presented to
of tbe
of Toronto
Mrs»Albert Gooderham
A MANUAL OF ZOOLOGY
p
A
MANUAL OF ZOOLOGY
BY
T. JEFFREY PARKER, D.Sc., F.R.S.
PROFESSOR OF BIOLOGY IN THE UNIVERSITY OF OTAGO,
DUNEDIN, N.Z.
AND
WILLIAM A. HASWELL, M.A., D.Sc., F.R.S.
PROFESSOR OF BIOLOGY IN THE UNIVERSITY OF SYDNEY, N.S.W.
RE VISED AND ADAPTED FOR THE USE OF AMERICAN
SCHOOLS AND COLLEGES
A^*3
\'L***
THE MACMILLAN COMPANY
LONDON : MACMILLAN & CO., LTD.
IQOO
All rights reserved
COPYRIGHT, 1900,
BY THE MACMILLAN COMPANY.
Set up and electrotyped January, 1900. Reprinted September,
1900.
Nortoooti
J. S. Gushing & Co. - Berwick & Smith
Norwood Mass. U.S.A.
PREFACE
IN planning the present work the aim of the authors has
been to provide a manual embodying a course of study
adapted to the requirements of the student chiefly in higher
classes of schools, and to some extent in junior classes of
universities. To make this, within the necessarily narrow
limits of space imposed, anything more than a bare synopsis,
it has been necessary to restrict the extent of the ground
covered. This has been done (i) by leaving out altogether
certain classes of existing animals; (2) by omitting all de-
scriptions of extinct groups ; (3) by dealing only very briefly
with embryology. Opinions must differ as to the best selec-
tion of groups for an elementary manual of this kind. But
broadly, there can, it has appeared to us, be little doubt that
what should be omitted, or only briefly dealt with, are the
groups of rare occurrence and uncertain relationships, the
greater part of the space being devoted to the more familiar
representatives of the large phyla.
A course of laboratory and museum instruction, supple-
mented by work in the field and on the seashore, is abso-
lutely necessary in order that any sound knowledge of
vi PREFACE
zoology may be attained. The present manual does not
provide such instruction, but is intended to be used in
association with it, and the examples selected for de-
scription are such as may under most circumstances be
readily obtained.
The general plan is similar to that followed in the Text-
Book of Zoology by the same authors, but the restricted
space has necessitated considerable modifications. We
have not adopted the method, followed in various recent
manuals, of beginning with one of the larger Invertebrata
or with a vertebrate, and working from that upwards and
downwards. The reasons given for such a mode of treat-
ment we understand to be that if we begin with the simplest
animals, the Protozoa, we discourage and embarrass the
beginner by introducing him at once into a world entirely
new to him, requiring him at the same time to learn the use
of an entirely unfamiliar instrument the microscope. But in
our opinion, the difficulty is much less than is alleged by the
advocates of the alternative method, and the advantage of
presenting the facts at the outset in a natural and logical
order by far outweigh any such disadvantages. We are con-
vinced that any general acquaintance which the student may
possess beforehand with a rabbit or a crayfish will be of little
real value to him when he begins to take up seriously the
study of its structure. Moreover an elementary knowledge
of the use of the microscope is absolutely essential to any
adequate study of Zoology as an intellectual discipline, and
this difficulty, such as it is, may as well be met first as last.
PREFACE vii
Owing to the lamented death of Professor T. Jeffrey
Parker, at a time when but little progress had been made
with this work, his actual share in it has been but slight :
but as it was planned between us, and the earlier parts had
the advantage of his revision, and more especially as it owes
a great deal to his work in the Text-Book it has been
thought right to let it appear under our joint names as origi-
nally intended.
I have to express very great indebtedness to Professor W.
Newton Parker for the pains he has taken in revising the
proof-sheets and for many valuable suggestions which he has
made during the progress of the work.
WILLIAM A. HASWELL.
PREFACE TO THE AMERICAN EDITION
THIS American edition of Parker and HaswelPs useful
and concise " Manual of Zoology " has been adapted for the
use of American schools. Common American forms closely
similar to the European or Australasian ones described in
the English edition, have been mentioned, so that the
student can use the book in examining the allied typical
forms from his own country. In the majority of cases the
European species differ only in trivial characteristics, so
that one general description will answer for both.
In a very few cases the American editor has revised and
corrected views or statements not believed to be correct.
For example, few, if any, American zoologists would regard
Limulus as an undoubted Arachnidan.
A few additional American animals have been referred to
and figured, while a few cuts not reproduced in the English
edition have been copied from Parker and HaswelPs
"Text-book of Zoology," and also from Sedgwick's "Text-
book of Zoology."
ix
CONTENTS
PAGE
PREFACE TO THE ENGLISH EDITION ,v
PREFACE TO THE AMERICAN EDITION . . . . ix
LIST OF ILLUSTRATIONS . ... . ... xvii
INTRODUCTION . . . . •'/. . . . . i
Definition of zoology . . . ."..'. . I
Binomial nomenclature 2
Individual variations . . ... . . . . 3
Hybrids . . . 3
Definition of morphology . . . , . . 4
Definition of histology . . . . . * . . 4
Definition of embryology 4
Classification . 5
Phyla . .......... 7
Organic evolution . . . • . . . . . 9
Genealogical tree . 9
Palaeontology . . 10
Fossils 10
Succession of life in time . . . . . ' . . n
Phylogeny . . . : * . ... .n
Distribution of animals, in space and in time , . . 1 1
The plankton '. . . .12
The necton . . . . . . . . . .12
The benthos 12
Definition of a fauna 12
Zoo-geographical regions 12
Definition of physiology 12
Definition of ethology or binomics 13
CONTEXTS
SECTION I
PAGE
PHYLUM PROTOZOA 14
Class i. The Rhizopoda 14
Example of the Class — Amceba proteus .... 14
Class 2. The Mastigophora 34
Example of the Class — Euglena viridis .... 34
Class 3. The Infusoria 45
Example of the Class — Paramcecium caudatwn . . 45
Class 4. The Sporozoa 55
Example of the Class — Monocystis agilis . 55
SECTION II
THE METAZOA 59
Oosperm or egg 59
Male cell or sperm 60
Fertilisation . 60
Segmentation of the oosperm 60
Germinal layers 62
Tissues, epithelium 63
Glands, ducts 63
Connective tissues 65
Fibrous tissue 65
Fat 65
Cartilage 66
Bone 66
Muscular tissue 66
Nerve tissue, ganglia, nerves 66
Organs 66
Exoskeleton 67
Endoskeleton 67
Organs of digestion 68
Organs of respiration 70
The blood 70
Blood vascular system 70
Heart 71
Organs of excretion 71
CONTENTS xiii
PAGE
The brain . . . 71
Reproduction 72
The phyla of the animal kingdom 74
Tabular view of the phyla 75
SECTION III
PHYLUM PORIFERA 76
Example of the Phylum and Class — Sycon gelatinosum . 76
SECTION IV
PHYLUM CCELENTERATA 90
Class i. The Hydrozoa „• .91
Example of the Class — Obelia . . . . 91
Class 2. The Scyphozoa 108
Example of the Class — Aurelia aurita .... 108
Class 3. The Actinozoa 1 14
Example of the Class — Tealia crassicornis . . .114
Class 4. The Ctenophora 125
Example of the Class — Hormiphora plumosa . . .125
SECTION V
PHYLUM PLATYHELMINTHES 129
Class i. The Trematoda 129
Example of the Class — Distomum hepaticum . . .129
Class 2. The Turbellaria 137
Example of the Class — Planaria torva . . . .138
Class 3. The Cestoda 138
Example of the Class — Tania solium . . . .138
Class 4. The Nemertinea 145
Example of the Class — Tetrastemma .... 145
SECTION VI
PHYLUM NEMATHELMINTHES 149
Class. The Nematoda 149
Example of the Class — Ascaris lumbricoides . . . 149
xiv CONTENTS
SECTION VII
PAGE
PHYLUM ECHINODERMATA 157
Class i. The Asteroidea 157
Example of the Class — Asterias vulgaris . . '157
Class 2. The Ophiuroidea 169
Example of the Class — Ophioglypha lacertosa . .169
Class 3. The Echinoidea 170
Example of the Class — Strongylocentrotus . . . 1 70
Class 4. The Holothuroidea 1 73
Example of the Class — Holothuria ednlis . . . 1 73
Class 5. The Crinoidea 174
Example of the Class — Ante don 174
SECTION VIII
ROTIFERA, POLYZOA, AND BRACHIOPODA 178
Class i. Rotifera 178
Example of the Class — Brachionus rubens , . .178
Class 2. Polyzoa 181
Example of the Class — Bugula avicularia . . .181
Class 3. Brachiopoda 184
Example of the Class — Magellania flavescens . . .184
SECTION IX
PHYLUM ANNULATA 188
Class i. The Chaetopoda 188
Example of the Class — Nereis dumerilii . . . .189
Class 2. The Hirudinea 203
Example of the Class — Hirudo medicinalis . . . 203
SECTION X
PHYLUM ARTHROPODA 212
Class i. The Crustacea 213
Example of the Class — Astacus fluviatilis . . . 213
Class 2. The Onychophora 236
Example of the Class — Peripatus 236
CONTENTS xv
PAGE
Class 3. The Myriapoda 239
Example of the Class — Scolopendra morsitans . . . 239
Class 4. The Insecta 241
Example of the Class — Periplaneta americana . . 241
Class 5. The Arachnida 254
Example of the Class — Scorpio 254
SECTION XI
PHYLUM MOLLUSCA . . 264
Class i. The Pelecypoda 265
Example of the Class — Anodonta cygnea . . . 265
Class 2. The Amphineura 281
Example of the Class — Chiton spinosus .... 281
Class 3. The Gastropoda 284
Example of the Class — Helix nemoralis .... 284
Class 4. The Cephalopoda 296
Example of the Class — Nautilus pompilius . . . 298
SECTION XII
PHYLUM CHORDATA 310
Subphylum i. The Adelochorda 311
Example of the Subphylum — Balanoglossus . . .311
Subphylum 2. The Urochorda 314
Example of the Subphylum — Ascidia . . . .314
Subphylum 3. The Vertebrata 322
Examples of the Subphylum — Amphioxus, Petromyzon,
Pisces, etc 322
Division A. The Acrania 323
Example of the Division — Amphioxus lanceolatus . . 323
- Division B. The Craniata 328
Examples of the Division, the dogfish, lizard, and rabbit . 328
Class i. Cyclostomi 360
Example of the Class — Petromyzon marinus . . . 360
Class 2. Pisces 365
Examples of the Class — Sharks, perch, and lung fishes . 365
xvi CONTENTS
PAGE
Subclass i. Elasmobranchii 366
Example of the Subclass — Scyllium and Mustelus . . 366
Subclass 2. Holocephali (omitted) 394
Subclass 3. Teleostomi 394
Example of the Subclass — Salmofario .... 395
Subclass 4. Dipnoi . . . 405
Example of the Subclass — Ceratodus fosteri . . . 405
Class 3. Amphibia . . . . . . . 407
Example of the Class — Rana temporaries . . . 408
Class 4. Reptilia 433
Examples of the Class — Lizards, turtles, crocodile . . 434
Class 5. Aves 456
Example of the Class — Columba livia . . . -457
Class 6. Mammalia 491
Example of the Class — Lepus cuniculus .... 491
LIST OF ILLUSTRATIONS
FIG. PAGE
1. Amoeba proteus 15
2. Amoeba polypodia 18
3. Quadrula, Hyalosphenia, Arcella, Difflugia .... 20
4. Forms of Foraminifera 22
5. Shells of Foraminifera 25
6. Actinophrys sol ......... 26
7. Actinosphierium eichhornii 27
8. Forms of Heliozoa . . . • . . . . . 29
9. Liteocircus annularis 31
10. Actinomma asteracanthion 32
11. Collozoum inerme ......... 33
12. Euglena viridis 35
13. Forms of Mastigophora 37
14. Forms of Choanoflagellata 39
15. Forms of Dinoflagellata 40
16. Noctiluca miliaris . 41
17. Volvox globator . . . 43
1 8. Paramoecium caudatum 47
19. Forms of Ciliata ......... 49
20. Forms of Tentaculifera . . . . . . . .51
21. Forms of Ciliata • • • 53
22. Vorticella ., . . 54
23. Monocystis agilis . . 56
24. Gregarina -57
25. Ovum of a sea-urchin 60
26. Diagram of maturation and fertilization of ovum . 6l
27. Segmentation of the oosperm 62
28. Forms of epithelium ........ 64
29. Diagram illustrating the structure of glands .... 65
xviii LIST OF ILLUSTRATIONS
FIG. PAGE
30. Bones of arm with biceps muscle . ... . . -67
31. Viscera of male frog 69
32. Hydra 73
33. Sycon ciliatum 76
34. Sycon gelatinosum 77
35. Sycon gelatinosum, magnified 78
36. Sycon gelatinosum, transverse section 80
37. Ascetta primordialis .84
38. Section of Spongilla 85
39. Skeleton of sponges 87
40. Sponge spicules 88
41. Obelia colony 93
42. Nematocysts of Hydra 96
43. Dissection of Medusa . . 97
44. Development of Laomedea and Eudendrium ... 99
45. Structure of Hydra 100
46. Petasus and Glossocodon . 102
47. Bougainvillea ramosa ........ 103
48. Physaiia 106
49. Physaiia arethusa 106
50. Halistemma tergestinum 107
51. Aurelia aurita, partly dissected 109
52. Aurelia aurita, development in
53. Tessera princeps 113
54. Tealia crassicornis 115
55. Sea-anemone, in sections 116
56. Common sea-anemone 118
57. Corallium rubrum 118
58. Alcyonium palmatum 119
59. Tubipora musica 120
60. Pennatula sulcata 121
61. Flabellum curvatum 122
62. Astraea pallida 123
63. Dendrophyllia nigrescens and Madrepora aspera . . .124
64. Cancrisocia on back of a crab . . . . . .125
65. Hormiphora plumosa . . . . . . . .126
66. Hormiphora plumosa, section of a tentacle . . . .127
67. Idyia roseola 128
LIST OF ILLUSTRATIONS xix
FIG. PAGE
68. Distomum hepaticum, natural size 130
69. Distomum hepaticum, anatomy 131
70. Distomum hepaticum, development 135
71. Trematodes : Amphistomum and Homalogaster . . . 136
72. Structure of a triclad turbellarian 137
73. Planaria polychroa 138
74. Taenia solium 139
75. Taenia solium, head magnified 140
76. Taenia solium, proglottis . 141
77. Development of tape-worm 142
78. Cyst of Taenia echinococcus with daughter-cyst and scolices 144
79. Diagram of organs of a Nemertine ..... 146
80. Tetrastemma, structure •- . 147
81. Ascaris lumbricoides .- . . . . . . 150
82. Ascaris lumbricoides, dissection of female . . . . 151
83. Diagram of nervous system of Nematoda .... 152
84. Ascaris lumbricoides, posterior end of male dissected . . 153
85. Trichina spiralis . . . . . . . . 155
86. Starfish, showing tube feet .158
87. Starfish, vertical section through an arm . . . .161
88. Starfish, diagrammatic sections . . . . ... 164
89. Asterias rubens, digestive system 165
90. Ambulacral systems of a starfish .166
91. Anthenea, dorsal surface 167
92. Anthenea, ventral surface . . . . . . .168
93. Ophioglypha lacertosa 169
94. Strongylocentrotus 171
95. Corona of sea-urchin 172
96. Apical systems of plates of sea-urchin 172
97. Cucumaria planci 174
98. Antedon . . . 175
99. Metacrinus interruptus 177
100. Brachionus rubens 179
101. Bugula avicularia 182
102. Plumatella 183
103. Pedicellina 184
104. Magellania flavescens 185
105. Magellania lenticularis, sagittal section .... 186
xx LIST OF ILLUSTRATIONS
FIG. PAGE
1 06. Nereis dumerilii, natural size 189
107. Nereis dumerilii, parapodium 190
1 08. Nereis dumerilii, setae 191
109. Nereis dumerilii, anatomy ....... 192
no. Nereis dumerilii, transverse section ..... 194
in. Section through the eye of Nereis 196
112. Brain and connecting nerves of Nereis . . . . 197
113. Serpuke in their tubes 198
114. Trochosphere of Eupomatus 199
115. Lumbricus agricola 200
116. Lumbricus, setae 201
117. Hirudo medicinalis 204
118. Head of Hirudo medicinalis, showing the three jaws . . 205
119. Head of Hirudo quinquestriata 206
1 20. Nephridium of the medicinal leech 208
121. Transverse section of Hirudo ...... 209
122. Diagram of blood-channels of leech ..... 210
123. Astacus fluviatilis 214
124. Appendages of Astacus 217
125. Astacus fluviatilis, dissection from right side . . .221
126. Respiratory organs of Astacus fluviatilis .... 223
127. Thorax of crayfish, transverse section 225
128. Diagram of the circulation in the crayfish .... 226
129. Nervous system of Astacus fluviatilis 227
130. Reproductive organs of Astacus fluviatilis .... 229
131. Cancer pagurus 230
132. Pagurus bernhardus 231
133. Apus glacialis 232
134. Development of Apus 233
135. Cyclops and Calocalanus 234
136. Lepas anatifera 235
137. Peripatus capensis ........ 237
138. Peripatus capensis, head, etc. ...... 237
139. Internal organs of Peripatus ...... 238
140. Scolopendra 240
141. Periplaneta americana 242
142. Mouth-parts of the cockroach 243
143. Pieris rapae, larva, and pupa 244
LIST OF ILLUSTRATIONS xxi
FIG. PAGE
144. Carpet beetle, larva, and pupa 245
145. Culex and larva 246
146. Internal organs of cockroach ...... 247
147. Periplaneta, its tracheal system 248
148. Periplaneta, nervous system 249
149. Honey bee, queen, worker, and drone .... 253
150. Red ant, male, worker, and female 253
151. Euscorpio 255
152. Scorpion, ventral side 256
153. Scorpion, internal organs 258
154. Epeira diadema 259
155. Cattle tick 260
156. Itch mite 260
157. Limulus, ventral view 261
158. Anodonta cygnea, entire animal 265
159. Anodonta cygnea, right valve, and animal .... 268
1 60. Anodonta, section of shell and mantle .... 269
161. Anodonta cygnea, animal 270
162. Anodonta cygnea, dissection from left side . . . . 273
163. Anodonta cygnea, sections of gills . ... . 274
164. Anodonta, diagram of circulatory system .... 276
165. Anodonta, embryo and glochidium . . ... 278
1 66. Mytilus edulis 279
167. Teredo navalis . . . ... ... . . 280
1 68. Chiton spinosus . . 281
169. Chiton, ventral view 282
170. Chiton, nephridial and genital systems .... 283
171. Helix nemoralis 285
172. Triton nodiferus, shell 286
173. Triton nodiferus, median section of shell . . . . 287
174. Solarium perspectivum, under side . . .- . . 288
175. Terebra oculata, shell 289
176. Cyprsea moneta, animal expanded, in its shell . .... 290
177. Doris tuberculata 290
178. Shell-bearing Pteropoda . 291
179. Patella vulgata, animal, ventral view 292
1 80. Limax, lung-cavity, etc 293
181. Triton nodiferus 294
xxii LIST OF ILLUSTRATIONS
FIG. PAGE
182. Sepia cultrata 297
183. Nautilus pompilius 298
184. Nautilus pompilius, section of shell 299
185. Spirula peronii 301
1 86. Sepia cultrata, shell 301
187. Loligo vulgaris 302
1 88. Argonauta argo 303
189. Chromatophore of Sepia 304
190. Sepia cultrata, dissected 305
191. Nautilus pompilius, anatomy 306
192. Sepia officinalis, jaws 307
193. Sepia officinalis, enteric canal 307
194. Nautilus pompilius, oral surface of male and female . . 309
195. Balanoglossus 311
196. Balanoglossus, diagrammatic sagittal section of anterior end . 312
197. Ascidia . 314
198. Ascidia 315
199. Ascidia, diagram of longitudinal section . . . . 317
200. Ascidia mammillata, larva . 320
201. Diagram of metamorphosis of larva into fixed Ascidian . 321
202. Botryllus violaceus 322
203. Amphioxus lanceolatus, ventral and side view . . . 323
204. Amphioxus, diagram of anatomy 325
205. Amphioxus lanceolatus, sections 327
206. Dogfish, fins, etc. 329
207. Lacerta viridis ......... 330
208. Lepus cuniculus, lateral view of skeleton with outline of body . 331
209. Scyllium, vertebrae 334
210. Lizard, vertebrae of 335
211. Lepus cuniculus 336
212. Scyllium canicula 338
213. Lacerta agilis, three views of skull 340
214. Fore and hind limbs of vertebrate, diagram . . . 341
215. Tooth, longitudinal section, semi-diagrammatic . . . 343
216. Scyllium canicula, dissection 345
217. Lacerta agilis, viscera in their natural relations . . . 348
218. Circulation of a fish, diagram 351
219. Scyllium canicula, brain, dorsal view 353
LIST OF ILLUSTRATIONS xxiii
FIG. PAGE
220. Eye of man, diagrammatic horizontal section . . -357
221. Petromyzon marinus 361
222. Myxine glutinosa, head 362
223. Petromyzon marinus 363
224. Scyllium canicula, side view of skull 371
225. Scyllium, pectoral arch 373
226. Scyllium canicula, dissection 376
227. Diagram of the vascular system of a fish .... 378
228. Scyllium catulus 382
229. Dogfish, egg-case 385
230. Scyllium, embryo, with gills, etc. 386
231. Lamna cornubica - . 387
232. European sting-ray (Urolophus cruciatus) .... 388
233. Skeleton of Urolophus testaceus 390
234. Heptanchus, side view of skull . . . . . 391
235. Salmo fario, fins, etc 395
236. Salmo fario, caudal end of vertebral column . . . 397
237. Pleuronectes cynoglossus 398
238. Ctenoid and ganoid scales . . . . . . . 399
239. Polypterus birchir . . 399
240. Skull of sturgeon . 400
241. Salmo fario, entire skull, left side ." . . * . 401
242. Premaxillae of Sargus 402
243. Hippocampus (sea-horse) 404
244. Ceratodus fosteri 405
245. Ceratodus fosteri, anterior portion of skeleton . . . 406
246. Rana temporaria 409
247. Rana temporaria, skeleton 412
248. Rana temporaria, skull, different views . , . .413
249. Rana esculenta, shoulder girdle 415
250. Rana esculenta, pelvic girdle from right side . . .416
251. Rana temporaria, dissection from left side . . . .417
252. Rana temporaria, heart with cavities laid open . . . 420
253. Rana temporaria, arterial system, etc 421
254. Rana temporaria, venous system, etc. ..... 424
255. Rana esculenta, brain from above and below . . . 426
256. Rana esculenta, urinogenital organs of male .... 428
257. Rana esculenta, urinogenital organs of female . . . 429
xxiv LIST OF ILLUSTRATIONS
FIG. PAGE
258. Rana temporaria, stages in life-history .... 430
259. Salamandra maculosa 432
260. Siren lacertina 433
261. Pygopus lepidopus 437
262. Hatteria punctata 438
263. Grecian tortoise, Testudo graeca 439
264. Skeleton of crocodile 441
265. Cistudo lutaria 442
266. Chelone midas 443
267. Skull of rattlesnake 445
268. Pectoral arch and sternum of Lacerta agilis . . . 446
269. Heart of monitor, Varanus 448
270. Brain of alligator, from above 449
271. Pineal eye of Hatteria punctata, section . . . .451
272. Poison apparatus of rattlesnake 454
273. Columba livia, diagram with most of feathers removed . 458
274. Columba livia, feather 460
275. Pterylosis of Columba livia 462
276. Columba livia, bones of the trunk 463
277. Columba livia, cervical vertebra 464
278. Columba livia, sacrum of nestling 465
279. Columba livia, skull of young 466
280. Columba livia, hyoid apparatus 467
281. Columba livia, bones of left wing 468
282. Columba livia, bones of left manus of nestling . . . 469
283. Columba livia, left innominate of nestling .... 470
284. Columba livia, bones of left hind-limb . . . -471
285. Columba livia, part of left foot of embryo .... 472
286. Columba livia, muscles of left wing 473
287. Columba livia, dissection from right side .... 475
288. Heart of pigeon, dorsal aspect 478
289. Columba livia, brain, different views 479
290. Eye of pigeon 480
291. Columba livia, right membranous labyrinth of ear . .481
292. Columba livia, male urinogenital organs .... 482
293. Columba livia, female urinogenital organs .... 482
294. Feather of cassowary 484
295. Wing of nestling of Opisthocomus and of adult Apteryx . 486
LIST OF ILLUSTRATIONS xxv
FIG. PAGE
296. Callus bankiva, domestic fowl, egg at time of hatching . 489
297. Lepus cuniculus, side view of skeleton with outline of body 492
298. Lepus cuniculus, atlas and axis .- . 494
299. Lepus cuniculus, skull, side, and ventral view . . . 497
300. Lepus cuniculus, shoulder girdle . . . . . 501
301. Lepus cuniculus, distal end of fore-leg and carpus . . 502
302. Lepus cuniculus, innominate bones and sacrum . . . 503
303. Lepus cuniculus, bones of hind foot ..... 504
304. Lepus cuniculus, lateral dissection of head, neck, and thorax 506
305. Lepus cuniculus, stomach, intestine, and liver, etc. . . 508
306. Lepus cuniculus, heart, from right side .... 509
307. Lepus cuniculus, the vascular system 511
308. Lepus cuniculus, larynx, ventral and dorsal views . . 513
309. Lepus cuniculus, brain, dorsal and ventral view . . . 514
310. Lepus cuniculus, two dissections of brain .... 516
311. Lepus cuniculus, longitudinal vertical section of brain . 518
312. Lepus cuniculus. urogenital organs 519
313. Lepus cuniculus, anterior end of vagina, with right uterus, etc. 521
314. Duck-bill, Ornithorhynchus anatinus 526
315. Spiny ant-eater, Echidna aculeata ..... 527
316. Virginian Opossum, Didelphys virginiana .... 528
317. Dasyure, Dasyurus viverrinus 529
318. Rock wallaby, Petrogale xanthopus 530
319. Koala, Phascolarctos cinereus 531
320. Unau, or two-toed sloth 532
321. Tatu armadillo, Dasypus sexcinctus 533
322. Scaly ant-eater, Manis pentadactyla 534
323. Aard-vark, Orycteropus capensis 534
324. Killer, Orca gladiator 535
325. Section of upper jaw, with baleen plates, of Babenoptera . 536
326. Harbor seal, Phoca vitulina 540
327. Bat, Synotus barbastellus . 542
MANUAL OF ZOOLOGY
INTRODUCTION
Zoology, the branch of Natural History which deals with
animals, is one of the two subdivisions of the great science of
Biology, which takes cognizance of all organisms, or things
having life, as distinguished from such lifeless natural objects
as rocks and minerals. The second of the two subdivisions
of Biology is Botany, which deals with plants.
The subject-matter of Zoology, then, is furnished by the
animals which inhabit the land-surface, the air, and the
salt and fresh waters of the globe ; the aim of the science
is to find out all that can be known of these animals,
their structure, their habits, their mutual relationships, their
origin.
The first step in the study of Zoology is the recognition
of the obvious fact that the innumerable individual animals
known to us may be grouped into what are called species,
the members of which resemble one another so closely that
to know one is to know all. The following example may
serve to give the reader a fairly accurate notion of what
zoologists understand by species, and of the method of
naming species which has been in use since the time of the
great Swedish naturalist Linnaeus.
B I
2 MANUAL OF ZOOLOGY
The domestic cat, the European wild cat, the ocelot, the
leopard, the tiger, and the lion are animals which agree with
one another in the general features of their organisation —
in the number and form of their bones and teeth, in the
possession of retractile claws, and in the position and
characters of their internal organs. No one can fail to
see that these animals, in spite of differences of size, colour,
markings, etc., are all, in the broad sense of the word,
" cats." This is expressed in the language of systematic
Zoology by saying that they are so many species of a single
genus.
According to the system of binomial nomenclature intro-
duced by Linnaeus, each kind of animal receives two names
— one the generic name, common to all species of the
genus ; the other the specific name, peculiar to the species
in question. Both generic and specific names are Latin in
form, and are commonly Latin or Greek in origin, although
frequently modern names of persons or places, with Latinised
terminations, are employed. In giving the name of an ani-
mal, the generic name is always placed first, and is written
with a capital letter, the specific name following it, and
being written, as a rule, with a small letter. For instance,
to take the examples already referred to, the domestic cat is
called Felis domestica, the European wild cat F. catus, the
leopard F. pardus, the tiger F. tigris, the lion F. leo. Thus
the systematic name of an animal is something more than a
mere appellation, since it indicates the affinity of the species
with other members of the same genus : to name an animal
is, in fact, to classify it.
It is' a matter of common observation that no two indi-
viduals of a species are ever exactly alike : two tabby cats,
for instance, however they may resemble one another in the
general characters of their colour and markings, invariably
INTRODUCTION 3
present differences in detail by which they can be readily
distinguished. Individual variations of this kind are of
universal occurrence. Moreover, it often happens that
the members of a species are divisible into groups distin-
guishable by fairly constant characters : among domestic
cats, for instance, we find white, black, tabby, gray, and tor-
toiseshell cats, besides the large long-haired Persian breed,
and the tailless Manx cat. All these are distinguished as
varieties of the single species, Felis domestica.
It is often difficult to decide whether two kinds of ani-
mals should be considered as distinct species or as varieties
of a single species, and no universal rule can be given for
determining this point. Among the higher animals mutual
fertility is a fair practical test, the varieties of a species
usually breeding freely with one another and producing fer-
tile offspring, while distinct species either do not breed
together or produce infertile hybrids or mules. Compare,
for instance, the fertile mongrels produced by the union of
the various breeds of domestic dog with the infertile mule
produced by the union of the horse and ass. But this rule
is not without exception, and in the case of wild animals is,
more often than not, impossible of application : failing it,
the only criterion of a "good species" is usually the pres-
ence of constant differences from allied species. Suppose,
for instance, that a naturalist receives for description a
number of skins of wild cats, and finds, after an accurate
examination, that in some specimens the tail is two-thirds
the length of the body and the skin of a uniform reddish
tint with a few markings on the head, while in the rest the
tail is nearly half as long as the body and the skin tawny
with black stripes. If there are no intermediate grada-
tions between these two sets of individuals, they will be
placed without hesitation in distinct species: if, on the
4 MANUAL OF ZOOLOGY
other hand, there is a complete series of gradations between
them, they will be considered to form a single variable
species.
As, therefore, animals have to be distinguished from one
another largely by structural characters, it is evident that
the foundations of a scientific Zoology must be laid in
Morphology, the branch of science which deals with form
and structure. Morphology may be said to begin with an
accurate examination of the external characters ; the divi-
sions of the body, the number and position of the limbs,
the characters of the skin, the positions and relations of the
mouth, eyes, ears, and other important structures. Next the
internal structure has to be studied, the precise form, posi-
tion, etc., of the various organs, such as brain, heart, and
stomach being made out : this branch of morphology is
distinguished as Anatomy. And, lastly, the various parts
must be examined by the aid of the microscope, and their
minute structure, or Histology, accurately determined. It
is only when we have a fairly comprehensive knowledge of
these three aspects of a given animal — its external charac-
ters, its rough anatomy, and its histology — that we can with
some degree of safety assign it to its proper position among
its fellows.
An accurate knowledge of the structure of an animal in
its adult condition is not, however, all-sufficient. Nothing
has been made more abundantly clear by the researches of
the last half-century than that the results of anatomy and
histology must be checked, and if necessary corrected, by
Embryology — i.e. by the study of the changes undergone
by animals in their development from the egg to the adult
condition. A striking instance is afforded by the common
barnacles which grow in great numbers on ships' bottoms,
piers, etc. The older zoologists, such as Linnaeus, grouped
INTRODUCTION 5
these creatures, along with snails, mussels, and the like, in
the group Mollusca, and even the great anatomical skill of
Cuvier failed to show their true position, which was made out
only when Vaughan Thompson, about fifty years ago, proved,
from a study of the newly hatched young, that their proper
place is among the Crustacea, in company with crabs,
shrimps, and water-fleas.
Given a sound knowledge of the anatomy, histology, and
embryology of animals, their Classification may be attempted
—.that is, we may proceed to arrange them in groups and
sub-groups, each capable of accurate definition.
The general method of classification employed by zoolo-
gists is that introduced by Linnaeus, and may be illustrated
by reference to the group of cats which we have already
used in the explanation of the terms genus, species, and
variety.
We have seen that the various kinds of true cat — domes-
tic cat, lion, tiger, etc. — together constitute the genus
Felis. Now there is one member of the cat-tribe, the
cheetah, or hunting leopard, which differs from all its allies
in having imperfectly retractile claws and certain peculiari-
ties in its teeth. It is therefore placed in a distinct genus,
Cyn&lurus, to mark the fact that the differences separating
it from any species of Felis are of a more fundamental char-
acter than those separating the species of Felis from one
another.
The nearest allies of the cats are the hyaenas, but the
presence of additional teeth and non-retractile claws — to
mention only two points — makes the interval between
hyaenas and the two genera of cats far greater than that
between Felis and Cynselurus. The varying degree of differ-
ence is expressed in classification by placing the hyaenas in
a separate family, the Hycenida, while Felis and Cynaelurus
6 MANUAL OF ZOOLOGY
are placed together in the family Felidce. Similarly the
civets and mongooses form the family Viverridce ; the dogs,
wolves, jackals, foxes, etc., the family Canidcz; bears, the
family Ursidce; and so on.
All the foregoing animals have sharp teeth adapted to a
flesh diet, and their toes are armed with claws. They there-
fore differ fundamentally from such animals as sheep, deer,
pigs, and horses, which have flat teeth adapted for grinding
vegetable food, and hoofed feet. The differences here are
obviously far greater than those between any two of the
families mentioned above, and are emphasised by placing
the flesh-eater in the order Carnivora, the hoofed animals
in the order Ungulata. In the same way gnawing animals,
such as rats, mice, and beavers, form the order Rodentia ;
pouched animals, such as kangaroos and opossums, the
order Marsupialia; and so on.
Carnivora, Ungulata, Rodentia, Marsupialia, etc., although
differing from one another in many important respects, agree
in the possession of a hairy skin and in the fact that they all
suckle their young. They thus differ from birds, which have
a covering of feathers, and hatch their young from eggs.
The differences here are considerably more important than
those between the orders of quadrupeds referred to, and are
expressed by placing the latter in the class Mammalia, while
birds constitute the class Aves. In the same way the scaly,
cold-blooded lizards, snakes, tortoises, etc., form the class
Reptilia; the slimy-skinned, scaleless frogs, toads, and sala-
manders the class Amphibia ; and the finned, water-breathing
fishes the class Pisces.
Mammals, birds, reptiles, amphibians, and fishes all agree
with one another in the possession of red blood and an inter-
nal skeleton — an important part of which is the backbone
or vertebral column — and in never having more than two
INTRODUCTION 7
pairs of limbs. They thus differ in some of the most funda-
mental features of their organisation from such animals as
crabs, insects, scorpions, and centipedes, which have colour-
less blood, a jointed external skeleton, and numerous limbs.
These differences — far greater than those between classes
— are expressed by placing the backboned animals in
the phylum or sub-kingdom Chordata, the many-legged
armoured forms in the phylum Arthropoda. Similarly, soft-
bodied animals with shells, such as oysters and snails, form
the phylum Mollusca, polypes and jellyfishes the phylum
Ccelenterata. And, finally, the various phyla recognised by
zoologists together constitute the kingdom Animalia.
Thus the animal kingdom is divided into phyla, the phyla
into classes, the classes into orders, the orders into families,
the families into genera, and the genera into species, while
the species themselves are assemblages of individual animals
agreeing with one another in certain constant characters. It
will be seen that the individual is the only term in the series
which has a real existence : all the others are mere groups
formed, more or less arbitrarily, by man.
To return to the animal originally selected as an example,
it will be seen that the zoological position of the domestic
cat is expressed as follows : —
Kingdom — ANIMALIA.
Phylum — CHORDATA.
Class — MAMMALIA.
Order — CARNIVORA.
Family — Felidce.
Genus — Felis.
Species —F. domes fica.
The object of systematic zoologists has always been Jo
8 MANUAL OF ZOOLOGY
find a natural as opposed to an artificial classification of
animals. Good instances of artificial classification are the
grouping of bats with birds on the ground that both possess
wings, and of whales with fishes on the ground that they both
possess fins and live in the water. An equally good example
of a natural classification is the grouping of both bats and
whales under the head of Mammalia because of their agree-
ment, in all essential points of anatomy, histology, and
embryology, with the hairy quadrupeds which form the bulk
of that class.
With the older zoologists the difficulty was to find some
general principle to guide them in their arrangement of
animals — some true criterion of classification. It was
believed by all but a few advanced thinkers that the in-
dividuals of each species of animal were descended from
a common ancestor, but that the original progenitor of each
species was totally unconnected with that of every other,
having, as Buffon puts it, "participated in the grace of a dis-
tinct act of creation." To take an instance : all wolves were
allowed to be descended from a pair of ancestral wolves, and
all jackals from a pair of ancestral jackals, but the original
pair in each case was supposed to have come into being by
a supernatural process of which no explanation could or
ought to be offered. Nevertheless it was obvious that a
jackal was far more like a wolf than either of them was like
a tiger, and that in a natural system of classification this fact
should be expressed by placing the wolf and jackal in one
family, the tiger in another.
All through the animal kingdom the same thing occurs :
no matter what group we take, we find the species com-
posing it resemble one another in varying degrees, or, as it
is sometimes expressed, have varying degrees of relationship
to one another. On the view that each species was sepa-
INTRODUCTION 9
rately created, the word relationship was used in a purely
metaphorical sense, as there could, of course, be no real
relationship between two groups of animals having a totally
independent origin. But it was assumed that creation had
taken place according to a certain scheme in the Divine
Mind, and that the various species had their place in this
scheme like the bits of glass in a mosaic. The problem of
classification was thus to discover the place of each species
in the pattern of the unknown design.
The point of view underwent a complete change when,
after the publication of Darwin's Origin of Species in 1859
the Doctrine of Descent or of Organic Evolution came to
be generally accepted by biologists. A species is now
looked upon, not as an independent creation, but as having
been derived by a natural process of descent from some pre-
existing species, just as the various breeds of Domestic Fowl
are descended from the little jungle-fowl of India. On this
view the resemblances between species referred to above are
actually matters of relationship, and species are truly allied
to one another in varying degrees, since they are descended
from a common ancestor. Thus a natural classification
becomes a genealogical tree, and the problem of classifica-
tion is the tracing of its branches.
This, however, is a matter of extreme difficulty. Repre-
senting by a tree the whole of the animals which have ever
lived on the earth, those existing at the present day would
be figured by the topmost twigs, the trunk and main
branches representing extinct forms. Thus the task of
arranging animals according to their relationships would be
an almost hopeless one but from two circumstances : one,
that remains of many extinct forms have been preserved :
the other, that the series of changes undergone by an ani-
mal in its development from the egg often forms an epitome
io MANUAL OF ZOOLOGY
of the changes by which, in the course of ages, it has been
evolved from an ancestral type. Evidence furnished by the
last-named circumstance is, of course, furnished by embry-
ology : the study of extinct animals constitutes a special
branch of morphology to which the name Palaeontology is
applied.
The solid crust of the earth is composed of various kinds
of rocks divisible into two groups : (i) Igneous rocks, such
as granite and basalt, the structure of which is due to the
action of the internal heat of the globe, and which originate
below the surface and are not arranged in layers or strata ;
(2) Aqueous or sedimentary rocks, which arise by the disin-
tegration, at the surface of the earth, of pre-existing rocks,
the fragments or debris being carried off by streams and
rivers and deposited at the bottom of lakes or seas. Being
formed in this way by the deposition of successive layers or
strata, the sedimentary rocks have a stratified structure, the
lowest being in every case older than the more superficial
layers. The researches of geologists have shown that there
is a general order of succession of stratified rocks ; that they
may be divided into three great groups, each representing
an era of time of immense but unknown duration, and that
each group may be subdivided into more or fewer systems
of rocks, each representing a lesser period of time.
Imbedded in these rocks are found the remains of various
extinct animals in the form of what are called fossils. In
the more recent rocks the resemblance of these to the hard
parts of existing animals is perfectly clear; we find shells
hardly differing from those we pick up on the beach, bones
easily recognisable as those of mammals, birds, or fishes,
and so on. But in the older rocks the fossils are in many
cases so different in character from the animals existing at
the present day as to be referable to no existing order. We
INTRODUCTION II
find birds with teeth, great aquatic reptiles as large as whales,
fishes, molluscs, Crustacea, etc., all of an entirely different
type from any now existing. We thus find that the former
were in many cases utterly unlike the present animal inhabi-
tants of the globe, and we arrive at the notion of a succession
of life in time, and are even able, in exceptionally favourable
circumstances, to trace back existing forms to their extinct
ancestors.
By combining the results of comparative morphology,
embryology, and palaeontology we get a department of
Zoology called Phytogeny, the object of which is to trace
the pedigrees of the various groups. There are, however,
very few cases in which this can be done with any approach
to exactness; most " phylogenies " are purely hypothetical,
and merely represent the views at which a particular zoolo-
gist has arrived after a more or less exhaustive study of the
group under discussion.
Animals may also be studied from the point of view of
Distribution. One aspect of this study is inseparable from
Palaeontology, since it is obviously necessary to mention in
connection with a fossil the particular system or systems of
rocks in which it occurs : thus we distinguish geological
distribution or distribution in time.
The distribution of recent forms may be studied under
two aspects, their horizontal or geographical distribution,
and their vertical or bathymetrical distribution. To men-
tion the latter first, we find that some species exist only on
plains, others — hence called alpine forms — on the higher
mountains ; that some marine shells, fishes, etc., always keep
near the shore (littoral species), others live at great depths
(abyssal species) , while others (pelagic species) swim on the
surface of the ocean. Among aquatic animals, moreover,
whether marine or fresh-water, three principal modes of life
12 MANUAL OF ZOOLOGY
are to be distinguished. There are animals such as jelly-
fishes, which float on or near the surface of the water, and
are carried about passively by currents ; such forms are
included under the term Plankton. Most fishes, whales, and
cuttle-fishes, on the other hand, are strong swimmers, and
are able to traverse the water at will in any direction ; they
together constitute the Nekton. Finally, such animals as
crabs, oysters, sponges, zoophytes, etc., remain permanently
fixed to or creep over the surface of the bottom, and are
grouped together as the Benthos.
Under the head of geographical distribution we have such
facts as the absence of all land-mammals, except bats in
New Zealand and the Polynesian Islands, the presence of
pouched Mammals, such as kangaroos and opossums, only
in some parts of America and in Australia and the adjacent
islands, the entire absence of finches in Australasia, and so
on. We find, in fact, that the fauna — i.e. the total animal
inhabitants — of a country is to a large extent independent
of climate, and that the faunae of adjacent countries often
differ widely. In fact, it is convenient in studying the geo-
graphical distribution of animals largely to ignore the ordi-
nary division into continents, and to divide the land-surface
of the globe into what are called zoo-geographical regions.
There are still two departments of zoological science to
be mentioned. As it is impossible to have a right under-
standing of a machine without knowing something of the
purpose it is intended to serve, so the morphological study
of an animal is imperfect without some knowledge of its
Physiology, i.e. of the functions performed by its various
parts, and the way in which they work together for the
welfare of the whole.
Not only may we study the action of a given animal's
organs, but also the actions of the animal as a whole, its
INTRODUCTION 13
habits, its relations to other animals, whether as friends, as
enemies, or as prey, to the vegetable kingdom, and to its
physical surroundings, such as temperature, humidity, etc.
In a word, the whole question of the relation of the organism
to its environment gives us a final and most important
branch of Natural History which has been called Ethology
or Bionomics.
SECTION L— PHYLUM PROTOZOA
1. THE RHIZOPODA
THE simplest members of the animal kingdom are for the
most part, too small to be visible without the aid of a micro-
scope, or at least so small as to appear to the unassisted eye
as extremely minute specks, not distinguishable, unless in
unusually active movement, from small particles of non-living
matter. Representatives of this class of simple minute ani-
mals are to be found living under a variety of different con-
ditions ; they are abundant in fresh water, running or
stagnant, and they are equally numerous in the sea, while
they are also to be found living in the fluids of cavities in
the bodies of higher animals. An example which will serve
to illustrate some of the main features of the class is the
Proteus animalcule or Amoeba. Amoeba (Fig. i) is some-
times to be found by searching with the aid of the micro-
scope in water from stagnant pools. To the unpractised
beginner it is a difficult task to discriminate between the
microscopic particles of non-living matter which form the
main part of the sediment at the bottom of such a pool —
de"bris of animals, vegetable or mineral nature — and the
object of which he is in search. Numerous minute bodies
will doubtless be seen which their active movements among
the motionless particles show to be endowed with life. But
SECT, i PHYLUM PROTOZOA 15
Amoeba is not one of these. It is to be recognised as a
glassy-looking, irregularly shaped particle with a definite out-
line. From a particle of some crystalline mineral substance,
to which such a description would equally well apply,
Amoeba would soon be distinguishable owing to the cir-
cumstance that it is constantly changing its shape.
This change is effected by the pushing out of projections
or processes, called pseudopods or pseudopodia (psd), which
FIG. i. — Amoeba proteus , a living specimen, c. vac, contractile vacuole,
nu, nucleus; psd, pseudopods. (From Parker's Biology, after Gruber.)
undergo various alterations of size and shape, and may be-
come withdrawn, other similar processes being developed
in their place. At the same time careful watching shows
that the Amoeba is also, with extreme slowness, changing its
position. This it effects by a kind of streaming motion. A
projection forms itself on one side, and the entire substance
of the Amoeba gradually streams into it ; a fresh projec-
tion appears towards the same side, the streaming move-
ment is repeated, and, by a constant succession of such
movements, an extremely gradual locomotion, which it often
takes very close watching to detect, is brought about. In
these movements, it is to be noticed, the Amoeba is influenced
16 MANUAL OF ZOOLOGY SECT.
to some extent by contact with other minute objects ; when
the processes come in contact with small grains of sand or
other similar particles, their movements are modified in such
a way that the Amoeba, in its slow progress onwards, passes
on one side of them, so that it might be said to feel its way
among the solid particles in a drop of sediment.
Judging from the nature of the movements, we are obliged
to infer that the substance of which this remarkable object is
composed must be soft and semi-fluid, yet not miscible with
the water, and, therefore, preserving a sharp contour. These
and other characteristics to be mentioned subsequently
enable us to conclude that we have to do with the substance
of complex chemical composition termed protoplasm, which
constitutes the vital material of all living organisms whether
animals or plants. In Amoeba the protoplasm is clearly dis-
tinguishable into two parts, an outer homogeneous, glassy-
looking layer completely enclosing a more granular internal
mass.
Examination of the Amoeba with a fairly high powe'r of the
microscope reveals the presence in its interior of two objects
which with a low power we should be likely to overlook. One
of these is a small rounded body of a homogeneous appear-
ance, which preserves its form during all the changes which
the Amoeba as a whole undergoes. This is termed the
nucleus (Fig. i, nu) • it is enclosed in an extremely delicate
membrane, and consists of a protoplasmic material differing
from that which forms the main bulk of the Amoeba in con-
taining a substance which refracts the light more strongly
and which has a stronger affinity for certain colouring
matters. The other minute object to be distinguished in the
interior appears as a clear rounded space (c. vac} in the
protoplasm. When this is watched it will be observed to
increase gradually in size till it reaches a maximum of, let us
I PHYLUM PROTOZOA 17
say, a fifth of the total diameter of the Amoeba, when by a
sudden contraction of its walls, it suddenly disappears, to
reappear presently and gradually grow again to its maxi-
mum size. This pulsating clear space is the contractile
vacuole.
By watching the Amoeba carefully for some time we may
be enabled to observe that the movements of the proto-
plasm of the body not only effect locomotion, but are con-
nected also with the reception of certain foreign particles
of organic nature — i.e., either entire minute animals or
plants, or minute fragments of larger forms — which form the
foodvi the Amoeba, — into the interior of the protoplasm.
A process of the protoplasm is pressed against such a par-
ticle of food, which becomes sunk in the soft substance,
and passes gradually into the interior. Here it becomes
surrounded by a little globule of watery fluid, and by
degrees partially or wholly disappears ; the part, if any,
which remains, subsequently passes outwards from the pro-
toplasm into the surrounding water. The matter which dis-
appears evidently mixes with the protoplasm and adds to its
bulk.
When food is abundant the Amoeba increases in bulk —
more food being ingested. than is required for simply main-
taining the size unaltered — and soon a remarkable change
takes place. The processes become withdrawn, and a fissure
appears dividing the Amoeba into two parts (Fig. 2). This
fissure grows inwards, and the two parts become more and
more completely separated from one another, till eventually
the separation becomes complete, and we have two dis-
tinct Amoebae resulting from the division of the one. While
the protoplasm has been undergoing this division into two
halves the nucleus also divides, and each of the two new
Amoebae possesses a nucleus similar to the original one,
c
iS
MANUAL OF ZOOLOGY
SECT.
and developed from it by division. It is mainly by this
simple process of division into two, or binary fission, as it is
called, that reproduction or multiplication takes place in the
Amoeba.
FIG. 2. — Amoeba polypodia in successive phases of division. The light spot is the
contractile vacuole; the dark the nucleus. (From Lang's Text-Book, after
F. E. Schulze.)
Amoeba thus consists of an undivided particle of proto-
plasm containing a nucleus. To such a particle the term
cell is applied. In higher groups the animal when fully
developed, consists of a number of such cells, usually differ-
ing in character in different parts ; and simple animals, such
i PHYLUM PROTOZOA 19
as Amoeba, in which the entire animal consists throughout
life of a single cell, are distinguished as unicellular from the
multicellular form in which a number of cells are combined.
The whole of the great group or phylum of animals — the
Protozoa — to which Amceba belongs, are distinguished from
all the remaining groups of the animal kingdom — the
Metazoa — by their unicellular character.
Among the Protozoa a large number resemble Amoeba in
the possession of pseudopodia or processes of the protoplasm.
The pseudopodia-bearing Protozoa constitute one of the great
divisions or classes into which the Protozoa are divided by
zoologists — the class known as the Rhizopoda. In only a
comparatively small proportion of the members of this class
have the pseudopodia the comparatively short and blunt
shape which they have in Amceba. All the Rhizopoda with
comparatively short and thick pseudopodia are grouped
together to form one of the leading divisions or orders of
Rhizopoda — the order Lobosa. Amoeba is one of the
simplest of these. The largest among the near relatives of
Amoeba is Pelomyxa, which may be as much as 8 mm. in
diameter, so that it is readily visible to the naked eye ; its
pseudopodia are very short and broad, and, instead of a
single nucleus, it contains a large number as well as many
contractile vacuoles. Other Lobosa differ from Amceba in
the presence of a shell or test enclosing the protoplasm.
One of these is Difflugia (Fig. 3, D), which is very common
in fresh water. Difflugia has a flask-shaped test formed of
agglutinated sand-grains and other foreign particles. The
main bulk of the protoplasm is contained in the interior of
the shell, but comparatively long pseudopodia are capable of
being pushed out through the mouth of the flask. It pierces
the wall of the cells of Spirogyra, inserts its pseudopods, lift-
ing the entire cell-contents out and passing them into its
20
MANUAL OF ZOOLOGY
SECT.
body within the shell (Stokes). An even commoner member
of the group is Arcella (Fig. 3, C). Arcella has a shell
much wider than that of Difflugia, convex on one side, flat on
the other. In the middle of the flat surface is a rounded
opening. The shell of Arcella is of a transparent, tough
FIG. 3.— A, Quadrula symmetrica; B, Hyalosphenia lata; C, Arcella vulgaris;
D, Difflugia pyriformis. (From Lang's Comparative Anatomy, after Schulze
and Wallich.)
material, which is said to be chitinoid from the fact that it
appears to resemble a substance termed chitin, of a horny
consistency, very general in its occurrence in the integument
of animals. This chitinoid test exhibits a minute pattern
when examined under a high power of the microscope.
I PHYLUM PROTOZOA 21
The bulk of the protoplasm is, as in Difflugia, enclosed
within the test, but a considerable portion of it may be
pushed out in the form of pseudopods. Several nuclei and
a contractile vacuole are contained in the protoplasm. The
body of the animal is colourless, and is attached to its test,
says Stokes, " by fine threads of its own substance." There
are several species in our fresh-water pools, among them
Arcella vulgaris (Fig. 3, C).
All the rest of the Rhizopoda differ from the Lobosa in
having the pseudopodia in the shape of slender threads.
Of these a remarkable and interesting group is the order
Foraminifera. A Foraminifer has a shell which is nearly
always composed of carbonate of lime. This we can readily
demonstrate by placing a drop of hydrochloric or nitric acid
on a mass of the shells, when they dissolve with efferves-
cence. In some Foraminifera the shell has a wide opening
on the exterior as in Difflugia and Arcella ; in others there
is no large opening, but the wall of the shell is perforated
by a number of minute pores scattered over its surface.
The greater part of the protoplasm is enclosed within the
shell, but part of it (Fig. 4) streams out from the single
large opening, or from the pores, in the form of slender
thread-like radiating pseudopodia, which, when they come
in contact with one another, may coalesce, and may in this
way give rise to a network. The protoplasm in the interior
contains a nucleus, but no contractile vacuole. The shape
of the shell is sometimes spherical, sometimes flask-shaped,
sometimes oval or elliptical. Only in a comparatively small
number of Foraminifera does it remain simple (/, 2) ; in the
great majority, though the shell when first formed is simple,
a little process or bud of protoplasm soon projects through
the wide opening or through the pores; this increases in
size, and becomes enclosed in a shell like the original one,
22
MANUAL OF ZOOLOGY
SECT.
3.Squammufina
4.M i I i o I a
FIG. 4. — Various forms of Foraminif era. In 4, Miliola,«, shows the living animal;
b, the same killed and stained; a, aperture of shell; f, food particles; nu,
nucleus; sh, shell. (From Blitschli's Protozoa and Claus's Zoology.)
I PHYLUM PROTOZOA 23
but usually a size larger, remaining in firm connection with
it, the cavities of the two remaining in communication with
one another through the original opening or openings at
which the bud first appeared. From this second shell in
turn a bud is given off in the same manner, and the process
is repeated again and again, until, instead of a single particle
of protoplasm enclosed in a single shell, there is formed a
composite structure, made up of a number of particles of
protoplasm, each with its nucleus, and each enclosed in a
shell, the whole of the shells being firmly united togethei,
and the whole of the particles of protoplasm being in con-
tinuity through the apertures of communication. The
several parts of such a compound shell, which are known as
the chambers, are variously arranged in different Forami-
nifera (Fig. 5), according to the way in which the succes-
sive buds have been given off. In some the buds succeed
one another in a straight line, and the compound shell
which results (j) has consequently its chambers arranged
in a straight row. Or the chambers may be developed
alternately on opposite sides of the original cell (5), or
with the new chambers entirely overlapping their prede-
cessors (4). In other cases the development of the buds
takes a winding course, the resulting shell having its cham-
bers arranged in some form of spiral, like the spiral of a
watch-spring or of a corkscrew. Such a spiral shell (6 — //)
assumes a great variety of forms in different Foraminifera,
owing to differences, not only in the shape of the chambers
themselves, but also in the nature of the spiral in which they
are arranged.
In many cases the shell is further complicated by the
development of what is termed the supplemental shell (Fig.
5, 8 b), a deposit of carbonate of lime outside the original
shell, traversed by a complex system of fine canals contain-
24 MANUAL OF ZOOLOGY SECT.
ing protoplasm, and sometimes produced into a number of
relatively large spines.
Though the great majority of Foraminifera have dense
shells composed of carbonate of lime, there are many in
which the shell resembles that of Difflugia in being com-
posed of foreign particles, such as sand-grains, cemented
together ; these are termed the arenaceous Foraminifera ;
some of these have one large opening, some a number of
pores. In certain fresh-water forms, such as Gromia, the
shell is chitinoid. In Gromia (Fig. 4, i) the chitinoid shell
has a wide mouth through which the protoplasm protrudes
to form a layer enclosing the shell and giving off the
pseudopodia.
Little is known of the reproduction of the Foraminifera.
But in some a remarkable mode of reproduction has been
observed. The protoplasm in the interior of the shell divides
up into a number of particles. Each of the bodies thus
formed possesses, instead of pseudopodia, a single delicate
whip-like appendage — the flagellum — which lashes to and
fro and propels the embryo Foraminifer through the water.
Such a flagellum-bearing embryo is termed zflagellula.
All the Foraminifera, with the exception of Gromia and
one or two allied forms, are marine, and the greater number
are pelagic — i.e., live in the surface waters of the open sea —
though they occur also inshore, and at almost all depths.
The pelagic Foraminifera are most abundant in warm lati-
tudes, where they occur in enormous numbers. The ocean
floor at depths of five hundred to twenty-eight hundred
fathoms is covered in many places with a mud-like deposit
which effervesces and dissolves when acid is added, and
which, when examined under the microscope, is found to
consist mainly of the shells of Foraminifera, which must
have fallen down from above on the death of the animals.
PHYLUM PROTOZOA
2.Logena
4.Frondicularia G.GIobigerma
Aflfc,
O.Pianorbulina
ll.Nummulires
FIG. 5. — Shells of Foraminif era . In 3, 4, and j, a shows the surface view, and b a
section; 8a is a diagram of a coiled cell without supplemental skeleton; 8b of
a similar form with supplemental skeleton (s. sk) ; and 10 of a form with over-
lapping whorls; in na half the shell is shown in horizontal section; b is a ver-
tical section; .*, aperture of shell; i — 15, successive chambers, i being always
the oldest or initial chamber. (After Carpenter, Brady, and Butschli.)
26 MANUAL OF ZOOLOGY SECT.
From the name of the genus — Globigerina (Fig. 5, 6) —
which occurs in the greatest abundance in this deposit, it is
known as the Globigerina ooze. In the deepest parts of the
ocean the Globigerina ooze is entirely absent, the calcareous
shells of the Foraminifera apparently becoming entirely dis-
solved before they can reach such great depths. It is inter-
esting to note that similar deposits were formed in previous
geological periods — the beds of chalk of the Cretaceous
period consisting, like the Globigerina ooze, in great measure
of the shells of Foraminifera, though apparently not formed
under the same conditions of depth. Another case of
massive deposition of Foraminifera in a former geological
period is the Nummulitic Limestone, a bed of limestone
made up, for the most part, of the shells of comparatively
gigantic Foraminifera, the Nummulites (Fig. 5, //).
A Rhizopod by no means uncommon in fresh water is
the so-called sun-animalcule, Actinophrys sol. The body
FIG. 6. — Actinophrys sol. a, axial filaments of pseudopods; «, nucleus;
/, pseudopod. (From Lang's Comparative Anatomy, after Greenacher.)
of Actinophrys (Fig. 6) is nearly spherical, and contains a
large nucleus and numerous vacuoles, some of which, situ-
ated near the surface, are contractile. The most charac-
teristic feature is formed by the pseudopodia, which, instead
I PHYLUM PROTOZOA 27
of being comparatively short and thick, as in Amceba and in
the other Lobosa, or extremely delicate, flexible, and thread-
like, as in the Foraminifera, are slender, but comparatively
stiff, and stand out straight from the surface of the sphere
in a radiating manner : they are capable of only very slow
28 MANUAL OF ZOOLOGY SECT.
movements. The pseudopodia owe their stiffness to the
presence of a rod of chitinoid material which lies in the axis
of each, and extends inward toward the middle of the pro-
toplasm. A large nucleus lies in the centre of the body. A
good many other genera are known which have pseudopodia
of the same general character as those of Actinophrys, and
these are accordingly grouped together as an order of
Rhizopoda — the order Heliozoa. Of these other genera of
Heliozoa, Aetinosph&rium (Fig. 7) is somewhat more com-
plex in structure than Actinophrys, the protoplasm being
divided into a central mass — the endosarc — in which the
vacuoles are small, and an outer layer — the ectosarc — in
which they are very large. Numerous nuclei are present,
and bodies containing chlorophyll — the characteristic green
colouring matter of plants. It frequently occurs in com-
pany with Actinophrys, among the leaves of Lemna and
other plants, and feeds on microscopic forms, ajso Rotifers
(Stokes). Some of the Heliozoa, instead of being composed
like Actinophrys entirely of soft protoplasm, have support-
ing and protecting hard parts. Such hard, or compara-
tively hard, parts in any animal, whatever form they may
assume, whether that of an enclosing shell or crust, or a
system of internal bones or other firm structures, are known
under the general term of skeleton. In those Heliozoa in
which a skeleton occurs it is sometimes a shell of aggluti-
nated sand-grains, like the shell of Diffiugia, or of the arena-
ceous Foraminifera; or it may consist of loosely matted
needle-like bodies composed of silica (Fig. 8, /) ; or there
may, as in C/athrulina, be a sphere of silica, perforated by
numerous openings, enclosing the protoplasm. Clathrulina
elegans (Fig. 8, j) is common in many ponds, attached to
the rootlets of Lemna, or duck- weed (Stokes).
Reproduction takes place, as in Amoeba, by binary fission.
PHYLUM PROTOZOA
c.-vac
2.Nuclean'a
3-Clahhr-uJina
FIG. 8. — Various forms of Heliozoa. ja, the entire animal; 36, the flagellula;
c. vac, contractile vacuole; ^gelatinous investment; nit, nucleus; psd, pseudo-
pods; sk, siliceous skeleton; sp, spicules. (From Biitschli's Protozoa, after
Schulze and Greeff.)
3o MANUAL OF ZOOLOGY SECT.
But in some genera the process of fission under some circum-
stances remains incomplete, the two protoplasmic bodies
to which the fission gives rise remaining connected together
by a bridge or isthmus of protoplasm, instead of becoming
separated off in the shape of two independent animals, as in
Amoeba. Further, these two bodies may each in turn divide
in the same incomplete way, so that four Heliozoans are
developed, all remaining connected together; and by further
repetitions of the same process a structure may be formed
consisting of a large number of units all connected together
by living substance. A structure of this kind, formed as a
result of repeated incomplete division (or, in other cases,
budding) from an original simple animal, is termed a colony,
and the elements or units of which it is composed are termed
zooids. How such a colony of unicellular Protozoa is to
be distinguished from a multicellular animal or Metazoan
(p. 19) will be explained at a later stage. It will at once be
apparent that the compound Foraminifera are of the nature
of colonies of unicellular zooids, each occupying one of the
chambers of the shell, formed as the result of a process
of repeated budding.
In addition to the process of multiplication by fission
multiplication also takes place in some Heliozoa by a pro-
cess known as the formation of spores. In spore-formation
(a form of which has already been referred to as occurring in
the Foraminifera) the protoplasm breaks up into numerous
small parts, each of which eventually develops into the form
of the parent. Usually the Protozoan passes into a qui-
escent condition before this takes place; the pseudopodia
become withdrawn, and the whole becomes enclosed in a
firm envelope or sporocyst; this process is known as encysta-
tion. The spores in some of the Heliozoa, when set free,
are provided each with two flagella (Fig. 8, j, b) which
PHYLUM PROTOZOA
subsequently become lost, pseudopodia appearing in their
place.
The Radiolaria are marine Rhizopoda which have exceed-
ingly delicate, thread-like pseudopodia (Fig. 9, psd) and a
skeleton usually composed of silica. This skeleton may be
composed of loosely woven needle-like bodies or spicules ;
more usually it is in the form of a globular, conical, star-
shaped, or disc-shaped shell, perforated by numerous open-
ings, and often supported by spines which radiate out from
psd
Int.caps.fr
cent caps
SKel.
~jExt.caps.pr.
FIG. 9. — Liteocircus annularis. cent, caps, central capsule; ext. caps, pr, extra-
capsular protoplasm; int. caps, pr, intra-capsular protoplasm; nu, nucleus;
psd, pseudopods; skel, skeleton; z, cells of Zooxanthella. (After Biitschli,
from Parker's Biology.}
the centre ; sometimes (Fig. 10) there are several such
shells one within the other. In some Radiolaria the skele-
ton is composed not of silica, but of a chitinoid substance
called acanthin. Embedded in the protoplasm is a perfor-
ated membranous sac, the central capsule (Figs. 9 and 10,
cent, caps), in the protoplasm within which is a single
nucleus or a number of nuclei, and a number of oil-drops.
There is no contractile vacuole, but in many Radiolaria the
protoplasm outside the central capsule contains numerous
non-contractile vacuoles, the presence of which gives it a
frothy appearance.
MANUAL OF ZOOLOGY
SECT.
Radiolaria which give rise to colonies are exceptional, but
a few cases occur. In these (Fig. n) the central capsule
divides again and again giving rise to a number of central
capsules which remain embedded in a firm gelatinous sub-
stance — the vacuolated protoplasm outside the central cap-
sules. Such a mass, which may attain considerable size,
floats about freely in the sea.
PHYLUM PROTOZOA
33
In addition to reproduction by simple binary fission,
spore-formation also occurs in some of the Radiolaria. The
protoplasm contained in the central capsule breaks up into
small masses, each of which becomes a flagellula provided
with a flagellum (Fig. 44, E, F).
In most of the Radiolaria there occur in the extra-capsular
protoplasm minute yellow cells (Fig. 9, z), which multiply
FIG. ii. — CollOZOUm inerme. A— C, three forms of the entire colony, nat. size;
D, a small colony showing the numerous capsules (c. caps} and extra-capsular
protoplasm with vacuoles (vac} ; E, spores containing crystals (c) ; mega- and
microspore. (From Blitschli's Protozoa, after Hertwig and Brandt.)
independently by binary fission. It has been proved that
these are microscopic unicellular plants (Zooxanthella) of
the class Algae, which live in the substance of the protoplasm
of the living Radiolarian. Such an intimate association
between two living organisms is known as symbiosis. There
can be no doubt that this association is beneficial both to the
Radiolarian and to the Alga. It is characteristic of the
plant cell that under the action of light and in the presence
34 MANUAL OF ZOOLOGY SECT.
of the specially vegetable green colouring matter, chlorophyll,
it is able to utilise for its nutrition the carbon dioxide
or " carbonic acid gas " present in the air. The carbon is
seized and made use of by the plant cell for the building up
of such compounds as starch and sugar, while the oxygen is
set free. The animal cell, on the other hand, is continually
using up oxygen and giving off carbon dioxide in the process
of respiration, while it is unable, in the absence of chloro-
phyll, to manufacture such substances as starch and sugar.
Thus in this close association or symbiosis between the Zoox-
anthella and the Radiolarian, the latter benefits the former
by supplying it with carbonic acid and other substances by
which it is nourished, while the Alga contributes to the
respiration of the Radiolarian by the oxygen which it gives
off, and to its nutrition by the sugar and other substances
which it forms.
2. THE MASTIGOPHORA
We have seen that the spores by which multiplication is
effected in some of the Rhizopoda (Heliozoa, Radiolaria)
are characterised by the presence of slender whip-like
appendages — the flagella. In a great number of Protozoa
such a flagellate condition of the cell is not merely a tempo-
rary larval one, as in the cases already dealt with, but is the
ordinary and permanent condition of the adult animal.
These permanently flagellate Protozoa constitute the class
Mastigophora — a very numerous group, mostly of very
small size. A good example of this class, very abundant in
fresh-water pools, in which it may be present in such
enormous numbers as to impart to the water a distinct
green colour, is Euglena viridis (Fig. 12). Another species
or variety of Euglena viridis, is so abundant at times as to
colour the water blood-red (Stokes).
PHYLUM PROTOZOA
35
The body of Euglena (E, H} is spindle-shaped, and has
at the blunt anterior end a depression, the gullet (F. ces),
from the inner surface of which springs a single long flagellum
The organism is propelled through the water by the
lashing movements of the flagellum, which is always directed
forwards ; it can also perform slow, worm-like movements of
contraction and expansion (A — £>), but anything like the
36 MANUAL OF ZOOLOGY SECT, i
free pseudopodial movements which characterise the Rhizo-
poda, is precluded by the presence of a very thin skin or
cuticle which invests the body. There is a nucleus (nu)
near the centre of the body, and at the anterior end a con-
tractile vacuole (H, c. vac), leading into a large non-con-
tractile space or reservoir (r) which discharges into the
gullet.
The greater part of the body is coloured green by the
characteristic vegetable pigment, chlorophyll, and contains
grains of paramylum (H, /), a carbohydrate allied to
starch. In contact with the reservoir is a bright red speck,
the stigma (pg), formed of a pigment allied to chlorophyll
and called hamate chrome. It seems probable that the
stigma is a light-perceiving organ or rudimentary eye.
Euglena is nourished like a typical green plant ; it de-
composes the carbon dioxide of the air dissolved in the
water, assimilating the carbon and setting free the oxygen.
Nitrogen and other elements it absorbs in the form of min-
eral salts in solution in the water. But it has also been
shown that the movements of the flagellum create a whirl-
pool by which minute fragments are propelled down the
gullet and into the soft internal protoplasm. There seems
to be no doubt that in this way minute organisms are taken
in as food. Euglena thus combines the characteristically
animal (holozoic) with the characteristically vegetable (Jwlo-
phytic) mode of nutrition.
Sometimes the active movements cease; the animal comes
to rest and surrounds itself with a cyst or cell-wall of cellulose
(the characteristic material of the cell- wall of plants), from
which, after a quiescent period, it emerges to resume active
life. It is during the resting condition that reproduction
takes place by the division of the body in a median plane
parallel to the long axis ( G) . Under certain circumstances
3.Astasiof>is
S.Oikomonas (?)
ll.Dinobryon 12. Sy ncr y p r a 13. Anhhojjhysa H.Rhi^idodendron
FIG. 13. — Various forms of Mastigophora. In 2, flagellate (a) and amoeboid (b)
phases are shown; in j, flagellate (a) and heliozoan (£) phases; in 8 are shown
two stages in the ingestion of a food particle (f ) ; chr, chromatophores;
c. vac, contractile vacuole; f, food particle ; g, gullet; nu, nucleus; /, lorica;
/, protoplasm; per, peristome; v. i, vacuole of ingestion. (Mostly from Biit-
schli's Protozoa, after various authors.)
37
38 MANUAL OF ZOOLOGY SECT.
nuiltiple fission takes place, and flagellulce, i.e., young pro-
vided with flagella, are produced, which, sometimes after
passing through an amoeboid stage, develop into the adult
form.
In the other Mastigophora the body may have a shape
similar to that of Euglena, or may be longer and narrower,
or, on the other hand, may be short and thick, ovoid or
globular. Anterior and posterior ends are nearly always
distinguishable, the former being that which is directed
forwards in progression. Usually there are distinct dorsal
and ventral surfaces, the former being that which is habitually
directed upwards. In most cases the body is equal-sided
or bilaterally symmetrical, i.e., is capable of being divided
into two equal lateral portions along the median vertical
plane ; but sometimes it is unsymmetrical, one side differ-
ing more or less from the other. In most the body is, as
in Euglena, naked ; but some have a chitinoid shell or lorica,
while others have a firm cell-wall of cellulose which may
present an elaborate pattern of strips, dots, etc., and may be
produced into long processes. Most of the Mastigophora
are, like Euglena, free-swimming, but some are permanently
attached by means of a slender stalk (Fig. 13, 10, ij, 14;
Fig. 14, 1,3}.
The number and arrangement of the flagella vary greatly.
The number may be one, as in Euglena, or two, three, or four.
In forms with two flagella these are both attached at or near
the anterior end, and often take on different functions, one
of them, directed forwards, being alone used in locomotion,
while the other is trailed behind when the animal is swim-
ming freely, or is used to anchor it to various solid bodies.
In one large group of Mastigophora, the Choanoflagellata
(Fig. 14), there is, surrounding the base of the flagellum, a
remarkable vase-like prolongation of the protoplasm, ex-
PHYLUM PROTOZOA
39
ceedingly delicate and transparent, called the collar. This
is conuactile, and, though its precise functions are not yet
certainly known, there is evidence to show that its move-
ments cause a flow of water, with minute particles in sus-
pension, up the outside of the collar and down the inside,
4o
MANUAL OF ZOOLOGY
SECT
the solid particles being then ingested in the soft protoplasm
between the base of the flagellum and that of the collar.
Both collar and flagellum may be withdrawn, and the animal
pass into an Amoeba-like or amoeboid form. In another
group — the Dinoflagellata (Fig. 15) — there are two fla-
gella, one springing from a longitudinal groove extending
along the anterior half of the body, and the other lying in a
PHYLUM PROTOZOA
transverse groove which completely encircles the body ; the
former alone acts as an organ of locomotion, the latter lies
habitually in the groove and performs undulating move-
ments. Noctiluca (Cystoflagellata) (Fig. 1 6), which is the
largest member of the class, being about half a millimetre
in diameter, has two flagella, one of which is modified in
a remarkable manner. The body of Noctiluca is globular,
with a cleft along one side so that it resembles a miniature
peach. From this springs a very large and stout flagellum
u
.^rl.' •" '>/ I
fI=%&k
m
FIG. 16. — Woctiluca miliaris.
ult animal;
, c , flagellulae; bg, tentacle;
f, flagellum; m, mouth; n, nucleus. (From Lang, after Biitschli.)
or tentacle t which is marked with a number of transverse
lines or striations ; and a second flagellum, of comparatively
small size, lies in the gullet.
Though all the Mastigophora are characterised by the
possession of flagella, there are a few, such as Mastigamceba
(Fig. 13, 4), which also possess pseudopodia, and may be
capable of amoeboid movements.
Nutrition is effected in a variety of different ways. Some
forms live in decaying organic infusions, not taking in solid
food-particles, but absorbing nourishing matter in a dis-
42 MANUAL OF ZOOLOGY SECT.
solved form from the substances in the infusion. Others,
living in. internal cavities of the bodies of higher animals,
receive, in a similar way, nourishment from the juices of the
animal they infest. Organisms, whether plants or animals,
which receive their nourishment in the former of these two
ways, are said to be saprophytic as regards their nutrition,
while such as obtain it from other living organisms are said
to be parasitic. But a large proportion of the Mastigophora
are neither saprophytes nor parasites, and are nourished in
one of two other ways, or in both of them. Many take in
minute solid particles of organic matter, usually in the form
of minute living organisms. In many such cases, there is,
as in Euglena, an aperture, the mouth, opening into a short
passage, the gullet, by which the food is received into the
protoplasm in the interior of the body ; but this is not
always present, and in such cases (Fig. 13, 8) the food-parti-
cles are taken in by a process not unlike that which we have
seen to occur in Amoeba. But, on the other hand, many of
the Mastigophora are not distinguishable from plants by their
mode of nutrition ; and on that ground, taken in connection
with their structure, which is in nearly all respects that of
a typical unicellular plant, have almost equal claims to be
ranked in either the vegetable or the animal kingdom.
They have a cell-wall of cellulose like a plant cell, they
contain chlorophyll or a red colouring matter, hczmato chrome,
of similar composition, and they have no mouth. They
must, therefore, be nourished precisely after the manner
of a green plant, and, if they are assigned to the animal
kingdom instead of to the vegetable, it can only be because
the possession of flagella seems to ally them with forms that
are of undoubted animal character.
Colonies are of frequent occurrence among the Mastigo-
phora. Sometimes there is a branching slender stalk
PHYLUM PROTOZOA
43
bearing a single zooid or a group of zooids at the end of
each of the branches (Fig. 14, j), the whole colony being
fixed by the base of the main stalk, and the flagellum serving
for the capture of food-particles and not for locomotion.
FIG. 17. — Volvox globator. A, entire colony, enclosing several daughter-colonies;
B, the same during sexual maturity; C, four zooids in optical section; D1— D5,
asexual formation of daughter-colony; E, zooid which has become converted
into a mass of microgametes ; F, microgamete; G, megagamete surrounded by
microgametes ; H, zygote; a, early stages in the formation of daughter-colonies:
_/?, flagellum; ov, ovy, megagametes; pg, pigment spot; spy, zooids containing
microgametes. (From Parker's Biology, after Cohn and Kirchner.)
Sometimes (Fig. 17) the colony is of a more massive char-
acter, the zooids being embedded in a clump of gelatinous
material, with the end bearing the flagellum projecting on
the exterior : usually such colonies are free-swimming.
44 MANUAL OF ZOOLOGY SECT.
Multiplication is effected most commonly by the simple
process of binary fission (Fig. n, 2b), which may take place
either in the active or in an encysted condition. In some
cases the fission is multiple, the protoplasm dividing not
merely into two, but into a greater number of parts, each
destined to develop into the adult form.
We also meet in the Mastigophora with what may be
regarded as the simplest mode of sexual reproduction. In
some forms two individuals come together and become
completely fused, the process being known as conjugation?
and the body formed by the union of the cells being known
as a zygote. The protoplasm of the latter divides by mul-
tiple fission into very minute spores. These, when first
liberated by the rupture of the zogote, are mere granules,
but soon the flagella are developed. In some cases the con-
jugating cells or gametes are of two sizes, union always taking
place between a large cell or megagamete and a small cell or
microgamete. In Volvox, which is a free-swimming spheri-
cal colony (Fig. 17, £, F, G) this difference between the
two sets of conjugating cells reaches its extreme, pro-
ducing a condition of things closely resembling what we
find in the sexual reproduction of higher forms. Certain
of the zooids enlarge and form megagametes, others divide
repeatedly and give rise to groups of microgametes, each
of the latter having the form of a rod-like body with two
flagella. The microgametes escaping, swim about freely and
conjugate with the motionless megagametes to form a zygote,
which, after a time divides to give rise to a new colony.
Mastigophora occur under the most various conditions,
to some of which reference has been already made. Many
kinds live in fresh water; others are abundant in the sea.
Noctiluca and others among the marine forms are phos-
1 Conjugation has also been observed to occur in many Rhizopods.
I PHYLUM PROTOZOA 45
phorescent, and are usually the agents by means of which
the diffuse phosphorescence of the sea is produced. Others,
again, are saprophytes, while others are parasites of higher
animals.
3. THE INFUSORIA
Often to be found in great numbers, in stagnant pools,
organic infusions, etc., is Paramoecium, the " slipper-shaped
animalcule," a Protozoan of comparatively large size, about
J mm. in length, which moves about very actively like
Euglena, but with a more regular and more rapid move-
ment, and by means of organs of locomotion differing in
character from the flagellum of the latter. The .body of
Paramoecium (Fig. 18, A, B) is covered with what appear
under the microscope like small delicate hairs arranged in
longitudinal rows. These are the cilia; they are in inces-
sant to-and-fro vibration, and it is by their means that the
Paramcecium moves about and obtains its food. In shape
the body is somewhat cylindrical, rounded at the anterior
and bluntly pointed at the posterior end. On one side,
the ventral, is a large oblique depression, the buccal groove
(hue. gr), leading into a short gullet (gut), which, as in
Euglena, ends in the soft internal protoplasm. The proto-
plasm is differentiated into a firmer superficial layer, the
cortex (corf), and a semi-fluid central mass, the medulla
(med), and is covered superficially by a thin cuticle. The
cilia are prolongations of the cortex, and perforate the
cuticle.
In the cortex are found two nuclei. One of these, the
meganucleus (nu), is a comparatively large ovid body; the
other, the micronucleus (pa. nu), is a small rounded body
closely applied to the meganucleus. Two contractile
46 MANUAL OF ZOOLOGY SECT. I
vacuoles (c. vac} are present. Each is connected with a
series of radiating spindle-shaped cavities in the protoplasm
which serve as feeders to it ; after the contraction of the
vacuole these cavities are seen gradually to fill, apparently
receiving water from the surrounding protoplasm ; they then
contract, discharging the water into the vacuole, the latter
rapidly enlarging while they disappear from view ; finally
the vacuole contracts and discharges its contents externally.
The cortex contains minute radially-arranged sacs called
trichocysts (trch}. When the animal is irritated, more or
fewer of these suddenly discharge a long delicate thread
(C), which, in the condition of rest, is very probably coiled
up within the sac.
Food, in the form of small living organisms, is taken in
by means of the current caused by the cilia of the buccal
groove. The food-particles, enclosed in a globule of water,
or " food- vacuole " (/. vac], circulate through the proto-
plasm, where the soluble parts are gradually digested and
assimilated. Effete matters are egested at a definite anal
spot posterior to the mouth, where the cortex and cuticle
are less resistant than elsewhere. The whole feeding pro-
cess can readily be observed in this and other Infusoria by
placing in the water some insoluble colouring matter, such
as carmine or indigo, in a fine state of division, the minute
particles of the colouring matter, which are taken into the
mouth in the way described, being readily observed as they
become received into food-vacuoles and circulate in the
central protoplasm.
Multiplication takes place by transverse fission (D), the
division of the body being preceded by that of both nuclei.
It has been proved, however, that multiplication by binary
fission cannot go on indefinitely, but that after it has been
repeated a certain number of times, it is interrupted by
B
c.vac
c.vac.
/T"A ///
:/\:
.;# 1-
pa.nu
FIG. 18. — Paramcecium caudatum. A, the living animal from the ventral aspect;
B, the same in optical section : the arrow shows the course taloen by food-particles ;
C, a specimen which has discharged its trichocysts; D, diagram of binary fission;
buc. .g-r, buccal groove; corf, cortex; cu, cuticle; c. vac, contractile vacuole; _/".
vac food vacuole; gul, gullet; wed, medulla; ««, meganucleus; fa. nu, micro-
nucleus; trch, trichocysts. (From Parker's Biology.')
47
48 MANUAL OF ZOOLOGY SECT, i
conjugation. In this very remarkable and characteristic
process two Paramcecia become applied by their ventral
faces, but do not fuse ; their meganuclei break up and dis-
appear, and an interchange of the substance of the micro-
nuclei of the two conjugating individuals takes place, with
the result that each develops a new meganucleus, and a
new micronucleus, partly formed of the substance of its own
micronucleus, partly that of the other Paramoecium.
The possession of cilia is the distinctive feature of the class
Infusoria among the Protozoa. But in one section of the
class — the order Tentaculifera — cilia are only present in
the young, their place in the adult being taken by append-
ages known as tentacles. The form of the body in the
Infusoria (Fig. 19) is very varied ; it may be globular,
ovoid (/), kidney-shaped (2), trumpet-shaped (j), vase-
shaped (9), produced into a long, flexible, neck-like pro-
cess (5), or into large paired lappets (6), flattened from
above downwards, or elongated and divided into a series
of segments. Most are free-swimming, but many are fixed,
usually by means of a slender stalk (), or the tentacle may be
branched (4), the extremity of each of the branches being
suctorial. In some forms (j") the tentacles are devoid of
sucker-like extremities, and can be moved about actively to
catch the prey.
The meganucleus is often ovoid, as in Paramcecium. In
other cases it may be long and band-like (Fig. 19, j,
mg. nu}, horseshoe-shaped (p), very long and constricted
PHYLUM PROTOZOA
S.Rhynchel-a
7.0|>hryodenclron
8.Ef)helol"
Q. Dendrosoma
FIG. 20. —Various forms of Tentaculifera. ia and b, two species of Ppdophrya ;
c, a tentacle much enlarged; 2a, Acineta jolyi ; sbt A. tuberosa; in b the ani-
mal has captured several small Ciliata; 8a, a specimen multiplying by budding;
8b, a free ciliated bud; Qa, the entire colony; qb, a portion of the stem; QC, a
liberated bud; a. organism captured as food; b. c, brood cavity: bd, bud;
c. vac, contractile vacuole; nig. nu, meganucleus; mi. nn, micronucleus;
t, tentacle. (After Butschli and Baville Kent.)
52 MANUAL OF ZOOLOGY sEcr.
at intervals so as to look like a string of beads, or branched.
In nearly all cases one or more micronuclei are present.
In Vorticella and others there is a single contractile vacuole
which opens, as in Euglena, through the intermediation of
a reservoir into the gullet. In other Infusoria there may
be one, two, or many contractile vacuoles. In some instances
the protoplasm is hollowed out by numerous non-contractile
vacuoles. Trichocysts mainly occur in the forms with a uni-
form coating of cilia : more complicated bodies of similar
character termed nematocysts (9, c) occur in some cases.
A mouth is absent in many parasitic forms, and nourish-
ment is obtained by the absorption of the digested food of the
animal in which the infusorian is parasitic. In the Tentacu-
lifera, in which a mouth is also absent, nourishment is drawn
in by means of the tentacles in the manner already described.
In the rest there is a mouth and gullet, usually situated, as in
Paramcecium, at the end of a buccal groove, or peristome.
In Vorticella and its allies (Fig. 19, p, and Fig. 22) the
body is in the shape of a wine-glass, the stem of which is
represented by a slender stalk (sf), while the rim is the
equivalent of the peristome (per) ; in the area which the
peristome encloses is an elevated disc of protoplasm, be-
tween which and the peristome on one side is the opening
of the mouth (mtJi) : the only cilia present run in a spiral
band round the peristome, round the edge of the disc, and
down into the gullet (gull). An anal spot is present in
Vorticella and many other forms ; in a few there is, instead,
a distinct anal aperture (Fig. 19, 2 a).
A chitinoid skeleton (Fig. 21) occurs in a few forms;
usually it is bell-shaped, sometimes it is perforated by a
number of apertures (/) so that it resembles in appearance
the skeleton of some of the Radiolaria. A chitinoid lid or
operculum (2, j, op) may be fixed to the edge of the peri-
PHYLUM PROTOZOA
53
stome, and when the animal is retracted into its case, accu-
rately closes the mouth of the latter.
Colonies occur in many of the Infusoria. Some allies of
Vorticella (Fig. 19, 9) develop highly complex colonies, the
slender stalk branching again and again, and each terminal
branch ending in a zooid. A remarkable colonial form is
54
MANUAL OF ZOOLOGY
SECT.
Dendrosoma (Fig. 20, p), one of the Tentaculifera : it has
a creeping stem from which branches spring upwards,
each terminating in a zooid with suctorial tentacles ; and
FIG
. 22. — Vorticella. A, B, living specimens in different positions; C, optical
section; D1, D2, diagrams illustrating coiling of stalk; E1, E2, two stages in
binary fission; E3, free zooid; F1, F2, division into mega- and microzooids;
G1, G2, conjugation; H1, multiple fission of encysted form; H2, H3, develop-
ment of spores; ax.f, axial fibre; cort, cortex; cu, cuticle; c. -vac, contractile
vacuole ; d, disc ; gull, gullet; m, microzooid; wM, mouth; MM, meganucleus;
per, peristome. (From Parker's Biology, partly after Saville Kent.)
I PHYLUM PROTOZOA 55
the single nucleus extends as a narrow branching cord
throughout the axis of the entire colony.
Transverse fission is the universal method of reproduc-
tion ; and budding also occurs. Spore-formation has been
observed in a few forms.
Conjugation, in the form of a temporary union of two
individuals, with interchange of the substance of the micro-
nuclei, occurs in many of the ciliate Infusoria. In some
forms the conjugating individuals become completely fused.
The effect of the process of conjugation seems to be in-
creased activity in multiplication by fission.
In mode of life the Infusoria are as varied as the Mastigo-
phora. Some are holozoic, some saprophytic, some parasitic.
Of the parasitic forms some give rise to definite diseases
in the bodies of their hosts. The skin affection known as
eczema, for example, seems to be caused by the presence
of parasitic Vorticellae.
4. THE SPOROZOA
In the interior of certain organs, termed the seminal
vesicles, of the earthworm will often be found a parasitic
Protozoan — Monocystis agilis (Fig. 23) — which exempli-
fies another of the classes of the phylum, the class Sporozoa.
It is flattened, elongated, pointed at both ends, and performs
slow movements of expansion and contraction (A, B),
reminding us of those of Euglena. There are neither
pseudopodia, nor flagella, nor cilia. There' is a firm
cuticle, and the protoplasm is divided into a denser
superficial portion, the cortex, and a central semi-fluid mass,
the medulla. There is a large clear nucleus, but no trace of
contractile vacuole, or of mouth or gullet. Reproduction
takes place by a peculiar and characteristic process of spore-
formation. Either a single individual, or two individuals
56 MANUAL OF ZOOLOGY SECT.
closely applied together, but not actually fused, become
encysted. Multiple fission then takes place, the proto-
plasm becoming divided (C) into an immense number of
spindled-shaped spores, each surrounded by a strong
chitinoid coat, and thus differing markedly from the naked
spores of Rhizopoda and Mastigophora. The protoplasm
of each spore then undergoes fission, becoming divided
PHYLUM PROTOZOA
57
into a number of somewhat sickle-shaped bodies, which are
arranged within the spore-coat somewhat like a bundle of
sausages. By rupture of the spore-coat these falciform
young, as they are termed, are liberated, and at once begin
active movements, the thin end of the body moving to and
fro like a clumsy flagellum. They enter the clumps of devel-
oping sperms of the earthworm, and afterwards escape into
the cavity of the seminal vesicle and grow into the adult form.
58 MAXL'AL OF /OOLOGY >i • r. i
All the Sporozoa are parasitic, and all are characterised
by the absence of pseudopodia, flagella, and cilia; and of
mouth and gullet, and by the formation of spores enclosed
in chitinoid coats. Gregarina (Fig. 24) differ from Mono-
cystis in having the medullary part of the protoplasm divided
into two sections, known as the protomerite (pr), and'
deutomerite (tieu}, by a sort of partition, with, in the young
condition, a third division, the epimerite (ep) in front; and
in the more complex form of the cysts, which have delicate
canals or sporoducts (spd) through which the spores escape.
Some of the Sporozoa ( Coccidium and others) are parasites,
not like Monocystis and Gregarina, in the cavities of organs,
but in the interior of cells, such as the cells lining the intes-
tine of higher animals. The various forms of the disease
known as malaria in Man have been proved to be due to the
presence of a Sporozoan (H&mamcebA laverani ) which in-
vades and destroys, at a certain stage in its life-history, the
red corpuscles of the blood. Another form (Apiosoma
bigeminum) causes the Texas fever in cattle, the infection
being carried by ticks. These parasites cause high fever,
anaemia, bloody urine, and the number of red-blood corpus-
cles is diminished in one week to one-sixth of the normal
amount. Babesia bovis in the blood of the ox causes the dis-
ease known as haemoglobinurea, and another form produces
a similar disease in sheep. A parasite of the tzetse fly, which
is a flagellate hsematozoan, is the cause of the tzetse disease
in southern Africa. These organisms live in the marrow and
lymphatics, and flush at intervals into the general blood
stream. The disease is communicated by the tzetse fly from
the wild game, the herds of which are the fester spots which
maintain the disease. The silkworm disease called pebrine
is due to one of the Myxosporidia, Ghtgea bombycis, which
inhabits all the tissues of the caterpillar of Bombyx mori.
SECTION II. — THE METAZOA
WHILE the Protozoa are predominantly unicellular, and of
extremely simple structure, the rest of the animal kingdom,
grouped together under the comprehensive title of Metazoa,
are all multicellular in the adult condition, and have, except
in some of the lowest groups, a more or less elaborate struc-
ture owing to the presence of complicated systems of organs
for carrying on the various functions of animal life. Such
an animal as a lobster or a frog, for example, may readily
be ascertained to be made up of a complicated system of
parts, — skeleton, muscles, digestive organs, blood vessels,
and so on, — and it requires only the most superficial micro-
scopic examination of the substance of these various parts
to render it evident that each is built up of an immense
multitude of cells. A lobster or a frog, however, or any
other Metazoan, consists, in the earliest stage of its fyisr-
ence, of a single cell, the oosperm. formed bv the union
of a male cejl or sperm with a female cell or ovum. The
ovum (Fig. 25) is usually spherical in shape, with one or
more enclosing membranes, with cell-protoplasm enclosing
a large nucleus (germinal vesicle, as it is often termed in
this case), in which are contained one or more small,
rounded bodies (germinal spot or spots"). The ovum may
contain, in addition to the protoplasm, a quantity of non-
protoplasmic material or yolk.
59
6o
MANUAL OF ZOOLOGY
SECT.
Before the changes begin which lead to the formation
of the multicellular Metazoan, another cell, the male cell or
sperm, has to unite with the ovum or female cell. Before
this takes place, the ovum throws off portions of its substance
(Fig. 26, pot} in the form of two little rounded bodies —
the polar bodies. This preliminary process is known as the
maturation of the ovum. The male cell or sperm is a
relatively small cell, usually motile, which penetrates into
FlG. 25. — Ovum of a Sea-Urchin, showing the radially striated cell-membrane, the
Srotoplasm. containing yolk-granules, the large nucleus (germinal vescicle), with
:s network of chromatin and a large nucleolus (germinal spot). (From Bal-
four's Embryology, after Hertwig.)
the ovum, and coalesces with it — the coalescence being
what is termed fertilisation or impregnation — and the
immediate result being that, instead of separate ovum and
sperm, we have a compound body, the oosperm, formed by
their union, but not differing at first in any marked degree
from the simple ovum, and containing a single nucleus
representing both the nucleus of the sperm and that of the
ovum.
On impregnation follows the process of segmentation of
the oosperm. The nucleus first divides into two ; then the
THE METAZOA
mem
sey.nud.
FIG. 26. — Diagram illustrating the maturation and fertilisation of the ovum. A. formation of
first polar globule; B, beginning of fertilisation, sperms approaching the micropyle or
aperture in the enclosing membrane of the ovum through which the sperm enters; C, forma-
tion of the male pronucleus; D, approximation of the male and female pronuclei; E, forma-
tion of segmentation-nucleus; 9 cent, female centrosome; $ cent, male centrosome (the
centrosomes are cell-structures not further referred to in this work); mem, egg-membrane;
microp, micropyle; pol, polar bodies; 9 pron, female pronucleus; $ pron, male pronu-
cleus; seg. nucl, segmentation nucleus.
62
MANUAL OF ZOOLOGY
SECT.
substance of the protoplasm becomes cleft into two parts
(Fig. 27), each half containing one of the nuclei, so that
two complete cells result. This process, it will be observed,
is essentially the same as the binary fission of Amoeba and
Other Protozoa : in the Metazoan, however, the two cells
do not become separated from one another as the two
parts of the divided Amoeba do, but remain in contact and
undergo further changes. Each of them divides (Fig. 27)
FIG. 27. — Various stages in the segmentation of the oosperm. (From Gegenbaur's
Comparative Anatomy.}
in the same manner into two — four cells being thus formed ;
the four divide to form eight, the eight to form sixteen,
and so on ; until, by this process of division and sub-
division, the oosperm becomes segmented into a large
number of comparatively small cells. In this mass of cells
an arrangement into layers, I\\Q germinal layers, becomes by
and by discernible ; and from these layers of cells are
developed eventually all the parts of the body of the
Metazoan.
ii THE METAZOA 63
This mode of development is, however, not entirely with-
out parallel among the Protozoa. In the colonial Volvox
(p. 43, Fig. 1 7) it will be remembered that male cells or
microgametes (sperms) and female cells or megagametes
(ova) are developed, and that by the coalescence of a
microgamete with a megagamete a compound cell, the
zygote (oosperm), is formed, which undergoes division to
give rise to an adult Volvox.
As the various parts become gradually moulded from the
cells of the germinal layers, the form and arrangement of
the cells of the different parts become modified in different
ways, so that the cellular structure comes to differ widely;
and, as a result, we find in the fully formed animal a
variety of different kinds of material, — tissues, as they are
termed, — such as muscle, bone^gri^^, -t>erver ^11 derived
from the cells of the germinal layers. Of such tissues the
following are the most important. An epithelium is a thin
stratum of cells covering some surface, external or internal :
it may be one cell thick, or several cells thicks The cells of ^
which an epithelium is composed vary greatly in form in
different cases (Fig. 28) : they may be beset at their free
surfaces with cilia (a), like the cilia of the Infusoria, or with
flagella, like those of the Mastigophora (/), or may be
amoeboid (-#), sending out pseudopodia like a Rhizopod.
The epithelium which covers the outer surface is known
as the epidermis or deric epithelium ; that which lines the
interior of the digestive organs is the enteric epithelium.
Glands (Fig. 29) are formed by modification of epithe-
lial cells. In many cases a single cell of the epithelium
forms a gland, which is then termed a unicellular gland
(A, It). The secretion (or substance which it is the func- y
tion of the gland to form or collect) gathers in such a case
in the interior of the cell, and reaches the surface of the
64
MANUAL OF ZOOLOGY
SECT.
FIG 28. — Various forms of epithelium, a, ciliated epithelium; £, columnar; d, sur-
face view of the same; c, tessellated; e, the same from the surface; f, flagellate
epithelium with collars; g, flagellate epithelium without collars; A, epithelium
of intestine with pseudopodia; /, stratified epithelium; k, deric epithelium of a
marine planarian with pigment cells, rod cells, and sub-epithelial glands. (From
Lang's Comparative Anatomy.)
IT THE METAZOA 65
epithelium through a narrow prolongation of the cell, which
serves as the duct of the gland. In other cases the gland is
multicellular (£>, G), formed of a number of cells of the
epithelium, lining a depression or infolding, simple or com-
plex in form, of the latter. In the central cavity of such a
ands in an
communicating
FIG. 29. — Diagram to illustrate the structure of glands. A , unicellular gl
epithelium; B, unicellular glands lying below epithelium and comi
with the surface by narrow processes (ducts) ; C, group of gland cells; D, group
of gland cells lining a depression; E and F, simple multicellular gland; G,
branched multicellular gland. (From Lang.)
gland the secretion collects to reach the surface through
a passage, the duct.
The general name of connective tissues is applied to a
number of tissues which play a passive part in the economy
of the animal, connecting and supporting or protecting the
various organs. Sometimes connective tissue is gelatinous
in character, sometimes fibrous. Fat or adipose tissue is
66 MANUAL OF ZOOLOGY SECT.
usually developed by modification of fibrous connective
tissue, the cells becoming distended with oily matter.
Cartilage is a firm but elastic material, readily cut with a
knife, which forms an important constituent of the skeleton
in higher animals. Bone differs from cartilage in being
much denser and harder, owing to its being strongly
impregnated with limey matter (carbonate and phosphate
of lime).
Muscular tissue is the material by means of which nearly
all the movements of the Metazoa are effected. It consists
of bundles of microscopic fibres, which in the living condi-
tion have the special property of contractility, contracting,
i.e. becoming shorter and thicker, when stimulated. Bundles
or bands of these form the organs known as muscles. Nerve
tissue, which is the sensitive, conducting, and stimulating
tissue of the body, consists of nerve-cells and nerve-fibres ;
groups of the former constitute nerve- ganglia ; bundles of
the latter form nerves.
Associated with the multicellular character of the Metazoa
is the possession of a variety of different parts or organs
adapted to carrying out different functions in the life of
the animal. Such a formation of organs is faintly fore-
shadowed in the unicellular body of the Protozoa; the
contractile vacuoles, the nucleus, the pseudopodia, flagella,
and cilia, the gullet, etc., are all to be looked upon as organs
subserving certain functions. But in the Metazoa, with the
exception of some of the lower groups, the development
of organs for the carrying on of the functions of animal life
— organs of locomotion, organs for protection and support,
organs of digestion, respiration, and reproduction — is
carried much further.
Some of the chief functions which are carried on in the
body of an animal have already been briefly referred to in
Ii THE METAZOA 67
the account of the Protozoa. The special study of these
constitutes, as already pointed out in the Introduction, the
science of Physiology, which forms accordingly an important
part of the study of Zoology, and a part to which frequent
reference will be made in dealing with the structure of the
various groups of animals.
The various internal parts of an animal are supported
and protected by the skin and the skeleton. The skin or in-
tegument consists of a layer of cells — the epidermis — with,
FIG. 30. — Bones of the human arm and fore-arm with the biceps muscle, showing
the shortening and thickening of the muscle during contraction and the conse-
quent change in the relative position of the bones — viz., flexion of the fore-arm
on the upper arm. (From Huxley's Physiology.}
superficial to it, in many animals, a non-cellular layer known
as the cuticle, and below it usually a fibrous layer, the
dermis. The skeleton is, as already explained in the
section on the Protozoa, a system of hard parts, external or
internal, serving for the protection and support of the softer
substance of the body. When these hard parts are external
they form an exoskeleton, when internal an endoskeleton.
An exoskeleton is formed by the thickening and hardening
of portions of one or other of the layers of the integument,
— cuticle, epidermis, or dermis. An endoskeleton usually
68 MANUAL OF ZOOLOGY SECT.
consists either of cartilage, or of bone, or of both. The
parts of the skeleton in the higher animals, whether external
or internal, usually consist of a number of distinct pieces
which are movably articulated together, and these have the
additional important function of serving for the attachment
of muscles, constituting a jointed framework on which the
muscles act in bringing about the various movements of the
body and its appendages (Fig. 30).
The nutrition of the Metazoa is in some cases, as in some
of the Protozoa, effected by food being absorbed in a
dissolved form through the general surface. In the great
majority, however, the food, liquid or solid, is received
through an opening — the mouth — into a cavity in the
interior of the body — the digestive or enteric cavity. In
most cases this has the form of a longer or shorter tube or
canal, beginning at the mouth and ending at a second exter-
nal opening — the anus. This digestive or enteric canal
consists usually of a number of different parts, through which
the food passes in succession, each part having its special
function to perform in connection with nutrition. In most
cases there are organs in the neighbourhood of the mouth
serving for the seizure of food ; these may be simply tentacles,
or soft, finger-like appendages, or they may have the form of
jaws, by means of which the food is not only seized but torn
to pieces, or ground into small fragments, in the process
of mastication. In general we can distinguish in the enteric
canal a buccal cavity, a pharynx, an oesophagus or gullet, a
stomach, and an intestine. It is in the stomach and anterior
part of the intestine that the food becomes acted upon by
certain digestive secretions, the effect of which is to render
the various ingredients soluble, and thus fitted to be absorbed
through the wall of the enteric canal, so as to reach the
various parts of the body and supply them with nourish-
THE METAZOA
69
ment. These digestive secretions are partly produced by
the cells of the epithelium of the canal, which are modified
to form unicellular or multicellular glands (p. 65), partly by
certain large special digestive glands, salivary glands, liver,
and pancreas. The nutrient parts of the food are by this
means so acted upon that they are ready to be absorbed,
and in most animals pass into the blood, to be distributed
FIG. 31. — General view of the viscera of a male frog, from the right side, a,
stomach; b, urinary bladder; c, small intestine; cl, cloacal aperture; d, large
intestine; e, liver; f, bile duct; g, gall bladder; k, spleen; /, lung; k, larynx;
/, fit body; tn, testis; «, ureter: o, kidney; /, pancreas; s, cerebral hemi-
sphere; sp, spinal cord; t, tongue: «, auricle; ur, urostyle; v, ventricle;
v.s, vesicula seminalis; , triradiate spicules; sp' , oxeote
spicules of dermal cortex (dc) ; .«•/", tetraradiate spicules of gastral cortex (gc);
ec, ectoderm; en, endoderm; /./«, pore membrane; /)/, prosopyles ; ap, apopyle ;
di, diaphragm; exc, excurrent passage; PC, paragastric cavity; em, early
embryo; em' , late embryo. The arrows indicate the course of the water through
the sponge.
80
SECT, in PHYLUM PORIFERA 81
flagellate canals (R} — rather wider, octagonal in cross-
section, and lined by endoderm continuous with the lining
of the paragastric cavity. The incurrent canals end blindly
at their inner extremities, not reaching the paragastric
cavity; externally each becomes somewhat dilated, and the
dilations of neighbouring canals often communicate. These
dilated parts are closed externally by a thin membrane —
the pore membrane, perforated by three or four openings —
the inhalant pores already referred to. The flagellate canals
are blind at their outer ends, which lie at a little distance
below the surface ; internally, each communicates with the
paragastric cavity by a short, wide passage, the excurrent
canal (exc). Incurrent and flagellate canals run side by
side, separated by a thin layer of sponge substance, except
at certain points, where there exist small apertures of com-
munication — the prosopyles ( // ) — uniting the cavities
of adjacent incurrent flagellate canals.
The ectoderm lining of the incurrent canals is of the
same character as the ectoderm of the outer surface. The
endoderm (fi) of the flagellate canals, on the other hand, is
totally different from that which lines the paragastric cavity.
It consists of cells of columnar shape, ranged closely together
so as to form a continuous layer. Each of these flagellate
endoderm cells, or collared cells, as they are termed, is not
unlike one of the choanoflagellate Protozoa (p. 38) ; it has
its nucleus, one or more vacuoles, and, at the inner end, a
single, long, whip-like flagellum, surrounded at its base by a
delicate, transparent, collar-like upgrowth, similar to that
which has already been described as occurring in the
Choanoflagellata. If a portion of a living specimen of the
sponge is teased out in sea- water, and the broken fragments
examined under a tolerably high power of the microscope,
groups of these collared cells will be detected here and
82 MANUAL OF ZOOLOGY SECT.
there, and in many places the movements of the flagella
will be readily observed. It is to these movements that the
formation of the currents of water passing along the canals
is due.
The short passage or excurrent canal, which leads inwards
from the flagellate canal to the paragastric cavity, differs
from the former in being lined by flattened cells similar to
those of the paragastric cavity ; it is partly separated from
the flagellate canal by a thin diaphragm (Fig. 36, <#),
perforated by a large circular central aperture — the apopyle
(ap) — which is capable of being contracted or dilated ; its
opposite aperture of communication with the paragastric
cavity, which is very wide, is termed the gastric ostium of
the excurrent canal.
The effect of the movement of the flagella of the cells in
the flagellate canals is to produce currents of water running
from without inwards along the canals to the paragastric
cavity. This causes water to be drawn inwards through the
prosopyles from the incurrent canals, and, indirectly, from
the exterior through the perforated membranes at the outer
ends of the latter.
Between the ectoderm of the outer surface and of the
incurrent canals, and the endoderm of the inner surface and
of the flagellate canals, are a number of spaces filled by an
intermediate layer — the mesoderm or mesoglcea — in which
the spicules of the skeleton are embedded. The
spicules (Fig. 36, sp.}, each of which is developed in a
single cell of the middle layer, are regularly arranged, and
connected together in such a way as to protect and support
the soft parts of the sponge. Most are, as already noticed,
of triradiate form. Large numbers, however, are of simple
spear-like or club-like shape (sp'). The sexual reproductive
cells — the ova (Fig. 36, ov) and sperms — are developed
in PHYLUM PORIFERA 83
immediately below the flagellate endoderm cells of the
flagellate canals, and in the same situation are to be found
developing embryos (em, em').
The simplest sponges are vase-shaped or cylindrical in
form, either branched or unbranched, and, if branched,
with or without anastomosis or coalescence between neigh-
bouring branches. But the general form of the less sim-
ple sponges differs widely from that of such a branching
cylinder as is presented by Sycon (Fig. 34).
From the point to which the embryonic sponge becomes
attached, it may spread out horizontally, following the ir-
regularities of the surface on which it grows, and forming
a more or less closely adherent encrustation like that of an
encrusting lichen. In other cases the sponge grows at first
more actively in the vertical than in the horizontal direction,
and the result may be a long, narrow structure, cylindrical
or compressed, and more or less branched. Sometimes
vertical and horizontal growth is almost equal, so that event-
ually there is formed a thick, solid mass of a rounded or
polyhedral shape, with an even, or lobed, or ridged surface.
Very often, after active vertical growth has resulted in the
formation of a comparatively narrow basal part or stalk,
the sponge expands distally, growing out into lobes or
branches of varying forms, and frequently anastomosing.
Sometimes after the formation of the stalk with root-like
processes for attachment, the sponge grows upwards in such
a way as to form a cup or tube with a terminal opening.
Sometimes the sponge grows from a narrow base of attach-
ment into a thin flat plate or lamella ; this may become
divided up into a number of parts or lobes, which may
exhibit a divergent arrangement like the ribs of an open
fan.
MANUAL OF ZOOLOGY
SECT.
Sycon belongs to a type of sponges intermediate between
the very simplest forms on the one hand, and the more
complex on the other. The
simplest and most primitive
of known sponges is one
named Ascetta primordialis
(Fig. 37). It is vase-shaped,
contracted at the base to
form a sort of stalk, by the
expanded extremity of which
it is attached ; at the oppo-
site or free end is the circular
osculum. So far there is a
considerable resemblance to
Sycon gelatinosum ; but the
structure of the wall in Ascetta
is extremely simple. Regu-
larly arranged over the sur-
face are a number ' of small
rounded apertures, the in-
halant or incurrent pores ;
but, since the wall of the
sponge is very thin, these
apertures lead directly into
the central or paragastric
cavity, the long passages or
canals through which the
communication is effected in
Sycon being absent. The
wall consists of the same
three layers as in Sycon ; but
the middle one, though it contains a small number of
spicules, is very thin ; the endoderm, which lines the
FIG. 37. — Ascetta primordialis. A
portion of the wall of the vase-like
sponge removed to show the para-
gastric cavity. (After Haeckel.)
Ill
PHYLUM PORIFERA
paragastric cavity, consists throughout of flagellate collared
cells similar to those of the flagellate canals of Sycon.
The majority of sponges, however, are more complicated
in structure than Sycon. One of the causes of their
complexity being that the canals, instead of being simple
and straight, become branched, forming a system, often
highly complicated, of ramifying channels. In these more
complex sponges the flagellate collared cells are confined to
In
FIG. 38. — Vertical section of a fresh-water sponge (Spongilla) , showing the arrange-
ment of the canal-system. C, ciliated chambers; DP, dermal pores; Ex,
excurrent canals; GO, openings of the excurrent canals; PG, paragastric
cavity; SD, subdermal cavities; O, osculum. (Modified from Leuckart and
Nitsche's diagrams.)
certain rounded dilatations of the canals — the flagellate
chambers.
Moreover, in the more complex forms the development
of branches from the originally simple sponge, and the
coalescence of neighbouring branches with one another,
greatly obscure the essential nature of the sponge as a
colony of zooids similar 'to the branches of Sycon ; and
this effect is increased by the development of a variety of
infoldings of the ectoderm which appear in the higher
forms.
86 MANUAL OF ZOOLOGY SECT.
The elements* of the skeleton differ in character in the
two sub-classes into which the sponges are divided. In
the Calcarea, of which Sycon is an example, they consist
of calcareous spicules, usually triradiate in form. In the
Non-Calcarea the skeleton either consists of spongin fibres
alone (Fig. 39, A), or of siliceous spicules alone, or of a
combination of spongin fibres with siliceous spicules (B) :
in some (Myxospongias) skeletal parts are altogether
absent. Spongin is a substance allied to silk in compo-
sition ; the fibres are exceedingly fine threads, which branch
and anastomose, or are woven and felted together in such a
way as to form a firm, elastic supporting structure. The
siliceous spicules (Fig. 40) are much more varied in shape
than the spicules of the Calcarea, and in a single kind of
sponge there may be a number of widely differing forms of
spicules, each form having its special place in the skeleton
of the various parts of the sponge-body. In most Non-
Calcarea siliceous spicules and spongin fibres combine to
form the supporting, framework, the relative development of
these two elements varying greatly in different cases. But in
certain groups of the Non-Calcarea, including the common
washing sponges, spicules are completely absent, and the
entire skeleton consists of spongin. In some Non-Calcarea
which are devoid of spicules, the place of these is taken
by foreign bodies — shells of Radiolaria, grains of sand, or
spicules from other sponges (Fig. 39, C). In others, again,
such as the Venus's flower-basket (Euplectelld], the glass-
rope sponge (Hyalonema), and others, the skeleton consists
throughout of siliceous spicules bound together by a siliceous
cement.
Reproduction in the Sponges is effected either sexually or
asexually. The process by which, in all but the simplest
forms of sponges, a colony of zooids is formed from the
Ill
PHYLUM PORIFERA
originally simple cylinder or vase, may be looked upon as
an asexual mode of reproduction by budding. Asexual
A.EusfDongia
B.Pachychalina
FIG. 39. — Microscopic structure of the skeleton in various sponges. A, Euspongia,
network of spongin fibres; B, Pachychalina , spongin strengthened by siliceous
spicules; C, Spongelia, spongin strengthened by various foreign siliceous
bodies, fragments of spicules of other sponges, etc. (After Vosmaer.)
88
MANUAL OF ZOOLOGY
multiplication also assumes the form in some cases of a
process of production of internal buds in the shape of
groups of cells called gemmules^ which eventually become
detached and develop into new individuals. In the fresh-
water sponges (Spongillida) multiplication takes place very
actively by means of such gemmules, each of which is a
spherical group of cells enclosed in an envelope composed
of peculiarly shaped siliceous spicules, termed amphidiscs
(Fig. 40, right side). All sponges multiply by a sexual
process — by means of male cells, or sperms, and female
FIG. 40. — Various forms of sponge spicules. (From Lang's Text-Book.)
cells, or ova. Ova and sperms are developed in the same
sponge, but rarely at the same time. The cell destined to
form sperms divides into a number of small cells, giving
rise to a rounded mass of sperms. The latter, when
mature, have oval or pear-shaped heads and a long taper-
ing appendage or tail. Each cell destined to form an ovum
enlarges, and eventually assumes a spherical form. After a
sperm has penetrated into its interior and effected impreg-
nation, it usually becomes enclosed in a brood-capsule
formed for it by certain neighbouring cells, and in this
situation, still enclosed in the parent sponge, it undergoes
iii PHYLUM PORIFERA 89
the earlier stages of its development. Eventually it becomes
free as a ciliated larva, which pursues a free existence for a
time, swimming about by the agency of the cilia, till after
a time it becomes fixed and develops into the adult form.
Fresh-water sponges (Spongilhda) live in rivers, lakes, etc.
Marine sponges occur in all seas, and at all depths, from the
shore between tide marks to the deepest abysses of the ocean.
Sponges do not appear to be edible by fishes, or even
the higher crustaceans or molluscs. Countless lower animal
forms, however, burrow in their substance, if not for food,
at least for shelter, and the interior of a sponge is frequently
found to be teeming with small crustaceans, annelids, mol-
luscs, and other invertebrates. None of the sponges are
true parasites. The little boring sponge, Cliona, burrows
in the shells of oysters and other bivalves, and even into
solid limestone, but for protection and not for food. But
the sponge frequently lives in that close association with
another animal or plant to which the term messmateism, or
commensalism is applied — associations which benefit one or
both. Thus some species of sponge are never found grow-
ing except on the backs or legs of certain crabs. In these
cases the sponge protects the crab and conceals it from its
enemies, while the sponge benefits by being carried from
place to place, and thus obtaining freer oxygenation. Cer-
tain cirripede crustaceans (members of the order to which
the barnacles and acorn-shells belong) are invariably found
embedded in certain species of sponge. Frequently a
sponge and a zoophyte grow in intimate association, so
that they seem almost to form one structure. Thus the
glass-rope sponge (Hyalonema} is always found associated
with a zoophyte (Pafythoa), and there are many other in-
stances. Sponges often also grow in very close association
with certain low forms of plants (Alga).
SECTION IV. — PHYLUM CGELENTERATA
IN the previous section we saw that the simplest type
of sponge has the general character of a cylinder, closed
at one end and open at the other, and having the walls
perforated by minute pores, and composed of three layers,
— ectoderm, mesogloea, and endoderm, the last consisting
of collared flagellate cells.
In such an organism as this, imagine the pores to disap-
pear, the internal cavity thus coming to communicate with
the exterior by a single terminal aperture ; the mesogloea
to be replaced by a very thin, structureless layer containing
no cells ; the endoderm cells to lose their collars ; and a
circlet of arm-like processes, or tentacles, formed of the
same layers as the body-wall, to be developed round the
terminal aperture. The result would be a polype, and
would serve as a type of the general structure of the group
of animals with which we are now concerned.
The most familiar examples of Coelenterata are the horny,
seaweed-like hydroids, or, as they are sometimes called,
"zoophytes," to be picked up on every sea- beach, jelly-
fishes, sea anemones, and corals. The phylum is divided
into four classes as follows : —
Class i. — Hydrozoa, including the fresh- water polypes,
zoophytes, many jellyfishes, — mostly of small size, — and a
few stony corals.
90
SECT, iv PHYLUM OELENTERATA 91
Class 2. — Scyphozoa, including most of the large jelly-
fishes.
Class j. — Actinozoa, including the sea-anemones, and
the vast majority of stony corals.
Class 4. — Ctenophora, including certain peculiar jelly-
fishes known as "comb-jellies."
1. THE HYDROZOA
Obelia, which is a good example of the class, is a common
zoophyte occurring in the form of a delicate, whitish, or light
brown, almost fur-like growth on the wooden piles of piers
and wharfs. Obelia commissuralis occurs on the coast of
New England almost at low-water mark, being exposed only
at the lowest tides. With it, north of Cape Cod, may be
found Obelia gelatinosa, a rather stouter species, but similar
in general appearance. Obelia geniculata is abundant on
Laminaria or the "devil's apron," giving the fronds when
submerged a downy appearance. The following account
refers to a common European species : It consists of
branched filaments about the thickness of fine sewing
cotton ; of these, some are closely adherent to the timber,
and serve for attachment, while others are given off at right
angles, and present at intervals short lateral branches, each
terminating in a bud-like enlargement. The structure is best
seen under a low power of the microscope. The organism
(Fig. 41) is a colony, consisting of a common stem or axis,
on which are borne numerous zooids.
The large majority of the zooids have the form of little
conical structures (P, i-P, 4}, each enclosed in a glassy,
cup-like investment or hydrotheca (hth), and produced dis-
tally into about two dozen arms or tentacles (/) : these
zooids are the polypes or hydranths. Less numerous, and
92 MANUAL OF ZOOLOGY SECT, iv
found chiefly towards the proximal region of the colony, are
long cylindrical bodies or blastostyles (bis), each enclosed
in a transparent case, the gonangium or gonotheca (gth),
and bearing numerous small lateral offshoots, varying greatly
in form according to their stage of development, and known
as medusa-duds (m.bd). By studying the development of
these structures, and by a comparison with other forms, it
is known that both blastostyles and medusa-buds are zooids,
so that the colony is trimorphic, having zooids of three
kinds.
To make out the structure in greater detail, living speci-
mens should be observed under a high power. A polype
is then seen to consist of a somewhat cylindrical, hollow
body, of a yellowish colour, joined to the common stem by
its proximal end and produced at its distal end into a
conical elevation, the manubrium or hypostome (mnb),
around the base of which are arranged the twenty-four
tentacles in a circle. Both body and manubrium are hol-
low, containing a spacious cavity, the enteron (enf), which
communicates with the outer world by a mouth (mth), an
aperture placed at the summit of the manubrium. The
mouth is capable of great dilatation and contraction, and
accordingly the manubrium appears now conical, now
trumpet-shaped. Under favourable circumstances small
organisms may be seen to be caught by the tentacles and
carried towards the mouth to be swallowed. The hydro-
theca (hth) has the form of a vase or wine-glass, and is
perfectly transparent and colourless. When irritated — by
a touch, or by the addition of alcohol or other poison — the
polype undergoes a very marked contraction : it suddenly
withdraws itself more or less completely into the theca, and
the tentacles become greatly shortened and curved over the
manubrium (P. 2).
FIG. 41. — Obelia sp. A, portion of a colony, with certain parts shown in longi-
tudinal section; B, medusa; C, the same, with reversed umbrella; D, the same,
oral aspect; tid. i, 2, buds; bis, blastostyle ; COP, coenosarc ; ect, ectoderm:
end, endoderm ; ent, enteric cavity: gth, gonotheca (gonangium) : hth, hydro-
theca; /, lithocyst ; m.bd, medusa-bud: mnb, manubrium ; ntsgl, mesoglcea :
tnth, mouth: /, perisarc: P. i, 2, 3, 4, polypes: rad.c, radial canal; /,
tentacle ; vl, velum.
93
94 MANUAL OF ZOOLOGY SECT.
The various branches of the common stem show a very
obvious distinction into two layers : a transparent, tough,
outer membrane, of a yellowish colour and horny con-
sistency, the perisarc (/), and an inner, delicate, granular
layer, the ccenosarc (tee), continuous by a sort of neck or
constriction with the body of each hydranth. The coenosarc
is hollow, its tubular cavity being continuous with the
cavities of the polypes, and containing a fluid in which a
flickering movement may be observed, due to the presence
of vibrating cilia. In the blastostyle both mouth and tenta-
cles are absent, the zooid ending distally in a flattened disc ;
the hydrotheca of the polype is represented by the gono-
theca (gth}, which is a cylindrical capsule enclosing the
whole structure, but ultimately becoming ruptured at its
distal end to allow of the escape of the medusa-buds.
These latter are, in the young condition, mere hollow off-
shoots of the blastostyle : when fully developed they have
the appearance of saucers attached by the middle of the
convex surface to the blastostyle, produced at the edge into
sixteen very short tentacles, and having a blunt process, the
manubrium, projecting from the centre of the concave sur-
face. They are ultimately set free through the aperture in
the gonotheca as little medusae or jellyfish (B-D), which
will be described hereafter.
The microscopical structure of Obelia reminds us, in its
general features, of that of such a simple sponge as Ascetta,
but with many characteristic differences. The body is
composed of two layers of cells, the ectoderm and the
endoderm, the latter ciliated ; between them is a very
delicate transparent membrane, the mesoglcea or supporting
lamella, which, unlike the intermediate layer of sponges,
contains no cells and is practically structureless.
The perisarc or transparent outer layer of the stem shows
IV PHYLUM CfELENTERATA 95
no cell-structure, but only a delicate lamination. It is, in
fact, not a cellular membrane or epithelium, like the ecto-
derm and endoderm, but a cuticle, formed, layer by layer,
as a secretion from the ectoderm cells (see p. 67). It is
of chitinoid or horn-like consistency, and, like the lorica
of many Protozoa, serves as a protective external skeleton.
Embedded in the ectoderm are numerous clear, ovoid
bodies, the stinging-capsules or nematocysts (Fig. 42), serving
as weapons of offence. Each consists (A) of a tough, ovoid
capsule, full of a gelatinous material, and invaginated at one
end in the form of a hollow process continued into a long,
coiled, hollow thread. The whole apparatus is developed in
an interstitial cell called a cnidoblast (cnb], which, as it ap-
proaches maturity, migrates towards the surface, and becomes
embedded in one of the large ectoderm cells. At one point
of its surface the cnidoblast is produced into a delicate pro-
toplasmic process, the cnidocilov trigger-hair (cnc} : when this
is touched — for instance by some small organism brought
into contact with the waving tentacles — the cnidoblast un-
dergoes a sudden contraction, and the pressure upon the
stinging-capsule causes an instantaneous eversion of the
thread (B), at the base of which are minute barbs. The
threads or the gelatinous substance are poisonous and
exert a numbing effect on the animals upon which the
Obelia preys.
The structure of the Medusae — formed as we have seen
by the development of medusa-buds liberated from a
ruptured gonangium — yet remains to be considered. The
convex surface of the bell or umbrella (Fig. 41, B-D) by
which the zooid was originally attached to the blastostyle, is
distinguished as the ex-umbrella, the concave inner surface
as the sub-umbrella. From the centre of the sub-umbrella
proceeds the manubrium (mn&), at the free end of which is
96
MANUAL OF ZOOLOGY
SECT.
the four-sided mouth (mfh}. Very commonly as the medusa
swims the umbrella becomes turned inside out, the sub-
f^cnb
^^ att n"
crib
FIG. 42. — Nematocysts of hydra. A, undischarged; B, discharged; C, nerve-
supply; cnb, cnidoblast; cnc, cnidocil; u/t, nucleus; ntc, nematocyst; nv.ct
nerve-cell. (From Parker's Biology, after Schneider.)
umbrella then forming the convex surface, and the manu-
brium springing from its apex (Fig. 41, C).
IV
PHYLUM OELENTERATA
97
The mouth (Figs. 41, C, D, and 43, mth) leads into an
enteric cavity which occupies the whole interior of the
manubrium, and from its dilated base sends off four delicate
tubes, the radial canals (rad. c), which pass at equal
distances from each other through the substance of the
umbrella to its margin, where they all open into a circular
canal (cir. c), running parallel with and close to the
margin. By means of this system of canals the food, taken
end.fam
FIG. 43 — Dissection of a medusa with rather more than one-quarter of the umbrella
and manubrium cut away (diagrammatic). The ectoderm is dotted, the endo-
derm striated, and the mesogloea black, cir. c, circular canal; end. lam,
endoderm lamella; gon, gonad; /, lithocyst; mnb> manubrium; mth, mouth;
rad. c, radial canal; vl, velum.
in at the mouth and digested in the manubrium, is dis-
tributed to the entire medusa.
The edge of the umbrella is produced into a very narrow
fold or shelf, the velum (Fig. 43, z>/), and gives off the
tentacles (/), which are sixteen in number in the newly-born
medusa (Fig. 41, D), but which are very numerous in the
adult. At the bases of eight of the tentacles — two in each
quadrant — are minute globular sacs (/), each containing a
H
98 MANUAL OF ZOOLOGY SECT.
calcareous particle or lithite. These are the marginal sense-
organs or lithocysts : they were formerly considered to be
organs of hearing, and are hence frequently called otocysts :
in all probability their function is to guide the medusa by
enabling it to judge of the direction in which it is swim-
ming. The marginal organs, in this case, may therefore be
looked upon as organs of the sense of direction.
In the description of the fixed Obelia-colony no mention
was made of cells set apart for reproduction, like the ova and
sperms of a sponge. As a matter of fact, such sexual cells
are only found, in their fully developed condition at least, in
the medusae. Hanging at equal distances from the sub-
umbrella, in immediate relation with the radial canal, are
four ovoid bodies (Fig. 43, gon), each containing a mass of
cells which are developed either into ova or into sperms. As
each medusa bears organs of one sex only (testes or ovaries
as the case may be), the individual medusae are dioecious.
When the gonads are ripe, the sperms of the male
medusae are shed into the water and carried by currents to
the females, impregnating the ova, which thus become
oosperms or unicellular embryos. The oosperm undergoes
complete segmentation (Fig. 44, A~F}, and is converted
into an ovoidal ciliated body called &planula (G, H). The
planula swims freely for a time (ff), and then settles down
on a piece of timber, seaweed, etc., fixes itself by one end
(K}, and becomes converted into a hydrula or simple polype
(Z, M), having a disc of attachment at its proximal end,
and at its distal end a manubrium and circlet of tentacles.
Soon the hydrula sends out lateral buds, and, by a frequent
repetition of this process, becomes converted into the com-
plex Obelia-colony with which we started.
This remarkable life-history furnishes the first example we
have yet met with of alternation of generations, or metagenesis.
IV
PHYLUM CCELENTERATA
99
The Obelia-colony is sexless, having no gonads, and develop-
ing only by the asexual process of budding ; but certain of
its buds — the medusae — develop gonads, and from their
impregnated eggs new Obelia-colonies arise. We thus have
an alternation of an asexual generation — the Obelia-colony
— with a sexual generation , the medusa.
FIG. 44. — Stages in the development of two zoophytes (A-H, Laomedea. I-M,
Eudendrium) allied to Obelia; A-F, stages in segmentation; G, the planula
enclosed in the maternal tissues; H, the free-swimming planula; I-M, fixation
of the planula and development of the hydrula. (From Parker's Biology, after
Allman.)
The majority of the Hydrozoa resemble Obelia in form-
ing fixed colonies ; but there are a few exceptional cases in
which the animal remains simple. One of these is Hydra,
the Fresh-water Polype. In Hydra the entire organism (Fig.
45) consists of a simple cylindrical body with a conical hypos-
FIG 45. — Hydra. A vertical section of entire animal; B, portion of transverse
section, highly magnified: C, two large ectoderm cells: D, endoderm cell cf
H. viridis ; E, large nematocyst; F, small nematocyst; G, sperm; a, ingested
diatom; bd.lt bd.z, buds; chr, chromatophores; cnbl, cnidoblast; cnc, cnidocil;
ect, ectoderm; end, endoderm; ent. cav, enteric cavity; eiit. cav1, its prolonga-
tion into the tentacles; _ft, flagellum; hyp, hypostome or manubrinm; int. c, in-
terstitial cells; m.pr, muscle processes; ntth, mouth; tnsgl, mesoglcea; net,
large, and tttc1, small nematocysts; ttu, nucleus; av, ovum; ovy, ovary; psd,
pseudopods ; spy, spermary ; vac. vacuole.
100
SECT, iv PHYLUM OELENTERATA 101
tome and a circlet of from six to eight tentacles surrounding
the mouth. It is ordinarily attached, by virtue of a sticky
secretion from the proximal end, to weeds, etc., but is capable
of detaching itself and moving from place to place after the
manner of a looping caterpillar. The tentacles are hollow,
and communicate freely with the enteron. There is no
perisarc. Buds are produced which develop into Hydrae ;
but these are always detached sooner or later, so that a
permanent colony is never formed. There are no special
reproductive zooids, but simple ovaries (ovy) and testes
(spy} are developed, the former nearer the proximal, the
latter nearer the distal end of the body.
In nearly all the remaining Hydrozoa that do not form
colonies the form assumed is not that of the polype, but that
of the medusa (Fig. 46), a polype stage never being
developed, and the animal resembling in all essential
respects the medusae of Obelia; the chief difference of
importance being the presence of sense-organs in the form
of hollow, club-shaped appendages, the tentaculocysts, con-
taining calcareous bodies of lithites. These simple free-
swimming medusiform Hydrozoa (TrachyIin(K) develop ova
and sperms which give rise to free-swimming ciliated larvae ;
but the latter, instead of becoming fixed and developing into
plant-like colonies, remain free, and develop directly into
medusae like those from which they originated. The fixed
zoophyte stage is thus absent in the life-history, and an
alternation of generations is not recognisable.
In the colonial Hydrozoa, which constitute the great
majority of the class, the colony in most instances resem-
bles that of Obelia in being a fixed structure consisting of a
slender branching stem, covered over by perisarc, and bear-
ing zooids and blastostyles. In many the perisarc is
produced to form hydrothecas and gonothecae for the
102
MANUAL OF ZOOLOGY
SECT.
protection of the polypes and blastostyles respectively ;
but in others (Fig. 47) these protecting structures are
absent. The polypes resemble those of Obelia in all es-
1"
% V
fli
sential respects, but differ in the number and arrangement
of the tentacles and other minor points. In many medusae
are developed from blastostyles as in Obelia, and when
fully formed become free. The shape of the medusa
IV
PHYLUM CGELENTERATA
103
differs in different forms, more particularly as regards the
umbrella. There is always a manubrium, with gastric
t
FIG. 47. — Bougainvillea ramosa. A, entire colony, natural size; B, portion of the
same magnified ; C, immature medusa ; dr. c, circular canal ; cu, cuticle or
perisarc ; ent. cav, enteric cavity ; hyd, polype or hydranth ; hyp, hypostome or
manubrium ; med, medusa; muo, manubrium ; rad. c, radial canal ; t, tentacle ;
v, velum. (From Parker's Biology, after Allman.) This is closely allied to the
New England B. super cilians.
104 MANUAL OF ZOOLOGY SECT.
cavity, and a marginal and four radial canals, and a velum
is universally present. But lithocysts are not present in all,
their place being taken by specks of red or black pigment
— the ocelli or rudimentary eyes — at the bases of the ten-
tacles. The number and arrangement of the tentacles is
subject to considerable variation. The gonads are some-
times, as in Obelia, developed in the radial canals, some-
times in the manubrium. In size the medusae range from
about i up to 400 millimetres (16 inches) in diameter.
In many of the zoophytes, however, the medusae never
become detached from the colony, developing the ova and
sperms without becoming free. 'In such cases the charac-
teristic medusa structure is more or less imperfectly de-
veloped, and in many forms is not at all recognisable, the
buds corresponding to those which in Obelia give rise to
medusae merely developing into rounded outgrowths termed
sporosacs, in the interior of which the ova and sperms are
formed.
The reproductive buds are not in all cases formed, as in
Obelia, on distinct, peculiarly modified, mouthless zooids.
In many instances, whether they are destined to give rise
to medusae or sporosacs, the buds spring directly from the
ccenosarc, or from the ordinary zooids.
A small group of Hydrozoa — the Hydrocorallina — in-
cluding the Millepores {Millepord) and Stylaster, form
colonies, the supporting material of which, instead of being
chitinoid, is of calcareous and stony character, like the
substance of a coral.
The colonies of Hydrozoa are not in all instances at-
tached, like those of Obelia and the other hydroid zoo-
phytes. In one large order, the Siphonophora, the colonies
of zooids float or swim freely in the sea. In some Siphono-
phora there are no organs for active locomotion, and the
IV PHYLUM CCELENTERATA 105
colony drifts about, completely at the mercy of wind and
tide, buoyed up by a bladder-like float or pneumatophore
containing air. Such a passively floating form is the
Portuguese Man-of-war {Physalia) (Figs. 48, 49) which has
an elongated float, pointed at the ends, and produced above,
along its upper edge, into a crest or sail (cr.). At one end
is a minute aperture communicating with the exterior.
From the under side of the float hang polypes (/), feelers,
groups of medusa-buds looking like bunches of grapes of
a deep blue colour, and long retractile tentacles, sometimes
several feet in length, and containing batteries of stinging-
capsules powerful enough to sting the hand as severely as a
nettle. The male reproductive buds remain attached and
take the form of sporosacs, while the female buds apparently
become detached as free medusae. Physalia arethusa is
common in the West Indies, and, borne northward by the
Gulf Stream, is occasionally met with on the coast of
southern New England, and off Nova Scotia.
In such a Siphonophoran as Halistemma (Fig. 50), on
the other hand, there is a long, slender, flexible stem or
coenosarc, at the upper end of which is a comparatively
small float. Next to this come a number of closely set,
transparent structures (net), having the general characters
of unsymmetrical medusas without manubria, each being a
deep, bell-like body, with a velum and radiating canals.
During life these swimming-bells or nectocalyces contract
rhythmically, — i.e., at regular intervals, — thus serving to
propel the entire organism through the water. Below the
last nectocalyx the character of the structures borne by the
stem changes completely : they are of several kinds, and
are arranged in groups which follow one another at regular
intervals.
Some of these are unmistakable polypes (/) differing,
io6
MANUAL OF ZOOLOGY
SECT.
cr-
FIG. 48 — Physalia. The living animal
floating on the surface of the sea. cr,
crest ; p, polype ; pn, pneumatophore,
float, or air-sac. (After Huxley.)
FIG. 49. — Physalia arethusa, natural
size. (After Agassiz.)
HYLUM CCELENTERATA
FIG. 50.— Halistemma tergestinum. A, the entire colony; B, a single group of
zooids; cos, coenosarc; dz, dactylozooid ; hph, hydrophy Ilium or bract: net,
nectocalyx or swimming-bell; ntc. battery of nematocysts; p. polype; />«,
pneumatophore or float; J, *', sporocysts; ^tentacle. (After Claus.)
io8 MANUAL OF ZOOLOGY SECT.
however, from those we have hitherto met with, in having
no circlet of tentacles round the mouth, but a single, long,
branched tentacle (/) arising from its proximal end, and
bearing numerous groups or " batteries " of stinging-capsules
(ntc}. Others are dactylozooids or feelers (dz) — mouth-
less polypes, each with an unbranched tentacle springing
from its base. Near the bases of the polypes and dactylo-
zooids spring groups of sporosacs (B, s, s'), some male,
others female ; and finally delicate, leaf-like transparent
bodies — the bracts or hydrophyllia (hph) — partly cover the
sporosacs. Halistemma occurs in the Atlantic and Mediter-
ranean. A closely related form (Agdlmopsis cara) occurs
off the coast of New England.
2. THE SCYPHOZOA
Aurelia, which may be taken as an example of the
Scyphozoa, is the most common of our larger jellyfishes,
and is often found cast up on the sea-shore, where it is
readily recognisable by its gelatinous saucer-shaped umbrella,
from eight to twelve, and sometimes fifteen inches in diam-
eter, having near the centre four red or purple horseshoe-
shaped bodies — the gonads — lying embedded in the
jelly.
The general arrangement of the parts of the body (Fig.
51) is very similar to what we are already familiar with in
the hydrozoan jellyfishes (Figs. 41 and 43). Most con-
spicuous is the concavo-convex umbrella, the convex sur-
face of which, or ex-timbrella, is uppermost in the ordinary
swimming position. The outline is approximately circular,
but is broken by eight notches, in each of which lies a pair
of delicate processes, the marginal lappets (nig. lp) with a
peculiar sense-organ; between the pairs of lappets the edge
IV
PHYLUM OELENTERATA
109
of the umbrella is fringed by numerous close-set marginal
tentacles (/).
In the centre of the lower or sub-umbrella surface is a
four-sided aperture, the mouth (mtli), borne at the end of
99"
FIG. 51. — Aurelia aurita. Ventral view— two of the oral arms are removed; tt.r.c,
radial canal; gon, gonads; i.r.c, radial canal; mg. Ifi, marginal lappet; mtht
mouth; or. a, oral arm; p.r.c, radial canal; s.g.p, sub-genital pit; /,
tentacles.
an extremely short and inconspicuous manubrium: sur-
rounding it are four long delicate processes, the oral arms
no MANUAL OF ZOOLOGY SECT.
(or. a), situated one at each angle of the mouth and uniting
round it.
At a short distance from each of the straight sides of the
mouth is a nearly circular aperture leading into a shallow
pouch, the sub -genital pit (s. g. p), which lies immediately
beneath one of the conspicuously coloured gonads (gon).
The mouth leads by a short tube or gullet, contained
in the manubrium, into a spacious stomach, which is
produced into four wide inter-radial gastric pouches, which
extend about halfway from the centre to the circumference.
In the outer or peripheral wall of each gastric pouch are
three small apertures, leading into as many radial canals
(a.r.c, i.r.c, p.r.c), which pass to the edge of the umbrella
and then unite in a very narrow circular canal.
Each gonad (gon.) is a horseshoe-shaped frill-like structure
situated on the floor of the gastric pouch. When mature, its
products — ova or sperms — are discharged into the stomach,
and pass out by the mouth. The sexes are lodged in distinct
individuals.
Lying parallel with the inner or concave border of each
gonad is a row of delicate filaments supplied with stinging-
capsules. These are the gastric filaments : their function
is to kill or paralyse the prey taken alive into the stomach
(compare Fig. 53, g.f).
The development and life-history of Aurelia present
several striking and characteristic features. The impreg-
nated egg-cell or oosperm becomes converted into a closed
two-layered sac or planula (Fig. 52, A), similar to that of
a Hydrozoon. The planula swims about by means of the
cilia with which its ectodermal cells are provided, and, after
a brief free existence, settles down, loses its cilia, and be-
comes attached by one pole. At the opposite pole a mouth
is formed. On two opposite sides of the mouth hollow
IV
PHYLUM OELENTERATA
in
FIG. 52. — Aurelia aurita. development A, planula: B, C, formation of the gullet
or stomodaeum; D, transverse section of youn» scyphula; E, scyphula; F,
longitudinal section of same', G, division of scypnnla into ephyrulae; H, ephy-
rula from the side: I, the same from beneath. In AD and F the ectoderm
is unshaded, the endoHerm striated, and the mesoglcea dotted, a, lobes of
umbrell<; mnb, manubrium; wM, mouth; s f, septal funnel; st, stomodaeum;
t, tentacle: in, taenioles, or gastric ridges. (From Korschelt and Heider's
Embryology )
112 MANUAL OF ZOOLOGY SECT.
processes grow out, forming the first two tentacles; soon
two others appear at right angles to these. Subsequently
other tentacles appear. At the same time the attached or
proximal end is narrowed into a stalk-like organ of attach-
ment (E).
The outcome of all these changes is the metamorphosis
of the planula into a polype (F), not unlike a Hydra. The
Scyphozoon-polype is called a Scyphula. The Scyphula some-
times multiplies by budding. After a time it undergoes a
process of transverse fission (G), becoming divided by a series
of constrictions which deepen until the polype assumes the
appearance of a pile of saucers, each with its edge produced
into eight bifid lobes. Soon the process of constriction is
completed, the saucer-like bodies separate from one another,
and each, — except the first topmost one, which falls off and
dies, — turning upside down, begins to swim about as a small
jellyfish called an Ephyrula (H, I), which grows rapidly
and eventually develops into the adult Aurelia.
The rest of the Scyphozoa resemble Aurelia in the gen-
eral features of their structure, but there is a good deal
of variation in certain points (Fig. 52). Thus the umbrella,
instead of being a saucer-shaped disc, as in Aurelia, is often
conical or cup-shaped or cubical. In some, tentaculocysts
are not developed, and in others the oral arms are absent.
Lucernaria differs somewhat widely from the rest in being
attached by means of a short stalk developed from the centre
of the ex-umbrella. In the Rhizostomece the mouth is
obliterated by the union of the bases of the oral arms, the
food being taken in through a large number of minute orifices
scattered over the surface of the arms, and leading into a
system of fine canals, which join together to form larger
canals, eventually opening into the gastric cavity. Many of
the Scyphozoa pass through an alternation of generations
IV
PHYLUM CCELENTERATA
similar to that which has been described in the case of
Amelia, with a fixed scyphistoma stage ; but in others the
ciliated larvse developed from the ova give rise directly to
i.r.
frr.t
FIG. S3.- Tessera princeps. A, external view; B, vertical section; g. /, gastric
filament; gon, gonad; i.r.t, tentacle; mnb, manubrium; mth, mouth; p.r.t,
tentacle: j^, stomach; tn, taeniole or gastric ridge. Antarctic Ocean. (After
Haeckel.)
jellyfishes like the parent, without the intercalation of any
fixed stage.
The Scyphozoa are all marine, and the majority are
pelagic, i.e., swim freely in the surface waters of the ocean,
i
ii4 MANUAL OF ZOOLOGY SECT.
A few inhabit the deep sea, and have been dredged from
as great a depth as 2000 fathoms. Nearly all are free-
swimming in the adult state ; some, however, live on coral-
reefs or mud-banks, and are found resting, in an inverted
position, on the ex-umbrella ; and a few, such as Lucernaria,
are able to attach themselves at will by a peduncle. Many
are semi-transparent and glassy, but often with brilliantly
coloured gonads, tentacles, or radial canals. In many cases
the umbrella, oral arms, etc., are highly coloured, and some
species are phosphorescent. They are all carnivorous, and,
although mostly living on smaller organisms, are able, in the
case of the larger species, to capture and digest crustaceans
and fishes of considerable size.
3. THE ACTINOZOA
The simplest and most familiar of the Actinozoa are the
Sea-anemones, which are to be found attached to rocks,
seaweeds, shells, etc., on the sea-shore. When expanded a
sea-anemone has the form of a cylindrical column attached
to a rock or other support by a broad base. The distal or
free surface of the column, termed the disc or peris to me,
bears in the middle an elongated, slit-like aperture — the
mouth. Springing from the disc and encircling the mouth
are numerous cylindrical tentacles, disposed in circlets, their
total number being some multiple of five.
Obviously the sea-anemone is a polype, formed on the
same general lines as a polype of the Hydrozoa. But
certain important differences from the Hydrozoan polype
become manifest when we examine the internal structure
(Fig. 54). The mouth does not lead at once into a spacious
undivided enteric cavity, but into a short tube (gitl), having
the form of a flattened cylinder, which hangs downward
iv PHYLUM CCELENTERATA 115
into the interior of the body, and terminates in a free edge.
This tube is called the gullet or stomodaeum. Its inner
surface is marked with two longitudinal grooves (sgph),
known as the gullet-grooves or siphonoglyphes. The gullet
does not simply hang freely in the interior cavity, but is
connected with the body-wall by a number of radiating
cst.f
FIG. 54. — Tealia crassicornis. Dissected specimen; gon, gonads; gult gullet;
/. m, longitudinal muscle; Ip, lappet; ntes. I, primary, mes. 2, secondary,
mes. 3, tertiary mesenteries; mes. F, mesenteric filaments; mth, mouth;
ost. /, ost. 2, ostia or aperture in mesenteries; /. tn, parietal muscle; sgph,
siphonoglyphe; s. m, sphincter muscle; t. nt, transverse muscle.
partitions, the complete or primary mesenteries (mes. '/) ;
between these are incomplete secondary mesenteries (mes. 2),
which extend only part of the way from the body-wall to
the gullet, and tertiary mesenteries (mes. 3), which are
hardly more than ridges on the inner surface of the body-
MANUAL OF ZOOLOGY
SECT.
wall. Thus the entire enteric cavity of a sea-anemone is
divisible into three regions : (i) the gullet or stomodseum,
communicating with the exterior by the mouth, and opening
below into (2) a single main digestive cavity, the stomach,
which gives off (3) a number of radially arranged cavities,
the inter-mesenteric chambers. The free edges of the
mesenteries below the gullet are produced into curious
iv PHYLUM CCELENTERATA 117
twisted cords, the mesenteric filaments (mes. F), answering
to the gastric filaments of Scyphozoa. Stinging- capsules
occur in the ectoderm, and are also very abundant in the
mesenteric filaments. They resemble in general character
the nematocysts of Hydrozoa, but are of a more elongated
form, and the thread is usually provided at the base with
very numerous slender barbs.
In virtue of possessing both stinging-capsules and gland-
cells, the mesenteric filaments perform a double function.
The animal is very voracious, and is able to capture and
swallow small fishes, molluscs, sea-urchins, etc. The prey
is partly paralysed before ingestion by the nematocysts of
the tentacles, but the process is completed, after swallowing,
by those of the mesenteric filaments. Then, as the captured
animal lies in the stomach, the edges of the filaments come
into close contact with one another and practically surround
it, pouring out at the same time a digestive juice secreted
by their gland-cells.
Sea-anemones are dioecious, the sexes being lodged in
distinct individuals. The gonads — ovaries or testes — are
developed in the substance of the mesenteries (Fig. 54,
gon}, a short distance from the edge, and, when mature,
often form very noticeable structures. The development
of sea-anemones resembles, in its main features, that of
Scyphozoa, but there is no alternation of generations.
Our common sea-anemone, Metridium marginatum (Fig.
56), lives under stones near low- water mark.
Two main divisions or sub-classes of the Actinozoa are
recognised, — the Zoantharia and the Alcyonaria, the
former including the sea-anemones, the Madrepores, and
other stony corals, and the horny black corals ; the latter
the "dead men's fingers," red coral, organ-pipe coral,
"sea-fans," and "sea-pens." The principal distinguishing
u8
MANUAL OF ZOOLOGY
SECT.
features of the two sub-classes are, that in the Zoantharia
the tentacles and mesenteries are usually very numerous,
and are arranged, as a rule, in multiples of five or six, and
FIG. 56. — The common Sea-anemone.
(After Emerton.)
FIG. 57. — Corallium rubrum, portion of
colony. Enlarged twice. (After Lacaze-
Duthiers.)
that the tentacles are simple in form ; while in the Alcyo-
naria (Fig. 58) the tentacles and mesenteries are always
eight in number, and the tentacles are pinnate, *>., each
of them consists of a main stem with two rows of lateral
branchlets.
Only the sea-anemones (with a few exceptions) and a
few Madrepore corals remain simple, the rest all giving
rise to more or less extensive colonies, of a variety of differ-
ent forms, by continuous budding. The structure of the
zooids is similar to that of the sea-anemone in all essential
respects. In many of the Alcyonaria two forms of zooids
are to be distinguished in each colony (dimorphism of the
zooids), ordinary zooids, and siphonozooids, which are smaller,
and are devoid of tentacles and of gonads.
PHYLUM OELENTERATA
"9
None of the sea-anemones have a true skeleton ; in some,
however, there is a thick cuticle, and several kinds enclose
themselves in a more or less complete tube, which may be
largely formed of discharged nematocysts. In some Alcyo-
FIG. 58. — Alcyonium palmatum. A, entire colony natural size; B, spicules.
Mediterranean Sea. (After Cuvier.)
naria, such as the " dead men's fingers " (Alcyonium, Fig. 58),
the skeleton consists of minute, scattered, irregular deposits
of carbonate of lime called spicules. Alcyonium carneum
occurs below tide- mark off the New England coast. In
Tubipora (the "organ-pipe coral") (Fig. 59) there is a con-
120
MANUAL OF ZOOLOGY
SECT.
tinuous calcareous tube for each polype. In the red coral
of commerce (P"ig. 57), which inhabits the Mediterranean
Sea, there is an extremely hard calcareous branched rod
which extends as an axis through the ccenosarc. In the
black corals (Antipathes and allies) there is a horn-like
axis ; and in Gorgonia there
is a similar skeleton, some-
times partly calcareous, with the
addition of numerous spicules.
In the sea-pens (Fig. 60) the
colony is supported by an un-
branched horny axis. Pennatula
aculeata lives in deep water in
the North Atlantic.
In the Madrepore corals we
have a skeleton of an entirely
different type, consisting, in fact,
of a more or less cup-like calca-
reous structure secreted from the
ectoderm of the base and column
of the polype. When formed by
a solitary polype such a " cup-
FIG. sg.-TuWporamusica. Skei- coral" is known as a corallite ;
eton of entire colony. Natural
size //.platform. indianOcean. in the majority of species a large
(After Cuvier.)
number — sometimes many thou-
sands — of corallites combine to form a corallum, the skele-
ton of an entire coral-colony.
The structure of a corallite is conveniently illustrated by
that of the solitary genus Flabellum (Fig. 61, A, B). It
has the form of a short conical cup, much compressed,
so as to be oval in section. Its wall or theca is formed
of dense stony calcium carbonate, the proximal end pro-
duced into a short stalk or peduncle. From the inner
IV
PHYLUM CCELENTERATA
121
surface of the theca a number of radiating partitions, the
septa, proceed inwards or towards the axis of the cup,
some of them meeting in the middle to form an irregular
central mass or columella, which in some kinds of corals
forms an independent, pillar-like
structure arising from the middle
of the base.
In the living condition the
polype fills the whole interior of
the corallite, and projects beyond
its edge to a greater or less degree
according to its state of expan-
sion. The septa alternate with
the mesenteries, each being in-
vested by an in-turned portion of
the body-wall ; so that, though
having at first sight the appear-
ance of being internal structures,
they are really external, lying alto-
gether outside the enteric cavity,
and are in contact throughout
with the ectoderm.
The almost infinite variety in
form of the compound corals is FIG. 60. — Pennatula sulcata.
. . Entire colony. Natural size.
due, in the main, tO the Various /, lateral branch. (After
methods of budding. According
to the mode of budding, massive corals are produced in
which the corallites are in close contact with one another,
as in Astr&a (Fig. 62) ; or tree-like forms, such as Den-
drophyllia (Fig. 63, A), in which a common calcareous
stem, the ccznenchyma, is formed by calcification of the
ccenosarc,1 and gives origin to the individual corallites.
1 See p. 94.
122
MANUAL OF ZOOLOGY
SECT,
FIG. 61. — A, B, two views of Flabellum curvatum. Natural size. C, semi-dia-
grammatic view of a simple coral; D, portion of a corallite; E, F, diagram of a
simple coral in longitudinal and transverse section; ectoderm dotted, endoderm
striated, skeleton black, b.pl, basal plate; col, cplumella; e. th, epitheca; gult
gullet; mes., mes. i, mes. 2, mesenteries; mes. f, mesenteric filaments; sep,
septa; /, tentacle; th, theca. (A and B after Moseley; C and D after Gilbert
Bourne.)
iv PHYLUM CCELENTERATA 123
It is by this last-named method, the coenosarc attaining
great dimensions, and the individual corallites being small
and very numerous, that the most complex of all corals,
the Madrepores (Fig. 63, B), are produced.
The Actinozoa are remarkable for the variety and brill-
iancy of their colour during life. Every one must have
noticed the vivid and varied tints of sea- anemones ; but in
FIG. 62. — Astraea pallida, the living colony. Natural size. Fiji Islands. (After
Dana.)
life the corals also exhibit a marvellously varied and gor-
geous colouring ; and the same holds good of many of the
Alcyonaria.
Many Actinozoa, like many sponges (p. 89), furnish
examples of commensalism, a term used for a mutually
beneficial association of two organisms of a less intimate
nature than occurs in symbiosis. An interesting example
is furnished by the sea-anemone Adamsia palliata. This
species is always found on a univalve shell — such as that of
a whelk — inhabited by a hermit-crab. The sea-anemone
is carried from place to place by the hermit-crab, and in
I24
MANUAL OF ZOOLOGY
this way secures a more varied and abundant food-supply
than would fall to its lot if it remained in one place. On
the other hand, the hermit-crab is protected from the attack
of predaceous fishes by retreating into its shell and leaving
exposed the sea-anemone, which, owing to its toughness,
FIG. 63. — A, Dendrophyllia nigrescens; B, Madrepora aspera. Natural size.
co, corallites ; cs, coenosarc; /, polypes. Pacific Ocean. (After Dana.)
and to the pain caused by its poisonous stinging-capsules,
is usually avoided as an article of food.
A similar case is that of Cancrisocia, of the China seas,
which lives on the back of a crab (Dorippe facchino,
Fig. 64). The crab carries, for its protection when young,
a small shell over its back, which it holds in this position by
iv PHYLUM CCELENTERATA
'25
means of its two reversed pairs of hind legs. The sea-
anemone appears to have fixed itself when young to the
FIG. 64. — Cancrisocia living as a commensal on the back of a crab. (After Verrill.)
shell, and afterwards, by its growth, spread over the back of
the crab, taking the place of the shell.
4. THE CTENOPHORA
The Ctenophora or comb-jellies are a group of free-
swimming, gelatinous, transparent animals which occur, some-
times in enormous numbers, in the surface waters of the sea.
The animal (Fig. 65) has the appearance of a mass of clear
jelly, usually of a globular shape ; and no pulsating move-
ments, such as those by means of which a Medusa propels
itself, are to be observed. Running over the surface, nearly
from pole to pole of the globular body, there will be observed
a series of eight bands of flashing points of light. These are
found, when examined more closely, to consist of rows of
long cilia, which run at right angles to the long axis of -the
126
MANUAL OF ZOOLOGY
SECT.
band. The cilia of each row are cemented together at
their bases, free from one another distally, so that each row
is comb-shaped, the basal cemented parts of the cilia
forming the back of the comb, the free portions the teeth.
It is by the paddling action of the numerous swimming
FIG. 65.— Hormiphora (Cydippe) plumosa. A, from the side; B, from the aboral
mth, mouth; s. pi, swimming plates; t and b, tentacles. Natural size.
Mediterranean Sea.
(After Chun.)
combs of these eight bands that the ctenophore is propelled
through the water.
Laterally there is situated a pair of long slender tentacles,
each provided with numerous little tag-like processes, and
having its base lodged in a sheath into the interior of which
the whole tentacle can be retracted. At one pole, the oral,
is an opening, the mouth : and at the opposite pole is
a pair of minute pores, the excretory pores, which are the
IV
PHYLUM CCELENTERATA
127
openings of a pair of canals given off from the enteric cavity.
Between the two excretory pores is a remarkable structure,
which is the nerve-centre as well as an organ of special
sense. The mouth leads into a flattened tube, the gullet,
and this again leads into a cavity, the infundibulum, which
ad.c
ad.c.
•s c
B
FIG. 66.— Hormiphora plumosa. A, transverse section of one of the branches of
a tentacle; B, two adhesive cells (ad c,~) and a sensory cell (j. c) highly magni-
fied, cu, cuticle; ««, nucleus. (After Hertwig and Chun.)
probably corresponds to the stomach of the sea-anemone.
From this cavity certain canals are given off.
Stinging-capsules are not developed, their place being
taken by a number of peculiar cells called adhesive cells, with
which the branches of the tentacles are covered. An
adhesive cell (Fig. 66, B) has a convex surface, produced into
small papillae, which readily adheres to any surface with
which it comes in contact, and is with difficulty separated.
In the interior of the cell is a spirally coiled filament, the
delicate inner end of which can be traced to the muscular
axis of the tentacular branch. These spiral threads act as
springs, and tend to prevent the adhesive cells from being
128
MANUAL OF ZOOLOGY
SECT. IV
torn away by the struggles of the captured prey. An allied
form is Pleurobrachia^ very abundant off our shores.
In some of the Ctenophora the body is produced into a
pair of lateral lobes. In fierce, instead of being globular, it
is more nearly cylindrical, with an extremely wide mouth
and gullet, and without tentacles. In
the "Venus's girdle" (Cestus), it is
compressed and almost ribbon-like.
All are free-swimming ; colonies are
never formed ; and there is never any
kind of skeleton.
The Ctenophora are usually per-
fectly transparent, and quite colour-
less, save for delicate tints of red,
brown, or yellow on the tentacles or
FIG. 67. — idyia roseola, on ridges on the inner surface of the
V halT natural size™**, a'nal gullet. CeStUS has, hoWCVCr, a deli-
/?£•!£ cate vi°let nuej and, when irritated,
(After shows a beautiful blue or bluish-green
fluorescence ; while Beroe is coloured
rose-pink, and Idyia is of a brilliant pink. The most
primitive form to be found on our coast is Idyia (Fig. 67),
which is a simple oval sphere, the interior of which forms an
immense digestive cavity, in which entire large animals may
be engulfed.
paddles
SECTION V. — PHYLUM PLATYHEL-
MINTHES
THE Platyhelminthes or Flat-worms are a group of animals
which, though of a low type of organisation, yet show in
many cases a great advance on the Ccelenterata, in the
possession of systems of organs of a more or. less elaborate
character for the carrying on of the various functions.
Many are internal parasites of higher animals; others are
parasites on the outer surface (external parasites) ; others
again are non-parasitic.
1. THE TREMATODA
A good and easily procurable example of the flat- worms
is the Liver-fluke of the sheep (Distomum hepaticum),
which lives as a parasite in the liver, in the interior of the
larger bile-ducts of the infested animal. It is a soft-bodied
worm, of flattened, leaf-like shape (Fig. 68), with a trian-
gular process, the head lode, projecting from the broader
end. When the liver-fluke is compared with a zooid oiObelia,
or with a Medusa or a sea-anemone, a striking difference in
the general disposition or symmetry of the parts is at once
recognisable. In the latter, as in the Coelenterata in general,
the prevailing arrangement is a radial one, the parts being
disposed in a radial manner round the main axis of the body,
which is an imaginary line running through the middle of
K 129
130
MANUAL OF ZOOLOGY
SECT.
FIG. 68. — Distomum hepaticum.
Natural size, excr, excretory
pore; mo, mouth; repr, repro-
ductive aperture; sckr, pos-
terior sucker.
the mouth and enteric cavity. In the fluke, on the other
hand, the parts are disposed to the right and left of an
imaginary median vertical plane,
along which the entire animal
is capable of being divided into
two completely symmetrical,
right and left, halves. The type
of symmetry here exemplified is
termed bilateral; it has already
been met with in some of the
Protozoa, and is characteristic
of nearly all animals higher than
the Coelenterata.
The broader end of the body
is determined as anterior, ow-
ing to the mouth and the central part of the nervous
system being situated at that extremity. One of the broad
flat surfaces is the dorsal, the other the ventral. The
mouth (tno), situated at the anterior extremity of the head-
lobe, is surrounded by a muscular oral sucker, and some
distance back, on the ventral surface, just behind the head-
lobe, is a second much larger posterior sucker (sckr).
Between the two suckers is a median aperture, the genital
opening (repr), through which a curved muscular process,
the cirrus or penis, may be protruded. In the middle of
the posterior end of the body is a minute opening, the
excretory pore (excr).
The surface is covered with innumerable minute spinules,
but vibratile cilia are absent.
The mouth (Fig. 68, mo) leads to a small, bulb-like body,
the pharynx (Fig. 69, pti), with thick muscular walls and a
small cavity. From this a short passage, the oesophagus,
leads to the intestine. The latter (inf) is frequently a very
v PHYLUM PLATYHELMINTHES 131
conspicuous structure, owing to its being filled with the
dark biliary matter on which the fluke feeds. It divides
almost immediately into two main limbs, right and left, and
from each of these are given off, both internally and ex-
FIG. 69. — Distomum hepaticum. Internal organisation. General view of the
anterior portion of the body, showing the various systems of organs as seen from
the ventral aspect, ej, ejaculatory duct; f, female reproductive aperture; int,
anterior portion of the intestine (the rest is not shown) ; od, commencement of
oviduct; ov, ovary; /, penis; ph, pharynx; sh, shell-gland; te, testes; ut,
uterus; vdlt left vas deferens; ?' right vas deferens; vit, lobes of vitelline
glands; vs, vesicula seminalis. (After Sommer.)
ternally, a number of blind branches or cceca, those on the
inner side being short and simple, while those on the outer
side are longer and branched. The two limbs of the intes-
tine, with their branches, thus form a complicated branching
MANUAL OF ZOOLOGY SECT.
system, the ramifications of which extend throughout the
whole of the body. There is no anus, or aperture of com-
munication between the intestine and the exterior, the only
external opening of the alimentary system being through the
mouth.
A branching system of vessels — the water-vessels or
vessels of the excretory system — ramify throughout the body.
A longitudinal main trunk opens outwards by means of the
excretory pore. In front it gives off four large trunks, each
of which branches repeatedly, the branches giving off smaller
vessels, and these again still smaller twigs, until we reach a
system of extremely fine microscopic vessels, or capillaries.
Each of these ends internally in a slight enlargement
situated in the interior of a large cell, a flame-cell, with a
bunch of vibratile cilia, or a single thick cilium, in the
interior.
The fluke has a nervous system, the arrangement of
which partakes of the bilateral symmetry of the body. The
central part of this system consists of a ring of nerve matter,
which surrounds the oesophagus, and presents two lateral
thickenings or ganglia containing nerve-cells, and a single
ganglion situated in the middle line below. From this are
given off a number of nerves, of which the chief are a pair
of lateral cords running back to the posterior end and
giving off numerous branches. There are no organs of
special sense.
The reproductive organs are constructed on the hermaph-
rodite plan, i.e., both male and female organs occur in the
same individual. The male part of the apparatus consists of
testes, sperm-ducts or vasa deferentia, and cirrus. The testes
(te) are two greatly ramified tubes which occupy the middle
part of the body, one situated behind the other. From each
testis there runs forward a duct, the vas deferens, the two
v PHYLUM PLATYHELMINTHES 133
vasa deferentia (v. d) opening anteriorly into an elongated
sac, the vesicula seminalis (v. s), from which a narrow tube —
the ejaculatory duct (ej) — leads to the male aperture at the
extremity of the cirrus. The female part of the apparatus
consists of a single ovary, an oviduct, a uterus, vitelline or
yolk-glands, vitelline ducts and shell-glands. The ovary (ov)
is a branched tube situated on the right side in front of the
testes : the branches open into a common duct, the oviduct
(od) . The vitelline glands (vif) consist of very numerous
minute rounded follicles, which occupy a considerable zone
in the lateral regions of the body. The two main vitelline
ducts, right and left, run transversely inwards to open into a
small sac — the yolk reservoir. From this a single median
duct passes to join the oviduct. Around the junction is a
mass of unicellular shell-glands (sh.gl). The uterus (uf) is
a wide convoluted tube formed by the union of the median
vitelline duct and the oviduct. In front it opens close to
the base of the penis. A canal termed the canal of Laurer
leads from the junction of the oviduct and median vitel-
line duct to open externally on the dorsal surface of the
body.
Each ovum on impregnation becomes surrounded by a
mass of vitelline matter or yolk, derived from the yolk-
glands. It then becomes enclosed in a chitinous shell,
the substance of which is derived from the secretion of the
shell-glands. The completed egg remains for a time in the
uterus ; afterwards it is discharged, and, passing down
the bile-ducts of the sheep into the intestine, reaches the
exterior with the faeces. When it escapes from the egg,' the
ciliated embryo, as it is termed (Fig. 70, A), has the form of
a somewhat conical body, covered all over with vibratile
cilia, and with two spots of pigment, the eye-spots, near the
broader or anterior end, which is provided with a triangular
134 MANUAL OF ZOOLOGY SECT.
head-lobe (pap) . There is no vestige of internal organs, with
the exception of a pair of flame-cells. The ciliated larva swims
about in water, or moves over damp herbage for a time, and
perishes unless it happens to reach a pond-snail (Limncea),
as a parasite of which it is alone able to enter into the next
phase of its life-history. When it meets with the snail,
destined to form the second or intermediate host of the
parasite, the embryo bores into it by means of the head-
lobe. Established in the interior, it grows rapidly into the
form of an elongated sac, the sporocyst (Fig. 70, B), with an
internal cavity. Eventually cells are budded off from the
interior of the sporocyst, each of which gives rise to a body
called a redia (C). When fully formed the redia is a
cylindrical body, having a mouth leading to a pharynx, fol-
lowed by a simple sac-like intestine, and a system of excre-
tory vessels. The rediae, after escaping from the interior of
the sporocyst, bud off internally cells which either give rise
to a fresh generation of rediae or to bodies termed cercaricz.
The latter (D) are provided with long tails, with anterior
and posterior suckers, a mouth and pharynx, and a bifid
intestine. These escape through an aperture in the wall of
the redia, and, moving actively by means of their tails, force
their way out from the body of the snail. They then, losing
the tail, become encysted, attached to blades of grass or
herbage. The transference of the larval fluke to its final
host, the sheep, is effected if the latter swallow the grass on
which the cercaria has become encysted. The young fluke
then escapes from the cyst, and forces its way up the bile-
ducts to the liver, in which it rapidly grows, and, developing
reproductive organs, attains the adult condition.
The liver-fluke is an example of the class of flat-worms
known as Trematoda. These are all parasitic. Some are
internal parasites, and in the adult condition inhabit, for the
PHYLUM PLATYHELMINTHES
J35
most part, the enteric canal, the liver, or the lungs of some
animal of the Vertebrate or back-boned class (fishes, amphib-
ians, reptiles, birds, or mammals), swallowing the digested
eye
FIG. 70. — A-D, development of Distomum hepaticum.
A, ciliated larva; B, sporocyst, containing rediae in
various stages of development; C, redia, containing a
daughter redia, and cercariae; D, fully developed cer-
caria. b.op^ birth opening; etit, enterqn of redia; eye,
eye-spots; gist, gastrula stage of redia; germ, early
stages in the formation of cercariae; int, intestine of
cercaria; mor, morula stage in the development of
cercariae; ces, oesophagus; or.su, oral sucker; pap,
head-lobe of ciliated embryo; ph, pharynx; proc, pro-
cesses of redia; vent su, ventral (posterior) sucker.
(After Thomas.)
food or various secretions of their host. Others are external
parasites, living on some part of the outer surface of their
host, and feeding on mucus or other secretions of the- in-
136
MANUAL OF ZOOLOGY
SECT.
tegument. The leaf-like form exemplified in the liver-fluke
prevails in most (Fig. 71), but a more elongated form some-
times occurs. The anterior end is distinguished from the
posterior by its shape, by the arrangement of the suckers,
and, in many of those Trematodes that are external para-
sites, by the presence of eyes. Suckers are universal in
their occurrence. They are always ventrally placed, their
chief function being to fix the parasite to the surface of its
FIG. 71. — Trematodes. A, Amfhistomum; B, Homalogaster. gp, genital
aperture; tn, mouth; s, posterior sucker; te, testes; vit, vitelline glands.
(After M. Braun.)
host in such a way as to facilitate the taking in by the
mouth of animal juices and epithelial debris. Their number
and arrangement vary considerably. There are nearly
always present an anterior set (or, as in the liver-fluke,
a single anterior sucker surrounding the mouth), and
a posterior set or a single large posterior sucker. There
PHYLUM PLAT YH ELM INTHES
137
In
are no cilia on the surface, and a well-developed enteric
canal is always present.
A remarkable series of
metamorphoses, such as
that which has been de-
scribed in the liver-fluke,
is characteristic of the
internally parasitic forms ;
in the ectoparasitic or
externally parasitic Tre-
matodes development is
direct, the young animal
when it escapes from the
egg differing little from
the adult except in size.
2. THE TTJRBELLARIA
The Turbellaria are a
class of flat-worms which,
though for the most part
non-parasitic, resemble the
Trematodes ver^^J^sely,
the chief differerBBbeing
the presence of a coating
of vibrating cilia, and the
absence, in the majority,
of suckers. The leaf form
is the prevailing one (Fig.
72), but in many the body
is elongated and ribbon-
like, or subcylindrical. In
some the anterior end is
FIG. 72. — General plan of the structure of a
Triclad Turbellarian. en, brain; e, eye;
g, ovary; t\, median limb of the intestine;
/2, left limb; z'3, right limb; In, longitudinal
nerve-cord; m, mouth; od, oviduct; ph,
pharynx; t, testes; te, tentacles; vd, vas
deferens; n, uterus; $ , ejaculatory duct;
5 , vagina; tf $ , common genital aperture.
(After Von Graff.)
retractile, and may be everted as
138
MANUAL OF ZOOLOGY
SECT.
a proboscis. The mouth is never at the extreme anterior
end, but is always ventrally placed, sometimes behind the
middle. A few multiply by budding, and these may give
rise to chains of individuals, which subsequently become
separated. In the lowest Tur-
bellaria the intestine is repre-
sented merely by a nucleated
mass of protoplasm ; in others it
is a simple sac ; in the major-
ity it is branched. The general
structure of the other internal
organs very closely resembles
that of the corresponding parts
in the Trematodes.
FlG. 73. — Planar£apolychroa(a), Turbcllaria OCCUr in the SCa,
Ivgubris (&}, torva (c), about , . j i • j
thrice the natural size. (After in fresh water, and also in damp
Schmidt, from Claus.) , , . . , , „.,.
localities on land. The great
majority are non-parasitic, their food consisting of minute
aquatic animals and plants of various kinds. An example
is Planaria torva of our fresh-water pools and streams
(Fig. 73,6-).
3. THE CESTO
The class Cestoda or tape-worms ^Kill internal parasites,
and in the adult condition live in the enteric canal of verte-
brates. The tape-worms are much more completely adapted
to a life of parasitism than the Trematodes : they have no
digestive system, and are nourished by the imbibition,
through the general surface, of liquid nutriment derived
from the digested food of the vertebrate host. The shape
of a typical tape-worm is widely different from that of a
trematode. A tape-worm (Fig. 74) is flattened like a
trematode, but is extremely elongated, the length being
PHYLUM PLATYHELMINTHES
139
FIG. 74. — Taenia solium. Human tape worm. Entire
specimen reduced, cap, head. (After Leuckart.)
140
MANUAL OF ZOOLOGY
SECT.
many times, often hundreds of times, the greatest breadth,
so that the animal assumes the form of a long, narrow ribbon
or tape. This ribbon is not continuous, but is made up of
a string of segments or proglottides. Towards one end the
body becomes narrower, terminating in a rounded knob —
the head or scolex. On the head (Fig. 75) is a circlet
of hooks borne on a rounded prominence, the rostellum,
which is capable of being protruded and retracted to a
certain extent ; at the sides are four suckers. By means of
these hooks and suckers the head is
attached to the wall of the intestine
of the host, the elongated body lying
free in its interior. The part of the
body just behind the head (neck) is
not divided into segments. The most
anterior segments are much shorter than
those further back, and not so distinctly
separated off from one another. The
surface is devoid of cilia, as in the
Trematodes. A digestive cavity is, as
already stated, absent; but there is a
distinct nervous system, and a system
FIG. 75.— Head of Taenia of water-vessels with flame-cells. In the
SOlium, magnified. . . . . . .
(After Leuckart.) posterior region of the body each pro-
glottis (Fig. 76) is found to contain a
complete set of hermaphrodite reproductive organs similar
in general plan to those of the liver-fluke. The ova, when
fertilised, are enclosed in a chitinoid shell, and received
into a uterus. In the most posterior segments the uterus
is a large branched tube distended with enormous quantities
of these eggs, and the other parts of the reproductive appa-
ratus have become absorbed. These "ripe" proglottides,
as they are termed, drop off, one by one, from the pos-
PHVLUM PLATYHELMINTHES
141
terior end, and reach the exterior with the faeces of the
host. At the same time new proglottides are constantly
being formed by the appearance of new ring-like grooves
behind the neck region. This dropping off of ripe proglot-
tides from the posterior end, and the formation of new ones
behind the neck, results in a gradual shifting backwards of
the proglottides. As each proglottis passes backwards from
its point of origin, it gradually develops the various parts
of the reproductive apparatus in its interior, until, when
can,.eoccret
cart.excret
— ne.rv.1
gl.vit
FIG. 76. — A proglottis of Taenia solium with mature reproductive apparatus.
can- excret, longitudinal excretory canals with transverse connecting vessels;
gl. vz't, vitelline glands; nerv. /, longitudinal nerves; ov,ov, ovaries; por. gen,
genital pore; schld, shell-glands; uter, uterus; vag, vagina; vas. def, vas
deferens. The numerous small round bodies are the lobes of the testes.
Leuckart.)
(After
it has reached the posterior region, it possesses a com-
plete set of reproductive organs, and, as it reaches the
extreme posterior end, it has become ripe, i.e., has its uterus
distended with eggs.
In the interior of each of the eggs in the ripe proglottides
is an embryo consisting of a rounded mass of cells bearing
six chitinoid hooks — the six-hooked or hexacanth embryo
(Fig. 77, A). After the egg has been discharged from the
free proglottis, it has to reach the enteric canal of a second
142
MANUAL OF ZOOLOGY
SECT.
kind of animal — a second or intermediate host — in order
that the embryo may be enabled to enter the next phase of
its life-history. In the case of some tape-worms, this second
or intermediate host is, like the first or permanent host, a
vertebrate animal : in the case of others it is some inver-
FIG. 77. — Development of Tape-worm. A, hexacanth embryo; B, Proscolex of
Tania saginata; C-E, stages in the formation of the scolex of the same; C,
thf invagination before the hooks and suckers have become developed; D, after
thv, appearance of the hooks and suckers; E, partly evaginated; F, fully
evaginated scolex of T. solium with caudal vesicle; G, scolex of T. serrata
with the remains of the vesicle; H, young tape- worm of T. serrata. (After
Leuckart.)
tebrate animal such as an earth-worm, a centipede, or an
insect. This transference of the hexacanth embryo to the
second host is a passive migration, not an active one, as in
v PHYLUM PLATYHELMINTHES 143
the case of the ciliated embryo of the Trematodes, the egg
being received into the enteric canal of the second host with
the water or food. The digestive fluids of this second host
dissolve the egg-shell and set free the contained embryo,
which bores its way by means of its hooks to some part of
the body in which it is destined to pass through the next
phase of its life-history, and there becomes encysted (B).
The phase which follows presents two main varieties. In
cases in which the second host is an invertebrate animal, the
hooked embryo develops into a form to which the name of
Cysticercoid is given ; when, on the other hand, the inter-
mediate host is a vertebrate, the form assumed is nearly
always that termed Cysticercus or bladder-worm. In both
cases a tape- worm head is developed, with the rostellum,
hooks, and suckers of the adult. In the Cysticercus (C-H)
this is formed from the wall of a relatively large cyst or
bladder into which the hooked embryo develops.
In a very small number both of Cysticercoids and of
Cysticerci more than one tape-worm head is formed. Thus
Tcznia ccenurus of the dog has a bladder-worm stage
occurring in the sheep and rabbit, which gives rise to several
tape-worm heads. But the most striking instance of mul-
tiple production of tape-worm heads in a bladder-worm is
Tcenia echinococcus, well known as the cause of the disease
termed hydatids, common in man and in various domestic
animals. In this case the hooked embryo develops into a
large mother-cyst, from the interior of which daughter-cysts
are budded off. Eventually from the walls of these daughter-
cysts (Fig. 78) are formed numerous tape-worm heads.
The transference to the first or final host is effected by the
second or intermediate host, or the part of it containing the
Cyticercus or Cysticercoid, being taken into the enteric canal
of the final host. Sometimes, if the intermediate host is
144 MANUAL OF ZOOLOGY SECT.
a small animal, such as a water-flea, this may take place
"accidentally"; in other cases the intermediate host
actually forms the food of the final host. Thus, to give two
instances, a Cysticercoid having as an intermediate host an
earth-worm is taken with the latter into the enteric canal of
a sea-gull — its final host ; a Cysticercus which occurs in the
liver of rats and mice is received into the enteric canal of
the cat. In this way the Cysticercus or Cysticercoid is set
free in the enteric canal of the final host; the tape-worm
head becomes attached by means of its hooks and suckers
to the wall of the intestine, and the long segmented body
of the tape-worm is developed behind.
FIG. 78.— Cyst of Taenia echinococcus with the developing daughter-cyst and
scolices. (After Leuckart.)
The commonest human Cestode parasites in the United
States and Canada are Tcenia solium and T. saginata ( T.
mediocanellata) , the latter being the more common pest.
The Cysticercus stage of the former occurs chiefly in the
flesh of the pig ; that of the latter in the flesh of the ox ;
and the relative prevalence of these two tape- worms in
different countries varies with the habits of the people with
regard to flesh-eating : where more swine's flesh is eaten
in an imperfectly cooked state Tcenia solium is the more
prevalent, where more beef, T. saginata.
v PHYLUM PLATYHELMINTHES 145
Bothriocephalus latus, a very large tape-worm without
hooks, is a common human parasite in eastern countries.
Its Cysticercus occurs in the pike and certain other fresh-
water fishes. It has not become endemic, or naturalized,
in the United States.
4. THE NEMERTINEA
The Nemerteans are non-parasitic, unsegmented worms,
most of which are marine, only a few forms living on land
or in fresh water. They are commonly looked upon as
nearly related to the Turbellaria, and were formerly in-
cluded in that class ; but they are in some respects higher
in organisation than the Turbellaria, and they exhibit cer-
tain special features distinguishing them from the rest of the
lower worms.
The body (Figs. 79 and 80) is narrow and elongated,
cylindrical or depressed, unsegmented, and devoid of ap-
pendages. In length it varies, in different species, from a
few millimetres to as much as ten metres. The entire sur-
face is covered with vibratile cilia.
The mouth (m) is at or near the anterior extremity on
the ventral aspect. Close to it above there is an opening
through which can be protruded a very long muscular organ,
the proboscis (fir), the possession of which is one of the
most characteristic features of this class of worms. The
proboscis is hollow : when it is extended to its utmost, a
part still remains which is not capable of being everted, and
at the junction between the eversible and non-eversible
parts, i.e., at the extremity of the organ when it is fully
protruded, there is in many of the Nemerteans a pointed or
serrated stylet (Fig. 80, st), which probably permits of the
proboscis being used as a weapon : when a stylet is absent,
L
i46
MANUAL OF ZOOLOGY
SECT.
the surface of the extremity is sometimes abundantly
provided with stinging-capsules ; sometimes it is beset with
glandular adhesive papilla. The proboscis is capable of
long.nc
dir
FIG. 79. — Diagram of the organs of a Nemertine, from below, a, anus; br, brain;
div, coeca; long, nc, longitudinal nerve-cords; tn, mouth; «, nephridia; ov,
ovaries; pr, probosis. (After Hubrecht.)
being retracted within the interior of an investing sheath,
the proboscis sheath.
PHYLUM PLATYHELMINTHES
ftrop. afa
ciigr
Irrob
retr.mue
FIG. Bo. — Tetrastemma. General view of the internal organs, an, anus: <«:. st,
accessory stylet ; cer. g, brain : cil.gr, ciliated groove ; dors, ves, dorsal vessel ;
lat. ne, lateral nerve; lat. ves, lateral vessel; neph, nephridium ; op. neph,
nephridial aperture ; profr, eversible part of proboscis : prob*, non-eversible part
of proboscis; prob. ap, aperture for the protrusion of the proboscis; retr. mus,
retractor muscle of the proboscis ; st, stylet. (From Hatschek's Lthrbuch,}
148 MANUAL OF ZOOLOGY SECT, v
The alimentary canal (Fig. 79) is a simple tube distin-
guishable into oesophagus with longitudinally folded walls,
and intestine with lateral coeca (div). It ends in an anal
opening (a) situated near the posterior extremity of the
body.
The Nemerteans possess a system of blood-vessels with
well-defined walls formed of an epithelium and a layer of
muscle. There are three principal longitudinal trunks — a
median dorsal and two lateral. The blood follows no
regular course through the vessels, but is moved about by
the muscular contractions of the body.
The excretory vessels of the Platyhelminthes are repre-
sented in the Nemertine worms by a pair of greatly coiled
and branched tubes (Fig. 80, nep/i), opening on the exterior ;
the fine terminal branches of the system are provided with
ciliary flames, and cilia occur also in the course of the
vessels themselves.
The nervous system is in some respects more highly
developed than in the Turbellaria. The brain (Fig. 80,
cer.g) is composed of two large ganglia with lobed surfaces,
connected together by two commissures, dorsal and ventral,
between which pass the proboscis and its sheath. From the
brain pass backwards a pair of thick nerves which run
throughout the length of the body.
Eyes are present in the majority of Nemerteans, and in
the most highly organised species occur in considerable
numbers.
Most species are dioecious. The ovaries (Fig. 79, ov) and
testes are situated in the intervals between the intestinal
cceca. The ovary or testis is a sac, the cells lining which
give rise to ova or spermatozoa ; when these are mature each
sac opens by means of a narrow duct leading to the dorsal
surface, where it opens by a pore.
SECTION VI. — PHYLUM NEMATHEL-
MINTHES
THE Nemathelminthes or round- worms are so named
because the body instead of being compressed from above
downwards, as in the flat-worms, is rounded, i.e., cylindrical.
The majority of the members of the phylum belong to the
class of the Nematoda or round-worms in a more restricted
sense. A good example of these is the common round-
worm of man (Ascaris lumbricoides), which is a common
parasite in the human intestine ; or the nearly allied Ascaris
suilla of the pig. When fresh the animal is of a light
yellowish-brown colour ; it is marked with four longitudinal
streaks, two of which, very narrow and pure white in the
living worm, are respectively dorsal and ventral in position,
and are called the dorsal (Fig. 81, d. /) and ventral (v. /)
lines : the other two are lateral in position, thicker than the
former and brown in colour, and are distinguished as the
lateral lines. The mouth is anterior and terminal in position,
and is bounded by three lobes, or lips, one median dorsal
(d. lp), the other two ventro-lateral (v. lp). A very minute
aperture on the ventral side, about two millimetres from
the anterior end, is the excretory pore (ex. p). At about the
same distance from the pointed and down-turned posterior
end is a transverse aperture with thickened lips, the anus
(an), which in the male serves also as a reproductive
aperture, and gives exit to a pair of needle-like chitinoid
149
MANUAL OF ZOOLOGY
SECT.
bodies, the penial seta (pn.s}. In the female the repro-
ductive aperture or gonopore is separated from the anus, and
1 31
is situated on the ventral surface about one-third of the
length of the body from the anterior end (Fig. 82, gnp).
The outer surface of the body is furnished by a delicate,
transparent, elastic membrane, of a chitinoid nature, the
VI
PHYLUM NEMATHELMINTHES
cuticle. It is wrinkled trans-
versely so as to give the animal
a segmented appearance. Be-
neath the cuticle is a proto-
plasmic layer containing scat-
tered nuclei and longitudinal
fibres, and representing a syn-
cytial ectoderm, i.e., an ecto-
derm in which the cell-bodies
are not differentiated, and its
cellular nature is recognisable
only by the nuclei.
Beneath the ectoderm is a
single layer of muscular fibres
of peculiar structure, arranged
longitudinally, and bounding
the body-cavity.
The muscular layer is not
continuous, but is divided into
four longitudinal bands or
quadrants, two dorso-lateral
and two ventro-lateral, owing
to the fact that at the dorsal,
ventral, and lateral lines the
ectoderm undergoes a great
thickening and projects in-
wards, between the muscles,
in the form of four longitudi-
nal ridges. It is this arrange-
ment that gives rise to the
lines seen externally.
The mouth leads into the
anterior division of the enteric
152
MANUAL OF ZOOLOGY
SECT.
•din
canal, the pharynx or stomodaeum (Fig. 82, ph], with very
muscular walls. Posteriorly the
pharynx opens into the intestine
(inf)> a thin walled tube, flattened
from above downwards. Posteriorly
the intestine narrows considerably
to form the short rectum, which
opens externally by the anus (an).
The food, consisting of the semi-
fluid contents of the intestine of the
host, is sucked in by movements of
the pharynx, and is then absorbed
into the system through the walls
of the intestine. The food being
already digested by the host, there
is no need of digestive gland-cells
such as occur in animals which pre-
pare their own food for absorption.
Between the enteric canal and
the body-wall is a distinct space, the
coelome or body-cavity, containing a
clear fluid.
The excretory system presents a
certain resemblance to that of Pla-
todes. It consists of two longitu--
dinal canals (ex. v), one in each
lateral line. Anteriorly they pass
to the ventral surface, unite with
v
FIG. 83. — Diagram of nervous one another, and open by the
system of Nematoda. c, com- . , .
missures; din, dorsal nerve; minute CXCrCtOry pore (ex. p) al-
hsn, posterior lateral nerve; , . .
on, upper and ««, under ready nOtlCCQ.
portion of nerve-ring; sg. rr-.i • r
lateral swellings ; vin, ventral The nervOUS System COnSlStS of a
nerve. (From Lang, after / x •,• ,•> i
Butschii.) nng (nv. r) surrounding the pharynx
• Jwm
VI
PHYLUM NEMATHELMINTHES
'S3
and giving off six nerves forwards and six backwards (Fig.
83). Of the latter, two are
of a considerable size and
run in the dorsal and ven-
tral lines respectively (din,
vlri).
The reproductive organs a
are formed on a peculiar
and very characteristic pat-
tern. The testis (Fig. 84, ^
ts) is a long coiled thread,
occupying a considerable
portion of the body-cavity.
At its posterior end it is
'continuous with the vas
deferens. The vas deferens,
in its turn, becomes con-
tinuous with a wide canal,
the vesicula seminalis (vs.
sem\ which opens by a
short, narrow, muscular
tube, the ductus ejaculato-
rius, into the rectum. Be-
hind the rectum, and open-
ing into its dorsal wall, are
paired muscular sacs (/)
containing the penial seta
(/. ns) already noticed.
The anterior end of the
testis consists of a solid
mass of sexual cells ; pass-
ing backwards there is
found a cord or rachis occupying the axis of the tube and
154 MANUAL OF ZOOLOGY SECT, vi
having the sperm-cells attached to it ; still further back the
sperms become gradually differentiated, and are finally set
free in the vas deferens.
The organs of the female (Fig. 82) resemble those of
the male, but are double instead of single. There are two
coiled, thread-like ovaries (pvy}> each passing insensibly
into a uterus (ut). In the ovary, as in the testis, the eggs
are developed in connection with an axial cord or rachis.
The two uteri unite in a short muscular vagina (yag) which
opens, as already seen, on the ventral surface of the body
{gn£) at about one-third of the entire length from the head.
The Nematodes in general vary greatly in size, from about
i mm. or less to two metres (six feet) in the case of the
Guinea-worm, the length always being great in proportion to
the diameter, and the body being always bluntly pointed at
the anterior end, and either pointed or forked posteriorly.
The mouth is frequently armed with spines by means of
which the worms draw blood from the intestinal blood-
vessels of their host. Many free-living forms have a sharp
stylet for piercing the tissues of the plants on which they
feed, and a suctorial apparatus for absorbing their juices.
The nervous system has in most the same general struc-
ture as in Ascaris, and the same holds good of the repro-
ductive apparatus. A few are hermaphrodite, but, instead
of a double set of reproductive organs as in Platyhelminthes,
they have organs similar to those of the female Ascaris, the
gonads producing first sperms and afterwards ova.
One of the most terrible parasites of man is a nematode
called Trichina spiralis (Fig. 85), a minute worm, the male
(C) a little over i mm. (^ inch) in length, the female (B)
about 3 mm. (-J- inch). In the adult or sexual condition it
lives in the intestine of man, the pig, and other mammals.
Internal impregnation takes place, the eggs develop in the
B
FIG. 85. — Trichina spiralis. A, encysted form in muscle of host; B, female; C,
male, bh, connective tissue envelope; cy, cyst; tie, ejaculatory duct; e, em--
bryos; y, fat globules; h, testis; nt. f, muscle fibre; oe, pharynx; ov, ovary;
wo, gonopore; zh, cell masses in intestine. (From Langs Comparative
Anatomy, after Clans.)
155
156 MANUAL OF ZOOLOGY SECT, vi
uterus of the female, and the minute young (B, e), to the
number of at least about a thousand, are born alive. Soon
after birth the young worms migrate through the walls of
the intestine and reach the voluntary muscles of the host,
such as those of the limbs, back, tongue, etc. Each worm
enters a muscle- fibre and coils itself up in the muscle-
substances (A) ; a spindle-shaped cyst (cy). is formed round
it, and the muscle undergoes more or less degeneration.
This process gives rise to various morbid symptoms in the
host, but, after some months the cysts become calcified and
the danger to the infected individual is over. In order that
further development of the encysted and sexless Trichinae
should take place, it is necessary for the infected flesh of
the host to be eaten by another animal in which the worm
is capable of living, e.g., that of man by pig or rat, or that
of a pig by man. When this is done the cysts are dissolved
by the digestive juices, the worms escape, develop repro-
ductive organs, and copulate, the young migrating into the
muscles and producing the disease as before.
It will be noticed that in this case the parasite is able to
exist in various hosts, and that both sexual and asexual stages
are passed through in the same host, dispersal of the species
taking place by the flesh of an infected animal being eaten
by another, either of the same or of a different species.
The female Guinea- worm (Dracunculus medinensts) attains
a length of 30-200 cm. (1-6 feet), and lives in the sub-
cutaneous connective tissue of man. The eggs develop in
the uterus, and the newborn young pass out of the body of
the host through abscesses caused by the presence of the
parasite. If, as must often be the case, they escape into
water, they make their way into the body of a water-flea
(Cyclops}, and in this condition probably reach their human
host once more in his unfiltered drinking water.
SECTION VII.— PHYLUM ECHINODER-
MATA
THE starfishes, brittle-stars, sea-urchins, feather-stars, and
their allies, many of which are familiar objects on the sea-
shore, are grouped together as the phylum Echinodermata.
Even a superficial comparison of a starfish, a brittle-star, and
a sea-urchin will reveal unmistakable points of agreement.
All have a hard surface more or less abundantly provided
with pointed spines : in all the symmetry is distinctly
radial ; and, if the animals are examined in the living
condition while immersed in sea-water, it will be found that
all are provided with rows of soft retractile tubular append-
ages acting in the starfish and sea-urchin as the organs of
locomotion by means of which the animal creeps slowly
along. Examination of the external structure shows, as will
presently become evident, that the resemblance is not a
merely superficial one, but extends to all the systems of
internal organs.
1. THE ASTEROIDEA
The body of a starfish, such as the common English red
starfish, Asterias rubens, or A. vulgaris, of our American
coast, is enclosed in a tough, hard integument, containing
numerous plates or ossicles, as they are termed, of calcareous
material. This exoskeleton is not completely rigid in the
158 MANUAL OF ZOOLOGY SECT.
fresh condition, but presents a certain limited degree of
flexibility. The body (Fig. 86) is star-shaped, consisting of
a central part, the central disc, and five symmetrically
arranged processes, the arms or rayst which, broad at the
base, taper slightly towards their outer extremities. There
are two surfaces, one the dorsal or abactinal, directed up-
FlG 86. — Starfish. General view of the ventral surface, showing the tube-feet.
(From Leuckart and Nitsche's Diagrams.)
wards in the natural position of the living animal ; the other,
the ventral or actinal, directed downwards. The dorsal sur-
face is convex, the ventral flat ; the colour of the former is
much darker than that of the latter.
In the centre of the ventral surface (see Fig. 92) is a five-
rayed aperture, the actinostome, and running out from this in
a radiating manner are five narrow grooves, each running
along the middle of the ventral surface of one of the arms
vii PHYLUM ECHINODERMATA 159
to its extremity. Bordering each of the ambulacral grooves
there are either two or three rows of movable calcareous
spines, the ambulacral spines. External to the ambulacral
spines are additional rows of stout spines, which are not
movable. -
On the convex dorsal surface there are a number of short,
stout spines arranged in irregular rows parallel with the long
axes of the rays. These are supported on irregularly shaped
ossicles buried in the integument. In the soft interspaces
between the ossicles are a number of minute pores, the
dermal pores, scarcely visible without the aid of a lens.
Through each of these pores projects a very soft filiform
process, one of the dermal branchicz or papules. (Fig. 88,
Resp. ca}, which is capable of being entirely retracted.
Very nearly, though not quite, in the centre of the dorsal
surface is an aperture, the anus (an), wide enough to admit
of the passage of a moderately stout pin. On the same sur-
face, midway between the bases of the two rays, is a flat,
nearly circular plate, the surface of which is marked by
a number of radiating, narrow, straight, or slightly wavy
grooves : this is the madreporite.
Attached to the spines of the ventral surface, in the inter-
vals between them, and in the intervals between the spines
on the dorsal surface, are a number of very small, almost
microscopic, bodies, which are termed the pedicellaria (Fig.
88, Fed}. Each of these is supported on a longer or shorter
flexible stalk, and consists of three calcareous pieces, a
basilar piece at the extremity of the stalk, and two jaws,
which are movably articulated with the basilar piece, and
are capable of being moved by a certain set of muscular
fibres, so as to open and close on one another like the jaws
of a bird.
In a well-preserved specimen there will be seen in each
160 MANUAL OF ZOOLOGY SECT.
of the ambulacral grooves two double rows of soft tubular
bodies ending in sucker-like extremities ; these are the tube-
feet (Figs. 86, 88, T. F}, of which, in Asterias, there are
four rows in each arm. In a living specimen they will
be seen to act as the locomotive organs of the animal. They
are capable of being greatly extended, and when the star-
fish is moving along, it will be observed to do so by the
tube-feet being extended outwards and forwards (i.e., in the
direction in which the animal is moving), their extremities
becoming fixed by the suckers, and then the whole tube-
foot contracting so as to draw the body forward ; the hold
of the sucker then becomes relaxed, the tube-foot is stretched
forwards again, and so on. The action of all the tube-feet,
extending and contracting in this way, results in the steady
progress of the starfish over the surface. With the aid of
the tube-feet the starfish is also able to right itself if it is
turned over on its back.
At the extremity of each of the ambulacral grooves is to
be distinguished a small bright red spot, the eye (Fig. 88, A,
oc)t and over it a median process, the tentacle (/), similar
to the tube-feet but smaller and without the terminal sucker.
The tentacles have been ascertained by experiment to be
olfactory organs, the starfish being guided to its food much
more by this means than by the sense of sight. If one of
the arms be cut across transversely (Fig. 87 and Fig. 88, B)
and the cut surface examined, the dorsal part of the thick,
hard wall of the arm will present the appearance of an arch
(with its convexity upwards), and the ventral part the form
of an inverted V, the ends of the limbs of which are con-
nected with the ventral ends of the dorsal arch by a very
short, flat, horizontal portion. Enclosed by these parts is a
space, a part of the ccelome or body-cavity, and below, be-
tween the two arms of the V, is the ambulacral groove.
VII
PHYLUM ECHINODERMATA
161
The dorsal arch is supported by a number of irregular
ossicles. The V-shaped ventral part of the body- wall —
i.e., the walls of the ambulacral groove — is supported
by two rows of elongated ossicles, the ambulacral ossicles
(Fig. 88, Amb. os), which meet together at the apex or
summit of the groove like the rafters supporting the roof
of a house, but with a movable articulation allowing of
FIG. 87. — Starfish. Vertical section through an arm. amp, ampullae ; ep. epider-
mis : rad. amb, radial vessel of the ambulacral system; s points to the septum
dividing the blood-vessel into two parts; rad. tie, radial nerve of the epidermal
system; sp, spaces in mesoderm of body-wall; t.f, tube-feet. (From Leuckart,
after Hamann.)
separation or approximation of the two rows so as to open
or close the groove. Between the ambulacral ossicles of
each row are a series of oval openings, the ambulacral pores ',
one between each contiguous pair of ossicles. In the ventral
groove lie the tube-feet (/./). Each tube-foot is found to
correspond to one of the ambulacral pores. When the tube-
foot is drawn upon, it is seen to be continuous with one of
M
1 62 MANUAL OF ZOOLOGY SECT.
a series of little bladder-like bodies, the ampulla, which lie
on the other side of the ambulacral ossicles, i.e., in the
cavity of the arms. When one of them is squeezed the cor-
responding tube-foot is distended and protruded, the cavities
of the tube-foot and the ampulla being in communication
by means of a narrow canal running through the ambulacral
pore ; and it is in this way that the foot is protruded in the
living animal. The corresponding ampulla being contracted
by the contraction of the muscular fibres in its walls, the
contained fluid is injected into the tube-foot and causes its
protrusion. «
Running along the ambulacral groove, immediately below
where the ambulacral ossicles of opposite sides articulate, is
a fine tube, the radial ambulacral vessel (Fig. 87, rad. amb ;
Fig. 88, B, Rad. Amb. V; Fig. 90, r), which appears in
the transverse section as a small rounded aperture. From
this short side branches (Fig. 90 r) pass out on either side
to open into the bases of the tube-feet. Below the radial
ambulacral vessel is a median thickening of the integument
covering the ambulacral groove ; this marks the position of
the radial nerve (Figs. 87 and 88, Rad. ne} of the epidermal
nervous system, and is traceable as a narrow thickened band
running throughout the length of the groove, and terminat-
ing in the eye at its extremity, while internally it becomes
continuous with one of the angles of a pentagonal thickening
of a similar character, the nerve-pentagon, which surrounds
the mouth.
The two radial nerve-bands of the deep nervous systems
are thickenings of the lining membrane of a space overlying
the radial nerve and underlying the radial ambulacral system.
A channel throughout the length of the arm above the
radial nerve forms part of a system of channels which are
usually regarded as constituting a blood-vascular system.
vii PHYLUM ECHINODERMATA 163
This radial blood-vessel, as it is termed, is divided lon-
gitudinally by a vertical septum into two lateral halves.
Internally it communicates with an oral ring-vessel surround-
ing the mouth and likewise divided into two by a septum.
When the dorsal wall of the central disc is dissected away,
the remainder of the organs come into view. The rows of
ambulacral ossicles appear on this view as ridges, the
ambulacral ridges, one running along the middle of the
ventral surface of each arm to its extremity, and extending
inwards to the corresponding angle of the mouth. At the
sides of each of these ridges appear the rows of ampullae.
Within the pentagonal actinostome is a space, the peristome,
covered with a soft integument, and in the centre of this is a
circular opening, the true mouth, the size of which is capable
of being greatly increased or diminished.
The mouth is found to open through a short passage, the
esophagus, into a wide sac, the cardiac division of the stomach
(Fig. 88, st; Fig. 89, card. si}. This is a five-lobed sac,
each of the lobes of which is opposite one of the five arms.
The walls of the sac are greatly folded, and the whole is
capable of being everted through the opening of the mouth,
folded over some object desired as food, and then retracted
into the interior, the retraction being effected by means of
special retractor muscles which arise from the sides of the
ambulacral ridges. This cardiac division of the stomach
communicates dorsally with a much smaller chamber, the
pyloric division of the stomach, and this in turn opens into a
very short conical intestine, which leads directly upwards to
open at the small anal aperture. The pyloric division of
the stomach is pentagonal, each angle being drawn out to
form a pair of large, tree-like appendages, the pyloric caca
(Figs. 88 and 89, pyl. ccec}, which extend to near the
extremity of the arm. The walls of the pyloric caeca are
i64
MANUAL OF ZOOLOGY
SECT.
glandular : they secrete a digestive fluid, and are therefore to
be looked upon as digestive glands. It is found by experi-
menting with this digestive fluid that it has an action on
FIG. 88. — Diagrammatic sections of a starfish. A vertical section passing on the
right through a radius, on the left through an inter-radius. The off-side of the
ambulacral groove with the tube-feet (T. F) and ampullae (Amp) are shown in
perspective. B, transverse section through an arm. The ectoderm is coarsely
dotted, the nervous system finely dotted, the endoderm radially striated, the
mosoderm evenly shaded, the ossicles of the skeleton black, and the coelomic
epithelium represented by a beaded line, amb.os, ambulacral ossicles; amp,
ampullae; an, anus; C. Amb. V, circular ambulacral vessel; C. B. K, septum
of ring blood-vessel; Cd. cee, cardiac caeca; Ccel, ccelome; Ccel. Epithm,
coelomic epithelium; Der. Epithm, deric epithelium; Derm, mesoderm; Ent.
Epthm, enteric epithelium; Int. cce, intestinal caeca; Mdpr, madreporite; Mes,
mesentery; Mth, mouth; Nv. R, nerve ring; oc, eye; os, ossicles of body-wall;
ovd, oviduct; Ped} pedicellariae; ph, perihaemal spaces; pyl. c, Polian vesicles; c,
circular canal; m, madreporite; m', madreporic canal; /, tube-feet; r, radial
vessels; r', branches to ampullae. (After Gegenbaur.)
Accompanying the madreporic canal there is an organ, —
the ovoid gland, — the relationships and function of which
have given rise to a considerable amount of difference of
opinion. It is a fusiform body, the interior of which is
divided up into a number of freely communicating spaces.
VII
PHYLUM ECHINODERMATA
167
The starfish is unisexual, each individual possessing
either ovaries (Fig. 88, ov) or festes, which appear very
similar until they are examined microscopically. They
consist of masses of rounded follicles, like bunches of
minute grapes, a pair in each inter-radial interval. The
ducts, by means of which the ova, or sperms, reach the
FIG. 91. — Anthenea. View of dorsal surface. (After Sladen.)
exterior, open on the dorsal surface (Fig. 88, A, Ovd}
through a number of perforations on a pair of sieve-like
plates, situated inter-radially close to the bases of the arms.
Other starfishes, while resembling Asterias in most re-
spects, differ from it in a number of less important points.
Thus though the number of arms is usually five, in some
species it is eight, in others more, and in some of those with
i68
MANUAL OF ZOOLOGY
SECT.
more than five arms the number is inconstant. The pro-
portions borne by the arms to the central disc also vary
greatly in different kinds, the arms being in many instances
relatively longer, in many relatively shorter than Asterias, and
in the latter case (Figs. 91 and 92) the central disc is cor-
respondingly increased in extent. In some extreme instances
of this modification the starfish assumes the form of a five-
FIG. 92. — Anthenea. View of ventral surface. From New Zealand. (After Sladen.)
angled disc, in which the arms are represented merely by the
angles. In all cases the arms are hollow, each containing
a prolongation of the body-cavity containing the caeca; and
in all the mouth is in the centre of the ventral surface, and
narrow ambulacral grooves run out from it in a radiating
manner to the extremities of the arms. In some starfishes
there are but two rows of tube-feet in each arm. An anus
VII
PHYLUM ECHINODERMATA
169
is sometimes absent; in Asterias vulgaris it is minute,
almost closed. The spines and pedicellariae differ in their
form and arrangement in different kinds of starfish, as also,
though in a less degree, the tube-feet. The starfishes con-
stitute one of the five classes of living Echinodermata, the
class Asteroidea.
2. THE OPHIUROIDEA
The Brittle-stars bear many resemblances to the true star-
fishes, but have a number of special features of sufficient
FIG. 93.— Ophioglypha lacertosa. A. outline, of the natural size; B, central disc,
dorsal view; C, the disc, ventral view showing the mouth and genital fissures.
(From Nicholson and Lydekker's Paleontology.)
importance to justify their being regarded as constituting a
separate class, which is termed the Ophiuroidea. Like
170 MANUAL OF ZOOLOGY SECT.
Asterias, the brittle-star (Fig. 93) has a star-shaped body
with a central disc and five radiating arms. But the arms,
instead of appearing merely as radiating prolongations of the
central disc, are sharply marked off from it, and have rather
the appearance of appendages. They are solid, long, slender,
and tapering, clothed with plate-like ossicles and beset
laterally with spines. They are highly flexible, and instead
of creeping along slowly like a starfish the brittle-star moves
with comparative activity by means of lateral movements
of the arms. As in the starfish there are distinct dorsal
and ventral surfaces, the former having the mouth in its
centre. An anus is absent, and the madreporite is on the
ventral surface instead of the dorsal. There are no ambula-
cral grooves, and the tube-feet project at the side of the
arm. The internal structure is similar in most respects to
that of the starfish, but the radial prolongations of the
body-cavity into the arms are absent, and there are no
pyloric caeca. In certain of the Ophiuroidea the arms are
branched.
3. THE ECHINOIDEA
The Sea-urchins (Class Echinoidea) differ much more
widely from the starfishes than the brittle-stars. The body
(Fig. 94) is not star- shaped, but globular. At one pole is
the mouth, at the other the anus. The body is enclosed in
a shell or corona (Fig. 95), formed of firmly united plate-
like ossicles arranged in rows which run from oral to aboral
poles. Supported on these are numbers of long, slender,
sharp-pointed, freely movable spines (Fig. 94). Running
over the surface from near the oral to near the aboral poles
are five bands of tube-feet which are capable of being
extended into long slender tubes (Fig. 94). These have
vii PHYLUM ECHINODERMATA 171
sucker-like extremities and, like the tube-feet of the starfish,
are the organs of locomotion. A remarkable and charac-
FIG. 94. — Strongylocentrotus. Entire animal, with the tube- feet extended beyond
the ends of the spines. (From Brehm's Thierleben.)
teristic feature of the internal structure is the presence of a
complicated apparatus for mastication known as Aristotle's
lantern, consisting of five jaw-like parts, each bearing a
I72
MANUAL OF ZOOLOGY
Ap
SECT.
FIG. 95. — Corona of sea-urchin with the spines removed to show the arrangement
of the plates, lateral view. Amb, ambulacra! zone with its perforated plates;
Ap, apical (aboral) pole; Int. amb, inter-ambulacral zones. (From Bronn's
Thierreich.)
sharp tooth. The points of these five teeth can be seen
through the opening of the mouth. The enteric canal has
no radiating coeca. The five
ducts of the reproductive or-
gans open on five ossicles, the
genital plates (Fig. 96, geri),
which with five smaller ocu-
lar plates (oc) each bearing
a rudimentary eye, form a
complete ring round the
space (peripr) at the anal
pole, in the middle of which
of a sea-urchin. amb, ambulacral • ,1
zones; gen, genital plates; int. amb, IS the attUS ; a
inter-ambulacral zones; madr, madre- • orv,<,lfTOrr,,,4.,i/4
porite; oc, ocular plates; peripr, peri- 1S amalgamated
proct. (After Leuckart.) the genital platCS.
rvf
Ot
vii PHYLUM ECHINODERMATA 173
In the Heart-urchins (Spatangus) the body is heart-shaped
instead of globular, and in the Cake-urchins (represented by
our Echinarachnius parma) it is flattened and disc-like. In
most respects, however, these irregular sea-urchins are very
closely allied to the ordinary or regular forms, and with the
latter they constitute the third class of Echinodermata, the
Echinoidea.
4. THE HOLOTHUROIDEA
Also widely different from the starfishes in the general
form of the body are the Holothurians (class Holothuroidea) .
Some of these are known as sea-slugs from their slug-like
appearance, others as sea-cucumbers. One is termed the
" cotton-spinner " from the cottony filaments which it dis-
charges when irritated or removed from the water. Certain
large tropical forms which abound on coral reefs in the Pacific,
are used as food and form the object of a fishing industry in
connection with which they are known as Beche-de-mer
or trepang {Holothuria edulis). Our Floridan trepang is
H. floridana ; a more northern form is Pentacta frondosa.
A Holothurian (Fig. 97) is roughly comparable to a sea-
urchin the body of which has been drawn out in the direc-
tion of the line joining mouth and anus, so that it has
assumed a long and slender form. But there is only
exceptionally a rigid shell of plates, the body-wall being
nearly always flexible and sometimes quite soft and sup-
ported by calcareous spicules, and usually one side, habitu-
ally directed downwards, is often modified as a ventral
surface. A circlet of tentacles surrounds the mouth. Five
regular zones of tube-feet sometimes run from mouth to
anus : sometimes those on the dorsal surface may be modi-
fied ; sometimes the tube-feet are scattered over the entire
174
MANUAL OF ZOOLOGY
surface, in some forms (such as the worm-like Synapta and
its allies) tube-feet are entirely absent.
FIG. 97. — Cucumaria planci. Entire animal seen from the ventral surface, with the
tentacles expanded, and the tube-feet projected outwards. (From Hertwig's
Lekrbuck, after Ludwig.)
5. THE CRINOIDEA
The Feather-stars and their allies constituting the class
Crinoidea, bear some superficial resemblances to the star-
fishes and brittle-stars, but with some important points of
difference. The body of a feather-star (Fig. 98) is star-
shaped, with a central disc and five arms which are bifurcate
VII
PHYLUM ECHINODERMATA
175
at their bases. On that surface of the central disc which is
directed upwards in the natural position of the animal, is in
the centre the mouth and on one side the anus. On the
opposite surface are attached whorls of slender curved cy-
lindrical appendages, the cirri, by means of which the
animal is able to anchor itself temporarily to a rock or a
seaweed. The arms are long, flexible and tapering, shaped
176 MANUAL OF ZOOLOGY SECT.
somewhat like a feather, with a main axis and a pair of
lateral rows of short slender branches, the pinnules. The
arms act as the locomotive organs of the animal, their wav-
ing movements propelling it slowly through the water. Tube-
feet are not developed as such ; but are represented by a
great number of very minute simple processes, the tentacles,
which border grooves running along the upper surfaces of
the arms and of the pinnules.
Some of the Crinoidea, the stalked Crinoids (Fig. 99),
chiefly occurring at great depths in the sea are supported on
a long slender stalk by which they are permanently fixed.
In the ordinary feather- stars the larva passes through a
stage in which it is attached by means of a stalk like the
stalked Crinoids : after a time the stalk becomes absorbed
and the young feather-star becomes free.
Our two species of Antedon live in deep water off the
New England coast.
A remarkable feature of the Echinodermata is the prevail-
ing radial arrangement vi their parts, a feature in which they
resemble the very much more simply organised Ccelenterata.
But underlying this there is to be detected a more obscure
arrangement of the body in right and left halves, just as in
the bilateral animals we have been more recently dealing
with. This deeper bilateral symmetry is almost completely
disguised by the radial arrangement of most of the parts.
In the larva the symmetry is strongly bilateral and it is only
by passing through a remarkable metamorphosis in which
parts of the larva are sometimes altogether discarded that
the radially constructed adult form is developed.
VII
PHYLUM ECHINODERMATA
177
FIG 99. — Metacrinus interruptus. (After P. H. Carpenter.)
N
SECTION VIII. — ROTIFERA, POLYZOA
AND BRACHIOPODA
1. THE ROTIFERA
A group of Metazoa of microscopic size, the Rotifera or Wheel
Animalcules, which are of exceedingly common occurrence in fresh
water, and are also found, though much less abundantly, in the sea, are
readily mistaken on a superficial examination for Infusoria on account
not only of their minuteness and the general resemblance in shape of
many of them to certain members of that class, but of the presence of
cilia as organs of locomotion. A more careful examination, however,
shows that these minute creatures are relatively highly organised multi-
cellular animals, and reveals certain general features of resemblance
between them and the Trochosphere, which is the characteristic larval
form in a phylum to be subsequently dealt with, the Annulata (Section
IX.).
The majority of the Rotifera are free-swimming. The cilia, by means
of which the swimming movements are effected, are confined to one
extremity of the body, the anterior or oral, and are borne on a very
characteristic organ termed the trochal disc (Fig. 100, tr. d). This is in
its simplest form a disc with a prominent rim, fringed with strong cilia,
and surrounds the oral end. The mode of movement of the cilia is
such as to cause the trochal disc to assume the appearance of a rapidly
rotating wheel, and it is to this circumstance that the name Rotifera or
Wheel-bearer is applied to the group. Sometimes, however, the form
of the trochal disc is less simple, the disc with its circlet of cilia becom-
ing divided into lobes, or drawn out into long processes. In some
forms ciliated prominences are present within the circlet of cilia, and
in others there is a second circlet internal to the first.
The body is usually distinguishable into the trunk and the tail (f).
The latter, which is situated at the extremity of the body most remote
178
SECT, vin ROTIFER A, POLYZOA, AND BRACHIOPODA 179
from the trochal disc, is frequently divided by a series of freely-movable
joints into a number of tubular segments like the parts of a telescope.
It is provided at its extremity in many forms with a pair of processes
which act like the blades of a pair of forceps in enabling the animal to
tn.
FIG. too. — Brachionus rubens. A, from the dorsal aspect ; B, from the right side.
a, anus ; br, brain ; d. f dorsal feeler ; c. gl, cement gland ; cl, cloaca ; c. I,
ciliary lobes ; c. v, contractile vesicle ; e, eye-spot ; int, intestine ; lrt lorica ;
I. f, lateral feeler : m, muscular bands ; nph, nephridial tubes ; ov, ovary ; ph,
pharynx ; st, stomach ; /, tail ; tr. d, trochal disc ; vt> vitellarium. (After
Hudson and Gosse.)
temporarily attach itself. In many forms in which the tail is well-
developed locomotion may be effected not only by swimming by the
movements of the cilia of the trochal disc, but by creeping or looping
i8o MANUAL OF ZOOLOGY SECT.
movements like those of a leech, the oral end and the extremity of the
tail being alternately attached. In Rotifers, which are permanently
fixed, attachment is effected through the intermediation of the tail,
which is drawn out to form a long narrow stalk. In others the tail is
absent, or represented only by a pair of ciliated processes.
The trunk is in some Rotifers enclosed in a glassy cuirass or lorica
formed of a thickening of the cuticle. One remarkable form — • Pedalion
— has six hollow appendages terminated by feathered setae : and a few
other forms are provided with simple or fringed setae.
The stalked forms inhabit tubes into which the animal can completely
retract itself, the substance of the tube being either a delicate gelatinous
material, or composed of pellets of mud, or of the animal's faeces.
The structure of the internal organs is simple. The alimentary
canal usually terminates in an anal aperture (a). There is a large
pharynx (//£) containing a masticatory apparatus, the mastax, usually
consisting of three chitinous pieces, or jaws, of complicated form. The
nervous system consists of a single ganglion (&r), situated towards the
oral end ; and there are usually one or several very simple eyes (£), stomach (stom), and intestine (ini),
suspended within a wide body-cavity. There is no vascular system, and
the central part of the nervous system consists of a single ganglion
(Fig. 102, £**«£•), placed between mouth and anus. The sexes are
united, and there is a free-swimming cilia larva.
Probably allied to the ordinary Polyzoa thus briefly characterised,
and usually assigned to that class, are three genera, Pedicellina (Fig.
103), Loxosoma and Urnatella, the first two colonial, the third solitary,
which, among other special features, have the anus situated within the
circlet of the tentacles. These are known as the Endoprocta, as
FIG. ioi. — Bugula avicularia. Two zpoids, magnified, an, anus; az'i'c, avicularia;
enib> embryo enclosed in the ooecium; funic, funiculus; gast, muscular bands
passing from the stomach to the body-wall; int, intestine; »io, mouth; oaec,
ooecium ; ces, oesophagus ; ov, ovary '.pit, pharynx ; ret, parieto- vaginal muscles ;
sf, spermatidia : stom, stomach.
182
SECT, vin ROTIFERA, POLYZOA, AND BRACHIOPODA 183
distinguished from the Ectoprocta or ordinary Polyzoa, in which
the anus, as we have seen, is external to the lophophore and tenta-
cles.
1 84
MANUAL OF ZOOLOGY
tent
SECT.
tent
FIG. 103. — Pedicellina. Showing successive stages (numbered / to 6) in the
development of zooids by budding, an, anus; gang, ganglion; mo, mouth;
tent, tentacles (retracted). (After Hatschek.)
3. THE BRACHIOPODA
The Brachiopoda, or Lamp-shells, are a group of marine animals
which present certain important features of resemblance to the Polyzoa,
and on that account are placed with them in a special phylum to which
the name Molluscoida is applied. The Brachiopoda are solitary,
never giving rise to colonies like those of the Polyzoa, and one of their
most striking characteristics is the possession of a calcareous shell which
bears a remarkable resemblance to that of the members of a widely
different group, the Pelecypoda of the phylum Mollusca, the group to
which the mussels, oysters, and clams belong. The shell (Fig. 104)
consists of two pieces or valves, one dorsal (d. v), the other ventral
(v. v), and the animal is attached by a horny stalk or peduncle (Fig.
ic>5,/
viii ROTIFERA, POLYZOA, AND BRACHIOPODA 187
situated in the middle of the anterior body-wall within the lophophore,
leads into a V-shaped digestive canal (st. inf), which may or may not
terminate in an anal aperture. A heart is present in the form of a con-
tractile sac, and there is a feebly developed vascular system. The
central part of the nervous system is in the form of a nerve ring,
with ganglia, which surrounds the oesophagus. There is a pair of large
funnel-shaped nephridia («///) which act also as reproductive ducts,
leading from the coelome to the mantle-cavity. The sexes are some-
times separate, sometimes united.
The Brachiopoda are all marine. They are widely distributed geo-
graphically, and live at various depths, from between tide-marks to
twenty-nine hundred fathoms. At the present day the class includes
only about twenty genera and a hundred species, but in former geo-
logical periods the Brachiopoda were much more numerous, 106 genera
being known from the palaeozoic rocks, there being nearly two thou-
sand fossil species.
Lingula pyramidata occurs in sand at or near low water from Chesa-
peake Bay to Florida. Our common northern species, Terebratulina
septentrionalis, lives north of Cape Cod, attached to rocks in from ten
to fifty fathoms.
SECTION IX. — PHYLUM ANNULATA
AN earthworm, a lobworm, and a leech, when compared
with one another, will at once be seen to possess certain
features in common. Each is bilaterally symmetrical, long
and relatively narrow in shape, is transversely ringed or
jointed, and has a soft integument ; each has a mouth open-
ing towards the anterior end and a smaller anal aperture
towards the posterior end. The earthworm and the lob-
worm, moreover, resemble one another in possessing a
number of bristles, extremely short in the former, disposed
regularly in groups along the rings of the body. The ringed
or annulate appearance is found, on a closer inspection, to
be due to the elongated body being made up of a row of
similar parts, the segments or mefameres, which are remark-
ably uniform throughout the length of the body, not only in
external appearance, but in internal structure. A general
correspondence is found to exist in the disposition of the
internal organs of all the three, and the conclusion is arrived
at that they are all members of one phylum. The phylum
in question, the Annulata, comprises the earthworms, the
class of the marine segmented worms or Annelids to which
the lobworm belongs, the leeches and certain other groups.
1. THE CILETOPODA
The rows of bristles above referred to as disposed along
the segments of the body in the earthworm and the lobworm
188
SECT, ix PHYLUM ANNULATA 189
constitute one of the distinguishing features of the class
Chaetopoda or " bristle-footed " worms of the phylum
Annulata. Of these a good and common example is Nereis
— a marine Annelid of common occurrence under stones
and among shells and seaweed on the
sea- shore in all parts of the world. The
following account of the European Nereis
dumerilii will apply, with slight differences,
to our common Nereis virens.
In shape (Figs. 106-109) the body,
which may be about 7 or 8 centimetres
in length, is long and narrow, approxi-
mately cylindrical, somewhat narrower
towards the posterior end. A very distinct
head, bearing eyes and tentacles, is recog-
nisable at the anterior end; the rest is
divided by a series of ring-like narrow
grooves into a corresponding series of seg-
ments or metameres, which are about eighty
in number altogether ; and each of these
bears laterally a pair of movable muscular
processes called the parapodia, provided
with bundles of bristles or seta. The head
(Fig. 109) consists of two parts, the pro-
stomium (prcest) and the peristomium
(peris t). The former bears on its dorsal
surface four large rounded eyes, in front FIG. 106.- Nereis du-
a pair of short cylindrical tentacles (tent),
and further back a pair of somewhat
longer stout appendages or palpi (palp}. The peristo-
mium, which presents some resemblance to the segments of
the body, though wanting the parapodia. bears laterally four
pairs of long slender cylindrical tentacles (perist, tent} :
190 MANUAL OF ZOOLOGY SECT.
on its ventral aspect is a transversely elongated aperture,
the aperture of the mouth. The segments of the body
differ little in external characters from one another through-
out the length of the worm. Each bears laterally a pair of
parapodia which in the living animal are usually in active
movement, aiding in creeping, or acting as a series of oars
for propelling it through the water. When one of the para-
podia (Fig. 107) is examined more attentively it is found
to be biramous, or to consist of two distinct divisions — a
dorsal, which is termed the notopodium (noto), and a ventral,
dors, cirr
noto
neuro
"^^Bb^
vent.cirr
FIG. 107. — Nereis dumerilii. A single parapodium magnified, ac, aciculum;
dors, cirr, dorsal cirrus; neuro, neuropodium; noto, notopodium; vent, cirr,
ventral cirrus. (After Claparede.)
which is termed the neuropodium (neuro). Each of these
is further subdivided into several lobes, and each bears a
bundle of setae. Each of the bundles of setae is lodged in
a sac formed by in vagi nation of the epidermis, the setigerous
sac, and is capable of being protruded or retracted and
turned in various directions by bundles of muscular fibres
in the interior of the parapodium. In each bundle there
is, in addition to the ordinary setae, a stouter, straight, dark-
coloured seta (ac), the pointed apex of which projects only
a short distance on the surface ; this is termed the aciculum.
The ordinary setae (Fig. 108) are exceedingly fine, but
IX PHYLUM ANNULATA 191
stiffish, chitinous rods, of which two principal kinds are
recognisable; both have a terminal blade articulating with
the main shaft of the seta by a distinct joint. On the
dorsal side of the parapodium is a short cylindrical, tentacle-
like appendage, the dorsal cirrus
(Fig. 107, dors, cirr), and a similar,
.somewhat shorter, appendage, the
ventral cirrus (vent, cirr} , is situated
on its ventral side. The last segment
of the body, the anal segment, bears
posteriorly a small rounded aperture,
the anus ; this segment is devoid of
parapodia, but bears a pair of appen-
dages, the anal cirri, similar in'char-
acter to the cirri of the ordinary
segments, but considerably longer.
On the ventral surface, near the
bases of the parapodia, there is in
each segment a pair of very fine aper-
tures, the openings of the nephridia.
The enteric canal is a straight tube
running throughout the length of the
body from the mouth to the anus.
Between the outer surface of this
tube and the inner surface of the wall
of the body is a considerable space FIG Io8 _Nerei8duTeriiii.
— the cceZom, body cavity, or peri-
visceral cavity — filled with a fluid, the
cozlomic fluid. The space is divided by a series of transverse
partitions or septa passing inwards from the body- wall to the
walls of the alimentary canal opposite the grooves between
the segments, and thus dividing the ccelom into a series of
chambers, each of which corresponds to one of the seg-
FIG. 1 09. — Nereis dumerilii. Semi-diagrammatic view of the anterior portion of
the body, with the dorsal body-wall removed, so as to show the alimentary canal,
the septa, the blood-vessels and the nephridia; a portion of the intestine removed
so as to show the ventral blood-vessel and nerve-cord which lie below, dors, vess,
dorsal vessel; gl, cesophageal glands; int, beginning of intestine; ne. co, nerve
cord; neph, nephridia; ass, oesophagus; palp, palp; para, parapodia; perist,
peristome; perist. tent, peristomial tentacles; /*, pharynx with its jaws; freest*
prostomium; vent, vess, ventral vessel.
I92
SECT, ix PHYLUM ANNULATA 193
ments. These partitions are not complete, spaces being
left around the alimentary canal and elsewhere, through
which neighbouring chambers communicate.
The mouth leads into a wide cavity, the buccal cavity
continued back into a pharynx (Fig. 109, ph). In the
pharynx are a number of very small dark brown chitinous
denticles, which are very regularly arranged. The posterior
part of the pharynx has very thick walls composed of
bundles of muscular fibres, which are concerned in the
movement of a pair of laterally placed chitinous jaws.
Behind the pharynx the alimentary canal narrows con-
siderably to form a tube, the oesophagus (&s}, which runs
through about five segments to open into the intestine.
The anterior part of the alimentary canal is capable of
being everted as a proboscis until the jaws are thrust forth
and thus rendered capable of being brought to bear on some
small living animal, or fragment of animal matter, to be
seized and swallowed as food.
Into the oesophagus open a pair of large unbranched
glandular pouches, or cceca (gl), which probably are of the
nature of digestive glands. The intestine (int} is a straight
tube of nearly uniform character throughout, regularly con-
stricted between the segments.
Nereis has a well-developed system of vessels filled with
blood of a bright red colour. A main dorsal vessel (Figs.
109 and no, dors, vess) runs from one end of the body to the
other above the alimentary canal, and is visible in places
through the body-wall in the living animal. It, as well as
the majority of the vessels, undergoes contractions which are
of a peristaltic character — waves of contraction passing
along the wall of the vessel so as to cause the movement of
the contained blood. These peristaltic contractions are
more powerful in the case of the dorsal vessel than in that
o
194
MANUAL OF ZOOLOGY
of any of the others, and run with great regularity from
behind forwards, so as to drive a current of blood in that
direction.
Along the middle of the ventral surface below the alimen-
tary canal runs another large longitudinal vessel, the ventral
vessel (vent, vess), in which the current of blood takes a
IX PHYLUM ANNULATA 195
direction from before backwards. Connecting the dorsal
and ventral vessels, there are in each segment two pairs of
loop-like transverse vessels which give off branches to the
parapodia, the alimentary canal, and neighbouring parts.
There is a well-developed nervous system (Fig. 112) which
is bilateral and metameric in its arrangement, like the other
systems of organs. Situated in the prostomium is a large
bilobed mass of nerve-matter containing numerous nerve-
cells, the cerebral ganglion or brain (c). This gives off
tentacular nerves to the tentacles and palpi, and two pairs
of short thick optic nerves to the eyes. Behind, two thick
nerve strands, the cesophageal connectives (//), curve round
the mouth in the peristomium to meet on the ventral aspect
behind the mouth and below the pharynx. The cesophageal
connectives, with the cerebral ganglion, thus form a ring
around the anterior part of the enteric canal. Running
backwards from the point of union of the cesophageal con-
nectives, along the entire length of the body of the worm,
on the ventral aspect, is a thick cord of nerve-matter, the
ventral nerve-cord (h) . In each segment this cord presents
a little dilatation from which nerves are given off to the
various parts of the segment : and each of these enlarge-
ments is really double, consisting of a pair of closely-united
ganglia. The intermediate parts of the cord, between suc-
cessive pairs of ganglia, are also double, consisting of a pair
of longitudinal connectives enclosed in a common sheath.
Given off behind from the cerebral ganglion is a system of
fine nerves with occasional small ganglia, the stomatogastric
or visceral system, distributed to the anterior part of 'the
alimentary canal.
The tentacles and palpi, as well as the cirri, are probably
organs of the sense of touch. The only other sense-organs
are the four eyes, situated on the prostomium. The eye
t96
MANUAL OF ZOOLOGY
SECT.
(Fig. in) consists of a darkly pigmented cup, the retina
(re), with a small rounded aperture, the//////, and enclosing
a mass of gelatinous matter, the lens (/) .
CO
FIG. in. — Section through an eye of Nereis, co, cornea; cu, cuticle; /, lens; r,
layer of rods; re, retina. (After Andrews.)
The organs which are supposed to perform the function
of excretion are a series of metamerically arranged pairs of
internally ciliated tubes, the segmental organs or nephridia
(Figs. 109 and no, neph) occurring in all the segments of
the body. Each of these has an external opening or nephri-
diopore, a fine circular pore capable of being widened or
contracted, situated on the ventral surface not far from the
base of the ventral cirrus, and opening internally into the
coelom through a ciliated bell or funnel, the nephrostome,
projecting through the mesentery into the cavity of the seg-
ment next in front of that in which the body of the organ
lies.
IX
PHYLUM ANNULATA
197
Nereis is unisexual. The sexual elements, ova or sperms,
are formed from temporary masses of cells (ovaries or testes],
which are developed towards the breeding season by a pro-
n>
FIG. 112. — Nereis. Anterior portion of nervous system, comprising the brain, the
oesophageal connectives, and the anterior part of the ventral nerve-cord. .(After
Quatrefages.)
liferation of the cells of the membrane (peritoneum) lining
the coelom and the structures it contains.
Ova and sperms, when fully ripe, are discharged, reaching
198 MANUAL OF ZOOLOGY SECT.
the exterior, in the case of the sperms probably through the
nephridia ; in the case of the ova, which are much too large
to pass out in this way, probably through apertures tempo-
rarily formed by rupture of the body- wall ; and impregnation
takes place by contact between the two sets of elements
while floating freely in the sea-water.
FIG. 113. — Serpulae with their tubes. (After Quatrefages.)
Other annelides which may be collected along with Nereis
on the sea-shore will be found to resemble it in the seg-
mented character of the body, and the presence of para-
podia with setae, but to differ from it in the general shape,
the number of the segments, the form of the parapodia, and
the arrangement and shape of the setae, the form of the
head with its eyes and tentacles, and other points. Many
IX
PHYLUM ANNULATA
199
possess branchice, organs which are absent as such in Nereis,
in the form of simple or branched vascular processes ar-
ranged in pairs on the dorsal side of the parapodia, through-
out the whole or a part of the length of the body, or (Fig.
113) confined to the head-end. All such marine worms
belong to the sub-class Polychseta of the Chaetopoda.
Though many of them move about freely like Nereis, others
live permanently in tubes of a membranous or shelly mate-
THrf
FIG. 114. — A, Tt, C, three stages in the development of the Trochosphere of
Eupomatus, from the side, an, anus; fh, blastocoele; ;«, polar cells of the
mesoderm; md, mid-gut; «. larval head-nephridium; ot, otolith; sp, neural
plate; st, stomodaeum; ivk, preoral ciliated ring; iuklt post-oral ciliated ring.
(From Lang's Comparative Anatomy.}
rial. The tube-inhabiting Polychaeta (Fig. 113) usually
present marked modifications of form in accordance with
their mode of life. The branchiae when present are usually
confined to the head-end, so that they can easily be thrust
out through the opening of the tube, and the body is fre-
200
MANUAL OF ZOOLOGY
SECT.
quently divisible into regions owing to more or less marked
differences in the development of the parapodia and other
points, between the anterior part which may be thrust out
B
FIG. 115. — Lumbricus agricola. A, entire specimen, lateral view ; B, ventral view
of anterior portion of the body, magnified. /, 77, 33, first, fifteenth, and thirty-
third segments. The black dots represent the setae. (After Vogt and Jung.)
of the tube and the posterior parts which habitually remain
enclosed in it. All the Polychaeta, with one or two ex-
ceptions, have the sexes separate, and have a free-swimming
IX
PHYLUM ANNULATA
201
pelagic larva, the Trochosphere (Fig. 114), provided with one
or several circlets of cilia.
When a common earthworm is compared with Nereis,
certain resemblances are at once discernible. The earth-
worm (Fig. 115) has the same elongated cylindrical body,
divided by ring-like grooves into a large number of seg-
ments or metameres. But the well-developed head-region
is absent, as are the eyes, palpi, and tentacles, and the
parapoda are not present, nor the dorsal and ventral cirri.
Setae, however, are present (Fig. 116), though so short as to
be distinguishable with difficulty ; two
double rows run along each side of the
ventral surface, so that there are alto-
gether eight of these short setae on each
segment. A thickened zone — the saddle
or clitellum — is to be observed extend-
ing over five segments, in front of the
middle of the body. In internal struc-
ture there is a considerable resemblance ;
but the reproductive organs are her-
maphroditic in arrangement and more
complex in structure than in Nereis.
There are two special male ducts or vasa FIG. n6. — Lumbricus,
setae, highly magnified.
deferentia, opening on the ventral sur-
face of the fifteenth segment, and female ducts or oviducts
opening on the fourteenth.
The fertilised ova of the earthworm are enclosed, together
with a quantity of an albuminous fluid in a cocoon, the wall
of which is formed of a viscid secretion from the glands of
the clitellum, hardened and toughened by exposure to the
air. The cocoon is deposited in the earth, and the embryos
develop into complete, though minute, worms before they
make their escape. At a certain stage the embryos are
202 MANUAL OF ZOOLOGY SECT.
nourished by swallowing the albuminous fluid contained in
the cocoon.
The earthworms, together with a number of allied fresh-
water forms, constitute the sub-class Oligochaeta of the
Chaetopoda. As a group they are distinguished from the
Polychseta by the sexes being united in the same individual,
with the ovaries and testes compact and few in number, by
the absence of parapodia and cirri, the non-development of
a distinct head-region, and the absence of a free larval stage.
Very few Chaetopoda are true parasites, but a considerable
number are to be set down as commensals, habitually associ-
ating with another animal for the sake of food and shelter.
The earthworms burrow in soil containing decaying vegetable
matter, passing the mould through their intestine and subse-
quently throwing it off in the shape of "castings" on the
surface. They also feed on decaying leaves, and sometimes
on animal substances. Some of the fresh-water Oligochaeta
manufacture tubes of mud held together by a tenacious
secretion from glands in the integument. Some of the
Polychaeta move about freely or burrow in sand, or even in
rock or in the shells of molluscs ; some occupy temporary
tubes ; others inhabit permanent tubes sometimes of parch-
ment-like consistency, sometimes hardened by deposition of
grains of sand, small fragments of shell or -other foreign
bodies, sometimes of dense, shelly, calcareous material.
These tubes are usually firmly fixed to a rock or a seaweed
or other foreign body. While the free-living Polychaeta are
carnivorous in their diet, those that inhabit permanent tubes
are vegetable feeders.
A few Polychaeta are pelagic. The majority live among
sand, mud, rock, or seaweed in shallow water, or actually
between high- and low-water limits ; but they also occur at
all depths in the ocean.
IX PHYLUM ANNULATA 203
2. THE HIRUDINEA
A good example of the Hirudinea is the medicinal leech
(Hirudo), various species of which are to be found in ponds,
swamps, and slowly flowing streams in various parts of the
world.
It is a vermiform animal, some 6-10 cm. (2-3 inches) in
length, but is capable of contracting and elongating itself
so as to produce great alterations in form and proportion.
It moves by " looping " movements, and is also a good
swimmer. The body (Fig. 117) is depressed or flattened
dorso-ventrally, the dorsal surface convex, the ventral flat-
tened. The anterior end presents a ventrally directed, cup-
like hollow, the anterior sucker (a. s), in the middle of which
is a small aperture, the mouth (mth}. The hinder end bears
a disc-like posterior sucker (p.s), also directed downwards,
and at its junction with the trunk, on the dorsal surface, is
the very small median anus (a).
The whole body is encircled by close-set transverse grooves,
dividing it into annuli. These, like the annuli of some
earthworms, are more numerous than the true segments or
metameres, the study of the internal organs showing that,
except at the two extremities, each segment contains five
annuli. On the ventral surface of the fifth annulus of each
segment is a pair of minute apertures, the nephridiopores
or excretory apertures (n. p. 1-17 ) ; of these there are
altogether seventeen pairs, marking the fifth rings of the
sixth to the twenty-second segments.
The anterior sucker bears on its dorsal surface five pairs
of small black spots, the eyes (e. i, e. j).
The perfectly definite and comparatively small number of
metameres in the leech offers a striking point of contrast
B
nfi.it
FIG. 117. — Hirudo medicinalis. A, dorsal; B, ventral aspect, a, anus; a. s,
anterior sucker; e. I. first pair of eyes; e. 5, fifth pair; gp. rf , male gonopore;
gp. $, female gonopore; »ith, mouth; «/. /, first pair of nephridiopores;
np. 77, seventeenth pair; /. s, posterior sucker; s.p, sensory papillae; I-XXVI,
segments. (Partly after Whitman.)
204
SECT. IX
PHYLUM ANNUL AT A
205
FIG. 118
with what we have met with in the Chaetopoda, and is to be
looked upon as a mark of higher differentiation.
The alimentary organs are greatly modified in accordance
with the blood-sucking habits of the animal. Surrounding
the mouth are three jaws,
one median and dorsal, the
other two ventro - lateral.
Each has the form of a com-
pressed muscular cushion,
with a sharp, evenly curved,
free edge covered with chi-
tin, which is produced into
numerous serrations or teeth
(Fig. 1 1 8) . By means of its
muscles each jaw can be
moved backwards or for-
wards through a certain arc,
and the three, acting to-
gether, produce the characteristic triradiate bite in the skin
of the animal upon which the leech preys.
The mouth leads into a muscular pharynx (Fig. up,//*),
situated in the fourth to seventh segments. Radiating
muscles pass from its walls to the integument, and by their
contraction dilate its cavity and suck in blood made by the
jaws. Around the pharynx are numerous unicellular sali-
vary glands, which open close to the mouth ; their se-
cretion has the effect of preventing the coagulation of the
blood taken as food.
The pharynx communicates by a very small aperture with
the second and largest division of the enteric canal, the
huge crop (^rr), a thin- walled tube extending from the eighth
to the eighteenth segment, and produced into eleven pairs of
lateral pouches (cr, cr. i, //). The crop is capable of great
Head of Hirudo medici-
nalis, showing the three jaws(£): b,
one of the jaws isolated, with the finely
toothed free edge. (After Sedgwick.)
I
v.et
FIG. ng. — Hirudo quinquestriata. Dissection from the dorsal aspect, «,anus;
^f, brain; cr. /, first diverticulum of crop, contracted; cr. /', the same expanded;
cr. //, the last diverticulum of the crop, contracted; cr. /', the same expnnded;
. d, vas deferens ; v. sew, vesicula seminalis.
206
SECT, ix PHYLUM ANNULATA 207
dilation, and its form varies greatly according to whether it
is empty or gorged with blood. Posteriorly the crop com-
municates by a minute aperture with the stomach (.$•/), a
tubular chamber which is the digestive portion of the canal ;
the blood is passed into it from the crop with extreme
slowness, and undergoes an immediate change, its colour
turning from red to green. The digestion of a whole
cropful of blood takes many months. The stomach is
continued into a narrow intestine (int) ; this passes into a
somewhat dilated rectum (ret), which turns slightly upwards
and opens by the anus (an) in the last annulus.
The excretory system consists of seventeen pairs of
nephridia (nph. i-if), situated in segments 6-22. A
typical nephridium (Fig. 120) has the general form of a loop
passing upwards from the ventral body-wall, produced into an
offshoot which extends inwards (mesially) to the correspond-
ing testis, and connected posteriorly with a small bladder or
vesicle (Fig. 120, vs). The free end is swollen into a lobed
mass which lies in a blood sinus (Fig. 114, nst) ; comparison
with other Hirudinea shows that this dilated end of the
nephridium represents a nephrostome which has lost its open
funnel-like end in correlation with the absence of a distinct
ccelom.
There is a complex vascular system, containing, like that of
the earthworm, red blood, the plasma coloured with haemo-
goblin and containing sparsely distributed colourless corpus-
cles. But a striking difference from the preceding anneli-
dan types is found in the fact that the blood-containing spaces
are of two kinds, — blood-vessels proper, having muscular walls,
and blood-sinuses, the walls of which are devoid of muscle.
The two principal blood-vessels are lateral in position
(Figs. 119 and 122, /. v), running fore and aft at the level of
the middle of the nephridia and uniting with one another at
208
MANUAL OF ZOOLOGY
SECT.
the anterior and posterior ends of the body. They send off
branches both dorsally and ventrally, some of which anasto-
mose with one another. The ultimate branches break up
into capillaries in the integument, nephridia, etc.
The two principal sinuses are respectively dorsal (d. s) and
ventral (v. s), the former lying just above the enteric canal
in the middle dorsal line, the latter occupying a similar
FIG. 120. — Nephridium of the medicinal leech, a. I, apical lobe; m. I, middle lobe;
n. pt nephridiopores; nst, nephrostome; r. /, recurrent lobe; /. /, testis lobe;
vs, vesicle ; -vs. d, vesicle duct. (After Bourne.)
position on the ventral side, and enclosing the ventral
nerve-cord.
The nervous system is of the usual annulate type. There
is a small brain (Fig. 119, br} situated above the anterior
end of the pharynx immediately behind the median dorsal
IX
PHYLUM ANNULATA
209
jaw. It is connected by a very short pair of cesophageal
connectives with the ventral nerve-cord, which consists of
twenty-three well-marked rounded ganglia (gn. 1-23) united
by delicate double connectives. The first, or sub-cesopha-
geal ganglion is larger than the others, and is shown by
development to be made up of five united embryonic
ganglia : the last ganglion is also of unusual size, and results
from the fusion of six distinct ganglia in the embryo* The
ventral nerve-cord is contained in the ventral sinus.
d.s
FIG. i2i. — Transverse section of Hirudo : diagrammatic; cr, crop; d. s, dorsal
sinus which encloses the dorsal vessel ; /. v, lateral vessel ; n. c, nerve cord;
nph., nephridium; nst., nephrostome ; ov, ovary; ts, testis ; v. s, ventral sinus.
(After Bourne.)
The principal sense organs are the eyes, of which there are
five pairs situated round the margin of the anterior sucker
on the dorsal side, one pair in each of the five segments.
They occupy positions taken in the succeeding segments by
a series of papillae, the lateral sense-organs, with which they
are obviously homologous. The margin of the anterior
sucker also bears a large number of goblet-shaped organs,
which are very probably organs of taste. The minute
structure both of these and of the lateral sense organs is
MANUAL OF ZOOLOGY
SECT.
very similar to that of the eyes. The function of the lateral
sense organs is unknown.
The leech is monoecious. There are nine pairs of testes
(Fig. 119, ts), in the form of small spherical sacs situated in
segments 12-20. Each gives off from its outer surface a
narrow efferent duct, which opens into a common vas deferens
(v. d}. In the tenth segment the vas deferens increases in
width and forms a complex coil, the vesicula seminalis
its
FIG. 122. — Diagram of principal blood channels of leech ; d. s, dorsal sinus ; /.
lateral vessel ; v. s, ventral sinus containing nerve-cord.
(v. sem}, from which is continued anteriorly a somewhat
dilated muscular tube, the ductus ejaculatorius (d. ej}.
From each ejaculatory duct a narrow tube passes to the base
of the penis (/), a curved eversible muscular organ which
opens on the ventral surface of the second annulus of the
tenth segment, in the middle line.
The ovaries are coiled filamentous bodies, each enclosed
ix PHYLUM ANNUL ATA 211
in a small globular ovarian sac (ov. s), situated in the
eleventh segment. From each ovarian sac a short oviduct
passes inwards and backwards, and unites with its fellow in
a median duct which opens into a curved muscular tube, the
vagina (va), which opens in the middle line on the ventral
surface of the second annulus of the eleventh segment, i.e.,
one segment behind the male aperture.
The leeches are a comparatively uniform group ; but
some of the class differ from the medicinal leech in more
or less important points. Thus in one section there are no
jaws, and the anterior end of the body is capable of being
retracted within the part immediately behind it or thrust
forward as a proboscis or introvert. In the great majority
respiration takes place through the skin, as in the medicinal
leech ; but in one genus, Braiuhellion, which is an external
parasite on certain fishes, gills are present in the form of
delicate lateral outgrowths of the segments.
The majority of the Hirudinea are inhabitants of fresh
water, and live, like the medicinal leech, by sucking the
blood of higher animals. Others are permanent external
parasites ; others again are carnivorous, feeding on snails
and other Mollusca.
SECTION X. — PHYLUM ARTHROPODA
IF we examine and compare, even quite superficially, a
crayfish, a scorpion, a centipede, and a blue-bottle fly, we
see at once that, while they manifestly do not belong to any
of the groups of animals studied hitherto, they are all con-
nected together by certain broad common features. They
all have a hard, or at least tough, integument ; they all have
the body more or less clearly divided into segments, and
they all have a system of appendages, feelers, jaws, legs, etc.,
adapted to different uses in the different animals mentioned,
and in different parts of the body of the same animal, but
agreeing in being covered with a hard or tough integument
like that of the body itself, and in being divided into seg-
ments by a number of joints. These features, together with
certain points in the arrangement and structure of the
internal parts, are characteristic of the members of the phy-
lum Arthropoda, a group of very great extent, comprising,
among others, four large classes, each exemplified by one of
the four familiar animals above referred to.
Of these the crayfish differs from the rest in being an
aquatic animal and in having organs of respiration, gills, or
branchiae adapted to this mode of life. The remaining
three are, with a few exceptions, air-breathers. The cray-
fish is a representative of the class Crustacea of the phylum
Arthropoda ; the scorpion of the class Arachnida, the cen-
212
SECT. X PHYLUM ARTHROPODA 213
tipede of the class Myriapoda, and the blue-bottle fly of the
class Insecta.
1. THE CRUSTACEA
The class Crustacea comprises a very large number of
Arthropods, the great majority of which are inhabitants
either of fresh water or of salt. Familiar examples of Crus-
tacea are the crayfishes, lobsters, shrimps, and prawns, the
crabs and hermit-crabs, the sand- hoppers, and woodlice,
the barnacles, and acorn-shells. As an example of the
Crustacea the Fresh-water Crayfish should be studied.
The following description applies more especially to the
common European crayfish (Potamobia pallipes),1 but the
American species of Astacus will be found to correspond in
all essential respects, while the lobster also presents but slight
differences.
It is to be noticed, in the first place, that the crayfish,
like Nereis, is a bilaterally symmetrical animal, and that the
bilateral symmetry is complete, the right and left halves of
the body being exactly alike. The crayfish, it is to be
noticed, also resembles Nereis and the leech in being
metamerically segmented, the segmentation being most
clearly distinguishable in the posterior region of the body.
Here, however, the external resemblance ceases. Instead
of the soft integument of Nereis and the leech, the crayfish
has a hard enclosing crust or exoskeleton formed of the
thickened and calcified cuticle, and, in place of the un-
jointed, short parapodia of Nereis, there are a series of
variously modified appendages, feelers, jaws, legs, etc.,
which, like the body itself, are enclosed in a hard exo-
skeleton, having a jointed character, the appendages thus
1 More commonly named Astacus fluviatilis.
214
MANUAL OF ZOOLOGY
SECT.
being divided into series of movable segments which are
termed \hepodomeres.
The body of the crayfish (Fig. 123) is divided into two
regions — an anterior, the cephalothorax (cth), which is
covered by a broad shield or carapace ; and a posterior,
the abdomen (at>), which is divided into distinct segments,
movable upon one another in a vertical plane. The cepha-
FIG. 123. — Astacus fluviatilis, side view of male, a^, antennule; a%, antenna;
ab, abdomen; cth, cephalothorax; kd, gill-cover; r, rostrum; 8, third maxilli-
pede; 9, first leg;-/o-/j, remaining legs; ig, uropod; XIV, first abdominal
segment ; XIX, sixth abdominal segment. (From Lang's Comparative
A natomy. )
lothorax is again divided into two regions — an anterior, the
head, and a posterior, the thorax — by a transverse depres-
sion, the cervical groove. The carapace is developed from
the dorsal regions of both head and thorax, and is free only
at the sides of the thorax,1 where it forms a flap or gill-cover
1 This was the view of Huxley, but it is the opinion of American authors
that the carapace is the enlargement of the fused tergites or dorsal region of
two head-segments, i.e., the second antennal and mandibular; those of
the succeeding cephalothoracic segments being atrophied. — AMERICAN
EDITOR.
X PHYLUM ARTHROPODA 215
(kit) on each side, separated from the actual body-wall by
a narrow space in which the gills are contained. The cara-
pace is made of chitin, strongly impregnated with carbonate
of lime so as to be hard and but slightly elastic.
The abdomen is made up of seven segments : the first six
(XIV-XIX) of these are metameres in the strict sense of
the word, and have a ring-like form, presenting a broad
dorsal region or tergum; a narrow ventral region or sternum;
and downwardly directed lateral processes, the pleura. The
seventh division of the abdomen is the telson; it is reduced
in size, flattened horizontally, and divided by a transverse
groove into anterior and posterior portions. All seven seg-
ments are calcified, and are united to one another by chiti-
nous articular membranes ; the first segment is similarly
joined to the thorax.
It has been stated that the abdominal segments are
movable upon one another in a vertical plane, i.e., the
whole abdomen can be extended or straightened, and flexed
or bent under the cephalothorax ; the segments are incapa-
ble of movement from side to side. This is due to the fact
that, while adjacent segments are connected dorsally and
ventrally by flexible articular membranes, they present at
each side a hinge, placed at the junction of the tergum and
pleuron, and formed by a little peg-like process of one seg-
ment fitting into a depression or socket in the other. A line
drawn between the right and left hinges constitutes the axis
of articulation, and the only possible movement is in a plane
at right angles to this axis.
The ventral and lateral regions of the thoracic exoskeleton
are produced into the interior of the body in the form of a
segmental series of calcified plates, so arranged as to form a
row of lateral chambers in which the muscles of the limbs
lie, and a median tunnel-like passage or sternal canal, con-
2i 6 MANUAL OF ZOOLOGY SECT.
taining the thoracic portion of the nervous system. The
entire endophragmal system, as it is called, constitutes a kind
of internal skeleton.
The head exhibits no segmentation ; its sternal region is
formed largely by a shield-shaped plate, the epistoma, nearly
vertical in position. The ventral surface of the head is, in
fact, bent so as to face forwards instead of downwards. The
cephalic region of the carapace is produced in front into a
large median spine, the rostrum (Fig. 123, r): immediately
below it is a plate from which spring two movably articu-
lated cylindrical bodies, the eye-stalks, bearing the eyes at
their ends.
Among the appendages one's attention is attracted by the
long feelers (Fig. 123, alf a.2) attached to the head, the
five pairs of legs (9-13) springing from the thorax, and
the little fin-like bodies arising from the sterna of the abdo-
men. It will be convenient to begin with the last-named
region.
The third, fourth, and fifth segments of the abdomen bear
each a pair of small appendages, the abdominal feet or pleo-
pods (Fig. 1 24, 10} . Each consists of an axis or protopodite,
consisting of a very short proximal (pr. i) and a long distal
(pr. 2) podomere, and bearing at its free end two jointed
plates, fringed with setae, the endopodite (en} and exopodite
(ex). These appendages act as fins, moving backwards and
forwards with a regular swing, and probably aiding in the
animal's forward movements.
In the female a similar appendage is borne on the second
segment, while that of the first is more or less rudimen-
tary. In the male the first and second pleopods (p) are
modified into incomplete tubes which act as copulatory
organs (gonopoda). The sixth pair of abdominal limbs (//)
are alike in the two sexes ; they are very large, both endo-
PHYLUM ARTHROPODA
217
and exopodite having the form of broad flat plates ; in the
natural position of the parts they lie one on each side of the
telson, forming with it a large five-lobed tail-fin ; they are
O.CofJulafopy Organs lO.Swimming FooC
ll.Uropod 3.
FIG. 124. — Typical appendages of Astacus. en. 1-5, podomeres of endopodite;
ep, epipodite; ex, exopodite; A. flagella; g, gill; pr. i, pr. 2, podomeres of
protopodite; /-j, podomeres of axis of antennule. (After Huxley.)
therefore conveniently called uropods or tail-feet. The telson
itself bears no appendages.
218 MANUAL OF ZOOLOGY SECT.
The thoracic appendages are very different. The four
posterior segments bear long, slender jointed legs (8), upon
which the animal walks ; in front of these is a pair of very
large legs terminating in huge claws or chela, and hence
called chelipeds (Fig. 1 23, p) . The three anterior segments x
bear much smaller appendages, more or less leg-like in
form, but having their bases toothed to serve as jaws ; they
are distinguishable as maxillipeds or foot-jaws (Fig. 1 24, 6, 7) .
The structure of these appendages is best understood by
a consideration of the third maxilliped (7). The main por-
tion of the limb is formed of seven podomeres arranged in
a single series, strongly calcified, and, with the exception of
the second and third, which are fused, movably articulated
with one another. The second podomere, counting from the
proximal end, bears a many-jointed, feeler-like organ (ex),
and from the first springs a thin folded plate (cp), having a
plume-like gill (g) attached to it. Obviously such an ap-
pendage is biramous, but with one of its branches greatly in
excess of the other ; the first two segments of the axis (pr. i,
pr. 2) form the protopodite, its remaining five segments
(en. 1-5) the endopodite, and the feeler, which is directed
outwards, or away from the median plane, the exopodite
(ex) . The folded plate (ep) is called the epipodite ; in the
natural position of the parts it is directed upwards, and lies
in the gill-cavity between the proper wall of the thorax and
the gill-cover.
The five legs (8) differ from the third maxilliped in their
greater size, and in having no exopodite ; in the fifth or last
the epipodite also is absent. The first three of them have
undergone a curious modification, by which their ends are
1 By most authors the maxillipedes are regarded as belonging to the
head, the number of pairs of thoracic appendages being considered as
five. — AMERICAN EDITOR.
x PHYLUM ARTHROPODA 219
converted into pincers or chelce ; the fourth segment (en. 4)
of the endopodite (sixth of the entire limb) is produced
distally so as to form a claw-like projection (en. 4'), against
which the terminal segment (en. 5) bites. The first leg is
much shorter than any of the others and its chela is of im-
mense size, and forms an important weapon of offence and
defence. The second maxilliped resembles the third, but is
considerably smaller ; the first (6) has its endopodite greatly
reduced, the two segments of its protopodite large and leaf-
like, and no gill is connected with the epipodite.
The head bears a pair of mandibles and two pairs of
maxillae in relation with the mouth, and in front of that aper-
ture a pair of antennules and one of antennae. The hindmost
appendage of the head is the second maxilla (5), a markedly
foliaceous appendage; its protopodite (pr. i, pr. 2) is cut
up into lobes; the exopodite (ex) is modified into a
boomerang-shaped plate, which, we shall see, is an impor-
tant accessory organ of respiration. The first maxilla (4) is
a very small organ, having neither exo- or epipodite. The
mandible ( j) is a large, strongly calcified body, toothed along
its inner edge, and bearing on its anterior border a little
three-jointed, feeler-like body, the palp.
The antenna (2) is of great size, being nearly as long as
the whole body. It consists of an axis of five podomeres,
the fifth or last of which bears a long, flexible, many-jointed
structure, or flagellum (7?), while from the second segment
springs a scale-like body or squame (ex) .
The antennule (/) has an axis of three podomeres (/-j),
ending in two many-jointed flagella (fl. / and 2) .
The eye-stalks, already noticed, arise just above the an-
tennules, and are formed each of a small proximal and a
large distal segment. They are sometimes counted as
appendages serially homologous with the antennae, legs, etc.
220 MANUAL OF ZOOLOGY SECT, x
If, as seems probable, the eye-stalks and antennules are to
be looked upon as belonging to a preoral region corre-
sponding to the prostomium, of Nereis, then it will be seen
that the body of the crayfish consists of a prostomium,
eighteen metameres, and a telson. The prostomium bears
eye-stalks and antennules ; the first four metameres are fused
with the prostomium to form the head, and bear the an-
tennae, mandibles, first maxillae, and second maxillae; the
next eight metameres (5th-i2th), constitute the thorax,
and bear the three pairs of maxillipeds and the five pairs of
legs; the remaining six metameres (i3th-i8th), together
with the telson, constitute the abdomen, and bear five pairs
of pleopods and one of uropods.
The digestive organs (Fig. 125) are somewhat complicated.
The mouth lies in the middle ventral line of the head, and is
bounded in front by the labrum, at the sides by the mandi-
bles, and behind by a pair of delicate lobes, the paragnatha.
It leads by a short wide gullet («) into a capacious stomach,
which occupies a great part of the interior of the head, and
is divided into a large anterior or cardiac division (c. s) , and
a small posterior or pyloric division (ps) ; the latter passes
into a narrow and very short small intestine (md), from
which a somewhat wider large intestine (M) extends to the
anus (an), situated on the ventral surface of the telson.
In the cardiac division of the stomach the chitinous lining
is thickened and calcified in certain parts, so as to form a
complex articulated framework, the gastric mill, on which
are borne a median and two lateral teeth, strongly calcified
and projecting into the cavity of the stomach. Two pairs
of strong muscles arise from the carapace, and are inserted
into the stomach ; when they contract they move the mill in
such a way that the three teeth meet in the middle and com-
plete the comminution of the food begun by the jaws. The
FIG. 125. — Astacus fluviatilis, dissection from the right side, aa, antennary
artery; abt abdomen; an, anus; b. d, bile duct; bf. 4, cheliped; bm, ventral
nerve-cord; cs, cardiac division of stomach; cth, cephalo-thorax : em, dorsal
muscles; fm, ventral mucles; g, brain; h, heart; hd. large intestine; Ir, liver;
md, small intestine; a, ostium; oa, ophthalmic artery ; oaa, superior abdominal
artery; ae, gullet; //. /-j, pleoppds; //. 6, uropod; ps, pyloric division of
stomach; sa, sternal artery; t, testis and telson; uaa, inferior abdominal artery;
vd, vas deferens ; vdo, male genital aperture. (From Lang after Huxley.)
221
222 MANUAL OF ZOOLOGY SECT.
separation of the teeth is effected partly by the elasticity of
the mill, partly by delicate muscles in the walls of the
stomach. The pyloric division of the stomach forms a
strainer; its walls are thickened and produced into nu-
merous setae, which extend quite across the narrow lumen
and prevent the passage of any but finely divided particles
into the intestine. Thus the stomach has no digestive func-
tion, but is merely a masticating and straining apparatus.
On each side of the cardiac division is found at certain
seasons of the year a plano-convex mass of calcareous
matter, the gastrolith.
The digestion of the food and to some extent the absorp-
tion of the digested products are performed by a pair of
large glands (Ir), lying one on each side of the stomach
and anterior end of the intestine. They are formed of
finger-like sacs or cceca, which discharge into wide ducts
opening into the small intestine, and are lined with glandu-
lar epithelium derived from the endoderm of the embryo.
The glands are often called livers, but as the yellow fluid
they secrete digests proteids as well as fat, the name hepato-
pancreas is often applied to them, or they may be called
simply digestive glands. The crayfish is carnivorous, its food
consisting largely of decaying animal matter.
The digestive organs and other viscera are surrounded by
a body-cavity, which is in free communication with the blood-
vessels and itself contains blood.
There are well -developed respiratory organs, in the form
of gills, contained in a narrow branchial chamber, bounded
internally by the proper wall of the thorax (Fig. 127, ef),
externally by the gill-cover or pleural region of the carapace
(kd). Each gill consists of a stem giving off numerous
branchial filaments, so that the whole organ is plume-like.
The filaments are hollow, and communicate with two paral-
PHYLUM ARTHROPOD A
223
FIG. 126. — Respiratory organs of Astacus fluviatilis. In A the gill-cover is removed
and the gills undisturbed; in B the podobranchiae are removed and the outer
arthrobranchiae turned down. alt antennule; a*, antenna; at>lt first; abz,
second abdominal segment; arb. 7-12, inner arthrobranchiae; arb-^. 7 12, outer
arthrobranchiae : ep. J, scaphognathite; plb. 11-13, pleurobranchiae; pdb. 7-13,
podobranchs; //. /, first pleopod; 6-/J, thoracic appendages. (From Lang's
Comparative Anatomy, after Huxley.)
lei canals in the stem — an external, the afferent branchial
vein, and an internal, the efferent branchial vein.
According to their point of origin, the gills (Fig. 126) are
224 MANUAL OF ZOOLOGY SECT.
divisible into three sets, — first, podobranchia or foot-gills,
springing from the epipodites of the thoracic appendages,
from which they are only partially separable ; secondly,
arthrobranchicz or joint-gills, springing from the articular
membranes connecting the thoracic appendages with the
trunk ; and thirdly, pleurobranchicz or wall-gills, springing
from the lateral walls of the thorax, above the attachment of
the appendages.
At the base of each antenna is an organ of a greenish
colour, the antennary or green gland, by which the function
of renal excretion is performed. The gland is cushion-
shaped ; it discharges into a thin-walled sac or urinary
bladder which opens by a duct on the proximal segment of
the antenna. The glands already referred to as occurring in
the gills are also supposed to have an excretory function.
The circulatory organs are in a high state of development.
The heart (Figs. 125, 127, h) is situated in the dorsal region
of the thorax, and is a roughly polygonal muscular organ
pierced by three pairs of apertures or ostia (0) guarded by
valves which open inwards. It is enclosed in a spacious
pericardial sinus (Fig. 127, pc}, which contains blood.
From the heart spring a number of narrow tubes, called
arteries, which serve to convey the blood to various parts of
the body. At the origin of each artery from the heart are
valves which allow of the flow of the blood in one direction
only, viz., from the heart to the artery. From the anterior
end of the heart arise five vessels, and from the posterior
end two, which are practically united at their origin.
All these arteries branch extensively in the various organs
they supply, becoming divided into smaller and smaller
offshoots, which finally end in microscopic vessels called
capillaries. These latter end by open mouths which com-
municate with the blood- sinuses (Fig. 128, s), spacious
PHYLUM ARTHROPODA
225
cavities lying among the muscles and viscera, and all com-
municating, mediately or immediately, with the sternal sinus
(st. s), a great median canal running longitudinally along the
thorax and abdomen, and containing the ventral nerve-cord
and the sternal and ventral abdominal arteries. In the
FIG. 127. — Transverse section of thorax of crayfish, diagrammatic, abm, ventral
abdominal muscles; bf, leg; bm, ventral nerve-cord; d, intestine; dbm, dorsal
muscles of abdomen; legs; mxp. 3, third maxillipedes. (A, after Bell.)
PHYLUM ARTHROPODA
231
the appendages, and the essential features of the internal
anatomy. The crabs and the hermit-crabs differ from the
other forms mentioned, mainly in the abdomen being re-
duced. In the crabs (Fig. 131) this region is extremely
small, its appendages are only feebly developed, and it is
FIG. 132. — Pagurus bernhardus. ch, chela of first right leg; /. 4, 1. 5, fourth and
fifth legs; t, abdominal terga; up, uropods. (After Bell.)
permanently flexed on the sternal surface of the cephalo-
thorax, so that it is completely concealed from view when
the animal is looked at from above.1 In the hermit-crabs
1 The European Cancer is represented by our common Cancer irro-
ratus, and the explanation of Fig. 131 will equally well apply to our species.
MANUAL OF ZOOLOGY
SECT.
(Fig. 132) the abdomen with its appendages is imperfectly
developed, and not enclosed completely in a hard exoskele-
ton, this region being sheltered in the shell of a whelk
or other univalve mollusc
which the hermit-crab drags
about with it.1
The crustaceans enumer-
ated above, together with
the sand-hoppers, woodlice
and their allies, and a large
number of others, form one
or two sub-classes into which
the class Crustacea is di-
vided— the sub-class Mala-
costraca. The Malacostraca
are highly organised Crus-
tacea, usually of consider-
able size, and nearly all
have a thorax of eight and
an abdomen of seven seg-
ments. The appendages
are highly differentiated.
There is a gastric mill, and
the renal organs are in the
form of antennary glands.
The other sub-class is
the Entomostraca. The
Bernard') ' Entomostraca, which are
even more numerous than
the Malacostraca, are of comparatively simple organisation,
and usually of small, often almost microscopic, size. The
1 Our common American hermit-crab is Eupagurus pollicaris ; the
right chela is still larger than in Pagurus bernhardus of the European coast.
133. — Apus glacialis, ventral aspect.
abd.f, abdominal feet; ant. i, anten-
nule; ant. 2, antenna; Ibr, labrum; md,
mandible; mx, first maxilla; ov, aper-
ture of oviduct; s.f. pi, sub-frontal
plate ; sh. gl, shell-gland ; th.f, thoracic
feet; t/i.f. i, first thoracic foot. (After
PHYLUM ARTHROPODA
233
number of segments is variable, and the appendages are not
so highly differentiated as in the Malacostraca. A carapace
developed from the head is often present. There is no gas-
tric mill, and the renal organs are not antennary glands, but
FIG 134. — Three stages in the development of Apus. fs, frontal sensory organ;
L, digestive gland; s, carapace; 1-4, cephalic appendages; I-X 1 1 1, body seg-
ments and appendages. (From Lang's Comparative Anatomy.)
shelf-glands opening at the bases of the second maxillae. The
larva nearly always leaves the egg as a characteristic form
called the Nauplius (Fig. 134, A), which occurs also, though
234
anlf
MANUAL OF ZOOLOGY
,. a.nt.2,
SECT.
FIG.
2,Calo'calanus
135. — ia, female Cyclops, from the right side; b, dorsal view; C, antenna of
male; D, swimming-foot, aid I, first abdominal segment; ant. /, antennule;
ant. 2, antenna; c. th, cephalo-thorax ; e, median eye; en, endopodite; e. s, egg-
sac; ex, expedite; ov, ovary ; pr. /, pr. 2, protopodite ; r, rostrum; s.f, swim-
ming-feet; th. 2, th. b, thoracic segments. (After Huxley, Gerstaecker, Hartog,
and Giesbrecht.)
PHYLUM ARTHROPODA
235
exceptionally, as a free-swimming stage in the Malacostraca,
the Nauplius stage in that sub-class being usually passed
through in the egg. The Nauplius 'is an oval unsegmented
body with a median eye, and three pairs of short appen-
dages provided terminally with long hairs.
FIG. 136. — Lepas anatifera. A, the entire animal; B, its anatomy, a', antennule;
c, carina; cd, cement gland; /, digestive gland; m, adductor muscle; od, ovi-
duct; ov, ovary; /, (in B) penis and (in A) peduncle; s, scutum; t, tergum and
testis; vd, vas deferens. (From Lang's Comparative Anatomy, after Darwin
and Claus.)
.Most of the Entomostraca are free-swimming, and the
majority of them, such as the water-fleas (Fig. 135) and
their allies, are of almost microscopic minuteness, though a
few, such as Apus and the brine-shrimp, are of compara-
tively large size. Many Entomostraca, however, become
236 MANUAL OF ZOOLOGY SECT.
fixed in the adult condition as external parasites, mainly
of fishes. Many of those parasitic Entomostraca undergo
a degradation of structure, a retrograde metamorphosis, as it
is termed. Comparatively highly organised in their free-
swimming larval stages, these lose when they attain the adult
parasitic condition some, if not all, of their characteristic
crustacean features, and may lose all trace of segmentation
and of jointed appendages. Also characterised by degrada-
tion of structure, though in a less degree than some of the
parasitic forms, are the barnacles (Fig. 136) and acorn-
shells (Cirripedes), which are not parasitic, but are perma-
nently fixed in the adult condition to a rock or a beam of
timber or other submerged object. In the larval condition
these are free-swimming, distinctly segmented, and provided
with a number of jointed appendages ; in the adult state they
become fixed, lose their segmentation, though retaining some
of their jointed appendages, and become enclosed in a fold
of the integument in which are developed a series of cal-
careous plates. The attachment of the cirripede is by the
head; while the posterior portion of the body is free, and is
capable of being thrust out with a series of six pairs of many-
jointed appendages or cirri, borne on the thorax through a
slit in the enclosing shell. In the barnacles the head-region
is drawn out into a stalk (A, /) ; in the acorn-shells the stalk
is absent.
2. ONYCHOPHORA
The class Onychophora comprises only the aberrant genus Peripatus,
which is interesting owing to certain primitive features which it presents
— features which afford some reason for regarding it as intermediate
between such forms as the Annulata on the one hand, and the higher
Arthropoda on the other.
Peripatus (Fig. 137) is a caterpillar-like animal of approximately
cylindrical form, and not divided into segments; it has a fairly well-
X PHYLUM ARTHROPODA 237
marked head and a series (14-42) of short stumpy appendages. The
integument is thrown into a number of fine transverse wrinkles and is
FIG. 137. — Peripatus capensis, lateral view. (From Balfour.)
beset with numerous conical papillae, each capped with a little chitinous
spine. The head (Fig. 138) bears a pair of antennas, a pair of eyes, a
FIG. 138. — Ventral view of head of Peripatus capensis, with antennae, jaws, oral
papillae, and first pair of legs. ('After Balfour.)
pair of jaws, and a pair of short processes — the oral papilla. On the
surface of the oral papillae are situated a pair of glands, the slime glands.
238
MANUAL OF ZOOLOGY
SECT.
-dycn
FIG. 139. — Dorsal view of the internal organs of PeripatuS. an, anus; ant, an-
x PHYLUM ARTHROPOD A 239
Each jaw is composed of two curved, falciform, chitinous plates; they
lie at the sides of the mou^h enclosed by a circular lip. The jaws, as
well as the oral papillae, are developed as modified limbs. The legs are
not jointed; each consists of a proximal part and a small distal part or
foot, terminating in a pair of horny claws.
In the internal anatomy (Fig. 139) the most important features are the
presence of organs of respiration in the form of tracheae, unbranched or
little branched tubes, groups of which open on little depressions of the
integument, the external openings or stigmata of which are in some
species distributed irregularly over the surface, in others arranged in
longitudinal rows; the presence of a series of pairs of nephridia (iiepti)
similar to those of the Annulata, and of a nervous system consisting
of a brain (brri), situated in the head, and two widely separate nerve
cords (ne. co) which run parallel with one another throughout the
length of the body, and are not dilated into distinct ganglia. The
sexes are distinct.
The various species of Peripatus are all terrestrial, and are found in
damp localities under bark, or dead timber, or stones. Four species
occur in South Africa, one in South America, and one in the West
Indies, one in New Zealand, and two in Australia.
3. THE MYRIAPODA
The class Myriapoda, including the centipedes and the
millipedes, consists of tracheate Arthropoda, which bear
many features of resemblance to the insects. There is a
distinct head, bearing a single pair of many-jointed antennae,
a pair of eyes, and from two to four pairs of jaws ; and a
trunk, not distinguishable into regions, but consisting of
a number of similar segments, each bearing either one pair
of legs or two. A system of air-tubes or tracheae similar to
those of Peripatus or the insects open by a series of stigmata
(in centipedes on alternate segments) on the sides or lower
surfaces of the segments.
The head in the Myriapoda (Fig. 140) is as well marked
off as in an insect ; it appears to be composed of about four
240
MANUAL OF ZOOLOGY
SECT.
fused segments. The antenna consist sometimes of many,
sometimes of comparatively few seg-
ments. A pair of eyes, situated on
the dorsal surface of the head, con-
sist of aggregations of ocelli except
in Scutigera, in which there are com-
pound eyes, differing, however, in
their structure from those of insects.
There are in millipedes a movable
labrum, a pair of mandibles, and a
pair of fused maxilla. In the cen-
tipede there are three pairs of jaws
in front of the poison- fangs. The
mandibles have no palps ; one or
both pairs of maxillae usually possess
palps.
The number of segments in the
body varies from 12 to 173. In the
millipedes (Diplopoda) the dorsal
walls of the segments are very
strongly arched ; in the centipedes
(Chilopoda) the segments are all
dorso-ventrally compressed, with dis-
tinct tergal and sternal shields
(scuta) separated laterally by inter-
vals of comparatively soft skin on
which the stigmata open. In the
centipede each segment bears a pair
of jointed legs ; of these the most
anterior pair is extended forwards
to form a pair of poison-fangs, at
FIG. 140.— Scoiopendra, orcen- the extremity of the pointed ter-
tipede. (FromCuvier's/l«- .... /• i • i i j
imai Kingdom.-) minal joint of which opens the duct
x PHYLUM ARTHROPODA 241
of a poison gland. In the millipedes each segment behind
the fourth or fifth bears two pairs of legs, the four or five
most anterior having only one pair each, except one segment
which is footless. In most of the millipedes and their allies
the appendages of the seventh segment are modified in the
male to form copulatory organs.
The enteric canal is straight and is much simpler in
character than that of the Insecta. The heart is in the form
of a long tube, consisting of as many chambers as there are
segments in the body. The breathing organs are air-tubes
or tracheae, resembling those of larval insects, such as cater-
pillars.
4. THE INSECTA
The class Insecta, comprising the cockroaches, grass-
hoppers, dragon-flies, beetles, butterflies, house-flies, and
bees, with their many allies, though it is a very extensive one,
including as it does a larger number of species than any
of the other classes of the Arthropoda, is yet characterised
by a remarkable degree of uniformity, no such extremes of
modification occurring as are observable among the Crustacea.
The body of an insect, like that of a crustacean, is segmented,
and bears a series of pairs of jointed appendages. The
surface is covered with a chitinous cuticle, forming an exo-
skeleton, which is sometimes comparatively thin, sometimes
thick and hard. Like the body of the crustacean, that of
the insect is divisible into certain regions. In the Insecta
these regions are quite constant in their disposition, and are
always three in number, — head\i\ front, thorax in the middle,
and abdomen behind. The head is found, when its develop-
ment is traced, to be formed by the union with the head-lobe
of the embryo of some five segments, but in the adult no
trace of segmentation is distinguishable. The thorax always
242 MANUAL OF ZOOLOGY SECT.
consists of three segments, which are usually firmly united
together. The abdomen contains from ten to eleven seg-
ments.
The appendages are also very constant in their arrange-
ment throughout the Insecta, though variously modified in
form in the different orders,
in accordance with differ-
ences in mode of life. The
head (Fig. 141) bears a
pair of antennae, a pair of
mandibles, and two pairs
of maxillae. The antennae
vary a good deal in size
and shape in different
insects. The mandibles
(Fig. 142, md) lie at the
FIG. 141.— Periplanetaamericana. Lateral c\Ae^ nf the month in
view of the head and its appendages. S .Ul, ]
cerv, one of the cervical sclerites; ey front Qf which is a ITlOVa-
eye; £V?«,gena; man, mandible; max1,
first pair of maxillae; max*, second pair ^\Q labnim Or Upper lip
of maxillae (labium).
(Ibr). Each mandible is
a single solid piece, and is devoid of palp. The second pair
of maxillae (mx. 2) are united in their basal portions to form
a lower lip (labium). Jointed palpi (pnt) are borne both
by the first pair of maxillae (maxillary palpi) and by the
second (labial palpi). All the jaws become differently
modified in the different orders in accordance with differ-
ences in the nature of the food. Insects, which like cock-
roaches and beetles, masticate hard substances, have the
mandibles strong and sharp and the maxillae well developed,
and adapted to act as masticatory organs. Insects which,
like cicadas, bugs, lice, and plant-lice, live on the juices of
plants or animals, have the jaws in the form of sharp stylets,
enclosed in a sheath or proboscis, for piercing the integu-
PHYLUM ARTHROPODA
243
ment. Intermediate conditions also occur. In the Hyme-
noptera (bees, wasps, etc.), for example, the mouth-parts are
adapted both for biting and for licking and sucking; the
mandibles and maxillae are sharp and lancet-like, the middle
part of the labium is produced into a long median tongue,
at the sides of which are a pair of accessory tongues (para-
mx,
M,
FIG. 142. — Mouth-parts of the Cockroach, lor, labrum; md, mandible; mx ^ an-
terior pair of maxillae; >«, mentum; me and mi, outer and inner divisions of the
second pair of maxilla;; //, labial palp; pm, maxillary palp; st, stipes; sm,
submentum. (From Lang's Comparative Anatomy.)
glossa). In the Hemiptera (bugs, lice, etc.) the labium is
modified to form a sucking proboscis enclosing the stylet-
like mandibles and maxillae.
In the Diptera (house-flies, gnats, etc.) the mandibles,
244 MANUAL OF ZOOLOGY SECT.
usually not developed in the males, are biting or piercing
organs, while the basal parts of the labium form a proboscis
enclosing a sharp spine developed from a process on the
roof of the mouth (hypopharynx).
In the Lepidoptera, or butterflies and moths, the mandi-
bles are aborted in the adult and the maxillae are developed
into elongated half-tubes, which are united and form a com-
plete tube capable of being coiled up in a spiral manner
under the head, the extremity in some cases being provided
with hooks or spines for rupturing the nectaries of flowers.
FIG.
143. — Butterfly (Pieris rapae) , with caterpillar and chrysalis stages.
(After Riley.)
Each of the three segments of the thorax always bears
a pair of jointed legs which do not present such marked
modifications as the appendages of the head. The terminal
part (tarsus) is made up of a number (not more than five)
of short segments, and ends in a pair of claws, often with
an adhesive pad or sucking disc between them.
In addition to the legs, the second and third segments of
the thorax usually bear each a pair of wings. The wings
are thin transparent expansions of the integument sup-
ported by a system of branching ribs, called veins, or ner-
PHYLUM ARTHROPOD A
245
vures. In most of the butterflies and moths (Fig. 143) the
wings are opaque, owing to their being covered with numer-
ous overlapping microscopic scales to which the various
colours of the wing are due. In the beetles (Fig. 144),
locusts, and others, on the other hand, the posterior wings
alone are membranous, the anterior pair being converted
into hard and tough cases — the elytra — which, when
folded up, cover over and protect the delicate posterior
wings. In the bugs and their allies, the anterior wings are
FIG. 144. — d, Carpet beetle (Anthrenus scrophulariae) with larva a, b, and pupa, c.
(After Riley, from Bulletin of Division of Entomology, United States Depart-
ment of Agriculture.)
thick and opaque at the bases only. In the house-flies,
gnats (Fig. 145), and their allies (order Diptera), the ante-
rior wings alone are developed, the posterior being rep-
resented by vestiges, the halteres or balancers. In the
bee-parasites the posterior pair of wings are alone devel-
oped, the anterior pair being vestigial. In some insects
(springtails, lice, fleas) wings are entirely absent in all
stages. In others again, as certain moths, they are present
in one sex — usually the male — and absent in the other.
246
MANUAL OF ZOOLOGY
SECT.
The abdomen is devoid in the adult, except at the
posterior extremity, of any paired limbs. At the posterior
end there are frequently appendages forming the sting,
ovipositor and genital processes, which may be of the
nature of modified limbs.
FIG. 145. — Culex, mosquito, and larva. (After Guerin and Percheron.)
The digestive canal (Fig. 146) consists of a number of
parts. It is nearly always considerably longer than the
body, and is longer in vegetable-feeding than in carnivorous
forms. The mouth leads into a buccal cavity into which
the ducts of a pair of large salivary glands open.
Following upon this is a narrow (esophagus (n, ventral view. tem comprises an oesophageal nerve-
an, anus; cten, ctenidia; ft, foot;
mant, mantle edge; mo, mouth, ring, consisting of a thicker dorsal
cerebral portion not differentiated into
ganglia, and a thinner ventral buccal commissure. Two pairs of longi-
tudinal nerve-cords, pedal and pallial, are given off from this poste-
riorly. The former, which give off nerves to the foot, are joined by
numerous commissures passing beneath the enteric canal. The large
cords contain nerve-cells throughout their length.
The conspicuous organs of special sense present on the head of Gas-
tropods (see p. 289) are absent in the Chitons. A pair of processes
situated in front at the sides of the mouth have the character of labial
palps. Remarkable sensory organs, the micrcesthetes and the megalas-
thetes, lie in the canals already mentioned as occurring in the super-
X!
PHYLUM MOLLUSCA
283
ficial layer of the shell valves. The megalaesthetes may take the form
of eyes, with cornea, lens, pigment layer with iris, and retina.
There are two symmetrical nephridia (Fig. 170) opening internally
into the pericardium by a ciliated funnel-like opening (n.peri. #/), and
mo
den
neph.
€171
FIG. 170. — Chiton, nephridial and genital systems, an, anus; cten, ctenidia; gen.
ap, genital aperture; gon, gonad; gonod, gonoduct; mo, mouth; neph. ap,
nephridial aperture; n.peri. ap, aperture from nephridia to pericardium. (From
Simroth, after Haller and Lang.) «
opening on the exterior {neph. «/), between two of the posterior
ctenidia. Each consists of a looped main tube, into which open
numerous minute tubules which ramify among the viscera. The sexes
are distinct. The testis and ovary (gon} are similar in appearance,
284 MANUAL OF ZOOLOGY SECT.
differing only in colour when the products are mature. Each is an un-
paired sac marked by a series of slight lateral constrictions. The larva
is a Trochosphere.
All the Amphineura are marine. The Placophora (Chitons) occur
at all depths, thougn most abundant on the shores between tidal limits.
The shell-less forms (Aplacophora),on the other hand, are rare in very
shallow water, and absent altogether from the littoral zone; some have
been found at considerable depths (down to 1250 fathoms). The Placo-
phora are all vegetable feeders, their food consisting of minute algae
and diatoms. The Aplacophora subsist on small animals. The Placo-
phora, when at rest, adhere firmly to the surface of a rock or a block
of coral by means of the sucker-like foot. When forcibly detached the
animal curls itself up into a ball, and will only after a considerable time
slowly extend itself again. All their movements are extremely slug-
gish. The Aplacophora are unable to fix themselves in this way; many
of them occur twined round the stems of zoophytes, sometimes attached
by a thread of viscid mucus.
3. THE GASTROPODA
The class Gastropoda comprises the snails and slugs,
limpets, whelks, periwinkles, sea-hares, and the like.
They are distinguished by the possession of a shell of a
univalve character, consisting of a single piece, and by the
mantle not being developed into two lateral folds, as in the
Pelecypoda. There is a distinct head, bearing eyes and
tentacles. The body is inequilateral, and the foot is ven-
trally situated, forming a large creeping disc.
If we look at a living Gastropod, such as a snail (Fig.
171) when fully extended, the want of symmetry appears
at first sight to be limited' to the spiral shell, which is in
itself unsymmetrical, and is held obliquely, the head part
and the "tail " part appearing when superficially examined,
quite bilaterally symmetrical. But a closer examination,
especially after removal of the shell, shows that the depar-
xi PHYLUM MOLLUSCA 285
ture from symmetry is very marked. The left side of the
body has become very much more strongly developed than
the right, and this side of the body is drawn out into a
spirally twisted prominence — the visceral spiral — enclos-
ing the liver and other organs. The anal aperture, instead
of being median and posterior, is situated on the right side,
and in front of it on the same side is the reproductive
aperture.
oc.tent
lent
FIG. 171. — Helix nemoralis. an, anus ; gen. ap, genital aperture ; oc. tent, pos-
terior eye-bearing tentacles ; pulm, opening of pulmonary sac ; tent, anterior
tentacles. (After Pelseneer.)
The shell is of simple conical form in the limpets. In
most of the Gastropoda it is in the shape of a spiral (Figs.
J72» 173) with the turns usually in close contact with one
another, the inner walls of the turns coalescing to form an
axial, hollow, or solid column — the columella. By far the
greater number of such spiral shells are dextral, i.e., if we
begin at the apex of the spiral to reach the opening of the
shell we have to pass from left to right with the columella
always on our right-hand side ; in a few cases, however, the
spiral is sinistral, taking the opposite direction from that
of the ordinary dextral shell. The form of the shell varies
with the degree of obliquity with which the whorls are set
286
MANUAL OF ZOOLOGY
SECT.
on the axis. When the obliquity is very slight (Fig. 174),
the spiral is nearly flat; when the obliquity is great, an
elongated tapering shell, such as that represented in Fig.
175, is the result. Sometimes the later whorls completely
FIG. 172. — Shell of Triton nodiferus. Natural size. New Zealand.
cover over the earlier ones, so that the spiral form of the shell
is concealed. Sometimes only the apical portion of the shell
is spiral, the remainder being a straight or sinuous cylinder.
The mouth of the shell has usually a prominent margin or
XI
PHYLUM MOLLUSCA
287
peristome, which is sometimes entire and continuous, some-
times is broken by a deep notch or a spout-like prolonga-
tion or canal, formed in connection with the development
FIG. 173. — Longitudinal median section of the shell of Triton nodiferus.
of a spout-like prolongation of the mantle, the siphon,
which lies in it. The mouth of the shell in many Gastro-
poda is capable of being closed by means of an operculum
288 MANUAL OF ZOOLOGY SECT.
borne on the foot. In some terrestrial forms in which an
operculum is absent, the opening may be closed up during
winter by a layer of hardened mucous matter to which the
name of epiphragm is applied. Lateral folds of the mantle
are in some of the Gastropoda (Fig. 176) reflected over
the shell, and may completely cover it. In some cases
these folds unite by their edge, so that the shell comes to
be enclosed in a complete sac of the mantle; such enclosed
shells are always imperfectly developed and incapable of
covering the body. Thus in Aplysia (the "Sea-hare ") and
FIG. 174. — Shell of Solarium perspectivum from the under side.
(From the Cambridge Natural History.)
other allied forms the shell is greatly reduced, thin and
horny, and concealed within the mantle, while in the
nudibranch (Fig. 177), members of the same sub-order, it
is entirely absent. The shell is also completely absent in
some of the pelagic forms (Hctcropoda and Pteropoda) \ in
others, though present and external, it is too small to
enclose the animal. In the slugs the shell is vestigial and
concealed by the mantle.
The Gastropoda have a well-marked head, separated
from the body by a constriction or neck. The mouth,
XI
PHYLUM MOLLUSCA
289
situated at the anterior end of the head on its ventral
aspect, is in many instances provided with a protrusible
probosis or introvert, sometimes of considerable length.
On the dorsal surface of the head are a
pair of tentacles which vary a good deal in
shape, but are usually cylindrical or club-
shaped. In most cases the eyes are situ-
ated on tubercules at the bases of the ten-
tacles, or elevated towards the middle;
but in the snails and slugs (Pulmonata)
(Fig. 171) the eyes are elevated on the
extremities of a second, longer pair of
tentacles (pc. tent} placed behind the first.
The mantle is usually developed into a
fold, the mantle-flap, originally posterior,
but subsequently becoming shifted round
to the right-hand side. This covers over
a cavity, the mantle-cavity, situated ante-
riorly, in which are situated the anal and
nephridial apertures and the ctenidia. The
edges of the mantle-flap may become united
together in such a way as to form a cham-
ber opening on the exterior by a compara-
tively narrow opening. In many the edges
of this aperture are drawn out into a spout-
like prolongation open ventrally, the
siphon, which lies in the corresponding
prolongation of the peristome of the shell,
and serves as a channel for the ingress FIG. 175. — Shell of
and egress of water. In some Gastro-
pods, however, there is no definite mantle-cavity, the anus,
nephridial apertures, and ctenidia merely lying under cover
of a comparatively slightly developed lateral mantle-flap.
290
MANUAL OF ZOOLOGY
SECT.
The foot varies in the extent of its development in the
different families of the class. It usually presents an
elongated, flat, ventral surface on which the animal creeps
FIG. 176. — Cypraea moneta (Cowrie). Showing the mantle, provided with marginal
tentacles, partly enveloping the shell. Br, branchia; M, M, mantle; F, foot;
T, tentacles at the edge of the mantle. (From Cooke, after Quoy and Gaimard.)
by wave-like contractions of the muscular tissue. In the
typical Gastropods the foot is usually distinguishable into
three parts, a middle part or mesopodium which is the most
lr
FIG. 177. —Doris (Archidoris) tuberculata. a, anus; 6r, branchiae; nt, penis;
rh, rh, tentacles. (From the Cambridge Natural History.')
important, with a smaller anterior propodium and posterior
metapodium. The whole foot becomes reduced in a few
Gastropods that remain fixed. The metapodium very fre-
XI
PHYLUM MOLLUSCA
291
quently bears a disc or stopper, the operculum, usually
horny, or partly calcified, by means of which the aperture
of the shell is closed when the animal is retracted.
In some forms, such as the sea-hares (Aplysia), the foot
develops a pair of lateral lobes, the epipodia, which act as
fins; and in the Pteropods (Fig. 178), which are specially
modified for a pelagic existence, these constitute the largest
part of the foot.
The organs of respiration in the majority of the aquatic
Gastropoda are in the form of gills or ctenidia, usually plume-
shaped appendages consisting'of a central stem bearing two
FIG. 178. — Shell-bearing Pteropoda. /,/, fins; /, liver; o, ovary; sk, shell.
(From Cooke, after Souleyet.)
rows of compressed filaments or lamellae, or a single row.
Two ctenidia may be present or only one may be developed;
they are enclosed in the mantle-cavity.
In the Nudibranchs two ctenidia are absent, but their
place as breathing organs is taken by a number of secondary
branchia, sometimes simple, sometimes branched or pin-
nate processes, which are distributed over the dorsal surface,
as in Eolis, or as in Doris (Fig. 177), forming a circlet
surrounding the anus, or, as in Pleurophyllidia, a row on
each side beneath the mantle-flap.
292 MANUAL OF ZOOLOGY SECT.
In the limpets (Patella and its allies1) (Fig. 179) the
true ctenidia are represented only by a pair of vestiges,
and respiration is carried on by a number of secondary
branchiae (g. /) in the form of lamellae situated between the
short lateral fold of the mantle and the foot. In the Pul-
monata, and in some members of other groups, ctenidia are
absent, and the mantle-cavity, completely enclosed except
sh
TUB-
FIG. 179. —Patella vulgata, seen from the ventral side. /, foot;^. /, circlet of
gill lamellae; m. e, edge of the mantle; mu, attachment muscle; si, slits in the
attachment muscle; sh, shell; v, efferent branchial vessel; v't aorta; ve, smaller
vessels. (From the Cambridge Natural History.}
for a small rounded opening, has the function of a pul-
monary sac or Jung (Fig. 180), its roof being richly sup-
plied with blood-vessels; in the aquatic forms its function
is apparently as much hydrostatic as respiratory. In some
of the Pulmonata there is a return to a completely aquatic
mode of respiration accompanied by the development of
1 Our common eastern American limpet is Acmaa testudinalis.
xi PHYLUM MOLLUSCA 293
secondary gills — vascular processes of the wall of the
mantle-cavity.
FIG. 180. — Pulmonary cavity and related parts in a slug (Limax). aort, aorta;
aur, auricle; neph, nephridium; peric, pericardium, laid open; pul. ap, pul-
monary aperture ;/«/. v, pulmonary vein with its ramifications; rect, rectum;
ur, ureter; vent, ventricle. (After Pelseneer.)
Digestive Organs. — In many Gastropods there is a long
proboscis capable of being everted and retracted, at the
extremity of which the mouth is placed. A single curved
horny jaw lies on the roof of the buccal cavity in the Pul-
monata; in most marine Gastropoda the place of this is
taken by two lateral pieces.
A characteristic feature of the alimentary canal of the
Gastropoda, which, however, they share with some Amphi-
neura and with the Cephalopoda, is the possession of an
odontophore and radula, situated in a thick-walled chamber,
the buccal cavity, into which the mouth opens. From the
floor of the cavity rises an elevation, the odontophore, which
is somewhat elongated in the direction of the long axis of
the body and compressed laterally. Over the summit of
the odontophore runs longitudinally a narrow strap-like
body, the radula or lingual ribbon (Fig. 181, rad), beset
294
MANUAL OF ZOOLOGY
SECT.
with numerous minute horny or siliceous teeth arranged in
transverse row?. Posteriorly this toothed ribbon extends
into a narrow curved pouch, the radular sac (Fig. 181, rad.
sac), extending backwards from the posterior and lower
aspect of the buccal cavity. Anteriorly it does not extend
beyond the odontophore prominence. The latter contains
cartilages (cart), serving for the support of the whole appa-
ratus, and is capable of being extruded, with the radula
which it bears, through the opening of the mouth by the
contraction of sets of protractor muscular fibres. Inserted
bod.
Jaw
rCLCJt-.SCLC
FIG. 181. — Triton nodiferus. Diagrammatic longitudinal vertical section of buccal
cavity, bod. cav, body cavity; cart, cartilage of odontophore; jaw, right jaw;
ces, oesophagus; rad, radula; rad. sac, radula sac.
into the radula itself are sets of bands of muscular fibres by
which it can be drawn backwards and forwards over the
odontophore as over a pulley, the effect being a rasping of
any hard substance against which it is pressed. The entire
buccal cavity is capable of being drawn forwards towards
the mouth opening, or backwards into the introvert, by the
contraction of strands of muscular fibres passing from its
wall to the wall of the body.
The heart is enclosed, as in the fresh-water mussel, in a
Xi PHYLUM MOLLUSCA 295
cavity, the pericardium. It consists, in nearly all cases, of
only two chambers, an auricle and a ventricle.
The nervous system and organs of special sense are in
most Gastropoda more highly developed than they are in
the fresh-water mussel. There are distinct cerebral and
pleural, as well as pedal and visceral, ganglia. Well-
developed eyes are present in the majority, and there are
otocysts, osphradia or water-testing organs, and usually
olfactory organs in the shape of special groups of cells on
the tentacles.
The nephridia are granular tubes or chambers communi-
cating, as in the fresh-water mussel, with the pericardial
cavity on the one hand, and with the exterior on the other.
Two nephridia right and left may be present, or only one.
The sexes are separate in some Gastropoda; in others,
such as the snails and slugs, they are united; and in the
latter case their structure is highly complex. The larva is
a Trochosphere, which subsequently develops into a form
known as the Veliger. In the Veliger the prototroch, or
ciliated prae-oral ridge of the Trophosphere, becomes drawn
out into a bilobed flap bordered with strong cilia. There
is a shell, a distinct foot bearing an operculum, and ten-
tacles and eyes are present on the head-region. The shell
is at first of simple conical form and the anus is placed in
the middle line posteriorly. It is only as development
advances that one side of the body becomes more rapidly
developed than the other, and the anus becomes shifted
forwards, the shell at the same time in the great majority
taking on a spiral form, and the visceral prominence
enclosed within it acquiring a corresponding shape.
Two main divisions or sub-classes of the Gastropoda are
recognised — the Streptoneura and the Euthyneura. The
former comprises the majority of the marine univalves,
296 MANUAL OF ZOOLOGY SECT.
such as the limpets, ear-shells, cowries, tritons, whelks, and
cones. The latter includes the water-breathing sea-hares
and nudibranchs and the air-breathing snails and slugs.
The chief general points of distinction between the two
groups are that in the Streptoneura the visceral nerve-cords
are twisted into a figure 8, and the sexes are separate,
while in the Euthyneura the twisting of the nerve-cords is
absent and the sexes are united in the same individual.
Only a few aberrant families of Gastropoda are parasites.
Most are aquatic, all the most primitive forms being in-
habitants of the sea. Of the marine families the majority
move by creeping over the sea-bottom, some burrowing in
mud or sand, some in solid rock; some are able to float in
a reversed position, adhering to frothy mucus secreted by
the glands of the foot; certain exceptional forms such as
Vermetus are fixed in the adult condition by the substance
of the shell. A few families — the Heteropoda and the
Pteropoda — are specially modified for a pelagic mode of
existence, and swim through the water by flapping move-
ments of the lobes of the foot, which act as fins. Gastro-
pods are found at considerable depths — up to nearly three
thousand fathoms — in the ocean. Many forms, however,
are inhabitants of fresh water, while many Pulmonata are
terrestrial, and occur even towards the summits of the
highest mountains.
4. THE CEPHALOPODA
The class Cephalopoda, including the cuttle-fishes, squids,
Octopi, argonauts, and Nautili, is the highest of the Mollusca,
its members being very much more active and powerful
in their movements than the rest of the Mollusca, and much
more highly endowed as regard their higher senses. The
xr
PHYLUM MOLLUSCA
297
body (Figs. 182, 183, 185, 187) is bilaterally symmetrical.
The foot, instead of extending along the ventral surface
FIG. 182. — Sepia cultrata.
Entire animal viewed from the dorsal aspect. New
Zealand.
of the body in the region behind the mouth, as it does in
Pelecypoda and Gastropoda, occupies a more anterior posi-
298
MANUAL OF ZOOLOGY
SECT.
tion, and surrounds the mouth. A distinct head is pres-
ent, and the foot assumes the appearance of a system of
appendages of the head. In the cuttle-fishes (Fig. 182),
jaws inf
cart
manl -
sejbt
FIG. 183. — Nautilus pompilius, diagrammatic lateral view of a female specimen
enclosed in its shell, cart, cartilage; cten, ctenidia; hd, hood; inf, funnel;
jaw s, jaws; mant, mantle: ntant' , dorsal mantle-fold overlapping the coil of the
shell; mus, position of lateral mass of muscle; nid, nidamental glands; sept,
first septum; siph, siphuncle. (After Keferstein. 1
squids (Fig. 187), Octopi, and Argonauts (constituting the
sub-class Dibranchiata) the main part of the foot is composed
XI
PHYLUM MOLLUSCA
299
of either eight or ten long, highly extensible and contractile
appendages, the arms, the inner surfaces of which are beset
with numerous suckers, rendering them powerful grasping
organs. These are arranged in a circlet surrounding the
mouth. The posterior part of the foot appears to be repre-
sented by the funnel, a wide tube through which water is
ch"
FIG. 184. — Section of the shell of Nautilus pompilius, showing the septa (s, s), the
septal necks (s. «., s. «.), the siphuncle (si, represented by dotted lines), and the
large body-chamber (ch}. (From the Cambridge Natural History.}
driven out from the mantle-cavity. In the Nautili (Fig. 183),
(sub-class Tetrabranchiata), the place of the arms with their
suckers is taken by a number of lobes bearing sheathed
tentacles surrounding the mouth, and a funnel is also pres-
ent, though it does not form a complete tube.
'si
300 MANUAL OF ZOOLOGY SECT.
To compare such a cephalopod as a cuttle-fish or squid
with a fresh-water mussel or a snail, it is advisable to place
it in a position which it quite naturally assumes when not
swimming, with the head and its arms downwards and
the body sloping away from this upwards and backwards.
In this position we distinguish antero-dorsal and postero-
ventral surfaces, oral and aboral extremities, and right and
left borders. A shell is present in nearly all Cephalopods,
but is only external in the female argonaut and in Nautilus.
In the latter (Fig. 184) it is in the form of a flat spiral, the
interior of which is divided by a series of transverse partitions
or septa into a corresponding series of chambers. The last
chamber opens widely on the exterior, and this alone lodges
the body of the animal, the remaining chambers being filled
with gas.
Perforating the middle of all the septa in succession is a
spiral tube — the siphuncle — continuous with the centro-
dorsal region of the visceral prominence. In the course
of its growth the body of the Nautilus shifts forwards at
intervals into a newly formed chamber, and a new sep-
tum is formed closing the latter off from the cavity last
occupied.
The Nautilus inhabits the coral reefs of the Pacific, at a
depth of a few fathoms. Of existing Dibranchiata, Spirula
(Fig. 185) alone has a shell comparable to that of Nautilus.
The shell of Spirula is of spiral form, the turns of the spiral,
however, not being in close contact. Internally it is divided
into chambers by a series of septa, and these are perforated
by a siphuncle. Again, as will be seen by comparing Figs.
183 and 185, the relation of the soft parts to the shell is the
reverse of what obtains in Nautilus, the shell of Spirula curv-
ing backwards, that of Nautilus forwards. Moreover the
shell of Spirula is an internal structure, being almost com-
XI
PHYLUM MOLLUSCA
301
pletely covered by the mantle,
cast ashore on Nantucket.
In the other Dibranchiata the shell
may consist of three parts, — a horny
pen or pro-ostracum, a calcareous
guard, and a part termed the phrag-
mocone. The last, which alone repre-
sents the shell of Spirula, has the
form of a cone divided internally by
a series of septa perforated by a si-
phuncle. These parts are most com-
pletely developed in the extinct genus
Belemnites, in which the shell con-
sists of a straight, conical, chambered
phragmocone, with a siphuncle, en-
closed in a calcareous
sheath, the guard, pro-
, , . , FIG. 18
duced into a horny or ia
Its shell has been found
. 185. — Spirula peronii,
teral view, d, terminal
sucker; f, funnel; j,, s2,
projecting portions of the
shell, the internal part of
which is indicated by dotted
lines. (From Cooke.)
calcareous plate, the
pro-ostracum. In the
cuttle-fish of the Medi-
terranean Sea (Sepia) the shell is a leaf-like
body, with a rounded and comparatively
broad oral end, and a narrower aboral pro-
vided with a sharp projecting spine. The
main mass of the shell consists of numerous,
closely arranged, thin laminae of calcareous
composition, between which are interspaces
containing gas. The spine-like projecting
point represents the guard, and the main
Sepia cuitrata, substance of the shell is to be looked upon
posterior view,
reduced. as the pro-ostracum and phragmocone, the
septa of the latter being represented by the calcareous
302
MANUAL OF ZOOLOGY
SECT.
lamellae. In Loltgo1 (the squids) the shell (Fig. 187, B) is
long, narrow, and completely horny ; it corresponds to the
pro-ostracum, the phragmocone being entirely absent.
FIG. 187. — Loligo vulgaris. A, entire animal, dorsal view; B, horny internal shell
or pen. (From Keferstein.)
In Octopus the shell is represented only by a pair of
rudiments with which muscles are connected. In Argonauta
there is no shell in the male, but the female has an external
shell (Fig. 1 88) of a remarkable character. This is a deli-
1 Our common American species is Loligo pealii.
XI
PHYLUM MOLLUSCA
3°3
cate spiral structure, the internal cavity of which is not
divided into chambers. It is not secreted by the mantle
like the shells of other Mollusca, but by the surfaces of a
pair of the arms ending in expanded disc-like extremities,
which become applied to its outer surface ; its chief func-
tion is to carry the eggs. The argonaut inhabits deep water,
70 to 100 miles off the coast of New England, its shells
being in very rare cases found cast ashore on our coast
south of Cape Cod.
FIG. 188. — Shell of Argonauto argo.
In addition to the shell there is in all the Cephalopoda an
internal skeleton of cartilage supporting and protecting the
nerve-centres and other parts.
The cuttle-fishes and other Dibranchiata when alive will
be observed to undergo frequent changes of colour, 'and
blushes of different hues are to be noticed passing over the
surface. These are due to the presence of numerous con-
tractile, pigment-containing cells or chromatophores, situated
in the deeper layers of the integument over the entire
304 MANUAL OF ZOOLOGY SECT.
surface, which contract and expand under nervous influence
(Fig. 189).
On the postero-ventral aspect of the body the mantle
encloses a wide cavity, the mantle-cavity (Figs. 190, 191),
in which the ctenidia are lodged, and on the wall of which
are situated the anal, excretory, and reproductive apertures.
The mantle-cavity communicates at its oral end by a wide
slit with the exterior; but this is capable of being closed,
771
FIG. 189. — Chromatophore of Sepia, magnified, nuc, nuclei in wall of sac ; pignt,
pigment ; rad. mus, radiating strands of muscle. (After Vogt and Jung.)
so that, when the walls of the cavity contract, a stream of
water is ejected through the funnel, and the animal is
propelled in the aboral direction. Swimming is also effected
in the Dibranchiata by means of a pair of fins in the shape
of muscular, lateral flaps. The ctenidia (cten} are plume-
like, and are either two (Dibranchiata} or four (Tetra-
branchiata) in number.
The mouth is provided with a pair of horny or calcified
jaws (Fig. 192, B) similar in shape to the jaws of a parrot.
The buccal cavity contains an odontophore. Opening into
XI
PHYLUM MOLLUSCA
305
FIG. 190. —Sepia cultrata, female seen from the posterior aspect, the wall of the
mantle-cavity divided along the middle line and the two flaps thus formed spread
out so as to expose the contents, ac, nid ', accessory nidamental glands ; an,
anal aperture with its lateral appendages : f, membranous fold attaching the
ctenidium to the wall of the mantle-cavity ; in/, external opening of funnel ; inf.
cart, infundibular cartilage: ink. s, ink-sac; ink. d, ink duct; lig, ligamentous
band which extends from the anterior wall of the mantle-cavity to the ovary, cut
across ; liv, liver : /. cten, left ctenidium ; /. neph, left nephridial aperture ; l.nid,
left nidamental gland ; /. st. g, left stellate ganglion : matii. cart, mantle cartilagf ;
mo, mouth ; mus, neck muscles ; ov, ovary ; ovid, oviduct; rec, rectum.
306
MANUAL OF ZOOLOGY
SECT.
the terminal part of the intestine close to the anal aperture
is the duct of a peculiar gland — the ink gland (Fig. 193, j).
This secretes a black substance, the ink, which is discharged
when the animal is irritated or alarmed, and mingling with
the water in the mantle-cavity is discharged as a dark cloud,
under cover of which the animal may elude the pursuit of
an enemy.
The heart and vascular system reaches a high stage of
development. The heart consists of a median ventricle and
FlG. 191. — Nautilus pompilius, interior of mantle-cavity of a male specimen with
the postero-ventral wall reflected, a. I. neph.af>,o\&\ left nephridial aperture;
an, anus • cten, ctenidia : /. J1 ap, left reproductive aperture : / ant. 0s, left oral
osphradium : / vise rt/, left viscero-pericardial aperture : want, flaps of mantle;
pen, penis : / /. neph ap, aboral left nephridial aperture : p. r. neph. ap, aboral
right nephridial aperture; post, os, aboral osphradia ; r. vise, ap, right viscero-
pericardial aperture.
two or four elongated lateral auricles or branchio-cardiac
vessels conveying the blood from the ctenidia to the ventricle.
The nervous system is highly developed, and its principal
central parts, representing the cerebral, pedal, and visceral
ganglia of other molluscs, with their commissures and con-
XI
PHYLUM MOLLUSCA
307
nectives, form a ring round the gullet. There are a pair of
large eyes situated on the head. In the cuttle-fishes and
other Dibranchiata these have a highly complicated structure,
FIG. 192. — Sepia officinalis, jaws. A, in
situ; B, removed and slightly enlarged.
( From the Cambridge Natural History,)
FIG 193. - Sepia officinalis, enteric
canal, a, anus; b. d, one of the
bile ducts; b. m, buccal mass; c,
caecum; z', ink-sac; i. d, ink-duct;
j, jaws; /, /, liver lobes; ce, oesoph-
agus; p, pancreatic appendages1;
r, rectum; s. g, salivary glands;
st, stomach (From the Cambridge
Natural History.)
and contain representatives of all the principal parts of the
eye of a fish or other vertebrate. In Nautilus the eye is of
1 This organ is by Sedgwick regarded as renal in its nature, being the
unpaired portion of the kidneys. (See Sedgwick's Text-book of Zoology,
i, pp. 433,437.)
3o8 MANUAL OF ZOOLOGY SECT.
much simpler structure. There is a pair of otocysts, and
sensory processes or depressions supposed to be olfactory
are also present. Osphradia occur only in Nautilus.
There are either two (Dibranchiata) or four (Tetra-
branchiata) nephridia, which are in the form of sacs opening
into the mantle-cavity, and in the Dibranchiata communi-
cating with the pericardium. Through each of these runs
one of the principal veins, round which the secreting tissue
of the nephridium is aggregated.
The sexes are distinct. The ova are always large, con-
taining a large quantity of yolk. No metamorphosis, such
as is general in other groups of Mollusca, is known to occur
in any Cephalopod.
The Cephalopoda 'are all marine, "and range from tidal
limits to a considerable depth. Squids swim like fishes in
schools, rising to the surface and darting out of the water,
and sometimes leaping so vigorously as to fall on the decks
of large vessels. A large number are pelagic. They are,
nearly without exception, carnivorous. In length they range
from an inch or two to as much as fifty feet — the gigantic
members of the group, such as Architeuthis , being by a long
way the largest of invertebrate animals, and like the other
classes of Mollusca they are most abundant in tropical and
warm temperate seas.
As already stated, the class is divided into two sub-classes,
the Dibranchiata and the Tetrabranchiata — the latter com-
prising only the Nautili (in addition to many fossil forms),
the former including all the rest of the living members of
the class. In the former the forefoot assumes the character.
of a circlet of either eight or ten arms bearing suckers sur-
rounding the mouth. The funnel forms a complete tube.
The shell is usually internal ; when external its cavity is not
divided by septa. There are two ctenidia, two nephridia,
XI
PHYLUM MOLLUSCA
309
and two auricles. An ink gland is present. In the latter,
on the other hand, the forefoot has the character of lobes
bearing tentacles ; the funnel does not form a complete
FIG. 194. — Oral surface of a male (A) and female (B) Nautilus pompilius in an
expanded state, J natural size, linear, a, shell; b, external annular lobe carry-
ing 19 tentacles on each side, and anteriorly enlarged to form the hood; c, right
and left inner lobes, each carrying 12 tentacles in the female, and divided in the
male into two parts; d, posterior inner lobe; e, oral cone; _/", tentacles of the
outer annular lobe projecting from their sheaths; g, two anterior tentacles of this
lobe belonging to the hood; /, superior, k, inferior, ophthalmic tentacle; /, eye;
«, lamellated organ on the posterior inner lobe of the female; tn, paired lami-
nated organ on each side of the posterior inner lobe of the female; o\ funnel;
/, spadix; g, antispadix. (After Bourne, from Sedgwick.)
tube. There is an external, chambered, spiral shell. There
are four ctenidia, four nephridia, and four auricles. The
ink gland is absent.
SECTION XII.— PHYLUM CHORDATA
THE Phylum Chordata comprises all the vertebrate ani-
mals (fishes, amphibians, reptiles, birds, and mammals),
together with the Urochorda or Aseidians, and the^Adelo^
Chorda or Balanoglossus and its allies. The name Chordata
is derived from one of the most important of the few but
striking common features by which the members of this
extensive phylum are united together — the possession,
Cither in the^min^cojidition^ or throughout ..life— of a .
structure termed the chorda dorsalis or notochord. This is
^ __ - -- — .— . • - — —
acord only^f cells, typically developed from the endoderm,
extending along the middle line on the dorsal side of the
enteric cavity, and on the ventral side of the central part
of the nervous system. It becomes enclosed in a firm
sheath and forms an elastic supporting structure. In the
Vertebrata (with the exception of Amphioxus and the lam-
preyTand"liag3shes) it becomes in_the adult replacejjjrinre.
or less completely by a segmented bony or cartilaginous
axis — the spinal or vertebral column. Another nearly uni-
versal common feature of the Chordata is the perforation
of the wall of the pharynx, either in the embryonic or larval
condition only, or throughout life, by a system of clefts —
the branchial clefts ; and a third is the almost universal
presence at all stages, or only in the larva, of a cavity or
system of cavities, the neuroctzle, in the interior of the body,
lying above the central nervous system/^
310
SECT, xii PHYLUM CHORDATA
1. TflV ADELOCHORDA
Of somewhat doubtful relationships both to
one another and to the other Chordata are cer-
tain remarkable marine animals which have
been grouped together under the name of
Hemichorda or Adelochorda. These are
Balanoglossus •&&& its allies, which occur in.
shaTjoy water on the coasts of rnnst of the
warmer parts of the world, ancJLtwo are deep-
sea animals, Rhabdopleura and Cephalodiscus.
Balanoglossus (Fig. 195) is a soft-bodied,
cylindrical, worm-like animal, the surface of
which is uniformly ciliated. It is divisible into
three regions ^Lm front there is a large, club-
shaped, hollow organ — the
diately behind the proboscis and encircling its
base is a prominent fold — the collar ;(^jjf\o.
third region or trunk is long and nearly cylin-
drical, but somewhat depressed.
Balanoglossus lives in the sea, burrowing
in sand or mud by means of its proboscis. It
occurs as far north as Salem, Mass., between
tide-marks. Numerous glands in the integu-
ment secrete a viscid matter to which grains
of sand adhere in such a way as to form a
fragile temporary tube. The proboscis (Fig.
195, pr, Fig. 196, proti) has muscular walls;
its cavity opens on the exterior usually by a
single minute aperture — the proboscis pore
(Fig. 196, prob. po} — rarely by two. The
collar (Fig. 195, cd) is also muscular, and
contains one cavity or two (right and left)
separated from one another by dorsal and
ventral mesenteries, and completely cut off
from the proboscis. The collar cavity com-
municates with the exterior by a pair of collar
pores — ciliated tubes leading into the first
gill-slit or first gill-pouch.
-br
312
MANUAL OF ZOOLOGY
SECT.
On the dorsal surface of the anterior part of the trunk is a double
row of small slits — the gill-slits (Fig. 195, br^) — each row situated in
a longitudinal furrow; these slits increase in number throughout. The
div
prob. ske-l
dors.v
FIG. 196. — BalanoglOSSUS. Diagrammatic sagittal section of anterior end. card,
s, cardiac sac; div, diverticulum (supposed notochord) ; dors, n, dorsal nerve
strand; dors, sin, dorsal sinus; dors, v, dorsal vessel; mo, mouth; prob, pro-
boscis; prob. po, proboscis pore; prob. skel, proboscis skeleton; vent, n, ven-
tral nerve strand; vent, v, ventral vessel. (After Spengel.)
ccelom of the trunk is divided into two lateral closed cavities by a verti-
cal partition (dorsal and ventral mesenteries).
The mouth (Fig. 196, ;«0,) is situated ventrally at the base of the
proboscis, within the collar. Into the dorsal half of the anterior portion
Xii PHYLUM CHORDATA 313
of the alimentary canal open the internal gill-openings. The gill-
pouches are supported by a chitinoid skeleton consisting of a number
of separate parts.
The posterior part of the alimentary canal is a nearly straight tube
with, in its middle part, paired hepatic cceca (Fig. 195, hep}, which
bulge outwards in a series of external prominences. Posteriorly it
terminates in an anal aperture situated at the posterior extremity of the
body. Throughout its length it Hes between the dorsal and ventral
divisions of the vertical partition, which act as mesenteries.
In front the dorsal wall of this anterior portion of the alimentary
canal gives off a diverticulum (Fig. 196, div], the lumen of which
extends nearly to the anterior end. This diverticulum consists of
epithelium with gland cells and of a sort of retiform connective tissue;
it is supposed to be homologous with the notochord of the typical
Chordata.
There is a blood-vascular system with dorsal (dors, z/) and ventral
(vent, v} longitudinal trunks. The nervous system consists of dorsal
{dors, n) and ventral strands (vent. «), which extend throughout the
length of the body. The part of the dorsal cord which lies in the collar
lies deeper than the rest, and contains a canal or a number of spaces.
Between the collar and the trunk the dorsal and ventral strands are
connected by a ring- like thickening. There are no organs of special
sense.
The sexes are separate; the ovaries and testes are saccular organs
arranged in a double row along the branchial region of the trunk and
further back; they open on the exterior by a series of pores.
The course of the development differs in different species. In some
it is comparatively direct; in others there is a metamorphosis. In the
latter case the embryo assumes a larval form termed Tornaria, which
is somewhat like an Echinoderm larva, with a pair of ciliated bands,
one of which is considered prae-oral, and the other post-oral, and an
independent circlet of strong cilia at the posterior end.
Usually associated with Balanoglossus are two aberrant animals —
Cephalodiscus and Rhabdopleura — formerly regarded as Polyozoa.
These both resemble Balanoglossus in having the body divided into
three parts or regions — a proboscis, with a proboscis cavity, a collar
with a collar-cavity communicating with the exterior by a pair of collar-
pores, and a trunk with two distinct lateral cavities; and in the presence
of a structure resembling a notochord with the same relations to the
MANUAL OF ZOOLOGY
SECT.
nervous system as in Balanoglossus. They both differ from Balano-
glossus in having the alimentary canal bent on itself, so that the anal
opening is situated not far from the mouth, in the presence of tentacles
arising from the collar; and in the comparatively small size of the
proboscis.
2. THE UROCHOIIDA
«
Still more unlike a vertebrate in general appearance than Balano-
glossus, and yet, as the earlier stages show, indubitably to be assigned
to the Chordate phylum, are the Ascidians or Sea-squirts and their
allies.
Sea-squirts are familiar objects on rocky sea-
shores, where they occur often in large associa-
tions, adhering firmly to the surface of the rock.
They also live free in sand and in mud, at differ-
ent depths, some being deep-sea forms. When
touched the Ascidian ejects with considerable
force two fine jets of sea-water, which are found
to proceed from two apertures on its upper end.
The shape of the Ascidian, however, can only
be profitably studied in the case of specimens
that are completely immersed in the sea-water,
specimens not so immersed always undergoing
contraction. In an uncontracted specimen l
(Fig. 197) the general shape is that of a short
cylinder with a broad base by which it is fixed
to the rock. The free end presents a large
rounded aperture, and some little distance from
it on one side is a second of similar character.
FIG. 197. — Ascidia, en-
tire animal seen from The former aperture is termed the oral, the
the right - hand side.
(After Herdman.)
latter the atrial. A strong current of water
will be noticed, by watching the movements of
floating particles, to be flowing steadily in at the former and out of the
latter. When the animal is removed from the water both apertures
become narrowed, so as to be almost completely closed, by the contrac-
1 The European species, whose anatomy is here described, is approxi-
mately represented by our common large Ascidia callosa, which lives in
deep water off the Maine coast.
XII
PHYLUM CHORDATA
3'5
tion of sphincters of muscular fibres which surround them. At the same
time the walls *of the body contract, streams of water are forced out
through the apertures, and the bulk becomes considerably reduced.
or.ap
at rap
FIG. 198. — Dissection of Ascidia from the right-hand side. The greater part of the
test and mantle has been removed from that side so as to bring into view the
relations of these layers and of the internal cavities and the course of the aljmen-
tary canal, etc. an, anus; atr. ap, atrial aperture; end, endostyle; gon, gonad;
gonod, gonoduct; hyp, hypophysis; hyp.d, duct of hypophysis; mant. mantle;
ne.gn, nerve-ganglion; aes. ap, aperture of oesophagus; or.ap, oral aperture;
ph, pharynx; stom, stomach; tent, tentacles; test, test. (After Herdman.)
The outer layer of the body-wall is composed of a tough translucent
substance forming a thick test or tunic (Fig. 198, test}. This proves,
3i6 MANUAL OF ZOOLOGY SECT.
when analysed, to consist largely of the substance cellulose, which has
already been referred to (p. 36) as a characteristic component of the
tissues of plants, and which is rare in its occurrence in the animal
kingdom.
When the test is divided (Fig. 198), the soft wall of the body or
mantle (manf), as it is termed, comes into view, and the body is
found to be freely suspended within the test, attached firmly to the lat-
ter only round the oral and atrial apertures. The mantle follows the
general shape of the test, and at the two apertures is produced into short
and wide tubular prolongations, which are known respectively as the oral
and atrial siphons (Fig. 199, atr. siph}. These are continuous at their
margins with the margins of the apertures of the test, and round the
openings are the strong sphincter muscles by which closure is effected.
Within the body-wall is a cavity, the atrial or peribranchial cavity
(atr. cav) communicating with the exterior through the atrial aperture.
The oral aperture leads by a short and wide oral passage into a
chamber of large dimensions, the pharynx or branchial chamber (ph).
This is a highly characteristic organ of the Urochorda. Its walls are
pierced by a number of slit-like apertures, the stigmata (Fig. 199, stig}
arranged in transverse rows. Through these the cavity of the pharynx
communicates with the atrial or peribranchial cavity, which completely
surrounds it except along one side. The edges of the stigmata are
beset with numerous strong cilia, the action of which is to drive currents
of water from the pharynx into the atrial cavity. It is to the move-
ments of these cilia lining the stigmata that are due the currents of
water already mentioned as flowing into the oral and out of the atrial
apertures, the ciliary action drawing a current in through the oral
aperture, driving it through the stigmata into the atrial cavity, whence
it reaches the exterior through the atrial aperture. The stigmata are
all vertical in position; those of the same row are placed close together,
separated only by narrow vertical bars; neighbouring rows are sepa-
rated by somewhat thicker horizontal bars ; in all of these bars run
blood-vessels.
It has been already mentioned that the atrial cavity does not com-
pletely surround the pharynx on one side. This is owing to the fact
that on the side in question, which is ventral in position, the wall of the
pharynx is united with the mantle along the middle line. Along the
line of adhesion the inner surface of the pharynx presents a thickening
in the form of a pair of longitudinal folds separated by a groove. To
XII
PHYLUM CHORDATA
this structure, consisting of the two ventral longitudinal folds with the
groove between them, the term endostyle is applied. The cells covering
Unt
Ual
br.car
fLSc.br
slom,
ca.rtl.viao
FIG. 199. — Ascidia, diagram of longitudinal section from the left-hand side, the test
and mantle removed, atr. cav, atrial cavity; air. siph, atrial siphon; br.car,
branchio-cardiac vessel; card, vise, cardio-visceral vessel; gpnod, gonoduct;
hi, heart; hyp, hypophysis ; mant, mantle; n.gn, nerve-ganglion; aes. cesopha-
gus ; ov, ovary: rect, rectum ; stig, stigmata; stont, stomach; tent, tentacles;
test, testis; tr. v, transverse vessel; vent, v, ventral vessel; vise, br, viscero-
branchial vessel. (After Herdman.)
the endostyle are large cells of two kinds — ciliated cells and gland cells,
— the former beset at their free ends with cilia, the action of which is
3i 8 MANUAL OF ZOOLOGY SECT.
to drive floating particles that come within their influence outwards
towards the oral aperture, the latter secreting and discharging a viscid
mucous matter. Anteriorly the endostyle is continuous with a ciliated
ridge which runs circularly round the anterior end of the pharynx. In
front of this circular ridge, and running parallel with it, separated from
it only by a narrow groove, is another ridge of similar character; these
are termed the peri-pharyngeal ridges, the groove between them is the
peri-pharyngeal groove. Dorsally, i.e., opposite the endostyle, the
posterior peri-pharyngeal ridge passes into a median, much more
prominent, longitudinal ridge, the dorsal lamina, which runs along the
middle of the dorsal surface of the pharynx to the opening of the
oesophagus. The mucus secreted by the gland cells of the endostyle
forms viscid threads which entangle food-particles (microscopic organ-
isms of various kinds) ; the cilia of its ciliated cells drive these forwards
to the peri-branchial groove, around which they pass to the dorsal
lamina, and the cilia of the cells of the latter drive them backwards to
the opening of the oesophagus.
Some little distance in front of the anterior peri-pharyngeal ridge, at
the inner or posterior end of the oral siphon, is a circlet of delicate
tentacles (Fig. 198, tent).
The oesophagus leads from the pharynx (near the posterior end of
the dorsal lamina) to the stomach, which, together with the intestine,
lies embedded in the mantle on the left-hand side. The stomach is a
large fusiform sac. The intestine is bent round into a double loop, and
runs forwards to terminate in an anal aperture, situated in the atrial
cavity. There is no liver; but the walls of the stomach are glandular,
and a system of delicate tubercles which ramify over the wall of the
intestine is supposed to be of the nature of a digestive gland.
The Ascidian has a well-developed blood system. The heart is a
simple muscular sac, situated near the stomach in a pericardium forming
part of the primitive ccelom. Its mode of pulsation is very remarkable.
The contractions are of a peristaltic character, and follow one another
from one end of the heart to the other for a certain time; then follows
a short pause, and, when the contractions begin again, they have the
opposite direction. Thus the direction of the current of blood through
the heart is reversed at regular intervals.
The nervous system is of an extremely simple character. There is a
single nerve-ganglion, which lies between the oral and atrial apertures,
embedded in the mantle. This is elongated in the dorso-ventral direc-
xii PHYLUM CHORDATA 319
tion, and gives off at each end nerves which pass to the various parts
of the body.
Lying on the ventral side of the nerve -ganglion is a gland — the sub-
neural gland. A duct runs forward from it and opens into the cavity
of the pharynx; the termination of the duct is dilated, and this terminal
dilatation is folded on itself in a complicated way to form a tubercle,
the dorsal tubercle, which projects into the cavity of the pharynx.
The excretory system is represented by a single nephridium, which
consists of a mass of clear vesicles, without a duct, lying in the second
loop of the intestine.
The sexes are united. The ovary and the testis are closely united
together, and lie on the left-hand side of the body in the intestinal
loop. Continuous with the cavity of each is a duct — oviduct or spermi-
duct, as the case may be — which opens into the atrial cavity close to
the anus.
So far we have met with no feature that could with certainty be looked
upon as indicating alliances with the Chordata. But, though the adult
Ascidian is devoid of any such features, there is in the course of its life-
history a larval stage in which Chordate affinities are unmistakably
indicated. In this stage the young Ascidian is free-swimming, and in
general shape bears some resemblance to a minute tadpole, consisting
of an oval trunk and a long, laterally compressed tail. The tail is fringed
with a caudal fin, which is merely a delicate outgrowth of the thin test
covering the whole of the surface ; running through the delicate fringe
are a series of striae presenting somewhat the appearance of the fin-rays
of a fish's fin. At the anterior end are three processes, the adhesive
papillae. In the axis of the tail is the notochord (noto}, which at this
stage consists of a cylindrical cord of gelatinous substance enclosed in a
layer of cells. Parallel with this runs, on the dorsal side, the, narrow rai^.
dal portion of the nerve-cord, and at the sides are bands, or muscular
fibres. In the trunk the nerve-cord is dilatedf and, further forwards,
expands into a vesicle, the sense vesicle {sens, ves} with an otocyst (g/g)
and a well-developed eye {eye}. The entericcanal is distinguishable
into pharynx, oesophagus, stomach, and intestine. The pharynx opens
on the exterior by the mouth : in its ventral floor the endostyle (end}
has become developed; its walls are pierced by stigmata, the number
of which varies; a ciliated sac opens in*6 it below the trunk part of
the nerve-cord. The atrial cavity has become formed round the phar-
ynx, and opens on the exterior by a single aperture (atr}. The heart
320 MANUAL OF ZOOLOGY SECT.
and pericardial cavity have become developed. In this tailed, free-
swimming stage the larva remains only a few hours; it soon becomes
fixed by the adhesive papillae, and begins to undergo the retrogressive
metamorphosis by which it attains the adult condition.
The chief changes involved in the retrogressive metamorphosis (Figs.
200 and 201) are increase in the number of pharyngeal stigmata, the
diminution, and eventually the complete disappearance, of the tail with
the contained notochord and caudal part of the nerve-cord, the dis-
appearance of the eye and the otocyst, the dwindling of the trunk part
of the nervous system to a single ganglion and the formation of the
reproductive organs. Thus, from an active, free-swimming larva, with
well-developed organs of special sense, and provided with a notochord
and well-developed nervous system, there is a retrogression to the fixed
FIG. 200 — Free- swimming larva of Ascidia mammillata, lateral view, adh, adhe-
sive papillae; all, alimentary canal; atr, atrial aperture; cil.gr, ciliated groove;
end, endostyle; eye, eye; med, nerve-cord; noto, notochord ; oto, otocyst; sens,
•ves, sense vesicle ; stig, earliest stigmata. (From Korschelt and Heider, after
Kowalewsky.)
inert adult, in which all the parts indicative of affinities with the Ver-
tebrata have become aborted.
A remarkable feature of the Ascidians is that, though many remain
simple, others give rise to colonies by a process of budding. In some
of these compound forms, distinguished as the Composite Ascidians, the
tests of the zooids are united together to form a mass of gelatinous
consistency in which the zooids of the colony lie embedded (Fig. 202).
These compound forms, such as Amaroucium, are common on the New
England coast in shallow water.
A minute animal which swims about in the surface waters of the sea
has in most respects an extremely close resemblance to the tailed larva
XII
PHYLUM CHORDATA
A
321
&r
FIG. 201. — Diagram of the metamorphosis of the free, tailed larva into the fixed
Ascidian. A, stage of free-swimming larva; B, larva recently fixed; C, older
fixed stage, adk, adhesive papillae; atr, atrial cavity; cil.gr, ciliated groove;
end, endostyle; ht, heart; med, ganglion of trunk; n. gn, nerve-ganglion; noto,
notochord; or, oral aperture; rect, rectum; sens ves, sense vesicle; stfg, stig-
mata; stol, stolon; t, tail. (From Korschelt and Heider, after Seeliger.)
322 MANUAL OF ZOOLOGY SECT.
of an Ascidian, being of similar shape, with a rounded body and a long
tail-like appendage attached to the ventral side, and with a distinct
notochord. This, however, is an adult animal, known as Appendicula-
ria. It never becomes fixed and retains permanently its chordate
characteristics.
cZ
07*
FIG. 202. — BotryllUS violaceus . or, oral apertures ; cl, opening of common cloacal
chamber. (After Milne-Edwards.)
A number of other Urochorda are permanently free-swimming, but
these are all almost, if not quite, as thoroughly metamorphosed as the
Ascidians, so that their true affinities only become clear when their
life -histories are followed.
3. THE VERTEBBATA
The Sub- phylum Vertebrata comprises the lancelets, the
lampreys and their allies, the fishes, the amphibians, the
reptiles, the birds, and the mammals. The lancelets occupy
an extremely isolated position with regard to the other mem-
XII
PHYLUM CHORDATA
323
bers of the sub-phylum, and are best regarded as consti-
tuting by themselves a division, which, for reasons which
will be manifest shortly, is designated Acrania, the rest of
the sub-phylum being known as Craniata.
A. THE ACRANIA
This isolated group, the Acrania, comprises only a single family, the
two genera (Br&nchiostoma and Asymmetrori) of which are distin-
guished from one another by comparatively slight differences.
Branchiostoma (more widely known under the name of Amphioxus) ,
the lancelet, is a small transparent animal, occurring in the sea near
the shore and burrowing in sand; its length does not exceed 5.8 cm.
FIG. 203. —Amphioxus lanceolatUS. A. ventral; B, side view of the entire animal.
an, anus; atrp, atriopore; cd. f, caudal fin; ctr, cirri; dors, f, dorsal fin;
dors.f. r. dorsal fin-rays; gon, gonads; mtfll, metapleure; ntyotn, myomeres;
nek, notochord; or. kd, oral hood; vent, f, ventral fin; vent. f. r, ventral fin-
rays. (After Kirkaldy.)
or less than two inches. Its form will be obvious from Fig. 203. The
body is elongated, pointed at either end, and compressed. The anterior
two-thirds is roughly triangular in transverse section, presenting right
and left sides, inclined towards one another, above, and a convex ven-
tral surface. The posterior third is nearly oval in section, the right
and left sides meeting above and below in a somewhat sharp edge.
Extending along the whole of the dorsal border is a median longi-
tudinal fold, the dorsal Jin {dors, /"); this is continued round the
324 MANUAL OF ZOOLOGY SECT.
posterior end of the body and extends forwards, as the ventral Jin
(vent. _/"), as far as the spot where the oval gives place to the trian-
gular transverse section. The portion of the continuous median fold
which extends round the pointed posterior extremity of the body is
somewhat wider than the rest, and may be distinguished as the caudal
Jin (cd.f}. In the anterior two-thirds of the body there is no median
ventral fin, but at the junction of each lateral with the ventral surface
is a paired longitudinal fold, the metapleure (mtpl}, which extends
forward to the oral hood mentioned in the next paragraph.
Below the pointed anterior extremity is a large median aperture
surrounded by a frill-like membrane, the oral hood ( or. kd\ the edge
of which is beset with numerous tentacles or cirri. The oral hood
encloses a cup-shaped cavity or vestibule, at the bottom of which is the
mouth (Fig. 204, mth). Immediately in front of the anterior termina-
tion of the ventral fin and partly enclosed by the metapleures is a
rounded aperture of considerable size, the atripore (atrp*}, and a short
distance from the posterior extremity of the body is the anus (an),
placed unsymmetrically on the left side of the ventral fin. The post-
anal portion of the body is distinguished as the tail.
Amphioxus ordinarily lives with the greater part of the body buried
in sand, only the anterior end with the expanded oral hood protruding.
It also swims in the vertical position, and frequently lies on one side
on the sand; it burrows, head foremost, with great rapidity. It occurs
on the American coast as far north as Cape Hatteras. A current of
water is constantly passing in at the mouth and out at the atriopore.
The muscular layer (my} is remarkable for exhibiting metameric
segmentation. It consists of a large number — about sixty — of muscle
segments or myomeres, separated from one another by partitions of
connective tissue, the myocommas, and having the appearance, in a
surface view, of a series of very open V's with their apices directed
forwards (Figs. 203 and 204).
The chief of the skeletal or supporting structures of the lancelet is
the notochord (Figs. 203 and 204, ncfi), a cylindrical rod, pointed at
both ends, and extending from the anterior to the posterior end of the
body in the median plane. It lies immediately above the enteric tract
and between the right and left myomeres. It is composed of a peculiar
form of cellular tissue, known as notochordal tissue, formed of large
vacuolated cells extending from side to side of the notochord, and
having the nuclei confined to its dorsal and ventral regions. Around
XII
PHYLUM CHORDATA
325
these cells is a notochordal
sheath of connective tissue
which is produced dorsally
into a canal for the ner-
vous system.
The oral hood is sup-
ported by a ring (Fig. 204,
sK) of cartilaginous con-
sistency, made up of sepa-
rate rod-like pieces ar-
ranged end to end, and
corresponding in number
with the cirri.
The pharynx is sup-
ported by delicate oblique
rods of a chitinoid mate-
rial, the gill-rods (br. r).
The dorsal fin is supported
by a single series, and the
ventral fin by a double
series, of Jin rays (dors,
f. r), short rods of con-
nective tissue.
The mouth (mtK), as
already mentioned, lies at
the bottom of the vestibule
or cavity of the oral hood
(or. Jid). It is a small cir-
cular aperture surrounded
by a membrane, the velum
(vl} acting as a sphincter,
the free edge of which is
produced into a number
of velar tentacles (vl. /).
The mouth leads into
the largest section of the
enteric canal, the pharynx
(pfc), a high compressed
chamber extending through
the anterior half of the
326 MANUAL OF ZOOLOGY SECT.
body. Its walls are perforated by more than a hundred pairs of narrow
oblique clefts, tf\Q gill-slits or branchial apertures (br. c), which place
the cavity of the pharynx in communication with the atrium (see
below). From the posterior end of the pharynx goes off the tubular
intestine (inf) which extends backwards, almost in a straight line to
the anus.
On the ventral wall of the pharynx is a longitudinal groove, the
endostyle, lined by ciliated epithelium containing groups of gland-cells.
Like the homologous organ in Ascidia (p. 317), the glands secrete a
cord of mucus in which food particles are entangled and carried by the
action of the cilia to the intestine. A somewhat similar structure, the
epipharyngeal groove, extends along the dorsal aspect of the pharynx;
its sides are formed by ciliated cells, which, at the anterior end of the
groove, curve downwards, as the peri-pharyngeal bands, and join the
anterior end of the endostyle.
From the ventral region of the anterior end of the intestine is given
off a blind pouch, the liver (/;-) or hepatic caecum, which extends for-
wards to the right of the pharynx; it is lined with glandular epithelium
and secretes a digestive fluid.
The gill-slits (br. <:/) are long narrow clefts, nearly vertical in the
expanded condition, but very oblique in preserved and contracted
specimens — hence the fact that a large number of clefts always appear
in a single transverse section (Fig. 205).
The branchial septa or lamellae (Fig. 204, br. sep~}, or portions of the
pharyngeal wall separating the clefts from one another, are covered
by an epithelium composed, except on the outer face, of greatly elon-
gated and ciliated cells. Each septum is supported towards its outer
edge by one of the chitinoid branchial rods (br. r) already referred
to.
The gill-clefts lead into a wide chamber occupying most of the space
between the body-wall and the pharynx and called the atrium (Fig.
204, atr}. It is crescentic in section, surrounding the ventral and
lateral regions of the pharynx, but not its dorsal portion. It ends
blindly in front; opens externally, behind the level of the pharynx, by
the atriopore (atrf) ; and is continued backwards by a blind, pouch-
like extension (atr} lying to the right of the intestine. As in Ascidia
the cilia lining the gill-clefts produce a current setting in at the mouth,
entering the pharynx, passing thence by the gill-slits into the atrium
and out at the atriopore. The current, as in Tunicata and Balano-
XII
PHYLUM CHORDATA
327
glossus, is both a respiratory and a food current, the animal feeding
passively on the minute organisms in the surrounding water.
There is a system of blood-vessels, but no heart. A contractile
median ventral vessel, the ventral aorta, runs forward in the ventral
wall of the pharynx, and gives off lateral branches, the afferent bran-
chial vessels, which pass upwards in the branchial lamelke. Efferent
branchial vessels receive the blood from the wall of the pharynx and
open dorsally into a pair of longitudinal vessels, the dorsal aorta. The
FIG. 205, — Amphioxus lanceolatus. A, transverse section of the pharyngeal re-
gion, a, dorsal aorta; b, atrium: c, notochord: co, coelom; e, endostyle; g,
gonad; kb, branchial lamella;; &/, pharynx; /, liver; my, myomere; n. neph-
ridium; r, neuron or dorsal nerve tube; sn, spinal nerves; sp, gill-slits. B,
transverse section of the intestinal region; air, atrium; coel, coelom; d. ao,
dorsal aorta: int, intestine; myom, rnyomere: nc h, notochord: neu, neuron;
j. int. v, subintestinal vein. (A, from Hertwig, after Lankester and Boveri; B,
partly after Rolph.)
latter join to form a median dorsal aorta, which runs backwards imme-
diately below the notochord and above the intestine.
The principal organs of excretion are about ninety pairs of peculiarly
modified nephridia (Fig. 204, npJi) situated above the pharynx and in
relation with the main ccelomic cavities.
An excretory function has also been assigned to a.single pair of
organs called the brown funnels (Fig. 204, br.f}, also situated on the
dorsal aspect of the pharynx at its posterior end.
328 MANUAL OF ZOOLOGY SECT.
The central nervous system is a rod-like organ, the neuron or dorsal
nerve-cord (Fig. 204), contained within and completely filling a median
longitudinal neural canal which lies immediately above the notochord.
It is traversed by an axial canal, which becomes dilated at the anterior
extremity. From this nerve-cord regularly arranged nerves are given
off.
At the level of the anterior end of the nerve-cord is a narrow ciliated
depression, the olfactory pit (Fig. 204, olf. p} opening externally on
the left side of the snout and connected at its lower end with a median
hollow process of the nerve-cord. This structure is supposed to be an
organ of smell.
The organ of sight is an unpaired pigment spot (^) in the front wall
of the brain; it is therefore a median eye. A peculiar structure, the
groove of Hatschek, on the roof of the oral hood, is supposed to have a
sensory fanction, and may be an organ of taste. Lastly, the sensory
cells on the buccal cirri give those organs an important tactile function.
The sexes are separate, but there is no distinction, apart from the
organs of reproduction, between male and female. The gonads (Fig.
204, goti) are about twenty-six pairs of pouches arranged metamerically
along the body- wall and projecting into the atrium so as largely to rill
up its cavity.
When ripe the inner walls of the gonadic pouches burst, and the ova
or sperms make their way into the atrium and thence by the atriopore
to the external water, where impregnation takes place.
B. THE CRANIA TA
The fishes, amphibians, reptiles, birds, and mammals are
grouped together under the general designation Craniata,
derived from one of the features which these animals have
in common, viz., the presence of a skull or cranium. In
order to understand the general characteristics of the Craniata,
it will be advisable to examine and compare representatives
of some of the principal classes. For this purpose a dogfish,
a lizard,1 ancl a rabbit will be a good and convenient selection.
1 The anatomy of the Anolis or " American chameleon " of the Southern
States is essentially like that of the European lizard.
XII
PHYLUM CHORDATA
329
Not only must entire and,
if convenient, living speci-
mens be examined, but
prepared skeletons of all
three must be availa-
ble for examination, and
preparations showing the
various systems of inter-
nal organs, notably the di-
gestive system, the heart,
and the brain.
An external comparison
appears at first sight to
reveal few points of agree-
ment between the three
selected examples. The
skin, the general shape,
the movements, are all
widely different. A few
features common to all
three are, however, to be
recognised. It will be
observed that in all three
are distinguishable a head
region, in front, a- trunk
region (by far the largest),
in the middle, and a tail
region, differing greatly in
its development, behind.
The head region bears
anteriorly the opening
of the mouth, bounded
above and below by jaws
330
MANUAL OF ZOOLOGY
SECT.
bearing teeth ; near the mouth are a pair of smaller aper-
tures — the nostrils or nasal apertures, and at the sides
of the head region are the pair of conspicuous eyes ;
while further back the pair of prominent auricles or pin-
nae, with the wide apertures at their bases, mark very
conspicuously the position of the auditory organs in the
FIG. 207. — Lacerta viridis. (After Brehm. )
rabbit, less clearly indicated in the lizard, and still less
in the dogfish. On the lower (ventral) surface, towards
the posterior end of the trunk, will be observed in all three
apertures which serve as the orifices through which the
intestine and the ducts of the urinary and genital organs
communicate with the exterior. A further resemblance
XII
PHYLUM CHORDATA
331
between the lizard and the rabbit consists in the presence
of two pairs of jointed limbs, anterior and posterior, the
principal divisions of which correspond in their general
arrangement. In the dogfish these are found to be rep-
resented by very different-looking structures, the paired fins.
At this point all external resemblance ceases, and we see
nothing but differences.
The skin of the dogfish, though almost smooth, is harsh to
the touch, and, when we examine it with a lens, this is found
to be due to the presence of innumerable minute hard gran-
FIG. 208. — LepUS cuniculus. Lateral view of skeleton with outline of body.
ules, set closely together so as to give the surface the charac-
ter of a fine file. The general shape of the body is adapted
to cleaving the water rapidly, — long and narrow, nearly
fusiform, pointed at the ends, — and the fins are obviously
swimming organs. The fins are all of the same general
character, so far as their superficial appearance is con-
cerned ; they are all of the nature of flap-like outgrowths,
thick at the base, where they are obviously supported by
hard parts, thinner towards the margins, where their sole
332 MANUAL OF ZOOLOGY SECT.
support is a series of slender fibres of horny character.
Besides the two pairs of fins which have already been re-
ferred to as taking the places of the anterior and posterior
pairs of limbs in the lizard and rabbit, certain others are to
be recognised which are of a totally different character,
being median or unpaired ; these, which are not in any
way represented in either the lizard or the rabbit, are the
two dorsal, the single ventral, and the single caudal, the
last fringing the tail.
Behind the eye in the dogfish will be noticed a small
aperture which seems to occupy very nearly the position
occupied by the opening of the ear in the rabbit. This
opening, however, the spiracle, does not lead into the ear,
but into the cavity of the pharynx. Further back there
are, on each side, five slit-like apertures in a row : these
are the branchial or gill-clefts, and are not present in the
lizard or the rabbit. In the living fish it will be observed
that there are regular movements of the mouth, spiracles,
and branchial clefts, indicating that water is being rhythmi-
cally taken in through the mouth and expelled by the
spiracles and branchial clefts. Those are the movements
of respiration.
The mouth is situated some little distance behind the
anterior extremity of the head, on the ventral side. In
front of it are tne nasal openings (nostrils), which are also
ventrally situated.
In the lizard the surface is covered with a system of
overlapping horny scales. The head is separated from the
trunk by a distinct constricted region, the neck. The tail
is extremely long and narrow. The two pairs of limbs,
anterior and posterior, or pectoral and pelvic, are adapted to
running on the surface of the ground. Each consists of
three divisions, — arm, fore-arm, and hand, — the anterior
Xii PHYLUM CHORDATA 333
limb, thigh, leg, and foot in the posterior ; and each hand
and each foot contains five slender digits, each provided
at its extremity with a curved and pointed horny claw.
Slight rhythmical movements of dilatation and contraction
of the anterior portion of the trunk are the movements of
respiration, by means of which air is alternately drawn into
and expelled from the lungs through the nostrils.
In the rabbit the place of the scales of the lizard is taken
by the coating of hairs constituting the fur. The limbs
present the same main divisions as in the lizard, though the
proportions of the parts are very different, and the hind foot
has only four toes. Between the head and trunk the neck
region is more sharply marked off than in the lizard. Aris-
ing from the posterior part of the head, behind the eyes,
are a pair of very prominent auditory pinna or auricles, at
the base of each of which is the corresponding ear-opening.
Movements of respiration resembling those of the lizard,
but much more marked, are to be detected in the living
animal.
When the skeletons of these three animals are examined
and compared, it will be found that they are constructed on
the same general plan with differences in details. In the
dogfish it is mainly composed of cartilage ; in the others,
mainly of bone. In all there is a rod-like axis, the spinal
or vertebral column supporting the trunk and tail, but not
continued into the head, where its place is taken by the
skull. The spinal column consists of a row of similar
segments, the vertebra, which articulate with one another.
Each vertebra consists of a neutral solid portion, the 'cen-
trum or body ; an arch of bone or cartilage, the neural
arch, situated on the dorsal side of the centrum, and cer-
tain processes. The series of centra form together a strong
axial support for the entire body and tail; the series of
334
MANUAL OF ZOOLOGY
SECT.
neural arches enclose a canal, the neural canal, on the
dorsal side of the centra. By the interlocking of certain
processes — the articulating processes — of the neural arches
the vertebrae in the lizard and rabbit are yet more firmly
united together.
In the dogfish the centra have deeply concave anterior
and posterior faces, so that when the vertebrae are in posi-
ha.
FIG. 209. — A, three trunk vertebrae of Scyllium from the side; B, a single trunk
vertebra viewed from one end; C, three caudal vertebrae from the side; D, a
single caudal vertebra from one end. c, centrum; h. a, haemal arch; n. a, neural
arch; tr. fr, transverse process. (After Hasse.)
tion there are hollows of considerable extent between the
centra formed by the apposition of these concave faces.
This form of centrum is termed amphiccelous. The entire
spinal column is distinguishable into two regions, — the
region of the trunk in front and the region of the tail
XII
PHYLUM CHORDATA
335
behind. In the region of the trunk the vertebrae bear very
small ribs in the form of short rods of cartilage ; in the
caudal region ribs are absent ; but each vertebra bears, in
addition to the neural arch, a ventrally situated arch of
similar shape — the h&mal arch.
In both the lizard and the rabbit the vertebrae are com-
posed entirely of bone. In the former the centra have
concave anterior and convex posterior surfaces — and the
vertebrae are accordingly said to be precocious. In the lat-
ter the surfaces are flat, and the discs of fibro-cartilage, the
inter-vertebral discs, are intercalated between the vertebrae.
FIG. 210. — Vertebrae of Lizard. A, anterior, B, posterior, view of a thoracic ver-
tebra; C, lateral, D, anterior, view of atlas vertebra; E, lateral view of axis.
cent, centrum; hyp, hypapophysis of axis; lat, lateral piece of atlas; lig. liga-
mentous band dividing the ring of the atlas into two; neur, neural arch of atlas;
od, odontoid process; pr. zy, pre-zygapophysis; pt. zy, post-zygapophysis; rb,
rib; sp, spine; -vent, ventral piece of atlas.
In both the spinal column is divisible into five regions, — the
cervical, the thoracic, the lumbar, the sacral, and the caudal.
The cervical region is the most anterior. In the rabbit the
vertebrae of the cervical region are devoid of ribs; in. the
lizard they have short ribs with the exception of the first
three. The first and second vertebrae in both the rabbit
and the lizard are specially modified in connection with the
movements of the head on the trunk. The vertebrae of the
336
MANUAL OF ZOOLOGY
SECT.
thoracic region are characterised by the possession of ribs,
which, in the case of the most anterior, are connected with
the breast-bone or sternum by slender cartilaginous sternal
ribs. In the lumbar region there are no ribs. The sacral
region is distinguished by its relations with the hind limb.
The caudal region, short in the rabbit, very long in the
lizard, lies behind the sacral. The ribs connected with the
thoracic vertebrae are slender curved rods, which lie in
the side walls of the anterior part of the trunk ; the most
anterior of them with their continuations, the sternal ribs,
form half-loops extending from the spinal column dorsally
cent
Sac,
FIG. 211. - Lepus Cuniculus. A, atlas and axis, ventral aspect; od, odontoid pro-
cess of axis. B, lateral view of axis; art, articular facet for occipital condyle;
od, odontoid process; pt. zy, post-zygapophysis; sp, neural spine. C, thoracic
vertebrae, lateral view, cent, centrum; fac, facet for rib; met, metapophysis;
pr. zy, pre-zygapophysis; pt. zy, post-zygapophysis; rb, rib; sp, spinous process.
to the sternum ventrally. The sternum or breast-bone,
absent in the dogfish, lies in the middle of the wall of the
ventral region of the trunk. In the lizard it is a rhomboidal
plate of cartilage ; in the rabbit it is bony, and divided up
into a number of segments known as the sternebra.
In the embryo of each of the three forms used as illus-
trations, the spinal column passes through a stage in which
it consists merely of a continuous cylindrical rod of cells —
the notochord, corresponding to the notochord of Amphi-
oxus — which becomes enclosed in a sheath. In some
xii PHYLUM CHORDATA 337
Craniates it never passes beyond this stage, but remains of
the nature of a persistent notochord, as it is termed. But in
the great majority the notochord becomes enclosed in a
sheath of cartilage, and thus becomes divided up into a
number of segments. Eventually ossification sets in, and
the series of completely formed bony vertebrae become^
developed.
As already mentioned, the spinal column does not extend
into the head region. The skeleton of this region is the
complex cartilaginous or bony structure known as the skull.
The chief part of this is a case, the cranium, in the interior
of which the brain is lodged, and the walls of which afford
support to three pairs of organs of special sense, — the nasal
or olfactory organs in front, the eyes in the middle, and the
ears or auditory organs behind. The cavity of the cranium
opens behind by a rounded foramen, the foramen magnum,
into the anterior end of the neural canal enclosed by the
neural arches of the vertebrae ; and the posterior region of
the cranium articulates movably with the first vertebrae of
the spinal column. In addition to the cranium the skull
or skeleton of the head comprises certain elements known
as the visceral arches. The foremost of these forms the
jaws, the second is the hyoid, and mainly supports the
tongue, the remainder are the branchial arches.
In the dogfish the cranium remains in the primitive
condition of a cartilaginous case, with complete walls and
floor, but with the roof partly formed of fibrous membrane.
In the lizard and rabbit the substance of the cartilage is
replaced by a number of cartilage bones, i.e, bones which
take the place of pre-existing cartilage, to which are super-
added a number of membrane bones, i.e., bones, the site of
which was not preoccupied by cartilage ; the whole united
together so as to form a structure of considerable com-
z
MANUAL OF ZOOLOGY
SECT.
Xii PHYLUM CHORDATA 339
plexity. The visceral arches in the dogfish are composed
of a system of rods of cartilage. The first visceral arch
forms the upper and lower jaws, between which the open-
ing of the mouth is situated. The jaws are connected on
each side with the skull behind by means of a cartilage
known as the hyomandibular, which is a part of the second
or hyoid arch ; the rest of the hyoid arch and the branchial
arches, which are five in number, lie in the lateral and ven-
tral walls of the pharynx and support the gills.
In both the lizard and the rabbit the branchial arches
are not present as such, the only well-developed visceral
arches being the first and second. The upper jaw is
formed of certain membrane bones, and in the lower jaw
also the cartilage completely disappears, its place being
taken by bones which are early completely united together,
so as to form the bony lower jaw or mandible. In the
lizard the mandible articulates on each side with the pos-
terior region of the skull through the intermediation of a
bone known as the quadrate, which is an element of the
first visceral arch. In the rabbit the articulation between
the mandible and the skull is direct, no quadrate inter-
vening.
The skeleton of the limbs in the dogfish differs widely
from that of the lizard and rabbit. In all three we dis-
tinguish the limb-arch from the skeleton of the free part
of the limb itself. The limb-arch (pectoral or pelvic) is a
cartilage or a system of bones with which the base of the
free part of the limb articulates, and has the function of
connecting the limb with the trunk and serving for the
origin of many of the muscles moving the limb. In the
dogfish the entire skeleton of the limbs is composed of
cartilages which are so arranged as to support the thin
broad expanse of the fin. In both the lizard and the
pmac
Cacl.nar
para
ang
dent
FIG. 213. - Skull of Lacerta aplis. A, from above; B, from below; C, from the
side, ting, angular: art, articular; bas oc, bast-occipital ; has. ptg, basi-pterygoid
processes; bas.sph, basi-sphenoid ; col, epi-pterygoid; cor, coronary; dent,
dentary; eth, ethmoid: ex oc. ex-occipital: ext. iiar, external nares; for mag,
foramen magnum: fr, frontal; int. nar, internal nares; ju, jugal; Icr, lacyr-
mal; max, maxilla; nas, nasal; oc. cond, occipital condyle; olf, olfactory
capsule; of>.ot, opisthotic: opt n, optic nerve; pal, palatine; par, parietal;
par. parasphenoid; par.f, parietal foramen; p. vix, pre-maxil!ae; pr.fr, pre-
frontal; ptg, pteryjjoid, H.f>rb, post orbital; qit, quadrate; s. ang, supra-
angular; s. orb, supra-orbitals; sq, squamosal; supra, t.'1, supra-temporal i;
supra t?. supra-temporal 2; trans, transverse; supra, oc. supra-occipital; vom,
vomer. (After W. K. Parker.)
340
PHYLUM CHORD ATA
341
rabbit the skeleton of the limbs is constructed on a general
plan, common to the limbs of all Craniata but the fishes,
and known as the pentadactyle, in allusion to the five digits
in which the limb typically terminates. In the pectoral
limb the upper arm has a single long bone known as the
humerus ; at its proximal end this is movably articulated
with the pectoral arch. The forearm contains two long
SCP
B
FE
PU
mils. 5
J57
FIG. 214. — Diagrams of the fore (A) and hind (B) limbs with the limb-girdles. actb,
acetabulum; gl, glenoid cavity; p. cor, procoracoid; I-V, digits. Cartilage
bones — cn.i, cn.2, centralia; COR, coracoid; dst. 5-1, distalia; FE, femur;
FI, fibula; fi, fibulare; HU, humerus; IL, ilium; int, intermedium; IS,
ischium; mtcp. 1-5, metacarpals; mt. ts. 1-5, metatarsals; ph, phalanges;
PU, pubis; RA, radius; ra, radiale; TI, tibia; ti, tibiale; UL, ulna; ill,
ulnare, membrane bone; CL, clavicle.
bones — radius and ulna — articulating proximally with the
distal end of the humerus. The skeleton of the hand con-
sists of three principal parts, — the carpus, the metacarpus,
342 MANUAL OF ZOOLOGY SECT.
and the phalanges. The carpus or wrist consists of a num-
ber of small irregularly shaped bones arranged in two trans-
verse rows, proximal and distal, with a central bone between
the rows. The metacarpus consists of five narrow bones
forming the support of the basal parts of the five digits,
and articulating proximally with the distal row of carpals.
The rest of the skeleton of the digit is formed of a row
of small bones, the phalanges, the last of which — ungual
phalanx — is modified in shape to support the horny claw.
The skeleton of the hind-limb corresponds closely with
that of the fore-limb. The pelvic arch consists on each side
of three bones which become firmly united together, one
of these, the ilium, is dorsal in position, the other \wQ,pubis
and ischium, are ventral, the pubis being anterior to the
ischium. The ilia articulate firmly with the sacral region
of the spinal column ; the pubes unite ventrally in an articu-
lation known as the pubic symphysis, and in the lizard the
ischia are similarly connected. Laterally where the three
bones unite is a cup-like cavity — the acetabulum — which
forms the socket for the head of the thigh-bone.
The thigh has a single long bone, the femur. The leg
has two bones, the tibia and fibula, the former, which is
internal, being the larger of the two, and the latter in the
rabbit not being distinct from the former towards the distal
end. In the foot are a number of tarsal bones correspond-
ing to the carpals of the hand, a series of metatarsals corre-
sponding to the metacarpals and a series of phalanges.
When the skin of the trunk of the dogfish is removed
there will be found immediately beneath it a thick layer
of muscle. This is distinctly divided into segments or
myomeres similar to those of Amphioxus, and this, with the
division of the vertebral column into segments or vertebrae
(which, however, do not exactly correspond in arrangement
XII
PHYLUM CHORDATA
343
ZS
with the myomeres), indicates that the body, like that of
Nereis or an Arthropod, is metamerically segmented. In
the lizard and rabbit the metamerism of the muscular sys-
tem, though distinguishable at an early stage, becomes lost
in the adult, and the muscles take on a much more compli-
cated arrangement.
On the jaws are a series of teeth, the function of which
is to seize the food, and in the rabbit cut it into fragments,
and crush it into yet smaller particles, in order to prepare it
for the process of digestion. In the dogfish the teeth are
numerous and of uniform character throughout, small with
sharp points directed backwards. At
their bases they are fixed to the surface
of the cartilage of the jaw by means of
dense fibrous tissue. In the lizard the
teeth are also of uniform character
(homodont dentition]. They are of a
simple conical shape, and fixed to the
bone of the jaws. In the rabbit the
teeth are distinctly visible into sets, dif-
fering from one another in shape and
function (heterodont dentition). Their
bases are lodged in sockets or alveoli in
the substance of the jaws.
The structure of the tooth is the same
in all three cases. The main mass of
the tooth consists of dentine, a densely FIG. 215. — Longitudinal
, .- , . , . . . ,. section of a tooth, semi-
Calcified material permeated by delicate diagrammatic. PH,
parallel tubules. The free surface is '
•ze
sheim>s Vertebrata^
covered with a layer of still harder mate-
rial, the enamel, and the basal portion is
covered with a layer of cement, which is similar in micro-
scopic structure to bone.
344 MANUAL OF ZOOLOGY SECT, xn
The anterior part of the cavity into which the mouth
leads is the buccal cavity ', the posterior part is the pharynx.
On the floor of the buccal cavity is, in the lizard and in the
rabbit, a mobile muscular prominence, the tongue, repre-
sented in the dogfish by a much less prominent and little
mobile process.
From this a wide tube leads backwards to open into a
spacious chamber, the stomach. From the stomach the
intestine, a more or less coiled tube, leads eventually to the
anal aperture. In the dogfish and in the lizard the anus
opens into a chamber, the cloaca, which also receives the
ducts of the urinary and reproductive organs. In the rabbit
a cloaca is absent, and the anus is separate from the urino-
genital opening. The mucous membrane of the enteric
canal contains numerous glands, the secretions of which play
an important part in digestion ; the most important of these
secretions is the gastric juice secreted by the glands of the
stomach. In addition, special large digestive glands are
present producing secretions, also having the function of
acting on the various components of the food in such a way
as to facilitate the passage of the useful ingredients from the
cavity of the alimentary canal to the blood-vessels. In the
rabbit these special large digestive glands are the salivary
glands, the liver, and the pancreas ; in the dogfish and
lizard the salivary glands are absent, though in the latter
there are numerous small glands, the buccal glands, in the
wall of the buccal cavity. The secretion of the salivary
glands, the saliva, enters the cavity of the mouth through
the ducts of the glands. It contains a ferment, ptyalin,
which has the property of converting starch into sugar.
The liver is in all three a relatively large organ, fixed by
folds of peritoneum to the dorsal wall of the abdominal
cavity and divided by fissures into a number of lobes. Its
ty C S l * ••
346 MANUAL OF ZOOLOGY SECT.
duct, the bile duct, conveys its secretion, the bile, into
the most anterior part of the intestine known as the duo-
denum. The duct gives off a diverticulum which expands
into a rounded sac, the gall-bladder ; this acts as a recep-
tacle for the bile when it is not required. The bile has an
important action on the fatty matters of the food, converting
them into an emulsion and decomposing a small proportion
into glycerine and fatty acid. In addition to secreting the
bile the liver has another function to perform : it acts as
a storehouse for surplus carbohydrates absorbed from the
food. The carbohydrates — compounds of the nature of
starch and sugar — are converted in the liver into a sub-
stance known as glycogen or animal starch, which becomes
stored up in the cells to be given out again to the blood as
it is required for nutrition during the intervals of fasting ;
this function of the liver is known as the glycogenic function.
The pancreas, which is a much smaller gland than the
liver, produces a secretion, the pancreatic juice, which has
the effect of converting starch into sugar, proteids into
soluble modifications known as peptones, and of assisting in
the emulsification of fats. The duct of the pancreas also
opens into the duodenum. The nutrient matters of the
food, rendered soluble by the action of the various digestive
fluids, pass into the blood contained in the blood-vessels in
the wall of the enteric canal, and are thus conveyed through-
out the body to be distributed. The fatty matters, however,
pass into a system of minute vessels — the lacteals — which
ramify in the wall of the intestine. The lacteals are not
blood-vessels, but belong to the lymphatic vascular system to
be referred to presently. The lacteals combine together
and in the rabbit open into a large trunk — the thoracic duct
— by means of which the absorbed emulsion, or chyle as it is
termed, is conveyed to one of the great veins.
xii PHYLUM CHORDATA 347
The body-cavity in which the enteric canal and other
organs are contained is lined with a membrane, the peri-
toneum. This is reflected over the surface of the contained
structures, and folds of it serve to suspend the various organs
and connect them together. The best developed of these
folds is the mesentery (defective in the dogfish), by means
of which the intestine is attached to the dorsal wall of the
body-cavity.
The organs of respiration of the dogfish are gills adapted
for receiving oxygen from the air dissolved in sea-water;
those of the lizard and the rabbit are lungs adapted for
breathing air directly. The movements of respiration have
been already referred to. In the dogfish these movements
have the effect of causing water to be taken in by the mouth,
and to pass out from the pharynx to the exterior through
the gill-slits. In passing out, the water flows over the gills,
which are sets of vascular elevations on the walls of a series
of five pairs of chambers — the branchial sacs opening
internally into the pharynx, and externally communicating
with the surrounding water through the branchial slits. In
this way the needed oxygen is constantly being taken up,
and the carbon dioxide given off. The walls of the branchial
sacs are supported by the hyoid and branchial arches.
Inspiration and expiration of air in the lizard and rabbit
take place through the nostrils. The nasal chambers into
which the nostrils lead communicate internally with the
mouth-cavity or the pharynx through a pair of apertures
known as the internal or posterior nares. On the floor of
the pharynx behind the root of the tongue is a slit-'like
aperture, the glottis, opening behind into a chamber known
as the larynx, the wall of which is supported by cartilages.
From the larynx the air passes backwards along a tube, the
trachea, the wall of which is supported by numerous rings
348
MANUAL OF ZOOLOGY
SECT.
-Tr
ff
of cartilage. The trachea bifurcates when it enters the
body- cavity, each of the two branches, or bronchi as they
are termed, passing to the
corresponding lung. In the
lizard the lung is in essence
a thin-walled sac with elas-
tic walls. In the wall of
the sac immediately out-
side, the delicate internal
epithelium is a rich net-
work of blood-vessels, into
the blood contained in
which oxygen from the air
in the cavity of the lung
readily passes, while the
carbonic acid is at the
same time given off. In
the rabbit the lung is of
much more complicated
structure, but the essential
relations are the same.
In the lizard the lungs
lie in the anterior part of
the general body-cavity.
In the rabbit the anterior
part of the body-cavity,
containing the lungs and
the heart, is separated off
from the posterior part,
FIG. 217. — Lacerta agilis. General view
„*-.*.„ :„•„ „ fu^ o-v^o^v
Containing the greater
of the viscera in their natural relations.
Bl, urinary bladder; Ci, post-caval vein ;. f: r t^ ^nt^nV runal imrl
ED, rectum; GB, gall-bladder; H, tlOn Ol the CntCriC Canal and
heart; Lg, Lg , the lungs; M, stomach;
MD, small intestine; Oe, oesophagus;
Pn, pancreas; Tr, trachea. (After
Wiedersheim.)
partition concave posteri-
Xli PHYLUM CHORDATA 349
orly, — the diaphragm, — the anterior portion of the cavity
being known as the cavity of the thorax, and the posterior
as that of the abdomen.
The air in the lungs, as it is constantly losing oxygen and
gaining carbon dioxide, requires to be frequently renewed ;
and the respiratory movements which have already been
referred to are the movements indicative of this renewal ; in
the movement of respiration air is drawn into the lungs,
which become fully distended ; in that of expiration, the
greater part of the air is driven out again, and the lung
collapses. In the rabbit inspiration and expiration are
effected by the movements of the ribs and of the diaphragm,
by which the dimensions of the cavity of the thorax are
increased or diminished.
The blood-vascular system is highly developed in all the
three examples. The blood is of a red colour, owing to
the presence of red corpuscles containing a red colouring
matter termed hcemoglobin.
The blood-vessels are of three kinds, — arteries, veins, and
capillaries. The arteries have firm and elastic walls, which
do not collapse when the vessel is empty; they contain
arterial blood, i.e., blood which contains abundance of
oxygen. The veins have thin, non-elastic walls which col-
lapse when the vessel is empty and contain valves ; the con-
tained venous blood is darker in colour than the arterial, and
has been deprived of oxygen in the tissues. Both arteries
and veins ramify extensively, the ultimate branches being of
very small size. Connecting together the ultimate branches
of the arteries and the ultimate branches of the veins is a
system of microscopic vessels — the capillaries.
The heart is ventral and anterior in position. In the dog-
fish it will be found to lie in a space, the pericardial cavity,
between the two rows of gills, and separated behind from the
350 MANUAL OF ZOOLOGY SECT.
general body-cavity (abdomen) in which the majority of the
internal organs are contained, by a transverse fibrous parti-
tion. It consists of four chambers, — the sinus venosus, auri-
cle, ventricle, and conus arteriosus. The venous blood enters
the sinus venosus from the great veins and passes through
the other three chambers in succession in the order given.
All the chambers contract rhythmically, and by their con-
tractions the blood is propelled from chamber to chamber,
and finally driven out from the heart, its passage in the
opposite direction being prevented by the presence of
valves. These are placed in the openings leading from
chamber to chamber, and are so arranged that while they
permit the ready passage of the blood in the direction above
given, they close up the opening when pressure is exerted in
the opposite direction ; thus, for example, when the auricle
contracts, the valve guarding the opening leading back into
the sinus venosus closes that opening, while the valve in the
opening leading into the ventricle opens freely, and the
blood passes readily in that direction. The ventricle is by
far the most muscular of the four chambers, since it is
mainly by its contractions that the blood is forced through
the system of vessels. The blood which is forced out from
the heart by the contractions of the ventricle passes into a
series of vessels which carry it all to the gills. Here it
enters a system of capillaries in the gills, and these being
separated from the surrounding water only by a thin mem-
brane, oxygen readily enters the blood, and the carbon
dioxide collected in the various tissues and organs of the
body is given off. The blood then enters a set of larger
vessels, which combine to form a large trunk, the dorsal
aorta. Branches from this distribute blood to all parts of
the body, where it enters the systems of capillaries, and
whence it is carried back again to the heart by the veins.
XII
PHYLUM CHORD ATA
351
In the lizard the heart and the circulation are somewhat
more complicated than in the dogfish. There is a sinus
venosus as before. The auricle is completely divided into
two chambers, right and left, by a partition. Into the right
auricle the sinus venosus drives the venous blood from the
great veins ; into the left open the pulmonary veins, bring-
ing the oxygenated blood from the lungs. Both the auricles
open into the ventricle, the cavity of which is partly divided
by a septum. From the ventricle are given off the main
arteries (systemic arteries) which branch throughout all parts
d an
br.a.
a bra.
i' IG. 218 — Diagram illustrating the course of the circulation in a fish. Vessels
containing aerated blood, red; those containing non-aerated blood, blue; lym-
phatics, black. B, capillaries of the body generally; E, of the enteric canal;
G, of the gills; K, of the kidneys; L. of the liver; T, of the tail. a. br. a,
afferent branchial arteries; au, auricle; c. a, conus arteriosus; d. ao, dorsal
aorta; e br. a, afferent branchial arteries; h. p v, hepatic portal vein; h. v,
hepatic vein; Ic, lacteals; ly, lymphatics; p-r. ci>. v, pre-caval veins; r, p. v,
renal portal veins; s. v, sinus venosus; v, ventricle; v. ao, ventral aorta. The
arrows show the direction of the current.
of the body, and the pulmonary arteries, which pass direct
to the lungs. By various arrangements of the parts which
need not be described at present, the venous blood from
the right auricle is mainly guided into the pulmonary arte-
ries, and passes to the lungs to obtain oxygen and part with
its carbon dioxide ; while the arterial blood is mainly guided
352 MANUAL OF ZOOLOGY SECT.
to the systemic arteries. A certain degree of mixing, how-
ever, of the venous and arterial currents takes place as they
pass through the ventricle.
In the rabbit this mixing of the arterial and venous cur-
rents is entirely prevented, owing to the ventricle being
completely divided into two chambers — right and left.
The right auricle opens into the right ventricle, and fills it
with venous blood from the great veins. From the right
auricle the blood is driven through a pulmonary artery to the
lungs. From the lungs the oxygenated blood is returned
by means of the pulmonary veins to the left auricle ; from
the left auricle it enters the left ventricle, and from the
latter is driven out through the system of systemic arteries
to all parts of the body. There are thus two distinct cur-
rents of blood constantly passing simultaneously through the
heart, but entirely cut off from one another, viz., a venous
current on the right side and an arterial on the left. The
blood of the rabbit has a much higher temperature than
that of the dogfish or lizard.
In all the three examples the veins which carry the
venous blood towards the heart from the stomach, intestine,
and pancreas unite together to form a large vein, the hepatic
portal, which ramifies in the substance of the liver, and
forms the main source of the blood supply of that organ.
In the dogfish and lizard, but not in the rabbit, veins con-
vey blood from the posterior region to the kidneys, forming
what is termed a renal portal system.
The nervous system is highly developed. The central
nervous system consists of the brain and spinal cord. The
brain is, as already stated, contained in the cavity of the
cranium ; the spinal cord, continuous with the posterior end
of the brain, extends through the neural canal roofed over
by the series of neural arches of the vertebrae.
XII
PHYLUM CHORDATA
353
The spinal cord is similar in essential respects in all three
examples. It is a cylindrical cord of nerve matter, having
running along the middle of its dorsal surface a fissure, the
Zol
FIG. 919. — Dorsal view of the brain of Scyllium canicula. The posterior division
of the brain is the medulla oblongata (NH), on the dorsal surface of which is
shown one of the central ventricles (F. rho). The large cerebellum (HH}
nearly covers the optic lobes (MH}. The diencephalon (ZH) shows in the
middle one of the central ventricles, and the place of attachment of the pineal
body (Gp}. The prosencephalon (VH} gives off the olfactory lobes (Tro, L. ol).
The following nerves are shown: optic (//), trochlear (IV}, trigeminal (V)t
facial (VII}, auditory (VIII}, glossopharyngeal (IX}, and vagus (X}.
(From Wiedersheim.)
dorsal longitudinal fissure, and along the middle of its ven-
tral surface, a second fissure, the ventral longitudinal fissure.
2A
354 MANUAL OF ZOOLOGY SECT.
Through its substance from end to end runs a narrow canal,
the central canal.
In the brain of the dogfish the most anterior portion is
a thick mass of nerve matter indistinctly divided into two
lateral portions by a shallow depression. This is the pro-
sencephalon of the fore-brain. A pair of lobes given off
from this in front are the olfactory lobes. The prosencepha-
lon with a narrow region, diencephalon or thalamencephalon,
behind it, constitute the fore-brain. Behind the fore-brain
a pair of oval lobes, the optic lobes, constitute the dorsal
portion of the mid-brain, which comprises, in addition, a
thick mass of longitudinal nerve-fibres, lying below, and
connecting the hind-brain with the fore-brain. An elon-
gated median mass, indistinctly divided into lobes, is the
cerebellum, the anterior portion of the hind-brain. The
posterior division of the hind-brain, — medulla oblongata, —
broad in front, tapers posteriorly where it passes into the
spinal cord.
The central canal of the spinal cord expands in the me-
dulla oblongata into a wide shallow cavity, roofed over only
by a thin membrane ; this is known as the fourth ventricle.
From this runs forwards a narrow passage, the iter or aque-
duct of Sylvius, expanding in front in the thalamencephalon
into a laterally compressed cavity, the third ventricle. From
this are given off a pair of lateral ventricles, passing into
the prosencephalon, each giving off a prolongation into the
corresponding olfactory tube.
The roof of the third ventricle is very thin ; it is pro-
duced into a slender process — the epiphysis or pineal body.
Its side walls are formed of two masses, the optic thalami;
its floor is produced into a hollow prolongation, the infun-
dibulum, to the end of which a vascular body, the hypophysis
or pituitary body is applied.
xii PHYLUM CHORDATA 355
In the brain of the lizard the same parts are recognisa-
ble as in the dogfish, the chief differences being that the
prosencephalon is deeply divided by a median longitudinal
fissure into two lobes, the cerebral hemispheres, and that
the cerebellum is very small. In the rabbit also we rec-
ognise the same parts. But the whole brain is larger in pro-
portion to the bulk of the body ; the cerebral hemispheres
are much more highly developed, and the cerebellum is not
only of large relative size, but is of complicated structure.
The peripheral nervous system consists of the spinal and
cerebral nerves given off from the spinal cord and the brain
respectively, with their ramifications through all parts of the
body. A pair of spinal nerves emerge from the neural
canal between each adjoining pair of vertebrae. Each
spinal nerve arises from the spinal cord by two roots — a
dorsal and a ventral ; the former is dilated into a ganglion.
Experiments prove that the dorsal root contains the sensory
fibres of the nerves, i.e., those fibres which are concerned
in carrying impulses from the various parts to the nerve
centres to be translated in consciousness into sensations.
When, for example, the skin of some part of the body is
touched, the impulse by means of which we become con-
scious of the contact passes from the surface through
branches of the spinal nerves, and enters the spinal cord
through the dorsal root, in order to be transmitted to the
brain. The ventral root, on the other hand, contains the
motor fibres ; the fibres through which impulses which lead
to the contraction of muscles pass outwards from the central
nervous system.
More or less extensive intercommunications take place
between the spinal nerves that are situated opposite the
origin of the limbs ; these spinal nerve plexuses give off the
nerves to the limbs.
356 MANUAL OF ZOOLOGY SECT.
The cerebral or cranial nerves correspond pretty closely
in their general arrangement in the three examples. The
olfactory nerve-fibres, which originate from the olfactory
lobes, the optic nerves, which are derived from the thalamen-
cephalon, and the auditory nerves which originate from the
medulla oblongata, are the nerves of the special senses of
smell, sight, and hearing respectively, the first ending in the
epithelium of the nasal cavities, the second in the retina of
the eye, and the third in the epithelium of the interior of
the inner ear. Other cranial nerves supply the muscles
that move the eyeball, the skin of the head, the muscles of
the jaws, the tongue, pharynx, heart, stomach, etc.
The structure of the eye is in all essential respects the
same in all the three examples ; such differences as there
are will be referred to later. The eye of a bullock or a
sheep, being larger, may with advantage be substituted.
The eyeball is globular, and is encased in a rough opaque
capsule, the sclerotic. It lies in the cavity of the orbit, and
is capable of being turned about in various directions by a
number of muscles inserted into it. On the side of the
eyeball directed towards the light, the opaque sclerotic is
replaced by a transparent membrane, the cornea, which
forms a window through which the rays of light enter the
eye. Within the sclerotic is a more delicate pigmented
layer, the choroid. Towards the cornea the choroid passes
into a circular pigmented diaphram, the iris, the opening
of which is known as the pupil. Through the pupil, the
size of which is capable of being increased or diminished,
the light is admitted into the interior of the eye. The sen-
sitive part of the eye, the part on which the image produced
by the rays of light proceeding from an object must fall in
order to produce the sensation of sight, is a soft gray layer
lining that part of the cavity of the eye which lies within the
XII
PHYLUM CHORDATA
357
iris. The rays of light are brought to a focus on the retina
mainly by means of the crystalline lens, a firm, glassy body
situated within the iris. The cornea also assists in this, as
does a gelatinous substance, the vitreous humour, which fills
the part of the cavity of the eyeball internal to the lens.
The ear in the dogfish is imbedded in the cartilage of
the posterior part of the skull (auditory region). It con-
sists of a somewhat complicated structure termed the
e.c
FIG. 220. — Diagrammatic horizontal section of the eye of man. c, cornea; ch.
choroid (dotted); C. P, ciliary processes; e. c, epithelium of cornea; e. cj,
conjunctiva; f. c{ yellow spot; /, iris; L, lens; ON, optic nerve; OS, ora
serrata; o-x, optic axis; /. c. R, anterior non- visual portion of retina; P. £,
pigmented epithelium (black); R, retina; sp. I, suspensory ligament; Scl,
sclerotic; V. H, vitreous body. (From Foster and Shore's Physiology.)
membranous labyrinth, with soft walls and an internal
epithelium in which the fibres of the auditory nerve termi-
nate. Contained in the interior of the labyrinth is a fluid,
the endolymph, in which there are suspended particles of
358 MANUAL OF ZOOLOGY SECT.
carbonate of lime, the otoliths. In the lizard and rabbit
there are superadded to this, the essential part of the ear,
certain accessory parts. The most important of these is
the tympanum or drum of the ear. This is a cavity to the
outside of the auditory region of the skull (the region in
which the membranous labyrinth is enclosed). The tym-
panum communicates with the pharynx through a passage
known as the Eustachian passage. Externally the cavity of
the tympanum is closed by a tense, drum-like membrane,
the tympanic membrane. The tympanic membrane is set
in vibration by the waves of sound, and the vibrations are
transmitted across the tympanic cavity by a slender rod of
bone (in the lizard) or a chain of minute bones (in the
rabbit). The inner end of the rod or chain of bones is
inserted into a membrane covering over a small aperture in
the outer wall of the auditory region of the skull, which
forms the inner wall of the tympanic cavity, and by this
means the vibrations are communicated to the endolymph
of the membranous labyrinth and affect the terminations
of the auditory nerve-fibres. In the lizard the tympanic
membrane is nearly on a level with the skin of the head,
and its position is conspicuously indicated by a brown
patch situated behind the eye. In the rabbit the tympanic
membrane is more deeply sunk, and a wide passage, the
passage of the outer ear, leads to it from the exterior. The
ear of the rabbit also differs from that of the lizard in the
presence of the prominent auricle or pinna of the ear to
which reference has been already made.
The kidneys, or organs of renal excretion, though they
differ in form in the three examples are not widely different
in essential structure. Their function is the secretion of
urine, which consists of water containing various nitrogenous
waste matters in solution. Essentially the kidney is a mass.
xii PHYLUM CHORDATA 359
of tubules by whose agency the process of secretion is car-
ried on, the whole being richly supplied with blood-vessels.
Eventually the tubules open into a duct, the ureter. In the
lizard and the rabbit there is present a median thin-walled
sac, the urinary bladder, in which the urine is stored, to be
discharged at intervals. In the rabbit the ureters open into
the bladder, and the latter opens on the exterior by a median
canal, the tirethra. In the lizard the ureters and the bladder
have independent openings into the cloaca, and the bladder
is filled only by regurgitation from the latter chamber.
The sexes are distinct in all three. There are two testes,
each with its duct or vas deferens. In the female there are
two ovaries, which are solid bodies in which the ova lie im-
bedded. In the dogfish, when mature, the ova are of large
size, containing a great quantity of food-yolk. The ova of
the rabbit are extremely small, while those of the lizard are
of a size intermediate between those of the other two.
Each ovum is enclosed in a follicle — the Graafian follicle —
with a wall composed of small cells. When the ovum
approaches maturity the follicle projects on the surface of
the ovary, and eventually the wall becomes ruptured and
the ovum escapes into the body-cavity.
The oviducts, of which there are two, are not connected
with the ovaries, each opening anteriorly into the body-
cavity by a wide opening. In the dogfish and the lizard
the oviducts remain practically distinct from one another
throughout; in the rabbit the posterior parts are united to
form a median chamber, the body of the uterus, and a
median passage, the vagina, leading to the exterior. The
ova in all three, when discharged from the ovaries, enter the
wide openings of the oviducts and are impregnated during
their passage backwards. In both the dogfish and the lizard
each fertilised ovum becomes enclosed while in the oviduct
360 MANUAL OF ZOOLOGY SECT.
in a tough shell, and is discharged when development has
only begun. In the rabbit the fertilised ovum is received
into the uterus and there undergoes its development, the
young rabbit when born differing little, save in size, from the
adult. The nourishment of the/az/us or uterine young of
the rabbit is effected by means of a special vascular structure
known as the placenta, by means of which nutrient material
passes from the blood of the mother to that of the foetus ;
and after birth the young rabbit receives its nourishment
for a time exclusively from the secretion of a set of glands
of the mother — the mammary or milk glands.
CLASS I. CYCLOSTOMI
The lowest of existing Craniate Vertebrates are certain
fish-like animals known as "lampreys" and "hag-fishes,"
or " slime-fishes," which are looked upon as constituting the
class of Craniata, to which the name of Cyclostomi is ap-
plied. Of them it is here possible only to make the briefest
mention. The lampreys (Petromyzon and other genera)
and the hag-fishes or slime-fishes (Myxine and Bdellostoma)
are somewhat eel-like in general shape, that is to say, they
have a long and narrow body without marked external dis-
tinction into regions, and with a soft and slimy integument.
Of the fins of such a fish as the dogfish the median or un-
paired series alone are represented, paired fins corresponding
to the limbs of the higher Craniata being entirely absent.
There is a dorsal fin divided into two in the lampreys, undi-
vided in the hag-fishes, which is continued as a tail fin round
the posterior or caudal extremity of the body. On the
lower or ventral surface of the anterior or head-end is a deep
hollow — the buccal funnel, much more conspicuous in the
lampreys than in the hags, at the bottom of which the small
XII
PHYLUM CHORDATA
opening of the mouth is situated. There are no jaws, but
on the inner surface of the buccal funnel and on the tongue
— a fleshy (?) process below the opening of the mouth. In
Myxine the funnel is edged with slender, flexible processes
or tentacles. At the sides of the head are the eyes, well
developed and conspicuous in the lamprey, imperfect and
buried beneath the skin in Myxine, and on the upper surface
is a single median aperture, the nostril. Further back at
na.ap
FlG. 221. — Petromyzon marimiS. Ventral (A), lateral (B), and dorsal (C) views
of the head. br. cl. /, first gill-cleft; buc.f, buccal funnel; eye, eye; mth, mouth;
na. ap, nasal aperture; /, papillae : pn, pineal area; 1. I, t. 2, t. 3, teeth of buccal
funnel; /. 4, teeth of tongue. (After W. K. Parker.)
the sides of the head are, in the lamprey, a series of seven
pairs of slits, the gill-slits, leading to the gill-pouches ; in
Bdellostoma there are six pairs of small gill-slits, in Myxine
only a single aperture on each side.
The skeleton is very unlike that of the true fishes, and
362
MANUAL OF ZOOLOGY
SECT. XII
is in some respects extremely primitive. The spinal col-
umn is represented merely by a thick persistent notochord,
enclosed in a sheath, with, in the lampreys, small carti-
na..ap
mlh
oe.s.cl.d
FIG. 222. — Head of Myxine glutinosa (A) and of Bdellostoma forsteri (B), from
beneath, br. ap, branchial aperture; br. cl. i, first branchial cleft ; mth, mouth;
na. ap, nasal aperture; oes. ct. d, oesophageo-cutaneous duct. The smaller open-
ings in A are those of the mucous glands. (After W. K. Parker.)
laginous processes representing neural and haemal arches.
The skull is cartilaginous, and is peculiarly modified. Be-
hind it in the lamprey is a remarkable basket-like apparatus,
ligililiJJL
364 MANUAL OF ZOOLOGY SECT.
composed of cartilaginous processes. This branchial basket,
as it is termed, supports the gill-sacs.
The gill-sacs, of which there are either six or seven pairs,
are the organs of respiration, representing the gills of the
true fishes. In the lamprey each of these communicates
with the exterior by the corresponding gill-slit, and inter-
nally opens into a common passage, the respiratory tube
which leads in front into the buccal cavity. In Bdellostoma
each gill-pouch has its own internal opening through a
narrow tube into the pharynx, as well as its external open-
ing through a small gill-slit. In Myxine, on the other
hand, though each pouch has a separate internal commu-
nication with the pharynx, the tubes leading outwards from
the gill-pouches of each side all join to form a common
tube, which opens on the exterior by the single gill-slit.
The other systems of organs are not so remarkable. The
alimentary canal, the heart, and the brain are not widely
different from those of the true fishes. A peculiar feature
is that there is only a single nasal sac (opening by the single
nasal aperture already referred to) instead of the pair
developed in all other Craniates ; in Myxine its cavity com-
municates by a passage with the cavity of the mouth. In
the lamprey, in addition to paired eyes having the typical
vertebrate structure, there is connected with a lobe in the
roof of the fore-brain a median or pineal eye of simpler
structure and imperfectly understood function.
Lampreys live mainly in rivers and estuaries. Their food
consists chiefly of small aquatic animals, such as worms,
small crustaceans, etc. ; but they also sometimes attach
themselves to the bodies of fishes, by means of the sucker-
like buccal funnel, and rasp off portions of the flesh with the
horny teeth of the tongue. Myxine actually makes its way
into the interior of the bodies of large fishes, such as the
xil PHYLUM CHORDATA 365
cod, consuming the flesh in its passage, and thus becomes
for a time an internal parasite — the only example among
the Vertebrata of such a condition. In the free state Myxine
usually lies buried in the sand, with only the anterior end,
with the nasal aperture, projecting on the surface. By
means of the passage leading from the nasal sac to the
mouth, water passes in and out through the nasal aperture,
and the process of respiration is carried on while the ani-
mal remains almost completely hidden.
The geographical distribution of the Cyclostomi is some-
what remarkable. Petromyzon is found on the coasts and
in the rivers of Europe, North America, Japan, and West
Africa. Of the allied genera one, Ickthyomyzon, occurs on
the western coast of North America ; another, Mordacia, in
Tasmania and Chili; a third, Geotria, in the rivers of Chili,
Australia, and New Zealand. Myxine occurs in the North
Atlantic and on the Pacific Coast of South America, includ-
ing the Straits of Magellan; Bdellostoma on the coasts of
South Africa, New Zealand, and Chili.
CLASS q:. PISCES
The class Pisces or Fishes includes the Elasmobranchii or
cartilaginous fishes_( sharks, dogfishes, and rays), the Teleo-
stomi or bony fishes (such as perch, pike, mackerel, cod,
sole, salmon, sturgeon, and bony pike), and the Dipnoi or
lung-fishes. In these the organs both of respiration and
of locomotion are adapted for an aquatic mode of life. The
chief and, in the majority, the only organs of respiration
are the gills, which are in the form of series of vascular
processes attached to the branchial arches and persisting
throughout life. The organs of locomotion are the paired
pectoral and the pelvic fins, and the unpaired dorsal,
366 MANUAL OF ZOOLOGY SECT.
ventral, and caudal ; these are all supported by fin-rays of
dermal (p. 372) origin. A hard external covering of scales
developed in the dermis is usually present. In the en-
doskeleton the notochord is usually replaced more or less
completely by cartilaginous or bony vertebrae ; there is a
well-developed skull and a system of well-formed visceral
arches, of which the first forms the upper and lower jaws, the
latter movably articulating with the skull, and both nearly
always bearing teeth. An air-bladder is frequently present,
and in certain exceptional cases acquires the function of a
lung or chamber for breathing air.
Sub-class I. Elasmobranchii
A dogfish may be selected as a convenient example of
the sub-class and of the class Pisces. Dogfishes occur at
slight depths off the coasts in all quarters of the globe. The
commonest European forms are the rough hound {Scyllium
canicula}, the lesser spotted dogfish (S. catulus}, the
piked dogfish (Acanthias vulgaris], and the smooth hound
(Musfelus vulgaris}. Allied species of the southern hemi-
sphere are Scyl/ium, Acanthias, and Mustelus anarcticus.
On the coast of Northeastern America the common dogfish
is Mustelus cants. For the description which follows, any
of these species will be found to serve very well.
A slight general account of the dogfish has already been
given in the introduction to the Craniata ; this has now to be
extended and supplemented. The general shape (Fig. 206)
may be described as fusiform ; at the anterior or head-end it
is broad and depressed ; posteriorly it tapers gradually and
is compressed from side to side. The head terminates
anteriorly in a short blunt snout. The tail is narrow and
bent upwards towards the extremity. The entire surface is
XIT PHYLUM CHORDATA 367
covered closely with very minute hard placoid scales or
dermal teeth somewhat larger on the upper surface than
on the lower. These are pointed, with the points directed
somewhat backwards, so that the surface appears rougher
when the hand is passed over it forwards than when it is
passed in the opposite direction. When examined closely,
each scale is found to be a minute spine situated on a
broader base. The spine consists of dentine covered with a
layer of enamel; the base is composed of bone, and the
whole scale has thus the same essential structure as a tooth.
Along each side of the head and body runs a faint depressed
longitudinal line or slight narrow groove, — the lateral line.
As in fishes in general, two sets of fins are to be
recognised, — the unpaired or median fins, and the paired or
lateral. These are all flap-like outgrowths, running vertically
and longitudinally in the case of the median fins, nearly
horizontally in the case of the lateral; they are flexible,
but stifrlsh, particularly towards the base, owing to the
presence of a supporting framework of cartilage. Of the
median fins, two — the dorsal — are situated, as the name
indicates, on the dorsal surface : they are of triangular
shape ; the anterior, which is the larger, is situated at about
the middle of the length of the body, the other a little
further back. The caudal fringes the tail ; it consists of a
narrower dorsal portion and a broader ventral, continuous
with one another round the extremity of the tail, the latter
divided by a notch into a larger, anterior, and a smaller,
posterior lobe. The tail is heterocercal, i.e., the posterior
extremity of the spinal column is bent upwards and lies -in
the dorsal portion of the caudal fin. The ventral or
so-called anal fin is situated on the ventral surface, opposite
the interval between the anterior and posterior dorsals ; it
resembles the latter in size and shape.
368 MANUAL OF ZOOLOGY SECT.
Of the lateral fins there are two pairs, the pectoral and the
pelvic. The pectoral are situated at the sides of the body,
just behind the head. The pelvic, which are the smaller, are
placed on the ventral surface, close together, in front of the
middle of the body. In the males the bases of the pelvic fins
are united together in the middle line, and each has connected
with it a clasper or copulatory organ. The latter is a stiff rod,
on the inner and dorsal aspect of which is a groove leading
forwards into a pouch-like depression in the base of the fin.
The mouth — a transverse, somewhat crescentic opening
— is situated on the ventral surface of the head, near its
anterior end. In front and behind it is bounded by the
upper and lower jaws, each bearing several rows of teeth
with sharp points directed backwards. The nostrils are sit-
uated one in front of each angle of the mouth, with which
each is connected by a wide groove, the nasobuccal groove.
A small rounded aperture, the spiracle, — placed just behind
the eye, — leads into the large mouth-cavity or pharynx.
Five pairs of slits running vertically on each side of the neck,
the branchial slits, also lead internally into the mouth-
cavity. A large median opening on the ventral surface at
the root of the tail, between the pelvic fins, is the opening
leading into the cloaca, or chamber forming the common
outlet for the intestine and the renal and reproductive organs.
A pair of small depressions, the abdominal pores, situated
behind the cloacal opening, lead into narrow passages open-
ing into the abdominal cavity.
The skeleton is composed entirely of cartilage, with, in
certain places, depositions of calcareous salts. As in Verte-
brates in general, we distinguish two sets of elements in the
skeleton, — the axial set and the appendicular, the former
comprising the skull and spinal column, the latter the limbs
and their arches.
xii PHYLUM CHORDATA 369
The spinal column is distinguishable into two regions, —
the region of the trunk and the region of the tail. In the
trunk region each vertebra (Fig. 209, A] consists of a centrum
(c}, neural arch (na), and transverse processes (tr.pr).
In the caudal region there are no transverse processes, but
inferior or hcemal arches (D, h. a} take their place. The
centra of all the vertebrae are deeply biconcave or amphi-
coslous, having deep conical concavities on their anterior
and posterior surfaces. Through the series of centra runs
the notochord, greatly constricted in the centrum itself,
dilated in the large spaces formed by the apposition of the
amphicoelous centra of adjoining vertebrae. The concave
anterior and posterior surfaces of the centra are covered
by a dense calcified layer, and eight radiating lamellae of
calcified material run longitudinally through the substance
of the centrum itself. Each neural arch consists of a pair
of rod-like neural processes, which form the sides, and two
pairs of compressed neural plates (one placed opposite the
centrum, the other or intercalary cartilage, opposite the
interval between adjoining centra), which form the roof of
the arch, together with usually two nodules — the repre-
sentatives of neural spines — which form the keystones.
The transverse processes are very short : connected with
each of them is a cartilaginous rudimentary rib about half
an inch in length.
The cranium (Fig. 224) is a cartilaginous case, the wall
of which is continuous throughout, and not composed, like
the skulls of higher vertebrates, of a number of distinct ele-
ments (bones) fitting in together. At the anterior end is a
rostrum, consisting of three cartilaginous rods converging as
they extend forwards and meeting at their anterior ends.
At the sides of the base of this are the olfactory capsules
(olf. cp), — thin rounded cartilaginous sacs opening widely
370 MANUAL OF ZOOLOGY SECT.
below, — the cavities of the two capsules being separated
from one another by a thin septum. The part of the roof of
the cranial cavity behind and between the olfactory capsules
is formed, not of cartilage, but of a tough fibrous membrane,
and the space thus filled in is termed the anterior fontanelle ;
in contact with the lower surface of the membrane is the
pineal body, to be afterwards mentioned in the account of
the brain. Each side wall of this part of the skull presents
a deep concavity, the orbit over which is a ridge-like
prominence, the supra-orbital crest, terminating anteriorly
and posteriorly in obscure processes termed respectively the
pre-orbital and post-orbital processes. Below the orbit is a
longitudinal infra-orbital ridge.
Behind the orbit is the auditory region of the skull (aud.
cp), a mass of cartilage in which the parts of the mem-
branous labyrinth of the internal ear are embedded. On
the upper surface of this posterior portion of the skull are
two small apertures situated in a mesial depression. These
are the openings of the aqueductus vestibuli (endolymphatic
ducts), leading into the vestibule of the membranous laby-
rinth. Behind this again is the occipital region, forming the
posterior boundary of the cranial cavity, and having in the
middle a large rounded aperture, the foramen magnum,
through which the spinal cord contained in the neural canal
and protected by the neural arches of the vertebrae becomes
continuous with the brain, lodged in the cranial cavity. On
either side of this is an articular surface, the occipital
condyle, for articulation with the spinal column.
A number of smaller apertures or foramina, chiefly for
the passage of nerves, perforate the wall of the skull.
In close connection with the cranium are a number of
cartilages composing the visceral arches (Fig. 224). These
are incomplete hoops of cartilage, mostly segmented, which
XII
PHYLUM CHORDATA
371
!^l|l|
o-.S.23^<
372 MANUAL OF ZOOLOGY SECT.
lie in the sides and floor of the mouth-cavity or pharynx.
The first of these forms the upper and lower jaws. The
upper jaw, or palato-quadrate (»/./), consists of two stout
rods of cartilage firmly bound together in the middle line
and bearing the upper (or anterior) series of teeth. The
lower jaw, or Meeker s cartilage (/. /), likewise consists of
two stout cartilaginous rods firmly united together in the
middle line, the union being termed the symphysis. At their
outer ends the upper and lower jaws articulate with one
another by a movable joint. In front the upper jaw is
connected by a ligament with the base of the skull.
Immediately behind the lower jaw is the hyoid arch. This
consists of two cartilages on each side, and a mesial one in
the middle below. The uppermost cartilage is the hyo-man-
dibular (hy. m) ; this articulates by its proximal end with a
distinct articular facet on the auditory region of the skull ;
distally it is connected by ligamentous fibres with the outer
ends of the palato-quadrate and Meckel's cartilage. The
lower lateral cartilage is the cerato-hyal (hy. en}. Both the
hyo-mandibular and cerato-hyal bear a number of slender
cartilaginous rods — the branchial rays of the hyoid arch
(br. r). The mesial element, or basi-hyal, lies in the floor
of the pharynx. Behind the hyoid arch follow the branchial
arches, which are five in number. Each branchial arch con-
sists of several cartilages and bears branchial rays.
The skeleton of all the fins — paired and unpaired — pre-
sents a considerable degree of uniformity. The main part
of the expanse of the fin is supported by a series of flattened
segmented rods, the pterygiophores or cartilaginous fin-rays,
which lie in close apposition ; in the case of the dorsal fins
these are calcified along their axes. At the outer ends of
these are one or more rows of polygonal plates of cartilage.
On each side of the rays and polygonal cartilages are a
xii PHYLUM CHORDATA 373
number of slender horny fibres of dermal origin. In the
smaller median fins there may be an elongated rod of carti-
lage constituting the skeleton, or cartilage may be entirely
absent. In the pectoral fin (Fig. 225) the fin- rays are
supported on three basal cartilages articulating with the
pectoral arch. The latter is a strong hoop of cartilage in-
complete dorsally, situated immediately behind the last of
d.f..
FIG 225. —Ventral view of pectoral arch of Scyllium with right pectoral fin. The
pectoral arch is divisible into dorsal (pet. g) and ventral (pet. g'} portions,
separated by the articular facets (art./) for the fin. The pectoral fin is formed
of three basal cartilages (bs. 1-3) and numerous radials (rad} ; its free edge is
supported by dermal rays (d.f. r). (Modified from Marshall and Hurst.)
the branchial arches. It consists of a dorsal, or scapular,
(pet. g) and a ventral, or coracoid, portion (pct-g')> the
coracoid portions of opposite sides being completely con-
tinuous across the middle line, while the scapular are sepa-
rated by a wide gap in which .the spinal column lies.
Between the two portions are the three articular surfaces
for the three basal cartilages. The three basal cartilages of
374 MANUAL OF ZOOLOGY SECT.
the fin are named, respectively, the anterior, pro-pterygium
(bs. /), the middle, meso-pterygium (bs. 2), and the pos-
terior, meta-pterygium (bs.j). Of these the first is the
smallest, and the last the largest. The pelvic fin has only a
single basal cartilage, articulating with the pelvic arch, with
which also one or two of the fin-rays articulate directly. The
pelvic arch is a nearly straight bar of cartilage which runs
transversely across the ventral surface of the body, just in
front of the cloacal opening.
The mouth leads into a very wide cavity, the pharynx
(Fig. 216, ph), into which opens at the sides the internal
apertures of the branchial clefts and of the spiracle. From
this runs backwards a short wide tube, the oesophagus (gut),
which passes behind into the stomach. The stomach is
a U-shaped organ, with a long left limb (cd. st) continuous
with the oesophagus, and a short right (pyl. st) passing
into the intestine. At the pylorus — the point where the
stomach passes into the intestine — is a slight constriction
followed by a thickening. The intestine consists of two
parts, — small intestine or duodenum, and large intestine.
The former is very short, only an inch or two in length.
The latter (int) is longer and very wide ; it is divisible into
two portions, — the colon in front and the rectum behind.
The former is very wide and is characterised by the pres-
ence in its interior of a spiral valve, a fold of the mucous
membrane which runs spirally round its interior and both
retards the too rapid passage of the food, and affords a
more extensive surface for absorption. The rectum differs
from the colon in being narrower and in the absence of the
spiral valve ; it opens behind into the cloaca.
There is a large liver (I. Ir, r. Ir) consisting of two elon-
gated lobes. A rounded sac, the gall-bladder, lies em-
bedded in the left lobe at its anterior end. The duct of
xii PHYLUM CHORDATA 375
the liver, the bile duct, runs from the liver to the intes-
tine. Proximally it is connected with the gall-bladder and
by branch ducts with the right and left lobes of the liver.
It opens into the commencement of the colon.
The pancreas (pa?i) is a light-coloured compressed gland
consisting of two main lobes with a broad connecting isthmus
lying in the angle between the right-hand limb of the stomach
and the small intestine. Its duct enters the wall of the small
intestine and runs in it for about half an inch, opening event-
ually at the point where the small intestine passes into the
colon.
Connected with the rectum on its dorsal aspect is an oval
gland, the rectal gland (rct.gl), about three-quarters of an
inch in length.
The spleen (spf) is a dark-red or purple body attached to
the convexity of the U-shaped stomach, and sending a narrow
lobe along the right-hand limb.
The organs of respiration in the dogfish are the gills,
situated in the five gill-pouches. Each gill-pouch is an
antero-posteriorly compressed cavity opening internally into
the pharynx and externally by the gill-slit. The walls of the
pouches are supported by the branchial and hyoid arches with
their rays, the first pouch being situated between the hyoid
and first branchial arches, the last between the fourth and
fifth branchial arches. On the anterior and posterior walls
of the pouches are the gills, each hemibranch consisting of a
series of close-set parallel folds or plaits of highly vascular
mucous membrane. Separating adjoining gill-pouches and
supporting the gills are a series of broad interbranchial septa,
each containing the corresponding branchial arch with its
connected branchial rays. The most anterior hemibranch is
borne on the posterior surface of the hyoid arch. The last
gill-pouch differs from the rest in having gill-plaits on its
SECT, xii PHYLUM CHORD ATA 377
anterior wall only. On the anterior wall of the spiracle is a
rudimentary gill, the pseudo-branch or spiracular gill, in
the form of a few slight ridges.
The heart Is situated in the pericardial cavity, on the ventral
aspect of the body, in front of the pectoral arch and between
the two series of branchial pouches. The heart consists of
four chambers^ — sinus venosus (s. ?;)., auricle (au\ ventri^
cle (v), and rnnus arfp.rinsus (c. art), through which the
blood passes in the order given. The sinus venosus is a thin-
walled, transverse, tubular chamber, into the ends of which
the great veins open. It opens into the auricle by an aper-
ture, the sinu- auricular aperture. The auricle is a large,
triangular, thin-walled chamber, situated in front of the sinus
venosus and dorsal to the ventricle. Its apex is directed
forwards, and its lateral angles project at the sides of the
ventricle ; it communicates with the ventricle by a slit-like
aperture guarded by a two-lipped valve. The ventricle is a
thick-walled, globular chamber, forming the most conspicu-
ous part of the heart when looked at from the ventral sur-
face. From it the conus arteriosus runs forwards as a
medium stout tube to the anterior end of the pericardial
cavity, where it gives off the ventral aorta. It contains two
transverse rows of valves, anterior and posterior, the former
consisting of three, the latter of three or four. The ventral
aorta (Fig. 227, v. ao} gives origin to a series of paired affer-
ent branchial arteries (a. br. a), one for each branchial
pouch.
From the gills the blood passes by means of the efferent
branchial arteries (e.&r.a). These efferent vessels form a
series of loops, one running around the margin of each of
the first four internal branchial clefts : a single vessel runs
along the interior border of the fifth branchial cleft and
opens into the fourth loop. The four main efferent bran-
£>,
2
t* o - •- **
.= C V c V.' -
c .- o'C g-
IPMI
SECT, xii PHYLUM CHORDATA 379
chial vessels run inwards and backwards from the loops
under cover of the mucous membrane of the roof of the
mouth to unite in a large median trunk — the dorsal aorta
(d. ao) . From the first efferent vessel, that from the first
or hyoidean gill, arises the carotid artery, which runs for-
wards and bifurcates to form the internal and external
carotid arteries {c.a}, supplying the head with arterial
blood.
The dorsal aorta runs backwards throughout the length
of the body- cavity, giving off numerous branches, and is
continued as the caudal artery (cd.a), which runs in the
canal enclosed by the inferior arches of the caudal vertebrae.
The veins are very thin-walled, and the larger trunks are
remarkable for their dilated character, from which they
have obtained the name of sinuses, though they are true
vessels and not sinuses in the sense in which the word is
used in dealing with the Invertebrates.
The venous blood is brought back from the head by a
pair of jugular or anterior cardinal sinuses (/. v), and from
the trunk by a pair of posterior cardinal sinuses (crd. v) . At
the level of the sinus venosus the anterior and posterior car-
dinals of each side unite to form a short, nearly transverse
sinus, fat precaval sinus or ductus Cuvieri (pr. cv. v) which
Ts continued into the lateral extremity of the sinus venosus.
There are two portal systems of veins, the renal portal
and fat hepatic portal (k.p.v], by which the kidneys and
liver, respectively, are supplied with venous blood. The cau-
dal vein (cd.v), which brings back the blood from the tail,
running, along with the caudal artery, through the inferior
arches of the vertebrae, divides on entering the abdominal
cavity into right and left renal portal veins (r.p.v}, which
end in a number of afferent renal veins supplying the kidneys.
The hepatic portal vein (fi.p. v) is formed by the conflu-
380 MANUAL OF ZOOLOGY SECT.
ence of veins derived from the intestine, stomach, pancreas,
and spleen, and runs forwards to enter the liver a little to
the right of the middle line. The blood from the liver
enters the sinus venosus by two hepatic sinuses (Ji. v) placed
close together.
The fore-brain consists of a rounded, smooth prosen-
cephalon (Fig. 219, V. H), divided into two lateral parts by
a very shallow median longitudinal groove. From its antero-
lateral region each half gives off a thick cord, which dilates
into a large mass of nerve matter, the olfactory lobe (L. le or third ventricle (dia) occupying
the interior of the diencephalon. From this opens in front
a median prosocxle, which gives off a pair of paracoeles
(para) extending into two lateral portions of the prosen-
cephalon.
A series of nerves arise in pairs from the brain and spinal
cord. From the spinal cord the nerves arise segmentally,
one pair corresponding to each myomere, and pass through
apertures in the neural arches of the vertebrae. Each arises
by two roots, a dorsal and a ventral. The dorsal root is
dilated into a ganglion, and contains only sensory fibres ;
the ventral root is non-ganglionated, and is motor. A
longitudinal ganglionated sympathetic nerve, extending along
the dorsal region of the coelome, is connected with the
spinal nerves, and sends branches to the viscera, blood-
vessels, etc.
From the brain arise ten pairs of nerves, some of which
are sensory, others motor, others mixed. Three are the
nerves of the principal sense organs : the first, or olfactory,
supplying the organ of smell (Fig. 228, olf. s) ; the second,
or optic, the retina of the eye, and the eighth, or auditory,
the organ of hearing. The third, or oculomotor, the fourth,
382
MANUAL OF ZOOLOGY
SECT.
or trochlear {path), and the sixth, or abducent, go to the
muscles of the eye; the fifth, or trigeminal (oph. V, mx. V,
mnd. V), to the snout and jaws ; the seventh, or facial (oph.
sjy-co
FIG. 228. — Scyllium catulUS. Dissection of the brain and spinal nerves from the
dorsal surface. The right eye has been removed. The cut surfaces of the
cartilaginous skull and spinal column are dotted. The ophthalmicus profundus
and the buccal branch of the facial are not represented, cl. /-<:/. j, branchial
clefts; ^A^epiphysis; ext. rect^ external rectus irmsrle of *hp py^-paii: gi.~T>Ti.
jjlU^opharvngear, /tor. can\ horizontal semicircular canal; hy. mnd. V"
mandibular portion ol tne iacial ;
internal rectus muscle; fat, vttg, '.
-, . r . . i ,i
divlBlOn ui Hii1 in^eminal;
'6JTT.
n, supei
ophthalm
lerior oblique muscle: int.
if. ool, inlerior oDiique nms
teral brancn 01 vagus; mx
_ v, maxillary
"ulfuctory gap^ultj1; — olf~ s, "oir^t^fy gar;
tranches 01 trigeminal and laciaj; path.
lourtTi nervel ff. Vll, palatine D ancn of Iacial; sp. co, spinal cord; spir,
spiracle; s. rect, superior rectus m scle; s. obi, superior oblique; vag, vagus;
vest, vestibule. (From Marshall and Hurst.)
VII.pl. VII, hy. mnd. VII), to the palate, lower jaw, and
hyoid arch; the ninth, or glossopharyngeal (gl.ph), to the
xii PHYLUM CHORDATA 3$3
hyoid and first branchial arches ; and the tenth, or vagus
(vag), to the remaining branchial arches, as well as to the
heart, stomach, and lateral line.
Besides the lateral line, which is probably the seat of a
delicate tactile sense, and the tongue, which is presumably
an organ of taste, there are the three pairs of characteristic
sensory organs, the structure and position of which are very
characteristic of vertebrates. These are the olfactory organs,
the eyes, and the auditory organs. The olfactory organs are
a pair of cup-like sacs on the under side of the snout, en-
closed in the olfactory capsules and opening externally by
the nostrils. They are lined with mucous membrane, which
is raised up into ridges so as to increase the surface. The
general structure of the eyes has already been described
(p. 356). The ear consists of the membranous labyrinth
(p. 357), which is enclosed in the cartilage of the auditory
region of the skull. It consists of a sac called the vestibule
(Fig. 228, vest), with which are connected three tubes,
called from their form the semicircular canals. Two of these,
the anterior and posterior canals, are vertical in position,
and are united with one another at their adjacent ends ; at
the other end each is dilated to form a bulb-like swelling,
the ampulla. The third, or horizontal canal (hor. can),
opens at each end into the vestibule, and has an ampulla
at its anterior end. The vestibule gives off a tube, the
endolymphatic duct, which opens at the auditory aperture
already referred to on the top of the head. Endolymph
containing otoliths (p. 358) fills the interior of the labyrinth,
and it is immediately surrounded externally by a space con-
taining a similar watery fluid, the perilymph. The fibres of
the auditory nerve are distributed to various parts of the
internal epithelium of the vestibule and semicircular canals.
There seems little doubt that the membranous labyrinth
384 MANUAL OF ZOOLOGY SECT.
has not only an auditory, but also an equilibrating function,
i.e., that the fish is enabled by its means to maintain its
equilibrium in the water.
The kidneys (Fig. 227, k) are long flat lobulated
bodies lying one on each side of the backbone in the
posterior part of the abdominal cavity. From the ventral
surface of each spring numerous delicate ducts which unite
into a single tube, the ureter, opening directly into the
cloaca in the female, in the male into a small paired cham-
ber, the urogenital sinus (ug. s), which opens into the
cloaca (cl).
In the male dogfish the testes are a pair of large soft
organs situated in the body-cavity, and united with one
another posteriorly. From the anterior end of each arise
numerous delicate efferent ducts, which enter a long convo-
luted spermiduct or vas deferens (z>. def} leading posteriorly
to the urogenital sinus. In the female there is a single
ovary suspended to the dorsal body-wall by a fold of peri-
toneum. In the adult it is studded all over with rounded
projections, the ova. There are two oviducts, a right and a
left, which extend along the whole length of the dorsal wall
of the ccelom below the kidneys. Anteriorly they unite
with one another below the gullet, and just in front of the
line and at the point of junction is a single aperture of con-
siderable size, by which both tubes communicate with the
coelom ; posteriorly they open into the cloaca. About the
anterior third of each oviduct is narrow ; its posterior two-
thirds is wide and distensible, and at the junction of the
parts is a yellowish glandular mass, the shell-gland.
Internal impregnation takes place, the spermatic fluid of
the male being passed, by means of the claspers, into the ovi-
ducts of the female. The ova, when ripe, break loose from
the surface of the ovary into the coelom, and thence pass,
XII
PHYLUM CHORDATA
385
through the common aperture, into one or other of the ovi-
ducts, where fertilisation (p. 393) occurs. As it passes into
the dilated portion of the oviduct, the oosperm (p. 60) of
Scyllium becomes surrounded by a horn-like egg-shell (Fig.
229), secreted by -the shell-gland, and having the form of a
pillow-case produced at each of its
four corners into a long tendril-like
process. The eggs are laid among
seaweed, to which they become
attached by their tendrils. In some
other dogfishes (Acanthias, Mus-
telus} a mere vestige of the egg-shell
is formed, and the eggs undergo the
whole of their development in the
oviducts, the young being eventu-
ally born alive with the form and
proportions of the adult.
The great size of the egg is due
to the immense quantity of yolk
which it contains ; its protoplasm
is almost entirely aggregated at one
pole in the form of a small disc.
When segmentation of the oosperm
takes place, it affects the protoplasm
alone, the inactive yolk taking no
part in the process. The disc of
protoplasm divides to form a little
heap of cells, the blastoderm, situ-
ated at one pole of the undivided sphere of yolk. The
blastoderm subsequently spreads out as a sheet of cells
over the yolk which it ultimately completely encloses.
While this extension of the blastoderm is taking place, its
middle part becomes raised up into a ridge-like thick-
2C
FIG. 229. — Dogfish, egg-case.
(After Dean.)
386 MANUAL OF ZOOLOGY SECT.
ening, which is moulded, step by step, into the form of
the embryo fish. The head, trunk, and tail acquire dis-
tinctness, and become more and more clearly separated off
from the bulk of the egg, the latter taking the form of a
yolk-sac attached by a narrow stalk to the ventral surface of
the embryo (Fig. 230).
In this condition the various parts of the adult fish can
be recognised, but the proportions are different, and the
FIG. 230. — A, embryo of Scyllium with yolk-sac (x i|); 13, under-side of head
enlarged, br. f, branchial filaments protruding through gill-clefts; §r. f ',
branchial filaments projecting through spiracle; cd.f, caudal fin; d. f, dorsal
fins; e, eye; ex. br. ap. external branchial apertures; mth, mouth; na, nostrils;
pet. f, pectoral fin: p'<. f, pelvic fin; st, yolk-stalk; v. f, ventral fin; yk. s,
yolk-sac. (After Balfour, slightly altered.)
head presents several peculiarities. The gill-filaments (br.f)
are so long as to project through the external branchial
apertures and the spiracle (br. f) in the form of long threads
abundantly supplied with blood-vessels, and apparently
serving for the absorption of nutriment — the albumen in
the egg-shell in the case of Scyllium, secretions of the ovi-
duct in the viviparous forms. Besides this mode of nutrition
the yolk-sac communicates with the intestine by a narrow
duct, through which absorption of its contents is constantly
xii PHYLUM CHORDATA 387
going on. By the time the young fish is ready to be born
or hatched, the greater part of the yolk-sac has been drawn
into the coelom, a mere vestige of it still dangling from the
ventral surface of the body.
In all the most important features of their organisation
there is a considerable degree of uniformity among the
Elasmobranchii.
In general shape the sharks (Fig. 231), for the most part,
are somewhat fusiform and slightly compressed laterally. In
the rays (Fig. 232), on the other hand, there is great dorso-
FIG. 231. — Shark (Lamna cornubica). (From Dean's Fishes.)
ventral compression. The head is in many cases produced
forwards into a long rostrum, which is of immense length
and bordered with triangular teeth in the saw- fish shark
{Pristiophorus} and saw-fish ray (Pristis}. In the hammer-
head shark the anterior part of the head is elongated trans-
versely.
There are well-developed median and paired fins. The
caudal fin is well developed, and, as a rule, strongly hetero-
cercal in the sharks and shark-like rays, feebly developed
in most of the latter group. The dorsal and ventral fins
are large in the sharks, the former completely divided into
two ; in the rays the dorsal fin is usually small, and the ven-
388
MANUAL OF ZOOLOGY
SECT.
tral absent. The paired fins are very differently developed
in the two groups. In the sharks both pairs are well devel-
oped, the pectoral being the larger. In the rays or skates
the pectoral fins are extremely large, very much larger than
the pelvic, fringing the greater part of the length of the
flattened body, and becoming prolonged forwards on either
FIG. 232. — European sting-ray (Urolophus cruciatus). (After Giinther.)
side and even in front of the head, so that the animal presents
the appearance of a broad fleshy leaf.
In all recent Elasmobranchs the male has, connected with
the pelvic fins, a pair of grooved appendages, the daspers
or pterygodia, which subserve copulation.
The mouth is situated on the ventral surface of the head,
usually a considerable distance from the anterior extremity.
xii PHYLUM CHORDATA 389
In front of each angle of the mouth on the ventral surface
is the opening of one of the olfactory sacs, each of which
is connected by a groove, the naso-buccal groove, with the
mouth-cavity. Behind the mouth, on the dorsal surface
in the rays, and at the side in the sharks, is the spiracle.
Along the sides of the neck in the sharks, and on the ven-
tral surface in the rays, is on either side a row of slit-like
apertures, the branchial slits or branchial clefts. These
are usually five in number on each side ; but in Hexanchus
and Chlamydoselachus there are six, and in Heptanchus
seven. A large cloacal opening is situated just in front of
the root of the tail, and a pair of small openings placed in
front of it, the abdominal pores, lead into the abdominal
cavity.
When the integument develops any hard parts, as is the
case in the majority of the Elasmobranchs, they take the
form, not of regular scales, as in most other fishes, but of
numerous hard bodies, which vary greatly in shape, are
usually extremely minute, but are in some cases developed,
in certain parts of the surface, into prominent tubercles or
spines. When these hard bodies are, as is commonly the
case, small and set closely together in the skin, they give
the surface very much the character of a fine file ; and the
skin so beset, known as " shagreen," is used for various
polishing purposes in the arts. This is the placoid form of
exoskeleton, to which reference has been already made.
Each of the hard bodies has the same structure as a tooth,
being composed of dentine, capped with enamel, and sup-
ported on a bony base, representing the cement or crusta
petrosa of the tooth, The dermal fin-rays are horny. The
skeleton is composed of cartilage, with, in many cases,
deposition of bony matter in special places, notably in the
jaws and the vertebral column. The entire spinal column
390
MANUAL OF ZOOLOGY
SECT.
may be nearly completely cartilaginous (Hexanchus and
Hcptanchus}, but usually the centra are strengthened by
tab
tas.
FIG. 233. — Skeleton of sting-ray (UrolOpllUS testaceus), ventral view. a. v. /,
anterior vertebral plate; bas. br, basi-branchial plate; br.i-br.j, branchial
arches. The branchial rays are represented as having been removed, the round
dots indicate their articulations with the arches cl, skeleton of clasper; h, m,
hyomandibular; ky, hyoid arch; lab, labial cartilage; lig, ligament connecting
the hyomandibular with the palato-quadrate and Meckel's cartilage; mck,
Meckel's cartilage; ms. J>t, mesopterygium; mt.pt, metapterygium of pectoral
fin; ml.pt', metapterygium of pelvic fin; nas, nasal cartilage; pal, palato-
quadrate ; pect, pectoral arch ; //, pelvic arch ; pro. pt, propterygium ; sp, spiracu-
lar cartilage.
XII
PHYLUM CHORDATA
391
radiating or concentric lamellae of calcified cartilage or
bone, or they may be completely calcified. They are
deeply amphiccelous, the remains of the notochord per-
sisting in the large spaces between the concave surfaces
of contiguous centra. In the rays the anterior part of the
spinal column becomes converted into a continuous solid
cartilaginous and bony mass — the anterior vertebral plate
(Fig. 233, a. v. p). Two main regions only are distinguish-
pt. orb
FIG. 234. — Lateral view of the skull of Heptanchus. mck, Meckel's cartilage;
pal. au, palato-quadrate; pt. orb, post-orbital process of the cranium, with
which the palato-quadrate articulates. (After Gegenbaur.)
able in the spinal column — the pre-caudal region and the
caudal, the latter being distinguished by the presence of in-
ferior or haemal arches. In the pre-caudal region short ribs
may be developed, but these are sometimes rudimentary or
entirely absent.
The skull is an undivided mass of cartilage, hardened, in
many cases, by deposition of osseous matter, but not con-
taining any separate bony elements. In all, the jaws are
392 MANUAL OF ZOOLOGY SECT.
connected with the skull through the intermediation of a
hyomandibular cartilage, or proximal element of the hyoid
arch ; in the great majority this is the sole articulation of
the jaws with the skull posteriorly, and the skull is on that
account said to be hyostylic ; but in Hexanchus and Hep-
tanchus (Fig. 234) the upper jaw has a direct articulation
with the skull behind the orbit, and the arrangement is
termed amphistylic. There are always five pairs of bran-
chial arches, except in Hexanchus and Chlamydoselachus,
which have six, and Heptanchus, in which there are seven.
The basal cartilages of the pectoral fin are typically three,
as in the dogfish, but there are sometimes four, and the
number may be reduced to two. There are usually two
such cartilages in the pelvic fin, and one alone may be
present.
Electric organs — organs in which electricity is formed
and stored up, to be discharged at the will of the fish —
occur in several Elasmobranchs. They are best developed
in the electric rays {Torpedo and Hypnos) in which they
form a pair of large masses running through the entire thick-
ness of the body between the head and the margin of the
pectoral fin. By means of the electric shocks which they
are able to administer at will to animals in their immediate
neighbourhood, these torpedo rays are able to ward off the
attacks of enemies and to kill or paralyse their prey.1
Teeth are developed in all on the palato-quadrate or
upper jaw and Meckel's cartilage or the lower jaw. They
are arranged in several parallel rows, and are developed
from a groove at the back of the jaw, successive rows
coming to the front, and, as they become worn out, falling
off and becoming replaced by others. In the sharks the
teeth are usually large and may be long, narrow, and pointed,
1 Torpedo occidentalis occurs on the southern coast of New England.
xii PHYLUM CHORDATA 393
or triangular with serrated edges, or made up of several
sharp cusps; in the rays, however, the teeth are more or
less obtuse, sometimes, as in the eagle rays, forming a con-
tinuous pavement of smooth plates covered with enamel,
adapted to crushing food consisting of such objects as
shell-fish and the like.
The various divisions of the enteric canal are similar in
all members of the class to what has already been described
in the case of the dogfish. A spiral valve is always present
in the large intestine, though its arrangement varies con-
siderably in the different families. The rectum always ter-
minates in a cloaca into which the urinary and genital ducts
also lead.
The respiratory organs have in all the same general
arrangement as in the dogfish. The inter-branchial septa
are of considerable breadth and the gill-filaments are
attached to them along their entire length.
The heart also has in all essential respects the same
structure throughout the group, the most characteristic
feature being the presence of a conus arteriosus which is
rhythmically contractile and contains several rows of valves.
Impregnation is internal in all the Elasmobranchii with
the exception of the Greenland shark (Lcemargus}, the
claspers acting as intromittent organs by whose agency the
semen is transmitted into the interior of the oviducts. In
all Elasmobranchs the ova are very large, consisting of a
large mass of yolk with, on one side, a disc of protoplasm,
the germinal disc. The ripe ovum ruptures the delicate
wall of the follicle in which it is enclosed and escapes' into,
the abdominal cavity to enter one of the oviducts, as already
stated in the case of the dogfish. Impregnation takes place
in the oviduct, and in the oviparous forms the impregnated
ovum becomes enclosed in a chitinous shell secreted by the
394 MANUAL OF ZOOLOGY SECT.
shell-gland. Enclosed in the shell, the form of which varies
in different groups, the egg passes to the exterior and under-
goes development until the young fish is fully formed, when
it escapes by rupturing the egg-shell. In the viviparous
forms, on the other hand, the ovum undergoes its develop-
ment in the uterus ; and the young fish, when it escapes to
the exterior, has assumed all the features of the adult.
The habits of the active, fierce, and voracious sharks,
which live in the surface waters of the sea waging war on
all and sundry, are in strong contrast with those of the more
sluggish rays, which live habitually on the bottom, usually in
shallow water, and feed chiefly on crustaceans and molluscs,
with the addition of such small fishes as they can capture.
As a group, the Elasmobranchs, more particularly the
sharks, are distinguished by their muscular strength, the
activity of their movements, and also by the acuteness of
their senses of sight and smell. The only deep-water
Elasmobranch known is a species of ray, which extends to
a depth of over 600 fathoms.
Sub-class III. Teleostomi1
The great majority of existing fishes belong to the sub-
class Teleostomi. As a matter of convenience we may look
upon the Teleostomi as consisting of two main divisions, —
the Teleostei, in which are included all the commonest and
most familiar fishes, such as the perch, pike, mackerel, cod,
sole, herring, eel, salmon, etc., and the Ganoidei or Ganoids,
such as the sturgeon, body pike (Lepidosteus), and bow-fin
(Amid} of North America, and the Polypterus of the Nile.
They are distinguished from Elasmobranchs by the posses-
1 Sub-class II, the small group Holocephali, or Chivnaeras and their
allies, is one of the groups omitted from this work. See Preface.
XII
PHYLUM CHORDATA
395
sion of an operculum or gill-cover, by the absence of a
cloaca, by having the primary skull and shoulder-girdle
complicated by the addition of membrane-bones, and by
possessing bony instead of horn-like fin-rays.
A typical Teleostomian, such as a trout (Fig. 235) l or a
herring, has a long compressed body nearly half of which
is formed by the tail, pointed anterior and posterior ends, a
large vertical tail-fin, a head of moderate size, and a terminal
mouth. Such a form is eminently fitted for progression
through the water. But from this characteristic fish form
op
FIG. 235. — Salmo fario. a. I, adipose lobe of pelvic fin; an, anus; c. f, caudal
fin; d.f. /, first dorsal; d.f. 2, second dorsal or adipose fin; /. /, lateral line;
op, operculum ; pet. f, pectoral fin ; pv . f, pelvic fin ; v. f, ventral fin. (After
Jardine.)
there are many striking deviations. The body may be
greatly elongated and almost cylindrical, as in the eels ; or
of great length and strongly flattened from side to side, as
in the ribbon-fishes ; or the head may be of immense pro-
portional size and strongly depressed, as in certain shore-
fishes, such as the fishing-frog ; or, as in the beautiful reef-
fishes, the whole body may be as high as it is long. The
mouth sometimes has a ventral position, as in the Elasmo-
branchs, with the snout prolonged over it ; this is the case,
1 Our common brook trout in the northeastern states is Salmo fontinalis.
396 MANUAL OF ZOOLOGY SECT.
for example, in the sturgeons (Fig. 240). On the other
hand, in the ground-feeding " star-gazers " and some others,
the lower jaw is underhung like that of a bull-dog, and the
mouth becomes dorsal in position. A beak may be pro-
duced by the elongation of the upper jaw, as in the sword-
fish, or of the lower jaw, as in the half-beak or czar-fish, or
of both jaws as in the bony pike.
An operculum or gill-cover (op), a flap which covers the
gills of each side and bounds in front the single, usually
crescentic gill-opening, is always present, and is supported
by four membrane bones. Ventrally the operculum is pro-
duced into a thin membranous extension, the branchio-
stegal membrane, which is in nearly all cases supported by a
series of bony rays. Spiracles are absent except in certain
of the Ganoids.
There are dorsal, ventral, and caudal median fins. The
dorsal is usually divided into two ; in a few it is partly or
wholly supported by a series of finlets. The caudal is in
the majority of a type to which the term homocercal is
applied. The homocercal caudal fin is divided into two
equal or sub-equal lobes, upper and lower, so that it appears
symmetrical externally, though the posterior portion of the
spinal column which supports it is strongly bent upwards
and terminates in the upper lobe. In some of the Ganoids,
however, this upward curvation of the caudal part of the
spinal column does not occur, and the tail is symmetrical
internally as well as externally ; in these the tail is said to
be diphycercal. In many Ganoids the tail is heterocercal, as
in nearly all the Elasmobranchs (p. 367). In some Teleos-
tomi dorsal, caudal, and ventral fins are united into a con-
tinuous fold. The dermal fin-rays of the caudal fin and a
portion or all of those of the rest of the fins are slender
flexible rods divided into a series of short segments and
xii PHYLUM CHORDATA 397
usually branching at the free ends. In many, however, the
anterior portions of the dorsal, ventral, and pelvic fins are
supported not by flexible jointed rays, but by stiff unjointed
sharp spines.
The paired fins, pectoral and pelvic, are usually thin and
flexible, supported mainly, or exclusively, by jointed rays.
The pectorals always retain their normal position, just
behind the gill-cleft, but the pelvics always become more or
less shifted forwards from their typical position beside the
vent; when they are not placed as far forwards as the
UST
JJ.EJt
FIG. 236. — Salmofario. Caudal end of vetebral column. CN, centrum; D.F.R,
dermal fin-rays; H. SP, haemal spine; H. ZYG, haemal zygapophysis ; N. SP,
neural spine; N. ZYG, neural zygapophysis; UST, urostyle.
middle of the abdomen, they are said to be abdominal in
position ; when further forwards, nearly beneath the pectorals,
they are said to be thoracic ; when still further, actually in
front of the pectorals and beneath the throat, they are said
to be jugular in position.
A very remarkable deviation from the typical form occurs
in the flat-fishes (Pkurontetida> including the soles, plaice,
flounders, turbots, etc.). The body (Fig. 237) is very
deep and strongly compressed ; the fish habitually rests on
the bottom, in some species on the right, in others on the
398
MANUAL OF ZOOLOGY
SECT.
left side. The under side is usually pure white, the upper
dark. The eyes are both on the upper side, and the skull
is distorted so as to adapt the orbits to this change of
position.1
le.
FIG. 237. — Pleuronectes cynoglOSSUS (craig-fluke), from the right side. d. f,
dorsal fin; I e, left eye; pet f, pectoral fin; pv. _/, pelvic fin; r. e, right eye;
v.f, ventral fin. (After Cuvier.)
In many Teleostei, such as the eels, the skin is devoid
of hard parts ; but in most cases there is an exoskeleton
developed in the derm. In the majority this takes the form
of scales, rounded plates of bone embedded in pouches of
the derm, and overlapping one another from behind for-
wards. When the free border of the scales presents an
even curve, they are called cycloid scales ; when the free
edge is produced into small spines, they are distinguished
as ctenoid scales (Fig. 238). In exceptional cases the scales
may be so large and strong as to form a rigid armour.
1 Our common flounders are Paralichthys dentatus from the southern
coast of New England, and Pseudopleuronectes americanus from the coast
north of Cape Cod.
XII
PHYLUM CHORDATA
399
Sometimes there is an armour formed of stout bony plates,
or scutes, while in other cases, as in the " file-fishes," the
exoskeleton takes the form of minute spines like the
FIG. 238. — A, ctenoid scale; B, ganoid scale. (After Giinther.)
shagreen of sharks, or as in many globe-fishes of long bony
spines ; lastly, in Polypterus (Fig. 239) and Lepidosteus are
found rhomboid or ganoid scales in the form of rhomboidal
plates of bone covered externally by a layer of enamel or
ganoin and joined together by pegs and sockets.
FIG. 239. — Polypterus birchir. A, entire animal ; B, ventral
view of throat, an, anus; br. tit, branchiostegal membrane;
c.f, caudal fin; d.f, dorsal finlets; jug //.jugular plates;
elvic fin; v.
., .,
na, nostril: pet./, pectoral fin; pv.f, pel
tral fin. (After Cuvier.)
.f, ven-
In the sturgeon the spinal column consists of a persistent
notochord with cartilaginous arches ; in the rest bony verte-
brae are present, the centres of which are nearly always
bi-concave.
400
MANUAL OF ZOOLOGY
SECT.
In the sturgeons (Fig. 240) and their allies the cranium
is an undivided mass of cartilage with a few isolated carti-
lage bones, and covered over dorsally by membrane bones.
In most of the other members of the group it is mainly or
entirely composed of numerous cartilage and membrane
bones (Fig. 240). Both upper and lower jaws are bounded
by membrane bones (/. mx, mx, dent}. The jaws are con-
nected with the skull by the intermediation of a hyomandib-
FIG. 240. — Skull of sturgeon, with the membrane bones removed, a, pharyngo-
branchial; AF, antorbital process; AR, articular; b, epibranchial; c, cerato-
branchial; C, notochord; Cop, basi-branchials; d, hypobranchial; De, dentary;
Gff, auditory capsule; HM, hyomandibular; ky, hyoid cornu; /A, inter-hyal;
Md, mandible; Na, nasal capsule; Gb, neural arches; PF, post-orbital pro-
cess; PQ, palato-quadrate; Ps. Ps' . Ps" , parasphenoid; Psp, neural spines;
Qu, quadrate; R. rostrum; Ri, ribs; Sp. TV", foramina for spinal nerves; Sy,
symplectic; WS, vertebral column; «, vagus foramen; I-V, branchial arches.
(From Wiedersheim's Comparative Anatomy.}
ular (hyom) which, however, probably does not correspond
with the cartilage so named in the dogfish and other Elas-
mobranchs. The pectoral arch is complicated by the addi-
tion of membrane bones, of which the most constant are a
pair of large clavicles. The pelvic arch is vestigial or absent.
Two genera of Teleostomi possess electric organs, — the
electric catfish (Malaptervrus) and the electric eel (Gym-
notus) ; the former occurs in fresh waters of tropical Africa,
XII
PHYLUM CHORD ATA
401
and the latter in Brazil and the Guyanas. Some Teleostomi
are toothless, but in most instances teeth are present, and
may be developed, not only on the pre-maxilla and maxilla
of the upper jaw, and the dentary of the lower, but on a
2D
402
MANUAL OF ZOOLOGY
SECT.
number of other bones in the wall of the mouth. In most
of the Teleostei the maxilla is devoid of teeth, and does not
enter into the upper boundary of the mouth opening. In
the great majority the teeth are small and very numerous,
adapted for preventing the struggling prey from slipping out
of the mouth, but quite unfitted for either tearing or crush-
ing ; but in many instances teeth are comparatively large and
few in number, and in some (Fig. 242) there is a marked
differentiation of the teeth, those in front of the jaws being
FIG. 242. — Premaxillae of Sargus, showing teeth. (After Owen.)
pointed or chisel-shaped, and adapted for seizing or cutting,
while the back teeth have rounded surfaces adapted for
crushing. The teeth may be either simply embedded in the
mucous membrane so as to be detached when the bones
are macerated or boiled, or they may be implanted in the
sockets of the bone or ankylosed to it. Their succession
is perpetual, i.e., injured or worn-out teeth are replaced at
all ages. The Ganoids have a spiral valve in the intestine ;
this is absent in the Teleostei. Cceca (the pyloric CKCO)
are commonly developed at the junction of the stomach and
small intestine. The anus is always distinct from, and in
front of, the urogenital apparatus, there being no cloaca
such as occurs in Elasmobranchs. The gills are usually
Xii PHYLUM CHORDATA 403
comb-like, consisting of rows of slender branchial filaments.
The inter-branchial septa are reduced as compared with
those of the Elasmobranchs, the branchial filaments project-
ing freely beyond them. As a rule, the gills are developed
in the first four branchial arches.
A characteristic structure of the Teleostomi is the air-
bladder or swimming bladder, which, however, is not present
in all. It is an elongated sac with elastic walls situated in
the body-cavity immediately below the spinal column. In
some cases (Ganoids and some Teleostei) it communicates
with the gullet by a duct, the pneumatic duct ; in the rest it
is a closed sac. It is sometimes divided into compartments,
or produced into lateral offshoots. In some of the Ganoids
its wall is sacculated, assuming an appearance not unlike
that of the lung of one of the higher air-breathing verte-
brates. The air-bladder seems able to act as a sort of
accessory organ of respiration. Its normal function, how-
ever, appears to be hydrostatic, i.e., it serves to keep the fish
of the same specific gravity as the water ; variations in press-
ure, as the fish ascends or descends, are regulated by ab-
sorption or secretion of gas.
In the Ganoids the heart has a structure very similar to
that of the dogfish, consisting of a sinus venosus, auricle,
ventricle, and conus arteriosus — the last being rhythmically
contractile like the other chambers, and containing rows of
valves. In Teleostei there is no such conus arteriosus; but
there is always a large bulb-like dilation of the base of the
ventral aorta, the bulbus aortce. The optic nerves of the
Ganoids agree with those of Elasmobranchs and of Verte-
brates in general in forming a chiasma, whereas in the
Teleostei they simply cross one another or decussate.
Most Teleostomi are oviparous, the eggs being impreg-
nated after they are laid. Many instances of parental care
404
MANUAL OF ZOOLOGY
of the young are known, the most familiar being that of the
male stickleback, which constructs a nest of weeds fastened
together by a glutinous secretion of the kidneys, and
jealously guards the developing young. In the sea-horse
{Hippocampus, Fig. 243) and the pipe fish (Sy-ngnafhus)
the young are developed in a pouch in the abdomen of the
male. In Aspredo, one of the cat-fish tribe, the eggs are
B
FIG. 243. — Hippocampus (sea-horse). In B, the operculum is removed to show the
gills, br. ap, branchial aperture; brd. p, brood-pouch; d.f, dorsal fin; g. gills;
pet./, pectoral fin. (From Claus and Giinther.)
pressed into the soft spongy skin of the belly, and thus
carried about by the parent. The ova, although containing
a large proportional amount of yolk, are always small as
compared with those of Elasmobranchs, never exceeding
5 to 10 mm. in diameter, and being usually much smaller.
xii PHYLUM CHORDATA 405
They are rarely protected by
an egg-shell. They are pro-
duced in immense numbers,
a single female sometimes lay-
ing several millions. In such
cases the mortality among
the unprotected embryos and
young is immense. The eggs
may be pelagic, i.e., so light
as to float when laid, as in the
cod, haddock, turbot, sole,
etc., or demersal, i.e., so heavy
as to sink to the bottom, as in
the herring, salmon, trout, etc.
Sub-class IV. Dipnoi
The Dipnoi or lung-fishes,
comprising as their living rep-
resentatives only the Queens-
land Ceratodus (Fig. 244),
or Burnet salmon, and the
mud-fishes, Protopterus and
Lepidosiren, of certain South
African and South American
rivers respectively, are fishes
of such well-marked and spe-
cial features that by some
zoologists they are separated
from the true fishes and re-
garded as constituting a sepa-
rate class of Vertebrates. One
of their peculiar features is
4o6
MANUAL OF ZOOLOGY
SECT.
indicated by their name Dipnoi ; not only do these animals
breathe by means of gills like ordinary fishes, but they have
a highly developed apparatus for the respiration of air —
a single lung in the case of Ceratodus, a pair of lungs
(united in front) in the other two genera. They have bony
scales and dermal fin-rays ; but the paired fins are con-
structed on a totally different type from those of any other
living fish. The fin, pectoral or pelvic as the case may be,
is leaf-like, or very long and narrow, and the skeleton (Fig.
245) consists of a central axis in the form of a slender, taper-
FIG. 245. — Ceratodus Forsteri. Lateral view of the anterior portion of the skeleton.
A, anterior median membrane bone of the roof of the skull; B. posterior median
membrane bone. r~, otic process; /. c. hy, posterior cornu of hyoid;
PMX, premaxilla: PR. OT, pro-otic; RA. UL, radio-ulna; SP. ETH, sphenethmoid; SQ,
squamosal; S. SCP, supra-scapula: SHS, suspensorium; TI. FI, tibio-fibula ; tr. pr, transverse
process: UST, urostyle; V. i, cervical vertebra; V. 9, sacral vertebra; VO, vomer; I-V
digits. B, the fourth vertebra, anterior face. a. zyg, anterior zygapophysis ; en. centrum;
Im, lamina; «. sf, neural spine; pd, pedicle; tr. pr, transverse process. (After Howes,
slightly altered.)
SECT. XII
PHYLUM CHORDATA
413
union of a pair of frontals in front with a pair of parietals
behind. Over the olfactory capsules are a pair of triangular
nasals (NA), and applied to their ventral surfaces small
» O W.Q
""*. "^ ^Js S-'S
flrfHilgf
Ils, s-inus venosus; tngt
tongue; ts, testis; ur, ureter; ur' , its aperture into the cloaca; UST, urostyle;
v, ventricle; T ly.s, ventral lymph sinus; i'o. t, vomerine teeth; vs. sent,
vesicula seminalis.
Eustachian tubes (eus. /, vide infra). On its floor is the
large tongue (tng), attached in front and free behind, where
it ends in a double point ; by means of its muscles it can be
2 E
4i 8 MANUAL OF ZOOLOGY sECt.
suddenly projected, point foremost, from the mouth, and is
used in the capture of insects. Immediately behind the
tongue is the glottis (gl). Teeth are arranged in a single
series round the edge of the upper jaw, attached to the pre-
maxillse and maxillae ; there is also a small patch of teeth
(vo. /) on each vomer just internal to the posterior nostril.
The teeth are small conical bodies, their bases ankylosed to
the bones ; their only use is to prevent the polished or slimy
bodies of the prey — insects and worms — from slipping out
of the mouth.
The buccal cavity narrows towards the pharynx, which
leads by a short gullet (gul) into a stomach (st) consisting of
a wide cardiac and a short, narrow pyloric division. The
duodenum (du), or first portion of the small intestine, passes
forwards parallel with the stomach ; the rest of the small
intestine is twisted into a coil. The large intestine or rectum
(ret) is very wide and short, and passes without change of
diameter into the cloaca (el) .
The liver (Ir) is two-lobed ; between the right and left
lobes lies a large gall-bladder. The pancreas (pn) is an
irregular gland surrounding the bile duct, into which it
pours its secretion; the spleen (spl) is a small, red globular
body attached near the anterior end of the rectum.
The lungs (I. Ing, r. Ing) are elastic sacs lying in the
anterior part of the coelom above the heart and liver ; their
size and appearance vary greatly according to their state of
distention. Each contains a spacious cavity, and has its
walls raised into a complete network of ridges abundantly
supplied with blood-vessels. The two lungs open anteriorly
into a small laryngo-tracheal chamber which communicates
with the mouth by the narrow slit-like glottis. The walls of
the laryngo-tracheal chamber are supported by a cartilagi-
nous framework, and its mucous membrane is raised into a
Xii PHYLUM CHORDATA 419
pair of horizontal folds, the vocal chords, by the vibration of
which the croak of the frog is produced.
In breathing, the frog keeps its mouth closed, and, by
depressing the floor of the mouth draws air into the buccal
cavity through the nostrils. The floor of the mouth is then
raised, the nostrils are closed, and the air is forced through
the glottis into the lungs. The skin is also an important
respiratory organ.
'The pericardium (Fig. 25 i,pcd) is not a separate cham-
ber, as in fishes, but the heart, enclosed in a pericardial
membrane, lies in the general coelomic cavity between the
gullet above and the epicoracoids below. The heart con-
sists of a sinus venosus (Figs. 251 and 252, s. #), right
and left auricles (r. au, /. au), a ventricle (v, vt), and a
conus arteriosus (c. art) . As in Dipnoi, the sinus venosus
opens into the right auricle, the pulmonary veins into the
left ; a striking advance is seen in the greatly increased size
of the left auricle and its separation by a complete partition,
the septum auricularum (Fig. 252, spt. aur), from the right.
The two auricles open by a common auriculo-ventricular
aperture, guarded by a pair of valves (au. v. v), into the sin-
gle ventricle. The conus springs from the right side of the
base of the ventricle ; it is separated from the latter by three
small semilunar valves, and is traversed obliquely along its
whole length by a large flap-like longitudinal valve (Iv)
which springs from its dorsal wall and is free ventrally. The
conus passes without change of diameter into a bulbus aorta,
the two being separated by a semilunar valve and by the
free end of the longitudinal valve. The bulbus gives off two
branches, right and left, each of them divided by two longi-
tudinal partitions into three vessels, — an inner or anterior,
the carotid trunk (car. tr), a middle, the systemic trunk or
aortic arch, and an outer or posterior, the pulmo-cutaneous
420 MANUAL OF ZOOLOGY SECT.
trunk (put. cu. tr}. The carotid and systemic trunks com-
municate separately with the bulbus, the two pulmo-cuta-
neous trunks communicate with the anterior end of the
conus by a single aperture placed just below the free end of
the longitudinal valve.
car.gl n -
]L r^
^^*^^*~ •
car.a.-
syst.tr
f>ul.cu,.tr'^**
FlG. 252. — Rana temporaria. The heart from the ventral aspect with the cavities
laid open, a, a', bristle in left carotid trunk; art. v. v, auriculo-ventricular
valves; b,b' ', bristle in left systemic trunk; c, c', bristle in left pulmo-cutaneous
trunk; car. a, carotid artery; car. gl, carotid plexus; c. art, conus arteriosus;
car. tr, carotid trunk; /. an, left auricle; Ig. a, lingual artery; /. ?', longitudinal
valve; finl. cu tr, pulmo-cutaneous trunk; flttl v, aperture of pulmonary veins;
r. au, right auricle; .r. an. ap, sinu-auricular aperture; spt. aur, septum auricu-
larum; v. v', valves; vt, ventricle.
After being bound together in the way described for a
short distance, the carotid, systemic, and pulmo-cutaneous
trunks separate from one another. The carotid trunk divides
XII
PHYLUM CHORD ATA
421
w
cZAcar.tr \^1
^*-V^sbk /^r/c"
S&^M^vert
FIG. 253. — Rana temporaria. The arterial system, with the heart, lungs, kidneys,
and left testis, from the ventral aspect, car, carotid artery; car. gl, carotid
gland; c. art, conus arteriosus; car. tr, carotid trunk; ccel. mes, cceliaco-
mesenteric artery; CM, cutaneous artery; d. ao, dorsal aorta; du, duodenal
artery; gs, gastric artery; hp, hepatic artery; il, iliac artery; int, intestinal
arteries; kd, kidney; /. an, left auricle; Ig, lingual artery; pul, pulmonary
artery; pul. cu. tr, pulmo-cutaneous trunk; r. an, right auricle; rn, renal
arteries; spl, splenic artery; sys. tr, systemic trunk; spin, spermatic artery;
is, testis; v, ventricle.
422 MANUAL OF ZOOLOGY SECT.
into carotid (Figs. 252, car. a and 253, car) and lingual (Jg)
arteries for the supply of the head, the former having at its
base a small swelling, the carotid gland (car.gl}, consisting
of a plexus of blood-vessels. The systemic trunks curve
round the gullet and unite with one another above it to form
the dorsal aorta (d. ao), from which, or from one of the
systemic trunks themselves, the arteries to all parts of the
body, except the head, the lungs, and the skin, are given off.
The pulmo-cutaneous trunk divides into two, a pulmonary
artery (put) to the lung, and a cutaneous artery (cu) to the
skin.
The blood from the head and fore-limbs is returned by
veins which unite to form a pair of large trunks, the pre-
cavals, which open separately into the sinus venosus.
One portion of the blood from the hind-limb is carried
forward by a vein which unites with its fellow of the oppo-
site side to form the abdominal vein (Fig. 254, abd), which
passes forwards, in the ventral body-wall, to the level of
the sternum, where it turns inwards and divides into two
branches, both breaking up into capillaries in the liver.
Just as it enters the liver it is joined by the hepatic portal
vein (hp.pt), bringing the blood from the stomach, intes-
tine, spleen, and pancreas. The rest of the blood from
the hind-limb is carried by the renal portal vein to the
corresponding kidney.
The blood is collected from the kidneys by the renal
veins (rn), which unite to form the large unpaired post-caval
vein (pt. cv). This passes forward through a notch in the
liver, receives the hepatic veins (hp) from that organ, and
finally opens into the sinus venosus. Thus the blood from
the hind-limbs has to pass through one of the two portal
systems on its way back to the heart ; part of it goes by the
renal portal veins to the kidneys, and thence, by the renal
xir PHYLUM CHORDATA 423
veins to the post-caval, part by the abdominal vein to the
liver, and thence by the hepatic veins to the post-caval.
Lastly, the blood which has been purified in the lungs is
returned by the pulmonary veins (////) directly to the left
auricle.
It will be perceived that the blood poured into the right
auricle is mostly impure or venous, that poured into the
left fully aerated or arterial. When the auricles contract,
which they do simultaneously, each passes its blood into the
corresponding part of the ventricle, which then instantly
contracts, before the venous and arterial bloods have time
to mix. Since the conus arteriosus springs from the right
side of the ventricle, it will at first receive only venous
blood, which, on the contraction of the conus, might pass
either into the bulbus aortse or into the aperture of the
pulmo-cutaneous trunks. But the carotid and systemic
trunks are connected with a much more extensive capillary
system than the pulmo-cutaneous, and the pressure in them
is proportionally great, so that it is easier for the blood to
enter the pulmo-cutaneous trunks than to force aside the
valves between the conus and the bulbus. A fraction of a
second is, however, enough to get up the pressure in the
pulmonary and cutaneous arteries, and in the meantime the
pressure in the arteries of the head, trunk, etc., is constantly
diminishing, owing to the continual flow of blood towards
the capillaries. Very soon, therefore, the blood forces the
valves aside and makes its way into the bulbus aortae. Here
again the course taken is that of least resistance ; owing to
the presence of the carotid gland the passage of blood into
the carotid trunks is less free than into the wide, elastic,
systemic trunks. These will, therefore, receive the next
portion of blood, which, the venous blood having been
mostly driven to the lungs, will be a mixture of venous and
424
MANUAL OF ZOOLOGY
SECT.
p*
FIG. 254. — Rana temporaria. The venous system with the heart, lungs, liver,
kidneys, and right testis, from the dorsal aspect. abd, abdominal vein; br,
brachial vein ; cd, .cardiac vein; efs. littb, dorso-lumbar vein ; du, duodenal vein;
ext. jit, external jugular vein; fin, femoral vein; gs, gastric vein; ///, hepatic
ein; hp . pt, hepatic portal vein ; int, intestinal veins; int ju, internal jugular
ein; kd, kidney; /. an, left auricle; Ing, lung; for, liver; ms. en, musculo-
utaneous vein; pr. cv, pre-caval vein; pt. cv, post-caval vein; pul, pulmonary
ein; pv, pelvic vein; r. au, right auricle; rn, renal veins; rn. pt, renal portal
ein; sc, sciatic vein : spl^, splenic vein; spm, spermatic vein; s. i>^ sinus venosus;
ts, testis; ves, vesical veins.
Xii PHYLUM CHORDATA 425
arterial. Finally, as the pressure rises in the systemic trunks,
the last portion of blood from the ventricle, which, coming
from the left side, is arterial, will pass into the carotids and
so supply the head.
The lymphatic system is very well developed, and is
remarkable for the dilatation of many of its vessels into
immense lymph sinuses. The lymph is pumped into the
veins by two pairs of lymph-hearts, one situated beneath
the supra-scapulae, the other beside the posterior end of the
urostyle.
The brain (Fig. 255) has a very small cerebellum (H If),
large optic lobes (Mff), a well-developed diencephalon,
and large hemispheres and olfactory lobes, the latter fused
in the median plane.
The first spinal nerve performs the function of the
hypoglossal, one of the cranial nerves of higher Vertebrates
supplying the muscles of the tongue : it passes out between
the first and second vertebrae. The spinal cord is short,
and ends in a delicate filament, the filum terminate. In
correspondence with the number of vertebrae there are only
ten pairs of spinal nerves, of which the second and third
unite to form a brachial plexus giving off the nerves to the
fore-limb, while the seventh to the tenth join to form a
lumbo- sacral plexus giving off the nerves to the hind-limb.
The olfactory sacs have each two openings: the anterior
nans or external nostril and the posterior nan's (Fig. 251,
/. na), or internal nostril, which opens into the mouth
immediately external to the vomer.
The eye and the auditory organ have the usual structure,
but in connection with the latter there is an important
accessory organ of hearing not hitherto met with. Bounded
externally by the tympanic membrane, and internally by the
outer wall of the auditory capsule, is a considerable space,
426
MANUAL OF ZOOLOGY
SECT.
the tympanic cavity {cav), which communicates with the
mouth by the short Eustachian tube already noticed (Fig.
251, eus. /), so that a probe thrust through the tympanic
membrane from outside passes directly into the mouth. In
ftfVil
ff } 1
•E
-MR
-M.d)
FIG. 255. — Rana esculenta. The brain. A, from above; B, from below, ch. opt,
optic chiasma; HH, cerebellum; Hyp, pituitary body; /«/, infundibulum;
L. ol, olfactory lobe; Med, spinal cord; MH, mid brain; NH, medulla ob-
longata; Th. opt, optic thalamus; Tr. opt, optic tract; I'H, cerebral hemi-
sphere; ZH, diencephalon ; I—X, cerebral nerves; XII. (/), hypoglossal (first
spinal) nerve. (From Wiedersheim's Comparative Anatomy}
the roof of the tympanic cavity lies a slender rod of bone
and cartilage, the columella, its head, or extra-columella,
attached to the inner surface of the tympanic membrane, its
*n PHYLUM CHORDATA 427
handle united to the stapes, a nodule of cartilage which is
fixed in the membrane of the fenestra ovalis (p. 358).
Sonorous vibrations striking the tympanic membrane are
communicated by the columella and stapes to the fenestra
ovalis, thence to the perilymph, and thence to the mem-
branous labyrinth. The connection of the Eustachian tube
with the mouth obviates undue compression of the air in
the tympanic cavity.
The kidneys (Figs. 251 and 253, Kd, and Figs. 256
and 257, N) are flat, somewhat oval bodies of a dark
red colour, lying in the posterior region of the ccelom.
On the ventral face of each is an elongated, yellow adrenal,
and irregularly scattered nephrostomes occur on the same
surface. They do not, however, communicate with the
urinary tubules, but with the renal veins, and serve to propel
the lymph from the coelom to the venous system. The
ureters ( Ur) pass backwards from the outer borders of the
kidney, and open into the dorsal wall of the cloaca ( Cl) .
Opening into the cloaca on its ventral side is a bilobed,
thin-walled, and very delicate sac, the urinary bladder (Fig.
251, <£/), into which the urine passes by gravitation from
the cloaca when the anus is closed.
The testes (Fig. 256, Ho) are white ovoid bodies lying
immediately ventral to the anterior ends of the kidneys, to
which they are attached by folds of peritoneum. From the
inner edge of each pass a number of delicate vasa efferentia,
which enter the kidney and become connected with the
urinary tubules. The spermatic fluid is thus passed into
the urinary tubules and carried off by the ureter, which is
therefore a urinogenital duct in the male frog. A vesicula
seminalis opens by numerous small ducts into the outer side
of the ureter. Attached to the testis are lobed bodies of a
bright yellow colour, the fat-bodies (FK) .
428
MANUAL OF ZOOLOGY
SECT.
The ovaries (Fig. 257, Ov) are large folded sacs, on the
surface of which the black and white ova project. A fat-
body is attached to each. The oviducts (Od} are greatly
convoluted tubes, the narrow anterior ends of which open
CvAo
FK
into the ccelom by small
apertures ( Of) placed close
to the bases of the lungs.
Their posterior ends are
wide and thin- walled (£//),
and open into the cloaca
(P) . The ova break loose
from the surface of the
ovary and enter the cce-
lomic apertures of the ovi-
ducts, the walls of which
are glandular, and secrete
an albuminous fluid having
the property of swelling up
in water. The eggs receive
a coating of this substance
as they pass down the ovi-
ducts, and are finally stored
up in the thin-walled pos-
terior portions of those
FIG. 256. — Rana esculenta. Urmogenital r
organs of the male. Ao, dorsal aorta; tubes, which in the
Cl, cloaca; Cv, post-caval vein ; FK, fat .
bodies; HO, testes; N, kidneys; S, mg SCaSOn become
apertures of ureters into cloaca; Ur, .. .
ureters. (From Wiedersheim's Com- mensely dilated and
parative Anatomy.) . ..
as uteri. The eggs are laid
in water in large masses ; each has one black and one white
hemisphere, the former always directed upwards, and is sur-
rounded by a sphere of jelly. During oviposition the male
sheds his spermatic fluid over the eggs, and the sperms
making their way through the jelly impregnate them.
XII
PHYLUM CHORD ATA
429
When the embryo escapes from the egg by the rupture of
the egg-membrane it swims about as a little fish-like creature
or tadpole, with two pairs of branched external gills and a
(3d—
FIG. 257. — Rana CSCUlenta. Urinogenital organs of the female. N, kidneys;
Od, oviduct; Of, its coelomic aperture; Ov, left ovary (the right is removed);
P, cloacal aperture of oviduct; 6". S' ' , cloacal apertures of ureters; Ut, uterine
dilatation of oviduct. (From Wiedersheim's Comparative Anatomy.)
long tail. There is no mouth, and eyes have not yet become
developed. On the lower surface of the head is a pair of
430
MANUAL OF ZOOLOGY
SECT.
suckers by which the tadpole is able to attach itself to
water-weeds. Soon a pair of external gills appears, the
mouth and gill-slits are formed, and the eyes appear. The
mouth is small, bounded by lips beset with horny papillae,
•hatched
FIG. 258. — Rana temporaria. Stages in the life-history, from the newly-hatc
Tadpoles (/) to the young Frog (5). 2a is a magnified view of 2. (F
Mivart.)
and provided with a pair of horny jaws. The enteric canal
grows to a great length and is coiled like a watch-spring, and
the tadpole browses upon the water-weeds which form its
xii PHYLUM CHORDATA 431
staple food, though it also eats decaying leaves and the flesh
of dead animals.
Soon the external gills show signs of shrivelling, and at
the same time internal gills, like those of fishes, are devel-
oped on the branchial arches. A fold of skin, the operculum,
appears on each side, in front of the gills, growing from the
region of the hyoid arch, and extends backwards until the
gill-slits and external gills are covered and there is only a
single small external branchial aperture on each side. On
the right side the operculum soon unites with the body- wall
so as to close the branchial aperture, but on the left side
the opening remains for a considerable time as the sole exit
of the water. At this time the tadpole is to all intents
and purposes a fish.
The lungs now appear, and the larva is for a time truly
amphibious, rising periodically to the surface to breathe air ;
the single branchial aperture, however, soon closes, and
henceforth respiration is purely aerial.
In the meantime the limbs are developed. The hind-
limbs appear as little rounded buds, one on each side of the
root of the tail. The fore-limbs arise beneath the operculum,
and are therefore hidden at first ; soon, however, they
emerge by forcing their way through the operculum. As
the limbs increase in size, the tail undergoes a progressive
shrinking. The mouth widens, the intestine undergoes a
relative diminution in length, and vegetable is exchanged
for animal diet. The little tailed frog can now leave the
water and hop about upon land ; its tail is soon completely
absorbed, and the metamorphosis is complete.
The frogs and toads are all closely allied as regards all
the main features of their structure — the chief differences
between the many genera and species being in such super-
ficial characteristics as coloration and proportions. In
432
MANUAL OF ZOOLOGY
SECT.
some teeth are altogether absent; in others the webs
between the toes are not developed; in some tree-frogs
(Hyla and allied genera) the toes terminate in sucking
discs. A less superficial point of divergence from the
structure of the common American frogs is to be observed in
some members of the group, such as the tree-frogs and toads
(Hyla, Bufo, and others), in which the two halves of the
shoulder-girdle, instead of being firmly united in the mid-
FIG. 259. — Salamandra maculosa. (After Cuvier.)
die line, overlap one another. In one small group the
tongue is absent. In some, again, there is no fish-like, gill-
bearing larva or tadpole — the young animal emerging from
the egg with the limbs formed, with no gills and no tail.
All the frogs and toads are grouped together to form an
order of Amphibia — the Anura or tailless Amphibia.
The newts and salamanders (Fig. 259), with a number of
other less widely known forms, differ from the frogs and
toads in the possession in the adult of a well-developed tail.
These constitute the order Urodela or tailed Amphibians.
Of these tailed Amphibians, some, such as the newts and
XII PHYLUM CHORDATA 433
salamanders, lose both gills and gill-
slits completely in the adult : while in
others (such as Proteus, Necturus, and
Siren), either gills are retained through-
out life, or, as in the American Meno-
poma, or hell-bender, gill-slits remain
as a permanent record of their pres-
ence in the larva. In some of the
tailed Amphibians the limbs are well-
developed ; in others they are very
small.
Widely different in many respects
from both the Anura and Urodela are
a group of Amphibia — the Gymno-
phiona — which are quite snake-like
in appearance, owing to the elongated
and narrow form of the body and the
entire absence of limbs. The group is
represented by the blind snake (Cos-
cilia} of Central and South America.
CLASS IV. REPTILIA
The class Reptilia comprises the
lizards and snakes, the tuataras, the
turtles and tortoises, and the alligators
and crocodiles. On a superficial com-
parison of these with the Amphibia, it
might be inferred that there is a close
alliance between the two groups ; but
this impression becomes weakened
when a closer examination is made of
the structure and development, and it Fl&na26o'(FromrMivaftC)r"
2 F
434 MANUAL OF ZOOLOGY SECT.
at length becomes evident that in the Reptilia we have
to do with a class of Vertebrates which stand on a dis-
tinctly higher plane than the Amphibia. One significant
feature of the Reptilia which marks them off sharply
from the Amphibia is that the lungs are the sole organs
of respiration, gills never being developed at any stage.
Another is the development in the embryo of two struc-
tures known as the amnion and the allantois, not devel-
oped in lower groups of Vertebrates, but present in the
embryos of all the higher. The amnion is a thin membrane
which covers over the body of the embryo, the space between
it and the latter being tensely filled with a watery fluid. The
amnion thus forms a sort of water-cushion, protecting the
delicate and fragile embryo from the effects of any shocks
which may be sustained by the eggs. The allantois, repre-
sented in the frog by the urinary bladder, is a membranous
structure developed as a hollow outgrowth of the enteric
canal at its posterior end. It becomes highly vascular, and
acts as an embryonic respiratory organ.
There are four well-marked orders of living reptiles : —
1. The Squamata, comprising the Lacertilia or lizards
(including the iguanas, monitors, skinks, geckos, chamaeleons,
and others), and the Ophidia or snakes (including the vipers
and rattlesnakes, pythons, boas, sea-snakes, etc.).
2. The Rhynchocephalia, including only the New Zealand
Tuatara (Hatteria).
3. The Chelonia, including the land tortoises, soft tor-
toises, river and marsh tortoises, and the turtles.
4. The Crocodilia, including the crocodiles, gavials, the
alligators and caimans.
The most striking external difference between a typical
lizard (Fig. 207) and the frog are in the covering of scales
in the case of the former, the comparative smallness of its
xii PHYLUM CHORDATA 435
head, and the presence of a distinct neck, the great length
of the caudal region, the shortness of the limbs, and the
approximate equality in length of the anterior and posterior
pairs. The anterior limbs are situated just behind the
neck, springing from the trunk towards the ventral surface.
The fore-limb, like that of the frog, is divided into three
parts, the upper-arm or brachium, the fore-arm or anti-
brachium, and the hand or manus ; there are five digits
provided with horny claws, the first digit or pollex being
the smallest. The hind-limbs arise from the posterior end
of the trunk towards the ventral aspect; each, like that of
the frog, consists of three divisions — thigh or femur, shank
or crus, and foot or pes. The pes, like the manus, termi-
nates in five clawed digits, of which the first or hallux is the
smallest. The head is somewhat pyramidal, slightly de-
pressed ; the openings of the external nares are situated
above the anterior extremity. The mouth is a wide slit-
like aperture running round the anterior border of the head.
At the sides are the eyes, each provided with upper and
lower opaque movable eyelids, and with a transparent third
eyelid or nictitating membrane, which, when withdrawn, lies
in the anterior angle of the orbit. Behind the eye is a
circular brown patch of skin, — the tympanic membrane, —
corresponding closely to that of the frog, but somewhat
sunk below the general level of the skin. The trunk is
elongated, strongly convex dorsally, flatter at the sides and
ventrally. At the root of the tail on the ventral surface is
a slit-like transverse aperture — the anus or cloacal aperture.
The tail is cylindrical, thick in front, gradually tapering to
a narrow posterior extremity ; it is nearly twice as long as
the head and trunk together.
There is an exoskeleton of horny epidermal scales covering
all parts, differing in size in different positions.
436 MANUAL OF ZOOLOGY SECT.
In some groups of lizards the tail is comparatively short
and thick; and in others it is depressed and expanded into
a leaf-like form. In the chamaeleons the long and tapering
tail is used as a prehensile organ, the coiling of which
round branches of the trees in which the animal lives, aids
in maintaining the balance of the body in climbing from
branch to branch.
In the limbs there is likewise a considerable amount of
variation in the different groups of the Lacertilia. Moder-
ately long pentadactyle limbs, like those of Lacerta, are the
rule. In the chamaeleons both fore- and hind-limbs become
prehensile by a special modification in the arrangement and
mode of articulation of the digits. In these remarkable
arboreal reptiles the three innermost digits of the manus are
joined together throughout their length by a web of skin,
and the two outer digits are similarly united ; the two sets
of digits are so articulated that they can be brought against
one another with a grasping movement much analogous to
the grasping movements of a parrot's foot or the hand of
man. A similar arrangement prevails in the pes, the only
difference being that the two innermost and three outermost
digits are united. In some groups of Lacertilia, on the
other hand, such as the blind-worms (Anguit), limbs are
entirely absent, or are represented only by mere vestiges ;
and numerous intermediate gradations exist between these
and forms, such as Lacerta, with well-developed limbs. The
limbless lizards, such as the glass-snake, and Pygopus (Fig.
261), bear a very close resemblance to the snakes, not only
in the absence of the limbs, but also in the general form of
the body and the mode of locomotion.
The body of a snake is elongated, narrow, and cylindrical,
usually tapering towards the posterior end, sometimes with,
more usually without, a constriction behind the head. In
XII
PHYLUM CHORDATA
437
the absence of limbs, the beginning of the short caudal
region is only indicated by the position of the cloacal open-
ing. The fore-limbs are never represented even by vestiges ;
in some pythons there are inconspicuous vestiges of hind-
limbs, in the form of small claw-like processes. The mouth
of the snake is capable of being very widely opened by the
free articulation of the lower jaw, and it is this mainly which
distinguishes it from the snake-like lizards. But other, less
FlG. 261. — PygOpUS lepidopus. (After Brehm.)
conspicuous, points of distinction are the absence of movable
eyelids in the snake, and also the absence of a tympanum.
Hatteria, the New Zealand Tuatara (Fig. 262), the only
living representative of the Rhynchocephalia, is a lizard-like
reptile with a well-developed laterally-compressed tail, and
pentadactyle extremities, very similar to those of a typical
lizard. The upper surface is covered with small granular
scales, and a crest of compressed spine-like scales runs along
the middle of the dorsal surface. The lower surface is
covered with transverse rows of large squarish plates.
438
MANUAL OF ZOOLOGY
In the Chelonia (Fig. 263) the body is short and broad,
enclosed in a hard "shell," consisting of a dorsal part or
carapace and a ventral part or plastron. These are firmly
united, apertures being left between them for the head and
neck, the tail and the limbs. The neck is long and mobile ;
the tail short. The limbs are fully developed, though short.
In some (land and fresh-water tortoises) they are provided
each with five free digits terminating in curved horny claws ;
in the turtles the digits are closely united together, and the
FIG. 262. — Hatteria punctata. (After Brehm.)
limb assumes the character of a " flipper " or swimming
paddle. The cloacal aperture is longitudinal.
The Crocodilia, the largest of living reptiles, have the
trunk elongated and somewhat depressed, so that its breadth
is much greater than its height. The snout is prolonged,
the neck short, the tail longer than the body and compressed
laterally. The limbs are relatively short and powerful, with
five digits in the manus and four in the pes, those of the
latter being partly or completely united by webs of skin.
XII
PHYLUM CHORDATA
439
The eyes are very small ; the nostrils placed close to the
end of the snout and capable of being closed by a sphincter
muscle. The cloacal aperture is a longitudinal slit.
Characteristic of the Squamata is the development in the
epidermis of horny plates, the scales, which cover the entire
surface, overlapping one another in an imbricating manner.
Sometimes they are similar in character over all parts of the
surface ; usually there are specially developed scales — the
FIG. 263. — Grecian tortoise (Testudo graeca). (After Brehm.)
head shields — covering the upper surface of the head. In
the majority of snakes the ventral surface is covered with a
row of large transversely elongated scales, the ventral shields.
In some lizards (chamaeleons and geckos) the scales are
reduced and modified into the form of minute tubercles or
granules. In some lizards special developments of the
scales occur in the form of large tubercles or spines.
In the snake-like Amphisbaenians there are no true scales,
440 MANUAL OF ZOOLOGY SECT.
with the exception of the head shields, but the surface is
marked out into annular bands of squarish areas.
In addition to the modification of the scales, the integu-
ment of the chamaeleons is remarkable for the changes of
colour which it undergoes, these changes being due to the
presence in the dermis of pigment cells which contract
or expand under the influence of the nervous system,
in a way that reminds one of the integument of the
Cephalopoda.
In the Chelonia, scales, when developed, are confined to
the head and neck, the limbs and the tail, but in all of them,
with the exception of the soft tortoises, both dorsal and ven-
tral surfaces are covered by a system of large horny plates.
A series of horny head-shields usually cover the dorsal sur-
face of the head. Beneath the horny plates of the dorsal
and ventral surfaces are the bony carapace and plastron,
partly composed of dermal bones, but so intimately united
with elements derived from the endoskeleton that the entire
structure is best described in connection with the latter
(P- 443).
In the Crocodilia, the dorsal surface is covered with longi-
tudinal rows of sculptured horny plates, beneath which are
bony dermal scutes of corresponding form. The ventral
surface of the body is covered with scales like those of a
lizard. The horny plates of the dorsal surface of the tail are
elevated into a longitudinal crest.
A periodical ecdysis or casting and renewal of the outer
layers of the horny epidermis takes place in all the Reptilia.
Sometimes this occurs in a fragmentary manner ; but in
snakes and many lizards the whole comes away as a con-
tinuous slough.
The vertebra are always fully ossified. Only in the
geckos and Hatteria are the centra amphiccelous, with
XII
PHYLUM CHORDATA
441
remnants of the notochord in
the inter-central spaces. In
most of the others the centra
are precocious, a ball-like con-
vexity on the posterior surface
of each centrum projecting
into a cup-like concavity on
the anterior face of the next.
The various regions of the
spinal column are well marked
in most of the lizards, in the
Chelonia, and in the Croco-
dilia (Fig. 264). In the snakes
and many of the snake-like
lizards only two regions are
distinguishable — pre - caudal
and caudal. In the others
there is a sacral region com-
prising two vertebrae, which
have strong transverse pro-
cesses for articulation with
the ilia. The first and sec-
ond vertebrae are always modi-
fied to form an atlas and
axis. Ribs are developed in
connection with all the ver-
tebrae of the pre-sacral or pre-
caudal region; in the caudal
region they are usually replaced
by inferior arches. In the fly-
ing lizards {Draco) a num-
ber of the ribs are greatly
produced, and support a pair
ti
ii
T
o 6
tr
11
§1
II
442
MANUAL OF ZOOLOGY
SECT.
of wide flaps of skin at the sides of the body, acting as
wings or rather as parachutes. In Hatteria and Crocodilia
(Fig. 264) each rib has connected with it posteriorly a flat-
tened curved cartilage, the uncinate.
FIG. 265. — CiStudO lutaria. Skeleton seen from below; the plastron has been
removed and is represented on one side. C. costal plate; Co, coracoid; e, ento-
plastron; Ep, epiplastron; f, fibula; fe, femur; H, humerus; //, ilium; ts,
ischium; M, marginal plates; Nu, nuchal plate; Pb, pubis; Pro, pro-cora-
coid; Py, pygal plates; R, radius; Sc, scapula; T, tibia; U, ulna. (From
Zittel.)
In the Chelonia (Fig. 265) the total number of vertebrae
is always smaller than in the members of the other orders.
The cervical and the caudal are the only regions in which
the vertebrae are movable upon one another. The vertebrae
xii PHYLUM CHORDATA 443
of the trunk, usually ten in number, are immovably united
together. Each of the neural spines, from the second to
the ninth inclusively, is expanded into a flat plate, and the
row of neural plates (Fig. 266, V), thus formed constitutes
the median portion of the carapace. The ribs are likewise
immovable ; a short distance from its origin each passes
into a large bony costal plate (C), and the series of costal
plates uniting by their edges form a large part of the cara-
pace on either side of the row of neural plates. The cara-
pace is made up of the neural and costal plates supplemented
by a row of marginal plates (Figs. 265 and 266, M) running
along the edge, and nuchal (Nu) and pygal (Py) plates
FIG. 266. — Chelone midas. Transverse section of skeleton. C, costal plate; C,
centrum; M, marginal plate; P, lateral element of plastron; R, rib; V, expanded
neural plate. (After Huxley.)
situated respectively in front of and behind the row of
neural plates.
The bony elements of the plastron of the Chelonia are an
anterior and median plate and six pairs of plates — the six
pairs probably being, of similar nature to the abdominal
ribs of the Crocodilia.
The sternum in the Lacertilia is a plate of cartilage with a
bifid posterior continuation. In the Ophidia and Chelonia
it is absent. In the Crocodilia it is a broad plate with a
posterior continuation or hyposternum, extending backwards
as far as the pelvis.
444 MANUAL OF ZOOLOGY SECT.
A series of ossifications — the abdominal ribs, with a mesial
abdominal sternum — lie in the wall of the abdomen in the
Crocodilia (Fig. 264, Sta), and similar ossifications occur
also in the monitors and in Hatteria. The elements of
the plastron of the Chelonia are probably of a similar
character.
In the skull ossification is much more complete than in
the Amphibia, the primary chondrocranium persisting to a
considerable extent only in some lizards and in Hatteria,
and the number of bones is much greater.
The parasphenoid is reduced, and its place is taken by
large basi-occipital, basi-sphenoid, and pre-sphenoid bones.
The lower jaw articulates with the skull through the interme-
diation of a quadrate bone, which is movable in the lizards
and snakes, fixed in Hatteria, the Chelonia, and Crocodilia.
A remarkable feature of the skull of the snakes (Fig. 267),
is the free articulations of the bones of the jaws, permitting
of the mouth being opened very wide so as to allow the
passage of the relatively large animals which the snake
swallows whole ; this wide opening of the mouth is further
aided by the two halves of the mandible not being firmly
fixed together anteriorly, but merely connected together by
means of elastic tissue, so that they are capable of being
widely separated from one another.
In accordance with their purely aerial mode of respira-
tion, the visceral arches are much more reduced in the
Reptilia than in the Amphibia in general. The only well-
developed post mandibular arch is the hyoid, and even
this may undergo considerable reduction (Ophidia). The
branchial arches, except in so far as they may contribute to
the formation of the tracheal rings, are not represented in
the adult, with the exception of most Chelonia, in which the
first branchial arch persists.
Xii PHYLUM CHORDATA 445
In the lizard (Fig. 268) and crocodiles there is a cross-
shaped membrane-bone, the interclavide or episternum (epist),
in relation to the pectoral arch and sternum. In the limb-
less lizards the pectoral arch may be absent or may be well
developed ; it is completely wanting in all snakes. In the
pelvic arch the ischium is separated from the pubis by a wide
space not developed in the Amphibia. Slight vestiges of hind-
limbs occur in some pythons alone among the Ophidia.
FIG. 267. — A, lateral view of skull of rattlesnake (Crotalus). B. O, basi-occipital;
B. S, basi-sphenoid; E. O, exoccipital; F. <9, fossa ovalis; La, conjoined lac-
rymal and pre-frontal; L. f, articulation between lacrymal and frontal; Mn,
mandible; MX, maxilla; Na, nasal; PI, palatine; Pmx, pre-maxilla; P. Sph,
pre-sphenoid ; Pt, pterygoid; Qu, quadrate; Sq, squamosal; //. V, foramina
of exit of the second and fifth cranial nerves. B, transverse section at point
lettered B in Fig. A; T, trabeculae. (After Huxley.)
In the lizards teeth are present in the pre-maxillae, the
maxillae, the mandible, and usually the palatines. These
are in most lizards small and simple, and uniform in shape
and arrangement. A Mexican Lizard, Heloderma, which
also occurs in Utah and Arizona, differs from all the rest in
446
MANUAL OF ZOOLOGY
SECT.
having teeth which are perforated for the ducts of poison-
glands. In the snakes (Fig. 267) teeth are rarely devel-
oped on the pre-maxillae, but are present on the maxillae,
palatines, pterygoids, and sometimes the transverse bones,
as well as the dentary of the mandible. They may be of
the same nature throughout, solid, elongated, sharp-pointed
teeth, which are usually strongly recurved, so that they have
the character of sharp hooks, their function being rather to
episl
7T/
r.s
773
FIG. 268. — Pectoral arch and sternum of a lizard (Lacerta agilis). cl, clavicle;
cor, coracoid; ep. cor, epicoracoid; epist, episternum; glen, glenoid cavity for
head of humerus; pr. cor, pro-coracoid ; r. I — r. 4, first to fourth sternal ribs;
sc, scapula; st, sternum; supra, sc, supra-scapula. (After Hoffman.)
hold the prey and prevent it slipping from the mouth while
being swallowed than to masticate it. Non-venomous snakes
possess teeth only of this character. In the venomous snakes,
more or fewer of the maxillary teeth assume the character
of poison-fangs. These are usually much larger than the
ordinary teeth, and either grooved or perforated by a canal
xii PHYLUM CHORDATA 447
for the passage of the duct of the poison-gland. In the
vipers there is a single large curved poison-fang with small
reserve-fangs at its base, these being the only teeth borne
by the maxilla, which is very short ; in the venomous colu-
brine snakes the poison-fangs are either the most anterior or
the most posterior of a considerable range of maxillary teeth.
In the vipers the large poison-fang is capable, owing to the
maxilla in which it is fixed being movable on a hinge -joint,
of being rotated through a considerable angle, and moved
from a nearly horizontal position, in which it lies along the
roof of the mouth, embedded in folds of the mucous mem-
brane, to a nearly vertical one when- the snake opens his
mouth to strike its prey.
In Hatteria there are pointed, triangular, laterally-
compressed teeth, arranged in two parallel rows, one along
the maxilla, the other along the palatine. The teeth of the
lower jaw, which are of similar character, bite in between
these two upper rows, all the rows becoming worn down
in the adult in such a way as to form continuous ridges.
Each pre-maxilla bears a prominent, chisel-shaped incisor,
represented in the young animal by two pointed teeth. In
the young Hatteria a tooth has been found on each vomer —
a condition exceptional among reptiles.
In the Chelonia, teeth are entirely absent, the jaws being
invested in a horny layer in such a way as to form a structure
like a bird's beak.
The Crocodilia have numerous teeth which are confined
to the pre-maxillae, the maxillae, and the dentary. They are
large, conical, hollow teeth, devoid of roots, each lodged in
its socket or alveolus, and each becoming replaced, when
worn out, by a successor developed on its inner side.
In the enteric canal of the Reptiles the principal special
features to be noticed are the muscular, gizzard-like stomach
448
MANUAL OF ZOOLOGY
of the Crocodilia, the presence of a rudimentary caecum at
the junction of small and large intestines in most Lacertilia
and in the Ophidia, and the presence of numerous large
cornified papillae in the oesophagus of the Turtles.
The Reptiles have all an
elongated trachea, the wall
of which is supported
by numerous cartilaginous
rings. The anterior part
of this is dilated to form the
larynx, the wall of which
is supported by certain spe-
cial cartilages — the cricoid
and the arytenoids. The
trachea bifurcates posteri-
orly to form two bronchi,
right and left, one passing
to each lung.
The lungs of the Lacer-
tilia and Ophidia are sim-
ple and sac-like, like those
of the frog. In the Croco-
dilia and Chelonia they are
of a more complex char-
acter, being divided inter-
nally by septa into a number
of chambers.
. In the heart (Fig. 269)
the sinus venosus is always
distinct, and is divided into
two parts by a septum ;
its aperture of communication with the right auricle is
guarded by valves. There are always two quite distinct
BA-
FlG. 269. —Heart of monitor (Varanus)
dissected to show the cavity of the
ventricle and the vessels leading out
from it. A. ^', auricles; A o, dorsal
aorta; Ap. Ap' ', pulmonary arteries;
Asc, subclavian artery; Ca. Ca' , caro-
tids; RA. RA, roots of dorsal aorta;
Trca, innominate trunk ; V, ventricle ;
t, right aortic arch; *, left aortic arch.
(From Wiedersheim.)
XII
PHYLUM CHORDATA
449
auricles, as in the Amphibia, the right receiving the venous
blood from the body, the
left the oxygenated blood
brought from the lungs by
the pulmonary veins. But
a vital point of difference
between the heart of the
reptile and that of the am-
phibian is that in the
former the ventricle is al-
ways more or less com-
pletely divided into right
and left portions. In all the
Lacertilia, Ophidia, and
Chelonia the ventricle is
incompletely divided by
a septum which does
not entirely cut off the
two portions of the
cavity from one another.
But in the Crocodilia
the cavity is completely
divided, so that we may
speak of distinct right
and left ventricles.
The brain of Reptiles
is somewhat more highly
organised than that of the
Amphibia. The Cerebral FIG. 270. - Brain of aUigator, from above.
hemispheres are well de-
veloped in all. The mid-
brain consists usually of
two closely approximated oval optic lobes. The cerebellum
2G
Mtl
B. ol., olfactory bulb ; G. /, epiphysis ;
HH, cerebellum ; Met) ' , spinal cord ; Mff,
optic lobes ; NH, medulla oblongata ;
VH, cerebral hemispheres ; / — XI, cra-
nial nerves ; i, 2, first and second spinal
nerves. (After Wiedersheim.)
450 MANUAL OF ZOOLOGY SECT.
is always of small size, except in the Crocodilia (Fig. 270),
in which it is comparatively highly developed, and consists
of a median and two lateral lobes.
The eyes are relatively large, with a cartilaginous sclerotic
in which a ring of bony plates is developed in some cases.
Most reptiles have both upper and lower eyelids and nicti-
tating membrane. The greater number of the geckos and
all the snakes constitute exceptions, movable eyelids being
absent in both these groups. In the chamaeleons there is
a single circular eyelid with a central aperture.
The middle ear is absent in the snakes, though a colu-
mella auris is present, embedded in muscular and fibrous
tissue.
Developed in close relation to the epiphysis there is in
many lizards (Lacerfa. Varanus, Anguis, Grammatophora,
and others) and in Hatteria, a remarkably eye-like organ —
the pineal eye (Fig. 271), which is situated in a foramen of
the cranial roof immediately under the integument, and
covered over by a specially modified, transparent scale.
Like the epiphysis itself, the pineal eye is developed as a
hollow outgrowth of the roof of the diencephalon ; the
distal end of this becomes constricted off as a hollow sphere,
while the remainder becomes converted into a nerve. The
nerve degenerates before the animal reaches maturity, so
that the organ would appear — though evidently, from its
structure, an organ of sight — to have now entirely or nearly
lost its function.
Though fertilisation is always internal, most Reptilia are
oviparous, laying eggs clothed in a tough, parchment-like or
calcified shell. These are usually deposited in holes and
left to hatch by the heat of the sun. In the crocodiles they
are deposited in a rough nest and guarded by the mother.
In all cases development has only progressed to a very early
XII
PHYLUM CHORDATA
45 i
stage when the deposition of the eggs takes place, and it is
only after a more or less prolonged period of incubation that
the young, fully formed in almost every respect, emerge
from the shell and shift for themselves. Many lizards,
k
8t
FIG. 271. — Section of the pineal eye of Hatteria punctata. g> blood-vessels; h,
cavity of the eye filled with fluid; k, capsule of connective tissue; /, lens; m,
molecular layer of the retina; r, retina; st, stalk of the pineal eye; x, cells in
the stalk. (From Wiedersheim, after Baldwin Spencer.)
however, and a few snakes are viviparous, the ova being
developed in the interior of the oviduct, and the young
reaching the exterior in the completely formed condition.
452 MANUAL OF ZOOLOGY SECT.
The lizards are for the most part terrestrial animals,
usually extremely active in their movements and endowed
with keen senses. The majority readily ascend trees, and
many kinds are habitually arboreal ; but the chamaeleons
are the only members of the group which have special modi-
fications of their structure in adaptation with an arboreal
mode of life. The skinks and the amphisbaenians are
swift and skilful burrowers. The geckos are enabled by the
aid of the sucker-like discs on the ends of their toes to run
readily over vertical or overhanging smooth surfaces. A
few lizards, on the other hand, live habitually in fresh water.
The flying lizards (Draco) are arboreal, and make use of
their wings — or, to speak more accurately, aeroplane or para-
chute (thin folds of skin supported by the greatly produced
ribs) — to enable them to take short flights from branch to
branch. Chalmydosaurus and certain other genera are
exceptional' in frequently running on the hind-feet, with the
fore-feet entirely elevated from the ground. A tolerably
high temperature is essential for the maintenance of the
vital activities of lizards, low temperatures bringing on an
inert condition, which usually passes, during the coldest
part of the year, into a state of suspended animation or
hibernation. The food of lizards is entirely of an animal
nature. The smaller kinds prey on insects of all kinds, and
on worms. Chamseleons, also, feed on insects, which they
capture by darting out the extensile tongue covered with a
viscid secretion. Other lizards supplement their insect diet,
when opportunity offers, with small reptiles of various kinds,
frogs and newts, small birds and their eggs, and small mam-
mals, such as mice and the like. The larger kinds, such as
the monitors and iguanas prey exclusively on other ver-
tebrates ; some, on occasion, are carrion-feeders. Most
lizards lay eggs enclosed in a tough calcified shell. These
xii PHYLUM CHORDATA 453
they simply bury in the earth, leaving them to be hatched
by the heat of the sun. Some, however, are viviparous ; in
all cases the young are left to shift for themselves as soon as
they are born.
Snakes are also usually extremely active and alert in their
movements ; and most are very intolerant of cold, under-
going a hibernation of greater or less duration during the
winter season. Many live habitually on the surface of the
ground — some kinds by preference in sandy places or
among rocks, others among long herbage. Some (tree-
snakes) live habitually among the branches of trees.
Others (fresh-water snakes) inhabit fresh water; others
(sea-snakes) live in the sea. The mode of locomotion of
snakes on the ground is extremely characteristic, the
reptile moving along by a series of horizontal undulations
brought about by contractions of the muscles inserted into
the ribs, any inequalities on the surface of the ground
serving as fulcra against which the free posterior edges
of the ventral shields (which are firmly connected with the
ends of the ribs) are enabled to act. The burrowing blind-
snakes and other families of small snakes feed on insects
and worms. All the rest prey on vertebrates of various
kinds — fishes, frogs, lizards, snakes, birds and their eggs,
and mammals. The pythons and boas kill their prey by
constriction, winding their body closely round it and draw-
ing the coils tight till the victim is crushed or asphyxiated.
Some other non-venomous snakes kill with bites of their
numerous sharp teeth. The venomous snakes sometimes,
when the prey is a small and weak animal such as a frog,
swallow it alive : usually they first kill it with the venom of
their poison-fangs.
When a venomous snake strikes, the poison is pressed out
from the poison-gland by the contraction of the masseter
454
MANUAL OF ZOOLOGY
SECT.
(Fig. 272, Me), one of the muscles which raise the lower
jaw : it is thus forced along the duct ( Gc) to the aperture
(za), and injected into the wound made by the fang. The
effect is to produce acute pain with increasing lethargy and
weakness, and in the case of the venom of some kinds of
snakes, paralysis. According to the relative amount of the
poison injected and the degree of its virulence (which differs
not only in different kinds of snakes, but in the same snake
under different conditions) the symptoms may -result in
death, or the bitten animal may recover. The poison is a
FIG. 272. — Poison apparatus of rattlesnake. A , eye ; Gc, poison-duct entering
the poison-fang at f ; Km, muscles of mastication partly cut through at * ; Me,
masseter or constrictor muscle ; Me' , continuation of the constrictor muscle to the
lower jaw ; N, nasal opening ; S, fibrous poison-sac ; 2, tongue ; za, opening of
the poison-duct ; zf, pouch of mucous membrane enclosing the poison-fangs.
(FromWiedersheim. )
clear, slightly straw-coloured or greenish liquid ; it preserves
its venomous properties for an indefinite period, even if
completely desiccated. The poisonous principles are cer-
tain proteids not to be distinguished chemically from other
proteids which have no such poisonous properties. Immu-
nity against the effects of the poison, and relief of the symp-
toms after a bite has been inflicted, have been found to be
conferred by injections of the serum of animals which have
xii PHYLUM CHORDATA
455
been treated with injections of increasing doses of the
poison.
The majority of snakes are viviparous. Some, however,
lay eggs, which, nearly always, like those of the oviparous
lizards, are left to be hatched by the heat of the sun, some
of the Pythons being exceptional in incubating them among
the folds of the body.
Hatteria lives in burrows in company with mutton-birds
(Puffinus), and feeds on insects and small birds. It lays
eggs enclosed in a tough parchment-like shell. The eggs
are laid in November, and the embryos pass the winter in
a state of hibernation unknown to any other vertebrate
embryo, not emerging from the egg until nearly thirteen
months have elapsed (Dendy).
Of the Chelonia some (land- tortoises) are terrestrial;
others (fresh- water tortoises) inhabit streams and ponds,
while the sea-turtles and luths, or leather-backed turtles,
inhabit the sea. Even among reptiles they are remarkable
for their tenacity of life, and will live for a long time after
severe mutilations, even after the removal of the brain ; but
they readily succumb to the effects of cold. Like most
other reptiles, the land and fresh-water tortoises living in
colder regions hibernate in the winter ; in warmer latitudes
they sometimes pass through a similar period of quiescence
in the dry season. The food of the green turtles is exclusively
vegetable ; some of the land tortoises are also exclusively
vegetable feeders ; other Chelonia either live on plant food,
together with worms, insects, and the like, or are com-
pletely carnivorous. All are oviparous, the number of eggs
laid being usually very great (as many as 240 in the sea-
turtles) ; these they lay in a burrow carefully prepared in
the earth, or, in the case of the sea-turtles, in the sand of
the sea-shore, in a round hole about fifteen or twenty inches
456 MANUAL OF ZOOLOGY SECT.
deep and ten inches in diameter, and having covered them
over, leave them to hatch.
The crocodiles and alligators, the largest of living reptiles,
are in the main aquatic in their habits, inhabiting rivers,
and, in the case of some species, estuaries. Endowed with
great muscular power, these reptiles are able, by the move-
ments of the powerful tail and the webbed hind- feet, to
dart through the water with lightning-like rapidity. By
lying in wait motionless, sometimes completely submerged
with the exception of the extremity of the snout bearing
the nostrils, they are often able by the suddenness and
swiftness of their onset to seize the most watchful and timid
animals. In the majority of cases the greater part, and in
some the whole, of their food consists of fishes ; but all the
larger and more powerful kinds prey also on birds and
mammals of all kinds, which they seize unawares when they
come down to drink or attempt to cross the stream.
On land their movements are comparatively slow and
awkward, and they are correspondingly more timid and
helpless.
The Crocodilia are all oviparous, and the eggs, as large in
some species as those of a goose, are brought forth in great
numbers (sometimes 100 or more), and either buried in the
sand or deposited in rough nests.
CLASS V. AVES
In many respects birds are the most highly specialised of
Craniata. As a class they are adapted for aerial life, and
almost every part of their organisation is modified in ac-
cordance with the unusual environment. The non-conduct-
ing covering of feathers; the modification of the fore-limbs
as wings, of the sternum and shoulder-girdle to serve as
XII PHYLUM CHORDATA 457
origins of the wing-muscles, and of the pelvic girdle and
hind-limbs to enable them to support the entire weight of
the body "on land ; the perfection of the respiratory system,
producing a higher temperature than in any other animals,—
all these peculiarities are of the nature of adaptations to
flight.
The common or domestic pigeon is known under many
varieties which differ from one another in size, proportions,
coloration, details in the arrangements of the feathers, and
in many points of internal anatomy.
The following description refers especially to the common
dovecot pigeon.
In the entire bird (Fig. 273) the plump trunk appears to
be continued insensibly into the small, mobile head, with its
rounded brain-case and prominent beak formed of the upper
and lower jaws covered by horny sheaths. The head, neck,
and trunk are invested in a close covering of feathers, all
directed backwards and overlapping one another. Posteriorly
the trunk gives origin to a number of outstanding feathers
which constitute what is ordinarily called the tail. From
the anterior region of the trunk spring the wings, also
covered with feathers, and, in the position of rest, folded
against t"he sides of the body. The legs spring from the
hinder end of the trunk, but, owing to the thick covering
of feathers, only the feet are to be seen in the living bird,
each covered with scales and terminating in four digits
(dg /' — dg 4'), three directed forwards and one backwards.
In order to make a fair comparison of the outer form
with that of other craniate types, it is necessary to remove the
feathers. When this is done the bird is seen to have a
long, cylindrical, and very mobile neck, sharply separated
both from head and trunk. The true tail is a short, conical
projection of the trunk, known as the uropygium, and giving
458
MANUAL OF ZOOLOGY
SECT.
origin to the group of large feathers (ret) to which the word
" tail " is usually applied. On the dorsal surface of the
uropygium is a papilla bearing on its summit the opening of
FIG. 273. — Columba livia. The entire animal from the left side with most of the
feathers removed ad. dg. rmx, ad-digital remex; al. sp, ala spuria; an, anus:
au. ap, auditory aperture; cb. ring, cubital remiges; cr, cere; dg. I, 2, $, digits
ofmanus; dg /', 2', 3', 4, digits of pes; hu fit, humeral pteryla; Ig, ligament
of remiges; md. dg rmg, mid-digital remiges; na, nostril; net. m, nictitating
membrane; o. gl, oil gland; pr. dg. rmg, pre-digital remises; pr. ptgm , pre-
patagium; //. ptgm, post-patagium ; ret, mesial rectrix of right side; ret', sacs
of left rectrices; sp- pt, spinal pteryla; ts. mtts, tarso-metatarsus; v. apt,
ventral apterium, or featherless space.
xii PHYLUM CHORDATA 459
a large gland, the oil-gland (o.gl), used for lubricating or
"preening" the feathers.
The wings show the three typical divisions of the fore-
limb, upper arm, fore-arm, and hand, but the parts of the
hand are closely bound together by skin, and only three
imperfectly marked digits, the second (dg 2) much larger
than the first (dg i) and third (dg j), can be distinguished.
In the position of rest the three divisions of the wing are
bent upon one another in the form of a Z : during flight the
entire wing is straightened out at right angles to the trunk.
In the hind-limb the short thigh is closely bound to the
trunk : the foot is clearly divisible into a proximal portion,
the tarso-metatarsus (ts. mtts} and four digits, of which one,
the hallux (dg /'), is directed backwards, the others, the
second, third, and fourth of the typical foot, forwards.
The mouth is terminal and is guarded by the elongated
upper and lower beaks ; it has, therefore, a very wide gap.
On each side of the base of the upper beak is a swollen
area of soft skin, the cere (cr) surrounding the nostril (no),
which has thus a remarkably backward position. The eyes
are very large, and each is guarded by an upper and a lower
eyelid and a transparent nictitating membrane (net. m). A
short distance behind the eye is the auditory aperture
(au. ap\ concealed by feathers in the entire bird, and lead-
ing into a short external auditory meatus, closed below
by the tympanic membrane. The amis or cloacal aper-
ture (an), is a large, transversely elongated aperture placed
on the ventral surface at the junction of the uropygium with
the trunk.
The exoskeleton is purely epidermal, like that of the
lizard, which it also resembles in consisting partly of horny
scales. These cover the tarso-metatarsus and che digits of
the foot, and are quite reptilian in appearance and structure.
460
MANUAL OF ZOOLOGY
SECT.
Each digit of the foot is terminated by a claw which is also
a horny product of the epidermis, and the beaks are of the
same nature. The rest of the body, however, is covered by
feathers, a unique type of epidermal product found nowhere
outside the present class.
inf.uittb
FIG. 274. — Columba liyia. A, proximal portion of a remex. cal, .calamus; inf.
umb, inferior umbilicus; rch, rachis; sup. umb, superior umbilicus. B, fifo-
plume. C, nestling-down. (C, from Bronn's Thierreich.)
A feather (Fig. 274) is an elongated structure consisting
of a hollow stalk, the calamus or quill (cat), and an ex-
panded distal portion, the vexillum or vane. At the
proximal end of the quill is a small aperture, the inferior
umbilicus (inf. umb), into which fits, in the entire bird, a
xii PHYLUM CHORDATA 461 .
small conical prolongation of the skin, the feather papilla.
A second extremely minute aperture, the superior umbilicus
(sup. umb), occurs at the junction of the quill with the vane
on the inner or ventral face of the feather, i.e., the face
adjacent to the body.
The vane has a longitudinal axis or rachis (rch) contin-
uous proximally with the quill, but differing from the latter
in being solid. To each side of the rachis is attached a kind
of membrane forming the expanded part of the feather and
composed of barbs, delicate thread-like structures which
extend obliquely outwards from the rachis. In an uninjured
feather the barbs are closely connected so as to form a con-
tinuous sheet, but a moderate amount of force separates
them from one another, and it can readily be made out with
the aid of a magnifying glass that they are bound together
by extremely delicate oblique filaments, the barbules, having
the same general relation to the barbs as the barbs themselves
to the rachis.
Adjacent barbules interlock by means of a system of min-
ute hooklets and flanges, and in this way the parts of the
feather are so bound together that the entire structure offers
great resistance to the air.
Among the contour feathers which form the main cover-
ing of the bird and have the structure just described, are
found filpplumes (Fig. 274, B), delicate hair-like feathers
having a long axis and a few barbs, devoid of locking
apparatus, at the distal end. Nestling pigeons are covered
with a temporary investment of down feathers (C), in which
also there is no interlocking of the barbs : when these first
appear each is covered by a horny sheath like a glove finger.
Feathers, like scales, arise in the embryo from papillae of
the skin formed of derm with an epidermal covering. The
papilla becomes sunk in a sac, the feather-follicle, from
462
MANUAL OF ZOOLOGY
SECT.
which it subsequently protrudes as an elongated feather-germ,
its vascular dermal interior being the feather-pulp. The
horny substance of the feather is formed from the epidermis
of the feather-germ.
The feathers do not spring uniformly from the whole sur-
face of the body, but from certain defined areas (Fig. 275),
c.
FIG. 275. — Pterylosis of Columba livia. A, ventral; B, dorsal, al. pt, alar
pteryla or wing-tract; c. pt, cephalic pteryla or head-tract; cd. pt, caudal
pteryla or tail-tract; cr. pt, crural pteryla; cr. apt, cervical apterium or neck-
space; fm. pt, femoral pteryla; hit. pt, humeral pteryla; lat. apt, lateral
apterium; sp.pt, spinal pteryla; i>. apt, ventral apterium; v. pt, ventral pteryla.
(After Nitsch.)
the feather tracts or pteryla (sp.pt, hu. pt, etc.), separated
from one another by featherless spaces or apteria (y. apt,
etc.), from which only a few filoplumes grow.
In the wings and tail certain special arrangements of the
feathers are to be distinguished. When the wing is stretched
XII
PHYLUM CHORDATA
463
CtCT?
out at right angles to the trunk, twenty-three large feathers
(Fig. 273) are seen to spring from its hinder or post-axial
border': these are the remiges or wing-quills. Twelve of
them are connected with the ulna and are called cubitals
or secondaries (cb. rmg) . The rest are known as primaries.
In the tail there are twelve long rectrices {ret) or tail-quills
springing in a semicircle from the uropygium. The whole
feather-arrangement is known^as the pterylosis.
f. trs
$cb
FIG. 276. — Columba livia. The bones of the trunk, acr. cor, acrocoracoid ;
a. tr, anti-trochanter; actb, acetabulum; car, carina sterni; cd. v, caudal verte-
brae; cor, coracoid; cv. r, cervical ribs; _/ trs, probe passed into foramen
triosseum; fur, furcula; gl. cv, glenoid cavity; z7, ilium; is, ischium; is. for,
ischiatic foramen; obt. n, obturator notch; pu, pubis; pyg. st, pygostyle; scp.
scapula; s. scr, syn-sacrum; st, sternum; st. r, sternal ribs; th. -v. I, first, and
th. v. 3, last thoracic vertebra; unc, uncinates; vr. r, vertebral ribs.
The vertebral column is distinguished from that of most
other Craniata by the great length and extreme mobility of
the neck, the rigidity of the trunk region, and the shortness
of the tail. There are fourteen cervical vertebrae, the last
two of which have double-headed ribs (Fig. 276,^. r) each
464
MANUAL OF ZOOLOGY
SECT.
CTV
having its proximal end divisible into the head proper articu-
lating with the centrum of the vertebra, and a tubercle with
the transverse process : their distal ends are free, not uniting
with the sternum. In the third to the twelfth there are
vestigial ribs (Fig. 277, rb), each having its head fused with
the centrum, and its tubercle with the transverse process.
The whole rib thus has the appearance of a short, backwardly
directed transverse process perforated at its base.
The centra of the cervical vertebrae differ from those of
all other Vertebrata in having saddle-shaped surfaces, the
anterior face (Fig. 277, A) being
concave from side to side and
convex from above downwards.
This peculiar form of vertebra is
distinguished as heteroccelous.
The first two vertebrae, the
atlas and axis, are specially
modified. The atlas is a ring-
like bone with an articulation on
its anterior surface for the single
occipital condyle of the skull.
The axis has projecting forwards
FIG. 277. — Columba livia. Cer-
vical vertebra; A, anterior; from itS Centrum, a peg-like pro-
B. posterior face. a. zyg, an-
terior zygapophysis; en, cen- CCSS, the odontoid prOCCSS, which
trum; n.a, neural arch; p.zyg,
posterior zygapophysis; rb,ri\>; llCS in the lower part of the ring
•vrb.f, vertebrarterial foramen.
of the atlas.
Between the last cervical vertebra and the pelvic region
come four thoracic vertebrae (Fig. 276), the first three
united into a single mass, the fourth free. They all bear
ribs, each consisting of a vertebral (vr. r) and a sternal
(st. r) portion, and articulating with the vertebra by a double
head. Springing from the posterior edge of the vertebral
rib is an uncinate (Fig. 276, unc), resembling that of Hatteria
XII
PHYLUM CHORDATA
465
t p
and the crocodile, but formed of bone and ankylosed with
the rib.
Following upon the fourth thoracic are about twelve
vertebrae all fused into a single mass (Fig. 276, s. scr)y and
giving attachment laterally to the
immense pelvic girdle. The
whole of this group of vertebrae
has, therefore, the function of a
sacrum, differing from that of a
reptile in the large number of
vertebrae composing it. The
first of them bears a pair of free
ribs, and is, therefore, the fifth
or last thoracic (th. v. j). The
next five or six have no free
ribs, and may be looked upon
as lumbar (Fig. 278, I1 — s3).
Next come two sacral vertebrae
(^r1) homologous with those of
the lizard. The remaining five
vertebrae of the pelvic region are
caudal. Thus the mass of ver-
tebrae supporting the pelvic girdle
in the pigeon is a compound
sacrum, or syn-sacrum, formed by the fusion of the posterior
thoracic, all the lumbar and sacral, and the anterior caudal
vertebrae.
The syn-sacrum if- followed by six free caudals and the
vertebral column ends posteriorly in an upturned, compressed
bone, the pygostyle or ploughshare-bone (Fig. 276, pyg. sf),
formed by the fusion of four or more of the hindermost
caudal vertebrae.
The sternum (Fig. 2*76, sf) is one of the most character-
2H
FIG. 278. — Columba livia. Sac-
rum of a nestling (about
fourteen days old), ventral
aspect, c1, centrum of first
sacral vertebra; c1, centrum of
fifth caudal; c. r, first sacral
rib; 71, centrum of first lumbar;
Is, of third lumbar; s1. of fourth
lumbar; s*, of sixth lumbar;
tr. p, transverse process of
first lumbar; tr. p, of fifth
lumbar; tr p" , of first sacral.
(From Parker's Zootomy.)
466
MANUAL OF ZOOLOGY
SECT.
istic parts of the bird's skeleton. It is a broad plate of bone
produced ventrally, in the sagittal plane, into a deep keel or
carina sterni (car), formed, in the young bird, from a separate
centre of ossification. The posterior border of the sternum
presents two pairs of notches, covered, in the recent state,
an
FIG. 279. — Columba livia. Skull of young specimen. A, dorsal; B, ventral; C,
left side. al. s, alisphenoid; an, angular; ar, articular; b 0, basi-occipital;
d. dentary; e. o, ex-occipital; eu, aperture of Eustachian tube;y". m, foramen
magnum; f-r, frontal; i. o. s, inter-orbital septum; ju, jugal; Ic, lachrymal; Ib. s,
lambdoidal suture; m. eth, mesethmoid; >«_r, maxilla; mx. p, maxillo-palatine
process; na, no.', net" , nasal; o. c, occipital condyle; or.fr, orbital plate of
frontal; pa, parietal; pa. s, parasphenoid (rostrum); //, palatine; /. mx, pre-
maxilla; pt, pterygoid; qu, quadrate; s. an, supra-angular; s. a, supra-occipital;
sg, squamosal; ty. tympanic cavity; II. — XII, foramina for cerebral nerves.
(From Parker's Zootomy.)
XII
PHYLUM CHORDATA
467
b.hy
by ligament ; its anterior edge bears a pair of deep grooves
for the articulation of the coracoids.
The skull (Fig. 279) is distinguished at once by its
rounded brain- case, immense orbits, and long pointed beak.
The foramen magnum (/. m) looks downwards as well as
backwards, so as to be visible in a ventral view, and on its
anterior margin is a single, small, rounded, occipital condyle
(o. c}. Most of the bones, both of the cranial and facial
regions, are firmly ankylosed in the adult, and can be made
out only in the young bird.
The premaxillas (Fig. 279, /. mx) are united into a large
triradiate bone which forms
practically the whole of the
upper beak. The maxillae
(Fig. 279, mx), on the other
hand, are small, and have
their anterior ends produced
inwards into spongy maxillo-
palatine processes (Fig. 279,
mx.p). The slender poste-
rior end of the maxilla is
continued backwards by an
equally slender jugal (ju)
and quadrato - jugal to the
quadrate. The latter (Fig.
279, qu) is a stout three-
rayed bone articulating by FIG. 280 —Columbia livia. Hyoid ap-
r • i L r paratus. The cartilaginous parts are
tWO facets With the rOOf dotted. J.Ar./.basi-branchials; b hy,
r .1 • . j basi-hyal ; c . br, cerato - branchial ;
of the tympanic cavity, and c, hj hyoid comu; */. br, epi-
presenting below a condyle
for articulation with the mandible : the mandible of the
young bird consists of a cartilage bone, the articular (Fig.
279, ar), and four membrane bones, which all coalesce in the
b.br.3.
468
MANUAL OF ZOOLOGY
SECT.
adult. The hyoid apparatus (Fig. 280), is of characteristic
form, having an arrow-shaped body (b. hy) with a short pair
of anterior cornua (c. hy) derived from the hyoid arch, and
a long pair of posterior cornua (c. br., ep. br) from the first
branchial. The colu-
mella is a rod-shaped
bone ankylosed to the
stapes, and bearing at
its outer end a three-
rayed cartilage or ex-
tra-columella fixed to
the tympanic mem-
brane.
The shoulder-girdle
(Fig. 276) is quite un-
like that of other Cra-
niates. There is a pair
of stout, pillar - like
coracoids (cor) articu-
lating with deep facets
on the anterior border
of the sternum and
directed upwards, for-
wards, and outwards.
The dorsal end of each
is produced into an
acrocoracoid process
(acr. cor), and below
this, to the posterior
FIG. 281.— Columba livia. Skeleton of the left aspect of the bone, is
wing. cp. mtcf>, carpo-metacarpus; hu, hu- , , . ,.
merus; ph.i, phalanx of first digit; ph. 2', attached by ligament a
ph. 2" ', phalanges of second digit; ph-3, i L j /
phalanx of third digit; f>n. for, pneumatic Sabre-Shaped SCapllM
foramen; fa, radius; ra . radiale; ul, ulna; * ,\ u* u A
ul', ulnare. (s#) Vvhich extends
rat
XII
PHYLUM CHORDATA
469
backwards over the ribs, and includes, with the coracoid, an
acute angle, the coraco-scapular angle. The glenoid cavity
(gl. cv) is formed in equal proportion by the two bones ; in-
ternal to it the scapula is produced into an acromion process.
In front of the coracoids is a slender V-shaped bone, the
furcula (fur) or " merrythought," the apex of which nearly
reaches the sternum, while each of its extremities is attached
by ligament to the acromion and acro-coracoid processes
of the corresponding side in
such a way that a large aper-
ture, the foramen triosseum
(/„ frs) is left between the
three bones of the shoulder-
girdle. The furcula is a mem-
brane bone and represents
fused clavicles and inter-
clavicle.
Equally characteristic is the
skeleton of the fore-limb. The
humerus (Fig. 281, hu) is a
large, strong bone, with a
greatly expanded head and
a prominent ridge for the in-
sertion of the pectoral muscle.
The radius (ra) is slender
and nearly straight, the ulna
stouter and gently curved.
There are two large free car-
pals, a radiale (ra') and an ulnare (#/'), and articulating
with these is a bone called the carpo-metacarpus (cp. mtcp),
consisting of two rods, that on the preaxial side strong and
nearly straight, that on the postaxial side slender and curved,
fused with one another at both their proximal and distal
FIG. 282. — Columba livia. Left manus
of
parts
agtnous
radiale ;
cp. 2, ulnare; ntcp. i. 2,3, meta-
carpals; ph. i, phalanx of first digit;
ph. 2, ph. 2', phalanges of second
digit; ph. 3, phalanx of third digit;
ra, radius; ul, ulna. (From
Parker's Zootomy.)
470 MANUAL OF ZOOLOGY SECT.
ends ; the proximal end is produced pre-axially, into an
outstanding step-like process.
The study of its development shows that this bone is
formed by the union of the distal carpals with three meta-
carpals (Fig. 282), the second and third of which are the
two rod-like portions of the bone, the first, the step-like
projection. Articulating with the first metacarpal is a single
pointed phalanx (ph. i) ; the second metacarpal bears two
phalanges, the proximal one ( ph. 2') produced postaxially
into a flange, the distal one (ph. 2") pointed ; the third
metacarpal bears a single pointed phalanx (ph. j).
ac
»tt
FIG. 283. — Columba livia. Left innominate of a nestling. The cartilage is dotted.
ac, acetabulum; a. tr, anti-trochanter; il, pre-acetabular; and /'/', post-acetab-
ular portion of ilium; is, ischium; z. s. f, ischiatic foramen; ob. f, obturator
notch; pu, pubis. (From Parker's Zootomy.}
The pelvic girdle (Fig. 283). The ilium (il) is an
immense bone, attached by fibrous union with the whole
of the syn-sacrum and becoming ankylosed with it in the
adult. As usual it furnishes the dorsal portion of the acetab-
ulum. The ventral portion of the acetabulum is furnished
in about equal proportions by the pubis and ischium
(Fig. 283) : it is not completely closed by bone, but is
perforated by an aperture covered by membrane in the
recent state. Both pubis and ischium are directed sharply
XII
PHYLUM CHORDATA
471
backwards from their dorsal
nearly parallel. Neither is-
chiuin nor pubis unites ven-
trally with its fellow to form
a symphysis.
In the hind-limb the/emur
(Fig. 2%4,/e) is a compara-
tively short bone. Its proxi-
mal extremity bears a promi-
nent tro chanter (tr) and a
rounded head (hd} . Its dis-
tant end is produced into
pulley-like condyles. Articu-
lating with the femur is a
very long bone, the tibio-
tarsus (ti. ts} ; its distal end
is pulley-like, not concave
like the corresponding ex-
tremity of the tibia of other
Amniota. The study of its
development shows that the
pulley-like distal end of the
bone (Fig. 285, //*) con-
sists of the proximal tarsals,
— astragalus and calcaneum,
— which at an early period
unite with the tibia and give
rise to the compound shank-
bone of the adult. The fibula
(Fig. 284, /) is very small,
much shorter than the tibia,
and tapers to a point at its
distal end.
or ace tabular ends, and lie
472
MANUAL OF ZOOLOGY
SECT.
ti
ntl*-
Following the tibio- tarsus is an elongated bone, the tarso-
metatarsus (ts. mtts), presenting at its proximal end a con-
cave surface for the tibio-tarsus, and at its distal end three
distinct pulleys for the articulation of the three forwardly
directed toes. In the young bird the proximal end of
this bone is a separate cartilage (Fig. 285, tl'2), repre-
senting the distal tarsals, and followed by three distinct
metatarsals, belonging respectively
to the second, third, and fourth
digits. To the inner or preaxial
side of the tarso-metatarsus, near its
distal end, is attached by fibrous
tissue a small irregular bone, the
first metatarsal (mtfs. /) . The back-
wardly directed hallux has two pha-
langes, the second or inner toe
three, the third or middle toe four,
and the fourth or outer toe five. In
all four digits the distal or ungual
phalanx is pointed and curved, and
serves for the support of the horny
claw.
A further peculiarity* is the fact
that the larger proportion of the
bones contain no marrow, but are
filled during life with air, and are
therefore said to be pneumatic. The cavities of the various
bones open externally in the dried skeleton by apertures
called pneumatic foramina (Fig. 281., pn. for), by which, in
the entire bird, they communicate with the air-sacs (vide
infra).
As might naturally be expected, the muscles of the fore-
limb are greatly modified. The powerful downstroke of the
FIG. 285. — Columba livia.
Part of left foot of an un-
hatched embryo (magni-
fied). The cartilage is
dotted. mil. 2, second;
mil. 3, third ; and mtl. 4,
fourth metatarsal; //, tibia;
//. /, proximal tarsal car-
tilage; tl. 2, distal tarsal
cartilage. (From Parker's
Zootomy.)
PHYLUM CHORDATA
473
wing, by which the bird rises into and propels itself through
the air, is performed by the pectoralis (Fig. 286, pet}, an
immense muscle having about one-fifth the total weight of
the body ; it arises from the whole of the keel of the
sternum (car. si] , from the posterior part of the body of
FlG. 286 — Columba livia. The principal muscles of the left wing; the greater
part of the pectoralis (pet} is removed, car. st, carina sterni; cl, furcula; cor,
coracoid; cor. br. br, coraco-brachialis brevis; cor. br. Ig, cqraco-brach!alis
longus; cp. st, corpus sterni; ext. cp. rd, extensor carpi radialis; ext. cp. «/,
extensor carpi ulnaris; ft. cp. ul. flexor carpi ulnaris; gl. c, glenoid cavity: hu ,
head of humerus; hu' , its distal end; pet, pectoralis; pet', its cut edge; pet", its
insertion; prn. br, pronator brevis; prn. Ig, pronatpr longiis; pr. ptgm, pre-
patagium; pt.ptgni, post-patagium; sb ch>, sub-clavius; sb. civ', its tendon of
insertion passing through the foramen triosseum, and dotted as it goes to the
humerus; tns. ace, tensor accessorius; tns. br, tensor brevis; tns. Ig, tensor
longus; tns. m. p, tensor membranae posterioris alae.
that bone {cp. st), and from the clavicle \d), filling nearly
the whole of the wedge-shaped space between the body
and the keel of the sternum, and forming what is commonly
called the "breast" of the bird. Its fibres converge to
their insertion (/V/') into the ventral aspect of the humerus
474 MANUAL OF ZOOLOGY SECT, xn
(hu, Au'), which it depresses. The elevation of the wing is
performed, not, as might be expected, by a dorsally placed
muscle, but by the sub-clavius (sb. civ}, arising from the
anterior part of the body of the sternum, dorsal to the
pectoralis, and sending its tendon (sb. c/v') through the
foramen triosseum to be inserted into the dorsal aspect of
the humerus. In virtue of this arrangement, the end of the
foramen acting like a pulley, the direction of action of the
muscle is changed, the backward pull of the tendon raising
the humerus.
Digestive Organs. — The mouth (Fig. 287) is bounded
above and below by the horny beaks, and there is no trace
of teeth. The tongue (trig) is large and pointed at the tip.
The pharynx leads into a wide and distensible £•#//t. cv, post-caval; pty. b, pituitary body; pyg. st, pygo-
style; r. au, right auricle; r. br, right bronchus; ret, rectum; r. vnt, right
ventricle; sp. cd, spinal cord; spl, spleen (dotted behind liver); s. rhb, sinus
rhomboidalis; s. scr, syn-sacrum; st, carina sterni; syr, syrinx; tk. 7>. /, first,
and tk. v-j, fifth thoracic vertebrae: tng, tongue: tr, trachea; fs, right testis;
ur, aperture of left ureter; urdm, urodasum; v. df, aperture of left vaa deferens.
47S
476 MANUAL OF ZOOLOGY SECT.
The duodenum (duo} leaves the gizzard quite close to the
entrance of the proventriculus and forms a distinct loop
enclosing the pancreas. The rest of the small intestine is
called the ilium (/////) : it passes without change of diameter
into the rectum or large intestine (ra1), the junction between
the two being marked only by a pair of small blind pouches
or co2ca (cos) . The cloaca is a large chamber divided into
three compartments.
There are small buccal glands opening into the mouth, but
none that can be called salivary. The liver (Ir) is large, and
is divisible into right and left lobes, each opening by its own
duct (b. d. i, b. d. 2), into the duodenum : there is no gall
bladder. The pancreas (pn) is a compact reddish gland
lying in the loop of the duodenum, into which it discharges
its secretion by three ducts (pn. d. i-j). A thick- walled
glandular pouch, the bursa Fabricii (b. fabr), lies against
the dorsal wall of the cloaca in young birds, and opens into
the cloaca : it atrophies in the adult.
The spleen (spl) is an ovoid red body, of unusually small
proportional size, attached by peritoneum to the right side
of the proventriculus. There are paired thyroids at the base
of the neck ; and, in young pigeons, there is an elongated
thymus on each side of the neck. The adrenals (Fig. 292,
adr) are irregular yellow bodies placed at the anterior ends
of the kidneys.
The £/.77taae
FIG. 299. — Lepus cuniculus. Skull: A, lateral view; B, ventral view. aw/1. /r^»c, angular
Process of mandible; as, ali-sphenoid (external pterygoid process); b. oc, basi-occipital ;
. sph, basi-sphenoid; covd, condyle; fr, frontal; int pa, inter-parietal; ju, jugal; Icr,
lacrymal; max, maxilla; nas, nasal; opt. fo, optic foramen ; o. sph, orbito-sphenoid; pa,
parietal; pal, palatine; pal max, palatine plate of maxilla; par. oc, par-occipital pro-
cess; pal. p. max, palatine process of pre-maxilla; /. max, pre-maxilla; per, periotic;
pt, pterygoid; p. t. sq, post-tympanic process of squamosal; s. oc, supra-occipital; sq,
squamosal; ty. bul, tympanic bulla; vo, vomer; zyg. max, zygomatic process of maxilla.
2K
497
498 MANUAL OF ZOOLOGY SECT.
in position, which forms the floor of the most posterior part
of the cranial cavity ; it bears the lower third of the occipital
condyles. Articulating in front with the basi-occipital is a
plate of bone, also horizontal in position, which forms the
middle part of the floor of the cranial cavity. This is the
basi-sphenoid ; on its upper surface is a depression, the sella
turcica or pituitary fossa, in which the pituitary body rests.
In front of it is another median bone of laterally compressed
form, the pre-sphenoid. Connected laterally with the basi-
sphenoid and pre-sphenoid are two pairs of thin irregular
plates, the ali-sphenoid (as) behind and the orbito-sphenoid
(o-. sph) in front. The ali-sphenoids are broad wing-like
bones, each produced below into a bilaminate process, the
pterygoid process.
The boundary of the anterior part of the brain case is
completed by a narrow plate of bone, the cribriform plate
of the ethmoid, perforated by numerous small foramina for
the passage of the olfactory nerves. This cribriform plate
forms a part of a median vertical bone, the mesethmoid, the
remainder of which, or lamina perpendicularis, forms the bony
part of the partition (completed by cartilage in the un ma-
cerated skull) between the nasal cavities. Fused with the
mesethmoid are two lateral, thin-twisted bones, the ethmo-
turbinals, and with its inferior edge articulates a long median
bone with a pair of delicate lateral wings, the vomer. Roof-
ing over the part of the cranial cavity, the walls and floors of
which are formed by the sphenoid elements, is a pair of
membrane bones, the parietals (pa}, and further forward
another pair, \htfrontals (fr). Between the supra-occipital
and the parietals is a median ossification, the inter-parietal
(int. pa) . Below the parietal and frontal is a broad bone (sq),
the superior margin of which is bevelled off. This is the
squamosaL It gives off in front a strong zygomatic process^
xii PHYLUM CHORD ATA 499
which curves outwards, then downwards, and finally forwards,
to unite with ihejugal in the formation of the zygomatic arch.
Below the root of the process is a hollow, the gUnoid fossa.
Between the occipital and parietal bones, below and
behind the squamosal, are the tympanic and periotic bones.
The tympanic forms the bony part of the wall of the
external auditory meatus ; below it is dilated to form a
process (ty. but) projecting on the under surface of the
skull, the bulla tympani. The periotic (/. of) is a bone
of irregular shape enclosing the parts of the membranous
labyrinth of the internal ear ; externally it presents two
small openings, the fenestra ovalis and fenestra rotunda,
visible only when the tympanic is removed. The periotic
and tympanic are ankylosed together, but are loosely con-
nected with the surrounding bones.
Roofing over the olfactory cavities are two flat bones,
the nasals (nas). In front of the nasals are the pre-maxillce
— large bones which form the anterior part of the snout,
bear the upper incisor teeth, and give off three processes.
The maxilla (max), which form the greater part of the
upper jaw and bear the premolar and molar teeth, are
large, irregularly shaped bones, the upper surfaces of which
are spongy. They give off internally horizontal processes,
the palatine processes, which unite to form the anterior part
of the bony palate. A strong process which is given off
from the outer face of each maxilla and turns outwards and
then backwards to unite with the zygomatic process of the
squamosal and thus complete the zygomatic arch, is a
separate bone in the young, the malar or jugal (ju) .
The rest of the narrow bony palate, forming the roof of
the mouth and the floor of the nasal cavities, is formed by
the palatine plates of the palatine bones. The pterygoids
are small irregular bones, each of which articulates with
500 MANUAL OF ZOOLOGY SECT.
the palatine in front and the ali-sphenoid behind. The
lachrymals are small bones, one situated in the anterior
wall of each orbit, perforated by a small aperture — the
lachrymal foramen.
The mandible, or lower jaw, consists of two lateral halves
or rami, which articulate with one another in front by a
rough articular surface or symphysis, while behind they
diverge like the limbs of a letter V. In each ramus is a
horizontal portion (anterior), which bears the teeth, and a
vertical or ascending portion, which bears the articular
surface or condyle for articulation with the glenoid cavity
of the squamosal ; in front of the condyle is the compressed
coronoid process. The angle where the horizontal and as-
cending processes meet gives off an inward projection or
angular process.
The hyoid, which, as in the pigeon, is the only other
post-oral visceral arch represented in the adult, consists of
a stout thick body or basi-hyal, a pair of small anterior
cornua or cerato-hyals, and a pair of long backwardly directed
cornua or thyro-hyals.
The auditory ossicles, contained in the cavity of the middle
ear, and cut off from the exterior, in the unmacerated skull,
by the tympanic membrane, are extremely small bones,
which form a chain extending, like the columella auris of
the pigeon, from the tympanic membrane externally to the
fenestra ovalis internally.
The elements of the pectoral arch (Fig. 300) are fewer
than in the pigeon. There is a broad thin triangular scap'u-
lar, the base or vertebral edge of which has a thin strip of
cartilage (the supra-scapular cartilage) continuous with it.
Along the outer surface runs a ridge, the spine; the spine
ends below in a long process, the acromion process (a),
from which a branch process or metacromion (ma) is given
XII
PHYLUM CHORDATA
501
off behind. At the narrow lower end of the scapula is a
concave surface, the glenoid cavity, into which the head
of the humerus fits, and immediately in front of this is a
small inwardly curved process, the coracoid process (c),
which is represented by two separate ossifications in the
young rabbit. A slender rod, the clavicle (ct), is con-
nected with the acromion process externally and with the
sternum internally by means of fibrous tissue.
At the proximal end f
of the humerus are to
be recognised: (i) A
rounded head for ar-
ticulation with the
glenoid cavity of the
scapula ; (2) externally
a greater; and (3) in-
ternally a lesser tuber-
osity for the insertion
of muscles. At the
distal end are two ar-
ticular surfaces, one
large and pulley-like,
trochlea, for the ulna;
the other smaller, capi-
tellum, for the radius : laterally are two prominences or
condyles, an internal and an external.
The radius and ulna are firmly fixed together so as to be
incapable of movement, but not actually ankylosed. The
radius articulates proximally with the humerus, distally with
the scaphoid and lunar bones of the carpus. The ulna pre-
sents on the anterior aspect of its proximal end a deep fossa,
the greater sigmoid cavity, for the trochlea of the humerus ;
the prominent process on the proximal side of this is the
FIG
300. — Lepus cuniculus. Shoulder-girdle
with anterior end of sternum of young speci-
men, a, acromion; «/, pre-scapular fossa;
c, coracoid; cl, ossified clavicle; ma, meta-
cromion; mss, meso-scapular segment; ost,
pre-sternum; pc, pre-coracoid ; pf, post-scapu-
lar fossa; sr~, sternal ribs. (After Flower.)
502
MANUAL OF ZOOLOGY
SECT.
olecranon process. Distally it articulates with the cunei-
form.
The carpal bones (Fig. 301), nine in number, are all
small bones of irregular shape. Eight of these are arranged
in two rows, a proximal and a distal ; the ninth, centrale
(cent), lies between the two rows. The bones of the proxi-
mal row are — taken in
order from the inner to the
outer side — scaphoid (sc) ,
lunar (or semi- lunar) (lun),
cuneiform (cun), and pisi-
form. Those of the dis-
tal row are reckoned in
the same order, trapezium
( trpm ) , trapezoid ( trpz) ,
magnum (mag), and unci-
form (unc).
The five metacarpals are
all small but relatively nar-
row and elongated bones,
the first being smaller than
the rest. Each of the five
digits has three phalanges,
except the first which has only two. The distal (ungual)
phalanges are grooved dorsally for the attachment of the
horny claw.
The pelvic arch (Fig. 302) contains the same elements
as in the pigeon, but the union of the ilium with the sacrum
is less intimate, the acetabulum is not perforated, and the
pubes of opposite sides unite ventrally in a symphysis (sy).
The ilium and ischium meet in the acetabulum or articular
cavity, which they contribute to form for the head of the
femur, but the remainder of the cavity is bounded, not by
IG. 30
of fore-arm and carpus, dorsal view, the
bones bent towards the dorsal side so as
to be partly separated: cent, centrale;
cun, cuneiform; /««, lunar; mag, mag-
num; rad, radius; sc, scaphoid; trpz,
trapezoid; trpm, trapezium; uln, ulna;
unc, unciform; I-V, bases of metacar-
pals. (After Krause.)
XII
PHYLUM CHORDATA
5°3
the pubis, but by a small intercalated ossification, the
cotyloid bone. The ilium (it) has a rough surface for
articulation with the sacrum. Between the pubis (pub) in
front and the ischium (isch) behind is a large aperture, the
obturator foramen (obt). The femur has at its proximal
end a prominent head for articulation with the acetabulum,
external to this a prominent process, the great trochanter,
and internally a much smaller, the lesser trochanter, while
a small process or third
trochanter is situated on
the outer border a little
below the great trochan-
ter. At its distal end
are two prominences or
condyles, with a depres-
sion between them. Op-
posite the knee-joint, or
articulation between the
femur and the tibia, is a
small bone or knee-cap,
the patella. The tibia
has at its proximal end
two articular surfaces for
the condyles of the fe-
mur ; distally it has also
two articular surfaces,
one, internal, for the
astragalus, the other for
the calcaneum. The fibula is a slender bone which becomes
completely fused distally with the tibia.
The tarsus consists of six bones of irregular shape
arranged in two rows, one of the bones, the navicular
(Fig. 303, nav), being intercalated between the two rows.
— Lepus cuniculus. Innominate
bones and sacrum, ventral aspect. acet,
acetabulum; il, ilium; isch, ischium; obt,
obturator foramen; pub, pubis; sacrt
sacrum; sy, symphysis.
5°4
MANUAL OF ZOOLOGY
SECT.
cal
CIS?
In the proximal row are two bones, the astragalus {asi) and
the calcaneum (cal), both articulating with the tibia; the
calcaneum presents behind a long calcaneal process. The
distal row contains three bo'nes, the mesocuneiformt ectocunei-
form, and cuboid (cub) ; the ento-
cuneiform, which commonly forms
the most internal member of this
row in other mammals, is not pres-
ent as a separate bone.
There are four metatarsals, the
hallux or first digit being absent.
Each of the digits has three pha-
langes, which are similar in character
to those of the manus.
The ccelom of the rabbit differs
from that of the pigeon in being
divided into two parts by a trans-
verse muscular partition, the dia-
phragm. The anterior part, or
thorax, contains the heart and the
roots of the great vessels, the lungs
and bronchi, and the posterior part
of the oesophagus. The posterior
part or abdomen contains the stom-
jp. — ach and intestine, the liver and
pancreas, the spleen, the kidneys,
FIG. 303. — Lepus cuniculus.
Skeleton of pes; ast, astrag- ureters and urinary bladder, and the
alus; cal, calcaneum; cub, . ,
cuboid; cnn, cuneiforms; Organs OI reproduction.
The teeth (Fig. 299) are lodged
in sockets or alveoli in the pre-maxillae, the maxillae,
and the mandible. In the pre-maxillse are situated four
teeth, the four upper incisors. Of these the two anterior
are very long, curved, chisel-shaped teeth, which are
xii PHYLUM CHORDATA 5°5
devoid of roots, growing throughout life from persistent
pulps. Enamel is present as a thick layer on the ante-
rior convex surface only, which accounts for the .bevelled-
off character of the distal end, the layer of enamel being
much harder than the rest, which therefore wears more
quickly away at the cutting extremity of the tooth. The
second pair of incisors of the upper jaw are small teeth which
are lodged just behind the larger pair. In the lower jaw are
two incisors, which 'correspond in shape with the anterior
pair of the upper jaw. The remaining teeth of the upper
jaw are lodged in the maxillae. Canines, present in most
mammals as a single tooth on each side, are here entirely
absent, and there is a considerable space, or diastema, as it
is termed, between the incisors and the teeth next in order,
the pre-molars. Of these there are three in the upper jaw
and two in the lower. They are long, curved teeth devoid
of fangs, the first smaller than the others. Behind the pre-
molars are the molars, three on each side both in the upper
and lower jaws.
Opening into the cavity of the mouth are the ducts of
four pairs of salivary glands. On the floor of the mouth is
the muscular tongue, covered with a mucous membrane
which is beset with many papillae. The roof of the mouth
is formed by the palate. The anterior part, or hard palate,
is crossed by a series of transverse ridges of its mucous
membrane. The posterior part, or soft palate, ends behind
in a free pendulous flap (the uvula} in front of the opening
of the posterior nares. Behind the mouth or buccal cavity
proper is the pharynx. The pharynx is divided into two
parts, an upper or nasal division, and a lower or buccal
division, by the soft palate. Into the nasal division open in
front the two posterior nares and at the sides the openings
of the Eustachian tubes. The nasal division is continuous
5o6
MANUAL OF ZOOLOGY
SECT.
with the buccal division round the posterior free edge of
the soft palate. From the buccal division leads ventrally
the slit-like opening of the glottis into the larynx and
trachea; overhanging the glottis is a leaf-like movable
flap (Fig. 304, ep] formed of a plate of yellow elastic
cartilage covered with mucous membrane : this is the
epiglottis. Behind, the pharynx becomes continuous with
cbt
rtl.lng
FIG. 304. — LepUS cuniculus. Lateral dissection of the head, neck, and thorax. The
head and spinal column are represented in mesial vertical section: the left lung
is removed; the greater part of the nasal septum is removed so as to show the
right nasal cavity with its turbinals. aort, dorsal aorta; b. Ay, basi-hyal; cbl,
cerebellum; cer, cerebral hemispheres; cor. i>, coronary vein; dia, diaphragm;
ep, epiglottis; eu, opening of Eustachian tube into pharynx ; lar, larynx ; Lj. v,
left jugular vein; /. s6. a, left subclavian artery; /. sb. 7', left subclavian vein;
»z^,medulla; mes. eth, mesethmoid; mx. trb, maxilla-turbinal; a?s, oesophagus;
olf, olfactory lobe; pi. a., pulmonary artery; p. wax, pre-maxilla; pr. st, pre-
sternum; pt. c, post-caval vein; rt. Ing, root of left lung with bronchus and pul-
monary veins and artery cut across; s.gl, sub-lingual salivary gland; s. mx.gld,
sub-maxillary salivary gland; st, sternebrae; tng, tongue; tr, trachea; trb,
ethmo-turbinals; vel. pi, soft palate.
the (esophagus or gullet (as}. The latter is a narrow but
dilatable muscular tube, which runs backwards from the
pharynx through the neck and thorax to enter the cavity of
the abdomen through an aperture in the diaphragm, and
opens into the stomach.
xii PHYLUM CHORDATA 507
The stomach (Fig. 305) is a wide sac, much wider at the
end (cardiac}, at which the oesophagus enters, than at the
opposite or pyloric end, where it passes into the small
intestine. The small intestine is an elongated, narrow,
greatly coiled tube, the first part of which or duodenum
(du and di<) forms a U-shaped loop. The large intestine is
a wide tube, the first and greater part of which, termed the
colon, has its walls sacculated, a structure which is absent in
the short, straight posterior part or rectum (ret}. At the
junction of the small with the large intestine is a very wide
blind tube, the ccecum, which is of considerable length and is
marked by a spiral constriction, indicating the presence in
its interior of a narrow spiral valve. At its extremity is a
small, fleshy, finger-like vermiform appendix.
The intestine, like that of the pigeon, is attached through-
out its length to the dorsal wall of the abdominal cavity by
a mesentery or fold of the lining membrane or peritoneum.
The liver is attached to the diaphragm by a fold of the
peritoneum. Its substance is partly divided by a series of
fissures into five lobes. A thin-walled gall-bladder lies in a
depression on its posterior surface. The common bile duct,
(c. b. d} formed by the union of the cystic duct from the
gall-bladder and hepatic ducts from the various parts of the
liver, runs to open into the duodenum near the pylorus.
The pancreas (pri) is a diffused gland in the fold of
mesentery passing across the loop of the duodenum. Its
single duct, the pancreatic duct (pn. d), opens into the
distal limb of the loop.
The heart (Fig. 306) is situated in the cavity of the
thorax, a little to the left of the middle line, and lies
between the two pleural sacs enclosing the lungs. The peri-
cardial membrane enclosing the heart consists of two layers,
a parietal, forming the wall of the pericardial cavity, and a
*?•<*
FIG. 305. — Lepus cuniculus. The stomach, duodenum, posterior portion of rectum
and liver (in outline) with their arteries veins, and ducts. A. the coeliac artery of
another specimen (both x |). The gullet is cut through and the stomach some-
what displaced backwards to show the ramifications of the coeliac artery (cos. a) ;
the duodenum is spread out to the right of the subject to show the pancreas
(/«) ; the branches of the bile duct (c. b. d}, portal vein (p. v~) and hepatic
artery (h. a), are supposed to be traced some distance into the various lobes of
the liver, a. in. a, anterior mesenteric artery; cau, caudate lobe of liver, with
its artery, vein, and bile duct; c. b. d, common bile duct; cd. j^, cardiac portion
of stomach; c. il. a, common iliac artery; cae. a, cceliac artery; cy. a, cystic
artery; cy. d, cystic duct; d. ao, dorsal aorta; du, proximal, and du' , distal
limbs of duodenum; du. a, duodenal artery; du. ha, in (A), duodeno-hepatic
artery; g. a, gastric artery and vein; g. b, gall-bladder; h. a, hepatic artery;
b. d, left bile duct; /. c, left central lobe of liver, with its artery, vein, and bile
duct; I. g. 7% lieno-gastric vein; /. /, left lateral lobe of liver, with its artery,
vein, and bile duct; ins, branch of rr esenteric artery and vein to duodenum;
?«.y. r, mesorectum; m. v, chief mesenteric vein; ces, oesophagus; /. m. a,
posterior mesenteric artery; / m. v, posterior mesenteric vein; pn, pancreas;
pn. d, pancreatic duct; /. z/, portal vein; py. st, pyloric portion of stomach;
ret, rectum; r c, right central lobe of liver, with artery, vein, and bile duct;
spg, Spigelian lobe of liver, with its artery, vein, and bile duct; spl, spleen; sp. a,
splenic artery. (From Parker's Zootomy.}
508
SECT. Xii PHYLUM CHORD ATA 509
visceral, immediately investing the heart. Between the two
is a narrow cavity containing a little fluid, the pericardial
fluid. In general shape the heart resembles that of the
pigeon, with the apex directed backwards and slightly to
the left, and the base forwards. Like that of the pigeon, it
contains right and left auricles and right and left ventricles,
the right and left sides of the heart having their cavities
completely separated off from one another by inter-auricular
and inter-ventricular partitions.
sem.is
FIG. 306. — LepUS CUniculus. Heart, seen from the right side, the walls of the
right auricle and right ventricle partly removed so as to expose the cavities.
ao, aorta \ f. ov, fossa ovalis; /. pr. c, opening of pre-caval; m. pap, mr.sculi
papillares; pt. c, post-caval; //. c' , opening of post-caval; r.prc, right pre-
caval; r. pul, right pulmonary artery ; son. v, semi-lunar valves; tri, tricuspid
valve.
. Into the right auricle open three large veins, the right
and left pre-caval veins and the single posf-caval, the first
into the anterior part, the second into the left-hand side of
the posterior portion, and the third into the dorsal surface.
Projecting forwards from it is an ear-like auricular appendix.
On the septum is an oval area where the partition is thinner
510 MANUAL OF ZOOLOGY SECT, xil
than elsewhere ; this is the fossa ovalis, it marks the
position of an aperture, the foramen ovale, in the foetus.
The cavity of the right auricle communicates with that of
the right ventricle by the wide right auriculo-ventricular
opening. This is guarded by a valve, the tricuspid, com-
posed of three membranous lobes or cusps, so arranged and
attached that while they flap back against the walls of
the ventricle to allow the passage of blood from the
auricle to the ventricle, they meet together across the
aperture so as to close the passage when the ventricle
contracts. The lobes of the valve are attached to muscular
processes of the wall of the ventricle, the musculi papillares^
by means of tendinous threads called the chorda tendinetz.
The right ventricle, much thicker than the auricle, forms
the right side of the conical apical portion, but does not
extend quite to the apex. Its walls are raised up into
muscular ridges called columns carnece. It gives off in
front, at its left anterior angle, the pulmonary artery, the
entrance to which is guarded by three pouch-like semi-lunar
valves.
The left auricle, like the right, is provided with an
auricular appendix. Into this cavity on its dorsal aspect
open together the right and left pulmonary veins. A large
left auriculo-ventricular opening leads from the cavity of the
left auricle into that of the left ventricle ; this is guarded by
a valve, the mitral, consisting of two membranous lobes or
cusps with chordae tendineae and musculi papillares. In
the walls of the ventricle are columnar carneae rather more
strongly developed than in the right. At the basal
(anterior) end of the left ventricle is the opening of the
aorta, guarded by three semi-lunar valves similar to those
at the entrance of the pulmonary artery. The coronary
arteries, which supply the muscular substance of the heart,
FIG. 307. — LepUS CUniCUlus. The vascular system. The heart is somewhat dis-
placed towards the left of the subject; the arteries of the right and the veins
of the left side are in great measure removed. a, arch of the aorta; a. efg,
internal mammary artery; a. f, anterior facial vein; a. »/, anterior mesenteric
artery; a. ph, anterior phrenic vein; az. i>, azygos vein; br, branchial artery:
c. i7. a, common iliac artery; cae, coeliac artery ; d. ao, dorsal aorta; e. c, external
carotid artery; e. i7. a, external iliac artery; e il. v, external iliac vein: e. ju,
external jugular vein; fm. a, femoral artery; fm. v, femoral vein; //. ?', hepatic
veins; i. c, internal carotid artery; /. cs, intercostal vessels; t'.j'u, internal
jugular vein; / /, ilio-lumbar artery and vein; in, innominate artery; I. an,
left auricle; /. c. c, left common carotid artery; /. prc, left pre-caval vein;
/. v, left ventricle; in. sc, median sacral artery; /. a, pulmonary artery; p. epg,
epigastric artery and vein; p. ft posterior facial vein; p. in, posterior mesenteric
artery; p. ph, posterior phrenic veins; ptc, post-caval veins; /. v, pulmonary
vein; r, renal artery and vein; r. au, right auricle; r. c. c, right common
carotid artery; r.prc, right pre-caval vein; r. v, right ventricle; scl. a, right
sub-clavian artery; scl. v, sub-clavian vein; spin, spermatic artery and vein;
vs. s, superior vesical artery and vein; ut, uterine artery and vein; 7-r, vertebral
artery. (From Parker's Zootomy.}
5"
512 MANUAL OF ZOOLOGY SECT.
are given off from the aorta just beyond the semi-lunar
valves. The corresponding vein opens into the terminal
part of the left pre-caval. The pulmonary artery divides
into two, a right and a left, each going to the corresponding
lung.
The aorta gives origin to a system of arterial trunks by
which the arterial blood is conveyed throughout the body.
It first runs forwards from the base of the left ventricle,
then bends round the left bronchus, forming the arch of the
aorta (Fig. 307, a), to run backwards through the thorax
and abdomen, in close contact with the spinal column, as
the dorsal aorta (d. ao}.
The system of caval veins which open into the right
auricle consists of the right and left pre-cavals and of the
single post-caval. From the liver the blood is carried to the
post- caval by the hepatic veins.
The hepatic portal system consists, as in other vertebrates,
of a series of veins conveying blood from the various parts
of the alimentary canal to the liver, the trunks of the system
uniting to form the single large portal vein (Fig. 307, p. v).
There is no renal portal system.
Respiratory Organs. — The larynx (Fig. 308) is a cham-
ber with walls supported by cartilage, lying below and
somewhat behind the pharynx, with which it communicates
through a slit-like aperture. It contains the vocal cords.
Leading backwards from the larynx is the trachea or wind-
pipe (Fig. 308, tr), a long tube, the wall of which is sup-
ported by cartilaginous rings which are incomplete dorsally.
The trachea enters the cavity of the thorax and there divides
into the two bronchi, one passing to the root of each lung.
The lungs (Fig. 304) are enclosed in the lateral parts of
the cavity of the thorax. Each lung lies in a cavity lined
by a membrane — the cavity of the plenral sac or pleural
XII
PHYLUM CHORDATA
513
membrane. The right and left pleural sacs are separated
by a considerable interval owing to the development in the
partition between them of a space, the mediastinum, in
which lie the heart and other organs. The lung is attached
only at its root where the pleural membrane is reflected
over it. In this respect it differs widely from the lung of
the bird. It differs also in its minute structure. The
bronchus entering at the root divides and subdivides to
form a ramifying system of tubes, each of the ultimate
branches of which, or terminal bronchioles, opens into a
FIG. 308. — Lepus cuniculus. Larynx: A, ventral view; B, dorsal view; ary,
arytenoid: cr, cricoid ; ^/.epiglottis; sant, cartilage of Santorini; th, thyroid,
tr, trachea. (From Krause, after Schneider.)
minute chamber or infundibulum, consisting of a central
passage and a number of thin-walled air-vesicles or alveoli
given off from it.
The spleen is an elongated, compressed, dark red body
situated in the abdominal cavity in close contact with the
stomach, to which it is bound by a fold of the peritoneum.
The thymus, much larger in the young rabbit than in the
adult, is a soft mass, resembling fat in appearance, situated
in the ventral division of the mediastinal space below the
base of the heart. The thyroid is a small brownish, bilobed
glandular body situated in close contact with the ventral
surface of the larynx.
2L
MANUAL OF ZOOLOGY
SECT.
The neural cavity, as in the pigeon, contains the central
organs of the cerebro-spinal nervous system, the brain and
spinal cord. The brain (Fig. 309) of the rabbit contains
the same principal parts as that of the pigeon, with certain
differences, of which the following are the most important.
The surface of the cerebral hemispheres (Fig. 309, /. b,
XII PHYLUM CHORD ATA 515
Fig. 310, c. /i), which are relatively long and narrow, presents
certain depressions or sulci, which, though few and indis-
tinctly marked, yet divide the surface into lobes or con-
volutions not distinguishable in the case of the pigeon or
the lizard. A slight depression, the Sylvian fissure, at
the side of the hemisphere separates off a lateral portion or
temporal lobe (Fig. 311, ch2) from the rest. There are
very large club-shaped olfactory lobes at the anterior ex-
tremities of the cerebral hemispheres. Connecting together
the two hemispheres is a commissural structure, the corpus
callosum (Fig. 310, cp. cl), not present in the pigeon; this
runs transversely above the level of the lateral ventricles.
Below the corpus callosum is another characteristic structure
of a commissural nature, \hzfornix (b.fo), a narrow median
strand of longitudinal fibres which bifurcates both anteriorly
and posteriorly. Below the corpus callosum, between it and
the fornix, the thin inner walls of the hemispheres (septum
lucidum) (sp. lu.) enclose a small, laterally compressed cav-
ity, the so-called fifth ventricle or pseudocode; this is not
a true ventricle, but merely a space between the closely
apposed hemispheres.
The lateral ventricles of the cerebral hemispheres are
much more extensively developed than in the brain of the
pigeon, and of somewhat complex shape.
The floor of the anterior portion of the lateral ventricle
is formed of an eminence of gray matter, the corpus
striatum (cp. s). The right and left corpora striata are
connected together by a narrow transverse band of white
fibres, the anterior commissure (a. co).
The diaccele (z/3) is a laterally compressed cavity. From
the posterior part of the roof of the diaccele arises the
peduncles of the pineal body, and just beyond their point of
origin is the posterior commissure (p. co), a delicate trans-
Si6
MANUAL OF ZOOLOGY
verse band of fibres connecting together the posterior
parts of the optic thalami. The latter (o. tti) are large
•M10
FIG. 310. — Lepus CUniculus. Two dissections of the brain from above (nat. size).
In A, the left parencephalon is dissected down to the level of the corpus callq-
sum; on the right the lateral ventricle is exposed. In B, the cerebral hemi-
spheres are dissected to a little below the level of the anterior genu of the corpus
callqsum; only the frontal lobe of the left hemisphere is retained; of the right, a
portion of the temporal lobe also is left; the velum interpositum and pineal body
are removed, as well as the greater part of the body of the fornix, and the whole
of the left posterior pillar; the cerebellum is removed with the exception of a part
of its right lateral lobe; a. co, anterior commissure; a.fo, anterior pillar of for-
nix; a. pn, anterior peduncles of cerebellum; b.fo, body of fornix; cbl, superior
vermis of cerebellum; c62, its lateral lobe; c.gn, corpus genictilatum; c.h, cere-
bral hemisphere; ch.pl, choroid plexus; cp. cl, corpus callosum; cp. s, corpus
striatum; c. rs, corpus restiforme; d. p, dorsal pyramid; _fl, flocculus; hp. m,
hippocampus major; in, co, middle commissure; o. f1, anterior; o 1-, posterior
lobes of corpora quadrigemina; o. th, optic thalamus; otr, optic tract; /. co, pos-
terior commissure; p fo, posterior peduncles of cerebellum; /. i4, fourth ventricle. (From Parker's Zootomy.)
masses of mixed gray and white matter forming the lateral
portions of the diencephalon ; they are connected together
xii PHYLUM CHORD ATA 517
by a thick mass of gray matter, the middle or soft commis-
sure (m. co) passing across the diacoele. The floor of the
diencephalon is produced downwards into a mesial rounded
process, the tuber cinereum or infundibulum (inf) to which
the pituitary body is attached. In front of this, on the
ventral aspect of the brain, is a thick curved transverse
band of nerve fibres, the united optic tracts, from the ante-
rior border of which the optic nerves are given off. Behind
the tuber cinereum is a rounded elevation, the corpus
mammillare (c. ma).
In the mid-brain the dorsal part is remarkable for the
fact that each optic lobe is divided into two by a transverse
furrow, so that two pairs of lobes, the corpora quadrigemina,
are produced. On the ventral region of the mid-brain the
crura cerebri are far more prominent than in the lower
groups. In the hind-brain the cerebellum (Fig. 310, cb\ cb")
is very large ; it consists of a central lobe or vermis and two
lateral lobes divided by very numerous fissures or sulci into
a large number of small convolutions. Each lateral lobe
bears an irregularly shaped prominence, the flocculus. On
section (Fig. 311, cb) the cerebellum exhibits a tree-like
pattern (arbor vita) t brought about by the arrangement of
the white and gray matter. On the ventral aspect of the
hind-brain a flat band of transverse fibres, the pons Varolii,
connects together the lateral parts of the cerebellum.
The cranial nerves are similar to those of the pigeon in
most respects, differing in some of the particulars of their
arrangement and distribution.
The rabbit, like most other vertebrates, possesses a
sympathetic netvous system, consisting of a series of ganglia
united together by commissural nerves and giving off
branches to the various internal organs.
In the organs of special sense the following special
518 MANUAL OF ZOOLOGY SECT.
features are to be seen when a comparison is made with the
pigeon. In the eye, the sclerotic is composed entirely of
dense fibrous tissue ; the pecten is absent. In the ear the
principal point of difference is in the special development
of the cochlea. This part of the membranous labyrinth,
instead of retaining the simple curved form which it pre-
sents in the bird, is coiled on itself in a close spiral of two
and a half turns.
FIG. 311. — Lepus cuniculus. Longitudinal vertical section of the brain (nat. size).
Letters as in the preceding figure; in addition, cb, cerebellum, showing arbor
vitse; c. c, crus cerebri; chl, parencephalon; cA2, temporal lobe; c. ma, corpus
mammillare; _/. m, foramen of Monro; in/, infundibulum; iy, lyra; m. o, me-
dulla oblongata; o. ck, optic chiasma; olf, olfactory lobe; pty, pituitary body;
•vl. tp, velum interpositum; v. vn, valve of Vieussens; //, optic nerve. (From
Parker's Zootomy.}
The special features of the middle ear with its auditory
ossicles have been already referred to.
The kidneys are of somewhat compressed oval shape,
with a notch or hilus on the inner side. They are in
close contact with the dorsal wall of the abdominal cavity,
the right being somewhat in advance of the left. Towards
the hilus the tubules of the kidney converge to open into
a wide chamber, the pelvis, which forms the dilated
commencement of the ureter. When the kidney is cut
XII
PHYLUM CHORDATA
519
across, its substance is seen to be divided into a central
mass or medulla and a peripheral portion or cortex. An
adrenal (suprarenal) body lies in contact with the anterior
end of each kidney. The ureter (Fig. 312, ur) runs back-
ur
V€L .
II
3?
FIG. 312. — Lepus CuniculUS. The urogenital organs. A, of male; B, of female,
from the left side (half nat. size). The kidneys and proximal ends of the ureters,
and in B, the ovaries, Fallopian tubes and uteri are not shown, an, anus; bl,
urinary bladder; c. c, corpus cavernosum; c. s, corpus spongiosum; c.glt
Cowper's gland; g. cl, glans clitoridis; g. p, glans penis; p. gl, perineal gland;
/. ft', aperture of its duct on the perinea! space ; pr, anterior, pr , posterior, and
Pr ', lateral lobes of prostate; ret, rectum; r. gl, rectal gland; u. g. a, urino-
genital aperture; u. HI, uterus masculinus; ur, ureter; -va, vagina; vb, vesti-
bule; v. d, vas deferens. (From Parker's Zootomy.)
wards to open not into a cloaca but directly into the urinary
bladder (bl). The latter is a pyriform sac with elastic
walls which vary in thickness according as the organ is
520 MANUAL OF ZOOLOGY SECT.
dilated or contracted. In the male the openings of the
ureters are situated much nearer the posterior narrower
end or neck than in the female.
In the male rabbit the testes are oval bodies, which,
though in the young animal they occupy a similar position
to that which they retain throughout life in the pigeon,
pass backwards and downwards as the animal approaches
maturity until they come to lie each in a scrotal sac situated
at the side of the urogenital opening. The cavity of each
scrotal sac is in free communication with the cavity of the
abdomen by an opening, the inguinal canal. A convo-
luted epididymis, closely adherent to the testis, forms the
proximal part of the vas deferens. The vasa deferentia
(ltd) terminate by opening into a urogenital canal, or
urethra, into which the neck of the urinary bladder is con-
tinued. A prostate gland (pr) surrounds the commence-
ment of the urethra, the neck of the bladder, and the
terminal parts of the vasa deferentia. A diverticulum of the
urethra, the titerus masculinus (um), lies embedded in
the prostate gland close to the neck of the bladder. A
small pair of ovoid glands, Cowper's glands (c. gl), lie just
behind the prostate close to the side of the urethra.
The terminal part of the urethra traverses a cord of
vascular tissue, the corpus spongiosum (c. s), which forms the
dorsal portion of the penis. A loose fold of skin, the
prepuce, encloses the penis.
In the female the ovaries are small ovoid bodies attached
to the dorsal wall of the abdomen behind the kidneys. The
Graajian follicles enclosing the ova form only very small
rounded projections on their outer surface.
The oviducts in the anterior part of their extent (Fallopian
tubes} are very narrow and slightly convoluted. They open
into the abdominal cavity by wide funnel-shaped openings,
XII
PHYLUM CHORDATA
521
with fimbriated or fringed margins. Posteriorly each passes
into a thick-walled uterus. The two uteri open sepa-
rately into a median tube, the vagina (va). The vestibule
(Fig. 312, vb), or urogenital canal, is a wide median
passage, into which the vagina and the bladder open. On
its ventral wall is a small, hard, rod-like body, the clitoris,
corresponding to the penis of the male, and composed of
two very short corpora cavernosa attached anteriorly to the
fit lit
1Mb'
va.
T.Ut
FlG. 313. — Lepus cuniculus. The anterior end of the vagina, with the right uterus,
Fallopian tube, and ovary (nat. size). Part of the ventral wall of the vagina is
removed, and the proximal end of the left uterus is shown in longitudinal section
fl. t, Fallopian tube; fi. t' , its peritoneal aperture; /. ut, left uterus; /. nt' ', left
os uteri; r. ut, right uterus; r. nt' , right os uteri; s, vaginal septum; z>a,
vagina. (From Parker's Zootomy.')
ischia, with a terminal soft conical glans ditoridis (g. cl] .
The vulva, or external opening of the vestibule, is bounded
laterally by two prominent folds, the labia majora.
The rabbit is viviparous. The ovum, which is of rel-
atively small size, after it has escaped from its Graafian
follicle, passes into the oviduct, where it becomes fertilised,
and reaches the uterus, in which it develops into the fatus,
522 MANUAL OF ZOOLOGY SECT.
as the intra-uterine embryo is termed. The young animal
escapes from the uterus in a condition in which all the parts
have become fully formed, except that the eyelids are still
closed, and the hairy covering is not yet completed. As
many as eight or ten young are produced at a birth, and
the period of gestation, i.e., the time elapsing between the
fertilisation of the ovum and the birth of the young animals
is thirty days. Fresh broods may be born once a month
throughout a considerable part of the year, and, as the
young rabbit may begin breeding at the age of three
months, the rate of increase is very rapid.
During intra-uterine life the young rabbit is nourished by
an organ called the placenta, formed by an intimate union
between certain structures, the foetal membranes, derived
from the embryo, and a specially modified part of the wall
of the uterus. By means of the placenta a close connection
is established between the blood-system of the foetus and
that of the parent, and nourishment is thus received by the
former from the latter.
After birth the young rabbits are nourished for a time
wholly by the milk or secretion of the mammary glands of
the mother.
The following are the principal general features which
characterise the Mammalia as a class : —
The Mammalia are air-breathing vertebrates, with warm
blood, and with an epidermal covering in the form of hairs.
The bodies of the vertebrae are in nearly all mammals
ossified each from three independent centres, one of which
develops into the centrum proper, while the others give
rise to thin discs of bone, the epiphyses. Also charac-
teristic of the spinal column of mammals are the discs of
fibre -cartilage termed inter-vertebral discs, which intervene
between successive centra.
xii PHYLUM CHORD ATA 523
The skull has two condyles in connection with the atlas,
instead of the single condyle of the reptiles and birds ; and
the lower jaw articulates with the skull in the squamosal
region without the intermediation of the separate quadrate
element always present in that position in birds and reptiles.
Each of the long bones of the limbs is composed in the
young condition of a central part or shaft and terminal
epiphyses, the latter only becoming completely united with
the shaft at an advanced stage. In the pectoral arch the
coracoid of the birds and reptiles is usually represented
only by vestiges, which unite with the scapula in the adult.
Mammals are typically diphyodont> i.e., have two sets of
teeth — a milk or deciduous set, and a permanent set ; some
are monophyodont, i.e., have only one set. The teeth are
thecodont, i.e., the base of each tooth is embedded in a
distinct socket or alveolus in the substance of the bone of
the jaw ; and nearly always the teeth in different parts of
the jaw are clearly distinguishable by differences of shape
into incisors, canines, and grinding teeth, i.e., are heterodont ;
in some instances the teeth are all alike (Jwmodont). A
cloaca is absent except in the Prototheria.
A movable plate of cartilage, the epiglottis, overhangs the
glottis or passage leading from the pharynx into the cavity
of the larynx.
A partition of muscular fibres, usually with a tendinous
centre, the diaphragm, divides the cavity of the body into
two parts, — an anterior, the thorax, containing the heart and
lungs, and a posterior, the abdomen, containing the greater
part of the alimentary canal with its associated glands, the
liver and pancreas, and the renal and reproductive organs.
The lungs are freely suspended within the cavity of the
thorax. The heart is completely divided into two halves,
a right and a left, between which there is no aperture of
524 MANUAL OF ZOOLOGY SECT.
communication. Each half consists of an auricle and a
ventricle, opening into one another by a wide opening,
guarded by a valve composed of three membranous cusps
on the right side, two on the left. The right ventricle gives
off the pulmonary artery ; the left gives off the single aortic
arch, which passes over to the left side, turning round the
left bronchus in order to run backwards as the dorsal aorta.
The blood is warm. The red blood-corpuscles are non-
nucleated and usually circular.
The two cerebral hemispheres, in all but the monotremes
and marsupials, are connected together by a band of trans-
verse fibres, the corpus callosum, not represented in the
lower vertebrates. The dorsal part of the mid-brain is
divided into four optic lobes, the corpora quadrigemina.
On the ventral side of the hind-brain is a transverse band of
fibres, the pons Varolii, by which the lateral portions of the
cerebellum are connected together.
The ureters, except in the Prototheria, open into the
bladder.
Mammals are all, with the exception of the monotremes,
viviparous. The foetus is nourished before birth from the
blood-system of the parent through a special development
of the fcetal membranes and the lining membrane of the
uterus, termed the placenta. After birth the young mam-
mal is nourished for a longer or shorter time by the milk or
secretion of the mammary glands of the parent.
The class Mammalia is divisible into two main divisions
or sub-classes, the Prototheria and the Theria.
The Prototheria are mammals in which the mammary
glands are devoid of teats ; the oviducts are distinct through-
out, and there is a cloaca into which the ureters and the
urinary bladder open separately. In the centra of the
vertebrae the epiphyses are absent or more imperfectly de-
Xii PHYLUM CHORDATA 525
veloped ; the bones of the skull early coalesce by the oblit-
eration of the sutures ; there is a large coracoid articulating
with the sternum, and a T-shaped episternum, and there is a
pair of epipubic (marsupial) bones. In the brain a corpus
callosum is absent. The ova are discharged in an early stage
of their development, enclosed in a tough shell.
This sub-class comprises a single living order, the Mono-
tremata, including the duck-bill or Platypus (Ornithorhyn-
chus} and spiny ant-eater {Echidna).
The Theria are mammals in which the mammary glands
are provided with teats ; the oviducts are united in a longer
or shorter part of their extent, and there is no cloaca, the
ureters opening into the base of the bladder. The centra of
the vertebrae possess distinct epiphyses ; the bones of the
skull in most instances do not completely coalesce, most of
the sutures remaining distinguishable throughout life ; the
coracord is represented by vestiges, and an episternum is
absent as a distinct bone. The early development of the
young takes place in the uterus.
Of the Theria again there are two sections, the Metatheria
or Marsupialia and the Eutheria.
The section Metatheria comprises all the pouch-bearing
mammals or marsupials, such as the opossums, the dasyures,
the bandicoots, the wombats, the phalangers, and the kan-
garoo, nearly all, with the exception of the opossums, con-
fined to the Australian region. They are characterised by
the possession of a pouch or marsupium, within which the
young, born in rudimentary and helpless condition, are
sheltered. They also possess a pair of peculiar bones, the
epipubic or marsupial bones (present also in the Prototheria) ,
attached to the pubes.
In the Eutheria marsupium and marsupial bones are
absent. This section comprises the great majority of
526
MANUAL OF ZOOLOGY
SECT.
mammals, which, when the fossil forms are left out of
account, are capable of being arranged in nine orders : —
1. Edentata, comprising the sloths, ant-eaters, and arma-
dillos.
2. Cetacea, including the whales, porpoises, and dolphins.
3. Sirenia, or dugongs and manatees.
4. Ungulata, a very large order, comprising among others,
the horses, tapirs, and rhinoceroses, the ruminants (camels,
oxen, sheep, goats, antelopes, giraffes, and deer), the pigs
and hippopotami, the hyraxes, and the elephants.
FlG. 314. — Duck-bill (Ortutkorkyttckits anatinus). (After Vogt and Specht.)
5. Carnivora, or the cats, dogs, bears, weasels, and otters,
and the seals and walruses.
6. Rodentia, a large order, including, among many others,
the rats and mice, hares and rabbits, squirrels, beavers, and
porcupines.
7. Insectivora, including the moles, shrews, and hedge-
hogs.
8. Chiroptera, or bats, and fruit-eating bats (flying foxes).
XII
PHYLUM CHORD AT A
527
9. Primates, comprising the lemurs, apes, and monkeys,
and the human species.
The two genera of the Prototheria, Ornithorhynchus and
Echidna, differ somewhat widely from one another in gen-
eral appearance. The former (Fig. 314) has the surface
covered with a close soft fur, and has the upper jaw pro-
duced into a depressed muzzle, not unlike the beak of a
duck, covered with a smooth, hairless integument. The eyes
are very small, and there is no auditory pinna. The legs are
FIG. 315.— Spiny Ant-eater (Echidna acnleata). (After Vogt and Specht.)
short, and the five digits end in strong claws, and are con-
nected together by a web, so that the limbs are equally
adapted for burrowing and for swimming. The tail is elon-
gated and depressed, covered with fur. The male has a
sharp-pointed, curved spur on the inner side of the foot,
having the duct of a poison-gland opening at its apex.
Echidna (Fig. 315) has the body covered above with
strong-pointed spines, between which are coarse hairs ; the
528 MANUAL OF ZOOLOGY SECT.
lower surface is covered with hair only. The jaws are pro-
duced into a rostrum which is much narrower than that of
Ornithorhynchus. The eyes are small, and there is no audi-
tory pinna. The tail is vestigial.
The opossums (Didelphyida) (Fig. 316) are arboreal
rat-like marsupials, with elongated naked muzzle, with well-
developed, though nailless, opposable hallux, and elongated
prehensile tail. The Dasyuridae (Australian native cats,
tasmanian devil, thylacine, etc.) have the pollex often rudi-
FIG. 316. — Virginian Opossum (Didelphys virginiana}. (After Vogt and Specht.)
mentary, the foot four-toed, the hallux, when present, small
and clawless, and the tail not prehensile.
The bandicoots (PerameKdas) are burrowing marsupials,
the size of which varies from that of a large rat to that of
a rabbit. They have an elongated pointed muzzle, and, in
some cases, large auditory pinnae. The first and fifth digits
of the fore-foot are vestigial or absent, the remaining three
XII
PHYLUM CHORDATA
529
nearly equally developed. In the hind- foot the fourth toe
is much longer and stouter than the others, while the second
and third are small and slender, and united together by a
web of skin, and the first is vestigial or absent. The marsu-
pium has its opening directly backwards.
The wombats (Phascolomyida) are large, heavy, thick-
bodied, burrowing animals, with short flattened heads, short
thick limbs, provided with strong claws on all the digits
except the hallux, and with the second, third, and fourth of
:
FIG. 317. — Dasyure (Dasynrns riverrz'tiHs). (After Vogt and Specht.)
the hind-foot partly connected together by skin. The tail
is very short. The kangaroos and their allies (Macropodidce)
(Fig. 318) are adapted, as regards their limbs, for swift
terrestrial locomotion. They have a relatively small head
and neck, the fore-limbs small, and each provided with five
digits ; the hind-legs long and powerful ; rapid progression
is effected by great springing leaps, with the body inclined
forwards and the fore-limbs clear of the ground. The
foot is narrow and provided with four toes, the hallux
being absent ; the two inner (second and third) small and
2 M
530
MANUAL OF ZOOLOGY
SECT.
united together by integument, while the middle one is
very long and powerful. The tail is very long, and usually
thick. There is a large marsupium.
FIG. 318. — Rock wallaby (Petrogale xanthopus). (After Vogt and Specht.)
The Phalangers {Phalangcrida) are climbing Marsupials
which have both fore- and hind-feet prehensile ; the second
and third toes of the hind-foot slender and united by a
web, as in the kangaroo, but the hallux, which is nailless,
XII
PHYLUM CHORDATA
531
opposable to them ; the fourth and fifth nearly equal ; the
tail is well developed and prehensile. The koalas (Fig. 319)
differ from the phalangers mainly in the relatively thicker
body and the vestigial tail.
The sloths {Bradypodida) (Fig. 320) are more completely
adapted, in the structure of their limbs, to an arboreal life
FIG. 319. —Koala (Phascolarctos ctnereus). (After Vogt and Specht.)
than any other group of the Mammalia. They have a
short, rounded head, with small pinnae and long slender
limbs, the anterior much longer than the posterior, with
the digits, which are never more than three in number, long,
curved, and hook-like, adapted for enabling the animal to
hang and climb, body downwards, among the branches of
trees. The tail is rudimentary. The body is covered with
coarse hairs.
The ordinary ant-eaters {Myrmecophaga) have a greatly
532
MANUAL OF ZOOLOGY
SECT.
elongated snout, with the mouth as a small aperture at its
extremity, small eyes, and the auditory pinna sometimes
small, sometimes well developed. There are five digits in
the fore-foot, of which the third has always a very large,
FIG. 320. — Unau, or two-toed sloth (Chol&pus didactylus) .
(After Vogt and Specht.)
curved, and pointed claw, rendering the manus an efficient
burrowing organ. The toes of the hind-foot, four or five in
number, are sub-equal and provided with moderate-sized
XII
PHYLUM CHORDATA
533
claws. The tail is always very long, and is sometimes pre-
hensile. The body is covered with long hair.
In the armadillos {Dasypodida} (Fig. 321) the head is
comparatively short, broad, and depressed. The number of
complete digits of the fore-foot varies from three to five ;
these are provided with powerful claws, so as to form a very
efficient burrowing organ. The hind-foot always has five
digits with smaller claws. The tail is usually well developed.
FIG. 321. — Tatu armadillo (Dasypus sexcinctus). (After Vogt and Specht.)
The most striking external feature of the armadillos is the
presence of an armour of bony dermal plates. This usually
consists of a scapular shield of closely united plates covering
the anterior part of the body, followed by a series of trans-
verse bands separated from one another by hairy skin, and a
posterior pelvic shield. The tail is also usually enclosed in
rings of bony plates, and a number protect the upper surface
of the head. Dasypus occurs in southwestern Texas.
In the scaly ant-eaters (Manis} (Fig. 322) the head is
produced into a short pointed muzzle. The limbs are short
534
MANUAL OF ZOOLOGY
FIG. 322 —Scaly ant-eater (Manis peutadactyla). (After Vogt and Specht.)
FIG. 323. — Aard-vark (Orycteropus capensis). (After Vogt and Specht.)
XII
PHYLUM CHORDATA
535
and strong, with five digits in each foot. The upper surface
of the head and body, the sides of the latter, and the entire
surface of the tail are covered with an investment of rounded
horny epidermal scales. The lower surface is covered with
hair, and there are a few coarse hairs between the scales.
There are five digits in both manus and pes.
The aard-varks (Fig. 323) have a thick-set body, the head
produced into a long muzzle with a small tubular mouth, the
pinnae of great length, the tail long and thick. The fore-
limbs are short and stout, with four toes. The hind-limb
FIG. 324. — Killer ( Orca gladiator} . (After True. )
is five-toed. The surface is covered with thick skin with
sparse hairs.
The Cetacea (Fig. 324), among which are the largest of
existing mammals, are characterised by the possession of a
fusiform fish-like body, tapering backwards to the tail, which
is provided with a horizontally expanded caudal fin divided
into two lobes or " flukes," and a relatively large head, not
separated from the body by any distinct neck. A dorsal
:i
536
MANUAL OF ZOOLOGY
SECT.
median fin is usually present. The fore-limbs take the form
of flippers, with the digits covered over by a common integu-
ment and devoid of claws ; the hind-limbs are absent. The
mouth is very wide ; the nostrils are situated on the summit
of the head, and the auditory
pinna is absent. Hairs are
completely absent, or are rep-
resented only by a few bristles
about the mouth. In the
whale-bone whales (Fig. 325)
the nostrils have two exter-
nal slit-like apertures ; in the
toothed whales, porpoises, and
dolphins, on the other hand,
the two nostrils unite to open
by a single crescentic valvular
aperture.
In the Sirenia also the body
is fish-like, with a horizontal
caudal fin, the fore-limbs flip-
per-like, the hind-limbs absent,
and the integument almost
hairless. But the body is dis-
tinctly depressed, and the
head is by no means so large
FIG. 325. — Section of upper jaw with m proportion as in the Ceta-
baleen-plates, of Baleenoptera. (After
Owen-) cea, and has a tumid truncated
muzzle, not far back from the extremity of which the nostrils
are situated. There is no dorsal fin.
In the Ungulata vera the claws or nails of other mammals
are replaced by thick solid masses, the hoofs, investing the
ungual phalanges and bearing the weight of the body. The
number of digits is more or less reduced, and the limbs as a
xii PHYLUM CHORDATA 537
whole are usually specially modified to act as organs of
swift locomotion over the surface of the ground, their move-
ments being restricted by the nature of the articulations to
antero-posterior movements of flexion and extension. The
metacarpal and metatarsal regions are relatively very long.
In the sub-order Artiodactyla (or cattle, sheep, antelopes,
giraffes, deer, camels, pigs, and hippopotami) the third
and fourth digits of each foot form a symmetrical pair, and
in the majority are the only digits that are completely devel-
oped. Characteristic of the ruminants are the cephalic
appendages known as horns and antlers. The horns of the
oxen, sheep, goats, and antelopes, sometimes developed in
both sexes, sometimes only in the males, are horny sheaths
supported on bony cores, which are outgrowths of the frontal
bones. In the giraffes the horns, which are short and occur
in both sexes, are bony structures covered with soft skin, and
not at first attached by bony union to the skull, though sub-
sequently becoming firmly fixed. The antlers of the deer,
.which, except in the case of the reindeer, are restricted to
the male sex, are bony growths enclosed only while immature
in a layer of skin, the " velvet," covered with very soft short
fur. Antlers are shed annually, and renewed by the growth
of fresh vascular bony tissue from the summit of a§pair of
short processes of the frontal bones, the pedicles.
In the pigs the legs are relatively short, and the two lat-
eral toes of both manus and pes are fully developed, though
scarcely reaching the ground. The surface is covered with
a scanty coat of coarse bristles. There is a truncate mobile
snout, the anterior end of which is disc-shaped and free from
hairs. A remarkable feature of the males is the development
of the canine teeth of both jaws into large, upwardly curved
tusks.
In the hippopotami the body is of great bulk, the limbs
538 MANUAL OF ZOOLOGY SECT.
very short and thick, the head enormous, with a transversely
expanded snout, prominent eyes, and small pinnae. The
tail is short and laterally compressed. The toes are four in
each manus and pes, all reaching the ground. The surface
is naked, with only a few hairs in certain positions ; the skin
is of great thickness.
In the sub-order Perissodactyla (horses, tapirs, rhinoce-
roses) the third digit is either the only complete one in both
fore- and hind-foot (horses) or there are only three digits,
second, third, and fourth in each (rhinoceroses), or there
are four in the fore-foot and three in the hind (tapirs) . The
horses (Equidce) have the distal divisions of the limbs slen-
der, the metacarpals and metatarsals nearly vertical to the
surface of the ground, the single hoof massive and with a
broad lower surface. Though the head is elongated, the
nasal region is not produced into a proboscis. The tail is
short or moderately long, and is either beset throughout with
a large number of very long coarse hairs, or with a tuft of
such specially developed hairs at the extremity. A mane of
similar large hairs usually runs along the dorsal surface of the
neck. There is a wart-like callosity above the wrist, and in
the true horses a second a little below the heel or " hock."
The .tapirs have the body more massive than the horses,
and the limbs, especially the distal segments, shorter and
stouter. The nasal region is produced into a short proboscis.
The surface is beset with a scanty covering of hairs. The
tail is vestigial.
In the rhinoceroses the body is extremely massive, the
limbs short and stout, each digit provided with a hoof-like
nail. There is a short soft muzzle. Either one or two
remarkable median horns are borne on the nasal region, not
attached directly to the skull ; these are epidermal structures
which are formed of a dense aggregation of slender fibre-
xii PHYLUM CHORDATA 539
like elements. The eyes are small, the auditory pinna well
developed. The surface is devoid, or nearly devoid, of hairs,
and the skin is enormously thick, and in some species
thrown into deep folds. The tail is narrow and of moderate
length.
The hyraxes are small, somewhat rabbit-like animals,
with slender limbs and vestigial tail. There are four func-
tional digits in the manus and three in the pes, all provided
with short flat nails, except the innermost of the pes, which
has a curved claw. The body is covered with soft fur.
The elephants, the largest of existing terrestrial mammals,
have the limbs much more typically developed than in the
true Ungulates, there being five comparatively short digits,
enclosed in a common integument, in each foot, all of them
in the fore-, and three or four in the hind-foot terminating in
a broad flat nail. The limbs are very stout and pillar-like,
and the thigh and leg when at rest are in a straight line
instead of being, as in the Ungulata vera, placed nearly at
right angles to one another — a circumstance which gives a
characteristic appearance to the hind-quarters. The nasal
region is produced into a proboscis or " trunk," a mobile
cylindrical appendage, longer than the rest of the head, at
the extremity of which the nostrils are situated. There is
in the male a pair of enormous tusks, the incisors of the
upper jaw. The eyes are small, the pinna of the ear enor-
mous. The tail is small. The skin is very thick and pro-
vided with only a scanty hairy covering.
In the Carnivora the typical number of digits is sometimes
present, or, more usually, there are five in the fore- and four
in the hind-foot, or four in both. The extremities of the
digits are provided with compressed curved claws, which
may be very long and sharp, when they are capable, when
not in use, of being retracted into a sheath of skin situated
540 MANUAL OF ZOOLOGY SECT.
at their bases ; or relatively short and blunt, when they are
incompletely or not at all retractile. The otters (Lutra}
differ from the rest in having short limbs with the toes
connected by webs of skin.
The Pinnipedia, or seals and walruses (Fig. 326), have
the proximal segments of the limbs short, so that the arm
and thigh and nearly all the fore-arm and leg are enclosed
in the common integument of the trunk, and the manus and
pes elongated. The earless seals (Phocida) are much more
completely adapted to an aquatic life than the eared seals
FIG. 326. — Harbor Seal (Phoca vitulina).
{Otariidcz} and walruses (Trichechida) , being unable to flex
the thigh forwards under the body, so that the hind-limbs
may aid in supporting the weight, and thus being only able
to drag themselves along very awkwardly when on dry land.
The pinna of the ear is absent in the earless seals and
walruses, well developed in the eared seals. The surface in
all is covered with a thick soft fur. In the fur seals there
are two kinds of hairs, those of the one kind being longer
and coarser and scattered through the more numerous shorter
and finer hairs composing the fur proper. A remarkable
xii PHYLUM CHORDATA 541
feature of the walruses is the presence of a pair of large tusks,
the enlarged canine teeth, projecting downwards from the
upper jaw.
Though some of the rodents (beavers, water voles) are
aquatic, some (squirrels and tree-porcupines) are arboreal,
while others (the majority of the order) lead a terrestrial
life and are active burrowers ; they are on the whole a very
uniform group, and exhibit few such remarkable modifica-
tions as are to be observed in some of the other orders of
mammals. They are nearly all furry animals with five-toed,
plantigrade, or semi-plantigrade limbs. The tail is usually
elongated, and may be naked or covered with fur; but
sometimes, as in the rabbits and hares, it is very short. A
few special modifications, however, have to be noted in cer-
tain families of rodents. The flying squirrels have on each
side a fold of skin, the patagium, which serves as a parachute.
The African flying squirrels {Anomalurus} are remarkable
also on account of the presence of a series of overlapping
horny scales on the lower surface of the basal part of the tail.
The Jerboas (Diptis) and their allies are characterised by
the great relative length of the hind-limbs — the mode of
locomotion of these remarkable rodents being by a series of
leaps not unlike the mode of progression of the kangaroo —
and by the reduction of the number of the toes to three in
some of them. The porcupines (Hystricida) have numerous
elongated spines or " quills " among the hairs of the dorsal
surface, and some of them have prehensile tails.
The Insectivora are, in general, small, furry, burrowing
mammals with plantigrade limbs and an elongated muzzle.
But there is a considerable range of modification within the
order in adaptation to different modes of life. The cobegos
( Galeopithecus} have a fold of skin extending along each side
of the neck and body and continued between the hind-legs,
542 MANUAL OF ZOOLOGY SECT.
enclosing the tail ; the fore- and hind- feet are both webbed,
and the tail is prehensile. The hedgehog (Erinaceus) has
the surface beset with pointed spines. The moles (Tatpa)
and their allies, which are active borrowers, have the limbs
very short and stout and provided with extremely strong
claws. The jumping shrews (Macrosceledidce) have slender
limbs adapted to progressing by leaps on the surface of the
ground.
The Chiroptera (Fig. 327) are the only mammals which
are capable of active flight. The fore-limbs have the seg-
FIG. 327. — Bat {Synotus barbastelius}. (After Vogt and Specht.)
ments greatly elongated, especially the fore-arm and the
four ulnar digits, and these support a thin fold of the integu-
ment which stretches to the hind-limbs and constitutes the
wing. A fold also extends between the hind-limbs and may
or may not involve the tail. The pollex is much shorter
than the other digits, directed forwards, and terminates in a
well-developed curved claw ; in the Megachiroptera, but not
in the Microchiroptera, the second digit also has a claw; the
other digits are always clawless. The position of the hind-
limbs is peculiar, and the knee is directed backwards instead
xii PHYLUM CHORDATA 543
of forwards as in other mammals ; the five digits of the foot
are all provided with claws. So complete is the adaptation
of the limbs to the purpose of flight that bats are only able
to shuffle along with great difficulty on the ground, though
with the aid of their claws they are able to climb and to
suspend themselves from branches of trees by the hind-feet.
In the lemurs and their allies (Prvsimii) the body is
slender, and the limbs adapted for an arboreal existence.
The hallux is divergent from the other digits of the foot
and opposable to them, and the same holds good, in some
cases, of the pollex. In some, all the digits are provided
with claws, or all but the hallux. More commonly all the
digits are provided with flat nails, except the second of the
pes, which always has a claw. The eyes are very large.
The muzzle is sometimes elongated, sometimes short ; the
nostrils are slit-like. The tail is sometimes absent or short ;
more usually it is greatly elongated, but it is never prehen-
sile. The surface is always covered with soft fur.
Of the remaining groups of Primates the Hapilidae or
marmosets are small squirrel-like animals with all the digits
except the hallux provided with pointed claws, with the
pollex incapable of opposition, the tail non-prehensile, and
without cheek-pouches or callous patches over the ischia.
The Cebidae, or American monkeys, resemble the Hapalidae
in the negative characters of the absence of ischial callosities
and of cheek-pouches, and of the power of opposition in the
hallux. But the limbs are much longer, the digits are all
provided with flat nails, and the tail is frequently prehensile.
The Cercopithecidae, or baboons and macaques, all have
brightly coloured bare callous patches of skin (callosities)
over the ischia, and most of them have cheek-pouches for the
storage of food. All the digits are provided with flat nails.
The tail may be long or short or absent ; when present it is
544 MANUAL OF ZOOLOGY SECT. xn.
never prehensile. The pollex when developed is always
opposable to the other digits. In the Simiidae or man-like
apes, a tail is never developed, and there are no cheek-
pouches ; ischial callosities are only present in the gibbons.
The gibbons can walk in an upright position without the
assistance of the fore-limbs ; in the others, though in pro-
gression on the surface of the ground, the body may be held
in a semi-erect position with the weight resting on the hind-
limbs, yet the assistance of the long fore-limbs acting as
crutches is necessary to enable the animal to swing itself
along.
INDEX
Aard-vark, 535.
Abactinal end, of starfish, 158.
Acanthias vulgaris, 366.
Acanthin, 31.
Acetabulum, 342; of frog, 416.
Aciculum of Annelids, 190.
Acineta, 51.
Acmaea tesludinalis, 292.
Acrania, 323.
Acromion process, 500.
Actinobolus, 49.
Actinomma asteracanthion, 32.
Actinophrys sol, 26, 28.
Actinosphaerium, 27, 28.
Actinostome, 158.
Actinozoa, 91, 114.
Adamsia palliata, 123.
Adelochorda, 311.
Adrenals, of birds, 476; of frog, 427.
Agalmopsis cara, 108.
Air-bladder, 403.
Air-sacs, of birds, 472, 477; of in-
sects, 248.
Air-vesicles, 513.
Albatross, 490.
Alcyonaria, 118, 119.
Alcyonium carneum.ng; palmatum,
119.
Alisphenoid, 498.
Allantois, 434.
Alligator, 434, 438, 456 ; brain, 449.
Alveolus, 504.
Amaroucium, 320.
Ambulacral groove, 160, 161.
Ambulacral pores, 161.
Ambulacrum, 160.
Amnion, 434.
Amoeba, 14, 19 ; polypodia, 18 ; pro-
teus, 14.
Amphicrelous vertebrae, 334.
Amphineura, 281.
Amphibia, 407.
Amphidiscs, 88.
Amphioxus lanceolatus, 323.
Amphistomum, 136.
Ampulla, 162.
Anemone, sea, 115, 117.
Anguis, 436.
Animalcules, wheel, 178.
Annelida, 188, 191.
Annulata, 188.
Annuli of leeches, 203.
Anodonta cygnea, 265, 270, 273, 274 ;
fluviatilis, 265; circulatory system,
of, 276.
Anolis, 328.
Anomalurus, 541.
Anoplophyra, 49.
Ant-eater, 526, 531 ; scaly, 533 ; spiny,
525. 527-
Antedon, 175.
Antelope, 526, 537 •
Antenna, 219.
Antennule, 219.
Antlers, 537.
Anthenea, 167.
Anthophysa, 37.
Anthrenus scrophularise, 245.
Antipathes, 120.
Ant, red, 253; neuter, 253; soldier,
253 ; worker, 253.
Anura, 432.
Anus, 46; of Antedon, 175; of star-
fish, 159 ; absent in starfish, 170; of
2N
545
546
INDEX
round worms, 149 ; of birds, 459 ;
of reptiles, 435 ; of scorpion, 255.
Aorta, of mammals, 512 ; of molluscs,
275; of vertebrates, 350.
Ape, 544.
Aphides, 250.
Apiosoma bigeminum, 58.
Apis mellifica, 253; parthenogenesis
in, 250.
Aplacophora, 284.
Aplysia, 288, 291.
Apopyle, 82.
Appendicularia, 322.
Appendix vermiformis, 507.
Apteria, 462, 483.
Apteryx, 483.
Apus glacialis, 232, 275.
Arachnida, 254; lungs or pulmonary
sacs, 257.
Arachnidium, 259.
Arbor vitas of cerebellum, 517.
Arcella vulgaris, 20.
Arch, haemal, 335, 369; hyoid, 337,
372; pectoral, 339, 373, 406, 445,
446, 500; neural, 410; pelvic, 339,
416, 445, 470, 502.
Arches, branchial, 337, 372,407; vis-
ceral, 337, 370, 444.
Archidoris tuberculata, 290.
Archipterygium, 406.
Architeuthis, 308.
Argonauta argo, 302, 303.
Arteries, of vertebrates, 349, 379,419,
422; coronary, 510; pulmonary,
352, 407; systemic, 351.
Arthropoda, 212.
Armadillo, 526, 533.
Artiodactyla, 537.
Aristotle's lantern, 171.
Ascaris lumbricoides, 149, 151 ; suilla,
149.
Ascetta primordialis, 84.
Ascidia callosa, 314; mammillata,
320.
Ascidians, 314; blood system, 318;
heart, 318; larva of, 319; nervous
system, 318.
I Aspredo, 404.
Astacus fluviatilis, 213, 221.
Asterias rubens, 157 ; vulgaris, 157.
Asteroidea, 157.
Astraea, 121 ; pallida, 123.
Astragalus, 504.
Asymmetron, 323.
Atlas, 493 ; of birds, 464.
Atriopore, 326.
Atrium, 326.
Auditory capsules, 410.
Aurelia aurita, 108, in.
Auricles, of birds, 477 ; of mammals,
510 ; of rabbit, 333 ; of sharks, 377 ;
of vertebrates, 350, 407.
Aves, 456.
Avicularium, 181.
Axis, 493 ; of birds, 464.
Babesia bovis, 58.
Baboon, 543.
Balanoglossus, 311, 313.
Bandicoot, 525, 528.
Barbs, of feathers, 461.
Barbules, 461.
Basi-sphenoid, 498.
Bat, 526, 542.
Bdellostoma, 360, 361, 364.
Beak, of birds, 457 ; of bivalve shells,
267; of Brachiopod shells, 184; of
czar fish, 396; of sword fish, 396.
Bear, 526.
Beaver, 526, 541.
Bee, 250 ; honey, 253 ; parasites, 252.
Beetle, carpet, 245.
Belemnites, 301.
Bells, swimming, 105.
Beroe, 128.
Bile, 346.
Bill, of birds, 485; modifications of,
485-
Binomial nomenclature, 2.
Biology, definition of, I.
Bionomics, 13.
Birds, 456 ; colors of, 484 ; egg, 483,
489, 490 ; limbs of, 459 ; mouth of,
459; voice of, 488; wings of, 459.
INDEX
547
Bladder, air, 403; gall, 346, 374;
of molluscs, 275 ; swimming, 403 ;
urinary, 519; of Crustacea, 224;
frog, 427 ; vertebrates, 359.
Blastoderm, of sharks, 385.
Blastostyle, 92.
Blood, 70; corpuscles, 70 ; of insects,
249; vascular system of insects,
249 ; of birds, 488 ; of starfish, 162 ;
of vertebrates, 349, 422, 423.
Blood-vessels, 70; of annelid worms,
193, 207, 260; of Crustacea, 224,
226; nemertean worms, 148.
Body-cavity of starfish, 160.
Body, pituitary, 354.
Bojanus, organ of, 275.
Bombyx mori, 58.
Bone, 66.
Bone quadrate, 339.
Bones, of birds, 472; cartilage, 337,
411; epipubic, 525; marsupial,
525; membrane, 337, 411.
Bothriocephalus latus, 145.
Botryllus violaceus, 322.
Bougainvillea ramosa, 103; super-
cilians, 103.
Brachionus rubens, 179.
Brachiopoda, 184.
Bract, 108.
Bradypodidae, 531.
Brain, 71 ; of annelid worms, 195,
197,208; of birds, 479; of Crustacea,
227 ; of insects, 249 ; of Peripatus,
239 ; of mammals, 514 ; of reptiles,
449; of shark, 353, 380; fore, 354.
Branchellion, 211.
Branchial basket of lamprey, 364.
Branchiae, of annelid worms, 199;
secondary in Gastropod molluscs,
291.
Branchiostoma, 323.
Breast-bone, 336.
Brittle-stars, 169.
Bronchi, of birds, 476; of lizard, 348 ;
of mammals, 512.
Bronchioles, 513.
Bud, 73.
Budding, 72.
Buds, medusa, 92.
Bufo, 432.
Bugula avicularia, 182.
Bulbus aortae, 403, 419.
Bulla tympani, 499.
Bursa Fabricii, 476.
Buthus carolinianus, 259.
Byssus, 279.
Calamus, 460.
Calcaneum, 416, 504.
Calcarea, 86.
Calcar, of frog, 417.
Camel, 526, 537.
Canal, of gastropod shell, 287 ; ingui-
nal, 520 ; neural, 334 ; radial, 97.
Cancer irroratus, 231 ; pagurus, 230.
Cancrisocia, 124.
Capillaries of vertebrates, 349.
Capitulum, 495.
Capsule, central, 31.
Carapace, 214; of Crustacea, 233.
Cardium, 280.
Carina sterni, 466,
Carinatae, 483.
Carnivora, 6, 526, 539.
Carpal bones, 502.
Carpo-metacarpus, 469.
Carpus, 341.
Cartilage, 66 ; cerato-hyal, 372; hyo-
mandibular, 339, 372; intercalary,
369 ; Meckel's, 372.
Casque, 486.
Cassowary, 483.
Cat, 2, 5, 7, 526.
Caudal vertebras, 335.
Cavity, atrial, 315; pericardia!, 315,
349-
Cavity, buccal, 293, 294; of verte-
brates, 344, 459, 505.
Cebidae, 543.
Cell, 18 ; flame, 132, 140.
Cells, adhesive, 127 ; pigment, 303.
Cellulose, in ascidian test, 315.
Cement, of tooth, 343.
Centrale, 502.
548
INDEX
Centra, of birds, 464; of mammals,
493 ; of vertebrae, 333.
Cephalodiscus, 311, 313.
Cephalopoda, 296.
Cephalothorax of arachnida, 254.
Ceratium, 40.
Ceratodus fosteri, 405.
Cercaria, 134; of fluke-worm, 134.
Cercopithecidae, 543.
Cere, 459, 486 ; absence of, 486.
Cerebellum, 354; of birds, 479, 489;
of mammals, 517.
Cerebral hemispheres, 355, 480, 514,
Cervical vertebrae, 335.
Cestoda, 138.
Cestus, 128.
Cetacea, 526, 535.
Chaetopoda, 188.
Chalaza, 490.
Chalk, how formed, 26.
Chameleon, American, 328.
Chauna, 486.
Chela, of arachnida, 256; of Crusta-
cea, 218, 219.
Cheliceres, 257, 262.
Cheliped, 218.
Chelonia, 434, 438, 455.
Chiasma, optic, 380.
Chilaria of Limulus, 262.
Chilopoda, 240.
Chiroptera, 526, 542.
Chitin, 20.
Chitonellus, 281.
Chiton spinosus, 281.
Chlamydosaurus, 452.
Chlamydoselachus, 389.
Chlorophyll, 28.
Choanoflagellata, 38.
Chorda dorsalis, 310.
Chordata, 310.
Chromatophores, 303, 304.
Chrysalis, 252.
Chyle, 346.
Ciliata, 49.
Circulation of frog, 423.
Cirri of amphioxus, 323.
Cirrus, of annelid worms, 191; of cri-
noids, 175; of fluke-worms, 130.
Cistudo lutaria, 442.
Clam, 279; giant, 280.
Claspers, of sharks, 368.
Classification, 5, 8.
Clathrulina elegans, 28, 29.
Clavicle, 414, 501.
Clavicles, of sturgeon, 400.
Claws, 486 ; of birds, 460, 486.
Cliona, 89.
Clitellum, 201.
Clitoris, 521.
Cloaca, 344, 407, 476 ; of Prototheria,
523; of sharks, 393.
Cnidoblast, 95.
Cnidocil, 95.
Cobego, 541.
Coccidium, 58.
Cochlea, of birds, 489 ; of mammals,
518-
Cockle shell, 280.
Cockroach, 242, 243, 247.
Cocoon, of earthworms, 201.
Codonella, 49.
Coeca, of fluke-worms, 131 ; hepatic,
of Amphioxus, 326; hepatic, of
Balanoglossus, 313; hepatic, of in-
sects, 248; intestinal, of starfish,
165 ; pyloric, of starfish, 163 ; rec-
tal, of birds, 476; worms, 193.
Coecilia, 433.
Ccelenterata, 90.
Coelom, of mammals, 504; of mol-
luscs, 271 ; of starfish, 160 ; of
worms, 191.
Coenenchyma, 121.
Ccenosarc, 94.
Collar, 39.
Collozoum inerme, 33.
Colocalanus, 234.
Colonies, 42.
Colony, 30.
Colors of birds, 484.
Columba livia, 457.
Columella, 285 ; of birds, 468 ; of
corals, 121.
INDEX
549
Column, spinal, 333, 369; spinous,
335; vertebral, 335 ; of frog, 410.
Comb-jellies, 125.
Commissures of brain, 515.
Conchiolin, 269.
Condyle of skull of birds, 467.
Condyles, of bird's leg, 471 ; occipi-
tal, of frog, 411.
Condylostoma, 49.
Conjugation, 44, 48, 55.
Con us arteriosus, 350, 419; of Dipnoi,
407 ; of sharks, 377 ; of Teleostomi,
403-
Coracoid bone of birds, 468. .
Corallite, 120.
Corallum, 120.
Corallium rubrum, 118.
Coral, red, 120.
Cord, spinal, 353.
Cords, vocal, of frog, 419; of mam-
mals, 512.
Cornea of eye of Crustacea, 228.
Corona of Echinoidea, 170, 172.
Corpora, cavernosa, 521 ; quadri-
gemina, 517; restiformia, 381.
Corpus, callosum, 515; mammillare,
517; spongiosum, 520; striatum,
SIS-
Cortex, 45, 55 ; of kidneys, 519.
Cowrie, 290.
Crab, 124, 230 ; hermit, 231 ; king, 260.
Craniata, 323, 328.
Cranium, 328, 337 ; of sharks, 369.
Crayfish, 213.
Crinoidea, 174; stalked, 176.
Crocodilia, 434, 438, 456.
Crop, of birds, 474, 488 ; of insects,
246 ; of leeches, 205.
Crura cerebri, 380, 517.
Crustacea, 213.
Cryptomonas, 37.
Ctenidia, 271, 279, 282, 291, 304.
Ctenophora, 91, 125.
Cubitals, 463.
Cuboid, 504.
Cucumaria planci, 174.
Cucumber, sea, 173.
Cuneiform, 502, 504.
Cuticle, 95; of nematoid worms, 151,
Cuttlefish, 296, 300.
Cyclas, 280.
Cyclidium, 49.
Cyclops, 156, 234.
Cyclostomi, 360.
Cydippe, 126.
Cypraea moneta, 290.
Cyst, daughter of tape worms, 143;
mother of tape worms, 143.
Cysticercoid embryo, 143.
Cysticercus, 143.
Cystoflagellata, 41.
Dactylozooids, 108.
Dallingeria, 37.
Dasypus sexcinctus, 533.
Dasyurus, 525, 528, 529.
Deer, 526, 537.
Dendrocometes, 51.
Dendrophyllia, 121, 124.
Dendrosoma, 51, 54.
Dentine, 343.
Dentition, heterodont, 343; homo-
dont, 343.
Deutomerite, 58.
Devil, tasmanian, 528.
Diacoele, 515. .
Diaphragm, 349, 504, 523.
Dibranchiata, 298, 300, 301, 308.
Dictyocysta, 53.
Didinium, 49.
Difflugia, 19, 21, 24; pyriformis, 20.
Digestion, 69; in vertebrates, 344,
346.
Digestive glands of starfish, 164.
Digit, 341; of birds, 459; of frog,
409 ; of mammals, 502.
Dimorpha, 37.
Dimorphism, 118.
Dinobryon, 37.
Dinoflagellata, 40.
Dioecious worms, 148.
Diophrys, 49.
Diphyodont dentition, 523.
Diplomita, 37.
550
INDEX
Diplopoda, 240.
Dipnoi, 365, 405.
Diptera, 243, 245.
Dipus, 541.
Disc, trochal, 178.
Discorbina, 25.
Disease, cattle, 58; silkworm, 58.
Distomum hepaticum, 129, 135.
Distribution, bathymetrical, n; geo-
graphical, ii ; geological, n ; zoo-
geographical, ii.
Division, self, 18, 44.
Dog, 526.
Dogfish, 366.
Dolphin, 526, 536.
Dorippe facchino, 124.
Doris tuberculata, 290, 291.
Down feathers, 461.
Draco, 441, 452.
Dracunculus medinensis, 156.
Dromaeus, 483.
Duck-bill, 525.
Duct, 65; ejaculatory, of leech, 210;
pneumatic, 403.
Dugong, 526.
Duodenum, 346; of birds, 476; of
mammals, 507.
Ear, of bird, 459 ; of Crustacea, 228 ;
of frog, 426; of mammals, 518 ; of
vertebrates, 383.
Earthworm, 201, 202.
Ecdysis, 440.
Echidna, 525, 527.
Echinarachnius parma, 173.
Echinodermata, 157.
Echinoidea, 170.
Ectoderm, 79.
Ectoprocta, 183.
Ectosarc, 28.
Eczema, caused by a parasitic vorti-
cella, 55.
Edentata, 526.
Egg, 59, 60 ; segmentation of, 60.
Egg-shell, 360; of bird, 483; of mol-
luscs, 265; of sharks, 384.
Eggs, of crocodiles, 456 ; demersal,
405 ; of frog, 428 ; pelagic, 405 ; of
reptiles, 451 ; of sharks, 385 ; of
turtles, 455; summer and winter,
180 ; of reptiles, 452.
Elasmobranchii, 365.
Electric catfish, 400.
Electric eel, 400.
Elephant, 526.
Elytra, 245.
Embryo, ciliated, of flat-worms, 133 ;
cysticercoid, 143 ; hexacanth, 141.
Embryology, 4.
Embryo of shark, 386.
Emu, 403.
Enamel, 343.
Encystation, 30.
Endoderm, 79.
Endolymph, 357.
Endopodite, 216.
Endoprocta, 181.
Endosarc, 28.
Endoskeleton, 67.
Endostyle, 317, 319.
Enteron, 92.
Entomostraca, 232.
Entovalva, 281.
Eolis, 291.
Epeira diadema, 259.
Ephelota, 51.
Ephyrula, 112.
Epicoracoid bone, 414.
Epidermis, 63.
Epiglottis, 506.
Epimerite, 58.
Epipharynx of insects, 250.
Epiphragm, 288.
Epiphysis cerebri, 354, 380.
Epipodia, 291.
Epipodite, 218.
Episternum, of frog, 415 ; of reptiles,
445-
Epistoma of Crustacea, 216.
Epistylis, 48, 49.
Epithelium, 63, 64; deric, 63.
Equidae, 538.
Ethmoid, 498.
Ethmo-turbinals, 498.
INDEX
55'
Ethology, 13.
Euglena viridis, 34, 36.
Euplectella, 86.
Eupomatus, trochosphere of, 199.
Eurypterida, 260.
Euspongia, 87.
Eustachian tube, 358, 417, 505.
Eutheria, 525.
Euthyneura, 295.
Evolution, 9.
Excretion, 71.
Excretory pore of nematoda, 152.
Excretory system of nematoda, 152.
Excretory vessels of flat-worms, 132 ;
of nemertean worms, 148.
Exoccipital bones of frog, 411; of
mammals, 496.
Exopodite, 216.
Exoskeleton, 67; of sea urchin, 157,
of starfish, 157.
Eye, of birds, 459, 480, 489 ; choroid of,
356 ; compound, of Crustacea, 228 ;
iris of, 356 ; of frog, 408 ; of insects,
250; of mammals, 518; median, of
amphioxus, 328 ; of molluscs, 280,
283, 289, 307 ; of nemertean worms,
148; of nereis, 196; pineal, 364,
450 ; pupil of, 356 ; of starfish, 160 ;
of vertebrates, 356, 425, 450.
Eyeball, 356.
Eyelid, of frog, 408.
Eye-spot, of fluke-worm, 133.
Eye-stalk, 216, 219.
Facets of eye, 228.
Facial nerve, 382.
Fallopian tubes, 520.
Fat bodies of frog, 427.
Fauna, 12.
Feather, follicle of, 461 ; germ of, 462 ;
papilla of, 461 ; pulp of, 462 ; tracts,
462.
Feathers, 460, 483; colors of, 484;
contour of, 461 ; cubital, 463 ;
primaries, 463 ; rectrices, 463 ;
secondaries, 463.
Feather-stars, 174.
Felis, 2, 5, 7.
Femur, 342; of birds, 471.
Fibula, 342, 416 ; of birds, 471.
Fibulare, 416.
Filoplumes, 461.
Fimbrias of mussel, 266.
Finger, index, 409.
Fins, 332, 365, 372; lateral, 368;
median, 367; paired, 367; rays of,
365 ; of shark, 406 ; unpaired, 367.
Fin-skeleton, of ceratodus, 406.
Fish, circulation in, 351.
Fishes, 365; bony, 394; cartilaginous,
365 ; teeth of, 402.
Fission, binary, 18, 28, 44.
Flabellum, 120; curvatum, 122.
Flagellula, 24, 33, 38.
Flagellum, 24, 33, 36, 38 ; of Crustacea,
219.
Flat-fish, 397.
Flat-worms, 137.
Flight, muscles of, in birds, 474.
Flocculi, of bird's brain, 480.
Flounder, 397.
Fluid, coelomic, 191.
Fluke-worm, 129, 135.
Foeces, 69. -
Foetus, 360, 521.
Folliculina, 49.
Fontenelle, 570.
Foot, of frog, 409 ; of molluscs, 266,
280, 281, 290.
Foramen magnum, 337.
Foramina, 370 ; pneumatic, 472.
Foraminifera, 21, 25, 26.
Formica rufa, 253.
Fornix, 515.
Fossils, 10.
Fox, flying, 526.
Frog, brain, 425; eyes, 408; limbs,
408 ; metamorphosis of, 429 ;
mouth, 408; nervous system, 425;
nostrils, 408.
Frondicularia, 25.
Frontal bones of frog, 411; of lizard,
340.
Fron to-parietal bones, 411.
552
INDEX
Funnel of Cephalopoda, 299, 304.
Furcula, 488.
Galeopithecus, 541.
Gametes, 44.
Ganglion, optic, 249; of mussel, cere-
bro-pleural, 276; pedal, 276; vis-
ceral, 276.
Ganodei, 394.
Gastrolith, 222.
Gastropoda, 284.
Generations, alternation of, 98.
Genital opening of flat-worms, 130.
Genital plates of Echinoidea, 172.
Geotria, 365.
Germinal spot, 59.
Germinal vesicle, 59.
Gestation, 522.
Gibbon, 544.
Gill-cover, 214.
Gill-slits of Balanoglossus, 312.
Gill, spiracular, 377.
Gills, 70; of annelid worms, 199;
of Crustacea, 222; of frog, 431; of
molluscs, 267, 271, 279, 282, 291,
304 ; secondary, 293 ; tracheal, 248 ;
of ve'rtebrates, 347, 375.
Giraffe, 526, 537.
Girdle, pelvic, of birds, 470.
Gizzard, of birds, 474, 488 ; of insects,
247.
Gland, 63; byssus, 279; Cowper's,
520 ; digestive, 27 ; digestive of
starfish, 164; green, 224; mam-
mary, 360; milk, 360; of fluke-
worm, 133; ovoid, 166; prostate,
520 ; rectal, 375 ; salivary, 69 ; sali-
vary of vertebrates, 344; shell, 133,
233,384; subneural, 319.
Glands, buccal, 476; clitoridis, 521;
thyroid, 476.
Glenodinium, 40.
Globigerina, 25, 26 ; ooze, 26.
Glochidium, 277.
Glossocodon, 102.
Glottis, 347, 418 ; of birds, 476.
Glugea bombycis, 58.
Glycogen, 346.
Goat, 526.
Gonads, 72; of mussel, 277.
Gonangium, 92, 95.
Gonopoda, 216.
Gonopore of nematoid worms, 150.
Gonotheca, 92.
Graafian follicle, 359, 520.
Gregarina, 57, 58.
Gromia, 22, 24.
Groove, buccal, 45.
Growth, lines of, in bivalve shells, 267.
Guinea worm, 156.
Gymnophiona, 433.
Gymnotus, 400.
Haemamoeba laverani, 58.
Haemal arch, 335.
Haematochrome, 36.
Hag-fish, 360.
Hair, trigger, 95.
Halistemma, 105, 107.
Hallux, of birds, 459; of frog, 410.
Hand of frog, 409.
Hapilidae, 543.
Hare, 526; American, 491.
Hatschek, groove of, 328.
Hatteria, 437, 455.
Heart, 71 ; of birds, 477, 488 ; of crus-
tacea, 224 ; of Dipnoi, 407 ; of frog,
419; of mammals, 507; of mol-
luscs, 275, 294, 306 ; of reptiles, 448 ;
of sharks, 377 ; of vertebrates, 349.
Hedgehog, 526, 542.
Heliozoa, 28, 29.
Hell-bender, 433.
Heloderma, 445.
Hemichorda, 311.
Hemiptera, 243.
Hemispheres, cerebral, 355.
Hen's egg, 489.
Hepato-pancreas, 222.
Heptanchus, 389, 390, 392.
Hermaphroditism, in flat-worms, 132.
Heteropoda, 288, 296.
Hexanchus, 389, 392.
Hilus of kidney, 518.
INDEX
553
Hinge of bivalve shells, 267; teeth, 267.
Hippocampus, 404.
Hippopotamus, 526, 537.
Hirudinea, 203.
Hirudo, eyes of, 209; lateral sense-
organs, 209; medicinalis, 204;
quinquestriata, 206.
Histology, 4.
Hoatzin, 487.
Hock, 538.
Holothuria edulis, 173 ; floridana,
173-
Holothuroidea, 173.
Homalogaster, 136.
Hoof, 536.
Hormiphora plumosa, 126.
Horns, 537.
Horse, 526, 538 ; sea, 404.
Host, of guinea worm, 156; of para-
sitic worms, 134, 142, 144.
Hound fish, rough, 366.
Humerus, 341; of birds, 469.
Hyalonema, 89.
Hyalosphenia lata, 20.
Hybrids, 3.
Hydatids, 143.
Hydra, 73, 96, 99, 100.
Hydranths, 91.
Hydrocorallina, 104.
Hydrophyllia, 108.
Hydrotheca, 91.
Hydrozoa, 90, 91.
Hydrula, 98.
Hyla, 432.
Hyoid apparatus of birds, 468; of
frog, 411 ; of mammals, 500.
Hypopharynx, 244.
Hypophysis cerebri, 354, 380.
Hyposternum, 443.
Hypostome, 92.
Hyrax, 526, 539.
Hystricidae, 541.
Ichthyomyzon, 365.
Idyia roseola, 128.
Ilium, 342; of birds, 470, 476; of frog,
416; of mammals, 503.
Imago, 251.
Incisor teeth of rabbit, 491.
Incubation, 483, 490.
Infundibulum, 127, 354, 380; of
. brain, 513, 517.
Infusoria, 45.
Ink gland of Cephalopoda, 306.
Ink sac of Cephalopoda, 306.
Insecta, 241; abdomen, 242; head,
242: thorax, 242; appendages of
head, 242; of thorax, 242 ; muscu-
lar force of, 252.
Insectivora, 526, 541.
Interclavicle, 445.
Intestine of vertebrates, 374, 418, 447.
Introvert, 289.
Ischium, 342; of bird, 470; of frog,
416.
Itch mite, 260.
Jaws, of Cephalopoda, 304 ; of leech,
205; of Peripatus, 239 ; of starfish,
159 ; upper, of frog, 410 ; of verte-
brates, 343.
Jellyfish, 90.
Jerboa, 541.
Kangaroo, 525, 529.
Kidneys, of birds, 481 ; of frogs, 427 ;
of mammals, 518; of molluscs, 275,
283, 295 ; of vertebrates, 358, 384.
King crab, 260, 263.
Kiwi, 483.
Koala, 531.
Labia majora, 521.
Labrum, of Arachnida, 256; of in-
sects, 242; of Limulus, 262; of
Mvriapoda, 240.
Lacerta viridis, 330.
Lachrymal bones, 500.
Lachrymal foramen, 500.
Lacrymaria, 49.
Laemargus, 393.
Lagena, 25.
Lamellae of molluscan gills, 272, 274.
Lamellibranchiata, 265.
554
INDEX
Lampreys, 360, 364.
Lamp-shells, 184.
Larva, of annelid worms, 199 ; of in-
sects, 251.
Larynx, 347; of birds, 476; of mam-
mals, 506, 512.
Laurer, canal of, 133.
Layers, germinal, 62.
Leech, eyes of, 209; sense-organ of,
209; medicinal, 203.
Legs, of Crustacea, 218 ; of insects,
244 ; of mammals, 493 : of reptiles,
435-
Lemur, 543.
Lens, crystalline, 357.
Lepas anatifera, 235.
Lepidoptera, 251.
Lepidosiren, 405.
Lepus cuniculus, 491.
Limb of vertebrates, 332, 459, 493.
Limpet, 285, 292.
Limulus, 260, 263.
Line, lateral, 367, 383 ; pallial, 267.
Lingula pyramidata, 187.
Liteocircus annularis, 31.
Lithite, 98.
Lithocysts, 98.
Liver, 69; of birds, 476; of frog,
418 ; of vertebrates, 374.
Liver-fluke, 129, 135 ; of vertebrates,
344, 507.
Lizards, 436 ; flying, 441 ; habits,
452.
Lobe, temporal, of mammals, 515.
Lobes, olfactory, 354, 380 ; optic, 480.
Lobosa, 19.
Loligo pealii, 302 ; vulgaris, 302.
Lophomonas, 49.
Lophophore, of Brachiopods, 186 ; of
Polyzoa, 181.
Lorica, 38 ; of Rotifers, 180.
Loxosoma, 181.
Lucernaria, 112.
Lumbar vertebrae, 335.
Lumbricus agricola, 200.
Lunar bones, 502.
Lungs, 70 ; book, of Arachnida, 257 ;
of birds, 477 ; of fishes, 365, 405 ;
of frog, 418, 431 ; of lizards, 348,
448; of mammals, 512; of molluscs,
292.
Lutra, 540.
Lymphatic vessels, 425.
Macaque, 543.
Macropodidee, 529.
Macrosceledidae, 542.
Madrepora aspera, 124.
Madrepore, 120.
Madreporic canal, 165.
Madreporite, 159.
Magellania flavescens, 185 ; lenticu-
laris, 186.
Magnum, 502.
Malacostraca, 232.
Malapterurus, 400.
Malar bone, 499.
Malaria caused by Protozoa, 58.
Malphigian tubes, 248.
Mammalia, 491.
Mammary glands, 360.
Manatee, 526.
Mandible, of vertebrates, 339, 500.
Mandibles, of Crustacea, 217, 219 ; of
insects, 242 ; of Myriapoda, 240.
Manis, 533.
Mantle, of ascidians, 315 ; of molluscs,
266, 289; cavity, 271, 289, 304.
Manubrium, 92, 94, 95, 109.
Marmoset, 543.
Marsupium, 525.
Mastigamoeba, 37, 41.
Mastigophora, 34.
Maxilla, of Crustacea, 218, 219; of
insects, 242.
Maxillary palpus of insects, 242.
Maxilliped,2i8.
Medulla, 45, 55; of kidney, 519; ob-
longata, 354.
Medusa-buds, 92.
Megagamete, 44.
Megalaesthetes, 282.
Meganucleus, 45, 50.
Megapodius, 491.
INDEX
555
Meleagrina margaritifera, 280.
Membrane, branchiostegal, 396 ; nic-
titating, 435 ; tympanic, 408, 435 ;
undulating, 50.
Menopoma, 433.
Merostomata, 260.
Mesentery, 115, 347, 507.
Mesoglaea, 94.
Mesopodium, 290.
Metacarpus, 342.
Metacrinus interruptus, 177.
Metagenesis, 98.
Metameres, 189.
Metamorphosis, of Crustacea, 235 ; of
frog, 429 ; of insects, 251 ; retro-
grade, of ascidians, 320.
Metapleure, 323.
Metapodium, 290.
Metatarsal bones, 504.
Metatarsus, 342.
Metatheria, 525.
Metazoa, 19, 59.
Metridium marginatum, 117.
Mice, 526.
Micraesthetes, 282.
Microgamete, 44.
Micronucleus, 45.
Miliola, 22.
Milk, pigeon's, 483.
Mill, gastric, of crawfish, 220.
Millepora, 104.
Mite, 260; itch, 260.
Mole, 526, 542.
Molar teeth, 505.
Mollusca, 264; characters of, 364;
naked, 291, 296.
Molluscoidea, 184.
Monkey, 543.
Monocystis agilis, 55, 56.
Monotremata, 525.
Monosiga, 39.
Mordacia, 365.
Morphology, 4.
Mound-maker bird, 491.
Mouth, 92; of fishes, 368, 374; of
fluke-worms, 130 ; of frog, 408, 417.
Mud-fish, 405.
Multicilia, 49.
Muscle, adductor, of bivalve shells,
268, 271.
Muscle, of birds, 472; of vertebrates,
342.
Mussel, fresh water, 265, 270, 273,
274 ; brain of, 276 ; nervous system
of, 276 ; sea, 279.
Mustelus anarcticus, 366 ; canis, 366 ;
vulgaris, 366.
Mya arenaria, 279.
Myomeres, 342.
Myriapoda, 239.
Myrmecophaga, 531.
Mytilus edulis, 279.
Myxine, 360; glutinosa, 362, 364.
Myxospongiae, 86.
Nacre of shell, 269.
Naked molluscs, 291, 296.
Name, generic, 2 ; specific, 2.
Nares, 347, 417, 425, 505; of mam-
mals, 496.
Nauplius, 233.
Nautilus pompilius, 298, 300, 306, 309.
Nectocalyces, 105.
Necturus, 433.
Nematelminthes, 149.
Nematocysts, 52, 95, 96.
Nematoda, 149.
Nematodes, 154.
Nemertean worms, 145.
Nemertinea, 145.
Nephridia, of Amphioxus, 327; of
annelids, 196; of leech, 207, 208;
of molluscs, 275, 283, 295, 308.
Nephridiopores, 203.
Nephrostomes of frog, 427.
Nereis dumerilii, 189, 192, 194;
virens, 189.
Nerve cord of Amphioxus, 328.
Nerve-pentagon, 162.
Nerves, 71 ; auditory, 356; cranial,
356; cerebral, 356; hypoglossal,
425 ; olfactory, 356, 381 ; optic, 356,
381,517; peripheral, 355.
Nervous system, of annelids, 195; of
556
INDEX
Crustacea, 227 ; of insects, 249 ; of
molluscs, 275, 282, 295, 296, 306;
of Nematoda, 152; of nemertean
worms, 148 ; of fluke-worm, 132; of
starfish, 162; of tape-worm, 149; of
vertebrates, 355, 380, 381.
Nest, birds', 490.
Neuroccele, 310.
Neuropodium of annelid worms, 190.
Newt, 432.
Nictitating membrane, 408, 435, 492.
Noctiluca miliaris, 41.
Nodosaria, 25.
Nomenclature, binomial, 2.
Nostrils, in Apteryx, 486 ; of birds,
459 ; of frog, 408.
Notochord, 310, 313, 324, 336, 337,
366, 406.
Notochordal sheath, 325.
Notopodium of annelid worms, 190.
Nuclearia, 29.
Nucleus, 16, 45.
Nucula, 279.
Nudibranch molluscs, 291, 296.
Nummulites, 25.
Nyctotherus, 49.
Obelia, 99; commissuralis, 91 ; gela-
tinosa, 91 ; geniculata, 91.
Ocelli, 104.
Ocellus of insects, 250.
Octopus, 302.
Ocular plates of Echinoidea, 172.
Odontoid process, 493.
Odontophore, 293, 304.
Oesophagus of starfish, 163; of in-
sects, 246.
Oikomonas, 37.
Oil glands of birds, 459.
Olfactory capsules, 410.
Olfactory pit of Amphioxus, 328.
Olfactory sacs of frogs, 425.
Oligochaeta, 202.
Ommatidia, of Crustacea, 228; of
insects, 250.
Omosternum, 415.
Onychophora, 236.
Oosperm, 59, 60, 62.
Opalinopsis, 49.
Operculum, 52; of bony fish, 396; of
Dipnoi, 407 ; of gastropod molluscs,
291, 295 ; genital, of scorpion, 257 ;
of Limulus, 262; of Polyzoa, 181.
Ophioglypha lacertosa, 169.
Ophiuroidea, 169.
Ophrydium, 53.
Ophryodendron, 51.
Ophryoglena, 49.
Opisthocomus, 487.
Opossum, 525, 528.
Optic chiasma, 380.
Optic lobes, 380, 480.
Optic thalami, 354, 516; of sharks,
380.
Orbito-sphenoid, 498.
Organs, 66.
Ornithorhynchus, 525, 527.
Osculum, 77.
Osphradium, 277, 295; in Nautilus,
308.
Ossicles, ambulacra], 161 ; auditory,
500; of starfish, 157.
Ostium, 82.
Ostrich, 483.
Otaridae, 540.
Otocysts, 98; of mussels, 277; of
Cephalopods, 308.
Otoliths of vertebrates, 358.
Otter, 526, 540.
Ovaries,of birds, 482 ; of frog, 427, 428 ;
of mammals, 520; of shark, 384; of
starfish, 107; of vertebrates, 359.
Ovary, 101, 133; of Crustacea, 228.
Oviducts, of birds, 482 ; of Crustacea,
229; of mammals, 520; of verte-
brates, 359, 428.
Ovum, 59, 60; fertilization of, 61;
maturation of, 61 ; of mammals,
521 ; of vertebrates, 359, 384.
Oxen, 526, 537.
Oyster, pearl, 280.
Pachychalina, 87.
Paedogenesis in insects, 251.
INDEX
557
Pagurus bernhardus, 231.
Palaeontology, 10.
Palate, 505.
Palatine bone, 414, 499.
Pallial line, 267.
Pallium, 266.
Palpi, of annelid worms, 189 ; of mol-
luscs, 271, 282.
Palpus of insects, 242.
Palythoa, 89.
Pancreas, 69, 344, 346, 375, 418, 507 ;
of birds, 476.
Pancreatic appendages of molluscs,
Soy-
Papilla, adhesive, of nemertean
worms, 146.
Papulae of starfish, 159.
Paraglossae of insects, 243.
Paralichthys dentatus, 398.
Paramoecium caudatum, 45, 47.
Paramylum, 36.
Parapodia of annelids, 189.
Parasitic worms, 156.
Parasphenoid bone of frogs, 413.
Parietal bones of frogs, 413.
Parthenogenesis, in insects, 250; in
Rotifers, 180.
Patagium, 541.
Patella, 292 ; of mammalian leg, 503.
Pearl, mother of, 269; mussel, 265,
280; oyster, 280.
Pebrine, 58.
Pecten, 280; of eye of bird, 480,
489.
Pectines of scorpion, 257.
Pedalion, 180.
Pedicellina, 181, 184.
Pedicellariae, 159.
Pedicles, 537.
Pedipalpi, 256; of spider, 259.
Peduncle, 120.
Pelagic animals, 291, 308.
Pelecypoda, 265, 278, 280.
Pelomyxa, 19.
Pelvic arch, 445.
Pelvic fin, 374, 406.
Pelvis of mammalian kidney, 518.
Penis, of fluke-worms, 130 ; of mam-
mals, 520; nematoid worms, setae
of, 149.
Pennatula aculeata, 120; sulcata, 121.
Pen of cuttle-fish, 301.
Pentacta frondosa, 173.
Peptones, 346.
Peramelidse, 528.
Pericardium, 295; of frog, 419; of
molluscs, 271.
: Perilymph, 383.
! Periostracum, 268.
' Periotic bones, 499,
Peripatus, 236.
j Periplaneta americana, 242.
Perisarc, 94.
Perissodactyla, 538.
Peristome, 52, 163, 287.
Peristomium, 189.
Peritoneum, 347 ; of annelid worms,
197.
Pinna, auditory, 333.
Pinnipedia, 540.
Pinnules of crinoids, 176.
Pipe fish, 404.
Pisces, 365, 394; teeth of, 402.
Placenta, 360.
Placophora, 284.
Plaice, 397.
Planaria, lugubris, 138; polychroa,
138 ; torva, 138.
Plankton, 12.
Planorbulina, 25.
Planula, 98, no.
Plates, in reptiles, 443.
Platyhelminthes, 129.
Platypus, 525.
Pleopoda, 216.
Pleural membrane, 513.
Pleura sac, 513.
Pleurobrachia, 128.
Pleuronectes cynoglossus, 398.
Pleuronectidae, 397.
Petasus, 102.
Petromyzon, 360; marinus, 361,363.
Phalanges, 342, 502, 530 ; ungual, 342.
Pharynx, of Amphioxus, 325 ; of an-
558
INDEX
nelid worms, 193; of leech, 205;
ascidian, 365; of mammals, 505;
of vertebrates, 344.
Phascolomyidae, 529.
Phocidae, 540.
Phragmocone, 301.
Phylogenes, n.
Phylum, 7, 74, 75.
Physalia arethusa, 105.
Physiology, 12.
Pieris rapas, 244.
Pig. 526, 537-
Pigeon, domestic, structure of, 457.
Pigeon's milk, 483.
Pigment cells of molluscs, 303.
Pineal body, 354, 380; eye, 364, 450.
Pleurophyllidia, 291.
Ploughshare, 465.
Pneumatic duct, 403.
Pneumatophore, 105.
Podobranchise, 224.
Podomeres, 214.
Podophrya, 51.
Poison apparatus of reptiles, 454.
Poison fang of reptiles, 447, 453, 454.
Poison glands, of scorpion, 255 ;
of spider, 259 ; of reptiles, 453.
Poison, of reptiles, 454; immunity
against, 454.
Polar bodies, 60.
Polian vesicles, 165.
Polychaeta, 199.
Polykrikos, 40.
Polyoeca, 39.
Polype, 90.
Polypterus birchir, 399.
Polyzoa, 181.
Pons Varolii, 517.
Porcupine, 526, 541.
Pore, excretory, of fluke-worms, 130 ;
of round-worms, 149.
Porifera, 76.
Porpoise, 526, 536.
Portuguese man-of-war, 105.
Post-abdomen, 255.
Potamobia pallipes, 213, 221.
Prae-abdomen, of scorpions, 255.
| Pre-maxillae, 499.
j Pre-hallux, 417.
Premaxilla of frog, 414.
Prepuce of mammals, 520.
Pre-sphenoid, 498.
Presternum, 495.
Primates, 527, 543.
Pristiphorus, 387.
Pristis, 387.
Proboscis, of annelid worms, 193; of
Balanoglossus, 311; of gastropod
molluscs, 289, 293; of leech, 211 ;
of nemertean worms, 145; sheath
of, 146.
Process, articulating, 334; odontoid,
464.
Procoracoid bone of frog, 414.
Proglottis, 140.
Pro-ostracum, 301.
Pro-otic bones of frog, 411.
Propodium, 290.
Prorocentrum, 40.
Prorodon, 49.
Prosencephalon, 380.
Prosimii, 543.
Prosopyle, 81.
Prostomium of annelids, 189.
Proterospongia, 39.
Proteus, 433.
Protobranchia, 279.
Protomerite, 58.
Protoplasm, 16.
Protopodite, 216.
Protopterus, 405.
Prototheria, 524.
Prototroch, 295.
Protozoa, 14.
Proventriculus of birds, 474, 488.
Pseudocoele, 515.
Pseudopleuronectes americanus, 398.
Pseudopodia, 15.
Pteropoda, 288, 291, 296.
Pterygiophores, 372.
Pterygodia, 388.
Pterygoid, bones, 414, 499.
Pterygoid process, 498.
Pterylae, 462.
INDEX
559
Pterylosis, 462, 463.
Ptyalin, 344.
Pubis, 342; of birds, 470; of frog,
416 : of mammals, 503.
Pulmonary sacs of Arachnida, 257.
Pupa, 251.
Pygopus, 436, 437.
Pygostyle, 465, 487.
Pyxicola, 53.
Quadrate bone, 414.
Quadrato-jugal, 414.
Quadrula symmetrica, 20.
Quill, 460.
Rabbit, 331, 491, 526.
Rachis, 461.
Radiale, 469.
Radiolaria, 31.
Radio-ulna of frog, 415.
Radius, 341, 501 ; of bird, 469.
Radula, 293.
Radula sac, 293.
Rana esculenta, 408, 415, 429; tem-
poraria, 408, 412, 413, 417, 420, 421 ;
metamorphosis of, 430.
Rat, 526.
Ratitae, 483.
Rattlesnake, skull of, 445.
Ray, 388, 394 ; electric, 392 ; sting, 388.
Razor fish, 281.
Rectrices, 463.
Rectum, of molluscs, 271 ; of mam-
mals, 507.
Remiges, 463.
Reproduction, 18, 24, 72.
Reptilia, 433.
Respiration, 70; of vertebrates, 332,
349-
Rhabdopleura, 311.
Rhinoceros, 526, 538.
Rhipidodendron, 37.
Rhizopoda, 14, 19.
Rhizostomese, 112.
Rhyncheta, 51.
Rhynchocephalia, 434.
Ribbon, lingual, 293.
Rib, 336.
Ribs, of birds, 463, 494 ; false, 495 ;
floating, 495.
Rodentia, 526, 541.
Rostellum, 140.
Rostrum, 216.
Rotalia, 22.
Rotifera, 178.
Ruminants, 526.
Sac, scrotal, 520.
Saccammina, 25.
Sacral vertebrae, 335.
Sacrum, 494.
Salamander, 432.
Salamandra maculosa, 432.
Salmo, fario, 395, 401 ; fontinalis, 395.
Salmon, Burnet, 405.
Salpingoeca, 39.
Saprophytes, 45.
Saprophytic, 42.
Saw-fish, 387.
Scales, ctenoid, 398; cycloid, 398;
ganoid, 399; of legs of birds, 459;
placoid, 367 ; of reptiles, 435, 439.
Scallop shell, 280.
Scaphoid, 502.
Scapula, 414 ; of birds, 468.
Sclerotic, 356; plates of bird's eye,
480.
Scolex, 140.
Scolopendra, 240.
Scorpion, 255, 259 ; anatomy of, 258 ;
carapace of, 255.
Scuta, 240.
Scutes of bony fishes, 399.
Scutigera, 240.
Scyllium, canicula. 338, 345, 366, 371,
376; catulus, 366.
Scyphozoa, 91, 108.
Scyphula, 112.
Sea-hare, 288, 291, 296.
Sea-horse, 404.
Sea-squirts, 314.
Sea-urchins, 170.
Seal, 526, 540; earless, 540.
Segmental organs of annelids, 196.
56o
INDEX
Segmentation of egg, 60.
Segments of worms, 189.
Sella turcica, 498.
Sense organ, 108.
Sense organs of leech, 209; of mol-
luscs, 282.
Sepia cultrata, 297, 301, 305.
Septa, 121 ; of annelid worms, 191.
Serpula, 198.
Setae, of annelids, 190, 201 ; olfactory,
of Crustacea, 228 ; penial, 149, 150,
153-
Setigenous sac of annelids, 190.
Shark, Greenland, 393.
Sheath, proboscis, of nemertean
worms, 146.
Sheep, 526, 537.
Shell, Cephalopod, 300.
Shell-fish, 266.
Shell-gland of fluke-worm , 133.
Shell-glands, 133 ; of Crustacea, 233.
Shell membrane, 490 ; nacre of, 269 ;
periostracum, 269; prismatic layer
of, 269; supplemental, 23; vesti-
gial, 288.
Shells, dextral, 285 ; sinistral, 285.
Shields of reptiles, 439.
Ship-worm, 279.
Shoulder-girdle, of birds, 468; of
frog, 414.
Shrew, 526 ; jumping, 542.
Simiidae, 544.
Sinistral shells, 285.
Sinus venosus, 350, 407, 419.
Siphon, of molluscs, 266 ; of gastro-
pod mollusc, 289.
Siphonoglyphes, 115.
Siphons of ascidians, 315.
Siphonozooids, 118.
Siphophora, 104.
Siphuncle, 300.
Siren, 433.
Sirenia, 526, 536.
Skeleton, 28, 67; of birds, 487; of
fish, 368; of sponges, 79.
Skull, autostylic, 407; of birds, 467 ;
of frog, 410; of mammals, 495;
of reptiles, 444; of vertebrates, 328,
333. 337- 339-
Slits, branchial, of sharks, 368 ; gill, of
Amphioxus, 326; of Balanoglos-
sus, 312.
Sloth, 526, 531, 532.
Slug, 288, 293.
Snail, 284.
Snake, 436, 446, 453 ; glass, 436 ; ovi-
parous, 455 ; viviparous, 455.
Soldier ant, 253.
Sole, 297.
Solen, 281.
Species, 3; abyssal, n; alpine, n;
littoral, ii ; pelagic, n, 24.
Sperm, 59.
Spermiduct of shark, 384.
Sphaerophrya, 51.
Sphenethmoid bone of frog, 411.
Spicule, 31, 119.
Spicule of sponge, 79, 88.
Spider, 259.
Spine, caudal, of Limulus, 262.
Spines, ambulacral, 159; neural, 369.
Spinnerets, 259.
Spiracle of shark, 332, 368, 386.
Spiroloculina, 25.
Spirula peronii, 300, 301.
Spleen, 375, 418; of birds, 476; of
mammals, 513.
Sponges, 76.
Spongelia, 87.
Spongilla, 85, 89.
Spores, 30.
Sporocyst, 30, 134 ; of fluke-worm, 134.
Sporoduct, 58.
Sporozoa, 55.
Spot, anal, 46.
Spur of birds, 487.
Squamata, 434.
Squamosal bone, 414, 498.
Squammulina, 22.
Squid, 296, 300.
Squirrel, 526, 541 ; flying, 541.
Starfish, 157.
Stentor, 49.
Sternebrae, 336, 495.
INDEX
561
Sternum, 255, 336; of birds, 465, 488 ;
of frog, 415 ; of reptiles, 443.
Stichotricha, 53.
Stickleback, 406.
Stigma, 36.
Stigmata, of ascidians, 315; of in-
sects, 248; of scorpion, 257.
Stinging capsules, 52, 95, 108 ; of
nemertean worms, 146.
Stomach, chyle, 247.
Stomach, of mammals, 506; of star-
fish, 163 ; of vertebrates, 374, 418.
Stomach, sucking, of insects, 246.
Stomodaeum of Nematoda, 152.
Stomogastric nerves, 195.
Stone-canal of Echinoderms, 165.
Strepsiptera, 252.
Streptoneura, 295.
Strongylocentrotus, 171.
Struthio, 483.
Sturgeon, 399, 400.
Stylaster, 104.
Stylet of nemertean worms, 145.
Sucker of distoma, 130, 136.
Suprascapular bone of frog, 414.
Suspensorium, 414.
Sutures of skull, 496.
Swan mussel, 265.
Swift, 490.
Swimming, act of in squid, 304,
308.
Sycon ciliatum, 76; gelatinosum,
'76.
Sylvian fissure, 515.
Symbiosis, 33.
Symmetry, bilateral, of worms, 130 ;
radial, 176.
Sympathetic nerves of vertebrates,
381, 517-
Symphysis, of jaw, 500; pubic, 352,
502 ; of frog, 416.
Synapta, 174.
Syncrypta, 37.
Syncytial ectoderm, 151.
Syngnathus, 404.
Syn -sacrum, 465, 487.
Syrinx, 488.
20
Tadpole, 429.
Taenia ccenurus, 143 ; echinococcus,
143, 144; saginata, 142, 144; ser-
rata, 142; solium, 139, 141, 144.
Tail, diphycercal, 396; heterocercal,
367, 396 ; homocercal, 367, 396.
Tailor bird, 490.
Talpa, 542.
Tape-worms, 138, 144; human, 138,
141.
Tapir, 526, 538.
Tarso-metatarsus, 472.
Tarsus, 342, 411, 503 ; of insects, 244.
Tealia crassicornis, 115.
Teeth, dermal, 467 ; heterodont, 523 ;
homodont, 523 ; thecodont, 523 ; of
leech, 205 ; of sharks, 392 ; of shells,
267; stomach, of crawfish, 220; of
vertebrates, 343, 418, 446, 504 ; ca-
nine, 505 ; incisor, 504 ; molar,
505 ; premolar, 505.
Teleostei, 394.
Teleostomi, 394.
Telson, 217.
Tentacles, 48, 50, 91 ; of annelid
worms, 189; of crinoids, 176; of
molluscs, 289; of starfish, 160.
Tentaculifera, 48, 50, 51.
Tentaculocysts, 101.
Terebra oculata, 289.
Terebratulina septentrionalis, 187.
Teredo navalis, 279, 280.
Tergum, 255.
Tessera princeps, 113.
Test, 19; of ascidians, 315.
Testes, 101, 132; of birds, 481; of
Crustacea, 228 ; of fluke-worm, 132;
of frog, 427; of mammals, 520; of
Nematoda, 153; of starfish, 167;
of vertebrates, 359.
Tetrabranchiata, 299, 308.
Tetramita, 37.
Tetrastemma, 147.
Texas cattle disease, 260.
Texas cattle fever, 58.
Theca, 92, 120.
Thecodont teeth, 523.
562
INDEX
Theria, 524, 525.
Thoracic vertebras, 335.
Thorax, of insects, 241 ; of mammals,
504-
Thuricola, 53.
Thylacine, 528.
Thymus, 513 ; of birds, 476.
Thyroid, 513.
Thyroid glands, 476.
Tibia, 342, 416.
Tibio-fibula of frog, 416.
Tibio-tarsus of birds, 471.
Tick, 260 ; cattle, 260.
Tintinnidium, 49.
Tissues, 63.
Toad, 432.
Toe, great, of frog, 410.
Toes, of birds, 487.
Tongue, of birds, 474 ; of frog, 417 ;
of vertebrates, 344.
Torpedo occidentalis, 392.
Trachea, of birds, 476 ; of mammals,
512 ; of reptiles, 347, 448.
Tracheae of insects, 248.
Trachelomonas, 37.
Trachelius, 49.
Trachosphere of molluscs, 295.
Trachylinae, 102.
Trapezium, 502.
Trapezoid, 502.
Tree, genealogical, 9.
Trematoda, 134; ectoparasitic, 137.
Trichechidae, 540.
Trichina spiralis, 154.
Trichocysts, 46.
Triclad Turbellaria, 137.
Tridacna gigas, 280.
Trigeminal nerves, 382.
Trigger-hair, 95.
Trigonia, 280.
Triton nodiferus, 286, 294.
Trochanter, 471, 503.
Trochosphere of annelid worms, 201.
Trout, 395.
Tuatara, 437, 438.
Tube-feet, of Echinoideaji70 ; of Holo-
thuroidea, 173 ; of starfish, 160, 161.
Tubipora musica, 119.
Tunic of ascidians, 315.
Turbellaria, 137.
Turbot, 397.
Turtles, 434, 438, 455.
Tympanic bones, 499.
Tympanum, 358 ; of frog, 408.
Tzetse fly, 58.
Ulna, 341, 501 ; of birds, 469.
Ulnare, 469.
Umbilicus of feather, 460.
Umbo of shells, 267.
Umbrella, 95.
Unau, 532.
Unciform, 502.
Ungulata, 526, 536.
Unio complanatus, 265, 280; mar-
garitifer, 265.
Urchin, sea, egg of, 60.
Urchins, cake, 173; heart, 173.
Ureter, 359; of frog, 427; of mam-
mals, 519 ; of shark, 384.
Urethra, 359, 520.
Urinary tubes, 248.
Urine, 358.
Urnatella, 181.
Urochorda, 314; larva, 319.
Urodela, 432.
Urolophus testaceus, 390.
Uropoda, 217.
Uropygium, 457, 463.
Uterus, masculinus, 520; of Nema-
toda, 154; of tape-worm, 140; of
vertebrates, 359 ; of worms, 133.
Vacuole, contractile, 17, 36, 45 ; food,
46.
Vagina, of leech, 211 ; of vertebrates,
359- 521-
Vagus nerve, 383.
Valve, spiral, 374 ; of shark, 393, 402.
Valves, mitral, 510 ; semi-lunar, 510 ;
of shells, 265.
Vane of feather, 460.
Variation, 3.
Vascular system of a fish, 378.
INDEX
563
Vas deferens, of fluke-worm, 132; of
mammals, 520 ; of vertebrates, 359 ;
of worms, 132.
Vein, pulmonary, 407, 423; renal
portal, 422.
Veins, hepatic, 352; pulmonary, 351 ;
of vertebrates, 349, 350, 379.
Veliger, 295.
Velum, 97.
Velvet, of deer horns, 537.
Ventricle, of brain, fourth, 354, 380;
lateral, 354; third, 354; fifth, 514.
Ventricles of heart of vertebrates,
35°-
Venus's flower-basket, 86 ; girdle, 128.
Vermetus, 296.
Vermiform appendix, 507.
Vermis, 517.
Vertebra, 333, 440, 463 ; amphicoelous,
334, 440 ; heterocoelous, 464 ; pro-
coelous, 335, 410, 441.
Vertebrata, 322; brain of, 354; cir-
culation of, 349 ; nervous system of,
350; respiration of, 349.
Vertebral column, 333, 369; of birds,
463; of frog, 410; of mammals, 493.
Vesicles, Polian, 165 ; racemose, 166 ;
Tiedemann's, 166.
Vesicula seminalis of worms, 133.
Vessels, water, of flat worms, 132 ; of
Platyhelminths, 132.
Vexillum, 460.
Vibrissae of rabbit, 492.
Visceral arches, 337, 444.
Visceral mass of molluscs, 270.
Visceral nerves, of Crustacea, 227 ; of
worms, 195.
Viviparity, 72.
Voice of birds, 488.
Vole, 541.
Volvox globator, 43, 44.
Vomer bone, of frog, 413.
Vorticella, 48, 52, 54; parasitic, 55.
Vulva, 521.
Wallaby, 530.
Walrus, 526, 540.
Wasp, 250.
Weasel, 526.
Whale, 526, 536.
Wheel animalcules, 178.
Whelk, 296.
Wings, of birds, 459; muscles of,
474 ; of insects, 244 ; veins of, 244.
Wombat, 529.
Worker ant, 253.
Worm, blind, 436.
Xiphosura, 260, 263.
Xiphisternum, 415.
Yolk-sac, of shark, 386.
Zooecium, 181.
Zooid, 30, 91.
Zoology, definition of, i.
Zoophytes, 90.
Zooxanthella, 33.
Zygomatic arch, 499.
Zygomatic process, 498.
Zygapophysis of frog, 410.
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