a 
 depression of the skin, and lined by a continuation of the Epidermic 
 layer. From the bottom of this follicle there arises a cluster of cells, 
 which are Epidermic cells ; the exterior of this cluster is the bulb, 
 and the soft interior portion is the pulp. Although the follicle is ex- 
 tremely vascular, and even the bulb becomes reddened by minute in- 
 jection, yet no vessels have yet been traced to the interior of the hair. 
 The hairs of most animals present three elementary parts an exter- 
 nal cuticle, the cortical, horny, or fibrous substance, and an internal 
 medulla or pith ; these elements attain their highest development in 
 the quills, or modified hairs of the porcupine, and the English hedge- 
 hog (Erinaceus Europceus). 
 
 Two of the three layers above indicated, may be distinguished in 
 all hairs, without any exception the cortical, and the medullary : the 
 cuticular covering is sometimes wanting. 
 
 421. The cortical, or fibrous substance of a hair is longitudinally 
 striated (Fig. 114); it often presents dark spots, FJG 114 
 except in white hairs (in which it is transparent), 
 
 and is more or less deeply colored. The color is 
 sometimes distributed with tolerable regularity, 
 and sometimes more concentrated in granular 
 spots. 
 
 422. The medullary substance, or pith, is com- 
 posed of an aggregation of very large cells, which 
 
 * & Striated appearance of 
 
 do not possess fluid contents in that part of the the Cortical substance, 
 hair that is completely formed, but it is filled with 
 cells, usually containing pigment. 
 
 423. The feathers of Birds are precisely analogous to the hair 
 of animals; the cortical (horny) tube of a feather, represents the 
 like tissue in the hair of an animal ; and the cellular medulla con- 
 tained within the quill is the analogue of the medulla of a hair. 
 
 424. One striking difference exists, however, in hair, as com- 
 pared with the feather of a Bird ; it has been said that the hair-folli- 
 
78 
 
 ANIMAL PHYSIOLOGY. 
 
 [LESSON 26. 
 
 cle is so vascular that the bulb of the hair becomes red in a minute 
 injection, no vessels, however, being visible. The follicle of a feather, 
 on the contrary, is not only abundantly supplied with capillary blood- 
 vessels, but more, the cellular medulla is intensely vascular. In 
 other animals, as will be hereafter seen, when a hair is pulled out, it 
 
 FIG. 115. 
 
 FIG. 116. 
 
 Featherof a canary 
 bird. 
 
 Feather of a Eook injected. 
 
 bleeds; proving a tendency to vascularity in 
 this tissue, which, for all we yet know, may really 
 exist. This will be best understood by consult- 
 ing Fig. 115, which shows the feather of a Rook, 
 the medulla of which is beautifully injected. 
 
 The arrangement of the capillaries will be seen 
 to be peculiar, and characteristic; they are large, 
 as compared with human capillaries, to enable them to transmit the 
 larger-sized corpuscles of the blood. The corticle substance of the 
 feather is marked a, the vascular medulla b. 
 
 425. But feathers differ from hair in 
 another respect; the quill (a), termi- 
 nating in a shaft (5), (Fig. 116), is co- 
 vered on two sides by a feathered por- 
 tion called the vane (c). The feathers 
 of the vane are lamellated, or composed 
 of a series of distinct plates called 
 barbs (c); (Figs. 116, 117, d), these 
 barbs are made up of still smaller barbs, 
 called, therefore, barbules (e), (Fig. 117); 
 and these are found to be provided with 
 a series of very minute barbs or hooks, 
 hence called barbulince a still further 
 diminutive (Fig. 117, /). 
 
 The latter are slightly hooked, to 
 Barb of a feather magnified. enable them to attach the barbules to 
 
LESSON 26.J HAIR. 79 
 
 each other, so that the whole surface of the barbs, of which the vane 
 consists, may form a solid, continuous, firm, resisting membranous 
 expansion, by which a feather strikes the air, as an oar strikes the 
 water. 
 
 Were it not for this beautiful provision, the air would pass 
 through the feathers of the vane, and flight would be impossible. 
 
 426. The cuticular substance of human hair, is composed of a 
 series of flatened cells or scales, derived from the epidermis thrown 
 off or exfoliated, from the interior of the follicle. These cells or 
 scales, are disposed in an imbricated (imbrex, a tile) FlG 
 form, or overlap each other, like the arrangement of 
 
 shingles or tiles, on a nouse-top. This disposition of 
 the scales can be proved by a very simple experiment ; 
 place a hair between the thumb and finger, and pro- 
 ceed to spin it round, by moving the finger and 
 thumb contrary to each other ; the hair will inva- 
 riably pass through the root end first, which indi- 
 cates not only the imbricated arrangement of the E Human h 
 scales, but that they overlap from the root ; this is 
 shown in Fig. 118, the imbrications at the sides being exag- 
 gerated. 
 
 427. As these scales are attached one by one, as they become 
 detached from the sides of the follicle, and the hair is always growing, 
 it follows that no two of them can be deposited exactly in the same 
 place consequently they overlap ; the lower part of a scale previ- 
 ously there, being covered by the upper part of a scale newly added. 
 
 428. The cortical fibres of the shaft 
 of a hair are identical with the cells of 
 the bulb; they become elongated as 
 they are pushed upwards towards the 
 mouth of the follicle, by the production 
 of additional cells beneath, and are di- 
 minished in their diameter; consequent- 
 ly, the shaft of a hair is much less in diam- 
 eter than the bulb. 
 
 . Epidermic scales of Human hair. 
 
 429. The epidermic scales which cover 
 
 the cortical substance, can be separated by the application of caustic 
 soda, when they appear as represented in Fig. 119. 
 
 The dark spots, dots, or streaks, of the cortex are chiefly granu- 
 lar pigment ; cavities filled with air or fluid , or nuclei. 
 
 430. Caustic Potash and Soda, soften and swell up the cortical 
 
80 ANIMAL PHYSIOLOGY. [LESSON 26. 
 
 substance without destroying the spots, by which we see that they are 
 nothing but pigment granules, deposited in the plates of the hair ; 
 they are frequently found in dark hairs, but vary very much in size 
 and form. Other dark spots which, at first sight, appear to be pig- 
 Fro. 120. 
 
 FIG. 121. 
 
 Plates from the cortical substance of the shaft of 
 
 Human hair. Scales from the root of the hair. 
 
 ment granules, prove to be, on closer examination, little cavities filled 
 with air. 
 
 431. The root of the hair, especially the lower half of it, differs so 
 far from the foregoing description, which applies to the shaft, that 
 the scales, in this situation, appear as well formed elongated cells, 
 each one possessing a nucleus. In Fig. 120, scales from the shaft, 
 and in Fig. 121, from the lower half of the root, are shown ; those 
 from the shaft (Fig. 120) are flat and fusiform (spindled-shaped) 
 in shape; those from the root (Fig. 121) are broader, and generally 
 better formed, possessing a cylindrical, straight, or serpentine nu- 
 cleus. 
 
 432. The medulla forms but a small portion of a hair ; it is the 
 central streak or axis, and extends from the bulb to the point, nearly. 
 It is cylindrical in shape, and composed of a congeries of nucleated 
 cells. If white hairs be boiled in caustic soda till they swell and 
 coil up, simple pressure will generally demonstrate the cellular struc- 
 
 PIG 122 ture of the medullary cylinder, which 
 
 is then sufficiently transparent for 
 transmitted light. The medulla is re- 
 markable for the great quantity of air 
 which it contains; by its means the 
 medullary cells are broken up into a 
 series of distinct cylinders, of all 
 lengths some being much shorter than 
 others. In examining a hair from bulb 
 to point, it is curious to observe the 
 many breaks which the medulla sus- 
 tains, owing to the presence of air. A 
 
 White Hair of the head. representation is given (Fig. 122) of a 
 
 white hair from the head, which has been treated with caustic soda 
 
LESSON 26.] 
 
 HAIR. 
 
 81 
 
 FIG. 123. 
 
 magnified 250 diameters ; a, nucleated cells of the medulla, without 
 air ; b, cortical substance, with distinct nuclei ; c, cutic- 
 ular covering, showing the imbrications. 
 
 433. To demonstrate the presence of air in the me- 
 dullary cylinder, another illustration is necessary (Fig. 
 123) ; .the most conspicuous object is the bulb (a), in 
 which a dense aggregation of pigment cells is shown. 
 From this point the medulla remains intact to b, where 
 air is firstly found dividing the medulla ; thence we see 
 the frequent interruption of the medulla by the interven- 
 tion of air, until it ceases near the point, c. The original 
 specimen was a hair from the human eye-brow. 
 
 434. The whole of these facts, however, may be seen 
 with advantage by consulting thin transverse sections of 
 human hair (Fig. 124). 
 
 435. Here the cuticle (a), the cortical substance (b)j 
 and medulla (c), with its pigment cells, are well shown ; 
 the other figure (Fig. 125) was devoid of medullary pig- 
 ment cells, at the point where the section was made. 
 
 436. The human hair is very elastic; it has been 
 found by experiment that it will stretch to more than 
 one-third its length without breaking. It readily im- 
 bibes water, and as readily gives it out again ; consequent- 
 ly, it is sometimes dry and brittle, sometimes moist 
 and soft, according as the skin, or the atmosphere, con- 
 tains much or little moisture. Moreover, it becomes 
 
 longer or shorter, according to the quantity of moisture it contains. 
 
 437. The chemical composition of hair has not yet been satisfac- 
 
 Human eye- 
 
 dulla - 
 
 FIG. 124. 
 
 FIG. 125. 
 
 Transverse section, Human hair. 
 
 Transverse section, Human hair. 
 
 torily determined ; some authors suppose it to consist of a combina- 
 tion of proteine and sulphur, to which others add a small quantity 
 of a peculiar substance allied to gelatin. Hairs withstand putrefac- 
 tion better and longer than any other part of the body ; the hair of 
 mummies is always found to be quite perfect, 
 6 
 
82 
 
 ANIMAL PHYSIOLOGY. 
 
 [LESSON 26. 
 
 FIG. 126. 
 
 438. As regards the imbricated structure of the cuticular cover- 
 ing, human hair closely approximates to wool (Fig. 126) ; and a bold 
 attempt has been made in this country to prove that the hair of a 
 Negro and wool are identical, and that, therefore, the Negro is an in- 
 ferior animal, as compared with the white races of man- 
 kind. 
 
 This statement is supported in the work in question* 
 by figures professing to be transverse sections of the hair 
 of a white man, African, and full-blooded Indian, and 
 the author makes them disagree remarkably. That of 
 the white man, doubtless obtained from some accredited 
 work on human physiology, is correct ; the hair of the 
 Indian is represented as round as a circle described by 
 compasses ; and that of the African as a long oval. 
 
 They differ as much in size as in shape ; the Euro- 
 pean is shown as the smallest ; next in size, and inter- 
 mediate, is the Indian the African hair being double 
 the size of the latter. 
 
 439. In the following pages figures are given of the European, 
 Indian, and Negro hair, all faithfully copied from existing prepara- 
 tions ; these preparations have been measured by a Micrometer, and 
 found to be of the same size, nearly. That the shape of hair (of the 
 
 FIG. 127. FIG. 128. 
 
 Wool 
 
 Transverse section of hair, Negro. Transverse section of hair, Negro. 
 
 head) is various in the same individual, will be seen from the two 
 figures of hair from the white man, and two figures subjoined from the 
 Negro (Figs. 127 and 128). Each presents a specimen with and with- 
 
 *"Trichologia Mammalium," by Peter A. Brown, LL. D., Philadelphia. 
 
 The author has published a description of his " cutting machine," the very worst form 
 ever used ! It is no larger round than an ordinary pencil case ; the hair to be cut is imbedded 
 in cork, and the instrument held in one hand, whilst a razor held in the other performs the 
 cutting. The cortical substance renders hair a very tough, resisting tissue, and if only sup- 
 ported by cork, the latter yields to the pressure of the razor, and a very obUque section is the 
 best result hence the long oval that he has given of the Negro hair. 
 
 A cutting machine must be Jtoed, leaving both hands at liberty to use the razor, which 
 requires great pressure to make a thin section, and the hairs should be constantly moistened 
 vrith warm water to soften them, otherwise, with all possible care, the sections will be too 
 thick to transmit light, or show their true structure. 
 
LESSON 27.] 
 
 HAIR. 
 
 83 
 
 out pigment in the medulla ; that portion of the cortical substance 
 which joins the cuticle is much darker in color in the Negro and In- 
 dian than in the white races, and this remark applies to the cortical 
 substance generally. The hair from the head of a full-blooded Me- 
 nomonee Indian (Fig. 129) agrees in all general characteristics with 
 those already described. 
 
 440. Hairs of the beard are usually much larger and coarser 
 
 FIG. 130. 
 
 FIG. 129. 
 
 Transverse section of hair of 
 Menomonee Indian. 
 
 Hair of the beard, white man; a, cuticular 
 layer; >, cortical substance ; c, medulla. 
 
 than those of the head ; a figure of a transverse section of the hair of 
 the beard of a white man is given at Fig. 130 ; in shape it is iden- 
 tical with a hair from the head of the same person (Fig. 123) ; the 
 letters refer to the same tissues. All the foregoing specimens of 
 hair were examined, and drawings simultaneously made, under a 
 l-4th object glass. 
 
 441. In the Negro, or mulatto even, the imbrications are much 
 more distinct (because larger) than in the white races of mankind, 
 owing to the fact that the epidermic scales, which enter into the com- 
 position of the cuticular covering, are themselves deeply colored with 
 pigment, as already described in connection with the epidermis of 
 the skin, and the darker the skin the darker and coarser the epider- 
 mic scales. Beyond this fact, there is nothing to distinguish the 
 hair of a Negro, from that of any other specimen of the human 
 family. As a rule, whether in a white man or a black, strong, coarse 
 hair has a great disposition to curl. 
 
 LESSON XXVII. 
 
 HAIR, CONTINUED. 
 
 442. As a class of Microscopical objects, and as a valuable ad- 
 junct to Zoology, the structure of the hair of animals has excited 
 
84 ANIMAL PHYSIOLOGY. [LESSON 27. 
 
 great attention within the last few years. The Genera of an animal, 
 and frequently the species, can be accurately determined by the mi- 
 croscopical examination of a fragment of a hair. 
 
 In the higher mammalia, the hair appears to possess the same 
 tissues as those described as belonging to the human hair, that is to 
 say, the cuticle, the cortex, and the medulla. 
 
 443. Allusion has been made to the want of vascularity of the 
 bulb of the human hair, and the interior of the follicle ; if the whis- 
 ker (vibrissa) of a cat be pulled out, it will generally bleed, proving 
 vascularity in the follicle, if not in the bulb, of these particular 
 hairs. 
 
 444. If a thin, transverse section be made of a Tiger's whisker 
 (Fig. 131), the three tissues composing it are distinctly seen ; the 
 outer cuticular layer (a), the cortical substance (b), remarkable for 
 the great amount of pigmentary cells included in it; and lastly, the 
 
 FIG. 18L FIG. 132. 
 
 Transverse section, Tiger's "Whisker. Transverse section, Cat's Whisker. 
 
 medullary cylinder (c) in the centre, containing well-formed pigment 
 cells, but devoid of pigment where this section was made. 
 
 A similar section of a Cat's whisker (Fig. 132) shows the same 
 structure. 
 
 445. The Vibrissse, as the whiskers of animals are called, are in- 
 struments of great importance to a vast number of them, but espe- 
 cially to the Feline races. All the cats, from the majestic lion down 
 to our household pet, are not only carnivorous (feed on flesh), but 
 they are predaceous (prcsda, prey), seize living prey. 
 
 446. As soon as the eye discerns a victim, it is fixed with a deadly 
 and unfaltering gaze ; the creature creeps stealthily and noiselessly 
 along upon the soft cushions of the feet, the eye having no part what- 
 ever in the direction taken ; what then guides it ? the Vibrissae. 
 
 The Vibrissse, measured from point to point, exceed the diameter 
 of the widest part of the body ; wherever they can pass without 
 touching, the body therefore can follow. Their sensibility appears 
 
LESSON 27.] 
 
 HAIK. 
 
 85 
 
 to be exquisite, and in proportion as the point, or other part nearer 
 the bulb be touched, the animal knows exactly whether it can pass 
 or not. 
 
 447. For experiment sake, a cat has had her Vibrissse cut, and 
 then put into a box provided with a large round hole larger than 
 necessary for her body to pass through. But she has lost her gauge, 
 and no temptation can induce her to attempt to come out of the box. 
 Lions and tigers, following their prey in the jungle, are solely guided 
 by the refined sensibility of these organs, which (as already observed) 
 bleed when pulled out. 
 
 448. The true structure of hair can only be known by examining 
 transverse sections of it, which require to be cut sufficiently thin, or 
 they are useless. 
 
 449. Sections of the vibrissa of the Hat (Fig. 133), and of the 
 Raccoon (Fig. 134), show the same tissues as those described in man ; 
 the air which separates the cells in the medullary canal in human 
 
 FIG. 133. Fio. 134 
 
 Transverse section of vibrissa, Kat. Transverse section of vibrissa, Eaccoon. 
 
 hair, is equally found exerting the like division in these hairs. Like 
 the vibrissse of the Tiger and the Cat, those of the Rat and Raccoon 
 are remarkable for the general roundness of their figure. There can 
 be no doubt that these organs are as important to the two last 
 mentioned animals, as to the former ; in the first, they tend to 
 ensure the capture of living prey in the last, they facilitate 
 escape. 
 
 450. Hitherto, only one medullary canal has been described, as 
 being excavated (as it were) out of the cortical substance ; but in 
 the Pachydermatous (thick skinned) animals, to which the Elephant, 
 Hog, Horse, Rhinoceros, &c., belong, there are several medullary 
 canals apparent. 
 
 A thin transverse section of a hair from the proboscis of the 
 Elephant (Fig. 135), is almost identical with a similar section of a 
 Hog's bristle (Fig. 136), and in both, a plurality of medullas appear 
 
ANIMAL PHYSIOLOGY. 
 
 [LESSON 27. 
 
 FIG. 135. 
 
 FIG. 136. 
 
 Transverse section of hair from the Ele- Hog's bristle, 
 
 phant's proboscis. 
 
 (a), in the cortical substance (6). Another section of a Hog's bristle 
 
 (Fig. 137), made nearer to the lower 
 portion, shows greater density in the 
 outer part of the cortical substance, 
 but the several medullary canals in 
 its interior are fully apparent. 
 
 They are, however, still better 
 shown in the hair of the Elephant's 
 tail, especially if the section be made 
 near to the bulb ; such an illustra- 
 tion (Fig. 138) is quite conclusive of 
 the fact stated. The medullary ca- 
 nals (a, a), contain cells, most of 
 
 them provided with pigment, while the cortical substance (6), is re- 
 plete with pigment cells of the most perfect shape. 
 
 Fu>> m 451. Much difference, 
 
 too, exists in the form of 
 the hairs of the tail and 
 proboscis ; in the former 
 they nearly resemble that 
 of human hair ; the latter, 
 like the Hog's bristle, are 
 nearly round. 
 
 Plurality of medullary 
 canals may be seen in an- 
 other tissue, which is to 
 
 Transver.se section of hair from the Elephant's tail. a jj a pp earancc an y thing 
 
 but hair-like in its general characteristics. 
 
LESSON 27.] 
 
 HAIR. 
 
 87 
 
 If a thin transverse section be made of Baleen ( Whalebone), it 
 will be found to be composed of a dense aggregation of structures 
 resembling so many distinct hairs, each having its medullary canal, 
 surrounded by a cortical substance (Fig. 139). 
 
 If now a longitudinal section be made, the medullary canals will 
 be very distinctly seen, divided periodically into a series of cellular 
 cavities by septa (partitions) transverse in their direction (Fig. 140). 
 
 452. In structure, whalebone bears a wonderful resemblance to 
 hair (Fig. 139), agreeing most with the pachyderm type, which ad- 
 
 FIG. 140. 
 
 FIG. 139. 
 
 Transverse section of Whalebone. Longitudinal section of Whalebone. 
 
 mits a plurality of medullas. The cortical substance is divided into 
 a series of distinct bodies, each simulating a hair, and separate ; is 
 seen to be filled with medullary canals, which are, however, better 
 seen in the longitudinal section (Fig. 140). 
 
 In the hair from the mane of a Horse, there is an exception to 
 the rule of development of pachydermatous animals, as only one 
 medullary canal appears (Fig. 141). 
 
 453. The male Turkey (Meleagris galloparvo) is provided with 
 
 FIG. 141. 
 
 FIG. 142. 
 
 Transverse section of hair, Horse's mane. Transverse section of hair from Turkey's beard. 
 
 a tuft of very coarse hair, popularly known as the beard ; in trans- 
 verse section all the tissues are distinctly seen (Fig. 142). The 
 
88 
 
 AXIMAL PHYSIOLOGY. 
 
 [LESSON 27. 
 
 shape of it is very remarkable, and differs from all the other hairs 
 in this respect. The cortical substance is uniformly dark the 
 
 FIG. 143. FIG. 144. FIG. 145. 
 
 Hair of Stag, longitudinal. Hair of Wapeti Deer, longitudinal Hair of Goat, longitudinal. 
 
 result of pigment existing in a diffused condition ; the medullary 
 canal partakes of the same irregularity of form which distin- 
 146. guishes the entire hair, its cells are well shaped, and pig- 
 ment (when not interrupted by air) present. 
 
 454. The hair of the Ruminants (Ox, Sheep, Deer, 
 <&c.) is peculiar ; in them the cuticle cannot be found, be- 
 cause not present ; the cortical substance supplies its place , 
 and the medulla, transformed to large cells, filled only 
 with air, constitutes the bulk of the structure. 
 
 In the Stag (Gervus elephas) the cells of the medulla 
 (Fig. 143) are of great size ; the dark cells are still full 
 of air, which, in small portions, is always intensely black 
 under the microscope ; so too the hair of the Wapeti Deer 
 (Fig. 144) is equally cellular, but of great beauty and 
 smaller size. 
 
 455. In the hair of the Goat the two tissues (Fig. 145) 
 are all that meet our gaze. 
 
 456. The belly of the Duck-billed Platypus (Orni- 
 thorhyncus paradoxus), is covered with hairs of a very 
 curious form (Fig. 146). The bulb, at its extremity, is 
 almost pointed ; the shaft continues its course of nearly 
 equal size for a considerable distance ; at last it becomes 
 attenuated, and gives evidence of terminating (as hairs 
 usually do) in a very fine point. Instead of this, it sud- 
 denly and greatly enlarges, and this continues till it grad- 
 ually diminishes and ends in a fine point. 
 
 At a short distance from the bulb, the narrow portion 
 Hair of is filled with a series of well-formed cells (Fig. 147), like 
 
 O. paradoxus. 
 
LESSON 27.] HAIE. 89 
 
 the Ruminants ; these, however, terminate just prior to the com- 
 mencement of the enlarged portion. This latter at first contains 
 diffused coloring matter (Fig. 148), which soon ceases, and the re- 
 mainder of the hair is transparent. 
 
 457. The quills of the Porcupine (Hystrix cristata) are only 
 modified hairs; all the re- pw 14L pra 
 
 quired tissues being found in 
 these structures, especially in 
 the species quoted. The cu- 
 ticular covering (Fig. 149, a), 
 is seen as a delicate external 
 ring; but by far the most 
 remarkable structure is the 
 cortical substance, which is 
 
 transformed to horn, and Narrow part of the hair, Structure of enlarged por- 
 
 O. paradoxus, tion, O. paradoxus. 
 
 gives amazing strength to the 
 
 quill (b). Press it as hard as you will between the thumb and fin- 
 ger, no impression can be made on it, and to make a thin section it 
 musfc be firstly softened by .p. ug 
 
 boiling. The pigment of the 
 cortical substance is con- 
 tained in a series of well-de- 
 veloped cells (c). The cor- 
 tical layer consists of two 
 structures one (c) made up 
 of cells, possessing pigment ; 
 the other (b) a layer of 
 dense, non-nucleated horn. 
 
 In the centre, and every- 
 where amid the cortical layer, 
 the cells of the medulla (d) 
 are seen. 
 
 458. The quills of the Transverse section Quill of Porcupine. 
 
 English hedgehog (Erinaceous Europeans) exhibit a like structure 
 in a minor degree, but without cuticle. 
 
 Two tissues are there, but the cortical substance descends into 
 the interior of the medullary layer, without reaching the centre 
 (Fig. 150). 
 
 The arrangement of the medullary cells is best seen in a longi- 
 tudinal section (Fig. 151). 
 
 459. Lastly, the American porcupine (Hystrix dorsata) presents 
 
ANIMAL PHYSIOLOGY. 
 
 [LESSON 27. 
 
 FIG. 150. 
 
 a totally different aspect ; here the cortical substance is restricted 
 to a narrow ring, which forms the periphery of the circumference 
 
 all within it consists of me- 
 dullary cells (Fig. 152). 
 
 It is easy to understand 
 how the Indians can use these 
 quills in such varied pattern ; 
 they have no support, and can 
 be flattened with the greatest 
 ease. In the two last illus- 
 trations the cuticle ceases to 
 be present, and cannot there- 
 fore be shown. 
 
 460. Since we quitted the 
 examination of human hair and 
 
 wool, we have lost all trace of 
 Transverse section, quill of English Hedgehog. ^ external imbrications> - and 
 
 it might be inferred that these characteristics are confined to man, 
 and the sheep ; but this is by no means true, for, on the contrary, 
 many animals there are in which this particular arrangement is shown 
 in great perfection. 
 
 461. Thus, the hair of the seal (Phoca vitulina) presents them in 
 
 Fro. 151. 
 
 FIG. 152. 
 
 Longitudinal section, quill of 
 English Hedgehog. 
 
 Transverse section, quill of American 
 Porcupine. 
 
 a manner more nearly resembling a vegetable stem than any thing 
 animal (Fig. 153). 
 
 462. The hair taken from the belly of the mouse (Mus muscu- 
 lus) is very interesting (Fig. 154). The imbrications are well shown, 
 but its beauty consists in its cellular medulla ; some cells are nearly 
 white, others are intensely black ; in some parts of its structure the 
 
LESSON 27.] 
 
 HAIR. 
 
 91 
 
 Hair of Seal. 
 
 Mouse Hair. 
 
 black and white cells FlG - 153 - Fl - 154 - FIG. 165. 
 
 alternate, occupying 
 the whole diameter ; 
 in other portions the 
 black is broken up 
 into smaller rounded 
 bodies, and mixed 
 with the white. Nei- 
 ther is this all; the 
 hair enlarges gradu- 
 ally from the bulb, 
 then diminishes, and 
 
 continues to do this four times before it ends in a point. 
 Each enlargement, too, is always larger than that which 
 preceded it, and the last the largest of all. 
 
 A pretty little Marsupial animal (having a bag, or 
 pouch, like the Opossum), from Australia, Phascogale 
 penicillata, has hair somewhat resembling that of the 
 Mouse, inasmuch as each hair consists of four enlargements 
 (from the bulb), and corresponding diminutions. These Phascogale.' 
 hairs are of such great length, that it is out of the question to figure 
 an entire one, especially as the principal has been demonstrated in 
 the hair of Ornithorhyncus (Fig. 146). 
 
 But enlarged detached portions are illustrated : thus, a figure of 
 the bulb, and commencement of the shaft (Fig. 155), is ^given. To 
 
 Fin. 156. 
 
 FIG. 157. 
 
 FIG. 153. 
 
 Succeeding portion, 
 le. 
 
 Terminal enlarsred portion, 
 Phascogale. 
 
 Hair of Indian 
 Bat: 
 
 this succeeds a well imbricated structure (Fig. 156), the interior of 
 which displays medullary cells. 
 
 The latter structure now prevails throughout the remainder of 
 
92 
 
 ANIMAL PHYSIOLOGY. 
 
 [LESSON 27. 
 
 the hair, except in the attenuated portions, but to show the great dis- 
 parity of size in the terminal enlargement, a figure of it (Fig. 157) is 
 also given. 
 
 463. An exceedingly interesting and beautiful hair is obtained 
 from a species of Bat, common in India, the scientific name of which 
 is not known, although the hairs have been found in the cabinets of 
 microscopists for fully twenty years. The imbrications are arranged 
 as a whorl (Fig. 158) which surround the shaft. It is altogether un- 
 like the hair of any other known species. 
 
 464. But it is reserved for still lower animals to show what ex- 
 traordinary weapons hairs may become ; in a Marine worm (Aphro- 
 dita hispida) the hairs are transformed into darts, and used as such 
 (Fig. 159). The specimen from which the drawing was made, was 
 dissected from the body of a naked (without a shell) Sea-slug Ap- 
 lysia in whose integument a number of them were found It will 
 
 FIG. 159. FIG. 160. FIG. 161. 
 
 Hair of Aphrodita 
 hispida. 
 
 Hair, larva of Der- 
 mestes lardariua. 
 
 Hair, larva of Dermestes, (more 
 magnified). 
 
 be evident that, once in, there they must remain, as, from their struc- 
 ture, no power could extricate them, and consequently they were 
 broken off, that the Sea-mouse (as these Annellides are called) might 
 escape ; but, is it possible to imagine a better shaped harpoon ? 
 
LESSON 28.] EPITHELIUM. 93 
 
 465. A form of hair, from the larva of an insect (Dermestes lar- 
 darius) very common in larders in this country, is so curious in form, 
 that it were unpardonable to omit it ; moreover, it tends to show the 
 great display of Almighty wisdom, even in the construction of a 
 hair ! Two figures of this hair are given, as seen by different mag- 
 nifying power, and in different conditions ; the first (Fig. 160) is per- 
 fectly spear-shaped, the imbrications being most distinct : this is mag- 
 nified 300 diameters. In the second figure (161) the head of the 
 spear is opened like an umbrella, a state in which these hairs are fre- 
 quently found ; it is now magnified 500 diameters. 
 
 466. The larva (upon whose body these hairs are alone found) 
 does not exceed three-eighths of an inch in length, and appears to be 
 a very quiet, passive animal. Whatever use it makes of these most 
 remarkable hairs remains unknown, no one has even hazarded a con- 
 jecture in relation to them, notwithstanding there can be no reason- 
 able doubt that they are defensive, as those of Aphrodita are offen- 
 sive. Let the reader only imagine what the effect would be on 
 another animal, advancing to molest the larva of Dermestes, and 
 have all these hairs suddenly porrected (stretched forth), and the 
 umbrella-like processes suddenly opened in its face ! 
 
 The foregoing demonstrations have distinctly proved firstly, the 
 general character of imbrications as common to a majority of hairs ; 
 secondly, the important fact that hair, in man and most of the higher 
 animals, consists of three distinct tissues ; and, thirdly, that where a 
 tissue is lost (cuticular layer), it designates, most usually, the smooth 
 (non-imbricated) hairs. 
 
 LESSON XXVIII. 
 
 EPITHELIUM. 
 
 467. On the external surface of the body we found the skin pro- 
 tected by a layer of flattened horny scales, called Epidermis ; this 
 layer is continued over the outer surface of the lips, lining the whole 
 interior of the mouth, covering the surface of the tongue, descending 
 into and lining the (Esophagus, Stomach, and Bowels, but, in conse- 
 quence of its altered form, under the new name of Epithelium. 
 
 468. This peculiar tissue is also found covering all other Mucous, 
 Serous and Synovial membranes ; it lines the heart, blood-vessels and 
 
94 ANIMAL PHYSIOLOGY. [LESSON 28. 
 
 absorbents ; the follicles of the mucous membrane, and all the glands ; 
 the trachea (windpipe) and all its ramifications, no less than the air- 
 cells of the lungs. 
 
 469. Epithelial cells are various in figure, but resolve themselves 
 into two chief forms the tessellated or pavement epithelium, and the 
 cylindrical, or cylinder epithelium. 
 
 Both these forms may be provided with vibratile cilia, and each 
 has a tendency to run into the other. 
 
 470. The cells of the tessellated or pavement epithelium (Fig. 
 162) are flattened, and polygonal ; they are attached to each other 
 
 like the elements of a tessellated pave- 
 ment, by the numerous angular sur- 
 faces each scale presents hence the 
 name bestowed on this particular form 
 of epithelium. It occasionally hap- 
 pens, however, that they retain their 
 original rounded or oval form, and in 
 this case they are found separated by 
 an interval of space from each other. 
 471. All epithelial cells, without 
 respect to form, are remarkable for 
 the possession of a distinct nucleated 
 
 spot ; whence this nucleus is obtained is at this time a mystery ; it is 
 quite likely that they produce other epithelial cells, on the principle 
 of cell development, and this is all that is known in relation to the 
 subject. 
 
 472. The cylinder-epithelium is composed of elongated cells, cy- 
 lindrical in their form ; they are placed side by side, in a uniform se- 
 ries, the lower portion (frequently attenuated) constituting the base, 
 and the upper, exposed portion, projecting into the free space of the 
 tissue to which it is attached. 
 
 473. To see the well-formed cylindrical cell, a tissue should be 
 selected with a flat surface ; if it be convex, the lower ends of the 
 epithelial cells are always of less diameter than the upper portion 
 (attenuated), so that these epithelium scales much more resemble a 
 series of truncated cones, than cylinders ; this fact is well shown 
 in the epithelium covering the villi of the intestines, of which more 
 will be said in the proper place. 
 
 474. The Cylinder epithelium is found covering the entire sur- 
 face of the alimentary canal, from the cardiac orifice of the stomach 
 to its termination ; it is also found in the ducts of the glands which 
 
LESSON 28.] EPITHELIUM. 95 
 
 open into this canal, the duct (ductus choledochus) which conveys 
 the bile from the liver to the first of the small intestines (Duodenum), 
 the salivary, and other glands. 
 
 475. Both the forms of epithelium already described, are fre- 
 quently ciliated; the object of this arrangement appears to be to 
 propel fluids over the particular surface upon which they are placed, 
 and admirably they are adapted to this purpose ! When these organs 
 are moving in full activity, nothing can be seen but the incessant, 
 rapid whirl of particles of extraneous matter contained in the water ; 
 when their activity begins to cease, the exact form of the motion 
 then becomes visible. On such occasions it will be perceived that 
 the down stroke is given with great energy and activity, the cilia 
 recovering their position by a slower motion ; this can be successfully 
 imitated by striking the arm down very quickly, and lifting it back 
 in slower time. 
 
 476. It has been already remarked in the Introduction, that the 
 motion of vibratile cilia is alike independent of the will, and of vi- 
 tality, as its action can be distinctly seen in epithelium removed from 
 the body, long after death. 
 
 477. This phenomenon is not restricted to the human subject, or 
 to the higher mammalia, but is much better seen, and for a greater 
 length of time, in the lower forms of animal life. Thus : detached 
 epithelial scales from the mucous membrane of the human nose, have 
 been seen actively swimming through water by the agency of their 
 vibratile organs, some hours after their removal ; from the mucous 
 membrane lining the air- tubes of man (bronchi), for sixty hours after 
 death, and so vigorously, as to leave no doubt they would continue 
 in motion for a much longer period of time ; but the cilia of a Tor- 
 toise has been seen in active motion fifteen days after death, notwith- 
 standing the body was putrid ! 
 
 A view of ciliated cylinder-epi- FlQ - lf 
 
 thelium, of the truncated- cone form, 
 is given (Fig. 163), in which the 
 cilia (b) will be found occupying 
 the upper enlarged portion ; the 
 
 nuclei (a) are clearly seen in the ciliated epithelium. 
 
 centre of each cell. 
 
 478. If the tongue of a Frog be slightly scraped with a knife, 
 and the product placed in a drop of water, and examined by the mi- 
 croscope, masses of ciliated epithelium of the pavement kind will be 
 found (Fig. 164-1). These will be seen swimming through the water 
 
96 ANIMAL PHYSIOLOGY. [LESSON 28. 
 
 at a great rate, especially when first procured, and they will continue 
 so to do for a long time, or until the water evaporates. 
 
 479. The membrane covering the drum of the human ear (mem- 
 brana iympani) is also the seat of ciliated epithelium (Fig. 164 2) ; 
 
 likewise the human air-passages, as 
 already remarked, a representation 
 of which is given (Fig. 164-3). These 
 three last forms have been drawn to 
 scale so that their relative size may 
 be ascertained, and in all of them 
 
 1. Ciliated epithelium from the Frog's , . .. .- 11 
 
 mouth. 2. From the inner surface of nuclei are distinctly Visible, 
 human membrana tympani (drum of ton T -i ii 11 e -L TI 
 
 the ear) 8. From the human bron- 480. Like the Cells 01 the J^pl- 
 
 dermis, the Epithelial cells are con- 
 stantly being cast off, or exfoliated, and as constantly renewec 1 . 
 The time in which this is effected, however, is found to differ in tis- 
 sues ; thus, it is oftenest renewed in the mucous membranes devoted 
 to the function of nutrition, where, in healthy digestion, the epithe- 
 lium of the whole alimentary canal is said to be constantly thrown 
 off after every meal ; when this fails to be accomplished, disease is 
 supposed to be the never-failing result. 
 
 481. On the contrary, as there is little action on Serous surfaces, 
 the epithelium in such situations is much longer retained. 
 
 482. From the fact that two nuclei are not uncommonly found in 
 one cell (Fig. 162, c), and that cells sometimes present a constriction, 
 it is possible that they may be produced, like the vegetable cells, by 
 spontaneous division. 
 
 SEROUS AND SYNOVIAL MEMBRANES. 
 
 483. The free surface of these membranes is found to be covered 
 with Epithelium ; underneath, is a layer of condensed Areolar tis- 
 sue, which gives thickness, strength, and elasticity to the membrane. 
 The yellow fibrous element forms a large portion of the composition 
 of these membranes, and gives them elasticity in every direction. 
 
 484. Serous and Synovial membranes form closed sacs, which 
 contain a fluid ; that found in Serous membranes is nearly the same 
 with the serum of the blood, and the fluid of Synovial capsules is 
 the same, with an additional quantity of albumen. 
 
 485. Serous membranes are found in the abdominal cavity ; thus, 
 the membrane which lines the abdominal muscles, or the outer wall 
 of the abdomen peritoneum from a Greek word, signifying to ex- 
 tend around, is a serous membrane. 
 
LESSON 29.] THE OKGANS OF NUTRITION. 97 
 
 486. Serous membranes invest the abdominal viscera, and pass 
 from one viscus to another, until they have invested the whole of 
 them, when they are reflected on the parieties (sides). 
 
 487. The Synovial membrane is a thin membranous layer, which 
 covers the articular (joints) surface of the bones, from which it is 
 reflected upon the surfaces of the ligaments which surround and enter 
 into the composition of a joint. Like the serous membranes, these also 
 are shut sacs ; the peculiar fluid secreted by them is called synovia. 
 
 488. Certain sacs surrounding some of the joints are called 
 bursce mucosce (mucous purses) ; these are shut sacs, allied in struc- 
 ture to synovial membranes, and secreting a synovial fluid. 
 
 LESSON XXIX. 
 
 THE ORGANS OF NUTRITION. 
 
 489. If, during the summer months, a drop of water containing 
 animal or vegetable matter, or both, in a state of decomposition, be 
 examined with a microscope, it will display a world of animated 
 atoms ! 
 
 These compose the individuals forming the class known as " mi- 
 croscopical animal cula" The form and size, no less than other 
 characteristics of the individuals of this class, is extremely various ; 
 some of them (Monas crepusculus) being so minute that a single 
 drop of water would contain five hundred millions of them. Our 
 present object, however, is to inquire into the particulars of their 
 nutrition. 
 
 490. Prof. Ehrenberg long ago promulgated the idea that the 
 
 majority of these creatures are endowed with a 
 
 FIG. 165. 
 great but variable number of digestive sacs, each 
 
 of which (according to him) is independent of the 
 rest, but all of them communicating directly with 
 the oral cavity (Fig. 165, 6), as shown in the pro- 
 fessor's figure of the Monas termo supposed to 
 be the most minute animal revealed to our vision 
 even by the microscope. 
 
 491. Increased knowledge of these creatures 
 may probably demonstrate some mistake in con- 
 nection with this description, which is at variance with all that we 
 really know ; the figures (of the same authority) of larger animals 
 
 7 
 
98 
 
 AXIMAL PHYSIOLOGY. 
 
 [LESSON 29. 
 
 FIG. 166. 
 
 FIG. 167. 
 
 Alimentary canal, Vorticella 
 citrina. 
 
 Alimentary canal, Sten- 
 tor polymorphus. 
 
 of the same class, appear to be much more consistent j thus, the 
 
 alimentary canal of Vor- 
 ticella citrina (Fig. 166) 
 is distinctly sacculated, 
 and so, too, in Stentor 
 polymorphus (Fig. 165); 
 in all these figures the 
 ciliated oral (mouth) 
 aperture is marked a. 
 
 In the Vorticella 
 and Stentor (Figs. 166 
 and 167), the circular 
 intestine is perfectly 
 sacculated (c), or alter- 
 nately dilated and con- 
 tracted (b, Cj d) throughout its entire course. 
 
 Two of the figures (166 and 167) are represented as dissected out 
 of the body ; this has been done by the mind's eye, for no earthly 
 power is equal to such a task manually performed. 
 
 ROTIFERA. 
 
 492. The animals of this class have their vibratile 
 cilia placed in circular or semicircular groups, and 
 when in action they appear to revolve hence their 
 name. The so-called wheel animalcule, found in 
 leaden gutters, and in infusions of hay, is a Eotifer^ 
 a view of which is given (Fig. 168). The mouth is 
 seen at a ; eye-spots at b ; antenna (?) at d ; jaws 
 and teeth, ej alimentary canal,/, g (glandular, ?), 
 mass enclosing it ; h, longitudinal muscles ; i, tubes, 
 containing water, or blood ; k, young animals ; and 
 Z, cloaca. 
 
 The body of a Rotifer is more or less elongated ; 
 its posterior extremity is furnished with a pair of 
 forcipated instruments, or claspers, which, when not 
 required for use, can be retracted, and protected 
 within a sheath. 
 
 493. The vibratile cilia are arranged in from 
 two to five groups, placed on lobes, as shown in 
 Notommata clavulata (Fig. 169, a). 
 
 Eotifer vuigaris. This beautiful creature is as transparent as a 
 
LESSON 29.] 
 
 THE ORGANS OF NUTRITION. 
 
 99 
 
 glass, and all the organs described can be seen in the microscope, if 
 it remain quiet, with the utmost distinctness ; it will be apparent 
 that the alimentary canal, and all the organic structures, have made 
 a great advance from the simple sacculated condition, and only one 
 aperture of the Vorticella, and its allies. 
 
 494. These animals are remarkable for their tenacity of life. 
 As early as the year 1701, Leeuwenhoek had been examining some 
 specimens of Rotifer vulgaris, and left FlG 169 
 
 the water in which they were con- 
 tained to evaporate. Two days after- 
 ward, having added some rain water, 
 previously boiled, within half an hour 
 he saw a hundred of the Rotifera re- 
 vived, and moving about ! 
 
 A similar experiment was made, 
 with the same results, keeping the 
 animals dried up for a period of five 
 months ; and this has been repeated, 
 and confirmed by many subsequent 
 authorities, the time being extended 
 to three years. 
 
 ENTOZOA. 
 
 495. The Entozoa are parasitic 
 internal, or intestinal worms ; of 
 these, every known animal has its 
 own peculiar species, and usually 
 more than one ; in man, no less than 
 eighteen different species have been 
 detected, occupying the various cavi. 
 ties and tissues of the body. 
 
 496. Excluded from the influence 
 
 of light, they are almost uniformly white in color ; deprived of air 
 they do not possess organs of respiration ; they 
 are, in short, little (if any thing) but sacs for 
 the imbibition of nutriment. 
 
 497. The Acephdlocyst (Fig. 170) consists 
 of a globular or oval vescicle filled with fluid ; 
 sometimes suspended freely in the fluid of a cyst 
 of the surrounding condensed cellular tissue, de- 
 veloping smaller acephalocysts, which are discharged from the outer 
 or the inner surface of the parent cyst. 
 
 Notommata clavulata. 
 &, 6. Longitudinal muscles, which 
 shorten the "body. 
 
 c, c. Transverse muscles, which dimii 
 
 nish the breadth of the body. 
 
 d, d. Ganglions (nerve knots) of the 
 
 neck. 
 
 e. Cervical ganglion. 
 / Pharynx, containing the jaws. 
 g. Alimentary canal, terminating 
 
 h. a Cloacal outlet. 
 i. Glands, either salivary or liver. 
 Jc. Eeproductive tubuli. 
 m. Forcipated instruments for pre- 
 hension. 
 
 FIG. 170. 
 
 The Acephalocyst. 
 
100 ANIMAL PHYSIOLOGY. [LESSON 29. 
 
 498. They vary from the size of a pea to that of a child's head ; 
 in the larger ones the wall of the cyst has a laminated texture. 
 They are of a pearly whiteness, without fibrous structure, elastic, 
 spurting out their fluid when punctured. 
 
 499. So far as known, there are two species of this animal ; one 
 the Acephalocystis JEndogena, or the " pill-box Hydatid " of Hunter, 
 most commonly found in man ; and the Acephalocystis Exogena, 
 found in the Ox, and other domestic animals. All these animals 
 multiply by fissiparous division, precisely like the multiplication of 
 the cells of plants, to which they appear to be most nearly allied. 
 In the first named species, this process takes place from the internal 
 surface of the parent cyst, and in the last, from the external surface 
 hence their specific names, respectively. 
 
 500. Another parasite, closely allied to the above, the C&nurus 
 Cerebralis, is found in the substance of the brain of Sheep, Calves, 
 Pigs, Rabbits, and even Dogs, and produces a disease called (in 
 England) the " gid," or " mad staggers." 
 
 501. In this disease, the animal affected by it appears to be 
 " giddy," and staggers with the head down to the ground, or butting 
 
 FIG ill against extraneous substances in a state of apparent 
 
 unconsciousness. A figure of this parasite is 
 given (Fig. 171). 
 
 502. The Coanurus is one of the most simply 
 organized animals, consisting of a large bag (c) 
 always filled with water, at the end of a long neck 
 (5), the summit of which is provided with suctorial 
 mouths (a), adapted alike to adhesion to the tis- 
 sues by which it may be surrounded, and for the 
 procuration of nutriment. They are frequently 
 found provided with many heads, which can be 
 retracted within, or protruded without the com- 
 
 Comurus cerebral*. mon cygt 
 
 503. This Hydatid form is by no means uncommon as a parasite 
 in the animal kingdom and in man, and, wherever found, they in- 
 variably produce distressing, if not fatal disease. They have no sex, 
 and appear to propagate most abundantly by the mere act of spon- 
 taneous division, such as is common to plants, and to the Acephalo- 
 cysts. 
 
 Of course, there can be no cure for the Coenurus, and the best 
 that can be done is, to terminate the animal's suffering as soon as 
 the " gid " makes its appearance. After death, pass a saw round the 
 
LESSON 29.] 
 
 THE ORGANS OF NUTRITION. 
 
 101 
 
 skull, and remove the upper part, so as to expose the brain ; an ani- 
 mal, like the figure given, will be invariably found. 
 
 Many Cystoid animals there are closely allied to the Coenurus, 
 and afflicting alike domestic animals, and man, but their effects are 
 not immediately fatal. 
 
 504. The Echinococcus hominis, is a small animal cell, provided 
 at its summit with a remarkable circlet, or coronet of teeth, by which 
 it clings to the tissue, and four suctorial mouths for the imbibition 
 of nutriment ; they have been found in the liver and other organs of 
 the human body (Fig. 172) ; a, head ; b, suckers. 
 
 505. Another cellular animal (Cysticercus cellulosa) has been 
 met with in the eye, brain, substance of the heart, and the voluntary 
 muscles of the body (Fig. 173) ; in addition to the head, formed 
 like the last, this animal possesses a 
 
 long neck, which terminates in the nu- 
 trimental sac. The head, with its 
 coronet of spines, a/ the digestive 
 sac, b. 
 
 A magnified view of the coronet 
 of spines is given in Fig. 174 ; b, the 
 spines, or teeth ; a, the suctorial mouths. 
 
 506. These animals infest Pigs to an enormous extent, causing 
 what is called the measles ; and as the vitality of the ova is not de- 
 stroyed in the process of cooking, those persons who eat fresh pork 
 
 PIG. 172. 
 
 FIG. 173. 
 
 Echinococcus he- 
 minis. 
 
 Cysticercus cel- 
 lulosa. 
 
 FIG. 174. 
 
 Head of Cysticercus, magnified. 
 
 (not salted) need not be surprised to find themselves the victims of 
 507. TcBnia solium, or tape worm, of which it is now well known 
 
102 
 
 ANIMAL PHYSIOLOGY. 
 
 [LESSON 29. 
 
 FIG. 175. 
 
 FIG. 176. 
 
 the Cysticercus is the young. The head of the latter animal is, in 
 every respect, so identical with the former, that a figure 
 of it is unnecessary. 
 
 508. Two species of Distoma (dis, two ; stoma, 
 mouth) infest the human subject D. hepaticum, found, 
 as the specific name indicates, in the liver, and D. lan- 
 ceolatum ; of these animals, the former is also very abun- 
 dantly found in the Pig. It is also sometimes found in 
 large quantities infesting the liver of the Sheep, and 
 in them it causes the rot. They are supposed to take 
 up Planariae with the water they drink, which, under 
 D.tepaticum. a i tere( j circumstances of position, becomes a Distoma. 
 509. The nutrimental canal is very simple in both these animals. 
 In D. hepaticum (Fig. 175), a represents the suctorial mouth, b the 
 anterior sucker ; the second is imperforate, and is simply an organ 
 of adhesion. The alimentary canal is continued from the mouth for 
 a short distance as a single tube, and then divides ; the 
 divisions run parallel with each other, and surround the 
 ventral sucker, which-is placed between c, c, and is also 
 for the sole purpose of adhesion ; the parallelism of the 
 tubes is then continued to the caudal extremity. Each 
 tube gives off several branches from the outer, and but 
 few from the inner side ; many of these branches are 
 ramified, and all of them terminate in blind extremities 
 near the margin of the body. 
 
 510. In Distama lanceolatum, the suctorial pores 
 are larger than in D. hepaticum ; the anterior sucker is 
 perforated by the mouth (Fig. 176, a), and the alimen- 
 tary canal, commencing by a kind of pharynx, is con- 
 tinued as a very slender tube (c) for a short space, and 
 bifurcates, each division being continued without rami- 
 fication, on each side of the body to the tail, where it 
 ends in a blind extremity (d). The ovaria are seen at 
 
 y, and the oviducts at g. The second sucker is at b. 
 
 511. It is a very remarkable fact that nearly all 
 the animals parasitic in man, are found in only one 
 other animal the Pig ; and whether we obtain them 
 directly from itj or whether it be another point of close 
 affinity between the animal in question and humanity, 
 
 has yet to be determined. 
 
 Dist ia 1 tum nceo " 
 
LESSON 30.] 
 
 NUTRITION IN POLYPI. 
 
 103 
 
 FIG. 177. 
 
 LESSOR XXX. 
 
 ORGANS OF NUTRITION IN POLYPI. 
 
 512. We have now to consider the structure of an extremely in- 
 teresting class of animals, moderately minute in size, and of won- 
 drous beauty ! 
 
 The Polypi (poly, many ; pes, feet) are so called from their 
 general resemblance to the many armed Cuttle-fishes, and these ob- 
 tained the name of "many feet " from the Greek naturalists. They 
 are almost universal in their distribution ; inhabiting the fresh water 
 pools in great abundance, they form objects of surpassing interest to 
 the naturalist. 
 
 513. But for endless variety of external form, associated with 
 every shade of color, we must seek 
 
 for these charming creatures in the 
 Ocean. 
 
 The limits of this work will 
 not permit an extended notice of 
 these animals ; and in the present 
 connection we are in search of nu- 
 trimental organs, chiefly. 
 
 514. The fresh waters furnish 
 three species of Hydra; H. vul- 
 garis; H. fusca, and H. viridis, 
 or green Hydra. Of these, the H. 
 fusca is less common, and by far 
 the most beautiful (Fig. 177). The 
 tentacles, as the arms are called, 
 are shorter than the body in H. vul- 
 garis, but in this species they are 
 of very great length, and when seen 
 in a glass jar groping about, and 
 searching for prey, present an ob- 
 ject of incredible magnificence ! 
 
 515. The Hydrse are carnivo- 
 rous ; feeding upon the minute ani- 
 mals (especially Crustaceans) which 
 are found abundantly in the same 
 pools. The instant a tentacle 
 
 touches an animal, although its body may be rotected by a shell, it 
 
 Hydra fusca. 
 
104 ANIMAL PHYSIOLOGY. [LESSON 30. 
 
 dies, stung to death, paralyzed. It is then seized by the terminal 
 portion of the tentacle, and conveyed to the mouth, while the other 
 tentacles are incessantly in search of food, to supply the wants of an 
 ever hungry stomach. This organ occupies the whole interior of the 
 body there is no intestine ; the terminal portion of the body forms 
 a narrow base, provided with a suctorial disc, for the purpose of at- 
 taching itself to aquatic vegetation. 
 
 516. The simplicity of structure of these creatures may be in- 
 ferred from the fact, that they may be turned inside out without the 
 slightest detriment ; that which was the external surface instantly 
 assumes the function of a true digestive stomach, while the stomach 
 takes upon itself the office of a secreting organ, and produces young. 
 
 517. The mode of reproduction of the Hydrse is curious : a num- 
 ber of little bud-like processes make their appearance on the external 
 surface, which soon resemble the parent in all their external charac- 
 ters ; each possesses its mouth and tentacles, and although remaining 
 attached to the body of the parent, proceeds to provide for its own 
 
 wants. It is true that a canal 
 of communication exists between 
 the parent and the young bud, 
 through which nutriment passes 
 to help sustain it ; but after a 
 short time this canal closes up, 
 and the young continue attached, 
 or not, at their pleasure. A 
 figure is given of a family group, 
 such as those persons who have 
 kept, and bred these animals, 
 will immediately recognize (Fig. 
 178). The first figure (177) rep- 
 resents two perfect generations ; 
 the parent Polype (a), a young 
 bud (b), and a more advanced 
 one (c). 
 
 This figure (178) shows three 
 generations ; the original parent 
 (a), the first family (6, 6), and 
 nydra viridis. "^ the second family, produced from 
 
 the first (c, c). 
 
 But apart from the process of budding (gemmation), there is 
 another mode by which they can be produced in great quantity, 
 
LESSON 30.] NUTRITION IN POLYPI. 105 
 
 namely, by cutting them in pieces, when each portion will become a 
 perfect animal. 
 
 518. We have referred to the Marine Polypi ; do our readers 
 chance to know that the red coral of Commerce, which forms such a 
 pretty ornament for the necks of children, is composed of Carbonate 
 of lime, and once formed the internal skeleton of a family of Polypes, 
 by whom it was manufactured ? 
 
 519. The Order of Polypes, to which Corallium rubrum (red 
 coral) belongs, possess eight short, broad, leaflike tentacles around 
 the mouth, and in this species they are white. The deeply red- 
 colored skeleton is, as has been said, internal ; it is covered by a red 
 flesh, of paler color than the skeleton, and this is everywhere exca- 
 vated into little cavities, for the reception of the individual Polypes. 
 In this order the young continue to form a part of one common 
 family, which may number several hundred individual members ; 
 they bear the same relation to each other, and the group with which 
 they are connected, that the leaves bear to a tree. 
 
 520. The excess of nutriment FIG. iso. 
 due to the combined nutrition of so 
 
 many members, goes to extend the 
 common mass ; to make new bone, 
 cover it with new flesh, and to place 
 in its cells a new family of Polypes. 
 An illustration of this species is 
 
 FIG. 179. 
 
 Bed coral, polypes in situ. Polype of Corallium rubrum. 
 
 given (Fig. 179), in which the bone (a) is shown, covered with the 
 flesh (6), and the polypes, with the tentacula displayed (c), emerging 
 from the cells. 
 
 521. To show the general structure, and especially the alimentary 
 canal of this polype, a. magnified figure is given (Fig. 180). The ex- 
 
106 ANIMAL PHYSIOLOGY.. [LESSON 31. 
 
 panded tentacles are seen at a ; at the base of them (6) is the 
 mouth ; the stomach, provided with eight vertical partitions (d), oc- 
 cupies the centre of the animal. At the bottom of the stomach is 
 an outlet (e) for the transmission of the nutrient matter to a canal, 
 which communicates in like manner with the stomachs of all the 
 polypes, by which means the nourishment is made available for the 
 purposes of the commonwealth. Appended to the lower portion of 
 the stomach are the ovigerous (egg-producing) tubuli (/). 
 
 LESSON XXXI. 
 
 ACALEPHA. 
 
 522. The surface of the Ocean, during the summer months, pre- 
 sents a vast assemblage of soft-bodied, gelatinous forms, of every size, 
 from many feet diameter, down to an inconsiderable speck ; all of them 
 as transparent as glass, all luminous at night, and many of them 
 sharply stinging the hand that touches them : from this latter pro- 
 perty they obtain their name ; the Greek word signifying a nettle. 
 
 523. The best account of these animals is that given by Peron 
 and Leseueur, two French naturalists. 
 
 " The substance of a Medusa is wholly resolved by a kind of in- 
 stantaneous fusion into a fluid analogous to sea water ; and yet the 
 most important functions of life are effected in bodies that seem to 
 be nothing more than, as it were, coagulated water. The multipli- 
 cation of these animals is prodigious ; and we know nothing certain 
 respecting their mode of generation. 
 
 " They may acquire dimensions of many feet diameter, and weigh 
 occasionally from fifty to sixty pounds ; and their system of nutrition 
 escapes us. They execute the most rapid and continuous motions ; 
 and the details of their muscular system are unknown. Their secre- 
 tions seem to be abundant ; but we perceive nothing satisfactory as 
 to their origin. They have a kind of very active respiration ; its 
 real seat is a mystery. 
 
 " They seem extremely feeble, but fishes of large size are daily 
 their prey. One would imagine their stomachs incapable of action 
 on these latter animals ; in a few moments they are digested. 
 A great number of these Medusae are phosphorescent, and glare 
 amidst the gloom of night like globes of fire ; yet the nature, the 
 principle, and the agents of this wonderful property remain to be dis- 
 
LESSON 31.] 
 
 NUTRITION IN ACALEPHA. 
 
 107 
 
 FIG. 181. 
 
 covered. Some sting and inflame the hand that touches them ; but 
 the cause of this power is equally unknown." 
 
 524. Our ignorance of these animals is by no means so profound at 
 the present day, albeit much yet remains to be discovered. John Hun- 
 ter was the first to inject the stomach and communicating canals, and 
 thus discovered the extraordinary route by which the nutriment 
 
 reaches the digestive cavity, and also 
 the channels by which the digested 
 aliment is distributed for the sup- 
 port of the general system. 
 
 The animal on which the expe- 
 riment was made, belonged to the 
 Genus Ehizostoma (rhizoma, a root ; 
 stoma, a mouth), and a figure of it 
 is appended (Fig. 181). 
 
 525. Every part of the body of 
 this Bhizostoma Cuvieri is of the 
 utmost transparency, so that the 
 internal organs may be distinctly 
 seen through the external parietes 
 of the mantle. 
 
 The gastric cavity, or stomach 
 
 (d)j is in the centre, surrounded by four ovarial sacs (e, e, e). A 
 number of wide vessels extend from the circumference of this quad- 
 rangular stomach to the pur- 
 ple-colored, highly vascular, 
 lobed and respiratory margin 
 of the disc (Figs. 181 and 
 182, h, h). 
 
 The peduncle hangs sus- 
 pended from the centre of 
 the disc, and is divided into 
 eight branches (c, e), which 
 terminate in simple lobed di- 
 latations (a, a), having their 
 surface marked with numer- 
 ous depressions, which are the 
 orifices of internal canals (a, 
 5, c), leading upwards to the 
 stomach (d). In the middle 
 and upper parts of these section of EMzostoma. 
 
 FIG. 182. 
 
108 ANIMAL PHYSIOLOGY. [LESSON 31 . 
 
 eight branches there are fimbriated (fringed) membranous extensions 
 (181, /, 182, /, &), the numerous vessels of which also anastomose 
 with the principal ascending trunk of each peduncle. On making 
 a vertical section of this Rhizostoma, thus injected, through the 
 centre of the disc (182), the internal canals (5, c) are seen, commencing 
 from the orifices of the branches (a), receiving all the lateral absorbent 
 canals (/, k) in their course, and uniting above to form one large 
 03sophageal passage (m) before entering the central gastric cavity (d). 
 The peduncles divide and subdivide like the roots of a plant; the 
 cesophageal canals follow these ramifications, and ultimately termi- 
 nate in numerous pores (/), upon the margins of the branches and 
 clavate (clubbed) ends of the ramified peduncles. These pores are 
 the commencement of the nutritive system ; they are analogous to 
 the numerous polype-mouths of the compound coral animal. 
 
 Minute animalcules, or the juices of a decomposing larger ani- 
 mal, are absorbed by these pores, and conveyed by the successively 
 uniting oesophageal canal to the stomach. 
 
 The nutrient fluid passes by vessels which radiate from that 
 cavity, to a beautiful network (182, h, h) of large capillaries, which 
 spread upon the under surface of the margin of the disc. Thin 
 membranous partitions (182, Z, Z) separate the cavity of the stomach 
 (d) from the four ovarial sacs, which open externally by distinct 
 apertures (i, i). 
 
 526. In some of the higher Medusae, as in Cetonia aurita (hav- 
 ing lobes like the e,ar), the mouth is single, and opens directly from 
 the centre of the lower surface of the mantle, into a capacious sto- 
 mach, from which numerous vessels radiate to a circular canal sur- 
 rounding the margin of the disc. The mouth of Cetonia is of quad- 
 rangular form, supported by four curved cartilaginous plates, from 
 which are suspended four elongated, tapering lips, or tentacula (Figs. 
 183 and 184, a, a). On inverting the disc (184) the short, four- 
 sided oesophagus is seen in the centre, leading to a capacious gastric 
 cavity, partially divided into four sacs (183 and 184, c, c), and from 
 each of these sacs numerous alimentary canals (183 and 184, 5, b) 
 radiate towards the margin of the mantle, ramifying with great regu- 
 larity, but presenting few anastomoses compared with those of the 
 Rhizostomes. 
 
 Around the lower part of the stomach the four ovarial sacs (184, 
 c) are placed, containing the colored ovaries, and opening externally, 
 each by a distinct aperture. From around the margin of the stomach, 
 sixteen canals come off, alternately simple and ramified, which end ID 
 
LESSON 32.] NUTRITION IN THE ECHINODERMA. 
 
 109 
 
 the circular vessel (184, d) passing round the margin, and by placing 
 the living Medusa in sea water tinged with indigo, the stomach (18P, 
 c), the radiating vessels (184, b, 5), and the circular marginal canal 
 (184. d), are soon found to be filled with the blue coloring matter, 
 
 Fie. 183. FIG. 184. 
 
 Cetonia aurita. 
 
 Cetonia aurita. 
 
 while the rest of the animal remains colorless. The free margin of 
 the mantle is fringed with a row of minute tentacula, which appear 
 to be highly sensitive, and in constant motion ; the organs of vision 
 (according to Ehrenberg) are placed in the slight depressions around 
 the free edge of the disc (e, 183 ; /, 184). 
 
 LESSON XXXII. 
 
 ORGANS OF NUTRITION IN THE ECHINODERMA. 
 
 527. The bodies of Star- 
 fishes, Echini, &c., are more 
 or less covered with spines 
 (Fig. 185), and hence the 
 name of the class, which is 
 formed from echinus, a spine 
 and derma, skin ; frequently 
 they are called the prickly- 
 skinned animals. 
 
 528. The digestive ap- 
 paratus in the Star-fishes, Echinus. 
 
 and its immediate allies (Euryale, Ophiura, or brittle stars, Asterias, 
 
110 ANIMAL PHYSIOLOGY. [LESSON 32. 
 
 &c.), is very simple ; like the Hydra, it consists of a single sac, 
 with but one aperture. 
 
 In others (Comatula, Encrinus)^ the digestive canal is more 
 lengthened, and curves upon itself, and has an outlet distinct from 
 the mouth. 
 
 In the JEchinida (Sea-urchins) and Holothuridce (Sea-cucum- 
 bers) there is a long, narrow, convoluted intestine, passing through 
 the body, with very slight gastric enlargement. 
 
 In the higher forms of Star-fishes (Holothuridae) the folds of the 
 long intestine are connected by means of a highly vascular mesen- 
 tery, which, whether injected artificially or otherwise, presents an ob- 
 ject of surpassing beauty. 
 
 529. The mouth of the Asterias (Fig. 186) is placed in the cen- 
 tre of the inferior surface of the body, surrounded by long tubular 
 
 FIG Ig6 tentacula, and pro- 
 
 tected by fasciculi of 
 calcareous spines. 
 
 By means of a 
 very short oesophagus, 
 it leads directly to a 
 wide and very dilata- 
 ble stomach (a), pro- 
 vided with a distinct 
 internal mucous lin- 
 ing, and an external 
 muscular coat. 
 
 It occupies the 
 whole central part of 
 the body, from which 
 Nntrimental organs, Asterlus rnbens. the marginal divisions 
 
 originate. From the stomach two long, tapering, ramified cceca, 
 which commence by a single trunk, are given off opposite the com- 
 mencement of each ray, and are distributed through it in a central line, 
 so that collectively there are ten pairs of the coecal appendages (b, b). 
 
 530. Each of these cceca is attached to the integument along the 
 upper part of each ray, by a delicate vascular membrane. In addi- 
 tion to these appendages, the stomach is also provided with small, 
 short cceca (blind sacs) at its upper part within the disc, and at its 
 sides, between the great coecal trunks of the rays. 
 
 531. The Echinida (Fig. 187) present a more elevated form of 
 the nutrimental organs ; the mouth is furnished with five large and 
 
LESSON 32.] NUTRITION IN THE ECHINODERMA. 
 
 Ill 
 
 powerful teeth, called the " Lantern of Aristotle," for the comminu- 
 tion of the food (Fig. 188). It is a singular fact that, in this Class, 
 the number five, or its multiples, constantly meet us : Jive i&ys,Jive 
 teeth ; ten coscal appendages, and so on. In the Class Acalepha, 
 FIG. 1ST. FIG. 188. 
 
 The Lantern of Aristotle. 
 , The Teeth. 
 &, The Alveolar pro- 
 
 Nutrimental organs, Echinus. 
 
 c, Hooks for the attach- 
 ment of muscles. 
 
 four and its multiples are as constantly found ; the tentacles are four 
 in number or eight ; and this principle is constant in these two classes. 
 
 532. The teeth, (Fig. 188, a) are three-sided prisms, dense at the 
 lower, pointed extremity, softer at the base, with their inner edge 
 sharp and fit for cutting; they are each implanted in a larger trian- 
 gular pyramid (5), two sides of which are in close apposition with 
 opposite sides of the adjoining pyramids, and are transversely grooved, 
 like a file. 
 
 A further view of two of these teeth, in apposition by the alveo- 
 lar processes, is given (Fig. 189). The upper, soft portion of the 
 teeth is shown at a ; the terminal, hardened 
 part at b ; the alveolus at c. The secretion 
 of some simple salivary follicles assist in com- 
 pleting the mastication of the food. These 
 teeth are put in motion by a series of well- 
 developed muscles, said (by Valentin) to con- 
 sist of the striped fibre. 
 
 533. In the cavity of the lantern is the 
 pharynx, which is divided by five longitudinal 
 folds ; the salivary coeca are placed in its im- 
 mediate neighborhood. A slender oesophagus 
 
 FIG. 189. 
 
 Two of the Teeth of Echi- 
 nus, natural size. 
 
112 ANIMAL PHYSIOLOGY. LESSON 32. 
 
 (c) leads to the gastric portion of the intestine (d) ; and that canal 
 twice winds round the circuit of the abdominal cavity before its final 
 termination. The intestine is generally found loaded with fine sand ; 
 its surface, and that of the vascular mesentery, is covered with a rich 
 network of capillary blood-vessels. 
 
 534. Near the oesophagus is a fusiform, dilated, contractile vesicle ; 
 this is the heart, and by tying a small pipe in it, and passing injec- 
 tion through it, the whole vascular system will be beautifully dis- 
 played. A trunk proceeds from the heart, which forms a circle round 
 the oesophagus, at the base of the lantern ; a second trunk proceeds 
 from the opposite end of the heart, and forms a similar circle round 
 the vent ; an artery and a vein also run along the concave margin of 
 the intestine ; the blood is of a yellowish color, and exhibits a dis- 
 tinct nucleus. 
 
 HOLOTHUKIA. 
 
 535. These animals have been likened to a lengthened Echinus, 
 deprived of its calcareous plates, and with its axis extended in a lon- 
 gitudinal direction. The skin is usually soft and leathery ; in a few 
 genera, strengthened by calcareous spines. Five avenues of suckers, 
 terminating the long retractile tubular feet, divide the body into as 
 many longitudinal segments, which, in the majority, are of equal, or 
 
 nearly equal dimensions. In some species 
 
 FIG. 190. 11 IT-, 
 
 the suckers are developed only on one 
 side; in other species the body is entirely 
 covered with them ; the suckers are simi- 
 lar in every respect to those of Echini 
 and Star-fishes. 
 
 536. The mouth is surrounded by 
 plumose tentacula, usually of great beau- 
 ty; when complete, the number is al- 
 ways Jive, or its multiple (Fig. 190). 
 The tentacula can be withdrawn into 
 the mouth by means of its proper 
 muscles, and in captivity they frequent- 
 ly tantalize the eager naturalist by re- 
 taining them in the interior of the 
 body for days together ; nay, they often 
 die with them in this position. 
 
 537. They are provided with a circle 
 of teeth, analogous to those of the 
 
 Cucumaria frondosa. Echini. 
 
LESSON 32.] NUTRITION IN THE ECHINODERMA. 113 
 
 538. The oesophagus passes through this circle, and opens into 
 a more or less muscular stomach, from which an intestine, often very 
 complicated, proceeds to the posterior portion of the body, where 
 it dilates into a cloaca, from which two long ramified tubes (the 
 respiratory organs) originate. These facts are demonstrated in the 
 annexed figure of Holoihuria elegans (Fig. 191). 
 
 The mouth is shown at a / the tentacles, in this instance retract- 
 
 FIG. 191. 
 
 Holothnria elegans. 
 
 ed, at b ; the stomach is seen at d ; a biliary follicle (or, what is more 
 likely, the ampulla Poliana, a bottle), which would seem to be pecu- 
 liar to this species at c ; the very long, convoluted intestine is con- 
 tinued from the stomach, and designated by the same letter d, d, d, 
 8 
 
114 ANIMAL PHYSIOLOGY. [LESSON 32. 
 
 until it terminates in the cloaca,// it is connected to the body in 
 several places by a mesentery of great vascularity (e, e), which also 
 connects one fold of the intestine to another. 
 
 539. The branchise (gills, h), which arise from the cloaca, give 
 off a great number of ramified branches from the central stem. 
 They are always filled with sea water, from which the gills possess 
 the power of eliminating the oxygen ; the vesicles, or cells of the 
 gills, are described at m. The blood-vessels which pass from the 
 mesentery to the gills, conveying the blood to be aerated, are shown at 
 n / and the external opening of the cloaca at g. 
 
 Seen in a recently killed specimen, these gills form a very inter- 
 esting object ; they then seem to exhibit a constant vermiform mo- 
 tion, which continues long after the apparent death of the animal. 
 
 540. One fact in connection with Holothuria is too remarkable 
 to omit. Those persons who handle a living specimen for the first 
 time, will be surprised to find that, without the slightest provocation, 
 the integument suddenly bursts, and the whole contents of the body 
 are violently thrown out ; neither is this all, for, if the emptied skin 
 be thrown into a vessel of sea water (which should be renewed da'ly), 
 the alimentary canal, and all the lost organs including the teeth 
 and the tentacles will be reproduced. 
 
 541. This act appears to be due to the excessive irritability of 
 these animals, which, when once excited, appears to be beyond its 
 power to control. The muscular system is of enormous power, es- 
 pecially in the transverse direction of the body. 
 
 542. To enable the creature to shorten its length, and to retract 
 the head, strong tendinous chords are attached to the muscular coat ; 
 of these, five are devoted to the head alone. 
 
 543. The Cucumaria frondosa is the reputed largest Holothuria 
 known ; Fig. 190 is copied from a specimen, now in the Hunterian 
 Collection, England, which measures twelve inches in the dead state ; 
 beside it, in the Museum, is a preparation of another individual of 
 the same species, which, in life (sometimes) measured three feet 
 it did so at the moment it was killed, and at the instant contracted 
 to four inches, all that it measures now. 
 
 544. The sexes in these animals are separate ; the important 
 organs of the female the tubuli containing an immense quantity of 
 ova are seen at k. These, filled to repletion with their valuable 
 contents, form a very interesting object for the microscope, while the 
 rich orange color of the ova contributes greatly to the attractiveness 
 of such a preparation as that figured. 
 
LESSON 32.] NUTRITION IN THE ECHINODEKMA. 
 
 115 
 
 FIG. 192. 
 
 545. From the amazing number of ova deposited by the various 
 species of Holothuria during only one season, they ought to be the 
 most abundant of all animals, instead of being moderately rare ; the 
 probability is that their eggs are greedily eaten by -small fishes, Me- 
 dusae, some Zoophytes, and, in fine, by the host of small Carnivora 
 incident to the ocean. 
 
 A preparation of the Ovarium of Cucumaria frondosa, dissected 
 out of the body, is shown in Fig. 192. The tubuli are suspended by 
 
 the oviduct (a), the tubes 
 being quite full of ova, of a 
 rich orange color. The organs 
 of reproduction are placed in 
 the head, between the ten- 
 tacula; the external orifice 
 of the oviduct is a small, dark- 
 colored papilla, which (unless 
 carefully sought for) might 
 
 FIG. 193. 
 
 Ovarium, Cucumaria frondosa. Enlarged ovarian tubuli, C. frondosa. 
 
 easily elude detection. An enlarged view of these ovarian tubuli, 
 showing their contents, is given in Fig. 193. 
 
 546. One of the most elegant preparations the animal kingdom 
 can furnish, is the respiratory organs of Holothuria. 
 
 Those of Cucumaria frondosa are reduced from eleven inches in 
 height, and shown in Fig. 194. The cloaca (a) is entirely covered 
 with strong, flat muscles, which were attached to the muscular coat 
 of the integument. Great muscular power is necessary to this organ, 
 whose constant function it is to draw water from the ocean, pump it 
 up to the minutest sac, or modified air cell (d), and discharge it 
 when unfitted for further use. Beside the Cloacal outlet, there must 
 be a series of minute apertures, which have hitherto defied discovery 
 in connecting with this apparatus, for, if a specimen (previously ac- 
 customed to handling, by being tickled daily, in sea water) be care- 
 
116 
 
 AXIMAL PHYSIOLOGY. 
 
 [LESSON 32. 
 
 fully lifted out of the vessel containing it, on the palms of both 
 hands, five beautiful, minute jets of water, crossing each other in 
 various directions, will frequently be seen ; so great is the quantity 
 of water contained in the respiratory apparatus, and so small the 
 apertures, that the streams will continue steadily to flow for half an 
 hour. 
 
 547. The intestine, which, as before described, also terminates in 
 
 FIG. 194. 
 
 Respiratory organs, Cucumana frondosa. 
 
 the cloaca, is shown at 5 / the respiratory tubes, with their ramified 
 branches, at c. These organs, like the alimentary canal, are confined 
 to a given situation in the interior of the body : the latter, by means 
 of the mesentery, the former, by a series of round, white, tendinous 
 chords (e, e). 
 
 Authors who have only seen such a preparation, and know nothing 
 of its connections by manual examination, have greatly mistaken the 
 character of these tendons ; thus Grant (and others) describes them 
 
LESSON 32.] NUTRITION IN THE ECHINODERMA. 
 
 117 
 
 FIG. 195. 
 
 FIG. 196. 
 
 " as follicles," and add that " they pour their secretion into the respi- 
 ratory organs." * 
 
 SIPUNCULUS. 
 
 548. The rough Syrinx, Tube-worm, or Sipunculus, according 
 to modern classification, is a very curious animal, and as much (ap- 
 parently) unlike a Star-fish as can be imagined. It is, however, 
 closely allied to Holothuria. 
 
 549. The body is cylindrical, and covered with a strong coriaceous 
 (leathery) integument, generally rugous (wrinkled), except at the 
 posterior extremity, which is longitudinally grooved to its termi- 
 nation. A specimen, about two inches long, is represented in Fig. 
 195. On opening a simi- 
 
 ilar specimen, a very cu- 
 rious condition of the 
 nutrimental apparatus 
 presented itself; the gas- 
 tric cavity (Fig. 196, a), 
 is clearly distinguish- 
 able 5 this terminates in 
 an intestine (b) apparent- 
 ly filled with fine sand, 
 which is of considerable 
 length. It descends in 
 a tortuous course to the 
 posterior portion of the 
 body; it then winds upon 
 itself in a series of close 
 folds, and terminates by 
 a small tube (c) at the 
 vent, which is situate 
 near the base of the proboscis (the latter not exceeding one-tenth of 
 the body in length), close to the anterior extremity. The longitu- 
 dinal muscles are beautifully displayed, and several strong tendons, 
 some oblique in their position, are equally well shown. Two long, 
 narrow, sacculated bodies (d, d) are seen, but whether they are 
 glandular, or Ampullae (like a bottle ; the heart of Holothuria is 
 
 * In the year 1841, the author had thirteen living specimens of C. frondosa, in his posses- 
 sion in Edinburgh. After a variety of interesting experiments with the living animals, he 
 displayed their anatomy in a series of preparations now in the Hunterian Museum. Draw- 
 ings of them, of natural size, he possesses. 
 
 Sipunculus. 
 
 Nutrimental organs, Sipunculus. 
 
118 
 
 ANIMAL PHYSIOLOGY. 
 
 [LESSON 33. 
 
 FIG. 197. 
 
 so called usually with the addition of the name of its discoverer, 
 Poli thus : ampulla Poliana), or belong to the 
 reproductive function, is difficult to say most 
 likely the latter. Out of four animals of this 
 species dissected, and made into preparations 
 (which exist), no trace of tentacula was found 
 in either of them. 
 
 The muscular system in these animals, like 
 that of Holothuria, is powerfully developed. 
 It is arranged (as already shown) in longitudi- 
 nal parallel fibres, whilst the head can be re- 
 tracted by a very strong tendon, attached to it, 
 and inserted by a broad expanded base, below 
 the lower third of the animal's body. 
 
 A view of the muscular system, dissected 
 out of the integument, is given in Fig. 197. 
 The muscles are described at a, and the tendon, 
 
 above referred to, at b. 
 
 Muscular system, Sipun- 
 culus. 
 
 XXXIII. 
 
 ORGANS OF NUTRITION IN THE ANNELLATA. 
 
 550. The Latin name which distinguishes this class is derived 
 from anellus, a little ring, the bodies of all the individuals belonging 
 to it being composed of a series of little rings, or segments. 
 
 551. A peculiarity of this class is, that they all possess colored 
 blood, generally red, although in some species it is yellowish ; from 
 this circumstance they are very usually called " the red-blooded 
 worms." Many of these animals are Terrestrial (belonging to the 
 earth), as the common Earth-worm (Lumbricus terrestris), or Angle 
 worm, but by far the greater number are inhabitants of the ocean. 
 
 552. The most attractive portion of the structure of a majority 
 of the marine worms, is the respiratory tuft, which is placed (in 
 some species) at the summit of the head. A very common marine 
 worm is the Serpula contortuplicata, a figure of which is given 
 (Fig. 198). 
 
 553. When all is quiet, and the creatures are luxuriating in 
 
LESSON 33.] NUTRITION IN THE ANNELLATA. 
 
 119 
 
 their native element, they thrust their respiratory organs (c) far 
 above the head, the vibra- FlG . 193 . 
 
 tile cilia being, at the 
 same time, in rapid mo- 
 tion. But if any thing 
 chance to disturb them, 
 the respiratory tuft is 
 instantly withdrawn into 
 the tube (a) in which the 
 body is contained, and 
 the conical plug (5), form- 
 ed like the shell, of car- 
 bonate of lime, but cov- 
 ered with flesh, is drawn 
 tightly down, and effect- 
 
 ,-, -i ,1 Serpula coutortuplicuta. 
 
 ually closes the entrance 
 
 to the tube. At the top of the conical plug a pair of forcipated 
 instruments are placed ; it is their func- FIG. 199. 
 
 tion to collect sand, and " puddle " it 
 down, so that it fill entirely the concave 
 summit with a compact layer of sand ; 
 by this expedient they frequently es- 
 cape molestation by even pretty good 
 naturalists, who affirm that " the ani- 
 mal is dead, and the shell filled with 
 sand." 
 
 554. Much uniformity of plan pre- 
 vails in the structure of the nutri- 
 mental organs in this class, consisting 
 for the most part of a tube, generally 
 possessing enlargement of the gastric 
 cavity (stomach), which passes straight 
 through the body. 
 
 555. In some of the higher worms, 
 as in the Sea-mouse (ApJirodita acu- 
 leata), the strong, muscular, gizzard- 
 like stomach is supplied, at its terminal 
 portion, with the secretion of a great 
 number of long follicular glands. 
 
 556. In the annexed figure of it 
 
 (Fig. 199) the mouth is shown at a, a AJimentaiy canal, Aphroditaaculeata. 
 
120 
 
 ANIMAL PHYSIOLOGY. 
 
 [LESSON 33. 
 
 dense fleshy proboscis at 5, the central portion of the digestive tube, 
 which represents the stomach, at c; lateral, ccecal appendages at d, 
 and the vent at e. 
 
 557. The Leech presents an interesting form of the mitrimental 
 organs ; the mouth is triangular, and armed with three Fig. 202. 
 crescentic jaws (a, a, Fig. 200), presenting their sharp 
 
 convex margin toward the oral cavity, which margin 
 is beset with sixty small teeth (Fig. 201). 
 
 It is by the action of these little saws upon the 
 tense integument seized by the labial sucker that the 
 triradiate bite of the leech is made ; the muscles of 
 the jaws are marked 5, b (Fig. 200). 
 
 558. The oesophagus is short, and terminates in a 
 
 FIG. 200. 
 
 FIG. 201. 
 
 Mouth of Leech. Jaw of Leech. Nutrimental organs, Leech. 
 
 singularly complicated stomach, divided by deep constrictions into 
 eleven compartments, at the sides of which are coecal pouches, pro- 
 gressively though slightly increasing in length to the tenth, and dis- 
 proportionately elongated in the eleventh compartment (Fig. 202). 
 
 559. Army Surgeons, who have required more leeches, after an 
 engagement, than they possessed, have availed themselves of the 
 knowledge of this peculiarity in the structure of the creature's ali- 
 mentary canal, to make one leech do the work of several, by simply 
 cutting off the lower part of the body, when the blood pours out in 
 a rush, emptying the canal immediately. 
 
 Thereafter, the leech continues to suck blood, as long as he is 
 permitted to do so ; he always feels empty so his appetite continues 
 voracious. 
 
 560. It is a common practice (in Europe), after a leech has left 
 a patient, to throw salt upon it, to produce vomiting, which it in- 
 variably does, but it kills the leech. 
 
 561. The best plan is, to hold it firmly at the posterior portion 
 of the body with one hand, and draw it steadily through two fingers 
 
LESSON 33.] NUTRITION IN THE ANNELLATA. 
 
 121 
 
 FIG. 
 
 of the other hand, using some pressure at the same time. By this 
 mode of " stripping " the leech, the stomach, and the lateral pouches 
 will be entirely emptied, and the animal soon becomes ready to 
 renew his labors. 
 
 562. Although ever ready to relieve suf- 
 fering humanity of inflamed, or otherwise 
 diseased blood, this does not constitute the 
 natural food of the leech ; it is well known 
 in the sick room that, while the majority of 
 them die from the effects of their first san- 
 guinary meal, those of them that recover re- 
 main in a weakly condition for some weeks 
 afterwards ; and it rarely happens that one 
 leech will do duty a second time. 
 
 5G3. In the sand- worm (Arenicola pisca- 
 torium the fisherman's worm) the blood is 
 of a most brilliant red, and the highly vascu- 
 lar, respiratory tufts, form charming objects 
 (Z, /, Fig. 203), with or without the microscope. 
 The mouth is at a ; the gastro-intestinal 
 canal commences at the termination of the 
 oesophagus (b) by a sudden dilatation, into 
 which two coecal glandular pouches (c) pour 
 their secretion ; the rest of the canal is sim- 
 ple in its outward form, but its walls are 
 thickened by a stratum of minute secerning 
 cells (<?'), which prepare a greenish yellow 
 fluid. 
 
 The circulation of the blood in this worm 
 is very interesting ; there is on each side of 
 the 03sophagus, at its lower part, a contrac- 
 tile sac (/), which sends off a large and 
 short vessel downward, toward the middle 
 ventral line, where, meeting with its fellow 
 trunk, a ventral vessel (e) is formed. This 
 vessel (e) furnishes a pair of transverse 
 
 branches to each ring of the body, which, at the seventh segment, 
 penetrate the branchial tufts (I, I) attached to the sides of that and 
 succeeding middle segments of the body. The pulsations of the two 
 ossophageal ventricles (/) propel the blood into the ventral vessel 
 (e), through the vessels (ra, m) to the gills, where it receives a new 
 
122 
 
 ANIMAL PHYSIOLOGY. 
 
 [LESSON 34. 
 
 impulse by the contractions of these organs, and, after having been 
 oxygenized, it is returned, partly by vessels of the skin, but chiefly 
 by a direct and continuous lateral vessel (k, k), to the dorsal artery (g). 
 This artery extends from one end of the body to the other. At 
 its middle part it receives many transverse branches from the diges- 
 tive tube, and through them joins the inferior intestinal vein (7^;. 
 The vascular network thus formed around the intestine gives origin 
 to two veins at the sides (i), which terminate in the dorsal vessel, 
 immediately behind the ventricles (f, d). 
 
 LESSON XXXIY. 
 
 ORGANS OF NUTRITION IN THE EPIZOA. 
 
 FIG. 204. 
 
 Actheres percarum, female. 
 
 564. The Epizoa (epi, upon ; zoon, 
 an animal) form a most extraordinary 
 class of animals. They are external 
 parasites, usually on the bodies of 
 Fishes, where they attach themselves 
 to the skin, the eyes, and the gills. 
 Their number is prodigious, probably 
 exceeding that of the fishes they infest. 
 
 Limited space will not allow of 
 more than one illustration of this 
 class the Adheres percarum found 
 attached to the eye of the Perch. 
 
 565. The mode by which the Ler- 
 naea (as these animals were called by 
 Linnseus) adhere to their prey, is pe- 
 culiar, and characteristic of the class. 
 A pair of hollow, tubular feet, ad- 
 hering by their terminal extremities 
 (Fig. 204, Z, Z), gives origin to a cup- 
 shaped sucker (m) ; this is the instru- 
 ment of adhesion. 
 
 566. The mouth consists of upper 
 (b) and under jaws, the latter pro- 
 vided with feelers ; besides these, a 
 pair of jointed antennae, each termi- 
 nated by three small bristles (a). 
 The alimentary cacal is, as in all 
 
LESSON 35.] NUTRITION IN THE CIKRIPEDIA. 123 
 
 these animals, straight, and terminates by a vent, at the extremity 
 opposite to the head. The intestine is fusiform, and divided by a 
 series of slight constrictions into sacculi (minute sacs, d). 
 
 It is maintained in its position by a transverse muscle (h) ; the 
 walls of the abdomen are distinctively provided with longitudinal 
 (i) and transverse (k) fasciculi of muscular fibres. 
 
 567. The nervous system consists of a single cephalic ganglion, 
 placed on the ventral surface, from which are continued two princi- 
 pal chords (^, g) extending along the under surface of the body. 
 The heart may be seen in the middle line of the cephalo- thorax 
 (head, chest), propelling the blood forwards. Two canals pass 
 from it into the hollow feet ; the rest of the blood is distributed to 
 the head, and along each side of the commencement of the alimen- 
 tary canal to the under part of the body, where it passes backwards 
 in the vessel which accompanies the intestine. 
 
 568. The ovaria (o, o) at first appear as long, blind tubes, sac- 
 culated along the outer side. As the ova become developed, the 
 
 ovarium takes on the form of a bunch of grapes, 
 
 , . ,, . , ., , , FIG. 205. 
 
 and occupies the whole cavity of the abdomen ex- 
 ternal to the intestine ; each ovarium terminates 
 by a triangular, and somewhat prominent orifice, 
 to which the external ovisac (f) is appended. 
 This latter structure agrees with the form of ex- 
 ternal ovisac in the lower Crustacea, into which 
 the ova pass from the abdominal cavity (having 
 attained a certain degree of maturity) through the 
 oviduct e, for their full development, previous to 
 the fertilizing influence of the male. 
 
 569. The disparity of size in the sexes is considerable, as appears 
 by the annexed figure of the Male Actheres (Fig. 205). 
 
 LESSON XXXY. 
 
 ORGANS OF NUTRITION IN CIKEIPEDIA. 
 
 570. Like the Epizoa, many of these animals are parasitic, but 
 unlike the latter, these have only a residence on the bodies of ani- 
 mals, obtaining their food from oilier sources : thus the Tubicinella 
 is parasitic in the skin of the Whale, but it does not obtain its suste- 
 nance, or any portion thereof, from the animal whose skin it inhabits. 
 
124 
 
 ANIMAL PHYSIOLOGY. 
 
 [LESSON 35. 
 
 571. The Cirripeds (meaning curled feet) are divided into two 
 orders : those having a peduncle as an organ of attachment, are the 
 Lepads, and those which are sessile (sitting close upon the body), are 
 the Balanoids. The first, are commonly called Barnacles; the 
 second, Acorn-shells. 
 
 572. The visceral mass in this class is usually protected by a 
 calcareous shell composed of several pieces ; but in Otion cornuta, 
 the viscera is protected by the development of a horny sheath. 
 
 573. In the common Barnacle (Lepas anatifera), found so 
 abundantly adhering to ships' bottoms, the calcareous matter extends 
 from five centres, so as to afford protection to the whole body : the ce- 
 phalic pair of valves is the largest. All the valves are strongly marked 
 with lines of growth, formed by successive additions to their margins. 
 
 574. The sessile Cirripeds (Acorn-shells) are defended by a 
 multivalve shell j the base of which is generally formed by a calca- 
 reous plate, and the walls are apparently divided into twelve conical 
 compartments, six of which rise from the margin of the base and 
 terminate in a point at the free margin of the shell ; whilst the 
 other six, in the form of inverted cones, occupy the interspaces of 
 the preceding series. 
 
 575. One illustration of the structure of a Lepad will suffice : 
 
 animalcules, or other proper 
 food, are brought to the 
 mouth (a, Fig. 206) by the 
 cirrigerousfeet (6), and seized 
 by the lateral jaws; they 
 are then conveyed by a short 
 oesophagus to a dilated stom- 
 ach (c), which receives the 
 ducts of two salivary glands 
 (&). Groups of hepatic coaca 
 are developed from the walls 
 of the stomach. The intes- 
 tine (d) is bent upon the 
 stomach, and tapers with a 
 slightly sinuous course to ter- 
 minate at (e), the base of the 
 caudal appendage (/). In 
 these pedunculated Cirripeds, 
 slender conical branchiae (g) 
 are attached to the base of 
 the maxillary foot, and to that of some of the cirrigerous feet. 
 
 FIG. 206. 
 
 Lepas vitrea. 
 
LESSON 36.] NUTRITION IN THE CRUSTACEA. 125 
 
 In the pedunculated Cirripeds, a large granular, glandular mass 
 covers the viscera immediately beneath the muscular tunic of the 
 body ; its numerous ducts successively unite into three or four prin- 
 cipal trunks, which terminate in a lateral receptacle (h) at the side 
 of the intestine. In Lepas, a duct is continued from this receptacle, 
 which passes through the canal of the extensile tail (i). 
 
 LESSON XXXVI. 
 
 OKGANS OF NUTKITION IN THE CEUSTACEA. 
 
 576. In these animals we find a class of articulata, in which the 
 segments of the body are provided with articulated (jointed) limbs, 
 or appendages. They are aquatic ; only a few of them being able 
 to support themselves, and that for a short time, on land. 
 
 577. Their breathing organs, or branchiae, are organized for 
 aquatic respiration. 
 
 578. In the highest individuals of the class, the Crab, and the 
 Lobster, the external layer of the integument is hardened by the 
 addition of earthy material, consisting of the carbonate, with a very 
 small proportion of the phosphate of lime. In the smaller and lower 
 Crustacea, the tegumentary covering retains a flexible, horny texture. 
 
 In a great proportion of the class, the body consists of twenty- 
 one rings, of which seven are more or less soldered together to form 
 the head, seven more enter into the formation of the thorax, and 
 the remaining seven constitute the body. The great ponderosity of 
 the skeleton of the lobster, by the deposition of such inordinate 
 quantity of the Carbonate of lime, is essential to its well being, its 
 great weight having the effect of keeping the animal at the bottom, 
 notwithstanding the turbulence of the ocean. In these animals, the 
 smaller claw is provided with two rows of pointed, sharp, cutting 
 teeth, used as shears to divide its food ; the larger claw, on the con- 
 trary, is furnished with two or three short rounded tubercles, and 
 endowed as this claw always is with enormous muscular power, the 
 instrument becomes a most efficient anchor. 
 
 579. The means of locomotion of a lobster in the water is pro- 
 digious ; it expands the five plates, constituting the terminal portion 
 of the body (or tail, as it is usually called), and by a single down 
 stroke it is propelled a distance of from 16 to 20 feet ! 
 
126 
 
 ANIMAL PHYSIOLOGY. 
 
 [LESSON 36. 
 
 580. The mouth in the higher Crustacea is generally furnished 
 with a pair of strong palpigerous mandibles, and five or more pairs 
 of jointed under jaws, which move transversely, and support articu- 
 lated feelers ; the three outer pairs of under jaws are the largest, and 
 support gills at their base. 
 
 581. The entrance of the mouth presents an upper lip, a bifid 
 tongue, and sometimes an under lip. The mouth opens by a very 
 short, narrow ossophagus into a capacious stomach (Fig. 207), pro- 
 vided internally with a great number of minute (microscopical) 
 teeth; in addition to these, there are three very large calcareous 
 teeth, situated near the pyloric orifice of the stomach, their external 
 portion being remarkable for their redness. 
 
 In examining the external aspect of this stomach, the very short 
 
 FIG. 207. FIG. 208. 
 
 External view, stomach of Lobster. 
 
 Stomach of Lobster opened to show 
 gastric teeth in situ. 
 
 oesophagus (b) is seen to terminate immediately in the capacious di- 
 gestive sac (d), at the upper portion of which a pair of short, strong 
 jaws (c) are seen. A number of strong calcareous bones, longitudinal 
 in their direction, support the membranous portion of the stomach, 
 and form a solid basis for the support of the large teeth. The cen- 
 tral rounded tooth (5, Fig. 208) is supported upon a large, somewhat 
 triangular bone, transverse in its direction. The entire organ is cov- 
 ered externally with a layer of muscle's of great power. The pylo- 
 rus is shown at a (Fig. 207). 
 
 582. Two of these teeth (a, Fig. 208) resemble the grinding or 
 molar teeth of an Elephant, whilst the third, which is placed in 
 front, and somewhat below the former, has a rounded termination (b\ 
 The lateral teeth are employed to cut, divide, and comminute the 
 food, which is performed by a rounding motion, like the action of 
 one mill-stone upon another; the third tooth is employed in constant- 
 ly pushing the food, as it escapes between the grinding teeth, back 
 again, to be more thoroughly triturated. 
 
LESSON 36.] NUTRITION IN THE CEUSTACEA. 
 
 127 
 
 FIG. 
 
 The whole of this curious gastric apparatus (the three large teeth) 
 constitute what is popularly called " the lady, in the head of the 
 Lobster," and, when inverted, the rounded tooth personates " the 
 lady," who is supported by the two lateral grinding teeth. 
 
 583. The alimentary canal passes, without convolutions, through 
 the long axis of the body, and opens by distinct apertures at each 
 extremity. The mucous coat sometimes forms folds in the oesopha- 
 gus and stomach ; the muscular layer is strongest at the orifices of 
 the stomach, and there is no mesentery in the abdomen. The py- 
 loric extremity of the stomach receives on each side a short and wide 
 duct from the liver, but this part of the subject will be best under- 
 stood by reference to the accompanying figure. 
 
 A longitudinal section of a Lobster (Astacus marinus) is given 
 in Fig. 209. The under jaws (a), with their feelers, are placed on 
 the inferior aspect of the head, between the large claws and the two 
 pairs of antennae. 
 
 The short oesophagus opens into the 
 stomach (5), which is surrounded by the 
 numerous lobes of the liver (n, n). The 
 intestine (c) receives at its commence- 
 ment the two hepatic ducts, and passes 
 beneath the heart (e) ; the posterior aor- 
 ta (h) follows nearly a straight course to 
 the vent, which is situate below the last 
 segment of the body (d). 
 
 584. The anterior aortic vessel (/), 
 and the pulmonary vein (</), are both 
 distinctly seen. 
 
 585. In addition to the vascular sys- 
 tem already described, consisting of the 
 heart and arteries, there is yet another 
 portion of the utmost importance, name- 
 ly, venous sinuses. 
 
 586. Instead of veins, the blood is 
 returned to the heart by these struc- 
 tures, which are large, loose sacs, the 
 coat of which is of delicate transparen- 
 cy. The heart itself is enclosed in a ve- 
 nous sinus, and lies literally bathed in 
 blood. These sinuses communicate 
 
 freely with each other, and with the arterial system. The best way 
 
 Section of Lobster. 
 
128 ANIMAL PHYSIOLOGY. [LESSON 37. 
 
 to procure a minute injection of a lobster, is to put a pipe into a claw 
 and pass the iDJection through it. The venus sinuses will fill first, 
 afterwards the arteries and the heart. 
 
 587. If, in the ferocious combats to which the lobsters are always 
 exposed, one happen to wound a claw of its adversary, the injured 
 lobster instantly casts off the limb, always at a particular joint at 
 the second articulation. If this were not done, the animal would 
 soon bleed to death, in consequence of the lacerated venus sinus. 
 Cast off at the joint indicated, provision is made there, but nowhere 
 else, for the perfect contraction of all the soft parts, and, as the lob- 
 ster possesses the power of renewing lost portions of its structure, no 
 permanent injury results. 
 
 588. The membranes composing the walls of these sinuses are of 
 such extreme tenuity, that they can only be demonstrated by the aid 
 of the injecting syringe ; the most careful and accurate, dissection 
 fails to discover them. 
 
 LESSON XXXVII. 
 
 ORGANS OF NUTRITION IN INSECTS. 
 
 589. The intestinal canal of any animal is the tube which com- 
 mences at the mouth, and is devoted to the reception of nutriment, 
 whereby the growth and development of the individual may be pro- 
 moted, and the wear and tear, and positive loss since the last meal, 
 may be compensated for. In all the higher animals this canal pos- 
 sesses an opening at the opposite extremity ; that this is not essen- 
 tially necessary we have abundantly seen in relation to classes al- 
 ready discussed Infusoria; Entozoa ; many Polypi,- the Acale- 
 pha; and Asterias, amonst the Echinodermata. 
 
 Examples of this condition are not wanting in Insects, but it 
 rarely occurs, and is only met with in the infantile condition (larvae, 
 maggots), and never in the perfect insect. 
 
 590. This canal is subject to great modifications of distension 
 and constriction, whereby it is separated into a variable number of 
 divisions, and as the function of these divisions is dissimilar, they 
 have received different names. In addition to the partition of the 
 canal, there are peculiar processes, or appendages, which either origi- 
 nate from or open into it. 
 
I*ESSON 37.] NUTRITION IN INSECTS. 129 
 
 591. The intestinal canal of Insects consists of three membranes 
 the innermost membrane is smooth and textureless, and variously 
 armed with horny lines, ridges, or teeth. It is most distinct in the 
 pharynx, crop, and proventriculus, or gizzard. 
 
 The second layer is white and smooth, and, although usually thin, 
 is sometimes thick and spongy. 
 
 The third (outer) layer is a compact, firm, fleshy, muscular coat ; 
 it is not equally observable in all parts of the intestinal canal, but is 
 readily seen in the pharynx, stomach, and colon, but it is lost in the 
 crop, or craw. 
 
 592. The length of the intestine in Insects appears to be governed 
 by the same law that regulates it in other animals ; those that feed 
 on vegetable matter usually possess a longer and more distended in- 
 testine than those which feed on animal matter, in which it is shorter 
 and narrower. 
 
 593. In this class the intestinal canal is divided into the pha- 
 rynx, the oesophagus, the crop, or craw, the proventriculus, or giz- 
 zard, the stomach, the duodenum, the ileum, the ccecum, and the 
 colon. 
 
 594. The appendages are the salivary glands, the liver, and cer- 
 tain vessels supposed to constitute a kidney. 
 
 595. The several parts enumerated are never all present in the 
 same individual ; sometimes one part is wanting and sometimes 
 another. Thus, insects with a suctorial mouth have no need of a 
 pharynx ; neither do they possess a gizzard, for, feeding upon fluid 
 food only, they have no need of such an organ. The part most usu- 
 ally deficient is the duodenum, which has only been found in some of 
 the beetles ; after this the ccecum is less usually found, as it belongs 
 only to those insects which feed upon animal matter. 
 
 596. The biliary vessels are seldom wanting, the salivary glands 
 frequently, and the kidneys very generally. 
 
 597. THE PHARYNX is the funnel-shaped commencement of the 
 oesophagus, and is only found in mandibulate insects ; it is of large 
 size in grasshoppers, cockroaches, and most caterpillars. 
 
 598. THE (ESOPHAGUS extends from the pharynx to the stomach ; 
 it is distinguished from the pharynx by its smaller capacity, and from 
 the stomach, by its different structure. In the Lepidoptera (butter- 
 flies and moths) it is double for a space, and then united into one tube. 
 
 599. The separation of cesophagus from stomach is sometimes ef- 
 fected by a constriction ; sometimes it passes insensibly into it, and 
 sometimes the crop intervenes between them. 
 
 9 
 
130 ANIMAL PHYSIOLOGY. [LESSON 37. 
 
 600. It has been remarked that the crop is absent in insects pro- 
 vided with a suctorial mouth, but all these possess a peculiar organ 
 not found in other insects ; this is, sometimes, a bladder-shaped disten- 
 sion of the oesophagus ; in others it forms a distinct bag, which opens 
 into the oesophagus ; and in still another order it hangs appended to 
 the oesophagus by means of a long, thin duct, frequently far in front 
 of the stomach. 
 
 601. This organ is the sucking, or pumping stomach ; its func- 
 tion does not consist in being a receptacle for nutriment, but in pro- 
 moting the procuration of it, by distending at the pleasure of the in- 
 sect, and by the rarefaction of the air contained in it, facilitating the 
 ascent of fluids in the terminal proboscis, and oesophagus. But the 
 action of this organ will be more fully explained hereafter. 
 
 602. THE PROVENTB.ICULUS, or gizzard, is the third division of 
 the alimentary canal ; it is a small, narrow, and tubular cavity, fur- 
 nished with teeth, spines, or horny ridges. It lies in front of the 
 mouth (or commencement) of the stomach ; it is found in all insects 
 prone to feed on hard substances, which require thorough comminu- 
 tion previous to digestion. 
 
 Externally it has a roundish or ovate appearance, and is more 
 distinctly muscular than any other portion of the intestinal canal. 
 
 603. THE STOMACH is that portion of the canal which extends 
 from the end of the oesophagus, or of the crop, or of the gizzard, to 
 the opening of the evacuating ducts of the biliary vessels. Some 
 authors call it duodenum, because digestion commences in it, but from 
 the analogy of the higher animals it is probable that the stomach 
 ends prior to the connection with the bile vessels, and that their se- 
 cretion is poured into the first of the intestines proper. The subject, 
 however, is open to doubt, especially as we find commonly in the bi- 
 valve, and other Mollusca, that the bile is poured directly into the 
 stomach. 
 
 The divisions from the stomach are fewer and more simple than 
 those which precede it ; with the exception of the colon they are 
 much narrower than the stomach, and more delicate in their struc- 
 ture. 
 
 604. THE DUODENUM. When this intestine is present, it is sepa- 
 rated from the stomach by a distinct constriction, which is probably 
 a pylorus ; immediately beyond this the bile vessels enter the in- 
 testine. 
 
 605. THE ILEUM. Wherever the duodenum is wanting, the ileum 
 follows immediately upon the stomach, from which it is also sepa- 
 
LESSON 37.] NUTRITION IN INSECTS. 131 
 
 rated by the pylorus. Sometimes this intestine is wanting, and in 
 that case the stomach joins the colon. 
 
 606. The last division of the alimentary canal is THE COLON ; it 
 is usually divided from the preceding portion of the intestine by a 
 valve, which completely closes its aperture. The colon is subject to 
 great variety of form ; it is found cylindrical, clavate (club-shaped), 
 sac-shaped or longitudinally folded. The situation of the colon is 
 always determinate found at the apex of the abdomen, and sur- 
 rounded by the last segments. 
 
 607. THE CCECUM. In many insects a blind, sac-shaped appen- 
 dage is found in connection with the colon; this is the co3cum. 
 Like the intestine to which it is attached, this is also subject to great 
 variation in form ; this portion of the canal is peculiar to the carniv- 
 
 'orous tribes, although occasionally found in the butterflies. The ex- 
 act function of this organ is not known in any animal, but (in con- 
 junction with the colon) in the higher animals it is supposed to be as 
 a second stomach. 
 
 608. THE BILIARY VESSELS. These are narrow, filiform tubes, 
 which open into the duodenum, if present, or the ileum, where the 
 former is wanting ; the ends not connected to the intestines are either 
 free and closed, or pass into each other, and thus form one vessel, 
 which pierces the intestine at both ends. 
 
 609. THE SALIVARY GLANDS. These are various in form, num- 
 ber, and the situation where their secretion is poured. In some in- 
 sects they are tubular, in others vesicular, and in another series lobu- 
 lated. In some the secretion is emptied into the mouth, in others 
 the proboscis, and lastly, directly into the stomach. Some insects 
 have one pair of these glands, some two, and others (like the higher 
 animals) three pairs. Illustrations of them will be hereafter given. 
 
 610. Before proceeding further, it becomes necessary to show the 
 principles of classification of insects, which will render that portion 
 of the subject very simple, which, without its aid, would be involved 
 in great confusion. As the simplest, but by no means the best, the 
 Linnsean system will be adopted. 
 
 611. This naturalist selected the structure of the wings, thence 
 called the Alary (wing) system, as the basis of his classification ; he 
 had seven orders, the last being wingless. 
 
 In addition to the names of the orders, and translation of the 
 Greek compound names, an illustration of the structure of the wings 
 in each order is appended. 
 
132 
 
 ANIMAL PHYSIOLOGY. 
 
 [LESSON 38. 
 
 LESSON XXXVIII. 
 
 NUTRITION IN INSECTS, CONTINUED. 
 FIG. 210. 
 
 Fio. 211. 
 
 FIG. 214. 
 
 612. COLEOPTERA, 
 
 (koleos, a sheath; pteron, a wing.) 
 BEETLES. 
 
 HEMIPTERA, 
 
 (emisus, half; pteron, a wing.) 
 TREE-BUGS. 
 
 LEPIDOPTERA, 
 
 (lepis, a scale ; pteron, a wing.) 
 BUTTERFLIES AND MOTHS. 
 
 NEUROPTERA, 
 
 (neuron, a nerve ; pteron, a wing. ) 
 DRAGON-FLIES. 
 
 HYMENOPTERA, 
 
 (hymen, a membrane ; pteron, a wing.) 
 BEES, WASPS. 
 
LESSON 38.] 
 
 NUTRITION IN INSECTS. 
 
 133 
 
 DIPTERA, 
 
 isj two; pteron, a wing.) 
 HOUSE AND FLESH FLIES. 
 
 FIG. 215. 
 
 APTERA, 
 
 (a, without ; pteron, a wing.) 
 
 WINGLESS. 
 
 613. The structure of the mouth of an insect gives fair induc- 
 tive evidence of the general conformation of the nutrimental organs, 
 as there is a necessary connection between them. 
 
 614. The COLEOPTEROUS insects y or true beetles, whose delicate 
 wings are covered and protected by strong, bony sheaths, or wing- 
 covers, are mandibulate ; that is to say, their upper jaws, or man- 
 dibles, are well developed, and offer the best type of structure of these 
 organs. In the mouth of one of the predaceous and carnivorous 
 Tiger beetles (Cicindela hybrida), Fig. 216, is the well-formed, 
 slightly bilobed, upper lip (a) ; below, and on either side of it (b), 
 are the formidable upper jaws (mandibles), in this insect furnished 
 with a number of strongly formed teeth, the better to kill and divide 
 its living prey. 
 
 The under portion of this- mouth is shown in Fig. 217. The un- 
 
 FIG. 216. 
 
 FIG. 217. 
 
 Upper portion of the mouth of 
 Cincindela hybrida. 
 
 Under portion of the mouth of Cicindela 
 hybrida. 
 
 der jaws, maxillse (a), are furnished with two pairs of auxiliary 
 jointed appendages (6, c], which perform the function of hands in 
 conveying food to the mouth ; they are called palpi, or feelers, and 
 are supposed to be endowed with much sensibility. The trilobate 
 central piece (d) is the lower lip, to which is attached a long pair of 
 jointed feelers, beautifully fringed with hair(e) these are the labial 
 palpi (labium, the under lip), and the chin is shown at /. 
 
134 
 
 ANIMAL PHYSIOLOGY. 
 
 [LESSON 38. 
 
 615. It has been remarked that those animals that subsist on 
 * animal food, have a short and simple form of the n^trimenta! organs : 
 
 such is the case with the Tiger beetles ; moreover, they are not sub- 
 ject to much convolution, but are found nearly straight. 
 
 616. A figure of the alimentary canal of Cicindela campestris, 
 which is a beetle common in this country, and in Europe, is given 
 (Fig. 218). The oesophagus is shown at a; it soon dilates into a 
 
 FIG. 219. 
 
 FIG. 218. 
 
 Alimentary canal Cicindela campestris. 
 
 Crop of Dyticus marginalis. 
 
 large crop (6), the surface of it being covered with minute follicles. 
 This is succeeded by a small, but strong muscular gizzard (proven- 
 triculus), c, the interior of which is lined with teeth. The gizzard 
 opens directly into the true stomach (ventriculus), also covered with 
 follicular appendages (d). 
 
 At its lower portion the pyloric valve is placed, and in that 
 neighborhood the biliary ducts (e) pour in their secretion ; it is not 
 quite clear, however, whether the valve be situated below these bile 
 ducts or above them. 
 
 The intestine (/), commences beneath the biliary vessels, and 
 terminates in a short, dilated colon (g). 
 
 In the large aquatic beetle, Dyticus margindlis, found as abun- 
 dantly in the ponds of this country as of Europe, the crop is of large 
 size, and terminates in a gizzard provided with four large triangular 
 teeth (Fig. 219). The crop (a) is a capacious bag, its interior beset 
 with very minute teeth, and deeply furrowed ; the proventriculus, or 
 
LESSON 38.] 
 
 NUTRITION IN INSECTS. 
 
 135 
 
 FIG. 221. 
 
 FIG. 220. 
 
 gizzard (&), and its four teeth, are seen just in advance of the com- 
 mencement of the stomach. The crop is opened to show the teeth. 
 
 617. The mouth in the next order, Hemiptera, or the Tree bugs, 
 has undergone remarkable modification the whole of it is trans- 
 formed. In place of well-formed upper and under jaws, we have only 
 four delicate bristles ; and these are so fine and fragile, that when 
 not in use they require the protection of a sheath, which is specially 
 developed for their preservation. The mouth of these insects is dis- 
 tinguished by the possession of a jointed organ called the rostrum 
 (Fig. 221). This has from three to five joints. The organ itself 
 
 is simply an altered form of the 
 lower lip, which in these insects 
 forms the sheath or protecting case 
 alluded to. 
 
 The remainder of the apparatus 
 of this curiously formed mouth is 
 shown in Fig. 220. The upper 
 lip (a) is a long, slender, somewhat 
 triangular scale ; its office, however, 
 appears to be uncertain, the jaws 
 being confined in the rostrum. The 
 bristles representing the upper jaws 
 are seen at b, and the lower jaws at c. 
 
 Frequently these organs terminate in a fine point; at other times 
 their extremities are provided with cutting instruments, those of the 
 first pair always differing from those of the FlQ 2 22. 
 
 second. Although organized to pierce the 
 tough cortex (bark) of plants, these animals 
 never refuse the more nutritive juices of ani- 
 mals if opportunity favor them, as every prac- 
 tical Entomologist knows to his cost, and 
 the pain resulting from the bite of many of 
 them is very severe. 
 
 618. The best known insect of this order, 
 is the loathsome household tormentor, the 
 common bug (Cimex lectularius), and a figure 
 of its nutrimental organs is given (Fig. 222). 
 The mouth receives the secretion of two pairs 
 of salivary glands (h, i), in the form of sim- 
 ple follicles, terminated by minute vesicles Alimentary canal, Cimex 
 
 7 lectularius. 
 
 Upper portion of 
 mouth, Tree bug. 
 
 Eostrum of 
 Tree bug. 
 
136 
 
 ANIMAL PHYSIOLOGY. 
 
 [LESSON 38. 
 
 FIG. 223. 
 
 The short oesophagus dilates slightly to form a very small crop 
 (e), which communicates with a true stomach of some length (d). 
 In this, as in the former instance, the true position of the pyloric 
 orifice is by no means clear, but, either into the stomach, or im- 
 mediately at the commencement of the intestine, the bile vessels 
 (g) empty their secretion. The canal terminates in a short colon 
 (e, f ). The head is shown at a, the antennae at b, and the rostrum 
 at k. 
 
 619. The omnivorous Cockroaches (Blattaria) were erroneously 
 included in this order by Linnaeus ; they now form a distinct order, 
 under the name of Uictyoptera (diktos, to make lace ; pteron, wing). 
 The nutrimental organs present many points of great interest ; 
 the preparation from which the figure was made 
 (Fig. 223), remains connected to the head, 
 the parts of which it is not now necessary to 
 describe. The oesophagus (a) terminates in a 
 large crop (5), at the terminal portion of which, 
 eight (sometimes only six) large and strong 
 gastric teeth are found (Figs. 224 and 225). 
 The salivary glands are extensively developed 
 (c), and show a number of lobules terminating 
 in a lengthened sac, each gland communicating 
 with its proper duct. 
 
 The crop has had a portion removed, to 
 show the structure and folds of the mucous 
 membrane; this is easily done, as the prepa- 
 ration is preserved in fluid. 
 
 620. Immediately below the proventriculus 
 (gastric teeth), and at the commencement of 
 the stomach, there are eight long follicles disposed around it, usually 
 filled with a thick, white substance (d). These appendages in this 
 situation are peculiar ; whatever the nature of their secretion is un- 
 known ; but some authors suppose (with great probability consider- 
 ing the habits of the animal) that they are a second series of salivary 
 glands, pouring out their secretion on the food the instant it has 
 been duly and effectually comminuted by the gastric teeth. The 
 stomach (e) begins where the last described follicles connect, and is 
 a long, tortuous, convoluted tube, terminated by a distinct pylorus. 
 The Ileum (/) succeeds the stomach, and receives the contents of 
 the numerous short and slender biliary tubuli (g). 
 
 The large distended colon joins the ileurn ; after one convolution 
 
 Nutrimental organs, B. 
 Americana. 
 
LESSON 38.] 
 
 NUTRITION IN INSECTS. 
 
 137 
 
 it narrows to a size scarcely larger than the stomach, and slightly 
 enlarges again, prior to its termination. 
 
 The gastric teeth (Figs. 224 and 225), are shown in two views of 
 
 FIG. 224. 
 
 \\\:\ I 1 _IY ! '*i ! r/l ' 
 
 Gastric teeth, Cockroach. 
 FIG. 226. 
 
 FIG. 225. 
 
 Pavement e 
 cav 
 
 pithelium of funnel-shaped 
 dty, B. Americana. 
 
 Gastric teeth, B. Americana. 
 
 FIG. 227. 
 
 them. In the first (Fig. 224) r the crop has been cut open, and the 
 teeth seen in profile, whereby their entire figure is well shown. The 
 central teeth show their toothed processes very distinctly ; the lateral 
 teeth are somewhat foreshortened, and not quite so perfect. It will be 
 seen that the upper portion of these teeth is terminated by a long 
 and strong toothed process ; the lower portion also is indented, and 
 toothed, the whole forming a most efficient apparatus. 
 
 Moreover, they are based upon and supported by a series of bones. 
 
 In Fig. 225, the spectator looks down upon the teeth, and into 
 the funnel-shaped, valvular cavity beneath them. The teeth are 
 seen at a; strong fasciculi of muscles be- 
 tween them at b, and the membrane which 
 lines the funnel-shaped cavity, leading to the 
 stomach, is thrown into a number of large 
 rounded folds, c. This membrane is covered 
 with a beautiful surface of minute pavement 
 epithelium (Fig. 226). 
 
 621. A preparation, showing the salivary 
 glands entire, is figured in 227. The lob- 
 ules (b) are everywhere seen communicating 
 by short ducts, with the large duct common to 
 the glands on either side (&); the latter 
 coalesce, and form a common duct which emp- 
 ties its secretion into the mouth (c). 
 
 Salivary glands, B. 
 Americana. 
 
138 
 
 ANIMAL PHYSIOLOGY. 
 
 [LESSON 39. 
 
 Fio. 228. 
 
 LESSON XXXIX. 
 
 NUTBITION IN INSECTS CONTINUED. 
 
 622. The Linnaean order Hemiptera is, confessedly, an ill-ar- 
 ranged one; in addition to the Cockroaches, and other extraneous 
 insects, the Grasshoppers, Crickets, and their congeners, were ad- 
 mitted by the illustrious Swede. These have been removed by 
 modern Entomologists, but as the system here adopted is strictly 
 Linnaean, if it be necessary to speak of these insects at all, it can 
 only properly be done in legitimate connection. 
 
 623. These insects, called now Orthoptera, from the leathery 
 structure of their wing cases, are all voracious vegetable feeders, and 
 they present by far the best developed proventriculus of any insects 
 known to us. 
 
 624. The oesophagus in Locusta viridissima, soon terminates in 
 the crop (Fig. 228, a) ; at the lower portion this forms a kind of neck, 
 
 filled with small teeth, which ends in the 
 proventriculus, in these insects a distinct 
 organ (b). It lies slightly imbedded at 
 its lower portion in another digestive 
 sac, which is transverse in its direction 
 (c), and to which a plexus of fine tubes 
 (h), like the biliary tubuli, are attached. 
 To this succeeds the true ventriculus 
 (stomach), which is usually narrow, 
 and of some length (d). At its lower 
 portion, beyond the pyloric valve, the 
 biliary vessels are connected (e), and the 
 intestine proper commences. This at 
 first is a dilated sac (/), which becomes 
 Bttrf*i . Loc^ta attenuated, and after a convolution ends 
 
 viridissima. j n the Colon (g). 
 
 625. The salivary glands in Locusta viridissima^ the house, and 
 most field Crickets, resemble those of the Cockroaches, and are dis- 
 played at i. 
 
 626. The proventriculus is such a wonderful structure that it 
 merits a distinct notice, and a more highly magnified view to show it 
 (Fig. 229). 
 
 The preparation from which the drawing was made, was dis- 
 
LESSON 39.] 
 
 NUTRITION IN INSECTS. 
 
 139 
 
 FIG. 229 
 
 Proventriculus of Gryllotalpa. 
 
 sected from the Mole cricket (Gryllotalpa) from Jamaica, a much 
 smaller insect than the European species, but fearfully destructive. 
 The specimen and its 
 companions cost the 
 proprietor of a farm 
 there upwards of 60,- 
 000 sterling, $300,000, 
 by the entire destruc- 
 tion of his crop of sugar 
 cane. 
 
 Interiorly the giz- 
 zard is divided into 
 six compartments, by 
 means of six bones (a, 
 a), which occupy the 
 whole longitudinal length of the organ. Between every two of the 
 bones are three rows of teeth, and of these, the teeth in the centre, 
 or the central row, are the largest and most powerful. Outside of 
 the large teeth are two rows, one on each side of them, and still more 
 outside are other two rows. All the teeth in these several rows 
 differ somewhat in their structure ; in addition to these, there are 
 large teeth above and below the rows, and to assist their action the 
 external surface is covered with a muscular coat of extraordinary 
 power. The entire number of teeth contained in this gizzard is two 
 hundred and twenty-two. So great is their capability for tearing 
 and minutely dividing every substance presented to their action, that 
 they have been compared, most fitly, to the . machine used in cloth- 
 making, called " the Devil," for nothing can resist its action. 
 
 A still more enlarged view is given of the position of the bones 
 (a, Fig. 230), and of one row 
 of the teeth. The lateral 
 teeth, described above, are 
 here lettered 5 / the* central 
 row, including a large middle Enlarged view of one row of the teeth, Gryllotalpa. 
 
 and two lateral teeth, are marked c and d. 
 
 627. In the intestinal canal of man, and the higher animals, a 
 vast assemblage of glands, of minute size and uncertain function, are 
 found, some of them solitary, others aggregated. Their presence ap- 
 pears to be essential to the action of this' portion of the canal. 
 
 628. The Ileum of the house-cricket (Acheta domestic) exhibits 
 a wonderful development of similar glands. This intestine is dis- 
 
 FIG. 230. 
 
140 
 
 ANIMAL PHYSIOLOGY. 
 
 [LESSON 39. 
 
 played in Fig. 231, where the glands are aggregated. A more highly 
 magnified view of two of these glands is given in Fig. 232. 
 
 FIG. 231. 
 
 FIG 
 
 Iliac glnnds of Cricket. 
 
 Ileum of the House Cricket. 
 
 Fig. 233. 
 
 629. There appears to be great similitude between the perform- 
 ance of nutrition in the vegetable feeding insects and the vegetable 
 feeding ruminant quadruped. In both there are four distinct sacs, 
 devoted to this function ; in the insect, mastication is effectively per- 
 formed by the wonderful gizzard ; in the Ox, by the peculiarly con- 
 structed teeth. Saliva is abundant in both, and each possesses a 
 magnificent display of aggregated iliac glands. 
 
 630. The food that is intractable, and yields its nutriment with 
 difficulty to the herbivorous quadruped, is no less difficult and in- 
 tractable to the vegetating insect, and both require an extraordinary 
 adaptation of many organs to reduce it to subjection. 
 
 631. The next order, the Lepidoptera, presents an equally singu- 
 
 lar structure of its mouth ; here the 
 upper lip and the upper jaws are so 
 minute as almost to elude detection. 
 Of the three triangular plates pre- 
 sented at the upper part of the figure 
 (Fig. 233, a), the central portion is 
 the upper lip, and the upper jaws are 
 of the same size nearly, and shape, on 
 either side of it. 
 
 632. The Butterflies and Moths 
 rarely feed at all ; but when they do 
 condescend to perpetrate such vulgari- 
 ty, they manifest great indifference, 
 hovering over a flower, still on the 
 wing. At last, probably, (hey incline to take a mere sip of the 
 delicious fluid found in the nectary, and for this purpose unfold, and 
 make straight, their spirally wound under jaws (5), which, in some 
 
 Mouth of Cynthia cardui (painted lady) 
 Butterfly. 
 
LESSON 40.] NUTKITION IN INSECTS. 141 
 
 of them, are of great length (two inches long). The end of this 
 compound instrument is thrust deep into the coveted fluid, and 
 almost immediately the creature is on the wing again ; the sip has 
 been taken, the appetite is appeased. 
 
 633. The structure of the under jaws, when made straight, is 
 very curious. 
 
 Each one is a hollow tube, and the junction of the two forms 
 another, so that the apparatus consists of three tubes. The outer 
 surface is ringed, and each tube is really a tube and a half. To pro- 
 tect these important organs, a pair of inordinately large feelers are 
 found connected to the lower lip labial palpi therefore (c). 
 
 634. The oesophagus (as will be seen hereafter) is divided into 
 two branches, each one of which occupies an under jaw, so that either 
 might act independently of the other. The central canal, formed 
 by the junction of the two under jaws, receives and transmits the 
 secretion of the salivary glands ; so that the FIG. 234. 
 central tube is used to insalivate the food which 
 
 is sucked up by the two under jaws. The 
 under lip is much larger than the upper, but of 
 variable size. 
 
 635. The alimentary canal of the Cabbage 
 Butterfly (Pontia Brassica) is shown in Fig. 
 234. 
 
 636. The oesophagus (a), cut off below the 
 bifurcation, receives the tube connected with 
 the pumping stomach (c), and the food is re- 
 ceived into the stomach (d). The salivary glands 
 (n, ri), in this insect, are simple filiform tubes. 
 
 Below the pylorus, the bile vessels are con- 
 nected to the commencement of the Ileum (e) ; 
 the former are very delicate, and of great 
 
 , , 7 >. Nutrimental organs, Pon- 
 
 extent (k). tia Brassica. 
 
 The ccecum is seen (g) arising from the colon (h). 
 
 LESSON XL. 
 
 NUTEITION IN INSECTS, CONTINUED. 
 
 637. In the larval condition (maggots, caterpillars, and grubs) 
 of insects, the nutritive organs are straight in their direction, and 
 
142 
 
 ANIMAL PHYSIOLOGY. 
 
 [LESSON 40. 
 
 FIG. 235. 
 
 simple in their structure. The salivary glands, however, in some of 
 them are greatly developed ; thus, in the caterpillar of the Goat 
 Moth (Cossus ligniperda], where the creature is found in the interior 
 of the willow tree, for three years, constantly feeding on the heart 
 
 of the wood, large reservoir 
 bags are added to the glands 
 to hold a supply of this im- 
 portant secretion. The nu- 
 trimental organs of this in- 
 sect are shown in Fig. 235. 
 The drawing was made 
 from a preparation, and to 
 display all the parts the 
 salivary glands had to be 
 divided ; they were placed, 
 therefore, on either side 
 the nutrimental canal. 
 
 638. The ramified tu- 
 bular portion (a) at the 
 lower part, is the secreting 
 tube, or gland proper. 
 They coalesce, and form 
 one evacuating duct (5), 
 which transmits the secre- 
 tion to c, a large collecting 
 or reservoir bag. At the 
 summit of this bag is another tube (d) ; these combine to form one, 
 and through it the secretion of these glands, and another pair, not 
 present in the preparation, is delivered to, not the mouth, but to a 
 little bony tube connected with the lowef lip (Fig. 236), called the 
 spinneret, found only in those larvae which prepare a web for their 
 pupa change. 
 
 639. The elands not present are of great length, extending from 
 one end of the tody to the other, and almost filiform ; they are called 
 silk vessels, and are supposed to originate this material. And this 
 is true ; but the saliva is always combined with it, as necessarily it 
 must be when the four glands have only a common outlet. 
 
 640. When a Caterpillar is about to change into a Chrysalis, the 
 salivary glands are painfully distended with a secretion that will no 
 more be used for its legitimate purpose. 
 
 641. It is therefore poured out through the spinneret (in the 
 
 Nutrimental organs, Cossus ligniperda. 
 
LE96ON 40.] 
 
 NUTRITION IN INSECTS. 
 
 143 
 
 FIG. 236. 
 
 species possessing it), the gummy fluid becoming instantly inspissated 
 when brought into contact with the atmosphere (Fig. 236), and forms 
 a thread ; during all this time the poor crea- 
 ture's body is sadly contorted, and it gives 
 unmistakable evidence of great sickness, 
 pain, and suffering. That the change the 
 animal is about to undergo is really attend- 
 ed with such severe distress, is apparent 
 from the fact that many of them die during 
 the process. 
 
 642. The alimentary canal (235) com- 
 mences by a wide funnel-shaped cavity, the 
 
 pharynx (e) ; to this succeeds the oesophagus 8 P inneret ' Cossu8 Mgniperda. 
 (f), which dilates into a membranous crop, filled with deep longitudinal 
 folds, by which means its internal capacity can be greatly increased 
 (g). After the food has lain macerating here for a while, it is trans- 
 ferred to the long stomach (h), provided with a powerful muscular 
 coat externally, and lined with a mucous membrane. Here the food 
 is reduced to chyme, and allowed to pass through the pyloric valve 
 (i) into the ileum (&), where it meets with the biliary secretion 
 passed through the connecting gall ducts (Z, Z), and the chyme is 
 transformed to chyle. 
 
 The Ileum terminates in a short, straight colon, which, as com- 
 monly happens, enlarges slightly, prior to its termination. 
 
 643. The liver exhibits a series of pro- 
 tuberances, which are alternate. A highly 
 magnified view is given (Fig. 237), in which 
 it will be seen that they are cells, each being 
 filled with (apparently) globules, of an oily 
 fluid. 
 
 The cut ends of this portion of the liver 
 of a Caterpillar, have discharged an oil, 
 which, in the preserving fluid, has assumed 
 a globular form of variable dimensions, all 
 of them being very much larger than when 
 confined within the cells. This sacculated 
 form of the liver is common to most insects, and may be regarded as 
 characteristic ; moreover, it is always minute and uniform, and can- 
 not be confounded with the lobules of the salivary glands. 
 
 FIG. 237. 
 
 Liver of Caterpillar, 
 magnified. 
 
144 ANIMAL PHYSIOLOGY. [LESSON 41. 
 
 LESSOJST XLI. 
 
 NUTRITION IN INSECTS, CONTINUED. 
 
 644. The Neuropterous insects are, for the most part, predace- 
 ous and carnivorous ; always killing their prey on the wing, they 
 have hence been called " the Hawks amongst insects." 
 
 645. The most conspicuous insects of this order, and the best 
 known, are the bold and beautiful dragon flies, or, as they are called 
 in this country, "Devil's darning needles." Furnished with a head 
 almost all eyes, their sight is wonderfully piercing ; provided with 
 large, light wings, constructed of the most gauzy material, and abun- 
 dantly supported by an incredible number of the lightest conceivable 
 bones, their flight is as remarkable for its swiftness as their aim is 
 unerring. It is a pretty sight to see these creatures Hawking over a 
 pond, and remarkable the distance at which they see an insect once 
 seen, its death is certain ! Our obligations are great to this order 
 of insects, for they kindly free us from millions of pests, alike de- 
 tractive of our property and sorely tormenting to our persons. It 
 has pleased the Almighty dispenser of good to set up no end of an- 
 tagonisms in nature wherever a bane exists, there is the antidote ; 
 what a pity that man, in the plenitude of his ignorance, should take 
 so much pains always to destroy the antidote ! So important are 
 these insects, it is not too much to say that he who wantonly kills a 
 dragon fly commits a public wrong. 
 
 646. The smaller species of Libellula (Agrion), with a body less 
 in diameter than a moderate sized pin, consume immense quantities 
 of Mosquitoes, at the moment, too, when they emerge from the water 
 and assume the winged state. 
 
 647. The habits of other insects 
 frequently change with a new form, 
 but, whether as an inhabitant of 
 the water, or a denizen of the at- 
 mosphere, the dragon flies are al- 
 ways cruelly carnivorous, and as 
 such should be cherished. 
 
 648. The mouth of a Dragon 
 fly is mandibulate (Fig. 238). The 
 
 Upper part of month, Libellul, U PP 6r K P M is * el1 formed > the U f 
 
 per jaws (b) are short, remarkably 
 strong, possessing toothed processes, and supplied with muscles for 
 
LESSON 41.] 
 
 NUTRITION IN INSECTS. 
 
 145 
 
 Under part of mouth of Dragon fly. 
 
 closing the mouth (c) of great power. The antagonist muscle (d) is 
 simply required to open the mouth, and it is slight accordingly. The 
 under jaws (Fig. 239) are short, and not very powerful (a) ; each is 
 supplied with a small feeler (/), or palpus. 
 
 649. These organs are chiefly FIG. 289. 
 used as hands, to hold a living in- 
 sect while the upper jaws kill and 
 
 divide it, and afterwards convey 
 the pieces to the mouth. 
 
 650. The under lip (b) is un- 
 usually large, provided with two 
 processes with hinge joints, by 
 means of which they can either be 
 extended or remain closed ; this 
 
 apparatus forms a table, or platform, on which an insect can be 
 placed while the upper jaws act upon it. Such an arrangement was 
 necessary for an insect who kills and eats its j rey on the wing. The 
 mentum, or chin, is shown at c. 
 
 651. In the Hymenoptera, the mouth has undergone remarkable 
 modification, especially in the Bees. These insects require strong, 
 toothed jaws, for manifold purposes, and con- 
 sequently their mandibles are constructed upon 
 
 this type (Fig. 240, a). The upper lip is 
 shown at f. But the great business of their 
 lives is to procure the nectar from flowers, and 
 convert it into honey, and for this purpose an 
 especial apparatus is necessary. To this end, 
 the under jaws, and their dependences (palpi), 
 have become strangely metamorphosed; the 
 under jaws (b) are formed into a tube to re- 
 ceive and protect the rest of the mouth when 
 not required for use. "Within these (d, d) are 
 two long, jointed organs, gradually tapering 
 upwards, with short terminal processes nearly 
 at right angles ; these are the maxillary palpi, 
 or feelers of the under jaws. Their function appears to be that of 
 hands, to hold back the petals of a flower, whilst the long central 
 tongue (e) is busily engaged lapping up the nectar; for this purpose 
 they appear to be admirably adapted. The tongue (e) is much long- 
 er when extended than any other part of the mouth ; it is perforated 
 at its extremity, and has in its interior a canal, which is a continua- 
 10 
 
 FIG. 240. 
 
 Mouth of the honey bee, 
 Apis melliflca. 
 
146 ANIMAL PHYSIOLOGY. [LESSON 41. 
 
 tion of the oesophagus. The external surface is ringed, and exten- 
 sively covered with hair. At the base of this organ are two little 
 processes (c) called little tongues (paraglossae), the use of which is 
 unknown. For its protection, it folds up. 
 
 F 652. The structure of the nutrimental or- 
 
 gans is very interesting (Fig. 241) ; the oeso- 
 phagus (a) dilates into a large crop (5), or 
 collecting bag, having one side of it particu- 
 larly enlarged. 
 
 653. The pumping stomach is not devel- 
 oped in the Hymenoptera as a special organ, 
 but its function is shared with the crop. The 
 enlarged portion contains air ; by removing 
 the pressure of the muscles of the body, this 
 air becomes rarefied, and if the other extremi- 
 ty, the tongue, be made air tight, as it must 
 meiiifica. jjg wnen plunged deep into a viscid fluid, the 
 
 tube, from the pumping stomach downward, becomes exhausted, and 
 the fluid in which the tongue is placed necessarily ascends by a jerk. 
 Then the action ceases, until the tube be exhausted again, which oc- 
 curs directly the insect takes off the pressure by a deep inspiration, 
 and so the action continues. 
 
 654. The valvular projection of the true stomach is inserted far 
 into the crop (c) as a double tube, and must be withdrawn therefrom, 
 when the Bee desires to feed upon the honey it has gathered ; but so 
 long as they remain within the crop that organ is merely a collecting 
 bag, and retains the contents only until it can return to the hive, 
 where it is cast up, and deposited in the cells. 
 
 655. During the period it remains in the crop, it is macerating 
 in the salivary secretion, whereby its vitality is destroyed, and the 
 probability of acetous fermentation obviated. From this moment it 
 is preserved so effectually that it cannot decompose, in any time. So 
 far as is known, honey is the only substance which, having been duly 
 prepared in the stomach of the Bee, is cast up, and forms wholesome 
 and delicious food for man. 
 
 656. The stomach (d) is a long, muscular organ, which gradually 
 increases in size as it descends. Its lower portion is provided with 
 a pyloric valve, below which the ileum (e) commences. 
 
 The bile ducts (g) empty their secretion at the commencement 
 of the ileum, which terminates ultimately in the colon (/). 
 
LESSON 42.] NUTRITION IN INSECTS. 147 
 
 LESSON XLII. 
 
 NUTRITION IN INSECTS, CONCLUDED. 
 
 657. In the last order of winged insects, the Diptera, the mouth 
 is again transformed ; here we have a proboscis, or Haustellum, which 
 is membranaceous, or more or less fleshy. It descends in a perpen- 
 dicular direction from the orifice of the mouth, and is, in general, 
 shortly from its origin, kneed (shaped like a knee) forward, and ter- 
 minates in a flapper-shaped, suctorial surface. 
 
 658. In many of the predaceous Diptera (Tabini, Chrysops, 
 Stomoxys, &c.}, the bristles, or lancets lie, in a hollow groove exca- 
 vated in the upper surface of the proboscis, and covered and con- 
 cealed by a long corneous triangular scale, the upper lip. The Mos- 
 quito, Flea, and others, carry their lancets within a case, on the 
 principle of the Hemiptera. 
 
 659. Many of the vegetable feeding two-winged flies, are pro- 
 
 FIG. 242. 
 
 
 
 FIG. 243. 
 
 Fleshy under lip of 
 Helophilus tenax. 
 
 Upper part of mouth, Helophilus 
 tenax. 
 
 vided with a mouth, in every respect similar to the Tabini, and their 
 allies (Fig. 242). 
 
 660. The mouth of the rat-tailed worm-fly (Helophilus tenax), 
 to which Swammerdam did such ample justice, is a good illustration. 
 The insect in its perfect state feeds only on ripe fruit, which it first 
 stabs, or wounds, with its lancets, and then withdrawing them, places 
 the expanded fleshy under lip over the wound. 
 
 661. These, moistened with saliva, firmly adhere by means of 
 
148 
 
 ANIMAL PHYSIOLOGY. 
 
 [LESSON 42. 
 
 FIG. 244. 
 
 their rugous (wrinkled) surface the moisture contributing to make 
 them air-tight. In all these insects, the under lip is modified to 
 form the proboscis. The fleshy lips of the proboscis (a, 243), with 
 their rugous surface (6), are seen partly spread out for attachment. 
 
 The lancets, &c., are shown in the figure 242. The long trian- 
 gular upper lip (a) covers the remainder of the apparatus ; on either 
 side are seen the upper jaws (b), which are, in this insect, blunt- 
 pointed : the under jaws (c) are curved like a scymitar, and remarka- 
 bly thin, and sharp at their points. In the Tabini, and all their 
 
 allies, the upper jaws are sharp, 
 and lancet-shaped, while the under 
 jaws are blunt, or probe-pointed. 
 The long, leathery palpi (d) are 
 merely for additional protection. 
 
 662. The pumping stomach at- 
 tains its highest development in 
 the Diptera; in them it consti- 
 tutes an independent organ, which 
 is beautifully exemplified in the 
 nutrimental organs of the Flesh- 
 fly (Musca carnaria), or Blue-fly. 
 In this insect (Fig. 244), the long 
 delicate oesophagus (a) is continu- 
 ed from the muscular crop, to the 
 end of the proboscis, but not all the 
 way as the oesophagus ; a some- 
 what wider tube is excavated in 
 the proboscis, at the commencement 
 of which the ducts of the salivary 
 glands (b, 5), and oasophageal tube, 
 proper, terminate. 
 
 663. The salivary glands (c, c), 
 at their commencement, are robust, 
 
 remarkably convoluted, tubes; by degrees they become straighter, 
 and attenuated (d, d), and finally end as delicate tubes, parallel with 
 the lower third of the stomach. 
 
 664. The course of the oesophagus is direct to the commencement 
 of the crop, it then turns off, nearly at right angles, and ends in a 
 bladder-shaped bag, of large size the pumping stomach (e). 
 
 665. It is easy to understand that the small quantity of air, al- 
 ways found in this receptacle, becoming rarefied so as fully to distend 
 
 Nutrimental organs, Musca carnaria. 
 
LESSON 42.] NUTRITION IN INSECTS. 149 
 
 the sac, the tube in connecting with it becomes exhausted, and as 
 the other extremity has been previously made air-tight, the as- 
 cent of fluid, as a sudden jerk, is inevitable. Of course its tendency 
 is to rush into the pumping stomach, and if this could be achieved, 
 death would most likely be the immediate result, as much as if a 
 pail of water were suddenly poured into our lungs ; but long before 
 the air can reach the pumping stomach, reaction takes place, and 
 the fluid is driven through a very short tube, nearly at right angles, 
 but somewhat inclined to the oesophagus, into the crop, in whose cal- 
 lous margin a valve is placed to prevent regurgitation. Once in this 
 organ, the food macerates in the saliva, and becomes subject to the 
 action of its powerful muscles; in due time, it passes through a 
 valve at the lower portion, and enters the stomach (f). 
 
 666. This latter is a very long, slender, tortuous, and convo- 
 luted tube, having (according to some authors) three distinct 
 divisions in its interior ; it terminates by a pylorus just before the 
 commencement of the ileum (</), into which intestine the biliary 
 ducts, as usual^ enter. The liver (&, h) is of great size, and like the 
 same organ in the Caterpillar, appears to be filled with oil cells, 
 exceedingly minute, however. The ileum, too, is of unusual extent, 
 but at length terminates in the Colon (i). 
 
 667. Thus, as briefly as circumstances would permit, the chief, 
 and most remarkable characteristics of the nutrimental organs, and 
 the adapting forms of the mouth in the Linnsean orders of insects 
 have been described. It is unnecessary to speak of the Aptera, in- 
 asmuch as they really belong to the other orders, the want of wings 
 being a sexual distinction ; moreover, the majority of the individuals 
 of this order were not Insects at all, and have been removed to the 
 Classes to which they properly belong. 
 
 668. The structure of the nutrimental organs of insects is parti- 
 cularly interesting from the fact of their close agreement with like 
 structure in the Vertebrate animals. Thus, the ccecal appendages 
 around the pylorus of the Cockroach, bear close resemblance to a 
 similar structure found in many Fishes; in the latter they are sup- 
 posed to be salivary or pancreatic (pancreas, the sweetbread) in their 
 secretion, and this is, at least, equally probable with the Insect. 
 Feeding indiscriminately as the Blattaria do on whatever comes in 
 their way, upon flesh, or fruits, vegetables, linen, clothes of all kinds, 
 printed books and written manuscript, engravings or water-color 
 paintings, old boots and shoes, and not unfrequently nibbling the 
 toes (in hot climates) of persons while asleep, their power of digestion 
 had need be very perfect to get quit of such heterogeneous matter. 
 
150 ANIMAL PHYSIOLOGY. [LESSON 43. 
 
 669. The many digestive sacs of Locusta viridisima (large Eng- 
 lish grasshopper), and its allies, has its full representative in the four 
 digestive cavities of the herbivorous quadruped. The only great and 
 peculiar exception appears to be in relation to the pumping stomach 
 of the Lepidoptera, Hymenoptera, and Diptera, but even this, in 
 the opinion of some authors, but apparently with insufficient reason, 
 is met by the air-bladder of fishes. 
 
 670. The persistency with which the glandular system is develop- 
 ed in insects, is no less remarkable. 
 
 Salivary glands, to the extent of even three pairs, is by no means 
 uncommon, while few insects are entirely destitute of them. 
 
 The Liver is almost always found, and usually extensively pro- 
 duced, while in its ultimate structure (cellular) it bears great affinity 
 with the same organ in higher animals. In none of the illustrations 
 produced was a kidney found, but this organ is by no means rare. 
 
 Finally, in this class the most important problem, the ultimate 
 structure of glands, may be studied with great ease. In the higher 
 animals these organs are veiled by a parenchyma, which renders in- 
 vestigation difficult; but in insects, we find them already analyzed 
 existing as simple tubuli, and offering every facility for the most 
 minute examination of them. 
 
 When the like organisms in man and the higher animals have 
 been successfully treated, and reduced to their elemental condition, 
 lo ! they too, are simple tubes ! 
 
 LESSON XLIII. 
 
 OEGANS OF NUTEITION IN ARACHNIDA. 
 
 671. The general characteristics of this class have already been 
 given, together with the names of the orders into which it has been 
 divided. 
 
 The Arachnidans are placed above the insects in the scale of 
 being for the following reasons : they present a more concentrated 
 condition of the nervous system, and of the heart ; and the larger 
 species possess a higher condition of the respiratory system, which is 
 not only less diffused than in insects, but in some of them consists of 
 air-sacs, or rudimental lungs. If a Spider be examined, it will be 
 seen at a glance that the head is confluent with the chest, forming 
 
LESSON 43.] 
 
 NUTRITION IN ARACHNIDA. 
 
 151 
 
 the cephalo-thorax ; the remainder is the body, so that it exhibits 
 but two divisions ; and this is equally true of all the members of 
 this class. 
 
 672. Some of the lower Arachnida, so minute as to be quite 
 microscopical, are parasitic on man, and the history of one of these 
 parasites is not a little curious. It has already been observed that 
 the human hair grows out of a bag, or follicle ; this follicle re- 
 ceives the ducts of two fat secreting glands, called sebaceous glands. 
 
 673. Within the ducts of these glands, the parasite in question, 
 Demodex folliculorum (demos, lard; and dex, a boring worm), is 
 found (Fig. 245) ; in length, they range from the ^ th to the T th 
 of an inch. The figure gives a magnified view of a hair-follicle (a), 
 containing the bulb of the hair (b d) } the sebaceous gland (c), and the 
 
 FIG. 247. 
 
 FIG. 245. 
 
 Fro 246. 
 
 Demodex folliculorum. 
 
 Demodex from the scalp. 
 
 Demodex folliculorum ; 
 the perfect animal mag- 
 nified. 
 
 duct in which is the parasite (d). In adults, these creatures usually 
 abound on either side of the nose ; in young men, red pimples, of a 
 painful character, appear on the forehead, face, neck, &c., which, 
 when the inflammation subsides, is distinguished by a black spot. If 
 this spot be tightly squeezed, a white, tortuous, somewhat spiral 
 mass will appear spiral, because a cast in solid fat of the duct 
 placed in oil, the fatty or sebaceous substance will separate and 
 leave a specimen or more of the Demodex. 
 
 Another figure (246) is given, taken fVom the human scalp ; a, 
 the sebaceous glands ; b, a hair ; c, the ducts ; and d, d, the para- 
 sites. 
 
152 ANIMAL PHYSIOLOGY. [LESSON 43. 
 
 A highly magnified view of the animal is given in Fig. 247, where 
 it will be seen that it possesses eight feet (c), like all the arachni- 
 dans. 
 
 674. The mouth (b) is furnished with a proboscis, and is there- 
 fore suctorial ; it has also two short and thick maxillary palpi (a, a), 
 consisting of two joints, and above is a narrow upper lip. The ab- 
 domen is minutely ringed. 
 
 675. No nutrimental organs have yet been discovered in these 
 parasites, partly because of their opacity, and partly on account of 
 the shining character of their integument. 
 
 676. The next parasite originates the most loathsome, disgusting 
 disease that afflicts humanity the itch. Many medical men have 
 sought for this animal in vain, and hence they have concluded that 
 no such creature exists in connection with the disease. But their 
 failure has arisen from two causes : one, they have looked in the 
 wrong place, and the other, the animal is too minute to be seen by 
 unassisted vision, unless held up against the light. Usually they 
 are sought for in the pustule, characteristic of the' disease; but be- 
 fore the pustule can make its appearance, the Acarus has burrowed 
 off in another direction, and to succeed in finding it, the neighbor- 
 hood of the pustule should be explored with a needle. 
 
 677. The Acarus scabicel (Fig. 248) possesses all the true char- 
 
 acters of the Mites ; the legs in some mites, 
 terminate in suckers, but in this species (four 
 of them) in long setae (bristles a). 
 
 678. The mouth has a twofold character, 
 it is adapted either for suction or mastica- 
 tion. The whole form of the animal adapts 
 it eminently for the life it leads, constantly 
 burrowing beneath the surface of the skin, 
 where, having no use for visual organs, none 
 appear to be present, as in the Mole. 
 
 The Spiders are a very interesting class 
 of animals, the particulars in relation to them 
 requiring more space than the limits of this 
 Acarus scabitei wor ^ w afford ; suffice it to say, that the 
 
 organs of digestion are arranged on a very 
 simple plan, as befits an animal strictly carnivorous. 
 
 The mouth, as compared with the same structure in insects, is 
 also simple, and remarkably well adapted to the peculiar wants of 
 the animal. 
 
LESSON 43.] NUTRITION IN THE AEACHNIDA. 
 
 153 
 
 FIG. 249. 
 
 The short, strong upper jaws (Fig. 249) are provided with sharp 
 pointed, slightly curved teeth (6), which are hollow, like the poison 
 fang of a serpent, and for the same pur- 
 pose the transmission of the saliva. 
 
 The instant a Spider bites a fly, or 
 another individual of its own species, 
 the saliva is poured out abundantly 
 through the cavity of the tooth simul- 
 taneously with its insertion. 
 
 As a consequence, the victim is 
 poisoned, the body swells considerably, 
 and it dies immediately. 
 
 Now commences the process of feed- 
 ing, which simply consists in sucking up the juices of the slain. 
 
 To assist this process, the base of the teeth (a) is provided with 
 a double coronet of short, strong, pointed spines, upon which an 
 insect is literally impaled, whilst the killing and feeding progresses. 
 At the lower part of the jaws (d) two large cavities are seen, out 
 of which the muscles were extracted. 
 
 The under jaws (maxillge) are shown at a (Fig. 250), in the form 
 
 FIG. 250. 
 
 Upper jaws of the Spider. 
 
 Under jaws, Spider. 
 
 of short strong organs, whose function it is to hold the insect, whilst 
 the upper jaws kill it, and suck up its juices. 
 
 This operation is greatly assisted by the long, strong, five-jointed 
 feelers (b, 5), each of which terminates in a short hooked process (c). 
 Surely no better form of apparatus could have been contrived to 
 meet the special and peculiar requirement of a Spider. 
 
 680. In the domestic spider, the oesophagus (a, Fig. 251) passes 
 beneath the brain, and expands into a stomach almost as broad as 
 the sternum, which sends off a large coecal process into the base of 
 the maxillary palpi (6), and of each thoracic leg ten coecal appen- 
 dages in all. A shorter diverticulum (a turning) is continued 
 from the upper part of the stomach (d). Where the intestine 
 
154 
 
 ANIMAL PHYSIOLOGY. 
 
 [LESSON 43. 
 
 FIG. 251. 
 
 passes through the narrow pedicle of the abdomen, it is contracted ; 
 it slightly expands in its straight course (/) along that cavity, then 
 contracts and forms two short convolutions (g), and communicates 
 with a large globular coecuiu (h) from which the last short intestine 
 arises. Four bile ducts (i, i) open into each 
 side of the straight portion of the intestine. 
 Two long, slender tubes (k, k), constituting the 
 kidney, communicate with the commencement 
 of the co3cum. 
 
 681. There is a simple and easy mode of 
 finding the class to which the articulata belong, 
 at a glance : thus, if the body be divided into 
 three chief portions, it is sure to possess just 
 three pairs of legs ; therefore the creature is 
 an insect. But if four pairs of legs be 
 present, this character is invariably found as- 
 sociated with another of great importance; 
 that is to say, the body will have only two 
 divisions,' the head and the chest being sol- 
 dered together to form the cephalo-thorax (head, 
 ion ' Spid( chest), and the remainder constitutes the ab- 
 domen, or body. Here, then, we have the class Arachnida typified, 
 and the specimen is either a Spider (the Greek name of the class), a 
 Scorpion, or a Mite. If Jive, six, or more pairs of legs be present, 
 again we find the two divisions of the body indicating the same parts 
 as those already described (cephalo-thorax, and body), and these 
 form the characteristics of the Crustaceous animals. 
 
 682. To descend still lower in the scale : if the specimen pre- 
 sented to our notice have a variable number of distinct rings, or seg- 
 ments, any one of which is like all the rest, and the legs numbering 
 twenty-two, or more pairs, the specimen belongs to the class Myrio- 
 poda many feet to which the Centipedes, lulidce, Wood-lice, &c., 
 belong. Size has nothing to do with it ; the Mites (many of them 
 microscopical specks) having the required characteristics, as much 
 belong to the Arachnida as though they were as large as a Scorpion ; 
 and so of all the rest. 
 
LESSON 44.] NUTRITION IN THE TUNICATE MOLLUSCA. 155 
 
 LESSON XLIV. 
 
 OEGANS OF NUTRITION IN THE TUNICATE MOLLUSCA. 
 
 683. The Molluscous, or soft-bodied animals, appear to be organ- 
 ized for the perfecting of the nutritive function, to the development 
 of which every other consideration gives way. 
 
 684. The lower orders of this class (Tunicata, Brachiopoda, 
 Lamellibranchiata) are headless, and called, therefore, Acephala 
 (a, without ; cephale, a head) ; those with a head are the Pteropoda 
 (wing-foot), Gasteropoda (belly-foot), and Cephalopoda (head-foot). 
 
 685. The Tunicata are so called because their bodies are en- 
 closed in a gelatinous membrane, or sac ; they breathe either by a 
 vascular membrane, or by a ribbon-shaped gill stretched across the 
 common visceral cavity. There is no shell or calcareous deposit in 
 these animals ; moreover, in common with the headless Molluscs, 
 they are fixed to the rocks, and other submarine substances. 
 
 686. The Brachiopods (brachion, the arm ; pous, the foot) pos- 
 sess a bivalve shell, have two long, spiral, strongly ciliated arms, de- 
 veloped from the sides of the mouth, and breathe by means of their 
 vascular mantle. 
 
 687. The Lamellibranchiata are bivalve Molluscs, breathing by 
 means of lamellated gills (hence their name) attached to the mantle. 
 The Oyster and the Mussel are the best examples. 
 
 688. The Pteropods swim by two wing-like muscular appendages 
 attached to the sides of the (supposed) head. 
 
 689. The Gasteropods are the slugs and snails ; they walk upon 
 a foot, of greater or less dimensions, attached to the under surface 
 of the ventral surface hence their name, belly-foot. 
 
 690. The Gephalopods have their locomotive organs attached to 
 the head, generally in the form 252 
 
 of muscular arms, or tenta- 
 cles ; this is the only order 
 of the mollusca possessing an 
 internal skeletpn. 
 
 691. The Tunicate) are 
 frequently found in groups, 
 forming compound animals, 
 like many of the Polypes. 
 The outer gelatinous tunic is 
 
156 
 
 ANIMAL PHYSIOLOGY. 
 
 [LESSON 44. 
 
 FIG. 253. 
 
 warty in many species, but is always found to be smooth and lubri- 
 cous on its internal surface. 
 
 692. This tunic is lined by another, a muscular coat, of great 
 beauty as regards the arrangement of its fibres (Fig. 252) ; in this 
 animal (Cynthia pupa) the muscles consist of long diverging fasci- 
 culi, which originate from around the two orifices of the sac (a, b), 
 
 and extend round the entire body 
 of the animal. These fasciculi are 
 attached to various points of the 
 exterior tunic, but most intimately 
 around the respiratory (a) orifice, 
 and the vent (5), which are also 
 provided with distinct and strong 
 sphincter muscles (c, d), passing in 
 a circular manner around them. 
 
 693. The organs of nutrition 
 in these animals are peculiar in 
 their arrangement; thus, we find 
 the mouth proper, or entrance into 
 the nutrimental canal, placed at 
 the bottom of the sac (g, Fig. 253) ; 
 the food arrives at the mouth di- 
 rectly from the external respira- 
 tory aperture (a), being directed 
 to it by the spiral respiratory cur- 
 rent, caused by the vibratile cilia 
 
 lining the respiratory sac. The 
 organs, Cynthia pupa. m()uth leadg ^ ^ oesophagug Q 
 
 tolerable length, and ends in a well-formed, muscular cavity (&), 
 sometimes folded longitudinally, and perforated at the pyloric ex- 
 tremity by the wide ducts of the biliary follicles (/,/). 
 
 694. Neither teeth, jaws, nor salivary glands, are found in con- 
 nection with this very simple alimentary canal, but the liver is al- 
 ways found, under some follicular form, opening into the cavity of 
 the stomach, as in other mollusca. The intestine forms a distinct 
 curvature, in an upward direction, behind the respiratory sac ; it 
 terminates opposite to the vent (6), and ends with a margin of vibra- 
 tile cilia, to compel, by their action, the discharge of effete particles 
 of matter. 
 
 695. The ovaria (k) and the oviducts (m) lie on the inner side 
 of the intestine, the latter terminating by a margin of vibratile cilia, 
 
LESSON 45.] NUTRITION IN THE BKACHIOPODA. 
 
 157 
 
 like the intestine, and for the same purpose to compel FrG - 254 - 
 the mature ova to pass through the aperture of the 
 vent, when open. 
 
 696. In the beautiful and luminous Pyrosoma (Fig. 
 254) we have an interesting example of a compound 
 molluscan group. The external tunics of the individu- 
 als composing this group, are thin, soft, very trans- 
 parent, and of a bluish white color, and are the parts 
 by which they appear to be united together. 
 
 697. The Pyrosoma is a long tube shaped like a 
 finger, closed at the upper end (a), and open at the 
 lower extremity (6), and composed of a great number 
 of distinct individuals (c), which possess an internal 
 organization similar to the Cynthia. Like the latter, they also pos- 
 sess two orifices, but their position is different ; their respiratory 
 apertures are placed on the sides of the long projecting papillae (c), 
 and the apertures constituting the vents of all the separate individu- 
 als, open into the interior of the tube ; so that, solely by the com- 
 bined act of respiration, this elegant tube is carried through the seas. 
 
 The species of this animal common to the Atlantic (Pyrosoma 
 gigantium), is of about the length of two fingers, and when seen on 
 a still night, or, better still, if captured and conveyed in a basin of 
 sea- water into a cabin, is an object of remarkable beauty. 
 
 Pyrosoma gi- 
 gantium. 
 
 LESSON XLY. 
 
 NUTEITION IN THE BEACHIOPODA. 
 
 698. There are only three orders of this class, the Lingula^ Orbi- 
 cula, and Terebratula. These are all protected by shells, and attach 
 themselves to foreign substances, the Lingula (so called because 
 tongue-shaped) by means of a very long peduncle (Fig. 255 A), which 
 passes between the two valves : a, the shell, 5, the peduncle ; and 
 the Terebratula, by a much shorter peduncle, which projects through 
 a hole in a beak-shaped prolongation of one of the valves. 
 
 699. In the latter the alimentary tube is very short, of great 
 simplicity, and confined to a small space. The rest of the interior 
 of the lobes of the mantle is occupied by three long, strongly ciliated 
 arms, disposed in folds and spiral curves. The bases of the arms 
 
158 
 
 ANIMAL PHYSIOLOGY. 
 
 [LESSON 45. 
 
 join, and form a transverse fringed band above the mouth ; the bent 
 portions of the fringed arms are supported by slender, elastic, calca- 
 reous processes. 
 
 700. A figure of the nutrimental organs in situ is given (Fig. 
 FIG. 255 A. 255). The peduncle (e) for attachment is 
 
 seen in connection with that layer of the 
 mantle that forms the back ; a double heart 
 is said to exist in these animals, the auricles 
 of which (b, b) are placed on either side of 
 the alimentary canal, and above the point 
 of junction of the curled arms. It is, how- 
 ever, most probable that the so-called " hearts" 
 are simply the external openings of the 
 ovaria, by which the ripe ova effect their 
 escape. The stomach is entirely concealed 
 
 FIG. 255. 
 
 Lingula, natural size. Nutrimental organs in situ, T. Australia. 
 
 by a mass of biliary follicles (c), which completely cover it ; above, 
 it is covered with peritoneum. The intestine (d), which takes an 
 oblique direction, is not very conspicuous, owing to its depth ; two 
 of the arms, fringed with strong cilia (a), are seen on either side, and 
 in front the remains of the third arm (a), the curl having been cut 
 off, to show the other parts of the structure. Another, a side view 
 of Terebratula Australis, is given in Fig. 256; here the right 
 (lower) arm is partly seen, being concealed by the great curl usually 
 
LESSON 45.] NUTRITION IN THE BRACHIOPODA. 159 
 
 assumed by the central arm (e). To the right of the figure fe seen a 
 large orifice the tubular portion of the left arm, which has been 
 removed. The anterior and posterior portions of the mantle are 
 external in each direction (/). The trumpet-shaped mouth (a) is 
 seen just below the tendinous portion of one of the four strong mus- 
 cles (6), whose function it is to close the valves, and, crossing it ob- 
 liquely, a muscle of the second pair ; the white, glistening character 
 of the tendons of these muscles is very beautiful. The mouth leads 
 to a pharynx, and a very short oesophagus, which instantly terminates 
 in the stomach. The biliary follicles (c), as before seen, completely 
 
 FIG. 256. 
 
 FIG. 25T. 
 
 Alimentary canal, Terebratula Aus- 
 tralis, front view. 
 
 Terebratula Australia, side view. 
 
 conceal the stomach, and the short, trumpet-shaped intestine (h) may 
 be traced to its termination within the mantle. The peduncle for 
 attachment (g) is seen as before. 
 
 701. A better view of the alimentary canal is given in Pig. 257, 
 from a preparation of these organs dissected out of the body. Here 
 the mouth is seen surrounded with short, unusually strong cilia (a) ; 
 living and breathing under the weight and pressure of from sixty to 
 ninety fathoms of water, the cilia of the arms require to be strong 
 to compel the necessary currents of water to perform the circuit of 
 the interior of the valves ; charged with oxygen, for the supply of 
 the respiratory organs, it is, at the same time, laden with food (ani- 
 
160 ANIMAL PHYSIOLOGY. [LESSON 46. 
 
 malcules) for the supply of the animal's wants. To obtain this food 
 from the strong stream of water constantly being propelled through 
 its interior, the mouth has need of a special arrangement of ciliated 
 processes, which are found accordingly. The funnel-shaped pharynx 
 (b) is well shown in this view, and leads to the oesophagus (c) ; as 
 before, the biliary follicles (d) obscure the stomach. The reverse 
 side of this preparation (Fig. 258) shows the stomach (c?), and the 
 whole of the short intestinal canal (5), the mouth (a), and the 
 biliary follicles (c). 
 
 FIG. 258. FIG. 
 
 Back view of alimentary canal, T. 
 
 Australia. The arms of T. Australis. 
 
 Another preparation has been copied, to show the disposition of 
 the unmutilated arms, with their central one curled, and all of them 
 armed with remarkably strong cilia (Fig. 259). These are addition- 
 ally supported by a pair of strong calcareous (carbonate of lime) 
 bones, which are placed on either side, lying between a double mem- 
 brane, and just within the margin of the strong cilia. 
 
 The aperture at the upper portion of the figure passed around 
 the oasophagus, which had to be dissected out of it. The nervous 
 ring which surrounds the 03sophagus, and distributes branches to the 
 arms, is found in this situation. 
 
 LESSON XLYI. 
 
 NUTRITION IN THE LAMELLIBKANCHIATA, AND IN THE PTEROPODA. 
 
 702. In the common Oyster, the visceral mass occupies about 
 half the cavity of the shell next the hinge. The rest of the space be- 
 
LESSON 46.] NUTRITION IN THE LAMELLIBRANCHIATA. 
 
 161 
 
 FIG. 260. 
 
 Nutrimental organs, Oyster. 
 
 tween the lobes of the mantle, being almost entirely occupied with 
 the branchial laminae (gills), which 
 are four in number, equally divided, 
 and placed on each side of the vis- 
 ceral mass. The mouth is furnished 
 with two long, tapering, fleshy tentac- 
 ula (a, Fig. 260), and is continued 
 by a short oesophagus to an expanded 
 stomach, into which numerous rami- 
 fied hepatic follicles empty them- 
 selves (6). The intestine (c), after 
 describing a remarkable convolution, 
 ascending to the upper part of the 
 stomach, which it crosses, is contin- 
 ued along the interspace of the bran- 
 chiae towards their extremities which 
 are farthest from the mouth, where it terminates. The ovarium sur- 
 rounds the intestinal convolutions, and forms, with the liver, the chief 
 part of the visceral mass. 
 
 PTEEOPODA. 
 
 703. In all the Mollusca provided with a head, the capability of 
 locomotion is always considerable ; whereas in the acephalous (head- 
 less) molluscs it forms the exception not the rule. 
 
 704. The pteropods* are provided with two fin-like muscular ex- 
 pansions, attached to the sides of the neck, which, from their resem- 
 blance to wings, suggested pteropoda (iving-foot) as the name of the 
 class. Some of these animals are provided with a light and delicate 
 seinitransparent shell. 
 
 705. In the Hyalcea, it resembles a bivalve shell, of which the 
 two valves have been cemented together at the hinge, leaving a nar- 
 row fissure in front, and at the sides. In Cleodora, the two plates 
 of the shell are united together along the sides, as well as at the 
 base, leaving an opening only in front. Some (Clio, and others) are 
 naked, or unprovided with shells. 
 
 706. All the pteropods are of small size ; they float in the open 
 sea, often at a great distance from shore, and in latitudes that suit 
 them they swarm in such incredible numbers, as to discolor the sea. 
 The huge whale, with its remarkably small oesophagus, chiefly sub- 
 sists on the Clio borealis, and Limarcina^ both of which species 
 abound in the northern seas. 
 
 11 
 
162 
 
 ANIMAL PHYSIOLOGY. 
 
 [LESSON 47. 
 
 FIG. 261. 
 
 FIG. 262. 
 
 707. In the Hyalfea (Fig. 261), the head (a) and fins (b, I) form 
 together a large division of the body ; the portion containing the 
 viscera, and which is lodged in the shell (c), constitutes the abdomen. 
 
 708. The mouth is a 
 small longitudinal fis- 
 sure (a, Fig. 262) at 
 the apex of two diverg- 
 ing eminences; it con- 
 tains a tongue covered 
 with a thin, horny plate. 
 There are no salivary 
 Hyalaea, in its shell Nutrimental^-gans glands in this species, 
 
 but they are found well 
 
 developed in the Clio. In both these animals the narrow lengthened 
 03sophagus, which passes under a broad crerebral ganglion (g), and 
 dilates in the abdominal cavity into a membranous crop (6), is 
 slightly marked internally with longitudinal plicae (folds). This first 
 digestive cavity opens directly into a short cylindrical muscular giz- 
 zard (c), likewise marked with longitudinal folds on its inner surface, 
 and lying, like the crop, over the great retractor muscle (&), by 
 which the animal draws its head and fins (t, i) into its shell. From 
 the muscular gizzard, the long narrow intestine (d, e,f) makes a 
 double turn round the lobes of a small liver, and continues nearly of 
 uniform thickness to its termination on the right side of the neck, 
 under the right branchial fin. 
 
 LESSON XLY1I. 
 
 NUTRITION IN THE GASTEROPODA, AND CEPHALOPODA. 
 
 709. In the lower Gasteropods, the respiratory organs are ex- 
 posed, some on the back (Eolis), or the sides of the back ; some at 
 the lower part of the body, between the foot and the mantle ; and 
 some around the body, as in the patella (Limpet). 
 
 710. A figure is given of Eolis Inca (Fig. 263), in which the 
 back is nearly covered with a series of respiratory sacs. 
 
 711. The greater variety in the food, and habits of life of the 
 Gasteropodous Mollusca, renders a more complicated and varied 
 form of the nutrimental organs essentially necessary. Thus, the 
 
LESSON 47.] NUTRITION IN THE GASTEROPODA, ETC. 
 
 163 
 
 land species (Snails and Slugs) feed on the nutritive vegetables of 
 the earth ; many of the marine kinds (Doris, Eolis, Tritonia, &c.) 
 
 FIG. 263. 
 
 The short, narrow 
 
 03- 
 
 FIG. 264. 
 
 Eolis Inca. 
 
 on the lowest fuci of the Sea ; whilst many others are carnivorous, 
 and feed on living prey, 
 
 712. The Aplysia 
 faciata feeds on coarse 
 marine plants, and like 
 the herbivorous quad- 
 rupeds, presents a com- 
 plicated condition of 
 the alimentary appara- 
 tus. The broad labial 
 tentacula (a, Fig. 264) 
 are moved by strong 
 muscular bands (b). 
 The lips are supported 
 by two cartilaginous 
 (gristly) laminae (or 
 plates), and the tongue 
 is covered with minute 
 recurved teeth. 
 
 713. The wide 
 muscular cavity of the 
 mouth (c) receives the 
 terminations of two 
 salivary glands (e). 
 
 sophagus (d) dilates in- 
 to a large membranous 
 crop (i) ; this crop, or 
 
 paunch, occupies the Nutriment* organs, Aplysia faciata. 
 
 right side of the abdomen and opens laterally into the smallest, 
 middle stomach (&), which *is provided internally with numerous 
 
164 ANIMAL PHYSIOLOGY. [LESSON 47. 
 
 broad, flat, horny teeth, which serve to divide the softened vegetable 
 matter transmitted in small portions from the first stomach. 
 
 714. The third cavity (I) of this complex series of stomachs, is 
 placed on the left side of the abdomen; it receives by several wide 
 ducts, at its pylorio orifice, the secretion of a large, lobed liver (o), 
 and of a long, single pancreatic follicle ; its inner parietes are fur- 
 nished with several sharp, horny spines, to assist in subdividing the 
 coarse food, for the purpose of admitting the solvent gastric fluids. 
 The intestine (m) forms several convolutions round the liver (o), and 
 after a lengthened course, without forming an enlargement, it opens 
 on the right side (n), near the posterior portion of the body, and 
 immediately behind the heart (q, r) and the large gills (p). 
 
 715. In some of the Gasteropodous molluscs (as we have seen), 
 there are as many as four distinct gastric cavities ; horny teeth are 
 more or less found in the interior of one, or more, of these sacs, in 
 addition to the armature of the tongue, by teeth of various shapes 
 and sizes, which obtains extensively in this class. 
 
 Flo 265 716. A figure of the teeth of the tongue 
 
 of the common Whelk (Buccinum unda- 
 tum) is given in Fig. 265. In the Limpet, 
 the tongue is longer than the whole body, 
 and is covered with transverse rows of sharp 
 recurved spines, by which they are enabled 
 to file the coarse marine plants, on which 
 they subsist. 
 
 CEPHALOPODA. 
 
 717. These animals, for the most part, 
 are free, naked, and predaceous ; they are 
 Teeth mi^the tcmgn^of Buccin- provided with powerful organs of prehen- 
 sion, and mastication, and their short al- 
 imentary canal is furnished with highly developed salivary, biliary, 
 and pancreatic glands. The muscular bulb of the mouth contains, 
 in the naked species, two strong, curved, sharp, horny mandibles, 
 very like those of a parrot. 
 
 718. The short muscular tongue is covered with rows of sharp, 
 horny, recurved spines (as already noticed in other molluscs), attach- 
 ed to a cartilaginous base. There are two pairs of salivary glands ; 
 an upper smaller, and an inferior larger pair both of which are con- 
 glomerated (a round mass a batt)j and tabulated (composed of 
 lobes). 
 
LESSON 47.] NUTRITION IN THE GASTEROPODA, ETC. 165 
 
 719. In the Nautilus, a short pharynx (a, Fig. 266) leads to the 
 03sophagus (6), which dilates into a crop (c), with well marked lon- 
 gitudinal folds. Below this first cavity (c), a narrow tube conducts 
 to the second stomach, or muscular gizzard (d) ; this is situated on 
 the right side, and varies in its form, muscularity, and relative size, 
 and is provided with a thick, tough, coriaceous internal lining, to 
 protect it from the hard shells, and other dense 
 
 substances taken in with the food. 
 
 720. The muscles of the gizzard radiate from 
 around a circular tendinous part on each side, or 
 pass continuously over the sides of the cavity. 
 
 From the left side of the gizzard a passage, 
 generally short, and wide, leads to the third 
 stomach (e), which in many Cephalopods has a 
 convoluted spiral shape, and presents internally 
 numerous transverse folds of its mucous coat. 
 
 Passing to the left side from the third, or Nutrimentai organs, 
 
 & m Nautilus. 
 
 spiral stomach, the intestine (/) forms a short 
 single convolution near the left branchial heart, then ascends along 
 the fore part of the liver to terminate between two longitudinal 
 strong muscular bands near the base of the syphon, by a free external 
 orifice (g). 
 
 721. This third gastric cavity forms (in Nautilus) a globular 
 sac, plicated internally, with parallel folds. The intestine forms a 
 short, single convolution directed downwards, then ascends to the 
 fore part of the liver, to terminate between two strong muscular 
 bands, near the base of the syphon. 
 
 722. Destitute of a shell, as the great majority of the Cephalo- 
 pods are, they are left (apparently) without the means of protecting 
 themselves from the thousands of foes, ever ready to destroy them. 
 
 723. Their naked, plump, soft, gelatinous bodies, offer an irresist- 
 ible temptation to every fish that swims the ocean ; to Lobsters and 
 Crabs ; and to nearly every marine animal. 
 
 724. The* wisdom and beneficence of an all-wise Providence is 
 singularly exhibited in favor of the Cuttle-fishes, for he has given 
 them a passive means of defence, vastly more efficacious and superi- 
 or than physical power, or great warlike capabilities : he has simply 
 furnished them with a bag, full of intensely black ink ; if pursued by 
 an enemy, for even the shortest space, the creatures at once discharge 
 the contents of this bag, which instantly renders the ocean, for a 
 great space above, below, and around, exceedingly black and turbid, 
 
166 ANIMAL PHYSIOLOGY. [LESSON 47. 
 
 moreover, it affects the eyes of other animals : in the meanwhile, 
 the Cuttle-fish escapes ! 
 
 725. The situation of this bag differs in the various species, but 
 it is usually found adjacent to the liver. 
 
 720. The beautiful black pigment known as " Indian Ink," is 
 made by the Chinese from the inspissated (hardened) contents of the 
 ink-bag of one species, and the no less beautiful color, Sepia, from 
 the ink-bag of another species of Cuttle-fish, so that the Fine Arts 
 are greatly benefited by the means necessary to insure their lives. 
 
 727. But the most surprising fact in this connection is, that the 
 contents of the ink-bags of a number of fossil Cuttle-fishes has been 
 made into an ink (in England), and the frontispiece of a pamphlet 
 that went through a very large edition, printed with it ; in color, it 
 bears a close relation to Sepia.* 
 
 728. The Cuttle-fishes being shell-less, require a bone of some 
 kind for the attachment of their strong and powerful muscles, and 
 to give general support to the body. For these purposes, they are 
 provided with an internal skeleton the only animals amongst the 
 invertebrate (save certain polypes) similarly provided. This bone, 
 which extends nearly the whole length of the body, is called the 
 gladius (a sword), and is as varied in form as composition. 
 
 729. In some species it is long, and shaped like the feather of a 
 bird, the quill portion being inordinately long, whilst in substance it 
 is scarcely cartilaginous. In the common Cuttle-fishes (Sepia 
 officinalis) , it is thick, and broad in shape, having its animal mem- 
 brane consolidated by the carbonate of lime. 
 
 730. The bone of this animal is common in every Chemist's 
 shop, and (in this country) is placed in the cages of Canary and 
 other small birds ; considering that it is solidified by an earth so 
 weighty as carbonate of lime, it is, above all things, remarkable for 
 its extreme lightness ; we will see what causes it. 
 
 731. Take a portion of such a bone, break it, and place it under 
 the microscope the secret of its lightness will soon be revealed. 
 
 It will be seen that the structure consists of a number of strata, 
 or laminae, of inconceivable thinness; these are separated from each 
 other by a vast number of pigmy pillars (Fig. 267), which necessa- 
 rily admit of a current of air to pass freely between the laminated 
 plates, which not only imparts lightness to the fabric, but must give 
 great buoyancy to the animal. 
 
 * The Author possesses a copy of the pamphlet iu question. 
 
LESSON 48.] NUTRITION IN FISHES AND EEPTILES. 
 
 167 
 
 FIG. 267. 
 
 732. It is an inconceivably pretty sight to see a Cuttle-fish blush 
 blushing is by no means limited to them, for other naked (shell-less) 
 molluscs do the same occasionally, but 
 in an inferior degree. "When one of these 
 creatures is brought on deck from a 
 dredge, and placed in a dish of sea- 
 water, after a few minutes the whiteness 
 of its skin will disappear, and its entire 
 body and tentacles become suffused with 
 a pale pink color, which gradually be- 
 comes somewhat intensified : this is the 
 blush. 
 
 Left to itself, the animal will soon 
 
 resume its former color ; it is, however, easy to kill them preserving 
 the blush permanently in death. 
 
 Section of Cuttle-fish bone, mag- 
 nified 100 diameters. 
 
 LESSON XLYIII. 
 
 NUTRITION IN FISHES AND EEPTILES. 
 
 733. For the most part, these animals are predaceous, and swal- 
 low their prey entire ; their oesophagus is consequently short and 
 wide, their stomach capacious, and their intestine short. 
 
 734. Their accessory glands are moderately developed, and their 
 teeth are adapted to prehension rather than mastication ; of the 
 structure of these organs, more will be said hereafter. 
 
 735. The alimentary canal of fishes is generally more short and 
 simple than in higher vertebrata, which agrees with their predatory 
 habits, and their inferior position in the scale of being. 
 
 736. With a short oesophagus and a capacious stomach, with its 
 two orifices approximated, the whole digestive canal of fishes is often 
 shorter than the body, as seen in the common Herring (Glupea ha- 
 rengus), Fig. 268, where the narrow cardiac part of the oesophagus 
 (a) opens into a lengthened tapering stomach (5), communicating by 
 a long duct (m) with a large air-bladder (I). The duodenum, c 
 (twelve ; so called because the human duodenum is about twelve 
 fingers in length ; it is the first of the small intestines), is provided 
 with numerous pancreatic tubuli (d), which remind us of the eight 
 similar follicular appendages beneath the crop in the Cockroaches. 
 
168 ANIMAL PHYSIOLOGY. [LESSON 48. 
 
 From this point, a short intestine (e, e) arises, which opens into the 
 cloaca (/). The soft roe (h, h) of the male fish, like the ovarium of 
 the female, empties its contents through the common duct (i), and 
 
 FIG. 268. 
 
 Nutrimental organs, Herring. 
 
 finally by the aperture (k) beyond the cloacal outlet (/). This one 
 figure is a sufficient demonstration of the general arrangement of the 
 nutrimental organs in the class of Fishes ; the modifications to which 
 it is subject being too unimportant to need comment : we therefore 
 proceed to the class of 
 
 REPTILES. 
 
 737. These animals, like the Fishes, are predaceous in their 
 habits, and swallow their prey whole. They have loose and feeble 
 articulation of the jaws, which greatly favors such proceeding, while 
 their teeth are sharp, slender, and fitted as prehensile organs, but ill 
 adapted to the purposes of mastication. 
 
 738. The long, free bifid tongue of the Frog, covered with pa- 
 pillae, and muciparous (mucous) follicles, is the all important instru- 
 ment for the procuration of food. 
 
 739. It is attached by its apex to the inner surface of the under 
 jaw, the base being loose and free in the back part of the mouth. 
 A Frog will never touch any save a living insect, and of this fact it 
 requires such positive and conclusive evidence, that the latter often 
 escapes before the former is sufficiently stimulated to attempt its 
 capture. 
 
 "When once a Frog fixes his eye on a lively living insect, his whole 
 appearance is suddenly changed. The passive, sluggish animal of 
 the minute before, has suddenly assumed the aspect of ferocity. 
 
 740. If it be a fly at some distance from the frog, on the carpet, 
 the latter, his eyes full of malignity and craft, stretches out his 
 
LESSON 48.] NUTRITION IN FISHES AND REPTILES. 169 
 
 limbs to their utmost capacity, and creeps towards the insect in the 
 most stealthy, noiseless manner possible ; as soon as he arrives within 
 a certain distance of his victim, the tongue is thrown out so rapidly 
 that it escapes detection ; but the fly has been struck, glued to the 
 tongue by the mucus on the surface, and returns with it into the 
 Frog's mouth. 
 
 741. The senses of hearing, sight, and smell, are wonderfully acute 
 in these animals. No one would believe that a fly alighting on the 
 surface of a carpet, would be accompanied by any appreciable sound, 
 and (so far as our sensations are concerned) this is quite true ; not 
 so with a frog, however ; the fly may alight at a distant part of 
 the room, and the frog's back be turned from that direction, yet he 
 hears it instantly, turns round, and proceeds to effect its capture, in 
 which he very rarely fails ! 
 
 742. The mode by which a frog is enabled to seize its prey, is 
 in this wise : stimulated by the sight of it, the tongue becomes in- 
 jected with blood, through the influence of the imagination, until it 
 is quite turgid or erect ; at this instant, it can be thrown out and 
 used. The action is like letting the back of the hand fall quickly 
 from the elbow-joint, FIG 
 
 without moving the 
 wrist, and allowing it 
 quickly to rebound. 
 
 743. The process 
 requires to be swift, 
 for the breathing of 
 the frog is suspend- 
 ed so long as the 
 mouth remains open. 
 
 744. There is not 
 in nature a more 
 harmless or valuable 
 
 animal than a frog, nor one, whose presence in gardens should be 
 so much encouraged, for they consume only insects, spiders, and 
 slugs, and the quantity of these they destroy is quite incredible. 
 
 745. It has been remarked that the teeth have a prehensile 
 character in the frogs, but this cannot be demonstrated in Fig. 269, 
 copied from a minutely injected preparation of the palate of a frog, 
 because the spectator looks directly down upon the teeth, whereby 
 the pointed apices escape detection ; moreover, he desires to see the 
 blood-vessels, to do which, cuts off (apparently) the points of the 
 
170 AXIMAL PHYSIOLOGY. [LESSON 48. 
 
 teeth. The teeth (a, a) are seen in their sockets, but so slightly at- 
 tached that many of them are missing; neither is their sharp, pointed 
 character conspicuous, being concealed by Canada balsam. The 
 injection has run so minutely, that the pulps (6, b) of many of the 
 teeth are injected. Two eminences may be seen to the right; these 
 are the palatine bones, and to each, three and four teeth are arti- 
 culated ; in the frog the teeth are confined to these bones and the 
 upper jaw. The beauty of the vascular (vessels) arrangement of the 
 mucous membrane of the palate, need not be insisted on. 
 
 746. The strong muscular oesophagus is short, dilatable, and lon- 
 gitudinally folded ; it leads to a narrow, elongated stomach, placed 
 transversely from left to right, with thick, fleshy sides, especially at 
 the pyloric extremity, and covered above by the two lobes of a large 
 liver, always provided with a free and distinct gall bladder. 
 
 747. Injected, opened, and microscopically examined, the stomach 
 of a frog presents all the elements of a true digestive cavity. Its 
 mucous membrane is traversed with capillary blood-vessels, which 
 ramify on the surface of the cell-walls, everywhere conspicuous (Fig. 
 270). Mucus issues from the cells, and a gastric fluid is secreted 
 by the capillaries of the mucous membrane, so that the resolution of 
 the food is accomplished on precisely the same principle in a frog as 
 in a man. 
 
 748. The duodenum is remarkable for the entire absence of pa- 
 pillae (papilla, a teat or nipple), but it is provided with transverse 
 folds of the intestine, called valvulcs conniventes (valvular folds). 
 These valvular folds have edges like papillae, but, instead of being 
 distinct bodies, stretch across the intestine as one single fold. 
 
 FIG. 270. FIG. 271. 
 
 Stomach of Frog. Duodenum, Frog. 
 
 749. This is shown from the injected duodenum of a frog (Fig. 
 271). The villi (or papillae) of the duodenum, that we look in vain for 
 in the Frog, present themselves with all their characteristics well de- 
 veloped, in the duodenum of the Toad (Fig. 272). 
 
LESSON 48.] NUTRITION IN FISHES AND EEPTTLES. 1*71 
 
 The same short, broad, square-shaped organ that belongs per- 
 sistently to this portion of the intestinal canal in all the warm- 
 blooded animals, is equally characteristic of the duodenum of a lowly 
 Batrachian ! 
 
 The folds that were transverse in the duodenum, become lon- 
 gitudinal in the ileum, and display a beautiful arrangement of capil- 
 lary blood-vessels (Fig. 273), as shown in the figure, copied from an 
 injected preparation of the tissue. The large intestine (colon), al- 
 
 FIG. 272. Fio. 278. 
 
 Ileum of Frog. Duodenum of Toad. 
 
 though destitute of folds, presents a fine example of capillary dis- 
 tribution, and is shown in Fig. 274. 
 
 The mucous membrane of the large intestine presents great uni- 
 formity in both frogs and toads, and consists of a plexus of capillary 
 blood-vessels, which appear to cross the larger vessels of supply and 
 return (arteries and veins) which are situated in the sub-mucous tissue. 
 
 The mucous membrane is so thin and transparent in these ani- 
 mals, that the larger vessels can be distinctly seen in a well-injected 
 preparation, through its parietes; this is shown in the large intes- 
 tine of the Frog, Fig. 274. 
 
 750. The Batrachian reptiles (batrachos, a frog), which include 
 the frogs and toads, are not amphibious they are air-breathing an- 
 imals, and cannot respire at all under water. If a frog be kept be- 
 neath the surface of the water he dies, in 
 
 ,. f . FIG. 274. 
 
 not exceeding four hours. 
 
 751. There are reptiles, however, 
 supplied with permanent gills, for aquat- 
 ic respiration, and lungs, for breathing 
 air, and these constitute truly amphibi- 
 ous animals. The ponds of this country 
 teem with a very interesting amphibious 
 reptile the Menobranchus (permanent 
 gills), usually called " the mud sucker." 
 
 752. In form it is somewhat Lizard-like, having a long body, four 
 
172 
 
 ANIMAL PHYSIOLOGY. 
 
 [LESSON 48. 
 
 short legs, and a tail of moderate length. Its head is broad and 
 flat, at the base of which the " permanent gills," from which its 
 Greek name is derived, are seen on either side. 
 
 753. Its internal structure agrees, in general particulars, with the 
 frogs ; the stomach marks a slight advance in relation to the great 
 regularity and distinctness of the mucous cells, and of the deep-seated 
 
 FIG. 275. 
 
 FIG. 276. 
 
 
 Stomach of Mcnobrauchus. 
 
 ileum of Menobrauchus. 
 
 capillaries (Fig. 275) ; so, too, the ileum (Fig. 276) shows the lon- 
 gitudinal folds, and the capillary arrangement in great perfection. 
 
 754. Another of these Amphibise, the Menopoma (permanent 
 holes), like the former in size and general particulars, but presenting 
 a series of holes at its sides, like a Lamprey, and not yet found in 
 this country (so far as known), but indigenous to Africa, presents a 
 still further advance in the structure of the stomach (Fig. 277), by 
 displaying in each cell two mucous tubes. 
 
 755. It is deeply interesting to trace the gradual development 
 of such an important organ as the stomach, from its condition in a 
 batrachian reptile up to man, and this principle will be followed (as 
 far as expedient) henceforth. 
 
 i.. 
 
 756. Passing the Ophidian reptiles (snakes), and the Saurians 
 
 FIG. 
 
 FIG. 278. 
 
 Stomach of Menopoma. Stomach of the Snapping Turtle. 
 
 (lizards), we come to the Chelonian order (turtles, tortoises) ; here 
 we find that the nutrimental organs (especially the stomach) have 
 gained a great advance. The injected stomach of the Snapping 
 
LESSON 49.] NUTRITION IN BIRDS. 173 
 
 Turtle (Fig. 278) well illustrates this fact. We here see the gastric 
 cells of the mucous membrane of large size, and the capillaries me- 
 andering on their surface in a tortuous direction. 
 
 LESSOJST XLIX. 
 
 NUTEITION IN BIRDS. 
 
 757. In this class the alimentary apparatus is adapted for the 
 higher forms of animal and vegetable matter, which they obtain in 
 the air, in the waters, or on the earth. The jaws have their margins 
 covered with horny plates, like the Chelonian reptiles, which vary in 
 their forms according to the kind of food they are destined to 
 feed on. 
 
 758. The broad, depressed bills of Ducks, Geese, Swans, and 
 many other aquatic birds, with dentated edges and soft, sensitive lips, 
 are well adapted for obtaining worms, and other small objects under 
 water or in mud. The flat, spatulate jaws of the Spoonbills are 
 adapted for quick, lateral motion in the water, and for extracting mi- 
 nute animals from the moist banks of lakes and rivers. 
 
 759. The sub-maxillary pouch of the Pelican serves as a net for 
 seizing fishes ; the straight, sharp bills of Cranes and Storks dart 
 with precision through the water upon their moving prey, and the 
 long, compressed bills of Cormorants, Gulls, Albatrosses, and other 
 predaceous aquatic birds, terminate above in a sharp inverted hook, to 
 seiEe firmly the smooth, scaly bodies of fishes. The broad bills, with 
 cutting edges, of the Struthious (pertaining to the Ostrich, two- 
 toed) birds, are adapted to prune the leaves and shoots of plants, 
 and the long, narrow bills of Woodpeckers to be inserted into small 
 crevices to seize minute insects, and most of the insectivorous birds 
 have a similar structure on a smaller scale. 
 
 760. The long, tubular beak of the Humming-bird is suited for 
 insertion into the corollas of flowers. In the Grosbeaks and Cross- 
 bills, the Sparrows and Buntings, and all the granivorous (feeders 
 on grain) order, and in the common poultry, the bills form stronger 
 and shorter cones, broader at the base, to break down and remove 
 the hard coverings of grain. In the climbing Cockatoos, Parrots, 
 and Maccaws, the broad and powerful bills serve as prehensile organs, 
 and to break the hard, shelly coverings of seeds. The bills of Eagles, 
 
174 
 
 ANIMAL PHYSIOLOGY. 
 
 [LESSON 49. 
 
 FIG. 279. 
 
 Vultures, Hawks and Owls, and other rapacious birds, are strong, 
 short, compressed, arched, curved at the point, dense in their tex- 
 ture, and with sharp, cutting edges, to seize, and tear, and cut the 
 flesh of living prey. In fine, the external forms of the mouth cor- 
 respond with and indicate the structure of the internal organs of di- 
 gestion, and afford useful characters for the division of the class. 
 
 Want of space, however, will 
 not permit more than two il- 
 lustrations of the digestive or- 
 gans, and the birds selected 
 for this purpose are the com- 
 mon Fowl and the Crow. 
 
 761. The length of the nu- 
 trimental canal differs great- 
 ly in the several orders of 
 Birds ; it obeys the common 
 law of being shorter in the 
 flesh-consuming tribes, and 
 of greater length in those 
 feeding on a vegetable diet. 
 In nearly all the members 
 of this class, the food is de- 
 tained in a preliminary sac, 
 formed by the dilatation of 
 some part of the mouth, 
 pharynx, or oesophagus, be- 
 fore it passes into the sto- 
 mach, and in this receptacle 
 it frequently undergoes a 
 partial state of digestion. 
 In most of the small birds, 
 feeding upon grain, and in 
 the common poultry, a spe- 
 
 Alhnentary caiial, Fowl. c ia) gac j s developed from 
 
 the oesophagus, called the crop (6, Fig. 279). The food is allowed to 
 lie and macerate for some time in a fluid abundantly secreted by a 
 number of follicles situated in the walls of the crop, which prepares 
 it for the more perfect process of digestion, which it will receive in 
 the stomach. 
 
 762. From the crop the oesophagus (a) continues, exhibiting 
 
LESSON 49.] 
 
 NUTRITION IN BIEDS. 
 
 175 
 
 another but slight enlargement (c) before it enters the stomach ; this 
 second sac is called the " proventriculus " (pro, before ; ventricubts, 
 the stomach). This latter organ secretes a gastric fluid proper, which 
 additionally prepares the food for the stomach's action. The giz- 
 zard, or true stomach of these birds (d) next succeeds, and if its 
 structure be found on investigation to be peculiar, so at least is its 
 function. Examined carefully, it will be found to possess two pairs 
 of muscles ; of these, one pair is moderately, while the other is most 
 immoderately, developed ; the interior, too, is lined with a hard, cal- 
 lous, non-vascular, perfectly insensible, membrane. 
 
 763. The action of these muscles is to press the sides of the 
 stomach (gizzard) firmly together, and produce and sustain a lateral, 
 grinding motion, by which means the hard food may become thorough- 
 ly triturated (reduced to a very fine pulp). To assist this most 
 remarkable process, these birds always swallow small particles of 
 flint, for without its agency the probability is that the perfect reduc- 
 tion of the food could not be accomplished. These flinty particles, 
 combined with the constant, firm, lateral motion of the muscles, and 
 aided by the insensible lining membrane of the gizzard, form an ex- 
 cellent apparatus for the purpose required. 
 
 764. Those persons who keep Canaries, and other singing birds, 
 instead of sprinkling fine gravel on the bottom of the cage, that the 
 poor birds might help themselves to flint, to assist their digestion, 
 usually give them a piece of Cuttlefish-bone (Carbonate of lime !), 
 which is useless. 
 
 765. The consequence is, .the poor creatures sicken (of dyspepsia) 
 and die ; if any one will make the experiment, and try the effect of 
 some minute particles of .silica on their favorite song birds, the ex- 
 treme greediness with which it will be consumed will speedily assure 
 them of the necessity for its continuance. 
 
 766. The liver, of fair dimensions (e), discharges its secretion, 
 by its proper duct, into the duodenum ; the 
 
 well-formed gall bladder (jf ), and a pan- 
 creas, or sweetbread (g)- are also met 
 with. The duodenum (h) succeeds the 
 stomach, or gizzard ; if the latter be found 
 devoid of blood-vessels, the like cannot be 
 said of this commencement of the small 
 intestines, for, on the contrary, its inner 
 surface is densely covered with villi (like 
 the pile of velvet, and giving a velvety 
 
 FIG. 280. 
 
 VilU of the duodenum of a Fowl. 
 
176 
 
 ANIMAL PHYSIOLOGY. 
 
 [LESSON 49. 
 
 FIG. 281. 
 
 appearance to the intestines), of unusual size, and remarkable for the 
 squareness of their contour (Fig. 280) ; it will be seen, by reference 
 
 to the figure, that the villi are in- 
 tensely vascular. To this succeeds 
 the small intestine (i, i), the coacum 
 (&), and the large intestine (m), 
 terminating in the cloaca (o). 
 
 In the common Crow, the ali- 
 mentary canal possesses much gen- 
 eral agreement with the like organs 
 in the Fowl ; points of difference, 
 however, occur. 
 
 A portion of the oesophagus (a, 
 Fig. 281), together with the giz- 
 zard and commencement of the 
 duodenum, has been accurately 
 copied from a dissection. It will 
 be apparent that the enlargement 
 at the cardiac portion of the osso- 
 phagus (b) exceeds that of the 
 Fowl. 
 
 The pylorus (d) marks the 
 Gizzard, duodenum, &c., Crow. point where the duodenum (c) 
 
 commences. The gizzard (e), although not very large, possesses 
 
 muscles of great power. 
 These will be better under- 
 stood by consulting Fig. 
 282, in which this organ is 
 seen cut open. The lower 
 part of the oesophagus (a) 
 conducts to the cardiac en- 
 largement (b). A muscle 
 of the larger pair is cut 
 through at c, and a muscle 
 of the smaller pair at d. 
 The deep folds and wrinkles 
 of the interior of the sto- 
 mach (gizzard) are referred 
 
 Gizzard laid open, Crow. 
 
 to at e. 
 
 The intestines exceed in length those of the Fowl, and terminate 
 without the development of a coscal appendage. 
 
 FIG. 282. 
 
LESSON 50.] NUTRITION IN THE MAMMALIA. 
 
 LESSON L. 
 
 NUTRITION IN THE MAMMALIA. 
 
 767. The digestive organs vary more in this class than in any 
 other of the Vertebrated animals ; moreover, they present the high- 
 est type of development in the various organs connected with the 
 function of nutrition. 
 
 768. The high condition of their organs of sense assist these 
 animals to perceive minuter differences in the chemical and physical 
 properties of their food ,' while the structure and fixed position of 
 the teeth enable them to comminute their aliment, and mix it suffi- 
 ciently with the secretion of the salivary glands, for the final pur- 
 poses of digestion. 
 
 769. The Rodentia (gnawing) present some striking peculiarities 
 in connection with the development of their nutrimental organs. 
 Although possessing but one stomach, it 
 
 contains, nevertheless, the elements of 
 
 two very distinct organs. The stomach 
 
 of the common Bat (Fig. 283) offers a 
 
 good illustration ; the oesophagus (a) 
 
 communicates with nearly the centre of 
 
 the organ, and can, with the like ease, 
 
 deposit food on either side. By inflating 
 
 and drying such an illustration, a line of 
 
 demarcation will then be visible, clearly stomach of the Eat 
 
 dividing the organ into two distinct parts ; that towards the pylorus 
 
 (6), on the right side as it lies in situ (d), will appear to be fhick^ 
 
 as if composed (as in truth it is) of the three coats common to such 
 
 an organ ; on the left side (e) there is superior transparency, and a 
 
 number of lines, ridges, or furrows, transverse in their direction ; the 
 
 duodenum commences at c. In the figure the organ is reversed, but 
 
 it is everywhere described correctly. 
 
 770. If, instead of inflating and drying the stomach, it be cut 
 open for examination, the left side (e) will be found devoid of mucous 
 membrane, or muscular coat ; both of which, together with an ex- 
 ternal serous coat, are found in connection with the right side (d). 
 To render our examination complete, we should try the injecting 
 syringe, to ascertain the vascularity of the organ, and here a very 
 interesting fact is disclosed : the right side of the stomach is in- 
 
 12 
 
178 ANIMAL PHYSIOLOGY. [LESSON 50. 
 
 tensely vascular ; the left side consists of a hard, callous, insensible, 
 FIG 2g4 non-vascular membrane, comparable in 
 
 every respect to the membrane lining the 
 gizzard of the fowl. An injected prepa- 
 ration of the stomach of the Musk-Rat 
 (so far as it is vascular) is offered in 
 Fig. 284 ; it is useless to attempt to 
 show the other half, for not one single 
 vessel does it possess. But the mucous 
 MUCOUS membrane of stomach, membrane of a true digestive cavity is 
 admirably shown in the vascular portion. 
 
 771. Many of the Rodents (the common Rat, for example) are 
 omnivorous ; feeding indiscriminately upon all that comes in their 
 way ; at one time eating flesh, at another grain. 
 
 772. It has been supposed, therefore, that flesh would be placed 
 in the right side of the stomach, and digested on the principle com- 
 mon to all carnivorous animals ; and that, when a material as re- 
 fractory as wheat was purloined from a farmer's granary, it would be 
 transferred to the left side, and become subject to the same kind of 
 trituration as if found in the gizzard of a fowl. 
 
 773. But inasmuch as all the gnawing animals (Rodents, including 
 even the Mice) possess the same kind of stomach, and many of them 
 are strictly vegetable feeders (Musk-Rat, and others), this opinion must 
 be given up, and at the present moment we can only confess our ig- 
 norance of the intention and special use of this remarkable dual (two) 
 organ. 
 
 774. The wants of those animals designed to feed exclusively on 
 grass, are peculiar, and necessitate an arrangement of the nutrimen- 
 tal organs of such a kind, that no parallel can be found in the animal 
 kingdom, except in certain Insects, organized to consume the same 
 material, and there we find a like adaptation of parts. Of all the 
 various forms of food given to animals as their natural pabulum, none 
 is found to contain such a mere atom of nutrient material as grass. 
 Moreover, the nutriment, small as it is, is locked up in a particular 
 manner, so that the means in ordinary use for the resolution of other 
 substances, are altogether inadequate for the dissolution of a substance 
 so refractory and unyielding. 
 
 775. In the herbivorous quadrupeds (Cows, Sheep, Deer, &c.) we 
 find four distinct sacs, or stomachs, devoted to the reception, macer- 
 ation, and digestion of the food (Fig. 285). 
 
 776. In a state of nature, the herbivora, naturally timid, and 
 
LESSON 50.] NUTRITION IN THE MAMMALIA. 179 
 
 dreading assaults from their foes, the Feline animals, go to the pas- 
 tures in flocks, for mutual protection. Here they will be seen busily 
 engaged in cropping the herbage only, and Fw. 285. 
 
 when their hunger is satisfied, they hie 
 away to secure and shady retreats, to di- 
 gest, at their leisure, the material they 
 have provided for that purpose. 
 
 777. In a domesticated state they have 
 no cause for fear, and as soon as they feel 
 satisfied, they throw themselves lazily and 
 listlessly on the grass, to commence the 
 process known as " rumination," or " chew- 
 ing the Cud." Digestive sacs of the ruminant 
 
 778. While steadily engaged in crop- 
 ping the grass, the crude food is passed down the oesophagus (a) 
 to the first stomach, which is by far the largest (b). 
 
 779. This is called the ingluvies, or paunch, and is simply a 
 huge collecting bag, analogous to the crop of a bird, or an insect. 
 The food lies macerating in the paunch, in a fluid, apparently of no 
 chemical significance, secreted by the organ. 
 
 780. During the period the animal has been collecting grass, 
 some of it has been squeezed out of the over-distended paunch, into 
 the second stomach, or reticulum, so called from the honeycomb-like 
 structure of its interior. This stomach (c) is small, its internal sur- 
 face consisting only of honeycomb cells ; into these the morsels of 
 grass expressed from the paunch go, and by the action of the muscu- 
 lar coat of the stomach, aided by a little water generally found in 
 the cells, the grass becomes converted into a round ball. 
 
 781. When all is prepared for rumination, one of these balls is 
 suddenly jerked up the oesophagus into the mouth, and submitted, 
 for the first time, to the action of the grinding teeth. 
 
 782. These organs are of peculiar structure, as will be hereafter 
 seen ; a most lengthened process of mastication now commences, and 
 contemporaneously the food is thoroughly insalivated from the copious 
 secretion of the salivary glands, which are always well developed in 
 these animals. Thus the vitality of the grass is perfectly destroyed, 
 and it is at last fitted to descend the oesophagus, a second time, 
 with its tissues loosened, and prepared for the ultimate process of 
 resolution by the stomach proper. It descends the oesophagus, but 
 it passes neither into the first nor second stomach, but, by means of 
 two thick muscular folds placed across the opening of communication, 
 
180 ANIMAL PHYSIOLOGY. [LESSON 51. 
 
 a canal is formed which conducts to the third stomach, the omasum, 
 or many plies (d). 
 
 LESSON LI. 
 
 NUTKITION IN MAMMALIA, CONTINUED. 
 
 783. This stomach is of much greater dimensions than the second, 
 and much longer than wide ; its interior consists of a vast number 
 of folds of a membrane, hence the word many plies, or folds, whereof 
 every alternate fold is large and deep, and the intermediate one short 
 and shallow. The food gets impacted closely within these folds, and, 
 from its appearance, no less than the quantity of moisture found always 
 in the membranous folds of this stomach, its function appears to be 
 to press the food, and absorb from it all extraneous moisture. The 
 effect of these folds is like that of a series of damp towels, and it is 
 quite remarkable how compact and comparatively dry the food be- 
 comes in the omasum. In due time it passes through an aperture of 
 communication into the abomasum, or reed, the fourth and last sto- 
 mach (e). 
 
 784. Examined by the microscope, this is the only organ pos- 
 sessing a mucous membrane organized to secrete gastric juice and 
 mucus, and digestion of the food in this stomach appears to proceed 
 precisely on the same plan as in those animals possessing only one 
 stomach. These animals, therefore, in common with insects, possess 
 really but one digestive sac, all the others being auxiliary, and en- 
 dowed with functions extraneous to that of true digestion, but neces- 
 sary and essential, from the unmanageable nature of their food. The 
 duodenum is seen at/". 
 
 785. In the Camels and Dromedaries, the second stomach be- 
 comes of great importance, as its cells are employed as a reservoir to 
 contain large quantities of water to supply its daily need when trav- 
 ersing the dreary and parched deserts, where no water can be found. 
 The surface of these cells (in them) is covered with a layer of muscu- 
 lar fibres, and the animal possesses the power of opening these aper- 
 tures, to admit a small supply of water only to escape, and closing 
 them again, as soon as its immediate want is supplied. So great is 
 their thrift and economy in this respect, that Camels have frequently 
 been known to travel for thirty days without water. 
 
 786. The length of the intestinal canal is always great in vege- 
 
LESSON 51.] NUTRITION IN THE MAMMALIA. 181 
 
 table feeding animals ; thus, in the Sheep, the canal is upwards of 
 thirty times the length of the body, and it is of proportionate dimen- 
 sions in the Cow, &c. 
 
 787. In structure, the intestinal canal presents a villous mem- 
 brane of great beauty, and the glandular system of the intes- 
 tines, so well displayed in the Carnivora and in man, is no less 
 displayed in these animals. 
 
 788. In the small intestines, especially in the Ileum, patches of 
 glands more than a finger long present themselves ; these are the 
 glandulas aggregatse, or agmenatse (aggregated glands) of Peyer. 
 Usually these glands are non-vascular, but, in the figure of them 
 
 FIG. 286. FIG. 287. 
 
 Ileum and Peyer's glands, Calf. Colon, Calf. 
 
 presented, drawn from a preparation (Fig. 286), it will be seen that 
 the surface of each gland (5, b) is covered with a network of capil- 
 laries, having wide meshes ; the villi (a, a), in the midst of which 
 the glands are situated, are beautifully seen. 
 
 789. In all the higher animals it happens that the large intestine 
 (Colon) reproduces, as it were, the peculiar cellular structure which 
 distinguishes the stomach, and so very like it, that frequently it be- 
 comes very difficult, if not impossible, to discriminate between sto- 
 mach and colon ; this is the more surprising when we consider how 
 many yards of a totally different structure intervene between these 
 two organs. A figure of the Colon of a Calf is given (Fig. 287), in 
 which the cellular structure is shown. 
 
 790. In the Carnivorous animals the structure of the teeth is es- 
 sentially different from those of the herbivora, and better adapted as 
 organs of prehension, mastication, and for tearing and dividing their 
 food ; but there is yet another organ singularly modified to suit spe- 
 cial wants, and this is the Tongue. 
 
 791. The tongues of all the higher, and many of the lower verte- 
 brata, possess (usually) three forms of papillse-: the filiform (a thread 
 
182 . ANIMAL PHYSIOLOGY. [LESSON 52. 
 
 or filament), fungiform (mushroom shaped), and the circumvallatce 
 (surrounded by a ditch). All these forms are found without any ad- 
 dition in the feline animals, but in them the filiform papillae are 
 modified to subserve the purposes of teeth. 
 
 792. In a state of nature, these animals are subject to " a feast 
 and a fast," and frequently have to endure long intervals of absti- 
 nence from food ; whenever it is present, therefore, they make the 
 most of it; feeding to repletion, the first day or two, if the prey be 
 large, till at length the carcass is demolished, and nothing remains 
 but the bones. These are not yet reduced to the condition of a skel- 
 eton ; the attachments of the several muscles, and their tendinous 
 terminations, yet remain firmly connected to them. 
 
 793. Still they are much too short for the teeth to grasp, 
 and the animal must now depend upon the kindly offices of the 
 tongue, or starve. 
 
 794. It proceeds, therefore, to lick the bones, and the flesh peels 
 off at every effort ; this long, soft, flexuous organ can, and does, pen- 
 etrate all the cavities and sinuosities of a bone, especially at the ar- 
 ticulating surfaces ; nothing can resist its power ; even the periosteum 
 (the membrane that tightly covers a bone) is found to submit, and 
 all that remains, when the process of licking is over, is a white, per- 
 fectly clean, well-prepared skeleton. 
 
 795. Those persons who have suffered their hands to be licked by 
 an affectionate domestic cat, will have an idea of the potency of this 
 organ ; nay, they must be conscious that if they could endure the af- 
 fectionate demonstration for only a very few minutes, the cuticle 
 would be abraded, and blood would freely flow from the true skin. 
 
 LESSOR LII. 
 
 NUTRITION IN THE MAMMALIA, CONCLUDED. 
 
 796. In order to make the foregoing statement fully compre- 
 hended, a figure is given of a Cat's tongue (Fig. 288), copied from a 
 preparation. The tongue of a Lion is in every respect precisely simi- 
 lar, but larger. The filiform papillae (a) are found from the apex, 
 where they are interspersed with the fungiform (5), to about one-third 
 of the length of the tongue, and at this point they increase in size, and 
 
LESSON 52.] 
 
 NUTRITION IN THE MAMMALIA. 
 
 183 
 
 FIG. 288. 
 
 have their external surface covered with a dense horny layer. This in- 
 crease in size continues to, and beyond 
 the centre, at which point they have 
 assumed very formidable dimensions 
 (a). Near the base of the tongue, the 
 circumvallate papillaB (c) are found ; 
 they are six in number. These are 
 only greatly enlarged fungiform papil- 
 lae, and the ditch by which they are 
 surrounded is filled with mucus- 
 crypts, or the mucus-follicles of Lei- 
 berkuhn, who first described them. 
 They are the external outlets of mu- 
 cus-tubes, mucus being abundantly 
 poured out to lubricate the upper sur- 
 face of the tongue. 
 
 Beyond the Circumvallatae, are 
 other filiform papillae, but destitute of 
 a horny covering, their situation being 
 too remote to be effective as teeth; 
 they are covered with mucous crypts, 
 so well formed, that they possess a cal- 
 lous margin. From the peculiar cov- 
 ering of the filiform papillaB in the 
 Feline animals, it is probable that 
 they are not endowed with much sensibility as organs of taste, but 
 that this function is exercised by the fungiform papillae alone. 
 
 797. The stomach is well formed (as regards its ultimate or 
 
 FIG. 289. FIG. 290. 
 
 Cat's tongue. 
 
 Stomach of Cat' Ileum of Cat. 
 
 microscopical character), as might be expected in a true carnivorous 
 animal, and a figure of the Cat's stomach is given (Fig. 289). 
 
 798. Another remarkable modification of structure is met with 
 in the villi of the intestines, which in all these animals are singular- 
 
184 ANIMAL PHYSIOLOGY. [LESSON 52. 
 
 ly long and narrow ; nothing can exceed, however, the beautiful ar- 
 rangement of their capillary plexuses (Fig. 290). The small intes- 
 tine of the Cat shows this very nicely, but in the Lion (Fig. 291) it 
 is still better shown, as the capillaries in the Cat are of extreme 
 tenuity ; but in the latter the vessels and the villi both attain their 
 maximum development, so far as is consistent with this class. 
 
 799. The intestinal glandular system is also well developed in 
 these animals ; the form of the glands differs pretty much from those 
 we have already seen : thus, in the aggregated glands of the Lion 
 (Fig. 292), each gland stands in a cup, or surrounded by a ditch, 
 which is filled with mucus-crypts, the gland itself being somewhat 
 conical in form, the top constituting the larger portion. 
 
 800. But in addition to the aggregated, animals have, in their 
 
 FIG. 291. FIG. 292. 
 
 Ileum of a Lion. Feyer's glands, Ileum of ^ion. 
 
 small intestines, glands of the same character and form, dispersed 
 widely, and found singly : these are the solitary glands. The large 
 intestine has its glands also, always however of the solitary kind, and 
 being in structure the exact converse of those we have yet examined. 
 The glands hitherto seen were evolved (opened, expanded), those to 
 be described are involute (to envelop, to cover with surrounding 
 matter) ; in other words, they are funnel-shaped cavities, excavated 
 as it were out of the mucous membrane. In the first, we saw the 
 outside in the last, the inside ; both these glands are really shaped 
 alike, but they are reversed in their position. 
 
 801. Again, reference is made to the large intestine of the Lion 
 for the demonstration (Fig. 293) ; here the capillary structure of the 
 mucous membrane is everywhere seen ; it surrounds the cavities of 
 the solitary glands, and enters them to a certain depth. 
 
 To render this more intelligible, a section of the last prepara- 
 tion is figured (Fig. 294). The capillary plexuses of the mucous 
 membrane are seen upon the upper surface, and descending for a 
 space into the cavity of the gland, and finally, its funnel-shaped inte- 
 rior is well shown. 
 
LESSON 52.] NUTRITION IN THE MAMMALIA. 185 
 
 The large intestine (colon) of the Feline animals agrees in gen- 
 eral particulars with the characteristics usually exhibited in the ani- 
 mal kingdom, with respect to the great resemblance it uniformly 
 
 FIG. 293. FIG. 294. 
 
 Solitary glands of large intestine, Lion. Section of solitary gland, Lion. 
 
 bears to the structure of the stomach. A figure (295) of this part 
 of the intestine of a Cat is given. 
 
 If the papillary surface be carefully dissected from a well inject- 
 ed intestine, the sub-mucous tissue will be found to present a beauti- 
 ful view of the vessels which supply blood to the villi, and of those 
 which are employed to effect its return in other words, arteries and 
 veins. 
 
 As these vessels end or commence in capillaries, they are neces- 
 
 FIG. 295. FIG. 296. 
 
 Colon of Cat. Vessels of the sub-papillary layer, Lion. 
 
 sarily minute ; but in the layer immediately beneath, the larger 
 vessels, in connection with this particular plexus, are found. 
 
 A figure of this structure, from the small intestine of the Lion, 
 is given (Fig. 296), which shows all that has been described. 
 
 802. In the Canine animals (Dogs), many of the tissues differ 
 greatly from those of the Feline ; the tongue, for example, is re- 
 markable for its extreme softness and ductility. Possessing villi of 
 the same denomination, in these animals they appear to be endowed 
 with exquisite sensibility, at least the distribution of the gustatory 
 nerves (nerves of taste) would lead to such conclusion. 
 
186 
 
 ANIMAL PHYSIOLOGY. 
 
 [LESSON 52. 
 
 803. A figure of filiform papillae of the Dog, minutely injected, 
 is given in Fig. 297, and also of two circumvallate papillae in Fi<r. 
 298 ; in both instances the terminal nervous loops accompany the 
 capillaries, and necessarily impart great sensibility to these organ?. 
 The circuinvallatae are very small in the Dog. 
 
 FIG. 297. FIG. 299. 
 
 FIG. 293. 
 
 Circumvallate papillae 
 of the Dog. 
 
 papilla-, Tongue, Dog. 
 
 Mucous membrane of Stomach, 
 Dog. 
 
 FIG. 
 
 804. The structure of the mucous membrane of the stomach of a 
 Dog is highly interesting, as will be seen by reference to the accom- 
 panying figure of it (Fig. 299). Here the gastric cavities are beau- 
 tifully formed, their cell-walls consisting of a single, tortuous capil- 
 lary blood-vessel, and the deep-seated vessels which surround the mu- 
 cus-tubes are well shown. / 
 
 805. The line of demarcation which separates one tissue from 
 another is always remarkably abrupt. Some (theoretical) physiolo- 
 gists hold, that the change of one form of tissue into another is so 
 very gradual as to become quite insensible ; an opinion entirely op- 
 posed to fact : for example, the structure of the stomach continues 
 
 half way through the pyloric valve, the 
 other half of it being duodenum, as will 
 be seen in Fig. 300, from the Dog. It 
 is quite true that the stomach exhibits 
 papillae, in addition to its gastric cells, 
 prior to the commencement of the pyloric 
 valve, and within the stomach a fore- 
 shadowing of the important tissue here- 
 after to become, not the exception, but 
 the rule; they do not extend, however, 
 to the pylorus, and are more usual in 
 man than in the stomach of domestic animals. So, too, as regards 
 the ilio-caecal valve, which forms the junction of the ileum with the 
 caecum and colon ; the structure of the small intestine remains in- 
 tact half through the valve, when the caecum abruptly joins it. An 
 
 Junction of stomach and duo- 
 denum, Dog. 
 
LESSON 52.] 
 
 NUTKITION IN MAMMALIA. 
 
 187 
 
 FIG. 301. 
 
 artery, with its three distinguishing characteristic coats, ends ab- 
 ruptly, suddenly, in a capillary ; the structure is altered, and so is 
 the character of the circulation. In like manner, a capillary sud- 
 denly terminates, and a vein, with its characteristics of structure 
 and function, commences, and so with other tissues : each maintains 
 its own integrity without compromise, and ends only at the point of 
 junction with another tissue. 
 
 806. The duodenum of a dog is a most surprising sight. The 
 great length and breadth of the villi, conjoined with the large dis- 
 tribution of capillaries to each villus, renders the preparation under 
 the microscope a very gorgeous one. 
 
 This is represented, as far as art can go, in Fig. 301, but the 
 white lines on a black ground form but a sorry 
 substitute for the rich color of the vermilion 
 which has been injected into the vessels to 
 simulate arterial blood. 
 
 807. In the Jejunum (empty, and so call- 
 ed because this intestine is always found 
 empty), the form and size of the villi undergo 
 modification in all animals, and this is repeated 
 in the Ileum ; examples, however, are not ne- 
 cessary in this connection. 
 
 808. In the colon, as shown before, the 
 structure of the stomach is so nearly repro- 
 duced that it is extremely difficult to define one tissue from another ; 
 in fact, the only rule appears to be the following : generally the gas- 
 tric cells of the stomach are wider on the surface, and deeper than 
 the cells of the colon, consequently it is easy to penetrate many of 
 the former by the microscope, and see the capillaries on the floor of 
 the cell, around the mucus-tubes. (See 
 
 Fig. 299.) As there is no such struc- 
 ture in the cells of the colon, the attention 
 of the observer is necessarily restricted to 
 the surface, and here the identity with 
 the stomach appears to be perfect. 
 
 The colon of the Dog is shown in Fig. 
 302, and fully justifies all that has been 
 
 Said f i*' Colon of the Dog. 
 
 Enough has now been written, and 
 
 examples sufficient have been produced, to show the principles of nu- 
 trition, as displayed in the animal kingdom ; those subjects which 
 
 Villi of the duodenum, 
 Dog. 
 
 FIG. 302. 
 
188 ANIMAL PHYSIOLOGY. [LESSON 53. 
 
 have hitherto been lightly dealt with, notwithstanding their impor- 
 tant influence on the great question under discussion, have been re- 
 served designedly until the salient points in regard to the ultimate 
 structure of the (apparently) most important organs had been dis- 
 posed of; and because it was deemed more advisable to take such 
 subjects specially, in connection with the nutrition of man. These 
 are, the structure of the teeth, the structure, but more especially the 
 function of the salivary glands, and the properties of the gastric juice 
 and mucus. 
 
 LESSON LIU. 
 
 ' / 
 
 THE STRUCTURE OF THE TEETH. 
 
 809. The teeth claim priority, and, reversing the order of arrange- 
 ment hitherto pursued, in which the lower animals have served as 
 the basis for the consideration of more complicated structures, de- 
 voted to the performance of a kindred function in the higher forms 
 of animal life, it is intended to begin these inquiries with man, and 
 FlG 303 gradually descend in the scale of 
 
 being. 
 
 810. The mucous membrane 
 of the gums, which lies at the bases 
 of the teeth, is peculiar, and re- 
 quires description. 
 
 If a well injected preparation 
 be made, the mucous membrane 
 of the gum will be found covered 
 
 Mac membrane of the gum, tan.n. with papillae. These (in the adult) 
 
 are somewhat long, and consist of 
 
 a single looped capillary, which, through the tension of the injection, 
 becomes more or less twisted (Fig. 303). Their number is very con- 
 siderable, presenting, literally, a forest of them. The papillae of the 
 lips present a gorgeous sight, when well injected ; the loops, as in 
 the former case, twisting with the pressure of the injection. 
 
 THE TEETH. 
 
 811. These *gans, together with the bones, to which they are 
 closely allied, form the sclerogenous (hard) tissues of animals. 
 
 812. Human teeth, and the teeth of the higher mammalia, con- 
 
LESSON 53.] THE STRUCTURE OP THE TEETH. 189 
 
 gist of three distinct tissues ; the dentine, or ivory, which forms the 
 greater part of the tooth, and contributes to its form ; the enamel, 
 which covers and defends the outer, exposed surface of the tooth ; 
 and lastly the crusta petrosa, or cementum, which forms the external 
 covering of the fang. The interior of a tooth contains a cavity of 
 variable size, called the pulp cavity, in which, in a healthy tooth, the 
 vascular pulp, with its plexus of nerves, lies. 
 
 813. As the enamel first meets our gaze, it shall have priority of 
 description. This tissue, in the grinding teeth, is thickest on the 
 masticating surface. A delicate membrane, discovered by Nasmyth, 
 and known as " Nasmyth's membrane," covers the enamel, and is so 
 closely united with it, that they can only be separated by the em- 
 ployment of hydrochloric (formerly muriatic) acid. 
 
 814. The enamel is so much more brittle, and harder than the 
 other tissues of the teeth, that a knife scarcely marks it, and it 
 readily yields sparks when struck against steel. 
 
 815. This tissue presents a fibrous structure, due to its compo- 
 sition, which consists entirely of the prisms or fibres of the enamel. 
 These are long, solid prisms, irregular in shape, but usually hexa- 
 gonal, or pentagonal, generally occupying the whole substance of the 
 enamel, resting by one extremity on the dentine (ivory), and by the 
 other on Nasmyth's membrane. 
 
 816. In adult teeth it is easy to detect these elements in longi- 
 tudinal or transverse sections, but it is difficult to separate them for 
 any great length ; it is easier of accomplishment in young and devel- 
 oping teeth, where the enamel is so much softer that it may be 
 cut with a knife. The action of diluted hydrochloric acid is 
 necessary to effect the separation of the prisms, and, if not too 
 long continued, delicate transverse striae may be detected on their 
 surface. 
 
 817. The prisms of the enamel are very firmly united, but what 
 constitutes the bond of union, has not yet been satisfactorily demon- 
 strated; delicate tubes have been clearly established in connection 
 with this tissue in young animals, and although difficult of detection 
 in adults, the probability is that they are present, although it may 
 be in a calcified condition. 
 
 818. In making a section of a tooth, to show the facets of the 
 prisms of enamel, great care should be taken not to injure the ex- 
 ternal surface, but grind from behind until sufficiently thin. 
 
 819. A figure of such a section, from a human tooth so prepared, 
 
190 
 
 ANIMAL PHYSIOLOGY. 
 
 [LESSON 53. 
 
 is given (Fig. 304); here the facets are four, five, or six-sided, with 
 a nucleated spot apparent in each of them. 
 
 820. The isolated prisms are also given in Fig. 305 ; the trans- 
 verse lines serve to give them a jointed appearance ; the sides, too, 
 are remarkable for their irregularity. 
 
 821. If the mode by which the several prisms are connected to 
 
 FIG. 804. 
 
 FIG. "305. 
 
 Facets of the enamel, human. 
 
 Prisms of enamel, human. 
 
 FIG. 306. 
 
 each other, and enabled to form a solid tissue, be obscure, there can 
 be no doubt of the manner in which the dentine becomes firmly con- 
 nected to the enamel. The dentinal tubuli, as they approach the 
 enamel, divide and form Y-like terminations, which (in the molar 
 
 teeth) penetrate the enamel, 
 and thus form a bond of un- 
 ion; but in human canine 
 teeth, a much more efficient 
 plan is in operation, as shown 
 in Fig. 306, which repre- 
 sents the junction of the den- 
 tine and enamel in a human 
 canine tooth. Tubes of the 
 dentine (a, a) having entered 
 the enamel, become tortu- 
 ous, and greatly increase in 
 size, especially as they ap- 
 proach their terminations ; 
 they form a series of wedges, or dowells, which renders the contact 
 so firm that no earthly power can separate tissues so joined. Strike 
 a tooth on an anvil with a hammer, the blow will break the tooth in 
 all manner of directions, but no mechanical skill can separate the 
 
 Junction of dentine and enamel, human 
 Canine Tooth. 
 
LESSON 53.] THE STRUCTURE OF THE TEETH. 191 
 
 enamel of such a tooth from the dentine at its point of junction. 
 This plan of attachment appears only to be used for teeth like the 
 canines, that are brought violently into contact with resisting sub- 
 stances; other teeth, the molars for example, having a steady, uni- 
 form action to perform, do not require such extraordinary care, nei- 
 ther is it bestowed upon them. To show the mode of connection 
 with the enamel of a molar tooth, see Fig. 307. 
 
 The dentinal tubuli are seen at a, their terminations dividing into 
 two branches (b) prior to reaching the enamel (c), which forms the 
 mode of connection of the two tissues. 
 
 822. The junction of dentine with the crusta petrosa, or cemen- 
 tum, is also by the insertion, or interlacement, of the terminal bifid 
 dentinal tubuli with the cementum ; and as there is no strain or vio- 
 lence to any part of the fang, tins mode of connection appears to be 
 
 Fro. SOT. FIG. 308. 
 
 Connection of Ivory and Enamel, Molar Junction of Ivory and Crusta 
 
 Tooth. Petrosa. 
 
 all that is necessary. It is interesting to observe that whether the 
 dentine has to be connected to the enamel or to the crusta petrosa, 
 that its own tubuli are employed as the bond of union. 
 
 The fang of a tooth, from its position in the bony socket of the 
 jaw (alveolus), is greatly protected from acts of violence ; whilst the 
 same appliances are in use to join the crusta petrosa to the dentine, 
 the branches of the tubes of ivory are so minute as to be scarcely 
 distinguishable. For the most part, the junction of these tissues 
 rather indicates a dark line, of no great depth, in which the divided 
 tubes are scarcely apparent. This will be understood by consulting 
 Fig. 308, which shows the crusta petrosa (a), dentinal tubuli (J), and 
 the junction of the two (c) ; but such is the extreme minuteness and 
 shortness of the divided dentinal tubes in connection with this tissue, 
 that they are scarcely discernible. 
 
192 ANIMAL PHYSIOLOGY. [LESSON 54. 
 
 LESSON LIV. 
 
 THE STRUCTURE OF THE TEETH, CONTINUED. 
 
 823. Examined in transverse section, the prisms of enamel are 
 well seen throughout their course ; they are distinguished by a series 
 
 FIG 309 of transverse lme s at regular intervals (Fig. 
 
 309), which appear to divide the tissue into 
 small squares, or dice. When the prisms are 
 isolated (as we have seen), the same appearance 
 appears to be caused by the transverse lines on 
 their surface. On the other hand, it has been 
 
 supposed, and with probability, that these 
 
 section of transverse lines indicate the several stages of 
 growth of the tissue, and that, although division 
 of it in the direction indicated by the lines is impossible, the evi- 
 dence of demarcation defining its original stages of growth, is ren- 
 dered permanent. If the surface of enamel be destroyed, the facets 
 of the prisms are lost, as already indicated. 
 
 824. The dentine or ivory of a recent tooth is of a yellowish- 
 white color, and transparent ; in a dried tooth, air enters the tubuli, 
 and imparts to it a silky or satiny appearance. The dentine forms 
 the walls of a case, in which the pulp is received r so that the tubes of 
 this tissue have uniform contact with the vessels of the pulp. At the 
 lower part of the fang of a tooth there is a small aperture, through 
 which the vessels pass to supply the pulp, and through which also the 
 nerve, to be divided into a delicate looped plexus, is transmitted. 
 
 825. The dentine consists of minute canals, or tubuli, which 
 commence by open mouths on the inner wall of the pulp cavity, and 
 extend through the whole substance of the dentine to the cement and 
 enamel. Each tube has a wall, less than its own diameter in sub- 
 stance, which can easily be seen in transverse sections ; in longitudi- 
 nal sections it is almost invisible. In life these canals contain a 
 clear fluid, but in a dead tooth the tubuli become filled with air ; and 
 as air in small cavities always appears black under the microscope, 
 these tubuli appear as so many small, delicate black lines ; but if the 
 tooth be prepared in Canada balsam, the air is driven out of the tu- 
 buli by the heat employed in making the preparation, and the tur- 
 pentine of the balsam enters them; in this case they appear as deli- 
 cate tubes. 
 
 826. The direction of the tubuli in the dentine is rarely straight, 
 
LESSON 54.] 
 
 THE STRUCTURE OF THE TEETH. 
 
 193 
 
 FIG. 310. 
 
 but wavy ; they also present numerous ramifications and anastomo- 
 ses; towards the crown of a tooth they usually form an elegant 
 plume, which presents a fine object under the mi- 
 croscope. Each tube generally describes two or 
 three large, besides a great number of small cur- 
 vatures, which occasionally have the appearance 
 of zigzags, or spiral windings. 
 
 827. To show the connection of the three 
 tissues of the teeth, and their relation to each 
 other, a figure is given of a longitudinal section 
 of a human canine tooth (Fig. 310). The enamel 
 is marked #, the dentinal tubuli, 5, 6, the pulp 
 cavity, c, the crusta petrosa, or cementum, d, and 
 thin plates of dentine, e. 
 
 828. The cementum is a layer of true bone, 
 which covers the lower part of the teeth, and in the 
 many fanged teeth, not unfrequently cements them 
 all together. The cementum commences above, 
 at the point where the enamel ceases, so that the 
 dentine in a healthy tooth is never left ex- 
 posed to the atmosphere. It begins as a very thin 
 layer, gradually increasing in substance as it de- 
 scends, and attains its greatest dimensions at the 
 lower part of the fang. 
 
 829. As bone, it may readily be imagined that 
 
 it is the least hard of the dental tissues. Like bone, the cementum 
 contains bone cells, with their canaliculi, together with Haversian 
 canals and vessels. The bone cells are conspicuous for the great va- 
 riety which they present in number, form, and size, and for the unu- 
 sual number and length of their canaliculi (little tubes). 
 
 830. The canaliculi often resemble feathers and brushes, and un- 
 less the lacunae (bone cells) are isolated, connect them with each 
 other, and anastomose with the ends of the dentinal canals or tubes. 
 At the point of junction with the enamel, bone cells are invariably 
 absent; they first make their appearance about the middle of the 
 fang, but scattered and solitary. Towards the extremity of the 
 fang their number increases, and they frequently take on a very reg- 
 ular arrangement. 
 
 831. In old teeth it very commonly happens that the pulp 
 becomes obliterated, and the pulp cavity filled with cementum; 
 and in these cases the Haversian canals, lacunae, and their canali- 
 
 13 
 
 Longitudinal section 
 
 of Canine tooth, 
 
 Human. 
 
194 
 
 ANIMAL PHYSIOLOGY. 
 
 [LESSON 55. 
 
 FIG. 312. 
 
 FIG. 311. culi, are more than usually 
 
 distinct. 
 
 832. In the figure several 
 very thin transverse sections 
 of the dentine appear, attached 
 to the sides of the pulp cavity 
 (e) ; these exhibit the tubular 
 character of the canals very 
 satisfactorily. 
 
 833. Special reference is made to these thin sections of the tubes 
 as they are ordinarily seen, in another figure (Fig. 311) much more 
 highly magnified, indicating the tubes, and a more crowded con- 
 dition of them in Fig. 312. 
 
 Trnnsvor.*e section of 
 IX-ntinul tubes. 
 
 A raorfi crowded 
 view. 
 
 FIG. 313. 
 
 LESSON LY. 
 
 THE STEUCTUBE OF THE TEETH, CONTINUED. 
 
 834. In the teeth of the Dog the same tissues, arranged on the 
 same plan, are found, and present in the molar teeth a very inter- 
 esting appearance (Fig. 313). The enamel (a) is always distin- 
 guished by its apparent density, as compared with the other tissues , 
 towards the edges of the upper portion of the figure (5), the ter- 
 minal line of the enamel, and the commencement of the crusta pe- 
 trosa, is shown. From this point it (crusta petrosa) can be traced 
 descending the fangs, right and left, to their 
 termination, then ascending, and finally form- 
 ing a junction at the centre. On the inner 
 surface of the enamel, and crusta petrosa, 
 the dentine is seen (c), and within this tis- 
 sue the large, well-formed pulp cavity (d). 
 At the bend, which connects the two fangs, 
 the dentinal tubuli assume a curious and 
 very beautiful arrangement. 
 
 835. The molar tooth of a Cat displays 
 the same arrangement of the like tissues, 
 and the external form of the tooth bears 
 great resemblance to the molar of the Dog 
 (Fig. 314) ; a, the enamel; 5, crusta petrosa ; 
 c, dentine ; and d, pulp cavity. 
 
 Molar Tooth, Dog. 
 
LESSON 55.] THE STKUCTURE OF THE TEETH. 
 
 195 
 
 836. A transverse section of the canine tooth of a Horse pre- 
 sents the same tissues under a different aspect. The section has 
 been made so near to the crown of the tooth, that the enamel forms 
 a ring nearly surrounding the dentine (Fig. 315), with the apex of 
 
 FIG. 314. 
 
 FIG. 315. 
 
 Molar Tooth, Cat. . Canine Tooth, Horse, transverse. 
 
 the pulp cavity in the centre. Another section of the same tooth 
 (Fig. 316), made below the former, shows the enamel (a) round only 
 one half of the section, the other half being the crusta petrosa (b). 
 Between these tissues is the dentine (c), and in the centre the pulp 
 cavity (d). A third section (Fig. 317), made still lower than the 
 second section, from the same tooth, shows an entire absence of 
 
 FIG. 317. 
 
 FIG. 316. 
 
 Canine Tooth, transverse, Horse. 
 
 Canine Tooth, transverse, liurse. 
 
 enamel, and the crusta petrosa (a) surrounds the section. The den- 
 tine, in all these sections, is very nearly the same ; the pulp cavity 
 grows gradually larger from its apex to the base, but the most satis- 
 factory part of the demonstration is the number and density of the 
 bone cells, as seen in the last figure, but which is not sufficiently 
 magnified to be apparent in the representation of it. 
 
196 ANIMAL PHYSIOLOGY. [LESSON 55. 
 
 837. In a tusk of the Hog, as seen in longitudinal section (Fig, 
 318), the enamel covers the outer surface that portion which comes 
 in contact with resisting substances, and within it the ivory ; the 
 pulp cavity is seen at the lower part. 
 
 838. This is probably still better seen in a transverse section of 
 the same tooth (Fig. 319) ; in this view, the tooth appears to be tri- 
 angular in form. The large pulp cavity occupies the centre, which 
 
 FIG. 318. 
 
 IB 
 
 FIG. 319. 
 
 Longitudinal section, tusk of Hog. Transverse section, Hog's tusk. 
 
 is succeeded by the tubes of the ivory ; the enamel entirely surrounds 
 the section. 
 
 839. It is reserved for the Herbivorous quadruped to show the 
 most interesting and beautiful forms of teeth known to us among the 
 higher animals. The same three tissues are present here, but ar- 
 ranged in a different manner to meet a special want. 
 
 840. These animals having uniformly to masticate grass, either 
 in a dried or green state, have their teeth constantly brought in 
 contact with large quantities of pure silica, incorporated in the 
 cuticle of the grass. If the surface of the teeth were smooth, 
 they would be inadequate to perform the grinding motion assigned 
 to them. We know that the miller requires to have the surface of 
 his mill-stones hacked into cavities to form a grinding surface, and 
 this is precisely the want of the herbivorous quadruped in relation to 
 the surface of its teeth they must not be flat, but hollowed out into 
 unequal cavities. To meet this imperative want, the tissues enamel, 
 ivory, and bone are all arranged on the same plane. 
 
 841. Examine the crown of the molar (grinding) tooth of a Cow 
 or a Sheep ; its surface will present a series of ridges standing up 
 above the other tissues ; next to these are inclined planes of a differ- 
 ent tissue, descending from the ridges to large, hollow, unsightly 
 cavities lying at their base evidently another tissue. 
 
 842. Now it must happen that if flint be brought constantly in 
 
LESSON 55.] THE STRUCTURE OF THE TEETH. 
 
 197 
 
 FIG. 320. 
 
 contact with enamel, ivory, and bone, lying beside each other, they 
 will wear unequally ; the softest (the bone) will cut the fastest, and 
 form the deep hollows described ; the next in hardness, the ivory, 
 will wear less than the bone, but more than the enamel ; and lastly, 
 the enamel, wearing but little, will form the high ridges described. 
 
 843. But this is not all : to render the inequalities certain and 
 constant, there are three systems of enamel in the grinding teeth of 
 the upper jaw of the Cow (a, a, a, Fig. 320), and only two in those 
 of the lower jaw, so that enamel 
 
 never opposes enamel ; by all 
 these contrivances the teeth must 
 necessarily wear unequally, and 
 always present a rough, uneven, 
 grinding surface to the food. 
 
 844. To show the arrange- 
 ment of the enamel of a molar of 
 the upper jaw, a figure (320) is 
 given, but slightly magnified. 
 Crusta petrosa (b) is found sur- 
 rounding the tooth ; within this 
 a layer of enamel (a), which 
 passes irregularly round the outer 
 surface ; next to this is ivory, to 
 which succeeds crusta petrosa, on 
 
 the other side ef which ivory again appears, to be bounded by the 
 enamel. Take a given portion of a tooth, and the arrangement of 
 
 FIG. 321. 
 
 Molar of Cow. 
 
 Portion of Molar tooth, Sheep. 
 a, a, Enamel ; &, &, Dentine ; c, Cementum. 
 
198 ANIMAL PHYSIOLOGY. [LESSON 56. 
 
 the tissues will be invariably as follows : crusta petrosa in tbe centre, 
 bounded on each side by ivory, which always adjoins enamel ; crusta 
 petrosa and enamel never come together (except on the outer sur- 
 face) ; they are always separated by the ivory. 
 
 845. These facts are well illustrated by a figure of the grinder 
 of a Sheep (Fig. 321) ; here the enamel (a, a) is constantly seen in 
 connection with the ivory (5, 5), and inside of this the crusta petrosa 
 (c). The elegant wavy form of the dentinal tubuli renders this a 
 very charming object for the microscope. The crusta petrosa (more 
 properly called cementum in these teeth, as it performs the office of 
 a cement to the other tissues) forms, in many instances, little more 
 than a line in the centre of the ivory, yet quite sufficient for its soft- 
 ness to be felt, and the required hollow to be formed. 
 
 LESSON LYI. 
 
 THE STEUCTUEE OF THE TEETH, CONTINUED. 
 
 846. In the Rodentia, the form of the teeth is very interesting : 
 the enamel in the large, curved incisors, is always found upon the 
 opposing surface (front) alone. These teeth, in every member of the 
 class, are constantly being pushed, as it were, from behind, forwards ; 
 in other words, continually growing; and to gnaw, from which they 
 acquire their name, is in them an imperative necessity, to keep these 
 teeth in check, and reduce them within usable limits. Were Rats, 
 Mice, Rabbits, and their kindred, not to keep their ever-growing 
 teeth well cut down, by gnawing hard substances, by which the teeth 
 wear considerably, they would soon be unable to use them on legiti- 
 mate food, and die of starvation. 
 
 847. If a Rat, or Rabbit, chance to break one incisor tooth, the 
 * opposite tooth fails to oppose it ; the consequence is, it continues to 
 
 grow, and forms a perfect ring. The broken tooth also grows, and 
 having attained its original length, and finding no opposition, also 
 forms a ring. 
 
 848. To obtain such illustrations for Museum purposes, to show 
 the ever-growing nature of such teeth, one of them has frequently 
 been designedly cut with a fine saw, or wire-nippers, to procure 
 specimens of the curled, or even double-curled teeth ; such examples 
 are common in European Museums. 
 
LESSON 56.] THE STRUCTURE OF THE TEETH. 
 
 199 
 
 849. A figure (322) of a longitudinal section of the incisor of a 
 Rabbit is given. he enamel (a) forms a chisel-shaped cutting 
 instrument at the apex of the tooth ; within the point, the crusta 
 petrosa (&) forms a very delicate line, which is continued along the 
 inner surface of the tooth ; within this tissue, and the enamel, is the 
 dentine (c), and in the centre of it, the pulp cavity (d). 
 
 850. A transverse section of such a tooth (Fig. 323) is very in- 
 
 FIG. 322. 
 
 FIG. 323. 
 
 Transverse section, Incisor, Kabbit. 
 
 Longitudinal section, Incisor, Rabbit- 
 
 structive ; it is somewhat triangular in shape, the front being par- 
 ticularly flat, while the sides recede, and are rounded at the back. 
 The enamel (a) occupies the entire front, and for its security em- 
 braces the corners, and is gradually lost at the sides ; here the crusta 
 petrosa (b) begins, and completes the outer wall of the tooth. As in 
 the former illustrations, within these tissues is the dentine (c) , and 
 in the centre the pulp cavity (d). 
 
 851. As far as the alternation of tissues is concerned, the molar 
 teeth of the Rodents are formed on the same plan as those of the 
 herbivorous quadru- 
 ped, the arrangement 
 
 being, however, some- 
 what different. 
 
 852. A figure of a 
 Rabbit's molar tooth 
 is given in Fig. 324. 
 In preparing 'these 
 teeth, they almost in- 
 variably break into Transverse section of Molar tooth, Eabbit. 
 
 four pieces, in consequence of the brittleness of the crusta petrosa, 
 
 FIG. 324. 
 
200 
 
 ANIMAL PHYSIOLOGY. 
 
 [LESSON 57. 
 
 FIG. 325. 
 
 and such an accident befell this illustration, but which was subse- 
 quently repaired. Here the enamel forms partLy the outside of the 
 tooth, but a long, tortuous, zigzag portion also runs through the centre 
 (a, a). The arrangement of the enamel naturally divides the tooth 
 into four portions ; within each system of enamel is the dentine 
 (>, 5), with pulp cavities (c, c) in the centre. In addition, how- 
 ever, is a layer of crusta petrosa (d, d), which forms the bond of 
 union, or cement, by which the four distinct portions of the tooth are 
 united into one. 
 
 853. By far the most curious arrangement 
 is the molar tooth of the Musk-rat ; the tooth 
 is long, and formed of a reduplication of 
 parts, with the exception that the enamel is con- 
 tinuous from one end of the tooth to the other, 
 bounding the outer surface, and penetrating the 
 various sinuosities. Everywhere within the 
 enamel is the dentine, and, as in other Rodents, 
 the crusta petrosa lies in the centre of the ivory. 
 Cavities formed by the curious direction taken by 
 the enamel, are filled up with crusta petrosa, for 
 the double purpose of cementing this compound 
 tooth firmly together, and for preserving and 
 forming the outlines. A figure of this tooth is 
 given (Fig. 325) ; the enamel (a, a) is seen 
 everywhere surrounding the dentine (5), in the 
 centre of which is the crusta petrosa (c, c), 
 which, filling up the external cavities, is seen 
 at d, d. If the section be made low enough from the surface, the 
 pulp cavities appear. 
 
 Transverse section molar, 
 Musk-rat. 
 
 LESSON LYII. 
 
 THE STRUCTURE OF THE TEETH, CONCLUDED. 
 
 854. The teeth, hitherto examined, have presented all the tissues 
 characteristic of these organs in the higher animals, subject to a varied 
 disposition of the order of arrangement. Teeth are liable to de- 
 generation ; to a loss of tissue, and to a much altered form of the 
 tissue that remains. Of all these structures enamel is found to be the 
 least constant, and, when absent, its place is supplied by a dentine 
 (ivory) of superior hardness. 
 
LESSON 57.] THE STRUCTURE OF THE TEETH. 
 
 201 
 
 855. In the class of Reptiles, the Ophidians (Serpents) are en- 
 tirely destitute of enamel, and the same remark applies to nearly 
 the entire class of Fishes. In the latter, the dentine assumes new 
 characters ; in some Fishes the dentinal tubuli have their origin from 
 vascular canals, hence such a tissue is called vaso-dentine ; and in 
 other fishes the medullary canals are wavy, irregular, and prone to 
 anastomose (join), and is usually covered by a hard dentine ; this is 
 called osteo- dentine. 
 
 856. The teeth of the Pristis (Saw-fish), and the Myliobatis (a 
 Ray), well display the vaso-dentinal structure, and as such have 
 been selected for illustration. 
 
 857. In the Pristis the vascular canals are large, and remarkable 
 for their parallelism ; the tubes that are given off from the centre of 
 the tooth, are large in size, and few in number, but those canals 
 which approximate to the sides, give off a dense plexus of fine tubuli, 
 
 FIG. 
 
 FIG. 327. 
 
 Longitudinal section of tooth, Myliobatis. 
 
 Longitudinal section of tooth, 
 Pristis. 
 
 distributed to the sides and crown of the tooth, and forming the 
 vaso-dentine. This is shown in Fig. 326 ; the vascular canals (a) 
 are seen in the centre, giving off (comparatively) but few tubes. 
 The lateral tubes (b) distribute the great plexuses of fine dentinal 
 tubes to the crown and sides ; there is no pulp cavity in this tooth. 
 
 858. The vascular canals of vaso-dentine can only be well seen 
 in longitudinal sections; for this purpose such a section is given 
 of the tooth of Myliobatis (Fig. 327). Here the vascular canals 
 (a, a) are of great size, and, as is usual in this form of tissue, 
 parallel to each other ; the dentinal tubuli (b, b) are given off in 
 remarkably rich clusters of beautiful ramose tubuli, presenting, under 
 the microscope, a very fine appearance. 
 
202 
 
 ANIMAL PHYSIOLOGY. 
 
 [LESSON 5V. 
 
 859. But the extent of the ramified tubuli must be sought for in 
 a transverse section, a figure of which is given (Fig. 328) ; in the 
 centre is seen the section of the vascular canals, and the tubuli coming 
 off in profuse plexuses ; the tissue which separates the vascular 
 canals and dentinal tubuli, is a thin layer of cementum. 
 
 860. A fossil Shark's tooth (Fig. 329) shows the structure of 
 osteo-dentiue very satisfactorily, and, to add to the beauty of the 
 
 FIG. 323. 
 
 FIG. 829. 
 
 Transverse section of tooth of Myliobatis. Longitudinal section of tooth of Shark, Fossil- 
 
 preparation, as seen by the microscope, the blood contained in the 
 
 canals retaining its original color, is also fossilized ! 
 
 861. Here the canals (a) are seen to be wavy, and anastomosing 
 
 very freely ; the chief distribution of the dentinal tubuli is to the 
 
 sides and crown (b), as in the Pristis and Myliobatis. 
 
 Another fine example of osteo-dentine is met with in the teeth of 
 FIG. 330 the Maskanonge, call- 
 
 ed generally Husca- 
 longe. It is a trans- 
 verse section (Fig. 
 330), and shows the 
 amastomosing charac- 
 ter of the vascular ca- 
 nals very satisfactorily. 
 Near the outer margin 
 of the tooth a canal 
 
 Transverse section of tooth, Muscalomre. appears to run round 
 
 it, from whence the great distribution of osteo-dentine comes off. 
 In the central portion of the section these tubuli are seen anasto- 
 
LESSON 58.] THE SALIVARY GLANDS. 203 
 
 mosing very freely, and contribute to give a fine appearance to the 
 section. The distinction, then, in the tissues of the teeth of fishes 
 is, that in vaso-dentine the vascular tubes are parallel, whereas, in 
 osteo-dentine, they anastomose. 
 
 LESSON LYIII. 
 
 THE SALIVAKT GLANDS. 
 
 862. In the human subject, as in all the higher mammalia, there 
 are three pairs of salivary glands ; these are the parotid, submaxil- 
 lary, and sublingual glands. 
 
 868. The parotid gland (in man) is the largest of the three pairs, 
 and, situate immediately in front of the external ear, extends super- 
 ficially for a short distance over the masseter muscle, and behind the 
 ramus of the lower jaw. 
 
 864. The submaxillary gland is situated in the posterior angle 
 of the submaxillary triangle of the neck. 
 
 865. The sublingual is an elongated and flattened gland, situated 
 beneath the mucous membrane of the floor of the mouth, on each 
 side of the frenum (bridle) of the tongue. 
 
 866. In structure they are conglomerate glands, consisting of lobes 
 which are made up of angular lobules, and these of smaller lobules. 
 
 867. The smallest lobule is apparently made up of granules, 
 which are minute coecal pouches, formed by the dilatation of the 
 extreme ramifications of the ducts. 
 
 868. These minute ducts unite to form lobular ducts, and the 
 lobular ducts constitute, by their union, a single excretory duct. 
 
 869. The above description of these glands applies very generally 
 to the animals in which they are found. 
 
 870. It is not a little remarkable that these three pairs of salivary 
 glands are all found in the class of Reptiles, but never in the same 
 individual ; one animal possesses the parotid ; another, the sub- 
 maxillary ; while a third has only the sublingual. 
 
 871. Food received into the mouth is given at once to the grind- 
 ing teeth, for the double purpose of being thoroughly comminuted 
 and insalivated. One pair of the salivary glands (parotid) has its 
 evacuating duct on the inside of the cheek, opposite to the second 
 molar tooth of the upper jaw, and the action of the jaws, in the act 
 of mastication, not only compels the descent of the saliva in copious 
 streams from these, but simultaneously from the other glands. 
 
204 ANIMAL PHYSIOLOGY. [LESSON 58. 
 
 872. The salivary glands, and their secretion, appear to be so 
 much alike, that it has been difficult to say whether they all se- 
 crete a fluid possessing the same chemical properties or not. 
 
 873. But reasoning from analogy of the effects produced by ani- 
 mals possessing some of these glands, to the exclusion of the rest, 
 one would incline to the belief that each pair of glands possesses 
 different chemical properties, or, perhaps, that two pairs of them pos- 
 sess properties distinct from the third, and that the combination of 
 the whole is necessary to the production of the required effect. 
 
 874. Mastication of the food, the first act in the process of di- 
 gestion, is, at the same time, the most important one. If it be per- 
 formed in a hasty, slovenly manner, dyspepsia is the unfailing result ; 
 those persons who have once accustomed themselves to consume their 
 food, dispensing with this preliminary process, never can recover the 
 lost art, and sink into an early grave, the victims of suicide. 
 
 875. The saliva appears to possess three most important proper- 
 ties : firstly, it destroys vitality in all animal and vegetable matter ; 
 secondly, it loosens the tissues, thereby preparing them to receive 
 the saliva itself, and ultimately to admit the gastric juice; and 
 thirdly, it mechanically softens and dilutes hard or dry food. 
 
 876. When a Cow fills her paunch with grass, she places there a 
 large amount of living vegetable material ; lying in that organ, or 
 transferring it to the second stomach, no way affects its vitality, but 
 when thrown back into the mouth, and it comes in contact with the 
 saliva, then it instantly dies, and becomes materially altered in ap- 
 pearance. 
 
 877. Examine the contents of the first three stomachs of a Cow, 
 or a Sheep ; in the two first the food is evidently living grass, but 
 in the third it has the appearance of a thoroughly well-boiled vege- 
 table more nearly allied in color and appearance to spinach, and, 
 as yet, it has only come in contact with the saliva, which must be 
 held responsible for its changed condition. 
 
 878. Arrest a caterpillar in the act of eating the leaf of a cab- 
 bage ; kill it instantly, open its crop, and examine the leaf you saw 
 it consume but a minute before : it will have lost its bright green 
 color, and be reduced, in every respect, to the appearance of the 
 grass in the third stomach of the Cow. As it cannot have come in 
 contact with any other material than the salivary secretion, it is 
 surely justifiable to attribute its altered appearance to the action of 
 that fluid. 
 
 879. When man eats raw, ripe fruits,, he eats living vegetables, 
 
LESSON 59.] THE SALIVARY GLANDS. 205 
 
 and if he put them into his stomach in that state, there they will 
 remain, for no stomach has the power to destroy the vitality of any 
 thing, as, if it had, assuredly it would destroy and digest itself, a 
 contingency that always happens in death. Nothing is more com- 
 mon, at post-mortem examinations, than to find that a portion of the 
 stomach has actually thus acted upon itself ! 
 
 LESSON LIX. 
 
 THE SALIVAKY GLANDS, CONCLUDED. 
 
 880. To show the universality of this particular chemical prop- 
 erty of destroying life, let us see what takes place amongst the lower 
 animals. Bulk for bulk, weight for weight, can any thing exceed the 
 pain of a Mosquito bite, to say nothing of the long-continued after 
 consequences ? 
 
 881. What gives rise to this extreme suffering ? Surely it can- 
 not be the insertion of its tubular sheath and tiny jaws, because if 
 the flesh were stabbed at the same time with a dozen large stocking 
 needles, the pain would not be nearly so great, and the wound would 
 sooner heal. When a spider bites a fly, why does the insect die 
 instantly, and its body swell up prodigiously ? 
 
 882. If a rattlesnake, or other, so called, poisonous serpent, bite 
 a man, why is the wound almost universally fatal ? 
 
 883. If a Dog, not rabid, bite a man, or if a Cow, Horse, Hog, 
 Raccoon, Fox (and many other animals), do the same thing, or if one 
 man bite another, why, in any, or all these circumstances, should 
 the bitten person be liable to Hydrophobia ? 
 
 884. To these questions, which might be greatly extended, there 
 is but one answer, namely, that the person bitten has been in every 
 instance inoculated with the saliva of the other animal, and that one 
 of its chief properties is to destroy life. 
 
 885. To them, and to us, it is a natural secretion, and so harm- 
 less is it, under some circumstances, that a man may drink any 
 quantity of the poison (saliva) of a Rattlesnake, and it will have 
 none other effect than to help him to digest his food ! But if in- 
 oculated into the circulation of the blood, it becomes a virulent, a 
 fatal poison. 
 
 886. Who can doubt that, if a Mosquito were as large as a good 
 
206 ANIMAL PHYSIOLOGY. [LESSON 59. 
 
 sized dog, its saliva would be as immediately and certainly fatal as 
 the bite of a rattlesnake ? 
 
 887. The pain that we share with domestic and other animals, 
 from the bite of parasitic insects, is solely due to this cause inocu- 
 lation by their saliva. 
 
 888. The division of the salivary glands amongst the reptiles 
 would appear to throw some light on the function of each, or certainly 
 some of them ; thus : the poisonous reptiles possess only parotid 
 glands, the secretion of which descends by the channels of the fangs 
 
 of the upper jaw (Fig. 331, a) ; the use they make of 
 them would seem to establish the function and proper- 
 ties of these particular glands. 
 
 889. The Boa Constrictor (Python tigris) has no 
 parotid glands, neither can he destroy his prey by a 
 bite, but he entwines his body around his victim, and 
 kills him, as a bear would, by an embrace. But what 
 is now to be done ? he has no grinding teeth to enable 
 him to insalivate the food and loosen the tissues, by partially decom- 
 posing the body of the goat he has killed, and so prepare it for the 
 action of his stomach ; in other words, how can he perform the im- 
 portant function of insalivating it ? 
 
 890. He does it in this way : Tie licks it all over, and wherever 
 the tongue, covered with saliva, touches it, the flesh becomes almost 
 rotten under its influence. 
 
 891. Now, as it is well known that persons have been bitten by 
 a rabid dog and escaped hydrophobia, whilst other persons have been 
 bitten by sound and healthy dogs and yet this fearful disease has 
 supervened, how is this to be explained, unless we admit the differing 
 chemical property of the salivary glands respectively ? 
 
 892. If the teachings of the rattlesnake and the boa constrictor 
 have any practical value, it would appear that the parotid glands 
 alone possess the power of destroying life, and that the secretion of 
 the other glands can only be employed upon already dead matter, to 
 effect its speedy decomposition. 
 
 893. If this theory be true, it is very easy to explain the bites 
 and their consequences of the two dogs : in the case of the rabid dog 
 whose bite proved innocent, the saliva of inoculation may have 
 come only from the submaxillary and sublingual glands, and con- 
 sequently it was harmless ; whereas, in the case of the sound dog, 
 the saliva came from the parotid glands, and was therefore fatal. 
 
 894. This view is sustained by the following considerations : the 
 
LESSON 59.1 THE SALIVARY GLANDS. 207 
 
 ducts of the parotid glands are situated, as we have seen, in immedi- 
 ate proximity to the molar teeth, and the secretion is only evolved 
 by their action ; the probability is that the incisor teeth, used in bit- 
 ing, and the interior of the mouth, are usually lubricated by the se- 
 cretion of one or both of the other pairs of glands, whilst the parotid 
 glands are reserved for mastication alone. 
 
 895. Whatever light chemistry may throw upon this really im- 
 portant question, remains to be seen, but Comparative Anatomy, the 
 only sure guide in the settlement of abstruse and difficult subjects 
 of this kind, would appear to settle it conclusively, that the secre- 
 tion of the parotid glands affects solely the vitality of all tissues 
 presented to their action ; and the secretion of the other glands has 
 the power of rapidly decomposing or disintegrating tissues already 
 
 896. The third function of the saliva is no less important, name- 
 ly, to dilute or moisten dry food, and is common to all these glands. 
 
 The blood of man and animals is too rich and thick to be con- 
 sumed in its natural state by parasitic insects ; and the motive they 
 have for pouring their secretion liberally into the wound they have 
 made, is twofold, one to destroy the vitality of the blood, a func- 
 tion their stomach cannot perform, and the other to dilute it, to 
 make it thin enough to be pumped up with ease. 
 
 897. In insects, the anatomical position of their salivary glands 
 does not appear to warrant the opinion that they, at least, possess 
 parotid glands ; but the life-destroying character of the salivary se- 
 cretion in all the predaceous, carnivorous, and parasitic tribes, in ad- 
 dition to the same exhibition in all those insects feeding upon living 
 vegetable matter, too clearly points to the function and character of 
 the parotid secretion, notwithstanding the situation of their glands. 
 
 898. And why should it be necessary for such insects to have 
 two, and frequently three pairs of such glands, if they all possessed 
 the same capabilities ? From this circumstance alone, it would ap- 
 pear that the function is divided ; that one pair of these glands has 
 the power of destroying life, and the other pair (or pairs) of decom- 
 posing organic matter already dead both these processes being essen- 
 tial to the ultimate digestion of the food. 
 
 899. In the Nepa (water Scorpion), there are three pairs of sali- 
 vary glands three of them lying on the right and three on the left 
 side of the body. One pair of these glands possesses a distinct outlet, 
 and from the effects it produces by inoculation, entomologists have 
 long ago concluded that these especial glands secrete a poisonous 
 
208 ANIMAL PHYSIOLOGY. [LESSON 60. 
 
 fluid. Is it not much more probable that they are, in function, parotid 
 glands ? 
 
 900. To show the difficulties that surround this question, it may 
 be well to remark, that in the Calf, when cooked, all these glands 
 taste precisely like the (so-called) sweetbread, and have the same 
 general appearance. 
 
 901. The organ called by butchers the " throat-sweetbread," is, 
 in reality, the submaxillary gland ; and the " heart-sweetbread " is 
 the Thymus gland, which is always of great size in young animals. 
 
 902. The true sweetbread, or pancreas, is never eaten. 
 
 LESSON LX. 
 
 THE PEOPEETIES OF THE GASTBIC JUICE AND MUCUS. 
 
 903. If we eat a dry cracker, we cannot swallow it until it be 
 moistened with the saliva ; and the same thing takes place with 
 Cows and Sheep, when they are fed upon dry hay. 
 
 904. When food that has been properly insalivated, reaches the 
 stomach, it is destined to come in contact with two other elements, 
 both of which, so far as experiments on artifical digestion have ex- 
 tended, are imperatively necessary for its final resolution into chyme. 
 These are, the weak acid, known as gastric juice, and mucus / and 
 without the combination of the two, in their full integrity, there can 
 be no healthy digestion. 
 
 905. From the chemical composition of one of these agents (the 
 gastric juice), it must be evident that those persons who habitually 
 drink much water, must necessarily impair the function of the stom- 
 ach, as they thereby dilute an already weak acid, until it be power- 
 less ; in fact there can be no doubt that the practice of water- drink- 
 ing to excess is as much a vice as the too frequent indulgence in 
 strong potations, and leads to precisely the same consequences 
 death. * 
 
 906. Moreover, water taken in large quantities with a full meal, has 
 another very bad effect : when there is food in the stomach to digest, 
 the capillaries, previously nearly empty, are turgid with blood, which 
 has been withdrawn from the surface of the body and the limbs, to 
 meet an immediate, special want cold water thrown upon this ex- 
 
LESSON 60.] THE GASTRIC JUICE AND MUCUS. 209 
 
 cited capillary surface, at once represses this circulation and drives 
 it back to its former channels. The blood has been summoned to 
 the stomach, at the time it is specially needed, to supply the neces- 
 sary pabulum for the secretion of mucus and gastric juice> neither 
 of which is kept " on service." Once driven back, what is to be- 
 come of the food, how is it to be digested, when the material for 
 preparing the solvents for it has been sent away ? 
 
 907. "Water containing much lime in solution is altogether unfit 
 to drink, because dangerous. This earth is eliminated by the kid- 
 neys, and passed in the solid form to the bladder, where it concretes, 
 and forms calculi, which can only be removed by the most painful 
 and dangerous operation known to surgery. 
 
 908. Boiling such water has the effect of precipitating the great 
 excess of lime, but too much remains to render it desirable to use, if 
 it can be avoided. For comfort sake, and to have perfect immunity 
 from thirst, the less people drink of any thing the better ; a moderate 
 quantity (two cups) at breakfast, and the like at tea, are all that 
 nature requires, and any one can soon become accustomed to this 
 kind of moderation, by which the soundness of the stomach and the 
 general health will be greatly promoted. Such persons are never dys- 
 peptic, and never know the sensation of thirst, under any circumstances* 
 
 909. The tubes which secrete the mucus lie in the submucous 
 (sub, under, beneath) tissue of the stomach; they are surrounded by 
 the capillaries, which are going to form the capillary plexuses of the 
 mucous membrane* These tubes open upon the floors of the gastric 
 cells of the stomach ; their number is variable, but they average 
 from five to nine tubes in each cell. 
 
 910. A delicate distribution of capillaries with wide meshes runs 
 around the tubes, and these are the vessels seen in those cells, pre- 
 senting the most open surface, by which stomach may be discrimi- 
 nated from large intestine. 
 
 911. There is much obscurity surrounding the origin of the gas- 
 tric juice; some authors supposing that it is secreted by the vessels 
 of the mucous membrane of the stomach, but we now know that the 
 stomach, in its submucous tissue, is literally filled with glands, hence 
 called gastric glands ; these all secrete a fluid, and while some of 
 them are known to secrete the true gastric juice, the function of the 
 remainder remains to be discovered. 
 
 912. These glands are not so well developed nor so conspicuous 
 in man, as in other animals, and two views of them are selected, one 
 from the Dog, and the other from the Calf. 
 
 14 
 
210 
 
 ANIMAL PHYSIOLOGY. 
 
 [LESSON 61. 
 
 913. In the pylorus of a Dog, large glands (Fig. 332) exist, 
 lined with cylinder epithelium (a), and terminated by coacal append- 
 ages (5) ; the body of the gland is shown at c, 
 
 914. The gastric glands from the middle of the stomach are those 
 which secrete the gastric juice ; the function of those of the pylorus 
 is not known. 
 
 FIG. 332. 
 
 FIG. 88a 
 
 Gastric gland, Dog. 
 
 Gastric glands, Calf. 
 
 In the fourth stomach of the Calf these glands are particularly 
 numerous, a portrait of which is given in Fig. 333. Like the gas- 
 tric glands of the Dog, these also are lined with cylinder epithelium ; 
 there is an absence, however, of ccecal appendages at their termina- 
 tion, which becomes attenuated. 
 
 LESSON LXI. 
 
 NUTEITION IN MAN. 
 
 915. Before proceeding to describe the organs which, by their 
 united action, form the nutrimental system of Man, it will be desirable 
 to state briefly and succinctly the progressive order in which they are 
 used, and the particular function delegated to each to perform. 
 
 916. The teeth may be divided into two chief kinds : incisor (or 
 incision) teeth, placed in the front of the upper and lower jaw, their 
 function being to primarily cut or divide the food ; having done this, 
 it is directly transferred to the second order of teeth, the molars, 
 or grinders, whose function it is to grind and subdivide the food as 
 much as possible. 
 
LESSON 61.] 
 
 NUTRITION IN MAN. 
 
 211 
 
 917. During the time the molars are thus employed, the saliva 
 from the parotid glands is abundantly poured out from its ducts, 
 which open opposite to the second grinder, and in the meanwhile the 
 secretion from the other two pairs of salivary glands commingles 
 with the first, and thus the food becomes thoroughly insalivated, 
 whereby its living principle is destroyed, and incipient decomposition 
 induced. 
 
 918. During this time the tongue is not idle its business is to 
 turn the food so that every surface of it may be presented to the mo- 
 lar teeth ; neither is this all, for the tongue conveys the food from 
 the molars on one side of the mouth to those on the other side, and 
 when this first and most important operation is completed, the 
 tongue conveys the food to the funnel-shaped cavity at the back of 
 the mouth, called the pharynx, from whence it is passed to the ceso- 
 phagus to be conveyed to the stomach. 
 
 919. The tongue is used by man in suction ; the Canine and Fe- 
 line races employ the tongue to lap fluids ; the Giraffe twines this 
 organ around the leaves and branches of trees, and detaches them 
 with force. The Ant-eaters have a 
 
 remarkably long tongue, covered 
 with a slimy secretion ; this they pro- 
 trude, and upon it entrap their vic- 
 tims. The Cameleon among reptiles, 
 and the Woodpecker among birds, 
 have each a tongue enormously de- 
 veloped, for the purpose of prehen- 
 
 Fio. 884. 
 
 sion. 
 
 It has been already stated that 
 the human tongue, in common with 
 the like organ in other animals, pos- 
 sesses three distinct kinds of papillae ; 
 this will be best understood by con- 
 sulting the subjoined figure of the 
 human tongue (Fig. 334). The fili- 
 form papillae are seen at a, the fungi- 
 form at 2>, and the circumvallatae at 
 c. That the filiform papillae are en- 
 dowed with the sense of taste is cer- 
 tain, from the fact that the gustatory nerves (nerves of taste) are 
 extensively distributed to them; the precise function of the other 
 papillae is obscure. The white spots at the upper portion of the 
 
 Human tongue. 
 
212 ANIMAL PHYSIOLOGY. [LESSON 61. 
 
 tongue, above the circumvallate papillae, indicate the mucus-crypts 
 of Leiberkuhn, which are abundant in this situation. 
 
 920. The oesophagus is provided with two layers of muscles ; one 
 longitudinal, the other transverse. 
 
 921. By their united action the food is conveyed to the stomach, 
 and delivered to what is called the cardiac orifice. 
 
 922. In form the stomach very much resembles the bag of a bag- 
 pipe, to which it is generally compared. 
 
 923. It possesses three 
 coats, an internal mucus, a 
 muscular, and an external se- 
 rous coat derived from the 
 peritoneum, or the membrane 
 which lines the muscles of the 
 abdomen. 
 
 924. A figure of the ex- 
 ternal form of the stomach is 
 given (Fig. 335) ; the ossoph- 
 
 agus (a) enters the stomach 
 The human stomach. . v ' 
 
 at the cardiac orifice ; the 
 
 constriction at the other extremity marks the pyloric valve (b) ; and 
 the first of the small intestines, the duodenum, commences on the 
 other side the pylorus (c). 
 
 925. As soon as the food reaches the stomach, it comes in con- 
 tact with agents which exert a chemical influence upon it ; these are 
 the gastric juice, and mucus. Stimulated by the presence of food, 
 the muscles are in incessant action, constantly contracting on it, 
 moving it from side to side, literally churning it. 
 
 926. The combined action of the heat of the stomach, the mus- 
 cular action, and the solvent power of the gastric juice, aided by a 
 peculiar influence of the mucus, reduces the food to its elements, or 
 dissolves it into a pulpy state, called chyme. 
 
 927. In this form it makes application to pass through the py- 
 loric valve, and if there be no solid particles, it is permitted so to 
 do ; but undigested matter is sent back again to be thoroughly re- 
 duced before it can be allowed to go through the valve into the duo- 
 denum. If, however, the food chance to be of an unhealthy or in- 
 digestible character, the stomach soon casts it out, in the same state 
 that it entered the organ, and proceeds to act upon what may remain 
 of a better character. 
 
LESSON 62.] NUTRITION IN MAN. 213 
 
 LESSON LXII. 
 
 NUTRITION IN MAN, CONTINUED. 
 
 928. When it reaches the intestine, the chyme is subject to new 
 influences ; the Liver supplies its bile, and the pancreas (or sweet- 
 bread) the pancreatic juice, and by their means the chyme becomes 
 changed into chyle, or new blood, which is to circulate throughout 
 the body, to renew wasted material, and to promote growth. 
 
 929. When formed, the chyle is white and milk-like, and is asso- 
 ciated with innutritious materials ; from these it is separated, firstly, 
 in the duodenum, and what then escapes is subsequently constantly 
 being separated throughout the tract of the small intestines. 
 
 930. But the chyle is not blood ; it does not yet possess the ne- 
 cessary requirements of that fluid it has no life ; it wants, in fact, 
 another element, oxygen, and must go to the lungs to obtain it. 
 For this purpose the villi of the small intestines are provided with 
 certain tubes, or canals, called lacteals, from lacta, milk, and it is 
 their duty to take up or remove the chyle, still white, and convey it 
 upwards to a reservoir in the chest called the thoracic duct ; thence 
 to the heart, and finally to the lungs, from which latter organ it is re- 
 turned to the other side of the heart (the left side), of a beautiful 
 bright vermilion color, endowed with all the properties of new blood, 
 and forthwith to be distributed by the arteries to all parts of the 
 body, for the purposes of nutrition. 
 
 931. The injected preparation of the mucous membrane of the 
 stomach of the human subject (Fig. 336) 
 
 is a magnificent spectacle ! Here we 
 have a dense arrangement of honeycomb- 
 like cells, the walls of which are formed, 
 not of a single capillary as we have hith- 
 erto seen, but a plexus of very delicate 
 vessels. This particular arrangement is 
 only met with in the mucous membranes 
 of man, and the monkey ; in all other ani- 
 
 , -i -if ii n n Mucous membrane of human 
 
 mals single vessels form the cell walls ; stomach. 
 
 by this sole characteristic the human stomach (or monkey) may be 
 
 readily known. 
 
 932. The commencement of the duodenum, soon after its junc- 
 tion with the pylorus, abounds in glands, known as "Brunner's 
 glands," from their supposed discoverer ; in truth, however, these, in 
 
214 
 
 ANIMAL PHYSIOLOGY. 
 
 [LESSON 62. 
 
 FIG. 837. 
 
 common with the remainder of the intestinal glands, were really dis- 
 covered by Peyer, who describes them as being " as numerous as the 
 stars in the firmament of heaven." 
 
 933. These glands lie, not in the mucous but in the sub mucous 
 tissue, where they form a continuous layer of white, flat bodies, of 
 irregular size, surrounding the whole intes- 
 tine. Each gland consists of numerous 
 minute lobules, of which the ducts (a) 
 open into the mucous membrane of the 
 intestine. A figure of these glands is 
 given (Fig. 337). 
 
 934. The villi of the duodenum (Fig. 
 338) are usually larger and broader than 
 those of the Jejunum, and are remarkable 
 for the possession of a large vessel in the 
 centre of each villus ; throughout the small intestines, at the bases 
 of the villi, and surrounding them, are the mucus-crypts, or folli- 
 cles of Leiberkuhn. 
 
 935. They appear like so many minute holes upon the surface of 
 the mucous membrane ; examined by dissection, they are found to be 
 long, narrow, deep tubes, or cavities, giving the idea of a villus 
 pushed into the mucous membrane, and inverted, like inverting the 
 finger of a glove. In life these glands are filled with a clear, fluid 
 secretion, called the intestinal juice. 
 
 Brunner's glands. 
 
 FIG. 838. 
 
 FIG. 339. 
 
 Villi, of human Duodenum. Jejunum, human. 
 
 936. In the human jejunum the villi and Leiberkuhnian follicles 
 are well seen (Fig. 339) ; it will be readily perceived that, by the 
 arrangement of these follicular glands, the surface of the mucous 
 membrane is thereby greatly increased ; where there is not room for 
 another villus, there is yet room for a series of minute apertures at 
 its base. 
 
 937. The villi of the small intestines contain in their interior 
 
LESSON 63.] NUTBrnON IN MAN. 215 
 
 certain vessels, whose function it is to absorb the nutriment and con- 
 vey it into the circulation, to supply the blood positively lost by the 
 various glandular bodies, all of which have secreted or formed some- 
 thing from it ; these are the lacteals, already referred to. 
 
 LESSON LXIII. 
 
 NUTRITION IN MAN, CONTINUED. 
 
 938. The precise relation of the lacteals to the villi of man, has 
 not yet been determined, owing to the difficulty of meeting with villi 
 distended with chyle ; but in the lower animals we can feed, and sub- 
 sequently kill, at any required moment, a Dog, or Cat, &c., and at 
 once proceed to make the necessary examination. 
 
 939. These vessels appear to be much larger than capillary blood- 
 vessels, and one only is found in a villus which traverses its cen- 
 tral axis, and terminates in a coecal, or enlarged end. 
 
 940. But how does the chyle get into the lacteals ? This is a 
 very difficult question to answer, and one to which no satisfactory re- 
 ply has yet been given. Many theories have been advanced, but no 
 authenticated observations have as yet been published. 
 
 941. Some investigations made on this subject,* but not yet 
 given to the world, lead to the conclusion that the apices of the 
 viili open, and that the chyle is received directly in at the enlarged 
 termination of the lacteals ; it must be conceded, however, that this 
 fact is very difficult of verification, for the tissue, when first seen, is 
 covered with a deep layer of mucus : the epithelium at the summit 
 of the villi, is, like the organs themselves, porrect (standing up), 
 and worse, it so soon dies. The only favorable circumstance in con- 
 nection with a transient glance is, the uprightness of the villi, so 
 that the spectator looks down upon and readily perceives their open 
 
 * Thirty years ago, during the Author's studentship, desirous of obtaining information 
 on this subject, he killed a Cat, and proceeded to examine the small intestine as rapidly as 
 possible, whilst yet vitality remained in the tissue. He saw the summits of the villi attop&n, 
 apparently as wide as their own diameter, but they soon closed up, and remained shut. 
 
 Subsequently he repeated this experiment to a party of distinguished medical men, in 
 London, including some of his teachers. 
 
 Having to arrange the preparation under the microscope, he again saw the same sight, 
 but, owing to the rapid loss of vitality, the villi so soon closed that not more than two or three 
 of the gentlemen present had an opportunity of seeing any thing of this interesting exhibi- 
 tion, and then so hastily that it was far from satisfactory to them. He has not since repeated 
 this experiment. 
 
216 
 
 ANIMAL PHYSIOLOGY. 
 
 [LESSON 63. 
 
 mouths, but such experiments need confirmation at the hands of other 
 observers, before they can be received as true. 
 
 942. The human Ileum is chiefly remarkable for the number of 
 solitary and agmenated glands there found. The former are in every 
 respect like the latter, except that they are scattered amongst the 
 villi singly, instead of being grouped in masses. 
 
 943. These glands are rounded, flattened organs, always found 
 along that surface of the intestine which is opposite to the mesen- 
 tery. The " Peyer's patches " of these glands increase in size as 
 they approach the coecum, and attain their greatest dimensions just 
 within the iliac portion of the valve which separates the ileum from 
 the coscum ilio-coecal valve. 
 
 944. Each gland of a Peyer's patch is round, somewhat hemis- 
 pherical, but slightly flattened at the top ; no vessels have been de- 
 tected in them, except in the preparation of the Calf (Fig. 386), 
 where, it is supposed either that the gland was in some peculiar con- 
 dition, or that the form of injection used (Bi-chromate of potash) 
 ran more minutely than usual ; most likely the latter. 
 
 945. They contain a thickish gray matter, with which there is 
 but little fluid, and a number of nucleated cells, of round form, to- 
 gether with an abundance of free nuclei A figure of the aggregated 
 glands (Fig. 340) is given ; the glands are seen at a, and the villi of 
 the intestine at b. 
 
 946. These glands are particularly liable to take on disease in 
 
 typhoid fever, and patients are frequently con- 
 valescent of the fever, and yet die of Typhoid 
 Peyerian glands. When this disease supervenes, 
 the glands firstly ulcerate, and subsequently 
 slough off, destroying at last the walls of the in- 
 testine when the 
 patient dies. 
 
 A figure of 
 typhoid Peyerian 
 glands, copied from 
 a preparation, is 
 here given, (Fig. 
 341.) The healthy 
 villi of the intes- 
 tine are seen at a; 
 ^^___. at their bases lie 
 
 A "Fever's patch ."from ,-,., T , * -i /7\ i i , i 
 
 the ileum, human. the follicles of Leiberkuhn (0), whilst a large 
 
 FIG. 340. 
 
 FIG. 841. 
 
 Typhoid Peyerian glands, human. 
 
LESSON 63.] 
 
 NUTKITION IN MAN. 
 
 217 
 
 FIG. 342. 
 
 hole (white in the preparation) shows where the glands of Peyer have 
 sloughed off. In phthisis these glands are liable to become the seat 
 of tubercular deposit, and also of an ulcerative process, whence re- 
 sults the diarrhoea, so troublesome in that disease. In Asiatic chol- 
 era they become greatly enlarged from the accumulation of granular 
 matter in the vesicles. 
 
 Brunner's glands are remarkably free from tendency to disease. 
 
 947. The mucous membrane of the large intestine in man, as in 
 other animals, bears a close resemblance 
 
 to the like tissue of the stomach, but in 
 man (and the Monkey) again we find 
 that a delicate plexus of capillaries, not 
 single vessels, forms the boundaries of 
 the cells (Fig. 342). 
 
 948. Solitary glands are abundantly 
 found in the large intestine ; they are of 
 large size, and exhibit a funnel-shaped 
 cavity (see Fig. 293) or pit-like aperture, 
 
 which forms a depression of the mucous membrane ; at the bottom 
 of this follicle lies a closed, somewhat flattened gland, exactly the 
 same in structure, and possessing similar contents to the glands of 
 the small intestines. 
 
 It has already been observed that the mucous membranes in the 
 Monkey are identical with similar structures in man, and two illus- 
 trations are offered in confirmation of this fact. 
 
 The first (Fig. 343) is from the Jejunum, and exhibits villi of 
 
 Human Colon. 
 
 FIG. 343. 
 
 FIG. 344. 
 
 Jejunum, Monkey. Colon, Monkey. 
 
 the same size and shape, and the same display of mucus-crypts, as 
 the corresponding human intestine. 
 
 The second (Fig. 344) is from the Colon, and again the same 
 exact parallelism exists. While the cells of such tissue in all other 
 animals are surrounded by single vessels only, it is reserved for man 
 and the Monkey to display a plexus in the same situation. 
 
218 ANIMAL PHYSIOLOGY. [LESSON 64. 
 
 949. A carefully compiled description has thus been given of the 
 form of the nutrimental organs, and their accessory glandular ap- 
 pendages, in the several classes of the animal kingdom, commencing 
 with the lowest, and tracing its gradual development up to man. 
 
 LESSON LXIY. 
 
 NUTRITION IN MAN, CONTINUED. 
 
 950. In the class of ANIMALCULA, we saw a number of digestive 
 cavities possessing but one opening ; a little higher in the same class, 
 this cavity was extensively sacculated. 
 
 951. In the KOTIFEROUS animals, the alimentary canal possesses 
 two openings, and a glandular apparatus is superadded. 
 
 952. The ENTOZOA (intestinal parasites) are somewhat anomalous ; 
 the Acephalocyst, although allied to the Entozoa by its affinities, is 
 really lower than the lowest animalcule. It is provided with a nu- 
 trimental cavity, but destitute even of a mouth, and like the plants, 
 to which it is most closely allied, propagated by spontaneous division. 
 None of the Entozoa possess more than one cavity to their nutri- 
 mental organs. 
 
 953. In the POLYPI we found the same simple condition of the 
 nutrimental canal, and in those which possess a stomach with two 
 cavities, the lower one is solely devoted to the transmission of nutri- 
 ment for the extension of the commonwealth. 
 
 954. The ACALEPHA are equally simple, and the like must be said 
 of some of the 
 
 955. ECHINODERMATA, where Asterias possesses only one diges- 
 tive aperture. 
 
 956. In the remaining orders, a slight advance has been made ; 
 the alimentary canal is much more extensive, possesses convolutions, 
 and terminates in a distinct aperture, opposed to the mouth. 
 
 957. Amongst the lowest of the ANNELLIDES ranks the Leech ; 
 but although possessing only a stomach furnished with ccecal append- 
 ages, it has yet two apertures. The Aphrodita, in addition to its 
 numerous ccoca, has an intestine superadded. 
 
 958. In the lowly EPIZOA, we still have two apertures to the ali- 
 mentary canal, in addition to an intestine, which indicates a higher 
 grade of development. 
 
LESSON 64.] NUTRITION IN MAN. 219 
 
 959. In the CIRRIPEDS the same condition obtains. 
 
 960. The CRUSTACEA mark a higher advance, by the possession 
 of a large, well-developed liver, in addition to an intestine and two 
 apertures. 
 
 961. The INSECTS are truly remarkable for the great perfection 
 which their organization displays. Provided with mouths exquisitely 
 adapted to their varied food, the structure of their internal organs is 
 quite complicated. 
 
 962. Here we meet, not only with salivary glands, but frequently 
 existing to the extent of three pairs of them as many pairs as man 
 Jhimself possesses, and endowed, apparently, with similar functions. 
 In addition, they all have a liver, and some of them (Blatta) a pan- 
 creas, whilst the intestinal canal is divisible into nearly as many 
 portions as that of the human subject ; and, finally, many of them 
 possess kidneys. 
 
 963. The higher members of the class ARACHNIDA, the Spiders, 
 have a liver and a kidney. 
 
 964. In the MOLLUSCA we find no advance, but in many of its 
 members a falling off of development. 
 
 965. In the TUNICATA, the only accessory organ is a liver. The 
 like in the BRACHIOPODA and LAMELLIBRANCHIATA. In the G-ASTERO- 
 PODA, salivary glands are added. 
 
 966. The CEPHALOPODS, like many Insects, have a plurality of 
 stomachs, but no positive advancement is discernible ; as a whole, 
 the class Mollusca appears to be below the Articulata in general or 
 ganization. 
 
 967. The FISHES, as the lowest class of the Vertebrate sub-king- 
 dom, exhibit only a rudimentary condition of the nutrimental organs ; 
 a liver, however, is always found, and usually well developed ; the 
 salivary glands, for the most part, merge into the pancreatic folli- 
 cles so abundantly developed in the majority of them. 
 
 968. The KEPTILES, as a class, indicate a higher rank ; the sto- 
 mach is always well formed, particularly as regards the internal 
 structure of it ; neither are the accessories of a well-defined nutri- 
 mental function wanting. Although the Frogs are destitute of 
 salivary glands, the three pairs common to the higher animals are 
 distributed amongst the other members of the class. They are all 
 supplied with a liver, have the intestinal canal of sufficient length 
 and. properly divided, and possess kidneys. 
 
 969. The BIRDS, amongst their remarkable developments, pos- 
 sess, many of them, four pairs of salivary glands. Without jaws, 
 
220 ANIMAL PHYSIOLOGY. [LESSON 65. 
 
 without teeth, for the dividing and mastication of their food, 
 the stomach is wonderfully modified to suit an extraordinary 
 want. All the other requisites of a well-developed nutrimental func- 
 tion they are possessed of. 
 
 970. The most elaborate and perfect form of these organs is met 
 with in the class MAMMALIA. Notwithstanding the various modifi- 
 cations and complications of the nutrimental canal to meet special 
 wants, the general principle remains always the same, and the sever- 
 al accessory organs essential to perfect digestion of the several kinds 
 of food, upon which the members of the class are destined to sub- 
 sist, are there. 
 
 LESSON LXY. 
 
 NUTRITION IN MAN, CONCLUDED. 
 
 971. What a wonderful piece of mechanism is the human intes- 
 tinal tract, with its millions of villi all periodically actively engaged, 
 its mucus-crypts, its countless glands, its capillary, and its nervous 
 systems ! That it should at any time get out of repair is by no 
 means surprising ; the wonder is that it remains in a healthy condi- 
 tion, especially from the difficult and impossible labors many of us 
 call upon it to perform. The true rules for a sound and healthy 
 stomach are few and simple to eat when we are hungry, and to 
 drink only when nature requires it. 
 
 972. How many persons there are who occupy themselves inces- 
 santly in eating, and as incessantly in drinking water ! Has it ever 
 occurred to them that the highly complicated machinery necessary to 
 digest food requires repose ? 
 
 973. The muscular coat of the stomach having labored to digest 
 a meal, demands rest, and must have it, if its vigor be cared for. 
 On the other hand, if it be attempted to make the necessary organs 
 always work, they flatly refuse, and will not do any thing ; whereby 
 the worst form of dyspepsia results. A pint of water weighs one 
 pound, and the stomach must attempt the same means to get rid of it 
 as though it were the same weight of solid food, but with less suc- 
 cess ; all its contractions are in vain the water eludes these efforts 
 till the fatigued muscles yield in despair.. 
 
 974. But there are other forms in which we do ourselves a great 
 wrong, namely, by eating improper, because indigestible food, or by 
 eating food improperly prepared. ThuS young meats (Veal and 
 
LESSON 65.] NUTRITION IN MAN. 221 
 
 Lamb) are neither nutritious nor easy of digestion ; Beef, and espe- 
 cially Mutton, are by far the lightest and most nutritious of all meats. 
 
 Curious, but most satisfactory information, quite confirmatory of 
 the views already enunciated, have been furnished by a series of 
 carefully noted experiments, made at different times, and by a num- 
 ber of independent observers, upon the stomach of Martin, the cel- 
 ebrated Canadian with a permanent hole in his stomach, the result 
 of a gun-shot wound. The gastric juice, long supposed to be a myth, 
 inasmuch as no one had ever seen it, because it cannot be found in 
 death, appears to be secreted at the very time, and in the exact quan- 
 tity wanted. The physiological law that .all young meats are in- 
 digestible, is sustained by the fact that a tender young Chicken 
 requires two-thirds longer time to digest it than a tough old hen. 
 Chickens are frequently prescribed for invalids, but this appears to 
 be a mistake, as, to be easy of digestion and nutritious, the full de- 
 velopment of age would seem to be essential. But care and cau- 
 tion are necessary in the preparation of such food ; it should be put 
 into cold water after having been cut into pieces, and simmered 
 gently for many continuous hours, the time required depending upon 
 its age. If it once be suffered to boil, there is an end of the pro- 
 cess, for muscle consists of the two elements albumen and fibrin 
 and the too sudden application of heat, or the temperature of the 
 boiling point, coagulates one element (albumen), and corrugates 
 the other (fibrin). 
 
 Coagulation of albumen is the state to which the white of an egg 
 is reduced when boiled hard perfectly solidified. Corrugation of 
 fibrin is imitated by parchment brought under the influence of a 
 strong fire, in which the entire mass is shrivelled, or clewed up into 
 a small space ; in both cases the nutriment is locked up, and ren- 
 dered inaccessible to any stomach. 
 
 The flesh of an Ox or Cow is more readily digested than Veal ; 
 Mutton, than Lamb. 
 
 It is well known that the application of heat to butter or lard 
 decomposes them, and essentially alters their properties; for this 
 reason pie-crust is extremely unhealthy. A peep into the Canadian's 
 stomach, shows conclusively that cooked butter or lard is firstly sep- 
 arated ; it then floats upon the surface as a mass of grease, and ulti- 
 mately passes out of the stomach, without undergoing any digestion 
 whatever. 
 
 The skins of all kinds of fruit are entirely indigestible ; the sto- 
 mach refuses to have any thing whatever to do with them. 
 
222 ANIMAL PHYSIOLOGY. [LESSON 65. 
 
 Hot bread never digests at all ; after a long season of working 
 and tumbling about the stomach, it will begin to ferment, and in the 
 end, having submitted the organ to a great amount of fatigue, be 
 finally passed out of the stomach as a refractory and unmanageable 
 mass. But it never becomes assimilated, or absorbed by those organs 
 destined to appropriate nutriment. 
 
 Another remarkable fact has been developed, which proves the 
 truth of the old adage, " laugh and grow fat." It has been satisfac- 
 torily established that mirthfulness at and after a meal greatly facili- 
 tates digestion. On the other hand, if this man be made angry at 
 or immediately subsequent to a meal, bile rushes into the stomach 
 in a perfect stream, and digestion is retarded for some hours, and at 
 last feebly performed. 
 
 975. Besides hot, there is another form of bread demanding 
 notice, and the evils in connection with it are easy of demonstration ; 
 for example : the bones of a young Child are gelatinous (com- 
 posed of jelly), or, at the best, cartilaginous (gristly) ; to become 
 bone, they require the phosphate of lime to be deposited in the 
 meshes or interstices of the tissue. 
 
 976. Wheat contains the phosphate of lime, which, if allowed to 
 remain as such, would be duly appropriated ; but if alum form a 
 constituent of bread, this earth is neutralized, for a mutual decompo- 
 sition takes place between it and the constituents of alum. Alum is 
 the earth alumina, in combination with sulphuric acid ; but if phos- 
 phate of lime be present, the sulphuric acid having more affinity for 
 lime, quits the alumina, and forms a new compound sulphate of 
 lime, or plaster of Paris. The phosphoric acid and alumina are both 
 set free, and in the way of nutrition. Children fed upon bread thus 
 made are liable to rickets, caries (rotting) of the teeth, and a still 
 worse disease known as " spina ventosa," in which very painful tu- 
 mors are formed, sometimes as large as a human head. 
 
 977. Another very objectionable substance is in general use, to 
 supersede eggs, or yeast saleratus ; it is only necessary to remind 
 the reader, that this agent is simply a modified pearlash, which is a 
 poison. 
 
 978. But it is not only in the baker's bread that we go wrong ; it 
 has been already remarked, that the hot biscuits in common and daily 
 use are most objectionable, and no stomach can possibly digest them ; 
 moreover, they are rarely sufficiently baked. 
 
 979. Every good housewife knows, that whilst a loaf from the 
 baker is scarcely eatable on the second day, that her own sweet, 
 
LESSON 66.] MUSCULAR FIBRE. 223 
 
 pure, and nutritious "home-made," retains its freshness and softness 
 for at least a week, this is the best form of bread. 
 
 980. Unripe fruit and vegetables should be avoided as dangerous ; 
 consequently green corn, being an unripe, immature vegetable, is 
 most unhealthy. 
 
 981. Those persons who partake of this vegetable, are constrain- 
 ed to eat the hull, which, in the green state, is particularly thick 
 and tough, and cannot possibly be assimilated, as the experiments on 
 Martin's stomach fully testifies ; moreover, the corpuscles of starch, 
 so eminently desirable in the ripe corn, are not yet formed in its 
 green condition. Never eat or drink between meals. 
 
 982. These remarks might be extended with great propriety, but 
 the theme is neither a gracious nor a pleasant one ; it must be under- 
 stood, at the same time, that they are addressed ostensibly to the 
 younger members of the community, who will feel no difficulty in 
 beginning the right way, and continuing in it, whereby their life 
 will be prolonged, and their happiness promoted. 
 
 LESSON LXVI. 
 
 COMPOUND TUBULAR TISSUES. MUSCULAR FIBRE. 
 
 983. The flesh of animals is called technically muscle; examined 
 by the microscope it is found to be of two distinct formations 
 striped, and non-striped. The majority of the lower animals, espe- 
 cially those (Mollusca) in which the nutrimental function is devel- 
 oped at the expense of those properties which commonly distinguish 
 an animal, as locomotion, volition, &c., possess the non-striped mus- 
 cle only. 
 
 984. Insects, Crustacea, and other of the animals conspicuous for 
 their activity, possess, in addition to the non-striped, the striped 
 muscle. 
 
 985. In the lower, in common with all the higher animals, the 
 non-striped muscle belongs to the vegetative organs (nutrimental 
 canal) ; and the striped muscle to the organs of animal life (loco- 
 motion). 
 
 986. A singular and beautiful illustration of the muscular fibre 
 of the Molluscous class may be given from a specimen of fossil mus- 
 cular fibre, from the tentacles of the extinct Belemnite, which accu- 
 
224 
 
 ANIMAL PHYSIOLOGY. 
 
 [LESSON 66. 
 
 rately agrees with the structure of the muscular fibre of the tenta- 
 cles of the recent Cuttle-fishes (Fig. 345). 
 
 987. The fibres are of two sizes, those near the external surface 
 are remarkably fine (a, Fig. 345), whilst those of deeper layer (a, 
 
 FIG. 346. 
 
 FIG. 345. 
 
 Fossil muscular fibre, Belemnite. 
 
 Fossil muscular fibre, Belemnite. 
 
 FIG. 347. 
 
 Fig. 346) are much broader ; both present the same characteristics, 
 which consist chiefly in the possession of a great number of nuclei 
 (b, Fig. 345). Wherever two layers of fibres are found (in the deep- 
 seated muscle), one layer of fibres crosses the other at right angles 
 (c, Fig. 346). The fibres of the outer layer show the pigment cells 
 
 in great abundance, and in a 
 wonderful state of preserva- 
 tion (a, Figs. 346 and 347). 
 
 988. In addition to the 
 muscular fibre, a portion of the 
 integument (a, Fig. 347) is also 
 shown ; it occurs to some ex- 
 tent in connection with the 
 muscular fibre, in which situa- 
 tion it cannot well be seen, 
 but the detached portion is very interesting, as it shows epidermic 
 scales. In this preparation the fibres are seen singly, and the nuclei 
 well shown. 
 
 989. Amongst the active animals of the Articulate sub-kingdom, 
 the striped fibre prevails, except as regards the muscles of the nutri- 
 mental organs. This form of the fibre in insects, and lulidae, has 
 often been figured, but a general misconception appears to prevail 
 with regard to its true structure. 
 
 990. The transverse lines on an insect fibre are so well marked, 
 
 Fossil muscular fibre, a, Integument, Belemnite. 
 
LESSON 67.] MUSCULAR FIBRE. 
 
 225 
 
 that they give an idea of coarseness, and as such they have been de- 
 scribed; but a little careful examination of the subject will show 
 this opinion to be erroneous, for, on the contrary, the ultimate fibril- 
 lae in these animals are so remarkably delicate, that no amount of 
 magnifying power will succeed in showing a single transverse line 
 upon them, when examined singly in the mass they are seen. 
 
 991. This is shown in Fig. 348, copied from a preparation of the 
 muscles of Blatta Americana, made to show the ultimate fibrillaj ; the 
 muscular fibres on either side (a, a) show deli- 
 cate transverse lines, but the fibrillse torn 
 
 from, and still connecting them (6), do not 
 show the least indication of a transverse line, 
 still they are really there. 
 
 992. So, too, 
 lulus (Fig. 349), 
 in which the lines 
 on the fibre are 
 very coarse, the 
 fibrillae liberated 
 at the end, are 
 singularly fine, 
 and display no 
 
 transverse lines. Muscular fibre, B. Americana. Muscular fibre, itilus. 
 
 993. If we examine a muscle of the higher animals by the naked 
 eye, it will be seen to consist of a bundle of fibres, running in the 
 direction of the long axis of the muscle, and connected by means of 
 areolar tissue. 
 
 994. If a muscle be analyzed by dissection, it will be found to 
 consist of fasciculi, or bundles of fibres ; and if we succeed in ob- 
 taining an ultimate fibre, it will consist of a fasciculus or bundle of 
 ultimate fibrillce. 
 
 995. An ultimate fibre exhibits, under the microscope, the longi- 
 tudinally arranged fasciculi of ultimate fibrillas, their number being 
 so great, however, that their precise structure cannot be determined 
 until separated. 
 
 LESSON LXYII. 
 
 MUSCULAE FIBEE, CONTINUED. 
 
 996. In addition to the longitudinal lines, equi-distant trans- 
 verse lines, at right angles to the former, will also be seen, and the 
 
 15 
 
226 
 
 ANIMAL PHYSIOLOGY. 
 
 [LESSON 67. 
 
 FIG. 350. 
 
 Muscular fibre cleaving 
 transversely. 
 
 general appearance of the fibre will indicate a breaking up of the 
 entire structure into small dice, or square cells containing discs. 
 
 997. It is always uncertain in which direction a muscle will pre- 
 fer to split whether in the direction of its longitudinal elements, 
 the fibrillse, or in the direction of the transverse lines the cells. 
 A representation of cleavage in the latter direc- 
 tion may be seen at Fig. 350. 
 
 998. It has been remarked that the elements 
 of a muscle (fibres) are connected to each other 
 by areolar tissue; the elements of a fibre (ultimate 
 fibrillse) are similarly connected ; but a fibre is 
 enveloped in a distinct and characteristic tissue 
 the myolemma (sheath of the muscle), or 
 simple membrane in the animal kingdom. 
 
 999. This sheath is quite distinct from areo- 
 lar, or any other tissue. Its existence can easily 
 be demonstrated in any muscular fibre by sub- 
 jecting it to the action of fluids, which occasion 
 
 a swelling of its contents ; such is the effect of acids and alkalies, and 
 the result may be obtained by citric and tartaric acids, or by potash. 
 1000. There is no reason to believe that the myolemma is per- 
 forated, either by nerves or capillary blood-vessels ; it rather seems 
 
 to present an impenetrable barrier 
 between the real elements of muscu- 
 lar structure and the surrounding 
 parts. 
 
 1001. Muscular tissue, properly 
 so called, is extra (non) vascular ; for 
 its fibres are not penetrated by ves- 
 sels ; and the nutriment required for 
 its growth must be drawn by absorp- 
 tion through the myolemma. 
 
 1002. Still, the substance of mus- 
 cle, as a whole, is remarkably vascu- 
 lar ; the capillary vessels being dis- 
 
 a. Artery; 6, tributed in parallel lines, running in 
 the direction of the fibres, and united 
 by transverse branches in the minute interspaces between the fibres ; 
 so that, in all probability, there is no fibrilla which is not in close 
 relation to a capillary (Fig. 351). 
 
 1003. The striped muscles, or muscles of animal life, as they 
 
 FIG. 351. 
 
 c, Capillaries. 
 
LESSON 67.] 
 
 MUSCULAR FIBRE. 
 
 227 
 
 852. 
 
 are called, in contradistinction to the non-striped muscle, or muscle 
 of vegetative or organic life, 
 are, of all the tissues except the 
 skin, most abundantly supplied 
 with nerves. These, like the 
 blood-vessels, lie on the out- 
 side of the myolemma of the 
 several fibres ; and their influ- 
 ence must consequently be ex- 
 cited through it. 
 
 The general arrangement 
 of the nerves is shown in Fig. 
 352. 
 
 1004. The ultimate fibres 
 or tubes of the nerves, after is- 
 suing from the trunks, form a 
 series of loops, which return 
 either to the trunk from whence 
 they proceeded, or to an adja- 
 cent one. 
 
 1005. Having described the 
 
 general Structure of the Striped Distribution of nerves to muscle. 
 
 muscle, it only now remains to give its minute and ultimate characters. 
 
 * 1006. Obtain by tearing out the tissue an ul- FIG. 354. 
 timate fibril, or tear a fibre longitudinally, so that it 
 
 FIG. 353. 
 
 Muscle torn to show fibrillae. Ultimate fibrilla of mus- 
 
 cular fibre, Pig. 
 
 is held together only by a series of fibrillge, such as represented in 
 Fig. 353. 
 
 1007. Place it under the microscope, using for this purpose not less 
 than a fourth object-glass or a linear power of about 500 diameters. 
 
 1008. An appearance such as is shown in Fig. 354 will be seen. 
 
228 ANIMAL PHYSIOLOGY. [LESSON 68. 
 
 The fibrilla will now appear to be a delicate transparent tube, divid- 
 ed by well defined but very delicate transverse lines, by which the 
 structure is broken up into a series of symmetrical cells. 
 
 1009. In the centre of each cell is a solid, dark body the sarcous 
 element of Bowman. 
 
 1010. A fourth object-glass will only show a single transverse 
 line; but a superior twelfth object-glass will show that the line is 
 double divided by the least conceivable interval of space. 
 
 1011. If the structure be built up of cells (of which there ap- 
 pears no room for doubt), each cell should have an upper and lower 
 portion, and the approximation of two cells should show the top of 
 the one and the bottom of the other, and this is true. 
 
 1012. The transparent membrane around the sarcous element 
 has been named the sarcolemma (sheath of the fleshy element). 
 
 1013. Thus it will be seen that a primitive fasciculus is made up 
 of a number of fibrillae, running together in a longitudinal direction, 
 united together by areolar tissue ; when a fibre is formed, the entire 
 fasciculus is contained in the peculiar sheath, the myolemma. 
 
 Each fibrilla is again composed, as before stated, of an external 
 tubular sheath, the sarcolemma, in which is contained cells having 
 rectangular discs (sarcous elements) enclosed in chambers, or spaces, 
 formed by processes of the sarcolemma extending across the tube. 
 The fasciculi are united in bundles by areolar tissue, invested by the 
 myolemma to form the fibres of descriptive anatomy. 
 
 LESSON LXYIII. 
 
 MUSCULAR FIBRE, CONCLUDED. 
 
 1014. Such is the history of the structure of the muscular fibre 
 of animal life, and when compared with the representations of fresh- 
 water and marine algae, they will be seen to be identical. 
 
 1015. Thus Fig. 355 represents a very beautiful parasitic fresh- 
 water Alga, found upon the stems and leaves of the white and yellow 
 pond-lilies. The entire structure consists of a congeries of square- 
 shaped cells, each of which is a plant in itself, and containing an 
 equally square nucleus, or germinal spot. 
 
 1016. It should be remarked that the squareness of the cell, and 
 of the nucleus, form distinctive characters of this order of plants. 
 
LE3SOX 68.] 
 
 MUSCULAR FIBRE. 
 
 229 
 
 1017. The series of large, dark, circular masses (a) around the figure, 
 and near the margin, are the sporangia (spora, a seed ; aggos, a vessel ; 
 spore, that portion of a plant which performs the function of seeds). 
 
 FIG. 355. 
 
 Fresh-water Alga, parasitic on pond Lilies. 
 
 1018. In this order of plants propagation is effected by the spon- 
 taneous division of cells, and by spores, contained in what is called 
 " mother-cells " (perispores), the structures described (a) in the figure. 
 
 FIG. 857. 
 
 FIG. 856. 
 
 Callithalnaia Baileii. 
 
 Alga, from Barbadoes. 
 
 1019. In a beautiful Marine Alga, Callithalmia Baileii, its 
 specific name, in honor of the late Professor Bailey, of West Point, 
 
230 
 
 ANIMAL PHYSIOLOGY. 
 
 [LESSON 69. 
 
 FIG. 858. 
 
 we find an approximation to the structure (ultimate) of muscular 
 fibre (Fig. 354). The plant consists, like all the algae, of a congeries 
 of cells of exceedingly variable size, depending upon their maturity. 
 
 1020. A bud is shown, made up of cells equally variable in 
 size. In the interior of all these cells, without exception, is a nu- 
 cleus, of a reddish brown color, always bearing a close relation to 
 the size of the cell containing it (a). 
 
 1021. In another marine alga, from the Island of Barbadoes 
 (Fig. 357), we appear to be gazing upon a very highly magnified 
 ultimate fibre of the Pig. The arrangement of the longitudinal 
 lines, indicating ultimate fibrillse, is perfect, and the cells, somewhat 
 longer in one diameter than in the transverse one, and containing 
 the (as if) sarcous elements (a), renders the illusion as satisfactory 
 as can well be desired. 
 
 1022. But a still closer approximation is in store for us ; in 
 Lake Michigan, at Chicago, may be found, in great abundance, a 
 remarkably delicate fresh-water alga. Like all its kindred, it ex- 
 hibits, at the same moment, 
 every stage of development. 
 Small, detached portions of 
 this plant are extremely grace- 
 ful in the general arrangement 
 of their parts, as will be seen 
 by reference to the figure (Fig. 
 358). 
 
 1023. This plant, collected 
 in the height of summer, gave 
 indication of its amazingly ra- 
 pid growth, all the cells, devoid 
 of nuclei, indicating new cells ; 
 the cells of the stem, how- 
 ever, are more mature than 
 those of the branches, and 
 each one contains a nucleus 
 (a). 
 
 1024. It is only necessary 
 to refer the reader back (Fig. 
 354) to the highly magnified 
 view of the ultimate fibrilla 
 of muscular fibre, and making 
 
 Alga from Lake Michigan, Chicago. due allowance for the dig . 
 
LESSON 69.] MUSCULAR FIBRE. 231 
 
 parity of size in that figure and this, there can be no doubt that the 
 structure is the same. 
 
 1025. It is by no means the least remarkable fact that a tissue 
 purely animal, as is the muscular fibre of animal life, should exhibit 
 in its elements the true characteristics of a vegetable origin, and, still 
 more, of a lowly vegetable, such as an alga, but here we may trace 
 a distinct connection between the lowest plants and even the highest 
 animals. 
 
 1026. The ultimate element of a muscle, therefore, is a single 
 nucleated cell, such as forms the sole element of thousands of plants. 
 
 1027. Neither does the analogy end here, for it is well known 
 that in muscular fibre the cells are firstly formed, and the nucleus 
 (sarcous element) subsequently placed therein. 
 
 1028. It is highly probable that the sarcous elements of muscle 
 possess the same generative power as the nuclei of plants, and that 
 the tissue is extended by the subdivision of the sarcous element, and 
 the cell containing it. 
 
 1029. Very thin transverse sections of muscle show merely a 
 series of minute round dots the sarcous elements each one being 
 surrounded by a small circular white ring, de- Fl(J 
 
 noting the position of the rectangular body 
 within the tube (Fig. 359). 
 
 1030. The muscles of organic life, or vol- 
 untary muscles, as they are called, differ in 
 
 structure from the preceding. Transverse Action of 
 
 1031. They form a closer and more com- muscle> 
 
 pact tissue, and are far more difficult to manipulate with than the 
 muscles of animal life. 
 
 1032. It sometimes happens that their size is less than the fibres of 
 the striped muscle, although in some animals the contrary is the fact. 
 
 1033. These plain, non-striated fibres, are arranged like the 
 fibres of the other muscles, in a parallel manner, into bands, or 
 fasciculi ; but the fasciculi are usually woven into a network not 
 having any fixed points of attachment. 
 
 This is the nature of the muscular coat of the ossophagus, sto- 
 mach, intestinal canal, &c. ; it also occurs in most of the large gland 
 ducts, and in the iris (curtain of the eye). 
 
 1034. The Heart is composed of various forms of muscular fibre ; 
 some being distinctly striated, others quite plain, and others of in- 
 termediate character. 
 
 1035. The chief characteristic form of the non-striped muscular 
 
232 
 
 ANIMAL PHYSIOLOGY. 
 
 [LESSON 69. 
 
 FIG. 
 
 fibre consists in certain nodosities (bullae), developed at certain inter- 
 vals, and these are found to contain a nucleus. 
 
 1036. To render this latter fact apparent, it is 
 frequently desirable to employ acetic acid, but prep- 
 arations are not uncommon which have not been 
 subjected to the action of any re-agent, but in which 
 the nuclei are well seen. A figure of the non-striped 
 fibre is given (Fig. 360). 
 
 1037. The true structure of muscular fibre, as 
 revealed by the microscope, was first published in 
 the Philosophical Transactions, by Mr. William 
 Bowman, and that account has been made available, 
 in addition to original observations and preparations. 
 
 Non-striped mus- 
 cular fibres. 
 
 LESSON LXIX. 
 
 COMPOUND TUBULAR TISSUES, CONTINUED. NERVOUS SYSTEM. 
 
 1038. The late Baron Cuvier applied himself to correct the 
 errors in the classification of Animals which had been handed down 
 to us by Aristotle, the Father of Natural History, altered, but not 
 improved, by Linnaeus, and descended to our own times. 
 
 1039. To this end he devoted much time and untiring labor to 
 the dissection of the nervous systems, especially of the Invertebrate 
 animals. The result of these labors was, the division of the entire 
 animal kingdom into four primary divisions, or sub-kingdoms. 
 
 1040. Notwithstanding that the structure of the nervous system 
 really formed the basis of his classification, he contented himself with 
 the prominent external characters, as the means of designation of 
 his three lower classes, and only in the first class is an internal 
 character adopted. 
 
 1041. Thus the animal kingdom consisted, according to this 
 author, of the following divisions : 
 
 VERTEBRATA, . ARTICULATA, 
 
 MOLLUSCA, RADIATA. 
 
 1042. All the animals of the first class possess a bony vertebral 
 column, for the transmission and protection of the spinal chord. 
 
 1043. The MOLLUSCOUS animals were so called from the general 
 softness of their bodies, such as slugs, snails (marine, fresh-water, 
 and terrestrial), the inhabitants of bivalve (bis, two) and univalve 
 
LESSON 69.] NERVOUS SYSTEM. 233 
 
 (unus, one) shells, and the many forms of naked similar creatures 
 found in the ocean. 
 
 1044. The ARTICULATA have their bodies composed of a variable 
 number of distinct rings, or segments, jointed to each other, such as 
 Lobsters, Insects, Centipedes, Worms, &c. 
 
 1045. The RADIATA are so called from the several members of 
 the body radiating from the central portion, as in the Star-fishes. 
 
 1046. Dr. E. E. Grant, of Edinburgh, offered, some thirty years 
 ago, a classification of the animal kingdom which should be based 
 upon the development of the nervous system alone. Hence the new 
 classification, as compared with Cuvier's, stood thus : 
 
 1047. Cuvier. Grant. 
 VERTEBRATA, SPINI-CEREBRATA. 
 MOLLUSC A, CYCLO-GANGLIATA. 
 ARTICULATA, DIPLO-NEURA. 
 EADIATA, CYCLO-NEURA. 
 
 1048. The Oerebro-spinal (brain, spine) axis of man, and all 
 Vertebrates, originated the expression by which Grant designates 
 this sub-kingdom. 
 
 1049. The Mollusca were assumed by this author to possess a 
 nervous chord which surrounded the oesophagus, and upon which 
 ganglia were placed ; hence Cyclo-gangliata (circle ; ganglions.) 
 The nervous system of Cuvier's Articulata is found to consist, pri- 
 marily, of a double nervous chord, hence Diplo-neura (two ; nerves), 
 but on which ganglia are more or less found. 
 
 1050. The last sub-kingdom, the Radiata of Cuvier, presents (in 
 the Star-fishes, according to Tiedemann) a nervous ring surrounding 
 the oral aperture, but without any ganglion, therefore Cyclo-neura 
 (circular nerve). 
 
 1051. This classification was unquestionably an advance; but 
 another man, younger than Grant, and newer to science, desired to 
 prove the facts upon which the latter system was founded, and this 
 man was Owen. 
 
 1052. With regard to the Vertebrate division but little could be 
 done Cuvier's characters had covered the ground, and the nervous 
 system was found to be arranged on a uniform plan. 
 
 1053. However, in place of the " Spini-cerebrata" of Grant, Owen 
 proposed Myalencephala, as somewhat more expressive, the word 
 being derived from muelos, marrow, and egkephalon, brain. 
 
 1054. When the learned professor examined the Molluscous ani- 
 mals, he found Grant's character to fail ; in this class a nervous 
 
234 ANIMAL PHYSIOLOGY. [LESSON 70, 
 
 ring, beset wiih ganglia, is not found, except in rare cases ; it is a 
 nervous commissure (or band) connecting the cephalic ganglia, and 
 passing, not around, but behind the oesophagus. Then the pedal 
 ganglia (in those molluscs possessing a foot) and the branchial ganglia 
 are variously disposed now in one place, now in another hence 
 Owen, with far greater propriety, called Cuvier's Mollusca, Hetero- 
 gangliata (eteros, other ; genos, kind). 
 
 1055. The designation of the next sub-kingdom, by Owen, as 
 compared with Grant, is of less consequence ; and whether we ex- 
 press the " double nervous chord " with Grant, or speak of the sym- 
 metrical arrangement of the ganglia in this class, with Owen, who 
 calls them, from the latter circumstance, Homogangliata (omes, the 
 same; genos, kind), matters not, either expression being equally correct. 
 
 1056. We come to the last division of the animal kingdom, Ea- 
 diata of Cuvier, Cyclo-neura of Grant. 
 
 1057. Owen is content to take the statement of Tiedemann in re- 
 lation to the Star-fishes ; moreover, he has a preparation of Asterias 
 papposa, in the college Museum, prepared by the hand of the immor- 
 tal Hunter, but whether the author designed it to represent the ner- 
 vous system (which it certainly does not), or a portion of the vascu- 
 lar system (which it assuredly does), is left to conjecture. 
 
 1058. For those animals of the Radiate division in which Owen 
 believes a nervous system has been recognized, he proposes the word 
 Nematoneura (nema, a thread; neuron, a nerve). But in common 
 with many others, he is by no means satisfied that a nervous system 
 has been discovered in some of the class of Cuvier's Radiata ; and for 
 these he proposes a very significant designation Acrita, confused. 
 
 1059. The lower animals exhibit all the manifestations of a ner- 
 vous system, whether it can be detected or not. 
 
 1060. It is presumed, therefore, to exist, but under such circum- 
 stances that even the microscope fails to detect it as an independent 
 organism it is diffused or confused, and hence the expression is a 
 good one. 
 
 LESSON LXX. 
 
 NEBVOUS SYSTEM, CONTINUED. 
 
 1061. The classification of the three first classes of the animal 
 kingdom, especially by the last authority, is undeniably good ; much 
 doubt exists, however, as to whether a nervous system really exists 
 in any individual of the last (Radiata) or not. 
 
LESSON 70.1 NERVOUS SYSTEM. 235 
 
 1062. John Hunter left a preparation in his Museum of Asterias 
 papposa (a many-rayed Star-fish) ; a white, delicate ring is seen sur- 
 rounding the oral (mouth) aperture, from which a series of white 
 chords are traced into the several rays ; this has been assumed, by his 
 successors, to be the nervous system Hunter's notes, in relation to 
 his preparations, having been destroyed. 
 
 1063. Subsequently, Tiedemann published a valuable monograph 
 on the Echinodermata (prickly-skinned animals, in which class the 
 Star-fishes are included). He gave a description, accompanied by 
 beautiful figures, of the anatomy of the common five-rayed Star-fish 
 Asterias rubens and amongst the tissues figured was the nervous sys- 
 tem, a copy of which is appended (Fig. 361). 
 
 Here a white ring is distinctly seen sur- 
 rounding the oral aperture, and distributing 
 three branches to each of the five rays. 
 
 1064. He also described the vascular sys- 
 tem in the following remarkable words : " The 
 vessels which absorb the chyle from the di- 
 gestive sac, terminate after a series of reticu- 
 late anastomoses, in a circular trunk, which Nervous system of Asterias. 
 likewise receives branches from the radiated cceca. The venous cir- 
 cle communicates by means of a dilated tube, regarded as a rudimen- 
 tal form of heart, with an arterial circle surrounding the mouth, 
 from which branches diverge to the rays, and other parts of the body." 
 
 1065. Authority is not wanting to confirm the fact that the vascu- 
 lar system, so accurately described by Tiedemann, is the same structure 
 which himself and others have mistaken for a nervous system. 
 
 1066. In the uninjected state of the animal, the vessels are filled 
 with white, coagulated blood, and in roundness, fulness, color, and 
 general appearance, accurately simulate nerves. 
 
 1067. From all that is known of the necessities of a nervous 
 system, it appears to be quite improbable that any such condition 
 exists in the animal kingdom as that alleged to belong to the Kadiata. 
 
 1068. It is extremely difficult to understand a nervous system, 
 consisting only of a series of simple chords unprovided with a sin- 
 gle nervous centre, or ganglion. 
 
 1069. Now a ganglion is a knot of nervous matter ; a brain of a 
 kind ; a centre of reinforcement ; and the probability is that no ner- 
 vous system exists, without, at least, one ganglion. If this be true, 
 the nervous system in the Radiata has yet to be discovered. 
 
 Nerves possess distinct functions : thus, a nerve of sensation has 
 
236 ANIMAL PHYSIOLOGY. [LESSON 71. 
 
 no power to direct or organize motion ; neither is a motor nerve en- 
 dowed with sensation. 
 
 A nerve of vision cannot perform the function of smell, taste, 
 hearing, or touch ; neither can the nerves of one organ assume the 
 function of the nerves delegated to another organ; each has its own 
 duty to perform, preserves its individuality, and is so far distinct. 
 
 1070. A nerve and a ganglion, as will be hereafter seen, possess, 
 each of them, a peculiar and definite structure, and the only way to 
 be sure of their presence is to cut off a small portion, and examine 
 it with the high power of a compound achromatic microscope. 
 
 1071. Plants assimilate food, continue their kind, and the lower 
 orders of them are even endowed with locomotion ; the Venus' Fly- 
 trap, and the Sensitive Plant would seem to offer the indications 
 of a nervous system ; so far as is really known, the lower animals 
 appear to occupy a similar position with plants. 
 
 1072. From the foregoing statement, it will be advisable to com- 
 mence the inquiry into the nature and condition of the nervous sys- 
 tem, and its mode of development, in the Articulate sub-kingdom, all 
 the individuals included in this section being unmistakably endowed 
 therewith. 
 
 LESSON LXXI. 
 
 NEBYOTJS SYSTEM IN THE AETICULATA. ENTOZOA ANNELLIDA. 
 
 1073. In the lowest animals of this sub-kingdom, the parasitic 
 Entozoa, the nervous system is very imperfectly developed, and, from 
 their position within the bodies of other animals, but little required. 
 
 1074. In the intestinal parasite Strongylus gigas, a slender ner- 
 vous ring surrounds the beginning of the gullet, and a single chord 
 is continued from its inferior part, and extends in a straight line 
 along the middle of the ventral aspect to the opposite extremity of 
 the body, where a slight swelling (ganglion) is formed, immediately 
 anterior to the posterior part of the body, which is surrounded by a 
 loop, analogous to that with which the nervous chord commenced. 
 The abdominal nerve is situated internal to the longitudinal muscular 
 fibres, and is easily distinguishable from them with the naked eye, by 
 its whiter color, and the slender branches which it sends off on each 
 side. These transverse twigs are given off at pretty regular inter- 
 vals of about half a line, and may be traced round to nearly the op- 
 posite side of the body. 
 
LESSON 71.] NERVOUS SYSTEM. 237 
 
 1075. In the Ascarides, a dorsal nervous chord is continued from 
 the oesophageal ring, down the middle line of that aspect of the body 
 corresponding to the ventral chord on the opposite aspect. 
 
 1076. The nervous system of the ANNELLIDA, or red-blooded 
 worms, as they are commonly called, presents a marked advance be- 
 yond its condition in the white-blooded parasitic worms ; it consists 
 of a double median central chord, or chain of small ganglions, ex- 
 tending from one end of the body to the other ; the two chords di- 
 verge anteriorly to allow the passage of the oasophagus, and again 
 unite above that tube to form a distinct, though small, bilobed ce- 
 phalic ganglion. 
 
 1077. Most of the Annellides are provided with ocelli (eyes), and 
 in many of them the head supports soft cylindrical tentacles (feel- 
 ers), called (improperly) antennw : they are pj& g62 
 obviously organs of touch, but differ from the 
 
 antennae of insects in the absence of joints. 
 
 1078. In this class the nervous system has 
 reached a higher type and more constant plan 
 of arrangement. 
 
 1079. It always commences by a symmet- 
 rical bilobed ganglion, which, both by its situ- 
 ation above the mouth and the parts which it 
 supplies, merits the name of brain, which it 
 has generally received. 
 
 1080. In the medicinal leech there are sent 
 off from this ganglionic centre (Fig. 362, a), 
 ten distinct optic nerves (6, 5), Besides many 
 smaller filaments to the integument and other 
 parts of the head ; each optic nerve or fila- 
 ment terminates by expanding upon the base 
 of a black eye-speck or ocellus, ten of which 
 may be distinguished by the aid of a lens of 
 moderate magnifying power, dotting, as it were, 
 at equal distances, the upper margin of the 
 expanded suctorial lip. 
 
 1081. The principal nerves which arise 
 from the brain of the leech are what may be 
 called analogically the crura, which diverge as 
 they descend to embrace the oasophagus, and 
 are often called the oesophageal chords ; they 
 
 . , , . . . . , , Nervous system of the 
 
 then converge and reunite to join the large medicinal Leech. 
 
238 ANIMAL PHYSIOLOGY. [LESSON 71. 
 
 sub-oesophageal ganglion (c). From this ganglion the muscles of 
 the three serrated jaws, as well as the principal muscles of the oral 
 (mouth) sucker, derive their nervous influence. Those who have 
 watched the vigorous workings of this part in a hungry leech, begin- 
 ning its feast, will not be surprised at the great development of the 
 nervous centre of the suctorial and maxillary mechanism. 
 
 1082. Two chords, in such close apposition as to seem a single 
 nervous band, are continued from the sub-03sophageal ganglion (sub, 
 under, beneath) along the middle of the under part of the abdomen, 
 attached to the ventral (ventre, belly) integument, and enclosed, as it 
 were, by the great ventral vein. Twenty-one equidistant ganglions 
 are developed upon these chords, which distribute their filaments to 
 the adjoining segments by two diverging trunks on each side. The 
 segments indicated by the external circular indentations of the in- 
 tegument are much more numerous than the ganglions. A simple 
 nervous filament extending from the 03sophageal ganglion along the 
 dorsal aspect of the alimentary canal, has also been detected in the 
 leech, and this forms the first trace of a distinct sympathetic nerve 
 as yet seen in the animal kingdom. 
 
 1083. In the earth-worm (angle-worm) the brain or supra-oeso- 
 phageal ganglion (supra, above) consists of two lateral lobes, which 
 send off small nerves to the proboscis, and the two large connecting 
 cords to the sub-o3sophageal ganglion. The two ventral nervous 
 trunks are more distinct from each other than in the leech, but the 
 ganglions are relatively smaller and more numerous, corresponding 
 in number with the segments of the body. 
 
 1084. In the Nereis, a marine worm, some species of which grow 
 to the extent of two feet in length, the abdominal ganglions are more 
 distinctly bilobed than in the earth-worm, and the supra -oasophageal 
 ganglion is relatively larger, having to furnish nerves to both an- 
 tennae and ocelli. The pairs of ganglions developed upon the ven- 
 tral chord correspond with the segments of the body in number, and 
 are very close together. 
 
 1085. In the species which attains the great length indicated, 
 Eunice gigantea, the nervous system consists of upwards of 1,000 
 ganglia. 
 
 In the Epizoa, the nervous system of Actheres percarum (Fig. 
 1204) possesses a single cephalic ganglion, placed on the ventral sur- 
 face, from which are distributed two principal chords (g, g) } extend- 
 ing along the under surface of the body. 
 
LESSON 72.] 
 
 NERVOUS SYSTEM. 
 
 239 
 
 FIG. 
 
 LESSON LXXIL 
 
 NERVOUS SYSTEM OP CIREIPEDIA, AND MYRIOPODA. 
 
 1086. In the Cirripedia (cirrus, a curl ; pes, a foot), commonly 
 called Barnacles, or Acorn-shells, the nervous system is very simple. 
 
 1087. In the Lepas vitrea the oesophagus is surrounded by a 
 white oval ring, at the sides of which are placed the small ganglions 
 which supply the first pair of feet. The ring is completed below by 
 the ganglions of the second pair of feet. 
 
 The fifth and sixth pairs of ganglions are 
 approximated to each other ; there is no 
 cerebral ganglion, but filaments are given 
 off from the supra-oasophageal loop to the 
 peduncle and sides of the head (see Fig. 
 363). Two of these branches pass to a 
 small ganglion on either side, near the 
 stomach, from which the digestive organs 
 are supplied; the tubular extensile tail 
 receives the last two pairs of nerves. The 
 neurolemma (nerve sheath) is stained by a 
 dark brown pigment in the Lepas vitrea. 
 
 1088. The class Myriapoda (many 
 feet) contains the Wood-lice, lulidce (for 
 which there is no common name), and Cen- 
 tipedes (hundred legs). Both these latter 
 animals are found at the roots of trees ; 
 the lulus is about an inch in length (in 
 
 this country), the body very round, covered by a brittle, black, shin- 
 ing skeleton ; its legs numerous, having two pairs on each segment 
 of the body, and remarkably short. Some species, if touched, throw 
 themselves on their side, and curl into a close ring. 
 
 1089. In these animals the condition of the nervous system is of 
 much general interest. In them the corresponding ganglions of the 
 abdominal chords are much less conspicuous than in the earth-worms, 
 and the whole central axis of the nervous system, continued from the 
 brain, is almost as devoid of partial swellings as the spinal chord of 
 the apodal (without feet) vertebrates. 
 
 1090. A figure of the brain and chief distribution of the nerves, 
 from an original preparation of lulus, is shown at Fig. 364. 
 
 1091. The cephalic ganglion (a) of the lulus, is transversely 
 
 Nervous system, Lepas vitrea 
 
 (glassy). 
 
 a, Nervous ring, surrounding 
 the oesophagus. 
 
 5, c, Parallel nervous abdomi- 
 
 nal chords. 
 
 6, c, <?, e, f, Ganglia, supplying 
 
 nerves to the curled feet. 
 
240 ANIMAL PHYSIOLOGY. [LESSON 72. 
 
 elongated, and obscurely divided by a slight median indentation into 
 two side-lobes ; its upper and latter extremities are prolonged out- 
 wards into the optic lobes (c, c), which resolve themselves half-way 
 towards the compound eye into a plexus of filaments (optic nerves) 
 for its several divisions. Two separate antennal nerves, conjectured 
 by Straus Durcheim to be motory and sensory (d, d), are sent off on 
 each side below and in front of the optic nerves to the short, seven 
 
 FIG. 3&L 
 
 Brain and principal nerves of lulus. 
 
 jointed antennae. On each side, also, but below the antennal nerves, 
 arise the two nerves (b), united together by an anastomosing branch, 
 which supply the mandibles. 
 
 1092. The thick cssophageal chords (g) are continued from the 
 posterior and inferior angles of the brain ; and, though apparently 
 simple, consist essentially of two chords, which become separate at 
 the lower part of the pharynx ; the anterior chord girts the pharynx 
 by a transversely oval ring, formed by the confluence with its fellow ; 
 the posterior and normal columns converge, at an acute angle back- 
 wards, blend together, and expand into the commencement of the 
 abdominal nervous trunk ; thus enclosing the oesophagus by a second 
 and looser collar. 
 
 1093. The stomato-gastric, or sympathetic nerves (/), which 
 arise from the posterior part of the brain, immediately form a third 
 slender ring (e) about the cssophagus, from the middle of the upper 
 part of which the trunk of the sympathetic system is continued a 
 short way back upon the stomach, when it divides ; the two divisions 
 diverge at an angle of 45, bend abruptly backwards, and run parallel 
 with each other along the dorso-lateral parts of the wide and straight 
 alimentary canal. 
 
 1094. Two large nerves (h) are sent forwards from the beginning 
 of the thick sub-03sophageal or ventral chord (i), to supply the max- 
 
LESSON 72.] NERVOUS SYSTEM, 241 
 
 illse, which form the under lip ; the nerves of the two single pairs of 
 feet, belonging to the thoracic segments, next arise, and afterwards 
 the more numerous minute nerves to the little feet, which, by their 
 articulation to the segments in double pairs, indicate pw} gg5 
 such segments to be merely a confluence of two seg- 
 ments. The simplicity of the abdominal chords cor- 
 responds with the close approximation and great num- 
 bers of the organs from which they receive impres- 
 sions, and to which they transmit stimuli. 
 
 1095. In the Polydesmus maculatus (spatted), 
 (Fig. 365), the segments are fewer and larger than in 
 the lulus, and their lateral margins are produced; 
 each, however, with the exception of the first three, 
 which answer to the thorax in insects, supports two 
 pairs of legs but these are longer than in the lulus. 
 
 1096. The abdominal nervous chords show as lit- 
 tle trace of their median separation as in the luli, 
 swelling into two slight enlargements (a, a) opposite 2JA 
 each of the abdominal segments ; two nerves are sent 
 
 off from either side of each enlargement, and the an- BJ1 
 
 terior of these four pairs of nerves is directed at an 
 
 acute angle forwards and outwards to the stigmata; 
 
 it is doubtful, however, if these be nerves analogy 
 
 seems to indicate that they are arteries ; the remaining pairs supply 
 
 the muscles of the segment, and the legs, and are of equal size. 
 
 1097. In the Centipede (Scolopendra), a series of equal and equi- 
 distant ganglia is developed upon the" ventral surface of the two ab- 
 dominal chords. Only in the first and last of the abdominal gangli- 
 ons can any modification of size be detected. The anterior or 
 sub-cesophageal ganglion is larger than the rest, having to supply 
 the modified legs which perform the function of jaws and underlip ; 
 the chords diverging as they escape on each side of the oesophagus, 
 enclose it by uniting with the large bilobed brain above. The nerves 
 from this part (the brain) supply the large antennae and the aggre- 
 gated ocelli ; in other words, the organs of special sense. 
 
 1098. Even in animals so low in the scale of being as the class 
 Myriapoda, we find the full recognition of the leading physiological 
 divisions of a nervous system in the higher animals. 
 
 1099. Thus the supra-cesophageal ganglion or brain in these crea- 
 tures, so far corresponds with the cerebrum of Man, that it is sub- 
 servient to the functions of the special organs of sense, and is the 
 
 16 
 
242 ANIMAL PHYSIOLOGY. [LfcSSON 73. 
 
 centre whence voluntary impulse may be directed along the non- 
 ganglionic tracts of the nervous axis, and to which ordinary sensa- 
 tion may be transferred by similarly uninterrupted nervous filaments. 
 So, too, we find the function of the cerebellum simulated by the large 
 sub-cesophageal mass, which originating the nerves analogous to the 
 fifth pair in man, and the higher mammalia, for the masticating 
 organs and other parts of the head, may be regarded as analogous to 
 the base of the brain. 
 
 1100. The stomato-gastrie (sympathetic) nerves, complete this 
 complicated system. 
 
 LESSON LXXIII. 
 
 NERVOUS SYSTEM IN CEUSTACEA. 
 
 1101. In the numerous and diversified class of Crustacea, every 
 condition of the nervous system is met with, from that of the lowest 
 Annellide, or the earliest larval state, where scarcely a filament is yet 
 perceptible in the place of the nervous columns, to that concentration 
 of the nervous ganglia around the oesophagus, which connects the 
 highest Articulata with the Mollusca. 
 
 1102. The supra-oesophageal ganglia (brain) are generally larger 
 than those of Arachnida, and smaller than those of Insects ; they are, 
 for the most part, united into a single cerebral ganglion, devoted 
 chiefly to the large organs of the senses, and their nerves unite with 
 the sympathetic, as in Insects. 
 
 1103. The ganglia of the cephalo-thorax (head-chest, which in 
 these animals is soldered into one piece) vary much in their number, 
 magnitude, and degree of approximation, according to the form of 
 that part of the trunk, and the size of the several pairs of legs. 
 
 1104. Many of the lower Crustacea have the segments nearly 
 equally developed from the anterior to the posterior extremity of the 
 trunk, and this equal development is seen also in the nervous co- 
 lumns and ganglia of these segments, as shown in the subjoined figure 
 of the nervous system of Talitrus locusta, or Sand-hopper, so com- 
 mon on the sea-shore (Fig. 366). 
 
 1105. The slender longitudinal columns, and the minute ganglia 
 along their course, here remain distinctly separated from each other 
 by a small space on the median plain ; the ganglia are nearly of the 
 same size from the first pair (a), above the oesophagus (&), to the 
 caudal pair (c), and the pairs are almost equidistant along the whole 
 
LESSON 73.] NERVOUS SYSTEM IN CRUSTACEA. 
 
 243 
 
 FIG. 366. 
 
 FIG. 36T. 
 
 Nervous system of the 
 Cymothoa. 
 
 Nervous system of 
 Sand-hopper, a, Ce- 
 phalic ganglia ; 5, CE- 
 sophagus ; c, Cau- 
 dal ganglia. 
 
 trunk, in a longitudinal di- 
 rection. 
 
 1106. The same form of 
 the nervous columns is seen 
 in the highest Crustacea, 
 while yet in their embryo 
 condition in the ovum. In 
 the short and broad trunk 
 of the Cymothoa, where the 
 legs are still equally devel- 
 oped along the sides of the 
 body, the nervous columns 
 (Fig. 367) have already ap- 
 proximated to touch each 
 other on the median plane, 
 and the ganglia on the two 
 sides have coalesced to form 
 a single chain along the 
 middle of the abdominal 
 surface of the body. The 
 ganglia are still nearly equi- 
 distant, and equally developed along the columns ; but where the 
 minute posterior segments occur, the ganglia are closer 
 
 together and smaller in size. The transverse concen- 
 tration of the columns and ganglia towards the median 
 plain, thus seen in the lowest Crustacea, is succeeded 
 in higher species by a longitudinal movement of the 
 nervous matter, directed, as we have seen in inferior 
 classes of Articulata, chiefly to two points of the body, 
 the head and the thorax, from which the largest and 
 most important appendices of the body, whether for sen- 
 sation, mastication,or progressive motion, are developed. 
 
 1107. In the long-tailed Crustacea, as the Lobster 
 (Astacus marinus), Cray-fish (Astacusfluviatilis),^ 
 only is the sympathetic system of nerves derived from 
 the lateral ganglia of the stomach, but the ganglia 
 and columns have coalesced and met transversely 
 along the whole body; in the region of the thorax, 
 from which the five pairs of large extremities are de- 
 veloped, the ganglia have enlarged in size above those 
 of the post-abdomen, and considerably approximated 
 to each other in a longitudinal direction (Fig. 368). 
 
 FIG. 368. 
 
 Nervous system 
 of the Lob'ster. 
 
244 
 
 ANIMAL PHYSIOLOGY. 
 
 [LESSON 74. 
 
 In the higher Articulata the segments first coalesce on the anterior 
 and posterior portions of the trunk, and hence the enlarged form 
 presented by their cephalic and caudal ganglia, independent of the 
 great size often attained by the appendices developed from the 
 terminal parts of the body. 
 
 The cephalic ganglion is shown at a, and this, together with 
 the ganglia which succeed it, down to b, is of larger size than the 
 abdominal ganglia, with the exception of the last (c),) which in this 
 form of the nervous system always attains increased size. 
 
 1108. The most concentrated form of the nervous system met 
 with in the Crustacea, is that found in the short and broad trunks 
 of the Crabs (Fig. 369), where all the symmetrical ganglia of the 
 columns are collected into two masses, the one in the head, and 
 the other in the centre of the cephalo-thorax ; the sympathetic nerves 
 
 are confined to a nervous band around 
 the wide ossophagus. The supra-oeso- 
 phageal ganglion, or brain, is compara- 
 tively small in the Crabs, from the 
 smallness of the cephalic appendices, 
 which it supplies with nerves. 
 
 1109. The infra-cesophageal mass 
 is of great size, consisting of the whole 
 chain of ganglia, which was originally 
 extended along the body behind the 
 oesophagus, fused into one mass. It 
 sends out* numerous branches to the 
 
 surrounding viscera, and to the five 
 Nervous system, Crab. paipg Q legg which radiate from around 
 
 that point, and the columns are prolonged backwards, ramifying along 
 the short slender post-abdomen, as a simple nervous chord. 
 
 FIG. 369. 
 
 LESSON LXXIY. 
 
 NERVOUS SYSTEM IN INSECTS. 
 
 1110. In Insects the nervous system differs chiefly from that in 
 the Myriopoda in having its primary divisions more definitely devel- 
 oped, and in manifesting degrees of concentration corresponding with 
 the increase of bulk and strength in particular parts of the trunk, 
 
LESSON 74.] THE NERVOUS SYSTEM IN INSECTS. 245 
 
 and in the locomotive organs appended thereto. Most Insects, how- 
 ever, commence their career as worms ; the high form which they 
 are ultimately destined to attain in the articulate series, is at first 
 marked by the guise of a red-blooded worm. 
 
 1111. The larvae, which present larger and more perfect seg- 
 ments, most of which are provided with legs or prolegs, have a gan- 
 glionic centre for each segment, and intermediate chords. 
 
 1112. This worm-like type of the nervous system can be seen in 
 any caterpillar, and an illustration is given (Fig. 370) of the nervous 
 system of the larva of the Goat Moth, Oossus ligniperda immor- 
 talized by the wonderful dissections of Lyonnet, and the engravings, 
 by his own hand, which gave effect to his labors as an Entomotist 
 (one who dissects insects). 
 
 The abdominal nervous columns of insects have been regarded 
 by Lyonnet, Straus, Dufour, and Chiaje, no less than by modern au- 
 thorities, as analogous to the brain and spinal chord of vertebrated 
 animals. There are at first thirteen pairs of approximated ganglia, 
 corresponding with the original segments, and extending along the 
 middle of the ventral surface of the body, and the oesophagus passes 
 downwards, perforating the connecting nervous columns between the 
 first and second pairs of ganglia ; in other words, the oesophagus in 
 insects passes through the centre of the divided brain ; the first 
 pair of ganglia, therefore, are swpra-cesophageal (above the oesopha- 
 gus), or cephalic, and all the succeeding ganglia of the columns are 
 beneath the alimentary canal. 
 
 1113. The ganglia, at first like those of the worm and centipede, 
 are nearly at equal distances, and of equal size, like the segments 
 themselves of the young caterpillar. The columns and ganglia, orig- 
 inally separate (see Fig. 366, of the nervous system of the Sand- 
 hopper, which, although a lowly crustacean, illustrates this point,) on 
 the two sides, early approximate transversely, and unite, and a slow 
 movement of the ganglionic matter is at length observed in a longi- 
 tudinal direction. These transverse and longitudinal movements 
 of the nervous matter proceed to a very variable extent, according 
 to the degree of metamorphosis from the larva condition, to which 
 the individual is subjected in the various adult forms of this class. 
 In insects, as in the Myriopods, the first and second pairs of ganglia 
 are contained within the head, and constitute, together, the brain ; 
 the succeeding pairs are generally placed near the anterior limits of 
 the segments to which they belong. The third pair of ganglia 
 placed in the prothorax (first division of the chest) appear to be 
 
246 ANIMAL PHYSIOLOGY. [LESSON 74. 
 
 generally smaller than the fourth ; and the fifth, in the mesothorax 
 (middle division of the chest), smaller than the sixth, contained in 
 the metathorax (last division of the chest). 
 
 1114. The ganglia contained in the abdomen, like the segments 
 of that part of the body, are generally the least altered by develop- 
 ment from their primitive condition ; in the Coleopterous insects 
 (Beetles), however, the majority of them become obliterated in the 
 progress of development, and the like occurs in many of the Hemip- 
 tera (Tree bugs). The last pair of ganglia are generally the first 
 to advance forward and unite with the penultimate pair in the larva 
 state. 
 
 1115. In the larva of a Lepidopterous insect (butterfly), the co- 
 lumns are lengthened, and the cephalic ganglia widely separated to 
 allow the oesophagus to pass between them. The first of these ganglia, 
 equivalent to the cerebrum of man, gives off the nerves for the sup- 
 ply of organs of special sense ; these amount in caterpillars to eight 
 pairs, in addition to the nerves which connect the upper with the 
 lower part of the brain ; the latter are called the crura. They like- 
 wise give off filaments to the small lateral ganglia (c) of the head, 
 and to the commencement of the sympathetic series of ganglia 
 (Fig. 370). 
 
 1116. Between all the succeeding pairs of ganglia, a solitary 
 branch is seen coming through the loop formed by the division of the 
 chords in the upper part of the figure ; it divides into two branches, 
 one passing to the orifice of the spiracle (breathing mouth) on the 
 right side, and the other to the like organ, on the left. These 
 branches invariably come off above the ganglia. 
 
 1117. Ninety years ago these structures were described by Ly- 
 onnet, as motor nerves, and the fact that their ramification was dis- 
 tributed to the muscles employee! in respiration, favored this opinion. 
 The opinions of Lyonnet were adopted and maintained by all suc- 
 ceeding authorities, but 
 
 1118. In the Limulus polyphemus, or King Crab, found in con- 
 siderable numbers on the Jersey coast, the heart agrees with the 
 figures given of the heart in Insects, i. e., a straight vessel, from the 
 anterior chamber, terminating in three vessels, two of which are later- 
 al, and descend down to the nervous ring surrounding the oesopha- 
 gus, the middle one being lost in the head : thence a branch passes 
 along the dorsal surface of the ganglionic ventral chord, invariably 
 giving off branches in front of each ganglion, in fact the motor 
 and as some authors have designated it, respiratory tract of Insects. 
 
LESSON 75.] NERVOUS SYSTEM IN INSECTS. 247 
 
 If a small pipe be tied in the heart, and injection (size colored 
 with vermilion) be thrown in, these so-called nerves will be demon- 
 strated as arteries. If the same experiment be made from the heart 
 (dorsal vessel) of a caterpillar, the like results will be obtained, and thus 
 establish the true character of this structure in Insects, Myriopods, 
 and the lower Crustacea, and demonstrate beyond all doubt that the 
 so-called motor, and respiratory nerves, in all these animals, are a 
 system of arteries. Being always filled, however, with white, coagu- 
 lated blood, in death, the main trunk from which the branches are 
 distributed lying upon the upper surface of the gangliated nervous 
 chord, and exceedingly minute and attenuated in structure, they 
 much more resemble nerves than arteries. 
 
 LESSON LXXV. 
 
 NEKVOUS SYSTEM OF INSECTS, CONTINUED; 
 
 1119. The individuals composing the articulate sub-kingdom 
 have their bodies divided into a series of more or less distinct rings, 
 or segments, arranged in a linear series. This disposition is more 
 apparent in those animals which exhibit lowly organization, that 
 is to say, the Worms, Myriopods, and the larval condition of In- 
 sects. 
 
 1120. Carefully examined, it will be seen that in structure, in- 
 ternally, these segments present merely a repetition of parts, and 
 this statement is equally true of the nervous system. 
 
 1121. In the centre of each segment of a Centipede,.OT a caterpil- 
 lar, a nerve-knot or ganglion is invariably found ;, from this nervous 
 centre the muscles of the segment obtain their supply of nervous im- 
 pulse ; the only exception to this rule is in regard to the superior 
 portion of the brain the supra-oesophageal ganglion where we find 
 the nerves solely distributed to the organs of special sense, and to 
 the development of the frontal ganglion, from whence the sympa- 
 thetic nerves arise. An illustration is given of the nervous system 
 of the caterpillar of the Goat Moth, Cossus ligniperda (Fig. 370), 
 copied from an original preparation. 
 
 1122. The bilobed ganglion, having a long transverse diameter 
 (a), is the supra- cesophageal ganglion, or brain ; the nerves dis- 
 
248 
 
 ANIMAL PHYSIOLOGY. 
 
 [LESSON 75. 
 
 FIG. 370. 
 
 Nervous system of Cossus ligniperdt 
 
 tributed from this portion of 
 the nervous system are given 
 to the organs of vision, feeling, 
 taste ; supplying all the organs 
 devoted to special sense. Two 
 branches arise from the anterior 
 (front) portion which terminate 
 in a small ganglion, from which 
 a delicate nerve arises. 
 
 1123. This nerve returns, 
 as it were, and was hence called 
 by its discoverer, Lyonnet, the 
 nervus recurrens, or recurrent 
 nerve ; it is distributed upon 
 the oesophagus and stomach, 
 where it terminates : this is the 
 stomato-gastric (mouth stom- 
 ach), or sympathetic nerve. 
 
 1124. The superior portion 
 of the brain is connected with 
 the inferior or sub-cesophageal 
 ganglion (&), by a pair of nerv- 
 ous chords, widely separated, 
 to admit the oesophagus (d), or 
 gullet, which passes through 
 this divided brain. The great 
 necessity for such an arrange- 
 ment of the nervous system in 
 any animal, by which it is ren- 
 dered imperative that the ali- 
 mentary canal should pass 
 through the centre of the brain, 
 is, that the superior portion of 
 it (the brain) must necessarily 
 be always placed in the vertex, 
 to supply the organs of special 
 sense with nerves. The mus- 
 cles of the jaws, &c., receive 
 their supply of nerves from the 
 inferior surface of the brain, 
 which, by the contrivance re- 
 
LESSON 75.] NERVOUS SYSTEM IN INSECTS. 249 
 
 sorted to, is on the same plane ; and lastly, the protection of the 
 bulk of the nervous system requires it to be transferred from the 
 dorsal to the ventral surface. 
 
 1125. From its function of distributing the nerves of sense, there- 
 fore, the brain requires to be placed in the superior part of the head, 
 adjacent to the organs which it is destined to supply with nerves. 
 For a like reason (proximity to the structures to be supplied with 
 nerves), and, as stated in the preceding paragraph, for superior pro- 
 tection, the remainder of the nervous system is placed upon the ven- 
 tral surface of the body, and this could only be accomplished by di- 
 viding the brain, and transmitting the alimentary canal through the 
 space thus formed. 
 
 1126. All the nerves which arise from the base of the brain are 
 motor in their function, and they are, therefore, distributed to the 
 muscles of the jaws. Nerves arise from the lower surface of the 
 sub-cesophageal ganglion, one on each side, which terminate in a 
 minute ganglion (c) called lateral ganglia ; from these a few delicate 
 nervous twigs arise, which are distributed to the muscles of the 
 throat. 
 
 1127. The first thoracic ganglion (e) is near the base of the 
 brain ; its nerves are distributed to the muscles of the segment to 
 which it belongs. ** ^ 
 
 1128. The second (/) and third (h) thoracic ganglia are remark- 
 able for their increased size, and the chords connecting them for 
 their great divergence. Between the loops thus formed a branch is 
 seen descending from the inferior surface of the ganglia respectively 
 (g, g), and giving off a branch right and left. 
 
 1129. This structure is continued throughout the entire nervous 
 system, the branches being invariably given off above the ganglions. 
 By careful dissection their ultimate branches may be traced to the 
 muscles of the respiratory organs, and hence they have been thought 
 to constitute a distinct respiratory tract, combining a motor func- 
 tion. They are not such, however, but simply a system of arteries, 
 and these are the vessels which have been injected from the heart in 
 Insects, and in the Limulus, as already described. 
 
 1130. The remainder of the nervous system is simply a repetition 
 of what has been already described, until we reach the terminal, en- 
 larged ganglion (&). This is called the caudal (tail) ganglion, and 
 is formed by the junction of the llth and 12th ganglions. 
 
 1131. The most important portion of the nervous system of any 
 animal is the brain, and we present a much magnified view of that 
 
250 ANIMAL PHYSIOLOGY. [LESSON 75. 
 
 organ as it appears in the same Caterpillar (Fig. 371), and the fol- 
 lowing is the description of the nerves proceeding from it, and the 
 organs to which they are distributed : 
 
 FIG. 371. 
 
 Brain of a Caterpillar (Cossus ligniperda). 
 
 A. Cerebrum, superior portion of the brain. 
 
 B. Cerebellum, inferior portion of the brain. 
 a, a. Nerves of the eyes. 
 
 &, &. Of the antennae. 
 
 e. Cord passing around the oesophagus, proceeding from the cerebrum. 
 <?, d. Cord connecting the cerebrum and cerebellum, 
 e, e. Nerves of the mandibles (upper jaws). 
 f,f. Nerves of the maxillae (under jaws). 
 g, g. Second connecting nerve of the under lip, of which the nerve of the mandible is a 
 
 branch. 
 
 0*, g*. First nerves of the under lip, which give off a branch, M, to the muscles of the lower 
 , jaws. (The branches of the second nerve of the lip, g, g, give off a branch for a 
 
 muscle, N.) 
 
 O, O. Nerves of the muscles of the upper jaws and antennae. 
 P, P. Nerves of the muscles of the upper jaws. 
 
 R. K. Nerves that distribute themselves at the posterior portion of the skull. 
 S. S. Nerves of the muscles of the neck, which pass into the thorax (chest). 
 V, V. Connecting cords of the cerebellum and first thoracic ganglion. 
 
 D. The frontal ganglion, formed by the two branches, E, E, whence the sympathetic 
 nerve, F, originates. 
 
 1132. It would be easy to present a further and more enlarged 
 view of the Cerebrum, chiefly for the more perfect demonstration of 
 those parts which are somewhat obscure, from the complexity of the 
 preceding figure, but want of space forbids it. 
 
 1133. It has been shown that in the larval condition of an insect 
 
LESSON 70.] NERVOUS SYSTEM IN ARACHNIDA. 
 
 251 
 
 the ganglia are remarkably symmetrical, with the exception of the 
 brain, each having to supply precisely the same nerves to the like 
 organic structures. 
 
 In the perfect insect, however, it is found that great absorption 
 has occurred of ganglions no longer required, and Fm S72 
 
 a corresponding deposition of nervous matter, to 
 increase the size of certain ganglia whose influ- 
 ence is imperative. In illustration of this fact, 
 the nervous system (in situ, Fig. 372), of the 
 natural size, is offered from the Blatta Ameri- 
 cana (American Cockroach). Here the abdomi- 
 nal ganglia (d) are minimized, and the thoracic 
 ganglia are largely but unequally developed. 
 
 1134. From these nervous centres it is that 
 the large and powerful superior (wings) and in- 
 ferior locomotive organs (legs) obtain the nervous 
 influence necessary to the performance of their 
 functions. The first thoracic ganglion (a) having 
 only to distribute nerves to the smallest pair of 
 legs, is the least in size ; the second thoracic 
 ganglion (b) has to supply not only the interme- 
 diate pair of legs, which are larger, but the superior organs, which, 
 whilst they afford protection to the true wings, are also engaged to a 
 limited extent in the action of flight. 
 
 The third, and last thoracic ganglion (c), is required to give im- 
 pulsion to the last and very powerful legs, at the same time that it 
 does the like to the real organs of flight the wings. Here, there- 
 fore, we see a greatly increased size in the nervous centre, especially 
 devoted to this function. The abdominal ganglia (d) supply the 
 muscles of the abdomen only, and are minute and uniform in size. 
 
 Nervous system of the 
 
 natural size of B. 
 
 Americana. 
 
 LESSON LXXYI. 
 
 NEEVOUS SYSTEM IN AKACHNIDA. 
 
 1135. The nervous system in one class of articulate animals yet 
 remains to be examined, the Arachnida. The class contains the 
 Mites, Scorpions, and Spiders, and has usually been placed by natu- 
 ralists below the Crustacea, and between it and Insects. 
 
252 ANIMAL PHYSIOLOGY. [LESSON 76. 
 
 1136. These animals present a more concentrated form of the 
 nervous system and of the heart than the animals previously exam- 
 ined; the larger species likewise offer a higher condition of the 
 respiratory system, which is less diffused than in Insects, and in some 
 consists only of air sacs, or lungs. 
 
 1137. But the most essential mark of the superiority of the 
 Arachnida is the course of their development. The spider under- 
 goes no metamorphoses comparable with those of insects. It is at 
 no period of its development an apodal (legless) worm. 
 
 1138. The head is always, in the Arachnida, soldered to the 
 chest, which thus forms the cephalo-thorax before alluded to ; it is 
 also deprived of antennae. 
 
 1139. They all ha vefour pairs of legs, which of itself forms an 
 important characteristic ; thus, an Insect is divisible into three chief 
 portions of its body, head, chest, and abdomen, to which neither 
 more nor less than three pairs of legs are superadded. 
 
 1140. The Crustacea, like the Arachnida, are divided into only 
 two portions, head-chest and abdomen, the legs being never less than 
 .five pairs, and frequently a greater number. 
 
 1141. The majority, but not all of these animals, are, like the 
 Insects, air-breathing ; to this rule there are, however, some excep- 
 tions amongst the Mites, and certain Spiders. 
 
 1142. The Mites, as their common name imports, are exceedingly 
 minute ; many of them, too, are parasitic. 
 
 1143. Man is the victim of two species of them, one the Demodex 
 folliculorum (Figs. 245-'6-'7), being by far the most minute that 
 has yet been discovered, and the other is the Acarus scabisei, or 
 the itch animal. 
 
 1144. That most loathsome of all diseases which afflicts humanity, 
 the itch, and the mange in dogs, are both caused by the presence of 
 a microscopical mite ; the species, however, in man and the dog, differ. 
 
 1145. The animal which afflicts the human family is known as the 
 Acarus scabicei, or by its more modern name of Sar copies galei. 
 An illustration of this animal is given (Fig. 248). 
 
 1146. This disease never occurs in any but very dirty people ; 
 through unpardonable neglect of washing the skin, the accumulation 
 of matter constantly being thrown off from its surface, produces 
 disease, and this disgusting parasite, when all other means are 
 neglected, comes, as a physician, to effect a cure ; this process is, 
 however, generally a lengthy one, until the aid of a physician of 
 another kind be invoked. 
 
LESSON 77.] NERVOUS SYSTEM IN THE MOLLUSCA. 253 
 
 1147. From their remarkable minuteness, we have no direct 
 testimony in relation to the condition of the nervous system in the 
 Mites / but in the Scorpion we find the principal masses or ganglions 
 concentrated around the oesophagus in the cephalo- thorax. 
 
 1148. From the small bilobed cephalic mass are sent upwards 
 the optic filaments, in front the nerves of the large forcipated claws, 
 and, backwards, the sympathetic nerves ; the sub-ossophageal gan- 
 glionic columns distribute nerves to the great under jaws, and to the 
 four pairs of thoracic legs ; two slender continuations of the double 
 columns are continued along the jointed abdomen, or tail, and seven 
 small ganglions are developed upon them, from which nervous fila- 
 ments are distributed to the surrounding parts. 
 
 1149. In Spiders the central masses of the nervous system are 
 wholly, or in great part, concentrated in the cephalo-thorax. The 
 brain is a bilobed gan- FIG 373 
 
 glion (Fig. 373, c), send- 
 ing forwards and up- 
 wards the optic nerves 
 (o) from its anterior 
 angles, and below these, 
 the two large nerves (m) 
 to the mandibles; a short 
 and thick collar encloses 
 the narrow gullet, and Nervous system of Spider, 
 
 expands into a second very considerable stellate or radiated ganglion 
 (s) situated below the stomach ; it sends off five principal nerves on 
 each side : the first (p), to the feelers of the under jaw ; the second 
 (Z), to the feelers of the under lip ; the three posterior nerves supply 
 the remaining legs. 
 
 LESSON LXXYII. 
 
 NERVOUS SYSTEM IN THE MOLLUSCA. 
 
 1150. The nervous system in these animals is arranged on a to- 
 tally different plan from what we have seen in the Articulata. 
 
 1151. In contradistinction to the uniform system of arrangement 
 of the nervous system, so constantly displayed in the latter sub- 
 kingdom, the Mollusca are remarkable for the unsymmetrical form of 
 its development. The cephalic ganglia, when two in number, are 
 
254 ANIMAL PHYSIOLOGY. [LESSON 77. 
 
 separated by an interval of space, and connected by a nervous chord 
 which passes behind the oesophagus. 
 
 1152. In the Articulata we found the alimentary canal invariably 
 transmitted through a nervous ring which surrounded it ; thence the 
 remaining ganglia were periodically developed at stated intervals 
 upon a double nervous chord, extending in the direction of the long 
 axis of the body. 
 
 1153. In the Mollusca the ganglia are always connected by a sin- 
 gle, not a double, chord ; moreover, the number and disposition of all 
 except the cephalic ganglions, is extremely variable, and of these 
 only one is met with in the lowest animals of the class. 
 
 1154. Again : in the Articulata, the advance in the development 
 of the nervous system is most conspicuous in the organs peculiar to 
 animal life, and is chiefly manifested in the powers of locomotion, 
 and in the instincts which are so various and wonderful in the class 
 of insects. 
 
 1155. In the Mollusca, on the contrary, the organizing energies 
 seem to have been chiefly expended in the perfection of the nutri- 
 mental series of organs, and of those concerned in the immediate 
 preservation of the individual and of the species. 
 
 1156. The Mollusca are so called on account of the uniformly 
 soft, unjointed nature of their external integument. 
 
 1157. In a large number of the lower organized Mollusca, there 
 is no head, and no nervous centre is needed above the gullet for the 
 reception of the impressions received by special organs of sense. All 
 other Mollusca are provided with a head, which generally supports 
 feelers, or soft tentacula, eyes, and a mouth armed with jaws. 
 
 1158. Amongst the lowest of the molluscous animals, is the class 
 Tunicata ; in these creatures the nervous system is more rudimen- 
 tary than we have described it ; only one ganglion has yet been dis- 
 covered, from which the filamentous nervous system is distributed 
 throughout the body. 
 
 In Cynthia pupa (Fig. 253) the nervous system consists of a sin- 
 gle ganglion (n) connected to a nervous chord which surrounds the 
 respiratory orifice (a). Fine nervous twigs are distributed to the 
 large vibratile organs, and a chord (d), of more than ordinary di- 
 mensions, commences at e, and passes down, without distributing 
 branches, to the bottom of the sac, where it is lost. 
 
 1159. The second order of the class Tunicata, includes the Sal- 
 pians, which float in the open sea, and are characterized by their 
 transparent elastic outer tunic, which is elongated, compressed, and 
 open at both extremities. 
 
LESSON 77.] NERVOUS SYSTEM IN THE MOLLUSCA. 
 
 255 
 
 1160. The muscular fibres of the cloak, or mantle, are arranged 
 in flattened bands (Fig. 374, e, e). The mouth and stomach, the liver 
 and the heart, are aggregated in a small mass near the posterior aper- 
 ture of the tunic (d) ; the intestine (c) extends towards the opposite 
 .iperture (a), and terminates in the common cavity of the mantle. 
 The brain and nervous system are seen at f. 
 
 1161. In Salpa polycratica (Fig. 374), the nervous system will 
 be found beautifully developed, of which an enlarged view is given in 
 
 FIG. 374. 
 
 FIG. 375. 
 
 Magnified view of nervous system, 
 8. polycratica. 
 
 Salpa polycratica. 
 
 Fig. 375. The word Salpa is Greek, and means a small fish ; poly- 
 cratica poly, much ; cratica, from kraios, strength. 
 
 By reference to the figure it will be seen that the nervous system 
 consists of two lobes, or ganglia, not separated by an interval of 
 space, but lying one upon the other. All the nerves are, without any 
 exception, distributed from the larger lobe, which is the equivalent of 
 the base of the brain, or infra-oesophageal ganglion (&), and are dis- 
 tributed to all parts of the body ; the analogue of the supra-ossopha- 
 geal ganglion (a) sends off two branches at right angles, which ter- 
 minate in expanded lobes (c, c). Nerves are not given off from this 
 latter lobe, simply because the creature is destitute of organs of 
 
256 ANIMAL PHYSIOLOGY. [LESSON 78. 
 
 special sense, and this portion of the brain may be considered as ru- 
 dimentary. So, too, the transverse lobes (c, c), which form, in all 
 probability, the elements of organs hereafter destined to become 
 Optic lobes. It is curious, however, to observe that whilst the por- 
 tion assumed to be the supra-cesophageal ganglion is uniformly very 
 dark in color, perhaps caused by a dense aggregation of ganglion cor- 
 puscles, the lateral lobes are conspicuous for the great number of these 
 corpuscles they contain, which may be distinctly seen in the figure. 
 
 1162. From this remarkable condition of the nervous system, it 
 appears highly probable that the Salpa, as such, is simply in a tran- 
 sition state, and it may eventually happen that, when we have culti- 
 vated a more perfect acquaintance with it, it will be found to pro- 
 gress to another form, and a higher state of development. 
 
 LESSOR LXXYIII. 
 
 NEEVOUS SYSTEM IN THE BEACHIOPODA. 
 
 1163. In the Brachiopods (brachion, an arm; pous, a foot), a 
 class of Mollusca which anciently existed to an immense extent dur- 
 ing the secondary period, and are found most abundantly fossilized, 
 but now restricted to three Genera, i. e. y Lingula, Orbicula, and 
 Terebratula, we have animals of great physiological interest. 
 
 1164. In Terebratula Australis, only one ganglion is found, as 
 in the Tunicata, from whence the nerves are distributed to the vascu- 
 lar mantle, the strongly ciliated arms (from which the class obtains 
 its name), and to all parts of the body. It is very difficult to find 
 this ganglion, and for a long time it eluded detection; it is beauti- 
 fully displayed, however, in a preparation, a copy of which is repre- 
 sented at Fig. 377, a. 
 
 1165. The Terebratula lives at a great depth in the ocean not 
 less than from sixty to ninety fathoms / for security, it attaches it- 
 self to submerged rocks, by means of a strong pedicle which projects 
 through a hole in a beak-shaped prolongation of one of the valves. 
 All the individuals of this class are bivalves. 
 
 1166. The dorsal layer of the mantle (Fig. 376) presents a very 
 interesting spectacle. At the upper surface two pairs of very short, 
 powerful muscles (a, b) may be seen, for the purpose of closing the 
 valves. These muscles are somewhat triangular in shape, and ter- 
 minate each in a short, strong tendon, of great beauty, situate at 
 
LESSON 78.] NERVOUS SYSTEM IN THE BRACHIOPODA. 257 
 
 their summit. A large and very capacious vein (c, c) runs through 
 each side of the mantle, which divides into a great number of smaller 
 branches, distributed to the outer edge of the mantle. In the centre 
 of each of these veins, an artery (e, e) is distributed, and ramifies 
 everywhere upon their surface. In addition to the vascular system, 
 nervous filaments (f ) are extensively distributed ; they are given to 
 the muscles, and pass directly through the mantle to its edge. The 
 
 FIG. 376. 
 
 Dorsal mantle of Terebratula Austral!?. 
 
 sexes are distinct in Terebratula ; thus the Ovarium, filled with eggs, 
 is seen at g, and the external thickened margin of the mantle at h. 
 
 1167. Having to breathe under such an enormous weight and 
 pressure of water, something more than the ordinary form of respi- 
 ratory apparatus becomes essentially necessary. 
 
 1168. There are no special organs of respiration in these ani- 
 mals ; that function appears to be performed by the singularly vascu- 
 lar mantle, but accessory thereto is, doubtless, the very powerful 
 arms, with the no less powerful vibratile cilia. By their action, the 
 surfaces of the mantle are kept constantly laved with water for res- 
 piration, and as the fluid always makes a circuit in one uniform di- 
 rection in this, as in other bivalves, the food which is contained in it 
 is conveyed to and appropriated by the mouth, which is abundantly 
 supplied with its own vibratile organs for that purpose (Figs. 256 and 
 257, a, a). 
 
 17 
 
258 ANIMAL PHYSIOLOGY. [LESSON ^8. 
 
 1169. Each arm extends outwards, advances forwards, curves 
 slightly inwards, and bends abruptly back upon itself, the two parts 
 of the bend being connected together ; then the stem again curves 
 forward, and becomes united to the corresponding bend of the oppo- 
 site arm, the conjoined extremities describing spiral convolutions 
 turned towards the dorsal valve ; the bent portions of the fringed 
 arms are supported by slender and elastic calcareous processes. In 
 all the Brachiopods, the stem which supports the brachial fringe is 
 hollow. 
 
 1170. In the Terebratulcs, and Orliculce, the spiral terminations 
 of the arms have their central canal surrounded by a double oblique 
 series of muscular fibres ; the canal is filled with fluid, and, by the 
 contraction of the muscular fibres, the extremities are extended by 
 the pressure of the contained fluid which is'injected into them. 
 
 1171. The structure of the alimentary canal, and its accessory 
 appendages, have been described in their proper place (p. 159). 
 
 1172. So, too, the organs of circulation, consisting, as some au- 
 thors (Owen) have supposed, in a heart placed on either side of the 
 alimentary canal, from whence the blood is distributed to all parts 
 of the body, especially to the vascular mantle. The probability that 
 these views are erroneous has been already stated (p. 158). 
 
 1173. In the nervous system of Terebratula, we find a nervous 
 collar, with only one ganglionic enlargement, surrounding the oeso- 
 phagus the ganglion being placed above the latter (Fig. 377, a). 
 Nervous filaments are distributed to the ciliated arms (d), the adduc- 
 tor muscles, and to the vascular lobes of the mantle (5, b). 
 
 1174. Two pairs of short, powerful muscles arise from each valve, 
 some of which are lost in the opposite valve, and others lost in the pedicle. 
 
 1 175. The pedicle is surrounded by an elastic yellow horny layer 
 and a tubular prolongation of the mantle. 
 
 1176. The true history of these interesting animals has been given 
 in the following beautiful and graphic language, by Prof. Owen : 
 " Both the respiration and nutrition of such animals, which exist be- 
 neath such an amazing pressure as a column of ninety fathoms (540 
 feet !) of sea-water, are subjects suggestive of interesting reflections, 
 and lead one to contemplate with less surprise the great strength and 
 complexity of some of the minutest parts of the frame of these di- 
 minutive creatures. In the unbroken stillness which must pervade 
 those abysses, their existence must depend upon their power of excit- 
 ing a perpetual current around them, in order to dissipate the water 
 already laden with their effete particles, and to bring. within the reach 
 
LESSON 79.] NERVOUS SYSTEM IN LAMELLIBBANCHIATA. 259 
 
 of their prehensile organs the animalcules adapted for their suste- 
 nance." The microscopical examination of the contents of the sto- 
 
 FIG. 877. 
 
 Nervous system, Terebratula Australis. 
 a. Ganglion. 5, 5. Nerves of the mantle, c, c. Veins, d. Nerves of the arms. 
 
 machs of numerous Terebratulae, has uniformly disclosed to view 
 myriads of well known minute siliceous forms erroneously ascribed 
 by Ehrenberg to the animal kingdom. 
 
 LESSON LXXIX. 
 
 NEEVOUS SYSTEM IN THE LAMELLIBEANCHIATA (LAMELLA, A PLATE; 
 BRAG CHI A, GILLS); 
 
 1177. The relation of the contained soft parts to the bivalve shell 
 of the Brachiopoda is such that, in the Terebratula^ the perforated 
 valve must be regarded as the inferior or central one, and the imper- 
 forate or shorter valve the dorsal one. 
 
 1178. In the Lamellibranchiata one valve is applied to the right 
 and the other to the left side of the animal. 
 
 1179. The nervous system advances in a regularly proportional 
 degree with the complexity of the general organization, and especially 
 
ANIMAL PHYSIOLOGY. [LESSON 79. 
 
 with the muscular system ; the ganglion upon the posterior adductor, 
 which is most conspicuous in the Oyster, Mussel, Pecten, and other 
 Bivalves, is the largest and most constant. 
 
 1180. It supplies the branchiae with their nerves, and is called, 
 therefore, the branchial ganglion ; but it distributes an equal share 
 of nerves to the posterior dorsal and anterior parts of the mantle. 
 
 1181. In the common Mussel (Mytilus edulis) the labial or 
 cephalic ganglions may be distinguished by their rose color (when 
 fresh) at the base of the labial processes (a, Fig. 378). They are 
 connected by a short transverse nervous chord (6), which passes be- 
 hind the mouth. From each of these ganglions two principal nerves 
 are given off, one passing forwards to the anterior adductor (q), the 
 other backwards along the base of the foot and the visceral mass to 
 the posterior adductor (g, g). At a short distance from the cephalic 
 ganglia this latter nervous chord (g, g) sends off a branch (c, c), 
 which terminates in a ganglion at the base of the foot (d) ; as each 
 of these branches ends in a ganglion, for the supply of nerves to the 
 foot, they coalesce, and a bilobed pedal (pes, foot) ganglion is formed. 
 The cephalic (a), pedal (d) and branchial (h) ganglions, constitute 
 the important centres of the nervous system in this and other bi- 
 valves. The pedal ganglia distribute nerves in one direction to the 
 retractors of the foot; in another to the substance of the foot 
 (/) itself. The branchial ganglions (h } h) send off nerves, which are 
 distributed principally to the breathing organs (m, m), and two 
 large nerves which diverge as they pass over the adductor 
 muscle (/, J), to proceed to the base of the tentacular proceses 
 guarding the posterior lobes of the mantle ; these continue along the 
 margin of each lobe of the mantle, until they meet and anastomose 
 (join) with similar branches, which are continued over the anterior 
 adductor muscles descending from the cephalic ganglions. 
 
 1182. The most remarkable fact demonstrated by the prepara- 
 tion of which a copy has been given, is the surprising and persistent 
 connection of the ganglionic centres ; throughout this nervous system 
 it invariably occurs that a nerve which has its origin in one ganglion, 
 terminates in another. By this means the cephalic ganglions are 
 connected, and the circuit made perfect. 
 
 1183. The nerves (c, c), which arise from the cephalic ganglia 
 respectively, terminate in d, c?, the pedal ganglia, whilst these, in 
 their turn, are connected by the looped nerves, f, f. 
 
 1184. The cephalic are connected with the branchial ganglia, 
 through the medium of the dorsal chords, g, g j one branchial gan- 
 
LESSON 79.] NERVOUS SYSTEM IN LAMELLIBKANCHIATA, 
 
 261 
 
 glion connects with its fellow, by the agency of the commissural 
 nerve, i. 
 
 The demonstration of the figure is as follows : 
 FIG. 878. 
 
 a. 
 
 5. 
 
 c, c. 
 
 *,*. 
 
 1,1. 
 
 m, m. 
 
 n, n. 
 
 o, o. 
 
 P- 
 
 Nervous system of Mytilus edulis (common Mussel). 
 
 Cephalic, or labial ganglia. 
 
 Commissure, or nervous chord, passing behind the oasophagus, uniting them. 
 
 Nerves, derived from the cephalic ganglia. 
 
 Their termination in ganglia at the base of the foot. 
 
 Bilobed pedal (pes, foot) ganglia. 
 
 Nerves from the pedal ganglia distributed to the foot. 
 
 Nerves which originate in,the cephalic ganglia, and terminate in 
 
 The branchial ganglia. 
 
 Commissure, or nervous chord connecting branchial ganglia. 
 
 Branches from the branchial ganglia, which are distributed to the inner margin of the 
 mantle. 
 
 Nerves derived from .?,.;, and the branchial ganglioa, and distributed to the outer mar- 
 gin of the mantle. 
 
 Branch from branchial ganglion, distributed to the posterior part of the mantle. 
 
 Nerves distributed to the gills, forming the branchial plexus. 
 
 Terminal nerves from the branchial plexus, ending in the cephalic ganglia. 
 
 The gills. 
 
 Sympathetic nerves, derived from the cephalic ganglia, and distributed to the stomach. 
 
 Nerves distributed to the anterior adductor muscle. 
 
262 ANIMAL PHYSIOLOGY. [LESSON 79. 
 
 1185. The respiratory, or branchial nerves, have their origin in 
 the branchial ganglions on either side; they ascend one lamella of 
 the gills, giving off numerous minute branches, and forming plexuses ; 
 the main respiratory trunk then descends the next lamella, giving off 
 its plexuses by the way ; arrived at the lower portion, it again as- 
 cends, but prior to doing this it sends off a branch to the fourth and 
 last lamella of the gills, when the main trunks ascend lovingly side 
 by side, giving off their minute plexuses by the way, till they reach 
 the summit. Here the fourth lamella gives off the (now attenuated) 
 main nerve, which receives a branch from the third lamella, and con- 
 tinues its course till the circuit be completed in the cephalic ganglion. 
 
 1186. The pallial (pallium, a cloak or mantle) nerve, y, also 
 originates in the branchial ganglion ; we trace it throughout the 
 circumference of the mantle, accompanied by its fellow, &, till we 
 lose them both at the anterior portion of the body, in the cephalic 
 ganglion. 
 
 1187. The post-pallia! nerves (?, I) arise from the branchial 
 ganglion on one side, and form a loop which terminates in the other ; 
 to end this surprising history it is only necessary to add that the 
 sympathetic nerves are given off by one cephalic ganglion, and end 
 in the other. 
 
 1188. Reasoning from the facts adduced, it would appear that 
 the principle (so far as is known) firstly enunciated in a Lamelli- 
 branchiate mollusc, continues through the classes till it (probably) 
 culminates in man ; it is very far from reasonable that such an ar- 
 rangement pertains to these creatures alone. Whenever our dissec- 
 tions of the nervous system of man and the higher animals become 
 more perfect, it may result that the like connection of the great 
 nervous centres is equally complete. 
 
 The looping of terminal nerves in man and the higher mam- 
 malia is well known, as witness the nerves in muscle, Fig. 352 ; this 
 seems to be confirmatory of the principle here shown to exist, exten- 
 sively, throughout the entire nervous system of an animal. Should 
 such an arrangement be generally true, there would be no difficulty 
 in understanding the phenomena of the reflex action of the nervous 
 system, together with other and important ^phenomena in connection 
 with peculiar nervous affections, to which poor humanity is prone. 
 The series of preparations in which the foregoing facts are recorded, 
 were dissected for the Hunterian Museum, where they still remain. 
 
LESSON 80.] NERVOUS SYSTEM IN THE GASTEROPODA. 263 
 
 LESSON LXXX. 
 
 NERVOUS SYSTEM IN THE GASTEROPODA. 
 
 1189. The meaning of this word has already been given, and it 
 will be at once apparent that its application is to the slugs and 
 snails, whether inhabitants of the earth, fresh waters, or of the 
 ocean, the whole of which progress upon their belly-foot 
 
 1190. The majority, but not all, of these animals are androgy- 
 nous (aner, a man ; gune, a woman) ; both sexes are combined in 
 the same individual. 
 
 1191. From the great power of locomotion possessed by this 
 class, it is evident that the muscular system has acquired an increase 
 of development as compared with the Lamellibranchiata, and, cor- 
 responding to this, is the increase in development of the nervous 
 system, and the development of a brain. 
 
 1192. Thus we observe, in the lowest and least locomotive 
 Gasteropod^ a tendency in the nervous system to be aggregated at 
 the forepart of the body, the cerebral ganglions rising more to the 
 upper surface of the now well-developed head, and the branchial and 
 pedal ganglions beginning to concentrate themselves about the 
 mouth. 
 
 1193. In the slug and snail the principal centres of the nervous 
 system are a supra-oasophageal and a sub- 03sophageal ganglion, but 
 the complex character of the latter and larger mass is indicated by 
 the triple nervous chord, which completes on each side the collar 
 round the alimentary tube. From the inferior mass the nerves 
 radiate to the muscular foot, the soft and susceptible integument, 
 and the circulating and respiratory organs. The upper ganglion 
 gives off the large nerves of the tentacles and ocelli ; it also commu- 
 nicates on each side by two minute filaments proceeding from its 
 posterior and outer angles, with a small pair of sympathetic ganglions 
 situated on the side of the oesophagus. 
 
 1194. In the Bulla lignaria (Fig. 379) there is a small lobed 
 ganglion (a), anterior to the usual cephalic ring (0), which is situ- 
 ated below the bulb of the oesophagus. The cephalic ring (e) sur- 
 rounds the oesophagus, and at its sides are seen two large tri-lobate 
 ganglia (/), which send numerous branches to the surrounding mus- 
 cular parts, and two long branches (h, h) extend backwards from 
 them, along the sides of the abdomen, to two symmetrical ganglia 
 
264 
 
 ANIMAL PHYSIOLOGY. 
 
 [LESSON 80. 
 
 (i, i) placed above the muscular foot. Behind these are two sym- 
 pathetic ganglia (k), which send filaments to the digestive organs. 
 
 1195. In the simple form of the nervous system presented by the 
 Carinaria Mediterranea (Fig. 380), there is a close analogy with 
 the ordinary disposition of the symmetrical detached nervous columns 
 along the ventral surface of the abdomen in the inhabitants of bi- 
 valve shells. Lobed ganglia (g, h) are found in this animal at the 
 sides of the resophagus, and a transverse nervous band (i) connecting 
 them, and encompassing that passage. From this nervous cesopha- 
 geal ring (i) the two optic nerves pass laterally to the eyes (/,/), 
 
 Fig. 379. 
 
 Fio 
 
 Nervous system of Bulla lignaria. Nervous system of Carinaria Mediterranea. 
 
 and the tentacular branches pass upwards and forwards to the long 
 slender tentacula (e, e). Numerous branches extend downwards and 
 laterally, to ramify on the muscular parietes of the abdomen, and 
 two principal trunks (k, k), extending backwards along the ventral 
 surface of the abdomen, meet with a large compound quadrilobate 
 (four-lobed) ganglion (q) behind the stomach, and above the di- 
 verging muscles of the compressed foot. These two ventral (belly) 
 detached and converging columns (&, A), extending from the oeso- 
 phageal collar to the middle or pedal ganglion (q), can be traced 
 backwards from these ganglia, along the lower surface of the ab- 
 
LESSON 80.] NERVOUS SYSTEM IN THE GASTEROPODA. 265 
 
 dominal cavity beneath the intestine, to near the caudal extremity 
 of the trunk. A branch, constituting the sympathetic, extends 
 directly backwards from the brain, or 03sophageal collar, and is dis- 
 tributed to the viscera. Numerous branches come off from the 
 pedal ganglia (q), to ramify on the muscles of the foot and surround- 
 ing parts. The lateral ganglia of the nervous ossophageal collar are 
 the parts from which the two principal nervous chords are derived, 
 which extend backwards beneath the abdominal viscera. 
 
 1196. The Buccinum (Whelk) and the Harpa have the greatest 
 
 FIG. 881. 
 
 Nervous system of Harpa elongata. 
 
 portion of the ganglionic matter of the oesophageal nervous ring ac- 
 cumulated in a cerebral position above the entrance of the alimentary 
 canal, as shown in the annexed figure of the Harpa elongata (Fig. 381). 
 1197. The mantle (o) is opened to show the branchiae (d, e) and 
 
266 ANIMAL PHYSIOLOGY. [LESSON 82. 
 
 the siphon (c) on the left side of the figure. On opening the an- 
 terior part of the trunk the retracted proboscis (</), with its muscles 
 (h), are seen extending backwards to the right of the brain (i), which 
 rests on the inferior turn of the oesophagus. From this cerebral 
 mass (i) large nerves are seen extending forwards to the head (b), 
 the tentacula, with the eyes, at their base (s, s), and to the broad 
 fin-like anterior fold (a) of the long tapering foot. Other nervous 
 chords are seen extending downwards to the ventral surface of the 
 abdomen, and backwards to the sympathetics which supply the ab- 
 dominal viscera. 
 
 1198. This gradual concentration of the ganglionic matter of the 
 great O3sophageal nervous ring of the Gasteropods into a cephalic 
 position, may be regarded as preliminary to its enclosure in a distinct 
 cranial covering a condition which it attains in the Cephalopoda 
 (kephale, head ; pous, foot). 
 
 LESSON LXXXI. 
 
 NEKVOUS SYSTEM IN THE PTEEOPODA AND CEPHALOPODA. 
 
 1199. These animals are named from the Greek, pteron, a wing, 
 and pous, a foot, and are so called from the peculiar wing-like form 
 of their sole locomotive organs, which are placed near the head. 
 
 1200. All the animals of this class are minute, the largest (Clio 
 borealis) not exceeding an inch in length. They are marine, and 
 found for the most part in the Arctic seas, where they exist in im- 
 mense shoals. Some of them are encased in an extremely delicate 
 shell (Hyalea) ; others, like the Clio, are naked. They constitute, 
 especially (7. borealis, the chief food of the Whale, which is unable to 
 swallow any thing of larger size than the creatures now under con- 
 sideration ; and of these, from the smallness of its oesophagus, it can 
 only take one at a time. 
 
 1201. The nervous system in the Pteropods presents the same 
 general plan, and the same varieties of form in its cephalic masses, as 
 we have seen existing in the Gasteropods, especially in the naked species. 
 
 1202. Thus, in the Clio borealis, there is a double nervous collar 
 around the oesophagus ; two small ganglia approximate to each other, 
 to form a bilobate brain (a) (Fig. 382), and are placed above the 
 oesophagus, immediately behind the lips, and indicate by their di- 
 minished size the imperfect development of the organs of the senses 
 in this animal, which scarcely presents a trace either of eyes or ten- 
 
LESSON 81.] NERVOUS SYSTEM IN THE PTEROPODA. 
 
 267 
 
 Nervous system, 
 Clio borealis. 
 
 FIG. 38& 
 
 tacula. Behind these central ganglia are two larger FlG - 
 
 lateral ganglia connected together by a transverse 
 band below the oesophagus, and which supply the 
 principal nerves to the muscular-closed mantle en- 
 veloping the trunk. Two nervous bands proceed 
 from each of this middle pair of ganglia, one of which 
 connects them with the cerebral, and another proceeding backwards 
 connects them with a posterior pair of ganglia, which are united by a 
 transverse chord above the oesophagus. 
 
 CEPHALOPODA. 
 
 1203. The nearest approach to the vertebrated form of the ner- 
 vous system is that presented by the Cephalopods, the highest of the 
 mollusca, and of all invertebrata. The brain is enclosed in a dis- 
 tinct cranial cavity, numerous symmetrical ganglia are developed on 
 the great nervous axis, both before and behind that organ, and sym- 
 pathetic ganglia are observed in the abdominal cavity. 
 
 1204. The principal masses of the nervous system of the Pearly 
 Nautilus (Fig. 383) are concen- 
 trated in the head. The supra- 
 
 cesophageal part, or brain (a), 
 presents the form of a short, thick, 
 transverse, round chord, or com- 
 missure, connected at each ex- 
 tremity with three ganglionic 
 masses. The middle and supe- 
 rior of these (b) supplies the eye 
 and the inferior hollow tentacu- 
 liform organ; the anterior and 
 inferior ganglia (c, c) meet their 
 fellow below the oesophagus ; the 
 posterior ganglion (d), in like 
 manner, joins that of the oppo- 
 site side and forms a second and 
 posterior oesophageal ring. The 
 nerves given off immediately 
 from the supra-oesophageal gan- 
 glion supply the muscular and 
 other parts of the mouth, and 
 have small pharyngeal ganglions 
 developed upon them. The an- 
 terior OeSOphageal ring gives Off 1 Nervous system of the Pearly Nautilus. 
 
268 ANIMAL PHYSIOLOGY. [LESSON 82. 
 
 principally the nerves to the tentacula (/, /), and the two me- 
 dian ones (g,g) are connected with a ganglion (h,h), which supplies 
 the tentacula of the inferior labial processes, and the lamellated 
 organs on that part of the oral sheath. The tentacula nerves are 
 continued, like those of the arms in the higher cephalopods, along 
 the middle of the tentacle, attached by loose cellular tissue to the 
 vessels of the part. The posterior collar gives off numerous nerves 
 (m) of a flattened form, which supply the muscles of the shell. The 
 respiratory nerves form a small ganglion (q) at the base of each pair 
 of gills, from which branches are sent to those organs, and to the 
 heart. A plexus of more delicate visceral nerves (r) is continued 
 backwards along the interspace of the branchial nerves, and the chief 
 branches are connected with a small ganglion situated upon the 
 stomach ; the ophthalmic tentacula derive their nerves (n^ n) from the 
 immediate vicinity of the origin of the optic ganglion. The hol- 
 low plicated process beneath the eye, regarded by some authors as 
 the olfactory organ, likewise receives its nerves from the extremity 
 of the supra-cesophageal chord. 
 
 LESSON LXXX1I. 
 
 NERVOUS SYSTEM IN THE FISHES. 
 
 1205. The great axis of the nervous system occupies entirely a 
 dorsal (dorsum, back) position in the vertebrated classes ; it is en- 
 closed in an osseous (bony) sheath or spine, which is continued over 
 its posterior prolongation, and it is nowhere perforated by the ali- 
 mentary canal. 
 
 The fibrous structure of the encephalic portion (brain) which is 
 perceptible in the Cephalopods, becomes more distinct and obvious as 
 we ascend through the vertebrated classes ; and that anterior part 
 of the nervous axis becomes likewise proportionally larger, leaving 
 only slight traces, in the fourth ventricle, of its original opening for 
 the passage of the alimentary canal. 
 
 The spinal chord, the medulla oblongata, the optic lobes, the 
 cerebral, and cerebellic hemispheres, form the most constant ele- 
 ments of thJfc axis, but their relative and actual developments vary in 
 the different classes. Though much varied in the extent of its de- 
 velopment in the different classes, there is great similarity in the 
 successive stages of the development of this system in the embryos 
 
LESSON 82.] NERVOUS SYSTEM IN THE PISHES. 269 
 
 of all the vertebrated animals, and great uniformity of plan in all its 
 adult forms. Beginning with the two columns of the axis, like the 
 two chords of a worm, it becomes reinforced by filaments from every 
 part of the periphery, and gradually receives its ganglionic enlarge- 
 ments, as in all the inferior tribes, where they are most required by 
 the developing organs of the body. The great sympathetic or nervous 
 system of organic life, which is extended along the upper, or dorsal 
 side of the symmetrical axis in the inverted bodies of the articulata, 
 is here developed along the ventral or under surface of the spino- 
 cerebral (spine, brain) axis, and like the sympathetic system of the 
 highest articulata, it is enclosed with the viscera, in a cavity distinct 
 from that which envelops the nervous axis of animal life. 
 
 1206. In the long, worm- like form of the lowest fishes, as the 
 Lamprey, the Pride, and the Gastrobranchus, the two slender col- 
 umns extending along the back, and scarcely protected by a cartilag- 
 inous (cartilage, gristle) sheath, are nearly without cerebellum, and 
 destitute of ganglionic enlargements in their course to the head, 
 where the minute cerebral elements are .enclosed, like the ganglia of 
 a Cephalopod, in a cartilaginous tube, consisting of a single piece. 
 
 1207. This simple condition of the axis, presented by the lowest 
 fishes, resembles the primitive development of this system in the 
 highest vertebrata before the extremities began to shoot from the 
 sides of the trunk. 
 
 1208. In fishes, as in Cephalopoda, where a large exterior surface 
 of the skull is required for muscular attachments, the minute brain 
 does not fill the cavity of the cranium, and the space between the 
 dura mater, which lines the skull, and the pia mater, which invests 
 the cerebral organs, is occupied by the soft, transparent, semi-fluid 
 cellular tissue of the arachnoid coat, which passes down likewise 
 through the vertebral canal, enveloping the spinal chord. 
 
 1209. The spinal chord is nearly equal in its development 
 throughout the vertebral column, even in many of the osseous fishes, 
 from the smallness of the arms and legs not requiring those enlarge- 
 ments which we observe in most higher animals, where the nerves 
 are larger and more powerful extremities are given off. 
 
 1210. In species which have the arms of great magnitude, as 
 Rays, and Flying-fishes, there is a proportionate development of the 
 upper enlargements of the spinal chord. 
 
270 
 
 ANIMAL PHYSIOLOGY. 
 
 [LESSON 83. 
 
 LESSON LXXXIII. 
 
 NERVOUS SYSTEM IN FISHES, CONCLUDED. 
 
 1211. In the Trigla lyra (Fig. 384), where the pectoral fins are 
 of great size, a series of ganglionic enlargements (5, b) of the spinal 
 chord (a) are observed at its upper part, which corresponds in num- 
 ber with the number of the large detached rays of the pectoral fins 
 presented by the different species, Trigla cucullus having five en- 
 largements and five detached rays, and the Trigla lyra having six 
 of each. 
 
 1212. The demonstration of the figure is as follows : The spinal 
 chord is seen at a. The medulla oblongata which consists of six 
 ganglionic enlargements at b, b. At c, d, the cerebellum is seen, and the 
 cerebrum aty. In this superior portion of the brain, the optic lobes 
 (e, e), the olfactory lobes (g), and the olfactory nerves (h) are found. 
 
 FlG . 384. FlG . 385> 1213. The posterior extremi- 
 
 ty of the spinal chord is some- 
 times sensibly enlarged where 
 nerves proceed to the muscles of 
 a large caudal (tail) fin, and in 
 abdominal fishes (an order so 
 called from the attachment of the 
 ventral fins to the abdomen, be- 
 hind the pectorals, or chest fins), 
 an enlargement is observed, cor- 
 responding with the ventral, or 
 belly fins. 
 
 1214. In front of the medulla 
 Brain, Conger eel. oblongata and cerebellum in os- 
 seous fishes, there are three pairs 
 of rounded lobes placed in front of ach other along the floor of the 
 cranium, and occupying but a small portion of that capacious cavity, 
 as seen in the brain of the Conger eel (Murcsna conger, Fig. 385), 
 where these three pairs of lobes are nearly equally developed and 
 similar in form. 
 
 1215. The spinal chord is shown at a; to this succeeds the 
 cerebellum (b). The cerebrum is marked e, containing the optic 
 lobes (c), the olfactory lobes (/), the olfactory nerves (g,g), and the 
 pineal gland (d). 
 
 1216. The posterior pair of lobes (c), immediately before the 
 
 Nervous system, 
 Trigla lyra. 
 
LESSON 84.] NERVOUS SYSTEM IN EEPTILES. 271 
 
 cerebellum (6), are the optic lobes, which are hollow internally, as in 
 the human embryo, and give origin to the principal fibres of the 
 optic nerves. 
 
 1217. The second or middle pair of lobes (e) are the cerebral 
 hemispheres, which here, as in the human embryo, are destitute of 
 internal ventricles, and without external convolutions. 
 
 1218. The anterior pair (f) are the olfactory tubercles, which 
 are entirely appropriated to the olfactory nerves (g, g). 
 
 1219. In the Trigla lyra, where the medulla oblongata (Fig. 384, 
 b, b] is marked by ganglionic enlargements, and the cerebellum (c, d) is 
 proportionally small, the optic lobes (e, e) are much larger than the 
 cerebral hemispheres (/), and the olfactory tubercles (g) are much 
 inferior in size. 
 
 1220. In most fishes, as in the earliest condition of the human 
 brain, the optic lobes are larger than the hemispheres; they are 
 smooth and gray on the outer surface, and destitute of the transverse 
 sulcus (a furrow), which gives them a four-lobed (quadrigeminous) 
 appearance in the adult mammalia ; they are hollow within, and 
 have their inner walls lined with white medullary fibres. The ven- 
 tricles of the optic lobes communicate freely with each other, and 
 they open behind by a narrow aqueduct, into the fourth ventricle 
 beneath the cerebellum. 
 
 1221. The interior white medullary walls of these two lateral 
 cavities meet above on the median line, and form an extended com- 
 missure ; they descend along the median line to form a prominent 
 ridge, but not a complete septum, between the ventricles. 
 
 1222. Finally, the optic lobes of fishes, like their medulla oblon- 
 gata, are larger in proportion to the cerebral hemispheres than in any 
 of the higher vertebrata, and they present the same great propor- 
 tions the earlier we observe them in the human embryo. 
 
 LESSON LXXXIY. 
 
 NERVOUS SYSTEM IN REPTILES. 
 
 1223. In the Amphibia, and in the larva state of those which 
 lose the gills, the spinal chord, the medulla oblongata, and the cere- 
 bral parts contained within the cranium, present the same proportions 
 and general conditions which we observe as permanent characters in 
 
272 
 
 ANIMAL PHYSIOLOGY. 
 
 [LESSON 84. 
 
 FIG. 886. FIG. 887. 
 
 most of the osseous fishes ; but the cerebellum is generally smaller in 
 amphibia and reptiles than in all the other vertebrata. 
 
 1224. As in the lower fishes, the spinal chord in these inferior 
 forms of amphibia is prolonged, small, and tapering, without distinct 
 enlargement where the nerves usually come off to the arms and to 
 the legs. The medulla oblongata is yet broad and lobed, the cere- 
 bellum in form of a very small median transverse lobe without hem- 
 ispheres, the optic lobes large, gray, smooth without, hollow within, 
 and quite exposed, and the cerebral hemispheres extending longi- 
 tudinally, without internal ventricles, and smaller than the optic 
 lobe. 
 
 1225. The metamorphosis of the animals of this class, prone to 
 such phases, changes the condition of their nervous system, from that 
 of the lower fishes, to nearly that of the reptiles above them, in which 
 
 no metamorphosis occurs ; and these changes in the 
 nervous system are effected so rapidly, that we can 
 perceive a marked advancement in the development 
 of the nervous system of the Tadpole produced in 
 one day. 
 
 1226. In the Tadpole of the common frog, on 
 the fourth day (Fig. 386), the spinal chord is per- 
 ceptibly enlarged at its posterior part (a), and also 
 the medulla oblongata. The cerebellum (b) is 
 scarcely visible, extended across the median plain ; 
 the optic lobes (c), and the cerebral hemispheres (e) 
 are small, narrow, and so far separate longitudinal- 
 ly as to expose the optic thalami (d). 
 On the following, or fifth day (Fig. 387), besides the general in- 
 crease of the spinal chord (o), the cerebellum (b) is perceptibly en- 
 larged, the optic lobes (c) are proportionately broader and shorter 
 and the cerebral hemispheres (e), increased in every direction, begin, 
 to extend backwards over the optic thalami (d). As the tadpole ad- 
 vances in its development, and the legs and arms are extended from 
 the sides, the posterior and middle enlargements of the spinal chord 
 are proportionally increased, the cerebral hemispheres enlarge, but 
 they present no convolutions or ventricles. The anterior extremity 
 of the chord is enlarged from the first, as it gives origin to the crani- 
 al (head) nerves, and the posterior end is enlarged for the cauda 
 equina (the termination of the spinal chord in man, and other ani- 
 mals, is supposed to represent a Horse's tail, and is thus named 
 cauda, a tail ; equina, a Horse). 
 
 Nervous systems of 
 
 Frog on fourth and 
 
 fifth days. 
 
LESSON 85.] 
 
 NERVOUS SYSTEM IN BIEDS. 
 
 273 
 
 FIG. 388. 
 
 FIG. 389. 
 
 1227. The changes effected in the nervous system of the higher 
 amphibia closely resemble those produced by development in the 
 human embryo. Their sympathetic nerves, and ganglia, too, are 
 more distinct than in the class of fishes. 
 
 1228. By comparing the nervous system of the adult Frog 
 (Fig. 388), with those of the tadpole during the period of early de- 
 velopment, great and important changes will be apparent. Thus, 
 the olfactory ganglia and nerves (nerves to the nose), which did not 
 at all appear before, are now well formed (a) ; the cerebal hemis- 
 pheres (b) are greatly enlarged, the optic lobes (c) well developed, 
 and the cerebellum (d) remains so small that it does not cover the 
 fourth ventricle, or cavity left by the divergence of the columns of 
 the spinal chord (e) ; the caucla 
 
 equina (/,/) is also well produced 
 at the period of mature growth. 
 
 1229. From the foregoing it 
 will be seen that the chief advance 
 in the development of the Reptile 
 brain, as compared with that of 
 Fishes, consists in the greatly in- 
 creased size of the cerebral hemis- 
 pheres over the optic lobes, but the 
 cerebellum is smaller so small in 
 the Frog that it does not even cov- 
 er the fourth ventricle, and this is 
 common to nearly the whole class. 
 
 In confirmation of these facts a 
 figure is given of the brain of the 
 Turtle (Fig. 389); the olfactory 
 ganglia (a) are largely developed, 
 and form, with the eyes, the most important organs of special sense. 
 The cerebrum (b) is enormously produced, as compared either with 
 the optic ganglia (c), or the cerebellum (d). 
 
 Nervous system 
 of adult Frog. 
 
 Brain of the Turtle. 
 
 LESSON LXXXY. 
 
 NEKVOUS SYSTEM IN BIRDS. 
 
 1230. In this class the cerebral hemispheres attain a great in- 
 crease of development, and arch backwards, so as partly to cover the 
 18 
 
274 ANIMAL PHYSIOLOGY. [LESSON 85. 
 
 optic ganglia, and these are separated from each other and thrown 
 to either side. 
 
 1231. The cerebellum also is much increased in size, proportion- 
 ally to the medulla oblongata and its ganglia ; there is, however, no 
 appearance of a division into hemispheres. 
 
 1232. The optic ganglia bear a considerable proportion to the size 
 of the cerebrum; they are still hollow, as they are in the embryo 
 condition of man. We shall hereafter see that the brain of the Hu- 
 man embryo bears comparison in many respects to the brain of the 
 bird. 
 
 1233. The great increase of the cerebral hemispheres, arching 
 backwards over the Thalami, and optic ganglia, but destitute of con- 
 volutions, and imperfectly connected by commissures, the large 
 cavity still existing in the optic ganglia, and freely communicating 
 with the third ventricle together with the imperfect evolution of 
 the cerebellum make the correspondence in the two very remarkable. 
 
 1234. In the earlier periods of the Old World, Birds appear to 
 have been connected with the Reptiles, through the flying Lizard, 
 
 FIG 390 or Ptwodactylus, remains of which animal are now only 
 found in a fossilized condition. 
 
 1235. It is very instructive to examine the brain 
 of the chick, after two days of incubation (Fig. 390). 
 We here see that the two halves of the spinal chord (a) 
 are united posteriorly, and form the vesicular enlarge- 
 ment (&), corresponding to the cauda equina and pelvic 
 dilatation of the adult The cervical and dorsal ver- 
 tebrae begin to embrace the anterior (f) portion of the 
 chord, and three vesicular enlargements are seen on the 
 cephalic portion of the nervous axis. The posterior (c) of 
 these enlargements forms the rudimentary lobes of the medulla ob- 
 longata, the middle dilatation (d) constitutes the outline of the optic 
 lobes, the anterior (e) and smaller cephalic enlargement forms the 
 embryo condition of the cerebral hemispheres in the chick, and all 
 these lobes are disposed in a longitudinal direction, as they are found 
 in fishes, and in the embryos of mammalia. 
 
 1236. In the brain of the adult Stork (Fig. 391), the large cere- 
 brum (d, e) is partially divided into lobes ; it covers the optic thala- 
 mi (thalamus, a bed-chamber, bed of the optic nerves), and contains 
 a small ventricle, which extends forwards to the olfactory (nerves of 
 smell) tubercles (/). 
 
 1237. These latter commence from two medullary tracts (h) on 
 
^ 
 
 LESSON 85.] NERVOUS SYSTEM IN BIRDS. 275 
 
 the inferior surface of the hemispheres, and taper forwards to the 
 olfactory nerves. The optic lobes, from whence the optic nerves 
 arise, are shown at c, the nerves of motion of the eye, or motor oculi 
 (</), are also well developed. 
 
 1238. The large cerebellum (ra), with its lateral lobes (I), is also 
 well seen; the medulla oblongata (b) terminates in the spinal 
 chord (a). 
 
 1239. An illustration is offered of the brain of the Buzzard 
 
 FIG. 391. 
 
 Brain of the Stork. 
 
 (Fig. 392) ; the olfactory ganglia are entirely concealed, in this view, 
 by the great size of the cerebral hemispheres (a). The optic gan- 
 glia (b) are seen of large size ; the cerebellum (c), and the pineal 
 gland (d))j with (e) the spinal chord, completes the view. 
 
 1240. The sensitive spinal nerves of birds have the ganglia larger, 
 and approximate more nearly to their origin than in reptiles ; and 
 from the retraction and high termination of the spinal chord, as well 
 as the comparative magnitude of the legs in this class, the posterior 
 ganglionic enlargement is remarkable for its size, and at this place 
 the motor and sensitive roots pass out through separate foramina 
 (holes) of the numerous sacral (sacrum, the back) vertebra. 
 
 The twelve pairs of cranial nerves are distinct, as in reptiles and 
 mammalia. The smallness of the facial nerve corresponds with the 
 immobility and insensibility of the superficial parts of the face, and 
 the magnitude of the acoustic nerve, with the great development of 
 
276 ANIMAL PHYSIOLOGY. [LESSON 86. 
 
 their internal ear, and their acute sense of hearing, especially in noc- 
 turnal birds. 
 
 The spinal nerves are chiefly cervical (cervix, the neck), and sa- 
 cral (sacrum, the lower part of the back), from the number of ver- 
 tebrae composing these parts of the column. 
 
 LESSON LXXXYI. 
 
 NEKVOUS SYSTEM IN MAMMALIA AND MAN. 
 
 1241. It has been shown that the nervous system in the lowest 
 animals possessing such a structure, exists in the form of a single 
 chord, presenting a lengthened axis, and in the Entozoa only one 
 ganglion is found. 
 
 1242. To this succeeds a double chord, and with this single or 
 double chord, ganglia, or knots of nervous matter, varying alike in 
 situation and number, are associated. 
 
 1243. Thus, in the lower Articulata, we find a ganglion, or little 
 brain, or nervous mass of reinforcement, placed in the centre of each 
 segment of the body, which are motor in their function, and supply 
 nerves only to the system of muscles found in the segments respec- 
 tively. The nerves of distribution are uniform in number, and dis- 
 tributed to similar structures in each instance the only exception 
 being in relation to the supra-sesophageal ganglion, or brain, the nerves 
 proceeding from which, with the exception of the sympathetic nerves, 
 are distributed solely to the organs of special sense. 
 
 1244. In the Leech we found only eyes to be supplied, and thus 
 the brain distributed only optic nerves, and may be considered as 
 simply an optic ganglion. In this animal the lower portion of the 
 brain, infra-oesophageal ganglion, greatly exceeds the superior portion 
 in size the muscles to be supplied with nerves being much more 
 abundant than the organs of special sense. 
 
 1245. In proportion as organs of sense are increased, so will the 
 brain be found to increase in size, and the greater will be the num- 
 ber of nerves distributed from its superior portion ; compared with 
 the Leech, a Caterpillar claims a much higher organization, and 
 hence the superior development of its brain, and the vast assemblage 
 of nerves in connection with it. In the Cirripeds, no organs of 
 special sense were found, neither is a superior portion of the brain de- 
 veloped, but the ganglions connected with the double chord, are mo- 
 
LESSON 86. J NERVOUS SYSTEM IN MAMMALIA AND MAN. 277 
 
 tor in their function, with the exception of the sympathetic nerves 
 originating from the supra-oasophageal loop. In the Myriapods, 
 however, a large and well developed brain is found, to supply the in- 
 creased number of the organs of special sense, and to originate a well 
 formed sympathetic system. In Insects another and remarkable 
 change, of a strictly progressive character, awaits us. In their lar- 
 val, or infantile condition, their energies are in abeyance, and their 
 organs of special sense are few, compared to their condition in the 
 perfect insect ; the superior portion of the brain, therefore, is much 
 smaller than it is hereafter destined to become. The energy, activi- 
 ty, and great irritability of the perfect Insect, contrasts remarkably 
 with the dull, sluggish, almost impassible life of the same animal in 
 its young condition. In a caterpillar, any one segment or ring of the 
 body (except the head) is like all the rest, and has the same func- 
 tions, even of locomotion, to perform hence the necessity of a gan- 
 glionic enlargement, or little brain in each segment, to keep up, or 
 maintain, the nervous force necessary for the due performance of 
 their functions respectively. The brain is much larger than their 
 inferior portions in the perfect Cockroach (Fig. 417), and Mantis 
 religiosa (Fig. 419). 
 
 1246. In the bivalve-mollusca, we find a creature in which the 
 nutritive system appears to be developed at the expense of all the 
 other organs ; consequently there is little special sense, and no need 
 of nerves to supply organs that do not exist. 
 
 1247. Destitute of vision, optic nerves are unnecessary; devoid of 
 smell and taste, there are neither gustatory nor olfactory nerves, and 
 the brain (or that which is analogous to it, as some authors suppose) is 
 reduced to the two cephalic ganglions, which are placed on either side 
 of the oesophagus, and much smaller in size than the branchial gan- 
 glia. From all analogy of the distribution of nerves from special 
 centres, and the organs they supply, the cephalic ganglia of the bi- 
 valve mollusca appear to constitute, not the superior, but only the 
 inferior surface of the brain. Headless, and entirely destitute of 
 organs of special sense, there is no need of a supra-cesophageal gan- 
 glion, and none such is developed; the branchial ganglions, with 
 their mixed function, appear to be the most important. The same re- 
 marks apply to the still lower Tunicata and Terebratulce. 
 
 1248. But in the Slugs and Snails, whether naked or testaceous 
 (testa, a shell), we find animals endowed with that superior organiza- 
 tion that renders a higher development, no less than a local position 
 and concentration of the brain, imperatively necessary. With a 
 
278 ANIMAL PHYSIOLOGY. [LESSON 86. 
 
 head, and abundant organs of special sense, a well developed supra- 
 oesophageal ganglion is found. 
 
 1249. From these animals we make a rapid ascent to the fishes ; 
 in the lowest of these, the anterior portion of the double chord dis- 
 plays a succession of five pairs of ganglia. 
 
 1250. The higher fishes, and the amphibious reptiles, appear to 
 have a different disposition of these primitive ganglia. ' The first 
 two have become fused into a single ganglion, and then follow only 
 three pairs of symmetrical ganglia. But if the larger pair be un- 
 folded after being hardened in alcohol, it will then be seen that the 
 whole number of ganglia exists, but that four have become concealed 
 by a thin covering that has spread across them. 
 
 1251. This condition of the brain carries us upwards in the scale 
 of being, even to the mammalia ; in the dog, or cat, for example, 
 we find, first a single ganglion, the cerebellum ; then three pairs 
 following each other in succession ; and if we unfold the middle 
 pair, we shall be at once convinced that it is indeed composed of two 
 pairs of primitive ganglia, concealed by an additional development. 
 
 1252. Again it will be observed that the primitive ganglia of 
 opposite sides, at first separate and disjoined, become connected by 
 means of transverse fibres of communication, or commissures. The 
 oflice of these commissures is the association in function of the two 
 symmetrical portions. 
 
 1253. Carpenter, in his human physiology, has truly said, " Hence 
 we arrive at the general and important conclusion, that the brain 
 among the lower animals consists of primitive chords, primitive 
 ganglia upon those chords, and commissures which connect the 
 substances of the adjoining ganglia, and associate their actions." 
 
 1254. In the development of the cerebro-spinal axis of man, the 
 earliest indication of the spinal chord is presented under the form of 
 a pair of minute longitudinal filaments placed side by side. 
 
 1255. Upon these, towards the anterior extremity, five pairs of 
 minute swellings are observed, not disposed in a straight line, as in 
 fishes, but curved upon each other so as to correspond with the 
 direction of the future cranium. 
 
 1256. The posterior pair soon becomes cemented upon the mid- 
 dle line, forming a single ganglion ; the second pair also unite with 
 each other ; the third and fourth pairs, at first distinct, are speedily 
 veiled by a lateral development, which arches backwards and con- 
 ceals them ; the anterior pairs, at first very small, decrease in size 
 and become almost lost in the increased development of the pre- 
 ceding pairs. 
 
LESSON 86.1 NERVOUS SYSTEM IN MAMMALIA AND MAN. 279 
 
 1257. This is represented to some extent, in three views of the 
 human brain from an Embryo (Figs. 393, 394, and 395). The first 
 (Fig. 393) is seen from behind ; a, the optic lobes, or, as they are 
 called, from their four-lobed character in the human subject, corpora 
 quadrigemini ; b, the cerebral hemispheres ; d, cerebellum ; *, me- 
 dulla oblongata. 
 
 1258. The second (Fig. 394) and the third (Fig. 395) have the 
 same letters of reference down to e ; the second is a side, and the 
 third a sectional (perpendicular) view ; g, the floor of the third ven- 
 tricle ; i, olfactory nerve ; /, optic thalamus. 
 
 1259. We see here a chain of resemblances corresponding with 
 the progressive development observed in the lower animals ; the 
 
 FIG. 393. Fia. 394. FIG. 395. 
 
 Brain of human Embryo, Side view. Sectional view. 
 
 from behind. 
 
 human brain passes through the phases of improving development, 
 which distinguishes the highest from the lower creatures ; and we 
 are naturally led to the same conclusion with regard to the archi- 
 tecture of the human brain, that we are led to establish as the 
 principle of development in the inferior creatures that it is com- 
 posed of primitive chords, primitive ganglia upon those chords, 
 commissures to connect the ganglia, and developments from those 
 ganglia. 
 
 The human brain, therefore, may be supposed to consist of a 
 number of elements, which are more or less diffused amongst the 
 lower animals, and which in them constitute the several ganglionic 
 masses that we find them to possess. 
 
 The more widely these elements are diffused, and the more fre- 
 quent the repetition of these little brains, the lower the individual in 
 the scale' of being. 
 
 Thus, the Nereis nuntia, with its 1,000 ganglions, is lower than 
 a Caterpillar ; which is, in its turn, lower than the perfect Insect ; 
 for in the latter we find a greater concentration of the Cerebrum, to 
 supply an increased number of organs of special sense, all of which 
 have attained a higher, a more refined development. 
 
 The organs of locomotion in the perfect insect have also become 
 
280 ANIMAL PHYSIOLOGY. [LESSON 86. 
 
 concentrated ; hence the absorption of ganglions in the abdomen, 
 where they are no longer wanted, and the deposition of increased 
 nervous matter in the thoracic ganglions, where it is imperatively 
 needed. 
 
 These facts are beautifully illustrated in the disparity of size and 
 number of the nervous centres (ganglions) of the active Slugs and 
 Snails, as compared with the passive bivalve-mollusca. 
 
 It has been remarked, with great propriety, that, in the progress 
 of his development, man passes successively through all those phases 
 of existence at which the remainder of the animal kingdom, respec- 
 tively, remain permanent. 
 
 He has never been, in reality, an Animalcule, an Insect, a Mol- 
 lusc, Fish, or Reptile, but he has passed through the conditions at 
 which they remain stationary. 
 
 It has been shown that, in the development of the human brain 
 and spinal chord, two nervous chords, unprovided with ganglia, first 
 exist. 
 
 The next stage exhibits a single ganglion, and at this moment 
 the human embryo is on the same plane with those animals in whom 
 a sole ganglion becomes permanent ; as the ganglia increase slowly 
 in number, so the embryo attains a higher rank in the scale of being. 
 
 But it is equally true that, prior to the production of even a 
 nervous chord, a still lower type was indicated, for, although the 
 statement is somewhat humiliating to the " lord of creation," we yet 
 commence our career in a form far less animal than vegetable. At 
 one period of the development of the ovum, a single cell exists ; 
 presently it divides into two ; these sub-divide into four, and this 
 process continues until the yelk consists entirely of a congeries of 
 cells. 
 
 Now this is precisely the plan upon which, as we have seen, 
 plants owe their being, and in both kingdoms the primary cells are 
 employed to organize the tubular tissues spiral and lactiferous ves- 
 sels in plants, nutrimental organs and blood-vessels in animals. 
 
 The probability is that man possesses a stomach, not only before 
 the advent of any portion of the nervous system, but prior to the 
 formation of an intestinal canal, thereby reducing him to the level 
 of the polypes. When the intestine is superadded, he has attained 
 a higher grade of development. 
 
 Again, the stomach is completed, like that 'of the polype, with 
 only one aperture ; when other cells are added, to form a rudimen- 
 tary and short intestine, the septum (partition) becomes absorbed. 
 
LESSON 87.] NEKVOUS SYSTEM IN MAMMALIA AND MAN. 281 
 
 So, too, "blood-vessels are formed, and the blood freely circulated 
 long before the existence of a heart. This may be beautifully seen 
 in the ova of Fishes, and especially in the egg of the domestic fowl, 
 on the fourth day of incubation. 
 
 But the character of this circulation is more nearly allied to the 
 vegetable than to the animal kingdom, and closely resembles the 
 circulation, or rotation, as it is called, so beautifully seen in the 
 hairs of many plants, Tradescantia, the cells of Chara, Nitella, Va- 
 lisneria, Frog bit, &c. 
 
 Still, in his early development, man maintains his supremacy, 
 for, during these progressive changes which take place in secret 
 unseen his external form is always human ! 
 
 LESSON LXXXYII. 
 
 NERVOUS SYSTEM IN MAMMALIA AND MAN, CONTINUED. 
 
 1260. The spinal chord of the adult man (Fig. 896, 5, i) is 
 smaller, compared with the cerebral mass contained within the 
 cranium, than in other mammalia, and short, from the want of caudal 
 prolongation of the trunk ; its posterior and middle enlargements 
 (c, d) are conspicuous, and of a lengthened form, from the magnitude 
 and number of the nerves which proceed from them to the sacral 
 extremity ; the cauda equina (a, b) is of great length ; the motor 
 roots (nerves of motion, Z, Z) and anterior columns are smaller than 
 the sensitive, and the ganglia of the posterior or sensitive roots (k) 
 of the spinal nerves are here larger than in other mammalia. 
 
 1261. The medulla oblongata, though comparatively small, has 
 its component fasciculi most deeply marked, and the quantity of 
 internal ganglionic matter in the course forwards of these white 
 fibrous fasciculi corresponds with their great development in the 
 human cerebral and cerebellic hemispheres, where the convolutions 
 (g) arid laminae (h, i) surpass in number and depth those of almost 
 all inferior animals. 
 
 1262. It now only remains to ascertain the microscopical charac- 
 ters which distinguish a nerve and a ganglion in all animals 3 * and 
 these characters are found to be remarkably constant. 
 
 1263. The fine, white chord, called a nerve, when placed under 
 the microscope, is found to consist of three tissues ; of these, the 
 
282 
 
 AXIMAL PHYSIOLOGY. 
 
 [LESSON 87. 
 
 outer one is a delicate, structureless sheath, called the Neurolemma 
 Fir 8% (neuron, a nerve ; lemma, a sheath). 
 
 1264. Within this sheath are the 
 nerve fibres, as they have been called, 
 which are really tubes containing a me- 
 dulla, or pulp. 
 
 1265. These ultimate tubes possess a 
 structureless sheath of extreme delicacy; 
 they are found composing the nerves of 
 all descriptions ; belong as much to the 
 gray, or cortical, as to the white, or me- 
 dullary substance of the brain, of the 
 spinal chord (where it exists), and of the 
 ganglia. 
 
 1266. The pulp, contained in the 
 tubes, known as the " white substance" of 
 Schawn, who first described it, is, when 
 quite fresh, perfectly homogeneous, fluid, 
 and viscid, like a thick oil, but every 
 method known of preserving it, coagulates 
 or otherwise alters it. For this purpose a 
 saline solution (eight ounces of salt, to one 
 quart of water) appears to be the best 
 adapted, as it changes it the least. 
 
 1267. It has been remarked that it 
 readily dissolves in water (Mollusca), 
 leaving only a series of empty tubes, and 
 this is true even in the human subject. 
 Preparations of nerves, made for the mi- 
 croscope, are subject to pressure, and 
 under its influence the whole contents of 
 the nerve tubes (in time) become squeezed 
 out. 
 
 1268. In addition to the white sub- 
 stance of Schawn, these tubes contain in 
 their centre a tube of the most delicate 
 transparency ; this is called the axis- 
 cylinder. 
 
 1269. A figure of the axis-cylinder 
 obtained by pressure from a preparation of the median nerve (human), 
 is given in Fig. 397. The same preparation also displays the white 
 
 Cerebio-spinal axis (brain, spinal 
 chord) of man. 
 
LESSON 87.] NERVOUS SYSTEM IN MAMMALIA AND MAN. 
 
 283 
 
 substance (Fig. 398), obtained by the same agency; nothing can exceed 
 the transparency, combined with brilliancy, of these two last prepara- 
 tions. It will be seen that the white substance consists of nucleated 
 cells. 
 
 1270. Another axis-cylinder, containing some corpuscles of the 
 white substance, copied from the same preparation, is given (Fig. 
 
 FIG. 897. 
 
 FIG. 398. Fm. 399. 
 
 White substance of Schawn ; from the 
 median nerve, human. 
 
 Axis-cylinder contain- 
 ing white substance, 
 median nerve. 
 
 Axis-cylinder. 
 
 399) ; it will readily be perceived that they differ considerably in 
 size. A common occurrence is, to find the axis-cylinder with the 
 white substance covering the termination of it (Fig. 400). 
 
 1271. The appearance of the tubes of the median nerve is shown 
 in Fig. 401, the granular contents indicating the white substance. 
 
 1272. The nerve tubes of the sympathetic system differ from 
 
 FIG. 400. FIG. 401. FIG. 402. 
 
 Median nerve. 
 
 Sympathetic nerve, human. 
 
 "White substance covering ter- 
 mination of axis cylinder. 
 
 those just described ; firstly, they are so much smaller that they do 
 not exceed one-third the diameter of the former ; and, secondly, they 
 do not present the two distinct substances within the tubular invest- 
 ment, which has been shown to exist in the ordinary nervous tubuli. 
 1273. A figure of the tubes of a sympathetic nerve is given at 
 Fig. 402 ; the contents of these tubes appear to be perfectly homo- 
 
284 
 
 AXIMAL PHYSIOLOGY. 
 
 [LESSOX 87. 
 
 geneous, although, when treated with acetic acid, they exhibit cell 
 nuclei (a). 
 
 1274. In addition to nerve tubes, which, as before remarked, are 
 common to all nerves, ganglions possess solid corpuscles, liable to 
 much variety of shape ; these have been (erroneously) called " gan- 
 glion globules," but when removed from the tissue many of them 
 present an irregular figure, and are caudate (tailed). A figure of a 
 thin section of a ganglion of the neck (human) 
 is given (Fig. 403) ; these corpuscles are ex- 
 tremely numerous, and, when seen in their nat- 
 ural situation, have a reddish appearance. 
 
 FIG. 404. 
 
 FIG. 405. 
 
 Sympathetic ganglion of Corpuscles from the gray substance Nerve of B. Americana, 
 the neck, human. of the spinal chord, human. 
 
 Removed from the tissue with which they aBe connected, these cor- 
 puscles are very variable in size and shape. 
 
 1275. The ganglion corpuscles are common to the gray or corti- 
 cal substance on the external surface of the Brain, and of all the 
 ganglia, and the corresponding gray matter in the interior of the 
 human spinal chord. A view of these corpuscles, obtained from the 
 latter situation, is given in Fig. 404 ; in addition to their caudate 
 terminations, these corpuscles also present nuclei. 
 
 1276. The remarkable constancy in the structure of nerve and 
 ganglion in the animal kingdom has been adverted to, and illustra- 
 tions obtained from a class as low as the Insects will be sufficient to 
 prove the statement. A portion of a nerve given off from the last 
 
 FIG. 406. (caudal) ganglion of a Cockroach (B. Ameri- 
 
 cana} is given in Fig. 405 ; the Neurolemma 
 (nerve sheath) is distinctly seen on either side 
 (a, a), and within it the nerve tubes containing 
 the white substance* 
 
 1277. A section of the caudal ganglion of 
 
 Ganglion, B. Americana, the' same insect (Fig. 406) displays the nerve 
 tubes greatly reduced in size, and the crowded ganglion corpuscles 
 
LESSON 88.] NERVOUS SYSTEM IN MAMMALIA AND MAN. 
 
 285 
 
 (a), which, in the preparation, are slightly red, as they are in man. 
 All the figures of nerve tissue have been drawn under a one- 
 fourth object glass, and to scale. 
 
 FIG. 407. 
 
 LESSON LXXXYIII. 
 
 NEEVOUS SYSTEM IN MAMMALIA AND MAN, CONCLUDED. 
 
 1278. Vascularity of Nerves. Nerves, like muscles, appear to 
 be highly vascular ; the vessels, however, will be found restricted to 
 the outer sheath, and are not allowed to penetrate amongst the tubu- 
 lar structure. This rule also applies to the brain, which is nourished 
 and sustained, not by vessels passing into the interior of its substance, 
 
 "but by a highly vascular membrane, the pia mater, which every- 
 where surrounds it. 
 
 1279. Nerves, it is well known, always accompany the arteries 
 and veins into whatever tissue they are distributed, but the nerves 
 do not gain any advantage from their near proximity to arteries 
 during the course of their joint dis- 
 tribution, for the nerves carry their 
 
 own vascular system with them. 
 
 1280. In good injected prepara- 
 tions the nerves will be found to have 
 participated in the general success; 
 if one of these be dissected out, placed 
 on a slip of glass, dried, and mounted 
 in Canada Balsam, the probability is 
 that an appearance will present itself, 
 under the microscope, similar to Fig. 
 407, which shows an injected nerve. 
 On one side of the sheath will be seen 
 an artery (a), and on the opposite 
 side a vein (5), and these two vessels 
 
 are connected by a series of capillaries (c), which ramify everywhere 
 on the surface of the sheath. 
 
 1281. Such a preparation as the foregoing, is very instructive, as 
 it teaches a lesson not easily forgotten ; it demonstrates the peculiar- 
 ity of the distribution of vessels in this particular tissue, and enables 
 one to detect a nerve, under circumstances in which it would other- 
 wise elude detection. 
 
 Nerve injected. 
 
286 
 
 ANIMAL PHYSIOLOGY. 
 
 [LESSON 88. 
 
 1282. In a portion of human pericardium (the bag in which the 
 heart hangs) very minutely injected, and presenting a most gorgeous 
 sight under the microscope, three somethings are seen entering the 
 tissue at a particular point, somewhat deep seated, and to some extent 
 veiled by a plexus of capillaries belonging to that layer of tissue which 
 covers them ; what are they ? Many circumstances lead to the con- 
 clusion that the outer vessel on one side (6, Fig. 408) is an artery, 
 distributing blood to the pericardium, and that the outer vessel, on 
 the opposite side (a), is the vein, receiving and returning the blood 
 from this tissue ; but what is the third something which lies between 
 them ? Let us examine it closely, and see if we can discover what 
 it is ; two vessels make their appearance, one on either side of this 
 something the one is much smaller than the other, and both appear 
 to be connected with the capillary plexus (c) ramifying between them ; 
 no connection whatever appears to subsist between the outer vessels 
 
 FIG. 409. 
 
 FIG. 409. 
 
 Portion of human pericardium. 
 
 Vascularity of a ganglion, with the vessels of 
 supply and return. 
 
 of the unknown tissue and the artery and vein outside of it ; the 
 question hence arises, in what tissue is such a distribution a peculiari- 
 ty? To this there can be but one reply a nerve and this some- 
 thing which, in the dried state of the tissue, more nearly resembles 
 another blood-vessel, is indeed the nerve which invariably accom- 
 panies the artery throughout its distribution. 
 
 1283. If the circulation of the blood to a nerve be peculiar, it is 
 no less so to the ganglions ; for an example, a copy is given (Fig. 
 409) of a preparation of a sympathetic ganglion of the neck 
 (human). 
 
 1284. Here the artery and vein are not at all connected with the 
 tissue to be supplied, but the former, while passing in its course of 
 general distribution, gives off a twig (a) to the ganglion, which in- 
 stantly breaks up into a plexus of capillaries, which ramify all over 
 
LESSON 89.] ORGANS OF SPECIAL SENSE. THE EYE. 287 
 
 the entire surface of the ganglion, and ultimately yield up their con- 
 tents, by another twig (b) to the vein, which passes it into the jugu- 
 lar vein, and thence to the heart. 
 
 1285. Such, then, are the peculiarities which characterize the vas- 
 cular system of nerves and ganglia, and by which they may be at all 
 times recognized, as no such distribution pertains to any other tissue. 
 
 LESSON LXXXIX. 
 
 OKGANS OF SPECIAL SENSE. THE EYE. 
 
 1286. Want of space in this small volume will not permit a full 
 inquiry into the subjects which form the title of this lesson, but one 
 organ, from its almost universal distribution in the animal kingdom, 
 together with its importance, claims special attention the Eye. 
 
 1287. As far as our knowledge of it extends, the eye is strictly 
 an optical instrument a camera and as capable of performing cor- 
 rectly in death, as in the living organ. To prove this fact it is only 
 necessary to remove, carefully, the posterior portion of the sclerotic 
 coat of the fresh eye of a Sheep or an Ox, leaving untouched the 
 retina. If the eye, thus prepared, be presented to any object, a mi- 
 nute, inverted, and most beautiful view of the picture will appear 
 upon the retina, arrayed in all its natural colors. If the picture so 
 formed be magnified with a lens of moderate amplifying power (one 
 inch, or 1^ inch focus), a very charming sight will be offered to the 
 spectator. 
 
 1288. A well formed visual organ appears to require the follow- 
 ing parts : a transparent cornea, or outer covering ; an aqueous (wa- 
 tery) humor; an iris, or curtain of the eye, to limit and control 
 the quantity of light to be admitted ; a crystalline lens ; a vitreous, 
 or glassy humor; a pigment or paint, frequently but not always 
 black, to absorb the excess of light which has entered the eye, and 
 thereby give increased sharpness and intensity to the picture ; a 
 retina, or thin membraneous expansion of the optic nerve, forming 
 the white curtain (similar to the ground-glass of a camera) upon 
 which the images are depicted ; and finally, an optic nerve, whose 
 function it is to transmit faithfully to the brain, the full particulars 
 of color, and general appearance of the picture formed upon the 
 retina. 
 
288 ANIMAL PHYSIOLOGY. [LESSON 89. 
 
 1289. That the combination of these tissues is necessary to the 
 production of vision, is evidenced by the fact that they are all, or 
 nearly all, found in various stages of modification, down to animals 
 of otherwise lowly organization. 
 
 1290. There are, however, many animals altogether destitute of 
 eyes, and yet they are visibly affected by light. This is especially 
 well seen in the Animalcules, Zoophytes, and others, where some of 
 them (Hydra) seek the light, and others (Actinia, and many other 
 Zoophytes) contract their bodies, and shun its influence. 
 
 1291. Plants, guided by light, open or close their flowers and 
 their leaves, and follow with flowers expanded the daily course of the 
 sun, or seek his light with branches and leaves slowly moving in the 
 direction he takes ; yet they possess no nervous system, neither do 
 the animals above mentioned, but both appear to be influenced by 
 perceptions altogether unknown to us. 
 
 1292. Some authors (Ehrenberg and others) have supposed that 
 many animals, acknowledged to be destitute of a nervous system, 
 possess eyes ; thus red spots seen in many (supposed) animalcules, to 
 say nothing of other lowly organized creatures, have been described 
 by Ehrenberg, as visual organs, notwithstanding that many of these 
 have subsequently been discovered to be plants ! 
 
 1293. This red coloring-matter, so prominently developed in the 
 lowest plants, as in the plant called "fied snow;" the Protococcus 
 pluvialis, found in rain-water ; the Hcematococcus sanguined, found 
 frequently on stale bread ; is but a slightly altered chlorophylle, and 
 into which it can be converted, made green. 
 
 1294. These facts clearly demonstrate the fallacy of attributing 
 the function of vision to the red spots, unless supported by more 
 convincing testimony than mere color. ' Eyes sometimes have a red- 
 dish tint from the red-brown pigment which shows through the 
 transparent cornea. 
 
 1295. The possession of eyes in the Radiate sub-kingdom, appears 
 to be open to much doubt, notwithstanding that visual organs have 
 been claimed for the Medusae, Starfishes, &c. 
 
 1296. In the Articulata, on the contrary, there is no question 
 of their very general development, although they are not found in 
 the Epizoa, generally, nor in the Cirripeds, at all. 
 
LESSON 90.] THE EYE IN THE ANNELLATA, ETC. 289 
 
 LESSON XC. 
 
 THE EYE IN THE ANNELLATA, CRUSTACEA, MYRIAPODS, AND INJECTS. 
 
 1297. In the Annellata (red-blooded worms), eyes are constantly 
 found, and in variable number ; thus in the several species of Pla- 
 naria, they vary from one to three pairs, and in one species (Prosto- 
 ma armatum) the head is literally covered with them. 
 
 1298. In the medicinal Leech (Fig. 362) there are ten simple 
 eyes ; in Nereis nuntia there are four large eyes on the upper part 
 of the head, and nearly one hundred smaller visual organs disposed 
 in rows and groups on all the prominent lobes about the mouth. 
 
 1299. But in the higher forms of this class the eyes are reduced 
 to two. In all these animals the eyes consist of a transparent cornea, 
 a minute crystalline lens; a pigment, not always, but generally black, 
 and an optic nerve ; whether other organs are superadded is not 
 known, the extreme minuteness of the eyes forbidding further inves- 
 tigation. 
 
 1300. In the higher forms of Crustacea (Lobsters and Crabs), 
 the eyes are pedunculated and movable, by means of muscles inserted 
 within their sclerotic covering ; in the inferior Crustacea, they are 
 sessile (sitting close upon the body, without support) and immovable, 
 and in the lower Crustacea the two sessile eyes are frequently united 
 on the median plane, and appear to form but one organ (Monoculus, 
 Daphniaj &c.). 
 
 1301. The eyes themselves are constructed on the same plan as 
 those of Insects, hereafter to be described, with one remarkable ex- 
 ception : the facets in the transparent cornea of Insects are hexago- 
 nal (see Fig. 420), but in the Lobster they are perfectly square (Fig. 
 410), and resemble a ruled glass micrometer ; pio 410 
 moreover, it consists of a series of laminae 
 
 (plates). It will be shown hereafter that in 
 the Insect eye a great tendency to the square 
 form of the facet prevails, notwithstanding it 
 is always found associated with the pure hex- 
 agonal figure. 
 
 1302. In the Myriapods (Centipedes, lu- 
 lidse) the eyes of some species resemble those 
 of the Annellides, whilst others approximate 
 
 to the Insects; most of them present numerous separate simple 
 19 
 
290 ANIMAL PHYSIOLOGY. [LESSON 90. 
 
 eyes, grouped together on the two sides of the head. The eyes of 
 Scolopendra (Centipede) consist each of a group of about twenty- 
 three small, distinct eyes, approximated and placed in lineal rows, and 
 the aggregated eyes of lulus are also composed of several rows. 
 
 1303. In Insects the eyes, like most other organs of the body, at- 
 tain a high degree of development ; moreover, two kinds of visual 
 organs are found in many of them, one series of eyes being adapted 
 for long, and the other for short sight. The great Dorr-beetle, or 
 May-bug, as the Melolontha vulgaris (Cockchafer) is commonly 
 called, is a familiar example of an Insect endowed with very short 
 vision. Persons walking in the fields, especially at twilight at the 
 latter end of the month of May, or during June, will find these In- 
 sects constantly striking them in the face, and flying against other 
 parts of their body, with so much force that the creature frequently 
 falls, as if stunned by the concussion. 
 
 1304. The facetted, or compound eye, so conspicuous in all the 
 perfect insects, appears to have but a short focal range, and even this 
 differs to a large extent, as may be seen by the superior and remark- 
 able convexity of these eyes, in many of them. 
 
 1305. Those insects which feed on the juices of plants, or ani- 
 mals, require very short vision, as their food lies at their feet, and 
 hence their eyes are singularly convex. 
 
 1306. Amongst the predaceous beetles, longer vision is required, 
 and the convexity of the compound eyes is greatly reduced. 
 
 1307. The Bees, on the other hand, need telescopic vision to 
 guide them in their long flights in search of honey and wax ; but, 
 when engaged in the act of collecting, or in making, and hermetically 
 sealing their beautiful cells, near vision becomes necessary, and hence 
 much convexity of their compound eyes. 
 
 1308. The telescopic form of eye, when present, is in the form of 
 two or three single, distinct eyes, of larger size than any of the facets 
 of the compound eye, and placed in the best possible position for the 
 exercise of their function on the vertex (crown of the head). Cat- 
 erpillars have only a variable number of these single eyes, grouped 
 together, however, as a common mass, with but a moderate interval 
 of space between them. 
 
 1309. Much disagreement prevails in regard to the true structure 
 of the Insect eye, and of the three authorities who have chiefly ex- 
 amined it, no two of them hold the same opinion. These authorities 
 are, Marcel de Serres, Straus-Durckheim, and J. Miiller. 
 
 1310. According to Straus, the epidermis continues over the ex- 
 
LESSON 91.] THE EYE IN INSECTS. 291 
 
 posed surface of the eye, as in serpents ; it is colorless and transpa- 
 
 rent. Beneath this transparent external covering, are placed the 
 
 transparent facets, or cornieae of the several minute compound eyes, 
 
 and beneath this lat- 
 
 ter layer the conical, 
 
 transparent lenses. To 
 
 render the description 
 
 plain, a figure (according 
 
 to this authority) is 
 
 given (Fig. 411). 
 
 1311. The structure 
 of the insect eye by 
 Marcel de Serres, was 
 
 Subsequently Superseded Structure of the eye"of Me- Miiller's views, eye of Libel- 
 
 11 lolontha vulgaris, Straus. lula. 
 
 by tne Statements Ol ^ Continuous layer of trans- a. Transparent cornea. 
 
 Vm+ a fr-nay "hi a parent hexagonal corneae. &. Crystalline lens. 
 
 but a truer hlS- 5. The con ical transparent c. Conical lens. 
 
 torv i<5 o-ivPTi "hw T lenses. d. The pigment. 
 
 .ory is given Dy J . c The optic filaments? con . e> The * p ^ filament 
 
 nected to the apices of 
 the conical lensesT 
 
 1312. He discards 
 
 the "epidermic covering of the cornea "of Straus, which really has 
 no existence. 
 
 1313. Beneath the cornea, Miiller found a minute double-convex 
 lens, possessing (like the crystalline lens of man and the higher ani- 
 mals) two curves; the flatter or shallower curve being placed in 
 front, and the deeper curve behind. 
 
 1314. The bases of the conical lenses, according to Straus, are 
 perfectly flat, but Miiller found them to be convex, and that they 
 touched the greater curve of the crystalline lens, only at the centre 
 the surrounding space being filled by the pigment. 
 
 1315. To illustrate this theory a figure is given (Fig. 412). 
 
 LESSON XCI. 
 
 THE EYE IN INSECTS, CONTINUED. 
 
 1316. Miiller, however, has not exhausted all the facts in relation 
 to the structure of this important organ of sense. 
 
 1317. Behind the horny substance of the transparent cornea, is 
 a whitish membrane, divisible into laminae, or layers, which contains 
 the crystalline lenses; with moderate care it may be detached, re- 
 
292 
 
 ANIMAL PHYSIOLOGY. 
 
 [LESSON 91. 
 
 FIG. 413. 
 
 FIG. 414. 
 
 Transparent cornea, with 
 
 lenses in situ; M. 
 
 carnaria. 
 
 Lamina of the transparent 
 cornea, containing the len- 
 ses, Caterpillar. 
 
 taining the lenses in situ. In some Insects this membrane is partic- 
 ularly delicate, and in these cases it is more likely to remain attached 
 to the transparant cornea, showing the lenses, when viewed by trans- 
 mitted light, in the centre of the facets, severally; this is shown 
 from a preparation of the Flesh-fly (Musca carnaria), Fig. 413. A 
 beautiful specimen of the membrane, detached, with the lenses, was 
 obtained from a small Caterpillar of this country, name unknown ; 
 
 a figure of it is given 
 (Fig. 414). In this 
 specimen the lenses are 
 of unusual size, the pos- 
 terior surface being of 
 great convexity. 
 
 1318. The conical 
 bodies are usually col- 
 ored, but very delicate 
 in texture, and possessing a semi-transparency. 
 
 1319. They have generally a faint yellow color, and they become 
 decomposed in a very short time in water ; neither can they be pre- 
 served very well any how ; in spirit they contract so much as not to 
 be visible, and in other preserving fluids it is extremely difficult for 
 
 the well-practised eye to detect them ; 
 hence they should be sought for in 
 freshly caught insects. 
 
 1320. All authors agree in believ- 
 ing the conical lenses to represent the 
 vitreous humor of the eyes of the 
 higher animals, a fact confirmed by 
 the difliculty of preserving them. 
 
 1321. They are undoubtedly con- 
 vex at their large extremity, and in 
 some insects (M. carnaria) remarka- 
 bly so. 
 
 1322. The optic filaments are not 
 attached to the terminal points or api- 
 ces of the cones as represented by au- 
 thors, but, on the contrary, pass en- 
 Conical bodies, Cone of a cater- tirel y through their centre (b, Fig. 
 
 M carnaria. pillar. 415) an( j are some times Seen pro- 
 
 a. Cone. /' * 
 
 6. Optic filament. jecting through the large end (base 
 
 of the cone). In Musca carnaria, examined by a fourth object-glass, 
 
 FIG. 415. 
 
 FIG. 416. 
 
LESSON 91.] 
 
 THE EYE IN INSECTS. 
 
 293 
 
 they appear to be of great size ; they have consequently been re- 
 duced in the figure given of them (Fig. 416). 
 
 1323. In the perfectly fresh state in which they were seen, each 
 optic filament formed a very beautiful sight, possessing, in every in- 
 stance, an axis-cylinder ; the white substance was too transparent to 
 be visible. 
 
 1324. The cones of the Caterpillar, above referred to, are still 
 larger (Fig. 416), and these have been preserved, fortunately, in a 
 saline solution, but they are opaque, and, whether the nervous fila- 
 ment enters the cone or not, cannot now be determined ; the bases 
 of these cones are much flatter than those of Musca. 
 
 1325. The mode of connecting the several lenses of the compound 
 eye of an Insect with the FlG 417 
 
 brain, is shown in a figure 
 copied from a preparation 
 of the brain of Blatta 
 Americana (Fig. 417). 
 
 1326. The inferior por- 
 tion of the brain, or iufra- 
 oesophageal ganglion, can- 
 not be seen in this Insect, 
 in viewing the brain from 
 the upper surface, because 
 it lies immediately below 
 the supra-03sophageal gan- 
 glion, and, being much 
 smaller, is concealed by 
 it, and can only be seen 
 from the under surface. 
 
 1327. There is one fact in connection with the compound eyes 
 of Musca carnaria, that has escaped the observation of the authori- 
 ties, namely, that all the important elements 
 
 of a visual organ rest upon and are supported 
 by an aggregated arrangement of fat lobules, 
 of exquisite beauty, and, as might be expected, 
 existing in a state of the most perfect analysis. 
 A figure of these lobules is given (Fig. 418). 
 
 1328. When the plan of connection of the Fat i obu ies of the eye, 
 compound, or facetted eye, with the brain is 
 
 considered, it is not difficult to understand its action ; each individ- 
 ual organ transmits to the optic lobe a picture of what it sees, and 
 
 Brain, Blatta Americana. 
 
 a. The Cerebrum, or supra-oesophageal ganglion. 
 &. The optic nerves, terminating in the optic lobes. 
 
 c. Optic filaments, one of which is iu connection with. 
 
 each individual eye. 
 
 d. Facetted external cornea. 
 
 e. Antenneal nerves. 
 
 /. Nerves connecting the brain with the first thoracic 
 ganglion. 
 
 FIG. 418. 
 
294 ANIMAL PHYSIOLOGY. [LESSON 91. 
 
 the combination of a vast number of detached portions of even a 
 large picture makes upon the optic lobe a perfect and undivided 
 whole, the impression of which is conveyed to the brain by the optic 
 nerve, not as a divided, but as a single picture. An Insect, there- 
 fore, has no business to know from any practical results that it pos- 
 sesses more than a single eye on each side of its head. 
 
 1329. The necessity for such a vast number of distinct organs 
 of vision, is a consequence of their fixity of position ; it is essential 
 for their well being, to guard and protect themselves from their nu- 
 merous enemies, ever ready to destroy them, that they possess vision 
 in every conceivable direction, and the predaceous varieties require 
 a no less perfect development of the organ to enable them to discern 
 their nimble prey. The large extent of surface occupied by the 
 compound eyes, fully effects this desirable object ; above, below, be- 
 fore, behind and laterally, asleep or awake, are an infinite number 
 of vigilant guardians, never closed nor veiled by eyelids, but ever 
 on the alert and ready to give the alarm. 
 
 1330. The number of distinct organs in the facetted eye has been 
 computed (by the aid of a micrometer), by those persons curious in 
 such matters, thus : the House-fly possesses 4,000 ; Libellula (Dragon- 
 fly), 12,554; Papilio, 17,355; Cossus ligniperda, 11,300; Mordella 
 (a small beetle), 25,088. 
 
 1331. Hairs are frequently found connected with the compound 
 eyes ; they are placed in the depressions between the corneao, and 
 afford protection (like eyelashes) to the organs. 
 
 1332. Bees have to enter the expanded cup of flowers, in search 
 of the nectar ; their eyes might suffer abrasion and become opaque 
 from the frequent contact with the petals, or they might be obscured 
 and rendered useless by aggregated pollen masses. But no such 
 contingencies can occur to them, in consequence of the protection 
 afforded by their eyelashes. 
 
 1333. The telescopic, or simple eyes, are differently constructed. 
 Usually, these are of great size, as compared with any of the facets 
 of the compound eye. 
 
 1334. Immediately behind the hemispherical, convex, trans- 
 parent cornea, is a well-shaped, double-convex, crystalline lens. 
 Like those already described, it possesses two curves, the deeper 
 one being behind. This latter surface fits accurately into a vitreous 
 humor, the posterior portion of which is rounded, and is received 
 into a bowl-shaped expansion of the optic nerve a true retina ; in 
 addition, there is a choroid coat, and a pigmentary layer, so that all 
 
LESSON 92.] THE EYE IN INSECTS. 295 
 
 the elements are here found of a well-developed visual organ. A 
 distinct optic nerve is given to each simple eye, which at once trans- 
 mits to the brain the image formed upon the retina. 
 
 LESSON XCII. 
 
 THE EYE OF INSECTS, CONCLUDED. 
 
 1335. To show the connection of the optic nerves of the single 
 eyes with the brain, a figure, copied from a preparation of the brain 
 of Mantis religiosa, is given (Fig. 419). The large, well-formed 
 
 FIG. 410. 
 
 Brain, Mantis religiosa. 
 
 cerebrum is shown at a ; posterior to which, at some distance, the 
 cerebellum (5), is seen; the crura, which connect the two hemispheres, 
 are marked c, c ; the optic nerve of the compound eye is shown at d ; 
 the optic lobe is marked e ; the optic filaments, which spring from 
 the optic lobe, are shown at jf ; the nerves distributed to the antennae 
 at h ; the optic nerves of the simple eyes at i, i ; and the bowl- 
 shaped retinal expansion of optic nerves of the simple eyes at k. 
 
 1336. From the mathematical figure of its several component 
 parts, the transparent cornea is an important part of the optical 
 apparatus. Authors have not agreed with regard to its figure ; some 
 claim it to be plano-convex, the plane surface within ; others assert 
 that it is double-convex ; whilst the truth appears to be that it is 
 neither, but, like the human transparent cornea, it is a meniscus 
 (from the Greek, signifying a little moon] ; in other words, it is con- 
 vex on its outer surface, and concave within. 
 
296 ANIMAL PHYSIOLOGY. [LESSON 92. 
 
 1337. The crystalline lenses fit into the concave surfaces of the 
 cornea, but how accurately is not known, nor whether a space is 
 reserved for an aqueous humor these, at present, are matters of 
 conjecture. 
 
 1338. From the fact that the pigment, which limits the aperture 
 of the lens by coating its sides, from the circumference towards the 
 centre, and thus forms an iris, there is great probability of the 
 presence of an aqueous humor. 
 
 1339. If a carpenter had to fill a given space with boxes of uni- 
 form size, he must adopt one of three mathematical figures : they 
 must be either square, triangular, or hexagonal the first and last 
 are used in the formation of the corneas of insects. 
 
 1340. The eyes in the centre of the facetted organ are always 
 the largest, and most perfect hexagons in form. As they approach 
 the margins, they begin to assume a square form, which, at the ex- 
 treme edge, is perfected ; so that both these figures exist in the same 
 
 FIG. 420. FIG. 421. FIG. 422. 
 
 Centre of the transparent Transparent cornea, towards Transparent cornea, at 
 
 cornea, M. carnaria. the edge, M. carnaria. the edge, M. carnaria, 
 
 eye, chiefly ^ it would appear, for the economy of space. This is well 
 shown in the transparent cornea of Musca carnaria (Fig. 420) ; first 
 we see the perfect hexagons in the centre of the cornea ; secondly 
 (Fig. 421), the gradual change to a square form; the process of 
 change is still further continued, till at last a series of perfectly 
 square cells are formed (Fig. 422). 
 
 1341. In the cornea of a Beetle a similar arrangement occurs, 
 but the square cells are not so sharply formed ; so, too, in the Drag- 
 on-fly, although in this insect the hexagons glide into parallelograms 
 rather than squares, the like arrangement generally prevails ; but 
 there are exceptions. 
 
 1342. Such may be the structure of the eye in some insects, but 
 some important differences, not yet recorded, occur in the eyes of 
 other insects. A large Beetle, Prionus longimanus (its specific 
 name signifying " long arms," and applied to the great length of the 
 first pair of legs), commonly known as the " Harlequin-beetle," from 
 the many colors it possesses, and the peculiarity of their arrange- 
 
LESSON 92.] THE EYE IN INSECTS. 297 
 
 ment, has compound eyes of unusual size, and which offer great facil- 
 ities for studying the structure of the transparent cornea, and espe- 
 cially of the lenses. 
 
 1343. It has been already remarked that the cornea is lined with 
 a membrane, to the posterior portion of which the crystalline lenses 
 are attached, and removing this from the cornea of Prionus, and sub- 
 mitting it to the microscope, an interesting scene presents itself. 
 
 1344. The lines which separate the corneas severally, are strongly 
 marked ; the cells are, generally, perfectly round, although those to- 
 wards the margins are oval, and quite flat; these cells are so many 
 open holes (Fig. 423), as if to admit the anterior portion of the true 
 crystalline lens ; moreover, being smaller, they act as stops to a struc- 
 ture yet to be described. 
 
 1345. If we now examine the cornea from which this membrane 
 has been detached, a very remarkable sight meets us. 
 
 1346. The cells, or the transparent spaces of the cornea, are fill- 
 ed with a series of crystalline prisms, Fre 
 
 which stand up far above the level of 
 the membrane in which they are situ- 
 ated ; some of them are round, others 
 
 Fro. 423. 
 
 Posterior layer of the transparent Prismatic lenses in situ, Prionus Ion- 
 
 cornea, P. longimanus. gimanus. 
 
 oval; hexagons (six sides), pentagons (five sides), cubes, and even 
 triangles, are all represented in one or other of these prisms (Fig. 
 424). They appear to be so firmly impacted in the cells, that it is 
 only reasonable to suppose that they fit it accurately ; in this case 
 the anterior portion must be convex, fitting the concave inner surface 
 of the cornea. The terminal portions now presented to the specta- 
 tor, and which were applied to the round holes of the membrane 
 removed, are perfectly flat, but much larger than the round holes, 
 which, as before remarked, act as stops. This would give a series 
 of plano-convex lenticular bodies, sealed up, as it were, in the sub- 
 
298 ANIMAL PHYSIOLOGY. [LESSON 92. 
 
 stance of the transparent cornea a structure that may (and doubt- 
 less does) prevail to some extent in insects, and justify the peculiar 
 figure of the cornea of the Melolontha vulgaris, given by Straus- 
 Durckheim, and of Libellula by Muller. 
 
 1347. These prismatic, or lenticular bodies, are wider at their 
 anterior than at the posterior extremity ; they possess precisely the 
 appearance that a human crystalline lens, preserved in alcohol, pre- 
 sents they transmit light, but have lost the power of defining ob- 
 jects ; at best, they now possess but semi- transparency. 
 
 1348. It must be understood that this arrangement of lenses 
 (very like a Stanhope lens), in the transparent cornea, is in addition 
 to the double-convex lens, vitreous humor, &c., neither of which 
 were preserved in the beetle in question ; it had once been in spirit, 
 but had become dry long prior to dissection. 
 
 1349. At the margins of the cornea, the lenses have in some 
 instances fallen out, and display the entire depth of it admirably. 
 The horny transparent portion is thin, but the partitions between 
 the transparent portions have great substance, thus leaving deep 
 cells for the reception of the lenticular, prismatic bodies. 
 
 1350. Probably a transverse section of this cornea, undissected, 
 would have presented a figure very similar to that of Straus and 
 Muller, both of whom agree in making this portion of the compound 
 eye of insects of great depth. 
 
 1351. They only differ in one respect, as regards this tissue : 
 Straus says it is plano-convex ; Muller, that it is double-convex. 
 
 . 425. 1352. These preparations, therefore, demon- 
 
 strate that the horny layer which forms the trans- 
 parent cornea is concavo-convex ; instead of being 
 of great depth, as represented, it is a thin layer ; 
 that the interspaces between the facets of this tis- 
 sue descend, to a considerable space, in the pos- 
 terior direction, thereby leaving long and deep 
 cells for the reception of the plano-convex 
 prismatic crystalline bodies ; that these are shut 
 in by a layer filled with round holes, smaller than 
 the plane surface of these prisms ; that the an- 
 terior part of the true crystalline lens passes 
 through these round holes, the large margins of 
 which cut off the light, and form a kind of iris ; 
 and that the posterior portion of the last mei;- 
 
 fiection of the eye of .",., 
 
 Prionus longimanus. tioned lenses, with their deeper curve, touch the 
 
LESSON 93.] THE EYE IN AEACHNIDA, MOLLUSCA, ETC. 299 
 
 convex part of the conical vitreous humor, the space around the 
 point of contact being filled with pigmentary matter. 
 
 1353. This is illustrated by Fig. 425. The convex portion of 
 the transparent cornea is shown at a ; the concave surface of it at 
 b ; the descending walls of the cornea at c ; the prismatic bodies, 
 that are included in its substance, at d / the posterior layer, which 
 encloses the prisms, at #/ the crystalline lens is shown at /, its 
 posterior portion, in apposition with the conical vitreous humor, at 
 g ; and the conical vitreous humor, h. 
 
 LESSON XCIII. 
 
 THE EYE IN AEACHNIDA, MOLLUSCA, AND FISHES. 
 
 1354. In the Arachnida, the simple eyes are the largest and 
 most perfect forms of ocelli met with in the articulated classes. In 
 the Spiders they are generally eight in number, arranged symmetri- 
 cally in one or two transverse rows on the upper and forepart of the 
 cephalo-thorax. The largest forms of these organs are met with in 
 the Scorpions, in which they have been the most frequently ex- 
 amined. 
 
 1355. Beneath the transparent cornea, in the eye of the Scorpion, 
 there is a spherical, firm, transparent lens ; beneath this, a vitreous 
 humor, which fills half of the eyeball, surrounded by the pigmentuin 
 and the choroid, excepting on the forepart, where it bounds the pupil 
 like an iris, and on the back part, where it is penetrated by the 
 optic nerve. The optic nerve expands into a well-formed retina, 
 investing all the convex posterior portion of the vitreous humor. 
 
 1356. Organs of vision are not required, neither are they devel- 
 oped in the fixed or slow-moving Molluscous animals ; and in those 
 individuals of this class which possess them, they are not aggregated 
 together like those of the Worms, the Myriopods, or the Arachnida, 
 neither are they compound organs, like the eyes of the Crustacea and 
 Insects. 
 
 1357. In the Gasteropods the eyes are always two in number, 
 movable, and generally pedunculated frequently found at the sum- 
 mit of one pair of tentacles, as in the Slug and the Snail. Some of 
 the naked Gasteropods, as the Eolis (Fig. 263), the Doris, and 
 
300 ANIMAL PHYSIOLOGY. [LESSON 93. 
 
 others, appear to be destitute of eyes ; in the naked Aplysia they 
 are but minute black dots. 
 
 1358. In some of the Gasteropods (Harpa elongata, Fig. 381) 
 the eyes are placed on tubercles, at the bases, or near the bases of 
 the tentacles. Such is the arrangement in the beautiful Cyprea 
 tigris from the South Seas (Fig. 426). 
 
 1359. In this animal the two long tentacula (a, a) present, near 
 
 FIG. 426. 
 
 
 
 Cyprea Tigris, or Leopard Cowry. 
 
 their bases, two prominent, round, black, and movable eyes (c, c), 
 with smooth, transparent, glistening corneas. The tentacula being 
 placed above the mouth (b) and in front of the syphon (d), the eyes, 
 which are raised on tubercles at some distance from the base of tHe 
 long, slender tentacula, have a considerable range of vision. Above 
 the expanded foot (g, g) is seen the inner surface of the mantle (e), 
 turned up over a portion of the shell (&), and covered with small 
 ramified tentacular extensions (f), which warn the animal of danger 
 from behind. 
 
 1360. In the Carinaria Mediterranea the optic nerves are seen 
 passing directly to the eyes from the cerebral ring (Fig 380, i). 
 
 1361. In the general plan of their formation, the eyes of the 
 Molluscous animals form a near approach to the ordinary condition 
 of these organs in Fishes, and the higher vertebrated classes. 
 
 1362. In all the vertebrata the eyes are two in number, and 
 symmetrically disposed on the sides of the head, and the differences 
 which they present relate chiefly to the density of the media through 
 which the various animals receive the rays of light, and the extent 
 of development of the external protecting parts of these delicate 
 organs. 
 
 1363. From the imperfect development of the nervous system in 
 Fishes, and the obscurity of the element through which they move, 
 their organs of vision are of great size, and, from the density of the 
 
LESSON 94.] ORGANS OF VISION IN THE HIGHER ANIMALS. 301 
 
 watery medium around them, they have little necessity for an aqueous 
 humor, and their cornea is flat. To preserve this flatness in front, 
 the sclerotic coat is thickened and consolidated ; and it is also to 
 prevent its assuming the spherical form in Birds, by the equal pres- 
 sure of the contained fluids, that the sclerotic is there strengthened 
 with bony plates, which preserve the tubular form of the eye, and 
 the great convexity of the cornea in that class. 
 
 1364. The crystalline lens in Fishes is composed of minute trans- 
 parent fibres, disposed in concentric layers, and united FIG. 427. 
 by their serrated edges, as seen in the Codfish (Fig. 
 
 427), the layers increasing in density from the sur- 
 face to the centre of the lens. 
 
 1365. The organs of vision are smallest in such 
 Fishes as burrow in the mud and sand ; they are 
 larger in predaceous Fishes, which frequent the dark 
 
 _ & . . r . Fibres of the crys- 
 
 depths of the ocean, than in those which reside on taiiine lens, Codfish. 
 the shallow coasts, or in fresh waters. Ciliary processes are rarely 
 developed in this class. 
 
 LESSON XCIV. 
 
 ORGANS OF VISION IN THE HIGHER ANIMALS 
 
 1366. As the eyes, we must henceforth consider, possess a more 
 complicated structure than the organs hitherto examined, it appears 
 to be desirable to give a brief enumeration of the parts which col- 
 lectively form a visual organ in the higher animals. 
 
 1367. The globe of the eye is composed of tunics and humors. 
 The tunics are three in number, the 
 
 1. Sclerotic and cornea. 
 
 2. Choroid, iris, and ciliary processes. 
 
 3. Retina, and zonula ciliaris. 
 
 1368. The sclerotic (skleros, hard) and cornea form the external 
 tunic of the eye-ball, and give to it its peculiar form. The sclerotic 
 is much thicker behind than before ; it is pierced at its posterior 
 surface by the optic nerve, ciliary nerves, and arteries. The cornea 
 is attached to its anterior part, by means of a bevelled edge ; its an- 
 terior surface is also covered by a thin tendinous layer, the tunica 
 albuginea (white tunic), which is covered for a part of its extent by 
 the mucous membrane of the front of the eye, the conjunctive mem- 
 
302 ANIMAL PHYSIOLOGY. [LESSON 94. 
 
 brane, or conjunctiva : such is the brilliancy of its whiteness at this 
 part, that it is commonly called "the white of the eye." The con- 
 junctiva (human) is a tissue of great vascularity, and a figure of it, 
 
 copied from a preparation, is given (Fig. 
 428). The portion of the preparation 
 selected for illustration, is where the 
 membrane approaches the margin of the 
 upper eye-lid ; in this situation (seen at 
 the lower part of the figure) the capil- 
 laries are very minute, and densely ag- 
 gregated the general surface of the 
 
 Conjunctiva injected, human. membrane ( of both Ms) ig CQvered by 
 
 arteries, veins, and loosely scattered capillaries, such as form the 
 greater part of the figure. The Conjunctiva still lines the upper and 
 lower eye-lids, upon which it is displayed ; and so dense and minute 
 is the arrangement of the capillary plexuses along the line of the 
 lids, that, to unassisted vision, they appear to consist of simple lines 
 of intense redness. 
 
 1369. The choroid is a vascular membrane of a rich chocolate 
 brcwn color upon its external surface, and of a deep black color 
 within. Externally it is connected to the sclerotic coat, internally 
 to the retina. It is pierced posteriorly for the passage of the optic 
 nerve, and anteriorly it is connected with the iris, ciliary processes, 
 and junction of the cornea and sclerotic, by a dense white structure, 
 the ciliary ligament, which surrounds the circumference of the iris 
 like a ring. 
 
 1370. This membrane is composed of three layers : 1. An ex- 
 ternal or venous layer, which consists of veins arranged in a peculiar 
 manner, called vence vorticosce. 2. Middle, or arterial layer, is 
 formed by the ramifications of minute arteries, and secretes upon its 
 surface the pigmentum nigrum. 3. The internal layer presents a 
 beautiful appearance under the microscope ; it is composed of several 
 laminae of hexagonal cells, which contain the granules of pigmentum 
 nigrum (black paint). 
 
 1371. In animals the pigmentum nigrum is replaced by a layer 
 of considerable extent, and of metallic brilliancy, called the tapetum. 
 
 1372. The iris (a rainbow) is so called from its variety of color 
 in different individuals ; it forms a curtain or septum (partition) be- 
 tween the anterior and posterior chambers of the eye, and is pierced 
 in its centre by. a circular opening, called the pupil. 
 
 1373. The ciliary processes consist of a number of highly vascu- 
 
LESSON 94.] ORGANS OF VISION IN THE HIGHER ANIMALS. 303 
 
 lar, triangular folds, formed (apparently) by the plaiting of tlie in- 
 ternal layer of the choroid. They are about sixty in number (in 
 man), and may be divided into large and small, the latter being 
 situated in the spaces between the former. These processes are 
 covered by a thick layer of pigmentum nigrum. 
 
 1374. The retina is the expanded portion of the optic nerve, and 
 is'the medium, equivalent to the ground glass of the Camera obscura, 
 upon which all images seen by the eye are painted. Notwithstand- 
 ing its extreme delicacy, it consists of three layers ; these are, the 
 external, or Jacob's membrane ; middle, or nervous membrane ; in- 
 ternal, or vascular membrane. 
 
 1375. The zonula ciliaris is a thin vascular layer, which con- 
 nects the anterior margin of the retina with the circumference of the 
 lens. It presents upon its surface a number of small folds corres- 
 ponding with the ciliary processes, between which they are received. 
 
 1376. The HUMORS of the eye are also three ; these are, the 
 aqueous humor, situated in the anterior and posterior chambers of 
 the eye. 
 
 1377. The anterior chamber is the space between the cornea in 
 front, and the iris and pupil behind, 
 
 1378. The posterior chamber is the narrow space bounded by 
 the posterior surface of the iris and pupil in front, and by the ciliary 
 processes and lens behind. 
 
 1379. The crystalline humor, or lens, is situated behind the 
 pupil, and is ' surrounded by the ciliary processes, which slightly 
 overlap its margin. It is more convex on the posterior than on the 
 anterior surface, and is embedded in the anterior part of the vitreous 
 humor, from which it is separated by the y IG . 429. 
 
 hyaloid membrane. It is invested by a 
 
 proper capsule, which contains a small FIG. 430. 
 
 quantity of fluid, and is retained in its 
 
 place by the attachment of the zonula 
 
 ciliaris. In its ultimate structure the 
 
 crystalline lens consists of a multitude of 
 
 fibres, the edges of which are wavy, or 
 
 undulate (Fig. 429). In other animals 
 
 they are serrated, and by this means lock 
 
 J ' J Fibres of the crys- 
 
 into each other, and form a tissue. This taiiine lens, human. 
 
 can be seen, in the higher animals, in the fibres of the Ox (Fig. 430). 
 
 1380. The vitreous humor forms the principal bulk of the globe 
 of the eye. It is enclosed in a delicate membrane, the hyaloid, 
 
304 ANIMAL PHYSIOLOGY. [LESSON 95. 
 
 which sends processes into its interior, forming cells in which the 
 humor is retained. A small artery may sometimes be traced through 
 the centre of the vitreous humor to the capsule of the lens. 
 
 1381. The sclerotic coat is a tunic of protection, and the cornea 
 a medium for the transmission of light. The choroid supports the 
 vessels destined for the nourishment of the eye, and by its pigraentum 
 nigrum absorbs all loose and scattered rays that might confuse the 
 image impressed upon the retina. The iris, by means of its powers 
 of expansion and contraction, regulates the quantity of light admit- 
 ted through the pupil. 
 
 1382. The transparent cornea, and the humors of the eye, have 
 for their office the refraction of the rays in such proportions as to 
 direct the image in the most favorable manner upon the retina. 
 
 1383. Such, then, are the several parts, and such their uses in 
 the eyes of the higher animals, and it only now remains to point out 
 the peculiarities of structure which distinguish classes, or the indi- 
 vidual members of classes in the ascending scale of being. 
 
 LESSON XCY. 
 
 THE EYES IN REPTILES, BIRDS, AND MAMMALIA. 
 
 1384. The eyes of Reptiles are more fitted to receive the rays 
 of light from the rare medium of the atmosphere than those of 
 fishes ; their cornea is generally more convex, their aqueous and 
 vitreous humors more abundant, and their lens less spherical in form ; 
 they also possess two movable eyelids, and a membrana nictitans (a 
 thin membrane, drawn rapidly across the front of the eye, by which 
 its surface is wiped, and obstructions removed ; the exercise of this 
 organ is said to simulate winking). 
 
 1385. In many of the Crocodilian reptiles, and the Tortoises and 
 Turtles, the sclerotic, at its anterior part, supports a circle of osseous 
 plates, which surround the transparent cornea, as in birds (Fig. 
 431). These plates around the cornea existed in the Ichthyosaurus, 
 and are found abundantly in the fossilized condition. 
 
 1386. In the eye of a Tortoise (Emys Europcea, Fig. 432) the 
 cornea (a) is pretty convex, from the abundance of aqueous humor 
 (b) in the anterior chamber, and the margin of the cornea is sup- 
 ported by ten osseous plates (Fig. 431), imbricated like those of 
 birds, and placed in the anterior part of the sclerotic (d, d), near to 
 the ciliary processes (/), and to the fixed margin of the iris (e). 
 
LESSON 95.] THE EYES IN REPTILES, BIRDS, ETC. 
 
 305 
 
 FIG. 431. 
 
 Eye of Emys Europcea. 
 
 The crystalline lens (g) has a compressed FIG. 432. 
 
 elliptical form, and a smaller axis than 
 the vitreous humor (h). The retina 
 terminates with a thickened edge at the 
 beginning of the cil- 
 iary processes, and a 
 similar structure is 
 presented in most of 
 the Chelonian rep- 
 tiles. 
 
 1387. In the 
 
 Snapping Turtle, the middle coat of the choroid presents a magnifi- 
 cent spectacle, when its vessels have been minutely injected, a figure 
 of which is given (Fig. 433), copied from a preparation. 
 
 1388. The posterior part of the choroid, it will be seen, is pierced 
 for the transmission of the optic nerve (a) ; it is called the foramen 
 of Soemmering. 
 
 1389. It will be seen that the vessels at this part are very mi- 
 nute, and that they gradually and steadily increase in size to the 
 anterior portion, just below the ciliary processes. At this point they 
 assume a very beautiful arrangement, and one that is peculiar, as 
 compared with other choroids. 
 
 FIG. 433. FIG. 434. 
 
 Choroid coat of the eye, Snapping Turtle. 
 
 20 
 
 Ciliary processes, Snapping Turtle. 
 
306 ANIMAL PHYSIOLOGY. [LESSON 95. 
 
 1390. The ciliary processes are also well developed in this Tur- 
 tle (Fig. 434) ; they are, however, remarkable for their shortness 
 and thickness, as compared with the same organs in other animals. 
 The lower part of this preparation joins the upper part of 433. 
 
 1391. In Birds the round pupil is capable of great and rapid 
 changes of dimension, aided by the remarkable mobility of the iris. 
 This highly movable and bright colored iris, with its black uvea (the 
 posterior coat of the iris), appears sometimes detached from the free 
 anterior margin of the choroid, and its colored surface presents ag- 
 gregations of minute globules, like those of the choroidal pigment. 
 
 1392. Birds possess a membrana nictitans, very perfect upper 
 and lower eye-lids, which are provided with tarsal cartilages and 
 Meibomian glands, and even eye-lashes, in addition to the necessary 
 muscles for their elevation and depression. 
 
 1393. The eyes are large in most of the Herbivorous mammalia, 
 especially the ruminantia, the rodentia, and most of the pachyder- 
 mata (thick-skinned animals), and also in most of the nocturnal 
 species. They are very small, even in the adult state, in the bur- 
 rowing animals, as Moles, Shrews, &c. 
 
 1394. The same circumstances which modify the form of the eye, 
 and the proportions of its refractive parts in other classes and ani- 
 mals, affect the organ in this ; thus in the visual organ of swimming 
 mammalia, there are many affinities with the eyes of fishes ; those of 
 bats approach those of birds ; and intermediate forms are allied to 
 the eyes of reptiles. 
 
 1395. In Cetaceous animals, which constantly reside in water, 
 and receive the rays of light through that dense refractive medium, 
 the eyes have little aqueous humor, the cornea is flat, the crystalline 
 lens is large, dense, and spherical, and the vitreous humor is less 
 abundant than in terrestrial quadrupeds ; and in order to preserve 
 this flatness of the forepart of the eye, the sclerotic coat, like that 
 of fishes, is thick, firm, and elastic, especially over the back and the 
 anterior parts of the eye. The sclerotic is an inch thick at the back 
 and the anterior parts of the eye in the Whale. 
 
 1396. The large eye of the ruminantia, and of most other her- 
 bivorous quadrupeds, often presents a greater lateral than vertical di- 
 rection of the transparent cornea, the pupil, and even of the entire 
 eye-ball, by which the lateral range of vision is extended in these 
 timid and watchful animals, during the inclined position of the 
 head. 
 
 1397. The visual requirements of these animals are peculiar; 
 
LESSON 96.] THE EYES IN MAMMALIA AND MAN. 
 
 307 
 
 when the head is bowed down to the ground, and the creatures are 
 occupied in cropping the herbage, microscopic vision is required ; but 
 when seeking the best pastures, or keeping a watchful look-out for 
 fear of surprises from their natural enemies, the feline species, tele- 
 scopic vision is essential. For this purpose they possess a seventh 
 muscle to the eye-ball one more than belongs to other animals 
 this is called the retractor muscle, and its office is to draw the eye- 
 ball back into the orbit, thereby effecting great alteration in its focal 
 capabilities. The eyes of a dead Cow, or Sheep, are generally re- 
 tracted deep into the orbit, by the contraction of these muscles. 
 This muscle may be fitly compared to the coarse adjusting screw of 
 a microscope; the fine adjustment has yet to be explained. 
 
 1398. While the muscles of the eye in all animals contribute, by 
 their action, in altering the focal length of the eye, the last act, by 
 which thorough sharpness of definition is acquired, is reserved for 
 the ciliary processes. It has been stated that these bodies impinge 
 upon the crystalline lens, at its margins ; in 
 
 addition to being highly vascular, they are 
 also provided with erectile tissues, and when 
 the capillaries are distended with blood, the 
 processes become erect. In this condition 
 their combined action slightly moves the lens, 
 by which means the last process of perfect ad- 
 justment prevails, and is made complete. 
 
 1399. The ciliary processes of the rumi- 
 nant are without parallel in the animal king- 
 dom ; they consist, even in the injected state, 
 of a vast number of folds (Fig. 435), and 
 when straightened out by the action of the 
 erectile tissue, they must exercise an unusual 
 influence on the position of the lens. 
 
 FIG. 435. 
 
 Ciliary processes, Ox. 
 
 LESSON XCYI. 
 
 THE EYES IN MAMMALIA AND MAN, CONTINUED. 
 
 1400. In the Feline animals, the ciliary processes are beautifully 
 developed, and more nearly resemble those of Man. 
 
 1401. In the domestic Cat (Fig. 436), they consist of a number 
 
308 
 
 ANIMAL PHYSIOLOGY. 
 
 [LESSON 96. 
 
 of plates, of great breadth at their anterior portion ; the vessels at 
 the posterior portion gradually glide into the vessels (arteries) of 
 the middle layer of the choroid. 
 
 1402. The veins (venae vorticosae) of the external membrane of 
 the choroid, are well seen in a preparation of them from the Dog (Fig. 
 437). Some of them are of large size, and all of them (in the prepa- 
 ration) distinguished by great roundness. 
 
 1403. But it is in the visual apparatus of Man, organized for 
 seeing in the erect position of the trunk, that we find the most com- 
 plete protection of the -orbits, by solid osseous parietes, and the 
 most parallel direction of their axes. Shaded externally by the eye- 
 rie. 437. 
 
 FIG. 486. 
 
 Ciliary processes, eye of the Cat. 
 
 Venae vorticosae, choroid of Dog. 
 
 brows, which are moved by their proper muscles, and protected by 
 two highly movable eye-lids, which continue over the forepart of the 
 organ, the human eye presents only a small rudiment of the third 
 eye-lid, or membrana nictitans, so highly developed in most of the 
 inferior vertebrata. 
 
 1404. The eye-balls are nearly spherical in form, with their axes 
 parallel, and perforated behind by the optic nerves ; they are sup- 
 ported on the back part by a large deposit of adipose substance (fat) , 
 and are moved by four recti (straight) , and two oblique muscles. 
 
 1405. A longitudinal section of the human eye will be found 
 at Fig. 438. 
 
 The function of the optic nerve is to inform the brain of all the 
 details of form, color, &c., of any object pictured upon its thin ex- 
 pansion, the retina. 
 
 The tubes, or fibres, as they have been erroneously described, 
 which enter into the composition of an optic nerve, decussate (di- 
 
LESSON 96.] THE EYES IN MAMMALIA AND MAN. 309 
 
 vide, intermingle) with the tubes of the other optic nerve. By this 
 arrangement, an object seen by one eye has its history given, simul- 
 taneously, to that part of the brain with which the other optic nerve 
 communicates, directly through its agency. 
 
 If one eye be closed, by the hand or a bandage, objects seen by 
 the open eye are not sharp and distinct, because it has lost half its 
 ordinary power. 
 
 In looking through Telescopes and Microscopes, it is most impor- 
 
 FIG. 438. 
 
 Longitudinal section of the human eye. 
 a. The sclerotic coat. 
 6. The cornea, connected to the former by means of a bevelled edge. 
 
 c. The choroid, connected anteriorly with 
 
 d. The ciliary ligament, and 
 
 e. The ciliary processes. 
 / The iris. 
 
 g. The pupil. 
 
 h. The third layer of the eye, the retina. 
 
 i. The canal of Petit, which encircles the lens (m); the thin layer in front of this canal is the 
 
 zonula ciliaris. 
 
 k. The anterior chamber of the eye, containing the aqueous humor. 
 I. The posterior chamber. 
 
 m. The lens, more convex behind than before, and enclosed in its capsule. 
 n. The vitreous humor, enclosed in the hyaloid membrane, 
 o. Tubular sheath of the hyaloid membrane, which serves for the passage of the artery of the 
 
 capsule of the lens. 
 
 p. Neurilemma (sheath) of the optic nerve. 
 q. The arteria centralis retina, embedded in its centre. 
 
 tant to keep both eyes open, and this can easily be done by turning 
 the head aside, and thus diverting the axis of vision. Those persons 
 who shut one eye never see an object distinctly, and what is worse, 
 they have created pain in both eyes ; the open one has been strained 
 to do impossibilities, and the closed eye intensely excited but not 
 permitted to be active. If properly managed, the spectator will 
 have a clear view of the object in the microscope, and distinctly see, 
 at the same time, objects on the table, and at a wide angle. 
 
 1406. The ciliary processes may be seen in two ways, either 
 
310 
 
 ANIMAL PHYSIOLOGY. 
 
 [LESSON 96. 
 
 by removing the iris from its attachment to the ciliary ligament, 
 when a front view of the processes will be obtained, or by making a 
 transverse section through the globe of the eye, when they may be 
 examined from behind, as in Fig. 439. 
 
 1407. In addition to the figure (slightly enlarged) displaying the 
 arrangement of the full series of ciliary processes, a more highly 
 magnified view of them, with their vessels injected, is given in 
 Fig. 440. 
 
 1408. The vessels derived from the arteria centralis retina, and 
 
 Fio. 439. 
 
 TV,. 440. 
 
 Ciliary processes, human, 
 a. The divided edge of the three tunics, 
 
 sclerotic, choroid, and retina. 
 &. The pupil. 
 
 c. The iris. 
 
 d. The ciliary processes. 
 
 e. The scalloped anterior border of the 
 
 retina. 
 / Choroid. 
 
 Ciliary processes, human. 
 
 distributed to the vascular membrane of the retina, form, when in- 
 jected, an object of great interest; it is shown in Fig. 441. 
 
 1409. In the progress of development of the human organs of 
 vision, during embryo life, the crystalline lens is found embedded 
 between two highly vascular membranes ; the one is the anterior, 
 and the other the posterior ', capsule of the lens. These membranes 
 appear to attain their maximum (greatest) development at a certain 
 given period, from which time the vessels begin to disappear by ab- 
 sorption, and at the time of birth are entirely removed. 
 
 1410. The capillaries of the anterior capsule (Fig. 442) are de- 
 rived from the ciliary arteries, and form a beautiful series of loops 
 divided into four somewhat triangular spaces, which collectively oc- 
 cupy the entire membrane, save the centre. In the process of ab- 
 sorption, the central portion is first removed, in each triangle, and 
 
LESSON 96.] THE EYES IK MAMMALIA AND MAN. 
 
 311 
 
 this process continues until four arched vessels alone remain attached 
 to the inner circumference of the membrane, and finally these dis- 
 appear. 
 
 1411. This membrane is sometimes (at a certain age) found at- 
 tached to the crystalline lens, and sometimes it is detached ; when 
 
 FIG. 442. 
 
 FIG. 441. 
 
 Vessels of the arteria centralis 
 retina, human. 
 
 Anterior capsule of the lens, human. 
 
 FIG. 443. 
 
 the latter occurs, it has been usual to .call it " membrana pupillaris " 
 it is in reality the anterior capsule of the lens. 
 
 1412. The posterior capsule lies between the crystalline lens and 
 the vitreous humor. To perform its function, it requires to be vas- 
 cular, but from the peculiarity of its position it appears to be cut 
 off from all sources of supply. 
 
 1413. The arteria centralis retina passes through the vitreous 
 humor, and having reached the 
 
 posterior capsule, terminates in a 
 plexus of capillaries distributed 
 to that membrane, but which are 
 not nearly so numerous as those 
 of the anterior capsule ; they are 
 represented in Fig. 443 ; a is the 
 terminal portion of the arteria 
 centralis retina. 
 
 1414. The vessels of the pos- 
 terior, like those of the anterior 
 capsule, are removed by absorp- 
 tion when their function has ceas- 
 
 ed, and the lens fully formed ; it Posterior capsule of the lens. 
 
 sometimes, but rarely, happens that they become permanent, and 
 
312 ANIMAL PHYSIOLOGY. [LESSON 96. 
 
 when this occurs they produce a form of blindness for which there 
 is no remedy. 
 
 1415. Amongst other tissues which enter into the composition 
 of the eye-lids, are two thin lamellae of fibro-cartilage, called the 
 tarsal cartilages, which give form and support to the eye-lids. 
 
 1416. Between "these cartilages, and embedded in them, lie the 
 Meibomian glands, so called from Meibomius, their discoverer. 
 They consist of a long duct, which opens upon the edge of the eye- 
 lids, surrounded by a cluster of follicles, which conceal the tube, ex- 
 cept at its terminal portion. As these glands extend the whole width 
 of the cartilages, they are necessarily longer in the upper than the 
 under eye-lid ; they differ in number in the two lids, there being 
 twenty-four in the upper and thirteen in the lower lid. 
 
 1417. These glands secrete a fatty matter, and may be regarded 
 as a form of sebaceous glands. Their chief function appears to be 
 to keep the margins of the eye-lids soft (greasy), and prevent adhesion. 
 They can at all times be well seen upon the inner surface of the lids, 
 shining and glistening like so many rows of pearls (Fig. 444). In 
 
 Fitt. 444. 
 
 Meibomian glands, in situ. 
 
 composition they consist of a lengthened tube, or duct, which extends 
 from one end of the gland to the other. On either side a number 
 of small follicles are found, so densely clustered as to entirely con- 
 ceal the duct, except at its termination. The tarsal cartilages are 
 grooved for the reception of these glands, which are retained in their 
 place by a layer of cartilage, which folds over each gland, and another 
 similar layer, which folds over the former. By lifting up these two 
 folds, a gland can be easily lifted out of the groove in the lower 
 cartilage, not being in any way attached to it. An enlarged figure 
 of a gland, so obtained, is shown in Fig. 445; when magnified, 
 
LESSON 96.] THE EYES IN MAMMALIA AND MAN. 
 
 313 
 
 each gland is seen to consist of a basement mem- Fl - 445 - 
 
 brane (a), and an epithelium (6) containing seba- 
 ceous matter ; c represents the orifice of the duct. 
 These glands are subject to disease, especially in 
 children, which appears to partake of a congested 
 character; the secretion is suspended, and the 
 ducts closed up ; in this form of disease the mar- 
 gins of the lids become inflamed, and the loss of 
 the eye-lashes invariably follows. 
 
 1418. Thus we have seen these complicated 
 optical instruments, the most universal in their 
 distribution in the animal kingdom, and by far the 
 noblest organs of sense, gradually advancing to 
 perfection, from the animals of lowly organization, 
 in which we first found them, up to man, where all 
 their internal essential parts, and their external 
 accessory apparatus, are the most exquisitely fin- 
 ished, and most minutely adjusted. It is chiefly 
 through their means that he is connected to the 
 external world, that he is enabled to provide for 
 
 A MeiDomian gland, re- 
 
 his wants, to acquire the materials of thought, moved and magnified. 
 to enjoy the sublime spectacle of the starry Heavens, and to gaze 
 with fervent admiration upon the wonders and beauties of ever 
 changing Nature, as revealed to him in this magnificent World ! 
 
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