Elements of comparative zoology

ELEMENTS

OF

COMPARATIVE ZOOLOGY

BY

J. S. KINGSLEY, S D.

Professor of Zoology in Tufts College

NEW YORK

HENRY HOLT AND COMPANY
f-- 1897,

Copyright, 1897,

BY
HENRY HOLT & CO.

ROBERT DRUMMOND, ELHCTROTYPER AND PRINTER, NEW YORK.

PREFACE.

THE present volume is intended as an introduction to
the serious study of zoology. It embraces directions for
laboratory work upon a selected series of animal types and
a general account of related forms. Laboratory guides
are somewhat numerous, but general outlines of zoology
adapted to beginners are few. By combining the two,
it has been possible to emphasize the comparative side of
the subject. A knowledge of isolated facts, no matter how
extensive, is of little value in education, excepting as the
powers of observation are trained in ascertaining those
facts. Nature studies are truly educational only when the
student is trained to correlate and classify facts. A con-
siderable experience with students of different ages has
resulted in the conviction that it is not sufficient to ask one
to compare a grasshopper and a beetle, pointing out their
resemblances and points of difference; leading questions
must be asked. When the student has answered the ques-
tions under the headings " Comparisons" in the following
pages, he has a tolerably complete statement of the princi-
pal characters of the larger groups of the animal kingdom.

Several considerations have had weight in the selection
of types to be studied in detail. In the first place, so far
as possible, these should be such as are readily obtainable
in any locality. But there are certain important groups,
all the members of which are marine. The forms of these
which have been used can be purchased of dealers in labor-

iii

iv PREFACE.

atory supplies (see Introduction) at a cost of less than sixty
cents per pupil. In the second place, the number of forms
studied and the extent to which details of structure are
worked out must be such that the work outlined can be
done by students of average ability, in the time usually al-
lotted to such work in the ordinary course. Especial care
has been taken that time shall not be wasted in working
out features of no morphological importance. Counting
tail-feathers or fin-rays has no place in elementary zoology.

Again, the work has been made largely macroscopic in
character. Microscopes are expensive, and many institu-
tions feel that they cannot afford to provide each student
with one of these instruments. Then, too, there are
enough important facts to be discovered with scalpel and
hand-lens. Too many beginners have been lost among cell-
theories and drowned in staining-fluids. These properly
come after the elements of the study have been mastered.

In order of treatment the author has followed the se-
quence which he believes productive of the best results.
A strictly logical course would lead from the simple to the
complex, but in practice this has not been found as valu-
able as the order adopted here.

A number of illustrations have been prepared especially
for this work. Most of the others are credited to the
author from which they are taken. It may interest some
to know that Figures 2 and 127 were engraved for the
second part of Agassiz and Gould's " Principles of Zool-
ogy," which was never published.

TUFTS COLLEGE, MASS., June 14, 1897.

CONTENTS.

PAGE

Introduction 1

Dissection of Bony Fish 9

Dissection of Dogfish 17

Comparisons of Fishes 20

Selachii 21

Teleosts 24

Comparisons of Fishes 32

Pisces 33

Dissection of Frog 40

Dissection of Tadpole 47

Comparisons of Ichthyopsida 48

Batrachia, or Amphibia 49

Comparisons of Ichthyopsida 54

Ichthyopsida 55

Dissection of Turtle 56

Dissection of Snake 58

Dissection of Bird 59

Comparisons of Sauropsida 63

Reptilia 64

Aves 71

Comparisons of Sauropsida 84

Sau ropsida 85

Dissection of Rat 86

Comparisons of Vertebrates 96

Mammals 97

Comparisons of Vertebrates 125

Vertebrata 127

Chordata 153

Dissection of Crayfish or Lobster , 157

Dissection of Sow-bug 162

Comparison of Crustacea 163

v

vi CONTENTS.

PAGE

Decapoda 164

Tetradecapoda 168

Dissection of Grasshopper 170

Dissection of Cricket 176

Dissection of June-bug 177

Dissection of Dragon-fly 178

Dissection of Bee or Wasp 179

Comparisons of Mandibulatae 179

Orthoptera 181

£oleoptera 184

Hymenoptera 188

Dissection of Squash-bug 192

Dissection of Butterfly 193

Comparisons of Haustellatae 193

Hemiptera 194

Lepidoptera 199

Comparisons of Arthropods 205

Crustacea 208

Hexapoda 213

Comparisons of Arthropods 225

Arthropoda 226

Dissection of Earthworm 235

Comparisons of Segmented Animals 238

Annelida 239

Vermes 242

Dissection of Clam 248

Dissection of Oyster 251

Dissection of Squid 252

Comparisons of Molluscs 256

Acephala 258

Cephalopoda 264

Comparisons of Mollusca 268

Mollusca 269

Dissection of Starfish 278

Dissection of Sea-urchin 282

Comparisons of Echinoderms 284

Asteroida 285

Echinoida • 288

Comparisons of Echinoderms 290

CONTENTS. vii

PAGE

Echinoderma 291

Dissection of Sea-aneinone 296

Study of Hydroid 299

Comparison of Coelenterates 300

Scypliozoa 301

Hydrozoa 305

Comparisons of Ccelenterates 309

Coelenterata 310

Dissection of Sponge 314

Sponges 316

Metazoa 318

Protozoa 321

Comparative Physiology 324

Morpliology of Animals 331

The Animal Kingdom 337

Appendix 341

Index.. . 345

ELEMENTS OF COMPAEATIVE ZOOLOGY,

INTKODUCTION.

Every true teacher must have his own methods, but
some suggestions as to the way in which this book is
intended to be used may be of value. In the first place,
the laboratory work is regarded as most important, since
through it the student is trained in observation — a train-
ing utterly lacking in all the non-scientific studies of the
school curriculum; and also since by it he acquires an
autoptic knowledge of the animals studied. It is be-
lieved that every point mentioned in the laboratory direc-
tions can be made out by students in the high-school

Each student should make all the drawings called for.*
Drawing the object seen is one of the greatest aids to
observation, and every pupil, no matter how lacking in
artistic ability, can make intelligent sketches of all points
called for. These sketches have great value for the
teacher, since by their aid one can see at a glance any
errors or difficulties. All questions- asked should be an-
swered in the note-book.

At various points are questions grouped under the head-
ing " Comparisons." These questions are based upon the

* The expression " X 2," " X 6," etc., means magnified two times,
six times, etc,

1

2 ELEMENTS OF COMPARATIVE ZOOLOGY.

previous dissections, and are intended to bring out clearly
in the student's mind the essential points of resemblance
and of difference in the forms studied, and the bearings of
the facts discovered. Laboratory work trains the powers
of observation; the answering of the questions leads to a
systematization of knowledge and an exercise of the rea-
soning powers. The value of nature studies lies more in
the training of the mind than in the acquisition of facts.
Hence each pupil should be required to hand in answers to
these questions, and to make these answers as detailed
as possible.

Following each laboratory section is a general account of
allied forms and a statement of the principal character-
istics of the group, thus giving a completeness to the
knowledge which otherwise would be utterly lacking. In
these general statements there are frequent references to
the sections where the student has worked out the point
for himself. The work throughout is based upon the in-
ductive method, and finally the animal kingdom is shown
as a whole.

APPAKATUS NECESSARY.

The room used for laboratory purposes should be well
lighted and should be furnished with running water.
There should be receptacles for waste, and the students
should be made to keep everything clean.

The tables for laboratory work should be low (not over
29 inches from the floor), and should afford each student
at least six square feet of surface. It is best that there
should be no varnish upon them, as this makes trouble
when alcohol is spilled.

Each student should have the following instruments : A
scalpel ; a pair of scissors j a pair of forceps ; two dissecting-

INTRODUCTION. 3

needles (made by inserting the eye end of a needle in a
stick about the size of a lead-pencil) ; a magnifying-glass
(a simple lens of about one-inch focus) ; a dissecting-pan ;
a jar of alcohol (70$) ; a note-book, pencils, and drawing-
paper. As the animals to be dissected are small, the
instruments should be of moderate size, delicacy being
preferable to strength. The dissecting-pans (preferably of
copper) should be about 6 by 12 inches, with flaring sides
an inch and a half in height. The bottom should be
covered to about one quarter of an inch in depth with
wax, so that the specimen may be pinned out during dissec-
tion. For most purposes it is better if the wax be black-
ened by lampblack.* At the close of each dissecting
period the specimen should be placed in the jar of alcohol
for preservation until the next time. For this purpose the
three-pound glass butter-jars with screw-tops are good.

The pencils should be hard (6H, Faber), and the points
should be kept sharp with a file or emery-paper. For
drawings a smooth, hard-surfaced unruled paper is best,
Bristol-board, aside from expense, being preferable. The
drawings should be in outline only; shading should not
~be attempted. Frequently the use of colored pencils will
make the sketches more intelligible, and for this purpose
the following conventional colors may be suggested :

Arterial circulation, red. Venous circulation, blue.

Alimentary canal, brown. Liver, green.

Kidneys, purple. Keproductive organs, yellow.
Nerves, gray.

The laboratory should be provided with an oil-stone for

* Instead of wax, the cheaper ozokerite (to be obtained of wholesale
druggists) may be used.

4: ELEMENTS OF COMPARATIVE ZOOLOGY.

sharpening instruments ; a pair of bone forceps * for cut-
ting hard substances; a hypodermic syringe and other ap-
paratus for injection (see Appendix) ; a skeleton of at least
one representative of each great group of Vertebrates ; and
at least one good compound microscope.

MATERIALS FOE DISSECTION.

The forms selected for study are, so far as possible, such
as can readily be obtained in any locality by taking a little
pains at the proper season. There are, however, certain
groups of animals which occur only in the sea, and repre-
sentatives of these must be obtained from the shore.
These marine forms selected are Embryo Dogfish (Squalus),
Squid (Loligo), Sea-urchin (Arbacia), Starfish, Sea-anemone
(Metridiiim), Hydroid (Pennaria), and Calcareous Sponge
(Grantia). The series may be obtained from dealers f at
a cost not exceeding sixty cents per student. Orders for
these should be placed in the early summer, so that no
difficulty or delay may occur later. Much of the other
material may be obtained when wanted, but such as can-
not be had in the colder months — frogs, tadpoles, snakes,
turtles, crayfish, insects, earthworms, etc. — should be col-
lected in the summer and preserved in alcohol or formol J

* In place of the expensive bone forceps of dealers in surgical in-
struments one can use the oblique-cut pliers to be purchased at any
hardware dealer's.

f Supply Department, Marine Biological Laboratory, Wood's Hole,
Mass.

Prof. H. W. Conn, Middletown, Conn.

F. W. Walmsley, Bridgeton, N. J.

Leland Stanford University; Stanford University P. 0., California.

These dealers issue price-lists.

| See Appendix for preservative fluids and methods

INTRODUCTION. 5

for use later. Those which require injection should be so
prepared before being placed in the preservative fluid.

As far as possible, all dissections should be performed
under water. This buoys up the various parts, and makes
their shapes and relationships more evident than they
otherwise would be.

REFERENCE BOOKS.

In the classroom there should be some works of reference,
and the teacher should have and use others. As an aid in
selection of these works the following remarks may be of
value :

There are a number of guides for the dissection of ani-
mals. One of the oldest and best of these is the " Practical
Biology " of Huxley and Martin (Macmillan & Co.), which
deals with both plants and animals in a thorough manner,
although but a few forms are included. Of a somewhat
similar character is Dodge's "Elementary Practical Biology"
(Harper & Brothers), which enters more into the physio-
logical side of the forms studied. Descriptions of more
forms will be found in Bumpus' "Invertebrate Zoology"
(Holt), Brooks' "Invertebrate Zoology" (Cassino), and
Parker's " Zootomy " (Macmillan & Co.), the latter includ-
ing only vertebrates. The works of Brooks and Parker are
illustrated.

For general accounts of the structure of animals, giving
general statements for all groups, Jackson's edition of
Rolleston's " Forms of Animal Life " (Macmillan) and
Gegenbaur's " Comparative Anatomy" (out of print; only
to be found second-hand) are good. The general structure
of invertebrate forms is covered by Lang's " Text-book of
Comparative Anatomy " (Macmillan), Shipley's " Inverte-
brate Zoology" (Macmillan), McMurrich's " Invertebrate

6 ELEMENTS OF COMPARATIVE ZOOLOGY.

Morphology " (Holt), and Huxley's (t Anatomy of the Inver-
tebrates " (Appleton). Of these Lang's work is the most
detailed ; Huxley's is rather old ; Shipley's is the simplest.
The structure of. the vertebrates will be found in Wieders-
heim's " Comparative Anatomy of the Vertebrates" (Mac-
millan), Huxley's "Anatomy of the Vertebrates" (Appleton).

The development of animals is discussed in the following
works : Balfour's " Treatise on Comparative Embryology "
(Macmillan), Korschelt and Heider's "Text-book of Em-
bryology" (Macmillan; one volume published so far), Hert-
wig's " Text-book of Embryology " (Macmillan), and
Minot's " Human Embryology" (Wm. Wood & Co). Bal-
four's treatise is a standard, but is rather old. Korschelt
and Heider deal only with invertebrates ; Hertwig and
Minot only with vertebrates.

Good general zoologies are comparatively few. Under
this head are here included works which treat of the struc-
ture, development, and classification of animals. Possibly
the most widely used work is Claus's " Elementary Text-
book of Zoology,'* 2 vols. (Macmillan & Co.), which, how-
ever, is largely based upon European forms. The " River-
side Natural History, "6 vols. (Hough ton, Mifflin & Co.), is
more popular in style, and deals largely with American ani-
mals. Somewhat similar English works are the " Cambridge
Natural History," 10 vols. (Macmillan & Co.), and the
" Royal Natural History " (edited by Lydekker).

The broader and more general biological principles,
without reference to classification and description of forms,
maybe found in Parker's "Elementary Biology" (Macmil-
lan) and Hertwig's " General Principles of Zoology" (Holt).

Besides these there are a number of good works treating
of special groups of animals. The student at the seashore
of our New England States finds Smith and VerriU's " In-

INTRODUCTION. 7

vertebrates of Vineyard Sound " indispensable. This was
published in the Eeport of the U. S. Fish Commission for
1871-2, but separate copies may be had from dealers in
scientific books. Emerton's " Life on the Seashore" (Cas-
sino) covers much the same ground, but in a more elemen-
tary manner. For the identification of vertebrates Jordan's
" Manual of the Vertebrates" (McClurg) is the standard.
There are two good works upon molluscs, Woodward's
" Manual of the Mollusca " (London) and Tryon's " Struc-
tural and Systematic Conchology," 3 vols. (Philadelphia),
both well illustrated. The insects are treated well in Corn-
stock's " Manual of the Study of Insects" (Comstock Pub.
Co., Ithaca, N. Y.) and Hyatt and Arms' "Insecta"
(Heath, Boston). An older work, but still of great value, is
Harris' "Insects Injurious to Vegetation " (Boston).

There are several works dealing with birds. Of these
possibly Coues' "Key to North American Birds" (Estes &
Lauriat) is most widely known. Ridge way's " Manual of
North American Birds" (Lippincott) is also good, as is
Chamberlain's edition of Nuttall's " Ornithology " (Boston).

There are also several more special works which are of
great value in the laboratory or study-room. Among these
are Huxley's "Crayfish" (Appleton & Co.), Ecker's
" Anatomy of the Frog " (Macmillan), Darwin's " Earth-
worms and Vegetable Mould" (Appleton), and his "Coral
Reefs." Dana's " Corals and Coral Islands " (Dodd, Mead
& Co.) is a later work. The teacher will find much valu-
able material in the zoological articles in the Encyclopedia
Britannica, though these are very unequal in treatment.
Some of the best of them have been reprinted in " Zoologi-
cal Articles " by Lankester and others (A. & C. Black).

A dictionary of scientific terms is frequently asked for.
Any of the more recent unabridged English dictionaries.

8 ELEMENTS OF COMPARATIVE ZOOLOGY.

will contain almost every zoological term one runs across in
most books. Several so-called dictionaries of scientific
terms have been published, but as yet not a single one of
any value has appeared.

The teacher should remember that science is continually
growing, and that text-books and manuals grow old. He
should therefore have access to some of the scientific jour-
nals. Among those most valuable to the teacher of natu-
ral history are the American Naturalist (Philadelphia) and
Natural Science (London). Nature (London) and Science
(New York) are weekly publications which include all
sciences.

LABORATORY WORK: FISH.

For this purpose any common fish — perch, sucker, pout,
etc. — from ten to twelve inches in length will answer. If
time permit, it will prove very advantageous to take two
different fishes and work out the following points, compar-
ing their resemblances and differences.

I. EXTERNAL CHARACTERISTICS.

TOPOGRAPHY OF BODY. Distinguish in the fish anterior
and posterior, a back (dorsum) and a belly (venter), and
right and left sides. Make out the regions : head, trunk,
and tail. Is there a neck ? Where is the mouth ? the
vent ?

How many fins can you find ? How many are in pairs ?
How many single ? Are any in the median line of the
body ? Is there a skeleton to the fins ? Could you regard
a fin as a fold of the skin supported on soft or spiny
rays?

Of the median fins the caudal terminates the tail, the
dorsal is on the back, the anal is just behind the vent.
Are there two of any of these ? Are the upper and lower
lobes of the caudal equal (homocercal) or unequal (hetero-
cercal).

Can the paired fins be compared in position to your
own limbs? By feeling, ascertain if there be any solid
support in the body for either pair. How does this con-
dition compare with that in man ? The anterior paired

9

10 ELEMENTS OF COMPARATIVE ZOOLOGY.

fins are the pectorals; the posterior are the pelvic or ven-
tral fins.

INTEGUMENT. On the trunk and tail are scales. Are
they regularly arranged ? Are there scales on the head ?
Do they extend on the fins ? Is there any skin over the
scales ? Is there skin on the head ? Can you trace the
skin of the head into the mouth ? Find dark pigment
spots on the body. Does the color belong to the scale or to
what ? Settle by pulling out a scale.

Notice the lateral line running along a row of scales on
either side of the body. Does it continue on the head ?
Examine the scales with a hand-lens and see what causes
the line. Examine any scale with the hand-lens. Is it
margin regularly rounded (cycloid), or is it toothed or spiny
behind (ctenoid) ?

THE HEAD. How many eyes are there ? Where are
they placed ? Are they movable ? Are eyelids present ?
Notice in each eye the colored iris around the central
black pupil.

What is the position of the mouth ? See that it has a
bony framework, the upper jaw being composed of a pre-
maxillary in front, and behind this a maxillary which
when the mouth is open slides over the dentary or lower
jaw. Do any of these bones bear teeth ? Open the mouth
and examine the tongue. How much can it move ? Can
you find teeth anywhere inside of the mouth ? Feel with
a pin.

How many nostrils, and where . situated ? Probe with a
bristle. Do they communicate with the mouth ? Can you
find any ears ?

THE BRANCHIAL APPARATUS. Find the gill-opening,
a crescentic slit on the side bounding the head behind. In
front of it is the gill-cover or operculum, which may be

DISSECTION OF A BONY FISH. 11

divided into the operculum proper (composed of several
parts) and the branchiostegal membrane, supported by the
bony branchiostegal rays, which completes the apparatus
below. Connecting the branchiostegal region with the
trunk is the narrow isthmus, separating the gill-openings
of the two sides.

Lift the operculum and see the gills. Each is composed
of rows of red gill-filaments supported on a branchial arch.
Between the successive arches are the gill-clefts. How
many are there of these ? Open the mouth and see how
the gill-clefts are connected with the posterior part (pharynx)
of the cavity. Could you regard them as slits in the wall
of a tube ? Notice that each arch contains a solid support.
Can you see a red blood-vessel running along each arch ?

Draw a sketch of the left side of the body, inserting and
naming all parts that can be seen from the surface.

INTERNAL STRUCTURE.

With scalpel and forceps remove a piece of skin from one
side of the fish, exposing the underlying muscles. Notice
that these are arranged in chevron-like plates, eacli plate
(myotome) extending from back to belly, and being divided
into dorsal and ventral portions. Pick among the ventral
parts of the muscle-plates. Do you find any ribs ? How
are they arranged with regard to the myotomes ?

Open the fish by cutting with the scissors from just in
front of the vent, forward, in the median line, to the
pectoral fins, taking care to cut nothing but the body- wall.
Make other incisions transverse to the first, so that the body-
wall on either side may be turned out like a flap, thus
opening up the body-cavity, or coelom, containing the
viscera. Without further dissection notice the membrane
(peritoneum) lining the cavity. Is it silvery or pigmented ?

12 ELEMENTS OF COMPARATIVE ZOOLOGY.

In the front part of the cavity is the large reddish or
brownish liver ; turn this over to the left and expose the
stomach, connected apparently with the front wall of the
body-cavity. Pass a probe from the mouth through the
oesophagus or gullet into the stomach. From the stomach
the intestine passes back to the vent. From what part of
the stomach does it arise.* Is it straight? How is it sup-
ported in its position ?

Study the liver more carefully. On its anterior surface
see blood-vessels (hepatic veins). Where do they go ? On
its posterior surface is the thin-walled green or yellow gall-
bladder. Can you trace any connection between liver and
intestine ?

Where is the thin membrane (mesentery) supporting the
intestine attached to the body-wall ? Can you find blood-
vessels in it ? From where do they seem to come ?

Pull the intestine to one side, and expose the reproduc-
tive organs in the posterior part of the body-cavity. The
testes are usually white, the ovaries yellow or pink. Both
vary in size according to the season. Are either of these
structures paired ? Trace their ducts backwards, and see
where they empty. In the dorsal part of the body-cavity
look for the air-bladder (lacking in some fishes). Can you
find a duct connecting it with the oesophagus ?

Make a drawing from the side showing the organs studied,
and leaving space for additions. Then cut away these parts
and find, dorsal to the air-bladder, the long, dark red
kidneys. Are they enlarged in front (head-kidneys) ? Can
you trace the kidney duct ?

Continue the median ventral incision forward between

* In many fishes worm-like blind tubes (pyloric caeca) arise at the
junction of stomach and intestine. Their purpose is to increase the
surface secreting the digestive fluids.

DISSECTION Off A BONY FISH. 13

the pectoral fins nearly to the isthmus, taking care as before
not to cut the underlying parts. Cut away the thin parti-
tion (false diaphragm) just in front of the liver. This will
lay open the pericardial cavity (part of the coelom).

In the pericardial cavity lies the heart. It consists of a
triangular ventricle below (in the normal position of the
fish) and a more dorsal auricle. In front the ventricle gives
off a blood-vessel, which at first has a conical enlargement
(arterial bulb), and then is continued forward as the ven-
tral aorta. Behind the heart is a blood-cavity (venous
sinus) extending across the body-cavity in front of the false
diaphragm. How are the hepatic veins (p. 12) related to
this?

Inject the blood-system by inserting the canula of an
injecting syringe (see Appendix) in the arterial bulb and
forcing some colored fluid * forward through the ventral
aorta. After the injection follow the ventral aorta forward,
tracing its branches (afferent branchial arteries) into the
gill-arches (p. 11). What relations do these branchial
arteries and ventral aorta bear to the pharynx ?

Now cut away the floor of the throat and trace in the
gill-arches the efferent branchial arteries to their union
above the gullet in the longitudinal blood-vessel, the dorsal
aorta. Can you find this aorta in the roof of the peritoneal
cavity ? Could the blood-system, so far as you have studied
it, be described as two longitudinal vessels lying on either
side of the alimentary canal, and connected by a series of
paired transverse vessels ? What must be the course of the
blood in the different parts of the system ? Draw a dia-
gram illustrating the relations of the circulatory apparatus
to the alimentary canal and gill-slits.

* None of the gelatine mixtures answer well here, as the necessary
heat weakens the walls of the blood-vessels.

14 ELEMENTS OF COMPARATIVE ZOOLOGY.

Pick into the side of the tail until the backbone (vertebral
column) is reached. Take out a small piece of it and clean
it by boiling a few minutes. . Wash away the flesh, and see
that it is made up of a series of bones (vertebrae), arranged
one after the other. Examine a single vertebra, making out
the following parts: (1) A body or centrum, shaped like an
hour-glass and hollow at either end, (amphicoelous). Do
the hollows of the two ends connect ? (2) Arising from
the centrum two bony plates (neural processes), uniting
above into a single neural spine. These together form a
neural arch; so-called, since the great nervous (neuron,
nerve) structure, the spinal cord, passes through it. (3)
On the opposite or ventral side of the centrum a similar
haemal arch, composed of haemal processes and haemal spine.

Examine in the same way a vertebra in the trunk region.
Can you find the same parts ? Do the ribs correspond to
neural arches or to haemal arches, or are they something
different from either ?

Draw a front view of trunk and caudal vertebrae, naming
the parts

In another bit of the back-bone, near the head, see the
spinal cord passing through the neural arch. Can you find
any nerves given off from it ? How are they arranged ?

In the tail region see blood-vessels passing in a similar
manner through the haemal arch (Jiaima, blood). Pull
apart two vertebrae and see what fills the cavities in the
ends.

Cut off the head, and after picking away the muscles at
the hinder part of the skull above, carefully slice off the top
of the skull with a strong knife, taking only thin slices and
exercising great care after the cavity of the skull is ex-
posed. Enlarge the opening by picking, and then with
great care pull away the loose gray matter which covers the

DISSECTION OF A BONY FISH. 15

white or pinkish brain. When this is exposed make out in
it the following parts, beginning in front :

(1) The olfactory lobes tapering in front into the nerves
going to the nasal pits (p. 10).

(2) Two rounded oval masses (cerebral hemispheres)
meeting in the middle line in front, and together constitut-
ing the cerebrum.

(3) The 'twixt-brain, also two-lobed, but lying at a
lower level.

(4) The large, paired, rounded optic lobes.

(5) The unpaired cerebellum crowded in between the
optic lobes behind and extending back over the base of —

(6) the medulla oblongata, also unpaired, which in
turn tapers into the spinal cord.

Draw the ' brain from above, three times the natural
size, naming the parts.

Cut off the tops of the various regions of the brain. Do
you find cavities (ventricles) in any of them ? Can you
find any nerves going from the brain ?

Boil the head of another fish for a few minutes, and then
pick away the flesh as far as possible with the forceps,
taking care not to pull any of the bones from their proper
positions. This will expose the skull, composed of numer-
ous bones. See that these can be grouped in the following
regions :

(1) The opercular apparatus, consisting of the several
bones composing the gill-cover (p. 10).

(2) The facial portion, made up of the jaws and parts
connected with them; numerous small bones around the
eye, etc. See how the lower jaw is suspended from the
skull. Does anything like this occur in man ?

(3) The cranium, consisting of a number of bones
which form a box to enclose and protect the brain.

16 ELEMENTS OF COMPARATIVE ZOOLOGY.

Remove the other bones from the cranium and notice
the various openings through which nerves and blood-ves-
sels find passage, and especially the large opening (fora-
men magnum) through which the spinal cord passes from
the brain to extend along the back. Can you find a place
especially fitted for the junction (articulation) of skull and
vertebral column ?

On the sides of the hinder parts of the cranium are the
thin-walled ear-capsules. Cut into one and open the sac
(vestibule) of the ear containing a large ear-bone (otolith).

LABOKATOBY WORK: EMBRYO DOGFISH.

EXTERNAL CHARACTERS.

How do the fins compare with those of the fish already
studied ? Have they a supporting skeleton ? Answer by
pulling off a bit of the skin from the pectoral fin. Is the
caudal fin homocercal or heterocercal (p. 9) ?

Place a bit of the skin in a drop of glycerine on a slide,
and after an hour examine it under the microscope. No-
tice the scales. How do they differ from those of the bony
fish ? This kind of scale is called placoid.

THE HEAD. — Are the eyes in the same position as in the
other fish ? Where are the nostrils ? Do they communi-
cate with the throat? Where is the mouth? Open it
and look for teeth. Do you find them in the same places
as in the bony fish ? Is there a tongue ? Behind each eye
is a hole (spiracle). Does it communicate with the mouth ?
On the sides of the "neck" occur the gill-slits. How
many are there ? How does this condition compare with
that in the bony fish ?

Draw the fish from the side.

INTERNAL STRUCTURE.

Open, as in the bony fish, by cutting from the vent for-
ward to the pectoral fins. Make cross-cuts and pin out the
walls. Can you see the myotomes (p. 11) ?

Trace the alimentary canal, In the front part of the

17

18 ELEMENTS OF COMPARATIVE ZOOLOGY.

body-cavity is the two-lobed liver, and between its lobes
find the u-shaped stomach. The intestine begins at the
end of the u. Cut off a bit of its wall with the scissors
and see the spiral valve inside. What function can you
suggest for it ? Is there a mesentery ?

Remove the alimentary canal, and on the roof of the ab-
dominal cavity see two long ridges on either side of the
mesentery. The outer ones are the kidneys, the inner pair,
much shorter, the reproductive organs.

Cut off the skin between the pectoral fins and clean the
muscles from the support of the fins (pectoral girdle)
which crosses the median line. Is this composed of bone ?

Cut through the pectoral girdle and lay open the peri-
cardial cavity. Is the heart like that of the bony fish ? In
front of the ventricle is an arterial cone. How does this
differ from the arterial bulb (p. 13) ? Trace the ventral
aorta into the afferent branchial arteries by carefully pick-
ing away the muscles.

Now cut back from either angle of the mouth along the
lower margin of the gill-slits, and turn back the lower jaw
as a flap. Now the gills can be studied, and in the cut
arches the gill-cartilages can be seen. How do the gills
differ from those of the bony fish ?

Slit the skin on the roof of the mouth and carefully
remove it with the forceps. This will expose the efferent
branchial arteries, which can readily be traced to their
union into the dorsal aorta.

Cut off the tail, and in the cut surface make out
the following points : In place of bony structures in the
position of the centrum (p. 14) a gelatinous notochord
forming the axis of the column, surrounded by a tough
notochordal sheath. Above and below neural and haemal
arches surrounding spinal cord and blood-vessels. On the

DISSECTION OF A DOGFISH (SHARK). 19

sides of the body, just beneath the skin, find the canal of
the lateral line (p. 10).

Split the skin in the median line on top of the head and
pull it off. On its under surface find the branching canals
of the lateral line system.

Now carefully slice off the top of the skull, exposing the
brain. Enlarge the opening and compare the brain with
that of the bony fish. Notice especially the difference in
relative size of parts. Draw the whole brain.

Cut away carefully the side walls of the cranium, expos-
ing the nerves coming from the brain. In this process you
will lay open the semicircular canals of the ear, behind the
spiracle, and, deeper down, the vestibule (p. 16). In this
last will be found a granular mass. Examine some of
it under the microscope in a drop of water and notice the
character of the small particles (otoliths). The principal
nerves that you will find will be the olfactory, going to the
nose; the optic, arising from the lower surface of the brain
and going to the eye ; the trigeminal, arising from the
anterior sides of the medulla and passing forward to supply
the "face." Just behind this is the combined auditory
and facial supplying the ear and face, and still farther
back the large vagus, which goes back to the gills, the
lateral line, and the viscera. Trace these nerves as far as
possible, and insert them in your sketch of the brain.

Cut off the snout by an incision passing through the nos-
tril, and in the cut surface see the folds of the olfactory
membrane.

Have you found bone in any part of the dogfish ?

20 ELEMENTS OF COMPARATIVE ZOOLOGY.
COMPARISONS.

Divide a page of your note-book by a vertical line; label
one column Bony Fish and the other Dogfish, and in each
write the answers to the following questions, numbering
them as they are here :

(1) What kind of scales? (2) Where is the mouth?
(3) What is the shape of the caudal fin ? (4) How do the
gills differ ? (5) Where are the nostrils ? (6) What is the
character of the hard parts ? (7) Is there a spiral valve in
the intestine ? (8) What parts occur in the heart? (9) Is
there a swim-bladder ? (10) Is there an operculum ?

SELACHII (SHAKES AND SKATES).

These forms, of which the dogfish is an example, are
almost all marine. They are sharply marked off from the
Teleosts (p. 24) by several important characters. The
body is covered with placoid scales, the mouth and nostrils
are always on the ventral side of the body, the caudal fin is
heterocercal, the gill-slits (usually five in number) open
separately to the exterior, the skeleton is cartilaginous, the
heart has an arterial cone, and the intestine is provided
with a spiral valve. An air-bladder is lacking. There is
usually also a spiracle (p. 17). There are two orders of
Selachians.

ORDER I. — SQUALI (Sharks).

In the sharks the body is more or less cylindrical, and
the gill-slits open upon the sides of the neck. About 150
species are known, some, like the dogfish, being small,
others reaching an enormous size. Those forms which feed
on fish and the like have sharp cutting teeth, and these are
arranged in rows, one behind another, so that only one row
is in use at a time, the other serving as a reserve supply if
one of the front row be lost. In other sharks, which feed
on shell-fish, the teeth are flattened plates, the whole form-
ing a mill for crushing the shells. Most of the species are
much like the dogfish in their general appearance, but
there are strange forms. Thus in the hammer-head sharks
the sides of the front of the head are drawn out like a

21

22 ELEMENTS OF COMPARATIVE ZOOLOGY.

mallet, the eyes being on the outer ends of the lobes. In
the sawfishes the snout is drawn out in a long beak, either
edge of which is armed with sharp teeth.

FIG. 1.— Sawfish
(Pristis pecti-
natus). After
Goode.

FIG. 2.— Common Skate (Raia erincea).

ORDER II. — RAIJE (Skates, Rays).

In the skates and rays the body is usually flattened, and
the gill-slits are on the under surface. In most forms the
body is sharply marked off from the tail, but in those saw-
fishes which belong to this order the body is shark-like.
The width of body in the true skates is partly due to

SELACHII. 23

the fact that the pectoral fins are enclosed in it, the whole
making a disk, rounded or four-sided in outline. Most of
them are bottom feeders, living upon shell-fish, and hence
have flattened pavement- teeth. The torpedoes are remark-
able for their electrical powers. In them certain muscles
on the sides of the head are metamorphosed into an elec-
trical battery, the discharge of which is under control of
the will. The current is strong enough to kill small
animals which come into contact with the creature. The
largest of the skates are the huge tropical devil-fish, which
reach a length of twelve or more feet and a weight of 1200
Ibs.

TELEOSTS (BOKY FISHES).

The great majority of the forms which we ordinarily call
fishes belong to the group of Teleosts or bony fishes, so
called from the abundant bony matter in the skeleton. In
all, the mouth is at the tip of the snout, the nostrils on the
upper surface, and the caudal fin, though heterocercal in
the young, is homocercal in the adult. The skull is covered
with numerous bony plates, and the body is covered with
either cycloid or ctenoid scales. Sometimes (trout) scales
are apparently lacking, but this apparent absence may be
due to their small size and their being buried in the skin.
The gills are covered by an operculum. Of the internal
features which characterize the group may be mentioned
the absence of a spiral valve in the intestine, the presence
of an arterial bulb in the heart, and, very frequently, of a
swim-bladder.

The thousands of species of bony fishes are variously
subdivided by naturalists accordingly as different structures
are made the basis of classification. One of the simplest
of these schemes recognizes six of these subdivisions or
orders, and is adopted here. To which does the specimen
you studied belong ?

ORDER I. — PHYSOSTOMI.

Bony fishes in which the gill-filaments are arranged on
the branchial arches like the teeth of a comb; with the pre-
maxillary and maxillary bones movable (p. 10) ; the dorsal,
anal, and ventral fins supported only by soft rays (p. 9) ;

24

TELE08TS. 25

and the ventral fins, when present, placed near the vent.
A swim-bladder is almost always present, and is connected
with the gullet by a tube through which it can be emptied
of air. The scales are usually cycloid (10). Most of the
forms belong in fresh water.

The catfishes and horned pout, with long filaments or
barbels about the mouth, belong here. In our Eastern
waters the species are small, but in the Mississippi basin
occur large species, some weighing a hundred pounds or
more. Many more species occur in the tropics of Africa
and South America, and some of these have the scales

FIG. 3.— Atlantic Salmon (Salmo salar). After Goode.

developed into a bony armor protecting the body. In
Africa occurs a species which, like the electrical eel, can
give a severe electrical shock.

The carp and minnows abound in fresh water, but,
excepting as they furnish food for other fishes, they are of
little importance, the carp of Europe being the least bad
food.

Much more valuable is the group of trout and salmon,
which are among the most important of food fishes. As a
rule these have a soft fin behind the rayed dorsal. The
salmon, of which there are one species on the Atlantic and
four on the Pacific coast, live in the sea and come into the
rivers to lay their eggs. The whitefish of the lakes are
closely allied forms.

26 ELEMENTS OF COMPARATIVE ZOOLOGY.

The "blind fish of Mammoth Cave should be mentioned
here. In this form a life in total darkness has resulted in
the degeneration of the eyes, which are buried beneath the
skin.

The savage, swift-swimming pike, pickerel, and muska-
longe, the latter reaching a length of eight feet, are, with
one exception, confined to America. They are noted for

FIG. 4.— Herring (Clupea harengus).

their voracity, and have been termed " mere machines for
the assimilation of other organisms."

Among the marine members of the order are the herrings,
shad, menhaden, fishes of great importance to man, both
as food and for the oil and fertilizers which are made from
them. They occur in large schools, and afford food for
numerous predaceous fishes.

Differing from the forms already mentioned are those
which may be grouped together as eels, fishes with elongate
bodies and without ventral fins. Most of the species are
marine, and those which live in fresh water go to the sea to
spawn. All are voracious creatures, and one South Ameri-
can species has marked electrical powers.

ORDER II. — ANACANTHINI.

These have the gills comb-like (p. 24) ; the dorsal, anal,
and ventral fins without spines; the ventral fins, when

TELEOSTS. 27

present, placed far forward between the pectorals; the
swim-bladder without connection with the gullet; and the
scales either ctenoid or cycloid. Mostly marine.

FIG. 5.— Cod (Gadus morrhua). After Storer.

But few of these forms need mention. Most important
of all are the cod and haddock, which stand beyond all
others as food fishes. They occur in the northern parts of

FIG. 6.— Winter Flounder (Pseudopleuronectes americanus). After Goode.

both oceans, and find their favorite feeding grounds on
those shallow spots known as " banks." The Grand Banks
of Newfoundland are constantly visited by fishermen from

28 ELEMENTS OF COMPARATIVE ZOOLOGY.

Europe and America, and have aptly been said to be the
richest banks in the world, honoring every draft upon them.
Allied to the cod is the strange group of flat fishes, the
halibut, flounders, turbot, and the like. In early life these
are symmetrical like other fishes, but as they grow older
they turn over on one side, and then the eye of that side
migrates to the upper surface, twisting the bones of the skull
in its progress. Henceforth the fish lives constantly in this
peculiar position, the side of the body turned downward
being white, the other colored. The halibut, occurring in
all northern seas, are among the largest fishes, occasionally
weighing 350 to 400 Ibs.

ORDER III. — ACANTHOPTERI (Spiny-finned Fishes).

In this, the largest order of bony fishes, the gills are
comb-like, the jaw-bones are movable (p. 10), and the
dorsal, anal, and ventral fins have spiny rays in front. In
some there is a swim-bladder, but it is without connection

FIG. 7.— Remora (Remoropsis ~brachypterd) . After Goode. The sucker is
shown on the top of the head.

with the gullet. Among the strange modifications in the
group are the suck-fish or Eemoras, in which part of the
dorsal fin is modified into a sucker, by which they attach
themselves to other fishes or floating objects, and are thus
carried about.

In the swordfishes the bones of the upper jaw are modified
into a long, stiff sword terminating the snout, and used as
a weapon of offence and defence. The largest species

TELEOSTS. 29

reaches a length of fifteen feet. In other points of structure
the swordfish are much like the mackerels, pompanos, and
bluefish, so well known as food fish. Of these the largest

FIG. 8.— Mackerel (Scomber scombrus).

is the tunny or horse-mackerel, which sometimes weighs
1500 Ibs.

In another group of perch-like formg the spines of the
fins are more developed. Here belong the perch, sea-bass
and porgies, the sheepshead and sunfish, sculpins, and a
long series too numerous to mention.

ORDER IV. — PHARYXGOGNATHI.

These are Acanthopteri in which the last branchial arches
are fused into a single bone, which thus resembles an addi-

FIG. 9.— Gunner (Ctenolabrus cmruleus). After Goode.

tional jaw in the throat, whence the name. All of the
species are marine, and with few exceptions they are trop-

30 ELEMENTS OF COMPARATIVE ZOOLOGY.

FIG. 10.— Swellfish (Chilomycterus geometricus) . After Goode.

FIG. 11.— Sunfish (Mold rotunda). After Putnam.

TELEOSTS. 31

ical. On our east coast are found the cunner and tautog;
on the Pacific occurs a group of surf -fishes (Embiotocidae),
remarkable for bringing forth living young.

ORDER V. — PLECTOGNATHI.

In this group of peculiar forms, almost all of which are
marine, the upper jaws are immovably united to the skull.

FIG. 12.— Sea-horse <• Hippocampus 'heptagonus) . After Goode.

Some are naked, others have the skin covered with spines
or bony plates. The spiny forms (swellfish) can erect the
spines by swelling out the body, and thus gain additional
protection. In the trunk-fishes the bony plates unite to

32 ELEMENTS OF COMPARATIVE ZOOLOGY.

form a solid box. In the sunfishes, which may weigh
500 Ibs., the body is almost circular in outline, and has a
distinctly chopped-oif appearance. As a whole, the order
bears most resemblance to the Acanthopteri. None are ol
the slightest economic importance.

ORDER VI. — LOPHOBRANCHII.

These are the most aberrant of bony fishes. The gills,
as the name implies, are tufted, and composed of small
rounded lobes packed in the gill-chamber. The opercular
apparatus is reduced to a simple plate, the small, toothless
mouth is at the end of a long snout, the skin is covered with
bony plates arranged in rings around the body. The
species, which are all small, are known, from their fanciful
shapes, as pipefishes and sea-horses. Many have a remark-
able peculiarity in breeding habits, in that the young are
carried for a time in a pouch beneath the tail of the male.

COMPARISONS.

Prepare another sheet as before, with columns for bony
fish and dogfish, and give answers to the following ques-
tions :

(1) Where does the animal live? (2) Is the surface
naked or scaly? (3) Is there a skeleton to the median
fins ? (4) Is there anything which could be called a hand
or foot? (5) Do the nostrils connect with mouth or
throat ? (6) How does the animal breathe ? (7) How
many auricles and ventricles to the heart ?

PISCES (FISHES).

The forms to which the name Fishes is usually applied
have a body adapted in shape and structure for an aquatic
life. It is usually covered with scales, which lie between
the two layers (corium and epidermis) of the skin, the lat-
ter extending over them. These scales may be of four
kinds, the placoid, ctenoid, and cycloid already mentioned
(pp. 10 and 17), and the ganoid, either rhomboid or circu-
lar in outline, and covered externally with a peculiar
enamel layer.

The fins are adapted to fanning the water, being broad
plates with an internal stiffening skeleton. Usually both
anterior and posterior paired fins are present, and these
are supported on skeletal arches or girdles (pectoral in
front, pelvic behind), which extend around the body
beneath, but which have no connection with the vertebral
column, nor with any structure like a breast-bone. The
pectoral, however, is frequently joined to the skull. The
paired fins are largely organs of balancing; the caudal is
the chief swimming organ. The caudal fin presents three
interesting conditions. In all fishes it is at first diphy-
cercal; that is, the vertebral column runs out in a straight
line, dividing the fin into equal and symmetrical lobes.
This condition is retained in a few forms. In others, with
growth, the vertebral axis becomes bent upwards, and a
secondary lower lobe is developed which, as it is smaller
than the other, gives the heterocercal condition (p. 9).

33

34 ELEMENTS OF COMPARATIVE ZOOLOGY.

FIG. 13.— Different Forms of Tails of Fishes. A, diphycercal ; B, hetero-
cercal ; C, D, homocercal.

PISCES. 35

This condition is permanent in the Selachii and most
ganoids, but in the bony fishes the lower lobe grows out
equal to the other (the tail becomes homocercal (p. 9),
although the skeleton shows a bent back-bone (Fig. 13,
CD)).

The nasal sacs are two, although occasionally four nos-
trils are present. In no case is there a passage through
them to the mouth-cavity, although it is interesting "to
note that in the skates a groove leads back from each of
these organs to the mouth, recalling a transitory condition
in the young of higher forms.

The gill-slits start as paired outpushings from the throat,
which later break through to the exterior. These may all
retain their separate external openings, or they may be cov-
ered up by a fold from the back side of the head growing
over them and forming an operculum. Water taken in
through the mouth is forced out through these slits, and is
thus brought in close contact with the thin-walled gills
lining their sides.

In many forms an air-bladder occurs. This starts as an
outgrowth from the dorsal wall of the oesophagus or gullet,
and in many this connection persists throughout life
(Physostomi), but in others the duct is closed later. The
bladder serves as a hydrostatic apparatus, and when it is
expanded the specific gravity of the fish is lessened and the
animal can rise, while when it is compressed the animal
sinks. In some forms the bladder is used in producing a
noise.

In all fishes the heart, situated in a pericardial chamber,
consists of two portions: an auricle, which receives the
blood returning from the body, and a ventricle, which
forces it forward through the gills to all parts of the animal.
In leaving the heart proper the blood first passes through

36 ELEMENTS OF COMPARATIVE ZOOLOGY.

an arterial cone or an arterial bulb. These differ in this:
the arterial cone is really an outgrowth of the heart, and
contains, on its interior, valves to prevent the flow of the
blood back into the ventricle; the arterial bulb, on the
other hand, is merely a muscular thickening of the ventral
aorta, and contains no valves.

The blood, returning to the heart, bears with it the waste
from all parts of the body, and prominent among these is

FIG. 14.— Types of Fish-hearts, a, auricle ; fc, bnlbus ; c, conus ; v, ventricle.

carbonic dioxide; in short, it is what physiologists call
venous blood. This is forced forward, through the ventral
aorta and the branchial arteries, to the gills. Through the
thin walls of these it comes in close connection with the
water, and the carbonic dioxide is given off, while oxygen,
from the air dissolved in water, is taken into the blood,
which thus becomes arterial blood, and is distributed to all
parts of the system through the dorsal aorta and other

It is interesting to note why a fish dies when taken from
the water. It is simply because it cannot obtain air enough.
When the fish is in the water the gills are floated out so
that all parts of them are exposed to the stream passing

PISCES.

37

through the gill-slits. When the fish is out these delicate
filaments mat together, reducing the surface for breathing;
and then, too, the gills soon become dry, and then are less
favorable for the exchange of carbonic dioxide and oxygen.

Among the peculiarities of the skull are the numbers of
branchial arches and the ease with which these, the oper-
cular structures, and bones of the face can be separated
from the cranium (p. 15). In the Selachii these, like the
rest of the skeleton, are composed of cartilage. In the
Teleosts this is largely replaced by bone. Another pecu-
liarity is that the lower jaw does not directly join (articu-
late with) the skull, but certain parts intervene between
the two, forming what is known as a suspensory apparatus.

The group of Pisces is divided into five subclasses.

SUBCLASS I. — SELACHII (p. 21).

SUBCLASS IL — HOLOCEPHALT.

A group of less than ten species of strange marine car-
tilaginous fishes in which the upper jaw is firmly united to
the cranium, the gills are covered by an operculum, and a
spiracle is lacking. Mouth and nostrils are ventral, as in

FIG. 15 — Chimcera monstrosa.

the sharks. The name Chimaera, given to some forms, em-
phasizes their strange appearance,

38 ELEMENTS OF COMPARATIVE ZOOLOGY.

SUBCLASS III. — GADOIDS.

These are remnants of a group once very abundant on
the world's surface, but now showing less than fifty living
species in the whole world, and most of these in North
America. Some of them are much like Selachians, others
like Teleosts, and still others go off towards the Holocephali.
The skeleton is bony or cartilaginous; the body may be
covered with ganoid or cycloid scales, or with bony plates,
or it may be naked; the tail either homo- or heterocercal ;
the gills are covered with an operculum. The heart is
provided with an arterial cone, and the intestine has a spiral
valve. A swim bladder occurs, and this has its duct, which,
in one form, empties into the ventral side of the O3sophagus.
With this confusing mixture of characters it is not strange
that many naturalists have split up the group and distrib-
uted its members among the other subclasses.

FIG. 16.— Common Sturgeon (Acipenser sturio). After Goode.

To it belong the sturgeons, the most sharklike of all,
some of which live in fresh water, while the marine forms
ascend the rivers to lay their eggs. From their ovaries are
made caviare, while their swim -bladders furnish the isinglass,
now so largely supplanted in domestic economy by gelatine.
Though some attain an enormous size, all feed upon small
animals, worms, insect larvae, etc=, which they find in the
mud. The garpikes, with their strongly armored bodies,
which also belong here, on the other hand, are very vora-

PISCES. 39

cious. The bowfin of the United States is the most like
Teleosts of all.

FIG 17.— Garpike (Lepidosteus osseus). After Tenney.

SUBCLASS IV. — TELEOSTS (p. 24).
SUBCLASS V. — DIPNOI (Lung-fishes).

Three or four species, one from Australia, one from
Africa, and one or two from South America, are the sole
living representatives of this group, which however occurs

Fro. 18.- Lung-fish (Protopterus annectens). After Boas.

as fossils in very old rocks. They have scaly bodies,
diphycercal tail, spiral valve, and a swim-bladder which is
used as a lung. Both pectoral and ventral fins are present,
and these are supported by a peculiar skeleton, while the
skull shows many strange features.

LABORATORY WORK: FROG.

EXTERNAL CHARACTERS.

If live frogs can readily be had, the student should have
a chance to study them alive before dissection. Notice the
way in which the eyes can be retracted. Notice especially
the way in which the frog breathes. Watch the nostrils
during the operation. On the back, a little in front of the
vent, may be seen a pulsation. This is produced by lymph-
hearts beneath the skin. Kill the frogs by wrapping them
in a cloth moistened with chloroform, and put them in a
close jar for an hour.

Notice the shape of the body. Can you find scales any-
where ? Is there anything like a tail ? How many appen-
dages are there ? How do they compare with your own
limbs? Open the mouth; where do you find teeth?
Where are the nostrils ? Probe them with a bristle. Where
does this appear in the mouth ? How does the tongue
differ from your own ?

Behind and a little below the eye is a circular tympanic
membrane (connected with the auditory apparatus). Cut
through this and insert a probe. Where does this appear
in the mouth ? With what does this Eustachian tube most
nearly correspond in the shark ? See the way the mouth-
cavity narrows behind to form the gullet. In front of this
see the slit-like glottis in the floor of the mouth.

In the fore limbs do you find parts corresponding to
arm, forearm, wrist, palm, and fingers ? How many fingers ?

40

DISSECTION OF A FROG. 41

In the hind leg do you find any parts besides thigh,
shank, ankle, instep, and toes ? If you have any difficulty,
compare the way in which the joints bend with those in
your own body, and find where your trouble is.

INTERNAL STRUCTURE.

Beginning just in front of the vent, slit the skin of the
ventral surface in the middle line forward to a point be-
tween the shoulders. Turn back the skin on either side.
Is it firmly attached to the underlying muscles ? Are there
blood vessels on its inner surface ? Notice the muscles ;
can you find any muscle -plates (p. 11) ?

Next cut the muscles in the same way, a little to the
(animal s) left of the middle line, carrying the incision for-
ward through the hard parts between the shoulders, and
taking great care to keep the underlying parts uninjured.
This lays open the peritoneal cavity (ccelom). Insert a blow-
pipe into the gullet and inflate the stomach. Is there any
sharp boundary between it and the intestine ? Is the in-
testine more or less coiled than in fish or dogfish ? Is it
of the same size throughout ? How is it suspended ?

Does the liver cover the stomach ? Turn the liver for-
ward and look for the greenish, spherical gall-bladder and
the light-colored, lobulated pancreas. Do you find ducts
from either of these to the intestine ? Farther back, in
the mesentery, near the enlarged portion (rectum) of the
intestine, is the. red spleen. At the posterior portion of the
peritoneal cavity is the thin-walled urinary bladder. With
what is it connected ?

Draw the digestive organs, showing the position of the
deeper structures by dotted lines.

Turn the intestines, etc., out of the body, exposing the

42 ELEMENTS OF COMPARATIVE ZOOLOGY.

reproductive organs and kidneys. These will differ in
their appearance in the two sexes.

In the male a yellowish, rounded body (testis) occurs on
either side of the median line, and just in front of each
are the yellowish, lobulated fat-bodies. Beneath (dorsal to)
the testes are the reddish -brown kidneys, each having on
its ventral surface a yellowish or golden adrenal.

What is the shape of the kidneys ? Are the testes and
kidneys connected in any way ? Do you find the ducts
(ureters) leading back from the kidneys ? Where do they
end?

In the female, the ovaries, crowded with dark-colored
eggs, occur in the place of the testes, their size depending
upon the season. Near them are the coiled oviducts.
Trace these forward and back to their terminations. Do
you find the fat-bodies ? Do kidneys and adrenals corre-
spond to the conditions described for the male ? Are these
ureters distinct from the oviducts ? Draw the reproductive
and urinary organs of your specimen.

Insert a blowpipe in the glottis (p. 40) and inflate the
lungs. What is their shape ? Are they made up of little
chambers (air-cells) throughout ?

Between lungs and liver is the pericardial cavity, and
through its walls in the freshly killed specimen the beating
of the heart can be seen. Open the pericardium very care-
fully and expose the heart; make out the ventricle behind,
and the auricles in front. Arising from the ventricle and
crossing the auricles is the arterial trunk. Carefully clean
this from the surrounding tissues and trace* it to its

* This is best done in an injected specimen. The injection can be
made by opening the ventricle and through it inserting the canula
into the arterial trunk and tying it there. Then force in the in-
jecting fluid.

DISSECTION OF A FROG. 43

division. Then follow each trunk. The right one soon
divides into three branches; the anterior is the carotid, the
middle the aortic arch, the third the pulmonary artery.
How does the trunk of the left side differ ?

Trace the carotid arch ; where does it go ? What be-
comes of the aortic arch ? Do you find a dorsal aorta ?
On which side of the alimentary tract should the dorsal
aorta be (p. 13) ? To what organs is the pulmonary artery
distributed ? Do you find anything to compare with the
ventral aorta (p. 13) and afferent and efferent branchial
arteries ? Draw the circulatory system as made out.

Place a drop of blood of the frog on a slide, cover it
with a cover-glass, pressing it well down, and examine
under the higher power of a microscope. What is the shape
of the corpuscles ? Are all alike in shape and size ? Stain
with fuchsin (see Appendix) and study again. Are all
parts equally stained ?

Split the skin along the back and pull it away. Find the
point where the head joins the back-bone; and beginning
here, with a strong pair of scissors cut away the roof of the
skull bit by bit, taking great care not to injure the brain.
Then in the same way cut away the neural arches of the
vertebra. This will expose the brain and spinal cord. The
later work will be more easily followed if the animal be put
for a day or more in 70$ alcohol.

In the spinal cord notice the spinal nerves given off at
regular intervals on either side. How many are there?
What relationship do they bear to the bodies of the verte-
brae ? Examine these spinal nerves more closely, and see if
each is double (has dorsal and ventral roots). Follow one
out by carefully cutting away the bone, and see where the
roots unite. Has either root an enlargement (ganglion) ?
Look in the dorsal part of the body- cavity for these spinal

44 ELEMENTS OF COMPARATIVE ZOOLOGY.

nerves. Trace the posterior ones back to their union
(plexus) to form the sciatic nerve going to the hind limb.

In the brain, between the eyes, are the cerebral hemi-
spheres. Are they separate ? In front are the olfactory
lobes. Are they separate ? Behind the cerebrum, and at a
lower level, is the 'twixt-brain. Next come the optic lobes,
and behind them the medulla. What has become of the
cerebellum (p. 15) ?

Sketch the brain and spinal cord from above, inserting
all the nerves seen, and making the sketch twice the size of
nature.

Cut across the olfactory nerves and turn the brain back-
wards. This will show the optic nerves. Cut these as far
as possible from the brain, and do the same with other
nerves farther back, at last removing the brain from the
skull.

On its under surface trace the optic nerves back to the
brain. Does the right nerve connect with the right optic
lobe ? Behind the optic nerves is a small projection, the
pituitary body. How many nerves can you find arising
from the side of the medulla ?

"With a sharp scalpel split the brain horizontally and ex-
amine the cavities found. Are they all connected ? The
larger cavities are called ventricles. Those in the hemi-
spheres are the first and second, that in the 'twixt-brain the
third, and that in the medulla the fourth. Are there ven-
tricles in the optic lobes ? Draw the brain, showing all cavi-
ties and connections found.

From another frog make a skeleton by removing as much
of the flesh as possible with scissors and scalpel, then boil it
with a little soap in the water, and pick away as much
more as you can, taking care not to separate the joints.*

* Much better skeletons can be made by cleaning off the flesh and

DISSECTION OF A FROG. 45

In this preparation how many vertebrae do you find ? Can
you find neural and haemal arches (p. 14) ? On either side
of each vertebra find a transverse process. How do these
compare with the ribs of a fish (p. 14) ? Are they the
same ? Give the reasons for your conclusion. Notice the
long bone (urostyle) terminating the vertebral column.
'Connecting the hind limbs with the back-bone is the
pelvic arch. Is it a true girdle ? With what part of the
vertebral column does it join ? Connected with the fore
limbs is the shoulder-girdle. Does it join the vertebral
column ?

Extending along the median line beiow, in connection
with the shoulder-girdle, is the breast-bone, or sternum.
How many parts in it ? Are all equally hard ? Connecting
the breast-bone with the shoulder are two bones on either
side; the anterior is the clavicle, the posterior the coracoid.
Extending dorsally from the shoulder-joint is the shoulder-
blade (scapula), and above it the supra-scapula (partly car-
tilage) . At the junction of coracoid and scapula is the glenoid
fossa, in which fits the head of the first bone (humerus) of
the arm. Has a joint like this much freedom of motion ?
The bone of the forearm is the radio-ulna. Does it show
any signs of a double condition ? With what does it con-
nect below ? How many bones in the wrist (carpus) ? How
are they arranged ? How many in the palm (metacarpus)
and in each finger ? How does the thumb differ from the
others ?

On the outside of each half of the pelvic girdle is a deep
cup (acetabulum) , in which is the head of the thigh-bone

then soaking the frog for weeks in water, brushing the parts every
few days with a tooth-brush. If such a skeleton be soaked for a few
days in Wickersheimer's fluid (see Appendix) and dried, it will retain
its flexibility and usefulness for years.

46 ELEMENTS OF COMPARATIVE ZOOLOGY.

(femur). Below this comes the tibio-fibula. Is this
double ? Below this comes the ankle region (tarsus). The
first two bones of this are long, the second very short.
What effect does this have on the position of the heel (p. 41)?
Compare the tarsus with the carpus. Is there anything which
you could call a sixth toe ? Does it come on the inside or
outside of the foot ?

In the skull distinguish between cranium and face (p. 15).
Notice the way in which the upper jaw is attached to the
cranium behind. Are there teeth on the same bones as in
the teleost ?

THE TADPOLE.

If possible the pupils should have a chance to examine
tadpoles of different ages. These can readily be obtained
by collecting the eggs in the spring and allowing them to
hatch out in glass jars. A number of these can be killed
at various stages by means of picrosulphnric acid (see Ap-
pendix) used for a couple of hours, then washed two to three
hours in water, and preserved in 70$ alcohol. The earliest
stage necessary should show the external gills, the latest
should have the hind legs well formed.

In the earliest of these larvae the pupil should pay especial
attention to the gills; the tail with its fin, how does it
differ from that of fishes ? In the older larvae the jaws
should be examined. What is their nature ? What is the
size of the mouth compared with that of the adult ? On
the left side of the body see the opening of gill-chamber. Is
there one on the right side ? Carefully open this chamber.
Do the right and left sides of the gill-cavity connect ? Can
you find any traces of the fore limb ? Carefully open the
abdomen and notice the compact coiling of the intestine.
Is it relatively longer or shorter than in the adult ? Pick
away the muscles from one side of the body until the middle
line of the body is reached. Do you find any vertebrae ?
Lying in this median line find a continuous gelatinous cord,
the notochord.

47

4:8 ELEMENTS OF COMPARATIVE ZOOLOGY.

COMPARISONS.

Prepare a sheet of paper with two columns as before, one
for fishes and the other for the frog and tadpole, and give
answers to the following questions:

(1) Is the skin naked or scaly ?

(2) What kind of appendages occur ?

(3) Is the pelvic girdle united to the back-bone "

(4) Is there an Eustachian tube ?

(5) What differences are there in the heart ?

(6) What are the organs of respiration ?

(7) Do the nostrils communicate with the mouth ?

(8) Differences between transverse processes and ribs ?

(9) Is a sternum present ?

BATRACHIA, OR AMPHIBIA.

The frog may serve as an example of the Batrachia,
which, so far as living representatives are concerned, are
marked off from the fishes by the features brought out in
the comparisons, as well as by a number of other features
not easily made out by the beginner. With very few excep-
tions the Batrachia pass at least a part of their life in the
water, and many, in reaching the adult condition, pass
through great changes in structure (all are familiar with
the change of the tadpole into the frog), so that we must,
in considering the group, take into consideration the char-
acters of both larva and adult.

In all the skin is very glandular and in all, except the
tropical group of blindworms, scales are lacking, and, ex-
cepting again these same limbless forms, fins have given
place to legs, much like the limbs of man, and like them
ending typically with five digits. In the larvae of all there
is a tail, and some (salamanders) retain this structure during
life, while in others, as in the frog, it is absorbed (not
dropped off) during growth. The larval tail bears a median
fin, but this is never divided into dorsal, caudal, and anal
(p. 9), and it differs further from those of fishes in having
no internal skeleton.

Of internal features those most distinctive are the skele-
ton of the limbs, unlike that occurring in any fish; the
union of the pelvic girdle with the back-bone; the existence
of an Eustachian tube in connection with the ear ; the con-

49

50 ELEMENTS OF COMPARATIVE ZOOLOGY.

nection of the nostrils with the cavity of the mouth; and
the presence of two auricles in the heart.

In the larva respiration takes place by gills, recalling
those of fishes ; and in a few forms these are retained during
life. Besides gills, all, in the adult condition, develop
lungs,* which grow out from the pharynx, and always re-
tain their connection with it by means of a windpipe (tra-
chea) opening upon its floor (compare p. 35). The gills are
fewer in number than in any fish, and only three or four
gill-slits are formed. Between these slits are developed
external gills. Later the slits are closed in most sala-
manders which lose the gills by the growing together of the
slits. In the frogs the process is preceded by the forma-
tion of an opercular fold (compare fishes) in front of the
gill region on either side. These folds grow back over the

FIG. 19.— Side View of Tadpole, e, ever g gill-opening; I, hind leg'
m, mouth ; n, nostril : v, vent.

gill-slits, those of the two sides fusing below the throat and
uniting with the wall of the body above and behind the
gills, thus forming a large chamber outside the gills which
is connected with the exterior by a small opening on the
left side,f through which the water used in breathing

In the larva the heart is two-chambered, and the blood,

*It has recently been shown that some of the North American
salamanders never develop lungs _ but respire solely through the skin.

f Right and left openings occur in two tropical toads (Aglossa).
A few forms have a median opening.

BATRACH1A. 51

passing forward from it, traverses afferent and efferent
branchial arteries, as in fishes, and is collected, as in those
forms, in a dorsal aorta. With the loss of gills and the de-
velopment of lungs the gill circulation changes. The first
arterial arch becomes converted into the carotid artery,
supplying the head ; the second, the aortic arch, connects the
heart with the dorsal aorta; the third dwindles and usually
disappears; while the fourth, the pulmonary artery, carries
blood to the lungs and skin. As will be seen, the embryonic
circulation is like that of the fishes, but the different con-
dition in the adult is brought about not so much by new
formations as by modifications of pre-existing structures.

In the larva the heart pumps only venous blood, as in
the fish. With the development of lungs and the division
of the single auricle into two, different conditions occur.
Blood from the body (venous) is poured into the right
auricle, and blood from the lungs (arterial, because in the
lungs it comes into contact with the air) into the left.
From the auricles the blood goes to the single ventricle,
and thence through the arterial trunk to head, body, and
lungs. So at first sight it would appear as if all parts
must receive a mixture of arterial and venous blood, but
this is not exactly the case. By means which cannot
be described here the purest arterial blood goes to the head,
the next to the aorta, while the venous blood is sent to the
lungs.

In the larvae of the frogs and toads the mouth is small
and the horny jaws are adapted to scraping small plants
from submerged objects. Correlated with this vegetable
food is an extreme length of intestine, it being a noticeable
fact that herbivorous animals require a longer digestive
tract than carnivorous forms.

In the larvae there is also a well-developed lateral-line

52 ELEMENTS OF COMPARATIVE ZOOLOGY.

system, and this persists to some extent in the adult of
the aquatic salamanders, though disappearing in all other
forms.

The vertebral column varies greatly in length, and in all
except the footless forms it can be divided into neck (cer-
vical), breast (thoracic), sacral, and caudal or tail regions,
the sacral being that which connects with the pelvic girdle.
In some the bodies of the vertebrae are amphicoelous (p.
14) ; in most salamanders they are opisthoccelous (rounded in
front, hollow behind), while in the frogs and toads they are
proccelous (hollow in front). The transverse processes of
the vertebrae are different from anything in fishes in that they
arise from the neural arch and not from the centrum. In
some forms the ends of these processes are jointed, and
from this and other facts they must be regarded as in part
equivalent to ribs. It is to be noticed that these ribs never
reach the sternum (p. 45), which, by the way, is a struc-
ture lacking in all fishes.

A noticeable feature in the Batrachia is the metamor-
phosis during growth, the chief features of which have
already been mentioned, the result being that the adult
differs very considerably from the young.

All living Amphibia live either in fresh water or on the
land ; none occur in salt water. The existing forms are
comparatively small, the largest being the giant salamander
of Japan, which may be three to four feet in length.
Existing Batrachia are conveniently divided into three
groups or orders.

ORDER I. — URODELA (Salamanders, etc.).

These forms retain the tail throughout life, and haye the
extremities weakly developed, fitted for creeping rather than
jumping. Some live in the water throughout life, while

BATKACIUA. 53

others, as adults, are to be sought in moist places. In some
forms the external gills are retained permanently. The
order belongs almost exclusively to the northern hemisphere,
and is especially well developed in America. Allied to these

FIQ. 20.— Salamander (Plethodon).

forms are some enormous fossils, grouped under the name
STEGOCEPHALI, some of which had skulls five feet or more
in length.

ORDER II. — ANURA (Frogs and Toads).

These in the adult condition lack a tail, and have appen-
dages fitted for leaping. The lower jaw is without teeth.
The larvae are always tailed, and have at first external gills.
Frogs and toads differ in that frogs have a smooth skin, and
teeth in the upper jaw ; toads have a warty skin (caused by
numerous glands) and no teeth. Tree-toads are more frog-
like, but they have sucking disks on the ends of the toes,
by means of which they are adapted to a life in trees.
Another group occurs in the tropics, in which the tongue
is absent.

Some of the Anura have strange breeding habits. Thus
in the European Alytes the male wraps the long string of
eggs about his body and carries them there until they hatch.
In Nototrema of South America the skin of .the back forms
a pouch, in which the eggs are carried ; while in the Suri-
nam toad (Pipd) the skin of the back becomes very much
thickened, leaving little cups, in each of which an egg
occurs, and here the young are hatched out,

54 ELEMENTS OF COMPARATIVE ZOOLOGY.

Another interesting form is the flying tree-toad of the
East Indies, in which the feet with the web between the
toes become greatly enlarged, forming large disks, upon
which the animal sails, much as does a flying squirrel upon
its lateral folds of skin.

OKDER III. — CECILIA (Blindworms).

These are legless, worm-like Batrachia found in the
tropics of both hemispheres. They have a rudimentary
tail, degenerate eyes, and the larvae, so far as known, have
three pairs of gills. Some species form an exception to all
living Batrachia in having scales in the skin.

COMPARISONS.

Fishes and Batrachia. For the latter use your notes and
the preceding account.

(1) Is the blood cold or warm ?

(2) Are median fins present ?

(3) Are gills present in young or adult ?

(4) Are lateral-line organs present ?

ICHTHYOPSIDA (FISH-LIKE FORMS).

Under this name are grouped fishes and batrachians,
since they are alike in certain important respects. Thus
they have, either as larvae or adults, functional gills, they
have lateral-line organs, they have median fins, and the
blood is cold. Besides these there are several other points
of union, notably in the development, especially promi-
nent being the absence of two embryonic structures, the
amnion and allantois, which occur in higher forms. The
Ichthyopsida is divided into two classes:

CLASS I. — PISCES (FISHES) (p. 33).
CLASS II. — BATEACHIA, OR AMPHIBIA (p. 49).

55

LABORATORY WORK: TURTLE.

EXTERNAL.

The hard shell is composed of a dorsal portion, the
carapace,, and a flat ventral shield, or plastron. Are the
plates covering these arranged in the same way on both ?
How are carapace and plastron united ? Are head, legs,
and tail naked ? How many toes on the feet ? Are claws
present ? Open the mouth. Are teeth present ? Are
there lips ? Is there a tongue ? Do the nostrils connect
with the mouth ? At the inner angle of the eye see a fold,
the nictitating membrane. Pull it out with the forceps.
What purpose can it fulfil ? Is there an external ear ?

INTERNAL.

Open the body by sawing the hard parts connecting
carapace and plastron on either side, then cut the skin, etc.,
from the plastron, and remove that plate, leaving the ani-
mal in the carapace. This exposes the muscles and the
limb-girdles, and, after the removal of a thin membrane, the
viscera. Was either girdle fastened to plastron ? Just be-
hind the shoulder-girdle is the heart, and on either side of
this the dark liver. In the left lobes of the liver is the
stomach. Trace the intestine to the vent. Is there an en-
larged terminal portion ? Is the intestine supported by a
mesentery ? Do you find pancreas or spleen ? Turn the
liver inwards and see the lungs. Are they large ?

In the heart how many chambers ? From the front see

56

DISSECTION OF A TURTLE. 57

the vessels. Trace them out, making out carotids, aortic
arches, and pulmonary arteries, comparing your work step
by step with the frog. (The third of the primary arches
has entirely disappeared.) What differences do you find
between right and left aortic arches ?

In the body-cavity, behind, are the kidneys. Are they
smooth or lobed ? Where do their ducts empty ? Do you
find a urinary bladder arising from the intestine behind ?
The ovaries are a broad oval, and can usually be recognized
by the contained eggs. Where do the oviducts empty ?
The testes are smaller, long oval, and are outside and behind
the kidneys.

In the skeleton * look for the vertebral column on the
inside of the carapace. Is it firmly united to it ? Can you
find any traces of ribs ? If so, in what respects are they
peculiar ? What parts can you recognize in the shoulder
and pelvic girdles ? In either limb, beyond the humerus
or femur, make out two bones (radius and ulna in the fore
limb, tibia and fibula in the hind limb), and beyond this
the (how many ?) carpal or tarsal bones. How does this
explain certain peculiarities in the frog? Draw either
limb, naming parts, remembering that the radius is on the
side of the thumb, the tibia on that of the big toe.

In the skull is the socket (orbit) of the eye completely
enclosed in bone ? How does the lower jaw join the skull ?
What is the means for articulation of the skull with the
vertebrae of the neck ? Are the vertebrae of the neck hol-
low in front, behind, or on both surfaces ? What name is
to be given to the condition found (p. 52) ?

* Skeletons sufficient for these purposes can readily be made by
boiling the specimens and washing away the flesh, with the aid of a
nail-brush. It is well to boil the head separately.

LABORATORY WORK: SNAKE.

Are there any traces of limbs ? Can you divide the body
into head, neck, thorax, and tail ? If so, give reasons for
the divisions you recognize. What is the character of the
skin ? What marked difference exists between the skin of
the head and that of the body ? Are the dorsal and ven-
tral surfaces alike ? Where is the vent ? Examine a scale
carefully. Is there any skin outside it ? Can you pull the
scales away from the body ? Does a snake shed its skin ?

Examine the head. Open the mouth. Are teeth present,
and, if so, where ? See the tongue. What is its character ?
Pull it out with the forceps.

58

LABORATORY WORK: BIRDS.

The following account will apply to almost any common
bird. The English sparrow or the pigeon is possibly the
most convenient.

EXTERNAL.

Notice that the body presents the regions, head, neck,
trunk, and tail. How many paired appendages are found ?
What covers the body ? what the legs and feet ?

In the head notice the beak, composed of upper and
lower mandibles. With what is it covered ? Is the upper
mandible movable ? Open the mouth ; do you find teeth ?
What is the shape of the tongue ? Where are the nostrils ?
Do they connect with the mouth ? Behind the tongue, on
the floor of the mouth, will be found the glottis (p. 40).
How many eyelids do you find ? Look at the inner corner
of the eye for the nictitating membrane. Pull it out
with the forceps. Is it like the same structure in the
turtle ? Hunt among the feathers for the ear-opening.
Are the feathers around it different from the others ?

Extend the wing. Can you find parts corresponding to
arm, forearm, and hand T Are the feathers alike in all
parts ? * How much is the surface of the wing increased
by the feathers ?

* The feathers on different parts of the wing have special names.
The long quills on the hand are primaries ; on the forearm, secondar-
ies ; and those on the arm, when they occur, are tertiaries. The short

59

60 ELEMENTS OF COMPARATIVE ZOOLOGY.

Are the feathers essentially alike on all parts of the
body ? Are all parts equally well covered ? Pull out a
large wing-feather and notice the central axis or shaft sup-
porting the expanded portion or vane made up of small
side-branches (barbs), and these in turn having smaller
branches (barbules). Pull two of these barbs apart, watch-
ing with a lens to see the part played by the barbules.
Are the conditions the same at the base of the vane ? Can
you find a downy feather among the others ? Examine it
carefully and see how it differs from the quills described.
Pick the feathers from a part of the breast and study one
of the pin-feathers. What parts occur in it ?

Next pick the feathers from the whole bird. This will
be more easily done by dipping it in hot water. When
picking the feathers notice that they come from pits in the
skin. When the bird is picked, look for these pits. Are
they equally distributed on all parts of the body, or are
they arranged in feather-tracts ?

In the leg see the thigh and shank (drumstick). Where
is the heel ? Does the bird walk on the whole foot ? Con-
necting the shank with the toes is the tarso-metatarsus.
How many toes ? Do they all point the same way ?

INTERNAL STRUCTURE.

Cut through the skin in the median line below from the
neck to the vent, being careful not to injure the deeper
structures in the neck. Pull the skin away. Insert a blow-
pipe in the mouth and inflate. This will render the

feathers overlapping the large quills above and below are the upper
and lower wing-coverts. At the bend of the wing, just outside the
primary coverts, are short quills borne on the thumb and forming the
false wing (ala spuria).

DISSECTION OF A BIRD. 61

oesophagus very evident, and will show a specialized enlarge-
ment, the crop, if it exists. In front of the O3sophagus is
the ringed trachea or windpipe, while on either side are
veins (jugulars) usually gorged with blood.

Cut through the abdominal walls in the median line
from the breast-bone to the vent. Open, and, after inflat-
ing as before, notice the air-sacs. How many do you find ?

Next remove the limbs from one (the left) side, cutting
the muscles away from the keel of the breast-bone. Then
cut through the ribs where they join the breast-bone, and
next sever them near the back, removing the walls of the
body from one side. This will expose the reddish-brown
liver, and, partially covered by it, the muscular stomach or
gizzard ; farther in front and near the back-bone the lungs,
and in other parts the coils of the intestine. After draw-
ing the viscera in position, proceed with the dissection.

Pull the gizzard back, and inflate, this time through
the oesophagus in the neck. Where is the glandular
stomach (proventriculus) ? Where does the intestine con-
nect with the gizzard ? Is the intestine the same size
throughout ? Is a mesentery present ?

In front of the liver is the pericardium, containing the
heart. Open the pericardium and trace, as far as possible
without injection, the blood-vessels going from it. Make
out the carotids, aortic arch, and pulmonary arteries.
How many of each ? Which way (right or left) do they
turn ? Cut out the heart, and cut it open horizontally.
How many chambers are found ? Sketch the circulation
as far as made out.

In the hinder part of the body-cavity are the dark-colored
kidneys. Are they irregular in outline ? In front of them
are the reproductive organs. The testes are whitish and
oval ; the ovaries in the breeding season are filled with eggs

62 ELEMENTS OF COMPARATIVE ZOOLOGY.

in various stages of growth. Can you trace the ducts from
either kidney, or reproductive organs ? Where do they end ?

Open the skull very carefully, beginning at the top and
working down on the sides. If the head be cut off and put in
alcohol for twenty-four hours or more, the parts of the brain
will be better made out. In front are the cerebral hemi-
spheres, with the olfactory lobes showing in front and below.
Inserted in the angle between the two hemispheres is the
cerebellum, and on either side of the latter, and partially
covered by the cerebrum, are the optic lobes. What has
become of the 'twixt-train ? Do you find the medulla ?
Are all the parts of the brain smooth ? Draw the brain
from above and from the side.

The essential features of the skeleton can be made out
from the same specimen after boiling. The parts neces-
sary are the head, the shoulder-girdle, wing, leg, and a few
of the vertebras. What is the shape of the ends of the
vertebrae ? In the shoulder-girdle what parts can you
recognize ? What name must be given to the wish-bone, or
furcula ? (compare the frog.) In the wing humerus, radius,
and ulna are readily made out. How many carpal bones
do you find? In the "hand" how many fingers can you
distinguish? Sketch the carpus and "hand/' with the
ends of radius and ulna. In the leg recognize femur
tibia, and fibula. Wrhere is the heel ? What must the
bone above the toes be ?

Are the bones distinct in the skull ? Move the beak
upon the skull. Where do the bones slide ? Connecting
the angle of the upper jaw with the skull is the quadrate
bone. Is it movable ?

COMPARISON OF BIRD, TURTLE, AND SNAKE. t>3

COMPARISONS.

With two columns, one for bird, the other for turtle and
snake, answer the following questions:

(1) Is the blood warm or cold ?

(2) Are feathers present ?

(3) Are there any wings ?

(4) Is there an elongate true tail ?

(5) Are the carpus and tarsus long or short ?

(6) Are air-sacs present ?

(7) How many aortic arches ?

(8) How many ovaries ?

REPTILIA (REPTILES).

The living reptiles closely simulate the Batrachia, and
in fact the frogs, toads, and salamanders are reptiles in
popular parlance. The short-
bodied turtles are paralleled by the
frogs, the lizards by the sala-
manders, and the snakes by the
blindworms. Yet the differences
between the two groups are many
and important.

The body is more or less
completely covered with scales,
and the toes, when present, bear
claws. The scales differ from
those of fishes in being outside
of the outer layer of the skin.
These scales differ much in ar-
rangement, etc. The large plates
covering the carapace of the turtle
are but enlarged scales, while the
bony armor of the alligator is
composed of scales, rendered more
protective by the development of
bone in the deeper layer of the
; skin. In the snakes the scaly
fcacheeafi,t f £S§Stii£ covering is periodically shed.

By the greater development of

the neck the heart is carried back to a greater distance

64

REPTILES.

65

from the head than in the Batrachia. In all except the
alligators the heart is three- chambered, and in these the
ventricle is incompletely divided into two. There are two
aortic arches, but the left one, which also supplies the
stomach, is smaller where it joins its fellow to form the
dorsal aorta. The blood is cold.

The brain is small, no part being extremely developed,
and the optic lobes touch, or may touch, each other in the

FIG. 22. — Brain of Snake, c, cerebrum ; cl, cerebellum ; o, optic lobes ;
I, olfactory nerve ; II, optic nerve.

median line. In snakes, lizards, and turtles the cere-
bellum is small ; in the alligators it is larger.

The vertebrae are usually procoelous, and the vertebral
column is divisible into the regions of neck (ribless),

FIG. 23.— Skull of Garter-snake (Eutcenia sirtalis), showing the attach-
ment of the lower jaw to the skull by means of the quadrate bone, q.
(Slightly enlarged.)

thorax (with ribs), lumbar (ribless), sacrum (usually two
vertebrae which connect with the pelvis), and tail ; but in
snakes these distinctions fail, and only trunk and tail ver-
tebrae are recognizable. A breast-bone is present in lizards
and alligators, but none occurs in turtles or snakes. The

66 ELEMENTS OF COMPARATIVE ZOOLOGY.

skull articulates with the vertebral centrum by a single
surface (condyle). The hinder angle of the lower jaw is
connected with the skull by the quadrate bone, which
may be free or firmly united to the skull; and the pre-
maxillary and maxillary bones are firmly united to the
rest of the skull. Teeth are usually present, and in the
alligators these are inserted in sockets. The shoulder-
girdle (lacking in snakes) is much like that of frogs, the
clavicle, however, being absent in alligators. The pelvis
is lacking in most snakes, being represented by two bones
in the boas. The feet, when present, are usually of the
normal type, the bones of the forearm (ulna and radius)
and of the shank (tibia and fibula) being separate, and the
toes, five in number, provided with claws.

In the embryo, gill-slits are partially developed, but no
functional gills occur. The lungs are well developed ; the
left one being reduced or absent in the snakes and snake-
like lizards. Respiration is effected by means of the ribs,
except in the turtles, and there by a special muscle.

Both ovaries are developed. The eggs are large, and in
those reptiles which lay eggs, are covered with a limy shell.
A few snakes and lizards bring forth living young. In
the development of the eggs two structures, amnion and
allantois, are formed, which never occur in the Ichthy-
opsida.

Reptiles are most abundant in the tropics, and are lack-
ing in cold regions. They are mostly flesh-eaters, some
living on insects, others on larger forms. Some live on
land, some in fresh water, and some in the sea. All living
forms can be arranged in four orders.

REPTILES.

OEDEE I. — LACEETILIA (Lizards).

In these the quadrate bone is movable, but the under
jaw cannot be displaced (cf. Snakes). Legs are usually
present, but either or both
pairs may disappear. When
the legs are absent the
body is exceedingly snake-
like, but these forms, like
all other lizards, may be
distinguished at once from
the true snakes by the
presence of small scales on
the belly. Only one lizard
has the reputation of being
poisonous, but in former
times many, like the basi-
lisk, were fabled to have
most deadly powers. Among
the more interesting forms
are the " glass snakes," so
called from the ease with
which the tail breaks ; the
" horned toads/' which are
not toads, but true lizards;
and the chameleons, with
their wonderful powers of Fl°- 24<~GreenLJuifken (An°m- From
color change, a capacity
which is shared to a less degree by other forms.

OEDEE II. — OPHIDIA (Snakes).

These are like the lizards in the movable quadrate, but
they differ in the absence of limbs and of sternum,, the pres-

68 ELEMENTS OF COMPARATIVE ZOOLOGY.

ence of broad scales (scutellae) on the belly, and in the
fact that the lower jaw is connected with the cranium by
elastic ligaments, so that it can be displaced in swallowing
food. Many snakes are poisonous, the poison being con-
veyed into the wound by specialized teeth, the so-called
poison-fangs, which are either grooved or are tubular, the
grooved teeth being capable of being folded back when not
in use, the others being permanently erect. The rattle-
snakes and moccasins belong to the former group. The
largest snakes, the pythons of India and Africa and the
boas and anacondas of South America, kill their prey by
crushing, as do most of the smaller snakes — our black-
snakes, for example.

Some snakes are protected against their enemies by their
colors, which render them inconspicuous in their usual
haunts; others by the nauseous smell which they produce
by certain glands in the skin; still others by their poison-

Fio. 25.— Dissection of head of Rattlesnake. /, poison-fangs ; p,
poison-sac.

glands. Most of the snakes are terrestrial, but some,
like our water-snakes, take to the water, while in the Indian
Ocean are found truly aquatic snakes, which never go on

REPTILES. 69

land and which bring forth living young. These sea-
snakes are very poisonous. The rattlesnakes are the best
known poisonous forms in the United States. In these
the rattle is formed by bits of dry skin, which are not lost
at the time when the snake sheds the rest of its covering.
In this way a new joint is added to the rattle at each molt,
and so the whole becomes an approximate index of age.

OBDER III. — TESTUDIJTATA (Turtles).

The turtles and tortoises are characterized by their short
bodies, enclosed in a bony shell or box ; by the absence of
teeth ; and by the union of the quadrate bone with the
cranium. The shell, with its two parts, carapace and
plastron (p. 56), is composed of an outer layer of horny
plates (modified scales) and a deeper bony layer, with
which ribs and vertebrae are more or less completely united.
Into this protective case the head, tail, and legs may be
retracted, and in the box-tortoises a hinge in the plastron
allows the closure of the openings.

Some turtles are vegetarians, others are carnivorous.
Some live on land, some in fresh water, and some in the sea.
The largest of existing species are the giant land-tortoises
of the Galapagos Islands and Mozambique, and the leather-
back and the loggerhead turtles of tropical seas.

Tortoise-shell, before the days of celluloid, was furnished
by the dorsal plates of the large tortoise-shell turtle of
tropical seas. These plates have the peculiarity that they
can be united by heat, so that pieces of any desired size
may be obtained. While many turtles are most inoffensive
creatures, others, like our snapping- turtles and our soft-
shelled turtles, are ferocious, the young snapper showing its
temper as soon as it is hatched from the egg.

70 ELEMENTS OF COMPARATIVE ZOOLOGY.

ORDER IV. — CROCODILIA (Crocodiles and Alligators).

These forms have the highest development of brain and
heart of any of the reptiles, the heart being incompletely
four-chambered. In general shape they are closely like the
lizards, but in bony and other structural features they are
greatly different. Crocodiles and alligators are distin-
guished from each other by the fact that the former
have fully webbed feet and more slender snouts. The
gavials of the rivers of India have the snout even more
slender. The alligators are confined to the New World,
while the crocodiles occur in both hemispheres.

The fossil reptiles show a greater range of forms than
the living species. The Ichthyosaurs were the whales
among the reptiles of former times, while the Plesiosaurs,
also swimming forms, had extremely long necks. The
Dinosaurs were like the birds in many structural features,
although they lacked powers of flight and were terrestrial
or aquatic. Some were enormous in size, having thigh-
bones nine feet in length and vertebras five feet across.
The Pterodactyls were flying reptiles with wings like those
of the bats, except that the wing-membrane was supported
by a single finger.

AVES (BiKDS).

No one can have the slightest question as to whether a
certain animal is a bird or not. The feathers, the fore-
limbs fitted for flight, and the horny, toothless beak are
characteristic of all living forms.

Feathers arise from the outer layer or epidermis of the
skin, and each has its tip inserted in a pit or follicle in the
integument. Feathers vary considerably. Most prominent
are the large, strongly built contour feathers, which give
the animal its general shape. Beneath these are the down
and the pin-feathers. Feathers are not uniformly dis-
tributed over the body, but are gathered in feather tracts,
the arrangement of which varies in different birds. The
feathers are not permanent structures, but they are molted
or shed and replaced by a new growth, this taking place
usually once a year. In connection with the feathers
should be mentioned the oil-glands (the only glands in the
skin of birds) upon the tail, the secretion of which is used
in preening the feathers.

In their origin feathers are much like the scales found
on the feet, and are doubtless modifications of such struc-
tures. The scales on the feet may be small or broad, both
kinds sometimes occurring on the same foot. The spur of
the cock is but an extremely developed scale with a bony
core. These scales differ from those of fishes in that they
are developed on the outside of the outer layer of the skin
(compare p. 33). The toes are terminated by claws; short

71

72

ELEMENTS OF COMPARATIVE ZOOLOGY.

in the terrestrial, longer in the arboreal, forms. Claws
occur in some cases, especially in
young birds, upon the wings.

In all living birds teeth are absent,
and even in the embryos but the
slightest trace of their former exis-
tence can be found. In certain fossil
birds well-developed teeth occur. The
tongue is usually slender., stiff, and
horny, and in some forms (woodpeck-
ers, etc.) it is very extensible. The
oasophagus is long, and frequently a
part of it in the neck is swollen out
to form a reservoir of food or crop.
The stomach is divided into two parts.
The first of these (proventriculus),
which is glandular, appears much like
an enlargement of the gullet. The sec-
ond or muscular stomach (gizzard) is
a veritable chewing organ. It is most
developed in the seed-eating birds,
and in these often contains small stones
to assist in grinding the food.

The lungs are especially well devel-

FiG. 28.-Alimentary ,& .. . .

Tract of an Eagle, c, oped, and a peculiarity is, that con-
crop; m, muscular stom- . _ .,1,1

ach (gizzard) ; i, intes- nected with them are air-sacs which

tine; p, glandular stom- _ ,1,1

ach (proventriculus); extend among the other viscera and

t, trachea ; v, vent. . . <• n i ,,

even into some or the bones, as in the
wing.* These air-sacs serve to increase the respiratory sur-
face, and also to lessen the weight of the bird. They are

* A similar pneumaticity occurred in the bones of some of the
fossil reptiles (Dinosaurs).

BIRDS. 73

also possibly of use in changing the position of the centre
of gravity during flight.

The heart has four chambers, the single ventricle of lower
forms being divided into right and left portions. The large
blood-vessels which lead from it are, in the embryo, much
like those of the fish ; but with development some parts are
altered and others suppressed, so that the result is more modi-
fied than in the forms already discussed. Thus the left half
of the third arch, except for an artery going to the wing of
that side, has entirely disappeared, while the right half, here
called the arch of the aorta, connects the left ventricle
with the dorsal aorta. From this the first arch, modified
into carotids, seems to arise. The second arch is completely
suppressed, while the fourth arch, arising from the right
ventricle, carries the blood to the lungs. In returning
from the body the venous blood is emptied into the right
auricle and passes thence, through the right ventricle, to
the lungs for aeration ; while that from the lungs goes to
the other side of the heart, and thence to all parts of the
body. Hence there is here no mixing of arterial and venous
blood in the heart.

In the reproductive organs a constant feature is the
suppression of the right ovary, a rudiment of it existing in
a few forms. In the breeding-season the oviduct is very
large, and from its walls are secreted the white and the shell
of the egg. The eggs are large, and are always enclosed in
a limy shell. There is quite a difference in the condition in
which the young hatch from the egg. Some are nearly
naked and very helpless, while others are thickly clothed
with down and are able to run and to feed themselves.

The brain is large, and, in comparison with the lower
forms already studied, is noticeable for the great develop-
ment of the cerebrum and cerebellum, which by their growth

ELEMENTS OF COMPARATIVE ZOOLOGY.

FIG. 27.— Brain of Bird.

have forced the optic lobes apart and have covered over the
'twixt-brain. The eye is peculiar in
that it departs widely from the spheri-
cal form, being obtusely conical in
front, and in that a circle of bones are
developed in this conical portion.
There is a tube developed (external
meatus) leading from the side of the
head in to the ear, and this is sur-
rounded by a ring of regularly arranged
feathers.

In the skeleton division into neck,
thoracic, sacral, and caudal vertebrae,
occur. The number of neck vertebrae
varies from eight to twenty-four. The
sacral are noticeable for their number,
and really embrace, besides the true sacrals, some of the
lumbars and caudals. The anterior caudal vertebrae are
free, but the last six or eight are coalesced into the pygo-
style or plowshare bone. The bodies of the vertebrae in
living birds are concave vertically, convex transversely
behind, the conditions being reversed on the anterior
faces. The cervical vertebrae bear short ribs, free in the
young but firmly united in the adult. Each of the true
ribs has a small plate (uncinate process) on the posterior
margin, which connects it with the rib behind. The breast-
bone (sternum) is large and broad, and in flying birds
possesses a strong ridge or keel below, to which the muscles
of flight are attached. In some flightless birds the keel is
lacking.

The skull is noticeable from the great extent of the
fusion of the separate bones; for the single condyle for
articulation with the neck and for the suspension of the

BIRDS. 75

lower jaw by means of a quadrate bone, as in the lizards,
snakes, etc.

The shoulder girdle consists of scapula, coracoid, and
clavicles, the latter noticeable for their union into a V-
shaped " wish-bone " or furcula. In the wing the reduction
in bones near the end is remarkable. The bones of the
wrist are all united into two, while the tfrree fingers which

FIG. 28.— Skull of Quail. <?, quadrate bone.

remain have few joints and are partly united. In the hind
limb the fibula is short, but especially noticeable is the
great lengthening of two of the ankle-bones, the result being
that the heel is elevated some distance from the ground.

Birds are grouped in three divisions or subclasses, the
first two of which are extinct; the third contains the ten
thousand known species of living forms.

CLASS I. — SAURUR^; (Tailed Birds).

These forms, found fossil in the lithographic stone of
Bavaria, had tails of extreme length, the feathers being
arranged on either side of the long tail vertebrae; and they
had teeth in the jaws. Only two specimens are known, the

76 ELEMENTS OF COMPARATIVE ZOOLOGY.

smaller being about the size of a crow, the other somewhat
larger. They are called Archaeopteryx,

SUBCLASS II. — ODOKTOKNITHES (Toothed Birds).

These forms, which have been found only in American
rocks, are more like modern birds than is Archaeopteryx,

FIG. 29.— Skeleton of Wingless Toothed Bird (Hesperornis). From Marsh.

but they differ from all existing birds in having teeth.
They had normal tails, and one form apparently was wing-

BIRDS. Y7

less, only a rudimentary humerus persisting. Some of
these toothed birds were about as large as a pigeon; one
was about three feet in height.

SUBCLASS III. — ORNITHURJE (Modern Birds).

In all living birds teeth are lacking and the tail is re-
duced ; and, excepting a few forms, all have well-developed
wings. The recent subdivisions of the subclass are based

FIG. 30. — South American Ostrich or Nandu (Rhea americana). From Liitkeru

upon characters not readily grasped by elementary students,
so we must content ourselves with a classification founded

7$ ELEMENTS OF COMPARATIVE ZOOLOGY,

on external features. The student should, however, re-
member that the so-called "orders" are in no wise equiva-
lent to orders in other groups.

ORDER I. — STRUTHII (Ostriches).

The ostrich-like birds have long running legs and wings
so reduced as to be useless in flight, and with this the keel
of the sternum (p. 74) has disappeared. The foot contains
usually three, occasionally but two, toes. These birds are
mostly large, and embrace the true ostriches of Africa, so
valuable for their feathers; the South American nandus;
the emeus and cassowaries of Australia, and the nearly
wingless kiwi of Australia.

*
ORDER II. — RASORES (Scratching Birds).

These, like all the remaining birds, have a keeled sternum.
They have a weakly curved beak, feet well fitted for run-
ning, with three toes in front, and a fourth at a higher
level behind. Here belong the grouse, the pheasants, and
the domestic fowl and turkeys, as well as a considerable
number of tropical forms. Our common hens, in all their
numberless varieties, are descendants of the wild fowl of
India. The turkeys are natives of America.

ORDER III. — NATATORES (Swimming Birds).

In these the short feet are adapted for swimming by
having a web between the anterior toes. The body varies
greatly in shape. In the penguins the wings have lost the
powers of flight, the wing-feathers being short and scale-
like. On the other hand, they are strong swimmers, and
the loons almost equal them in this respect. The other ex-

BIRDS.

79

FIG. 31.— Penguin (Aptenodytes longirostris). From Llitken.

FIG. 32.— Wood-duck (Aix sponsa). After Audubon.

80 ELEMENTS OP COMPARATIVE ZOOLOGY.

treme is reached in those strong fliers, the albatross, tropic
birds, gulls, etc. More useful to man are the ducks and
geese, while the swans, auks, and cormorants must be
mentioned as members of the order.

ORDER IV. — GRALLATORES (Wading Birds).

The wading birds have long legs, the tarsal region being
extremely long, and the shank partly naked. Correlated
with length of leg is length of neck. Here belong a long
series of forms, some of which, like the snipe, are of value

FIG. 33.— Wilson's Snipe (Gallinago urilsoni). After Wilson.

to man as game-birds ; while others, like the cranes, herons,
storks, etc., have less importance. Some, like the ibis and
the flamingo, are brightly colored, while marabou and egret
furnish feathers for human adornment.

In all the foregoing groups of birds the hinder toe is,
as a rule, small and of little use. In all that follow it is
usually well developed.

BIRDS. 81

ORDER V. — RAPTORES (Birds of Prey).

The owls, hawks, eagles, and their allies are characterized
by short, stout, curved beaks, strong feet and large wings;
all structures admirably adapted to the capture of prey and
the tearing of flesh. Some, like the eagles, hawks, and
vultures, are strong fliers with excellent powers of sight;
the owls, on the other hand, are more dependent upon
catching their prey by stealth; and their eyes are adapted
to their nocturnal habits. The buzzards and vultures depend
upon decaying flesh for their food, and their value as
scavengers leads to their protection by law in the regions
where they occur.

In the birds of prey, like all that have preceded them in
our account, the young, when hatched, are covered with
feathers (usually down feathers), and have their powers
well developed. In all the remaining orders the young are
helpless and nearly naked when they escape from the shell.

ORDER VI. — COLUMBINE (Pigeons).

The pigeons stand nearest to the Rasores from which,
however, they differ in the weaker legs, the large pointed
wings, and the fleshy membrane at the base of the beak,
pierced for the nostrils. The five hundred different kinds
of pigeons show little variety in form. Our domestic
pigeons, with their wonderful variations, have descended
from the rock-pigeon of Europe. The extinct dodo of the
islands east of Africa was a flightless pigeon of large size.
The species died out some two hundred years ago.

ORDER VII. — SCANSORES (Climbing Birds).

These birds have the feet adapted for climbing, two of
the toes being directed forwards and two backwards. Some,

82 ELEMENTS OF COMPARATIVE ZOOLOGY.

like the toucans, have enormous bills, others have the beak
of moderate size. Here belong the cuckoos, with their
reprehensible egg-laying habits, and the well-known wood-

FlQ. 34.— Carolina Paroquet (Conurus carolinensis). After Wilson.

peckers. The large group of parrots also belong to the
group of climbing birds. In these last the tongue is fleshy,
and the feet are very efficient organs of prehension.

ORDER VIII. — PASSERES (Perching Birds).

In these the feet have three toes in front, one directed
backward and all on a level, and no naked skin on the
beak. They are usually subdivided into the Clamatores or
crying birds, and the Oscines or singing birds, the latter
having a complicated muscular apparatus in connection
with the vocal organs. To the Clamatores belong the
Asiatic hornbills, which recall the American toucans ; the

BIRDS. 83

kingfishers, with their large strong beaks; and those gems
of bird-life, the humming-birds. To the Oscines belong an

FIG. 35.— Bird of Paradise (Paradisea apoda). After Levaillant.

enormous series of feathered songsters, the mere enumera-
tion of which would take a volume the size of the present

84: ELEMENTS OF COMPARATIVE ZOOLOGY.

one, the whole series reaching its apex in that pestilential
immigrant, the English sparrow. Among these singing
birds are some which, like the crows, are not noted for
their musical abilities, and their near relatives, the birds

FIG. 36.— Winter Wren. From Coues.

of paradise. We can only mention, in addition, the star-
lings, flycatchers, wrens, orioles, warblers, and thrushes,
forms which make our woods vocal and beautiful.

COMPARISONS.

With columns for Birds and Reptiles, answer the follow-
ing questions:

(1) Are scales present ?

(2) Are claws present ?

(3) How many occipital condyles ?

(4) Is there a distinct quadrate bone connecting the
upper jaw with the skull ?

(5) Are true ribs present ?

(6) How many chambers to the heart ?

(7) What is the size of the eggs ?

(8) Are functional gills ever developed ?

(9) Do the urinary and reproductive ducts empty into
the hinder part of the alimentary canal ?

SAUKOPSIDA.

Although we naturally associate the birds with the warm-
blooded, hair-bearing animals (Mammals), yet structurally
they are more allied to the reptiles; a fact indicated by our
heading, which means lizard-like. Some of these common
features are a body-covering of scales or feathers derived
from the epidermis; the articulation of the skull with the
neck by a single condyle ; the existence of the quadrate as a
suspensor (p. 37) of the lower jaw, the presence of true
ribs, a three- or four-chambered heart, no functional gills,
large eggs with an abundance of yolk, and the existence of
a cloaca into which digestive, reproductive and excretory
organs empty. There are two classes of Sauropsida.

CLASS I. — REPTILIA (p. 64).

CLASS II. AVES (p. 71).

85,

EAT: LABORATORY WORK.

If possible, the student should be provided with two
specimens, one injected, the other not. If rats are not
easily obtained, a single injected specimen will suffice. Rats
may be injected by cutting into the left ventricle and in-
serting the canula into the aorta from this opening, ligating
it by tying in front of the heart. A gelatine mass works
best, but care must be taken lest the delicate vessels be
broken. Only a small amount of fluid is necessary to fill
all the vessels.

EXTERNAL.

With what is the body covered ? Is there hair on the
tail ? Do you find scales on the tail ? In what respect do
they resemble and in what differ from those of reptile or
fish?

How many toes on the fore-feet ? Do you find any trace
of a thumb ? Are the toes provided with claws i* Sketch
the sole, bringing out the callous spots. How many toes
in the hind-foot ? Sketch the sole and compare with that of
fore-foot.

How many nostrils ? Of what use to the animal are the
" whiskers " of the upper lip ? Examine eyes and look for
third eyelid at inner angle of the eye. Does it resemble any
structure you have found in the animals previously studied ?
Is there anything similar in your own eye ?

86

DISSECTION OF A EAT. 87

INTERNAL.

Cut the skin along the ventral median line from near the
vent to a point behind the jaw. Lay the skin back, separat-
ing the loose connective tissue which binds it to the deeper
parts. See the thin muscles covering the abdomen. Feel
for breast-bone, and open up the body by cutting through
muscular walls from between hind-legs to breast-bone.
Make transverse cuts on either side, and fold the walls out-
wards. This opens the peritoneal cavity. In this, with-
out disturbing parts, can now be seen, in front, the dark-
colored liver, behind this the coils of the intestine, and be-
tween the hinder coils of this tube the urinary bladder.

Tip the liver to your left and find the stomach. Sketch
from the side, showing the entrance of the gullet (oesophagus)
and the beginning of the intestine. Notice how liver and
stomach are connected by thin membrane (mesentery).
Tip the stomach forward and notice the spleen suspended
in another portion of the mesentery.

Trace the intestine, without cutting anything. It is also
held by its mesentery. It makes first a large loop back-
wards (duodenum) and then comes forward to form numer-
ous convolutions. Find a largo pocket (caecum) given off
from the intestine. All of the tube in front of this is
called the small intestine; back of it the large intestine.
In the latter two portions — (1) colon, (2) rectum — can
readily be distinguished by the different appearance of the
walls.

Spread out a portion of the mesentery supporting the in-
testine and notice in it small vessels. Some of these will
be found to be single, others double. The double vessels
are arteries and veins. They can be distinguished by trac-
ing them towards the middle line of the body. The veins

88 ELEMENTS OF COMPARATIVE ZOOLOGY.

unite in a large vein (mesenterial vein) which follows along
the colon, thence forward into an anterior fold, where it is
joined by other veins (gastric) from the stomach and
(splenic) from the spleen. From the union of these is
formed the portal vein which enters the liver from behind.
The small arterial branches arise from a mesenterial artery
which accompanies the mesenterial vein for some distance
and then can be traced back to the median line of the
dorsal surface of the body-cavity, where it joins the great
arterial trunk, the aorta. From the aorta, just in front of
the origin of the mesenterial artery, arises the cceliac artery,
which gives off. a branch to the liver (hepatic artery), and
then divides into splenic and gastric arteries, going to the
spleen and stomach respectively. Trace these arteries.
Where does the hepatic enter the liver ?

The single vessels in the mesenteries are the lymphatics.
Their purpose is to carry the products of digestion forward,
and eventually empty them into the blood-vessels. These
lymphatics unite in a lymphatic duct, which runs closely
parallel to the mesenterial artery and empties into a thoracic
duct running parallel with the aorta.

Sketch the blood-vessels (X 2) so far made out, on a
sheet large enough to accommodate the whole circulatory
apparatus of the rat.

In the mesentery supporting the duodenum find the
fatty-looking, irregular pancreas. Where does its duct
enter the intestine ?

How many lobes are there in the liver ? Are they sym-
metrically placed ? Beside the portal vein and the hepatic
artery is the bile-duct. Trace it forward and see how its
branches arise from the liver-lobes. Trace it backwards and
see where it enters the intestine. Look on the posterior
surface of liver for the gall- bladder. Tip the liver back-

DISSECTION OF A HAT. 89

wards (i.e., towards the tail). See how it is attached by
mesenteries to a muscular partition (diaphragm) bound-
ing the peritoneal cavity in front. See the oesophagus and
a blood-vessel (postcava) extending from the liver through
the diaphragm. Sketch the alimentary canal.

Cut through the oesophagus just in front of the stomach
and through the rectal portion of the intestine, and cutting
the mesentery remove the alimentary canal.

In the body-cavity see, dorsal to the liver, the kidneys.
Are they at the same level ? Covering the anterior end of
each kidney is a triangular supra-renal capsule. Trace
from each kidney (median surface) backwards a whitish
tube, the ureter. In the median line of the body-cavity is
the aorta already mentioned. Trace it backwards, finding
the arteries (renal) going to the kidneys. Farther back
the aorta divides into a pair of common iliac arteries.
Trace these into the legs. Do you find them to divide ?

Just behind the point of division of the aorta into the
common iliacs can be seen the common iliac veins, which
return from the legs and unite into a vessel, the postcava,
which passes forward, at first dorsal to the aorta. A little
farther forward the postcava receives an ileo-lumbar vein
from either side, and then a renal vein from each kidney.
From the kidneys trace the postcava forward through the
liver. This may readily be done by cutting away the ven-
tral part of the liver and then, inserting the point of the
scissors into the postcava, make a cut. Continue this
until the whole vessel is laid open up to the diaphragm.
On the inner surface of the postcava, inside the liver, notice
the openings of the hepatic veins. These bring to the
postcava the blood which entered the liver by the portal
vein.

90 ELEMENTS OF COMPARATIVE ZOOLOGY.

Add these parts to the sketch of the blood system
already begun.

With a sharp scalpel split a kidney horizontally. In the
cut section make out on the median side a cavity (the
pelvis of the kidney) from which arises the ureter. Into
the pelvis projects from the outer wall a papilla. In the
thick outer wall notice the difference in appearance between
the outer cortical substance and the more central medullary
substance. Sketch the cut section.

Notice the direction of the muscle-fibres in the dia-
phragm. What would be the effect of their contraction
upon the diaphragm ? Cut through the diaphragm ventral
to the postcava, and continue the cut along the ventral sur-
face of the body to one side of the median line. Cut the
ribs with stout scissors. This will lay open the pleural
cavity.

In the pleural cavity, behind, will be seen the postcava,
and dorsal to it the ossophagus. These pass forward be-
tween the lobes of the lungs. Notice the thin membrane
(mediastinum) passing dorsally from the breast-bone to the
heart and lungs. The heart itself will be found to be
enclosed in its own thin sac (pericardium). Sketch the
contents of pleural cavity.

Cut open the pericardium and study the heart. Its apex
is directed backward and to the (animal's) left ; its broader
base in front and to the right. Tip the heart to your right,
and notice how the postcava enters it near the base on the
right side. Just before its entrance into the heart it re-
ceives a similar vessel (the precava) from in front. Follow
the precava forward, cutting away the fatty-looking thymus
gland just in front of the heart in order to trace the vessel.
Soon it divides into right and left branches (jugulars) each
of which receives a vessel (subclavian vein) from the cor-

DISSECTION Off A RAT. 91

responding fore limb. Trace the jugulars forward to head ;
do they divide ? Insert precava and its branches as well as
anterior end of postcava in the sketch of the blood-vessels.

Arising from the left side of the base of the heart is the
aorta. Follow this forward; to which side of the body
does it turn ? From the arch which the aorta makes trace
the following vessels: (1) Right brachiocephalic artery,
which soon divides into the right subclavian artery and
the right common carotid artery. Follow the subclavian
into the limb, and the common carotid towards the head.
Where does the common carotid divide into internal and
external carotids? (Just outside the common carotid
will be found a white thread-like nerve. It is the vagus
(pneumogastric) nerve and supplies the stomach, heart,
and lungs). (2) The left common carotid; and (3) close
to it in its point of origin from the aortic arch the left
subclavian artery. Trace these as before. Do you notice
any differences between these vessels on the two sides of
the body ?

Tip the heart to your left and trace the course of the
aorta from the origin of the left subclavian back to the
origin of the coeliac artery already found. On which side,
(dorsal or ventral) of the oesophagus does the aorta pass ?
On which side is the heart ? Insert the vessels now made
out in the sketch, which should now represent the principal
vessels of the systemic circulation.

Dissect the aortic arch loose from the surrounding tissue,
lift it up, and see dorsal to it the pulmonary arteries going
to the lungs. From what part of the heart do they arise ?
Tip the heart to the animal's right and see the pulmonary
veins, which bring the blood back from the lungs to the
heart. On which side, with reference to the pre- and post-
cava, do they enter the heart ? The pulmonary arteries

92 ELEMENTS OF COMPARATIVE ZOOLOGY.

and pulmonary veins belong to the pulmonary circulation.
Add them to the sketch.

Cut through the cavas, pulmonary vessels, and aorta, and
remove the heart. On the base on either side will be found
small lobes — the auricles. Split the heart with a sharp
scalpel parallel to the horizontal plane of the animal, keep-
ing in mind which side of the organ was originally right,
and which left. Make out two pairs of cavities (usually
containing clotted blood, which should be carefully re-
moved). Which of these has the thicker walls — the right or
the left ? The basal cavities are the auricles, the apical the
ventricles. Which parts, auricles or ventricles, would you
suppose to play the greater part in forcing the blood
through the circulation ? Study the connections between
auricles and ventricles. Do the two auricles connect with
each other ? Is the same true of the ventricles ? Notice
what vessels enter the left auricle. Where do the pre-
and postcava enter ? Where does the blood go from the
left ventricle ? Insert a diagram of the heart, with its
chambers, in the sketch of the circulation.*

Between the common carotids is the ringed trachea, or
windpipe. Dissect it loose and cut near the head. Insert
a blowpipe in the hinder portion and inflate the lungs by
blowing. Are the rings of the trachea complete ? Trace
the trachea forward and notice enlarged anterior portion
(larynx), and just in front, and ventral to it, the hyoid
bone. Beneath the trachea (dorsal to it) is the oesophagus.

Remove the skin from the head. Notice the large
muscles attached to the jaw, and just in front of the ear
the salivary (parotid) gland. Cut through the jaw muscles,

* The heart of a cat, sheep, or pig will show these points much
better.

DISSECTION OF A RAT. 03

and, beginning at the angles of the mouth, carefully cut
backwards through the cheeks, so as to allow the lower jaw
to be bent back. In the mouth-cavity study the teeth.
In front are the incisors, and further back the molars.
How many of each in each jaw. "With a knife test the
hardness of the front and back surfaces of the incisors.
Which is the harder ? Why are these teeth always sharp ?
Is there any such arrangement in the molars ?

Between the molars is the hard palate, its surface with
transverse folds. Farther back is the soft palate, bounded
behind by the place (internal narial opening) where the
nostrils communicate with the back part of the mouth-
cavity. How many of these openings do you find ? Slit
soft palate with the scissors and see how this arrangement
is brought about.

Opposite the internal narial opening (i.e., on the floor
of the pharyngeal region) is an opening — the glottis, sur-
rounded by a raised rim, which is enlarged in front into
a soft epiglottis. Inside of the glottis may be seen two
folds (vocal chords), which narrow the opening. Insert a
probe into the glottis. Where does it appear ?

Split the skin down the back, and remove it from the
body, and then with the bone forceps break through the
cranial walls at the back of the head,* taking pains not to
injure the underlying structures, When the opening is
made enlarge it by removing the skull bit by bit with a
strong knife from the dorsal surface and right side. Then
continue the process back in the neck region as far as the
shoulders.

* The points relating to the brain can be made out more easily on
the cat or sheep, but with a little pains the directions here given can
be followed on the rat.

94 ELEMENTS OF COMPARATIVE ZOOLOGY.

In the brain make out, viewed from above, in front the
olfactory lobes; next the large cerebrum, and behind this
the cerebellum, and following the cerebellum the medulla
oblongata, broad in front and tapering behind into the
spinal cord. Are any of these parts paired ? The line
between medulla and spinal cord is not a sharp one, and the
place of passage through the skull may be regarded as the
boundary. Sketch these parts in outline from above and
from the side, X 2.

Over the whole brain is a rather tough membrane, the
dura mater, which is next to be removed from the dorsal
surface. Do you find any convolutions on the cerebrum ?
Cut through the olfactory lobes as far forward as possible,
and lift the cerebrum very carefully from in front. It
will be found to be tied by the optic nerves, going from
the ventral surface. Cut these as close to the skull as pos-
sible. Do the olfactory lobes arise from the tip of the
cerebrum ? Roll the brain very carefully to the left side,
looking at the same time at the right side of the medulla
for nerves. From its anterior angle (below the cerebellum)
will be found a strong nerve, the trigeminus, and just
behind it another nerve, the facial and auditory com-
bined. Some distance farther back, yet still inside the
skull, arises a more complex nerve, consisting in reality
of three, the glossopharyngeal, the vagus, and the spinal
accessory. (Thus we can easily make out in the rat the
following nerves: I, olfactory; n, optic; v, trigeminal;
vn, facial; vin, auditory; ix, glossopharyngeal ; x, vagus
or pneumogastric ; xi, spinal accessory. The other nerves
are not easily made out on so small a form.)

Tip the cerebrum forward, and notice between it and the
cerebellum the optic lobes behind and the 'twixt-brain in
front. How does this compare with what was found in the

DISSECTION OF A RAT. 95

dogfish? Tip the cerebellum forward, and see the large
triangular opening in the roof of the medulla.

On the lower surface of the brain see the cut optic
nerves. From which division of the brain do they arise ?
Behind the optic nerve find a median lobe, the hypophysis.

With a sharp scalpel make a series of cross sections through
the cerebrum. Are the two halves completely separate ?
In each half find a cavity (ventricle), and above it in the
solid tissue a transverse lighter band (corpus callosum).
Draw the section. Make similar sections through the 'twixt-
brain and the optic lobes. How many cavities do you find
here ? Draw each section.

Cut a longitudinal vertical section through the cerebel-
lum to left of median line, and notice the way in which the
cerebellum is folded. The somewhat bush-like structure is
known as the arbor vitae. Make a sketch of it. Cut
transversely through the rest of cerebellum and medulla,
and in the section see the folds of cerebellum cut in the
opposite direction; and, below, the thick floor (pons varolii)
of the medulla. Cut through the medulla farther back.
Do you find a central canal in the section ?

On the ventral surface of the neck, just outside the caro-
tids, dissect away carefully, keeping the fore legs stretched
out, until you find nerves (white cords) going from the ver-
tebral region to the sides of neck. Can you make out two
roots to each nerve ? Just in front of the ribs notice that
the nerves are larger, and that they go to the fore limb just
in front of subclavian artery and vein. How many of
these nerves as they arise from the neck interlace to form
the brachial plexus (the network from which the limb
nerves arise). Trace them into the limb. Sketch the
plexus.

Separate the muscles in the bend of the knee, exposing

96 ELEMENTS OF COMPARATIVE ZOOLOGY.

the large sciatic nerve. Trace the nerve backwards towards
the trunk. Does it pass through any bones ? Trace the
nerve inside the dorsal wall of the body-cavity. Do you
find a plexus like that of the fore limb ? If so, how many
nerves enter into its formation ?

COMPABISONS.

With three columns, for Ichthyopsida, Sauropsida, and
Bat respectively, answer the following questions :

(1) Is hair present ?

(2) Do you find true scales or feathers ?

(3) Is there an external ear ?

(4) Do you find anything like gill-slits?

(5) How many chambers in the heart ?

(6) How many aortic arches ?

(7) Do the aortic arches bend to the right or to the left ?

(8) Is a diaphragm present ?

(9) Do they produce eggs ?

MAMMALIA (MAMMALS).

The name Mammalia is applied to all those forms which,
like the mouse, cow, and man, have warm blood, a body
covered with hair, and which bring forth living young,
nourished during the early stages by milk secreted by the
mother. These characters at once distinguish any mammal
from any other animal, but other features of equal or
greater importance occur.

Hair occurs in the young of all mammals, and is usually
found also in the adult; but in the case of the whales it is
absent in the fully grown animal, and even in the young it
is only found near the mouth. Hair is a product of the
outer or epidermal layer of the skin. At places this layer
dips down into the deeper layer (dermis), forming a pit or
follicle from the bottom of which the hair grows, continual
additions being made at this point, commonly known as the
" root." The hair itself is a solid column, varying consid-
erably in shape in different animals, from the delicate fur of
the fur-seal, to the bristles of the pig or the spines of the
porcupine. There are usually glands present which open
into the follicle and which secrete a fluid, the object of
which is to keep the hair moist ; and besides, each follicle
is provided with muscles which serve to erect the hair at
times of fright (as in cats and dogs), or in cold weather.

Closely related to hair are nails, claws, hoofs, and horn.*

* Here is intended such horns as those of the cow, sheep, antelope,
and rhinoceros ; the horns of the deer are true bone.

97

98 ELEMENTS OF COMPARATIVE ZOO LOOT.

In fact these structures must be regarded as hairs united
throughout their length. At other times a similar consoli-
dation of hair gives rise to protective scales covering the
body, as in the case of the pangolins.

The bodies of the vertebrae usually have flat faces, and
the vertebral column in most forms can be divided into five
regions — cervical, thoracic, lumbar, sacral, and caudal.
The cervical vertebrae occur in the neck; they bear no ribs,
and, except in three rare forms, they are constantly seven
in number, the long-necked giraffe and the short-necked
whale having the same number of these bones. The tho-
racic vertebrae are more variable in number. They bear ribs,
some of which extend downward and unite with the breast-
bone or sternum. Between the thoracic and pelvic regions
occur the ribless lumbar vertebrae, while the sacral verte-
brae are those which unite with the pelvic bones. The cau-
dal vertebrae are found in the tail. In the whales only
cervical and thoracic vertebrae can be distinguished, since
the absence of a pelvis in these forms allows no line to be
drawn between lumbar, sacral, and caudal regions.

In the skull there is a tendency for bones which are dis-
tinct in the fishes and reptiles to fuse with each other, so
that the number of distinct elements is considerably re-
duced. The skull is borne on the first cervical vertebra,
upon which it slides by means of two rounded surfaces or
condyles. The lower jaw articulates directly with the
skull, and is never suspended by a quadrate bone, as in the
forms already studied.

The fore limbs are always present; the hind limbs are
absent in the whales and manatees, being represented in a
few forms by one or two bones imbedded in the muscles of
the trunk. Except in the Monotremes (p. 102), the cora-
coid does not occur as a distinct bone, but as a small prom-

MAMMALS. 99

inence joined to the shoulder-blade (scapula), while in many
the collar-bone (clavicle) also is lacking. The feet have
typically five toes, but not infrequently this number is re-
duced by a disappearance of the outer digits, the reduction
reaching its extreme in the cow, which has but two, and
the horse, which walks upon the tip of its middle toe.

FIG. 37.— Brain of Dog. (After Weidersheim.) II-XII, the cranial nerves
(see page 94).

The most marked characteristic of the nervous system is
the great relative increase in size of the cerebrum, and, to
a less extent, of the cerebellum; the optic lobes and the
medulla, so prominent in the lower forms, being over-
shadowed by these parts. The cerebrum is the seat of in-
telligence, and this increase in size is correlated with the
higher mental powers of the mammals. Microscopic study
of the brain has shown that this organ is composed of two
different portions, called, according to their colors, white and
gray, and that the gray matter is the true brain substance,
while the white is composed of nerve-cords to transmit
nerve impulses. The gray matter is on the outside of the
cerebrum, hence the larger the brain the more surface it
has, and consequently the more gray matter it can have.
In the higher mammals the amount of surface of the cere-
brum is greatly increased by folds or convolutions, and the

100 ELEMENTS OF COMPARATIVE ZOOLOGY.

extent and complexity of these convolutions correspond
well with the intelligence of the form.

In the eyes the nictitating membrane or "third eyelid"
of the bird is reduced to a small fold at the inner angle of
the eye. Except in the whales, and some seals, moles,
etc., external ears are developed, while the internal parts of
the ear become considerably modified. Thus the quadrate
and one other bone pass in to the middle ear, where they,
together with a third bone, form a chain to convey sound-
waves to the sensory portions. In the inner or sensory
portion a spiral outgrowth, the cochlea, occurs (Fig. 64),
and in this is a most wonderfully intricate sensory appa-
ratus— the organ of Corti — the functions of which are as
yet uncertain.

The mouth is usually provided with fleshy lips, and all
mammals, except some edentates and whales, have teeth.
These teeth are always confined to the jaws (cf. Fishes, p.
10), being inserted by one or more roots into sockets in the
bone. Some mammals have but a single set of teeth
throughout life, but the majority have a first or milk den-
tition, which is soon lost and replaced by a permanent
dentition. Occasionally, as in the sperm-whale, etc., all the
teeth are similar in shape, but usually several different
kinds occur, the extreme being reached when four types
are present — incisors, canines, premolars, and molars.
The incisors have but a single root, and are found in the
premaxillary bone and in the corresponding position in the
lower jaw. The first teeth in the maxillary, if single-rooted
and pointed, are called canines; and behind these come
the molars, with two or more roots. These in turn are
subdivided into premolars, which appear in both milk and
permanent dentitions, and molars proper, which occur only
in the permanent set. The number of teeth and their

MAMMALS. 101

arrangement vary considerably in different mammals, and
the characters which they furnish are of great value in group-
ing the various forms. To express these characteristics
briefly a dental formula has been introduced, in which the
different kinds of teeth are indicated by initials, while the
number in either jaw is represented by a figure above or
below a horizontal line. Thus the permanent dentition of
man is expressed thus: i 8, c |, pm f, m f ; which indi-
cates that in man there are two incisors, one canine, two
premolars, and three molars in each half of each jaw. The
pig has, i 3, c {, pm f , m f ; the cow, i J, c f, pm J, m f,
incisors and canines being absent from the upper jaw.

The body-cavity is divided by a transverse muscular par-
tition, the diaphragm, into two chambers — an anterior
pleural cavity containing the heart and lungs, and a poste-
rior peritoneal cavity in which is situated the stomach,
liver, intestine, etc.

The heart, placed a little to the left of the median line,
is four-chambered, having, like that of the birds, two
auricles and two ventricles. Of these the auricle and ven-
tricle of the right side receive the blood from the body and
send it to the lungs, while those of the left side take the
blood as it comes from the lungs and send it through the
aorta to all parts of the body. The aorta, which bends
backward and to the left, represents the left arch of the
fourth pair of the primitive branchial vessels, the right of
the same pair being partially represented in the artery
(subclavian), which carries the blood to the right fore limb
— a condition just the reverse of what occurs in the birds.
The fifth pair of arches form part of the arteries (pulmo-
naries) which convey blood from the heart to the lungs.
The blood of the mammals differs from that of all other

102 ELEMENTS OF .COMPARATIVE ZOOLOGY.

forms in that the red corpuscles are circular in outline and
are not nucleated.

The monotremes form the only exceptions to the state-
ment that the mammals bring forth living young. These
lay eggs, one species having the eggs about the size of a
pigeon; but the young which are hatched from these eggs
are nourished by milk secreted by the mother, as is the case
with all other mammals.

The Mammalia are divisible into three large groups or
subclasses: Monotremata, Marsupialia, and Placentalia.

SUBCLASS I. — MONOTREMATA.

This subclass contains three or four species of animals
which are found only in Australia and its immediate
neighborhood. They present resemblances to the birds, or

FIG. 38.— Duckbill (Ornithorhynchus paradoxus) . From Ltitken.
better, to the reptiles in the following points, in all of
which they differ from the other mammals: They lay
eggs; they have well-developed coracoid bones; and repro-
ductive and excretory organs empty into the posterior por-
tion (cloaca) of the intestine, and thence pass by a common
opening to the exterior.

MAMMALS. 103

The monotreines include the duckbill and the spiny
ant-eaters. The duckbill is an aquatic animal, and re-
ceives its common name from the fact that it has a horny
bill much like that of the duck. It lives in burrows in the
banks of streams, and feeds on beetles, shrimps, etc., which
it catches in the water and crushes with its horny teeth, its
true teeth being lost at an early age. The spiny ant-eaters
resemble the duckbill in their burrowing habits, but they
live exclusively on the land, where they feed on ants.
They are, like the true ant-eaters (p. 106), entirely toothless,
and receive the adjective spiny of their common name from
the fact that their hair takes the shape of long stout spines,
recalling those of the porcupines.

SUBCLASS II. — MARSUPIALIA.

This subclass receives its name from the fact that in the
female a curious pouch or marsupium is developed on the

FIG. 39.— Pelvis of Opossum. (After FIG. 40.- Opossum (Diclelphys vir-
Minot.) M, marsupial bone; ii, mniana). After Audubon and
ilium ; is, ischium ; p, pubis. Bachman.

lower surface of the body of the female, in which the young
are placed by the mother immediately after birth, and where
they remain until able to take care of themselves. This

104 ELEMENTS OF COMPARATIVE ZOOLOGY.

pouch is supported by a pair of bones which extend forward
from the pelvis — the marsupial bones, — and these, as well as
a peculiar inbending of the angle of the lower jaw, serve at
once to distinguish any marsupial skeleton. Were these
the only characters to be considered we should not be war-
ranted in placing these forms in a subclass by themselves,
but there are other characters connected with reproduction
which justify this course. The living marsupials have a
peculiar distribution : they are restricted to warmer Amer-
ica and the chain of islands extending from Australia to
Celebes. Fossil forms are found in Europe as well.

The American species are all opossums — forms with pre-
hensile tails — and have given rise to the expression
' ( playing 'possum," from their habit of feigning death when
disturbed. Their food is chiefly insects, but birds, eggs,
etc., are not despised.

Australia is the real home of the marsupials; indeed at
the time of its discovery this continental island contained
only marsupials, if we except the dingo, or native dog.
In this region are found forms which recall animals of
different groups occurring in other parts of the' world.
Thus the wombat resembles in size and teeth the beaver;
the thylacines in habits and in form are dog-like, while
the phalangers in size and appearance are like the flying
squirrels, and, like those animals, they have that same fold
of skin which enables them to glide through the air from
tree to tree. Most familiar of all the Australian forms are
the large grass-eating kangaroos, in which the fore legs
have become almost useless for locomotion, the animal
jumping with its hind legs, and when resting, supporting
itself upon these members and its enormously developed
tail. There are also fossil marsupials in Australia, some
of them of enormous size. Thus Thylacoleo was as large

MAMMALS.

105

as a lion, while Diprotodon had a skull three feet in length
and a thigh-bone two feet from tip to tip.

SUBCLASS III. — PLACENTALIA.

The great majority of mammals belong in this division.
They are marked off from the other subclasses by the
absence of those characters which have been mentioned as
distinguishing these, as well as by a structure now to be
mentioned. These mammals are not born until their in-
ternal organization has been well advanced; and in order
that they may be supplied with nourishment a peculiar
vascular structure is formed, — the placenta, — by means of
which blood is brought to the growing embryo. Such a
structure is lacking in both monotremes and marsupials.
The Placentalia are divided by details of structure into
many groups or orders, eleven of which are represented in
the world to-day.

ORDER I. — EDENTATA.

The edentates, the lowest of the placenta! mammals,
receive their name from the fact that incisor teeth are

FIG. 41.— Nine-banded Armadillo (Dasypus novemcinctus). From Lutken.

always lacking, while in the ant-eaters no teeth occur.
The feet are armed with strong claws. The group is a
tropical one, and has its greatest representation in Amer-
ica. Here belong the armadillos, in which the deeper

106 ELEMENTS OF COMPARATIVE ZOOLOGY.

layer of the skin becomes converted into bone, forming an
armor over the body. In the fossil Glyptodou this armor
formed one solid piece, enclosing the trunk much like the
armor of a turtle; but in the living forms it becomes
broken into several transverse bands, which move upon
each other, so that the animal can coil itself into a ball.

The sloths are larger forms which, back downward,
crawl with the slowest motions along the branches of the
trees, holding themselves by their hook-like claws. Upon
the ground they walk with difficulty, their long claws
being in the way. In geological times there were forms

FIG. 42. — Pangolin (Mania longicaudato). From Monteiro.

allied to the sloths, but of much larger size. One, the
Megatherium of South America, had a skeleton 18 feet in
length. Another form found in North America receives
interest from the fact that it was first described by Thomas
Jefferson.

The ant-eaters are true edentates in that they are wholly
without teeth. As their name implies, ants form the chief
part of their food; their claws are well adapted for digging

MAMMALS.

into the nests, the tongue is very long and extensible, while
the salivary glands pour out a thick, sticky secretion which
fastens the ants to the tongue. The true ant-eaters are
natives of South America, but in Africa and India are
allied forms with teeth, which also feed upon ants.
Among these are the pangolins, in which the whole upper
surface of the body is covered with scales, arranged some-
what like those of a pine-cone. These scales, as already
mentioned (p. 98), are to be regarded as modified hair.

ORDER II. — RODESTTIA (The Gnawers).

The rodents are the gnawers, the well-known abilities of
rats and mice in this direction being shared by all mem-
bers of the order. They have no canine teetn ; the molars

FIG. 43.— Skull of rauskrat (enlarged), showing the gnawing incisors and absence

of canines.

are usually f, while the incisors vary between f , ^, and f .
These incisors demand a moment's attention. These teeth
have persistent pulps, i.e., they continue to grow through-
out life. As fast as they wear away they are renewed from
below. In each incisor two parts can be distinguished:
the anterior face of the tooth is covered with a very hard
layer (enamel), while the posterior surface is composed of
a much softer dentine. This dentine wears away much

108 ELEMENTS OF COMPARATIVE ZOOLOGY.

faster than the enamel, and the result is that the teeth are
constantly kept at a chisel-edge.

Lowest of the rodents come those forms familiarly
known as hares and rabbits, with disproportional hind legs
and long ears. The distinction between the two — hares
and rabbits — is very slight, the true rabbit being a native
of southern Europe. All the rest are hares. In America,
however, the term rabbit is usually restricted to the small
burrowing forms.

The porcupines, with some of their hair changed to long
sharp spines, — efficient weapons of defence, — come next.
These occur in both hemispheres, but the American forms
are mostly arboreal, while those of the Old World burrow.
Allied to them in structure, but differing in fur, are the
chinchilla and the coypu of South America, the latter fur-
nishing the well-known "nutria fur." The same country
furnishes the stupid, so-called guinea-pigs, — whose young
shed their milk-teeth before birth, — and the giants of
rodents, the capybara, with a body four feet in length.

Rats and mice are the great pests of the order. Our
common brown rat is a recent immigrant. The early set-
tlers brought with them the black rat, the brown rat being
then unknown in western Europe, but about 1720-30 the
latter came west from the Volga region, and gradually
spread all over western Europe and then over America,
the black rat disappearing before the invader. There are
many rat-like forms, among them the lemmings of the
Arctic regions, vast hordes of which occasionally overrun1
Norway; the dormice, which hibernate in winter; the
gopher and pocket-rats, which burrow through the soil in
the Western States; the familiar muskrat, and the less
familiar jumping mice, which resemble the kangaroos in
their locomotion.

MAMMALS. 109

Another series of rodents contains the beaver, common
to the Old World and the New, which furnishes furs of
great value. These live most of their lives in the water,
building dams so that they may always have plenty of it;
while their near relatives, the woodchucks, and their west-
ern representatives, the prairie-dogs, have no such depend-
ence upon water. Highest of all the rodents are the
ground - squirrels, the true squirrels, and the flying
squirrels.

ORDER III. — INSECTIVORA (Insect-eaters).

These are small forms, in which all four types of teeth
are developed, and which are marked off from all other
orders by characters rather difficult of expression. As
their name implies, they feed largely upon insects, but
worms and other small animals are not despised. The
species are largely tropical, but the shrews and moles are
found in cooler climates. Most of the species are noctur-
nal and burrowing animals, consequently their eyes are
small, while their fore legs are adapted for digging.

ORDER IV. — CHEIROPTERA (Bats).

The bats are the only mammals which truly fly. In the
rv.ise of the flying squirrel and the rest, the animals glide
Liirougli the air on the plane formed by the lower surface of
the body, the tail, and the broad membrane which extends
between the limbs; and they can never ascend to the level
from which the flight started. With the bats, on the other
hand, there are no such limitations to the flight. The wing
in the bats consists of a very thin membrane supported
upon a framework composed of the body and the bones of
the fore limbs. These latter are elongated, four of the
fingers excessively so ; and between these fingers and ex-

110 ELEMENTS OF COMPARATIVE ZOOLOGY.

tending back to the body and the hind limbs is the web of
the wing. The thumb, however, is not involved in the wing,
but forms a claw of great use in supporting the body,
although when at rest they usually hang by the five claws
of the hind feet. The jaws are provided with incisors,
canines, premolars, and molars. Bats are social animals,
occurring in large numbers in caves, deserted buildings, and

FIG. 44.— Skeleton of bat.

the like, where they spend the day, and it is remarkable
that these colonies are usually entirely male or female. In
a rough way the bats may be divided into fruit-eating and
insect-eating forms, their habits being correlated with
peculiarities of structure. To the fruit-eating species
belong the large bats of the East Indies known as flying
foxes. All of our bats are insect-eating. Some of the
South American bats (not the one called the vampyre by
Liune) are known to suck the blood of other mammals.

MAMMALS. Ill

In the four orders Edentates, Rodents, Insect! vores, and
Bats the surface of the cerebrum is smooth; in all the re-
maining orders it is at least fissured, and in most it is con-
voluted (see Fig. 37), this increase in surface reaching its
greatest development in man. Since this line of division
corresponds in a way with the intelligence of the forms,
the four orders already mentioned are grouped together as
Ineducabilia; the others are associated as Educabilia.

ORDER V.— CETE (Whales).

The whales have a fish-like body, the resemblance being
frequently heightened by the development of a dorsal fin ;
and yet in all points of structure they are mammals. The
anterior limbs contain the same bones (except that the
number of joints in the fingers may be increased) as do our

FIG. 45.— Pigmy whale (Kogia floweri). From Gill.

own, but the whole has been modified into a " flipper" for
use in swimming. The hind limbs are absent externally,
but imbedded in the flesh on either side is a bone, variously
interpreted as a part of the pelvis or as the bone of the
thigh. The body terminates in a bilobed caudal fin
("flukes"), but this, instead of being vertical, as in the
fish, is horizontal. All of the whales have teeth in the
young stages ; some retain them through life, while others
lose them long before maturity, sometimes even before
birth. The stomach is remarkable for having several
(4-7) chambers, this complication recalling the condition
in the cow.

112 ELEMENTS OF COMPARATIVE ZOOLOGY.

According to the presence or absence of teeth the living
whales are divided into two groups. In some of the .toothed
whales but two teeth are present ; others may have a large
number ; and usually these cannot be well distributed
among incisors, canines, etc., as all are essentially alike in
size and shape. In the male narwal, however, one of the
upper teeth on one side (apparently a canine) grows straight
forward into a long twisted spear eight or nine feet in
length, while the other teeth disappear at an early age.
The killer-whales are comparatively small, but are among
the most voracious of mammals, not hesitating to attack
the largest whales. Here also belong the blackfish, por-
poises, and dolphins. The sperm-whales are larger, and
have no teeth in the upper jaw, while the lower jaw is abun-
dantly supplied. They derive their common name from the
spermaceti which they produce. This is a solid granular
substance found in the "case," a cavity occurring on the
right side of the front of the head between the skin and the
skull.

The toothless whales are also known as whalebone whales,
from the fact that they bear
upon the lower sides of the
upper jaw hundreds of long par-
allel plates of so-called whalebone
or baleen. These plates are
fringed at the end, and the whole
apparatus forms an efficient
strainer, used in separating the

FIG. 46 — Section through the ,, , -. . -. ,-,

head of a whalebone whale Small animals Upon Which these

(after Boas), showing how the , , _ , „ ,-, -.

plates of baleen (w) are ar- whales feed from the surround.

ranged on either side of the . T, . , ,

mouth-cavity (m) The true ing water. It is among these

bones are shown black. 111 i_ i 1 1 i 1-1

whalebone whales that the giants

among mammals occur. The right whales of the Arctic

MAMMALS. 113

seas reach a length of sixty feet, the razor-back whales are
still larger, while the sulphur bottoms and silver bottoms
(so called on account of the color of the lower surface)
attain a length of from 90 to 95 feet.

ORDER VI. — SIREKIA (Sea-cows).

These are whale-like animals, with the same flippers and
the same horizontal tail, but they differ from the whales in
the possession of an evident neck, and of sparse hair or
bristles all over the body. Besides these features all, ex-
cept the extinct Rytina, have flat-crowned molar teeth. The
living forms are very few. Rytina, which lived near Ber-
ing Strait, was exterminated in the last century. The
dugong is the representative of these forms in the Indian
Ocean, while the three species of manatees come, one from
Africa, the other two from the eastern coasts of America.
All the sea-cows are vegetable feeders, living upon sea-
weed or, in the case of the manatees, upon the plants found
in fresh-water streams as well.

ORDER VII. — PROBOSCIDIA (Elephants).

The elephants are the giants among the land mammals.
They have five toes, each encased in its own hoof; they
have no incisors in the lower jaw, while the pair in the
upper jaw are developed into large tusks. Canines are
lacking, but there are seven molars in each half of each
jaw. These molars are flat-crowned, the surface of the
crown being crossed by several ridges of harder enamel.
Only two, or at most three, of these molars are in use at
once, but as the old ones wear out they drop out at the
front of the jaw, and are replaced by new ones from behind
until the seven are gone. The skull is enormous, but it is

114 ELEMENTS OF COMPARATIVE ZOOLOGY.

comparatively light on account of the numerous cavities in
the bone. Most striking of all is the proboscis, which is

FIG. 47. — A manatee (Trichechus americanus) feeding. After Elliott.

merely an enormously developed nose, with capacities which
only one who has studied an elephant can realize. The

MAMMALS. 115

skin is almost entirely naked, hairs being scarce, and on the
tail taking the shape of long wiry bristles.

To-day two species of elephants exist, one having its
home in India, the other in Africa. In the later geological
ages there were several others, one having lived in America
and others in Europe. Towards the end of the last century
remains of hairy elephants — even the flesh being preserved
—were found imbedded in the ice in northern Siberia
Allied to the elephants were the somewhat larger mas-
todons, in which the molar teeth bore conical cusps, while
the tusks were frequently enormous. Some mastodons had
incisors in the lower jaw as well.

ORDER VIII. — HYRACOIDEA (Coneys).

This order contains but two or three species, distributed
from Syria south into Africa. In having long curved
incisors and absence of canines they recall the rodents, in
other points their structure is like that of the rhinoceros,
while the foot-pads on their feet recall those of the cat or
dog. The hyrax of Syria is probably the coney of the
Old Testament.

ORDER IX. — UNGULATA (Hoofed Animals).

To this order belong the great majority of important
mammals. They are herbivorous, usually of large size,
and lack collar-bones. The feet are used solely in walking,
and not in prehension, each toe having its tip enclosed in
a horny hoof, and in living forms there are never more than
four toes developed on a foot. The living ungulates are
arranged in two series, according to the number — even or
odd — of toes upon their hind feet. The odd- toed forms are
called PERISSODACTYLA, the even-toed are ARTIODACTYLA.

116 ELEMENTS OF COMPARATIVE ZOOLOGY.

To the perissodactyls belong, of living forms, the tapirs,
rhinoceroses, and horses. The tapirs live in the forest
regions of the tropics of both continents. They have a
hog-like body, large prehensile upper lip; teeth, i |, c \, pm
j, m |; while their fore feet have four toes, the hind feet
three. Yet, although the fore feet have an even number
of toes, these are not symmetrically arranged, as in artio-
dactyl forms, the pig for example, but one (third) is en-
larged and bears most of the weight of the body.

The rhinoceroses have three toes on each foot; the skin

FIG. 48.— Sumatran rhinoceros (Ceratorhinus sumatrensis) . From Liitken.

is extremely thick; the snout bears one or two well-
developed horns, in which there is no bony core; and
canine teeth are not developed even in the young. There
are six species known, those occurring in Africa having
two horns, while in the East Indies are both one and two-
horned forms.

In the horses the reduction of toes has gone still farther,

MAMMALS.

117

there being but one (the middle or third) in each foot. In
the skeleton, however, traces of two more can
be found in the "splint-bones," two small
bones occurring alongside the large "cannon-
bone." All of the existing horse-like forms
have the teeth i }, c |, p £-, m f , and all are
natives of the Old World, none existing in
America at the time of its discovery. All
evidence goes to show that the home of the
domestic horse was in Central Asia, and indeed
four different species of horse run wild there
to-day. The asses have their centre around
the eastern end of the Mediterranean, while
the zebras or striped horses are all African. In
geological time, however, America had horses,
and the fossils in our Western States give the Fro. 4g._Foot
history of the race from small forms about the showing the
size of a fox, and with three toes behind and
four in front; later, those as large as a sheep,
with three functional toes in each foot; and
still later, three-toed forms as large as a donkey. In
domestication horses vary extremely in size as in other
respects.

Lowest of the artiodactyls, or even-toed ungulates, come
the two species of hippopotamus, in which there are four
toes, large canine teeth, and a huge, clumsy body, some-
times fourteen feet in length. In the pigs the canines are
still large, and the toes are four in number, but the outer
ones are lifted above the ground so that they are useless as
organs of locomotion. Our domestic swine have descended
from the wild-boars of Europe. In the warmer parts of
America the peccaries represent the group.

The hippopotamus and the pigs have the axis of the

118 ELEMENTS OF COMPARATIVE ZOO LOOT.

F.O.SO.-Diagram of the stomach

foot passing up between the middle toes; in other words,
they have cloven hoofs. In all other artiodactyls the cloven
hoof occurs, and besides, they chew the cud, and hence they
are associated as a group of ruminants. The stomach is
di rided into four chambers, and when a cow, for instance,

feeds, it swallows the grass
without chewing it. It passes
down to the first stomach and
thence to the second. In these
it becomes mixed with digestive
fluids and softened. It is then
brought up into the mouth,
thoroughly chewed, and again
swallowed. This time it passes

int° the thM Sumach, and

frOm this int° the fourth> and
so into the intestine.

To the ruminants belong the most valuable domesticated
animals. In South America are found the llamas and
alpacas, which were the cattle and beasts of burden of the
ancient Peruvians ; while in Asia and Africa the camels, in
part, take their place. Two kinds of camels occur, one
with one and the other with two humps upon the back.
These humps are merely large masses of fat. Some forty
years ago the United States Government introduced some
camels into our southwestern territory, and the descendants
of these are still to be found in Arizona.

We associate together under the common name of deer
all those ruminants which have horns consisting of solid
bone. These horns are annually shed and grow out anew
each year, usually increasing in size with the age of the
animal. When first formed the horns are covered with a
thin skin with short hairs. The horns in this condition are

MAMMALS. 119

said to be in the velvet. When the horn is fnlly formed
the skin dies and is worn off. In some deer horns are borne
only by the male, but sometimes both sexes, as with the
reindeer, are provided with them. The long-necked giraffes
are closely related to the deer.

In other ruminants the horns are never shed. In these
the horns consist of a central core of bone, covered on the

FIG. 51— Prong-horned antelope (Antilocapra americana).

outside with a horny structure — in reality modified hair
(p. 97). Here belong our domestic cattle, which are be-
lieved to have arisen from four different kinds, which
formerly were wild in Europe. This wild stock is almost
extinct. One of these forms at least was closely similar to
our American bison, which has so nearly approached ex-
tinction from the desire for "buffalo " robes. The true
buffalo are all natives of the Old World, and occupy a posi-
tion between the ancestors of domestic cattle and the long
series of forms grouped together as antelope, most of

120 ELEMENTS OF COMPARATIVE ZOOLOGY.

which belong to Africa, but which are represented in
America by the prong-horned antelope of our Western
States. Other members of the same group with permanent
horns are the sheep and the goats, the series ending with
the so-called musk-ox of the arctic regions, a form nearer
the goats than to the domestic cattle in its structure.

As a whole, we may say that in points in structure —
especially in the characters of feet and teeth — the group of
ungulates are among the most specialized of the mammalia,
the whales, bats, seals, and possibly the elephants alone ex-
celling them in this respect.

ORDER X. — CARNIVORA (Beasts of Prey).

The beasts of prey are specialized in the direction of
flesh-eating. Their bones are slender, but strong; their
feet (usually five- toed) are furnished with claws; while on
the top of the skull is a crest for the attachment of the
strong muscles of the jaws. All four kinds of teeth are
present, and one of the molars or premolars is flattened
vertically, so that, meeting its fellow of the opposite jaw, it
cuts like a pair of shears. In the lower mammals we find
the lower jaw so hinged upon the skull that it can move
back and forth in grinding the food. In the carnivores^
on the other hand, no such motion is possible.

The carnivores are divided into two groups, one embrac-
ing the typical land-inhabiting forms; the other, which
includes the walrus and the seals, is modified for an aquatic
life; the differences being most marked in the structure of
the appendages. In the first group the legs are elongate
and the toes are distinct, whence the name FISSIPEDIA;
while in the other division (PINNIPEDIA) the legs are
shortened, the fingers are webbed, and the feet are thus
effective paddles,

MAMMALS. „ 121

Lowest of the fissipedia are the bears and their allies, in
which the whole sole of the foot is applied to the ground in
walking, and hence are called plantigrade, in opposition to
those digitigrade forms, like the cat and dog, which walk
upon the tips of their toes. The bears are widely distrib-
uted over the earth, America having at least three species.
The racoon is distributed throughout the United States,
and in tropical America is represented by that exceedingly
interesting animal, the coati.

Another group of carnivores includes the otters, mink,
ermine, sable, and marten — all of which are valuable for the
furs which they afford, — as well as the weasels and ferrets,
and the well-known skunks. These are partly plantigrade,
partly digitigrade.

The dogs, foxes, wolves, and jackals are all digitigrade.
They have the teeth, i J, c ^, pm J, m f . Foxes and
wolves are wild, and many believe that our domestic dogs
have descended from some wolf stock; but others think
that dogs and wolves are distinct, and even that our common
dogs represent several originally distinct kinds or species.

The hyaenas are intermediate between the cats and dogs
in many respects. They have the back teeth fitted for
crushing. In the cats, of which there are more than fifty
species, the teeth are usually i f , c -}-, pm f , m {, while
the claws are retractile into sheaths. Our domestic cat
apparently had its origin in Egypt, while ancient Greece and
Itcme lacked our familiar puss, its place being taken by
domesticated martens. Among the cats the tiger, lion,
panther, leopard, and puma rank first, and with them are
associated the wildcats and lynxes.

In external form the seals and walruses have little re-
semblance to the other carnivores, but in structure, and
especially in their skulls, there is great resemblance — to the

122 ELEMENTS Off COMPARATIVE ZOOLOGY.

bears and otters in particular. As has been said, their feet
are modified into paddles, and only the distal region is dis-
tinct from the body. Lowest are the large walruses, of
which there are two species in northern seas, in which the
upper canines are enormously developed. They can use
their hind feet in walking. The eared seals are so-called
because they have small external ears. The largest of these
are the sea-lions, but the most valuable are the fur seals, of

FIG. 52.— The harbor seal (Phoca vitulina). After Elliott.

which two species are known. The one which occurs in the
southern hemisphere has been almost exterminated, while
the Alaskan species is rapidly following the same road.

The true seals lack all external ears, and since their skins
are less valuable, a longer lease of life seems assured them.
They occur on all shores, and from their fish-eating habits
are frequently a nuisance to fishermen.

MAMMALS. 123

ORDER XL — PRIMATES.

The term Primates is given to that group which includes
the monkeys, apes, and man, from the fact that they are
the first or highest group in the animal kingdom. Collar-
bones are always present; the feet are very primitive, and
the fingers and toes are armed with nails, claws but rarely
occurring. Intelligence, not structure, assigns them the
leading place.

Lowest come the group of lemurs or " half apes," which
have their metropolis in Madagascar, but have relatives in
Africa and in the East Indies. They are largely nocturnal,
and eat fruit or insects or other small animals. They are
noticeable from the fact that the second finger is provided
with a claw.

The marmosets are small squirrel-like forms found in
South America. They are provided with claws on all digits
except the great toe, and the tail is incapable of grasping,
while the thumb is scarcely capable of being opposed to the
fingers.

The remaining American monkeys — the howlers, sapajous,
spider-monkeys, and the like — have a broad septum of the
nose, causing the nostrils to be wide apart; the thumb is
scarcely opposable, and in some is lacking; while the teeth
differ from those of the Old World monkeys, and of man, in
having pm f. Many have a prehensile tail.

The Old World monkeys have the nostrils closer together,
the thumb as well as the great toe is opposable^ and the
tail never takes the place of a fifth hand. In their teeth
they resemble man : i f , c {, pm |, m f . The baboons,
distributed across Asia and Africa, have large cheek pouches
for the storage of food, etc., and naked callous patches on

124 ELEMENTS OF COMPARATIVE ZOOLOGY.

which they sit. Some have long tails, others no tails at
all. The macaques and mangabeys are allied Asiatic forms.
In the anthropoid apes tail, cheek pouches, and callous
spots are lacking; as the name indicates, they are man-
like. There are three of these. The orang-utan (the
name is Malay for Man of the Woods) lives in Borneo and
Sumatra. The chimpanzee and the gorilla are African.

FIG. 53— Chimpanzee (Troglodytes niger) . After Brehm.

Each of these has certain points in which it is more like
man than are the others.

The highest mammal is man, who differs from the other
primates less in structure than in intelligence.

COMPARISONS Of VERTEBRATES. 125

COMPARISONS.

With five columns, one for fish and dogfish, one for frog,
one for turtle and snake, and one each for bird and rat,
answer the following questions:

(1) Is the body bilaterally symmetrical ?

(2) Are paired appendages present ?

(3) How many nostrils ?

(4) How many eyes ?

(5) How many ears ?

(6) Are the skeletal parts external or internal ?

(7) Is the vent dorsal or ventral ?

(8) Is there a skull ?

(9) In what plane do the jaws move ?

(10) Is the back-bone a single structure ? If not, of what
is it composed ?

(11) Are both shoulder and pelvic girdles present ?

(12) On what side of the alimentary canal is the central
nervous system ?

(13) What parts are found in the central nervous system ?

(14) To what organs do the first pair of nerves go ?

(15) To what organs do the second pair of nerves go ?

(16) How many and what parts do you find in the brain ?

(17) Are there cavities inside the brain ?

(18) Is there a peritoneal cavity ?

(19) In what way is the alimentary canal supported ?

(20) Do you find in each form liver, spleen, and pan-
creas ?

(21) In what part of the cavity do you find the kidneys ?

(22) What cavity surrounds the heart ?

(23) What chambers do you find in the heart ?

(24) Is the heart dorsal or ventral to alimentary canal ?

126 ELEMENTS Off COMPARATIVE ZOOLOGY.

(25) Is the aorta dorsal or ventral to alimentary canal ?

(26) What vessels carry blood to the head ?

(27) Are the respiratory organs connected, either directly
or indirectly with the alimentary canal ?

(28) Are any parts (if so, what) repeated one after an-
other in the body ?

(29) Draw a diagram of a transverse section through the
body in the region of the heart, showing the heart, spinal
cord, oesophagus, vertebra, aorta, and body-walls.

(30) Draw a similar section through the kidneys, show-
ing the peritoneal cavity, intestine, mesentery, spinal cord,
kidneys, aorta, vertebra, etc., and the body-walls.

VERTEBKATA.

All of the forms so far studied or described are associated
together as a group or branch — Vertebrata — the name of
which implies that they all possess a " back-bone " composed
of separate bones or vertebrae. This one character of itself
would hardly warrant this grouping, especially since some
forms have the vertebrae but feebly developed, while in other
features they are closely similar to those with a well-devel-
oped back-bone. This presence of vertebrae is closely asso-
ciated (correlated) with other features of equal or even of
more importance, and it is this totality of similarity that
justifies the group.

All vertebrates have an inner supporting skeleton, and a
few forms, like the turtles, have in addition an external
skeleton derived from the skin. The internal skeleton, for
convenience of treatment, may be divided into one portion
lying in the axis of the body, and a second portion pertain-
ing to the limbs and appendages. Besides these there is a
third part, the visceral skeleton, developed in connection
with the gills.

The axial skeleton consists of the vertebral column (back-
bone), the skull, and the ribs. In all vertebrates, at least
in the young stages, a solid rod of cartilage runs through
the body between the central nervous system and the
alimentary canal. In front it terminates near the middle
of the brain; behind it runs to the end of the body. This
rod is the notochord. In the higher vertebrates it dis-
appears long before the animal becomes adult; but in the

127

ELEMENTS off COMPARATIVE ZOOLOGY.

lower, as in the sharks, it can be recognized throughout
life. This notochord is enveloped in a membranous noto-
chordal sheath, and in this sheath are formed rings of
cartilage which give rise to the bodies (centra) of the verte-
brae. Between these rings no cartilage is formed and hence
the whole column is jointed and flexible. In the sharks
these rings and other parts of the skeleton remain carti-
laginous; in other vertebrates any or all may be con-
verted into bone. In a typical vertebra, for instance, in
the tail of a fish (p. 14), outgrowths from the centrum
occur above and below, forming two arches. The upper of

FIG. 54.— Different vertebrae and connected structures. A* in tail region
of teleost ; B, in body region of teleost ; C, in tail region of salamander ;
D, in mammal ; c, centrum ; 7i, haemal arch (rib in JB) ; w, neural arch ;
r, rib ; s, sternum ; t, transverse process.

these (neural arch) encloses the spinal cord, the lower
(haemal arch) extends around the blood-vessels of the tail.
Farther forward, in the trunk region of the bony fish, the
two halves of the haamal arch do not meet below, but form
slender threads (ribs) which support the flesh around the
viscera. In the forms above the fishes an outgrowth
(transverse process) may rise on either side of the vertebral
centrum, and the ribs, when they occur, are continuations of
these transverse processes, and have nothing to do with the

VERTEBRATA.

129

haemal arches. Hence it follows that the ribs in a fish and
those in a higher vertebrate — a bird or man, for example —
are not identical; i.e., are not homologous. The centra of
the vertebrae may be hollow at either end (amphicoelous) as
in fishes, or they may be hollow behind and rounded in
front (opisthoccelous) as in the salamanders; or again they
may be rounded in front and concave behind (proccelous)
as in many reptiles; or lastly, they may have flat surfaces,
as in most mammals.

The vertebral column is capable of division into regions.

/

FIG. 55. — Diagram of the skeleton of a mammal, showing regions of verte-
bral column, etc. d, cervical; e, thoracic; /, lumbar; gr, sacral; /j,
caudal vertebrae ; i, scapula ; /c, humerus ; Z, radius ; m, carpus ; n, ulna ;
o, metacarpus; p, pelvis; r, femur; *s. fibula : f, tibia; tt, tarsus ; v, meta-
tarsus; it?, phalanges; j/, sternum.

In the fishes there are two of these, trunk and caudal, the
former being distinguished by bearing ribs. In the Batra-
chia a cervical region is distinguished from the trunk by the
absence of transverse processes from its single vertebra,
while the caudal is separated from the trunk by a sacral
region, the vertebra of which is connected with the bones
(girdle) supporting the hind limbs. In the higher verte-

130 ELEMENTS OF COMPARATIVE ZOOLOGY.

brates the trunk vertebrae can be divided into thoracic and
lumbar regions, the former with, the latter without, ribs.
As we have just seen, there may be two kinds of ribs —
those of fishes and those of the higher verte-
brates. In reptiles, birds, and mammals the
ribs of one side fuse at their ventral ends with
their fellows of the opposite side. The fused
regions separate from the ribs and unite
together, giving rise to the breast-bone or
sternum. In some sterna the separate ele-
ments can be traced; in others the fusion is
complete. The sternum in the Batrachia
has no connection with the ribs, and may
therefore be different from the breast-bone
in Sauropsida and Mammalia.

The skull consists of two portions: the
cranium and the face. The former affords
Pro Action to the brain and support to the
mentepo™wh1ch organs °f sense; the facial portions cluster
it is composed. ar0und the mouth and nose.
In the sharks the cranium is a continuous box of carti-
lage, only perforated for the passage of nerves and blood-

FIG. 57— Skull and branchial arches of a shark. 7i, hyoid, and Tim,
hyomandibular form the suspensor of the lower jaw, m (Meckel'a
cartilage); p</, upper jaw (palato-quadrate) ; s, spiracle; I — V, gill-arches,
between which are shown the gill-clefts.

vessels. In the other vertebrates some or all of this carti-
lage becomes replaced by bone, either by direct conversion

VERTEBRATA. 131

(ossification) or by substitution. The bony cranium (unlike
the cartilaginous cranium) is not a continuous wall, but is
composed of separate bones firmly united together, the
number varying between wide limits, being most numerous
in the lower and reduced by fusion in the higher forms.

In the sharks the facial skeleton is very simple, being
represented by the upper and lower jaws, and by a few car-
tilages supporting the lips. The upper jaw is not firmly
united to the cranium, but is held in position by muscles
and ligaments, while the lower jaw is hinged to the upper,
and not to the cranium. Comparisons, which cannot be
described here, show that the upper jaw of the shark is not
the same as the upper jaw in the other vertebrates. In
them numbers of other bones are added to the skull, and

FIG. 58 —Skull of cod. (After Hertwig.) The dotted portion is the
equivalent of the upper jaw of the shark (Fig. 57).

the upper jaw of the shark is only comparable to three pairs
of bones, known to the anatomist as the palatines, ptery-
goids, and quadrates.

The visceral skeleton consists of bars of cartilage on either
side of the throat between the gill-slits, the series being
united below (Fig. 57). These gill-bars serve to keep this
region, weakened by the openings, from collapse. The most

132 ELEMENTS OF COMPARATIVE ZOOLOGY.

anterior of these gill-bars has the special name of hyoid.
There is some evidence tending to show that the lower jaw
and the palato-quadrate bar are but modified gill-bars.
With the disappearance of gills in the higher vertebrates
the branchial arches tend to disappear, and in birds and

FIG. 59.— Diagram (after Wiedersheim) showing the relation of permanent
structures (dark) to the gill-bars of the embryo (dotted). 7i, hyoid
arch ; I, cartilages of larynx ; I, 11, III, gill-bars. At the front of h and
I is shown in black the hyoid bone of the adult, with its two horns; be-
hind the ear, at the other end of the hyoid arch, is (black) a piece (styloid
process) which joins the skull.

mammals only parts of the hyoid and first gill-bar remain
in the adult, where they are largely employed as supports
for the tongue.

There are never more than two pairs of appendages in
the vertebrates. These are the fore and hind limbs. In
their skeletons these are much alike, and in each can be
recognized arches of bone (girdles) uniting the limb to the
trunk, and the skeleton of the limb proper. These girdles
are known respectively as the shoulder or pectoral and the
pelvic girdle. In the fishes the girdles are simple arches,
and the skeleton of the limbs is largely composed of fin-rays
to support the flattened swimming organ.

VERTEBRATA. 133

In those vertebrates which support the weight of the body
upon the limbs the appendicular skeleton is more compli-
cated. In its typical condition the shoulder-girdle consists
of three bones, which meet * to afford attachment for the
skeleton of the fore limb. One of these bones, the
shoulder-blade (scapula), is dorsal. It never joins the ver-
tebrae, but is united to the trunk by muscles and ligaments.

Fro. 60.— Diagram of fore and hind limbs of a terrestrial vertebrate, with
one half of their girdles, c, carpus ; cl, clavicle ; co, coracoid ; f, fibula ;
e, femur ; 7j, humerus ; il, ilium ; is, ischium ; me, metacarpus ; mt, meta-
tarsus ; p, pubis ; r, radius ; s, scapula ; t, tarsus ; u (in upper) ulna, (in
lower) tibia ; 1 — 5, digits, each composed of phalanges. "

The other two extend ventrally from the shoulder-joint and
meet the sternum. Of these the anterior is the collar-bone
(clavicle), the posterior the coracoid.

In the pelvic girdle there are likewise three bones, which
at their point of junction give rise to the hip-joint. The
dorsal bone is the ilium, which articulates with the sacral
vertebras (p. 129), while below are found the ischium and
pubis, the latter being the more anterior. Ischium. and
pubis unite with their fellows of the opposite side, thus
completing the arch.

In the pelvic girdle the parts mentioned are pretty con-
stant, but in the shoulder-girdle other bones may be added,

* The clavicle frequently does not enter into the formation of the
shoulder- joint.

134 ELEMENTS OF COMPARATIVE ZOOLOGY.

or either coracoid, or coracoid and clavicle may disappear.
In the birds the clavicles unite, forming the wish-bone
(furcula .

The bones of the fore limb (Fig. 60) are : a single bone
(humerus) in the arm; two bones (ulna and radius) side by
side, in the forearm ; a series of nine bones (carpals) in the
wrist; five longer bones (metacarpals) in the palm; and
several rows (phalanges) of five bones in the digits. In the
hind limb the conditions are closely similar : a single femur
in the thigh, tibia and fibula in the shank, nine tarsals in
the ankle, five metatarsals succeeding these, and finally the
phalanges of the toes.

These are the typical numbers, but they may be reduced
through disappearance or fusion, and this reduction usually
appears first in the toes, and may proceed so far, as in the
horse, that one toe alone remains functional.

The nervous system consists of a central and a peripheral
portion, the latter consisting of nerves going from the cen-
tral system to all parts of the body. To these should be
added the organs of general and special sense.

The central system consists. of an anterior brain, passing
behind into the spinal cord. The brain is contained in the
cranium, the spinal cord passes through the tube formed by
the neural arches of the vertebrae.

The spinal cord is somewhat cylindrical, tapering behind,
and contains in its centre a
small canal. Nerves arise from
the cord in pairs in regular se-
quence, and pass out between the
FIG. 6i.-DiagTammatic section vertebra to all parts of the body

^^g^nu^f^T^K and to the limbs- Each of th^
nerve-root ;u<, white matter. spinal nerveS has two places of

origin (roots) from the cord — one near the dorsal, the other

VERTEBRATA. 135

near the ventral surface, but after a short course these roots
unite into a common trunk. These roots differ in structure
and function. The dorsal root bears a nervous enlargement
or ganglion ; the ventral has no such structure. Experiment
shows that the dorsal root is concerned in bringing sensa-
tions to the central nervous system, and, if it be cut, the
parts to which it goes will be without feeling. The ventral
root, on the other hand, is motor; i.e., it controls the
action of muscles, etc. If this root be cut, the muscles,
glands, etc., which it supplies are paralyzed. Hence we
may speak of the dorsal roots as afferent, since they bring
sensations to the central nervous system ; while the ventral
roots are efferent, because they carry nervous impulses in
the opposite direction.

The brain must be recognized as an enlarged and special-
ized portion of the central nervous system. The canal of
the spinal cord continues into the brain, enlarging them into
four cavities or ventricles, connected by narrower portions.

FIG. 62.— Diagram of vertebrate brain, c, cerebrum; cb, cerebellum; 7i,
infundibulum ; m, medulla ; o, olfactory nerve ; ol, optic lobes ; s, spinal
cord ; 1 — 4, ventricles.

In the brain five portions may be distinguished. Beginning
in front, these are: (1) the cerebrum, composed of right
and left halves or hemispheres, and containing in their in-
teriors the first and second ventricles; (2) the smaller
'twixt-brain, with thin walls and enclosing the third ven-
tricle; (3) the thick- walled optic lobes; (4) the cerebel-
lum ; (5) the medulla oblongata, the fourth ventricle being

136 ELEMENTS OF COMPARATIVE ZOOLOGY.

contained in cerebellum and medulla. In the lower verte-
brates these five regions are nearly equal in size, but the
higher we go in the scale the larger proportionately do the
cerebrum and the cerebellum become, until in man the
cerebrum weighs about nine tenths of the whole brain.

Prom the brain are given off, typically, twelve pairs of
nerves, which are spoken of both by numbers and by their
proper names. The majority of these are unlike the spinal
nerves in that they have but a single root, and are corre-
spondingly either sensory or motor. Thus the first or olfac-
tory nerve, which goes to the nose; the second or optic
nerve, to the eye ; the eighth or auditory nerve, distributed
to the ear, — are purely sensory. On the other hand, the
third, fourth, and sixth (oculomotor, trochlearis, and
abducens) nerves go to the muscles of the eye ; the eleventh*
(accessorius) goes to the muscles of the shoulder-girdle;
and the twelfth (hypoglossal) goes to the muscles of the
tongue. These nerves are purely motor, but it must be
remembered that the twelfth in the young of a few forms
has a dorsal ganglionated root. The remaining nerves are
like the spinal nerves in so far as they have both sensory
and motor functions. The fifth or trigeminal supplies the
sense organs of the head and the principal muscles of the
jaws. The seventh (facial) goes to the superficial facial
muscles, and in the lower vertebrates supplies certain sense
organs in the skin, but in man has lost its sensory functions.
The ninth (glossopharyngeal) goes to the tongue and
pharynx; while the tenth (vagus or pneumogastric) sup-
plies the sense organs of the lateral line (p. 137) of the trunk
and sends branches to the stomach, lungs, gills, heart, etc.

Connected with the nervous system are the sense organs,

* Tbis occurs in no icbthyopsidan vertebrate.

VERTEBRATA.

13V

The skin contains small touch organs connected with
afferent nerves, and these are for the recognition of pressure
and temperature. Possibly allied to these are the organs
of the lateral line, which are found only in the aquatic
Ichthyopsida. These organs are sometimes free on the sur-
face, sometimes in pits, while not infrequently the pits are
connected by canals running beneath the surface, with
openings to the exterior here and there. This line of organs
is plainly seen on the side of the body in most fishes. On
the head, however, it frequently branches greatly and be-
comes enormously extended in this way. The occurrence of
these structures in aquatic forms only would suggest that
their function is connected with that element; but what
that function is, is not well understood.

The taste organs are within the mouth, principally on the
tongue. They are poorly developed in some vertebrates,
better in others.

The olfactory organs are always placed in front of the
mouth. They consist of a membrane folded so as to expose
a great amount of surface, and this surface is covered with
the sense structure, connected with the ends of the olfactory
nerve. In the fishes the sacs containing this membrane

Fro. 63.— Relations of the olfactory organ, A, in fishes, B, in higher
vertebrates, b, brain ; i, internal nostril ; n, external nostril. The sen-
sory surface is folded.

have only external nostrils, but in all others they are placed
at one side of a tube, which leads from the external nostril

133 ELEMENTS OF COMPARATIVE ZOOLOGY.

to the back part of the mouth. Hence a fish can perceive
odors in the water only as it swirls in and out of the nasal
sac. In the air-breathing forms, odors in the air are drawn
with the breath over the sensory surface.

The essential part of the ear consists of a thin mem-
branous sac on either side of the head. In three places this

sac is so pinched as to form
small tubes (semicircular
canals) open at either end into
the main sac. The whole is
filled with fluid in which are
numerous minute solid parti-
cles (otoliths). At one end
of each tube and at places in

FIG. 64.-Diagram of mammalian the SaC are SenSOI7 OrganS

ed with the auditory
Sound-waves entering

by

waves to the inner parts. the sensory organs and thus

to stimulate the nerve.

In the sharks this ear-sac is placed behind and medial to
the spiracle (p. 17). In the higher vertebrates the spiracle
becomes closed on the outside, but the rest of the structure
remains, and is known as the Eustachian tube, and as its
outer end comes between the ear and the external world,
one or more bones usually extend across the tube to convey
the sound-waves to the sac. In the frogs the outer end of
the Eustachian tube is closed by the large tympanic
membrane on the side of the neck.

In the higher vertebrates an external ear occurs. This
consists of a tube leading inward to the tympanic mem-
brane, and to this tube are frequently added structures to

VERTEBRATA. 139

catch and reflect the sound-waves into the tube. It should
be mentioned that the ear is more than an organ of hearing ;
it is also an organ for maintaining the balance, for if the
ear or the auditory nerve be injured the animal can no
longer maintain its equilibrium.

The eye is built on the plan of a photographic camera.
The essential parts are a lens which brings the rays of light
to a focus on the retina, and means for causing the image
on the retina to stimulate the optic nerve. To these are
added various accessory structures for protection, for regu-
lating the amount of the light, etc. In the lower forms
eyelids are absent, but higher in the scale folds of flesh are
developed which can close over the organ. Many animals
have three of these eyelids, two working vertically, the
third, the nictitating membrane, extending from the inner
angle eye' over the transparent cornea. This nictitating
membrane occurs in the eye of man as a small fold (semi-
lunar fold), which has entirely lost its primitive protective
function.

Over the whole globe of the eye is a tough layer, the
sclerotic coat, which is usually white, and which may be
cartilaginous or may even have bone deposited in it, as in
many reptiles and birds. In front this layer becomes per-
fectly transparent, and is there known as the cornea. Inside
of the sclerotic is found a densely black layer (choroid), and
still within this the transparent retina, the outer portion of
which is imbedded in the choroid. In front the choroid is
continued into the iris, a circular muscle with an aperture
the pupil, in its centre. This iris, which is colored, regu-
lates by its enlargement and contraction the amount of light
which is admitted to the visual parts of the eye. Back of
the iris and held in position by a circular muscle and liga-
ment is the transparent lens. In front of this lens is a

140 ELEMENTS OF COMPARATIVE ZOOLOGY.

watery fluid (aqueous humor), while behind it and between
it and the retina is the somewhat denser vitreous humor.

The optic nerve enters the eye from behind, passing
through sclerotic, choroid, and retina, and is then dis-
tributed over the inner surface of the latter layer.

The eyeball is moved by six muscles, which are essentially

FIG. 65.— Diagram of vertebrate eye. c, choroid ; «, iris ; Z, lens ; n, optic
nerve ; r, retina ; s, sclerotic.

alike in all vertebrates. Four of these are straight or rectus
muscles, two are oblique. These muscles are controlled by
the three eye-muscle nerves (p. 136).

The alimentary canal runs through the body from mouth
to vent. In it several parts can be distinguished.

The mouth, at or near the anterior end, is without fleshy
lips, except in the mammals. The mouth is frequently
armed with teeth, and even in those groups, like the turtles
and the birds, where they are absent the germs occur in the
young, a fact which points to the descent of these from
toothed ancestors.

The tongue is formed as a fold of the floor of the mouth,
and is usually supported by a skeleton (hyoid, p. 132) derived

VERTEBRATA.

from the first or first and second visceral arches. In some
it is without powers of motion, but frequently it is very
mobile. Usually it is attached behind, the front margin
being free, but in many batrachia it is attached in front
and folded back in the mouth.

The mouth-cavity is succeeded by the pharynx, a region
distinguished by containing the respiratory openings (inter-
nal nostrils, gill-slits, glottis, p. 93).

Behind the pharyngeal region is the digestive tract proper.
In some vertebrates it is scarcely possible to distinguish

FIG. 66.— Diagram of the digestive tract of a mammal, if), brain ; d,
diaphragm ; ft, heart ; i, intestine ; fr, kidney ; i, liver ; o, oasophagus ;
p, pancreas ; s, stomach ; sp, spleen ; v, vent.

regions in it, but in most cases several distinct portions
occur. Those usually to be recognized are the following:

The pharynx communicates with the gullet or oesopha-
gus, a muscular tube which frequently serves only to carry
food back to the stomach. On the other hand, a part of this
tube may be expanded into a glandular food-reservoir or
crop (birds).

In some fishes and batrachia the stomach is hardly differ-
entiated from the oesophagus, but in other forms it is well
developed, with muscular and glandular walls. It may
even be divided into several portions. Thus in birds (Fig.

ELEMENTS OF COMPARATIVE ZOOLOGY.

26) we frequently find two parts, one chiefly glandular
while the other (gizzard) is extremely muscular. In the
ruminants (p. 118) the specialization is carried farther, and
we find four divisions to the organ.

The intestine is the absorptive portion of the alimentary
canal. In some it is short and straight, in others long and
convoluted, there being usually a correlation between length
of intestine and the character of the food, this region being
longer in the vegetable feeders. Increased absorptive sur-
face is obtained in several ways, in addition to lengthening
of the intestine. In the lower Ichthyopsida this is accom-
plished by the development of an extensive internal fold
(spiral valve). In others there are numerous small longi-
tudinal folds, while in the highest vertebrates transverse
folds occur on which are minute finger-like outgrowths
(villi). In the lower vertebrates the hinder part of the
intestine receives the ducts of the excretory and reproduc-
tive organs, and at such times is called a cloaca. In the
mammals, the monotremes excepted, no cloaca is formed.
The vent is on the lower surface, in the median line.

There are several accessory structures connected with the
alimentary canal. Thus frequently salivary glands are
present, emptying into the mouth. Behind the stomach
the ducts of the liver and pancreas pour in their secretions,
while in many fishes well-developed pyloric caeca occur,
just behind the stomach, which have a digestive function.

The digestive organs are supported in the body-cavity by
a thin membrane (mesentery) which bears blood-vessels,
etc., and which is attached to the dorsal wall of the body-
cavity. This mesentery in reality is but the continuation
of the lining (peritonaeum) of the body-cavity.

Vertebrates respire in three ways: by gills, by lungs, and
by the skin. Gills arise first as outpushings or pouches in

VERTEBRATA.

143

the sides of the pharynx, and then these break through to
the exterior, giving rise to gill-slits or clefts, through which
water taken in at the mouth can pass out. On the sides of
these clefts the gills proper are developed. These are thin-
walled leaves or filaments with a rich blood-supply, and
through these thin walls there is an exchange of dissolved
gases (oxygen and carbon dioxide) between the water and
the blood.

In the septa between the gill-slits are the gill-bars or car-
tilages (p. 131) ; and from the septa there grow out, in the

FIG. 67.— Relations of gills, gill-openings, etc., in a shark (left) and a

teleost (right).

larval -batrachia, fleshy fringes, the external gills. In most
batrachia these external gills are later absorbed and replaced
by internal gills, which in turn may disappear upon the
assumption of an aerial respiration.

The number of these clefts varies between four and eight,
but in all the anterior cleft has largely lost its respiratory
function. In the sharks it becomes modified into the

144 ELEMENTS OF COMPARATIVE ZOOLOGY.

spiracular cleft; in the higher vertebrates it enters into the
structure of the ear, giving rise to the cavity of the drum
and to the Eustachian tube.

In the sharks each cleft opens separately to the exterior;
but in ganoids and teleosts the hyoid septum gives rise to a
fold (operculum) or " gill-cover," which grows back over
the external openings, so that there is apparently but a
single slit externally. A little con-
sideration will show that there is little
real modification. In the anurous
batrachia a similar fold is found, but
this unites again with the body-wall
behind the gills, thus enclosing the
external openings in an atrium, with
but a single opening to the exterior
(p. 50) . In the sauropsida and mam-
Fio.68.— Human embryo mals gill pouches are formed in the

(after Hertwig), with r ...

the floor of mouth and embryo, but according to recent ob-

and throat removed, ,, .. , ,, .

to show the rudimen- servers these never break through, so

tary gill-slits, g. I, «r-n

lung; n, nostril, still that no real clefts are formed. With

connected with the ,. .. , .. „ . , .,

mouth. growth all but the first pair of these

pouches disappear, the first persisting as the Eustachian
tube.

In all vertebrates above fishes, gills are supplemented
(batrachia) or replaced by lungs. These are paired sacs
richly supplied with blood-vessels, and connected with the
external world by means of a tube (windpipe or trachea)
which opens by the glottis upon the floor of the pharynx.
The trachea is usually strengthened by the development of
cartilages in its wall, some of which may become large, as
in the case of the human "Adam's apple." The lungs
themselves may be simple sacs, but usually they become
greatly folded, thus increasing the respiratory surface. In

VERTEBRATA. 145

the batrachia, which lack diaphragm and ribs, air is forced
into the lungs by swallowing; in the reptiles and birds it is
drawn in by means of the muscles (intercostals) between
the ribs; in the mammals the intercostals are reinforced by
a transverse muscle (diaphragm), Fig. 66, which crosses the
body-cavity.

In the ganoids and bony fishes exists a structure, the
swim-bladder or air-bladder, which is usually thought to
represent the lungs. In the lower teleosts (Physostomi) it
is connected with the alimentary canal by a duct opening
on the dorsal wall of the pharynx, but in others (Physo-
clisti) this duct closes long before the adult condition is
reached. In the lung-fishes, on the other hand, the struc-
ture is double and its duct ventral.

Connected with the respiratory system are two glands of
problematical function. One of these, the thyroid, is
formed from the floor of the pharynx. The other (the
thymus) arises from the gill-pouches, and in the higher
vertebrates disappears in adult life. In the calf it forms
the " neck sweetbread." Both these glands are without
ducts, and the part they play is obscure.

In the circulatory system three parts may be recognized :
(1) a central propelling organ, the heart; (2) arteries,
carrying the blood away from the heart; and (3) veins
bringing it back. Between arteries and veins are interposed
minute tubes, the capillaries.

The heart is a muscular organ, enclosed in a special sac
of the body-cavity, the pericardium. In the heart can
always be distinguished a receptive portion (auricle), which
receives the blood as it comes from the veins, and passes it
on to the true propelling organ, the ventricle. This latter
has strong muscular walls, and when it contracts, the
blood, prevented by a valve from returning to the auricle, is

146 ELEMENTS OF COMPARATIVE ZOOLOGY.

forced out through the artery (ventral aorta) connected
with the ventricle.

In all fishes there is but a single auricle and a single ven-
tricle, but when lungs appear, as in the batrachia, the
auricle becomes divided, and now one half (the right)
receives the blood from the body, while the left auricle
takes the blood returning from the lungs. These both
pour the blood into the single ventricle. In the reptiles we
find the beginning of a division of the ventricle, which
becomes complete in the crocodiles and continues in birds
and mammals. In these forms the left auricle pours its
blood into the left ventricle, while the same relations exist
between the auricle and ventricle of the right side.

In the fishes the blood leaves the ventricle by an arterial
trunk, in which, when best developed, we can distinguish a
conus with valves inside to prevent the blood flowing back
into the ventricle; or a bulbus, without valves, and in front
of these the ventral aorta. From this lateral vessels
(afferent branchial arteries) are given off, and these pass up
through the branchial septa. Consequently the number of
these arteries primarily depends upon the number of gill-
clefts. In the septa the arteries break up into capillaries
which pass through the gills, and collect in efferent bran-
chial arteries which pass above the pharynx. Here they
unite and give rise to the main trunk, the dorsal aorta,
which runs, above the alimentary canal, through the body,
giving off vessels to all parts.

From these vessels the blood passes through the capillaries
and is collected in veins which bring it back to the heart to
repeat the circuit. In this circulation the blood changes
in its character. When it enters the heart it bears nourish-
ment obtained from the alimentary canal, and waste from
all parts of the body. Its color is a dark purplish red. In

VERTEBRATA.

147

its passage through the gills it rids itself of one kind of
waste (carbon dioxide) and absorbs oxygen from the water.
This exchange is accompanied by a change of color to bright
red. The other waste is gotten rid of in the kidneys. In

FIG. 69.— Diagram of the arterial arches and their modificaitons in vari-
ous vertebrates. A, fish ; B, batrachia ; C, snake ; D, bird ; E, mammal.
a, ventral aorta ; c, internal carotid ; d, dorsal aorta ; e, external carotid ;
p, pulmonary artery ; s, subclavian. Drawn by Dr. F. D. Lambert.

the capillaries of the body it gives np its oxygen and
nourishment to the surrounding parts, and becomes loaded
anew with carbon dioxide and other waste, changing color
again to the dark red. From this account it will be seen

148 ELEMENTS OF COMPARATIVE ZOOLOGY.

that in the fish only blood charged with impurities passes
through the heart.

From the arrangement of blood-vessels found in the fishes
(sharks) all the conditions found in the higher vertebrates
may be derived, simply by enlarging some vessels and sup-
pressing others. Some of the changes involved may be
made out from the accompanying diagrams (Fig. 69) in
comparison with your dissections, the explanatory statement
being made that in embryo birds and mammals paired
branchial arteries occur, while in the adult this symmetry
is largely lost.

One point particularly to be mentioned is that with the
development of lungs, arteries going to these organs are
developed from the hinder pair of branchial arteries.

When the gills are lost and the lungs function as respi-
ratory organs, the conditions of the circulation are changed.
The blood, in leaving the heart, passes partly to the various
parts of the body, partly to the lungs. That going to the
latter organ loses its carbon dioxide, and takes up oxygen
and changes to bright red. It now returns along with
blood from other parts to the heart, which therefore now
receives both light and dark blood and forces the same out
again. But when the lungs are developed the auricle of
the heart divides, and one auricle receives the dark, the
other the light blood, both emptying their contents in turn
(in frogs and reptiles) into the single ventricle. It was
therefore formerly thought that the blood sent out through
the ventral aorta must necessarily be mixed; but this is
not the case. By means of a peculiar valve the red blood
is sent to the body, the dark blood to the lungs.

As has already been mentioned, in crocodiles, birds, and
mammals the ventricle is also divided, and now one half of

VERTEBRATA.

149

the heart contains only bright, the other only dark, blood.
The division is also carried farther, for
the last arch (going to the lungs) becomes
connected with the half of the heart
which receives the dark blood, while
the rest of the arches are similarly
related to the other half of the heart.

The blood itself should have a mo-
ment's attention. It consists of a fluid
(plasma) in which float myriads of
minute solid bodies (corpuscles). The
plasma is a pale yellow in color, the red
of the blood being due to certain of the
corpuscles, which are therefore known
as the red corpuscles. Other corpuscles
are colorless, and are called white cor-
puscles or leucocytes. The red corpuscles
carry the oxygen and carbon dioxide,

FIG. 70— Diagram of the the plasma the nourishment and the

circulation in a mam-
mal. The arrows show other waste. The plasma is further
the direction of the *

flow; the vessels carry- pecuiiar in that when withdrawn from

ing red blood are r

shown white, those the veins it soon solidifies or "clots."

carrying dark blood,

shaded, ^o, auricles; The excretory organs (kidneys or
K?rtv£ '^ Ringing nephridia) are very complicated struc-

the blood from the in- * . ' J x

testine ; v, ventricle, tures. In a few words, they may be
described as a pair of organs lying in the dorsal wall of the
body-cavity close to the median line. Each kidney is richly
supplied with blood, and it extracts from this fluid the
nitrogenous waste and pours it into an excretory or urinary
duct which empties behind, near the anus.

The reproductive system is closely related to the excretory
organs. In all except a few fishes the sexes are separate.
In the females, eggs are formed in special structures, the

150 ELEMENTS OF COMPARATIVE ZOOLOGY.

ovaries, and when ripe the eggs are passed out to the
exterior by means of a tube (oviduct) developed from the
urinary duct. This passage may be rapid, or the egg may
remain for a time in the oviduct and there undergo its
development, as is the case in certain members of all groups
of vertebrates except birds.

In the male, corresponding to the ovaries in position,
etc., are the testes, which produce the male reproductive
element, which is also carried off by a part of the primitive
excretory duct.

All vertebrates produce eggs, but these vary considerably
in size. In the mammals the diameter is about T^ of an
inch, the ostrich lays an egg about 5 inches in diameter,
while the egg of one of the extinct birds of Madagascar
was equal in size to 150 hen's eggs.

The Vertebrates are divided into Cyclostomes and
Gnathostomes.

CYCLOSTOMATA.

The Cyclostomes include a few eel-like forms, commonly
known as lampreys and hagfishes. These differ from the
other Vertebrates in many points, some of which are
mentioned here. Bone is entirely lacking, and cartilage
is feebly developed. Vertebrae are scarcely recognizable,
and there are no traces of paired fins, although dorsal and
caudal fins may occur. The mouth, as the name Cyclo-
stome implies, is circular, but is incapable of closure like
that of other vertebrates, since movable jaws are lacking.
Inside of the mouth are horny teeth (few in the hagfishes,
many in the lampreys), but these are chiefly used for
holding, not for biting or crushing. The tongue is very
large.

There is but a single nostril on top of the head, The

CYCLOSTOMES, LAMPREYS, AND HAGFISHES. 151

gills are placed not in simple slits, but in large pouches on
the sides of the neck, and these pouches may either open
separately to the exterior or by means of a tube which leads
to a single opening. The number of gill pouches ranges
between six and fourteen on either side.

The Cyclostomes are subdivided into two groups, accord-
ingly as the nostril communicates with the throat or not.
As examples of the first, the hagfishes may be cited. These
are all marine, and are capable of secreting a large amount
of mucus from their bodies, so that a few hagfish in a pail
will convert the water into a jelly-like mass. These fishes
are parasites, and work their way into various fishes, like
the cod, and when once inside they eat up all the flesh
and viscera, leaving nothing except the skin and bones.

The second group is represented by the lampreys. Some
of these are marine, others live in fresh water, while many

FIG. 71.— Lamprey (Petromyzon marinus). After Goode.

of the marine forms ascend streams in spring to lay their
eggs. By means of their circular mouths, horny teeth,
and sucking tongues, the lampreys attach themselves to
fishes, from which they suck the mucus and frequently
the blood. In some places the large sea-lampreys are
regarded as delicacies, but usually they are not esteemed
as food.

152 ELEMENTS OF COMPARATIVE ZOOLOGY.

GNATHOSTOMATA.

In the Gnathostomata jaws are always developed; the
skeleton, whether of cartilage or bone, is a true support to
the body ; usually paired limbs occur, and the nostrils are
always paired. The general account of the Vertebrata in
the preceding pages applies especially to the Gnathostomes.
This group is divided into three subbranches :

SUBBRA^CH I. — ICHTHYOPSIDA (p. 55).

SUBBRANCH II. — SAUROPSIDA (p. 85).
SUBBRANCH III.— MAMMALIA (p. 97).

CHORDATA.

There are a few characters of the Vertebrates which are
shared by other forms. These features are: (1) the posses-
sion of gill-slits ; (2) a nervous system which is entirely on
one side of the alimentary canal; and (3) a notochord which
lies between the alimentary canal and the nervous system.
The existence of this notochord has given the name Chordata
to the assemblage. There are four divisions or branches of
the Chordata, only three of which need mention here.

BRANCH I. — LEPTOCAKDII (Lancelots) .

The few species of lancelets (Ampliioxus) are all marine,
and occur in warmer seas. They have a body which is
fish-like, but they differ from all fishes in the absence of a
true heart and of a skull. The gill-slits are numerous

FIG. 72.— Diagram of Amphioxns (after Hertwig and Boveri). Above
(dotted) is the nervous system ; below it (cross-lined), the notochord ; the
mouth is surrounded by the circle of tentacles ; below the notochord is
the region of gill-slits ; the vent is near the posterior (right) end below.

(about sixty), and these empty into a gill-chamber recalling
in some features that of the tadpoles. The notochord runs
the whole length of the body, and a stomach is lacking,
the liver emptying into the intestine just behind the gills.
Limbs or paired fins are absent, but there is a median fin

153

154 ELEMENTS OF COMPARATIVE ZOOLOGY.

at the end of the body. The animals are about two or three
inches long, are almost perfectly transparent, and bury
themselves in the sand, only the mouth end, encircled by a
fringe of delicate filaments, appearing above the surface.
They are without any economic importance, but their
extremely simple structure makes them intensely interesting
to the naturalist.

BRANCH II. — TTOICATA.

The fact that these forms had any relationship to the
Vertebrates would never have been suspected had one
studied only the adults. When, however, the development
was studied, it was perceived that these forms had larvae in
which there was a notochord, gill-slits, and a nervous system
much like that of the Vertebrates ; in short, that in shape
and in structure these young Tunicates were decidedly
tadpole-like. Then these tadpoles settled down upon some
object and passed through a metamorphosis in which the
tail was lost, the nervous system was contracted into a mass,
and the body became more or less saccular and covered
with an external envelope or " tunic," which gives the
name to the group.

Of these Tunicates there are many varieties, but the
essential features of the adult can be made out from the
generalized figure given. The body is globular, and shows
on the outside two openings. One of these is the mouth,
which communicates with a gill-region perforated by
numerous gill-slits. At the bottom of this pharyngeal
region is the oesophagus, which leads to stomach and intes-
tine, the latter twisting so as to terminate at the bottom of
a cloacal chamber, which opens to the exterior by the other
aperture mentioned. The water, which passes through the

CHORD AT A, 155

gill-slits, is collected, and passes into the same cloacal
chamber. The nervous system consists of a centre or
ganglion between the two openings, from which nerves
radiate to the various parts. There is a heart at the

FIG. 73.— Diagram of a Tunicate. Z), branchial chamber, perforated by
gill-clefts, and connecting at the bottom with the oesophagus which leads
to the globular stomach, and thence by the intestine to the vent, v ; h,
heart ; n, nervous system ; m, mouth.

opposite side of the body, and a peculiarity of this organ
is that it regularly changes in its action, the blood flowing
in a direction opposite to that which it followed a moment
before.

The species of Tunicates are numerous, and show great
variety of form. A characteristic of many is the power to
reproduce by budding, and as a result there are formed

156 ELEMENTS OF COMPARATIVE ZOOLOGY.

large colonies, the members of which are more or less inti-
mately connected with each other. In some cases the ani-
mals resulting from budding produce eggs, and these eggs
grow into forms unlike their parents but like those from
which the parents were budded. In other words, the child
does not resemble the parents, but the grandparents.
This peculiarity is called "alternation of generations."

The tunicates are all marine, and they abound in the
seas of all parts of the world. Some of them are known
from their shapes and color as " sea-peaches," others as
"sea-pears," while a common name for all is "sea-squirts,"
due to the fact that they squirt water from the openings
upon being disturbed.

BRANCH III. — VERTEBRATA (p. 127).

CEAYFISH OE LOBSTEE: LABOEATOEY WOEK.

EXTEK^AL.

Each pupil will require at least two specimens. One
of these should be opened along the back, as described
below, and placed for some days in alcohol in order that
the internal parts may become hardened, thus better fit-
ting them for dissection.

Can you distinguish two regions in the body ? How
many joints (segments or somites) can you distinguish in
the posterior region or abdomen ? Can you see segments
in the anterior region (cephalothorax) ?

Examine a segment (the third) of the abdomen. How is
it joined to the segments in front and behind ? Are the
parts between the segments as hard as the walls of the seg-
ment ? What is gained by this arrangement ? How does
the wall of the segment differ from a ring ? To what part
of the ring are the appendages (swimmerets) attached ?
How many of these are there on the segment ? In a swim-
meret make out the basal joint (basiopodite), having two
leaf -like branches, one towards the median line of the body
(endopodite), the other outside of this (exopodite). Draw
the segment and appendages from in front.

Compare the segments behind the third with that one.
Do all have the two-branched appendages ? How are the
swimmerets of the sixth segment modified ? How does the
last segment (telson) differ from the others ? Where is the
vent? Compare the appendages of the first and second

157

158 ELEMENTS OF COMPARATIVE ZOOLOGY.

abdominal somites with those of the third. In the male
they are peculiarly modified. What numerical relations do
you find between somites and appendages in the abdomen ?
(Savigny's law).

Examine the lower surface of the cephalothorax, and
see if you can find traces of segments, especially in the
region near the abdomen. How many appendages on one
of these somites ? How many pairs of large legs, includ-
ing the " pincers," do you find ? In the hinder pair of legs
how many joints do you find ? Can you distinguish exop-
odite and endopodite ? Compare this leg, joint by joint,
with the big claw. What change would make it into a
pinching-organ ? How many of these legs are furnished
with pincers ? Look on the inside of the basal joints of
the legs for openings (outlets of the reproductive organs).
If they occur on the middle pair the specimen is a female;
if on the last pair it is a male. What is the sex of your
specimen ?

Study the appendages (mouth-parts) in front of the big
claws. In order to do this properly it will be necessary to
remove those of one side one by one, by grasping the base
of the appendage with the forceps and pulling it out.
Be careful to get all of each appendage, and nothing
else. The three hindermost (or outer) mouth-parts are the
jaw-feet (maxillipeds). Compare the hinder pair with the
third swimmeret. Do you find basiopodite, exopodite, and
endopodite? Compare it with one of the walking-legs.
Which part, exopodite or endopodite, is lacking in the
latter ? Draw each of the maxillipeds.

In front of the maxillipeds come two pairs of accessory
jaws (maxillae). Eemove them carefully, and draw.
Look on the hinder maxilla for a large expansion, the gill-
bailer. Kemoving these parts exposes the mouth, on

DISSECTION OF CRAYFISH. 159

either side of which is a strong jaw (mandible). How do
these jaws move in comparison with those of man ? Take
one out, and see of how many joints it is composed.

The cephalothorax is covered above by a large continu-
ous plate, the carapax.* Does this show signs of seg-
ments. With the forceps lift the hinder corner of the
carapax on the side where the mouth-parts still remain,
and see where it joins the body. Then with the scissors
cut away the free portion, thus laying open the gill-
chamber, and exposing the body- wall and the numerous
gills or branchiae. Are any of these attached to the legs or
to the body-wall ? Move the maxillae, and see the opera-
tion of the gill-bailer. Can water obtain free access to the
gills ?

In front of the mouth occur the "feelers" or antennae.
Could these be compared to the legs ? Can you find exop-
odite or endopodite in them ? Examine the basal joint
of the larger or posterior one (the antenna proper), and
find an opening, the outlet of the green gland (see below).
Is it in any way comparable in position to the reproductive
opening ? In the smaller feelers (antennulae) look for the
ear-sac on the upper surface of the basal joint. (It is
covered with a thin membrane, around which hairs are
arranged.) Above the antennulae are the eyes. Are they
movable ? Examine the black portion (cornea), and see
the small portions (facets) of which it is composed.

Make a tabular arrangement of the appendages of the
body,f and ascertain by Savigny's law (p. 158) how many
segments there are in the body of the crayfish. Compare
the segments, and see how their diversity is brought about

* Often written carapace. The spelling here adopted is preferable.
f For reasons which cannot be discussed here, the eyes are not re-
garded as appendages comparable to the others.

160 ELEMENTS OF COMPARATIVE ZOOLOGY.

by under- development (atrophy) of one part and over-
development (hypertrophy) of another. (The carapax is
really but the dorsal portions of the antennal and mandib-
ular somites, the line crossing its middle being the line of
union of these two.)

Make a side view of the crayfish, twice the natural size,
naming the parts.

INTERNAL STRUCTURE.

The dissection should be made under water, the speci-
cimen, back upwards, being held in position by being
pinned to the wax bottom of the dissecting-pan, the pins
passing through the telson and large claws. Open the
crayfish along the back by cutting away the carapax with
the scissors, taking care not to injure the underlying parts.
Continue the cuts backward, removing the upper surface of
the abdomen.

Just beneath the carapax, behind the impressed line
crossing it, is the oblong whitish heart. How many open-
ings through its walls can you find ? How many tubes
(arteries) leading from it ? With the forceps gently tip
the heart to the side. Can you find more openings or
more arteries ? Is there a chamber (pericardium) around
the heart ? Trace the arteries as far as you can without
injuring other parts.

Beneath the heart, and projecting from beneath it, are
the paired reproductive organs. Do those of the two sides
connect ? Can you find the ducts leading down from
them ? Where do they end ? Still farther in front is the
large thin-walled stomach, and on either side of this, and
reaching back to the heart, is the liver, reddish in the
crayfish, green in the lobster. Tip the stomach back-

DISSECTION OF CRAYFISH. 161

wards and see the oesophagus or tube leading to it from
the mouth. Tip it forwards and find the intestine. Can
you find the ducts leading from the liver to the intestine ?

Draw the viscera, etc., as far as made out, adding the
intestine later.

Cut away heart, liver, reproductive organs, and trace
the intestine to the vent. Is it the same size throughout ?

Take out the stomach, being very careful not to injure
other structures when cutting the oasophagus. Open the
stomach and find the teeth; how many ? Try to see how
the teeth grind the food.

In the front part of the body, close to the antennae, find
the green glands (paired). Their openings have already
been found. They are excretory in function (kidneys).

Cut away the (white) muscles in the abdomen, being
careful as you approach the floor, and expose the hinder
part of the central nervous system (ventral cord). How
are the enlargements (ganglia) arranged with reference to
the segments of the abdomen ? Are the nerves given off
from the ganglia, or from the cord (commissure) connecting
them ? Trace the ventral cord forward into the cephalo-
thorax, carefully breaking away the hard parts which cover
it, and follow it forward to the brain, in front of the
mouth. How many ganglia do you find in the cephalo-
thorax ? Do any show signs of being double ? Is the
commissural cord single or double in this region ? Is there
a ring of the nervous system around the oesophagus ? Can
any of the nervous system be said to be above, or any
below, the alimentary canal ? From what part do the
nerves to the antennae and eyes arise ?

Draw the nervous system from above.

SOW-BUG: LABORATORY WORK.

Can you make out three regions in the body: head,
thorax, and abdomen ? Where would you draw the lines
between the regions ?

Examine a thoracic segment. Does it resemble in any
way an abdominal segment of a crayfish ? Study the legs.
Can you find exopodite and endopodite? How many legs
do you find ? Are any of them terminated with pincers ?
Look beneath the thorax for thin overlapping membranes
attached to the bases of the legs. They will be found only
in females. Between them and the lower surface of the
body is a chamber or brood-pouch to contain the eggs or
young. Do you find anything in this cavity ?

How many segments do you find in the abdomen ?
Notice the last pair of abdominal appendages extending
behind the body. Turn the animal on its back, and with
the needle pull apart the flattened plates on the lower sur-
face of the abdomen. These are the gills. Do they pre-
sent any of the characteristics of appendages ? How many
of these gills do you find ? Examine them all and see
which ones bear white spots (air-chambers). Draw a pair
of these gills.

Examine the head. Where are the eyes ? Are they
on stalks ? What are the peculiarities of the antennae ?
Can you, with the lens, find another pair of minute an-
tennae ? The mouth-parts form a short, thick projection

162

COMPARISON OF SOW-BUG AND CRAYFISH. 163

beneath the head. Pick this apart with the needle. How
many pairs * of mouth- parts can you find ? Counting all
the appendages of the head, how many segments should
there be in this region ?

COMPARISONS.

With one column for crayfish, the other for sow-bug,
give answers to these questions :

(1) Are head and thorax united ?

(2) Are the eyes on movable stalks ?

(3) How many pairs of walking-feet, counting the
pincers as such ?

(4) Where are the gills ?

(5) Are both exopodites and endopodites present ?

* The two of the hinder pair are united, but should be counted as
a pair.

DECAPODA.

Those forms which are commonly known as crayfish,
shrimps, lobsters, prawns, and crabs are collectively known
as Decapods, from the fact that, including the large claws,
they have ten walking-feet. Besides this we find that they
all have eyes on movable stalks, the anterior part of the
body (thirteen segments) is covered by a fold of the integu-
ment known as the carapax, and the gills are (usually)
borne packed away in a gill-chamber above the walking-
legs.

This group of Decapoda is subdivided into three divisions,
or " suborders," according, among other things, to the
characters presented by the abdomen. In the MAGRURA
it is, as shown in the crayfish, very large, and is carried
well extended; in the BRACHYURA it is much smaller,
not nearly so large as the cephalothorax, and is folded up
beneath the latter region so that it is not visible from above.
In the third group, the ANOMURA, the abdomen is inter-
mediate between the conditions found in the other groups,
and frequently it is much softer than the other regions.

Of the Macrura the most important are the lobsters,
which are large marine forms differing in few points, except
size, from the fresh-water crayfish. These play a great
part in the food-supply of northern Europe and the east-
ern United States. They are mostly captured by sinking
large wooden traps (lobster-pots) baited with refuse fish,
and at intervals hauling up the pots. The number thus

164

DECAPOD CRUSTACEA.

165

taken upon tne shores of New England and Canada amounts
to oetween twenty and thirty
million annually. Crayfish
are used largely as food in
Europe, and are bred in ponds
for the market, but in Amer-
ica they are largely neglected.
Shrimps and prawns are
largely salt-water forms, but
some of the prawns occur in
fresh water in the warmer
parts of the world. The line
between the two is not easily
drawn except by saying that
the body of the shrimp
is flattened (depressed) from
above downwards, while that
of the prawn is compressed
(flattened from side to side).
In America, " shrimp salad "
is almost universally made
from prawns.

Of the Anomura, the most
interesting are the so-called
hermit-crabs. These are somewhat lobster-like, but the
abdomen is but slightly hardened, and so, to protect this
vulnerable part of the body, the crab inserts it in a deserted
snail-shell, and this "house" he carries about with him
wherever he goes, retreating into it and closing the opening
at the approach of danger with his solid pincing-claws.
With increase in size the crab must move into a larger
shell. In other Anomura the back is. soft, and these

FIG. 74.— Common shrimp (Crangon
vulgaris). From Emerton.

166 ELEMENTS OF COMPARATIVE ZOOLOGY.

" false hermits " carry half a clam-shell about with them
to cover their weak point.

FIG. 75.— Hermit-crab (Eupagurus berrihardw) in a snail-shell. From

Emerton.

Only a few of the true crabs or Brachyura live in fresh
water. In the tropical and semi-tropical regions are those

FIG. 76. — Shore-crab (Cancer irroratus).

which live on the land ; but the great majority — a thousand
different kinds — live in the sea. The larger species have

DECAPOD CRUSTACEA. 167

some economic value as food, but all of them are important
as scavengers. In America " soft-shelled crabs" are
prominent in our markets at the proper season of the year.
During the rest of the time this crab, known as the "blue
crab," has as hard a shell as any crab, but when the proper
moment comes the shell splits across the hinder margin,
and out from this opening comes the body covered only
with the thinnest skin, and at this time alone is it a " soft
shell." All other crabs molt or shed their skin in the same
way, the new skin rapidly growing hard again, but the
blue crab is the only one taken in sufficient abundance
at this time to be of economic importance.

TETRADECAPODA.

Contrasted to the Decapods are the fourteen-footed or
Tetradecapodous forms, of which the sow-bug is one type.
In these we can distinguish clearly head, thorax, and
abdomen, the joints of the thorax being freely movable on
each other. The eyes are not placed upon movable stalks,
but are scarcely elevated above the general surface of the
head. Most of these forms are marine; a few live in fresh
water, and still fewer, like the sow-bugs and pill-bugs, upon
the land. All are small, those which reach two inches in
length being the veritable giants among the group.

There are two subdivisions of Tetradecapods : Isopoda
and Amphipoda.

In the Isopoda the body is depressed, as in the sow-bug,
and the gills are borne under the abdomen. Most of the
Isopoda feed upon decaying matter, but some have become
parasites upon other animals, and have consequently so
changed their appearance that one knowing only the adult
would never regard them as Isopods at all. But the young
settle the question, since before they begin their parasitic
life they are regular Isopods.

In the Amphipods the body is compressed from side to
side, and the gills are borne on the thoracic region between
the legs. These forms are familiar to all visitors to the
shore under the common name of " beach-fleas/' a name
which those forms living under dried seaweed, etc., have
won for themselves through their leaping powers. Others

168

TETRADECAPOD CRUSTACEA. 169

live in the ocean itself. None of them have any economic
importance aside from their acting as scavengers and
serving as i'ood for fishes.

FIG. 77.— Beach-flea (Gammarus ornatus). From Smith.

GRASSHOPPER: LABORATORY WORK.

Can you distinguish three regions — head, thorax, and
abdomen — in the body ? Where would you draw the lines
between these regions ? and why at these points ?

Notice that the abdomen is made up of a series of rings
(segments or somites) essentially like each other. Exam-
ine a ring at about the middle of the abdomen, and see that
it is made up of dorsal and ventral hardened halves, united
by a more flexible membranous portion. Look at the side
of the somite and find a small opening (spiracle). How
many somites bear similar spiracles ? Has any somite more
than a pair of spiracles ? Could you speak of these spiracles
as being segmentally arranged ?

Examine the base of the abdomen and see that its first
segment is incomplete. Look at the lower surface and see
if you can find the lower half of this ring. On the sides of
this first ring notice a large oval thin spot (tympanic mem-
brane), the so-called ear. Can you find a spiracle near
the ear ?

The tip of the abdomen varies in shape in the two sexes.
In the female it is provided with two pairs of pointed out-
growths (ovipositor). The male lacks these, and the tip is
rounded and frequently upturned. Study this region care-
fully in each sex, making out the following points :

In the male notice that the ventral halves of the terminal
segments are much larger than the dorsal portions. (This
overgrowth is called hypertrophy.) Counting from the
base, how many rings can you find in the whole abdomen ?

170

DISSECTION OF GRASSHOPPER.

Are any except the first incomplete ? Lift the parts on
the dorsal side of the tip of the abdomen and find the vent.
On the dorsal side between the vent and the tenth somite
is a broad plate (supra-anal plate), and on either side of
this is a small outgrowth from the tenth segment (anal
cercus). Are these anal cerci movable ? Could they be
regarded as jointed appendages ? To which somite do they
belong ?

In the female study the terminal somites in the same way
as in the male. Do you find the same dorsal and ventral
halves ? Are any of them hypertrophied ? Do you find
vent and anal cerci ? Examine the ovipositor.* Are its
parts movable ? See if they are attached to the eighth and
ninth segments.

Draw side and dorsal views of male and female abdo-
mens, making each sketch at least five inches long. Insert
all features made out, lettering everything.

In the thorax recognize three segments: prothorax,
mesothorax, metathorax, the first overlapping the others
something like a cape. How many legs are attached to the
prothorax ? Look in the membrane joining the pro- to the
mesothorax for a spiracle. Study a prothoracic leg. It is
made up of a series of joints. Joining the leg to the body
are two short joints (coxa and trochanter), then comes a
long femur, next an almost equally long tibia, and lastly,
a several-jointed foot or tarsus. Notice how freely the
head moves upon the prothorax by means of a flexible

* As its name implies, the ovipositor is of use in laying the eggs.
By means of it the grasshopper bores a hole in the earth, and then the
packets of eggs, passing down through the tube formed by the four
members of the ovipositor, are deposited in the ground. Other allied
species use the ovipositor for placing the eggs in leaf -buds or in the
stems of certain plants.

172 ELEMENTS OP COMPARATIVE ZOOLOGY.

" neck." Separate the prothorax from the head and from
the mesothorax, and draw it from the side.

Study meso- and metathorax together. Notice that on
the back the line between these somites is very distinct;
trace this line upon the side, and thence to the ventral
surface. Do you notice any other lines which seem to
divide meso- and metathorax ? Can you trace them on all
surfaces ? Do you find any spiracles in this region ? How
are the legs related to the somites ? Can you recognize in
each the same parts found in the prothoracic legs ? Where
are the wings ? Are they alike ? What is the prevailing
direction of the ribs or " veins " in them ? Can either pair
be folded like a fan ? Is there anything to protect the
hinder pair when at rest ?

Draw a side view of meso- and metathorax, inserting ex-
panded wings, legs, etc.

Eemembering what was found out about the crayfish
and sow-bug, and considering the thorax and tip of the
abdomen of the grasshopper, do you find anywhere a seg-
ment bearing more than a pair of jointed appendages ? *
So far as your present knowledge goes, would you be justi-
fied in saying that a pair of jointed appendages indicates
a somite of the body ? (Savigny's law.)

Notice that the head is made up of a large solid piece
(epicranium), to which are attached various movable por-
tions. On either side of the head is a large compound eye.
With a sharp knife slice off one of these eyes and examine it
under a low power of the microscope. Why is it called
compound ? What is the shape of the parts (facets) of
which it is composed ?

Look on the front of the head for the smaller bead-like

* For reasons which cannot be discussed here, the wings of grass-
hoppers, etc., are not considered as jointed appendages.

DISSECTION Of GRASSHOPPER.

simple eyes or ocelli. How many of these do you find, and
how are they arranged ?

On the front of the head, below the eyes, is a broad fold,
the clypeus, to which is attached a movable upper lip
(labrum) covering the mouth in front. Near the eyes arise
two long, slender feelers or antennae. Could they be re-
garded as jointed appendages ?

On the lower side of the head is the mouth, surrounded
by a series of appendages or mouth-parts. Beginning be-
hind, remove these one after another with forceps and
needle. The most posterior is the lower lip or labium.
It is in reality double, and consists of the united basal
joints and, arising from these on either side, a several-jointed
palpus. Draw the labium X 10, and then take off and draw
the pair of appendages, the maxillae, next in front. Notice
that in these the basal joints are enlarged, one forming a
sharp cutting-organ, the other a more fleshy portion to hold
the food in position. The terminal parts form a palpus,
somewhat similar to the labial palpus. Still further in
front come the jaws or mandibles. Move these with the
forceps. Do they work in the same way that your own
jaws do ? Draw them, and then draw front and side views
of the head, labelling all the parts.

Have you found any traces of segments in the head ?
How many pairs of jointed appendages have you found ?
According to Savigny's law, how many segments* must
there be ?

INTERNAL STRUG TUBE.

The internal structure of the grasshopper in its larger
features is readily made out. Select a large female for the

* Study of the embryos of some insects makes it probable that there
is one more segment in the head than is shown by Savigny's law.

174 ELEMENTS OF COMPARATIVE ZOOLOGY.

purpose of dissection; pin it out, back uppermost, in the
dissecting-pan, in water just deep enough to cover it, and
with fine scissors cut away the dorsal wall of the abdomen,
taking great pains to remove nothing but the hard parts.
In spite of all care the beginner will probably remove the
heart — a delicate tube lying along the middle of the back —
with the dorsal wall. Continue the cuts forward, removing
the dorsal wall of the thorax. Notice the large muscles which
move the wings. If the specimen has been freshly killed,
the most striking feature will be a series of silvery-appear-
ing air-tubes, tracheae, which connect with the spiracles
and ramify all parts of the body. In alcoholic "hoppers"
these are distinguishable only with difficulty. Between the
body-wall and the viscera will be found the light-colored
fat-body.

In the anterior part of the abdomen, on either side, is
a cluster of long oval yellow eggs, and from each mass of
eggs a delicate tube (oviduct) may be traced backwards to
the region of the ovipositor. Separate the masses of eggs
and find, between and below them, the dark-colored ali-
mentary canal. Follow this forward and back and make
out in it the following parts: In the hinder half of the
abdomen the intestine, which in front passes into the much
larger stomach. At the junction of the stomach and intes-
tine are a number of fine tubes (Malpighian-tubes) which
are excretory in function. At the anterior end of the
stomach are a number of larger double-cone shaped tubes,
the gastric caeca, and in front of these is the large brown
crop. The crop is connected with the mouth by a narrow
tube, the gullet or oesophagus.

Remove the alimentary canal by cutting through oesoph-
agus (close to the crop) and intestine, and look upon the
floor of the abdomen for the nervous system. Can you find

DISSECTION OF GRASSHOPPER. 175

enlargements (ganglia) in this ? How are they arranged
with regard to the somites ? Follow the nervous system for-
ward, if possible, into the head. Can you find cords pass-
ing around the oesophagus as in the crayfish ? Is there a
brain above the gullet ? Does the alimentary canal pass
through the nervous system ?

Draw a diagram of a section passing through the thorax,
showing the body-wall, wings, legs, spiracles, egg-masses,
nervous cord, alimentary canal, and heart-in their relative
positions.

THE CRICKET : LABORATORY WORK.

Do you find the same regions as in the grasshopper ?
Are there the same number of segments in the abdomen ?
and in the thorax ? Are the wings and the feet the same
in number in the two forms ? In the place of the cerci
what do you find ? Could you call these jointed appen-
dages ? How many parts do you find in the ovipositor of
the female ? What changes in the grasshopper ovipositor
would be necessary to make it like that of the cricket ?
Can you split any of the parts of the ovipositor of the
cricket ? Can you find the ear ?

In the head are there the same eyes, antennae, and mouth-
parts ? Do the mandibles work in the same way ? Look
on the second long joint (tibia) of the foreleg for the ear.

176

« JUNE-BUG " (BEETLE) : LABORATORY WORK.

How does the size of the head compare with that of the
grasshopper ? Can you find both ocelli and compound
eyes ? Notice the antennse on the front of the head.
Draw one. What changes would you need to make in the
antenna of a grasshopper to make it like that of the June-
bug? Can you find labrum, mandibles, maxilla, and
labium as in the grasshopper ?

How many pairs of walking-legs do you find ? Do you
find segments to correspond ? What name must be given
to the large segment just back of the head ? Examine a
leg : Do you find in it the same segments that occur in the
leg of the grasshopper ?

Lift one of the hard outer wings (elytra). Do you find
veins, like those of the grasshopper, in the elytron ? Is
there a second pair of wings ? Are they as long as the
elytra ? How are they folded ?

Study the abdomen. Can you find the membranous
portion uniting dorsal and ventral halves of the somites ?
Are spiracles present ? Can you find any * ( ears " ? How
many segments can you count in the abdomen ? Do you
find anal cerci, or ovipositor? Separate the flaps at the
hinder end of the abdomen. Can you find any additional
segments ? Draw a beetle from above with elytra and
wings extended,

177

DRAGON-FLY: LABORATORY WORK.

Which pair of wings are the larger? What is the
genera! arrangement of the veins in the wings ? Is the
head freely movable ? What is the size of the compound
eyes ? How many simple eyes do you find ? How would
you describe the antennae ?

Are the mouth-parts fitted for biting ? Do they move
like those of a grasshopper? Do you find upper lip
(labrum) ? maxillae ? labium ? What is the character of
the mandibles ? Are they toothed ? Have any of the
mouth-parts palpi ?

Do you find all three of the thoracic segments? Are
those present of equal size? Are they firmly united to
each other ? What is the relative size of the legs ? How
many joints in the foot ?

How many segments do you find in the abdomen ? Are
any of them partially divided ? On what ones do you find
spiracles ? Are there appendages on any of the abdominal
segments ?

178

BEE OR WASP: LABORATORY WORK.

What peculiarities do you find in the antennal joints ?
Are both compound eyes and ocelli present? Are the
mandibles, like those of the grasshopper, fitted for biting ?
How do the other mouth-parts compare in shape with
those of the grasshopper ? Do you find a " tongue " ?

How many thoracic segments ? Are all freely movable ?
Which is the smallest ? Which bear wings ? Which pair
of wings is the largest ? Are the veins of the wings many
or few ? Are the wings transparent ?

Does the abdomen join the thorax by its whole width,
as in the grasshopper ? or is there a slender stalk joining
the two ? How many abdominal segments do you find ?
Squeeze the abdomen and look for the sting. Does it
compare in any way with the ovipositor of other insects ?
Where was it before pressure was applied ?

COMPARISONS.

Rule a sheet of paper with columns for Grasshopper,
Beetle, Dragon-fly, and Wasp, and write the answers in
each to the following questions :

(1) Are ocelli present ?

(2) Are the antennal joints equal in size ?

(3) Are the maxillae and labium short and stout, or
long and slender ?

(4) Are any of the thoracic rings free ?

179

180 ELEMENTS OF COMPARATIVE ZOOLOGY.

(5) Which thoracic ring is the largest ?

(6) Which pair of wings is the larger ?

(7) Describe the general structure of the fore wings.

(8) How many segments in the abdomen ?

(9) Are any appendages besides those of the ovipositor
present on the abdomen ?

(10) With which column should the cricket be placed ?

ORTHOPTERA.

The name Orthoptera, which is given to the group
containing the grasshoppers, crickets, locusts, cockroaches,
etc., means straight-winged, and alludes to the general
course of the veins of the wings of most forms. This is,
however, not a feature of great importance, for indeed we
find species which are absolutely lacking in wings, but
which are, in other respects, so closely related to the
grasshoppers that they too must be included in the Orthop-
tera. When we take all of these Orthopterous forms we
see that they agree in a number of points, some of which
may be mentioned. The jaws are strong and fitted for
biting hard substances; the antennae are usually long and
thread-like; ocelli are always present; the prothorax moves
freely on the meso thorax; the abdomen is ten-jointed, and
it usually bears on its tenth somite movable cerci; the
ovipositor is large and cannot be withdrawn into the abdo-
men; the anterior wings serve as covers for the second
pair, and these last are folded longitudinally, when at rest,
like a fan.

Besides these points, which should have been made out
by the student, there is another feature not readily discovered
in the classroom. The young Orthopteran hatches from
the egg with all the legs and segments of the adult, which
it resembles much in general appearance, except in the
following particulars : it is smaller in size, with a dispro-
portionately large head, and it lacks the wings characteristic
of the full-grown form. It is most voracious, and with

1ft

182 ELEMENTS OF COMPARATIVE ZOOLOGY.

much eating increases rapidly in size. But since it is
enclosed in a hard outer wall, incapable of growth, it has
frequently to cast off this non-elastic "skin" and to grow
a new one, larger than the old. This molting is accom-
plished by a splitting of the old skin down the back, and
from this hole the animal draws itself, and now, its skin
being soft, it can readily increase in size. Gradually, how-
ever, the skin becomes thicker and harder, and the process
of molting must be repeated. With each of these molts
the animal grows more like the adult, the wings appearing

FIG. 78.— Young grasshopper with the wings just beginning to appear.
After Emerton.

first as small pads upon the back, and with later molts
attaining the final size. It is an easy matter to follow
these changes by catching the young hoppers in the spring,
and keeping them in a breeding-cage, feeding them fre-
quently with fresh grass and leaves. The student must
keep this history in mind when studying the peculiarities
of the beetles.

With few exceptions the Orthoptera are injurious to
human interests, since they are vegetable-feeders, and, as
they often occur in immense numbers, they can destroy all
crops throughout large districts.

Possibly the most disagreeable members of the group are
the cockroaches, flattened forms,, many of them wingless,

ORTHOPTERA.

183

which are familiar from the persistence with which they
haunt our dwellings, etc., after they have once been intro-
duced. Our familiar " Croton bug" is an immigrant from
Europe, but we have also our native species. Insect-
powder and eternal vigilance are
the only means known to rid a \.
building of these pests. \

Strangest of our Orthoptera are
the " walking-sticks"; long, wing-
less animals which feed upon the
oak and which, as they stand mo-
tionless upon a twig, can scarcely
be distinguished from the twigs
themselves. The species figured is
foreign.

Grasshoppers and locusts are
much alike, and are usually con-
fused by most people. Both are
leaping forms, but the locusts have
short antennae and short oviposi-
tors, while the grasshoppers have
these parts long. The katydid is
a grasshopper, while the "grass-
hopper" which in 1873-76 did
such damage in our Western States
is a locust. Closely allied are the
crickets, whose ceaseless chirp is so Fl«
monotonous upon summer nights.
These make their song by rubbing their wing-covers
together, and it is interesting that only the male can make
the noise. The "ear" of the cricket is not upon the
abdomen, but upon the fore legs. It is not certain that
any of these structures are really for hearing.

79. — Walking - stick
(Acanihoderus). From Hert-

COLEOPTERA (BEETLES).

The beetles are all grouped under a common head of
Coleoptera, the name of which means sheath-wings. Of
beetles there are known over a hundred thousand different
kinds, but all these agree in the following points: The
mouth-parts are fitted for biting; ocelli rarely occur; the
pro thorax is large; the anterior wings* are converted into
thick, horny wing-covers or elytra, beneath which are
folded the much larger hinder wings.

From the egg of the beetle there hatches out a somewhat
worm-like form popularly known as a "grub." This
larva, as it is called, bears but the slightest resemblance to
its parents. It eats and grows, without essentially altering
its appearance until at last it undergoes a molt which re-
sults in a sudden change in its appearance. It is no longer
worm-like, but looks more like the adult beetle. This
stage, which is called the pupa, does not eat, but lies quiet
in some cavity ; after a longer or shorter period of rest it
molts again and emerges the perfect beetle, after which,
no matter how long it may live, it undergoes no further
changes, nor does it increase at all in size. Forms which,
like the beetles, pass through these abrupt changes are
said to undergo a complete metamorphosis.

The beetles are divided into two great groups. In the
one (Rhynchophora) that part of the head which bears the

* The elytra of beetles are apparently not the same organs as the
anterior wings of grasshoppers or butterflies, but the distinction be-
tween the two cannot be made clear here,

134

COLEOPTERA. 185

mouth is prolonged into a snout; in the other there is no
such prolongation. These are called the normal Coleoptera.

Of the normal Coleoptera some are beneficial to man,
since they feed upon other insects. Here may be enumer-
ated the brilliant tiger-beetles and the caterpillar-hunters,
the habits of which have given them their common names.
They are all extremely active. The water-beetles should
be placed in the same category, for they and their larvae
feed upon the insects of our streams and ponds, and do not
a little towards keeping the mosquitoes within bounds.

Another large group of beetles have the antennae ending
in a club or knob. Some of these, like the carrion-beetles,
are of value, since they lay their eggs in decaying flesh,
where the larvae live and flourish, converting what other-
wise would be a nuisance into another crop of beetles.
Others, like the "ladybugs," are predaceous, feeding upon
the smaller insects; but still others are unmitigated nui-
sances, since they have a taste for dried animal matter.
Among these are the bacon-beetle and the far better known
" buffalo-bug," which plays havoc with our silks and wool-
ens, our carpets, and the specimens in our museums. In
this same group belong the rove-beetles, forms in which the
wing-covers are very short, not covering half of the long
abdomen. Disturb one and notice the threatening way it
moves its abdomen about, as if to sting. It is, however,
perfectly harmless.

The spring-beetles and the fireflies agree in having the
antennae toothed something like a saw. The spring-beetles
receive their common name from the fact that when laid
upon their backs they will suddenly throw the body into
the air. When opportunity offers, study the actions of one
of these and see how the spring is arranged. Some of
these spring-beetles are serious pests, for their larvae are the

186 ELEMENTS OF COMPARATIVE ZOOLOGY.

well-known wireworms. The fireflies are interesting from
their phosphorescent powers. Underneath the abdomen
are the light-giving spots. Much attention has been given
to this light-producing apparatus in the hopes of obtaining
a solution of the problem of producing light without heat.

A large number of beetles have the terminal portion of
the antennae, like that of the June-bug, with a club
formed of leaf-like joints. These are known as Scara-
baaans, from the sacred beetle (Scarabceus) of the Egyptians
which belongs to the group. These sacred forms are repre-
sented in our country by the tumble-bugs, which lay their
eggs in balls of manure which they trundle along the road
until they find a suitable place to bury them. From the
similar habits of the Scarabaeus the Egyptians worked out
quite a symbolism. " The ball which the beetles were
supposed to roll from sunrise to sunset represented the
earth; the beetle itself personified the sun, because of the
sharp projections on its head, which extend out like rays of
light; while the thirty segments of its six tarsi represented
the days of the month." Other members of the Scara-
baeans, like our June-bugs, are vegetarians and do no little
damage. As larvae they feed upon the roots of the grass
and other plants; as adults they devour the foliage. In
the tropics occur Scarabaeans of enormous size, some having
bodies six inches in length.

The long-horn beetles live as larvae in the solid portions
of trees and shrubs, where they bore long tubes. The
species usually have long antennae, and many of them are
beautifully colored. Structurally much like these borers
are the shorter and more oval leaf -beetles, which do so much
damage. Here belong- the cucumber-beetles, the Colorado
potato-beetle, and others which feed upon the grape, the

VOLEOPIERA.

asparagus, etc. ; and near them are the so-called weevils
which attack peas and beans.

The oil-bottles and blister-beetles are a curious group,
since in their young stages many of them are parasitic
upon other insects, while when adults they contain a pecu-
liar substance which will raise a blister upon human flesh.
Hence some of these are killed, dried, and form a regular
article of commerce under the name of Spanish flies.

FIG. 80.— Pea- weevil (Bruchus pM\ FIG. 81.— Hazel-

natural size and enlarged, b, pea nut- weevil (Bo-

containing a weevil. laninus nasicus.)

The snout beetles (Rhynchophora) or true weevils are all
injurious, since as larvae and adults they feed upon vegeta-
tion. Some attack fruits, some eat grain, and others nuts.
Certain ones burrow between the bark and solid woods
of trees, excavating curious mines, while others bore into
the solid wood.

EYMENOPTERA (BEES, WASPS, ANTS.)

Bees, wasps, and ants are the better known represen-
tatives of this group, all the members of which agree in
having four membranous wings (the front pair the larger)
with comparatively few cross-veins. The mouth-parts are
fitted both for biting and for sucking. There is a com-
plete metamorphosis. So far as we can judge, these are the
most intelligent of all insects, and the student who investi-
gates their habits is continually rewarded by new facts,
which show that their small brains are most highly devel-
oped. In other points of structure, however, they are
much less complicated.

In the lower forms the female is provided with an ovi-
positor, frequently of great length, which is well adapted
for boring. In the higher this ovipositor is modified into
a sting — a weapon of offence and defence, the efficiency of
which is increased by an associated poison-gland.

The lowest forms are the sawflies, the larvae of which are
vegetable-feeders, some eating the leaves of plants, others
boring in the solid wood. A little higher in the scale come
the gall-flies, those forms which lay their eggs in various
plants and in some way so stimulate the vegetable tissue
that strange growths — galls — are formed. Allied to these
last are the ichneumon-flies, which lay their eggs in other
insects. Here the larvae hatch out, feed upon the host,
at last destroying it. Then pupation comes, and the per-
fect insect emerges to repeat the process. Naturally these
188

HTMENOPTBRA. 189

ichneumon-flies are an important agent in keeping down
injurious insects.

FIG. 90.— Ichneumon-fly, enlarged. From Riley.

The ants are possibly the most interesting of all insects.
They are true communists. In them, as in the white
ants (p. ), there is a differentiation of the individuals
into males, females, and workers, the latter being wingless.
A.ny adequate treatment of these forms would of itself
demand a book larger than this volume. The males and
females take " wedding-flights," after which the male soon
dies, while the females bite off their wings and henceforth
have nothing to do except to lay eggs. These eggs are

190 'ELEMENTS OF COMPARATIVE ZOOLOGY.

cared for by the workers, which, as the name implies
perform all the labor of the colony. They obtain the
food, take care of the immature insects, build the nests,
and carry on the wars. In their battles some ants always
take prisoners, and these are kept as slaves. Some species
of ants have depended on slaves so long that they are only
able to fight, while did the slaves not feed them they would
starve. No group of insects will better reward careful
study than these.

The digger-wasps make mines in the earth or in wood in
which they lay their eggs, usually placing with the eggs a
supply of food for the young. Some use as food pollen
and nectar of plants, while others store up insects or spiders
which have been so stung that they are paralyzed, not
killed. In this way the food will keep for a long time.

The true wasps are some solitary, some colonial, and in

FIG. 91.— Sand- wasp (Sphex).

the colonial forms we find again, as in the ants, males,
females, and workers, the workers being winged. Most of
these true wasps (and hornets are wasps) build nests usu-

HYMENOPTERA. 19 1

ally of half -decayed wood, which they chew into a kind of
paper. Inside are the cells in which the eggs are placed
and in which the young undergo their metamorphosis.
Males and workers die in the autumn, but the females live
through the winter and start new colonies in the spring.

Among the bees the honey-bees occupy the first place from
their value as honey-storers. Indeed, so great is their value
that hundreds of books and dozens of journals have been
published dealing wholly with them. In each colony there
are males (drones), females (queens), and workers, the
latter imperfectly developed females. Soon all the drones
are killed, and all the queens except one, and her sole duty
is to lay eggs. If the queen be lost, the workers can take a
larva that would otherwise develop into a worker, and by
different food convert it into a queen. Wax is a secretion
of the bee, honey is the nectar obtained by the bees from
flowers, while the bee-bread is the pollen of flowers.

SQUASH-BUG: LABORATORY WORK.

Can you distinguish three regions in the body ? How
many legs do you find ? Have these the same joints as in
the grasshopper ? How many joints in the tarsus ? Do
you find compound eyes, ocelli, and antennae on the head ?
Examine the lower surface of the head and find the beak.
See if with needles you can separate it in several needle-like
parts. This can only be done with great care in so small
a form as the squash-bug. The student, if successful, will
find four needle-like pieces (mandibles and maxillae)
sheathed in a groove-like labium. Could this beak be
used for biting and chewing, or for piercing and sucking ?
Notice the wings, drawing one of each pair. In the
anterior wing are the basal and distal parts equally thick ?
How many joints in the abdomen? Where are the
spiracles ?

192

BUTTERFLY: LABORATORY WORK.

Notice the relative size of the wings. How are they
carried when the insect is at rest? Rub the wings and
notice your fingers. Scrape a wing with a scalpel and
study the "dust" under the microscope. With what is
the body covered ? Sketch the veins in the wings.

Study the head. Below, notice the proboscis. Straigh-
ten it out with a needle. At the sides of the base of the
proboscis see the labial palpi. Are the antennas of the
same size throughout their length ? Sketch the head in
outline, then remove the hairs, etc., which cover it and
look for eyes and ocelli, inserting what you find in the
drawing.

Do you find in the legs the same joints as in the legs of
grasshoppers ? Have the tarsi of all the legs the same
number of joints ? Is the base of the abdomen as broad as
the thorax ? Do you find cerci or ovipositor ?

COMPARISONS.

With columns for Squash-bug and Butterfly, answer the
following questions:

(1) What is the relative size of the two pairs of wings ?

(2) How are they carried when at rest ?

(3) Are they naked or covered with scales ?

(4) Are either pair thickened at the base ?

(5) Are distinct labial palpi present ?

(6) Can the proboscis be used as a piercing- organ ?

193

HEMIPTERA (BUGS).

The Hemiptera are the true bugs. This term is fre-
quently loosely applied, but any true bug has the following
characteristics : Its mouth-parts are not fitted for biting,

FIG. 83.— Head of seventeen-year locust to show the mouth-parts, etc. a,
antennae ; e, compound eye ; J, labium ; met, mandible ; raz, maxilla.

but for piercing and sucking. They are prolonged into a
beak, consisting of a fleshy grooved sheath (labium) with
four needle-like bristles (mandibles, maxillae) in the groove.
This organ is used for making holes in plants or flesh, and

194

HEMIPTERA. 195

also serves as a tube through which the bug sucks up the
juices found. The bugs have an incomplete metamorpho-
sis (p. 182), hatching from the egg much in the adult con-
dition, except that wings are lacking.

Almost all the Hemiptera. when adult, have four wings,
though -there are a number of wingless forms. These wings
are built upon two distinct patterns, and this serves as a
means of subdividing the Hemiptera into two groups. In
the one (HETEROPTERA) the basal half of the anterior
pair of wings is thickened while the rest is membranous,
and the wings themselves are held in an overlapping manner
upon the back when at rest. This condition is familiar in
the squash-bug. In the other group (HOMOPTERA) there
is no such thickening of the basal portion of the first pair
of wings, and these organs, when at rest, are placed upon
the sides of the abdomen.

While most of the bugs are injurious to human interests,
there are some which are a benefit to man, since they feed
on injurious insects ; and still others, like the cochineal- and
lac-bugs, produce substances of value to man.

Of the Heteropterous forms some are aquatic, and of
these the water-skaters, gliding over the surface of still
water, are familiar to all. Others live most of their lives
beneath the surface, and some of the larger of these water
bugs can kill small fish, sticking the beak into them and
sucking their blood.

Of the terrestrial forms none is more widely known than
the bedbug, a form which is famed for its attacks on man.
It is one of the bugs which never develop wings. From
the pecuniary standpoint the chinch-bug is more important,
since it attacks fields of grain, doing sometimes millions of
dollars of damage in a single year. The young attack first
the roots and underground stems, and later the stems

196 ELEMENTS OF COMPARATIVE ZOOLOGY.

themselves, killing them before they have had time to
ripen the grain.

The squash-bug, which does such damage to pumpkin- and
squash-vines, is another form of Heteropteran, as are those
familiar forms which have no other common name than
"stink-bug." No one who has ever taken into his mouth
a berry over which one of these animals has travelled can

Ci

FIG. 83.— Seventeen-year locust (Cicada septendecim). From Riley. a.
pupa ; b.pupa-case from which the adult, c, has escaped ; d, twig bored
for the deposition of eggs.

doubt the appropriateness of the name. However, these
bugs are not alone in their malodorous qualities; many
others, like the squash-bug and bedbug, also secrete a
strong-smelling fluid, which of course protects them from
birds and other insect-eating animals.

Among the Homopteran forms the cicadas come first.
One of these, the " dog-day locust" (it is not a locust at
all), is familiar from its shrill note heard during the hottest

HEMIPTERA. 197

days of summer. This form requires two years to come to
its full maturity, but its cousin, the seventeen-year locust,
requires, typically, seventeen years from the time the eggs
are laid until the animals are ready to lay another series of
eggs. These eggs are laid in the twigs of trees. The
young when hatched from these eggs drop to the ground,
and, burrowing beneath its surface, spend the next seven-
teen years * sucking the juices of the roots of the trees.

Another group of Homopterans are the " spittle-in-
sects," small forms which, settling upon a blade of grass or
twig of shrub, soon surround themselves with a frothy mass.
They suck the juices of the plant, and after having token
out what they desire eject the rest as a mass of foam.
Examine one of these bits of froth and you will find the
immature bug inside. Allied to them are the tree-hoppers
and leaf -hoppers, so common and so injurious to vegetation.

The plant-lice deserve a little more attention. They
occur on almost every kind of plant, sucking its juices and
reproducing as rapidly as possible. One does but little
damage, but the havoc wrought by thousands is very con-
siderable. In the summer the colonies of these forms will
be found to be largely wingless, and these wingless forms
are all females capable of reproduction without males. In
some species they lay eggs, in others they bring forth liv-
ing young. These in time reproduce in the same way, and
so rapidly do they increase that one plant-louse may be the
progenitor of 100,000,000 in five generations. At the
close of the season appear the true sexual forms, the males
always winged. These sexual forms produce eggs which
last through the winter. All of the plant-lice are destruc-
tive to vegetation, and some, like the Phylloxera of the
grape, are extremely so.

* In the South the period is thirteen years, in the North seventeen.

198 ELEMENTS OF COMPARATIVE ZOOLOGY.

The scale-bugs or bark-lice are also serious pests, doing
great damage to fruit-trees, etc. The males are winged,
but the female is scale-like and adheres closely to the
branch or the fruit, sucking its juices. Oranges and lemons
are frequently covered with these forms. A few, however,
are of value to man. The pigment carmine is made from
the dried bodies (cochineal) of a scale-louse of the cactus,
while lac — from which shellac is prepared — is the secretion
of a tropical tree-inhabiting species.

Besides the Heteroptera and the Homoptera, the Hemip-
tera embraces a third division, the PARASITA, or lice. These
are all wingless forms, living as parasites in the hair and on
the skin of mammals, and sucking the blood of their hosts.

LEPIDOPTERA (Moras AND BUTTERFLIES).

The millers, moths, and butterflies are grouped together
as Lepidoptera, and all agree in having four membranous
wings covered with dust-like scales, in having a long suck-
ing "tongue " formed of the two maxillae, and in having
a complete metamorphosis (p. 188) in which there hatches

FTO. 84.— Army- worm, larva of Leu- FIG. 85 .— Pupa of a Bombycid
cania unipuncta, showing five (pairs moth a, antenna; Z, first pair
of) abdominal legs. of legs ; w, wings.

from the egg a worm-like larva. This stage is commonly
known as a caterpillar or "worm," but it differs from all
true worms in having legs, and those who wish to call
things by their true names should never speak of them as
worms. These larvae always have sharp jaws and simple
eyes, and are provided with from eight te sixteen legs. Of

m

200 ELEMENTS OF COMPARATIVE ZOOLOGY.

these, three pairs are on the thoracic segments, while the
abdomen has from one to five pairs. These larvae, when
they hatch from the egg are small, but by feeding they
grow, increase in size being rendered possible by frequent
moltings of the skin. At last there comes a molt by which
the appearance is greatly changed and the pupal stage is
reached. In the pupa the abdominal legs are lost, the body
is shortened and covered with a harder skin, in which
one can trace the legs, antennae, and wings of the future
moth or butterfly, folded over the breast. Many caterpillars
of the moths, as a preparation for pupation, spin silken
nests or cocoons, the silk being the product of glands which
empty into the mouth. The pupae of butterflies have
usually no such silken protection, but are free. From the
fact that many of these butterfly pupae are marked with
patches and spots of gold, they are frequently called chry-
salides (sing, chrysalis).

The pupal stage lasts for some time (months), during
which no food is taken and no motion possible except of
the abdominal rings; then the pupal skin is molted and
the perfect insect (imago) emerges. In those forms which
have a cocoon the silken threads are softened by fluids
secreted by the imago, and in some there are hooks at the
bases of the wings which aid in tearing an opening for the
escape of the moth.

When the imago first comes out it is soft and flabby, and
the wings are soft bags. They are rapidly distended by
blood pumped into them, and, held expanded, are rapidly
dried by the air into efficient organs of flight. The
wings are covered with scales, and to these is the color-
pattern due. These scales are merely modified hairs like
those which cover the whole body. When removed the
wing is seen to have a framework of supporting " veins "

LEPIDOP^ERA. 201

which are really not veins at all. These veins vary greatly
in their arrangement in different moths and butterflies,
and are used as a basis of classification.

FIG. 86.— Army- worm moth (Leucania unipuncta\ From Riley.

While the larvae are biting insects, the adult is adapted
for taking liquid nourishment by means of a so-called
" tongue" which when not in use is coiled beneath the head
like a watch-spring. This tubular structure, which, in
function, is so like the beak of the bugs, is much different
in structure, as it is formed by the union of the two max-
illae, while the other parts — labrum, mandibles, maxillary
palpi, and labium, are present, but in a more or less reduced
condition.

There are two great divisions of the Lepidoptera, the but-
terflies and the moths of common language. The day-flying
butterflies hold the wings erect over the back when at rest,
and they have the antennae enlarged into clubs at the tip.
In the moths, which are mostly nocturnal, the wings are
carried nearly horizontally when at rest, and the antennae,
while frequently feathered, are never clubbed.

Among the smallest, and at the same time the most
troublesome, of the moths are those pests, the clothes-moths
and their relatives, which do such damage to woolen goods,
furs, etc. These are among the few larvae of moths which

202 ELEMENTS OF COMPARATIVE ZOOLOGY.

have left a vegetarian diet and taken to food of animal or-
igin. Another exception is found in the bee-moth, the larva
of which is found in apiaries, feeding upon the wax and
spinning its silk all through the comb.

Of the leaf-rolling moths the codling-moth is the best
known. Its larva is the worm so frequently found near
the core of apples. Other allied species tie the leaves of
apple-trees, roses-bushes, etc., together and live in the nest
thus formed.

The Geometrids include those moths whose larvae are com-
monly known as measuring-worms from their looping gait.
All of these are pests, and the canker-worms exceed all the
rest in this respect. These are especially noticeable from
the fact that the adult female is wingless.

The sphinx-moths or hawk-moths are large narrow- winged
forms, the larvae of which are injurious to many plants.
From the attitude assumed by some larvae when at rest the
name sphinx was applied to the group ; the other common
name, hawk-moths, has reference to their powers of flight.

FIG. 87.— Sphinx-moth (Everyx myron). From Riley.

Another group of moths are known as Bombycids. While
some of these are unmitigated pests, others are of value to
man, the silkworms leading in this respect. These are, in
fact, the most valuable of all insects. The true silkworm is

LEPIDOPTERA. 203

a native of China, but has been distributed to all of the
warm parts of the earth. Like other caterpillars, they form
their cocoons, and then these are heated to kill the pupa and
the silk of the cocoon is unwound, and after proper treat-
ment becomes the silk of commerce. We have several spe-
cies of silkworms in this country some of which make a
stronger silk than the Chinese species; but although a few
articles have been made from it, it has no economic impor-
tance. These large American silkworm-moths are known
as Polyphemus-, Promethea-, Cecropia- and lo moths, and
they, together with the beautiful green luna-moth, are great
favorites with collectors.

The skippers are a group of small butterflies in which
the clubbed antennae are bent into a hook at the tip. They
are called skippers on account of their jerky flight.

The swallowtails are well-known forms of butterflies in
which the hind wings are prolonged into tails, whence the
name. The larvae of these forms are usually brightly col-
ored, but they are protected by a pair of " stink-horns,"
which they can project at will from the region of the neck,
and which give off, in most cases, a most offensive odor.

Another group of butterflies, whitish-yellow or orange
in color, are typified by the cabbage-butterflies. We had
some of these which were bad enough ; but a few years ago
the European cabbage-butterfly came to this country and
became the greatest pest of all our butterflies.

Of smaller size — the most delicate of all our butterflies
— are those forms which have received the common names
of the blues, the coppers, and the hair-streaks, from their
predominant colors and from the ornamentation of the
wings.

Of larger size are the group of " four-legged" butterflies,
so called because the first pair of legs are so small as to be

204 ELEMENTS OF COMPARATIVE ZOOLOGY.

of no use to the animal. Of these forms there are hun-
dreds of species, including the milkweed-butterflies, the

FIG. 88.— A four-legged butterfly (A rgynnis aphrodite), under side shown

on right.

painted-beauty, the mourning-cloak (the first butterfly to
appear in the spring) , and numbers of others, the catalogue
of the names of which would prove
dry reading. Only one needs more
mention. This is the White Moun-
tain butterfly, found only on the tops
of the White Mountains, on the tops
of the higher peaks of Colorado, and
in Labrador. It is supposed that
this form is a remnant of an Arctic
fauna which extended over the North -
ern United States when the country
butterfly (CEnete semtdea) . was covered by the great ice-sheet (see
Geology), and on the retreat of the glacier these colonies
were left stranded upon these points as the only places cold
enough for them.

COMPARISONS.

With two columns, one for grasshopper, squash-bug,
beetle, and butterfly, and the other for crayfish and sow-
bug, answer the following questions :*

1. How many pairs of antennae ?

2. How does the animal breathe ?

3. How many segments in the head-region ?

4. How many walking-feet ?

5. Are there appendages on the abdomen ?

6. Where are the reproductive openings ?

7. Are any appendages two-branched ?

* If the points have not been made out for all forms, answer for
those about which you know.

205

CKUSTACEA.

The crayfish and sow-bug may be taken as types of the
Crustacea, or crab-like forms. These all have two pairs of
antennae or appendages in front of the mouth ; they have a
varying number of segments at the front of the body, cov-
ered by a common shell or carapax, and, excepting gill-less
microscopic forms, they all breathe by means of gills at-
tached to some of the feet.

The number of segments in the body varies ; in the higher
groups it is constantly twenty, but in the lower it may fall
far short of, or far exceed, that number. The regions also
vary in extent and cannot be compared throughout the
group. Taking the segments connected with the senses
and with eating as constituting the head, this region may
contain as few as five or as many as eight segments. Not
infrequently the head and the next region of the body are
united so that they are called a cephalothorax. The abdo-
men is usually well developed, but it may be reduced to a
mere stump, as in the barnacles. Any of the segments ex-
cept the last one may bear appendages. Those most usually
present are two pairs of antennae,* a pair of mandibles, two
pairs of maxillae, and a varying number of maxillipeds and
walking-feet.

If we study these appendages in the young, or in the
adult of some forms, we find that they each consist of a

* One pair is very small in the sow-bug, but it can be seen with a
lens.

208

CRU8TACBA. 207

basal joint, bearing two jointed branches, the exopodite
and endopodite. With growth of the animal the exopo-
dite frequently disappears.

The gills by which most Crustacea breathe are thin out-
growths of the body, usually closely connected with some of
the appendages, either of the thorax or of the abdomen. In
shape they may be plates or plumes or sacs, but all are trav-
ersed by blood-vessels so that the blood is brought in close
proximity to the water. In some cases these gills hang
freely into the water, in others they are placed in special
gill-chambers, and then there is an arrangement of parts
for pumping fresh water over them. In the terrestrial
Crustacea these gills still serve as breathing-organs, as in
the sow-bugs, and are constantly kept moist. In some of
the lower Crustacea there are no special organs of respira-
tion, the thin walls of the body affording sufficient surface
for the purpose.

The alimentary canal is nearly straight, and there is usu-
ally a chewing-stomach in which the food is ground by hard
teeth in the walls, and beyond this there is frequently a
straining-stomach. A large so-called liver is always present,
pouring digestive juices into the alimentary canal behind
the stomach. The eyes are either simple or compound. In
the simple eyes there is a single lens for the whole structure,
while the compound eyes are composed of many separate
eyes, each with its own lens. In some cases these eyes are
placed on jointed stalks, at others they are in the walls of
the head. Ears have been found in some forms. Usually
they are sacs in the base of the antennulae, but in the opos-
sum-shrimps they occur near the end of the abdomen. The
hairs which occur over the body are organs of touch, and
possibly some of them serve as organs of taste and smell as
well.

208 ELEMENTS OF COMPARATIVE ZOOLOGY.

A heart is lacking in a few forms. When present it is
dorsal in position, but may he either in thorax or abdomen.
It may be a long tube with several chambers, or a short thick
muscular organ without divisions. The blood returning
from, the gills enters the heart and is forced thence to all
parts of the body, a condition quite different from what we
found in the fish. It does not flow throughout its course
in closed vessels, but escapes from them and comes into large
spaces (lacunae) between the various organs and muscles, and
from the largest of these lacunae, near the floor of the body,
it again goes to the gills.

In the Crustacea there are excretory organs (nephridia)
which open to the exterior entirely independently of the
alimentary canal. In the higher Crustacea (crayfish, etc.)
these nephridia are known as " green-glands " and open at
the base of the antennae (second segment); in the lower
Crustacea they are called "shell-glands" and open at the
base of the second maxillae (fifth segment).

The sexes are separate in all except the barnacles, and the
ducts of the reproductive organs open to the exterior in
the thoracic region, never in the abdomen. In almost all
forms the eggs are carried about by the mother until they
are hatched. In almost all the lower Crustacea the young
escapes from the egg in a very immature condition, known
as a Nauplius, a name given years ago under the belief
that it was an adult. The nauplius has an unsegmented
body, a single median eye, and only three pairs of appen-
dages— antennulae, antennae, and mandibles — the anten-
nulae being solely sensory, while antennae and mandibles
are used in both swimming and eating. In the higher
Crustacea the nauplius stage is passed in the egg, and the
young hatches in a more advanced condition — sometimes

CRUSTACEA. 209

closely like the adult in all except size. Growth is allowed
for by frequent molts of the external cuticle of the body.

Over 10,000 species of Crustacea are known, almost all
of them aquatic, and the majority marine. Only a few,
like the sow-bugs and land-crabs, live on the land. A few
are vegetarians, some are parasites on other animals, but
the majority are scavengers, feeding on decaying organic
matter. The Crustacea may be conveniently divided into
two "subclasses": Malacostraca and Entomostraca.

SUBCLASS I. — MALACOSTRACA.

This group contains the larger and higher Crustacea, in
which the body consists of twenty somites,* all of which
except the last (telson) may bear appendages. Compound
eyes are usually present ; and the nauplius stage (p. 208) is
usually passed in the egg. Besides several unimportant
groups, this subclass contains the orders Decapoda and
Tetradecapoda.

ORDER I. — DECAPODA (p. 164).
ORDER II. — TETRADECAPODA (p. 168).

SUBCLASS II. — ENTOMOSTRACA.

This division contains a large number of forms, mostly
small, or even microscopic in size. The number of body-
segments is usually less than twenty, but occasionally there
may be many more. Some are decidedly shrimp-like in
form, but in others parasitic habits have resulted in such
changes that there is little external resemblance to a cray-
fish or a crab. In fact, this degeneration may go so far in

* Twenty-one in Nebalia.

210 ELEMENTS OF COMPARATIVE ZOOLOGY.

certain fish-parasites (so-called fish-lice) that the adults
would never be suspected of being crustaceans were it not

cut 9

FIG. 92.— An Entomostracan (Cyclops). From Hertwig.

for the young. When the development is studied, these,

CRUSTACEA.

211

like all other Entomostraca, are found to have a free-
swimming nauplius stage.

The only ones of the Entomostraca (aside from the fish-
parasites) which have received a com-
mon name are the barnacles, so familiar
at the seashore. In these the body
is enclosed in a hard calcareous shell,
which is either directly attached to
some solid support, as in the acorn-
barnacles, or there is a fleshy support,
as in the goose-barnacles. Inside the

FIG. 93.— Goose - barna-
cles (Lepas anatifera).
After Schmarda.

shell is the animal, and a
cursory examination of its
two-branched feet and its
other features would con-
vince any one that these
forms are truly crustacean.

Mention should be made
here of a large group of ex-
tinct animals, the Trilobites,
which recent investigations
have shown to be crusta-
ceans, but which cannot be
more definitely placed within
that group. They agree with
neither Entomostraca nor Malacostraca in their structure.
They have a flattened body, in which head, thorax, and

FIG. 94.— Restoration of the under
surface of a Trilobite, showing the
appendages. After Beecher.

212 ELEMENTS OF COMPARATIVE ZOOLOGY.

abdomen are readily distinguished, and in which both thorax
and abdomen consist of an axial portion, and two lateral
regions or lobes, whence the name of the group. The
head bears a pair of compound eyes, a single pair of an-
tennae, and four pairs of appendages, which served at once
for walking and for taking food. Each segment of thorax
and abdomen supports a pair of two-branched appendages.
Trilobites appear in the earliest fossil-bearing rocks, and
the group died out soon after the period of coal-formation
(in the Permian).

HEXAPODA (INSECTS).

The group of Insects contains more species than all the
rest of the animal kingdom together, a conservative esti-
mate placing the number of distinct forms at over half a
million. Yet all of these agree in certain essential points.
Thus, in all, the hody is divided into three regions, head,
thorax, and abdomen, and of these the thorax alone bears
organs of locomotion. Three pairs of legs are always pres-
ent (whence the name Hexapoda — six-footed — given to the
group). Of wings there may be one or two pairs. The
head bears four pairs of appendages, one pair (the antennae)
being sensory ; the others (mouth-parts) being used in
eating. Breathing is by means of tubes (tracheae) which
open on the sides of the body and which penetrate to all
parts of the interior. The sexes are always separate, and
the reproductive organs open at the hinder end of the body
just beneath the vent.

In the head no evidence of segments is seen, except as
shown by the appendages. The antennae, of which there
are only a single pair, are sensory in function. In many
cases they clearly bear organs of smell, and in some they
may also be hearing-organs. In the primitive condition
the mouth-parts are fitted for biting and eating hard sub-
stances, the mandibles being strong jaws, while the maxillae
and labium serve to hold the food in place. These latter
bear jointed prolongations — the palpi — which are sensory.
In other insects these mouth-parts are modified and united

£13

214 ELEMENTS OF COMPARATIVE ZOOLOGY.

into a sucking- tube which frequently is a piercing- organ
of no mean capabilities.

The thorax is composed of three segments, named, from
in front backwards, the prothorax, mesothorax, and meta-
thorax. Of these the first is frequently movable. Each
segment bears a pair of legs, made up of several joints, the
number varying according to the number in the " foot"
(tarsus), the rest of the member usually consisting of four
joints. On the dorsal surface of the meso- and metathorax
occur the wings, the characters of which are largely used
in the classification of insects. They are entirely lacking
in the lowest insects (Thysanures) as well as in individuals
of other groups, as ants, many parasites, and the females
of certain moths. In the flies the posterior wings are
greatly reduced, so that they appear like a pair of knobbed
hairs, termed "balancers," since if they be removed the fly
cannot control its motions. Frequently both pairs of
wings are used in flight, but in certain groups the front
pair are much thickened and hardened, so that they are con-
verted into wing-covers (elytra) which protect the hinder
wings when at rest.

The abdomen is normally composed of ten segments, but
this number may be reduced. In some insects the ab-
domen joins the thorax by its whole width, while in others
it is contracted in front to a slender stalk as in the wasps.
The appendages of the abdomen, in the adult, are never
locomotor in function. In the lowest insects rudimentary
appendages may occur on all segments of the abdomen, but
in the higher groups only three pairs, at most, occur, and
two of these are modified into an organ (ovipositor) for
laying the eggs. In the bees, wasps, etc., the ovipositor is
at the same time an offensive weapon, the sting.

The alimentary canal has few convolutions. Into the

INSECTS. 215

mouth-cavity open the salivary glands. In those forms
which eat solid food a "chewing-stomach" with hard
horny teeth occurs. Behind this comes the true stomach,
and following this the intestine, to which are attached a
varying number of Malpighian tubes (2-100 or more)
which, like the kidneys of higher forms, serve to carry away
nitrogenous waste from the body.

The circulatory organs are poorly developed. A dorsal
tube, or heart, is present, lying above the alimentary canal,
and this pumps the blood forward, into an aorta of varying
length. Soon, however, the blood leaves this tube and
flows between the muscles and viscera and finds its way to
the hinder part of the body, where it again enters the heart
through openings in its sides. This imperfection in the
blood-vessels is compensated for by the peculiar character
of the organs of breathing (respiration). These consist of
a number of tubes (tracheae) which open to the outside by
paired openings (spiracles) in the sides of the body. These
spiracles occur in the thorax and. abdomen, and never ex-
ceed a pair to a somite, and from three to ten pairs may
occur. Internally the tracheae branch again and again,
until the finest twigs penetrate to every part of the body.
Frequently the various tracheae are connected on either side
of the body, and in the strong-fliers these connecting tubes
are enlarged into air-sacs, which thus render the body
lighter. Air is drawn into the tracheae by the enlarge-
ment of the abdomen, and thus reaches all the of tissues of the
body. Since breathing is accomplished through the spira-
cles in the sides of the body, one can see that one cannot
readily kill an insect by putting chloroform on its head.

The nervous system consists of an enlargement or
"brain" in the head, in front of the mouth, and from
this nerves go to the eyes and antennae, while a stronger

216 ELEMENTS OF COMPARATIVE ZOOLOGY.

nerve-cord passes on either side of the gullet, to unite in a
second enlargement (ganglion) behind. Thus, as will readily
be understood, the alimentary canal passes through the
nervous system, a condition which is totally different from
anything found in the vertebrates. Behind the infra-
cesophageal ganglion a double nerve-cord extends along the
floor of the body, connecting a series of similar ganglia.
In the lower insects there is a ganglion in each segment,
but in the higher these tend to move forward and to unite
with each other into a few masses or compound ganglia.

The eyes are always on the head. In the adult insects
compound eyes are usually present, and besides these
there may also be simple eyes. In the latter there is but a
single lens, while the compound eyes are composed of
many distinct visual structures, each with its own lens.
Organs, which are regarded as ears, occur in various forms.
In the grasshoppers these organs are on the base of the
abdomen ; in the crickets, on the legs ; in many groups the
antennae are supposed to have auditory powers. Taste
resides chiefly in the lower lip, while touch,- though found
all over the body, is especially developed in the antennas
and the palpi of labium and maxillae. In some insects the
sense of smell is strongly developed, and there is reason to
believe that the olfactory organs are in the antennae.

The group of Insecta may be subdivided in two ways,
accordingly as different characters are employed. If we
follow one method the mouth-parts form the basis of
division, and we have a mandibulate group in which the
jaws are fitted for biting, as in the grasshopper and beetle;
while in the Uaustellate group the mouth-parts are no longer
fitted for biting, but form a tube through which liquid food
is sucked, as in the bugs and butterflies.

The second method of subdivision depends upon the

INSECTS.

217

facts of life-history. In the first or ametabolous group the
young leaves the egg with much the general shape of the
adult, and the growth is gradual, without any sharply marked
lines between the different stages. Such is the case with
the grasshopper and the bug. In the other or metabolous
group we can distinguish three stages sharply marked off

FIG. 95.— Colorado potato-beetle (Doryphora decemli neata) . a, eggs; b,
larva ; c, pupa ; rf, adult.

from each other — larva, pupa, and adult. These are exem-
plified in the beetle and butterfly.

These two classifications do not agree, as can be seen from
the following tables :

MAKDIBULAT^;. HAUSTELLAT.^.

Thysanura. Hymenoptera.*

Orthoptera. Hemiptera.

Pseudoneuroptera. Lepidoptera.

Neuroptera. Diptera.

Coleoptera.

* The Hymenoptera have the mouth-parts adapted for both biting
and sucking.

218 ELEMENTS OF COMPARATIVE ZOOLOGY.

AMETABOLA. METABOLA.

Thysanura. Coleoptera.

Orthoptera. Neuroptera.

Pseudoneuroptera. Hymenoptera.

Hemiptera. Lepidoptera.

Diptera.

As will be seen from the foregoing tables, the group of
Hexapoda, or Insecta, is subdivided into nine groups or
orders.*

ORDER I. — THYSAKURA.

These are small wingless insects without any general
common name except those of "bristle-
tails" and springtails, which have been
manufactured for them. The springtails
live in damp places — in cellars, under
leaves in the forest, etc., and they have
a spring beneath the body by means of
which they can jump to great distances.
The bristletails have the body terminating
in two long filaments. To this last group
belong some pests known commonly as
"silverfish" — soft-bodied shining forms,
which eat paper, starched clothing, etc.
FIG. 96.— "silver- Aside from this silver-fish or "fish-moth"

fish" (Lepisma , . .

saccharina). the group has little general interest; but

to the naturalist it is very interesting because it is so
primitive.

ORDER II. — ORTHOPTERA (see p. 181).

* Many authorities recognize more orders than these, the difference
chiefly lying in the extent to which the Neuroptera and Pseudoneu-
roptera are subdivided.

INSECTS. 219

ORDER III. — PSEUDOITEUROPTERA.

These forms, like the Orthoptera, have biting mouth-
parts, and have a gradual change from the young to the
adult, but they differ from those forms in having both
pairs of wings alike, usually very thin and transparent,
with very numerous veins, and not capable of being folded
like those of the Orthoptera. There are two divisions of
these Pseudoneuroptera. In the first the younger stages
are passed in the water, in the second on land.

Examples of the first are seen in the dragon-flies
(ODONATA); their larvae live in the water, where they
feed upon other insects, etc., and especially on the larvae
of mosquitoes. When the adult stage is reached and they
take to the air, they are veritable dragons, feeding upon
insects, which they catch on the wing. Here, too, belong
the May-flies or day-flies with an aquatic life of from one
to three years, a life in the air of but a few days, or even a
few hours. These May-flies often appear in great numbers
in the cities near the Great Lakes.

The celebrated white ants or termites may represent the
forms with a solely terrestrial life-history. These are not
"ants" -at all in the true sense of the word, but they
resemble them in several points. They form large colonies
consisting of several distinct "castes" with different
structure. Only the kings and queens are winged, and
only these are capable of reproduction. Besides these
there are "workers" and '•' soldiers." The workers build
the nests, gather the food for the whole colony, and bring
up the young. The soldiers have enormous heads, and
protect the others. The termites are miners, and make
their burrows beneath the earth and inside of dead wood.
They avoid the light, and where they cannot otherwise

220 ELEMENTS OF COMPARATIVE ZOOLOGY.

make their way they build covered ways, sometimes for
hundreds of feet. They feed upon dead wood, and will
sometimes utterly eat out the inside of the timbers of a
house, leaving posts and joists but a mere shell. They are
comparatively rare in colder climates, but in the tropics

FIG. 97.— White ant (Termes flavipes). a, larva; b, winged male; c,
worker ; d, soldier ; e, queen ; /, pupa. From Riley.

they become a terrible pest. The queen is kept a prisoner
in the nest, is fed by the workers, and develops* so many
eggs that her abdomen is swollen out of all proportion.
As the eggs escape they are cared for by the workers.

ORDER IV. — NEUROPTERA.

These forms have the wings much as in the Pseudonen-
roptera, the mouth-parts for biting or much reduced, but
they have a complete metamorphosis. The majority of
these forms are inconspicuous, and their existence is hardly
recognized except by naturalists. Here belong the "dob-

INSECTS.

sons/' or hellgrammites, larvae of a large insect, which are
used as bait by anglers. Here, too, belong the ant-lions,

c

FIG. 98.— Adult male hellgrammite (Corydalis cornutus). From Riley.

which build little pitfalls for the ants on which they feed.
Last to be mentioned are the caddis-flies, the aquatic larvae
of which protect themselves by building cases of stones,
sticks, etc., in which they hide and which they carry about

222 ELEMENTS OF COMPARATIVE ZOOLOGY.

with them in their search for food. These caddis-flies, in
the adult stage, have the mouth-parts much reduced, and

FIG. 99.— Adult ant-lion (Myrmeleon).

are supposed to represent pretty closely the ancestors of the
butterflies and moths (Lepidoptera).

ORDER V. — COLEOPTERA (see p. 184).

ORDER VI. — HYME^OPTERA (seep. 188).

ORDER VII. — HEMIPTERA (see p. 194).

ORDER VIII. — LEPIDOPTERA (see p. 199).

ORDER IX. — DIPTERA (Flies).

This order contains the true flies, and these forms are
sharply marked off from other insects. The name means
two- wings, and the flies have but a single pair of these
organs, while on the metathorax is a pair of knobbed hairs,
the so-called balancers. The mouth-parts are fitted for
sucking. The larvae, commonly known as maggots, are
worm-like, lack feet, and in some species even lack a dis-
tinct head. In some the pupa is motionless, but in others,
as in the mosquito, it has great powers of motion. The
balancers are sensory organs, and they also serve as a
means of maintaining the equilibrium, for if they be cut off
from a fly, the animal can no longer direct its motions.

The group of flies is very large in number of species,
some being beneficial, while others are decided pests.
Among the latter are those forms which feed upon other

DIPTERA.

223

insects, as well as those which in their larval stages feed
upon decaying organic matter.

Most familiar of all is the common house-fly. This lays
its eggs in horse-manure, each female producing ahout
150 eggs. In about ten to fourteen days these eggs become
perfect insects, so that with this rapidity of multiplication
it is no wonder that flies are abundant towards the end of
summer. Allied to this is the blow-fly which lays its eggs
in meat and other provisions.

FIG. 100. — Head and Proboscis of
blow-fly. After Kraepelin. e, egg ;
p, maxillary palpi.

FIG. 101.— Larva (maggot) of
house-fly.

The bot-flies are parasitic in various domesticated animals.
These flies lay their eggs upon horses, cattle, or sheep, and
the larvae enter the animal and cause serious injury or even
death. The horse-bot larvae are taken into the stomach;
the ox-bot or " ox-warble " lives beneath the skin of cattle ; and
the sheep-bot enters the cavities connected with the nose or
even the horns, producing the disease known as " si

224: ELEMENTS OF COMPARATIVE ZOOLOGY.

FIG. 103.— Common house-fly (Mused).

FIG. 103. — Larva (a) and pupa (ft) of mosquito.

DIPTERA. 225

More familiar are the mosquitoes, which lay their eggs on
stagnant water. The larvae hatch out and are known as
"wrigglers." They pupate beneath the surface, and
finally the perfect insect emerges to make itself an unmit-
igated nuisance about our persons. Many proposals have
been made for reducing the number of these torments.
The best is, possibly, the pouring of kerosene upon the
surface of all stagnant water. This will kill the eggs as
they are laid, while it also destroys the perfect insects as
they come from the water.

COMPARISONS.

With two columns, one for grasshopper, beetle, squash-
bug, and butterfly, the other for crayfish and sow-bug,
answer the following questions :

(1) Is the body made up of a series of segments ?

(2) Do any of the segments have jointed appendages ?

(3) Do you find more than one pair of appendages on one
segment ?

(4) Are the hard parts (skeleton) external or internal ?

(5) Do the jaws work in a vertical or in a lateral plane ?

(6) Can the jaws be compared to the other appendages of
the body ?

(7) Is the heart above or below the alimentary canal ?

(8) Is the brain above or below the oesophagus ?

(9) Where is the largest part of the nervous system ?

(10) Is there any relationship between nerve-enlargements
(ganglia) and the external segments of the body ?

ARTHROPODA.

The word. Arthropoda means "jointed foot/' and is very
characteristic of all that immense series of forms which,
like the grasshopper and the crayfish, have an external
skeleton which only permits of motion by a thinning or
jointing at intervals. In this way both body and limbs
have this jointed appearance, but with the body this joint-
ing or segmentation of the external surface is associated
with features of internal structure which must have a
moment's attention. This external jointing of the body
divides it into a series of essentially similar rings or somites,
and in each of these we find parts of all the internal organs.
That is, the segmentation is not confined to the external
surface, but is characteristic of all parts.

In an ideal arthropod each of these segments would be
an exact repetition of its fellows, but in nature we find that
certain segments or parts of certain segments become over-
developed (hypertrophied), and this produces an under-
development (tendency towards atrophy) in others. Thus
every segment in our ideal arthropod would bear a pair of
jointed appendages, but our studies have shown us that
these appendages are frequently atrophied on some of the
segments. Again, there is a tendency in some regions,
and especially in the head, for a more or less complete
fusion of segments, so that the number can only be ascer-
tained by the appendages or by the features presented in
development.

226

ARTHROPODA. 227

Usually these segments can be grouped in regions, of
which, at most, three can be distinguished: in front the
head; next, the thorax; and behind, the abdomen. The
head is largely concerned in the taking of food, and is the
seat of the special senses. The thorax is the locomotor

FIG. 104.— Diagram of grasshopper showing the body divided into the three
regions : head, thorax, and abdomen.

region, while in the abdomen the primitive segmentation
is most marked.

Through the body as an axis runs the alimentary canal,
the mouth being on the under surface of the head, while
the vent is at the tip of the abdomen. Above the digestive
tract lies the heart, which in some forms has a chamber in
each of several somites of the body; that is, the heart is
segmented. On the floor of the body, below the alimentary
canal, is the nervous system, which exhibits this segmen-
tation in a more marked degree. In each segment there is
a paired enlargement or ganglion from which nerves go to
the various organs of the segment. These ganglia of the
successive segments are connected with each other by a
double nerve-cord, so that all are in communication with
each other. At the front end of the body one of these
nerve-cords passes on one side of the oesophagus, the other
on the other, and above it they unite with a large compound
ganglion, the so-called brain. In this way a part of the
nervous system is brought above the alimentary canal,
while the rest lies below. In other words, the digestive
tract passes through the nervous system, a condition which

228 ELEMENTS OF COMPARATIVE ZOOLOGY.

is without parallel in the vertebrates, but which is usually
met with in the non-vertebrate animals.

The organs of respiration are never connected with the
alimentary canal. They are always developments of the
surface of the body. In the case of gills we have outgrowths
of the body- wall, usually much folded or divided to afford
additional surface, and in these are blood-vessels. In the
case of gills, then, we may say that the blood is brought
to the oxygen dissolved in the water for that exchange of
gases (carbon dioxide and oxygen) upon which respiration
depends. With tracheae, on the other hand, the respira-
tory surface is obtained by a forcing of the external surface
into the deeper parts, much as one might invert the finger
of a glove into the palmar region. In the tube thus formed
air can enter, and thus the oxygen is brought to the blood
and other tissues of the body.

The Arthropoda are by far the largest group of animals,
the number of forms living to-day being estimated from
half a million to a million or more.

The Arthropoda are subdivided into three groups or
"classes" : Crustacea, Acerata, and Insecta.

CLASS L— CEUSTACEA (p. 206).
CLASS II.— ACERATA.

In these arthropods the body is divided into two regions,
a cephalothorax in front and an abdomen behind. The
cephalo thorax bears the eyes (of which there may be several
pairs) and six pairs of appendages, none of which can be
considered as antennas. The abdomen may have or may
be without apparent appendages. The respiratory organs
are confined to the abdomen, and in their development are
always connected with the abdominal limbs. They may
be of three kinds: (1) External gills borne on the abdomi-

ARTHROPOD A. 229

nallegs; (2) internal sacs (lungs) with numerous leaf- like
folds ; (3) air-tubes or tracheae, strikingly like those of the
Insecta, but with a different history. The reproductive
organs open near the middle of the body.

SUBCLASS I. — MEEOSTOMATA.

Here belong the horseshoe crabs of our east coast (and a
number of fossil forms), which breathe by means of leaf-
like gills, whicli have both simple and compound eyes, and
which have the bases of the walking-feet of the cephalo-
thorax modified to serve as jaws. Recent investigations
show that the horseshoe crabs are not related to the true
crabs, but are to be rather closely associated with the
scorpions. These forms live in the sea, feeding on worms,
etc., found in the sea-bottom, coming to the shore in
spring and early summer to lay their eggs. The horse-
shoe crabs are without any economic importance, as they
are useless as food, but they are extremely interesting to
the naturalist, as they are the last remnants of forms which
were once abundant in the seas of past times.

SUBCLASS II. — ARACHNTDA.

With few exceptions, the Arachnids are terrestrial forms.
They breathe by internal lungs or by tracheae, and they
lack compound eyes. There are several orders of Arach-
nids, but only a few of them need be mentioned here, as
some are inconspicuous, while others occur only in the
warmer regions of the globe.

ORDER I. — SCORPIO^IDA.

The scorpions have a single pair of jaws (mandibles) and
a pair of large pincers, much like those of lobster or crab.
The long abdomen is distinctly jointed, the seven basal

230 ELEMENTS OF COMPARATIVE ZOOLOGY.

joints being much larger than the terminal five. The ab-
domen ends in a very efficient poison-sting. On the lower
surface of the basal abdominal segments are the openings
to four pairs of lungs. Scorpions are not found in cold

v-

FIG. 105. — Under surface of scorpion (Buthus) showing the combs and
outlines of the lung-sacs.

climates, but in the warmer regions they abound, and their
stings, which rarely prove fatal to man, renders them un-
pleasant companions.

ORDER II. — ARAKEIDA.

The Araneida, or spiders, have the cephalothorax and ab-
domen unsegmented, but sharply separated from each other
by a narrow waist. In front are the poison-jaws (man-
dibles), each with a poison-gland inside. At the tip of the
lower surface of the abdomen are two or three pairs of
spinnerets. These are modified appendages with numbers
of small openings at the tip. Connected with each spinneret
is a gland which secretes a fluid with the property of hard-
ening as soon as it comes in contact with the air. This is

ARTHROPODA.

231

forced out at will through the spinnerets, and forms the
silk with which the spiders wind their prey, wrap up their
eggs, and build those marvellous webs, interesting to all

FIG. 106.— Round- web spider (Epeira insularis). After Emerton.

FIG. 107.— A harvestman laying eggs. After Henking.

except the housekeeper. The poison-jaws are strong, and
venomous enough to kill the insects upon which these ani-

232 ELEMENTS OF COMPARATIVE ZOOLOGY.

mals feed; but the alleged cases of serious or fatal poison-
ing of man as the result of spider-bites need authentication.

OBDER III. — PHALANGIDA.

This name is given to the animals familiarly known as
"harvestmen " and "daddy-longlegs," with small bodies
in which there is no waist between thorax and abdomen,

FIG. 108.— Harvestman (Phala.ngium ptetum).

and with extremely long legs. These forms feed upon
small insects, but are perfectly harmless to larger animals.

ORDER IV. — ACARIXA.

Here belong the mites, in which the unsegmented abdo-
men is fused to the cephalothorax, and in
which the first two pairs of appendages are
modified into a piercing-organ. By means
of this structure, the ticks burrow into the
skin of cattle or of man, the itch-mite makes
its way into the thin skin between the fin-
gers, and the red mite sucks the juices of
plants. As a rule the Acarina are para-
sites, and hence the group is largely made

Fio.109.- Cheese- to J

mite, enlarged. up of pests.

ARTHROPODA.

233

CLASS III.— INSECTA.

In the Insects there is a distinct head con-
sisting of four segments; respiration is effected
by tracheae opening along the sides of the body,
while the reproductive organs open near the tip
of the abdomen.

SUBCLASS I. — HEXAPODA (p. 213).
SUBCLASS II. — CHILOPODA (Centipedes).

In the Chilopods, which include the centi-
pedes and similar forms, the head is succeeded
by a long series of body-segments, each with a
pair of locomotor appendages (legs), and with
no distinction between thorax and abdomen.
Most of the group are carnivorous, and the
larger forms, at least, are provided with poison-
glands which open in the last pair of cephalic
appendages. The chilopods of northern lati-
tudes are small, insect-feeding forms, but in the
tropics occur the centipedes, the larger species FIG! no.— A
of which are said to be extremely venomous.

Usually the Chilopods are associated with another group,
the DIPLOPODA (thousand-footed worms), as a class or sub-
class, Myriapoda, but the differences between them are too
great for this. The Diplopods have but three segments in
the head, and, after the first three, each segment of the
body bears two pairs of legs, while the reproductive organs
open far forward. The thousand-legged worms live in

234 ELEMENTS OF COMPARATIVE ZOOLOGY.

moist places, where they feed upon decaying vegetable
matter. They are harmless forms, but several species se-

FIG. 111.— A Diplopod (Spirostrephon), showing the two legs to a segment.
From Packard.

crete a strong-smelling substance, which protects them
against their foes.

LABORATORY WORK: EARTHWORM.

The student should be supplied with a live earthworm,
and also with a specimen killed by placing in a dish in
which is a bit of cloth dampened with chloroform, the
whole being covered so as to prevent escape of the fumes.
After death the worm should be pinned out straight, and
hardened in plenty of alcohol.

Is the body cylindrical throughout? Is it bilaterally
symmetrical ? Can you distinguish between dorsal and
ventral surfaces ? Is the body apparently made up of seg-
ments ? Are they all essentially alike ? Draw the worm
through the fingers; does it move with equal ease in both
directions ? Examine the head end for the mouth ; is it dorsal
or ventral in position ? Is the ring (preoral lobe) in front
of the mouth complete ? How is it attached to the next
ring ? Examine the surface of the body with a lens for
bristles (setae). Do you find them on each segment ? How
are they arranged on the segment ? Where is the vent ?
About one fourth the length of the body from the anterior
end notice that certain rings are enlarged and swollen, and
that the lines between the segments tend to be obliterated.
This is the clitellum. How many segments are included
in it ? The clitellum is a glandular structure to secrete
the cases or cocoons in which the eggs are laid.

Hold a living worm near the anterior end. Does it pro-
ject a proboscis from the mouth ? Look on the back and
see the red dorsal blood-vessel showing through the skin.

235

236 ELEMENTS OF COMPARATIVE ZOOLOGY.

Study the segments in front of the clitellum, looking for
openings of the reproductive organs on the ventral surface.
How many pairs of these do you find, and on what seg-
ments are they ? Leave a dead worm in water for several
hours; can you separate from it an external transparent
cuticle ?

Draw a worm from the side, being careful to get in the
right number of segments, back to the posterior end of the
clitellum, and bringing out as many of the points dis-
covered as possible.

Pin a worm, which has been in alcohol, with pins pass-
ing through the preoral lobe and the hinder end of the
body, in a dissecting-pan. With the scissors open the
dorsal wall of the body from just behind the clitellum to
the anterior end, taking care to cut through only the dor-
sal wall. It is best to make this cut just a little to one
side of the median line. As you start to lay open the body,
notice the partitions (dissepiments) running in from the
body-wall and holding the parts together. Do these dis-
sepiments correspond in position to the external rings or
to the spaces between them ? Do they divide up the body
into a series of body-cavities ? Do the cavities of the right
side correspond in position with those of the left ?

Cut the dissepiments with the scissors, and pin out the
body -wall. This exposes the digestive tract lying in the
axis of the body. In it make out the following regions :
(1) A pear-shaped enlargement (pharynx) occupying about
half a dozen segments in front. Notice the muscle-fibres
going to the pharynx from the body-wall. (2) A narrower
tube (oesophagus) leading back through about ten segments
from the pharynx, and expanding about segment 16 into
(3) a heart-shaped crop, which in turn is followed by (4) a
second enlargement (gizzard) of about the same size. (5)

DISSECTION OF EARTHWORM. 23T

From the gizzard the intestine can be traced back to the
vent.

Lying above the alimentary tract is the dorsal blood-
vessel. From it are given off transverse vessels. Are
these in pairs ? Do they correspond to the segments in
number and position ? Are any of them enlarged ? In
what direction do they go ? Can you find (by tipping the
alimentary canal) a ventral blood-vessel beneath ? Do any
vessels connect with it ?

On the top of the anterior end of the oesophagus are two
pear-shaped bodies, the brain. Can you find nerve-cords
(commissures) leading downward and backward from the
brain ?

Arising from either side and extending upwards so as
to overlap the esophagus above are lobes of the repro-
ductive organs. Draw the parts so far made out, viewed
from above, and then cut through the pharynx and care-
fully lift up the alimentary canal as far back as the be-
ginning of the intestine, cutting it off at that point. Now
sketch the reproductive organs, lifting them up to see if
any organs occur beneath.

Examine the cut end of the intestine. Is the inside a
circular tube ? On the dorsal surface of the intestine see
the dark green chloragogue organ (a digestive gland, sup-
posed to be something like liver or pancreas in its action).

On the middle line of the floor of the body find the
ventral nerve-cord, with its numerous enlargements (gan-
glia). Are these latter equal in number to the somites ?
Do they occur in or between the somites ? Trace the
nervous system forwards, and find out how it Connects with
the brain. Draw the brain and twenty ganglia of the ven-
tral chain connected together. Just outside the ventral
nervous cord find in each segment (except a few anterior)

238 BLSmNTS Off COMPARATIVE ZOOLOGY.

a minute coiled tube (nephridium). These are the kidneys
of the worm, and each opens separately to the exterior
between the rows of setae.

COMPAEISONS.

With columns for Vertebrate, Arthropod, and Earth-
worm, answer the following questions :

(1) Are paired appendages present ?

(2) Do you find an evident body-cavity ?

(3) Is the alimentary canal supported by a mesentery ?

(4) Is the greater part of the nervous system dorsal or
ventral in position ?

(5) Is there any segmentation visible from the outside ?

(6) Is there anything which you could call internal seg-
mentation ? If so, what parts are repeated ?

(7) Is there an external cuticle ?

(8) Does the alimentary canal pass through the nervous
system ?

(9) Is there an internal skeleton ?

(10) Bumming up these points, what two forms do you
consider to be most similar ?

(11) Draw transverse diagrams of a vertebrate, an
arthropod, and an earthworm, showing skeleton, body-
cavity, dorsal vessel, aorta, ventral vessel, heart, kidneys,
nervous system, appendages, etc., as far as you find them in
each. Which two seem most alike ?

(12) Can you better bring all three diagrams into har-
mony by turning any one wrong side up ? If so, what one
must be turned ?

(13) Can you recall any such connection, in any verte-
brate, between the dorsal and ventral blood-vessels, as you
find in the earthworm ? If so, where and what ?

ANNELIDA (SEGMENTED WORMS).

The earthworm may be taken as a representative of this
group, the members of which have a marked external seg-
mentation of the body, but which lack jointed appendages.
They also have a dorsal brain and a ventral ganglionic
nerve-cord; the ganglia, like all other parts, being segment-
ally arranged. There are nephridia in each segment, while
the circulatory system consists of a dorsal vessel in which
the blood goes forward, a ventral vessel in which the flow
is towards the tail, and segmen tally arranged transverse
vessels which connect the two. The annelids are divisible
into several groups or orders, only two of which need be*
mentioned here.

ORDER I. — CH^ETOPODA.

In these the body-cavity is well marked, as in the earth-
worm ; and each segment of the body bears setae, which
serve as locomotor organs. In some (OLIGOCH^ET^:) the
bristles are comparatively few, and they arise directly from
the body-wall, while appendages of all kinds are lacking.
A few of the Oligochsetes live in the sea ; more occur in
fresh water, but the great majority are terrestrial, and are
familiarly known as "earthworms" or " angleworms,"
the latter name being given from their use in baiting fish-
hooks. The earthworms burrow in the soil, feeding upon
decaying vegetable matter in the earth. They swallow
earth and all, and come to the surface to deposit their well-

.339

240 ELEMENTS OF COMPARATIVE ZOOLOGY.

known castings. In this way they work over the soil, and
are of immense value to agriculture, as Darwin has shown in a
most interesting volume on these lowly forms. Our earth-
worms are moderate in size, but in Africa, South America,
and Australia giant earthworms, four to six feet in length
and an inch in diameter, occur.

In other Chaetopods (POLYCH^T^;) the bristles are
numerous in each segment, and
are borne on fleshy outgrowths
(parapodia) from the sides of the
body. The head bears fleshy
feelers or tentacles, there are fre-
quently horny jaws in the mouth,
while eyes are commonly present
— structures which are lacking in
the Oligochaetes. The Poly-
chaetes are largely marine, and Fl?- 112.— Anterior end of

> * clam- worm (.ZVereis),showing

occur in large numbers burrowing jays, eyes, tentacles, and

bristle-bearing parapodia.

in the mud of the shores or sea-
bottoms. Many of them are brightly colored, and marine
worms are among the most beautiful objects in nature.
They are largely carnivorous, and some of them are, to the
associated life, terrible animals of prey.

ORDER II. — HIRUDIKEI (Leeches).

The leeches have the body-segments ringed, so that one
examining the outside would conclude that there were
more segments than are really present. There are no bris-
tles on the segments, but the hinder end always bears a
sucking disc, while usually there is a second sucker around
the mouth. The body-cavity is not distinct. There are
two great groups of leeches — those with jaws around the
mouth, and those which lack jaws.

WORMS. 241

The jawless leeches are aquatic, and occur in fresh water ;
more rarely in the sea. They live largely upon fishes,
feeding upon the mucus covering the body. The jawed
leeches have three jaws radiating from the mouth, and each
jaw has its edge finely toothed. With these jaws they are
able to cut the skin of vertebrates, upon the blood of which

FIG. 113.— A tube-inhabiting Polychaete (Amphitrite). At the upper end are
the tentacles, and just below to the left the gills.

they feed. This blood-sucking habit led to the use of
leeches in medicine in those days when it was believed that
if a man were sick his cure could be effected by still fur-
ther weakening him. Most of the jawed leeches live in
fresh water, but in the warmer parts of the Old World land
leeches occur in the moist forests, and these form almost
intolerable pests.

VERMES (WORMS).

Under this heading are included a large number of forms
commonly known as worms, but which are incapable of
strict definition. In general it may be said that they have
elongate bodies, without internal skeleton, without appen-
dages, with a marked bilateral symmetry, and distinct dorsal
and ventral surfaces. Further than this we can hardly go
in a definition which will at once include all worms and at
the same time not include other forms. Some of these
worms are terrestrial, some aquatic, and some live as para-
sites on or in other animals. Omitting a number of micro-
scopic forms and small groups, we may divide the Vermes
into four classes : Plathelminthes or flat- worms, Nemathel-
minthes or round-worms, Annelids or segmented worms, and
Molluscoidea.

CLASS I.— PLATHELMINTHES (FLAT-WORMS).

In the flat-worms the body is flattened, is without appen-
dages or skeleton; the mouth when present is on the ven-
tral surface, and no vent occurs. There is no body-cavity
aside from the digestive tract. Some are leaf-like, others
are more elongate, and a very few are nearly cylindrical.
The free-living and some of the parasites have an alimen-
tary canal, but to this there is only a single opening, the
mouth. Aside from the digestive cavity, the body is solid
throughout, there being no such body-cavity as we have seen
in all forms hitherto studied. The nervous system consists
of a centre or ' ' brain, " always in the dorsal front portion of
the body, from which nerve-cords run to various parts, there

343

WORMS.

243

being usually two long cords which run backwards in a
nearly parallel direction. Eyes may be
present on the dorsal surface near the
brain.

The capacity of reproduction by di-
vision is very well developed in these
forms, especially in the non-parasitic
groups. In these a second mouth will
appear at about the middle of the body,
then the body will constrict in front of
the new mouth, and finally will divide
into two worms. Not infrequently a
new mouth will appear in each of the
halves before the division is complete, so
that we can have a chain of four or even
eight animals connected together, and
all the result of division of a single pa-
rent. Besides this reproduction by di-
vision, reproduction by means of eggs
occurs. The Plathelminthes are divided
into three orders — Turbellaria, Trema-
toda, and Cestoda.

OKDEK I. — TUKBELLAKIA.

Fiq. 114. — Process of
division in Microsto-
•nnim. After Graff, wi,

cessive

planes of division.

These are small free-living forms
which occur in fresh or salt water, and
occasionally in moist earth. They are
common in our ponds and streams,
crawling over the bottoms or upon submerged sticks and
stones. They have a mouth and digestive tract.

OKDER II. — TREMATODES.

Like the last, these have mouth and digestive tract, but
they differ in being parasitic on or in other animals, and in

244 ELEMENTS OF COMPARATIVE ZOOLOGY.

having sucking discs (from one to many) developed upon the
body. Some of them become serious pests. One form, the
liver-fluke, produces the disease known as " liver-rot" in
sheep. Other forms occur in man, especially in the tropics,
being introduced in drinking-water. They cause serious
sickness.

ORDER III. — CESTODES (Tapeworms).

The Cestodes are all parasitic in other animals. They
differ from the Trematodes in the complete absence of
mouth and digestive tract, since they absorb their nourish-
ment through the skin. Usually they have ribbon-like
bodies, and hence are commonly known as tapeworms. At
the anterior end are the means of attach-
ment (hooks or suckers) by which the
animal attaches itself to the lining of
the intestine of its host, while usually
the body becomes broken up into a se-
ries of joints or proglottids. There is
continually a formation of new proglot-
tids near the head, while the older pro-
glottids, loaded with eggs, drop off and
are carried out with the waste of the
digestive tract. These tapeworms ob-
tain entrance into the body in the food,
man usually receiving his from raw or
partially cooked beef or pork, and more
rarely from fish. The proglottids and

FIG. 115.— T a p e w o r m

(Tmnia) with progiot- eggs, passing from the body, may fall

tids from different re-
gions of the body, /i, where they may be eaten by cattle or

head enlarged. . J. n ^ . J

swine. Inside their bodies, they undergo
partial development in the muscles, and then when taken
into the human body they complete their development.

WORMS.

245

Other vertebrates than man possess tapeworms. The cat
gets hers from the mouse, the dog his from cattle and rab-
bits, the sharks from other fish, etc.

CLASS II.— KEMATHELMINTHES.

In these round-worms the body is long and cylindrical,
and is covered with a firm cuticle. Usually both mouth
and vent are present, but there is never any division of the
body into segments. Some live freely in the water, some
are parasitic in plants, and some infest animals. Among
them are to be mentioned the vinegar and paste "eels,"
which are occasionally found in these substances. Here,
too, belong the " horsehair- worms," which are frequently
believed to be horsehairs converted into worms by soaking
in water. These hairworms are at one period of their
lives parasitic in insects, especially in grass-
hoppers. Some of the roundworms occur
as parasites in man. The stomach- worms
and pinworms of children belong to the
round-worms, and these obtain entrance to
the human system only as the exceedingly
minute eggs are taken into the stomach
by way of the mouth.

Worst of all the parasitic Nemathel-
minthes is the Trichina, which when adult
is scarcely an eighth of an inch in length,
and yet which not infrequently causes
death. Man is usually infected with them
by eating raw or partially cooked pork. In
the pig they first appear in the alimentary
canal, where the mothers bring forth myri- encysted in hul

, „ . . . man muscle. Af-

ads oi living young. These young burrow ter Leuckart.
outwards into the muscles and there enclose themselves in a

2±6 ELEMENTS OF COMPARATIVE ZOOLOGY.

capsule, where they remain indefinitely. If this infested
flesh be eaten raw, the capsule is dissolved by the stomach,
the young are soon born, and they in turn wander through
the muscles, and, when numerous, this boring into the flesh
causes severe sickness, and even death. The worst epidemic
of this disease, known as trichinosis, on record occurred
near Emmersleben, Saxony, in 1884. From one pig three
hundred and sixty-four persons were infected, and of these
fifty-seven died within a month. The moral which we
have to learn from tapeworms and trichina is that our
beef and pork should never be eaten raw, but should be
cooked through.

CLASS III.— ANNELIDA (p. 239).
CLASS IV.— MOLLUSCOIDEA.

Under this heading are grouped a few forms, which in
time past were considered as Molluscs (see p. 269), but
which are now known to have only superficial resemblances
to the clams, etc. There are two orders of these Mol-
luscoids.

OKDER I. — POLYZOA (Moss Animals).

The Polyzoa are individually small, but by budding they
form colonies of considerable size, the tentacles of the in-
dividuals giving the colony a mossy appearance. These
tentacles surround the mouth in a more or less modified
circle, and by them the animals obtain their food. The
body is sac-like, and the alimentary canal is bent upon
itself so that the vent is near the mouth. Many of the
colonies secrete an external skeleton, which may be horny
or calcareous. Most of the Polyzoa are marine, but a few
occur in fresh water.

WORMS. 247

ORDER II. — BRACHIOPODA (Lamp shells).

From the fact that the Brachiopoda possess a bivalve
shell, these forms were formerly included among the
molluscs near the clams. A little examination, however,
shows that the resemblance between them is but slight.
The two valves of the Brachiopod are unequal in size, and
are dorsal and ventral, rather than right and left, as in the
clams. Near the point where the two parts (valves) are

FIG. 117.— Diagram of a Brachiopod. b, tentacles around mouth, m ; i, in-
testine ; the shell black, the stalk to the right.

hinged together there is usually an opening * in the larger
valve through which a fleshy peduncle or stalk projects, by
means of which the animal is fastened to some support.
Inside the valves, which can be closed by muscles, are the
principal organs. Near the mouth are found a number of
delicate tentacles (much like those of the Polyzoa), the disk
which bears them being frequently rolled into a spiral.
The alimentary canal is bent, but a vent is occasionally
lacking.

The Brachiopods are all marine. There are few in
existing seas; but they are among the oldest inhabitants,
for the shells are found fossil in all rocks from the oldest
down to the present time.

* In some the peduncle extends from between the valves instead of
having a special opening.

THE CLAM: LABORATORY WORK.

For this purpose the student can use either the fresh-
water clam or the long clam of the Northern sea-shore.
For the study of the nervous system clams which have
been a few days in alcohol are better than fresh specimens.

EXTERNAL.

Notice the shell ; of how many parts or valves is it com-
posed ? Are the valves equal in size ? They are joined by
a hinge, dorsal in position, and each valve has a promi-
nence (umbo) near the hinge. On each valve see the lines
of growth running parallel with the free margin of the
shell. Draw a line from the umbo to the free margin of
the shell, perpendicular to the latter. This divides the
valve into unequal parts, and of these the smaller is the
anterior. Now with these facts tell which is the right
and which the left valve of the shell. Draw one of the
valves, inserting all points made out.

INTERNAL.

Remove the left valve from the clam by inserting a knife
at either end close to the shell, and cutting the muscles
which lie near the hinge-line. Then carefully remove the
valve, seeing that all fleshy portions are left in the right
valve. If properly done, this will leave the animal covered
with a thin membrane, the mantle. Projecting through
this, near the dorsal line, are the adductor muscles, which
keep the shell closed, and which were cut in removing the
valve. According to their position, these are known as
the anterior and posterior adductors. Are the edges of the

248

DISSECTION OF CLAM. 249

mantle thickened ? Are the mantles of the right and left
sides united anywhere along the free margin of the shell ?

Cut through the mantle near its ventral edge and fold
hack. Is it free back to the hinge line ? Cutting through !
the mantle opens the mantle or branchial chamber. In
this several structures are to be noticed. Arising from the
side of the body are plaited folds (how many ?), the
branchiae or gills. Are there branchiae on the right side
as well ? Extending downward between the gills is the
soft abdomen, terminated at the anterior ventral angle by a
more solid foot. In front, just ventral to the anterior
adductor, are two pairs of fleshy flaps, the labial palpi,
and where they meet at their junction with the body is
the mouth. At the posterior end of the animal look for
two fleshy tubes (siphons) formed by the edge of the man-
tle. * Run a wire in each from the outer end, and see where
it appears inside the shell. The ventral siphon is the in-
current or branchial siphon; the dorsal is the excurrent or
cloacal siphon. Draw the parts so far made out.

Just beneath and behind the hinge is the heart, its
position in the living animal being readily seen by its
pulsations. Carefully cut into the chamber in which it is
situated and make out a central ventricle, rather dense in
texture, and leading to it on either side a delicate tubular
auricle which brings the blood from the gills to the
ventricle. Notice the intestine passing through the ven-
tricle. Just in front of the posterior adductor is the dark
organ of Bojanus or kidney. Draw the parts made out.

The alimentary canal and the nervous system are best
followed in specimens which have been in alcohol a few
days. In such a specimen insert a probe into the excur-

* These are small in the fresh-water clams, but are greatly de-
veloped, and form the part commonly but erroneously called the
"head," in the long clam.

250 ELEMENTS OF COMPARATIVE ZOOLOGY.

rent siphon. Notice that it does not enter the branchial
chamber. Cut through the thin membrane between the
gills of the right and left sides, posterior to the abdomen.
This lays open the cloacal chamber into which the probe
extends. In the dorsal wall of this chamber, just below
the posterior adductor, see a pinkish or orange body, the
parieto-splanchnic ganglia. From this trace backward
nerves which curve forwards along the base of the gills.
Also trace two nerves forward, one on either side of the
body, until they meet in a pair of cerebral ganglia just
above the mouth. Are the two cerebral ganglia connected
directly with each other ? From the cerebral ganglia trace
a pair of nerves downward to the pedal ganglia lying
between the abdomen and the foot. Sketch the nervous
system.

Beginning with the intestine where it leaves the heart,
trace it posteriorly. On which side of the posterior
adductor does it pass ? Where does it empty ? Trace it
forward from the heart, carefully picking away the sur-
rounding tissue with the needles, into and through the
abdominal mass, and plot the coils which it makes. It
will be found to pass into a rather large saccular stomach,
on either side of which is the dark-green liver.* Trace
the oesophagus from the stomach to the mouth.

Take a clam which has been hardened for a couple of
weeks in strong alcohol or formol. Cut it transversely in
slices a quarter of an inch thick, using a sharp scalpel for
the purpose. Draw the sections and name all the parts
found. This can be done easily if the previous dissection
has been intelligently done.

* In a pocket of the stomach in the long clam will be found 'a
structure of unknown function, the crystalline style, transparent, an
inch or more in length.

THE OYSTER.

Oysters in the shell should be used. Find the hinge as
in the clam, Do you find lines of growth ? In the same
way as in the clam distinguish anterior and posterior, right
and left valves. Is the right or the left valve convex ?

Break the shell at the hinder end and, inserting a knife,
cut the adductor muscle so as to remove the left valve.*
How many adductors do you find ? Is the mantle edge
thickened and united as in the clam ? Do you find any
siphons ? What other peculiarities do you find in the edge
of the mantle ?

Remove the mantle from the left side and trace the parts.
How does the foot compare with that of the clam ? How
do the palpi differ ? How many gills ? Which adductor —
anterior or posterior — is absent ? Find the heart, just in
front of the adductor. Lay open the pericardium. How
many auricles and how many ventricles are present ? Trace
the alimentary canal through the body from the mouth to
the vent. How is it related to the heart ?

* If you do not know where the adductor is, study a shell already
removed and find the scar made by it.

251

SQUID: LABORATORY WORK.

EXTERNAL FORM.

The head, separated from the body by a "neck," bears at
its anterior end a circle of tentacles ; how many ? Are all of
these of equal length ? If not, which pair is the longer ?
On the side of the head are the eyes; behind the eye is a fold
of the skin, the olfactory organ. The body is surrounded
with a mantle, bearing at the posterior end a pair of large
fins. Is the mantle joined to the body all around ? If not,
where is it attached ? Projecting from the mantle opening
is the end of a fleshy tube, the siphon. The side of the
body on which the siphon occurs is usually called the ven-
tral side.

Sketch the squid from the side, showing these points, not
omitting the color spots (chromatophores) .

Examine the tentacles more carefully. On their inner
surfaces see the stalked suckers. Are they sim ilarly arranged
on all the arms ? Examine a sucker with the hand-lens,
making out the fleshy lip, the horny hooks, and a fleshy
bottom (piston) in the central cavity. Sketch a sucker,
considerably enlarged.

INTERNAL STRUCTURE.

Place the squid in the dissecting-pan, siphon uppermost.
Cut the mantle longitudinally a little to one side of the
middle, beginning at the free edge and carrying the incision
to the end of the body. This lays open the mantle chamber.

253

DISSECTION OF SQUID. 253

Lift the cut edges carefully, looking for the median mantle
artery running from the body to the mantle. Pin out the
mantle and make out the following points :

The siphon; notice its inner end; just behind it is the
end of the intestine. On either side of the siphon are the
siphonal cartilages, grooved on the surface. Look on the
edge of the mantle and find a ridge. Close up the mantle
and see how the parts interlock.

Behind the siphon, at either side of the body, are the
gills. What structure have they ? Can you see any vessels
connected with them ? Follow the intestine back from the
vent. Is it free, or is it tied down to the underlying struc-
tures ? Notice that it passes across a dark-colored sac —
the ink-sac. Some distance behind the gills see a vessel,
the post-cava, coming from the side of the mantle forward
to the body.

The other features vary considerably accordingly as the
specimen is male or female. In the female the hinder part
of the body is occupied with eggs, while upon that part
between the gills is the large transversely striated nida-
mental gland.* When these are carefully removed the
structures are much as in the male.

On either side of the intestine, a little behind the ink-sac,
is the small opening of the kidney; the kidneys themselves
stretch back behind the base of the gills. They are irregu-
lar in shape. When they are removed f there will be seen
in the median line the systemic heart. Behind, it gives
off an arterial trunk, which soon divides to form the median
mantle artery already noticed, and the lateral mantle
arteries which follow the postcavse. On either side it

* These secrete the capsules in which the masses of eggs are laid.
\ Cut through the thin wall of the kidney just behind the gill,
pull off the thin skin, and wash away the granular contents.

254 ELEMENTS OF COMPARATIVE ZOOLOGY.

receives a branchial vein, coming from the gill; while in
front it gives off an anterior aorta, which runs forward.

Look on the side of the gill nearest the mantle and see
the branchial artery. Trace it towards the middle line
and find the branchial heart, just behind the branchial
vein. This receives the blood from the postcavae already
noticed, and also from a precava which comes from in
front through the kidney, but is not so easily traced. The
course of the circulation may be briefly described as fol-
lows: The blood is forced to all parts of the body by the
systemic heart. After supplying these regions it collects
in the pre- and postcavas and is brought to the branchial
hearts, which pump it through the branchial arteries to
the gills. From the gills it returns to the systemic heart
by way of the branchial vein to repeat its circuit. Sketch
all parts made out.

Carefully trace the intestine backwards from the vent,
removing the systemic heart and the remains of the kid-
neys. Just behind the level of the systemic heart it will
be found to enter the thick- walled, muscular stomach.
This stomach gives off, behind, a large, thin-walled blind
sac, which extends far back into the body mass. Close to
where the intestine leaves the stomach the oesophagus
enters it. Trace the oesophagus forward to the region of
the neck, ~but not farther at present. In its course it can
be followed through the liver. Sketch the alimentary
tract as if viewed from the side, inserting intestine, ink-
sac, stomach, blind sac, liver, and oesophagus, leaving
room for the anterior end of the latter to be inserted later.

With a single stroke of a sharp scalpel split the head
longitudinally, making the cut as nearly as possible in the
median plane. In the section thus made the anterior end

DISSECTION OF SQUID. 255

of the alimentary tract and the central part of the nervous
system can be easily studied.

Just inside the mouth, which is placed in the centre of
the circle of arms, is the oval buccal mass, which is only
slightly connected with the rest of the head. In this find
the two horny jaws, black at the tips, and shaped some-
thing like the beak of a parrot. Do these jaws work in a
vertical or in a horizontal plane? The cavity of the
mouth lies inside these jaws and passes nearer to the dorsal
jaw. Just inside the mouth-cavity is a pocket given off
on the ventral side, in which will be found a horny lingual
ribbon, covered with minute horny teeth. Could this
ribbon be used in rasping the food after it had passed the
jaws ? Notice that the bulk of the buccal mass is made
up of muscles arranged to move jaws and lingual ribbon.

From the buccal mass trace the oesophagus backward to
the point where it was left in the previous dissection. Do
not cut at first in tracing it, as you would be apt to injure
other portions. If the section of the head be in the
median plane, the course of the oesophagus will be easily
followed without dissection. If not, it can be traced later
after the nervous structures have been studied.

A little back of the buccal mass some harder, cartilage-
like structures will be seen in the cut surface of the head.
These form a brain capsule, resembling in some respects
the vertebrate skull. In the dorsal side of this will be
found a large centre, the cerebral ganglion, while on the
ventral side two somewhat smaller ganglia occur. The
anterior of these is the pedal ganglion, and from it nerves
can be traced running into the arms. The posterior is the
visceral ganglion. Between the cerebral on the one hand
and the pedal and visceral ganglia on the other passes the
oesophagus. In one half of the head demonstrate by dis-

256 ELEMENTS OF COMPARATIVE ZOOLOGY.

section that these ganglia are connected. Except that the
ganglia are much closer together and the connections cor-
respondingly shortened, are the relations the same as in
the clam ?

Just ventral to the visceral ganglion is an enlargement
of the cerebral capsule; this is the ear. Cut into this and
notice that it has an irregular cavity. Is there a similar
structure on the other side of the head? Sketch the
section of the head, showing the ganglia, jaws, lingual
ribbon, oesophagus, and ear, in the drawing already made
of the alimentary tract.

Split one half of the head in a horizontal plane, having
the section pass through the middle of the eye. In the
section thus made study first the eye itself. This is covered
externally with a transparent cornea, and inside contains
two chambers, separated from each other by the solid lens.
The outer chamber in turn is partially divided by a circular
fold, the iris. The inner chamber is bounded internally
by the retina, the outer surface of which is marked by a
thin layer of black pigment. Behind and dorsal to the eye
is the optic ganglion, bounded posteriorly by a cartilage wall.
Trace the connections of the optic and cerebral ganglia.

Cut into the dorsal region of the mantle from the outside
and find the horny pen. Continue the cutting so that it
may be taken out. Sketch it.

COMPAKISONS.

With two columns, one for oyster and clam and one for
squid, answer the following questions :

(1) Is there a distinct head ?

(2) Are there cephalic tentacles ?

(3) Is there a bivalve shell ?

DISSECTION OF SQUID. 257

(4) Is the siphon, if present, a part of the mantle ?

(5) Did you find any eyes ?

(6) Are adductor muscles present ?

(7) Is there a bivalve shell ?

(8) Are the gills leaf -like or plume-like ?

(9) Are there jaws ?

(10) Is there a lingual ribbon ?

(11) Are there branchial and systemic hearts ?

(12) Is there an ink-sac ?

ACEPHALA.

In the Acephala, as the name implies, there is no distinct
head. The ootiy is flattened from side to side, and the two
sides are almost exact repetitions of each other. On either
side of the body there is a strong outgrowth of the body
wall, the mantle, which secretes on its outer surface the
shell, which is divided in the median line so that two halves
or valves result. Between the mantle folds and the body
is the mantle-chamber, and into this on either side there
usually hangs down a pair of leaf-like gills.* From the
lower surface of the body projects a muscular foot. 'With
these features the animal presents a marked resemblance to
a book in which the valves represent the covers; the mantle,
gills, body, and foot, seven leaves.

Where the two valves are hinged together there is an
elastic ligament which tends constantly to open the valves,
which are closed by means of adductor muscles extending
from one valve to the other. Usually there are two of
these muscles — anterior and posterior, but the anterior of
these may disappear.

In some, as in the oyster, the mantle edges are free from
each other throughout their extent; but not infrequently
they become fused in places, leaving openings between.
At the posterior end this fusion frequently results in the
formation of two tubes or siphons connecting the outer

* It is not necessary here to include the gill features of Cuspidaria,
Silenia, etc,

358

ACEPHALA. 259

world with the mantle-chamber. When these siphons
become greatly developed there are connected with them
strong retractor muscles, to
draw them back at times of
danger, etc. All of these
muscles — adductors, retract-
ors, etc. — leave their impress
on the shell, so that the stu-
dent, with the shell alone,
knows of some of the struc-

of thp soft mrts Fl^' 1^8 ~~ Insid® of. Wvalve shell

1 Wie bOlt pdl Lb. showing muscular impressions, rt,

ia rlrnwn infn tVin anterior adductor ; p, posterior ad-
IS arawn into ine ductor ; ,x, siphonal muscle.

mantle-cavity by means of

very minute hair-like structures (cilia) which cover the
gills and other parts. These cilia are in constant motion,*
and thus currents of water are produced, flowing always in
one direction. This water brings oxygen to the gills and,
through them, to the blood. It also brings minute animals
and plants. These are passed on to the labial palpi, which
are similarly covered with cilia, and from these organs the
cilia force the food into the mouth.

In the nervous system we always find cerebral, pedal, and
visceral ganglia, the first being above, the others beside
or below, the alimentary canal. Ears are present, connected
with the pedal ganglia; and eyes may be present, either
upon the edges of the mantle or at the tips of the siphons.

The alimentary canal is always provided with stomach
and liver. Connected with the stomach a blind sac fre-
quently occurs, and in this there may be a peculiar trans-
parent rod, the crystalline style, of uncertain use. The

* The teacher should demonstrate this ciliary action under the
compound microscope.

260 ELEMENTS OF COMPARATIVE ZOOLOGY.

intestine goes from the stomach first towards the foot, then
mounts towards the hinge-line, and frequently passes through
the ventricle of the heart.

The heart consists of a single ventricle and usually two
auricles, but sometimes there is but one of the latter. The
heart is situated in a chamber (pericardium), which is
connected by means of a pair of convoluted kidney tubules
(organ of Bojanus) with the exterior.

A thoroughly satisfactory classification of the Acephala
has not yet been worked out. Possibly the best is that
based upon the structure of the gills, but a more convenient
one for our purposes is based upon the presence or absence
of a siphon.

ORDER I. — ASIPHOKIDA.

The edges of the mantle free ; no siphon present. Most
prominent of this order are the oysters. These are all
marine, species being found in all but the colder seas. In
these forms the animal lies upon one side, and there results
an inequality of the valves. On our east coasts oysters
extend from the Gulf of Mexico to Cape Cod. Further
north (except in the Bay of Chaleur) they are not found
native, but are "planted." The centre of the oyster
industry is Baltimore. In 1894 the oyster-fishery of the
United States amounted to over $16,000,000.

In the scallops the shell is fluted, and the valves may be
unequal or similar in shape. These molluscs can swim
freely by rapidly opening and closing the valves of the shell ;
and they are further noticeable from the fact that around
the edge of the mantle are a series of rather complicated
eyes. The "scallops" of the markets are the adductor
muscles of these molluscs, In the pearl-oysters the inner

ACEPIIALA. 261

layer of the shell has a pearly appearaoce, and these forms
also produce, like some other molluscs, the precious pearls.
These pearls are really the shell-forming secretions of the

FIG. 119.— Scallop (Pecten irradians). From Binney's Gould.

mollusc around some foreign body, and they receive their
beauty from the way in which the shell is deposited around

FIG. 130.— Salt- water mussel (Mytilus edulis).

the centre. Fresh-water mussels, to be referred to a few
lines below, also form pearls of value. The shell of the
pearl-oyster also has its value, for it furnishes the mother-

262 ELEMENTS OF COMPARATIVE ZOOLOGY.

of-pearl used for knife-handles, for inlaying, etc. The
pearl-oysters occur in the Indian Ocean, and also in the
Bay of Panama.

The salt-water mussels, so abundant on the mud flats all
along Northern shores have a peculiar gland in the foot
which secretes strong silky threads (byssus) by which these
animals anchor themselves. The common species, which
occurs both in Europe and New England, is called the edible

FIG. 121. — Quahog (Venus mercenaria) , with foot and siphons extended.

mussel; but not infrequently severe sickness follows its
use as food. The fresh-water mussels are especially abun-
dant in America, the Mississippi basin being their centre.
They are useless as food, owing to their strong taste.
There are possibly a hundred species of these forms in
America; over six hundred so-called species have been
described. In their siphonal structure they form a transi-
tion to the next group,

ACEPHALA.

263

ORDER II. — SIPHONATA.

In these the margins of the mantle have grown together
posteriorly into a double tube or siphon, and accordingly as
this siphon is developed the an-
imal can burrow below the sur-
face and still obtain its necessary
supplies of water and food; for
these tubes can reach the surface,
and through them there is a
continual flow of water — inward
through the ventral, outwards
through the dorsal, passage.

The great majority of bivalve
molluscs belong here, but there
are comparatively few of general
interest. The largest of all
clams, the giant clam of the East
Indies, with shells sometimes
weighing over 300 pounds, be-
longs here, as do the quahog and
the long clam, which are used as
food. One of these forms, the
Teredo or ship-worm, is a serious
pest, as it bores in wood, destroy-
ing the piles of wharves, the
bottoms of boats, etc. Their
burrows run to long distances,
but all their food and water
must be drawn in through the l%U8ii£CI^B£SF-fB
siphons. One great inundation ££e°sYshonsW the currents m
in Holland at the beginning of

the last century was directly due to the borings of these
forms,

CEPHALOPODA (SQUID AND CUTTLEFISH).

The Cephalopods derive their name from the fact that
the circle of tentacles or arms around the mouth (i.e., on
the head) was compared to the foot of other molluscs. Later
investigations show that these tentacles represent but a part
of the foot, the siphon also belonging to the same category.
These same arms, which are either eight or ten in number,
bear sucking organs by means of which these animals hold
fast their prey. In only the pearly nautilus are the arms
lacking, and here they are replaced by about a hundred
smaller organs.

The head, which is separated from the body by a distinct
neck, bears a pair of eyes — simple in the nautilus, but al-
most as complex as those of man in the other forms. In
these more highly developed eyes there is retina, lens, iris,
cornea, and cavities resembling those occupied by the
aqueous and vitreous humors. Yet the resemblances are
superficial; the structures are in reality totally different.

The mantle is connected with the body in the region of
the so-called back. Below, it encloses a good-sized mantle-
cavity, open in front. It is very muscular, and the open-
ing about the neck can be closed at will, so that the only
connection between the mantle-chamber and the outside
world is through the tube of the siphon. If one of these
animals fill its mantle with water, close the neck opening,
and then force out the water by contracting the mantle,
the water will stream from the siphon in a strong jet, which

364

CEPHALOPODA. 265

by its reaction forces the animal in the other direction.
This apparatus forms with many, and especially with the
squid, the chief organ of locomotion, and in these the tip
of the siphon can be bent in any direction, so that the ani-
mal may go forwards, backwards, etc., according as it
wishes.

In the mantle-cavity are one or two (Nautilus) pairs of
feather-like gills, and into the same chamber empty the
ducts of the kidneys and reproductive organs, as well as
the intestine, and the ink-sac connected with it. This last
organ secretes a dark-colored fluid, which when discharged
into the water makes a cloud, and thus the animal is en-
abled to escape unseen. From this ink the pigment sepia
and some kinds of India-ink are manufactured.

Imbedded in the skin of the mantle are pigment spots or
chromatophores, which are interesting from the fact that
they can be enlarged or contracted by the nervous system.
When enlarged they nearly touch each other, and thus give
the body their general hue (red). When contracted they
appear as minute black points, while the general body color
(translucent white) then prevails. As a result we have in
these animals a power of color-change far more striking
than that of the chameleons.

Most living Cephalopods have no external shell. Inside
of the back, however, is a shell — the pen — which may be
either feather-shaped and horny, or broader, thicker, and
calcareous. In this last condition it furnishes the " cuttle-
bone" so often given to cage-birds. The paper nautilus
has a shell which is formed only by the female ; it is secreted,
not by the mantle, but by one pair of the arms, and this
shell is really a protection for the eggs. In the pearly nau-
tilus, on the other hand, there is a true shell, which is
coiled in a spiral and is divided by partitions into a series

266 ELEMENTS OF COMPARATIVE ZOOLOGY.

of chambers, only the outer one being occupied by the ani-
mal. Similar chambered shells are very abundant among
fossils.

The mouth is armed with a pair of horny jaws shaped
much like those of a parrot. These are very efficient in
biting food; but any morsels taken into the mouth are sub-
jected to further subdivision by means of the lingual rib-
bon, which is, as its name implies, a ribbon-like membrane,
bearing on its surface numbers of minute teeth, which rasp
the food into fine shreds.

The heart is situated in a pericardium and is systemic;
that is, it pumps the blood returning from the gills to the
various parts of the body. A peculiarity of the circulatory
system is that in all, except the pearly nautilus, the vessel
carrying blood to the gills develops a special pumping
organ, the branchial heart.

The various ganglia of the nervous system are (except
the stellate ganglia) placed close together in the head, and
from this centre nerves radiate to all parts of the body,
those going to the tentacles being connected with each
other by a circular cord.

The Cephalopods are all marine. They are carnivorous,
feeding upon fishes, etc. , which they capture with their
arms and hold fast by their numerous suckers. The
larger forms might be no mean antagonist for man; but
the monster described by Victor Hugo is without counter-
part in nature. The Cephalopods are divided into two
orders, according to the number of gills.

OKDER L- TETRABRAKCHIATA.

In the Tetrabranchs there are two pairs of gills (i.e., four
in all) ; the head bears numerous short tentacles without
suckers, and the body is enclosed in a chambered shell.

CEPHALOPODA. 267

The pearly nautilus is the only living representative of this
group. It occurs in the East Indian seas, and, while the
shells are very common, the animal is very rare in museums.
In geological times allied forms were very abundant, and
are known as Ammonites (with tightly coiled shells), and
Orthoceratites (with straight shells), etc.

ORDER II. — DIBRAKCHIATA.

These have two gills (one pair), and long, sucker-bearing
arms. An ink-sac is always present. The order is sub-
divided into the OCTOPODA, in which there are eight arms,

FIG. 123.— Octopus bairdii. From Verrill. One arm on the right side is
modified for purposes of reproduction.

and the DECAPODA, in which the number is increased to ten
by the addition of a pair of longer arms. In the Octopoda
there is no internal shell, and the body is saccular. Here
belong the octopus, poulpes, etc., as well as the paper nau-
tilus, which does not sail with its shell as a boat, and its

268 ELEMENTS OF COMPARATIVE ZOOLOGY.

broadened arms erect to catch the wind, as it is often said
to do. The Decapoda include the squid, the sepia, and other
forms. The smaller squid are abundant, and are caught in
large numbers for bait in fishing for cod. Near Newfound-
land, and in other parts of the world, giant squid are occa-
sionally found, the largest one known having a body length
of twenty feet. The length of the arms was not mentioned
in the account.

COMPAEISONS.

With two columns, as before, for clam, oyster, and squid,
answer the following questions :

(1) Is the body bilaterally symmetrical ?

(2) Is there a mantle ?

(3) Are gills present ?

(4) Is there a foot ?

(5) Do you find cerebral, pedal, and visceral ganglia ?

(6) Does the alimentary canal pass through the nervous
system ?

MOLLUSCA.

Oysters, Clams, Snails, and Cuttlefish may be taken as
examples of the ten thousand different species which are
known as Molluscs. The name comes from the Latin
mollis, soft, and alludes to the fact that, aside from the shell,
the body has no conspicuous hard parts. This, however, is
a point of no real importance in classifying animals.

Molluscs vary greatly in appearance; but if we carefully
compare the points which all possess in common, we can
construct an ideal mollusc, from which any form may be
derived by additions here and modifications there. Such
a typical mollusc is described below.

The body is saccular, and bilaterally symmetrical. There

FIG. 124.— Transverse and longitudinal sections of a schematic Mollusc, a,
auricle ; c, cerebral ganglion ; d, digestive tract ; /, foot ; fir, gill ; to, heart ;
t, intestine ; ?, liver ; *n, mouth ; w, nervous system ; p, pedal ganglia ;
pc, pericardium ; s, stomach ; v, vent.

is, above, a conical visceral mass; below, a muscular foot;
while from either side a fold of the body-wall extends out-
wards and downwards as a mantle. Between the mantle

270 ELEMENTS OF COMPARATIVE ZOOLOGY.

and the body and foot is a mantle chamber, or, since it
frequently contains the gills (branchiae), it is frequently
called the branchial chamber.

The outer surface of the mantle and the dorsal part of
the body frequently have the power of secreting a shell
composed, chiefly, of carbonate of lime. This shell in
some forms becomes split along the median line, so that
two halves or valves result. In most other forms the shell
becomes coiled into a spiral, and when this occurs the
primitive symmetry becomes lost in part.

Shells increase in size during the life of the animal.
The mantle is continually laying down new layers of shell
inside of those first formed, hence the older parts are thicker
than the newer portions. Then the mantle is larger when
the new layers are secreted, so these project beyond the
layers outside of them. As a consequence there occur on
the outside lines of growth.

In many species there are colored bands or spots upon
the mantle, and these parts secrete carbonate of lime
similarly colored, the result being that the shell is corre-
spondingly striped or spotted. Again, in some, the edge
of the mantle is produced into finger-like lobes, etc., and
these produce spines and the like upon the shell.

Shells are frequently spoken of as the houses or homes
in which the animals live. As will be seen from the above,
the shells are as much a part of the animal as is the
carapax of a lobster or the wings of a butterfly. The
oyster or snail can never leave its shell.

In most molluscs folds of the skin extend from the body-
wall into the mantle-chamber. These are the branchiae or
gills. Inside of them are blood-vessels, and through their
thin walls the blood is brought into close connection with
the oxygen dissolved in the water, just as is the case in

MOLLUSC A. 271

the gills of a fish. In the common terrestrial molluscs gills
are absent, but the inside of the mantle-chamber is lined
with a fine network of blood-vessels, so that the whole
organ resembles somewhat a lung, and has received that
name.

In the flow of the blood there is a great difference be-
tween the mollusc and the fish. In the mollusc the blood
returns at once from the gill to the heart, and is then
forced by this organ to all parts of the body. The heart is
situated in a chamber or pericardium, and consists of one or
two (right and left) auricles which receive the blood, and
a ventricle which pumps it to the body. In the squid ac-
cessory or branchial hearts are added. These are placed at
the bases of the gills and force the blood through these
organs, from which they return to the other or systemic
heart, to go to all parts of the body.

In all molluscs except the Acephala the region of the
mouth is provided with a lingual ribbon. This is a band
of horny material, bearing on its free surface rows of hard
and sharp teeth, so that the whole resembles a flexible file.
It is supported in such a way that it may be moved back
and forth, thus rasping the food. In some Gasteropods it
can even be used in boring holes in the shells of other
molluscs. This lingual ribbon is constantly growing at its
deeper end, so that the loss by wear in front is continually
made good. The teeth on the ribbon vary in number and
shape in different species. In some there are but three in
a transverse row, while in others there may be over one
hundred.

In the ideal mollusc the alimentary canal goes straight
through the body from mouth to vent. In nature it
usually has some convolutions, increasing* the amount of
digestive surface. In the Cephalopods and in most Gas-

272 ELEMENTS OF COMPARATIVE ZOOLOGY.

teropods it becomes bent on itself, so that the vent is far
in front, either upon the right side or even in the median
line. In the Gasteropods, when it is median, it is close to
and dorsal to the mouth. In the Cephalopods it is ventral.

The nervous system consists of at least three pairs of
ganglia and the cords or commissures connecting them,
as well as the nerves going to the various parts. These
ganglia are the cerebral, above the mouth; the pedal,
primarily in the foot; and the visceral, farther back in the
body. Both pedal and visceral ganglia are below the in-
testine; the pedal supplying the foot, the visceral the body
and the mantle. To these three pairs others are frequently
added. Sometimes the ganglia are widely separated, when
the commissures are correspondingly lengthened; or they
may be brought close together, with shortened connecting
cords.

Some molluscs lack organs of special sense; others have
eyes and ears. The ears are little sacs, usually near the
pedal ganglion, but the eyes may have various positions.
They may be on the sides of the head (squid), or on the
sides or tips of tentacles arising from the head (snails), or
scattered over the back (some slugs and chitons), or on the
edges of the mantle (scallops), or on the end of the siphon
(some clams). In some they are merely spots which have
the power to distinguish between light and darkness, and
from these all degrees of development may be found to the
extreme in the squid, where these organs are scarcely infe-
rior to those of vertebrates in structure.

For kidneys the molluscs have one or two organs consist-
ing of convoluted tubes opening at their inner end into the
pericardium and communicating with the exterior at the
other.

In some the sexes are separate ; in others, like our land

MOLLUSC A. 273

snails, they are united in the same individual. All mol-
luscs, with very few exceptions, lay eggs, from which the
next generation is produced.

Molluscs are divided in different ways by different au-
thorities. For our purposes we may recognize four divi-
sions or classes: Placophora, Gasteropoda, Acephala, and
Cephalopoda.

CLASS I.— PLACOPHORA.

Here belong a few forms known as Chitons. They are
separated from all other molluscs by many points of inter-
nal structure, while externally they may always be recog-
nized by having a dorsal shell composed of eight transverse
plates, which overlap from in front backwards, like the
shingles on a roof. All are marine.

CLASS II— GASTEROPODA.

The Gasteropods receive their name from the fact that
the foot usually forms a large sole or creeping disc extend-
ing along the ventral side of the body. There is a distinct
head, which usually bears sensory tentacles, and the eyes are
commonly placed at the bases or on the tips of one pair of
these structures. In some cases, as in most land-snails,
these tentacles can be pulled back into the body.

In the majority of forms gills are developed in the mantle-
chamber. In a few there is a pair of these organs, but in
many one gill disappears, while in other species both true
gills entirely disappear, and are either replaced by secondary
gills developed on the back or in other regions; or the
mantle-chamber may be richly lined with blood-vessels and
thus be converted into an organ (lung) for breathing air.
This is the case in all of our common land-snails.

274 ELEMENTS OF COMPARATIVE ZOOLOGY.

In all Gasteropods a shell is present in the young, but in
many it is lost before the animal becomes adult. It is
never a bivalve structure, but is either plate-like or is coiled
in a spiral. In some the spiral is flat, in others it may be
elongate, and the turns may be either to the right or to the
left, right-handed shells being in the great majority. In a
large number of Gasteropods a shell-like structure (oper-
culum) is developed on the dorsal surface of the hinder
part of the foot, and when the animal withdraws itself into
the shell this operculum closes the opening after all the soft
parts are inside.

Some of the peculiarities of the nervous system form the
basis of the subdivision of the Gasteropods. In one group
(Euthyneura) the ganglia and the cords connecting them
are much as in the clam. In the other (Streptoneura) the
cords leading back from the brain become crossed so that
the nerve which starts from the right side goes to a ganglion
on the left, and vice versa.

In all Gasteropods a lingual ribbon (p. 270) is present, and
this works against a plate or "jaw " on the upper side of
the mouth. The alimentary canal is rarely straight.
Usually there are convolutions, and the whole is so bent
upon itself that the vent is carried far forward, and may be
placed upon the neck just above the mouth. Sometimes it,
or the liver connected with it, become greatly branched.

SUBCLASS I. — STREPTONEURA.

In these the nervous system is twisted ; there is but a
single pair of tentacles upon the head; and the gills are
placed in front of the heart, a condition which leads many
naturalists to call the group "Prosobranchs."

MOLLUSC A.

275

ORDER I. — DIOTOCARDIA.

In these forms the body retains its bilateral symmetry to
a considerable degree, and externally may appear perfectly
symmetrical. The name implies the
existence of two auricles to the heart.
In the limpets the shell is a flattened
cone; in the abalones it is somewhat ear-
shaped and very weakly spiral, but in
the top shells it is strongly spiral. The
abalones alone have any economic
value. Their shells, remarkable for
having a series of holes in them, are
composed of a greenish mother-of-pearl,
which is extensively used in inlaid

Work. FIG. 125.— Limpet (Ac-

meed testudinalis).

ORDER II. — MONOTOCARDIA. Gould Bhmey's

Here belong the great majority of marine snails, all of

which agree in having but a single gill and a single auricle
to the heart. Few of them have any
economic interest aside from those which
feed upon oysters and other valuable
shellfish. These injurious forms — com-
monly known as "drills" — are able to
bore holes through the shells of oysters,
etc., by means of their lingual ribbons.
Many, however, are great favorites with
collectors, among them the strombs,
cones, cowries, and olives. Some of the

FIG. 126. — stromb cones are noticeable from the fact that

(Strombus pugilis).

After Woodward, they have a poison-gland connected with
the lingual ribbon. Some species formerly grouped as a

276 ELEMENTS OF COMPARATIVE ZOOLOGY.

distinct order of Heteropoda are especially modified for a
life on the high seas.

SUBCLASS II. — EUTHYNEURA.

In the Euthyneura the nervous system is without a
twist, and the head almost always bears two pairs of
tentacles.

ORDER I. — OPISTHOBRANCHIA.

These forms are all marine, and have but two divisions to
the heart — an auricle and a ventricle, the latter being in
front of the former. Some are provided with a spiral shell,
while others — called Nudibranchs or naked molluscs — are

Fio. 127.— Naked mollusc (Doris), showing the gills, above to the right.

without such protection. In the nudibranchs there are
commonly developed gills upon the dorsal surface, and in
the living condition these forms are, from their bright colors
among the most attractive of molluscs. Here, too, are
forms (Pteropods) especially developed for a life on the sur-
face of the ocean, the foot being modified into a pair of
wing-like structures.

ORDER II. — PULMOKATA.

The great majority of the land and fresh- water snails
and slugs belong here. In them gills have disappeared, and
the mantle-cavity has been modified into an organ (lung)
for breathing air, the opening to which is to be seen on the

MOLLUSCA. 277

right side of the body. Over six thousand species belong
here, some (snails) having a well-developed spiral shell,
while the slugs are apparently shell-less; but in these slugs
one can frequently find a rudimentary shell imbedded in the
mantle.

CLASS III.— SCAPHOPODA (TOOTH-SHELLS).

In these the mantle edges are fused below, forming a tube,
and as a result there is formed a tubular shell, open at both
ends, in shape something like the tusk of an elephant.
The foot is large, and adapted for digging in the sand, in
which these animals live. There is no distinct head, but
the mouth is provided with a lingual ribbon. In the
anterior part of the mantle-cavity are a pair of bunches of
long threads of unknown function; possibly they are sen-
sory, possibly respiratory, in nature. All of the tooth-shells
are marine.

CLASS IV.— CEPHALOPODA (see p. 264).
CLASS V.— ACEPHALA (see p. 257).

STAEFISH: LABORATORY WORK.

EXTERNAL.

The body is shaped like a five-rayed star; in it distin-
guish the central disc and the arms or rays. In the centre
of the disc find the mouth. The side on which it occurs
is called the oral surface. Running along the oral surface
of each arm are the fleshy tube-feet or ambulacra, and the
regions of the oral surface in which they occur are known
as the ambulacral areas. Sketch this surface in outline,
showing the parts.

The surface opposite the mouth is the aboral surface.
Does it have ambulacra ? By feeling and bending see that
this surface is composed of numerous hard (calcareous)
plates, and that many of these bear spines. On the aboral
side of the disc is a rounded body, the madreporite. Is it
radial or interradial in position ; that is, does it lie in the
line of a ray or between two rays ? Sketch the aboral sur-
face, and draw a line through it dividing it into symmetrical
halves. How many such lines can be drawn ? The arm
opposite the madreporite is known as the anterior ray.*

With the needle demonstrate that the calcareous plates
are not on the outside. What covers them ? Are the
spines movable on the plates ? Scattered over the aboral

* The reasons why this is called anterior rather than posterior
cannot be worked out on the forms selected for dissection, but can
only be seen by a comparison with the heart-urchins (Spatangoids),
etc.

278

DISSECTION OF STARFISH. 279

surface are numbers of fleshy, finger-like projections, the
branchiae. Look at the very tip of the arm, and find the
rounded red eye- spot (recognized with difficulty in pre-
served material).

INTEBKAL STKUCTUKE.

Cut into the side of one of the arms, carrying the inci-
sion outward to near the tip, crossing to the opposite side
and then back towards but not quite to the disc. Fold
back the flap thus separated, and notice the following struc-
tures :

Attached to the aboral surface the lobular hepatic caeca,
each supported by a thin membrane (mesentery).

On the floor (oral surface) a series of thin- walled vesicles,
the ampullae. By means of a needle ascertain if these am-
pullae are connected with the ambulacra.

Continue the removal of the aboral surface from the rest
of the body, taking care that all soft parts are separated
from it and left in the oral portion, and that the portion
immediately around the madreporite be left intact, and that
one arm be left untouched. Now find on the aboral sur-
face of each hepatic caecum the hepatic duct. Trace these
ducts inward until they enter a saccular structure, the
pyloric part of the stomach. Do they unite before joining
the stomach ? On the aboral surface of the pylorus is a
small lobular structure, the branchial tree. How many
branches has it ? Is it radial or interradial in position ?
Draw a line through the starfish passing through the bran-
chial tree, dividing the animal into symmetrical halves ; how
does this symmetry compare with that obtained from the
madreporite ? Near the centre of the pylorus is the small
tubular intestine (frequently torn in removing the external
wall). It empties by a vent on the centre of the disc; diffi-

280 ELEMENTS OF COMPARATIVE ZOOLOGY.

cult to demonstrate this in the preserved specimen. Notice
the openings into the branchiae.

Eemove the hepatic caeca from one arm and find the
lobular reproductive organs near the base of the ray. Where
does this duct connect with the external wall ? Would you
consider this point (at which the duct opens to the exte-
rior) as radial or interradial ?

Below (that is, oral to) the pylorus is the cardiac portion
of the stomach, produced into gastric pouches in each of
the rays. Trace from these pouches the thin retractor
muscles into the ray to their attachment to its floor.

Make a sketch of your dissection, showing in the centre
the stomach, in one arm the hepatic caeca, in a second the
reproductive organs, a third with cardiac retractors and am-
pullae, a fourth with the dorsal surface, and leave the other
arm for structures, to be added later.

Carefully cut away stomach a little inside the mouth,
and then trace the stone-canal (a hard S-shaped tube)
downward from the madreporite to the region around the
mouth. Examine this circumoral region from the aboral
side, and find the ten Polian vesicles (much like the ampul-
lae) and, inside of these, the small sacculated racemose vesi-
cles. How many are there of these ? What do you find
in the place of the one needed to make symmetry ? Beside
the stone-canal is a thin-walled sac, the so-called heart.
Sketch the organs in this paragraph, and keep the drawing
for further additions.

Remove the ampullae, membranes, etc., from the floor of
one of the rays and see the ambulacral plates which meet
in the median line. Notice the openings in this ambulac-
ral area by means of which the ampullae connect with the
ambulacra. Are these ambulacral pores in or between the
plates ? How many rows of them do you find in an arm ?

DISSECTION Of STARFISH. 281

Sketch these plates in the ray of the drawing left incom-
plete.

Turn this same ray over, remove the ambulacra, and see
the ambulacral plates from the oral surface. They meet,
forming an ambulacral groove, the edges of which are
formed by smaller plates (interambulacrals) bearing mov-
able spines.

Cut off the arm as yet left intact about half an inch from
the disc, and draw the section, including in the sketch the
ambulacral plates forming the roof of the ambulacral
groove; outside of these the interambulacrals, and then the
plates of the aboral surface. Add to these parts the bran-
chiae, ambulacra, ampullae, hepatic caeca, and mesenteries in
their proper position.

In the groove of that part of the arm which remains at-
tached to the disc notice a tube, the radial canal. Insert
into this the canula of a hypodermic syringe or other in-
jecting apparatus (see Appendix), and force in some colored
fluid (solution of carmine or Prussian blue). What happens
to the ampullae and ambulacra ? Part the ambulacra and
follow the colored radial canal to the region of the mouth,
and see how this is surrounded by a ring-canal. Are stone-
canal, racemose vesicles, or Polian vesicles filled with the
fluid ? Insert the radial and ring canals, ampullae, and
ambulacra in the drawing of the stone-canal, etc.

Beneath the radial canal is a thickening of the skin, the
radial nerve which connects with circumoral ring-nervt:
just below the ring-canal.

SEA-URCHIN: LABORATORY WORK.

EXTERNAL.

What is the general shape ? Are the spines movable ?
Can you find ambulacra between the spines ? In how many
areas are they arranged ? At one pole of the urchin find
the oral area closed by a thin membrane (peristome) and in
its centre, teeth (how many ?). Do the ambulacra radiate
from this mouth ? If so, where should you look for the
eye-spot (compare starfish) ?

In a cleaned specimen * make out the ambulacra! areas
radiating from the region of the mouth. They may be
recognized by the presence of the ambulacral pores. Do
these pores pass through or between the plates ? How does
this condition compare with that found in the starfish ?
Between each two sets of ambulacral plates are found the
larger interambulacrals. Which plates, ambulacral or in-
terambulacral, bear rounded prominences for the articula-
tion of the spines ? Making a comparison with a starfish,
where would you draw the line between two rays of the sea-
urchin ? Illustrate by a sketch.

Follow a ray from the oral area to the pole opposite the
mouth. Notice in the centre of this pole a circular anal

* For this purpose the parts of the shell (test) of specimens used
in previous years may be employed. They are easiest cleaned by
rubbing off the spines and then bleaching in Eau de Javelle or Labar-
raque's solution (potassium or sodium hypochlorite), to be had of
druggists.

DISSECTION OF SEA-URCHIN. 283

area, made up of small anal plates. How many plates
make up the boundary of this circle ? Examine them
under the lens and decide which one compares in structure
with the madreporite of the starfish. Is it radial or inter-
radial in position ? How many of these plates bear small
pores ? Sketch this region, showing the anal area and the
tips of the rays, and label the parts, deciding which of the
perforated plates must be genital and which must be
ocular plates by comparing with their relative position,
radial or interradial, in the starfish. With what is the
madreporite associated ? What parts must belong to the
aboral surface of the starfish ?

INTERNAL STRUCTURE.

Open an alcoholic urchin by breaking into the equator
of the test, and then continue the opening around by
breaking, bit by bit, with the forceps around the shell,
taking care that the fleshy parts beneath be not injured.
Then carefully lift the aboral pole and, separating every-
thing from it, leave all the soft portions in the oral half.

Most prominent at first will be the yellowish reproduc-
tive organs occupying a position above everything else.
Are its lobes connected ? Can you trace the ducts of this
organ ? Sketch the reproductive system and then remove
it. This will expose the alimentary canal (brown in color)
supported by a mesentery. Trace its course, making draw-
ings as you proceed. How many turns does it make ? At
its oral end the alimentary canal connects with a compli-
cated apparatus — Aristotle's lantern — composed of numer-
ous harder portions and muscles to move them. Have the
teeth any relations to this apparatus ? Look on the inside
of the test for the ampullae, and between them for the
radial canal.

284 ELEMENTS OF COMPARATIVE ZOOLOGY.

Usually in preserved urchins the stone-canal becomes so
tender as to be easily destroyed. It goes downward from
the madreporite to the inner end of Aristotle's lantern,
where it connects with a ring-canal, and from this arise
the radial canal, in much the same way as in starfishes, the
whole forming a water- vascular system. As in the star-
fish, the nervous system follows this water- vascular system.

COMPAEISONS.

With columns for starfish and sea-urchin, answer the
following questions :

(1) What is the general shape of the body ?

(2) Are the radial canals inside or outside the hard body-
wall ?

(3) Do you find branchiae ?

(4) Are all the spines movable ?

(5) Is an Aristotle's lantern present ?

(6) How many divisions to the reproductive organs ?

(7) Are hepatic caeca present ?

(8) Do you find a branchial tree ?

(9) Do you find gastric pouches ?

ASTEROIDA (STARFISHES).

In the starfishes the flattened body is either pentagonal,
or has a number of arms, or rays (usually five), giving it
the shape of a star. In the body- wall are numerous calca-
reous plates, movable on one another. In the axis of each
ray, on the side of the body with the mouth (oral surface),
are regularly arranged ambulacra! plates, margined on
either side by interambulacral plates similarly arranged.
In the rest of the surface (aboral surface) no such regularity
of plates occurs. The mouth is in the centre of the disc
which unites the rays, and is always without jaws or other
hard parts. The mouth opens directly into a capacious
stomach, the extent of which is increased by gastric pouches.
The stomach is also partially divided by a constriction into
two chambers, an oral, cardiac, and an aboral, pyloric,
division. From the latter a short intestine runs to the
aboral pole, where it may open by a vent, but in some no
vent occurs. Into the pyloric chamber empty the ducts of
five pairs of glands (hepatic caeca) which secrete the digestive
fluids, while from the intestine arise from one to five
saccular outgrowths, the branchial trees, the function of
which is uncertain.

The organs of locomotion consist of tube-feet or ambula-
cra on the oral surface of each arm. These are connected
with sacs or ampullae inside the ray, and each of these
systems is in turn connected by lateral canals with a

285

286 ELEMENTS OF COMPARATIVE ZOOLOGY.

radial canal running below the arm in the median line.
These radial canals unite to form a ring-canal around the
mouth, and this in turn communicates with a stone-canal
which leads to the aboral surface, and thence to the exterior
through pores in a specialized plate, the madeporite. This
whole system is known as the water-vascular system. By
means of ampullar muscles the ambulacra can be ex-
tended, while ambulacral muscles serve for their retraction.
At the end of each ambulacra is a sucking-disc.

The nervous system consists, chiefly, of a nerve-ring
around the mouth and a radial nerve in each ray, the
whole paralleling the water-vascular system. Eye-spots,
one at the end of each ray, are the only specialized sense-
organs present.

The circulatory organs consist of a so-called heart beside
the stone-canal, from which vessels run in various directions,
the chief portion running between nervous and water-
vascular tracts. The only respiratory organs are the thin-
walled branchiae, which are outpushings of the body-cavity
upon the dorsal surface.

The reproductive organs occur at the bases of the arms,
one organ on either side of each ray, the ducts emptying
in the angle between the arms. From the eggs there hatch
out larvae which are free-swimming and bilateral, and
which show not the slightest trace of the radial shape of
the parent.

The starfishes are all marine. They feed largely on
clams, oysters, and other molluscs, and are regarded as one
of the greatest pests on oyster-beds. The way in which the
starfish feeds is interesting. It has no hard parts to break
the shell, while the mouth is too small to admit of swallow-
ing the oyster. So it everts its stomach through the
mouth and wraps it around the shell it wishes to devour.

ASTEROIDA. 287

The retractor-muscles noticed in your dissection (p. 280)
aid in pulling back the stomach after a meal.

Most of the starfishes have five rays, but this number
may be exceeded, the number reaching occasionally twenty
or more.

ECHINOIDA (SEA-URCHINS).

In the sea-urchins the body is spherical, heart-shaped, or
disc-like, and the ambulacral areas extend, like meridians,
from oral to anal regions. In short, sea-urchins are easiest
compared with starfishes, if we imagine the arms of the
latter bent backwards until they meet above. In this way
the terminal eye-spots would be brought next to the anal
area, while the reproductive openings, by the union of the
arms, would be forced into a position between the oculars,
and the madreporite would become pressed against one of
the reproductive (genital) plates.

All of the plates are firmly united to one another, while
the spines are freely movable, and share, with the ambu-
lacra, locomotor functions. The mouth is armed with five
teeth, and to aid in the movement of these a calcareous
framework is found just inside the mouth, known from its
first describer as Aristotle's lantern. In some, as in our
common urchins, this framework and its muscles are com-
plicated. From the mouth the tubular alimentary canal
pursues a winding course (usually folding on itself) to the
vent. Hepatic caeca, gastric pouches, and branchial trees
are lacking. The reproductive organs become fused into
five lobes by the union of those of the same interradius.

The Echinoida are divided into three orders :

ORDER I. — REGULARIA.

In these, which embrace the more common urchins, the
mouth is at one pole, the vent at the other, and the body
is approximately spherical.

ECHINOIDA.

289

ORDER II. — CLYPEASTROIDEA (Sand-cakes).

In the "Sand-cakes" and "Sand-dollars" we have
urchins in which the test is disc-shaped and the ambulacra
are confined to the upper surface. The mouth is in the
centre of the lower surface; the vent is on the margin

a A

FIG. 128.— .4, oral, and B, aboral surfaces of Sand-dollar (Echinarachnius).
a, vent; 0, genital pores; z, ambulacral areas; m, madreporite ; o,
mouth.

of the disc, or near the margin on the lower surface. It is
interradial in position. In a few of the sand-cakes the
margin of the disc is notched, while in others there may
be perforations extending through from upper to lower
surface.

ORDER III. — SPATANGOIDS (Heart-urchins).

In these the body, flat below, arched above, has a heart-
shaped outline, and both mouth and vent are eccentric in
position upon the lower surface. The ambulacra are all on
the upper surface, but the anterior row is lacking.

290 ELEMENTS OF COMPARATIVE ZOOLOGY.

COMPAKISONS.

With columns for sea-urchin and for starfish, answer
the following questions :

(1) Of what is the skeleton composed ?

(2) Are spines present upon the outside of the body ?

(3) Can you speak of the parts as being radiately ar-
ranged ?

(4) Can you also speak of them as bilateral ?

(5) Do you find in both ampullae and ambulacra ?

(6) Does the nervous system surround the mouth ?

(7) Is there a body-cavity ?

(8) Is there a madreporite and a stone-canal ?

(9) Do you find radial canals ?

ECHINODERMA.

This term means spiny skin, and both starfishes and sea-
urchins possess this peculiarity in a high degree. But
besides this external characteristic there are many other
features which distinguish the
group. In fact, there is scarcely
a division in the whole animal
kingdom more sharply marked
off from other forms than this.
In all the body is built on that
radiate plan which is so promi-
nent in starfish and urchin,
and in all except a few starfish
there are five rays, although in
some the rays may subdivide.
This radiate condition affects
not only the external surface,
but may extend to every sys- /Y \\

tern as well. And vet we may

J J FIG. 139.— Larva of a starfish, en-

trace in every form a bilateral- larged. m, mouth ; v, vent,
ity, and development shows that the bilateral condition is
primitive, the radial character being acquired with growth.
Another characteristic is the ambulacral apparatus with its
water- vascular system, and a third feature is the possession
of a large body-cavity distinct from the alimentary canal.
In all there is the formation of calcareous plates in the
skin, and in all except the Holothurians these plates are
developed into a more or less solid skeleton. All possess a

292 ELEMENTS OF COMPARATIVE ZOOLOGY.

bilateral larva, and in its development the young goes
through most wonderful changes. The Echinoderms are
all marine. The group is subdivisible into five classes:

CLASS I.— HOLOTHURIDEA (SEA-CUCUMBERS).

The Holothurians are cylindrical Echinoderms, with
mouth and vent at the end of the body, and usually with

FIG. 130.— Sea-cucumber (Pentacta frondosa). From Emerton.

the ambulacra scattered over the surface in such a way as
to make the comparison with a cucumber most apt. Around
the mouth is a circle of tentacles (in reality enormously

ECHINODERMA. 293

developed ambulacra), and with these the animals obtain
their food. Inside, the pharynx is surrounded by calcareous
plates, the whole resembling slightly the lantern of the sea-
urchin, but no teeth are ever developed. In most species
the madreporite is inside the body, and in many the bran-
chial trees (p. 285) become developed into large tree-like
structures. Along our shores two groups or orders occur;
PEDATA, in which there are ambulacra and branchial
trees; and APODA, in which both these structures are
lacking, and the body is decidedly worm-like.

CLASS IL— ECHINOIDEA (SEA-URCHINS) (see p. 288).
CLASS III.— ASTEROIDEA (STARFISHES) (see p. 285).
CLASS IV.— OPHIUROIDEA (BRITTLE-STARS).

The brittle-stars, or serpent-stars as they are frequently
called, are much like the true starfishes, the chief distinc-
tions being that in the brittle-stars the arms and the disc
are sharply distinct from each other, and that the extremely
mobile arms are long, slender, and somewhat snake-like.
A little closer examination shows that the ambulacral

groove has been carried into
the interior of the arms, and
that here one must search for
the ambulacral plates. There
is no vent, and the madre-
porite occurs on the lower

FIG. 131.— Brittle-star (Ophiopholis). FIG. 132.— Cross-section of arm of
From Morse. brittle-star, a, ambulacral plate ;

ao, ambulacral opening.

side of the body, usually covered by one of the plates sui>

294 ELEMENTS OF COMPARATIVE ZOOLOGY.

rounding the month. There are a few forms in which the
arms branch again and again, and since when captured these
forms bend the arms inwards towards the mouth, giving

FIG. 133.— Crinoid (Pentacrlnus) half FIG. 184.— Mouth area of a crinoid
natural size. From Brehm. ( Comatula) showing the course of

the intestine leading from the
mouth (m > to the vent (a). 0, grooves
leading from anus to mouth.

a somewhat basket-like appearance, these are known as
"basket-fish/' The name brittle-stars is due to the fact
that in some the arms are very easily broken. A few
brittle-stars produce living young.

ECHINODERMA. 295

CLASS V.— CRINOIDEA (SEA-LILIES).

While all other echinoderms are free throughout their
lives, the crinoids are characterized by being fixed to some
firm support by a long stalk arising from the aboral surface
of the body. In most the stalk persists throughout life,
but in a few, after the adult condition is reached, the body
separates from the stalk and thereafter follows a free life.
From the central disc or calyx radiate the five (usually)
branching arms, and these arms and their branches bear
small branchlets, so that as these animals rest in their
ordinary position, the whole forms a funnel-like net with
the mouth at the small end. On the upper (oral) side of
all these branches run grooves converging at the mouth,
and so any object which falls anywhere on the funnel is
brought to the animal as food. The alimentary canal runs
spirally through the calyx, and the vent is on the oral
surface. The stalk, like the calyx, is strengthened by
calcareous plates, those of the stalk being disc-like and
piled one on another.

Crinoids, with the exception of the free forms (Comatuld),
are among the rarities of museums, as they are found only
in the deeper seas. In past time, however, they were very
abundant, and whole layers of rock in certain localities are
made up of their remains. The fossil forms present a
greater variety of shape than do the living representatives.

SEA- ANEMONE:* LABORATORY WORK.

In the prepared specimen notice that the body is cylin-
drical and may be described as consisting of a column,
with a base by which the animal was attached, and an
oral disc bearing a large number of finger-like tentacles,
in the centre of which is the mouth. Which tentacles,
inner or outer, are the larger ? If there be an increase in
number of tentacles during growth, which ones would
probably be the older ? What is the shape of the mouth ?
How many thickened places do you find in the mouth ?
These thickened portions are called siphonoglyphes. Could
they be used to indicate bilateral symmetry ? Make a
drawing of the animal showing the column, oral disc, etc.
Cut off a few tentacles, and see if they be hollow or solid.

INTERNAL STRUCTURE.

Cut the animal with a sharp knife into two portions,
the incision being made parallel to the oral disc and pass-

* It requires some patience to prepare sea-anemones for laboratory
work. If merely collected and placed in the preservative fluid, the
result will be a shapeless mass, in which the student will find every-
thing confused. The anemones should be placed in shallow dishes
of salt water, allowed to expand, and then gradually be stupefied by
the addition of crystals of sulphate of soda (Glauber's salts); and
then, when completely stupefied, kill and harden by transferring to
a \% solution of chromic acid for three hours. The specimens are
then washed for half an hour in running water and transferred to
the preservative fluid — formalin or alcohol (see Appendix).

296

DISSECTION OF A SEA-ANEMONE. 297

ing through the body about half an inch from the mouth
end. In the upper portion (i.e., that nearest the oral
disc) will be found an oesophagus extending inwards from
the mouth. Can you trace the siphonoglyphes into this
tube ? Extending inwards from the outer wall to the
oesophagus are six * pairs of partitions, the primary mesen-
teries or septa. The result of this is that the space inside
of the body is divided into a series of chambers. The
chambers between the septa of a pair are called the intra-
radial, those between the pairs of septa the interradial
chambers. The interradial chambers will be found to be
partially subdivided by other pairs of septa (secondary,
tertiary, etc.) which extend outwards from the body- wall,
but which do not reach the oesophagus.

Examine the primary septa and find on each a muscle
extending in the direction from oral disc to base. Are
these muscles on the inter- or iritra- radial sides of the septa ?
Examine all the primary septa before deciding this ques-
tion. Then sketch the cut surface, inserting body-wall,
oesophagus, and primary septa ; and on each of the septa
put the muscles on the proper surface. If this be done, it
will be found that there is but one plane which will divide
the animal into exactly symmetrical halves. The septa
through which this plane passes are the directives. Do
they correspond in position to the siphonoglyphes ? Study
a few of the incomplete septa. Have these muscles like
the others ? At the oral ends of the septa look for open-
ings through these partitions.

Split the other part of the animal lengthwise, and pin out
under water. Notice that the oesophagus does not reach

* Occasionally variations will be found in the number and arrange-
ment of the septa ; these exceptional forms should be compared with
the more normal specimens.

298 ELEMENTS OF COMPARATIVE ZOOLOGY*

the base. Could food pass from the oesophagus into the
inter- and in tra- radial chambers ? Do you find any body-
cavity distinct from the digestive cavity ? Do you find any
opening to compare with a vent ?

Along the free edges of the mesenteries are the coiled
mesenterial filaments. Do they present the same appear-
ance nearer the oral disc that they do farther down ? On
the sides of the septa near the mesenterial filaments are the
reproductive organs (not always plainly visible).

A HYDROID * (Pennaria).

Examine a colony under the hand lens or low power of
the microscope, and notice the branching stem (hydro-
caulus), bearing on their tips the fleshy hydranths or
zooids. The hydrocanlus is covered with a horny, tube-
like perisarc. Does this present any striking peculiarities ?
Sketch the whole colony.

In a single hydranth see that there is a balloon-shaped
body, the neck of the balloon being the proboscis, at the
end of which is the mouth. The hydranth is covered with
tentacles. Is there any regularity in their arrangement ?
Are they all similar ? Look on various hydranths for

* For this purpose it is well to have some alcoholic material, and
also some mounted slides, which can be used, year after year, with
successive classes. To make these mounts the alcoholic material
should be washed for half an hour in water, and then stained for
twenty-four hours in alum cochineal (made by soaking 7 parts of
crushed cochineal insects and 7 parts of a'um in 700 of water for
twenty-four hours. Then boil until the amount is reduced to 400
parts. Allow to stand twenty-four hours, filter, and add a little
thymol to keep it from spoiling). After staining, the specimens
should be rinsed in water and placed in 80#, 95#, and absolute alcohol
for at least two hours each, and then left the same length of time in
oil of clove. The best specimens may then be selected, placed upon
the microscope-slides, the oil drained off, and a drop or two of Can-
ada balsam added, and a bit of thin glass (cover-glass) placed on the
specimen. The slides should be allowed to b come dry and hard
(which will take some weeks) before being placed in the hands of the
student. It must be borne in mind that all of the above details are
necessary ; omissions will result in failure

299

300 ELEMENTS OF COMPARATIVE ZOOLOGY.

globular outgrowths, medusa-buds. Sketch a hydranth en-
larged, showing the points made out.

Study a mounted specimen under higher microscopic
powers, and see that the zooids are made up of two layers
and that they contain a central digestive cavity. Can you
trace the layers and the cavity into the hydrocaulus ?
Could food taken into one of the hydranths pass to another
hydranth ? Are the tentacles solid or hollow ? Examine
the tip of a tentacle of the series nearest the mouth, and
see the large oval nettle-cells imbedded in it. (In favor-
ble specimens threads can be seen extending from the net-
tle-cells). Sketch a hydranth enlarged, showing layers,
digestive tract, etc., and a medusa-bud.

Look carefully over the hydranths and see if you can find
any traces of an oesophagus turned into the body as in the
sea-anemone ; of septa, and of mesenterial filaments. Do
any individuals show a bilateral nature ?

COMPARISONS.

With columns for Sea-anemone and for Hydroid, answer
the following questions :

(1) Are the animals simple or do they form colonies con-
nected tegether ?

(2) Can you find traces of bilaterality in the animals ?

(3) Are septa present ? Is the digestive cavity simple,
or is it subdivided into chambers ?

(4) Is there an inturned oesophagus ?

(5) Are the tentacles hollow or solid ?

SCYPHOZOA (SEA-A^EMO^ES, CORALS, ETC.).

All those animals which, like the sea-anemone, have an
oesophagus turned into the body (much as one might turn
in the mouth of a bag), and which have the digestive cavity,
subdivided by radially arranged partitions or septa, are
called Scyphozoa. To these characteristic features may
be added others. Thus there is a circle of (usually hollow)
tentacles surrounding the mouth, and the edges of the
septa bear long mesenterial filaments which are digestive
in function. By the septa the digestive cavity has its
surface greatly increased, so that the substances rendered
soluble by the secretions of the mesenterial filaments can
be more readily absorbed. Further details of structure are
better given in treating of the two subclasses into which
the Scyphozoa are divided; merely saying here that all are
marine.

SUBCLASS I. — ACTIKOZOA (Sea-anemones and Corals)
In these the animal is fixed; it never swims freely, and
the body in general has much the same structure as was
found in the sea-anemone dissected. In some the indi-
viduals (polyps) are separate; in others the individuals re-
produce by division or by budding, and the new polyps
thus formed never completely separate from their parents,
so that large aggregations or colonies result. In these one
can distinguish the mouths, and usually the tentacles of
the individual polyps, but the division does not affect the
digestive tract, so all are connected, and the food which is
taken in at one mouth may serve to nourish any part of the

301

30:2 ELEMENTS OF COMPARATIVE ZOOLOGY.

whole colony. In some the outer surface of the body is
naked, but in many of the solitary and in most of the colo-
nial forms the base or both base and column secrete car-
bonate of lime, thus forming a solid support for the body.
This solid support is the well-known coral. In most spec-

FIG. 135. -Diagram of a bit of coral to show the FIG. 136. — Section of a
way in which the polyps are connected. The coral cup showing the
coral is black ; the digestive cavity shaded. calcareous septa. Af-

ter Pourtales

imens of coral one can readily recognize the cups in which
the separate polyps were situated; and in these cups, in
most cases, are calcareous partitions much like the septa of
the soft parts.* As long as the colony remains alive it is
constantly budding off new polyps, and thus the colony and
the coral grow. Those species which live in cold water
produce but little coral, but in tropical waters the coral-
producing forms abound, and by their combined secretions
the coral islands are made.

The great majority of the Actinozoa may be subdivided,
according to the number of septa, into two orders:

* These calcareous septa do not coincide with, but alternate in posi-
tion with, the fleshy septa.

&CYPHOZOA.

ORDER I. — OCTOCORALLA.

303

In these the separate polyps are small, and each has but
eight septa and eight tentacles. They produce but little
coral, but rather those kinds of coral which are known as
sea-fans and sea-whips. One form is especially noticeable
since it produces the precious red coral so often carved into
beads, etc.

ORDER II. — HEXACORALLA .

As the name indicates, the septa and tentacles here occur
in multiples of six. Here belong all the sea-anemones and
the true corals which produce coral-reefs and islands. The

FIG. 137. — Sea-anemone (Metridium). From Emerton.

reef-building species are limited in their distribution by
temperature, for they cannot live where the temperature of
the water falls below 60° Fahr. (13° C.).

304 ELEMENTS OF COMPARATIVE ZOOLOGY.

SUBCLASS II.— SCYPHOMEDUS^: (Jellyfishes).
At first sight these Scyphomedusae differ greatly from
the Actinozoa. They are free-swimming forms in which
the body is developed into an umbrella-shaped structure,

FIG. 138.— Common white jellyfish (Aurelid). After Agassiz.

the mouth is at the end of a long proboscis, and all is
semitransparent. Yet when the details of structure are ana-
lyzed there are found the same inturned oesophagus, the
same septa and filaments, and the same tentacles; and
hence these forms must be somewhat closely associated with
the sea-anemones. The jelly-like consistency of their bodies
has given them the name of Jellyfishes. A rather more
accurate name for them is medusae, the tentacles being
compared to the snaky locks of that mythical monster.
They swim through the water by a lazy flapping of their
umbrellas, feeding upon whatever may come in their way.
While some are small, others become veritable giants, the
large blue jellyfish of the New England coast sometimes
measuring seven feet across ; its tentacles streaming behind
for a hundred feet as it swims through the water.

HYDKOZOA (HYDROIDS, ETC.).

In contrast with the Scyphozoa the Hydrozoa lack the
inturned oesophagus and the septa dividing the digestive
tract, while they have solid tentacles. In size they are on
the average much smaller, and colonial forms predominate.
In their life-history we frequently meet some wonderful
changes, and to describe these we may follow through the
life-cycle of the Pennaria, studied in the laboratory work.

From the egg there hatches out a little oval, free-swim-
ming embryo, which soon attaches itself by one end to
some submerged rock, while a mouth breaks through at the
other, and tentacles grow out around the sides of the body.
When a mouth is formed feeding and growth are possible.
As the animal grows larger little buds appear on the sides,
and these, forming mouths and tentacles, grow into
hydranths like the parent. These buds never become free,
but the whole colony thus formed has a common digestive
tube by which all are connected. On the outside a tubular
protecting sheath, the perisarc (p. 299), is developed. After
a while buds appear on the sides of the hydranths, and
these have a much different history, for they develop into
free-swimming jelly fishes.

These jellyfishes (see Fig. 139) are much like those of
the Scyphomedusae (p. 304), being bell-shaped or umbrella-
shaped, the mouth being at the end of the handle, while
branches of the digestive tract riin to the margin of
the umbrella. However, these hydrozoan jellyfishes differ
from the Scyphomedusse in the absence of mesenterial fila-

305

306 ELEMENTS OF COMPARATIVE ZOOLOGY.

ments and inturued oesophagus, and are further distin-
guished by the fact that the aperture of the umbrella is
partially closed by a thin membrane (velum) lacking in the
other jellyfishes. These jellyfishes produce the eggs from
which are developed other colonies like that studied.

FIG. 139.— A Hydroid (BougainviUea. After Allman, from Lang. 7i, feed-
ing polyp ; rn/c, medusa-buds ; m, a f ree-swiming medusa. At the base
are seen the root-like stolons connecting the colony together.

Here is a point which needs emphasis. From the egg is
developed a hydranth which by budding develops numer-
ous other hydranths, and each of these in turn, by budding
produces several medusae. In other words, we have here
au animal which reproduces asexually. These medusae are

HYDROZOA. 307

the sexual forms, and they produce eggs which grow not
into other jellyfishes but into the fixed forms. This phe-
nomenon is known as an alternation of generations, the
young resembling not the parent, but, rather, the grand-
parent.

ORDER I, — HYDRIDE.

Here belongs the fresh- water Hydrozoan — the Hydra —
in which there is no medusa stage, the animals producing
eggs which develop directly into other Hydra?. The fresh-
water Hydrae, which are green or brown in color, and about
a quarter of an inch in length, abound in fresh water

ORDER II. — HYDROMEDUSJE.

The Pennaria is typical of this group. In most there is
that alternation of fixed and free-swimming forms which has
already been described. In the fixed stage the colony is
usually protected by a perisarc which occasionally may be
developed into cups protecting the hydranths. On the
other hand some of these Hydromedusae exist only as jelly-
fishes, the eggs which they produce developing directly into
other jellyfishes. The Hydromedusae are abundant in all
seas, and are among the most beautiful and interesting
of all the animals with which the naturalist has to deal.
Only two or three species occur in fresh water.

ORDER III. — SIPHONOPHORA.

These may be defined as colonies of jellyfishes, arising
by budding. In these colonies the medusae become special-
ized in different directions. This specialization in some
forms may go so far that we have the jellyfishes modified
into (1) a float supporting the colony; (2) swimming-
bells by means of which it moves; others (3) for feeding,
still others (4) for digestion, and again others (5) for re-

308 ELEMENTS OF COMPARATIVE ZOOLOGY.

production, etc.
from the colony.

Usually one or more of these is absent
The most familiar of the Siphonophores

FIG. 140.— Diagram of a Siphonophore.
c, covering scale ; d, digestive sac ;
f, float ; m, mouth of feeding indi-
vidual; r, reproductive bell; s,
swimming-bell; t, tentacle.

FIG. 141. — Portuguese man-of-war
(Physalia). After Agassiz.

is the "Portuguese man-of-war," which occasionally drifts
on our shores. In this beautifully-colored species the float
is large and the swimming-bells are absent.

COMPARISON OF C(ELENTERATES. 309

COMPARISONS.

Answer the following questions for sea-anemone and for
hydroid :

(1) Has either a radial arrangement of parts ?

(2) Are tentacles present ?

(3) Is there a body-cavity apart from the digestive
cavity ?

(4) How many openings to the digestive tract ?

CCELENTERATA.

The Ccelenterata and the Echinoderma were formerly
united into a group Radiata, the basis of association being
the radiate type of structure so noticeable in a starfish or a
coral. Later studies showed that the two divisions had
very few points in common, and that the differences be-
tween them were very great. Remembering the account of
the Echinoderms, the following facts regarding the Ccelen-
terata will have significance :

In the Coelenterates there is but a single opening into the
digestive tract, which thus serves at once for mouth and
vent. Through it all food enters, and all indigestible por-
tions are cast out. The mouth connects with the digestive
tract, which extends to all parts of the body, so that the food
is brought close to every portion, there being no circulatory
apparatus. There is no body-cavity distinct
from the digestive tract. Around the
body, usually close to the mouth, is a circle
of tentacles, and on these abound some
structures which need a slight description
— the nettle-cells.

These nettle-cells are small bodies which
occur all over the body, but are especially
numerous upon the tentacles. Each is in
FIG. 142. — A dis- reality a sac, one end of which is drawn
thffh^e^coliS out into a long and slender tube, coiled up

around the cell. inside Qf the ^^ Thege nettle-Cells Can

be " discharged" by the animal, and this discharge consists

310

C(ELENTERATA. 311

in a forcing out of the tube in the same way in which one
may blow out the inturned finger of a glove. These
cells contain a strongly irritant poison, and at the discharge
this poison escapes. These nettle-cells furnish a means of
defense, and they are also used in obtaining food, the poison
being strong enough to paralyze instantly small animals.
In some forms it is strong enough to affect man. For in-
stance, the tentacles of the Portuguese man-of-war will
quickly raise a bright red ridge on the hand or arm of man,
and produce an almost intolerable burning sensation in
the parts thus touched.

In many Coelenterates there is no specialized nervous
system, the general surface of the body having sensory and
nervous powers. In others there is a central nervous system
arranged in a ring around the body ; and some of the jelly-
fishes may have organs, the structure of which leads to
their being regarded as simple types of eyes and ears.

With very few exceptions, the Ccelenterates are marine.
Some move about freely, some are as firmly fixed as is any
plant ; but, as has already been explained (p. 305), both fixed
and free conditions may occur in the life-history of a single
species. All of the Coelenterates reproduce by means of
eggs, but, besides, most forms have the power of forming
buds which grow into new individuals, sometimes like,
sometimes greatly different from, tbe parent. The Coelen-
terates are divided into two classes, accordingly as they
possess or lack an inturned oesophagus.

CLASS I. — HYDROZOA (p. 305).
CLASS II. — SCYPHOZOA (p. 301).

CTENOPHORA.

Usually a number of free-swimming jellyfishes are closely

associated with the Hydrozoa and Scyphozoa under the

313

CTENOPHORA. 313

name Ctenophora. They receive this name (meaning comb-
bearers) from the fact that the usually globular body has
eight rows of vibratile organs, each row being composed of
series of hairs arranged much like the teeth of a comb.
They have an alimentary canal, which branches so that a
portion underlies each row of combs. They, however, differ
from all true Coelenterates in the absence of nettle-cells, and
in a number of other features which need not be described
here. All of the Ctenophores are marine.

SPONGES: LABOEATORY WORK.

A. — A CALCAREOUS SPONGE (Grantid).

Notice the shape. Is the surface smooth ? How many
openings do you find ? What differences do you find
between the ends ? Split the sponge lengthwise with a
sharp scalpel, laying open the central cavity (cloaca).
Where is the large opening (ostium) hy means of which the
cloaca is connected with the exterior ? By what is it sur-
rounded ? In the walls of the cloaca notice the openings
(excurrent canals) — best seen after the sponge has dried.
In the cut walls see the small chambers (ampullse). Draw
one half of the sponge, naming the parts. Cut the other
half of the sponge transversely, and notice the radially
arranged ampullaB. Place a bit of the sponge in weak
hydrochloric acid. What occurs? Boil another bit in
caustic potash (a few drops of a 5-per-cent solution), then
place the fluid on a slide ; examine under the microscope.
Draw the spicules which you see. Crush a dry bit of the
sponge in the fingers. Has it any elasticity ?

B. — A BATH SPONGE.

Select small rounded sponges for this purpose. Notice
the irregularity of the surface. Do you find any large open-
ing in any way comparable to the ostium of the calcareous
sponge ? If so, split the sponge through this opening and
study the section. Can you find canals branching from the
ostium ? If so, sketch their arrangement.

314

STUDY OF A SPONGE. 315

Crush a bit of the dry sponge between the fingers. How
does it compare with the other form ? Examine a very thin
bit of it under the microscope ; can you find spicules ?

It is to be noted that in the bath-sponge only the hard
or skeletal parts are present, the flesh having been washed
away. In the calcareous sponge, as put up for laboratory
use, flesh and skeleton are both present.

SPONGES (PORIFERA).

Sponges differ from other animals in so many respects
that for along time naturalists were uncertain as to whether
they were animals or plants, but this matter has long been
settled beyond dispute.

All sponges are composed of the following parts : On the
outside are numbers of small openings or pores (whence the
name Porifera), and these lead to small tubes or incurrent
canals, which extend inward to small chambers (ampullae) ,
the digestive organs, which also contain the apparatus for
keeping up the flow of water through the canals. With the
water numerous small particles of food are drawn into the
ampullae, and are there taken up, while the water leaves the
chambers by means of a second system of tubes (excurrent
canals), passes into a central space (cloaca), and thence to
the exterior by a large opening (ostium). This same system
of canals also serves for respiration, but special muscular,
circulatory, nervous, sensory, and excretory organs are lack-
ing.

In a few sponges there is no skeleton, but most species
have a firm support for the soft parts. This skeleton may
consist of small particles (spicules) of carbonate of lime or
of silica, often much like crystals in form ; or of fibres of a
horny substance; or again, both spicules and fibres may
occur together. In the sponges of the stores we have noth-
ing but the horny fibres, all of the flesh having been washed
away; but in this skeleton we can trace roughly the systems
of canals, the cloaca, and the ostium.

Sponges reproduce by budding and by eggs. In budding

316

SPONGES. 317

smaii outgrowths occur, and these gradually become larger,
and finally an ostium is formed. From the eggs are formed
little free-swimming embryos, which later settle down and
grow into the adult.

Sponges are largely marine, only a few forms, and these
of no economic importance, occurring in fresh water. The
sponges of commerce come from the Mediterranean, the

FIG. 144.— Sponge (Dactyocalyx). From Liitken.

Red Sea, and Florida and the West Indies. They are
brought up by divers, or by hooks which are dragged over
the bottom. The fleshy portions are allowed to decay,
then the skeleton is washed, and the sponges are packed in
bundles for the market. There are different grades of elas-
ticity and fineness of fibre, and consequently different values.
The finest sponges come from the eastern part of the
Mediterranean. Sponges occur as fossils, especially in the
Cretaceous rocks.

There are two great groups of sponges. In the first,
called CALCAEEA, the skeleton is composed of carbonate of
lime; in the second, SILICEA, there is sometimes a skeleton
consisting of silica (quartz), sometimes of horny fibres,
sometimes of both horny fibres and siliceous spicules; and
again, there are a few forms which have no skeleton.

METAZOA.

All of the divisions or groups of animals so far studied
are united by naturalists under the name Metazoa for the
following reasons: A careful consideration of their struc-
ture leads to the conclusion that, in all, the body is of
appreciable size, and that, in each and every one, certain
portions or organs are specialized for the performance of
certain functions necessary in the economy of the individual.
Thus we find in all reproductive organs which have solely
to do with the perpetuation of the species; in all (except
a few degenerate parasites) there is a mouth for taking in of
food and an alimentary tract for its digestion ; in all there is
a more or less distinct nervous system ; and in all, parts of
the body are more or less specialized for respiration.

A little deeper insight leads to another conclusion which
farther justifies the group of Metazoa. In
all animals so far studied the body is com-
posed of layers, at least two in number;
one on the outside forming the skin, and a
a second on the inside forming the lining
of the digestive tract. To these two layers
are given names, ectoderm and entoderm,
meaning respectively outer and inner skin.

In the Ccelenterata all of the functions
of the animal are performed by either one
or the other of these two layers. In all
the other divisions a third layer occurs FIG. 145.— Diagram of

a two-layered ani-

between ectoderm and entoderm — the mai, based upon a

nydroid. ec, ecto-

mesoderm (middle skm), and this meso- derm; en, entoderm.
derm takes some of the functions which are divided between

318

METAZOA. 319

the ectoderm and entoderm of the Coelenterata. The study
of the development of these three-layered animals shows a
very interesting fact. At first there are but two layers in
the body, and later the mesoderm develops between these
two. In other words, all of the higher Metazoa pass through
a stage in which they exhibit a coelenterate condition.

These three layers reach their highest condition in the
Vertebrates, and it may be interesting to see how all the
various structures which have been studied in a shark or in
a rat are related to these layers.

To the ECTODERM belong the outer layer of the skin,
the outer layer of scales, the hair, feathers, sweat-glands,
the enamel of the teeth, the nervous system, the sensory
portions of sensory organs, and the lens of the eye.

The ENTODERM furnishes the lining of the alimentary
canal, the notochord, gills, tracheal lining, lungs, liver,
pancreas, urinary bladder.

The contributions of the MESODERM to the body are more
extensive. They include the deeper layers of the skin,
fat, muscles, connective-tissue, cartilage, bones, ligaments,
blood-vessels, blood, the lining (pleural and peritoneal mem-
branes) of the body-cavity, the deeper layer of the scales,
the dentine of the teeth, the outer layers of the alimentary
canal, and the reproductive and excretory organs and their
ducts.

If we study any part of any one of the animals already
dissected or mentioned under the higher powers of the
microscope — having first treated it so as to bring out details
— we will discover another fact of great importance. Every
one of these animals will be found to be made up of small
parts, essentially like each other, just as the wall of a build-
ing is built up of separate bricks. These separate parts or
elements of the Metazoa are known as cells. Each one of

320 ELEMENTS OF COMPARATIVE ZOO LOOT.

these cells is microscopic in size, with an average diameter
of about ^ny of an inch ; and each consists of a semi-fluid
substance known as protoplasm, in the centre of which is a
mass of slightly different protoplasm, known as the nucleus.
Now, since each and every metazoan is built up of cells, we
may speak of the Metazoa as many-celled animals.

These cells vary greatly in shape, but no matter how
different they may appear at first sight, they all agree with
the description given in the last paragraph. Some may be
spherical, others cubical or flattened, and still others
branched, yet in all there is the same nucleus. Cells of the
same general shape are united together to form tissues, so
that we have bone-tissue made up of what may be called
bone-cells; muscular tissue, of muscle-cells; and nervous
tissue, of nerve-cells; etc.

In the Metazoa the tissues are built up into organs for
the performance of certain purposes; and usually a single
organ is composed of several kinds of tissues, while the same
kind of tissue may reappear in different organs. Thus the
hand of man is an organ of grasping; in it we find mus-
cular, bony, connective, and nervous tissues; while in the
heart of the shark muscular, connective, and nervous
tissues appear.

The Metazoa are subdivided into groups or " branches"
which may be arranged in order of their complexity in the
following manner:

BRANCH I. — CCELENTERATA (p. 310).

BRANCH II. — SPONGIDA (p. 316).

BRANCH III. — VERMES (p. 242).

BRANCH IV. — MOLLUSCA (p. 269).

BRANCH V. — ARTHROPODA (p. 226).

BRANCH VI. — ECHINODERMA (p. 291).

BRANCH VII. — CHORD ATA (p. 153).

PROTOZOA.

In contrast to the Metazoa, which have just been defined
as animals made up of many cells, and these cells arranged
in two or three layers and grouped into tissues, comes the
group of Protozoa, which may be defined as animals each
consisting of a single cell. A little thought will show that
this difference is in reality very great. In the metazoan
certain groups of cells become adapted (specialized) for the
performance of certain work in the body, and the more
specialized they become the more restricted are they in
their lines of work. Thus in man the cartilage and bone-
cells are solely for the support of the body, muscle-cells for
the moving of parts or of the body as a whole. When,
however, we turn to the Protozoa, composed of but a single
cell, we find that this one cell has to do all the work which
in the Metazoa is shared by the several groups of cells. It
has to feed, to move, to excrete waste matters, and to re-
produce its kind. In a word, the cells of the Metazoa are
differentiated in various directions; those of the Protozoa
are undifferentiated.

The Protozoa show great variety in shape, appearance,
and habits. In some there is no differentiation between the
different regions of the cell which composes the body, ex-
cepting the fact that a nucleus is usually (if not always)
present. Food may be taken in at any point ; any portion
may be used for locomotion; and indigestible portions may
pass out anywhere on the surface. By feeding they grow,

321

322 ELEMENTS OF COMPARATIVE ZOOLOGY.

and when growth reaches a certain limit the animal (cell)
divides, and we have now two individuals in the place of the
original one.

In other Protozoa different regions in the cell may be
specialized in different directions. A single example must
suffice. In the form figured we have but a single cell, but
it is a cell of definite shape. Exter-
nally the body is covered with a
denser layer, comparable in position
and use to a skin. A little deeper
are developed longitudinal lines of
contractile material which act in the
same way as the muscles of the
Metazoa, moving one part on another.
Over the outer surface are minute
hair-like organs (cilia) which are in
constant motion, and when the ani-
mal casts itself loose these serve like
so many oars to propel it through the
water. At the larger end of the body
these hair-like organs become much
larger, and they are here arranged in
a spiral. The effect of their constant
motion is to create a minute whirlpool
in the water, the centre of which is
in an opening in the larger end. This
K mav kg compared to a mouth. The

FIG. 146. — Diagram of a * . .., ... ,. •,

Protozoan based upon water brings with it minute particles

Stentor. c, large cilia , .. .. »• •* T n

around the oral disc ; cv, suitable for food, and these pass

contractile vacuole; gr, , , ., . , . , .,

gullet; wi, mouth; nm, through the mouth into a cavity com-

muscular bands; n, nu- ., . , . -, ,-,

cieus; w, nerve-ring. parable to a gullet, from which they
pass into the central part of the cell, where they are
digested. Then the indigestible portions are at last passed

PROTOZOA. 323

out from the body at a fixed point, the functional vent.
The large cilia always move in a regular and rhythmic man-
ner— a fact which would imply that they were connected
and controlled in some manner in their action; and high
microscopic powers shows at their bases a cord of somewhat
denser material which takes the place of a central nervous
system. If this be cut, the cilia no longer work in har-
mony. Finally, all animals, in doing work, produce nitrog-
enous waste, which must be gotten rid of by means of
kidneys. In the form figured the kidneys are replaced by
a space on the interior (contractile vacuole) which regularly
enlarges and contracts, and at each contraction this waste
is forced out into the surrounding water. All of this is in
a single cell.

The Protozoa, of which many thousand different kinds
have been described, are all very minute, only a very few
being even visible without a microscope. The great
majority are aquatic, some being found in fresh water and
many in the sea. A few live in moist earth, and more are
parasitic in other and higher animals, where they may at
times be productive of disease.

COMPARATIVE PHYSIOLOGY.

An animal is a machine, and the preceding laboratory
exercises are intended to give a student a knowledge of the
different kinds of mechanism in the several animal types.
Our knowledge of a machine is not complete when we know
its structure ; we must also understand the way the differ-
ent parts perform their work. The study of the structure
of an animal is the province of anatomy, while that branch
of science which deals with the action of the various parts
— the working of the whole — is called physiology.

It is a far more difficult task to ascertain from the speci-
mens themselves the function of the parts and the action of
the animal machine as a whole, than it is to make out the
details of structure and so a general summary is given here.

Any and every machine, in order that it may perform
work, must be supplied with energy, and the animal obtains
this energy by the slow combustion (oxidation) of food, just
as the steam-engine gets its energy from the rapid combus-
tion of coal. In the case of a steam-engine there is an
engineer who supplies the fuel, regulates the action of the
parts, and disposes of the waste. The animal must be its
own engineer. It must have the means of obtaining fuel
(food), of putting it in such position that all the energy pro-
duced by its oxidation can be utilized to its fullest extent,
and all waste can be properly disposed of. This has led, in
the first place, to the formation of a digestive tract, in which
the food is put in such shape as to be most advantageously
used by the organism.

324

COMPARATIVE PHYSIOLOGY. 325

In the lowest animals (lowest Protozoa) we find that the
whole body (cell) serves as a digestive tract, and that food
can be taken in at any point on the surface. A little higher
(p. 322) an organ which we must call a mouth is formed in
the body, and this opening for the taking in (ingestion) of
food is found in all higher animals, except a few parasites
which, living in liquid food, need no such opening. With
larger animals a definite digestive cavity or canal is formed,
the lining of which has certain definite work to perform.
Most articles of food are insoluble as taken into the body ;
a bit of meat or starch can be soaked indefinitely in pure
water or can even be boiled for days without passing into
solution. In the digestive tract juices are produced which
alter these substances so that they can be dissolved ; and it
is only when they are in solution that they can pass through
the walls of the alimentary canal to those parts where they
are to be utilized.

In the lower animals all parts of the digestive tract seem
able to act at once as formers of digestive fluids, and in the
taking up of the dissolved food, but as we pass higher in
the scale complications of various kinds are introduced. In
the first place, we find certain organs, like the salivary
glands, stomach, pancreas, and liver, set apart for the secre-
tion of digestive fluids, and even in animals as low as the
sea-anemone the mesenterial filaments appear to have the
same power. On the other hand, the other portions, while
they may secrete, are pre-eminently the region for the
absorption of the liquefied food. Another complication is
this : A given amount of surface can absorb only so much
in a given time ; so to obtain the necessary amount of food
the surface must be increased. This explains in part the
folding of the wall of the digestive tract in the sea-anemone,
as well as the lengthening and coiling of the intestine in

326 ELEMENTS OF COMPARATIVE ZOOLOGY.

tadpole and rat, and the spiral valve in the shark. In many
vertebrates the surface is still further increased by numerous
minute foldings and outpushings of the lining of the intes-
tine which, though so small as to be invisible to the naked
eye, still more than double the surface.

With most food there are certain portions which are in-
digestible. These of course must be gotten rid of. In
the Coelenterates and flatworms the only opening through
which they can pass out is the same one by which they
entered, and so this opening, usually called the mouth,
serves at once as mouth and vent. In the higher forms
the alimentary canal becomes a complete tube with two dis-
tinct openings, one — the mouth — for the taking in of food,
the other — anus or vent — for the ejection of non-nutritious
portions.

After its solution the food (nourishment) must be trans-
ferred to the parts which are to do the work. In the Pro-
tozoa the same parts which digest do the work. In the
sea-anemone and flatworms the pouching of the digestive
tract renders the transfer easy, for the pouches extend to
all parts. Above these forms we find circulatory organs
present, one of the functions of which is the carrying of the
dissolved food from the digestive tract to the working parts.
These circulatory organs are tubes through which the fluid
flows, but a flow can only be produced by some mechanism
which shall propel the fluid. In most cases this is effected
by muscles in the walls of the vessels, which by waves of
contraction force the fluid along. The tendency is con-
stantly towards a concentration of these pumping muscles
in one region, and thus a heart results.

So far, we have traced the fuel to the working parts.
In order to do work the fuel must be oxidized, and this
means that oxygen must also be brought to these parts.

COMPARATIVE PHYSIOLOGY. 327

This oxygen is found either in the air or dissolved in the
water in which the animal lives. In the Ccelenterates, flat-
worms, and many other forms, the general surface of the
body is sufficient for the absorption of the oxygen, but where
the animal is larger and needs more oxygen special provi-
sions are needed.

A very simple condition, physiologically, is found in the
insects, where air-tubes (tracheae) extend inwards from the
outside, their fine branches reaching to every part of the
body. Air is drawn into these tubes by an enlargement of
the body by suitable muscles, and then, when the oxygen
is absorbed, contraction forces out the remainder. This
breathing process can be seen by watching the abdomen of
a grasshopper or a wasp. In many Crustacea, molluscs,
worms, vertebrates, the conditions are more complicated.
In these the nutrient fluid is also the bearer of the oxygen;
and, in order that the fluid may obtain this element special-
ized portions are developed, where the circulatory fluid may
come into close relationship with the water (gills) or the air
(lungs). In some (see the figure of Doris, p. 276) the gills
project freely into the water, and there is no special appa-
ratus for changing the fluid. In other forms the gills are
protected by enclosure in a branchial chamber, and then the
water containing the oxygen must be brought here. In the
oyster and clam this is effected by numerous minute hair-
like structures (cilia) which by their constant motion draw
water over the gills. The squid gets its supply by enlarging
and contracting its mantle-cavity, the crayfish by pumping
water over the gills by means of its "gill-bailer," and the
fish and tadpole by taking water into the mouth and forcing
it out through the gill-slits. The lungs of the higher ver-
tebrates possess a resemblance to the tracheae of the insects
in that air is drawn into them; but here the similarity

328 ELEMENTS OF COMPARATIVE ZOOLOGY.

ceases, for in the vertebrates the air is brought from the
lungs to the working parts by the intervention of the
nutrient fluid (blood).

The methods by which air is drawn into the lungs vary.
The frog swallows the air by aid of the muscles extending
across the throat between the halves of the lower jaw, and
that this swallowing is the only way of forcing air into the
lungs is shown by the fact that if the mouth be kept from
closing the animal will suffocate.* In the Sauropsida the
muscles between the ribs and those forming the walls of the
abdomen are concerned in the inspiration and expiration of
air; while in mammals the muscular partition (diaphragm)
which divides the body-cavity becomes an efficient organ
in the process.

We naturally think of work in terms of motion, and in
the case of an animal the contraction of a muscle or the
movement of a part or the whole of the body naturally sug-
gest themselves as examples. These, however, are but a
part of the work which the animal does. The performance
of any function of the body is really work. When a gland
secretes, a nerve acts, an intestine absorbs, or the mind
carries on its operations, the expenditure of energy is called
for just as in the contraction of a muscle. So all parts
must have both food and oxygen.

When coal is burned in an engine, besides energy there
is a production of waste. A part of this waste passes off in
a gaseous condition as water vapor and part as ashes.
When any part of the animal body works there is a similar
formation of waste, and the carbon dioxide and water vapor
are carried away by the same structures (tracheae in the
insects, blood-vessels and gills or lungs in many other forms)
which brought the oxygen to the parts.

* The skin is a very important organ in the respiration of the
Batrachia (see p. 50).

COMPARATIVE PHYSIOLOGY. 829

The animal, besides, needs for its fuel substances known
to the chemist as nitrogenous food, and the combustion of
this produces, besides the carbon dioxide and water, nitrog-
enous waste, and this, in all of the higher animals, is gotten
rid of by means of organs which can be grouped under the
common name of kidneys. Here are to be placed not only
those structures specifically called kidneys in the foregoing
pages, but also the green gland of the crayfish, the Malpi-
ghian tubes of insects, the nephridia of the earthworm, and
the organ of Bojanus in the clam. Even the contractile
vacuole of the Protozoa is to be regarded as an organ for
the excretion of nitrogenous waste.

We have seen that the fluid propelled by the heart has a
large series of different purposes to fulfil. It must carry
nourishment from the digestive tract to the different parts
of the body ; it has to carry oxygen from the gills and lungs
to these various structures, and to carry the carbon dioxide
and water produced by work to the same lungs and gills,
while the nitrogenous waste must be carried to the kidneys.
The fluid which does all this is the blood.

There is another aspect of animal physiology to be re-
viewed. The animal needs to be aware of the presence of
food and of the proximity of things injurious, to it. This
implies the formation of a sensory system, and naturally this
system must be on the outside of the body, for from with-
out comes both food and danger. The knowledge of the
presence of good or of evil would be of little value to the
animal were it without ability to avail itself of this knowl-
edge. Hence this sensory system is connected with a
nervous system; which directs and controls the actions of
the animal. In the lower animals this nervous system is
on the surface, but as this superficial position is dangerous
to such an important structure, we find in all the higher

330 ELEMENTS OF COMPARATIVE ZOOLOGY.

animals that it becomes removed to a deeper position, which
necessitates the development of nerve-cords to connect it
with the sensory system and with the muscles and other
parts. It is interesting that in all animals, even in man,
no matter how deeply situated or how thoroughly protected
it may be in the adult, the central nervous system arises
from the outer surface, and secondarily attains its perma-
nent position.

Since most animals must search for their food, we find
that one end becomes adapted for always going in front,
and in this way a head has come into existence, and here are
situated the brain and the most important sensory organs,
as well as the mouth, since this part of the body first comes
into the neighborhood of substances useful as food or likely
to be injurious to the animal.

So far we have treated of the animal as an automatic self-
regulating machine, but in one respect it differs from all
machines of human production. No amount of fuel put
under the boiler of a steam-engine will cause this mechanism
to increase in size or to give rise to other bits of mechanism
like itself. The animal machine grows by the taking in of
food, and like the steam-engine, it wears out. It, however,
has the power of reproducing the kind, by the formation of
small parts (either buds or eggs) which eventually grow into
animals like the parent which produced them, and thus the
species is perpetuated, the young taking the place of the
generation which has worn itself out.

MORPHOLOGY OF ANIMALS.

We are now in position to review some of the facts we
nave already discovered, and to draw some general conclu-
sions.

Excepting some Protozoa, each and every animal can be
placed under one of two heads. In the one, the body is
bilaterally symmetrical. In it we can recognize anterior
and posterior; dorsal and ventral; right and left. Under
the other we place those forms in which these features do
not exist; there is no right and left, but the parts are
radially arranged around an axis, like the spokes around
the axle of a wheel. To this latter group belong the
sponges and coelenterates ; to the first, all other divisions
reviewed in this volume. Even the Echinoderms belong
to the bilateral type, for their development shows that in
the early stages they have not a trace of radial symmetry,
but only acquire it later in life.

In the bilateral animals, in turn, two types can be
recognized: the segmented and the unsegmented. The
segmented forms show their peculiarities in the most
striking manner in some of the Annelids, like the earth-
worm (p. 235). In these the body is made up of a series
of rings or segments, each essentially like its fellow, and
each containing a portion of all systems of organs — muscu-
lar, nervous, circulatory, digestive, excretory, etc. In the
arthropods this segmentation again appears, but here there
are tendencies in two directions : towards a fusion of seg-
ments, and towards an increase of one segment at the
expense of another. In annelids and arthropods this

331

332 ELEMENTS OF COMPARATIVE ZOOLOGY.

segmentation is visible externally; in the vertebrates it is
not so plainly shown, but it nevertheless exists. The trunk
muscles (see p. 11) are thus arranged; the spinal nerves
and the vertebrae correspond to the muscle segments, as do
also certain blood vessels (intercostals), while in their early
history the kidneys are segmen tally arranged.

On the other hand, the lower worms show no traces of
segmentation, while the molluscs show it to a very slight
extent.* In the echinoderms there is a repetition of
ambulacra and ambulacral plates, but this is supposed to be
different in its origin from that in the segmented animals.

All animals above the Protozoa reproduce by eggs.
These eggs, when carefully studied, are found to agree in
their essential characteristics. Each, in fact, is a cell
(p. 320) containing a nucleus; but to these essentials other
structures — shell, white, yolk, etc. — may be added. Each
egg, under proper conditions, is capable of growing into a
form like that which produced it. The essential condition
is that a peculiarly modified cell, the spermatozoan, unites
with the egg, and then the compound cell is capable of
development, f Keduced to its simplest terms, the process
of development may be briefly stated thus :

After union with the sperm cell (fertilization) the egg
divides again and again, the result being the formation of
a large number of cells, all connected together, which later
arrange themselves in layers (p. 318), and then develop into
organs. This type of reproduction is known as sexual
reproduction, since egg-cell and sperm-cell are produced
by animals of different sexes.

* The gills, kidneys, and heart of the Chitons (p. 273) and the
Nautilus (p. 267) are supposed to present indications of segmentation.

f In a few cases, as in the honey-bee, the eggs can develop without
union with a spermatozoan.

MORPHOLOGY Of1 ANIMALS. 333

In many Protozoa something similar occurs. Here we
find a union of different individuals, and as each protozoan
is a single cell, this union of individuals is comparable, to
a certain extent, to the union of egg-cell and sperm-cell.
With the Protozoa, however, after this union (conjugation)
the individuals separate and each divides, thus producing
new individuals (cells), which differ from the cells produced
by the division of the egg in that they never arrange
themselves into layers, but each forms a distinct individual
like the parent.

Besides this sexual reproduction many animals possess
the power of reproducing asexually. In these cases the
animal Lmay divide into two, or a small portion may pro-
trude as a bud which will eventually produce an individual
more or less like the parent. This asexual reproduction is
very common among the ccelenterates, but it may also oc-
cur among the lower worms (p. 243), the Polyzoa, the
tunicates, etc.

In many instances this asexual reproduction does not re-
sult in the formation of distinct and separate animals, but
buds and parents may remain somewhat intimately con-
nected with each other, the result being the formation of
what are known as colonies, of which Pennaria may be
taken as a type. Here we are met with a difficulty in the
use of terms. We have spoken heretofore of individuals ;
but is each zooid in a colony of Pennaria an individual, or
is the colony itself to be so regarded, the zooids being re-
garded as organs ?

In many cases this reproduction by budding results in
the formation of parts very different from each other. Thus
in the hydroid (Fig. 147) abundant on shells inhabited by
hermit-crabs, the colony consists of three different kinds of
hydranths: (1) the feeding hydranths (/) which take

334 ELEMENTS OF COMPARATIVE ZOOLOGY.

nourishment for the whole colony; (2) the protective hy-
dranths (p) which lack mouths, but which are richly pro-
vided with nettle-cells; and (3) the reproductive hydranths
(r), the sole function of which is the reproduction of the
species. In the Siphonophores this differentiation is carried

FIG. 147.— Part of a colony of the hydroid, Hydractinia^ an illustration of
polymorphism. /, feeding individuals ; p, protective individuals ; r, re-
productive individual.

still farther (p. 307), for here seven different forms may be
developed. When there are but two different forms in the
history of the species it is called dimorphic (from the
Greek meaning two forms) ; if more than two, the species
is polymorphic.

Besides the di- or polymorphism produced by budding,
similar conditions may arise in other ways. Thus fre-
quently we find sexual dimorphism, in which the male and

MORPHOLOGY OF ANIMALS. 335

female of the same species are greatly different in their
appearance. An example of this is familiar in the can-
kerworm-moths, the male of
which is winged, the female
wingless. Again, we have to
recognize a seasonal dimor-
phism. Thus certain butter-
flies produce several broods in
a year. Those of the summer
broods are so different from

FIG. 148.— Male (m) and female (/)

those Which COme from CO- of one of the isopod Crustacea, an
n . , , .. extreme example of sexual di-

coons which have passed morphism.

through the winter, that without following through the

whole history the relationships would not be suspected.

Closely connected with this polymorphism is the phenom-
enon of alternation of generations, of which instances are
abundant in some groups of the animal kingdom (p. 307).
Thus in the butterflies just mentioned, from the eggs of the
winter-brood individuals are produced the summer brood
presenting far different appearances from the parents, while
the eggs of the summer brood produce in turn the winter
brood. Again, in certain gall-wasps the difference between
two generations is so great — both in appearance and in
habits — that they would never be regarded as belonging to
the same species, or even to the same genus, were it not
that the whole history had been followed, so that it was
ascertained that each generation resembles, not its parents,
but its grandparents.

Many animals in the course of their development pass
through a metamorphosis, which is not to be confused with
polymorphism. In forms where a metamorphosis occurs
the young, as it hatches from the egg, is greatly different
from the parent, but by successive changes of form it at

336 ELEMENTS OF COMPARATIVE ZOOLOGY.

last reaches the adult condition in which it resembles closely
the parent. These metamorphoses at times give us clues
as to the past history of the group. Thus the larvas of
Echinoderms (p. 291) and the tadpoles of the Anura (p.
50) point to the fact that the first group has descended from
markedly bilateral ancestors, and that the radiate condition
of the adult has been secondarily acquired; while the his-
tory of the frog is evidence that these batrachians have
sprung from tailed water-breathing ancestors. In the In-
sects, on the other hand, the larval and pupal stages have
far less significance, but apparently have been introduced
into the history the better to adapt these forms to the
various conditions of their existence.

THE ANIMAL KINGDOM.

All of the different forms already enumerated — both
protozoan and metazoan — are called animals,* in contrast
with another great group of living forms, the plants, which
form the Vegetable Kingdom.

At first sight the animals and the plants seem entirely
distinct. "We say that animals move, have sensation, have
organs of feeding, of respiration, motion, etc., and that the
plants lack all these. When we contrast a cat and a cab-
bage these and many other points of difference are at once
forced upon us, while the features in which they resem-
ble one another seem to be extremely few. When, how-
ever, we carry our comparisons farther and take the lower
forms into account we soon find that these distinctions fail.
We find many animals which are as firmly fixed as any
tree, while we find many undoubted plants which move
through the water as freely as any fish. We find, again,
many plants which have undoubted powers of sensation.
House-plants in a window turn their leaves towards the
source of light; the leaves of the sensitive-plant droop if
they be touched; while the reproductive elements (zoo-
spores) of many low aquatic plants will recognize the pres-
ence of and swim towards a trace of malic acid. On the
other hand, sensory organs are as poorly developed in
sponges, and in many Protozoa, as in many plants.

* Frequently the term animal is restricted to members of the group
of mammals. Thus we hear one say "animals and birds." This is
not correct. A bird, a fish, or a clam is as truly an animal as a cat.

337

338 ELEMENTS OF COMPARATIVE ZOOLOGY.

Plants really have their organs of feeding and of respi-
ration in their roots and leaves, while animals as high as
the parasitic worms have no organs for taking food or for
respiration, the absorption of nourishment taking place
at any spot on the surface of the body.

Several other tests have been suggested to separate ani-
mals from plants. Plants reproduce by seeds, by spores,
and by buds; animals by means of eggs. Plants take up
carbon dioxide and give off oxygen; animals use oxygen
and give off carbon dioxide. Plants take either liquid or
gaseous nourishment, while animals partake of solid food.
Plants may have a peculiar green coloring substance called
chlorophyl, lacking in animals. Plants produce a peculiar
chemical substance known as cellulose. These features
when accurately analyzed are all seen to have their excep-
tions. Many animals reproduce by budding, while the
sexual reproduction of animals and of plants is essentially
the same. Plants require oxygen as much as animals, and
it is only the green plants which give off oxygen ; a mush-
room or a toadstool takes up oxygen and gives off carbon
dioxide the same as does any animal. Quite a number of
animals possess chlorophyl, while it is lacking from many
plants; and cellulose is found even in the Tunicata. In
the matter of food the distinction is a little sharper. While
some animals like the parasitic worms take only nourish-
ment in solution, no plant takes solid nourishment.

Yet, although we cannot frame a perfect definition which
will at once separate all animals from all plants, we prac-
tically have little difficulty in deciding in any given case
that is likely to arise in our every-day experience as to
whether the form in question shall be placed in the one
kingdom or in the other.

The difficulty of framing a definition arises from the fact

THE ANIMAL KINGDOM. 339

that both animals and plants are both members of the liv-
ing world, and hence have many features in common, which
may be summarized in the expression that both are alive.
We do not know what life * is ; we only know it by the
phenomena which it exhibits, which may be briefly stated
as follows :

All living beings are composed of a peculiar substance (or
group of substances) known as protoplasm, and this proto-
plasm is known only as the product of life. When un-
mixed with other substances it is semifluid, transparent, and
slightly heavier than water. It contains a large number of
chemical elements — carbon, oxygen, hydrogen, nitrogen,
sulphur, and phosphorus predominating — but how these are
arranged is as yet one of the mysteries. When treated with
the reagents of the chemist it dies and is no longer proto-
plasm.

This protoplasm, and consequently the animals and plants
which contain it, exhibits certain properties. It can take
non-living substances and convert them into a part of itself,
that is, make them alive. The bread and the roast beef
which we eat are dead; yet we know that they become
parts of ourselves, not in the shape of bread and roast beef,
but as our own protoplasm. This process is known as
assimilation, and continued assimilation results in growth.
A snow-ball grows by accretions on the outside, but the
growth of animals and plants occurs all through the body
and throughout every part of it. It is a growth of the
protoplasm.

Protoplasm has the power of spontaneous motion. Under

* Frequently the expression ' ' vital force " is used, as if there were
some distinct force in nature exhibiting itself only in living forms.
This is entirely unnecessary, for each and every phenomenon of life
can be explained by physical and chemical means,

340 ELEMENTS OF COMPARATIVE ZOOLOGY.

favorable conditions we can see its particles changing their
relative position, or we may see the mass move as a whole.
It moves also in response to external influences, or, as the
physiologist expresses it, it reacts to stimuli. Thus some
protoplasm will turn to the light, other kinds will try to
avoid it. Heat, up to a certain degree, will increase its
action, while electricity will cause it to contract.

Protoplasm has the power of reproduction, by which we
mean that portions can separate from the parent mass and
can then carry on all the processes which could be per-
formed before the separation took place.

These, and a number of other features not so easily de-
scribed, are characteristic of protoplasm, and they occur in
no non-living substance. These are, too, the phenomena
of life, and hence protoplasm has been aptly termed the
physical basis of life.

APPENDIX.

Alcohol. — The most important of all reagents. It can
be purchased, tax-free, by incorporated institutions upon
the fulfilment of certain conditions.* As it comes from
the distiller it is usually about 95$ alcohol, the rest being
water. This is too strong for most purposes, and for the
preservation of material it should be reduced to 70$ by the
addition of water.

Specimens for dissection should be kept in 70$ alcohol,
but in putting them up a weaker grade (50$) should be
used first, and this should be changed every day or two at
first. Plenty of alcohol should be used, otherwise the
specimens will spoil.

Instead of alcohol for preservative purposes, other solu-
tions are sometimes used with fairly good results. Among
these may be mentioned :

Formol. — This is a 40$ solution of formaldehyde, and
for use this should be reduced by addition of water to a
2$ solution (i.e., 1 part formol to 49 of water), in which
specimens may be kept in good condition for some months.
The same care must be exercised as with alcohol to
change the fluid frequently while hardening the specimens.
Formol has the disadvantage of evaporating readily, and
so the jars must be tightly sealed. It also has the disad-
vantage of freezing.

* These may be learned by application to tlie Collector of Internal
Revenue in any district in the United States.

341

342 ELEMENTS OF COMPARATIVE ZOOLOGY.

A second substitute for alcohol is Wickersheimer's fluid.
This is made by dissolving 100 grams of alum, 25 of com-
mon salt, 12 of saltpetre, 60 of potassic carbonate, and 20
of white arsenic (arsenious acid) in 3 litres of boiling
water. To this, when cold, add 1200 grams of glycerine
and 300 of alcohol. Change the specimens once or twice,
and keep them in at least twice their bulk of the fluid.

Injections are made as a means of more readily following
tubular structures, especially blood-vessels, and consist in
forcing into these tubes colored material which will render
them more easily recognized. For many injections simple
apparatus may be used. Thus frequently a glass tube
drawn out to a point can be filled with the injecting fluid
and then, when the end of the tube is inserted into the
blood-vessel, the fluid can be forced into the artery or vein
by the pressure of the breath. It is, however, more satis-
factory to use the regular injecting syringe, sold by all
dealers in naturalists' supplies. These are provided with
small tubes (canulas) for insertion into the vessel to be in-
jected, and these are grooved at the tip so that they may
be firmly tied into the artery or vein.

Most of the injections called for in the present work
can be made either through the aorta or through the ven-
tricle. The ventricle is cut open, and the canula is forced
through this opening into the aorta, around which a string
is passed and tied, thus holding the tube firmly in place.
The syringe is then filled with the injecting fluid (see
below) and connected with the canula, when a pressure
upon the piston will force the fluid into the blood-vessels.
Too much pressure should not be exerted, as the vessels are
liable to rupture.

Various injecting fluids have been proposed, but the
following are ample for all purposes, and they have, be-

APPENDIX. 343

sides, the advantage of not requiring heat, which in the
case of some forms causes a softening of the walls of the
blood-vessels.

Starch Injection Mass. — Grind together in a mortar one
volume of dry starch, one of a 2|$ aqueous solution of chloral
hydrate, and one-fourth volume each of 95$ alcohol and
of the "color." The "color" consists of equal volumes
of dry color (vermilion, chrome yellow, Prussian blue, etc.)
glycerine and alcohol. The mixture will keep indefinitely,
but requires thorough stirring before use and quick usage,
as the starch and color settle rapidly.

Gum Injection Fluid. — Make a rather thick solution of
gum arabic in water ; color it with carmine or soluble Prus-
sian blue, and strain through muslin. With the addition
of a little thymol the fluid will keep well if tightly corked.
After injection, place the animal in alcohol, which hardens
the gum.

By using both injection masses in succession the complete
circulatory system may be injected (double injection). To
accomplish this, first inject with the gum fluid, colored blue,
and then follow with the starch mass colored red. The gum
will flow through the finest vessels, but the starch mass will
stop at the capillaries.

Study of Vertebrate Brains. — If material be abundant,
the study of the brain and its nerves will be much facili-
tated by putting heads of the various forms in the fluid
mentioned below a week or two before the dissection is to
take place. The fluid, which should be changed two or
three times, softens (decalcifies) the bones, and at the
same time hardens the nervous structures. It is composed
of equal parts of 95$ (commercial) alcohol and 10$ nitric
acid. The heads should be washed for an hour or two

344: ELEMENTS OF COMPARATIVE ZOOLOGY.

in water before dissection, as otherwise the acid will attack
the dissecting instruments.

Fuehsin is one of the most easily used stains. It is made
by dissolving one part of the aniline dye in two hundred
parts of water.

Picrosulphuric Acid is used for killing many animals with-
out distortion. It is made by dissolving picric acid in water
until no more will be taken up, and then adding to one
hundred parts of the solution two parts of sulphuric acid.
It is allowed to stand a day, is filtered, and is prepared for
use by adding three parts of water to one of the stock solu-
tion. Specimens killed in this fluid are stained yellow,
and should be washed in several changes of water before
being placed in alcohol or formol. It takes from one to
three hours to kill.

INDEX.

Abalone, 275

Abducens nerve, 136

Acanthoderus, 183

Acanthopteri, 28

Acarina, 232

Accessorms nerve, 136

Acephala, 258, 277

Acerata, 228

Acetabulum, 45

Acmaea, 275

Acorn barnacles, 211

Actinozoa, 301

Adam's apple, 144

Adductor muscles, 248

Adrenal, 42

Aglossa, 50

Air-bladder, 12, 35, 145

Air-cells, 42

Air-sacs of bird, 61, 72

Air-tubes, 174

Aix, 79

Ala spuria, 60

Albatross, 80

Alcohol, 341

Allantois, 55, 66

Alligators, 70

Alpaca, 118

Alternation of generation, 307,

335

Alytes, 53
Ambulacra, 278
Ambulacral plates, 280
Ambulacra! groove, 281
Ametabola, 217
Ammonites, 267
Amnion, 55, 66
Amphibia, 49
Amphiccelous, 14, 129
Amphipoda, 168

Amphitrite, 241

Amphioxus, 153

Ampulla of sponge, 314, 316

Ampulla of starfish, 279

Anacanthini, 26

Anaconda, 68

Anal area, 282

Anal plates, 283

Anatomy, 324

Angleworm, 239

Animal kingdom, 337

Annelida, 239, 246

Anolis, 67

Anomura, 164

Ant-eater, 106

Antelope, 119

Antennae, 159

Antennulse, 159

Anthropoid apes, 124

Antilocapra, 119

Ant-lion, 221

Ants, 189

Anura, 53

Aorta, 13, 88

Aortic arch, 43

Apes, 124

Apoda, 293

Apparatus, 2

Aptenodytes, 79

Aqueous humor, 140

Arachnida, 229

Araneida, 230

Arbor vita?, 95

Arch, haemal, 14

Arch, neural, 14

Archaeopteryx, 76

Argynnis, 204

Aristotle's lantern, 283, 288

Armadillo, 105

345

346

INDEX.

Army- worm, 199, 201
Arterial blood, 36, 148
Arterial bulb, 13, 36
Arterial cone, 18, 36
Artery, afferent, 13
Artery, bracliiocephalic, 91
Artery, branchial, 13, 146
Artery, carotid, 43, 91
Artery, cceliac, 88
Artery, efferent, 13
Artery, gastric, 88
Artery, hepatic, 88
Artery, iliac, 89
Artery, mesenterial, 88
Artery, pulmonary, 91
Artery, splenic, 88
Artery, subclavian, 91
Arthropoda, 226, 320
Artiodactyls, 117
Asipkonida, 260
Ass, 117

Assimilation, 339
Asteroida, 285, 293
Atrophy, 160
Atrium, 144

Auditory nerve, 19, 95, 136
Auks, 80
Aurelia, 304
Auricle, 13, 145
Australian dog, 104
Aves, 71
Axial skeleton, 127

Baboon, 123
Back-bone, 127
Balancers, 222
Balaninus, 187
Baleen, 112
Bark-lice, 198
Barnacles, 211
Basiopodite, 157
Basket-fish, 294
Bass, sea, 29
Batrachia, 49
Bats, 109
Beach-flea, 169
Bears, 121
Beaver, 109
Bedbug, 195
Bees, 191

Beetles, 184
Bilateral animals, 330
Bile-duct, 88
Bird, dissection of, 59
Bird of paradise, 84
Birds, 71
Birds of prey, 81
Bison, 119
Blackfish, 112
Blindfish, 26
Blind worms, 54
Blister-beetle, 187
Blood, 36, 43, 149
Blow-fly, 223
Boa, 68

Body cavity, 11
Body layers, 318
Body of vertebra, 14
Bojanus, organ of, 249
Bombycids, 202
Bony-fish, dissection of, 9
Bony-fishes, 24
Bot-flies, 223
Boring beetles, 186
Bougainvillea, 306
Bowfin, 39
Brachial plexus, 95
Brachiocephalic artery, 91
Brachiopoda, 247
Brachyura, 164
Brain of vertebrates, 134
Brain of dog, 99
Branchiae of starfish, 279
Branchial apparatus, 10
Branchial arch, 11
Branchial artery, 13, 18
Branchial heart, 253, 271
Branchial tree, 279
Branchiostegals, 11
Breast-bone, 130
Bristle-tails, 218
Brittle-stars, 293
Brood-pouch, 162
Bruchus, 187
Buccal mass, 255
Buffalo, 119
Buffalo-bug, 185
Bugs, 194

Bulbus arteriosus, 146
Buthus, 230

INDEX.

347

Butterflies, 201
Butterfly, dissection of, 193
Buzzards, 81
Byssus, 262

Caddis-flies, 221
Cecilia, 54
Calcarea, 317
Calcareous sponge, 314
Camel, 118
Cancer, 166
Canines, 100
Canker-worm, 202
Capillaries, 145
Carapace of turtle, 56
Carapax, 159
Carmine, 198
Carnivora, 120
Carotid artery, 43, 91
Carp, 25
Carpals, 134
Carpus, 45
Cassowary, 78
Caterpillars, 199
Caterpillar hunters, 185
Catfish, 25
Cats, 121
Cattle, 119
Caudal vertebra, 14
Caudal region, 129
Caviare, 38
Cells, 319
Centipedes, 233
Centrum, 14, 128
Cephalopoda, 264, 277
Ceratorhinus, 116
Cerebellum, 15, 135
Cerebral hemispheres, 15
Cerebrum, 15, 135
Cervical region, 129
Cestodes, 244
Cete, 111
Chaetopoda, 239
Cheiroptera, 109
Chilomycterus, 30
Chilopoda, 233
Chimsera, 37
Chimpanzee, 124
Chinch-bug, 195
Chinchilla, 108

Chitons, 273
Chloragogue organ, 237
Chordata, 153, 320
Chromatophores, 252, 265
Chrysalis, 200
Cicada, 196
Cilia, 259
Circulation, 326
Circulation, systemic, 91
Circulation, pulmonary, 92
Clam, dissection of, 248
Clamatores, 82
Clams, 261
Clam-worm, 240
Clavicle, 99, 133
Claws, 97
Climbing birds, 81
Clitellum, 235
Cloaca, 85, 102, 142
Clupea, 26
Clypeastroidea, 289
Clypeus, 173
Coati, 121
Cochineal, 198
Cochlea, 100
Cockroaches, 182
Cod, 27

Codling-moth, 202
Ccelenterata, 310, 320
Coeliac artery, 88
Co3lom, 11
Coleoptera, 184, 222
Collar-bone, 99
Colon, 87
Columbinae, 81
Comatula, 294
Commissure, 161
Compound eye, 172
Condyle, 66, 98
Coney, 115
Conjugation, 332
Connective tissue, 87
Contractile vacuole, 323
Conurus, 82
Conus arteriosus, 146
Coracoid, 45, 133
Coral, 302
Corium, 33
Cormorants, 80
Cornea, 139

Corpus caUosum, 95

Corpuscles of blood, 43, 149

Corydalis, 221

Coypu, 108

Cowry, 275

Coxa, 171

Crab, horseshoe, 229

Crabs, 166

Crane, 80

Crayfish, 164

Crayfish, dissection of, 157

Cranial nerves, 136

Crangon, 165

Cricket, dissection of, 176

Crinoidea, 295

Crocodiles, 70

Crop, 61, 72

Croton-bug, 183

Crow, 83

Crustacea, 206, 228

Crystalline style, 250

Ctenoid scales, 10

Ctenolabrus, 29

Ctenophora, 312

Cuckoos, 82

Cunner, 29, 31

Cuttlebone, 265

Cuttlefish, 264

Cycloid scales, 10

Cyclops, 210

Cyclostomes, 150

Dactyocalyx, 317
Daddy-long-legs, 232
Dasypus, 105
Day-flies, 219
Decapoda, 164, 267
Deer, 118

Dental formula, 101
Dentary, 10
Dentine, 107
Dermis, 97
Devil-fish, 24
Diaphragm, 89, 101, 145
Dibranchiata, 267
Didelphys, 103
Digestion, 325
Digger-wasps, 190
Digitigrade, 121
Dimorphism, 334

Dingo, 104

Dinosaurs, 70, 72

Diotocardia, 275

Diphycercal, 33

Diplopoda, 233

Dipnoi, 39

Diprotodon, 105

Diptera, 222

Directives, 297

Dissecting-pans, 3

Dissepiments, 236

Dobsons, 220

Dodo, 81

Dog, 121

Dog-day locust, 196

Dogfish, dissection of, 17

Dolphin, 112

Dormice, 108

Doryphora, 217

Dorsal blood-vessel, 237

Dorsal root of nerves, 43

Dragon-fly, dissection of, 178

Dragon-flies, 219

Drills, 275

Drumstick of bird, 60

Duckbill, 102

Ducks, 80

Duodenum, 87

Dura mater, 94

Eagles, 81

Ear of vertebrates, 138

Earthworm, 239

Earthworm, dissection of, 235

Echinarachnius, 289

Echinoderma, 291, 320

Echinoida, 288, 293

Ectoderm, 318

Edentata, 105

Educabilia, 111

Eels, 26

Efferent arteries, 146

Efferent nerve, 135

Eggs, 331

Egret, 80

Electrical fishes, 23, 25, 26

Elephants, 113

Elytra, 177

Embiotocidge, 31

Emeu, 78

349

Enamel of tootb, 107
Endopodite, 157
Entoderm, 318
Entomostraca, 209
Epeira, 231
Epicranium, 172
Epidermis, 33, 97
Epiglottis, 93
Ermine, 121
Eupagurus, 166
Eustachian tube, 40, 138
Eutainia, 65
Euthyneura, 276
Everyx, 202
Excretion, 328
Excurrent canals, 314, 316
Exopodite, 157
Eye of vertebrates, 139
Eye muscles, 140

Facets, 172
Facial nerve, 94, 136
Fat body, 42, 174
Feathers, 59, 71
Feather tracts, 71
Femur, 46, 134
Ferret, 121
Fertilization, 332
Fibula, 134
Fins, 9, 33, 132
Fireflies, 185
Fish, dissection of, 9
Fishes, 33
Fish-lice, 210
Fish-moths, 218
Fissipedia, 120
Flamingo, 80
Flatfish, 28
Flatworms, 242
Flies, 222
Flounder, 27
Flukes of Whale, 111
Fluke- worms, 244
Fly-catchers, 84
Flying fox, 110
Foramen magnum, 16
Foot of molluscs, 258, 269
Formol, 341
Formaldehyde, 341
Fowl, 78 "

Fox, 121

Frog, dissection of, 40

Frogs, 53

Fuchsin, 344

Furcula, 75, 134

Gadus, 27

Gall-bladder, 12, 88

Gall-flies, 188

Gallinago, 80

Galls, 188

Gammarus, 169

Ganglion, 43, 135, 161

Ganoids, 38

Garpike, 38

Gastropoda, 273

Gastric artery, 88

Gastric vein, 88

Gavial, 70

Geese, 80

Genital plates, 283

Geometrids, 202

Geophilus, 233

Gill-bailer, 158

Gill-bars, 131

Gill-cartilages, 18

Gill-chamber, 159

Gill-cover, 15, 144

Gills, 10, 11, 35, 143

Gill-slits, 131

Gill-slits of reptiles, 66

Giraffe, 119

Girdles, 18, 33, 132

Gizzard of birds, 72, 142

Glass-snake, 67

Glenoid fossa, 45

Glossopharyngeal nerve, 136

Glottis, 40, 93, 144

Glyptodon, 106

Gnathostomata, 152

Goats, 120

Goose barnacles, 211

Gopher, 108

Gorilla, 124

Grallatores, 80

Grantia, 314

Grasshopper, dissection of, 170

Gray matter. 99

Green glands, 161, 208

Grouse, 78

350

INDEX.

Grub, 184
Guinea-pigs, 108
Gulls, 80

Haddock, 27
Haemal arch, 128
Hagfishes, 151
Half-apes, 123
Hair, 97
Hairworms, 245
Halibut, 28
Hares, 108
Harvestman, 232
Haustellatse, 216
Hawk-moths, 202
Hawks, 81
Heart, 145
Heart- urchins, 289
Hellgrammites, 221
Hemiptera, 194, 222
Hen, 78

Hepatic veins, 89
Hepatic artery, 88
Hepatic caeca, 279
Hermit-crab, 165
Heron, 80
Herring, 26
Heterocercal, 9, 33
Heteropoda, 276
Heteroptera, 195
Hexapoda, 213, 233
Hippocampus, 31
Hippopotamus, 117
Hirudinei, 240
Holocephali, 37
Holothuridea, 292
Homocercal, 35
Homoptera, 195
Honey-bee, 191
Hoofed animals, 115
Hoofs, 97
Horn, 97
Horn-bills, 82
Horned pout, 25
Horned toad, 67
Hornets, 190
Horse, 116

Horsehair- worms, 245
Horse-mackerel, 29
Horseshoe crab, 229

Horse-fly, 223
Humerus, 45, 134
Humming-birds, 83
Humors of eye, 140
Hyaena, 121
Hydra, 307
Hydractinia, 333
Hydranths, 299
Hydridse, 307
Hydrocaulus, 299
Hydroid, dissection of, 299
Hydroids, 305
Hydromedusae, 307
Hydrozoa, 305, 311
Hymenoptera, 188, 222
Hyoid bone, 132, 140
Hypertrophy, 160, 170
Hypoglossal nerve, 136
Hypophysis, 95
Hyracoidea, 115
Hyrax, 115

Ibis, 80

Ichneumon-flies, 188
Ichthyopsida, 55
Ichthyosaurus, 70
Iliac vein, 89
Iliac artery, 89
Ilium, 133
Imago, 200
Incisors, 100
Incurrent canals, 316
India ink, 264
Individual, 332
Ineducabilia, 111
Infundibulum, 135
Injections, 342
Ink-sac, 253
Insecta, 213, 233
Insectivora, 109
Intercostal muscles, 145
Interradial plane, 278
Interambulacrals, 281
Iris, 139
Ischium, 133
Isinglass, 38
Isopoda, 168
Isthmus, 11
Itch-mite, 232
Jackal, 121

INDEX.

351

Jaws, 131

Jelly-fishes, 304, 305, 307
Jugular veins, 61, 90
Jumping mice, 108
June-bug, 186
June-bug, dissection of, 177

Kangaroo, 104
Katydid, 183
Keel of sternum, 74
Kidney, 12, 90
Kingfishers, 83

Labium, 173
Labrum, 173
Lac, 198
Lacertilia, 67
Ladybugs, 185
Lampreys, 151
Lamp-shells, 247
Lancelots, 153
Larva, 49, 184
Larynx, 92
Lateral line, 10, 137
Leaf-beetles, 186
Leaf-hoppers, 197
Leeches, 240
Lemming, 108
Lemurs, 123
Lens, 139
Leopard, 121

Lepas, 211

Lepidoptera, 197, 222

Lepidosteus, 39

Leptocardii, 153

Leucania, 199

Leucocytes, 149

Lice, 198

Lice, fish, 210

Lice, plant, 197

Life, 339

Limpets, 275

Lines of growth, 248, 270

Lion, 121

Lingual ribbon, 255, 271

Liver, 142

Liver-fluke, 244

Liver-rot, 244

Lizards, 67

lama, 118
Lobster, 164

Lobster, dissection of, 157
Locusts, 183
Loon, 78

Lophobranchii, 32
Lumbar region, 130
Lung-fishes, 39
Lungs, 50
Lymphatics, 88
Lymph-heart, 40
Lynx, 121

Macaques, 124

Mackerel, 29

Macrura, 164

Madreporite, 278

Maggots, 222

Malacostraca, 209

Malpighian tubes, 174, 215

Mammalia, 97

Man, 124

Manatee, 113

Mandibulatse, 216

Mandible, 159

Mandibles of birds, 59

Mangabey, 124

Manis, 106

Mantle, 248, 269

Marabou, 80

Marmosets, 123

Marsupialia, 108

Marten, 121

Mastodon, 115

Maxillae, 158

Maxillary, 10

Maxillipeds, 158

May-flies, 219

Measuring- worm, 202

Mediastinum, 90

Medusa-buds, 300

Medusae, 304

Medulla oblongata, 15, 135

Megatherium, 106

Menhaden, 26

Merostomata, 229

Mesenterial artery, 88

Mesenterial filaments, 298

Mesenterial vein, 88

Mesenteries of sea-anemone, 297

352

INDEX.

Mesentery, 12, 142
Mesentery of starfish, 279
Mesoderm, 318
Mesotliorax, 171
Metabola, 217
Metacarpals, 134
Metacarpus, 45
Metamorphosis, 184, 335
Metatarsals, 134
Metathorax, 171
Metazoa, 318
Metridium, 303
Mice, 108
Microstomum, 243
Milk dentition, 100
Millers, 199
Mink, 121
Minnows, 25
Mites, 232
Moccasin, 68
Mola, 30
Molars, 93, 100
Moles, 109
Mollusca, 269, 320
Molluscoida, 246
Monkeys, 123
Monotocardia, 275
Monotremata, 102
Mosquitoes, 225
Moss animals, 246
Mother-of-pearl, 262
Moths, 199
Motor nerve, 135, 136
Mouth parts, 158
Mourning-cloak, 204
Myotome, 11
Myrmeleon, 222
Mytilus, 261
Musca, 224
Muscle-plates, 11
Muscles of eye, 140
Muskalonge, 26
Musk-ox, 120
Muskrat, 107, 108
Mussels, 261

Nails, 97

Naked molluscs, 276
Nandu, 78
Narwal, 112

Nasal organs, 35

Natatores, 78

Nauplius, 208

Nautilus, 267

Nemathelminthes, 245

Nephridia, 208

Nereis, 240

Nettle-cells, 300, 310

Nerves of head, 136

Nervous system of vertebrates

134

Neural arch, 128
Neuroptera, 220
Nictitating membrane, 56, 139
Nidamental gland, 253
Nose, 137
Nostrils, 137
Notochord, 18, 127
Notochordal sheath, 127
Nototrema, 53
Nudibranchs, 276
Nutria fur, 108

Oblique muscles, 140
Ocelli, 173
Octocoralla, 303
Octopoda, 267
Octopus, 267
Ocular plates, 283
Oculomotor nerve, 186
Odonata, 219
Odontornitb.es, 76
(Eneis, 204
Oesophagus, 12, 141
Oil-bottle, 187
Oil-glands, 71
Olfactory lobes, 15, 94
Olfactory nerve, 19, 136
Olfactory organs, 137
Oligochaetae, 239
Olive-shells, 275
Operculum, 10, 144
Operculum of molluscs, 274
Ophidia, 67
Ophiopholis, 293
Ophiuroidea, 293
Opisthobranchia, 276
Opisthoccelous, 129
Opossum, 103
Optic lobes, 15, 135

INDEX.

Optic nerve, 94, 136

Orang-utan, 124

Orbit, 56

Organ of Bojanus, 249, 260

Organ of Corti, 100

Organs, 318, 320

Orioles, 84

Ornithorhynclius, 102

Ornithurse, 77

Orthoceratitis, 267

Ortboptera, 181, 218

Oscines, 82, 83

Ossification, 131

Ostriches, 78

Ostium, 314, 316

Otoliths, 16, 138

Otter, 121

Ovary, 12, 42

Oviduct, 42

Ovipositor, 170

Owls, 81

Ox-warble, 223

Oyster, dissection of, 251

Oysters, 260

Palate, 93

Painted-beauty, 204

Palatine, 131

Palpi, 173

Pancreas, 142

Pangolin, 107

Panther, 121

Parotid gland, 92

Paper-nautilus, 267

Paper-wasps, 191

Paradisea, 83

Parapodia, 240

Parasita, 198

Parrots, 82

Passeres, 82

Paste-eels, 245

Pearl-oysters, 260

Pearls, 261

Pearly nautilus, 267

Peccary, 117

Pecten, 261

Pectoral girdle, 18, 132, 133

Pedata, 293

Pelvic girdle, 45, 132

Penguin, 78

Pen of squid, 256
Pennaria, 299
Pentacrinus, 294
Pentacta, 292
Pericardial cavity, 13
Perisarc, 299
Peristome, 282
Peritoneum, 11, 142
Peritoneal cavity, 101
Perissodactyls, 116
Permanent dentition, 100
Perch, 29
Perching birds, 82
Petromyzon, 151
Phalanger, 104
Phalanges, 134
Phalangida, 232
Phalangium, 232
Pharynx, 11, 141
Pharyngognathi, 29
Pheasant, 78
Phoca, 122
Phylloxera, 197
Physalia, 308
Physiology, 324
Physostomi, 24
Pickerel, 26

Picrosulphuric acid, 344
Pig, 117
Pigeons, 81
Pike, 26
Pill-bug, 168
Pipa, 53
Pipe-fish, 32
Pinnipedia, 120
Pin-worms, 245
Pisces, 33
Pituitary body, 44
Placenta, 105
Placentalia, 105
Plaooid scales, 17
Placophora, 273
Plantigrade, 121
Plant-lice, 197
Plants, 337
Plasma, 149
Plastron, 56
Plathelniintb.es, 242
Plectognathi, 31
Pleisosaurs, 70

354

INDEX.

Plethodon, 53
Pleural cavity, 90, 101
Plexus, 95
Plowshare-bone, 74
Pneumogastric nerve, 91, 136
Polian vesicles, 280
Polychaetae, 240
Polymorphism, 334
Polyps, 301
Polyzoa, 246
Pompano, 29
Pons varolii, 95
Porcupine, 108
Porgy, 29
Porifera, 316
Porpoise, 112
Portal vein, 88
Portuguese man-of-war, 308
Postcava, 89, 253
Poulpes, 267
Pout, 25
Prairie-dog, 109
Prawn, 165
Precava, 90, 254
Premaxillary, 10
Premolars, 100
Preoral lobe, 235
Primates, 123
Pristis, 22
Proboscidia, 113
Proccelous, 129
Proglottids, 244
Prosobranchs, 274
Prothorax, 171
Protoplasm, 320, 339
Protopterus, 39
Protozoa, 321
Proventriculus, 61, 72
Pseudoneuroptera, 219
Pseudopleuronectes, 27
Pterodactyls, 70
Pteropods, 276
Pterygoid, 131
Pubis, 133

Pulmonary artery, 91, 101
Pulmonary circulation, 92
Pulmonary veins, 91
Pulmonata, 276
Pupa, 200
Pupil of eye, 139

Pygostyle, 74
Pyloric caeca, 142
Python, 68

Quadrate, 62, 1(0, 131
Quahog, 263

Rabbits, 108

Racemose vesicles, 280

Raccoon, 121

Radial canal, 281

Radial nerve, 281

Radial plane, 278

Radio-ulna, 45

Radius. 134

Raia, 22

Raptores, 81

Rasores, 78

Rat, dissection of, 86

Rats, 108

Rays, 22

Rectus muscles, 140

Rectum, 87

Reference- books, 5

Regularia, 288

Remora, 28

Remoropsis, 28

Renal vein, 89

Reproduction, 330, 331

Reproduction by division, 243

Reptiles, 64

Respiration, 326

Retina, 139

Rhea, 77

Rhinoceros, 116

Rhynchophora, 184, 187

Ribs, 128

Ring canal, 281

Ring nerve, 281

Rodentia, 107

Roundworrns, 245

Rove-beetles, 185

Ruminants, 118

Rytina, 113

Sable, 121
Sacral region, 129
Salmon, 25
Salamanders, 52
Salivary gland, 92

INDEX.

Sand-cakes, 289

Sand-dollars, 289

Sapajou, 123

Sauropsida, 85

SaururaB, 75

Savigny's law, 158

Sawfish, 22

Sawflies, 188

Scale-bugs, 198

Scales, 33. 64, 71, 98

Scallops, 260

Scansores, 81

Scaphopoda, 277

Scapula, 99, 133

Scarabseans, 186

Sciatic nerve, 96

Sclerotic coat, 139

Scomber, 29

Scorpions, 229

Scratching-birds, 78

Sculpin, 29

Scutellae, 68

Scyphomedusse, 304

Scyphozoa, 301, 311

Sea-anemones, 301

Sea-bass, 29

Sea-cows, 113

Sea- cucumbers, 292

Sea-fans, 303

Sea-horse, 31

Sea-lilies, 295

Sea-lion, 122

Sea-peach, 156

Sea-pear, 156

Sea-squirt, 156

Sea-urchin, dissection of, 282

Sea-urchins, 288

Sea-whips, 303

Seal, 121

Segmented animals, 330

Segments, 157, 170

Selachii, 21, 37

Semicircular canals, 19, 138

Semilunar fold, 139

Sensation, 329

Sense-organs of vertebrates, 187

Sensory nerve, 135,136

Sepia, 264, 268

Septa, 297

Serpent-stars, 293

Setae, 235

Seventeen-year locust, 197

Shad, 26

Sharks, 21

Sheath of notochord, 128

Sheep, 120

Sbeepshead, 29

Shell, 258

Shell-gland, 208

Shellac, 198

Ship- worm, 263

Shoulder-blade, 45

Shoulder-girdle, 45, 132

Shrews, 109

Shrimp, 165

Silicea, 317

Silkworms, 202

Silver-bottom, 113

Silver-fish, 218

Simple eyes, 173

Singing-birds, 82

Siphon, 249, 252

Siphonata, 263

Siphonoglyphes, 296

Siphonophora, 307

Sirenia, 113

Skates, 21,22

Skeleton of vertebrates, 127

Skippers, 203

Skull, 130

Skunk, 121

Slugs, 277

Sloth, 106

Snails, 273, 277

Snake, glass, 61

Snake, study of, 58

Snakes, 67

Snipe, 80

Somites, 157, 170

Sow-bug, 162

Sparrow, 84

Spatangoids, 289

Spermaceti, 112

Spermatozoan, 331

Sperm-whale, 112

Sphex, 190

Sphinx-moths, 202

Spicules of sponge, 314, 316

Spiders, 230

Spinal accessory nerve, 94

356

INDEX.

Spinal cord, 134
Spinal nerves, 43, 134
Spinnerets, 230
Spiny ant-eaters, 103
Spring-beetles, 185
Spiracle, 17, 138, 144, 171
Spiral valve, 18, 142
Spirostreplion, 234
Spittle-insects, 197
Splenic artery, 88
Splint-bone, 117
Sponge, dissection of, 314
Sponges, 316, 320
Springtails, 218
Squash-bug, 192, 196
Squid, 268

Squid, dissection of, 252
Squirrels, 109
Staggers, 223
Starfish, dissection of, 278
Starfishes, 285
Starling, 84
Stegocephali, 53
Sternum, 45, 130
Sting, 188
Stink-bug, 196
Stomach- worms, 245
Stone canal, 280
Stork, 80
Streptoneura, 274
Stromb, 275
Struthii, 78
Sturio, 38
Sturgeon, 38
Styloid process, 132
Subclavian artery, 91
Subclavian vein, 90
Suck- fish, 28
Sulphur bottom, 113
Sunfish, 29, 30, 32
Supra-anal plate, 171
Supra-renal, 89
Supra-scapula, 45
Surf-fish, 31
Surinam toad, 53
Swallow-tails, 203
Swans, 80
Sweetbread, 145
Swell-fish, 30
Swim-bladder, 145

Swimmeret, 157
Swimming-birds, 78
Swordfish, 28
Swine, 117

Systemic circulation, 91
Systemic heart, 271

Tadpole, dissection of, 47

Ta^nia, 244

Tailed birds, 75

Tape-worms, 244

Tapirs, 116

Tarsals, 134

Tarso-metatarsus, 60

Taste-organs, 137

Teeth of mammals 100

Teleosts, 24, 39

Telson, 157

Teredo, 263

Termes, 220

Termites, 219

Test, 282

Testes, 12

Testudinata, 69

Tetrabranchiata, 266

Tetradecapoda, 168

Thoracic duct, 88

Thoracic region, 130

Thousand-footed worm, 233

Thrushes, 84

Thylacine, 104

Thylacoleo, 104

Thymus gland, 145

Thyroid gland, 145

Thysanure, 218

Tibia, 134

Tibio-fibula, 46

Tiger, 121

Tiger-beetles, 185

Ticks, 232

Tissues, 320

Toads, 53

Tongue of vertebrates, 140

Toothed birds, 76

Tooth-shells, 277

Torpedo, 24

Tortoise, 69

Tortoise-shell, 69

Toucans, 82

Touch, 137

INDEX.

357

Trachea, 61, 144

Trachea? of insects, 213, 215

Transverse process, 45. 12S

Tree-hoppers, 197

Trematodes, 243

Trichechus, 114

Trichina, 245

Trichinosis, 246

Trigeniinal nerve, 136

Trilobites, 211

Trochanter, 171

Trochlearis nerve, 136

Troglodytes, 124

Tropic birds, 80

Trout, 25

Tube-feet, 278

Tumble-bug, 186

Tunicata, 156

Turbellaria, 243

Turbot, 28

Turkey, 78

Turtle, dissection of, 56

Turtles, 69

Twixt-brain, 135

Tympanic membrane, 138, 170

Ulna, 134
Umbo, 248
Uncinate process, 74
Ungulata, 115
Ureter, 89
Urinary bladder, 41
Urodela, 52
Urostyle, 45

Vagus nerve, 19, 136
Valve, spinal, 18
Valves, 248
Veins, 88-91
Velum, 306
Venous blood, 148
Venous sinus, 13
Ventral aorta, 146
Ventral blood-vessel, 237
Ventral cord, 161
Ventral root of nerve, 43
Ventric e of heart, 145
Ventricles of brain, 135

Venus, 262
Vermes, 242, 320
Vertebra, 14, 128
Vertebrata, 127
Vestibule, 16
Villi, 142
Vinegar- eels, 245
Visceral mass, 269
Visceral skeleton, 127, 131
Vital force, 339
Vitreous humor, 140
Vocal cords, 93
Vultures, 81

Wading-birds, 80

Walking-stick, 183

Walrus, 121

Warblers, 84

Wasps, 190

Water-beetles, 185

Water-vascular system, 284, 286

Weasel, 121

Weevil, 187

Whalebone, 112

Whales, 111

White ants, 219

Whitefish, 25

White matter of brain, 99

Wickersheimer's fluid, 342

Wild-boar, 117

Wildcat, 121

Wilson's snipe, 80

Wing-covers, 60

Wish bone, 75, 134

Wire worms, 186

Woodchuck, 109

Wood-duck, 79

Woodpeckers, 82

Wolf, 121

Wombat, 104

Worm, thousand footed, 233

Worms, 242

Wren, 83

Wrigglers, 225

Zebra, 117
Zooids, 299

HENRY HOLT 6- CO.'S WORKS ON SCIENCE.

Hertwig's General Principles of Zoology. From the Third Edition of
Dr. Richard Hertwig's Lehrbuch der Zoologie. Translated and
edited by GEORGE WILTON FIELD, Professor in Brown Univer-
sity. 226 pp. 8vo. $1.60 net.

Howell's Dissection of the Dog. As a Basis for the Study of Physi-
ology. By W. H. HOWELL, Professor in the Johns Hopkins
University. 100 pp. 8vo. $1.00 net.

Jackman's Nature Study for the Common Schools. (Arranged by the
Months.) By WILBUR JACKMAN, Teacher of Natural Science,
Cook County Normal School, Chicago, 111. 448 pp. I2mo.
$1.20 net.

Kerner & Oliver's Natural History of Plants. Translated by Prof. F.
W. OLIVER, of University College, London. 410. 4 parts.
With over 1000 illustrations and 16 colored plates. $15.00 net.

Macalister's Zoology of the Invertebrate and Vertebrate Animals. By
ALEX. MACALISTER. Revised by A. S. PACKARD. 277 pp.
i6mo. 80 cents net.

MacDougal's Experimental Plant Physiology. On the Basis of Gels'
PJianzenphysiologische Versuche. By D. T. MAcDouGAL, Unu
versity of Minnesota* vi -f- 88 pp. 8vo. $1.00 net.

Macloskie's Elementary Botany. With Students' Guide to the Exam-
ination' and Description of Plants. By GEORGE MACLOSKIE,
D.Sc., LL.D. 373 pp. I2mo. $1.30 net.

McMurrich's Text-book of Invertebrate Morphology. By J. PLAYFAIR
MCMURRICH, M.A., Ph.D., Professor in the University of Cin-
cinnati, vii -j- 661 pp. 8vo. New Edition. $3.00 net.

McNab's Botany. Outlines of Morphology, Physiology, and Classi-
fication of Plants. By WILLIAM RAMSAY McNAB. Revised by
Prof. C. E. BESSEY. 400 pp. i6mo. 8oc. net.

Martin's The Human Body. See American Science Series.

*Merriam's Mammals of the Adirondack Region, Northeastern New
York. With an Introductory Chapter treating of the Location
and Boundaries of the Region, its Geological History, Topogra-
phy, Climate, General Features, Botany, and Faunal Position.
By Dr. C. HART MERRIAM. 316 pp. 8vo. ^.^Q net.

Newcomb & Holden's Astronomies. See American Science Series.

*Noel's Buz ; or, The Life and Adventures of a Honey Bee. By
MAURICE NOEL. 134 pp. i2mo. $1.00.

Noyes's Elements of Qualitative Analysis. By WM. A. NOYES, Pro-
fessor in the Rose Polytechnic Institute. 91 pp. 8vo. 8oc. net.

Packard's Entomology for Beginners. For the use of Young Folks,
Fruit-growers, Farmers, and Gardeners. By A. S. PACKARD.
xvi -\- 367 pp. I2mo. Third Edition, Revised. $1.40 net.

Postage 8 per cent additional on net books. Descriptive list free.

HOLT & CO.'S WORKS ON SCIENCE.

Packard's Guide to the Study of Insects, and a Treatise on those
Injurious and Beneficial to Crops. For Colleges, Farm-schools,
and Agriculturists. By A. S. Packard. With 15 plates and
670 wood-cuts. Ninth Edition. 715 pp. 8vo. $4. ^Q net.

- Outlines of Comparative Embryology. By A. S. PACKARD. Copi-
ously illustrated. 243 pp. 8vo. $2.00 net.

- Zoologies. See American Science Series.

Perkins's Outlines of Electricity and Magnetism. By CHAS. A. PERKINS,
Profesrr- in the University of Tennessee. 277 pp. I2mo.
$1.10 nfi,

Pierce's Problems in Elementary Physics. Chiefly numerical. By

E. DANA PIERCE, of the Hotchkiss School. 194 pp. i2mo.
6oc. net.

Price's The Fern Collector's Handbook and Herbarium. By Miss SADIE

F. PRICE. With 72 plates. {November, 1896.)

Remsen's Chemistries. See American Science Series.

Scudder's Butterflies. By SAMUEL H. SCUDDER. x -f 322 pp. i2mo.
$1.20 net.

- - Brief Guide to the Commoner Butterflies. By SAMUEL H. SCUDDER.

xi -j- 206 pp. I2mo. $1.00 net.

- The Life of a Butterfly. A Chapter in Natural History for the
General Reader. By S. H. SCUDDER. 186 pp. i6mo. 8oc. net.

Sedgwick and Wilson's Biology. See American Science Series.

*Step's Plant Life. By EDWARD STEP. Popular Papers on the
Phenomena of Botany. I2mo. 148 Illustrations. '$i.oonet.

Underwood's Our Native Ferns and their Allies. By LUCIEN M. UNDER-
WOOD, Professor in DePauw University. Revised. 156 pp.
I2mo. $i.oo net.

Williams's Elements of Crystallography. By GEORGE HUNTING-TON
WILLIAMS, late Professor in the Johns Hopkins University.
x -j- 270 pp. I2mo. Revised and Enlarged. $1.25 net.

Williams's Geological Biology. An Introduction to the Geological
History of Organisms. By HENRY S. WILLIAMS, Professor of
Geology in Yale College. 8vo. 395 pp. $2.80 net.

Woodhull's First Course in Science. By JOHN F. WOODHULL, Pro-
fessor in the Teachers' College, New York City.

/. Book of Experiments, xiv -j- 79 pp. 8vo. Paper. SQC. net.
II. Text-Book, xv +133 pp. I2mo. Cloth. 6$c.nef.
III. Box of Apparatus, f 2.OO net (actual cost to the publishers).

Zimmermann's Botanical Microtechnique. Translated by JAMES ELLIS
HUMPHREY, S.C. xii -f 296 pp. 8vo. $2.50 net.

HENRY HOLT & CO., 29 WEST 230 ST., NEW YORK.

July, 1897.

SCIENCE

REFERENCE AND TEXT-BOOKS

PUBLISHED BY

HENRY HOLT & COMPANY,

29 WEST 230 STREET, NEW YORK.

Books marked * are chiefly for reference and supplementary use, and are
to be found in Henry Holt &" CoSs List of Works in General Literature.
l''or further particulars about books not so marked see Henry Holt &* Co. 's
Descriptive Science Catalogue. Either list free on application. Except-
ing JAMES' PSYCHOLOGIES and WALKER'S POLITICAL ECONOMIES, both in
the American Science Series, this list contains no works in Philosophy or
Political Economy. Postage on net books 8 per cent, additional.

Smcncan Science Scries

I. Astronomy. By SIMON NEWCOMB, Professor in the Johns Hopkins University,
and EDWARD S. HOLDEN, Director of the Lick Observatory, California.
Advanced Course. 512 pp. 8vo. $2.00 net.
The same. Briefer Course. 352 pp. 12010. $1.12 net.

2. Zoology. By A. S. PACKARD, JR., Professor in Brown University. Advanced

Course. 722 pp. 8vo. $2.40 net.

The same. Briefer Course. 338 pp. i2ino. $1.12 net.
The same. Elementary Course. 290 pp. 12010. 80 cents net.

3. Botany. By C. E. BESSEY, Professor in the University of Nebraska.

Advanced Course. 6npp. 8vo. $2.20 net.

The same. Briefer Course. (Entirely new edition, 1896.) 356 pp. 12010.
$1.12 net.

4. The Human Body. By H. NEWELL MARTIN, sometime Professor in the Johns

Hopkins University.

Advanced Course. (Entirely new edition, 1896.) 685 pp. 8vo. $2.50 net.

Copies without chapter on Reproduction sent when specially ordered.
The same. Briefer Course. 377 pp. 12010. $1.20 net.
The same. Elementary Course, 261 pp. i2mo. 75 cents net._
The Human Body and the Effect of Narcotics. 261 pp. 12010. $1.20 net.

5. Chemistry. By IRA REMSEN, Professor in Johns Hopkins University.

Advanced Course (Inorganic). 850 pp. 8vo. $2.80 net.

The same. Briefer Course. (Entirely new edition, 1893.) 435 PP- $1-12 net.
The same. Elementary Course. 272 pp. 12010. 80 cents net.
Laboratory Manual (to Elementary Course). 196 pp. 12010. 40 cents, net.
Chemical Experiments. By Prof REMSEN and Dr. W. W. RANDALL. (For
Briefer Course.) No blank pages for notes. 158 pp 12010. SQC *">t.

6. Political Economy. By FRANCIS A. WALKER, President Massachusetts Insti-

tute of Technology. Advanced Course. 537 pp. 8vo. $2.00 net.
The same. Briefer Course. 415 pp. 12010. $1.20 net.
The same. Elementary Course. 423 pp. 12100. $1.00 net.

7. General Biology. By Prof. W. T. SEDGWICK, of Massachusetts Institute of

Technology, and Prof. E. B. WILSON, of Columbia College. (Revised and
enlarged, 1896.) 231 pp. 8vo. $1-75 net.

8. Psychology. By WILLIAM JAMES, Professor in Harvard College. Advanced

Course. 689 -j- 704 pp. 8vo. 2 vols. $4.80 net.
The same. Briefer Course. 478 pp. 12010. $1.60 net.

9. Physics. By GEORGE F. BARKER, Professor in the University of Pennsylva-

nia. Advanced Course. 902 pp. 8vo. $3.50 net.

10. Geology. By THOMAS C. CHAMBERLIN and ROLLIN D. SALISBURY, Professor*
in the University of Chicago. (In Preparation.)

HENRY HOLT & CO.'S WORKS ON SCIENCE.

Allen's Laboratory Exercises in Elementary Physics. By CHARLES R.
ALLEN, Instructor in the New Bedford, Mass., High School.
Pupils' Edition: x -f- 209 pp. I2mo. 8oc. net. Teachers'
Edition : $1.00 net.

Arthur, Barnes, and Coulter's Handbook of Plant Dissection. By J. C.

ARTHUR. Professor in Purdue University, C. R. BARNES, Pro-
fessor in University of Wisconsin, and JOHN M. COULTER, Presi-
dent of Lake Forest University, xi -f- 256 pp. i2mo. $1.20 net.

Barker's Physics. See American Science Series.

Seal's Grasses of North America. For Farmers and Students. By
W. J. BEAL, Professor in the Michigan Agricultural College.
8vo. Copiously illustrated. 2 vols. Vol. I., 457 pp. $2.50 w<?/.
Vol. II., 707 pp. $5.00 net.

Bessey's Botanies. See American Science Series.

Black and Carter's Natural History Lessons. By GEORGE ASHTON
BLACK, Ph.D., and KATHLEEN CARTER. (For very young
pupils.) x -(- 98 pp. I2mo. SQC. net.

Bumpus's Laboratory Course in Invertebrate Zoology. By HERMON C.
BUMPUS, Professor in Brown University, Instructor at the Ma-
rine Biological Laboratory, Wood's Holl, Mass. Revised. vi-}~
157 pp. I2mo. $r.oo net.

Cairns's Quantitative Chemical Analysis. By FREDERICK A. CAIRNS.
Revised and edited by Dr. E. WALLER. 417 pp. 8vo. $2.00
net.

Champlin's Young Folks' Astronomy. By JOHN D. CHAMPLIN, Jr.,

Editor of Champlin's Young Folks' Cyclopedias. Illustrated,
vi -f~ 236 pp. i6mo. 48c. net.

Crozier's Dictionary of Botanical Terms. By A. A. CROZIER. 202 pp.
8vo. $2.40 net.

Hackcl's The True Grasses. Translated from " Die natiirlichen
Pflanzenfamilien " by F. LAMSON-SCRIBNER and EFFIE A.

SOUTHWORTH. V -f- 228 pp. 8vO. $1.50.

Hall's First Lessons in Experimental Physics. For young beginners,
with quantitative work for pupils and lecture-table experiments
for teachers. By EDWIN H. HALL, Assistant Professor in Har-
vard College, viii + 120 pp. I2mo. 6sc. net.

Hall and Bergen's Text-book of Physics. By EDWIN H. HALL,
Assistant Professor of Physics in Harvard College, and
JOSEPH Y. BERGEN, Jr., Junior Master in the English High
School, Boston, xviii -\- 388 pp. I2mo. $1.25 net.

Postage 8 per cent additional on net books. Descriptive list free.

PSYCHOLOGY

ETHICS AND PHILOSOPHY
REFERENCE AND TEXT-BOOKS

PUBLISHED BY

HENRY HOLT & COMPANY

29 WEST 230 STREET, NEW YORK

Books marked * are chiefly for reference and supplementary use, and to
be found in Henry Holt & CoSs List of Works in General Literature.
For further particulars about books not so marked see Henry Holt &" CoSs
Descriptive Educational Catalogue. Either list free on application.
Postage on net books 10 per cent, additional.

*Bain's John Stuart Mill. A Criticism with Personal Recollections.

By Prof. ALEXANDER BAIN of Aberdeen. I2mo. 214 pp. $1.00.

* James Mill. A Biography. With portrait. I2mo. 498 pp.

$2.00.

Baldwin's Handbook of Psychology. By Prof. JAMES MARK BALDWIN
of Toronto. 2 vols. (sold separately). 8vo.
Vol. I. Senses and Intellect. 357 pp. $1.80, net.
Vol. II. Feeling and Will. 406 pp. $2.00, net.

Elements of Psychology. 372pp. i2mo. $1.50, net.

Descartes : The Philosophy of Descartes. Selected and translated by
Prof. H. A. P. TORREY of the University of Vermont. (Sneath's
Modern Philosophers.) xii-{-345 pp. I2mo. $1.50, net.

Falckenberg's Modern Philosophy from Nicolas of Cusa to the Present
Time. By Prof. RICHARD FALCKENBERG of Erlangen. Trans-
lated with the author's co-operation by Prof. A. C. ARMSTRONG,
Jr., of Wesleyan. 665 pp. 8vo. $3.50, net.

Hegel : Philosophy of Hegel. Translated extracts from Hegel's
works, with an introduction by Prof. JOSIAH RoYCEof Harvard.
(Sneath's Modern Philosophers.} {In preparation.}

"Hillebrand's German Thought. From the Seven Years' War to
Goethe's Death. Six Lectures delivered at the Royal Institu-
tion of Great Britain. By CARL HILLEBRAND. I2mo. 306 pp.
$1-75.

"Holland s Rise of Intellectual Liberty, from Thales to Copernicus. A
History. By FREDERICK MAY HOLLAND. 8vo. 458 pp. $3.50.

Hume: The Philosophy of Hume. Extracts from the "Treatise of
Human Nature." With an introduction by HERBERT A. AIKINS,
Professor in Western Reserve University. 176 pp. I2mo.
(Sneath 's Modern Philosophers.} $1.00, net.

Hyde's Practical Ethics. By Pres. WM. DE WITT HYDE of Bowdoin.
I2mo. 219 pp. 80 cents, net.

HENRY HOLT & CO.'S WORKS ON PHILOSOPHY.

James' Principles Of Psychology. (American Science Series.) Advanced
Course. By Prof. WM. JAMES of Harvard. 2 vols. 8vo. 701
-j- 710 pp. $4.80, net.

Psychology. Briefer Course. I2mo. 491 pp. $1.60, net.

Jastrow's Chapters in Modern Psychology. By Prof. JOSEPH JASTROW
of the University of Wisconsin. (In preparation.')

Kant : The Philosophy of Kant. Selected and translated by Prof.
JOHN WATSON of Queen's College, Canada. x-|-356 pp. i2mo.
(Sneath's Modern Philosophers.) $1.75, net.

Locke: The Philosophy of Locke. Extracts from the "Essay con-
cerning Human Understanding." Edited by Prof. JOHN E.
RUSSELL of Williams College. 160 pp. I2mo. (Sneath's Modern
Philosophers.) $1.00, net.

*Martineau's Essays, Philosophical and Theological. By JAMES MARTI-

NEAU. 2 Vols. 8VO. 428 -\- 438 pp. $5-OO.

*Maude's The Foundation of Ethics. By JOHN EDWARD MAUDE. Ed-
ited by Prof. WM. JAMES of Harvard. I2mo. 224 pp. $1.50.

*MHPs Three Essays on Religion, and Berkeley. By JOHN STUART
MILL. 8vo. 313 pp. $2.00.

* The Autobiography. 8vo. 319 pp. $2.00.

* Dissertations and Discussions. 5 vols. 8vo. $2.00 per vol.

* Examination of Sir William Hamilton's Philosophy. 8vo. 354 pp.

$2.75-

* Comte's Positive Philosophy. 8vo. 182 pp. $1.25.

*Mill, John Stuart : His Life and Works. Twelve sketches by HERBERT
SPENCER, HENRY FAWCETT, FREDERIC HARRISON, and other dis-
tinguished authors. i6mo. 96 pp. $1.00.

*Nicholls' The Psychology of Time. By HERBERT NICHOLLS, Fellow of
Clark. 8vo. 140 pp. $1.50, net.

Paulsen's Introduction to Philosophy. By Prof. FRIEDRICH PAULSEN of
Berlin. Translated with the author's sanction by Prof. FRANK
THILLY of the University of Missouri. With a preface by
Prof. WM. JAMES of Harvard. xxiv-(-437 pp. 8vo. $3.50, net.

Reid : The Philosophy Of Reid. The " Inquiry into the Human Mind
on the Principles of Common Sense." Edited by Dr. E. HER-
SHEY SNEATH of Yale. viii-J-368 pp. i2mo. (Sneath' s Modern
Philosophers.) $1.50, net.

Spinoza : The Philosophy of Spinoza. Parts I, II, V of the " Ethics,"
and Extracts from III, IV. Translated and edited by Prof.
GEO. STUART FULLERTON of the University of Pennsylvania.
Second Edition, Enlarged. vi-(-358 pp. I2mo. (Sneath' s Mod-
ern Philosophers.) $1.50, net.

Zeller's Outlines of the History of Greek Philosophy. By Dr. EDWARD
ZELLER. Translated with the author's sanction by SARAH F.
ALLEYNE and EVELYN ABBOTT. i2mo. 377 pp. $1.40, net.

Postage on net books 8 per cent additional. Descriptive list free.

HENRY HOLT & CO., 29 WEST 230 ST., NEW YORK.
September, 1895.

SOME ENGLISH TRANSLATIONS

About, Edmond : The Man with the Broken Ear. 16mo. $1.— The

Notary's Nose. 16mo. $1.

Auerbach, B.: The Villa ou the Rhine. (Davis.) 2 vols. 16mo. $2.
—On the Heights. (Stern.) 2 vcls. 16mo. $2.— On the Heights.
(Buonett). 16mo. Paper. 1 vol. 30c.

Bacourt, Chevalier de : Souvenirs of a Diplomat. 12mo. $1.50.

Berlioz, Hector : Selections from his Letters and Writings. (Apthorp.)
12mo. $2.

Brink, Bernhard ten: English Literature. Vol.1. (Kennedy.)
Large 12mo. $2. Vol. II. (Robinson.) Large 12mo. $2.—
Five Lectures on Shakespeare. (Franklin.) 12nio. $1.25.

Chevrillon, Andre: In India. (Marchant ) 12ino. $1.50.

Falke, Jakob von: Greece and Rome: Their Life and Art. (Browne.)
Quarto. $10.

Firdusi : The Epic of Kings. (Zimmern.) 12mo. $2.50.
Gautier, Leon: Chanson de Roland. (Rabillon). 12mo. $1.25.

Gautier, Theophile : A Winter in Russia. (Ripley.) 12mo. $1.75.—
Constantinople. (Gould.) 12mo. $1.75.

Gavard, Charles : A Diplomat in London. (Hodder.) 12mo.

Goethe, J. W. von : Poems and Ballads. (Gibson.) (Library of For-
eign Poetry.} IGmo. $1.50.

Guerin, Maurice de : Journal. (Fisher.) 12mo. $1.25.
Guyau, Jean Marie : The Irreligion of the Future. (Hodder.)

Heine, Heinrich : Book of Songs. (Leland.) (Library of Foreign
Poetry.} 16mo. 75c.— The Romantic School. (Fleishman).
12mo. $1.50.— Life Told in His Own Words. (Dexter.) 12mo.

$1.75.

Hertz, Henrik : King Rene's Daughter. (Martin.) (Library of Foreign
Poetry.} 16mo. $1.25.

Heyse, Paul : The Children of the World. 12mo. $1.25.
Kalevala. Selections. (Porter.) 16mo. $1.50.

Kalidasa: Shakuntala. (Edgren.) (Library of Foreian Poetry.)
16mo. $1.50.

SOME ENGLISH TRANSLATIONS

Klaczko, Julian : Rome and the Renaissance. (Marchaut.)
Knortz, Karl : Representative German Poems. 12mo. $2.50.

Leasing, G. E. : Nathan the Wise. (Frothiugham.) (Library of For-
eign Poetry.) 16ino. $1.50.

Lockhart, J. G. : Ancient Spanish Ballads. (Library of Foreign
Poetry.) 16ino. $1.25.

Moscheles. Ignatz : Recent Music and Musicians. (A. D. Coleridge.)
ISino. $2.

Roumanian Fairy Tales. (Percival.) 12mo. $1.25.

Rousselet, Louis : Ralph, the Drummer Boy. (Gordon.) 12mo.
$1.50.

Rydberg, Victor : Magic of the Middle Ages. (Edgren.) 12mo.
$1.50.

Sainte-Beuve, C. A.: English Portraits. 12mo. $2.

Spielhagen, Frederick : Problematic Characters. (deVere.) 16ino.
Paper. 50 cents. — Through Night to Light. (de Vere.) 16mo.
Paper. 50 cents. — The Hohensteins. (de Vere.) 16mo. Paper.
50 cents. — Hammer and Anvil. (Browne.) 16mo. Paper. 50
cents.

Sylva, Carmen : Pilgrim Sorrow. 16mo. $1.25.

Taine, H. A.: Italy, Rome and Naples. (Durand.) Large 12mo.
$2.50. — Ilaly, Florence and Venice. (Duraud.) Large 12mo.
$2.50.— Notes on England. (Rae.) Large 12mo. $2.50. — A Tour
through the Pyrenees. (Fiske.) Large 12rno. $2.50.— Notes on
Paris. (Stevens.) Large 12mo. $2.50. — History of English Lit-
erature. (Van Laun.) 2 vols. Large 12mo. $5. The same.
12mo. 1vol. $1.25. The same. Large 12m o. 4 vols. In press.
— On Intelligence. (Haye.) 2 vols. Large 12mo. $o. — Lectures
on Art. First Series. (Durand.) Large 12mo. $2.50. — Lectures
on Art. Second Series. (Durand.) Large 12mo. $2.50. — The
Ancient Regime. (Durand.) Large 12mo. $2.50. — The French
Revolution. (Durand.) 3 vols. $7.50.— The Modern Regime.
Vol. I. Large 12mo. $2.50.— The Modern Regime. Vol. II.
Large 12mo. $2.50.

Tegner, Esaias : Frithiof s Saga. (Blackley.) 16mo. $1.50.

Wagner, Wilhelm Richard : Art Life and Theories of Richard Wag-
ner. (Burlingame.) 12mo. $2. — Ring of the Nibelung. (Dip
pold.) 12mo. $1.50.

Witt, C.: Classic Mythology. (Younghusband.) 12mo. *$1.
* denotes net price.

HENRY HOLT & CO., NEW YORK.

m