: h iV;

II. Secondary Age.

I Palaeozoic Age.
Metamorphic Rocks.

G&F TH1

Upper Tertiary Formation

Lower Tertiary "
Cretaceous

Oolitic "

Trias "

Carboniferous "

Devonian "

Upper Silurian "

Lower Silurian "

PRINCIPLES OF ZOOLOGY:

TOUCHING

THE STRUCTURE, DEVELOPMENT, DISTRIBUTION,
AND NATURAL ARRANGEMENT

RACES OF ANIMALS, LIVING AND EXTINCT

WITH NUMEROUS ILLUSTRATIONS.
PART I

COMPARATIVE PHYSIOLOGY.

FOR THE USE OF SCHOOLS AND COLLEGES.
BY

LOUIS AGASS1Z AND A. A. GOULD,

REVISED EDITION.

BOSTON:
OOULD AND LINCOLN,

50 WASHINGTON STREET.

NEW YOKK: SHELDON AND COMPANY.
CINCINNATI : GEO. S. BLANCUAKD.

1869.

Entered, according to Act of Congress, in the year 1851

BY GOULD AND LINCOLN,
In the Clerk's Office of the District t'oort tor the District of Massachusetts.

PREFACE.

THE design of this work is to furnish, an epitome of the leading
principles of the science of Zoology, as deduced from the present
state of knowledge, so illustrated as to be intelligible to the begin-
ner. No similar treatise now exists in this country, and, indeed,
some of the topics have not been touched upon in the English lan-
guage, unless in a strictly technical form, and in scattered articles.
On this account, some of the chapters, like those on Embryology
and Metamorphosis, may, at first, seem too abstruse for scholars in
our common schools. This may be the case, until teachers shall have
made themselves somewhat familiar with subjects comparatively new
to them. But so essential have these subjects now become to a correct
interpretation of philosophical zoology, that the study of them will
hereafter be indispensable. They furnish a key to many phenomena
which have been heretofore locked in mystery.

Being intended for American students, the illustrations have been
drawn, as far as possible, from American objects : some of them are
presented merely as ideal outlines, which convey a more definite
idea than accurate sketches from nature ; others have been left im-
perfect, except as to the parts especially in question ; a large propor-
tion of them, however, are accurate portraits from original drawings.
Popular names have been employed as far as possible, and to the
scientific names an English termination has generally been given ;
but the technical terms have been added, in brackets, whenever mis-
understanding was apprehended. Definitions of those least likely
to be understood, may be found in the Index.

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

The authors gratefully acknowledge the aid they have received,
in preparing the illustrations and working out the details, from Mr.

6 PREFACE.

E. Desor for many years an associate of Professor 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 first part is devoted to Comparative Anatomy, Physiology,
and Embryology, as the basis of Classification, and also to the illus-
tration of the geographical distribution and the geological succession
of Animals ; the second to Systematic Zoology, in which the prin-
ciples of Classification will be applied, and the principal groups of
animals will be briefly characterized.

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

BOSTON, June 1, 1848.

PREFACE TO THE REVISED EDITION.

IN revising the present work, the authors have endeavored to
render more precise those passages which admitted of too broad a
signification or of a double interpretation; and to correct such errors
as had arisen from inadvertence, or such as the rapid progress of Sci-
ence has disclosed. They are indebted for many suggestions on
these points to several distinguished teachers who have used the work
as a text book, and more especially to Professor Wyman, of Harvard
University. Several entirely new paragraphs have also been added.

A list of some of the principal authors who have made original
researches, or of treatises which enter more into detail than was ad-
missible in an elementary work, has been given at the close of the
volume* for the use of those who would pursue the subject of
Zoology in a more extended manner.

The work having thus been revised and enlarged, the authors sub-
mit it to the public with increased confidence in its accuracy and
usefulness.

BOSTON, February 1, 1851.

TABLE OF CONTENTS.

Page

INTRODUCTION .... ... 17

CHAPTER FIRST.

THE SPHERE AND FUNDAMENTAL PRINCIPLES OP ZOOLOGY . '-5

CHAPTER SECOND.
GENERAL PROPERTIES OF ORGANIZED BODIES . . , 35

SECTION I.
Organized and Unorganized Bodies ....... 85

SECTION II.
Elementary Structure of Organized Bodies .... 36

SECTION III.
Differences between Animals and Plants . . • • 41

CHAPTER THIRD.

FUNCTIONS AND ORGANS OF ANIMAL LIFE . 44

SECTION I.
0] the Nervous System and General Sensation . . M

TABLE OF CONTENTS.

SECTION II. p^

Of the Special Senses . .48

1. Of Sight . 48

2. Of Hearing ... 65

3. Of Smell 60

4. Of Taste . 62

5. OfTouch . 63

6. Of the Voice . 34

CHAPTER FOURTH.

OF INTELLIGENCE AND INSTINCT . 67

CHAPTER FIFTH.

OP MOTION ... 73

SECTION I.

Apparatus of Motion ... 73

SECTION II.

Of Locomotion 7^

1. Plan ol the Organs of Locomotion . 82

2. Of Standing, and the Modes of Progression ... 88

Walking 90

llunning . 91

Leaping 91

Climbing 92

Flying 92

Swimming ... 93

•

CHAPTER SIXTH.

OP NUTRITION 96

SECTION I.

Of Digestion 9?

Digestive Tube .... .... 9?

Chymification 100

Chylification 100

Mastication ... . .... 101

Insalivation ....... . 108

Deglutition ... . ... 108

TABLE OF CONTENTS.

CHAPTER SEVENTH.
OP THE BLOOD AND CIRCULATION .... .111

CHAPTER EIGHTH.
OF RESPIRATION 118

CHAPTER NINTH.
OF THE SECRETIONS 126

CHAPTER TENTH.
EMBRYOLOGY 1^J

SECTION I.

Of the Egg 131

Form of the Egg

Formation of the Egg 1^

Ovulation

Laying •

Composition of the Egg . ... 137

SECTION II.
Development of the Young within the Egg 138

SECTION III.
Zoological Importance of Embryology ....... V>3

CHAPTER ELEVENTH.
PECULIAR MODES OF REPRODUCTION . 156

SECTION I.
Qemmiparous and Fissiparous Reproduction ... 156

SECTION II.
Alternate and Eqidvocal Reproduction 158

10 TABLE OF CONTENTS.

SECTION III.

Fagk

Consequences of Alternate Generation .... ,16?

CHAPTER TWELFTH.

METAMORPHOSES OF ANIMALS ..... 174

CHAPTER THIRTEENTH.

GEOGRAPHICAL DISTRIBUTION OF ANIMALS . i8G

SECTION I.
General Laios of Distribution .... , l&G

SECTION II.

Distribution of the Faunas ..... 194

I. Arctic Fauna ...... .. 197

II. Temperate Faunas ..... 198

III. Tropical Faunas ..... . 204

SECTION III.
Occlusions ....... ... 207

CHAPTER FOURTEl'A'rH.

GEOLOGICAL SUCCESSION OF ANIMALS; OB, Tpaa

IN TIME .......... '214

SECTION I.

Structure of 'he Earth's Crust ...'.... 214

SECTION II.

Ages of Nature .......... 221

Palaeozoic Age .......... 223

Secondary Age . ........ 227

Tertiary Age .......... 233

Modern Age .... .... 235

Conclusions . . ; ?3?

EXPLANATION OF THE FIGURES.

FRONTISPIECE. — The diagram opposite the title page is intended to
present, 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 221, are represented
by four zones, of different shades, each of which is subdivided by circles
indicating the number of formations of which they are composed. The
whole disk is divided by radiating lines into four segments, to include the
four great departments of the Animal Kingdom ; the Vertebrates, with
Man at their head, are placed in the upper compartment, the Articulates
at the left, the Mollusks at the right, and the Radiates below, as being
the lowest in rank. Each of these compartments is &gain subdivided tc
include the different classes belonging to it, which are named at the outer
circle. At the centre is placed a figure to represent the primitive egg,
with its germinative vesicle and germinative dot, (278,) indicative of the
universal origin of all animals, and the epoch of life when all are appar-
ently alike, (275, 276.) Surrounding this, at the 'point from which each
department radiates, are placed the symbols of the several departments,
as explained on page 155. The zones are traversed by rays which repre-
sent the principal types of animals, and their origin and termination in-
dicates the age at which they first appeared or disappeared, all those which
reach the circumference being still in existence. The width of the ray in-
dicates the greater or less prevalence of the type at different geological
ages. Thus, in the class of Crustaceans, the Trilobites appear to com-
mence in the earliest strata, and to disappear with the carboniferous for-
mation. The Ammonites also appeared in the Silurian formation, and
did not become extinct before the deposition of the Cretaceous rocks.
The Belemnites appear in the lower Oolitic beds ; many 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 later than in the earlier Ages.

Below the circle is a section, intended to show more distinctly the rel-
ative position of the ten principal formations of stratified rocks (461)
composing the four great geological ages ; the numerals corresponding to
those on the ray leading to Man, in '.he circular figure. See also figure 154.

12 EXPLANATION OF THE FIGURES.

THE CHART OF ZOOLOGICAL REGIONS, page 195, is intended to show
the limits of the several Faunas of the American Continent, correspond-
ing to the chmatal regions. And as the higher regions of the mountains
correspond in temperature to the climate of higher latitudes, it will be
seen 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.

FlQ.

1. Simple cell, magnified, as seen in the house-leek.

2. Cells when altered by pressure upon each other ; from the pith of elder.

3. Nucleated cells, (a,) magnified; b, nucleolated cells.

4. Cartilaginous tissue from a horse, magnified 120 diameters.

5. Osseous tissue from a horse, magnified 450 diameters.

6. Nervous fibres, showing the loops as they terminate in the skin of a

frog.

7. Gray substance of the brain, magnified.

8. Head of an embryo fish, to show its cellular structure throughout

9. Diagram, to'show the nervous system of the Vertebrates, as found

in a monkey.

10. Diagram of the nervous system of the Articulates, as seen in a lobster.

11. Diagram of the nervous system of the Mollusks, as found in Natica

heros.

12. Diagram of the nervous system of the Radiates, as found in Scutella,

( Echinarachnius parma. )

13. Section of the eye. a, optic nerve ; b, sclerotic coat ; c, choroid coat;

d, retina ; e, crystalline lens ; /, cornea ; gt iris ; A, vitreous body ;
iy chamber, divided by the iris.

14. Diagram, showing the effect of the eye on rays of light.

15. Position of the eye of the snail.

16. Eyes (ocelli) of the spider.

17. Eye-spots of a star-fish, (Echinaster sanguinolentus.)

18. Compound eyes, showing the arrangement of the faoettes, and theii

connection with the optic nerve, as seen in a crab's eye.

19. Diagram of the human ear, to show the different chambers, canals,

and bones.

20. Tympanum and small bones of the ear, twice the natural size ; a.

tympanum ; m, malleus ; n, incus ; «?, orbiculare : s, stapes.
21 Section of the brain of a crow, showing the origin of the nerves of
the special senses.

22. Diagram of the larynx, in man.

23. Larynx of the merganser, (Mergus merganser.)

24. Nests of Ploceus Philippinus, male and female.

25. Distribution of nerves to the muscular fibres.

26. Test, or crust-like covering of an Echinoderra, (Cidarts.)

EXPLANATION OF THE FIGURES. 13

Fio
$7. Muscular ribbons of the willow-moth> ( Cossw ligniperda. )

28. Vertebra of a cod-fish.

29. Disposition of the muscles of the trout, (Salmo trutta.)

30. Disposition of the muscles of an owl, (Strix brachyotis.)

31. Jelly-fishes, (Stomobrachium cruciatum, Hippocrene Bougaimrittv*}

32. Leech, showing the terminal cups.

33. Portion of a Nereis, showing the gills as organs of motion.
34-43. Modifications of the fore-arm.

34. Monkey. 35. Deer. 36. Tiger. 37. Whale. 38. Bat.
39. Pigeon. 40. Turtle. 41. Sloth. 42. Mole. 43. Whale.

44, Leg of a beetle.

45. Leg of a lizard.

46 Skeleton of a tiger.

47 Cuttle-fish, (Loliyo illecebrosa.)

48 Sea-anemone, (Actinia marginata-) a, mouth ; 6, stomach ; c, general

cavity of the body.

49. Planaria, showing the mouth, stomach, and its branches.

50. Jaws, stomach, and intestine of a sea-urchin, (Echinus lividus.)

61. Plan of the digestive organs of an insect.

62. Plan of the digestive organs of a land-slug, ( Tebennophorus Carolina

ensis.)

53. Globules of chyle.

54. Portion of intestine, showing the lacteals of man, and their entrance

into a vein.

55. Jaws of an Echinoderm, (Echinarachnius parma

56. Jaws of a sea-urchin, (Echinus granulatus.)

57. Beak of a cuttle-fish.

58. Portion of the tongue of a mollusk, (Natica heros,) magnified.

59. Jaws of an Annelide, (Nereis.)

60. Trophi (organs for taking food) of a beetle.

61. " of a bee.

62. 63. " of a squash-bug.

64. " of a butterfly.

65. " of a Rotifer, (Brachionus.)

66. Jaws of ditto, magnified.

67. Skull of a tiger, showing the muscles for mastication.

68. Head of a snapping-turtle, (Emysaurus serpentina.)

69. Head of a Whale, showing the whalebone.

70. Head of an ant-eater.

71. Head of an alligator.

72. Head of a skate-fish, (Mijliobatis,') showing the palate bcne.

73. Head of a monkey, showing the three different kinds of teeth.

74. Teeth of an insectivorous animal, the mole.

75. Teeth of a carnivorous animal, the tiger.

76. Teeth cf a rodent

14 EXPLANATION OF THE FIGURES

PIG.

77. A polyp, ( Tubularia indimsa ;) m, mouth; o, ovaries;//. tantaoT??.

78. Blood disks in man, magnified.

79. " " in birds, "

80. " " 'in reptiles, "

81. " " in fishes, "

82 Porti on of a vein opened, to show *he valves

83. Network of capillary vessels.

84. Dorsal vessel of an insect, with its valves.
85 Cavities of the heart of mammals and birds.

86. " " " of a reptile.

87. " " " of a fish.

88. Heart and bloodvessels of a gasteropod mollusk, (Natica.)
80, Trachese, or air tubes of an insect ; *, stigmata ; t, trachea.

90. Relative position of the heart and lungs in man.

91. Respiratory organs of a naked mollusk, (Polycera illuminata )

92. Respiratory organs (gills) of a fish.

93. Vesicles and canals of the salivary glands.

94. Section of the skin, magnified, to show the sweat glands ; a, the cut •

ft. blood-layer ; c,epidermis ; g, gland imbedded in the fat-layer,^

95. Egg of a skate-fish, (Myliobatis.)

96. Egg of hydra.

97. Egg of snow-flea, (Podurella.)

98. Section of an ovarian egg ; d, germinative dot ; g, germinative vesi

cle ; s, shell membrane ; v, vitelline membrane.

99. Egg cases of Pyrula.

100. Monoculus bearing its eggs, a a.

101. Section of a bird's egg ; a, albumen ; c, chalaza ; et embryo ; s, shell

y, yolk.

102. Cell-layer of the germ.

103. Separation of the cell-layer into three layers ; s, serous or nervou;

layer ; m, mucous or vegetative layer ; v, vascular or blood layer.

104. Embryo of a crab, showing its incipient rings.

105. Embryo of a vertebrate, showing the dorsal furrow.

106—8. Sections of the embryo, showing the formation of the dorsal canaL
109. Section, showing the position of the embryo of a vertebrate, in re-
lation to the yolk.

110 Section, showing the same in an articulate, (Podurella.)

111 -22. Sections, showing the successive stages of development of the

embryo of the white-fish, magnified.
123 Young white-fish just escaped from the egg, with the yolk not yet

fully taken in.
124, 125. Sections of the embryo of a bird, showing the formation of the

allantois ; e, embryo ; x x, membrane rising to form the amnios ;

a, allantois ; y, yolk.
126. The same more fully developed. The allantois (a) >s further de-

EXPLANATION OF THE FIGURES. 15

Fio.

veloped, and bent upwards. The upper part of the yol* (d d ) is
nearly separated from the yolk sphere, and is to become the in
testine. The heart (h) is already distinct, and connected by
threads with the blood-layer of the body.

127. Section of the egg of a mammal ; v, the thick vitelline membrane,

or chorion ; y, yolk ; s, germinative dot ; g, germinative vesicle.

128. The same, showing the empty space (k) between the vitelline sphere

and chorion.

129. Shows the first indications of the germ already divided in two layers,

the serous layer, (s,) and the mucous layer, (m.)

130. The mucous layer (m) expands over nearly half of the yolk, and be-

comes covered with many little fringes.

131. The embryo (e) is seen surrounded by the amnios, (b,) and covered

by a large allantois, (a;) p e, fringes of the chorion ; p m, fringes
of the matrix.

132. Hydra, showing its reproduction by buds.

133. Vorticella, showing its reproduction by division.

134. Polyps, showing the same.

135. A chain of Salpae.

136. An individual salpa ; m, the mouth ; a, embryos

137. Cercaria, or early form of the Distoma.

138. Distoma, with its two suckers.

139. Nurse of the Cercaria.

140. The same, magnified, showing the included young.

141. Grand nurses of the Cercaria, enclosing the young nurses.

142. Stages of development of a jelly-fish, (Medusa ;) o, the embryo in

its first stage, much magnified ; 6, summit, showing the mouth ;
C;/» ff, tentacles shooting forth ; e, embryo adhering, and form-
ing a pedicle ; h, i, separation into segments ; d, a segment be-
come free ; kt form of the adult.

143. Portion of a plant-like polyp, (Campanularia, ) a, the cup which

bears tentacles ; b, the female cup, containing eggs ; ct the cups
in which the young are nursed, and from which they issue.

144. Young of the same, with its ciliated margin, magnified.

145. Eye of the perch, containing parasitic worms, (Distoma.)

146. One of the worms magnified.

147. Transformations of the canker-worm, (Geometra vemalis ;) a, the

canker worm ; b, its chrysalis ; c, female moth ; d, male moth.

148. Metamorphoses of the duck-barnacle, (Anatifa;) a, eggs, magnified;

b, the animal as it escapes from the egg ; c, the stem and eye ap-
pearing, and the shell enclosing them ; d, animal removed from
the shell, and further magnified ; e,f, the mature barnacle, affixed.

149. Metamorphoses of a star-fish, (Echinaster sanguinolentus,} showing

the changes of the yolk, (e ;) the formation of the pedicle, {/»;)
and the gradual change into the pentagonal and rayed form.

16 EXPLANATION OF THE FIGURES.

FlO.

150. Cornatula, a "West India species, in its early stage, with, its stem

151. The same detached, and swimming free.

152. Longitudinal section of the sturgeon, to show its cartilaginous ver

tebral column.

153. Amphioxus, natural size, showing its imperfect organization.

154. Section of the earth's crust, to show the relative positions of the

rocks composing it ; E, plutonic or massive rocks ; M, metamor-
phic rocks ; T, trap rocks ; L, lava. 1. Lower Silurian forma-
tion ; 2. Upper Silurian ; 3. Devonian ; 4. Carboniferous ; 5.
Trias, or Saliferous ; 6. Oolitic ; 7. Cretaceous ; 8. Lower Terti-
ary or Eocene ; 9. Upper Tertiary, or Miocene, and Pleiocene ;
10. Drift.

155. Fossils of the Palaeozoic age ; a, Lingula prima ; b, Leptsena alter-

nata ; c, Euomphalus hemisphericus ; d, Trocholites ammonius ;
e, Avicula decussata ; ft Bucania expansa ; g, Orthoceras fusi
forme ; i, Cyathocrinus ornatissimus, Hall ; j, Cariocrinus orna-
tus, Say ; k, Melocrinus amphora, Goldf. ; I, Columnaria alveo ,
lata ; m, Cyathophyllum quadrigeminum, Goldf. ; n, o, Caninia
flexuosa ; p, Chaetetes lycoperdon.

156. Articulata of the Pakeozoic age ; a, Harpes ; b, Arges ; c, Brontes ,

dt Platynotus ; e, Euryptei;us remipes.

157. Fishes of tbe Palaeozoic age ; a, Pterichthys ; b, Coccosteus ; ct

Dipterus ; d, palatal bone of a shark ; et spine of a shark.

158. Representations of the tracks of supposed birds and reptiles in the

sandstone rocks.

159. Supposed outlines of Ichthyosaurus, (a,) and Plesiosaurus, (b.)

160. Supposed outline of Pterodactyle.

161. Shells of the Secondary age; a, Terebratula; b, Goniomya; c,

Trigonia ; d, Ammonite.

162. Supposed outline of the cuttle-fish, (a,) furnishing the Belemnite.

163. Radiata from the Secondary age ; a, Lobophyllia flabellum ; b, Litho-

dendron pseudostylina ; c, Pentacrinus briareus ; d, Pterocoma
pinnata ; e, Cidaris ; ft Dysaster ; g, Nucleolites.

164. Shells of the Cretaceous formation ; a, Ammonites ; b, Criocerns j

c, Scaphites ; d, Ancyloceras ; e, Karaites ; /, Baculites ; g,
Turrilites.

165. Shells of the Cretaceous formation ; a, Magas ; 5, Inoceramus ; £>,

Hippurites ; d, Spondylus ; e, Pleurotomaria.

166. Radiata from the Cretaceous formation ; a, Diploctenium cordatura

6, Marsupites ; d, Galerites ; c, Salenia ; e Micraster con

anguinum.
167 Nummulite.
168. Supposed outline of Paleotherium.

169 Supposed outline of Anoplotherium.

170 Skeleton of the Mastodon, in the cabinet of Dr. J. C. Warren.

INTRODUCTION.

EVERY art and science has a language of technical terms
peculiar to itself. With those terms every student must
make himself familiarly acquainted at the outset ; and, firsi
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 Fells leo, the
lion, Felis tigris, the tiger, Felis catus, the cat, Canis lupus,
the wolf, Canis vulpes, the fox, Canis familiaris, 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 in every
object 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
2*

18 INTRODUCTION.

ibunded upon some of the minor peculiari/ies of anat.raica.
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 cf their feet, claws, and teeth, and they belong to
the genus Felis ; while the dog, fox, jackal, 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 color, size, proportions, sculpture, &c. Thus we
have different kinds, or species, of duck, different species
of squirrel, different species of monkey, &c., varying from
each 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 peculiarities, generally induced by some modification
of native habits, such as are seen in domestic animals.
These are called varieties, 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 ale wives, herrings,
shad, &c., form a family called Clupeidse ; the crows, black-
birds, jays, &c., form the family Corvidse. Families are
combined to form orders, and orders form classes, and finally,
classes are combined to form the four primary divisions or
departments, of the Animal Kingdom.

For each of these groups, whether larger or smaller, \ve
involuntarily 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 employ 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
•deas of the class, family, or genus to which it belongs.

INTRODUCTION. 19

Thus, we have a general idea of a bird ; but this idea does
not correspond to any particular bird, or any particulai
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 because 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, and so on.

As we must necessarily make frequent allusions to ani-
mals, with reference to their systematic arrangement, it seems
requisite 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.

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

I. The department of Vertebrates.
II. The department of Articulates.

III. The department of Mollusks.

IV. The department of Radiates.

1. The department of VERTEBRATES 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.

INTRODUCTION.

3. Reptiles.

4. Fishes.

The class of MAMMALS is subdivided into three orders •,
a Beasts of prey, ( Carnivora.)
b Those which feed on vegetables, (Herlivora.)
c. Animals of the whale kind, (Cetaceans.)

The class of BIRDS is divided into four orders, namely,

a. Perching Birds, (Insessores.)

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, (Rhizodonts.)

b. Lizards, (Lacertians.)

c. Snakes, ( Ophidians.)

d. Turtles, (Chelonians.)

e. Frogs and Salamanders, (Batrachians.)

The class of FISHES is divided into four orders :

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

(Ganoids,) fig. 157, c.
ft. Those with the skin like shagreen, as the sharks and

skates, (Placoids.)
c. Those which have the edge of the scales toothea,

and usually with some bony rays to th? iins, as the

perch, ( Ctenoids.)

INTRODUCTION. 21

d. Those whose scales are entire, ind whose fin rays
are soft, like the salmon, (Cycloids.)

II. Department of ARTICULATES. 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 with a trunk for sucking fluids, like the butter*

fly, (Suctoria,) fig. 62-64.

b. Those which have jaws for dividing their food, (Man-

ducata,} fig. 60.

c. Those destitute of wings, like spiders, fleas, millipedes

&c., (Aptera.)

The class CRUSTACEANS may be divided as follows :

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

ster, (Malacostraca.)

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

c. An extinct race, intermediate between these two,

(Trilobites,) fig. 156.

The class of WORMS comprises three orders :

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

( Tubulilranchiates.)

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

sibranchiates.)

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

(Abrancliiates,) and also the Intestinal Worms.

22 INTRODUCTION.

III. The department of MOLLUSXS is divided into tfirec
classes, namely :

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

cuttle-fish, (Cephalopods,) fig. 47.

2. Those which creep on a flattened disk or foot, like

snails, (Gasteropods,) fig. 88.

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

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

The CEPHALOPODS may be divided into

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

fig. 47.

b. Those having a shell, divided by sinuous partitions

into numerous chambers, (Ammonites,) fig. 164.

c. Those having a chambered shell with simple par-

titions, (Nautilus.)

The GASTEROPODS contain four orders :

a. The land snails which breathe air, (Pulmonates.)

b. The aquatic snails which breathe water, (Branch-

ifers,) fig. 88.

c. Those which have wing-like appendages about the

head, for swimming, (Pteropods.)

d. A still lower form allied to the Polyps by their gen-

eral appearance, (R/iizopods or Foraminifera.)

The class of ACEPHALS contains three orders :

a. Those having shells of two valves, (bivalves,) like the
clam and oyster, (LamellibrancMates.)

6. Those having two unequal valves, and furnished with
peculiar arms, (Brachiopods.)

INTRODUCTION 23

c. Mollusks living in chains or clusters, like the Salp;i, fig.
135 ; or upon plant-like stems, like Flustra, (Bryo-
zoa.)

IV. The department of RADIATES is divided into -three
:lasses :

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

odernis,) figs. 12, 26.

2. Jelly-fishes, (Acalephs,) fig. 31.

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

arms around the mouth, figs. 48, 77, 143.

The ECHINODERMS are divided into four orders :

a. Sea-slugs, like biche-le-mar, (Holot/iurians.)

b. Sea-urchins, (Echini,) fig. 26.

c. Free star-fishes, (Asterida,) fig. 17.

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

figs. 150, 151.

The ACALEPHS include the following orders :

a. Those furnished with vibrating hairs, by which they

move, (Ctenophora.)

b. The Medusse, or common jelly-fishes, (Discophora,)

figs. 31, 142.

c. Those provided with aerial vesicles, (Siphonophorte.)

The class of POLYPS includes two orders.

a. The so-called fresh-water polyps, and similar marine

forms, with lobed tentacles, (Hydro'ids,) fig. 143.

b. Common polyps, like the sea-anemone and coral

polyp, (Actinoids,) fig. 48.

in addition to these, there are numberless kinds of micro-

24 INTRODUCTION.

scoplc animalcules, commonly united under the name of
infusory animals, (Infusoria,) from their being found specially
abundant in water infused with vegetable matter. These
minute beings do not, however, constitute a natural group in
the Animal Kingdom. Indeed, a great many that were for-
merly supposed to be animals are now found to be vegetables.
Others are ascertained to be crustaceans, mollusks, worms
of microscopic size, or the earliest stages of development ot
larger species. • In general, however, they are exceedingly
minute, and exhibit the simplest forms of animal life, and
are now grouped together, under the title of Protozoa. But,
as they are still very imperfectly understood, notwithstand-
ing the beautiful researches already published on this sub-
ject, and as many of them are likely to be finally distributed
among vegetables, and the legitimate classes in the Animal
Kingdom to which they belong, we have not assigned any
special place for thorn.

PHYSIOLOGICAL ZOOLOGY

A CHAPTER FIRST.

THE SPHERE AND FUNDAMENTAL PRINCIPLES OP
ZOOLOGY.

1. ZOOLOGY is that department of Natural History wh;c^
relates to animals

2. To enumerate and name the animals which are found
on the globe, to describe their forms, and investigate their
habits and modes of life, are the principal, but by no means
the only objects of this science. Animals are worthy of our
regard, not merely when considered as to the variety and ele-
gance of their forms, or their adaptation to the supply of our
wants ; but the Animal Kingdom, as a whole, has a still
higher signification. It is the exhibition of the divine thought,
as carried out in one department of that grand whole which
ws call Nature ; and considered as such, it teaches us mos*
rnportant lessons.

3. Man, in virtue of his twofold constitution, the spiritual
and the material, is qualified to comprehend Nature.

3

26 SPHERE AND FUNDAMENTAL

Being made .'n 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
other animals, he is also in a condition to understand the
mechanism of organs, and to appreciate the necessities of
matter, as well as the influence which it exerts over the in-
tellectual element throughout the domain of Nature.

4. The spirit and preparation we bring to the study of
Nature, is a matter of no little consequence. When we wou'.d
study with profit a work of literature, we first endeavor to
make ourselves acquainted with the genius of the author;
and in order to know what end he had in view, we must
have regard to his previous labors, and to the circumstances
under which the work was executed. Without this, although
we may perhaps enjoy its perfection as a whole, and ad-
mire the beauty of its details, yet the spirit which pervades
it will escape us, and many passages may even remain un-
intelligible.

5. So, in the study of Nature, we may be astonished at
the infinite variety of her products; we may even study
some portion of her works with enthusiasm, and neverthe-
less remain strangers to the spirit of the whole, ignorant of
the plan on which it is based, and fail to acquire a proper
conception 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
destioying the proper meaning of the whole.

6. Besides the beings which inhabit the earth at the pres-
ent time, this picture also embraces the extinct races which
are now known to us by their fossil remains only. And
these are of the greatest importance, since they furnish us
with the means of ascertaining the changes and modifica-
tions which the Animal Kingdom has undergone in the sue-

PRINCIPLES* OF ZOOLOGY 27

aessive creations, 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
knowledge in Zoology. A century ago, the number of
known animals did not exceed 8000; that is to say, from
the whole Animal Kingdom, fewer species were then
known than are now contained in many private collections
of certain families of insects merely. At the present
day, the number of living species which have been satisfac-
torily made out and described, is more than 50,000.* The
fossils already described exceed 6000 species ; and if we

* The number of vertebrate animals may be estimated at 20,000.
About 1500 species of mammals are pretty precisely known, and the num-
ber 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 number about the same as the Mammals, 1500 described
species, and they 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
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, therefore,
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 la
25,000 species ; and it is quite probable, that by uniting the principal cd
lections of insects, 60 or 80,000 species might now be counted; f*.r the
whole department of artieulata, comprising the Crustacea, the eirrhipeda,
the insects, the red-blooded worms, the intestinal worms, and the infuso-
ria so far as they belong to this department, the number would already
amount to 100,000 ; and we might safely compute the probable number of
sf ecies actually existing at double that sum.

Add to these about 10,000 for radiata, including echini, star-fishes, me-
dusa;, and polypi, and we have about 250,000 species of living animals ; and
supposing the number of fossil species only to equal them, we b'< ve, at »
veiy moderate computation, half a million of species.

28 SPHERE AND FUNDAMENTAL

consider that whatever any one stratum of the eaiJi has
been well explored, the number of species 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.*

8. 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 enlarged, it at the same time, becomes more
:ntelligible to those who are competent to seize its promi-
nent 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 and extent of the vol-
umes already published upon the various departments of
Natural History show, that only a mere outline of a domain
so vast could be fully .sketched >in an elementary work, and
that none but those who make it their special study can be
expected to survey its individual parts.

10. Every well-educated person, however, is expected tc
have a general acquaintance with the great natural phe-
nomena constantly displayed before his eyes. There is a
general knowledge of man and the subordinate animals*
embracing their structure, races, habits, distribution, mutual
relations, &c., which is not only calculated to conduce es-

* In a separate work, entitled " Nomenclator ZoOlogictts," by L. AGAS-
8iz, 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 ki cw in detail the genera and families in each class of the Animal
Kingdom

PRINCIPLES OF ZOOLOGY. 29

sentially to our happiness* but which it would be quite inex-
cusable to neglect. This general view of Zoology, «t is the
purpose of this work to afford.

11. A sketch of this nature should render prominent the
more general features of animal life, and delineate the ar-
rangement of the species according to their most natural
relations and their rank in the scale of being ; thus giving
a panorama, as it were, of the entire Animal Kingdom,
To accomplish 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
pecies has its definite sphere of action, whether more or

less extended, — its own peculiar office in the economy of
nature ; and a complete adaptation to fulfil all the purposes
of its creation, 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 functions, y

13. In this physiological point of view, an animal may be
xsaid 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, an animal, like a quad-
ruped, or a bird, which has the five senses fully developed,
and which has, moreover, the faculty of readily trans-
porting 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 perform-
ance of its function. Thus, the eye-spots of the star-fish
and jelly-fish are probably endowed with merely the fac

3*

30 SPHERE AND FUNDAMENTAL

ulty of perceiving light, without the power of distinguishing
objects. The keen eye of the bird, on the contrary, dis-
cerns minute objects at a great distance, and when compared
with the eye of a fly, is found to be not only more perfect,
but constructed on an entirely different plan. It is the
same with every other organ.

15. We understand the faculties of animals, and appre-
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 exam-
ination of their structure ; they must never be disjoined,
and must 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 even serve for very dif-
ferent uses. Analogy, on the contrary, indicates the simi-
larity of purposes or functions performed by organs of dif-
ferent structure.

17. 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
hereafter 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 different purposes, the one for flight, and the other
for climbing, they are both constructed on the same plan.
Accordingly, the bird is more nearly "allied to the monkey
than to the butterfly, though they both have in common
the faculty of flight. Affinities, and not analogies, therefore,
must g'lide us in the arrangement of animals.

PRINCIPLES OF ZOOLOGY. 81

18. Our investigations should not be limited to adul
ajimals, but should also include 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 predomi-
nant 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 individu-
als, we might be induced to divide all animals into two
groups, according to their mode of respiration ; uniting, on
the one hand, all those which breathe by gills, and, on the
other, those which breathe by lungs. But this distinction
loses its importance, when we consider that various animals,
for example, frogs, which respire by lungs in the adult
state, have only gills when young. It is thence evident thai
the respiratory organs cannot be taken as a satisfactorj
basis of our fundamental classification. They are, as we
shall see, subordinate to a more important system, namely,
the nervous system.

20. Again, we have a means of appreciating the relative
grade of animals by the comparative study of their devel-
opment. It is evident that the caterpillar, in becoming a
butterfly, passes from a lower to a higher state. Clearly,
therefore, animals resembling the caterpillar, the worms, for
instance, must occupy a lower rank than those approaching
the butterfly, like most insects. There is no animal which
does not undergo a series of changes similar to those of t!ie
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 egg some days
previous to the time of hatching, we find in it a living ani-
mal, which, although imperfect, is nevertheless a chicken •

'42 SPHERE AND FUNDAMENTAL

it lias been developed from a hen's egg, and we know thai,
should it continue to live, it would infallibly display all the
characteristics of the parent bird. Now, if there existed in
Nature an adult bird as imperfectly organized as the chicken
on the day, or 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 at length be-
come entirely dissimilar. For example, the myriads of
minute aquatic animals embraced under the name of Infu-
soria, generally very simple in their organization, 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 are found
members of all the lower classes of animals, mollusks,
crustaceans, worms, &c. ; and many of them are even found
to belong to the Vegetable Kingdom.

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 thei>* turn,
differ from those of tropical regions. Certainly, no one will
maintain 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 by chance merely the white bear and
reindeer inhabit only cold regions.

24. Nor is it by chance that most of the largest animals,
of every class, the whales, the aquatic birds, the sea-turtles,
the crocodiles, dwell in the water rather than on the land.
And while the water affords freedom of motion to the largest,
it is also the home of the smallest of living beings, allow-
ing a degree of liberty to their motion, which they could nol
enjoy elsewhere.

VK1NCIPLES OI ZOOLOGY. 33

25. Nor are 3ur researches to be limited to the animals
now living. 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 present day. Many of those
remains present forms so extraordinary that it is almost im-
possible to trace their alliance with any animal now
living. In general, they bear a striking analog}' to the em-
bryonic forms of existing species. For example, the curi-
ous fossils known under the name of Trilobites (Fig. 156)
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 do not hesitate to refer them to the
crustaceans. We shall also see tha. some of the Fishes
of ancient epochs present shapes altogether peculiar to them-
selves, (Fig. 157,) but resembling, in a striking manner, the
embryonic forms of our common fishes. A determination
of the successive appearance of animals in the order of time
is, therefore, of much importance in assisting to decide the
relative rank of animals.

26. Besides the distinctions to be derived from the varied
structure of organs, there are others less subject to rigid
analysis, but no less decisive, to be drawn from the imma-
terial principle with which every animal is endowed. It is
this which determines the constancy of species from genera-
tion to generation, and which is the source of all the varied
exhibitions of instinct and intelligence which we see dis-
played, from the simple impulse to receive the food which is
brought within their reach, as observed in the polyps, through
the higher manifestations, in the cunning fox, the sagacious
elephant, the faithful dog, to the exalted intellect of man,
which is capable of indefinite expansion.

27. Such are some of the general aspects in which we •
are to contemplate the animal creation. Two points of

34 FUNDAMENTAL PRINCIPLES OF ZOOLOGY.

view should never be lost sight of, nor 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 vague and
profitless pantheism. He who beholds in Nature nothing
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 mate-
rialist.

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
physical laws by virtue of which all beings preserve their
characteristics, will be very likely to confound the Creator
with the creature.

29. It is only as it contemplates, at the same time, matter
and mind, that Natural History rises to its true character
and dignity, and leads to its worthiest end, by indicating to
us, in Creation, the execution of a plan fully matured in the
beginning, and undeviatingly pursued ; the work of a God
infinitely wise, regjlating Nature according to imrni table
laws, which He has himself imposed on her.

CHAPTER SECOND.

GENERAL PROPERTIES OF ORGANIZED BODIES
SECTION I.

ORGANIZED AND 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 organ-
ized bodies, (vegetables and animals.) These two groups
have nothing in common, save the universal properties of
matter, such as weight, extension, &c. They differ at the
same time as to their form, their structure, their chemical
composition, and their mode of existence.

32. The distinctive characteristic of inorganic bodies is
•est ; the distinctive trait of organized bodies is independent

motion, LIFE. The rock or the crystal, once formed, nevei
changes from internal causes ; its constituent parts or mole-
cules invariably preserve the position which they have once
taken in respect to each other. Organized bodies, on the
contrary, are continually in act '.on. The sap circulates in

36 ELEMENTARY STRUCTURE OF ORGANIZED BODIES*.

the tree, the blood flows through the animal, and in both
there is, besides, the incessant movement of growth, decom
position, and renovation.

33. Their mode of formation is also entirely different.
Unorganized bodies are either simple or made up of ele-
ments unlike themselves ; and when a mineral is en-
larged, 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 interstitially, by the successive assimilation
of new particles, derived from various sources.

34. Finally, organized bodies are limited in their duration.
Animals and plants are constantly losing some of their parts
by decomposition during life, which at length cease to be
supplied, and they die, after having lived for a longer or
shorter period. Inorganic bodies, on the contrary, contain
within themselves no principle of destruction ; and unless
subjected to some foreign influence, a crystal or a rock would
never change. The limestone and granite of our mountains
remain just as they were formed in ancient geological
epochs ; while numberless generations of plants and ani-
mals 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
essential 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 pene

ELEMENTARY STRUCTURE OF ORGANIZED BODIES 37

trates 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 to liquids. There
is no part of the body, no organ, however hard and compact
it may appear, which has not this peculiar structure. It ex-
ists in the bones of animals, as well as in their flesh and fat ;
tn the wood, however solid, as well as in the bark and flowers
of plants. It is to this general structure that the terrr or-
ganism is now applied. Hence the collective name of
organized beings,* which includes both the animal and the
vegetable kingdoms.

37. The vegetable tissues and most of the organic struc-
tures, 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 Fig. 1.

from each other are called intercellular passages or spaces
(m.) When the cellules are very numerous, and crowd
each other, their outlines become angular, and the intercel-
lular spaces disappear, as seen in figure 2, which represents

* Formerly, animals and plants were said to ^organized, because they
are furnished with definite parts, called organs, which execute particular
functions. Thus, animals nave a stomach, a heart, lungs, &e ; plants
have leaves, petals, stamens pistils, roots, &c.? which are indispensable
to the maintenance of life and the perpetuation of the species. Sinco
the discovery of the fundamental identity of structure of animal and
vegetable tissues, a common denomination for this uniformity of textuie
has been justly preferred; and the existence of tissues is now regarded
as the basis of organization.

4

38 ELEMENTARY STRUCTURE OF ORGANIZED BODIES

the pith of the elder. They then
have the form of a honey-comb ;
whence they have derived their
name of cellules.

38. All the organic tissues, whether
animal or vegetable, originate from

cells. The cell is to the organ- Fig. 2.

ized body what the primary form of the crystal is to the
secondary, in minerals. As a general fact, it may be stated
6 that animal cells are smaller than vegetable
—p. jsi cells ; but they alike contain a central dot or
vg) (jjj) vesicle, called nucleus. Hence such cells are
called nucleated cells, (Fig. 3, a.) Sometimes
the nucleus itself contains a still smaller
dot, called nucleolus, (b.)

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 exam
ination, 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
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. The areolar tissue consists of a network of delicate
fibres, intricately interwoven so as to leave numberless
communicating interstices, filled with fluid. It is inter-
posed in layers of various thickness, between all parts of
the body, and frequently accompanied by clusters of fat
cells. The fiUvous and the serous membranes are mere
modifications of this tissue.

42 The cartilaginous tissue is composed of nucleated

ELEMENTARY STRUCTURE OF dlGANIZED BODIES.

39

Fig- 4.

Fig. 5.

cells, the intercellular spaces being filled with a more com
pact substance, called the hyaline matter. Figure 4 repre-
sents a slip of cartilage from the horse, under
a magnifying power of one hundred and twen-
ty diameters.

43. The osseous or bony tissue differs from
the cartilaginous tissue, in having its meshes
filled with salts of lime, instead of hyaline sub-
stance, whence its compact and solid appear-
ance. 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, as
is seen in figure 5, representing a section of a
bone of a horse, magnified four hundred times.

44. The muscular tissue, which forms the flesh of ani-
mals, 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. In the muscles
under the control of the will, the fibres 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. The nervous tissue is of different kinds. In

nerves proper, it is composed of

very delicate fibres, which return

back at their extremities, and

form loops, as shown in figure 6,

representing nervous threads as

they terminate in the skin of a

frog. The same fibrous structure

is found in the white portion of the brain.

the gray substance of the brain is composed of
vory minute granulations, interspersed with clusters of larger
cells, as seen in figure 7.

the

Fig. 7.

Fig. 6.

But

40 ELEMENTARY STRUCTURE OF OKj.,NIZED BODIES.

46. The tissues above enumerated differ from each othei
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 made up of nothing but cells
in contact with each other. Such is the case with the
polyps; yet they contract, secrete, absorb, and repro-
duce; and most of the Infusoria move freely, by means of
little fringes on their surface, arising from a peculiar kind
of 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 salr=on, for instance, con-
tains not only all the tissues we have mentioned, namely,

bone, cartilage, muscle, nerve, brain,
and membranes, but also bloodves-
sels, glands, pigments, &c. Let
us, however, examine it during the
embryonic state, while it is yet in
Fig. 8. the egg, and we 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 sur-
rounding the eye a little larger, and those beneath being still
larger, (Fig. 8.) It is only at a later period, after still further
development, 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.

DIFFERENCES BETWEEN ANIMALS AND PLANTS 41

SECTION III.

DIFFERENCES BETWEEN ANIMALS AND PLANTS.

49. At first glance, nothing would seem more widely
different than animals and plants. What is there in coin-
mon, for instance, between an oak or an elm, and the bird
which seeks shelter amid their foliage ?

50. The differences are usually so obvious, that this
question would be superfluous if applied only to the higher
forms of the two kingdoms. But this contrast diminishes,
in proportion as their structure is simplified ; and as we
descend to the lower forms, the distinctions are so few
and so feebly characterized, that it becomes at length dif-
ficult 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 of the polypi, that they have generally
been classed among animals, although in reality they be
long to the vegetable kingdom.

51. Animals and plants differ in the relative predomi-
nance of the elements, oxygen, carbon, hydrogen and nitro-
gen, of which they are composed. In vegetables, only a
small proportion of nitrogen is found ; while it enters largely
into the composition of the animal tissues.

52. Another peculiarity of the Animal Kingdom is, the
presence of large, distinctly limited cavities, usually intended
for the lodgment of certain organs ; such is the skull and
the chest in the higher animals, the cavity of the gills in
fishes, and of the abdomen, or general cavity of the body
which exists in all animals, without exception, for the pur-
pose of digestion, or the reception of the digestive organs.

53. The well-defined and compact forms of the organs

4»

42 ' DIFFERENCES BETWEEN ANIMALS AND FLINTS.

lodge*, in these cavities, is a peculiarity belonging to animals
only. I& 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 lungs, instead of being condensed into one
organ, are scattered independently in countless numbers over
the branches. Nor is there any organ corresponding to the
brain, the heart, the liver, or the stomach.

54. 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, through the trunk
and al! the branches, to the whole plant, before they arrive
at the leaves, where they are to be digested. In animals,
on the contrary, the food is at once received into the diges-
tive cavity, where it is elaborated ; and it is only after it has
been thus dissolved 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 substances ; and they produce albumen,
sugar, starch, &c., while animals consume them.

55. Plants commence their development from a single
point, the seed, and, in like manner, all animals are devel-
oped 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, generally 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 develop-

DIFFERENCES BETWEEN ANIMALS AND PLANTS. 43

ment of new branches. Some of the lowest animals, how-
ever, the polyps for instance, increase in a somewhat analo-
gous manner, (§ 329, 330.)

56. 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 de-
structive to animal life ; while plants, by respiration, which
they in most instances perform by means of the leaves,
reverse the process, and thus furnish oxygen, which is so
essential to animals. If an animal be confined in a small
portion of air, or water containing 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 no difficulty is experienced.
The practical effect of this compensation, in the economy of
Nature, is obviously most important ; vegetation restoring
to the atmosphere what is consumed by animal respiration,
combustion, &c., and vice versa.

57. But there are two things 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 perceiv-
ing other objects or their influences ; in other words, volun-
tary motion and sensation.

58. All animals are susceptible of undergoing 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 de-
gree of cold, or to the action of poisons But they have no
consciousness of these influences, and suffer no pain ; while
animals under similar circumstances suffer. Hence they
have been called animate beings, in opposition to plants
which are inanimate oeings.

J

CHAPTER THIRD.

FUNCTIONS AND ORGANS OF ANIMAL LIFE,
SECTION L

OF THE NERVOUS SYSTEM AND GENERAL SENSATION.

59. LIFE, in animals, is manifested by two sorts of func-
tions, viz. : First, the peculiar functions of animcd life, or
those of relation, which include the functions of sensation
and voluntary motion ; those which enable us to approach,
and perceive our fellow beings and the objects about us, and
to bring us into relation with them : Second, the functions
of vegetative life, which are nutrition in its widest sense,
and reproduction ; * those indeed which are essential to the
maintenance and perpetuation of life.

60. The two distinguishing characteristics of animals,
namely, sensation and motion, (57,) depend upon special
systems of organs, which are wanting in plants, the nervous
system and the muscular system under its influence. 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.

* 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 uppe.
.layer, and the second from the lower layer of the germ of the animal
See Chapter on Embryology, p. 112.

NKRVOUS SYSTEM AND GENERAL SENSATION. 45

61. Greatly as the form, the arrangement, and the volj
ame of the nervous system

vary in different animals,
they may all be reduced to
four principal types, which
correspond, moreover, to the
four great departments of the
Animal Kingdom. In the
vertebrate animals, namely,
the fishes, reptiles, birds, and
mammals, the nervous sys-
tem is composed of two prin-
cipal masses, the spinal mar-
row, (Fig. 9, c,) which runs
along the back, and the
brain, contained within the
skull.* The volume of the
brain is proportionally larger
as the animal occupies a
more elevated rank in the
scale of being. Man, who
stands at the head of Crea-
tion, is in this respect also the
most highly endowed being. Fig-

62. With the brain and spinal marrow are connected tho
nerves, which are distributed, in the form of branching
threads, through every part of the body. The branches
which unite with the brain are twelve pairs, called ihe cere-

* 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 9 and 21.) The spinal marrow is made up
by the union of four nervous columns

46 NERVOUS SYSTEM AND GENERAL SENSATION.

bral nerves, and are designed chiefly for the organs of
sense located in the head. Those which join the spinal
marrow 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 nerve is double, in fact, being composed
of two threads, which at their junction with the spinal mar-
row are separate, and afterwards accompany each other
throughout their whole course. The anterior thread trans
mits the commands of the will which induce motion ; the
other receives and conveys impressions to the brain, to pro-
duce sensations.

63. In the Articulated animals, comprising the crabs,

barnacles, worms, spi-
ders, insects, and oth-
er animals formed of
rings, the nervous sys-

Fig. 10. tern consists of a se-

ries of small centres or swellings, called ganglions, (Fig. 10,)
placed beneath the alimentary canal, on the floor of the gen-
eral cavity of the body, and connected by threads ; and of a
more considerable mass placed above the oesophagus or
throat, connected with the lower ganglions by threads which
form a collar around the alimentary canal. The number of
ganglions generally corresponds to the number of rings.

64. In the Mollusks, (Fig. 11,) the nervous system con-

sists of a single gangl ionic
circle, the principal swell-
ings of which are placed
symmetrically above and
below the oesophagus, and
from whence the filaments,
Fig. 11. which supply the organs

in different directions, take their origin.

NERVOUS SYSTEM AND GENERAL SENSATION. 47

65. In the Radiata, (Fig. 12,) the nervous system is re-
duced to a single ring, encircling

the mouth, and giving off .threads
towards the circumference. It dif-
fers essentially from that of the
Mollusks, by being disposed in a
horizontal position, and by its star-
like form.

66. The nerves branch off and
diffuse sensioility to every portion

of the body, and thereby men and Fig- 12-

the higher animals are enabled to gain a knowledge of the
general properties 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, &c. There
are some parts, however, the ends of the fingers, for exam-
ple, in which this sensibility is especially acute, and these
also receive a larger supply of nerves.

67. On the contrary, those parts which are destitute of
sensibility, such as the feathers of birds, the wool of ini-
mals, or 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.

68. There are animals in which the faculty of percep-
tion is limited to this general sense ; 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 /or certain kinds of per-
ceptions, which are acted upon by certain kinds of stimuli,
as light, sound and odor, and which are called the SENSES.
These are five in number, namely : sight, hewing,
taste, and

-f-

<18 SPECIAL SENSES

SECTION II.

OF THE SPECIAL SENSES.

1. Of Sight.

69. Sight is the sense by which light is perceived, and
by means of which the outlines, dimensions, relative posi-
tion, color and brilliancy of objects are discerned. Some
of these properties may be also ascertained, though in a less
perfect manner, by the sense of touch. We may obtain an
idea of the size and shape of an object, by handling it ; but
the properties that have a relation to light, such as color and
brilliancy, and also the form and size of bodies that are be-
yond our reach, can be recognized by sight only.

70. 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 connec-
tion with particular nerves, called the optic nerves, (Fig. 13,
a.) In the vertebrates, these are the second pair of the cer-
ebral nerves, and arise directly from the middle mass of the
brain, (Fig. 21, Z>,) which, in the embryo, is the most con-
siderable of all.

71. Throughout the whole series of vertebrate animals

the eyes are only two in num-
ber, and occupy bony cavities
of the skull, called the orbits.
The organ is a globe or hollow
sphere formed by three princi-
pal membranes, enclosed one
within the other, and filled with
transparent matter. Figure 13
represents a vertical section

OF SIGHT. 49

through the eye, from before backwards, and will give an
idea of the relative position of these different parts.

72. The outer coat is called the sclerotic, (b ;) it is a
thick, firm, white membrane, having its anterior portion
transparent. Th^s transparent segment, which seems set in
the opaque portion, like a watch-glass in its rim^is called the
cornea, (f.)

73. The inside of the sclerotic is lined by a thin, dark-
colored 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 gives to the eye
its peculiar color, and is called the iris, (g.) The iris read-
ily contracts and dilates, so as to enlarge or diminish an open-
ing at its centre, the pupil, 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 sidewise, as in the sheep.

74. The third membrane is the retina, (d.) It is formed
by the optic nerve, which enters the back part of ihe eye, by
an opening through both the sclerotic and choroid coats, and
expands upon the interior into a whitish and most delicate
membrane. It is upon the retina that the images of objects
are received, and produce impressions, which are conveyed
by the nerve to the brain.

75. 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, (c.)
It is tolerably firm, perfectly transparent, and composed of
layers of unequal density, the interior being always more
compact than the exterior. Its form varies in different classes
of animals. In general, it is more convex in aquatic than in
land animals; whilst with the cornea it is directly the con-
trary, being flat in the former, and convex in ihe latter.

76. By means of the iris, the cavity, (i,) in front of the crys-

5

50 SPECIAL SENSES.

talline lens is divided into two compartments, called .he an
terior and posterior chambers. The fluid which fi is tnese
chambers is a clear watery liquid, called the aqueous humor
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. Tnis
is called the vitreous humor, (h.)

77. The object of this apparatus is to receive the rays of
light, which diverge from all points of bodies placed before
it, and to bring them again to a point upon the retina. It is
a well-known fact, that when a ray of light passes obliquely
from one medium to another of different density, it will be
refracted or turned out of its course more o- loss, according
to the difference of this density, and the obliquity at which
the ray strikes the surface. This may be illustrated by the
following figure, (Fig. 14.)

Fig. 14.

The ray a c, which strikes the cornea A B perpendicularly,
continues without deviation, until it reaches the bottom ot
the eye at c. But the rays a m and a n, which strike the eye
obliquely, change their direction, and instead of proceeding
onward to m g and n d, take the direction m i and n f A
still further refraction, though less considerable, is occasioned
by passing through the crystalline lens C D, and the vitreous
humor, so that the two rays, m i and nf, will at last meet in
?jt point. This point is called the focus, (c,) and in distinc
vision \s always precisely at the retina, E F.

78. From this arrangement, the image found upon the

OF SIGHT. 51

retina will be inverted. We may satis.fy ourselves c f this
by direct observation. The eye of the white rabbit being
destitute of the black pigment of the choroid, is quite trans-
parent. Take the eye, soon after the death of the animal,
and arrange it in one end of a tube, so that the cornea will
face outwards ; then if we look in at the other end of
the tube, we may see objects to which it is directed exactly
pictured upon the retina, but in a reversed position.

79. The mechanical structure of the eye may be per-
fectly imitated by art. Indeed, the camera obscura is an
instrument constructed on the very same plan. By it, exter-
nal objects are pictured upon a screen, placed at the bottom
of the instrument, behind a magnifying lens. The screen
represents the retina ; the dark walls of the instrument
represent the choroid ; and the cornea, the crystalline lens
and the vitreous humor 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 adapt-
ing itself so as to discern with equal precision very remote,
as well as very near, objects.

80. By means of muscles which are attached to the bali,
the eyes may be rolled in every direction, so as to view ob-
jects 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 lid, which is vertical ;
this is also found in most of the reptiles and a few man.-
mals. In fishes, the lids are wanting, or immovable.

81. The eye constructed as above described is called a
simple eye, and belongs more especially to the vertebrate
animals. In man, it arrives at its highest perfection. In
him, the eye also performs a more exalted office Uan mere
vision. It is a mirror, in which the inner man is reflected.
His passions, his joys, and his sorrows, his inmost self, are

52 SPECIAL SENSES.

revealed, with the utmost fidelity, in the expression of his
eye, and it has been rightly called " the window of the
soul."

82. Many of the invertebrate animals have the eye
constructed upon the same plan -as that of the vertebrate
animals, but with this essential difference, that the optic
nerve which forms the retina is not derived from a ner-
vous centre, analogous to the brain, but arises from one
of the ganglions. Thus, the eye of the cuttle-fish contains
all the essential parts of the eye of the superior animals,
and, what is no less important, they are only two in number,
placed upon the sides of the head.

83. The snail and kindred animals have, in like manner,

only two eyes, mounted on the tip
of a long stalk, (the tentacle,) or
situated at its base, or on a short

, ^s pedestal by its side. Their struc-

" — -~^Xb ture is less perfect than in the cuttle-

Fig. 15. fish, but still there is a crystalline lens,

and more or less distinct traces of the vitreous body. Some
bivalve mollusks, the scollops for example, have likewise
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.

84. In spiders, the eyes are likewise simple, and usually

eight in number. These
little organs, usually called
ocelli, instead of being
placed on the sides of
the body or of the head,
occupy the anterior part
of the back. All the essen-
Fig. 16. tial parts of a simple eye

the corner , the crystalline lens, the vitreous body, are found in

OF SIGHT. 53

hem, and even the choroid, which presents itself in the
form of a black ring around the crystalline lens. Many in
sects, in their caterpillar state, also have simple eyes.

85. Rudiments of eyes have been observed in very
many of the worms. They, generally appear as small
black spots on the head ; such as are seen on the head
of the Leech, the Planaria and the Nereis. In these latter
animals there are four spots. According to Muller, 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, without the power
of discerning objects.

86. 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, at the mar-
gin of many Medusae, and in
some Polypi. Ehrenberg has
shown that similar spots also
exist in a large number of the

Infusoria. Fig. 17.

87. In all the above-mentioned animals, 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 of the 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

54

SPECIAL SENSES.

natural transition to the compound eyes of insects, to which
we now give our attention.

88. 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 pedestals, as in the crabs.
But if we examine an eye of this kind by a magnifying lens,
we find its surface to be composed of an infinite number of
angular, usually six-sided faces. If these fapettes are re-
moved, we find beneath a corresponding number of cones, (c,)
side by side, five or six times as long as they are broad,
and arranged like rays around the optic nerve, from
which each one receives a little filament, so as to
present, according to Muller, the following disposition.

(Fig. 18.) The cones are per-
fectly transparent, but sepa-
rated from each other by
walls of pigment, in such a
manner that only those rays
which are parallel to the
axes can reach the retina A ;
all those which enter ob-
liquely are lost ; so that of
Fig. 18. all the rays which proceed

from the points a and £, only the central ones in each
pencil will act upon the optic nerve, (d ;) the others will
strike against the walls of the cones. To compensate
for the disadvantage of such an arrangement, and for the
want of motion, the number of fa£ettes is greatly multi-
plied, 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 number of
small image? each of them representing a portion of the
figure. Tht entire picture is of course, more perfect,

OF HEARING. 55

in proportion as the pieces are smaller and more nu-
merous.

89 Compound eyes are destitute of the optical apparatus
necessary to concentrate the rays of light, and cannot adapt
themselves to the distance of objects ; they see at a certain
distance, but cannot look at pleasure. The perfection of
their sight depends on the number of fayettes 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 directions, 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.

90. If there be animals destitute of eyes, they are either
of a very inferior rank, such as most of the polypi, or else
they are animals which live under unusual circumstan-
ces, such as the intestinal worms. Even among the ver-
tebrates, there are some that lack the faculty of sight, as
the Myxine glutinosa, 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 example, that curious fish (Amblyopsis spelceus,)
which lives in the Mammoth Cave, and which appears to
want even the orbital cavity. The craw-fishes, (Astacus
pellucidus,) of this same cave, are also blind ; having
merely the pedicle for the eyes, without any traces of
fayettes.

2. Hearing.

91, To hear, is to perceive sounds. The faculty of per-
ceiving sounds is seated in a peculiar apparatus, the EAR,
which is constructed with a view to collect and augment the
sonorous vibrations of the atmosphere, and convey them to

56 SPECIAL SENSES.

the acoustic or auditory nerve, which arises from the poste-
rior part of the brain. (Fig. 21, c.)

92. The ears never exceed two in number, and are
placed, in all the vertebrates, at the hinder part of the head.
In a large proportion of animals, as the dog, horse, rabbit,
and most of the mammals, the external parts of the ear
are generally quite conspicuous ; and as they are, at the
same time, quite movable, they become one of the promi-
nent features of physiognomy.

93. These external appendages, however, do not const!
tute the organ of hearing-, properly speaking. The true seat
of hearing is deeper, quite in the interior of the head. It is
usually a very complicated apparatus, especially in the supe-
rior animals. In mammals it is composed of three parts, the
external ear, the middle ear, and the internal ear ; and its
structure is as follows : (Fig. 19.)

Fig. 19.

94. The external ear, which is popularly regarded as the
rar, consists of the conch, (#,) and the canal which leads
from it the external auditory passage, (&.) The first is a

OF HEARING 57

gristly expansion, in the form of a norn or a funnel, the
object of which is to collect the waves of sound ; for this
reasor. , animals prick up their ears when they listen. • The
ear of man is remarkable for being nearly immovable.
Therefore, persons, whose hearing is deficient, employ an
artificial trumpet, by which the vibrations from a much
more extended surface may be collected. The external
ear is peculiar to mammals, and is wanting even in some
aquatic species of these, such as the seals and the Orni-
thorhyncus.

95. The middle ear has received the najme of the tym-
panic cavity, (k.) It is separated from the auditory passage
by a membranous partition, the tympanum or drum, (c ;)
though it still communicates with the open air by means
of a narrow canal, called the Eustachian tube, (i,) 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 distinguished
by the names of malleus, (Fig. 20, c,)
incus, (n,) stapes, (s,) and os orbicu-
lare, (o;) which are articulated to-
gether, so as to form a continuous
chain, as here represented, magnified.

96. The internal ear, which is

also denominated the labyrinth, is an irregular cavity formed
in the most solid part of the temporal bone, beyond trie
chamber of the middle ear, from which it is separated by a
bony partition, which is perforated by two small holes, called,
from their form, the round and the oval apertures, the fora-
men rotundum, (Fig. 19, g,) and the foramen ovale, (A.) The
first is closed by a membrane, similar to that of the tympa-
num, while the latter is closed by the stapes, one of the little
bones n the chamber.

58 SPECIAL SENSES.

97. Three parts a:e to be distinguished in the labyrinth,
namely, the vestibule, which is the part at the entrance of the
cavity ; the semicircular canals, (d,) which occupy its uppei
part, in the form of three arched tubes; and the cochlea^
which is a narrow canal placed beneath, at the lower part
of the vestibule, having exactly the form of a snail-shell, (e.)
The entire labyrinth is filled with a watery fluid, in which
membranous sacs or pouches float. Within these sacs, the
auditory nerve (f) terminates. These pouches, therefore,
are the actual seat of hearing, and the most essential parts
of the ear. The auditory nerve is admitted to them by a
long passage, the internal auditory canal.

98. 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
tympanum. The tympanum, by its delicate elasticity, aug-
ments 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 covering the round aperture, (#•,)
and produces vibrations there, corresponding to those of the
tympanum. After all these modifications, the sonorous
vibrations at last arrive at the labyrinth and the auditory
nerve, which transmits the impression to the brain.

99. But the mechanism of hearing is not/so complicated
in all classes of animals, and is found to be more and more
simplified as we descend the series. In birds, the middle
and interior ears are constructed on the same plans as in the
mammals ; but the outer ear no longer exists, and the audi-
tory passage, opening on a level with the surface of the head
behind the eyes, is merely surrounded by a circle of peculi-
arly formed feathers. The bones of the middle ear are also
less numerous there being generally but one.

OF HEARING. 59

100. In reptiles, the whole exterior ear disappears ; the
auditory passage is always wanting, and the tympanum be-
comes external. In some toads, even the middle ear also is
completely wanting. The fluid of the vestibule is charged
with salts of lime, which frequently give it a milky appear-
ance, and which, when examined by the microscope, are
found to bo composed of an infinite number of crystals.

101. In fishes, the middle and external ear are both
wanting; and the organ of hearing is reduced to a mem-
branous vestibule, situated in the cavity of the skull, and
surmounted by semicircular canals, from one to three in
numoer. The liquid of the vestibule contains chalky con-
cretions of irregular forms, which are called Otolites, the
use of which is doubtless to render the vibration of sounds
more sensible.

102. In crabs, the organ of hearing is found on the lower
face of the head, at the base of the large antennse. It is a
bony chamber closed by a membrane, in the interior of
which is suspended a membranous sac filled with water. On
this sac, the auditory nerve is expanded. In the cuttlefish,
the vestibule is a simple excavation of the cartilage of the
head, containing a little membranous sac, in which the audi-
tory nerve terminates.

103. Finally, some insects, the grasshopper for instance,
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 beeii
sought for in the head only..

104. It appears from these examples, that the part of the
organ of hearing which is uniformly present in all animals
furnished with ears, is precisely that in which the auditory
nerve ends. This, therefore, is the essential part of the or-
gan. The other parts of the apparatus, the tympanum,
audit .iry passage, a- id even the semicircular canals, have for

60

SPECIAL SENSES.

their object merely to aid the perception of sound with more
precision and accuracy. Hence we may conclude that the
sense of hearing is dull in animals where the organ is re-
duced to its most simple form ; and that animals which have
merely a simple membranous sac, without tympanum an!
auditory passage, as the fishes, or without semicircular
canals, as the crabs, perceive sounds in but a very imper-
fect manner. J/

3. Of Smell

105. SMELL is the faculty of perceiving odors, and is

a highly important
sense to many ani-
mals. Like sight
and hearing, smell
depends upon special
nerves, the olfacto-
ry, (a,) which are
the first pair of cer-
p. 21 ebral nerves, and

which, in the em-
a, olfactory nerve; b, optic nerve; c, audi- i j-

, bivo, are direct pro-

tory nerve ; a, cerebrum ; e, cerebellum ;

/, nostril. longations of the

brain.

106. The organ of smell is the NOSE. Throughout the
series of vertebrates, it makes a part of the face, and in
man, by reason of its prominent form, it becomes one of tne
dominant traits of his countenance ; in other mammals, the
nose loses this prominency by degrees, and the nostrils no
longer open downwards, but forwards. In birds, the position
of the nostrils is a little different ; they open farther back
and higher, at the origin of the beak, (/.)

107. The nostrils are usually two in number. Some fishes
have four. They are similar openings, separated by a par-
tition upon the middle line of the body. In man and the

OF SMELL. 61

mammals, the outer walls of the nose are composed of carti-
lage ; but internally, the nostrils communicate with bony cav-
ities situated in the bones of the face and forehead. These
cavities are lined by a thick membrane, the pituitary mem
biuue, on which are expanded the nerves of smell, namely,
the olfactory nerves, and some filaments of the nerve which
goes to the face.

108. The process of smelling is as follows. Odors are
particles of extreme delicacy which escape from very many
bodies, and are diffused through the air. These particles
excite the nerves of smell, which transmit the impressions
made on them to the brain. To facilitate th'e perception of
odors, the nostrils are placed in the course of the respiratory
passages, so that all the odors which are diffused in the a;r
inspired, pass over the pituitary membrane.

109. The acuteness of the sense of smell depends on the
extent to which the membrane is developed. Man is not so
well endowed in this respect as many animals, which have
the internal surface of the nostrils extremely complicated, as
it is especially among the beasts of prey.

110. The sense of smell in Reptiles is less delicate than
in the mammals ; the pituitary membrane, also, is less de-
veloped. Fishes are probably still less favored in this
respect. As they perceive odors through the medium of
water, we should anticipate that the structure of their
apparatus would be different from that of animals which
breathe in the air. Their nostrils are mere superficial pouch-
es, lined with a membrane gathered into folds which gen-
erally radiate from a centre, but are sometimes arranged
in parallel ridges on each side of a central band. As 'he
perfection of smell depends on the amount of surface
exposed, it follows that those fishes which have these
folds most multiplied are also those in which fiis sense is
most acute.

6

62 SPECIAL SENSES.

111. No special apparatus for smell has yet been found in
Invertebrates. And yet there can be no doubt that insects,
crabs, and some moliusks perceive odors, since they are
attracted from a long distance by the odor of objects. Some
of these animals may be deceived by odors 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 plar ts
which have the smell of tainted flesh.

4. Of Taste.

112. TASTE is the sense by which the flavor of bodies is
perceived. That the flavor of a body may be perceived, it
must come into immediate contact with the nerves of taste ;
these nerves are distributed at the entrance to the digestive
tube, on the surface of the tongue 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 inti-
mate connection between the taste and the smell, so that
both these senses are called into requisition in the selection
of food.

113. 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 an
isolated part of the brain. The tongue, in particular, receives
nerves-from several trunks; and taste is perfect in proportion
as the nerves which go to the tongue are more minutely dis-
tributed. The extremities of the nerves generally terminate
in little asperities of the surface, called papilla. Sometimes
these papillae are very harsh, as in the cat and the ox ; and
again they are very delicate, as in the human tongue, in that
of the dog, horse, &c.

114. Birds have the tongue cartilaginous, sometimes be-
set with little stiff points; sometimes fibrous or fringed
at the edges. In the parrots, it is thick and fleshy

OF TOUCH. 63

or it is even barbed at its point, as in the woodpeckers.
In some reptiles, the crocodile for example, the tongue
is adherent ; in others, 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, generally adherent, and
its surface is frequently covered with teeth.

115. It is to be presumed, that in animals which have a
cartilaginous tongue, the taste must be very obtuse, especial-
ly 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 thcil
readily swallowing artificial bait. It is probable that they
are guided in the choice of their prey by sight, rathei
than by taste or smell.

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

*

5. Of Touch.

117. The cense of TOUCH is merely a peculiar manifesta-
tion of the general sensibility, seated in the skin, and
dependent upon the nerves of sensation, which expand over
the surface of the body. By the aid of this general sensi-
bility, we leavn whether a body is hot or cold, wet or dry.
We may also, by simple contact, gain an idea, to a certain

64 SPECIAL SENSES.

extent, of the form and consistence of a body, as, for exam*
pie, whether it be sharp or blunt, soft or hard.

118. 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 other fingers, is capable of so moulding
itself around objects, as to multiply the points of contact.
Hence, 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.

119. In some animals, this faculty is exercised by other
organs. Thus the trunk of the elephant is a most perfect
organ of touch ; and probably the mastodon, whose numer-
ous relics 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.

120. 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.

121. Animals employ their voice either for communica-
tion with each other, or to express their sensations, their en-
joyments, their sufferings. Nevertheless, this faculty « en
joyed Bby but a small minority of animals ; with but very
few exceptions, only the mammals, the birds, and a few
reptiles are endowed with it. All others are dumb.
Worms ard insects have no true voice ; for we must not

OF THE VOICE, 65

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, (grasshopper,) caused by the friction of
his legs against his wings ; nor the shrill noises of the cricket,
or the tell-tale call of the katydid, produced by the friction
of the wing covers upon each 'other, and in numerous similai
cases which might be cited.

122. Consequently, were the mammals, the birds, and the
frogs to be struck out of existence, the whole Animal King-
dom would be dumb. It is difficult for us, living in the midst
of the thousand various sounds which strike our 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 be-
fore man, the birds, and the mammals were called into being.

123. In man and the mammals, the voice is formed in an
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 Adam's

apple, is composed of several cartilaginous

pieces, called the thyroid cartilage, (&,) the ^^_?:^.

cricoid cartilage, (c,) and the small arytenoid

cartilages. Within these are found two large

folds of elastic substance, known by the name Fig. 22.

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, ana

of the interior of the glottis in man, is indicated by dotted

lines, in Fig. 22.

124. The mechanism of the voice is as follows : the air,
o- its way to the lungs, passes the vocal cords. So long as
these are in repose, no sound is produced ; but the mome it
they are made tense they narrow the aperture, and oppose

6*

66

OF THE VOICE.

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

125. Some mammals have, in addition, large cavities
which communicate with the glottis, and into which the air
reverberates, as it passes the larynx. This arrangement is
especially remarkable in the howling monkeys, which are dis-
tinguished above all other animals for their deafening howls.

126. 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 inferior
larynx, which is very complicated in structure. It is a kind

of bony drum, (a,) having with-
in it two glottides, formed at the
top of the two branches (bb) of
the windpipe, (c,) each provided
with two vocal cords. The dif-
ferent pieces of this apparatus
are moved by peculiar muscles,
the number of which varies in
different families. In birds which
have a very monotonous cry,
such as the gulls, the herons,
the cuckoos, and the mergansers

(Fig. 23,) there is but one or two pairs ; parrots have three

and the birds of song have five.

127. Man alone, of all the animal creation, has the power
of giving to the tones he utters a variety of definite or ar-
ticulate sounds ; in other words, he alone has the gift of
speech.

Fig. 23.

V

CHAPTER FOURTH.

OF INTELLIGENCE AND INSTINCT.

128. 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
phenomena of life. It originates with the body, and is de-
veloped 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 devel-
opment and rank of animals.

129. The constancy of species is a phenomenon depend-
ing 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 ; anJ no in-
spection would 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 essentially modify,
and determines the growth of the future being. The egg of
the hen, for instance, cannot be made to produce any other
animal than a chicken, and the egg of the codfish 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.

130. PERCEPTION is a faculty springing from this princi-
ple, The organs of sense are the instruments for receiving

68 INTELLIGENCE AND INSTINCT.

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 perrei»e
them not. We 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 perceives is directed to the object.

131. In addition to the faculty of perceiving sensations,
the higher animals have also the faculty of recalling past
impressions, or the power of memory. Many animals retain
a recollection of the pleasure or pain they have experi-
enced, and seek or avoid the objects which may have pro-
duced these sensations ; and, in doing so, they give proof
of judgment.

132. 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
reasoning.

133. -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
splendor. God u 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 ex-
ternal world; 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 conscious-
ness of his own nature, and even conceive of that Infinite
Spirit, " whom none by searching can find out."

INTELLIGENCE AND INSTINCT 69

134. 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 thei conduct is
frequently regulated by another principle of inferior order
still derived from the immaterial principle, called INSTINCT.

135. Under the guidance of Instinct, animals are enabled
to perform certain operations, without instruction, in one
undeviating manner. 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 be-
cause his associates have informed him, that these materials
are more suitable for the purpose. But the bee requires no
instructions in building her comb. She selects at once the
fittest materials, and employs them with the greatest econo-
my ; 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 appearances, without the consciousness of its
utility, being in some sense impelled to it by a blind impulse.

136. If, however, we judge of the instinctive acts of ani-
mals when compared with 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.

137. The instinctive actions of animals relate either to

70 INTELLIGENCE A! ID INSTINCT.

the procuring of food, or to the rearing of their young ; m
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.

138. 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, labors in view of the future ; and
she has become the emblem of order and domestic economy.

139. 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 made exceedingly comfortable. Others show very
great ingenuity in concealing their nests from the eyes of
their enemies, 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 sew together the leaves
of trees for its nest.

140. 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 tho
mullein leaf, is calculated equally for comfort and for es-
caping observation. An East Indian bird, (Ploceus Philippi-
uus,) mt only exhibits wonderful devices in the construction,

INTELLIGENCE AND INSTINCT. 71

security, and comfort of its nest, but displays a still furthel
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 com-
plete thatch. The entrance
is through a long tube, run-
ning downwards from the
edge of the nest ; and its
lower end is so loosely woven,
that any serpent or squirrel,
attempting to enter the aper-
ture, would detach the fibres,
and fall to the ground. The
mule, however, who has no
occasion for such protection,
builds his thatched dome, sim-
ilar to that of the female, and FiS- 24-
by its side ; but makes simply a perch across the base of
the dome, without the nest-pouch or tube.

141. But it is among insects that this instinctive solici-
tude for the welfare of the progeny is every where exhibited
in the most striking manner. 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 ap-
propriate for the nourishment of the future young.

142. It is by the dictate of instinct, also, that vast numbers
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.

143. Other animals live naturally in large societies, and
labor in common. This is the case with the ants and bees.
Among tin latter, even the kind of labor for each member
of the community is determined beforehand, by instinct.

72 INTELLIGENCE AND INSTItfflfN

Some of them collect only honey and wax ; while others
are charged with the care and education of the young ; and
still others are the natural chiefs of the colony.

144. Finally, there are certain animals so guided by their
instinct as to live like pirates, on the avails of others*
labor. The Lestris or Jager will not take the trouble to
catch fish for itself, but pursues the gulls, until, worn out
by tKe pursuit, they eject their prey from their crop. Some
ants make war upon others less powerful, take their young
away to their nests, and oblige them to labor in slavery.

145. There is a striking relation between the volume of'
ihe brain compared with the body, and the degree of intelli-
gence 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 ;ts brain bears a greater
resemblance to that of man.

146. The relation between instinct and the nervous
system 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 ver-
tebrates, since they have only ganglions, without a proper
brain. There is even a certain antagonism between instinct
and intelligence, so that instinct loses its force and peculiar
character, whenever intelligence becomes developed.

147. Instinct plays but a secondary part in man. He is
not, however, entirely devoid of it. Some of his actions are
entirely prompted by instinct, as, for instance, the attempts of
the infant 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.

148. THE power of voluntary motion is the second grand
characteristic of animals, (57.) Though they may not all
have the means of transporting themselves from place to
place, there-is no one 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 cell, and retires again at
its will.

149. The movements of animals are effected by means of
muscles, which are organs designed expressly for this pur-
pose, and which make up that portion of the body which
is commonly called flesh. They are composed of threads,
which are readily seen in boiled meat. These threads
are again composed of still more delicate fibres, called mus-
cular fibres, (45,) which have the property of elongating
and contracting.

150. The motions of animals and plants depend, therefore,
upon causes essentially different. The expansion and closing
of the leaves and blossoms of plants, which are their most

7

74 APPARATUS) OF MOTION.

obvious motions, are due to the influence , f ligl. , heal
moisture, cold, and similar external agents ; but all the mo
tions peculiar to animals are produced by a cause residing
within themselves, namely, the contractility of muscular
fibres.

151. The cause which excites contractility resides in the
nerves, although its nature is not precisely understood.

We only know that each
muscular bundle receives
one or more nerves, whose
filaments pass at intervals
across the muscular fibres,
as seen in Fig. 25. It has
also been shown, by experi-
ment, that when a nerve
Fig. 25.

entering a muscle is sev-
ered, the muscle instantly loses its power of contracting
under the stimulus of the will, or, in other words, is par-
alyzed.

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

153. In the great majority of animals, motion is greatiy
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 so as to act as levers, to in-
crease the precision and sometimes the force of movements.
The solid parts are usually so arranged as to form a sub-

APPARATUS OF MOTION. 75

stuntial framework for the body, which has heen varioi sly
designated in the several classes of animals, as the test, shell
carapace, skeleton, fyc. The study of these parts is one of the
most important branches of comparative anatomy. Their
characters are the most constant and enduring of all others.
Indeed, these solid parts are nearly all that remains of
tue numerous extinct races of animals of past geological
eras ; and from these alone are we to determine the struc-
ture and character of the ancient fauna.

154. Most of the Radiata have a calcareous test or crust)
shell. In the Polypi, this structure, when it exists, is usually
very solid, sometimes assuming the form of a simple inter-
nal skeleton, or forming extensively branched stems, as
in the sea-fans ; or giving rise to solid masses, furnished
with numerous cavities opening at the surface, from which
the movable parts of the animals are protruded, with the
power, however, of retracting themselves at pleasure, as in
the corals. In the Echinoderms, the test is intimately con-
nected with the structure of the soft

parts. It is composed of numer-
ous little plates, sometimes con-
solidated and immovable, as in
the sea-urchins, (Fig. 26,) and
sometimes so combined, as to
allcw of various motions, as in
the star-fishes, (Fig. 17,) which use their projecting rays,
both for crawling and swimming.

155. In the Mollusks, 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 parts which they cover. These shells are geneially so
constructed as to afford complete protection to the animal
within their cavities. In a few, the shell is too small for this
purpose ; and in some it exists only at a very early period.

76 APPARATUS OF MOTION.

and is lost as the animal is developed, so that at last nere is
no other covering than a slimy skin. In others, the skin
becomes so thv^k 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. As a general thing,
the solid parts do not aid in locomotion, so that the mol-
lusks are mostly sluggish animals. It is only in a few rare
cases that the shell becomes a true lever, as in the Scollops,
(Pecten,) which use their shells to propel themselves in
swimming.

156. The muscles of mollusks either form a flat disk un-
der the body, or large bundles across its mass, or are dis-
tributed 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 the disposition may be, they
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 other animals.
This peculiar aspect no doubt arises from the numerous
small cavities extending between the muscles, and the secre-
tion of mucus which takes place in them.

157. In the Articulated animals, the solid parts are ex-
ternal, 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 structure. The rings differ in the severa
classes of this department, merely as to volume, form, solid-
ity, 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 we see in the
crabs. In others, they are membranous, and the body is
capable of assuming various forms, as in the leeches and
worms generally

APPARATUS OF MOTION.

77

158. A variety of appendages are attached to these
rings, such as jointed legs, or in place of them stiff bristles
oars fringed with silken threads, wings either firm or mem
branous, antennae, movable pieces which perform the office
of jaws, &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, com-,
bine to form but a single internal cavity, in which all the or-
gans are enclosed, the nervous system, as well as the organs
of vegetative life, (63.)

159. The muscles which move
all these parts have this peculiar-
ity, that they are all enclosed with-
in the more solid framework, and
not external to it, as in the verte-
brates ; and also that the muscular
bundles, which are very consider-
able in number, have the form of
ribbons, or fleshy strips, with par-
allel fibres of remarkable white-
ness. Figure 27 represents the

Fig. 27.

disposition of the muscles of the caterpillar which destroys
the willow, (Cossus ligniperda.) The right side represents
the superficial layer of muscles, and the left side the deep-
seated layer.

160. The Vertebrata, like the articulated animals, have
solid parts at the surface, as the hairs and horns of mam-
mais, the coat of mail of the armadillo, the feathers and claws
of birds, the bucklers and scales of reptiles and fishes, &c.
Hut they have besides this, along the interior of the whole
body, a solid framework not found in the invertebrates, well
known as the SKELETON.

161. T.he skeleton is composed of a series of separate
bpnes called vertebras, united to each other by ligaments.

7*

78

APPARATUS OF MOTION.

Each vertebra has a solid centre with four 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 (a) along
the region of the trunk, which encloses
the spinal marrow, and in the head re-
ceives the brain, (frh) The lower arches
(b) form another >cavity, similar to the
superior one, which contains the organs of
nutrition and reproduction ; their branch-
es generally meet below, and when dis-
joined, the deficiency is supplied by
fleshy walls. Every part of the skeleton
may be reduced to this fundamental typt
the vertebra, as will be shown, when treating specially of the
vertebrate animals ; 'so that between the pieces composing
the head, the trunk, or the tail, we have only differences
in the degree of development of the body of the ver-
tebra, or of its branches, and not in reality different plans
of organization.

162. The muscles which move this solid framework of
the vertebrata are disposed around the vertebra?, as is

Fig. 28.

Fig. 29.

woll exemplified among the fishes, where there is a band
of muscles for each vertebra. In proportion as limbs

LOCOMOTION.

79

are developed, this intimate relation between the muscles
and the vertebrae diminish-
es. The muscles are un-
equally distributed and are
concentrated about the
limbs, where the greatest
amount of muscular force
is retired. For this rea-
son, the largest masses of
flesh in the higher verte-
brates are found about the
shoulders and hips ; while
in fishes they are concen-
trated about the base of the Fig. 30.
tail, which is the part principally employed in locomotion.

SECTION II.

OF LOCOMOTION.

163. One of the most curious and important applic it ions
of this apparatus of bones and muscles is for LOCOMO-
TION. By this is understood the movement which an animal
makes in passing from place to place, in the pursuit of pleas-
ure, sustenance, or safety, m distinction from those motions
which are performed equally well while stationary, such as
the acts of respiration, mastication, &c.

164. 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

80 LOCOMOTION.

equally concerned in effecting locomotion, or only some of

its parts are employed for the purpose.

165. The jelly-fishes (Medusae) swim
by contracting their umbrella-shaped
bodies upon the water below, and its
resistance urges them forwards. Other
animals are provided with a sac or
siphon, which they may fill with water
and suddenly force out, producing a jet,
which is resisted by the surrounding
water, and the animal is thus propelled.

The Biche-le-mar, (Holothuria,) the cuttle-fishes, the Salpae,

&c., move in this way.

166. Others contract small portions of the 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 boJy
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.

167. Some have, at the extremities of the body, a cup or
some other organ for maintaining a firm hold, each extremity
acting in turn as a fixed point. Thus the Leech has a cup
or sucker at its tail, by which it fixes itself; the body is then

elongated by the contraction
of the muscular fibres which
encircle the animal ; the mouth
is next fixed by a similar suck-
Fig. 32. er and by the contraction of
muscles running lengthwise the body is shortened, and the
tail, losing its hold, is brought forwards to repeat the same
nrocess. Most of the bivalve mollusks, such as the clams.

LOCOMOTION. 81

move from place to place, in a similar way. A fleshy organ,
called the foot, is thrust forward, and its extremity fixed
in tha mud, or to some firm object, when it contracts,
and thus draws along the body and the shell enclosing
it. Snails, and many similar animals, have the fleshy under
surface of their body composed of an infinitude of very short
muscles, which, by successive contractions, so minute, indeed,
as scarcely to be detected, enable them to glide along
smoothly and silently, without any apparent muscular effort.

168. In the majority of animals, however, locomotion is
effected by means of organs specially designed for the pur-
pose. The most simple are the minute, hair-like cilia,
which fringe the body of most of the microscopic infu-
sory animalcules, and which, by their incessant vibrations,
cause rapid movements. The sea-urchins and star-fishes
have little thread-like tubes issuing from every side of the
body, furnished 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,
and usually wings also. 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 fringe-like gills for paddles. (Fig. 33.)

169. Among the Vertebrata, we find the greatest diversity
in the organs of locomotion and the modes of their applica-
tion, as well as the greatest perfection, in whatever element

82 ORGANS OF LOCOMOTION.

they may be employed. The sailing of the eagle, the hound-
ing of the antelope, the swimming of the shark, are riot
equalled by any movements of insects, This superiority is
due to the internal skeleton, which, while it admits a great
display of force, gives to the motions, at the same time, a
great degree of precision.

1. Plan of the Organs of Locomotion.

170. The organs of progression in vertebrated animals
nt'ver exceed four in number, and to them the term limbs is
more particularly applied. The study of these organs, a3
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 ob-
serve the modifications, oftentimes very slight, by which a
very simple organ is adapted to every variety of move-
ment. No part of the animal structure more fully illustrates
the unity of design, or the skill of the Intellect which has
so adapted a single organ to such multiplied ends. On this
account, we shall illustrate this subject somewhat in detail.

171. It is easy to see that the wing which is to sustain
the bird in the air must be different from the leg of the stag,
which is to serve for running, or the fins of the fish that
swims. But, notwithstanding their dissimilarity, 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. In order to show this, it is necessary to give a short de-
scription of the composition of the arm or anterior extremity.

172. The anterior member, in the vertebrates, is invaria-
b*y composed of the following bones: 1. The shoulder-
blade, or scapula, (a,) a broad and flat bone, applied upon
the b )nes of the trunk • 2. The arm, (Z»,) formed of a single

OHGANS OF LOCOMOTION.

S3

-a

long cylindrical bone, the humerus ; 3. The fore-arm com-
posed of two long bones, the radius, (c,) and ulna, (d,)
which are often fused into one ; 4. The hand, which :.s
composed of a series of bones, more
or less numerous in different classes,
and which is divided into three parts,
namely, the carpus, or wrist, (e,) the
metacarpus, or palm, (/,) and the pha-
langes, or fingers, (g.) The clavicle or
collar-bone, (o,) when it exists, belongs
also to the anterior member. It is a
bone of a cylindrical form, fixed as
a brace between the breast-hone and
shou.der-blade. Its use is to Veep the
shoulders separated ; to this end, we
find it fully developed in all animals
which raise the limbs from the sides, as
the birds and the bats. On the other
hano, it is rudimentary, or entirely want-
ing in animals which move them back-
wards and forwards only, as with most
auadrupeds.

,173. The following outlines, in which corresponding bones
are indicated by the same letters, will give an idea of the
modifications which these bones present in different classes.
In the arm of man, (Fig. 34,) the shoulder-blade is fiat
and triangular ; the bone of the arm is cylindrical, and en-
larged at its extremities ; the bones of the fore-arm are
somewhat shorter than the humerus, but more slender ; the
hand is composed of the following pieces, namely, eight
small hones of the carpus, arranged in two rows, five meta-
carpal bones, which are elongated, and succeed those of the
wrist; five fingers of unequal length, one of which, the
thumb is opposed to the four others.

Fig. 34.

84

ORGANS OF LOCOMOTION.

174. In the stag, (Fig. 35,) the bones of the fore-arm
are rather longer than that of the arm, and the radius no
longer turns upon the ulna, but is blended with it; the meta-
rurpal, or cannon bone, is greatly developed ; 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.

175. In the arm of the lion, (Fig. 36,) the arm bone is

Fig. 36.

stouter, the carpal bones are less numerous, and the fingers
are short, and armed with strong, retractile claws. In the
whale, (Fig. 37,) the bones of the arm and fore-arm <are
much shortened, and very massive ; the hand is broad, the
fingers strong, and distant from each other.

Fig. 38. S- •

In the bat, the thumb, which is represented by a small
hook, is entirely free, (Fig. 38 ;) but the fingers are elon-
gated in a disproportionate manner, and the skin is stretched

ORGANS OF LOCOMOTION.

85

across them, so as to serve the purpose of a wing. In birds
the pigeon for example, (Fig. 39,) there are but two fingers
which are soldered together, and destitute of nails ; and the
thumb is rudimentary.

176. The arm of the turtle (Fig. 40) is peculiar in having,

Fig. 42.

besides the shoulder-blade, two clavicles ; the arm-bone is
twisted outwards, as well as the bones of the fore-arm, so
that the elbow, instead of being behind, is turned forwa~ds;
the fingers are long, and widely separated. In the Sloth,
(Fig. 41,) the bones of the arm and fore-arm are very greavly
elongated, and at the same time very slender ; the hand is
likewise very long, and the fingers are terminated by enoi-
mous non-retractile nails. The arm of the Mole (Fig. 42)
is still more extraordinary. The shoulder-blade, which is
usually a broad and flat bone, becomes very narrow ; the
arm-bone, on the contrary, is contracted so much as to seem
nearly square ; the elbow projects backwards, and^the hand
is excessively large and stout. <^/r

177. In fishes, the form and arrangement of Hke bonos is
so peculiar, that it is often difficult to trace their correspond-
ence to all the parts found in other animals ; nevertheless
the bones of the fore-arm are readily recognized. In the Cod
8

86 ORGANS OF LOCOMOTION.

(F g. 43N tlipro are two flat and broad bones, one of which,
the ulna, (rf,) presents a long point, anteriorly. The bones of

c

the carpus are represented by four nearly square little bones.
But in these again there are considerable variations in dif-
ferent fishes, and in some genera they are much more irreg-
ular in form. The fingers are but imperfectly represented
by the rays of the fin, (g,) which are composed of an infini-
tude of minute bones, articulated with each other. As to
the humerus and shoulder, their analogies are variously in-
terpreted by different anatomists.

178. The form of the members is so admirably adapted to
the special offices which they are designed to perform, that
by a single inspection of the bones of the arm, as repre-
sented 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 its ulna, the delicate and pliable fingers,
and the thumb opposed 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 incon-
venient for walking on the ground, but appropriate for seizing
upon the branches of the trees, on which these animals live.
The short fingers, armed with retractile nails, indicate the
lion, at first glance, to be a carnivorous animal. The arm
of the stag, with his very long cannon-bone, and that of the
horse, also, with its solitary finger, enveloped in a hoof, are
organs especially adapted for running. The very slondcr
and greatly elongated fingers of the bat are admirably COD

ORGANS OF LOCOMOTION. 87

trived for the spread of a wing, without in Creasing the
weight of the body. The more 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 the mass of the flesh, presents,
externally, a mere delicate balancer, the pectoral fin.

179. The posterior members are identical in their structure
with the anterior ones. The bones of which they are
composed, are, 1. The pelvis, (Fig. 46,) which corresponds
to the shoulder blade ; 2. The thigh bone, or femur, which
is a single bone, like the humerus ; 3. The bones of the leg,
the tibia andjibula, which, like the radius and ulna, some-
times coalesce into one bone ; and lastly, the bones of the
foot, which are divided, like those of the hand, into three
parts, the tarsus or ankle, the metatarsus or Instep, and the
toes. The modifications are generally les? marked than in
the arm, inasmuch as there is less diversity of funttion ; for
in all animals, without exception, the posterior extremities
are used exclusively for support or locomotion.

180. The anterior extremity of the vejftebraies, however
varied in form, whether it be an

arm, a wing, or a fin, is thus
shown to be composed of essen-
tially the same parts, and con-
structed upon the same general
plan. This affinity does not ex-
tend to the invertebrates ; for al-
though in many instances their Fig. 44. Fig. 45.
limbs bear a certain resemblance to those of the vertebrates,
and are even used for similar purposes, yet they have no real

88 OF STANDING AND PROGRESSION.

affinity. Thus the leg of an insect, (Fig. 44,) and tha
of a lizard, (Fig. 45 ;) the wing of a butterfly and the
wing of a bat; are quite similar in form, position, and use,
but in the bat and the lizard, the organ has an internal bony
support, which is a part of the skeleton ; while the leg of
the insect has merely a homy 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, (157.) It
is by ascertaining and regarding these real affinities, or
the fundamental differences, existing between similar organs,
that the true natural grouping of animals is to be attained.

2. Of Standing, and the Modes of Progression.

181. 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 poste-
rior 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 horizontal. Man alone is designed to stand upright,
with his head supported on the summit of the vertebral col-
umn. Some monkeys can rise upon the hind legs into the
erect posture ; but it is evidently a constrained one, and not
their habitual attitude.

182. That an animal may stand, it is requisite that the
limbs should be so disposed that the centre of gravity, in
o'ther words, the point about which the body balances itself,
should fall within the space included by the feet. If the
centre of gravity is outside of these limits, the animal falls
to he side to which the centre of gravity inclines. On
thifa account, the albatross, and some other aquatic birds

OF STANDING. 89

which have the feet placed very far back, cannot use them
for walking.

183. The more numerous and the more widely separated
are the points of support, 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 the\ should have a broad base. Thus we see that
mos: quadrupeds have slender legs, touching the earth by
only a small surface. 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.
Moreover, the muscles of the toes are so disposed that the
weight of the bird causes them to grasp firmly ; hence it
is enabled to sleep standing in perfect security upon the roost,
without effort.

Fig. 46.

184. In quadrupeds, the joints at the junction of the limbs
with the body bend freely in only one direction, 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 antag-
onism 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 ; whi'e the arm bends
8*

90 MODES OF PROGRESSION.

backwards, and the fore-arm forwards. Different terms have
been employed to express the various modes of progression,
aecoid'ng to the rapidity or the succession in which the
limbs are advanced.

185. 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 while one leg sustains the body, the other is thrown
forwards to prevent it from falling, and to sustain it in turn.
For this reason, walking has been defined to be a continual
falling forwards, continually interrupted by the projection of
the legs.

186. The throwing forwards of the leg, which would
require 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 suffi-
cient of itself to maintain the limbs in place, without the as-
sistance of the muscles. This may be proved by experi-
ment. If we cut away all the muscles around the hip joint, the
thigh bone still adheres firmly to the pelvis, but separates the
moment a hole is pierced, so as to admit air into the socket.

187. In ordinary walking, the advancing leg touches the
ground just before the other is raised ; 30 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, but with this difference, that the body always
rests on at least two legs. The limbs are raised in a deter-
minate order, usually in such a manner that the hind-leg of
one side succeeds th fore-leg of the opposite side. Some

MODES OF PROGRESSION. 91

animals, as the giraffe, the lama, and the bear, raise both
legs of one side at the same moment. This is called am-
bling, or pacing.

188. RUNNING consists in the same succession of motions
as walking, so accelerated that there is a moment be-
tween 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 to say, 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-limbs are raised to-
gether as well as the hind-legs ; it is then termed a gallop.

189. 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 again at a certain distance in
advance. 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 all leaping animals have the posterior members
very much more robust than the anterior, as the frog, the
kangaroo, jerboa, and even the hare. Leaping is also com-
mon among certain birds, especially among the sparrows,
the thrushes, &c. Finally, there is also a large number of
leaping insects, sush as the flea, the large tribe of grass*
hoppers and crickets, in which we find that pair of legs
with which leaping is accomplished much more developed
than the others.

92 MODES OF PROGRESSION.

190. CLIMBING is merely walking upon an inclined or
even upright surface. It is usually accomplished by means of
sharp nails ; and hence many carnivorous animals climb
with great facility, such as the cat tribe, the lizards ; and
many birds, the woodpecker, for instance. Others employ
their arms for this purpose, like the bears when they clirnb
a tree ; or their hands, and even their tails, like the mon-
keys ; 'or their beaks, like the parrots. Lastly, there are some
whose natural mode of progression is climbing. Such are
the sloths, with their arms so long, that, when placed upon
the ground, they move very awkwardly ; and yet their struc
ture is by no means defective, for in their accustomed move
ments upon trees they can use their limbs with very great
adroitness.

191. 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 PodurellaB. Still 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.)

192. FLIGHT 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 support, for the
mcment, upon which the bird is sustained. But as this
support very soon yields, owing to the slight density of the
air, it follows that the bird must make the greater and more

MODES OF PROGRESSION. 93

raf id efforts to compensate for this disadvantage. Kence 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. 30.) To facili-
tate its prDgress, the bird, after each flap of the wings, brings
them against the body, so as to present as little surface as
possible to the air ; for a still further diminution of resistance,
all birds have the anterior part of the body very slender,
Their flight would be much more difficult if they had large
heads and short necks.

193. Some quadrupeds, such as the flying-squirrel and
Galeopithecus, have a fold of the skin at the sides, which
may be extended by the legs, and which enables them to
leap from branch to branch with more security. But this
is not flight, properly speaking, since none of the peculiar
operations of flight are performed. There are also some
fishes, whose pectoral fins are so extended as to enable them
to dart from the water, and sustain themselves for a consider-
able time in the air ; and hence they are called flying-fish.
But this is not truly flight.

194. SWIMMING is the mode of locomotion employed by
the greater part of the aquatic animals. Most animals which
live in the water swim with more or less facility. Swimming
has this in common with flight, that the medium in which it
is performed, the water, becomes also the support, and read
ily yields also to the impulse of the fins. Only, as water is
much more dense than air, and as the body of most aquatic
animals is of very nearly the same specific gravity as water,
it follows that, in swimming, very little effort is requisite to
keep the body from sinking. The whole power of the mus-
cles is consequently employed in progression, and hence
swimming requires vastly less muscular force than flying.

195. Swimming is accomplished by means of various or-
gans designated under the general term, fins, although in an

94 MODES OF PROGRESSION.

anatomical poiri: of view these may represent very different
parts. In the Whales, the anterior extremities ar. i the tail
are transformed into fins. In Fishes, the pectoral fins, which
represent the arms, and the ventral fins, which represent the
legs, are employed for swimming, but they are not the prin-
cipal organs ; for it is by the tail, or caudal fin, that pro-
gression is principally effected. Hence the progression of
the fish is precisely that of a. boat under the sole guidance
of the sculling-oar. In the same manner as a succes-
sion of strokes alternately right and left propels the boat
straight forwards, so the fish advances by striking alternately
right and left. To advance obliquely, it has only to strike
a little more strongly in the direction opposite to that which
he wishes to take. The Whales, on the contrary, swim by
striking the water up and down ; and it is the same with a
few fishes also, such as the rays and the soles. The air-
bladder facilitates the rising and sinking of the fish, by ena-
bling it to vary the specific weight of the body.

196. 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 thtr beaver, or which
feed on marine animals, as the otter and duck, have webbed
feet ; that is to say, the fingers are united by a membrane
which, when expanded, acts as a paddle.

197. There is also a large number of invertebrate animals
in which swimming is the principal or the only mode of
progression. Lobsters swim by means of their tail, and, like
the Whales, strike the water up and down. Other Crustacea
have a pair of legs fashioned like oars ; as the posterior legs
in sea-crabs, for example.. Many insects likewise, swim
wilh their legs, which are abundantly fringed with hairs to
give them surface ; as the little water boatmen, (Gyrinus,
Dytiscus,) whose mazy dances on the summer streams every
one must have observed. The cuttle-fish uses its long ten-

MODES OF PROGRESSION. 95

tacles as oars, (Fig. 47 ;) and some star-fishes (Comatula,
Euryale) use their arms with great adroitness, (Fig. 151.)
Finally, there are some insects which have their limbs con-
structed for running on the surface of water, as the water-
srulers, (Ranatra, Hydrometra.)

Fig. 47.

198. A large number of animals have the faculty of mov
ing both in the air and on land, as is the case with most birds,
and a great proportion of insects. Others move with equal
facility, and by the same members, on land and in water, as
some of the aquatic birds and most of the reptiles, which latter
have even received the name Amphibia, on this account.
There are some which both walk, fly, and swim, as the ducks
and water-hens ; but they do not excel in either mode of
progression.

199. However different the movements and offices pei-
formed by the limbs may appear to us, according to the ele-
ment in which they act, we see that they are none the less
ihs effect of the same mechanism. The contraction of the
same set of muscles causes the leg of the stag to bend for
laaping, the wing of the bird to flap in the air, the arm of
the mole to excavat1 the earth, and the fin of the whale to
strike the water. ,

CHAPTER SIXTH.

NUTKITION.

200. THE second class of the functions of animals are
those which relate to the maintenance of life and the per-
petuation of the species ; the functions of vegetative life, (59.)

201. The increase of the volume of the body must re
quire additional materials. There is also an incessant waste
of particles which, having become unfit for further use, are
carried out of the system. Every contraction of a muscle
exp&ftds the energy of some particles, whose place must be
supplied. These supplies are derived from every natural
source, the animal, vegetabte, and even the mineral king-
doms ; 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 appropriation of it to the
growth and sustenance of the body, is called NUTRITION in
the widest sense of that term.

202. In early life, during the period of growth, the amount
of substances appropriated is greater than that which is lost
At a later period, when growth is completed, an equilibrium
between 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.

203. The solids and fluids taken into the body as food are

OF DIGESTION. 9*7

subjected to a process called Digestion, by which the sclid
portions are reduced to a fluid state also, the nutritive sepa
rated 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
require 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 breathe, by a process called 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 reno-
vated or expelled. This circuit is what is termed the Circu-
lation. The function of Nutrition, therefore, combines sev-
eral distinct processes.

SECTION I.

OF DIGESTION.

'204. Digestion, or the process by which the nutritive parts
of food are elaborated and pre-
pared to become part of the body,
is effected in certain cavities, the
stomach and intestines, or alimen-
tary canal. This canal is more or
less complicated in the various
classes of animals ; but there is no
animal, however low its organiza-
tion, without it, in some form, (54.)

205. In the polypi, the digestive
apparatus is limited to a single
cavity. In the Sea Anemone, ( Ac-
tinia,) for example, it is a pouch, (Fig 48, b) suspended in
9

Fig. 48.

98

NUTRITION.

Fig. 49.

the interior of the body. When the fooc has been s jffi /lently
digested there, it passes, by imbibition, into the general cav-
ity of the body, (c,) which is filled with water, and mingling
with it, flows thence into all parts of the an-
imal. The jelly-fishes, (Medusse,) and
some Worms, have a distinct stomach, with
appendages branching off in every directior ,
(Fig. 31,) in which a more complete elabo-
ration takes place. The little worms known
by the name of Planaria, present a striking
example of these ramifications of the intes-
tine, (Fig. 49, e.) But here, likewise, the
product of digestion mingles with the fluids
of the cavity of the body which surround
the intestine (d) and its branches, and cir-
culation is not yet distinct from diges-
tion.

206. As we rise in the scale of animals, the functions
concerned in nutrition become more and more distinct from
each other. Digestion and circulation, no longer confounded,
are accomplished separately, in distinct cavities. The most
important organs concerned in di-
gestion are the stomach, and the
small and large intestine. The
first indications of such a distinc-
tion are perceived in the higher
Radiata," such as the sea-urchins,
(Fig. 50,) in which the stomach (s)
is broader than either extremity of
the intestine. The dimensions and
Fig- 50. form of the cavities of the intestine

very considerably, according to the mode of life of the ani-
mal; but the special functions assigned to them are invaria-
ble ; aria the three principal cavities succeed each other, in

OF DIGESTION.

99

every.. animal where they are found, in an i:. variable order:
first, the stomach, (s,) then the intestine, which is small al
first, but often enlarged
towards its termination.
This arrangement may
be seen by the follow-
ing diagrams from a bee-
tle and a land mollusk,
where the same letters
indicate corresponding
parts, (Figs. 51, 52.)

207. From the mouth,
(m,) the food passes into
the stomach through a
narrow tube in the neck,
called the oesophagus -or
gullet, (o.) This is not FiS-61- Fis-52-

always a direct passage of uniform size ; but there is some-
times a pouch, the crop, (c,) into which the food is first intro-
duced, and which sometimes acquires considerable dimen-
sions, especially in birds, and in some insects and mollusks.
(Fig. 51.) In the stomach, the true digestive process is be-
gun. The food no sooner arrives there than changes com
mence, under the influence of a peculiar fluid called the gas-
trie juice, which is secreted by glands lining the interior of
the stomach. The digestive action is sometimes aided by the
movements of the stomach itself, which, by its strong contrac-
tions, triturates the food. This is especially the case in the
gizzard of some birds, which, in the hens and ducks, for in-
stance, is a powerful muscular organ. In some of the Crus-
tacea and Mollusks, as the Lobster and Aplysia, there are
even solid organs for breaking down the food within the
stomach itself.

208 The result of this process is the reduction of the food

100 NUTRITION.

.o a pulpy fluid called chyme, which varies in its> nature with
ths food. Hen.ce the function of the stomach has been
named chymification. With this, the function of digestion is
complete in many of the lower animals, and chyme is circu-
lated throughout the body ; this is the case in Polypi and Jelly-
fishes, and some Worms and Mollusks. In other animals,
however, the chyme thus formed is transferred to the intes-
tine, by a peculiar movement, like that of a worm in creep-
ing, which has accordingly received the name of vermicular
or peristaltic motion.

209. The form of the small intestine (i) is less variable
than that of the stomach. It is a narrow tube, with thin walls,
coiled in various directions in the vertebrate animals, but
more simple in the invertebrates, especially the insects. 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 res cut of this elaboration is to produce a complete sepa
ration of the truly nutritious parts, in the form of a milky
^quid called chyle. The process is called chylification ; and
there are great numbers of animals, such as the Insects,
Crabs, and Lobsters, some Worms, and most of the Mollusks,
in which the product of digestion is not further modified by
respiration, but circulates throughout the body as chyle.

210. The chyle is composed of minute, colorless globules

of a somewhat flattened form, (Fig. 53.) In
the higher animals, the Vertebrates, it is taken
up and carried into the blood by means of very
minute vessels, called lymphatic . vessels or
lacteals, which are distributed every where in
the walls of the intestine, and communicate

OF DIGESTION. 101

with the veins, forming also in their course several glandular

masses, as seen in a portion of intestine connected with a vein

in Fig. 54 • 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. Flg' 54<

211. The organs above described constitute the most es
sential for the process of digestion, and are found more or less
developed in all 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
the mouth of those animals that feed on solid substances, which
serve for cutting or bruising the food into small fragments
before it is swallowed ; and, in many of the lower animals,
these organs are the only hard portions of the body. Thia
process of subdividing or chewing the food is termed masti>
cation.

212. Beginning with the Radiata, we find the apparatus
for mastication partaking of the star-like arrangment which
characterizes those animals. Thus in Scutella, (Fig. 55,)
we have a pentagon composed of five triangular jaws, con-
verging at their summits towards a central aperture \\hich
corresponds to the mouth, each one bearing a cutting 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 ob-
jects which come between them. In some of the sea-urchins

9*

102 NUTRITION.

(Echinus,) this apparatus, which has been called Aristotle's

Fig. 55.

Fig. 56.

lantern, (Fig.t56,) consists of 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 Scutella ; only instead oT being placed horizontally,
they form an inverted pyramid.

213. Among the Mollusks, a few, like the cuttle-fishes,
have solid jaws or beaks closely resembling
the beak of a parrot, (Fig.
57,) which move up and
down as in birds. But a
much larger number rasp
their food by means of a flat
Fig. 57. blade coiled up like a watch- Fig. 58.

spring, the surface of which is covered with innumerable
minute tooth-like points of a horny consistence, as seen in a
highly magnified portion -of the so-called tongue of Natica,
(Fig. 58, a,) which, however, is only a modification of the
beaks of cuttle-fishes.

214. The Articulata are remarkable, as
a class, for the diversity and complication
of their a^ paratus for taking and dividing
their food. In some marine worms, Nereis
for exarr pie, the jaws consist of a pair of
Fig. 59. curved, horny instruments, lodged in ~8

sheath, (Fig. 59 ) In spiders, these jaws are external, and

OF DIGESTION.

103

sometimes mounted on long, joined stems. Insects which
masticate their food have, for the most part, at least two pairs
of horny jaws, (Figs. 60, 61, m,j?) besides several. additional
pieces which serve for seizing and holding their food.
Those which live on the fluids which they extract either from
plants or from other animals, have the masticatory organs
transformed into a trunk or tube for that purpose. This
trunk is sometimes rolled up in a spiral manner, as in the
butterfly, (Fig. 64;) or it is stiff", and folded beneath the

t-

Fig. 60. Fig. 61. Fig. 62. Fig. 63. Fig. 64.

chest, as in the squash-bugs, (Fig. 62,) containing several
piercers of extreme delicacy, (Fig. 63,) adapted to penetrate
the skin of animals or other objects whose juices they extract ;
or they are prolonged so as to shield the tongue when thrust
out in search of food, as in the bees, (Fig. 61, t.) The crabs
have their anterior feet transformed into a kind of jaws, and
several other pairs of articulated appendages performing ex-

Fig. 65. Fig. 66.

cljsively masticatory functions. Even in the microscopic
Rotifers, we find very complicated jaws, as seen in a Brachi
onus, (Fig. 65,) and 'still more magnified in Fig. 66. But

104

NUTRITION.

amidst this diversity of ^paratus, there is one thing ,\ nich
characterizes all the Articulata, namelv, the jaws always
move sideways ; while those of the Vertebrates and Mollusks
move up and down, and those of the Radiata concentrically.

21 5. In the Vertebrates, the jaws form a part of the bony

skeleton. In most of them the
lower jaw only is movable, and
is brought up against the upper
jaw by means of very strong mus-
cles, the temporal and masseter
Fig. 67. muscles, (Fig. 67, t, m,) which

perform the principal motions requisite for seizing and mas-
ticating food.

216. The jaws are usually armed with solid cutting

instruments, the TEETH, or else are
enveloped in a horny covering, the
beak, as in the birds and tortoises,
(Fig. 68.) In some of the whales,
the true teeth remain concealed in the
jaw-bone, and we have instead a range
of long, flexible, horny plates or fans, fringed at the margin,
which serve as strainers to separate the minute marine ani-
mals on which they feed
from the water drawn in
with. them, (Fig, 69.)
A few are entirely des-
titute of teeth, as the
ant-eater, (Fig. 70.)

217. Though all the
vertebrates possess jaws.

Fig. 69. it must not be in/erred

that they all chew their food. Many swallow their prey
whole ; as most birds, tortoises, and whales. Even many of
chose which are furnished with teeth do not masticate their

Fig. 68.

Of DIGESTION.

105

food, some using them merely for seizing 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 the alligator, (Fig. 71,)
Ihe porpoises, and many fishes. A few of the latter, some of

Fig. 71. Fig. 72.

the Rays, for example, have a sort of bony pavement, (Fig.
72,) composed of a peculiar kind of teeth, with which they
crush the shells of the mollusks and crabs on which they
feed.

218. The Mammals, however, are almost the only verte
brates which can properly be said to masticate their food
Their teeth are well
developed, and pre-
sent great diversity
in form, arrangement
and iflode of inser-
tion. Three kinds
of teeth are usually
distinguished in most
of these animals,
whatever may be . Fig. 73.

their mode of life; nar'ely, the cutting teeth, incisors; the

a

106 NUTRITION.

tusks or carnivorous teeth, canines ; and the grinders, molars
(Fig. 73.) The incisdrs (a) occupy the front of the mouth,
the upper ones being set in the intermaxillary bones ; they
are the most simple and the least varied, have generally
a thin cutting summit, and are employed almost exclusively
for seizing food, except in the elephant, in which they assume
the form of large tusks. The canines (b) are comcal, mc:e
elongated 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 carnivora 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 mastica-
tion ; as in the baljyroussa, &c. The molars (c) are the most
important 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, to those with
broad and level summits, as in the ruminants and rodents.
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.

219. The harmony of organs already spoken of (22-24)
is illustrated, in a most striking manner, by the study of the
teeth of the mammals, aH especially of their molar teeth.
So constantly do they correspond with the structure of the
other parts of the body, that a single molar is sufficient not
only to indicate the mode of life of the animal to which i
belongs and show whether it feeds on flesh or vegetables, or
bo' i, bit also to determine the particular group to which it is
related. Thus, those beasts of prey which feed on insects,
and which on that account have been called Insectivora, such

OF DIGESTION. 107

*

as the moles and bats, have the molars terminated by several

Fig. 76. Fig. 75.

sharp, conical points, (Fig. 74,) so arranged that the eleva-
tions of one tooth fit exactly into the depressions of the tooth
opposite to it. In the true Carnivora, (Fig. 75,) on the con-
trary, the molars are compressed laterally, so as to have
sharp, cutting edges, as in the bats ; and they- shut by the
side of each other, like the blades of scissors, thereby di
viding the food with great facility.

220. 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,) like the
elephant, and some of the gnawers, (rodentia,) like the hare,
(Fig. 76,) 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 subsist. Finally, the omnivora,
those which feed on both flesh and fruit, like man and the
monkeys, have the molars terminating in several rounded
tubercles, being thus adapted to the mixed nature of their
food.

221. Again, the mode in which the molars are combined
with the canines and incisors furnishes excellent means of

"characterizing families and genera. Even the internal struc-
ture of the teeth is so peculiar in each group of animals, and
yet subject to such invariable rules, that it is possible to
determine with precision the general structure of an animal

108 NUTRITION.

merely by investigating the fragment of a tooth under a mi
croscope.

222. Another process, subsidiary to digestion, is called
tnsalivation. Animals which masticate their food ha\e
glands, in the neighborhood of the mouth, which secrete 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 mastication. After it has been masticated and min-
gled with saliva, it is moved backwards by the tongue, and
passes down through the oesophagus, into the stomach. This
act is called deglutition or swallowing.

223. The wisdom and skill of the Creator is strikingly
illustrated in. the means he has afforded to every creature for
securing the means for subsistence. Some animals ha\e
no ability to move from place to place, but are fixed to the
soil ; as the oyster, the polyp, &c. These are dependent for
subsistence upon such food as may stray or float near, and
they have the means of securing it when it comes within
their reach. The oyster closes its shell, and thus entraps its
prey ; the polyp has flexible arms, (Fig. 77,) capable of

great extension, which it throws instantly
„ v around any minute animal that comes in con-
'' -^"^ tact with it. The cuttle-fish, also, has elongated
arms about the mouth, furnished with ranges
of suckers, by which it secures its prey,
(Fig. 47.)

224. Some are provided with instruments
Fig. 77 for extracting food from places which would

be otherwise inaccessible. Some of the mollusks, with their
rasp-like tongue, (Fig. 58,) perforate the shells of other ani
mals, and thus reach and extract the inhabitant. Insects
have vario is piercers, suckers, or a protractile tongue for the

OF DIGESTION. 109

same purpose, (Figs. 61-64.) Many Annelides, the leeches
for example, have a sucker, which enables them to produce
a vacuum, and thereby draw out blood from the perforations
they make in other animals. Many microscopic animals are
provided with hairs or cilia around the mouth, (Fig. 65,)
which by their incessant motion produce currents that bring
within reach the still more minute creatures or particles CD
which they feed.

225. 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
even movable, and admirably adapted for the purpose. The
woodpeckers have long, bony tongues, barbed at the tip,
with which they draw out insects from deep holes and crevi-
ces 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 his tongue,
the enlarged end of which is covered with a glutinous sub-
stance to which they adhere. The elephant, whose tusks
and short neck prevent him from bringing 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 abundant in this country,
was fuinished with a similar organ. Man and the monkeys
employ the hand exclusively, for prehension.

226. Some animals drink by suction, like the ox, others
by lapping, like the dog. Birds simply fil the beak with
water, then, raising the head, allow it to run down into the
nrop. It is difficult to say how far aquatic animals re-
quire water with their food ; it seems, however, impossible
tha1" they should swallow their prey without introducing n$
the same time some water into their stomach. Of many
among the lowest animals, such as the Polyps it is well

10

110 OF DIGESTION.

known that they frequently fill the whole cavity of their body
with water, through the mouth, the tentacles, and poiea
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.

226 a. Besides the more conspicuous organs above de-
scribed, there are among the lower animals various micro-
scopic apparatus for securing their prey. The lassos of polypi
have been already mentioned incidentally, (223.) They are
minute cells, each containing a thin thread coiled up m its
cavity, which may be thrown out by inversion, and extend to
a considerable length beyond the sac to which it is at
tached. Such lassos are grouped in clusters upon the ten-
tacles, or scattered upon the sides of the Actinia and of
most polypi. They occur also in similar clusters upon the
tentacles and the disk of jelly-fishes. The nettling sensa-
cion produced by the contact of many of these animals 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 movable stalk. The clasps, which may open and shut al-
ternately, 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 diameter may seize and retain shr mps of half
that length, notwithstanding their efforts to dise.«tf igle them-
selves.

CHAPTER SEVENTH.

CF THE BLOOD AND CIRCULATION.

227. THE nutritive portions of the food are poured into
the general mass of fluid which pervades every part of tin-
body, out of which every tissue is originally constructed,
and from time to time renewed. This fluid, in the general
acceptation of the term, is called blood ; but it differs greatly
in its essential constitution in the different groups of the
Animal Kingdom. In polypi and medusai, it is merely
chyme, (208 ;) in most mollusks and articulates it is chyle,
(209 ;) but in vertebrates it is more highly organized, and
constitutes what is properly called BLOOD.

228. 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 disks

Fig. 78. Fig. 79. Fig. 80. Fig. 81.

These vary in number with the natural heat of the animal
*ro:n which the blood is taken. Thus, they are more nu

112 OF THE BLOOD

merous 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, (Fig. 78 ;) they are' some-
what larger, and of an oval form, in birds and fisiies, (Figs
79, 81 ;) and still larger in reptiles, (Fig. 80.)

229. The color of the blood in the vertebrates is bright
red ; but in some invertebrates, as the crabs and mollusks,
the nutritive fluid is nearly or quite colorless ; while in the
worms and some echinoderms, it is variously colored yellow,
orange, red, violet, lilac, and even green.

230. The presence of this fluid in every part of the body
is one of the essential conditions of animal life. A per-
petual current flows from the digestive organs towards the
remotest parts of the surface ; and such portions as are not
required for nutriment and secretions return to the centre of
circulation, 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 in
the Hv3r. The blood is kept in an incessant CIRCULATION
for this purpose.

231. 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, which occupy a
somewhat higher rank, a similar liquid is distributed by pro-
longations of the principal cavity to different parts of the
body, (Fig. 31.) Currents are produced in these, partly by
the .general movements of the animal, and partly by means
of the incessant vibrations of microscopic fringes, called
vibratile cilia, which overspread the interior. In most of
the mollusks and articulates, the blood (chyle) is also 'n
immediate contact with the viscera, water being mixe<i with
it in mollusks ; the vessels, if there are any, not forming a

AND CIRCULATION.

113

complete circuit, but emptying into various cav ties which
interrupt their course.

232. In animals of still higher organization, as the verte-
brates, we find the vital fluid enclosed in an appropriate sei
of vessels, by which it is successively conveyed throughout
the system to supply nutriment and secretions, and to the
respiratory organs, where it absorbs oxygen, or, in other
words, becom 3s oxygenated.

233. The vassels in which the blood circulates are of two
kinds : 1. The arteries, of a firm, elastic structure, which
may be distended or contracted, according to the volume of
their contents, and which convey the blood from the centre
towards the surface, distributing it to every point of the
body. 2. The veins, of a thin, membranous
structure, furnished within with valves, (Fig.

82, v,) which aid in sustaining the column of
blood, only allowing it to flow from the peri-
phery towards the centre. The arteries con-
stantly subdivide into smaller and smaller
branches ; while the veins commence in minute
twigs, and are gathered into branches and larger
trunks, to unite finally into a few stems, near the
centre of circulation.

234. The extremities of the arteries and veins are con-
nected by a net-work of extremely

delicate vessels, called capillary ves-
sels, (Fig. 83.) They pervade every
portion of the body, so that almost
no point can be pricked without
drawing blood. Their office is to
distribute the nutritive fluid to the
organic cells, where all the important processes of nutrition
are performed, such as the alimentation and growth of all
organs and tissues, the elaboration of bile, milk, saliva, anc
10*

Fig. 82.

Fig. 83.

114 OF THE BLOOD

other important products derived from blood, the removal of
effete particles and the substitution of new ones, and al)
those changes by which the bright blood of the arteries be
comes 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.

235. 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 ves-
sel contracts, the blood can
flow only towards the head, and, being thence distributed to
ths body, is returned again into the dorsal vessel, (Fig. 84,)
by fissures at its sides.

236. In all the higher animals there is a central organ,
the heart, which forces the blood through the arteries to-
wards 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, independ-
ently 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 respiratory organs, and indicate
the higher or lower rank of an animal, as determined by the
quality of the blood distributed in those organs.

237. In the mammals and birds the heart is divided by a
vertical partition into two cavities, each of which is again
divided into two compartments, one above the other, as seen
in the diagram, Fig. 85.) The two upper cavities are called

AND CIRCULATION/ 115

auricles^ and the two lower ventricles. Reptiles have two

Fig. 85. Fig. 86. Fig. 87.

auricles and one ventricle, (Fig. 86.) Fishes have one auri-
cle and one ventricle only, (Fig. 87.)

238. 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 a valve, to prevent its reflux ;
while the ventricles, by their contractions, force the blood
through arteries into the lungs, and through the body gen-
erally.

239. The two auricles dilate at the same instant, and also
contract simultaneously ; so also do the ventricles. These
successive contractions and dilatations constitute the pulsa-
tions of the heart. The contraction is called systole, and the
dilatation is called diastole. Each pulsation consists of two
movements, the diastole or dilatation of the ventricles,
during which the auricles contract, and the systole or con-
traction 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
heats per minute.

240. The course of the blood in those animals which have
four cavities t:> the heart is as follows, beginning with the
left ventricle (Fig. 85, 1. v.) By the contraction of this

116 OF THE BLOOD

ventricle, the blood is driven through the main arterial trunk,
called the aorta, (Fig. 90, a,) and is distributed by its
branches thi :>ughout the body ; it is then collected by the
veins, carried back to the heart, and poured into the right
auricle, (Fig. 85, r a,) which sends it into the right, ventricle
rv.) The right ventricle propels it through another set of
arteries, the pulmonary arteries, (Fig. 90, p,) to the lungs,
(Z ; ) it is there collected by the pulmonary veins, and con-
veyed to the left auricle, (Fig. 85, / a,) by which it is returned
to the left ventricle, thus completing the circuit.

241. Hence the blood in performing its whole circuit
passes twice through the heart. The first part of this cir-
cuit, 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 cir-
culation : this double circuit is said to be a complete circu-
lation. In this case the heart may be justly regarded as
two hearts conjoined, and in fact the whole of the lesser cir-
culation intervenes in the passage of the blood from one side
of the heart to the other ; except that during the embryonic
period there is an opening between the two auricles, which
closes as soon as respiration commences.

242. In reptiles, (Fig. 86,) 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 sep
arate the two kinds of blood received from the auricles ; bui
ihe mixture soon takes place by means of a special artery,
which passes from the pulmonary artery to the aorta.

243 In fishes, (Fig. 87,) the blood is carried directly

AND CIRCULATION. 117

from the -\ ?ntricle to the gills, which are their chief respir
atory organs; thence it passes into arteries for distribution
to the system in general, and returns by the veins to the
auricle. Here the blood, in its circuit, passes but once
through the heart ; but the heart of a fish corresponds nev-
ertheless to the heart of a mammal, and not to one half of
it, as has often been maintained, for the gills are not lungs.

244. Crabs and other Crustacea have but a single ventri-
cle, without an auricle.
In the mollusks, there is
likewise but a single ven-
tricle, as in Natica, (Fig.
88, h.) Some have in
addition one or two auri-
cles. These auricles are
sometimes so disjoined
as to form so many isolated hearts, as in the cuttle-fish.
Among Eadiata, the sea-urchins are provided with a tubular
heart

CHAPTER EIGHTH.

OF RESPIRATION.

245. F 3R the maintenance of its vital properties, the olood
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 RESPIRATION to
bring the blood into communication with the air.

246. Among animals which breathe in the open air,

some have a series of tubes branching
through the interior of the body, called
trachea, (Fig. 89, *,) opening externally
upon the sides of the body, by small aper-
tures, called stigmata, (s ; ) as in insects
and in some spiders. But the most com-
mon mode of respiration is by means of
LUNGS, a pair of peculiar spongy or cel-
lular organs, in the form of large pouches,
which are the more complicated in pro-
portion to the . quantity of a'r to be con-
sumed.

247. In the lower vertebrata, provided with lungs, they
form a single organ ; but in the higher classes they are in pairs,
placed in the cavity formed by the ribs one on each side of

Fig. 89.

OF RESPIRATION. 119

the vertebral column, and enclosing the heart fh) between
them, (Fig. 90, 1 L) The lungs communicate with the atmos-
phere by means of a tube composed of cartilaginous rings
which arises from the back part of the mouth, and divides
below, first into a branch for each organ, and then into in-
numerable branches penetrating their
whole mass, and finally terminating in
minute sacs. This tube is the trachea
or ivindpipe, (w,) and its branches are
the bronchi. In the higher air-breath-
ing animals the lungs and heart occupy
an apartment by themselves, the chest,
which is separated from the other con-
tents of the lower arch of the vertebral
column, (161,) by a fleshy partition,
called the diaphragm, passing across
the cavity of the body, and arching up into the chest. The
only access to this apartment from without is by the glottis,
(Fig. 22, 0,) through the trachea.

248. The mechanism of respiration by lungs may be com-
pared to the action of a bellows. The cavity of the chest is
enlarged by raising the ribs, the* arches ofwhjch naturally
slope somewhat downward, but more especially by the con-
traction of the diaphragm, whereby its intrusion into the
chest is diminished. This enlargment causes the air to rush
in through the trachea, distending the lung so as to nil the
additional space. When the diaphragm is again relaxed,
and the ribs are allowed to subside, the cavity is again dimin-
ished, and the air expelled. These movements are termed
inspiration or inhalation, and expiration. The spongy pul-
monary substance being thus distended by air, the blood sen.
from the heart is brought into such contact with it as to allow
the requisite interchange to take place, (235.)

249. The respiration of animals breathing in water is ac-

120

OF RESPIRATION.

Fig. 92.

free access to them

complished by a different apparatus. The air is to be
/3 derived frorr. the water, in which

more or less is always diffused.
The organs for this purpose are
Fig. 91 called branchiae, or gills, and are

either delicate tufts or plumes floating outside of the body,
as in some of the marine worms,
(Fig. 33,) and many mollusks, (Fig.
91, £•;) or they consist of deli-
cate combs and brushes, as in fishes,
(Fig. 92,) crabs, and rnost mollusks,
(Fig. 88, g.) These gills are al-
ways so situated that the water has
In the lo^e/- aquatic animals, such as
the polypi, and some jelly-fishes and mollusks, respiration
takes place by the incessant motions of vibratory cilia, which
fringe both the outside and the cavities of the body ; the cur-
rents they produce bringing constantly fresh supplies of water,
containing air, into contact with the respiratory surface.

250. Many animals living in water, however, rise to the
surface and breathe the atmosphere there, or are furnished
with the means of carrying away a temporary supply of air,
whilst others are furnisht.d with reservoirs in which the blood
requiring oxygenation n.ay be accumulated, and their stay
under water prolonged. This is the case with the seals,
whales, tortoises, frogs, many insects and mollusks, &c.

251. 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 <> f a very different character, namely, car-
bonic acid gas, will have taken its place. The essential
office of respiration is to supply oxygen to the- blood, at the
same time fhat carbon is removed from it.

OF RESPIRATION. 121

252. An immediately obvious effect cif respiration in the
red-blooded animals is a change of color; the blood, in
passing through the respiratory organs, being changed from
a very dark purple to a bright scarlet. In the great circula-
tion (241) the scarlet blood occupies the arteries, and is usu-
ally called red blood, in contradistinction from the venous
blood, which is called Hack blood. In the lesser circulation,
on the contrary, the arteries carry the dark, and the veins
the red blood.

253. The quantity of oxygen consumed by various am
mals in a given time has been accurately ascertained by ex-
periment. It has been found, for instance, that a common-
sized man consumes, on an average, about 150 cubic feet in
twenty-four hours ; and as the oxygen constitutes but 21 per
cent, of the atmosphere, it follows that he inhales, during a
day, about 700 cubic feet of atmospheric air. In birds, the
respiration is still more active, while in reptiles and fishes it
is much more sluggish.

254. The energy and activity of an animal is, therefore
.somewhat dependent on the activity of its respiration. Thus
the toad, whose movements are very sluggish, respires much
more slowly than the mammals, birds, and even insects ; and
it has been ascertained that a butterfly, notwithstanding its
comparatively diminutive size, consumes more oxygen than
a toad.

255. The circulation and respiration have a reciprocal in-
fluence upon each other. If the heart be powerful, or if
on violent exercise a more rapid supply of blood to repair
the consequent waste is demanded, (201,) respiration must be
proportionally 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 is rendered
more stimulating by greater oxygenation, and ca'uses an ac-

11

122 OF RESPIRATION.

celeration of the circulation. The quantity of air consumed
varies, therefore, with the proportion of the blood which is
sent to the lungs.

256. The proper temperature of an animal, or what is
termed ANIMAL HEAT, depends on the combined activity of
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 *he
surrounding medium. Thus, birds maintain a temperature
of about 108° Fahrenheit ; and in a large proportion of mam-
mals it is generally from 95° to 105°. These bear the
general designation of warm-blooded animals.

257. Reptiles, fishes, and most of the still lower 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
often, however, a little above it when the external tempera-
ture 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 respiratory organs, are among them, (243.)

258. The production of animal heat is obviously connected
with 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 a.s 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

OF RESPMATIOIN. 123

uniform distribution of heat through the body, Its not yet
been satisfactorily ascertained.

259. 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 HIBERNATION,
or the hibernating sleep. The marmot, the bear, the bat,
the crocodile, and most reptiles, furnish examples. During
this s*ate tfte 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
attending it fully illustrate the laws already stated, (254-8.)

260. There is another point of view in which respiration
should be considered, namely, with reference to the buoy-
ancy of animals, or their power of rising in the atmosphere,
and their ability to live at different depths in the water, under
a diminished or increased pressure. The organs of res-
piration of birds and insects are remarkably adapted for the
purpose of admitting at will a greater quantity of air into
their body, the birds being provided with large pouches ex-
tending from the lungs into the abdominal cavity and into
the bones of the wing. In insects the whole be dy is pene-
trated 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 micro-
scopic tubes, penetrating from the surface into the substance,
or the cavities of the body, 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 mollusks they are
more mnrerous in the fleshy parts, as, for example, in the

124 OF RESPIRATION.

foot, which they help to distend, and communicate with the
main cavity of the body, supplying it also with liquid ^ in
echinoderms they pass through the skin, and even through

260 a. In order fully ;o appreciate the homologies between the
various respiratory apparatus observed in different animals, it is ne-
cessary to resort to a strict comparison of the fundamental connec-
tions of these organs with the whole system of organization, rather
than to the consideration of their special adaptation to the elements
in which they live. In Vertebrates, for instance, there are two seta
of distinct respiratory organs, more or less developed at different pe-
riods of life, or in different groups. All Vertebrates, 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 res-
piration 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 growth. Again, all Vertebrates have
lungs, opening in or near the head ; but the lungs are fully devel-
oped only in Mammalia, birds, and the higher reptiles, in propor-
tion as the branchial respiration is reduced ; whilst in fishes the air-
bladder constitutes a rudimentary lung.

260 b. In Articulates, there are also two sorts of respiratory or-
gans ; aerial, called tracheae in insects, and lungs in spiders ; and
aquatic, in Crustacea and worms, called gills. But these tracheae and
lungs open separately upon the two sides of the body, (air never
being admitted through the mouth or nostrils in Articulates ;) the
gills are placed in pairs ; those which are like the tracheae occupying
a similar position, so that there are nearly as many pairs of tracheae
and gills as there are segments in these animals, (Figs. 89 and 33.)
The different respiratory organs in Articulates are in reality mere
modifications of the same apparatus, as their mode of formation and
successive metamorphoses distinctly show, and cannot be compared
•with either the lungs or gills of Vertebrates ; they are special organs
not found in other classes, though they perfi rm the same functions.
The same may be said of the gills and lungs of mollusks, which
are essentially alike in structure, the lungs of snails and slugs being
only a modification of the gills of aquatic mollusks ; but these two
kinds of organs differ again in their structure and relations from the
tracheae and gills of Articulates, as much as from the lungs and gills

OF RESPIRATION. 125

i.he hard shell, whilst in polyps they perforate the walls of
the ge.ieral cavity of the body, which they constantly fili
with water.

of Vertebrates. In those Radiates which are provided with distinct
respiratory organs, such as the Echinoderms, we find still anothei
typical structure, their gills forming bunches of fringes around the
mouth, or rows of minute vesicles along the radiating segments of
ttib body.

11*

CHAPTER NINTH.

OF THE SECRETIONS.

261. V/u LE, by the process of digestion, a homogeneous
fluid is prepared from the food, and supplies new material to
»he 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
purposes, 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.
SECRETION.

262. The organs by which these operations are per-
formed are much varied, consisting either of flat surfaces or
membranes, 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 sur-
face of the body is covered by them, and they either dis-
charge their products directly upon the surface, as on the
mucous membrane, or they unite in clusters and empty into
a common duct, and discharge by a single orifice, as is the
case with some of the intestinal glands, and of those from
which the perspiration issues upon the skin, (Fig. 94.)

OF THE SECRETIONS 127

263. In the .:igher 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,
such as the salivary glands, the kidneys,
and Vie liver. In these, clusters of sacs
open into a common canal, and this canal

unites with similar ones forming larger trunks, such as we
find in the salivary glands, (Fig. 93,) and finally they all
discharge by a single duct.

264. 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 retained in the blood with impunity ; or, the fluids
selected are such as are positively injurious, and cannot
r3main in the blood without soon destroying life. These

atter are usually termed EXCRETIONS.

. 265. 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.

266. We have already seen (37) that all animal tissues
admit of being traversed by liquids and gases. This mutual
transmission of fluids from one side of a membrane to the
other is termed endosmosis and exosmosis, or imbibition and
transudation, and is a mechanical, rather than a vital, phe-
nomenon, inasmuch as it takes place in dead as well as in

128 OF THE SECRETIONS.

living tissues. The bloodvessels, 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 superficial loss is termed exhalation. It is
most active where the bloodvessels most abound, and accord
ingly 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 exhalation, five eighths of the whole weight
of the substances received into it.

267. The skin, or outer envelop of the body, is otherwise
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 some-
times gradual and continual, as in man. In fishes and many
mollusks, it comes off in the form of slime, which is, in fact,
composed of cells detached from the surface of the skin.
Sometimes the loss is periodical, when it is termed moulting.
Thus, the mammals cast their hair, and the deer their horns,
the birds their feathers, the serpents their skins, the crabs
their test, the caterpillars their outer envelop, with all the
hairs growing from it.

268. The skin presents such a variety of structure in the
different groups of animals as to furnish excellent distinctive
characters of species, genera, and even families, as will
hereafter be shown. In the vertebrates we may recognize
several distinct layers, of unequal thickness, as may be seen
in figure 94, which represents a magnified section of the
human skin, traversed by the sudoriferous canals. The
lower and thickest layer, (a,) is the cutis, or true skin, and
is the part which is tanned into leatner. Its surface presents
numerous papillae, in which the nerves of general sensation
terminate; they also contain a fine network of bloodvessels,

OF THE SECRETIONS.

129

Fig. 94.

usually termed the vascular layer. The
Bupsrficial layer (c) is the epidermis,
or cuticle. The cells of which it is com-
posed are distinct at its inner portion,
but become dried and flattened as they
are pushed outwards. It is supplied with
neither vessels nor nerves, and, conse-
quently, is insensible. Between these
two layers, and more especially con-
nected with the cuticle, is the rele muco-
sum, (1),) 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 coverings of the Crustacea, are
merely modifications of the epidermis. On the other hand,
the feathers of birds and the scales of fishes arise from the
vascular layer.

269. Of all the Excretions, if we except that from the
Lungs, the bile seems to be the most extensive and im-
portant ; and hence a liver, or some analogous organ, by
which bile is secreted, is found in animals of every depart-
ment ; while some, or all, of the other glands are want-
ing in the lower classes of animals. In Vertebrates, the
liver is the largest of all the organs of the body. In rnol-
lusks, it is no less preponderant. In the gasteropods, like the
snail, it envelopes the intestine in its convolutions, (Fig. 52 ;)
and in the acephala, like the clam and oyster, it generally
surrounds the stomach. In insects it is found in the shape of
long tubes, variously contorted and interlaced, (Fig. 51.) In
the Radiata, this organ is largely developed, especially
among the echinoderms. In the star-fishes 't extenis into

130 OF THE SECRETIONS.

all the recesses cf the rays ; and, in color and stiuctuie, re
sembles the liver of mollusks. Even in polyps, we find pe-
culiar brDwn cells lining the digestive cavity, which, proba-
bly, perform functions similar to those of the liver in the
higher animals.

270. The great importance of the respiratory organs in
discharging carbon from the blood has already been spoken
of, (245, 251.) The substances removed by the liver and
the lungs are of the same class, being those which are desti-
tute of nitrogen. These organs seem, in some sense, sub-
sidiary to each other ; and hence, in those animals where
the respiratory organs are largely developed, the biliary
organs are comparatively small, and vice versa. Another
and opposite class of impurities, and no less pernicious if
retained in the blood, is removed by the KIDNEYS ; and,
consequently, organs answering to the kidneys are found
very far down in the series of animals. Most of the peculiar
ingredients of the urine are capable of assuming solid, crys-
talline forms ; and, in some animals, as in reptiles and
birds, the whole secretion of the kidneys is solid. In mosi
cases, however, the urinary salts are largely diluted with
water; and, as the lungs and liver are supplementary to
each other in the removal of carbon, so the lungs, the kid-
neys, and the skin mutually relieve each other in the removal
of the watery portions of the blood.

CHAPTER TENTH

EMBRYOLOGY.
SECTION I

OF THE EGG.

271. THE functions of vegetative life, of which we nave
treated in the preceding chapters, namely, digestion, circu-
lation, respiration, and secretion, have for their end the pres-
ervation of the individual. We have now to treat of the
functions that serve for the perpetuation of the species,
namely those of reproduction, (200.)

272. It has been generally admitted 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 individ-
uals differing from themselves ; but recent investigations
have modified to a considerable extent this view, as we shall
see hereafter.

273. Reproduction in animals is almost universally accom
plished by the association of individuals of two kinds, males
and females, living commonly in pairs or in flocks, each of
them characterized by peculiarities of structure and external
appearance. As this distinction prevails throughout the ani-
mal kingdom, it is always necessary, if we would obtain a
correct and complete idea of a species, to take into account
the peculiarities of both sexes. E veiy one is familiar with the
differences between the cock and the hen, the lion and the
lioness, frc. Less prominent peculiarities are observed in

132 EMBRYOLOGY.

most Vertebrates. Among Articulata, the differences are no
less striking, the males being often of a different shape and
color, as in crabs, or having even more complete organs, as
in many Bribes of insects, where the males have wings, while
the females are destitute of them, (Fig. 1-17.) Among mol-
lusks, the females have often a wider shell.

2,74. Even higher distinctions than specific ones are based
upon peculiarities of the sexes ; 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 peculiar liquid, the milk, secreted by herself. Again,
the Marsupial, such as the opossum and kangaroo, are dis-
tinguished by the circumstance that the female has a pouch
into which the young are received in their immature con-
dition at birth.

275. 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
incipient animal is enclosed within an egg. It is then called
an embryo, and the period passed in this condition is called
the embryonic period.

276. Before the various classes of the animal kingdom
had been attentively studied during the embryonic period,
all animals were divided into two great divisions : the ovip-
arous, 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

OF THE EGG.

133

Fig. 95.

egga should therefore, be considered as a universal charac
terislic of the Animal Kingdom.

277. Form of 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 constant, that the term oval has been universally
adopted to designate it. But this is by no means the usua'
form of the eggs of other animals.

Fn most instances, on the contra-
ry they are spherical, especially
among the lower animals. Some
have singular appendages, as those
of the skates and sharks, (Fig. 95,) which are shaped like
a hand-barrow, with four hooked horns at the corners. The
eggs of the hydra, or fresh water
polyp, are thickly covered with
prickles, (Fig. 96.) Those of
certain insects", the Podurella, for
example, are furnished with fila-
ments which give them a hairy
aspect, (Fig. 97 ;) others are cylindrical or prismatic ; and
frequently the surface is sculptured.

278. Formation' 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 minute in size, in
this condition they are called ovarian, or primitive eggs.
They are identical in all animals, being, in

fao.t, merely little cells (v) containing yolk,
(yy) and including other smaller cells, the
germinative vesicle, (g,) and the germinative
dotf, (d.) The yolk itself, with its membrane,
(v,) is formed while the egg remains in the
ovary. It is afterwards enclosed in another
envelope, the shell membrane, which may remain soft,
12

Fig. 96.

Fig. 97-

Fig. 98.

134 EI I BRYOLOGY.

or be further surrounded by calcareous deposits, the shell
proper, (Fig. 101, 5.) 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.

279. Ovulation. — Having attained a certain degree of
maturity, which varies in different classes, the eggs leave
the ovary. This is called ovulation, and must not le con-
founded with the laying of the eggs, which is the subsequent
expulsion of them from the abdominal cavity, either imme-
diately, or through a special canal, the oviduct. Ovulation
takes place at certain seasons of the year, and never be-
fore 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 number of years consecutively,
generally in the spring in terrestrial animals, and frequently
several times a year ; most of the lower aquatic animals, how-
ever* 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 but-
terfly and most insects die, shortly after having laid their eggs.

280. The period of ovulation is one of no less interest tc
the zoologist than to the physiologist, since the peculiai
characteristics of each species are then most clearly marked.
Ovulation is to animals whit flowering is to plants ; and,
indeed, 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 ornamented with much brighter
colo-s at this period

OF THE EGG.

135

281. 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.

282. Eggs are sometimes laid one by one, as in birds ;
sometimes collectively and in great numbers, as in

the frogs, the fishes, and most of the invertebrates.
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 envelop ; in others they are Fi
enclosed in cases or between membranous disks,
forming long strings, as in the eggs of the Pyrula shell, (Fig
99.) 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 in nests constructed
for thc»t purpose by the parent. Other animals
carry their eggs attached to their bodies ;
sometimes under the tail, as in the lobsters
and r rabs, sometimes hanging in large bun-
dles nn both sides of the tail, as in the Mo-
nocul-is, (Fig. 100, a.)

233. Some toads carry them on the back, and, what is
most extraordinary, it is the male which undertakes this
olfice. Many mollusks, the Unio for example, have them
enclosed between the folds of the gills during incubation,
In the jelly fishes and polyps, they hang in clusters, either

Fig. 100.

136 EMBRYOLOGY.

outside, (Fig. 77, o,) or inside, at the bottom of tie 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 mollusks. 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.

284. The development of the embryo does not always
take place immediately after the egg is laid. A considera-
ble 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 genelal, 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. The seeds, which are
equivalent to eggs, preserve for years, and even for ages
their power to germinate. Thus, there are some well-
authenticated cases in which 'wheat taken from the ancient
catacombs of Egypt has been made to sprout and grow.

285. 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 tem-
perature, corresponding to the natural heat of the future
chicken, which is naturally supplied by the body of the
parent. In other words, incubation is necessary for t«heir
growth. Incubation, however, is not a purely vital phenom-
enon, but may be easily imitated artificially. Some birds
of warm climates dispense with this task ; for example, the
ostrich often contents herself with depositing her eggs in the
sand of the desert, lea ing them to be hatched by the gun. In

OF THE EGG. 137

like manner, th? 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 »;ggs, as the sticklebacks, sun-fishes, and cat-fishes ; but
whether they impart heat to them or not, is doubtful.

Before entering into the details of embryonic transfer
mations, a few words are necessary respecting the composi
tion of the egg.

286. Composition of the Egg. — The egg is composed
of several substances, varying in structure, as well as in
appearance. Thus, in a hen's egg, (Fig. 101,) we have first
a calcareous shell, (s,) lined by a double membrane, the shell
membrane, (m ;) then an albuminous substance, the white,
(a,) in which several layers may be distinguished ; within
this we find the yolk, (y,) enclosed in its membrane ; and
before it was laid, there was in the midst of the latter a mi-
nute vesicle, the germinative vesicle, (Fig. 98, g,) containing
a still smaller one, the germinative dot* (d.) These different
parts are not equally important in a

physiological point of view. The
most conspicuous of them, namely,
the shell and the white, are not es-
sential parts, and therefore are often
wanting ; while the yolk, the ger-
minative vesicle, and the germina- Fig. 101
tive 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 by Fig. 101, e.

287. The vitellus or yolk (Fig. 101, y) is the most essen-
tial part of the egg. It is a liquid of variable consistence,
sometimes opaque, as in the eggs of birds, sometimes trans-
parent and colorless, as in the eggs of some fishes and
mollusks. On examination under the microscope, it appears
to be composed of an accumulation of granules and oil-drops.

12*

138 EMBRYOLOGY.

The yelk is surrounded by a very thin skin, the vitellme
membrane, 'Fig. 98, v.) In some insects, when the albumen
is wanting, this membrane, surrounded by a layer of pecu-
liar cells, forms the exterior covering of the egg, which, in
sucli cases, is generally of a firm consistence, and sometimes
even horny.

288. The germinative vesicle (Fig. 98, g) is a cell of ex-
treme delicacy, situated, in the young egg, near the middle
of the yolk, and easily recognized by the greater transpar-
ency of its contents when the yolk is in some degree opaque,
as in the hen's egg, or by its outline, when the yolk itself is
transparent, as in eggs of fishes and mollusks. It contains
one or more little spots, somewhat opaque, appearing as
small dots, the germinal dots, (rf.) On closer examination,
these dots are themselves found to contain smaller nucleoli.

289. The albumen, or white of the egg, (Fig. 101, a,) is
a viscous substance, generally colorless, but becoming
opaque white on coagulation. Voluminous as it is in birds'
eggs, it nevertheless plays but a secondary part in the histo-
ry 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 ovi
duct is wanting, are generally without the albumen. In
birds, the albumen consists of several layers, one of which,
the chalaza, (c,) is twisted. Like the yolk, the albumen is
surrounded by a membrane, the shell membrane, (m,) which
is either single or double, and in birds, as also in some
reptiles and mollusks, is again protected by a calcareous
covering, forming a true shell, (s.) In most cases, how-
ever, tbis envelop continues membranous, particularly in the
eggs of the mollusks, most crustaceans and fishes, salaman-
ders, frogs, &c. Sometimes it is horny, as in the sharks
and skates.

DEVELOPMENT OF THE YOUNG WITHIN THE ECG. 139

SECTION H.

DEVELOPMENT OF THE YOUNG WITHIN THE EGG.

290. The formation and development of the young ani-
mal within the egg is a most mysterious phenomenon. From
a hen's egg, for example, surrounded by a shell, and com-
posed, as we have seen, (Fig. 101,) of albumen and yolk,
with a minute vesicle in its interior, there is produced, at the
end of a certain time, a living animal, composed apparently
of elements entirely different from those of the egg, en-
dowed with organs perfectly adapted to the exercise of all
the functions of animal and vegetative life, having a pul-
sating heart, a digestive apparatus, organs of sense for the
reception of outward impressions, and having, moreover, the
faculty of performing voluntary motions, and of experi-
encing pain and pleasure. These phenomena are certainly
sufficient to excite the curiosity of every intelligent person.

291. 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 incu-
bation 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 developed. Modern researches have taught us that
these gradual changes, although complicated, and at first
sight so mysterious, follow a constant law in each great
division of the Animal Kingdom. *

292. The study of these changes constitutes that peculiar
branch of Physiology called EMBRYOLOGY. As there are
differences in the four great departments of the AnimaJ

140 EMBRYOLOGY.

Kingdom perceptible at an early stage of embryonic life,
quite as obvious as those found at maturity, and as the
phases of embryonic development furnish important indi-
cations for the natural classification of animals, we propose
to give the outlines of Embryology, so far as it may have
reference to Zoology.

293. 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, (39.) These cells, however, are more or less diversi-
fied and modified, or even completely metamorphosed in the
full grown animal ; but, at the commencement of embry-
onic life, the whole embryo is composed of minute cells of
nearly the same form and consistence, originating within the
yolk, and constantly undergoing changes under the influence
of life. New cells are successively formed, while others
disappear, or are modified and so transformed as to become
bones, muscles, nerves, &c.

294. We may form some idea of this singular process,
by noticing how, in the healing of a wound, new substance
is supplied by the transformation of blood. Similar changes
take place in the embryo, during its early life ; only, instead
of being limited to some part of the body, they pervade the
whole animal.

295. 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 yol-k,
which at first consists of a mass of uniform appearance, grad-
ually assumes a diversified aspect. Some portions become
more opaque and others more transparent ; the germinal
vesicle, whicn was in the midst of the yolk, rises to its upper
part where the germ is to be formed. Tiaese early changes

DEVELOPMENT OF THE YOUNG WITHIN THE LGG. Ill

are accompanied, in some animals, Dy a rotation of the yolk
within the egg, as may be distinctly seen in some of the
mollusks, especially in the snails.

296. 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 sub-
divided into two more, and so on, till the whole yolk as-
sumes the appearance of a mulberry, each of the spheres of
which it is composed having in its ' interior a transparent
vesicle. This is the case in mammalia, most mollusks,
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.

297. But whether complete or partial, this process leads
to the formation of a germ comprising the whole yolk, or
rising above it as a disk-shaped protuberance, composed of
little cells, which has been variously designated under the
names of germinative disk, proligerous disk, 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 disk again
gradually enlarges, until it embraces the whole, or nearly
the whole, of the yolk.

298. At this early epoch, namely, a few days, and some-
times a few hours,

after development
has begun, the
germ proper con-
sists of a single
layer composed Fig. 102. Fig. 103.

* In the Birds and higher reptiles we find, in the mature egg, a peculiar
organ, called cicatricula, which may. nevertheless, have been formed by
a similar proc ?ss before it was laid.

142 EMBRYOLOGY.

of very minute cells, all of which are alike in appearance
and form, (Fig. 102, g.) But soon after, as the germ increases
in thicRness, several layers may be discerned, in vertebrated
animals, (Fig. 103,) which become more and more distinct.

299. The upper layer, (s,) in which are subsequently
formed the organs of animal life, namely, the nervous sys-
tem, the muscles, the skeleton, &c., (59,) has received the
name of serous or nervous layer. The lower layer, (m,)
which gives origin to the organs of vegetative life, and espe-
cially to the intestines, is called the mucous or vegetative
layer, and is generally composed of larger cells than those
of the upper or serous layer. Finally, there is a third
layer, (v,) interposed between the two others, giving rise to
the formation of blood and the organs of circulation ; whence
it has been called blood layer, or vascular layer.

300. From the manner in which the germ is modified, we
can generally distinguish, at a very early epoch, to what de-
partment of the animal kingdom an individual is to belong.
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. 104.)
The germ of the vertebrated ani-
mals, on the other hand, displays
a longitudinal furrow, which marks
Fig. 104. Fig. 105. the pOSition the future back-bone
is to occupy, (Fig. 105.)

301. The development of this furrow is highly important,
a> 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.*

* In these figures, the egg is supposed to be cut down through the mid-
dle, so that mly the cut edge of the embryo is seen ; whereas, if viewed

DEVELOPMENT OF THE YOUNG WITHIN THE EGG. 113

At first the furrow (Fig. 106, Z>) is very shallow, and a lit-

I

Fig. 106. Fig. 107. Fig. 108.

tie transparent, narrow band appears under it, called the
primitive stripe, (a.) The walls of the furrow consist of two
raissd 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 ap-
proach each other, as seen in Fig. 107 ; at last they meet
and unite completely, so that the furrow is now changed
into a closed canal, (Fig. 108, b.) This canal is soon filled
with a peculiar liquid, from which the spinal marrow and
brain are formed at a later period.

302. 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 founo
in the embryos of all vertebrates, 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 vertebrates has two cavities, namely,
the upper one, which is very small, containing the nervous
system, and the lower, which is much larger, for the intes-
tines, (161.)

303. In all classes of the Animal Kingdom, the embryo
proper rests upon the yolk, and covers it like a cap. Bui
the direction by which its edges approach each other, and

from above, it would extend over the yolk in every direction, and the
furrow at b, of Fig. 106, would appear as in Fig. 105.

144

EMBRYOLOGY.

Fig. 109.

unite tc form the cavity of the body, is very unlike in dif
ferent animals ; and these several modes

are of high importance in classification.
Among the Vertebrates, the embryo lies
with its face or ventral surface towards
the yolk, (Fig. 109,) and thus the suture,
or line at which the edges of the germ
unite to enclose the yolk, and which in
the mammals forms the navel, is found
in front. Another suture is found along
the back, arising from the actual folding upwards of the
upper surface of the germ, to form the dorsal cavity.

304. The embryo in the Articulata, on the contrary, lies
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
vertebrates is found on the belly, is here
found on the back. In the Cephalopoda
the yolk communicates with the lower
side of the body, as in Vertebrates, but
there is no dorsal cavity formed in them.
In the other Mollusks, as also in the Worms, there is this
peculiarity, that the whole yolk is changed at the beginning
into the substance of the embryo ; whilst in Vertebrates, and
the higher Articulates and Mollusks, a part of it is reserved,
till a later period, to be used for the nourishment of the em-
bryo. Among Radiata, the germ is formed around the yolk,
and seems to surround the whole of it, from the first.*

805. The development of the embryo of the vertebrated
animals may be best observed in the eggs of fishes. Being

Fig. 110.

* These facts show plainly that the circumstance of embryos arising
from the whole or a part of the yolk is of no systematic importance.

DEVELOPMENT OF THE YOUNG WITHIN THE EGG. 145

transparent, they do not require to be cut open, and, by
sufficient caution, the whole series of embryonic changes
may be observed upon the same individual, and thus the suc-
cession in which the organs appear be ascertained with pre-
cision ; whereas, if we employ the eggs of birds, which are
opaque, we aro obliged to sacrifice an egg for each obser-
vation.

306. To illustrate these general views as to the develop- \
nient of the embryo, we will 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.

Fig. 111. Fig. 112. Fig. Il

307. The egg, when laid, (Fig. 11 1,) is spherical, about the
size of a small pea, and nearly transparent. It has no albu-
men, and the shell membrane is so closely attached to the
membrane of the yolk, that they cannot be distinguished.
Oil-like globules are scattered through the mass of the yolk,
or grouped into a sort of disk, under which lies the germina-
tive vesicle. The first change in such an egg occurs a few
hours after it has been laid, when the shell membrane sepa-
rates from the yolk membrane, in consequence of the ab-
sorption of a quantity of water, (Fig. 112,) by which the
egg increases in size. Between the shell membrane (s m)
and the yolk, (y,) there is now a considerable transparent
space, which corresponds, in some respects, to the albumen
found in the eggs of birds.

308. Soon afterwards we see, in the midst of the oil-like

13

146

EMBr>.y. LOGY.

globules, a swelling in the shape of a transparent vesicle,
(Fig. 113, g,) composed of very delicate cells. This is tlm
first indication of the germ. This swelling rapidly enlarges
until it envelops a greai part of the yolk, when a depression

Fig. 114.

Fig. 115.

Fig. 116.

is formed upon it, (Fig. 114.) This depression becomes by
degrees a deep furrow, and soon after a second furrow ap-
pears at .right angles with the former, so that the germ now
presents four elevations, (Fig. 115.) The subdivision goes
on in this way, during the second and third days, until the
germ is divided into numerous little spheres, giving the sur-
face the appearance of a mulberry, (Fig, 116.) This ap-
pearance, 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.

309. On the tenth day, the first OM* lines of the embryo
begin to appear, and we soon distinguish in it a depression
between two little ridges, whose edge* ^ustantly approach

Fig. 117. Fig. 118. Fig. 119.

each other until they unite and form a canal, ^Fig. 117, £,

DEVELOPMENT OF THE YOUNG WITHIN THE EGG. 147

us has been before shown, (Fig. 107.) At the same time,
an enlargement at one end of the furrow is observed. This
is the rudiment of the head, (Fig. 118,) in which may soon
be distinguished traces of the three divisions of the brain,
(Fig. 119,) corresponding to the senses of sight, (m,) hear-
ing, (e,) and smell, (p.)

310. Towards the thirteenth day, we see a transparent,
cartilaginous cord, in the place afterwards occupied by the
back-bone, composed of large cells, on which transverse

Fig. 120. Fig. 121. Fig. 122.

divisions are successively forming, (Figs. 120, 121, c.) This
is the dorsal cord, a part of which, as we have before seen, is
common to all embryos of vertebrated animals. It always
precedes the formation of the back-bone ; and in some
fishes, as the sturgeon, 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. 121, x) is afterwards
formed. At the same time we see, at the posterior part
of the head, an elliptical vesicle, which is the rudiment of the
ear. At this period, the distinction between the upper and
ihe lower layer of the germ is best traced ; all the changes
mentioned above appertaining to the upper layer.

311. After the seventeenth day, the lower layer divides
into two sheets,, the inferior of which becomes the intestine

148 EMBRYOLOGY.

The heart shows itself about the same time, under the form
of a simple cavity, (Fig. 121, A,) 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 perceived, and the globules
of blood are seen to rise and fall in conformity with these
motions.

312. 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. 122,) with similar returning
currents. At this time the liver begins to be formed. Mean-
while, the embryo gradually disengages itself, at both ends,
from its adherence to the yolk ; the tail becomes free, and
the young animal moves it in violent jerks.

313. The embryo, although still enclosed in the egg, now
unites all the essential conditions for the exercise of the
functions of animal life. It has a brain, an intestine, a pul-
sating heart and circulating blood, and it moves its tail spon-
taneously. But the forms of the organs are not yet complete
nor have they yet acquired the precise shape that character-
izes the class, the family, the genus, and the species. The
young White-fish is as yet only a vertebrate animal in gen-
eral, and might as well be taken for the embryo of a frog.

314. 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
surrounds the body ; the anterior limbs, which were indicated
only by a small protuberance, 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.

315. In this state, the young white-fish escapes from the

DEVELOPMENT OF THE YOUNG WITHIN THE EGG.

tgg, about the sixtieth day after it is laid, (Fig. 123,) but
its development is^still
incomplete. The out-
lines are yet too indis-
tinct to indicate the
genus and the species F{g> 123.

to which the fish be-

loi.gs ; a* most we distinguish its order only. The opercula
or gill-covers are not formed; the tee.h are wanting; the
fins have as yet no rays ; the mouth is underneath, and it
is some time before it assumes its final position 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 si2e, until it is at length completely taken
into the animal, (304.) The duration of these metamorphoses
varies extremely in different fishes ; some accomplish it in the
course of a few days, while in others, months are required.

315 a. In frogs and all the naked reptiles, the development is very
similar to that of fishes. It is somewhat different in the scaly rep-
tiles, (snakes, lizards, and turtles,) which have peculiar membranes
surrounding and protecting the embryo during its growth. From
one of these envelopes, the allantoTs, (Fig. 125, a,) is derived theii
common name of Attantoldian Vertebrates, in opposition to the naked
reptiles and fishes, which are called Anallantoldian.

315 6. The AllantoTdian Vertebrates differ from each other in
several essential peculiarities. Among Birds, as well as in the scaly

Fig. 124. Fig. 125.

; we find at a certain epoch, when the embryo is already dis-
13*

150 EMBRYOLOGY.

316. As a general fact, it should be further stated, that
the envelopes which protect 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 innumer-
able eggs of fishes, discharged almost without protection

engaging 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. 124, x x.) These walls, converging from
all sides upwards, ris3 gradually till they unite above the middle of
the back, (Fig. 125.) When the junction is effected, which in the
hen's egg takes place in the course of the fourth day* a cavity is
formed between the back of the embryo (Fig. 126, e) and the new
membrane, whose walls are called the amnios. This cavity becomes
filled with a peculiar liquid, the amniotic icater.

315 c. Soon after the embryo has been enclosed in the amnios, a
shallow pouch forms from the mucous layer, below the posterior ex-
tremity of the embryo, between the tail and the vitelline mass. This
pouch, at first a simple little sinus, (Fig. 125, a,) grows larger and
larger, till it forms an extensive sac, the allantois, turning backwards
and upwards, so as completely to separate the two plates of the am-
IUOF, (Fig. 126, a.) and finally enclosing the whole embryo, with us

Fig. 126.

amnios, in another large sac. The tubular part of this sac, which is
nearest the embryo, is at last transformed into the urinary bladder.
The heart (A) is already very large, with mniute arterial threads

DEVELOPMENT OF THE YOUNG WITHIN THE EGG. 151

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.

317. 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

Fig. 127.

Fig. 128.

passing off from it. At this period there exist true gills upon the
sides of the neck, and a branchial respiration goes on.

315 d. The development of
mammals exhibits the folio-wing
peculiarities. The egg is ex-
ceedingly minute, almost micro-
scopic, although composed of the
same essential elements as those
of the lower animals.* The vitel-
line membrane, called chorion, in

this class of animals, is comparatively thicker, (Fig. 127, v,) always
soft, surrounded by peculiar cells, being a kind of albumen. The
chorion soon grows proportionally larger than the vitelline sphere
itself, (Fig. 128, y,) so as no longer to invest it directly, being sepa-
rated from it by an empty space, (&.) The germ is formed in the
same position as in the other classes of Vertebrates, namely, at the top
of the vitellus, (Fig.
129 ;) and here also
two luyers may be
distinguished, the up-
per or serous layer, (*,)
and the lower or mu-
cous layer, (m.) As
it gradually enlarges,
the surface of the
chorion becomes cov-
ered with little fringes, which, at a later epoch, will be attached to
the mother by means of similar fringes arising from the walls of
the matrix, or organ which contains the embryo.

315 e. The pmbryo itself undergoes, within the cnorion changes

Fig. 129.

Fig. 130.

152

EMBRYOLOGY.

contrary, in the mammals, the chorion, which cor responds
to the vitelline membrane, is vivified, and finally becomes
attached to the maternal body, thus establishing a direct con-
nection between the young and the mother ; a connection
which is again renewed in another mode, after birth, by the
^rocess of nursing.

similar to those described in birds : its body and its organs are
formed in the same way ; an amnios encloses it, and an allantolfs
grows out of the lower extremity of the little animal. As soon as the
allantoYs has surrounded the embryo, its blood vessels become more
and more numerous, so as to extend into the
fringes of the chorion, (Fig. 131, pe;) while,
on the other hand, similar vessels from the
mother extend into the corresponding
fringes of the matrix, (p m,) but without
directly communicating with those of the
ehorisn. These two sorts of fringes soon
become interwoven, SD as to form an intri-
cate organ filled with blood, called the pla-
centa, to which the embryo remains sus-
pended until birth.

315 /. From the fact above stated, it is clear that there are three
modifications of embryonic development among vertebrated animals,
namely, that of fishes and naked reptiles, that of scaly reptiles and
birds, and that of the 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 tie peripheric part of the embryo and an allantoYs
growing out of lie iower cavity, both enclosing and protecting the
germ.

Fig. 131.

ITS ZOOLOGICAL IMPORTANCE. 153

SECTION III.

ZOOLOGICAL IMPORTANCE OF EMBRYOLOGY.

318. As a general result of the observations which ha,ve
been mide, up to this time, on the embryology of the various
classes of the Animal Kingdom, especially of the veite
brates, it may be said, that the organs of the body are suc-
cessively fcrmed in the order of their organic importance,
the most essential 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.

319. Thus we have seen that, in the fish, the first changes
relate to the segmentation of the yolk and the formation of
the germ, which is a process common to all classes of ani-
mals. It is not until a subsequent period that we trace the
dorsal furrow, which indicates that the formiiig animaj will
have a double cavity, and consequently belong to the di\lsion
of the vertebrates; an indication afterwards fully confirmed
by the successive appearance of the brain and the organs
of sense. Later still, the intestine is formed, the limbs be-
come 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 extremit es, mark the genus and species.

320. Hence the embryos of different animals resemble
each otner more strongly when examined in the earlier
stages of the! r growth We have already stated that, during

154 EMBRYOLOGY.

almost the whole period of embryonic life, the young fish
and the young frog scarcely differ at all, (313 :) 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 further back in
the history of development, we come to a period when n3
appreciable difference whatever is to be discovered between
the embryos of the various departments. The embryo of
the snail, when the 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 ; the class and the group are not yet
indicated.

321. After this account of the history of the development
of the egg, the importance of Embryology to the study of
systematic Zoology cannot be questioned. For evidently, if
the formation 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 classifi-
cation. 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 Vertebrates, the Articulates, the Mollusks, and the
Radiates, corresponds perfectly with the gradations displayed
b/ Embryology.

322. This classification, as has been already shown, (61,)
is founded essentially on the organs of animal life, the ner-
vous system and the parts belonging thereto, as found in the
perfect 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 vegetative life, on which is founded the division into
classes, orders, and families, such as the heart, the respirator"
apparatus, and the jaws, are not distinctly formed until after-

ITS> ZOOLOGICAL IMPORTANCE. 155

wards. Therefore 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.

323. Combining these two points of view, that of Embry
ology with that of Anatomy, the four divisions of the Anima)
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.

324. The type of Vertebrates, 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 cen-
tre, and closing above, as well as below.

325. The type of Articulata, having bu^t one cavity, grow-
ing from below upwards, and the nervous system forming
a series of ganglions, placed below the intestine, is repre-
sented by a single crescent, with the horns directed up-
wards.

326. The type of Mollusks having also but one cavity, the
nervous system being a simple ring around the oesophagus,
with ganglions above and below, from which threads go off
to all parts* is represented by a single crescent with the
hoins turned downwards.

327. 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 L

GEM \IIPAROTTS AND FISSIPAROUS REPRODUCTION.

328. WE have shown in the preceding chapter, that ovuU-
(ion, 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 fissip-
arous reproduction, or propagation by division ; and also
some still more extraordinary modifications yet involved in
much obscurity.

329. Reproduction by buds occurs among the polyps, me-

dusae, and some of the infusoria. .On the stalk,
or even on the body of the Hydra, (Fig. 132,)
and of many infusoria, there are formed
buds, like those of plants. On close exam-
ination they are found to be young animals
at first very imperfectly formed, and commu*
nicating at the base with the parent body,
from which they derive their nourishment. By

T 1 ^*?

degrees, the animal is developed ; in most
cases, the tube by which it is connected with the parent

GEMMIPAROUS AND FISSIPAROUS REPRODUCTION. 157

withers away, and the animal is thus detached 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 the polyps, as in trees, budding
is only an accessory mode of reproduction, which pre-
supposes a trunk already existing, originally the product ol
ovulation.

330. Reproduction ly division, or fissiparous reproduction
is still more extraordinary ; it takes place only in polyps and
some infusoria. A cleft or fissure at some part of the body
takes place, very slight at first,
but constantly increasing in
depth, so as to become a deep
furrow, like that observed in the
yolk, at the beginning of embry-
onic development ; at the same
time the contained organs are di-
vided 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 Vorticella, (Fig,
133,) and in some Polyps, (Fig. 134,) and sometimes trans-

Fig. 133.

Fig. 134.

versely. In some Infusoria, the Paramecia, for instance,

this division occurs as often as three or four times in a day.

331. 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 t le ai ms of the star-fishes. The tail of a lizard is also

14

158

REPRODUCTION

readily reproduced. Salamanders even possess the facu'ty
of reproducing parts of the head, including the eye with al)
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.

332. 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 polyp, be divided into several pieces,
the injury is soon repaired, each fragment speedily becoming
a perfect animal. Something like this reparative faculty is
seen in the vegetable kingdom, as well as the animal. A
willow branch, planted in a moist soil, throws out roots below
and branches above ; and thus, after a time, assumes the
shape of a perfect tree.

333. 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 Vorticella, according to Ehrenberg, all three jflodes are
found ; it is propagated by eggs, by buds, and by division.
Ovulation, however, is, the most con non mode of reproduc-
tion , the other modes, and also alternate reproduction, are
only additional means employed by Nature to secure the per-
petuation of the species.

••-•

SECTION II.

ALTERNATE AND EQUIVOCAL REPRODUCTION.

334. It is a matter of common observation, that individuals
of the same species have the same general appearance, 1 y
which theii peciliar organization is indicated. The Iran*

ALTERNATE AND EQUIVOCAL REPRODUCTION. 159

mission 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, unhesitatingly adopt the new definition
of Dr. S, G. Morton, who defines species to be " primordial
organic forms."

335. But it does not follow that animals must resemble
their parents in every condition, and at every epoch of their
existence. On the contrary, as we have seen, this resem-
blance is very faint, in most species, at birth ; and some,
such as the caterpillar and the tadpole, undergo com-
plete metamorphoses before attaining their final shape as the
butterfly and 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.

336. 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 genera-
tion. The son does not resemble the father, but the grand-
father ; and in some cases the resemblance reappears only
at the fourth or fifth generation, and even later. This sin-
gular mode of reproduction has received the name of alter-
nate generation. 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 to several problems alike interesting in a zoological
and in a philosophical point of view.

337. Alternate generation was first observed among tl e
Salpae. These are marine mollusks, without shells, belong-
ing to the family Tunicata. They are distinguished by ihu
curious peculiarity of being united together in considerable
numbers so as to form long chains, which float in the sea.

160 REPRODUCTION.

he mouth, (m,) however, being free in each, (Fig. 135)

Fig. 135.

Fig. 136.

The individuals 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. 136,) 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 their parent, (a,) and these
again bring forth solitary individuals, &c.

338. In some parasitic worms, alternate generation is
accompanied by still more extraordinary phenomena, as is
shown by the late discoveries of the Danish naturalist, Steen-
strup. Among the numerous animals which inhabit stagnant
pools, in which fresh-water shells, particularly Lymnea and
Paludina, are found, there is a small worm,
know to naturalists under the name of Cer-
caria, (Fig. 137.) 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. Va-
rious viscera appear within, and, among
others, a very distinct forked cord, (c.,)
which embraces the sucker, and which is
thought to be the liver.

339. If we watch these worms, which
always abound in company with the shells
mentioned, we find them after a while attaching themselves,
by mear.s of 'heir sucker, to the bodies of the mollusks. When

Fig. 137.

ALTERNATE AND EQUIVOCAL REPRODUCTION.

161

Fig. 138.

The fol

fix 3d they soon undergo considerable alteration. The tail,
which was previously employed for locomotion, is now use-
less, falls off, and the animal surrounds itself with a .ttucous
substance, in which it remains nearly motionless,
like the caterpillar on its transformation into the
Pupa. If, however, after some time, we remove
the litile animal from its retreat, we find it to be
no longer a Cercaria, but an intestinal worm,
called Distoma, having the shape of Fig. 138,
with wo suckers. The Distoma, therefore, is
only a particular state of the Cercaria, or, rather,
the Cercaria is only the larva of the Distoma.

340. What now is the origin of the Cercaria ?
lowing are the results of the latest researches on this point.
At certain periods of the year, we find in the viscera of the
Limnea (one of the most common fresh-water mollusks) a
quantity of little worms of an elongated form,
v ith a well marked head, and two posterior
projections like limbs, (Fig. 139.) On examin-
ing these worms attentively, under the micro-
scope, 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 CercariaB, the tail and the characteristic
furcated organ (a) within it being distinctly visible, (Fig.
140.) These little embryos
increase in size, distending
the worm which contains
them, and which seemingly
has no other office than to
protect and forward the de- Fig. 140.

ve\opment of the young

Cercaria. It is, as it were, their living envelop. On this
account, i« has been called the nurse.
14*

Fig. 139.

162 REPRODUCTION.

341. When they have reached a certain size, the young
Cercurioe lea~'e the body of the nurse, and move freely in
the abdornina cavity of the mollusks, or escape from it intc
the water, to fix themselves, in their turn, to the body of
another rnollusk, and begin their transformations anew.

342. But this is not the end of the series. The nurses of

the Cercaria are themselves the offspring of little
worms of yet another kind. At certain seasons,
we find in the viscera of the Limnea, worms
somewhat like the nurses of Cercaria in shape,
(Fig. 141,) but rather longer, more slender, and
having a much more elongated stomach, (5.)
These worms contain, in the hinder part of the
body, little embryos, («,) which are the young
nurses, like Figures 139, 140. This generation
has received the name of grand-nurses.

343. Supposing these grand-nurses to be the immediate
offspring of the Distoma, (Fig. 138,) as is probable, we have
thus a quadruple series of generation. Four generations
and one metamorphosis are required to evolve the perfect
animal ; in other words, the parent finds no resemblance to
himself in any of his progeny, until he comes down to the
great-grandson.

344. 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 females, 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 prefect state ; and, as each member of the succession is

ALTERNATE AND EQUIVOCAL REPRODUCTION. 163

an incomplete animal, we cannot better explain their office,
than by considering them analogous to the larvae of the
Cercaria, that is, as nurses.*

345. The development of the Medusse is not less instruc-
tive. According to the observat ons of 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 animals have no resemblance whatever to the
perfect Medusa. They are little cylindrical bodies, (Fig.
142, a,) much resembling infusoria, and, like them, covered
with minute cilia, by means of which they swim with much
activity.

346. After swimming about freely in the water for some
days, the little animal fixes itself by one extremity, (Fig.
142, e.) At the opposite extremity a depression is gradu-

* There is a certain analogy between the larvse 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 favor 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 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 gen-
eration, 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 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 confided to other individuals, -o the
jjueen 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 look upon them merely as
nurses

164 REPRODUCTION.

ally formed the four corners (b f) become elongated, and
by degrees, are transformed into tentacles, (c.) • Tnese

0 CO

2

g Fig. 142. k

tentacles rapidly multiply, until the whole of the upper
margin is covered with them, (g.) Then transverse
wrinkles are seen on the body, at regular distances, ap-
pearing first above and extending downwards. 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 ap-
pearance of a pine cone, surmounted by a tuft of tentacles,
(h ;) 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 divisions are united by only a very slender axis, and
resemble a pile of cups placed within each other, (i.)
The divisions are now ready for separation ; the upper ring
first disengages itself, and then the others in succession.*
Each segment (d) then continues its development by itse'f,
until it becomes a complete Medusa, (k ;) while, according
to recent researches5 the basis or stalk remains and pro-
duces a new colony.

347. It is thus, by a series of metamorphoses, that the
little animal which, on leaving the egg, has the form of the

* These free segments have been described as peculiar animals, ui der
he narie of Ephyra.

ALTERNATE AND EQUIVOCAL REPRODUCTION. 165

Infusoria, passes in succession through all the phases we
have described. But the remarkable point in these meta-
morp. loses is, that what was at first a single individual is
thus transformed, by transverse division, into a number of
entirely distinct animals, which is not the case in ordinary
metamorphoses. Moreover, the upper segment does not
follow the others in their development. Its office seems to
be accomplished so soon as the other segments begin to be
independent, being intended merely to favor their develop-
ment, by securing and preparing the substances necessary
to their growth. In this respect, it resembles the nurse of
the Cercaria.

348. The Hydroid 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 extremity of

the branches, (a,) and which appear first,
are furnished with long tentacles, where-
with they seize their food, (Fig. 143.)
Those in the axils of the branches, and
which appear late, are females, (£,) and
have no such tentacles. Inside of the lat-
ter, little spherical bodies are found, each
having several spots in the middle ; these
are the eggs. Finally, there is a third
form, different from the two preceding,
produced by budding from the female polyp, to which it in
some sort belongs, (c.) It is within this that the eggs ar-
rive, 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.

349. Tr.3 little animal, on becoming free, has not the

166 REPRODUCTION.

slightest resemolaiue .o the adult polyp. As in the yc jng
Medusa, the body is cylindrical, covered with
delicate cilia. After having remained free for
some time, the young animal fixes itself and as-
sumes a flattened form. By degrees, a little swell-
ing rises from the centre, which elongates, and at
last forms a stalk. This stalk ramifies, and we
Fig. 144. soon recognize in it the animal of figure 143,
with the three kinds of buds, which we may
consider as three distinct forms of the same animal.

350. The development of Campanularia presents, in
some respects, an analogy to what takes place in the re-
p reduction of plants, and especially of trees. They should
be considered as groups of individuals, and not as single
individuals. The seed, which corresponds to the embryo
of the Hydroid, puts forth a little stalk. This stalk soon
ramifies by gemmiparous reproduction, that is, by throwing
out buds which become branches. But ovulation, or repro-
duction by means of seeds, does not take place until an ad-
vanced 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 com-
monly united in one flower, but which in some instances are
separated, as in the hickories, the elders, the willows, &c.*

* Several plants are endowed with organs similar to the third form of
buds, as seen in the Campanularia ; for example, the liverwort, (Marchan-
tia polymorpha,) which has at the base of the cup a little receptacle, from
the bottom of which little disk-like bodies are constantly forming, which,
when detached, send out roots, and gradually become complete individu-
als. Besides that, we find in these animals, as in plants, the important
peculiarity, that all the individuals are united in a common 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 reproduction has been
observed, we find that the progress displayed in each type consists pre-
cisely in the ir creasing freedom of the individual in its various forms. At

CONSEQtfLNCES OF ALTERNATE GENERATION 167

SECTION III.

OONSEQTENCES OF ALTERNATE GENERATION.

351. These various examples of alternate generation ren-
der it evident, that this phenomenon ought not to be consid-
ered as an anomaly in Nature ; but as the special plarrof de-
velopment, 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 inverte-
bratH animals ; while among the Vertebrates it is as yet
unknown. It would seem that individual life in the lowei
animals is not defined within so precise limits as in the
higher types ; owing, perhaps, to the greater uniformity and
independence of their constituent 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 metamorphoses, which are
a sort of second birth.

352. Many analogies may be discovered between alternate
reproduction and metamorphosis. They are parallel lines
that lead to the same end, namely, the development of the
species. Nor is it rare to see them coexisting in the same

first, we have all the generations united in a common trunk, as in the
lower Polyps and in plants; then in the Medusae and in some of the
Hydroid Polyps the third generation begins to disengage itself. Among
some of the intestinal worms, (the Distoma,) 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 generations, the
nuises as well as the perfect animals, are separate individuals.

168 REPRODUCTION.

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.

353. 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 pro-
duces the Cercaria is manifestly an inferior state, just as the
chrysalis is inferior to the butterfly.

354. But there is this essential difference between the
metamorphoses 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.

355. It follows, therefore, that the general practice of de-
riving 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, en-
dowed 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 Infusoria, 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

CONSEQUENCES OF ALTERNATE GENERAnrN. 169

separate individuals, the grand-nurse, the nurse, the larva or
Cercaria, and the Distoma, in which the sexes are not sepa-
rate. Among the Aphides, the number is much greater
still.

356. The study of alternate generation, besides making
us better acquainted with the organization of the lower ani-
mals, greatly simplifies our nomenclature. Thus, in future,
instead of enumerating the Distoma and the Cercaria, or the
Strobila, *he Ephyra, and the Medusa, as distinct animals,
belonging to different 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.

357. Alternate generation always presupposes several
modes of reproduction, of which the primary is invariably
by ovulation. Thus, we have seen that the Polyps, the
Medusa, the Salpa, &c., produce eggs, which are generally-
hatched within the mother. The subsequent generation, on
the contrary, is produced in a different manner, as we have
shown in the preceding paragraphs ; as among the Medusae,
by transverse division ; among the Polyps and Salpae, by
buds, &c.

358. 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 development,
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 sthe Campanularia,
are barren, and have none of the attributes of maternity,
except that of watching over the development of the species,
being themselves incapable of producing young.

359. Another important result follows from the above ob-
servations namely, that the differences between animals
which are produced by alternate generation are less, the

15

170 REPROIUCTION.

earlier the epoch at which we examine them. No two ani
mals can be more unlike than an adult Medusa (Fig. 31
and an adult Campanularia, (Fig. 143;) they even seem to
belong to different classes of the Animal Kingdom, the for-
mer being considered as an Acaleph, the latter as 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 depart-
ment, have nearly the same form, at one'period of their life.
Farther still, this resemblance extends to plants. The
spores of certain sea-weeds have nearly the same appear-
ance as the young Polyp, or, the young Medusa; and what
is yet more remarkable, 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 for only a short
time ; soon it becomes fixed, and from that moment the
resemblance ceases.

360. 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, bo-
cause their germs are similar? On the contrary, we thinK
nothing is better calculated to strengthen the idea of the
original separation of the various groups, as distinct and
independent types, than the study of their different phases.
In fact, a difference 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

CONSEQUENCES OF ALTERNATE GENERATIC N. 171

deny the realty of natural groups, because of these early
resemblances, would be to take the semblance for the
reality. It would be the same as saying that the frog and
the fish are one, because at one stage of embryonic life it is
impossible, with the means at our command, to distinguish
them.

361. The account we have above given 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 occur-
rence mysterious. We need only to recollect how the
Cercaria insinuates itself into the

skin and the viscera of mollusks,
(339, 342,) to understand how
admission may be gained to the
most inaccessible, parts. Such be-
ings occur even in the eye of many Fig. 145. Fig. 14b.
animals, especially of fishes ; they

are numerous in the eye of the common fresh-water perch
of Europe. To the naked eye they seem like little white
spots, (Fig, 145;) but when magnified, they have the form
of Fig. 146.

362. 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 tlveir
history. At certain periods of the year, the Sculpins of the
Baltic are infested by a particular species of Taenia or tape-
worm, from which they are free at other seasons. Mr. Esch-
richt found that, at certain seasons, the worms lose a great
portion of the long chain of rings of which they are com-
posed. On a careful examination, he found that earh ring

172 REPRODUCTION.

contained several hundred eggs, which, on heing freed from
their envelop, float in the water. As these eggs are innu-
merable, it is not astonishing that the Sculpins should occa-
sionally swallow some of them with their prey. The eggs,
being thus introduced into the stomach of the fish, find con-
ditions favorable 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
s-.vallowed are probably lost.

363. All animals swallow, in the same manner, with their
food, and in the water they drink, numerous eggs of such
parasites, any one of which, finding in the intestine of the
animal favorable conditions, may be hatched. It is probable
that each animal affords the proper conditions for some par-
ticular species of worm ; and thus we may explain how it is
that most animals have parasites peculiar to themselves.

364. As respects the Infusoria, we also know that most
of them, the Rotifera especially, lay eggs. These eggs,
which are extremely minute, (some of them only -rs^iny °f
an inch in diameter,) are scattered every where 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.

365. This being the case, it is much more natural to
suppose that the Infusoria * are products of like germs, than

* In this connection, it ought to he 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 refeired to the Vegetable Kingdom.

SPONTANEOUS GENERATION. 173

.o assign to them a spontaneous origin altogether incompati-
ole with what we know of organic development. Their
rapid appearance is not at all astonishing, when we reflect
ihat 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
generation among the lower animals, no substantial difficul-
ties to the ax'om " omne vivum sx ovo" (275,) any longer

exist.

15*

CHAPTER TWELFTH.

METAMORP IOSES OF ANIMALS.

366. UNDER the name of metamorphoses are included
lliose changes which the body of an animal undergoes after
its birth, and which are modifications, in various degrees, of
»ts organization, form, and its mode of life. Such changes
are not peculiar to certain classes, as has been so long sup-
posed, but are common to all animals, without exception.

367. Vegetables also undergo metamorphoses, but with
this essential difference, that in vegetables the process con-
sists 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 woody layers to the trunk. In animals, the
whole 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 be-
comes an air-breathing animal ; its tail and the gills disap-
pear; lungs and legs are being developed, and, finally, it is
to live and move on land.

368 The nature, the duration, and importance of meta-
morphoses, as also the epoch at which they take place, are
infinitely varied. The most striking changes which naturally
present themselves to the mind when we speak of metamoi

METAMORPHOSES OF ANIMALS. 175

phoses, 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 modified.
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 air-tubes, and breathes in the atmosphere. It passes by,
with indifference, objects which before were attractive, and
its new instincts prompt it to seek conditions which would
have been most pernicious 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.

369. 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
!t ceases to feed, spins its silken cocoon, casts its skin, and
remains enclosed in its chrysalis state.* During this period
of its existence, most extraordinary changes take place. The
jaws with which it masticated mulberry leaves are trans-
formed into a coiled tongue ; the spinning organs are reduced t
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 elon-
gated and narrow. The dorsal vessel is shortened. The
ganglions of the thoracic region approach each other, and
unite into a single mass. Antennas and palpi are developed on
the head, and instead of simple eyes appear compound ones.

* In the raising of silk-worms this period is not waited for, but «he ani
mal is killed as soon as it has spun its cocoon.

176 METAMORPHOSES OF AN1MAL3.

The muscles, which before were uniformly distributed, (159,)
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, burst-
ing the envelop of its chrysalis, issues in the form of a winged
moth.

370 The different external forms which an insect may
assume is well illustrated by one which is unfortunately too
well known in this country, namely, the canker-worm. Its
eggs are laid on posts and fences, or upon the branches of our
apple-trees, elms, and other trees. They are hatched about
the time the tender leaves of these trees begin to unfold.
0-6 o d

r

Fig. 147.

The caterpillar (a) 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 en-
ters the earth to the depth of four or five inches, and having
excavated a sort of cell, is soon changed into a chrysalis or
nymph, (b.) 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.

371. Tiansformations no less remarkable are observed
among the Crustacea. The metamorphoses in the family of
Cirrhipedes are especially striking. It is now known that
the barnacles, vBalanus,) which have been arranged among
the mollusks, are truly crustaceans ; and this result of modern
researches has been deduced in the clearest manner from the

METAMORPHOSES OF ANIMALS.

m

study of their transformations. The following figures repre-
sent the different phases of the duck-barnacle, (Anatifa.)

a b e

Fig. 148.

372. The Anatifa, like all Crustacea, is reproduced by
eggs, specimens of which, magnified ninety diameters, are
represented in figure 148, a. From these eggs little ani-
mals issue, which have not the slightest resemblance to the
parent. They have an elongated form, (ft,) a pair of ten-
acles, and four legs, with which they swim freely in the
water.

373. Their freedom, however, is of but short duration.
The little animal soon attaches itself by means of its tenta-
cles, having previously become covered with a transparent
shell, through which the outlines of the body, and also a very
distinct eye, are easily distinguished, (Fig. 148, c.) Figure
148, d, shows the animal taken out of its shell. It is plainly
seen that the anterior portion has become considerably en-
larged. Subsequently, the shell becomes completed, and
the animal casts its skin, losing with it both its eyes and its
tentacles. On the other hand, a thick membrane lines the
interior of the shell, which 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, ana the animal soon acquires a definite shape, such

178 METAMORPHOSES OF ANIMALS.

as it is rep escnted in figure 148, /, attached to a piece of
floating wood

374. There is, consequently, not only a change of organi-
zation in the course of the metamorphoses, but also a change
of faculties and mode of life. The animal, at first free,
becomes fixed ; and its adhesion is effected by totally
different organs at different periods of life, first by means of
centacles, which were temporary organs, and afterwards
by means of a fleshy stem developed especial.y for that
purpose.

375. The Radiata also furnish us with examples of vari-
ous metamorphoses, especially among the star-fishes. A
small species living on the coast of New England (EcM~
naster sanguinolentus) undergoes the following phases,
(Fig. 149.)

Fig. 149.

376. If the eggs are examined by the microscope, each
one is found to contain a small, pear-shaped body, which
is the embryo, (e,) surrounded by a transparent envelop.
On escaping 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 disk also assumes a pen-
tagonal 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.)

METAMORPHOSES OF ANIMALS.

179

Fig. 151.

377. Analogous transformations take place in the Cc nat-

ula. In early life
(Fig. 150) it is
fixed to the ground
by a stem, but be-
comes detached at
a certain epoch,
and then floats
freely in the sea,
(Fig. 151.) On
the other hand,

the Polypi seem to follow a icverso
course, many of them becoming fixed to
the ground after having been previously
Fig. 150. free.

378. The metamorphoses of mollusks, though less
striking, are not less worthy of notice. Thus, the oyster,
with which we are familiar in its adhering shell, is free
when young, like the clam (Mya) and most other shell-
fishes. Others, which are at first attached or suspended to
the gills of the mother, afterwards become free, as the Unio.
Some naked Gasteropods, the Acteon or the Eolis, for ex-
ample, are born with a shell, which they part with shortly
after leaving the egg.

379. The study of metamorphoses is, therefore, of the
utmost importance for understanding the real affinities of
animals very different in appearance, as is readily shown by
(he 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 out
ward appearance. But, on comparing the caterpillar and
the worm, these two animals closely resemble each- other.
The analogy, however, is only transient; it lasts only
during the larva state of the caterpillar, and is effaced as it

180 METAMORPHOSES OF ANIMALS.

passes to the chrysalis and butterfly states. The latter be
comes a more and more perfect animal, whilst the worm
remains in its inferior state.

380. Similar instances are furnished by animals belong
ing to all the types of the Animal Kingdom. Who would
think, at first glance, that a Barnacle or an Anatifa were
more nearly allied to the crab than to the oyster? And,
nevertheless, we have seen, (372,) in tracing back the Anat-
ifa to its early stages, that it then bears a near resemblance
to a little Crustacean, (Fig. 148, d.) It is only when full
grown- that it assumes its peculiar mollusk-Iike covering.

381. Among the Cuttle-fishes there are several, the
Loligo, (Fig. 47,) 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 com-
pare the young, we find that in both animals the tentacles
are all equal, though they differ in number. The inequality
in the tentacles is the result of a further development.--

382. Among the Radiata, the Pentacrinus and the Comat-
ula exemplify the same point. The two are very different
when full grown, the latter being a free-swimming star-fish,
(Fig. 151,) while the former is attached to the soil, like a
Polyp. But we have seen (377) 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, a/id floats freely in the water.

383. In the type of Vertebrates, the considerations drawn
from metamorphoses acquire still greater importance in ref-
erence to classification. The Sturgeon and the White-fish,
before mentioned, (306,) 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

METAMORPHOSES OP ANIMALS. 181

resolved by an examination of their anatomical structure.
The White-fish has a skeleton, and, moreover, a vertebral
column, composed of firm bone. The Sturgeon, (Fig.152),

Fig. 152.

on the contrary, has no bone in the vertebral column, except
the spines or apophyses of the vertebra?. The middle part,
or body of the vertebra, is cartilaginous ; the mouth is trans-
verse, and underneath the head ; and the caudal fin is un-
equally forked, while in the White-fish it is equally forked.

384. If, however, we observe the young White-fish jusl
after it has issued from the egg, (Fig. 123,) the contrast will
be less striking. At this period the vertebrae are cartilagi-
nous, like those of the Sturgeon ; its mouth, also, is trans-
verse and inferior, and its tail undivided ; at that period the
White-fish and the Sturgeon are, therefore, much more alike.
But this similarity is only transient ; as the White-fish grows,
its vertebras become ossified, and its resemblance to the
Sturgeon is comparatively slight. As the Sturgeon has no
such transformation of the vertebras, 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 inferior in rank.

385. This relative inferiority and superiority strikes us
still more when we compare with our most perfect fishes
(the Salmon, the Cod) some of those worm-like animals, so
different from ordinary fishes that they were formerly placed
among the worms. The Am-

phioxus, represented of its nat-
ural size, (Fig. 153,) not only
16

182 METAMORPHOSES OF ANIMALS.

has no bony skeleton, but not even a head, properly spoak
ing. Yet. the fact that it possesses a dorsal cord, extending
from one extremity of the body to the other, proves that it
belongs to the type of Vertebrates. But as this peculiar
structure is found only at a very early period of embiyonic
development, in other fishes, we conclude that :he Amphi-
oxus holds the very lowest rank in this class.

386. 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 picvious
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 differ-
ent 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 metamorphoses which take place subse-
quently to birth in others.

387. We have already shown that embryonic develop-
ment consists in a series of transformations ; the young ani-
mal enclosed in the egg differing at each period of its de-
velopment, from what it. was before. But because these
transformations precede birth, and are, there fore, not generally
observed, they are not less important. To be satisfied that
these transformations are in every respect similar to those
which follow birth, we have only to compare the changes
which immediately precede birth with those which immediate-
ly follow it, and we shall readily perceire that the latter arc
simply a continuation of the former, till all are completed.

388. Let rs recur to the development of fishes for llus

METAMORPHOSES OF A.IIMALS. 183

trntion. The young White-fish, as we have seen, (315,) 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.

389. Similar inferences may be drawn from the develop-
ment of the chicken. 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. Thus we 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.

390. In certain Mammals, known under the name of
Marsupials, (the Opossum and Kangaroo,) the link between
the transformations which take place before birth, and those
that occur 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 remain,
each one fixed to a teat, until they are entirely developed.
Even those animals which are born nearest to the complete
state, undergo, nevertheless, embryonic transformations.
Ruminants acquire their horns; and the lion his mane. Mosi
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 aliments.

184 METAMORPHOSES OF ANIMALS.

391. 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 after-
wards, the circumstance that some precede and others
succeed birth cannot mark any radical distinction be-
tween them. Both are processes of the life of the indi-
vidual. Now, as life does not commence at birth, but
goes still farther back, it is quite clear that the modifi-
cations which supervene during the former period are
essentially the same as, and continuous with, the latei
ones ; and hence, that metamorphoses, far from being
exceptional i# the case of Insects, are one of the gen-
eral features of the Animal Kingdom.

392. 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 differ-
ences ; and that there should be, as in the class of Rep-
tiles, some families that undergo important metamor-
phoses, (the frogs, for example,) and others in which
nothing of the kind is observed after birth, (the Lizards
and Tortoises.)

393. It is only by connecting the two kinds of trans-
formations, namely, those which take place before, and
those after birth, that we -are furnished with the means
of ascertaining 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 will force upon us tne convic-
tion that there is an immutable principle presiding over
all these changes, and regulating them in a peculiar
manner in each animal.

394. These considerations are exceedingly impor-
tant, not only from their bearing upon classification,
but not less so from the application which may be
made of them to the study of fossils. If we exam-
ine attentively the fishes that have been found in
the different strata of the earth, we remark that

METAMORPHOSES OF ANIMALS. 185

those of the most ancient deposits have, in general, preserved
only the apophyses of their vertebra?, whilst the vertebrae
then selves are wanting. Were the Sturgeons of the Amer-
ican rivers to become petrified, they would be found in a
similar state of preservation. As the apophyses are the
only bony portions of the vertebral column, they alone
would be preserved. Indeed, fossil Sturgeons are known,
which are in precisely this condition.

395. 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 living ones, and will, probably, be
true of all classes of the Animal Kingdom, when fully studied
as to thsir geological succession.
16*

*"

CLAPTER THIRTEENTH.

GEOGRAPHICAL DISTRIBUTION OF ANIMALS
SECTION I.

GENERAL LAWS OF DISTRIBUTION.

396 No animal, excepting man, inhabits every part of the
surface of the earth. Each great geographical or climatal
region 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 acci-
dent 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 perfectibility of his social condition.

397. A group of animals which inhabits 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
families, genera, and species, and in the preponderance of
certain 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, alto

GENERAL LAWS OF DISTRIBUTION. 187

getlier peculiar, and not found on the nearest cont.nents.
There are numerous animals ,n 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 ocnclude that those regions
have the same Fauna, any more than that the Flora of Lap-
land and England are alike, because some of the sea-weeds
found on both their shores are the same.

398. 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 similffi
animals, (401, 402.) Hence the faunas of the two hemis-
pheres have been distributed into three principal divisions,
namely, the arctic, the temperate, and the tropical faunas ;
in the same manner as we have arctic, temperate, and tropi-
cal floras. Hence, also, animals dwelling at high elevations
upon mountains, where the temperature is much reduced
resemblWhe animals of colder latitudes, rather than those of
the surrounding plains.

399. In some -respects, the peculiarities of the fauna of a
region depend 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 limi-
tation of a fauna is less intimately dependent on climate
than that of a flpra. Plants, in truth, are for the most part
terrestrial, (marine plants being relatively very few,) wh:le
animals are chiefly aquatic. The ocean is the true home of
the Animal Kingdom ; and while plants, with the excep
tion 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 extreme limit of flower-
ing plants,

188 GEOGRAPHICAL DISTRIBUTION OF ANIMALS.

400. The influence of climate, in the colder regions, acvs
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 t.ie temperatg regions, on the contrary, the
species differ on each of the continents, but they still pre
serve the same general features. The types are the same
but they are represented by quite different species. In
consequence of these general resemblances, the first colo-
nists 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, the animals of temperate Asia differ more from those
of Europe than they do from those of America.

401. Under the torrid zone, the Animal Kingdom, as well
as the Vegetable, attains its highest development. The ani-
mals of the tropics are not only different from those of the
temperate zone, but, moreover, they present the greatest
variety among themselves. The most gracefully propor-
tioned forms are found by the side of the most grotesque,
decked with every combination of brilliant coloring. At the
same time, the contrast between the animals pf different con-
tinents 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.

402. This diversity upon different continents cannot de-
pend simply on any influence of the climate of the tropics

GENERAL LAWS OF «ISTRIBUTION. 189

if it were so uniformity ought to be restored in proportion
as we recedi from the tropics towards the antarctic tern
perate regions. But, instead of this, the differences con-
tinue to increase ; — so much so, that no faunas are more in
contrast than those of Cape Horn, the Cape of Good Hope,
and New Holland. Hence, other influences must be in oper-
ation besides those of climate; — influences of a highei
order, which are involved in a general plan, and intimately
associated with the development of life on the surface of the
earth.

403. 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 moun
tains, like the Rocky Mountains. Again, a desert may in-
tervene, like the desert of Sahara, which separates the fauna
of Central Africa from that of the Atlas and the Moorish
coast, the latter being merely an appendage to the fauna
of Europe. But the sea effects the most complete limita-
tion. 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 frcm 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 desert. Not only are no
materials found there for sustenance, but it is doubtful if ani-
mals could sustain the pressure of so great a column of
water, although many of them are provided with a system of
pores, (260,) which enables them to sustain a much g-eater
pressure than terrestrial animals.

404. When there is no great natural limit, the transition
from one fa ana to another is made insensibly. Thus, in
passing fronn he arctic to the temperate regions of North

190 GEOGRAPHICAL DISTR1BUT ON OF ANIMALS

America, one species takes th3 place of anott er, a third suc-
ceeds the second, and so on, until finally the fauna is found
to be completely changed, though it is not always possible
to mark the precise line which divides the one from the
other.

405. 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 the St. Lawrence 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, there is no
chance of its return to a former limitation, inasmuch as, being
fixed, and consequently unable to choose positions for its
eggs, they must be left to th^ 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.

406. 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 con-
fined in their range than herbivorous ones ; because their
food is almost every where to be found. The herbivora, on
the contrary, are restricted to the more limited regions
Co/responding to the different zones of vegetation. The
same remark may be made with respect to Birds. Birds of
prey, such as the eagle and vulture, have a mich wider range
than the granivorous and gallinaceous birds. Still, notwith-
standing the facilities they have for change of place, even
the birds tl at wander widest recognize limits which they do

GENERAL LAWS OF DISTRIBUTION. 191

not overstep. The Condor of the Cordilleras does not do
scend 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 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 piey.

407. 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
prairies of the West, the Pampas of South America, the
Steppes of Asia, the Deserts of Africa ; — and, for marine
an-mals, 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.

408. Finally, to obtain a true picture of the zoological
distribution of animals, not the terrestrial types alone, 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 defined than those of
the terrestrial faunas, 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, con-
fined to the vicinity of the shores, their distribution must be
subjected to laws similar to those which regulate the terres-
trial faunas. As to the fresh-water fishes, not only do the
species vary in the different zones, but even the different
rivers of the same region have species peculiar to them, and

192 GEOGRAPHICAL DISTRIBUTION OF ANIMALS.

not found in neighboring streams. The garpikes (Lepi-
dosteus) of the American riveVs afford a striking example ol
this kind.

409. A very influential cause in the distribution of aquatic
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
different zones at different elevations in ascending moun-
tains, (398.) 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 coloring, in particular, var es, ac-
cording to the quantity of light they receive, as has also
been shown to be the case with the marine plants.

410. 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, exclusive of the animals of the surrounding
country, merely because 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 exam-
p.e, is the fauna of the great steppe, or plain of Gobi, in
Asia ; and such indeed that of the chain of the Rocky Moun-
tains may prove to be, when the animals inhabiting them shall
bt- batter known.

GENERAL LAWS OF DISTRIBUTION. 193

411. 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
nabitual abode. As to Birds, which of all animals wander
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 belong to the temperate faunas, notwith-
standing their migration during winter to the confines of the
torrid zone. This rule does not apply to the fishes who an-
nually 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
coast of Maine and Nova Scotia.

412. 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,
after a very long journey, return again in Autumn to their
quarters, 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 of the Lemmings are marked by the devas-
tations they commit along their course, as they come down
from the borders of the Frozen Ocean to the valleys of
Lapland ard Norway ; but their migrations are not period*
ical.

17

194 GEOGRAPHICAL DISTRIBUTION 'oF ANIMALS.

SECTION II

DISTRIBUTION OF THE FA'JNAS

413. We have stated that all the faunas of the globe may
be divided into three groups, corresponding to as manygreal
climatal divisions, namely, the glacial or arctic, the temperate
and the tropical faunas. These three divisions appertain to
both hemispheres, as we recede from the equator towards 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.

414. No continent is better calculated to give a correc'
idea of distribution into faunas, as determined by climate
than the continent of America ; extending as it does across
both hemispheres, and embracing all latitudes, so that all
climates are represented upon it, as shown by the chart on the
following page.

415. 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 observation will be
very much as follows. Along the coast of Greenland and
Iceland, and also along Baffin's Bay, he will meet with an
unvaried fauna, 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.

416. 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

©

N.POLE

I.

II.
III.
IV.

V.
VI.

FAUNAS.

North Glacial or Arctic.
Northern Temperate.
Northern Warm.
Tropical.
Southern Warm.
Southern Temperate.

196 GEOGRAPHICAL DISTRIBUTION OF ANIMALS.

various animals which dwell only in forests. Here the tem-
perate fauna commences. Still the number of species is not
5Tet very considerable ; but as he 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 a* length entirely disappear, some few acci-
dental or periodical visitors excepted, who wander, during
winter, as far south as the Carolinas.

417. 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 which people the for-
ests, the prairies, the rivers, and .the sea-shores, most of which
he will also find to be different from those of the northern
continent. By this extraordinary richness of new forms, he
will become sensible that he is now in the domain of the
tropical fauna.

418. 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 animals will be less varied, and the whole picture will
recall to him, in some measure, what 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 ex-
tremity of the continent, the fauna and the flora becoming
more and more impoverished as he approaches Cape Horn.

419. Finally, we know that there is a continent around
the South Pole. Although we have as yet but very imper-
fect notions respecting the animals of this inhospitable clime
still, the few which have already been observed there present

DISTRIBUTION OF THE FAUNAS. 197

a close analogy to those of the arctic region. It is another
glacial fauna, namely, the antarctic. Having thus sketched
the general divisions of the faunas, it remains to point out
the principal features of each of them.

420. I. ARCTIC FAUNA. — The predominant feature of the
Arctic Fauna is its uniformity. The species are few in num-
ber ; but, on the other hand, the number of individuals is
immense. We need only refer to the clouds of birds which
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 great
uniformity, also, in the form and color 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, gan-
nets, &c., all belonging to the lowest orders of Birds. Rep-
tiles are altogether wanting. The Articulata are represented
by numerous marine worms, and by minute crustaceans of
the orders Isopoda and Amphipoda. Insects are rare, and
of inferior types. Of the type of Mollusks, 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 con-
clude with the Echinoderms, there are several star-fishes
and Echini, but few Holothurise. The class of Polypi is
very scantily represented, and those producing stony corals
are entirely wan ing.

198 GEOGBAPHICAL DISTRIBUTION OF ANIMALS.

421. 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.

422. It has already been said, (400,) 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 numer-
ous 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
and animals. On the North American continent it extends
much farther southward on the eastern shore than on the
western. From the peninsula of Alashka, it bends north-
wards towards the Mackenzie, then descends again towards
the Bear Lake, arid comes down nearly to the northern shore
of Newfoundland.

423. II. TEMPERATE FAUNAS. — The faunas of the tern-
pei ate 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 colors, though less brilliant than those found in
tropical regions. Those parts of the country covered with
forests especially swarm with insects, which become the food
of other animrls ; worms and terrestrial and flip-iadle mol-

usks are also ibundant.

DISTRIBUTION OF THE FAUNAS. 199

424. 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
approach of the cold season, and vegetation is arrested for a
lunger or shorter period. Insects retire, and the animals
which live upon them no longer find nourishment, and are
ohliged to migrate to warmer regions, on the borders of the
tropics, where, amid the ever-verdant vegetation, they find
fbe means of subsistence.

425. 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
during the warm season. The Carnivora, the Ruminants,
and the most active portion of the Rodents, are the only ani-
mals 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.

426. Taking the contrast of the vegetation as a basis, and
the consequent changes of habit imposed upon the denizens
of the forests, the temperate fauna has been divided into
two 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 the deciduous trees, coincides, in general, with the limit
of the pines, it may be said that the cold region of the tem-
perate fauna extends as far as the pines. In the United
States this coincidence is not 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 consider as belonging to the southern portion

200 GEOGRAPHICAL DISTRIBUTION OF ANIMALS.

of the temperate region that part of the country south of
the la itude where the Palmetto'or Cabbage-tree (Chanuzrops)
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.

427. 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 demarkation above mentioned,
namely, at Cape Hatteras. It has been observed that of
one hundred and ninety-seven Mollusks inhabiting the coast
of 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-
four being common to both sides of the Cape. A similar
limitation of the range of Fishes has been noticed by Dr.
Storer ; and Dr. Holbrook has found the Fishes of South
Carolina to be different from those of Florida and the West
Indies. In Europe, the northern part of the temperate re-
gion extends to the Pyrenees and the Alps ; and its south-
ern portion consists of the basin of the Mediterranean, to-
gether with the northern part of Africa, as far as the desert
of Sahara.

428. 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 5m-
liiense extent of country embraced, the same stamp is every
where exhibited. Generally, the same families, frequently
chs same genera, represented by different species, are
found. There are even a few species of terrestrial animals
regarded as identical on the continents of Europe and

DISTRIBUTION OF THE FAUNAS. 201

America ; but their supposed number is constantly dimin-
ished, as more accurate observations are made. The pre-
dominant types among the mammals are the bison, deer, ox
horse, hog, numerous rodents, especially squirrels and hares,
nearly all the insectivora, weasels, martens, wolves, foxes.,
wildcats, &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 birds. Of Reptiles, there are lizards and
tortoises of small or medium size, serpents, and many ba-
trachians, but no crocodiles. Of fishes, there is the trout
family, the cyprinoids, the sturgeons, the pikes, the cod, and
especially the great family of Herrings and Scomberoids, to
which latter belong the mackerel and the tunny. All classes
of the Mollusks are represented ; though the cephalopods are
less numerous than in the torrid zone. There is an infinite
number of Articulata of every type, as well as numerous
Polyps, though the corals proper do not yet appear abun-
Jantly.

429. On each of the two continents of Europe and Amer-
ica there is a certain number of species, which extend from
one extreme of the temperate zone to the other. Such, for
example, are the deer, the bison, the cougar, the flying-squir-
rel, 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 Behr-
ing'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 muskrat,
which is found from the mouth of Mackenzie's River to
Florid i. The field-mouse has an equal range in Europe,
Other species, on the contrary, are limited to one region

202 GEOGRAPHICAL DISTRIBUTION OF ANIMALS.

The Canadian elk is confined to the northern portion of the
fauna ; while the prairie wolf, the fox-squirrel, the Bassaris,
and numerous birds, never leave the southern portion.*

430. 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
(hose in the others, though very closely allied. 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 furcifer,}
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 dis-
tinct species.

431. The faunas or zoological provinces of the Old World
which correspond to these are :

* 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, (Gondylura
cristata,) which replaces the Mygale of the Old World ; several genera
of rodents, especially the muskrat. Among the types characteristic of
America must also be reckoned the snapping-turtle among the tortoises ;
the Menobranchus and Menopoma, among the Salamanders ; the Gar-
pike and Amia among the fishes ; and finally, among the Crustacea, the
Limulus 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 which live in America
have been br )ught from the Old World

DISTRIBUTION OF THE FAUNAS. 203

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 fajna 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 i* the Reptiles — as it it also in the flora.

Lastly, it is in the temperate zone of the northern hemi-
sphere that we meet with the most striking example 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.

432. The faunas of the southern temperate regions differ
from those of the tropics as much as the northern temperate
fauna? 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
contrasts. Each of the three continental peninsulas which
jut 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 and fishes, insects
and mo.iusks. Among the most characteristic animals of
the south irn extremity of America are peculiar species of
seals and especially, among aquatic birds, the penguins.

204 GEOGRAPHICAL DISTRIBUTION OF ANIMALS.

433. New Holland, with its marsupial mammals, with
which are associated insects and mollusks no less singulai
furnishes a fauna still more peculiar, and which has no sinri
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
prevail over the whole continent, in its temperate as well as
its tropical portions, the species only being different at dif-
ferent localities.

434. 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 rep-
resented, and all contain numerous genera and species.
We need only refer to the tribe of humming-birds, which
numbers not less than 300 species. It is very important to
notice, that here are concentrated the most perfect, as well
as the oddest, types of all the classes of the Animal King-
dom. The tropical region is the only one occupied by the
Quadrumana, the herbivorous bats, the great 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 essentially
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
marine animals, as a whole, are equally superior to those of
other regions ; the seas teem with crustaceans and numerous
cephalopods, together with an infinite variety of gasteropods
and acephala. The Echinoderms there attain a magnitude

DISTRIBUTION OF THE FAUNAS. 205

and variety elsewhere unknown ; and lastly, the Po'yps there
display an activity of which the other zones present no ex-
ample. Whole groups of islands are surrounded with coral
reefs formed by those little animals.

435. 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, ac-
cording as they are found on different continents. Thus,
the monkeys of America have flat and widely separated
nostrils, 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.

436. But these differences, however important they may
appear at first glance, are subordinate to more important
characters, 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^ a natural con-
sequence of the distribution of the palms ; for as these trees,
which constitute 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.

437. Several well-marked faunas may be distinguished in
the tropical part of the American continent, namely :

1. The fauna of Brazil, characterized by its gigantic rep-
tiles, its monkeys, its Edentata, its tapir, its humming-buds,
and its astonishing variety of insects.
18

206 GEOGRAPHICAL DISTRIBUTION OF ANIMALS.

2. The fauna of the western slope of the Andes, com-
prising Chili and Peru ; and distinguished by its Llamas,
vicunas, and birds, which differ from those of the basin of
the Amazon, as also do the insects and mollusks.

3. The fauna of the Antilles and the Gulf of Mexido.
This is especially characterized by its marine animals, among
which the Manatee is particularly remarkable ; an infinite
variety of singular fishes, embracing a large number of
Plectognaths ; also Mollusks, and Radiata of peculiar species.
[t is in this zone that the Pentacrinus caput-medusa is found,
the only representative, in the existing creation, of a family so
numerous in ancient epochs, the Crinoidea with a jointed stem.

The limits of the fauna of Central America cannot yet be
well defined, from want of sufficient knowledge of the ani-
mals which inhabit those regions.

438. The tropical zone of Africa is distinguished by a
striking uniformity in the distribution of the animals, which
corresponds 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
hippopotamus 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 conditions of vegetation very similar, over wide
countries. Some 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 elephant, the crocodile of the
Nile, a vast number of Antelopes, and especially two species
of Orang-outang, the Chimpanzee and the Engeena, a large
and remarkable animal, only recently described. The fishes
of the N'le have a tropical character, as well as the animals

CONCLUSIONS. 207

of Arabia, which are more allied to those of Africa tl \n tc
those of Asia.

439. The tropical fauna of Asia, comprising the two
peninsulas of India and the Isles of Sunda, is not less marked.
It is the country of the gibbons, the red orang, the royal
tiger, the gavial, and a multitude of peculiar birds. Among
the fishes, the family of Chetodons is most numerously
represented. 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 mol-
lusks are no less strongly characterized. Among others is
the nautilus, the only living representative of the great fam-
ily of large, chambered-shells which prevailed so extensively
over other types, in former geological ages.

440. The large Island of Madagascar has its peculiai
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 particularly characteristic.

SECTION III

CONCLUSIONS.

441. From the survey we have thus made of the clistribu
ti jn 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 animal? constitute the faunas of different regions.

208 GEOGRAPHICAL DISTRIBUTION OF ANIMALS.

2d. The diversity of faunas is not in proportion to the
distan :e 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 arc
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
temperate and polar regions.

4th. There is a no less striking relation between the fauna
and flora, the limit of the former being oftentimes deter-
mined, so far as terrestrial animals are concerned, by the
extent of the latter.

442. 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 mon-
key would perish with hunger in the polar regions. Animals
which store up provisions are all peculiar to temperate or coM
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.

443. However intimately the climate of a country seems to
be allied with the peculiar character of its fauna, we are not
to conclude that the one is the consequence of the other
Tho differences which are observed between the animals of

CONCLUSIONS. 209

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 necessa-
rily find all animals precisely similar, when placed under
the same circumstances. 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 iden-
tity ; and the particulars in which they differ, though ap-
parently trifling, are yet constant.

444. 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 exam-
ination, that there is the closest resemblance between spe-
cies that dwell far apart from each other, while species of
the same genus, that live side by side, are widely different.
This may be illustrated by a single example. The Menopo-
ma, 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 legs, while others are only provided
with two ; and also in having either two or four legs.
Hence we might be tempted to refer them to different types,
did we not know intermediate animals, completing the series,
namely, the Proteus and Megalobatrachus. Now, the for-
mer exists only in the subterranean lakes of Austria, and
the latter in Japan. The connection in this case is conse-
quently established by means of species which inhabit con-
tinents widely distant from each other.

445. Neither the distribution of animals, therefore, any
more than their organization, can be the effect of external

18 •

210 3EOGRAPHICAL DIS~RIBUTION OF ANIMALS.

influences. We must, on the contrary, see in it the reahza
tion of a plan wisely designed, the work of a Supreme Intel
ligence who created, at the beginning, each species of am«
mal at the place, and for the place, which it inhabits. To
each species has been assigned a limit which it has no dis-
position to overstep, so long as it remains in a wild state.
Only those animals which have been subjected to the yoke
of man, Dr whose subsistence is dependent on man's social
habits, are exceptions to this rule.

446. As the human race has extended over the surface
of the earth, man has more or less modified the animal popu-
lation of different regions, either by exterminating certain
species, 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 Ameri-
ca 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 welcome animals have followed man in his pere-
grinations ; 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.

447. Among the species which have disappeared, under
the influence of man, we may mention the Dodo, a pecu-
liar species of bird which once inhabited the Mauritius,
some remains of which are preserved in the British and
Ashmolean Museums ; also a large cetacean of the north,
(Rytina Stelleri,) formerly inhabiting the coasts of Behring's
Straits, aid which has not been seen since 1768. Ac-cord-
ing to al] appearances, we must also count among these the

CONCLUSIONS. 211

great stag, the skeleton and horns of which have been found
buried in the peat-bogs of Ireland. There are also manj
species of animals whose numbers are daily diminishing,
and whose extinction may be foreseen ; as the Canada deer
( Wapiti,) the Ibex of the Alps, the Lammergeyer, the
bison, the beaver, the wild turkey, &c.

448, 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
vhe 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 larva? of
insects, and may, probably, serve as depositories for the eggs
of fishes, Crustacea, and mollusks. It is possible, also, that
aquatic birds may contribute in some measure to the diffu-
sion of some species of fishes and mollusks, either by the
eggs becoming attached to their feet, or by means of those
which they evacuate undigested, after having transported
them to considerable distances. Still, all these circum-
stances exercise but a very feeble influence upon the dis-
tribution of species in general ; and each country, none the
less, preserves its peculiar physiognomy, so far as its animals
are concerned.

449. There is only one way to account for the distribu-
tion of animals as we find them, namely, to suppose that
they are autochthonal, 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 o ' the same zone ; an inference which we
must make from The distribution of aquatic animals, especial-
ly that of Fishes. If we examine the fishes of ihe different

212 GEOGRAPHICAL DISTRIBUTION OF ANIMALS.

rivers of the United States, peculiar species will be fo jnd in
each basin, associated with others which are con.mon to
several basins. Thus, the Delaware River contains species
not found in the Hudson. But, on the other hand, the pick-
erel 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 versa, which it
could only have done by passing along the sea-shore, or by
.eaping over large spaces of terra Jirma ; that is to say> in
both cases it would be necessary to do violence to its organi-
zation. Now, such a supposition is in direct opposition to
the immutability of the laws of Nature.

450. 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.

451. 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 recognized ; 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, corresponding to the arctic fauna, (400,) and,
like it, identical on the three continents, having for its
southern limit the region of trees, (422.) In Africa, we
have the Hottentot and Negro races, in the south and central
portions respectively, while the people of northern Africa
are a lied to their neighbors in Europe; just as we have
seen to be the case with the zoological fauna in general

CONCLUSIONS 213

(403.) The inhabitants of New Holland, like its animals
are the most grotesque and uncouth of all races, (433.)

452. 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
decided. 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 dif-
ferences. • It could not indeed be expected, that a people
constantly subjected to cold, like the people of the North,
and living almost exclusively on fish, which is not to be
obtained without great toil and peril, should present the same
characteristics, either bodily or menta , as. those who idly
regale on the spontane >us bounties of tropical vegetation

CHAPTER FOURTEENTH

GEOLOGICAL SUCCESSION OF ANIMALS; OR, THEIR
DISTRIBUTION IN TIME.

SECTION L

STRUCTURE OF THE EARTH'S CRUST,

453. 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.

454. But man and the animals which now surround him
are not the only kinds which have had a being. The sur-
face of our planet, anterior to their appearance, was not a
desert. Tnere 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.

455. In general, their hard parts are the only relics of
them which have been preserved, such as the skeleton and
teeth of Vertebrates ; the shells of the Mollusks and Radiata ;
the shields of the Crustaceans, and sometimes the wing-cases
of Insects. Most frequently they have lost their original

STETTCTURE OF THE EARTHS CRUST. 215

chemical composition, and are changed into stone ; and
hence the name of petrifactions or fossils, under which lat-
ter term are comprehended all the organized oodles of
former epochs, obtained from the earth's crust. Others have
entirely disappeared, leaving only their forms ai d sculpture
impressed upon the rocks.

456. The study of these remains and of their position in
the rocks constitutes PALEONTOLOGY ; 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
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 stu-
pendous length of time they have required, it is necessary to
sketch the principal outlines of Geology.

457. The rocks* which compose the crust of our globe
are of two kinds :

1. The Massive Rocks, 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.

458. 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

* Rocks, in a geological sense, include all the materials of the earth.
the loose soil and gravel, as well as the firm rock.

216 GEOLOGICAL SUCCESSION OF ANIMALS.

layers or strata, have become, as they hardened, limestones,
slates, marls, or grits, according to their chemical and me-
chanical composition, and contain the remains of the animals
and plants \vhich were scattered through the waters.*

459. The different strata, when undisturbed, are arranged
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 undergone,
the strata have been ruptured, and many points of the surface
have been elevated to great heights, in the form of moun-
tains ; and hence it is that fossils are sometimes found at the
summit of the highest mountains, though the rocks contain-
ing 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 upturned strata, where they appear or crop out in suc-
cession, at the surface, or on the slopes of mountains, as seen
in the diagram, (Fig. 154.)

460. The sedimentary rocks are the only ones which have
been found to contain 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 com-
parison and detailed study of them belongs to Geology, of

* 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. 154,
AT,) being probably sedimentary rocks, which have undergone consider-
able changes. The Plutonic rocks, as well as the metamorphic rocks,
are not always confined to the lower levels, but they are often seen rising
to considerable heights, and forming many 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
Jo at the present era, (Fig. 154, T. L.)

STRUCTURE OF THE EARTH'S CRUST.

211

w.iich Paleontology forms an essential part. A group of
strata extending over a certain geographical extent, all of
which contain some fossils in common, no matter what may
be the chemical character of the rock, whether it be lime-
stone, sand, or clay, is termed a geological Formation. Thus,
the coal beds, with the intervening slates and grits, and the
masses of limestone, between which they often lie, constitute
but one formation — the carboniferous formation.

461. Among the stratified rocks we distinguish ten prin-
cipal Formations, each of which indicates an entirely new
era in the earth's history ; while each of the layers which
compose a formation indicates but some partial revolution.
Proceeding from below upwards^ they are as follows, as
indicated in the cut, and also in the lower diagram on the
Frontispiece.

Fig. 15*.

l*t The Lower Silurian. This is a most extensive for-
mation, no less than eight stages of which have been made
out by Geologists in North America, composed of various
limestones and sandstones.*

* 1. Potsdam Sandstone ; 2. Calciferous 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.

19

218 GEOLOGICAL SUCCESSION Ol ANIMALS.

2d. The Upper Silurian. It is also a very extensive for-
mation, since about ten stages of it are foui-d in the State of
New York.*

3d. The Devonian, including in North America no less
than eleven stages.t It occurs also in Russia and Scotland,
where it was first made out as a peculiar formation.

4th. The Carboniferous Formation, consisting of three
grand divisions. J

5th. The Trias, or Saliferous Formation, which, contain-
ing the richest deposits of Salt on the continent of Europe,
comprises three stages,^ to one of which the Sandstone of
the Connecticut valley belongs.

6th. The Oolitic Formation, only faint traces of which
exist on the continent of America. It comprises at least four
distinct stages. ||

7th. The Cretaceous, or Chalk Formation, of which three
principal stages have been recognized, two of which are
feebl) represented in this country, in the Southern and Mid-
dle States.

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.

* 1. Onei da Conglomerate; 2. Medina Sandstone; 3. Clinton Group;
4. Niagara Group ; 5. Onondaga Salt Group ; 6. Wuter Limestone ;
7. Pentamerus Limestone ; 8. Delthyris Shaly Limestone ; 9. EncrinaJ
Limestone ; 10. Upper Pentamerus Limestone.

•f 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.

J 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.

|| 1. The Lias ; 2. The Lower Oolite ; 3. The Middle Oolite ; 4 The
Upper Oolite

bTRUCTURE OF THE EARTH'S CRUST. 219

9tli. The Upper Tertiary, or Miocene and
found also in the United States, as far north as Martha s
Vineyard and Nantucket, and very extensive in Southerr.
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
history, indicating a more or less extensive and important
change in the condition of its surface.

462. All the formations are not every where 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 easy to under-
stand how 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 sediment 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 towards 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.

(EC LOGICAL SUCCESSION OF ANIMALS

463. 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 and
died, not scattered at random, though sometimes mingled to-
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.

464. In most geological formations, the number of spe-
cies 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 limestone in the neighborhood of Paris,
which is only one stage of the lower tertiary, contains not
less than 1200 species of shells ; whereas the species now
living in the Mediterranean do not amount to half that num-
ber. Similar relations may be pointed out in America.
Mr. Hall, one of the geologists of the New York Survey, has
described, from the Trenton limestone, (one of the ten stages
of the lower Silurian,) 170 species of shells, a number almost
equal tD that of all the species found now living on the coast
of Massachusetts.

465. Nor was the number of individuals less than at
present. Whole rocks are entirely formed of animal re-
mains, particularly of corals and shells. So, also, coal is
compos 3d of the remains of plants. If we consider the slow

OF NATURE. 221

ness with wl ich corals and shells are formed, it will give us
some fa nt 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 thick-
ness. 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.

466. 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 low-
est grade, such as the Polyps, the Echinoderms, to which
succeeded the Mollusks, then the Articulated Animals, and,
last of all, the Vertebrates. This theory, however, is now
untenable ; since fossils belonging to each of the four depart
ments have been found in the fossiliferous deposits of every
age. Indeed, we shall see that even in the lower Silurian
formation there exist not only Polyps and other Radiata, but
also numerous Mollusks, Trilobites, (belonging to the Articu-
lata,) and even Fishes.

SECTION II.

AGES OF NATURE.

467. Each formation, as has been before stated, (460,)
contains remains peculiar to itself, which do not extend into
the neighboring deposits above or below it. •Still there is u
connection between the different formations, more strong in
proportion to their proximity to each other. Thus, the ani-
mal remains of the Chalk, while they differ from those of all
other formations, are, nevertheless, much more nearly related
19*

222 GEOLOGICAL SUCCESS ON OF ANIMALS

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.

468. 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 surface
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 condi-
tion, and illustrated by contemporaneous monuments, so, in
the history of the earth, also, are distinguished several great
periods, which may be designated as the various Ages of
Nature, illustrated, in like manner, by their monuments, the
fossil remains, which, by certain general, traits stamped upon
them, clearly indicate the eras to which they belong.

469. We distinguish four Ages of Nature, corresponding
to the great geological divisions, namely :

1st. The Primary or Palceozoic Age, comprising the lower
Silurian, the upper Silurian, and the Devonian. During this
age there were no 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 for-
mation, the Trias, the Oolitic, and the Cretaceous formations.
This is the epoch in which air-breathing animals first appear.
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.

4th. The Modern Age, characterized by the appearance
of the most perfect of all created beings. This is the Reign
of Man.

AGES OF NATURE.

583

Let us review each of these four Ages of Nature, with
reference to the diagram at the beginning of the volume.

470. THE PALAEOZOIC AGE. Reign of Fishes. — The
palaeozoic fauna, being the mos* remote from the present
epoch, presents the least resemblance to the animals now
existing, as will easily be perceived by a glance at the fol-

Fig. 155.

lowing sketches, (Fig. 155.) In no other case do we mees
with animals of such extraordinary shapes, as in the strata
of the Palaeozoic age.

471. We have already stated (466) that there are found,
in each formation of the primary age, animal remains of all
the four great departments, namely, vertebrates, articulata,
mollusks, and radiata. We have now to examine to what
peculiar classes and farrilies of each department these re-
mal'is belong, with avieu o ascertain if any relation between

224 GEOLOGICAL SUCCESSION OF ANIMALS.

the structure of an animal, and the epoch of its first appear
arice on the earth's surface, may be traced.

472. 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, which are the least perfect of the class. We
have represented, in the above sketches, several of the most
curious forms,* as well as of the Polyps, of which there are
some quite peculiar types from the Trenton limestone, and
from the Black River limestone.

473. Of the Mollusks, the bivalves or Acephab are nu-
merous, but, for the most part, they belong to the Brachiopo-
da, that is to say, to the lowest division of the class, including
mollusks with unequal valves, having peculiar appendages
in the interior. The Leptcena alternata, (£,) which is found
very abundantly in the Trenton limestone, is one of these
shells. The only fossils yet found in the Potsdam sandstone,
the oldest of all fossiliferous deposits, belong, also, to this
family, (Lingula prima, a.) Besides this, there are also
found some bivalves of a less uncommon shape, (Avicula
decussata, e.)

474. The Gasteropods are less abundant ; some of them
are of a peculiar shape and structure, (Bucania expansa,f;
Euomphalus hemisphericus, c.) Those more similar to our
common marine snails have all an entire aperture ; those
with a canal being of a more recent epoch.

475. Of the Cephalopods we find some genera not less
curious, part of which disappear in the succeeding epochs ;

* (i)Cyathocrinus ornatissimus, Hall ; (J ) Melocrinus Amphora, Goldf. ;
(A) Cariocrinus ornatus, Say; (I) Columnaria alveolata; (m) Cyatho-
phyllum qur.d*igeminum, Goldf. ; (nt 6) Caninia flexuosa ; (p) Chcetetes
lycopwdon.

AGES OF NATURE.

225

suci, in particular, as those of the straigh., chambered shells
called Orthoceratites, some of which are twelve feet in length,
(Orthoceras fusiformc, g.) There are also found some of a
coiled shape, like the Ammonites of the secondary age, but
having less complicated partitions, (Trocholites ammonius,d.)
The true cuttle-fishes, which are the highest of the class,
are not yet found. On the contrary, the Bryozoa, which
have long been considered as polyps, but which, according
to all appearances, are mollusks of a very low order, are
very numerous in this epoch.

476. The Articulata of the Paleozoic age are mostly
Trilobites, animals which evidently belong to the lower
order of the Crustaceans, (Fig. 156.) There is an incom-
pleteness and want of development, in the form of their
body, that strongly reminds us of the embryo among the
crabs. A great many genera have already been discovered.

Fig. 156.

We may consider as belonging to the more extraordinary
the forms here represented, (Harpes, a ; Arges, b ; Bron*
tes, c ; and Platynotus, d ;) the latter, as well as the Isotelus
the largest of all, being peculiar to the Paleozoic deposit of
this country. Some others seem more allied to the crusta-
ceans of the following ages, but are nevertheless of a very
extraordinary form, as Eurypterus remipes, (e.) There are
a. so found, in the Devonian, some very large Entomostraca.
The class of WDrms is represented only by a few Serpulse,

226

GEOLOGICAL SUCCESSION OF ANIMALS.

which are marine worms, surrounded by a solid sheath. The
class DI Insects is entirely wanting.

477. The inferiority of the earliest inhabitants of our
earth appears most striking among the Vertebrates. There
are as yet neither reptiles, birds, nor mammals. The fishes,
as we have said, are the sole representatives of this division
of animals.

478. But the fishes of that early period were not like
ours. Some of them had the most extraordinary forms, so
that they have been often mistaken for quite different ani-
mals ; for example, the Pterichthys, (a,) with its two wing-

Fig. 157.

like appendages, and also the Coccosteus (b) of the samo
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, (e,) as well as palatal bones, (rf,) the latter of a
very peculiar kind. Even those fishes which have a more
regular shape, as the Dipterus, (c,) have not horny scales
like our common fishes, but are protected by a coat of bony
plates, covered with enamel, like the gar-pikes of the
American rivers. Moreover, they all exlybit certain char-
acteristic features, which are very interesting in a physio-
logical point o/ view. They all have a broad head, and a
tail terminafing in two unequal lobes. What is still more
curious, the best preserved specimens show no indications

AGES OF NATURE. 227

of the bodies of vertebrse, but merely of their spinous pro-
cesses ; from which it must be inferred that the body of the
vertebra was cartilaginous, as it is in our Sturgeons.

479. 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 the Sturgeon, arrested, as it were, in their devel-
opment ; since we have shown that the Sturgeon, in its or-
ganization, agrees, in many respects, with the Cod or Salmon
at an early age.

480. Finally, there was, during the Paleozoic age, but
liitle variety among the animals of the different regions of
the globe ; and this may be readily explained by the pecu-
liar configuration of the earth at that epoch. Great moun-
tains did not then exist ; there were neither lofty elevations
nor deep depressions. The sea covered the greater part, if
not the whole, of the surface of the globe ; and the animals
which then existed, and whose remains have been preserved,
were all, without exception, aquatic animals, breathing by
gills. This wide distribution of the waters impressed a very
uniform character upon the whole Animal Kingdom. Be-
tween the different zones and continents, no such strange
contrasts of the different types existed as at, the present
epoch. The same genera, and often the same species, were
found in the seas of America, Europe, Asia, Africa, and
New Holland ; from which we must conclude that the
climate was much more uniform than at the present day.
Among the aquatic population, no sound was heard. All
creation w^s then silent.

481. THE SECONDARY AGE. Reign of Reptiles. — The
Secondary age displays a greater variety of animals as well
as plants. The fantastic forms of the Palseozoic age disap«
pear, and in their place we see a greater symmetry of shape.
The advance is particularly marked in the series of verte-

228 GLOLOGICAL SUCCESSION OF ANIMALS.

brates. Fishes are no longer the sole representatives ol
that department. Reptiles, Birds, and Mammals successive
ly make their appearance, but Reptiles are preponderant
particularly in the oolitic formation ; on which account we
have called this the Reign of Reptiles.

482. 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 Mollusks.* Besides these, we meet here
with the first air-breathing animals, which are Insects and
Scorpions. At the same time, land-plants first make their
appearance, namely, ferns of great size, club-mosses, and
other fossil plants. This corroborates what has been already
said concerning the intimate connection that exists, and
from all times has existed, between animals and the land-
plants, (399.) The class of Crustaceans has also improved
during the epoch of the coal. It is no longer composed ex-
clusively of Trilobites, but the type of horse-shoe crabs also
appears, with other gigantic forms. Some of the Mollusks
seem also to approach those of the Oolitic period, particularly
the Bivalves.

483. In the Trias period, which immediately succeeds the
Carboniferous, the fauna of the Secondary age acquires its
definitive character ; here the Reptiles first appear. They are
huge Crocodilian animals, belonging to a peculiar order, the
Rhizodonts, (Protosaurus, Notosaurus, and Labyrinthodon.)
The well-known discoveries of Professor Hitchcock, in the
red sandstone of the Connecticut, have made us acquainted

* This circumstance, in connection with the absence of Reptiles, has
caused the coal-measures to be generally referred to the Palaeozoic epoch.
But there are other reasons which induce us to unite the carboniferous
pa;iod with the secondary age, especially when considering that here the
land animals first appear, whereas, in the Palaeozoic age, there are only
marine animals, breathing by gills ; and, also, that a luxuriant terrestrial
vegetation Avas developed at that epoch.

AGES OF NATURE.

229

with a grca number of birds' tracks (Fig. 158, a, fc) belong-
ing to this epoch, for the most part indicating birds of gigan-
tic size. These impressions, which he has designated under
the name of Ornithichnites, are some of them eighteen inches

a Fig. 158.

in length, and five feet apart, far exceeding in size the tiacks
of the largest ostrich. Other tracks, of a very peculiar shape,
have been found in the red sandstone of Germany, and in
Pennsylvania. They were probably made by Reptiles which
have been called Cheirotherium, from the resemblance of the
track to a hand, (c.) The Mollusks, Articulates, and Raaiates
of this period, approach to the fauna of the succeeding period.
484. The fauna of the Oolitic formation is remarkable for
the great number of gigantic Reptiles which it contains. In

Fig. .159.

this formation we find those enormous Amphibia, known
under the names Ichthyosaurus, Plesiosaurus, Megdlosaurus*
and Iguanodon. The first, in particular, the Ichthyosaurus,
(Fig. 159, a,) greatly abounded on the coast of the continents
of that period, and their skeletons are so well preserved, that
we are enabled to study even the minutest details of their
structure, which differs essentially from that of the Reptiles
of the present day. In some respects they form an inter-
mediate link between the Fishes and Mammals, and may be
considered as the prototypes of the Whales, having, like
20

230 GEOLOGICAL SUCCESS- ON OF ANIMALS.

then), limbs in the form of oars. The Plesiosaurus (b)

agrees, in many respects, with
the Ichthyosaurus, in its struc-
ture, but is easily distinguished
by its long neck, which resem-
bles somewhat the neck of
some of our birds. A still
more extraordinary Reptile is
Fig. 160. the Pterodactylus, (Fig. 160,)

with its long fingers, like those of a bat, and which is thought

to have been capable of flying.

485. It is also in the upper stages of this formation that
we first meet with Tortoises. Here also we find impressions
of several families of insects, (Libellulce, Coleoptera, Ichneu-
mons, fyc.) Finally, in these same stages, the slates of
Stonesfield, the first traces of Mammals are found, namely
the jaws and teeth of animals having some resemblance to
the Opossum.

486. The department of Mollusks is largely represented
in all its classes. The peculiar forms of the primary age
have almost all disappeared, and are replaced by a much
greater variety of new forms. Of the Brachiopods only one

a b c d

Fig. 161.

type is very abundant, namely, the Terebratula, (Fig. 161, a.)
Among the other Bivalves there are many peculiar forms, as
the Goniomya (b) and the Trigonia, (c.) The Gasteropods
display a great variety of species, and also the Cephalopods,
among which the Ammonites are the most prominent, (d.)
There are also found, for the first time, numerous represen-
tatives of the Cutth-fishes, under the form of Belemnites^

AGES OF NATURE.

231

(Fig. 162 ) an extinct type of animals, protected by a sheath,
and terminating in a conical body, somewhat similar to the
bone of the Sepia, which a
commonly is the only
part preserved, (b.)
487. The variety is

not less remarkable

Fig. 162. b

among the Kadiates.

There are to be found representatives of all the classes ,
even traces of Jelly-fishes have been made out in the
slate of Solenhofen, in Bavaria. The Polyps were very
abundant at that epoch, aspecially in the upper stages, one
of which has received the name of Coral-rag. Indeed,
there are found whole reefs of corals in their natural po-
sition, similar to those which are seen in the islands of the

Pacific. Among the most remarkable types of stony Polyps
may be named the fan-like Lobophyllia, (L.flabellum, a,)
and various forms of tree-corals, Lithodendron pseudosty-
tina, b.) But the greatest variety exists among the Echino-
derms. The Crinoids are not quite so numerous as in
former ages. Among the most abundant are the Pentacri-
7iM5, (c.) There are also Comatula-like animals, that is to
say, free Crinoids (Pterocoma pinnata, d.) Many Star-
fishes are likewise observed in the various stages of this
formation. Finally, there is an extraordinary variety of

232

GEOLOGICAL SUCCESSION OF ANIMALS

Echini, among them Cidaris, (e,) with large spines, and
several other types not found before, as, for example the
Dysaster, (f) and the NucleoUtes, (g.)

488. 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 Ich-
thyosauri and Plesiosauri, that characterize the preceding
epoch, are succeeded by gigantic Lizards, more nearly
approaching the Reptiles of the present day. Among the
Mollusks, a great number of new forms appear, especial-
ly among the Cephalopods,* some of which resemble the

Fig. 164.

Gasteropods in their shape, but are nevertheless cham-
bered. The Ammonites themselves are quite as numerous

Fig. 165

as in the Oolitic period, and are in general much orna-
mented, («.) The Acephala furnish us, also, with peculiai
types, not occurring elsewhere, Magas, (a,) the Inoceramus

* («0 Ammonites; (b) Crioceras ; (c) Scaphites ; (d) Ancyloceras
(e) Hamites- (/) Baculites; (g] Turrilites.

AGES OF NATURE. 233

(5,) the Hippurites, (c,) and peculiar Spondyli, with long
spines, (d.) There is also a great variety of Gastro-
pods, among which are some peculiar forms of Plcu

Fig. 166.

Totomaria, (e.) The Radiates are not inferior to the others
in variety.*

489. TERTIARY AGE. Reign of Mammals. — The most
significant characteristic of the Tertiary faunas is their
great resemblance to those of the present epoch. The am
mals belong in general to the same families, and mostly
to the same genera, differing only as to the species. And
the specific differences are sometimes so slightly marked,
that a considerable familiarity with the subject is required,
in order readily to detect them. Many of the most abundant
types of former epochs have now disappeared. The changes
are especially striking among the Mollusks, the two great
families of Ammonites and Belemnites, which present such
an astonishing variety in the Oolitic and Cretaceous epochs,
being now completely wanting. Changes of no less impor-
tance 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

* (a) Diploctenium cordatum ; (b) Marsupites ; (c) Salenia ; (d) Ga
leritet ,* \?) Micrayfer cor-arquinum.
20*

234

GEOLOGICAL SUCCESSION OF ANIMALS.

Fig. 167.

remains of a very peculiar type of animals, almost
unknown to the former ages, as well as to
the present period. They are little cham-
bered shells, known to geologists under the
name of Nummulites, from their coin-like ap-
pearance, and form very extensive layers of
rocks, (Fig. 167.)

490. But what is more important in a philosophical point
of view is, that aquatic animals are no longer predominant
in Creation. The great marine or amphibian reptiles give
place to numerous mammals of great size ; for which rea-
son, we have called this age the Reign of Mammals. Here
are also found the first distinct remains of fresh-water
animals.

491. The lower stage of this formation is particularly
characterized by great Pachyderms, among which we may
mention the Paleotherium and Anoplotherium, which have
acquired such celebrity from the researches of Cuvier.
These animals, among others, abound in the Tertiary forma-
tions of the neighborhood of Paris. The Paleotheriums, of

Fig. 168. Fig. 169.

which several species are known, are the most common ;
they resemble, (Fig. 168,) in some respects, the Tapirs,
while the Anoplotheriums are more slender animals, (Fig.
169.) On this continent 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 have boon detected.

AGES OF NATURE. 235

492. The fauna of the upper stage 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 aiimals, some
of them much surpassing in size the lions and tigers of our
day. We meet also gigantic Edentata, and Rodents of great
size.

493. The distribution of the Tertiary fossils also revoals
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 ba 'ns,
which, like the Gulf of Mexico, or the Mediterranean of this
day, contained species not found elsewhere. Such was the
basin of Paris, that of London, and, on this continent, that of
South Carolina.

494. In this limitation of certain types within certain
bounds, we distinctly observe another approach to the present
condition of things, in the fact that groups of animals which
occur only in 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 as in its present fauna ; and Marsupials were
formerly as numerous in New Holland as they now are,
though in general of much larger size.

495. THE MODERN EPOCH. Reign of Man. — ThePreseii*
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 every where around us The
climate 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, became much colder at the end of this period,
causing the polar glaciers to advance south, much beyond

236 GEOLOGICAL SUCCESSION OF ANIMALS.

their previous limits. It was this ice, either floating like ice-
bergs, or, as there is still more reason to believe noving
along the ground, like the glaciers of the present day, that, in
its movement towards the South, rounded and polished the
hardest rocks, and deposited the numerous detached frag-
ments brought from distant localities, which we find every
where scattered about upon the soil, and which are known
under the name of erratics, boulders, or grayheads. This
phase of the earth's history has been called, by geologists,
the Glacial or Drift period.

496. After the ice that carried the erratics had melted
away, the surface of North America and the North of Europe
was cov-ered by the sea, in consequence of the general sub-
sidence of the continents. It is not until this period thai
we find, in the deposits known as the diluvial or pleistocene
formation, incontestable traces of the species of animals now
living.

497. 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 organization, it is impossible that they
should have migrated from other countries, we must conclude
that they were created at a more recent period than our
marine animals.

498. Among these 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 Mastodon , the remains of which ore found in the upper-

CONCLUSIONS. 237

most strata of the earth's surface, and probably the very
last large animal which became extinct before the creation
of man.*

Fig. 170.

499. 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 appeart nee, and
at their head MAN.!

CONCLUSIONS.

500. From the above sketch it is evident that there is a
manifest progress in the succession of beings on the surface

* The above diagram is a likeness of the splendid specimen disinterred
at Newburg, N. Y., 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.

f The former of these phases is indicated in the frontispiece, by a nar-
row circle, inserted between the upper stage of the Tertiary formation
and the Reign of Ma-' properly so called.

238 GEOLOGICAL SUCCESSION OF ANIMALS.

of the earth. This progress consists in an increasing simu
larity to the living fauna, and among the Vertebrates, espe
cially, in their increasing resemblance to Man.

501. But this connection is not the consequence of a
direct lineage between the faunas of different ages. There
is nothing like parental descent connecting them. The
Fishes of the Paleozoic age are in no respect the ancestors
of the Reptiles of the Secondary age, nor does Man descend
from the Mammals 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 himself, whose aim, in forming
the earth, in allowing it to undergo 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 the surface of our globe.
Man is the end towards which all the animal creation
has tended, from the first appearance of the first Palaeozoic
Fishes.

502. In the beginning His 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,
thousands 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 earth those vast stores of granite, marble, coal,
salt, and the various metals, the products of its several revo-
lutions ; and thus was an inexhaustible provision made for
his necessities, and for the development of his genius, age
in anticipation of his appearance.

503. To study, in this view, the succession of animals in
time, and their distribution in space, is, therefore, to become
acquainted with the ideas of God himself. Now, if the suc-
cession of created beings on the surface of the globe is the
realization of an infinitelj wise plan, it follows that there

CONCLL SIGNS. 239

must be a necessary relation between the races of ani
mals and the epoch at which they appear. It is necessary,
therefore, in order to comprehend Creation, that we com-
bine 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 ani-
mals.

INDEX AND GLOSSARY.

Abd6men, the lower cavity of the
body, 41.

Abranchiates, without gills, 21.

Acalepha, a class of Radiates, many
species of which produce tingling
of the skin when handled, 23.

Acephala, mollusks having no dis-
tinct head, like clams, 22.

Acoustic, pertaining to the sense of
hearing, 56.

Actinia, digestive apparatus of, 97.

Actinoids, 23.

Affinity, relationship, 30, 87.

Ages of Nature, 221.

Albumen, the white of egg, 42, 111,
138.

Alimentary canal, 97.

Alimentation, the process of nutri-
tion, 42.

Allantois, Allantoidian, 149.

Alligator, teeth of, 105.

Alternate reproduction, 159 ; con-
sequences of, 167 ; difference be-
tween, and metamorphosis, 167.

Ambling, 91.

Amblyopsis spelseus, 55.

Ammonites, 22, 230, 232, 233.

Amnios, 150.

Amphibia, 95.

Amphipods, a family of crusta-
ceans.

Amphioxus. its place 181.

Amphiuma, 209.

Analogy, 30.

Ana Ufa, metamorphoses of, 177.

Ancyl6ceras, 232.

Animalcule, a minute animal, 24.

Animal heat, 122.

Animal life, 44 ; organs of, 44.

Animals, number of, 27 ; distribu-
tion in space, 186 ; in time, 214.
21

Animals and plants, difference* be»

tween, 41.
Animate, possessed of animal life,

43.

Anoplotherium, 234.
Antenna, the jointed feelers ol lob-
sters, insects, &c., 77.
Aorta, the great bloodvessel arising

from the heart, 116.
Aphides, reproduction of, 162, 163.
Apophysis, a projection from the

body of a bone, 181.
Apparatus of motion, 73.
Aptera, wingless insects, 21.
Aquatic, living in water.
Aqueous, like water.
Aqueous humor, 50.
Arctic fauna, 197.
Areolar tissue, 38.
Arges, 225.

Aristotle's lantern, 102.
Arm, 82 ; different forms of, 83.
Artery, 113.
Articulates, composed of joints, like

the lobster or caterpillar, 21;

number of, 27.
Ascidia, bottle-shaped mollusks

without a shell.
Assimilation, the change of blood

into bone, muscle, &c., 122.
Astacus pellucidus, 55.
Asteridae, the family of star-fishes,

23.
Auditory, pertaining to the sense

of hearing, 56.
Auricle, a cavity of the heart, like

a little ear, 115.
Avicula decussata, 224.
Axolotl, 209.

Baculites, 232.

242

INDEX ^ND GLOSSARY.

Balanus, the barnacle, 176.
Basilosaurus, 234.
Batrachians, the frog tribe, 20.
Beak, 104.

Belemnites, 230, 233.
Bird-tracks, in red sandstone, 229.
Birds, number of, 27.
Bivalve, having two shells, like the

clam, 27-
Blastoderm, the embryonic germ,

141.

Blind-fishes, 55.
Blood, 111, 121.
Boulders, 236.
Brachionus, jaws of, 103.
Brachiopods, a class of mollusks,

22.

Brain, 45.

Branchiae, gills, 120.
Branchifers, univalve mollusks

breathing by gills, 22.
Bronchi, tubes branching from the

windpipe in the lungs, 119.
Brontes, 225.
Bryozoa, 23, 225.
Bucania expansa, 224.

Calcareous, composed of lime, 75,

Campanularia, reproduction of, 165,

170.

Canine teeth, 106.
Caninia flexuosa, 224.
Canker-worm, metamorphoses of,

176.

Cannon-bone, 86.
Canter, 91.

Capillary vessels, 113.
Carapace, the upper covering of the

crab or tortoise, 75.
Carbon, the basis of charcoal and

most combustibles, 41.
Carboniferous rocks, 218, 228.
Cariocrinus ornatus, 224.
Carnivora, animals feeding on flesh,

20; teeth of, 107.
Carpus, the wrist, 83.
Cartilage, gristle, 39.
Cartilaginous tissue, 38.
Cell, 37 ; nucleated, 38.
Cellule, a little cell, 37.
Cephalopods, mollusks with arms

surrounding the head, like the

cuttle-fish, 22.

Cercaria, reproduction of, 160, 171.
Cerebral, pertaining to the brain, 45.
Cestracion Philippi, 204.

Cetaceans, marine animals whiefc
nurse their young, like the whale,
porpoise, &c., 20.

Chaetetes lycoperdon, 224.

Chalaza, the albuminous thread by
which the yolk of the egg is sus-
pended, 138.

Chalk formation. £1 3.

Chambers of the eye, 60.

Chamois, 192.

Cheirotherium, 229.

Chelonians, reptiles of the tortoiftj
tribe, 20.

Chorion, 151.

Choroid, coat of the eye, 49.

Chrysalis, the insect in its passage
from the worm to the fly state.
174.

Chyle, 100, 112.

Chyme, 100, 112.

Cicatricula, 141.

Cilia, microscopic hairs, like eye
lashes, 81, 112, 116, 120.

Circulation, 97 ; great, 111 ; pulmo-
nary or lesser, 116; complete,
116; incomplete, 116.

Cirrhipedes, Crustacea having curled
feelers, like the barnacles, 27.

Class, 18.

Clavicle, the collar-bone, 83.

Climate, influence on a fauna, 188.

Climbing, 92.

Coccbsteus, 22b.

Cochlea. 58.

Cold-blooded animals, 122.

Coleopterous, insects with hard
wing cases, like the dor-bug, 27.

Collar-bone, 83.

Columnaria alveolata, 224.

Comatula, metamorphosis of, 179
180.

Condor, 191.

Constancy of species, 67.

Coral-rag, 231.

Cornea, the transparent portion of
the eye, 49.

Corpuscles, minute bodies, 39.

Cossus ligniperda, muscles of, 77-

Cretaceous, or chalk formation, 218

Cricoid, ring-like, 65.

Crinoid, lily-like star-fishes, 23

Cri6ceras, 232.

Crustacea, articulated animals hav-
ing a crust-like covering, like the
crab and horse-shoe, 27 : heart
of, 117.

Crystalline lens, 49.

INDEX AND GLOSSARY.

243

O.enoids, fishes which ht.ve the

edge of the scales toothed, 20.
Cteuophori, soft, radiated animals,

moving by cilia, 23.
Cutis, 128.
Cuttle-fish, jaws of, 102; heart of,

117; metamorphosis of, 180;

mode of swimming, 95.
Cyathocrinus ornatissimus, 224.
Cyathophyllum quadrigemiuum,

224.
Cycloids, fishes with smooth scales,

Deciduous, not permanent during a

lifetime, 199.
Deglutition, the act of swallowing,

108.
Dentition, form and arrangement

of the teeth.
Department, a primary division of

the animal kingdom, 18.
Development of the white-fish,

145.

Devonian rocks, 218.
Diaphragm, the partition between

the chest and abdomen, 74, 119.
Diastole, the dilatation of the heart,

115.

Digestion, 97.

Diploctenium cordatum, 233.
Dipterus, 226.
Discophori, disk-shaped animals,

like the jelly-fish, 23.
Disk, a more or less circular, flat-
tened body, 14.
Distoma, reproduction of, 161 ; in

the eye of the perch, 171.
Distribution of animals, laws of,

186 ; in space, 186 ; in time, 214.
Dodo, its disappearance, 210.
Dorsal cord, 143.
Dorsal vessel, 114.
Dorsibranchiates, mollusks having

gills upon the back, 21.
Drift, 219, 236.
Drinking, 109.

Duck-barnacle. See Anatifa.
Dysaster, 232.

Ear, 55.

Echinoderms, radiate animals arm-
ed with spines externally, like
the sea-urchin, 23.

Fchmus, the sea-urchin, 23; jaws
of, 102 ; heart of U7 ; mode of
progres%ion, 81.

Echinus sangumolentus, metamor-
phosis of, 178.

Egg, 131 ; form of, 133 ; formation
of, 133 ; ovarian, 133 ; laying of,
135 ; composition of, 137 ; devel-
opment of, 139 ; of Infusoria, 172.

Elementary structure of organized
bodies, 36.

Embryo, the young animal before
birth, 33, 132 ; development of,
139.

Embryology, 131, 139; importance
of, 153.

Endosmose, 127. See Exosmose.

Engeena, a large orang, 206.

Entomostraca, 21.

Eocene formation, 218.

Ephyra, 164, 169.

Epidermis, the scarf-skin, 129.

Epithelium-cells, 126.

Equivocal reproduction, 158.

Erratics, rolling stones, 236.

Euomphalus hemisphericus, 224.

Eurypterus remipes, 225.

Eustachian tube, 57.

Excretions, 127.

Exhalation, 128.

Exosmose and Endosmose, the pro-
cess by which two fluids pass
each way through a membrane
which separates them, so as to
become mingled, 127.

Eye, 48 ; simple, 51 ; aggregate,
53 ; compound, 54 ; destitution
of, 55 ; compared to a camera
obscura, 51.

Fa9ette, a very small surface, 54.
Family, a group including several

genera, 18.

Fauna, 186 ; distribution of, 194.
Femur, the thigh bme, 87.
Fibula, the smallest ol the two

bones of the leg, 87.
Fins, 93.
Fishes, number of, 27; heart of,

116 ; reign of, 222, 223.
Fissiparous reproduction, propaga

tion by fissure or division, 156.
Flight, 92.

Flora, influence on a fauna, 187.
Fluviatile, pertaining to rivers, 27.
Foraminifera, 22.
Formation, geological, 217.
Fossil, dug from the earth, applied

to the remains of animals and

plants.

244

AND GLOSSARY.

Function, the office which an organ
is designed to perform, 29.

Galeopithecus, its facilities for
leaping, 93, 207.

Galerltes, 233.

Gallinaceous, birds allied to the do-
mestic fowl, 190.

Gallop, 91.

Ganglions, scattered nervous mass-
es, from which nervous threads
arise, 46.

Ganoids, fishes having large, bony,
enamelled scales,mostly fossil, 20.

Gar-pike, 192.

Gasteropods, mollusks which crawl
by a flattened disk, or foot, on
the under part of the body, like
the snail, 22.

Gastric juice, 99.

Gavial, a crocodile, with a long,
slender head.

Gemmiparous reproduction, propa-
gation by budding, 156.

General properties of organized
bodies, 35.

Genus, 17-

Geographical distribution of ani-
mals, 186 ; conclusions, 207.

Geological succession of animals,
214

Germ, the earliest manifestation of
the embryo, 42, 141.

Germinative disk, 133, 137, 141;
vesicle, 133, 137, 138; dot,137,138.

Gestation, the carrying of the young
before birth, 135.

Gills, 31, 120, 124.

Gizzard, 99.

Glacial period, 236.

Glands, 127 ; salivary, 127.

Globules of chyle, 100.

Glottis, 65.

Goniomya, 230.

Grallatores, birds with long legs for
wading, 20.

Grand-nurses of Cercaria, 162.

Granivorous, birds feeding on grain

Grit, coarse sandstone, 216.

Gullet, 99.

Hamites, 232.

Hand, 83.

Harmony of organs. 106

Harpes,225.

Hearing, 53

Heart, 114

Herbivora, animals feeding on grass
and leaves, 20.

Hibernation, torpid state of ani«
mals during winter, 123.

Hippurltes, 233.

Holothurians, soft sea-slugs, biche-
le-mar, 23.

Homogeneous, uniform in kind, 126.

Homology, 30.

Humerus, the shoulder-bone, 81.

Hyaline matter, pure, like glass, 39.

Hydra, egg of, 133 ; propagation of,
156, 158.

Hydrogen, a gas which is the prin-
cipal constituent of water, 41.

Hydroids, a family of polyps, 23.

Ichthyosaurus, 229, 232.

Icterus Baltimore, nest of, 70.

Igneous, that have been acted upon
by fire, 215.

Iguanodon, 229.

Imbibition, 127.

Inanimate, destitute of life, 43.

Incisor teeth, 106.

Incubation, hatching of eggs by the
mother, 136.

Infusoria, microscopic animals in-
habiting water, not yet fully ar-
ranged in their proper classes, 24,
32 ; motions of, 40 ; generation of
172.

Inocoramus, 232.

Inorganic,not made up of tissues,35.

Insalivation, 108.

Insects, number of, 27.

Insessores, perching birds, like
birds of prey, 20.

Instinct, 67, 69.

Intelligence, 67, 68.

Intercellular passages, 37.

Invertebrates, animals destitute of
a back-bone.

Iris, the colored part of the eye 40

Is6telus, 225.

Jelly-fish. See Medusa.
Judgment, 68.

Kidneys, 130.

Labyrinthodon, 228.

Lacertans, animals of the lizard

tribe, 20.
Lacteals, vessels which take up the

nutriment, 100
Lamellibranchiates, mollusks hav

INDEX AND GLOSSARY.

245

ing gills '.rranged. in sheets, like

the clam and oyster, 22.
Larva, the caterpillar or worm state

of an insect.
Larynx, 65.
Lasso-cells, 110.
Layers of the embryo, 142.
Leaping, 91.
Lemming, 190, 197.
Leptaena alternata, 224.
Lestris, 72.
Life, 35, 44.
Limbs, 54.

Limnea, parasites of, 160, 162
Lingula prima, 224.
Lithodendron pseudostylina, 231.
Liver, 129.

Lobophyllia flabellum, 231.
Lobsters, mode of swimming, 94 ;

nervous system, 46.
Locomotion, 79; organs of, 82;

modes of, 88.
Loligo, arms of, 180.
Lungs, 118.
Lymphatic vessels, 100.

Magas, 232.

Malacostraca, 21.

Mammals, animals which nurse
their young, 19 ; number of, 27 ;
reign of, 222, 233.

Man, reign of, 222, 234 ; races of,
212 ; his twofold nature, 25.

Manatee, 206.

Manducata, insects furnished with
jaws, 21.

Marchantia polymorpha, reproduc-
tion of, 166.

Marl, earth principally composed
of decayed shells and corals, 216.

Marsupials, animals with a pouch
for carrying their young, as the
opossum ; gestation of, 183.

Marsupkes, 233.

Mastication, 101.

Mastodon, 236.

Matrix, the organ in which the em-
bryo is developed, 152.

Medulla oblongata, continuation of
the brain into the back-bone.

Medusa, jelly-like animals living in
the sea, 23 ; development of, 163 ;
digestive organs, 98 motion 80.

Megalobatrachus, 209.

Megalosaurus, 229.

Melocrhius amphbra, 224.

Mem>ry, 68.

21*

Menobranchus, 202, 209.

Menop6ma, 202, 209.

Merganser, an aquatic bird allied to
the goose, 66, 193.

Metacarpus, the wrist, 83.

Metatarsus, 87.

Metamorphic rocks, 216, 174.

Metamorphosis, 149, 167; of the
silk-worm, 175 ; canker-worm,
176: duck-barnacle, 177; star-fish,
178; comatula, 179.

Micraster cor-anguinum, 232.

Miocene formation, 219.

Modern age, 222, 235.

Molar teeth, 106.

Molecules, very minute particles, 35.

Mollusks, soft animals of the snail
and oyster kind; heart of, 117;
liver of, 129 ; number of, 27 ; meta-
morphosis of, 179.

Monkey, teeth of, 107, 205.

Mon6culus, mode of carrying eggs,
135 ; motion, 73 : apparatus of, 73.

Moulting, the shedding of feathers,
hair, &c., 128.

Muscles, 73; disposition of, in in-
sects, 77 ; in, fishes, 78 ; in birds,
79.

Muscular tissue, 39.

Myxine glutinosa, its eye, 55.

Natatores, birds with webbed feet
for swimming, 20.

Natica, tongue of, 102 ; heart of, 117.

Nautili, 22.

Neptunian rocks, 215.

Nereis, jaws of, 102 ; gills of, 81 ;
eye, 53.

Nervous system, 44 ; in mammals,
45 ; in articulates, 46 ; in crusta-
ceans, 46 ; in radiates, 47.

Nervous tissue, 39.

Nest of Baltimore oriole, 70 ; of tai-
lor bird, 70 ; of Ploceus, 71.

Nomenclature, the naming of ob-
jects and their classes, family, &c.

Nostrils, 60.

Notosaurus, 228.

Nucleolites, 232.

Nucleolus, a little nucleus, 38.

Nucleus, a kernel, or condensed
central portion, 38.

Nudibranchiates, mollusks having
the gills floating externally, fig. 91

Nummulites, 234.

Nurses, of Cercaria, 162; of ants
and bees, 163.

246

INDEX AND GLOSSARY.

Nutrition, 96.

Ocelli, minute eyes, 52.

Octopus, arms of, 180.

Odors, 61.

(Esophagus, the gullet, 46, 99.

Olfactory, pertaining to the sense

of smell, 45, 60.
Omnivora, feeding upon all kinds

of food, 107.
Oolitic formation, 218.
Operculum, a cover for the aperture

of a shell.
Ophidians, animals of the serpent

kind, 20.
Optic nerves, 48.
Orbits, 48.
Orders, 18.
Organism, 37.
Organized bodies, general properties

of, 35 : elementary structure, 36,

37.

Ornithichnites, 229.
Orth6ceras fusiforme, 225.
Osseous tissue, 39.
Otolites, little bones in the ears of

mollusks and Crustacea, 59.
Ovary, the organ in which eggs

originate, 133.
Oviduct, the passage through which

the egg is excluded, 134.
Oviparous, producing eggs, 131.
Ovis montana, 192.
Ovo-viviparous, animals which

hatch their eggs within their

body, 135.
Ovul/ition, the production of eggs,

134.

Oxygen, its consumption in respira-
tion, 41, 113, 121.

Pachydermata, thick-skinned ani-
mals, like the elephant, hog, &c.,
107, 234.

Pacing, 91.

Paleont61ogy, 215.

Palaeozoic age, 222, 223.

Paleotherium, 234.

Palpation, the exercise of the touch,

Palpi, jointed organs for touch,
about the mouth of insects, 64.

Papilla, a little pimple, 62.

Paramecia, reproduction of, 157.

Parasitic, living on other objects.

Passerine birds of the sparrow kind
201.

Peduncle cr Pedicle, a slender stem.

Pelvis, the cavity formed by the
hip bones, 87.

Pentacrinus, 231 ; metamorphosis
of, 180.

Perception, 67.

Perchers, a class of birds, 20.

Peripherie, exterior surface, 152.

Peristaltic motion, 100.

Petrifactions, 215.

Phalanges, 83.

Pigment, a coloring substance, 40.

Pituitary membrane, 61.

Placenta, the organ by which the
embryo of mammals' is attached
to the mother, 152.

Placoids, fishes with a rough skin,
like the shark or skate, 20.

Planaria, its digestive apparatus,
98 ; an eye of, 53.

Plant-lice. See Aphides.

Plants compared with animals, 41.

Platynotus, 225.

Pleiocene formation, 219.

Plesiosaurus, 229, 232.

Pleurotomaria, 233.

Ploceus Philippinus, nest of, 70.

Plutonic rocks, 215.

Podurella, mode of leaping, 92 ; em-
bryo of, 144 ; egg of, 133.

Polyps, a small animal fixed at one
end, with numerous flexible feel-
ers at the other, 27, 53; repro-
duction of, 158.

Prehension, act of grasping, 109.

Primary age, 222.

Primitive stripe, 143.

Progression, 88, 90.

Proligerous, the part of the egg
bearing the embryo, 141.

Pr6teus, 209.

Protosaurus, 228.

Protractile, capable of being ex-
tended.

Pterichthys, 226.

Pter6coma pinnata, 231.

Pterodactylus, 230.

Pteropods, mollusks with wing-like
expansions for swimming, 22.

Pulmonary, relating to the lungs,
116.

Pulmonates, mollusks which
respire air, 22.

Pupil, 40.

Pyrula, egg-cases of, 135.

Quadrumanous, four-handed, 201

INDEX AND GLOSSARY.

247

Quadruped, animals with four legs,
40.

Radiata, animals whose organs ra-
diate from a centre, 23, 27.

Radius, one of the bones of the
arm, 83.

Reign of fishes ; of man, 235 ; of
mammals, 233 ; of reptiles, 238.

Relation, functions of, 44.

Reproduction, 131 ; peculiar modes,
156.

Reptiles, number of. 27; reign of,
222, 227.

Respiration, 97, 118.

Rete mucosum, 129 ; retina, 49.

Retractile, that may be drawn
back, 84.

Rhizodonts, 20 ; of the trias, 228.

Rhizopods, 22.

Rocks, classification of, 215; defi-
nition of, 215.

Rodents, quadrupeds with teeth for
gnawing, 107.

Rotifers, jaws of, 103 ; eggs of, 172.

Ruminants, quadrupeds which chew
the cud, 107.

Running, 91.

Rytma Stelleri, 210.

Salenia, 233.

Saliferous formation, 218.

Saliva, 108.

Salivary glands, 127.

Salpa, reproduction of, 159 ; motion
of, 80.

Scansores, birds adapted for climb-
ing, 20.

Scaphites, 232.

Scapula, 82.

Sclerotic, the principal coat of the
eye, 49.

Scutella, jaws of, 101.

Sea-anemone. See Actinia.

Sea-urchin, eye of, 53 ; digestive
organs, 98; heart, 117.

Secondary age, 222, 227.

Secretions, 97, 126.

Sedimentary rocks, 215.

Segment, portion of a circle or
sphere.

Sensation, general, 43, 47.

Senses, special, 48.

Sepia, 231.

Serous, watery, 142.

Shark, egg of, 133.

Shoulder-blade, 82.

Sight, 48.

Silex, flinty rock.

Siliceous, made of mnt.

Silk-worm, metamorphosis of, 176.

Silurian rocks, lower, 217; upper
218.

Sinuous, bending in and out, 22.

Siphonophori, 23.

Siren, 209.

Skeleton, 74, 77.

Skin, structure of, 128.

Smell, 60.

Species, constancy of. 67; definition
of, 17, 159.

Spinal marrow, 45.

Spondyli, 233.

Sponges not animal, 41.

Spontaneous generation, 171.

Spores, the germs of sea-weeds
ferns, &c., 170.

Standing, 88.

Stapes, 57.

Star-fish, metamorphoses of, 178
eye of, 53 ; mode of progression,
81 ; reproduction of parts, 126.

Stigmata, openings in insects for
the admission of air, 118.

Stomach, 97.

Stratified rocks, 215.

Stratum, a layer.

Strobila, 164, 169.

Structure of the earth's crust, 214

Sturgeon, compared with white-
fish, 180.

Suctoria, insects taking their food
by suction, 21.

Swimming, 93.

Sylvia sutoria, nest of, 70.

Systole, the contraction of the heart
to force out the blood, 115.

Tape-worm, reproduction of, 140.

Tapir, 204, 234.

Tarsus, the ancle, 87.

Taste, 62.

Teeth, 104.

Temperate faunas, 198.

Temporal, relating to the temples,

Tentacle, the horn-like organs on
the head of mollusks, usually
bearing the eyes, 52.

Terebratula, 230.

Tertiary age, 222, 233.

Tertiary formation, lower, 218 ; up
per, 219.

248

INDEX AND GLOSSARY.

Test, the bristle crust covering the
crustaceans, &c., 75.

Teuthidcans, the family of cuttle-
fishes, 22.

Tibia, one of the bones of the leg, 87.

Tissues, 37 ; areolar, 38 ; cartilagi-
nous, 38 ; muscular, 39 ; osseous,
39 ; nervous, 39.

Tongue, 62.

Touch, 63.

Trachea, the windpipe, 119.

Tracheae, the air-tubes of insects,
118, 123.

Transudation, 127.

Trias formation, 218, 228.

Trigonia, 230.
rUobites, 21, 32.

TrochoUtes ammonius, 225.

Trophi, organs for feeding, of in-
sects, crabs, &c.

Tropical faunas, 204.

Trot, 91.

Tubulibranchiates, 21.

Tunicata, mollusks with a leathery
covering, 159.

Turrilites, 232.

Tympanum, a drum ; the membrane
separating the internal and exter-
nal ear, 57.

Type, an ideal image, 18.

Ulna, one of the bones of the arm,

83.

Ultimate, final.
Univalve, having a single shell, like

the snail, 27.

Vascular, composed of vessels, 129
Vegetative life, 44, 96; layer, 142.
Veins, lia

Ventricle, a cavity of the heart, 116

Vermicular, 100.

Vertebra, a joint of the back -bone,

46, 77.
Vertebrate, having a back-bone, 19,

Vertical, in a perpendicular direc-
tion, 48

Vesicle, a small membranous bag,
37.

Vestibule, a porch ; the entrance to
one of the cavities of the ear, 58.

Vibratile, moving to and fro, 112.

Viscera, 159.

Vitelline membrane, 138.

Vitellus, 137.

Vitreous humor, 50.

Viviparous, producing living young,
131.

Vocal cords, 65.

Voice, 64.

Voluntary, under control of the will,
43.

Vorticella, reproduction of, 157, 158

Walking, 90.

Wapiti, 211.

Warm-blooded animals, 122.

Water-tubes of aquatic animals, 123.

Whale, fans of, 104.

Whales, mode of swimming, 94.

White-fish, development of, 145.

Windpipe, 119.

Worms, 21 ; eye of, 53.

Zoology, its sphere, 25.
Zoophytes, animals of a very lo\V

type, mostly fixed to the ground.

of a plant-like form.

249

LIST OF THE MOST IMPORTANT AUTHORS

WHO » AY BE CONSULTED IN REFERENCE TO THE
SUBJECTS TREATED IN THIS WORK

GENERAL ZOOLOGY.

Aristotle's Zoology; Linnseus, System of Nature; Cuvier's Animal
Kingdom; Oken's Zoology; Humboldt's Cosncos, 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, Mailer, 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 OP ANATOMY AND PHYSIOLOGY MAY BB
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.

Kolliker, Theory of the Animal Cell.

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 Boussin
gault, Liebig, Matteucci, Beaumont.

INSTINCT AND INTELLIGENCE.
Kirby, Blumenbach, Spurzheim, Combe.

250

EMBRYOLOGY.

D' Alton, Von Baer, Purkinje, Wagner, Wolfe, Rathke, Bischoff
Velpeau, Flourens, Barry, Leidy.

PECULIAR MODES OF REPRODUCTION.
Ehrenbcrg, Trembly, ROsel, Sars, Loven, Steenstrup, Van Beneden.

METAMORPHOSIS.

St. Merian, Rosel, De Geer, Harris, Kirby and Spence, Bunneister
Reaumur.

GEOGRAPHICAL DISTRIBUTION.

Zimmerman, Milne Edwards, Swainson, A. Wagner, Forbes, Pennant,
Richardson, Ritter, Guyot.

GEOLOGY.

The Works of Murchison, 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 volumes, but are scattered through the volumes Oi
Scientific Periodicals ; such as the

Transactions of the Royal Society of London.

Annals and Magazine of Natural History.

Annales, and Archives, du Museum d' Hist. Natuielie.

Annales des Sciences Naturelles.

Wiegmann's Archiv fdr Naturgeschichte.

Mailer'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.

END OF PART I,

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