IV Modern Age
III Tertiary A^P

irSecoiid-d

•••••MMHH*

LPalceozoieA^e. "^1

Met aTnoiiilric R o cks .

Drift or

Tertiary ForrriaJicn/
"Lower Jertiaay. "

a AS HP01 ff

OUTLINES

OF

COMPARATIVE PHYSIOLOGY,

TOUCHING

THE STRUCTURE AND DEVELOPMENT

OF THE

RACES OF ANIMALS, LIVING AND EXTINCT.

FOR THE USE OF SCHOOLS AND COLLEGES.

BY

LOUIS AGASSIZ

AND

A. A. GOULD.

from t{)e Kebfeefc iStritton, anir grratls

BY

THOMAS WRIGHT, M D.

•>

WITH 390 ILLUSTRATIONS.

LONDON:

BELL & DALDY, YORK STREET, COVENT GARDEN.

1870.

LONDON' :
PRINTED BY WILLIAM CLOWES AND SONS,

STAMFORD STREET AXD CHARING CROSS.

THE EDITOR'S PREFACE.

THE distinguished position occupied by Professor Agassiz,
from his numerous and important works on Natural Science,
especially his " Recherches sur les Poissons Fossiles," renders
any eulogium on the contributions of so eminent a naturalist
to zoological literature unnecessary.

The " Principles of Zoology," of which the present volume
forms the first part, was designed by Professor Agassiz, in
conjunction with Mr. Gould, as a text-book for the use of
higher schools and colleges, for which it is undoubtedly well
adapted, as the style is simple, the arrangement clear, and
the range of subjects 'important and comprehensive: it is,
moreover, well suited for imparting to the general reader a
sound knowledge of Physiology and the Philosophy of Natural
History.

In introducing the present edition of this work to the English
public, the Editor desires to state that he has endeavoured still
farther to increase its value, by large additions to several of
the chapters. In doing so, he has availed himself of the
treatises of Cuvier, Carus, and Meckel, on Comparative Ana-
tomy ; and those of Tiedeman, Miiller, Valentin, and Wagner,
on Physiology. From Dr. Willis's excellent translation of the
Elements of the latter profound author much additional matter
has been derived.

The additions from Wagner are duly acknowledged in the
body of the work : those by the Editor are indicated by his

IV PEEFACE.

initials, and both are enclosed in brackets, so that the reader
may readily distinguish between MM. Agassiz and Gould's
text, and the additions made thereto,

The number and excellence of the wood-cuts form an im-
portant feature in this edition. With the exception of those
belonging to the chapters on Embryology, and the Meta-
morphoses of Animals, they are nearly all additional, by which
the original number is more than doubled : the American
edition having only 170 wood-cuts, whilst the present con-
tains 390. The beautiful drawings illustrative of human
Osteology were engraved by Branston for the valuable Manual
on the Bones by John F. South, Esq. ; those illustrating the
chapters on Circulation, Respiration, Secretion, and the De-
velopment of the Chick, are chiefly from Wagner's " Icones
Physiologies" and were engraved for the English translation
of that author's Elements of Physiology ; the other figures
are selected from various sources, references to which are
given in the Table of illustrations.

It has been the study of the Authors and of the Editor to
exclude as much as possible a technical phraseology from
the following pages ; but as the use of scientific terms could
not altogether be dispensed with, the Editor has given an
interpretation of them in a copious Glossarial Index.

T.W.

Cheltenham, October, 1851.

PKEFACE.

THE design of this work is to furnish an epitome of the leading
principles of the science of Zoology, according to the present
state of knowledge, so illustrated as to be intelligible to the
young student. No similar treatise exists in this country, and
indeed some of the topics have not been touched upon in the
language, except in a strictly technical form, and in scattered
articles. On this account, some of the chapters, such as those
on Embryology and Metamorphosis, may at first seem too
abstruse for the beginner. But so essential have these sub-
jects now become to a correct interpretation of philosophical
zoology, that the study of them will hereafter be indis-
pensable. They furnish a key to many phenomena which
have heretofore been locked in mystery.

The illustrations have been drawn from the best authorities ;
some of them are merely hypothetical outlines, which convey
a more definite idea than if drawn from nature ; others have
been left imperfect, except as to the parts especially in ques-
tion ; a large proportion of them, however, are complete and
original. Popular names have been employed as far as pos-
sible, and Definitions of those least likely to be understood,
will be found in the Glossary.

The principles of Zoology developed by Professor Agassiz
in his published works have been generally adopted in this,
and the results of many new researches have been added.

VI PEEFACE.

The Authors gratefully acknowledge the aid they have re-
ceived in preparing the illustrations and working out the
details from Mr. E. Desor, for many years an associate of Pro-
fessor Agassiz ; from Count Pourtales and E.C.Cabot, Esq.;
and also from Professor Asa Gray, by valuable suggestions in
the revision of the letter-press.

The present volume is devoted to Comparative Physiology
as the basis of classification ; the second will comprise Sys-
tematic Zoology, in which the principles of classification will
be applied, and the principal groups of animals briefly charac-
terised.

Should our aim be attained, this work will produce more
enlarged ideas of man's relations to Nature, and more ex-
alted conceptions of the plan of Creation and its Great
Author.

BOSTON, JUNE 1, 1848.

TABLE OF CONTENTS.

INTRODUCTION xix

CHAPTER FIRST.

THE SPHERE AND FUNDAMENTAL PRINCIPLES OF ZOOLOGY . 1

CHAPTER SECOND.

GENERAL PROPERTIES OF ORGANIZED BODIES ... 9

SECTION I.
Organized and Unorganized Bodies . . . 9

SECTION II.
Elementary Structure of Organized Bodies . 1C

SECTION III.
Differences between Animals and Plants .... .20

CHAPTER THIRD

ORGANS AND FUNCTIONS OF ANIMAL LIFE 28

SECTION I.

Of the Nervous System and General Sensation . . . .28

Structure of the primary Fibres of Nerves, 29 — Termination
of the primary Fibres, 34 — The Cerebro- spinal system of Man—
The Cerebrum, 40— The Cerebellum, 41— The Optic Lobes, 42—
The Spinal Cord, 42 — Nervous system of Fishes, 44 —Amphibia,
45 — Scaly Reptiles, 45 — Birds, 45 — Mammalia, 46 — Cerebr«m
Nerves, 49 — Nervous system of Articulata, 54 — Couchifera, 55 —
Gasteropoda, 55 — Cephalopoda, 56 — Radiata, 57.

SECTION II.

Of the Special Senses 58

1. Of Sight, 58— The Eye, 58— Dioptrics of the Human Eye, 60
— 2. Of Hearing, 70 — Comparative Anatomy of the Organ of
Hearing, 70—80—3. Of Smell, 80— The Nose, 80—4 Of Taste,
81—5. Of Touch, 82—6. The Voice, 83.

VLU TABLE OF CONTEXTS.

Page

CHAPTER FOURTH.

OF INTELLIGENCE AND INSTINCT ..... 86

Perception ...... ... 86

CHAPTER FIFTH.
OF MOTION 91

SECTION I.
Apparatus of Motion .... .... 91

Voluntary and Involuntary Muscles, 92 — Microscopic Anatomy
of Muscular Fibre, 90— 94— Ciliary Motions, 95— Skeleton of
Polyps, 100— Echinidre, 101— Astejriadae, 102— Crinoidese, 103
— Mollusca, 104— Articulata, 105— Vertebrata, 106.

SECTION II.

Organs of Locomotion . 109

Skeleton of Man, 111 — Composition of tbe Bones in Fishes, 113
• — Reptiles, 113 — Birds, 113 — Mammals, 113 — Analysis of Bones,
114 — Microscopic Structure of Bones, 115 — The Head, 116 —
The Orbits, 123— The Trunk, 126— The Cervical Vertebra, 127
—The Dorsal Vertebras, 129 — The Lumbar Vertebras, 130—
The Sacrum, 131— The Coccyx, 131— The Vertebras, 131—
Comparative Table of the number of the Vertebrae, 134 —
The Thorax, 135- The Pelvic Arch, 136— The Thigh, 138—
The Leg, 139— The Foot, 139— The Tarsus, 140— The Meta-
tarsus, 140— Toes, 140— The Scapular arch, 141 — The Scapula'
142— The Clavicle, 143— The Humerus, 143— The Hand, 146
—The Carpus, 146— The Metacarpus, 146— The Phalanges,
147 — 1. Plan of the Organs of Locomotion in the Vertebrata,
148 — 2. Of Standing, and the Modes of Progression, 152 —
Walking, 154— Running, 155— Leaping, 155 — Climbing, 155 —
Flight, 156 — Swimming, 157.

CHAPTER SIXTH.
NUTRITION ... 159

SECTION I.
Of Digestion 160

The Polypifera, 160— The Infusoria, 161— The Acalephae, 162
— The Eohinoderms, J 63— The Bryozooan Polypifera, 165— The
Tunicated Mollusca, 166 — The Conchifera, 166 — The Gastero-
poda, 167— The Cephalopoda, 171— The Annelida, 172— The
Crustacea, 173 — The Arachnida, 174 — Insects, 174 — The Ver-
tebrata, 178 — Organs of Mastication, 185 — Insalivation, 191 —
Prehension, 193.

TABLE 01" CONTENTS. IX

Page

CHAPTER SEVENTH.

OF THE BLOOD AND CIRCULATION ...... 194

Blood globules in Man, 194 — Mammalia, 196 — Birds, Reptiles,
and Fishes, 197, 198— Blood vessels, 199— Heart, 200— Circu-
lation of the Blood in Mammals and Birds, 202 — Reptiles, 203 —
Fishes, 204 — Crustacea, Mollusca, and Insecta, 205 — Capillary
Vessels, 207 — Circulation of the Blood in the Web of the Frog's
foot, 208—212 — Circulation in the Lungs of the Triton, 213.

CHAPTER EIGHTH.

OF RESPIRATION ......... 216

The Echinoderms, 27— The Tunicata, 218— The Conchifera, 219
—The Gasteropoda, 219— The Pteropoda, 220— The Cephalo-
poda, 220— The Crustacea, 220— The Annelida, 220— Fishes,
221 — Insects, 223 — Air-breathing Vertebrata, 225 — Develop-
ment of the Lungs, 226 — 231 — Respiration in Gases other than
Atmospheric Air, 234.

CHAPTER NINTH.

OF THE SECRETIONS ......... 241

Endosmose and Exosmose, 243 — Structure of Glands, 246 — Ele-
mentary parts of Glands, 263 — Origin of Glands, 265 — Dis-
tribution of the Vessels in Glands, 269.

CHAPTER TENTH.

EMBRYOLOGY .... .... 272

SECTION I.

Of the Egg 27J

Form of the Egg, 272— Formation of the Egg, 273.

SECTION II.

Development of the Young within the Egg .... 278
Development of Fishes, 280 — 289 — Development of the Chick,
290 — Structure of the Egg as just laid, 290 — Detachment of the
Ovum from the Ovary, and completion of its formation in the
Oviduct, 292 — Earliest Period in the Development of the Chick,
from the first appearance of the Embryo to the first traces of Cir-
culation, 295 — Second Period of the Development of the Chick,
to the Evolution of the Second Circulation, 308 — Third Period
in the history of the Development of the Incubated Egg : from
1he commencement of the Circulation in the Allantois to the Ex-
elusion of the Embryo, 324— Birth of the Chick, 333— Phy-
sical and Chemical changes in the Egg during Incubation, 334.

SECTION III
Zoological Importance of Embryology . . . 336

.< TABLE OF CONTENTS.

Page

CHAPTER ELEVENTH.
PECULIAR MODES OF REPRODUCTION 339

SECTION I.
Gemmiparous and Fissiparous Reproduction .... 339

SECTION II.

Alternate and Equivocal Reproduction . . . . .348

SECTION III.
Consequences of Alternate Generation . ... 348

CHAPTER TWELFTH.
METAMORPHOSES OF ANIMALS ....... 353

CHAPTER THIRTEENTH.

GEOGRAPHICAL DISTRIBUTION OF ANIMALS . . . 363

SECTION I.
General Laws of Distribution ....... 363

SECTION II.
Distribution of the Faunas . . . . . . . 369

1. Arctic Fauna, 371 — 2. Temperate Faunas, 373 — Tropical
Faunas, 377-

SECTION III.
Conclusions .......... 380

CHAPTER FOURTEENTH.

GEOLOGICAL SUCCESSION OF ANIMALS ; OR, THEIR DISTRIBUTION

IN TIME .... ..... 390

SECTION I.
Structure of the Earth's Crust 3^0

SECTION II.

Ages of Nature ........ 396

The Palaeozoic Age, 397 — The Secondary Age, 402 — The
Tertiary Age, 414 — The Modern Epoch, 415 — Conclusion, 417.

List of the most important Authors who may be consulted in

reference to the Subjects treated in this Work . . . 419
GLOSSARIAL INDEX .... ... 421

EXPLANATION OF THE FIGURES.

FRONTISPIECE. — The diagram opposite the title-page is intended to pre-
sent, at one view, the distribution of the principal types of animals, and
the order of their successive appearance in the layers of the earth's crust.
The four Ages of Nature, mentioned at page 190, are represented by four
zones, each of which is subdivided by circles of different shades, indicat-
ing the number of formations of which it is composed. The whole disc
is divided by radiating lines into four segments, to include the four
great departments of the animal kingdom ; the Vertebrata are placed in
the upper compartment, the Articulata at the left, the Mollusca at the
right, and the Radiata below, as being the lowest in rank. Each of these
compartments is again subdivided to include the different classes belonging
to it, which are named at the outer circle. At the centre is placed a figure
representing the primitive egg, with its germinative vesicle and germinative
dot C § 436), indicative of the universal origin of all animals, and the epoch
of life when all are apparently alike. Surrounding this, at the point from
which each department radiates, are placed the symbols of the several de-
partments, as explained on page 337. The zones are traversed by rays
which represent the principal types of animals ; their origin and termi-
nation indicate the age at which they first appeared or disappeared ; all
those which reach the circumference being still in existence. The width
of the ray indicates the greater or less prevalence of the type at dif-
ferent geological ages. Thus, in the class of Crustaceans, the Trilobites
commence in the earliest strata, and disappear with the carboniferous
formation. The Ammonites also appeared in the Silurian formation,
and became extinct with the deposition of the Cretaceous rocks. The
Belemnites appear in the lower Oolitic beds ; many new forms commence
in the Tertiary; a great number of types make their appearance only in
the Modern age ; while only a few have continued from the Silurian,
through every period to the present. Thus, the Crinoids were very nu-
merous in the Primary Age, and are but slightly developed in the Tertiary
and Modern Age. It is seen, at a glance, that the animal kingdom is
much more diversified in the latter, than in the earlier ages.

Below the circle is a section, intended to show more distinctly the re-
lative position of the ten principal formations of stratified rocks (§ 648),
composing the four great geological ages ; the numerals corresponding to
those on the ray leading to Man, in the circular figure. See also figure 376.

Xil

EXPLANATION OF THE FIGURES.

The CHART OF ZOOLOGICAL REGIONS, page 370, is intended to show
the limits of the several Faunas of the American Continent, corresponding
to the climatal regions. As the higher regions of the mountains cor-
respond in temperature to the climate of higher latitudes, it will be seeu
that the northern temperate fauna extends, along the mountains of Mexico
and Central America, much farther towards the Equator, than it does on
the lower levels. In the same manner, the southern warm fauna extends
northward, along the Andes.

Fig.

1 Tissue of the house leek- Agassiz

2 Pith of the elder . Ibid.

3 Microscopic structure of carti-

lage . . . Schwann

4 Branchial cartilage of the larva

of a frog . . Ibid.

5 Evolution of cellular tissue. Ibid.

6 Evolution of muscular fibre. Ibid.

7 Evolution of nervous fibre. Ibid.

8 Nucleated cells from the granula-
tions of the umbilical cord. Breschet

9 Primary fibres of a human

nerve . . . Wagner

10 Branch of a nerve distributed to

a muscle of the eye . Ibid.

11 Primary fibres of the olfactory

nerve in man . Valentin

12 Terminal plexus of the auditory

nerve (pike) . . Wagner

13 Terminal plexus from the ciliary

ligament (duck) . Valentin

14 Terminal fibres (central) from

the yellow substance of the ce-
rebellum . . Wagner

15 Abdominal ganglion of the sym-

pathetic nerve . . Ibid.

16 Primary fibres of the intercostal

nerve of the sparrow . Ibid.

17 Thin slice from the cervical

ganglion of the calf. Valentin

18 Primary fibres and ganglionic glo-

bules of the human brain. Ibid.

19 The nervous system of Man.

[Milne Edwards

20 A section of the human brain,

shewing likewise the point of
union of the cerebral nerves
therewith . . Ibid

21 The brain and spinal cord of

the Cyprinu& aiburnus. Cams

Fig.

21*A portion of the spinal cord shew-
ing the double union of the
nerves . . Edwards

22 The brain of the eel seen from

above . . . Carus

23 The brain of the eel seen from

below . . . Ibid.

24 The brain of the tortoise seen

from above . . Bojanus

25 The brain of the tortoise seen

from below . . Ibid.

26 The brain of the turkey seen from

above . . . Carus

27 The brain of the pigeon seen

from below . . Ibid.

28 The brain and spinal cord of

the rat ... Ibid.

29 The brain of the hare . Ibid.

30 The brain of the common cat. Ibid.

31 The brain and spinal cord of

the racoon . . Ibid.

32 The brain of a monkey laid

open .... Ibid.

33 The brain of a monkey seen

from below . . Ibid.

34 The nervous system of the gar-

den beetle . . . Ibid,

35 The nervous system of Pa-

hidina vivipara . Cuvier

36 The nervous system of the star-

fish . . Tiedeman

37 Section of the globe of the

eye . . . Agassiz

38 Diagram shewing the effect of

the eye on rays of light. Wagner

39 Diagram shewing the effect of

the eye on rays of light. Wagner

40 Ditto ditto . . Ibid.

41 Ditto ditto . . Ibid.

42 Ditto ditto Ibid

EXPLANATION OF THE FIGUBES.

• • •

Xlll

Fig.

43 Optical diagram . Wagner

44 Compound eyes of insects and

Crustacea . . . Miiller

45 Vertical section of the organ of

hearing in man . Edwards

46 Malleus or hammer-bone of the

internal ear . . South.

47 Incus or anvil bone ditto. Ibid.

48 Stapes or stirrup ditto. Ibid.

49 Chain of bones in situ. Ibid.

50 Relative situation of the tympa-

num and labyrinth. Soemmering

51 Views of the labyrinth. Ibid.

52 Ditto of the cochlea. Ibid.

53 Ditto of the semicircular canals.

[Ibid.

54 Ditto ditto ditto. Ibid.

55 The cochlea, base and apex. Ibid.

56 The spiral laminae of the

cochlea . . . Ibid.

57 The external shell of the cochlea

removed . . . Ibid.

58 Horizontal section of the coch-

lea ... South

59 From view of the human

larynx.

60 The larynx of the merganser

(Mergns Merganser'} .

60 A muscular fasciculus of the ox.

[Wagner

61 The structure of human muscle.

[Ibid.

62 Muscular fibre, after Skey. Skey

63 Muscles from the back of the

rattle-snake . Wagner

64 Muscular fibres from the inver-

tebrata . . . Ibid.

65 Muscular fibres from the eso-

phagus . . . Skey

66 Streaked muscles of the Scolo-

pendra Afro, . . Wagner

67 Cilia arising from the epithelial

cylinders . . . Ibid.

68 Epithelial cells producing cilia.

[Ibid.
69, 70 Litharcea Websteri. Sowerby

71 The test of an echinus. Edwards

72 Apiocrinus rotunda . Miller

73 Encrinus moniliformis . Ibid.

74 Cyprceacdssis ru/a. Stutchbury

Fig.

75 Astacus Vectensis, from Isle of

Wight . . Mantell

75* External skeleton of Dasypus
sexcinctus.

76 The muscular system of the

perch . . . Carus

77 The muscular system of the

Falco nisus . . . Ibid.

78 The skeleton of man. Cheselden

79 The human cranium . South
80—83 The temporal bones. Ibid.

84 The calvaria of the human

skull . . . Ibid.

85 The temporal bones . Ibid.

86 and 87 External and internal

views of ditto . . Ibid.
88 and 89 Anterior and posterior

faces of petrous portion. Ibid.
90, 90* External and internal views

of the occipital bone. Ibid.

91 The sphenoid and ethmoid. Ibid.

92 The superior and inferior max-

illaries . . . Ibid.

93 Internal view of the superior

maxillary . . . Ibid.

94 The partition of the nostrils. Ibid.

95 A vertical section of the or-

bits, nostrils, and palate. Ibid.

96 The lateralboundary of ditto. Ibid.

97 The orbits . . . Ibid.

98 and 99 Views of the internal

structure of the nose . Ibid.
100, 101 The internal and external sur-
face of the superior maxilla. Ibid.
102 The osseous roof of the
mouth . . . Ibid.
103, 104 External and internal sur-
faces of the superior maxilla.

rlbid.

105 The dorsal vertebrae. Ibid.
106, 107 The cervical ditto. Ibid.
108 and 109 The atlas . Ibid.

110 The axis . . . Ibid.

111 The seventh cervical vertebra.

[Ibid.

112, 113 The dorsal vertebrae. Ibid.
114 The mode of articulation of
the dorsal vertebras . Ibid.
115,116 Lumbar vertebrae. Ibid.
117 The fifth lumbar vertebra. Ibid,

XIV

EXPLANATION OF THE FIGURES.

Fig.

113, 119, 120 Different views of

the sacrum . . South

121 The front view of the spinal

column . . . Ibid.
] 22 The back view of ditto. Ibid.

123 The lateral view of ditto. Ibid.

124 The thorax . . Ibid.
125, 126 Views of the male and

female pelvis . . Ibid.
127, 128 The ossa innominata. Ibid.
129, 130 The outlet of the pelvis

[Ibid.

131 The acetabulum . . Ibid.

132 The position of the pelvis, the

axis .... Ibid.

133, 134 The anterior and posterior

view of the femur. Ibid.

137 The tibia, fibula and patella.

[Ibid.

138 The tarsus, metatarsus and

toes .... Ibid.

139 Tibio-tarsal articulation. Ibid.
140, 141 The two rows of tarsal

bones . . . Ibid.

142 The metatarsus. . . Ibid.

143 The toes . . Ibid.

144 The scapular arch. . Ibid.
145, 146, 147 Different views of

the scapula . . Ibid.
148 The clavicle . . . Ibid.
149, 150 Front and back view of

the humerus . . Ibid.
151, 152 The condyles of ditto.

[Ibid.

153 The radius and ulna. Ibid.

154 The carpus, metacarpus and

phalanges . . . Ibid.

155. 156 The two rows of carpal
bones . . . Ibid.

157, 158 The upper and lower sur-
faces of the carpal bones Ibid.

158* The metacarpus . Ibid.

159 The phalanges of the thumb

and fingers . . Ibid.

160 The anterior extremity of the
stag . . . Agassiz

161 Ditto of the lion . Ibid.

162 Ditto of the whale . Ibid.

163 Ditto of the bat . Ibid.

164 Ditto of the bird . Ibid. !

Fig.

165 The anterior extremity of the

sloth . . [Agassiz

166 Ditto of the turtle . Ibid.

167 Ditto of the mole . Ibid.

1 68 Ditto of a fish . . Ibid.

169 The skeleton of the camel.

[Edwards

170 The fresh-water polyp (Hydra

viridis) . . . Ibid.

171 Leucophrys patula . Ehrenberg

172 Eosphora najas . Ibid.

1 73 A vertical section oiRhizostoma

Cuvieri . Eysenhardt

174 Anatomy of the sea urchin,

Echinusescidentus. Delle Chiaje

175 Plumatella repens . Edwards

176 The anatomy of the common

oyster (Ostrea edulis) . Poll

177 The anatomy of the sea-hare

(Aplysia Camelus) . Cuvier

178 The anatomy of the leech (Hiru-

do medicinalis) . Carus

179 The digestive organs of a

beetle . . Edwards

180 The thoracic and abdominal vis-

cera of a monkey . Ibid.

181, 182 The gastric glands from

the stomach of man. Wagner

183 Magnified diagram of these

glands . . . Ibid.

184 Other forms of glands of this

class . . . Ibid.

185 Stomach of the plover (Vanel-

lus cristatus}. . . Ibid.

186, 187, 188 Gastric glands of

birds . . . Ibid.

189 The chyliferous vessels and

glands . . Edwards

190 The jaws of an urchin (Echi-

narachnius parma). Agassiz

191 The jaws of an urchin (Echi-

nus granulatus) . Ibid.

192 The jaws of a cuttle fish. Ibid.
193, 194 The dental organs of Nerita

and Patella . Wright

195 The anatomy of the mouth of

a beetle . . Edwards

196 Ditto of the bee . . Ibid.

197 Ditto of the bug , . Ibid.

198 Ditto lancets of ditto . Ibid.

EXPLANATION Of THE PIGUEES.

XV

Fig.

199 The anatomy of the mouth of

the butterfly . Edwards

200 The jaws of the snapping tur-

tle (Emysaurus serpentina).

[Agassiz

201 The head of a whale, shewing

the whale-bone . . Ibid.

202 The head of an ant-eater.

[Ibid.

203 The head of an alligator. Ibid.

204 The head of a skate-fish (My-

liobatis), shewing palate teeth.

[Ibid.

205 The skull of the horse.

206 The skull of a squirrel.

207 The skull of a tiger.

208 Globules of the blood of man.

[Wagner

209 Ditto of the common goat (Ca-

pra domestica) . . Ibid.

210 Blood and lymph globules of

the pigeon (Columba domes-
tica) . . . Ibid.

211 Blood globules of the Proteus

anyuinus . . Ibid.

212 Blood and lymph globules of

the Triton cristatus . Ibid.

213 Blood globules of the Rana

esculenta . . . Ibid.

214 Blood and lymph globules of the

Cobitis fossilis . . Ibid.

215 Blood globules of the A mmocetes

branchialis . . Ibid.

216 Vein laid open to shew the

valves . . Cloquet

217 Diagram of the course of the

blood in mammals and birds.

[Edwards

218 Diagram of an ideal section of

the human heart . Ibid.

219 Diagram of the circulation in

reptiles. . . . Ibid.

220 Diagram ol the circulation in

fishes . . . Ibid.

221 The heart and vascular system

of the Doris . . Ibid.

222 The vascular system of the

lobster . . . Ibid.

223 The organs of circulation in a

nenropterous insect Ibid.

Fig.

224 Capillary vessels of the intestinal

villus of a hare . Wagner

225 Circulation of the blood in the

inter-digital membrane of the
hind foot of a frog, magnified
three diameters . Ibid.

226 The same, magnified forty-five

diameters . . . Ibid.

227 The same, magnified one hun-

dred and ten diameters. Ibid.

228 A venous branch, magnified three

hundred and fifty times. Ibid.

229 View in outline of a vein, mag-

nified six hundred times. Ibid.

230 A portion of the lung of a living

triton, drawn under the micro-
scope, magnified one hundred
and fifty times . . . Ibid.

231 Capillary circulation in the

lung .... Ibid.

232 The anatomy of the Holothuria

tubulosa . Delle Chiaje

233 The branchias of the Arenicola.

[Edwards

234 The respiratory apparatus of the

Nepa cinerea. Leon Dufour

235 Lungs, heart, and principal blood-
vessels of man . Edwards

236 Lung of the triton, magnified.

[Wagner

237 Lung of the triton, injected. Ibid.

238 Lungof the frog, magnified. Ibid.

239 Lung of the tortoise ditto. Ibid.

240 Lung of the serpent ditto. Ibid.

241 Terminal vesicles of the human

lung .... Ibid.

242 Portion of the lung of a hog. Ibid.

243 Portion of the human lung mag-

nified two hundred times. Ibid.

244 Rudiment of the lung from the

embryo of a fowl . Ibid.

245 Rudimentary lung from the em-

bryo of a sheep . Miiller

246 Termination of the bronchi of

the embryo of a hog. Rathke

247 Diagram of experiment to illus-

trate Endosmose andExosmose.

248 Glands from the auditory pas-

sage of the human subject.

[Wagner

XVI

EXPLANATION OF THE FIGURES.

Fig.

249 Sudoriparous glands from the

palm of the hand. Wagner

250 Do. do. . . Gurlt

251 Thin layer of the scalp mag-

nified . . . Ibid.

252 The salivary glands of insects

[Ramdohr and Succow

253 Glands of insects . Ibid.

254 Do. do. . Ibid.

255 Harderian gland of the Pe-

lecanns onocrotalus. Wagner

256 Cowper's gland of the hedge-

hog (Erinaceus*) . Ibid.

257 Parotid gland of a new-born

infant . . . Weber

258 Kidney and supra-renal capsule

of an infant . . Wagner

259 Portions of do. magnified. Ibid

260 Do. magnified 60 diameters. Ibid.

261 Termination of one of the tubuli

magnified 250 times . Ibid.

262 Kidney of the porpoise (Delphi-

nus phoccena) . . Miiller

263 Lobules of the human liver.

[Wagner

264 A branch of the hepatic vein and

liver lobules . . Ibid.

265 Superficial lobules of the liver.

[Kiernan

266 The intra-lobular plexus of

biliary vessels . . Ibid.

267 A transverse section of the

lobes of the liver . Ibid.

268 A view, magnified 40 times, of

the liver of a newt. Wagner
269—272 Show the development of

the liver . . Miiller
273 Ramifications of the bronchi

from the embryonic Falco tin-

nunculus . . Wagner
274, 276 Rudimentary form of the |

parotid gland . . Miiller i

277 Lobules of the parotid gland.Ibid.

278 Development of the liver in the

Falco tinnunculus Wagner

279, 280 Malpighian bodies from the

kidney of the Triton and Strix

aluco . . Huschke

281 The egg of a skate-fish (Mylio-

batis).

Agassiz

Fig.

282 The ova of a fresh-water polyp

(Hydra) . . Agassiz

283 The egg of an insect — the

snow-flea (Podurella). Ibid.

284 The primary ova of a bird

magnified . . Wagner

285 TheeggsoftliePyrwfo. Agassiz

286 The ovarial sacs of a Monoculus,

[Ibid.

287 Ideal section of a fowl's egg.

[Baer

288 Cell layer of the germ. Agassiz

289 Separation of the cell layer in-

to three laminae . . Ibid.

290 Embryo of a crab, showing the

incipient rings . . Ibid.

291 Embryo of a vertebrate animal,

showing the dorsal furrow.Ibid.
292—294 Sections of the embryo,
showing the formation of the
dorsal canal . . Ibid

295 Section showing the position of

the embryo of a vertebrate
animal in its relation to the
yolk . . . Ibid.

296 Section showing the same in an

articulate animal . Ibid.

297 — 308 Sections showing the suc-
cessive stages of development
of the white-fish magnified.

[Ibid.

309 The young white-fish just es-
caped from the egg, with the
yolk not yet fullytakenin. Ibid.

310 — 311 Sections of the embryo of
a bird, showing the formation
of the allantois : e, embryo ; x,x,
membrane arising to form the
arnnios ; a, the allantois ; y,
the yolk.

312 The same fully developed; the
allantois (a} is further deve-
loped and bent upwards ; the
upper part of the yolk (d, d}
is nearly separated from the
yolk sphere, and is to become
the intestine ; the heart (h ) is
already distinct and connected
by threads with the blood
layer of the body.

Jy OP THE "FIGURES.

XVU

Fig. \ Fig.

313, 314 Sections of the egg of a 334
mammal ; v, the thick vitelline
membrane or chorion ; y, the
yolk ; s, the germinative spot ;
g, the germinative vesicle ;
k, the empty space between
the vitelline sphere and cbo-

non.

315 Shows the first indication of
the germ dividing into layers,

335
336
337

338

the serous
cous (m).

(s) and the mu- 339—

is seen sur-

343
344,

346

347

348

316 The mucous layer (m) expands

over nearly half the yolk, and
becomes covered with many j
little fringes.

317 The embryo (c)

rounded by the amnios (6), and
covered by the large allantois
(a) ; p, e, fringes of the cho-
rion ; /;, m, fringes of the ma-
trix

318 One of the chalazae of a jack-

pulled straight.

[\Vagner

319 "Vitellus of a hen's egg Ibid.

320 The yolk of a jackdaw's egg.

[Ibid.

321 Section of a yolk almost ripe

included in its calyx . Ibid.

322 The ovary of a fowl . Ibid.
323, 324 The" vitellus twelve hours I 359

daw's egg

after incubation

Ibid. 360

325 Magnified view of the blasto-[361
derma . Ibid.

326 Ideal sections

Baer

327 Yolk after eighteen hours' in-

•\-f

cubation

Wagner

328 The pellucid area magnified.

[Ibid.

329 Ideal sections of 327, 328. Ibid.

330 Yolk after twenty-four hours'

incubation . . . Ibid.

331 Magnified view of the pellucid

area .... Ibid.

332 Ideal sections of 329—331.

[Ibid.

333 Yolk of the natural size after

thirty-six hours' incubation.

[Ibid.

Magnified view of the pellucid
area of the vitellus Wagner
Ideal sections of the embryo.

[Ibid.

Incubated vitellus of the jack-
daw's egg . . Ibid.
Anterior extremity of an em-
bryo .... Ibid.
Ideal section of an embryo.

[Ibid.

342 Views of embryos mag-
nified . . . [Ibid.
Ideal section of ditto . Ibid.
345 Outlines of embryos of the
fowl .... Ibid.
View of the vitellus magnified.

[Ibid.

View of the embryo of the
yolk .... Ibid.
Yolk of the hen's egg . Ibid.
349 — 354 Views of embryos in dif-
ferent stages of development.

[Ibid.

355 Embryo of a lizard (Lacerta

agilis) . . . Ibid.

356 Vorticella, showing its reproduc-

tion by buds . Agassiz

357 Vorticella, showing its repro-

duction by division . Ibid.

358 Polyps, showing the same phe-

nomenon . . . Ibid.
A chain of Salpae . Ibid.

An individual Salpa . Ibid.
Cercaria, or early form of the

Distoma . . Steenstrup

362 Distoma, with its two suckers.

[Ibid.

363 Nurse of the Cercaria . Ibid.

364 The same magnified, showing

the included young . Ibid.

365 Grand nurses of the Cercaria,

including the young nurses.

[Ibid.

366 Stages of development of the

Acalephae (Mtdusa) : a, the
embryo in its first stage, much
magnified ; b, summit, show-
ing the mouth; c, f, g, ten-
tacles shooting forth; e,
embryo adhering, and forming
6

XVU1

EXPLANATION OP THE FIQUEES.

Fig.

a pedicle ; h, i, separation into
segments; da segment become
free; k, form of the adult.

[Sars

367 Portion of a horny sheathed

polyp (Campanularia) : a,
cup, which bears tentaculae ;
fc, the female cell, containing
eggs ; c, the cells in which the
young are nursed, and from
which they issue . Steenstrup

368 The young of the same, with

its ciliated margin, magnified.

369 Transformations of the canker

worm (Geometra vemalis) :
a, the canker worm ; b, its
crysalis; c, female moth;
d, male moth. . Agassiz

370 Metamorphoses of the Duck-

barnacle (Anatifa); a, eggs
magnified ; b, the animal as
it escapes from the egg ; c,
the stem and eye appearing,
and the shell enclosing them ;
d, animal removed from the
shell, and further magnified ;
e,f, the mature barnacle af-
fixed by its pedicle . Ibid.

371 Metamorphoses of a star-fish

(Eckinaster sangidnolentus),
showing the changes of the
yolk, e ; the formation of the
pedicle, p ; and the gradual
change into the pentagonal
and rayed form . . Ibid.

372 Comatula, a West Indian spe-

cies, ia its early stage attached
w a ivsoi . . Agassiz

i Fig.

I 373 The same, detached and swim-
ming free . . . Ibid.

374 Longitudinal section of the stur-

geon, to show its cartilaginous
vertebral column . Ibid.

375 Amphioxus, natural size, show-

ing its imperfect organiza-
tion .... Ibid.

376 Section of the earth's crust,

showing the relative position
of the rocks composing it.

[Agassiz

377 Fossils of the Palaeozoic age.

[Murchison.

378 Homalonotus delphinocephalus.

[Konig

379 Pterichthys . . Miller

380 Coccosteus cuspidatus . Ibid.

381 The Flora of the coal period.

[Richardson

382 Foot-prints of birds . Ibid.

383 Plesiosaurus rugosus . Owen

384 Pterodactylus crassirostris.

[Goldfuss

385 Jaw of the Thylacotheriwn,

magnified. . Richardson

386 Fossils, shells, and Hemicidaris
\ from the oolitic rocks.

[Phillips

387, 388 Fossil shells from the
greensand strata of the Isle of
Wight . . . Mantell

389 Fossil shells, and Mammalian

remains, from the locustrine
tertiary strata of the Isle of
Wight, to illustrate the fauna
of that period . . Ibid.

390 The Megatherium.

[Pander and D'Alton

INTRODUCTION.

EVERY art and science has a language of technical terms
peculiar to itself. With those terms the student must make
himself familiarly acquainted at the outset ; and first of all,
he will desire to know the names of the objects about which
he is to be engaged.

The names of objects in Natural History are double, that
is to say, they are composed of two terms. Thus, we speak
of the white-bear, the black-bear, the hen-hawk, the sparrow-
hawk ; or, in strictly scientific terms, we have Felis leo, the
lion ; Felis tigris, the tiger; Felis catus, the cat ; Canis lupus,
the wolf ; Canis vulpes, the fox ; Canis familiar is, the dog, &c.
They are always in the Latin form, and consequently the
adjective name is placed last. The first is called the generic
name ; the second is called the trivial, or specific name.

These two terms are inseparably associated with every ob-
ject of which we treat. It is very important, therefore, to
have a clear idea of what is meant by the terms genus and
species; and although the most common of all others, they
are not the easiest to be clearly understood. The Genus is
founded upon some of the minor peculiarities of anatomical
structure, such as the number, disposition, or proportions of
the teeth, claws, fins, &c., and usually includes several kinds.
Thus, the lion, tiger, leopard, cat, &c., agree in the structure
of their feet, claws, and teeth, and they belong to the genus
Felis ; while the dog, fox, jackall, wolf, &c., have another
and a different peculiarity of the feet, claws, and teeth, and
are arranged in the genus Canis.

The species is founded upon less important distinctions,
such as colour, size, proportions, sculpture, &c. Thus we
have different kinds, or species, of duck, different species of
squirrel, different species of monkey, £e., varying from each

XX INTRODUCTION.

other in some trivial circumstance, while those of each group
agree in all their general structure. The specific name is the
lowest term to which we descend, if we except certain peculi-
arities, generally induced by some modification of native habits,
such as are seen in domestic animals. These are called vari-
eties, and seldom endure beyond the causes which occasion
them.

Several genera which have certain traits in common are
combined to form a family. Thus, the alewives, herrings,
shad, &c., form a family called CLTJPEID^;, among fishes ;
the crows, black-birds, jays, &c., form the family CORYIDJE,
among birds. Families are combined to form orders, and
orders form classes, and finally, classes are combined to form
the four primary divisions of the animal kingdom, namely,
the departments.

For each of these groups, whether larger or smaller, we in-
voluntarily picture in our minds an image, made up of the
traits which characterize the group. This ideal image is called
a TYPE, a term which there will be frequent occasion to em-
ploy, in our general remarks on the animal kingdom. This
image may correspond to some one member of the group ;
but it is rare that any one species embodies all our ideas of
the class, family, or genus to which it belongs, Thus, we
have a general idea of a bird ; but this idea does not corre-
spond to any particular bird, or any particular character of a
bird. It is not precisely an ostrich, an owl, a hen, or a sparrow ;
it is not because it has wings, or feathers, or two legs ; or be-
cause it has the power of flight, or builds nests. Any, or all
of these characters would not fully represent our idea of a
bird ; and yet every one has a distinct ideal notion of a bird,
a fish, a quadruped, &c. It is common, however, to speak of
the animal which embodies most fully the characters of a
group, as the type of that group. Thus, we might perhaps
regard an eagle as the type of a bird, the duck as the type of
a swimming-bird, and the mallard as the type of a duck.

As we must necessarily make frequent allusions to animals,
with reference to their systematic arrangement, it seems re-
quisite to give a sketch of their classification in as popular
terms as may be, before entering fully upon that subject, and
with particular reference to the diagram fronting the title-
page.

INTRODUCTION. XXI

The Animal Kingdom consists of four great divisions which
we call DEPARTMENTS, namely,

I. The department of Vertebrata.
II. The department of Articulata.

III. The department of Mollusca.

IV. The department of Radiata.

I. The department of VERTEBRATA. includes all animals
which have an internal skeleton, with a back-bone for its axis.
It is divided into four classes.

1 . Mammals (animals which nurse their young) .

2. Birds.

3. Reptiles.

4. Fishes.

The class of MAMMALS is subdivided into three orders.

a. Beasts of prey (Carnivord).

b. Those which feed on vegetables (Herbivord).

c. Animals of the whale kind (Cetaceans).

The class of BIRDS is divided into four orders.

a. Birds of prey (Incessores) .

b. Climbers (Scansores).

c. Waders (Grallatores) .

d. Swimmers (Natatores).

The class of REPTILES is divided into five orders.

a. Large reptiles with hollow teeth, most of which are

now extinct (RhizodotUs\

b. Lizards (Lacertans).

c. Snakes (Ophidians).

d. Turtles (Cheionians).

e. Frogs (Batrachians).

The class of FISHES is divided into four orders :

a. Those with enamelled scales, like the gar-pike

Lepidosteus (Ganoids].

b. Those with the skin like shagreen, as the sharks

and skates (Placoids).

c. Those which have the edge of the scales toothed,

and usually with some bony rays to the fins, as the
perch (Ctenoids).

d. Those whose scales are entire, and whose fin ravs are

v

soft, like the salmon (Cycloids).

XX11 INTRODUCTION.

II. Department of ARTICULATA. Animals whose body is
composed of rings or joints. It embraces three classes.

1. Insects.

2. Crustaceans, like the crab, lobster, &c.

3. Worms.

The class of INSECTS includes three orders.

a. Those which have jaws for dividing their food (Man-
ducata], fig. 195.

I. Those with a trunk for sucking fluids, like the but-
terfly (Suctoria), fig. 199.

c. Those destitute of wings, like fleas (Apterd).

The class of CRUSTACEANS may be divided as follows : —

a. Those furnished with a shield, like the crab and lob-

ster (Malacostracd).

b. Such as are not thus protected (Entomostraca).

c. An extinct race, intermediate between these two

(Trilobites), fig. 3/8.

The class of WORMS comprises three orders :

a. Those which have thread-like gills about the head

(Tubulibranchiatd).

b. Those whose gills are placed along the sides (Dor-

sibra?ichiata).

c. Those which have no exterior gills, like the earth-

worm (Abranchiata).

III. The department of MOLLUSCA is divided into three
classes, namely :

1. Those which have arms about the head, like the

cuttle-fi sh ( Ceph a lopodd) .

2. Those which creep on a flattened disc or foot like

snails (Gasteropoda).

3. Those which have no distinct head, and are enclosed

in a bivalve shell, like the clams (Acephala).

The CEPHALOPODA may be divided into —

a. The cuttle-fishes, properly so called (Teuthideans) .

b. Those having a shell, divided by sinuous partitions into

numerous chambers (Ammonites).

c. Those having a chambered shell with simple partitions

(Nautilus).

xx

The GASTEKOPODA contains three orders :

a. The land-snails which breathe air (Pulmonata).

b. The aquatic snails which breathe water (Branchiferci).

c. Those which have wing-like appendages about the

head, for swimming (Pteropoda).

The class of ACEPHALA contains three orders :

a. Those having shells of two valves (bivalves), like the

clam (Lamellibranchiatd).

b. Those having two unequal valves, and furnished with

peculiar arms (Brachiopodd).

c. Those living in chains or clusters, like the Safya, or

upon plant-like stems, like the Flustra. — Bryozoa.

IV. The department of RADIATA is divided into three
classes :

1. Sea-urchins, bearing spines upon the surface (Echi-

nodermata).

2. Jelly-fishes (Acahpha).

3. Polyps, fixed like plants, and with a series of flexible

arms around the mouth.

The EcmisroDEKMS are divided into four orders :

a. Sea-slugs, like the biche-le-mar (Holotkurians).

b. Sea-urchins (Echini), fig. /I.

c. Free star-fishes (AsteriadfB), fig. 36.

d. Star-fishes mostly attached by a stem (Crinoidee),

figs. 69, 70.

The ACALEPHA includes the following orders :

a. The Medusae, or common jelly-fishes (Discophori),

fig. 173.

b. Those provided with aerial vesicles (Siphonopkori).

c. Those furnished with vibrating hairs, by which they

move (Ctenophori).

The class of POLYPS includes three orders :

a. Fresh-water polyps, and similar marine forms (Hy-

dro'ids), fig. 170.

b. Marine polyps, like the sea-anemone and coral-polyp

(Actinoids) .

c. A still lower form, allied to the mollusca by their

shell (Rhizopods}.

XXIV INTRODUCTION.

In addition to these, there are numberless kinds of micro-
scopic animalcules, commonly called infusory animals (Infu-
soria), from their being found specially abundant in water
infused with vegetable matter. Indeed, a great many that
were formerly supposed to be animals are now known to be
vegetables. Others are ascertained to be crabs, mollusks,
worms, &c. in their earliest stages of development. In
general, however, they are exceedingly minute, exhibiting
the simplest forms of animal life, and are now grouped
together, under the title of Protozoa. But, as they are still
very imperfectly understood, notwithstanding the beautiful
researches already published on this subject, and as most of
them are likely to be finally distributed among vegetables
and various classes of the animal kingdom, we have not
assigned any special place to them.

PHYSIOLOGICAL ZOOLOGY.

CHAPTER FIRST.

THE SPHERE AND FUNDAMENTAL PRINCIPLES OF

ZOOLOGY.

§ 1 . ZOOLOGY is that department of Natural History which
relates to Animals.

§ 2. The enumeration and naming of the animals which
are found on the globe, the description of their forms, and
the investigation of their habits and modes of life, are the
principal, but not the only objects of this science. Ani-
mals are worthy of our regard not only in respect to the
variety and elegance of their forms, and their adaptation to
the supply of our wants ; but the Animal Kingdom, as a
whole, has also a still higher signification. It is the exhi-
bition of the divine thought, as it is carried out in one de-
partment of that grand whole which we call Nature ; and
considered as such, it teaches us the most important lessons.

§ 3. Man, in virtue of his twofold constitution, the spiritual
and the material, is qualified to comprehend Nature. Having
been made in the spiritual image of God, he is competent to
rise to the conception of His plan and purpose in the works
of Creation. Having also a material body, like that of ani-
mals, he is 'prepared to understand the mechanism of organs,
and to appreciate the necessities of matter, as well as the in-
fluence which it exerts over the intellectual element, through-
out the whole domain of Nature.

§ 4. The spirit and preparation we bring to the study of
Nature, is not a matter of indifference. When we would
study with profit a work of literature, we first endeavour to
make ourselves acquainted with the genius of the author ;

B

2 SPHEBE AND FUNDAMENTAL

and in order to know what end he had in view, we must* have
regard to his previous labours, and to the circumstances under
which the work was executed. Without this, although we
may perhaps enjoy the perfection of the whole, and admire
the beauty of its details, yet the spirit which pervades it will
escape us, and many passages may even remain unintelligible.

§ 5. So, in the study of Nature, we may be astonished at
the infinite variety of her products, and may even study some
portion of her works with enthusiasm, and nevertheless re-
main strangers to the spirit of the whole, ignorant of the plan
on which it is based ; and may fail to acquire a proper con-
ception of the varied affinities which combine beings together,
so as to make of them that vast picture, in which each animal,
each plant, each group, each class, has its place, and from
which nothing could be removed without destroying the proper
meaning of the whole.

§ 6. Besides the beings which inhabit the earth at the pre-
sent time, this picture also embraces the extinct races which
are now known to us by their fossil remains only. These are
of very great importance, since they furnist us with the means
of ascertaining the changes and modifications which the Ani-
mal Kingdom has undergone in the successive creations which
have taken place since the first appearance of living beings.

§ 7. It is but a short time since it was not difficult for a
man to possess himself of the whole domain of positive know-
ledge in Zoology. A century ago, the number of known
animals did not exceed 8000 ; that is to say, in the whole
Animal Kingdom, fewer species were then known than are
now contained in many private collections of certain families
of insects alone. At the present day, the number of living
species which have been satisfactorily made out and described,
is more than 50,000.* The fossils already described exceed

* The number of vertebrate animals may be estimated at 20,000.
About 1500 species of mammals are pretty precisely known, and the
number may probably be carried to about 2000.

The number of Birds well known is 4 or 5000 species, and the probable
number is 6000.

The Reptiles, like the Mammals, number about 1500 described species,
and will probably reach the number of 2000.

The Fishes are more numerous ; there are from 5 to 6000 species in the
museums of Europe, and the number may probably amount to 8 or 10,000.

The number of Mollusks already in collections, probably reaches 8 or

PRINCIPLES OF ZOOLOGY. 3

i

6000 species ; and if we consider that wherever any one stra-
tum of the earth has been well explored, the number of spe-
cies discovered has not fallen below that of the living species
which now inhabit any particular locality of equal extent, and
then bear in mind that there is a great number of geological
strata, we may anticipate the day when the ascertained fossil
species will far exceed the living species.*

§ S. These numbers, far from discouraging, should, on the
contrary, encourage those who study Natural History. Each
new species is, in some respects, a radiating point which throws
additional light on all around it ; so that as the picture is en-
larged, it at the same time becomes more intelligible to those
who are competent to seize its prominent traits.

§ 9. To give a detailed account of each and all of these
animals, and to show their relations to each other, is the task
of the Naturalist. The number arid extent of the volumes
already published upon the various departments of Natural
History show, that only a mere outline of so vast a domain
could be given in an elementary work like the present, and
that none but those who make it their special study can be
expected to survey its individual parts.

10,000. There are collections of marine shells, bivalve and univalve,
which amount to 5 or 6000 ; and collections of land and fluviatile shells,
which count as many as 2000. The total number of mollusks would there-
fore probably exceed 15,000 species.

Among the articulated animals it is difficult to estimate the number of
species. There are collections of coleopterous insects which number 20
to 25,000 species ; and it is quite probable, that by uniting the principal
collections of insects, 60 or 80,000 species might now be counted ; for the
whole department of articulata, comprising the Crustacea, the cirrhipeda,
the insects, the red-blooded worms, the intestinal worms, and the infuso-
ria, as far as they belong to this department, the number would already
amount to 100,000 ; and we might safely compute the probable number
of species actually existing at double that sum.

Add to these about 10,000 for radiata, echini, star-fishes, medusse, and
polypi, and we have about 250,000 species of living animals ; and sup-
posing the number of fossil species only to equal them, we have, at a very
moderate computation, h~lf a million of species.

* In a separate work, entitled " Notneviclator Zoologicus" by L. Agas-
siz, the principles of nomenclature are discussed, and a list of the names
of genera and families proposed by authors is given. To this work those
are referred who may desire to become more familiar with nomenclature,
and to know in detail the genera and families in each class of the Animal
Kingdom.

B 2

4 SPHERE AXD FUNDAMENTAL

§ 10. Every -well-educated person, however, is expected to
have a general acquaintance with the great natural phenomena
constantly displayed before his eyes. A general knowledge
of man and the subordinate animals, embracing their structure,
races, habits, distribution, mutual relations, &c., is calculated
not only to conduce essentially to our happiness, but is a study
which it would be inexcusable to neglect. This general know-
ledge, which is given by the science of Zoology, it is the pur-
pose of the present work to afford.

§ 1 1 . A sketch of this nature should render prominent the
more general features of animal life, and delineate the arrange-
ment of the species according to their most natural relations
and their rank in the scale of being ; and thus give a pano-
rama, as it were, of the entire Animal Kingdom. To accom-
plish, this, we are at once involved in the question, what is it
that gives an animal precedence in rank ?

§ 12. In one sense, all animals are equally perfect. Each
species has its definite sphere of action, whether more or less
extended, — its own peculiar office in the economy of nature ;
and is perfectly adapted to fulfil all the purposes of its crea-
tion, beyond the possibility of improvement. In this sense,
every animal is perfect. But there is a wide difference among
them, in respect to their organization. In some it is very
simple, and very limited in its operation ; in others, extremely
complicated, and capable of exercising a great variety of func-
tions.

§ 13. In this physiological point of view, an animal may
be said to be more perfect in proportion as its relations with
the external world are more varied ; in other words, the more
numerous its functions are. Thus, a quadruped, or a bird,
which has the five senses fully developed, and which has,
moreover, the faculty of readily transporting itself from place
to place, is more perfect than a snail, whose senses are very
obtuse, and whose motion is very sluggish.

§ 14. In like manner, each of the organs, when separately
considered, is found to have every degree of complication,
and, consequently, every degree of nicety in the performance
of its function. Thus, the eye-spots of the star-fish and jelly-
fish are probably endowed with the faculty of perceiving
light, without the power of distinguishing objects. The keen
eye of the bird, on the contrary, discerns minute objects

PRINCIPLES OF ZOLOOGT.

at a great distance, and when compared with the eye of a fly,
is found to be not only more complicated, but constructed
on an entirely different plan. It is the same with every other

organ.

§ 15. We understand the faculties of animals, and appro
ciate their value, just in proportion as we become acquainted
with the instruments which execute them. The study of the
functions or uses of organs therefore requires an examination
of their structure ; Anatomy and Physiology must never be
disjoined, and ought to precede the systematic distribution of
animals into classes, families, genera, and species.

§ 16. In this general view of organization, we must ever
bear in mind the necessity of carefully distinguishing be-
tween affinities and analogies, a fundamental principle re-
cognized even by Aristotle, the founder of scientific Zoology.
Affinity or homology is the relation between organs or parts
of the body which are constructed on the same plan, how-
ever much they vary in form, or serve for different uses. Ana-
logy, on the contrary, indicates the similarity of purposes or
functions performed by organs of different structure.

§ 1 7. Thus, there is an analogy between the wing of a bird
and that of a butterfly, since both of them serve for flight.
But there is no affinity between them, since, as we shall here-
after see, they differ totally in their anatomical relations. On
the other hand, there is an affinity between the bird's wing
and the hand of a monkey, since, although they serve for dif-
ferent purposes, the one for climbing, and the other for flight,
yet they are constructed on the same plan. Accordingly, the
bird is more nearly allied to the monkey than to the butterfly,
though it has the faculty of flight in common with the latter.
Affinities, and not analogies, therefore, must guide us in the
arrangement of animals.

§ 18. Our investigations should not be limited to adult
animals, but should also be directed to the changes which
they undergo during the whole course of their development.
Otherwise, we shall be liable to exaggerate the importance of
certain peculiarities of structure which have a predominant
character in the full-grown animal, but which are shaded off,
and vanish, as we revert to the earlier periods of life.

§ 19. Thus, for example, by regarding only adult indivi-
duals, we might be induced to divide all animals into two

SPHERE AND FUNDAMENTAL

groups, according to their mode of respiration ; uniting iu
one group all those which breathe by gills, and, in the
other, those which breathe by lungs ; but this distinction loses
its importance, when we consider that various animals, as, for
example, frogs, which respire by lungs in the adult state,
have only gills when young : hence it is evident that the
respiratory organs cannot be taken as a satisfactory basis
for fundamental classification. They are, as we shall see,
subordinate to a more important organism, namely, the ner-
vous system.

§ 20. Again, we ave a means of appreciating the relative
grade of animals by the comparative study of their develop-
ment. It is evident that the caterpillar, in becoming a butter-
fly, passes from a lower to a higher state ; clearly, therefore,
animals resembling the caterpillar, as, for instance, worms,
occupy a lower rank than insects. There is no animal which
does not undergo a series of changes similar to those of the
caterpillar or the chicken ; only, in many of them, the most
important ones occur before birth, during what is called the
embryonic period.

§ 21. The life of the chicken has not just commenced when
it issues from the egg ; for, if we break the shell some days
previous to the time of hatching, we find in it a living animal,
which, although imperfect, is nevertheless a chicken ; it has
been developed from a hen's egg, and we know that, should it
continue to live, it will infallibly display all the character-
istics of the parent bird. Now, if there existed in nature an
adult bird, as imperfectly organized as the chicken on the day
before it was hatched, we should assign to it an inferior rank.

§ 22. In studying the embryonic states of the mollusks or
worms, we observe in them points of resemblance to many
animals of a lower grade, to which they afterwards become
entirely dissimilar; for example, the myriads of minute aquatic
animals embraced under the name of Infusoria, whose organ-
ization is generally very simple, remind us of the embryonic
forms of other animals. We shall have occasion to show that
the Infusoria are not to be considered as a distinct class of
animals, but that among them, there are found members of all
the lower classes of animals, as mollusks, crustaceans, polyps,
and even vegetable organisms.3

3 And a;' grouped in the families Desmidice and Diatomacece. — ED.

PRINCIPLES OF ZOOLOGY. 7

§ 23. Not less striking are the relations that exist between
animals and the regions they inhabit. Every animal has its
home. Animals of the cold regions are not the same as those
of temperate climates ; and these latter, in their turn, differ
from those of tropical regions. Certainly, no one will main-
tain it to be the effect of accident that the monkeys, the most
perfect of all brute animals, are found only in hot countries ;
or that it is by chance that the white bear and reindeer in-
habit only cold regions.

§ 24. Nor is it by chance that the largest of all animals, of
every class, as the whales, the aquatic birds, and the sea-
turtles, dwell in the water rather than on the land ; and while
this element affords freedom of motion to the largest, so is it
also the home of the smallest of living things.

§ 25. In the study of zoology we must not confine our re-
searches to animals now in existence. There are buried, in
the crust of the earth, the remains of a great number of
animals belonging to species which do not exist at the pre-
sent day ; many of these remains present forms so extraor-
dinary, that it is almost impossible to trace their connection
with any animals now living. In general, they bear a striking
analogy to the embryonic forms of existing species ; for ex-
ample, the curious fossils known under the name of Tri-
lobites (Fig. 378) have a shape so singular, that it might well
be doubted to what group of articulated animals they belong ;
but if we compare them with the embryo crab, we find so
remarkable a resemblance, that we hesitate not to refer them
to the crustaceans. We shall also see that some of the fishes
of ancient epochs present shapes entirely peculiar to them-
selves (Fig. 3/9), resembling in a striking manner the em-
bryonic forms of some of our common fishes. A determina-
tion of the successive appearance of animals, in the order of
time, is therefore of much importance in assisting us to deter-
mine their relative zoological rank.

§ 26. Besides the distinctions derived from the varied struc-
ture of organs, there is another less subject to rigid analysis,
but no less decisive, to be drawn from the immaterial principle,
with which every animal is endowed. It is this vital principle
which determines the constancy of species, from generation to
generation, and which is the source of all the varied exhibi-
tions of instinct and intelligence which we see displayed, from

8 TUoSDAMEXTAL PEIXCIPLES OF ZOOLOGY.

the simple impulse in the polyps to receive the food which is
brought within their reach through the higher manifestations,
as observed in the cunning fox, the sagacious elephant, the
faithful dog, and the exalted intellect of man, which is capable
of indefinite expansion.

§ 27. Such are some of the general aspects in which we
shall contemplate the animal creation. Two points of view
should never be lost sight of, or disconnected, namely, the
animal in respect to its own organism, and the animal in its
relations to creation as a whole. By adopting too exclusively
either of these points of view, we are in danger of falling
either into gross materialism, or into a vague pantheism. He
who beholds nothing in Nature besides organs and their
functions, may persuade himself that the animal is merely a
combination of chemical and mechanical actions and reactions,
and thus becomes a materialist.

§ 28. On the contrary, he who considers only the manifes-
tations of intelligence and of creative will, without taking into
account the means by which they are executed, and the phy-
sical laws, by virtue of which all beings preserve their charac-
teristics, will be very likely to confound the Creator with the
creature.

§ 29. It is only by a simultaneous contemplation of matter
and mind, that Natural History rises to its true character and
dignity, and attains its noblest end, namely, the indication
throughout the whole of creation of a plan fully matured in
the beginning, and invariably pursued ; the work of a God
infinitely wise, regulating Nature according to the immutable
laws which He has himself imposed on her.

CHAPTER SECOND.

GENERAL PROPERTIES OF ORGANIZED BODIES.

SECTION I.

OKGAISTIZED AXD UNORGANIZED BODIES.

§ 30. NATURAL HISTORY, in its broadest sense, embraces the
study of all the bodies which compose the crust of the earth,
or which are dispersed over its surface.

§ 31. These bodies may be divided into two great groups ;
inorganic bodies (minerals and rocks), and living or organic
bodies (vegetables and animals). These two groups have
nothing in common, save the universal properties of matter,
such as weight, colour, &c. They differ at the same time in
form, structure, composition, and mode of existence.

§ 32. The distinctive characteristic of inorganic bodies is
rest; while that of organic bodies is independent motion,
LIFE. The rock or the crystal, once formed, never change ;
their constituent parts or molecules invariably preserve the
position which they have once taken in respect to each
other. Organized bodies, on the contrary, are continually
in action. The sap circulates in the tree, the blood flows
through the animal, and in both there is, besides, the inces-
sant movement of growth, decomposition, and renovation.

§ 33. Their mode of formation is also entirely different.
Unorganized bodies are either simple, or made up of elements
unlike themselves ; and when a mineral is enlarged, it is
simply by the outward addition of particles constituted like
itself. Organized bodies are not formed in this manner.
They always, and necessarily, are derived from beings similar
to themselves ; and once formed, they always increase inter-
stitially by the successive assimilation of new particles derived
from various sources.

§ 34. Finally, organized bodies are limited in their dura-
tion. Animals and plants are constantly losing some of their
parts by decomposition during life, which at length cease to

10 ELEMENTARY. STRUCTURE OF ORGANIZED BODIES.

be supplied, and they die, after having lived their appointed
period. Inorganic bodies, on the contrary, contain within
themselves no principle of destruction ; and unless subjected
to some foreign influence, would never change. The lime-
stone and granite of our mountains remain just as they were
formed in ancient geological epochs ; while numberless gene-
rations of plants and animals have lived and perished upon
their surface.

SECTION II.

ELEMENTARY STRUCTURE OF ORGANIZED BODIES.

§ 35. THE exercise of the functions of life, which is the es-
sential characteristic of organized bodies (§ 32), requires a
degree of flexibility of the organs. This is secured by means
of a certain quantity of watery fluid, which penetrates all
parts of the body, and forms one of its principal constituents.

§ 36. All living bodies, without exception, are made up of
tissues so constructed as to be permeable by liquids. There
is no part of the body, no organ, however hard and compact
it may appear, which has not this peculiar structure. It
exists in the bones of animals, as well as in their flesh and fat ;
in the wood, however solid, as well as in the bark and flowers
of plants. It is to this general structure that the term organism
is now applied. Hence the collective name of organized
which includes both the animal and the vegetable

kingdoms.

§ 37. The vegetable tissues, and most organic structures,
when examined by the microscope, in their
early states of growth, are found to be
composed of hollow vesicles or cells. The
natural form of the cells is that of a sphere
or of an ellipsoid, as may be easily seen
in many plants ; for example, in the tissue
of the house-leek (Fig. 1). The intervals
which sometimes separate them from each
other are called intercellular spaces (wi)-
F- ^~~ When the cellules are very numerous, and

* Formerly, animals and plants were said to be organized because they
are furnished with definite parts, called organs, which execute particular
functions. Thus, animals have a stomach, a heart, lungs, &c. ; plants

ELEMENTARY STRUCTURE OF ORGANIZED BODIES. 1 1

crowd each other, their outlines become angular, and the
intercellular spaces disappear, as seen in figure 2, which repre-
sents the pith of the elder. They
then have the form of a honey-comb,
whence they have derived their name
of cellules.

§ 38. All organic tissues, whe-
ther animal or vegetable, originate
from cells. The cell is to the or-
ganized body what the primary form
of the crystal is to the secondary in ^S- 2-

minerals. As a general fact, it may be stated that animal
cells are smaller than vegetable cells, but they alike contain a
central dot or vesicle, called the nucleus. Hence such cells
are called nucleated cells (Figs. 3 and 48). Sometimes the
nucleus itself contains a still smaller dot, called the nucleolus.

§ 39. The elementary structure of vegetables may be ob-
served in every part of a plant, and its cellular character has
been long known. But with the animal tissues there is far
greater difficulty. Their variations are so great, and their
transformations so diverse, that after the embryonic period, it
is sometimes impossible, even by the closest examination, to
detect their original cellular structure.

§ 40. Several kinds of tissues have been designated in the
animal structure ; but their differences are not always well

tf

marked, and they pass into each other by insensible shades.
Their modifications are still the subject of investigation, and
we refer only to the most important distinctions.

§ 41. 1st. The aveolar tissue consists of a network of deli-
cate fibres intricately interwoyen, so as to leave numberless
communicating interstices filled with fluid. It is interposed,
in layers of various thickness, between all parts of the body,
and frequently accompanied by clusters of fat cells. The
fibrous and the serous membranes are mere modifications of
this tissue.

have leaves, petals, stamens, pistils, roots, &c., all of which are indispen-
sable to the maintenance of life, and the perpetuation of the species. Since
the discovery of the fundamental identity of structure of animal and vege-
table tissues, a common denomination for this uniformity of texture has
been justly preferred ; and the existence of vital tissues is now regarded as
the basis of organization.

12 ELEMENTARY STRUCTURE OF ORGANIZED BODIES.

§ 42. 2ndly. The cartilaginous tissue is composed of
nucleated cells, the intercellular spaces being filled with a
more compact substance, called the hyaline matter.

§ 43. 3dly. The osseous or bony tissue, which differs from
the cartilaginous tissue, in having the meshes filled with salts
of lime, instead of hyaline substance, whence its compact and
solid appearance. It contains besides minute, rounded, or star-
like points, improperly called bone-corpuscles, which are found
to be cavities or canals, sometimes radiated and branched.

§ 44. 4thly. The muscular tissue, which forms the flesh of
animals, is composed of bundles of parallel fibres, which pos-
sess the peculiar property of contracting or shortening them-
selves, under the influence of the nerves, the muscles under
the control of the will, are commonly crossed by very fine lines
or wrinkles, but not so in the involuntary muscles. Every one
is sufficiently familiar with this tissue, in the form of lean meat.

§ 45. 5thly, the nervous tissue is of different kinds. In the
nerves proper, it is composed of very delicate fibres, which
return back at their extremities, and form loops, as shown in
figures 12 and 13, representing the primary fibres of the au-
ditory nerve from the auditory sac of the pike. The same
fibrous structure is found in the white portion of the brain.
But the grey substance of the brain is composed of very mi-
nute granulations, interspersed with clusters of large cells, as
seen in fig. 14.

§ 46. The tissues above enumerated differ from each other
more widely, in proportion as they are examined in animals
of a, higher rank. As we descend in the scale of being, the
differences become gradually effaced. The soft body of a
snail is much more uniform in its composition than the body
of a bird, or a quadruped. Indeed, multitudes of animals
are known to be composed of nothing but cells in contact with
each other. Such is the case with the polyps ; yet they con-
tract, secrete, absorb, and reproduce ; and most of the Infuso-
ria move freelv, by means of little fringes on their surface,

•/•*•/ cj

arising from modified cells.

§ 47. A no less remarkable uniformity of structure is to
be observed in the higher animals, in the earlier periods of
their existence, before the body has arrived at its definite form.
The head of the adult salmon, for instance, contains not only
all the tissues we have mentioned — namely, bone, cartilage,

ELEMESTABY STEUCTUHE OF OEGAXIZED EDDIES. 13

muscle, nerve, brain, and membranes, but also blood-vessels,
glands, pigments, £c. If we examine it during the embryonic
state, while it is yet in the egg, we shall find that the whole
head is made up of cells which differ merely in their dimen-
sions ; those at the top of the head being very small, those
surrounding the eye a little larger, and those beneath still
larger. It is only at a later period, after still further deve-
lopment, that these cellules become transformed, some of them
into bone, others into blood, others into flesh, &c.

§ 48. Again, the growth of the body, the introduction of
various tissues, the change of form and structure, proceed in
such a manner as to give rise to several cavities, variously
combined among themselves, and each containing, at the end
of these transformations, peculiar organs, or peculiar systems
of organs.

[§ 49. " All organic tissues," says Dr. Schwann, " how-
ever different they may be, have one common principle of
development as their basis — viz., the formation of cells ;*
that is to say, nature never unites molecules immediately into
a fibre, a tube, and so forth, but she always, in the first in-
stance, forms a round cell, or changes, where it is requisite,
cells into the various primary tissues in which they present
themselves in the adult state. The formation of the elementary
cells takes place, in the main points, in all the tissues accord-
ing to the same laws ; the farther formation and transforma-
tion of the cells is different in the different tissues.

[§ 50. " The primary phenomena of cells are the follow-
ing : — there is first a structureless substance present (cyto-
blastema), which is either contained in pre-existing cells, or
exists on the outside of these. Within this, cell-nuclei gene-
rally first arise — round or oval, spherical or flat corpuscles —
which usually include one or two small dark points (nuclear-
corpuscules) . Around these cell-nuclei the cells are produced,
and in such wise that they at first closely surround the nuclei.
The cells expand by growth, and indeed by intussusception,
ind the same thing very commonly happens, for a certain
period, in regard to the nuclei. When the cells have attained
a certain stage of development, the nuclei generally disappear.
With reference to the place at which the new cells arise in

* These observations have been confirmed by Wagner, Valentin, Kolli-
ker, Schleiden, Mohl, Niigeli, and others. — ED.

14 ELEMENTARY STRUCTURE OF ORGANIZED BODIES.

any tissue, the law is, that they constantly appear where the
nutritive fluid penetrates the tissue most immediately ; there-
fore it is that the formation of new cells in the unorganized
tissues only takes place at the points where they are in con-
tact with the organized matter ; in the completely organized
tissues, again, where the blood is distributed to the whole of
the texture, new cells are produced in the entire thickness of
the tissue.

[§ 51. " The process by which the cells evolve themselves
into the elementary formations of the individual tissues is
very multifarious. The most remarkable differences are the
following : — 1 . The elongation of the cell into a fibre, which
probably takes place in consequence of one or more parts of
the cell- wall increasing in a greater degree than the others.
2. The division into so many isolated fibres, of a cell elon-
gated in different directions. 3. The blending of several
simple or primary cells into one secondary cell.

[§ 52. " CARTILAGE. — The cartilages are distinguished
among all the tissues of the human body, by containing the

largest quantity of cytoblastema, which is
also extremely consistent (fig. 3). The
quantity of cytoblastema, however, differs
greatly in different cartilages. It is, for
instance, much smaller than usual in the
branchial cartilages of the larva of the frog
(fig. 4). Here the cells may be observed
flattening one another as soon as they
touch. The first formation, and subse-
Fig. 3.— Cartilage; the quent growth of cartilage, take place in
nidus of the os ileum, J n ? } . p^tohlaatema is first nrn
but as yet without Sucn W S > ma Cyl° na 1S nrst Pro"

earthy deposit, from the duced, m which cells then form, whilst, at

foetus of the sow. the same time, fresh cytoblastema arises,

within which, again, cells are evolved as
before, and so the process goes on. As the cartilage is without
vessels at first, the formation of new cells only proceeds on the
superficies of the substance, or, at all events, in its vicinity ;
in the situation, therefore, where the cartilage is in immediate
contact with the nutritive matter. The production and growth
of the cells of cartilage are exhibited in figure. 4 . In the cyto-
blastema, on the surface of the cartilage at a, or between the
new-formed cells at b, new cell- nuclei are arising. Around

ELEMENTARY STRUCTURE OF ORGANIZED BODIES. 15

these, cells will by and by be formed, as at c and d, which still
surround the nucleus intimately, and are very thin in the
walls. These cells expand by growth, and their walls, at the
same time, become thicker. The nuclei also grow in a very
slight degree for a while. The
cells now contain a clear fluid,
then a granular precipitate,
which generally first forms it-
self around the nucleus, as at
e, figure 4, for example. In the
old cells young cells occasion-
ally arise. By and by cavities
or canals are formed in the car-
tilages in a way which has not
yet been investigated with suffi-
cient care, through which these
vessels also take their course. Fig< 4 represents the branchial
If, after this epoch, any new cartilage of a very young larva of
cells are produced, we may pre- the frog. The lower edge of the
sume that their evolution takes preparation is the natural limit of
place, not only from the sur-
face of the cartilage, but also around these vascular cavities
and canals ; and, perhaps, it is from this circumstance that,
after ossification, the cells are found disposed in laminse,
partly concentric around the cavity of the medullary canal,
partly parallel with the surface of the cartilage. In the pro-
cess of ossification, the earth is first deposited in the cytoblas-
tema of the cartilage. The cells of the cartilage, at the same
time, suffer a remarkable change, which seems to consist in
their becoming elongated in different directions into hollow
processes or canals, and thus acquiring a stellated appearance
(stellated cells). The nuclei of the cells, during this process,
are absorbed. At length, and finally, the cells themselves, and
the canals proceeding from them, appear to become filled with
calcareous earth.

[§ 53. CELLULAR TISSUE. — The cytoblastema of the cellular
tissue is a structureless, gelatinous looking, transparent sub-
stance, uot unlike the vitreous humour of the eye. Within
this arise small round granular-looking cells, furnished with
nuclei (fig. 5 a.) Here, too, the nucleus appears to be the
part first formed, the cell being developed around it. As the

16 ELEMENTARY STRUCTURE OE ORGANIZED BODIES.

Cb

cellular tissue contains blood-vessels, the evolution of new
cells also proceeds through the entire substance of the tissue.
The cells grow, but scarcely attain to twice the diameter of
the nuclei they enclose ; at a very early period, however, they

begin to length-
en out in two
opposite direc-
tions into fibres
(figure 5 b).
The fibres then
stretch on either
hand into seve-
ral branches (c,
d), and these,
in their turn, di-
vide into still
smaller fibres.
This fibrillation
of the branch-
es, however, by
and by proceeds
Fig. 5. — Various stages in the evolution of the eel- backwards, to-
lular tissue of the fetus of the sow; the stages are in -yyar(Js the stem
the order of the letters of reference; c and d are f •> /-i

mere varieties.

ing immediately

from the body of the cell ; so that at a later period, instead of
a single fibre, a bundle of isolated fibres is seen proceeding from
either side of the body of the cell (fig. 5 e). Finally, the body
of the cell itself also splits into fibres, and then, instead of a
cell, we have a bundle of separate fibres, to which the nucleus
of the former cell still continues attached. This process con-
sists, therefore, in a kind of splitting up of a single cell into
a multitude of hollow fibres. At a subsequent period, the
nucleus is taken away, so that the fibres alone remain, and
compose the filaments of the cellular tissue, as we find them
in adults. It would appear, however, that they must suffer a
chemical change, in addition to the changes in form, inasmuch
as the cellular tissue at first affords no proper gelatine.

[§ 54. " MUSCLE. — The researches of Valentin have shown
that the muscles are composed of globules arranged in rows,
like strings of beads, which then unite into a fibre, — the pri-

ELEMENTARY STRUCTURE OF ORGANIZED BODIES. 17

mary muscular fibre. The fibre thus evolved is a hollow

cylinder, in the cavity of which, cell-nuclei lie near to one

another (fig. 6, a).

From this it is „, £ c A

probable that the

globules which

compose the fibre

were hollow, —

were cells, — and

that the nuclei,

£

included in the
cylinder, are the

nuclei belonging Fig. 6. a, b, c. Different stages in the evolution
to these primary of muscular fibre ; d, a muscular bundle imper-
cells. The earlier fectly developed, standing on its edge.

process of evolution must therefore have been as follows : —
the globules or primary cells arranged themselves in a row,
or coalesced into a cylinder, and then the septa, by which
this cylinder must have been divided, underwent absorption.
The nuclei are flat, and lie within the cylinder, not in its
axis, but on its walls. This cylinder, rounded and closed at
its ends, — this secondary muscular cell, grows continually, like
a simple cell, but only in the direction of its length, for it either
gains nothing in point of breadth, or it becomes actually thinner.
The growth lengthwise, however, does not proceed from the
ends only, but through the entire extent of the cylinder, as is
obvious, from the fact of the nuclei, which at first lay close to
one another, getting more and more distant, and even themselves
elongating often in no inconsiderable degree. In this way, the
muscular bundle a, (fig. 6) is changed into the bundle 6. At
this period, the deposition of a new substance upon the inner
surface of the parietes of the cylinder, or cellular membrane of
the secondary muscular cell, takes place, by which its wall is
thickened (compare the fibre c with the fibre b, fig. 6). That
the thickening of the wall here, is no thickening of the cell-
membrane itself, as is in the case of cartilage, appears from
this, that the nuclei are not forced inwards, towards the hollow
of the cylinder, but outwards, and continue lying in front 'of
the secondary deposition, as is seen in d (fig. 6). The secon-
dary deposition in question, goes on until the cylinder is com-
pletely filled. The deposited substance changes into very

c

18 ELEMENTARY STRUCTURE OF ORGANIZED BODIES.

delicate fibres, which run in the direction of the length of the
cylinder. These are the primary muscular fibres ; together
they constitute a bundle, and this is the primary muscular
fasciculus, which is inclosed externally by a peculiar struc-
tureless wall — the cell-membrane of the secondary muscular
cell. A process, in all respects analogous, occurs, according to
Meyen, in the cells of the liber, or inner bark of vegetables.
Here, too, simple cells arise, which arrange themselves in rows,
and by coalescing at the points where the cellular parietes are
in contact, subsequent absorption of the septa being produced,
change into a secondary cell, the wall of which increases in
thickness by means of secondary deposition ; the only thing
wanting in the resemblance is, that this thickening should
take place by means of longitudinal filaments.

[§ 55. " NERYE. — The nerves appear to be formed after the
same manner as the muscles, viz. by the fusion of a number
of primary cells arranged in rows into a secondary cell. The
primary nervous cell, however, has not yet been seen with
perfect precision, by reason of the difficulty of distinguishing
nervous cells, whilst yet in their primary state, from the in-
different cells out of which entire organs are evolved. When
first a nerve can be distinguished as such, it presents itself as
a pale cord, with a coarse longitudinal fibrillation, and in this
cord a multitude of nuclei are apparent (fig. 7, a). It is easy

to detach individual
dm l\ filaments from a cord
of this kind, as the
figure just referred to
shows, in the interiors
of which many nuclei
are included, similar to
those of the primitive
muscular fasciculus,
but at a greater dis-
tance from one an-
Fig. 7.— Different stages in the development other. The filaments
of nerve ; a and b, of a very young fetal are pale, granulated,
sow ; c and d, nervous vagus, from the cranium anc[ (as appears by
of a foetal calf. their fartiier develop-

ment) hollow. At this period, as in muscle, a secondary
deposit takes place upon the inner aspect of the walls of

ELEHENTABY STBUCTUKE OF OBGANIZED BODIES. ly

the fibrils, or upon the inner aspect of the cell-.membrane of
the secondary nervous cell. This secondary deposit is a
fatty white-coloured substance, and it is through this that
the nerve acquires its opacity (fig. 7, b). Superiorly, the fibril
is still pale ; inferiorly, the deposition of the white substance
has occurred, and its effect, in rendering the fibril dark, is ob-
vious. With the advance of the secondary deposit, the fibrils
become so thick, that the double outline of their parietes comes
into view, and they acquire a tubular appearance (fig. 7, c).
On the occurrence of this secondary deposit, the nuclei of the
cells are generally absorbed ; yet a few may still be found to
remain for some time longer, when they are observed lying
outwardly between the deposited substance and the cell-mem-
brane (fig. 7 c), as in the muscles. The remaining cavity of
the secondary nervous cell appears to be filled with a pretty
consistent substance, the band of Remak, and discovered by
him. In the adult a nerve consequently consists, 1st, of an
outer pale thin cell-membrane — the membrane of the original
constituent cells, which becomes visible, when the white sub-
stance is destroyed by degrees (ex. yr. fig* 7, d) ; 2nd, of a
white fatty substance, deposited on the inner aspect of the
cell-membrane, and of greater or less thickness ; 3rd, of a
substance which is frequently firm or consistent, included
within the cells, the band of Remak.*
[§56. From this resume, it would

appear that the universal elementary

form of every tissue is the CELL, which / «

is preceded by the NUCLEUS as medi- **"

ate, and the JSTUCLEOLUS as immediate

products of the formative power. Cells

and nuclei seem to stand in mutual and

relative opposition; so that generally, Fig- 8.— Cells from the
i • • 11 Vi • i -i I granulations of the umbi-

perhaps invariably, the one is evolved at fical cord of the calf Th

the expense of the other (fig. 8). After bear a striking resem-
these transition stages are accom- blance to the cellular tis-
plished, the tissue attains individuality sue of vegetables ; nuclei

according to the general character and are sef lfludtef in the

i ,-, -T. several cells. After Bres-

place it occupies m the system. Dur- chet and G1 (Ann des

uig this last stage the more distant Sc.Nat.t.\iu.-pl. 6,fig.5).
* Dr. Schwann, in Professor Wagner's Physiology, p. 222.

c2

20 DLFFEEENCES BETWEEN ANIMALS AND PLANTS.

organic parts enlarge, as is distinctly seen in the cells of the
epithelium, in the muscular fibres, and in the primary fibrous
fasciculi of the nerves ; whilst mere nuclei, as the blood,
lymph, or pus-globule, remain, or suffer diminution in the
course of farther development.]*

SECTION III.

DIFFERENCES BETWEEN ANIMALS AND PLANTS.

§ 57. AT first sight, nothing would appear more widely
different than animals and plants. What is there in common,
for instance, between an oak and the bird which seeks shelter
amidst its foliage ?

§ 58. The difference, indeed, is usually so obvious, that the
question would be superfluous, if applied only to the higher
forms of the two kingdoms ; but as we descend to the simpler
and therefore lower forms, the distinctions become so few, and
so feebly characterized, that it is at length difficult to pronounce
whether the object we have before us is an animal or a plant.
Thus, the sponges have so great a resemblance to some polyps,
that they have generally been included in the animal, although
in reality they belong to the vegetable kingdom.')*

§ 59. Animals and plants differ in the relative predomi-
nance of their component elements, oxygen, carbon, hydrogen,
and nitrogen. In vegetables, only a small proportion of nitro-
gen is found, while this element enters largely into the com-
position of animal tissues.

§ 60. Another peculiarity of the animal kingdom is the
presence of large, distinctly limited cavities, for the lodgment
of certain organs ; such is the skull and the chest in the higher
animals, the branchial chamber in fishes, and the abdomen
or general cavity of the body, which exists in all animals, with-
out exception, for the reception of the digestive organs.

§ 61. The well-defined and compact forms of the organs
lodged in these cavities is a peculiarity belonging to animals
only. In plants, the organs designed for special purposes are
never embodied into one mass, but are distributed over various
parts of the individual ; thus the leaves, which answer to the

* Wagner's Physiology, p. 221.

f The animality of sponges is maintained by some of our most dis-
liuguibhed naturalists. — ED.

DIFFERENCES BETWEEN ANIMALS AND PLANTS. 21

lungs of animals, instead of being condensed into one organ,
are developed on the stem and branches ; nor is there any
organ corresponding to the brain, the heart, the liver, or the
stomach.

§ 62. Moreover, the presence of a proper digestive cavity
involves marked differences between the two kingdoms, in
respect to alimentation, or the use of food. In plants, the
fluids absorbed by the roots are carried to every part of the
plant, before they arrive at the leaves ; in animals, on the
contrary, the food is at once received into the digestive cavity,
where it is elaborated ; and it is only after it has been dis-
solved and prepared, that it is introduced into the other
parts of the body. The food of animals consists of organized
substances, while that of vegetables is derived from inorganic
elements ; vegetables produce albumen, sugar, starch, &c.,
whilst animals consume them.

§ 63. Plants commence their development from a single
point, the seed, and, in like manner, all animals are developed
from the egg. But the animal germ is the result of successive
transformations of the yolk, while nothing similar takes place
in the plant. The subsequent development of individuals is
for the most part different in the two kingdoms. No limit is
usually placed to the increase of plants ; trees put out new
branches and new roots as long as they live. Animals, on
the contrary, have a limited size and figure ; and these once
attained, the subsequent changes are accomplished without
any increase of volume or essential alteration of form ; while
the appearance of most vegetables is repeatedly modified, in
a notable manner, by the development of new branches. Some
of the lowest animals, however, as the polyps, increase in a
somewhat analogous manner.

§ 64. In the effects they produce upon the air, by respira-
tion, there is an important difference. Animals consume the
oxygen, and give out carbonic acid gas, which is destructive to
animal life ; while plants, by respiration, which they, in most
instances, perform by means of the leaves, reverse the process,
and furnish oxygen, which is essential to the life of animals. If
an animal be confined in a small portion of air, or water con-
taining air, this soon becomes so vitiated by respiration as to
be unfit to sustain life ; but if living plants are enclosed with
the animal at the same time, the air is maintained* pure, and

22 DIFFERENCES BETWEEN ANIMAL3 AND PLANTS.

no difficulty is experienced. The practical effect of this com-
pensation, in the economy of nature, is obviously most im-
portant ; vegetation restoring to the atmosphere what is con-
sumed by animal respiration, combustion, &c., and vice versa.

§65. But there are two properties which, more than all
others, distinguish the animal from the plant, namely, the
power of moving itself or its parts at will, and the power of
perceiving objects and the influences produced by them ; in
other words, voluntary motion and sensation.

§66. All animals are susceptible of pleasure and pain.
Plants have also a certain sensibility. They wither and fade
under a burning sun, or when deprived of moisture ; and they
die when subjected to too great a degree of cold, or to the
action of poisons. But they have no consciousness, and there-
fore suffer no pain ; while animals under similar circum-
stances endure it. • Hence they have been called animate beings,
in opposition to plants, which are inanimate beings.

[§ 67. If we take a general view of the animal and vegeta-
ble kingdoms, we find that each kingdom may be grouped
into three divisions.

IN THE ANIMAL. IN THE VEGETABLE.

1. Zoophyta. 1. Acotyledons.

2. Mollusca and Articulata. 2. Monocotyledons.

3. Vertebrata. 3. Dicotyledons.

[§ 68. The first great division of the animal series compre-
hends the zoophytes ; their bodies have a circular or radiated
form like some of the lowest vegetables, and are composed of a
simple organic tissue, which is soft, pulpy, more or less trans-
parent, and possessed of irritability and contractibility, although
muscular fibres have not been observed in many groups of
this division. They manifest a high degree of sensibility,
although distinct nerves and ganglia have been only discovered
in the acalephae and echinodermata. In these classes the gan-
glia form so many centres of life, and each segment of the
body has its own special ganglion. Through this simple con-
dition of the nervous system many zoophytes possess the
power of reproduction by scission or slips, and by buds or
gemmules, after the manner of plants. The most inferior
forms have no distinct organ except a digestive cavity, which

DUTEBENCES BETWEEN ANIMALS AND PLANTS. 23

is sometimes furnished with small coeca ; they have no per-
ceptible blood-vessels nor special organs for respiration and
reproduction ; they are all aquatic, and are analogous to the
lowest division of the vegetable series, the acotyledonous or
cellular plants, both in form, consistence, and chemical com-
position.

[§69. The acotyledons all possess a soft, pulpy tissue of
the most simple organisation, deprived of fibres. The repro-
ductive organs are altogether absent, or are united on the same
individual ; they have no medullary substance, and are merely
expansions of simple cells, in which no special organs are de-
veloped for any of the functions.

[§ 70. The second division of the animal series comprehends
all those in which we find the nervous system disposed in cords
in a body more or less symmetrical, extending from the head
to the posterior extremity, under the intestinal canal. In all
the classes of this great section the nervous trunks lie on
the ventral surface of the body, and are provided at intervals
with a number of ganglia, from which leashes of fila-
ments emanate to supply the different organs. The nervous
centre we call the brain, is formed in them of a double gan-
glion, situated above the esophagous ; from it two branches
arise to unite in ganglia situated below that tube, thus em-
bracing the esophagous like a necklace or collar : from this
nervous circle filaments proceed to be distributed to the different
organs of the body. In all the mollusca, the nervous system
preserves this general character ; but among the articulata, as
Crustacea, insects, and annelides, each ring of the body pos-
sesses a ganglion, which distributes filaments to the organs
contained therein. The number of ganglia in the series cor-
responds to the segments comprised in the length of the
body, the whole being connected together by a double cord,
emanating from the lateral parts of the esophagean gan-
glion. From this disposition of the nervous system, life is
not confined to a single centre (as in the vertebrata), each
ganglion presiding, as it were, over the vital manifestations of
the organs proper to the individual segments : it is thus
they can reproduce many important parts that may have been
removed, or lost by accident, as the claws of the crab and
lobster, &c.

[§71. The nutritive functions of the mollusca and articulata

24 DIFFEKENCES BETWEEN ANIMALS AND PLANTS.

are under the empire of a ganglionic cord, similar to the
sympathetic nerve in man. These two great classes never
present an internal articulated skeleton ; their muscles are
attached to the skin, which is more or less indurated. The
Crustacea and mollusca have a heart and blood-vessels, for
propelling and circulating their nutritive fluids, with branchiae
for aquatic and pulmonary sacs for seriform respiration. In
the arachnida, insects, and annelides, the circulation is carried
on by a pulsating dorsal vessel, and respiration is accomplished
by sacs, branchiae, or trachiee, that ramify, like blood-vessels,
through every part of the body : their jaws move on a hori-
zontal plane, and many of them are provided with a proboscis
or a suctorial apparatus. They possess the senses of vision,
and even those of smell and hearing ; touch and taste, being
refined modifications of sensibility, are enjoyed in a greater or
less degree by ah1 animals. The reproductive organs in the
acephalous mollusca (as the oyster) are united in the same in-
dividual : they are separate, however, in the gasteropoda (as
the snail) and cephalopoda (as the cuttle-fish), as well as in
the Crustacea and insects.

[§ 72. This division of the animal series is analogous to
the monocotyledonous plants. The marrow or pith is inter-
woven with their vegetable fibres, as the nervous system
is disseminated by ganglia through the bodies of the inver-
tebrata ; there is no osseous skeleton in the one, nor is there
any true wood in the other, but in both the circumference is
more solid than the centre. We see among some families of
this section (as the grasses, lilies, and palms, &c,, the same as
among insects, Crustacea, and annelides), the integument more
or less indurated, and in some families containing a quantity
of silicious particles, just as the external skeleton of insects is
composed of peculiar animal substances, termed chitine and
coccine, and consolidated by minute proportions of the phos-
phates of lime, magnesia, and iron ; or that of Crustacea, which
is hardened with nearly half its weight of the carbonate of lime,
and a considerable proportion of the phosphate, with traces of
magnesia, iron, and soda. The knotty-jointed stems of many
grasses represent the articulated bodies of worms, Crustacea,
and myriapods. Many families of this division produce seed
only once in their lives, like some worms and insects which cease
to exist after having deposited their ova. Their leaves are

DIFFEEENCES BETWEEN ANIMALS A1STD PLANTS. 25

simple, and their nerves are, in general, parallel : their flowers
possess only three stamens, or their multiples (6 or 9), and
they are often incomplete in many of their parts. None of
these endogenous vegetables grow by layers, but by a swelling
out of their internal structure, just as the horny or calca-
reous envelope of insects and Crustacea is periodically shed
to allow of a general increase from within. Among some
classes and families of both kingdoms there are many groups
which are aquatic in their habits.

[§ 73. The third great division of the animal kingdom, called
vertebrata, comprehends all those animals provided with two
distinct nervous systems ; the one formed of a series of gan-
glia extending through the body, and called the ganglionic
or sympathetic system, which presides over the functions of
internal life or nutrition. The other, consecrated to exter-
nal life or relation, is composed of the brain, spinal cord,
and nerves, the principal centres of which are enclosed in
the cranium and the canal of the vertebral column ; they
all possess an internal framework or skeleton, the several
jointed pieces of which are moveable on each other. The
most perfect possess five senses ; four of these occupying the
cavity of the cranium, and there are never more than four
members disposed in pairs. They have all a heart with red
blood, and respire by lungs, or branchiae, and the sexes are
separate. They are usually parted into two great groups, the
vertebrata with cold blood and feeble respiration, fishes
and reptiles, and the vertebrata with warm blood and a com-
plete respiration, birds and mammals. The nervous system,
in this division of the series, attains its greatest development,
presenting the most perfect centralisation, from which the most
noble faculties emanate.

[§ 74. We compare with this group of animals the dicotyle-
donous vegetables, or those whose embryo possesses two coty-
ledons or seed lobes. The form of their reproductive organs
is always the most perfect, being composed of the number
five and its multiples. Their trunks or stems grow by the
addition of concentric layers or rings of wood made to their
outer surface. Being thus exogenous, they display more or
less solidity internally, like the osseous skeleton of the verte-
brata. The central marrow or pith is enclosed in a sheath
(analagous to the spinal canal) extending through the entire

26

DIFFERENCES BETWEEN ANIMALS AND PLANTS.

length of the plant from the collar of the root to the terminal
flowers of the stem, and branches. This division comprehends
the most highly developed families of the vegetable series in
which the manifestations of life display themselves in their
fullest perfection. Here we meet with all the most vivacious
plants, all the large trees, and all those which manifest the
most marked irritability, as the sensitive plant, &c. &c.

[§ 75. In resume we observe in animals and plants certain
functions that are analogous, and contain organic traits that
are different in each kingdom. The following table will
enable the student to understand these analogies and dif-
ferences : —

IN THE YEGETABLE.

1. The roots are external,
and are implanted in the earth,
and all the special vital organs
are situated externally.

2. Nourishment surrounds
the vegetable, which it ab-
sorbs by the external organs
(the roots, leaves, &c.)

3. The sap ascends and de-
scends by the agency of the
vessels, aided by absorption
and exhalation, through the
influence of light and heat.

4. The leaves are the aerating
organs or lungs of plants, and
are usually of a green colour,
and situated externally.

5. The vegetable absorbs
carbonic acid gas, retains the
carbon, and exhales the oxy-
gen through the influence of
the solar rays.

IN THE ANIMAL.

1 . The absorbent vessels or
internal roots penetrate the
membranes of the digestive
canal, and the vital organs are
concealed internally.

2. The animal is compelled
to search for its pasture, or its
prey, and absorbs the juices by
internal organs.

3 . The blood (whether white
or red) circulates by means of
one or more hearts, or by the
contractility of the vessels
themselves.

4. The respiratory organs
of animals are sacs, tracheae,
branchiae or lungs, and are
usually placed internally, and
tinged of a red colour, from
the blood that circulates
through them.

5. The animal absorbs the
oxygen of the atmosphere, or
that contained in the water,
and exhales carbonic acid.

D1FFEKENCES BETWEEN ANIMALS AND PLANTS.

27

IN THE VEGETABLE.

6. The vegetable is a com-
pound of many plants that are
divisible and capable of mul-
tiplication by buds, slips,
suckers, or seeds.

7. The plant has a circular
or radiated form, both sexes
being often united on the same
individual.

8. The reproductive organs
in the vegetable fall every year.

9. Fructification is the great
end of vegetable existence, by
the development of the flower
and fruit.

10. The movements in the
vegetable are involuntary, de-
pending on a state of turges-
cence in the vessels, or in a
degree of irritability peculiar
to their tissues.

11. The vegetable is en-
dowed with an organic sensi-
bility without consciousness.

12. Vegetables possess de-
fensive or protective weapons,
and many have poisonous or-
gans.

IN THE ANIMAL.

6. Animals, some polyps
and mollusca excepted, form a
whole that is indivisible, being
composed of central organs,
as the brain, spinal cord, heart,
&c.

7. Animals have mostly a
binary form, each half being
the counterpart of the other :
the sexes are usually separate,
although they are united in
the inferior classes of mol-
lusca and radiata.

8. In the animal they are
permanent during life.

9. Sensibilityandconscious-
ness are the highest conditions
of animal life, through the ope-
ration of the brain and nerves.

10. The motions of animals
are voluntary, depending on
the energy of their muscular
system, regulated by the will
acting through the nerves.
Some movements belong to the
involuntary class .

v

1 1 . The nervous system con-
fers on animals sensibility,
accompanied with conscious-
ness.

12. Animals, in addition,
are furnished with offensive in-
struments for seizing and des-
troying prey ; some have a
venomous, and others an elec-
trical apparatus to accomplish
the same end. — T. W.]

CHAPTER THIRD.

ORGANS AND FUNCTIONS OF ANIMAL LIFE.
SECTION I.

OF THE NEEVOUS SYSTEM AND GENERAL SENSATION.

§ 76. LIFE, in animals, is manifested by two kinds of
functions, viz.: First, the functions of animal life, or those
of relation, which include sensation and voluntary motion ;
those which enable us to approach, and perceive our fellow-
beings and the objects around us, and bring us into relation
with them : Second, the functions of vegetable life, which are
nutrition in its widest sense, and reproduction ;* those in-
deed, which are essential to the maintenance and perpetuation
of life.

§ 77. The two distinguishing characteristics of animals,
namely, sensation and motion (§ 65), depend upon special
systems of organs, wanting in plants, and which are called the
nervous and muscular systems. The nervous system, therefore,
is the grand characteristic of the animal body. It is the
centre from which all the commands of the will issue, and to
which all sensations tend.

§ 78. Greatly as the form, the arrangement, and the volume
of the nervous system vary in different animals, they may all
be reduced to four principal types, which correspond, more-
over, to the four great divisions of the animal kingdom.
In the vertebrate animals, namely, fishes, reptiles, birds,

* This distinction is the more important, inasmuch as the organs of
animal life, and those of vegetative life, spring from very distinct layers of
the embryonic membrane. The first are developed from the upper layer,
and the second from the lower layer of the germ of the animal. See
Chapter on Embryology.

NERYOUS SYSTEM AND GENERAL SENSATION. 29

and mammals, the nervous system is composed of two prin-
cipal masses, the spinal cord (fig. 19), which runs along the
back, and the brain (fig. 20), contained within the skull.*
The volume of the brain is proportionally larger, as the animal
occupies a more elevated rank in the scale of life. Man,
who stands at the head of creation, is in this respect also the
most highly endowed being.

§ 79. With the brain and spinal cord the nerves are con-
nected, which are distributed, in the form of branching threads,
through every part of the body. The branches which unite
with the brain are nine pairs, called the cerebral nerves, and
are destined chiefly for the organs of sense located in the head.
Those which join the spinal cord are also in pairs, one pair
for each vertebra or joint of the back. The number of pairs
varies, therefore, in different classes and families, according to
the number of vertebrae. Each spinal nerve is double, being
composed of two threads, which at their junction with the
cord are separate, and afterwards accompany each other
throughout their whole course. The anterior thread transmits
the commands of the will, which induce motion ; the pos-
terior receives and conveys impressions to the brain, to pro-
duce sensation.

STRUCTURE OF THE PRIMARY FIBRES OF NERVES.

[§ 80. Whoever would acquire a knowledge of the minute
anatomy of the nervous system, had better begin by examining
one of the peripheral nerves. Let a piece of one of the trunks
or branches of a nerve, that can easily be dissected out, be
chosen, and laid upon a glass plate : here let the nervous
bundles be separated or teazed out by the aid of a needle in
either hand, until free spaces of the glass plate appear ; let
the preparation now have a drop of serum or of albumen added
to it, and then be covered with a piece of thin glass. Under
a magnifying power of from three to four hundred diameters,
numbers of transparent cylindrical, straight, or slightly
sinuous filaments will- be perceived as the chief structure,

* The brain is composed of several distinct parts, which vary greatly, in
their relative proportions, in different animals, as will appear hereafter.
They are : 1. The medulla oblongata; 2. Cerebellum; 3. Optic lobes;
4. Cerebral hemispheres ; 5. Olfactory lobes ; 6. The Pituitary body ;
7. The Pineal body. See figures 19, 20. The spinal cord is composed of
four nervous columns.

30

NERVOUS SYSTEM AND GENERAL SENSATION.

having a mean diameter of from 1 -200th to 1 -300th of a line,
and always proceeding distinct from one another, never anas-
tomosing. These are the PRIMITIVE FIBRES of the nerve (figs.

9, et seq.) If these
fibres have under-
gone little or no
change, each is se-
verallv seen to be

*

bounded by a dou-
ble contour — an
appearance which
must be viewed as
the optical expres-
sion of a transpa-

\\lilltltl fj/ '»! rent covering or

membrane. The

middle space is
completely trans-
parent. When the
Fig. 9. — A, Primary fibres of a human body, nerve has suffered
B, primary fibres (more highly magnified) of the change from pres-
^rain* sure, imbibition of

water, or the like, the appearance is altered. In the middle clear
space granular or grumous particles or masses are perceived,
which, under pressure, escape from the divided ends of the'
primitive fibres (fig. 9, A, to the right). Other changes, but
more difficult of apprehension, also take place in the lateral
contours of the fibres, which are made up of the double lines.
To observe the primitive fibres of nerves in their normal
situation, the best subject is the delicate flat muscle of some
small animal — one of the muscles of the eye of the common
sparrow, for example (fig. 10) — which must be gently pressed
between two plates of glass. Here, in the middle trunk (a),
which, to the naked eye, looked finely fasciculated only, a
great number of primitive fibrils are perceived lying over one
another, but without running altogether parallel, inasmuch as
some diverge a little to the right, others a little to the left,
some proceed from below upwards, others from above down-
wards, but all preserve the main course onwards. They lie
BO close, and cover each other so much, that their structure
individually cannot be distinctly made out. At the parts

KEEYOUS SYSTEM AOT) GEtfEEAL SENSATIOK.

31

where smaller branches are sent off transversely, however,
(fig, 10, b, b,) the structure of the primary fibres running iu
a parallel direction
may be seen as dis-
tinctly as when they
are separated by
art. It frequently
happens that we may
tear fresh primitive
fibres in such a way
that the broader,
clear, middle por-
tion alone retains
its continuity, the
bounding lines hav-
ing given way trans-
versely ; the middle
portion is then seen
to be enclosed with-
in an extremely de-

_ .

hcate contour. From
all this, it may be
inferred that each
primitive fibre con-
sists of a very clear Fig' 10' — Branch of a nerve distributed to one

i -i -• •, 3 of the muscles of the eye of a sparrow,

included substance,

and a transparent tubular sheath. The double line or contour
of either side being the optical expression of the inner and
outer wall of this tube. Other observers admit a more com-
pound structure, and some have even spoken of a ciliary epi-
thelium, lining the inner aspect of the sheath.

[§ 81. These primary tubes or fibres of the peripheral
nerves are similar, with very slight modifications, in every
part of the nervous system. It is necessary, however, to ex-
cept from this general rule the first and second cerebral
nerves. In the auditory nerve the fibres are somewhat more
delicate than elsewhere. They also very commonly appear
rather finer than wont where they traverse ganglions. They
appear to be distributed over the periphery of the body, with-
out, in any instance, anastomosing. They have a central and
a peripheral termination. With reference to the first, or

NERVOUS SYSTEM AND GENERAL SENSATION.

where they enter the brain or spinal cord as roots of nerves,
they pass immediately into the white medullary fibres, or cen-
tral parts, and at the same time become by one-half, or even
two-thirds, smaller. The primary fibres of the brain and
spinal cord, as well as those of the olfactory and auditory
nerves, are in some cases so delicate, that they measure but
the 1 - 1 000th of a line in diameter : frequently, however, they
are thicker, from the 1 -400th to the 1-5 00th of a line in
diameter. These fibrils, of different dimensions, are constantly
observed running over, and under, and near to one another.

(Figs. 9, 10, B, and
11, C.) Examined in
the most recent state
possible, they are, for
the major part, cy-
lindrical, but in part
also knotty or vari-
cose, inasmuch as
they exhibit little oval
or rounded enlarge-
ments in their course.

(Figs. 9, B, H,A,B.)
It is doubtful whe-
ther or not this vari-
cose state is acciden-
tal only, or is really
peculiar to certain
primary fibres in the
living state. So much
Fig. 11. — A, primary fibres of the olfactory is certain, that the
nerve of man. B, a primary fibre from the tho- knots are constantly
racic portion of the spinal cord of man. C, a seen arisin0* under
thin slice from the outer aspect of the ophthalmic , •• f & , j

ganglion of man. After Valentin. tne e?e °? "

server, and that they

are frequently effects of the methods of investigation pur-
sued. There is nevertheless this peculiarity to be noted in re-
gard to the primary fibres of the central parts, that they are
much more apt to assume the varicose condition than those
of the periphery — a peculiarity that seems to be connected with
their structure. The sheaths, in fact, of the central primary
fibres are much more delicate, although in general still charac-

KERYOUS SYSTEM AND GENERAL SENSATION.

33

terised by the double contour, than those of the peripheral
fibres. In the central fibres, too, the sheath and contents appear
to be far more intimately connected ; in many cases they are
completely inseparable, so that the contrast as betwixt sheath
and contents disappears. These delicate primary fibrils of
the central masses run in such a variety of ways, crossing and
interlacing, and forming such a tangled skein, that it is
impossible to follow them to the roots of the nerves, or towards
the periphery of the brain and cord, and so to make certain
that they never anastomose. To all appearance, however, they

Fig. 12. — A small portion of the terminal plexus of primary fibres of the
auditory nerve in the auditory sac of the pike (Esox lucius.)

34

NERVOUS SYSTEM AND GENERAL SENSATION.

never divide ; and they seem no more to run into one another,
or to communicate by anastomoses here, than they do in the
peripheral parts of the body. But these fine primary fibres
of the central parts enlarge conspicuously and immediately
at the entrances of the different nerves into the brain and
spinal cord.

TERMINATION Or THE PRIMARY FIBRES.

[§ 82. A very important question, which naturally presents
itself in connexion with the primary fibrils, is this : how do
they end? Although generally traced with difficulty, the
peripheral terminations of the nervous fibrils are still much
more easily demonstrated than those of the centres. United
into bundles, and surrounded with cellulo-membranous sheaths
(neurilema), the primary fibres penetrate all the organs nearly

to their peripheral confines, to where
they are covered with epithelial or
epidermic formations. Here it is that
the bundles of primary fibres separate
and form plexuses — terminal plex-
uses, as they have been designated ;
at last single primary fibres form
loops, or rather two primary fibres
meet and form a loop — terminal
loops. These loops are smaller or
larger in different tissues. (Figs.
12, 13.) Wherever the primary
fibres of nerves have been distinctly
traced to their extremities, this mode
of termination in loops has been
observed, so that it appears to be
general, and even to extend to the
nerves of special sense, with the sin-
gle exception of the olfactory and
optic nerves, in the peripheral ex-
pansions of which, no loopings have

„ been positively ascertained to exist,

Fig. 13. — Terminal primary 1,1 i J •>

fibres from the ciliary liga- Chough no one has yet conde-

ment of the common duck, scended upon any other mode of

After Valentin. termination in regard to these two

NERVOUS STST.E3I AXD GENERAL SENSATION.

Fig. 14. — Central terminal
fibres from the yellow sub-
stance of the cerebellum of
the common pigeon : a, ter-
minal plexus of primary fi-
bres ; b, loopings of the ter-
minal fibres ; c, ganglionic
globules.* A ganglionic cell

nerves. It has been stated that
the mode of termination of the
primary fibres is much more
difficult of demonstration in the
central parts than in the peripheries.
It is impossible at present to say
positively that they again turn round
loop-wise, on the surface of the
brain, as certain observations would
lead us to conclude that they did.
(Fig. 14.)

[§ S3. Besides the tubular or
primary fibrous formations now
described, there is a second and

general elementary structure in the

J ,.,, -, ,,
nervous system, entitled the gang-

lionic, or nervous globules, better the
ganglionic cells or corpuscles. These
corpuscles are met with in the brain, from the Gasserian ganglion

spinal cord, and ganglia, and also °,f ™an' j™™* fro™ *s
, , , . & &. i sheath and highly magnified,

here and there in particular nerves.

The cineritious, or grey nervous substance, wherever it occurs, be
it deep seated or superficial, consists
of aggregations of these ganglionic
corpuscles. They have always a
certain quantity, more or less, of the
tubular or primary fibrous structure
mixed with them ; the more abun-
dant the primary fibres, the lighter
is the mass ; the fewer they are, the
darker is its colour. The ganglionic
corpuscles, particularly in the brain
and spinal cord, are much more de-
licate and easily destroyed than the
primary fibres. To study them, it is
well to begin with the Gasserian

ganglion of a small animal, such as

?u ., ,1 . r p Fig. 15. — Second abdomi-

a rabbit, or a thoracic ganglion of a nal gsanglion of the gympatbe.

small bird (figs. I 6, B. 1 7, a). Here tic nerve of the Fringilla spi-
they mostly appear as globular or oval, mis, to show the course of the
indistinctly granular bodies, having primary fibres.

I) 2

36

XERYOUS SYSTEM AND GENEEAL SENSATION.

i

Fig. 16. — A, single primary fibres from an intercos-
tal nerve of the common sparrow. B, several primary
fibres and ganglionic cells, from one of the thoracic
ganglions of the same bird. *A single ganglionic cell,
with a clear nucleus and darker nucleolus.

I

internally a clear ve-
sicular-looking nu-
cleus, which in its
turn mostly includes
a nucleolus. They
are composed of ex-
tremely fine mole-
cules, connected to-
gether by a semi-
fluid, glutinous, or
viscid, amorphous
substance. It is
doubtful whether or
not they possess a
delicate transparent
proper capsule. For
the major part, however, each gan-
glionic corpuscle is surrounded by
a cellulo-membranous capsule or
sheath : extremely delicate, greyish
or reddish coloured cellulo-mem-
branous fibres, furnished with nu-
clei, are interwoven into true cap-
sules ; but from these the ganglio-
nic corpuscles very readily become
detached and fall out. Frequently,
as, for instance, in the cervical por-
tion of the sympathetic nerve (fig.
17, A and B), this cellulo-mem-
branous sheath is so highly de-
veloped, that the gangliouic cor-
puscles (A, a, a) appear to be
bedded in a kind of matrix, which
is only intersected here and there
by single primary fibres (B, a, a) ;
these, like the corpuscles, seeming
to be separated and kept apart
by the abundant cellular tissue.

Fig. 17. — A, thin slice from the superior cervical ganglion of the calf; «, gangli-
globules ; I, primitive fibre ; c, involucrum of the ganglionic cells. B, thin slice
trom the soft nerve of the plexus maximus carotidis of the calf; «, a, a, isolated pri-
mary fibres ; b, b, thick sheaths of the same. After Valentin.

NERYOUS SYSTEM AND GENERAL SENSATION.

37

This cellular tissue, with its nucleated fibres, has been errone*
ously described as a third and distinct special element of the
nervous system, under the name of the organic fibrils, proba-
bly from their abundance in the sympathetic and its ganglia,
or of the nodulated fibrils — fibrillse nodulosse.

The ganglionic corpuscles present numerous varieties in re-
gard to form, size, arrangement, and the structure of their re-
moter elements. They are singularly delicate and destructible
in the central masses. Here the cellular sheath, just de-
scribed, is entirely wanting ; and the finely granular substance
of which they consist, and the clear nucleus which they con-
tain, are so diffluent, that it is seldom we succeed in finding
more under our microscopes than a homogeneous, finely granu-
lar mass. Whether from the great nervous centres., or from
the more peripheral ganglia, they are generally either round
or oval in figure (figs. 14, 16*, 17, «, and 18, a) ; frequently,
however, they
are elongated,
sausage shaped,
four - cornered,
tetrahedral, and
furnished with
off-sets or pro-
cesses (fig. 18,
B) ; it is seldom
that two are seen
connected by a
bridge. The nu-
cleus is always
clear, roundish,
or lengthened
and simple; the
micleolus is ex-
tremely small.
In their gene-
ral external ap-
pearance, these
ganglionic cor-
puscles have a
surprising re-
semblance to

Fig. 18. — Primary fibres and ganglionic globules from
the human brain. A, ganglionic globules in the
substance of the thalamus, mixed with varicose pri-
mary fibres, a, a single ganglionic globule or cell,
highly magnified; 6, a blood-vessel. B, B, ganglionic
globules with processes of various form, as they are
met with in the black substance of the crura cerebrL
After Valentin.

38 XEBVOUS SYSTEM AXD GEKEBAL SENSATION.

primitive ova ; they are constituted after the general type of
cellular formations, although they have more of the character
of solid bodies than of true cells with fluid contents.*]

[§ 84. The general form and distribution of the nervous sys-
tem of animal life is shown in the annexed plate (fig. 19),
which represents the cerebro- spinal system, and the course of
the principal nerves in man. At a are seen the two hemi-
spheres of the cerebrum ; at b those of the cerebellum ; and at
c the spinal cord. The principal motory nerve, passing to the
muscles of the face, is seen at d ; and at e, the brachial plexus
formed by the interlacing of five spinal nerves, destined to give
off branches to the upper extremities. The principal of these
are, the median nerve, f, which passes down the arm ; the
ulnar nerve, y, which passes round the inner condyle of the
humerus, is distributed to the integument and muscles, and
sends terminal twigs to the ring, and fourth fingers ; the
internal cutaneous nerve, h ; and the radial and muscular
nerves, i, which are in like manner distributed to the integu-
ment and muscles of the fore-arm, hand, and fingers. From
the spinal cord are given off the intercostal nerves, j, which,
escaping through the holes formed in the spinal column, pass
between the ribs, and are lost in the skin and muscles of
the trunk. The lumbar plexus, k, sends nerves to the front of
the thigh and leg ; the sacral plexus, /, gives origin to the
principal nerves of the lower extremities. The great sciatic
nerve — the largest nerve in the body — proceeds down the back
of the thigh, and at the ham divides into the tibial nerve, ?n,
the external peroneal, or fibular nerve, n, and the external
saphenous nerve, o.

[§ 85. THE BEAUST is a compound organ, enclosed in the
skull, and surrounded by three membranes: these are, the dura-
mater, the external or fibrous, the pia-mater, the middle, or
vascular; and the arachnoid, the internal or serous. These mem-
branes are prolonged into the canal of the spinal column for
lodging the cord, and invest in like manner this central portion
of the nervous system. Figure 20 will serve to give the
student a general idea of the different parts which compose
the brain. It represents a vertical section of the cerebrum, a ;
the cerebellum, d ; the medulla oblongata, e ; and shews the

* Professor Wagnei's Elements of Physiology, p. 464, et seg.

ig. i9._The Nervous System of Man.

40

NERVOUS SYSTEM AND GENERAL SENSATION.

primary course of the cerebral nerves, and their points of union
with the brain and medulla obkmgata.

/

Fig. 20. — Section of the Brain of Man, shewing the primary course of the

Nerves.

[§ 86. THE CEREBRUM (a) is in man the most voluminous
part of the brain. It occupies all the upper portion of the
cranium, from the frontal to the occipital bone (fig. 79). It
is of an ovoid form, with the largest extremity directed back-
wards. Superiorly and posteriorly it is divided into two
hemispheres, separated from each other by a fold of the
dura mater, called the falx cerebri, which descends between
them. Inferiorly, the hemispheres are limited by a broad
band, f, caUed the corpus callosum, which extends its fibrous
structure into both hemispheres, and unites them organi-
cally together. The surface of the cerebrum presents a num-
ber of elevations and depressions, which wind in a tortuous
manner, resembling the foldings of the small intestine in the
abdomen. These are called the convolutions of the brain, and
arise from the great development of the nervous substance
being thus folded to pack into a small compass ; the convo-
lutions are more or less deep in proportion to the development
of the cerebrum. In infancy they are shallow, as well as

NERVOUS SYSTEM AIJTD GENERAL SENSATION. 41

in the cerebrum of the higher orders of mammals, whilst in
some of the lower orders, as the rodentia (figs. 28 and 29),
they entirely disappear. The inferior surface of the cerebrum is
divisible into three lobes, separated from each other by trans-
verse furrows (fig. 20). a is the anterior, b the middle, c the
posterior lobes. Near the median line we observe two round
eminences, the optic lobes, g ; and two large masses of neurine,
the peduncles of the brain, which pass downwards to be con-
tinued into the medulla oblonyata. It is from the base of the
brain, likewise, that the nerves proceed which are classed under
the division cerebral. The surface of the cerebrum is formed
almost entirely of grey nervous substance, which covers the in-
ternal white neurine. When we cut off the hemispheres parallel
to the corpus callosum, we observe that the cerebrum contains
internally several cavities communicating with each other,
called the ventricles of the brain. In these chambers several
bodies are found, the study of which more especially belongs
to the professed anatomist.

[§ 87. The CEREBELLUM occupies the posterior and inferior
part of the skull (fig. 19, b. fig. 20, d) : its weight, as com-
pared with that of the brain, is, in man, 1 : 9, whilst in other
mammals it varies from 1 : 2 to 1 : 14. It is protected from the
pressure of the posterior lobes of the cerebrum by a large ex-
tension of the dura mater (tentorium cerebelli), which becomes
an osseous plate in the carnivora. The cerebellum is divided
into two large lateral lobes, and one small central lobe. The
lateral lobes are separated by a membranous process (falx
cerebelli), and the middle lobe is situated in a depression be-
hind and below them. In the quadrumana (figs. 32 and 33),
the third lobe is proportionally larger ; and in the rodentia
(figs. 28 and 29) it equals in volume a lateral lobe. The
nervous substance is folded into a series of transverse con-
centric lamellae, placed perpendicularly on their edges, and
enclosed one within the other. If the sulci are carefully
opened, several other lamellae will be found enclosed within
them, but smaller in size, more irregular, and with various
degrees of inclination. The distribution of the neurine is
seen on making a vertical section of one of the lateral lobes,
as shown at (d) figure 20. The white substaatce is found so
disposed as to resemble the stem and branches of a tree, and
hence called the arbor vitce. The branches project into the
lamellae, and are invested with a covering of grey substance.

42 NERVOUS STSTEM: AND GENERAL SENSATION.

A horizontal section shows that the quantity of white suo-
stance considerably exceeds that of the gray. The cerebellum
is connected with the brain and spinal cord by three pairs of
medullary fasciculi. From the interior of the lobes two fasci-
culi (processus e cerebello ad testes) pass forwards and up-
wards to the optic lobes, g. In their ascent they converge,
and are connected by a fold of neurine, called the valve of
Vieussens.* Two round white processes, corpora restiformia,
pass obliquely downwards, and are continued into the posterior
columns of the medulla oblongata. The largest of the fasci-
culi are the crura cerebelli, which incline forwards and in-
wards, and become continuous with the fibres of the pons
Varolii.f This bridge of neurine bears the same relation to
the cerebellum that the corpus callosum does to the cerebrum ;
it is composed of converging fibres, and may therefore be re-
garded as the ccrebellar commissure.

[§ 88. THE OPTIC LOBES. When we raise the posterior
lobes of the brain, we observe between this organ and the
cerebellum four small round eminences, placed in pairs on
each side of the median line (fig. 20, g), upon the superior
surface of the medullary prolongations, which ascend from the
spinal cord to expand in the cerebrum ; these are the optic
lobes, which are developed in a direct ratio with the volume of
the optic nerves.

[§ 89. THE SPINAL CORD is that division of the cerebro-
spinal system, inclosed in all the vertebrata, within the
spinal canal. In man it reaches from the lower border of the
pons Varolii to the first or second lumbar vertebra, whilst in
the foetus it extends throughout the whole length of the spinal
canal ; in this respect representing the permanent condition ot
the spinal cord in reptiles and fishes. We observe three dis-
tinct enlargements of the cord, in different parts of its course.
The cranial swelling, or medulla oblongata, exhibits a conside-
rable expansion, near the margin of the pons, which diminishes
before entering the foramen magnum : on its lateral parts are
three eminences, the pyramidal, olivary, and restiform bodies.
The second enlargement corresponds to the interval between
the third and fifth cervical vertebrae ; the third, to that be-

* Vieussens, a great anatomist ; his Neurographia Universalis was pub-
lished at Lyons in 1685.

t In honour of a celebrated anatomist of the sixteenth century, Varoli.

NEKYOUS SYSTEM AND GENEEAL SENSATION. 43

tween the tenth dorsal and first lumbar vertebrae ; its inferior
termination presents considerable variety ; the spinal cord is
divided into two lateral halves by sulci, extending, on its ante-
rior and posterior surfaces, throughout its entire length ; it is
composed of white and grey substance : the grey occupying the
centre, and the white the periphery of the organ. About an
inch below the pons the pyramidal bodies of the anterior
columns communicate very freely. The white fibrous layer
dips into the sulcus, and its fibres interlace along the median
line ; those from the right column passing into the left, and
vice versa, whilst on the posterior columns no such interchange
of fibres is observed : experiments have proved that the an-
terior columns are the motory, the posterior columns the sen-
sitive centres of the cord.

[§ 90. The spinal cord gives attachment to thirty-one pairs of
nerves, which are regular, symmetrical, and double-rooted ; one
of the roots of each nerve (fig. 21*, d] is united to the anterior
column, the other (6) to the posterior column of the cord ; on
the posterior root a ganglion (c) is formed ; the anterior root (d)
joins the posterior (A)external to it, and thus forms a nerve (e, f)
compound in structure and function.
Sir Charles Bell, Mayo, Majendie, and
others, have proved by experiments
that sensation depends on the posterior
root, and the power of voluntary motion
on the anterior root. The cord is at-
tached, throughout its whole length,
to the tube of the dura mater by a
thin shining membrane, derived from Y 21*.— A segment of
the pia mater, which sends out about the spjnal c'ord) to °how (he
twenty dentate processes, to pin it double origin of the spinal
to that fibrous sheath ; this ligament nerves : b, the posterior

is hence called membrana dentata : it root 5 c» the ganglion of

-, c , i P , that root ; d, the anterior

extends from the foramen magnum to root; g>'the uud

the first lumbar vertebra, and forms nerve.
a vertical septum, separating the

anterior from the posterior roots of the nerves. The sheath
of the dura mater is not entirely occupied by the spinal cord,
but contains a considerable quantity of limpid fluid, in which it
is suspended. By this admirable provision this nervous centre
is preserved from pressure and commotion, in violent move-
ments of the vertebral column.

t

NEEVOUS SYSTEM AND GE^EBAX SENSATION.

[§91. Comparative anatomy, and the history of
animal evolution, have shed an important light upon
the relative importance of the different masses that
compose the brain ; a general survey, therefore, of the
morphology of this organ may illuminate the stu-
dent's path, and enable him to comprehend more
clearly its complicated structure.

[§92. We can easily trace a progressive develop-
ment of the structure of the brain, in the entire series
L- of the vertebrated animals. In FISHES its consti-
tuent parts appear in the form of globular masses,
which lie behind each other on the same plane. The
volume of the brain is small in proportion to the mass
of the body; thus it is 1-720 in Gadus lata, 1-1305
in Esox Indus, 1-1837 in Silurus glanis, and only
1-37440 in Scommher thynnus. Its relative propor-
tion to the spinal cord is seen in the annexed figure
of the cerebro-spinal system of the bleak, Cypri.nus
alburnus (fig. 21), where a, is the ganglia of the
hemispheres ; b, is the optic lobes ; c, the cerebellum ;
d, the medulla oblongata; e, the spinal cord. The
cord presents anterior and posterior columns, as in
man, and enlarges into the medulla oblongata, which
may be regarded as an integral part of the brain ;
from it arises most of the cerebral nerves ; the cere-
bellum (c) is single, and occupies the median line ; it
exhibits various phases of development in the dif-
ferent families. In front of the cerebellum
we find a pair of ganglia — the optic lobes
(b) — which in bony fishes give origin to the
optic nerves ; they are hollow, and exhibit
internally the rudiments of parts that are
more fully developed in the higher classes ;
transverse bands of neurine unite these gan-
glia together. Before the optic lobes a se-
cond pair of ganglia are placed — the cere-
bral hemispheres (a) ; they are small, and
he apart, but are united by a transverse
band in bony fishes : with these masses the
olfactory nerves (fig. 22, 1) are connected,
which sometimes form ganglia before they
are distributed to the nose (figs. 22 and 23,

Fig. 22.

Fig. 23

NEEYOUS SYSTEM AM> GENERAL SENSATION.

45

c* a**). The optic nerves (fig. 22, 2) decussate in most fishes
like two fingers laid crosswise ; in the skate the right nerve
goes through a fissure in the left ; in bony fishes the nerves
cross without any organic intermixture.

[§ 93. In the AMPHIBIA, as the frog and newt, the brain
exhibits many of the essential features of the fishes type. In
front of the medulla oblongata we observe the small single-
lobed cerebellum, c ; before it lies the optic lobes, b, and pineal
gland ; and before these are the hemispheres, a, more developed
than in fishes.

[§ 94. In SCALY Fig. 24. Fig. 25.

REPTILES, serpents,
lizards, and tortoises,
(figs. 24 and 25) the
optic lobes and pineal
gland preserve the
same relations ; but
the hemispheres (fig.
24, a) are much in-
creased in volume, and
the olfactory nerves
(fig. 25, c) arise from
their anterior parts.
The hemispheres ap-
pear in the form of
rolled laminae, and
enclose lateral ventri-
cles ; on their floor we
observe the corpora
striata, through which
the ascending fibres of the hemispheres are seen to pass.

[§ 95. BIEDS present a stillfurther development, and exhibit a
very uniform arrangement of the cerebral parts.

Fig. 26 represents the brain of a turkey.
The medulla oblongata, d, is considerably
expanded ; a true pons is absent, but some
transverse medullary fibres represent the ru-
diment of this cerebellar commissure. The
cerebellum, c, exhibits the middle lobe,
with feeble indications of lateral expansi-
ons, c*. It is divided into lamellee by trans- Fig. 26. The brain
verse fissures ; portions of the posterior co- of a turkey.

Fig. 24 represents the brain of a tortoise,
in which a, is the hemispheres ; b, the optic
lobes ; c, the cerebellum ; d, the pineal gland ;
5, 9, 10, 11, the pairs of nerves.

Fig. 25 shows the base of the same brain:
b, are the hemispheres ; c, the olfactory
nerves; 1 , the optic nerves ; 2, the auditory
nerve ; c, the medulla oblongata.

46

NERVOUS SYSTEM AND GENERAL SENSATION.

lumns of the medulla expand in its interior, giving off branches
which are covered by grey substance, and forming an arbor
vitse. The optic lobes are considerably developed, and seen
at b, behind the hemispheres. When these bodies are separated,
/• we observe the anterior commissure bound-

ing the third ventricle ; pineal and pituitary
bodies are distinct ; the hemispheres are
greatly increased in volume in this class ;
they are still smooth, without convolutions
and' posterior lobes. The absence of the
latter permits us, when we open the skull,
to see the optic lobes lying behind them.
Fig. 27. — The brain The olfactory nerves, with their ganglionic
of a pigeon. enlargement, are seen in fig. 27, which re-
presents the base of the brain of a pigeon, a, is the hemi-
spheres; b, the optic lobes; c, the cerebellum ; 1 to 6, pairs of
nerves. The olfactory nerves arise at the an-
terior and inferior parts of the anterior lobes
7j of the hemispheres; the corpus callosum is re-
presented by a feeble rudiment in this class.
£ [§96. The Brain presents many phases of de-
velopment in the different orders of the MAM-
- MALTA. In the monotremata, and marsupialia,
the hemispheres are not much more developed
than in birds ; and the corpus callosum is still
rudimentary. In the ornithorhyncus, the cere-
bellum, like that of birds, is one-lobed, with
indications only of the lateral lobes, and the he-
mispheres become narrow and pointed as they
advance. In the rodentia, as in fig. 28, which
represents the brain and spinal cord of a rat
(Musdecumanus] the hemispheres, a, are smooth,
and without convolutions, and the posterior
lobes are undeveloped ; the cerebellum, d, lies
free and uncovered, as do also the optic
lobes, 6, and pineal gland ; the middle lobe of
the cerebellum, c, c, is more highly developed
than the lateral lobes, d, d ; the superior
enlargement of the spinal cord, e, extends
Fi 28 . _ The into the middle swelling ; /, is the inferior
brain and spinal enlargement, terminating in the cauda equiua ;
coM of P rot 1 i:- -*•' fl->^ ^factory nerves.

NERYOUS SYSTEM AND GENERAL SENSATION.

47

Fig. 29.— The brain of
a hare.

at---

Fig. 29 is the brain of a hare (Lepus timidus), seen from
above, with the right hemisphere laid open. 1, 1, the ganglia
of the olfactory nerves ; a, a, the cerebral hemispheres, without
convolutions; b, c, the optic lobes of the right side ; d, the pos-
terior border of the corpus callosum ;
y the corpus striatum of the right
side ; g, the cornu ammonis ; h, the
posterior part of the right lateral
ventricle ; i, the root of the right
optic nerve ; k, the right ganglion of
the hemispheres ; /, the cerebellum •
m, its lateral lobes ; n, the lateral
lobules ; o, the medullary laminae at
the surface of the cerebellum ; p,
the fourth ventricle ; q, the arbor
vitse.

In the ruminantia and carnivora, the convolutions exist as
seen in the brain of thecommoncat, (Feliscatus), fig. 30, where
1, 1, are the ganglia of the olfactory
nerves, and 1*, the cavity which they
contain ; 2, the commissure of the
optic nerves ; 3, the roots of the third
pair ; 8, the roots of the eighth pair ; a, ,
the anterior lobes; b, the middle lobes
of the cerebrum ; a, the white root
of the olfactory nerve ; c, the grey
matter of the infundibulum ; d,
crura cerebri ; e, the pons Varolii ; f,
corpora restiformia ; g, corpora py-
ramidalia ; h, medulla oblongata ; i,
the cerebellum; k, corpora albicantia. Fig- 30. —The brain of the cat.

Fig. 31 represents the brain and spinal cord of the raccoon,
(Procyon lotor}. a, the cerebral hemispheres ; 1, the ganglia of
the olfactory nerves ; 6, the optic lobes ; c, the cerebellum ; d,
the superior, and e, the inferior enlargement of the spinal cord ;
fy the cauda equina. The spinal sheath is laid open, to show
the cord and the double roots of the spinal nerves. In the
rounded brain of the porpoise, and in that of the raccoon (fig.
31) and the cat (fig. 30), the convolutions are well developed ;
in the brain of the elephant they are deep, numerous, and iso-
lated from one another ; the optic thaiami increase in size as we
ascend the animal series °^;| ^"

a-.

Fig.

.1

tf

>

NERVOUS SYSTEM.

rn a direct ratio with that of the hemispheres,
as is also the pons Varolii with that of the late-
° ral lobes of the cerebellum.

In the monkeys, as the Cercopithecus sabceus,
the brain (figs. 32 and 33) evidently resembles
that of man in its general configuration. The
hemispheres (fig. 33, a, a', #"). are well deve-

31. loped, both in their anterior andposterior lobes ;
the latter almost cover the cerebellum (in fig.
33, c, c} ; they are relatively of large size, and
have well-developed lateral lobes (fig. 32). The
medulla oblongata, d, is large, and presents the
pyramidal olivary, and restiform eminences,
as in man. The internal structure of the brain
of this monkey is seen at fig. 32, where a is
the corpus callosum ; b} the anterior commis-
sure; c, corpora striata; d, optic thalami ; e, the
radiated disposition of the medullary fibres, as
they pass through the thalami and striated bo-
dies ; f, the pineal gland ; ff, the anterior tu-
bercles ; A, the posterior tubercles, nates, and
testes, of the corpora quadrigemina ; i, the
posterior termination of the lateral ventricle ;
I, the fourth ventricle ; m, the medulla oblon-
gata ; n, the lateral lobes of the cerebellum,
divided to show the arbor vitee.

Fig. 33 is the base of the same brain : 1, the
olfactory nerves ; 2, the optic nerves ; 3, the
third ; 4, the fourth ; 6, the sixth pairs of
nerves : a, the anterior ; a', the middle ; a', the
posterior lobes of the hemispheres ; c, the cere-
bellum; c', the pons Varolii. The corpora albi-
cantia form a single projection behind the in-
fundibulum; the olfactory nerves have no mam-
millary swelling like the olfactory of man; the

> posterior cornu of the lateral ventricles, and
the pes hippocampi, are wanting. The brain of
the ourang, and particularly that of the chim-
pansee, bear a still closer resemblance to that
of man : the hemispheres are more largely deve-
loped, the convolutions more numerous and

NERVOUS SYSTEM AND GENERAL SENSATION.

49

symmetrical ; the cerebellum is relatively larger to the cerebrum
than in man ; the trapezium, which is present in the lower
monkeys, is absent in them, as it is in man ; corpora albicantia
are distinct; the posterior cornu of the lateral ventricle becomes
developed with the pes hippocampi of the cornua ammonis,
parts which are only found in the human brain besides.

Fig. 32.

Fig. 33.

TV'

Brain of Cercopithecus Sabeeus
laid open.

a

Base of the same brain, showing
the cerebral nerves.

[§ 97. CEREBEAL NERVES. We have shown in fig. 20 the
primary course of the cerebral nerves, and their union with
the brain. The olfactory ganglia are large in the cold-blooded
vertebrata, but very small in man, consisting merely of an en-
largement of the trunk of the olfactory nerves (1), which are
the first pair that unite with the brain. From the olfactory
ganglia, reposing on the cribriform plate of the ethmoid bone,
numerous fine filaments proceed to the nasal cavity, and are
distributed to the mucous membrane of the nose.

[§ 98. The optic nerves (2) may be traced from the globe
of the eye to their union with the optic lobes, which are de-
veloped in a direct ratio with these nerves (§ 88). Behind
the eye we observe the third, fourth, and sixth pairs of
nerves.

[§ 99. The third pair are the principal motory nerves of
the muscles of the eye : they distribute branches to the three
recti, and the inferior oblique muscles, and send fibrils to regu-
late the motions of the iris. Reflex motions of the parts to

£

50 NEETOUS SYSTEM AND GENERAL SENSATION".

which these nerves are distributed are occasioned by impres-
sions made upon the optic nerve ; as such motions cease when
the trunk of that nerve is divided.

[§ 100. The fourth pair consist of motory fibrils. They
take a long course, and are distributed to the superior oblique
muscles, to which they are especially destined.

[§ 101. The sixth pair are likewise motory nerves. Their
distribution is restricted to the external straight muscles of
the eye-ball. The function of these nerves has been proved,
both by experiments and pathological observations.

[§ 102. The fifth pair resemble in their origin, structure,
and distribution, compound spinal nerves. Their anterior
roots are distributed exclusively to the muscles of mastication.
The posterior roots impart sensation to the integuments of the
forehead, temples, eyelids, nose, mouth, the greater part of
the ear, the conjunctiva, the mucous membrane of the nasal
fossae, a great part of the mouth, pharynx, upper surface of
the tongue, teeth, and gums. These great nerves divide into
three branches, 1st, the opthalmic (5) passes into the orbit, en-
dows the eye with sensibility, and comes out beneath the eye-
brow, to be distributed on the forehead and temples ; 2nd,
the superior maxillary (5) traverses a canal beneath the orbit,
and distributes leashes of filaments to the skin of the cheeks,
nose, and upper lip; 3rd, the inferior maxillary (5") is distri-
buted to the tongue, pharynx, tonsils, mouth, teeth, gums, chin
and lips.

[§ 103. The Facial Nerve (fig. 19, d, fig. 20, 7) is the
true motory nerve of the muscles of the face, and enables the
countenance to reflect the varied emotions of the mind. This
nerve does not impart sensation, that function being performed
by the branches of the fifth pair. Beneath the origin of the
facial nerve is seen the divided trunk of the acoustic, or audi-
tory nerve.

[§ 104. The Glosso-pharyngeal Nerve (9) is distributed to
the tongue and pharynx : its function is not so clear as that of
the preceding nerves. By some it is regarded as the special
nerve of taste ; by others as a moto-sensitive nerve, as it con-
tains motory and sensitive fibrils.

[§ 105. The Pneumo-gastric Nerve (10) is distributed to
the larynx, air passages, lungs, heart, esophagus, and stomach.
It sends branches, likewise, to the plexuses which surround the

NERVOUS SYSTEM AND GENERAL SENSATION. 51

roots of the great arteries that supply the viscera; it possesses
motory and sensitive filaments ; through the whole of its. ex-
tensive course it confers sensibility on the vocal and respira-
tory organs, and on the stomach.

[§ 1 06. The Spinal Accessory ( 1 2) is seen ascending along the
spinal cord, and passing backwards beneath the cerebellum. It
is distributed principally to the great respiratory muscles, and
is a motory nerve.

[§ 107. The Lingual Nerve (11) is the motory nerve of the
tongue, special sensibility being imparted to that organ by the
fifth pair, common sensation by the glosso-pharyngeal, and
motion by the lingual. It guides the muscles of the tongue in
the various operations of chewing, swallowing, and articulating,
as often as that organ comes into play in the latter act.

[§ 108. The Spinal Nerves, we have already shown (§ 90),
unite with the spinal cord by two roots. The posterior roots
are furnished with ganglia, over which the primary fasciculi
of the anterior roots pass without mixing. Immediately be-
yond the ganglia, the primary fibres of both roots blend
together, and form compound nerves. At 14 and 15 (fig 20),
the two first pairs of spinal cervical nerves are seen : these
enter into combination with several cerebral nerves. Their
sensitive fibres supply the skin of the occiput, ear, chin, and
cheek, and send motory fibres to several of the muscles of the
tongue. The phrenic nerve chiefly derived from the fourth
cervical, although it obtains filaments from other nerves, is
distributed to the diaphragm, and regulates the involuntary
respiratory movements effected by the rising and falling of that
muscle. The general distribution of the other spinal nerves
has been indicated in our outline 'of fig. 19.

[§ 109. The Great Sympathetic Nerves are placed along the
sides of the vertebral column, and extend from the base of the
skull to the os coccyx. They may be said to consist of a chain
of ganglia, communicating with all the cerebral and spinal
nerves, those of the three higher senses excepted. They are
destined to preside over the processes of nutrition, and have
their great centre, the solar plexus, situated in the abdomen;
from the ganglia of the sympathetic, branches proceed to the
heart and blood vessels, the lungs and air passages, the stomach
and intestinal canal, the liver, kidneys, and other glands. From
this distribution of the sympathetic nerves, to the organs sub-

E 2

52 NERVOUS SYSTEM AND GENERAL SENSATION.

servient to nutrition, they are called the nervous system of
organic life, in contradistinction to the cerebro-spinal, which
is called the system of animal life. The function of the
great sympathetic nerves has been so well described by Pro-
fessor Wagner, that we quote his conclusions on this sub-
ject.—T. W.]

[§ 110. " In regard to the sympathetic nerve, and its func-
tions, two mutually opposed views are at the present time en-
tertained by physiologists. One party, and this has hitherto
been the predominating one, considers the sympathetic as a dis-
tinct nervous system, independent, to a certain extent, of the
I rain and spinal cord, and comprises it under the special de-
signation of the ORGANIC NERVOUS SYSTEM. Besides its con-
nections with the brain and spinal nerves, from which it receives
fasciculi, it is held to include peculiar organic fibres, the exist-
ence of which is problematical. The sympathetic appears much
rather to comprise no peculiar or intrinsic fibres. The grey
aspect of particular bundles depends on an admixture of gan-
glionic matter with their fibrils; the dirty reddish hue of other
nerves is connected with the presence of an unusual quantity
of highly vascular filamentous tissue, which often surrounds
single primary fibres abundantly. We have, in fact, no evi-
dence of the existence of any other than the ordinary motory
and sensitive fibres in the sympathetic, these being derived
from the other cerebral and spinal nerves, and being plentifully
surrounded in the different ganglia of the head, neck, thorax,
and abdomen, with ganglionic globules or cells. The primary
fibres seem at most only to become somewhat thinner in the
ganglions than they are beyond them. In this view, conse-
quently, the sympathetic nerve is virtually a cerebro-spinal
nerve, and such is the light in which it now begins to be very
generally regarded.

[§ 111. "From recent investigations, it appears certain that
the sympathetic receives twigs from the whole of the cerebral
nerves, except those of the three higher special senses — smell,
sight, hearing; and farther, from both the anterior and poste-
rior roots of the spinal nerves at large. The primitive fibrils
of the sympathetic form plexuses within its numerous ganglia,
and have numerous gauglionic corpuscles interposed between
them. They emerge unchanged from the ganglia, from which
no new or particular fibrils appear to originate.

fS 112. " Comparative anatomy brings many arguments in

NEKYOTJS SYSTEM AND GENERAL SE^SATIOIT. 53

favour of the view, that the sympathetic is nothing more than
a cerebro-spinal nerve. In the cyclostomes among fishes, the
sympathetic is either wholly, or in major part, replaced by the
par vagum, the eighth pair ; the same thing occurs among ser-
pents, in which, moreover, branches proceed directly from tha
spinal cord to the viscera. It is a remarkable anatomical fact
also, that in man and the mammalia, the lachrymal gland,
arid several other organs of secretion, such as the mammae,
are supplied with nerves directly from the cerebro-spinal sys-
tem, not mediately from the sympathetic.

[§ 113. "The nerves which the sympathetic supplies to the
viscera, are the instruments of their sensations and motions,
It is, for example, easy to demonstrate by experiment, that the
peristaltic motions of the intestines in the rabbit, dog, and
other animals, is powerfully and permanently increased by the
stimulation of the solar plexus, or of any particular branch
proceeding directly to the intestines. By other experiments of
the same kind, the motory power of other fibres, and their in-
fluence upon the viscera, can also be shown : the heart is ex-
cited by stimuli applied to the inferior cervical ganglion, and
also, but in a much inferior degree, by irritating the superior
thoracic ganglion. It has even been said, that the great vas-
cular trunks of the thorax and abdomen have been seen to
contract under the influence of stimuli applied to the thoracic
ganglia. Stimulation of the cervical ganglia induces contrac-
tions in the oesophagus ; and movements of the stomach follow
excitement of the four inferior cervical pairs, and of the two
superior thoracic ganglia. Many branches of the sympathetic
and other nerves minister to the motions of the small intestines.
Stimulation of the lower lumbar and superior sacral nerves is
followed by powerful contractions of the great intestines, urin-
ary bladder, uterus, and oviduct. The greater splanchnic nerve
having been stimulated in the horse, the ductus communis
choledochus has been seen to contract, and in birds this fact is
easily demonstrated, and very remarkable. In the same way,
motions have been observed in the ureters, on applying stimuli
to the abdominal ganglia, and to the roots of the abdominal
spinal nerves. The bladder receives its nerves principally from
the sacral portion of the sympathetic ; the vas deferens, and
vesiculae seminales, contract upon the two inferior lumbar
ganglia being stimulated.

54 NERVOUS SYSTEM A^D GENERAL SENSATION.

[§ 114. " If we agree, then, that the sympathetic in general
performs the functions of the cerebro-spinal nerves at large, we
must still admit that it exhibits numerous peculiarities. It not
only extends over all the vegetative organs of the abdomen,
and in part also of the thorax, but, by its fibrils detached
from the ganglia, it accompanies the great blood-vessels in their
course, and with these penetrates every part of the body. In
its motory, as well as hi its sensitive functions, it also exhibits
essential modifications : the motions of the parts to which it is
distributed are abstracted from the empire of the will. These
involuntary, and in the healthy state, unconscious, motions,
extend to the most remote structures with which it is in com-
munication, by means of ganglia, such as the iris, for example.
Reaction upon stimulation generally lasts longer than the sti-
mulus, which is exactly the reverse of what happens in refer-
ence to the muscles of voluntary motion, when the reaction so
constantly ceases before the stimulus is removed. The sensi-

*-

bility, as already observed, is extremely slight in the healthy
state. The conduction from the peripheral to the central parts,
has therefore undergone a manifest alteration, and even partial
interruption, as it would seem. The central parts receive no
impressions from the organs which are supplied with nerves
from the sympathetic ; and they have, farther, no power of
controlling the motions of these organs. These remarkable
effects can only be referred to the influence of the ganglions."*]
[§ 115. The nervous system of the articulata is arranged dif-
ferent from, that of the vertebrata. The absence of an internal
osseous skeleton in the former removes the nervous centres into
new relations : and accordingly, we find it associated with the
tegumentary and muscular systems, and ruled by the law which
regulates their development. We still, however, distinguish
cerebro-spinal, and sympathetic nerves. The brain is situated,
without exception, above the anterior extremity of the digestive
tube, and connected by two lateral trunks with the spinal
cord. Instead of being situated in the dorsal region of the body,
as in the vertebrata, it is found, on the contrary, without ex-
ception, along the abdominal line. This difference in the dispo-
sition of the nervous system constitutes one of the essential
characters distinguishing the two great primary subdivisions

* Wagner's Physiology, p. 512, et seq.

j^ERYOUS SYSTEM AND GENERAL SENSATION.

55

of the animal series. The number of the ganglia in the simpler
forms of the articulata, corresponds in general to the number of
the ringsof thebody : butin the
higher groups there is often a
fusion of two or more ganglia
into one. This change is well
exemplified in the development
of insects, spiders, and crus-
taceans : the spinal cord of
the articulata, like that of the
vertebrata, is composed of
motory and sensitive columns.
In insects, a special nervous
system, the sympathetic, is dis-
tributed to the organs of vege-
tative life. The annexed figure Fig 34-_The nervous system of
(34) shows the distribution of Carabus nemoralis, a garden beetle,
the cerebro-spinal system in a The cephalic ganglia supply nerves
beetle, Carabus nemoralis. to the eyes> antennae, parts of the

r& llfi Trirriprnnllnsra thp mouth, &c. ; the thoracic ganglia
p . in me monusca, me , neryes to the thorax> thethree

principal centre of the nervous pairs of legs and the wings . tne ab_
system surrounds the gullet, in dominal ganglia send branches to the
the form of a gangliated collar ; organs contained in the abdomen,
but it exhibits many phases of development in the different
classes of this sub-kingdom. In the CONCHIFERA, which are
acephalous, as the mussel (Mytilus edulis), distinct organs exist
for the ingestion of the food, respiration, and locomotion, and
each of these possesses ganglia, in immediate relation with the
function over which it presides. Hence we find —

1st. Msophageal ganglia, which surround the gullet, and re-
present the brain. These nerves proceed to the labial pro*
cesses, that serve for taste and touch.

2nd. Branchial ganglia presiding over the respiratory func-
tion. From these ganglia, likewise, the muscles concerned in
the act of respiration, the adductors of the shell, the folds of the
mantle, and the intestine are supplied.

3rd. Pedal ganglia vary with the presence or absence of a
foot for locomotion. The whole of these ganglia are united
into a nervous chain by connecting filaments.

In the GASTEEOPODA we observe a further development o<
the nervous system. They possess a head; and the brain

5b

KEEYOUS SYSTEM AST) GENERAL SE3 SATIOtf.

as in the river snail (Paludina vivipara), fig. 35, consists of
two oval lobes, u, u, united by a nervous commissure. From

the cerebral masses
nerves proceed to the
eyes, tentacules, and
mouth; another gan-
glionic centre, the pe-
VM " Sal, occupies thebody,
from which fibrils pass
to the muscular foot,
whilst other ganglia
supply the respiratory
and digestive organs.
In the CEPHALO-
PODA, as the cuttle-
fish, the brain is
still more developed.
Fig. 35. — The anatomy of Paludina vivi- Laro-e optic nerves are
para (river snail), a, the foot ; 6, the oper- distributedtothehigh-
culum, fixed to the posterior part of the | j i

foot ; d, the respiratory tube, prolonged under ty organised eyes, and
the right tentacule; g, the branchiae ; /, the
canal of the mucous organ ; n, the heart and
auricle ; p, the pharynx ; q', the second cur-
vature of the esophagus ; r', the stomach ; s, ~a~hTf the i tenta'cula
first turn of the intestine ; s', the second turn ; Ce.n1 La>

*", point where the intestine enters the bran- eight or ten in num-
chial cavity ; v, v, salivary glands ; u, u, supra- ber, that surround the
esophageal ganglions, which represent the head. We find, like-
brain ; x, principal nerve to the muscular en- wise m this class a

vel°Pe- rudimentary skull, in

the form of a cartilaginous plate, extended over the brain.
The ganglia placed beneath the esophagus are very large,
and give origin to many branches. Ganglia are moreover
scattered among the nutritive organs, which are regarded as
belonging to the sympathetic system.

§ 117. In the radiata, the nervous system is reduced to a
single ring, encircling the mouth. It differs essentially from
that of the mollusca, by its star-like form and horizontal posi-
tion. In the anatomy of Asterias aurantiaca (common sea-
star), fig. 36, the typical form of the nervous system of the
radiata is shown. We observe the mouth surrounded by a
nervous ring ; at the centre of each ray of the body is a

auditory nerves to the
rudimentary ears, and
branches are sent to

SYSTEM AJfD GENEBAL SENSATION.

57

ganglion, from which nerves proceed to the organs contained in
that segment of the animal. — T. \V.]

§ 117. The nerves
branch off and diffuse
sensibility to every por-
tion of the body, and
thereby animals are en-

v

abled to gain a know-
ledge of the general pro-
perties of the objects
which surround them ;
every point of the body
being made capable of
determining whether an
object is hot or cold, dry
or moist, hard or soft.
There are some parts,
however, the ends of the
fingers, for example, in
which this sensibility is
especially acute, and these
also receive a larger supply of nerves.

§ 118. On the contrary, those parts which are destitute of
sensibility, such as the feathers of birds, the wool of animals,
and the hair of man, are likewise destitute of nerves. But the
conclusive proof that sensibility resides in the nerves is, that
when the nerve which supplies any member of the body is
severed, that member at once becomes insensible.

§ 119. There are animals in which the faculty of percep-
tion is limited to this general sensation ; but their number is
small, and, in general, they occupy the lowest place in the
series. Most animals, in addition to the general sensibility,
are endowed with peculiar organs for certain kinds of percep-
tions, which are called the SENSES. These are five in number,
namely : sight, hearing, smell, taste, and touch-

Fig. 36. — The Anatomy of Asterias
aurantiaca.

58 SPECIAL SENSES.

SECTION II.

OF THE SPECIAL SENSES.

1. Of Sight.

§ 120. SIGHT is the sense by which light is perceived, and
by means of which, the outlines, dimensions, relative position,
colour, and brilliancy of objects are discerned. Some of these
properties may be also ascertained, though in a less perfect
manner, by the sense of touili. We may obtain an idea of
the size and shape of an obji-rf, by handling it ; but the pro-
perties that have a relation t-> light, such as colour and bril-
liancy, and also the form and size of bodies that are beyond
our reach, can be recognized by sight only.

§121. The EYE is the organ of vision. The number, struc-
ture, and position of the eyes in the body is considerably
varied in the different classes. But whatever may be their
position, these organs, in all the higher animals, are in con-
nection with particular nerves, called the optic nerves (fig. 13,
a). In the vertebrata, these are the second pair of the cerebral
nerves, and arise directly from the middle mass of the brain (fig.
20, b), which, in the embryo, is the most considerable of all.
§ 122. Throughout the whole series of vertebrate animals,

the eyes are only two in number,
and occupy bony cavities of the
skull, called the orbits. The
eye is a globe or hollow sphere,
formed by three principal mem-
branes enclosed one within the
other, and filled with transpa-
rent matter. Fig. 37 represents
a vertical section through the or-
gan, and will give an idea of the
relative position of these different
parts.

§ 1 23. The outer coat is called the sclerotic (b); it is a thick,
firm, white membrane, having its anterior portion transparent.
This transparent segment, which seems set in the opaque
portion, like a watch-glass in its rim, is called the cornea (/).
§ 124. The inside of the sclerotic is lined by a thin, dark
coloured membrane, the choroid (c). It becomes detached
from the sclerotic when it reaches the edge of the cornea,
and forms a curtain behind it. This curtain give- to the eye

or SIGHT. 59

its peculiar colour, and is called the iris (g). The iris readily
contracts and dilates, so as to enlarge or diminish the open-
ing in its centre, the piipil, according as more or less light
is desired. Sometimes the pupil is circular, as in man, the
dog, the monkey ; sometimes in the form of a vertical ellipse,
as in the cat ; or it is elongated transversely, as in the sheep.

§ 125. The third membrane is the retina (d). It is formed
by the optic nerve, which enters the back part of the eye by
an opening through both the sclerotic and choroid coats, and
expands into a whitish and most delicate membrane upon the
vitreous humour (h). It is upon the retina that the images of
objects are received, and produce impressions, which are con-
veyed by the nerve to the brain.

§ 126. The fluids which occupy the cavity of the eye are
of different densities. Behind, and directly opposite to the
pupil, is placed a spheroidal body, called the crystalline
lens (e). It is tolerably firm, perfectly transparent, and com-
posed of layers of unequal density, the interior being always
more compact than the exterior. Its form varies in the differ-
ent classes. In general, it is more convex in aquatic than in
land animals ; whilst with the cornea, it is the reverse, being
flat in the former, and convex in the latter.

§ 127. By means of the iris, the cavity (i) in front of the
crystalline is divided into two compartments, called the anterior
andi posterior chambers (?'). The fluid which fills these cham-
bers is a clear watery liquid, called the aqueous humour. The
portion of the globe behind the lens, which is much the largest,
is filled by a gelatinous liquid, perfectly transparent, like that
of the chambers, but somewhat more dense. This is called
the vitreous humour (ti).

§ 128. The mechanical structure of the eye may be
imitated by art ; — indeed, the camera obscura is an instru-
ment constructed on the same plan. By it, external objects
are pictured upon a screen, placed at the bottom of the
instrument, behind a magnifying lens. The screen repre-
sents the retina ; the dark walls of the instrument represent
the choroid ; and the cornea, the crystalline and the vitreous
humour combined, are represented by the magnifying lens. But
there is this important difference, that the eye has the power of
changing its form, and of adapting itself so as to discern, with
equal precision, very remote, as well as very near objects.

§ 129. By means of muscles which are attached to the

60 SPECIAL SENSES.

ball, the eyes may be rolled in every direction, so as to view
objects on all sides, without moving the head. The eyes are
usually protected by lids, which are two in the mammals, and
generally furnished with a range of hairs at their edges, called
eye-lashes. Birds have a third, or vertical lid, which is also
found in most reptiles, and a few mammals. In fishes, the
lids are wanting, or immovable.

DIOPTEICS OF THE HUMAN EYE.

[§ 130. " The rays of light which attain the retina, and there
unite to form images, must of course pass through the whole
of the refracting media described in the preceding paragraphs.
The refracting powers of these media, which are spoken of
collectively as the humours of the eye, differ in conformity
with the fashion, structure, density, and chemical constitution
of each.* These humours are farther the principal cause of
the form of the eye-ball, which not only differs in reference
to kinds, but also among individuals of the same kind. In
man, the eye-ball, in a general way, presents the form of an
ellipsoid open in front, where it is met and completed by a
small segment of a sphere engrafted upon it. The axis of the
eye corresponds with the optic or visual axis, and extends
from the centre of the cornea backwards to the foramen of
Soemmerring, a little to the outside of the point at which the
optic nerve makes its entrance. This optic axis of the eye
measures on an average from 10^ to 11 lines, arid differs from
the axis of the optic nerve which passes from the outer third
of the cornea, to the middle of the point of entrance of the
optic nerve, crossing the optic axis at an angle of about 20
degrees. In its general condition, the eye is so fashioned that
the rays which arrive from a point divergingly upon the
cornea, are immediately made to converge, and this in such
measure precisely, that they meet in a focus as they attain the
retina. It is of course the central ray alone of a pencil of
rays that passes through dioptric media unrefracted ; all the
other rays suffer refraction, and are approximated to the

* [We have various estimates of the refracting powers of the transparent
media of the eye, a summary of which is given by Weber in his edition of
Hildebrand's Anatomy, IV. 103. The numbers of the several humours of
the human eye, according to Brewster, are the following: Cornea, 1,386 ;
aqueous humour, 1,3366 ; lens, as a whole, 1,3767 ; middle portion of the
same, 1,3786; nucleus of ditto, 1,3999 (according to Young, 1,4025J ;
vitreous humour, 1,3394.]

OF SIGHT.

61

central ray. The rays composing a pencil falling upon the
cornea are refracted in different degrees by the transparent
media of the eye, in proportion to the difference between the
density of these media and that of the air, and in proportion
to the curves presented by their several surfaces. The rays
are in the first place refracted by the cornea, by the membrane
of the aqueous humour, and by the aqueous humour itself;
then, and very particularly, by the crystalline lens, and that
differently, by different strata of this body in the ratio of their
several densities ; finally, by the vitreous humour ; having
passed through which they have come to a focus, and reached
the retina at one and the same moment.

[§ 131. "When the object from which the rays of light
proceed has extent in space, — Fig- 38.

length and breadth, suppose, for
example, that it is the arrow a,
b, in fig. 38, then must the ob-
ject of necessity appear reversed
upon the retina c, d; that which is
superior in the object becomes in-
ferior, that which is to the right
appears to the left in the image.*
As every object emits rays from
every point in all directions, which
then proceed in straight lines, the
axal rays e, f, g, of the different
pencils proceeding from either end,
and the middle of the arrow, a, b,
must cross at some point within
the eye. Numerous observations
satisfy us that this point lies very
near the centre of the eye (h),
somewhat behind the crystalline
lens (#). The prime rays, e, f, g, which proceed from
the object may be^named, in reference to the eye, rays of
direction, because every prime or axal ray of a pencil de-
termines the direction of the* other rays, in order that all of
them may meet in a focus upon the retina. The point at

* [It is most easy to obtain conviction of this reversed position of objects
upon the retina, by taking the eye of a white rabbit, free from pigment,
clearing the globe from fat, muscles, &c., and then presenting it with the
cornea in front to the window ; all the objects before it, such as trees

62

SPECIAL SENSES.

Fig. 39,

which the rays must diverge, if a clearly defined image is to
be formed, is called the point of intersection, or focal centre.*
The position of this point is determinable, with the assistance of
an instrument for measuring angles ; it lies somewhat behind
the crystalline lens, and very near the centre of the eye. The
intersecting axal rays of two objective points (fig. 38) inclose
an angle (a, h, b, for the object a, b; i, k, h, for the object
i, k), which is called the visual angle. This angle diminishes
with the distance of the two objects from the eye, and the
retinal image is in the same proportion smaller. The arrow,
i, k, is only half the distance of the arrow, a, b, from the eye ;
the visual angle, i, h, k, is therefore twice as large as the angle
a, h, b, and the same thing is true in reference to the images
depicted upon the retina. It is on this account that objects of
different magnitudes seen at different distances, but of which the
visual angles are the same, form retinal images of the same size.
[§ 132. All images falling upon the retina through the

houses, &c., are perceived, forming a very elegant little picture, but re-
versed or upside down upon the posterior wall
of the transparent eye. If a simple or double
glass lens be now placed at a proper distance,
the reversed image which the objects refracted
by the crystalline lens form, may be projected
on a sheet of paper.

* [Volkmann instituted many very able
experiments upon the condition of retinal
images, and from this inferred the focal centre.
An experiment easily performed is the fol-
lowing : — Upon an horizontal table let a num-
ber of straight lines (fig. 39) a a', b b', &c.,
he drawn, all of which intersect at the point
c; upon this point, c, let a prepared white
rabbit's eye, E, Y, E, be so placed, that the
axis of the eye coincides with the line a7, d1.
If the anterior part of the cornea, Y. stand at
the due distance from c, then will objects at
a, &, d, e, /, form their appropriate retinal
images at a", 6", d", e," /". The chamber
being darkened, let tapers be placed at «, 6,
d, e, /, and the spectator look successively at
a, from a', at 6, from b', at d, from d\ cVc.,
and it will be found that the line of vision
will cut the retinal image of a, at a", of b, at
&", &c. The retinal images of the whole of
the tapers lie in straight lines, which intersect
at the focal point, c.

or SIGHT.

63

dioptrical media of the eye are appreciated, but all are not
seen with equal distinctness. Images appear by so much the
more indistinct, as they are formed more remotely from the
point upon which the optic axis of the eye falls. This point
corresponds very accurately to the foramen of Soemmerring.
Whether the peculiar distinctness of vision at this point de-
pends on the structure of the retina there, or is to be ascribed
to this, that in the usual position of the eyes their axes are so
directed towards objects, that the principal rays from these
strike through the centres of the lenses, remains doubtful.
The latter view is, however, the more probable. For as those
rays of a pencil of light that strike through the edges of the
lens must be differently refracted from those that pass through
its centre ; in consequence of the difference of density between
these edges and the centre, &c.> they cannot all unite in the
same focus ; hence there is unequal dispersion and ill-de-
fined images. It is not unimportant to observe, that we
do not in fact see more than a single point of an object
with perfect distinctness ; if we seem to take in more,
it is only from the rapidity with which Fig. 40.

the eyes travel and survey each point
in succession one after the other. In
surveying a picture closely, we are
conscious of this — we look at one part
after another ; at a distance, indeed, we
receive a general impression of the
work, but this is only because the rays
then come from the object at large in
a pencil so delicate, that it passes en-
tirely by the centre of the lens. There
is a particular circumscribed spot at the
bottom of the eye, corresponding to
the place of entrance of the optic nerve,
or, at all events, to the centre of this
part, which the arteria centralis retinae
perforates, where we have no sense of
visual perception.*

* Marrotti was the first who described the
disappearance of the visual image at the en-
trance point of the optic nerve. To make the
experiment, let two black objects be taken
and placed at a and b (fig. 40), upon a white

a 9

64

SPECIAL SENSES.

[§ 133. The motions of the eye are of great importance in
the act of vision. As in the steady contemplation of objects
we have to bring them into the focal centre of the produced
visual axis, we necessarily move the eye-ball in the act of
looking around and studying the details of objects successively,
according to determinate laws. It has been ascertained that
in this motion the eye-bah1 revolves accurately round a point, —
the point of revolution of the eye — which remains unaltered ;
it is at once the point of intersection of the rays of direction

Fig. 41 and of those of vision.

In this point (fig. 41),
a, in the appended di-
agram, all the diame-
ters of the eye inter-
sect, and many of
these diameters are at
the same time the
axes of revolution
with reference to the
actions of the muscles
of the eye. If the
two eyes be directed
to the points b and b\
'the axal rays fall upon
c and c'. Both eyes

m

then look forwards,
and also somewhat
convergingly, so that
the two axes b c, and
6' c', do not run pre-
cisely parallel, but diverge slightly, by which c and c' are
further from one another than b and b'. In the horizontal

ground. From the diagram it is seen that in the right eye, the spot, a, falls
upon the point of the retina, a', whilst the cross, b, falls in the middle of the
entrance point of the optic nerve, precisely where the central artery and
vein of the retina are situated. Now if the left eye be closed, and the
point a, and cross 6, are regarded at the usual distance for distinct vision,
the attention being, however, particularly directed to a, the cross b,
will be found to disappear the moment the pencil of rays proceeding
from it comes to fall upon the middle of the entrance place of the optic
nerve.

OF SIGHT. (55

transverse diameter, d e, which runs from the temporal to the
nasal side of the eye-hall, lies the axis of the organ in refer-
ence to the action of the superior and inferior straight muscles.
The perpendicular diameter passes from above downwards
through the point of revolution a, cutting the transverse
diameter at a right angle, and is at the same time the axis of
revolution of the internal and external straight muscles of the
eye. A line drawn from the outer margin of the cornea, ft to
the inside of the entrance place of the optic nerve, #, represents
the horizontal diagonal axis of the eye-ball, and is at the
same time the axis of revolution in reference to the two oblique
muscles. The superior oblique turns the pupil downwards
and outwards ; the inferior oblique turns it upwards and
outwards. The action of the whole muscles of the eye is pro-
ductive of no change in the position of the eye-ball, but only of
a revolution upon its axis. The faculty, however, which
enables us to judge of distances, and to adjust the eye so as to
obtain distinct vision at different distances, although it is pro-
bably only gradually acquired, is generally exerted uncon-
sciously. The power of thus accommodating the eye is pos-
sessed in very different degrees by different individuals ; it is
particularly remarkable in some of the higher animals ; and in
some men is either totally wanting or is reduced to a minimum.
Short-sightedness depends almost invariably on a loss of the
power of accommodation in the eye, as a consequence generally
of early and undue exercise of the organ upon objects close at
hand. This defect is therefore almost entirely confined to per-
sons in a certain rank of life, or having certain pursuits : the
majority of scholars and men of letters are short-sighted. In
the same way also far-sightedness is frequently an effect of the
want of the power of accommodation in the eye : sailors, who
are always looking at the horizon, are all but invariably far-
sighted. Both short-sightedness and far-sightedness are but
the limits to innumerable and individual departures from that
which may be held the standard in the structure of the eye.

[§ 134. There are many experimental ways of proving the
different positions which the images of near and distant objects
occupy upon the retina. One of the best known is that of
Scheiner,* which has been variously modified by different

* Father Sclieiner made this experiment more than two hundred years

7

ago: RWJ ur^ta, &c 1G2G— 29.

66

SPECIAL SENSES.

observers. If in a card (fig. 42, * *) two small holes be pricked,
over or to the side of one another, but not more distant than the

diameter of the pupil, A,
B, and a small object, such
as a pin, be looked at
through them, it will be
seen single only when it is
at a certain distance from
the eye, say at a ; for the
rays of the pencil which
proceeds from the object at
c, come precisely to a focus
upon the retina, at c. If
the pin be now placed at
b, the rays will centre at
g, in front of the retina, and
the object be then seen
double at d and f. The
same thing happens when
the pin is removed to a
greater distance than a,
say to e; the pencil of rays
in this case could only cen-
tre after their refraction by
the lens at h, far beyond
the retina, so that the sin-
gle object is necessarily
again seen double at i and
k. Double vision of this
kind sometimes occurs
along with partial opaci-
ties, streaks and specks of
the cornea.

[§ 135. Although there
are two images formed by
the refracting media upon
the retina of the two eyes,
still in ordinary vision we
see objects single, not double. This depends on the condi-
tion or quality of particular spots of the two retinae. Ob-
jects, to wit, are seen single when the axes of the two eyes
meet in the object contemplated. In this case the point fixed

OF SIGHT.

67

by the eyes, I, in the accompanying diagram (fig. 43), falls upon
the two terminal points of the two eyes' axes, a and I. The
points in the two eyes, A and B, which correspond or are
similarly situated, with reference to all surrounding points

m

are entitled IDENTICAL, inasmuch as they comport themselves
subjectively as if they were in reality but a single point, and
images impressed upon them excite in the mind the idea of
but one image. Besides these, there are other points of the
retina which are also identical or correspondent ; in other
words, which present single mental conceptions of double
retinal impressions ; but it is a law that the objects and cor-
responding points of the retina rnnst lie in a certain circle,

SPECIAL SENSES.

which is designated the HOEOPTER, — a circle (fig. 43) which
passes at once through the point of coincidence, /, of the visual
axes, I a, I b, and the points of decussation, c c\ of these axes
with the lines of direction.]*

§ 135. The eye constructed as above described, is called a
simple eye, and belongs more especially to the vertebrate ani-
mals. In man, it arrives at its highest perfection. In him,
the eye also performs a more exalted office than mere vision.
It is a mirror in which the inner man is reflected. His pas-
sions, his joys, and sorrows, are reflected with the utmost
fidelity, in the expression of his eye, and hence it has been
called " the window of the soul."

§ 136. Many of the invertebrate animals have the eye con-
structed upon the same plan as that of the vertebrate animals ;
the optic nerves, which form the retinae, are derived from the
cephalic ganglia, a nervous centre analogous to the brain.
The eye of the cuttle-fish contains all the parts essential to
that organ in the superior animals, and, what is no less im-
portant, the eyes are only two in number, and placed upon the
sides of the head.

§ 137. The snail and kindred animals have, in like manner,
only two eyes, mounted on the tip of a long stalk (the ten-
tacle), or situated at its base, or on a short pedicle by its side.
Their structure is less perfect than in the cuttle-fish, but still
there is a crystalline lens, and more or less distinct traces of

v

the vitreous body. Some bivalved mollusca, the pectens for
example, have a crystalline lens, but instead of two eyes, they
are furnished with numerous eye spots, which are arranged
like a border around the lower margin of the animal.

§ 138. In spiders, the eyes are likewise simple, and usually
eight in number. These little organs, called ocelli, instead of
being placed on the sides of the body or of the head, occupy
the anterior part of the cephalo-thorax. All the essential parts
of a simple eye, the cornea, the crystalline lens, the vitreous
body, are found in them, and even the choroid, which presents
itself in the form of a black ring around the crystalline lens.
Many insects, in their caterpillar state, have also simple eyes.

§ 139. Rudiments of eyes have likewise been observed in
many worms. They generally appear as small black spots
on the head ; such as are seen on the head of the leech, the

* Professor \Vagner 's Physiolcy. p. 577 — 585.

OP SIGHT.

planaria and the nereis. In these latter animals there are
four spots. According to Miiller, they are small bodies,
rounded behind, and flattened in front, composed of a black,
cup-shaped membrane, containing a small white, opaque body,
which seems to be a continuation of the optic nerve. It cannot
be doubted, therefore, that these are eyes ; but as they lack
the optical apparatus which produces images, we must suppose
that they can only receive a general impression of light, with-
out the power of discerning objects.

§ 140. Eye-spots very similar to those of the nereis are
found at the extremity of the rays of some of the star fishes ;
in the sea-urchins they are placed around the border of the
apical disc, and at the margin of many medusae, and in some
polyps. M. Ehrenberg has shown that similar spots also exist
in a large number of the infusoria.

§ 141. In all the animals mentioned above, the eyes, what-
ever their number, are apart from each other. But there is
still another type of simple eyes, known as aggregate eyes.
In some millipedes, the pill-bugs, for instance, the eyes are
collected into groups, like those of spiders ; each eye inclosing
a crystalline lens and a vitreous body, surrounded by a retina
and choroid. Such eyes consequently form a natural transi-
tion to the compound eyes of insects and Crustacea, to which
we now give our attention.

§ 142. Compound eyes have the same general form as simple
eyes ; they are placed either on the sides of the head, as in
insects, or supported on pedicles, as in crabs. If we examine
an eye of this kind by a magnifying lens, we find its surface com-
posed of an infinite number of
angular, usually six-sided facettes
(fig. 44) . If these facettes are re-
moved, we find beneath, a corre-
sponding number of cones (c),
side bv side, five or six times as

V

long as they are broad, and ar-
ranged like rays around the op-
tic nerve, from which each one
receives a little filament, so as to
present, according to Midler,
the following disposition. The
cones are perfectly transparent,
hut separated from each other by walls of pigment, in such.

Fig. 44.

TO SPECIAL SENSES.

a manner, that only those rays -which are parallel to the axes
can reach the retina (A) ; all those which enter obliquely are
lost ; so that of all the rays which proceed from the points a
and b, only the central ones in each pencil act upon the
optic nerve, d : the others strike against the walls of the
cones. To compensate for the disadvantage of such an ar-
rangement, and for the want of motion, the number of fa-
cettes is greatly multiplied, so that no less than 25,000 have
been counted in a single eye. The image on the retina, in this
case, may be compared to a mosaic, composed of a great num-
ber of small images, each of them representing a portion of
the figure. The entire picture is, of course, more perfect, in
proportion as the pieces are smaller and more numerous.

§ 143. Compound eyes are destitute of the optical appa-
ratus necessary to concentrate the rays of light, and cannot
adapt themselves to the distance of objects ; they see at a cer-
tain distance, but cannot look at pleasure. The perfection of
their sight depends on the number of facettes or cones, and the
manner in which they are placed. Their field of vision is wide,
when the eye is prominent ; it is very limited, on the contrary,
when the eye is flat. Thus the dragon-flies, on account of the
great prominency of their eyes, see equally well in all direc-
tions, before, behind, or laterally, whilst the water-bugs, which
have the eyes nearly on a level with the head, can see to only
a very short distance before them.

§ 144. If there be animals destitute of eyes, they are either
of a very inferior rank, such as most of the polyps, or else
they are animals which live under unusual circumstances,

V

such as the intestinal worms. Even among the vertebrata,
there are some that lack the faculty of sight, as the Myxine
ylutinosa, which has merely a rudimentary eye concealed under
the skin, and destitute of a crystalline lens. Others, which
live in darkness, have not even rudimentary eyes, as, for ex-
ample, that curious fish (AmUyopsis spelceus), which lives in
the Mammoth cave, and which appears to want even the
orbital cavity. The crawfishes (Astacus pelhicidus) of this
same cavern are also blind ; having merely the pedicle for the
eyes, without any traces of facettes.

2. OF HEARING.

§ 145. To hear, is to perceive sounds. The faculty of per-
ceiving sounds is seated in a peculiar apparatus, the EAE, which

OF HEABDfG.

if? constructed with a view to collect and augment the sonorous
vibrations of the atmosphere, and convey them to the acoustic
or auditory nerve (fig. 45, 0), which arises from the posterior
part of the brain (fig. 20).

§ 146. The ears never exceed two in number, and are placed,
in all the vertebrata, at the hinder part of the head. In a
large pro-
portion of
animals,
as the dog,
horse, rab-
bit, and
most of the
mammals,
the exter-
nal parts of
the ear are
generally
quite con-
spicuous,
and as they
are at the
same time
moveable,
they be-
come one
of the pro-
minent
features of
the physi-
ognomy.

§ 147.
These ex-

Fig. 45. — Vertical Section of the Organ of Hearing in
Man. — The internal parts are enlarged, to make them more
evident, a, b, c, the external ear ; d, the entrance to the
auditory canal,/; e, e, petrous portion of the temporal bone,
in which the internal ear is excavated ; g, membrane of the
tympanum ; h, cavity of the tympanum, the chain of bones
tp"*nnl n" being removed ; i, openings from the cavity into the cells,
j, excavated in the bone ; on the side opposite the mem-
pendages, brana tympani are seen the foramen ovale and foramen ro-
however, tundum ; k, the Eustachian tube ; /, the vestibule ; m, the se-
micircular canals ; n, the cochlea ; o, auditory nerve ; p, the
canal for the passage of the carotid artery to the brain ; g,
part of the glenoid fossa, for receiving the head of the lowr-r
jaw ; r, the style-like process of the temporal bone, which
gives attachment to muscles ; s, the mastoid process of the

do not,
properly
speaking,
constitute

the organ temporal bone.

72 SPECIAL SENSES.

of hearing. The true seat of that sense is in the interior of
the head. It is usually a very complicated apparatus, espe-
cially in the superior animals. In mammals it is composed of
three parts ; the external ear, the middle ear, and the internal
ear, as shewn in fig. 45.

§ 148. The external ear consists of the conch («), and the
canal which leads from it, the external auditory passage (c, rf).
The first is a gristly expansion, in the form of a horn or a
funnel, the object of which is to collect the waves of sound ;
for this reason, animals prick up their ears when they listen.
The ear of man is remarkable for being nearly immoveable ;
therefore, persons whose hearing is deficient employ an arti-
ficial trumpet, by which they collect vibrations from a much
more extended surface. The external ear is peculiar to mam-
mals, and is wanting even in some aquatic species, such as
the seals and the ornithorynchus.

§ 149.. The middle ear has received the name of the tym-
panic cavity (h}. It is separated from the auditory passage
by a membranous partition, the tympanum or drum (y) ;
thoughit still communicates with the open air by means of anar-
row canal, called the Eustachian tube (k), which opens at the
back part of the mouth. In the interior of the chamber, are four
little bones of singular forms, which anatomists have distin-
guished by the names of malleus (fig. 49, «), incus (6), stapes

P. ,c (d), and os orbiculare (c] ; which are articulated
rig. 4b. t v / • ,.

together, to form a continuous chain „

[The malleus, or hammer (fig. 46), has a rounded
head (1), a smooth articular surface connected by
a short neck (2) with the shaft of the bone,
which has a short process (3). The shaft or
handle (4) is lengthened and curved, and from
the front thereof proceeds a long delicate pro-
Fig. 47. cess (5).

The incus, or anvil (fig. 4 7), resembles a bicuspid
tooth; its head (l)is hollowed out to receive the
head of the malleus ; the short process (2) serves
for the attachment of a ligament ; and the long
process (3) for its articulation with the orbicular
bone, which is early soldered to it.

The stapes, or stirrup (fig. 48), is placed horizontally, with its
base resting upon the foramen ovale, and its head articulated

OF HEARING.

73

with the round nodule at the extremity of the long process
of the incus ; the base of the bone (3) is of the ri ,g
same figure as the foramen ; the lateral walls
of the arch (2, 2) are connected by a mem-
brane, and surmounted by a small head (1),
which articulates with the os orbiculare. These
four bones, when united together, form a chain, as shown
in fig. 49, where the membrane of Fig. 49.

the tympanum is seen at (1), and
a, h, c, (I, are the bones by which
the membrane of the tympanum
is connected with that of the fo-
ramen ovale, the handle of the mal-
leus being attached to the tympanum,
and the base of the stapes being ap-
plied to the vestibular membrane.
The motions of this chain are regu-
lated by four small muscles, three of
which are inserted into the malleus, an d
one is attached to the stapes. — T. W. J

§ 150. The internal ear, which is also denominated the
labyrinth, is an irregular cavity formed in the most solid part
of the temporal bone, beyond the chamber of the middle ear}
from which it is separated by a bony partition, and per-
forated by two small holes, called, from their form, the round
and the oval apertures, the foramen rciundum and the fora-
men ovale,
/.(fig. 45).
The first
is closed
by a mem-
brane simi-
lar to that
of the tym-
panum,
while the
latter is

closed by

the stapes. %' ^0.— Relative situation of the Tympanum and Labyrinth.

[The relative position of the tympanum and labyrinth is
shown in figure 50. (1), is the tympanum, with its tubes

74

SPECIAL SENSES.

and bony chain; (1 1), A, the labyrinth, in which the nervous
expansion floats; B, the semicircular canals; andC, the cochlea.
The labyrinth is the true auditory organ, and is more or less
developed wherever audition exists as a special sense. Com-
parative anatomy shows many phases of structure in this
intricate apparatus.

[§ 151. The labyrinth is situated (fig. 45) I, m, in the most
solid portion of the temporal bone : it consists of three portions
(fig. 51); the vestibule (a) ; the semicircular canals (5) ; and
the cochlea (c).

Fig. 51. — Views of Labyrinth.

Posterior.

Anterior.

Inferior.

surface.

Posterior.

canals.

Anterior.

[§ 152. The vestibule (Fig. 51, a) is placed at the inner side of

the drum, with which it corn-
Fig. 52.— Vertical Section ; internal rnunicates by the oval hole (fig.

on Wo /in . J, ill

52, 11) ; it is surrounded by
the cochlea and semicircular
canals. This small chamber is
about the size of a grain of
wheat; into it open the five am-
pulla of the semicircular ca-
nals (19, 19, 19, 19, 19) ;
the opening for the passage of
the auditory nerve (20) ; on
the fore and under part is a hole leading to the cochlea (21);

,,. B • • i and behind is the aqueduct of the ves-

Elg. 53. — Semicircular ., , ,__,.

tibule (22).

[§ 153. The semicircular canals (fig.
53, 6) rise from the superior and pos-
terior part of the vestibule, immediately
behind the tympanum. They are three
in number, in the form of tubes, with
flask-like swellings at their extremities.
From their position they are named the
vertical, or superior (23) ; the oblique,
or posterior (24) ; and the horizontal, or
Anterior View. inferior (25). As two of the canals ter-

OF HEABIffG.

75

ruinate in a common orifice, there are only five openings from
them into the vestibule. Fig. 54 exhibits a section of the
semicircular canals.

Fig. 54. — Section of
Canals.

^7.

Fig. 55. — Views of the Cochlea.

in-

Anterior internal

Surface. Base' APex'

[§ 154. The cochlea (fig. 51, c, and 55) is a singular organ, in
form very like the shell of a garden snail. Its cavity (fig. 56) is
divided by a longitudinal partition, half os-
seous and half membranous, called the spi-
ral lamina (fig. 57, 29), which makes two
and a-half turns round a central pillar, the
modiolus (fig. 58, 26), the apex of which
is called the cupola (28). One of these

passages (fig. 57, 33) leads to the fora- Fig. 5 6. -Anterior _
men ovate (22), of the vestibule, and is ternal surface of spiral
called scala vestibuli; the other (32) ter- tube; the lamina spiralis
minates in the foramen rotundum of the removed,
tympanum, and is called scala tympani.
These passages are freely perforated, to
give transit to filaments of the auditory
nerve, which enters the cochlea through
the cribriform base of the central pillar

(fig. 58, 35). The whole of the internal

ear is filled with a limpid fluid, perilymph, Fig. 57. — Lamina spi-
in which the membranous and nervous ralis; the external shell
parts of the semicircular canals and coch- of the cochlea removed,
lea are suspended. This membranous labyrinth contains a
similar fluid, the endolymph.* — T. W.]

§ 155. By this mechanism, the vibrations of the air are
first collected by the external ear, whence they are conveyed
along the auditory passage, at the bottom of which is the tym-

* The figures of the internal ear, the last excepted, are copied from
Soemmering.

76 SPECIAL SENSES.

panum. The tympanum, by its delicate elasticity, augments
the vibrations, and transmits them to the internal ear, partly by

means of the little bones in the chamber,
which are disposed in such a manner that
the stapes exactly fits the oval aperture
(foramen ovale) ; and partly by means of
the air which strikes the membrane cover-
ing the round aperture (foramen rotun-
duiri), and produces vibrations there, cor-
responding to those of the tympanum.
Fie 58*— Horizontal After all these modifications, the sonorous
section through tube, vibrations arrive at last at the labyrinth
lamina, modiolus, and and the auditory nerve, which transmits
meatus internus. the impression to the brain,

§ 156. The mechanism of hearing is not so complicated
in all classes of animals, but is found to be more and more
simplified, as we descend the series. In birds, the middle
and internal parts of the ear are constructed on the same
plan as in mammals , but the outer ear no longer exists, and
the auditory passage, opening on a level with the surface of
the head behind the eves, is surrounded onlv by a circle of

«/' V V

peculiarly formed feathers. The bones of the middle ear are
also less numerous, there being generally but one.

[The owls have a large membranous crescentic fold, provided
with tufts of short feathers, and which can be used as a valve.
The largest ear-conch is met with in the long-tufted hibou
(Strix otus). A true chain of ossicles may be distinguished in
the tympanum, one of which is style-shaped and bony, while
the others remain in a cartilaginous state. The principal bone
represents the stapes : its base forms an oval plate, which is
applied to the foramen ovale, and through this the sonorous
vibrations are transmitted to the aqueous fluid of the labyrinth.
Only one muscle can be detected for moving the ossicles, which
is thought to represent the laxator of the tympanum. The la-
byrinth consists of compact bony walls, surrounded by spongy
osseous tissue. The vestibule is small ; the semicircular canals
are large, and vary in size, being broad and elevated in rapa-
cious and passerine birds, and thick and depressed in the
grallae, gallinse, and palmipedes. The cochlea consists of a
sh°:htlv curved osseous cone. In the membranous sac of the

fc,

vestibule minute masses of crystallized phosphate of lime (oto-
iithsj are found, as in mammals. — T. W.J

OF HEAEIXG. ', 7

§ 157. In reptiles, the external ear disappears ; the auditory
passage is wanting, and the tympanum becomes external. In
some toads, the middle ear also is completely wanting. The
fluid of the vestibule is charged with salts of lime, which
frequently give it a milky appearance, and which, when exa-
mined by the microscope, are found to be composed of an infi-
nite number of crystals.

[The tympanic cavity is absent in the proteus and salaman-
der, and both the skin and muscles are continued over the ex-
ternal ear. The foramen ovale is closed by a cartilaginous
operculnm, on which is inserted a style-shaped ossicle, called
columella, regarded as the four bones soldered into one.
The Eustachian tube is absent : the tympanic cavity is also
absent in serpents. In frogs it consists of a membranous
chamber, which commences by a funnel-shaped cartilaginous
ring, upon which a naked membrana tympani is stretched.
The colurnella rests its oval base on the foramen ovale, and its
gristly head on the tympanum. In the crocodile, the rudiment
of an external ear exists in the form of a tegumentary fold,
containing a bony plate, and which can be made to shut
down, like a valve, by a muscle. The internal ear presents nu-
merous phases of development in the different groups of rep-
tiles : in all it is lined by a membrane, and separated from the
cranial cavity. The vestibule varies in form and size, and con-
tains crystalline cretaceous masses, or otoiiths : the semi-
circular canals expand into ampullee : the cochlea is absent
in frogs and salamanders, but exists in serpents, tortoises, and
lizards, in the form of a hollow cone, with a blunt and dilated
apex ; it includes a pair of cartilages, covered by a plicated
membrane, turned towards each other, and upon which the
auditory nerve expands its delicate fibrils, as upon the lamina
spiralis of the human ear. — T. \V.]

§ 158. In fishes, the middle and external ear are both want-
ing ; and the organ of hearing is reduced to a membranous
vestibule, situated in the cavity of the skull, and surmounted
by semicircular canals, from one to three in number. The liquid
of the vestibule contains chalky concretions of irregular forms,
the use of which is doubtless to render the vibration of sounds
more sensible.

[The structure of the organ of hearing m this class exhibits
an interesting series of gradations, ranging from the simple
primitive type of the invertebrata, to the more complicated

78 SPECIAL SENSES.

mechanism described in amphibious reptiles. In osseous
fishes, the membranous labyrinth lies for the most part full
within the cranial cavity, and adjacent to the brain ; or it
is only imperfectly and partially enclosed in bones, as the
skin and muscles are continued over the skull. The sonorous
vibrations propagated by the water are communicated through
the walls of the cranium, as no openings exist for the special
reception of waves of sound. The labyrinth consists — 1st, of
a simple vestibule, or transparent sac, which receives the am-
pullae of the arched canals, and is provided with nervous
expansions : 2nd, the auditory sac is separated from the
vestibule by a partition, and divided into two chambers, which,
with the vestibule, contain the ossicles and calcareous parts,
surrounded by the fluid of the labyrinth : 3rd, the semicircular
canals, which are more or less developed in different genera,
and open by ampullse into the vestibule. In the rays and
sharks, the labyrinth is separated from the cranial cavity, and
imbedded in a mass of cartilage, which is more solidified around
the membranous labyrinth. We find two openings, closed by
membranes, on each side of the skull, which communicate with
the internal ear, and represent the round and oval foramina of
the labyrinth. Between each of these openings and the integu-
ment a membranous sac is placed, which is filled with a calca-
reous mass, and extends into the membranous vestibule. A pair
of otoliths, composed of the carbonate of lime, are appended to
the walls of the sacs. Osseous fishes are furnished with three
of these concretions, almost as hard as porcelain: one is lodged
in the vestibule, the others occupy the chambers of the sac.
In the cyclostome fishes, as the petromyzon, the ear is simple,
consisting of a cartilaginous part, and a pair of hard yellow
oval capsules, connected with the skull, and enclosing, like a
bony labyrinth, a membrane lining the same, and having in-
terposed between them a fibro-membranous layer. The mem-
brane of the labyrinth consists of a small sac, divided into two
cells, two wide depressed semicircular canals, which enter the
vestibule by one common ampulla, a rudimentary auditory sac,
which appears as an appendage to the vestibule. The auditory
nerve sends two branches to supply the labyrinth. In the
myxine the ear is still more simple : the auditory capsule is filled
with a membranous labyrinth, within which a single arched
canal is blended with the vestibule. Otoliths and calcareous

OP HEAEING. 79

salts are not found in the labyrinth of cyclostomes, although
such bodies exist in the cuttle-fish, among the invertebrata.
No vestige of an auditory organ has been detected in the am-
phioxus, which forms, in this respect, an exception to the law
which prevails in all other vertebrata. — T. W.]

§ 159. In crabs, the organ of hearing is found at the lower
surface of the head, at the base of the large antennae. It is a
bony chamber, closed by a membrane, in the interior of which
is suspended a membranous sac, filled with fluid. On this sac
the auditory nerve is expanded. In the cuttle-fish, the vesti-
bule is a simple excavation of the cartilage of the head, contain-
ing a little membranous sac [and otolith], in which the auditory
nerve terminates.

§ 160. Finally, some insects, as, for instance, the grass-
hopper, have an auditory apparatus, no longer situated in the
head, as with other animals, but in the legs ; and from this fact
we may be allowed to suppose, that if no organ of hearing has
yet been found in most insects, it is because it has been sought
for in the head only.

[Much doubt exists as to the true seat of the organ of
hearing in insects. Treviranus thought it was situated in
Blatta orientalis, at the base of the antennae. Ramdohr con-
sidered a vesicle placed at the base of the jaws of the bee as an
organ of hearing. Straus-Durckheim thinks the seat of this
sense in the cockchaffer is in the plates of the antennae.
D'Blainville thought that certain vesicles situate in the sides of
the body, and covered by a membrane, were organs of audition.
These differences of opinion about a matter of fact, is a proof
that we as yet possess no certain knowledge of the true seat of
this sense, although there can be no doubt that insects hear. —
T.W.]

§ 161. It appears from these examples, that the part of the
organ of hearing uniformly present, is that in which the audi-
tory nerve ends ; this, therefore, is the essential part of the
organ. The other parts of the apparatus, the tympanum,
auditory passage, and the semicircular canals, have for their
object merely to aid, with more precision and accuracy, the
perception of sound. Hence we may conclude, that the sense
of hearing is dull in animals where the organ is reduced to
its most simple form ; and that animals which have merely
a simple membranous sac, without a tympanum and audi-

80 SPECIAL SENSES.

tory passage, as fishes, or without semicircular canals, as crabs,
perceive sounds in a very imperfect manner.

3. OF SMELL.

§ 162. SMELL is the faculty of perceiving odours, and is
a highly important sense in many animals. Like sight and
hearing, smell depends upon special nerves, the olfactory, which
form the first pair of cerebral nerves (fig. 20, z), and which,
in the embryo, are direct prolongations of the brain.

§ 163. The organ of smell is the NOSE. Throughout the
series of vertebrata it makes a part of the face, and in man, by
reason of its prominent form, it becomes one of the dominant
traits of his countenance ; in other mammals, the nose, by de-
grees, loses this prominency, and the nostrils no longer open
downwards, but forwards. In birds, the position of the nos-
trils is a little different ; they open farther back, and higher
up, at the origin of the beak.

§ 164. The nostrils are usually two in number — some fishes

j «/

have four. They are similar openings, separated by a partition
upon the middle line of the body. In man and the mammals,
the outer walls of the nose are composed of cartilage ; but
internally, the nostrils communicate with cavities situated in
the bones of the face and forehead. These cavities are lined
by a thick membrane, the pituitary, on which are expanded
the olfactory nerves, [and some filaments of the fifth pair.]

§ 165. The process of smelling is as follows. Odours are
particles of extreme delicacy, which escape from very many
bodies, and are diffused through the air. These particles make
an impression on the nerves of smell, which transmit the im-
pressions to the brain. To facilitate the perception of odours,
the nostrils are placed in the course of the respiratory passages,
so that many of the odours diffused in the air, which are in-
spired, pass over the pituitary membrane.

§ 166. The acuteness of the sense of smell depends on the
extent to which that membrane is developed. Man is not so well
endowed in this respect as many mammals, which have the in-
ternal surface of the nostrils extremely complicated. Such is
especially the case among the carnivora.

§ 167. The sense of smell in reptiles is less delicate than
m mammals; their pituitary membrane being less developed.

OF TASTE. 81

Fishes are probably still less favored in this respect. As they
perceive odours through the medium of water, we should anti-
cipate that the structure of their apparatus would be different
from that of animals which breathe air. Their nostrils are
mere superficial pouches, lined with a membrane gathered into
folds, which generally radiate from a centre, but are sometimes
arranged in parallel ridges on each side of a central band. As
the perfection of smell depends on the amount of surface ex-
posed, it follows that those fishes which have these folds most
multiplied are also those in which this sense is most acute.

§ 168. No special apparatus for smell has yet been found
in the invertebrata. And yet there can be no doubt that insects,
crabs, and some mollusca perceive odours, since they are at-
tracted from a long distance by the odour of objects. Some of
these animals may be deceived by odours similar to, those of
their prey ; which clearly shows that they are led to it by this
sense. The carrion fly will deposit its eggs on plants which
have the smell of tainted flesh.

4. Or TASTE.

§ 169. TASTE is the sense by which the flavour of bodies is
perceived. That the flavour of a body may be perceived, it
must come into immediate contact with the nerves of taste,
and hence these nerves are distributed at the entrance to
the digestive tube, on the surface of the tongua and the palate.
By this sense animals are guided in the choice of their food,
and warned to abstain from what is noxious. There is an
intimate connexion between taste and smell, so that both
these senses are called into requisition in the selection of
food.

§ 1/0. The nerves of taste are not so strictly special as those
of sight and hearing. They do not proceed from one single
trunk ; and, in the embryo, do not correspond to a particular
part of the brain. The tongue receives nerves from several
trunks ; and taste is perfect in proportion as the nerves which
go to the tongue are more minutely distributed. The extremi-
ties of the nerves generally terminate in the little asperities of
the surface, called papillce. Sometimes these papillae are very
harsh, as in the cat and the ox ; and, again, they are very deli-
cate, as in the human tongue, in that of the dog, horse, &c.

§ 171. Birds have the tongue cartilaginous, sometimes be-

o

82 SPECIAL SENSES.

set with little stiff points ; sometimes fibrous, and fringed at
the edges. In the parrots, it is thick and fleshy ; or it is even
harbed at its point, as in the woodpeckers. In some reptiles,
the crocodile, for example, the tongue is adherent; mothers, on
the contrary, it is capable of extensive motion, and serves as an
organ of touch, as in the serpents ; or it may be thrust out to a
great length, to take prey, like that of the chameleon, toad, and
frog. In fishes it is usually cartilaginous, as in birds, and is
generally adherent, and has its surface frequently covered with
teeth.

§ 1/2. It is to be presumed, that in animals which have a
cartilaginous tongue, the taste must be very obtuse, especially
in those which, like most fishes, and many granivorous birds,
swallow their prey without mastication. In fishes, especially,
the taste is very imperfect, as is proved by their readily swal-
lowing artificial bait. It is probable that they are guided in
the choice of their prey by sight, rather than by taste or smell.

§ 173. Some of the inferior animals select their food with
no little discernment. Thus, flies will always select the sugary
portions of bodies. Some of the mollusca, as the snails, for
example, are particularly dainty in the choice of their food. In
general, taste is but imperfectly developed, except in mam-
mals, and they are the only animals which appear to enjoy the
flavour of their food. With man this sense, like others, may be
greatly improved by exercise ; and it is capable of being brought
to a high degree of delicacy.

5. OF TOUCH.

§ 174. The sense of TOUCH is merely a peculiar* manifesta-
tion of the general sensibility, seated in the skin, and depend-
ent upon the nerves of sensation which expand over the surface
of the body. By the aid of this general sensibility, we learn
whether a body is hot or cold, wet or dry. We may also, by
simple contact, gain, to a certain extent, an idea of the form
and consistence of a body, as, for example, whether it be sharp
or blunt, soft or hard.

§ 175. This faculty resides more especially in the hand,
which is not only endowed with a more delicate tact, but,
owing to the disposition of the fingers, and the opposition of
the thumb to the others, is capable of so moulding itself
around objects, as to multiply the points of contact. Hence

THE TOICE. 83

touch is an attribute of man rather than of other animals ; for
among these latter, scarcely any, except the monkeys, have
the faculty of touch in their hands, or, as it is technically
termed, of palpation.

§ 1/6. In some animals, this faculty is exercised by other
organs. Thus the trunk of the elephant is a most perfect or-
gan of touch ; and probably the mastodon, whose numerous
remains are found scattered in the superficial layers of the earth's
crust, was furnished with a similar organ. Serpents make use
of their tongue for touch ; insects employ their palpi, and
snails their tentacles for the same purpose.

6. THE VOICE.

§ 177. Animals have not only the power of perceiving, but
many of them have also the faculty of producing sounds of
every variety, from the roaring of the lion to the song of the
bird as it salutes the rising sun. It is moreover to be remarked,
that those which are endowed with a voice, likewise have the
organ of hearing well developed.

§ 1/8. Animals employ their voice, either for communica-
tion with each other, or to express their sensations, en-
joyments, or sufferings. Nevertheless, this faculty is pos-
sessed by a small minority of animals : with but very few
exceptions, only mammals, birds, and a few reptiles, are en-
dowed with it. All others are dumb. Worms and insects
have no true voice ; for we must not mistake for it the buzzing
of the bee, which is merely a noise created by the vibration
of the wings ; nor the grating shriek of the locust, caused by
the friction of his legs against his wings ; nor the shrill noise
of the cricket, or the tell-tale call of the ratydid, produced by
the friction of the wing covers on each other. And in nu-
merous similar cases which might be cited.

§ 1/9. Consequently, were mammals, birds and frogs, to
be struck out of existence, the whole animal kingdom would
be dumb. It is difficult for us, living in the midst of the
thousand various sounds which strike the ear from all sides,
to conceive of such a state. Yet, such a state did doubtless
prevail for thousands of ages on the surface of our globe, when
the watery world alone was inhabited, and before man, the
mammals, and birds were called into being.

G2

84

SPECIAL SENSES.

-o

•m

§ 180. In man and the mammals, the voice is formed in <*u
Fig. 59. organ called the larynx, situated at the upper
part of the windpipe, below the bone of the
tongue (a). The human larynx, the part called
n Adam's apple, is composed of several cartilagi-
nous pieces, called the thyroid cartilage (6), the
cricoid cartilage (c), and the small arytenoid car-
tilages. Within these are found two large folds
of elastic substance, known by the name of the
vocal cords (m). Two other analogous folds,
the superior ligaments of the glottis (n), are situated a little
above the preceding. The glottis (o) is the space between
these four folds. The arrangement of the vocal cords, and of
the interior of the glottis' in man, is indicated by dotted lines
in fig. 59.

§181. The mechanism of the voice is as follows : the air, on its
way to the lungs, passes the vocal cords. So long as these are in
repose, no sound is produced ; but the moment they are made
tense, they narrow the aperture, and oppose an obstacle to the
current of air, and it cannot pass without causing them to
vibrate. These vibrations produce the voice ; and as the vocal
cords are susceptible of different degrees of tension, these

Fig. 60.

tensions determine different sounds ;
giving an acute tone when the ten-
sion is great, and a grave and dull
one when the tension is feeble.

§ 182. Some mammals have, in ad-
dition, large cavities which commu-
nicate with the glottis, and into which
the air reverberates, as it passes the
larynx. This arrangement is espe-
cially remarkable in the howling mon-
keys, which are distinguished above
ah1 other animals, for their deafening
howls.

§ 183. In birds, the proper larynx
is very simple, destitute of vocal cords,
and incapable of producing sounds ;

but at the lower end of the windpipe there is a second or infe-
rior larynx, which is very complicated in structure. It is a
kind of 'bony drum (fig. 60 a), having within it two glottides,

i-f

THE VOICE.

formed at the top of the two branches (b,b) of the windpipe (c).
each provided with two vocal cords. The different pieces of this
apparatus are moved by peculiar muscles, the number of which
varies in different families. In birds which have a very mono-
tonous cry, such as the gulls, the herons, the cuckoos, and the
margansers (fig. 60), there is but one or two pairs ; parrots
have three ; and the birds of song have five.

§ 184. Man alone, of all the animal creation, has the power
of giving, to the tones he utters, a variety of definite or arti-
culate sound? ; in other words, he alone has the gift of
epeech.

CHAPTER FOURTH.

OF INTELLIGENCE AND INSTINCT.

§ 185. BESIDES the material substance of which the body is
constructed, there is also an immaterial principle, which,
though it eludes detection, is none the less real, and to which
we are constantly obliged to recur in considering the pheno-
mena of life. It originates with the body, and is developed
with it, while yet it is totally apart from it. The study of
this inscrutable principle belongs to one of the highest branches
of philosophy ; and we shall here merely allude to some of its
phenomena which elucidate the development and rank of
animals.

§ 186. The constancy of species is a phenomenon depending
on the immaterial nature. Animals, and plants also, produce
their kind, generation after generation. We shall hereafter
show that all animals may be traced back, in the embryo, to a
mere point in the yolk of the egg, bearing no resemblance
whatever to the future animal, and no inspection could enable
us to declare with certainty what that animal is to be ; but
even here, an immaterial principle is present, which no external
influence can modify, and which determines the growth of the
future being. Essentially the egg of the hen, for instance,
cannot be made to produce any other animal than a chicken ;
and the egg of the cod-fish produces only the cod. It may
therefore be said with truth, that the chicken and the cod
existed in the egg before their formation as such.

§ 187. PERCEPTION is a faculty springing from this prin-
ciple. The organs of sense are the instruments for receiving
sensations, but they are not the faculty itself, without which
they would be useless. We all know that the eye and ear
may be open to the sights and sounds about us, but if the
mind happens to be preoccupied, we perceive them not. We

OF INTELLIGENCE AND INSTINCT. 87

may even be searching for something which actually lies within
the compass of our vision ; the light enters the eye as usual,
and the image is formed on the retina ; but, to use a common
expression, we look without seeing, unless the mind that per-
ceives is directed to the object.

§ 188. In addition to the faculty of perceiving sensations,
the higher animals have also the faculty of recalling past im-
pressions, or the power of memory. Many animals retain a
recollection of the pleasure or pain that they have experienced,
and seek or avoid the objects which may have produced these
sensations ; and in doing so, they give proof of judgment.

§ 189. This fact proves that animals have the faculty of
comparing their sensations and of deriving conclusions from
them ; in other words, that they carry on a process of rea-
soning.

§ 190. These different faculties, taken together, constitute
intelligence. In man, this superior principle, which is an
emanation of the divine nature, manifests itself in all its
splendour. God " breathed into him the breath of life, and
man became a living soul." It is man's prerogative, and his
alone, to regulate his conduct by the deductions of reason ;
he has the faculty of exercising his judgment not only upon
the objects which surround him, and of apprehending the
many relations which exist between himself and the external
world ; but he may also apply his reason to immaterial things,
observe the operations of his own intellect, and, by the analysis
of his faculties, may arrive at the consciousness of his own
nature, and even conceive of that Infinite Spirit, " whom none
by searching can find out."

§ 191. Other animals cannot aspire to conceptions of this
kind; they perceive only such objects as immediately strike their
senses, and are incapable of continuous efforts of the reasoning
faculty in regard to them. But their conduct is frequently
regulated by another principle of inferior order, called INSTINCT,
still derived from the immaterial principle.

§ 192. Under the guidance of instinct, animals are enabled
to perform certain operations, in one undeviating manner,
without instruction. When man chooses wood and stone, as
the materials for his dwelling, in preference to straw and
leaves, it is because he has learned by experience, or because
his associates have informed him that these materials are

88 OF INTELLIGENCE AND INSTINCT.

more suitable for the purpose. But the bee requires no in-
structions in building her comb. She selects at once the fittest
materials, and employs them with the greatest economy ; and
the young bee exhibits, in this respect, as much discernment
as those who have had the benefit of long experience. She
performs her task without previous study, and, to all appear-
ance, without the consciousness of its utility, being in some
sense impelled to it by a blind impulse.

§ 193. If, however, we judge of the instinctive acts of animals,
when compared with the acts of intelligence, by the relative
perfection of their products, we may be led into gross errors,
as a single example will show. No one will deny that the
honey-comb is constructed with more art and care than the
huts of many tribes of men. And yet, who would presume
to conclude from this, that the bee is superior in intelligence
to the inhabitant of the desert or of the primitive forest ? It
is evident, on the contrary, that in this particular case we are
not to judge of the artisan by his work. As a work of man, a
structure as perfect in all respects as the honey-comb would
indicate very complicated mental operations, and probably
would require numerous preliminary experiments.

§ 194. The instinctive actions of animals relate either to
the procuring of food, or to the rearing of their young ; in
other words, they have for their end the preservation of the
individual and of the species. It is by instinct that the leopard
conceals himself, and awaits the approach of his prey. It is
equally by instinct that the spider spreads his web to entangle
the flies which approach it.

§ 195. Some animals go beyond these immediate precau-
tions ; their instinct leads them to make provision for the
future. Thus the squirrel lays in his store of nuts and acorns
during autumn, and deposits them in cavities of trees, which
he readily finds again in winter. The hamster digs, by the
side of his burrow, compartments for magazines, which he
arranges with much art. Finally, the bee, more than any
other animal, labours in view of the future ; and she has
become the emblem of order and domestic economy.

§ 196. Instinct exhibits itself, in a no less striking manner,
in the anxiety which animals manifest for the welfare of their
anticipated progeny. All birds build nests for the shelter and
nurture of their young, and in some cases these nests are

OF INTELLIGENCE AND INSTINCT. S9

made exceedingly comfortable. Others show very great in-
genuity in concealing their nests from the eyes of their ene-
mies, or in placing them beyond their reach. There is a small
bird in the East Indies, the tailor bird (Sylvia sutoria), which
works wool or cotton into threads, with its feet and beak, and
uses it to sow together the leaves of trees for its nest.

§ 197. The nest of the fiery hang-bird (Icterus Baltimore),
dangling from the extremity of some slender, inaccessible
twig, is familiar to all. The beautiful nest of the humming-
bird, seated on a mossy bough, and itself coated with lichen,
and lined with the softest down from the cotton-grass or the
mullein leaf, is calculated equally for comfort and for es-
caping observation. An East Indian bird, (Ploceus Philippi-
nus}) not only exhibits wonderful devices in the construction,
security, and comfort of its nest, but displays a still further
advance towards intelligence. The nest is built at the tips of
long pendulous twigs, usually hanging over the water. It is
composed of grass, in such a manner as to form a complete
thatch. The entrance is through a long tube running down-
wards from the edge of the nest; and its lower end is so
•loosely woven, that any serpent or squirrel attempting to enter
the aperture, would detach the fibres, and fall to the ground.
The male, however, who has no occasion for such protection,
builds his thatched dome similar to that of the female, and by
its side ; but simply makes a perch across the base of the
dome, without the nest-pouch or tube.

§ 198. But it is among insects that this instinctive solicitude
for the welfare of the progeny is every where exhibited in the
most striking manner. The bees and wasps not only prepare
cells for each of their eggs, but take care, before closing the
cells, to deposit in each of them something appropriate for the
nourishment of the future young.

§ 199. It is by the dictate of instinct, also, that vast num-
bers of animals of the same species associate, at certain periods
of the year, for migration from one region to another ; as the
swallows and passenger pigeons, which are sometimes met
with in countless flocks.

§ 200. Other animals live naturally in large societies, and
labour in common. This is the case with the ants and the
bees. Among the latter, even the kind of labour for each
member of the community is determined beforehand, by in-

90 OF INTELLIGENCE AND INSTINCT.

stinct. Some of them collect only honey and wax, others
are charged with the care and education of the young, whilst
others are the natural chiefs of the colony.

§ 201. Finally, there are certain animals so guided by their
instinct as to live like pirates, on the fruits of others' labour.
The lestris or jager will not take the trouble to catch fish for
itself, but pursues the gulls, until, worn out by the pursuit,
they eject their prey from their crop. Some ants make war
upon others less powerful, take their young away to their
iiests, and oblige them to labour in slavery.

§ 202. There is a striking relation between the volume of
the brain, compared with the size of the body, and the degree
of intelligence which an animal may attain. The brain of
man is the most voluminous of all, and among other animals
there is every gradation in this respect. In general, an animal
is the more intelligent, in proportion as its brain bears a greater
resemblance to that of man.

§ 203. The relation between instinct and the nervous sys-
tem does not present so intimate a correspondence as exists
between the intellect and the brain. Animals which have a
most striking development of instinct, as the ants and bees,
belong to a division of the animal kingdom where the nervous
system is much less developed than that of the vertebrata,
since they have only ganglia, without a proper brain.
There is even a certain antagonism between instinct and in-
telligence, so that instinct loses its force and peculiar character
whenever intelligence becomes developed.

§ 204. Instinct plays but a secondary part in man; he is
not, however, entirely devoid of it. Some of his actions are
prompted by instinct, as, for instance, the attempts of the in-
fant to nurse. The fact again, that these instinctive actions
mostly belong to infancy, when intelligence is "but slightly
developed, goes to confirm the two last propositions.

CHAPTER FIFTH.

OF MOTION.
SECTION I.

APPARATUS OF MOTION.

§ 205. THE power of voluntary motion is the second grand
characteristic of animals (§ 65). Though they may not all have
the means of transporting themselves from place to place,
there is no animal which has not the power of executing some
motions. The oyster, although fixed to the ground, opens
and closes its shell at pleasure ; and the little coral animal
protrudes itself from its retreat, and retires again at its will.

§ 206. The movements of animals are affected by means of
muscles, which are organs designed expressly for this purpose,
and make up that large portion of the body, commonly called
flesh. They are composed of a series of bundles, which are
readily seen in boiled meat. These bundles are again composed
of parcels of still more delicate fibres, called muscular fibres
(§ 215), which have the property of elongating and contracting.

§ 207. The motions of animals and plants depend, there-
fore, upon causes essentially different. The expansion and
closing of the leaves and blossoms of plants, which are their
most obvious motions, are due to the influence of light, heat,
moisture, cold; and other external agents ; but all the motions
peculiar to animals are produced by an agency residing within
themselves, namely, the contractility of muscular fibres.

§ 208. The cause which excites contractility resides in the
nerves, although its nature is not precisely known. We only
know that each muscular bundle receives one or more nerves,
whose filaments pass at intervals across the muscular fibres.
It has also been shown, by experiment, that when a nerve
entering a muscle is severed, the muscle instantly loses its
power of contracting, under the stimulus of the will, or, in
other words, is paralyzed.

92 APPARATUS Or MOTION.

§ 209. The muscles may be classified according as they are
more or less under the control of the will. The contractions
of some of them are entirely dependent on the will, as in the
muscles of the limbs which are used for locomotion. Others
are quite independent of it, like the contractions of the heart
and stomach. The muscles of respiration ordinarily act in-
dependently of the will, but are partially subject to it ; thus,
when we attempt to hold the breath, we arrest, for the mo-
ment, the action of the diaphragm.

[§ 210. The movements of animah are therefore divided
into VOLUNTARY and INVOLUNTARY ; the immediate agent of
the former is the muscular tissue, which is most intimately
associated with the nervous system, and is brought thereby
under the control of the will. The motions characterised as
involuntary, are for the most part effected by means of mus-
cular tissue ; but the fibres of the involuntary muscles present
histological characters, which distinguish them from that of
the voluntary class. The muscular tissue passes by insensible
gradations into other forms of contractile fibrous tissue, so
that it is difficult to define the limits between them.

[§ 211. Besides muscular movements, animals execute mo-
tions which appear to be altogether independent either of the
muscular or the nervous systems. These are called CILIARY
MOTIONS ; they are most extensively performed, and may be
best studied in the lowest classes of the invertebrata, although
they take place in connection with some of the organic func-
tions in all.

[§ 212. When studied by the aid of the microscope, with a
quarter of an inch object-glass, true muscular fibres present
two distinct histological forms. 1st. The simple unstreaked
fibrillse of organic life. 2nd. The compound streaked fibrillae
of animal life.

[§ 213. The first class consists of pale-coloured smooth
cylindrical fibres, arranged parallel to each other, and forming
bundles connected by a delicate cellular tissue. This class
is met with in the form of layers, investing the hollow
organs, as the stomach, intestines, and bladder ; it is likewise
found surrounding the excretory ducts of the larger glands,
and enters into the structure of the veins. The ultimate
fibrillse are estimated at about 1-1 000th of a line in diameter.

[§ 214. The second class consists of fibrillse mostly of a red

THE MUSCLES. 93

colour, which, when separated and examined by the micro-
scope, exhibit an infinite number of cross streaks. All the
muscles known as voluntary ; the muscles of the eye-ball,
the internal ear, tongue, and palate, a great part of the
esophagous, the diaphragm, the sphincters, and those of the
trunk and extremities, belong to this class. The muscular
fibres of the heart are, however, faintly streaked, although
this organ occupies the centre of the system of organic life.
Cross-streaked muscles are found in many of the invertebrated
classes ; they are well seen in insects, Crustacea, and spiders,
and may be observed in the fibrous layer on the under side of
the umbrella of some medusae. In various animals, however,
possessing voluntary motions, the simple class of muscular fibres
is only observed; but it may be assumed as a general propo-
sition, subject, however, to some exceptions, that the streaked
muscles belong to the system of animal life, and the un-
streaked muscles to that of organic life, and that the former
are developed from the serous, the latter from the mucous
layer of the germinal membrane.

[§ 215. Much difference of opinion exists as to the cause of
the cross streaks observed in the fibrillse of voluntary muscles.
We refer to the works of Wagner, Valentin, Bowman, and
others for a statement of their various opinions, and proceed
to describe the appearance presented by a beautiful preparation
of a portion of one of the voluntary muscles of a pig in fluid now
before me, viewed with one-eighth of an inch object-glass, each
fibrilla appears to be composed of an investing membrane or
sarcolemma, from which transverse processes extend across the
tube, dividing it into a number of square discs ; these cells
or discs, it is presumed, are occupied by the primitive sub-
stance of the muscular tissue ; the discs are of a rectangular
form, and have the same dimensions in the long as in the trans-
verse diameter ; in those fibrillse which are stretched the discs
appear oblong, but in one unstretched fibril, which lies most
advantageously for observation, the diameters are equal ; the
ultimate fibre of muscular tissue therefore, appears to consist
of a longitudinal row of rectangular discs placed end to
end, as seen in Figs. 60 and 63. A number of fibrillae united
by delicate tissue form a primitive fasciculus, and many fas-
ciculi united by areolar tissue, make the common fibres of
muscle as seen by the naked eye. From this arrangement of

94

APPARATUS OF MOTION.

the fasciculi into fibres, we can readily understand one feature
of voluntary muscle — the tendency which it shews to separate
in the longitudinal direction by a kind of natural cleveage.
The following figures from. Wagner illustrate most clearly the
different forms of muscular tissue. — T.W.]

In Fig. 60 we have a fresh muscular fasci-
culus of the ox, one-thirtieth of a line in thick-
ness. The upper extremity of the bundle
exhibits transverse stria? only ; but they ap-
pear to fail here and there, and these gaps
seem as if they separated fibrils or bundles of
fibres at some little distance from one ano-
ther ; the opposite or lower end of the fasci-
culus, on the contrary, shows nothing but
longitudinal striae or primitive fibrils, an effect
which is entirely due to the focussing of the
microscope. At the place where the muscular
bundle is torn through (inferiorly) a scaleform
appearance is perceived very beautifully brought
out by the different layers of the primitive fibrils,
which have contracted again in different de-
grees after yielding to the tearing force ; in
the middle of the specimen the microscope is
so focussed that transverse and longitudinal
striae are perceived at the same time ; here
the former, there the latter, more distinctly,
according to the difference of level of the
surface of the fibre examined. The trans-
verse strias are in a general way extremely
constant, and a highly characteristic indi-
cation of the muscular fibre of animal life, so
that the smallest portion of a muscle belong-
ing to this system is at once recognized under
the microscope by their presence. The trans-
verse stria3, however, become extremely faint
under many circumstances ; in bodies with
very soft or flabby muscles, and in very young
animals, for example ; but even here they are often very distinct, and are
readily studied in the living larva of the frog, near to the spinal column
in the tail. They are very distinct in boiled and roasted meat, and in
muscle that has been macerated in spirit (Fig. 61, 62, B), in which, indeed,
they often present themselves as absolute transverse rug33, with lateral
notchings, so that we should be very apt to suppose that a peculiar sheath
enveloped the muscular bundles, a supposition which gains strength from
the fact, that towards the torn ends of the specimen, the primitive fibrils
are often seen free, isolated, and without any appearance of cross-barring
(Fig. 62, A). On the other hand, however, we frequently recognize the

CILIARY MOTIONS.

CILIARY MOTIONS.

[§ 21 G.We have already stated that ciliary motions take place
independent of either the muscular or nervous systems (§ 211).

transverse streaking upon the several isolated primitive fibrils (Fig. 63, A.
and B). It would seem that transverse sections ought to supply the
surest grounds for conclusions ; but no such thing as a sheath can ever

Fig. 61.

Fig. 61.— Structure
of human muscle ; a
portion of the attol-
lens auriculas, which
had been long kept
in spirit. A, A num-
ber of primary mus-
cular fasciculi mag-
nified about 200
diameters. B, A sin-
gle fasciculus more
highly magnified. C,
Some fibres of cellu-
lar tissue interposed
between the muscu-
lar fasciculi.

Fig, 62.—
Muscular fibre,
after Skey.
(Philo8.Trans.
1837.) A, Fi-
bra Muscularis
— primitive
muscular fasci-
culus. Supe-
riorly the pri-
mitive fibres
are separated
from each
other ; the glo-
bules are blood-
discs to serve
as standards for
the estimation
of their diame-
ter. B, A pri-
mitive muscu-
lar fibre, to

show how the transverse striae are produced, and that they may be ^ eve-
rally seen as elevations.

96

CILIAET MOTIONS.

The peculiar motory phenomena that fall under this class were
known to the older naturalists, but their more successful inves-
tigation was reserved for our day.

Ciliary motions may be most conveniently studied with the
microscope, on portions of the mucous membranes ; that from
the mouth of the frog is most readily obtained, placed on a
glass slide in a drop of water, then covered with a small piece
of thin glass, and viewed with a fourth or an eighth of an inch

with certainty be shown in the circumference of the muscular fibres, how.
ever prepared by hardening, &c. The intimate structure is excellently
displayed, both by Bowman and Henle, as also in the accompanying figures.

Fig. 63. j .. Fig. 63.— Two

primary mus-
cular fasciculi
from the dor-
sal muscles of
a rattle-snake,
which had been
long kept in
spirits. At *
and* fine fibres
are seen dis-
tinctly brought,
into view by
separating the
muscular bun-
dles ; they seem
each to consist
of several pri-
mary or ulti-
mate fibres. B, Two of these fine filaments, seen under a power of 800,
which exhibit crossmarkings. The sinuous filament is cellular tissue.

Fig. 64.

Fig. 64.— A, A bun-
dle of fibres with-
out cross striae, from
the adductor muscle
which closes the
shell of Unio pic-
torum. B, A muscu-
lar bundle without
cross-streaking from
the Distoma dupli-
catum. C, The same
bundle thrown into
ziz-zags at the mo-
ment of contraction -,

CILIAEY MOTIONS.

If we take a small piece of the margin of the mantle, or a

I particularly recommend the muscular elements of the dorsal vessel or
heart of Scolopendra for Yig. 65.

the study of the natural »

resolution of the muscu-
lar fasciculi into fibres,
and of their termination
in elastic tissue. (Vide
Fig. 66.)

Fig. 65. — Muscular fibre
from the esophagus, about
three inches below the
pharynx, to show the
union of muscular fibres
of the animal (a, a) and
of the organic (b, b) life,
after Skey. B, Plan figure
of the spiral fibre, which,
according to some, sur-
rounds the primary mus-
cular fasciculi, and gives
the appearance of cross-
streaking. After Mandl,
Anat. Microscop.

Fig. 66.

Fig. 66. — A piece of a wing-shaped muscle from the Scolopendra Af a
inserted at * * * into the dorsal vessel of the insect. The transition ot
the striated muscular fasciculi into a net of elastic tissue is ver "beauti-

98 CILIARY MOTIONS.

portion of the gills of the fresh-water mussel (Anodon cygneus),

it will be found to exhibit cilia and their motions to great

advantage ; viewed with a quarter of an inch object-glass, the

Fig. 67.* cilia are then seen to consist of

delicate filaments like hairs, set more
or less regularly in rows, and moved
with rapidity. In this mollusk, the
cilia are about 1-1 00th of aline in
length, as seen in (c, c\ and are set
d a^ upon rounded cells (5, 5), as upon

bulbs ; their motion is hook-like, or,
in other words, the point of each cilia successively bends to-
wards its base, and is rapidly stretched out again. These
motions are performed more or less vividly in different ani-
mals, and in different states of the same animal. The infusoria
(fig. 171) exhibit this phenomenon in an admirable manner ;
the surface of their bodies is covered with rows of cilia, which
perform various motions ; a great number of the embryos of
sponges, polyps, acalephse (fig. 368), and mollusca are covered
with vibritile cilia during the first periods of their existence, and
these microscopic filaments play an important part in many of the
organs of the invertebrata. The sides of the bodies of heroes, and
the tentacula of medusse, exhibit these motions ; they are seen
in the interior of the tentacula of Actinia and other ZOAK-
THID J3 ; on the oral lobes of the rotifera (fig. 1 72) ; on the
exterior of the tentacula of Flustra, Alcyonellay and other
BETOZOID^; (fig. 1 75) ; the membrane lining the test of
urchins, CIDAKIDJE, and sea-stars, ASTEBIAD^E ; the anterior
parts of the bodies of the fresh-water mollusca, and the
branchiae of all univalve and bivalved genera, with those of
cirrhipedes and Crustacea (fig. 370), are provided with vibra-
tile cilia.

In the vertebrated animals ciliary motions are seen on many
parts of their bodies. On the mucous membrane covering
the gills of the tadpoles of frogs and salamanders, and on the
respirating organs as well as on the membrane lining the
mouth, fauces, and nasal passages of amphibia, reptiles,
birds, and mammals. Ciliary motions are intended to renew
the stratum of water or air bathing the surface covered by these

* There ought to be no space betwixt the epithelial cylinders that sup-
port the cilia, and the cilia themselves, as in the above figure, which is a
mistake of the artist ; they are immediately sessile upon the epithelium, as
in the plan (fig. 68),

CILIAKT MOTIONS.

99

filaments, they thus become important aids to the due perform-
ance of the function of respiration in the invertebrate classes ;
and are the chief agents by which it is performed in the sub-
kingdom radiata.

[§ 217. The most singular fact connected with the history
of ciliary motions, is their independence of the nervous sys-
tem, or even of the life of the organism itself. In the
fresh-water mussel, ciliary motions are observed for many
days on the surface of the membranes detached from the
body, even when the putrefactive process has considerably
advanced, and the same fact has been observed on the mucous
membranes of decapitated tortoises ; but in birds and mam-
mals, they cease in a few hours after death. Wherever ciliary
motions have been detected, cilia are seen as their instruments.
Set upon a particular form of cylinder-epithelium, composed of
closely arranged conical cells, implanted perpendicularly upon
the subjacent tissues (fig. 68), each cell supporting from six
to eight cilia upon its free summit (b, b, b), and containing
internally a distinct nucleated nucleus (c, c, c) ; the cilia and
nucleated cells are deciduous formations, and are cast off
and rapidly reproduced. The functions of this form of epi-
thelium are still obscure, and we know nothing of the cause
and the mechanism of the motions of the cilia. — T. W.J

Fig. 68.

B

Fig. 68. — Some of the cylindrate epi-
thelial cells are produced inferiorly into
a point, a*, in which case the nucleus, c,
occurs about the middle of the formation.
B, is a transverse section of the nuclei
and nucleoli. To obtain a view of the
ciliary motions in man, we have but to
draw the extremity of the handle of the
scalpel over the mucous membrane of the
nose, and to transfer the mucus thus ob-
tained, properly prepared, to the stage of
the microscope ; it rarely happens that
one or more epithelial cylinders with active
cilia are not discovered. The tessulai
epithelium of the mucous membrane of
the mouth may be procured by lightly
c scraping the inner surface of the cheek,
and should be examined at the same time,
by way of contrast. — WAGNER.]

H 2

100

THE SKELETON OF POLYPS.

§ 218. In the great majority of animals, motion is aided
by the presence of solid parts, of a bony or horny structure,
which either serve as firm attachments to the muscles, or,
being arranged to act as levers, they increase the force and
precision of the movements. The solid parts are usually so
constructed as to form for the body a substantial frame-work,
which has been variously designated in the several classes of
animals, the test, shell, carapace, and skeleton. The study
of these parts is one of the most important branches of com-
parative anatomy, as their characters are the most constant and
enduring of all others. Indeed, these solid parts are nearly all
that remain to us of the numerous extinct races of animals of

69. past geological eras;

and from these a-
lone, we are en-
abled to determine
the structure and
character of the an-
cient fauna.

§ 219. Most of
the radiata have a
calcareous test or
shell. In the po-
lyps, this structure,
when it exists, is
usually very solid,
sometimes assum-
ing the form of a simple inter-
nal skeleton, or forming exten-
sively branched stems, as in the
sea-fans; and sometimes solid
masses, furnished at the sides
with numerous cavities, in which
the animals are lodged, with the
power, however, of protruding
and retracting themselves at
pleasure, by means of their mus-
cles, as in the corals.

\_Litharcea Websteri (fig. 69)
___ is a fossil coral, from the ter-

Figs.69and70.-JL^^ut65^ri.tiary sands of Bracklesham Bay,

Fitr. 70.

TllE SKELETON OF ECHDSTODEEMS.

101

showing the skeleton of one of these lithophytes. The natu-
ral size of the polypary is seen at fig. 69, and a magnified vie-*
of one of the cells, with its rays, is given in fig. 70.]

In the echinoderms, the test is brittle, and intimately united

§/

with the soft parts. It is composed of numerous little plates,
sometimes consolidated and immoveable, as in the sea-urchins,
or combined, so as to allow of various motions, as in the star-
fishes (fig. 36), and in the sea-lilies (figs. 72 and 73), which
use their arms both for crawling and swimming.

Fig. 71. — The test of an Echinus. On the right side are seen the
spines and tubular suckers : on the left side, those parts have been re-
moved, to show the surface of the test, composed of the ambulaeral ares,
with the small plates, and poriferous avenues at their margins, and the
interambulacral areae, composed of the large polygonal plates. The plates
of both area? being covered with tubercles, for supporting spines.

[In the ECHrNiDj;, or sea urchins, the test is of a spherical
or pentagonal form, constructed of many series of calcareous
polygonal plates articulated together, and divided into two
groups, of which five form the ambulaeral areae, and five the
interambulacral arese, each area being composed of two columns
of plates (fig. 71 and 174, d, e). The ambulaeral alternate
with the interambulacral arese, and they are separated from
each other by ten rows of small perforated plates, through the
holes of which numerous tubular retractile suckers pass : the

102

THE SKELETON OF ECHIXODEEMS.

mouth occupies the base of the test ; the opening is of a cir-
cular or decagonal form, in which a complicated mechanism of
five jaws and five teeth, with their muscles, are lodged (figs.
190 and 191). The anus in this group opens at the vertex of
the test ; the opening is surrounded by a circle of ten plates,
five of which are perforated to give passage to ducts from the
genital organs, and called ovarial plates, and five are per-
forated for lodging the eyes, and called ocular plates. The sur-
face of the ambulacral and interambulacral plates is covered
with tubercles of various sizes, in general raised upon prominent
eminences, the tubercles having a round smooth head, to which
a spine with a concave base is fitted and moved by muscles ;
the entire surface of the test and spines is covered by an or-
ganised skin ; the skeleton therefore is enclosed hi mem-
branes, participating in the life and growth of the animal,
and forming an integral part of the urchin.

In the ASTEEIADJE, or sea stars (figs. 36 and 373), a similar
complicated skeleton exists, with this difference, that the ambu-
lacral and interambulacral arese, instead of being united to
form a hollow case, are stretched out into rays, at the ex-

Fig. 72. — Apiocrinus rotunda. Fig. 73. — Encrinus moniliformi*

THE SKELETON OF MOLLUSCA.

103

tremity of which the eyes are situated, corresponding to their
position in the echinidse ; the summits of the arese being ana-
logous to the extremities of the rays bent up towards the
anal pole.

In the CKIKOIDEJE, or sea lilies, which may be likened to
sea-stars supported upon many jointed columns, the skeleton is
very complicated, being composed of many thousand separate
pieces, beautifully and nicely fitted to each other. Fig. 72
represents the pear encrinite (Apiocrinus rotunda), from the
Bradford clay ; and fig. 73, the lily encrinite (Encrinus mo-
niliformis), from the Muschelkalk. These stalked echinoderms
attained a great generic development in the palaeozoic rocks,
entire strata being sometimes composed of their broken
skeletons ; their forms are less numerous in the triasic and
oolitic periods ; a few only are found in the chalk, and one
rare species lives in the warm regions of our present seas.
— T. W.]

Fig. 74. — Cyprceacdssis rufa; a, mature, b, immature state of the same

shell.

• § 220. In the mollusca, the solid parts are secreted by the
skin, most frequently in the form of a calcareous shell of one,
two, or many pieces, serving for the protection of the soft

104 THE SKELETON OF MOLLUSCA.

parts which they cover. These shells are generally so con-
structed as to aiford complete protection to the animal within
their cavities. In a few, the shell is too small for this pur-
pose ; in others it exists only at a very early period, and is
lost as the animal is developed., so that at last there is no
other covering than a slimy skin. In some the tegumentary
membrane becomes so thick and firm as to have the consistence
of elastic leather, or it is gelatinous or transparent; and what
is very curious, these tissues may be the same as those of woody
fibre, as, for example, in the ascidia. In general the solid parts
do not aid in locomotion, so that the mollusca are mostly slug-
gish in their movements. It is only in a few rare cases that
the shell becomes a true lever, as in the scallops (Pecten\
which use the valves thereof to propel themselves in swimming.

[The shells of a great majority of the gasteropoda are uni-
valve, and rolled obliquely, in consequence of the unequal de-
velopment of the body of the animal. They consequently
form a helix or oblique spiral ; sometimes the coil is towards
the right, but in general it is towards the left side. Some
univalve shells have a patelloid form, and are symmetrical,
without being spiral ; and there are various intermediate
groups, by which these forms blend into each other. Some
of the shells vary very much in form at different stages of their
growth, as shown in the beautiful Cypr&aeussis rufa, from the
coral reefs of the South Pacific. Fig. 74, a, is the mature
form of that shell, with its greatly developed right lip ; and 6,
the young, or immature form of the same. — T. W.]

§ 221 . The muscles of mollusca either form a flat disc under
the body, or large bundles across its mass, or they are distributed
in the skin, so as to dilate and contract it, or are arranged
about the mouth and tentacles, which they put in motion.
However varied in their disposition, the muscles always form
very considerable masses, in proportion to the size of the
body, and have a soft and mucous appearance, such as is not
seen in the contractile fibres of the other divisions of the animal
kingdom. This peculiar aspect no doubt arises from the nu-
merous small cavities extending between the muscles, and the
secretion of mucus which takes place in them.

§ 222: In the articulated animals (fig. 34), the solid parts are
external, in the form of rings, generally of a horny structure, but
sometimes calcareous, and successively fitting into each other
at their edges. The tail of a lobster gives a good idea of this

THE SKELETON OF AETICULATA.

105

structure. The rings differ in the several classes of this divi-
sion, merely as to volume, form, solidity, number of pieces,
and the degree of motion which one has upon another. In
some groups they are consolidated, so as to form a shield or
carapace, such as is seen in the crabs. In others, they are
membranous, and the body is capable of assuming various
forms, as in the leeches and worms generally. Fig. 75 is a
beautiful fossil Astacus, from the lower greensand, which exhi-
bits the character of the skeleton of the Crustacea.

\Leti. Jtc

Fig. 75. — Astacus f'ectensis, from the lower greensand, Isle of Wight.

§ 223. A variety of appendages are attached to these rings,
such as jointed legs (fig. 34), or, in place of them, stiff bristles,
oars fringed with silken threads, wings either firm or mem-
branous (fig. 369), antennae, moveable pieces which perform
the office of jaws (fig. 195), &c. But, however diversified this
solid apparatus may be, it is universally the case that the
rings, to which every segment of the body may be referred,
as to a type, combine to form but a single internal cavity, in
which all the organs are enclosed, the nervous system, as well
as the organs of vegetative life (§ 76).

§ 224. The muscles which move all these parts have this
peculiarity, that they are enclosed within the more solid frame-
work, and are not external to it, as in the vertebrata ; and
also that the muscular bundles, which are very considerable
in number, have the form of ribbons, or fleshy strips, with pa-
rallel fibres of remarkable whiteness.

§ 225. The vertebrated, like the articulated animals, have

106

THE SKELETON OF YERTEBRATA.

•Ay-

parts at the surface, as the hairs and horns of mammals,
the coat of mail of the armadillo (fig. 75*), the feathers and

claws of birds, the buck-
lers and scales of rep-
tiles and fishes, &c. But
they have, besides this,
along the interior of
the whole body, a solid
framework, not found
in the invertebrata, well
known as the SKELE-
TON.

Fig. 75*.— External skeleton of the Dasypus § 226. Theskeletonis
sexcmctus. composed of a series of

separate bones, called vertebrae, united to each other by liga-
ments. Each vertebra has a solid centre with several branches,
two of which ascend and form an arch above, and two descend,
forming an arch below the body of the vertebra. The upper arches
form a continuous cavity along the region of the trunk, which
encloses the spinal cord, and in the head receives the brain
(§ 85 and § 89). The lower arches form another cavity, similar
to the superior one, for containing the organs of nutrition and
reproduction ; the branches generally meet below, and when
disjoined, the deficiency is supplied by fleshy walls. Every
part of the skeleton may be reduced to this fundamental type,
the vertebra, as will be shown when treating specially of the
vertebrate animals; so that, between the pieces composing the
head, the trunk, and the tail, we have only differences in the de-
gree of development of the body of the vertebra, or of its
branches, and not in reality different plans of organization.

§ 227. The muscles which move this solid framework of the
vertebrata are disposed around the vertebrae, as is well exem-
plified among fishes, where there is a band of muscles for each
vertebra (fig. 76). In proportion as limbs are developed, this
intimate relation between the muscles and the vertebrae dimi-
nishes. The muscles are unequally distributed, and are con-
centrated about the limbs, where the greatest amount of
muscular force is required. For this reason the largest
masses of flesh, in the higher vertebrata, are found about the
shoulders and hips (fig. 77); while in fishes they are concen-
trated about the base of the tail, the part on which they princi-
pally depend for motion.

MUSCULAR SYSTEM OF FISHES.

107

a \ ff////f////M

[Fig. 76 represents the Ahtscles of the Peroh.' — a, inferior half of the
great lateral muscular mass ; a', the superior half; b and c, points where
these masses divide for the passage of the rays of the pectoral and ventral
fins; de, the middle inferior longitudinal muscles ;/, the middle superior; g,
muscles for moving the ventral fin ; h, the muscles special to the pectoral
fin ; h h, the particular muscles of the dorsal fin ; i, the muscles of the
anal fin ; k, the muscles of the caudal tail fin ; / I', the muscles com-
mon to the jaws ; m, the muscles of the operculum and the first inter-
costal of the cranium ; /3, attachment of the latero-superior muscles of
the occiput ; i//, the lateral line between the muscular masses ; the great
lateral nerve has been removed, and the superior muscular mass pushed
upwards. — Cuvier, Histoire des Poissons.

[Fig. 77. — Muscular system of Birds. — The muscles of the Falco
nisus : 1, the great complexus ; 1 a, its tendon ; 1 b, its superior head ;
1 c, its inferior head ; 2, the small complexus ; 3, the lateral flexor of the
head ; 4, the long flexor of the head ; 5, the great extensor of the neck ;
6, the descending cervical; 7,7', the demi-spinal muscles of the neck and
back ; 8, the superior flexor of the head ; 9, the inferior, or long flexor
of the head; 10, 10, the anterior and posterior inter - transverse muscles
of the neck; 11, the elevator of \he coccyx ; 12, the depressor of
the coccyx; 13, the cruri-coccygean ; 14, the pubi-coccygean ; 15, the
eschio-coccygean ; 16, the quadratus ; 17, the external oblique of the abdo-
men ; 18, the trapezium ; 19, the great serratus ; 20, the great pectoral ;
21, the latissimus dorsi; 22, the deltoid; 23, the subscapular ; 24, the
coraco-brachialis ; 25, the biceps brachialis ; 26, the supinator ; 27, the
long anconaeus ; 28, the short anconseus ; 29, the small anconaeus ; 30, the
anterior extensor of the skin of the wing ; 30 a, the portion which goes to
the carpus ; 30 b, the portion which goes to the radius ; 31, the posterior
extensor of the skin of the wing, divided • 32, the long extensor of the
metacarpus ; 33, the short extensor of the metacarpus ; 34 a; the com-
mon flexor of the thumb and second finger ; 34 b, the extensor of the

108

MUSCULA.E, SYSTEM! OE BIRDS.

second and third phalanx of
thumb ; 35, the radial flexor

s&TL<f.

{^^4^^-^,~
^t^^fe4lfe

-57

--0

F:g. 77. — Muscular system
Falco m'.sws.

the second toe ; 34 c, the short flexor of the
of the metacarpus ; 36, the ulnar flexor of
the metacarpus ; 37, the great glu-
teus ; 38. the first adductor of the
thigh ; 39, the sartorius; 40, the large
muscle of the thigh ; 41, the small
muscle of the thigh, the tendon of
which passes upon the knee, and
joins the flexor of the toes; 42, the
common extensor of the leg, the
vastus externus and internus ; 43,
the first anterior flexor of the leg ;
44, the third flexor of the leg, the
semimembranosus ; 45, the fourth
flexor, or semi-tendinosus ; 46,
the gastrocnemius ; 47, the internal
part of this muscle ; 48, the pyra-
midal muscle which opens the jaws;
49, the temporal ; 50, the long liga-
ment of the lower jaw ; 51, the cu-
taneous muscle of the head ; 52, the
anterior masseter ; 53, the coniform
~^f muscle of the hyoid bone ; 54, the
-"anterior tibial; 55, the posterior

«L ' -76 tibial 5 56' the extensor of the toe »

57, the flexor of the toe ; 58, the
long head of the common flexor of
the toes ; 59, the tendon of the ex-
tensor of the toes ; 60, the abductor
of the internal toes ; 61, the perfo-
rated flexor of the three toes ; 62,
the fibuJar muscle ; 63, the abductor
of the little toe ; 64, the abductor
of the great toe ; a, the pharynx ;
i, the trachea ; c, the hyoid ; d, the
ear ; e, the humerus ; /; the radius ;
ff, the ulna ; A, the thumb ; z, the
tibia ; k, the metatarsus ; I, the great
toe ; m, the internal toe ; n, the
median toe ; o, the external toe.—
Ca*-as,Ana?omie Compcree.— T . W. j
of the

OF LOCOMOTION. 109

SECTION II.

OF LOCOMOTION.

§ 228. ONE of the most curious and important applications of
this apparatus of bones and muscles is for LOCOMOTION. By
this is understood the movement which an animal makes in pass-
ing from place to place, in the pursuit of pleasure, sustenance,
or safety, in distinction from those motions which are performed
equally well while stationary, such as the acts of respiration,
mastication, &c.

§ 229. The means which nature has brought into action to
effect locomotion, under all the various circumstances in which
animals are placed, are very diversified ; and the study of their
adaptation to the necessities of animals is highly interesting in
a mechanical, as well as in a zoological point of view. Two
general plans may be noticed, under which these varieties
may be arranged. Either the whole body is equally concerned
in effecting locomotion, or only some of its parts are employed
for that purpose.

§ 230. The medusae (fig. 173) swim by contracting their
umbrella-shaped bodies upon the water below, and its resist-
ance urges them forwards. Other animals are provided with
a sac or syphon, which they may fill with water, and suddenly
force out, producing a jet, which is resisted by the surround-
ing water, and the animal is thus propelled. The Holothitria
(fig. 232), the cuttle-fishes, the salpse, &c. move in this way.

§ 23 1 . Others contract small portions of their body in suc-
cession, which being thereby rendered firmer, serve as points
of resistance, against which the animal may strive in urging
the body onwards. The earth-worm, whose body is composed
of a series of rings united by muscles, and shutting more
or less into each other, has only to close up the rings, at one
or more points, to form a sort of fulcrum, against which the
rest of the body exerts itself in extending forwards.

§ 232. Some have, at the extremities of trie body, a disc, or
some other organ, for maintaining a firm hold, each extremity
acting in turn as a fixed point. Thus the leech (fig. 178) has
a disc, or sucker, at its tail (o), by which it fixes itself; the
bodv is then elongated by the contraction of the muscular

V V

fibres which encircle the animal ; the mouth (a) is next fixed by
a similar sucker, and by the contraction of muscles running
lengthwise the body is shortened, and the tail, losing its hold, if

110 OF LOCOMOTION.

brought forwards to repeat the same process. Most of the bi-
valved mollusca, such as the clams, move from place to place in a
similar way. A fleshy organ, called the foot, is thrust forward,
and its extremity fixed in the mud, or to some firm object, when
it contracts, and thus draws along the body and the shell en-
closing it. Snails, and many similar animals (fig. 35), have the
fleshy under-surface of their body (a, 6) composed of an infinitude
of very short muscles, which, by successive contractions — so mi-
nute, indeed, as scarcely to be detected — enable them to glide
smoothly and silently along, withoutany apparentmuscular effort.

§ 233. In the majority of animals, however, locomotion is
effected by means of organs specially designed for the purpose.
The most simple are the minute hair-like cilia, fringing the
body of most of the microscopic infusory animalcules (fig.
171), and which, by their incessant vibrations, cause rapid move-
ments. The sea-urchins (fig. 174) and star-fishes (fig. 36) have
little thread-like tubes issuing from every side of the body, fur-
nished with a sucker at the end. By attaching these to some
fixed object, they are enabled to draw or roll themselves along ;
but their progress is always slow. Insects are distinguished for
the number and great perfection of their organs of motion: they
have at least three pairs of legs (fig. 34), and usually two pairs
of wings (fig, 369), but those that have numerous feet, like the
centipedes, are not distinguished for agility. The Crustacea
generally have at least five pairs of legs, which are used for both
swimming and crawling. The worms are much less active ;
some of them have only short bristles at their sides ; some
of the marine species use their gills for paddles.

§ 234. Among the vertebrata, we find the greatest diversity
in the organs of locomotion, and the modes of their application,
as well as the greatest perfection, in whatever element they may
be employed. The sailing of the eagle, the bounding of the
antelope, the swimming of the shark, are not equalled by any
movements of insects. Tli:3 superiority is due to the internal
skeleton, which, while it endows tlt£ j.\.iniiil with great force, gives
to the motions, at the same time, a nice degree of precision.

[§ 235. Before entering upon the study of the various mo-
tions of the vertebrate animals, and the means by which these
are performed, it is important to put the student in posses-
sion of a standard by which he will be enabled to compare the
form of the osseous elements and the modifications they undergo
in fishes, reptiles, birds, and mammals. With this view we

THE SKELETON.

Ill

proceed to give an outline of the structure of the Skeleton cf
Man (fig. 78), and the uses of its several parts. This bony frame-
work is formed of 249 separate pieces, articulated together iu

Fig. 78.— The Skeleton of Maa.

112 THE SKELETON.

various ways, and divided into the HEAD, TETJNK, and EXTHE-
MITIES. Some of the bones are single, and disposed on the
median line of the body, in which case they are always formed
of two halves, the counterpart of each other ; the great ma-
jority, however, consist of pairs. The following table exhibits
the distribution of the bones.

rOs frontis .................................... 1

Ossa parietalia .................................. 2

Os occipitis .................................... 1

Ossa temporum ................................ 2

Ossicula audit us . . .............................. 8

Os sphenoides ................................. 1

Os ethmoides .................................. 1

Ossa malarum .................................. 2

Ossa maxillaria superiora ........................ 2

Ossa nasi ...................................... 2

Ossa lachrymalia .............................. 2

Ossa palatina .................................. 2

j Ossa turbinata .................................. 2

Vomer ........................................ 1

Os maxillare inferius ............................ 1

Dentes .......................... ............. 32

_ Os hyoides .................................... 1

3 fVertebra3 .................................... 24

4 Costje ....................................... 24

? Sternum .................................... 2

H i Ossa innominata ................................ 2

£ Os sacrum .................................. ...

d Os coccygis ....... .................... ........ 1

0 I. 2

Claviculpe .................................... • •

CO

V

O

<M

PO

r

Scapulae
Ossa humeri
Ulna3

*

Radii

Ossa carpi ^

Ossa metacarpi *"

Phalanges digitorum manus *°

£ j Ossa sesamoidea

•^^ I *x

^ Ossa femoris

• •••••••*•••«** "

2

Ed
o

C

Patella?

'I'ibiro

Fibulae 4

Ossa tarsi . _

Ossa metatarsi iV

Phalanges digitorum pedis . « **

Ossa sesamoidea

249

COMPOSITION OP BONES.

113

[§ 236. The internal skeleton of the vertebrata is formed,
for the most part, of bone, a substance which is peculiar
to this primary division of the animal kingdom. It consists
of an organic gelatinous matter, hardened by inorganic earthy
particles distributed regularly throughout the animal tissue.
The relative proportion of the organic to the inorganic matter
varies in the different classes of the vertebrata; the bones of fishes
have the least, those of birds the greatest proportion of inorganic
elements, whilst reptiles and mammals occupy an intermediate
position ; the mammals, however, especially the active preda-
cious genera, having a larger proportion than the reptiles. From
a series of experiments recently made, and conducted with
great care, by Bibra,* on thoroughly dried bones of fishes, rep-
tiles, birds, and mammals, the following results were obtained.

[§ 237. FISHES.

SALMON. CARP.

Salmo salar. Cyprinus carpio.

Organic 60.62 40.40

Inorganic 39.38 59.60

COD.

Gadus morrhua,
34.30
65.70

Organic . .
Inorganic

1000

FROG.

Sana esculenta.
... 35.50
64.50

1000

DOLI 'TIN.

Lelphinus 4?lphis.

Organic 35.90

Inorganic . . 64.10

1000

1000
REPTILES.

SNAKE.

Coluber natrlx.

31.04

68.96

1000

MAMMALS,
ox.f

Bos taunts.
31.00
69.00

1000

1000

LIZARD.

Lacerta agilis.

46.67
53.33

1000

WILD CAT.f

Felis catus.

27.77
72.23

1000

MAN.f
Homo.
31.03
68.97

1000

BIRDS.

TURKEY.f
Meleaaris gallo-pavo.
30.49
69.51

HAWK.f

gallinarius.

26.72
73.28

GOOSE.f
Anser.

Organic 32.91

Inorganic 67.09

1000

* Chemische Untersuchungen iiber die Knochen u. Zahne des Mens-
Chen u. der Wirbelthiere, 1844.
t From the femur.

1000

1000

114

ANALYSIS OF BOXES.

[§238. The chemical composition of the inorganic consti-
tuents of bone in the four classes, is shewn in the following
table.

ANALYSIS OF BONES.

Phosphate of Lime with a trace of Fluate

Hawk.
64.39
7.03

Man.
59.63
7.33

Tortoise.
52.66
12.53

Cod.
57.29
4.90

Phosphate of Magnesia

0.94

1.32

0.82

2 40

Sulphate, Carhonate, and Chlorate of Soda

0.92
25.73

0.69
29.70

0.90
31.75

1.10
32,31

Oil

0.99

1.33

1.34

2.00

1000

1000

1000

1000

[§ 239. The primitive basis of bone, is a subtransparent
glairy fluid, resembling mucus in its chemical composition,
and containing a multitude of minute corpuscles. When it
passes into the stage of cartilage, a number of elliptical
nucleated cells make their appearance ; in proportion as the
cells increase in size and number, the cartilage hardens, and
at the point where ossification is about to commence, they ar-
range themselves in linear rows. In the long bones the cell
rows are parallel to the axis of the bone, and in the flat
bones, they run in rays from the centre to the periphery.
The nucleated cells are the agents by which the earthy parti-
cles are arranged in order ; and in bone, as in teeth, there may
be discerned in this predetermined arrangement, the same re-
lation to the acquisition of power and resistance with the great-
est economy in the building material, as in the disposition of
the beams and columns of a work of human architecture.*

[§ 240. The intimate structure of bone can only be studied
by the aid of the microscope ; for this purpose, very thin
sections of the bones of fishes, reptiles, birds, and mammals,
should be prepared and mounted on glass slides in Canada
balsam, and covered with very thin glass ; by this means a
series of comparative observations may be made. If we take
a transverse section of one of the long bones of man, the
femur, for example, and examine it with a power of about
two hundred linear, we observe that it is traversed by a num-
ber of canals called Haversian, which transmit blood-vessels

* Professor Owen's Comparative Anatomy of Fishes contains ample
details on this subject.

MICROSCOPIC STRUCTURE OF BONES. 115

through the substance of the bone ; around each of these
canals a series of bony laminae are concentrically arranged,
as if they resulted from rings of growth, and reminding
us of a transvere section of the branch of a dicotyledonous
tree. Between the laminae a number of peculiar spider-like
bodies are arranged likewise in a concentric manner ; they
have an irregular oval form, with jagged edges, and send
out from their circumference a number of small branching
tubes, which anastomose freely with the tubes from other cells,
forming thereby a complete network of tubes and reservoirs,
which traverse the osseous tissue in all directions. The sides
of the spider-like bodies lying nearest the Haversian canals,
send their small tubes to open into them, by which nutritive
fluids passing through the canals are absorbed and trans-
mitted through the osseous tissue, so that it is possible to inject
the spider-like bodies and the whole system of tubes, by forcing
fluids into any of the canals. The spider-like bodies have
received different names, as osseous corpuscles, calcigerous
cells, lacunae, or bone cells, according as the observer consi-
dered them to be solid or hollow. The spider-like bodies or
bone-cells in man, measure, on an average, about 1-1400 to
1 -2400th of an inch in their long diameter, and about from
1 -4000th to 1 -8000th of an inch in their shortest diameter.
The structure between the bone cells has been shewn by Mr.
Tomes* to consist of a cellular basis, in which the granular
earthy matter of bone is deposited. The granules vary from
l-6000th to the 1-14, 000th of an inch in size, and are best
shewn in a bone which has been long subjected to the
action of boiling water or steam. The microscope, there-
fore, enables us to demonstrate that bone is composed of — 1st,
granular earthy matter, distributed throughout the cellular
tissue ; — 2nd, bone cells and branching tubes, traversing the
osseous structure; the former being the hardening material ;
the latter for the distribution of nourishment through its
substance. This view of the function of the bone cells and
tubes is supported by the fact, that there is a constant relation
between the size of the bone cell and that of the blood cor-
puscle of the same animal, thus :

In birds, a transverse section of the femur shews that the
Haversian canals are more numerous and smaller, and that

* Cyclopaedia of Anatomy and Physiology. Art. Osseous Tissue, p. 843.

12

116 MICROSCOPIC STRUCTURE OF BONE.

fewer radiating tubes proceed from the bone cells ; in the os-
trich the bone cells are from l-1300th to l-2200th of an inch
in their long diameter, and from l-5425th to 1 -9600th in their
shortest. In reptiles the Haversian canals are few in number,
but large in size, and in the same section we observe the
canals and the bone cells arranged both vertically and longi-
tudinally. The bone cells in the turtle measure 1-3 75th of an
inch in length ; in the amphibia, as the siren, they measure
1 -290th of an inch in length. Fishes present considerable
variety in the intimate structure of the osseous tissue ; their
bone cells have a singular quadrate form ; the ramifying tubes
are few in number, and of considerable size, and anastomose
freely with the tubes from neighbouring cells, forming thereby
a well marked trellis-work in the osseous substance. The
specimen before me, a thin section of the scale of an osseous
fish, shews this anastomosis most distinctly. The size of the
bone cells has been found to bear a remarkable relation to that
of the blood corpuscle in the different classes of the ver-
tebrata.*

[§ 241. THE HEAD is composed of two parts, the cranium,
or skull, and the face. The cranium (fig. 79) is a bony case
,of an oval form, occupying the upper and back part of the
head ; it lodges the brain (§ 80), and protects it from injury,
and in two of its bones is situated the organ of hearing.
The walls are formed of the frontal bone (3), which forms the
forehead ; the two parietal bones (1) occupy the sides and
roof of the skull ; the two temporal (2) form the walls of the
temporal region ; and the occipital (4) is situated at the
posterior and inferior part. These bones are firmly united
to each other by sutures, the character of which varies in dif-
ferent parts of the cranium, and their evident intention being
to afford the best kind of mechanism for resisting external
violence. Thus, a blow upon the vertex tends to separate the
parietal bones from each other and from the frontal, and to
force their lower borders outwards ; but this accident is admi-
rably provided against by the different kinds of sutures which
unite the parietal to the frontal, occipital, and temporal bones,
thus a serrated suture locks them together above, to the occi-

* For much valuable information on this subject, consult Mr. John
Quekett's papers in the Trans, of the Microscopic Soc. London, vol. ii. part 2.

BONES OF THE SKULL.

117

pital behind, and to the frontal before, whilst the temporal bones
form the buttresses of this arch, overlapping in a spliced manner

Fig. 79.

Fig. 80.

the lower border of the parietals, to prevent that portion being
thrust outwards. The same mechanical provision prevents
the temporal bones from
being driven inwards by
blows given on the tem-
poral region.

Fig 80 shews the Fron-
to-temporal portion of the
frontal bone (os frontis],
bounded below by the
frontal prominences (1,1),
and above by the suture
by which it is connected
with the parietals. 4, 4,
are the temporal arches ;
5, 5, the temporal fossae,
in which the temporal
muscles are lodged; 10,
10, the superciliary arches ; 11, 11, the supra-orbital holes
through which the nerves of that name pass.

118

BO^ES OF THE SKULL.

Fig. 81 is the in-
ternal surface of the
samebone, shewing the
broad and shallow de-
pressions (17 and 18)
produced by the con-
volutions of the ante-
rior lobes of the cere-
brum and the internal
crest (19 and 20), which
gives attachment to the
dura mater.

Fig. 82 represents
the external surface of
the parietals (ossa pa-
rietalia) . At its upper
(6), anterior (5), and
posterior borders (7),
are seen the serrated
5 edges of the suture, and
at its lower border (8),
the bevelled edge,
which is overlapped by
the temporal bone.

Fig. 83 is the inter-
nal surface of the same
bone, and at the lower
anterior angle is shewn
the canal (12) for lodg-
ing the middle artery
of the dura mater,
which is here seen to
groove the bone with
its numerous branches

On the internal sur-
face of the parietal
bones (fig, 84) we ob-
serve the longitudinal
groove, sulcus longi-
tudinalis (1, 1, 1), .for
the longitudinal sinus

BONES OF THE SKTTLL.

119

of the brain, and a number of little pits (2, 2, 2, 2), more
or less deep, in which the glandulse pacchionse are situated :
there are also the impressiones digitatse (3, 3, 3, 3), and emi-
uentise ma- Fig- 84.

millares,
(4, 4, 4, 4),
produced
by the con-
volutions of
the brain ;
the groov-
ings for the
meningeal
arteries are
seen at 5,
5, 5, 5, and
the parietal
holes at 6, 6.
[§ 244.
The tempo-
rals (ossa
temporum),
fig. 85, are
of an irre-
gular form,
and consist
of three
portions,
the squa-
mous (I),
the mammillary (II), and the petrous (III.)

Fig. 86, represents the ex-
ternal surface of the squam-
ous portion (a\ with the root
of zygomotic process (2),
and the glenoid cavity for the
head of the lower jaw (6).
The internal surface of the
same portion (fig. 87) exhi-
bits the bevelled edge that
overlaps the parietals, and the
depressions (6) for receiving
the convolutions of the cerebrum.

Fig. 86.

External surface

120

BONES OF THE SKULL.

Fig- 87-

Internal surface.

Fig. 88.

14.

Figs. 88 and 89 represent the anterior and posterior surfaces
of the petrous portion of the temporal bone in which the in-
ternal ear is situated. These
parts, consisting of the tym-
panum and its ossicles, the
labyrinth with the vestibule,
semicircular canals, and coch-
lea, have been already de-
scribed in our section on the
internal ear. § 150 to 154.

[§ 245. Fig. 90 shews the
external surface of the occi-
pital bone (os occ^zYz's), with
its arched protuberances (10),
for giving attachment to the
muscles of the neck, and
the large aperture (foramen
magnum) (13) serving for
the passage of the spinal
cord. The basal portion is
seen at (14) ; at each side of
the foramen magnum are seen
the condyles (16, 16), by
which the skull rests upon
the first vertebra of the neck,
and moves backwards and for-
wards thereon.

Fig. 90* represents the in-
ternal surface of the os occi-
pitis, which behind the fora-
men magnum (13), is divided
into four cavities by a crucial
ridge (23, 23,24, 24). To the
vertical spine, above the trans-
verse portion, is attached the
falx cerebri, and to that below,
the falx cerebelli, whilst to the

transverse ridge the tentorium is attached : the cavities above
the transverse spine (21, 21) are for lodging the posterior
lobes of the cerebrum, and those below (22, 22), for the cere-
bellum; the upper surface of the basal process (14) is hol-
lowed out to receive the medulla oblongtita.

Anterior face.
Fig- 89.

Posterior face.

BONES Or THE SKULL.

121

The nead is almost
in equilibrium on the
condyles ( 1 6, 16), but
that portion situated
in front of the joint
is heavier than that
placed behind it,
hence it overweighs
the latter : this ne-
cessitates the presence
of more powerful
muscles in the pos-
terior region of the
neck, to maintain the
head erect upon the
spinal column; when
these become relaxed,
as in sleep, the head
falls forward upon the
chest.

[§ 246. The sphe-
noid and ethmoid
bones, Fig. 91 (1,2),
are wedged between
the cranial bones at
the base of the skull,
and may be said to be
common to the cra-
nium and the face.

[§ 247. The face is
formed by the union
of fourteen different
shaped bones, which
form five large cavi- 4
ties for lodging the
organs of vision, smell,
and taste. All the
bones of the face, the
lower jaw excepted,
are completely im-
moveable, and firmly
united to each other

Fig. 90.

122

BONES OF THE SKULL.

Fig. 91.

and to the bones of the skull ; the principal of these are the
superior maxillaries, Fig. 92 (2), forming nearly the whole of

the upper jaw, an d which
are connected with the
frontal bone in such a
manner as to contribute
to the formation of the
orbits (4) and the nasal
cavities (fig. 93,6); they
form the anterior part
of the roof of the mouth,
and unite with the malar
bones (1), to constitute
the prominence of the
cheeks ; behind they
unite with the palate
bones. In the interior of
the nasal fossee are found two spongy bones (figs. 94 and 95),
curiously folded, upon which the mucous membrane of the nose
Fig. 92.

Fig. 93.

is spread. It is through the horizontal cribriform plate of the
ethmoid bone, which separates the nasal cavity from that of the
skull, that the olfactory nerves proceed into the nasal fossae

BONES OF THE SKULL.

123

(13); this plate, being pierced with numerous holes for their
transit ; the cavity of the nose is further increased by commu-
Fig. 94. Fig. 95.

Partition of Nostrils. Transverse vertical section of Orbits,

Nostrils, and Palate.

nications established between it and the sinuses existing

in the frontal and superior max- Fig. 96.

illary bones, and which are lined

by a continuation of the nasal

membrane.

Fig. 96 shews the lateral boun-
dary of the nose, and the passages
leading to and from the frontal
and maxillary sinuses.

VJll

Lateral boundarv.

[§ 248. Fig. 97. THE CEBITS (10)
are two deep conical cavities, with
their base directed outwards ; they are destined to lodge and
protect the eyes. Thereof of the or- Fig- 97.

bit is formed by a thin plate of the /
frontal bone (fig. 81, 18); the
floor chiefly by the superior max-
illary (11), the internal wall by the
ethmoid and lachrymal (3,4) ; the
latter bone is grooved for the passage
of the nasal duct(l 1), which conveys
the tears into the nose ; the external

124

BOXES OF THE SKULL.

Fig. 98.

wall is formed by the malar (6) and a part of the sphenoid
bones; the latter bounds the apex of the orbital cone ; in it
are pierced holes for the passsage of the optic and other nerves
appertaining to the organ of vision. The orbit contains the
muscles that move the eye-ball, and in its upper and outer
region, the lachrymal gland.

Fig. 99. [§ 249. The greater

*- part of the nose is form-
ed by cartilages, so that
L a\ii(jjf in the skull the anterior

IRrHiaJMr . ., , -

opening or the nasal
1 cavity (fig. 98, 29) is
very large, and the
"^ osseous portion of the
nose formed by the
two small nasal bones
(fig. 99, 2), makes an
inconsiderable promi-
nence. The nasal ca-

Anterior boundary. Posterior boundaiy. vitv is divided by a
vertical partition into two fossse, as seen in fig. 99, 5 and 28,
which shews the posterior boundary of the nose ; superiorly it is
hollowed out of the ethmoid bone, the interior of which is
full of cells ; and its floor is formed by the superior maxillary.

Fig. 100. Fig. 101. [§ 25°- Tne

superior maxil-
lary bones (figs,
100 and 101)
contain the teeth
oftheupperjaw;
in infancy this
bone is compos-
ed of several ele-
ments, one of
which, called the
intermaxillary,
remains as a per-
manently dis-
tinct bone in

monkeys and other quadrupeds, whilst in man it is early sol-
dered to the superior maxillary. Fig. 100 shews the internal,

BONES OF THE SKULL.

125

and fi01. 101 the external surface of the superior maxillary,
with the sixteen teeth, four incisors, Fig 102>

two canine, and ten molars in situ.

Fig. 102 exhibits the palate plates
of the superior maxillary (2), and the
palatine bones (3), together with
the arch formed by the sixteen teeth
(1, 1).

[§251. The lower jaw, in the adult,
is composed of a single bone ; in the
infant, it consists of two branches united along the median
line ; and this separation is permanent in a great many animals,
whilst in reptiles and fishes each branch consists of several
distinct bones united together.

In man the lower jaw
(figs. 1 03 and 1 04) has some
resemblance to a horse shoe
with the branches bent up-
wards at an obtuse angle ;
it contains sixteen teeth,
and is articulated to the
glenoid cavity of the tem-
poral bone by a prominent
condyle (12) ; in front of
the condyle rises a second
eminence, called the coro-
noid process (14), serving for the attachment of the tem-
poral muscle. The elevatory muscles of the lower jaw

Fig. 103.

External surface.

Fig. 104.

are all attached near its
angle (3), they conse-
quently act at a short dis-
tance from the fulcrum,
the condyle (12), whilst
the resistance is situated at
a distance from the power;
the masseter and ptery-
goid muscles are fixed to the
inside as well as to the out-
side of the lower jaw ;
theyare fleshy and powerful, Internal surface.

for the purpose of raising the jaw with force, for crushing

126

BONES OF THE TEUNK.

and dividing the substances introduced between tbe teeth.
The mechanical disadvantage arising from having the power
thus placed so near the fulcrum, is compensated by the greater
rapidity of motion which such an arrangement permits, whilst
sufficient vital power is given to the elevatory muscles to
admit of the sacrifice of lever power. When a hard body is
introduced between the teeth, requiring an unusual force to
break it, we instinctively carry the body far back in the mouth,
in order to bring it more immediately under the power of the
lever. The motions of the jaws of quadrupeds will be treated
of more in detail, when the anatomical structure of the rumi-
nants, carnivora, and rodents is under special investigation.

THE TRUNK.

[§ 252. The most essential part of the skeleton is the verte-
bral column, of which the skull may be considered an expan-
sion, consisting, as it does, of three vertebra, the elements of
which have undergone great development, to encompass and
enclose the three primary divisions of the brain. The osseous
appears to follow the cerebro-spinal system, in the various
phases of its development, and may be regarded as a satellite
moving round the primary nervous centres. The vertebral
column occupies the middle line of the body, forming the
central axis, which sustains all the other parts of the skeleton.
It is composed in man of thirty-three vertebrae, arranged
into those of the neck, back, loins, sacrum, and coccyx.

[§ 253. A vertebra (fig. 105) is one of the segments of

Fig. 105.

the internal skeleton constituting this axis, and forming canals

CEEYICAL YEETEBE^E.

127

for protecting the central trunks of the nervous and vascular
systems, and to which, likewise, sometimes, appendages are
attached. A typical vertebra consists of a centre (centrum),
and ten processes (apophyses). From the upper part of
the centrum rise two neurapophyses, which form an arch
for enclosing the spinal cord and brain. These are sur-
mounted by a spine, called the neural spine. From the sides
of the centrum two transverse processes, or parapophyses, pro-
ject, which sometimes carry ribs, or pleurapophyses. From the
under side of the centrum two processes descend to enclose the
vascular trunks, in the same manner as the neurapophyses en-
close the spinal cord, they are called h&mapophyses ; from
them descends a single haemal spine. The vertebral elements un-
dergo various phases of development in the different classes,
and in different regions of the spinal column of the same animal ;
it is therefore only by taking a philosophical view of their
structural development in the animal series that we obtain a
knowledge of the beautiful law which produces such endless
variety out of a few simple elements.

[§ 254. THE CEEYICAL YERTEBEJE (figs. 106 and 107) are
smaller than the p. infi p.

others. We ob-
serve in them a
deviation from
the typical form
existing in the
dorsal region,
fig. 105 ; the
transverse pro-
cesses, fig.

107 (g, g), parapophyses, and ribs, pleurapophyses, are rudi-
mentary, and soldered together, forming a hole (8), through
which the vertebral artery passes to the brain ; the hcema-
pophyses are absent. This explanation of the structure of the
transverse processes of the cervical vertebras is beautifully
illustrated in the neck of struthious birds. In all mammals we
find seven cervical vertebrae. The first vertebra of the neck,
the atlas (figs. 108 and 109), supports the skull ; it is more
moveable than the others, and differs considerably from the
typical form; the centrum (i) is much reduced to receive a
toothlike process, rising from the centrum of the second ver-
tebra (fig. 110, k) ; around this pivot the atlas revolves, aud

128

CERVICAL

the lateral movements of the head are accomplished thereby,
whilst the upward and downward movements are performed by

Fig. 108. Fig. 109.

the play of the condyles of the occipital bone (fig. 90, 16) on the
broad concave articular surfaces of the atlas (fig. 108, 2). Fig.
108 shews the superior, and fig. 109 the inferior surface of this
vertebra. A firm ligament is stretched across the ring, dividing
it into two apertures ; the anterior hole (1) receives the tooth-
like process of the axis, the posterior hole (6) gives passage to
the spinal cord. The essential element of a vertebra is the
centrum, the next in constancy are the two neurapophyses, the
other elements undergo various phases of development. We
rarely find all the elements present in one vertebra ; some
are absent, others are rudimentary, and others expand into
disproportionate dimensions, in order to accomplish some
destined end. A typical vertebra with all its elements, presents
four channels disposed around the centrum; we find this
typical vertebra in the thorax of mammals, birds, and lizards.
Let us take, for example, the third, fourth, or fifth dorsal
vertebra of man (fig. 105) : the centrum (a, b) is broad, solid,
and slightly biconcave ; from its posterior part arise the two
neurapophyses (fig. 105, 7), which arch over and enclose the
spinal cord (6), and terminate in the neural spine (5) ; the two
transverse or parapophyses are seen at (4, 4) ; to the sides of the
centrum the dorsal ribs or two pleurapophyses are attached (fig.
1 24y,ihehtemapophyses are represented by the sternal cartilages,
which are united to the distal extremity of the ribs; the htemal
element is a broad flat bone, forming one of the segments of the
sternum ; these five elements unite to form one of the large hoops
of the thoracic cage (fig. 124), for enclosing and protecting
the heart and the great trunks of the vascular system ; the
lateral channels giving transit to the nerves and blood-vessels.

DOESAL VEETEBE.2E.

Fig. 110 is the axis or second vertebra of the neck, with the
round tooth-like process (k) rising from pig. no.

its centrum (1) ; from the extremity of
this process two strong ligaments pass
obliquely outwards, to be attached to
the occipital bone ; (2) is the articular
surface, which plays on a like process
of the atlas (fig. 109, 3).

The seventh vertebra (fig. Ill) differs
from the other cervical, in being larger, having the transverse
processes (4, 4) single, with a hole in
each for the transmission of the vertebral
veins ; constituting a transition to the
typical form met with in the middle re-
gion of the thorax.

[§ 255. THE DOESAL VEETEBEJE (figs.
1 1 2 and 113) diminish in size from the
first to the fourth or fifth, from which
they increase to the twelfth, which is the
largest of all. The centrum (1, «, 6,) is
longest in the antero-posterior direction ;
the parapophyses (4, 4,) are short and stout, and the neurapo-

Fig. 111.

Fig. 112.

Fig. 113.

10

physes (6)
broad, and
inclined to
form a
complete
osseous tile-
like case for
protecting
the spinal
cord ; the
neural spine
(5) is long,
and direct-
ed obliquely downwards, terminating in a tubercle for muscular
attachment. The number of the dorsal vertebrae corresponds with
the number of the ribs, which in man amounts to twelve pair.
Fig. 114 shews the articulation of the xth, xith, and xnth
dorsal vertebrae, and the changes of form which the centrum and

K

130

LUMBAR YERTEBR.E.

4

XII

apophyses present, when compared with the fourth and fifth ;

(figs. 112 and 113) the parapophy-
ses and pleurapophyses are short,
and the hcemapophyses have disap-
peared. We here see a transition
form, for blending with the ver-
tebras of the loins.

[§ 256. THE LUMBAR VERTE-
BRA (figs. 115 and 116) are of a
larger size than those in the dor-
sal region ; they are five in num-
ber, and have the long diameter
of the centrum in the trans-
verse direction ; the neural spine
presents a considerable surface
for the tendinous attachment of
the muscles of the back and
loins ; tlieparapophyses are short,

and the pleurapophyses are absent.

Fig. 115.

i£. 116.

Fig. 117 represents the fifth lumbar vertebra, which differs
from the others in having the under surface of its centrum
oblique, so that the anterior is deeper than the posterior
part, whereby it is better adapted for articulating with the sa-
crum, and affording us another example of a phase of transi-
tion from one form to another.

SACEUM AND COCCYX.

131

[§ 257. The SACEUM (fig. 118) is of a triangular shape, its
base (1) facing upwards and forwards ; its apex, which is
Fig. 117. Fig. 118

13

truncated (2), also facing forwards. It is concave before
from above downwards, and irregularly convex behind (fig. 1 20,
a) in the same direction. Fig. 119. Fig. 120.

In the young subject it
consists of five verte-
brae, which in the adult
become soldered into
a single bone. In
mammals it is much
narrower than in man,
and forms in them a
straight line with the
spine ; the separate
pieces thereof remaining permanently united by ligaments. In
animals which sometimes hold themselves erect, as monkeys,
bears, sloths, and many rodents, it is proportionally larger than
in other mammals. On the concave anterior surface of the sacrum
we observe holes (4) for the passage of the nerves ; and on its
posterior surface (fig. 120), similar apertures (11, 11, 11) for
the same purpose are seen. Fig. 119 is a profile of this bone.

[§ 258. The COCCYX consists of four small bones, which re-
tain only a rudimentary centrum, and are soldered together in
man (fig. 119, 2.) These bones are, in fact, the rudiment of an
organ, the tail, which attains great importance and dimensions
in some animals, as shown in the comparative table (§ 260).

[§ 259. The VEETEBE.E are firmly united together by pro-
cesses of bone (fig. 1 1 4 — 1 1 6, 2 and 3) that lock into each other.
Bet ween every two vertebrae, an elastic fibro- cartilaginous cushion

K2

132

SPINAL COLUMN.

is interposed. By this arrangement the chain of bones is
converted into a strong elastic central axis, more or less move-

Fig. 121.

Fig. 122.

m different animals, ac-
cording to the general struc-
ture and habits of each.

Fig. 121 exhibits a front
view of the spinal column of
man. It is of a pyramidal
form, the base of the pyramid
rests upon the sacrum, and
the apex supports the skull.
We observe, likewise, that the
diameter of the bodies of the
vertebrae differs in different
regions, being broad in the
neck, narrow in the back,
and broad again in the loins.

Fig. 122 represents a pos-
terior view of the spinal co-
lumn. The different forms of
the neurapophyses, in the cer-
vical, dorsal, and lumbar re-
gions, are here shewn. They
are observed to project back-
wards and a little downwards
in the neck ; they lie obliquely
downwards in the back, and
stand backwards in the loins.
On each side of the neural
spines, a groove is seen formed
by a junction of the arches of
all the vertebrae ; bounded
internally by the neural&pmes,
and externally by the para-
popliyses ; in this groove the
muscles are lodged that im-
part motion to the column.

Fig. 1 23 is a lateral view
of the spinal column, which
presents anteriorly two con-
vex, and one concave surface.

SPINAL COLUMN.

133

The upper convexity is formed by the lower cervical and the
upper dorsal vertebrae, and the lower convexity by the lum-

Fig. 123.

bar vertebrae ; whilst the central conca-
vity is formed by the middle dorsal ver-
tebrae. Behind the centra we see the
lateral holes for giving transit to the spinal
nerves, and formed by the junction of the
notches in the neurapophyses. The direc-
tion of the neurapophyses and parapophy-
ses is likewise well seen in this figure.

[§ 260. The following table* shows the
number of the vertebrae in the different
regions of the spinal column, in a few
familiar examples from mammals, birds,
reptiles, and fishes. It is important -to
note, that the number seven prevails in
the cervical vertebrae of all mammals,
whether we study these bones in the rudi-
mentary condition in which they exist in
whales, or in the enormous development
they attain in the neck of the giraffe.
The increased number of the bones in
the same region, in birds, is a compensa-
tion for the want of anterior prehensile
members, the neck, in birds, being used
as an arm. The number of the dorsal
vertebrae ranges from 7 to 320 ; the lum-
bar, from 2 to 9 ; and the coccygeal, from
4 to 115. The table might have been
greatly extended ; but those who wish for
further information on this interesting
branch of comparative osteology, are re-
ferred to the great work from which it is
extracted : —

J

* Cuvier, Lemons D'Anatomie Comparee, torn. i.

134

NL'MBEB OF THE YEETEBEZE.

COMPARATIVE TABLE OF THE NUMBER OF THE

VERTEBRA.

MAMMALIA.

Cervi-
cal.

Dorsal.

Lumbar.

Sacral.

Coccy-
geal.

Total:

Man

7

12

K.

5

4

33

Long-tailed Monkey . .

7
7

12
13

7
7

3
3

31

26

60
56

Long-tailed Opossum . .
Long-tailed Ant-eater . .
Elephant

7
7
7

16
16
20

6
3
3

2
6
4

36
40
27

64
72
61

Giraffe

7

14

5

4

18

48

Whale

7

15

9

1

27

59

BIRDS.
Vulture

15

7

13

6

41

Swallow

13

7

10

7

37

Turkey

14

7

15

6

42

1 Q

9

19

q

55

17

10

15

p.

48

2^

11

16

Q

58

REPTILES.
Tortoise

q

10

Q

90

49

Monitor (Lizard)

ft

21

2

2

1 46

Python (Boa)

320

102

itV

429

Rattle-Snake

171

^

907

Land Salamander ....

i

2

14
18

—

1

ou
26

49

£U /

44

fi9

FISHES.
Perch

21

91

\}£i

49

Mackerel

15

1 6

Ql

Trichiurus

60

100

160

Salmon

34

99

56

Cod

19

Q A

5^

Conger Eel

60

Ot
IflO

oo
162

Electric Eel

236

Shark

95

970

3fi=»

L.l\)

OOu

BOXES OF THE THOEAX.

135

[§ 261. The THOEAX is formed by the twelve dorsal ver-
tebrae, the ribs, and sternum ; the vertebrae have their elements
well developed in this region, to form an osseous cage for pro-
tecting the heart, lungs, and great bloodvessels (fig. 1 24). The

Fig. 124.

ribs,

pophyses, are
attached by a
head to the cen-
trum, and by a
tubercle to the
parapophyses;
the hcemapo-
pJiyses, or car-
tilages, are un-
ossified, and
removed to the
distal end of the
ribs; they unite
before with the
hcema /bones, or
sternum, which
is here placed
in the median
line,

The haemal
elements play
an important
part in the eco-
nomy of many
animals. In

birds and tortoises, the sternum is widely expanded, its deep
keel affording a large surface for the attachment of the
pectoral muscles in birds (fig. 77), and for the same muscles
in the mole and the bat among mammals. In man, only seven
of the twelve ribs form a complete hoop, as the hcemapophyses
of the five inferior ribs are united together, and the haemal ele-
ments of these are wanting. In crocodiles, the hcemapophyses,
or sternal ribs, are ossified ; and similar ossified apophyses are
continued along the fore part of the abdomen to the pubis.
Rudiments of these abdominal ribs are seen in the transverse
tendinous intersections of the rectus abdominis muscles in

13(5

THE PELYIC ARCH.

man and other mammals ; which attain their culminating
point in the reptilian type of structure, where they exist under
the form of true abdominal ribs.

[§ 262. The extremities are united to the trunk by two

girdles of bone, composed in the upper of the scapular, and

Fig. 125. Fig. 126.

Female. Male.

in the lower of the pelvic arches. The scapular arch presents
many modifications, to adapt the anterior members as instru-
ments for prehension and locomotion. The pelvic arch is of a
more uniform structure, as the posterior extremities form in-
struments of locomotion alone.

§ 263. The PELYIC AECH (fig. 125) is composed of three pair
of bones, which are separate in infancy, but soldered together
in the adult. One of these bones, the ilium (a), is firmly

Fisr. 127. Fiff. 128.

THE PELYIC ARCH.

137

united to the sacrum, and another, the pubis, joins its fellow
from the opposite side, forming the crown of the arch, whilst
the ischium is wedged in between them ; these three bones form
the ossa innominatum of the human anatomist.

Figs. 127 and 128 represent these haunch bones, (i) is the
ilium (n), the ischium, and (in) the pubis. The broad iliac
bones form the brim of the pelvis (fig. 125), they afford sup-
port to the viscera of the abdomen, and give attachment by both
their surfaces to the large and powerful muscles by which
the thigh is moved, and the trunk retained erect upon the
lower extremities. The brim of the pelvis («, «, a, a) differs in
the two sexes. In the male (fig. 126), the greatest diameter is
in the antero-posterior ; in the female (fig. 125), in the trans-
verse direction. A comparative view of the outlet (b, b, b, b)
(figs. 129 and 130) in a male and female pelvis, shews this
opening to be of a diamond form, having the angles before,
behind, and on the sides. In the male (fig. 130), the outlet is

Fig. 129. Outlet. Fig. 130^

Female.

Male.

small; in the female (fig. 129), it is large. The greatest
diameter is from the sacrum to the pubis in the female, in con-
sequence of the sacrum being less curved than in the male. The
space comprised between the brim and the outlet is called the
true pelvis, in which the pelvic viscera are lodged. On each
side of the pubic arch a large oval hole (obturator foramen),
is formed by the ischium and pubis. It Fig. 131.

gives passage to blood vessels and nerves,
and is partly closed by a ligament. On
each side of the obturator hole, but some-
what behind that opening, is the cup-
shaped cavity for receiving the head of the
thigh bone (acetabulum) (fig. 131, e),
formed by the junction of the ilium (i),

138

THE THIGH BONE.

the ischium (n), and pubis (in). The continuity of the mar-
gin is interrupted at the under and fore part, by a notch (/),
which is filled up with ligament. Opposite the notch is a cavity
(#), to which the round ligament of the / emur is attached. The
axis of the pelvis is so placed that the weight of the trunk

Fig. 132. Fig. 133. Fig. J34. '

does not rest on the
outlet, but upon the tu-
berosities of the ischia
(fig 132, a). The open-
ing of the outlet, there-
fore, points downwards
and backwards, and
that of the brim for-
wards and np wards.

[§ 264. THE THIGH
is composed of a single
bone, the femur (figs.
133 and 134). It con-
sists of a head, neck,
tro chanters, body, and
condyles. The round
head (1) has a pit for
the insertion of the
round ligament (2), which is accurately adapted to the ace-
tabulum and retained therein by ligaments and atmospheric
pressure. The neck (3) connects the head with the shaft or
body. At the point where it joins the latter, we observe two

BOXES OF THE LEG.

139

large projections. The larger (5) is called the great, and the
smaller (7) the lesser trochanter, which serve for the attach-
ment of the principal motory muscles of the thigh. The body
(9 9) is arched before, and slightly concave behind, where we
observe a rough projecting line (linea aspera) (10), which like-
wise affords a firm surface for the attachment of the muscles of
the thigh. The lower end of the body expands into two large
condyles (12, 13), of which the inner (13) is longer and larger.
Fig. 134 represents a front view, and fig. 133 a back view of the
femur. The coudyles move upon the head of the Fig. 137.
tibia only in one plane. The knee joint is, there-
fore, apure hinge, its motions being restricted by
lateral and crucial ligaments, whilst the round
head of the femur forms, with the acetabulum,

a ball and socket joint, and executes thereby

movements in all directions.

[§ 265. THE LEG- (fig. 137) consists of two

bones, the tibia (n) and fibula (in). The

tibia has a broad head, on which the condyles

of the femur play ; to its upper surface is

attached, by a ligament, a small round bone,

the patella (i), or knee-pan, which protects

the joint in front, and changes the direction

of the tendons descending from the thigh to

be inserted into the tibia, and thereby enabling

them to act more advantageously upon the leg.

The fibula (in) is a slender bone placed at the

external side of the tibia. It affords attachment

to muscles, and assists in the formation of the

ankle joint. The latter joint, however, being

formed chiefly by the lower end of the tibia; that

bone supporting the entire weight of the body.
[§ 266. THE FOOT consists of the TARSUS,

METATARSUS, and TOES. Fig. 138 shews

these parts of the foot. A is the tarsus, B the

Fit?. 138.

Tin

III

140

BONES OF THE TOOT.

Ill

Fig. 140.

Fig. 141.

IV

VII

VII

metatarsus, c the phalanges of the toes. The TAHSTJS con-
sists of seven bones arranged in two rows. In the first row
Fige 139. (fig. 139) is the astragalus (i), os

i naviculare (n), os calcis (m). The

articulation with the leg is formed
by the astragalus, which projects
above the rest, and fits into the
space between the tibia and the
fibula. The astragalus (i) rests upon
the heel bone, os calcis, (in), which
projects backwards, and is connected before with the navi-
cular bone (11). The second row (Fig. 140) consists of three

wedge-shaped
bones, ossa cu-
neiformia (rv,
V,YI), and the
cuboid bone,
05 cuboides
(YII). The con-
cave posterior

surfaces (i, i, i, T) articulate with the first row of the tarsal

bones and the convex an-
terior surfaces (fig. 141, 2,
2, 2, 2) with the metatarsal
bones.

[§ 267. The METATAKSUS
consists of five bones (fig. 142),
of which the first, or that of the
great toe, is the shortest and
largest, and that of the second
he longest. The bases (A)
have flat articular surfaces to
join them with the tarsus, and
heads (c) or articular sur-
faces for the phalanges ; the
middle part is the body (B),
which is convex above and
broad beneath.

[§ 268. THE TOES consist of
fourteen bones (fig. 143), of
which there are but two rows

THE SCAPULAE AECH.

141

to the great toe (i), and three to the other toes (11, in, iv, T) ;
their division is similar to that of the fingers, into base, body, and

Fig. 143.

Under surface.

head, but they are much shorter
and flatter.

The foot of man is distin-
guished from the corresponding
part in the quadrumana by its ca-
pability of being planted flat upon
the ground, and the strength of
the base thus afforded ; the paral-
lelism and magnitude of the
great toe, the advanced position
of the astragalus, the backward
extension of the heel, the fixed
condition of the tarsus, the
strength of the metatarsal bones and those of the phalanges,
form the distinctive differences between the foot of man and
that of monkeys : when we notice an ourang or chimpanse
attempting to walk erect, the foot is seen resting on its outer
side, the heel scarcely projecting, and they can only sustain
the erect position by supporting their hands upon some body.

[§268*. The internal side of the foot is constructed as an arch,
for lodging and protecting the blood vessels, nerves, and tendons
of the toes ; this arch likewise forms a spring by which sudden
shocks are diminished, the elasticity of the tarsal and meta-
tarsal articulations contributing to this end ; the jar being
broken thereby before it is transmitted to the limb. This pro-
vision is still further developed in the feet of certain animals,
like the cats, which bound after their prey ; in addition to
the elasticity of the tarsus and metatarsus, their feet are sup-
plied with elastic pads, to break the shocks occasioned by their
springing habits.

[§ 269. THE SCAPULAE, like the pelvic arch, consists of three
pair of bones, the scapula, the coracoid and the clavicle,
which are the homologues of the ilium, the ischium, and the
pubis ; early in life, in man, the coracoid becomes soldered to
the scapula, and is described as a process of the latter bone,
but it exists as a distinct element of the scapular arch in rep-
tiles and birds, and in the ornythorhyncus among the mono-
trematous mammalia.

Fig. 144 shews the right half of the scapular arch of manz'w

142

BOXES OF THE SHOULDER.

situ. The clavicle (1) is seen resting its internal head upon the

Fisr. 144.

first bone of the sternum,
and having its external
end attached by ligaments
to the acromion process
of the scapula ; the clavi-
cle maintains the shoulder
at a fixed distance from
the trunk.

[§ 2/0. THE SCAPULA
is a large flat bone, situ-
ated on the upper and
external part of the back.
It is of a triangular
form, and at its upper

. •*• L
and external angle expands to form a shallow cavity, called

Fig. 145.

Fig. 146.

the glenoid cavity (4), in which the head of the humerus
is received ; on the upper part of the body a prominent
ridge of bone rises (13), which passes upwards and out-
wards, and terminates in the acromion process (14), which
is expanded over the top of the joint, forming the bony
projection of the shoulder. The coracoid process (16)
is attached by a thick root to the anterior and upper part
of the neck of the bone (5), and curves forwards and out-

BONES OF THE AEM.

143

wards before the glenoid cavity ; the scapula is articulated
by the smooth face of the acromion process (15), to the
clavicle ; and affords an extensive attachment to the muscles
of the shoulder and those belonging to the arm and fore-arm ;
this bone is present in all animals possessing anterior members,
although its form undergoes many changes in birds and rep-
tiles. Fig. 145 represents the posterior view. Fig. 146, the
anterior view. Fig. 147, a profile of the scapula.

[§ 271. THE CLAYICLE, so called from its resemblance to
an ancient key, is divided into a Pigt 143.

body, two extremities, two arti-
cular surfaces, and two processes.
Its shape is that of a small Italic
/, placed horizontally ; its inner
or sternal extremity (1) is very
large, and irregularly cylindri-
cal ; upon its point is a large
articular surface (2), by which it
joins with the interarticular car-
tilage placed between it and the sternum ; the round arched
body expands and forms the scapular extremity (4), having
on its under surface a tuber (5), for the attachment of liga-
ments, and upon the outer extremity a plain articular sur-
face (6), by which it is united to the acromion process of
the scapula. The principal use of this bone is to keep the
shoulders apart, and complete the resistance of the scapular
arch in those animals, as the quadrumana and rodents, that
use their anterior members as prehensile instruments, and in
the bats and birds, whose anterior members are organs of flight ;
as the down-stroke of the wing tends to force the humerus
inwards ; in birds, likewise, the coracoid bone appears as a
distinct element of the arch.

[§ 272. THE HUMERTJS (fig. 149) is the homologue of the
femur, and, like it, is formed of a head, neck, body, and con-
dyles. The large round head (1) is received into the shallow
glenoid cavity (fig. 147,4), by which great freedom of motion
in ail directions is obtained ; the neck (5) is short and thick,
and the body (6) appears as if the upper part were twisted out-
wards, and the lower part inwards, the outer side of the body
presenting a rough surface (9) for the attachment of muscles.
The lower extremity of the shaft is enlarged to form a pulley-like
surface, upon which the ulna moves in one plane ; the outer

144

BONES OF THE ABM.

Fig. 149.

Fig. 150.

condyle (13) projects but little, whilst the inner condyle (14)

forms a considerable promi-
nence which projects inwards;
the condyles afford an exten-
sive surface for the attach-
ment of the muscles of the
fore-arm ; behind the inner
condyle is a deep fossa (19),
for receiving the olecranon pro-
cess of the ulna, and above
the condyles, on the front of
the bone, is a pit (18) for
receiving the coronoid pro-
cess of the same. Fig. 149
gives a front view, fig. 150
a back view of the humerus ;
fig. 151, the round head and
tubercles (3, 4) ; fig. 152,
the lower surface of the con-
dyles, (15) is the surface on
which the head of the radius
plays, (16) receives the sig-
t , moid cavity of the ulna, and
(17) is a groove for the pas-
sage of the ulnar nerve.

[§ 273. The fore-arm con-
sists (fig. 153) of two bones,
the RADIUS and the ULNA,
which are the homologues
of the tibia and the fibula.
These bones lie nearly pa-
rallel to each other, the ra-
FiS- 15i- FiS- 152- dius (1) on the outer, and the

ulna (11) on the inner side of the arm; they are united by
ligaments, and by a fibrous membrane stretched across the
interspace between them ; they have, however, a considera-
ble range of motion upon each other and upon the humerus.
The flexion and extension of the forearm is performed by the
ulna (1), which forms, with the humerus, a true hinge joint.
At its upper part we observe the olecanon process (fig.
153), which locks into a cavity (fig. 150, 19) on the posterior

OF THE FORE-ABM.

145

surface of the hurnerus ; which acting as a stop, renders exten-
sion beyond the straight line impossible. The hand is attached
to the lower end of the radius ; and as that part was Yig. 153
designed to perform pronation and supination, a
peculiar mechanical provision was necessary for
these important motions. The round head of the ra-
dius (fig. 153, n) is bound by a firm annular liga-
ment to the ulna (i), and the concavity on its sur-
face is received in a corresponding convexity on the
outer condyle of the humerus. Hence both bones
move upon the humerus, in acts of flexion and
extension, whilst the radius rolls upon the ulna,
carrying with it the hand in pronation and
supination, separate sets of muscles being as-
signed to each class of movements. It is only among
the higher mammals that any motion is permitted
between the bones of the fore-arm. These motions =1
are most important in man ; for without them
the hand would be incapable of a vast variety
of movements so necessary to the full develop-
ment of the purposes for which that instrument
was designed. When the free motions between
the bones of the fore-arm are impaired by injury

Fig. 154.

146

BONES OF THE CARPUS.

Fig. 155.
I 11 HI

Fig. 156.

Lower surface. 1

IV. Upper surface

Fig. 157.

VI VII

VIII

Fig. 158.

VIII VII VI

or disease, we learn the amount of importance they confer
upon the hand.

[§ 2/4. The HAND consists of the CARPUS, METACARPUS,
and PHALANGES; of these, part of the carpus (fig. 154 A), with
the radius, form the wrist joint ; the metacarpus (B) forms the
palm of the hand, and the phalanges (c) the fingers.

[§ 275. The CARPUS consists of eight bones, forming an

arch, (figs. 155 —
158), the concavity
of which is placed be-
fore, and the con-
vexity behind. These
eight bones are ar-
ranged in two rows,
four in each row ;
there are, in the first row (figs. 155, 156), on the outside the os
scaphoides (i), on its inner side the os lunare (n), next it the os
cuneiforme (in), and on the front of that bone the os pisiforme
(iv) : in the second row (figs. 157, 158), on the outside is the

os trapezium
(v), next to it
the os trape-

zoides (YI), to
its inner side,
the os mag-
num (vii),
and next to

that the os unciforme (vm). Of these bones the first row is
articulated above with the radius, and the interarticular car-
tilage at the extremity of the ulna, and below with the second
row ; the second row articulates above with the first row, and
below with the bases of the metacarpal bones.

[§ 2/6. The METACARPUS consists of five bones (fig. 158*),
each of which is divided into its upper part, or basis (A) ;
middle or body, corpus (B) ; and lower part or head, caput (c),
which forms the knuckle, and projects when the fingers are
bent. Upon the bases are articular surfaces for the carpal
bones.

[§ 277. The thumb and fingers of each hand consist of four-
teen pieces, or phalanges (fig. 159) ; of these twelve belong to
the fingers, and are disposed in three rows, those of the middle
finger (in) being longest, and of the little finger (v) shortest ;

Lower surface.

Upper surface

BONES OF THE HETACAEPUS AND PHALANGES.

147

Fig. 158.*
Bases.

an.

Front.

whilst the thumb (i) has but two, its middle phalanx being de-
ficient, but they are strong-
er than those of the fin-
gers.

[§ 277. The PHALANGES
consist of base (fig. 159)
(1), body (2), and head
(3) ; they taper from the
base, or upper part of the
head, the intermediate part
or body being rounded be-
hind, and flat before, with
two projectinglateral edges
for giving attachment to
the sheaths of the ten-
dons.

[§ 278. In reviewing the
structure of the upper ex-
tremity, we have seen that
it consists of a series of
levers joined together, and diminishing progressively in length.
Thus, the arm is longer
than the fore-arm ; the lat-
ter is longer than the
and each joint

hand ;
of the

er than the one which it
succeeds. By this admi-
rable arrangement the nu-
merous joints in the hand
permit that useful instru-
ment to vary its motions in a
thousand different ways, to
adapt it to the various bo-
dies itis designed to handle,
grasp, and touch; whilst the
long levers formed by the
arm and fore-arm allow the hand to be rapidly changed to a con-
siderable distance in all directions. It is principally by the
movements of the humerus upon the scapula, that the direction
of the limb is given ; the flexion and extension of the fore-arm

L2

Fig. 159.

Front.

fingers is short-

n

in

148 ORGANS OF LOCOMOTION

regulating the length ; whilst the multiplied movements of the
thumb and fingers perform the special acts which the hand waa
designed so admirably to execute. The quadrumana, like man,
have the thumb opposable to the other fingers. It is this, in fact,
which forms the true character of the hand. But the bones of
the thumb in man are more lengthened and powerful, in propor-
tion to the other fingers, than in monkeys, whose hand does
not equal his in perfection ; for monkeys can neither seize
minute objects with that precision, nor grasp and support large
ones with that firmness which is so essential to the dextrous
performance of the multitudinous purposes for which the hand
of man was designed. — T. W.]

1. PLAN OF THE ORGANS OF LOCOMOTION.

§ 279. The organs of progression in vertebrated animals
never exceed four in number, and to them the term limbs is
more particularly applied. The study of these organs, as
characteristic of the different groups of vertebrate animals, is
most interesting, especially when prosecuted with a view to
trace them all back to one fundamental plan, and to observe
the modifications, oftentimes very slight, by which a very sim-
ple organ is adapted to every variety of movement. No part
of the animal structure more fully illustrates the unity of de-
sign, or the skill of the Intellect, which has so adapted a single
organ to such multiplied ends. On this account we shall
illustrate the subject somewhat in detail.

§ 280. It is easy to see, that the wing which is to sustain
the bird in the air (fig. 1 64), must be different from the leg of
the stag (fig. 160), which is to serve for running, or the fin of
the fish (fig. 168) that swims. But, notwithstanding their dis-
similarity, the wing of the bird, the leg of the stag, and the
shoulder fin of the fish, may still be traced to the same plan of
structure ; and if we examine their skeletons, we find the same
fundamental parts.

§ 281. In the arm of man (fig. 78), the shoulder-blade is
flat and triangular ; the bone of the arm is cylindrical, and
enlarged at its extremities ; the bones of the fore-arm are
nearly the same length as the humerus, but more slender ; the
hand is composed of the eight small bones of the carpus,
arranged in two rows, five metacarpal bones, which are elon-
gated, and succeed those of the wrist , five fingers of unequal
length, one of which, the thumb, is opposed to the four others.

VERTEBRATED ANIMALS.

149

§ 282. In the stag (fig. 160), the bones of the fore-arm
(c, e?,) are rather longer than that of the arm (b), and the
radius no longer turns upon the ulna, fig. 160.

but is blended with it ; the metacarpal
or cannon-bone (/), is greatly deve-
loped ; and being quite as long as the
fore-arm, it is apt to be mistaken for it.
The fingers (#) are reduced to two, each of
which is surrounded by a hoof, at its
extremity.

§ 283. In the arm of the lion (fig. 161),
the arm bone (6) is stouter, the carpal bones
(<?) are less numerous, and the fingers (/")
are short, and armed with strong, retrac-
tile claws (#). In the whale (fig. 162), the
bones of the arm (6) and fore-arm (c, c/,) are
much shortened, and very massive ; the
hand is broad, the fingers (g} strong, and
distant from each other. In the bat (fig.
1 63), the thumb, which is represented by a
small hook, is entirely free, but the fingers
Fie. 161. Fig. 162.

-ft

Fig. 163.

Fig. 164.

are elongated in a disproportionate manner, and the skin is
stretched across them, so as to serve the purpose of a

wing.

150

ORGANS OP LOCOMOTION

In birds, the pigeon, for example (fig. 164), there are but two
fingers (</), which are soldered, and destitute of nails ; and
the thumb is rudimentary.

§ 28-4. The arm of the turtle (fig. 166) is peculiar in having,

Fig. 165

Fig. 166.

Fig, 167.

besides the shoulder-blade («), the coracoid bone and the cla*
vicle; the arm-bone (6) is twisted outwards, as well as the bones
of the fore-arm (c, d\ so that the elbow, instead of being be-
hind, is turned forwards ; the fingers (g) are long, and widely
separated. In the sloth (fig. 165), the bones of the arm (b] and
fore-arm (c,d] are very greatly elongated, and at the same time
very slender ; the hand is likewise very long, and the fingers (g}
are terminated by enormous non-retractile nails. The arm of
the mole (fig. 167) is still more extraordinary. The shoulder-
blade («), which is usually a broad and flat bone, becomes very
narrow ; the arm-bone (b), on the contrary, is contracted so
much as to seem nearly square, the elbow projects backwards,
and the hand (e, f, g] is excessively large and stout.

§ 285. In fishes, the form and arrangement of the bones is so
peculiar, that it is often difficult to trace their correspondence to
all the parts found in other animals ; nevertheless, the bones of
the fore-arm (c, d] are readily recognized. In the cod (fig. 1 68),

Fig. 168.

there are two
flat and broad
bones, one of
which, the
ulna (d), pre-
sents a long
point, anteri-

IN YERTEBRATED ANIMALS. 151

orly. The bones of the carpus (e) are represented by four
nearly square little bones ; but in these, again, there are
considerable variation in different fishes, and in some genera
they are much more irregular in form. The fingers are but
imperfectly represented by the rays of the fin (<?), which are
composed of an infinitude of minute bones, articulated with
each other. As to the humerus and shoulder, their analogies
are variously interpreted by different anatomists.

§ 286. The form of the members is so admirably adapted to
the especial offices which they are designed to perform, that by
a single inspection of the bones of the arm, as represented in
the preceding sketches, one might infer the uses to which they
are to be put. The arm of man, with its radius turning upon
the ulna, the delicate and pliable fingers, and the thumb op-
posed to them, bespeak an organ for the purpose of handling.
The slender and long arm of the sloth, with his monstrous claws,
would be extremely inconvenient for walking on the ground,
but appropriate for seizing upon the branches of trees, on
which these animals live. The short fingers, armed with re-
tractile nails, indicate the lion, at first glance, to be a carnivo-
rous animal. The arm of the stag, with his very long cannon-
bone, and that of the horse also, with its single finger en-
veloped in a hoof, are organs especially adapted for running.
The very slender, and greatly elongated fingers of the bat are
admirably contrived for the expansion of a wing, without in-
creasing the weight of the body. The firm and solid arm
of the bird indicates a more sustained flight. The short arm
of the whale, with his spreading fingers, resembles a strong oar.
The enormous hand of the mole, with its long elbow, is con-
structed for the difficult and prolonged efforts requisite in bur-
rowing. The twisted arm of the tortoise can be applied to no
other movement than creeping ; and, finally, the arm of the
fish, completely enveloped in muscles (fig. 76), presents, ex-
ternally, a mere delicate balancer, the pectoral fin.

§ 287. The posterior members are identical in their struc-
ture with the anterior. The bones of which they are com-
posed are, 1. The pelvis (figs. 125 and 169), which corre-
sponds to the shoulder blade ; 2. The thigh bone, or femur,
which is a simple bone like the humerus ; 3. The bones of the
leg, the tibia and fibula, which, like the radius and ulna, some-
times coalesce into one bone ; and lastly, the bones of the foot,

152 'IHE MODES OF PROGRESSION*.

which are divided, like those of the hand, into three parts, the
tarsus, metatarsus, and toes. Their modifications are generally
less marked than in the arm, inasmuch as there is less diversity
of function ; for in all animals, without exception, the poste-
rior extremities are used exclusively for support or locomotion.
§ 288. The anterior extremity of the vertebrata, however
varied in form, whether it be an arm, a wing, or a fin, is com-
posed of essentially the same parts, and constructed upon the
same general plan. This affinity does not extend to the in-
vertebrata, for although in many instances their limbs bear a
certain resemblance to those of the vertebrata, and are even
used for similar purposes, yet they have no real affinity. Thus
the leg of an insect (fig. 34), and that of a camel (fig. 169),
the wing of a butterfly, and the wing of a bat^ are quite similar
in form, position, and use ; but in the bat (fig. 1 63) and the camel
(fig. 169), the organ has an internal bony support, which is a
part of the skeleton ; while the leg of the insect has merely
a horny covering, proceeding from one of the rings of the
body, and the wing of the butterfly is merely a fold of the
skin ; showing that the limbs of the articulata are constructed
upon a different plan. It is by ascertaining and regarding
these real affinities, or the fundamental differences existing
between similar organs, that the true natural grouping of ani-
mals is to be attained.

2. OF STANDING, AND THE MODES OF PROGRESSION.

§ 289. STANDING, or the natural attitude of an animal, de-
pends on the form and functions of the limbs. Most of the
terrestrial mammals, and the reptiles, both of which employ
all four limbs in walking, have the back-bone horizontal, and
resting at the same time upon both the anterior and posterior
extremities. Birds, whose anterior limbs are intended for a
purpose very different from the posterior, stand upon the latter,
when at rest, although the back-bone is still very nearly hori-
zontal. Man alone is designed to stand upright, with his head
supported on the summit of the vertebral column. Some
monkeys can rise erect upon their hind legs ; but this is evi-
dently a constrained posture, and not their habitual attitude.

§ 290. In standing, it is requisite that the limbs should
be so disposed that the centre of gravity may fall within the
space included by the feet. If the centre of gravity be with-

THE MODES OF PKOGRESSION.

153

out these limits, the animal falls to that side towards which
the centre of gravity inclines. On this account, the albatros,
and some other aquatic birds which have their feet placed very
far back, cannot use them for walking.

§ 291. The more numerous and the more widely separated
the points of support are, the firmer an animal stands. On
this account, quadrupeds are less liable to lose their balance
than birds. If an animal has four legs it is not necessary
that they should have a broad base. Thus we see that most
quadrupeds have slender legs touching the ground by only a
small surface (fig. 169). Broad feet would interfere with
each other, and only increase the weight of the limbs, without
adding to their stability. Birds are furnished with long toes,
which as they spread out, subserve the purpose of tripods.

•PS

Fig. 169.— The Skeleton of the Camel.

v 0, cervical vertebrae ; v d, dorsal vertebrae ; v I, hrnbar vertebras ; v s,
the sacrum ; v g, caudal vertebrae ; c, the ribs ; o, scapula ; h, the humerus;
c a, the carpus ; m c, the metacarpus ; p h, the phalanges; cu, the radius
and ulna ; / e, the femur ; r o, the patella ; t i, the tioia ; t a, the tarsus :
m t, the metatarsus.

154 THE MODES OF PROGRESSION.

Moreover, tlie muscles of the toes are so disposed that the
weight of the bird causes them to contract firmly, hence birds
are enabled to sleep standing, in perfect security, upon their
perch, and without effort.

§ 292. In quadrupeds, the joints at the junction of the limbs
with the body bend freely in one direction only, that is, to-
wards the centre of gravity ; so that if one limb yields, the
tendency to fall is counteracted by the resistance of the limbs
at the other extremity of the body. The same antagonism is
observed in the joints of the separate limbs, which are flexed
alternately in opposite directions. Thus the thigh bends
forwards, and the leg backwards ; while the arm bends back-
wards, and the fore-arm forwards. Different terms have been
employed to express the various modes of progression, accord-
ing to the rapidity or the succession in which the limbs are
advanced.

§ 293. PROGRESSION is a forward movement of the body,
effected by successively bending and extending the limbs.
WALKING is the ordinary and natural gait, and other paces
are only occasionally employed. When walking is accom-
plished by two limbs only, as in man, the body is inclined
forwards, carrying the centre of gravity in that direction, and
whilst one leg sustains the body, the other is thrown for-
wards to prevent it from falling, and to sustain it in turn.
For this reason, walking has been defined to be a continual
falling forwards, interrupted by the projection of the leg.

§ 294. The throwing forwards of the leg, which would re-
quire a very considerable effort were the muscles obliged to
sustain the weight of the limbs also, is facilitated by a very
peculiar arrangement ; that is, the joints are perfectly closed
up, so that the external pressure of the atmosphere is sufficient
of itself to maintain the limbs in place, without the assistance
of the muscles. This may be proved by experiment. If we cut
away all the muscles around the hip-joint, the thigh-bone still
adheres firmly to the pelvis, but the moment a hole is pierced,
so as to admit air into the socket, it separates.

§ 295. In ordinary walking, the advancing leg touches the
ground before the other is raised ; so that there is a moment
when the body rests on both limbs. It is only when the
speed is very much accelerated, that the two actions become
simultaneous. The walking of quadrupeds is a similar process,

THE MODES OF PROGRESSION. 156

but with this difference, that the body always rests on two legs
at least. The limbs are raised in a determinate order, usually
in such a manner that the hind-leg of one side succeeds the
fore-leg of the opposite side. Some animals, as the giraffe, the
lama, and the bear, raise both legs of one side at the same mo-
ment. This is called ambling or pacing.

§ 296. RuNjSTisrG consists of the same successions of motion
as walking, so accelerated that there is a moment between two
steps when none of the limbs touch the ground ; in the horse
and dog, and in most mammals, a distinction is made between
the walk, the trot, the canter, and the gallop, all of which have
different positions or measures. The trot has but two measures.
The animal raises a leg on each side, in a cross direction ; that
is, the right fore leg with the left hind leg, and so on.
The canter has three measures. After advancing the two fore
legs, one after the other, the animal raises and brings forward
the two hind legs, simultaneously. When this movement is
greatly urged, there are but two measures ; the fore legs are
raised together, as well as the hind legs, it is then termed a
gallop.

§ 297. LEAPING consists in a bending of all the limbs, fol-
lowed by a sudden extension of them, which throws the body
forwards with so much force as to raise it from the ground,
for an instant, to strike it again at a certain distance in ad-
vance. For this purpose, the animal always crouches before
leaping. Most animals make only an occasional use of this
mode of progression, when some obstacle is to be surmounted ;
but in a few instances, this is the habitual mode. As the hind
legs are especially used in leaping, we observe that ah1 leaping
animals have the posterior members very much more robust
than the anterior ; as frogs, kangaroos, jerboas, and hares.
Leaping is also common among certain birds, especiaUy among
sparrows, thrushes, &c. Finally, there is also a large number
of leaping insects, such as fleas, grasshoppers and crickets, in
which we find the posterior pair of legs much more developed
than the others.

§ 298. CLIMBIKG is merely walking upon an inclined or
upright surface. It is usually accompli shed by means of sharp
nails ; and hence many carnivorous animals climb with great
facility, such as the cat tribe, lizards, &c., many birds, the
woodpeckers and parrots, &c., have the toes arranged in two

156 THE MODES OF PROGEESSION.

divisions, so as to grasp branches like a forceps. Others like
the bears employ their arms for this purpose ; monkeys use
their hands and tails ; and parrots their beaks. Lastly, there
are some whose natural mode of progression is climbing ; such
as the long-armed sloths, which, when placed upon the ground,
move very awkwardly ; yet their structure is by no means
defective, for in their accustomed movements upon trees, they
use their limbs with very great adroitness.

§ 299. Most quadrupeds can both walk, trot, gallop, and
leap ; birds walk and leap ; lizards neither leap nor gallop,
but only walk and run, and some of them with great rapidity.
No insect either trots or gallops, but many of them leap. Yet
their leaping is not always the effect of the muscular force of
their legs, as with the flea and grasshopper ; but some of them
leap by means of a spring, in the form of a hook, attached
to the tail, which they bend beneath the body, and which,
when let loose, propels them to a great distance, as in the
Podurellce. Others leap by means of a spring, attached
beneath the breast, which strikes against the abdomen when
the body is bent; as the spring-beetles (Elaters).

§ 300. FLIQHT is accomplished by the simultaneous action
of the two anterior limbs, the wings, as leaping is by that of
the two hinder limbs. The wings being expanded, strike
and compress the air, which thus becomes a momentary
support, upon which the body of the bird rests. But as
this support very soon yields, owing to the slight density
of the air, it follows that the bird must make greater and
more rapid efforts to compensate for this disadvantage.
Hence it requires a much greater expenditure of strength to
fly than to walk ; and therefore, we find the great mass of
muscles in birds concentrated about the breast (fig. 77). To
facilitate its flight, the bird, after each stroke of the wings,
brings them against the body, so as to present as little re-
sisting surface to the air as possible, and for the same end
all birds have the anterior part of the body very slender.

§301. Some quadrupeds, as the flying squirrel, Galeopithe-
cus [and flying lizard, Draco volcms], have a fold of the skin at
the sides, which in some extends to the legs, thereby enabling
them to leap from branch to branch with more facility. But
this is not flight, properly speaking, since none of the peculiar
operations of this act are performed. There are also some

THE MODES OF PROGRESSION. 157

fishes, whose pectoral tins are so extended as to enable them to
dart from the water, and sustain themselves for a short time in
the air ; and hence they are called flying fishes. But this is
not truly flight.

§ 302. SWIMMING is the mode of locomotion employed by
the greater number of aquatic animals. Swimming has this in
common with flight, that the medium in which it is performed
being also the support of the body, readily yields to the impulse
of the fins. But water being much more dense than air, and
the body of most aquatic animals being nearly the same weight
as the water it displaces, it follows, that in swimming, very little
effort is requisite to keep the body from sinking. The whole
power of the muscles is consequently employed in progression,
and hence swimming requires much less muscular force than
flying.

§ 303. Swimming is accomplished by means of various
organs, designated under the general term fins, although, in
an anatomical point of view, these represent very different
parts. In whales, it is the anterior extremities, and the tail,
which are transformed into fins. In fishes, the pectoral fins,
which represent the arms, and the ventral fins, which repre-
sent the legs, are employed for swimming, but they are not
the principal organs ; for it is by the tail, or caudal fin, that
progression is principally effected. Hence the swimming of
a fish is precisely that of a boat under the sole guidance of
the sculling-oar. In the same manner as a succession of
strokes, alternately right and left, propels the boat straight
forwards, so the fish advances by striking alternately right and
left with its tail. To advance obliquely, it has only to strike
in the opposite direction. Whales, on the contrary, swim
by a vertical movement of the tail ; and it is the same with a
few fishes also, such as the rays and the soles. The air-blad-
der facilitates the rising and sinking of the fish, by enabling it
to vaiy the specific weight of its body.

§ 304. Most land animals swim with more or less ease, by
simply employing the ordinary motions of walking or leaping.
Those which frequent the water, like the beaver, or which feed
on marine animals, as the otter, the duck, and other palmi-
pedes, have webbed feet, the toes being united by membranes,
which, when expanded, act as paddles.

§ 30.5. There is also a large number of invertebrate animals,

158 THE MODES OF PROGRESSION.

in which swimming is the principal, or the only mode of pro-
gression. Lobsters swim by means of a vertical motion of
their tail. Other Crustacea have a pah- of legs fashioned like
oars ; as the posterior legs in sea crabs, for example. Many
insects, likewise, swim with their legs, which are abundantly
fringed with hairs, to give them surface ; as the little water
boatmen (Gyrinus, Dytiscus), whose mazy dances on the sum-
mer streams every one must have observed. The cuttle-fish
uses its long arms as oars, and some star-fishes (Cotnatula,
Euryale), use their rays with great adroitness. Finally, there
are some insects which have their limbs constructed for run-
ning on the surface of water, as the water spiders (Ranatra,
Hydrometra) .

§ 306. A large number of animals have the faculty of mo-
ving both in the air and on the land, as is the case with most
birds, and a large proportion of insects. Others move with equal
facility, and by the same members, on land and in water, as
some aquatic birds and most reptiles. The latter have received
the name amphibia on this account. There are some which
walk, fly, and swim, as ducks and water-hens ; but they do
not excel in either mode of progression.

§ 307. However different the movements of the limbs may
appear to us, according to the element in which they are per-
formed, we see that they are the effect of the same mechanism.
The contraction of the same set of muscles, causes the leg of
the stag to bend in leaping, the wing of the bird to flap in
flying, the arm of the mole to strike outwards in digging, and
the fin of the whale to row in swimming.

CHAPTER SIXTH.

NUTRITION.

§ 308. THE second class of functions are those which relate
to nutrition and the perpetuation of the species ; the functions
of vegetative or organic life.

§ 309. The increase of the Tolume of the body requires
additional materials. There is also an incessant waste of par-
ticles, which, haying become unfit for further use, require to be
carried out of the system. Every contraction of a muscle ex-
pends the energy of some particles, whose place must be sup-
plied by others. These supplies are derived from every natural
source, the animal, vegetable, and mineral kingdoms ; and are
received under every variety of solid, liquid, and gaseous form.
Thus, there is a perpetual interchange of substance between the
animal body and the world around. The conversion of these
supplies into a suitable material, its distribution to all parts,
and the assimilation and appropriation of it to the growth and
sustenance of the body, is called NTJTBITIOJS, in the widest

V '

sense of the term.

§ 310. In early life, during the period of growth, the amount
of substances received is greater than that which is lost. At
a later period, when growth is completed, an equilibrium be-
tween the matters received and those rejected is established.
At a still later period, the equilibrium is again disturbed, more
is rejected than is retained, decrepitude begins, and at last
the organism becomes exhausted, the functions cease, and
death ensues.

§311. The solids and fluids taken into the body as food are
subjected to a process called Digestion, by which the solid
portions are reduced to a fluid state, the nutritive particles
separated from the excrementitious, and the whole prepared to
become blood, bone, muscle, &c. The residue is afterwards
expelled, together with those particles of the body which re-
quire to be renewed, and those which have been derived from
the blood by several processes, termed Secretions. Matters in
a gaseous form are also received and expelled with the air we

160

KUTBITI03T.

oreathe, by a process palled Respiration. The nutritive fluids
are conveyed to every part of the body by currents, usually
confined in vessels, and which, as they return, bring back the
particles which are to be either renovated or expelled. This
circuit is termed the Circulation. The function of Nutrition,
therefore, combines several distinct processes.

SECTION I.

OF DIGESTION.

§ 312. DIGESTION, or the process by which the nutritive
parts of food are elaborated and prepared to become blood, is
effected in certain cavities, the stomach and intestines, or ali-
mentary canal. This canal is more or less complicated in the
various classes of animals ; but there is no animal, however
low its organization, which is destitute of a digestive sac.

[§ 313. In the Hydraform POLYPIFERA, as in the common
fresh-water polype (Hydra viridis], the body consists of a diges-
tive sac, with a row of simple tentacula disposed around the
mouth, fig. 170. When the polype is watching for its prey
Fig. 170. it remains expanded, with its tentacula

•widely spread in all directions, to seize
a passing victim. No sooner does a
larve, or worm, or crustacean, impinge
upon one of these organs, than it is
arrested in its course as if by some ma-
gical influence : it appears fixed to the
almost invisible thread, and in spite of
its efforts, is unable to escape. The
prey, seized in this manner, and repre-
sented in fig. 1 70, is conveyed into the sto-
mach («), which has the appearance of a
delicate film, stretched over the contained
animal. If we watch attentively the pro-
cess of digestion, we observe the outline
of the included victim gradually becom-
ing more indistinct : soon are the soft
The Hydra viridis. parts dissolved, and reduced to a fluid
mass; and if any hard parts remain, as the shells of Cypris or
Daphnia, these are expelled through the oral aperture. It is
impossible to say by what process the nutritive product of

POLYPS AND INFUSORIA.

161

digestion enters the system of the hydra, as no vessels have
been discovered in them ; that the colour of the granular
parenchyma depends in some measure on the nature of the
food is satisfactorily shown ; thus, when a polype feeds upon
red larvae, or upon black planarise, the granules acquire a
similar hue, although the fluid in which they float remains
colourless; these granules move about in the parenchyma of
the animal, and give the appearance of globules of blood un-
dulating at large through the general tissue of the polype.
Should the Hydra be made to fast for a considerable time,
the granules lose their colour, and become almost transparent,
in a manner similar to that by which the blood-globules of
frogs lose their redness during the winter months, when de-
prived of nourishment.

[§ 314. The researches of Ehrenberg have demonstrated
that the INFUSORIA admit of a natural division into two
groups, founded on the degree of development of their diges-
tive organs ; the one group comprehends those in the interior
of whose bodies numerous cellular globules are seen, into which
alimentary matters pass : from the many gastric cavities pos-
sessed by these animalcules they are called POLTGASTRICA (fig.
171). In the second group we find a more perfect organization ;
the mouth is large, opening into an esophagus and stomach,
in which are found gastric teeth, a distinct intestine, and anus ;
around the head are numerous ball-shaped bodies, furnished
with cilia, which perform motions resembling those of a revolv-
ing wheel. The group is therefore called ROTIFERA (fig. 172).
The structure of the digestive organs of many of the inferior
forms of polygastrica is still involved in much obscurity ; but in
the higher forms, as in Leucophrys patula
(fig. 171), these organs become visible when
the animalcule has been fed with minute
particles of carmine diffused through the
water. The body is covered with long cilia,
which form a circle round the mouth,
their vibrations causing currents of water
to flow therein, together with the minute
particles on which Leucophrys subsists ;
the intestine is seen taking a winding
course through the body, having appended
to its walls numerous globular cells, many -pis. 171.— Leucophryi
of which are distended with colouring patula.

162

OllGAKS OF DIGESTION.

matter, and forming a natural injection of the gastric cavi-
ties ; the anus opens at *, from which egesta are often seen
exuding.

[§ 314. The Eosphora najas is typical of the rotifera. The

body (fig. 1 72) is enclosed in a double
elastic tunic, into which the muscles are
inserted ; its anterior part is truncated,
and furnished with globular bodies armed
with vibratile cilia; this rotatory apparatus
is moved by muscles inserted into the
"" base of the ciliiferous organs ; the eyes are
seen at #, a, b ; the pharynx (c) is large
and capacious, and the stomach (d) is
provided with a triturating apparatus,
which in many allied genera is armed with
jawrs. The intestine terminates in the anus
at d; the ovary, with many ova, is seen at/".
The posterior extremity of the body is fur-
nished with a pair of forceps, by which
the rotiferse attach themselves at pleasure.
[§315. The digestive organs in the ACA-
LEPH.& present many phases of develop-
Fig. 172. — Eosphora ment ; in some, their pendant arms are
najas. traversed by tubes, through which aliments

pass to reach the gastric cavity. The most remarkable structure
of this class exists in the Rhisostoma Cuvieri, of which a Ion si-

O

tudinal section is seen in fig. 1 73 ; the gastric cavity (6), sur-
rounded by four respiratory chambers, occupies the upper part
of the disc ; the peduncle, hanging from the centre of the disc,
divides into eight arms, four of which are seen terminating in
spongy expansions, and perforated with numerous apertures,
leading into a common channel (c) ; these vessels traverse the
centre of the tentacula ; in the middle and upper part of
each of the arms are numerous fimbriated folds, in which ves-
sels ramify that likewise open into the central canals ; these,
uniting two and two, enter the gastric cavity by four principal
trunks. The walls of the stomach are divided by delicate
septee from the four ovarial sacs ((/), which open externally by
distinct apertures (a, a) ; from the periphery of the stomach
sixteen vessels radiate, which divide and anastomose as they
proceed towards the margin of the disc, where they form a net-

ACALEPn,! AND ECHINODERMS.

163

work of vessels, in which the blood is exposed to the oxygen-
ating influence of the water, whilst the rhizostome floats like
a gigantic animalcule through the sea. The aliments gain ad-
mission to the stomach
only throueh these ab-

J o

sorbent tubes, which re-
mind us of a type of
structure so common in
plants ; in the Medusa
aurita the mouth is large
and patent, and can be
closed by a sphincter
muscle ; the stomach is
divided by septse ; in
these cavities fishes are
sometimes found, in dif-
ferent states of digestion.
The ciliograde tribe,
as in the Beroe pileus,
have a digestive tube,
passing straight through
the body : from the walls Fi§- * 73.— Rhizostoma Cuvieri.

• '

of which numerous vessels take their origin, to traverse the
structure of this most elegant acalephe, the marvels of whose
organization can only be understood after patient observation
with the microscope.

[§ 316. The ECHITSTODEEMS afford a striking illustration of
the law of progressive development, in the structure of their
skeleton, and internal organs. In the Asterias the mouth is
surrounded by tubular tentacula, and protected by fasciculi of
spines ; the short esophagus leads into a capacious stomach,
occupying the central disc, provided with a mucous lining,
and covered by a muscular layer ; from the stomach branches
proceed into each ray ; around these canals a number of csecal
processes cluster, regarded as rudimentary glands : in Ophiura
and Euryale the csecrJ processes are absent. In Comatuhi,
which connects the sea-stars with the urchins, the stomach
occupies the central disc, and leads into a long intestine, which
makes two turns around that organ. The mouth forms a larse

• *~*

opening at one side of the under surface, and the intestine
terminates in a prominent aperture, at the opposite side. Ill

M 2

104

ORGAN'S OF DIGESTION.

the urchins the mouth is for the most part armed with jaws
and teeth, and the oral and anal openings, gradually becoming
more separate, occupy distinct positions on the shell; in Echinus
and Cidaris, the mouth is found at the under pole, and the
anus at the upper pole of their globular shells. Fig. 1 74 shows
the structure of a common urchin (Echinus esculentus); the test

Fig. 174. — The anatomy of the Echinus esculentus.

ts divided near its equator, and the small section is raised
to shew the mouth from above ; k, h is the lantern, with the
pyramids and teeth ; the esophagus (m) is long and delicate,
and continuous with the stomach (») ; the first convolution
of the intestine is seen at o, and the second at q, r ; the
rectum (s) terminates in the centre of the opening formed by
the circle of ovarial plates, and surrounded by the branching

ECHI1STODERMS AND BRYOZOOA. 165

ovaries (t), which open by canals passing through each of the
five ovarial plates. The auricles surrounding the mouth (i)
give attachment to the lantern ; the ambulacral avenues (e}
give passage to tubular feet ; the simple spines (a) arming
the shell are moved by muscles ; the small trident spines, or
pedicellarise (b), move like forceps, and the long tubular feet
(c) are protruded by the injection of a fluid ; an oblong vesi-
cle (/) opens near the mouth ; the intestine is retained in situ
by a delicate mesentery (p), on which blood-vessels ramify ;
currents of water flow constantly through the shell, their course
being directed by the vibratile cilia covering the lining mem-
brane of the test ; the net-work of blood-vessels ramifying
upon these membranes is therefore bathed by the sea-water,
and maintained in a state of oxygenation, so that the whole in-
terior of the shell of urchins is a great respiratory chamber.

In the Holothuria (fig. 232) the long and uniform intestinal
canal makes several convolutions before terminating in the
cloaca; around the mouth are numerous csecal salivary ves-
sels ; a mesentery retains the intestine, and affords an ex-
tensive surface for the ramification of blood-vessels ; the re-
spiratory tubes are distinct from the general cavity of the
body, and form an arborescent organ like a rudimentary
lung.

[§ 317. In the BRYOZOOAN POLYPIEERA, as the Pluma-
teUa (fig. 175), the digestive organs present a much higher
phase of development than in the hydraform group, and mani-
fest an approach to the type of the tunicated mollusca. The
mouth is surrounded by a circle of ciliated tentacula, the vibra-
tions of which cause currents of water to flow towards the
oral aperture ; the possession of ciliated tentacula forming one
of the distinctive features of this group. The mouth, situated
in the centre of the tentacular circle, leads into a long saccu-
lated stomach, the walls of which are studded with glandular
specks, or biliary follicles. From about the middle of the
stomach the intestine proceeds, and ascending close to its walls,
opens by a rectum near the mouth (c), in such a position that
the excrementitious matter ejected therefrom is at once carried
away by the currents sweeping round this region ; the in-
testinal canal is attached to the sac by muscular bands, and
floats freely in the visceral cavity. The tegumentary sheatii
is an organic portion of the polype, and, after enclosing

166

ORGANS OF DIGESTION.

the internal organs, is reflected over the aperture of the cell,
and becomes continuous with the tentacular circle. In con-
sequence of
this union be-
tween the po-
lype and its
cell, it follows,
that when the
animal retires
therein, that
portion of the
tunic (c)
pushed out-
wards by the
exit of the po-
lype, is drawn
inwards on its
retreat by a
process of in-

Fig. l/o. — Plumatella repens. — a, natural size; b, the vagination, SO
same magnified. that tne flex_

ible extremity of the cell is at the same time a sheath for
the body, a support to the tentacula, and a door for closing
it. In fig. 175, muscular bands are seen passing from the
inner membrane of the cell to the body of the polype, by
which the retraction of the animal and the invagination of
the superior part of the cell is effected. At a, we see the
natural size of the polypedom of Plumatella; at b and c, the
cells and polyps magnified and protruded in search of prey ;
at d, the polype withdrawn into its cell, and the orifice closed
by the retraction (c) of the integument.

[§318. In the TUNICATED MOLLUSC A the digestive organs
are very simple. At the bottom of the cavity formed by the
muscular mantle is found the mouth, a simple absorbent
tube, opening into the stomach ; that organ is surrounded
by the follicles of the liver, the ducts from which enter its
cavity ; the short intestine terminates near the ventral aperture
of the muscular sac.

[§319. In the CONCHIPERA, as in the oyster (Ostrea edulisy
fig. 176), the mouth, surrounded by four labial plates (r\
opens into an oval stomach (a) ; the intestine (d,f} makes

CO^CHIFEROUS MOLLUSCA.

I

two turns through the body, terminating in the rectum
(g\ at the posterior border of the shell ; the liver (i) is very
large, surrounding the
digestive tube, and the
biliary ducts open into

the stomach, as in the
tunicata ; the large
branchial leaflets (h,
k] for respiration are
covered by the mantle
(/); in them we find
the cells for lodging
the ova ; the adductor
muscle (G, H) serves
for closing the valves

of the shell, and at
its internal side is seen
the heart (z).

[§ 320. The GAS-
TEROPODA possess
more perfect organs
of prehension than Fig. 176. — The anatomy of the Ostrea edulis.

the preceding class ; here we find not only complicated tubes
for absorbing, but likewise organs for mastication and de-
glutition. Some gasteropoda (Buccinum Murex Valuta) are
furnished with a singular and powerful organ, the proboscis,
which they can protrude at pleasure to a considerable dis-
tance from the mouth. In the Buccinum (whelk) it is in the
form of a hollow tube, surrounded by muscular fibres ; on
laying open this sheath we find a bifid cartilaginous tongue,
provided with sharp, silicious recurved teeth, and sending out
two long processes behind, into which numerous powerful
muscles are inserted ; on the right side of the tongue is the
opening of the esophagus. The proboscis, in a state of re-
pose, is lodged in a distinct cavity, into which it is retracted
by numerous longitudinal muscles, having a close analogy in
their arrangement with the fleshy columns in the heart of the
mammalia. At the point where the esophagus diverges from
the proboscis, in Paludina viuipara (fig. 35), it is surrounded
by two salivary glands, which insert their ducts at this part ;
these glands are always considerably developed in this class ;

168 ORGANS OF DIGESTION.

the esophagus now runs a short course, and near the sto-
mach dilates into a small crop, opening into a round mem-
branous stomach, surrounded or imbedded in the substance
of the liver ; the length of the intestine is considerably
less than that of the esophagus ; it describes a turn, di-
lates into a wide colon, and terminates on the right side,
under the open mantle ; the liver is of considerable size, occu-
pying the spiral turns of the shell, and, as in the preceding
classes, pours its secretion by numerous ducts into the sto-
mach. The digestive organs of other gasteropoda are formed
after the same type.

The Patella (or limpet) feeds on marine vegetables, and is
always found in situations where they are most abundant. It
is deprived of a proboscis, but the mouth is armed with a
long, slender, convoluted tongue, studded with rows of sharp,
silicious recurved teeth (fig. 194), by which it exercises a filing
process on its vegetable food. The wide sacculated esopha-
gus opens into a large stomach of a lengthened form, sur-
rounded by the liver ; the long convoluted intestinal canal
makes several turns through the structure of this organ, and
finally opens into a dilated rectum ; the long salivary vessels
empty themselves into the esophagus.

The Helix (snail) and Limax (slug) have large lips, which may
be regarded as the rudiments of a proboscis ; the upper jaw
of the garden snail (Helix aspera) is furnished with sharp
teeth, which perforate and file down the leaves of plants. The
short esophagus, having passed through the nervous collar, di-
lates into a large membranous stomach, contracted in the centre,
into the posterior half of which the biliary ducts enter ; the in-
testine, having made a turn through the liver, passes up along
the right side of the body, and opens by a small orifice at the
margin of the respiratory sac.

In the Pleuro-branchus the digestive organs are remarkable
for their complex structure, and for the resemblance the stomach
bears to the compound stomach of ruminating quadrupeds.
The esophagus is dilated into a membranous bag, or paunch,
into which the biliary ducts open ; to this succeeds a globular
muscular organ, analogous to the second or honeycomb sto-
mach of ruminants ; this leads to a membranous organ, provided
internally with longitudinal folds of the lining membrane, the
analogue of the leaflet, or manyplies, and, lastly, into a fourth,

GASTEROPODOTJS MOLLUSCA..

169

or true chylific membranous stomach ; the second chamber is
traversed by a muscular gutter, leading from the first to the
third stomach.

The digestive organs of Aplysia Camelus (sea hare, fig. 1/7)
are not less singular,
being not only equally
complex, but in addi-
tion, having the inter-
nal membrane of the
second stomach, or giz-
zard, armed with carti-
laginous bodies. The
pharynx (a) is large and
muscular ; the straight
esophagus (b) having
traversed the nervous
collar (m), soon dilates
into an ample membra-
nous crop (o, o\ turned
into a semilunar form.
This leads into a strong
muscular gizzard (p),
internally armed with
rhomboidal semi-cartila-
ginous plates, their ac-
tion being analogous to
the teeth found in the
stomach of the lobster,
and, like them, perform-
ing a similar bruising
function. This muscu-

lo-cartilaginous

organ

Fig. 177. — The anatomy of the Aplysia
Camelus.

opens into a third chy
lific stomach (</), the in-
ternal surface of which
is furnished with sharp recurved horny spines, most numerous
around the pyloric orifice ; into this region of the canal the
ducts from the liver (u, «), and the termination of a glandular
csecal appendage, the pancreas, pour their secretions. It is
extremely interesting, in a physiological point of view, to study

170 OEGANS OF DIGESTION".

the development of the glandular organs connected with the
assimilating functions. In Holothuria we have seen salivary
vessels developed in the form of a series of blind processes
surrounding the mouth. In the mollusca these organs are
glandular, and extend through nearly half the body in Aplysia
(s, v) ; the liver in the mollusca is likewise glandular, whilst
in the articulated animals it is composed of a series of con-
voluted vessels. A rudimentary pancreas exists in some
mollusca, which, like the salivary vessels in Holothuria,
assumes the form of a long blind secreting sac. The intes-
tinal canal (s) in Pleuro-branchus and Aplysia presents
nothing very remarkable ; it makes several turns through
the structure of th liver, terminating in the rectum (£),
which opens near the branchial, or respiratory aperture (cT) ;
the ovary (v), the oviduct (V) and its appendage (y) occupy
the posterior part of the body, surrounded by the testes (w)
and the epididymus (x) ; ascending from the latter is seen
the common generative canal (z, z) ; the heart, consisting of an
auricle (/3) and a ventricle (3), is placed near the branchiae
(B) ; the principal artery (£) runs forwards to supply the dif-
ferent organs situated at the anterior part of the body ; the
gastric artery (T) and the hepatic (T') artery are given oif from
the root of the principal trunk.

In Bulla lignaria the plates lining the muscular sto-
mach, or gizzard, acquire the consistence of shell ; they
are moved by powerful muscles, and perform the part of
stomach jaws. Among the gasteropodous mollusca the liver
is a very voluminous organ, divided into many lobes, and
very distinct from the intestine ; thus, in the garden snail,
whelk, &c., it occupies the several turns of the shell, embracing
the convolutions of the intestine, and pouring its secretion, by
distinct ducts, into the cavity of the stomach. In the slug and
sea-hare it occupies a great portion of the muscular sac,
common to the general visceral cavity. The liver of the
Doris is remarkable, from the circumstance of possessing,
besides ducts for pouring the biliary secretion into the sto-
mach, a particular canal running in a direct course from the
liver to the anus, and conveying a portion of the bile out
of the system, without traversing the intestinal tube. This
anatomical fact clearly proves that a portion of the bile is

CEPHALOPODOUS HOLLUSCA. 171

excrement! tious ; and that the liver is partly an eliminating
organ, destined to separate impure carbonaceous materials
from the blood.

[§ 321. In the CEPHALOPODA the mouth is situated in the
centre of the tentacular circle, and armed with two horny
jaws, resembling the bill of a parrot, imbedded in the flesh,
and moved by powerful muscles. In the interior of the
mouth is a moveable cartilaginous tongue ; the pharynx,
lodged at the anterior part of the cephalic cartilage, is
very large and muscular ; the long and straight esophagus
is surrounded by the nervous collar ; the stomach, like that
of Aplysia, presents three enlargements, forming a crop, a
gizzard, and a true digestive stomach. The crop is a dilata-
tion of the esophagus, leading into the second globular sto-
mach ; it is very muscular, and communicates by a narrow
opening with the third, or true digestive cavity, remarkable
for possessing a singular spiral valve, formed by a fold of the
lining membrane winding round its inner surface ; a modi-
fication of structure which we shall find repeated in some
cartilaginous fishes, with which the cephalopoda are closely
connected in many points of organization. Into this third
chamber the ducts from the liver and pancreas pour their
several secretions. The short intestinal canal, commencing at
the pyloric orifice of the third stomach, ascends in front
of the liver, and terminates in a valvular opening within
the funnel, situated at the under part of the neck. The
liver in the whole of this class is very large, and its copious
secretion is poured by two ducts, along with the vessel, from
the follicular pancreas into the third stomach, their orifices
being provided with a valvular apparatus ; the salivary glands,
four in number, insert their superior pair of ducts into the
pharynx, and their inferior pair into the esophagus.

The naked cephalopods, as the cuttle-fish, have a peculiar
black, inky fluid, prepared by the glandular lining membrane
of a particular bag, provided with a duct opening into the
funnel. This fluid is secreted in great abundance, and being
very miscible with water, forms a black cloud when injected
into the sea ; and by means of this singular provision these
naked, defenceless animals are enabled to elude the pursuit
of their numerous enemies. The inky fluid, abounding iu

172

ORGANS OF DIGESTION.

carbon, may probably be the excrementitous portion of the
biliary secretion, eliminated from the system by a distinct
organ, and thus made to serve a double use ; it may, in fact,
be analogous to that portion of the bile which is carried di-
rectly out of the body by a separate canal in the Doris.

[§ 322. In the ANNELIDA the digestive tube passes straight
through the body. The mouth is provided with jaws, and the
glands of the intestine are in the form of lateral caecal appen-
dages. The circulation is carried on by arteries and veins ;
their blood is red, and their respiratory organs are in the form
of branchiae, or internal air sacs.

Fig. 178. — The anatomy of the Hirudo medicinalis.

[§ 323. The Leech (Hirudo medicinalis, fig. 178) has a trian-
gular-shaped mouth (a), armed with three small teeth, a pharynx,
composed of numerous muscles (c) ; the action of which is seen
when the animal is engaged in sucking ; the pharynx opens
into a very large capacious sacculated stomach, with mem-
branous parietes, united by small folds to the enveloping elastic
tunic. The stomach is divided into numerous separate cham-
bers (/>/,//,/), by transverse processes of the lining mem-
brane, communicating with each other by central oval open-
ings ; it extends through about three parts of the entire length
of the body, where it enters the intestine (m) by a valvular
funnel-shaped opening ; this tube passes between the two pos-
terior caecal appendages of the stomach, and terminates in a
small aperture (n), at the margin of the posterior disc. The
gangliated nervous chain (g) is uniform in its development
throughout the body, giving off nerves at each ring ; the
respiratory vesicles (A) and the lateral vessels («') encircle
the body ; the caeca of the digestive tube are seen at q ; the

ANNELIDA A]ST> CRUSTACEA. 1/3

female genital parts at r, the male organs at s, and the anal
sucker at o.

[§ 324. In some annelida the mouth is provided with a pro-
jectile proboscis, formed of the anterior part of the intestinal
canal (fig. 233). This organ can be protruded and inverted
like the finger of a glove, and, like the proboscis of predacious
mollusca, has a set of muscles consecrated to effect its move-
ments ; in the Nereis it is very complicated, its free extremity
being armed with long jaws, like the pincers of Crustacea.
The proboscis is regarded by some physiologists as a pharynx,
armed with teeth, like those of star-fishes and echini ; and
being like them, capable of eversion. The stomach of Nereis
is large, and from its posterior part two csecal appendages pro-
ject ; its inner surface is armed with two small white teeth ;
the intestine passes straight through the body, and terminates
in an aperture at the posterior part.

In the Arenicola, or sand-worm (fig. 233), we observe an
additional complication of structure ; to the short esophagus
succeeds a complicated stomach, the first portion of which is
simple, and the second very complex ; into the latter division
of the organ an immense number of branched appendages
open, which appear to be a repetition of the biliary caeca ob-
served in the star-fish ; the stomach passes imperceptibly into
the intestine, which terminates at the posterior part of the
body. In the Aphrodita aculeata, or sea-mouse, a similar
arrangement of the internal organs exists.

[§ 325. In the CRUSTACEA the digestive organs, when com-
pared with those of the annelida, present a greater develop-
ment of the organs of mastication. The jaws, which are nume-
rous, move horizontally by powerful muscles ; the mouth of
the lobster and crab is situated on the under surface of the
body, on each side of which we find the first pair of jaws ex-
panded into a broad form, and sending out behind long pe-
dicles for the insertion of powerful muscles, which have
their points of attachment at the internal surface of the dorsal
shield ; succeeding these we find a second, third, fourth, fifth,
and sixth pair of jaws : they are all, especially the three first
pair, provided with sensitive palpi, in which it is probable
the sense of taste resides. The esophagus is short, opening
into a singularly complicated stomach, extended on a carti-

174 OEGA1STS OF DIGESTION.

lagiuous skeleton, which renders it better adapted for bruising
the aliments ; the framework is composed of five semi-osseous
pieces, provided internally with five teeth, surrounding the
pylorus ; three are large and two are small, being a repetition
of the type of organization we have already described in some
mollusca ; the several plates of this skeleton are moved by
muscles, so as to render it a powerful organ for bruising and
fracturing the shells of the smaller mollusca, on which
the Crustacea prey ; the calcareous parts of the stomach,
like the external shell, are periodically cast off; the intes-
tine forms a straight tube, extending from the pylorus to
the tail, and terminating at the under surface of the central
plate.

[§ 326. In the ABACHISTDA, as the common domestic spider
(Teyenaria domestica), the mouth is provided with a pair of
mandibles, armed with sharp claws, a venomous apparatus,
and maxillae or jaws ; the mandibles are used for seizing,
wounding, and retaining prey, whilst with the maxillse they
squeeze out and suck the contained juices of their victim.
The esophagus is short, of a delicate texture, and opens into
four crops, or stomachs ; the tube then continues a straight
and narrow canal, soon expanding into a muscular organ, sur-
rounded by numerous adipose granules ; this dilatation again
contracts, and, before terminating in the rectum, undergoes
another swelling ; into this enlargement the biliary vessels ter-
minate ; the apparatus for spinning is formed of four hollow
cylinders, the inferior parts of which are perforated like a
sieve, their superior apertures communicating with ducts, from,
ramified vessels, destined for the secretion of the viscous fluid
forming the filaments of the web ; these tubes occupy a con-
siderable portion of the abdomen, surrounding the termination
of the intestine, and their sole function being the secretion of
this fluid.

[§ 327. In INSECTS (fig. 179) the digestive organs are ex-
ceedingly varied and complicated ; in some the mouth is pro-
vided with jaws for bruising (fig. 195), in others with an
apparatus for sucking (fig. 196) ; the intestinal canal presents
many enlargements, and, in some orders, is extremely con-
voluted, terminating at the posterior part of the body ; there
are distinct organs for the secretion of the bile and the saliva,
and in some a rudimentary pancreas exists. Insects pass

ARACffiSTIDA AND INSECTA.

175

through a series of metamorphoses, presenting changes both
in their external form and in-
ternal structure, peculiar to
each successive stage; from
the egg is produced a vermi-
form animal, the larva; this,
after a time, becomes the chry-
salis, which finally develops
the perfect insect. The jaws of
insects (figs. 195 to 199) are
constructed after the type we
have already described in an-
nelida, Crustacea, and arach-
nida, that is to say, they are
placed laterally, and moved by
powerful muscles ; we recog-
nize two pair, an external pair,
or mandibulse (fig. 195, m\
and an internal pair, or maxil-
Ise (j) ; the mouth is furnished
with a superior lip, or labrum,
and an inferior lip, or labium.
The development of the jaws
is in strict relation with the
natural food of the insect. The
suctorial apparatus of the hy-
menoptera, that of the common
bee (fig. 1 9G), for example, is
very singular; projecting from
between the jaws we observe a
sucker (/), composed of nume-
rous rings ; this organ, called
by Treviranus the fleshy
tongue, is situated at the com-
mencement of the esophagus,
in a horny sheath, formed by
a prolongation of the labise,
into which it can be with-
drawn at pleasure. The canal
of the sucker is very incon-

Fig. 179. — Digestive Organs of a
Beetle.

a, the head which supports the
jaws ; b, the crop and gizzard ; d,
the chylific stomach ; c, the biliary
vessels ; d, the intestine ; e, secreting
organs ; /, the anus.

176 ORGANS OF DIGESTION.

siderable, opening into a bag situated before the esophagus,
into which it leads ; the function of this bag appears, ac-
cording to Burmeister, to be simply the rarefaction of its
contained air, by which fluids in the proboscis and esopha-
gus are pumped up into the first stomach. Insects pro-
vided with organs of mastication are deprived of this suck-
ing apparatus ; so that the development of maxillae and suc-
torial instruments stand in an inverse ratio to one another.
Burmeister is of opinion that, in insects deprived of a pro-
boscis, the sucking bag is converted into a crop. The
digestive organs of coleopterous insects present considerable
variety in their structure ; two sections of the order are
formed on this difference alone ; to the one section belongs
those which have a globular muscular stomach, and short
intestinal canal ; to the other, those having a large mem-
branous stomach, furnished with caeca, and a long tortuous
intestine : the first group are carnivorous, the second phyto-
phagous.

In Cicindila campestris, a carnivorous beetle, belonging
to the first group, the short esophagus is dilated into a
large glandular crop, opening into a small muscular giz-
zard, furnished internally with horny teeth, to perforate,
rub down, and divide the aliments. In this muscular sto-
mach we recognize a repetition of the type already described
in some mollusca. To this organ, called by Ramdohr the
plaited stomach, succeeds a flask-shaped chylific organ, fur-
nished with a number of small glandular follicles, for secreting
the gastric juice ; at the point where this organ emerges
into the pylorus, the ramified biliary vessels enter its cavity
by four ducts ; the intestine is short and straight, and de-
velops a large muscular colon, soon terminating in an anal
aperture.

The Melolontha vulgaris (common cockchafer) is an ex-
ample of the structure of these organs in the coleoptera, com-
prised in the second group. Here we find the entire canal
much increased in length and diameter ; in this vegetable-
eating insect the glandular organs are more voluminous, and
from the sides of the ramified vessels numerous csecal appen-
dages are produced. The esophagus is dilated into a membra-
nous crop ; the gizzard is merely rudimentary ; the stomach is
in the form of a long glandular sac, twisted in a spiral man-

INSECTA. 177

ner on itself, and receiving at its pyloric extremity the ducts
of the highly complicated biliary organs ; the small intestine is
short, and the colon has three dilatations in passing to the anal
aperture ; the biliary vessels are very numerous, and their
secreting surface is much increased by the development of in-
numerable small caeca from the sides of the large glandular ves-
sels ; these two examples sufficiently prove that in the struc-
ture of the digestive organs of carnivorous and phytophagous
insects a marked difference exists.

In the orthoptera, the grasshopper for example, the esopha-
gus is dilated into a crop, opening into a round muscular
stomach, the internal surface of which is armed with horny
teeth ; the true chylific stomach succeeds this muscular organ,
and is abundantly supplied with minute follicular appendages,
and the secreting surface of its internal membrane is greatly
increased by being thrown into delicate folds.

In the neuroptera the stomach and intestinal canal are allied
to the preceding ; being nearly all predacious, their masticatory
organs are highly developed, and the intestine passes nearly
straight through the body.

Among the hymenoptera the digestive organs of the bee are
the most interesting, as, in addition to the functions of nutri-
tion, they form two important products, wax and honey. The
sucker (fig. 196), leads into a large bag, situated on the anterior
part of the esophagus, with which it communicates ; here the
nectar obtained from flowers is converted into honey, which
the bee disgorges at pleasure into the cells of the honeycomb.
The esophagus terminates in a small gizzard, to which suc-
ceeds a large sacculated stomach ; into its pyloric portion the
biliary vessels enter ; the diameter of the small intestine is
inconsiderable, but that of the colon is very ample, the inter-
nal membrane of which has a glandular character, probably
intended for the secretion of the wax.

In the hemiptera, the common bug has been examined with
great care by Ramdohr ; he found its digestive organs to con-
sist of two stomachs, the first being very capacious, and serving
as a reservoir for the imbibed juices ; the second being very
complicated, and provided with caeca ; to the small intestine
succeeds a colon of considerable dimensions, provided with
caecal appendages. Connected with the termination of the in-

178 ORGANS OF DIGESTION.

testinal canal of hymenopterous insects we find in some genera
a venomous apparatus, consisting of a sting, a poison-bag, and
secreting glandular organs. In the bee the sting is situated on
the last segment of the abdomen, above the opening of the
rectum ; its base is surrounded by a small bag, embraced at
its superior part by numerous muscles ; two vessels, or caeca,
enter this reservoir with their poisonous secretion ; the sting
is composed of two portions, the corresponding surfaces of
which are grooved in a semilunar manner, so that, when ap-
proximated, a channel is formed ; into this the duct of the poi-
son-gland opens ; each half being armed with small sharp re-
curved teeth, for retaining it in the wound. The sting has a
sheath for its reception, and a particular set of muscles, under
the control of the will, for effecting its movements.

Insects possess salivary vessels opening into different situa-
tions ; some pour their secretion into the mouth, others into the
commencement of the stomach (fig. 179). When we survey the
varied forms which the biliary organs assume in theinvertebrated
animals, we may remark that among the articulata, respiring
atmospheric air, these organs present an arrangement and
structure very different from that observed in the aquatic ar-
ticulata and mollusca ; we are thus led to study more particu-
larly the relations existing between the function of the liver
as a secreting organ, and the respiratory apparatus as an ex-
halant system; the latter rejecting from the economy car-
bonaceous matter in a gaseous form, whilst the liver is con-
stantly eliminating from the system secretions abounding in
carbon and hydrogen, with other greasy and resinous materials.

[§ 328. The vertebrate animals resemble man in the general
arrangement and division of the digestive organs (fig. 180) ;
their principal differences depending upon the nature of the
food ; the purely carnivorous species having a shorter and
simpler apparatus than those which are frugivorous : among
the latter the stomach is often a compound organ. In the ro-
dents, as the rat, there are two compartments, and in ruminants
four distinct cavities, whilst in the carnivora it forms a simple
bag, as in man. The intestinal canal bears a constant relation,
in its length and development, to the kind of food to be di-
gested. In general, the length of the intestine is greatest in
the ruminants, varying from fifteen to twenty times the length

YERTEBRATA.

179

of the body ; in the sheep its proportionate length is as 28 to
I, whilst in the carnivora the proportion is about 4 to 1. In

Maxillary gland.
Trachea. '

Lungs. *
Heart.

Liver.
Gall bag.

Colon.

Caecum.

Small intestine.

Parotid gland.

Pharynx.
Esophagous

Thorax.
Aorta.

Diaphragm.

Stomach.

Pancreas.

Spleen,

Kidneys.

Colon.

Abdomen.

Rectum.
Bladder.

Fig. 180. — The Digestive Organs of a Monkey.

animals living upon a mixed diet of animal and vegetable food,
the proportionate length of the intestine occupies an inter-
mediate position ; in many rodents and monkeys the propor-
tion is about 5 to 1 ; in man about 6 to 1 . It may be stated,
as a general rule, that the stomach is simple when the food
consists of easily-digested animal substances, and is more
complicated when the harder vegetable substances form the
sustenance of the animal ; wherever a plurality of stomachs
exist, there is one which is the true digestive cavity, the others
subserving the processes of maceration and preparation.

[§ 329. Upon minute examination with the microscope, the
mucous membrane of the stomach is found to be covered with
small glandular follicles, which open internally ; these aper-
tures are surrounded by an abundant vascular network, which
also extends more deeply, and includes the csecal and some-
what racemiform follicles. The glands are sometimes simple and

180

ORGANS OF DIGESTION.

Fig. 181.

Tig. 182.

cylindrical, as in fig. 181, which represents the gastric glands
of the pyloric portion of the stomach ; at others they are com-
pound. Fig. 182 represents the gastric
glands in Man ; at A is a section of the
stomach with all its elements, magnified
about three diameters ; B represents the
same glands, with their racemiform ter-
minations distended with fluid, as seen
with the microscope, and magnified about
twenty diameters ; the contents of these
glands are always dark and granular, and
the membranous walls are of extreme deli-
cacy. Lying between these are other glands
of a larger size, and having a much more
compound racemiform structure ; they lie
separate from each other, and contain a
transparent fluid, destined for a purpose
different to that secreted by the gastric
glands. Fig. 1 83 is an outline and highly
magnified view of one of these glands,
from the middle part of the human sto-
mach ; the excretory duct is composed of
three branches, which proceed from a mul-
titude of blind cells. Fig. 184 is another
gland of the same class, from the vicinity
of the pylorus, where they are more com-
mon than in other parts of the stomach ;
it is viewed under the same magnifying
power as fig. 181 ; this gland is more com-
pound in structure, and its contents are
more transparent than those of the other
gastric glands. Much difference of opi-
nion prevails regarding these organs :
we have followed Wagner in our de-
scription, as they accord with our own
microscopic investigations.*

_ [§ 330. The stomach of birds presents

^^s>=^fiii a repetition of the type of structure which

we have already seen in insects. In the

* The stomach should be examined very soon after death, if correct
observations are to be made.

GA.STRIC GLANDS.

181

Fig. 183.

common plover (Vanellus cristatus, fig. 1 85), the esophagus (a)
opens into the proventriculus (6), the walls of which are stud-
ded with gastric glands, and the
muscular stomach, or gizzard (c),
is continued into the duodenum (d) .
The gastric glands have their blind
extremities turned towards the pe-
riphery, and their orifices open in-
to the proventriculus, the granular
contents are there voided under the
most gentle pressure. These glands
are, for the most part, simple ex-
ternally ; sometimes they form
caecal follicles (fig. 186, B) ; they
are well-developed in the rasores,
where they are racemiform and
lobular (<?), or divided into many
clusters, as in/". The common fowl,
or goose, form excellent subjects
for study, and they can always be
procured in a fresh state. Fig. 187
represents the gastric glands in the
glandular layer of the proventricu-
lus of the common fowl ; A is the
gland of its natural size, and B is a
magnified representation of the
same, where the caeca appear like
clusters of berries attached to a
stem. In young birds the cellular
structure of these glands is very
conspicuous. Fig. 188, at A, are
seen the simple gastric glands of a
young owl, of the natural size ; and
at B, the same magnified, to shew
the cellular structure of these organs. The relation in which
these glands stand to the secretion of the gastric juice is not yet
satisfactorily ascertained ; the microscope shows that the orifices,
and inner lining of the glands, are covered with a fine tessellated
epithelium, whilst the parenchyma of the gland consists of
minute granular corpuscules, about 1 -200th of a line in dia-
meter, not always nucleated, but formed of an uniform granular

182

ORGANS OF DlitESTIOtf.

mass, rather than of elements having a cellular character ; the
wall of the gland is formed of a transparent structureless mem-
Pig. 184. brane- Be~

sides these

granular cor-
puscles an al-
buminous
fluid exudes
from the walls
of the sto-
mach, and
mingles with
that yielded
by the gastric
glands ; the
gastric juice
appears to be
loaded with
corpuscles,
having a pe-
culiar acid
mixed with it,
secreted by

tt

an appropri-
ate set or
glands, from
which it is
expressed by
the contrac-
tion of the muscular coat of the stomach, when excited into
action by the presence of food. — T. W.]

§ 331. The result of this process is the reduction of the
food to a pulpy fluid called chyme, which varies in its nature
with the food. Hence the function of the stomach has been
named chymification. With this the function of digestion is
complete in many of the invertebrata, and chyme is circulated
throughout the body ; this is the case in polyps, acalephae,
some worms, and mollusca. In other animals, however, the
chyme thus formed is transferred to the intestine, by a pecu-
liar movement like that of a worm in creeping, which has
accordingly received the name of vermicular or peristaltic
motion.

GASTRIC GLANDS.

183

§ 332. The form of the small intestine is less variable than
that of the stomach. It is a narrow tube with thin walls, coiled

Fig. 185.

"

Fig. 186.

B

Fig. 186.— B, glands
of the proventriculus of
different birds ; a, of the
peacock (Pavo crista-
tus}. b, of the Catkar-
tes percnopterus. c, of
Casuarius galeatus. d,
of Falcopygargus. e,of
the fowl. /, of the os-
trich. — After Home,
Lecture on Comp. Anat.
ii. pi. 56.

in various directions in the vertebrate animals (fig. 180), but
more simple in the invertebrata, especially the insects (fig. 1 79),
Its length varies according to the nature of the food, being in
general longer in herbivorous than in carnivorous animals.
In this portion of the canal, the aliment undergoes its com-
plete elaboration, through the agency of certain juices which
here mingle with the chyme, such as the bile secreted by the
liver, and the pancreatic juice secreted by the pancreas. The
result of this elaboration is to produce a complete separation
of the truly nutritious parts, in the form of a milky liquid
called chyle. The process is called chylification ; and there
are great numbers of animals, as insects, crabs, lobsters, some
worms, and most of the mollusca, in which the product of

184

OEGANS OF DIGESTION.

digestion is not further modified by respiration, tut circulates
through the body as chyle.

Fig. 187.

15 •

A

§ 333. The chyle is composed of minute, colourless glo-
bules, of a somewhat flattened form. In the vertebrata, it is
taken up and carried into the blood by means of very minute
vessels, called lymphaticvessels or lacteals, which are distributed
everywhere in the walls of the intestine, and communicate with

t/

the veins, forming also in their course several glandular
masses, as seen on a portion of intestine connected with a vein
(fig. 189), and it is not until thus taken up and mingled with
the circulating blood that any of our food really becomes a
part of the living body. Thus freed of the nutritive portion
of the food, the residue of the product of digestion passes on
to the large intestine, from whence it is expelled in the form
of excrement.

§ 334. The organs above described constitute the most es-
sential for the process of digestion, and are found more or less
developed in afl. but some of the radiated animals ; but there
are, in the higher animals, several additional ones for aiding in
the reduction of the food to chyme and chyle, which render
their digestive apparatus quite complicated. In the first place,
hard parts, of a horny or bony texture, are usually placed about

OEGANS OF MASTICATION".

185

the mouth of those animals that feed on solid substances,
which serve for cutting or bruising the food into small frag-
ments before it Fig, 139.

is swallowed , Aorta Thoracic duct Lymphatic glands.

and, in many of
the lower ani-
mals, these or-
gans are the only
hard portions of
the body. This
process of subdi-
viding or chew-
ing the food is
termed mastica-
tion.

§ 335. Begin-
ning with the
radiata, we find
the apparatus
for mastication
partaking of the
star - like ar-
rangement Lymphatic Mesentery.
which character-
izes those animals. Thus, in the Scutella (fig. 190), we have a
pentagon composed of five triangular jaws, converging at their
summits towards a central aperture corresponding to the
mouth, each one bearing a plate or tooth, like a knife-blade,
fitted by one edge into a cleft. The five jaws move towards
the centre, and pierce or cut the objects which come between
them. In some of the sea-urchins, Echinidce, this apparatus,
which has been called Aristotle's lantern (fig. 191), consists of
Fig. 190. Fig. 191.

f Roots of
I the chy-
1 liferous
• [ vessels.

— Iiiteetine.

186

OBQANS OF DIGESTION.

numerous pieces, and is much more complicated. Still, the
five fundamental pieces or jaws, each of them bearing a tooth
at its point, may be recognized, as in the Scutella; only, instead
of being placed horizontally, they form an inverted pyramid.
§ 336. Among the mollusca, a few, like the cuttle-fishes,

Fig. 192.

Fig. 194.

Fig. 193.

Fig. 193.— The dental organ of Fig. 194.— The dental organ of a

the Nerita Ascensionensis. Patella, from the Straits of

Magellan.

have solid jaws closely resembling the beak of a parrot
(fig. 192), which move up and down, as in birds. [But a much
larger number rasp their food by means of a tongue sometimes
coiled like a watch-spring, the surface of which is covered
with innumerable tooth-like points, as in the highly mag-
nified portions of the dental organ of Nerita (fig. 193)
and Patella (fig. 194). The teeth present a great variety
of patterns, which are constant in the different genera, and
even characterize the species. They consist of variously-co-
loured silicious bodies, generally of hook-like forms, ar-
ranged in triple rows upon a musculo-membranous band,

ORGANS OF MASTICATION. 187

as in figs. 193 and 194. The central part is called the
rachis, and the lateral parts pleurce. The rachidian teeth
sometimes form a row of plates, as in Nerita ; or they have
a tile-shaped disposition, with pectinated borders, as in Buc-
cinum. The lateral series exhibit an immense variety of
forms, some having fringed processes, as in Nerita (fig. 193).
By the aid of this singular dental organ the gasteropoda bruise,
rasp, or pierce the vegetable or animal substances on which they
subsist, and bore through the shells of mollusca, on which
they prey. The tongue of the whelk (Buccimim) is fur-
nished with upwards of one hundred rows of pectinated
teeth, but the number of the dental rows on the lingual
ribbon varies in different genera, and at the different periods
of life of the individual. The dental organ of the common
limpet (Patella vuigata) is more than twice the length of the
animal, and in a state of repose is folded back into the digestive
tube. The dental membrane is wide in the mouth, and con-
tracted in the esophagus; and after a course of nearly three
inches, terminates near the small transverse stomach. The new
teeth, like those of rays and sharks, are developed from be-
hind, and are brought into use when required, a new series
arising with the age of the individual.* — T. W.]

§ 337. The articulata are remarkable, as a class, for the
diversity and complication of the apparatus for taking and
dividing their food. In some marine worms, Nereis, for ex-
ample, the jaws consist of a pair of curved, horny instru-
ments, lodged in a sheath. In spiders, they are external, and
sometimes mounted on long, jointed stems. Insects which
masticate their food have, for the most part, at least two pairs
of horny jaws (figs. 195, 196 m)) besides several additional
pieces serving for seizing and holding their food. Those living
on the fluids extracted either from plants or from the blood
of other animals, have the masticatory organs transformed
into a trunk or tube for that purpose. This trunk is some-
times rolled up in a spiral manner, as in the butterfly (fig.

* Loven's Memoir on the Teeth of Mollusca is nearly all that we pos-
sess on this subject.

Figures 193 and 194 were drawn by Mr. Etheridge, of the Bristol In-
stitution, from specimens dissected and prepared by my friend John W.
Wilton, Esq., F.R.C.S., Gloucester. The position of the dental organ of
the Patella (fig. 194) on the slide does not permit the left lateral teeth of
the specimen to be seen.

188

OEGANS OF DIGESTION.

199) ; or it is stiff, and folded beneath the chest, as in the
squash-bugs (fig. 197), containing several piercers of extreme
delicacy (fig. 198), adapted to penetrate the skin of animals or
other obj ects whose j uices they extract ; or the parts of the mouth
are prolonged, so as to shield the tongue when thrust out in search
of food, as in the bees (fig. 196,.;', p}. The crabs have their

Fi-. 195. Fig. 196. Fig. 197. Fig. 198. Fig. 199.

anterior feet transformed into jaws, and several other pairs of
articulated appendages perform exclusively masticatory func-
tions. Even in the microscopic rotifera, we find very com-
plicated jaws, as seen in the interior of Esophora (fig. 172).
But amidst this diversity of apparatus, there is one circum-
stance which characterizes all the articulata, namely/ the
jaws move sideways ; while those of the vertebrata and mol-
lusca move up and down, and those of the radiata concen-
trically.

§ 338. In the vertebrata, the jaws form a part of the
bony skeleton. In most of them the lower jaw (fig. 103)
only is moveable, and is brought up against the upper jaw by
means of the temporal and masseter muscles, which perform
the principal motions requisite for seizing and masticating
food.

§ 339. The jaws are usually armed with solid cutting in-
struments, the TEETH, or else are enveloped
in a horny covering, the beak, as in birds
and tortoises (fig. 200). In some of the
whales, the true teeth remain concealed in
the jaw bone, and they have instead, a range
of long, flexible, horny plates or fans, fringed
at the margin, serving as strainers to separate
the minute marine animals on which they feed from the water
drawn in with them (fig. 201). A few are entirely destitute of
teeth, as the ant-eaters (fig. 202).

Fig. 200.

OHGANS OF MASTICATION.

189

Fig. 201.

§ 340. Though all the vertebrata possess jaws, it must not
be inferred that they all chew their food. Many swallow their
prey whole ; as most
birds, tortoises, and
whales. Even many
of those which are
furnished with teeth
do not masticate their
food ; some using
them merely for seiz-
ing and securing their
prey, as the lizards,
frogs, crocodiles and
the great majority of fishes. In such animals, the teeth are
nearly all alike in form and structure, as, for instance, in

Fig. 202.

Fig. 204.

Fig. 203.

the alligator (fig. 203) ; the porpoises and many fishes. A
few of the latter, some of the rays, for example, have a sort
of bony pavement (fig. 204), composed of a peculiar kind of
teeth, with which they crush the shells of the mollusca and
crabs on which they feed.

§ 34 1 . The mammals, however, are almost the only verte-
brata which can be properly said to masticate their food. Their
teeth are well developed, and present great diversity in form,
arrangement, and mode of insertion. Three kinds of teeth are
usually distinguished in most of these animals, whatever may
be their mode of life ; namely, the cutting teeth, incisors ; the

190

OEGAISTS OF DIGESTION.

tusks, or carnivorous teeth, canines ; and the grinders, molars

(fig. 205). The
incisors occupy
the front of the
mouth ; they are
the most simple
and the least va-
ried ; they have
a thin cutting
summit, and are
empl6yedalmost
Fig. 205. — The skull of a horse. exclusively for

V

seizing food, except in the elephant, in which they assume the
form of large tusks. The canines are conical, more prominent
than the others, more or less curved, and only two in each jaw;
they have but a single root, like the incisors, and in the carni-
vora become very formidable weapons. In the herbivora they
are wanting, or, when existing, they are usually so enlarged
and modified as also to become powerful organs of offence and
defence, although useless for mastication, as in the babyroussa.

The molars are the most impor-
tant for indicating the habits and
internal structure of the animal, they
are, at the same time, most varied in
shape. Among them we find every
transition, from those of a sharp and
pointed form, as in the cat tribe (fig.
Fig. 206.— The skull of a 207), to those with broad and level
squirrel. summits, as in the ruminants and

rodents (fig. 206) ; still, when most diversified in the same
animal, they have one character in common, their roots being
never simple, but double or triple, a peculiarity which not only
fixes them more firmly, but prevents them from being driven
into the jaw in the efforts of mastication.

§ 342. The harmony of organs, already spoken of, is illus-
trated, in the most striking manner, by the study of the teeth
of mammals, and especially of their molar teeth. So constantly
do they correspond with the structure of other parts of the
body, that a single molar is sufficient not only to indicate the
mode of life of the animal to which it belongs, and to show
whether it fed on flesh or vegetables, or both, but also to de-

ORGANS OF INSALIVATION.

191

termine the particular group to which it is related ; thus, those
beasts of prey which feed on insects, and which, on that ac-
count, have been called in-
sectivora, such as the moles
and bats, have the molars
terminated by several sharp,
conical points, so arranged
that the elevations of one
tooth fit exactly into the de-
pressions of the tooth oppo-
site to it. In the true car-
nivora (fig. 207), on the con-

Fig. 207. — The skull of a tiger.

trary, the molars are compressed laterally, so as to have 'sharp-
cutting edges, as in the cats, and shut by the side of each
other, like the blades of scissors, thereby dividing the food
with great facility.

§ 343. The same adaptation is observed in the teeth of her-
bivorous animals. Those which chew the cud (ruminants),
many of the thick-skinned animals (pachydermata), (fig. 205),
like the horse and the elephant, and some of the gnawers (ro-
dentia), like the squirrel (fig. 206), have the summits of the
molars flat, like mill-stones, with more or less prominent
ridges, for grinding the grass and leaves on which they sub-
sist ; finally, the omnivora, those which feed on both flesh and
fruit, like man and the monkeys, have the molars terminating
in several rounded tubercles (fig. 102), being thus adapted to
the mixed nature of their food.

§ 344. Again, the mode in which the molars are combined
with the canines and incisors furnishes excellent means for cha-
racterizing families and genera ; even the internal structure of
the teeth is so peculiar in each group, and yet subject to such
invariable rules, that it is possible to determine with precision
the general structure of an animal, merely by investigating
fragments of its teeth under a microscope.

§ 345. Another process, subsidiary to digestion, is called
insalivation. Animals which masticate their food have glands,
in the neighbourhood of the mouth, for secreting a fluid called
saliva. This fluid mingles with the food as it is chewed, and
prepares it also to be more readily swallowed. The salivary
glands are generally wanting, or rudimentary or otherwise
modified, in animals which swallow their food without masti-

192 ORGANS OF DIGESTION.

cation. After it has been masticated, and mingled with saliva,
it is moved backwards by the tongue, and passes down through
the esophagus into the stomach ; this act is called deglutition,
or swallowing.

§ 346. The wisdom and skill of the Creator is strikingly
illustrated in the means afforded to every creature for securing
its appointed food. Some animals have no ability to move
from place to place, but are fixed to the soil, as the oyster,
the polype, &c. ; these are dependent for subsistence upon such
food as may stray or float near them, and they have the
means of securing it only when it comes within their reach.
The oyster closes its shell, and thus entraps its prey ; the polype
has flexible tentacula (figs. 170 and 175), capable of great ex-
tension, which it throws instantly around any minute animal
coming in contact with them ; the cuttle-fish has elongated arms
about the mouth, furnished with ranges of suckers, by which
it secures its victim.

§ 347. Some are provided with instruments for extracting
food from places which would be otherwise inaccessible. Some
of the mollusca, with their rasp-like tongue (fig. ] 93;, perforate
the shells of other animals, and thus reach and extract the in-
habitant. Insects have various piercers, suckers, or a protrac-
tile tongue for the same purpose (figs. 195 to 199). Many of
the annelida, the leeches for example (fig. 178), have a sucker,
which enables them to produce a vacuum, and thereby draw
out blood from the perforations they make in other animals.
Many infusoria and rotifera are provided with hairs, or cilia,
around the mouth (figs. 171, 172), which, by their incessant
motion, produce currents that bring within reach the still more
minute creatures, or particles, on which they feed.

§ 348. Among the vertebrata, the herbivora generally em-
ploy their lips or their tongue, or both together, for seizing the
grass or leaves they feed upon. The carnivora use their jaws,
teeth, and especially their claws, which are long, sharp, and
moveable, and admirably adapted for the purpose. The wood-
peckers have long, bony tongues, barbed at the tip, with which
they draw out insects from deep holes and crevices in the bark
of trees ; some reptiles also use their tongue to take their prey ;
thus, the chameleon obtains flies at a distance of three or four
inches, by darting out its tongue, the enlarged end of which is
covered with a glutinous substance, to which they adhere. The
elephant, whose tusk and short neck prevent him from bringing

OF DIGESTION. 193

his mouth to the ground, has the nose prolonged into a trunk,
which he uses with great dexterity, for bringing food and
drink to his mouth. Doubtless the mastodon, once so abun-
dant in the pre-Adamite earth, was furnished with a similar
organ ; man and the monkeys employ the hand, exclusively,
for prehension.

§ 349. Some animals drink by suction, like the ox ; others
by lapping, like the dog. Birds simply fill the beak with
water, then, raising the head, allow it to run down into the
crop. It is difficult to say how far aquatic animals require
water with their food ; it seems, however, impossible that they
should swallow their prey without introducing at the same time
some water into their stomach. Of many among the lowest
animals, such as the polyps, it is well known that they frequent-
ly fill the whole cavity of their body with water, through the
mouth, the tentacles, and pores upon the sides, and empty it
at intervals through the same openings. And thus the aquatic
mollusks introduce water into special cavities of the body, or
between their tissues, through various openings, while others
pump it into their blood-vessels, through pores at the surface
of their body. This is the case with most fishes.

Besides the more conspicuous organs above described, there
are among the lower animals various microscopic apparatus
for securing prey. The lassos of polypi have been already
mentioned incidentally. They are minute cells, each containing
a thin thread coiled up in its cavity, which may be thrown out
by inversion, and extended to a considerable length beyond the
sac to which it is attached. Such lassos are grouped in clus-
ters upon the tentacles, or scattered upon the sides of the
actinia, and of most polypi. They occur also in similar clus-
ters upon the tentacles and the disc of jelly-fishes. The net-
tling sensation produced by the contact of many of these ani-
mals is undoubtedly owing to the lasso cells. Upon most of
the smaller animals, they act as a sudden, deadly poison. In
echinoderms, such as star-fishes, and sea-urchins, we find other
microscopic organs in the form of clasps, placed upon a move-
able stalk. The clasps, which may open and shut alternately,
are composed of serrated or hooked branches, generally three
in number, closing concentrically upon each other. With
these weapons, star-fishes not more than two inches in diame-
ter, seize and retain shrimps of half that length, notwithstand-
ing their efforts to disentangle themselves.

o

CHAPTER SEVENTH.

OF THE BLOOD AHD CIRCULATION.

§ 350. THE nutritive portions of the food are poured into
the general mass of fluid pervading every part of the body,
out of which every tissue is originally constructed, and from.
ii]2ae to time renewed. This fluid, in the general accepta-
tion of the term, is called blood ; but it differs greatly in its
essential constitution : in the different groups of the animal
kingdom, in polyps, and medusae, it is merely chyme; in most
mollusca and articulata it is chyle; but in vertebrata it is more
highly organised, and constitutes what is properly called blood.
§ 351. The BLOOD, when examined by the microscope, is
found to consist of a transparent fluid, the serum, consisting
chiefly of albumen, fibrin, and water, in which float many
rounded, somewhat compressed bodies, called blood discs, or
globules. These yary in number with the natural heat of the
animal from which the blood is taken. Thus, they are more
numerous in birds than in mammals, and more abundant in
the latter than in fishes. In man and other mammals they
are very small, and nearly circular (figs. 208 and 209) ; they
are somewhat larger, and of an oval form, in birds and fishes
(figs. 210, 214, 215) ; and still larger in reptiles (figs. 211,
212, 213). [The blood-globules in man appear distinctly dis-

Fig. 208.— Globules
of the blood of man,
the blood having been
-~k drawn from a vein and
^ beaten, to separate the

A 0& *& ^ B C fibrin. A, blood glo-

bules, seen, a, on the
flat aspect ; b, standing

on the edge ; *, three-quarter view. B, a congeries of blood-globules,
with their Iflat surfaces in opposition, and forming columns such as are
made by a number of coins laid one upon another. C, a blood globule in
process of alteration, such as simple exposure to the air will produce. D,
a lymph globule, mingled with the proper blood globules.

N.B. The subjects of this and the succeeding figures of blood discs from
Wagner's Icones Physiologicce, are all magnified to the same extent, viz.
about nine hundred diameters.

OF THE BLOOD AND CIBCTJLATION.

195

coidal (fig. 208, A), and vary between the 300th to the 400th
of a line in diameter. They are rarely seen either larger or
smaller. That they are flat, disc-like bodies, is discovered by
examining them on different sides. At the beginning of an
observation, before the drop has spread itself abroad com-
pletely, and the globules have come to rest, or at any time
when the port-object is inclined a little one way or another,
numbers of them are always seen on their edges (A, 6), when
they appear as long-shaped bodies, bounded by two parallel
lines. They are also seen falling, or rolling over (*), and with
everything at rest, finally sinking down upon their flat sides (a).
The blood-discs are severally so pale in colour, and so transpa-
rent, that when one lies over another, the undermost is seen
distinctly shining through the uppermost (a inferiorly). If
quite normal, a delicate semicircular shadow upon the flat sur-
face gives the observer the idea that the blood- discs are very
slightly hollowed out, or sunk, in the manner of a concave
lens. In a short time, sometimes after the lapse of a few se-
conds only, particularly when the diluting medium has not
been well selected, though it also happens from the action of
the air, the blood-discs begin to suffer change ; they appear
puckered and uneven ; they acquire notched edges, and are
stellated ; they seem to be made up of very minute globules,
or they look like mulberries or raspberries (C). The blood-
discs seem to have a natural tendency to approximate by their
flat surfaces, and go to form columns such as are produced by
pieces of money piled one upon another (B).

[§ 352. It is a matter of interest to compare the blood-cor-

\S

o

V

Fig. 209.— Blood
globules of the com-
mon goat (Capra
domes tied).

B

Fig. 210.— A, blood and lymph globules of
the pigeon (Columbadomesticaj. B, a blood-
globule, treated with diluted acetic acid ; C,
with water, by which the central nucleus be-
comes visible.

o 2

196

OF THE BLOOD ATTD CIKCULATIOff.

puscles of the lower animals with those of man. In the mam-
malia they are in all essential -respects the same as in man,
round and discoidal ; for the most part, however, particularly
among the ruminants, decidedly smaller (fig. 209). In the
monkeys, again, they are very nearly of the same size.* In
birds, on the other hand, the blood-corpuscles are very differ-
ent, having an elongatedoval shape (fig. 210, A), and their broad
sides, instead of being depressed, are vaulted or raised (5).
They are on an average from 1-1 25th to 1-1 50th of a line in
length, and about half as broad. It is among the amphibia that
we meet with the largest blood-corpuscles. They are here, as
in birds, oval-shaped, but relatively somewhat broader ; and
their surface is rather depressed than vaulted. They are par-
ticularly large in the naked amphibia : in the Pro feus, for ex-
ample, they are from l-30th to l-50th of a line in the long
diameter, and are even distinguishable as little points by the

Fig. 211. — Blood-gl o^aies of the Proteus anguinus. In the glohule a*
the nucleus is seen, and m the glohule, d, which has heen treated with
water, it is still more apparent ; c is a lymph granule.

* The blood-corpuscles of the monkeys are in no wise to he distin-
guished from those in man. In different human subjects, — men, women,
children, negroes, — no difference can be perceived.

OF THE BLOOD AND CIRCULATION.

197

C

CL*

naked eye (fig. 211, a b). They are, consequently, from eight

to ten times larger here than in man. After the Proteus, we

observe the largest

blood-corpuscles in ^

the land salamanders,

where they measure

in the long diameter

from the 1-5 Oth to

the 1-6 Oth of a line.

In the water sala-

manders they are still

very large, — from the

l-TOth to the l-80th

of a line in length

(fig. 212). In the

frog and toad they Rg> 212>_Blood and lyraph.g]obules Of the
are from the 1 -bOth to great water-newt (Triton cristatus). «, b,
the 1-1 00th of a line blood-globules; a*, a blood-globule with eccen-
in length (fig. 213). trie nucleus ; c, lymph-granules, d, e, blood-
In the lizards ser- globules in progress of development ; they are
-i , surrounded with delicate involucra. Globules

its, ana 1 ,s, Qf this description are found abundantly in the

they are throughout blood of well-fed animals generally.
smaller, though still
measuring from the 1-1 22d to the 1-1 50th of a line in length.

In the majority of
fishes, and particu-
larly in all the bony
fishes, the blood-cor-
puscles are of a
rounded oval (fig.
214), not much long-
er than broad, flat-
tened, and from the
1-1 50th to the 1 -200th pig. 213.— A, a, a, a, b, blood-globules of
of a line in the long the edible frog (Rana esculentn} ; c, lymph
diameter. In the granule. B, blood-globules after the action
skates and sharks, of acetic acid.

again, they are notably larger, and very similar to those of the
frog ; they are as much as from the 1-5 Oth to the 1-1 00th of a
line in the long axis. It is remarkable that in the cycios-
tomes they greatly resemble those of man, being rounded,
discoidal, vaulted, slightly bi-concave (fig. 215, a, b}, and mea-

198

OF THE BLOOD AND CIBCTJLATION.

suring 1 -200th of a line in diameter ; they are, therefore, only
somewhat larger than in man. In the invertebral series of
animals they are generally irregular, granular, rounded cor-
puscles.*]

Fig. 214. — Blood and lymph glo- Fig. 215. — Blood-globules of

bules of the loach (Cobitis fossilis); the Ammocetes branchialis ; a,

a, a, b, perfect blood-globules ; d, a, b, perfect blood-globules ; c,

a blood-globule altered by the ac- lymph-globule. The blood-glo-
tiou of water, and shewing its nu- bules are exactly similar in the
cleus ; c, lymph granules. lamprey (Petromyzon], and un-

like those of all other fishes, whe-
ther cartilaginous or bony.

§ 353. The colour of the blood in the vertebrata is bright
red ; but in some invertebrata, as the crabs and mollusca,
the nutritive fluid is nearly or quite colourless, while in the
worms, and some echinoderms, it is variously coloured, yellow,
orange, red, violet, lilac, and even green.

§ 354. The presence of this fluid in every part of the body
is one of the essential conditions of animal life. A perpetual
current flows from the digestive organs towards the remotest
parts of the surface ; and such portions as are not required for
nutriment and the secretions, return to the centre of circu-
lation, mingled with fluids, which need to be assimilated to
the blood, and with particles of the body which are to be
expelled, or before returning to the heart are distributed
through the liver. The blood is kept in an incessant circula-
tion for this purpose.

§ 355. In the lowest animals, such as the polypi, the nutri-
tive fluid is simply the product of digestion, chyme, mingled
with water in the common cavity of the viscera, with which it
comes in immediate contact, as well as with the whole interior
of the body. In the jelly-fishes, Medusa, which occupy a some-
what higher rank, a similar liquid is distributed by prolongations
of the principal cavity to the different parts of the body (fig.
173). Currents are produced in these, partly by the general
* Professor Wagner's Physiology, p. 233, et seq.

OF THE BLOOD AT»i> CIRCULATION.

199

a

movements of the animal, and partly by means of the incessant
vibrations of cilia, which overspread the interior. In most of
the mollusca and articulata, the blood, chyle, is also in imme-
diate contact with the viscera, water being mixed with it in the
mollusca ; the vessels, if there are any, forming a complete
circuit, but not emptying into various cavities which interrupt
their course.

§ 356. In animals of still higher organization, as the verte-
brata, we find the vital fluid inclosed in an appropriate set of
vessels, by which it is successively conveyed throughout the
system, to supply nutriment and secretions, and to the respi-
ratory organs, where it absorbs oxygen, or, in other words, be-
comes oxygenated.

§ 357. The vessels in which the blood circulates are of two
kinds : 1 . The arteries, of a firm, elas-
tic structure, which may be distended,
or contracted, according to the volume
of their contents, and which convey
the blood from the centre towards the
periphery, distributing it to every point
of the body. 2. The veins, of a thin,
membranous structure, furnished with-
in with valves (fig. 216, v), which aid in
sustaining the column of blood, only
allowing it to flow from the periphery
towards the centre. The arteries con-
stantly subdivide into smaller and
smaller branches, while the veins com-
mencing in minute twigs, are gathered Fig. 216.— Vein laid open,
into branches and larger vessels, to to shew the valves, t;, t?.
unite finally into a few trunks near the centre of circulation.

§ 358. The extremities of the arteries and veins are con-
nected by a net-work of extremely delicate vessels, called capil-
lary vessels (figs. 224, 225) ; which pervade every portion of
the body, so that almost no point can be pricked without
wounding some of them. Their office is to distribute the nu-
tritive fluid to the organic cells, where all the important pro-
cesses of nutrition are performed, such as the alimentation and
growth of all organs and tissues, the elaboration of bile, milk,
saliva, and other important products derived from the blood,
the removal of effete particles, and the substitution of new
ones, and all those changes by which the bright blood of the ar-

200

OF THE BLOOD AFD CIRCULATION.

teries becomes the dark blood of the veins ; and again, in the
cells of the respiratory organs, which the capillaries supply,
the dark venous blood is oxygenated, and restored to the
bright scarlet hue of the arterial blood.

§ 359. Where there are blood-vessels, in the lowest animals,
the blood is kept in motion by the occasional contraction of
some of the principal vessels, as in the worms. Insects have a
large vessel running along the back, furnished with valves so
arranged that, when the vessel contracts, the blood can flow
only towards the head, and being thence distributed to the
body, is returned again into the dorsal vessel (fig. 223), by
fissures at its sides.

§ 360. In all the higher animals there is a central organ,
the heart, which forces the blood through the arteries towards
the periphery, and receives it again on its return. The HEART is
a hollow muscular organ, of a conical form, which dilates and
contracts at regular intervals, independently of the will. It is
either a single cavity, or is divided by walls into two, three, or
four compartments, as seen in the following diagrams. These
modifications are important in their connection with the respi-
ratory organs, and indicate the higher or lower rank of an

Fig. 217.

Lesser circulation.

Pulmonary artery.

Right auricle.
Heart.

5=3g?\$\, ^-'Pulmonary veins.

Left auricle.

Aorta.

\Left ventricla.

Greater circulation.

OF THE BLOOD AND CIRCULATION. 201

animal, as determined by the quality of the blood distributed
in those organs.

§ 361. In mammals and birds the heart is divided, by a
vertical partition, into two cavities, each of which is again di-
vided into two compartments, one above the other (fig. 217).
The two upper cavities are called auricles, and the lower ones
are called ventricles. Reptiles have two auricles and one
ventricle (fig. 219) ; fishes have one auricle and one ventricle
only (fig. 220). The plan (fig. 217) represents the course of
the blood in mammals and birds, in which we have a double
circulation ; a lesser one through the lungs, and a greater one
through the body.

§ 362. The auricles do not communicate with each other,
in adult animals, nor do the ventricles. The former receive
the blood from the body and the respiratory organs through
veins, and each auricle sends it into the ventricle beneath,
through an opening, guarded by valves to prevent its reflux ;
while the ventricles, by their contractions, force the blood
through arteries into the lungs, and through the body generally.

§ 363. The two auricles dilate at the same instant, and also
contract simultaneously ; so, also, do the ventricles. These
successive contractions and dilatations constitute the pulsations
of the heart. The contraction is called systole, and the dilata-
tion is called diastole. Each pulsation consists of two move-
ments, the diastole, or dilatation of the ventricles, during
which the auricles contract, and the systole, or contraction of
the ventricles, while the auricles dilate. The frequency of the
pulse varies in different animals, and even in the same animal,
according to its age, sex, and the degree of health : in adult
man, they are commonly about seventy beats per minute.

§ 364. The course of the blood, in those animals which
have four cavities to the heart, is as follows, beginning with
the left ventricle (fig. 218, /, v). By the contraction of this
ventricle, the blood is driven through the main arterial trunk,
called the aorta (#), and is distributed by its branches through-
out the body ; it is then collected by veins, carried back to
the heart, and poured into the right auricle (r, a], which sends
it into the right ventricle (r, v}. The right ventricle propels
it through another set of arteries, the pulmonary arteries ( p],
to the lungs ; it is there collected by the pulmonary veins, and

202

OF THE BLOOD A2TD CIBCTJLATIOISr.

conveyed to the left auricle (/, a), by which it is returned to
the left ventricle, thus completing the circuit.

Sup. vena cava. Pul. art. Aorta (a). Pulmonary artery (/>).

\ i
Pulmonary veins (p v). \ ^-^ ^ / ^Pulmonary veins (p i>).

Right auricle (r a).

Tricnspid valve.
Inferior vena cava.

Right ventricle (r v}.

Left auricle (I a).
Mitral valve.

Left ventricle (I v}.

Partition. Aorta descending (a).
Fig. 218. — Ideal section of the human heart.

§ 365. Hence the blood, in performing its whole circuit,
passes twice through the heart. The first part of this circuit,
the passage of the blood through the body, is called the great
circulation, and the second part, the passage of the blood through
the lungs, is the lesser or pulmonary circulation : this double
circuit is said to be a complete circulation (fig. 217). In this
case, the heart may be justly regarded as two hearts conjoined,
and, in fact, the whole of the lesser circulation intervenes in the
passage of the blood from one side of the heart to the other ;
except that during the embryonic period, when there is an
opening between the two auricles, which closes as soon as
respiration commences.

§ 366. In reptiles (fig. 219) the venous blood from the
body is received into one auricle, and the oxygenated blood
from the lungs into the other. These throw their contents
into the single ventricle below, which propels the mixture in
part to the body, and in part to the lungs ; but as only the
smaller portion of the whole quantity is sent to the lungs in a
single circuit, the circulation is said to be incomplete. In the
crocodiles, the ventricle has a partition which keeps separate
the two kinds of blood received from the auricles ; but .,he

OF THE BLOOD ATTD CIRCULATION. 203

mixture soon takes place by means of a special artery which
passes from the pulmonary artery to the aorta. [The reptiles
have a heart with one ventricle, and two auricles ; the right
auricle receives the impure venous blood from the body, the
left auricle receives the pure arterial blood from the lungs, and
both pour their contents into the same ventricle, where they
are min°ied together. This mixed blood is transmitted by the
ventricular contractions partly into the lungs and partly into
the body ; in the crocodile a partial partition divides the ven-
tricle into a right side and a left side, as in birds and mammals.
Fig. 219 is a plan of the circulation in reptiles; the arrows
indicating the course of the blood.

Lesser circulation.

Yena cava.

— Heart.

Aorta.

'« Single ventricle.

Greater circulation.
Fig. 219. — Circulation in reptiles.

[§ 367. In fishes the heart possesses two cavities, an auricle
and a ventricle, and only receives and transmits venous blood ;
it therefore represents the right side of the heart of birds and
mammals. The venous blood returned by the systemic veins
is poured into the auricle and ventricle, from whence a highly
elastic artery arises, which divides into five pairs of branches ;
these branchial arteries distribute the blood throughout the
gills ; from these organs it is conveyed into a large single vessel,

204

OF THE BLOOD AXD CIECULAT10X.

Auricle.

Lesser circulation.

lying along the spine, and byits branches is distributed through-
out the body. Fig. 220 is a plan of this type of circulating
organ.

[§ 368. In the
mollusca the heart
consists of a ven-
tricle and an au-
ricle, as in fishes ;
Heart. but it differs in

this, that it is
destined to pro-
pel the blood
the sys-

Ventricle.

"Veins —

^Dorsalartery.

through

Veins.

Greater circulation.
Fig. 220. — Circulation in fishes.

through the gills,
as in that class.

[Fig. 221 repre-
sents the circula-
ting organs of the
Doris; the heart
consists of a ven-
tricle (a), from
whence arises the

aorta (6), which sends branches to all parts of the body ; and a
single or double auricle (c), in which the veins (d) of the bran-
chial organs (e) terminate, the branchiae being developed in the
form of external vascular tufts. The blood purified in these or-
gans is conveyed to the heart, and transmitted by arteries through
the body ; it is collected by the radicles of the veins, which
terminate in a large trunk (f). By this vena cava it is dis-
tributed through the gills (<?), and from these organs it is re-
turned to the heart. In the CEPHALOPODA the circulation
through the gills is aided by branchial ventricles, situated at
the bases of these organs, but in other respects their circu-
latory apparatus resembles that of the mollusca in general.

[§ 369. In the Crustacea (fig. 222), the circulation is after
the type of the mollusca. The heart (a) consists of a ven-
tricle only, from which several arteries arise ; the opthalmic
(b), the antennal(c), the hepatic (d), the superior abdominal (e),
and the sternal (/*). After having circulated through the body,
the blood is collected in certain reservoirs (g g), which take the

OF THE BLOOD A7TD CIRCTJLATI01S'.

205

place of veins ; these venous sinuses swell out at the base, and
send a branch to each bran-
chia. After having circulated
through these organs, the
blood is returned to the

heart, to perform a similar cir-
cuit.

[§ 370. In insects (fig.
223) the circulation is main-
tained by a dorsal vessel («),
which acts the part of a
heart : it is divided into seve-
ral chambers bv valves, which

it

permit the blood to flow only
towards the head ; the vessel
here appears to cease, and the
blood seems to flow in the
interspaces of the tissues ; cur-
rents of globules form arches
in the anteunse, wings, legs,
and the prolongations of the
abdomen ; lateral currents
are seen at b, the direction of
their course being indicated
by the arrows. The circulation in insects can only be

Fig. 222.

221'~Circ^0a^g

Vascular system of the lobster.

studied in transparent aquatic larva, as those of the
ephemera, in which it forms a beautiful spectacle for the
microscopist. The chyle globules enter the dorsal vessel by

206

OF THE BLOOD AKD CIECULATIOIST.

lateral slits, which are protected by valves. The simplicity
of the circulating organs in insects forms a striking contrast

Fig. 223.— Circulation of insects.

to the preceding classes ; but we shall see, when treating of
the function of respiration, that in insects the air is so com-
pletely conveyed to all parts of their bodies, that a simple
arrangement suffices for the perfect eeration of their blood.

[§371. We have seen that the arteries terminate in the veins
in the periphery of all the organs ; these two divisions of the
vascular system are connected by the capillary vessels. A view
of these vessels can only be obtained by successful minute
injections, and the aid of the microscope ; size injections of
the skin, and the mucous membranes of the lungs and
intestinal canal, exhibit the peripheral capillary system in
great variety. The web of the frog's foot, the fishes' 'tail, and
the branchiae of the tadpoles* of frogs, a.nd salamanders, shew
the splendid spectacle of the vascular system in action. — T. W.]

[§ 372. However different the more minute capillary reticu-
lations in the various organs appear, they may nevertheless be

* Every season of the year is not alike favourable for making observa-
tions on the circulation. It is only in the spring that tadpoles are to be
had, but they are excellent subjects. They should be rolled up in moist

Or THE BLOOD AKD CIBCITLA.TION.

207

all reduced to a single fundamental type, a type which is most
readily observed in the vascular distribution of the intestinal
villi (fig. 224) : the terminal
twig of an artery (b, b) bends
round into the terminal twig of
a vein (a, a), and the two are
repeatedly connected by means
of delicate loop-like twigs, these
in their turn being formed into
meshes by cross or intermedi-
ate branches. The fundamental
type of the peripheral vascular
system is therefore an arterial
and a venous branchlet — pro-
per capillary vessels, and an in-
terposed net-work of fine vas-
cular canals — vasa intermedia.
A distinct separation between
capillaries, and intermediate
vessels, as this is perceived in
the intestinal villi more especi-
ally, is not generally to be ob-
served, the two blend or are
lost insensibly in one another.
The parenchyma, or organic
substance lying between the
finest vascular subdivisions, Fig. 224.— Vessels of one of the
forms islets of very various size intestinal villi of the hare; after
j ,, •71. ,1 an extremely beautiful dry prepa-

and figure, according as the ration by Doellinger. The villul is
meshes of the mtercurrerit ves- magnified about 45 times. The vein
sels are open or closer, and as a, a, is injected with white ; the
they are rounded or angular, artery, b b, with red; between the

The intimate structure of every fw° a most beautiful rete of c^'

,, IP- JP lanes is apparent.

organ, the mode or union and or

the grouping of its elementary parts, and the diameter of the

blotting-paper, nearly to the end of the tail, and so laid upon a plate of
glass of sufficient size, and placed under the microscope, the wrapper of
bibulous paper being kept constantly moist by a few drops of water 'let fall
on it from time to time. In this way the circulation may be watched for
hours, and the tadpole set free at the end of the observation is nothing the
worse. Young and still transparent fishes may also be treated in the same

208

OF THE BLOOD AND CIRCULATION.

vessels which appertain to it, give rise to the greatest diversity
of form in the peripheral vascular system, which has never-
theless so determinate a character in each tissue, that an ex-
amination with the microscope of the smallest particle of a
finely injected preparation enables us to say with certainty
from what part of the body it was obtained.*

[§ 373. When a transparent part of a cold-blooded animal,
the web of the frog's foot, for example, is examined under a

I

i

''//in,

Fig. 225.— Membrane between two of the toes of the frog's (Rana
escnlenta) hind-foot, with the vessels and their anastomoses, drawn under
the lens, and magnified three diameters, a c, Veins, b b, Arteries.

way, and are excellent subjects, but they require more delicate handling
than tadpoles. The circulation in the allantois of the young embryos of
lizards and snakes is also a very beautiful sight, when these subjects can
be had at the proper point of evolution ; they require to be removed from
the ova, and observed covered with fluid albumen in a watch-glass. In
the winter, frogs are the best subjects ; fishes are then much less proper.
In the web of the hind foot of the common frog (Rana temporarid], the
circulation is perhaps seen to as great advantage as anywhere. All our
better microscopes are now provided with a stage adapted for placing the
animal, which is best secured by being put into a linen or calico bag, with
tapes at each corner to tie it down.

* Professor Wagner's Physiology, p. 286.

OF THE BLOOD AtfU CIECULATION.

209

low magnifying power, the directions of the arterial and ve-
nous currents are readily discovered (fig. 225, a a, b b). The
anastomoses of both orders of vessels are seen distinctly.
Under a higher power (figs. 226 and 227) a net-work of very
fine vessels is perceived lying
now over, now under the
larger branches, and con-
nected with these by small

twigs.

In the larger ves-

sels the arterial and venous
currents are distinguished,
not merely by their opposite
directions, but also by the
kind of motion appropriate
to each : that of the arteries
is distinctly jerking or pul-
satory, but it gets ever less
and less, so as the minuter
subdivisions are attained,
and in the intermediate and
finest vessels of all it be-
comes a continuous stream, Fig. 226.— A portion of the web of a
which has the character ap- frog's foot, exhibiting the included
propriate to the venous cur- network of vessels, magnified45 times,
rent. In all the vessels, even The angular unnucleated cells c c,

in the very finest, a distinct °f ^ P™*^ ^8 Between

, J ' . the different vessels, are beautifully

boundary, formed by a sim- shown; a is a deeper-lying venous

pie dark line, is perceptible ; trunk, with which two smaller capil-
the surrounding paren- fciry veins, b b, communicate. The
chyma, now distinctly eel- superficial net-work of capillaries is

lular (fig. 226), now rather ^Y^^ ^Af^ 8fei °f
; & , '' blood-globules. All the vessels here

granular and fused, though figured are furnished with distinct
still including individual parietes.
ramified pigmentary cells

within it (fig. 227), is sharply limited ; the vessels never appear
as simple channels pierced through its substance and without
distinct parietes. Larger vessels (figs. 227 and 228) are ob-
viously enough furnished with darker parietes, composed of
various layers of fibres. In the most minute vessels there is
room for no more than a single row of blood-corpuscles, and
even these can only pass by their long diameters through the

210

OF THE BLOOD AND CIRCULATION.

axis of the vessel. The larger vessels admit several blood-
corpuscles together, and in the decidedly arterial or venous
branches they are observed passing on in' all positions — three,
four, and five abreast, over and near to one another, but those
in the centre of the current always in more rapid motion than
those on its outside and in contact with the walls of the
vessel. (Figs. 227 and 228.) Occasionally we observe single
vessels of larger calibre running very immediately under the
epithelium (a), which is made up of tubular cells with nuclei
(b, I, b, L), through which the fibrous parietes of the vessel are
seen shining (fig. 228).

o .--.r -v

Fig. 227. — Vascular rete and circulation of the web of the hind-foot of
Runa temporarily magnified 110 times. The individual cells of the paren-
chyma are indefinite and obscure. The black spots, some of them star-
shaped, are depositions of pigmentary matter. The deep venous trunk,
a, composed of three principal branches, b, 6, b, is covered with a rete of
smaller vessels. Mingled with the oval-shaped blood-globules, the smaller
and rounder lymph-globules are apparent ; here, under the blood- globules,
there, more on the outside of the stream.

OF THE BLOOD AXD CIKCULATIOX.

211

[§374. A magnifying power of from two to three hundred
diameters is required, to make out the particular details of the
peripheral circulation. The blood in mass, or in the larger
channels, is seen to flow more rapidly than in the smaller.
Here the blood-corpuscles advance with great rapidity, espe-
cially in the arteries, and with a whirling motion, and 'form a
closely crowded stream in the middle of the vessel, without
ever touching its parietes.
With a little attention a
narrower and clearer but
always very distinct space
is seen to remain betwixt

.1

the great middle current
of blood-corpuscles and
the bounding walls of the
vessel, in which a few of
the lymph-corpuscles are
moved onwards, but at a
vastly slowerrate (figs. 22$
and229,#,«). Theseround
lymph-corpuscles swim in
smaller numbers in the
transparent liquor san-
guinis, and glide slowly,

and in general smoothly, Fig. 228. — A venous branch from the
though sometimes they ad- web of Ran, temporana magnified 350
vance bv fits and starts times, nmning immediately under the siir-
". -!•• i • .-, • lace. The cells of the epidermis, o. o. o, o,

more rapidly, but with in- flattened> mostly shjsille(i, connected

tervemng pauses, and, as a Hke a piece of pavement, and generally

general rule, at least from provided with nuclei, are seen extended

ten to twelve times more over the vessel. The closely serried co-

slowlvthan the corpuscles luran of Wood-globules, some with their

c , i ' i mu edges, others with their broad faces

of the central stream The tunipd to the eve> is dlsti%mished . in

clear space filled with li- the clear space betwixt the blood-globules

quor sanguinisand lymph- and the parietes of the vessel, which ap-

corpuscles is obvious in all pear made up of longitudinally disposed

the larger capillary vessels, parallel fibres, the round, clear, and more

whether artpvifll nr venous • slugglishl>' moving lymph-globules are ap-
parent. The object is represented under

but it ceases to be apparent a -weak light.

hi the smaller intermediate

vessels, which admit but one or two ranks of blood-corpuscles

P2

212

OF THE BLOOD AND CIRCULATION.

(fig. 229). In these vessels the round lymph-corpuscles
f«,0,a,0) are seen swimming under, over, and behind the oval

blood-discs (b, b),
both of them pro-
ceeding paripassu
here, and having
the same mode-
rated motion : still
it is impossible not
to observe that the
blood-corpuscles
are possessed of a
greater degree of
lubricity, that they
evidently glide
more readily over
one another and
over the smooth

//^V' \/l!// ^V/V\C~H55^ walls of the ves-

//YV&Lj/y ^ r^S^^J _ Sels, than the

lymph-corpuscles,
which seem often
to get set fast at

the bendings of
Fig. 229. — View in outline of a large vein of the ,1 1 1 <-

frog's foot magnified GOO times. The blood-glo- Ls' £

bules, b and c, present sometimes their thin edges,
sometimes their broad surfaces, here they lie pa-
rallel, there diagonally, and elsewhere athwart the branches are
course of the vessel. The lymph-globules, a, a, are
principally conspicuous in the clear space near the
walls of the vessel.

I

the angles where
anastomosing

re-
ceived or given

/r .-, .-, °
off » tnere, ^ey re-
main sticking tor
an instant, and then are suddenly carried on again. Single
blood-corpuscles, too, may frequently be observed hurled
by a wave, as it were, against angles of the containing
vessels, and remain hanging for a brief interval ; at these
times they may be seen quivering or oscillating, in spite
of the pressure they must undergo ; but their stoppages
are never long, they soon fly off again, or, becoming in-
volved in the general stream, they are borne onwards. In
tAniiumplating the circulation under these circumstances, a
byeciacle of the most interesting kind is presented to the eye:

OF THE BLOOD AND CIBCULATION.

213

the little molecules of the blood are seen in ceaseless motion
and alive, but altogether without inherent activity, now borne
forward as upon gentle waves, and then pushed more im-
petuously along ; now advancing in serried ranks, now
threading their way in single files, the entire phenomena de-
pendent upon the activity of the central organ. In the most
minute intermediate vessels of all, a great degree of repose is

Fig 230. — Portion of the lung of a live Triton drawn under the micro-
scope, and magnified 150 times; a, 6, c, streams of venous blood; <7, a
branch of the pulmonary artery. The very delicate capillaries sen-ing as
bonds of union between the pulmonary vessels, are seen playing round
little islets of the substance of the lung. The clear space between the
current of the blood and the walls of the vessels observed in the larger
branches is almost entirely wanting here. The lymph granules, therefore,
are observed mixed with the general torrent. The arrows indicate the
course of the currents.

214

OP THE BLOOD AXD CIKCULA-TTON".

apparent ; single streams are often only recognizable by tlieir
bounding parietes ; comprehended within two dark lines,
these vessels are usually filled with the liquor sanguinis
alone ; it is at intervals only that a blood-corpuscle, more
rarely a lymph-corpuscle, from some neighbouring and larger
streamlet, detaches itself and makes its way into the canal,
which till now had appeared empty ; one corpuscle entering
in this way is frequently followed by several others in pretty
rapid succession, and then, or without anything of the kind
occurring, the vessel for a long time circulates nothing but
the limpid plasma. Whether there are any vessels or not
that never circulate aught but plasma, refusing, by reason of
the smallness of their diameters, at all times to admit the
blood-corpuscles, is doubtful.

[§ 375. Such is the peripheral systemic circulation in every
tissue susceptible of special examination. In the peripheral
vessels of every part yet examined, the separation into the
quicker stream of blood-corpuscles in the centre, and of the
slower one of liquor sanguinis in the circumference above in-
dicated, has been observed. But the circulation of the respi-
ratory apparatus, whe-
ther lungs or gills, offers
a most remarkable ex-
ception to this rule, so
uniform in reference to
the circulation at large.
The capillaries of the
respiratory organ are
filled with blood gene-
rally, i. e. liquor san-
guinis, with its super-
added blood and lymph-
corpuscles, — to their

Fig. 231.— One of the pulmonary islets very walls (figs. 230 and
bounded by capillaries on three sides, by a 231.) It is only in the
larger venous branch on the fourth side, larger capillary vessels
a, b, c are lymph-globules mingled with the tjiat a tllin stratum of
blood-globules. The object is magnified i • f h •

about 300 times. plasma is

contact with theparietes,

which are much more delicate than those of the systemic
circulation, and not, like them, formed of a series of dark

OF THE BLOOD AND CIECTJLATION. 215

fibrous layers. The circulation through the lungs of the water
newt is a very beautiful object (fig. 230). The pulmonary
arteries (d} here expand very speedily into a fine-meshed
net- work of intermediate vessels, which in general admit no
more than single files of blood-corpuscles playing around very
minute islets of the parenchyma of the lung (fig. 231). The
vessels always appear with distinct parietes, and terminate
partly in capillary veins of the same character as themselves
(fig. 230), partly in larger venous trunks. The blood-corpus-
cles mixed with lymph-corpuscles (fig. 231, c),as already stated,
fill both arteries and veins close to their parietes. The same
appearances are presented in the branchial fringes of the larva
of the water-newt.]*

* Professor Wagner's Physiology, page 294, et seq.

CHAPTER EIGHTH.

OF RESPIRATION.

§ 376. FOR the maintenance of its vital properties, the
blood must be submitted to the influence of the air. This is
true of all animals, whether they live in the atmosphere or in
the water. No animal can survive for any considerable period
of time without air ; and the higher animals almost instantly
die when deprived of it. It is the office of KESPIRATION to
bring the blood into communication with the air.

[§377. In the lowest classes of animals no special organ is
developed for the exposure of the nutritive fluid to the oxygen-
ating influence of the air contained in the water in which they
live. In them, the general cutaneous surface is a respiratory
organ • such is the case in infusoria, polyps, medusae, and
many other invertebrata. Many parts of the cutaneous mem-
brane on the exterior of their bodies, or that lining the diges-
tive organs, are covered with vibratile cilia, by the motions of
which, currents of water are made to flow over these surfaces,
and thfveby oxygenating the nutritive fluids circulating in
them.

[§378- In the echinodermata special organs exist ; the up-
per surface of the tegumentary membrane of the Asterias is
covered with innumerable small transparent fleshy tubes, which
in the living state are seen advancing and receding through
openings in the integument. The interior of these tubes is
lined with cilia, and by their vibrations currents of water are
made to flow through them into the visceral cavity, into which
they open. The peritoneal membrane lining this cavity pre-
sents a considerable extent of surface continually in contact
with the surrounding medium, and appears to be the principal
seat of respiration. Its surface is covered with cilia, by which
currents of water »*e made to flow in a determinate direction,

OF RESPIRATION".

217

and thus the stratum in contact with the vascular membrane
is incessantly renewed, and respiration thereby maintained.

[In the Echinidce (fig. 174), the space comprised between
the viscera and the test is filled with water, which is drawn
into and rejected from the body by five pairs of mem-
branous respiratory tubes, collected into ten tuft-like organs,
situated around the circumference of the oral aperture, and
opening internally by two perforated pits, as in Asterias.
The water thus introduced into the interior of the test
Hows along the membrane, covering its surface, and over
the peritoneal layer, investing the digestive organs and
tubular feet and ovaria by the action of cilia, so that the in-
terior of the
test of the
Echinus is in-
cessantly tra-
versed by re-
spiratory cur-
rents, whilst
the blood,
circulating
through

the

coriaceous in-
tegument, is
in like man-
ner aerated by
currents flow-
ing over its
surface by the
vibrations of
cilia.

In the Ho-
lothuria (fig.
232), the re-
spiratory
function is
limited to a
pair of or-
gans formed
after a type
which attains

Fig. 232. — The anatomy of the Holothuria tnbuio a.

218 OF RESPIRATION.

its full development, among the air-breathing vertebrata, in-
stead of entering the general visceral cavity by tubes, and
flowing over the surface of the peritoneum by the motions
of cilia, as in the Asteriadae and Echinidce ; the water is
inspired through a single chamber, called the cloaca (g, fig.
232) ; and by the contraction of its muscular walls flows
into two tubular branched organs (i, k\ attached by a process of
the peritoneum to the walls of the body ; upon the membra-
nous lining of these organs, which divide and subdivide, like
a tree, into branches, terminating in tuft-like cells (in) ; the
blood-vessels ramify like the pulmonary vessels on the bron-
chial tubes in the air-breathing vertebrata, which they further
resemble in the rythmic movements of dilatation and contrac-
tion, which take place three times in a minute in the Holo-
thuria tubulosa (fig. 232), the water, after each inspiration, re-
maining about twenty seconds in the body.

[§ 379. The respiratory organs, in all the other classes of
the animal series, may be grouped into three principal forms ;
branchiae, tracheae, lungs. The plan manifested in the structure
of these organs is to fold up, into the smallest possible space,
a large extent of membranous surface, upon which a net-work
of blood-vessels may be spread. It is impossible to imagine a
more perfect fulfilment of these conditions than is accomplished
in the structure of the branchiae and lungs, whereby the whole
circulating fluid of the body is made to traverse a vascular net-
work, and is brought thereby into mediate or immediate con-
tact with the air of the atmosphere, or that held in solution in
the water : as a general rule, it may be stated that branchiae
are adapted for aquatic, and lungs for aerial respiration.

[§ 380. Most of the mollusca respire by branchiae. In the
TFNICATA they occupy the interior of a cavity which is tra-
versed by currents of water, entering at one orifice and escaping
at another, and caused by the vibrations of cilia. In the
Sa1p<B the branchia has the form of a tube, formed by a fold
of the internal membrane, disposed transversely in spiral turns,
which gives an annulated appearance to the cavity, and has
caused it to be likened to the tracheae of insects. The su-
perior border of this membrane is provided with an infinity of
small vessels, running parallel with each other ; in other genera
the branchia forms a more continuous lining of the respiratory

OF RESPIRATION. 219

pac ; the inhaled currents are made to traverse the body by
the cilia, encircling the afferent aperture, and developed on the
surface of the branchial membrane.

In the CONCHIFERA the mantle presents two orifices, the
one for the entrance and the other for the exit of the water
from the branchial cavity. In the oyster (fig. 1/6), the bran-
chiae form four leaflets (h, K), attached by their contiguous
upper margins, and free below ; they consist of innumerable
elongated filaments, covered by a delicate membrane, on
which a rete of capillary blood-vessels is spread ; vibratile
cilia are developed on the surface of this membrane, as well
as on that of the branchial cavity, by which currents of water
are made to traverse the respiratory organs in a determinate
direction ; in the conchifera, burrowing in rocks, sand and
mud, the branchiae are greatly elongated, and the mantle is
prolonged into tubes, for conducting water into the palleal
cavity. The vibratile cilia are of large size in Mytilus and
Anodon, covering the entire surface of the branchial filaments,
and lining all parts of the respiratory cavity ; a small portion
of the branchiae, detached from the living animal, is seen to
row itself, like an animalcule, through the water, by the
motion of its cilia.

Nearly all the GASTEKOPODA respire by branchiae, which, in
most of the naked marine species, are in the form of tufts,
fans, or combs, variously disposed on the surface of the body,
and in the testaceous kinds are concealed under a fold of the
mantle. In the Doris (fig. 221) the branchiae (e) form elegant
ramose tufts, disposed around the anal opening ; in Thethys
they are composed of two dorsal rows of alternately tufted and
crested organs. In Aplysia (fig. 177) they occupy the right
side of the body, and are protected by a delicate peUucid
shell. In the numerous pecteni-branchiate gasteropods, as the
Paludina (fig. 35), inhabiting univalve turbinated shells, the
branchiae ((/} are placed under an extended fold of the mantle,
and in many of the carnivorous genera the water is con-
ducted into the branchial chamber, through a muscular si-
phuncle, lodged in a canal of the shell, and flowing over the
surface of the filamentary gills, by the vibrations of the cilia,
is discharged through an opening in the palleal cavity, carrying
with it the excreted materials from the glands and intestinal
canal.

220

OF RESPIRATION.

[In the PTEROPODA, as the Clio and Hyalea, the branchiae
resemble membranous expansions, like fins, or lamellae, on
the surface of the body. In the CEPHALOPODA they form two
or four organs, lodged in a distinct chamber, into which the
water is inspired, and expelled through a funnel-like tube,
situated on the under side of the neck.

[§381. The CRUSTACEA present various phases of
branchial development ; in the lowest forms, no
special organ exists; the tegumentary membrane
forming a general aerating surface. In the bran-
chiopods, the last joints of the feet are flattened
and covered with a vascular membrane, adapted
for respiration ; these organs having a continual
oscillating movement. In the Squill a, the bran-
chiae are limited to the abdominal members ;
whilst in the decapoda, as the crab and lobster
(fig. 222), they are formed like those of mollusca
and fishes, and lodged in separate cavities under
the thoracic shield ; the renewal of the water being
effected by the motion of distinct appendages.
In those Crustacea, as the land crabs, which live
for a time on shore, the branchiae are kept moist
by the membrane lining, the cavities being disposed
in folds, to serve as reservoirs for water ; and
sometimes it presents a spongy texture for the
same end.

[§ 382. The marine AKNELIDA respire by bran-
chiae variously disposed, on different parts of their
bodies ; in those living in tubes, as Serpula and
Sabella, they resemble the tentacula of polyps, and
form plumelike coloured organs, sometimes with a
spiral winding. When fully expanded in the water,
they are adorned with the most beautiful colours.
In the Amphitrite they are pectinated ; in Terebelhe
they resemble small trees planted round the neck.
In the genera which swim freely through the
water, they are disposed in longitudinal lines ; in
the Arenicola (fig. 233), they form a series of tufts,
rich in bloodvessels. In Eunices, they have a
of pectinated form, and in Aphrodita they are placed
the Arenicola. on scales along the back. In the Ilirudo (fig.

or EESPiRATio]*. 221

1 78) a series of vesicles lined with mucous membrane, and
richly supplied with blood vessels, are regarded as respirating
sacs.

[§ 383. Fishes respire by branchiae, or gills, for the sup-
port and protection of which a complicated framework of
bones, cartilages, ligaments, and muscles is provided ; the
form and arrangement of this apparatus varies in the different
families and genera. It may, however, be classified into — 1st.
The lingual bone and branchiostegous rays ; 2nd. The bran-
chial arches ; 3rd. The opercula or gill covers.

The gills are for the most part attached to the branchial
arches, which extend from the sides of the os hyiodes, back-
wards to the cranium. They are, in general, four in number
on each side of the head, and are composed of numerous la-
mellse, placed closely together, and arranged in a regular series
over the whole external convex margin of the branchial arches,
like the barbs of a feather, or the teeth of a comb. Every-
thing is arranged to afford the greatest possible extent of sur-
face for the contact of the water with the mucous membrane
on which a rich vascular network is spread. In the common
ray, the extent of surface of the mucous membrane of the
gills is estimated at 2250 square inches. In osseous fishes,
as the pike and perch, the gills adhere by their superior bor-
der, and are covered by moveable opercula. In the carti-
laginous genera, as the rays and sharks, they are attached by
both borders, and there are no opercula ; the water, which
hi the former enters by the mouth and escapes by the oper-
cula, in the latter is expelled by a series of fissures situated
at the sides of the neck. In the Hippocampus and Synynathus,
the gills are disposed in the form of tufts along the surface
of the branchial arches, resembling the tufted branchiae of
gastropoda and annelida. In sucking fishes, as the lamprey,
Petromyzon, they are in the form of vesicular sacs, ar-
ranged on each side of the neck, into which the water is
introduced by a canal coming from the cavity of the mouth,
and discharged through the holes situated at the sides of
the same region.

Most fishes, besides gills, possess a hollow organ analagous
to a lung, and called the air-sac, or swim-bladder ; it is situated
in the abdominal cavity, lying along the under side of the ver-

L22 or RESPIRATION.

tebral column, and, in general, communicating with the pha-
rynx, or stomach, by a membranous canal. Numerous blood-
vessels and nerves, derived from the eighth pair and the sym-
pathetic, are distributed on its walls ; this organ is most de-
veloped in those fishes which come frequently to the surface
of the water, and are remarkable for their vehement and
prolonged muscular movements, as the Lepidostens of the
American rivers. The air-sac in this fish is divided into two
chambers, the lining membrane presenting an arrangement
of cells like the lung of a reptile ; the duct from this air-sac,
surmounted by a rudimentary larynx, opens high up in the
throat, and, although a simple membranous tube, is the homo-
logue of the trachea of air-breathing vertebrata. In the Lepi-
dosiren the air-sac is a double organ, each division being divided
into several lobes ; it is situated behind the kidneys, against the
ribs, and is internally cellular, like the lung of a serpent ; an-
teriorly it opens by a tolerably long, narrow membranous
tube into the esophagus ; each division of the air-sac receives
a branch of the pulmonary artery, arising from the branchial
arteries. For these reasons the air-sac of fishes is regarded as
a rudimentary lung, performing an accessory part in the great
function of respiration. It is least developed, or even wanting,
in those species which live at the bottom, and burrow in sand
or mud, as the lampreys, rays, and Plenronectidce. Many
fishes respire by the intestinal canal, the air which they swallow
at the surface being employed for that purpose, as it escapes
from the intestine loaded with carbonic acid gas. The fact of
fishes swallowing air may be seen in the electric eel, and in
fishes kept in vases, the water of which has been deprived of
its air by their respiration.

[§ 384. The higher forms of reptiles, as serpents, lizards,
and turtles, breathe by lungs. In the amphibia, one group
comprising the frogs and salamanders, respire, during a term
of their embryonic development, by vascular tufted gills ; but
these organs are subsequently absorbed, as the lungs become
developed ; and, during adult life, they breathe air by lungs,
respiration being aided by the general surface of their smooth,
naked, tegumentary membrane. In another group the gills
are persistent through life, and co-exist with the lungs. Such
is the case in the Amphiuma, Menobraiichus, Proteus, Siren,

OF KESPIEATIOtf. 223

Axolotl ; all these amphibia, like fishes, have branchial arches
attached to the hyoid bone, and situated at the under part of
the head; in the Proteus, there are three pairs of branchiae, with
ramified filaments, extending in the form of vascular branched
organs to a considerable distance beyond the branchial
apertures ; the water enters by the mouth and escapes by the
inter-branchial spaces. Besides gills, the pereimibranchiate
amphibia possess lungs resembling the air-sacs of fishes, and
which we shall describe in treating of the development of these

organs.

[§ 385. The second form of respiratory organs, called tra-
chea, is met with in myriapoda, insecta, and some arachnida.
The tracheae are air-tubes which divide and subdivide, and be-
come smaller and smaller in diameter, and penetrate the sub-
stance of all the organs ; sometimes they are enlarged into
vesicular sacs, of different forms and sizes (fig. 234). These
tubes convey atmospheric air to the interior of all the tissues,
and, as they are everywhere surrounded by the blood, diffused
through the body of insects, a perfect aeration of that fluid is
effected ; the extensive ramification of the tracheae being a
compensation for the imperfection of their organs of circula-
tion. The large quantity of air contained in the bodies of in-
sects impart the necessary lightness and elasticity to them,
and the highly oxygenated condition of their circulating fluids
imparts energy to the muscular system, and precision and
activity to their movements ; to the same cause we must like-
wise attribute the high temperature which their bodies so
often acquire. Fig. 234 exhibits the respiratory system in
the Nepa cinerea. The air is admitted by the spiracles, or stig-
mata, into two great lateral tubes, which subdivide and ramify
through the body ; the tracheae are lined with a soft mucous

~ *- -

membrane, and covered externally with a dense, shining,
serous coat ; between these is interposed an elastic fibrous
tunic, formed of a cartilaginous filament rolled into a spiral
form, like the spiral vessels in plants. This admirable struc-
ture, affording as it does one of those striking examples of
creative wisdom and design, extends through all the ramifi-
cations of the tracheae, giving the necessary elasticity and
patency to tubes destined to convey air, and to ramify like
blood-vessels through all parts of the head, antennae, palpi,
legs, tarsi, wings, muscular, nervous and digestive systems ;

224

OF EESPIRATTON.

the stigmata, or spiracles, are provided with muscles to open
and close them, and with valves, processes, and hairs, va-

HeaO.

1st pair of legs

1st segment of
the thorax.

Origin of the
wings.

2d pair of legs.
3d pair of legs.

Trachese.

Spiracle.

Vesicular air
sacs.

Fig. 234. — Respiratory apparatus of the Nepa cinerea.

riously modified in the different families, to protect them from
the entrance of foreign bodies. The abdominal segments of
the body exhibit rythmic contractions and expansions during:
respiration, which are well seen in the dragon-fly, and resem-
ble the muscular movements of the thorax and abdomen during
the same act in the pulmonated vertebrates. — T. W.]

KESPIRATlOTf.

220

§ 386. In the lower vertebrata provided with 1 rings the/

form a single or-

gan

Luii;:

t Lungs

but in the
higher classes
they are in pairs,
placed in the
cavity formed
by the ribs, one
on each side of
the vertebral co-
lumn, and en-
closing the heart
between them
(fig. 235). The
lungs communi-
cate with the
atmosphere by
means of a tube,
composedpf car-
tilaginous rings,
arising at the
back part of
the mouth, and
dividing below,

first into a branch for each organ, and then into innumerable
branches penetrating their whole mass, and finally terminating
in minute cells. This tube is the trachea (/), and its branches
are the bronchi. In the higher air-breathing animals the lungs
and heart occupy an apartment by themselves, the chest (fig.
124), which is separated from the other contents of the lower
arch of the vertebral column by a fleshy partition, called the
diaphragm (fig. 180), passing across the cavity of the body,
and arching into the chest. The only access to this apartment
from without is by the glottis through the trachea (fig. 235, t).
§ 386*. The mechanism of respiration by lungs may be
compared to the action of a bellows. The cavity of the chest
is enlarged by raising the ribs, the arches of which naturally
slope somewhat downward, but more especially by the con-
traction of the diaphragm, whereby its intrusion into the chest
is diminished. This enlargement causes the air to rush in
through the trachea, distending the lungs so as to fill the ad-

Q

Fig. 235. — LUNGS, HEAUT, and principal blood-
vessels of MAN.

a r, right auricle : v r, right ventricle ; v I, left
ventricle ; a, aorta ; v c, vena cava ; a c, carotid
arteries ; vj, jugular veins ; a s, subclavian ar-
tery ; v s, subclavian veins ; t, trachea.

226

BESPIEATION.

t

Fig. 236. — Lung of the water

newt (Triton cristatus) :

ditional space. When the dia-
phragm is again relaxed, and the
ribs are allowed to subside, the
cavity is again diminished, and
the air expelled. These move-
ments are termed-inspiration and
expiration. The spongy pulmo-
nary substance being thus dis-
tended with air, the blood sent
from the heart is brought into such
contact with it as to allow the re-
quisite interchange to take place.
[§ 387. The minute anatomy
of the lungs, in vertebrate ani-
mals, exhibits many interesting
varieties. The structure is sim-
plest in the naked amphibia,
where it is but little more com-
plex than in the snails.* In the
water-newt, for instance, the
lungs present themselves as a
pair Of simple elongated sacs

vein.

'rf* «X* & *%Iw&. «^ ;
C*/CV^B^^i^*.l

•W*%\f

&ivV-*-

A, the /fi 236), attached to an ex-
<-mely short rudimentary la-
rynx, and internally exhibiting
no projection ; the air distends
the entire hollow internal sac, or
cavity. In the frogs the mem-
branous surface of the lungs is
increased by the development of
cells upon their internal aspects
(figs. 237 and 238), upon the
bottoms of which cells other secon-
dary and smaller ones can be per-
ceived ; all these pulmonic cells,

Fig. 237. — Portion of the lung
of the Triton cristatus* The ves-
sels are injected with fine size and
vermilion, and form so dense a net-
work that minute islets only of
j'-arcnrhvmn ro-""'" T-C^-I-

* The lung presents itself in its
very simplest form in the snails and
slugs. The contractile respiratory ori-
fice here leads to a simple smooth in-
ternal cavity lined with a delicate
mucous membrane, upon which the
n"lrnnnarv vessels are distributed.

EESPIRATION.

227

fcH

however, are merely parietal, and communicate directly with tht
middle cavity of the lung,
which is filled with atmo-
spheric air, and upon the
membranous walls of which,
as well as upon their bot-
toms, the blood-vessels ra-
mify. In the turtles (fig.
239) and crocodiles the cel-
lular subdivisions increase
in number and decline in
size, andthe common cavity Fig- 238. — Portion of the frog's lung
is divided by various bands frora within» to shew the open parietal
and septa stretching across ^~ figure drawn twice the size of
it, into a number of mutually

communicating sacs or pouches; the whole lung thus acquires a
more compact orparenchy-
matous appearance. In the
serpents (fig. 240), in which
one only of the two lungs is
ever completely evolved, this
at the upper part is covered
with small parietal cells ;
but these gradually become
smaller and smaller, less
and less distinct, and finally
disappear entirely, so that
the lower part of the lung
is completely vesicular and
un vascular.

[§ 388. In the class of

birds we observe, in the p:_ 9oQ A

rig. 239.— A, several cells from the

same interesting manner, lung of a Tortoise. A portion of one of

the general type of the these cells is exhibited in B, magnified

lung preserved, but the sur- five hundred times— part of the septum,

face of contact is greatlvin- a> a' which ^'ides this cell from those

creased bv means of narif next to il> ° and d' is seen' The ves'

- Pane; sels are injected with size'and vermilion,
tal cells, which are repeated and form such thick masses, that the
again and again. This mo- islets of pulmonic parenchyma betwixt
dification is made necessary taem almost disappear.
by the larger quantity of blood which is here transmitted to

/

..»->>• e "« • r ""- "7 »" - •>

228

EESPIEATIOB .

the respiratory system, and the consequent augmented amount

of respiratory process, by
which a larger extent of
membranous surface became
indispensable. The bronchi
in birds are continued into
the lungs, where they divide
into membranous tubes,
which permeate their sub-
stance; the deeper tubes
stand like organ-pipes, and
open into the superficial
tubes ; and all are covered
with small parietal cells,
upon which vessels are dis-
tributed ; the cells form very-
elegant, delicate microscopic

e ^ ~t reticulations, and generally

Fie. 240. — A piece from that part of , ,

the Serpent's lung which is most scan- present themselves as six-

tily supplied with vessels, magnified sided spaces,
four hundred times. The vessels here [§ 389. The lungs of man
form a very beautiful rete, with wide and fae mammalia are form-
meshes ; they have been successfully ed after another and a differ.

injected with fine size and vermmon. , , ,

eiit type ; the trachea here

divides and subdivides, like
the branches of a tree, into
finer and finer branches,
which at first contain carti-
lages in their constitution,
but which by and by become
membranous, and finally end
in blind sacculi, or rather
in hollow berry or bud-like
Fig. 241.— Terminal vesicles of the and clustered vesicles (figs.
human lung, hanging to a branch of 241 and 242). The pulmo-
the bronchi as berries hang to their nic ce}ls Of man and the
stalk, and distinct from one another. mamma]ia consequently,
The figure is half a plan, and the mag- parietal, but termi-

nifvmg power used very high. ^ _ ^ ^ from ^

Gth to the 18th of a line in magnitude, the majority of them
measuring between the 8th to the 10th of a line in diameter.

EESPIRATION.

223

Delicate arcuate fibres, of the nature
round these terminal vesicles, and
hold them distended, whilst the
vessels spread freely over their sur-
face (fig. 242).

[§ 390. The development of the
lungs is extremely interesting. In the
embryo of the bird and mammal
they first appear in the shape of a
simple, and then of a double projec-
tion from the esophagus (fig. 244, a),
which soon divides more distinctly
into two, becomes separated from
this part, and is finally supported
upon a pedicle — the future trachea
(fig. 244, 6). In birds these little
sacs are then drawn out into hollow
into the paral-
lel pipes above
described (§
387). In the
mammalia
they divide,
after the man-
ner of branch-

es, into twigs
and minute
vesicles (figs.
241 and 242),
which advance
in develop-
ment, and be-
come the future
terminal cells
(fig- 242, B).

[§391. The
capillary vas-
cular net- work
of the lungs,
as already
stated, exhi-

of elastic tissue, sui

Fig. 242— A, portion of the
lung of a hog. The terminal
vesicles are filled with mer-
cury, and of the natural size.
B, the same part seen under
a simple lens.

tubes, which pass over

Fig. 243. — Small portion of lung from the body of
a man examined shortly after death, under a magnify-
ing power of 200 times. The vessels, b, b, &c., still
turgid with blood, include very minute islets of paren-
chyma between them ; the semicircular fibres, a, a, a,
surround the smallest terminal cells of the lungs.

230

EESPIEATION.

in the embryo of the sixth day.
Both figures twice the size of
nature.

bits a peculiar structure, which may be studied very readily in

the lungs of the live newt (fig.
230), or in preparations of the
same part that have been finely
injected. From the whole extent
of the pulmonary artery a vast
number of very small arteries arise,
, the orifices of which give the inner

Fig. 244.— a, Rudiment of the surface of its principal branches
lung in the embryo of the fowl the appearance of a regularly per-
of the fourth day ; b, the lung forated sieve ; these minute ves-
sels form a very close irregular
hexagonal intermediate net-work,
without resolving themselves into
branches and twigs like a tree,
and so forming a capillary rete.
Yet single larger vessels (fig.
230, d) proceed from the
pulmonary artery to reach some
more remote part of the lung.
The pulmonary vein, like the pul-
monary artery, is partly perforated
at every point in its course for the
reception of smaller vessels, and
is partly formed by larger venous
trunks, which collect and bring

sheep, an inch and a half long, the blood from greater distances
seen under the microscope (af- /fi^ 230, c). The islets of the

A. «« A/T :i11«vM 71 s* ffl nvin G£>/*OV*<Y* . ...

thin and indistinctly cellular pa-
renchyma, are often of a di-
ameter inferior to that of the ves-
sels which surround them ; this
is the case in the tortoise, for ex-
ample (fig. 239), and appears to
be the case in man also (figs. 241,
242). It is remarkable that
even in the more conspicuous
branches of the pulmonary vas-
system, the layer of trans-

Fig. 245. — The greater part
of the right lung of a fetal

ter Miiller, De Gland, secern,
struct, penit. T. xvii. f. 7).

Fig 246. — Termination of one
of the branchings of the bronchi

from the lung of a very young "Uli" ^ m» ^ ia^c
embryo of the hog after Rathke parent lymph in immediate con-

Cfig. viii. T. xviii.)

j- •> -*.

tact with the walls of the vessels

RESPIRATION. 231

should either be wanting, or of the greatest delicacy ; and that
no lymph-corpuscles should be visible swimming in it apart
from the general current, but that they should be observed
mingled with the common stream (fig. 230 a, b, c).]*

[§ 3.Q2. The organs which serve in man and the various
classes of animals for respiration, and the mechanical part of
the function of these organs, have now been described. The
very essence of respiration, however, consists in this : that the
air of the atmosphere brought into contact with the blood
within the lungs effects certain changes in that fluid which are
indispensable to the maintenance of life. The air, it is true,
does not come into direct contact with the blood even in the
lungs, but is separated from it by the parietes of the pulmo-
nary cells and the walls of the blood-vessels. The air, how-
ever, readily penetrates these moist tissues, for it combines
with the watery fluid which permeates them, and so makes its
way even immediately to the blood. f As the lungs contain
air at all times, the influence which the elastic fluid exerts
upon the blood, and the changes wThich the blood undergoes,
are not connected with the alternate assumption and rejection
of so much air. These are but means to an end : the proper
respiratory process, or that process for which inspiration and
expiration are instituted, goes on incessantly. Inspiration
and expiration are merely provisions for changing the air,
which must be renewed at intervals, longer or shorter, if the
object of respiration is to be attained. — Before entering on
the peculiar chemical processes occurring in respiration, it is
proper to inquire into the changes which, 1st, the air, and 2nd,
the blood, experience in its course.

[§ 393. The earliest accurate researches into the nature of
respiration, were instituted with a view to determine the
changes which the air experienced in passing through the
lungs, and our information upon this part of the function

* Professor Wagner's Physiology, pp. 358, et seq.

f The penetration of the moist parietes of the air-cells and blood-
vessels is a general physical phenomenon, and independent of any peculiar
power or property inherent in the lungs ; any moist animal membrane
without or within the living body is gradually penetrated by the air of the
atmosphere and other gases. (§ 413). The extensive subdivision which the
blood undergoes in the minute vessels of the lungs is obviously calculated
greatly to assist the operation of the air.

232 RESPIRATION.

may be said to be pretty full. The air of the atmosphere
consists of a mixture of nitrogen and oxygen, with a
slight addition of carbonic acid and of hydrogen gases :
100 parts of atmospheric air consist, according to the
latest analyses, very constantly of 79 parts of nitrogen, and
21 of oxygen ; the admixtures of carbonic acid and hydrogen,
on the contrary, are extremely variable in amount ; the
carbonic acid has been ascertained to vary between 0,0003
and 1,0 per cent. ; the hydrogen may amount to about
1 per cent. The air that is expired yields very nearly the
same quantity of nitrogen as the air that is inspired; but it
contains less oxygen, and a larger quantity of carbonic acid,
and also of hydrogen ; it likewise contains some volatile
organic matters. The quantities of oxygen and carbonic
acid, in the air, have altered relatively during respiration, in
suchwise that the volume of the oxygen which has disappeared
is rather greater than that of the carbonic acid which has
made its appearance. Sir Humphrey Davy breathed during
one minute, making 19 inspirations in the time, 161 cubic
inches of air, which in 100 parts consisted of 72,7 nitrogen,

26.3 oxygen, and 1,0 carbonic acid ; and during this time he
expired 152 cubic inches of air, of which 100 parts contained

73.4 nitrogen, 15,1 oxygen, and 1 1,5 carbonic acid. In this ex-
periment, consequently, if we disregard the disappearance of
9 cubic inches of air and a slight increase of nitrogen, it appears
that from the respired air 1 1,2 per cent of oxygen had vanished,
and 10,5 per cent, of carbonic acid had appeared. In the
experiments of Allen and Pepys, 100 parts of expired air were
found to consist of 79 nitrogen, 13 oxygen, and 8 carbonic acid;
supposing, therefore, the air which was breathed to have been
of the normal constitution, 8 per cent, of oxygen had disap-
peared, and rather more than 8 per cent, of carbonic acid had
been evolved. Like results were come to by Dulong, Des-
pretz, Lavoisier, and Seguin. In the quantity of the absorbed
oxygen and of the added carbonic acid, however, the state-
ments of the different observers differ. Davy, for example,
found that the quantity of the added carbonic acid amounted
to from 3,95 to 4,5 per cent. ; in the particular experiment
quoted above, it was as much as 10,5 per cent. Allen and
Pepys state it at from 8 to 8,5 per cent. ; Berthollet at from
5,53 to 13 per cent. ; Menzies at 5 per cent. ; Prout at from

CHANGES IN THE AIR. 233

j,3 to 4,6 per cent. ; Murray at from 6,2 to 6,5 per cent. ;
Fyfe at 8,5 per cent., and Irvine at 10 per cent. The mean
of tke whole of these observations is about 5,8 per cent. If
WP ^esume that errors had crept into some of these experi-
ments, it is still obvious that the quantity of carbonic acid
eliminated by different individuals, and at different times, is not
always the same. Front, whose skill in observation inclines
us to place the most implicit reliance on his results, found by
direct experiment that the time when the smallest quantity of
carbonic acid was produced, was shortly after midnight ; it
increased towards morning, and rose continually towards mid-
day, when it attained its maximum ; in the afternoon it
declined again, and sank continually through the course of
the evening, until it reached its minimum about midnight.
The formation of carbonic acid, therefore, experiences regular
fluctuations in accordance with the times of the day. Prout
observed, farther, that a larger quantity of carbonic acid was
produced in states of mental tranquillity, during gentle exer-
cise and with a low state of the barometer ; and that, on the
contrary, less was formed under the influence of active exer-
tion, depression of mind, and the use of spirituous liquors.
The estimates which we have of the absolute quantity of car-
bonic acid eliminated during a given time also vary greatly.
According to Lavoisier and Seguin, the quantity formed in
twenty-four hours amounts to 8,534 grains French ; according
to Davy, it is 17,811 grains English; according to Allen and
Pepys, it is 18,612 grains English. But these quantities
Berzelius has shown are far too great with reference to the
quantity of food consumed in the same interval of time.*

* Berzelius observes (Thierchemie, 3tte Auf. S. 124), that upwards of
six pounds of solid aliment daily would be required to replace this loss of
carbonic acid, even were the whole of the carbon of the food to be elimi-
nated by the lungs in the shape of carbonic acid, and none to pass off with
the foeces, the bile, the urine, &c., which, however, is very far from being
the case. The above quantities must, therefore, be looked upon as exag-
gerated, though the observations themselves may be perfectly correct ;
the error, probably, lies in the reckoning ; during the short period that
such experiments last — one or two minutes — inspiration and expiration are
almost certainly forced or exaggerated ; the air is more rapidly changed,
and more carbonic acid is eliminated than during ordinary respiration.
The indications afforded by two minutes, under such circumstances, ap-
plied to the whole of the twenty-four hours, obviously raise the general
result far above the proper standard.

234 EESPIEATION.

The quantity of water contained in the expired air amounts,
taking the mean of the estimates of a great number of ob-
servers, to about 8,000 grains, or one pound in the four-and-
twenty hours.*

RESPIRATION IN GASES OTHEE THAN AT^tOSPHEETC AIE.

[§ 394. With a view of obtaining still more precise informa-
tion regarding the changes induced in air by its assumption
into the lungs, experiments have been instituted on the respi-
ration of different kinds of gas. These experiments, however,

* See Miiller's Physiology, by Baly, vol. i. p. 330. The statements
in the -text refer particularly to man ; but they also apply very closely
to animals which breathe by lungs, with this difference, that in cold-
blooded animals the quantities of oxygen absorbed, and of carbonic acid
eliminated, are relatively smaller. Dulong found, no matter what animal
he made the experiment upon, that there was rather more oxygen ab-
sorbed than carbonic acid evolved. The excess in graminivorous animals
amounts to one-tenth ; in carnivorous creatures, it was from one-fifth to
one-half more than the carbonic acid. Despretz observed the same thing.
Allen and Pepys, on the other hand, found the quantity of oxygen that
disappeared, and of carbonic acid that was generated, to be equal. The
oxygen which disappears is used up in the combustion of hydrogen, the
product of which is watery vapour. Treviranus and Miiller instituted
comparative experiments upon the respiration of some of the lower
animals, and the quantity of carbonic acid formed in a given time, con-
trasted with the weight of the animal, from which it appears that
mammals, for every one hundred grains of their weight, produce 0.52 of
cubic inch of carbonic acid in one hundred minutes ; that birds, consi-
dered in the same way, produce 0.97 of a cubic inch ; that amphibia (the
frog), still considered in the same way, produce 0.05 of a cubic inch. The
respiratory process performed by the medium of water is precisely the
same as that which goes on with the direct contact of air : the air dis-
solved in the water comes into contact with the blood which circulates
through the gills, and oxygen disappears, and carbonic acid appears as
usual. Water, in general, contains from five to five and a quarter per cent.
of its bulk of air dissolved in it — this air, however, having a somewhat
greater relative proportion of oxygen than the air of the atmosphere,
oxygen being somewhat more soluble in water than nitrogen. We have
very admirable researches on the respiration of fishes by A. von Humboldt
and Provencal. The water in which the fishes were put in these experi-
ments contained 20,3 per cent, of air, which, in one hundred parts, con-
sisted of 29,8 oxygen, 66,2 nitrogen, and 4,0 carbonic acid. After having
been used for respiration, the water still contained 17,6 per cent, of ah*,
which consisted, in one hundred parts, of 2,3 oxygen, 63.9 nitrogen, and
33,8 carbonic acid. Here, therefore, oxygen was also absorbed, and carbonic
acid evolved.

EESPIEATION OF KTTROGEN. 235

almost necessarily extended to the consideration of the effects
which breathing different gases produced upon the organism,
as well as to the changes which the gases suffered in the
process. We shall therefore here consider the two together.
During healthy respiration, the atmospheric air that supplies
the lungs is constantly changed. If this renewal of the air is
not provided for, but the same air is breathed over and over
again, the circumstances attending respiration are altered.
In the same proportion, for example, as the oxygenous con-
tents of the air dimmish, and the carbonaceous contents in-
crease, less and less oxygen is absorbed, less and less carbonic
acid is evolved ; and when the air comes to have a certain
proportion of carbonic acid mixed with it, which, from the
experiments of Allen and Pepys, appears to be ten per cent.,
no more carbonic acid is formed, and the elastic fluid no
longer suffices for respiration, although it still contains some-
thing like ten per cent, of oxygen. A little oxygen, indeed,
continues to disappear, but the respiration becomes laborious,
and cannot be carried on without imminent risk of suffocation to
any of the higher animals. This is the source of the oppressive
sensation experienced when many persons, crowded together in
a limited space, continue to breathe the same atmosphere. In
pure oxygen gas respiration goes on as readily as in atmospheric
air, but a feeling of uneasiness and of exhaustion is soon ex-
perienced. The changes produced in the gas are of the same
nature as when the common atmospheric air is breathed —
oxygen disappears, and carbonic acid is engendered ; the
quantity of the latter, according to Allen and Pepys, being,
however, greater than under ordinary respiration — it amounts,
instead of eight per cent., to between eleven and twelve per
cent. The same experimenters also found that nitrogen gas
was evolved during -the respiration of oxygen gas. Nitrous
oxyde gas (consisting of sixty-four nitrogen, thirty-six oxygen),
like oxygen, will support life for a time, but it produces a pe-
culiar intoxicating effect upon the economy. A portion of
the gas is dissolved by the blood, which assumes a purple red
colour ; and the face and hands, in consequence of this
change, acquire a livid and cadaverous hue. Nitrogen and traces
of carbonic acid are found in the expired nitrous oxyde gas.
Pure nitrogen, although it can be taken readily into the lungs,
and is not at all poisonous, is quite incompetent to support-

o

36 RESPIRATION.

life ; small animals immersed in it, therefore, soon die as-
phyxiated. Pure hydrogen, too, can be breathed, but will
not support life ; it is either without effect on the economy,
or exerts a soporific influence. The experiments of many in-
quirers, however, have shown that cold-blooded animals, such
as frogs, can exist for hours in pure nitrogen and hydrogen ;
they become asphyxiated at length, and are apparently dead ;
but if not kept too long immersed in the gases, they recover
when brought into contact with the air of the atmosphere.
All observers, too, are agreed that these animals eliminate car-
bonic acid when confined in nitrogen and hydrogen. In a mix-
ture of four parts hydrogen and one part (volume) oxygen,
animals were found by Allen and Pepys to become sleepy,
^without any prejudicial effect upon the health appearing to
ensue. Oxygen disappeared, and carbonic acid was evolved
precisely as when atmospheric air was breathed ; at the same
time, however, nitrogen made its appearance, and in such quan-
tity, too, that in the course of an hour the volume eliminated
equalled, and even exceeded by a half, the volume of the
animal wrhich was the subject of experiment. Other gases
are true poisons to the economy — carburetted, phosphuretted,
sulphuretted, arseniuretted hydrogen, &c. Air that contained
no more than l-1500th of its bulk of sulphuretted hydrogen
was sufficient to prove fatal to a bird ; 1 -800th destroyed a
dog, 1 -250th killed a horse. Some gases inspired in a state
of purity, or but little diluted, induce spasm, and complete
closure of the glottis, and consequent death ; more largely
diluted, they excite violent cough. To this list belong chlorine,
the vapour of iodine, nitric oxyde, ammoniacal gas, fluoboric
and fluosilicious gas, and the greater number of the strong
acid vapours, such as those of nitric acid, sulphuric and sul-
phurous acid, succinic acid, &c. The greater number of the
particulars related in the preceding paragraph have been made
known to us through the admirable researches of Sir
Humphrey Davy,]*

§ 395. The vivifying power of the air upon the blood is
due to its oxygen. If an animal be confined for a time in a
closed vessel, and the contained air be afterwards examined,
a considerable portion of its- oxygen will have disappeared,
and another gas of a very different character, namely, carbonic

* Dr. Julius Vogel, in Wagner's Physiology, p. 366.

BESPIEATIOX. 237

acid gas, will have taken its place. The essential office of
respiration is to supply oxygen to the blood, at the same
time that carbon is removed from it.

§ 396. An immediately obvious effect of respiration in the
red-blooded animals is a change of colour ; the blood, in
passing through the respiratory organs, being changed from a
very dark purple to a bright scarlet. In the great circulation
the scarlet blood occupies the arteries, and is usually called
red blood, in contradistinction to the venous blood, which is
called black blood. In the lesser or pulmonary circulation, on
the contrary, the arteries carry the dark, and the veins the
red blood.

§ 396*. The quantity of oxygen consumed by various ani-
mals in a given time has been accurately ascertained by expe-
riment. It has been found, for instance, that a common-
sized man consumes, on an average, about one hundred and
fifty cubic feet in twenty-four hours ; and as the oxygen con-
stitutes but twenty-one per cent, of the atmosphere, it follows
that he inhales, during a day, about seven hundred cubic feet
of atmospheric air. In birds, the respiration is still more
active, while in reptiles and fishes it is much more sluggish.

§ 397. The energy and activity of an animal is somewhat
dependent on the activity of its respiration. Thus the toad,
whose movements are very sluggish, respires much more slowly
than mammals, birds, and even insects ; and it has been ascer-
tained that a butterfly, notwithstanding its comparatively
diminutive size, consumes more oxygen than a toad.

§ 398. The circulation and respiration have a reciprocal
influence upon each other. If the heart be powerful, or if
violent exercise demand a more rapid supply of blood to
repair the consequent waste, respiration must be propor-
tionally accelerated to supply air to the greater amount of
blood sent to the lungs. Hence the panting occasioned by
running or other unusual efforts of the muscles. On the
other hand, if respiration be hurried, the blood being ren-
dered more stimulant by greater oxygenation, causes an ac-
celeration of the circulation. The quantity of air consumed
varies therefore with the proportion of the blood which is
sent to the lungs.

§ 339. The proper temperature of an animal, or what is
termed ANIMAL HEAT, depends on the combined activity of

238 KESPIEATIOX.

the respiratory and circulating systems, and is in direct pro-
portion to it. In many animals the heat is maintained at a
uniform temperature, whatever may be the variations of the
surrounding medium. Thus birds maintain a temperature of
about 108° Fahrenheit ; and in a large proportion of mammals
it is generally from 95° to 105°. These bear the general de-
signation of warm-blooded animals.

§ 400. Reptiles, fishes, and most of the invertebrate animals,
have not this power of maintaining a uniform temperature.
The heat of their body is always as low as from 35° to 50°,
but varies perceptibly with the surrounding medium, being,
however, often a little above it when the external temperature
is very low, though some may be frozen without the loss of life.
For this reason they are denominated cold-blooded animals;
and all animals which have such a structure of the heart, that
only a part of the blood which enters it is sent to the respira-
tory organs (§ 366), are among them.

§ 401. The production of animal heat is obviously con-
nected wit»h the respiratory process. The oxygen of the
respired air is diminished, and carbonic acid takes its place.
The carbonic acid is formed in the body by the combination
of the oxygen of the air with the carbon of the blood. The
chemical combination attending this function is, therefore,
essentially the same as that of combustion. It is thus easy
to understand how the natural heat of an animal is greater,
in proportion as respiration is more active. How far nutri-
tion in general, and more particularly assimilation, by which
the liquid parts are fixed and solidified, is connected with the
maintenance of the proper temperature of animals, and the
uniform distribution through the body, has not yet been satis-
factorily ascertained.

§ 402. Some of the higher warm-blooded animals do not
maintain their elevated temperature during the whole year ;
but pass the winter in a sort of lethargy, called HIBEENATIOK,
or the hibernating sleep. The marmot, the bear, the bat, the
crocodile, and most reptiles, furnish examples. During this
state the animal takes no food ; and as it respires only after
very prolonged intervals, its heat is diminished, and its vital
functions generally are much reduced. The structural cause
of hibernation is not ascertained ; but the phenomena at-
tending it fully illustrate the lavs already stated (§397 — 401).

RESPIRATION. 239

§ 403. There is another point of view in which respiration
should be considered, namely, with reference to the buoyancy
of animals, or their power of rising in the atmosphere, and
their ability to live at different depths in the water, under a di-
minishedor increased pressure. The organs of respiration of birds
and insects are remarkably adapted for the purpose of admit-
ting at will a greater quantity of air into their body, birds being
provided with large pouches extending from the lungs into the
abdominal cavity and into the bones of the wing ; insects have
their whole body penetrated by air-tubes, the ramifications of
their tracheae, which are enlarged at intervals into wider cells,
whilst most of the aquatic animals are provided with minute,
almost microscopic tubes, penetrating from the surface into the
substance, or the cavities of the body for admitting water into
the interior, by which they thus adapt their whole system to
pressures which would otherwise crush them These tubes may
with propriety be called water-tubes. In fishes, they penetrate
through the bones of the head and shoulder, through skin
and scales, and communicate with the blood vessels and
heart, into which they pour water; in mollusca they are more
numerous in the fleshy parts, as, for example, in the foot,
which they help to distend, and communicate with the main
cavity of the body, supplying it also with liquid ; in echino-
derms they pass through the skin, and even through the hard
shell, whilst in polyps they perforate the walls of the general
cavity of the body, which they constantly fill with water.

§ 404. In order fully to appreciate the homologies between
the various respiratory apparatus observed in different animals,
it is necessary to resort to a strict comparison of the fundamen-
tal connections of these organs with the whole system of or-
ganization, rather than to the consideration of their special
adaptation to the elements in which they live. In vertebrata,
for instance, there are two sets of distinct respiratory organs,
more or less developed at different periods of life, or in dif-
ferent groups. All vertebrata, at first, have gills arising from
the sides of the head, and directly supplied with blood from
the heart ; but these gills are the essential organs of respira-
tion only in fishes and some reptiles, and gradually disappear in
the higher reptiles, as well as in birds and mammalia, towards
the close of their embryonic life (§ 489). Again, all ver-
tebrata have lungs opening in or noar the head ; but the lun°-s

2-10 RESPIRATION.

are fully developed only in mammalia, birds, and the higher
reptiles, in proportion as the branchial respiration is reduced;
whilst in fishes the air-bladder constitutes a rudimentary lung.
§ 405. In the articulata, there are also two sorts of respiratory
organs ; aerial, called tracheae in insects, and lungs in spiders;
and aquatic, called gills in Crustacea and worms. But the
tracheae and lungs open separately upon the two sides of the
body (air never being admitted through the mouth or nostrils
in the articulata) ; the gills are placed in pairs ; those which are
like the tracheae occupying a smilar position, so that there are
nearly as many pairs of tracheae and gills as there are seg-
ments in these animals. The different respiratory organs in
the articulata are in reality mere modifications of the same appa-
ratus, as their mode of formation and successive metamor-
phoses distinctly show, and cannot be compared with either
the lungs or gills of the vertebrata; they are special organs not
found in other classes, though they perform the same func-
tions. The same may be said of the gills and lungs of niol-
lusca, which are essentially alike in structure, the lungs of
snails and slugs being only a modification of the gills of
aquatic mollusca ; but these two kinds of organs differ again
in their structure and relations from the tracheae and gills of ar-
ticulata, as much as from the lungs and gills of vertebrata.
In those radiata which are provided with distinct respiratory
organs, such as the echinoderms, we find still another type
of structure, their gills forming bunches of fringes around the
mouth, or rows of minute vesicles along the radiating seg-
ments of the body.

CHAPTER XINTH.

OF THE SECRETIONS.

§ 400. WKILE, by the process of digestion, a homogeneous
fluid is prepared from the food, for supplying new material to
the blood, another process is also going on, by which the
blood is analyzed, as it were ; some of its constituents being
selected and so combined as to form products for useful pur-
poses, while other portions of it, which have become useless or
injurious to the system, are taken up by different organs,
and expelled in different forms. — This process is termed
SECBETIOF.

§ 407. The organs by which these operations are performed
are much varied, consisting either of flat surfaces or mem-
branes, of minute simple sacs, or of delicate elongated tubes,
all lined with minute cells, called epithelium cells, which
latter are the real agents in the process. Every surface of
the body is covered by them ; and they either discharge their
products directly upon the surface, as on the mucous mem-
brane, or they unite in clusters, and empty into a common
duct, and discharge by a sing e orifice, as is the case with
some of the intestinal glands, and of those from which the
perspiration issues from the skin.

§ 40S. In the higher animals, where separate organs for
special purposes are multiplied, numerous sacs and tubes are
assembled into compact masses called glands. Some of these
are of large size, as the salivary glands, the kidneys, and
the liver. In these, clusters of sacs open into a common canal,
and this canal unites with similar ones, forming larger trunks;
and finally, they all discharge by a single duct, as we find in
the salivary glands.

§ 409. By the organs of secretion two somewhat different
purposes are effected, namely, fluids of a peculiar character
are selected from the blood for important uses, such as the
saliva, tears, milk, &c., some of which differ but little in
their composition from that of the blood itself, and might be

o
R

242 OF THE SECRETIONS.

retained in the blood with impunity ; or the fluids selected
are such as are positively injurious, and cannot remain in the
hlood without soon destroying life. These latter are usually
termed excretions.

§ 410. As the weight of the body, except during its period
of active growth, remains nearly uniform, it follows that
it must daily lose as much as it receives ; in other words, the
excretions must equal in amount the food and drink taken,
with the exception of the small proportion discharged by the
alimentary canal. Some of the most important of these outlets
will be now indicated.

§ 411. We have already seen that all animal tissues admit
of being traversed by liquids and gases, This mutual trans-
mission of fluids from one side of a membrane to the other is
termed endosmose and exosmose, or imbibition and transu-
dation, and is a mechanical rather than a vital phenomenon,
inasmuch as it takes places in dead as well as in living tissues.
The blood-vessels, especially the capillaries, share this property.
Hence portions of the circulating fluids escape through the
walls of the vessels, and pass off at the surface. This super-
ficial loss is termed exhalation. It is most active where the
blood-vessels most abound, and accordingly is very copious
from the air tubes .of the lungs, and from the skin. The loss
in this way is very considerable, and it has been estimated
that, under certain circumstances, the body loses, by exhala-
tion, five-eighths of the whole weight of the substances re-
ceived into it.

§ 412. The skin, or outer envelope of the body, is other-
wise largely concerned in the losses of the body. Its layers are
constantly renewed by the tissues beneath, and the outer dead
layers are thrown off. This removal is sometimes gradual and
continual, as in man; in fishes and many mollusca, it comes off
in the form of slime, which is, in fact, a collection of cells de-
tached from the surface of the skin ; sometimes the loss is pe-
riodical, when it is termed moulting. Thus, mammals cast
their hair, and the deer their horns, birds their feathers, serpents
their skin, crabs their test, and caterpillars their outer en-
velope, with the hairs growing from it.

§ 413. The skin presents such a variety of structure, in
the different groups of the animal kingdom, as to furnish
exceUent distinctive characters of species, genera, and even

OF THE SECRETIONS.

243

families, as will hereafter be shown. In the vertebrata it is
composed of three very distinct layers of unequal thickness
(fig. 250) ; the lower and the thickest layer is the corium,
(c, c), or true skin, and is the part which is tanned into
leather. Its surface presents numerous papillae, in which the
nerves of general sensation terminate ; they also contain a fine
net-work of blood-vessels, usually termed the vascular layer.
The superficial layer is the epidermis, or cuticle ; the cells of
which it is composed are distinct at its inner portion, but
become dried and flattened as they are pushed outwards. It
is destitute of vessels and nerves, and, consequently, is in-
sensible. Between these two layers, and more especially
connected with the cuticle, is the rete mucosum, a very thin
layer of cells, some of which contain the pigment which gives
the complexion to the different races of men and animals.
The scales of reptiles, the nails and claws of mammals, and the
solid covering of the Crustacea are merely modifications of the
epidermis; on the other hand, the feathers of birds, and the
scales of fishes, are derived from the vascular layer.

[§ 413*. Dutrochet investigated the phenomena called endos-
mose and exosmose more carefully than had yet been done,

Fig. 247.

and designated them by these names.*
Berzelius has given an excellent con-
densed view of the subject : " The phe-
nomena exhibited by bodies in solu-
tion," he observes, " in traversing
solid living parts, do not depend solely
on the properties which bodies in solu-
tion have of diffusing themselves evenly
through the fluids which are their men-
strua ; the animal membranes and the
water contribute their share, inasmuch
as the water passes with the dissolved
substance, and from this results a phe-
nomenon, which in its effects resembles
in every respect an absorption. For the
sake of illustration, let a, a, fig. 247, be a tube open at both
ends, but having a piece of moist bladder tied around its lower
extremity ; let a solution of any salt be now poured into the

* Memoires pour servir a 1'Histoire Anatomique et Physiologique des
Vegetaux et Anitnaux, Paris, 1837.

E2

\a

i

<.

I

L

: •]» ; i«

a

244 STRUCTURE Ol' GLAKDS.

tube, and this be plunged into a larger vessel, c, d, containing
water, the tube being immersed till the solution, a, b, is at the
same level, e, e, as the water in the outer vessel, c, d. After a
little time it will be found that the fluid in a, a has risen,
and got above the level, e, e, to b, for example, and that it is
continuing to rise, and will go on rising until the two fluids,
on the opposite sides of the bladder, are of the same density,
so that, if the tube, a, a, be not of sufficient length, the
fluid may even run over, having filled it completely. If
the tube, a, a, instead of containing a saline solution, contain
water, .and the recipient, c, d, instead of water, contain a
saline solution, things being disposed as before, the fluid in
a, a, far from rising, will begin to fall, and instead of fall-
ing in c, d, it will begin to rise. When the tube and
the recipient contain solutions of different salts respec-
tively, but as nearly as may be of the same density, the level
of the fluid in neither will be altered, perceptibly ; but, after
a certain time, the two salts will be discovered mingled to-
gether in both the tube and the recipient, or in the fluid on
both sides of the bladder. If the densities of the two saline
solutions have been different, the surface of that which is the
more dense will rise, that which is less dense will fall ; but it
will be found, nevertheless, that from the solution of greatest
density a portion will have passed into that of least density ;
the penetration has not therefore been all one way, but reci-
procally from each to the other, only in greatest measure from
the less to the more dense fluid. This phenomenon does not
take place only when moist animal membranes are the inter-
media between the two heterogeneous but miscible fluids ; it
also occurs when the interposed body is of an inorganic nature,
but thin and porous, and possessed of strength enough to sup-
port the increasing column of the denser fluid, such as thin
slices of slate, earthenware, &c. In general it may be said that
the power producing the phenomenon in question belongs to all
bodies which can absorb and retain a fluid in extremely delicate
pores."* The blood-vessels, especially the capillary vessels,
share this property of permeability to liquids ; hence, while
the circulation goes on, portions of the circulating fluid, espe-
cially its watery parts, escape through the walls of the vessels,
and pass off at the surface. This superficial loss, termed exha-
* Chimie, 4te. Aufl. B. ix S. 161.

STuUCTUEE OF GLANDS. 24 j

lation, is most active where vessels most abound, and accord
ingly most copious from the surface of the lungs. It has been
estimated that, under certain circumstances, the human body
loses, by exhalation, five-eighths of the whole weight of sub
stances taken into it.

[§ 414. SECRETION is a more complicated process than ex-
halation. It is not a mere mechanical operation, but is ac-
complished by means of organs, called glands ; which elaborate
peculiar juices, such as the sweat, the tears, the milk, the saliva,
the bile, the urine, &c.

[§415. At first glance there would seem to be nothing in
common between the organs which secrete the tears and that
which produces the bile, or between the kidneys and the
salivary glands. Still they all have the same elementary
structure. Every gland is composed of minute vesicles, or
extremely thin membranous sacs, generally too small to be
discerned by the naked eye, but easily distinguished by the
microscope. Sometimes these vesicles are single, and open
separately at the surface ; they are then called crypts or fol-
licles, but more frequently they unite to form clusters opening
into a common canal, which itself unites with the canals of
similar clusters to form trunks of various sizes, such as are
found in the salivary glands (figs. 257 and 2/7), in the mam-
mse, or in the liver (figs. 265, 267), which is a very large
gland receiving a great quantity of blood from the veins of
the alimentary canal

[§ 416. Sometimes the canals of the little clusters do not
unite, but open separately upon the surface of the body or
into its cavities, as in the intestinal glands or those from which
the perspiration issues (fig. 250, e). Occasionally the canals
themselves combine into bundles composed of a multitude of
parallel tubes, as we find in the kidneys, figs. 260 — 262. — T. W. I

§ 417. The operation of the glands is one of the most
mysterious phenomena of animal life. By virtue of the pe-
culiar properties with which they are endowed, they select
from the blood, which penetrates to their remotest ramifica-
tions, the elements of the special humours they are designed
to elaborate. Thus the liver extracts the elements of the bile ;
the salivary glands the elements of saliva ; the pancreas those
of the pancreatic juice ; and the sodoriferous glands those
of the sweat,

246 STRUCTURE OF GLANDS.

§ 418. Of the secretions thus formed by the different glands,
' some are immediately expelled from the body, as the sweat,
the urine, &c. ; these are denominated excretions. Others,
on the contrary, are destined either to be used as food for the
young, as the milk ; or to take part in the different functions
of the body, as the saliva, the tears, the gastric and pancreatic
juices, and the bile, which are properly denominated secretions.
Of all the secretions, if we except that from the lungs, the bile is
the most important; and hence a liver, or some analogous organ
by which bile is secreted, is found in all animals, while some or
all of the other glands are wanting in the lower classes. In the
vertebrata the liver is the largest of all the organs of the body.
In the mollusca it is no less preponderant. In the gastero-
poda, like the snails, it envelops the intestine in its convolu-
tions (fig. 177) ; and in the conchifera, like the clam and oyster
(fig. 176), it generally surrounds the stomach. In insects it
is in the form of long tubes variously contorted and interlaced
(fig. 179). In the radiata this organ is largely developed,
especially among the echinoderms. In the star-fishes (fig. 36)
it extends into all the recesses of the rays ; and in colour and
structure resembles the liver of the mollusca. Even in bryo-
zoan polyps (fig. 1 75) we find brown cells lining the digestive
cavity, which probably perform functions similar to those of
the liver of higher animals.

STRUCTURE OF GLANDS.

[§ 419. The type or elementary form of every secreting
gland is either a simple capsule, an elongated blind sac, or a
rounded vesicle, upon the outer aspect of which vessels are
ramified, and which on the inside generally exhibits numbers
of small cellular projections or depressions, and an outlet
through which the secreted matter escapes. Many of the
cutaneous and mucous glands, as also the simple glands of
the stomachs of birds (fig. 186, B. «, d), and the Lieberkiih-
nian glands of the intestines, afford examples in point ; but
they soon begin to get more complex, coalescing, dividing,
and sending forth new lateral lobules (fig. 185, B. e), and
by repetitions of the same process even acquiring a pretty
complicated mulberry appearance (fig. 184, B. /). The
ventricular glands of mammals are already somewhat more
compound (fig. 181, et seq.). The extent of secreting sur-

STRUCTURE OF GLANDS.

24?

face can be increased without any additional external com-
plexity, by a capsule or canal extended in length, and at the
same time rolled up or convoluted upon itself. We have an
example of this kind of gland in the ceruminous glands of the
ear (fig. 2-48, A. B), and in the sudoriparous glands (fig. 249,
A. B). We have only to conceive these two forms farther
subdivided, ramified, and the several parts connected by
means of vessels and cellular tissue, to have a perfect idea of
the most complex parenchymatous gland. The skeleton of
every gland is the ramified excretory duct, formed in the man-
ner already described, to which are attached the secreting

«/

blind sacs, vesicles, or tubes, connected together by cellular
tissue, and surrounded by net-works of capillary vessels.

B

Fig. 248. — Glands from the meatus auditorius externus of a young fe-
male of eighteen. A, section of the skin, seen magnified three diameters ;
b, b, hairs ; c, c, superficially situated sebaceous glands ; a, a, larger and
more deeply seated glands, which are coloured yellow, and appear to
secrete the cerumen. B, a gland of this kind more highly magnified ;
a, <z, the tortuous canal composing the gland and passing over into the
excretory duct b ; c, a. small vessel, with its branches. C, a hah- of the
auditory passage, penetrating the epidermis at c, and at d, contained
within its double follicle e, e ; a, a, sebaceous follicles of the hair, with
their excretory ducts.

248

STRUCTURE OF GLANDS.

[§ 420. The best picture we
possess of the vast variety existing
in the structural connection of the
several parts of the glandular skele-
ton, is in the secreting organs of in-
sects, particularly the salivary glands
(fig. 252). Here we observe the most
elegant and singular forms, having
frequently much of the vegetable
character in then: appearance. The
salivary glands present themselves
now as filiform canals (fig. 252, B),
now thicker and convoluted, now
with a sacculate end (c), here ex-
tending into a simple (E) or a
double vesicle (M), there branched

Fit? 249 -Sudoriparous gland from the palm of the hand of a young
person eighteen years of age. A, a gland entire with its excretory duct
manned forty times; a, a, the convoluted cana Is forming the gaud, and
from which two excretory ducts arise, 6, 6, winch unite to form tne smgle
spiral duct, which, at c, passes through the lamm« of the epidermis, and
opens on the surface at d; c, c, surrounding fat cells B, he same gland
more highly magnified. Around the canal of the gland play the vessel*,
fr, b. U, a few fat-globules from the emptied fat-cells.

STRUCTURE OP GLANDS.

»49

like the horns of a deer (G), or in the guise of a pair of
long shaped canals ending in many smaller saccules, or form-
ing a tuft or corymb of blind canals (H), or a cluster of
vesicles connected like a bunch of grapes or berries to a com-
mon duct (A, ~$}.

" b

a

Fig. 250. — Two sudoriparous
glands after Gurlt, Mayaz. f. d.
gesammte Thitrkeilk. 1835, Tab.
2, fig. 1. a, epidermis ; b, tactile
papillae ; c, corium ; d, adipose
tissue ; e, sudoriparous glands.

Fig. 251. — A thin layer from
the scalp of the human subject.
a, a. sebaceous glands ; b, a hair
with its follicle, c. After Gurlt,
Mag. f. d. gesam, Thierheil-
kunde, 1835.

The varieties in form presented by the seminal organs or
testicles are still greater, new inquiries constantly offering new
shapes to our notice. From the simple, linear and filiform
canal of Julus (fig. 253), to the highly complicated yet beau-
tiful appearance, comparable to a leafy tree lac'-en with fruit,
which we observe in Silpha obscura (fig. 253, 10), theitt are
forms of every intermediate degree of complexity, but always
as varieties of the same elementary type. Even the simple
canalicular or sacculate form presents numerous variations.
In one case it is the straight pretty regular canal already indi-
cated ( 1 ) ; in another the canal is irregular, of different thick-

250

STEUCTURE OF GLANDS.

nesses in different parts, and tortuous (2) ; in a third it is
spirally twisted (3), or is rolled up into a skein simple or
double, and with club-shaped ends (4), in every case for the
A B C

E

H

Fig. 252. — Salivary glands of insects, to show the variety in the form
and combination of the secreting follicles, from the simple lobular or
filiform canal and blind sac to the greatly complicated raceme.

A. Part of the salivary gland of Nepa cinerea. After Ramdohr.

B. Salivary vessel of Asida grisea. After S\iccow,Anat.physiolog. Unters.

C. Salivary vessel of Musca deviens. After the same.
E. The same of Musca carnaria. After the same.

G. The same of Blaps gigas. After the same.
H. The same of Cicada ormi. After the same.
M. The same of Pulex irritans. After Ramdohr.
N. The same of Scolopendra Afra. After nature.
(All these figures, with the exception of that indicated by N, are more
or less magnified.)

STRUCTURE OF GLANDS.

251

obvious purpose of saving room ; in other instances, still, the
organ presents itself in the shape of one or more club -like
canals nearly straight (5), or bent at an angle with corn-

Fig. 253.

I.

2.

3.

5.

1. Testis of Julus.

2. Tipula crocata.

3. Ranatra linearis.

4. Harpalus ruficornis.

5. Cercopis spumaria.

mencing divisions at the end, or with the end forming a
rounded vesicle ; or otherwise two ccecal canals are connected
like hooks, or they are finger-shaped, or form tufts of dif-
ferent kinds — quiver-like, star-shaped (6), or like the flowers
of syngenesious plants (7), or they form small saccules in the
shape of pannicles (8), or they are clustered like grapes or
berries, and attached to styles (9). In this way do the forms
of this gland alter in nearly allied species in the insect world;

252

STEUCTURE OF GLAXDS.

so rich in varied forms.* The peculiar constitution and
mode of distribution of the blood of the insect division of the

Fig. 253 (continued).

6.

10.

9.

6. Capsus tricolor.

7. Bostrichus capucinus.

8. Staphylinus maxillosus.

9. Prionus coriarius.
10. Sih)ha obscura

* There are few divisions of comparative anatomy so much calcu-
lated to set in a clear light the importance of this science in connexion
with the study of general morphology, as the sketch just given of the
vast variety of form presented hy the glandular system. If we would give
plans or ideal outlines of the principal forms of the different elements of

STETTCTrEE OF GLAXDS.

253

animal kingdom (§ 370) probably required the singular un-
folding of the glandular elements which we observe among its

B

Fig. 254. — The glands of insects which secrete the acrid or corroding
juice, after Leon Dufour, An. d. Sc. Nat. T. vii. pi. 19 and 20. A, of
Chlaenius velutinus. B, of Brachinus crepitans. C, of Calathus fulvipes.

the glandular system in man and the more perfect animals, no better
method could be followed than to pursue a single gland through the class
of insects. As supplementary to this part of our subject, the elegant
forms which the clustered canals and vesicles of others of the special
secreting organs of insects exhibit may be referred to in the subjoined
figures.

254

STKTJCTUKE OF GLANDS.

members. The blind extremities of the glands are surrounded
immediately by the blood, which is poured freely into all the
interstices of the body, and so attract the substances from its
mass which the glands of other and higher animals have
brought to them by finely divided capillary reticulations, to be
subjected to their peculiar elective attractions.

[§ 420*. It is infinitely more difficult to form an ideaofthe
glandular skeleton of man and the vertebrata, in the fully
formed condition, the composition of this being much ob-
scured by the connecting cellular tissue and intermingled net-
works of vessels. Still there are cases even here, where,
without peculiar difficulty, the two principal types in glandu-
lar architecture may be seized. As examples, the Harderian
glands of birds generally (fig. 255), and the Cowper's glands
of the hedgehog (fig. 256) may be quoted. Into both struc-
tures a quicksilver injection flows readily, and renders the
arrangement of their parts perfectly distinct even to the naked-
eye. The gland of Harder of the pelican (fig. 255) is seen
as a considerable lobulated body, each lobe being subdivided
into smaller rounded or elongated or angular lobules, which
again present themselves as small hollow pannicles or berries,

B

Fig. 255. — A, a Harderian gland of the Pelecanus onocrotalust \vii\\ the
excretory duct of the natural size injected with mercury. B, a portion of
the same slightly magnified. Some vascular ramifications are still appa-
rent between the lobules.

STEUCTUBE OF GLANDS.

255

attached to the enlarged excretory duct, these, in their turn,
having still smaller, rounded blind cells (fig. 255, B) sur-
rounded by vascular net-works attached to them, an arrange-
ment by which the whole structure acquires a cauliflower
appearance. The Cowper's glands of the hedgehog, on the
other hand (fig. 256, A), afford an example of that form in
which the ramified excretory duct divides into elongated,
pretty even, and slender cocca, which subdivide at their ends
into finger-shaped processes (fig. 256, B), partly straight,
partly sinuous, which are then applied to one another in the
form of flat lobules, these, in their turn, being connected by
cellular tissue into larger lobes.

[§ 421. In B

man and the
higher verte-
brata, glands of
the simple fol-
licular form (as
they exist in the
Lieberkiihnian
glands of the
intestines, for
example) attain
to the highest
degree of com-
plexity— in the
liver, for in-
stance.The com-
pound glands

may be arranged according to their structure into four
groups. 1. Compound follicles, the short excretory canal
passing without farther ramification at once into pedicu-
lated vesicles or racemiform lobules ; or the outwardly simple
sac exhibiting internally open cellular projections or shallow
pits ; to this head belong the greater number of the larger
mucous and cutaneous glands. 2. Glands with tree-like
ramifications of their excretory duct, and enlargements of the
terminal branches into racemiform or cauliflower-like aggre-
gated vesicles, which are visible with the naked eye, and vary
in magnitude from the 25th of a line to one line. To this
group belong the lachrymal glands, the salivary glands, and

Fig. 256. — A, the Cowper's gland of the hedge-
hog, with the excretory duct, a. The coeca composing
the gland are filled in the most beautiful manner
with the mercury ; the object is not magnified. B,
a few of the blind sacs seen slightly magnified.

2,56 STEUCTUKE OF GLANDS.

the pancreas. The lung of the mammal, with its terminal
vesicles attached to the minute ramifications of the bronchi,
may serve as a prototype of this form of gland, which is made
up of repetitions of the same fundamental structure, as we
have seen in the preceding paragraph to be the case with
regard to the Harderian gland. 3. Glands with a tubular
structure ; the secreting canals are here extremely slender, of
great length, convoluted, blind at the ends, not ramified, or
only once or twice divided, not sensibly or but very slightly
enlarged at the extremities, sometimes anastomosing by re-
current loops, or connected by cross branches, and from the
tenth of a line to half a line in thickness ; to this category
belong the kidneys and the testicles especially. The Cowper's
gland of the hedge-hog (fig. 256) may serve as a prototype
of the form of which that of the organs just mentioned may
be viewed as an extension. 4. Acmous (/lands. The excretory
duct here ramified through the substance of the gland, divides at
length into extremely minute branches ; all the branches and
twigs are beset with compact lobules, consisting of very small,
firm, angular cells, which effect the secretion. To this division
belongs the liver of vertebrate animals generally.

[§422. Compound follicles or glands of the first descrip-
tion, are progressive or more complex forms of the rounded or
elongated inversion, which we have seen constituting the
simple follicle of the mucous membrane and of the skin (§419);
no precise line of demarcation can, in fact, be drawn between
them and the simple follicle, or the sudoriparous or cerummous
gland. The large glands of the stomach and intestines may
serve as types of this kind of gland (fig. 182), or the numerous
glands which are in connection with the skin. All these glands
consist of ramifications of the excretory ducts, which swell out
into single saccules, that do not combine into true racemes or
lobes. The glands which areconnected with the hairs (fig. 248
c, #, a, and 25 1, ad) are small follicles, with rough external sur-
faces, and internally presenting the appearance of projecting pa-
rietal cells. To this division also belong the associated un-
branched saccules arranged along the excretory duct like the
grains of an ear of barley, which compose the Meibomian
glands.* Among animals a multitude of variously formed

* Figured by Miiller — De Gland, structura, Tab. v. figs. 1 and 2.

STRUCTURE OF GLANDS. 257

glands of the skin, other than the sudoriparous and sebaceous
glands are encountered.*

[§ 423. The progressive development of the last form of
gland is observed in the lachrymal, salivary and lacteal glands, f
in all of which a greater amount of ramification, an increase in
the quantity of vesicles and racemes produced, and a greater
degree of separation of the individual parts into lobes, are
observed. The lachrymal gland of man, of mammals and of
birds, exhibits terminal cells, which in the latter class are
large and conspicuous ; in man, on the contrary, they are
much smaller. The salivary glands of man are formed in the
same way (fig. 257). The cells of the terminal vesicles of
the parotid may still be readily
filled with mercury in young sub-
jects ; they are two or three times
smaller than the finest pulmonary
cells, measuring no more than from
the 30th to the 60th of a line in di-
ameter. The structure of the pan-
creas is similar, and the terminal
vesicles of this gland are very easily
filled with mercury or with air, in
birds especially, measuring when
thus distended from a 50th to a
30th of a line in diameter!^ The Fi& 257.— A very smal.
mammary glands in the ornithorhyn- piece of the parotid gland of
chus are extremely simple, and ex- anew-born infant, filled with
hibit the commencement of a series ™erc"ry and magnified five
of evolutions that end with the diameters- After Weber.
most complicated raceme ; the structure here consists of a con-

* To this number belong, for example, the musk bag, and the anal sacs
of many animals — the marten, the otter, &c., which exhale a peculiar
odour or stench. They are, in fact, extensive involutions of the skin, of
simple structure, occupied internally by shallow pits ; these structures
might be regarded as simple follicles, which, upon occasion, however,
may become more complicated, as they do in the anal sac of the hyaena,
for example, which is made up of several racemes clustered together.

•f On the structure of the glands in general, and of each of those men-
tioned in particular, see the work of M tiller, and the Elementary Treatises
on Anatomy of E. H. Weber and of Krause.

J The pancreas of fishes has been very commonly quoted as affording
an example or type of the successive evolution of glands from the simplest

S

258

STHUCTTJRE OF GLANDS.

geries of very large unramified cceca ; * but in the higher mam-
malia and in man the wide excretory ducts pass over into
finer branched canals, upon which the terminal cells form
botryoidal clusters; the cells are on an average from 1 -20th to
1-1 5th of a line in diameter.

[§424. Among the glands having tubular vessel -like secret-

^$MC--W

•F

ml

B

Fig. 258. — Kidney and supra-renal gland
of the new-born child, of the natural size,
a, kidney ; b, supra-renal gland ; c, artery ;
d, veins ; e, ureter.

Fig. 259. — A, B, por-
tions of the kidney repre-
sented in fig. 258 injected.
A, of the natural size ; the
Malpighian bodies, a, a, ap-
pearing as points in the cor-
tical substance ; b, the pa-
pilla of one of the tubular
pyramids. B, a small por-
tion of A, seen under a
simple lens and slightly
magnified; «, Malpighian
bodies ; b, tubuli uriniferi.

ccecal tubes to the most complex form observed in the glandular system.
Recent inquiries, however, rather lead us to conclude that the bony fishes
in general have a pancreas, which is comparable \n ; 11 respects to that of
the other vertebrate animals ; perhaps the coecal appendages which were
so long mistaken for the pancreas have a totally different function.

* See Meckel : Ornithorhynchi paradoxi descript. Anatom. Tab. viii.
and Owen on the Mammary Gland of the Ornithorhynchus, in Philos.
Trans.

STRUCTURE OF GLANDS.

ing canals, the
KIDKEYS de-
serve particu-
lar notice. The
development

Fig. 260.— A
still smallerpiece
of the same kid-
ney magnified
about sixty di-
ameters, and
drawn in part as
a plan, so that
the relations of
the tubuli to one
another and to
the vascular glo-
meruli may be
distinctly seen
and understood.
a, a simple ter-
minal tubulus
uriniferus ; b, bt
tubuli, forming
loops and return-
ing ; c, c, tubuli
terminatinginbi-
furcated points ;
di e, fi points
where the tubuli
join, continuing
their course to-
wards the papil-
la 5 ff, ff, 9, arte-
rial glomerules
or convolutions,
connected with
one another by a
general vascular
rete ; h, a larger
arterial trunk,
which feeds this
rete and the con-
nected glomeru-
li (the Malpighi-
«a bodies).

260

STRUCTURE OP GLAKDS.

of the kidneys in the vertebrate series is of especial interest.

In fishes and amphibia the entire tissue of the kidney con-
sists of tortuous canals, which
end partly in blind extremi-
ties, and partly pass into one
another in loops, but which,
from their great length and
intimate connection, cannot be
demonstrated singly. They
are not divided into single py-
ramids or lobules, a peculiarity
that first makes its appearance

among birds.

Here the highly

tortuous uriniferous tubules
are furnished with lateral

branches, which come off like

spicuous. Magnified 250 times.

Fig. 261 — Termination of one of
the tubuli uriniferi from the kidney
of aji adult, examined soon after the tines of a stag's horn ; in
death. The cellular structure is con- &u probability they pass over

the one into the other by means
of loops. In the mammalia
the tubuli uriniferi form many
pyramids or lobes, each a
system by itself (figs. 258 and
259, A). In the cortical sub-
stance of the human kidney
the tubuli can be traced, al-
though with difficulty, wind-

V *

ing among the vascular plex-
uses or skeins, mostly looped
towards the margin of the or-
gan, and running into one
another (fig. 260, b, b}, or
Fig. 262.— A lobe of the kidney ending blindly («), more

$2^*£tiSJ?*ll~ TlV11^1;. «*5&* and

club-shaped (fig. 261), occa-
sionally also cleft (fig. 260, c). The entire cortical substance
consists of convolutions of the uriniferous tubules, which are
found to present a very nearly uniform diameter, and which,
on an average, may be from about' the 50th to the 60th of a
line. They unite two and two as they approach the tubular
or medullary structure, becoming at the same time somewhat

STETJCTTKE OF GLANDS.

thicker, and then they run quite parallel to one another to
their termination (fig. 262).

[§ 425. Among the whole of the vertebrata, the parts which
are the efficient agents of
secretion in the liver are
so intimately connected
into a compact and little
lobular organ, by means
of the vessels and cellular
substance, that it is ex-
tremely difficult to form a
proper notion of its struc-
ture. Perhaps the follow-
ing is the true account of FiS- 263.— A, four lobules from the

the structure of the liver, Uver °f a *uman sulf ct f^*™ * a?e'
, <? M £ -i • magnified twice ; a branch of the hepatic

when fully formed m man vein> a> receives a more minutely ramified

twig from each lobule. B, some of the
cells of which the lobules of the liver are
composed, seen under a magnifying power
of 200 ; in the greater number the clear
nucleus is apparent.

B

It

and the mammalia

is easy to obtain convic-

•/

tion of the fact, that the
ends of the secreting parts
of the liver are leaf-like
lobules with blunt projec-
tions, which, in prepara-
tions of the organ, are
most apt to remain at-
tached to the minute ve-
nous twigs (fig. 263, A, a,
and 264, a, b, b). These
lobules are composed of
compact angular and
rounded cells (fig. 263,
B) Betwixt the several di- Flg- 264'~~ a' a branch of the hepatic

JJ / • J-*\_/ V IT A-.W L ±1 ^ ij\s V V-l CdjL. V1.X • • , i ,f j_ •! j • /• i • -i ! -i

/ . „ ^ * Xl vein with the tributary twigs of which the

visions of the cells of the lobules of the liver are connected, as leaves
individual lobules, the are with the final branches of a tree. The
branches of the gall-ducts venous ramuscles (vencs intralobulares) lie
penetrate (fi°* 266) and ™ t^ie middle of each lobule, as is seen in
there form anastomosing the two next succeeding figures which re-
, . , , . ° present transverse sections of the hepatic

retes, which surround sin- lobules magnified. After Kiernan.
gle groups of cells like

islets. Some observers describe the final ends of the secreting
element of the liver of mammals as hollow acini or vesicles

262

STRUCTURE OF GLAXDS.

a

with thin parietes, from the 40th to the 50th of a line in

diameter, and
capable of being
distended by air,
introduced into
the gall - ducts
with which they
are connected.
For this struc-
ture we have the
assurance of ana-
logy, from what
we witness in the
constitution of
Fig. 265. — Lobules of the liver, superficially si- the other glands,

tuated, divided horizontally ; a, o, intralobular

veins ; b, b, clefts between the several lobules, in

which cellular tissue, minute subdivisions of the

hepatic ducts of the vena portse and hepatic artery,

are included ; the middle portion of each lobule is

here in a state of congestion. After Kiernan.

XPS
f^PK,

mlf$

t^Sf

Vi]

llasr
it^JT

mode of evo-
lution of the li-
ver itself, and
the structure of
the organ in the
invertebrate se-
ries of animals ;
in fact, if we
turn to the cray-
fish and common
garden snail, we
find the precise
structure in ques-
tion. In the
cray-fish the li-
ver consists en-
tirely of small
Fig. 266. — The intralobular plexus of biliary ves- p0inted cseca,
sels, as figured by Kiernan— although the injection Clustered ' ijW
of these vessels was not so complete as it is here re-
presented ; d, d, two lobules divided across, with the grapes ; m
ramifications of the hepatic vein, a, a, the twigs of snail it is made
which perforate their centres ; b, b, b, b, branches up of blind,
of the hepatic duct, as they take their rise from the rounded termi-
plexus of biliary vessels, which are here injected, and -, vpsirlps

surround the uninjected portions of the substance of 1-1 i '

the lobules, d, d; c, cellular substance between the wmcn may
lobules. blown up with

>gfe

*%iiMNoi

STRUCTURE OP GLANDS.

263

air from the biliary ducts. If we farther examine the liver
of the larva of the water-newt (fig. 268, B) we see distinct
clusters of csecal ca-
nals, or round ter-
minal cells, like is-
lets, surrounded by
subdivisions of the
hepatic vein ; but
these csecal canals,
at all events, are not
thin- walled cells ;
they are almost as
compact as the acini
of the fully formed

m

liver of the highest
mammal.

I

I

ELE11EXTART PARTS

Or GLAKDS.

rn. <\O(\ TV. ^'1S- 2^7. — ^rigw °f three lobules of the liver

[_y 4zO. Lne pro- cut acrosS) the centre of each occupied by the

per substance of ramifications of the intralobular (the hepatic)

glands is liotformed vein, a, a, a. b, b, b, Branches of the vena

by or out of the or- P°rtae which course in the spaces between the

rlivmrv rpllnlnr «nh lobules, surrounding these and constituting the

\^LL i 1 1 1 1 \ ^t-L.1 LI 1 ill oU-U1™.. -IT i • XT l

" , , , intralobular veins. Numerous ramuscles pene-

stance, but by and trate into the interior of the lobules and anasto-

from other more mose with the intralobular or hepatic veins. The

or less distinctly rounded and oval interspaces or islets between

cellular elements these vessels are filled or possessed by the bi-

This anatomical if7 .vfssels<^ 266), and form the acini of

Malpigni. After Kiernan.
is particu-

-
truth

larly evident in the liver (fig. 263, A). Here the parietes
of the acini consist entirely of compact, irregularly rounded
or angular cells, of about l-200th of a line in magnitude.
The cells of the liver enclose a distinct clear nucleus and
a vellowish-coloured molecular matter in their interior.

*

The cells are like the stones of a piece of ancient masonry,
irregularly applied to one another. Externally, where th^
blood-vessels play around them, fibres of cellular tissue are
added. An epithelial covering of flat tessellated cells first
makes its appearance in the larger branches and trunks
of the gall-ducts. In other cases, as in the glands of
the stomach, for instance (§ 32!)), the substance of the

264

ELEMENTARY PARTS OF GLANDS

glandular parietes consists of rounded dark granules, not ob-
viously formed like cells, which appear to be arranged or

A

Fig. 268.— A,
a larva of the
water-newt of
the natural size ;
c, liver; b, sto-
mach; c, gall-
bladder.

B, the liver of
this larva mag-
nified 40 times.
The dark co-
loured stream-
lets of hlood are
seen surround-
ing the hepatic
lobules, which
consist of aggre-
gated racemi-
form ccEca. The
vascular chan-
nels represented
are those of the
hepatic vein.

OEIGIN OF THE GLANDS.

260

packed between a very delicate external envelope turned to-

wards the blood-vessels, and an internal epithelial investment.

The cellular structure of the parietes of the ventricular glands

is, however, very apparent in young birds (fig. 186, B). In

other glands, moreover, we recognize the cellular structure

with different degrees of distinctness — in the tubuli uriniferi,

for example, where the cells have nuclei, but are far from

being so compact, and are not nearly so readily isolated as in

the liver (fig. 261). It is difficult to say in how far this cel-

lular structure, which may be followed to the very ends of

the canaliculi, belongs to the innermost layer of the glandular

paries, or is connected with the epithelial investment, ap-

pertaining to the trunk and larger branches of the excretory

duct of every gland. Apparently, however, there are always

several layers of flattened cells placed one upon another, over

which a structureless membrane is drawn externally, and this

is the part that is surrounded immediately by the vascular

reticulation. Certain it is, that wherever we find secreting

follicles, they consist of a number of more or less distinctly

cellular or fibrous layers, which lie as the proper substance

of the gland betwixt the external net-work of blood-vessels

and the inner wall whence the secreted matter distils away.

OF THE GLATO)S.

[§ 427. The greater number of the secreting glands arise from

Fig. 269. — Rudiments of the
liver formed by evolution from the
tractus intestinalis in the embryo
of the fowl of the fourth day.
After Mailer— De Gland, &c.

Fig. 270. — Liver and pancreas
of an embryo of the fowl at the
end of the fourth day, magnified
twelve times linear, a, the liver;
b, the pancreas; c, the stomach;
d, d, the lungs.

2C6

ORIGIN OF THE GLANDS.

the mucous lamina of the germinal membrane, and, like the

salivary glands, the lungs,
the liver, the pancreas,
are to be regarded as
evolutions of this mem-
brane, or of the intesti-
nal canal. This view is
liable to misapprehen-
sion, by the process of
evolution being conceiv-
ed in a purely mechani-
cal way. The general
plan of the evolution of
the secreting glands is
as follows. At the place

where the gland is to be

Fig. 271.— The same parts in another fnrTT1Pd.— take ti,e liver
embryo more highly magnified, to exhibit lormecl-
the undoubtedly cellular and racemose or the pancreas as a par-
structure of the liver and pancreas. The ticular instance (figs. 269,
references are likewise the same. 270,and271,a, 6),arongh

projection appears upon the intestine. This projection consists

of a delicate, finely granular,
and pale tissue — the blastema, as
it is called, which was in former
times looked upon as without
structure. By watching this part
we see how particular divisions
make their appearance within it
(fig. 272), which by and by form
lobules or club-shaped bodies,
and are the elements or ground-
Fig. 272.— The liver more ad- work of the future csecal canals,
vanced than in the last figure from ^here these are to appear. It

is now that a kind of solution of
the internal contents of the mass
or masses takes place, or rather
that distinct walls with double
contours are produced. This is to be seen most beautifully
displayed in the lungs (fig. 273).* And now appears the

* The lungs are to be viewed as the prototype of all secreting glands.

an embryo of the fowl ^of the sixth
day. It is not onlv divided into
two lobes, but shows minute coeca
n its interior. After Muller.

ORIGIN OF THE GLANDS.

267

true glandular skeleton, as it has been described in speaking
of the conformation of the glands. Would we follow this
generation of
the glands
step by step,
a gland must
be chosen in
which the ra-
mifications of
the excretory
duct can be
seen amidst
the clearer
blastema,
from the sim-
ple rudiment
to the term of
extreme com-
plexity. In
young em-
bryos of the
sheep (fig.

2/4) we can, by the aid of
duct of the parotid still
simply branched, the seve-
ral branches enlarged like
buds at their extremities,
and but seldom divided.
The same thing may be seen
in small human embryos
(fig. 276). To follow the
onward evolution, embryos

v

successively more and more
advanced mustbe procured,
and, the parotid being re-
moved, it is to be examined
with a low power and as an
opaque object (fig. 277).
The clearer blastema of the
gland now appears dark,
and the excretory duct,

Fig. 273. — "Ramifications of the bronchi from the
embryonic Falco tinnunculns, to show the way in wh>cn
they sprout as blind canals. Both figures are magnified
about 150 times.

a simple lens, see the excretory

Fig. 274. — Rudiments of the parotid
gland in the embryo of a sheep, two
inches in length magnified. After
M Oiler.

ORIGIN OF THE GLANDS.

wmcn consists of a firmer granular mass, appears white, and in

the form of an ele-
gant and numerously
branched tree. The
leaf-like ends now
undergo transform-
ation into blind vesi-
cles, whilst the branch-
es and twigs of the
tree become hollow,
and unite themselves to

Fig. 276.— First appearance of the parotid the excretory duct (fig.
gland in a human embryo of the seventh 277). The blood-
week ; magnified twice. vessels are seen enter-
ing the blastema in the
shape of dark ramifica-
tions (fig. 2 7 7), but of
much smaller diame-
ters than those of the
ramified glandular
canal. The finest ele-
ments of the secreting
follicles do not consist
properly of cells ; in
the liver, for example
(fig. 2/8), they are ex-
tremely soft, roundish,
granular corpuscles,
which give to the larger
lobules (A) a racemi-
form appearance. It
is betwixt these major
divisions or lobules
that the blood-vessels
make their entrance

Fig. 277.— Lobules of the parotid gland (fig- 278, B, «, «),

wiih the excretory ducts from the embryo of a none ever penetrating

sheep four inches long, magnified eight" times, betwixt the finest ele-

After Muller. ments of all>

DISTRIBUTION OF VESSELS IN GLANDS. 269

DISTRIBUTION OF THE VESSELS IN GLANDS.

[§ 428. Glands in general derive their blood from arteries,
and all that is not used for purposes of secretion returns in
the usual way through veins and lymphatics into the general
current of the circulation. The lymphatics of glands are often
very large and conspicuous ; those of the liver are particularly
so. Among vertebrate animals the liver receives but a small
portion of its blood from an arterial source, and this appears
to be exclusively expended upon the gall-bladder, the gall-
ducts, and the coats of the larger vascular trunks, though
branches of the hepatic artery can also be followed, entering
along with the cellular substance of the organ between its
several component lobules. The blood from which the bile is
prepared is received from the portal vein, which ramifies
through the substance of the liver, and at length anastomoses
with the finest subdivisions of the hepatic vein, which spring
from the deeper parts, and then flow round about the clusters
of hepatic cells united into ccecal-looking lobules (fig. 267).
In the two lower classes of vertebrate animals, there is an
extension to the kidneys of the same system of circulation
which we observe confined to the liver among the two higher
classes. In amphibia and fishes a portion of the blood
returning from the hind-legs, tail, abdominal parietes, and
A B

Fig. 278. — A couple of feathery lobules Irom the embryo of the Falco
tinnunculus or Hobby, fourteen lines in length ; the substance of the liver
is seen composed of large pale granulated particles (cells) ; betwixt the
lobules a blood-vessel is seen well filled with blood-discs.

270

DISTBIBUTTOX OE VESSELS IX GLAKDS.

even some of the viscera, is distributed to the kidneys. But
whether the material for the secretion of the urine is afforded
from this source or not is doubtful ; for the kidneys here
still receive arteries of considerable magnitude, the finer twigs
of which form such tangled knots as we observe in the same
organs of birds and mammals. These tangled knots of ves-
sels, Malpighian bodies as they are called, constitute a form of

vascular distribution that is pe-
culiar to the kidneys. They
are skein-like convolutions of the
arteries, which run in straight
lines between the tubuli uriniferi,
before resolving themselves into
the finest capillary net-works

Fig. 279.-Malpighian bodies (fif ' 27? and 2<*°)- .They occ^

of the kidney of the water-newt m largest numbers interspersed

(rrtVo»^afcw<ra),afterHuschke, among the tubuli uriniferi of the

in Tied. n. Trevir. Zeitschrift, cortical substance (fig. 259, A and

B. 4, Tab. vi. B^ but ^ey are ajso ODserVed

more thinly scattered in the medullary substance. The vessels

of the most minute vascu-
lar net-works are every-
where much smaller — from
twenty to thirty times small-
er— than the finest ccecal
and secreting glandular tu-
bules, and never terminate
in these, as they were once
universally, and as they
have even very recently,
been supposed to do. They
rather play round the in-
dividual terminal portions
of the glandular skeleton,
they never even penetrate
between the constituent cel-
lular elements of this. The
parietes of the blood-vessels

appear to be of the very thinnest and most delicate description

in the glands.*]

* This admirable article on the structure of glands is from Professor
Wagner's Physiology, pp. 384, et seg. — ED.

Fig. 280. — Malpighian bodies
from the kidney of an owl (Strix
aluco), fully injected and largely
magnified.

CHAPTER TENTH.

EMBRYOLOGY.
SECTION I.

OF THE EGG.

§ 429. THE functions of vegetative life, of which we have
treated in the preceding chapters, namely, digestion, circula-
tion, respiration and secretion, have for their end the preser-
vation of the individual. We have now to treat of the
functions that serve for the perpetuation of the species,
namely those of reproduction (§ 308).

§ 430. It is a law of nature that animals as well as plants
are the offspring of individuals of the same kind, and vice
versa, that none of them can give birth to individuals differing
from themselves ; but recent investigations have modified to a
considerable extent this view, as we shall hereafter see.

§ 431 . Reproduction in animals is almost universally accom-
plished by the association of individuals of two kinds, males
and females, living commonly in pairs or flocks, and each of
them characterized by peculiarities of structure and external
appearance. As this distinction prevails throughout the animal
kingdom, it is always necessary for obtaining a correct and
complete idea of a species, to bear in mind the peculiarities of
both sexes. Every one is familiar with the differences between
the cock and the hen, the lion and the lioness. Less promi-
nent peculiarities are observed in most vertebrata. Among the
articulata, . the differences are no less striking, the males being
often of a different shape and colour, as in crabs ; or having
even more complete organs, as in many tribes of insects, where
the males have wings, while the females are deprived of
them. Among the mollusca the females have often a wider
shell.

§ 432. Even higher distinctions than specific ones are based
upon peculiarities of sex ; for example, the whole class
of mammalia is characterized by the fact that the female is
furnished with organs for nourishing her young with a pecu-

272

OF THE EGG.

liar liquid, the milk, secreted by herself. Again, the mar-
supialia, such as the opossum and kangaroos, are distinguished
by the circumstance that the female has a pouch, into "which
the young are received in their immature condition at birth.

§ 433. That all animals are produced from eggs (Omne
vivum ex ovo), is an old adage in zoology, which modern
researches have fully confirmed. In tracing back the phases
of animal life, we invariably arrive at an epoch when the in-
cipient animal is enclosed within an egg. It is then called
an embryo, and the period passed in this condition is called
the embryonic period.

§ 434. Before the various classes of the animal kingdom
had been attentively compared during the embryonic period,
all animals were divided into two great divisions : the ovi-
parous, comprising those which lay eggs, such as birds,
reptiles, fishes, insects, mollusks, &c., and the viviparous,
which bring forth their young alive, like the mammalia, and
a few from other orders, as the sharks, vipers, &c. This
distinction lost much of its importance when it was shown
that viviparous animals are produced from eggs, as well as
the oviparous ; only that their eggs, instead of being laid
before the development of the embryo begins, undergo their
early changes in the body of the mother. Production from

eo^s should therefore be considered as a universal character-

p
istic of the animal kingdom.

§ 435. FORM or THE EGG. — The general form of the egg is
more or less spherical. The eggs of birds have the form of an
elongated spheroid, narrow at one end ; and this form is so con-
stant, that the term oval has been
universally adopted to designate it.
But this is by no means the usual
form of the eggs of other animals.
In most instances, on the contrary,
they are spherical, especially among
the lower animals. Some have sin-
gular appendages, as those of the
skates and sharks (fig. 281), which
are shaped like a hand-barrow,
with four hooked horns at the cor-
ners. The eggs of the Hydra, or
fresh water polype, are thickly co-
vered with prickles (fig. 282). Those of certain insects, for

Fig. 281.

Fig. 282. Fig. 283.

OF THE EGG.

o-

4. I

example, the Podurella, are furnished with filaments which
give them a hairy aspect (fig. 283) ; others are cylindrical, or
prismatic, and frequently the surface is sculptured.

§436. FOEMATIOX OF THE EGG. — The egg originates
within peculiar organs, called ovaries, which are glandular
bodies usually situated in the abdominal cavity. So long as
the eggs remain in the
ovary, they are very

•/ •* •/ v

minute in size. In this
condition they are

V

called ovarian or pri-
mitive eggs. They are
identical in all animals,
being, in fact, merely
little cells containing
yolk-substance (&), in-

Fig. 284. — Primary ova of the bird, mag-
nified ; scarcely to be seen by the naked
eye ; a, stronia, or substance of the ovary,
composed of thick fibres ; c, chorion, cr
theca of the ovum, so thick as to be seen in
the guise of a ring ; b, yolk ; d, germinal
vesicle ; e, germinal spot. The structure of
the smaller ovum is the same.

eluding other similar
cells, namely, the ger-
minative vesicle (d}
and the e;erminative
dot (e). The yolk it-
self with its membrane
formed while the

s

egg remains in the ovary ; it is afterwards enclosed in another

envelope, the shell membrane, which may remain soft, or be
further surrounded by calcareous deposits, the shell proper
(fig. 287). The number of these eggs is large in. proportion as
the animal stands lower in the class to which it belongs. The
ovary of a herring contains more than 25,000 eggs ; while
that of birds contains a much smaller number, perhaps one
or two hundred only.

§ 437. Ovulation. — Having attained a certain degree of
maturity, which varies in different classes, the eggs leave the
ovary. This is called ovulation. It must not be confounded
with the laying of the eggs, which is the subsequent expulsion
of them from the abdominal cavity, either immediately, oar
through a special canal, the oviduct. Ovulation takes place at
certain seasons of the year, and never before the animal has
reached a particular age, which is commonly that of its full
growth. In a majority of species, ovulation is repeated for a
nn™K~- of vears consecutively, generally in the spring, in

T

274

OF THE EGG.

terrestrial animals, and frequently several times a-year; most of
the lower aquatic animals, however, lay their eggs in the fall,
or during winter. In others, on the contrary, it occurs but
once during life, at the period of maturity, and the animal soon
afterwards dies. Thus the butterfly and most insects die
shortly after having laid their eggs.

§ 438. The period of ovulation is one of no less interest to
the zoologist than to the physiologist, since the peculiar cha-
racteristics of each species are then most clearly marked.
Ovulation is to animals what flowering is to plants ; and, in-
deed, few phenomena are more interesting to the student of
nature than those exhibited by animals at the pairing season.
Then their physiognomy is the most animated, their song the
most melodious, and their attire the most brilliant. Some
birds appear so different at this time, that zoologists are always
careful to indicate whether or not a bird is represented at the
breeding season. Fishes and many other animals are orna-
mented with much brighter colours at this period .

§ 439. Laying. — After leaving the ovary, the eggs are either

discharged from the animal, that is, laid ;
or they continue their development within
the parent animal, as is the case in some
fishes and reptiles, as sharks and vipers,
which for that reason have been named
ovo-viviparous animals. The eggs of the
mammalia are not only developed within
the mother, but become intimately united
to her ; this peculiar mode of development
has received the name of gestation.

§ 440. Eggs are sometimes laid one
by one, as in birds ; sometimes collec-
tively and in great numbers, as in frogs, fishes, and most
of the invertebrata. The queen ant of the African termites
lays 80,000 eggs in twenty-four hours ; and the common
hair worm (Gordius) as many as 8,000,000 in less than one
day. In some instances they are united in clusters by a
gelatinous envelope ; or are enclosed in cases or between
membranous discs, forming long strings, as in the eggs of the
Pynda shell (fig. 285). The conditions under which the
eggs of different animals are placed, on being laid, are very
different. The eggs of birds, and of some insects, are deposited

Fig. 285. Fig. 286.

OF THE EGG. 275

in nests constructed for that purpose by the parent. Other
animals carry their eggs attached to their bodies ; sometimes
under the tail, as in the lobsters and crabs, sometimes hanging
in large bundles on both sides of the tail, as in the Monoculus
(fig. 286, a).

§ 4-10*. Some toads carry them on the back, and, what is
most extraordinary, it is the male which undertakes this office.
Many mollusca, the Unio for example, have them enclosed be-
tween the folds of the gills during incubation. In the medusae
and polyps, they hang in clusters either outside or inside, at
the bottom of the cavity of the body. Some insects, such as
the gad-flies, deposit their eggs on other animals. Finally,
many abandon their eggs to the elements, taking no further
care of them after they have been laid ; such is the case with
most fishes, some insects, and many mollusca. As a general
rule, it may be said that animals take the more care of their
eggs and brood, as they occupy a higher rank in their respective
classes.

§ 441. The development of the embryo does not always
take place immediately after the egg is laid. A considerable
time even may elapse before it commences. Thus, the first
eggs laid by the hen do not begin to develop until the whole
number which is to constitute the brood is deposited. The
eggs of most butterflies, and of insects in general, are laid in
autumn, in temperate climates, and remain unchanged until
the following spring. During this time the principle of life
in the egg is not extinct, but is simply inactive, or in a latent
state. This tenacity of life is displayed in a still more striking
manner in plants. Their seeds, which are equivalent to eggs,
preserve for years, and even for ages, the power of germinating.
Thus, there are some well-authenticated cases in which wheat
taken from the ancient catacombs of Egypt has sprouted and
grown.

§ 442. A certain degree of warmth is requisite* for the
hatching of eggs. Those of birds, especially, require to be
submitted for a certain length of time to a uniform tempera-
ture, corresponding to the natural heat of the future chicken ;
and which is naturally supplied by the body of the parent. In
other words, incubation is necessary for their growth. In-
cubation, however, is not a purely vital phenomenon, but may
be readily imitated by artificial means. Some birds of warm

T 2

27G OF THE EGG.

climates dispense with this task ; the ostrich, for example,
often contents herself with depositing her eggs in the sand
of the desert, leaving them to be hatched by the sun. In like
manner, the eggs of most birds may be hatched, by main-
taining them at the proper temperature, by artificial means.
Some fishes are also known to build nests, and to sit upon
their eggs, as the stickle-backs, sun-fishes, and cat-fishes ; but
whether they impart heat to them or not is doubtful. Before
entering into the details of embryonic transformations, a few
words are necessary respecting the composition of the egg.

§ 443. Composition of the Egg. — The egg is composed of
several substances, varying in structure, as well as in appear-
ance. Thus, in a new-laid hen's egg (fig. 287), we have first
a calcareous shell lined by a double membrane, the shell mem-
brane (c) ; then an albuminous substance, the white ; in which
several layers may be distinguished (e, /) ; within this, we find
the yolk enclosed in its membrane (Ji) ; and before it was laid,
there was in the midst of the latter a minute vesicle, the ger-
minative vesicle (fig. 284, d), containing a still smaller one,
the germinative dot (e). These different parts are not equally
important in a physiological point of view. The most con-
spicuous of them, namely, the shell and the white, are not
essential parts, and therefore are often wanting ; while the
volk, the germinative vesicle, and the germinative dot are found
in the eggs of all animals ; and out of these, and of these only,
the germ is formed, in the position shown in figs. 284 — 28".

§ 444. The rife/his, or yolk (fig. 287, h), is the most essen-
tial part of the egg. It is a liquid of variable consistence,
sometimes opaque, as in the egg of birds, sometimes transpa-
rent and colourless, as in the eggs of some fishes and mollusca.
On examination under the microscope, it appears to be com-
posed of an accumulation of granules and oil drops. The yolk
is surrounded by a very thin skin, the vitelline membrane (fig.
284, c). In some insects, when the albumen is wanting, this
membrane, surrounded by a layer of peculiar cells, forms the
exterior covering of the egg ; which in such cases is generally
of a firm consistence, and sometimes even horny.

§ 445. The germinative vesicle (fig. 284, d) is a cell of ex-
treme delicacy, situated, in the young egg, near the middis of
the yolk, and easily recognized by the greater transparency
of its contents when the yolk is in some degree opaque, as in

OF THE EGG

27?

the hen's ess:, or by its outline, when the yolk itself is trans-

CO- * v

parent, as in the eggs of fishes and mollusca. It contains on«
or more little spots, somewhat opaque, appearing as small dots,
the germinal dots (e). On closer examination, these dots aro
themselves found to contain still smaller nucleoli.

§ 446. The albumen, or white of the egg (fig. 287, e, e}, ia
a viscous substance, generally colourless, but becoming opaque
white on coagulation. Voluminous as it is in bird's eggs, it
nevertheless plays but a secondary part in the history of their
development. It is not formed in the ovary, like the yolk,
but is secreted by the oviduct, and deposited around the yolk
during the passage of the egg through that canal. On this
account the eggs of those animals in which the oviduct is
wanting, are generally destitute of albumen. In birds the
albumen consists of several layers, one of which, the cha-
lazce (g, g),
is twisted.
Like the
yolk, the al-
bumen is
surrounded
by a mem-
brane, the
shell mem-
brane (c\
which is
either single
or double ;
and in birds,
as also in
some rep-
tiles and
mollusca, is
again pro-
tected by a
calcareous

covering,
for min j; a

Fig. 287. — Ideal section of an extruded hen's egg, with
slight alterations from Bae'r. (Entu'ickelung. der Thiere,
B. I. Tab. III). A, blunt pole: B, sharp pole; a, a,
shell ; b, space filled with air ; c. membrane of the shell,
which, at d, d, splits into two layers ; e, e, limits of the
second and thicker albumen ; /, /, limits of the third and
thickest albumen clinging to the chalazae ; g, a. chalaza? ;
h, yolk ; j, central cavity of the yolk, from which a canal
or duct, &, leads to the cicatricula ; I, cumulus prolige-
rus ; m. germ (blastos).

true shell (d). In most cases, however, this envelope continues
membranous, particularly in the eggs of the mollusca, most
crustaceans and fishes, salamanders, frogs, &c. Sometimes it
is homv AS in the sharks and skates.

278 EMBEYOLOGY.

SECTION II.

DEVELOPMENT OF THE YOUNG WITHIN THE EGG.

§ 447. THE formation and development of the young animal
within the egg is a most mysterious phenomenon. From a
hen's egg, for example, surrounded by a shell, and composed,
as we have seen (fig. 287), of the albumen and the yolk, with
a minute vesicle in its interior, there is produced, at the end of
a certain time, a living animal, composed apparently of ele-
ments entirely different from those of the egg. Endowed with
organs perfectly adapted to the exercise of all the functions of
animal and vegetative life, having a pulsating heart, a digestive
apparatus ; organs of sense for the reception of outward im-
pressions, and having, moreover, the faculty of performing
voluntary motions, and of experiencing pleasure and pain.
These phenomena are certainly sufficient to excite the curi-
osity of every intelligent person.

§ 448. By opening eggs which have been subjected to incu-
bation during different periods of time, we may easily satisfy
ourselves that these changes are effected gradually. We thus
find that those which have undergone but a short incubation
exhibit only faint indications of the future animal ; while
those upon which the hen has been sitting for a longer
period include an embryo chicken proportionally more deve-
loped. Modern researches have taught us that these gradual
changes, although complicated, and at first sight so mysterious,
follow laws which are uniformly the same in each department
of the animal kingdom.

§ 449. The study of these changes constitutes that branch of
Physiology called EMBEYOLOGY ; as there are differences in the
four great departments of the animal kingdom perceptible at an
early stage of embryonic life, quite as obvious as those found
at maturity; and, as the phases of embryonic development af-
ford important indications for the natural classification of
animals, we propose to give the outlines of Embryology, so
far as it may have reference to zoology

§ 450. In order to understand the successive steps of em-
bryonic development, we must bear in mind that the whole
animal body is formed of tissues, the elements of which are
cells. These cells are more or less diversified and modified, or

DEVELOPMENT OF THE YOUNG WITHIN THE EGG. 279

even completely metamorphosed, in the full-grown animal ;
but, at the commencement of embryonic life, the whole em-
bryo -is composed of minute cells of nearly the same form
and consistence, originating within the yolk, and constantly
undergoing new change^ under the influence of life. New cells
are successively formed, while others disappear, or are mo-
dified, and so transformed as to become blood, bones, muscles,
nerves, &c.

§ 451. We may form some idea of this singular process,
by noticing how, in the healing of a wound, a new substance
is supplied by the transformation of the blood. Similar
changes take place in the embryo, during its early life ; only,
instead of being limited to one part of the body, they pervade
the whole animal.

§ 452. The changes commence in most animals soon after
the eggs are laid ; and are continued, without interruption,
until the development of the young is completed ; in others,
birds for example, they proceed only to a certain extent, and
are then suspended until incubation takes place. The yolk,
which at first consists of a mass of uniform appearance,
gradually assumes a diversified aspect. Some portions be-
come more opaque, and others more transparent; the germinal
vesicle, which was in the midst of the yolk, rises to the
upper part of it, where the germ is to be formed. These
early changes are accompanied, in some animals, by a rotation
of the yolk within the egg, as may be distinctly seen in the
eggs of some of the mollusca, especially the snails.

§ 453. At the same time the yolk undergoes a peculiar
process of segmentation. It is first divided into halves,
forming distinct spheres, which are again regularly subdivided
into two more, and so on, till the whole yolk assumes the ap-
pearance of a mulberry, each of the spheres, of which it i&
composed, having in its interior a transparent vesicle. This
is the case in mammalia, most mollusca, worms, £c. In
many animals, however, as in the naked reptiles, and fishes,*
this segmentation is only partial, the divisions of the yolk not
extending across its whole mass.

§ 454. But whether complete or partial, this process leads

* In the birds and the higher reptiles, we find in the mature egg a pecu-
liar organ called cicatricula, which may, nevertheless, have been formed
by a similar process before it was laid.

280

EMBRYOLOGY.

to the formation of a germ comprising the whole yolk, or
rising above it as a disc-shaped protuberance, composed of
little cells, which has been variously designated under the names
of germ inative disc, proligerous disc, blastoderma, germinal
membrane. In this case, however, that portion of the yolk
which has undergone less obvious changes, forms nevertheless
part of the growing germ. The disc again enlarges, until it
embraces the whole, or nearly the whole, of the yolk,

§ 455. At this early epoch, namely, a few days, and, in

Fig. 288. Fig. 289. *ome animals, a

fewhours after de-
velopment has be-
gun, the germ pro-
per consists of a
single layer com-
posed of very mi-
nute cells, all of them alike in appearance and form (fig.
2^8, </). But soon after, as the germ increases in thickness,
several layers may be discerned in vertebrate animals (fig.
289), which become more and more distinct.

§ 456. The upper layer (s), in which are subsequently
formed the organs of animal life, namely, the nervous system,
the muscles, the skeleton, &c. (§ 7C), has received the name
of serous or nervous layer. The lower layer (ni), which gives
origin to the organs of vegetative life, and especially to the
intestines, is called the mucous or vegetative layer, and is
generally composed of cells larger than those of the' upper or
serous layer. Finally, in the embryos of vertebrated animals,
there is a third layer (#), interposed between the two others,

giving rise to the formation of the blood and the organs of cir-
culation ; whence it has been called the blood layer or vascular
layer.

§ 457. From the manner in which the germ is modified, we

can generally distinguish, at a very
Fig.291. early epoch, to what department of the
animal kingdom an individual is to be-
iong. Thus in the articulata, the germ
is divided into segments, indicating the
transverse divisions of the body, as, for
example, in the embryo of the crabs
(fig. 290). The germ of the verte-
brated animals, on the other hand, displays a longitudinal fur-

DEVELOPMENT OF THE YOUXG WITHIN THE EGG. 281

row, marking the position which the future back-bone is to

occupy (fig- 291).

§ 458. The development of this furrow is highly impor-
tant, as indicating the plan of structure of vertebrated animals
in general, as will be shown by the following figures, which
represent vertical sections of the embryo at different epochs.*

Fig. 292. Fig. 293. Fig. 294.

At first the furrow (fig. 292, b) is very shallow, and a little
transparent narrow band appears under it, called the primitive
stripe (a). The walls of the furrow consist of two raised
edges, formed by a swelling of the germ along both sides of
the primitive stripe. Gradually, these walls grow higher, and
we perceive that their summits have a tendency to approach
each other, as seen in fig. 293 ; at last they meet and unite
completely, so that the furrow is now changed into a closed
canal (fig. 294, 6). This canal is soon filled with a peculiar
liquid, from which the spinal cord and brain are formed at a
later period.

§ 459. The primitive stripe is gradually obliterated by a
peculiar organ of a cartilaginous nature, the dorsal cord,
formed in the lower wall of the dorsal canal. This is found
in the embryos of all vertebrata, and is the representative of
the back-bone. In the mean time, the margin of the germ
gradually extends farther and farther over the yolk, so as
finally to enclose it entirely, and form another cavity, in which
the organs of vegetative life are to be developed. Thus the
embryo of the vertebrata has two cavities, namely, the upper
one, which is very small, containing the nervous system, and
the lower, which is much larger, for the intestines (§ 226).

§ 460. In all classes of the animal kingdom, the embryo
proper rests upon the yolk, andcoversitlike a cap. Butthe direc-

* In these figures the egg is supposed to be cut down through the
middle, so that only the cut edge of the embryo is seen ; whereas, if
viewed from above, it would extend over the yolk in every direction ;
and the furrow at b, of fig. 292, would be seen as in fig. 291.

EMBRYOLOGY.

tion by which its edges approach each other, and unite to form

the cavity of the body, is very unlike in
Fig. 295. different animals ; and these several modes

are of high importance in classification.
Among the vertebrata, the embryo lies with
its face or ventral surface towards the yolk
(fig. 295), and thus the suture, or line at
which the edges of the germ unite to en-
close the yolk, and which in the mam-
mals forms the navel, is found in front.
Another suture is found along the back,
arising from the actual folding upwards of the upper sur-
face of the germ, to form the dorsal cavity.

§ 461. The embryo in the articulata, on the contrary, lies
9ng with its back upon the yolk, as seen in

the following figure, which represents an
embryo of Podurella ; consequently the
yolk enters the body on that side ; and the
suture, which in the vertebrata is found on
the belly, is here, as also in the worms, found
on the back. In the cephalopoda the
yolk communicates with the lower side of
the body as in the vertebrata, but there is no dorsal cavity
formed in them. In the other mollusca there is this peculiarity,
that the whole yolk is changed at the beginning into the sub-
stance of the embryo ; whilst in the vertebrata and the higher
articulata and mollusca, a part of it is reserved, till a later
period, to be used for the nourishment of the embryo. Among
the radiata the germ is formed around the yolk, and seems to
surround the whole of it, from the first.*

§ 462. The development of the embryo of vertebrated
animals may be best observed in the eggs of fishes. Being
transparent, they do not require to be cut open, and by suffi-
cient caution, the whole series of embryonic changes may be
observed upon the same individual, and thus the succession
in which the organs appear, maybe ascertained with precision ;
whereas, if we employ the eggs of birds, which are opaque,
we are obliged to sacrifice an egg for each observation.

§ 463. To illustrate these general views as to the develop-

* These facts show that the circumstance of emhryos arising from the
whole or a part of the yolk is of no systematic importance.

jjEVELOPMENT OF THE YOUNG WITHIN THE EGG.

233

ment of the embryo, we shall briefly describe the principal
phases, as they have been observed in the white-fish of Eu-
rope, which belongs to the salmon family. The following
magnified sections will illustrate this development, and show
the period at which the different organs successively appear.

§ 464. The egg when laid (fig. 297) is spherical, about the
size of a small pea, and nearly transparent.

Fig. 297.

Fie. 298.

Fig. 299.

It has no albumen, and the shell-membrane is so closely at-
tached to the membrane of the yolk, that they cannot be dis-
tinguished. Oil-like globules are scattered through the mass of
the yolk, or grouped into a sort of disc, under which lies the
germinative vesicle. The first change in such an egg occurs a
few hours after it has been laid, when the shell-membrane
separates from the yolk-membrane, in consequence of the ab-
sorption of a quantity of water (fig. 298), by which the
egg increases the size. Between the shell-membrane (s, m)
and the yolk (y] there is now a considerable transparent
space, corresponding, in some respects, to the albumen found
in the eggs of birds.

§ 4b'5. Soon afterwards we see, in the midst of the oil-like
globules, a swelling in the shape of a transparent vesicle
(fig. 299, g), composed of very delicate cells. This is the
first indication of the germ. The swelling rapidly enlarges
until it envelops a large part of the yolk, when a depression is
formed in it (fig. 300). This depression becomes by degrees

Fig. 300.

Fig. 301.

Fig. 302.

a deep furrow, and soon after a second furrow appears at
right angles with the former, so that the germ now presents

284

EMBRYOLOGY.

four elevations (fig. 301). The subdivision goes on in this
way during the second and third days, until the germ is
divided into numerous little spheres, giving the surface the ap-
pearance of a mulberry (fig. 302). This appearance, however,
does not long continue ; at the end of the third day, the fissures
again disappear, and leave no visible traces. After this, the
germ continues to extend as an envelop around the yolk, which
it at last entirely encloses.

tt

§ 465*. On the tenth day, the first outlines of the embryo
begin to appear, and we soon distinguish in it a depression
between two little ridges, whose edges constantly approach
each other until they unite and form a canal (fig. 303, 5), as
has been before shown (fig. 293). At the same time an en-
largement at one end of the furrow is observed. This is the
rudiment of the head (fig. 304), in which may soon be dis-
tinguished traces of the three divisions of the brain (fig. 305),
corresponding to the senses of sight (m), hearing (<?), and
smell (/)).

Fig. 303.

Fig. 304.

Fig. 305.

§ 466. Towards the thirteenth day we see a transparent,
cartilaginous cord, in the place afterwards occupied by the
back-bone, composed of large cells, in which transverse di-
visions are successively forming (figs. 306, 307, c]. This is
the dorsal cord, a part of which, as we have before seen, is
common to all embryos of the verteb rated animals. It always
precedes the formation of the back-bone ; and in some fishes,
as the sturgeon (fig. 374), this cartilaginous or embryonic state
is permanent through life, and no true back-bone is ever formed.
Soon after, the first rudiments of the eye appear, in the form
of a fold in the external membrane of the germ, in which the
crystalline lens (fig. 307, x) is afterwards formed. At the same
time we see at the posterior part of the head an elliptical vesicle,

DEVELOPMENT OF THE YOUNG WITHIN THE EGG. L'Sf)

which is the rudiment of the ear. At this period, the dis-
tinction between the upper and the lower layer of the germ is
best traced ; all the changes mentioned above appertaining to
the upper layer.

§ 467. After the seventeenth day, the lower or mucous layer
divides into two sheets, the inferior of which becomes the in-
testine ; the heart shows itself about the same time, under the
form of a simple cavity (fig. 307, /?), in the midst of a mass of
cells belonging to the middle or vascular layer. As soon as the
cavity of the heart is closed in, regular motions of contraction
and expansion are observed, and the globules of blood are
seen to rise and fall in conformity with these motions.

Fig. 306.

Fig 307.

Ficr. 308.

§ 468. There is as yet, however, no circulation. It is not
until the thirtieth day that its first traces are manifest in the
existence of two currents, one running towards the head, the
other towards the trunk (fig. 308), with similar returning cur-
rents. At this time the liver begins to form. Meanwhile the
embryo gradually disengages itself at both extremities from its
adherence to the yolk ; the tail becomes free, and the young
animal moves it in violent jerks.

§ 469. The embryo, although still inclosed in the egg, now
unites all the essential conditions for the exercise of the func-
tions of animal life. It has a brain, an intestine, a pulsating
heart and circulating blood, and it moves its tail spontaneously ;
but the forms of the organs are not yet complete, nor have
tliev acquired the precise shape characterizing the class, the
family, the genus, and the species. The young white-fish is as
yet only a vertebrate animal in general, and might be taken
for the embryo of a frog.

286

EMBRYOLOGY.

§ 470. Towards the close of the embryonic period, after the
fortieth day, the embryo acquires a more definite shape. The
head is more completely separated from the yolk, the jaws
protrude, and the nostrils approach nearer and nearer to the
end of the snout ; divisions are formed in the fin which sur-
rounds the body ; the anterior extremities, which were indi-
cated only by small protuberances, assume the shape of fins ;
and, finally, the openings of the gills appear, one after the
other, so that we cannot now fail to recognize the type of
fishes

§ 471. In this state the young white-fish escapes from the
egg about the sixtieth day after it is laid (fig. 309) ; but its

development is still in-
309. complete. The outlines

are yet too indistinct to
indicate the genus and
the species to which
the fish belongs ; at
most we distinguish its

order only ; the opercula, or gill-covers are not formed, the
teeth are wanting, the fins have as yet no rays, the mouth is
underneath, and it is some time before it assumes its final posi-
tion at the most projecting point of the head. The remainder of
the yolk is suspended from the belly, in the form of a large
bladder, but it daily diminishes in size, until it is at length com-
pletely taken into the animal (§461). The duration of these
metamorphoses varies extremely in different fishes ; some accom-
plish it in the course of a few days, while in others months are
required.

§ 47 2. In frogs, and all the naked reptiles, the development
is very similar to that of fishes ; it is somewhat different in the

Fig. 310.

Fig. 311.

DEVELOPMENT Or THE YOUNG WITHIN THE EGG. 287

scaly reptiles (snakes, lizards, and turtles), which have pecu-
liar membranes surrounding and protecting the embryo during
its growth. From one of these envelopes, the allantois (fig.
311, a), is derived their common name of allantoidicm rer-
tebrata, in opposition to the naked reptiles and fishes, which
are called anallantoidian.

§ 4/3. The allanto'idian vertebrata differ from each other
in several essential peculiarities. Among birds, as well as in
the scaly reptiles, we find at a certain epoch, when the embryo
is already disengaging itself from the yolk, a fold rising around
the body from the upper layer of the germ, so as to present, in
a longitudinal section, two prominent walls (fig. 310, x, x).
These walls, converging from alJ sides upwards, rise gradually
till they unite above the middle of the back (fig. 311). When
the junction is effected, which in the hen's egg takes place in
the course of the fourth day, a cavity is formed betwreen the
back of the embryo (fig. 312, e] and the new membrane,
whose walls are called the amnios. This cavity becomes filled
with a peculiar liquid, the amniotic water.

Fi?. 312.

§ 4/4. Soon after the embryo has been enclosed in the
amnios, a shallow pouch forms from the mucous layer below
the posterior extremity of the embryo, between the tail and
the vitelline mass. This pouch, at first a simple little sinus
(fig. 311, «), grows larger and larger, till it forms an extensive
sac, the allantois turning backwards and upwards, so as com-
pletely to separate the two plates of the amnios (fig. 312, a),
and finally enclosing the whole embryo, with its amnios, in

288

EMBRYOLOGY.

another large sac. The tubular part of this sac, which is
nearest the embryo, is at last transformed into the urinary
bladder. The heart (k) is already very large, with minute
arterial threads passing off from it. At this period there
exist true gills upon the sides of the neck, and a branchial
respiration goes on.

$ 475. The development of mammals exhibits the following
peculiarties : the egg is exceedingly minute, almost microsco-
pic, although composed of the same essential elements as
those of the lower animals. The vitelline membrane, called
chorion, in this class of animals, is comparatively thicker
(fig. 313, v), always soft, surrounded by peculiar cells, being

a kind of albumen. The
chorion soon grows propor-
tionally larger than the vitel-
line sphere itself (fig. 314,
y), so as no longer to invest
it directly, being separated
from it by an empty space
(k). The germ is formed in
the same position as in the
other classes of the vertebrata, namely, at the top of the vitellus
(fig. 315) ; and here also two layers may be distinguished,

the upper, or se-
Ficr. 315. Fig. 316.

Fig. 313.

Fig. 314.

rous layer
and the lower,
or mucous layer
(m). As it gradu-
ally enlarges, the
surface of the cho-
rion becomes co-
vered with little
fringes, which, at
a later epoch, become attached to the mother by means of
similar fringes, arising from the walls of the matrix, or organ
which contains the embryo.

§ 470. Tbe embryo itself undergoes, within the chorion,
changes similar to those described in birds ; its body and its
organs are formed in the same way, an amnios incloses it,
and an allantois grows out of the lower extremity of the little

THE EGtt IS THE OVIDUCT.

289

Fig. 317.

animal. As soon as the allanto'is has surrounded the embryo,
its blood-vessels become more and more numerous, so as to
extend into the fringes of the chorion
(fig. 317, p, e), while, on the other
hand, similar vessels from the mother
extend into the corresponding fringes
of the matrix (p, m), but without di-
rectly communicating with those of
the chorion. These two sorts of fringes
soon become interwoven, so as to form
an intricate organ filled with blood,

called the placenta, to which the embryo remains suspended
until birth.

§ 477. From the fact above stated, it is clear that among
the vertebrated animals there are three modifications of em-
bryonic development, namely, that of fishes and naked reptiles,
— that of scaly reptiles and birds, — and that of mammals, which
display a gradation of more and more complicated adaptation.
In fishes and the naked reptiles, the germ simply encloses the
yolk, and the embryo rises and grows from its upper part. In
the scaly reptiles and birds there is, besides, an amnios arising
from the peripheral part of the embryo, and an allanto'is grow-
ing out of the lower cavity, both inclosing and protecting the
germ.

§ 478. As a general fact, it should be further stated, that
the envelopes protecting the egg, and also the embryo, are
the more numerous and complicated as animals belong to a
higher class, and produce a smaller number of eggs. This is
particularly evident when contrasting the innumerable eggs $f
fishes, discharged almost without protection into the water,
with the well-protected eggs of birds, and still more with the
growth of young mammals within the body of the mother.

§ 479. But neither in fishes, nor in reptiles, nor in birds,
does the vitelline membrane, or any other envelope of the egg,
take any part in the growth of the embryo ; while, on the con-
trary, in mammals, the chorion, which corresponds to the
vitelline membrane, is vivified, and finally becomes attached to
the maternal body, thus establishing a direct connection be-
tween the young and the mother : a connection which is
again renewed in another mode, after birth, by the process of

nursing.

u

290 EMBEYOLOGY.

STETJCTTJEE OF THE EGG AS JUST LAID.

[§ 4 SO. The egg of the common fowl is surrounded exter-
nally with a hard calcareous shell (fig. 287, #), consisting
almost wholly of carbonate of lime. It is, indeed, without
obvious pores, but is nevertheless permeable to air : some part
of its watery constituent escapes during the process of hatch-
ing, and eggs that are covered with a coat of varnish die.
Internally the shell is full of pits or depressions, in which
small warty or shaggy processes of the lining membrane of the
shell (the mernbrana testae} are implanted (fig. 287, c, c).
This membrane consists of two laminse, the outer of which is
made rough and uneven by the processes just mentioned ;
the inner, which is turned towards the white, is smooth and
polished. The two laminae separate at the blunt end of the
egg (fig. 287, d, d), so that here they are most easily demon-
strated, and contain the air-space, or air-chamber (folliculus
aeris) between them, which first appears shortly after the egg
is laid, and is very much enlarged by keeping and the heat of
incubation. The membrane of the shell is formed of a com-
pact fibrous tissue, and shows the chemical properties of
coagulated albumen. Betwixt the membrane of the shell and
the yolk is interposed the white (cilbumen ovi), the outer
stratum of which (fig. 287, between c and e) is extremely
watery and fluent, and consequently readily drained off
when the shell is pierced ; the inner layer, again, or that
which lies nearer the yolk, is more viscid and thicker
(fig. 287, between e and /), clings more closely to the
yolk, especially by its inmost stratum, which immediately
surrounds that part and the chalazse (fig. 287, /, /). The
white of an egg shows alkaline reaction, and contains a^bu-

\ /*

Fig. 318. — One of the chalazae of the jackdaw's egg pulled straight.
The way in which the twisted fibres of the part diverge into a funnel-
shaped expansion as they approach the volk, and so form the innermost
stratum of the albumen, is displayed.

STRUCTURE OF THE EGG.

291

men, salivary matter, and the common sulphates and hydro-
chlorates in small quantity. The chalazce (figs. 287, g, g,
320, b, 5) are a couple of spirally-twisted ropes, composed of
delicate fibres, or of a fine membrane, which, as the chalazi-
ferous membrane (membrana chalazifera), closely surrounds
the yolk, and then going off in the fashion of a funnel towards
either pole of the egg, becomes twisted into a rope (figs. 287
and 318, 320). A white streak, in the shape of a band, may
usually be seen extending over the
yolk from one chalaza to the other ;
this is the zone or belt (zona), which,
however, is not constant, and is
of no particular importance. The
chalazae vary exceedingly in point
of form and development ; they
appear to consist of coagulated al-
bumen. The yolk, or yolk-ball
(vitellus), is somewhat lighter than
the white, so that, in whatever
position the egg is held, it always
rises towards the side that is up-
permost. The vitellary membrane
(cuticula vitelli) (fig. 319, a) is

a perfectly simple, transparent,

,,J ,. A .'
and slightly glistening membrane. ture area vasculosa) . .

It closely surrounds the yolk tral transparent part of the

(fig. 287, i). Immediately under germ (the future area pelluci-

the vitellary membrane, and at da)- In the yolk here figured,

a point which in an opened egg the first dight effects of incu-

,. , r , bation are apparent — viz.. in

is always directed upwards, the the separation in the germ,

cicatricula (fig. 320, A, c, and which often takes place from
B), or tread, is seen shining transient exposure of the egg
through in the shape of a round to a hiSh temperature (hand-
whitish spot. The cicatricula con- ^g) or when the eggs have
r- • n i- been laid some time, and the

sists superficially of a membra- temperature of the air has
nous stratum (stratum proligerum been high.
— fig. 320, B), from a line and a

half to two lines in diameter, in which the germinal vesicle
was imbedded at an earlier period. This is the germ from
which in the beginning of the brooding the germinal mem-
brane, blastodernia, is produced. The germ in recent eggs

u 2

Fig. 319.— Vitellus, or yolk
of a hen's egg, seen from
above ; a, a, vitelline mem-
brane ; b, vitellus ; c, c, ha-
lones ; d, darker, more exter-
part of the germ (the fu-

ceu-

292

EMBRYOLOGY.

I

is generally slightly adherent to the vitellary membrane; in

such as have
been kept for
some time, it
is more de-
tached ; un-
der all circum-
stances it is
readily difflu-
ent, little con-
sistent. In
the centre it
is somewhat
clearer and
more transpa-
rent than else-
where (fig.
319, e), and
allows the
germinal cu-
«,«/„, (ciirmi-

I If, LI/ 1' ttO • I O It //C-Cv

7 , > ,

lusprohgerm)

to be seen

through it. This germinal cumulus is a loose whitish-yellow,
and somewhat conically formed granular layer, sunk in the
substance of the yolk ; betwixt it and the discus proliyerus,
or germinal disc, there is a minute interval, which is filled
with a fluid that appears to communicate with the canal of
the central cavity of the yolk.*

Fig. 320. — A, the unincubated yolk of the jack-
daw'segg (corvus corone) ; a, the vitellus ; b, b,

.-•,... j i * j • 1

tne chalazse ; c, the cicatncula.
B, the cicatricula magnified.

DETACHMENT OF THE OVUM FROM THE OYARY, AND COM-
PLETION OF ITS FORMATION IN THE OYIDUCT.

[§ 481. The chorion, or outer covering of the ovum in the
ovary, coalesces with a layer of the ovarian stroma into a firm
capsule or theca (fig. 321, a). This capsule is surrounded ex-
ternally with cellular tissue and blood-vessels, and is particu-
larly thick in that part of its circumference towards the pedicle

•

* In the foregoing description and terminology, Bae'r has been followed
as closely as possible. Vide his second volume, p. 10, et seq.

THE EGG IN THE OYIDTJCT.

293

The yolk, or vitelline-ball, lies within this capsule, and
as it advances to maturity forms a more and more completely
pediculated growth, like a berry, of which every ovarium pre-
sents many in different stages (fig. 322). On that side of each
capsule, or berry, which is opposite the pedicle, a curved,
pretty broad, white streak is observed ; this is the cicatrice
(stigma), (fig. 322, 6), which appears not to be vascular, for
although the blood-vessels entering by the pedicle form a
conspicuous rete with rhomboidal meshes on every other part
of the capsule, none are seen to cross or to penetrate the cica-
trice. The capsule is thinnest at this point, and the yolk is
here in most intimate contact, or even appears to be connected
with it (fig. 321, at the lower
part) ; the capsule at length
gives way, yielding in the line
of the cicatrice, and forming a
transverse rent with double
flaps, through which the yolk
escapes. The rupture of the
capsule in the line of the cica-
trice is easily effected by slight
pressure, even in ova that are
far from maturity (fig. 322, d) ;
it happens naturally to the ripe
ova after impregnation. When
the yolk has escaped, the capsule
which had inclosed it presents
itself as a hollow membranous
funnel, the calyx (fig. 322, d),
which remains hanging by its

pedicle, and shrivelling up or brane"; d, ge'rainal 'vesicle, which
shrinking into the stroma of the by and by becomes the cumulus
ovary, soon leaves no trace of its proligerus of ^Baerjfoe nucleus
former existence. The detach-
ment of the vitellus is accom-
plished either by the perfected
growth of this body, its size
proving sufficient at length to burst the cicatrice, or by an
increase in the thickness of the capsule towards the pedi-

Fig. 321.— Section of a yolk
almost ripe, included in its theca
and calyx : — b, petiole or stalk
connecting the calyx with the
ovary ; a, thicker substance of
the calyx united with the theca
of the ovum ; c, vitellary mem-

cicatriculae of Pander ; e, pro-
ligerous disc ; i, central cavity of
the vitellus, its duct proceeding
upwards.

cle, by which the vitellus is forced as

it were against

the

294

EMBEYOLOGT.

cicatrice (fig. 321) ; the whole process is very similar to
that which occurs among the mammalia when the Graafian
vesicle gives way and the corpus luteum is formed. The

oviduct attaches it-
self, by a kind of
suction, by its patu-
lous infundibulum
or bevelled abdomi-
nal end to the cap-
sule which contains
the ripest ovum,
and receives this as
it escapes. From
this point the ovum
makes its way mov-
ing spirally along
the muscular ovi-
duct, which is now
very much enlarged,
highly vascular, and
pouring out from its

mucous surface the
Fig. 322,-Ovaiy of the fowl, with vitelli or albumen which is
yolks, ripe and approaching maturity: — «, a _,. , ,

ripe yolk within its calyx or cup, the cicatrice disposed around
of which, b, b, is seen as a transverse non-vascu-
lar streak ; c, c, smaller yolks, with the vascular
rete of their cups and their cicatrices ; d, a
calyx empty, the part having given way along
the line of the cicatrice — smaller yolks (e) are
enveloped by calices so transparent that the ci- ls a consequence or
catricula is seen through them. the rotatory motion

upon its axis which

the ovum receives in the oviduct, and of the setting of the
albumen. The lower part of the oviduct is dilated into a
receptacle for the egg, and here are added the membrane of
the shell, and finally the shell itself, the milky calcareous
fluid secreted by this part being precipitated upon the egg in
crystals, which are at first isolated, but very soon run together
and cohere. The egg remains over twenty-four hours in the
receptacle. The germ at the firnt entrance of the egg into the
oviduct has already assumed the appearance proper to it at any

a

yolk in the different
layers but just de-
scribed. The forma-
tion of the chalazEe

DEVELOPMENT OF THE CHICK — FIRST PERIOD. 295

period anterior to the commencement of incubation, the ger-
minal vesicle having burst ; the upper disciform layers of the
germ and germinal cumulus only separate more and more.
After the egg is thus perfected, it is forced rapidly through
the cloaca. In other birds, it is here perhaps that the egg
receives, in part at least, the beautiful colours, red, green, yel-
low, brown, &c., in various shades, which are so frequently
met with, and which appear to be so many tints of the colour-
ing matter of the blood chemically altered.

EARLIEST PERIOD IN THE DEVELOPMENT OF THE CHICK,
FROM THE FIRST APPEARANCE OF THE EMBRYO TO THE
FIRST TRACES OF CIRCULATION.

[§ 482. The first period in the development comprehends
about two days. In the first hours of incubation, the germ
separates itself more from the vitellus and vitellary membrane,
to which, however, it still continues in some sort attached ;
the °;erm acquires more of a membranous consistence, and
the space between it and the germinal cumulus, which is filled
with fluid, becomes somewhat larger. Towards the sixth, or
between that and the eighth hour, a parting or resolution in
the now foliaceous germinal membrane, which proceeds from
the centre towards the periphery, is apparent ; a clear rounded
space, about a line in diameter, is produced in the middle,
this is the area pellucida s. yerminativa — the pellucid or ger-
minal area (fig. 319, e) ; the germinal membrane at the same
time becomes darker in the circumference, and surrounds the
transparent pellucid area like a ring, which is also about a line
in breadth (fig. 319, d) ; this is the future area vasculosa, or
vascular area. The cumulus proligerus is seen in the deeper
parts shining through the centre of the germinal membrane.
At this time two or three annular lines appear drawn around
the circumference of the germinal membrane — the halones
(fig. 319, c, c] ; these are circular ridges or walls formed in
the vitellus, between which there are furrows filled with thin-
ner fluid. Now also the germinal membrane may be observed
to show a disposition to separate into two layers, which are,
indeed, still intimately connected, but even at this early period
are in point of structure different. They are always particu-
larized as the lamina of the germinal membrane, the superior

29G

EMBRYOLOGY.

lamina being entitled the serous or animal layer, the inferior
the mucous or vegetative layer ; the former is limited to the
extent of the area pellucida, the latter extends farther in the
periphery, stretching beyond the area vasculosa. The albu-
men disappears in a great measure over the germinal mem-
brane, and the vitellus approaches the lining tunic of the shell
more closely ; in this situation, the vitellus becomes more pro-
minent, forming a segment of a lesser sphere, like the cornea
of the eye ; a circumstance which may likewise be frequently
observed in the egg before incubation (fig. 287, over m). It
is not unimportant to observe that these, the earliest observ-
able changes, not unfrequently take place in eggs that are laid
in summer, and when the weather is very warm, though, of
course, much short of brood-heat.

[§ 483. About the middle
of the first day, after from
twelve to fifteen hours of in-
cubation, the blastoderma,
or germinal membrane, is
completely detached from
the vitellary membrane, and
may be cut out as a con-
nected lamina, and washed
away from the membrane of
the yolk (figs. 323 and 324 . )
The germinal area (area pel-
lucida s. germinativa) has
now an elongated, often a

Fig. 323.-Vitellus or yolk after somewhat pyriform appear-
from twelve to fourteen hours' incuba- ance (figs. 323 and 325, 6),
tion, of the natural size (this and the and is two lines in length,
other figures of the vitellus look larger rpjie darker vascular area
than proper, from their having been ,fi 323 and 325 ^ hag
placed in flat saucers to be drawn, by \ ° , , , \ , ,

which they became somewhat flat- also lengthened out, and the
tened) : a, the yolk ; 6, area pellucida, germinal membrane extends
in the middle of which the notaprima- as a foliaceous formation
tiva, or primary streak, the first trace of indefinitely over it into the
the embryo is perceived ; c, outer area hal which now begin

pellucida. the future area vasculosa. , , P

The halones are indicated by the three to lookless regularthanthey
concentric circles. were originally. This outer

DEVELOPMENT OF THE CHICK FIRST PEEIOD.

portion of the blastoderma
is called theareavitellina.
About this period also the
separation of the blasto-
derma, in the direction
of its thickness, becomes
more apparent; between
the serous layer, which
still continues limited to
the germinal area, and
the mucous layer, which
extends into the vitelline
area, there appears a
new lamina, which, how-
ever, is only distinctly
denned towards the pe-
riphery, where it ap-
proaches the limits of
the area vasculosa ; in
the direction of the thick-
ness this lamina lies in
the blastoderma as if it
belonged to both of the
other layers, and pene-
trated into their sub-
stance ; to distinguish
this less separated lami-
na, it is spoken of as the
vascular lamina, the
blood and blood-vessels
first making their ap-
pearance within its sub-
stance. This formation
first becomes distinctly
visible between the six-
teenth and twentieth hour
of incubation (fig. 329,

297

Fig. 324.— The same vitellus, but
with a piece of the vitellary membrane
and the subjacent blastoderma re-
moved at a, by which the nucleus of
the cicatriculae, or cumulus proligerus,
a dark disciform substance implanted
in the vitellus, is brought into view.

Fig. 325. — Magnified view of the portion of the blastoderma removed
iu fig. 319. — a, the nota, or primary streak ; b, the oblong area pellucida ;
c, the oval area vasculosa.

298

EMBRYOLOGY.

A, B, d}. Somewhat earlier than this, namely, about the
fourteenth hour, the first rudiments of the embryo become
distinctly visible in the middle of the germinal area, in the
guise of a delicate white elongated streak, about a line and a
half in length ; it is designated nota primitiva — the primitive
streak, and lies in the line of the long axis of the germinal
area, which itself lies in the transverse axis of the egg (fig. 325, a) .
Under the nota primitiva, the cumulus proligerus, deeply seated,
may still be seen very plainly glistening through (fig. 326, A,

B, d). The nota primitiva rises slightly above the level of
the germinal area (fig. 326, b) ; it is thicker and blunter ante-
riorly, or towards that end which becomes the head of the
embryo, thinner, and tending to a point posteriorly. The nota
primitiva is probably the groundwork of the brain and spinal
cord.

[§ 484. The nota primitiva, an aggregate of dark granules

in the first instance, becomes
more fluent by and by, and
presents itself as a layer of de-
licate, transparent masses, by
the side of which, between the
sixteenth and eighteenth hour,
a pair of new formations arise
symmetrically, near the mid-
dle line. These are the lami-
nce s. plicfB dorsal es — the dor-
sal laminae, two cylindrical
rolls or enlargements, which

B

Fig. 326. — Ideal sections of fig.
323 (after Bae'r, with slight varia-
tions).— A, transverse section ; B,
longitudinal section ; a, vitelline
membrane, indicated by a finely
dotted line ; b, nota, or primitive
streak, with the serous layer of the

arise parallel to the nota primi-
tiva, and form a couple of cris-

tse, or ridges, one on either
. , „ ., 9~ 00- -• Qr>o

, Slde, of lfc (%s- 327 and 32f '

blastoderma, corresponding to the &, »), which diverge anteriorly

area pellucida ; c, mucous layer of and posteriorly, being nearest

the blastoderma, corresponding to about the middle of their

the area vasculosa ; d, cumulus pro- len«th an^ sloping somewhat

hgerus s. nucleus cicatncuke. „ .,, ^

from without inwards, or to-
ward? one another. The angles of the ridges are softly
rounded off; each ridge has the appearance of a clear broad
line, which is included within two darker lines. The germinal

DETELOPMEIN'T OF THE CHICK — FIRST PERIOD-

299

c, area

area presents a pyriform outline (figs. 327 and 328). Under
the canal for the spinal
cord, which is bounded by
the dorsal laminae, we ob-
serve the chorda dorsalis —
the dorsal cord (figs. 330
and 332, A, e, and fig.
331, /), an extremely fine
elongated streak, surround-
ed by a transparent sheath ;
both the dorsal cord and
the sheath go to constitute
the cartilaginous column
which appears later, and out
of which, by its becoming
divided into pieces, the ver- 327.-Yolk of the natural size

tebral column is produced after eighteen hours of incubation : a.
(§466). The embryo with vitellus ; b, area pellucida;
its laminae dorsales now vasculosa.
bends itself forward, at the
same time that it here forms
a sickle-shaped transparent
fold (fig. 328, c), the future
involucrum capitis — the
cranial envelope or cap.
From the twentieth to the
twenty-fourth hour, the
transparent germinal area
is observed to become
longer and more fiddle-
shaped. The cristae, or

folds of the dorsal laminae,

i ,1 i Fig. 328. — The pellucid area of

where they run closest to- |27 magnified;\ the peUucid

gether, appear somewhat area? now become pear-shaped ; in-

siimously bent (fig. 331, stead of the nota, or primary streak,

b,b} ; here, too, inthepecto- the two dorsal laminae or folds (lami-

ral region, on both sides of n" s- PKc<e dorsales) b, b, are seen ;

... i i the involucrum capitis, or cranial en-

the dorsal laminae, near velope? c> a faldfo^ fold| or kind of

their cnstEe, there appear reflex blastoderma, begins to be de-
dark, four-cornered looking veloped.

,300

EMBRYOLOGY.

plates, the future vertebral arches

Fig. 329.— Ideal sections of figs. 327
and 328. — A, tranverse section ? B, longi-
tudinal section; a, vitellary membrane;

b, serous layer of the blastoderma, or ger-
minal membrane, depressed in the middle
by reason of the rounded elevations of
the dorsal laminae on either side ; e, chor-
da dorsalis ; c, mucous layer of the blasto-
derma ; d, vascular lamina, between b and

c, indicated by a finely-dotted line.

Fig. 330. — Vitellus of the natural size
after twenty-four hours of incubation, the
germinal membrane with the rudiments
of the embryo farther advanced than in
fig. 327. The references are the same in
this as in figure 327.

(fig. 331, c, c, fig. 332,
A,/), which form at first
but three or four pairs ;
the cristae of the dorsal
laminae are observed to
approximate more and
more, in order to close
and complete the verte-
bral canal (fig. 332, A )
over the chorda dorsalis
(e). Anteriorly they se-
parate to a greater ex-
tent from each other to
form the head (fig. 331,
d), and also posteriorly
to form the future sa-
crum ; the enveloping
fold, the future involu-
crum capitis, is thrown
farther back (fig. 33],
e, e} ; the vascular and
mucous laminae of the
germinal membrane fol-
low this bending in (fig.
332, /), by which the
beginning of the intesti-
nal canal is produced,
which as yet is nothing
more than a depression
on the vitelline side of
the serous lamina of
the germinal membrane.
The embryo lies like
a flat-bottomed boat
turned over upon the
germinal membrane (fig.
332, B) ; the head is
already strongly indi-
cated (fig. 332, B, e}.
[§ 485. With the se-

DEVELOPMENT OF THE CHICK — FIRST PEKIOD. 301

cond day of incubation the embryo disconnects itself c-ven
more and more from the ger-
minal membrane and the
yolk, and rises more dis-
tinctly over the germinal
area. This takes place by
the anterior plait or fold (in-
volucrum capitis) continu-
ing to recede still farther
backwards (fig. 334, e}, and
the development posteriorly
of a second plait or fold,
sickle-shaped or crescentic
in the first instance also (fig.
334, g), the future involu-
crum caudce; the sides now
begin to turn inwards also,
by which the transparent
germinal area is drawn in
and bent laterally, and
made to assume a complete
fiddle-shape (figs. 333 and

334). The embryo is three

' . , ,{ , Fig. 331, — Magnified view of the

lines m length ; the broader pellucid area of the yolk> fig> 330 . the

and more strongly bent ex- area has now lost its pear-shape in a
treniity, with its transverse great degree, and become somewhat
plait or envelope, is visible fiddle-shaped (biscuit-shaped in the

original). In the middle are seen the
slightly sinuous edges of the dorsal
lamina, b, b, separating from one ano-
ther anteriorly and posteriorly ; on
their outsides lie four square plates,
c, c, rudiments of the vertebral co-

Jumn ' *• *ntf or ,c^ebral c!u. '. e> *>
. , , transparent edge of the cranial invo-

completely, close the canal lucrum> shining through; /, dorsal
for the spinal cord (fig. 335, cord.
A, g], beneath which the

more delicate chorda dorsalis with its sheath (e) extends. The
four-cornered laminae, the future vertebral arches, have in-
creased in number, new ones springing up in front and be-
hind ; and, about the thirty-sixth hour, as many as from ten

to the naked eye. The cris-
tae of the dorsal laminae
have become approximated
through a larger space,
touch each other (fig. 334,
b, 6), and finally coalescing

302

EMBRYOLOGY

3

to twelve "pairs may be reckoned (fig. 334, c, c, c). At
this time the dorsal laminae separate still more from one
another in front, so that many spaces or cells become dis-
tinctly visible be-
tween them ; the
largest or most
anterior of these
cells (fig. 334, d)
has become some-
what pointed for-
wards, and curved
underneath ; late-
rally it presents
wide bending in-
lets, which indi-
cate the first for-
mation of the
eyes ; it is the
cell of the thala-
mi and crura of
the cerebrum ;
the second small-
er cell (d2) is the
cell of the cor-
pora quadrigemi-
na ; the third, an
elongated cell
(</3), belongs to
the medulla ob-
longata. The
transparent mass
of the brain and
spinal cord ac-
quires greater
consistency, and

is covered with a
f ijr. 333. — Yolk of the natural size after thirty- fi , , . , ,

six hours of incubation ; a, yolk ; b, fiddle-shaped

I ellucid area, in the middle of which the embryo transparent lay-
is seen. In the vascular area, c, c, the insulae er, the future
sanguinis, or blood islets, begin to appear. membranous ill-

Fig. 332.— Ideal sections of fig. 331.— A,
transverse section ; B, longitudinal section. In
A,/, section of the vertebral laminae. In B,
formation of the head by the reflection of the
blastoderma ; e, margin of the involucrum capitis,
and entrance into the,future intestinal canal (fovea
cardiaca of Wolff). The other references are the
same as in fig. 329.

DEVELOPMENT OF THE CHICK — 3TIKST PERIOD.

303

volucra of the nervous centres ; the brain, and medulla ob-
longata, up to this
time, are, therefore,
in fact, shut vesicles,
which, on account of
their transparency
only, appear as open
spaces lying between
the sinuous cristse of
the dorsal laminae.
Outwardly, from the
cristae of the dorsal
laminae, and the four-
cornered laminae of
the vertebral arches,
proceeds the serous
lamina of the germi-
nal membrane, thick-
ening as it grows,
and bending from
both sides at the
same time slightly
inwards ; in this part
a number of small
dark leaflets make
their appearance si-
multaneously, which
become particularly
plain in the trans-
verse section (fig.
335, A, and especi-
ally fig. 338, A, b2)-
these are the rudi-
ments of the trans-
verse processes of
the vertebrae, and,
farther out, of the

Fig. 334. — Magnified view of the area pellucida of the vitellus, fig. 329
— b, b, crests of the dorsal laminae, receding from each other anteriorly
to form the cerebral cells ; dl, cell of the eyes and thalami ; d-, cell of the
corpora quadrigemina ; d3, cell of the medulla oblongata ; c, c, c, c, laminre
dorsales, of which ten are present on either side ; e, anterior fold of the

304

EMBRYOLOGY.

ribs likewise; these lateral prolongations of the serous Ja-

mina are called
the lamina ven-
tral es, ventral
laminae. As the
dorsal laminae
arise more per-
pendicularly in
plaits, and con-
verge to close the
spi-nal canal, so
the ventral la-
minae spread
more in breadth,
bend in inferior-
ly, and converge
Fig. 335. — Ideal sections of the embryo of fig ^o form the la-
330 ; letters of reference as in fig. 329. A, over ^^ parietes OI
the chorda dorsalis, e, is seen g, the canal for the * , ,

spinal cord, formed by the union of the cristae of abdomen,

the dorsal laminae. B, longitudinal section. The and finally to
heart, d2, is evolved as a thickening of the lamina close this cavity,
vasculosa. The vascular and

mucous layers follow the turnings and general course of the
serous layer, and decline anteriorly under the head of the
embryo, by which the fovea cardiaca, the anterior depres-
sion which marks the commencement of the intestinal canal,
becomes deeper (figs. 332, B, /, and 335, B). From this
sinus the vascular and mucous layers turn more posteriorly,
and immediately again proceed forwards, to be continued
in the plane of the germinal membrane (fig. 335, B, where
the heart, d2, is indicated). This part of the germinal mem-
brane, then, covers the head of the embryo when it is viewed
from below, and on this account is called the involucrum capi-
tis — the cranial envelope or cap — among writers on develop-
ment ; it is not any independent formation.

Whilst these changes in the form of the serous layer are
going on, others are proceeding, pari passu, in the vascular
lamina, in the following order, from the end of the first day

blastoderma, from which the involucrum capitis is formed, shining through ;
g, posterior fold of the blastoderma, still very narrow, from which is
formed the involucrum caudse ; /, chorda dorsalis

DEVELOPMENT OF THE CHICK PIEST PERIOD. 305

to the middle of the second. The area vasculosa (figs. 330
and 333, c) has enlarged, and from a form rather elongated,
has assumed one that is rounder. Its outer circumference is
beset with darker aggregated-looking masses (fig. 333) ; sin-
gle isolated points appear, and between these clefts are formed,
that by and by run together and form channels, which unite in
meshes with one another ; in these channels a clear colourless
or extremely pale yellow fluid can by and by be distinguished
in motion — this is the blood. The halones (fig. 330), which
had become more sinuous towards the beginning of the second
day, now vanish entirely. Along with these occurrences in
the periphery of the vascular lamina, the development of the
heart has been advancing in the centre, under the transparent
germinal area and the serous layer of the embryo. The vas-
cular lamina becomes thicker, and appears darker in this
point ; the heart shows itself as a somewhat sinuous sac, in-
terposed between and pushing apart the mucous and serous
laminae (fig. 335, B, eP). As the development advances, the
heart is observed from the under or abdominal aspect of the
embryo as a sac, simple and undefined anteriorly, of greater

a

Fig. 336. — An incubated vitellus of the jackdaw's egg ; A, of the na-
tural size ; B, magnified — a, vitellary membrane ; b, b, b, halones ; c,
embryo ; d, area pellucida , e, area vasculosa. (^Compare with figs. 330
and 333.)

306

EMBETOLOQY.

breadth posteriorly, and terminating in two (fig. 337, d, f)

or three (fig. 337, e] crura ; these
are the future great venous
trunks, which as yet are lost in-
sensibly in the germinal mem-
brane. Even at this period un-
dulating motions, rhythmical
contractions of the heart, may
be perceived, by which the
somewhat wavy appearance of
the organ is produced; the same
clear or nearly colourless fluid
is in motion in the heart as in
the vessels in the periphery.
The heart occupies the whole
space from the involucral point
of the germinal membrane to
the cranial end of the embryo,
Fig. 337.— Anterior end of an ancl is consequently, when the
embryo scarcely of greater age embryo is contemplated from
than that of fig. 330, seen from below, covered by the part of
the abdominal (the vitellary) as- the serous membrane which at
pect, to show the first formation ,1 ? .-, • -,

of the sacculate heart, a, with the Sam6 tmie f°r^S the involu'
its immerging vascular (venous) crum capitlS. The embryo,
trunks, d, e, f; b, b, crests of which at the end of the first day
the laminae dorsales seen shining bore some resemblance to a punt
throuSh- or flat-bottomed boat, by the

middle of the second day has acquired the form of an ordi-
nary small boat turned over, the sides of which (the ventral
laminse) converge, whilst the head is much curved or beak-
fashioned (the bending down of the head), and furnished
with a particular cover (the involucrum capitis) ; the pos-
terior part is also somewhat recurved, but much less so than
the anterior part, by the commencing development of the
caudal envelope. The ventral channel extends from the pos-
terior margin of the heart (fig. 337) to the crescentic plait of
the caudal envelope (fig. 334, from e to g, seen through the
back of the embryo).

[§ 486. The changes that occur during the second half of
the second day, from the thirty-sixth to the fiftieth hour, fire
the following : the dorsal laminse are closed along the whole

DEVELOPMENT OF THE CHICK — SECOND PEEIOD. 307

line of their course ; the head curves itself more and more
under the body, so also does the tail ; and the involucra both
of the head and tail again bend towards the dorsal aspect ;
the ocular sinuses are separated more distinctly from the an-
terior cerebral cell, which now lies completely underneath ;
the cell of the corpora quadrigemina is much enlarged ; from
the cell of the medulla oblongata the organ of hearing arises
as a vesicular eminence, and in its anterior part, a particular
contraction of the cerebellum is very commonly to be per-
ceived ; the spinal cord is now a laterally compressed tube.
The blood collects in the periphery of the vascular lamina
within a circular sinus or annular vessel, the future sinus s.
vena terminalis. The heart soon parts the ventral laminae
from one another, like a wedge, and so forms a hernia behind
the point of reflection of the germinal membrane to the cra-
nial involucrum ; it is here that the venous trunks penetrate
which carry the blood from the periphery of the vascular
lamina to the heart. The heart itself has now become a
relatively narrower, and more curved or spirally twisted sac,
which contracts with greater vigour than heretofore. The an-
terior extremity of the heart divides into two crura, which
proceed to the cover of the future oral cavity, and run for a
certain way under the vertebral column, where they blend into
the future aorta, separate again, and give off two great trans-
verse branches, which lose themselves in the germinal mem-
brane towards the periphery of the vascular area. The blood
by degrees acquires a red colour. The transparent germinal
area continues fiddle-shaped. In the periphery the serous
lamina recedes still more from the other laminae of the ger-
minal membrane that lie under it, at the same time that it is
raised round the whole circumference into a fold which grows
with great rapidity in the beginning of the third day (fig. 338,
A, B, f). The whole embryo is still more bent on itself ; the
cell of the corpora quadrigemina forms its anterior and su-
perior end ; the caudal end is turned in more than ever, and
the mucous layer following the bending, a depression is here
formed in the same way as we have seen one produced towards
the anterior extremity, at the fovea cardiaca ; the digestive
cavity is now a channel of considerable depth ; which, how-
ever, is still largely patulous towards the vitellus ; from which
undoubtedly it derives formative materials.

x2

308

.EMBRYOLOGY.

SEC01SD PEEIOD OF THE DEVELOPMENT OF THE CHICK, TO
THE EVOLUTION OF THE SECOND CIECULATION.

[§ 487. THE second period in the history of the development
of the chick begins with the third day, in the course of which
the circulation in the vitelline vessels is completely established
(figs. 339 and 346), and embraces farther the changes that
take place during the fourth and fifth days, till the allantois
has appeared, the membrane of the shell has been attained,
and the second circulation is established ; the first, which had
reached its highest development at the end of the fourth day,
now beginning to suffer an arrest, and to decline in extent and
activity (figs. 341 and 345). In the course of this period the
embryo is completely detached from the germinal membrane,
and becomes enveloped in peripheral productions of the same
part. The third day is the most remarkable in the whole

f

rt 7) .7 I a

Fig. 338. — Ideal section of an embryo somewhat younger than that of
fig. 339. A, transverse section ; a, vitelline membrane ; b,b, laminae dorsales
et vertebrales ; b-, b~, laminae abdominales and transverse processes ; c,c,
lamina mucosa, which is seen bending round under the chorda dorsalis (e),
to form the intestinal canal ; d, d, lamina vasculosa ; /, /, peripheral por-
tion of the lamina serosa, proceeding to form the lateral involucra and the
amnion ; g, medulla spinalis. — B, longitudinal section ; a, vitellary mem-
brane ; b, lamina serosa, and dorsum of the embryo ; b~, head of the
embryo ; c, c, lamina mucosa ; d, lamina vasculosa ; d2, heart ; d3, branchial
arteries ; c?4, aorta ; d5, artery of the blastoderma (arteria vitellina).

DEVELOPMENT OF THE CHICK SECOND PEEIOD. 309

history of the development, as, from the general vigour of the
formative processes, all the organs now begin to be evolved,

Fig. 339. — View of an embryo, four lines long, magnified about eight
diameters. The embryo is seen from the abdominal surface ; the time is
the middle of the third day. a, Area pellucida ; b, anterior cerebral cell
(the hemispheres) ; c, cell of the thalami and crura cerebri ; d, corpora
quadrigemina ; e, cerebellum and medulla oblongata ; /, the eye, a wide
cleft inferiorly ; g, the auditory vesicle lying in front of the medulla
oblongata ; h, h, h, vertebral lamina ; i, ventricle of the heart ; k, atrium
cordis ; kl, superior, and £2, inferior vein of the blastoderma ; I, bulb of
the aorta, giving off the four branchial arteries, over which lie three
branchial arches, 1, 2, 3 ; m, m, arteries of the blastoderma proceeding
from the divided trunk of the aorta ; inwards from either aorta the bodies
of the vertebral laminae are united by suture ; ?z, the allantois just
budding forth ; o, o, o, o, margins of the abdominal cavity, reflected su.
periorly into the involucrum capitis, p ; inferiorly into the involucrum
cauda?, §-, q. The mesentery, Wolffian bodies, &c., which have by this time
began to appear, are left out. The actual length of the embryo is indicated
by the line with the asterisk.

310

EMBRYOLOGY.

and the characteristic form of the embryo to be more particu-
larly declared. We shall speak of the different appearances in
groups, as they are associated with the several laminae of the
germinal membrane, tracing each principal formation, and
each individual organ, in its progress from the beginning to
the end of the period we are now considering.

[§ 488. The dorsal laminae have increased in size, and the
rudiments of the vertebrae within them (the vertebral laminae)
are growing both anteriorly and posteriorly (fig. 339, h, h) ;
they surround the spinal canal on the sides, are also to be seen
over the medulla oblongata, and several even exist anterior to
the ear (fig. 340, at d}. In the vicinity of the chorda dorsalis,

outwardly, between it and the
vertebral laminae, arise the
first cartilaginous rudiments of
the bodies of the vertebrae,
which blend superiorly with
the laminae of the vertebral
arches, close in the canal of
the spinal cord below, and
surround the cartilaginous co-
lumn (sheath) of the chorda
dorsalis. Towards the fifth
day the chorda dorsalis begins
to disappear ; the spinal cord

,. is laterally compressed, and

Fig. 340. — Anterior end of an „ , f ,

embr'vo somewhat more highly mag-

(L

falls into two halves, each of

nified, and a few hours older than
that of fig. 339. a, a, Cranial in-

which is again divided into
an upper and an under fas-

volucrum ; b, b, vertebral laminae ciculus. It is on the fifth day
near the crests of the now closed ^ t ^ mdimentary eiilarge-
dorsal lammse; c, spinal cord pass- '. ,. 9
ing into the medulla oblongata, d, ments or processes, indicative
which in its turn passes by a de- of the position of the future ex-
pression (the fourth ventricle) into tremities, make their appear-
the corpora quadrigemina, e ; /, ance . the earliest traces of the
mesocephalon (thalami and crura cerebral envelopes were already
cerebn) : a, hemispheres ; n, supe- - . _ , ,
rior maxillary bone ; i, auditory conspicuous on the fourth day.
vesicle ; k, branchial arches ; I, The medulla oblongata (fig.
atrium cordis ; m, the heart hang- 340, between c and d) is ex-
ing forwards ; n, bulb of the aorta, tremely flat above, in conse-
quence of the divergence of the superior fasciculi from one

DEVELOPMENT OF THE CHICK — SECOND PEKIOD. 311

another, and thus is the basis laid of the fourth ventricle,
which appears to be covered with its own peculiar medul-
lary and enveloping lamina. Anteriorly, the fasciculi of
the medulla oblongata ascend towards the corpora quadrige-
mina in two perpendicular laminae, which, on the fifth day,
become applied to one
another, and so cover the
fourth ventricle superiorly
and anteriorly ; thus is
the cerebellum produced,
visible from the side as
an enlargement (figs. 339
e, 340 d, 341 and 345
a2), behind which the
fourth ventricle presents
itself as a deep depres-
sion (figs. 341 and 345,
«?). The corpora quad-
rigemina form a simple
and very considerable cell,
which projects forwards
in an arched or vaulted
manner, but, with the in- Fig. 341.— Embryo of the fowl, nearly
creasing declension of ^ve lines m length, at the seventy-se-
the head turns alwavs cond hour of incubation (transition from

more and more down- fe .thifd tof the.fourthtl *?): The ab-

, an A* nominal surface 1S partly laid open, and

•as (ngs. 66$ and 347 the parts separated; the amnion is re-

d, 340 e, 341 and 345 moved, a, corpora quadrigemina ; b, the

a, 343 B, a, 342 b, 344 hemispheres; c, the nasal depression;

e). The laminae, which *' the fourth ventricle> in front of which

f™ , *i,^ v, n "es ^e cerebellum, a-, which is now

form the cerebellum, pro- more distinctly defined ; e, the ear;/,

ceed upwards, blending in the eye, in the choroid of which, already

the corpora quadrigemi- furnished with its pigment, a cleft is

na, under which the seen » ffl—ff4> the four branchial clefts ;

fourth ventricle is con- ^' ^e ^eart 5 *> the h'ver ; k, the intesti-
nal canal, with its open vitellary duct I ;

tinned as the aqueductus. ^ the rectum stm eifcling in a b^lind sac;

Anteriorly to the corpora n, the allantois ; o, the anterior, and p,
quadrigemina lies the the posterior, extremity ; g, q, g, g,
asymmetrical, smaller, )yolffian bodies ; r, upper jaw ; s, under
middle cerebral cell (figs. ^aw'
339 and 345 c, 340 and 341 /, 343 B, before r), formed by

312

EMBETOLOGT.

the advancing laminae of the medulla oblongata as the crura
cerebri ; it is open superiorly, and extends, as the third ventri-
cle, with a wide opening into the infundibulum, which on the
second day was directed straight downwards, but which now,
from the great bending in of the head, is turned backwards,
and even upwards. In this cell, which was the first formed,
and foremost cerehral cell (fig. 334, d1), the thalami make
their appearance towards the end of the period. The most

Fig. 342 A. — Embryo of the fowl of the fifth day, much magnified ;
after Huschke (/sw, 1828, § 163.) — a, a, hemispheres; b, corpora quad-
rigemina; c, upper jaw; d, under jaw; e, first branchial arch (os
hyoides) ; f, meatus auditorius externus ; <?1, </2, g3, first, second, and
third branchial fissures ; A1, A2, #3, the three branchial arteries ; i, the
heart ; k, the eye, with the cleft /; m, descending aorta ; D, cavity of the
mouth and fauces ; n, acoustic pouch.

Fig. 342. — B (after Huschke), front view of the embryo of the fowl, of
the fourth day ; a, hemispheres ; b, corpora quadrigemina ; c, eye ; d,
upper jaw; e, lower jaw; /, enlargement of the os hyoides; g, ventricle
of the heart ; h, atrium cordis ; D, oral aperture arid faucial cavity.

DEVELOPMENT OF THE CHICK — SECOND PERIOD. 313

anterior cerebral cell, at the present epoch, is symmetrical,
and contains the hemispheres (figs. 339, 341, and 345 b,
340 g, 344 d, 343 B, p] ; according to the natural curvature
of the embryo, it lies completely downwards. The optic nerve
appears as a vesicle, betwixt the middle and anterior cerebral
cell, in which the external envelopes (the outer portion of the
serous membrane), preparatory to the formation of the eye ball,
bend circularly inwards, in the shape of a sac, and externally
form a projection, which opens downwards as a cleft ; this is
closed by degrees, and at length forms a colourless thin streak,
whilst the rest of the bulb, from the deposition of the pigmen-
tum nigrum, is dark or deeply coloured ; the lens makes its
appearance very early (on the third day), forming a particular
closed capsule within the sac of the external envelopes (the
ball of the eye), and lying in the midst of an albuminous
ball, the vitreous humour.* The organ of hearing, at first a
simple vesicle arising from the medulla oblongata, soon be-
comes a distinct sac, which, examined from behind, appears
attached to the medulla oblongata by means of a pedicle — the
acoustic nerve (fig. 340, i) ; distinct from it a cleft appears
(fig. 342, A,/), which increases over against the acoustic sac,
and sinking into it, forms the external meatus audj£orius. If
the embryo be lying upon its side, the acoustic sac, which
subsequently forms the labyrinth, is seen as a rounded en-
largement (figs. 339 g, 341 e, 342 A, n), which in the course
of the period under consideration, comes continually forward.
About the beginning of the third day, the olfactory nerve
shows itself towards the basis of the cell of the hemispheres ;
at a later period the nasal holloiv (fig. 341, c) is observed as a
broad depression with puffed edges ; on the fifth day both
nasal hollows have become deeper, and are now distinct from
one another.

§ 489. Very important metamorphoses go on during this
period in the ventral laminae lying on either side of the dorsal
laminae, or middle portion of the embryo ; so far these ventrai
laminae are formed from the serous layer of the germinal mem-
brane only ; they separate into a superficial thinner layer (figs.
338 and 343, A, 52 and /), which, like a cuticle, loses itself
in the periphery of the embryo upon the deeper stratum ; and,
as it has already suffered a reflection anteriorly opposite the

* On the metamorphosis of the eye, consult figs, from 339 to 310.

314

EMBRYOLOGY.

heart, and formed the involucrum capitis ; so, towards the pos-
terior part, it has hent over as the involucrum caudse, and been
formed into plaits or folds laterally, as the lateral envelopes.
Thus is the serous layer of the germinal membrane, or upper
layer of the ventral laminae, raised on every side to converge
into an elliptical plait towards the back of the embryo ; on the
fourth day, these plaits have approached each other very closely ;

a

i--/

y } fa,

~^r- /-.

Fig. 343.— Ideal section of an embryo nearly at the end of the third
day : — A, transverse section ; a, vitelline membrane, &, b, laminae dorsales,
&c., as in fig. 338. B, longitudinal section. The cranial and caudal in-
volucra approximate, and at length meeting, they close the arnnion; g, the
eye ; k, entrance into the mouth, or fovea cardiaca ; i, the oesophagus,
with the rudimentary lung budding out as a diverticulum from it ; k, ex-
pansion of the alimentary tract, marking the seat of the stomach ; /, pos-
terior shut extremity of the intestine, from which proceeds the allantois, e,
surrounded by the vascular lamina dj m, the mesenteric lamina ; n, pas-
sage from the vitellus to the open abdomen ; 0, anterior part of the head
(corpora quadrigemina) ; p, hemispheres ; r, superior maxilla ; s, inferior
maxilla ; I, oral cleft or aperture ; 1, 2, 3, three branchial clefts. Other
references as in fig. 338.

DEVELOPMENT OF THE CHICK SECOND PEEIOD. 315

the anterior is now called the vagina capitis ; the posterior va-
gina caudcB (fig. 343, B, f, backwards) ; the lateral folds may,
in like manner, be entitled the vaginae later ales (fig. 343, A,
/, /) ; they coalesce at the end of the fourth day, and form a
visible cicatrice over the lumbar region of the embryo. In this
way we have a complete vesicular envelope thrown around the
embryo, — the AMFION (fig. 344, a, a), which is filled with
fluid. The upper layer of the fold (fig. 343, A and B, lying
under the vitelline membrane, a\ covers the whole germinal
membrane, and grows around the yolk as a serous capsule or
cyst, vesica serosa — the false amnion of Pander. At the place
where the embryo lies, this layer is separated from the rest of

Fig. 344. — Outline of the embryo of the fowl, at the end of the fifth
day, much magnified ; a, a, amnion ; 6, allantois ; c, corpora quadrige-
mina ; d, hemispheres ; e, eye ; /, anterior ; and g, posterior extremity.
The natural dimensions of this, as of many of the other figures, are indi-
cated by a line, or lines, with an asterisk.

316 EMBRYOLOGY.

the germinal membrane by a considerable space. The inferior
layer of the serous ventral lamina forms the ventral paries, and
gives origin to the bones and muscles which compose the neck
and trunk. Inferiorly, the vascular lamina lies upon it, and
this, with the serous lamina, evolves the formations which are
now to be described. On either side, under the vertebral
column, there is a lamina detached, which grows thicker, and
increases in a direction perpendicularly downwards ; these are
the lamina mesenteries, between which there is, at first, an
open triangular-shaped channel or cleft, the foramen mesen-
terii ; both the mesenteric laminae push the mucous layer be-
fore them, and speedily unite, at an acute angle, in the suture
(fig. 343, A, h, B, m). The furrow, or foramen of the mesen-
tery, resembles an equilateral triangle, with one of its angles
pointing directly downwards. After the union of the two
mesenteric laminae, the resulting structure grows most rapidly
posteriorly, opposite the middle of the body, and here forms a
septum, dividing the abdominal cavity into two halves.

It is at the beginning of the intestinal canal, where the ven-
tral laminae are converging, that the branchial arches are deve-
loped ; the parietes of the body here become thinner ; and in
this, the cervical region, several clefts or fissures make their
appearance, which sink downwards, and penetrate through
the mucous layer ; there are three pairs, or, with the oral
aperture, four pairs of such fissures, but the posterior pair are
extremely small ; they are called the branchial fissures — fissurae
branchiales ; between them lie three segments, or divisions of
the ventral laminae, which are blunt and rounded anteriorly,
bevelled off towards the digestive cavity, and therefore sickle-
shaped ; these are named the branchial arches — arcus bran-
chiales (figs. 339, 340, 341, 343, &c.) ; the fourth branchial
arch is placed hindmost, and is not yet distinct from the ven-
tral lamina. On the fourth day, the two most anterior bran-
chial arches increase in thickness (fig. 341, between #4 and
ff2) ; a new fissure is formed posteriorly (fig. 347, ff}) ; on the
fifth day, the foremost fissure closes (fig. 342, A, between d
and e),'and the foremost branchial arch unites with its fellow
of the opposite side, and forms the lower jaw (fig. 342, A, d,
B, e) ; the next in succession is transformed into the os hyoides
(fig. 342, A, e, B, /). The two last branchial fissures close

DEVELOPMENT OF THE CHICK — SECOND PERIOD. 317

up on the fifth day ; at the same time the first is lost en-
tirely; but the second
continues longer open

On the

(fig. 342, A,

third and fourth days,
the part of the ventral
lamina, which is situated
in front of the lower jaw
thickens and resolves
itself into the upper
jaw (fig. 341, r, and
345, 1 above 2); this
part is more strongly
marked on the fifth day
(fig. 342, A, c). The
two sides of the upper
jaw do not meet in the
first instance ; they co-
alesce at a later period, Fig< 345._Emrjryo of the fowl of the
through the medium of first half of the fourth day ; a, corpora
thefrontalprocess, which quadrigemina ; b, hemispheres; c, meso-
is developed betwixt the cephalon (thalami) ; d, fourth ventricle ;
eves rfio- S4'? -R OVPV /> eye, the cleft in the choroid beginning

\_ \ v^ o i j.j ^_ • \j*.jt** -«-*} »_/>trj. i i a j i _£• j j

to close ; gl, g~, the first and second
branchial spaces still entirely open ; g*, g*,
the third and fourth spaces open be-
hind only ; h, the ventricle of the heart,
now of a rounded form ; i, aorta ; n, al-

D).

The rudiments of the
ribs begin to be formed
in the parts of the ven-

tral laminae lying behind

lantois ;

and p, posterior ex-

T.-I- tremity. 1, 2. Upper and under jaw.

the branchial arches ; The line ^1th the asterisk indicates the

the extremities show natural length of the embryo,
themselves upon the ex-
ternal aspects of the same laminae. Of the extremities there is
still no trace to be discovered in the first half of the third day
(fig. 339), but in the second half of that day they arise on
the sides of the ventral laminae as narrow edgings, which by
the close of the day have turned more upwards, gained the
outer margins of the ventral laminae, and changed into
rounded offsets (fig. 341, o, p\ the posterior pair being dis-
tinguished from the anterior by somewhat greater breadth
(fig. 345, o, p) ; on the fifth day they recede still more up-

318

EMBRYOLOGY.

wards towards the dorsal laminae, become pediculated, and
present a broad shovel-shaped termination (fig. 344, f, g).

[§ 490. The vascular lamina in its development follows the
phases of the first, or vitellicular circulation, which, as has
been stated, attains its height on the fourth day (fig. 346).

Fig. 346. — View of the vitellus, magnified rather more than two diame-
ters, exhibiting the circulation of the blastoderma completely developed : —
a, Vitellus ; b, vena s. sinus terminalis ; ft2, point of approximation to the
embryo of the terminal sinus, and its communication with the veins, g, g ;
c, aorta ; d, punctum saliens, or pulsating point of the heart ; /, /, arte-
ries of the blastoderma ; g, g, veins of the same (one inferior, two supe-
rior ; sometimes there is but one above as well as below) ; e, e, the fiddle
or guitar-shaped area pellucida ; h, the eye. (This figure will be found to
correspond in almost every particular with that of Pander, tab. iv. fig. 1,
of his well known work, Entwickelungsgeschichte des Huhnchens im Eie).
The more delicate ramifications of the vessels and their numerous inos-
culations with the bounding sinus are omitted.

DEVELOPMENT OF THE CHICK SECOND PEEIOD. 319

Immediately under the head of the embryo, three blood-red
bounding points are seen (fig. 346, d), the expression of the
alternating contractions of the three divisions of the heart,
which are now in the course of formation, — the sinus venosus
(fig. 339 A", 340 /), which receives the veins, and towards the
end of the third day shows traces of the two auricles, the
ventricle (339 i, 340 m), and the bulbus aorta (339 /, 340 ri),
divided from the ventricle by a contraction. In this period
the heart presents such diversities that it may be said to be in
a state of ceaseless metamorphosis, both as regards form and
position. On the second day, it is a somewhat spirally
twisted canal lying under the brain (fig. 339, i) ; on the
third day, it has drawn itself more backwards, become more
concentrated, and bent round, as it were, into a kind of loop
(fig. 340, m\ when it appears to project in the form of a tu-
mour between the ventral laminse (figs. 340 m, and 341 h],
first inclining to the left and then to the right, and being
all the while within the compass of the involucrum capitis
(fig. 347, /). The ventricle, which during the third day is
still canalicular, becomes more globular on the fourth day
(fig. 345, h\ and pointed underneath, so that it acquires the
proper heart-shape (fig. 342, B, g] ; it then lies very much
to the right, whilst the sinus venosus, which is become more
distinct from it, lies more to the left (fig. 345, behind K).
At the end of the third day, the constriction between the
ventricle and aortal bulb is already well marked (fig, 340, n).
On the fourth day, the muscular mass of the heart and the
septum ventriculorum is produced ; in the sinus venosus the
septum is not begun to be formed till the fifth day, and the
two apices into which the veins even on the third day were
seen to plunge (fig. 340, below I}, enlarge, and become the
auricles. Some time before the bulbus aortse becomes distinctly
pinched off (fig. 347, /), it divides at the beginning of the third
day into four pairs of vascular arches, which show themselves
through the abdominal laminae, the most posterior of the four
being the smallest (fig. 347, 1 — 4) ; after the formation of the
branchial fissures they He behind the sickle-shaped branchial
arches (figs. 339, 340, 343, B) ; they unite on either side
upon the vertebral column into an aortal root ; the two
roots blend more posteriorly, and form the common aorta
(fig. 347, h). The vascular arches undergo considerable

320

EMBEYOLOGT.

changes in the course of the fourth day : the first pair
gradually disappears and is at length obliterated, and the se-
cond becomes smaller ; but on either side there is a fifth arch
formed, which becomes larger on the fifth day, whilst the
second now disappears ; so that on this day there are three
vascular arches present, all of nearly equal magnitude (fig. 342,
A, hl, A2, 7i3). The carotid, and by and by the vertebral, arte-
ries now make their appearance, arising from the aortal roots,

and the bulbus aortse
undergoes a division in-
to two passages. On the
fourth day the aorta
gives off distinct vessels
between the several divi-
sions of the vertebrse ; it
then divides and fur-
nishes two principal
branches, which go off
in transverse directions
(figs. 348 c, 347 i, i, 339
m, m, 346,ff), and split-
ting intobranchlets, form
an extremely beautiful
network upon the out-
spread germinal mem-
brane ; the aorta after-
Fig. 347. — Embryo of the yolk depicted wards proceeds, first di-
in fig. 348, seen from the abdominal as- yided and then single
pect, magnified, a, Vagina s. involucrum ^ ^ yertebral &CQ1

capitis : b, vagina s. involucrum caude (a • «?

and b, folds of the germinal membrane lumn> glves off a niesen-
enveloping the head and tail) ; c, c, ante- teric artery (figs. 338,
rior passage of the involucrum capitis into 343, B, d 5), and finally
the lateral involucra ; d, vault of the mass splits into two branches
appertaining to the corpora quadrigemina ;
e, anterior cerebral mass or lobe; /, heart;
y, termination of the venous trunks in the
future atrium cordis ; h, aorta ; 1, 2, 3, 4,
the four branchial arteries ; z, i, arteries
of the blastoderma ; &, A translucent

that ramify upon the
allautois (figs. 341, 345,
n) . Almost simultane-
ously with the formation
of the arteries an accom-

crests of the dorsal laminae, rendered • f

somewhat \vavy by the water in which 111 \,

the embryo is immersed ; I, I, vertebral 1S developed ; the veins

of the germinal mem-

ammse.

DEVELOPMENT OF THE CHICK — SECOND PERIOD. 321

brane, however, are so far in opposition to the arteries, that
whilst these are directed
transversely towards the si-
nus terminalis (fig. 346, /,
/), those run parallel with
the long axis of the embryo ;
one inferior, larger vein ly-
ing on the left (figs. 346, g,
339, k~\ to which comes a
second, smaller, often scarce-
ly perceptible one, situated
on the ri2;ht, and either one

O *

or two superior veins (figs.
346, g, g, 339, k1} bringing

the blood from the vascular

area to the heart. The sys- Fig- 348.— Yolk of the hen's egg,

tern of the venae cavae is °f the, ?aturai size' ^flattened

, . , , , ,, , through loss of support, at the be-

evolved in the bodyot the ginning Of the third day of incubation,

embryo at a still earlier pe- exhibiting the earliest traces of the

riod than the arterial sys- circulation. — a, Vitellus ; b, embryo ;

tern, and the portal system c> c> arteries of the blastoderma ; d, d,

is distinctly separated on the ™ns °f. the blastoderma; *> ** sj™s

J ., . terminalis.

fourth day, and ramifying

in the liver. The circulation upon the germinal membrane is,
therefore, avitellicular circulation ; the blood courses from the
embryo through the two arteriae vitellinae s. omphalo-mesen-
tericae (fig. 346, /j/), to the sinus terminalis or vascular circle,
which on the fourth day appears quite full of blood ; from this
the blood is returned to the heart through the four venous
trunks — the venae vitellinae s. omphalo-mesentericae (fig. 346,
g, g, g). The smallest arteries and veins also communicate
with one another by their most delicate extremities, and form
a beautiful rete with rhomboidal-shaped meshes.

[§ 491. There is a very peculiar formation belonging to the
foetus alone, and having a temporary or transitory character,
which must now be mentioned, namely, the Wolffian bodies,
— corpora Wolffiana, or primordial, kidneys. These bodies
are a product of the vascular membrane, though the serous
layer would also seem to have some share in their formation.
They make their first appearance in the second half of the
third day, as a pair of narrow but thick striae, which sprout

322 EMBKYOLOGY.

outwardly from each mesenteric lamina, in the angle formed
between this and the ventral lamina in the line of the verte-
bral column, from the region of the heart as far as the allan-
tois. Even at this early period they exhibit interchanging
elevations and notches, and a canal or duct running in the
line of their long axis. On the fourth day the corpora Wolf-
iiana are recognized as being formed out of hollow coecal-like
appendages, which are attached along the course of the duct
or canal (fig. 341, q, q, q, q) ; on the fifth day they look very
broad and thick, and the coecal appendages are convoluted.
The germ-preparing sexual organs, the testicles and ovaria,
make their appearance as delicate striae on the inner sides of
the corpora Wolfiiana.

§ 492. The metamorphoses of the mucous layer of the ger-
minal membrane begin, during this period, with the formation
of the intestinal canal. After the mucous layer, above the
involucrum capitis, has struck in under the head, and formed
the anterior access to the intestinal canal, fovea cardiaca, the
same layer also bends in at the opposite extremity, over the
involucrum caudae or caudal envelope, and here forms the
posterior access to the intestine, foveola inferior ; by the
increased curvature of the embryo, and the growth of the
ventral laminae, these depressions form funnel-shaped hollows,
which terminate, in blind extremities, towards the head and
tail. Almost simultaneously with the formation of the bran-
chial fissures, or perhaps a little earlier, the space between
the fore end of the head and the heart grows thin, and the
mouth and fauces break through, so that a free communica-
tion results betwixt the fovea cardiaca and the cavity of the
amnion (fig. 343, B, h). The intestinum rectum, on the
other hand (the posterior funnel-shaped involution of the
mucous layer), continues longer closed. By the formation of
the mesenteric laminae the mucous layer is detached from the
ventral laminae, and pushed downwards (fig. 338, A, under e) ;
as soon as the mesenteric laminae have coalesced, the mucous
layer also converges from both sides under the mesentery,
and where it is accompanied by the prolongations of the vas-
cular lamina, which proceed from the mesenteric laminae, two
new laminae present themselves, the intestinal lami/ice, —
laminae intestinales, which run perpendicularly downwards

DEVELOPMENT OF THE CHICK — SECOND PERIOD. 323

(fig. 343, A, under h\ and the mucous layer being thus bent
inwards in a canalicular manner, forms the intestinal cleft —
an open canal in communication with the yolk, running for-
wards funnel-shaped, towards the faucial cavity, and backwards
in the same manner to the rectum. At the beginning of the
fourth day the intestinal cleft has contracted, and exhibits but
a very small opening, which, extending soon after into a canal
or sac (fig. 341, k, I), passes over the peripheral mucous layer
as the intestinal canal (fig. 343, B, n), and throws itself com-
pletely around the yolk. The oral and faucial cavity gapes
widely, and extends into a narrower part or canal, the esopha-
gus, from which, inferiorly and posteriorly, a diverticular sac-
culus sprouts (fig. 343, B, z), the first rudimentary appearance
of the lungs ; a little farther on, an elongated enlargement of
the intestine is perceived, which indicates the situation of the
future stomach (fig. 343, k) ; the intestine then expands, and
goes off funnel-shaped towards the yolk (fig. 343, n, and in a
later form, fig. 341, k, /), and in like manner towards the rec-
tum, which still terminates in a blind sac ; the limits between
the small and large intestines are indicated by the evolution of
a couple of diverticula — the capita coeca — towards the end of
the third day. About the middle of the third day various
other parts are indicated in connection with the intestinal
canal, which enlarges in the places where these are to appear,
and sprouts out towards or into the vascular layer ; thus, two
little hollow offsets show themselves as the rudiments of the
liver, in which a venous net-work by and by appears, that re-
solves itself into the portal system. At the beginning of the
fourth day the two lobes of the liver appear as lappets of some
breadth (fig. 341, i), in which the composition, by means of an
aggregation of blind sacs, is apparent somewhat later ; another
small offset, or bunch, also shows itself in the vascular laver,

V

between the lobes of the liver ; this is the rudimentary pan-
creas; it grows slowly, but, on the fifth day, when the convo-
lutions of the small intestine begin to be formed, it has enlarged
considerably ; at this time the spleen also makes its appear-
ance as a small red body. The pulmonic sac divides, and be-
comes more distinct, from the esophagus appearing first
pinched off from that part, and then provided with a pedicle —
the future trachea ; on the fifth or sixth day the lung of the
one side is completely distinct from that of the other, and each

Y 2

324 EMBRYOLOGY.

is attached to the common pedicle by a particular branch, the
future bronchi ; the pedicle has farther extended, as the trunk
of the trachea.

In the course of the first half of the third day, a small
vesicular-looking protuberance arises from thrt intestinum
rectum (fig. 339, n) ; this proves to be the allantois, which
grows into the caudal involucrum, and distends it. The al-
lantois is covered externally with a stratum of the vascular
layer (fig. 343, B, e, d), which it carries with it in its growth.
The growth of this part is very rapid, in the course of the
fourth day (figs. 341, 345, n) forcing its way through the
caudal involucre, and the part by which it is attached being
drawn out into a hollow pedicle. The external covering from
the vascular layer shows ramifications of the aorta, which
form a beautiful vascular rete. On the fifth day, the allantois
presents itself as a large peduncuhted bladder protruding
from the umbilicus (fig. 344, 5), which, bending to the right,
has penetrated between the mesenteric and ventral lamina, and
lies betwixt the amnion .and the serous envelope. At this
time, the allantois is nearly as large as the entire embryo
(fig. 344), being almost five lines in diameter,*

THIRD PERIOD IN THE HISTORY OF THE DEVELOPMENT OF THE
INCUBATED EGG : FROM THE COMMENCEMENT OF THE CIR-
CULATION IN THE ALLANTOIS TO THE EXCLUSION OF THE
EMBRYO.

[§ 493. The third and last period comprises the interval
from the sixth to the twenty-first day. The two first days,
however, comprehend almost all of general physiological inte-
rest which happens in this period, so that a shorter review
of the grand features of the changes which take place in the
embryo and ovum through its course will be sufficient. If
the egg be opened at the beginning of this period, it must be
done with great care, as the albumen has now entirely disap-
peared, and the embryo lies close to the membrane of the
shell ; the vitellary membrane has become exceedingly thin, is
very easily torn, and indeed is soon resolved entirely ; the
air-space at the blunt end of the egg has greatly increased in

* According to Rathke, the lungs are evolved from the first as a pair ;
he describes them, on the fourth day of the incubation, as two small,
laterally compressed, thin laminae, tapering off from before backwards, and
ending in a blunt point, which spring from the oesophagus.

DEVELOPMENT OF THE CHICK THIRD PERIOD.

325

size. The germinal membrane now extends over the whole
of the yolk ; or the mucous layer of this part has almost en-
tirely grown around, and so
given origin to a sac-like co-
vering, the vitellary sac
(vitelliculum, or vitellicle,
Owen), which encloses the
yolk ; the vascular layer has
grown around nearly two-
thirds of the yolk. The si-
nus terminalis of this layer
is now a mere seam in the
periphery of the area vascu-
losa, and in the course of the
next few days disappears en-
tirely ; the veins, and then
the arteries of the vascular
layer of the vitellary mem-
brane, disappear somewhat
later. On the other hand,
the allantois is growing with
great rapidity, and, on the
sixth day, forms a pretty large flattened bladder (fig. 349),
which, however, in the course of the seventh day, acquires
nearly twice its former size, and inclines so much to the
right side, that with the amnion, it covers the embryo com-
pletely, and comes in contact superiorly by means of its most
vascular side with the serous envelope, which is consequently
now completely separated from the amnion, to the formation
of which it had in the first instance contributed. After the
rupture of the vitellary membrane, all that remains of the al-
bumen collects at the sharp end of the egg, and is now much
more consistent ; the yolk, on the contrary, has become
much thinner and more diffluent, and the number of its glo-
bules has very greatly diminished ; the embryo lies more to-
wards the blunt pole of the egg, and on the sixth day, after
breaking open the shell, the first appearance of motion is
observed in slight twitchings of the extremities.

[§ 494. The most remarkable metamorphoses of the indi-
vidual organs on the sixth and seventh days are the following :
the spinous processes are now formed on the vertebral arches ;

Fig. 349.— Embryo of the fowl
with the allantois, a, already of
great size, and depressed or flat-
tened, the umbilical vessels, b,
branching over it ; c, external ear,
indicated by a depression ; d, cere-
bellum ; e, corpora quadrigeinina ;
/, hemispheres.

32G

EMBRYOLOGY.

a

the rudiments of the ribs become more conspicuous ; the imme-
diate tegument of the brain and spinal cord is perceived to be

composed of two layers ;
the largely developed
corpora quadrigemina
seem to advance with
less rapidity of growth
towards the end of the
seventh day, and the he-
mispheres soon equal
them in size (fig. 353,
c, c, d, d) ; the fornix is
evolved over the still open
third ventricle ; the cor-
pora striata and thalami
become conspicuous ; the
optic nerves, distinct from
one another at first, now
become connected in the

Fig. 350.— Embryo of the jackdaw chiasma ; the infundibu-
(corvus corone) nearly four lines in lum ig gtm d andwide ;
length, drawn under the simple lens. The ., ., ., r, i

amnion, a, a, surrounds it closely on the pituitary body ap-
every side ; the allantois, 6, protrudes pears ; the cerebellum is
from the abdominal sulcus ; the extremi- formed ; but the fourth
ties are visible as simple lamellae ; nume- ventricle is still widely
rous segments of the vertebrae and the ftnd g over ^

several cerebral cells are conspicuous; 1, „ „

behind the corpora quadrigemina appears a deeP posterior furrow of
the cerebellum, and then the depression the spinal cord. The eye
for the fourth ventricle; the ear is seen is developed in every part,
as a pediculated vesicle, c, springing from
the medulla oblongata : under it lie the
branchial arches and fissures ; d is the
eye ; e, the nasal fossa, behind which the
heart is perceived.

auditory vesicle the semi-
circular canals and cochlea are formed ; the nasal depression
has lengthened downwards into a nasal passage, which runs
between the superior maxillary bone and the frontal process,
the opposite halves of which have now become united. In
the extremities, the arm and thigh, both extremely short, can
be distinguished ; in the hand the rudiments of the three
digits, and in the foot those of the four toes, can be made

and is very large ; the
external opening of the
ear is conspicuous, and
connexion with the

in

I)ETELOPMEXT OF THE CHICK — THIRD PEE LOU. 327

out (fig. 352, B). The amnion is more and more distended,
and at the umbilicus is brought more together, so that it
becomes
drawn out
into an um-
bilical cord,
in which lie
the pedun-
cle of the
allantois
and a noose
of the intes-
tine (fig.
352, A, b] ;
the neck ad-
vances in
its evolu-
tion, and
the lower

jaw-bones Fig. 351.— An embryo similar to the last, but somewhat

are elon°-a- furtner advanced. The references arethe same as infig.350.

ted and assume the fashion of a beak. The heart acquires
the form it possesses in after-life, the several parts having
approximated and become more closely conjoined : the
auricles are divided, and cover the ventricles, which can
now even from without be perceived to be double ; the
aortal bulb at the same time appears produced from both
ventricles in an arched form, arising directly over the septum,
and being divided into two canals, the separation between
which becomes visible outwardly on the seventh day ; the
pericardium is formed. From the aorta there now arise
but two vascular arches on either side, and to the right a
middle third arch ; this and the two anterior arches are the
later chief divisions of the aorta, and are filled by the stream
of blood transmitted from the left ventricle ; the two poste-
rior arches are supplied on the seventh day with blood exclu-
sively from the right ventricle of the heart, and are the future
pulmonary arteries ; the arches all terminate in the descend-
ing aorta. The Wolffian bodies, and the formations that take
place upon or in connexion with them, have many remark-
able relations during this period. The shut sacs of which

J28

EMBRYOLOGY.

they are composed become longer and more tortuous ; they
evidently secrete, and with their elongated common ducts, to

which they look as if they
were attached, terminate in
the cloaca ; betwixt their
component shut sacs num-
bers of small points, which
consist of little convoluted
hanks of vessels, in every
particular like the Malpi-
ghian bodies of the kidney,

mav be observed. The kid-

it

neys show themselves be-
hind and above the Wolffi-
an bodies on either side of
the spinal column ; at first
they are lobulated greyish
masses, which sprout by
the outer edges of the
Wolffian bodies; this is
plainly to be seen on the
sixth day, perhaps even
sooner ; the ureters are
formed afterwards as their
especial excretory ducts.
The kidneys arise as inde-

Fig. 352.— Cluck with part of the
yolk, a, a, which communicates, hy
means of the delicate vitello-intestinal
duct, with the noose of the jejunum i,
which at this time lies within the
funis umbilicalis ; c, c, vasa lutea. B,
separate views of the anterior extremity,
which shows a distinct division into

three digits, a, and of the posterior ex- pendent formations ; and,
tremity, which shows traces of four independently of them, the

capsulse supra-renales are

evolved on their upper or anterior edge. The reproductive
organs, which had appeared as little marginal lappets, now
form two longish-shaped white bodies, and lie behind the
supra-renal capsules, at some little distance from these, on the
inner edge of the Wolffian body ; they are still of like size,
and it is impossible to distinguish whether testicles or ovaria
will be produced; so that of all the principal organs the ge-
nital are those thM are the latest recognizable in their rudi-

v_^

ments, and distinguishable in their future special forms.
The vessels of the allantois are developed with great vigour ;
two arteries arise from the aorta, and a large vein runs on
the under edge of the liver to the vena cav^, along with the

DEVELOPMENT Of THE CHICK — THIRD PEKIOD.

329

hepatic vein. The vessels of the ailantois become the umbi-
lical vessels.

The alterations that trans-
pire in the mucous layer are
of less moment : the or-
gans already formed in crease
in size ; the faucial cavity is

m

elongated as the oral cavity
in the bill-shaped maxillae ;
the esophagus extends; the
division into crop and mus-
cular stomach is distin-
guishable ; behind the loop
for the duodenum, andwhich

1 ,1 ,-1 A'i&« Ui»j. — rxn ciiiijivu ounicv> licit

encloses the pancreas, the ()lderethan that represented in fig. 349,
jejunum forms a noose of surrounded by the amnion as an am-
ple vesicle ; a, the amnion ; the eyes,
b, b, are very large ; c, c, the corpora
quadrigemina, now scarcely larger than
the hemispheres d. d ; the space be-
tween them is the third ventricle.

Fig. 353. — An embryo somewhat

the same length and tenui-
ty, which lies completely
out of the abdomen within
the umbilical cord, where,
bv means of a delicate short

tt

conduit, it communicates with the vitellicle or yolk-sac, — the
ductus mtello-intestinalis (fig. 352, A, «). The liver is large
and gorged with blood ; the trachea and lungs are entirely
separated from the esophagus ; the larynx makes its appear-
ance as a small enlargement upon the trachea.

[§ 495. The principal changes from the ninth to the eleventh
day are as follow : the hemispheres of the brain enlarge
greatly, at the cost, apparently, of the corpora quadrigemina,
and span the third ventricle posteriorly ; the cerebellum in-
creases, particularly in its middle or vermiform portion, by which
the fourth ventricle isnow completely hidden; in the spinal cord
the enlargements corresponding to the two pairs of extremi-
ties, become more conspicuous ; the fibrous structure of the
brain and spinal cord is apparent ; the eyes proceed in their
development, and attain still more colossal relative dimensions ;
the eyelids appear as a circular-shaped fold of the skin ; the
external organ of hearing increases in width and depth. The
bulbs of the feathers become apparent in certain districts, first
along the middle line of the back, upon the haunches, and
over the rump ; the joints of the extremities are more solidly

330 EMBRYOLOGY.

and distinctly evolved ; the muscular parts are very apparent,
and separated into bundles under the skin ; the nerves are
more conspicuous, and the motions of the embryo are stronger;
the neck lengthens greatly. In the heart the external separa-
tion of the bulbus aortse into two distinct canals follows ; the
vessel proceeding from the left ventricle gives off larger
carotids from its anterior arches ; on these appear the little
thyroid bodies. These two aortal arches (trunci anonymi)
represent the earlier third branchial vascular arch ; the
asymmetrical vascular arches appearing behind them, on
the right side, is the future aorta clescendens. From the stem
arising out of the right ventricle proceed the two most poste-
terior (the earlier fifth) of the branchial vascular arches ;
they do not yet give off any pulmonary branches, and still
terminate posteriorly in the aorta ; at a later period they be-
come the proper pulmonary arteries. The corpora Wolffiana
become shorter, and smaller every way, and their excretory
duct longer ; the kidneys increase in size. The germ-pre-
paring sexual organs begin about this time to differ manifestly
in their form : the testicles become elongated, cylindrical, and
continue of equal size ; the ovaries remain flattened, grow un-
equally, the right first ceasing to make any progress and then
disappearing, the left enlarging proportionally with the other
parts. The oviducts are distinct, but the right, like the ovary
to which it corresponds, is arrested in its development. The
gall-bladder becomes conspicuous as a diverticulum of the
biliary duct. The bursa Fabricii emerges from the cloaca;
the allantois grows still more over the embryo. The vessels
on the vitellary membrane, especially on its under-surface,
are numerous and large ; the veins are turgid and tortuous
(fig. 352, A, c), and appear stained of a yellow colour,
whence they are often called vasa lutea.

[§ 496. It is in the course of the last days of the second
week that the epidermic formations are produced — the feather
bulbs, the nails, and the scaly coverings of the feet ; ossifi-
cation also begins in many bones, the muscular parts get
stronger, the eyelids are well formed, and in the ear the tvm-

O v *

panum has appeared. The Wolffian bodies are ever shorter
and smaller ; the testes acquire their excretory ducts ; the left
ovary is conspicuous, and the corresponding oviduct is hollow,
whilst the same parts on the right side have shrunk entirely.

DEYELOPMEirT OF THE CHICK — THIED PERIOD.

33 1

The intestine makes several turns outside of the umbilicus,
and continues in communication with the vitellary sac by
means of the vitellary duct ; upon the inner surface of the
vitellary sac, and over the tortuous veins, membranous pro-
ductions— puckered or wrinkled folds — make their appear-
ance ; and at the same time similar formations occur upon the
mucous membrane of the intestine. The allantois has now
grown completely around the embryo, so that the ovum — the
vitellary sac, the remaining albumen, &c. included — is com-
pletely enve-
loped anew as
it were,and will
now retain its
form even after
the shell is re-
moved (fig. 354,

b ; from the
Kestril — Falco
tinnunculus) ;
the serous co-
vering disap-
pears.

[§ 497. In
the beginning
of the third
week, the em-
bryo, straitened
for room, from
the transverse
axis of the egg
comes more and
more into the

Fig. 354. — Embryo of the Falco tinnuncnlns,
much farther advanced than that of the fig. 353. Jt
is represented enclosed in its membranes, and of the
natural size ; but heing removed from the shell, its
weight has caused it to spread, and to look longer
than it is in fact. The embryo of this falcon, by
reason of the transparency of the membranes, is pe-
culiarly fitted to serve for the demonstration of the
long axis, which, relative position of the several parts: a, the embryo
it finally fills ; shining through the membranes ; /, /, the eyes of

great size, seen from above ; b, b, the ailantois, has
grown completely around the embryo, and so forms
a perfect envelope, the chorion, whose principal vas-
cular branches are perceived ; c, c, the amnion ; d. d,

the head is
turned towards
the breast, and

_ , . «J A «-VA « \_ ti v^ u u,.a »_> UW.JU WW« 1 UV* B ^ 1 \> *.L\J H. 1. L 1 UAXSU • U*' . I V.

mostly lies un- the yolk-sac ; e. the albumen ; g, the coccyx, with the

der the

right

feathers beginning to sprout.

the al-
lantois has inclosed the whole embryo and vitellary sac, and

wing;

332

EMBRYOLOGY.

having contracted adhesions with itself, forms an uninter-
rupted cyst or envelope for the entire contents of the egg,

being everywhere in imme-
diate contact with the mem-
brane of the shell, from which
it must be peeled when they
are separated ; in the inte-
rior of the allantois, white

\V~ * ~\_X"" J / r~(* A\\

V;u ^<(vy f) i flocculent precipitates from

the urine occur, and these
accumulate at length to such
an extent that they conceal

,. , the embryo in a greater or
Fior. 355. — Magnified view of the , , J mi n

embrvo of the Lacerta ayilis, two less degree' The allantois,
and a half lines in length, for con- as the complete fcetal enve-
trast with the other embryos figured : lope, is entitled the chorion.
a, corpora quadrigemina ; b, cleft of jn the brain, the corpora
the eye ; c olfactory depression ; d, quadrigemina, which have
branchial fissures already disappear- . & , , , , . ,

ing ; C, anterior extremity ; /, hinder remained very much behind
extremity; ff, tail. in development, are thrown

backwards under the hemi-
spheres ; the pineal gland and cerebellum increase ; the latter
becomes marked with deep scissures. Over the eye, the eye-
lids grow till they meet, but without uniting ; the iris advances,
the cornea rises, the lenticular prominence remains, whilst the
lens recedes, and so the anterior chamber, which had hitherto
been wanting, is produced ; there is no appearance of pupillary
membrane. In the ear, the labyrinth becomes osseous at the
beginning of the third week. In the heart, the valvular sys-
tem is evolved ; the anterior arteries are detached more and
more from the descending aorta, and disappear altogether to-
wards the end of the period ; the pulmonary arteries become
much larger, and their terminations in the aorta have con-
tracted and become mere anastomosing channels — ductus ar-
teriosi. The kidneys grow rapidly. The corpora Wolffiana
shrink continually, but in male embryos they may still be de-
tected as rudiments near the testes, even after the epoch of
foetal life is over. The right ovary, as has been stated, is ar-
rested in its growth, and is soon after birth completely absorbed ;
the right oviduct also disappears, although a trace of it may be
discovered in some birds at every period of their life. From

BIRTH OF THE CHICK. 333

the testes delicate vasa efferentia are developed, which, after
passing through the Wolffian bodies, unite into a filiform vas
deferens, which in its turn is evolved out of, or, more cor-
rectly, into the excretory duct of the Wolffian body. The vitel-
lary sac shrinks more and more, its contents diminishing in
quantity, and becoming still more consistent. It is drawn into
deep sacculated compartments by the main trunks of the um-
bilical vessels ; the albumen and amniotic fluid are lessening
continually in quantity. The tegumentary umbilicus is still
freely open at the beginning of the last week ; and with the
advancing growth of the intestinal canal, a greater number of
convolutions of the bowel pass out of the abdominal cavity ;
on the nineteenth day the prolapsed intestine returns in some
degree into the abdomen again, and draws the yolk, with
which it is still in uninterrupted connexion by means of the
very considerable vitellary duct, along with it into the belly,
upon which the mucous and vascular layers of the vitellary
sac follow, whilst the serous layer increases, becomes thicker,
and detaches itself from both the other layers. The whole
vitellary sac is not thus taken up into the abdomen, only a
part of it enters, and this expands in the cavity, whilst the
part that is excluded is cut off by the contracting umbilical
ring. The vitellary duct is of considerable width, and arises
funnel-shaped from the intestine ; long after birth there is still
a little diverticulum of the jejunum to be discovered in its for-
mer situation ; nay, in some birds this diverticulum continues
through life as a normal feature in their structure. The com-
munication with the vitellus is at length obliterated, becoming
a mere thread, on which a yellow knot, the last remains of the
yolk, may not unfrequently be observed.

BIRTH OF THE CHICK.

[§ 498. Two days before its exclusion, the chick may occa-
sionally be heard chirping feebly within the shell, for the cho-
rion (the allantois) is readily torn by the point of the beak,
which then comes into contact with the air contained in the
air-chamber ; along with the imperfect respiration that now
goes on, the circulation through the umbilical vessels proceeds
unimpeded. The violent motions of the chick occasion cracks
in the shell ; the beak assists, and holes are produced. The
bill, so soft in all other parts, is furnished at this period with

354 EMBRYOLOGY.

a very remarkable, hard, horny process near its point, evidently
to enable the young creature to break through the shell, for
the process in question falls off very shortly after the escape
of the bird. The labour of getting free from the shell gene-
rally lasts half-a-day ; at length the upper part is raised, the
chick pushes out its feet, draws its head from under its wing,
and erecting itself quits the shell completely. The remain-
der of the chorion and amnion, which, with the closure of
the umbilicus, could no longer be nourished, shrivel, fall off,
and are left behind in the shell.

PHYSICAL AND CHEMICAL CHANGES IN THE EGG DTJKING

INCUBATION.

[§ 499. Various physical and chemical changes take place in
the egg during the period of incubation. It loses weight : in
the first week, to the extent of five per cent. ; in the second,
the amount is thirteen per cent. ; and in the third, sixteen per
cent. So that an incubated egg, with an embryo ready to
emerge from it, is altogether lighter than one that is just laid;
a new-laid egg sinks in water, — an egg at the end of the
period of incubation swims. The cause of this loss of weight
lies in the evaporation of the watery part of the albumen ;
the same thing happens, though more slowly, in unincubated
eggs from keeping ; the greater rapidity of the loss in the
incubated egg arises merely from the greater heat to which it
is subjected. Another consequence of the evaporation is the
formation and rapid enlargement of the air-space, which, as
we have seen (§ 477), is first produced after the egg is laid.
It is probable that the evaporation in question is connected
with chemical changes, for the air contained in the blunt end
of the egg is not simple atmospheric air, but contains a
larger proportion of oxygen, the amount varying between
twenty-five and twenty-seven per cent. This hyper-oxyge-
nated air serves the embryo in the process of respiration, or
aeration, that is carried on by the medium of the allantois ;
for eggs may be incubated to the perfect maturity of the ein-
bryo, even without the contact of the external atmospheric
air, and may be hatched alike well in pure oxygen and in va-
rious irrespirable gases ; for example, pure hydrogen, nitro-
gen, &c. At the beginning of the incubation the fluid albu-
men contains a small quantity of oil, apparently communicated

CHANGES IK THE EGG DTJR1XG INCUBATION. 335

to it from the yolk ; when the incubation has advanced con-
siderably, the albumen loses almost the whole of its water and
salts ; these seem to be transferred to the yolk, which admits
of explanation, for the vitellary sac bursts and draws the
albumen, now changed into a thick mass, into it. ]3y this
accession of matter, the yolk enlarges during the first half of
the period of incubation, but becomes thinner ; the incessant
demand upon it, however, for materials for the growth of the
embryo, causes it again to shrink and to become more consis-
tent towards the end of the period (§ 494). The proportion
of chemical elements of the vitellus and white vary consider-
ably ; the quantity of phosphorus contained in the albumen
lessens, but increases in the yolk, and again appears in com-
bination with oxygen and calcium as a phosphate of lime,
which in the period of ossification is plentifully required
for the consolidation of the bones ; as the quantity of lime
contained in an egg at the time it is laid is extremely small,
and becomes very large at a subsequent period, the earth must
be acquired in some way with which we are not at present
well acquainted. As it is not very probable that the lime is
derived from the shell, it may perhaps be produced from other
matters under the influence of the organic agencies ; the same
may be said of the iron, the quantity of which increases
greatly during incubation.] *

* The whole of this article on the development of the chick is from
Professor Wagner, Elements of Physiology, p. 84, et seg. It forms a
valuable complement to the chapter on Embryology. — ED.

336 EMBRYOLOGY.

SECTION III.

ZOOLOGICAL IMPORTANCE OF EMBRYOLOGY.

§ 500. As a general result of the observations which have
been made, up to this time, on the embryology of the various
classes of the animal kingdom, especially of the vertebrata,
it may be said, that the organs of the body are successively
formed in the order of their organic importance, the most es-
sential being always the earliest to appear. In accordance
with this law, the organs of vegetative life, the intestines and
their appurtenances, make their appearance subsequently to
those of animal life, such as the nervous system, the skeleton,
&c. ; and these, in turn, are preceded by the more general
phenomena belonging to the animal as such.

§ 501. Thus we have seen that, in the fish, the first changes
relate to the segmentation of the yolk and formation of the germ,
which is a process common to all classes of animals. It is not
until a subsequent period that we trace the dorsal furrow, which
indicates that the forming animal will have a double cavity,
and consequently belong to the division of the vertebrata ;
an indication afterwards fully confirmed by the successive ap-
pearance of the brain and the organs of sense. Later still,
the intestine is formed, the limbs become evident, and the
organs of respiration acquire their definite form, thus enabling
us to distinguish with certainty the class to which the animal
belongs. Finally, after the egg is hatched, the peculiarities
of the teeth, and the shape of the extremities, mark the genus
and species.

§ 502. Hence the embryos of different animals resemble
each other more strongly when examined in the earlier stages
of their growth. We have already stated that, during
almost the whole period of embryonic life, the young fish and
the young frog scarcely differ at all : so it is also with the
young snake compared with the embryo bird. The embryo
of the crab, again, is scarcely to be distinguished from that of
the insect ; and if we go still farther back in the history of
development, we come to a period when no appreciable differ-
ence whatever is to be discovered between the embryos of the
various departments. The embryo of the snail, when the

ZOOLOGICAL IMPORTANCE OF EMBRYOLOGY. 337

germ begins to show itself, is nearly the same as that of a fish
or a crab. All that can be predicted at this period is, that the
germ which is unfolding itself will become an animal ; but
the class and the group are not yet indicated.

§ 503. After this account of the history of the develop-
ment of the egg, the importance of embryology to the study
of zoology cannot be questioned. For evidently, if the for-
mation of the organs in the embryo takes place in an order
corresponding to their importance, this succession must of
itself furnish a criterion of their relative value in classification.
Thus, those peculiarities that first appear should be considered
of higher value than those that appear later. In this respect,
the division of the animal kingdom into four types, the ver-
tebrata, the articulata, the mollusca, and the radiata, cor-
responds perfectly with the gradations displayed by embry-
ology.

§ 504. This classification, as has been already shown, is
founded essentially on the organs of animal life, the nervous
system and the parts belonging thereto, as found in the per-
fect animal. Now, it results from the above account, that in
most animals the organs of animal life are precisely those that
are earliest formed in the embryo ; whereas those of vege-
tative life, on which is founded the division into classes, orders,
and families, such as the heart, the respiratory apparatus, and
the jaws, are not distinctly formed until afterwards. There-
fore a classification, to be true and natural, must accord with
the succession of organs in the embryonic development. This
coincidence, while it corroborates the anatomical principles of
Cuvier's classification of the animal kingdom, furnishes us
with new proof that there is a general plan displayed in
every kind of development.

§ 505. Combining these two points of view, that of Embry-
ology and that of Anatomy, the four divisions of the animal
kingdom may be represented by the four figures which are to
be found, at the centre of the diagram, at the beginning of
the volume.

§ 506. The type of VERTEBRATA, having two cavities, one
above the other, the former destined to receive the nervous
system, and the latter, which is of a larger size, for the intes-
tines, is represented by a double crescent united at the centre;,
and closing above, as well as below

z

338 EMBiiYULOGZ.

§ 507. The type of AETICULATA, having but one cavity, grow-
ing from below upwards, and the nervous system forming a
series of ganglions, placed below the intestine, is represented
by a single crescent, with the horns directed upwards.

§ 508. The type of MOLLTTSCA having also but one cavity,
the nervous system being a simple ring around the esophagus,
with ganglions above and below, from which threads go off
to all parts, is represented by a single crescent with the horns
turned down.

§ 509. Finally, the type of RADIATA, the radiating form of
which is seen even in the youngest individuals, is represented
by a star.

CHAPTER ELEVENTH.

PECULIAR MODES OF REPRODUCTION.
SECTION I.

GEMMIPAKOTJS AXD FISSIPAKOUS EEPKODUCTIO^.

§ 510. WE have shown, in the preceding chapter, that ovula-
tion, and the development of embryos from eggs is common to
all classes of animals, and must be considered as the great
process for the reproduction of species. Two other modes
of propagation, applying, however, to only a limited number
of animals, remain to be mentioned, namely, gemmiparous
reproduction, or multiplication by means of buds, and fissi-
parous reproduction, or propagation by division, and also some
still more extraordinary modifications yet involved in much
obscurity.

§511. Reproduction by buds occurs among polyps, medusae,
and some infusoria. On the stalk, or even on the body of

v

the Hydra (fig. 170), and of many infusoria (fig. 356), there
are formed buds, like those of plants. On
close examination they are found to contain Fig. 356.

young animals, at first very imperfectly
formed, and communicating at the base with
the parent body, from which they derive
their nourishment. By degrees the animal
is developed ; in most cases the tube by
which it is connected with the parent
withers away, and the animal is thus de-
tached, and becomes independent. Others
remain through life united to the parent
stalk, and in this respect present a more striking analogy to
the buds of plants ; but in polyps, as in trees, budding is
only an accessary mode of reproduction, which presupposes
a trunk already existing, originally the product of ovulation.
§ 512. Reproduction by division, or fissiparous reproduc-

z -1

340

EEPHODUCTI01ST.

Fig. 357.

Fig. 358.

tion, is still more extraordinary ; it takes place only in polyps

and some infusoria. A cleft, or fis-
sion, at some part of the body takes
place, very slight at first, but con-
stantly increasing in depth, so as
to become a deep furrow, like that
observed in the yolk, at the begin-
ning of embryonic development ; at
the same time the contained organs
are divided and become double, and
thus two individuals are formed of
one, so similar to each other that it
is impossible to say which is the
parent and which the offspring.
The division takes place sometimes
vertically, as, for example, in Vorti-
cella (fig. 357, c, d), and in some po-
lyps (fig. 358, a, d) ; and sometimes
transversely. In some infusoria, the
ParameeiafoY instance, this division
occurs as often as three or four
times in a day.

§ 513. In consequence of this
same faculty many animals are able
to reproduce various parts of their
bodies when accidentally lost. It is well known that crabs
and spiders, on losing a limb, acquire a new one. The same
happens with the rays of star-fishes ; the tail of a lizard
is also readily reproduced; salamanders even possess the
faculty of reproducing parts of the head, including the eye
with all its complicated structure. Something similar takes
place in our own bodies, when a new skin is formed over a
wound, or when a broken bone is reunited.

§ 514. In some of the lower animals this power of repara-
tion is carried much farther, and applies to the whole body,
so as closely to imitate fissiparous reproduction. If an earth-
worm or a fresh-water polype be divided into several pieces, the
injury is soon repaired, each fragment speedily becoming a per-
fect animal. Something like this reparative faculty is seen in the
vegetable as well as in the animal kingdom. A. willow-branch,
planted in a moist soil, throws out roots below and branches

ALTEENATE AND EQUIVOCAL EEPEODUCTION. 341

above ; and thus, after a time, assumes the shape of a perfect
tree.

§ 515. These various modes of reproduction do not exclude
each other. All animals which propagate by gemmiparous or
fissiparous reproduction also lay eggs. Thus the fresh-water
polyps (Hydra) propagate both by eggs and by buds. In For-
ticella, according to Ehrenberg, all three modes are found ; it
is propagated by eggs, by buds, and by division. Ovulation,
however, is the common mode of reproduction, the other modes,
and also alternate reproduction, are only additional means
employed by nature to secure the perpetuation of the species.

SECTION II.

ALTEENATE AND EQUIVOCAL EEPEODUCTIQN.

§ 51G. IT is a matter of common observation, that individuals
of the same species have the same general appearance, by
which their peculiar organization is indicated. The transmis-
sion of these characteristics, from one generation to the next,
is justly considered as one of the great laws of the animal and
vegetable kingdoms. It is, indeed, one of the points on which
the definition of species is generally founded. We would,
however, adopt the new definition of Dr. S. G. Morton, who
defines species to be "primordial organic forms."

§ 517. But it does not follow that animals must resemble
their parents in every condition, and at every epoch of then*
existence ; on the contrary, as we have seen, this resemblance
is very faint in most species at birth, and some undergo com-
plete metamorphoses before attaining their final shape, such
as the caterpillar and the tadpole, the butterfly and the frog.
Nevertheless, we do not hesitate to refer the tadpole and the
frog to the same species ; and so with the caterpillar and the
butterfly, because we know that there is the same individual
observed in different stages of development.

§ 518. There is also another series of cases in which the
offspring not only do not resemble the parent at birth, but
moreover remain different during their whole life, so that their
relationship is not apparent until a succeeding generation.
The son does not resemble the father, but the grandfather; and
in some cases the resemblance reappears only at the fourth or
fifth generation, and even later. This singular mode of re-
production has received the name of alternate generation.

342

REPRODUCTION.

The phenomena attending it have been of late the object of
numerous scientific researches, which are the more deserving
of our attention, as they furnish a solution of several problems
alike interesting in a zoological and philosophical point of
view.

§ 519. Alternate generation was first observed among the
Scilpce, marine mollusca, without shells, belonging to the
family tunicata. They are distinguished by the curious pe-
culiarity of being united together in considerable numbers,
so as to form long chains, which float in the sea (fig. 359),
the mouth (m), however, being free in each. The indivi-
duals thus joined in floating colonies produce eggs ; but in
each animal there is generally but one egg formed, which is
developed in the body of the parent, and from which is hatched
a little mollusk (fig. 360), which remains solitary, and differs
in many respects from the parent. This little animal, on the
other hand, does not produce eggs, but propagates by a kind
of budding, which gives rise to chains already seen within the
body of the parent (a), and these again bring forth solitary
individuals, &c.

Fi?. 359. Fig. 360.

§ 520. In some parasitic worms, alternate generation is
Fig. 361. accompanied by still more extraordinary phe-
nomena, as shown by the late discoveries of
Steenstrup, a Danish naturalist. Among the
numerous animals inhabiting stagnant pools,
in which fresh-water-mollusca (particularly
Lymncca and Paludina) are found, there is a
small worm, known to naturalists under the
name of Cercaria (fig. 361). When examined
with a lens, it looks much like a tadpole, with a
long tail, a triangular head, and a large sucker
(a) in the middle of the body. Various viscera
appear within, and among others a very dis-
tinctly forked cord (c), embracing the sucker
and winch is thought to be the liver.

ALTERNATE AND EQUITOCAL KEPRODUCTION.

343

Fig. 363.

§ 521. If we watch these worms, which always abound in
company with the mollusks mentioned, we find them after a
while attaching themselves, by means of their sucker, to the
bodies of these animals. When fixed they soon undergo con-
siderable alteration. The tail, which was pre-
viously employed for locomotion, is now useless, Fig. 362.
and falls off, and the animal surrounds itself with
a mucous substance, in which it remains nearly
motionless, like a caterpillar on its trans-
formation into the pupa. If, however, after
some time we remove the little animal from its
retreat we find it to be no longer a Cercaria,
but an intestinal worm called Distoma, with two
suckers, having the shape of fig. 362. The
Distoma, therefore, is only a particular state of
the Cercaria, or rather the Cercaria is only the
larva of the Distoma.

§ 522. What now is the origin of the Cerca-
ria ? The following are the results of the latest
researches on this point. At certain periods of
the year, we find in the viscera of the Lymncea
(one of the most common fresh-water mollusks)
a quantity of little worms of an elongated form,
with a well-marked head, and two posterior pro-
jections like limbs (fig. 363). On examining
these worms attentively under the microscope
we discover that the cavity of their body is
filled by a mass of other little worms, which a
practised eye easily recognizes as young Cer-
cari<z,* the tail and the ther characteristic fur-
cated organ (fig. 364, a) being distinctly visible
within it. These little embryos increase in

V

size, distending the worm containing them, and
which seemingly has no other office than to
protect and forward the development of the
young CercaricB. It is, as it were, their living
envelope. On this account, it has been called
the nurse.

§ 523. When they have reached a certain size, the young
Cercarice leave the body of the nurse, and move freely in the
abdominal cavity of the Lijmncea, or escape from it into the

Fig. 364.

344 KEPRODUCTION.

water to fix themselves, in their turn, to the body of another
mollusk, and begin their transformations anew.

§ 524. But this is not the end of the series. The nurses of

the Cercaria are themselves the offspring of little
Fig. 365. worms of yet another kind. At certain seasons,

we find in the viscera of the Lumn&a worms some-

v

what like the nurses of the Cercaria in shape (fig.
365), but rather longer, more slender, and having a
much more elongated stomach (s). These worms
contain, in the hinder part of the body, little em-
bryos (a), which are the young nurses of figures
363, 364. This generation has received the name
of grand-nurses.

§ 525. Supposing these grand-nurses to be the
immediate offspring of the Distoma (fig. 362), as
is probable, we have thus a quadruple series of
generation. Four generations and one metamorphosis are re-
quired to evolve the perfect animal ; in other words, we find
no resemblance to the parent in any of its progeny, until we
arrive at the fourth generation or the great-grandson

§ 526. Among the Aphides, or plant-lice, the number of
generations is still greater. The first generation, which is
produced from eggs, soon undergoes metamorphoses, and then
gives birth to a second generation, which is followed by a
third, and so on ; so that it is sometimes the eighth or ninth
generation before the perfect animals appear as males and fe-
males, the sexes being then for the first time distinct, and the
males provided with wings. The females lay eggs which are
hatched the following year, to repeat the same succession.
Each generation is an additional step towards the perfect state;
and as each member of the succession is an incomplete ani-
mal, we cannot better explain their office, than by considering
them analogous to the larvse of the Cercaria, that is, as nurses.*

* There is a certain analogy between the larvae of the plant-louse
(Aphis] and the neuters or working ants and bees. This analogy has
given rise to various speculations, and, among others, to the following
theory, which is not without interest. The end and aim of all alternate
generation, it is said, is to favour the development of the species in its
progress towards the perfect state. Among the plant-lice, as among all
the nurses, this end is accomplished by means of the body of the
nurse. Now a similar end is accomplished by the working ants and

ALTERNATE AND EQUIVOCAL EEPKODUCTIOX.

345

Fig. 366.

§ 527. The development of the Medusae is not less instruct-
ive. According to the observations of M. Sars, a Norwegian
naturalist, the Medusa brings forth living young, which, after
having burst the covering of the egg, swim about freely for
some time in the body of the mother. When born, these ani-
mals have no resemblance whatever to the perfect Medusa.
They are little cylindrical bodies (fig. 366, a), much resembling
infusoria, and like them covered with minute cilia, by means
of which they swim with much activity.

§ 528. After swimming about freely in the water for some
days, the little animal fixes
itself by one extremity (fig.
366, e). At the opposite ex-
tremity a depression is gra-
dually formed, the four cor-
ners (b, /) become elongated,
and by degrees are trans-
formed into tentacles (c).
These tentacles rapidly mul-
tiply, until the whole of the
upper margin is covered with
them (g). Then transverse wrinkles are seen on the body at
regular distances, appearing first above and extending down-
wards. These wrinkles, which are at first very slight, grow
deeper and deeper, and, at the same time, the" edge of each
segment begins to be serrated, so that the animal presents the
appearance of a pine cone, surmounted by a tuft of tentacles (h) ;

bees, only, instead of being performed as an organic function, it is
turned into an outward activity, which makes them instinctively watch
over the new generation, and nurse and take care of it. It is no longer
the body of the nurse, but its own instincts, which become the instrument
of the development. This seems to receive confirmation from the fact that
the working bees, like the nurses of the plant-lice, are barren females. The
attributes of their sex, in both, seem to consist only in their solicitude
for the welfare of the new generation, of which they are the natural
guardians, but not the parents. The task of bringing forth young is con-
fided to other individuals, to the queen among the bees, and to the female
of the last generation among the plant-lice. Thus the barrenness of the
working bees, which seems an anomaly as long as we consider them
complete animals, receives a very natural explanation so soon as we regard
them merely as nurses.

346

REPRODUCTION.

whence the name of Strobila, which was originally given to it,
before it was known to be only a transient state of the jelly-
fish. The separation constantly goes on, until at last the divi-
sions are united by only a very slender axis, resembling a
pile of cups placed within each other (i) . The divisions are
now ready for separation ; the upper ring first disengages it-
self, and then the others in succession.* Each segment (d)
then continues its development by itself, until it becomes a
complete Medusa (k) ; while, according to recent researches,
the basis or stalk remains and produces a new colony.

§ 529. It is thus, by a series of metamorphoses, that the
little animal which, on leaving the egg, has the form of the
infusoria, passes in succession through all the phases we have
described. But the remarkable point in these metamorpho-
ses is, that what was at first a single individual is thus trans-
formed, by tranverse division, into a number of entirely dis-
tinct animals, which is not the case in ordinary metamor-
phoses. Moreover, the upper segment does not follow the
others in their development. Its office seems to be accom-
plished as soon as the other segments begin to be indepen-
dent ; being intended merely to favour their development, by
securing and preparing the substances necessary to their
growth. In this respect it resembles the nurse of the Cer-

cana.

Fig. 367.

§ 530. The Hydraform-Polyps present phenomena no less

numerous and strange. The Campanularia
has a branching, plant-like form, with little
cup-shaped cells on the ends and in the axils
of the branches, each of which contains a
little animal. These cups have not all the
same organization. Those at the extre-
mity of the branches (a], and which appear
first, are furnished with long tentacles,
wherewith they seize their food (fig. 367).
Those in the axils of the branches, and
which appear late, are females (b), and
have no such tentacles. Inside of the lat-
ter, little spherical bodies are found, each

* These free segments have been described as peculiar animals, under
the name of Ephyra.

ALTEEXATE A1STD EQTIIYOCAL EEPEODUCTTOX. 347

having several spots in the middle ; these are the eggs.
Finally, there is a third form, different from the two prece-
ding, produced by budding from the female polyp, to which
it in some way belongs (c). It is within this that the eggs
arrive, after having remained some time within the female.
Their office seems to be to complete the incubation, for it is
always within them that the eggs are hatched.

§ 531. The little animal, on becoming free, has not the
slightest resemblance to the adult polyp. As in
the young Medusa, the body is cylindrical, and co- Fig. 368.
veredwith delicate cilia (fig. 368) . After having re-
mained free for some time, the young animal fixes it-
self and assumes aflattened form. By degrees alittle
swelling rises from the centre, which elongates, and
at last forms a stalk. This stalk ramifies, and we
soon recognize in it the animal of fig. 367, with
the three kinds of buds, which we may consider
as three distinct forms of the same animal.

§ 532. The development of the Campanularia presents, in
some respects, an analogy to what takes place in the repro-
duction of plants, and especially of trees. They should be
considered as groups of individuals, and not as single indivi-
duals. The seed, which corresponds to the embryo of the
polyp, puts forth a little stalk. This stalk soon ramifies by
gemmiparous reproduction, that is, by throwing out buds
which become branches. But ovulation, or reproduction by
means of seeds, does not take place until an advanced period,
and requires that the tree should have attained a considerable
growth. It then produces flowers with pistils and stamens,
that is, males and females, which are commonly united in one
flower, but which in some instances are separated, as in the
hickories, the elders, the willows, &c. &c.*

* Several plants are endowed with organs similar to the third form
of the Polyps, as seen in the Campanularia : for example, the liver-
wort (Marc/iantia polymorpha}, which has at the base of the cup a small
receptacle, from the hottom of which little disk-like bodies are constantly
forming, these, when detached, send out roots, and gradually become
complete individuals. Besides that, we find in some polyps, as in piants,
the important peculiarity, that all the individuals are united in a com-
mon trunk, which is attached to the soil ; and that all are intimately
dependent on each other, as long as they remain united. And if we
compare, in this point of view, the various species in which alternate re-

348 BEPRODTJCTION.

SECTION III.

CONSEQUENCES OF ALTERNATE GENERATION.

§ 533. THESE various examples of alternate generation render
it evident, that this phenomenon ought not to be considered
as an anomaly in nature ; but as the special plan of develop-
ment, leading those animals in which it occurs to the highest
degree of perfection of which they are susceptible. Moreover, it
has been noticed among all types of the invertebrated animals ;
while among the vertebrata it is as yet unknown. It would
seem that individual life in the lower animals is not denned
within such precise limits as in the higher types, owing, perhaps,
to the greater uniformity and independence of their consti-
tuent elements, the cells ; and that instead of passing at one
stride, as it were, through all the phases of their development,
in order to accomplish it, they must either be born in a new
form, as in the case of alternate generation, or undergo meta-
morphoses, which are a sort of second birth.

§ 534. Many analogies may be discovered between alter-
nate reproduction and metamorphosis. They are parallel
lines leading to the same end, namely, the development of
the species. Nor is it rare to see them coexisting in the same
animal. Thus, in the Cercaria, we have seen an animal pro-
duced from a nurse afterwards transformed into a Distoma,
by undergoing a regular metamorphosis.

§ 535. In each new generation, as in each new metamor-
phosis, a real progress is made, and the form which results is
more perfect than its predecessor. The nurse that produces
the Cercaria is manifestly an inferior state, just as the chry-
salis is inferior to the butterfly.

production has been observed, we find that the progress displayed in each
type consists precisely in the increasing freedom of the individual in its
various forms. At first, we have all the generations united in a common
trunk, as in the lower polyps and in plants ; then in the Medusa and in some
of the hydraform polyps (the Coryne), the third generation hegins to disen-
gage itself. Among some of the intestinal worms (the D-istoma), the third
generation is enclosed within its nurse, and this in its turn is contained
in the body of the grand nurse, while the complete Distoma lives as a
parasitic worm in the body of other animals, or even swims freely about
in the larva state, as Cercaria. Finally, in the plant-lice, all the genera-
tions, the nurses as well as the perfect animals, are separate individuals.

CONSEQUENCES OP ALTERNATE REPRODUCTION. 349

§536. But there is this essential difference between the meta-
morphoses of the caterpillar and alternate reproduction, that
in the former case, the same individual passes through all the
phases of development ; whereas, in the latter, the individual
disappears, and makes way for another, which carries out
what its predecessors had begun. It would give a correct idea
of this difference to suppose that the tadpole, instead of
being itself transformed into a frog, should die, having first
brought forth young frogs ; or that the chrysalis should, in
the same way, produce young butterflies. In either case, the
young would still belong to the same species, but the cycle
of development, instead of being accomplished in a single
individual, would involve two or more acts of generation.

§ 537. It follows, therefore, that the general practice of
deriving the character of a species from the sexual forms
alone, namely, the male and the female, is not applicable to all
classes of animals ; since there are large numbers whose various
phases are represented by distinct individuals, endowed with
peculiarities of their own. Thus, while in the stag the species
is represented by two individuals only, stag and hind, the
Medusa, on the other hand, is represented under the form of
three different types of animals ; the first is free, like the in-
fusoria; the second is fixed on a stalk, like a polyp ; and the
third again is free, consisting in its turn of male and female.
In the Distoma also, there are four separate individuals, the
grand nurse, the nurse, the larva or Cercaria, and the Distoma,
in which the sexes are not separate. Among the Aphides the
number is much greater still.

§ 538. The study of alternate generation, besides making us
better acquainted with the organization of animals, greatly
simplifies our nomenclature. Thus, in future, instead of enu-
merating the Distoma and the Cercaria, or the Strobila, the
Ephyra and the Medusa, as distinct animals belonging to dif-
ferent classes and families, only the name first given to one
of these forms will be retained, and the rest be struck from
the pages of zoology, as representing only the transitory phases
of the same species.

§ 539. Alternate generation always pre-supposes several
modes of reproduction, of which the primary is invariably by
ovulation. Thus we have seen that the polyps, the medusae,
the salpse, &c., produce eggs, which are generally hatched
within the mother. The subsequent generation, on the con-

350 EEPEODUCTION.

trary, is produced in a different manner, as we have shown
in the preceding paragraphs ; as among the medusae, by trans-
verse division ; among the polyps and the salpse, by buds, &c.

§ 540. The subsequent generations are moreover not to
be regarded in the same light as those which first spring
directly from eggs. In fact, they are rather phases of de-
velopment than generations properly so called ; they are either
without sex, or females whose sex is imperfectly developed.
The nurses of the Distoma, the Medusa, and the Campamdaria,
are barren, and have none of the attributes of maternity, ex-
cept that of watching over the development of the species,
being themselves incapable of producing young.

§ 541. Another important result follows from the above
observations, namely, that the differences between animals
which are produced by alternate generation are less, the
earlier the epoch at which we examine them. No two
animals can be more unlike, than an adult Medusa (fig.
366, k}, and an adult Campanularia (fig. 367) ; they even
seem to belong to different classes of the animal king-
dom, the former being an acaleph, the latter a polyp. On
the other hand, if we compare them when first hatched
from the egg, they appear so much alike, that it is with the
greatest difficulty they can be distinguished. They are then
little infusoria, without any very distinct shape, and moving
with the greatest freedom. The larvae of certain intestinal
worms, though they belong to a different department, have
nearly the same form, at one period of their life. Further
still, this resemblance extends to plants. The spores of cer-
tain sea-weeds have nearly the same appearance as the young
polyp, or the young Medusa ; and what is yet more remark-
able, they are also furnished with cilia, and move about in a
similar manner. But this is only a transient state. Like the
young Campanularia and the young Medusa, the spore of the
sea-weed is free only for a short time ; it soon becomes fixed,
and from that moment the resemblance ceases.

§ 542. Are we to conclude, then, from this resemblance of
the different types of animals at the outset of life, that there
is no real difference between them ; or that the two king-
doms, the animal and the vegetable, actually blend because
their germs are similar ? On the contrary, we think nothing
is better calculated to strengthen the idea of the original sepa-
ration of the various groups, as distinct and independent

CONSEQUENCES OF ALTERNATE REPRODUCTION. 351

types, than the study of their different phases. In fact, a differ-
ence so wide as that between the adult Medusa and the
adult Campanularia must have existed even in the young ;
only it does not show itself in a manner appreciable by our
senses ; the character by which they subsequently differ so
much, being not yet developed. To deny the reality of na-
tural groups, because of these early resemblances, would be to
take the resemblance for the reality. It would be the same as
saying that the frog and the fish are identical, because at one
stage of embryonic life it is impossible, with the means at our
command, to distinguish them.

§ 543. The account we have given above of the develop-
ment, the metamorphoses, and the alternate reproduction of
the lower animals, is sufficient to undermine the old theory
of spontaneous generation, which was proposed to account for
the presence of worms in the bodies of animals, for the sudden
appearance of myriads of animalcules in stagnant water,
and, under other circumstances, rendering their occurrence
mysterious. We need only recollect how the Cercaria in-
sinuates itself into the skin and the viscera of mollusca (§ 520,
§ 521), to understand how admission may be gained to the
most inaccessible parts. Such beings occur even in the eye
of many animals, especially of fishes ; they are numerous in
the eye of the common fresh-water perch of Europe.

§ 544, As to the larger intestinal worms found in other
animals, the mystery of their origin has been entirely solved
by recent researches. A single instance will illustrate their
history : — At certain periods of the year the sculpins of the
Baltic are infested by a particular species of Tcenia, or tape-
worm, from which they are free at other seasons. M. Esch-
richt found that, at certain seasons, the worms lose a great
portion of the long chain of rings of which they are composed.
On a careful examination he found that each ring contained
several hundred eggs, which, on being freed from their enve-
lope, float in the water. As these eggs are innumerable, it
is not astonishing that the sculpins should occasionally swallow
some of them with their prey. The eggs, being thus intro-
duced into the stomach of the fish, find conditions favourable
to their development ; and thus the species is propagated, and
at the same time transmitted from one generation of the fish to
another. The eggs which are not swallowed are probably lost.

352 EEPRODUCTICXN".

§ 545. All animals swallow, in the same manner, with their
food, and in the water they drink, numerous eggs of such pa-
rasites, any one of which, finding in the intestine of the animal
favourable conditions, may be hatched. It is probable that
each animal affords the proper conditions for some particular
species of worm ; and thus we may explain how it is that most
animals have parasites peculiar to themselves.

§ 546. As respects the infusoria, we also know that most of
them, the Rotifer a especially, lay eggs. These eggs, which
are extremely minute (some of them only 1-1 2,000th of an
inch in diameter), are scattered everywhere in great profusion,
in water, in the air, in mist, and even in snow. Assiduous
observers have not only seen the eggs laid, but, moreover,
have followed their development, and have seen the young
animal forming in the egg, then escaping from it, increasing
in size, and, in its turn, laying eggs. They have been able,
in some instances, to follow them even to the fifth and sixth
generation.

§ 547. This being the case, it is much more natural to sup-
pose that the infusoria* are products of like germs, than to
assign to them a spontaneous origin altogether incompatible
with what we know of organic development. Their rapid
appearance is not at all astonishing, when we reflect that
some mushrooms attain a considerable size in a few hours,
but yet pass through all the phases of regular growth ; and,
indeed, since we have ascertained the different modes of gene-
ration among the lower animals, no substantial difficulties any
longer exist to the axiom " omne vivum ex ovo" (§ 433).

* In this connection it ought to be remembered that a large proportion
of the so-called Infusoria are not independent animals, but immature
germs, belonging to different classes of the animal kingdom, and that
many must be referred to the vegetable kingdom.

CHAPTER TWELFTH.

METAMORPHOSES OF ANIMALS.

§ 548. UNDEE, the name of metamorphoses are included those
changes which the body of an animal undergoes after birth,
and which are modifications, in various degrees, of its organ-
ization, form, and mode of life. Such changes are not pe-
culiar to certain classes, as has been so long supposed, but
are common to all animals without exception.

§ 549. Vegetables also undergo metamorphoses, but with
this essential difference, that in vegetables the process consists
in an addition of new parts to the old ones. A succession of
leaves, differing from those which preceded them, comes on
each season ; new branches and roots are added to the old
stem, and woodv layers to the trunk. In animals the whole

J •/ t/

body is transformed, in such a manner that all the existing
parts contribute to the formation of the modified body. The
chrysalis becomes a butterfly ; the frog, after having been
herbivorous during its tadpole state, becomes carnivorous,
and its stomach is adapted to this new mode of life ; at the
same time, instead of breathing by gills, it becomes an air-
breathing animal, its tail and gills disappear, lungs and legs
are formed, and finally it lives and moves upon the land.

§ 550. The nature, the duration, and importance of meta-
morphoses, and also the epoch at which they take place, are
infinitely varied. The most striking changes naturally pre-
senting themselves to the mind, when we speak of meta-
morphoses, are those occurring in insects. Not merely is
there a change of physiognomy and form observable, or an
organ more or less formed, but their whole organization is modi-
fied. The animal enters into new relations with the external
world, while at the same time, new instincts are imparted to it.
It has lived in water, and respired by gills ; it is now furnished
with tracheae, and breathes air ; it passes by with indifference
objects which before were attractive, and its new instincts
prompt it to seek conditions which would have been most per-

A. A

354 METAMOEPIIOSES OK? ANIMALS.

nicious during its former period of life. All these changes are
brought about without destroying the individuality of the
animal. The mosquito, which to-day haunts us with its shrill
trumpet, and pierces us for our blood, is the same animal
that, a few days ago, lived obscure and unregarded in stagnant
water, under the guise of a little worm.

§ 551. Every one is familiar with the metamorphoses of the
silk-worm. On escaping from the egg the little worm or
caterpillar grows with great rapidity for twenty days, when it
ceases to feed, spins its silken cocoon, casts its skin, and re-
mains inclosed in its chrysalis state.* During this period of
its existence most extraordinary changes take place. The jaws
with which it masticated mulberry leaves are transformed into
a coiled tongue, the spinning organs are reduced, the gullet
is lengthened and more slender, the stomach, which was nearly
as long as the body, is now contracted into a short bag, the
intestine, on the contrary, becomes elongated and narrow ;
the dorsal vessel is shortened. The thoracic nervous ganglia
approach each other, and unite into a single mass. Antennae
and palpi are developed on the head, and simple eyes are
exchanged for compound ones. The muscles, which before
were uniformly distributed, are now gathered into masses.
The limbs are elongated, and wings spring forth from the
thorax. More active motions then reappear in the digestive
organs, and the animal, bursting the envelop of its chrysalis,
issues in the form of a winged moth.

§ 552. The different external forms which an insect may

assume is well illustrated by one

i f

Fig. 369. which is unfortunately too well known

in this country, namely, the canker-
worm (fig. 369). Its eggs are laid on
posts and fences, or upon the branches
of the apple, elm, and other trees.
They are hatched about the time the
tender leaves of these trees begin to
unfold. The caterpillar («) feeds on

.the leaves, and attains its full growth at the end of about four
weeks, being then not quite an inch in length. It then
descends to the ground, and enters the earth to the depth of

* In the raising of silk-worms this period is not waited for, but the
animal is killed as soon as it has spun its cocoon.

METAMORPHOSES OF AKTMALS.

355

a

four or five inches, and having excavated a sort of cell, is
soon changed into a chrysalis or nymph (6). At the usual time
in the spring it bursts the skin, and appears in its perfect state,
under the form of a moth (d). In this species, however,
only the male has wings. The perfect insects soon pair,
the female (c) crawls up a tree and having deposited her
eggs, dies.

§ 553.

Transform- Fig- 370.

ations no
less remark-
able are ob-
served
among the
Crustacea.
The meta-
morphoses
in the class
cirrhipoda
are es-
pecially

striking. It is now known that the barnacles (Balanus), which
have been arranged among the mollusca, are truly crusta-
ceans ; and this result of modern researches has been deduced
in the clearest manner from the study of their transformations.
Figures 3/0, a — -f, represent the different phases of develop-
ment of the duck-barnacle (Anatifd) .

§ 554. The Anatifa,like all Crustacea, is reproduced by eggs,
specimens of which, magnified ninety diameters, are repre-
sented in fig. 3/0, a. From these eggs little animals issue,
which have not the slightest resemblance to the parent. They
have an elongated form (6), a pair of tentacles, and four legs,
with which they swim freely in the water.

§ 555. Their freedom, however, is of but short duration.
The little animal soon attaches itself by means of its tentacles,
having previously become covered with a transparent shell,
through which the outlines of the body, and also a very distinct
eye, are easily distinguished (c). Fig. 370, dt shows the
animal taken out of its shell. It is plainly seen that the
anterior portion has become considerably enlarged ; subse-
quently, the shell becomes completed, and the animal casts its

A A 2

356

METAMORPHOSES OF

Fig. 371.

skin, losing with it both its eyes and its tentacles. On the
other hand, a thick membrane lining the interior of the shell,
pushes out and forms a stem (e), by means of which
the animal fixes itself to immersed bodies, after the loss of its
tentacles. This stem gradually enlarges, and the animal soon
acquires a definite shape, such as is represented in fig. 370, f,
attached to a piece of floating wood.

§ 556. There is, consequently, not only a changs of organ-
ization in the course of the metamorphoses, but also a change
of faculties and mode of life. The animal, at first free, be-
comes fixed ; and its adhesion is effected by totally different
organs at different periods of life, first by means of tentacles,
which were temporary organs, and afterwards by means of a
fleshy stem, especially developed for that purpose.

§ 557. The radiata also furnish us with examples of vari-
ous metamorphoses, especially
among the star-fishes. A small
species, living on the coastof New
England (Echinaster sanguino-
lentus), undergoes the following
phases (fig. 371).

§ 558. If the eggs are ex-
amined by the microscope, each
one is found to contain a small,
pear-shaped body, which is the
embryo (e), surrounded by a
transparent envelope. On es-
caping from the egg the little
animal has an oblong form, with
a constriction at the base ; this constriction, becoming deeper
and deeper, forms a pedicle, (p\ which soon divides into
three lobes. The disc also assumes a pentagonal form, with
five double series of vesicles ; the first rudiments of the rays,
are seen to form in the interior of the pentagon. At the same
time the peduncle contracts still more, being at last entirely
absorbed into the cavity of the body, and the animal soon
acquires its final form (m).

§ 559. Analogous transformations take place in the Coma-
tula. In early life it is fixed to the ground by a stem (fig.
372), but becomes detached at a certain epoch, and then floats
freely in the sea (fig. 373). On the other hand, the polypi

METAMORPHOSES OF ANIMALS.

357

Fig. 372.

seem to follow a reverse course, many of them becoming per-
manently fixed after having been previously free.

§ 560. The metamorphoses of the
mollusca, though less striking, are
not less worthy of notice. Thus,
the oyster, with which we are fami-
liar in its adhering shell, is free
when young, like the clam (My a)
and most other shell-fishes. Others,
which are at first attached or sus-
pended to the gills of the mother,
afterwards become free, as the Unio.
Some naked gasteropods, the Ac-
teon and the Eolis, for example, are
born with a shell, which they part
with, shortly after leaving the egg.

§ 561. The study of metamor-
phosis is therefore of the utmost
importance for understanding the
real affinities of animals very dif-
ferent in appearance, as is readily
shown by the following instances.
The butterfly and the earth-worm
seem, at the first glance, to have
no relation whatever. They differ
in their organization no less than in
their outward appearance. But on
comparing the caterpillar and the
worm, these two animals are seen
closely to resemble each other. The
analogy, however, is only transient;
it lasts only during the larva state of

*/

the caterpillar, and is effaced as it
passes to the chrysalis and butter-
fly conditions. The latter becoming a more and more perfect ani-
mal, whilst the worm remains in its inferior state.

& 562. Similar instances are furnished by animals belong;-

J 4/

ing to all the types of the animal kingdom. Who would
suppose, at the first glance, that a barnacle, or an anatifa, were
more nearly allied to the crab than to the oyster ? And,
nevertheless, we have seen (§ 553), in tracing back the anatifa

Fig. 373.

358 METAMOEPHOSES OF ANIMALS.

to its early stages, that it then bears a near resemblance to a
little crustacean (fig. 370 d). It is only when full grown
that it assumes its peculiar mollusk-like covering.

§ 563. Among the cuttle-fishes there are several, the
Loliffo, for example, which are characterized by the form
of their tentacles, the two interior being much longer than
the others, and of a different form ; whilst, in others, as the
Octopus, they are all equal. But if we compare the young,
we find that in both animals the tentacles are all equal, though
they differ in number. The inequality in the tentacles being
the result of a further development.

§ 564. Among the radiata, the Pentacrinus and the Co-
matula exemplify the same point. The two are very different
when full grown, the latter being a free-swimming star-fish
(fig. 373), while the former is attached to the soil, like a
polyp. But we have seen (§ 559) that the same is the case
with Comatula in its early period ; and that in consequence
of a further metamorphosis, it becomes disengaged from its
stem, and floats freely in the water.

§ 565. In the type of thevertebrata,the considerations drawn
from metamorphoses acquire still greater importance in re-
ference to classification. The sturgeon and the white-fish
before mentioned (§ 463) are two very different fishes ; yet,
taking into consideration their external form and bearing
merely, it might be questioned which of the two should take
the highest rank ; whereas, the doubt is very easily resolved
by an examination of their anatomical structure. The white-
fish has a skeleton, and moreover a vertebral column com-
posed of firm bone. The sturgeon (fig. 374), on the con-
Fig. 374.

trary, has no bone in the vertebral column, except the spines
or apophyses of the vertebrae. The middle part, or body of
the vertebra, is cartilaginous ; the mouth is transverse, and
underneath the head ; and the caudal fin is unequally forked,
while, in the white-fish, it is equally forked.

METAMORPHOSES OP ANIMALS. 359

§ 566. If, however, we observe the young white-fish just
after it has issued from, the egg (fig. 309), the contrast will
be less striking. At this period the vertebrae are cartilaginous,
like those of the sturgeon ; its mouth also is transverse, and
its tail undivided ; at that period the white-fish and the stur-
geon are therefore much more alike. But this similarity is
only transient; as the white-fish grows, its vertebrse become
ossified, and its resemblance to the sturgeon is comparatively
slight. As the sturgeon has no such transformation of the
vertebrae, and is in some sense arrested in its development,
while the white-fish undergoes subsequent transformation, we
conclude that, compared with the white-fish, it is really in-
ferior in rank.

§ 567. This relative inferiority and superiority strikes us
still more, when we compare with our most perfect fishes
(the salmon, the cod &c.) some of those worm-like animals, so
different from ordinary fishes that they were formerly placed
among the worms. The Amphioxus, represented of its natural
size (fig. 375), not only has no bony skeleton, but not even a
head, properly speaking. Yet
the fact that it possesses a dor- Fig. 375

sal cord, extending from one ex-
tremity of the body to the other,
proves that it belongs to the type
of the vertebrata (§458). But as
this peculiar structure is found only at a very early period of
embryonic development, in other fishes, we conclude that the
Amphioxus holds the very lowest rank in this class.

§ 568. Nevertheless, the metamorphoses of animals after
birth will, in many instances, present but trifling modifica-
tions of the relative rank of animals, compared with those
which may be derived from the study of changes previous to
that period, as there are many animals which undergo no
changes of great importance after their escape from the egg,
and occupy nevertheless a high rank in the zoological series,
as, for example, birds and mammals. The question is, whether
such animals are developed according to different plans, or
whether their peculiarity in that respect is merely apparent. To
answer this question, let us go back to the period anterior to
birth, and see if some parallel may not be made out between
the embryonic changes of these animals, and the metamor-
phoses which take place subsequently to birth in others.

360 METAMORPHOSES OF ANIMALS.

§ 569. We have already shown that embryonic development
consists in a series of transformations ; the young animal en-
closed in the egg differing, at each period of its development,
from what it was before. But because these transformations
precede birth, and are therefore not generally observed, they
are not less important. To be satisfied that these transfor-
mations are in every respect similar to those which follow
birth, we have only to compare the changes which immedi-
ately precede birth with those which immediately follow it,
and we shall readily perceive that the latter are simply a con-
tinuation of the former, till all are completed.

§ 570. Let us recur to the development of fishes for illus-
tration. The young white-fish, as we have seen (§ 471), is far
from having acquired its complete development, when born.
The vertical fins are not yet separate ; the mouth has not yet
its proper position ; the yolk has not yet retreated within the
cavity of the body, but hangs below the chest in the form of
a large bag. Much, therefore, remains to be changed, before
its development is complete. But the fact that it has been
born does not prevent its future evolution, which goes on
without interruption.

§ 571. Similar inferences maybe drawn from the develop-
ment of the chick. The only difference is, that the young
chicken is born in a more mature state, the most important
transformations having taken place during the embryonic
period, while those to be undergone after birth are less con-
siderable, though they complete the process begun in the
embryo. Thuswe see it, shortly after birth, completely changing
its covering, and clothed with feathers instead of down ; still
later its crest appears, and its spurs begin to be developed.

§ 5/2. In certain mammals, known under the name of
marsupials (the opossum and kangaroo), the link betAveen
the transformations which take place before birth, and those
occurring at a later period, is especially remarkable. These
animals are brought into the world so weak and undeveloped,
that they have to undergo a second gestation, in a pouch with
which the mother is furnished, and in which the young re-
main, each one fixed to a teat, until they are entirely developed.
Even those animals which are born nearest to the complete
states undergo, nevertheless, embryonic transformations. Ru-
minants acquire their horns ; and the lion his mane. Most

METAMORPHOSES OF ANIMALS. 361

mammals, at birth, are destitute of teeth, and incapable of
using their limbs ; and all are dependent on the mother and
the milk secreted by her, until the stomach is capable of
digesting other aliment.

§ 573. If it be thus shown that the transformations which
take place in the embryo are of the same nature and of the
same importance as those which occur afterwards, the cir-
cumstance that some precede and others succeed birth, cannot
mark any radical distinction between them. Both are pro-
cesses of the life of the individual. Now, as life does not
commence at birth, but goes still farther back, it is quite clear
that the modifications which supervene during the former
period are essentially the same as the later ones ; and hence
that metamorphoses, far from being exceptional in the case
of insects, are one of the general features of the animal king-
dom.

§ 5/4. We are therefore perfectly entitled to say that all
animals, without exception, undergo metamorphoses. Were
it not so, we should be at a loss to conceive why animals of
the same division present such wide differences ; and that
there should be, as in the class of reptiles, some families that
undergo metamorphoses (the frogs, for example), and others
in which nothing of the kind is observed after birth (the
lizards and tortoises).

§ 575. It is only by connecting the two kinds of trans-
formation— namely, those which take place before, and those
after birth, that we are furnished with the means of ascer-
taining the relative perfection of an animal ; in other words,
these transformations become, under such circumstances, a
natural key to the gradation of types. At the same time,
they force upon us the conviction that there is an immu-
table principle presiding over all these changes, and regulat-
ing them in a peculiar manner in each animal.

§ 576. These considerations are important, not only from
their bearing on classification, but not less so from the appli-
cation which may be made of them to the study of fossils.
If we examine attentively the fishes that have been found in
the different strata of the earth, we remark that those of the
most ancient deposits have in general preserved only the
apophyses of their vertebrae, whilst the vertebrae themselves
are wanting. Were the sturgeons to become petrified, they

362 METAMOKPHOSES OF ANIMALS.

would be found in a similar state of preservation. As the
apophyses are the only bony portions of their vertebral column,
they alone would be preserved. Indeed, fossil sturgeons are
known, which are precisely in this condition.

§ 577. From the fact above stated, we may conclude that
the oldest fossil fishes did not pass through all the metamor-
phoses which our osseous fishes undergo, and consequently
that they were inferior to analogous species of the present
epoch, which have bony vertebrae. Similar considerations
apply to the fossil Crustacea and to the fossil echinoderms,
when compared with their living types ; and it will probably be
true of all classes of the animal kingdom, when they are fully
studied as to their geological succession.

CHAPTER THIRTEENTH.

GEOGRAPHICAL DISTRIBUTION OF ANIMALS.

*

SECTION I.

GENERAL LAWS OF DISTRIBUTION.

§ 578. No animal, excepting man, inhabits every part of the
surface of the earth. Each great geographical or climatal re-
gion is occupied by some species not found elsewhere ; and
each animal dwells within certain limits, beyond which it does
not range while left to its natural freedom, and within which
it always inclines to return, when removed by accident or
design. Man alone is a cosmopolite ; his domain is the whole
earth ; for him, and with a view to him, it was created ; his
right to it is based upon his organization and his relation to
nature, and is maintained by his intelligence and the perfecti-
bility of his social condition.

»

§ 579. A group of animals inhabiting any particular
region, embracing all the species, both aquatic and terrestrial,
is called its FAUNA, in the same manner as the plants of a
country are called its FLORA. To be entitled to this name it is
not necessary that none of the animals composing the group
should be found in any other region ; it is sufficient that
there should be peculiarities in the distribution of the fami-
lies, genera, and species, and in the preponderance of cer-
tain types over others, sufficiently prominent to impress upon
a region well-marked features ; thus, for example, in the
islands of the Pacific are found terrestrial animals, altogether
peculiar, and not found on the nearest continents. There are
numerous animals in New Holland differing from any found
on the continent of Asia, or, indeed, on any other part of the
earth : if, however, some species, inhabiting both shores of a
sea which separates two terrestrial regions, are found to be
alike, we are not to conclude that those regions have the same
Fauna, any more than that the Flora of Lapland and England

364 GE1STEEAL LAWS OF DISTEIBUTION.

are alike, because some of the sea-weeds found on both their
shores are the same.

§ 580. There is an evident relation between the fauna of
any locality and its temperature, although, as we shall here-
after see, similar climates are not always inhabited by similar
animals. Hence the faunas of the two hemispheres have been
distributed into three principal divisions, namely the arctic,
the temperate, and the tropical, in the same manner as we
have arctic, temperate, and tropical floras ; hence, also, ani-
mals dwelling at high elevations upon mountains, where the
temperature is much reduced, resemble the animals of colder
latitudes, rather than those of the surrounding plains.

§ 581. In some respects the peculiarities of the fauna of a
region depends upon its flora, at least so far as land animals
are concerned ; for herbivorous animals will exist only where
there is an adequate supply of vegetable food ; but, taking the
terrestrial and aquatic animals together, the limitation of a
fauna is less intimately dependent on climate than that of a
flora. Plants, in truth, are for the most part terrestrial (marine
plants being relatively very few) while animals are chiefly
aquatic. The ocean is the true home of the animal kingdom ;
and while plants, with the exception of the lichens and mosses,
become dwarfed or perish under the influence of severe cold,
the sea teems with animals of all classes, far beyond the ex-
treme limit of flowering plants.

§ 582. The influence of climate, in the polar regions, acts
merely to induce a greater uniformity in the species of animals.
Thus, the same animals inhabit the northern polar regions of the
three continents ; the polar bear is the same in Europe, Asia,
and America, and so are also a great many birds ; in the tempe-
rate regions, on the contrary, the species differ on each of the
continents, but they still preserve the same general features ;
the types are the same, but they are represented by different
species. In consequence of these general resemblances, the first
colonists of New England erroneously applied the names of
European species to American animals. Similar differences are
observed in distant regions of the same continent, within the
same parallels of latitude. The animals of Oregon and of
California are not the same as those of New England. The
difference, in certain respects, is even greater than between
the animals of New England and Europe. In like manner,

GENERAL LAWS OF DISTRIBUTION. 3G5

the animals of temperate Asia differ more from those of
Europe than they do from those of America.

§ 583. Under the torrid zone the animal kingdom, as well
as the vegetable, attains its highest development. The animals
of the tropics are not only different from those of the tempe-
rate zone, but, moreover, they present the greatest variety
among themselves. The most gracefully proportioned forms
are found by the side of the most grotesque, decked with
every combination of brilliant colouring. At the same time,
the contrast between the animals of different continents is
more marked ; and, in many respects, the animals of the
different tropical faunas differ not less from each other
than from those of the temperate or frozen zones ; thus,
the fauna of Brazil varies as much from that of central Africa
as from that of the United States.

§ 584. This diversity upon different continents cannot de-
pend simply on any influence of the climate of the tropics ;
if it were so, uniformity ought to be restored in proportion as
we recede from the tropics towards the antarctic temperate
regions. But, instead of this, the differences continue to in-
crease ; — so much so, that no faunas are more in contrast than
those of Cape Horn, the Cape of Good Hope, and New Hol-
land. Hence other influences must be in operation besides
those of climate ; — influences of a higher order, which are in-
volved in a general plan, and intimately associated with the
development of life on the surface of the earth.

§ 585. Faunas are more or less distinctly limited, according
to the natural features of the earth's surface. Sometimes two
faunas are separated by an extensive chain of mountains, like
the Eocky Mountains. Again, a desert may intervene, like
the desert of Sahara, which separates the fauna of Central
Africa from that of the Atlas and the Moorish coast, the latter
of which is merely an appendage to the fauna of Europe.
But the sea effects the most complete separation. The depths
of the ocean are quite as impassable for marine species as high
mountains are for terrestrial animals. It would be quite as
difficult for a fish or a mollusk to cross from the coast of
Europe to the coast of America, as it would be for a reindeer
to pass from the arctic to the antarctic regions, across the
torrid zone. Experiments of dredging in very deep water
have also taught us that the abyss of the ocean is nearly a
dese . . Not only are no materials found there for sustenance,

3o6 GENERAL LAWS OF DISTRIBUTION.

but. it is doubtful if animals could sustain the pressure of so
great a column of water, although many of them are provided
with a system of pores (§ 403), which enables them to sustain
* much greater pressure than terrestrial animals.

§ 586. When there is no great natural limit, the transition
from one fauna to another is made insensibly. Thus, in pass-
ing from the arctic to the temperate regions of North America,
one species takes the place of another, a third succeeds the
second, and so on, until finally the fauna is found to be an
entirely new one, without its being always possible to mark
the precise limit between the two.

§ 587. The range of species does not at all depend upon
their powers of locomotion ; if it were so, animals which
move slowly and with difficulty would have a narrow range,
whilst those which are very active would be widely diffused.
Precisely the reverse of this is actually the case. The com-
mon oyster extends at least from Cape Cod to the Carolinas ;
its range is consequently very great ; much more so than that
of some of the fleet animals, as, for instance, the moose. It
is even probable that the very inability of the oyster to travel,
really contributes to its diffusion, inasmuch as having once
spread over extensive grounds, their is no chance of its return
to a former limitation, being fixed, and consequently unable .
to choose positions for its eggs, they must be left to the mercy
of currents ; while fishes, by depositing their eggs in the
bays and inlets of the shore, undisturbed by currents and
winds, secure them from too wide a dispersion.

§ 588. The nature of their food has an important bearing
upon the grouping of animals, and upon the extent of their
distribution. Carnivorous animals are generally less confined
in their range than herbivorous ones ; because their food is
almost everywhere to be found. The herbivora, on the othei
hand, are restricted to the more limited regions correspond-
ing to the different zones of vegetation. The same remark
may be made with respect to birds. Birds of prey, like
the eagle and vulture, have a much wider range than the
granivorous and gallinaceous birds. Still, notwithstanding
the facilities they have for change of place, even the birds
that wander widest recognize limits which they do not over-
pass. The condor of the Cordilleras does not descend into
the temperate regions of the United States ; and yet it is not
that he fears the cold, since he is frequently known to ascend

GENERAL LAWS OF DISTRIBUTION. 36?

even above the highest summits of the Andes, and disappears
from view where the cold is most intense. Nor can it be from
lack of prey.

§ 589. Again, the peculiar configuration of a country some-
times determines a peculiar grouping of animals into what
may be called local faunas. Such, for example, are the prai-
ries of the West, the pampas of South America, the steppes
of Asia, the deserts of Africa ; — and for marine animals, the
basin of the Caspian. In all these localities, animals are met
with which exist only there, and are not found except under
those particular conditions.

§ 590. Finally, to obtain a true picture of the zoological
distribution of animals, not the terrestrial types alo-ne, but the
marine species must also be included. Notwithstanding the
uniform nature of the watery element, the animals which dwell
in it are not dispersed at random ; and though the limits of
the marine may be less easily denned than those of the terres-
trial fauna, still marked differences between the animals of great
basins are not less observable. Properly to apprehend how
marine animals may be distributed into local faunas, it must
be remembered that their residence is not in the high sea, but
along the coasts of continents and on soundings. It is on the
Banks of Newfoundland, and not in the deep sea, that the
great cod-fishery is carried on ; and it is well known that when
fishes migrate, they run along the shores. The range of
marine species being therefore confined to the vicinity of the
shores, their distribution must be subjected to laws similar
to those which regulate the terrestrial faunas. As to the
fresh-water fishes, not only do the species vary in the dif-
ferent zones, but even the different rivers of the same region
have species peculiar to them, and not found in neighbouring
streams. The gar-pikes, Lepidosteus, of the American rivers,
afford a striking example of this kind.

§ 591. A very influential cause in the distribution of aqua-
tic animals is the depth of the water ; so that several zoological
zones receding from the shore may be defined according to the
depth of water, much in the same manner as we mark dif-
ferent zones at different elevations in ascending mountains. The
mollusks, and even the fishes found near the shore in shallow
water differ, in general, from those living at the depth of twenty
or thirty feet, and these again are found to be different from
those which are met with at a greater depth. Their colouring,

368 GENERAL LAWS OF DISTRIBUTION.

in particular, varies, according to the quantity of light they re-
ceive, as has also been shown to be the case with marine plants.

§ 592. It is sometimes the case that one or more animals
are found upon a certain chain of mountains, and not else-
where ; as, for instance, the mountain sheep (Ovis montana),
upon the Rocky Mountains, or the chamois and the ibex upon
the Alps. The same is also the case on some of the wide
plains or prairies. This, however, does not entitle such regions
to be considered as having an independent fauna, any more
than a lake is to be regarded as having a peculiar fauna, ex-
clusive of the animals of the surrounding country, merely be-
cause some of the species found in the lake may not ascend
the rivers emptying into it. It is only when the whole group
of animals inhabiting such a region has such peculiarities as
to give it a distinct character, when contrasted with animals
found in surrounding regions, that it is to be regarded as a
separate fauna. Such, for example, is the fauna of the great
steppe or plain of Gobi, in Asia ; and such indeed that of the
chain of the Rocky Mountains may prove to be, when the
animals inhabiting them shall be better known.

§ 593. The migration of animals might at first seem to pre-
sent a serious difficulty in determining the character or the
limits of a fauna ; but 'this difficulty ceases, if we regard the
country of an animal to be the place where it makes its habi-
tual abode. As to birds, which of all animals wander the
farthest, it may be laid down as a rule, that they belong to the
zone in which 'they breed. Thus, the gulls, many of the ducks,
mergansers, and divers, belong to the boreal regions, though
they pass a portion of the year with us. On the other hand,
the swallows and martins, and many of the gallinaceous birds be-
long to the temperate faunas, notwithstanding their migration
during winter to the confines of the torrid zone. This rule
does not apply to the fishes, who annually leave their proper
home, and migrate to a distant region merely for the purpose
of spawning. The salmon, for example, comes down from
the North to spawn on the coasts of Maine, Nova Scotia, and
the British isles.

§ 594. Few of the Mammals, and these mostly of the tribe
of rodents, make extensive migrations. Among the most
remarkable of these are the Kamtschatka rats. In spring
they direct their course westward, in immense troops ; and

DISTRIBUTION OF THE FAUNAS. 369

after a very long journey return again in autumn to their quar-
ters, where their approach is anxiously awaited by the hunters,
on account of the fine furs to be obtained from the numerous
carnivora which always follow in their train. The migrations

v O

of the Lemmings are marked by the devastations they commit
along their course, as they come down from the borders of the
Frozen Ocean to the valleys of Lapland and Norway ; but their
migrations are not periodical.

SECTION II.

DISTRIBUTION OF THE FAUNAS.

§ 595. WE have stated that all the faunas of the globe may
be divided into three groups, corresponding to as many
great climatal divisions, namely, the glacial or arctic, the tem-
perate, and the tropical faunas. These three divisions apper-
tain to both hemispheres, as we recede from the equator to-
wards the north or south poles. It will hereafter be shown
that the tropical and temperate faunas may be again divided
into several zoological provinces, depending on longitude or
on the peculiar configuration of the continents.

§ 596. No continent is better calculated to give a correct idea
of distribution into faunas, as determined by climate, than the

•

continent of America ; extending as it does across both hemi-
spheres, and embracing all latitudes, so that all climates are
represented upon it, as shown by the chart on the following
page.

§ 597. Let a traveller embark at Iceland, which is situated
on the borders of the polar circle, with a view to observe, in a
zoological aspect, the principal points along the eastern shore
of America. The result of his observations will be very much
as foUows. Along the coast of Greenland and Iceland, and
also along Baffin's Bay, he will meet with an unvaried fauna

»/ J

composed throughout of the same animals, which are also for
the most part identical with those of the arctic shores of
Europe. It will be nearly the same along the coast of Labrador.
§ 598. As he approaches Newfoundland, he will see the
landscape, and with it the fauna, assuming a somewhat more
varied aspect. To the wide and naked or turfy plains of the
boreal regions succeed forests, in which he will find various
animals dwelling only therein. Here the temperate fauna

370

GEOGRAPHICAL DISTRIBUTION OF AXIMALS.

FATINAS.

I. North Glacial, or

Arctic.

II. Northern Tempe-
rate.

III. Northern Warm.

IV. Tropical.

V. Southern Warm.
IV. Southern Tempe-
rate.

CHART OF ZOOLOGICAL REGIONS,

DISTRIBUTION OF THE FAUNAS. 3/1

commences. Still the number of species is not yet very
considerable ; as lie advances southward, along the coasts of
Nova Scotia and New England, he finds new species gradually
introduced, while those of the colder regions diminish, and at
length entirely disappear, some few accidental or periodical
visiters excepted, who wander during winter as far south as
the Carolinas.

§ 599. But it is after having passed the boundaries of the
United States, among the Antilles, and more especially on the
southern continent, along the shores of the Orinoco and the
Amazon, that our traveller will be forcibly struck with the
astonishing variety of the animals inhabiting the forests,
the prairies, the rivers, and the sea-shores, most of which he
will also find to be different from those of the northern conti-
nent. By this extraordinary richness of new forms, he will
become sensible that he is now in the domain of the tropical
fauna.

§ 6 (JO. Let him still travel on beyond the equator towards
the tropic of Capricorn, and he will again find the scene
change as he enters the regions where the sun casts his rays
more obliquely, and where the contrast of the Seasons is more
marked. The vegetation will be less luxuriant ; the palms
will have disappeared to make place for other trees ; the ani-
mals will be less varied, and the whole picture will recall to
him, in some measure, the scene which he witnessed in the
United States. He will again find himself in the temperate
region, and this he will trace on, till he arrives at the extremity
of the continent, the fauna and the flora becoming more
and more impoverished as he approaches Cape Horn.

§ 601. Finally, we know that there is a continent around
the South Pole. Although we have as yet but very imperfect
notions respecting the animals of this inhospitable clime, still
the few which have already been observed there, present a
close analogy to those of the arctic region. It is another
glacial fauna, namely, the antarctic. Having thus sketched
the general distribution of the faunas, it remains to point out
the principal features of each.

§ 602. I. AECTIC FAUNA. — The predominant feature of
the Arctic Fauna is its uniformity. The species are few ;
but, on the other hand, the number of individuals is im-
mense. We need only refer to the clouds of birds which

B B 2

372 GEOGBAPHICAL DISTKilTlTTION OF ANIMALS.

i

hover upon the islands and shores of the North ; the shoals
of fishes, the salmon, among others, which throng the coasts
of Greenland, Iceland, and Hudson's Bay. There is uni-
formity also in the form and colour of these animals. Not a
single bird of brilliant plumage is found, and few fishes with
varied hues. Their forms are regular, and their tints as dusky
as the northern heavens. The most conspicuous animals are
the white bear, the moose, the reindeer, the musk-ox, the
white fox, the polar hare, the lemming, and various seals ; but
the most important are the whales, which, it is to be remarked,
rank lowest of all the mammals. Among the birds, may be
enumerated some sea-eagles and a few waders, while the
great majority are aquatic species, such as gulls, cormorants,
divers, petrels, ducks, geese, gannets, &c., all belonging to the
lowest orders of birds. Reptiles are altogether wanting. The
articulata are represented by numerous marine worms, arid
by minute crustaceans of the orders isopoda and amphipoda.
Insects are rare, and of inferior types. Of the mollusca,
there are acephala, particularly tunicata, fewer gasteropods,
and very few cephalopods. Among the radiata are a great
number of jelly-fishes, particularly the Beroe; and to conclude
with the echinoderms, there are several star-fishes and echini,
but few holothurise. The class of polypi is very scantily repre-
sented, and those producing stony corals are entirely wanting.

§ 603. This assemblage of animals is evidently inferior to
that of other faunas, especially to those of the tropics. Not
that there is a deficiency of animal life ; for if the species are
less numerous, there is a compensation in the multitude of
individuals, and also in this other very significant fact, that
the largest of all animals, the whales, belong to this fauna.

§ 604. It has already been said (§ 602) that the arctic fauna
of the three continents is the same ; its southern limit, how-
ever, is not a regular line. It does not correspond precisely
with the polar circle, but rather to the isothermal zero, that is,
the line where the average temperature of the year is at 32°.
of Fahrenheit. The course of this line presents numerous
undulations. In general, it may be said to coincide with the
northern limit of trees, so that it terminates where forest
vegetation succeeds the vast arid plains, the barrens of North
America, or the tundras of the Samoyedes. The uniformity
of these plains involves a corresponding uniformity of plants
<tmmals. On the .North American continent it extends

DISTRIBUTION OF THE FAUNAS. 373

much farther southward on the eastern shore, than on the
western. From the peninsula of Alashka it bends northwards
towards the Mackenzie, then descends again towards the Bear
Lake, and comes down near to the northern shore of New-
foundland.

§ 605. II. TEMPEBATE FAUNAS. — The faunas of the tem-
perate regions of the northern hemisphere are much more
varied than that of the arctic zone. Instead of consisting
mainly of aquatic tribes, we have a considerable number of
terrestrial animals of graceful form, animated appearance, and
varied colours, though less brilliant than those found in tropi-
cal regions. Those parts of the country covered with forests
especially swarm with insects, which become the food of other
animals : worms, terrestrial and fluviatile mollusca are also
abundant.

§ 606. Still, the climate is not sufficiently warm over the
whole extent of this zone to allow the trees to retain their
foliage throughout, the year. At its northern margin the leaves,
excepting those of the pines and spruces, fall, on the ap-
proach of the cold season, and vegetation is arrested for a
longer or shorter period. Insects retire, and the animals
which live upon them no longer find nourishment, and are
obliged to migrate to warmer regions, on the borders of the
tropics, where, amid the ever-verdant vegetation, they find
the means of subsistence.

§ 607. Some of the herbivorous mammals, the bats, and
the reptiles which feed on insects, pass the winter in a state
of torpor, from which they awake in spring. Others retire
into dens, and live on the provisions they have stored up dur-
ing the warm season. The carnivora, the ruminants, and the
most active portion of the rodents, are the only animals that
do not change either their abode or their habits. The fauna
of the temperate zone thus presents an ever-changing picture,
which may be considered as one of its most important features,
since these changes recur with equal constancy in the Old and
the New World.

§ 608. Taking the contrast of the vegetation, as a basis,
and the consequent changes of habit imposed upon the deni-
zens of the forests, the temperate fauna has been divided into
twro regions ; a northern one, where the trees, except the
pines, drop their leaves in winter, and a southern one, where
they are evergreen. Now, as the limit of the former, that of

GEOGRAPHICAL DISTRIBUTION OF ANIMALS.

the deciduous trees, coincides, in general, with the limit of the
pines, it may be said that the cold region of the temperate
fauna extends as far as the pines. In the United States this
coincidence is riot so marked as in other regions, inasmuch as
the pines along the Atlantic coast extend into Florida, while
they do not prevail in the Western States ; but we may con-
sider as belonging to the southern portion of the temperate
region, that part of the country south of the latitude where
the palmetto or cabbage-tree (Chamaerops) commences, namely,
all the States to the south of North Carolina ; while the
States to the north of this limit belong to the northern portion
of the temperate region.

§ 609. This division into two zones is supported by obser-
vations made on the maritime faunas of the Atlantic coast.
The line of separation between them, however, being influ-
enced by the Gulf Stream, is considerably farther to the north ;
— namely, at Cape Cod : although there is also another decided
limitation of the marine animals at a point nearly coinciding
with the line of demarcation above-mentioned, namely, at
Cape Hatteras. It has been observed, that of one hun-
dred and ninety-seven mollusca inhabiting the coast o^
New England, fifty do not pass to the north of Cape Cod,
and eighty- three do not pass to the south of it ; only sixty-foui-
being common to both sides of the Cape. A similar limita-
tion of the range of fishes has been noticed by Dr. Storer ;
and Dr. Holbrook has found the fishes of South Carolina to
be diiferent from those of Florida and the West Indies. In
Europe, the northern part of the temperate region extends to
the Pyrenees and the Alps ; and its southern portion consists
of the basin of the Mediterranean, together with the northern
part of Africa, as far as the desert of Sahara.

§ 610. A peculiar characteristic of the faunas of the tem-
perate regions in the northern hemisphere, when contrasted
with those of the southern, is the great similarity of the pre-
vailing types on both continents. Notwithstanding the im-
mense extent of country embraced, the same stamp is every-
where exhibited. Generally, the same families, frequently
the same genera, represented by diiferent species, are found.
There are even a few species of terrestrial animals regarded
as identical on the continents of Europe and America ; but
their supposed number is constantly diminished, as more
accurate observations are made. The predominant types

DISTRIBUTION OF THE FAUNAS. 375

the mammals are the bison, deer, ox, horse, hog, nu-
merous rodents, especially squirrels, and hares, nearly all the
insectivora, weasels, martens, wolves, foxes, wild cats, &c.
On the other hand, there are no edentata and no quadrumana,
with the exception of some monkeys on the two slopes of the
Atlas and in Japan. Among birds, there is a multitude of
climbers, passerine, gallinaceous, and many rapacious fami-
lies. Of reptiles, there are lizards and tortoises of small or
medium size, serpents, and many batrachians, but no croco-
diles. Of fishes, there is the trout family, the cyprinoids,
the sturgeons, the pikes, the cod, and especially the great
family of herrings and sconiberoids, to which latter belong
the mackerel and the tunny. All classes of the mollusca are
represented ; though the cephalopods are less numerous than
in the torrid zone. There is an infinite number of articu-
lata of every type, as well as numerous polyps, though the
corals proper do not yet appear abundantly.

§611. On each of the two continents of Europe and
America, there is a certain number of species extending
from, one extreme of the temperate zone to the other. Such,
for example, are the deer, the bison, the cougar, the flying-
squirrel, numerous birds of prey, several tortoises, and the
rattle-snake, in America. In Europe, the brown bear, wolf,
swallow, and many birds of prey. Some species have a still
wider range, like the ermine, which is found from Behring's
Straits to the Himalaya Mountains — that is to say, from the
coldest regions of the arctic zone to the southern confines of
the temperate zone. It is the same with the musk-rat, which
is found from the mouth of Mackenzie's River to Florida.
The field-mouse has an equal range in Europe. Other species,
on the contrary, are limited to one region. The Canadian elk
is confined to he northern portion of the fauna ; while the
prairie wolf, the fox-squirrel, the Bassaris, and numerous
birds, never leave the southern portion.*

* The types which are peculiar to temperate America, and are not found
in Europe, are the opossum, several genera of insectivora, among them
the shrew-mole (Scalops aquaticus), and the star-nose mole (Condylitra
cristata}, which replaces the My yule of the Old World ; several genera
of rodents, especially the musk-rat. Among the types characteristic of
America must also be reckoned the snapping-turtle among the tortoises ;
the Menobranchus and Menopoma among the Salamanders ; the Lepidos-
teus and Amia among the fishes ; and, finally, the Limulus among the

76 GEOGKAPHICAL blSTlllliUTlON OF ANIMALS.

§ 612. In America, as in the Old World, the temperate
fauna is further subdivided into several districts, which may
be regarded as so many zoological provinces, in each of which
there is a certain number of animals differing from those in
the others, though very closely allied to them. Temperate
America presents us with a striking example in this respect.
We have, on the one hand : —

1st. The fauna of the United States properly so called, on
this side of the Rocky Mountains.

2d. The fauna of Oregon and California, beyond those
mountains.

Though there are some animals which traverse the chain
of the Rocky Mountains, and are found in the prairies of the
Missouri as well as on the banks of the Columbia, as, for
example, the Rocky Mountain deer (Antilope fnrcifer), yet,
if we regard the whole assemblage of animals, they are found
to differ entirely. Thus, the rodents, part of the ruminants,
the insects, and all the mollusks, belong to distinct species.

§ 613. The faunas or zoological provinces of the Old World
corresponding to these are : —

1st. The fauna of Europe, which is very closely related to
that of the United States proper.

2d. The fauna of Siberia, separated from the fauna of
Europe by the Ural Mountains.

3d. The fauna of the Asiatic table-land, which, from what
is as yet known of it, appears to be quite distinct.

4th. The fauna of China and Japan, which is analogous to
that of Europe in the birds, and to that of the United States
in the reptiles — as it is also in the flora.

Lastly, it is in the temperate zone of the northern hemi-
sphere that we meet with the most striking examples of
those local faunas which have been mentioned above. Such,
for example, is the fauna of the Caspian Sea, of the steppes
of Tartary, and of the Western prairies.

§ 614. The faunas of the southern temperate regions differ
from those of the tropics as much as- the northern temperate

Crustacea. Among the types which are wanting in temperate America,
and which are found in Europe, may be cited the horse, the wild boar,
and the true mouse. All the species of domestic mice living in America,
have been brought from the Old World.

DISTRIBUTION OF THE FACJS'AS. 377

faunas do ; and, like them also, may be distinguished into
two provinces, the colder of which embraces Patagonia. But,
besides differing from the tropical faunas, they are also quite
unlike each other on the different continents. Instead of
that general resemblance, that family likeness, which we
have noticed between all the faunas of the temperate zone of
'the northern hemisphere, we find here the most complete con-
trasts. Each of the three continental peninsulas jutting
out southerly into the ocean represents, in some sense, a
separate world. The animals of South America, beyond the
tropic of Capricorn, are, in all respects, different from those
at the southern extremity of Africa. The hyenas, wild boars,
and rhinoceroses of the Cape of Good Hope have no analogues
on the American continent ; and the difference is equally great
between the birds, reptiles, fishes, insects and mollusks.
Among the most characteristic animals of the southern ex-
tremity of America are peculiar species of seals, and especially
among aquatic birds, the penguins.

§ 615. New Holland, with its marsupial mammals, with
which are associated insects and mollusks no less singular,
furnishes a fauna still more peculiar, and which has no simi-
larity to those of any of the adjacent countries. In the seas of
that continent, where every thing is so strange, we find the
curious shark, with paved teeth and spines on the back
(Cestracion Philippii), the only living representative of a
family so numerous in former zoological ages. But a most
remarkable feature of this fauna is, that the same types pre-
vail over the whole continent, in its temperate as well as its
tropical portions, the species only being different in different
localities.

§ 616. TROPICAL FAUNAS. — The tropical faunas are dis-
tinguished, on all the continents, by the immense variety of
animals which they comprise, not less than by the brilliancy
of their dress. All the principal types of animals are
represented, and all contain numerous genera and species.
We need only refer to the tribe of humming-birds, which
numbers not less than three hundred species. It is very im-
portant to notice, that here are concentrated the most per-
fect, as well as the most singular types of all the classes of the
animal kingdom. The tropical region is the only one occu-
pied by the quadrumana, the herbivorous bats, the great

378 GEOGRAPHICAL DISTRIBUTION OF ANIMALS.

pachydermata, such as the elephant, the hippopotamus, and
the tapir, and the whole family of edentata. Here also are
found the largest of the cat tribe, the lion, and tiger. Among
the birds we may mention the parrots and toucans, as essen-
tially tropical ; among the reptiles, the largest crocodiles and
gigantic tortoises ; and, finally, among the articulated animals,
an immense variety of the most beautiful insects. The ma-
rine animals, as a whole, are equally superior to those of other
regions : the seas teem with crustaceans and numerous cepha-
lopods, together with an infinite variety of gasteropods and
acephala. The echinoderms there attain a magnitude and
variety elsewhere unknown ; and, lastly, the polyps there
display an activity of which the other zones present no
example. Whole groups of islands are surrounded with coral
reefs formed by those little animals,

§ 617. The variety of the tropical fauna is further enriched
by the circumstance that each continent furnishes new and
peculiar forms. Sometimes whole types are limited to one
continent, as the sloth, the toucans, and the humming-birds
to America, the giraffe and hippopotamus to Africa ; and
again, animals of the same group have different characteristics,
according as they are found on different continents. Thus,
the monkeys of America have flat and widely-separated nos-
trils, thirty-six teeth, and generally a long, prehensile tail.
The monkeys of the old world, on the contrary, have nostrils
close together, only thirty-two teeth, and not one of them has
a prehensile tail.

§ 618. But these differences, however important they may
appear at first glance, are subordinate to more important cha-
racters, which establish a certain general affinity between all
the faunas of the tropics. Such, for example, is the fact that
the quadrumana are limited, on all the continents, to the
warmest regions ; and never, or but rarely, penetrate into the
temperate zone. This limitation is a natural consequence of
the distribution of the palms ; for as these trees, which con-
stitute the ruling feature of the flora of the tropics, furnish, to
a great extent, the food of the monkeys on both continents,
we have only to trace the limits of the palms, to have a pretty
accurate indication of the extent of the tropical faunas on all
three continents.

DISTEJIH TION OF THE FAUNAS. 379

§ 619. Several well-marked faunas may oe distinguished in
the tropical part of the American continent, namely :

1st. The fauna of Brazil, characterized by its gigantic reptiles,
its monkeys, its edentata, its tapir, its humming-birds, and the
astonishing variety of its insects.

2nd. The fauna of the western slope of the Andes, comprising
Chili and Peru, is distinguished by its llamas, vicunas, and
birds, which differ from those of the basin of the Amazon, as
also do the insects and mollusks.

3dly. The fauna of the Antilles and the Gulf of Mexico. This
is especially characterized by its marine animals, among which
the Ma n a f us is particularly remarkable ; an infinite variety of
singular fishes, embracing a large number of plectognaths ;
also mollusca, and radiata of peculiar species. It is in this
zone that the Pentacri/ms caput-medusfB is found, the only
representative, in the existing creation, of a family so nume-
rous in ancient epochs, the Crinoidea with a jointed stem.

The limits of the fauna of Central America cannot yet be
well defined, from a want of sufficient knowledge of the animals
inhabiting those regions.

§ 620. The tropical zone of Africa is distinguished by a
striking uniformity in the distribution of the animals, cor-
responding to the uniformity of the structure and contour of
that continent. Its most characteristic species are spread over
the whole extent of the tropics : thus, the giraffe is met with
from Upper Egypt to the Cape of Good Hope. The hippopo-
tamus is found at the same time in the Nile, the Niger, and
Orange River. This wide range is the more significant, as it
also relates to herbivorous animals, and thus supposes condi-
tions of vegetation very similar over wide countries. Some

O *

forms are nevertheless circumscribed within narrow districts ;
and there are marked differences between the animals of the
eastern and western shores. Among the remarkable species
of the African torrid region are the baboons, the African ele-
phant, the crocodile of the Nile, a vast number of antelopes,
and especially two species of ourang-outang, the chimpanzee
and t\\e Engeena, a large and remarkable animal, only recently
described. The fishes of the Nile have a tropical character,
as well as the animals of Arabia, which are more allied to
those of Africa than to those of Asia.

§ 621. The tropical fauna of Asia, comprising the two pe-

380 GEOGRAPHICAL DISTRIBUTION OF ANIMALS.

ninsulas of India and the isles of Sunda, is not less marked.
It is the country of the gibbons, the red ourang, the royal
tiger, the gavial, and a multitude of peculiar birds. Among
the fishes, the family of chetodons is most numerously repre-
sented. Here also are found those curious spiny fishes, whose
intricate gills suggested the name Labyrinthici, by which they
are known. Fishes with tufted gills are more numerous here
than in other seas. The insects and mollusks are no less
strongly characterized. Among others is the Nautilus, the only
living representative of the great family of large chambered-
shells, which prevailed so extensively over other types in for-
mer geological ages.

§ 622. The large island of Madagascar has its peculiar
fauna, characterized by its makis and its curious rodents. It
is also the habitat of the Aya-aya. Polynesia, exclusive of
New Holland, furnishes a number of very curious animals,
which are not found on the Asiatic continent. Such are the
herbivorous bats, and the Galeopithecus, or flying maki. The
Galapago islands, only a few hundred miles from the coast of
Peru, have a fauna exclusively their own, among which gigantic
land-tortoises are very characteristic.

SECTION III.

CONCLUSIONS.

§ 623. FROM the survey we have thus made of the distribution
of the Animal Kingdom, it follows :

1st. Each grand division of the globe has animals which
are either wholly or for the most part peculiar to it. These
groups of animals constitute the faunas of different regions.

2d. The diversity of faunas is not in proportion to the dis-
tance which separates them. Very similar faunas are found
at great distances apart ; as, for example, the fauna of Europe
and that of the United States, which yet are separated by a
wide ocean. Others, on the contrary, differ considerably,
though at comparatively short distances ; as the fauna of the
East Indies and the Sunda Islands, and that of New Holland ;
or the fauna of Labrador and that of New England.

3d. There is a direct relation between the richness of a
fauna and the climate. The tropical faunas contain a much
larger number of more perfect animals than those of the tem-
perate and polar regions.

4th. There is a no less striking relation between the fauna

381

and flora, the limit of the former being oftentimes determined,
so far as terrestrial animals are concerned, by the extent of
the latter.

§ 624. Animals are endowed with instincts and faculties
corresponding to the physical character of the countries they
inhabit, and which would be of no service to them under other
circumstances. The monkey, which is a frugivorous animal,
is organized for living on the trees from which he obtains his
food. The reindeer, on the contrary, whose food consists of
lichens, lives in cold regions. The latter would be quite out
of place in the torrid zone, and the monkey would perish with
hunger in the polar regions. Animals which store up provi-
sions are all peculiar to temperate or cold climates. Their
instincts would be uncalled for in tropical regions, where the
vegetation presents the herbivora with an abundant supply of
food at all times.

§ 625. However intimately the climate of a country may be
allied with the peculiar character of its fauna, we are not to
conclude that the one is the consequence of the other. The
differences observed between animals of different faunas are
no more to be ascribed to the influences of climate, than their
organization is to the influence of the physical forces of
nature. If it were so, we should necessarily find all animals
precisely similar, when placed under the same conditions. We
shall find, by the study of the different groups in detail, that
certain species, though very nearly alike, are nevertheless
distinct in two different faunas. Between the animals of the
temperate zone of Europe, and those of the United States,
there is similarity, but not identity ; and the particulars in
which they differ, though apparently trifling, are yet constant.

§ 626. Fully to appreciate the value of these differences, it
is often requisite to know all the species of a genus or of a
family. It is not uncommon to find, upon such an examina-
tion, that there is the closest resemblance between species
dwelling far apart from each other, while species of the same
genus, living side by side, are widely different. This may
be illustrated by a single example. The Menopoma, Siren,
Amphiuma, Axolotl, and the Menobranchus, are batrachians
which inhabit the rivers and lakes of the United States and
Mexico. They are very similar in external form, yet differ in
the fact that some of them have external gills at the sides of the
head, in which others are deficient ; that some have five toes,

382 GEOGRAPHICAL DISTRIBUTION OF ANIMALS.

while others have only two ; and also in having either two or
four legs. Hence we might be tempted to refer them to differ-
ent types, did we not know intermediate animals, completing
the series, namely, the Proteus and Meyalobatrachus. Now
the former exists only in the subterranean lakes of Austria,
and the latter in Japan. The connection in this case is con-
sequently established by means of species which inhabit dis-
tant continents.

§ 627. Neither the distribution of animals therefore, any
more than their organization, can be the effect of external in-
fluences. We must, on the contrary, see in it the realization
of a plan wisely designed, the work of a Supreme Intelligence,
who created, at the beginning, each species of animal at the
place, and for the place, which it inhabits. To each species
has been assigned a limit which it has no disposition to over-
pass so long as it remains in a wild state. Only those animals
which have been subjected to the yoke of man, or whose
subsistence is dependent on man's social habits, are exceptions
to this rule.

§ 628. As the human race has extended over the surface of
the earth, man has more or less modified the animal popula-
tion of different regions, either by exterminating certain spe-
cies, or by introducing others with which he desires to be
more intimately associated, — the domestic animals. Thus,
the dog is found wherever we know of the presence of man.
The horse, originally from Asia, was introduced into America
by the Spaniards ; where it has thriven so well, that it is
found wild, in innumerable herds, over the Pampas of South
America, and the prairies of the West. In like manner the
domestic ox became wild in South America. Many less wel-
come animals have followed man in his peregrinations ; as,
for example, the rat and the mouse, as well as a multitude of
insects, such as the house-fly, the cock-roach, and others
which are attached to certain species of plants, as the white-
butterfly, the Hessian-fly, &c. The honey-bee also has been
imported from Europe.

§ 629. Among the species which have disappeared, under
the influence of man, we may mention the Dodo, a peculiar
species of bird which once inhabited the Mauritius, some re-
mains of which are preserved in the British and Ashmolean
Museums ; a large cetacean of the north (Rytina Stelleri),
formerly inhabiting the coasts of Behring's Straits, and which

CONCLUSIONS. 383

has not been seen since 1768. According to all appearances,
we must also reckon among these the great stag, the skeleton
and horns of which have been found buried in the peat-bogs
of Ireland, and those of the Isle of Man. There are also
many species of animals whose numbers are daily diminishing,
and whose extinction may be foreseen ; as the Canadian deer
( Wapiti), the ibex of the Alps, the L'dmmeryeyer, the bison,
the beaver,, the wild-turkey, &c.

.§ 630. Other causes may also contribute towards dispersing
animals beyond their natural limits. Thus the sea-weeds are
carried about by marine currents, and are frequently met with
far from shore, thronged with little crustaceans, which are in
this manner transported to great distances from the place of
their birth. The drift-wood which the Gulf stream floats
from the Gulf of Mexico even to the western shores of Europe,
is frequently perforated by the larvae of insects, and may
probably serve as depositories for the eggs of fishes, Crustacea
and moliusks. It is possible also that aquatic birds may con-
tribute in some measure to the diffusion of some species of
fishes and moliusks, either by the eggs becoming attached to
their feet, or by means of those which they evacuate undi-
gested, after having transported them to considerable dis-
tances. Still, .all these circumstances exercise but a very
feeble influence upon the distribution of species in general, and
each country, none the less, preserves its peculiar physiog-
nomy, so far as its animals are concerned.

§ 631. There is only one way to account for the distribu-
tion of animals as we find them, namely, to suppose that they
are autochthonoi, that is to say, that they originated like
plants, on the soil where they are found. In order to explain
the particular distribution of many animals, we are even led
to admit that they must have been created at several points of
the same zone, an inference which we must make from the distri-
bution of aquatic animals, especially that of fishes. If we ex-
amine the fishes of the different rivers of the United States, pe-
culiar species will be found in each basin, associated with others
which are common to several basins. Thus, the Delaware
River contains species not found in the Hudson ; but, on the
other hand, the pickerel is found in both. Now, if all animals
originated at one point, and from a single stock, the pickerel
must have passed from the Delaware to the Hudson, or vice

384 GEOGRAPHICAL U1STRIBTJTIOX OF ANIMALS.

versa, which it could only have done by passing along the
sea-shore, or by leaping over large spaces of terra firma;
that is to say, in both cases it would be necessary to do vio-
lence to its organization. Now such a supposition is in direct
opposition to the immutability of the laws of nature.

§ 632. We shall hereafter see that the same laws of distri-
bution are not limited to the actual creation only, but that
they have also ruled the creations of former geological epochs,
and that the fossil species have lived and died, most of them,
at the place where their remains are found.

§ 633. Even man, although a cosmopolite, is subject, in a
certain sense, to this law of limitation. While he is every-
where the one identical species, yet several races, marked by
certain peculiarities of features, are recognised ; such as the
Caucasian, Mongolian, and African races, of which we are
hereafter to speak. And it is not a little remarkable, that
the abiding places of these several races correspond very
nearly with some of the great zoological regions. Thus we
have a northern race, comprising the Samoyedes in Asia, the
Laplanders in Europe, and the Esquimaux in America, cor-
responding to the Arctic fauna (§ 602), and like it, identical on
the three continents, having for its southern limit the region
of trees (§ 604). In Africa, we have the Hottentot and Negro
races, in the south and central portions respectively, while the
people of northern Africa are allied to their neighbours in
Europe ; just as we have seen to be the case with the zoolo-
gical fauna in general (§ 584). The inhabitants of New Hol-
land, like its animals, are the most grotesque and uncouth of
all races (§ 615).

§ 634. The same parallelism holds good elsewhere, though
not always in so remarkable a degree. In America, espe-
cially, while the aboriginal race is as well distinguished from
other races as is its flora, the minor divisions are not so de-
cided. Indeed, the facilities, or we might sometimes rather
say, necessities, arising from the varied supplies of animal
and vegetable food in the several regions, might be expected
to involve, with his corresponding customs and modes of
life, a difference in the physical constitution of man, which
would contribute to augment any primeval differences. It
could not, indeed, be expected, that a people constantly sub-
jected to cold, like the people of the north, and living almost

CONCLUSIONS. 385

exclusively on fish, which is not to be obtained without great
toil and peril, should present the same characteristics, either
bodily or mental, as those who idly regale on the spontaneous
bounties of tropical vegetation.

[§ 635. Many other causes still more intimately connected
with the aspect of our globe have also a great influence upon
the distribution of the animals and plants living on its
surface. The form of continents, the bearing of their shores,
the direction and height of mountains, the mean level of great
plains, the amount of water circumscribed by land, and form-
ing inland lakes or seas, each shows a marked influence upon
the general features of vegetation. Small low islands, scat-
tered in clusters, are covered with a vegetation entirely
different from that of extensive plains under the same lati-
tudes. The bearing of the shores, again, modifying the cur-
rents of the sea, will also react upon vegetation. Mountain
chains will be influential, not only from the height of their
slopes and summits, but also from their action upon the
prevailing winds. It is obvious, for instance, that a moun-
tain chain like the Alps, running east and west, and form-
ing a barrier between the colder region northwards and
the warmer southwards, will have a tendency to lower the
temperature of the northern plains, and to increase that of the
southern below or above the mean which such localities would
otherwise present ; while the influence of a chain running
north and south, like the Rocky Mountains and the Andes,
will be quite the reverse, and tend to increase the natural dif-
ferences between the eastern and western shores of the conti-
nent, laying open the north to southern influences and the
south to those of the north, thus rendering its climate ex-
cessive, i. e. its summer warmer and its winter colder.

[§ 636. Again, the equalizing influence of a large sheet ot
water, the temperature of which is less liable to sudden changes
than the atmospheric air, is very apparent in the uniformity of
coast vegetation over extensive tracts, provided the soil be of
the same nature ; and also in the slower transition from one
season into another along the shores, the coasts having less
extreme temDeratures than the main land. The absolute de-
gree of temperature of the water acts with equal power ; as
the aquatic plants of the tropical regions, for instance, those

c c

386 GEOGRAPHICAL DISTRIBUTION OF ANIMALS.

of Guyana, differ as widely from those of Lake Superior as
the palms differ from the pine forests.

[§ 637. But, however active these physical agents may be,
it would be very un philosophical to consider them as the
source or origin of the beings upon which they show so exten-
sive an influence. Mistaking the circumstantial relation under
which they appear for a causal connection, has done great
mischief in natural science, and led many to believe they un-
derstood the process of creation, because they could account
for some of the phenomena under observation. But, however
powerful may be the degree of the heat ; be the air ever so
dry, or ever so moist ; the light ever so moderate, or ever so
bright ; alternating ever so suddenly with darkness, or passing
gradually from one condition to the other ; these agents have
never been observed to produce anything new, or to call into
existence anything that did not exist before. Whether acting
isolated or jointly, they have never been known even to modify
to any great extent the living beings already existing, unless
under the guidance and influence of man, as we observe among
domesticated animals and cultivated plants. This latter fact
shows, indeed, that the influence of the mind over material
phenomena is far greater than that of physical forces, and thus
refers our thoughts again and again to a Supreme Intelligence
for a cause of all these phenomena, rather than to the so-
called natural agents.

[§ 638. The physical agents whose influence upon organized
beings we have just examined, show a regular progression in
their action, agreeing most remarkably with the degrees of
latitude on one side, and the elevation above the level of the
sea on the other. Hence the difference in the vegetation, as
we proceed from tropical regions towards the poles, or as
we ascend from the level of the sea to any height along the
slopes of a mountain. In both these directions there is a
striking agreement in the order of succession of the pheno-
mena, so much so, that the natural products of any given lati-
tude may be properly compared with those occurring at a
given height above the level of the sea ; for instance, the vege-
tation of regions near the polar circles, and that of high moun-
tains near the limits of perpetual snow under any latitude. The
height of this limit, however, varies, of course, with the lati-
tude. In Lapland, at 6/° north latitude, it is three thousand

CONCLUSIONS. 387

five hundred feet above the level of the sea ; in Norway, at
lat. 60°, it is five thousand feet ; in the Alps, at lat. 46°, about
eight thousand five hundred ; in the Himalaya, at lat. 30°, over
twelve thousand ; in Mexico, at lat. 1 9°, it is fifteen thousand ;
and at Quito, under the equator, not less than sixteen thou-
sand. At these elevations, in their different respective lati-
tudes, without taking the undulations of the isothermal lines
into consideration, vegetation shows a most uniform character,
so that it may be said that there is a corresponding similarity
of climate and vegetation between the successive degrees of
latitude and the successive heights above the sea. As a strik-
ing example, the fact may be mentioned of the occurrence of
identical plants in Lapland in lat. 67°, at a height of about
three thousand feet and less above the level of the sea, and
upon the summit of Mount Washington, in lat. 44°, at a height
of not less than six thousand feet ; while below this limit, in the
wooded valleys of the White Mountains, there is not one spe-
cies which occurs also about North Cape.

[§ 639. There is, nevertheless, one circumstance which shows
that climatic influences alone, however extensive, taking, for
instance, into account all the above-mentioned agents together,
will not fully account for the geographical distribution of or-
ganized beings ; as their various limits do not agree precisely
with the outlines indicating the intensity of physical agents
upon the surface of the earth. A few examples may serve to
illustrate this remark. The limit of forest vegetation round
the arctic circle does not coincide with the astronomical limits
of the arctic zone ; nor does it agree fully with the isothermal
line of 32° of Fahrenheit ; nor is the limit of vegetation
in height always strictly in accordance with the temperature,
as the Cerastium latifolium 'and Ranunculus ylacialis, for in-
stance, occur in the Alps as high as ten, and even eleven
thousand feet above the level of the sea. Again, eastern and
western countries within the same continent, or compared
from one continent to the other, show such differences under
similar climatic circumstances, that we at once feel that some-
thing is wanting in our illustrations, when we refer the dis-
tribution of animals and plants solely to the agency of climate.
But the most striking evidence that climate neither accounts
for the resemblance nor the difference of animals and plants
in different countries, may be derived from the fact, that the

C c 2

388 GEOGRAPHICAL DISTRIBUTION OF ANIMALS.

development of the animal and vegetable kingdoms differs
widely, under the same latitudes, in the northern and in the
southern hemispheres, and that there are entire families of
plants and animals exclusively circumscribed within certain
parts of the world ; such are, for instance, the magnolia and
cactus in America, the kangaroos in New Holland, the ele-
phants and rhinoceros in Asia and Africa, &c., &c.

[§ 640. From these facts we may indeed conclude, that
there are other influences acting in the distribution of animals
and plants besides climate ; or, perhaps, we may better put
the proposition in this form : that however intimately con-
nected with climate, however apparently dependent upon it,
vegetation is, in truth, independent of those influences, at
least so far as the causal connection is concerned, and merely
adapted to them. This position would at once imply the ex-
istence of a power regulating these general phenomena in such
a manner as to make them agree in their mutual connection ;
that is to say, we are thus led to consider nature as the work
of an intelligent Creator, providing for its preservation under
the combined influences of various agents equally his work,
which contribute to their more diversified combinations.

[§ 641. The geographical distribution of organized beings
displays more fully the direct intervention of a Supreme
Intelligence in the plan of creation, than any other adapta-
tion in the physical world. Generally, the evidence of such
an intervention is derived from the benefits, material, intel-
lectual, and moral, which man derives from nature around
him, and from the mental conviction which consciousness im-
parts to him, that there could be no such wonderful order in
the universe, without an omnipotent Ordainer of the whole.
This evidence, however plain to the Christian, will never be
satisfactory to the man of science, in that form. In these
studies evidence must rest upon direct observation and induc-
tion, just as fuUy as mathematics claims the right to settle all
questions about measurable things. There wih1 be no scien-
tific evidence of God's working in nature, until naturalists
have shown that the whole creation is the expression of a
thought, and not the -product of physical agents. Now what
stronger evidence of thoughtful adaptation can there be, than
the various combinations of similar, though specifically differ
ent assemblages of animals and plants repeated all over the

CONCLUSIONS. 389

world, under the most uniform and the most diversified cir-
cumstances ? When we meet with pine trees, so remarkable
for their peculiarities, both morphological and anatomical,
combined with beeches, birches, oaks, maples, &c., as well
in North America as in Europe and Northern Asia, under
similar circumstances ; when we find, again, representatives
of the same family with totally different features, mingling, so
to say, under low latitudes with palm trees, and all the luxu-
riant vegetation of the tropics ; when we truly behold such
scenes, and have penetrated their full meaning as naturalists,
then we are placed in a position similar to that of the anti-
quarian who visits ancient monuments. He recognizes at
once the workings of intelligence in the remains of an an-
cient civilization ; he may fail to ascertain their age correctly,
he may remain doubtful as to the order in which they were
successively constructed, but the character of the whole tells
him that they are works of art, and that men, like himself,
originated these relics of by-gone ages. So shall the intelli-
gent naturalist read at once in the pictures which nature pre-
sents to him, the works of a higher Intelligence ; he shall re-
cognize in the minute perforated cells of the Conifer^, which
differ so wonderfully from those of other plants, the hierogly-
phics of a peculiar age ; in their needle-like leaves, the escut-
cheon of a peculiar dynasty ; in their repeated appearance
under most diversified circumstances, a thoughtful and thought-
eliciting adaptation. He beholds, indeed, the works of a being
thinking like himself, but he feels at the same time that he
stands as much below the Supreme Intelligence, in wisdom,
power and goodness, as the works of art are inferior to the
wonders of nature. Let naturalists look at the world under
such impressions, and evidence will pour in upon us that all
creatures are expressions of the thoughts of Him whom we
know, love and adore unseen.*]

* Lake Superior, by Professor Louis Agassiz, page 104 at seq.

CHAPTER FOURTEENTH.

GEOLOGICAL SUCCESSION OF ANIMALS ; OR, THEIR DIS-
TRIBUTION IN TIME.

SECTION I.

STRTJCTUEE OF THE EAETH'S CEUST.

§ 642. THE records of the Bible, as well as human tra-
dition, teach us that man and the animals associated with
him were created by the word of God ; " The Lord made
Heaven and earth, the sea, and all that in them is ;" and
this truth is confirmed by the revelations of science, which
unequivocally indicate the direct interventions of creative
power.

§ 643. But man and the animals which now surround
him are not the only kinds which have had a being. The
surface of our planet, anterior to their appearance, was not a
desert. There are, scattered through the crust of the earth,
numerous animal and vegetable remains, which show that
the earth had been repeatedly supplied with, and long in-
habited by animals and plants altogether different from those
now living.

§ 644. In general, their hard parts are the only relics of
them which have been preserved, such as the skeleton and
teeth of vertebrata ; the shells of mollusca and radiata ;
the shields of crustaceans, and sometimes the wing-cases
of insects. Most frequently they have lost their original
chemical composition, and are changed into stone ; and hence
the name of petrifactions or fossils, under which latter term
are comprehended all the organized bodies of former epochs,
obtained from the earth's crust. Others have entirely dis-
appeared, leaving only their forms and sculpture impressed
upon the rocks.

§ 645. The study of these remains and of their position in
the rocks constitutes PALAEONTOLOGY ; one of the most essen-
tial branches of zoology. Their geological distribution, or
the order of their successive appearance — namely, the distri-
bution of animals in time, is of no less importance than the

STRUCTURE OF THE EARTH'S CRUST. 391

geographical distribution of living animals, their distribution
in space, of which we have treated in the preceding chapter.
To obtain an idea of the successive creations, and of the
stupendous length of time they have required, it is necessary
to sketch the principal outlines of geology.

§ 646. The rocks* which compose the crust of our globe
are of two kinds : —

1. The Massive R,ocks, called also Plutonic, or Igneous
Rocks, which lie beneath all the others, or have sometimes
been forced up through them, from beneath. They were
once in a melted state, like the lava of the present epoch, and,
on cooling at the surface, formed the original crust of the
globe, the granite, and later porphyry, basalt, &c.

2. The Sedimentary, or Stratified Rocks, called also Nep-
tunic Rocks, which have been deposited in water, in the same
manner as modern seas and lakes deposit sand and mud on
their shores, or at the bottom.

§ 647. These sediments have been derived partly from the
disintegration of the older rocks, and partly from the decay
of plants and animals. The materials being disposed in layers
or strata have become, as they hardened, limestones, slates,
marls, or grits, according to their chemical and mechanical
composition, and contain the remains of the animals and plants
which were scattered through the water s.f

§ 648. The different strata, when undisturbed, are ar-
ranged one above the other in a horizontal manner, like the
leaves of a book, the lowest being the oldest. In consequence
of the commotions which the crust of the globe has under-
gone, the strata have been ruptured, and many points of the

* Rocks, in a geological sense, include all the materials of the earth,
the loose soil and gravel, as well as the firm rock.

f Underneath the deepest strata containing fossils, between these and the
Plutonic rocks, are generally found very extensive layers of slates without
fossils (gneiss, mica-slate, talcose-slate), though stratified and known to
the geologist under the name of Metamorphic Rocks (fig. 376, M}, being
probably sedimentary rocks which have undergone considerable changes.
The Plutonic rocks, as well as the metamorphic rocks, are not always con-
fined to the lower levels, but they are often seen rising to considerable
heights, and forming mary of the loftiest peaks of the globe. The former
also penetrate, in many cases, like veins, through the whole mass of the
stratified and metamorphic layers, and expand at the surface ; as is the case
with the trap dykes, and as lava streams actually do now (fig. 376, T. L.)

392

GEOLOGICAL SUCCESSION OF ANIMALS.

surface have been elevated to great heights, in the form of
mountains ; and hence it is that fossils are sometimes found at
the summit of the highest mountains, though the rocks con-
taining them were originally formed at the bottom of the sea.
But even when folded, or partly broken, their relative age may
still be determined by an examination of the ends of the up-
turned strata, where they appear or crop out in succession, at
the surface, or on the slopes of mountains, as seen in the dia-
gram (fig. 376).

Fig. 376.

§ 649. The sedimentary rocks are the only ones containing
animal and vegetable remains. These are found imbedded in
the rock, just as we should find them in the mud now deposited
at the bottom of the sea, if laid dry. The strata containing
fossils are numerous. The comparison and detailed study of
them belongs to geology, of which Palaeontology forms an
essential part. A group of strata extending over a certain
geographical extent, all of which contain some fossils in com-
mon, no matter what may be the chemical character of the
rock, whether it be limestone, sand, or clay, is termed a
geological Formation. Thus, the coal beds, with the inter-
vening slates and grits, and the masses of limestone between
which they often lie, constitute but one formation, — the car-
boniferous formation.

§ 650. Among the stratified rocks, we distinguish ten prin-
cipal formations, each of wrhich indicates an entirely new
era in the earth's history ; while each of the layers com-
posing a formation indicates but some partial revolution.
Proceeding from below upwards, they are as follows, as

STRTJCTTTEE OP THE EAKTH'S CEUST. 393

shewn in the cut, and also in the lower diagram in the
frontispiece.

1st. The Lower Silurian. This is a most extensive forma-
tion, no less than eight stages of which have been made out
by geologists in North America, composed of various lime-
stones and sandstones.*

2d. The Upper Silurian. It is also a very extensive forma-
tion, since about ten stages of it are found in the State of
New York.f

3d. The Devonian, including in North America no less than
eleven stages. £ It occurs also in Russia and Scotland, where
it was first made out as a distinct formation.

4th. The Carboniferous Formation, consisting of three grand
divisions §

5th. The Trias, or Saliferous Formation, contains the richest
deposits of salt on the continent of Europe, and comprises
three stages,]] to one of which the sandstone of the Con-
necticut valley belongs.

6th. The Oolitic Formation, only faint traces of which exist
on the continent of America. It comprises at least four dis-
tinct stages.^]"

7th. The Cretaceous, or Chalk Formation, of which three
principal stages have been recognized : two of these are
feebly represented in the Southern and Middle States of North
America.

* 1. Potsdam Sandstone; 2. Calciferons Sandstone; 3. Chazy Lime-
stone ; 4. Bird's-eye Limestone ; 5. Black River Limestone ; 6. Trenton
Limestone; 7. Utica Slate ; 8. Hudson River Group; being all found in
the western parts of the United States.

t 1- Oneida Conglomerate ; 2. Medina Sandstone ; 3. Clinton Group ;
4. Niagara Group ; 5. Onondaga Salt Group ; 6. Water Limestone ;
7. Pentamerus Limestone ; 8. Delthyris Shaly Limestone ; 9. Encrinal
Limestone ; 10. Upper Pentamerus Limestone.

J 1. Oriskany Sandstone; 2. Cauda-Galli Grit; 3. Onondaga Lime-
stone; 4. Corniferous Limestone; 5. Marcellus Shale; 6. Hamilton
Group ; 7. Tully Limestone ; 8. Genesee Slate ; 9. Portage Group ;
10. Chemung Group ; 11. Old Red Sandstone.

§ 1. The Permian, extensively developed in Russia, especially in the
government of Perm ; 2. The coal measures, containing the rich deposits
of coal in the Old and New World ; 3 The Magnesian Limestone of
England.

|| 1. New Red Sandstone ; 2. Muschelkalk ; 3. Keuper.

f 1. The Lias ; 2. The Lower Oolite ; 3. The Middle Oolite ; 4. The
Upper Oolite.

394 GEOLOGICAL SUCCESSION OF ANIMALS.

8th. The Lower Tertiary, or Eocene, very abundant in the
Southern States of the Union, and to which belong the coarse
limestone of Paris, and the London clay in England.

9th. The Upper Tertiary or Miocene, and Pleiocene, found
also in the United States, as far north as Martha's Vineyard,
and Nan tucket, and very extensive in Southern Europe, as well
as in South America.

10th. The Drift, forming the most superficial deposits, and
extending over a large portion of the northern countries in
both hemispheres.

We have thus more than forty distinct layers already made
out, each of which marks a distinct epoch in the earth's his-
tory, indicating a more or less extensive and important change
in the condition of its surface.

§ 651. All the formations are not everywhere found, or are
not developed to the same extent, in all places. So it is
with the several strata of which they are composed. In other
words, the layers of the earth's crust' are not continuous
throughout, like the coats of an onion. There is no place on
the globe where, if it were possible to bore down to its centre,
all the strata would be found. It is easv to understand how

tt

this must be so. Since irregularities in the distribution
of water upon the solid crust have, necessarily, always existed
to a certain extent, portions of the earth's surface must have
been left dry at every epoch of its history, gradually forming
large islands and continents, as the changes were multiplied.
And since the rocks were formed by the subsidence of sedi-
ment in water, no rocks would be formed .except in regions
covered by water ; they would be thickest at the parts where
most sediment was deposited, and gradually thin out to-
wards their circumference. We may therefore infer, that all
those portions of the earth's surface which are destitute of a
certain formation were dry land, during that epoch of the
earth's history to which such formation relates, excepting,
indeed, where the rocks have been subsequently removed by
the denuding action of water or other causes.

§ 652. Each formation represents an immense period of
time, during which the earth was inhabited by successive
races of animals and plants, whose remains are often found,
in their natural position, in the places where they lived ana
died, not scattered at random, though sometimes mingled to-

STRUCTURE OF THE EARTH'S CRUST. 395

gether by currents of water, or other influences, subsequent
to the time of their interment. From the manner in which
the remains of various species are found associated in the
rock, it is easy to determine whether the animals to which
these remains belonged lived in the water, or on land, on the
beach or in the depths of the ocean, in a warm or in a cold
climate. They will be found associated in just the same
way as animals are that live under similar influences at the
present day.

§ 653. In most geological formations, the number of species
of animals and plants found in any locality of given extent, is
not below that of the species now living in an area of equal
extent, and of a similar character; for though, in some deposits,
the variety of the animals contained may be less, in others it is
greater than that on the present surface. Thus, the coarse lime-
stone in the neighbourhood of Paris, which is only one stage of
the lower tertiary, contains not less than 1 200 species of shells ;
whereas the species now living in the Mediterranean do not
amount to half that number. Similar relations may be
pointed out in America. Mr. Hall, one of the geologists of
the New York Survey, has described, from the Trenton lime-
stone (one of the ten stages of the lower Silurian), 170 species
of shells, a number almost equal to that of all the species
found now living on the coast of Massachusetts.

§ 654. Nor was the number of individuals less than at
present. Whole rocks are entirely formed of animal remains,
particularly of corals and shells. So, also, coal is composed
of the remains of plants. If we consider the slowness with
which corals and shells are formed, we may form some faint
notion of the vast series of ages that must have elapsed in
order to allow the formation of those rocks, and their regular
deposition, under the water, to so great a thickness. If, as
all things combine to prove, this deposition took place in
a slow and gradual manner in each formation, we must
conclude, that the successive species of animals found in them
followed each other at long intervals, and are not the work of
a single epoch,

§ 655. It was once believed that animals were successively
created in the order of their relative perfection ; so that the
most ancient formations contained only animals of the lowest
grade, such as the polyps and the echinoderms, to which

39C GEOLOGICAL SUCCESSION OF ANIMALS.

succeeded the mollnsca, then the articulated animals, and
last of all, the vertebrata. This theory, however, is now
untenable ; since fossils belonging to each of the four de-
partments have been found in the fossiliferous deposits of
every age. Indeed, we shall see that even in the lower Silu-
rian formation there exist not only polyps and other radiata,
but also numerous mollusca, trilobites (belonging to the arti-
culata), and even fishes and reptiles.*

SECTION II,

AGES OF NATURE.

§ 656. EACH formation, as has been before stated (§ 649),
contains remains peculiar to itself, which do not extend into
the neighbouring deposits above or below it. Still there is a
connection between the different formations, more strong in
proportion to their proximity to each other. Thus, the
animal remains of the chalk, while they differ from those of
all other formations, are nevertheless much more nearly re-

•J

lated to those of the oolitic formation, which immediately
precedes, than to those of the carboniferous formation, which
is much more ancient ; and in the same manner, the fossils of
the carboniferous group approach more nearly to those of the
Silurian formation than to those of the Tertiary.

§ 657. These relations could not escape the observation
of naturalists, and indeed they are of great importance for
the true understanding of the development of life at the sur-
face of our earth. And, as in the history of man, several
grand periods have been established, under the name of Ages,
marked by peculiarities in his social and intellectual condition,
and illustrated by contemporaneous monuments, so, in the
history of the earth also, are distinguished several great pe-
riods, which may be designated as the various Ages of Nature y
illustrated in like manner by their monuments, the fossil re-
mains, which, by certain general traits stamped upon them,
clearly indicate the eras to which they belong.

§ 658. We distinguish four Ages of Nature, correspond-
ing to the great geological divisions, namely :

1st. The Primary or Paleozoic Age, comprising the lower

* See an important communication, by Mr. Logan, on the Footprints of
Reptiles in the Potsdam sandstone of Lower Canada, Quart. Jour. Geol.
Soc. vol. vii. p. 247. — Eo.

AGES OF NATURE. 397

Silurian, the upper Silurian, and the Devonian. During this
age there were few air-breathing animals. The fishes were
the masters of creation. We may therefore call it the Reign
of Fishes.

2d. The Secondary Age, comprising the carboniferous,
the trias, the oolitic, and the cretaceous formations. This
is the epoch in which air-breathing animals more extensively
prevail. The reptiles predominate over the other classes, and
we may therefore call it the Reign of Reptiles.

3d. The Tertiary Age, comprising the tertiary formations.
During this age, terrestrial mammals, of great size, abound.
This is the Reign of Mammals.

v «/

4th. The Modern Age, characterized by the appearance of
the most perfect of all created beings. This is the Reign of
Man.

Let us review each of these four Ages of Nature, with re-
ference to the diagram at the beginning of the volume.

§ 659. THE PALEOZOIC AGE. Reign of Fishes. — The
palaeozoic fauna, being the most remote from the present epoch,
presents the least resemblance to the animals now existing, as
will easily be perceived by a glance at the following sketches
(fig. 377). In no other case do we meet with animals of
such extraordinary shapes, as in the strata of the palaeozoic
age.

§ 660. We have already stated (§ 655) that there are found,
in each formation of the primary age, animal remains of all
the four great departments, namely, vertebrata, articulata,
mollusca, and radiata. We have now to examine to what
peculiar classes and families of each department these remains
belong, with a view to ascertain if any relation between the
structure of an animal and the epoch of its first appearance
on the earth's surface may be traced.

§ 661. As a general result of the inquiries hitherto made,
it may be stated that the palaeozoic animals belong, for the
most part, to the lower divisions of the different classes.
Thus, of the class of echinoderms, we find scarcely any but
Crinoids (figs. 72 and 73), which are the least perfect of the
class ; of which there are some quite peculiar types from, the
Trenton limestone and from the Black River limestone.

§ 662. Of the mollusca, the bivalves or acephala are nu-
merous, but for the most part belong to the brachiopoda, that
is to say, to the lo^u-est division of the class, including molluska

398

GEOLOGICAL SUCCESSION OF ANIMALS.

with unequal valves, having peculiar appendages in the interior.
The Leptana alternately found very abundantly in the Trenton

limestone, is

Fig. 377. one of those

,5 shells. The

only fossils yet
found in the
Potsdam sand-
stone, the old-
est, of all fossi-
liferous depo-
sits, belong al-
so to this fa-
mily (Lingula
prima) . Be-
sides this, there
are also found
some bivalves
of a less un-
common shape
(Avicula de-
cussata) ; [and
in the upper
stages of the
Silurian group
in England we
find Or this or-

bicularis (1), Terebratula navicula (2), Orthis navicularis,
(3) Pentameus Knightii (4), Atrypd affinis (5), fig. 3/7-j

§ 663. The gasteropoda are less abundant ; some of them
are of a peculiar shape and structure, as Bucania expansa,
Euomphalus hemisphcericus. Those more similar to our
common marine snails have all an entire aperture ; those with
a canal being of a more recent epoch.

§ 664. Of the cephalopoda we find some genera not less
curious, part of which disappear in the succeeding epochs ;
such, in particular, as those of the straight, chambered shells
called orthoceratites, some of which are twelve feet in length
(Orthoceras ventricosum) . There are also found some of a
coiled shape, like the ammonites of the secondary age, but
having less complicated partitions (Lituites yiganteus, 7). The
true cuttle-fishes, which are the highest of the class, are not

AGES OF NATURE. 399

yet found. On the contrary, the Bryozoa, which have long
been considered as polyps, but which, according to all appear-
ances, are mollusks of a very low order, are very numerous
in this epoch.

§ 665. The articulata of the palaeozoic age are mostly
trilobites, animals which evidently belong to the lower order
of the crustaceans (fig. 3/8). There is an incompleteness
and want of
development in
the form of
their body, that
strongly re-

o v

minds us of the
embryo among
the crabs. A
great many ge-
nera have al- Fig. 37S.—Homalonotus delphinocephalus.—Komg.
ready been dis-
covered. The Silurian rocks of Bohemia have yielded up-
wards of two hundred species. Homalonotus (fig. 37H),
one of the family Calymenidce, will give a general idea of the
form of these palaeozoic crustaceans. Some others seem more
allied to the crustaceans of the following ages, but are never-
theless of a very extraordinary form, as Eurypterus remipes.
There are also found, in the Devonian, some very large
entomostraca. The class of worms is represented only by Nereis
and a few Serpula, which are marine worms, surrounded by a
solid sheath. The class of insects is entirely wanting.

§ 666. The inferiority of the earliest inhabitants of our
earth appears most striking among the vertebrata. There
are as yet neither birds nor mammals. The fishes, and a few
reptiles whose fossil foot-marks we only know, are the sole
representatives of this division of animals.

§ 667. The fishes of that early period were not like
ours. Some of them had the most extraordinary forms, so
tha'-; they have been often mistaken for quite different animals ;
for example, the Pterichthys (fig. 3/9), with its two winglike
appendages, and also the Coccosteus (fig. 380), of the same
deposit, with its large plates covering the head and the ante-
rior part of the body. There are also found remains of shark's
spines, as well as palatal bones, the latter of a very peculiar

400

GEOLOGICAL SUCCESSION OF ANIMALS.

kind. Even those fishes which have a more regular shape,
as the Dipterus, have not horny scales like our common fishes,

Fig. 379. — Pterichthys, from the Devonian rocks of Scotland. — Agass.

but are protected by a coat of bony plates, covered with
enamel, like the gar pikes (Lepidosteus) of the American
rivers. Moreover they all exhibit certain characteristic fea-
tures, which are very interesting in a physiological point of
view. They all have a broad head, and a tail terminating in
two unequal lobes. What is still more curious, the best
preserved specimens show no indications of the bodies of the
vertebrae, but merely the spinous processes ; from which it must
be inferred that the body of the vertebra was cartilaginous, as
it is in our sturgeons.

§ 66^. Recurring to what has been stated on that point in
Chapter Twelfth, we thence conclude that these ancient fishes
were not so fully developed as most of our fishes, being, like

AGES OF NATURE.

401

the sturgeon, arrested, as it were, in their development ; since
we have shown that the
sturgeon, in its organiza-
tion, agrees, in many re-
spects, with the cod or
F. ...... ;.,

\

salmon in their early age.
§ 669. Finally, there
was, during the palaeozoic
age, less variety among
the animals of the differ-
ent regions of the globe ;
and this may be readily
explained by the peculiar
configuration of the earth
at that epoch. Great
mountains did not then
exist ; there were neither
lofty elevations nor deep
depressions. The sea co-
vered the greater part, if
not the whole, of the sur-
face of the globe ; and the
animals which then exist-
ed, and whose remains
have been preserved, were
all, with the exception or
the reptiles which have
left their foot-marks on
the Potsdam sandstone,
aquatic animals, breathing
by gills. This wide dis-
tribution of the waters im-
pressed a very uniform
character upon the whole
animal kingdom. Between
different zones and conti-
nents, no such strange TC „

, , * ,, -..ff ° rig.JSO. — Coccosteus cuspidatus
contrasts of the different

types existed as at the present epoch. The same gen eft;, and
often the same species, were found in the seas of America,
Europe, Asia, Africa, and New Holland ; from which we must

D D

.— .-. /-asa.

402

GEOLOGICAL SUCCESSION OF ANIMALS.

conclude that the climate was much more uniform than at
the present day. Among the aquatic population, no sound
was heard. All creation was then silent.

§ 670. THE SECONDARY AGE. Reign of Reptiles. — The
Secondary age displays a greater variety of animals as well as
plants. The fantastic forms of the palaeozoic age disappear,
and in their place we see a greater symmetry of shape. The
advance is particularly marked in the series of vertebrata.
Fishes and a few reptiles are no longer the sole representatives
of that department. Reptiles, birds, and mammals succes-
sively make their appearance, but reptiles preponderate, par-
ticularly in the Oolitic formation ; on which account we have
called this age the Reign of Reptiles.

§ 671. The Carboniferous formation is the most ancient of
the Secondary age. Its fauna bears, in various respects, a
close analogy to that of the palaeozoic epoch, especially in
its Trilobites and mollusca.* Besides these, we meet here

b

a

f

ft d C y

Fig. 381. — The Flora of the coal period.

a Arborescent fern. d Neuropteris. g Araucaria.

b Pecopteris.

c Asterophyllites.

i

e Lepidodendron.
/ Calamites.

k'

h Casuerina.

This circumstance has caused the coal-measures to be generally referred

AGES OF NATTJBE. 403

vrith air-breathing animals, as insects, scorpions, and rep-
tiles. At the same time, land-plants first make their ap-
pearance, namely, ferns of great size, club-mosses, and other
fossil plants. Fig. 381 exhibits some of the most typical
forms of the flora of this period. This abundant vegetation
corroborates what has been already said concerning the inti-
mate connection existing between the animals and the land-
plants of all epochs. The class of crustaceans has also improved
during the coal period. It is no longer composed exclusively
of Trilobites, but the type of horse-shoe crabs also appears,
with other gigantic forms. Some of the mollusca, particularly
the bivalves, seem also to approach those of the Oolitic period.
§ 6/2. In the Trias period, which immediately succeeds
the Carboniferous, the fauna of the Secondary age acquires
its definitive character ; here the reptiles first appear in con-
siderable numbers, consisting of huge crocodilian animals,
belonging to a peculiar order, the Rhizodonts (Protosaurus,
Notosaurus, and Labyrinthodori). The well-known discoveries
of Professor Hitchcock, in the red sandstone of the Con-
necticut Valley, have made us acquainted with a great number
of birds' tracks belonging to this epoch, for the most part indi-
cating animals of gigantic size. These impressions, which he
has designated under the name of Ornithichnites, are some of
them eighteen inches in length, and five feet apart, far exceed-
ing in size the tracks of the largest ostrich. Other foot-marks
of a very peculiar shape, have been found in the red sandstone
of Germany (fig. 382), and in Pennsylvania. They were
probably made by reptiles, which have been called Cheiro-

Fig. 382. — Line of footmarks on a slab of sandstone, from
Hildburghausen, in Saxony.

to the palaeozoic epoch. But there are reasons which induce us to unite
the carboniferous period with the secondary age, especially when we
consider that a luxuriant terrestrial vegetation was developed at this epoch;
that here land animals first appear in any considerable number, whereas,
in the palaeozoic age, there were chiefly marine animals, breathing by gilis,
and a few reptiles known only by their foot-marks.

D D 2

404

GEOLOGICAL SUCCESSION OF AJSTIMALS.

therium, from the resemblance of the impressions to a hand.
The mollusca, articulate, and radiata approach those of the

fauna of the suc-
ceeding period.

§ 673. The
Oolitic fauna is
remarkable for
the great number
of gigantic rep-
tiles it contains.
In this formation
we find those
enormous amphi-
bia, known under
the name Ichthy-
osaurus, Plesio-
saurus, and Me-
galosaurus. The
first, in particular,
the Ichthyosauri,
greatly abounded
on the coasts of
the continents of
that period, and
their skeletons are
so well preserved,
that we are ena-
bled to study even
the minutest de-
tails of their struc-
ture, which differs
essentially from
that of the rep-
tiles of the pre-
sent day. In
some respects
they form an in-
termediate link
between fishes
and mammals,
Fig. 383.— Plesiosaurus rvgosus.—Ovren. and may be con-

AGES OF NATURE.

405

sidered as the prototypes of the whales, having, like them,
limbs in the form of oars. The Plesiosaurus (fig. 383) agrees,
in many respects, with the Ichthyosaurus in its structure,
but is easily distinguished by its long neck, which somewhat
resembles the neck of some aquatic birds. A still more ex-
traordinary reptile is the Pterodactylus (fig. 384), with its
long fingers, like those of a bat, for the support of wings, by
which it was enabled to fly.

Fig. 384. — Pterodactylus Gratsirostris* — Goldfuss*

§ 674. It is also in the upper stages of this formation that
we meet with the skeletons of tortoises. Here also we find
the remains of several families of insects (Lidellula, Coleop-
tera, Ichneumons, $-c.) Finally, in these same stages, the slates
of Stonesfield, the first traces of mammals are found, namely,
\he jaws and teeth of animals belonging to extinct forms of

406 GEOLOGICAL SUCCESSION OF ANIMALS.

Marsupialia, and having some resemblance to the opossum
(fig. 385).

Fig. 385. — Jaw of the Thylacotherium. from Stonesfield.

§ 6/5. The department of mollusca is largely represented
in all its classes ; Some of the most common forms are sketched
in fig. 386. The peculiar types of the primary age have
almost disappeared, and are replaced by a greater variety of
new forms. Of the brachiopoda only one type, namely, that
of the Terebratula (10), is abundant. Among the other bi-
valves there are many peculiar forms, as Gryph&a (1 and 2),
Cardium (4), Trigonia (5), Goniomya (6), and Gervillia (8).
The gasteropoda display a great variety of species, and the
genus Nerin&a (11) is an abundant form. The Cephalopoda
are very numerous, among which the Ammonites (9) are the
most prominent. There are also found, for the first time, the
representatives of the cuttle-fishes, under the form of Belem-
nites, an extinct type of animals, with an internal chambered
shell, protected by a sheath, and terminating in a conical
body somewhat similar to the bone of the Sepia, and which is
commonly the only preserved part.

§ 676. The variety is not less remarkable among the
radiata. There are to be found representatives of all the
classes; even traces of jelly-fisheshavebeenmadeoutinthe slates
of Solenhofen, in Bavaria. The' polyps were very abundant
at that epoch, especially in the upper stages, one of which,
from this circumstance, has received the name of Coral-rag.
Indeed, there are to be found whole reefs of corals in their
natural position, similar to those which are to be seen in the
islands of the Pacific. [Among the most remarkable types

Fig. 386. — Fossil Mollusca and Kadiata of the Oolitic period.

1. GryphseadilatataSow. — Kellowayrock

and Oxford clay.

2. Gryphsea incurva Sow. Lower lias.

3. Nucleolites clunicularis. Cornbrash.

4. Cardium truncatum Sow. Lias marl-

stone.

5. Trigonia costata Sow. Inferior oolite.

6. Goniomya V scripta Agass. Inferior

oolite.

7. Hemicidaris intermedia. Gt. Oolite

and Coral rag.

8. Gervillia acuta Sow. Lower oolites.

9. Ammonites Calloviensis Sow. Kello-

way rock.

10. Terebratula acuta Sow. Lias marl-
stone.

i 11. Nerinsa cingenda Voitz. Lower
oolites.

40S GEOLOGICAL SUCCESSION OF ANIMALS.

of the family ASTERIDJG the genera Stylina, Montlivaltia,
Thecosmilia, Rhabdophyllia, Cladophyllia, Goniocora, Isastrea,
Thamnastrea ; and of the family FUNGIBLE, the genera Como-
seris, Protoseris, are found in the Coral-rag of Wiltshire.
In the Great Oolite, besides species of many of these genera,
others belonging to Cyathophora, Convexastrea, Calamophyllia,
Cladophyllia, Clausastrea, occur. Similar coralbeds exist in the
limestones belonging to the Inferior Oolite, from whence the
genera Di&cocyathus, Trochocyathus, Axosmilia, Thecosmilia,
Latomeandra. Anabacia, with numerous species belonging to
many of the Coral-rag genera, are found. The echinoderms
present a great variety of forms. The crinoids are not quite
so numerous as in former ages. Among the most abundant
is the Pentacrinus. There are also comatula-like animals,
that is to say, free crinoids (Pterocoma pinnatd). Many
star-fishes are likewise found in the various stages of this
formation. Finally, there is an extraordinary variety of
urchins, among them Cidaris and Hemicidaris (fig. 386, 7)
with large spines, and several other types not found before, as,
for example, Pyy aster, Dysaster and Nucleolites (fig. 386, 3),]
§ 677. The fauna of the Cretaceous period bears the same
general characters as the Oolitic, but with a more marked
tendency towards existing forms. Thus the Ichthyosauri
and Plesiosauri, characterizing the preceding epoch, are suc-
ceeded by gigantic lizards, approaching more nearly the rep-
tiles of the present day. Among the mollusca, a great num-
ber of new forms appear, especially among the cephalopoda,
as Ammonites, Crioceras, Scaphites, Ancyloceras, Hamites,
Raculites, Turrilites, some of which resemble the gasteropoda
in shape, but are nevertheless chambered. The Ammonites
themselves are quite as numerous as in the Oolitic period, and
are in general much ornamented. The acephala furnish us
also with peculiar types, not found elsewhere, as Mayas, Ino-
ceramus, Hippurites, and peculiar Spondyli, with long spines.
There are also a great variety of gasteropoda, among which
some peculiar forms of Pleurotomaria, Rostellaria, and Ptero-
ceras, are very characteristic. The radiata are not inferior to
the other classes in the novelty and variety of their forms.
In figs. 387 and 388, some of the most characteristic fossil
shells from the lower greensand strata are represented.

AGES OF 2TATTJKE.

409

Fig. 387.— Fossil shells from the lower greensand of the Isle of Wight.

410

GEOLOGICAL SUCCESSION OF ANIMALS.

. 388. — Fossil shells from the lower greensand of the Isle of Wight.

V

AGES OF NATUKE. 411

DESCRIPTION OF FIG. 387.

1 . Corbis corrugata, from the sand-rock, Atherfield : the figure is one-

half the size in linear dimensions of the original.

2. Trigonia caudata, from the sand-rock, Atherfield.

3. Gervillia anceps, from the Cracker Rocks, Atherfield ; a denotes the

markings of the hinge, which are seen in consequence of the valves
being slightly displaced. It is represented half the size linear of the
original. These shells are often much larger, and more elongated
than in the figure.

4. Venus striato-costata ; a small shell, common in the Cracker Rocks at

Atherfield ; the figure is twice the size of the original in linear
dimensions.

5. Area Raulini, from the sand-rock, Atherfield.

6. Perna Mulleti, from the lower beds of sand in conjunction with the

Wealden, Sandown Bay ; the figure is but half the size of the origi-
nal : a, the structure of the hinge ; by comparing this figure with a,
No. 3, the difference of the hinge in the genera Perna and Gervillia
will be recognized. This large and remarkable shell is highly cha-
racteristic of the lower beds of the greensand.

7. Venus parva, from Shanklin Cliff.

DESCRIPTION OF FIG. 388.

1 . Thetis minor, from the ferruginous sand-rock at the base of Shanklin

Cliff.

2. Another view of the same, to show the beaks and hinge-line.

3. Exogyra sinuata, represented one-fourth the natural size ; it is often

found much larger. From the greensand at Shanklin, Ventnor,
Sandown, &c.

4. Tornatella albensis, from the Cracker Rocks, Atherfield.

5. Terebratula sella ; an abundant shell in the sand at Atherfield.

6. Nucula scapha, from the sand-rock, Atherfield.

The three follow ina shells are embedded in a fragment of the Cracker

Rock, from Atherfield.

7. Natica rotundata.
8 Pterocera retusa.

9. Rostellaria Robinaldini,

10. Cerithium turriculatum, from Atherfield.

11. Ancyloceras gigas, from Atherfield. The figure is one-third the size,

linear, of the original. This fossil is often found two feet in length,
associated with Ammonites equally gigantic.

412

GEOLOGICAL SUCCESSION OF ATS1MALS.

Fig. 389. — Fossil shells and Mammalian remains, from the fresh-water
strata of the Isle of Wight.

OF NATURE. 413

DESCRIPTION OF FIG. 389.

FOSSIL SHELLS AND TEETH OF MAMMALIA, FROM THE KRESI1-W^ FEU
EOCENE STRATA OF THE ISLE OF WIGHT.

SHELLS.

Fig. 1. — Potomomya gregaria ; from Headon Hill.

This shell is described by Mr. Sowerby in Mineral Conchology
as Mya gregaria. The genus Potomomya (river mussels)
comprises those species which inhabit rivers only, and are not
found in estuaries and brackish waters.

2. — Potamides concavus ; Headon Hill.

3. — Melanopsis fusiformis ; Headon Hill.

4. brevis ; Headon Hill.

5. — Neritina concava ; Colwell Bay.

6. — Melanopsis carinata ; Colwell Bay.

7. — Helix globosus ; Shalfleet.

8. — Potamides plicatus ; Headon Hill.

9. ventricosus ; Headon Hill.

MAMMALIAN REMAINS

10. — Upper canine tooth of Anoplotherium commune ; from Seafield

near Hyde.
J 1. — The grinding surface of&aupper molar, of Pakeotherium medium;

from Binstead.
12. — One side of the lower jaw of Palaotherium minus, with five

teeth ; from Seafield.*

13*. — A tooth of DicJiobune cervinum, from Binstead.
13. — The grinding surface of fig. 13".

With the exception of the gigantic snail-shell, fig. 7, the fossil shells here
delineated are abundant at Headon Hill, and in the clays and marls at
Colwell Bay. The Mammalian remains are of excessive rarity, and have
hitherto only been found in the quarries near Ryde, and at Headon Hill.
From the latter locality, Dr. Wright recently obtained a fine specimen of
the jaw of a Dicodon, a new genus established "by Professor Owen.

* See British Fossil Mammals, p. 323.

414 GEOLOGICAL SUCCESSION OF ANIMALS.

§ 6/8. TEETIAEY AGE. Reign of Mammals. — The most
significant characteristic of the Tertiary faunas is their great
resemblance to those of the present epoch. The animals be-
long in general to the same families, and mostly to the same
genera, differing only as to species. The specific differences,
however, are sometimes so slightly marked, that a consider-
able familiarity with the subject is required, in order readily
to detect them. Many of the most abundant types of for-
mer epochs have now disappeared. The changes are espe-
cially striking among the mollusca, the two great families of
Ammonites and Belemnites, which present such an astonish-
ing variety in the Oolitic and Cretaceous epochs, being now
completely wanting. Changes of no less importance take
place among the fishes, which are for the most part covered
with horny scales, like those of the present epoch, while in
earlier ages they were generally covered with enamel. Among
the radiata, we see the family of crinoids reduced to a very
few species, while, on the other hand, a great number of new
star-fishes and sea-urchins make their appearance. There
are besides, innumerable remains of a very peculiar type of
animals, almost unknown in the former ages, as well as in
the present period. They are little-chambered shells, known to
geologists under the name of Nummulites, from their coin-like
appearance, and which form in some countries very extensive
lavers of rocks.

tf

§ 679. But what is more important, in a philosophical
point of view, is, that aquatic animals are no longer predomi-
nant in Creation. The great marine or amphibian reptiles
give place to numerous mammals of great size. For which
reason we have called this age the Reign of Mammals.

§ 680. The lower stage of this formation is particularly
characterized by great pachyderms, among which we may
mention the PalcEotherium and Anoplotherium, which have
acquired such celebrity from the researches of Cuvier. These
animals, among others, abound in the tertiary formations of
the neighbourhood of Paris, and those of the Hampshire
basin. The Palteotheria, of which several species are known,
are the most common ; they resemble, in some respects, the
tapirs, while the Anoplotheria are more slender animals. In
America are found the remains of a most extraordinary
animal of gigantic size, the Basilosaurus, a true cetacean.
Finally, in these stages, the earliest remains of monkeys hav<

CONCLUSIONS. 4J 5

been detected. In fig. 389 are figured the jaw and teeth of
Palceotheria, from the tertiary strata of the Isle of Wight. 10
is the canine tooth of P. commune, and 1 1 the grinding sur-
face of, the molar tooth of P. medium; 12 is one half of the
lower jaw of P. minus, and 13 are the molars of a Dichobune,
another extinct genus of the PAL^OTHERLDJE. The mollusca
of the estuary beds of the same locality are figured ill this
plate. Potomomya gregaria (1), Potamides concavus (2),Mela-
nopsis fusiformis (3), M. brevis (4), Neritina concava (5),
Melanopsis carinata (6), Potamides plicatus (8) and P. ven-
tricosus (9), Helix globosus (7).

§ 681. The fauna of the upper stages of the tertiary forma-
tion approaches yet more nearly to that of the present epoch.
Besides the pachyderms, that were also predominant in the
lower stage, we find numbers of carnivorous animals, some
of them much surpassing in size the lions and tigers of our
day. We meet also gigantic edentata, and rodents of great
size.

§ 682. The distribution of the tertiary fossils reveals to
us the important fact, that in this epoch animals of the same
species were circumscribed in much narrower limits than
before. The earth's surface, highly diversified by mountains
and valleys, was divided into numerous basins, which, like the
Gulf of Mexico, or the Mediterranean of our day, contained
species not found elsewhere. Such was the basin of Paris, that
of London, and in the United States, that of South Carolina.

§ 683. In this limitation of certain types within certain
bounds, we distinctly observe another approach to the actual
condition of things, in the fact that groups of animals which
oc-cur only hi particular regions are found to have already existed
in the same regions during the Tertiary epoch. Thus the
edentata are the predominant animals in the fossil fauna of
Brazil as well of its present fauna ; and the marsupialia were
formerly as numerous in New Holland as they now are, though
they were in general of much larger size.

§684. THE MODERN EPOCH. ReiynofMan. — The present
epoch succeeds to, but is not a continuation of, the Tertiary
age. These two epochs are separated by a great geological
event, traces of which we see everywhere around us. The cli-
mate of the northern hemisphere, which had been, during the
Tertiary epoch, considerably warmer than now, so as to allow
of the growth of palm-trees in the temperate zone of our time,

4.16 GEOLOGICAL SUCCESSION OF ANIMALS.

became much colder at the end of this period, causing the
polar glaciers to advance south, much beyond their previous
limits. It was this ice, either floating as icebergs, or, as
there is still more reason to believe, moving along the ground,
like the glaciers of the present day, that, in its movement to-
wards the south, rounded and polished the hardest rocks, and
deposited the numerous detached fragments brought from dis-
tant localities, which we find everywhere scattered about upon
the soil, and which are known under the name of erratics,
boulders, or grey heads. This phase of the earth's history
has been called, by geologists, the Qlacial or Drift period,
and is represented by the second circle of the frontispiece.

§ 685. After the ice that carried the erratics had melted
away, the surface of North America and the North of Europe
was covered by the sea, in consequence of the general subsi-
dence of the continents. It is not until this period that
we find, in the deposits known as the diluvial or Pleistocene
formation, incontestable traces of the species of animals now
living.

§ 686. It seems, from the latest researches of geologists,
that the animals belonging to this period are exclusively
marine ; for, as the northern part of both continents was
covered to a great depth with water, and only the summits of
the mountains were elevated above it, as islands, there was no
place in our latitudes where land or fresh-water animals could
exist. They appeared therefore at a later period, after the
water had again retreated ; and, as from the nature of their or-
ganization, it is impossible that they could have migrated
from other countries, we conclude that they were created at a
more recent period than our marine animals.

§ 687. Among the land animals which then made their
appearance, there were representatives of all the genera and
species now living around us, and besides these, many types
now extinct, some of them of a gigantic size, such as the Masto-
don,* the remains of which are found in the uppermost strata of
the earth's surface, and probably the very last large animal which

* The gallery of fossil remains in the British Museum contains a fine
skeleton of the Mastodon, a splendid specimen of which, disinterred at
Newburg, N. Y., is now in the possession of Dr. J. C. Warren, in Boston ;
the most complete skeleton which has ever been discovered. It stands
nearly twelve feet in height, the tusks are fourteen feet in length and
nearly every bone is present, in a state of preservation truly wonderful.

CONCLUSIONS.

417

became extinct before the creation of man. In the continent
of South America are found, in the drift of that region, the re-
mains of another gigantic animal, the Megatherium (fig. ,390),
which resembles the armadillos of that country, but differs from
all other quadrupeds in the colossal dimensions of its skeleton.

Fig. 390. — The Megatherium.

§ 688. It is necessary, therefore, to distinguish two periods
in the history of the animals now living ; one in which the
marine animals were created, and a second, during which the
land and fresh-water animals made their appearance, and at
their head MAN.*

CONCLUSIONS.

§ 689. From the above sketch it is evident that there is a
manifest progress in the succession of beings on the surface of
the earth. This progress consists in an increasing similarity
to the living fauna, and among the vertebrata, especially, in
their increasing resemblance to Man.

§ 690. But this connection is not the consequence of a direct
lineage between the faunas of different a°;es. There is nothing

O O O

like parental descent connecting them. The fishes of the
Palaeozoic age are in no respect the ancestors of the reptiles
of the Secondary age, nor does Man descend from the mam-
mals which preceded him in the Tertiary age. The link by
which they are connected is of a higher and immaterial nature ;
and their connection is to be sought in the view of the Creator

* The former of these phases is indicated in the frontispiece, by a
circle, inserted between the upper stage of the Tertiary formation and
the Reiyn of Man properly so called.

E E

418 GEOLOGICAL SUCCESSION OF ANIMALS.

himself, whose aim, in forming the earth, in allowing it to un-
dergo the successive changes which geology has pointed out,
and in creating successively all the different types of animals
which have passed away, was to introduce Man upon its sur-
face. Man is the end towards which all the animal creation
has tended, from the first appearance of the first Paleeozoic
fishes.

§ 691 . In the beginning the Creator's plan was formed, and
from it He has never swerved in any particular. The same Being
who, in view of man's moral wants, provided and declared, thou-
sands of years in advance, that " the seed of the woman shall
bruise the serpent's head," laid up also for him, in the bowels
of the earthr those vast stores of granite, marble, coal, salt, and
the various metals, the products of its several revolutions ; and
thus was an inexhaustible provision made for his necessities,
and for the development of his genius, ages in anticipation of
his appearance.

§ 692. To study, in this view, the succession of animals in
time, and their distribution in space, is therefore to become ac-
quainted with the ideas of God himself. Now, if the succes-
sion of created beings on the surface of the globe is the reali-
zation of an infinitely wise plan, it follows that there must
be a necessary relation between the races of animals and the
epoch at which they appear. It is necessary, therefore, in
order to comprehend Creation, that we combine the study of
extinct species with that of those now living, since one is the
natural complement of the other.* A system of zoology will
consequently be true, in proportion as it corresponds with the
order of succession among animals.

* In investigating the " Ages of Nature" much lasting and invaluable
information will be derived from an earnest study of the magnificent col-
lection of fossil remains contained in the palaeontological department of
the British Museum. The arrangement and naming of these monuments
of nature, which mark the past revolutions of the earth, are now so far
advanced by the great talents and zeal of Messrs. Waterhouse and Wood-
ward, the present curators, that it has become a national educational
saloon for this branch of natural history. In his visits to the gallery of
organic remains, the student will obtain much aid and useful knowledge
from Dr. Mantell's recent work, " Petrifactions and their Teaching ; or, a
Hand-book to the Gallery of Organic Remains of the British Museum."
Bobn's Scientific Library, 1851. — EDITOR.

419

LIST OF THE MOST IMPORTANT AUTHORS

WHO MAT EE CONSULTED IN REFEEENCE TO THE
SUBJECTS TEEATED IN THIS WOEX.

GENERAL ZOOLOGY.

Aristotle's Zoology ; Linnaeus' System of Nature ; Cuvier's Animal
Kingdom ; Oken's Zoology ; Humboldt's Cosmos, and Views of Nature ;
Spix, History of Zoological Systems ; Cuvier's History of the Natural
Sciences.

ANATOMY AND PHYSIOLOGY.

Henle's General Anatomy ; and most of the larger works on Compara-
tive Anatomy, Physiology, and Botany, such as those of Hunter, Cuvier,
Meckel, Miiller, Burdach, Todd and Bowman, Grant, Owen, Carpenter,
Rymer Jones, Hassall, Quain and Sharpey, Bourgery and Jacob, Wagner,
Siebold, Milne Edwards, Carus, Schleiden, Burmeister, Lindley, Robert
Brown, Dutrochet, Decandolle, A. Gray.

ON SPECIAL SUBJECTS OF ANATOMY AND PHYSIOLOGY MAY BE

CONSULTED

Schwann, on the Conformity in the Structure and Growth of Animals
and Plants.

Dumas and Boussingault, on Respiration in Animals and Plants.

Valentin, on Tissues ; and Microscopic Anatomy of the Senses.

Soemmering, Figures of the Eye and Ear.

KollJker, Theory of the Animal Cell, and Mikroskopische Anatomie.

Breschet, on the Structure of the Skin

Locomotion; Weber and Duges.

Teeth; Fred. Cuvier, Geoff. St. Hilaire, Owen, Nasmyth, Retzius.

Blood; Dollinger, Barry.

Digestion; Spallanzani, Valentin and Brunner, Dumas and Boussiii-
gault, Liebig, Matteucci, Beaumont

INSTINCT AND INTELLIGENCE.

Kirby, Blumenbach, Spurzheim, Combe.

EE 2

420

EMBRYOLOGY.

D'Alton, Von Baer, Purkinje, Wagner, Wolfe, Rathke, Bischoff, Vel-
peau, Flourens, Barry, Leidy.

PECULIAR MODES OF REPRODUCTION.

Ehrenberg, Trembly, Rosel, Sars, Loven, Steenstrup, Van Beneden.

METAMORPHOSIS.

St. Merian, Rosel, De Geer, Harris, Kirby and Spence, Burmeister,
Reaumur.

GEOGRAPHICAL DISTRIBUTION.

Zimmerman, Miine Edwards, Swainson, A. Wagner, Forbes, Pennant,
Richardson, Ritter, Guyot.

GEOLOGY.

The Works of Murehison, Phillips, Lyell, Mantell, Hugh Miller, Agassiz,
D'Archiac, De Beaumont, D'Orbigny, De Verneuil, Cuvier, Brongniart,
Deshayes, Morton, Hall, Conrad, Hitchcock, Troost, and the Reports on
the various local Geological Surveys.

Very many of the papers of the authors above referred to are not pub-
lished in separate treatises, but are scattered through the volumes of Sci-
entific Periodicals ; such as the

Transactions of the Royal Society of London.

Annals and Magazine of Natural History.

Annales, and Archives, du Museum d' Hist. Naturelle.

Annales des Sciences Naturelles.

Wiegmann's Archiv fur Naturgeschichte.

M tiller's Archiv.

OKen's Isis.

Berlin Transactions.

Transactions of the American Philosophical Society.

Memoirs of the American Academy.

Journal of the Academy of Nat. Sciences, Philadelphia.

Silliman's Journal.

Journal of Boston Society of Natural History.

GENERAL AND GLOSSARIAL INDEX.

Note.— The Arabic figures refer, not to the pages, but to the numbered sections ;
the Roman numerals indicate the pages of the Introduction.

A, a Greek prefix, signifying gene-
rally " without," as in Abran-
chiata (without gills, fipayxia),
which see.

Abdo'men (Lat. abdo, I conceal), the
posterior and principal cavity of
the animal, containing the bowels
and many other viscera. The
abdomen is distinct from the
thorax in crustaceans, spiders and
insects, 60.

Abranchia'ta (Gr. a, without;
/3/oayxia, gills), mollusks devoid
of gills, xxii.

Acale'pha (Gr. aica\r]<j)rj, a nettle),
radiates with soft skins, which
have the property of stinging like
a nettle, xxiii.

Acalevphae, digestion in the, 315.

Ac'arus (Gr. d/capj, a mite), arach-
nides, as the cheese-mite and
allied species.

Aceph'ala, Aceph'alous (Gr. a, with-
out ; (C60a\»7, head), headless ;
animals in Which a distinct head
is never developed, xxii. 662.

Acetab'ula (Lat. acetabulum, a shal-
low cup), fleshy sucking cups,
with which many of the inverte-
brate animals are provided.

Acetab'ulum, the, in man, 263.

Ac'ini (Lat. acinum, a berry), the
secreting parts of glands, which
are suspended like grains or small
berries to a slender stem.

Acotyl'edons, plants without a dis-
tinct, cotyledon, 69.

Acous'tic (Gr. dicovo, I hear), ap-
pertaining to sound, or the orgaii
of hearing.

Ac'rita (Gr. dicpirog, confused), a
term applied to the lowest ani-
mals, in which the organs, and
especially the nervous system,
Avere supposed to be confusedly
blended with the other tissues.

Actin'ia (Gr. CIKTIV, a ray), polyps
with many arms radiating from
around the mouth.

Actino'ceras (Gr. OKTIV, a ray ;
Ktpag, a horn), a generic term
signifying the radiated disposition
of the horns or feelers.

Actin'oids, polyps, as the coral-
polyps, xxiii.

Adipose* (Lat. adeps, fat), fatty.

Affinities and analogies, 16.

Ages of nature, 656 — 690.

Air, changes effected in, by respir-
ation, 393.

A'lar (Lat. ala, a wing), belonging
to a wing.

Albuxmen (Latin), the white of an
egg, 446.

Albuminous, consisting of albumen.

Al'iform (Lat. aliformis), shaped like
a wing.

Alimentary canal, the, 312.

Alimentation, or nutrition, 62.

Allan'tois (Greek), a vesicular organ

422

INDEX.

in connection with the intestine,
which makes its appearance dur- i
ing the development of the
embryo, 472.

Alliga'tor, teeth of the, 340.

Allu'vium (Latin), sand, gravel, &c.,
orought down by rivers.

Alternate generation, 518 — 547.

Alter'nate reproduction, 516 — 532;
consequences of, 533, 547 ; dif-
ferences between, and metamor-
phosis. 536.

Ambula'cra (Lat. ambulacrum, an
avenue or place for walking), the
perforated series of plates in the
shell of the sea-star or sea-urchin.

Am'bulatory (Lat. ambulo, I walk),
an animal, or a limb for walking.

Amer'ica, distribution of the faunas
of, 596—619.

Am'monites, an extinct genus of
mollusks, allied to the nautilus, i
which inhabited a chambered shell,
called Ammonite, from its resem-
blance to the horns on the statues
of Jupiter Ammon, xxii. 675.

Amor'phous (Gr. a, without ; fiop^fj,
form), bodies devoid of regular
form.

Amphibious (Gr. ajw0i, two, (3iO£,
life), having the faculty of living
both in water and on land, 306.

Amphiox'us, a genus of fishes, pecu-
liar structure of the, 567.

Am'phipods (Gr. dp<f>i, on both
sides ; TTOWC, a foot), an order of
Crustacea which have feet for both
walking and swimming.

Amphistovma (Gr. dp^i, on both
sides ; aTopa, a mouth), sucto-
rial parasitic worms, which have
pores like mouths at both ends of)
the body.

Amphiuvma, a batrachian, 626.

Ampul'la (Lat. a bottle}, a mem-
branous bag, shaped like a leathern
bottle, 158.

An'aema (Gr. d, without ; al/jia,
blood), the name given by Aris-

totle to the animals which have
no red blood, and which he sup-
posed to be without blood.

An'alogue, a part or organ in one
animal which has the same func-
tion as another part or organ
in a different animal ; see HOMO-
LOGUE.

Anal'ogy, distinguished from affinity,
16.

Anas'tomose (Gr. aver, through ;
(rro/Lia, mouth), when the mouths
of two vessels come into contact
and blend together, or when two
vessels unite as if such kind of
union had taken place.

Anat'ifa, or duck barnacle, metamor-
phoses of the, 553 — 556.

Androg'ynous (Gr. dvrip, a man;
ywri, a woman), the combina-
tion of male and female parts in
the same individual.

Anella'ta (Lat. annellus, a little
ring), worms, in which the body
seems to be composed of a suc-
cession of little rings, character-
ised by their red blood.

Anel'lide, the anglicised singular of
Anellata.

An'enterous (Gr. or, without; tvTtpov,
a bowel), the animalcules of in-
fusions which have no intestinal
canal.

Animal heat, 399.

Animal life, organs and functions
of, 76—184.

Animal and vegetable kingdoms,
three great divisions of the, 67.

Animarcuie (dim. of animal), a very
minute animal.

Animals, extinct, 629.

Animals, geographical distribution
of, 578 — 641 ; general laws, 578
—594 ; the faunas, 595—622 ;
conclusions, 623 — 641.

Animals, geological succession of,
642—690.

Animals, metamorphoses of, 5-i8—
577.

TKDEX.

423

Animals and plants, differences be-
tween, 57 — 74 ; resume, 75.

An'imate, possessed of animal life.

Annel'ida, or Annel'ids, digestive
organs of the, 322 — 324 ; respira-
tion, 382.

AnnulaHed (Lat. annulus^ a ring),
when an animal or part appears
to be composed of a succession of
rings.

Anoplothevrium (Gr. dvo-rrXog, un-
armed ; 9r]piov, beast), an ex-
tinct mammal, somewhat resem-
bling the pig, but unprovided
with tusks or offensive arms, 680.

An'ourous (Gr. a, without ; ovpa, a
tail), tail-less.

Anten'na (Lat. a yard-arm}, applied
to the jointed feelers, or horns,
upon the heads of insects and
Crustacea ; and sometimes to the
analogous parts which are not
jointed in worms and other ani-
mals.

Anthozo'a (Gr. dvOog, a flower ;
£wov, an animal), polyps (in-
cluding the actinia and allied
species), commonly called animal
flowers.

Antiperistalt'ic (Gr. dvri, against ;
and peristaltic), when the vermi-
cular contractions of a muscular
tube follow each other in a direc-
tion the reverse of the ordinary
one; see PERISTALTIC.

Ant'lia (Lat. a pump), restrictively
applied to the spiral instrument
of the mouth of butterflies and
allied insects, by which they pump
up the juices of plants.

Aor'ta (Gr. doprri, the wind-pipe ;
and also the name of the great
vessel springing from the heart,
which is the trunk of the systemic
arteries) ; it is exclusively applied
in the latter sense in modern
anatomy.

Aphid'ian, belonging to the aphis.

A'phis (Greek), the aphis, or plant-

louse, one of the articulata, alter-
nate generation of the, 526.

Ap'ical (Lat. apex, the top of a
cone), belonging to the pointed
end of a cone-shaped body.

Ap'odal (Gr. a, without ; Troda,
feet), footless, without feet or
locomotive organs ; fishes are so
called which have no ventral fins.

Apoph'ysis (Greek), a projection
from the body of a bone.

Apparatus of motion, 205 — 227.

Ap'tera (a, without ; Trrtpov, awing),
wingless insects, xxii.

Ap'terous (Gr. d, without ; Trrtpov,
a wing), wingless species of in-
sects or birds.

Aquat'ic (Lat. aqua, water), living
in water.

Aquat'ic animals, water tubes of,403.

A'queous, like water.

Avqueous humour of the eye, 127-

Arach'nida (Gr. dpaxvtj, a spider),
a class of articulates ; as spiders
and allied animals.

Arach'nida?, or Arach'nids, digestive
organs of the, 326 ; jaws, 337 •
respiration, 385.

Aracb/noid membrane, 85.

Arbores'cent (Lat. arbor* a tree),
branched like a tree.

Arc'tic (Gr. 'Ap/croc, the Bear, a
northern constellation, thus signi-
fying northern) fauna, the, 602
—604.

Arevolar (Lat. areola, a nipple
tissue, 41.

Aristotle's lantern, jaws of the Echi-
nidag, so called, 335

Arm of man, 281 ; corresponding
organ in other animals, 282 — 286.

Arteries, 357.

Arthrovdial (Gr. dpdpov, a joint) ;
it is restricted to that form of
joint in which a ball is received
into a shallow cup.

Articulavta (Lat. articulus, a joint),
a department of the animal king-
dom, consisting of animals with

424

IKDEX.

external jointed skeletons or jointed
limbs ; as the leech, the spider, the
gnat, xxii.

Articula'ta, or Artic'ulates, 70 ; ner-
vous system, 115; jaws, 337; of
the trias period, 665, 670.

Ascid'ian (Gr. dvKoc, a bottle), shell-
less acephalous mollusks, shaped
like a leathern bottle.

Assimilation, the change of blood
into bone, muscle, &c. 401.

Asteriavdae (Gr. darpov, a star),
the family of star-fishes, xxiii.

Astre'idae, a family of polyps, found
in the Coral-rag, 674.

Au'ditory (Lat. audio, I hear), per-
taining to the sense of hearing.

Au'ricle(Lat.GMrz'cz/Jfl),a cavity of the
heart, shaped like a little ear,36 1 .

Australia, fauna of, 615.

Autoch'thonoi (Greek), Aborigines,
or first inhabitants, theory of, ap-
plied to the distribution of ani-
mals, 631.

Automatic (Gr. avTo^aro^, self-
moving), a movement in a living
body without the intervention or
excitement of the will.

Aves (Latin), birds ; the second class
of vertebrate animals, xxi.

Axil'la (Lat. arm-pit), applied to
other parts of the animal body
which form a similar angle.

Ax'olotl, a genus of reptiles, 626.

Az'ygos (Gr. a, without ; £vyo£,
yoke), single, without fellow.

BAC'ULITE (Lat. baculus, a staff), an
extinct genus of mollusks, allied
to the nautilus, which inhabited a
straight-chambered shell, resem-
bling a staff.

Bal'anoids (Gr. fiaXai'og, an acorn),
a family of sessile cirripeds, the
shells of which are commonly
called acorn shells.

Bar'nacle ; see Anatifa.

Bas'ilar (Lat. basis, a base), belong-
ing to the base of the skull.

Bas'ilosaurus, an extinct cetacean,
680.

Batra'chians (Gr. fla-pa-%oQ, a frog),
the order of reptiles including the
frog, xxi.

Batraxchians, peculiar species of, 626.

Belem'nite (Gr. j3k\tp,vo^, a dart),
an extinct genus of mollusks ;
animals allied to the sepia, and
provided with a long, straight,
cbambered conical shell in the in-
terior of the body, 673.

Bi, or Bis, a Latin prefix, signifying
"twice, " as in the following words :

BPfid, cleft into two parts, or forked.

Bifurcate, divided into two prongs
or forks.

BiMateral, having two symmetrical
sides.

Bi'lobed, divided into two lobes.

Bipartite, divided into two parts.

Bivpeds (Lat. bis, two, pes, a foot),
animals with two feet, as man and
birds.

Bird tracks, fossil, 670.

Birds, the second division of the ani-
mal kingdom, xxi.

Birds, muscular system of, 227 ;
stomach of, 330.

Bis (Latin), two, or twice; used in
composition only.

Biy valve, a shell of two parts, closing
like a double door, 662.

Blas'toderm, the embryonic germ.

Blood, the, and circulation, 350 — 375.

Blood, the, its constituents, '^50 —
351 ; corpuscles, 352; colour,
353 ; its presence an essential
condition of life, 354; circulation,
.361 — 375; changes that it under-
goes in circulation, 395.

Bone, analysis of, 238 ; basis, 239 ;
microscopic structure, 240 ; the
various bones of the human ske-
leton, 235, 241—278.

Bot'ryoi'dal (Gr. fiorpvs, a bunch of
grapes), having the form of a
bunch of grapes.

Bould'ers, 684.

INDEX.

425

Brach'ial (Gr. /Spa^iov, the arm),
belonging to the arm.

Brach'iopods(Gr. fipa-%iov, the arm ;
TroSa, feet), acephalous mollusks,
with two long spiral fleshy arms
continued from the side of the
mouth, xxiii.

Brachyuxra (Gr. (Spayvc, short,
oufitt, tail), Crustacea with short
tails, as the crabs.

BrachyuVous, short tailed, usually
restricted to the Crustacea.

Brain, 78; in man, 85 — 88; in fishes,
92; in the amphibia, 93 ; in scaly
reptiles, 94 ; in birds, 95 ; in
mammalia, 96.

Bran'chia (Gr. /Spayx1-*, the gills of
a fish), the respiratory organs
which extract oxygen from the air
contained in water.

Bran'chifers (Gr. /Spory^trt, gills ;
Lat./ero, I bear), univalve mol-
lusks breathing by gills, xxiii.

Bran'chiopods (Gr. /S^ay^ta, gills ;
TroSa, feet), Crustacea, in which
the feet support the gills.

Bron'chi, tubes branching from the
windpipe in the lungs.

Bron'tes, a genus of the family Tri-
lobitidas.

Bryozo'a (Gr. fipvov, moss ; £wov,
animal), a class of highly organ-
ized polyps, most of the species
of which incrust other animals or
bodies like moss, xxiii. 664.

Buc'cal (Lat. bucca, mouth or cheeks),
belonging to the mouth.

and C^CA (Lat. c&cus,
blind), a blind tube, or produc-
tions of a tube, which terminate
in closed ends.

CalcaVeous (Lat. calx, chalk), com-
posed of lime.

Camel, skeleton of the, 291.

Campanula' ria, alternate generation
of the, 350—352.

Canine' (Lat. canis.a dog) teeth, 341. '.

Canker-worm, metamorphoses of the,
552.

Can'non-bone, the metacarpal bone
of the horse and stag, 282, 286.

Cap'illary vessels (Lat. capillus, a
hair), the minute vessels through
which the arteries and veins are
united, 358, 371.

Carapace', the upper shell of the
crab and tortoise, 318.

Car'bon (Lat. carbo), the basis of
charcoal and most combustibles.

Carboniferous, or coal. formation, 650,
669.

Car'dia (Gr. Kapdia, the heart or
stomach), the opening which ad-
mits the food into the stomach ;
also the region called the pit of
the stomach.

Carniv'ora (Lat. caro, flesh ; voro,
I devour), animals which feed on
flesh, xxi.

Car'pus (Latin), the wrist, 275.

Cartilaginous, or gristly, tissue, 42,
52.

Cau'dal (Lat. cauda, a tail), belong-
ing to the tail.

Cau'da Equivna (Lat. horse-tail), the
leash of nerves which terminates
the spinal marrow in the human
subject, and the analogous part in
the lower animals.

Cell (Lat. cello), the universal ele-
mentary form of every tissue, 56.

Cellule\ a little cell.

Cel'lular tissue (Lat. cella, a cell),
the elastic connecting tissue of
the different parts of the body
which everywhere forms cells or
interspaces containing fluid,53,56.

Cen'tipecle (Lat. centum, a hundred ;
pes, a foot), a genus of insects
with very numerous feet.

Cen'trum (Gr. Ktvrpov, centre), the
body or essential elements of a
vertebra, around which the other
elements are disposed.

Cephal'ic (Gr. Ki<pa\rj, head), be-
longing to the head.

Cephalopoda (Gr. KifyaXr], head ;
, feet), mollusks in which

426

I1VDEX.

long prehensile processes or feet
project from the head, xxii, 663,
673.

Cephal'o-thovrax (Gr. Ke^aXrj, head ; !
Lat. thorax, chest), the anterior j
division of the body in spiders,
scorpions, &c., which consists of
the head and chest blended to-
gether.

Cerca'ria, alternate generation exem-
plified in the, 520—524.

Cerca'ria} (Gr. Kfpicoc, a tail), ani-
malcules whose body is termi-
nated by a tail-like appendage.

Cerebellum, or little brain,inman,87.

Cer'ebral nerves, 97—114.

Cer'ebrum, or brain, in man, 86.

Cestravcion Phil'lipii, a living repre-
sentative of the fishes of a former
age, 615.

Cetaxcea, or Cetaceans (Lat. cete, a
whale), marine animals, which nurse
their young, like the whale, por-
poise, &c., xxi. 304.

ChahVza, the albuminous thread by
which the yolk of the egg is sus-
pended, 446.

Chalk formation, 650.

Chart of zoological regions, 595 —
622.

Chelo'nia (Gr. ^t\Mvn, a turtle), the
order of reptiles including the tor-
toises and turtles, xxi.

Che'le (Gr. \rj\i], a claw), applied
to the bifid claws of the crusta-
cea, scorpions, &c.

Chick, development of the, first
period, 482 — 485; second period,
486—492 ; third period, 493—
497 ; birth, 498 ; physical and
chemical changes in the egg du-
ring incubation, 499.

Chil'ognatha (Gr. \ti\og, a lip ;
yvaQoQ, a jaw), the order of many-
footed insects, typified by the
gally-worm or julus.

Chi'tine (Gr. %iroi', a coat), the pe-
culiar chemical principle which
hardens the integument of insects.

Chol'edochus (Gr.

doxe, receptacle), the tube form-
ed by the union of the hepatic
and cystic ducts.

ChoVion, from the Greek word sig-
nifying the membrane which en-
closes the foetus, and applied ge-
nerally to the outer covering of
the ovum, 475.

Chovroid, one of the coats of the eye,
124.

Chrys'alis (Gr. xpvvos, gold), the
stage of the butterfly immediately
preceding its period of flight, when
it is passive, and enclosed in a
case, which sometimes glitters
like gold.

Chyle (Gr. ^uXoc, juice), nutrient
fluid extracted from digested food
by the action of the bile, 333.

ChylificaHion, 332.

Chyme (-^V^LOQ, juice), digested
food which passes from the sto-
mach into the intestines, 331.

Chymifica'tion, 331.

Cil'ia (Lat. cilium, an eye-lash), mi-
croscopic hair-like bodies, which
cause, by their vibratile action,
currents in the contiguous fluid,
or a motion of the body to which
they are attached, 216.

Cil'iary motions, 211, 216, 217.

Ciliavted, provided with vibratile cilia.

CiliobrachiaHa (Lat. cilium, an eye-
lash ; Gr. fi(>a%ioi>, the arm), po-
lyps, in which the arms are pro-
vided with vibratile cilia.

Ciliogradesx (Lat. cilium, an eye-
lash ; gradior, I walk), acalepha?
which swim by the action of cilia.

Circulation, the, 350 — 375; its
course in the mammalia, 364,
365 ; in reptiles, 366 ; in fishes,
367 ; in mollusca, 368 ; in crus-
tacea, 369 ; in insects, 370 ; in
cold-blooded animals, 373.

Cir'ri (Lat. cirrus, a curl), curled
filamentary appendages, as the feet
of the barnacles.

INDEX.

407
T*»y

Cirrig'^rous, supporting cirri.

Cirrigrades\ moving by cirri.

Cir'ripeds, or Cirripexdia (Lat. cirrus,
a curl ; pes, a foot), articulate
animals having curled jointed feet,
sometimes written cirrhipedia and
cirrhopoda.

Classes, a subdivision of the animal
kingdom, xx ; again divided into
orders, xx.

Cla'vate (Lat. clavus, a club), club-
shaped ; linear at the base, but
growing gradually thicker towards
the end.

Clav'icle, the, or shoulder blade, 271.

Climate, insufficient alone to ac-
count for the geographical dis-
tribution of animals and plants,
638—641.

Climate, the polar, its influence on
animals, 582.

Climbing, 298.

Cloa'ca (Latin, a sink), the cavity
common to the termination of
the intestinal, urinary, and gene-
rative tubes.

Clyp'eiform (Lat. clypeus, a shield ;
forma, shape), shield-shaped, ap-
plied to the large prothorax in
beetles.

Coal period, flora of the, 669.

Coc'costeus, an extinct genus of
fishes from the Devonian rocks,
667.

Coe'cyx, the, 258.

Coch'lea, one of the divisions of the
internal ear, 154.

Cold-blooded animals, as reptiles,
fishes, &c. 400.

Coleop'tera (Gr. Ko\t6g, a sheath
TTTtpov, a wing), the order of in-
sects in which the first pah* of
wings serves as a sheath to defend
the second pair, as the common
dor-beetle.

Columel'la (Lat. a small column),
used in conchology to signify
the central pillar around which
a spiral shell is wound.

Comat'ula, a genus of the family
Crinoidea.

Comat'ula, metamorphoses of the,
559.

Commis'surae (Lat. commit to, I sol-
der), belonging to a line or parx
by which other parts are con-
nected together.

Compa'ges (Latin), a system or
structure of united parts.

Con'chifers (Lat. concha, a shell ;
fero, I bear), shell-fish, usually re-
stricted to those with bivalve
shells.

Cor'al rag, a stage of the oolite, 674.

Coria'ceous (Lat. corium, hide),
when a part has the texture of
tough skin, 413.

Cor'nea (Lat, corneus, horny), the
transparent horny membrane in
front of the eye, 123.

Cor'neous, horny.

Cor'neule (diminutive of cornea},
applied to the minute transparent
segments which defend the corn-
pound eyes of insects.

Cor'nua (Lat. cornu, a horn), horns
or horn-like processes.

Cor'puscles (diminutive of corpus, a
body), minute bodies.

Cotyl'edon (Greek), a seed lobe.

Creta'ceous (Lat. creta, chalk), be-
longing to chalk.

Cretavceous formation, 650, 675 ;
fauna, 675.

Crinoidx (Gr. icpivov, a lily ; ft'cog,
like), belonging to the Echino-
derma, which resemble lilies ; the
fossils called stone lilies, or encri-
nites, are examples, xxiii.

Crio'ceras, a genus of the family
Ammonitida3.

Cru'ra (Lat. crus, a leg), the legs
of an animal, or processes resem-
bling legs.

Crusta'cea (Lat. cntsta, a crust), the
class of articulate animals with a
hard skin or crust, which they
periodically cast, xxii.

428

INDEX.

Crusta'cea, or Crustaceans, digestive
organs of the, 325 ; jaws, 337 ; cir-
culation, 369; respiration,381,405.

Crypts, or follicles, 415.

Crysvtalline-lens, a transparent len-
ticular body, situated behind the
pupil of the eye, 126.

Ctevnoids (Gr. KTEVIQ, a tooth), fishes
which have the edge of the scales
toothed, xxi.

Cte^nophori, soft radiated animals
moving by cilia, xxiii.

Cuttle-fish, jaws of, 321 ; metamor-
phosis of, 563 ; mode of escape,
321 ; mode of swimming, 305.

Cu'tis (Lat.), the true skin, the part
which is tanned to form leather.

CyvclobranchiaHa(Gr./cwKAoc, round;
fipfl7XLa> g'^8)' molluscous ani-
mals which have the gills disposed
in a circle.

Cy'cloids, fishes with smooth scales,
xxi.

DEC'APODA (Gr. fe/ccr, ten ; TTOVQ, a
foot), crustaceous and molluscous
animals which have ten feet.

Decid'uous, parts which are shed, or
do not last thelifetime of the animal.

Deflect'ed, bent down.

Deglutition, 345

Dendrit'ic (Gr. StvSpov, a tree),
branched like a tree.

Departments, primary divisions of
the animal kingdom, xxi ; sub-
divided into classes, xxi.

Der'mal (Gr. depict, skin), belonging
to the skin.

Development of the chick, 482 — 499.

Devonian formation, 650.

Diaphragm, the partition between
the chest and abdomen, 209.

Diastole, the dilatation of the heart,
363.

Di'branchiaHa (Gr. £t£, twice; /3p«y-
Xia, gills), cephalopods having
two gills.

Dicotyledons, plants with two seed-
lobes, 74.

Di'dactyle (Gr. c?i£, twice; and

, a finger), a limb termi-
nated by two fingers.
Digestion, 312, 349 ; in the infuso-
ria, 314 ; acalepha, 315 ; echino-
derma,316 ; polypifera, 317 ; mol-
lusca, 318—321 ; annelida, 322—
324 ; crustacea, 325 ; arachnida,
326; insects, 327; vertebrara,

328 ; microscopic examination,

329 ; the stomach, 330 ; chymi-
fication, 331 — 334 ; mastication,
335 — 341 ; harmony of organs,
342—344 ; insalivation, 345 ; de-
glutition, 346—349.

Digestive organs ; see Digestion.

Digitate^ (Lat. digitus, a finger),
when a part supports processes
like fingers.

Diluvvium (Latin), a deposit from the
water of a flood or deluge.

Dimidiate (Lat. dimidium, half),
divided into two halves.

Dimy'ary (Gr. SIQ, twice ; pvov, a
muscle), a bivalve whose shell is
closed by two muscles.

Dip'tera (Gr. Sig, twice ; TTTtpov, a
wing), insects which have two
wings.

Dis'coid (Lat. discus, a quoit), quoit-
shaped.

Discophoxri, soft radiates, or jelly-
fishes, xxiii.

Disk (Lat. discus, a quoit), a more
or less circular flattened body.

Disto'ma (Gr. <5ic, two; oro/ua,
mouth), the intestinal worms with
two pores.

Dist'oma, alternate generation ex-
emplified in the, 521.

Distribution, geographical, of ani-
mals, 578—641.

Distribution in time of animals, 642.

DiVerticulum (from the Latin for a
bye-road), applied to a blind tube
branching out from the course of
a longer one.

DoMo, an extinct bird, 629.

Dor'sal (Lat. dorsum, the back), to-
wards the back.

Dor'sai cord, in the germ, 459.

429

Dor'sal vessel, in insects, 359.

Dorsibranchia'ta (Lat. dot-sum, the j
back : Gr. ftpayxia, g'lls)« mo1-
lusks with gills attached to the
back, xxii.

Drift formation, 650, 684.

Duc'tus (Latin), a duct, or tube,
which conveys away the secretion
of a gland.

Duode'num (Lat. duodecim, twelve),
the first portion of the small in-
testine, which in the human sub-
ject equals the breadth of twelve
fingers.

Du^ra maxter, 85.

E, Ex, a Latin prefix, signifying
generally "without," or "from,"
as Edentata, Exosmose; which see.

Ear, the, 145—161.

Earth's crust, structure of the, 642
—655.

Echinas'ter sanguin'olentus, meta-
morphoses of the, 557, 558.

Ech'ini,anorderofEchinoderms,xxiii.

Echin'oderms (Gr. i%ivo£, a hedge-
hog ; C£|0jua, skin), the class of |
radiated animals, most of which
have spiny skins, xxiii.

Echin'oderms, 661 ; internal organs
of the, 316 ; jaws of the, 335.

Eden'tata (Lat. ex, without, dens, a
tooth), a class of mammals, in
which the teeth are in some degree
incomplete ; as in the armadillo.

Eden'tulous, from the Latin word
for toothless.

Egg, the, all animals produced from,
433, 434 ; form, 435 ; formation,
436 — 446 ; development of the
young, 447 — 479 ; structure as
just laid, 480 ; changes in, during
incubation, 499.

Elementary structure of organized
bodies, 35 ; of tissue, 56.

El'ytra (Gr. {\vrpov, a sheath), the
wing sheaths formed by the mo-
dified anterior pair of wings of
beetles.

Emar'ginate (Lat. emargmo, to re-
move an edge), when an edge or
margin has, as it were, a part bit-
ten out.

Em'bryo (Latin), the earliest stage
of the young animal before birtii,
433.

Embryol'ogy, 429—509 ; the eg?,
429 — 446 ; development of the
young, 447 — 499 ; zoological im-
portance of embryology, 500 —
509.

Enal'iosaur (Gr. eva\to£, marine ;
cravpr>£, a lizard), an extinct order
of marine gigantic reptiles allied
to crocodiles and fishes.

Enceph'ala(Gr.6i/,in; KtQaXr), head),
molluscous animals which have a
distinct head.

Endogenous, increasing by inward
addition, as the palrn tree, 72.

Endosmose' and exosmose\411,413.

Entomol'ogy (Gr. tvrojua, insects ;
A6yo£, a discourse), the depart-
ment of natural history which
treats of insects.

Entomos'tracans (Gr. tvrojua, in-
sect ; ocrrpaKov, shell), small crus-
taceans, many of which are en-
closed in an integument, like a
bivalve shell, xxii.

Entozova (Gr. fi/roe, within ; Z,a>ov,
animal), animals which exist with-
in other animals.

Eocene' (Gr. IM£, the dawn ; KCIIVOC,
recent), the stage of the tertiary
period, in which the extremely
small proportion of living species
indicates the first commencement
or dawn of the existing state of
animate creation, 650.

Epider'mal (Gr. eTridep/^i^, the cuti-
cle), belonging to the cuticle or
scarf skin, 413.

Epister'nal (Gr. era, upon ; arepvov,
the breast-bone), the piece of the
segment of an articulate- animal
which is immediately above the
middle inferior piece, or sternum.

430

Epithelium, the thin membrane
which covers the mucous mem-
branes : it is analogous to the epi-
derm of the skin.

Epizova (Gr. ewi, upon; %&ov, ani-
mal), the class of low organised
parasitic crustaceans which live
upon other animals.

Errat'ics, rolling stones, 684.

Eusta'chian tube, the, 146.

Exci'to-moHory, the function of the
nervous system, by which an im-
pression is transmitted to a cen-
tre, and reflected so as to produce
the contraction of a muscle with-
out sensation or volition.

Exog'enous, increasing by outward
addition, as in the case of most
trees, 74.

Exosinose^ (Gr. f £, out of ; o9t o, I
expel), the act in which a denser
fluid is expelled from a membra-
nous sac by the entry of a lighter
fluid from without, 411,413*.

ExuVium (Latin, the skin of a ser-
pent), the skin which is shed in
moulting.

Exuxvial, any part which is moulted.

Eye, the, 121 — 129; dioptrics of
the human, 130 — 134 ; simple,
135 — 140; aggregate, 141; com-
pound, 142,143 ; rudimentary, 144.

Eye-lids and eye-lashes, 129.

FAC/ETTE (French), a flat surface
with definite boundary, 142.

Facial nerve, 103.

Families, a group of the animal
kingdom, xx. ; divided into ge-
nera, xx.

Fas'cicle (Lat. fasciculus), a small
bundle.

Fau'na (Latin), the animals peculiar
to a country, 579 ; general con-
siderations, 579 — 594 ; the arctic,
602—604 ; the temperate, 605—
615; the tropical, 616—622;
conclusions, 623 — 641.

Fevmur (Latin), the thigh bone, 264.

FiVula, the smallest of the two bones
of the leg, 265.

Fil'iform (L&i.filum, a thread ; for-
ma, a shape), thread-shaped, 420.

Fishes, the fourth division of the
animal kingdom, xxi.

Fishes, 667 ; muscular system of,
227 ; jaws, 340 ; circulation, 367;
respiration, 383.

Fishes, reign of, 659—669.

Fissip'arous (Lat. findo, I cleave ;
pario, I produce), the multiplica-
tion of a species by the cleavage of
the individual into two parts, 510.

Fissip'arous and gemmip'arous repro-
duction, 510 — 515.

Flabel'liform (Lat. flabellum, a fan),
fan-shaped.

Flex'ors (Lat. fecto, I bend), the
muscles emploved in bending a
limb.

Flex'uous, a bending course.

Floxra (Latin), the plants peculiar to
a country, 579 ; of the coal period,
669 ; of the oolitic period, 671.

Flux viatile (Lat.ftuvius, a river), per.
taining to rivers.

Flying, 300.

Foe'tus (Latin), the animal in the
womb, after it is perfectly formed.

Foliavceous (Lat. folium, a leaf),
shaped or arranged like leaves.

Foriicles(Lat. folliculns,a small bag)*
minute secreting bags which com-
monly open upon mucous mem-
branes, 415, 421.

Food, various methods of securing,
by different animals, 34G — 349.

Foot, the, 266—268.

Footsteps, fossil, 672.

Foraminifera, a class of microscopic
radiated animals having many
chambered shells, the septai of
which are perforated.

Formations, geological, 649 — 655.

Fossiliferous (Lat./ossz/z's, anything
dug out of the earth \fero, I bear),
applied to the strata which con-
tain the remains of animals and

INDEX.

431

plants, to which remains geolo-
gists now resti'ict the term fossil.

Fossil remains, 25,652 — 682.

Frontispiece, explanation of, xi.

Func'tion, the office which an organ
is designed to perform.

Fun'gidae, found in the coralrag,673.

GALAPAGOS islands, faunaof the, 622.

Gan'glion (Gr. yayyXtW, a knot), a
mass of nervous matter forming a
centre, from which nervous fibres
radiate.

Gan'glion'ic cells, 83.

Gan'oids, fishes having large bony
enamelled scales, mostly fossil, xxi.

Gases, respiration in, other than
atmospheric air, 394.

Gaster'opods (Gr. y«<rrep, stomach ;
TTOVC, a foot), molluscous animals
which have the locomotive organ
attached to the under part of the
body, xxii. 673.

Gas'tric glands, 330.

Gas'tric juice, 330.

Gemmip'arous (Lat. gemma, a bud;
pario, I bring forth), propagation
by the growth of the young like a
bud from the parent, 510.

Gemmip'arous and fissip'arous repro-
duction, 510— 515.

Gemmule* (dim. of gemma), the
embryos of radiated animals at
that stage when they resemble
ciliated monads.

Gen'era (Genus, in the singular), a
group of the animal kingdom,
xix. ; divided into species, xix.

Generation, alternate, 518 — 532;
consequences of, 533 — 547; spon-
taneous, 543.

Geographical distribution of ani-
mals, 578— 64 1 , of vegetation,639.

Geolog'ical formations, 649.

Germ (Lat. germen), the earliest
manifestation of the embryo.

Germ, first indication of the, 4 >S.

GestaHion (Lat. gestatio), the carry-
ing of the young before birth, 439.

Gla'cial (Lat. glades, Jce), or Drift

period, 684.
Glands, structure of, 419 — 425 ;

elementary parts, 426; origin, 42 7 ;

distribution of the vessels, 428.
Globovse (Lat. globus,a. globe), globs-

shaped.
Glob'ules (diminutive of globe) of

chyle, 333.

Glossopharyn'geal nerve, 104.
Glot'tis. the, 180.
Grallatores, or wading birds, xxi.
Grand-nurses, what, 524.
Granulesx (dim. of granum, a grain),

little grains.
Graniv'orous (Lat granum, grain ;

voro, I devour), birds feeding on

grain.

Greyheads, or boulders, 684.
Gullet, the, 115, 345.

HAND, the, 274—278.

Hseinapophy'sis (Gr. alp.ct, blood ;
a7r60D<7ic, a process of bone) ;
the vertebral elements which de-
scend from the centrum, and en-
close the blood-vessels in the
cartilages of the ribs.

Haversian canals, 240.

Head, the, 241—251.

Hearing, sense of, 145 — 161.

Heart, the, 360 ; circulation of the
blood, 361—375.

Hemip'tera (Gr./^uccrv, half; -nrfpov,
a wing), the order of insects in
which the anterior wings are
hemelytrous ; see Elytra.

Hepat'ic (Lat. hepar, liver), belong-
ing to the liver.

Herbiv'ora (Lat. herba, grass ;
voro, I devour), animals which
subsist, on grass, xxi.

Hermaphrodite ('Ep/uf/g, Mercury ;
fA<ppodirj], Venus), an individual
in which male and female cha-
racteristics are combined.

Hex'apod (Gr. ££a, six ; TTVVQ, a
foot,) animals with six legs, sucii
as true insects.

432

INDEX.

Hibernation (Lat. hyems, winter),
the torpid state of animals during
winter, 40'Z.

Histolog'ical (Gr. IOTOC, a tissue ;
Xoyog, discourse), the doctrine
of the tissues which enter into
the formation of an animal and
its different organs, 210.

HolothuVians, soft sea slugs, biche-
le-mar, xxiii.

Homal'onotus delphinoceph'alus,665

Homoge'neous, uniform in kind.

Hom'ologue (Gr. 6/xoc, like ; Aoyoe,
speech), the same organ in dif-
ferent animals under every variety
of form and function.

Honiorogy, or affinity, 16.

Homop'tera (Gr. oftog, like ; ir-tpov,
a wing), the insects in which the
fuur wings have a similar struc-
ture, but restricted in its applica-
tion to a section of Hemiptera.

Hu'merus, or shoulder-bone, the, 272.

Hy'aline (Gr. vaXoc, crystal) matter,
the pellucid substance which de-
termines the spontaneous fission
of cells, 42.

Ilydat'id (Gr. iiSanc;, a vesicle), a
bladder of albuminous membrane,
containing serous fluid ; generally
detached ; sometimes with an or-
ganised head and neck.

Hy'dra (Gr. vBpa, a water-serpent),
the modern generic name of fresh-
water polyps.

HyVlriform, similarly-formed polyps.

Hyxdrogen (Gr. vSwp, water ;
ye wa.w, I produce ;) a gas which
is one of the constituents of
water.

Hy'droids, fresh-water polyps, xxiii.

Hydrozova (Gr. vdpa, water ; %u>ov,
animal), the class of Polypi or-
ganised like the Hydra.

Hymenop'tera (Gr. V/JLTJV, a mem-
brane ; TTTtpdv,' a wing,) the
order of insects, including the
bee, wasp, &c. which have four
membranous wings.

!chthyosau'rus(ix0fc, a fish;

a lizard), an extinct saurian, 673.

Ide, idae (Gr. tidog, resemblance),
a termination indicating likeness.
As Acarus, a mite ; Acaridas, re-
sembling the mite.

Ig'neous (Lat. ignis, fire) rocks, 646.

Iguan'odon, an extinct gigantic rep-
tile, resembling in its teeth the
iguana, an existing lizard.

Il'ium, the. 263.

Imbricated (Lat. imlricatus, tiled),
scales which lie one upon another
like tiles.

Inanimate beings, plants, 75.

Incesso'res, perching birds, like
birds of prey, xxi.

Incivsor (Lat. incido, I cut), or cut-
ting teeth, 341.

IncubaHion (Lat. incubatio), hatch-
ing of eggs by the mother.

Incubavtion, 442 ; physical and che-
mical changes in the egg during,
499.

In'cus, or anvil, the, 149.

Infusovria (Lat. in/undo}, microscopic
animals, inhabiting infusions of ani-
mal or vegetable substances, xxiv-

Infusoria, digestion in the, 314.

Inoper'cular, univalve shells which
have no operculum or lid.

Inorgan'ic, not made up of tissues.

InsalivaHion, 345.

In'sects, a class of the Articulates,
xxii.

In'sects, digestive organs of, 327 :
jaws of, 337 ; circulation, 370 ;
respiration, 385.

Instinct, 191—204.

Intelligence and instinct, 185 — 204.

Interambulavcra, the imperforate
plates which occupy the intervals
of the perforated ones, or ambu-
lacra in the shells of the Echino-
derms ; see AMBULACRA.

Intersti'tial (Lat. interstitium), rela-
ting to the intervals between parts.

Invertebravta (Lat. in, used in com-
position to signify not, like un ;

433

vertebra, a bone of the back) ani-
mals without back bones.

Tris, the coloured part of the eye.

Is'opoda (Gr. itrog, equal ; TTOVQ, a
foot), an order of crustaceans, in
which the feet are alike, and equal.

JAWS, of man, 251 ; of other ani-

mals, 334—344.
Jelly-fishes, fossil, 676.
Judgment, 188,

KIDNEYS, development of the, 424.

LA^BIUM, Latin for a lip ; but ap-

plied only to the lower lip in

Entomology.
Laxbrum, Latin for a lip, but ap-

plied only to the upper lip in

Entomology.
Lab'yrinth, a part of the internal

ear, 150.

Labyrin'thodon, an extinct reptile, 672
Lacer'tans, or lizards, xxi.
Lac'teals (Lat. lacteus, milky), ves-

sels which take up the nutriment
Lamellibranchia'ta (Lat. lamella, a

plate ; Gr. /Spcryxia, gills"), aceph

alous mollusca, with gills in the

form of membranous plates, xxiii.
Lamel'liform (Lat. lamella, thin

leaves), shaped like a thin leaf or

plate.
Lar'va (Lat. a mask}, applied to an in-

sect in its first active state, which

is generally a different form, and as

it were masks the ultimate form.
Lar'viform, shaped like a larva.
Lar'ynx (Gr. XdpvyK), the organ of

voice, situated at the top of the

trachea, 180.
Laying of eggs, 439.
Leaping, 297.
Leg, the, 265.

Lepidop'tera (Gr. \f-n-ig, a scale ;
, a wing), the order of in-

sects in which the wings are
clothed with fine scales, as butter-
flies and moths.

Life, the distinctive characteristic of
organic bodies, 32 ; animal life,
76 ; blood an essential condition
of, 354.

Lith'ophytes (Gr. Xt'Oog, a stone ;
(pvrov, a plant), a stone plant, or
coral.

Liver, structure of the, in man, 425.

Locomotion, 228 — 307 ; plan of the
organs of, 279 — 288; standing, and
modes of progression, 289 — 307.

Lower Silurian formation, 650.

Lower tertiary formation, 650.

Lungs, the, 386* ; their various
forms, 387—391.

Lymphat'ics, 333.

MALACOI/OGY (Gr. juaXaicoc;, soft ;
Xoyoc., discourse), the history of
the soft bodied or molluscous
animals, which were termed ma-
lakia by Aristotle.

Malacos'tracans, crustaceans, like
the lobster, xxii.

Mal'leus, the, or hammer, 149.

MammaMia, or Mam'mals (Lat. mam-
ma, a breast), the class of animals
which give suck to their young, xxi.

Mam'mals, jaws of, 338 ; alone mas-
ticate their food, 341 ; circulation
of the blood, 364, 365 ; structure
of the liver, 425.

Mam'mals, reign of, 658, 678.

Man, nervous system of, 84 — 91 ;
special senses, 120 — 184 ; skeleton
of, 235—278 ; circulation of the
blood in, 364 — 366 ; respiration,
386, 389, 390 ; structure of the
IIVPT* *4- 2 T

Man, reign of, 658, 684—686.

Mandibulaxta(Lat.m«?zrt%wfo, a jaw),
the insects which have mouths
provided with jaws for ma^ica-
tion ; the term mandible is re-
stricted in entomology to the
upper and outer pair of jaws.

ManducaHa, insects furnished with
jaws, xxii.

Man'tle, the external soft con-

Jf F

434

tractile skin of the mollusca,
which covers the viscera and a
great part of the body like a cloak.

Marl, earth principally composed of
decayed shells and corals, a mix-
ture of clay and lime.

Marsupial animals found in the
oolite, 674.

MarsupiaMia (Latin, marsvpium, a
purse), an order of the Mammalia
having a tegumentary pouch, in
which the embryo is received
after birth, and protected during
the completion of its development.

Alassive rocks, 646.

MasticaHion, 334 ; confined to the
mammalia, 341.

Mas'todon (Gr. /uaorog, a teat;
ooov, a tooth), a genus of extinct
quadrupeds allied to the elephant,
but having the grinders covered
with conical protuberances like
teats, 687.

Matrix, the organ in which the
embryo is developed, 475.

Matter and mind, to be contemplated
together, 29.

Maxilla (Lat. maxilla, a jaw-bone),
in entomology restricted to the
inferior pair of jaws.

MeMian, having reference to the
middle line of the body.

Medulla oblongaHa, the oblong me-
dullary column at the base of the
brain, from which the spinal
chord or marrow is continued, 89.

Meduvsa, development of the, 527 —
529.

Medu'sa, a class of soft radiated ani-
mals, or acalephs, so called because
their organs of motion and pre-
hension are spread out like the
snaky hair of the fabulous Medusa.

Megalosau'rus, an extinct reptile, 673.

Mergan'ser, an aquatic bird allied
to the goose, 593.

Memory, 188.

Mes entery (Gr. /uecroc, intermediate ;
and tvTtpo$, entrail), the mem-

brane which forms the medium
of connection between the small
intestines and the abdomen.

MesothoVax (Gr. yuetrof, middle;
9opa£, the chest), the intermediate
of the three segments which form
the thorax in insects.

Metacar'pus, the wrist, 276.

Metamor'phic rocks, 647.

Metamo/phoses (Gr. ^isra^op^wo-ig,
change of form), of animals, 548 ;
of vegetables, 549.

Metatar'sus, one division of the
bones of the foot, 267.

MetathoVax (Gr. JJ.STO, after ; 6opa%,
the chest), the hindmost of the
three segments which compose
the thorax of an insect.

Migration little prevalent among the
mammalia, 594.

Mil'lepeds (Lat. milk, a thousand ;
pes, a foot), animals with many-
feet, as the wood-louse.

Milleporesx (Lat. mille, a thousand ;
Gr. Tropoc, a minute hole"), a genus
of lithophytes, having their sur-
face penetrated by numerous little
holes.

Miocenex (Gr. fieiov, less ; ican'Of,
recent), the stage of the tertiary
epoch in which a minority of
the fossil shells are of recent
species, 650.

Modern age, the reign of man, 658,
684—686.

Mo'lar (Lat. molaris, grinding) teeth,
341.

Moleculesv (of moles, a mass), mi-
croscopic particles.

Mollusca (Lat. mollis, soft), or Mol'-
lusks, a primary division of the
animal kingdom, xxii.

Mollusca, 70, 662 ; of the trias
period, 670; in the oolite, 673;
nervous system, 116; digestive
organs, 318 — 321; jaws, 336;
circulation, 368 ; respiration, 380,
405.

Mon'ad (Gr. /tioi-rt'.;, unity), the

435

genus of the most minute and|
simple microscopic animalcules, j
shaped like spherical cells.

Monocotyledons, plants with a single j
seed lobe, 72.

Monoc'ulus (Gr. IJLOVOQ, single ; Lat.
oculusj&n eye), the animals which
have but one eye.

Monomy'ary (Gr. /xorog, single ;
Hvov, a muscle), a bivalve whose
shell is closed by one adductor
muscle.

Monothal'amous (Gr. /IOVOQ, single;
Oa\a/.io£, a chamber), a shell
forming a single chamber, like
that of the whelk.

Motion, 205 — 307 ; apparatus of,
205— 227; locomotion, 228—288;
standing, and modes of progression,
289—307.

Mo'tory, the nerves which control
motion.

Moulting, the shedding of feathers,
hair, &c., 412.

Mul'tivalve (Lat. multus, many ;
valva, folding doors).

Mus'cular tissue, one of the primary
forms of animal tissues having
the power of contraction, 44, 54.

Myri'apods (Gr. pvpioQ, ten thou-
sand ; 7rouf , foot), the order of
insects characterized by their nu-
merous feet.

NA'CREOUS (Fr. nacre), pearly, like

mother-of-pearl.
Natatoxres (Lat. nato, I swim), birds

withwebbedfeetforswimming,xxi.
Na'tatory, an animal or part formed

for swimming.
Natural history, extent of the study

of, 30.

Nature, ages of, 656 — 690.
Nautilus, cephalopods with cham-
bered shells, xxii.

Nep'tunic,orwater-formedrocks,646.
Nerves, structureof the primary fibres

of, 80, 81; tbeir termination, 82 —

119.

Nerves, pairs of, their several offices,
97—114.

Ner'vous system of man, 84 — 95 ; of
other classes of animated beings,
92 — 119; special senses,120 — 184.

Nervous system, the, and general
sensation, 76 — 79.

Ner'vous tissue, 45, 55 ; its structure,
80, 81 ; termination, 82.

Ner'vures (Lat. nervus, a sinew),
the delicate frame of the mem-
branous wings of insects.

Neurapoph'yses (Gr. vtvpov, nerve ;
aTTopucric, a process of bone),
those vertebral elements which
enclose and protect the spinal cord
and brain.

Neu'ral- spine, the spinous processes
of the vertebra.

Neuri'lemma (Gr. vtvpov, a nerve ;
\i]fip,a, a covering), the mem-
brane which surrounds the ner-
vous fibre.

Neurop'tera (Gr. vtvpov, a nerve ;
TTTepov, a wing), the order of in-
sects with four wings, character-
ized by their numerous nervures,
like those of the dragon-fly.

Noduxle (dim. of nodus, a knot), a
little knot-like eminence.

Nor'mal (Lat. norma, rule), accord-
ing to rule, ordinary or natural.

Notosau'rus, an extinct saurian, 672.

Nucleated, having a nucleus or cen-
tral particle ; applied to the ele-
mentary cells of animal tissues,
the most important properties of
which reside in the nucleus, 38,56.

Nuvcleus and nu^cleolus, 56

Nu'dibrachiate (Lat. nudus, naked ;
Gr. /3/oay^irt, arms), the polyps,
whose arms are not clothed with
vibratile cilia.

Nudibranchiatax (Lat. nudus, naked ;
Gr. (3pavx<-a, gills), an order of
gasteropods, in which the gills
are exposed.

Nutrition, 308—349 •, digestion, 312
—349

436

IJTDEX.

OCKL'LI (Latin), minute eyes, 138.

Oc'topods (Gr. o/cro, eight ; TTOVQ, a
foot), animals with eight feet ;
the name of the tribe of Cephalo-
pods with eight prehensile organs
attached to the head.

CEsoph'agus, the gullet, or tube lead-
ing from the inouth to the sto-
mach, 345.

Olfac'tory (Lat. olfactus, the sense
of smelling) nerves, 97.

Ornniv'ora (Lat. omne, all ; voro, I
devour), feeding upon all kinds
of food, 343.

Oolite' (Gr. wov, egg ; \i9og, stone),
an extensive group of secondary
limestones, composed of rounded
particles, like the roe or eggs of a
fish.

Oolit'ic formation, 650.

Opervculum (Latin, a lid}, applied
to the horny or shelly plate
which closes certain univalve
shells ; also to the covering of
the gills in fish, and to the lids
of certain eggs.

Optic lobes, in man, 88.

Optic nerves, 98, 99, 101.

Ophid'ians (Gr. 60ic, a serpent), ani-
mals of the serpent kind, xxi.

O'ral (Lat. os, the mouth), belong-
ing to the mouth or the speech.

Orders, a group of the animal king-
dom, xx. ; subdivided into families
and genera, xx.

Organism, 36.

Organized bodies, general properties
of, 30 — 75 ; organized and unor-
ganized bodies, 30 — 34 ; elemen-
tary structure of organized bodies,
35 — 56 ; differences between ani-
mals and plants, 57 — 75.

Ornithichni'tes (Gr. opvig, a bird),
the fossil footsteps of birds, 67U

Orthop'tera (Gr. opQog, straight
7TTi.p6v, a wing), the order of in-
sects with elytra and longitudi-
nally folded wings.

Os'seous (Lat. os, a bone) tissue, 43.

Oto'liths (Gr. ovg, an ear ; \i9og,
a stone), the stony or chalky bo-
dies belonging to the internal ear,
156.

Ova'rium (Lat. ovum, an egg), the
organ in which the eggs or their
elementary and essential parts are
formed.

Ovary, detachment of the ovum from
the, 481.

Ovig'erous (Lat. ovum, an egg ; gero,
I bear), parts containing or sup-
porting eggs.

Ovip'arous (Lat. ovum, an egg ; pario,
I bring forth), animals which
bring forth eggs, 434.

Ovo-vivip'arous (Lat. ovum, an egg ;
vivus, alive ; pario, I produce),
animals which produce living
young, hatched in the egg within
the body of the parent without
any connection with the womb,
439.

OvuUVtion, the production of eggs,
437, 438.

Oxvum (Lat. an egg}, detachment from

the ovary, 481.

Ox'ygen, quantity consnmedby vari-
ous animals, 396*.

PACHYDER'MATA (Gr. Tra^vq, thick,
dfcp/ia,skin),thick-skinned animals,
like the elephant, hog, &c., 343.

Palreontol'ogy (Gr. 7ra\aid'-, an-
cient ; ovra, beings ; \6yof, dis-
course), the history of ancient ex-
tinct organised beings.

Palreontol'ogy, an essential branch
of zoology, 645.

Palaeozoic age, 658, 659 — 667.

Palseothe'rium (Gr. 7ra\£, an-
cient; 9i]piov, beast), an extinct
genus of Pachydermata, 680.

Pal'lial (Lat. pallium, a cloak), re-
lating to the mantle or cloak of
the mollusca.

Palpation, the act of feeling, 175.

IXDEX.

437

Papilbe (Lat. a nijjple}, minute soft
prominences, generally adapted
for delicate sensation, 413.

Pal'pi (Lat. palpo, I touch), the or-
gans of touch developed from the
labium and maxilla} of insects.

Parasit'ic (Lat. parasitus), h'ving on
other objects.

Paren'chyrna, the soft tissue of
organs ; generally applied to that
of glands, 372.

Pari'etes (Lat. paries, a wall), the
walls of the different cavities of
an animal body.

=Pas'serine (Lat. passer, a sparrow),
birds of the sparrow kind

Patel'la, the, 2(35.

Pectinated (Lat. pecten, a comb),
toothed like a comb.

Pectinibranchia'ta (Lat. pecten, a
comb ; /Spayxicr, gillsj, the order
of gasteropods, in which the gills
are shaped like a comb.

Ped (Lat. pes), Poda (Gr. TTOI>C, a

foot), a termination classifying cer.

tain kinds of animals by their feet ;

as quadruped, gasteropod ; which

see.

Ped'iform (Lat. pes, a foot), shaped
like a foot.

Pedun'cle (Lat. pedunculus), a stalk.

Pelag'ic (Gr. TriXayoc, sea), belong-
ing to the deep sea.

Pel'vic arch, the, 263.

Pe'lvis (Latin), the cavity formed by
the hip bones.

Pentacrinitex (Gr. TTF vra, five; KOIVOQ,
hair), apedunculated star-fish with
five rays ; they are for the most
part fossil.

Peripheral circulation, 372 — 375.

Periph'ery (Gr. iripi, about ; <ptpio,
J bear), exterior surface.

Purist al'tic (Gr. TT?PI, about ; Lat.
stdlo, I range), motion, the vermi-
cular contractions and motions of
muscular canals, as the alimentary,
the circulating, and generative
tubes.

Peritoneal (Gr. Trtpirovcaoi;, the
covering of the abdomen j, re-
stricted to the lining membrane
of that cavity.

Perpetual snow, limits of, 638.

Phal'anges (Latin), the joints of the
fingers and toes, 277.

Pharynx, the dilated beginning of
the gullet.

Phytoph'agous (Gr. <pvr6v, a plant ;
0ayo, I eat), plant-eating animals.

Piax master, 85.

Pig'ment (Lat. pigmenturri), a colour-
ing substance.

Pin'nate (Lat. pinna, a feather or
fin), shaped like a feather, or pro-
vided with fins.

Pisces (Latin), fishes ; the fourth
class of vertebrate animals, xxi.

Pituitary (Lat. pituita, phlegm),
membrane, 164.

Placen'ta (Latin), the organ by which
the embryo of mammals is attached
to the mother, 476.

Plac'oids, fishes with a rough skin,
like the shark or skate.

Plant lice ; see Aphides.

Plants and animals, differences be-
tween, 57 — 74 ; resume, 75.

Plan'aria, a genus of worms.

Plas'ma, the fluid part of the blood,
in which the red corpuscles float,
also called liquor sanguinus.

Plas'tron, the under part of the shell
of the crab arid tortoise.

Pleiocenex (Gr. TrXetov, more ; KUL-
VOQ, recent), the stage of the
tertiary strata, which is more
recent than the miocene, and in
which the major part of the fossil
testacea belong to recent species,
650.

Pleistocene^ (Gr. TrAftoroe, most ;
Kaivoc, recent), the newest of the
tertiary strata, which contains the
largest proportion of living species
of shells, 685.

Plesiosau'rus (Gr. ir^rjaioq, almost;
t-, a lizard), an extinct inariue

438

INDEX.

saurian, remarkable for
neck, 671.

Pleurotomavria, an extinct genus of
univalve shells.

Plex'us (Gr. TrXtKo, I twine), a bun-
dle of nerves or vessels interwoven
or twined together.

Pli'cae (Lat. plica, a fold), folds of
membrane.

Plumosex (Lat.pluma, a feather), fea-
thery, or like a plume of feathers.

Plutonic or igneous rocks, 646.

PneumatMc (Gr. 7rvtv/.ia, breath),
belonging to the air, and air-
breathing organs.

Pneumogas'tric nerve, 105,

Podurel'la, a genus of insects, their
mode of progression, 299.

Polygas'tria (Gr. TTO\VQ, many ;
yaaTep, a stomach), infusorial
animalcules which have many
assimilative sacs or stomach.

Pol'ypi (Gr. TroAug, many ; TTOVQ, a
foot), i-adiated animals with many
prehensile organs radiating from
around the mouth.

Polypifera, digestion in the, 3J3,
317.

Prehen'sion, act of grasping.

Primary, or palaeozoic age, the reign
of fishes, 658, 659—669.

Primitive fibres of the nerve, 80.

Progression, modes of, 289 — 307.

Prolig'erous, the part of the egg
bearing the embryo.

Prothovrax (Gr. Trpo, before, and
0opa£), the first of the three seg-
ments which constitute the thorax
in insects.

Protraet'ile, capable of being ex-
tended.

Pro'teus, a genus of batrachian rep-
tiles, 626.

Protosau'rus (Gr. Trpwroc, first ;
ffavpog, a lizard), an extinct genus
of saurian reptiles, 672.

Protozoa (Trpwrog, first ; £wo?/, ani-
mal), the, assumed, simplest forms
of animal life, xxiv.

its long I Pterich'thys

(Gr. TTTfpov, awing;
a fish), an extinct fish, of
very peculiar form, 667.

Pterodac'tylus (Gr. -nrtpov, a "wing;
Sa,KTv\o(;, a finger), an extinct fly-
ing reptile, 67 1 .

Pter'opods (Gr. Trrepov, a wing;
TTOVQ, a foot), mollusks, in which
the organs of motion are shaped
like wings, xxiii.

Pul'mogrades (Lat. pulmo, a lung ;
gradior, I walk), medusae which
swim by contractions of the res-
piratory disc.

Pul'monata (Lat. pulmo,\\ing), gaste-
ropods that breathe by lungs, xxxiii.

Pu'pa (Latin, doll, or little image),
the passive state of an insect im-
mediately preceding the last.

Pyloxrus (Gr. 7rv\a>p6^, the aper-
ture which leads from the stomach
to the intestine.

Pyr'iform (Lat. pyrum, a pear), pear-
shaped.

Py'rula, a genus of univalve shells.

QUAD'RIFID (Lat. quatuor, four ;
findo, 1 cleave), cleft in four parts.

Quadruma'nous (Lat. guatuor, four ;
manus, a hand), four-handed ani-
mals, as monkeys.

Quad'ruped (Lat. guatuor, four; pes,
a foot), animals with four legs.

RADIAXTA (Lat. radius, a ray), or
Radiates, the lowest primary divi
sion of the animal kingdom, xxi.

Radia'ta, nervous system of the, 117;
jaws, 335 ; of the trias period,
670 ; of the oolite, ti/4.

Ravdius, one of the bones of the arm,
273.

Ramosex (Lat. ramus, a branch),
branched.

Reasoning, 189.

Relation, functions of, 76.

Remak. band of, 55.

Ren'iform (Lat. ren, a kidney), kid-
ney-shaped.

439

Reproduction, peculiar modes of, 510
— 547 ; gemmiparous and fissipa- ,
rous, 5 1 0 — 5 1 5 ; alternate and equi- 1
vocal, 516 — 532; consequences of
alternate generation, 533 — 547.

Rep'tiles or Reptil'ia, jaws of, 340 ;
circulation of the blood, 366 ; re- j
spiration, 384.

Rep'tiles, reign of, 658, 670—677.

Reptil'ia (Lat.repto, I creep), orRep'-
tiles ; the third class of vertebrate
animals with imperfect respiration
and cold blood, xxi.

Respiration, 376 — 405 ; in the echi-
nodermata, 378, 405 ; in mollusca,
380, 405 ; in Crustacea, 381, 405 ;
in annelida, 382 ; in fishes, 383 ;
iu reptiles, 384 ; in insects and
arachnida, 385 ; in man, 3S6 ; in
birds, 388 ; lungs of man and the
mammalia, 389, 390 ; two sorts of
respiratory organs inarticulata,405

Rest, the distinctive character of in-
organic bodies, 32.

Re'te mucovsum, the cellular layer
between the scarf-skin and true
skin, which is the seat of the pe-
culiar colour of the skin, 413.

Ret'ina (Latin), the seatof vision, 125.

Retracr'ile, that may be drawn back.

Rhivzodonts, an order of extinct rep-
tiles, xxi. 672.

Rhizo'poda ; see Foraminifera.

Rocks, what, in a geological sense,
646 ; their different kinds, 646,
647.

RoMents (Lat rodo, I gnaw), quad-
rupeds with teeth for gnawing,
343.

Rotif' era (Lat. rota, a wheel ; fcro,
I bear), infusorial animalcules
characterised by the vibratile ;ind
apparently rotating ciliary organs
upon the head.

Rotif era, eggs of the, 546.

Ru'minants (Lat. ruminus), quadru-
peds which chew the cud •, as the
bull and stag, 343.

Running, 296.

SAC'CIFORM, shaped like a sac or bag.

Salif'erous, or salt-bearing forma-
tion, 650.

Sal'pians (Gr. aaX-Trrj, a kind offish),
tunicated mollusks which float in
the open sea, xxiii. 519.

Sau'rians (Gr. aavpoQ, a lizard), a
class of reptiles, including the ex-
isting crocodiles, and many spe-
cies of large size, 673.

Scan'sores (Lat. scando, I climb),
birds adapted for climbing, xxi.

Scap'ula, the, or shoulder blade. 270.

Scap'ular arch, the, 269.

Sclerot'ic, the principal coat of the
eye, 123.

Sebaxceous (Lat. sebum, tallow)
like lard or tallow.

Secondary age, the reign of reutiles,
658, 670—677.

Secretions, the, 406 — 428 ; structure
of glands, 419 — 425 ; elementary
parts, 426 ; origin of glands, 427 ;
distribution of their vessels, 428.

Sediment'ary or stratified rocks, 646;
alone contain fossils, 649.

Seg'ment, portion of a circle or
sphere.

Segmentation, the act of dividing
into segments.

SernuVnar, crescent-shaped, like a
half moon.

Sensation, 76 — 119.

Senses, the special, 120 — 184

Sep'ta (Latin), partitions.

Se'rous, (Lat. serum), watery.

Serrat'ed (L&i.serra, a saw), toothed
like a saw.

Ses'sile (Lat. sessilis], attached by a
base.

Se'tae (Lat. seta, a bristle), bristles
or similar uarts.

Shell, 218.

Shoulder blade, the, 270.

Sight, sense of 120—144.

Si'lex (Latin), flinty rock.

Sili'ceous (Lat. silex, flint), flinty.

Silk-worm, metamorphoses of the,
551.

440

INDEX.

S'iu'rian formations, 650.

Sm'uous (Lat. sinuatus, winding),
bending in and out.

Sivnus (Latin), a dilated vein or
receptacle of blood.

Siphon'ophori, soft radiates, xxiii.

Skeleton, the, 225 ; of man, 235—
278 ; corresponding organs of loco-
motionin other animals, 282 — 288.

Skin, the, 412, 413.

Smell, sense of, 162 — 168.

Species, ordinarily the lowest term [
in the divisions of the animal
kingdom, xix. ; occurrence of va-
rieties, xx.

Species, living, their number, 7, and
note.

Speech, gift of, confined to man, 184.

Spermatozova (Gr. a-n-fpfjia, seed;
£<ioi/, an animal), the peculiar mi-
croscopic moving filament and es-
sential parts of the fertilising fluid.

Sphinc'ter (Gr. o-0tyr£p), the circu-
lar muscles which contractor close
natural apertures.

Spic'ula (Lat. spiculum, a point or
dart), fine pointed bodies like
needles.

Spinal cord, in man, 89 ; see Nerv-
ous system.

Spixnal nerves, 108.

Spir'acles (Lat. spiro, I breathe), the
breathing pores in insects.

Sponges, doubtful nature of, 58, and
note.

Spontaneous generation, old theory
of, unfounded, 543.

Spores, the germs of sea-weeds,
ferns, &c.

Squa'mous (Lat. squama, a scale),
arranged like scales.

Standing, and modes of progression,
289—307.

Stapes, the, or stirrup, 149.

Ster i i,', the aspect of the body
where the sternum or breast-bone
is situated.

Stig/mata (Gr. <rriyu«, a mark), the
breathing pores of insects.

Stomach ; see Digestive organs.

Stra'ta (Latin, beds or layers), ar»
rangement of, 648.

Strat'ified rocks, 646.

Sucto'ria (Lat. suyo, I suck), ani-
mals provided with mouths lor
sucking, and the appendages of
other parts organised for suck-
ing or adhesion, xxiii.

Supra-oesophaxgeal (Latin, supra,
above), above the gullet.

Supreme Intelligence, direct inter-
vention of the, in the geographical
distribution of organized beings,
641.

SuHure (Lat. suo, I sew), the im-
moveable junction of two parts
by their margins.

Swimming, 302.

Sympathetic nerves, great, 109 ; op-
posite views regarding, 110 — 115.

Sys'tole (Gr. oT'oroXrj), the contrac-
tion of the heart to force out the
blood, 363.

TARSUS (Gr. rapcrog, a part of the
foot), applied to the last segments
of the legs of insects'

Tar'sus, the, in man, 266

Taste, sense of, 169 — 173.

TectibranchiaHa (Lat. tego, I cover;

(3payxlai giHs)i mollusks in which

he gills are covered by the mantle.

Teeth, the, 339—341.

Temperate fauna, the, 605 — 615.

Temperature, equalizing effects of
large sheets of water on, 636.

Tem'poral (Lat. tempora), relating to
the temples.

Te'ntacle (Lat. tentaculum), the
horn-like organs on the head of
mollusks usually bearing the eyes.

Terebrat'ula (Lat. terebro, I bore), a
genus of brachiopodous mollusks.

TePgal (Lat. tergum, the back), be-
longing to the back.

Ter'tiary (Lat. tertius, the third) age,
the reign of mammals, 658, 676
—683.

INDEX.

441

Test, lie brittle crust covering the i

crustaceans, &c.

Test, what, 218 ; in the echinidae,
asteriadae, and crinoidae, 219 ; in
the mollusca, 220 ; in the articu-
lata, 222.

TetrabranchiaHa (Gr. Tfrpa, four;
/3payxia, gills), cephalopods with
four gills.
Teuthid'eans, the family of cuttle

fishes, xxii.

Thoracic, belonging to the thorax.
Tho'rax, the, or chest, 261, 262.
Thigh, the, 264.
Tib'ia, one of the bones of the leg,

265.

Tissues, the various, 41 — 56.
Toes, the, 268.
Torrid zone, development of animal

and vegetable life in the, 583.
Tortoises, first traces of, 674.
Touch, sense of. 174 — 176.
Tra'cheae (Gr. rpa^eta, the rough
artery or windpipe), the breath-
ing tubes of insects.
Trias formation, 650.
Trias period, fauna of the, 670.
Tril'obite (Gr. rptc, three ; \of3og, a
lobe), an extinct genus of crusta-
cea, the upper surface of whose
body is divided into three lobes,
xxii. 665, 671.
Tro'phi, organs for feeding, of insects,

crabs, &c.

Trop'ical fauna, the, 616—622.
Trunk, the, 252—263.
Tubulibranchiates, articulates, with

gills about the head, xxii.
TunicaHa (Lat. tunica, a cloak), ace-
phalous mollusks enveloped in an
elastic tunic not defended by a
shell.

Tym'panum (Lat. a drum), the mem-
brane separating the internal and
external ear, 150.

Type (Gr. rv7roe),an ideal image, xx.
Type of the vertebrata, 506 ; of the
articulata, 507 ; of the mollusca,
508 ; of the radiata, 509.

UI/NA (Latin), one of the bones of

the arm, 273.
Un'cinated (Lat. unyuis, a nail or

claw), beset with bent spines like

hooks.
ITnivalve (Lat. unus, one ; valvce,

doors), a shell composed of one

calcareous piece.
Upper Silurian formation, 650.
Upper tertiary formation, 650.

VARIETIES, in the animal kingdom,
on what based, xx.

Vas'cular (Lat. vasculum), composed
of vessels.

Vegetation, geographical distribution
of, 639—641.

Veins, 357. ±

Ven'tral (Lat. venter, the belly), re-
lating to the inferior surface of the
body.

Ventric'ular (Lat. ventriculus, a
ventricle or small cavity, like those
of the heart or brain), belonging
to a ventricle, 361.

Ver'mes (Lat. vermis, a worm),
worm -like animals : applied in a
very extensive sense by Linnaeus,
xxii

Vermic'ular, or worm-like, motion,
331.

Ver'tebrae, the, 259 ; number of, in
different animals, 260.

Vertebravta (Lat. vertebra, a bone of
the back ; from verier e, to turn),
or Vertebrates, the highest divi-
sion of the animal kingdom, cha-
racterised by having a back-bone,
xxi. 73; digestive organs, 328.
329 ; jaws of, 338—344.

\ esic'ulae (Lat. vesica, a bladder),
receptacles like little bladders.

Ves'tibule (Lat. vestidulum,a.})Qi:cti),
the entrance to one of the cavities
of the ear, 158.

Vixbratile (Lat. vibratilis), moving
to and fro.

Villi (Latin), small processes like
the pile of velvet.

O G

442

INDEX.

Vis'cus, Vis'cera, plural (Latin), intes-
tine^ bowels.

Vitelline (Lat. vitellus, yolk), of, or
belonging to the yolk.

Vitel'lus, or yolk of eggs, 444.

Vit'reous humour (Lat. vitreus,
glassy), the humour of the eye on
which the retina or expansion of
the optic nerve is extended, 127.

Vivip'arous (Lat. vivus, alive ;paric,
I bring forth), animals which
bring forth their young alive, 434.

Vocal cords, 180.

Voice, the, 177 — 184 ; speech con-
fined to man, 184.

Voluntary (Lat. vofo, I will), under
control of the wilL

Voluntary and involuntary motions,
211.

WALKING, 293—295.

Warm-blooded animals, as birds,

mammals, &c. 399.
Water, equalizing effects of large

sheets of, 636.

Water-tubes of aquatic animals, 403.
Whales, mode of swimming, 304, 307.
Worms, or Ver'mes, class of, xxii.

YOLK of egg, 444.

Young, development of the, 447 — 449.

ZOOLOG'ICAL regions, chart of, ex-
plained, xii.

Zool'ogy, its sphere and fundamental
principles, 1 — 29.

Zo'ophytes (Gr. ^wov, animal, QVTOV,
a plant), the lowest primary divi-
sion of the animal kingdom, which
includes many animals that are
fixed to the ground and have the
form of plants, 68.

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