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A MANUAL OF ZOOLOGY 


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. 


REVISED AND ADAPTED FOR THE USE OF AMERICAN 
SCHOOLS AND COLLEGES 


Neto Work 


THE MACMILLAN COMPANY 
LONDON: MACMILLAN & CO., Ltp. 


1900 


All rights reserved 


CopyRIGHT, 1900, 


By THE MACMILLAN COMPANY. 


Set up and electrotyped January, 1900. Reprinted September, 
1900. 


Norwood 3ress 
J. 8. Cushing & 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 (1) 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 
v 


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 Zext+ 
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 ZextBook 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. 


Wiiutiam A. HASWELL. 


PREFACE TO THE AMERICAN EDITION 


Tus American edition of Parker and Haswell’s 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 Haswell’s 
“Text-book of Zoology,” and also from Sedgwick’s “'Text- 
book of Zoology.” 


CONTENTS 


PREFACE TO THE ENGLISH EDITION . 
PREFACE TO THE AMERICAN EDITION 
List oF ILLUSTRATIONS 


INTRODUCTION 
Definition of zoology 
Binomial nomenclature 
Individual variations 
Hybrids 
Definition of auyohotogy 
Definition of histology . 
Definition of embryology 
Classification a . 
Phyla 
Organic evolution 
Genealogical tree 
Paleontology 
Fossils 
Succession of life i in time 
Phylogeny i : : 
Distribution of animals, in space ll in time 
The plankton 
The necton . 
The benthos 
Definition of a fauna 
Zoo-geographical regions 
Definition of physiology 
Definition of ethology or binomics 

xi 


xvii 


_ 


xil CONTENTS 


SECTION I 
PAGE 
PHYLUM PROTOZOA. F F Fi ‘ 14 
Class 1. The Rhizopoda . ‘ F : ; 14 
Example of the Class — 4maba proteus . . ; 14 
Class 2. The Mastigophora : ‘ 34 
Example of the Class — Luglena viridis 34 
Class 3. The Infusoria 45 
Example of the Class — Paramacium i deadlite 45 
Class 4. The Sporozoa ‘ , 55 
Example of the Class — .V/omecvstis estes “ “ 55 

SECTION IT 
THE METAZOA . : : . . - 59 
Oosperm or egg : . : 59 
Male cell or sperm : 2 . 5 . 60 
Fertilisation ; i F 60 
Segmentation of the oosperm ‘ : : : . 60 
Germinal layers. 62 
Tissues, epithelium i ¥ é . 63 
Glands, ducts : : 63 
Connective tissues : : : » 65 
Fibrous tissue : é : » 65 
Fat. ; : : é : 65 
Cartilage : : : : . 66 
Bone . : : 66 
Muscular tissue. . : ; 66 
Nerve tissue, ganglia, nerves é ‘ 66 
Organs ‘ : é 66 
Exoskeleton , - ; : : : ¢ 67 
Endoskeleton : ; . 67 
Organs of digestion 3 : 68 
Organs of respiration : “96 
The blood : ‘ i : . 70 
Blood vascular system é . . 70 
Heart . . ® . : . . 71 


Organs of excretion. . é ‘i ‘ $ , ee ( 


CONTENTS 


The brain 

Reproduction 

The phyla of the | asda 
Tabular view of the phyla 


SECTION III 


PHYLUM PORIFERA 
Example of the Phylum wail Cis Sites peldinonnte 


SECTION IV 


PHYLUM Ca@:LENTERATA 
Class 1. The Hydrozoa 4 
Example of the Class — Odedia . 
Class 2. The Scyphozoa 
Example of the Class— durelia aurita 
Ciass 3. The Actinozoa A 
Example of the Class — Zeadia crassicornis 
Class 4. The Ctenophora . : 
Example of the Class — Hor paar piers F 


SECTION V 


PHYLUM PLATYHELMINTHES : ‘ F . . 
Class 1. The Trematoda . 
Example of the Class — Distomum iepticum a 
Class 2. The Turbellaria 
Example of the Class — Planarta torva 
Class 3. The Cestoda 
Example of the Class — Tenia solium 
Class 4. The Nemertinea 
Example of the Class — Te¢rastemma 


SECTION VI 


PHYLUM NEMATHELMINTHES 
Class. The Nematoda 
Example of the Class — Ascaris iiaaieiaies 


xiii 


149 
149 


xiv CONTENTS 


SECTION VII 


Pay_um ECHINODERMATA 
Class 1. The Asteroidea 
Example of the Class ~ 4stertas vulgaris 
Class 2. The Ophiuroidea 


Example of the Class — Ophioglypha lacertosa 


Class 3. The Echinoidea 

Example of the Class — Sz piercer otus 
-Class 4. The Holothuroidea 

Example of the Class — //olothurta seus 
Class 5. The Crinoidea 

Example of the Class — -faédon 


SECTION VIII 


ROTIFERA, POLYZOA, AND BRACHIOPODA 
Class 1. Rotifera 
Example of the Class ~ Brachionus rudbens 
Class 2. Polyzoa : 
Example of the Class — Bugula avicularia 
Class 3. Brachiopoda 


Example of the Class -— JJ/agellenia flavescens . 


SECTION IX 


PHYLUM ANNULATA 
Class 1. The Chetopoda , 
Example of the Class — NVerezs as wit. 
Class 2. The Hirudinea 
Example of the Class — Airzdo ene 


SECTION X 


PiryLuM ARTHROPODA 
Class 1. The Crustacea 
Example of the Class — .fs/acus fluviatilis 
Class 2. The Onychophora 
Example of the Class — Peripatus 


PAGE 
157 
157 
157 
169 
169 
170 
170 
173 
173 
174 
174 


178 
178 
178 
181 
181 
184 
184 


188 
188 
189 
203 
203 


212 
213 
213 
236 
236 


CONTENTS 


Class 3. The Myriapoda i e 

Example of the Class — Siotistention: morsttans . 
Class 4. The Insecta 

Example of the Class — Peciioiaa: americana 
Class 5. The Arachnida 

Example of the Class — Scorpio 


SECTION XI 


PHYLUM MOLLUSCA 2 2 

Class 1. The Pelecypoda . 

Example of the Class — 4nodonta cygnea 
Class 2. The Amphineura 

Example of the Class — Chiton shies 
Class 3. The Gastropoda . 

Example of the Class — Helix nemoralis . 
Class 4. The Cephalopoda 

Example of the Class — Vautilus oe 


SECTION XII 


PHYLUM CHORDATA 
Subphylum 1. The Adelochorda 
Example of the Subphylum — Bullets 
Subphylum 2. The Urochorda 
Example of the Subphylum — Asctadia 
Subphylum 3. The Vertebrata . 


Examples of the Subplivlim—vanhinads Pein. 


Pisces, ete. 
Division A. The Acrania 
Example of the Division ee ee ean: 
Division B. The Craniata 


Examples of the Division, the dogfish, bard and Sutshit ‘ 


Class 1. Cyclostomi 
Example of the Class — Petromyzon marinus . 
Class 2. Pisces 


Examples of the Class — Sharks, perch, acl lung fishes 


xv 


xvi 


CONTENTS 


Subclass 1. Elasmobranchii 


Example of the Subclass — Sey//rvei aut Haste 5 


Subclass 2. Holocephali (omitted) 
Subclass 3. Teleostomi 
Example of the Subclass — Satna fee 70 
Subclass 4. Dipnoi 
Example of the Subclass — Ceratodus foster? 
Class 3. Amphibia : 
Example of the Class — Rana temporaria 
Class 4. Reptilia 
Examples of the Class — Lizards, ere srdeoétile 
Class 5. Aves 
Example of the Class — Cotta livia 
Class 6. Mammalia : 
Example of the Class — Lepus cuniculus . 


PAGE 
366 
366 
394 
394 
395 
405 
405 
407 
408 
433 
434 
456 
457 
49! 
491 


LIST: OF ILLUSTRATIONS 


FIG. PAGE 
1, Amceba proteus. 5 : . 7 . : e » 15 
2. Ameeba polypodia ‘ : ; : . 18 
3. Quadrula, Hyalosphenia, Agedila, Difflugia ‘ . ‘ . 20 
4. Forms of Foraminifera . : F : 22 
5. Shells of Foraminifera s 4 25 
6. Actinophrys sol. P . 26 
7. Actinosphzerium eichhornii : : 27 
8. Forms of Heliozoa és ; ae) 
g. Liteocircus annularis . 4 ‘ . 31 

1o, Actinomma asteracanthion A . 32 

11, Collozoum inerme . 283) 

12. Euglena viridis. ; : . 35 

13. Forms of Mastigophora ; . 37 

14. Forms of Choanoflagellata. : : « 39 

15. Forms of Dinoflagellata ; : : : + 40 

16. Noctiluca miliaris . 3 : .  4i 

17. Volvox globator . : : . : . : s 43 

18. Paramcecium caudatum 2 “ : z : : = 149 

19. Forms of Ciliata . F . is : , - 49 

20. Forms of Tentaculifera i ‘ 7 ' x ST 

ot, Forme of Ciliata F ‘ . : i is F « 53 

22. Vorticella é 2 ‘ , ‘ , a‘ F Sa 

23. Monocystis agilis . Z , s ‘ 3 . 56 

24. Gregarina : é é : . 57 

25. Ovum of a sea- Beat ‘ 5 . 60 

26. Diagram of maturation and fertilization of ovum . es 

27% Segmentation of the oosperm ‘ 5 5 7 F . 62 

28. Forms of epithelium 5 2 ‘ . 64 

29. Diagram illustrating the structure of Mende : i af . 65 


Xvi 


xvili LIST OF ILLUSTRATIONS 


. Bones of arm with biceps muscle 

. Viscera of male frog 

. Hydra . e en 

. Sycon ciliatum 

. Sycon gelatinosum 

. Sycon gelatinosum, Maen 

. Sycon gelatinosum, transverse section 

. Ascetta primordialis 

. Section of Spongilla 

. Skeleton of sponges 

. Sponge spicules 

. Obelia colony 

. Nematocysts of Hydra . 

. Dissection of Medusa 

. Development of Laomedea and adendui 
. Structure of Hydra 

. Petasus and Glossocodon 

. Bougainvillea ramosa 

. Physailia 

. Physalia arethusa . 

. Halistemma tergestinum 

. Aurelia aurita, partly dissected 

. Aurelia aurita, development . 

. Tessera princeps 

. Tealia crassicornis 

. Sea-anemone, in sections 

. Common sea-anemone . 

. Corallium rubrum 

. Alcyonium palmatum 

. Tubipora musica 

. Pennatula sulcata 

. Flabellum curvatum 

. Astreea pallida ‘ 
. Dendrophyllia nigrescens ae Nadepais aspera 
. Cancrisocia on back of a crab 

. Hormiphora plumosa 

. Hormiphora plumosa, section of a tentacle 
. Idyia roseola . 


PAGE 
67 
69 
73 
76 
77 
78 
80 
84 
85 
87 
88 
93 
96 
97 
99 

100 
102 
103 
106 
106 
107 
109 
II 
113 
115 
116 
118 
118 
119 
120 
121 
122 
123 
124 
125 
126 
127 
128 


LIST OF ILLUSTRATIONS 


. Distomum hepaticum, natural size 

. Distomum hepaticum, anatomy 

. Distomum hepaticum, development 

. Trematodes: Amphistomum and Homalogaster 

. Structure of a triclad turbellarian 

. Planaria polychroa 

. Teenia solium 

. Teenia solium, head seapniied 

. Taenia solium, proglottis 

. Development of tape-worm 

. Cyst of Tzenia echinococcus with deapiee eel and solide 
. Diagram of organs of a Nemertine 

. Tetrastemma, structure 

. Ascaris lumbricoides 

. Ascaris lumbricoides, dissection of feet 

. Diagram of nervous system of Nematoda : 

. Ascaris lumbricoides, posterior end of male dissected . 

. Trichina spiralis . 

. Starfish, showing tube feet . : 

. Starfish, vertical section through an arm 

. Starfish, diagrammatic sections 

. Asterias rubens, digestive system . 

. Ambulacral systems of a starfish . 

. Anthenea, dorsal surface. E : . 

. Anthenea, ventral surface 

. Ophioglypha lacertosa . 

. Strongylocentrotus 

. Corona of sea-urchin : 

. Apical systems of plates of sea-urchin . 

. Cucumaria planci 

. Antedon ‘ 

. Metacrinus interruptus 

100. 
IOr. 
102. 
103. 
104. 
105. 


Brachionus rubens 

Bugula avicularia 

Plumatella . 

Pedicellina . ; 

Magellania flavescens . 2 x 
Magellania lenticularis, sagittal section 


LIST OF ILLUSTRATIONS 


. Nereis dumerilii, natural size 

. Nereis dumerilii, parapodium 

. Nereis dumerilii, sete . 

. Nereis dumerilii, anatomy 

. Nereis dumerilii, transverse section 

. Section through the eye of Nereis 

. Brain and connecting nerves of Nereis 

. Serpulz in their tubes . 

. Trochosphere of Eupomatus 

. Lumbricus agricola 

. Lumbricus, setze 

. Hirudo medicinalis 

. Head of Hirudo medicinalis, crenata the three jaws 
. Head of Hirudo quinquestriata 

. Nephridium of the medicinal leech 

. Transverse section of Hirudo 

. Diagram of blood-channels of leech 

. Astacus fluviatilis 

. Appendages of Astacus 

. Astacus fluviatilis, dissection from sight ade 
. Respiratory organs of Astacus fluviatilis 

. Thorax of crayfish, transverse section 

. Diagram of the circulation in the crayfish 
. Nervous system of Astacus fluviatilis 

. Reproductive organs of Astacus fluviatilis 
. Cancer pagurus 

. Pagurus bernhardus 

. Apus glacialis 

. Development of Apus . 

. Cyclops and Calocalanus 

6. Lepas anatifera 

. Peripatus capensis 

. Peripatus capensis, head, etc. 

. Internal organs of Peripatus 

. Scolopendra 

. Periplaneta americana . 

. Mouth-parts of the cockroach 

. Pieris rapze, larva, and pupa 


FIG. 


144. 
145. 
146. 
147. 
148. 
149. 
150. 
ISf. 
152. 
153. 
154. 
155. 
156. 
157. 
158. 
159. 
160. 
161, 
162. 
163. 
164. 
165. 
166. 
167. 
168. 
169. 
170. 
171. 
172. 
173. 
174. 
175. 
176. 
iG 
178. 
179. 
180, 
181. 


LIST OF ILLUSTRATIONS 


Carpet beetle, larva, and pupa 

Culex and larva 

Internal organs of soskisadh 
Periplaneta, its tracheal system 
Periplaneta, nervous system é 
Honey bee, queen, worker, and drone 
Red ant, male, worker, and female 
Euscorpio 3 

Scorpion, ventral side . 

Scorpion, internal organs 

Epeira diadema 

Cattle tick 

Itch mite 

Limulus, ventral view . 
Anodonta cygnea, entire animal . 
Anodonta cygnea, right valve, and animal 
Anodonta, section of shell and mantle 
Anodonta cygnea, animal 

Anodonta cygnea, dissection from left dds 
Anodonta cygnea, sections of gills 
Anodonta, diagram of circulatory system 
Anodonta, embryo and glochidium 
Mytilus edulis 

Teredo navalis 

Chiton spinosus 

Chiton, ventral view 

Chiton, nephridial and genital ——! 
Helix nemoralis 

Triton nodiferus, shell 

Triton nodiferus, median section of shill 
Solarium perspectivum, under side 
Terebra oculata, shell 

Cyprza moneta, animal expanded, in its shell 
Doris tuberculata 

Shell-bearing Pteropoda 

Patella vulgata, animal, ventral view 
Limax, lung-cavity, etc. 

Triton nodiferus . . : : . 


288 
289 
290 
290 
291 
292 
293 
294 


xxll 


FIG. 


182. 
183. 
184. 
185. 
186. 
187. 
188. 
189. 
190. 
Ig]. 
192. 
193. 
194. 
195. 
196. 
197. 
198. 
199. 
200. 
201. 
202. 
203. 
204. 
205. 
206. 
207. 
208, 
209. 
210. 
211. 
212. 
213. 
214. 
215. 
216. 
217. 
218, 
219. 


LIST OF ILLUSTRATIONS 


Sepia cultrata 

Nautilus pompilius 

Nautilus pompilius, section of sien 

Spirula peronii 

Sepia cultrata, shell 

Loligo vulgaris 

Argonauta argo 

Chromatophore of denis 

Sepia cultrata, dissected 

Nautilus pompilius, anatomy 

Sepia officinalis, jaws 

Sepia officinalis, enteric canal 

Nautilus pompilius, oral surface of male id one 
Balanoglossus 

Balanoglossus, diagrammatic sagittal section of anterior aud: 
Ascidia 

Ascidia 

Ascidia, diagram of ipneitimieals section 

Ascidia mammillata, larva 

Diagram of metamorphosis of larva into fixed Ascidian 
Botryllus violaceus 

Amphioxus lanceolatus, vented ant side view 
Amphioxus, diagram of anatomy 

Amphioxus lanceolatus, sections . 

Dogfish, fins, etc. 

Lacerta viridis 


Lepus cuniculus, lateral view ee dkeleeawr with outline oebaay.. 


Scyllium, vertebree 

Lizard, vertebre of 

Lepus cuniculus . 

Scyllium canicula 

Lacerta agilis, three views of dealt 

Fore and hind limbs of vertebrate, diagram 
Tooth, longitudinal section, semi-diagrammatic 
Scyllium canicula, dissection 

Lacerta agilis, viscera in their natural relations 
Circulation of a fish, diagram 

Scyllium canicula, brain, dorsal view 


PAGE 
297 
298 
299 
301 
301 
302 
303 
304 
305 
306 
307 
307 
309 
3l I 
312 
314 
315 
317 
320 
321 
322 
323 
325 
327 
329 
330 
331 
334 
335 
336 
338 
349 
34t 
343 
345 
348 
351 
353 


FIG, 


220, 
221, 
222. 
223. 
224. 
225. 
226. 
227, 
228. 
229. 
230. 
231. 
232. 
233. 
234. 
235; 
236. 
237. 
238. 
239. 
240. 
241. 
242. 
243. 
244. 
245. 
246. 
247. 
248. 
249. 
250. 
251. 
252. 
253. 
254. 
255. 
256. 
257. 


LIST OF IILUSTRATIONS 


Eye of man, diagrammatic horizontal section 
Petromyzon marinus : Z z : 
Myxine glutinosa, head 2 : : . 
Petromyzon marinus . ; : ‘ 
Scyllium canicula, side view of sical 
Scyllium, pectoral arch 

Scyllium canicula, dissection 

Diagram of the vascular system of a ih 
Scyllium catulus . 

Dogfish, egg-case 

Scyllium, embryo, with wile. etc. 

Lamna cornubica 

European sting-ray (esiapha sedan} 
Skeleton of Urolophus testaceus . 
Heptanchus, side view of skull 

Salmo fario, fins, etc. 

Salmo fario, caudal end of etched cate 
Pleuronectes cynoglossus 

Ctenoid and ganoid scales 

Polypterus birchir 

Skull of sturgeon 

Salmo fario, entire skull, left aie 

Premaxille of Sargus 

Hippocampus (sea-horse) 

Ceratodus fosteri 

Ceratodus fosteri, anterior parton of deeleten 
Rana temporaria : 

Rana temporaria, skeleton . : 

Rana temporaria, skull, different views 

Rana esculenta, shoulder girdle 

Rana esculenta, pelvic girdle from right dae 
Rana temporaria, dissection from left side 
Rana temporaria, heart with cavities laid open 
Rana temporaria, arterial system, etc. . 

Rana temporaria, venous system, etc. 

Rana esculenta, brain from above and below 
Rana esculenta, urinogenital organs of male . 
Rana esculenta, urinogenital organs of female 


xxili 


390 
391 
395 
397 
398 
399 
399 
400 
401 
402 
404 
405 
406 
409 
412 
413 
415 
416 
417 
420 
421 
424 
426 
428 
429 


xxiv 


FIG. 

258. 
259. 
260. 


261. 
262. 
263. 
264. 
265. 
266. 
267. 
268, 
269. 
270. 
271. 
272. 
273. 
274. 
275. 
276, 
277. 
278. 
279. 
280. 
281. 
282. 
283. 


284. 


285. 
286. 
287. 
288. 
289. 
290. 


291. 
292. 
293- 
294. 
295. 


LIST OF ILLUSTRATIONS 


Rana temporaria, stages in life-history 
Salamandra maculosa 

Siren lacertina 

Pygopus lepidopus 

Hatteria punctata z 

Grecian tortoise, Testudo graeca . 

Skeleton of crocodile . 

Cistudo lutaria 

Chelone midas 

Skull of rattlesnake 

Pectoral arch and sternum of igen agile 
Heart of monitor, Varanus . 

Brain of alligator, from above 

Pineal eye of Hatteria punctata, section 

Poison apparatus of rattlesnake 

Columba livia, diagram with most of feabicds cued 
Columba livia, feather . 4 

Pterylosis of Columba livia js . ‘ 
Columba livia, bones of the trunk 

Columba livia, cervical vertebra . 

Columba livia, sacrum of nestling 

Columba livia, skull of young. 

Columba livia, hyoid apparatus 

Columba livia, bones of left wing 2 
Columba livia, bones of left manus of nestling 
Columba livia, left innominate of nestling 
Columba livia, bones of left hind-limb 

Columba livia, part of left foot of embryo 
Columba livia, muscles of left wing 

Columba livia, dissection from right side 

Heart of pigeon, dorsal aspect 

Columba livia, brain, different views 

Eye of pigeon 

Columba livia, right eniouniGan: labyrinth e ear 
Columba livia, male urinogenital organs 

Columba livia, female urinogenital organs 
Feather of cassowary . , 

Wing of nestling of Opisthocomus sal of adc donee 


PAGE 
430 
432 
433 
437 
438 
439 
441 
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458 
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463 
464 
465 
466 
467 
468 
469 
470 
471 
472 
473 
475 
478 
479 
480 
481 
482 
482 
484 
486 


LIST OF ILLUSTRATIONS 


. Gallus bankiva, domestic fowl, egg at time of hatching 

. Lepus cuniculus, side view of skeleton with outline of body 
. Lepus cuniculus, atlas and axis 

. Lepus cuniculus, skull, side, and ventral view 

. Lepus cuniculus, shoulder girdle : 

. Lepus cuniculus, distal end of fore-leg and carpus 

. Lepus cuniculus, innominate bones and sacrum . 

. Lepus cuniculus, bones of hind foot 

. Lepus cuniculus, lateral dissection of head, neck, and on 
. Lepus cuniculus, stomach, intestine, and liver, etc. 

. Lepus cuniculus, heart, from right side 

. Lepus cuniculus, the vascular system 

. Lepus cuniculus, larynx, ventral and dorsal views 

. Lepus cuniculus, brain, dorsal and ventral view 

. Lepus cuniculus, two dissections of brain 

. Lepus cuniculus, longitudinal vertical section of brain 

. Lepus cuniculus, urogenital organs : 
. Lepus cuniculus, anterior end of vagina, with deh uterus, etc. 
. Duck-bill, Ornithorhynchus anatinus 

. Spiny ant-eater, Echidna aculeata 

. Virginian Opossum, Didelphys virginiana 

. Dasyure, Dasyurus viverrinus 

. Rock wallaby, Petrogale xanthopus 


Koala, Phascolarctos cinereus 


. Unau, or two-toed sloth 

. Tatu armadillo, Dasypus sexcinctus 

. Scaly ant-eater, Manis pentadactyla 

. Aard-vark, Orycteropus capensis . 

. Killer, Orca gladiator . 

. Section of upper jaw, with baleen plates, of atenoper 
. Harbor seal, Phoca vitulina . 

. Bat, Synotus barbastellus 


XXV 


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 orxganisms, 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 Linnzeus. 

B 1 


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 dcnomial nomenclature intro- 
duced by Linnzeus, 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 Feds domestica, the European wild cat & catus, the 
leopard /. pardus, the tiger F. Herts, the lion F Zo. 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. Jndividual 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, Hedis 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 Ayé7ids 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 — 7.c. 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 Linneeus, 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 Linnzeus, 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, 
Cynelurus, 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 hyzenas, but the 
presence of additional teeth and non-retractile claws — to 
mention only two points— makes the interval between 
hygenas and the two genera of cats far greater than that 
between Felis and Cynelurus. The varying degree of differ- 
ence is expressed in classification by placing the hyzenas in 
a separate family, the Hyenide, while Felis and Cynzelurus 


6 MANUAL OF ZOOLOGY 


are placed together in the family Ae%de. Similarly the 
civets and mongooses form the family Viverride ; the dogs, 
wolves, jackals, foxes, etc., the family Canzde,; bears, the 
family Urstde, 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 Marsupiala; 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 ammadvia, while 
birds constitute the class dves. In the same way the scaly, 
cold-blooded lizards, snakes, tortoises, etc., form the class 
keptiia, the slimy-skinned, scaleless frogs, toads, and sala- 
manders the class Amphiéza ; 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 ie 


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 Chorda/a, the many-legged 
armoured forms in the phylum Arthropoda. Similarly, soft- 
bodied animals with shells, such as oysters and snails, form 
the phylum AZollusca, polypes and jellyfishes the phylum 
Celenterata. And, finally, the various phyla recognised by 
zoologists together constitute the kingdom Azimasa. 

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 zvdzzdual 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 — Cuorpata. 
Class — MAMMALIA. 
Order — CarRNIVORA. 
Family — Fehde. 
Genus — Felis. 
Species —F. domestica. 


The object of systematic zoologists has always been to 


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 hke 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 Ovigin 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 


$<e) 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 Paleontology is 
applied. 

The solid crust of the earth is composed of various kinds 
of rocks divisible into two groups: (1) eneous 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 débris 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 s¢ratvfied 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 growps, each representing 
an era of time of immense but unknown duration, and that 
each group may be subdivided into more or fewer syszems 
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 paleontology we get a department of 
Zoology called Phylogeny, 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 
Paleontology, 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 (4¢toral species), others live at great depths 
(abyssal species), while others ( fe/agic 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 Plank/on. 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 Mes/on. 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 Benthas. 

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 fawna — ze. the total animal 
inhabitants — of a country is to a large extent independent 
of climate, and that the faunze 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 200-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, ¢.c. 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 enwronment gives us a final and most important 
branch of Natural History which has been called Ethology 
or Bionomics. 


SECTION I.—PHYLUM PROTOZOA 


1. THE RHIZOPODA 


Tue 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 founc 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 Ameba. Amceba (Fig. 1) 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 — 
débris 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 

14 


SECT. I PHYLUM PROTOZOA 15 


Amceba 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, 
Ameeba 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 


Fic. 1.—Ameeba 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 Amceba 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 Amceba 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 Amceba 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 Amceba, 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 procoplasm, which 
constitutes the vital material of all living organisms whether 
animals or plants. In Amceba 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 Amceba with a fairly high power 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 Amceba as a whole undergoes. This is termed the 
nucleus (Fig. 1, mz) ; it is enclosed in an extremely delicate 
membrane, and consists of a protoplasmic material differing 
from that which forms the main bulk of the Amceba 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 Wy 


say, a fifth of the total diameter of the Amceba, 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 Amceba 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 —ze., either entire minute animals or 
plants, or minute fragments of larger forms — which form the 
Jood of 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 Amceba 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 Amceba 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 Amcebe 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 
Amcebee possesses a nucleus similar to the original one, 

€ 


18 MANUAL OF ZOOLOGY SECT. 


and developed from it by division. It is mainly by this 
simple process of division into two, or &/nary fission, as it is 
called, that reproduction or multiplication takes place in the 
Amoeba. 


Fic. 2.—Ameceba polypodia in successive phases of division. The light spot is the 
contractile vacuole; the dark the nucleus. (From Lang’s 7ext-Book, after 
F. E. Schulze.) 


Amceba 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 


{ PHYLUM PROTOZOA 19 


as Amceba, in which the entire animal consists throughout 
life of a single cell, are distinguished as unicel/ular from the 
multicellular form in which a number of cells are combined. 
The whole of the great group or phylwm 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 Amceba in 
the possession of pseudopodia or processes of the protoplasm. 
The pseudopodia-bearing Protozoa constitute one of the great 
divisions or c/asses 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 
Ameeba is Pedomyxa, 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 Ameeba in 
the presence of a shell or zes¢ enclosing the protoplasm. 
One of these is Difiugia (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 Avcedla (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- 


Fic._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 chitinotd 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 (z, 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. 


i 


An ! 


wy 


AY Ves 


3.Squammulina 4Miliota 


| In, 


ted 
Hy t 
1 


Fic. 4.— Various forms of Foraminifera. In 4, Miliola, 2, shows theliving animal; 
4, the same killed and stained; a, aperture of shell: /, food particles; x, 
nucleus; s/, shell. (From Biitschli’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 (7) 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 (¢). 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, hke the spiral of a 
watch-spring or of acorkscrew. Such a spiral shell (6—zz) 
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. 
5,64), a deposit of carbonate of lime outside the original 
shell, traversed by a complex system of fine canals contain- 


24 MANUAT. 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 avenaceous Foraminifera ; 
some of these have one large opening, some a number of 
pores. In certain fresh-water forms, such as Gromuia, the 
shell is chitinoid. In Gromia (Fig. 4, 7) 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 flage//um— which lashes to and 
fro and propels the embryo Foraminifer through the water. 
Such a flagellum-bearing embryo is termed a flagedl/u(a. 

All the Foraminifera, with the exception of Gromia and 
one or two allied forms, are marine, and the greater number 
are pelagic —7.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. 


I PHYLUM PROTOZOA 25 


a 


a 


3.Nodosaria 


« SSD 


i1.Nummulites 


9.Planorbulina 


Fic. 5.—Shells of Foraminifera. In 3, 4, and 5, a shows the surface view, and da 
section; 8a isa diagram of a coiled cell without supplemental skeleton; 84 of 
a similar form with supplemental skeleton (s. s#); and zo of a form with over- 
lapping whorls; in zza half the shell is shown in horizontal section; 8 is a ver- 
tical section; .2, aperture of shell; 1—z5, successive chambers, 1 being always 
the oldest or initial chamber. (After Carpenter, Brady, and Biitschli.) 


26 MANUAL OF ZOOLOGY SECT. 


From the name of the genus — G/odigerina (Fig. 5, 6) — 
which occurs in the greatest abundance in this deposit, it is 
known as the Géodigertna 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 cha/k 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 Mummulitic Limestone, a bed of limestone 
made up, for the most part, of the shells of comparatively 
gigantic Foraminifera, the Nummulites (Fig. 5, zz). 

A Rhizopod by no means uncommon in fresh water is 
the so-called sun-animalcule, Actinophrys sol. The body 


Fic. 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 


27 


PHYLUM PROTOZOA 


I 


of being comparatively short and thick, as in Amceba and in 


the other Lobosa, or extremely delicate, flexible, and thread- 


(1assx] pue Simpoyy Joye ‘vozozo47 Syyosing 
wor1g) ‘tayonu ‘2 feyNpaur ‘pawe saonoea apMoeIWOD ‘9v2 "2 + xI09 ‘7407 tosoydoyewoays ‘4 
tpayusem Ajysy ‘uoyiod yews e “g ‘wsiues10 aus oy “Y ‘ITTIOYYIIG umueydsounoy — “2 “O14 


ere ry 
a eA 
ae 


ENS. 
° vis Ak 

bt Ses aN : 
{5 an) VA 


‘ ie alll 
eee K 


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, Actinospherium (Fig. 7) is somewhat more com- 
plex in structure than Actinophrys, the protoplasm being 
divided into a central mass — the exdosarc — in which the 
vacuoles are small, and an outer layer — the ecfosarc — in 
which they are very large. Numerous nuclei are present, 
and bodies containing ch/orophyl/ — 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, also 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 ske/eton. In those Heliozoa in 
which a skeleton occurs it is sometimes a shell of aggluti- 
nated sand-grains, like the shell of Difflugia, or of the arena- 
ceous Foraminifera; or it may consist of loosely matted 
needle-like bodies composed of silica (Fig. 8, 7); or there 
may, as in Clathrulina, be a sphere of silica, perforated by 
numerous openings, enclosing the protoplasm. Clathrulina 
elegans (Fig. 8, 7) is common in many ponds, attached to 
the rootlets of Lemna, or duck-weed (Stokes). 
Reproduction takes place, as in Amceba, by binary fission. 


I PHYLUM PROTOZOA 29 


2.Nuclearia 


3.Clathrulina 


Fic. 8.— Various forms of Heliozoa. 3a, the entire animal; 34, the flagellula; 
c. vac, contractile vacuole; g, gelatinous investment; 2, nucleus; Asd, pseudo- 
pods; s&, siliceous skeleton; sf, spicules. (From BiitSshli’s Protozoa, after 
Schulze and Greeff.) 


30 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 
Amceba. 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 sfores. 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 sforocyst; this process is known as encys/a- 
zon. The spores in some of the Heliozoa, when set free, 
are provided each with two flagella (Fig. 8, 3, 4) which 


1 PHYLUM PROTOZOA 31 


subsequently become lost, pseudopodia appearing in their 
place. 

The Radiolaria are marine Rhizopoda which have exceed- 
ingly delicate, thread-hke pseudopodia (Fig. 9, psd) and a 
skeleton usually composed of silica. This skeleton may be 
composed of loosely woven needle-like bodies or sficzles ; 
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 


“S=- Int. caps. pr 


Fic. 9. — Liteocircus annularis. cen¢. caps, central capsule; ext. caps. pr, extra- 
capsular protoplasm; z#/. caps. fv, intra-capsular protoplasm; #, nucleus; 
psd, pseudopods; skel, skeleton; 2, cells of Zooxanthella. (After Biitschli, 
from Parker’s Bzology.) 

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. 


32 MANUAL OF ZOOLOGY SECT. 


Radiolaria which give rise to colonies are exceptional, but 
a few cases occur. In these (Fig. 11) the central capsule 
divides again and again giving rise to a number of central 
capsules which remain embedded in a firm gelatinous sub- 


3, inner 


the two outer spheres broken 
cent. caps, central capsule; 


B, section showing the relations of the skeleton to the animal: 
er, s&. 2, middle, s% 


's Protosea, alter Haeckel and Hertwig.) 


au, nucleus; s% 7, 0 


protoplasm, 


sphere of skeleton 


ex caps. pr, 


away; 


Fic. 10. — Actinomma asteracanthion A, the shell with portions of 


stance — the vacuolated protoplasm outside the central cap- 
sules. Such a mass, which may attain considerable size, 
floats about freely in the sea. 


I 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 flagellida provided 
with a flagelluin (Fig. 44, 2, &). 

In most of the Radiolaria there occur in the extra-capsular 
protoplasm minute yellow cells (Fig. 9, 2), which multiply 


Fic. t1.— 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 Biitschli's Profozea, after Hertwig and Brandt.) 


independently by binary fission. It has been proved that 
these are microscopic unicellular plants (Zooxanthella) of 
the class Algze, which live in the substance of the protoplasm 
of the living Radiolarian. Such an intimate association 
between two living organisms is known as symdézosis. 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 
D 


34 MANUAL OF ZOOLOGY SECT. 


of the specially vegetable green colouring matter, ch/orophyd/, 
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 
setfree. 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 slendér 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 Auglena viridis, is so abundant at times as to 
colour the water blood-red (Stokes). 


I PHYLUM PROTOZOA 35 


The body of Euglena (4, #) is spindle-shaped, and has 
at the blunt anterior end a depression, the gullet (F. @s), 
from the inner surface of which springs a single long flagellum 
(#). The organism is propelled through the water by the 


» gullet; 


; Eand H, enlarged 
(From Parker’s Brology, after 


3 ¢. vac, contractile 


ry fission 
»mouth; x, nucleus; es 


g euglenoid movements 


, resting form after bina 


ged; G 
+ ey, cyst; 7, flagellum; 2 


A—D, four views illustratin, 
; ££, pigment spot; x (in H), reservoir. 


Ne 


S. 


, paramylum bodies 


views; F, anterior end further enlar 
Kent and Klebs.) 


vacuole in H, reservoir in E and F 


Fic. 12. — Euglena viridis. 


lashing movements of the flagellum, which is always directed 
forwards ; it can also perform slow, worm-like movements of 
contraction and expansion (4—JD), but anything like the 


36 MANUAL OF ZOOLOGY SECT, 1 


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 (zz) 
near the centre of the body, and at the anterior end a con- 
tractile vacuole (7, ¢. 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 (HH, p), a carbohydrate allied to 
starch. In contact with the reservoir is a bright red speck, 
the sigma (pe), formed of a pigment allied to chlorophyll 
and called hamatochrome. 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 (Ao/ozoic) with the characteristically vegetable (/o/o- 
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.Astasiopis 


2. Oikomonas (?) ‘a 


“oz n 
6.Dallingeria ua” Q.Cryptomonas ; . 
B.0ikomonas = AO CRB Ion 


i. Dinobryon 12.Syncrypta  1t3.Anthophysa 14.Rhipidodendron 


Fic. 13. — Various forms of Mastigophora. In 2, flagellate (a) and amceboid (4) 
phases are shown; in 5, flagellate (2) and heliozoan (4) phases; in § are shown 
two stages in the ingestion of a food particle (f); chr, chromatophores; 
¢. vac, contractile vacuole; /, food particle; g, gullet; 7, nucleus; Z, lorica; 
2, protoplasm; fer, peristome; vw. z, vacuole of ingestion. (Mostly from Biit- 
schli’s Protozoa, after various authors.) 


37 


38 MANUAL OF ZOOLOGY SECT. 


multiple fission takes place, and fluge/ule, ¢.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, ¢.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 Zovica, 
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, 70, 73, 24; 
Fig. 14, 7, 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- 


I PHYLUM PROTOZOA 39 


ceedingly delicate and transparent, called the col/ar. This 
is contractile, and, though its precise functions are not yet 


(After Saville Kent.) 


4.Proterospongia. 


3.Polyoeca. 


2.Salpingoeca. 


Fic. 14.— Various forms of Choanoflagellata. 24 illustrates longitudinal fission; 2c, the production of flagell- 
ule; ¢, collar; ¢. vac, contractile vacuole; 7, flagellum; @, lorica; 72, nucleus. 


1.Monosiga. 


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 


; nu', micronucleus; 


4.Polykrikos 
3}. da is an undischarged, and 6a 


dinal flagellum; 77. 2, transverse 


meganucleus 


ly 
(From Biitschli’s Protozoa.) 


gitu: 


3.Prorocentrum 


3 
icteres 
vu 

- 2S 

vgs 

BES 

e235 

‘ar BBR 
4 uno ing 
; eee 
Ay BRS 
So Beem 
ss e ry} 
ro) “32 
vo 
0 > 
u g 
ou Fi 
& 
< 
by 
ww 


flagellum; /. gv, longitudinal groove 


discharged stinging-capsule; chy 
pg, pigment spot; 


1.Glenodinium 
Fic. 15.— Various forms of Dinoflagellata. 


pass into an Ameceba-like or ama@dotd 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 


I PHYLUM PROTOZOA 4! 


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. 16), 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 


Fic. 16.—Noctiluca miliaris. «, the adult animal; 4, c, flagellule; dg, tentacle; 
J, flagellum; 7, mouth; z, nucleus. (From Lang, after Biitschli.) 

or zentrcle, 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 Mastigameba 
(Fig. 13, Z), which also possess pseudopodia, and may be 
capable of amceboid 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 farasitic. 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 Amceba. 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, hematochrome, 
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 


I PHYLUM PROTOZOA 43 


bearing a single zooid or a group of zooids at the end of 
each of the branches (Fig. 14, 3), 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. 


Fic. 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; 
Ji, flagellum; ov, ovy, megagametes; Ag, pigment spot; sAy, zooids containing 
microgametes. (From Parker’s Bzology, 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. 11, 24), which may take place 
either in the active or in an encysted condition. In some 
cases the fission is muw/tiple, 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 sexva/ 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 gumeves are of two sizes, union always taking 
place between a large cell or megagameze and a small cell or 
microgamete. In Volvox, which is a free-swimming spheri- 
cal colony (Fig. 17, £, 7, G) this difference between the 
two sets of conjugating cells reaches its extreme, pro- 
ducing a conditioi of things closely resembling what we 
find in the sexual reprf@uction 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- 


+ 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 Paramecium, the “ slipper-shaped 
animalcule,” a Protozoan of comparatively large size, about 
4 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 
Paramcecium (Fig. 18, 4, B) is covered with what appear 
under the microscope like small delicate hairs arranged in 
longitudinal rows. These are the c/a; 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 ventrad, is a large oblique depression, the duccal groove 
(duc. gr), leading into a short gullet (gw/), which, as in 
Euglena, ends in the soft internal protoplasm. The proto- 
plasm is differentiated into a firmer superficial layer, the 
cortex (cort), 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 (¢. 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 ana/ 
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 limes, it is interrupted by 


Zz 
7g mem 


mu. 


Fic. 18, — Paramecium caudatum. A, the living animal from the ventral aspect; 
B, the same in optical section: the arrow shows the course taken by food-particles; 
C, a specimen which has discharged its trichocysts; D, diagram of binary fission; 
buc. gr, buccal groove; cort, cortex; cz, cuticle; c. vac, contractile vacuole; /. 
vac food vacuole; gu/, gullet; med, medulla; 2, meganucleus; fa. 2x, micro- 
nucleus; ¢rch, trichocysts. (From Parker’s Bzology.) 


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 Paramcecium. 

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 ¢enfacles. The form of the body in the 
Infusoria (Fig. 19) is very varied; it may be globular, 
ovoid (7), kidney-shaped (2), trumpet-shaped (3), 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 (g). 

The arrangement of the cilia also varies greatly. Some, 
like Parameecium, have small cilia of uniform character 
distributed over the entire surface. Others have different 
kinds of cilia on different parts of the surface, while in 
others the cilia are entirely confined to certain regions. 
An instance of the latter arrangement is the common 
stalked form VordiceHa, with its allies such as Zpustyhs (9), 
in which the cilia are confined to the free extremity. These 
cilia produce rapid currents, and the ZpishZs, says Stokes, 
select from them anything they may want, and let the rest 
sweep by. In another group, again, the body, which is of 
flattened shape, bears on its dorsal surface a small number 
of very fine motionless cilia, while on its ventral the cilia are 


a 


4.Godonella 
. 5. 


be ntny a t 
3. Stentor 


8.Anoplophyra = ¢ 
9.E pistylis 


12.Multicilia — 13.Lophomonas 


a , 18.Trachelius 19.0phryoglena 
15 Didinium _'6-Condylost paryes 


‘oma . 
170 pdlinopsis 


Fic. 19. — Various forms of Ciliata. ga shows part of a colony, 4 a single zooid, and 
¢ acouple of nematocysts; a, anus; ¢. vac, contractile vacuole; # vac, food 
vacuole; g, gullet; sg. #7, meganucleus; ez. 27, micronucleus; 7¢, mouth; 
uu, nucleus; wfc, nematocyst; 7, tentacle; z. #5, undulating membrane; vac, 
non-contractile vacuole; uws¢, vestibule. (From Biitschli’s votozoa, after vari- 
ous authors.) 


E 49 


50 MANUAL OF ZOOLOGY SECT. 


very strong, and are modified into the shape of hooks, bris- 
tles, or plates with fringed ends. The hooks and plates do 
not vibrate rhythmically like ordinary cilia, but are moved 
as a whole at the will of the animal, such Infusoria being 
able, in addition to swimming freely through the water, 
to clamber by the aid of these specially modified cilia over 
the surface of weeds, etc. Tentacles may be present in 
addition to cilia (14), and a number of other exceptional 
modifications (zo-z3) occur which cannot be specially re- 
ferred to here. 

In addition to cilia, many genera possess delicate sheets 
of protoplasm, or wndulating membranes (uw. mb) in connec- 
tion with the peristome. These contract so as to pro- 
duce a wave-like movement which aids in the ingestion 
of food. 

The #entacles, which, in the Tentaculifera (Fig. 20), take 
the place of cilia in the adult, are elongated cylindrical 
structures, capable of protrusion and retraction, and having 
the distal end expanded into a sucker. The tentacle is 
practically tubular, the core consisting of a semi-fluid proto- 
plasm, while the outer part is tolerably firm. Infusoria and 
other organisms are caught by the tentacles, the cuticle of 
the prey is pierced or dissolved where the sucker touches 
it, and the semi-fluid protoplasm can then be seen flowing 
down the tentacle into the body of the captor. A single 
tentacle alone may be present (7), or the tentacle may be 
branched (4), the extremity of each of the branches being 
suctorial. In some forms (5) 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 Parameecium. In 
other cases it may be long and band-like (Fig. 19, 3, 
mg. ni), horseshoe-shaped (9), very long and constricted 


PHYLUM PROTOZOA 


4.Dendrocometes 5. Ephelota 


3.Rhyncheta 


TO bieyedesehet oe shelota 


Fic. 20. — Various forms of Tentaculifera. za and 4, two species of Podophrya;s 
c,a tentacle much enlarged; 2a, Acineta jolyt ; 2b, A. tuberosa,; in 6 the ani- 
mal has captured several small Ciliata; 8a, a specimen multiplying by budding; 
8b, a free ciliated bud; ga, the entire colony; 94, a portion of the stem; gc, a 
liberated bud; a. organism captured as food; 4. c, brood cavity: dd, bud; 
¢. vac, contractile vacuole; mg. nu, meganucleus; mz. xt, micronucleus; 
#, tentacle, (After Biitschli and Saville Kent.) 


52 MANUAL OF ZOOLOGY SECT. 


at intervals so as to look like a string of beads, or branched. 
In nearly all cases one or more micronuclei are present. 
Tn 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, ¢) 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, 9, and Fig. 22) the 
body is in the shape of a wine-glass, the stem of which is 
represented by a slender stalk (st), while the rim is the 
equivalent of the peristome (Zev) ; 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 (mh) : the only cilia present run in a spiral 
band round the peristome, round the edge of the disc, and 
down into the gullet (gz/7). 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 (7) so that it resembles in appearance 
the skeleton of some of the Radiolaria. A chitinoid lid or 
operculum (2,3, 0p) may be fixed to the edge of the peri- 


I 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 


5. Stichotricha 


m, contractile fibre; of, operculum. 


a 
g 
€ 4 
3 2 
ano! a 
ae: 
if 2-5 
ad 

ma <5 
4Q 28 
Tes 
ee 
B aE 
8 38 
as 
iy ae 
oe 
FE as 
. bier ct 
| 
ort) ga 
Oo wg 
3 SE 
x ov 
~ 

a 

og 
oae 
- un 
o | 
os 
° > 
~ | 
oe Fy 
oO a 
— g 
Q oy 

<= 


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. 20,9), one of the Tentaculifera: it has 
a creeping stem from which branches spring upwards, 
each terminating in a zooid with suctorial tentacles ; and 


Fic. 22.---Vorticella. A, B, living specimens.in different positions; C, optical 
section; D!, D?, diagrams illustrating coiling of stalk; Et, E*, two stages in 
binary fission; E%, free zooid; F1, 2, division into mega- and microzooids; 
G}, G*, conjugation; H!, multiple fission of encysted form; H?, H3, develop- 
ment of spores; ax. /, axial fibre; cort, cortex; cz, cuticle; ¢. vac, contractile 
vacuole; d, disc; gz//, gullet; #z, microzooid; m#¢4, mouth; 2%, meganucleus; 
per, peristome. (From Parker’s Szology, 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 Vorticellee. ; 


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 (4, 4), 
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 cov7ex, 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 


earthworm; jJ/, young Monocystis: 


roup of sperm-cells of the earthworm; 
(After Biitschli and Huxley.) 


h 


oung (M) ina 
by sperms of t 


d 


sperm-cells of earthworm, 


A, B, two individuals in different stages of contraction; C, cyst 


stis surrounde 


i 


D—F, development of 
c 


G, newly liberated Mono: 
nz, nucleus; sf, sperms o! 


containing spores; 


Fic. 23.— Monocystis agilis. 


chitinoid coat, and thus differing markedly from the naked 
spores of Rhizopoda and Mastigophora. The protoplasm 
of each spore then undergoes fission, becoming divided 


57 


PHYLUM PROTOZOA 


into a number of somewhat sickle-shaped bodies, which are 
arranged within the spore-coat somewhat like a bundle of 


By rupture of the spore-coat these fadiform 


young, as they are termed, are liberated, and at once begin 


sausages. 


(‘vozozo4g Syosing wor) ‘syonporods ‘pgs ‘sarods jo sseu ‘gs ‘podopnasd Buoy ‘2 ‘-psg 
spodopnasd qsoys ‘7 ‘psg saytawojoid ‘2g ‘smaponu ‘ww $4sh9 Jo JUaUNsaAUT snouElad 
foyawoynap ‘zap %3sh0 a Sf vazuvs1g “H jo yuauidojaaap ay} ut sadeis 
tpadieyosip usaaq aaey Sarods aya fo ysour YoIyM WOIY ‘2w-4Y7707g 
ul fzeipavinp *D jo suaundads omy “egy ‘1g 


yseo st (ga) ayautda ay sYIVOIADOD JO sT[ao 


Fe “91g 


Teyaquida o1ajua ur pappaquia Apjred w4032079 “D Jo suauttoeds omy “W 


a 


They enter the clumps of devel- 
oping sperms of the earthworm, and afterwards escape into 


active movements, the thin end of the body moving to and 
fro like a clumsy flagellum. 


the cavity of the seminal vesicle and grow into the adult form, 


58 MANUAL OF ZOOLOGY SECT. 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. Grevarina (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 (dew), by a sort of partition, with, in the young 
condition, a third division, the ep/merite (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 ( Coeccidium 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 (Hemameba laverant) 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, 
anemia, bloody urine, and the number of red-blood corpus- 
cles is diminished in one week to one-sixth of the normal 
amount. Badesia doris in the blood of the ox causes the dis- 
ease known as hemoglobinurea, and another form produces 
asimilar disease insheep. A parasite of the tzetse fly, which 
is a flagellate heematozoan, 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 pedrine 
is due to one of the Myxosporidia, Glugea bomébyets, which 
inhabits all the tissues of the caterpillar of Bomdvy mort. 


SECTION II.—THE METAZOA 


Waite 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 exist- 
ence, of a single cell, the oosperm, formed by the union 
of a male cell 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 yoék. 

59 


60 MANUAL OF ZOOLOGY SECT. 


Before the changes begin which lead to the formation 
of the multicellular Metazoan, another cell, the made 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, po/) 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 


Fic, 25.— Ovum of a Sea-Urchin, showing the radially striated cell-membrane, the 
rotoplasm, containing yolk-granules, the large nucleus (germinal vescicle), with 
ts 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 oosferm, 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 


al THE METAZOA 61 


IN 
smh, 
a Se 


Fic. 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; oi cent, male centrosome (the 
centrosomes are cell-structures not further referred to in this work); #zevz, egg-membrane; 
microp, micropyle; fol, polar bodies; 9 Aron, female pronucleus; ¢ prox, male pronu- 
cleus; seg. xucl, 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 dzvary fission of Amceba and 
other Protozoa: in the Metazoan, however, the two cells 
do not become separated from one another as the two 
parts of the divided Amceba do, but remain in contact and 
undergo further changes. Each of them divides (Fig. 27) 


Fic. 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, the germina/ layers, becomes by 
and by discernible; and from these layers of cells are 
developed eventually all the parts of the body of the 
Metazoan. 


Ir THE METAZOA 63 


This mode of development is, however, not entirely with- 
out parallel among the Protozoa. In the colonial Volvox 
(p. 43, Fig. 17) 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, gristle, nerve, all derived 
from the cells of the germinal layers. Of such tissues the 
following are the most important. An efctheum is a thin 
stratum of cells covering some surface, external or internal ; 
it may be one cell thick, or several cells thick. 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 
amceboid (A), 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 ezéric 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 wnicellular gland 
(A, B). The secretion (or substance which it is the func- 
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. 


Fic 28.— Various forms of epithelium. a, ciliated epithelium; 4, columnar; d, sur- 
face view of the same, c, tessellated; ¢, the same from the surface; Sf flagellate 
epithelium with collars; g, flagellate epithelium without collars; 4, epithelium 
of intestine with psendopodia ; 2, stratified epithelium; 2, deric epithelium of a 
marine planarian with pigment cells, rod cells, and sub-epithelial glands. (From 
Lang’s Comparative Anatomy.) 


II THE METAZOA 65 


epithelium through a narrow proiongation of the cell, which 
serves as the duct of the gland. In other cases the gland is 
multicellular (D, 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 


Fic. 29 — Diagram to illustrate the structure of glands. A, unicellular glands in an 
epithelium; 4, unicellular glands lying below epithelium and communicating 
with the surface by narrow processes (ducts); C, group of gland cells; D, group 
of gland cells lining a depression; & 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 

F 


! 


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. Bove 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, 
7.e. becoming shorter and thicker, when stimulated. Bundles 
or bands of these form the organs known as muscles. Verve 
ussue, which is the sensitive, conducting, and stimulating 
tissue of the body, consists of nerve-cells and nerve-fibres ; 
groups of the former constitute zerve-gangla, bundles of 
the latter form zerves, 

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 


Wl 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 sm and the shele‘on. The skin or in- 
tegument consists of a layer of cells — the efidermis — with, 


Fic. 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 adgestive 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 #exZacles, 
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 cawty, a pharynx, an esophagus or gullet, a 
stomach, and an intes#ine. 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- 


II 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, safvary 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 


Fic. 31. General view of the viscera of a male dog from the right side. a, 
stomach; 4, urinary bladder; c, small intestine; * cloacal aperture; d, large 
intestine; ¢, liver; /, bile duct: g, gall bladder; h. ‘spleen: z, lung; &, larynx; 
2, fat body; #z, testis; 2, ureter: 0, kidney; #, pancreas; s, cerebral hemi- 
sphere; sp, spinal cord; #, tongue: z#, auricle; zw, urostyle; v, ventricle; 
w.s, vesicula seminalis; w, optic lobe; «, cerebellum; y, Eustachian recess; 
z, nasal sac. (From Marshall ) 


throughout the body. The insoluble and indigestible ingre- 
dients of the food pass on through the posterior part of the 
intestine, and reach the exterior through the anal aperture 
as the feces. 

A supply of oxygen is necessary for the carrying on of the 
chemical changes in the tissues on which vital activity is 
dependent. At the same time, as a result of these changes, 


470 MANUAL OF ZOOLOGY SECT. 


carbonic anhydride (carbonic acid gas) is constantly being 
produced. The taking in of oxygen and giving off of car- 
bonic anhydride is the process of respiration. The task of 
facilitating the entry of oxygen and the passage outwards of 
carbonic anhydride is in most of the Metazoa performed 
by a set of organs known as organs of respiration; but in 
many respiration takes place through the general surface, 
and special organs for carrying on this function are absent. 
When organs of respiration are present, they are either 
processes or gills (6ranchig) adapted for the respiration of 
air dissolved in water; or /vngs or other cavities which are 
adapted for the direct respiration of air. Through the thin 
membrane lining the gill, or lungs, the oxygen passes and 
enters the blood in vessels immediately underneath the 
membrane, to be conveyed, like the food, throughout the 
system and supplied to the several parts. At the same 
time the carbonic anhydride, brought to the gill or lung by 
the same means, passes outwards into the surrounding water 
or air, and is thus got rid of. 

The blood consists of a fluid f/asma, in which float 
numerous cells — the d/o0d corpuscles. Sometimes the blood 
is colourless ; usually it is bright red, owing to the presence 
of a red colouring matter, termed Aemoglobin, which is 
sometimes confined to certain of the corpuscles, sometimes 
diffused throughout the plasma. Haemoglobin has a strong 
affinity for oxygen, and is thus of importance in connection 
with respiration. 

In order to carry on its functions as a conveyer of 
nutriment and of oxygen throughout the body, the blood 
flows in a system of vesse/s —the blood vascular system — 
which ramify throughout all the organs. Through this 
system of vessels it is driven in a more or less regular 
course, either by pulsating contractions of the muscular 


ul THE METAZOA 7 


walls of the blood-vessels themselves, or by the agency of a 
special organ, the Aear?. ‘lhe heart is essentially a sac with 
muscular walls. Its cavity is in communication with the 
main blood-vessels, and its walls contract regularly and 
drive the blood through the system of vessels, the direction 
of flow being regulated by a system of valves. 

The nitrogenous waste-matters which are produced as a 
result of the chemical changes that accompany vital action 
in the various organs, are separated out and got rid of bya 
system of organs known as the organs of excretion, or renal 
organs —this process of elimination being known as the 
process of renal excretion. 

It is by means of the nervous system that the animal 
receives impressions from the exterior and from the internal 
organs, and that the various internal parts are brought into 
vital communication with one another. The nervous system 
extends as a complicated system of nerves or bundles of 
nerve-fibres throughout all parts of the body. Large 
aggregations of nerve-cells and nerve-fibres forming the 
centres of the system are known as nerve-ganglia. When 
one of these, or a group of them, situated towards the 
anterior end, preponderates in size over the others, it 
is termed the drazn. Forming an important part of the 
nervous system are the organs of the special senses, — 
sight, hearing, smell, and taste, each of which is an organ 
adapted for the reception of impressions of a special kind 
from the exterior, — the impressions of light, of sound waves, 
of the particles and substances that produce the sensations 
of smell and taste. The less specialised sense of touch and of 
heat and cold is diffused generally over the integument, in 
which there are frequently special cells, or groups of cells, 
with nerve-fibres terminating in them, that are concerned 
with such sensations. 


92 MANUAL OF ZOOLOGY SECT. 


The organs of sexual reproduction are the gova:ts, in 
which male and female cells or sperms and ova are 
produced, with the gonoducts or canals by which these 
cells reach the exterior. The gonads in which male cells 
or sperms are produced are called #sées, and their ducts 
are the sferm-ducts, The gonads in which female cells 
or ova are formed are called ovarves, and their ducts 
ovidtucts. Sometimes testes and ovaries occur in distinct 
male and female individuals, when the animal is said to be 
unisexual, or to have the sexes distinct. In other cases 
both ovaries and testes occur in the same individual, when 
the animal is said to be hermaphrodite, or to have the sexes 
united. In some instances the same gonad produces both 
sperms and ova— assuming the character of a hermaphrodite 
gonad or ovo-testis. 

In many animals the ova are fertilised by the sperms 
after they have passed out from the body, and the develop- 
ment takes place externally —a condition which is known 
as oviparity. But in others the ova are fertilised while still 
in the ovary or oviduct of the parent, and the development 
may take place in the oviduct, usually in a special dilated 
part of the latter —the wéerus—so that the young only 
escape to the exterior after they have attained a compara- 
tively advanced stage of their development— when the 
animal is said to be wivparous. 

Besides the sexual process of reproduction by means 
of ova and sperms, there are in many classes of animals 
various asexual modes of multiplication. One of these — 
the process of simple fission —has been already noticed in 
connection with the reproduction of Protozoa. The forma- 
tion of sfores is an asexual mode of multiplication which 
occurs only in the Protozoa, and has been clescribed in the 
account of that group. Multiplication by dudding takes 


II THE METAZOA ™ 


place in a number of different classes of animals. In this 
form of reproduction a process or dud (Fig. 32, dd) is given 
off from some part of the parent animal; this bud sooner 
or later assumes the form of the complete animal, and may 
become detached from the parent either before or after its 


Fic. 32. —Fresh-water polype (hydra), two specimens, the one expanded the other 
contracted, showing multiplication by budding. 4d1 3d*% Sd, buds in various 
stages of growth, (From Parker's Bzology.) 

development has been completed, or may remain in perma- 

nent vital connection with it. 

When the buds, after becoming fully developed, remain 
in vital continuity with the parent, a sort of compound 
animal, consisting of a greater or smaller number of con- 
nected units, is the result. Such a compound organism is 


74 MANUAL OF ZOOLOGY SECT. 


termed a co/ony, and the component units are termed zoozds. 
In some cases such a colony is produced by a process which 
is more correctly termed éncomplete fission than budding. 
The various systems of organs, — digestive, circulatory, 
nervous, excretory, etc.,—— present under one form or an- 
other in all the higher groups of animals, are variously 
arranged and occupy various relative positions in different 
cases, producing a number of widely different plans of 
animal structure. According as their structure conforms 
to one or another of these great plans, animals are referred 
to one or another of the corresponding great divisions or 
phyla of the animal kingdom. That animals do present 
widely differing plans of structure is a matter of common 
knowledge. We have only to compare the true fish, such 
as cod, haddock, etc., in a fishdealer’s shop with the 
lobsters and the oysters, to recognise the general nature 
of such a distinction. The first named are characterised by 
the possession of a backbone and skull, with a brain and 
spinal cord, and of two pairs of limbs (the paired fins) : 
they belong to the great vertebrate or backboned group — 
the division Vertebrata of the phylum Chordata. The 
lobsters, on the other hand, in which these special verte- 
brate structures are absent, possess a jointed body enclosed 
in a hard jointed case, and a number of pairs of limbs also 
enclosed in hard jointed cases, and adapted to different 
purposes in different parts of the body — some being feelers, 
others jaws, others legs: their general type of structure is 
that which characterises the phylum Arthropoda. The 
oysters, again, with their hard calcareous shell secreted by a 
pair of special folds of the skin constituting what is termed 
the mandle, and with a special arrangement of the nervous 
system and other organs which need not be described here, 
are referable to the phylum Jfo//usca. Other familiar 


Ir THE METAZOA 75 


animals are readily to be recognised as belonging to one or 
other of these great phyla A prawn, a crab, a bluebottle 
fly, a spider, are all on the same general plan as the 
lobster: they are jointed animals with jointed limbs, and 
they have the internal organs occupying similar positions 
with relation to one another. They are all members of the 
phylum Arthropoda. Again, a mussel, a snail, a squid, are 
all to be. set side by side with the oyster as conforming 
to the same general type of structure ; they are all members 
of the phylum A/ollusca. Finally a dog, a lizard, a fowl, are 
obviously nearer the fish: they all have skull and backbone, 
brain and spinal cord, and two pairs of limbs; they are all 
members of the great group Chordata. 
Altogether twelve phyla are to be recognised, viz. : — 


I. Protozoa VIL. Molluscoida 
II. Portfera VIII. Echinodermata 
III. Calenterata IX. Annulata 
IV. Platyhelminthes X. Arthropoda 
V. Nemathelminthes XI. Mollusca 


VI. Zrochelminthes XII. Chordata 


SECTION III. —PHYLUM PORIFERA 


Tue Porifera, or sponges, belong to the lowest group of 
the Metazoa. They live fixed to the surface of rocks, or to 
submerged timber or seaweeds, so as to be incapable of 
locomotion; and have, in most cases, a general form which 
suggests the vegetable rather than the animal kingdom. 
But, in essentials, as will presently become 
evident, the sponges are distinctly animal in 
character, and the resemblances to plants 
are entirely superficial. 

The majority of sponges are compli- 
cated and difficult to understand, owing to 
their elaborate mode of branching and the 
fusion of the branches, and to the exceed- 
ingly intricate character of the skeletal 
parts, aside from their cellular structure. 
. Some, however, are free from these com- 
Fi 33.- Syconcili- plications ; and it is in one of these that 
pee. the main characteristics of sponges are 

best studied. Such a simple form is Sycon, 
a small sponge living attached to rocks on the seashore 
towards or below low-water mark. Sycon gelatinosum* has 
the form of a tuft, one to three inches long, of branching 


1 This is an Australasian species, but the following account will apply in 
all essential respects to Sycon ciliatum (Fig. 33) and S. clarkii of the coast 
of New England. 


76 


SECT. III : PHYLUM PORIFERA 17 


cylinders (Fig. 34), all connected together at the base, 
where it is attached to the surface of seaweeds, rocks, or 
other solid bodies submerged in the sea. It is flexible, 
though of tolerably firm consistency. On the outer surface 
are to be detected, under the microscope, groups of minute 
pores — the zzhalant pores. At the free end of each of the 
cylindrical branches is a small but distinct opening, sur- 
rounded by what appears like a delicate fringe. When the 
branches are bisected longitudinally (Fig. 35), it is found 
that the terminal openings (g) lead into narrow passages, 


Fic. 34. —Sycon gelatinosum. Entire sponge, consisting of a group 
of branching cylinders (natural size). 


wide enough to admit a stout pin, running through the axis 
of the cylinders; and the passages in the interior of the 
various branches join where the branches join—the pas- 
sages thus forming a communicating system. On the wall of 
the passages are numerous fine apertures which require a 
strong lens for their detection. The larger apertures at the 
ends of the branches are the osci/a of the sponge, the pas- 
sages the paragastric cavities. If the living Sycon is placed 
in sea-water with which has been mixed some carmine pow- 
der, it will be noticed that the minute particles of the 
carmine seem to be attracted towards the surface of the 


78 MANUAL OF ZOOLOGY SECT. 


sponge, and will often be seen to pass into its substance 
through the minute pores already mentioned as occurring in 
groups between the elevations on the outer surface. This 
would appear to be due to the passage of a current of water 


Fic. 35.—Sycon gelatinosum. A portion slightly magnified; one cylinder (that 
to the right) bisected longitudinally to show the central paragastric cavity 
opening on the exterior by the osculum, and the position of the incurrent and 
radial canals; the former indicated by the black bands, the latter dotted. 7 
marks the position of three of the groups of inhalant pores at the outer ends of 
the incurrent canals; 0, osculum. 


into the interior of the sponge through these minute open- 
ings dotted over the surface; and the movement of the 


floating particles shows that a current is at the same time 
flowing out of each of the oscula. A constant circulation of 


111 PHYLUM PORIFERA 79 


water would thus appear to be carried on — currents moved 
by some invisible agency flowing through the walls of the 
sponge to the central paragastric cavities, and passing out 
again by the oscula. 

If a portion of the Sycon is firmly squeezed, there will 
be pressed out from it first sea-water, then, when greater 
pressure is exerted, a quantity of gelatinous-looking matter, 
which, on being examined microscopically, proves to be 
partly composed of a protoplasmic material consisting of 
innumerable, usually more or less broken, cells with their 
nuclei, and partly of a non-protoplasmic, jelly-like substance. 
When this is all removed there remains behind a toughish, 
felt-like material, which maintains more or less completely 
the original shape of the sponge. This is the she/e/on or 
supporting framework. A drop of acid causes it to dissolve 
with effervescence, showing that it consists of carbonate of 
lime. When some of it is teased out and examined under 
the microscope, it proves to consist of innumerable, slender, 
mostly three-rayed microscopic bodies (Fig. 36, sf) of a 
clear, glassy appearance. These are the calcareous spicules 
which form the skeleton of the Sycon. 

Covering the outer surface of the sponge is a single layer 
of flattened, scale-like cells—the ectoderm (Fig. 36, ec) — 


through which project regularly arranged groups of needle- 


like and spear-like spicules (s5f'). The paragastric cavities 
are lined by a layer of cells (ez), which are like those of the 
ectoderm in general shape; this is the endoderm of the 
paragastric cavity. Running radially through the thick 
wall of the cylinders are a large number of regularly 
arranged straight passages. Of these there are two sets, 
those of the one set—the éucurrent canals (fC) — nar- 
rower, and lined by ectoderm similar to the ectoderm of 
the surface; those of the other set—the radial or 


i 
ue 


\ 


Ah i 
Ne 
dc \ . 


vi 


Fic. 36. —Sycon gelatinosum. ‘l'ransverse section through the wall of a cylinder 
(parallel with the course of the canals), showing one incurrent canal (/C), and 
one radial (2) throughout their length; sf, triradiate spicules; sf', oxeote 
spicules of dermal cortex (dc); sf'’, tetraradiate spicules of gastral cortex (ge); 
ec, ectoderm; ex, endoderm; pz, pore membrane; Zf, prosopyles; af, apopyle; 
dz, diaphragm; exc, excurrent passage; PG, paragastric cavity; ev, early 
embryo; e7', late embryo. The arrows indicate the course of the water through 
the sponge 

80 


SECT. lI PHYLUM PORIFERA 81 


flagellate canals (&) —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 ower 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 ( pp) — 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 (2) 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 

G 


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, d), 
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 gastte 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 mesoglea — in which 
the spicules of the skeleton are embedded. The 
spicules (Fig. 36, sf.), 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 (sf'). The sexual reproductive 
cells —the ova (Fig. 36, ov) and sferms — are developed 


III PHYLUM PORIFERA 83 


immediately below the flagellate endoderm cells of the 
flagellate canals, and in the same situation are to be found 
developing embryos (ev, 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. 


84 


MANUAL OF ZOOLOGY 


SECT. 


Sycon belongs to a type of sponges intermediate between 
the very simplest forms on the one hand, and the more 


Fic. 37.— Ascetta primordialis. A 
portion of the wall of the vase-like 
sponge removed to show the para- 
gastric cavity, (After Haeckel.) 


the middle one, though it 


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 
contains a small number of 


spicules, is very thin ; the endoderm, which lines the 


Ill PHYLUM PORIFERA 85 


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 


Ps 


fe 


Fic. 38. — Vertical section of a fresh-water sponge (Spongilla), showing the arrange- 
ment of the canal-system, C, ciliated chambers; D/P, dermal pores; £2, 
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 se/e¢on differ in character in the 
two sub-classes into which the sponges are divided. In 
the Calearea, of which Sycon is an example, they consist 
of calcareous spicules, usually triradiate in form. In the 
Non-Calearea 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 (ZB) : 
in some (Myxospongie) 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 (Zuplectella), the glass- 
rope sponge (Ayalonema), 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 


Il PHYLUM PORIFERA 87 


originally simple cylinder or vase, may be looked upon as 
an asexual mode of reproduction by budding. Asexual 


A.Euspongia 


| B.Pachychalina 


Fic. 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 SECT. 


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 (Spongiliid@) 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 amphidises 
(Fig. 40, right side). All sponges multiply by a sexual 
process — by means of male cells, or sperms, and female 


Fic. 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 Jong 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 


in 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 (Spongi/iide) 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, CZona, 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 messmatetsm, 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 (Ayalonema) is always found associated 
with a zoophyte (fa/yéhoa), and there are many other in- 
stances. Sponges often also grow in very close association 
with certain low forms of plants (.4/@). 


SECTION IV.—PHYLUM CCELENTERATA 


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 fotfe, 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 7.— Hydrozoa, including the fresh-water polypes, 
zoophytes, many jellyfishes,—mostly of small size,—and a 
few stony corals. 

90 


SECT. IV PHYLUM CCELENTERATA 91 


Class 2.— Sceyphozoa, including most of the large jelly- 
fishes. 

Class 3.-—— Actinozoa, including the sea-anemones, and 
the vast majority of stony corals. 

Class g.—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. Ovelia 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 Odelia gelatinosa, a rather stouter species, but similar 
in general appearance. Odea genicudata 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, z-P, 4), each’ enclosed in a glassy, 
cup-like investment or hydrotheca (Ath), and produced dis- 
tally into about two dozen arms or /entacles (7): these 
zooids are the pohpes 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 d/astostyles (b/s), 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-buds (m.6d). 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 #imorphic, 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 manudbrium 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 eteron (ent), 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 (At) 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). 


Peo High 


Fic, 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; Bd. 7, 2, buds; dls, blastostyle; c@, ccenosarc; ect, ectoderm ; 
end, endoderm ; ext, enteric cavity: gt#, gonotheca (gonangium) : /4¢/, hydro- 
theca; 7, lithocyst; #.4d¢, medusa-bud: #6, manubrium; szsg?, mesoglea; 
mth, mouth; #, perisarc; P. 72, 2, 3, ¢, polypes; rad.c, radial canal; ¢, 
tentacle; v/, velum. 5 


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 ferisarc (f), and an inner, delicate, granular 
layer, the cenosarc (ce), continuous by a sort of neck or 
constriction with the body of each hydranth. The ccenosarc 
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 (gz), 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 medusz 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 mesoglea 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 CCELENTERATA 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 cwéicle, 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 sanging-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 cnzdoblast (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 cnidocil or trigger-hair (enc) : 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 Medusaze — 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-wmbrella, the concave inner surface 
as the sub-umbrella. From the centre of the sub-umbrella 
proceeds the manubrium (mz), at the free end of which is 


96 MANUAL OF ZOOLOGY SECT. 


the four-sided mouth (ch). Very commonly as the medusa 
swims the umbrella becomes turned inside out, the sub- 


Fic. 42.— Nematocysts of hydra. A, undischarged; B, discharged; C, nerve- 
supply; ev, cnidoblast; exc, cnidocil; xz, nucleus; wfc, nematocyst; xz.c, 
nerve-cell. (From Parker's Svodogy, after Schneider.) 


umbrella then forming the convex surface, and the manu- 
brium springing from its apex (Fig. 41, C). 


Iv PHYLUM CCELENTERATA 97 


The mouth (Figs. 41, C, D, and 43, m¢h) leads into an 
enteric cavity which occupies the whole interior of the 
manubrinm, 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 cévcudar 
canal (cir. c), running parallel with and close to the 
margin. By means of this system of canals the food, taken 


es 


spas 


Fic. 43. ~ Dissection of 4 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 mesoglcea black. c7r. c, circular canal; exd. lam, 
endoderm lamella; gox, gonad; 7, lithocyst; #5, manubrium; 1¢4, mouth; 
rad, c, radial canal; v/, 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 velwm (Fig. 43, v/), and gives off the 
tentacles (7), 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 (7), each containing a 

H 


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Ae SCALE Fon A 
“ca 


fic 45.—Hydra. A vertical section of entire animal; B, portion of transverse 
section, highly magnified: C, two large ectoderm cells: D, endoderm cell of 
H viridis; ¥, large nematocyst; I’, small nematocyst; G, sperm; a, ingested 
diatom; éd.1, ba.2, buds: chr, chromatophores; cv/, cnidoblast; cc, cnidocil; 
ect, ectoderm; end, endoderm; ext. cav, enteric cavity; evt caz, its prolonga- 
tion into the tentacles; /7, flagellum; Ay/, hypostome or manubrium; zw? c, in- 
terstitial cells; 7. fx, muscle processes; ath, mouth; msg/, mesoglea; xct, 
large, and z#c}, small nematocysts; 7, nucleus; ov, ovum; ovy, ovary; psd, 
pseudopods; sfy,spermary; vac, vacuole, 


100 


SECT. IV PHYLUM CCOALENTERATA 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 Hydre ; 
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 poZype, but that 
of the medusa (Fig. 46), a polype stage never being 
developed, and the animal resembling in all essential 
respects the medusz of Obelia; the chief difference of 
importance being the presence of sense-organs in the form 
of hollow, club-shaped appendages, the sentaculocysts, con- 
taining calcareous bodies of 4¢h7ztes. These simple free- 
swimming medusiform Hydrozoa (Z7achytine) develop ova 
and sperms which give rise to free-swimming ciliated larvee ; 
but the latter, instead of becoming fixed and developing into 
plant-like colonies, remain free, and develop directly into 
medusz 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 hydrothece and gonothece 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- 


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sential respects, but differ in the number and arrangement 
of the tentacles and other minor points. In many meduse 
are developed from blastostyles as in Obelia, and when 
fully formed become free. The shape of the medusa 


Iv PHYLUM CCELENTERATA 103 


differs in different forms, more particularly as regards the 


umbrella. There is always a manubrium, with gastric 


® 
Fic. 47. — Bougainvillea ramosa. A, entire colony, natural size; B, portion of the 
same magnified ; C, immature medusa ; ctr. c, circular canal; cz, cuticle or 
perisarc ; end. cav, enteric cavity ; Ayd, polype or hydranth ; yf, hypostome or 
manubrium ; sed, medusa; 2d, manubrium ; rad. c, radial canal ; ¢, tentacle ; 
v, velum, (From Parker’s Bzology, after Allman.) This is closely allied to the 


New England B, supercilians. 


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 oce/Z 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 meduse range from 
about 1 up to 400 millimetres (16 inches) in diameter. 

In many of the zoophytes, however, the medusz 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 
medusze 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 meduse 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 (A@iVepora) and Sfvlaster, 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 othér 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 (cv). At one end 
is a minute aperture communicating with the exterior. 
From the under side of the float hang polypes (J), 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 meduse. 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 (zc), having the general characters 
of unsymmetrical medusz without manubria, each being a 
deep, bell-like body, with a velum and radiating canals. 
During life these szimming-bells or nectocalyces contract 
rhythmically, —z.e., at regular intervals,—thus serving to 
propel the entire organism through the water. Below the 
last negtocalyx 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 (f) differing, 


106 MANUAL OF ZOOLOGY SECT. 


gn RDM 
‘a 
~ 


SOG’ 


x 


OA 


‘d 
% + 
SON 
g i 
g 4 
a ¢€ 


Sretecat Mec as ah Sy 0! 
aes 


capa 


Mbveyunt 


tf 
i 


at 
Fic. 48 —Physalia. The living animal Fic. 49.— Physalia arethusa, natural 
floating on the surface of the sea. cv, size. (After Agassiz.) 
crest ; , polype ; A, pneumatophore, 
float, or air-sac. (After Huxley.) 


107 


es 
F 


a e \ F 
NINN 


az 


N 
SSN 


Uf 


— 


PSfLINS 
AAS Hon 
wt * 
4 ad ‘S, 
f w—7tle 


Fic. 50 —Halistemma tergestinum. A, the entire colony; B, 4 single group of 
zooids; ca@, coenosarc; dz, dactylozooid; #f4, hydrophyllium or bract; xc?, 
nectocalyx or swimmuing-bell; xéc. battery of nematocysts; #. polype; fx, 
pneumatophore or float; s, s', sporocysts; 7, tentacle, (After Claus.) 


108 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 dracés or hydrophyllia (hph) — partly cover the 
sporosacs. Halistemma occurs in the Atlantic and Mediter- 
ranean. A closely related form (Agalmopsis 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 umdrella, the convex sur- 
face of which, or ex-umbrella, 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 (mg. ip) with a 
peculiar sense-organ,; between the pairs of lappets the edge 


Iv PHYLUM CCELENTERATA 109 


of the umbrella is fringed by numerous close-set marginal 
tentacles (2). 

In the centre of the lower or sub-umbrella surface is a 
four-sided aperture, the mowth (mth), borne at the end of 


Fic. 51 —Aurelia aurita. Ventral view—two of the oral arms are removed; a@.7.c, 
radial canal; gon, gonads; z.r.c, radial canal; mg. 7p, marginal lappet; mth, 
mouth; ov. a, oral arm; Z.7.c, radial canal; s.g.f, sub-genital pit; ¢, 
tentacles. 


an extremely short and inconspicuous manubrium: sur- 
rounding it are four long delicate processes, the oral arms 


110 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 swd-genital pit (s. g. £), which lies immediately 
beneath one of the conspicuously coloured gonads (gon). 

The mouth leads by a short tube or gw/ez, 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, t.r.c, prc), which pass to the edge of the umbrella 
and then unite in a very narrow crcular canal. 

Each gonad (go.) 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./). 

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 flanula (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 CCZLENTERATA 11 


Fic. 52. — Aurelia aurita, development A, planula: B, C, formation of the gullet 


or stomodeum; D, transverse section of young scyphula; E, scyphula; F, 
longitudinal section of same; G, division of scyphula into ephyrule; H, ephy- 
rula from the side; J, the same from beneath, In A D and F the ectoderm 
is unshaded, the endoderm striated, and the mesoglcea dotted. a, lobes of 
umbrella; 724, manubrium; stk, mouth; sf, septal funnel; s¢, stomodzeum; 
z, tentacle: ¢z, teenioles, 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 Scrphula. The Scyphulasome- 
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 Aphyruda (H, I), which grows rapidly 
and eventually develops into the adult Aurelia. 

The rest of the Seyphozoa 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 ARAczostomee 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 113 


similar to that which has been described in the case of 
Aurelia, with a fixed scyphistoma stage; but in others the 
ciliated larvee developed from the ova give rise directly to 


Fic. 53.—-Tessera princeps. A, external view; B, vertical section; g. /, gastric 
filament; gom, gonad; 7.x.¢, tentacle; v5, manubrium; ath, mouth; £.7.t, 
tentacle: s¢, stomach; ¢m, tzeniole 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, t.e., swim freely in the surface waters of the ocean. 
I 


114 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 dase. The distal or 
free surface of the column, termed the dsc or peristome, 
bears in the middle an elongated, slit-like aperture—the 
mouth, Springing from the disc and encircling the mouth 
are numerous cylindrical z“rc/es, 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 (gv/), having 
the form of a flattened cylinder, which hangs downward 


IV PHYLUM CQELENTERATA 115 


into the interior of the body, and terminates in a free edge. 
This tube is called the guwde¢ or stomodeum. Its inner 
surface is marked with two longitudinal grooves (sgh), 
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 


WIth 
ost.? 


mes. 1. ani > 4.3 HT eon 


mes. 3. 


TL3.2 


Fic. 54.—Tealia crassicornis. Dissected specimen; gon, gonads; gz/, gullet; 
Z m, longitudinal muscle; 4%, lappet; wes. z, primary, mes. 2, secondary, 
mes. 3, tertiary mesenteries; mes. F, mesenteric filaments; mth, mouth; 
ost. 1, ost. 2, ostia or aperture in mesenteries; Z. 7, parietal muscle; sgfh, 
siphonoglyphe; s. #, sphincter muscle; #4. #, transverse muscle. 


partitions, the complete or primary mesenteries (mes. I) ; 
between these are incomplete secondary mesenteries (mes. 2), 
which extend only part of the way from the body-wall to 


the gullet, and “rtiary mesenteries (mes. 3), which are 
hardly more than ridges on the inner surface of the body- 


116 MANUAL OF ZOOLOGY SECT. 


wall. Thus the entire enteric cavity of a sea-anemone is 
divisible into three regions: (1) the gwd/et or stomodeum, 
communicating with the exterior by the mouth, and opening 


The ectoderm 
ac, acontium; cz, cinclis or aperture in 


gloza black. i 
, intermesenteric chamber; »es, mesentery; ses. /, mesenteric 


-wall; gv, gullet: zit. mcs. ¢ 
; mth, mouth; es¢, ostium; Z, pore; #, tentacle. 


is dotted, the endoderm striated, the meso: 


body 
filament 


Fic. 55. — Diagrammatic vertical (A) and transverse (B) sections of a sea-anemone. 


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 dicecious, 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 


118 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 


SN ext era 
Ped 
y Al 


Fic. 56.— The common Sea-anemone. Fic. 57. —Corallium rubrum, portion of 

(After Emerton.) 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, z.e., 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 siphonozoords, which are smaller, 
and are devoid of tentacles and of gonads. 


Iv PHYLUM CCELENTERATA 119 


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- 


Fic. 58.—Alcyonium palmatum. A, entire colony natural size; B, spicules. 
editerranean Sea. (After Cuvier.) 


naria, such as the “ dead men’s fingers ” (A/cyonium, 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 (Fig. 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 (.dv/pathes 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. FPennatula 
aculeata lives in deep water in 
the North Atlantic. 

In the Afadrepore 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- 
Fic. 59.— Tubipora musica. Skel- coral” is known as a corallite ; 

eton of entire colony, Natural, ia : 

cen IndianQcean jn the majority of species a large 

number — sometimes many thou- 

sands — of corallites combine to form a coradlum, the skele- 
ton of an entire coral-colony. 

The structure of a corallite is conveniently illustrated by 
that of the solitary genus F/adellum (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 ¢heca 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. 5 

The almost infinite variety in 
form of the compound corals is Fic._60.—Pennatula sulcata. 

n 3 . Entire colony. Natural size. 
due, in the main, to the various Z, lateral branch. (After 
methods of budding. According pee 
to the mode of budding, massive corals are produced in 
which the corallites are in close contact with one another, 
as in Astrea (Fig. 62); or tree-like forms, such as Den- 
arophyllia (Fig. 63, A), in which a common calcareous 
stem, the cenenchyma, is formed by calcification of the 
ccenosarc,' and gives origin to the individual corallites. 


1See p. 94. 


122 MANUAL OF ZOOLOGY SECT. 


Fic, 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 ofa 
simple coral in longitudinal and transverse section; ectoderm dotted, endoderm 
striated, skeleton black. 4. f/, basal plate; co/, columella; e. t, epitheca; gu, 
gullet; mes., mes. 1, 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 CCZLENTERATA 123 


It is by this last-named method, the ccenosarc 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 


Fic. 62. — Astrea 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 


124 MANUAL OF ZOOLOGY SECT. 


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, 


Fic. 63.—A, Dendrophyllia nigrescens; B, Madrepora aspera. Natural size. 
co, corallites; cs, ccenosarc; #, 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 C(ELENTERATA 125 


means of its two reversed pairs of hind legs. The sea- 
anemone appears to have fixed itself when young to the 


Fic. 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 


Fic. 65.—Hormiphora (Cyd7ppe) plumosa. A, from the side; B, from the aboral 
ole. tk, mouth; s. 7, swimming plates; ¢ and 4, 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 orad, 
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 


£ 


Fic. 66.—Hormiphora plumosa. A, transverse section of one of the branches of 
a tentacle; B, two adhesive cells (ad c,) and a sensory cell (s. c) highly magni- 
fied. cz, cuticle; 2x, 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 papillz, 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 Beroé, 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 
Fic. 67.—Idyia roseola. On ridges on the inner surface of the 

pre ee gullet. Cestus has, however, a deli- 

Lene pee z cate violet hue, and, when irritated, 

ye paddles. (After Shows a beautiful blue or bluish-green 

fluorescence ; while Beroé is coloured 

rose-pink, and Idyia is of a brilliant pink. The most 

primitive form to be found on our coast is Zdj7a (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. 


SECTION V.—PHYLUM PLATYHEL- 
MINTHES 


TuE 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 Aead lode, projecting from the broader 
end. When the liver-fluke is compared with a zooid of ObeZa, 
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 radia/ one, the parts being 
disposed in a radial manner round the mazn axis of the body, 
which is an imaginary line running through the middle of 

K 129 


130 MANUAL OF ZOOLOGY SECT. 


the mouth and enteric cavity. In the fluke, on the other 
hand, the parts are disposed to the night and left of an 
mo imaginary median vertical plane, 
ge 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 dzdateral; it has already 
been met with in some of the 
Protozoa, and is characteristic 

‘ of nearly all animals higher than 
Fic. 68.—Distomum hepaticum. rae 

Natural size. exer, excretory the Ccelenterata. 

ee The broader end of the body 

eee 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 (so), situated at the anterior extremity of the head- 
lobe, is surrounded by a muscular oval 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, 70) leads to a small, bulb-like body, 
the pharynx (Fig. 69, pf), with thick muscular walls and a 
small cavity. From this a short passage, the esophagus, 
leads to the ¢uéestine. The latter (én?) is frequently a very 


eccr 


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- 


= AP rt 

=) ANE SEAM 
gp) pms IS 5 NERA 

past Pe et ONCINY] BINA 

Fic. 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. ¢7, ejaculatory duct; 7, female reproductive aperture; zt, 
anterior portion of the intestine (the rest 1s not shown); od, commencement of 
oviduct; ov, ovary; #, penis; #4, pharynx; sh, shell-gland; ¢e, testes; zt, 
uterus; way, left vas deferens; wds, right vas deferens; wz?, lobes of vitelline 
glands; vs, vesicula seminalis. (After Sommer.) 


ternally, a number of blind branches or caca, 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 


132 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 ac 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 capzllaries. 
Each of these ends internally in a slight enlargement 
situated in the interior of a large cell, a fame-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 cesophagus, 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 nuinber 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, 7.c., 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 ¢s¢es 
(ze) 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. 2) opening anteriorly into an elongated 
sac, the vestcula seminalis (v. s), from which a narrow tube — 
the eyaculatory duct (e7)— 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 witelline glands (vit) consist of very numerous 
minute rounded follicles, which occupy a considerable zone 
in the lateral regions of the body. The two main v¢elline 
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 she//-gland’s (sh.gl). The uterus (ut) 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 feeces. When it escapes from the egg, the 
ciliated embryo, as it is termed (Fig. 70, 4), has the form of 
a somewhat conical body, covered all over with vibratile 
cilia, and with two spots of pigment, the eye-sfods, 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 ofa 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 (Zzmnea), 
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 vedia (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 rediz, after escaping from the interior of 
the sporocyst, bud off internally cells which either give rise 
to a fresh generation of rediz or to bodies termed cercarie. 
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 


v PHYLUM PLATYHELMINTHES 135 


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 


Fic. 70.—A-D, development of Distomum hepaticum. 
A, ciliated larva; 4, sporocyst, containing redia in 
various stages of development; C, redia, containing a 
daughter redia, and cercaria; D, fully developed cer- 
caria. 46,0f, birth opening; emf, enteron of redia; eye, 
eye-spots; gast, gastrula stage of redia; germ, early 
stages in the formation of cercariz; zt, intestine of 
certaria; zor, morula stage in the development of 
cercariz; @s, cesophagus; o.sz, oral sucker; fap, 
head-lobe of ciliated embryo; p2, pharynx; proc, pro- 
cesses of redia; vent.sw, ventral (posterior) sucker. 
(After Thomas.) 


food or various secretions of their host. Cthers 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 


Fic. 71.— Trematodes. A, Amphistomum, B, Homalogaster, gf, genital 

hee. a rons Ss, posterior sucker; fe, testes; vé#, vitelline glands. 
host in such a way as to facilitate the taking in by the 
mouth of animal juices and epithelial ¢éris. 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 


v PHYLUM PLATYHELMINTHES 


137 


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 ecloparasitic 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 TURBELLARIA 


The Turbellaria are a 
class of flat-worms which, 
though for the most part 
non-parasitic,resemble the 
Trematodes very closely, 
the chief difference being 
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 


te 
cn 
é 
z, 
ra 
t, 
Zt 
u 
9 


Fi. 72. — General plan of the structure of a 
Triclad Turbellarian. cz, brain; e, eye; 
g, ovary; 2,, median limb of the intestine; 
Zp, left limb; 2, right limb; 7, longitudinal 
nerve-cord; 2, mouth; od, oviduct; pA, 
pharynx; 7¢, testes; ¢e, tentacles; vd, vas 
deferens; 2, uterus; , ejaculatory duct; 
¢, vagina; ¢' ¢, common genital aperture. 
(After Von Graff.) 


some the anterior end is 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 
b in the Trematodes. 
Fic. 73.— Planarda polychroa(a),  Turbellaria occur in the sea, 
lugubrzs (6), torva (c), about . ‘ 
thrice the natural size. (After in fresh water, and also in damp 
Schmidt, from Claus.) winch 1 
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, ¢). 


3. THE CESTODA 


The class Cestoda or tape-worms are all 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 


Fic. 74. — Tenia solium. Human tape worm, Entire 
specimen reduced. caf, 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 praglottides. ‘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 rosteHlum, 
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 (meck) 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 xervous system, and a system 


Fic. 75.—Head of Tania of wates-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 werus 
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- 


v PHYLUM PLATYHELMINTHES 141 


terior end, and reach the exterior with the feeces 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.excret can.excrel 


|_ neru.t 


Fic. 76.—A_proglottis of Tenia solium with mature reproductive apparatus. 
can. excret, longitudinal excretory canals with transverse connecting vessels; 
gi. vit, vitelline glands; xerv. 7, longitudinal nerves; ov, ov, ovaries; por. gen, 
genital pore; sch/d, shell-glands; wfer, uterus; vag, vagina; vas. def, vas 
deferens. The numerous small round bodies are the lobes of the testes. (After 
Leuckart.) 


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, 2.¢., 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- 


D 


« 


Fic. 77. — Development of Tape-worm. A, hexacanth embryo; B, Proscolex of 
Tenia sagtnata; C-F, stages in the formation of the scolex of the same; C, 
the invagination before the hooks and suckers have become developed; D, after 
th, appearance of the hooks and suckers; E, partly evaginated; F, fully 
evacinated scolex of 7. solzzs with caudal vesicle; G, scolex of 7. serrata 
with the remains of the vesicle; H, young tape-worm of J. 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 
Tenia cenurus 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 
Tenia echinococcus, well known as the cause of the disease 
termed Aydatds, 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. 


Fic. 78.—Cyst of Tania echinococcus with the developing daughter-cyst and 
scolices. (After Leuckart.) 


The commonest human Cestode parasites in the United 
States and Canada are Zenia solium and 7. 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 Zenta sohum is the more 
prevalent, where more beef, 7° saginaza. 


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 (pr), 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, z.¢., 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 


146 MANUAL OF ZOOLOGY SECT. 


the surface of the extremity is sometimes abundantly 
provided with s#nging-capsules ; sometimes it is beset with 
glandular adhesive papille. The proboscis is capable of 


Fic. 79. — Diagram of the organs of a Nemertine, from below. a@, anus; 47, brain; 
div, coeca; dong. uc, longitudinal nerve-cords; #, mouth; x, nephridia; ov, 
ovaries; fr», probosis. (After Hubrecht.) 


being retracted within the interior of an investing sheath, 
the proboscis sheath. 


PHYLUM PLATYHELMINTHES 147 


-- dors ves 
brobt 
ap. Teph 
4.) 
breb 2 i} dar3 ves 
a 
Ter mus 


Fic. 80.—Tetrastemma. General view of the internal organs. az, anus: ac. st, 
accessory stylet; cer. g, brain: cz/. gr, ciliated groove ; dors. ves, dorsal vessel ; 
lat. ne, lateral nerve; dat. ves, lateral vessel; xeph, nephridium; of. xeph, 
nephridial aperture ; 4v0d1, eversible part of proboscis ; 70d, non-eversible part 
of proboscis; 470. af, aperture for the protrusion of the proboscis; retr. mus, 
retractor muscle of the proboscis; sz, stylet, (From Hatschek’s Lehréuch.) 


148 MANUAL OF ZOOLOGY SECT. V 


The alimentary canal (Fig. 79) is a simple tube distin- 
guishable into ewsophagus with longitudinally folded walls, 
and ¢nfestine with lateral ceca (div). It ends in an anal 
opening (a) situated near the posterior extremity of the 
body. 

The Nemerteans possess a system of dlood-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 vesse?s of the Platyhelminthes are repre- 
sented in the Nemertine worms by a pair of greatly coiled 
and branched tubes (Fig. 80, zefh), 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 xervous system is in some respects more highly 
developed than in the Zurbellaria. The brain (Fig. 80, 
cer. g) is composed of two large ganglia with lobed surfaces, 
connected together by two comsmussurves, 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. 

Zvyes are present in the majority of Nemerteans, and in 
the most highly organised species occur in considerable 
numbers. 

Most species are diecious. 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 


Tue Nemathelminthes or round-worms are so named 
because the body instead of being compressed from above 
downwards, as in the flat-worms, is rounded, #.¢., 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 dorsa/ (Fig. 81, @. 2) and ventral (v. 2) 
Zines: 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 &Zs, one median dorsal 
(d. 2), the other two ventro-lateral (v. 4). 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 


150 MANUAL OF ZOOLOGY SECT, 


bodies, the penial sete ( pn.'s). In the female the repro- 
ductive aperture or govopore is separated from the anus, and 


(After 


v. Up, ventral lip. 


an, anus; d. 7p, dorsal lip; a. 2, dorsal line; ex. p, ex- 


cretory pore; #, papillae; gv.s, penial seta; wv. /, ventral line; 


Leuckart.) 


A, anterior end from above; B, the same from below; C, posterior 


D, of male, side view. 


end of female; 


Fic. 81. — Ascaris lumbricoides. 


is situated on the ventral surface about one-third of the 

length of the body from the anterior end (Fig. 82, gz). 
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 syz- 
cytial ectoderm, t.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 


_ 
wm 
_ 


cuticle; aer. eAthm, deric epithelium; 
fat. 7, lateral line; 7, muscular 


ft spread out; 4, pharynx, partly cut away; 


an, anus; CH, 
ly cut away; 


de in situ, the le 


gut, intestine part 


that of the right si 


Semi-diagrammatic dissection of the female. 
gnup, gonopore; 


ex. v, excretory vessel ; 
uu, Y, nerve-ring; ovy, ovary, 


ex. p, excretory pore; 
layer; si, mouth: 


Fic. 82. — Ascaris lumbricoides. 
wd, uterus, 


152 


MANUAL OF ZOOLOGY 


SECT. 


canal, the pharvnx or stomodeum (Fig. 82, 24), with very 


on 
ag 
un 
vuln 

ae 

ca 
In 

SI 


|— hon 


Fic. 83. — Diagram of nervous 
system of Nematoda. c¢, com- 
missures; d@/z, dorsal nerve; 
Asn, posterior lateral nerve; 
on, upper and wx, under 
portion of nerve-ring; sg, 
lateral swellings; 7/2, ventral 
nerve. (From Lang, after 
Biitschli.) 


muscular walls. Posteriorly the 
pharynx opens into the ¢nfestine 
(nt), a thin walled tube, flattened 
from above downwards. Posteriorly 
the intestine narrows considerably 
to form the short recévm, which 
opens externally by the anus (a7). 
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 
ceelome or Jody-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. 7), one in each 
lateral line. Anteriorly they pass 
to the ventral surface, unite with 
one another, and open by the 
minute excretory pore (ex. p) al- 
ready noticed. 

The nervous system consists of a 
ring (xv. 7) surrounding the pharynx 


VI PHYLUM NEMATHELMINTHES 


153 


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 (@/n, 
vin). 

The reproductive organs 
are formed on a peculiar 
and very characteristic pat- 
tern. The ées#s (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 eyaculato- 
rius, into the rectum. Be- 
hind the rectum, and open- 
ing into its dorsal wall, are 
paired muscular sacs (s) 
containing the penal sete 
(p. ns) already noticed. 
The anterior end of the 
testis consists of a solid 
mass of sexual cells ; pass- 
ing backwards there is 


cu 


wet 


> 


CaaS 


U 


der epthm, epidermis; 


, testis; vs. sem, vesicula seminalis. 


an, anus; cz, cuticle; 


mt, muscular layer; Az. s, penial seta; s, sacs containing penial seta; ¢s 


Fic. 84. — Ascaris lumbricoides, posterior extremity of male, dissected. 


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 vzaries (ovy), each passing insensibly 
into a uterus (7). 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 (vag) which 
opens, as already seen, on the ventral surface of the body 
(gup) at about one-third of the entire length from the head. 

The Nematodes in general vary greatly in size, from about 
Imm. 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 Zrichina spiralis (Fig. 85), a minute worm, the male 
(C) a little over 1 mm. (;); inch) in length, the female (B) 
about 3 mm. (finch). 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 


e 


NS 


oy 


7" 


RIS ETAY 
OK 


viet 


Fic. 85. — Trichina spiralis. A, encysted form in muscle of host; B, female; C, 
male. 4h, connective tissue envelope; cy, cyst; de, ejaculatory duct; e, em 
bryos; / fat globules; 4, testis; mz. /, muscle fibre; oe, pharynx; ov, ovary; 
wo, gonopore; 2, cell masses in intestine. (From Lang’s Comparative 


Anatomy, after Claus.) 
155 


156 MANUAL OF ZOOLOGY SECT. VI 


uterus of the female, and the minute young (B, ¢), 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 Trichinz 
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 medinensis) 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 4. vugaris, 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 

157 


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 ams or rays, which, broad at the 
base, taper slightly towards their outer extremities. There 
are two surfaces, one the dorsal or abactinal, directed up- 


Fic 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 wdulacral 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 branchie or papule (Fig. 88, 
Resp. ce), which is capable of being entirely retracted. 

Very nearly, though not quite, in the centre of the dorsal 
surface is an aperture, the aus (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 pedicellari@ (Fig. 
88, Ped). 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 saws, 
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 ¢de- 
feet (Figs. 86, 88, 7. #), 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 (¢.c., 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), and over it a median process, the fentacle (7), 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 Jody-cavity, and below, be- 
tween the two arms of the V, is the ambulacral groove. 


vu PHYLUM ECHINODERMATA 161 


The dorsal arch is supported by a number of irregular 
ossicles. The V-shaped ventral part of the body-wall— 
z.e., the walls of the ambulacral groove —is supported 
by two rows of elongated ossicles, the amdéulacral ossicles 
(Fig. 88, Amd. 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 


Fic. 87.— Starfish. Vertical section through an arm. am, ampulle ; eA. epider- 
mis; vad. amd, radial vessel of the ambulacral system; s points to the septum 
dividing the blood-vessel into two parts; rad. ve, radial nerve of the epidermal 
system; sf, spaces in mesoderm of body-wall; ¢. /, 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 amdbulacral pores, 
one between each contiguous pair of ossicles. In the ventral 
groove lie the tube-feet (4). 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 


162 MANUAL OF ZOOLOGY SECT. 


a series of little bladder-like bodies, the ampudle, which lie 
on the other side of the ambulacral ossicles, ze., 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, 7), which appears in 
the transverse section as a small rounded aperture. From 
this short side branches (Fig. go 7’) 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 xevve-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 dlocd-vascular system. 


vil 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 orad/ ring-vesseZ 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 ampulle. 
Within the pentagonal actinostome is a space, the pevistome, 
covered with a soft integument, and in the centre of this is a 
circular opening, the true mow/h, 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, s¢; Fig. 89, card. st). 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 z/estine, 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, pyé. cec), which extend to near the 
extremity of the arm. The walls of the pyloric ceca are 


164 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 


Fic. 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 (7 #) and ampulle (.4 #2) are shown in 
perspective. B, transverse section through anarm 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 ccelomic 
epithelium represented by a beaded line. asd. 0s, ambulacral ossicles; amp, 
ampulla; anv, anus; C. Amé, 1’, circular ambulacral vessel; C. 8. 1’, septum 
of ring blood-vessel; Cd. cw, cardiac ceca; Ca@/, celome; Cael. Epithim, 
coelomic epithelium; Der. Epzthm, deric epithelium; Derm, mesoderm; Ext. 
Epthm, enteric epithelium: /zt. ce, intestinal ceca; Mdpr, madreporite; Mes, 
mesentery; A/th, mouth; Vv R, nerve ring; oc, eye; os, ossicles of body-wall; 
ovd, oviduct; Ped, pedicellaria: A, perihamal spaces; fy'2. cec, pyloric czeca; 
Rad. amb. v, radial ambulacral vessel; Rad. 8B. V, points to septum in the 
radial blood-vessel; Rad. Nz, radial nerve; Resp. c@, dermal branchie; S#, 
stomach; Sz. c, stone-canal; 7, tentacle; 7./, tube-feet. (From Parker’s - 
Biology.) 


food-matters similar to that exerted by the secretion of the 
pancreas in the Vertebrata, converting starch into sugar, 
proteids into peptones, and bringing about the emulsification 


VIt PHYLUM ECHINODERMATA 165 


of fats. From the short intestine are given off inter-radially 
two hollow appendages, the znéestinal ceca (Fig. 89, int. 
c@c), each with several short branches of irregular shape. 
Running downwards from the madreporite to near the 
border of the mouth, is an S-shaped cylinder, the madvreporic 
or stone-canal (Fig. 88, S¢.c). The walls of this canal are 
supported by a series of calcareous ossicles. The interior of 


a 
PY. cuee 


Fic. 89,—Asterias rubens. Digestive system. am, anus; card. st, cardiac 
division of the stomach; zt. cwc, intestinal ceca; madr, madreporite; Aly. 
ce@c, pyloric ceca; pyl. st, pyloric division of the stomach. (From Leuckart.) 


the madreporic canal communicates above with the exterior 
through the grooves of the madreporite. Below, the canal 
opens into a wide, five-sided, ring-like canal, the 72mg-vessel 
of the ambulacral system. From this are given off the five 
radial ambulacral vessels, passing to the extremities of the 
arms. From the pentagonal canal are given off also a series 
of five pairs of appendages, the Pokan vesicles (Fig. 90, ap), 


166 MANUAL OF ZOOLOGY SECT. 


— pear-shaped, thin-walled bladders with long narrow necks, 
— which are placed inter-radially. On the sides of the neck 
of each Polian vesicle (except in the inter-radius containing 
the madreporic canal, where there is one on one side only) 
project inwards a pair of little rounded glandular bodies, the 
racemose vesicles, or Ttedemann's vesicles, the interior of 
each of which is divided into a number of chambers. 


Fic. go.— Ambulacral system of. a starfish. a, ampulla ; ap, Polian vesicles; c¢, 
circular canal; , madreporite; +‘, madreporic canal; #, tube-feet; », radial 
vessels; ~', branches to ampulla. (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. 


Vil PHYLUM ECHINODERMATA 167 


The starfish is wnisexual, each individual possessing 
either ovaries (Fig. 88, ov) or ¢estes, 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 


Fic. 91.— Anthenea. View of dorsal surface. (After Sladen.) 


exterior, open on the dorsal surface (Fig. 88, A, Ova’) 
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 


168 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. g1 and gz) the central disc is cor- 
respondingly increased in extent. In some extreme instances 
of this modification the starfish assumes the form of a five- 


Fic. 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 ceca; 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 


CHESTER JERMAIN HUNN. 


VII PHYLUM ECHINODERMATA 169 


is sometimes absent; in Astexias vulearis it is minute, 
almost closed. The spines and pedicellaricz 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 


Fic. 93.— Ophioglypha lacertosa. A, outline, of the natural size; B, central disc, 
dorsal view; Cine 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-lke 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 ceca. 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 tu 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- 


Fic. 94.— Strongylocentrotus. Entire animal, with the tube-feet extended beyond 
the ends of the spines. (From Brehm’s Thzerleden.) 


teristic feature of the internal structure is the presence of a 
complicated apparatus for mastication known as Azistotle’s 
Zantern, consisting of five jaw-like parts, each bearing a 


172 


Int. amb 


MANUAL OF ZOOLOGY 


SECT. 


Lntl.amb 


Fic. 95.-— Corona of sea-urchin with the spines removed to show the arrangement 


of the plates, lateral view. 
Ap, apical (aboral) pole; 
Thierretch.) 


Amé, ambulacral zone with its perforated plates; 
Int. amb, inter-ambulacral zones. 


(From Bronn’s 
~ 


sharp tooth. The points of these five teeth can be seen 
through the opening of the mouth. The enteric canal has 


aamISTOR, 
are foe ( 
BoM UEC 

y [S yapoesrl cs 


ra 


Fic. 96.— Apical system of plates and 
aboral extremities of zones of the shell 
of a sea-urchin, amd, ambulacral 
zones; gen, genital plates; zz. amd, 
inter-ambulacral zones; madr, madre- 
porite; oc, ocular plates: pertpr, peri- 
proct. (After Leuckart.) 


no radiating coeca. The five 
ducts of the reproductive or- 
gans open on five ossicles, the 
genital plates (Fig. 96, gen), 
which with five smaller ocz- 
far plates (oc) each bearing 
a rudimentary eye, form a 
complete ring round the 
space (peripr) at the anal 
pole, in the middle of which 
is the anus; a madreporite 
is amalgamated with one of 
the genital plates. 


VII PHYLUM ECHINODERMATA 173 


In the Heart-urchins (Spatangis) 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 zyvegu/ar 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 Béche-de-mer 
or trepang (Aolothuria edulis). Our Floridan trepang is 
Hi, 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 éentacles surrounds the mouth. Five 
regular zones of ¢vée-fee¢ 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 SECT, 


surface, in some forms (such as the worm-like Syvapéa and 
its allies) tube-feet are entirely absent. 


Fic. 97. — Cucumaria planci. Entire animal seen from the ventral surface, with the 
tentacles expanded, and the tube-feet projected outwards, (From Hertwig's 
Lehrbuch, 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 


vu 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 


(From Leuckart and 


European coasts. 


Nitsche’s Diagrams.) 


Antedon. Side view of entire animal. 


Fic. 98.— 


opposite surface are attached whorls of slender curved cy- 
lindrical appendages, the ¢rr7, 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 Arvnules. 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 zez/acles, 
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 sfa/k 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 of 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 é¢/ateral 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. 


177 


ECHINODERMATA 


PHYLUM 


Vil 


(After P, H. Carpenter.) 


Fic. 99. — Metacrinus interruptus. 


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 ¢rochad disc (Fig. 100, 77.2). 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 ¢rwn% and the said (2). 
The latter, which is situated at the extremity of the body most remote 


178 


SECT. vil ROTIFERA, 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 


Fic. roo. — Brachionus rubens. A, from the dorsal aspect ; B, from the right side. 
a, anus ; Sy, brain; @. f dorsal feeler; c. g/, cement gland, ¢/, cloaca; ¢ @, 
ciliary lobes ; c. v, contractile vesicle ; ¢, eye-spot ; zvé, intestine ; Zr, Jorica ; 
Z. f, lateral feeler : 7, muscular bands ; ~f/, nephridial tubes ; ov, ovary ; ph, 

harynx ; s¢, stomach; #4, tail; ¢7. d, trochal disc; w#, vitellarium. (After 
udson 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 


180 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 /orica 
formed of a thickening of the cuticle. One remarkable form — Pedalion 
—has six hollow appendages terminated by feathered setze: and a few 
other furms are provided with simple or fringed setze. 

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 feces. 

The structure of the internal organs is simple. The alimentary 
canal usually terminates in an anal aperture (a). There is a large 
pharynx (f/) containing a masticatory apparatus, the #asfax, usually 
consisting of three chitinous pieces, or jaws, of complicated form. The 
nervous system consists of a single ganglion (dr), situated towards the 
oral end; and there are usually one or several very simple eyes (e). In 
close relation to the brain are one or several processes, the ¢actile rods 
(d. f), tipped with non-motile cilia, connected with the ganglion by 
means of nerves. A pair of longitudinal excretory vessels (7/4), pro- 
vided at intervals with short branches terminating in flame-cells, usually 
open into a contractile vesicle which discharges into the terminal part 
of the intestine. 

*The males differ greatly from the females, being nearly always much 
smaller and degenerate in structure. ‘Three kinds of eggs are produced : 
large and small seer eggs which always develop without fertilisation 
( parthenogenesis) and thick-shelled winder eggs, which probably require 
to be fertilised. 

A few Rotifers live in the sea, but the majority are fresh-water forms, 
occuring in lakes, streams, ponds, and even in puddles the water of 
which is rendered foul and opaque by mud and sewage. Frequently 
the water in which they live is dried up, and the thick-shelled winter 
eggs may then be widely dispersed by wind. It is even stated that the 
adult animals may survive prolonged desiccation and resume active life 
when again placed in water. Many forms cling to the bodies of higher 
animals in order to obtain a share of their food, thus leading a sort 
of commensal existence. Others go a step further and become true 
external or internal parasites. 


VIII ROTIFERA, POLYZOA, AND BRACHIOPODA 181 


2. THE POLYZOA 


The Polyzoa are an extensive class of animals for the most part 
marine, which, from the general form that they assume, are readily 
mistaken for hydroid zoophytes (Hydrozoa, p. 91). They occur as 
fixed colonies, the form of which varies greatly, supported by an exo- 
skeleton which is sometimes gelatinous, sometimes chitinoid, sometimes 
calcareous. They either encrust rocks, forming little patches, or they 
grow up with a plant-like habit. Most usually the colony is a branch- 
ing, plant-like structure, though it may assume other forms. The 
whole consists essentially of a number of minute chambers, or zoec?a, 
as they are termed, each formed by the exoskeleton of one of the 
zooids. Each zocecium (Figs. 101 and 102) has an aperture, sometimes 
capable of being closed by a lid or operculum, through which the oral 
extremity of the zooid is capable of being protruded. At this pro- 
trusible oral end of the zooid is a circular or horseshoe-shaped ridge or 
lophophore bearing a number of simple, slender, ciliated tentacles 
(Zent). In many Polyzoa the colony bears a series of remarkable 
appendages, the evicudaria, of the nature of modified zooids. A typical 
avicularium (Fig. 101, vic) has very much the appearance of a bird’s 
head supported on a very short stalk, with a movable part representing 
the lower jaw, which becomes separated from or approximated to the 
part representing the upper jaw by movements which closely resemble 
the movements of opening and closing of the bird’s mouth. These are 
probably defensive organs. The mouth (7o) is a large aperture in the 
middle of the oral extremity within the lophophore: the anus is situated 
near it, but outside the lophophore. The digestive canal is a U-shaped 
tube, divided into pharynx ( f/), stomach (s/o), and intestine (277), 
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, gang), 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 


Fic. ror.— Bugula avicularia. Two zooids, magnified. az, anus; avic, avicularia; 
em, embryo enclosed in the ocecium; faze, funiculus; gast, muscular bands 
passing from the stomach to the body-wall; zv¢, intestine: #0, mouth; o@c, 


ocecium ; @s, cesophagus : ov, ovary ; pi, pharynx ; ve?, parieto-vaginal muscles ; 
sf, spermatidia : stom, stomach. 


182 


ROTIFERA, POLYZOA, AND BRACHIOPODA 183 


SECT. VIII 


P dh Cueunry tay) 
“sySEqoyEys ‘ozugs : yoeuIOys ‘7s Saposnur OW eIIAI ‘4za4 | pueys sarjonposdar ‘wga«c : snBvydosa ‘w 
Syinour ‘ow | sunsazut ‘772 S uoIpdued 


‘suvg “payluseu Auojod & jo uoniog *¥eI[a}eMIN[g— “Zor ‘1g 


distinguished from the Ectoprocta or ordinary Polyzoa, in which 


the anus, as we have seen, is external to the lophophore and tenta- 


cles. 


184 MANUAL OF ZOOLOGY SECT, 


tent 


Fic. 103. — Pedicellina. Showing successive stages (numbered 7 to 6) in the 
development of zooids by budding. ax, anus; gang, ganglion; 70, 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 (@. v), the other ventral 
(v. v), and the animal is attached by a horny stalk or peduncle (Fig. 
105, @) which passes through an aperture (Fig. 104 7) in a process, 
the deak (6), of the ventral valve. In the natural state the peduncle is 
attached to a rock or other support, and the animal lies with the ventral 
valve uppermost and the two valves gaping slightly. The end of the 
valve at which the peduncle is situated is regarded as posterior, the 


VIL ROTIFERA, POLYZOA, AND BRACHIOPODA 185 


opposite end as anterior. The two valves articulate together by a more 
or less distinct hinge situated at the posterior end, and the movements 
of both opening and closing of the shell about this hinge are effected 
by means of muscles passing internally between the valves. 


Fic, 104. Magellania flavescens. A, the entire shell from the dorsal aspect; B, 
from the left side ; C, interior of ventral valve; D, of dorsal valve ; ad. #, adduc- 
tor impressions ; 4, beak; c.f, cardinal process; @, deltidium : @. 1, divaricator 
impressions; @. v, dorsal valve; /, foramen; /. , protractor impressions; 
s, tooth-socket; s. 7, shelly loop; sf, septum; ¢, tooth; v. v, ventral valve. 
Australian seas, (After Davidson.) 


The body of the animal occupies a relatively small part of the space 
contained in the interior of the shell and lies toward the posterior end. 


186 MANUAL OF ZOOLOGY SECT. 


The rest of the space is lined by a pair of folds of the body-wall, the 
mantle-folds (Fig. 105), @. m, v. mt), the edges of which are beset with 
minute setee (s). In the space (mantle-cavity) lined by these mantle- 


pl. st, 
New Zealand 


d. gl, digestive gland: d@ #1, 
pa, peduncle: 


its coiled process ; sth, mouth; fh, nephridium ; 
. m, ventral lobe of mantle; v. v, ventral valve of shell. 


1 


d.z, dorsal valve of shell; gov, gon®, gonads; At, heart; zzz, intestine; /f, 7p', 
ph 


(ph, lophophore ; 
pallial sinuses; s, seta ; 


dorsal mantle-lobe ; 
coast. 


Fic. 105. — Magellania lenticularis. Sagittal section of the entire animal. 
lip: 


folds lies a /ophophore (iph), usually of complicated form, fringed with 
long ciliated tentacles, and supported in many cases by a delicate, 
sometimes simple, sometimes complicated, shelly process of the dorsal 
valve, the shelly loop (Fig. 104, s. 7). The mouth (Fig. 105, mth), 


VIIL ROTIFERA, POLYZOA, AND BRACHIOPODA 187 


situated in the middle of the anterior body-wall within the lophophore, 
leads into a V-shaped digestive canal (s¢. 27), 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 cesophagus. There is a pair of large 
funnel-shaped nephridia (7%) which act also as reproductive ducts, 
leading from the ccelome 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, 7erebratulina 
seplentrionalis, 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 metameres, 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 CHATOPODA 


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 
Chetopoda 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 WVerers 
dumeritit will apply, with slight differences, 
to our common JVereis 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 farapodia, provided 
with bundles of bristles or seve. ‘The head 
(Fig. 109) consists of two parts, the pro- 
stomium (prest) and the pertscomium 
(perist). The former bears on its dorsal 
surface four large rounded eyes, in front Fic. 106.—Nereis du- 

r ; a merilii. Natural 
a pair of short cylindrical entacles (tent), size. (After Clapa- 
and further back a pair of somewhat ie 
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 (peris?, sent) : 


PACS OR Eee 


cy 
b 
EI 


5 
¥ 
. 
ms 
a 
= 


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 voéepodium (note), and a ventral, 


dors. cur 


vent.cirp 


Fic. 107. —Nereis dumerilii, A single parapodium magnified. ac, aciculum; 
dors. ctrr, dorsal cirrus; neuro, neuropodium; voto, notopodium; vent, czrr, 
ventral cirrus. (After Claparéde.) 


which is termed the weuropodium (neuro). Each of these 
is further subdivided into several lobes, and each bears a 
bundle of sete. Each of the bundles of sete is lodged in 
a sac formed by invagination 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 sete, 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 sete (Fig. 108) are exceedingly fine, but 


IX PHYLUM ANNULATA Il 


stiffish, chitinous rods, of which two principal kinds are 
recognisable ; both have a terminal d/ade 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. cir), 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 aad cirrt, 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 ,.. Jog = Resets qumeriigh 
—the calom, body cavity, or pert- Siero oe 
visceral cavity — filled with a fluid, the 
calomic fluid. The space is divided by a series of transverse 
partitions or sep/a 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- 


proesk UR? pgp i 


aers.vess— 


vert. vess 


rte, Co—| 


Fic. 109.— 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; g?, esophageal glands; ¢#?, beginning of intestine; ve co, nerve 
cord; weph, nephridia; ws, esophagus; palp, palp; para, parapodia: perist, 
peristome; ferrst. tent, peristomial tentacles; 2, pharynx with its jaws; prest, 
prostomium; vert. vess, ventral vessel 


192 


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 duccal cavity 
continued back into a pharvnx (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 esophagus (es), 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 cesophagus open a pair of large unbranched 
glandular pouches, or ceca (g/), which probably are of the 
nature of digestive glands. The ¢adestine (int) is a straight 
tube of nearly uniform character throughout, regularly con- 
stricted between the segments. 

Nereis has a well-developed system of vesse/s filled with 
blood of a bright red colour. A main dorsal vessel (Figs. 
109 and 110, 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 

oO 


MANUAL OF ZOOLOGY SECT. 


194 


of any of the others, and run with great regularity from 


behind forwards, so as to drive a current of blood in that 


direction. 


‘wntaygida peauoyiad jo r9Avy peraosta {249g “257% {[aSSAA [esWIA 
‘ssan ‘guad La}oSnul yeUIpN Zuo peryuaa ‘see Wuop guar WuMiyayuds MWoTDI JO safe] yejoued ‘249g 
savy + Areao ‘a0 saposnui anbiygo ‘sve “7go ‘wnynoioe pue was erpodoyou ‘7as ‘yo ‘sajosnur ayy ya 
wnynoie pue xzyas jetpodoinau ‘yas non * piiydau ‘yf ! prod aatau ‘02 +32 | jLULD D11a]UD JO []EA JO 
aposnw jeurpnyisuoy ‘8720 Suop ‘stusapida *yv uintayyida o1ajzua ‘fa yea tfassaa [esIOp ‘ssa S4op *]]EM 
-Apoq Jo sayosntu [eUIpNysuoy [es1op ‘sr zee ‘Suop saop .a[ond 4722 twoyMDd '7a~7I + [BULd IIIaIUD JO ]]BA JO 
aposnur jo raAvy AepMosty ‘(yeusayur) s7ue 9427 typem-Apog Ju ayasnur yo JoAvy avjnosrd ‘(yeusayxa) sys °9429 


‘Apoq ay) JO uorSar aypplw ay) Jo uordsas asiaasuNsy MeWUVIDEIPTwWOS “THLOUINp Stadayt—“O1r Od 


CUP Daly 
ich Raley y 


a) 
Ti On 
Ay, 


ip 


aN 


ty 


SS ES 


Along the middle of the ventral surface below the alimen- 
tary canal runs another large longitudinal vessel, the veadva/ 
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 ope nerves to the eyes. Behind, two thick 
nerve strands, the esophageal 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 


196 MANUAL OF ZOOLOGY SECT. 


(Fig. 111) consists of a darkly pigmented cup, the reéina 
(ve), with a small rounded aperture, the pwpi/, and enclosing 
a mass of gelatinous matter, the /ens (/). 


Fic. 111.— Section through an eye of Nereis. co, cornea; cx, cuticle; 2, lens; 7, 
layer of rods; ve, 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 110, #efh) occurring in all the segments of 
the body. Each of these has an external opening or zephrt- 
adiopore, 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 
celom through a ciliated bell or funnel, the xephrostome, 
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- 


o | 
VW 


Fig. 112.— Nereis. Anterior portion of nervous system, comprising the brain, the 
cesophageal connectives, and the anterior part of the ventral nerve-cord. (After 
Quatrefages.) 

liferation of the cells of the membrane (fer7tonewm) lining 

the ccelom 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. 


Fic. 113. —Serpule 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 setz, 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 sete, the form of the 
head with its eyes and tentacles, and other points. Many 


Ix PHYLUM ANNULATA 199 


possess dranchie, 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 Polycheta of the Chetopoda. 
Though many of them move about freely like Nereis, others 
live permanently in tubes of a membranous or shelly mate- 


* i 


Fic. 114.—A4, B, C, three stages in the development of the Trochosphere of 
Eupomatus, from the side. am, anus; /%, blastoceele; 2, polar cells of the 
mesoderm; wd, mid-gut; , larval head-nephridium; of, otolith; s/, neural 
plate; s#, stomodzum; w&, preoral ciliated ring; wé,, post-oral ciliated ring. 
(From Lang’s Comparative Anatonty.) 


rial. The tube-inhabiting Polycheta (Fig. 113) usually 
present marked modifications of form in accordance with 
their mode of life. The branchiz 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 


Fic. 115.—Lumbricus agricola. A, entire specimen, lateral view; B, ventral view 
of anterior portion of the body, magnified. 7, 75, 33, first, fifteenth, and thirty- 
third segments. The black dots represent the sete. (After Vogt and Jung.) 

of the tube and the posterior parts which habitually remain 

enclosed in it. All the Polycheta, with one or two ex- 


ceptions, have the sexes separate, and have a free-swimming 


IX PHYLUM ANNULATA 201 


pelagic larva, the Zrochosphere (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. 
Setz, 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 setee 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 Fic. 116, — Lumbricus, 

7 , 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 Qligocheta of the 
Chetopoda. As a group they are distinguished from the 
Polychaeta 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 Cheetopoda 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 Oligochzeta 
manufacture tubes of mud held together by a tenacious 
secretion from glands in the integument. Some of the 
Polycheta 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 Polycheta 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, 
swainps, 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 an/erior sucker (a.s), in the middle of which 
is a small aperture, the souch (mzh). 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 aznui. 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 (7. p. 7-17); 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 eves (@. z, @. 5). 

The perfectly definite and comparatively small number of 
metameres in the leech offers a striking point of contrast 


ew 


i 
——_ ‘ a 
) wy C =) 
t 3 0 ¢ —3 
{ { 
———— = = 
if 
A} i, — B 

if { <3) 
C ia ) 
tf ¢ | 
if m ¢ ) 

{ a} 

id =) ) 

———— ae — 

{ 2 * 

_ 2 mm ) 

i zz 

e 

‘e 

C 

Aan pv. 

C 


¢ { 

¢ t — 

¢ { ECD | 

¢ i een | 

t = | 

oa c mae 


a 


pe 


Fic. 117. —Hirudo medicinalis. A, dorsal; B, ventral aspect. a, anus; a. s, 
anterior sucker; ¢. 7. first pair of eyes; e¢. 5, fifth pair; gf. gf, male gonopore; 
gp. &, female gonopore; mth, mouth; wf. 7, first pair of nephridiopores; 
np. 17, seventeenth pair; p.s, posterior sucker; s. 4, sensory papillae; I-XXVI, 
segments. (Partly after Whitman.) 

204 


SECT. IX PHYLUM ANNULATA 205 


with what we have met with in the Cheetopoda, 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 “eth 
(Fig. 118). By means of its 
muscles each jaw can be 


b 


Fic. 118.—@, Head of Hirudo medici- 


moved backwards or for- nalis, showing the three jaws (os 4, 
: one of the jaws isolated, with the finel. 
wards through a certain arc, toothed free edge. (After Sedgwick. 


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. 119, pA), 
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 sa/- 
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 (cr), a thin-walled tube extending from the eighth 
to the eighteenth segment, and produced into eleven pairs of 
lateral pouches (¢7, cv. z, 77). The crop is capable of great 


Fic. 1t9.—Hirudo quinquestriata. Dissection from the dorsal aspect, @, anus; 
br, brain; ev. 7, first diverticulum of crop, contracted; cv 7’, the same expanded; 
cr. rr, the last diverticulum of the crop, contracted; cv 1’, the same expanded; 
d. e7, ductus ejaculatorius; gx. 1-23, ganglia of ventral nerve-cord ; ¢vé. in- 
testine ; 2. v, lateral vessel ; up. 1-77, nephridia ; oz. s, ovarian sac; f, penis; 
ph, pharynx ; f. s, posterior sucker ; xcz, rectum; st, stomach ; fs. 7—gQ, testes; 
va, Vagina; 7. d@, vas deferens ; 7. sev, 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 (sf), 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 zntestine (int) ; this passes into a 
somewhat dilated rectum (7c), which turns slightly upwards 
and opens by the anus (@z) in the last annulus. 

The excretory system consists of seventeen pairs of 
nephridia (nph. z-z7), 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, zs?) ; 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 hemo- 
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,— 4lv0d-vessels proper, having muscular walls, 
and dblood-sinuses, the walls of which are devoid of muscle. 

The two principal blood-vessels are lateral in position 
(Figs. 119 and 122, 7. 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 


Fic. 120. — Nephridium of the medicinal leech. a. ?, apical lobe; ». 7, middle lobe; 
n. ~, nephridiopores; wst, nephrostome; ~. 2, recurrent lobe; ¢. 2, testis lobe; 
us, 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 Jrazn (Fig. 119, 67) 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 (gz. z-237) 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. 


Fic. 121.— Transverse section of Hzrudo: diagrammatic; cr, crop; d. s, dorsal 
sinus which encloses the dorsal vessel ; 7. uv, lateral vessel ; 7. c, nerve cord; 
nph., nephridium; zs¢., 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 papillz, the /atera/ sense-organs, with which they 
are obviously homologous. The margin of the anterior 
sucker also bears a large number of godlet-shaped organs, 
which are very probably organs of taste. The minute 
structure both of these and of the lateral sense organs is 

P 


210 MANUAL OF ZOOLOGY SECT. 


very similar to that of the eyes. The function of the lateral 


sense organs is unknown. 
The leech is moncecious. There are nine pairs of ¢esées 


(Fig. 119, 4), 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. 7). In the tenth segment the vas deferens increases in 
width and forms a complex coil, the vestcw/a seminalis 


Fic. 122.— Diagram of principal blood channels of leech; @. s, dorsal sinus; /. 
lateral vessel ; v.s, ventral sinus containing nerve-cord. 


(vw. sem), from which is continued anteriorly a somewhat 
dilated muscular tube, the ductus egaculatorius (d. 2&7). 
From each ejaculatory duct a narrow tube passes to the base 
of the penrs (/), 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 


1X PHYLUM ANNULATA 211 


in a small globular ovarian sac (ov. s), situated in the 
eleventh segment. From each ovarian sac a short oduct 
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, 7.c., 
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, Branchellion, 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 
branchiz 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),’ but the 
American’ species of As/acus 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 mght 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 the podomeres. 

The body of the crayfish (Fig. 123) is divided into two 
regions —an anterior, the cephalothorax (¢th), which is 
covered by a broad shield or carapace; and a posterior, 
the abdomen (ab), which is divided into distinct segments, 
movable upon one another in a vertical plane. The cepha- 


Fic. 123.— Astacus fluviatilis, side view of male. a@,, antennule; a5, antenna; 
aé, abdomen; cth, cephalothorax; #da, gill-cover; 7, rostrum; 8, third maxilli- 
pede; g, first leg; so-73, remaining legs; 79, uropod; XIV, first abdominal 
segment; XIX, sixth abdominal segment. (From Lang’s Comparative 
Anatomy.) 


lothorax is again divided into two regions —an anterior, the 
head, and a posterior, the zhorax — by a transverse depres- 
sion, the cerz’cal groove. The carapace is developed from 
the dorsal regions of both head and thorax, and is free only 
at the sides of the thorax,! where it forms a flap or gid/-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, z.e., the second antennal and mandibular; those of 


the succeeding cephalothoracic segments being atrophied. — AMERICAN 
EDITOR, 


x PHYLUM ARTHROPODA 215 


(4d) 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 addomen 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 /ergum, a narrow ventral region or sternum ; 
and downwardly directed lateral processes, the plewra. The 
seventh division of the abdomen is the #éson, 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, z.e., the 
whole abdomen can be extended or straightened, and fered 
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 Ainge, 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 nght and left hinges constitutes the ax7s 
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 s/ernal canal, con- 


216 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 efzs/oma, 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, 7): immediately 
below it is a plate from which spring two movably articu- 
lated cylindrical bodies, the eye-s/z/ks, bearing the eyes at 
their ends. 

Among the appendages one’s attention is attracted by the 
long feelers (Fig. 123, @,, @,) attached to the head, the 
five pairs of legs (g-z3) 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 p/eo- 
pods (Fig. 124,70). Each consists of an axis or profopodite, 
consisting of a very short proximal (fr. 7) and a long distal 
(pr. 2) podomere, and bearing at its free end two jointed 
plates, fringed with sete, the exdopodite (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. 

Tn 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 (g) are 
modified into incomplete tubes which act as copulatory 
organs (gonopoda). ‘The sixth pair of abdominal limbs (zz) 
are alike in the two sexes; they are very large, both endo- 


x 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 


ent eng 


CM. 


pre oo 
4.0 Maxi 


lah 
LAntennule p 3. Antenna 


6.1% Maxilliped 8.34 Leg 


ad i 
Beer Maele 7, 34 Maxilliped 


®.Copulatory Organs 10. Swimming Foor 


11.Uropod 


Fic. 124. Typical appendages of Astacus. ez. 1—5, podomeres of endopodite; 
ep, epipodite; ex, cx OpONe Ts flagella; g, gill; fr. 7, fr. 2, podomeres of 
protopodite; 7-3, podomeres of axis of antennule. (After Huxley. 


therefore conveniently called wropods 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 /egs (8), upon 
which the animal walks ; in front of these is a pair of very 
large legs terminating in huge claws or che/e, and hence 
called chelipeds (Fig. 123,9). The three anterior segments? 
bear much smaller appendages, more or less leg-like in 
form, but having their bases toothed to serve as jaws; they 
are distinguishable as maxid/ipeds or foot-jaws (Fig. 124, 6, 7). 

The structure of these appendages is best understood by 
a consideration of the “Aird 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 (cf), 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 ( p~. Zz, 
pr. 2) form the protopodite, its remaining five segments 
(en. 7-5) the endopodite, and the feeler, which is directed 
outwards, or away from the median plane, the exopodite 
(ev). The folded plate (¢f) is called the efipodite, 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 Zegs (&) 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 che/e ; the fourth segment (en. ¢) 
of the endopodite (sixth of the entire limb) is produced 
distally so as to form a claw-like projection (em. ¢'), against 
which the terminal segment (e7. 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 fst (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 
maxilla in relation with the mouth, and in front of that aper- 
ture a pair of antennules and one of antenne. The hindmost 
appendage of the head is the second maxilla (5), a markedly 
foliaceous appendage ; its protopodite (pr. 7, 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 (3?) is alarge, strongly calcified body, toothed along 
its inner edge, and bearing on its anterior border a little 
three-jointed, feeler-like body, the pa. 

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 (2), while from the second segment 
springs a scale-like body or sguame (ex). 

The antennule (z) has an axis of three podomeres (7-7), 
ending in two many-jointed flagella (7. z 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 antenne, 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- 
tennee, mandibles, first maxille, and second maxille; the 
next eight metameres (5th—r2th), constitute the thorax, 
and bear the three pairs of maxillipeds and the five pairs of 
legs; the remaining six metameres (13th-18th), 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 gw//ef (@) 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 /arge intestine (had) 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 gas/vic md, on which 
are borne a median and two lateral #erh, 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 


Fic. 125.—Astacus fluviatilis, Shea from the right side. @a, antennary 
artery; 24, abdomen; az, anus; 4. d, bile duct; f g, cheliped; 4%, ventral 
nerve- cord: C55 cardiac division 3 stomach; cth, cephalo-thorax: em, dorsal 
muscles; /7, ventral mucles; g, brain; 4, heart; hd, large intestine; Ir, liver; 
mad, small intestine; 09, ostium; oa, ophthalmic artery; oaa@, superior abdominal 
artery; @, gullet; "bi. I-5, pleopods; pl. 6, uropod; gs, pyloric division of 
stomach; sa, sternal artery; #, testis and telson; uaa, inferior abdominal artery; 
ud, 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 sete, 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 (/7), lying one on each side of the stomach 
and anterior end of the intestine. They are formed of 
finger-like sacs or c@ca, 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 heparo- 
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 gid/s, contained in a narrow branchial chamber, bounded 
internally by.the proper wall of the thorax (Fig. 127, ep), 
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- 


x PHYLUM ARTHROPODA 223 


ti b 
ard, aby, azby avb 


Fic. 126. — Respiratory organs of Astacus fluviatilis. In A the gill-cover is removed 
and the gills aadieeurbed: in B the podobranchiz are removed and the outer 
arthrobranchia turned down. a, antennule; a, antenna; a@é,, first; ado, 
second abdominal segment; a7é 7-12, inner arthrobranchie; ard,. 7 12, outer 
arthrobranchie: ef. 5, scaphognathite; 47d. rz-13, pleurobranchiz; Add. 7-73, 
podobranchs; A/. 7, first pleopod; 6-73, thoracic appendages. (From Lang’s 
Comparative Anatonty, after Huxley.) 


lel 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, podobranchie or foot-gills, 
springing from the epipodites of the thoracic appendages, 
from which they are only partially separable; secondly, 
arthrobranchté or joint-gills, springing from the articular 
membranes connecting the thoracic appendages with the 
trunk ; and thirdly, Alewrobranchie 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 avéennary 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 wrinary 
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 ina high state of development. 
The heart (Figs. 125, 127, 4) is situated in the dorsal region 
of the thorax, and is a roughly polygonal muscular organ 
pierced by three pairs of apertures or os#a (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 dlood-sinuses (Fig. 128, 5), spacious 


x PHYLUM ARTHROPODA 225 


cavities lying among the muscles and viscera, and all com- 
municating, mediately or immediately, with the sternal sinus 
(s¢.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 


Fic. 127. — Transverse section of thorax of crayfish, diagrammatic. adm, ventral 
abdominal muscles; 4/, leg; 4, ventral nerve-cord; d, intestine; dé, dorsal 
muscles of abdomen; ¢/. wall of thorax; 4%, heart; &, gills; 4d, gill-cover: 
Z, liver; ov, ovary; fc, pericardial sinus; sa, sx, sternal artery; vs, ventral 
sinus. The arrow shows the direction of the blood-current. (From Lang’s 
Comparative Anatomy.) 


thorax the sternal sinus sends an offshoot to each gill in the 

form of a well-defined vessel, which passes up the outer 

side of the gill and is called the afferent branchial veti: 

(af. br. v; see also Fig. 127). Spaces in the gill-filaments 
Q 


226 MANUAL OF ZOOLOGY SECT 


place the afferent in communication with the efferent 
branchial vein (ef. 6r. v), which occupies the inner side of 
the gill-stem. The efferent branchial veins open into six 
branchio-cardiac veins (br. ¢.v), which pass dorsally in close 
contact with the lateral wall of the thorax and open into the 
pericardial sinus (fed. s). 

The whole of this system of cavities is full of blood, and 
the heart is rhythmically contractile. When it contracts, 
the blood contained in it is prevented from entering the 


-wasG St.s 


Fic 128. — Diagram of the circulation in the crayfish; heart and arteries, scarlet, 
veins and sinuses containing non-aérated blood, blue: those containing aérated 
blood, pink. a, artery; af. br. uv, afferent branchial vein; dr. c¢ v, branchio- 
cardiac vein; of br v, efferent branchial vein; Ad, heart; pcd s, pericardial 
sinus; s, sinus st. s, sternal sinus; 21, ostium with ‘valves: v®, arterial valves. 
The arrows show the direction of the current. 


pericardial sinus by the closure of the valves of the ostia, 
and therefore takes the only other course open to it, viz., 
into the arteries. When the heart relaxes, the blood in the 
arteries is prevented from regurgitating by the valves at their 
origins, and the pressure of blood in the pericardial sinus 
forces open the valves of the ostia and so fills the heart. 
Thus in virtue of the successive contractions of the heart, 
and of the disposition of the valves, the blood is kept con- 


x PHYLUM ARTHROPODA 


stantly moving in one direction, viz., 
from the heart by the arteries to the 
various organs of the body, where it 
receives carbonic acid and other waste 
matters; thence by sinuses into the 
great sternal sinus; from the sternal 
sinus by afferent branchial veins to the 
gills, where it exchanges carbonic acid 
for oxygen ; from the gills by efferent 
branchial veins to the branchiocardiac 
veins, thence into the pericardial sinus, 
and so to the heart once more. 

The nervous system (Fig. 129) con- 
sists of a brain (g) and a ventral nerve- 
cord, united by cesophageal connectives 
(sc). The ventral cord is double, but the 
right and left halves have undergone 
partial fusion, so that the ganglia, and 
in the abdomen the connectives also, 
appear single instead of double. The 
ventral cord contains twelve of these 
ganglia, the first is infra-cesophageal, 
being larger than the others and formed 
by the union of the’ ganglia belonging 
to the last three cephalic and first three 
thoracic segments. All the remaining 
segments have their own ganglia, with 
the exception of the telson, which is sup- 
plied from the ganglion of the preced- 
ingsegment. There is a wsceral system 
of nerves (s) supplying the stomach, 
originating in part from the brain and in 
part from the. cesophageal connectives. 


224 


Fic. 129. — Nervous system 
of Astacus fluviatilis. 
4g, sub-cesophageal gang- 
lion; cs, commissural 
ganglion; g, brain; s, 
visceral nerve; sc, ce- 
sophageal connective; y, 
post-cesophageal commis- 
sure; IV-VIII, thoracic 
ganglia; 7-6, abdominal 
ganglia. (From Lang's 
Comparative Anatomy, 
after Vogt and Yung.) 


228 MANUAL OF ZOOLOGY SECT. 


Sensory organs. —'lhe eyes differ entirely in structure 
from those of any animal that has been described hitherto. 
Each is a compound structure, being made up of a large 
number of distinct elements termed the ommatidea. The 
chitinous cuticle covering the distal end of the eye-stalk is 
transparent, divided by delicate lines into square areas or 
facets, and constitutes the cornea. Each facet of the 
cornea marks the position of the outer end of an omma- 
tideum, optically separated from its neighbours by black 
pigment. 

The antennules contain two sensory organs, to which are 
assigned the functions of smell and hearing respectively. 
The offactory organ is constituted by a number of extremely 
delicate olfactory sete, borne on the external flagellum. The 
auditory organ is a sac formed by invagination of the dorsal 
surface of the proximal segment, and is in free communica- 
tion with the surrounding water by a small aperture. 

Reproduction. — The crayfish is dicecious, and presents a 
very obvious sexual dimorphism. The abdomen of the 
female is much broader than that of the male; the first 
and second pleopods of the male are modified into tubular 
or rather spout-like copulatory organs (Fig. 124,9); and the 
reproductive aperture is situated in the male on the proximal 
podomere of the fifth leg, in the female on that of the third. 

The ¢estis (Fig. 130, B, 4 ~) lies in the thorax, just 
beneath the floor of the pericardial sinus, and consists of 
paired anterior lobes (¢) and an unpaired posterior lobe (w). 
From each side goes off a convoluted vas deferens (vd), 
which opens on the proximal segment of the last leg. The 
sperms are curious non-motile bodies produced into a num- 
ber of stiff processes ; they are aggregated into vermicelli- 
like spermatophores by a secretion of the vas deferens. 

The ovary (A, ov, w) is also a three-lobed body, and is 


x PHYLUM ARTHROPODA 229 


similarly situated to the testis; from each side proceeds a 
thin-walled oviduct (od), which passes downwards, without 
convolutions, to open on the proximal segment of the third 
or antepenultimate leg. The eggs are of considerable size. 

The ova, when laid, are fastened to the sete on the 
pleopods of the female by the sticky secretion of glands 
occurring both on those appendages and on the segments 


B 


Fic. 130. — Reproductive organs of Astacus fluviatilis. A, female; B, male; od, 
oviduct ; oe, external opening of the same; ov, ovary; #4, testis; ~, unpaired 
posterior portion of gonad; wd, vas deferens. (From Lang’s Comparative 
Anatomy, after Huxley.) 


themselves ; they are fertilised immediately after laying, the 
male depositing spermatophores on the ventral surface of 
the female’s body just before oviposition. 

The lobsters, shrimps, prawns, crabs, and hermit-crabs 
all resemble the crayfish in the number and disposition of 
the segments, the presence of a carapace covering both 
head and thorax, the general structure and arrangement of 


230 MANUAL OF ZOOLOGY SECT. 


anes as Be. 


i 


ies 


Fic. 131. —Cancer pagurus. A, dorsal; B, ventral aspect. av#¢. 1, antennule; 
ant. 2, antenna; aéd. 1, abd. 3, abd. 7 abdominal segments; £, eye-stalk; 
4,1, 2.5, legs; map. 3, third maxillipedes. (A, after Bell.) 


x 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 


Fic. 132.— Pagurus bernhardus. cz, chela of first right leg; 7.4, 7.5, fourth and 
fifth legs; ¢, abdominal terga; ~f, 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.’ 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. 


232 MANUAL OF ZOOLOGY SECT 


(Tig. 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 molluse 
which the hermit-crab drags 
about with it." 

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 


133. — Apus glacialis, ventral aspect. 
abd. f, abdominal feet; azz. 7, anten- form of antennary glands. 


nule; azé. 2,antenna; /ér, labrum; wed, : 
mandible; zx, first maxilla; oz, aper- The other sub-class 1S 


ture of oviduct; s / f/, sub-frontal 
Vsheli-giand, *h of thoracic ~©the ~Entomostraca. The 


plate; sh. 
feet; Pie a first thoracic foot. (After 


Bethard) Entomostraca, which are 


even more numerous than 
the Malacostraca, are of comparatively simple organisation, 
and usually of small, often almost microscopic, size. The 


1Qur common American hermit-crab is Hupagurus pollicaris; the 
right chela is still larger than in Pagurus beruhardus of the European coast, 


x 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 


Fic 134.— Three stages in the development of Apus //s, frontal sensory organ; 
L, digestive gland; s, carapace; r-¢, cephalic appendages; I-XIII, body seg- 
ments and appendages. (From Lang’s Comparative Anatomy.) 


shell-glands opening at the bases of the second maxille. The 
larva nearly always leaves the egg as a characteristic form 
called the Mewplius (Fig. 134, A), which occurs also, though 


234 MANUAL OF ZOOLOGY SECT. 


2,Calacalanus 


Fic. 135. — sa, female Cyclops, from the right side; 3, dorsal view; C, antenna of 
male; D, swimming-foot. a@éd zs, first abdominal segment; avf. 7, antennule; 
ant. 2, antenna; c. #4, cephalo-thorax: e, median eye; ev, endopodite; e. s, egg- 
sac; ex, expodite; ov, ovary; pr. 7, pr. 2, protopodite: », rostrum; s. 7, swim- 
ming-feet; ¢ 2, ti. 6, thoracic segments. (After Huxley, Gerstaecker, Hartog, 
and Giesbrecht.) 


x 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. 


* sa 
a 
Fic. 136.— Lepas anatifera. A, the entire animal; B, its anatomy. a’, antennule; 
c, carina; cd, cement gland; /, digestive gland; #, adductor muscle; od, ovi- 
duct; ov, ovary; #, (in B) penis and (in A) peduncle; s, scutum; #, tergum and 
testis; vd, vas deferens. (From Lang’s Comparative Anatonty, 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 Afus 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 metamorphosts, 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 ( Czrripedes), 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 ¢7rr7, borne on the thorax through a 
slit in the enclosing shell. In the barnacles the head-region 
is drawn out into a stalk (A, f) ; 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 


AN 
Cees 
mein 3 Ff 


ANNAN NE HET 
his incan 


Fic. 137.— Peripatus capensis, lateral view. (From Balfour. ) 


beset with numerous conical papilla, each capped with a little chitinous 
spine. The head (Fig. 138) bears a pair of antenne, a pair of eyes, a 


Fic. 138.— Ventral view of head of Peripatus capensis, with antennz, jaws, oral 
papilla, 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 papille are situated a pair of glands, the slime glands. 


238 MANUAL OF ZOOLOGY SECT. 


Fic. 139. — Dorsal view of the internal organs of Peripatus. az, anus; azt, an- 
tennz; dv, brain; cox. gld, coxal gland of the seventeenth leg: ¢ gen, male 
genital aperture ; ze. co, nerve-cord; zeph, nephridia: phar, pharynx ; sal. gid, 
salivary gland; s/. g/d, slime gland ; stot, stomach, (Combined from Balfour.) 


x PHYLUM ARTHROPODA 239 


Each jaw is composed of two curved, falciform, chitinous plates; they 
lie at the sides of the mouth enclosed by a circular lip. The jaws, as 
well as the oral papillze, are developed as modified limbs. The /egs 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 trachex, unbranched or 
little branched tubes, groups of which open on little depressions of the 
integument, the external openings or s¢igmata 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 (sep) 
similar to those of the Annulata, and of a nervous system consisting 
of a brain (477), situated in the head, and two widely separate nerve 
cords (ze. 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 antenne, 
a pair of eyes, and from two to four pairs of jaws; anda 
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 trachez 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 segménts. The anfenne consist sometimes of many, 


oS 


Fic. 140, — Scolopendra, or cen- 
tipede. (From Cuvier’s 4 x- 
imal Kingdom.) 


sometimes of comparatively few seg- 
ments. A pair of eves, situated on 
the dorsal surface of the head, con- 
sist of aggregations of ocelli except 
in Scwdéigerva, 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 maxi@. 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 maxillze 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 
(scu¢a) 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 
the extremity of the pointed ter- 
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 tracheze, 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 vegéons. In the Insecta 
these regions are quite constant in their disposition, and are 
always three in number, — ead in front, ¢horax 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 
R 


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 antenne, a pair of 
mandibles, and two pairs 
of maxille. The antenne 
vary a good deal in size 
and shape in different 
insects. The mandibles 
(Fig. 142, md) lie at the 


Fic. 141. — Periplaneta americana. Lateral «; . 
view of the head and its appendages. sides of the mouth, In 


cerv, one of the cervical sclerites; ey, front of which is a mova- 
eye; gen, gena; man, mandible; max}, 
ree eee ee max*, second pair ble labrum or upper lip 
(4r). Each mandible is 
a single solid piece, and is devoid of palp. The second pair 
of maxille (sz. 2) are united in their basal portions to form 
a lower lip (4adzum). Jointed palpi (fw) are borne both 
by the first pair of maxille (maxillary palpi) and by the 
second (/adial 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 maxillz 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- 


x 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 maxillee 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 ( fara- 


lor 


Fic. 142. — Mouth-parts of the Cockroach. 67, labrum; wd, mandible; x4, an- 
terior pair of maxille; #, mentum; se and mz, outer and inner divisions of the 
second pair of maxille; AZ, labial palp; #2, maxillary palp; st, stipes; s7, 
submentum. (From Lang’s Comparative Anatomy.) 

gloss@). In the Hemiptera (bugs, lice, etc.) the labium is 

modified to form a sucking proboscis enclosing the stylet- 

like mandibles and maxille. 


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 (Aipopharynx). 

In the Lepidoptera, or butterflies and moths, the mandi- 
bles are aborted in the adult and the maxille 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. 


Fic. 143. — Butterfly (Pieris rape), 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 (4zrsws) 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- 


x PHYLUM ARTHROPODA 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 e/¢ra—which, when 
folded up, cover over and protect the delicate posterior 
wings. In the bugs and their allies, the anterior wings are 


Fic. 144.— d, Carpet beetle (Anthrenus scrophulariz) with larva a, 4, 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 Aa/teres or balancers. In the 
bee-parasites the posverior 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. 


Fic. 145. — Culex, mosquito, and larva. (After Guérin 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 (es), which 
dilates behind into a crop (cr) for the storage of food. 
The place of the crop in sucking insects is taken by a 
stalked sac, usually termed the sucking stomach, but which 
is more properly a food reservoir. The essential processes 


247 


PHYLUM ARTHROPODA 


of digestion are carried on in an elongated chamber with 
glandular walls, the chy/e stomach, which may be divided 


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Sometimes there is intercalated between 


the crop and chyle stomach a muscular chamber frequently 
containing chitinous teeth, the gezzard (giz), or proventricu- 


into several parts. 


248 MANUAL OF ZOOLOGY SECT. 


/us. Appended to the chyle stomach at its anterior end are 
in many insects a number of tubular pouches, the hepatic 
ceca (cac). At the junction of the chyle stomach with the 
small intestine, or further back, there open a number (from 
2 to over 100) of narrow tubular appendages, the Mal- 
pighian tubes (ma/p), which are the organs of renal ex- 
cretion. The intestine: is usually 
B elongated, its posterior portion is 
dilated to form a wide rectum, 
acd which opens in the anal aperture 
. on the last segment. Anal glands 
producing an odoriferous secretion 
often open into the rectum. 
The organs of respiration are a sys- 
tem of fine branching tubes, the ¢ra- 


He \{ chee (Fig. 147), which communicate 
ae ae with the exterior through valvular 


apertures known as s#igmaza situated 
A at the sides of the segments. These 
a tracheee form a completely ramify- 
ing system which conveys the air to 
all the parts of the body. The wall 
of the tubes is strengthened by a 
series of spirally wound chitinous 


ag 5 Gage ie enc of“ fibres, each fibre or thread making 


oe ae ae the trachea’ from one to four or five turns around 

Denny.) the tracheze. In some insects, mainly 
those adapted for active flight, the tracheal system is dilated 
in certain parts of the body to form large azr sacs. In the 
aquatic larvee of some insects there is a series of soft external 
simple or divided processes — the ¢racheal gills — attached 
to the abdominal segments, and richly supplied with tracheze 


which have no communication with the exterior. 


x PHYLUM ARTHROPODA 249 


The blood-vascular system is, in comparison with the 
other systems of organs, not very highly developed, the need 
of an elaborate system of vessels being greatly diminished 
by the thorough way in which all the organs are supplied 


with oxygen by means of the 
tracheze. The blood is colour- 
less, or faintly yellowish or green- 
ish. A contractile tubular heart 
divided internally into a row of 
eight chambers by a system of 
valves extends through the abdo- 
men on the dorsal aspect. 

The nervous system (Fig. 148) 
is on the same gereral plan as in 
the Crustacea. There is a double 
supra - cesophageal ganglion or 
brain (47), a sub-cesophageal 
ganglion (7z/), also double, and 
a series of thoracic and abdomi- 
nal pairs of ganglia, which are 
closely united together in the 
middle line. The brain is rela- 
tively large in the higher insects, 
and is divided into several lobes, 
It gives off nerves to the antennz 
and ocelli and the labrum, and 
on each side it gives off a large 
lobe, the optic ganglion, on which 
the compound eye rests. A pair 
of esophageal connectives (conn) 


Fic. 148.— Periplaneta. General 


view of the nervous system. 
abd. 6, sixth abdominal ganglion ; 
ant, antennary nerve ; 47, brain ; 
conn, cesophageal connective ; 
zuf, sub-cesophageal ganglion ; 
opt, optic nerve; thor. 1, thor. 2, 
thor. 3, first, second, and third 
thoracic ganglia. (After Miall 
and Denny.) 


pass backwards on either side of the mouth from the brain 


to the sub-cesophageal ganglia. 


These connectives are very 


short, and, as a consequence, the brain and sub-cesophageal 


Missing Page 


Missing Page 


252 MANUAL OF ZOOLOGY SECT. 


caterpillars, are worm-like, but with well-developed jaws, 
three pairs of jointed thoracic legs, and a number of un- 
jointed stumpy abdominal legs. Eventually the caterpillar 
spins a cocoon of a silky substance, enclosed within which, 
and covered with a tough skin, it passes through a quiescent 
or pupa condition —the condition of the chnsahs. From 
the interior of this the imago subsequently emerges with all 
the parts of the adult insect fully formed. 

In mode of life there is a very considerable difference 
between different orders and families of insects. Some 
are parasites in the strict sense throughout life. This is the 
case, for instance, in the Strepsiptera (bee-parasites), 
the females of which live permanently ensconced between the 
joints of the abdomen of their hosts. The lice and bird- 
lice are external parasites throughout life; bugs and fleas, 
though not adhering to their hosts, are parasites as regards 
their diet. Many insects are parasites in the larval condi- 
tion, though free in the adult state. This holds good, for 
example, of the larvee of the ichneumons, which develop in 
the interior of the bodies of other insect-larve, also of 
the larvee of the bot-flies, which inhabit the alimentary canal 
of mammalian hosts (horses, oxen, sheep, rhinoceroses, 
tapirs). 

In accordance with the high grade of the structure of 
their various systems of organs, insects exhibit a correspond- 
ingly high degree of functional activity. The quantity of 
food consumed and assimilated is great in comparison with 
the bulk of the body, and the energy expended in muscular 
contractions is of very considerable amount. It is estimated 
that while the muscular force exerted by a horse bears a ratio 
of about 0.7 to its own weight (reckoned as 1), the muscu- 
lar force of an insect bears a ratio to its weight of from 
about 14 to about 23. Insects are also distinguished among 


x PHYLUM ARTHROPODA 253 


the Invertebrata by the keenness of their senses. The 
sense of sight is, as we should expect from the elaborate 
character of the optic organs, the most highly developed, 
many insects having been shown by experiment to have a 
keen sense of colour ; but a sense of smell, the seat of which is 
in the antenne, can be shown to exist in a high degree, and 


a b c 


Fic. 149: — Honey bee (Apis mellifica). a@, queen (perfect female) ; 4, worker (im- 
perfect female); andc, drone (male). (After Brehm.) 
the parts about the mouth bear nerve-endings concerned in a 
well-developed sense of taste. A sense of hearing does not 
appear to be universally present, but is well marked in such 
forms as produce sounds. At the same time insects are 
remarkable for the instincts, often leading to results of an 
elaborate character, which guide them in the pursuit of food 


Fic. 150. — Red ant (Formica rufa). Male, worker, and female. 


and the protection and rearing of their young. Among 
the insects which are the most highly endowed in this respect 
are some — the ants, bees, wasps, and termites — which live 
together in organised associations or communities, the various 
individuals composing which are distinguishable into sexua/ 
individuals, neuter workers, and soldiers (Figs. 149 and 150), 


254 MANUAL OF ZOOLOGY SECT. 


each specially organised for the part which it has to play in 
the economy of the community. 


5. THE ARACHNIDA 


The Arachnida, comprising the scorpions and spiders, 
the mites and ticks, the king-crabs, and a number of other 
families, is a much less homogeneous group than the Insecta, 
approaching the Crustacea in the variety which it presents 
in the arrangement of the segments and their appendages. 
In most members of the class, however, there is an 
anterior region of the body —the cephalothorax — repre- 
senting both head and thorax, and a posterior part or 
abdomen, which is typically composed of a number of dis- 
tinct segments ; in some cases cephalothorax and abdomen 
are united. 

Scorpions are inhabitants of warm countries, the largest 
kinds being found in tropical Africa and America. They 
are nocturnal animals, remaining under stones or in holes 
and crevices during the day, and issuing forth at night to 
hunt for their prey, which consists of spiders and insects. 
These they seize with their pincer-claws and sting to death 
with their caudal spine, afterwards sucking their juices. 

There are a number of different species of scorpions, 
divided into several genera, which differ from one another 
in comparatively unimportant points, so that the following 
general description will apply almost equally well to any of 
them. 

A scorpion (Fig. 151) has a long narrow body, in super- 
ficial appearance not unlike that of a crayfish. There is a 
small cephalothoracic shield or carapace, covering over dor- 
sally a short anterior region or cephalothorax. This is followed 
by a long posterior region or abdomen, the terminal part 


x PHYLUM ARTHROPODA 255 


of which in the living animal is habitually carried over the 
back (Fig.151), constituting the “ tail,” at the end of which 
the sting is placed. The cara- 
pace bears a pair of large eyes 
about its middle, and several 
pairs of smaller eyes on the 
antero-lateral margin. The an- 
terior, broader part of the ab- 
domen, which is termed the 
pre-abdomen, consists of seven 
segments, each of which is pro- 
tected by firm, chitinous, dorsal, 
and ventral plates, or #7ga and 
sterna. The tergum and sternum 
of each segment are separated 
from one another laterally by 
intervals of soft skin, except in 
the seventh, where they are 
united laterally for a longer or 
shorter distance. The posterior, 
narrower part of the abdomen, 
known as the fost-abdomen, con-  * 
sists of five segments, each en- Fis. arenes oe 
closed in a complete investing 
ring of hard chitinous matter. Articulating with the last 
segment of the post-abdomen is a terminal appendage, the 
caudal spine or s#vg, swollen at the base and acutely pointed 
at the apex, where open the ducts of two fozson glands. 
The anal opening is situated on the ventral surface of the 
last segment of the post-abdomen, immediately in front of 
the sting. 

The aperture of the mouth, which is very small, is at the 
anterior end of the cephalothorax on its ventral aspect; a 


256 MANUAL OF ZOOLOGY SECT. 


lobe which overhangs it in front is the dedrum. On each 
side of the mouth is a three-jointed appendage — the chelicera 
(Fig. 152, che?) — which is terminated bya chela. Behind 
these are the very large prncer-claws, or pedipalpi ( ped), 
each composed of six podomeres and terminating in power- 
ful chele. The basal joint of each pedipalp has a process 


Fic, 152.—Scorpion. Ventral surface of the cephalothorax and pra-abdomen. 
chel, chelicerz; of, operculum; Zect, pectines; fed, pedipalpi; sézg, stigmata. 


which bites against the corresponding process of the other 
pedipalp, these processes thus performing the functions of 
jaws. Following upon the pedipalpi are four pairs of walk- 
ing legs, each composed of seven podomeres, the last of 
which is provided with a pair of small curved and pointed 


x PHYLUM ARTHROPODA 257 


horny claws. The basal segments of the first two pairs of 
walking legs are modified so as to perform to some extent 
the function of jaws. 

All the six pairs of appendages hitherto described — the 
cheliceree, the pedipalpi, and the four pairs of walking legs 
— belong to the cephalothorax. The first segment of the 
pree-abdomen (Fig. 152) has a narrow sternum, on which 
there is placed a soft rounded median lobe divided by a 
cleft ; this is termed the genital operculum (op.) ; at its base 
is the opening of the genital duct. To the sternum of the 
second segment of the pree-abdomen are attached a pair of 
remarkable appendages of a comb-like shape, — the fectines 
(pect), — each consisting of a stem, along the posterior mar- 
gin of which is a row of narrow processes, somewhat like the 
teeth of a comb; the function of these appendages is doubt- 
ful, but is probably sensory. The remainder of the segments 
of the pree-abdomen, and all those of the post-abdomen, are 
devoid of appendages. The sterna of the third, fourth, fifth, 
and sixth segments of the pra-abdomen, which are very 
broad, bear each a pair of oblique slits—the stigmata 
(s#g) — leading into the pulmonary sacs. 

All the appendages of the scorpion are post-oral in posi- 
tion, and the most anterior — the cheliceree —are probably 
best regarded as corresponding to the antennz of the cray- 
fish, the equivalent of the crayfish’s antennules and of the 
antenne of the cockroach not being present. The pedi- 
palpi would then be the homologues of the mandibles of 
the insect and the crustacean. 

The organs of respiration in the scorpions are in the form 
of pulmonary sacs or book-lungs (Fig. 153, pu), the stig- 
mata or external openings of which have already been 
referred to. Each pulmonary sac is a compressed chamber 


lined with a thin cuticle. The lining membrane is raised 
Ss 


SECT. 


MANUAL OF ZOOLOGY 


258 


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x PHYLUM ARTHROPODA 259 


up into numerous delicate lamin lying parallel with one 
another, like the leaves of a book. Into the numerous nar- 
row spaces between the laminz the air penetrates, and oxy- 
genates the blood which enters the interior of the lamin 
from the ventral blood-sinus. In the United States the 
common scorpion from Florida to North Carolina is Bu thus 
carolinianus ; other species occur in Utah, New Mexico, 
etc., and in Southern California. 

The Spiders (Fig. 154) differ from the scorpions in hav- 
ing the abdomen short, rounded, and unsegmented, in having 
the chelicerze subchelate and 
provided with poison glands, 
the ducts of which open at 
their extremities, and the pedi- 
palpi simple, the terminal joint 
in the male being expanded, 
and the whole appendage be- 
ing used as an intromittent 
organ for the transference of 
the sperm to the genital open- 
ing of the female. At the 
extremity of the abdomen is 
a peculiar apparatus, the a@rachmidium or spinning organ. 
This consists of four or six appendages, the sprnnerets, on 
the surfaces of which open the numerous ducts of the spin- 
ning glands secreting the material of which the web is com- 
posed. The fine threads of viscid secretion issuing from 
the ducts harden on exposure to the air, and are worked up 
into the web by means of the posterior legs. There are six 
or eight eyes on the carapace. The organs of respiration 
are either four pulmonary sacs similar to those of the scor- 
pion, or two pulmonary sacs, and a system of trachee 
resembling those of insects. 


Fic. 154.— Spider (Epeira diadema). 


260 MANUAL OF ZOOLOGY SECT. 


In the Mites and Ticks (Fig. 155) no distinction into 
regions is recognisable, but there are the same series of 
paired appendages as in the scorpions and spiders. The 
cheliceree and pedipalpi, and also the legs, differ somewhat 
in form in different groups, in accordance with differences 
in mode of life. Organs of respiration, when present, take 
the form of tracheze. The cattle tick, Zvodes bovis, is the 
medium of conveyance of the Texas cattle disease. 


Fic. 155.— Cattle Tick Above, nat. size, Fic. 156. — Itch mite (Sarcoptes scabi- 
side view; below, dorsal view, en- ei). (After Leuckart.) 
larged. (From Packard.) 


The Xiphosura or King-crabs, an order comprising the 
single genus Limz/ws, differ widely from the scorpions and 
spiders.’ Limulus (Fig. 157) is a marine arthropod breath- 


1 The Xiphosura, with their fossil allies, the Eurypterida, are by some 
authors regarded as forming a distinct class, by others they are included 
among the crustacea. It seems better to refer them to a distinct class, the 
Merostomata. — AMERICAN EDITOR. 


x PHYLUM ARTHROPODA 261 


ing by gills, in which the body consists of two regions, — the 
cephalothorax and the abdomen. The former is covered 


Fic. 157.— Ventral view of Limulus. 7-6, appendages of cephalothorax; add, 
abdomen; cefh, cephalothorax; oferc, operculum, behind which are seen the 
series of abdominal appendages; ¢e/s, caudal spine or telson. (From Packard, 
after Kingsley.) 


over by a broad shield or carapace, bearing two large com- 
pound and two smaller, simple eyes. The segments of the 


262 MANUAL OF ZOOLOGY SECT. 


abdomen (nine in number) are united together, being cov- 
ered dorsally by a continuous abdominal carapace. At the 
posterior end is attached a very long, narrow, caudal spine 
which is a modification of the ninth abdominal segment of 
the larva. The anterior appendages (Fig. 157) somewhat 
resemble those of the scorpion. In front of the mouth is 
a pair of short, three-jointed, chelate appendages, the che/- 
cer@, at the sides of a labrum or upper lip. Behind these 
follow a series of five pairs of legs, the bases of all of which, 
with the exception of the last, are covered with spines, and 
have the action of jaws, while the extremities are for the 
most part chelate. The first pair of appendages of the 
abdomen are flat plates, which are united together in 
the middle line and together form the broad operculum 
(oferc), overlapping all the posterior appendages ; on its 
posterior face are the two genital apertures. The posterior 
appendages, of which there are five pairs, are thin, flat 
plates to which the gills are attached; each of them is 
divided by sutures into a small inner ramus or endopodite, 
and a larger external ramus or exopodite. A labrum (7os5- 
trum) lies in front of the mouth, and between the sixth pair 
of appendages is a pair of processes, the chilaria. 

In their mode of life the Arachnida present almost as great 
a diversity as'‘the Insecta. Some Acarida are parasites 
throughout life. Most of the other groups of Arachnida 
are predaceous, preying for the most part on insects or 
other arachnids. To capture the insects which constitute 
their food, the majority of spiders construct a web formed 
of the threads secreted by the arachnidium. The primary 
function of the threads formed from the secretion of the 
spinning organ is to constitute the material for the manufac- 
ture of a cocoon for enclosing the eggs, and in some arach- 
nids this is the sole purpose to which they are devoted. In 


x PHYLUM ARTHROPODA 263 


others there is added a nest for the protection of the eggs 
and of the parent itself; this in many cases becomes a per- 
manent lurking place which the spider inhabits at all sea- 
sons, and from which it darts out to capture its prey; in the 
trap-door spider the nest has a closely fitting hinged lid. 
In very many spiders the secretion is used mainly to form 
the web by means of which the prey is snared, with the 
addition frequently of a nest in which the spider lies in 
wait. A subsidiary function of the threads is to aid in loco- 
motion, the spider being enabled by means of them to let 
itself down safely from considerable heights, and even to 
float in the air. 

Some of the mites, as already mentioned, are parasitic ; 
others feed on various kinds of fresh or decaying animal or 
vegetable substances. Most free Acarida are terrestrial, 
some are aquatic. 

The Xiphosura are marine, living from low-water mark to 
the depth of a few fathoms in warm seas, burrowing in sand ; 
their food consists of various kinds of marine annelids. 
Limulus polyphemus inhabits our coast from Florida to, and 
just east of the mouth of, the Kennebec River, Maine. 


SECTION XI.—PHYLUM MOLLUSCA 


GRoupeED together in the Phylum Mollusca are a large as- 
semblage of animals exhibiting as great a diversity in their 
structure as is observable among the Arthropoda. The ani- 
mals popularly known as “ shell-fish,” such as the mussels, 
oysters, and scallops, the whelks, limpets, and snails, to- 
gether with the cuttle-fishes and many others, are compre- 
hended within this extensive phylum. If we compare a 
mussel, a whelk, and a cuttle-fish, we may experience a 
difficulty in finding a sufficient number of features common 
to all three to justify us placing them together in one phylum. 
They are all unsegmented, and are devoid of the continuous 
enclosing crust and the jointed appendages of the Arthro- 
poda; and they all possess, in different forms, a calca- 
reous shell, with, in relation to it, a specially modified area 
of the skin, the mand/e ; but it is only on a careful analysis 
and comparison of the various parts that we are enabled 
to arrive definitely at the conclusion that they all present 
us with modifications of the same general plan of structure. 

Five classes are comprised in the phylum; (1) the Pele- 
cypoda, or bivalved shell-fish, such as mussels, cockles, 
oysters, scallops, etc. ; (2) the Amphineura ; (3) the Gastro- 
poda, including the univalved shell-fish, such as periwinkles, 
whelks, snails, slugs, etc. ; (4) the Scaphopoda or elephant’s 
tusk shells ;' and (5) the Cephalopoda, including the cuttle- 
fishes, squids, octopi, and nautili. 

1 Not further referred to in this work, 


264 


SECT. XI PHYLUM MOLLUSCA 265 


1. THE PELECYPODA 


A Fresh-water Mussel will serve as a convenient example 
of the Pelecypoda.!’ Fresh-water mussels are found in rivers 
and lakes in most parts of the world. Anodonta cygnea, the 
swan-mussel, is the commonest species in England; but 
the pearl-mussel, Unio margari#fer, is found in mountain 
streams, and other species of the same genus are universally 
distributed. Unio complanatus is the common fresh-water 
pearl-mussel in the Eastern United States, and Anodonta 
fluviattis represents the European A. cygnea. 


Fic. 158. — Anodonta cygnea. The entire animal. A, from the left side; B, from 
the posterior end. d. Z. a, dorsal pallial aperture; ex. sph, exhalant siphon; 
4s foot; 7. sph, inhalant siphon; 2g, ligament; 7. mantle; ##z, umbo. (After 

owes.) 


The mussel (Fig. 158) is enclosed in a brown shell formed 
of two separate halves or va/ves hinged together along one 
edge. It lies on the bottom, partly buried in the mud or sand, 
with the valves slightly gaping, and in the narrow cleft thus 
formed a delicate, semi-transparent substance (7) is seen, 


1 The earlier and quite as appropriate name of this class is Lamedlibran- 
chiata, — AMERICAN EDITOR. 


266 MANUAL OF ZOOLOGY SECT, 


the edge of the maué/e or pallium. The mantle really con- 
sists of separate halves or /odes corresponding with the 
valves of the shell, but in the position of rest the two lobes 
are so closely approximated as to appear simply like a mem- 
brane uniting the valves. At one end, however, the mantle 
projects between the valves in the form of two short tubes, 
one (ex. sph) smooth-walled, the other (zx. sf) beset with 
delicate processes or fimbrie. By diffusing particles of 
carmine or indigo in the water it can be seen that a current 
is always passing in at the fimbriated tube, hence called the 
inhalant siphon, and out at the smooth or exhalant siphon. 
Frequently a semi-transparent, tongue-like body (//) is 
protruded between the valves at the opposite side from the 
hinge, and at the end furthest from the siphons ; this is the 
Joot; by its means the animal is able slowly to plough its 
way through sand or mud. When the mussel is irritated, 
the foot and siphons are withdrawn and the valves tightly 
closed. In a dead animal, on the other hand, the shell 
always gapes, and it can then be seen that each valve is 
lined by the corresponding lobe of the mantle, that the 
exhalant siphon is formed by the union of the lobes above 
and below it, and is thus an actual tube ; but that the boun- 
dary of the inhalant siphon facing the gape of the shell is 
simply formed by the approximation of the mantle lobes, so 
that this tube is a temporary one. 

The hinge of the shell is dorsal, the gape ventral, the end 
bearing siphons posterior, the end from which the foot is 
protruded anterior; hence the valves and mantle-lobes are 
respectively right and left. 

In a dead and gaping mussel the general disposition of 
the parts of the animal is readily seen. The main part of the 
body lies between the dorsal ends of the valves; it is pro- 
duced in the middle ventral line into the keel-like foot, and 


XI PHYLUM MOLLUSCA 267 


on each side, between the foot and the corresponding mantle- 
lobe, are two delicate striated plates, the g7//. Thus the 
whole animal has been compared to a book, the back being 
represented by the hinge, the covers by the valves, the fly- 
leaves by the mantle-lobes, the two first and the two last 
pages by the gills, and the remainder of the leaves by the 
foot. 

When the body of the mussel is removed from the shell 
the two valves are seen to be united along a straight Aznge- 
fine (Fig. 159, A, 4.2), by a tough, elastic substance, the 
hinge-ligament (Fig. 158, 27) passing transversely from valve 
to valve. It is by the elasticity of this ligament that the 
shell is opened ; it is closed, as we shall see, by muscular 
action ; hence the mere relaxation of the muscles opens the 
shell. In Anodonta the only junction between the two valves 
is afforded by the ligament, but in Unio each is produced 
into strong projections and ridges, the Ainge-teeth, separated 
by grooves or sockets, and so arranged that the teeth of one 
valve fit into the sockets of the other. 

The valves are marked externally by a series of concentric 
lines (Fig. 158) parallel with the free edge or gape, and 
starting. from a swollen knob or elevation, the umdo (um), 
situated towards the anterior edge of the hinge-line. These 
lines are Zines of growth. The shell is thickest at the umbo, 
which represents the part first formed in the young animal, 
and new layers are deposited under this original portion, as 
secretions from the mantle. 

The inner surface of the shell also presents characteristic 
markings (Fig. 159,A). Parallel with the gape and at a 
short distance from it is a delicate streak (f/. 7) caused by 
the insertion into the shell of muscular fibres from the edge 
of the mantle; the streak is hence called the palial Line. 
Beneath the anterior end of the hinge the pallial line ends 


268 MANUAL OF ZOOLOGY SECT. 


in an oval mark, the anterior adductor impression (a. ad), 
into which is inserted one of the muscles which close the 


Fic. 159. Anodonta cygnea. A, interior of right valve; B, the animal removed 
from the shell. a@. ad, anterior adductor or its impression; @. ”, anterior retrac- 
tor or its impression; ‘ds g, digestive gland, seen through mantle; ea. sph, exhal- 
ant siphon; /Z, foot; g/, gills, seen through mantle; 4. 2, hinge- line; z#. sph, 
inhalant siphon; hd, idney, seen through mantle; &. 0, Keber’s organ, seen 
through mantle; 2, mantle: p. ad, posterior adductor or its impression; fc, 
pericardium, seen through mantle; pi. 2, pallial line ; f2. m, pallial muscles; 
pir, posterior retractor or its impression ; pre, protractor or its impression. 


shell. A similar but larger posterior adductor impression 
(p. ad) lies beneath the posterior end of the hinge. 


The shell consists of three layers. Outside is a brown 
horn-like layer, the pevtostracum (Fig. 160, prs), composed 


XI PHYLUM MOLLUSCA 269 


of conchiolin, a substance allied in composition to chitin. 
Beneath this is a prismatic layer (prc), formed of minute 
prisms of calcium carbonate separated by thin layers of 
conchiolin; and lastly, forming the internal part of the 
shell, is the macre (m) or “mother-of-pearl,” formed of 
alternate layers of carbonate of lime and conchiolin arranged 
parallel to the surface. The periostracum and the prismatic 
layer are secreted from the edge of the mantle only, the 
pearly layer from the whole of its outer surface. The hinge 


pre 


prs 


Fic. 160. —Vertical section of shell and mantle of Anodonta; c#, connective-tissue 
layer of mantle; ¢f.7, its outer epithelium; ¢f.2, its inner epithelium; ”, nacreous 
layer of shell; Jvc, prismatic layer; Avs, periostracum. (After Claus.) 

ligament is continuous with the periostracum, and is to be 

looked upon simply as a median uncalcified portion of the 
shell, which is therefore, in strictness, a single continuous 
structure. 

By the removal of the shell the Jody of the animal (Fig. 
159, B) is seen to be elongated from before backwards, 
narrow from side to side, produced on each side into a 
mantle-lobe (mm), and continued ventrally into a keel-like 


MANUAL OF ZOOLOGY SECT. 


270 


visceral mass (Fig. 161, v. m2), which passes below and in 


Thus each valve of the shell is in 


contact with the dorso-lateral region of the body of its own 


front into the foot (/¢). 


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side together with the corresponding mantle-lobe, and it is 


from the epithelium (Fig. 160, ¢f.7) covering these parts 


that the shell is formed as a cuticular secretion, 


The whole 


XI PHYLUM MOLLUSCA 271 


space between the two mantle-lobes, containing the gills, 
visceral mass, and foot, is called the mande-cavity. 

Of the muscles the largest and most important are the 
anterior and posterior adductors (Figs. 159 and 161, a, ad, 
p. ad), great cylindrical muscles, passing transversely across 
the body, and inserted at either end into the valves of the 
shell, which are approximated by their contraction. 

The ce/om is reduced to a single ovoidal chamber, the 
pericardium (Fig. 161, fc) lying in the dorsal region of the 
body, and containing the heart and part of the intestine. In 
the remainder of the body the space between the ectoderm 
and the viscera is filled by the muscles and connective 
tissue. 

The mouth (Fig. 161, mth) lies in the middle line just 
below the anterior adductor. On each side of it are two 
triangular flaps, the zzternal (2. int. pp) and external (2. ext. 
plp) labial palps; both are ciliated externally. The mouth 
leads by a short gudle¢ (Fig. 162, gw/) into a large stomach 
(st), which receives the ducts of a pair of irregular, dark- 
brown, digestive glands (d. gl). The zntestine (tnt) is given 
off from the posterior end of the stomach, descends into the 
visceral mass where it is coiled upon itself, then ascends 
parallel to its first portion, turns sharply backwards, and 
proceeds, as the recfum (rect), through the pericardium, 
where it traverses the ventricle of the heart, and above the 
posterior adductor, finally discharging by the anus (a) into 
the exhalant siphon or cloaca. The stomach contains, at 
certain seasons of the year, a gelatinous rod, the crystalline 
style. 

The gills consist, as we have seen, of two plate-like 
bodies on each side between the visceral mass and the 
mantle ; we have thus a vzghtand a eft outer (Fig. 161, 2. ext. 
gé) and a vightand a “eftinner gill (2. int. gl). Seen from the 


272 MANUAL OF ZOOLOGY SECT. 


surface each gill presents a delicate double striation, being 
marked by faint lines running parallel with, and by more 
pronounced lines running at right angles to, the long axis of 
the organ. Moreover, each gill is double, being formed of 
two similar plates, the :zzer and outer /amelle, uniting with 
one another along the interior, ventral, and posterior edges 
of the gill, but free dorsally. The gill has thus the form of 
a long and extremely narrow bag open above (Figs. 162 and 
163) ; its cavity is subdivided by vertical bars of tissue, the 
inter-lamellar junctions (2. ¢.7.), which extend between the 
two lamelle, and divide the intervening space into distinct 
compartments or wader tubes (w.t) closed ventrally, but 
freely open along the dorsal edge of the gill. The vertical 
striation of the gill is due to the fact that each lamella is 
made up of a number of close-set gid/-filaments (f) ; the 
longitudinal striation to the circumstance that these fila- 
ments are connected by horizontal bars, the zz¢er-flamental 
junctions (i. f.7). At the thin, free, or ventral edge of 
the gill the filaments of the two lamelle are continuous with 
one another, so that each gill has actually a single set of 
V-shaped filaments, the outer limbs of which go to form 
the outer lamella, their inner limbs the inner lamella. 
Between the filaments, and bounded above and below by 
the inter-filamental junctions, are minute apertures, or ostia 
(os), which lead from the mantle-cavity through a more or 
less irregular series of cavities into the interior of the water 
tubes. The filaments themselves are supported by chitinous 
rods (7), and are covered with ciliated epithelium, the large 
cilia of which produce a current running from the exterior 
through the ostia into the water tubes, and finally escaping 
by the wide dorsal apertures of the latter. The whole organ 
is traversed by blood-vessels. 

Owing to this arrangement it will be seen that the water 


273 


PHYLUM MOLLUSCA 


XI 


tubes all open dorsally into a suprabranchial chamber, 
continuous posteriorly with the cloaca and thus opening on 


the exterior by the exhalant siphon. 


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The physiological importance of the gills will now be 


By the action of their cilia a current is produced 


which sets in through the inhalant siphon into the pallial 


obvious. 


274 MANUAL OF ZOOLOGY SECT. 


cavity, and out at the exhalant siphon. The ingoing cur- 
rent carries with it not only oxygen for the aération of the 


Fic. 163.— Anodonta cygnea. A, transverse section of outer; B, of inner gill; 
C, diagram of gill-structure; D, transverse section of gill-filament. 4. c, blood- 
corpuscle; 4. v, blood-vessels; ch, chitin; /, branchial filaments; ef, epithelium; 
7. f. 7, inter-filamental junction; 2. Z, inner lamella; 2. 2. 7, inter-lamellar junction; 
o. 2, outer lamella; os, external ostium; os', internal ostium; 7, chitinous rods; 
w.t, water tubes. (A, B, and D, after Peck.) 


blood, but also diatoms, Infusoria, and other microscopic 
organisms, which are swept into the mouth by the cilia coy- 


XI PHYLUM MOLLUSCA 275 


ering the labial palps. The outgoing current carries with 
it the various products of excretion and the feces passed 
into the cloaca. The action of the gills in producing the 
food current is of more importance than their respiratory 
function, which they share with the mantle. 

The excretory organs are a single pair of curiously 
modified nephridia, situated one on each side of the body 
just below the pericardium. Each nephridium consists of 
two parts, a brown spongy glandular portion or kidney (Fig. 
162, kd), and a thin-walled non-glandular part or bladder 
(62) communicating with one another posteriorly, while in 
front the kidney opens into the pericardium (7. f. af), and 
the bladder on to the exterior by a minute aperture (7 a), 
situated between the inner gill and the visceral mass. Thus 
the whole organ, often called after its discoverer, the organ 
of Bojanus, is simply a tube bent upon itself, opening at one 
end into the ccelom, and at the other on the external 
surface of the body. 

The czvculatory system is well developed. The heart lies 
in the pericardium and consists of a single ven¢ricle (Figs. 
162 and 164, v) and of right and left auricles (au). ‘The 
ventricle is a muscular chamber which has the peculiarity 
of surrounding the rectum (Fig. 162); the auricles are 
thin-walled chambers communicating with the ventricle by 
valvular apertures opening towards the latter. From each 
end of the ventricle an artery is given off, the anterior 
aorta (Fig. 162, a. ao) passing above, the posterior aorta 
( p. a0) below the rectum. From the aortz the blood passes 
into arteries (Fig. 164, a7¢. z,art. 2) which, ramifying all over 
the body, finally form an extensive network of vessels, many 
of which are devoid of proper walls and have therefore the 
nature of sinuses. 

The nervous system is formed on a type quite different 


276 MANUAL OF ZOOLOGY SECT. 


from anything we have yet met with. On each side of the 
gullet is a small cerebro-pleural ganglion (Fig. 162, ¢. pl. 
gi) united with its fellow of the opposite side by a nerve- 
cord — the cerebral commissure passing about the gullet. 
Each cerebro-pleural ganglion also gives off a cord, the cere- 
bro-pedal connective, which passes downwards and backwards 
to a pedal ganglion ( pd. gn) situated at the junction of the 


Fic. 164.— Diagram of the circulatory system of Anodonta. Vessels containing 
aérated blood red, non-aérated blue. @/ 47. v, afferent branchial veins; ao, 
aorta; art.s, artery to mantle; av 2, artery to body generally; az, auricle; 
ef. br. 7, efferent branchial veins; 2p. v, nephridial veins; fc, pericardium; wv, 
ventricle; v.c, venacava. The arrows show the direction of the current. 

visceral mass with the foot; the two pedal ganglia are so 

closely united as to form a single bilobed mass. From each 
cerebro-pleural ganglion there further proceeds a long cere- 
bro-visceral connective which passes directly backwards 


through the kidney, and ends in a wsceral ganglion (v. gn) 


XI PHYLUM MOLLUSCA 277 


placed on the ventral side of the posterior adductor muscle. 
The visceral, like the pedal ganglia, are fused together. 

Sensory organs are poorly developed, as might be expected 
in an animal of such sedentary habits. In connection with 
each visceral ganglion is a patch of sensory epithelium form- 
ing the so-called olfactory organ or, better, osphradium, 
the function of which is apparently to test the purity of 
the water entering by the respiratory current. Close to the 
pedal ganglion a minute otocyst is sometimes found. Sen- 
sory cells — probably tactile — also occur round the edge of 
the mantle, and especially on the fimbriz of the inhalant 
siphon. . 

The sexes are separate. The gonads (Fig. 162, gom) are 
large, paired, racemose glands, occupying a considerable 
portion of the visceral mass amongst the coils of the intes- 
tine ; the testis is white, the ovary reddish. The gonad of 
each side has a short duct which opens (g. af) on the sur- 
face of the visceral mass just in front of the renal aperture. 

In the breeding season the eggs, extruded from the gen- 
ital aperture, pass into the suprabranchial chamber and so to 
the cloaca. There, in all probability, they are impregnated 
by sperms introduced with the respiratory current. The 
oosperms are then passed into the cavities of the outer gills, 
which they distend enormously. Thus the outer gills act as 
brood-pouches, and in them the embryo develops into a 
peculiar larval form known as Glochidium. 

The Glochidium (Fig. 165) has a bivalved shell produced 
ventrally into incurved hooks beset with spines. After a 
time it is ejected from the mantle-cavity and falls to the 
bottom of the water, where it lies until it has the oppor- 
tunity of becoming attached to the gills or skin of a fish. 
Fixed firmly by means of the hooked valves the larva remains 
as an external parasite for about ten weeks, becoming en- 


278 MANUAL OF ZOOLOGY SECT. 


cysted by an overgrowth of the skin or mucous membrane 
of their host. In the meantime a metamorphosis is taking 
place, and when the young mussel becomes free it has begun 
to assume the form and structure of the adult. 

The majority of the members of the class Pelecypoda 
resemble the fresh-water mussel in the main features above 
described. They are bilaterally symmetrical, laterally com- 
pressed, with a mantle consisting of paired right and left 
lobes, secreting a bivalved calcareous shell. A distinct head 
is never present. There is on the ventral surface a muscu- 


D.--~ 


Fic 165.— A, advanced embryo of Anodonta; B, free glochidium. //, provisional 
byssus: s, shell; sh, hooks ; sv, adductor muscle ; so, sense organs; w, cilia. 
(From Korschelt and Heider’s Embryology. ) 


lar foot ; there are two abductor muscles, and there are two 
pairs of gills. But, on looking over a collection of shells of 
various bivalves, it will be found that certain of them differ 
from that of the fresh-water mussel in not having the two 
valves of the shell alike. This inequality between the 
two valves of the shell is strongly marked in the scallops, 
and even more so in the oysters. The oysters are also 
examples of Pelecypods, which have only one adductor 
muscle instead of two; and the oyster, which is unable to 


XI PHYLUM MOLLUSCA 279 


move from place to place, and in the case of some species is 
permanently fixed to some rock or other solid body by the 
substance of the larger valve, has no foot. The inhalant 
and exhalant siphons are sometimes absent, sometimes 
much longer than in the fresh-water mussel, as in the clam 
(Mya arenaria). Posterior to the foot there is in many 
Pelecypods a gland termed the dyssus gland, secreting silky 
threads which serve to attach the animal temporarily or 
permanently, as, for example, in the sea mussel (AZpilus) 
(Fig. 166). In most Pelecypoda the gills (ctenidia, p. 271) 


Fic. 166.— Mytilus edulis, attached by byssus (By) toa piece of wood. F, foot; 
S, exhalant siphon. (From the Cambridge Natural History.) 

are simpler in character than in the fresh-water mussels. 

In one group, Protobranchia (Nucula, etc.), they take the 

form of a pair of plume-like organs, and are primitive in 

shape and structure. 

A remarkably modified member of this class of molluscs 
is the ship-worm, Zervedo, which is very destructive to ships’ 
timbers, piles of jetties, etc. The valves of the shell are 
extremely small, and the general surface of the mantle 
secretes a continuous shelly tube lining the burrow in which 
the elongated worm-like body of the mollusc lies. Highly 


280 MANUAL OF ZOOLOGY SECT. 


developed eyes are present in a row round the edge of the 


Fic. 167.—Teredo navalis, in 
a piece of timber. P, pallets; 
SS, siphons; T,tube; V, valve; 
of shell. (From the Caméridge 
Natural History.) 


mouth in the scallop (/ecten) and 
a few others. 

Although none of the Pelecy- 
poda are microscopic, they present 
a considerable range in size, from 
the little fresh-water Cyc/as, about 
1 cm. long, to the giant clam (Z77- 
dacna gigas) of the Indian and 
Pacific Islands, which is sometimes 
60 cm. (two feet) in length and 
500 pounds in weight. The nacre- 
ous inner layer of the shell of the 
pearl oyster (JA/eleagrina marga- 
ritifera), which is of unusual thick- 
ness, constitutes the “ mother-of- 
pearl” of commerce, employed 
for many ornamental purposes. 
Pearls are deposits of nacre formed 
around sand grains or other foreign 
bodies, either between the mantle 
and shell, or in the soft parts in 
the pearl oyster and the pearl mus- 
sel (Unio complanatus), etc. 

Most Pelecypoda are sluggish 
in habit, progressing only by slow 
movements of the foot, and some 
are permanently fixed during adult 
life by the byssus. The scallops, 
however, swim freely by clapping 
the valves together. The cockles 
(Cardium), Trigonia, etc., jump 
by sudden movements of the foot, 


XI PHYLUM MOLLUSCA 281 


and the razor-fish (So/em) jerks itself forward by suddenly 
withdrawing its very large foot, and thus ejecting water 
through the siphons. The only parasitic genus is /7/0- 
valva, found in the gullet of a Holothurian. 

Pelecypoda are abundant both in fresh water and the sea ; 
the marine forms are mainly littoral. None are pelagic or 
terrestrial. 


2. THE AMPHINEURA 


A class of molluscs which comprises only a small number of repre- 
sentatives, most of them of rare occurrence and of simple organisation, 
is the Amphineura. With the exception of the Chitons these have no 
shell and are devoid of a foot, so that though probably related to the 
more typical molluscs, and to be referred to the same phylum, they are 
wanted in some of the most characteristic features exhibited by the 
members of the other classes. All the 
Amphineura are bilaterally symmetri- 
cal, more or less elongated molluscs, 
with the mouth at the anterior and the 
anus at the posterior end. 

The commonest, as well as the most 
highly organised, of the Amphineura 
are the Chitons, marine molluscs which 
are to be found adhering firmly, like 
limpets, to rocks and stones on the “4 
seashore, or in deep water. The body 
is dorso-ventrally compressed, convex 
above, and presents below a broad flat 
foot (narrow in Chitonel/us), which acts 
not only as an organ for effecting creep- 
ing movements, but also as a sucker for 
enabling the animal when at rest to Fic. 168 —Chiton spinosus, dorsal 

: s view. (From the Caméridge 
adhere firmly, like a limpet, to the sur- Natural History.) 
face ofa rock. The most remarkable 
external feature of the Chiton is the presence on the dorsal surface of 
a calcareous shell (Fig. 168), made up of no fewer than eight trans- 
versely elongated pieces or valves, arranged in a longitudinal row, artic- 


282 MANUAL OF ZOOLOGY SECT. 


ulating together and partly overlapping one another. They are some- 
times partly, sometimes completely, covered over by the mantle. Each 
valve consists of two very distinct layers, a more superficial and a deeper, 
the latter formed of a compact calcareous substance, the former perfo- 
rated by numerous vertical canals for the lodgment of the sense organs, 
to be presently referred to. External to the valves the dorsal integu- 
ment (mantle) of Chiton and its allies is usually beset with a number 
of horny or calcified tubercles and spicules. The mantle develops only 
very slight lateral flaps, and under cover of these are a series of small 
gills or ctenidia (Fig. 169, c¢z), to the 
number of fourteen to eighty. The 
mouth and anus are both median, situ- 
ated at the anterior and posterior 
extremities respectively. 

The buccal cavity always contains a 
well-developed odontophore. The in- 
testine is elongated and coiled. There 
are salivary glands and a large paired 
liver. There is a well-developed heart, 
consisting of a median ventricle and 
two lateral auricles. The pericardial 
cavity in which it lies is a space of con- 
siderable extent in the posterior region 
of the body, below the two last valves 
of the shell. 

carn The central part of the nervous sys- 
Fic. 169.—Chiton, ventral view. tem comprises an cesophageal nerve- 

an, anus; cfen, ctenidia; /t, foot; meee 3 

mant, mantle edge; 70, mouth. ring, consisting of a thicker dorsal 

(Alter: Relseneet:) cerebral portion not differentiated into 


ganglia, and a thinner ventral ézeccal commissure. Two pairs of longi- 
tudinal nerve-cords, pedal and fallial, 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 mcresthetes and the megales- 
thetes, lie in the canals already mentioned as occurring in the super- 


XI PHYLUM MOLLUSCA 283 


ficial layer of the shell valves. The megalaesthetes may take the form 
of eyes, with cornea, lens,spigment layer with iris, and retina. 

There are two symmetrical nephridia (Fig. 170) opening internally 
into the pericardium by a ciliated funnel-like opening (7. perz. ap), and 


Fic. 170. —Chiton, nephridial and genital systems. am, anus; cten, ctenidia; gen. 
ap, genital aperture; gox, gonad; goxod, gonoduct; mmo, mouth; neph. af, 
nephridial aperture; 7. ferz. af, aperture from nephridia to pericardium. (From 
Simroth, after Haller and Lang.) 


opening on the exterior (wepfh. af), 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 (gow) are similar in appearance, 


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as 


286 af .. 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 


Fic. 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 cana/, formed in connection with the development 


Fic. 173. — Longitudinal median section of the shell of Triton nodiferus. 


of a spout-like prolongation of the mantle, the sphon, 
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 epfiphragm 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 4/édysza (the “Sea-hare’’) and 


Fic. 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 (AHeteropoda and Preropoda); 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 zeck. 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 zuérovert, 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 (Pu/monata) 
(Fig. 171) the eyes are elevated on the 
extremities of a second, longer pair of 
tentacles (vc. zent) 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 mand/e-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 
and egress of water. In some Gastro- 


Fic. 175. — Shell of 
Terebra oculata. 


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. 


ul 


290 MANUAL OF ZOOLOGY SECT. 


The /oo¢ 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 


Fic. 176. — Cyprea moneta (Cowrie). Showing the mantle, provided with marginal 
tentacles, partly enveloping the shell. 8», 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 


ee 
vets 
ef 

% 9, 


Fic. 177.—Doris (Archidoris) tuberculata. a, anus; dr, branchie; , 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 (Af/ysta), the foot 
develops a pair of lateral lobes, the efzpoaia, 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 c/enzdia, usually plume- 
shaped appendages consisting of a central stem bearing two 


Fic. 178. — Shell- sa Ptero enone SA,f, fins; 2, liver; 0, ovary; sh, shell. 


From Cooke, after Souleyet.) 


rows of compressed filaments or lamellee, 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 Zolis, or as in Dorts (Fig. 177), forming a circlet 
surrounding the anus, or, as in Pleurophyliidia, a row on 
each side beneath the mantle-flap. 


292 MANUAL OF ZOOLOGY SECT. 


In the limpets (Pr/e/a and its allies!) (Fig. 179) the 
true ctenidia are represented only by a pair of vestiges, 
and respiration is carried on by a number of secondary 
branchiz (g. 7) in the form of lamellz 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 


Ss 


aig 


Fic. 179. — Patella vulgata, seen from the ventral side. 7, foot; g.7, circlet of 
gill lamella; 7. e, edge of the mantle; #7, attachment muscle; s/, slits in the 
attachment muscle; s&, shell; 7, efferent branchial vessel; z', aorta; ve, smaller 
vessels. (From the Cambridge Natural History.) 

for a small rounded opening, has the function of a pu/- 

monary sac or lung (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 -femea testudinalis. 


XL PHYLUM MOLLUSCA 293 


Secondary gills— vascular processes of the wall of the 
mantle-cavity. 


Puly 


Fic. 180.— Pulmonary cavity and related parts in a slug (Limax). aort, aorta: 
aur, auricle; neph, nephrin: eric, pericardium, laid open; px/. af, pul- 
monary aperture; 4z/. v, pulmonary vein with its ramifications; ect, 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 éuccal 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, vad), beset 


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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 


XI PHYLUM MOLLUSCA 297 


body (Figs. 182, 183, 185, 187) is bilaterally symmetrical. 
The foot, instead of extending along the ventral surface 


Fic. 182.— Sepia cultrata. Entire aval picwed from the dorsal aspect. New 
ealand. 


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), 


Fic. 183.— Nautilus pompilius, diagrammatic lateral view of a female specimen 
enclosed in its shell. cart, cartilage; cten, ctenidia; 4d, hood; 7u/, funnel; 
jaws, jaws; mant, mantle: mant', dorsal mantle-fold overlapping the coil of the 
shell; zs, position of lateral mass of muscle; zd, nidamental glands; seft, 
first septum; szfh, siphuncle. (After Keferstein.) 


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 /wzne/, a wide tube through which water is 


Fic. 184. — Section of the shell of Nautilus pompilius, showing the septa (s, s), the 
septal necks (s. #., 5. 2.), the siphuncle (sz, represented by dotted lines), and the 
large body-chamber (ck). (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. 


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 s7phuncle — 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. Its shell has been found 


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 Sprru/a, 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- 
duced into a horny or 
calcareous plate, the 
pro-ostracum. In the 
cuttle-fish of the Medi- 


Fic. 185.— Spirula peronii, 
lateral view. d, terminal 
sucker; 7, funnel; sy, s9, 
projecting portions of the 
shell, the internal part of 
which is indicated by dotted 
lines. (From Cooke.) 


Fic 186.—Shell of 
Sepia cultrata, 
posterior view, 
reduced. 


septa of the 


terranean Sea (Sef7a) 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 laminz of calcareous 
composition, between which are interspaces 
containing gas. The spine-like projecting 
point represents the guard, and the main 
substance of the shell is to be looked upon 
as the pro-ostracum and phragmocone, the 
latter being represented by the calcareous 


302 MANUAL OF ZOOLOGY SECT. 


lamella. In Zofigo' (the squids) the shell (Fig. 187, B) is 
long, narrow, and completely horny; it corresponds to the 
pro-ostracum, the phragmocone being entirely absent. 


Fic. 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 47vonauta 
there is no shell in the male, but the female has an external 
shell (Fig. 188) of a remarkable character. This is a deli- 


1 Our common American species is Lolige peal, 


XI PHYLUM MOLLUSCA 303 


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. 


Fic. 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, 


Fic. 189. — Chromatophore of Sepia, magnified. #zc, nuclei in wall of sac; pig, 
pigment ; rad. mus, .adiating strands of muscle, (After Vogt and Jung.) 

so that, when the walls of the cavity coutract, 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 (c/n) are plume- 
like, and are either two (Dibranchiata) or four (Zetra- 
branchiatfa) 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 


mantl.cart 
liv 


St 
inka. 


acnid. 


Fic. 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. zd, accessory nidamental glands; az, 
anal aperture with its lateral appendages; “4, membranous fold attaching the 
ctenidium to the wall of the mantle-cavity ; 7/, external opening of funnel: zu. 
cart, infundibular cartilage; zz. s, ink-sac; zk. d, ink-duct; dzg, ligamentous 
band which extends from the anterior wall of the mantle-cavity to the ovary, cut 
across; /2v, liver; 2 cten, left ctenidium ; 7. meph, left nephridial aperture : Z.xcd, 
left nidamental gland; Z. s¢. g, left stellate ganglion: ant. cart, mantle cartilage 3 
mo, mouth; mzs, neck muscles; ov, ovary ; ovzd, oviduct; rec, rectum. 


x 


306 MANUAL OF ZOOLOGY SECT. 


the terminal part of the intestine close to the anal aperture 
is the duct of a peculiar gland — the znk gland (Fig. 193, 7). 
This secretes a black substance, the 7k, 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 


HAAN 
C.visc.ab cote 72. 


Yb.t neph af 


Post os 


Fic. 191. —Nautilus pompilius, interior of mantle-cavity of a male specimen with 
the postero-ventral wall reflected. a. 2. neph. af, oral left nephridial aperture ; 
an, anus: cten, ctenidia: 2. ¢ af, left reproductive aperture: /. av/. os, left oral 
osphradium ; 2 vise af, left viscero-pericardial aperture; szazzz, flaps of mantle; 
pen, penis; p 2. neph ap, aboral left nephridial aperture: 2. r. neph. ap, aboral 
right nephridial aperture; fost. os, aboral osphradia; ». wzsc. 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, 


Fic. 193. — Sepia officinalis, enteric 
canal. a, anus; 6. d@, one of the 
bile ducts; 4 7, buccal mass; c, 
cecum; z, ink-sac; 7. d, ink-duct; 
J, jaws; 2, 2, liver lobes; @, cesoph- 
agus; #, pancreatic appendages}; 


Fic. 192. Sepia officinalis, jaws. A, zz vr, rectum; s. g, salivary glands; 
situ, B, removed and slightly enlarged. st,stomach (From the Cambridge 
(From the Cambridge Natural History.) 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-b00k of Zoology, 
i, PP- 433, 437-) 


308 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 (Zefra- 
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 acirclet 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 


Fic. 194. — Oral surface of a male (A) and female (B) Nautilus pompilius in an 
expanded state, 4 natural size, linear. a@, shell; 4, 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; 7, superior, &, inferior, ophthalmic tentacle; /, eye; 
2, lamellated organ on the posterior inner lobe of the female; wz, paired lami- 
nated organ on each side of the posterior inner lobe of the female; 0, funnel; 
p, 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 


Tue Phylum Chordata comprises all the vertebrate ani- 
mals (fisheS, amphibians, reptiles, birds, and mammals), 
together with the Urochorda or Ascidians, 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, 
either in the young condition, or throughout life, of a 
structure termed the chorda dorsalis or notochord. ,This is 
a cord only of 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- 
preys and hag frstres) it becomes in the adult replaced more 
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 vewvrocele, tr the-mrtertor-ofthe—bery, 
Jping above the central nervous system. 


310 


SECT. XII PHYLUM CHORDATA 


1. THE 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 and its allies, which occur in 
shallow water on the coasts of most of the 
warmer parts of the world, and two are deep- 
sea animals, Khabdopleura and Cephalodiscus. 

Balanoglossus (Fig. 195) is a soft-bocied, 
cylindrical, worm-like animal, the surface of 
which is uniformly ciliated. It is divisible into 
three regions: in front there is a large, club- 
shaped, hollow organ — the frodoscis ; imme- 
diately behind the proboscis and encircling its 
base is a prominent fold—the co//ar; the 
third region or én 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, £7, Fig. 196, prod) has muscular walls; 
its cavity opens on the exterior usually by 4 
single minute aperture—the prodoscis pore 
(Fig. 196, prob. po) —rarely by two. The 
collar (Fig. 195, co) 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. 


311 


prominences formed by 


gion: co, collar; ge, genital ridges; hep, 


Entire animal. 


Fic. 195. — Balanoglossus. 


_6r, branchial re 
hepatic caeca; Ar, proboscis. 


(After Spengel.) 


312 MANUAL OF ZOOLOGY SECT. 


On the dorsal surface of the anterior part of the trunk is a double 
row of small slits —the g2//-s/its (Fig. 195, 67,) — each row situated in 
a longitudinal furrow; these slits increase in number throughout. The 


aors.v 


Fic. 196. —Balanoglossus. Diagrammatic sagittal section of anterior end. card. 
sg, cardiac sac; dv, diverticulum (supposed notochord); dors. 2, dorsal nerve 
strand: dors. siz, dorsal sinus; dors. v, dorsal vessel; 220, mouth; prod, pro- 
boscis; prob. po, proboscis pore; prod. skel, proboscis skeleton; vent. 2, ven- 
tral nerve strand; zext 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, z0,) 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 caca (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 lies 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, dv), 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 sofochord of the typical 
Chordata. 

There is a blood-vascular system with dorsal (dors. v) and ventral 
(vent. v) longitudinal trunks. The nervous system consists of dorsal 
(dors. 2) and ventral strands (vezd¢. 7), 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 7ornarza, which 
is somewhat like an Echinoderm larva, with 9 pair of ciliated bands, 
one of which is considered pree-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 ¢runk with two distinct lateral cavities; and in the presence 
of astructure resembling a notochord with the same relations to the 


314 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 UROCHORDA 


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? 
(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 

> nt it on one side is a second of similar character. 
Fic. 197.--Ascidia, en- ‘ 

tire animal seen from The former aperture is termed the ova/, the 
aie Lean eh side. latter the aériad. 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 Ascidta cadlosa, which lives in 
deep water off the Maine coast. 


XI PHYLUM CHORDATA 315 


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. 


Fic. 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 alimen- 
tary canal, etc. a, anus; atr. af, atrial aperture; exd, endostyle; gon, gonad; 
gonod, gonoduct; hyp, hypophysis; 2yf.d, duct of hypophysis; #anz, mantle; 
ue. gn, nerve-ganglion; @s. af, aperture of cesophagus; ov. af, oral aperture; 

pA, pharynx; stom, stomach; tev, tentacles; fest, test. (After Herdman.) 


The outer layer of the body-wall is composed of a tough translucent 
substance forming a thick des¢ or funze (Fig. 198, est). This proves, 


316 MANUAL OF ZOOLOGY SECT. 


when analysed, to consist largely of the substance ce//ose, 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 (mant), 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 ova/ 
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 
(a¢r. 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 pharyviex 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 


4 


XII 


PHYLUM CHORDATA 317 


this structure, consisting of the two ventral longitudinal folds with the 
groove between them, the term ezdosty/e is applied. The cells covering 


orsiph 

lent LY \ ner 
A 

TT “¥P 


stigm 


i] 
| 
i 


ECCI OE 


alr.siph 


ou) 


LARA 


alrcav 
(dors.v 
: an 


L, it H+-|-gornod 
{i recl 


_OV 


| wesc.or 


brecar 2 
—— [-OES 


ht 


card.viso 


Fic. 199. — Ascidia, diagram of longitudinal section from the left-hand side, the test 


and mantle removed. atv. cav, atrial cavity; afr. siph, atrial siphon; 47. car, 
branchio-cardiac vessel; card. visc, cardio-visceral vessel; gonod, gonoduct; 
hi, heart; 4yf,hypophysis; manzt, mantle; x. gv, nerve-ganglion; @s, cesopha- 
gus; ov, ovary; rect, rectum; s¢zg, stigmata; stow, stomach ; ¢ezz. tentacles; 
test, testis; ty. v, transverse vessel; vent. v, ventral vessel; vzsc. dx, viscero- 
branchial vessel. (After Herdman.) 


the endostyle are large cells of two kinds — c*/rated cells and gland cells, 
—the former beset at their free ends with cilia, the action of which is 


IN BUNN. 
ouseek JERMA 


318 MANUAL OF ZOOLOGY SECT. 


to drive floating particles that come within their influence outwards 
towards the oral aperture, the latter secreting and discharging 4 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 feri-pharyngeal ridges, the groove between them is the 
peri-pharyngeal groove. Dorsally, 7.e,, opposite the endostyle, the 
posterior peri-pharyngeal ridge passes into a median, much more 
prominent, longitudinal ridge, the dorsa/ /amina, which runs along the 
middle of the dorsal surface of the pharynx to the opening of the 
cesophagus. 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 cesophagus. 

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, fend). 

The cesophagus 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 ava/ 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 ina 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 sz- 
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 strize presenting somewhat the appearance of the fin-rays 
of a fish’s fin. At the anterior end are three processes, the adhesive 
papille. In the axis of the tail is the notochord (oto), 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 cau- 
dal portion of the nerve-cord, and at the sides are bands, or muscular 
fibres. Inthe trunk the nerve-cord is dilated, and, further forwards, 
expands into a vesicle, the sezse vesicle (sens. ves) with an otocyst (oto) 
and a well-developed eye (eye). The enteric canal is distinguishable 
into pharynx, cesophagus, stomach, and intestine. The pharynx opens 
on the exterior by the mouth: in its ventral floor the endostyle (ed) 
has become developed; its walls are pierced by stigmata, the number 
of which varies; a ciliated sac opens into 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 asingle aperture (a/v). 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 papillee, and begins to undergo the redrogressive 
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. ‘Lhus, 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 


ree TAG 


PS TSTe EPR eaeet 
Se 


Fic. 200 — Free-swimming larva of Ascidia mammillata, lateral view. adh, adhe- 
sive papille; a/z, alimentary canal; afr, atrial aperture; cz/. gr, ciliated groove; 
end, endostyle; eye, eye; med, nerve-cord; note, notochord; ofo, otocyst; sexs. 
ves, sense vesicle; st7g, 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 Comeposite 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 


X XII PHYLUM CHORDATA 321 


Fic. 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. adh, adhesive papillz; atr, atrial cavity; cz. gv, ciliated groove; 
end, endostyle; ht, heart; med, ganglion of trunk; ~. gx, nerve-ganglion; 70Z0, 
notochord; ov, oral aperture; rect, rectum; sews és, sense vesicle; st7g, stig- 
mata; séo/, stolon; 4, tail. (From Korschelt and Heider, after Seeliger.) 


Y 


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 4ppendicula- 
ria. It never becomes fixed and retains permanently its chordate 
characteristics. 


Fic. 202. — Botryllus violaceus. +, oral apertures; c/, 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 VERTEBRATA 


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 Cramiata. 


A. THE ACRANIA 


This isolated group, the Acrania, comprises only a single family, the 
two genera (Branchiostoma and Asymmetron) 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 5.3 cm. 


ZEpl 
a P alrp venk fr 


SS 


Fic. 203. — Amphioxus lanceolatus. A. ventral; B, side view of the entire animal. 
an, anus; atrf, atriopore; cd. f, caudal fin; ez, cirri; dors. f, dorsal fin; 
dors. f. r. dorsal fin-rays; gon, gonads; mt/, metapleure; myom, myomeres; 
nch, notochord; ov. Ad, oral hood; vent. /, ventral fin; vent /. 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 fin (dors. f); this is continued round the 


324 MANUAL OF ZOOLOGY SECT, 


posterior end of the body and extends forwards, as the ventral fin 
(vent. f), 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 (mépl), 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. hd), the edge 
of which is beset with numerous tentacles or cz77z, The oral hood 
encloses a cup-shaped cavity or vestibule, al the bottom of which is the 
mouth (Fig. 204, mth). Immediately in front of the anterior termina- 
tion of the ventral fn and partly enclosed by the metapleures is a 
rounded aperture of cunsiderable size, the atr7pure (atrp), and a short 
distance from the posterior extremity of the body is the aus (an), 
placed unsymmetrically on the left side of the ventral fin. The post- 
anal portion of the body is distinguished as the zaz?. 

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, #ch), 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 


PHYL 


325 


M CHORDATA 


U 


XII 


“*sa[9bjU9] 1e[3A 


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:proysojou ‘ys tsarauoAur ‘mcodue Sy nous Sygue t1BAt] “47 
-uy [esiop '4/ “sop ‘uy yesiop (f ‘s4op Swo[sd "7H9 1M 
‘244g threw ‘1 4 4g seljaweEy jeryouviq Aiwpuoges ‘2 Y¢2s 


ND 479 


raunsayul yer :peuos ‘was sjods-aha ‘gs ‘a ‘ays000;eydaoua 
uvo [e.yua. ‘9 -ywa2 uy [epnes /"pxvs ‘por yeryouerq Aawpuooes 
g :Aavund ‘1 gas 4g “jauuny uaroig "4g tsyapo jerpouesq ‘77 4g 


"9°72 sSumyaa ‘73a ‘tKex-uy pexyuaa (2 of guaa Suy peryuea {77222 ‘p09 
‘g fyo serpiaydou ‘ygu 
‘wo ua hex 


tureig ‘49 :a1odoye ‘gzgv :uotesuojoid zoraysod sir‘ 2gv ts uiniijze “470 ‘snue ‘uo “‘snxorqdury jo Aurojeur ay) jo weiseiq — ‘hoz “O1q 
EIQ ey. L 4 K I r Rote : : 


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Rigas See ebee ¢ 
KR AH an AN ow S 77) 
$2 : ¢ & 
SP be 2 than SSB a 
SB Se Se A ne 
Sav, BMa as" ex 
Foge 8 Bi = 9 Es 
ec z 8 5 
ey te ery 2 Be 
A“Aoo Ss — ~¢ £ € SS e ee 
noes Sem 8-3 4, 
fe 6. Uo Bee ge 
Gee Re ee kee 
Seg 8 SRESC 2 "EAS 2 
von sS a vo =I a Yo 
BS Bo BPE Seo PES 
aseeEee of 4ad SE 
Oo. Be a Sh £ Eo 


— 


OY 
Sele inrenareete 


Sos0p 


ported by delicate oblique 
rods of a chitinoid mate- 


(or. r). 


The dorsal fin is supported 


rial, the g@d-rods 


and the 


ventral fin by a double 


by a single series, 


AyD 


Figen’ 


Asi 


(dors. 


short rods of con- 


series, of fiz rays 
nective tissue. 


fr); 


The mouth (zh), as 


X 
AY 


zwdasug 


(12°F sSfssoz2 104 
e358 3 8 
nBooD Ss 
Vo Goes 
Ago e ee 
gPREE RB 
Ce aie 
Lo ee 
6824 o 
= eh BE Os 
Bee ws HG 
BO ee ay 
BHO ya 
a) 
Sean 
DBP ay 8 
ov Ob § 
esoQegS 
oO Oo. 8 8 
et Og Se a 
an oCS 4 


AN! 


(vl) acting as a sphincter, 
the free edge of which is 


produced into a number 
of velar tentacles (vl. ¢). 


TL 


hipuongouuuee 


pea 


The mouth leads into 
the largest section of the 


enteric canal, the pharynx 
(ph), « 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, the gé//-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 (int) 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 tu 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 per?-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 ver (i) or hepatic cecum, which extends for- 
wards to the right of the pharynx; it is lined with glandular epithelium 
and secretes a digestive fluid. 

The gil/-slits (dr. cl) 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 éranchial septa or lamelle (Fig. 204, dr. 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 dranchial rods (6r. 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 aérium (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 (a/7f); and is continued backwards by a blind, pouch- 
lke extension (@é) 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 veztral 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 lamelle. Efferent 
branchial vessels receive the blood from the wall of the pharynx and 
open dorsally into a pair of longitudinal vessels, the dorsal aorte, The 


coed 


Fic. 205, — Amphioxus lanceolatus. A, transverse section of the pharyngeal re- 
gion. a, dorsal aorta; 4, atrium: ¢, notochord: co, ccelom; e, endostyle; & 
gonad; 44, branchial lamella; Ad, pharynx; 2, liver; zy, myomere; 7, neph- 
ridium; 7, neuron or dorsal nerve tube; sz, spinal nerves; sf, gill-slits. B, 
transverse section of the intestinal region; af7, atrium; coe/, celom; d. ao, 
dorsal aorta: z##, intestine; szyom, myomere: uch, notochord: 22x, neuron; 
s. 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, nph) 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 drown 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 xeuron or dorsal 
nerve-cord (Fig. 204), contained within and completely filling a median 
longitudinal zeural 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, off 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 pigmenté spot (e) 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, gon) are about twenty-six pairs of pouches arranged metamerically 
along the body-wall and projecting into the atrium so as largely to hill 
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 CRANIATA 


The fishes, amphibians, reptiles, birds, and mammals are 
grouped together under the general designation Craniaza, 
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,’ and a rabbit will be a good and convenient selection. 


1 The anatomy of the .4zodis or ‘‘ American chameleon” of the Southern 
States is essentially Jike that of the European lizard, 


XID > PHYLUM 


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 “unk 
region (by far the largest), 
in the middle, and a “az 
region, differing greatly in 
its development, behind. 
The head region bears 
anteriorly the opening 
of the mouth, bounded 
above and below by jaws 


‘ull 


myr myc 


=A rein 


aint 
in 
pull 
Y 


CHORDATA 


i AD 
A 
i a tt 


Un 
cy y 


329 


27, 
> pu. J, pelvic 


ly removed to show the 


anchial apertures; 


v 


re; pct. f, pectoral fin 


; myc, Myocommas; mynz, myomeres; x. a, nasal apertu 
(From Parker’s Brology.) 


mth, mouth 
6, spiracle; v. #, ventral fin. 


nn; S, 


, anus; c. ad. /, caudal fin; d.f.7,d f.2, dorsal fins; e, eye; ext. dr. apf, external br: 


muscles. az 
lateral line; 


Fic. 206. — Side view of Dogfish (Mustelus antarcticus), with a strip of skin in the middle of the bod 


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- 
ne, with the wide apertures at their bases, mark very 
conspicuously the position of the auditory organs in the 


Fic. 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 twu 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- 


Fic. 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 sfzvac/e, 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 dranchial 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 the 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 veck. 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 


xu 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 pinne 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 spzna/Z 
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 verfebr@, 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 nevral 
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- 


Fic. 209. — A, three trunk vertebre of Scyllium from the side; B, a single trunk 
vertebra viewed from one end; C, three caudal vertebre from the side; D, a 
single caudal vertebra from one end. c, centrum; 4, a, hemal arch; w. a, neural 
arch; ¢7. or, 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 amphicelous. The entire 

spinal column is distinguishable into two regions, — the 


region of the ¢vw#& in front and the region of the ¢az/ 


xu PHYLUM CHORDATA 335 


behind. In the region of the trunk the vertebree 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 hema/ 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 
vertebre are accordingly said to be procelous. In the lat- 
ter the surfaces are flat, and the discs of fibro-cartilage, the 
inter-vertebral discs, are intercalated between the vertebra. 


Fic. 210. —Vertebre 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; Ay, hypapophysis of axis; /at, lateral piece of atlas; /zg. liga- 
mentous band dividing the ring of the atlas into two; ev, neural arch of atlas; 
od, odontoid process; fr. zy, pre-zygapophysis; ff. zy, post-zygapophysis; 7d, 
rib; sf, spine; vent, ventral piece of atlas. 


In both the spinal column is divisible into five regions, — the 
cervical, the thoracic, the Lemébar, the sacraé, and the caudal. 
The cervical region is the most anterior. In the rabbit the 
vertebre 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 vertebre in both the rabbit 
and the lizard are specially modified in connection with the 
movements of the head on the trunk. The vertebree of the 


336 MANUAL OF ZOOLOGY SECT. 


thoracie region are characterised by the possession of 77s, 
which, in the case of the most anterior, are connected with 
the breast-bone or sternum by slender cartilaginous séernal 
vios. In the Zeméar region there are no ribs. The sacral 
region is distinguished by its relations with the hind limb. 
The cauda/ region, short in the rabbit, very long in the 
lizard, lies behind the sacral. The ribs connected with the 
thoracic vertebre 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 


Fic, 211. ~ Lepus cuniculus. A, atlas and axis, ventral aspect; ed, odontoid pro- 
cess of axis. B, lateral view of axis; ar?, articular facet for occipital condyle; 
od, odontoid process; ft. sy, post-zygapophysis; sf, neural spine. C, thoracic 
vertebra, lateral view. cent, centrum; fac, facet for rib; set, metapophysis; 
pr. sy’, pre-zygapophysis; fz. zy, post-zygapophysis; 7d, rib; sf, spinous process. 


to the sternum ventrally. The szernum 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 stevnebre. 

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 vofochord, 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 becomes 
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 sud. 
The chief part of this is a case, the cran‘vm, 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 offactory organs in front, the eyes in the middle, and the 
ears ot 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 vertebra ; and the posterior region of 
the cranium articulates movably with the first vertebra of 
the spinal column. In addition to the cranium the skull 
or skeleton of the head comprises certain. elements known 
as the wsceral arches. The foremost of these forms the 
jaws, the second is the Ayozd, and mainly supports the 
tongue, the remainder are the dranchial 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, t.e, bones which 
take the place of pre-existing cartilage, to which are super- 
added a number of membrane bones, 1.¢., 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. 


338 


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XU 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 guwadraze, 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 


% 


supra. Li S 


Fic. 


213, —Skull of Lacerta agilis. A, from above; B, from below; C, from the 
side. ang, angular: art, articular: das ec. basi-occipital: das. pty, basi-pterygoid 
processes; fas sph, basi-sphenoid; col, epi-pterygoid; cor, coronary; dent, 
dentary; eth, ethmoid; ¢x ec, ex-occipital: ert. war, external nares; for mag, 
foramen magnum: /r, frontal; z7¢. vax, internal nares; 7, jugal; der, lacyr- 
mal: sax, maxilla; was, nasal; oc cond, occipital condyle; of, olfactory 
capsule; of. of, apisthotic: opt n, optic nerve; fal, palatine; far, parietal; 


par. parasphenoid; fav. 7, parietal foramen; 4 wx, pre-maxille; fr. fr, pre- 


frontal; /éy, pterygoid, #4. 0rd, post orbital: qu, quadrate; s. ang, supra- 
angular; s o74, supra-orbitals; sg, squamosal; supra. ¢.1, supra-temporal 1; 
supra t.* supra-temporal 2; fans, transverse; supra. oc, supra-occipital; vor, 
vomer. (After W. K Parker. ) 

340 


SECT, XII PHYLUM CHORDATA 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 penéadacty/e, 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 


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Fic. 214. — Diagrams of the fore (A) and hind (B) limbs with the limb-girdles. acté, 
acetabulum; g/, glenoid cavity; #. cor, procoracoid; (IV, digits Cartilage 
bones — cn.1, en.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; ul, 
ulnare, membrane bone; CZ, clavicle. 


bones — radivs and w/na — 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 efacarpus 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 — wngual 
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 z/m, is dorsal in position, the other two, pzzdzs 
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 #éza 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 ¢a/sa/ bones correspond- 
ing to the carpals of the hand, a series of mec/atarsals corre- 
sponding to the metacarpals and a series of phalanges. 

When the skin of the trunk of the dogfsh 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 


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 a/veot 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 Fic. 215.— Longitudinal 

e R section of a tooth, semi- 

calcified material permeated by delicate diagrammatic.” PH, 

pa i pulpcavity; PH", open- 

parallel tubules. The free surface is  ingofsame; ZZ, den- 

covered with a layer of still harder mate-  {Mmei (From Wieder. 
rial, the ename/, and the basal portion is “'™* '¢7#?r2#.) 

covered with a layer of cemen¢, which is similar in micro- 


scopic structure to bone. 


344 MANUAL OF ZOOLOGY SECT. xX 


The anterior part of the cavity into which the mouth 
leads is the ducca/ cavity, the posterior part is the pharyrx, 
On the floor of the buccal cavity is, in the lizard and in the 
rabbit, a mobile muscular prominence, the songue, 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 c/oaca, 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 sadvary 
glands, the fiver, and the fanercas, in the dogfish and 
lizard the salivary glands are absent, though in the latter 
there are numerous small glands, the ducca/ glands, in the 
wall of the buccal cavity. The secretion of the salivary 
glands, the sa/va, enters the cavity of the mouth through 
the ducts of the glands. It contains a ferment, pepadin, 
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 


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345 


346 MANUAL OF ZOOLOGY SECT. 


duct, the dz/e duct, conveys its secretion, the é2/, 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 gadl-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 emwésion 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 g/ycogen 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 fepéones, 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 /acwa/s — which 
ramify in the wall of the intestine. The lacteals are not 
blood-vessels, but belong to the Aiwphatic vascular system to 
be referred to presently. The lacteals combine together 
and in the rabbit open into a large trunk — the “horacic duct 
— by means of which the absorbed emulsion, or chyée 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 fev7- 
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 gz//s 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 dranchial 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 zzéernal or posterior nares. On the floor of 
the pharynx behind the root of the tongue is a slit-like 
aperture, the g/o¢#s, opening behind into a chamber known 
as the Jarynx, 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. 


of cartilage. The trachea bifurcates when it enters the 
body-cavity, each of the two branches, or d7venchi as they 
Oe 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, 


Fic. 217.— Lacerta agilis. General view +s 
of the viscera in their natural relations. containing the greater por- 


&/, urinary bladder; Cz, post-caval vein; 4: . 
Do vectim: CB, gallbladder; A, tion of the enteric canal and 


heart; Lg, Lg’. the lungs; AZ, stomach; 


AMD, small intestine; Oe, cesophagus; other organs, by a muscular 
Pu, pancreas; Tyr, trachea. (After 


Whiedersheim.) partition concave posteri- 


XII PHYLUM CHORDATA 349 


orly,—the daphragm, — the anterior portion of the cavity 
being known as the cavity of the ¢zorax, and the posterior 
as that of the abdomen. : Hunn 

The air in the lungs, as it is constantly GER ely ahh 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 vespfération 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 hemoglobin. 

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, ¢.¢., 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 /ear¢ 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 seus venosus, aust- 
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 verns. 


xIl PHYLUM CHORDATA 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 


Fic. 218 — Diagram illustrating the course of the circulation in a fish. Vessels 
containing aérated blood, red; those containing non-aérated 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. 47. a, 
afferent branchial arteries; az, auricle; c. a, conus arteriosus; d@. ao, dorsal 
aorta; e. 67. a, afferent branchial arteries; 2. wv, hepatic portal vein; 4. v, 
hepatic vein; éc, lacteals; 7y, lymphatics; fv. cv. v, pre-caval veins; 7. p. 7, 
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 pu/monary 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 pu/monary 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 arévial 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 vena/ 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 vertebree. 


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 


VH Lot 


Fic. 219. — Dorsal view of the brain of Scyllium canicula, The posterior division 
of the brain is the medulla oblongata (V/A/), on the dorsal surface of which is 
skown one of the central ventricles (F. rho). The large cerebellum (WH) 
nearly covers the optic lobes (WA’). The diencephalon (ZH) shows in the 
middle one of the central ventricles, and the place of attachment of the en 
body (Gf). The prosencephalon (YH) gives off the olfactory lobes (Tro, L. ol). 
The following nerves are shown: optic (//), trochlear (/V’), trigeminal (Vv ), 
facial (V//), auditory (V///), glossopharyngeal (/4°), and vagus (1). 
(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 thalamencephaien, 
behind it, constitute the fore-drain. Behind the fore-brain 
a pair of oval lobes, the offic /odes, 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, — medudla 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 zter or ague- 
duct of Sylvius, expanding in front in the thalamencephalon 
into a laterally compressed cavity, the “ird ventricle. From 
this are given off a pair of /tteral 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 thalamy ; 
its floor is produced into a hollow prolongation, the //fien- 
dibulum, to the end of which a vascular body, the Aypophysis 
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, z.¢., 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 spenal 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 
offactory nerve-fibres, which originate from the olfactory 
lobes, the epzic nerves, which are derived from the thalamen- 
cephalon, and the ava/fory 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 scderotic. 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 chorord. ‘Towards the cornea the choroid passes 
into a circular pigmented diaphram, the zris, the opening 
of which is known as the pugr7. 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 


XI PHYLUM CHORDATA 357 


iris. The rays of liglt are brought to a focus on the retina 
mainly by means of the crvstadline lens, a firm, glassy body 
situated within the iris. The cornea also assists in this, as 
does a gelatinous substance, the w¢reous 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 


Fic. 220. — Diagrammatic horizontal section of the eye of man. c, cornea; ch. 
choroid (dotted); C. P, ciliary processes; e. c, epithelium of cornea; ¢. ¢7, 
conjunctiva; fc, yellow spot; /, iris; Z, lens; ON, optic nerve; OS, ora 
serrata; o-x, optic axis; # c. R, anterior non-visual portion of retina; P. Z, 
pigmented epithelium (black); AR, retina; sf. 2, suspensory ligament; Sc/, 
sclerotic; V’. H, vitreous body. (From Foster and Shore’s Physzology.) 


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 o#ifhs. 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 Avmpanum 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 “mpanic 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 Aidneys, 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 


XI 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 w7eter. In the 
lizard and the rabbit there is present a median thin-walled 
sac, the w//nary 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 wethra. 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 éesées, 
each with its duct or vas deferens. In the female there are 
two ovaries, which are solid boclies 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 wéerus, and a 
median passage, the vagzna, 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 she//, 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 fe/ws or uterine young of 
the rabbit is effected by means of a special vascular structure 
known as the p/acenéa, 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 iowest 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 (Fefromyzon and other genera) 
and the hag-fishes or slime-fishes (A/)x7ne 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 asa 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 


xit PHYLUM CHORDATA 361 


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 


LE ‘ brela 
ie | 
| 
| 
\ 


/ 


\ 
2Qa.ap pr 


Fic. 22t.-— Petromyzon marinus. Ventral (A), lateral (B), and dorsal (C) views 
of the head. 47. c/. 1, first gill-cleft; dc. /, buccal funnel; eye, eye; mth, mouth; 
na. ap, nasal aperture; /, papilla: #2, pineal area; ¢. 7, ¢. 2, ¢. 3; teeth of buccal 


funnel; 4g, teeth of tongue. (After W. K. Parker.) {sey of paatote 


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 


EP MANUAL OF ZOOLOGY SECT. XI 


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- 


oes.ct.d 


Fic. 222. — Head of Myxine glutinosa (A) and of Bdellostoma forsteri (B), from 
beneath. 4x. af, branchial aperture; 47, cd. z, first branchial cleft; #¢, mouth; 
na. apf, nasal aperture; oes. ct. d, esophageo-cutaneous duct. The smaller open- 
ings in A are those of the mucous glands, (After W. K. Parker.) 


laginous processes representing neural and hemal arches. 
The skull is cartilaginous, and is peculiarly modified. Be- 
hind it in the lamprey is a remarkable basket-like apparatus, 


pavo wor possed apistq ‘x 
“a (anBuo} ‘7 ‘7 :smsousA 
“4 $anZuo} jo aposnur 
90 syeuvo yeuids ‘v2 “7% 
saBepyivs [eyo 


‘f sa[UINe OVI snsouaa snuts ySnoity WEA [euy 
vow [eIUDA ‘op "2 sefoliyuad 
4 tenZuoy JO Loywajar ‘7 “7e 
“fo syayns ‘sa tyoor eruwto 
‘pu spxoo yeurds ‘fee 
waa repnsnl ‘2f sounysayur 7772 + UloA Te) 
{jauuny yeoonq Mojaq eA0o01 
Op ‘op p :ulea [eUIps¥s 


sgUTSOWUT OFT JaT]NS wroIy pas 


(hiaozo07 § Jayseg 
Swnpea ‘72 syayseq jerqoursq Jo 7 


fsaposuu [e1uas “ue 12 
snuis ‘2 “s :ja][NB Sarpunosins 
gzoyoenoid ‘7 mw g tasvyizes jesiop 1 
tproqoojou * 94 ‘ou 
:Aqtaeo peoong ‘ze 
aoriayur ‘ef °2 UAT. 
fyeuvo yeinau jo anss 
suado ano jyeq taddn oy} 


yeurpnaiSuoy pesquea ‘9 "2 + 
‘é4 suopuay SW‘ 2 "2 
<Areao 20 sjauuny Peon 
« pu tyonod Areyn: 
[wus 67 :adepnqes yensul| 
q jo uoni0d '¢ -y 


or1ajsod ‘p “g twin 


[ensuyy OF payourse ase[yze9 

1Seq 0} JOMaIUE dE] [ese 
jo ainyiede jeuiay 
iseq puryaq aed | 
o[noLne MOYs 0} pauedo 
e sjied snouidepiyze9 oy 


‘nv taseyiyaieo Iepnuue “uv 
“snuLieM wozAMor}ed — “Eee “ONT 


pues Mojaq ainye 
jou ay} JO yJeays aq) pu 


‘geuiay JO UOIaSSICL 


363 


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 éach 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 


xi 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 sucha 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. Fe/romyzon is found on the coasts and 
in the rivers of Europe, North America, Japan, and West 
Africa. Of the allied genera one, /chthyomyzon, occurs on 
the western coast of North America; another, AZordacia, in 
Tasmania and Chili; a third, Geo¢ria, 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 II. 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 (SeV/ium 
canicula), the lesser spotted dogfish (S. catéuus), the 
piked dogfish ( Acan¢hias vulgaris), and the smooth hound 
(Mustelus vulgaris). Allied species of the southern hemi- 
sphere are Scy@ium, Acanthias, and ALlustelus anarcticus. 
On the coast of Northeastern America the common dogfish 
is Mustelus canis, 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 


xt PHYLUM CHORDATA 367 


covered closely with very minute hard placotd 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 Zateral Line. 

As in fishes in general, two sets of fins are to be 
recognised, — the wupaired or median fins, and the pazred 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 stiffish, particularly towards the base, owing to the 
presence of a supporting framework of cartilage. Of the 
median fins, two — the dorsa/— 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 cawzda/ 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, Z.¢., 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 aa/ 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 /ateral 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 ge/vzc, 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 sf7vac/e, — 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 aédominal 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, 4) consists of a centrum 
(¢), neural arch (v@), and transverse processes (¢r. pr). 
In the caudal region there are no transverse processes, but 
inferior or hemal arches (D, h. a) take their place. The 
centra of all the vertebrae are deeply biconcave or amphi- 
celous, having deep conical concavities on their anterior 
and posterior surfaces. ‘Through the series of centra runs 
the notochord, greaély constricted in the centrum itself, 
dilated in the large spaces formed by the apposition of the 
amphiccelous centra of adjoining vertebree. The concave 
anterior and posterior surfaces of the centra are covered 
by a dense calcified layer, and eight radiating lamelle 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 weura/ plates (one placed opposite the 
centrum, the other or énéercalary 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 77d 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 o/factory capsules 


(olf. cb),—thin rounded cartilaginous sacs opening widely 
2B 


370 MANUAL OF ZOOLOGY SECT. 


below, —the cavities of the two capsules being separated 
from one another bya 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 anéertor 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 oré7¢ 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 72/ra-orbita/ ridge. 

Behind the orbit is the a/rorv 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 agueductus 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 vertebra 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 


37! 


CHORDATA 


PHYLUM 


XII XII 


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uodn Surmoyjoy ‘wayy YM payoauuod are (97) sadeyyaes yeiqey [feuls pue (47 197) squawest om) Aq wield ayy 0} payore 
osje st mel raddn aqi !(#%2 47) nuios profy ayi 0} Mojaq JuaWTYe}e Surats pure ‘smef (/'7) ramo, pue (f-¢7) aaddn ayy yoddns 
0} Surdjay ‘(ve -fy) repnqipuewody ay} st ajnsdeo Aroypne ayy ym paiejnoury “saaisu (S “2az7) yeurwmasiy pue (2 “2az) odo 
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pouq,  Uudhy 


ayro 


3772 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-guadrate (up. 7), 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 Afeckel’s cartilage (2. 7), likewise consists of 
two stout cartilaginous rods firmly united together in the 
middle line, the union being termed the sympfyscs. 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 Avord 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-hva/ (hy. en). Both the 
hyo-mandibular and cerato-hyal bear a number of slender 
cartilaginous rods — the branchial rays of the hyoid arch 
(47.7). The mesial element, or dasz-Aya/, lies in the floor 
of the pharynx. Behind the hyoid arch follow the dranchial 
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 p/errgiophores 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 


RI 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 dasal cartilages articulating with the 
pectoral arch. The latter is a strong hoop of cartilage in- 
complete dorsally, situated immediately behind the last of 


Fic 225, — Ventral view of pectoral arch of Scyllium with right pectoral fin. The 
pectoral arch is divisible into dorsal (Acé. g) and ventral ( pct. g') portions, 
separated by the articular facets (a7¢. /) for the fin The pectoral fin is formed 
of three basal cartilages (4s, 7-3) and numerous radials (vad); its free edge is 
supported by dermal rays (d. /. ~). (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-pierygium 
(4s. 2), the middle, meso-prerygium (és. 2), and the pos- 
terior, mefa-pterygium (bs. 3). Of these the first is the 
smallest, and the last the largest. The pelvic fz 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 esophagus (gut), 
which passes behind into the stomach. The stomach is 
a U-shaped organ, with a long left limb (¢@. s¢) continuous 
with the cesophagus, and a short right (fy? s¢) passing 
into the intestine. At the fy/orus—the point where the 
stomach passes into the intestine —is a slight constriction 
followed by a thickening. The zzéestine consists of two 
parts, —small intestine or duodenum, and /arge intestine. 
The former is very short, only an inch or two in length. 
The latter (¢z¢) is longer and very wide ; it is divisible into 
two portions, — the co/on 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 “iver (2. Iv, r. dr) consisting of two elon- 
gated lobes. A rounded sac, the gal/-dladder, lies em- 
bedded in the left lobe at its anterior end. The duct of 


xu PHYLUM CHORDATA 375 


the liver, the dz/ 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 (fan) 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 (ret. gl), about three-quarters of an 
inch in length. 

The spleen (spl) 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 g7/s, 
situated in the five g7//-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 g7//s, 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 znterbranchial 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 


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SECT. XII PHYLUM CHORDATA 377 


anterior wall only. On the anterior wall of the spiracle is a 
rudimentary gill, the psewdo-branch or spiracular gill, in 
the form of a few slight ridges. 

The dear 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, — sénus venosus (s.v), auricle (au), ventri- 
cle (v), and conus arteriosus (c. art), through which the 
blood passes in the order given. The szzus 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 s¢mu-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 ventra/ 
aorta (Fig. 227, v. a0) 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.br.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- 


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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 
(¢@.a0). 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 ¢zernal and external 
carotid arteries (¢.a@), supplying the head with arterial 
blood. 

The dorsal aorta rans 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 vertebre. 

The veins are very thin-walled, and the larger trunks are 
remarkable for their dilated character, from which they 
have obtained the name of szzuses, 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 (7. 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, the precaval sinus or ductus Cuviert ( pr.cv.v) which 
is continued into the lateral extremity of the sinus venosus. 

There are two fortal systems of veins, the renal portal 
and the hepatic portal (h.p.v), by which the kidneys and 
liver, respectively, are supplied with venous blood. The caw- 
dal vein (cd. v), which brings back the blood from the tail, 
running, along with the caudal artery, through the inferior 
arches of the vertebree, divides on entering the abdominal 
cavity into right and left veza/ portal veins (7. p.v), which 
end in a number of afferent renal veins supplying the kidneys. 

The hepatic portal vein (4. p. 7) 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 hepadic sinuses (h. 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 o/factory lobe (L. of), 
closely applied to the posterior surface of the correspond- 
ing olfactory capsule. The diencephalon (2) is com- 
paratively small; its roof is very thin, while the floor is 
composed of two thickish masses, the optic thalami. At- 
tached to the roof is a slender tube, the epiphysis cerebri or 
pineal body (Gp), which runs forwards and terminates in a 
slightly dilated extremity fixed to the membranous part of 
the roof of the skull. Projecting downwards from its floor 
are two rounded bodies, the /od7 infertores, which are dilated 
portions of the znfundibulum ,; and attached to this, behind, 
is a thin-walled sac ,— the petwitary body or hypophysis cerebri 
having a pair of thin-walled vascular lateral diverticula, — the 
sacet vasculosi, and having on its ventral surface a median 
tubular body attached at its posterior end to the floor of the 
skull. In front of the infundibulum, and also on the lower 
surface of the diencephalon, is the oftc chiasma, formed by 
the decussation of the fibres of the two optic nerves. The 
mid-brain (J¢/7) consists of a pair of oval optic lobes 
dorsally, and ventrally of a band of longitudinal nerve-fibres 
corresponding to the crura cerebri of the higher vertebrate 
brain. The cerebellum (/7/7) is elongated in the antero- 
posterior direction, its anterior portion overlapping the 
optic lobes, and its posterior the medulla oblongata, Its 


XI PHYLUM CHORDATA 381 


surface is marked with a few fine grooves. The medulla 
oblongata (VA), broad in front, narrows posteriorly to pass 
into the spinal cord. The fourth ventricle (F.rho) is a 
shallow space on the dorsal aspect of the medulla oblongata 
covered only by a thin vascular membrane, the choroid 
plexus ; it is wide in front and gradually narrows posteriorly. 
At the sides of the anterior part of the fourth ventricle are a 
pair of folded ear-shaped lobes, the corpora restiformia. 

The fourth ventricle is continuous behind with the cen- 
tral canal of the spinal cord. In front it is continuous with 
a narrow passage, the z7ev (z#er), which opens anteriorly into 
a wider space, the dacale or third ventricle (dia) occupying 
the interior of the diencephalon. From this opens in front 
a median prosocele, which gives off a pair of paraceles 
(fara) 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 ccelome, 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, off 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 frochlear (path), and the sixth, or adducent, go to the 
muscles of the eye; the fifth, or “#7vgeminal (oph. V, mx. V, 
mnd. VW’), to the snout and jaws ; the seventh, or facial (oph. 


P~ EX 
hie 
sobl AGS 
path hy al 
inlrects KS \ 
sreet fi : 
a [ex \ pliyt 
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hegyrena vt 


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waren 


BH 


§p-CO lalvag 


Fic. 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. c?. r-c/. 5, branchial 
clefts; ef, epiphysis; ext. rect, external rectus muscle of the eye-ball; g/. ph, 
glossopharyngeal; ov. can, horizontal semicircular canal; Ay. mud. VII, hyo- 
mandibular portion of the facial; 7”f 0d/, inferior oblique muscle; zvt rect, 
internal rectus muscle; at. vag, lateral branch of vagus; mx. J", maxillary 
division of the trigeminal; o/f cfs, olfactory capsule; o/f, s, olfactory sac; 
ae V. VIZ, superficial ophthalmic branches of trigeminal and facial; path, 
fourth nerve; f/, }°//, palatine branch of facial; sf. co, spinal cord; ‘sfzr, 
spiracle; s. rect, superior rectus muscle; s. 042, superior oblique; vag, vagus; 
vest, vestibule. (From Marshall and Hurst.) 


VIL, pl. VIL, hy. mnd. VIL), to the palate, lower jaw, and 
hyoid arch; the ninth, or glossopharyngeal (g/. ph), to the 


XII PHYLUM CHORDATA 383 


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 o/factory 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 semcircular 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 (Aor. 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 perz/ymph. 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, 
z.e., that the fish is enabled by its means to maintain its 
equilibrium in the water. 

‘The kidneys (Fig. 227, %) 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 
inte a single tube, the wre/er, opening directly into the 
cloaca in the female, in the male into a small paired cham- 
ber, the wrogenifal sinus (ug. s), which opens into the 
cloaca (¢/). 

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 (v. 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 ceelom 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 
ccelom ; 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 she/-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 ccelom, 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 dogfshes (Acanthias, Afus- 
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 Fic. 229. — Dogfish, egg-case. 
heap of cells, the d/astoderm, situ- eee 
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 


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 


Fic. 230.— A, embryo of Scyllium with yolk-sac (x 13); B, under-side of head 
enlarged. 4». 7, branchial filaments protruding through gill-clefts; 47. /', 
branchial filaments projecting through spiracle; cd /, caudal fin; @ /, dorsal 
fins; e,eye; ex. 4x”, ap external branchial apertures, »v¢/, mouth; va, nostrils; 
pet. f, pectoral fin: pz. _f, pelvic fin; s¢, yolk-stalk; uv. f, ventral fin; y&. s, 
yolk-sac, (After Balfour, slightly altered ) 


head presents several peculiarities. The gill-filaments (47. /) 
are so long as to project through the external branchial 
apertures and the spiracle (47. 7) 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 ccelom, 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 ee 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- 


Fic. 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 (Pris#s). 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 


Fic. 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 claspers 
or prerygodia, 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 Aexanchus 
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 addominal 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 péacotd 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 
Heptanchus), but usually the centra are strengthened by 


BK en 5, 
Gy 
nas \\\ Wh 


Fic. 233. —Skeleton of sting-ray (Urolophus testaceus), ventral view. @.7z. A, 
anterior vertebral plate; das. 47, basi-branchial plate; 4”. 7-r..5, branchial 
arches _ The branchial rays are represented as having been removed, the round 
dots indicate their articulations with the arches _ c¢/, skeleton of clasper; 4. mz, 
hyomandibular; Ay, hyoid arch; éa4, labial cartilage; /zg, ligament connecting 
the hyomandibular with the palato-quadrate and Meckel’s cartilage; mck, 
Meckel’s cartilage; zs. pt, mesopterygium; wf pz, metapterygium of pectoral 
fin; wd. pt’, metapterygium of pelvic fin; as, nasal cartilage; Jal, palato- 
quadrate; fect, pectoral arch; A/, pelvicarch; pro. p?, propterygium; sf, spiracu- 
lar cartilage. 


XI PHYLUM CHORDATA 391 


radiating or concentric lamelle 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, @. v. £). Two main regions only are distinguish- 


Fic. 234.— Lateral view of the skull of Heptanchus. ck, Meckel's cartilage; 
pal. gu, palato-quadrate; ft, ord, 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 hamal 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 Ayosfic ; 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 ayphistylic. 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 (Zorpedo and Aypnos) 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. 

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 evzertc 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-fllaments 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 (Lemargus), 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 


304 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. Teleostomi ! 


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 (Lepidosews), and bow-fin 
(dmia) of North America, and the Folpterus of the Nile. 
They are distinguished from Elasmobranchs by the posses- 


1Sub-class II, the small group Holocephali, or Chimzeras 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) 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 


Fic. 235.—Salmo fario. a. 7, adipose lobe of pelvic fin; az, anus; c. /, caudal 
fin; @./. 7, first dorsal; df 2, second dorsal or adipose fin; /. /, lateral line; 
(ae operculum; gc¢. 7, pectoral fin; Av. /, pelvic fin; v. f, ventral fin, (After 

ardine.) 


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 Sadmo 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 deak 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 (of), 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 dranchio- 
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 


XU 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 


Fic. 236. —Salmo fario. Caudal end of vetebral column. CN,centrum; D.F.R, 
dermal fin-rays; H. SP, hemal spine; H. ZYG, hemal 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 (Pleuronectide, 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. 


4 Yuga \ 
Ll heg fe ply 
Fic. 237. — Pleuronectes cynoglossus (craig-fluke), from the right side. a. f, 


dorsal fin; 7 ¢, left eye; Act /, pectoral fin; Az. /, pelvic fen; ~. ¢, right eye; 
vf, 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 cyediu/ scales; when the free 
edge is produced into small spines, they are distinguished 
as cfenotd 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 dentafus trom the southern 


coast of New England, and Pseudopleuronectes americanus from the coast 
north of Cape Cod. 


XII PHYLUM CHORDATA 309 


Sometimes there is an armour formed of stout bony plates, 
or scuées, while in other cases, as in the “ file-fishes,” the 
exoskeleton takes the form of minute spines like the 


Fic. 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. 


oe SS TRONS 


; re / 
orm pol RUS an uf 


Fic. 239. — Polypterus birchir. A, entire animal; B, ventral 
view of throat. az, anus; 4. 7, branchiostegal membrane; 
c. f, caudal fin; @. f, dorsal finlets; zag. £7, jugular plates; 
na, nostril: pct. f, pectoral fin; gv. f, pelvic fin; v. f, ven- 
tral fin. (After Cuvier.) 


In the sturgeon the spinal column consists of a persistent 
notochord with cartilaginous arches ; in the rest bony verte- 
bree 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, wx, dent). The jaws are con- 
nected with the skull by the intermediation of a hyomandib- 


a 
t 


Fic. 240.— Skull of sturgeon, with the membrane bones removed. a, pharyngo- 
branchial; .4/, antorbital process: AA’, articular; 4, epibranchial: c, cerato- 
branchial; C, notochord: Cf, basi-branchials; @, hypobranchial; De, dentary; 
GK, auditory capsule; 4/1/, hyomandibular; Ay, hyoid cornu; /A, inter-hyal; 
Md, mandible; Na, nasal capsule; Gé, neural arches; PF, post-orbital pro- 
cess; PQ, palato-quadrate; Ps. Ps'. Ps'', parasphenoid; Psp, neural spines; 
Qu, quadrate: 2 rostrum; AZ, ribs; Sf. NV, foramina for spinal nerves; Sy, 
symplectic, J/7S, vertebral column; #2, vagus foramen; /-I”, branchial arches. 
(From Wiedersheim’s Comparative -uatomy.) 


ular (Ayem) 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 cZavicles. The pelvic arch is vestigial or absent. 

Two genera of Teleostomi possess electric organs, — the 
electric catfish (J/alaplerurvus) and the electric eel (Gim- 
notus) ; the former occurs in fresh waters of tropical Africa, 


401 


PHYLUM CHORDATA 


XII 


and the latter in Brazil and the Guyanas. Some Teleostomi 
are toothless, but in most instances teeth are present, and 


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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 


Fic. 242. — Premaxilla 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, 7.¢., 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 ceca) 
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. Asa rule, the gills are developed 
in the first four branchial arches. 

A characteristic structure of the Teleostomi is the azr- 
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 pueumatic 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, z.c., 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 dudbus aorte. 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 SECT. 


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 (Syrgnathus) 
the young are developed in a pouch in the abdomen of the 
male. In Aspredo, one of the cat-fish tribe, the eggs are 


Fic. 243. —Hippocampus (sea-horse). In B, the operculum is removed to show the 
gills. 4” af, branchial aperture; dxd. 4, brood-pouch; df, dorsal fin; g. gills; 
pet. f, pectoral fin. (From Claus and (siinther ) 

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 


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, t.c., so light 
as to float when laid, as in the 
cod, haddock, turbot, sole, 
etc., or demersal, t.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, Profopterus 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 


405 


(From Dean, after Gtinther.) 


Fic. 244. — Ceratodus Forsteri. Reduced. 


406 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- 


7 lam 


Fic. 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. éas, basal cartilage of the pectoral fin; 4%, branchial arches; 
nt, inter-operculum; Zam, plate overhanging branchial region; ck, Meckel’s 
cartilage; oce. 7, occipital rib; of, operculum; Aa/, palato-quadrate; pct, pec- 
toral arch; rés, ribs; sb. orb, sub-orbital bones; sz, squamosal; supra. se, 
supra-scapula. 


ing, jointed rod of cartilage, with a row of smaller jointed 
rods of cartilage on either side of it. This form of fin-skele- 
ton, which occurs in certain groups of fossil fishes, as well as 
in Dipnoi, has been termed the archipterygivum. The noto- 
chord is persistent, and the cranium (Fig. 245) consists of a 
mass of cartilage with little ossification, but with the addition 


XII PHYLUM CHORDATA 407 


of a number of membrane bones ; the skull is aufostylic, the 
lower jaw articulating with a palato-quadrate process (pa/), 
corresponding to the palato-quadrate of the dogfish, but im- 
movably fixed to the side of the skull. There are four or 
five cartilaginous branchial arches (47). The gills are cov- 
ered over by an operculum. A cloaca is present, and the 
intestine contains a spiral valve. The structure of the heart 
is more complicated than in ordinary fishes, owing to the 
sinus venosus and the auricle being both imperfectly divided 
into two parts. There is a contractile conus arteriosus, which 
has a spirally twisted form, and is partly or completely divided 
internally by a longitudinal septum. A pulmonary artery, 
carrying blood to the lung or lungs, is given off from the 
afferent branchial system. The blood is returned from 
the lung or lungs by means of a pulmonary vein, which 
opens into the left division of the sinus venosus, and 
through it reaches the left division of the auricle. 


CLASS III. AMPHIBIA 


The larve of the newts or efts, and those of the frogs 
(familiar to every one under the name of tadpoles), bear a 
close resemblance in form and movements to the fishes. 
But, as they approach maturity, these fish-like larvee undergo 
a metamorphosis, fitting them for the amphibious mode of 
life which gives its name to the class: pentadactyle limbs are 
developed, and lungs for breathing air take the place of gills 
as the organs of respiration, while a corresponding advance to 
a higher type of structure occurs in the other parts. The 
Amphibia thus occupy an intermediate position between the 
fishes on the one hand and the higher air-breathing Verte- 
brates (reptiles, birds, and mammals) on the other. In 
addition to the possession of limbs constructed on the pen- 


408 MANUAL OF ZOOLOGY SECT. 


tadactyle type, or type of the cheiropterygium, the Amphibia 
differ from the fishes in the entire absence of fin-rays, and 
from all fishes but the Dipnoi, in the presence of lungs for 
breathing air in the adult: the larval gills become absorbed 
in the majority of Amphibia before maturity is reached, but 
in some are retained throughout life, the animal breathing, 
like the Dipnoi, by means of both lungs and of gills. 

The most convenient example of the Amphibia for special 
study is a frog. ‘The following description and figures have 
reference more specially to the European species of the 
genus Rana,— R. temporaria and R. esculenta, — but they 
will be found to apply to any American frog or toad, except 
in a few features which are chiefly quite superficial, some of 
which will be referred to subsequently. 

The ¢unk is short and stout, and is continued, without 
the intermediation of a neck, into the broad depressed Aead. 
There is no trace of a tail, the anus being terminal. The 
mouth also is terminal, and is characterised by its ex- 
traordinary width, the gape extending considerably behind 
the eye. On the dorsal surface of the snout are the small 
nostrils; the eyes are large and prominent, and each is pro- 
vided with an wpper eyelid in the form of a thick fold of skin 
and a nictitating membrane —a much thinner fold which 
arises from the lower margin of the eye and can be drawn 
up over it. Close behind the eye is a circular area of 
tensely stretched skin, the Ampanic membrane, a structure 
not met with in any fish; as we shall see, it is an accessory 
part of the auditory organ. There is no trace of branchial 
apertures. 

The back has a peculiar bend or hump, in the sitting 
posture, marking the position of the sacral vertebra (see 
p. 410). The limbs are of very unequal size. The /ore- 
Zimbs are short, and each consists of an upper arm, which, 


XII PHYLUM CHORDATA 409 


in the ordinary position, is directed backwards and down- 
wards from the shoulder joint; a fore-arm, directed down- 
wards and forwards from the elbow ; and a ham, ending in 
four short tapering dig7¢s, directed forwards. The Aind-limd 
is of great size ; in the usual squatting posture the thigh is 
directed downwards, outwards, and forwards from the thigh- 
joint, the shank inwards, backwards, and upwards from the 


Fic. 246.— Rana temporaria. (From Mivart.) 


knee. The /vo/ consists of two parts,—a varsa/ region directed 
downwards from the heel-joint, and five long, slender agit 
united by thin folds of skin or weds. Thus the limbs are 
placed in such a way that the elbow and knee face one 
another, and the first digit —that of the hand probably rep- 
resenting the second or index-finger, that of the foot, the 


410 MANUAL OF ZOOLOGY SECT. 


hallux or great toe—is turned inwards or towards the 
median plane of the body. 

The skin is soft and slimy, owing to the secretion of 
mucous glands ; there is no trace of an exoskeleton. 

The vertebral column (Fig. 247) is remarkable for its 
extreme shortness ; it consists of only nine vertebrae (V. 1- 
V. 9), the last followed by a slender, bony rod, the wrostyle 
(UST). The second to the seventh vertebre are similar 
in character. The centrum (B, cv) is somewhat depressed, 
and has a concave anterior and a convex posterior face —a 
form known as procelous. Each half of the xeural arch 
consists of two parts, —a pillar-like pedicle (pd) springing 
from the centrum and extending vertically upwards, and a 
flat, nearly horizontal dzmcna (2m), forming, with its fellow, 
the roof of the neural canal. 

The zygapophyses (a. zg) or yoking processes are far 
better developed than in any fish. Laterally the neural 
arch gives off on each side a large outstanding sransverse 
process (tr. pr) ; its crown is produced into a very small and 
inconspicuous neural spine. The first or cerarcal vertebra 
(V. 1) has a very small centrum and no transverse processes. 
There are no anterior zygapophyses, but at the junction of 
centrum and arch there occurs on each side a large.oval 
concave facet for articulation with one of the condyles of the 
skull (see p. 411). The eighth vertebra has a biconcave 
centrum ; that of the ninth or sacral vertebra (V.9) is con- 
vex in front and presents posteriorly a double convexity 
articulating with a double concavity on the anterior end of 
the urostyle. 

The shud (Figs. 247, 248) consists of a narrow drain-case, 
produced behind into great outstanding evditory capsules, 
and in front into large o/factory capsules. The whole of the 
bones of the upper aw are immovably fixed to the cranium 


XII PHYLUM CHORDATA 411 


so that the only free parts are the fower jaw and a 
small plate, the Ayord apparatus, partly bony and partly 
cartilaginous, which supports the tongue, and is the sole 
representative of the entire visceral or gill-bearing skeleton 
of the fishes. 

A cartilaginous cranium comparable with that of the dog- 
fish, but very thin and delicate, forms the foundation of the 
skull of the frog; but superadded to this are a number of 
cartilage bones—or bones which replace portions of the 
cartilage, and membrane bones — or bones which are formed 
in membrane, independently of the cartilage. ‘There are 
five cartilage bones, the paired exoccipitals and pro-otics, and 
the median sphenethmoid. The exoccipitals (EX. OC) lie 
in the posterior or occ7gital region of the skull and bound the 
large opening or foramen magnum (for. mag) at the posterior 
end of the skull through which the spinal cord, contained in 
the neural canal enclosed by the neural arches of the vertebree, 
becomes continuous with the brain, contained in the cavity 
of the cranium. Below the foramen magnum are a pair of 
oval projections, the occipital condyles (oc. cn), for articu- 
lation with the first vertebra of the spinal column. The 
second pair of cartilage bones, the pro-o/ics (PR. OT), are 
ossifications in the roof of the auditory capsule, situated 
just in front of the exoccipitals, with which they become 
firmly united. The sphenethmoid (SP. ETH) is a peculiar 
ossification of somewhat complex form, which lies partly in 
the wall of the anterior portion of the cranial cavity, partly in 
the wall of the posterior portions of the nasal cavities or 
olfactory sacs. 

To this cartilaginous cranium with its cartilage bones 
certain membrane bones are added. Covering the roof 
of the brain-case are two long narrow bones called the 
Jronto-parietals (FR. PA), because they are formed by the 


Fic. 247. — Rana temporaria. A, the skeleton from the dorsal aspect: the left half of the shoulder 
girdle and the left fore and hind limbs are removed, as also are the membrane bones on the 
left side of the skull. Cartilaginous parts dotted. Names of cartilage bones in thick, those 


of membrane bones in italic capitals, @. ¢ 43, anterio: cornu of hyoid; acts, acetabulum; 
AST, astrazgilus; 4 “y, basi-hyal; C, cahar, CAL, sale weum, EX. OC, ex-occipital; FE, 
femur; fox. fon', fontanclles, FR. PA, frontoppomtid: HU, humerus; IL, iliom; JLX, 
maxilla; of. cf, olfactory capsule; cf fr, otic process: :, Ay, posterior cornu of hyoid; 
PAV, premaxilla, PR. OT, pro-otw, RA. UL, radin-ulna; SP H, sphenethmoid; SQ, 


squamosal; S. SCP, supra-scapul.: svs, suspensorium; TI. FI, tibio-fibula; z7. Av, transverse 
process: UST, urostyle; V. 1, cervical vertebra; V. 9, sacral vertebra; /’?O, vomer; -V 
digits. B, the fourth vertebra, anterior face, «. sy, anterior zygapophysis; cz. centrum; 
dm, lamina; 2. sp, neural spine; fd, pedicle; ¢v, pr, transverse process. (After Howes, 
slightly altered, ) 


413 


PHYLUM CHORDATA 


SECT. XII 


union of a pair of /rontads in front with a pair of parietals 


behind. 


Over the olfactory capsules are a pair of triangular 


nasals (VA), and applied to their ventral surfaces small 


(poraye Apysys ‘samopy sayy) ‘zawoa ‘yy ‘sadeys ‘dys ‘yesourenbs ‘G5 
‘prouriausyds ‘ALA “ag ‘yesnf-owspenb ‘7 7G ‘pioBAraid ‘N74 ‘on0-o1d ‘LO ‘Ad ‘eyxeur 
cad ‘yyy ‘opped ‘pag spiody yo nuros 101aysod ‘Ay 19 -¢ :prousydsered “F775 "pg ‘ayeipenb 
-oyejed ‘2b yog sauneyed ‘7p Gy fsseooid ono ‘ag ‘yo ‘ajnsdeo 10,0810 ‘¥9 “yo Sa[Apuos [eqdi990 
‘42°90 {SadtaU YIUaAas pue yyy 10) UduUEIO; ‘ZS “Ar fugureroy odo ‘e ‘aay tyeseu ‘pyr feypixew 
‘VA ‘ueraxoaw-ojuaw SIO “AL <qeiataed-oyuosy ‘Vd ‘M7 ‘wnuseu usuresoy Fou “40f fyeidr1990 
“x9 ‘00 “XH ‘Areuep “ZV ‘e]aumnjoo “7OQ ‘!prody jo Apoq ‘fy -g :proAy jo nusod r0119;Ue 
‘fy 2B “putyaq wor > Sprody pue afqipuew yim ‘apis ya] aq1 woy ‘gq f(ainsdy yo y9}) apis wysr 


ay} UO padoulad SsUog SULIqUISUT ay) YA ‘yWwouEq WOY ‘WY "NYS eyT, “ele1odw9} eUeY— gre ‘O1y 


On the ventral surface of the skull 
is a large T-shaped parasphenoid (PA. SPA), its stem 
underlying the base of the cranium, while its two arms ex- 


tend outwards beneath the auditory capsules. 


paired vomers (VO). 


414 MANUAL OF ZOOLOGY SECT, 


The palato-quadrate cartilage is unossified ; but in relation 
to its anterior portion is a palatine (PAZ) membrane bone 
and to its posterior portion a prerygoid (PTG). The former 
is a slender rod-like bone directed transversely on the lower 
surface of the skull. The latter is a larger three-rayed bone, 
having an anterior, an inner, and a posterior arm. The 
posterior portion of the palato-quadrate cartilage, the guad- 
rate or suspensorium (sus), connects the lower jaw with the 
posterior region of the skull. Internally it is covered over 
by the inner and posterior arm of the pterygoid ; externally 
a hammer-shaped membrane bone, the sguamosal (SQ) 
is applied to it. The upper jaw is formed by three mem- 
brane bones, the small premaxilla (PAX ) in front, then 
the long narrow maxil/a (AZX ), and finally the short guad- 
ratojugal (QU. /U) which is connected posteriorly with 
the quadrate. The mandible contains on each side a per- 
sistent Meckel’s cartilage as a sort of core, ossified at its 
anterior end, outside which are two membrane bones. The 
hyoid is a squarish plate of cartilage (4. Ay) with two pairs of 
processes (a.¢. hy, p. c. hy), the posterior of which is ossified. 

The scapula is ossified and is connected by its dorsal 
edge with a swpra-scapula (Fig. 247, S. SCP) formed partly 
of bone, partly of calcified cartilage, and developed from 
the dorsal region of the embryonic shoulder-girdle. The 
coracoid (Fig. 249, Co) is also ossified, while the procora- 
coid is represented by a bar of cartilage, having a membrane 
bone, the c/avicle (C7), closely applied to it. The supra- 
scapula overlaps the anterior vertebre ; the coracoid and 
procoracoid are connected ventrally by a cartilage, the epi- 
coracoid (Co'), which is in close contact with its fellow of 
the opposite side in the middle ventral line, so that the 
entire shoulder-girdle, like that of the dogfish, forms a 
single inverted arch. 


xu PHYLUM CHORDATA 415 


Passing forwards from the anterior ends of the united 
epicoracoids is a rod of bone, the episternum (Ep), tipped 
by a rounded plate of cartilage, the omosternum ; and passing 
backwards from their posterior ends is a similar but larger 
bony rod, the sternum (SZ), also tipped by a cartilaginous 
plate, to which the name x7phisternum (An) is applied. 


Fic. 249.— Rana esculenta. The shoulder girdle from the ventral aspect. Co, 
coracoid; Co', epicoracoid; CZ, clavicle; G, glenoid cavity; 2, episternum; 
Fe, fenestra between procoracoid and coracoid; KC, cartilage separating scapula 
and clavicle; A, xiphisternum; 2, junction of epicoracoids; S, scapula; 
Sz, sternum. (From Wiedersheim’s Comparative Anatomy.) 


The four limbs deviate from the typical structure (p. 341) 
chiefly in the fusion of the radius and ulna into a single 
radio-ulna (Fig. 247, RA. UL) and in the presence of only 
four complete digits with a vestigial one on the radial side. 
In all probability the latter represents the pollex,-and the 


416 MANUAL OF ZOOLOGY SECT. 


complete digits are the second to the fifth of the typical 
hand. Six carpals only are present. 

The pelvic arch (Figs. 24.7 and 250) 
is very peculiarly modified; it re- 
sembles in form a bird’s “ merry- 
thought,”” consisting of two long 
curved bars articulating in front with 
the transverse processes of the sacral 
vertebra and uniting posteriorly in 
an irregular vertical disc of mingled 
bone and cartilage which bears on 
each side a deep, hemispherical 
acetabulum (Fig. 250, G) for the ar- 
ticulation of the thigh-bone. The 
curved rods are the ea (f, P); 

they expand posteriorly and unite 

inns Fnac Ki, ou with one another in the median plane 
ae pete pdnatony.) to form the dorsal portion of the disc 
and about one-half of the acetabulum. 

The posterior portions of the disc and the acetabulum are 
furnished by the zschza (Zs), fused with one another in the 
sagittal plane, and their ventral portions by the similarly 
united pudes (An). The ilium and ischium are formed of 
true bone, the pubis of calcified cartilage ; the union of the 
elements in the median plane is called the symphysis. In 
the Aznd-liméd the tibia and fibula are fused to form a single 
tibio-fbula (Fig. 247, TI. FI), and the two bones in the 
proximal row of the tarsus, namely, the tibiale or as/raga- 
/us (AST) and the fibulare or calcaneum (CAL), are greatly 
elongated and provide the leg with an additional segment. 
There are three tarsals in the distal row, one of which ap- 
pears to represent a central, another the first distal carpal, 
and the third the fused second and third. There are five 


Fic. 250 — Rana esculenta. 
Pelvic girdle from the right 


XII PHYLUM CHORDATA 417 


well-developed digits, and on the tibial side of the first is a 
spur-like structure or ca/ar (C), formed of three bones, a 
metatarsal and two phalanges: such a rudimentary digit is 
called a pre-hallux. 

The mouth leads into a wide éuccal cavity having in its 
roof the posterior nares (Fig. 251, p. na), a pair of projec- 
tions due to the downward bulging of the large eyes, and the 

eel 


fF; z 
EL 2 
obfl. FR PAP! gt O73) ry s| sped Ling ring ;, 7f° USSe™ oy Zz’ 
SPHETH J |) zl ___y {| UST | ur ' 


Fic 251.— Rana temporaria. Dissection from the left side; the viscera somewhat 
displaced. az, anus; 6.d, bile duct; 4. hy, body of hyoid; 42, urinary bladder; 
6/', its opening into cloaca; ¢ art, conus arteriosus; cd/m, cerebellum; cé, 
cloaca; cz. 3, centrum of third vertebra; cf. ad, corpus adiposum; cvb h, cere- 
bral hemisphere: d. Zy. s, dorsal lymph sinus; dz, duodenum; ef. cor, epicora- 
coid; es. ¢, Eustachian tube; FR. PA, fronto-parietal; g/, glottis; gul, gullet; 


iL, ilium; 1s, ischium; Ad, kidney; 7. az, left auricle; 2 dzg, left lung; /r, 
liver; mM. MCK, mento-meckelian; . a. 7, neural arch of first vertebra; o/f 2, 
olfactory Iabe; oft 7, optic lobe; 0. sT, omo- and epi-sternum; fcd, peri- 
cardium; PILV, premaxilla; fx, pancreas; f xa, posterior naris; fx, pubis; 
ret, rectum; ». Zag, right lung; s. zzf, small intestine; sf. cd, spinal cord; 
SPH. ETH, sphenethmoid; sf/, spleen; s¢, stomach; s. 7, sinus venosus; fg, 
tongue; ¢s, testis; #7, ureter; 27’, its aperture into the cloaca; uSsT, urostyle; 
wv, ventricle; zw dy. s, ventral lymph sinus; vo. ¢, vomerine teeth; ws. sem, 
vesicula seminalis, 


Eustachian tubes (eus. t, vide infra). On its floor is the 

large fongue (tng), attached in front and free behind, where 

it ends in a double point ; by means of its muscles it can be 
2E 


418 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 (g/). Teeth are arranged in a single 
series round the edge of the upper jaw, attached to the pre- 
maxilla and maxille; there is also a small patch of teeth 
(vo. 2) 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 gud/e¢ (gu/) into a stomach (s?) consisting of 
a wide cardiac and a short, narrow pyloric division. The 
duodenum (du), or first portion of the saall intestine, passes 
forwards parallel with the stomach; the rest of the small 
intestine is twisted into acoil. The large intestine or rectum 
(re?) is very wide and short, and passes without change of 
diameter into the cloaca (¢/). 

The “ver (/r) is two-lobed ; between the right and left 
lobes lies a large gadl-bladder. The pancreas (pn) is an 
irregular gland surrounding the bile duct, into which it 
pours its secretion ; the sA/cen (sf7) is a small, red globular 
body attached near the anterior end of the rectum. 

The lungs (2 lig, r. dng) are elastic sacs lying in the 
anterior part of the ccelom 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 /aryvngo-tracheal chamber which communicates 
with the mouth by the narrow slit-like g/odt’s. 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. 251, ped) is not a separate cham- 
ber, as in fishes, but the heart, enclosed in a pericardial 
membrane, lies in the general ccelomic cavity between the 
gullet above and the epicoracoids below. The heart con- 
sists of a sinus venosus (Figs. 251 and 252, s.v), right 
and left auricles (7. au, /. au), a ventricle (v, vf), and a 
conus arteriosus (¢. a7). 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 (/) 
which springs from its dorsal wall and is free ventrally. The 
conus passes without change of diameter into a dudbus aorte, 
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 (pul. 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. 


cangl 


cara 


Fic. 252.— Rana temporaria The heart from the ventral aspect with the cavities 
laid open. a, a’. bristle in left carotid trunk; az. v. v, auriculo-ventricular 
valves; 4,4’, bristle in left systemic trunk; ¢,c’, bristle in left pulmo-cutaneous 
trunk; cay a, carotid artery; car gt, carotid plexus; ¢ art, conus arteriosus; 
car. tr, carotid trunk; 2, az, left auricle; dg. a, lingual artery: 2. 7, longitudinal 
valve; Aud. cu. tr, pulmo-cutaneous trunk; fz/ v, aperture of pulmonary veins; 
y.au, right auricle; s av. af, sinu-auricular aperture; sft. aur, septum auricu- 
larum; v.v', valves; wd, 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 


xl PHYLUM CHORDATA 421 


Fic. 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; c@/. mes, coeliaco- 
Mesenteric artery; cz, cutaneous artery; @. ao, dorsal aorta; dz, duodenal 
artery; gs, gastric artery; 4, hepatic artery; z/, iliac artery; zw, intestinal 
arteries; #a, kidney; 7. av, left auricle; Zg, lingual artery; pu/, pulmonary 
artery; fx/. cu. tr, pulmo-cutaneous trunk; 7. az, right auricle; 7, renal 
arteries; s#/, splenic artery; sys. ¢r, systemic trunk; sf, spermatic artery; 
ts, testis; v, ventricle, 


422 MANUAL OF ZOOLOGY SECT. 


into carotid (Figs. 252, car. a and 253, car) and Aingual (2) 
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 (ad. 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 (pul) to the lung, and a cuaneous artery (cw) 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, aa), 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 Aepate 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 vena/ portal vein to the 
corresponding kidney. 

The blood is collected from the kidneys by the rena/ 
veins (rn), which unite to form the large unpaired fost-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 


xu 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 pu/monary veins (pul) 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 aérated 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 aorte 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 bulbusaorte. 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. 


Fic. 254. —Rana temporaria. The venous system with the heart, lungs, liver, 
kidneys, and right testis, from the dorsal aspect. aéd, abdominal vein; 47, 
brachial vein; cd, cardiac vein; ds. dmb, dorso-lumbar vein; dz, duodenal vein; 
ext. Jit, external jugular vein; fre, femoral vein; gs, gastric vein; 4, hepatic 
vein; Ap pt, hepatic portal vein; zv#, intestinal veins; zv¢. 7x, internal jugular 
vein; d, kidney; 2. az, left auricle; dug, lung: dvr, liver; ms. cx, musculo- 
cutaneous vein; pr. cv, pre- -caval vein; fz. cz, post- caval vein; puZ, pulmonary 
vein; pv, pelvic vein; . aw, right auricle; 77, renal veins; xv. ft, renal “portal 
vein; s¢, sciatic vein; sf, splenic vein; sft, spermatic vein; s. v, Sinus venosus; 
zs, testis; ces, 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 Amphatic system is very well developed, and is 
remarkable for the dilatation of many of its vessels into 
immense 4wph sinuses. Vhe lymph is pumped into the 
veins by two pairs of Jymph-hearts, one situated beneath 
the supra-scapulz, the other beside the posterior end of the 
urostyle. 

The drain (Fig. 255) has avery small cerebellum (H A), 
large optic lobes (A7 #7), 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 ‘erminale. In 
correspondence with the number of vertebre 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 offactory sacs have each two openings: the anzerior 
naris or external nostril and the fosterior naris (Fig. 251, 
p- 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 fympante cavity (cau), which communicates with the 
mouth by the short Eustachian tube already noticed (Fig. 
251, ews. 2), So that a probe thrust through the tympanic 
membrane from outside passes directly into the mouth. In 


Fic. 255.— Rana esculenta. The brain. A, from above; B, from below. ch oft, 
optic chiasma; AH, cerebellum; Ay, pituitary body: //, infundibulum; 
L. ol, olfactory lobe; AZed, spinal cord; ALAM, mid brain; A.A, medulla ob- 
longata; Th. oft, optic thalamus; 7y. oft, optic tract; /°A, cerebral hemi- 
sphere; ZH, diencephalon; /— X, cerebral nerves; A’//. (1), hypoglossal (first 
spinal) nerve. (From Wiedersheim’s Comfarative Anatonty ) 


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 


XII PHYLUM CHORDATA 427 


handle united to the s/apes, 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, Ad, and Figs. 256 
and 257, JV) 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 ccelom 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 (C7). 

Opening into the cloaca on its ventral side is a bilobed, 
thin-walled, and very delicate sac, the urinary bladder (Fig. 
251, 4/), into which the urine passes by gravitation from 
the cloaca when the anus is closed. 

The “estes (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 vestcula 
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 fatdodies (FX). 


428 MANUAL OF ZOOLOGY SECT. 


The ovaries (Fig. 257, Oz) are large folded sacs, on the 
surface of which the black and white ova project. A fat- 
body is attached to each. The oz7ducts (Od) are greatly 
convoluted tubes, the narrow anterior ends of which open 
into the coelom by small 
apertures ( Of) placed close 
to the bases of the lungs. 
Their posterior ends are 
wide and thin-walled (C7), 
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 


Fic. 256.—Ranaesculenta Urinogenital : ‘ 
organs of the male. -f, dorsal aorta; tubes, which in the breed- 
Cl, cloaca; Cv, post-caval vein; AK, fat . : 
bodies; HO, testes; .V, kidneys; S, ing season become im- 
apertures of ureters into cloaca; Ur, i 
ureters. (From Wiedersheim’s Com- mensely dilated and serve 


parative clnatony.) ‘ : 
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 CHORDATA 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 ¢adpole, with two pairs of branched external gills and a 


Fic. 257.—Rana esculenta. Urinogenital organs of the female. J, kidneys; 
Od, oviduct; Oz#, its coelomic aperture; Ov, left ovary (the right is removed); 
P, cloacal aperture of oviduct; S.S', cloacal apertures of ureters; U#, 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 papillee, 


Fic. 258.—Rana temporaria. Stages in the life-history, from the newly-hatched 
Tadpoles (1) to the young Frog (8). 2a is a magnified view of 2, (From 
Mivart.) 

and provided with a pair of horny jaws. The enteric canal 

grows toa 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 zrv/ernad 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 aérial. 

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 
(74/a 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 
(7fi7a, Bufo, and others), in which the two halves of the 
shoulder-girdle, instead of being firmly united in the mid- 


Fic. 259. — Salamandra maculosa. (After Cuvier.) 


dle 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 


XIL 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 
2 group of Amphibia—the Gyzzno- 
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 (C@- 
ciia) 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 ee ee 

2F 


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, chameleons, 
and others), and theSphidia or snakes (including the vipers 
and rattlesnakes, pythons, boas, sea-snakes, etc.). 

3. The Rhynchocephalia, including only the New Zealand 
Tuatara (Hatterta). 

g. The Chelonia, including the land tortoises, soft tor- 
toises, river and marsh tortoises, and the turtles. 

#. 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 dvachium, the fore-arm or anfi- 
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 ges. 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 néctitating membrane, which, when withdrawn, lies 
in the anterior angle of the orbit. Behind the eye is a 
circular brown patch of skin, — the Ampanic 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 scaés 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 chameleons 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 chameleons 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 (.imgués), 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 


Fic. 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 SECT. 


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 flastron. hese 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 


Fic. 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 sca/es, 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 


Fic. 263. — Grecian tortoise (Testudo greca). (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 ven¢ra/ shields. 
In some lizards (chameleons 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 Amphisbeenians 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 chameleons 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 
(Pp. 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 ecdyszs 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 vertebre are always fully ossified. Only in the 
geckos and Hatteria are the centra amphiccelous, with 


XII PHYLUM CHORDATA 


remnants of the notochord in 
the inter-central spaces. In 
most of the others the centra 
are proccelous, 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 vertebra, which 
have strong transverse pro- 
cesses for articulation with 
the ilia. The first and sec- 
ond vertebrz are always modi- 
fied to form an atlas and 
axis. Ribs are developed in 
connection with all the ver- 
tebrz 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 


. 


S 


AZ, humerus; 
(From 


U, ulna. 


T, tibia; 


D, thoracic region of spinal column; F, fibula; Fe, femur; 


} C, caudal region; 
Z,ischium; Z, lumbar region; A, radius; Az, ribs; S, sacrum; Sc, scapula; Sta, abdominal ribs; 


Fic. 264. — Skeleton of crocodile, 
Zittel.) 


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 wxcinaze. 


Fic. 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- 

lastron; £f, epiplastron; F, fibula; /e, femur; AH, humerus; //, ilium; Zs, 

ischium; //, marginal plates; .V, nuchal plate; 7é, pubis; Pro, pro-cora- 

ea ie pygal plates; A, radius; Sc, scapula; 7, tibia; U, ulna. (From 
ittel. 


In the Chelonia (Fig. 265) the total number of vertebre 
is always smaller than in the members of the other orders. 


The cervical and the caudal are the only regions in which 
the vertebrze are movable upon one another. The vertebree 


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 cost/ 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 margina/ plates (Figs. 265 and 266, 47) running 
along the edge, and nuchal (Vu) and pygal (Py) plates 


Fig. 266.— Chelone midas. Transverse section of skeleton. C, costal plate; C’, 
centrum; 4, 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 hyZosternum, extending backwards 
as far as the pelvis. 


444 MANUAL OF ZOOLOGY SECT. 


A series of ossifications — the abdominal ribs, with a mesial 
abdominal sternum —-\ie in the wall of the abdomen in the 
Crocodilia (Fig. 264, Séz), 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 skz// 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 aérial mode of respira- 
tion, the zsceral 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 zzderclavicle 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. 


BS 


Fic. 267. — A, lateral view of skull of rattlesnake (Crotalus), 2. O, basi-occipital; 
B.S, basi-sphenoid; £. O, exoccipital; 7. O, fossa ovalis; La, conjoined lac- 
rymal and pre-frontal; Z. /, articulation between lacrymal and frontal; (x, 
mandible; 47x, maxilla; Ma, nasal; P?, palatine; Px, pre-maxilla; P. Sph, 
pre-sphenoid; P¢, pterygoid; Qx, quadrate; Sg, squamosal; //. V, foramina 
of exit of the second and fifth cranial nerves. B, transverse section at point 
lettered Bin Fig. A; 7, trabecule. (After Huxley.) 


In the lizards teeth are present in the pre-maxillz, the 
maxilla, 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 


gpESTER JERMAIN HUNN. 


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 maxille, 
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 


Fic. 268. — Pectoral arch and sternum of a lizard (Lacerta agilis). cd, clavicle; 
cor, coracoid; ef. cor, epicoracoid; epzst, episternum; g/ex, glenoid cavity for 
head of humerus; fv. cov, pro-coracoid; ~ 7 — ~. 4, first to fourth sternal ribs; 
se, scapula; st, sternum; swfra. 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 hes 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 Hatteriaa 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-maxille, the maxillz, 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 SECT. 


of the Crocodilia, the presence of a rudimentary cecum at 
the junction of small and large intestines in most Lacertilia 
and in the Ophidia, and the presence of numerous large 
cornified papillz in the cesophagus of the Turtles. 

The Reptiles have all an 
elongated ¢rachea, 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 Zungs 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- 


Fic. 269. — Heart of monitor (Varanus) 


guarded by valves. 


dissected to show the cavity of the 
ventricle and the vessels leading out 
from it. A. A’, auricles; Ao, dorsal 
aorta; Ap. Ap’, pulmonary arteries; 
Asc, subclayian artery ; Ca. Ca’, caro- 
tids; RA. RA, roots of dorsal aorta; 
Trea, innominate trunk: V, ventricle; 
t, right aortic arch; *, left aortic arch, 
(From Wiedersheim. i 


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 
There are always two quite distinct 


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. Inall 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 drain of Reptiles 
is somewhat more highly 
organised than that of the 
Amphibia. The cerebral 
hemispheres are well de- 
veloped in all. The mid- 
brain consists usually of 


Fic. 270.— Brain of alligator, from above. 
B. ol., olfactory bulb; G. /, epiphysis ; 
FH, cerebellum ; Me, spinal cord ; WHA, 
optic lobes; MA, medulla oblongata ; 
VH, cerebral hemispheres ; /— XJ, cra- 
nial nerves ; 1, 2, first and second spinal 
nerves. (After Wiedersheim.) 


two closely approximated oval optic lobes. The cerebellum 


2G 


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 chameleons 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 (Lacerta, 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 451 


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, 


Fic. 271. — Section of the pineal eye of Hatteria punctata. g, blood-vessels; 7, 
cavity of the eye filled with fluid; 4, capsule of connective tissue: 27, lens; #2, 
molecular layer of the retina; 7, retina; s¢, stalk of the pineal eye; -r, 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 chameleons 
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 amphisbzenians 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, aéroplane 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. Chameleons, 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, dZc), one of the muscles which raise the lower 
jaw: it is thus forced along the duct (Gc) to the aperture 
(sa), 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 


_ @ ae Cara: ?) 
“sis (gee S Less 
ESS eae 


Fic. 272.— Poison apparatus of rattlesnake. 4, eye; Gc, poison-duct entering 
the poison-fang at ¢ ; Av, muscles of mastication partly cut through at * ; A/c, 
masseter or constrictor muscle; Mc’, continuation of the constrictor muscle to the 
lower jaw ; 4V, nasal opening; S, fibrous poison-sac ; 2, tongue; sa, opening of 
the poison-duct ;_ 24 pouch of mucous membrane enclosing the poison-fangs. 
(From Wiedersheim. ) 


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 458 


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 dryseason. 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 


j 
i 


4 


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 roo 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 


xl 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 
coe hester J. Hunn 
The common or domestic pigeon is known hester. 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 deak formed of the upper 
and lower jaws covered by horny sheaths. The head, neck, 
and trunk are invested in a close covering of feadhers, 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 wngs, also 
covered with feathers, and, in the position of rest, folded 
against the 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 scaées and terminating in four digits 
(dg r'— 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 wropygium, and giving 


458 MANUAL OF ZOOLOGY SECT. 


origin to the group of large feathers (7c¢) 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 


Fic. 273. —Columba livia. The entire animal from the left side with most of the 
feathers removed. ad.dg. rmx, ad-digital remex; a/ sf,ala spuria; ax, anus; 
au ap, auditory aperture; cd. rmg, cubital remiges; cr,cere; @g. J, 2, 3, digits 
of manus; dg 7’, 2’, 3’, 4’, digits of pes; Aw ff, humeral pteryla; dg, ligament 
of remiges; md. dg rmg, mid-digital remiges; a, nostril; xc. me, nictitating 
membrane; 9. g?, oil gland; py. dg rmg, pre-digital remiges; pr. pig, pre- 
patagium; Af pig, post-patagium; cz, mesial rectrix of right side; vcé’, sacs 
of left rectrices; sf. A¢, spinal pteryla; ¢s. s#éts, tarso-metatarsus; v. aft, 
ventral apterium, or featherless space. 


XII PHYLUM CHORDATA 459 


a large gland, the oz/-g/and (0. g/), 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 7) and third (dg 3), 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 /arso-metatarsus (¢s. més) and four digits, of which one, 
the hallux (dg z'), 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 ceve (cr) surrounding the wos¢7i/ (7a), 
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 (mcf. 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 anus or cloacal aper- 
ture (az), 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. 


Fic. 274.— Columba livia. A, proximal portion of a remex. ca/, calamus; z#f. 
uuib, inferior umbilicus; rch, rachis; sup. #6, superior umbilicus. B, filo- 
plume. C, nestling-down. (C, from Bronn’s 7hzerretch.) 


A feather (Fig. 274) is an elongated structure consisting 
of a hollow stalk, the ca/amus or quill (ca7), and an ex- 
panded distal portion, the vex//um or vane. At the 
proximal end of the quill is a small aperture, the zx/ertor 
umbilicus (inf. umb), mto 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, z.c., 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 dards, 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 dardudes, 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 filoplumes (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 papille of. 
the skin formed of derm with an epidermal covering. The 
papilla becomes sunk in a sac, the /eather-follicle, from 


462 MANUAL OF ZOOLOGY SECT. 


which it subsequently protrudes as an elongated feather-gerim, 
its vascular dermal interior being the /eather-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), 


Fic. 275.—Pterylosis of Columba livia. A, ventral: B, dorsal. a@/. ft, alar 
pteryla or wing-tract; ¢. pz, cephalic pteryla or head-tract: cad. At, caudal 
pteryla or tail-tract; cr fz, crural pteryla; cv. aft, cervical apterium or neck- 
space; f/m. ft, femoral pteryla; Az. ft, humeral pteryla; Jat aft, lateral 
apterium; sf 2, spinal pteryla; «. af¢, ventral apterium; @ Aé, ventral pteryla. 
(After Nitsch.) 


the feather tracts or pleryle (sp. pt, hu. pi, etc.), separated 
from one another by featherless spaces or apseria (v. aft, 
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 


XU PHYLUM CHORDATA 463 


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 cuditals 
or secondaries (cb. rmg). The rest are known as primaries. 
In the tail there are twelve long rectrices (rc¢) or tail-quills 
springing in a semicircle from the uropygium. The whole 
feather-arrangement is known as the peeryosis. 


car 


Fic. 276.—Columba livia. The bones of the trunk. acy. cov, acrocoracoid; 
a. tr, anti-trochanter; acd, acetabulum; car, carina sterni; cd. v, caudal verte- 
bre; cor, coracoid; cv. 7, cervical ribs; f ¢7s, probe passed into foramen 
triosseum; fxr, furcula; gi. cv, glenoid cavity; 2, ilium; 7s, ischium; 7s. for, 
ischiatic foramen; od¢, x, obturator notch; px, pubis; pyg. st, pygostyle; scp. 
scapula; s. scr, syn-sacrum; sz, sternum; sZ. , sternal ribs; th. wT, first, and 
th. u. 5, last thoracic vertebra; zc, uncinates; wr. ~, 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 vertebra, the last 
two of which have double-headed ribs (Fig. 276, cv. 7) each 


464 MANUAL OF ZOOLOGY SECT. 


having its proximal end divisible into the Aead proper articu- 
lating with the centrum of the vertebra, and a ¢wberc/e 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, 78), 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 vertebre 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 heterocelous. 

The first two vertebra, 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. 
Hie. aye alata Tela Gee The ang has projecting forwards 

vical vertebra; A, anterior; from its centrum, a peg-like pro- 


B, posterior face. a. syyy an- 


terior zygapophysis: cz, cen- cess, the odontoid process, which 
trum; 2. @,neural arch; fp. syg, 


posterior zygapophysis: 7%, mb; lies 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 (77. 7) and a sternal 
(s¢. 7) portion, and articulating with the vertebra by a double 
head. Springing from the posterior edge of the vertebral 
rib is an uncinaze (Fig. 276, wc), resembling that of Hatteria 


XII PHYLUM CHORDATA 465 


and the crocodile, but formed of bone and ankylosed with 
the rib. 

Following upon the fourth thoracic are about twelve 
vertebre all fused into a single mass (Fig. 276, s. sev), and 
giving attachment laterally to the 
immense pelvic girdle. The 
whole of this group of vertebra 
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 (¢4. v. 5). The 
next five or six have no free 
ribs, and may be looked upon 
as lumbar (Fig. 278, /'—s°*). 


Fic. 278.—Columba livia. Sac- 


Next come two sacral vertebre rum of a_ nestling (about 
5 fourteen days old), ventral 

(c') homologous with those of aspect. cl, centrum of first 
z onal sacral vertebra; c!, centrum of 

the lizard. The remaining five fifth caudal; c. 7, first sacral 
i fi rib; 71, centrum of first lumbar; 

vertebra of the pelvic region are 2, of third lumbar; s?, of fourth 
lumbar; s, of sixth lumbar; 

caudal. Thus the mass of ver- zr. p, transverse process of 
i : ‘ first lumbar; ¢7. ', of fifth 

tebrze supporting the pelvic girdle lumbar; ¢ #", of first sacral. 


:d 5 , (From Parker’s Zootomy.) 
in the pigeon is a compound 


sacrum, or syz-sacrum, formed by the fusion of the posterior 
thoracic, all the lumbar and sacral, and the anterior caudal 
vertebrae. 

The syn-sacrum ig followed by six free caudals and the 
vertebral column ends posteriorly in an upturned, compressed 
bone, the Aygossle or ploughshare-bone (Fig. 276, pyg. sé), 
formed by the fusion of four or more of the hindermost 
caudal vertebre. 

The sternum (Fig. 276, st) is one of the most character- 

2H 


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, 


Fic. 279. —Columba livia. Skull of young specimen. A, dorsal; B, ventral; C, 
left side. ad. s, alisphenoid; ax, angular; av, articular; 4 0, basi-occipital ; 
d. dentary; e. 0, ex-occipital; ex, aperture of Eustachian tube; f. #, foramen 
magnum; /r, frontal; 2.0. s, inter-orbital septum; jz, jugal; Zc, lachrymal; 2. s, 
lambdoidal suture; ». eff, mesethmoid; m2, maxilla; x ?, maxillo-palatine 
process; wa, wa’, na"', nasal; 0. c, occipital condyle; or. Jr, orbital plate of 
frontal; fa, parietal; fa. s, parasphenoid (rostrum); Pi, palatine: p wx, pre- 
maxilla; p¢, pterygoid; gz, quadrate; s. az, supra-angular; s 0, supra-occipital * 
sg, squamosal; ¢y, tympanic cavity; II.—XII, foramina for cerebral nerves. 
(From Parker’s Zootomy.) 


XII PHYLUM CHORDATA 467 


by ligament; its anterior edge bears a pair of deep grooves 
for the articulation of the coracoids. 

The sku (Fig. 279) is distinguished at once by its 
rounded brain-case, immense orbits, and long pointed beak. 
The foramen magnum (f #) 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 
(0. ¢). 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 premaxille (Fig. 279, 2. mx) are united into a large 
triradiate bone which forms 
practically the whole of the 
upper beak. The maxille 
(Fig. 279, mx), on the other 
hand, are small, and have 
their anterior ends produced 
inwards into spongy maxzllo- 
palatine processes (Fig. 279, 
mx.p). The slender poste- 
rior end of the maxilla is 
continued backwards by an 
equally slender jugal (jz) 
and quadrato - jugal to the 
quadrate. The latter (Fig. 
279, gu) is a stout three- 
rayed bone articulating by fic. 280 --Columbia livia. Hyoid ap- 


: paratus. The cart:laginous parts are 
two facets with the roof dotted. 4. 4.7, basi-branchials; 3 Ay, 


: : si-hyal; c. dr, -b hial; 

of the tympanic cavity, and se oe Bee ep 
D branchial. 

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 


468 MANUAL OF ZOOLOGY SECT. 


adult. The hyoid apparatus (Fig. 280), is of characteristic 
form, having an arrow-shaped body (é. 4) with a short pair 
of anterior cornua (¢c. Ay) derived from the hyoid arch, and 
a long pair of posterior cornua (¢. 7., ep. 6r) from the first 

: branchial. The colu- 
mella is a rod-shaped 
bone ankylosed to the 
stapes, anc bearing at 
its outer end a three- 
rayed cartilage or ex- 
tra-columella fixed to 
the tympanic mem- 
brane. 

The showlder-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 
Fic. 28:.—Columba livia. Skeleton of the left aspect of the bone, is 

wing. cp. métcp, carpo-metacarpus; Az, hu- 2 

merus; pf.z, phalanx of first digit; #i.2', attached by ligament a 

ee States din Cee eke sabre-shaped scapula 


foramen: va, radius; va‘, radiale; x2, ulna; 


ui’, ulnare. (scp) which extends 


xu PHYLUM CHORDATA 469 


backwards over the ribs, and includes, with the coracoid, an 
acute angle, the coraco-scapular angle. The glenoid cavity 
(gé. 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 
Jurcula (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 
(7. tvs) 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, hw) is a 
large, strong bone, with a 
greatly expanded head and 
a prominent ridge for the in- ye. 282, — Columba livia. Left manus 
sertion o: the pectoral muscle. iti Cp) a gee ne 
The radius (ra) is slender ©: 2, ulnare; smcp 1. 2,3, meta- 


carpals; #4. 7, phalanx of first digit; 
and nearly straight, the nina  2f3-o%-4> palene’s a second 
stouter and gently curved. Ss aba ulna. “(Eom 
There are two large free car- 
pals, a radiale (ra') and an wlnare (wl'), 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 


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 nYetacarpal is a single 
pointed phalanx (ff. 7); the second metacarpal bears two 
phalanges, the proximal one ( pA. 2') produced postaxially 
into a flange, the distal one (pA. 2") pointed; the third 
metacarpal bears a single pointed phalanx (fA. ?). 


ob, f us pe 


Fic. 283.— Columba livia. Left innominate of a nestling. The cartilage is dotted. 
ac, acetabulum; a. ¢, anti-trochanter; 77, pre-acetabular; and 77’, post-acetab- 
ular portion of ilium: zs, ischium; ¢ s. f, ischiatic foramen; 04. /, obturator 
notch; Jz, pubis. (From Parker's Zootomy.) 


ac 


The pelvic girdle (Fig. 283). The thum (i7) 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 or acetabular ends, and lie 


nearly parallel. Neither is- 
chium nor pubis unites ven- 
trally with its fellow to form 
a symphysis. 

In the hind-limb the femur 
(Fig. 284, fe) is a compara- 
tively short bone. Its proxi- 
mal extremity bears a promi- 
nent ¢rochanter (tr) and a 
rounded head (Ad). Its dis- 
tant end is produced into 
pulley-like condyles. Articu- 
lating with the femur is a 
very long bone, the 7#z0- 
tarsus (i. 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 Aula 
(Fig. 284, 7%) is very small, 
much shorter than the tibia, 
and tapers to a point at its 
distal end. 


e,femur; 7, fibula; 2d, head; mts. 7, 
rth digit; ¢z. ¢s, tibio-tarsus; ts. wztts, 


Bones of the left hind-limb. cx. 7, cnemial process; 


first metatarsal; Aa/, patella; A. 7, phalanx of first digit; A%. 4, phalanx of fou 


tarso-metatarsus; ¢”, trochanter, 


Fic. 284. — Columba livia. 


472 MANUAL OF ZOOLOGY SECT. 


Following the tibio-tarsus is an elongated bone, the zarso- 
metatarsus (ts. mitts), 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, #°), 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 (md¢¢s.z). 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 
Fic. 28s. — Columba livia, phalanx is pointed and curved, and 


Part of left foot of a a 

hatched embryo (magni. Setves for the support of the horny 
fied). The cartilage is 

dotted’: onilc os seconds “Glas 


mil. 3, third; and wl. 4, +e : 
fourth metatarsal dictibies A further peculiarity is the fact 


ae aes ee; that the larger proportion of the 
pa ee (From Parker's 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 preumatic 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 


XII PHYLUM CHORDATA 473 


wing, by which the bird rises into and propels itself through 
the air, is performed by the secéoradis (Fig. 286, pct), 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. s¢), from the posterior part of the body of 


pee prpigm 
na lg ens. br Us Gee [exe ep.ra 


Au, 


Fic. 286.— Columba livia. The principal muscles of the left wing; the greater 
part of the pectoralis (fc¢) is removed. ca”. st, carina sterni; c/, furcula; cor, 
coracoid; cor. dr. br, coraco-brachialis brevis: cor. br, lg, coraco- brach’alis 
longus; ¢f. s¢, corpus sterni; ext. cp. rd, extensor carpi radialis; ext. cp. 2/, 
extensor carpi ulnaris; 77. cf, w/. flexor carpi ulnaris; g?. c, glenoid cavity; hu, 
head of humerus; /z’, its distal end; Act, pectoralis; pct’ ,its cut edge: pct"’, its 
insertion; prx. br, pronator brevis: fx. Zg, pronator longus; pr. plgm, pre- 
patagium; A¢. _pigm, post-patagium; sd c/z, sub-clavius; sé. clv’, its tendon of 
insertion passing through the foramen triosseum, and dotted as it goes to the 
humerus; és. acc, tensor accessorius; 75. ér, tensor brevis; ¢us. lg, tensor 
longus; Zs. 2. f, tensor membrane posterioris alz. 


that bone (cf. s¢), and from the clavicle (¢2), 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 (fc?') into the ventral aspect of the humerus 


474 MANUAL OF ZOOLOGY SECT. XII 


(Au, hu'), which it depresses. The elevation of the wing is 
performed, not, as might be expected, by a dorsally placed 
muscle, but by the swvdb-clavius (sb. clv), arising from the 
anterior part of the body of the sternum, dorsal to the 
pectoralis, and sending its tendon (sd. ¢/y') 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 (tng) is large and pointed at the tip. 
The pharynx leads into a wide and distensible gu//et (gud), 
which soon dilates into an immense reservoir or crop (crp) 
situated at the base of the neck, between the skin and the 
muscles and immediately in front of the sternum. In this 
cavity the food, consisting of grain, undergoes a process of 
maceration before being passed into the stomach. From 
the crop the gullet is continued backwards into the stomach, 
which consists of two parts, the proventriculus (pron) and 
the géssard (giz). The proventriculus appears externally 
like a slight dilatation of the gullet, but its mucous mem- 
brane is very thick and contains numerous gastric glands 
so large as to be visible to the naked eye. The gizzard has 
the shape of a biconvex lens; its walls are very thick and 
its lumen small. The thickening is due mainly to the im- 
mense development of the muscles which radiate from two 
tendons, one on each of the convex surfaces. The epi- 
thelial lining of the gizzard is very thick and horny, and 
of a yellow or green colour: its cavity always contains small 
stones, which are swallowed by the bird to aid the gizzard 
in grinding up the food. 


Fic. 287. Columba livia. Dissection from the right side. The body-wall, with 
the vertebral column, sternum, brain, etc., are in sagittal section; portions of the 
gullet and crop are cut away and the cloaca is opened; nearly the whole of the 
ilium is removed, and the duodenum is displaced outwards. @. ao, aortic arch; 
bd. 7, ad. 2, bile-ducts; 4. fadr, bursa Fabricii; cé/, cerebellum; ce, right 
coecum; cfdm, coprodeum; cr, cere; cré. h, left cerebral hemisphere; crf, 
crop; cv. v. 7, first cervical vertebre; d7. cw, diaceele; dwt, dentary; duo, 
duodenum; ezs. apf, aperture of Eustachian tubes; g7z, gizzard (dotted behind 
the liver); g?, glottis; guw/, gullet; zZz, ilium: 72. 07d. sf, inter-orbital septum; 
Ad, right kidney; dwg, right lung; Z~, liver (right lobe); ma, bristle passed from 
nostril into mouth; 042. sep, oblique septum; o. g/, oil gland; ped, pericardium; 
pmx, pre-maxilla; fx, pancreas; px. 6, pineal body; pzd. 1-3, pancreatic 
ducts; fv. cv, right pre-caval; prdm, proctodeum; fry, proventriculus 
(dotted behind liver); At. cv, post-caval; pty. 6, pituitary body: Ayg. st, pygo- 
style; 7. az, right auricle; ». dr, right bronchus; rect, rectum; 7 vut, right 
ventricle; sf. cd, spinal cord; sf/, spleen (dotted behind liver); s. 724, sinus 
rhomboidalis; s. scr, syn-sacrum; sé, carina sterni; sy, syrinx; ¢. v. JZ, first, 
and th. v. 5, fifth thoracic vertebrae: ‘ug, tongue: fr, trachea; fs, right testis; 
ur, aperture of left ureter; w7dm, urodxum; v. df aperture of left vas deferens, 


475 


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 zim (2/m) + it passes without change of diameter 
into the rectum or large intestine (rc¢), the junction between 
the two being marked only by a pair of small blind pouches 
or ceca (cw). The cloaca is a large chamber divided into 
three compartments. 

There are small dvcca/ glands opening into the mouth, but 
none that can be called salivary. The Aver (/) is large, and 
is divisible into right and left lobes, each opening by its own 
duct (4. d@. 7, 6. d. 2), into the duodenum: there is no gall 
bladder. The fancreas (fp) is a compact reddish gland 
lying in the loop of the duodenum, into which it discharges 
its secretion by three ducts (fz. d. z~7). A thick-walled 
glandular pouch, the dursa Fabric (6. fabr), lies against 
the dorsal wall of the cloaca in young birds, and opens into 
the cloaca: it atrophies in the adult. 

The spleen (sf/) is an ovoid red body, of unusually small 
proportional size, attached by peritoneum to the right side 
of the proventriculus. There are paired ¢hyrords 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 glottis (Fig. 287, g/) is situated just behind the root 
of the tongue and leads into the Zavux, which is supported 
by cartilages, but does not, as in other vertebrates, function 
as the organ of voice. From the larynx an elongated tube, 
the ¢rachea or windpipe, the wall of which is supported by 
numerous bony rings, runs back along the ventral aspect of 
the neck to enter the body-cavity, where it divides into the 
right (7. 67) and left dronchz, one passing to each of the lungs. 


XI PHYLUM CHORDATA 477 


At the junction of the trachea with the bronchi is found 
the characteristic vocal organ, the sy7ix (s)'"), occurring in 
no other class. 

The dungs (Fig. 287, /ug) are very small in comparison 
with the size of the bird, and are but slightly distensible, 
being solid, spongy organs, not mere bags with sacculated 
walls, as in Amphibia and many reptiles. Their dorsal sur- 
faces fit closely into the spaces between the ribs and have 
no peritoneal covering ; their ventral faces are covered by a 
strong sheet of fibrous tissue, the pu/monary aponeurosis or 
pleura, a special development of the peritoneum. Into this 
membrane are inserted small, fan-like costo-pulmonary mus- 
cles, which arise from the junction of the vertebral and sternal 
ribs. 

Each main bronchus gives off secondary bronchi, and 
these branch again, sending off tubes which end blindly near 
the surface of the lung and give off blind dilations commonly 
known as alveo#. In addition to these, each main bronchus 
also gives off branches which end in a series of thin-walled 
air-sacs, which lie in the body-cavity, and are in communi- 
cation with the pneumatic cavities of the bones. 

The Acar? (Fig. 288) is of great proportional size, and like 
that of the crocodile consists of four chambers, z.¢., the right 
and left auricles, and right and left ventricles. There is no 
sinus venosus, that chamber being, as it were, absorbed into 
the right auricle (Fig. 288, A, 7. av). The right ventricle 
(Fig. 288, B) partly encircles the left, the former having a 
crescentic, the latter a circular cavity in transverse sections. 
The left auriculo-ventricular valve has the usual membranous 
structure consisting of two flaps connccted with the wall of 
the ventricle by tendons, but the corresponding valve of the 
right side (R. V) is a large muscular fold, very characteristic 
of the class. 


478 MANUAL OF ZOOLOGY SECT. 


The right auricle receives the right and left pre-cavals 
(x. pre, 1. pre) and the post-caval (pz), the left, four large 
pulmonary veins (f. 7). The left ventricle (Fig. 288, 2 vz), 
as in the crocodile, gives origin to the right aortic arch 
(a. ae), but the right ventricle (7. vz) gives off only one 
trunk, the pulmonary artery, which soon divides into two 


TUN 


Fic. 288.—A, heart of the pigeon, dorsal aspect. @. ao, arch of aorta; dx. a, 
brachial artery; 4*.v, brachial vein; ¢.c, common carotid: 7, jugular; 2. az, 
left auricle; 2. 2 a, left pulmonary artery; /. 7, left ventricle; pe. v, left pre- 
caval; pic, post- caval: pé 7, pulmonary veins; 7. av. x. an’, right auricle; 7 pa, 
right pulmonary artery; 7. pre, right pre- caval: run, right ventricle. B, heart 
of a bird with the right ventricle opened L. Vv, septum ventriculorum; R. Vi 
right ventricle; V, right auriculo-ventricular valve, (A, from Parker’s Zootomy; 
B, from Headley’ s Birds.) 


(7. p.a.,2p.a). The left aortic arch is absent in the adult, 
and it is the right alone which is continued into the dorsal 
aorta. The result of this is that the systemic arteries re- 
ceive pure arterial blood from the left side of the heart, and 
the only mingling of aérated and non-aérated blood is in the 


Xu PHYLUM CHORDATA 479 


capillaries. This is perhaps the most important physiologi- 
cal advance made by birds over reptiles. 

The aortic arch curves over the right bronchus to reach 
the dorsal body-wall, and then passes directly backwards as 
the dorsal aorta. 


Fic 289.— Columba livia The brain; A, from above; B, from below; C, from 
the left side. cd, cerebellum; c. 4, cerebral hemispheres; /, flocculus; 7%/, in- 
fundibulum; 2. 0, medulla oblongata; 0. /, optic lobes; o. ¢, optic tracts; pz, 
pineal body; II-XIII, cerebral nerves; sf. 7, first spinal nerve. (From Parker’s 
Zootomy.) 


The Jrain completely fills the cranial cavity, and is re- 
markable for its short, broad, rounded form. The cerebellum 


480 MANUAL OF ZOOLOGY SECT. 


(Fig. 289, ¢. 2) is of great size, and has a large median portion 
and two small lateral lobes or floccud’ (7) ; the surface of 
the middle lobe is marked by grooves passing inwards in a 
radiating manner and carrying with them the grey matter, 
the extent of which is thus greatly increased. The hemz- 
Spheres (c. h) extend backwards to meet the cerebellum, 
and the optic lobes (0. 2) are thereby pressed outwards so 
as to take up a lateral instead of the usual dorsal position. 


Fic. 290 — The eye. A, in sagittal section; B, the entire organ, external aspect; 
cn, cornea; ch, choroid; c?. pr, ciliary processes; zr, iris; 2, lens; off nv, 
optic nerve; pct, pecten; 7¢, retina; sc/, sclerotic; seZ. p/, sclerotic plates. 
(After Vogt and Yung.) 


The ere (Fig. 290) is not even approximately globular, 
but has the form of a biconvex lens. Sclerotic plates 
are present, and there is a large ~ccf’ in the form of a 
plaited and strongly pigmented membrane projecting into 


XII PHYLUM CHORDATA 481 


the cavity of the eye from the entrance of the optic 
nerve. 

The auditory organ (Fig. 291) is chiefly distinguished 
from that of reptiles by the great development of the coch/ra. 
The tympanic cavity and columella have the same arrange- 
ment as in the frog; the narrow Eustachian tubes open by 
a common aperture (Fig. 287, 
eus. ap) in the roof of the 
pharynx. 

The Aidneys (Fig. 287, 2d, Figs. 
292 and 293, &) have a very 
characteristic form. Each is a 
flattened organ divided into three 
main lobes and fitted closely into 
the hollows of the pelvis. The 
ureters (ur) are narrow tubes 
passing directly backwards to 
open into the middle compart- 
ment, or the cloaca. 

The destes (Figs. 287 and 292, Fic. 291.— Columba livia. The 


3 : ‘ right membranous labyrinth, 
zs) are ovoid bodies, varying 
greatly in size according to the 
season, attached by the perito- 
neum to the ventral surfaces of 
the anterior ends of the kidneys. 
From the inner border of each 


outer aspect; FA, ampulla of 
posterior canal; FB, posterior 
canal: HA, ampulla of hori- 
zontal canal; AB, horizontal 
canal; Zag, cochlea or lagena; 
mr, membrane of Reissner; 
ph, basilar part of cochlea; S, 
sacculus; SA, ampulla of 
anterior canal; SZ, anterior 
(canal. From Wiedersheim, af- 
ter Hasse.) 


goes off a convoluted vas def- 

erens (va@), which passes backwards, parallel with the 
ureter, to open into the cloaca on the extremity of a 
small papilla. The posterior end of the spermiduct is 
slightly enlarged to form a vesicula seminalis (v.s). The 
female organs (Fig. 293) are remarkable for the more or 


less complete atrophy of the right ovary and oviduct. 
21 


482 MANUAL OF ZOOLOGY SECT. 


The £/t ovary (ov) is a large organ in the adult bird, its 
surface studded with follicles or ovisacs, varying in size 
from about 15 mm. in diameter downwards, and each 
containing a single ovum. The “/f oviduct (2 od) is 
long and convoluted ; its anterior end is enlarged to form 
a wide, membranous ccelomic funnel (2 od@"') into which the 


Fic. 292,—Columba livia Male Fic. 293. —Columba livia. Female urino- 


urino-genital organs, adr, ad- genital organs. c/.2, urodeum; cd. 3, 
renal; cZ 2, urodeum; c¢/ 3, proctodzum; &, kidney: ¢. od, left ovi- 
proctodaum; £, kidney; ¢s, duct; ¢. od’, its cloacal aperture; 2. od'', 
testis, that of the right side dis- its coelomic funnel; 2. od''', its coelomic 
placed; », ureter; wr’, aper- aperture; ov, ovary; ». od, right oviduct; 
ture of ureter; wa, vas deferens; vr. od', its cloacal aperture: 27, ureter; 
va’, its cloacal aperture; 7. s, ur’, its cloacal aperture, (From Parker’s 
vesicula seminalis, (From Par- Zootomry.) 


ker’s Zootomy.) 


ripe ova pass on their liberation from the ovisacs ; the rest 
of the tube has thick, muscular walls, lined with glandular 
epithelium, and opens into the urodeum. 

Internal impregnation takes place. As the ova or 


XII PHYLUM CHORDATA 483 


“yolks” pass down the oviduct, they are invested with the 
secretions of its various glands ; first with layers of a/éumen 
or “ white,”’ next with a parchment-like shell-membrane, and 
lastly with a white calcareous she//. They are laid, two at a 
time, in a rough nest, and are ¢zcubazed or sat upon by the 
parents for fourteen days, the temperature being in this way 
kept at about 40° C. (104° F.). At the end of incubation 
the young bird is sufficiently developed to break the shell 
and begin free life. It is covered with fine down, and is fed 
by the parents with a secretion from the crop, the so-called 
“ pigeon’s milk.” 

Of recent birds two main divisions are recognised — 
the Ratitee and the Carinatee — the former comprising only 
the emus (Dromeus), cassowaries (Caswvartus), and kiwis 
(Apeeryx), the South American ostriches (Rhea), and the true 
ostriches (S/ru¢hio) ; and the latter including all the rest. 

One of the most characteristic features of birds in 
general is the covering of feathers — peculiar epidermal 
structures which differ widely in shape and arrangement 
from their equivalents, the horny scales of reptiles and the 
hairs of mammals. The arrangement of the feathers 
follows closely that briefly described as observable in the 
pigeon, with great diversity in detail. The distribution of 
the contour feathers in feather tracts or pteryle separated 
from one another by featherless tracts or apferva is almost 
universal in the Carinatee, but is not distinguishable in the 
Ratite except in the young condition. In many birds 
each feather has a secondary vein or a/fter-shaft, as it is 
termed, springing from the main shaft near the umbilicus, 
and sometimes (Fig. 294) this may be as large as the main 
shaft itself. A shedding or “moulting” of the feathers 
takes place at regular intervals, usually annually —a new set 
of feathers growing from the pulps of the old ones. 


484 


= 
en 
tess 
to% 


MANUAL OF ZOOLOGY SECT. 


(From Headley.) 


Feather, showing after-shaft and disconnected barbs. 


Fic. 294. Casuarius (Cassowary). 


The colours of feathers present great 
variety. Black, brown, red, orange, 
and yellow colours are due to the pres- 
ence of definite pigments, ze. are 
absorption colours. White, and in some 
cases yellow, is produced by the total 
reflection of light from the spongy, air- 
containing substance of the feather, 
there being, as in nearly all other natu- 
ral objects, no such thing as a white 
pigment. Blue, violet, and in some 
cases green, are produced by the light 
from a brown pigment becoming bro- 
ken up as it passes through the super- 
ficial layer of the feathers in its passage 
to the eye; no blue or violet pigments 
occur in feathers, and green pigments 
are very rare. The beautiful metallic 
tints of many birds are entirely the 
result of structure, owing their existence 
to a thin, transparent, superficial layer, 
which acts as a prism: in such feathers 
the colour changes according to the 
relative position of the bird and of the 
eye of the observer with regard to 
the source of light. 

There is also infinite variety in the 
general coloration of birds. In many 
the colouring is distinctly protective, 
harmonising with the environment, and 
even changing with the latter, as in the 
ptarmigan, which is greyish brown in 
summer, white in winter, the former 


XII PHYLUM CHORDATA 485 


hue helping to conceal the bird among herbage, the latter on 
snow. Frequently, as in pheasants and birds of paradise, the 
female alone is protectively coloured, while the male presents 
the most varied and brilliant tints enhanced by crests, plumes 
or tufts of feathers on the wings, elongated tail, etc. etc. 
These have been variously explained as “ courtship colours” 
for attracting the female; as due simply to the exuberant 
vitality of the male bird, or as helping to keep the number of 
males within proper limits by rendering them conspicuous to 
their enemies. Such ornaments as the bars and spots on 
the wings and tail of many gregarious birds, such as plovers, 
fully exposed only during flight, and often widely different 
in closely allied species, have been explained as “ recog- 
nition marks,” serving to enable stragglers to distinguish 
between a flock of their own and of some other species. 
The toothless jaws with the horny sheaths forming the 
bill are universal in the class. But the dimensions and 
form of the bill vary very widely in different groups of birds. 
It may be extremely short and wide for catching moths and 
other flying insects, as in swifts and goatsuckers ; short and 
conical for eating fruit, as in finches; strongly hooked for 
tearing the bodies of animals, as in birds of prey, or for 
rending fruits of various kinds, as in parrots ; long, conical, 
and of great strength, as in storks; slender and elongated, 
as in swifts, ibises, and curlews; broad and flattened for 
feeding in mud, as in ducks and geese; expanded at the 
end, as in spoonbills; immensely enlarged, as in hornbills 
and toucans. It is most commonly bent downwards at the 
tip, but may be straight or curved upwards, as in the avocet, 
or bent to one side, as in the New Zealand crook-billed 
plover. It is sometimes, as in the toucans, brilliantly 
coloured, and there may also be bright coloration of the 
cere, as in the macaws, and of naked spaces on the head, 


486 MANUAL OF ZOOLOGY SECT, 


as in the cassowaries. In the latter the head is produced 
into a great horny prominence or “ casque,” supported by 
an elevation of the roof of the skull. ‘The cere is frequently 
absent. The nostrils are placed at the base of the beak, 
except in Apteryx, in which they are at the tip. 

The essential structure of the wing — apart from its feathers 
—is very uniform. As a rule all three digits are devoid of 
claws, as in the pigeon, but the ostrich has claws on all 


Fic. 295 — A, wing of nestling of Opisthocomus ; B, wing of adult Apteryx y both 
from the inner (ventral) aspect; cd, z, first cubital remex; dg. 1, dg. 2, dg. 3, 
digits; pr. pig, pre-patagium; pz, Ag, post-patagium. (A, after Pycraft; 
B, after T. J. Parker.) 


three digits; rhea on the first, and sometimes the second 
and third; the cassowary, emu, and kiwi (Fig. 295, B) 
on the second; and the crested screamer (Chauna) and 
two other species, and, as a rare abnormality, the common 
fowl and the goose, on the first. With these exceptions, the 


XII PHYLUM CHORDATA 487 


hand of the adult bird has lost all the characters of a fore- 
foot ; but in the young of the hoatzin ( Opisthocomus) claws 
are present on the first two digits (Fig. 295, A), which are 
sufficiently mobile to be used in climbing. Besides the 
true claws, horny spwrs are sometimes present on the carpus 
and metacarpus. 

There is almost every gradation in the proportional 
length of the hind-limb, from birds in which nothing but 
the foot projects beyond the contour feathers, and even the 
toes may be feathered, to the long-legged storks and cranes, 
in which the distal part of the tibio-tarsus is covered with 
scales as well as the foot. In aquatic forms a fold of skin 
or wed is stretched between the toes, sometimes including 
all four digits, as in the cormorants ; sometimes leaving the 
hallux free, sometimes forming a separate fringe to each 
digit, as in the coots and grebes. As to the toes them- 
selves, the commonest arrangement is for the hallux to be 
directed backwards, and Nos. 2, 3, and 4 forwards, but in 
the owls No. 4 is reversible, z.¢. can be turned in either 
direction, and in the parrots, woodpeckers, etc., it, as well 
as the hallux, is permanently turned backwards. In the 
swifts, on the other hand, all four toes turn forwards. The 
hallux is frequently vestigial or absent, and in the ostrich 
No. 4 has also atrophied, producing the characteristic two- 
toed foot of that bird. 

The following are the most essential general features of the 
skeleton of birds. More or fewer vertebrz from the regions 
in front of and behind the sacral fuse with the true sacral 
vertebree to form the composite syn-sacrum. The posterior 
caudal vertebra are fused together to form a pygostyle. 
The bones of the skull early unite, the sutures becoming 
entirely obliterated. There is a single rounded occipital 
condyle. The premaxillae are very large and form the 


488 MANUAL OF ZOOLOGY . SECT. 


greater part of the upper jaw. The sternum is broad, and 
is usually provided with a prominent keel or carina as in 
the pigeon, but the carina is absent in the Ratite, and 
is rudimentary or absent in some flightless Carinate. The 
clavicles and interclavicle unite to form a furcula. The 
distal carpals and metacarpals unite to form a carpo- 
metacarpus. The pubes and ischia run downwards and 
backwards parallel with one another; and neither the pubes 
nor the ischia unite in a symphysis, but remain widely 
separated at their distal ends, except in the ostrich, in 
which the pubes unite distally, and the South American 
ostriches in which the ischia unite while the pubes remain 
free. Universally characteristic of the skeleton of the hind- 
limb is the union of the tibia with the proximal element of 
the tarsus to form a tibio-tarsus, and of the distal element of 
the tarsus with the second, third, and fourth metatarsals to 
form a tarso-metatarsus, the ankle-joint being situated 
between these bones. The skeleton always contains air- 
cavities to a greater or less extent. 

The presence of crop, proventriculus, and gizzard, as in 
the pigeon, is universal among birds. The gizzard is most 
powerful in grain-eating birds, thinner-walled in flesh-eaters. 
There is a pair of cceca in most birds at the junction of the 
large and small intestines. The voice of birds is always 
produced not in the larynx, as in other higher vertebrates, 
but in a syrinx situated either, as in the pigeon, at the 
junction of the trachea and bronchi, or at the anterior ends 
of the bronchi, or the posterior end of the trachea. The 
system of air-sacs connected with the bronchi described in 
the account of the pigeon is of universal occurrence. 

The temperature of the blood is always high. The heart 
in all has the same main features as in the pigeon: it has 
four distinct chambers, two auricles and two ventricles, and 


XII PHYLUM CHORDATA 489 


there is a single aortic arch, situated on the right side. In the 
brain the most characteristic points are the short rounded 
hemispheres, the large folded cerebellum produced forwards 
to meet the hemispheres, and the laterally placed optic 
lobes. The internal ear has a large curved cgchlea, and 
the eye has a pecten. The right ovary and oviduct are 
more or less completely aborted. 


Fic. 296. —Gallus bankiva (domestic fowl). Semi-diagrammatic view of the egg 
at the time of hatching. a, air-space; a/4, dense layer of albumen; 2/6’, more 
fluid albumen; 4/, blastoderm; c&, chalaza; sh, shell; sh. m, shell-membrane; 
sh. 1, sh, 2, its two layers separated to enclose air-cavity. (From Marshall’s 
Embryology, slightly altered.) 


The ovum is always large, owing to the great quantity of 
food-yolk ; the protoplasm forms a small germinal disc at one 
pole. Impregnation is internal, and as the incipient egg or 
oosperm passes down the oviduct, it is coated by successive 
secretions from the oviducal glands. It first receives a coat 
of thick, viscid e/bumen (Fig. 296, a/b), which, as the egg 


490 MANUAL OF ZOOLOGY SECT. 


rotates during its passage, becomes coiled at either end into 
a twisted cord, the chadasa (ch). Next, more fluid albumen 
(alb') is deposited layer by layer, then a tough, parchment- 
like shell-membrane (sh. m) and finally a calcareous shell 
(sh). The shell-membrane is double, and at the broad end 
of the egg the two layers are separate and enclose an air- 
cavity (@). The shell may be white or variously coloured 
by special pigments: it consists of three layers, and is 
traversed by vertical pore-canals, which are unbranched in 
the Carinate and in Apteryx, branched in the other Ratite. 
The eggs may be laid on the bare ground or on the rocks 
by the seashore, as in penguins and auks, or on the ledges 
on inaccessible cliffs as in the sooty albatross (Déomedea 
fuliginosa) ; but as a rule a mest is constructed for their 
reception by the parent birds. This may be simply a hole 
in the sand, as in the ostrich ; a mere clearing on the hill- 
side surrounded by a low wall of earth, as in the wandering 
albatross (Diomedea exulans) ; or a cylinder with excavated 
top, built of grass, earth, and manure, as in the mollymawks 
(Diomedea melanophrys, etc.). It may take the form of a 
burrow, as in many petrels, kingfishers, and sand-martins, or 
it may be more or less elaborately built or woven of sticks, 
moss, leaves, hair, or feathers, showing every stage of con- 
structive skill from the rude contrivance of sticks of the 
pigeon and eagle, to the accurately constructed cup- or 
dome-shaped nests of many familiar Passeres. In the tailor- 
bird (Orchotomus) it is formed of leaves sewn together, the 
beak acting as needle: in a Malayan swift (CollocaHia) it is 
largely built of the secretion of the bird’s buccal glands. 
After the egg is laid, the process of development is ar- 
rested unless the temperature is kept up to about 40° C. 
(104° F.) : this is usually done by the heat of the body 
of the parent birds, one or both of which sit upon, or ¢zcu- 


xII PHYLUM CHORDATA 491 


bate, the eggs until the young are hatched, but in the Aus- 
tralian mound-makers (AZegapodius) the eggs are buried in 
heaps of decaying vegetable matter, the decomposition of 
which generates the necessary heat. 


CLASS VI. MAMMALIA 


The class Mammalia, the highest of the Vertebrata, com- 
prises the Monotremes and Marsupials, the hoofed and 
clawed quadrupeds, the whales and porpoises and sea-cows, 
the rodents, bats, and insectivores, the lemurs and apes, and 
the human species. All mammals, though many are aquatic, 
are air-breathers throughout life, lungs being, as in reptiles 
and birds, the sole organs of respiration. The blood of 
mammals has a high temperature, resembling in that re- 
spect the blood of birds, and differing from that of reptiles 
and amphibia. The scales of reptiles and the feathers of 
birds are replaced in mammals by peculiar epidermal struc- 
tures, the hairs, usually developed in such quantities as to 
form a thick soft covering or fur. 

The rabbit (Lepus cuniculus) will serve as a convenient 
example of the class.! 

The rabbit (Fig. 297) is a four-footed or quadrupedal ani- 
mal, having the whole surface of its body covered with soft 
fur. The head bears below its anterior extremity the mouth 
in the form of a transverse slit bounded by soft lips. The 
upper lip is divided by a longitudinal cleft, running back- 
wards to the nostrils and exposing the chisel-shaped zncisor 
teth. Behind the incisor teeth the hairy integument pro- 
jects on each side into the cavity of the mouth. At the end 
of the snout, above the mouth, are the nostrils in the shape 


1 The following account will apply in all but very slight details to our 
cotton-tail rabbit or to our American hare. 


492 MANUAL OF ZOOLOGY SECT, 


of two oblique slits. The large eyes, situated at the sides 
of the head, have each three eyelids, an upper and a lower 
hairy lid, and an anterior hairless third eyelid or wécttating 
membrane, supported by a plate of cartilage. Vabrisse — 
very long stiff hairs—are scattered above and below the eyes 
and on the snout. Behind the eyes and a little nearer the 
summit of the head, are a pair of very long flexible and 
movable external ears or gznn@. These are somewhat 
spout-shaped, expanding distally and are usually placed 
vertically with the concavity directed laterally and some- 


Fic. 297-—Lepus cuniculus. Lateral view of skeleton with outline of body. 


what forwards, leading to the external auditory opening. 
The neck is a distinct constriction, but relatively short as 
compared with the neck of the pigeon. The ¢ru is distin- 
guishable into “rerax in front and addomen behind. On 
the ventral surface of the abdomen in the female are four or 
five pairs of little papilla — the “eas. 

At its posterior end, below the root of the tail, is the aza/ 
opening, and in front of this in the male is the fers, with a 
smal] terminal wrinogenital aperture and with the zestes, each 
in a prominent scvota/ sac, at the sides : and in the female 


XIL PHYLUM CHORDATA 493 


the opening of the wz/ya. The tail is very short and covered 
with a tuft of fluffy hair. 

The fore- and hind-timds, both of which take part in loco- 
motion and in supporting the weight of the animal, differ 
considerably in size—the fore-limbs being much shorter 
than the hind-limbs. Both have the same general divisions 
as in the lizard. The upper arm is almost completely 
hidden by the skin, being applied closely against the side of 
the body. The manus is provided with five digits, each 
terminating ina horny claw. The thigh is also almost hidden 
by: the skin; the es has four digits only, all provided with 
claws. 

The spinal column of the rabbit is divisible, like that of 
the pigeon, into five regions — the cervical, the thoracic, the 
lumbar, the sacral, and the caudal. In the cervical region 
there are seven vertebree ; in the ¢horacic twelve or some- 
times thirteen, in the vmédar seven, or sometimes six, in the 
sacral four, and in the cauda/ about fifteen. 

The centra of the vertebrae in a young rabbit consists of 
three parts —a middle part, which is the thickest, and two 
thin discs of bone — the efzphyses — anterior and posterior, 
applied respectively to the anterior and posterior faces of 
the iniddle part or centrum proper. Between successive 
centra in an unmacerated skeleton and thin disc-like plates 
of fibro-cartilage — are the inder-vertebral discs. 

The first vertebra or a#/as (Fig. 298, B) resembles the cor- 
responding vertebra of the pigeon in being of the shape of 
a ring without any solid centrum like that of the rest. On 
the anterior face of its lateral portions are two concave arti- 
cular surfaces (arf) for the two condyles of the skull. The 
second vertebra or axzs (B and C) bears on the anterior face 
of its centrum a peg-like process — the odontord process (od) 
—which fits into the ventral part of the ring of the atlas. 


494 MANUAL OF ZOOLOGY SECT. 


The thoracic vertebre all have elongated spines. The 
transverse processes are short and stout; each bears near 
its extremity a small, smooth articular surface or tubercular 
facet for the tubercle of a rib. On the anterior and posterior 
borders of each vertebra is a little semi-lunar facet, the 
capitular facet, situated at the junction of the centrum and 
the neural arch. The two contiguous semi-lunar facets of 
successive vertebree form between them a cup-like concavity 
into which the head or capi¢udum of a rib is received. 


Fic. 298. — Lepus cuniculus. A, atlas and axis, ventral aspect. od, odontoid pro- 
cess of axis. BH, lateral view of axis. a@r?, articular facet for occipital condyle; 
od, odontoid process; ff. sv, post-zygapophysis; sf. neural spine. C, thoracic 
vertebra, lateral view. cez?, centrum; fac, facet for rib; wet, metapophysis; 
pr. zy, prezygapophysis; ff. zy, post-zygapophysis; 7%, rib; sf, spinous process. 


In the lumbar region the spines are comparatively short, 
and both transverse processes and bodies are devoid of 
facets. 

The sacral vertebre are firmly ankylosed together to 
form a single composite bone, the sacvwm. The first and 
second bear great expanded lateral plates — sacral ribs — 
with roughened external surfaces for articulation with the 
ilia. 

Of the caudal vertebrae the more anterior resemble those 
of the sacral region and have similar processes ; but as we 
pass backwards in the caudal region all the processes gradu- 


XII PHYLUM CHORDATA 495 


ally diminish in size, the most posterior vertebra being 
represented merely by nearly cylindrical centra. 

There are twelve pairs of 7zés, of which the first seven are 
true ribs, t.e. are connected by their cartilaginous sternal 
ribs with the sternum; while the remaining five, the so- 
called false or floating ribs, are not directly connected with 
the sternum. All, except the last four, bear two articular 
facets, one on the vertebral extremity or capitulum, and the 
other on a little elevation or ¢wbercée situated at a little dis- 
tance from this, the former for the bodies, the latter for the 
transverse processes of the vertebree. 

The sternum (Fig. 300) consists of six segments or s¢erne- 
bre. The first or manubrium sterni or presternum is larger 
than the rest, and has a ventral keel. With the last is con- 
nected a rounded cartilaginous plate, the xphisternum. 

The skuil (Fig. 299), if we leave the jaws out of account, 
is not at all unlike that of the pigeon in general shape. 
The length is great as compared with either the breadth or 
the depth; the maxillary region, or region of the snout 
(corresponding to the beak of the pigeon), is long in pro- 
portion to the rest, the orbits closely approximated, being 
separated only bya thin inter-orbital partition, and the optic 
. foramina united into one. But certain important differences 
are to be recognised at once. One of these is in the mode 
of union of the constituent bones. In the pigeon, as we 
have seen, long before maturity is attained, the bony ele- 
ments of the skull, originally distinct, become completely 
fused together so that their limits are no longer distinguish- 
able. In the rabbit, on the other hand, such fusion between 
elements only takes place in one or two instances, the great 
majority of the bones remaining distinct throughout life. 
The lines along which the edges of contiguous bones are 
united— the sutures as they are termed —are sometimes 


496 MANUAL OF ZOOLOGY SECT. XII 


straight, sometimes wavy, sometimes zig-zagged, serrations 
of the edges of the two bones interlocking ; in some cases 
the edges of the bones are bevelled off, and the bevelled 
edges overlap, forming what is termed a sgvamous suture. 

Another conspicuous difference between the skull of the 
rabbit and that of the pigeon is in the mode of connection 
of the lower jaw, which in the former articulates directly with 
the skull, the quadrate, through which the union is effected 
in the pigeon, being apparently absent. Certain large 
apertures which are distinguishable are readily identified with 
the large openings in the skull of the pigeon. In the pos- 
terior wall of the skull is a large rounded opening, the 
foramen magnum, flanked with a pair of smooth rounded 
elevations or condyles for articulation with the first vertebra, 
these obviously corresponding to the single condyle situated 
in the middle below the foramen in the pigeon. A large 
opening situated at the end of the snout and looking forwards 
obviously takes the place of the externa/ nares of the pigeon ; 
and a large opening in the roof of the mouth leading forward 
to the external nasal opening, plainly represents, though 
much wider and situated further back, the ¢zzerna/ or poste- 
vier nares of the pigeon ; while the rounded tubular opening 
situated at the side of the posterior part of the skull, some 
distance behind the orbit, is evidently the same as the 
auditory aperture of the pigeon. 

Surrounding the large opening of the foramen magnum 
are the bones of the occipzza/ region of the skull, the supra-ex- 
and éas?-occipitals. The first of these (s. 0c ) is a large plate 
of bone above the foramen magnum. The ex-oceiprtals lie 
at the sides of the opening and each bears the greater part 
of the somewhat oval prominence or condyle with which the 
corresponding surface of the atlas or first vertebra articulates. 
The dast-occipitaé is a median plate of bone, almost horizontal 


G.0C 
Fic. 299. — Lepus cuniculus. Skull: A, lateral view; B, ventral view. ang. proc, angular 
process of mandible; as, ali-sphenoid (external pterygoid process); 4, oc, basi-occipital ; 
6. sph, basi-sphenoid; cod, condyle; /r, frontal; zz¢ fa, inter-parietal; 7x, jugal; cr, 
lacrymal; max, maxilla; vas, nasal; oft. fo, optic foramen; o. sph, orbito-sphenoid; Aa, 
parietal; Za/, palatine; fal max, palatine plate of maxilla; par. oc, par-occipital pro- 
cess; pal. p. max, palatine process of pre-maxilla; f. max, pre-maxilla; fer, periotic; 
pt, pterygoid; %. z. sg, post-tympanic process of squamosal; s. oc, supra-occipital; sg, 
squamosal; ty. 6x/, 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 
bast-sphenoid ; on its upper surface is a depression, the se//a 
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 a/-sphenoid (as) behind and the ordito-sphenoid 
(0. sph) in front. The ali-sphenoids are broad wing-like 
bones, each produced below into a bilaminate process, the 
plerygotd process. 

The boundary of the anterior part of the brain case is 
completed by a narrow plate of bone, the ervbriform plate 
of the e¢hmoi?, perforated by numerous small foramina for 
the passage of the olfactory nerves. This cribriform plate 
forms a part of a median vertical bone, the mesethmord, the 
remainder of which, or damina perpendicularis, forms the bony 
part of the partition (completed by cartilage in the unma- 
cerated skull) between the nasal cavities. Fused with the 
mesethmoid are two lateral, thin-twisted bones, the e¢imo- 
turbinals, and with its inferior edge articulates a long median 
bone with a pair of delicate lateral wings, the comer. 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 fariefals (pa), and further forward 
another pair, the frontals (fr). Between the supra-occipital 
and the parietals is a median ossification, the /vter-parietal 
(it, pa). Below the parietal and frontal is a broad bone (sg), 
the superior margin of which is bevelled off. This is the 
sguamosal. It gives off in front a strong z1gomatic process, 


XII PHYLUM CHORDATA 499 


which curves outwards, then downwards, and finally forwards, 
to unite with the 7wga/ in the formation of the sygomatic arch. 
Below the root of the process is a hollow, the glenoid fossa. 

Between the occipital and parietal bones, below and 
behind the squamosal, are the qnpanic and periofic bones. 
The tympanic forms the bony part of the wall of the 
external auditory meatus; below it is dilated to form a 
process (4. dvZ) projecting on the under surface of the 
skull, the Juda tympani. The periotic (pf. 0Z) 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 zasals (nas). In front of the nasals are the pre-maxille 
—large bones which form the anterior part of the snout, 
bear the upper incisor teeth, and give off three processes. 
The maxille (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 pterygords 
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 yor’, which, as in the pigeon, is the only other 
post-oral visceral arch represented in the adult, consists of 
a stout thick body or éas?-Aya/, a pair of small anterior 
cornua or cerato-hyals, and a pair of long backwardly directed 
cornua or ¢hyro-hvals. 

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 scapu- 
lar, the base or vertebral edge of which has a thin strip of 
cartilage (the swvpra-scapular cartilage) continuous with it. 
Along the outer surface runs a ridge, the sfine,; the spine 
ends below in a long process, the acremion process (a), 
from which a branch process or mefacromion (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 coracotd process (c), 
which is represented by two separate ossifications in the 
young rabbit. A slender rod, the clavicle (cl), is con- 
nected with the acromion process externally and with the 
sternum internally by means of fibrous tissue. 

At the proximal end 
of the humerus are to 
be recognised: (1) 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 Serr a eam beri es 

men a, acromion; af, pre-scapular fossa; 
large and pulley-like, ¢, coracoid; cZ, ossified clavicle; ma, meta- 


cromion; mss, meso-scapular segment; ost 
trochlea, for the ulna ; pre-sternum; pe, pre-coracoid; £/, post-scapu- 


the other smaller, capt- lar fossa; sv, sternal ribs. (After Flower.) 
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 


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, cenzérale 
(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), 
Zunar (orsemi-lunar) (dun), 
cunetform (cun), and pist- 
form. Those of the dis- 
tal row are reckoned in 
the same order, “rapeztum 
(7pm), trapezoid (tps), 
magnum (mag), and unci- 
form (unc). 

Fic. 301.—Lepus cuniculus. Distal end The five metacarpals are 
of fore-arm and carpus, dorsal view, the aj] small but relatively nar- 


bones bent towards the dorsal side so as 


to be partly separated: cent, centrale; row and elongated bones 
cun, cuneiform; dz, lunar; mag, mag- ? 


num; rad, radius; sc, scaphoid; #2, the first being smaller than 

trapezoid: ¢f7v, trapezium; 222, ulna; 

unc, unciform; /-I’, bases of metacar- the rest. Each of the five 

pals. (After Krause.) he tia 

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 svwphysis (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 


XII PHYLUM CHORDATA 503 


the pubis, but by a small intercalated ossification, the 
cotylowd bone. The thum (a7) has a rough surface for 
articulation with the sacrum. Between the pudis (pub) in 
front and the ¢schiwm (isch) behind is a large aperture, the 
obturator foramen (obt). The femur has at its proximal 
end a prominent ead for articulation with the acetabulum, 
external to this a prominent process, the great trochanter, 
and internally a much smaller, the Zesser crochanter, while 
a small process or chird 
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 


Fic. 302.— Lepus cuniculus. Innominate 


two articular surfaces, bones and sacrum, ventral aspect. acet, 
5 acetabulum; 27, ilium; zsch, ischium; oé¢, 
one, internal, for the obturator foramen; fxd, pubis; sacr, 


sacrum; sy, symphysis. 
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, zav), being intercalated between the two rows. 


504 MANUAL OF ZOOLOGY SECT. 


In the proximal row are two bones, the as/ragalus (ast) and 
the calcaneum (cal), both articulating with the tibia; the 
calcaneum presents behind a long caécaneal process. The 
distal row contains three bones, the mesocuneiform, ectocunet- 
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 da- 
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 cesophagus. The posterior 
part or addomen contains the stom- 
ach and intestine, the liver and 

: pancreas, the spleen, the kidneys, 
Fic. 303.—Lepus cuniculus. 4 

Skeleton of pes; asz, astrag- ureters and urinary bladder, and the 

alus; cad, calcaneum; cv, f 

cuboid; cv, cuneiforms; organs of reproduction. 

eMC The teeth (Fig. 299) are lodged 
in sockets or afveoti in the pre-maxille, the maxille, 
and the mandible. In the pre-maxille 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 505 


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 maxilla. Canines, present in most 
mammals as a single tooth on each side, are here entirely 
absent, and there is a considerable space, or dastema, 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 mo/ars, 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 papilla. The roof of the mouth 
is formed by the fa/aze. The anterior part, or hard pala, 
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 wzzdz) 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 vasaZ 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 Zustachian tubes. The nasal division is continuous 


506 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, ef) formed of a plate of yellow elastic 
cartilage covered with mucous membrane: this is the 
epiglottis. Behind, the pharynx becomes continuous with 


olf Z 


mes.elh — i ve 
a 
trb 


max.trb. Y ra 


KL, 


mnes.elhy 


Fic. 304. — Lepus cuniculus. Lateral dissection of the head, neck, Pe thorax. The 
head and spinal column are represented in mesial vertical section: the left Jung 
is removed; the greater part of the nasal septum is removed so as to show the 
right nasal cavity with its turbinals. @ort, doxsal aorta; 4. Ay. basi-hyal; cd, 
cerebellum; crv, cerebral hemispheres: cov. 7, curonary vein; aa, diaphragm: 
ef, epiglottis:; ew, opening of Eustachian fate’ inte pharynx; Jar, larynx; LGU, 
left jugular vein; 27 sd. a, left subclavian artery: 7. sé. 7, left subclavian vein; 
med, medulla; mes. eth, mesethmoid: 22x, tré, maxilla-turbinal; @s, cesophagus; 
olf, olfactory lobe; f/. a, pulmonary artery: p. MAX, pre-manilla; pr. st, pre- 
sternum; ft. c, post-caval vein; +. Zzg, root of left lung with bronchus and pul- 
monary veins and artery cut across; s. g7, sub-lingual salivary gland; s. #2. g/d, 
sub-maxillary salivary gland; s¢, sternebrae; “vg, tongue; 7, trachea; ¢7d, 
ethmo-turbinals; ve/. 7, soft palate. 


the asephagus 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 cesophagus enters, than at the 
opposite or fyZoric 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 du) 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 (rect). At the 
junction of the small with the large intestine is a very wide 
blind tube, the ccm, 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 “ver 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 ézle duct, 
(¢c. 6. d) formed by the union of the cyste duct from the 
gall-bladder and hepatc ducts from the various parts of the 
liver, runs to open into the duodenum near the pylorus. 

The pancreas (pn) is a diffused gland in the fold of 
mesentery passing across the loop of the duodenum. Its 
single duct, the pancreatic duct (pn. @), 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 


Fic. 305.— Lepus cuniculus. The stomach, duodenum, posterior portion of rectum 


and liver (in outline) with their arteries veins, and ducts. A. the ceeliac 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 (ca. a); 
the duodenum is spread out to the right of the subject to show the pancreas 
(pu); the branches of the bile duct (c. 8. d), portal vein (f. v) and hepatic 
artery (/. a), are supposed to be traced some distance into the various lobes of 
the liver. @. #2. a, anterior mesenteric artery; caz, caudate lobe of liver, with 
its artery, vein, and bile duct; c. 6. 2, common bile duct; cd. st, cardiac portion 
of stomach; c. 27. a, common iliac artery; ca@. a, coeliac artery; cy a, cystic 
artery; cy. d, cystic duct; d@. ao, dorsal aorta; dz, proximal, and du’, distal 
limbs of duodenum; ad a, duodenal artery; dz. ha, in (A), duodeno-hepatic 
artery; g. @, gastric artery and vein; g. 4, gall-bladder; 4. a, hepatic artery; 
&. d, left bile duct; 2. c, left central lobe of liver, with its artery, vein, and bile 
duct; 2. gv, lieno-gastric vein; 2. 7, left lateral lobe of liver, with its artery, 
vein, and bile duct: ss, branch of p esenteric artery and vein to duodenum; 
ms.7, mesorectum: mz 7, chief mesenteric vein; @&s, cesophagus; /. 7. a, 
posterior mesenteric artery; # #. v, posterior mesenteric vein; A, pancreas; 
pr. d, pancreatic duct; ~ 7, portal vein; Ay. sZ, pyloric portion of stomach; 
ret, rectum; » c, right central lobe of liver, with artery, vein, and bile duct; 
spe, Spigelian lobe of liver, with its artery, vein, and bile duct; 527, spleen; sf. a, 
splenic artery. (From Parker’s Zootomy.) 


508 


SECT. XII PHYLUM CHORDATA 509 


visceral, immediately investing the heart. Between the two 
is a narrow cavity containing a little fluid, the pericardial 
fiuid. 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.- 


Fic. 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; 7. Av. c, opening of pre-caval; 7 pap, musculi 
papillares; Az. c, post-caval; ff. c’, opening of post-caval; ». pvc, right pre- 
ave r. pul, right pulmonary artery; sew. v, semi-lunar valves; ¢77, tricuspid 
valve. 


Into the right auricle open three large veins, the righ? 
and deft pre-caval veins and the single postcaza/, 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. XII 


than elsewhere; this is the fossa ovaiis, it inarks 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 ¢ricuspid, 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 mzsculi papillares, 
by means of tendinous threads called the chorde tendinee. 
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 columne carnea. It gives off in 
front, at its left anterior angle, the pulmonary artery, the 
entrance to which is guarded by three pouch-like sem-/unar 
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 mz¢ra/, consisting of two membranous lobes or 
cusps with chordz tendineze and musculi papillares. In 
the walls of the ventricle are columnz carnee 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, 


Svs 
tip 


Fic. 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; @. mm, anterior mesenteric 
artery; a. fh, anterior phrenic vein; az. v, azygos vein; br, branchial artery: 
¢. 7. a, common iliac artery; ca, coeliac artery; d@.ao, dorsal aorta; e.c, external 
carotid artery; ¢. 2/7. a, external iliac artery; ¢ 77. v, external iliac vein: @ ju, 
external jugular vein: fm. @, femoral artery; fi. v, femoral vein; 4. v, hepatic 
veins; 7. ¢, internal carotid artery; 7. ¢s, intercostal vessels; 7. fu, internal 
jugular vein; ¢ Z, ilio-lumbar artery and vein; 77, innominate artery; ¢. az, 
left auricle; 7. c.c, left common carotid artery; 7. prc, left pre-caval vein; 
Z. uv, left ventricle; 7. sc, median sacral artery; #. a, pulmonary artery; p. epg, 
epigastric artery and vein; # //, posterior facial vein; 4. 7, posterior mesenteric 
artery; #. £2, posterior phrenic veins; ffc, post- caval veins; p. v, pulmonary 
vein; 7, renal artery and vein; 7. av, right auricle; 7. ¢. ¢, right common 
carotid artery; 7. prc, right pre-caval vein; 7. v, right ventricle; s¢/. a, right 
sub-clavian artery; sel. v, sub- clavian vein; spm, spermatic artery and vein; 
vs. S, superior vesical artery and vein; z/, uterine artery and vein; 77, vertebral 
artery. (From Parker’s Zootomy.) 

git 


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 (ad. ao). 

The system of caza/ veins which open into the right 
auricle consists of the right and /eft 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, .v). 
There is no renal portal system. 

Respiratory Organs. — The /arynx (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 ¢rachea or wind- 
pipe (Fig. 308, 77), 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 érenchi, one passing to the root of each lung. 

The /ungs (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 plewral 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 “rminal bronchioles, opens into a 


Fic. 308. —Lepus cuniculus. Larynx: A, ventral view; B, dorsal view; ary, 
arytenoid: cv, cricoid; ef, epigiottis; savt, cartilage of Santorini; th, thyroid, 
tr, trachea, (From Krause, after Schneider, ) 


minute chamber or 7nfundibilum, consisting of a central 
passage and a number of thin-walled azr-vesicles or alveok 
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 ¢kymus, 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 ¢yrozd is a small brownish, bilobed 
glandular body situated in close contact with the ventral 
surface of the larynx. 

25; 


514 MANUAL OF ZOOLOGY SECT. 


The neural cavity, as in the pigeon, contains the central 
organs of the cerebro-spinal nervous system, the éra7v and 
spinal cord. Vhe brain (Fig. 309) of the rabbit contains 


og. —Lepus cuniculus. 


Wiedersheim ) 


3 
cm 


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, 7. 4, 


XII PHYLUM CHORDATA 515 


Fig. 310, ¢. 4), 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 Sy/tun fissure, at 
the side of the hemisphere separates off a lateral portion or 
temporal lobe (Fig. 311, ch) 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. cZ), 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, the fornix (4. 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 fi/th ventricle or pseudocele, 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 (v*) 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- 


516 MANUAL OF ZOOLOGY SECT. 


verse band of fibres connecting together the posterior 
parts of the optic thalamz. ‘The latter (0. #) are large 


Fic. 310.— Lepus cuniculus. Two dissections of the brain from above (nat. size). 
In A, the left parencephalon 1s dissected down to the level of the corpus callo- 
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 
callosum; 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 Jobe; a co, anterior commissure; a./o, anterior pillar of for- 
nix; a. pu, anterior peduncles of cerebellum; 3. 0, body of fornix: cé1, superior 
vermis of cerebellum: 2, its lateral lobe; c. gz, corpus geniculatum; c. 4, cere- 
bral hemisphere; ch. f/, choroid plexus; cf. c/, corpus callosum; cf. s, corpus 
striatum; c. xs, corpus restiforme; @., dorsal pyramid; 77, flocculus: Ap m2, 
hippocampus major; 7. co, middle commissure: 0. 21, anterior; o 22, posterior 
lobes of corpora quadrigemina; o. ¢#, optic thalamus; ofr, optic tract, p co, pos- 
terior commissure; # /o, posterior peduncles of cerebellum; 4 va, fibres of pons 
Varolii forming middle peduncles of cerebellum; sf. 7a, septum lucidum; s¢ Z, 
stria longitudinalis; ¢ s, teenia semicircularis; v. vz, valve of Vieussens; v°, 
third ventricle; v4, 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 CHORDATA 517 


by a thick mass of gray matter, the middle or soft commis- 
sure (m. co) passing across the diaccele. The floor of the 
diencephalon is produced downwards into a mesial rounded 
process, the ¢wber 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 
mammuillare (c. ma). 

In the mid-brain the dorsal part is remarkable for the 
fact that each optic Jobe is divided into two by a transverse 
furrow, so that two pairs of lobes, the corfora guadrigemina, 
are produced. On the ventral region of the mid-brain the 
crura cerebvt 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, cd) the cerebellum exhibits a tree-like 
pattern (arbor vite), 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 Varolit, 
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 nervous 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 cochtea. 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. 


olf COLE a inf on ia, Sy 2S 
Z A\ ™.€0. Pe YPN. 
ack, 5, ys cA e 


Fic. 311. — Lepus cuniculus. Longitudinal vertical section of the brain (nat. size). 
Letters as in the preceding figure; in addition, cd, cerebellum, showing arbor 
vitae; ¢. c, crus cerebri; ch1, parencephalon; c/?, temporal lobe: ¢. wa, corpus 
mammillare; /. +, foramen of Monro; zz/, infundibulum; @y, lyra; #2. 0, me- 
dulla oblongata; 0. ch, optic chiasma; o/f, olfactory lobe; pty, pituitary body; 
vi, zp, velum interpositum; v. vz, 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 Azévs 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 fe/’s, 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 medudla and a peripheral portion or cortex. An 
adrenal (suprarenal) bedy lies in contact with the anterior 
end of each kidney. he wreter (Fig. 312, ur) runs back- 


ur 


al 


an 


Sali 


Fic. 312.—Lepus cuniculus. The urogenital organs. A, of male; B, of female, 

rom 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. ax, anus; 62, 

urinary bladder; c. c, corpus Cavernosum; c.s, corpus spongiosum; c. &, 

Cowper’s gland; g° c/, glans clitoridis; g. f, glans penis; 4. g?, perineal gland; 

. g7', aperture of its duct on the perineal space; #7, anterior, Pee » posterior, and 

pr’, lateral lobes of prostate; vc, rectum; ». gé, rectal gland; w. & @, urino- 

genital aperture; #. #z, uterus masculinus; ur, ureter; va, vagina; v4, vesti- 
bule; wv. d, vas deferens. (From Parker's Zootonzy.) 


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 ¢s/es 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 zmguinal canal. A convo- 
luted efedidymis, closely adherent to the testis, forms the 
proximal part of the vas deferens. The vasa deferentia 
(vd) 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 werus masculinus (um), les embedded in 
the prostate gland close to the neck of the bladder. A 
small pair of ovoid glands, Cowfer’s glands (c. g/l), 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 
Graafian follicles enclosing the ova form only very small 
rounded projections on their outer surface. 

The ovéducés in the anterior part of their extent (/a//opian 
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 wterus. The two uteri open sepa- 
rately into a median tube, the vagina (va). The vestibule 
(Fig. 312, vd), 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 c/vorts, 
corresponding to the penis of the male, and composed of 
two very short corpora cavernosa attached anteriorly to the 


Slt Zut 


fi Lt rue 


Fic. 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 1s 

removed, and the proximal end of the left uterus is shown in longitudinal section 

Ji. t, Fallopian tube; 77. z', its peritoneal aperture; 2. w#, left uterus; 7. w¢’, left 

os uteri; ». «¢, right uterus; 7. wt’, right os uteri; s, vaginal septum; va, 
vagina. (From Parker's Zootomy.) 


ischia, with a terminal soft conical glans clitoridis (g. cl). 
The vulva, or external opening of the vestibule, is bounded 
laterally by two prominent folds, the /abza mayora. 

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 fedus, 


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, z.¢., 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 p/acenza, 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 
fibro-cartilage termed inter-vertebral discs, which intervene 
between successive centra. 


XII PHYLUM CHORDATA 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 @phyodont, i.e., have two sets of 
teeth — a milk or deciduous set, and a permanent set ; some 
are monophyodont, t.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, z.e., are heterodont ; 
in some instances the teeth are all alike (Aomodont). 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 feetus is nourished before birth from the 
blood-system of the parent through a special development 
of the foetal 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 
vertebre 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 ( Oratthorhyn- 
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 vertebree 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. Edenfata, comprising the sloths, ant-eaters, and arma- 
dillos. 

2. Cefacea, including the whales, porpoises, and dolphins. 

3. Strenia, or dugongs and manatees. 

4. Ungulata, avery 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. 


Fic. 314. — Duck-bill (Oruithorhynchus 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. Lnsectivera, including the moles, shrews, and hedge- 
hogs. 

8. Chiroptera, or bats, and fruit-eating bats (flying foxes). 


xu PHYLUM CHORDATA 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 


Fic. 315.—Spiny Ant-eater (Echidna aculeata). (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 (Didelphjyide) (Fig. 316) are arboreal 
rat-like marsupials, with elongated naked muzzle, with well- 
developed, though nailless, opposable hallux, and elongated 
prehensile tail. The Dasyuride (Australian native cats, 
tasmanian devil, thylacine, etc.) have the pollex often rudi- 


Fic. 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 (Peramelive) 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 pinne. ‘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- 
plum has its opening directly backwards. 

The wombats (Phascolomyide) 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 


Fic. 317. — Dasyure (Dasyurus viverrinus). (After Vogt and Specht.) 


the hind-foot partly connected together by skin. The tail 
isvery short. The kangaroos and their allies (AZacropodida) 
(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 
2M 


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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, 


Fic. 320. — Unau, or two-toed sloth (Cholepus 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 (Dasypodide@) (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. 


Fic. 321. — Tatu armadillo (Dasypus sexctuctus). (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 SECT. 


Fic. 322 —Scaly apt-eater (Wanis pevtadactyla), (After Vogt and Specht.) 


Fic. 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 
pinne of great length, the tail long and thick. The fore- 
limbs are short and stout, with four toes. ‘The hind-limb 


tid diiilldiad ill 


Fic 324.—Killer (Orca gladzator). (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 Jarge head, not 
separated from the body by any distinct neck. A dorsal 


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 
Face mace at sesame a" it in proportion as in the Ceta- 

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 Avofs, 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 anders. 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 pedzcles. 

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 pinne. 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 (£guid@) 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- 


XU 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 (Lucra) 
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 (Phocide) are much more 
completely adapted to an aquatic life than the eared seals 


Fic. 326.— Harbor Seal (Phoca vitulina). 


(Otartide) and walruses (Zrichechid@), 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 


. 


XI PHYLUM CHORDATA 54t 


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 (2zpus) 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 (Ays#7cid@) 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 (Zrinaceus) has 
the surface beset with pointed spines. The moles (Zaa) 
and their allies, which are active burrowers, have the limbs 
very short and stout and provided with extremely strong 
claws. The jumping shrews (Macrosceledide) 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- 


Fic. 327.— Bat (Synotus barbastellus). (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 


XI PHYLUM CITORDATA 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 (ProsimiZ) 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 Hapilide 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 Cebide, or American monkeys, resemble the Hapalidz 
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 Cercopithecide, 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. XII. 


never prehensile. The pollex when developed is always 
opposable to the other digits. In the Simiidee 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. 

Acmezea testudinalis, 2g2, a 

Acrania, 323. 

Acromion process, 500, 

Actinobolus, 49. 

aActinomma asteracanthion, 32. 

actinophrys sol, 26, 28. 

‘Actinospherium, 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,119; palmatum, 
Ig. 

Alispbenoid, 498. 

Allantois, 434. 

Alligator, 434, 438, 456; brain, 449. 

Alveolus, 504. 

Amaroucium, 320, 

Ambulacral groove, 160, 161. 

Ambulacral pores, 161. 

Ambulacrum, 160, 

Amnion, 434. 


2N 


Ameceba, 14, 19; polypodia, 18; pro- 
teus, I4. 

Amphiccelous vertebrze, 334. 

Amphineura, 281. 

Amphibia, 407. 

Amphidises, 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 scrophularize, 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 


545 


546 


round worms, 149; of birds, 459; 
of reptiles, 435; of scorpion, 255. 


Aorta, of mammals, 512; of molluscs, | 


275; of vertebrates, 350. 

Ape, 544. 

«phides, 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 vitze of cerebellum, 517. 

Arcella vulgaris, 20. 

Arch, heemal, 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, 379 444- 

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; 
320. 

Ascidians, 314; blood system, 318; 
heart, 318; larva of, 319; nervous 
system, 318. 


mammillata, 


INDEX 


| Aspredo, 404. 

| Astacus fluviatilis, 213, 221. 

a\sterias 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, 111. 

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. 

Beroé, 128. 

Bile, 346. 

Bill, of birds, 485; modifications of, 
485. 

Binomial nomenclature, 2. 

Biology, definition of, 1. 

Bionomics, 13. 

Birds, 456; colors of, 484; egg, 483, 


489, 490; limbs of, 459; mouth of, 
459; voice of, 488; wings of, 459. 


INDEX 


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, 
I93, 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, 
41I; epipubic, 525; marsupial, 
325; membrane, 937) 411. 

Bothriocephalus latus, 145. 

Botryllus violaceus, 322. 

Bougainvillea ramosa, 103; 
cilians, 103. 

Brachionus rubens, 179. 

Brachiopoda, 184. , 

Bract, 108. 

Bradypodide, 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. 

Branchiz, of annelid worms, I99; 
secondary in Gastropod molluscs, 
2gI. 

Branchiostoma, 323. 

Breast-bone, 336. 

Brittle-stars, 169. 

Bronchi, of birds, 476; of lizard, 348; 
of mammals, 512. 

Bronchioles, 513. 

Bud, 73. 


super- 


547 


Budding, 72. 

Buds, medusa, 92. 

Bufo, 432. 

Bugula avicularia, 182, 
Bulbus aorta, 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, 

Carinate, 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 vertebrze, 335. 

Cavity, atrial, 315; pericardial, 315, 
349. 

Cavity, buccal, 293, 294; of verte- 
brates, 344, 459, 505. 

Cebide, 543. 

Cell, 18; flame, 132, I40. 

Cells, adhesive, 127; pigment, 303. 

Cellulose, in ascidian test, 315. 

Cement, of tooth, 343. 

Centrale, 502. 


548 


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. 

Cercopithecide, 543. 

Cere, 459, 486; absence of, 486. 

Cerebellum, 354; of birds, 479, 489; 
of mammals, 517. 

Cerebral hemispheres, 355, 480, 514, 
524. 

Cervical vertebrae, 335. 

Cestoda, 138. 

Cestus, 128. 

Cetacea, 526, 535. 

Chzetopoda, 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. 


INDEX 


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, 527. 

Cloaca, 344, 407, 476; of Prototheria, 
523; of sharks, 393. 

Cnidoblast, 95. 

Cnidocil, 95. 

Cobego, s4r. 

Coccidium, 58. 

Cochlea, of birds, 489; of mammals, 
518. 

Cockle shell, 280. 

Cockroach, 242, 243, 247. 

Cocoon, of earthworms, 201. 

Codonella, 49. 

Cceca, 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. 

Ceecilia, 433. 

Ccelenterata, go. 

Ceelom, of mammals, 504; of mol- 
luscs, 271; of starfish, 160; of 
worms, IoI. 

Ceenenchyma, raz, 

Coenosare, 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 


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. 

Conus 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, 
igxS. 

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. 


549 


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; 
dont, 343. 

Deutomerite, 58. 

Devil, tasmanian, 528. 

Diaceele, 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, 4o. 

Dicecious worms, 148. 

Diophrys, 49. 

Diphyodont dentition, 523. 

Diplomita, 37. 


homo- 


55° 


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, 11; geo- 
graphical, 11; geological, 11; zoo- 
geographical, 11. 

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. 

Dromeeus, 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. 

Echinaracbnius parma, 173. 

Echinodermata, 157. 

Echinoidea, 170. 

Ectoderm, 79. 

Ectoprocta, 183. 

Ectosare, 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- 
luses, 265; of sharks, 384. 

Eggs, of crocodiles, 456; demersal, 


INDEX 


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. 

Equida, 538. 

Ethmoid, 498. 

Ethmo-turbinals, 498. 


INDEX 


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. 


551 


Felis, 2, 5, 7. 

Femur, 342; of birds, 471. 

Fibula, 342, 416; of birds, 471. 

Fibulare, 416. 

Filoplumes, 461. 

Fimbrize of mussel, 266. 

Finger, index, 4o9. 

Fins; 992, 965, 972% lateral, 363; 
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, 4o2. 

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, Io. 

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. 

Fronto-parietal bones, 411. 


552 


Funnel of Cephalopoda, 299, 304. 
Furcula, 488. 


Galeopithecus, 541. 

Gametes, 44. r 

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, 2T4. 

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 vertebrates, 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, qo. 

Globigerina, 25, 26; 00ze, 26, 

Glochidium, 277. 

Glossocodon, Io2. 

Glottis, 347, 418; of birds, 476. 

Glugea bombycis, 58. 


INDEX 


Glycogen, 346. 

Goat, 526. 

Gonads, 72; of mussel, 277. 
Gonangium, 92, 95. 

Gonopoda, 216s 

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. m 
Gymnophiona, 433. 

Gymnotus, 400. 


Hzemameeba laverani, 58, 

Heemal arch, 335. 

Heematochrome, 36. 

Hag-fish, 360. 

Hair, trigger, 95. 

Halistemma, Ios, 107. 

Hallux, of birds, 459; of frog, 410. 

Hand of frog, 409. 

Hapilidze, 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 


Hingeof 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. 

Hystricidze, 541. 


Ichthyomyzon, 365. 

Idyia roseola, 128. 

Ilium, 342; of birds, 470, 476; of frog, 
416; of mammals, 503. 


553 
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, go. 

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 
Myriapoda, 240. 

Lacerta viridis, 330. 

Lachrymal bones, 500. 

Lachrymal foramen, 500. 

Lacrymaria, 49. 

Leemargus, 393. 

Lagena, 25. 

Lamellz of molluscan gills, 272, 274. 

Lamellibranchiata, 265. 


554 


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; 
452. 

Lobe, temporal, of mammals, 515. 

Lobes, olfactory, 354, 380; optic, 480. 

Lobosa, I9. 

Loligo pealii, 302; vulgaris, 302. 

Lophomonas, 49. 

Lophophore, of Brachiopods, 186; of 
Polyzoa, 181. 

Lorica, 38; of Rotifers, 180. 

Loxosoma, 181. 

Lucernaria, 112. 

Lumbar vertebree, 335. 

Lumbricus agricola, 200. 

Lunar bones, 502. 


flying, 441; habits, 


INDEX 


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. 

Macropodide, 529. 

Macrosceledidz, 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. 

Mastigamceba, 37, 41. 

Mastigophora, 34. 

Maxilla, of crustacea, 218, 219; of 
insects, 242, 

Maxillary palpus of insects, 242. 

Mavxilliped, 218. 

Medulla, 45, 55; of kidney, 519; ob- 
longata, 354. 

Medusa-buds, 92. 

Megagamete, 4q. 

Megaleesthetes, 282. 

Meganucleus, 45, 50. 


Lungs, 70; book, of Arachnida, 257 ; 


Megapodius, 491. 


INDEX 


Meleagrina margaritifera, 280. 

Membrane, branchiostegal, 396; nic- 
titating, 435; tympanic, 408, 435; 
undulating, 50. 

Menopoma, 433. 

Merostomata, 260. 

Mesentery, 115, 347, 507. 

Mesoglezea, 94. 

Mesopodium, 290. 

Metacarpus, 342. 

Metacrinus interruptus, 177. 

Metagenesis, 98. 

Metametes, 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. 

Micreesthetes, 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, 50s. 

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. 


555 


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. 

Myxospongiz, 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, I92, 
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 


194; 


556 


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. 

Neuroceele, 310. 

Neuropodium of annelid worms, 190. 

Newt, 432. 

Nictitating membrane, 408, 435, 492. 

Noctiluca miliaris, 41. 

Nodosatria, 25. 

Nomenclature, binomial, «. 

Nostrils, in Apteryx, 486; of birds, 
459; of frog, 408. 

Notechord, 910, 913, 924; 336, (337, 
366, 406. 

Notochordal sheath, 325. 

Notopodium of annelid worms, Igo. 

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. 

(Esophagus of starfish, 163; of in- 
sects, 246. 

Oikomonas, 37. 

Oil glands ot birds, 459. 

Olfactory capsules, 410. 

Olfactory pit of Amphioxus, 328. 

Olfactory sacs of frogs, 425. 

Oligochzeta, 202. 

Ommatidia, of crustacea, 228; 
insects, 250. 

Omosternum, 415. 

Onychophora, 236, 


of 


INDEX 


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, q9. 

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, ambulacral, 161; auditory, 
500; of starfish, 157. 

Ostium, 82. 

Ostrich, 483. 

Otaridze, 540. 

Otocysts, 98; of mussels, 277; of 
Cephalopods, 308. 

Otoliths of vertebrates, 358. 

Otter, §26, 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. 
Pzedogenesis in insects, 251, 


INDEX 


Pagurus bernhardus, 231. 

Palzeontology, Io, 

Palate, 505. 

Palatine bone, 414, 499. 

Pallial line, 267. 

Pallium, 266, 

Palpi, of annelid worms, 189; of mol- 
luses, 271, 282. 

Palpus of insectgy2q2. 

Palythoa, 89. as 

Pancreas, 69, 344, 346, 375, 418, 507; 
of birds, 476. 

Pancreatic appendages of molluscs, 


307- 

Papilla, adhesive, of nemertean 
worms, 146. 

Papulze of starfish, 159. 

Paraglossze of insects, 243. 

Paralichthys dentatus, 398. 

Parameecium 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. 

Pedicellariz, 159. 

Pedicles, 537. 

Pedipalpi, 256; of spider, 259. 

Peduncle, 120. 

Pelagic animals, 291, 308. 

Pelecypoda, 265, 278, 280. 

Pelomyxa, I9. 

Pelvic arch, 445. 

Pelvic fin, 374, 406. 

Pelvis of mammalian kidney, 518. 


557 


Penis, of fluke-worms, 130; of mam- 
mals, 520; nematoid worms, setz 
of, 149. 

Pennatula aculeata, 120; sulcata, rar. 

Pen of cuttle-fish, 301. 

Pentacta frondosa, 173. 

Peptones, 346. 

Peramelidz, 528. 

Pericardium, 295; of frog, 419; of 
molluses, 271. 

Perilymph, 383. 

Periostracum, 268, 

Periotic bones, 499, 

Peripatus, 236. 

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, 4o2. 

Placenta, 360. 

Placophora, 284. 

Plaice, 397. 

Planaria, lugubris, 138; polychroa, 
138; torva, 138. 

Plankton, 12, 

Planorbulina, 25. 

Planula, 98, 110. 

Plates, in reptiles, 443. 

Platyhelminthes, 129, 

Platypus, 525. 

Pleopoda, 216. 

Pleural membrane, 513. 

Pleura sac, 513. 

Pleurobrachia, 128. 

Pleuronectes cynoglossus, 398. 

Pleuronectidze, 397. 

Petasus, 102. 

Petromyzon, 360; marinus, 361, 363. 

Phalanges, 342, 502, 530; ungual, 342. 

Pharynx, of Amphioxus, 325; of an- 


558 


nelid worms, 193; of leech, 205; 
ascidian, 365; of mammals, 505; 
of vertebrates, 344. 

Phascolomyida, 529. 

Phocidze, 540. 

Phragmocone, 301. 

Piylogenes, 11. 

Phylum, 7, 74, 75. 

Physalia arethusa, 105. 

Physiology, 12. 

Pieris rapie, 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. 

Podobranchiz, 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. 

Polychzeta, 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, I05. 

Post-abdomen, 255. 

Potamobia pallipes, 213, 221. 

Prze-abdomen, of scorpions, 255. 


INDEX 


Pre-maxillze, 499. 
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 an orms, 193; of 
Balanoglossus, 371; 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, Tyo. 

Pro-ostracum, 301. 

Pro-otic bones of frog, 411. 

Propodium, 290. 

Prorocentrum, 4o. 

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. 

Pseudoceele, 515. 

Pseudopleuronectes americanus, 398. 

Pseudopodia, Is. 

Pteropoda, 288, 291, 296. 

Pterygiophores, 372. 

Pterygodia, 388. 

Pterygoid, bones, 414, 499. 

Pterygoid process, 498. 

Pterylae, 462. 


INDEX 


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, 

Pyxicola, 


Quadrate bo 
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. 

Ratitze, 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. 
Rhizostomez, I12. 
Rhyncheta, 51. 
Rhynchocephalia, 434- 
Ribbon, lingual, 293- 


559 


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. 

Saprophbytes, 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. 


560 


Segmentation of egg, 60. 

Segments of worms, 189. 

Sella turcica, 498. 

Sense organ, 108. 

Sense organs of leech, 209; of mol- 
luses, 282. 

Sepia cultrata, 297, 301, 305. 

Septa, 121; of annelid worms, 191. 

Serpula, 198. 

Setze, of annelids, 190, 201; olfactory, 
of crustacea, 228; penial, 149, 150, 
T53. 

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; 
frog, 414. 

Shrew, 526; jumping, 542. 

Simiide, 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 


INDEX 


of reptiles, 444; of vertebrates, 328, 
333, 337, 339- 

Slits, branchial, of sharks, 368 ; gill, of 
Amphioxus, 326; of Balanoglos- 
sus, 312. 

Sloth, §26, $31, $72. 

Slug, 288, 293. 

Snail, 284. 

Snake, 436, 44 
parous, 455; 

Soldier ant, 253. 

Sole, 297. 

Solen, 281. 

Species, 3; abyssal, 11; alpine, 11; 
littoral, 11; pelagic, rz, 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. 

Sternebrze, 336, 495. 


S, 436; Ovi- 
» 455. 


INDEX 


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. 


Stomach, of m' Is, 506; of star- 
fish, 163; of vertebrates, 374, 418. 

Stomach, sucking, of insects, 246. 

Stomodzeum 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 


561 


Tadpole, 429. 

Teenia coenurus, 143; echinococcus, 
143, 144; saginata, I42, 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, Ior, 

Terebra oculata, 289. 

Terebratulina septentrionalis, 187. 

Teredo navalis, 279, 280. 

Tergum, 255. 

Tessera princeps, I13. 

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 


Theria, 524, 525. 

Thoracic vertebrae, 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. 

Tracheze of insects, 248. 

Trachelomonas, 37. 

Trachelius, 49. 

Trachosphere of molluscs, 295. 

Trachylinge, 102. 

Trapezium, 502. 

Trapezoid, 502. 

Tree, genealogical, 9. 

Trematoda, 134; ectoparasitic, 137. 

Trichechideae, 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 Echinoidea,170 ; of Holo- 
thuroidea, 173; of starfish,160, 161. 


INDEX 


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; df bitds) 469. 

Ulnare, 469. E : 

Umbilicus of feather, 460. 

Umbo of shells, 267, 

Umbrella, 95. 

Una, 592. 

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. 


Yer 


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 


Vas deferens, of fluke-worm, 132; of 
mammals, 520; of vertebrates, 359; 
of worms, 132. 

Vein, pulmonary, 407, 423; 
portal, 422. 

Veins, hepatic, 352; pulmonary, 351; 
of vertebrates, 349, 350, 379. 

Veliger, 295. 

Velim, 97, Ais, 

Velvet, of deer horns, 537. 

Ventricle, of brain, fourth, 354, 380; 
lateral, 354; third, 354; fifth, 514. 
Ventricles of heart of vertebrates, 

350. 

Venus'’s flower-basket, 86 ; girdle, 128. 

Vermetus, 296. 

Vermiform appendix, 507. 

Vermis, 517. 

Vertebra, 333, 440, 463 ; amphiccelous, 
334, 440; heteroccelous, 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. 

Vibrissee of rabbit, 492. 

Visceral arches, 337, 444. 

Visceral mass of molluscs, 270. 


renal 


563 


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. 


Zocecium, 181. 

Zooid, 30, 91. 

Zoology, definition of, 1. 
Zoophytes, go. 
Zooxanthella, 33. 
Zygomatic arch, 499. 
Zygomatic process, 498. 
Zygapophysis of frog, 410. 


A TEXT-BOOK OF ZOOLOGY 


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Professor of Biology in Untuerstty of Otago, Dunedin, N.Z. 


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