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A COURSE IN
INVERTEBRATE ZOOLOGY

A GUIDE TO THE DISSECTION AND COMPARATIVE
STUDY OF INVERTEBRATE ANIMALS

BY

HENRY SHERRING PRATT, Pu.D,

PROFESSOR OF BIOLOGY AT HAVERFORD COLLEGE AND INSTRUCTOR IN
COMPARATIVE ANATOMY AT THE MARINE BIOLOGICAL LABORA-
TORY OF THE BROOKLYN INSTITUTE OF ARTS AND
SCIENCES AT COLD SPRING HARBOR, L.I.

REVISED EDITION

GINN AND COMPANY, BOSTON
NEW YORK + CHICAGO - LONDON
ATLANTA - DALLAS - COLUMBUS - SAN FRANCISCO

4

COPYRIGHT, 1901, 1915, BY
HENRY SHERRING PRATT
ALL RIGHTS RESERVED

816,10

The Atheneum Press

GINN AND COMPANY: PRO-
PRIETORS » BOSTON - U.S.A.

PREFACE

THE plan of this course is to study each of the larger groups
of invertebrate animals, so far as possible, as a whole, instead
of detached types of different groups taken more or less at
random, as is usually done. The attention is directed con-
stantly to the main structural features which characterize the
entire group under consideration. The effort is thus made to
teach relationships, and to make the study truly comparative.

In order that the systematic position of the animals examined
and their larger affinities may be easily kept in mind, a synopsis
of the animal kingdom expressing the relationships of the
various groups has been added in an appendix.

The course begins with arthropods, because the natural
succession of forms from the lowest to the highest is more
apparent in them than in any other group of invertebrates,
and it is, consequently, easier for a beginner, by studying
them, to learn to appreciate the real significance of the blood-
relationship of animals. Arthropods are also perhaps the most
convenient animals with which to teach the fundamental prin-
ciples of invertebrate morphology. Whether, however, the
student begins his course with insects or with crustaceans,
and whether the first insect taken up is the wasp or the
grasshopper, will be matters for the decision of the teacher.
The course has been so arranged that any of these methods of
beginning may be adopted.

While the comparative feature runs through all the dissections

in the course, each one is usually complete in itself and does
iii

iv PREFACE

not depend upon any others. The teacher is thus enabled to
give his class such dissections as he wishes and is not compelled
to adopt the entire series in order to have his course complete.
In my own classes, I vary the order of the dissections from
year to year and never go through the entire course. I even
occasionally begin the course with the Protozoa and work
upward to the higher animals; but I do not consider this
usually so profitable a method of procedure for the pupil as
the one herein recommended.

An important feature of the plan of this course has been
adopted, in a somewhat different form, from Huxley and
Martin’s “ Practical Biology ”’ and Marshall and Hurst’s “ Prac-
tical Zodlogy.” It is to give the student such practical directions
that he can go on with his work intelligently and profitably
without having an instructor constantly at his elbow. It has
been my experience that far too much of the time of the average
youthful student is often wasted in the laboratory because the
instructor does not happen to be at hand at critical times to
direct his work. The student will often do the work wrong
in consequence, or perhaps he will not do anything at all; in
either case his time is wasted and perhaps his material spoiled.

In most of the dissections the directions are so arranged that
the student can complete the study with a single specimen, and
the order in which the different systems of organs are taken up
in each dissection is made dependent upon this feature. The
necessity of practicing economy of material is thus inculcated,
and the habit is acquired of studying and handling each
specimen with care and judgment.

I have been fortunate in procuring the codperation of a num-
ber of well-known teachers in the revision of the proofs, with
the aid of whom I have sought to eliminate errors so far as
possible. Portions of the proofs have been read critically by

PREFACE v

Professors A. 8. Packard, J. H. Comstock, H. H. Wilder, J. I.
Hamaker, Frank Smith, H. B. Ward, E. L. Rice, H. L. Osborn,
H. L. Clark, C. W. Hargitt, and H. S. Jennings. Their criti-
cisms and suggestions have been most helpful and important,
and I wish to acknowledge a heavy obligation to each of them.

H. S. PRATT

HAVERFORD, Pa.
October, 1901

PREFACE TO THE REVISED EDITION

The principal differences between the first and second editions
of this work consist in the addition of several dissections in the
second edition, and the revision of the scheme of classification in
the Appendix. The additional dissections are those of the house
fly, a spider, the oyster, a sea cucumber, Gonionemus, and a sea
anemone.

HAvERFORD, Pa.
June, 1915

Insecta

Myriapoda
Arachnida
Crustacea

Polychaeta
Oligochaeta

Turbellaria
Cestoda

CONTENTS

CHAPTER I
ARTHROPODA
A Wasp.
A BEETLE .
A Fiy

A GRASSHOPPER .

A CATERPILLAR .

A CENTIPED

A SPIDER Ss ig clky
A CRAYFISH OR A LOBSTER.
A CRAB

A Sow-Bue

AN AMPHIPOD

CAPRELLA . z
LarRvaL DEcApPopDs .

A CopEPpoD

DAPHNIA Ge

A Naupiius Larva

CHAPTER II
ANNELIDA
NEREIS .
An EarRTHWORM .
CHAPTER III
PLATHELMINTHES
A PLANARIAN Worm .

A TAPEWORM .
vii

61
67

76
80

Ectoprocta

Pelecypoda

Gastropoda
Cephalopoda

Ascidiacea

Asteroidea
Echinoidea
Holothurioidea

Hydrozoa

Anthozoa

CONTENTS

CHAPTER IV

BRYOZOA (POLYZOA)

BucuLa

CHAPTER V
MOLLUSCA

A FrrEsHWATER MussEL
AN OYSTER

A Harp-SHeLL CLAM
A Lanp SNAIL .

A Squip

CHAPTER VI

TUNICATA

A Simp.te AscipIAN .

CHAPTER VII

ECHINODERMATA

A STARFISH
A Sea UrcHIN
A HoLoTaurian

CHAPTER VIII

CNIDARIA

Hypra .

A TuBULARIAN HypROMEDUSAN.
A CAMPANULARIAN HypRoMEDUSAN

GONIONEMUS .
A Sea ANEMONE

PAGE
85

89
99
103
112
123

135

141
149
155

159
163
169
175

., 178

CONTENTS ix

CHAPTER IX
SPONGIARIA
PAGE
Calcarea GRANTIA ee ee ee 181
CHAPTER X
PROTOZOA
Infusoria PARAMECIUM . oe eg ee ea ae a a ae BL
VORTICELLA 188
Mastigophora) EuGirena 192
Sarcodina AMOEBA . 194
APPENDIX
A SYNOPSIS OF THE CLASSIFICATION OF ANIMALS... . . . 197
GLOSSARY . 207
INDEX 225

APPARATUS AND MATERIAL

THE apparatus necessary for a course in invertebrate zodlogy
need not be extensive. Each student should be provided with the
following instruments: two scalpels, a small one and one of
medium size; two pairs of scissors, a large straight pair and a
small pair preferably with curved tips; two pairs of forceps,
a small pair and one of medium size, both straight and with
corrugated tips ; one or two dissecting needles, a probe, a blow-
pipe, a hand lens.

Each student should have a shallow dissecting pan, in the bottom
of which is a layer of black wax; the depth of the pan should be
about an inch and a half. If the lobster be dissected, however,
a deeper pan will also be needed. The student should also be
provided with a number of pins of several sizes, which may be
conveniently kept, while not in use, stuck in a large cork.

It is intended that most of the drawings of dissections should
be outlines, usually more or less diagrammatic, made with a hard
drawing pencil in a large blank book, the paper of which is good
and firm, or upon sheets of drawing paper. The general use of
colors by a class is not recommended, not because the use of them
is not often helpful, but because in a class of young students it is
difficult to prevent their abuse by many. The careless or slothful
student will often be tempted to substitute the use of colors for
careful drawing. Outline drawings of a dissection on a sufficiently
large scale, and carefully made and labeled, will invariably be
perfectly clear.

For the study of many of the animals or parts of them in this
course, a compound microscope will be needed; a dissecting micro-
scope will also be most useful throughout the course, although not
indispensable. The student should be provided with a number of
glass slides and thick cover-glasses. Water may be used as a

xi

Xi APPARATUS AND MATERIAL

medium for making temporary mounts of most of the objects
examined under the microscope. A solution made of equal parts
of water and glycerine, however, is usually preferable to water, as
it will not dry up and, besides, renders the object more transparent.
None of the animals studied here need to be stained and mounted
in balsam or other permanent medium. In the case, however, of
the tapeworm, the hydroids, and perhaps one or two of the other
forms, the animal can be studied with greater profit if thus stained
and mounted, and it is recommended that the student be provided
with such specimens.

As a rule the material needed can be easily obtained. Most of
the animals studied may be purchased from the supply department
of the Marine Biological Laboratory at Woods Hole, Mass.; F. D.
Lambert, Tufts College, Mass.; H. M. Stephens, Carlisle, Pa.; or
other dealers in such supplies. Blackford’s, Fulton Market, New
York City, will furnish the crayfish, the lobster, the edible crab,
the French snail (Helix pomatia), and the squid. Powers & Powers,
Station A, Lincoln, Neb., will furnish live protozoans and hydras.

INVERTEBRATE ZOOLOGY

CHAPTER I
ARTHROPODA

INSECTA
A HYMENOPTEROUS INSECT. A WASP

Observe the shape, color, and external anatomy of the animal.
It is bilaterally symmetrical, 7.e., it has a right and a left side
which are alike; it has a dorsal and a ventral side which are
unlike, and also a forward and a hinder end which are unlike,
the forward or anterior end being distinguished by the posses-
sion of important organs of special sense and the mouth. All
of these features are characteristic of rapidly moving animals.
Can you explain why? On the ventral side are the legs, which
are also called appendages or extremities. On the dorsal side of
the insect are the wings, which are not called extremities, since
only those organs receive this designation, speaking strictly,
which are paired projections from the lateral or the ventral
surface of the body, and are either used for locomotion or are
homologous to locomotory organs, 7.¢., are directly descended
from organs which were primarily used for locomotion. Thus,
the wings of bats and birds are extremities, although those of
insects are not.

The external surface of the animal is very smooth. This
feature is also correlated with rapid motion. Do you know

how? The animal is encased in a hard shell, called the cuticula,
1

2 INVERTEBRATE ZOOLOGY

which is composed largely of a very hard and resistant substance
called chitin, and serves the double purpose of a protection for
the internal soft parts and a surface for the attachment of
muscles. It is, in fact, the skeleton of the animal, and is called
an exoskeleton, in contradistinction to an internal supporting
structure which would be called an endoskeleton. All inverte-
brate animals, except some of the lowest, are provided with a
cuticular exoskeleton, but it is only the arthropods in which it
is composed largely of chitin. In fact, the possession of such
a hard and resistant external covering is one of the reasons why
insects have so successfully maintained themselves in the uni-
versal struggle for existence.

Observe that the body of the animal is composed of a number
of serially arranged segments. These are called somites or meta-
meres, and the segmented type of structure presented by the
insect body is called a metameric type of structure. Observe
that the body is sharply divided into three divisions — the head,
thorax, and abdomen.

The head is unsegmented and bears on its anterior and dorsal
surface a pair of long, jointed feelers or antenne, which are impor-
tant sense-organs, a pair of large compound eyes, and three small,
dot-like eyes, called ocelli, which it may be necessary to look for
with a hand lens; on its ventral side are the mouth-parts, the
organs which taste, grasp, and masticate the food. Examine
these mouth-parts carefully with a hand lens ; notice that there
is a short overhanging upper lip, beneath which is a pair of
powerful jaws having a lateral or side position instead of a
dorso-ventral one like the jaws of vertebrates. Beneath the
jaws are two other pairs of mouth-parts, the maxille and the
under lip, which, however, will not be studied at present ; notice
the two pairs of elongated and segmented palps, which are
probably organs of taste.

The thorax is composed of three somites or metameres, which
are called, respectively, the pro-, meso-, and metathorax. Each

A WASP 3

somite bears a pair of legs on its ventral surface, and the meso-
and metathorax bear each a pair of wings on the dorsal surface ;
it is thus in the thorax that the organs of locomotion of the
animal are concentrated. Find the sutures between the thoracic
segments. The dorsal cuticula of each thoracic segment is
called the tergum; the ventral cuticula, the sternum; and that
of each lateral side, the pleurum. Thus we speak of the pro-,
meso-, and metasternum, etc.

In the abdomen the dorsal and the ventral portions of the
cuticula are composed each of a distinct plate in each somite,
which are called the tergite and the sternite, respectively. The
abdomen bears no appendages ; it contains most of the vegeta-
tive organs of the animal. At its hinder end are the vent or
anus and, in the female, the sting. Do you find a straight row
of minute dots on each side of the abdomen and the thorax?
These are the spiracles, the external openings of the tracheal
or respiratory system. In dark-colored wasps it may be impos-
sible to see them with a hand lens, and it may be necessary to
remove the cuticula from the side of the body and examine
it under a compound microscope. How many are there on each
side, and what relation do they bear to the segments?

Hxercise 1. Draw an outline of the side view of the wasp on a
scale of 4 or 5, indicating the segmentation and all the
parts observed. The three thoracic segments may be
difficult to distinguish at first, but if it be kept in mind
that each one of them bears a pair of legs, the task will be
easy. Number on your drawing the thoracic and abdominal
segments, and carefully label all the different parts and
organs.

Exercise 2. Draw an outline of the face on a scale of 10,
showing exactly the relative length and the segmentation
of the antenne, the position of the compound eyes and
ocelli and the upper lip, and label them all.

4 INVERTEBRATE ZOOLOGY

Bxercise 3. Remove a metathoracic leg and draw an outline
of it on a scale of 5. Its different segments, beginning
with the proximal one, i.e., the one nearest the body, are
the following: the coxa, by which the leg articulates with
the body ; the trochanter, a very small segment ; the femur
or thigh, a long segment ; the tibia or shank, also long ; the
tarsus or foot, which is composed of five small segments,
the last one of which bears the two claws. Label all of
these.

Exercise 4. Remove a mesothoracic wing, extend it, and draw a
picture of it on a scale of 5, indicating its venation.

Save your specimen in a dish of formalin or alcohol for future
use. We shall reserve the detailed study of the mouth-parts
until the grasshopper is taken up, when the mouth-parts of the
various orders of insects will be studied together. The internal
anatomy of all insects is exceedingly similar, and it will not be
necessary to study it in more than one animal; we select the
grasshopper as being the one best suited.

A BEETLE 5

INSECTA

A COLEOPTEROUS INSECT. A LARGE BEETLE

Compare the animal with the wasp. We notice, in the first
place, the heavier and clumsier body and the smaller head.
The animal is evidently much less active and also less intel-
Jligent than the wasp. We notice, also, that the wings lie close
to the body instead of being raised above it. The forward or
mesothoracic wings are hard and thick; they are not used for
flight, but cover the metathoracic pair and the hinder part of
the body and are called the wing-covers or elytra. They form,
thus, an additional protection to the back. The entire body of
most beetles, in fact, has a thicker cuticula and, consequently,
a more effective external covering than that of the wasp.
This feature may be correlated with the smaller intelligence of
the animal. Opening the elytra, we notice beneath them the
membranous metathoracic wings with which the animal flies;
we notice also that they are folded transversely as well as longi-
tudinally. These wings are wanting in some of the running
beetles, where the wing-covers are sometimes fused. Note the
scutellum, the small triangular plate, between the base of the
wing-covers. Find the eyes and note their small size. Are
ocelli present? Find the antenne; in some beetles they are
often concealed beneath the sides of the head.

Exercise 1. Draw an outline of the dorsal aspect of the
beetle on a scale of 4 or 5, First, however, spread
and pin the right wing-cover and wing. Number the
thoracic and abdominal segments and label all the parts
observed.

6 INVERTEBRATE ZOOLOGY

Exercise 2. Draw an outline on the same scale of the ven-
tral aspect of your beetle, tracing carefully the sutures
between the segments. Number the thoracic and abdomi-

nal segments.

Exercise 3. Remove a mesothoracic leg and draw an outline
of it on the scale of 5. Label the segments.

Exercise 4. Remove a wing and draw an outline of it on a scale
of 5, tracing in the veins.

Save your specimen in formalin or alcohol for future use.

THE FLY 7

INSECTA
A DIPTEROUS INSECT. THE FLY

Kill several bluebottle flies or large house flies, without injur-
ing them, and impale one on a slender insect pin or a needle.
Stick the pin or needle into a cork or a small piece of wood,
in order to be able to handle it easily, and study the external
anatomy of the fly with the aid of a hand lens.

Observe the compact body of the animal, and note that it is
distinctly divided, like that of the wasp, into three divisions —
the head, the thorax, and the abdomen. Observe the color and the
hairy surface of the body, including the legs and the wings.
These numerous hairs are projections of the cuticula, and perform
a useful function as tactile organs; that is, they are sensitive to
vibrations of the atmosphere, and thus function as sense organs
in that they aid in giving the animal a knowledge of its sui-
roundings. Note the three pairs of long, strong legs and the
single pair of wings. The fly has unusual locomotory powers.
Correlated with these powers are the long cuticular hairs just
mentioned, and also the very large composite eyes. An active,
rapidly moving animal like the fly needs well-developed organs
of orientation. The eyes are larger in the male than in the female,
and are closer together on the top of the head. The two sexes
may thus be distinguished.

Between the large eyes are the three minute accessory eyes or
ocelli. Note the peculiar form of the small antenna, with their
pinnate terminal portion. Extend the proboscis and observe its
complex structure and the oral lobes at the lower end. The fly
eats only fluid food, which it sucks up through its proboscis.

The thorax is of relatively large size, being almost entirely filled

8 INVERTEBRATE ZOOLOGY

with the very extensive musculature of the legs and wings. The
three thoracic somites are of unequal size. The middle one is
the largest and bears the wings. Note that the hinder margin
of the basal portion of the wing is divided into three prominent
lobes. The posterior thoracic somite is the smallest and bears the
balancers, which are the morphological equivalents of the second
pair of wings, possessed by most insects. These are a pair of
minute white, knobbed organs, which project backward from the
posterior wall of the somite, each one being covered by the basal
lobe of the wing on that side. They have a sensory function.

The abdomen is composed of eight somites in the male fly and
nine in the female. Of these, however, four somites are much
larger than the others, and make up the greater part of the
abdomen. The sixth, seventh, and eighth in the male are very
small and rudimentary. In the female the posterior four form
a long, tubular ovipositor, which is usually telescoped into the
abdomen but can often be squeezed out by a little pressure,
Each of the five anterior abdominal somites has a pair of spiracles.
Find them.

Exercise 1. Draw an outline of the dorsal aspect of the fly on a
scale of about 10, indicating the segmentation and the parts
observed, including the venation of the wings. Label all
the parts observed.

Exercise 2. ‘Turn the fly over on its back and draw one of its legs
on a large scale. ‘The names of the different segments of the
leg may be obtained from Exercise 3 on page 4. Note,
between the two claws on each foot, the two pulvilli—the
hairy adhesive pads by means of whose sticky secretions
the fly can walk on an inverted surface.

Bzercise 3. Draw, on a large scale, a side view of the head with
the proboscis extended. Note carefully the form of the
antenna and of the proboscis. The latter is homologous to
the under lip or labium of other insects.

A GRASSHOPPER 9

INSECTA
AN ORTHOPTEROUS INSECT. A LARGE GRASSHOPPER

Observe the shape, color, and external anatomy of the animal.
Note the long, vermiform body and the large head. The body,
as in all insects, is made up of a number of serially arranged
segments, called somites or metameres, which fall into two divi-
sions — the thorax and the abdomen. The head is unsegmented,
being composed of a number of completely fused somites, and
bears upon its dorsal and anterior surface a pair of long, jointed
feelers or antenne, which are important sense-organs, a pair of
large compound eyes, and three small, dot-like eyes, called ocelli,
which it may be necessary to look for with a hand lens; on its
ventral side are the mouth-parts, the organs with which it tastes,
grasps, and masticates its food. Examine these mouth-parts
with a hand lens. Observe the long, broad upper lip and pass a
needle under its ventral edge. Back of the upper lip will be
seen the strong mandibles, and by pressing these to the right and
left the two remaining pairs of mouth-parts, the maxille and
the under lip, will be seen. Note the two pairs of jointed palps
belonging to them, which are probably organs of taste. These
parts will all be studied later in detail.

The thorax is made up of three somites, which are called the
pro-, meso-, and metathorax. Notice that the thorax is not sepa-
rated from the abdomen by a constriction, as it is in the wasp,
but, however, that it may be easily distinguished from the
abdomen by its greater diameter. The prothorax is movable,
as in the beetle, and its dorsal and lateral surfaces are covered
by a large shield. On the ventral side of the prothorax,
between the prothoracic legs, is, in many grasshoppers, a short

10 INVERTEBRATE ZOOLOGY

projection. The meso- and metathorax are united immovably
with the abdomen and are covered by the two pairs of wings.
The anterior or mesothoracic wings are parchment-like and are
not functional in flying, but, like the wing-covers of beetles, are
held out at right angles to the body during flight. The meta-
thoracic wings are membranous and are folded longitudinally
like a fan beneath the forward wings, when at rest. Each
somite bears a pair of legs on its ventral surface. The cutic-
ula of each thoracic somite is composed of a number of
distinct plates. Those which constitute the dorsal and the
ventral surfaces form the tergum and the sternum of the somite,
respectively ; those constituting the lateral surfaces form the
pleura of the somite. Thus we speak of the pro-, meso-, and
metasternum, etc.

In the abdomen the cuticula of the dorsal and the ventral
portions of each somite is composed of a single plate, which is
called the tergite and the sternite, respectively. The abdomen is
made up of eleven somites, which are not all, however, perfect
segments, the sternite of several of the terminal somites being
wanting. The posterior end of the abdomen is different in the
two sexes, the female possessing an ovipositor, by means of
which she buries her eggs in the ground. The sternites of the
ninth, tenth, and eleventh somites are wanting in the female, the
last sternite being the eighth. Tergites of the three terminal
somites are, however, present. Projecting from the hinder end
of the abdomen is the ovipositor, which consists of two pairs of
short, movable, curved, and pointed structures. One of these
pairs is dorsal in position, and the anus is at its base; the other
is ventral, and at its base is the external opening of the
oviduct. Extending from the posterior border of the tenth
tergite is another pair of pointed projections, called cerci, which
may have a sensory function. Just beneath each cercus is a
plate called a podical plate. Between the two podical plates on
the dorsal side of the animal is the triangular eleventh tergite.

A GRASSHOPPER 11

In the male the ninth and tenth sternites are present, although
they may be fused so as to appear as one plate. An additional
ventral plate, called the genital plate, forms the posterior extremity
of’the body. The tenth tergite is very small; the podical plates
and the cerci are large. Beneath the eleventh tergite is the
anus. Compare a male with a female abdomen and identify the
parts above mentioned.

On the lateral side of the first abdominal segment note the
auditory organ, a large circular opening covered by a membrane.
With the aid of a hand lens find the spiracles of the thorax and
the abdomen. Ten pairs are present, one pair on the anterior
margin of both the meso- and the metathoracic segments, and
one pair on each of the eight anterior abdominal segments, that
on the first abdominal segment being just within the margin of
the auditory organ.

Exercise 1. Spread out and pin down all four wings and draw
an outline of the dorsal aspect of the grasshopper on a
scale of 2 to 4. Number the thoracic and the abdominal
segments, and label all the parts observed.

Exercise 2. Cut off the wings from the left side of the body
and draw an outline of the side view of the thorax and the
two anterior abdominal segments on a scale of 5 or 6.
Note that both the meso- and the metapleurum are divided
by a diagonal suture into two portions. Number the seg-
ments and label all the parts.

Exercise 3. Draw a side view of the posterior end of your
specimen (whether male or female) on a scale of 5 or 6,
showing accurately the arrangement of all the parts, and
label them all.

Exercise 4. Draw an outline of the ventral surface of the
thorax on a scale of 5 or 6. Note the dovetailing of the
anterior margin of the metasternum with the posterior

12 INVERTEBRATE ZOOLOGY

margin of the mesosternum and of that of the first
sternite with the metasternum, also the attachment of
the legs.

e

Exercise 5. Remove a metathoracic leg and draw an outline of it
on a scale of 8. The segment by which it articulates with
the body is the coxa; the next segment is the trochanter,
which in the grasshopper, however, is not a free segment,
but is fused with the following one, the femur; the latter
is the largest segment of the leg and has V-shaped muscle
impressions on its surface; the next segment is the tibia
or shank; the end segment is the tarsus or foot, which is
made up of five smaller segments; the terminal one of
these bears two claws between which is a structure called
the pulvillus. This organ is an adhesive pad which enables
the animal to walk and spring on smooth surfaces. Label
all of these parts.

Exercise 6. Draw an outline of the face on a scale of 5 or 6.
The large plate which forms the top, front, and sides of
the head, in which the eyes, ocelli, and antenne are situ-
ated, is called the epicranium. The sides of the epicranium,
back of the eyes, are the gene, the top is the vertex, and
that part which forms the anterior surface is the front.
Ventral to the epicranium is a broad, short, median plate
called the clypeus, beneath which is the upper lip. The
antenne are the first pair of appendages. Label all parts.

The mouth-parts. These consist of the median upper lip or
labrum, the paired mandibles, the paired maxille, the median hypo-
pharynx, and the paired under lip or Jabium. The paired mouth-
parts are the second, third, and fourth pairs of appendages, the
antenna being the first pair.

Exercise 7. Remove the labrum with scissors and draw it on a
scale of 5.

A GRASSHOPPER 13

Exercise 8. With strong forceps remove the dark-colored mandi-
bles and draw the inner surface of one of them on a scale

of 5.

Exercise 9. Remove the maxille, which lie just back of the
mandibles, being careful to take out the entire structure.
Mount them on a glass slide in glycerine or water with
the posterior side uppermost, and examine them under the
microscope. Note the following parts: the basal segment
or cardo, by which the maxilla articulates with the head;
the stipes, the broadest segment of the structure; the
inner and the outer lobes, which project from the distal edge
of the stipes; and the maxillary palp, which projects from
the lateral edge of the stipes. Draw a maxilla on a scale
of 5 and label all of these parts.

Exercise 10. Note between the maxille and just in front of the
labium a median projection, the hypopharynx. Remove
the labium, taking care to leave none of it in the animal,
mount it on a slide, and identify the following parts:
the basal segment or submentum, by means of which the
labium articulates with the head; the mentum, the succeed-
ing segment; the ligula, which projects from the distal
edge of the mentum; and the two labial palps, which project
from the lateral edges of the mentum. The labium is a
second pair of maxille fused in the median line. Trace
the homologies between the parts of the labium and those
of the maxille. Draw the labium on a scale of 5 and
label its parts.

The mouth-parts of the wasp and the beetle. The mouth-parts
of the grasshopper are called biting mouth-parts because the
insect bites or chews its food instead of licking or sucking it.
Biting mouth-parts characterize all the more primitive insects.
The mouth-parts of the beetle are similar to those of the grass-
hopper, although the former is a much higher insect.

14 INVERTEBRATE ZOOLOGY

Exercise 11. Remove carefully and with the aid of the dissecting
microscope, if necessary, the antenne, labrum, mandibles,
maxille, and labium of the beetle. Mount them on a
slide and draw them on a large scale. Label carefully
all the parts.

Bxercise 12. The mouth-parts of the wasp are much more
highly specialized than those of the beetle, as they are
adapted not only for chewing, but also for licking. Remove
the antenne and the mouth-parts of the wasp and mount
them on a slide. The labrum and the mandibles will be
seen to be similar to those already studied. The maxille
and the labium, also, do not differ materially from those of
the beetle or the grasshopper. The labium les between
the two maxille, and its ligula is elongated and modified
to form a licking organ. Draw an antenna and the mouth-
parts on a scale of 6.

Internal anatomy. Take the grasshopper in the hand and with
a pair of fine, sharp scissors cut a slit through the body-wall a
little to one side of the mid-dorsal line from one end of the
body to the other, using great care not to injure the organs
within. Place the animal, dorsal side up, in a shallow pan
with a wax-covered bottom containing water or 80% alcohol.
First, with two strong pins, pin the head to the wax and then
the extreme hinder end of the body, then carefully spread the
cut edges of the body-wall as widely as possible to the right
and left and pin them down, using many pins on each side.
Observe the organs as they lie in the body-cavity. In the
thorax will be seen the strong locomotory muscles. Lying
immediately beneath the dorsal abdominal wall in the median
line is the heart; this may have been destroyed by the incision,
but if not, it may be recognized as a narrow, transparent tube
of the diameter of a needle, flanked by paired triangular muscles

A GRASSHOPPER 15

which hold it to the body-wall. Immediately beneath the heart
is a loose network of yellowish fatty tissue, called the fat-body,
which covers the viscera. Remove this carefully. The alimen-
tary canal will be disclosed, a large tube running through the
median axis of the body; above the abdominal portion are the
paired reproductive glands, from which a duct passes on each
side around the alimentary canal to the ventral side of the
animal. Notice the silvery air-tubes or trachee and the air-sacs
on each side of the alimentary canal ; also observe the tangled
mass of delicate brown threads, the urinary or Malpighian
tubules, between the reproductive glands and the alimentary
canal.

Exercise 13. Make a sketch of the animal on a scale of 5, show-
ing the internal organs in situ, and label them all.

The digestive system. With fine scissors sever the alimentary
canal at its extreme posterior end, where it joins the anus.
With great care draw it forward between the ducts of the
reproductive organs and from beneath those organs, loosening
it from the surrounding tissues with a needle. Identify the
following divisions of the alimentary canal: the pharynx, the
space just back of the mouth; the esophagus, the narrow tube
which runs upward from the pharynx and, bending back,
enters the thorax, where it enlarges to form a pouch called the
crop; the salivary glands, a pair of delicate, branched organs, one
on each side of the crop, the ducts of which run forward to the
pharynx; the gastric ceca, eight elongated sacs which encircle
the base of the crop; the stomach-intestine, a large tube which
extends back to the point where the delicate urinary or
Malpighian tubules join the alimentary canal; the ileum, a
thick tube the diameter of which is the same as that of the
stomach; the colon, a narrow, slightly coiled tube; and the
rectum, which has six ridge-like rectal glands along its sides and
opens into the anus.

16 INVERTEBRATE ZOOLOGY

The excretory system. This system consists of the Malpighian
tubules. These are delicate tubular glands, about fifty in num-
ber, which unite with and discharge their products into the
alimentary canal at the point of juncture of the stomach-
intestine and the ileum. They extend freely into the body-
cavity and excrete urinary wastes from the blood, in which
they lie immersed.

Exercise 14. Make a drawing of the alimentary canal and the
Malpighian tubules on a scale of 7 and label all of the
parts.

The reproductive system; the female organs. The two ovaries
are closely bound together by a web of connective tissue and
trachee so as to form a single mass, which lies above the
intestine. If your specimen be a female, part this mass along
the median line and with a needle gently remove some of the
connective tissue surrounding it. Examine it with a hand lens;
each side is a separate ovary and will be seen to be a collection
of parallel, tapering tubules, their smaller ends being in the
median line, their longer ends projecting back to the tube-like
oviduct. These tubules are called ovarioles; it is in them that
the eggs develop. How many tubules do you count on each
side? Notice the elongated eggs in each ovariole. How many
do you see in each one? The two oviducts proceed from the
ovaries to the ventral side of the animal, where they unite to
form a median tube, the vagina, which opens to the outside
between the ovipositors. Just above the vagina is a small sac,
the receptaculum seminis, which is connected by a long sinuous
duct with the exterior. This sac becomes filled with sperma-
tozoa during pairing, which fertilize the eggs as they pass out
of the vagina.

Exercise 15. (2) Make a semidiagrammatic drawing represent-
ing all the parts of the female reproductive tract.

A GRASSHOPPER 17

The male organs. ‘The paired testes which secrete the sperma-
tozoa lie above the intestine, bound together by connective
tissue and fat. Each testis consists of a bundle of elongated
tubes with which a duct called the vas deferens connects poste-
riorly. The two vasa deferentia run, one on each side of the
intestine, to the ventral side of the animal, where they meet
to form a median tube, called the ductus ejaculatorius, which is
homologous to the vagina of the female. Connecting with
the ductus ejaculatorius are a number. of tubular prostate
glands which secrete the fluid in which the spermatozoa are
suspended.

Exercise 15. (6) Make a semidiagrammatic drawing representing
all the parts of the male reproductive tract.

The respiratory system. The spiracles have already been noted.
They are the external openings of the trachee, a system of fine
air-tubes which extend throughout the entire body of the
insect and through which fresh air is introduced into every
part of the body. The blood is thus constantly aérated, and
there is never any venous blood present. This arrangement
results in a very active metabolism, and is one of the causes of
the extraordinary amount of energy which characterizes most
insects. With the aid of a hand lens examine the trachee in
different parts of the body. They may be easily detected by
their silvery gleam. Notice the arrangement of the main
tracheal trunks, including those which connect with the spiracles,
also the arrangement of the air-sacs, which are expansions of
traches. Mount a small portion of the fatty tissue containing
tracheze in water or glycerine and examine them with a com-
pound microscope. Notice the spiral threads which line the
trachez.

Exercise 16. Make a drawing of a trachea seen under a high
power of the microscope.

18 INVERTEBRATE ZOOLOGY

The circulatory system. This system is very simple in insects,
owing to the great complexity of the respiratory system. In-
stead of the blood being carried to the respiratory organs to
be aérated, as is the case in vertebrates, rendering necessary
a complicated system of blood-tubes connecting the remotest
parts of the body with the respiratory organs, the respiratory
organs are themselves a system of tubes which introduce air to
every part of the body. The insect has a blood fluid which
lies in the body-cavity. The only circulatory vessel present is
the tubular heart. ‘This organ, whose position has already been
noted, has a closed hinder end and segmental valvular openings
along its sides. By its contractions the blood is sent into the
forward portions of the body, whence it flows back into the
hinder portions, and enters the heart again through the valvu-
lar openings. To observe the heart of an insect is not always
easy, owing to its position so near the dorsal body-wall
and its great delicacy of structure. An. easy method .is to
mount a live, transparent, aquatic insect larva, such as that
of the mosquito, on a slide in water and observe it under a
compound microscope. The heart and its action may be easily
studied.

The nervous system. Cut off the alimentary tract at its forward
end, taking care not to injure the two nerve connectives which
pass to the brain, and remove all the viscera from the body.
The nerve cord will be seen lying on the ventral body-wall of the
abdomen, in the median line, slightly concealed by fat. It will
be seen to be double and to contain, in the abdomen, five
enlargements, the ganglia, from each of which fine nerves radiate.
Trace the nerve cord from the abdomen into the thorax. It is
here protected by hard projections of the body-wall, which
must be carefully removed. Four large ganglia will be found
here, the three posterior ones of which are the thoracic ganglia.
The one in the forward portion of the prothorax really belongs
to the head and is called the subesophageal ganglion. From it

A GRASSHOPPER 19

a pair of nerve connectives passes to the dorsally situated
supracsophageal ganglion or brain. The brain is the largest
ganglionic mass in the body and is situated in the top of the
head between the eyes. Lay bare the brain. Notice the
optic lobes going to the eyes, and between them the much smaller
ocellar lobes sending nerves to the lateral ocelli. Beneath the
optic lobes are the antennal lobes, which send nerves to the
antenne, while near them in the median line is the median
ocellar lobe, which sends a nerve to the median ocellus.

Exercise 17. Make a large sketch of the nervous system, repre-
senting it in an outline of the animal’s body, and show in
which segments the different ganglia occur.

Exercise 18. Draw a diagram representing a side view of a
grasshopper on a scale of 3 or 4, in which the segmenta-
tion, the relative position of the heart, the alimentary
tract, and the nervous system are accurately indicated.

20 INVERTEBRATE ZOOLOGY

INSECTA
AN INSECT LARVA. A CATERPILLAR

Notice that the head, thorax, and abdomen are not set off
from one another. The body is thus worm-like in form, there
being almost no specialization of the body-parts. Determine
how much of the body is thorax and how much abdomen.
The thorax bears three pairs of jointed legs, each one termi-
nating in a single hook. The abdomen also bears several pairs
of legs which are not like those of the thorax. How many are
there and in what do they differ from the thoracic legs? Find
and count the spiracles, which are usually easily seen.

Exercise 1. Draw an outline representing a side view of the
animal on a scale of from 2 to 6; number the thoracic and
abdominal segments, show the spiracles, and label all the
parts.

Study the head with the aid of-a hand lens. Notice the pair
of large convex plates which, with the small median triangular
plate, form the wall of the head. Near the lower edge of each of
the convex plates are several minute ocelli; count them. On the
ventral side of the head find the antenne; how many joints are
there in each? The mouth-parts are between the antenne. The
labrum is bilobed, and beneath it are the dark-colored mandibles.
Just back of these are the maxille and the labium, the latter
being a median, elongated, conical organ between the maxille.
The external opening of the silk glands is in the labium.

Exercise 2. Draw a front view of the head on a scale of 7.

Internal anatomy. With fine scissors make a longitudinal
incision the length of the animal, in the dorsal integument, a

A CATERPILLAR 21

short distance to one side of the median line. Turn the integu-
ment to the right and left and pin it down. If it has not been
destroyed, observe the heart. It is a straight, transparent tube
lying in the mid-dorsal line just beneath the integument. Note
the large, tubular alimentary tract surrounded by delicate, glis-
tening trachee and by the white and often filamentous fat. Its
forward portion is the esophagus; the middle and largest portion
is the stomach-intestine; the narrow portion back of which is the
intestine ; while the dilated portion which communicates with
the anus is the rectum. In the forward portion of the body
cavity, along the wall of the cesophagus, is a pair of delicate
tubular salivary glands which extend forward and communicate
with the mouth. Note and trace the course of the much larger
tubular silk glands on the ventral body-wall; they are also a
single pair and communicate with an opening in the labium.
Find and carefully trace the course of the six Malpighian tubes,
which lie along the stomach and join it at its posterior end.

Exercise 3. Draw an outline of the opened animal on a scale of
6, showing the organs above described. Represent the
segmentation and show accurately the position of the
organs in their proper segments.

Sever the cesophagus and remove the stomach and the intes-
tine from the body. Study the nervous system. Note the
arrangement of the trachee with reference to the spiracles.
Note the longitudinal muscle bands which form a part of the
body-wall; also their segmental arrangement.

Exercise 4. Draw an outline of the opened body on a scale of
6, showing and numbering the segments. . Draw in it the
nervous system, representing accurately the number of
ganglia, and placing them in the proper segments, together
with the trachee and muscles.

The reproductive system consists of two small sexual glands
and a duct leading from each. There is no external pore.

22 INVERTEBRATE ZOOLOGY

MYRIAPODA
A CHILOPOD. A CENTIPED (Lithobius)

Myriapods are worm-like animals which live under logs and
stones, beneath the bark of decaying stumps and trees, and
in other dark, damp places. The two main groups of myria-
pods may be easily recognized by the differences in shape and
habits, — the Chilopoda being flattened and very active animals
with one pair of legs to a segment, the Diplopoda being usually
cylindrical animals with short legs, two pairs of which are
present on'most of the segments.

Observe the vermiform body, the well-marked segmentation,
and the segmented legs ; also the lack of specialization among
the segments, there being no division into thorax and abdomen.
The animal is plainly an arthropod, but it is not an insect ; it
is a lower animal than an insect, because its body shows less
specialization. Note the single pair of antenne and the insect-
like mouth-parts, also the large hook-like appendages just back of
the head. These latter are homologous to the first pair of
legs; they are the principal organs of prehension and are
provided with poison glands which open on the inner surface
near the end. Note the anal feelers; these are homologous to
the hindermost legs and enable the animal to perceive what is
back of it.

Exercise 1. Draw an outline of the dorsal aspect of the animal
on a scale of 5 and label all the organs observed.

Exercise 2. Draw a ventral view of the head on a scale of
10, showing the cephalic appendages in position. The
mouth-parts consist of a pair of mandibles and two pairs

A CENTIPED 23

of maxille, the second pair of which is homologous to the
labium of insects.

Exercise 3. Remove, under a dissecting microscope, the prehen-
sile hooks and the mouth-parts, beginning with the pos-
terior ones and working forward, and the antenne. Mount
them on a slide and draw an outline of each. Compare
the different structures of the mouth-parts with those
of the insect and label them all.

The internal organs. The digestive, circulatory, respiratory,
excretory, and nervous systems are essentially like the same
systems in insects. The reproductive system consists of a
pair of sexual glands with paired ducts, the posterior portions
of which unite to forma common duct. This opens to the
outside in the genital segment, which is the penultimate body
segment.

24 INVERTEBRATE ZOOLOGY

ARACHNIDA

A SPIDER

As large a spider as possible should be obtained for this study.
If a small one is used, it is usually well to stick a slender insect
pin through it, in order to be able to handle it easily, and it should
be studied with the aid of a hand lens. Observe the form and
color of the animal. The body is unsegmented (although the
body of the embryo spider is distinctly segmented) and is made
up of two parts, the cephalothorax and the abdomen. What does
the embryonic segmentation indicate as to the ultimate relation-
ships of spiders? Observe the hairs which cover the body and
legs. They are projections of the cuticula and are important
sense organs, being sensitive to vibrations of the atmosphere.
They thus aid in giving the animal information in regard to
what is going on about it.

The cephalothorax. This division of the body is equivalent to
the head and thorax of insects. Observe carefully the eight
eyes at or near its forward end, both the size and arrangement
of which vary much in the various species of spiders. The
ventral surface bears the six pairs of appendages, the mandibles,
the pedipalps, and the four pairs of legs.

The mandibles, the anterior pair, occupy a vertical position at
the front end of the body and consist each of a basal portion and
a terminal claw, near the tip of which is the pore from which
poison is injected into the bite. In consequence of the vertical
position of its mandibles the spider can only strike an insect
which is beneath it.

The second pair of appendages are the pedipalps. These are
leg-like and contain one less segment than the legs, the missing

A SPIDER 25

segment being the one next to the last. The basal segment of
the pedipalp is called the maxilla. The two maxille are flattened
structures situated on the underside of the cephalothorax just
back of the mandibles, their forward, medial margins, which cover
the mouth, being used to lacerate and squeeze the food so that
the animal juices can be sucked up. Spiders prey exclusively
upon living animals; but they can take in only liquid food.
The pedipalps of the female spider differ in shape from those of
the male, and the two sexes may be distinguished in this way.
In the female the pedipalp looks exactly like a small leg; in
the male the terminal portion is expanded and very complex in
structure, being used by the animal in the act of pairing.

The third, fourth, fifth, and sixth pairs of appendages are the
legs, each of which is composed of the following seven segments:
the coxa, trochanter, femur, patella, tibia, metatarsus, and tarsus.
The legs are used by the spider for a variety of purposes besides
walking. They are important as tactile organs, their great length
increasing their usefulness in this respect, and they undoubtedly
compensate the animal in a certain degree for the lack of an-
tenne. They are also of use in spinning and manipulating the
web, the complex structure of the claws being associated with
this function.

The median plate between the maxille on the ventral side of
the body is the labium; the one between the bases of the legs is
the sternum.

The abdomen. The dorsal surface is usually marked by several
pairs of depressions which mark the points of attachment of mus-
cles. At the hinder end, on the ventral surface, are three pairs
of spinnerets. Study these carefully with the aid of a hand lens.
At the end of each spinneret are numerous microscopic holes,
from which is exuded the semifluid silk. This is made up of
many soft strands, which harden as they unite to form the thread.

A study of the embryology of the spider shows that the spin-
nerets are homologous to abdominal legs.

26 INVERTEBRATE ZOOLOGY

Note the spiracles, the external openings of the respiratory
organs, the trachee and the lungs. A short distance in front
of the spinnerets in the ventral surface of the abdomen is the
single median, minute tracheal spiracle: it is often difficult to
see. The lung spiracles are a pair of large slits near the anterior
end of the abdomen, each one at the lateral end of a transverse
fold of the integument. Between them in the median line is the
genital pore. In the female spider it is covered by a large and
complex plate called the epigynum.

Exercise 1. Cut off the legs on the right side of the body and
draw an outline of a side view of the spider on a scale of
from 5 to 10, putting in only the basal portion of the legs
but all of the pedipalps and the mandibles. Carefully label
all the parts observed.

Exercise 2. Draw an outline of the ventral aspect of the body
on the same scale, putting in and labeling all the parts
observed.

Exercise 3. Draw the front end of the body on a scale of 10,
showing the mandibles and the eight eyes.

Exercise 4. Draw the pedipalp on a scale of 6.
Exercise 5. Draw one of the legs on a scale of 6.

Exercise 6. Cut off a tarsus and study it under a compound
microscope, noting the shape of the claws and the hairs
which often surround them. Draw them.

The internal anatomy of the spider will not be studied in this
dissection. The heart is an elongated tube which lies, enclosed
in a pericardial space, in the dorsal portion of the abdomen.
From its anterior end an aorta extends into the cephalothorax
and sends off a number of large branches to the legs and other
organs.

A SPIDER 27

The digestive system consists of a straight alimentary tube and
its many branches. In the cephalothorax, branches of it extend
to the legs, and a portion of it forms a sucking stomach, by
means of which the spider sucks up its fluid food. In the abdo-
men it becomes the intestine and gives off an extensive network
of tubules, which fills a large part of the abdomen and has the
appearance of a compact gland; its function, however, is not
secretory and it does not differ in structure from the rest of
the intestine. The end intestine possesses a large dorsal fecal
reservoir.

The kidneys are a pair of branching Malpighian tubules.

The brain lies just beneath the eyes. It is joined, by means of
broad connectives, with the large ventral ganglionic mass, from
which nerves extend into the abdomen and the appendages.

The organs of respiration are the lungs and the trachee. The
lungs are a pair of sacs which open to the outside through the
lung spiracles, each sac containing a series of lamelle, usually
called a lung-book, in which the blood circulates. The trachee
open to the outside through the tracheal spiracle.

The sexes are separate in spiders. In the male the testes are
a pair of tubular glands which are joined, by means of the coiled
sperm ducts, with the sperm vesicle, which opens to the outside
through the genital pore. The ovaries, in the female, are large
organs in the ventral portion of the abdomen, which are joined,
by means of the oviducts, with the uterus, which, after receiving
the paired receptacula seminis, opens to the outside through the
genital pore.

The siik glands are branched or tubular structures in the
ventral portion of the abdomen.

28 INVERTEBRATE ZOOLOGY

CRUSTACEA
A MACRURAN DECAPOD. A CRAYFISH OR A LOBSTER

These two animals are very common, the one in fresh and
the other in salt water. In external form and internal anat-
omy they are exceedingly similar to each other, and the same
directions for dissection may be made to apply to either. In
habits and general method of life the animals also resemble
each other; they move about at or near the bottom of the
water, preferring regions which are rocky or stony, and feed
upon small animals of all kinds and upon carrion.

Observe the shape, color, and external anatomy of the ani-
mal. It is bilaterally symmetrical; the body is composed of a
number of serially arranged segments, which are called somites
or metameres ; the dorsal and the ventral sides of the body are
unlike, the latter being characterized by the possession of a
series of paired and jointed appendages metamerically arranged;
z.e., each somite or metamere bears a pair of appendages; the
anterior and the posterior ends are also unlike, the former being
characterized by the possession of organs of special sense and
the mouth. The external covering of the body is a chitinous
cuticula which constitutes an exoskeleton. All of these fea-
tures are equally characteristic of insects and myriapods.

As in all crustaceans, and also in insects, the body of the
animal falls into three distinct divisions, — the head, thorax, and
abdomen. ‘The first two of these body-divisions do not, however,
articulate freely with each other as they do in insects, but, in
common with all the higher crustaceans, they are fused together
and form a single structure, which is called the cephalothorax.
The dorsal and the lateral surfaces of this division show no

A CRAYFISH OR A LOBSTER 29

segmentation, because of the fusion of the somites and the
presence of a hard, shield-like structure covering it, which is
called the carapace, but on the ventral side the segmentation is
distinctly seen. Extending along the entire ventral surface
of the animal are the paired appendages. Their metameric
significance may not be seen in the cephalothorax, but it will
be distinctly seen in the abdomen, where each somite except
the last bears a pair of appendages.

The cuticular exoskeleton is thicker and heavier than in
insects ; this is due to the presence, besides chitin, of salts
of lime. The crayfish or lobster moults its cuticula periodi-
cally, the adult animal probably once or twice a year, the
young animals oftener.

The animal is capable of two sorts of locomotion. By pow-
erful strokes of the broad, fin-like end of the abdomen it swims
rapidly backward, and it can walk on its thoracic legs. It is
well provided with special sense-organs. Most important to it
are the two pairs of feelers or antenne, which are characteristic
of all crustaceans, and the compound eyes on movable stalks. It
also possesses, in a pair of small cavities, on the upper surface
of the basal joints of the first or shorter pair of antenna, pecu-
liar, sense-organs, which were formerly supposed to be ears, but
are now known to be balancing organs. With the aid of them
the animal maintains its equilibrium.

The body of the crayfish or the lobster, as of all the higher
crustaceans, is made up of twenty somites or body-segments, of
which the thirteen anterior somites form the cephalothorax,
and the seven posterior ones the abdomen.

The cephalothorax. The anterior five somites forming this
body-division are cephalic, the remaining eight are thoracic,
and all are covered dorsally and laterally by the carapace. The
projection running forward from the anterior end of the
carapace is called the rostrum. A transverse groove is seen
near its middle; this is the cervical suture and marks the

30 INVERTEBRATE ZOOLOGY

boundary between the head and the thorax. In the crayfish
two semicircular, longitudinal grooves extend backward from
the outer ends of the cervical suture, which separate the sides
of the carapace from the median, dorsal portion. The sides of
the carapace are called the branchiostegites; they cover lateral
folds of the dorsal integument of the animal, which extend
over the sides of the body and enclose between themselves and
it the spaces within which lie the gills. These spaces, the gill-
chambers, thus communicate freely with the surrounding water.
Pass the handle of a scalpel or other flat object beneath the
lower edge of the branchiostegite and it will go into the gill-
chamber. During life a current of water passes constantly
into the gill-chamber along this lower edge, where it bathes the
gills and then passes out at the forward end.

Study the ventral side of the cephalothorax. The most
important organs here are the appendages. At the anterior
end of the body are the two pairs of antenne, the longer pair
being the second. On the lower surface of the basal joint of
each of the latter is an opening ; these are the external open-
ings of the kidneys or green glands. Back of the antenne is
the mouth. It is bounded in front by a lip-like structure called
the labrum, at the sides by the strong mandibles, and behind. by
a pair of delicate plate-like projections, called the paragnatha,
which are not appendages. Press the mandibles aside and
pass a probe into the mouth. Between the mouth and the
large claws are five pairs of appendages which assist in the
act of eating ; they are two pairs of delicate leaf-like maxille,
just back of the mouth, and three pairs of larger maxillipeds,
back of them. They are best identified by beginning with
the hinder pair of maxillipeds, which is just in front of the
large claws, and working forward, placing a needle or knife
between the appendages as they are identified. Back of the
maxillipeds come the large grasping claws or chelipeds, which form
the principal weapons of offense and defense of the animal, and

A CRAYFISH OR A LOBSTER 31

in the largest lobsters are powerful enough to crush a man’s
arm. Note the difference between the right and the left claw,
if any. Back of the chelipeds are four pairs of walking legs.
In the male animal the paired external openings of the genital
organs are at the base of the last pair of walking legs, in the
female at the base of the antepenultimate pair. Find them.

The abdomen. The seven somites forming this body-division
are all free and jointed with one another. Note the difference
in the thickness of the cuticula on the dorsal and the ventral
surfaces, also its thinness at the joints. The appendages on
the abdomen have various uses. They probably have a general
respiratory function. In the male the first two pairs are
functional in pairing, in the female the first five pairs hold
the eggs from the time they are laid until the young are
hatched. The last pair in both sexes is large and broad
and with the end-segment forms the swimming fin. The end-
segment is called the telson; it bears no appendages; the anal
opening is in its ventral side.

The natural color of the animal is usually a greenish black,
but hot water or alcohol turns it red.

Exercise 1. Draw an outline of the dorsal side of the animal
and label all the parts.

Cut off the right branchiostegite with the scissors, taking
care not to injure the gills beneath. Push aside the gills and
notice the thin integument which forms the lateral wall of the
cephalothorax. Observe the method of attachment of the gills.
They are feathery, thin-walled expansions of the body-wall and
are attached either to it or to the basal portions of the legs.
They present a very large surface to the surrounding water, and
the blood circulating through them is thus oxygenated. Notice
the epipodites, the skinny flaps which project from the basal
joints of many of the legs and separate the gills of a segment
from those of the next. They are not prominent in the crayfish.

32 INVERTEBRATE ZOOLOGY

Exercise 2. Without displacing the gills or epipodites make a
sketch of them as they lie in the gill-chamber.

Exercise 3. Draw a diagram representing an ideal transverse
section of the body-wall in the region of the walking
legs; show the relations of the branchiostegites, the legs,
and the gills to the body.

The appendages. Of these there are nineteen pairs, each
somite of the body, with the exception of the last one, bearing a
.pair. There are thus thirteen cephalothoracic appendages, of
which five are cephalic and eight thoracic, and six abdominal
appendages. All of these appendages, except the first pair,
however much they may differ from one another, are modifi-
cations of a single primitive type of structure. This type has
been least modified in certain of the abdominal appendages.
We shall, consequently, study these first.

Exercise 4. The abdominal appendages are called swimmerets
or pleopods. Cut off the right swimmeret of the fourth
abdominal somite close to the body, draw it on a large
scale, and label all its parts. It consists of a basal piece,
the protopodite, and two terminal branches, the inner or
endopodite, and the outer or exopodite. This type of structure
is characteristic of all crustacean appendages except the
pair belonging to the first somite; those appendages which
apparently differ from this type are modifications of it.

Exercise 5. Remove and draw on a large scale the right-hand
sixth swimmeret. It is quite different from the last one
drawn, and is sometimes called a uropod, but yet has the
typical parts. Label its parts.

Exercise 6. (a) If the animal be a male, remove and draw the
right-hand first and second swimmerets. These are modi-
fied from the typical structure to serve as copulatory
organs.

A CRAYFISH OR A LOBSTER 33

Bzercise 6. (b) If the animal be a female, remove and draw the
right-hand first swimmeret.

Exercise 7. The five pairs of walking legs (including the cheli-
peds) are called periopods and belong to the thorax. Remove
and draw the right-hand fourth periopod, disregarding the
gill attached to it, and label the parts. It consists of seven
segments, of which the two segments nearest the body con-
stitute the protopodite, and the five farthest from the body
the endopodite. The exopodite is not present.

Exercise 8. The cheliped is composed of the same segments as
the other periopods. With a strong knife split the claw
lengthwise into two equal halves. Examine the muscles
controlling the movable limb of the claw. There is a
strong adductor muscle which closes it, and a weaker extensor
muscle which opens it. Make a diagrammatic drawing
illustrating them.

Exercise 9. The three pairs of appendages directly in front of
the chelipeds are the maxillipeds; they are thoracic append-
ages which assist in the process of eating. Remove with
forceps and scissors the right-hand third (é.e., the posterior)
maxilliped; draw it on a large scale, disregarding the
gill which may be attached to it, and carefully label the
protopodite, exopodite, and endopodite.

Exercise 10. Remove with the forceps the right-hand second
maxilliped and draw it on a large scale.

Exercise 11. Remove and draw the right-hand first maxilliped.
The two large basal segments are the two segments of the
leaf-like protopodite, the endopodite is a very small struc-
ture next to the protopodite, and the exopodite is a much
longer structure next to the endopodite. A large epipodite
is present. Label all of these.

34 INVERTEBRATE ZOOLOGY

Exercise 12. The two pairs of delicate appendages in front of
the maxillipeds are the maxille; they are cephalic append-
ages. Remove with forceps the right-hand second maxilla
and draw a large outline of it. The protopodite is wide
and leaf-like; the endopodite is small; the exopodite is
wide and with the epipodite forms a broad plate, called the
scaphognathite, which is used by the animal to maintain a
current of water from the gill-chamber.

Exercise 13. Remove carefully and draw the right-hand first
maxilla. The protopodite is wide and leaf-like and similar
to that of the second maxilla; the endopodite is extremely
small; the exopodite is wanting.

Exercise 14. Extract with strong forceps and draw the right-
hand mandible. The biting portion of it, together with
the first joint of the small palp, forms the protopodite; the
two terminal joints of the palp are the endopodite; the
exopodite is wanting. Close to the posterior surface of
the mandibles are the delicate paragnatha.

Exercise 15. Remove at its base and draw the right-hand second
(the longer) antenna. The exopodite is a short, stiff, plate-
like expansion ; the endopodite is the long slender terminal
portion.

Exercise 16. Remove and draw the right-hand first antenna, or
antennule as it is also called. No exopodite and endopo-
dite are present in this appendage throughout the Crustacea,
there being typically but one terminal branch. In the cray-
fish and lobster this terminal branch is double.

-Exercise 17. Construct in your notebook a table showing the
relation of the appendages and somites, as follows:

A CRAYFISH OR A LOBSTER 35

No. oF SOMITE. NAME OF APPENDAGE. PROT. Ex. Enp.

Head...

aorWwWnN re

1st maxilliped + + +

Thorax...

Abdomen . j 17

Write opposite the number of each somite, in your notebook,
first, the name of the appendage belonging to it, then indicate
what parts that appendage possesses by a “+” and what parts
it lacks by a “—” under the appropriate head, as is shown
above in the case of the sixth somite.

The gills. Remove the left-hand branchiostegite. Place the
animal in water and study the gills on the left side. These
organs may occur on the eight thoracic somites, and on each
segment they may be attached either to the basal joint of the
leg, when they are called podobranchiz, to the flexible joint by
which the leg articulates with the body, when they are called
arthrobranchie, or to the body-wall just above the leg, when they
are called pleurobranchie. A single thoracic somite may bear
on each side four gills, —a pleurobranch, two arthrobranchs,

36 INVERTEBRATE ZOOLOGY

an anterior and a posterior, and a podobranch, — but on most of
the somites a less number is present.

Exercise 18. Construct in your notebook a table showing the
arrangement and number of the gills and also of the epip-
odites and their velations to the somites bearing them,
as follows:

No. OF

Popo. ANT. ARTH. |POST. ARTH. PLEU. EPIP. TOTAL.
SOMITES.

Begin with somite 13 and indicate by a “+” under the
proper head opposite the number of each somite the presence
of the gill or epipodite, and by a « —”’ its absence.

The internal organs. With strong scissors and forceps care-
fully remove the shell from the entire dorsal surface of the ani-
mal, taking great care not to disturb the organs lying beneath.
Notice just beneath the shell a pigmented membrane. This is
the under-skin; it is composed of a layer of connective tissue,
gland-cells, nerves, and blood, on the outer surface of which is
the layer of epithelial cells called the hypodermis, the matrix of
the shell. Entirely remove the under-skin. Study the organs
as they lie, without disturbing them. Notice in the cephalo-
thorax, first, the large sac-like stomach just back of the rostrum
and connected by muscles with the anterior body-wall. On
each side of the stomach will be seen the cut ends of a mass of
muscle fibres. ‘These are the mandibular muscles. Demonstrate
their connection with the mandibles. Just back of the stomach

A CRAYFISH OR A LOBSTER 37

is the white, shield-shaped heart, from the anterior end of which
five delicate arteries proceed,—a median artery, and two pairs of
lateral ones. Find these arteries and trace them forward as far
as possible without breaking them. On both sides of the stom-
ach and the heart and partly beneath them are the liver and the
reproductive organs. The former is a pair of large, soft, and
usually light-green organs which may fill a large portion of the
cephalothorax and may extend back into the abdomen. The
latter, if the animal be a female, are a pair of brownish or
yellowish organs, the ovaries, in which the ova can often be
seen; they are situated beneath the heart and in front of and
behind it, and vary in size and also in color with the develop-
ment of the ova. When these are approaching maturity the
ovaries are the most prominent organs in the body-cavity, and
often extend far back into the abdomen. In the male animal
the reproductive glands, the testes, are white in color and
very slender, and occupy the same position as the ovaries in
the female. Note the coiled vas deferens on each side.

Study the musculature and the other organs of the abdo-
men. There are two systems of muscles here. On the dorsal
side are longitudinal muscles, the extensors, which extend or
straighten the abdomen. Separate these muscles carefully
along the median line and observe beneath them the delicate,
colorless abdominal artery which carries the blood from the heart
throughout the abdomen. Trace it forward to the heart.
Notice the lateral branch-arteries. How many pairs are there?
Just beneath this artery lies the intestine, which often contains
dark-colored fecal matter. Beneath it and filling most of the
space within the abdomen are the flexor muscles, which are very
complex, whose function it is to bend or flex the abdomen. It
is by the use of these two sets of muscles that the animal swims.

Exercise 19. Draw an outline of the animal’s body, showing the
segmentation and the above-mentioned organs in situ, and
label them all.

38 INVERTEBRATE ZOOLOGY

The circulatory system. The heart lies within an enclosed space
called the pericardial sac, the walls of which, the pericardium, will
have been partially destroyed by the removal of the under-skin.
The heart, the abdominal artery with its lateral branches, and
the five anterior arteries have been studied and drawn. Care-
fully press aside the heart and note the median dorso-ventral artery
which leaves the abdominal artery near the heart and passes
ventrally. This artery supplies with blood a ventral longitudinal
artery, which lies in the mid-ventral line in the thorax and
abdomen.

Remove the dorsal abdominal artery and the heart from the
body and float them in clean water. Note the six valvular
openings of the heart, two being on the dorsal side, two on the
ventral, and one on each of the lateral sides. These can be
seen by blowing on the heart through a blow-pipe.

Exercise 20. Draw a dorsal view of the heart showing the
valves there present.

The course of the circulation of the blood is the following:
by the contraction of the heart the blood is sent through the
arteries to all parts of the body; after bathing the different
tissues it collects in a ventral blood-sinus, a passage in the
ventral portion of the body-cavity in which lie the ventral
nerve-chain and the ventral abdominal artery, and passes
towards the gills; from the ventral sinus it passes to the gills
through afferent veins, one of which runs to each gill and
along the outer edge of it; it then runs through the delicate
gill-filaments, where it is aérated, and passes by efferent veins
on the inner edges of the gills back to their base; here six
larger branchial veins collect the blood and carry it to the
pericardial sac, whence it is taken through the valvular open-
ings into the heart.

Exercise 21. Draw a diagram representing the entire circulatory
system.

A CRAYFISH OR A LOBSTER 39

The reproductive system. The female genital organs. The posi-
tion of the ovaries has already been observed. In the crayfish
their forward portions are paired, while their hinder portions
are fused and lie in the median line. In the lobster, however,
no such fusion takes place, but the two ovaries are united by a
bridge midway in their length. Find the paired oviducts which
lead from the ovaries to the genital openings. Remove both
ovaries and oviducts from the body and float them in water.

Exercise 22. (a) Make a diagrammatic sketch of them.

The male genital organs. The position of the testes has been
already noted. In the crayfish they are similar in shape and
position to the ovaries in the female animal, but are more
slender; in the lobster they are a pair of long white tubes
which extend forward as far as the stomach and back into the
abdomen. Find the paired vasa deferentia, which are long con-
voluted tubes connecting the testes with the external genital
openings. Remove the vasa deferentia with the testes from
the body and float them in a pan of water.

Exercise 22. (6) Make a diagrammatic sketch of the male
reproductive tract.

Cut open a vas deferens and examine its contents under a
high power of the microscope. Star-shaped spermatozoa will be
seen.

Exercise 22. (c) Draw a spermatozoan.

The digestive tract consists of the mouth, esophagus, stomach,
intestine, into which open the paired livers, and the rectum. Pass
a probe through the mouth into the stomach and notice the
dorso-ventral course of the esophagus, which joins the mouth
with the stomach. The paired ducts which unite the two lobes
of the liver with the intestine join that organ just back of
the stomach. Find them. With scissors sever the esophagus

40 INVERTEBRATE ZOOLOGY

just ventral to the stomach, taking care not to injure the brain,
which lies in front of the stomach, or the two slender nerve-
connectives, which lie on either side of the esophagus. Sever *
the rectum near the anus. Remove the entire digestive tract
from the body and place it in a pan of clean water. The liver
is so soft that it may not be possible to remove it entire.
Notice the boundary between the intestine and the somewhat
larger rectum. In the crayfish the rectum is much longer than
the intestine; in the lobster the opposite is true. In the lob
ster notice the blind-gut or appendix which joins the rectum near
its anterior end.

Exercise 23. Make a diagrammatic sketch of the digestive tract.

Cut open the stomach by a ventral incision and wash it out.
Observe its chitinous lining and the dark brown chitinous teeth.
This chitinous lining is a continuation of the cuticula which
covers the external surface of the body and is moulted with
the cuticula. During certain parts of the year a pair of large
calcareous bodies called gastroliths are imbedded in the lining of
the stomach. They remain in the stomach after the moulting
of the cuticula and furnish lime for the new cuticula, which at
onte grows rapidly.

Exercise 24. Make a sketch of the inner surface of the stomach
showing the teeth.

The excretory system. Notice in the extreme forward end of
the body-cavity, just in front of and below the stomach, a pair
of pale greenish bodies. These are the kidneys or green glands.
Each one is made up of two portions, the smaller glandular por-
tion, next to the body-wall, and the larger saccular portion, or
urinary bladder, next the stomach. From the latter the ureter
leads to the external openings which have already been noted.

Exercise 25. Draw a view of the forward end of the body-
cavity showing the kidneys as they lie in position.

,

A CRAYFISH OR A LOBSTER 41

The nervous system consists of a ventral double nerve cord
lying in the mid-ventral line in the body-cavity and extending
the length of the animal, with paired ganglia at intervals, also
of a brain situated just back of the eyes, which is united with
the ventral nerve by two nerve connectives, passing one on each
side of the cesophagus. The ventral ganglia have typically a
metameric significance, but many of the somites have lost their
ganglia, so that there are fewer ganglia than somites. The
double nature of the ventral nerve is best seen in the thorax.

Remove all the muscles and the viscera from the body. The
ventral nerve cord will be seen in the abdomen lying in the
mid-ventral- line. Notice the ganglia. How many do you
count? Notice the lateral nerve-branches. In the cephalo-
thorax the nerve cord is concealed beneath transverse ridges
of the ventral wall of the shell. Cut these with scissors and
expose the nerve, beginning at the hinder end of the cephalo-
thorax and working forward. How many thoracic ganglia do
you find? Just back of the cesophagus is the large subceso-
phageal ganglion which is connected with the brain by the two
connectives already mentioned. ‘The brain or supracesophageal
ganglion is just back of the eyes.

Exercise 26. Draw an outline of the body and in it the nervous
system, showing accurately the number of ganglia and the
segments in which they lie, together with the lateral nerves.

Exercise 27. Remove the brain and draw an outline of it on
a scale of 6 or 8, using a dissecting microscope or hand
lens. Show the antennal and the optic nerves.

Exercise 28. Draw a diagram representing an ideal sagittal
section of the animal in which the relative position of the
principal systems of organs is accurately shown.

42 INVERTEBRATE ZOOLOGY

CRUSTACEA
A BRACHYURAN DECAPOD. A CRAB

The crab is a representative of the more highly specialized
of the two divisions of the Decapoda, the Brachyura, which
include those decapods with short weak abdomens. The lobster
and the crayfish represent the other and less highly specialized
of the two divisions, the Macrura, which comprise those decapods
with long abdomens.

Compare the crab with the lobster or the crayfish. Note the
broad shield-shaped cephalothorax and the abdomen bent under it.
The abdomen of the male crab is narrow while that of the
female is broad. Which sex is your animal? In what ways is
the higher specialization of the cephalothorax and the abdomen
of the crab shown?

The body of the crab is composed of twenty somites, like that
of the crayfish and the lobster, thirteen of which belong to the
cephalothorax and seven to the abdomen. The cephalothorax
is covered by a carapace. Notice the short transverse suture
which separates the cephalic from the thoracic portion. At
the ends of this suture notice the longitudinal depressions
which mark off the lateral branchial areas and separate the
branchiostegites from the median portion of the carapace. The
branchiostegites are not applied closely to the body as they are
in the lobster and the crayfish, but stand out from it, very much
increasing the transverse axis of the cephalothorax and making
it longer than the longitudinal axis. This feature of its struc-
ture makes it easy for the crab to run sideways. Notice that
the ventral edge of the branchiostegite is closely applied to
the body, so that the respiratory water could hardly enter the

A CRAB 43

gill-chamber along this edge as it does in the crayfish and the
lobster. An opening is present, however, at the base of the
cheliped through which the water enters. Pass a probe into
the branchial chamber through this opening. Notice the
prominent stalked eyes; also the two pairs of delicate antenne.
Examine and identify the mouth-parts and the thoracic legs;
they will be found to correspond to those of the crayfish or
the lobster. Find the openings of the genital organs; in the
male on the ventral surface of the last and in the female of the
antepenultimate cephalothoracic segment.

The abdomen is relatively small and weak and usually
remains folded beneath the cephalothorax. It lacks the swim-
ming fin; most crabs cannot swim. The common blue crab,
however, swims very well by means of the fifth pair of perio-
pods. The number of abdominal segments is variable, fusion
having taken place between certain of the somites. This num-
ber is also not the same in the male and the female of the same
species. Raise the abdomen from the cephalothorax and observe
the swimmerets on its ventral surface. In the female note the
long chitinous hairs which fringe the swimmerets. It is to
them that the eggs and newly born young are attached. The
only swimmerets present in the male are the first two pairs,
which are functional in pairing.

Exercise 1. Draw a dorsal view of the animal with the abdomen
extended, being careful not to omit the antenne and the
eyes, and label all the parts observed.

Exercise 2. Construct in your notebook a table showing the
relation of the appendages and somites similar to that made
use of with the lobster or the crayfish. (See page 35.)

The gills. With stout scissors cut off the right branchios-
tegite and expose the gills. These will be found to be quite
different from those in the lobster or the crayfish, pleurobranchie
only being present. Note the enormously elongated epipodite

44 INVERTEBRATE ZOOLOGY

of the first maxilliped which extends across the gills to the
hinder part of the branchial chamber.

Exercise 3. Construct a table showing the relation of the gills to
the somites similar to that made use of in the dissection of
the lobster or the crayfish. (See page 36.)

Bxercise 4. Draw a diagrammatic cross section representing an
outline of the body-wall in the region of the walking legs;
show in this the relation which branchiostegites, legs, and
gills bear to the body.

Internal anatomy. With strong scissors and forceps remove
the shell from the entire dorsal surface of the body, taking care
not to injure the organs within. The arrangement of the organs
will be seen to be similar to that in the crayfish or the lobster.
The livers are a pair of extensive yellowish organs. The ante-
rior portion of each of these passes laterally into the cavity
of the branchiostegite; the posterior portion passes backward
beneath the heart. In the male animal the testes are whitish
organs which follow the course of the livers; the vasa deferentia
are slender, coiled tubes which lie on each side of the heart.
In the female animal the ovaries also accompany the livers; the
oviducts are a pair of tubes which pass to the genital openings,
the middle portion of each being expanded to form a large sac,
the receptaculum seminis.

Exercise 5. Draw an outline of the body and the organs as they
lie in situ. Label all carefully.

Remove all the viscera, taking care not to injure the brain
and the circumcesophageal nerves, and examine the nervous
system. The brain is just back of the eyes, as in the lobster
or the crayfish, and is united with the ventral nerves by means
of the lateral circumcsophageal connectives which pass on each
side of the cesophagus. There is, however, no long ventral
nerve cord with segmental ganglia, but a single large ganglionic

A CRAB 45

mass, in the shape of a ring, which occupies a central position
in the cephalothorax, and from which nerves radiate to the
different appendages. The dorso-ventral artery passes through
this rmg. Expose the entire nervous system.

Exercise 6. Draw a semidiagrammatic view of the nervous
system, being careful to represent accurately the nerves
radiating from the ganglionic ring and those going from
the brain to the eyes and to the antenne.

46 INVERTEBRATE ZOOLOGY

CRUSTACEA
A LAND ISOPOD. A SOW-BUG (Porce/lio, Oniscus, or Armadillidium)

This animal is one of the few terrestrial crustaceans. It may
be found at any time of the year under stones, logs, etc., and
in other moist, dark places, where it lives on decaying vegetable
matter.

The animal must be studied with the aid of a hand lens or a
dissecting microscope. Compare the animal with the crusta-
ceans already studied. Notice the flattened body. It is com-
posed of twenty somites, of which five are cephalic, eight are
thoracic, and seven are abdominal, and much less fusion has
taken place among them than is the case in the decapods. The
head and the thorax are not covered by a carapace and thus are
not joined together to form a cephalothorax. The apparent
head is composed of six fused somites, five of which are ce-
phalic and one thoracic. The remaining seven thoracic somites
are free and movable. Count them. Count the abdominal
segments. Six will be found, the last two abdominal somites
being fused together.

Find the eyes: they are not on stalks, but are sessile. Only
one pair of antenne appears, the first pair being rudimentary.
Notice the pair of anal feelers which extend back from the hinder
end of the body. These are homologous to the last pair of
appendages, like the cerci of orthopterous insects, and have a
similar function.

Bxercise 1. Draw a dorsal view of the animal on a scale of 10.
Number the thoracic and the abdominal segments.

Study the ventral side of the animal. Notice if it be a male
or a female. The male has a long dark-colored, tube-shaped

A SOW-BUG AT

copulatory organ which extends from the forward border of the
abdomen backward. The female, besides lacking this organ,
may have a brood-sac on the ventral surface of the thorax, which
is composed of plates attached to the inner side of the first five
pairs of walking legs and contains eggs or young.

The appendages. First observe the seven pairs of walking legs ;
they are the thoracic legs numbering from two to eight; ex-
opodites and gills are wanting in them. The gills, instead of
being thoracic structures, as in the decapods, are attached to
the abdominal legs. With a fine needle separate the flattened
appendages of the first five abdominal segments. The endopo-
dite serves as the gill, while the exopodite is large and plate-
like and covers the endopodite. The appendages of the head
may be best studied from the hinder pair forward. They con-
sist of one pair of maxillipeds, which belong to the first thoracic
somite, two pairs of maxille, one pair of mandibles, and one pair
of antenne, the second, the first pair of antenne being rudi-
mentary. The maxillipeds are plate-like and cover the other
mouth-parts. Carefully remove the maxillipeds and study the
mouth-parts.

Exercise 2. Construct a table showing the relation of the
appendages and the somites similar to that made use of
in the dissection of the crayfish or the lobster (page 35),
leaving out of consideration, however, the protopodites,
exopodites, and endopodites.

48 INVERTEBRATE ZOOLOGY

CRUSTACEA

A TYPICAL AMPHIPOD. A FRESHWATER SHRIMP (Gammarus)
OR A SAND-FLEA (Ta/orchestia)

The freshwater shrimp is common in many places in pools
and streams, and may be easily caught with a fine net; the
sand-flea is a marine animal and is extremely common along all
of our shores.

Notice the compressed and translucent body; this latter
feature is extremely wide-spread among the smaller aquatic
animals. Can you explain what is the advantage to a small
aquatic animal to be translucent or transparent? Note the two
pairs of long antenne. In common with all the higher crustacea,
the body is composed of twenty somites, of which five are
cephalic, eight thoracic, and seven abdominal. Like the isopod,
the animal has no carapace, the eyes are sessile, and the appar-
ent head is composed of six fused somites, five being cephalic
and one thoracic. There are thus seven free thoracic segments.
Note the broad movable plates, the epimeral plates, which depend
from the ventral side of certain of the thoracic segments,
extending the lateral surface of the body ventrally; note the
differences in form between the thoracic appendages. The
abdomen is composed of six free segments, the sixth and
seventh somites being fused. Count them. The first three
pairs of abdominal legs are swimming legs, the last three are
jumping legs.

Exercise 1. Draw an outline of the side view of the animal on
a large scale. Number the thoracic and the abdominal
segments.

AN AMPHIPOD 49

Study the appendages, beginning with the free thoracic ones.
With fine needles separate the legs and observe the gills
attached to the posterior borders. How many bear gills? In
the female observe the brood-sac when it is present ; it is formed
by plate-like projections of the inner side of certain thoracic
feet. In the abdomen observe the biramous appendages; they
bear no gills. The cephalic appendages are those typical of
crustacea. In front of the mouth is a median lip called the
labrum, which, however, is not an appendage. Then come the
mandibles and two pairs of maxille. The pair of appendages,
the maxillipeds, belonging to the first thoracic somite (which is
fused with the cephalic somites) form a kind of lower lip.

Exercise 2. Construct a table of somites and appendages similar
to that made use of in the dissection of the lobster or the
crayfish (page 35), leaving out of consideration, however,
the protopodites, exopodites, and endopodites.

50 INVERTEBRATE ZOOLOGY

CRUSTACEA
AN ABERRANT AMPHIPOD (Capre//a)

This is a very common marine amphipod which is found
along our shores clinging to hydroid colonies and to seaweed.
It is an interesting form because it illustrates an extreme
degree of modification from the typical amphipod type; a
modification which is the result of its peculiar environment.

Notice the irregular cylindrical form and the small number
of appendages. The apparent head is composed of seven fused
somites, of which five are cephalic and two are thoracic, the
first of these latter bearing a pair of maxillipeds, and the second
a pair of legs. There are thus six free thoracic segments, of
which the first, fourth, fifth, and sixth bear non-branchiate legs,
and the second and third bear gills but no legs. The abdomen
has lost its segmentation and its appendages and has been
reduced to a mere protuberance at the end of the thorax.

Exercise 1. Draw a large outline of the side view of the animal.
Number the segments and label the parts observed.

Exercise 2. Construct a table of somites and appendages similar
to that made use of in the dissection of the crayfish or the
lobster (page 35), leaving out of consideration, however,
the protopodites, exopodites, and endopodites.

LARVAL DECAPODS 51

CRUSTACEA

LARVAL DECAPODS: THE ZOEA OF THE CRAB; THE MEGALOPA OF THE
CRAB; THE MYSIS STAGE OF THE LOBSTER

These names have been given to certain larval forms of the
crab and the lobster, as well as to those of other of the higher
crustaceans. It is as zoée that the crab and the higher crusta-
ceans generally leave the egg. The zoéa of the crab grows
into the megalopa, which in time grows into the adult animal.
The stage in which the lobster is born is more advanced than
the zoéa and is called the mysis stage. All of these larve are
minute animals and are more or less common in the surface
waters of the sea along our coast.

Mount several zoée of the crab on a slide and study them
under the microscope. The body will be seen to be divided into
two body-divisions, a cephalothorax and an abdomen. ‘The former

‘is covered with a delicate carapace, from which project one or
more spines. When the animal is newly born it possesses the
typical five pairs of cephalic appendages, and the anterior two
or three pairs of thoracic appendages, «e., the maxillipeds,
which, however, are used for locomotion. The remaining tho-
racic and the abdominal appendages are wanting, but appear as
the animal increases in size, those anteriorly situated appearing
first. The animal has two stalked eyes.

Exercise 1. Draw a side view of a zoéa on a large scale, repre-
senting accurately the appendages, and label the parts
observed.

Mount a megalopa and study it under the microscope. We
observe that it is much larger than the zoéa, that it has acquired

52 INVERTEBRATE ZOOLOGY

a relatively much larger cephalothorax and abdominal append-
ages, and is much more crab-like than the zoéa. But it still
has a long abdomen, and at the end of this is a swimming fin.
The megalopa is a swimming animal, like the adult lobster,
but it is gradually assuming the characters of the adult crab.
Its two anterior maxillipeds have lost their locomotory char-
acter, which they possessed in the zoéa, and have assumed their
final form and function. Identify all the mouth-parts.

Exercise 2. Draw a dorsal view of the animal, with the legs
extended, on a large scale.

Mount several lobster larve in the mysis stage and study them
under the microscope. The lobster is born in a more advanced
condition than is the crab. The zoéa stage of the lobster is
passed over in the egg, and when the young animal emerges
from the egg it resembles Mysis, a schizopodous crustacean,
and hence is said to be in the mysis stage. The general form
of the animal does not differ much from that of the adult.
The abdomen bears no appendages. The cephalothorax is
very nearly like that of the adult and bears the same append-
ages. The third maxilliped, however, is a locomotory append-
age, as it is in Mysis, and with the five periopods is used for
swimming. Notice the biramous character of each periopod.

Exercise 3. Draw a side view of the animal on a large scale.

A COPEPOD 53

CRUSTACEA
A FREE-SWIMMING COPEPOD (Cyclops)

These minute animals are representatives of the division of
Crustacea called the Entomostraca. All of the crustaceans
heretofore studied belong to the higher group called Malacos-
traca. Copepods are extremely common in both fresh and salt
water. They may be obtained in almost any permanent pool
of water in the woods or fields or from the surface water of the
sea, often in large quantities, and are easily kept in aquaria.
The animals should be studied alive if possible. Place several
on a slide under a cover-glass and examine them under a micro-
scope. If the pressure of the cover-glass does not suffice to
keep them quiet, the withdrawal of some of the water from
under the cover-glass with blotting-paper will probably accom-
plish this result. Also stain and mount a number of copepods
in balsam or glycerine. Observe the cylindrical body and the
two pairs of long antenne with their sense-hairs; also the long
spines at the end of the abdomen. Note the division of the
body into abdomen and cephalothorax, and also that the latter is
not covered by acarapace. If the animal be a female it may be
carrying a pair of egg-sacs filled with eggs extending from the
anterior end of the abdomen. Note the median eye, also the
intestine and muscle fibers, through the transparent body-wall.

The body is made up of fifteen somites, the head, thorax, and
abdomen each containing five. The head is relatively large, and
its somites are fused together; they bear the cephalic append-
ages common to all crustaceans. The first pair of antenne is
longer than the second; in the male it is secondarily modified

54 INVERTEBRATE ZOOLOGY

to form clasping organs, by which the female is held during
pairing. In Cyclops, which is the commonest freshwater genus
of the Copepoda, the first thoracic somite is fused with the
head, leaving only four free thoracic somites. The abdomen
bears no appendages. In the female the first two abdominal
somites may be fused together.

Exercise 1. Draw a large outline of the dorsal aspect of a cope-
pod, not putting in any appendages except the antenna.
Represent accurately the sense-hairs on the antenne and
the caudal bristles. Number the thoracic and abdominal
segments and carefully label all the parts.

Study the appendages. The thoracic appendages are bira-
mous. They do not bear gills, and the fifth pair is rudimentary.
The cephalic appendages consist of two pairs of antennae, one
pair of mandibles, and two pairs of maxille, the second pair of
which are without protopodites. The exopodites and endopo-
dites of this second pair join the body separately in conse-
quence and may appear as independent appendages.

Exercise 2. Draw a side view of an animal showing the append-
ages in position.

Exercise 3. Draw an outline of a thoracic leg on a large scale,
showing accurately all the joints and hairs.

Compare the copepod with the young larva of the crab or the
lobster. Enumerate the points of structural similarity between
them.

Internal anatomy. This can be best studied in the live animal.
The alimentary tract is straight and of large diameter, and often
contains dark-colored feecal matter. The mouth has a ventral
position, as in other crustaceans, while the anus is dorsal. There
is no liver or other accessory glandular organ. The circulatory
system in Cyclops consists of the colorless blood fluid alone,
there being no heart. The blood is, however, kept in circulation

A COPEPOD 59

by the rhythmic contractions of the intestine. Other copepods
possess a dorsal heart. There are no special respiratory organs.
How is respiration carried on? The excretory system consists
of a pair of coiled tubes, called the shell glands, which lie in the
forward part of the cephalothorax and have external openings
near the base of the first pair of thoracic appendages.

The reproductive system consists of median or paired organs in
the dorsal portion of the cephalothorax above the intestine. In
the female the ovaries are often conspicuous as a pair of large
branched organs. The oviducts are paired and lead to the exter-
nal sexual openings in the first abdominal segment. Appended
to the first abdominal segment may be a pair of egg-sacs contain-
ing fertilized eggs which are cemented together by means of a
secretion of the oviduct. In the male the reproductive gland is
the median testis, which communicates by means of paired vasa
deferentia with the external sexual openings, which are also in
the first abdominal segment. The spermatozoa collect in the
terminal portion of each vas deferens and form there a small
mass known as a spermatophore. The two spermatophores, during
the act of pairing, pass to the female and fertilize the ova. The
male animals are much less numerous than the females.

The reproductive glands of the copepod can be observed as
above described only during times of sexual activity. At other
times they can be seen only in part or not at all.

The muscular system can be easily seen to consist of striated
muscle fibers. Longitudinal as well as converging fibers will
be seen at each appendage. .

The nervous system may be seen in favorable specimens as a
ventral strand in the cephalothorax connecting with the large
dorsal brain.

Exercise 4. Draw a side view of the animal, showing as many of
the internal organs as you have observed.

56 INVERTEBRATE ZOOLOGY

CRUSTACEA

A CLADOCERAN PHYLLOPOD (Daphnia)

This is a small freshwater crustacean common in lakes and
pools. It should be studied under the microscope and alive
if possible. Place several on a slide under a cover-glass and
draw off enough water to keep them quiet; also observe sev-
eral in a watch-glass in order to see them from above. The
body of the animal will be seen to differ in shape from those
crustaceans already studied. It is but indistinctly segmented,
and, except the head, is entirely covered by a bivalve shell.
This shell is the cuticular covering of paired folds of the
dorsal integument, one fold covering each side of the body.
Beneath the opening of the valves of the shell appear the
appendages and the abdomen; on the surface of the shell a mesh-
work of fine lines can usually be seen. Notice the large,
median eye; it may often be seen to tremble slightly. The
shell has a deep, ventral indentation near the base of the
antenne.

The first pair of antenne is very small, but may be easily seen
projecting downward just back of the eye. The second pair of
antenne is very long and biramous, the two branches being the
exopodite and endopodite; they are the principal organs of
locomotion. Just back of the antenne is a large flap, called
the upper lip, and back of this are the large mandibles. There is
but a single pair of maxille, and they are so small that they will
probably not be seen. Four to six pairs of thoracic appendages
follow, the function of which is probably exclusively respira-
tory. How many are present in your specimen? Notice
the leaf-like surface of these appendages (whence the name

DAPHNIA 57

phyllopod), in which we can recognize the basal protopodite
and two broad terminal pieces, the endopodite and exopodite.
The short abdomen articulates with the thorax and is bent
beneath it, where it may be seen often moving rapidly back
and forth.

Exercise 1. Draw an outline of a side view of the animal on
a large scale and label the appendages and other parts
observed.

Exercise 2. Draw a highly magnified view of one of the thoracic
appendages and label accurately all the parts.

Internal organs. The digestive tract passes from the mouth,
which is ventrally placed and lies back of the ventral cleft in
the shell, first forward, then turns dorsally and finally posteri-
orly and extends back to the anus near the end of the abdomen.
Near the anterior bend of the digestive tract a pair of colored,
curved pouches communicate with it; they are liver-sacs. The
sac-like heart may be seen beating rapidly above the intestine.
It possesses a pair of lateral openings into which the blood
streams from the body-cavity with each dilation, and an ante-
rior opening through which it is sent into the forward part of
the body with each contraction. There are no other blood
vessels. Below the heart is a pair of excretory glands, called
the shell glands, which open to the exterior near the mouth.
The nervous system consists of an optic ganglion and a brain, lying
back of the eye, and a ventral nerve containing seven ganglia.

The reproductive organs. The daphnias which are usually seen
are all parthenogenetic females, the males making their appear-
ance at certain times of the year only. The female animal is
larger than the male, and may be distinguished by its brood-sac.
This is a large space just beneath the dorsal wall of the thorax
in which the eggs and the young brood are carried. The ovaries
are a pair of tubular organs alongside the intestine, which com-
municate, by means of short oviducts, with the brood-sac. The

58 INVERTEBRATE ZOOLOGY

ovaries are easily detected by the presence of large ova in
them. These are in groups of four, of which but one, the
third, is destined to become an egg, the other three being
nutritive cells by which it is nourished. In the male the testes
occupy a position similar to that of the ovaries. Their external
openings are on the ventral side of the abdomen.

During the greater part of the summer the eggs pass into the
brood-pouch unfertilized and develop there parthenogenetically,
producing only females. The young animals pass out of the
brood-chamber through a posterior opening ; they soon become
adult and in their turn give birth to parthenogenetic females.
The eggs which thus develop are called summer eggs. At cer-
tain times of the year, however, as in the autumn, males are
also born. They fertilize the females, and the fertilized eggs
then produced differ from those which were unfertilized in
possessing thicker shells. They are called winter eggs and are
able to resist the cold of winter or the effect of drought. In
the springtime the winter eggs develop into parthenogenetic
females again.

Bxercise 3. Draw an outline of the animal and place in it all
the internal organs you have observed.

A NAUPLIUS LARVA 59

CRUSTACEA

A LARVAL ENTOMOSTRACAN. A NAUPLIUS LARVA

In an aquarium containing copepods or ostracods there are
sure to be numbers of the young larve of these animals. They
are minute, free-swimming forms and are called nauplii, and may
be recognized by the triangular or oval, unsegmented body,
which bears three pairs of appendages and a median eye.
Nauplii of marine entomostracans may also be met with in
large numbers among the small animals obtained by skimming
the surface waters of the sea with a fine net.

Examine in a watch-glass under a microscope water contain-
ing sediment taken from a jar in which are copepods or ostra-
cods. Find a nauplius; the ostracod nauplius differs from that
of the copepod by being enclosed in the characteristic bivalve
ostracod shell. If marine plankton is at hand, look for several
kinds of nauplii in it.

Study the structure of a nauplius. Observe the unseg-
mented body; if the animal is not newly born, signs of segmen-
tation may have begun to appear. Observe the three pairs
of segmented appendages ; the segmentation, however, is often
indistinct. These appendages are homologous to the first and
second pair of antenne and the pair of mandibles of the adult
animal. As in the adult, the first pair is uniramous; the
second and third pairs are biramous. Both of the latter two
pairs are used for locomotion, although it is probable that they
also act as jaws. The median eye will be seen, and the straight
digestive canal.

Exercise 1. Draw a nauplius on a large scale and label all the
parts above mentioned.

60 INVERTEBRATE ZOOLOGY

The nauplius larva is of great theoretical significance. It
appears as the youngest, free-swimming larval stage of almost
all the entomostracans and of several of the malacostracans,
and those malacostracans which are born in a later period of
their development pass through a nauplius stage (2.e., a stage
in which the body is unsegmented and bears three pairs of
appendages) while they are still in the egg. This universal
occurrence of the nauplius larva seems to indicate that it
repeats substantially the structure of the primitive ancestor of
all crustaceans.

In its further development and growth the nauplius larva
increases in size, gradually becomes segmented, and acquires
new appendages, its growth and the specialization of its organs
advancing from the anterior towards the posterior end. The
appendages, which were originally typical, unmodified crusta-
cean appendages, become differentiated to form the first and
second pairs of antennz and the mandibles, and finally the size
and structure of the adult are attained.

Exercise 2. Look for several nauplii which are somewhat
advanced in development and draw outlines of them.

CHAPTER II

ANNELIDA
A POLYCHAETOUS ANNELID (Were/s virens)

Nereis is a common marine worm which. lives in the sand
along the shores of our northern and middle states. Its food con-
sists of various kinds of small marine animals, which it catches
with its formidable, protrusile proboscis. A specimen should
be selected for study in which the proboscis is not thrust out.

Observe, in ,the first place, the long, segmented, and some-
what flattened body, the pair of appendages on each segment,
and the distinct head with special sense-organs at the forward
end; observe also that the body tapers towards the hinder end,
where is a pair of special sense-organs, the long caudal feelers.
All of these characters indicate an animal possessed of the power
of rapid locomotion. Count the somites or body-segments; note
that they are almost exactly alike. This lack of specialization
is in sharp contrast to the condition of the somites in most arthro-
pods. Observe carefully the appendages; they differ from those
of the arthropod in that each one is an unjointed expansion of
the body-wall, whereas the arthropodous appendage is segmented.
Each one is made up of several lobes and is provided with long
bristles or setez. Note the absence of a hard shell, the external
integumentary covering being the glistening cuticula, which
has not been stiffened by the presence of calcareous salts.

Observe the head and the forward portion of the body.

An annelid’s body is composed genetically of two portions:
61

62 INVERTEBRATE ZOOLOGY

the prosoma, or primitive head, and the metasoma, or the primitive
segmented trunk. The prosoma may be further divided into
the prostomium, which lies in front of the mouth and contains
the brain and the principal organs of special sense, and the
metastomium, which contains the mouth. In Nereis the pro-
stomium bears the following special sense-organs: a pair of palps,
large cylindrical projections extending forward at its anterior
end; a pair of tentacles, two delicate organs between the palps;
and two pairs of eyes, small bead-like organs near the base of
the palps. Carefully identify all of these organs and notice
whether the palps and tentacles are jointed. The metastomium
is, in Nereis, fused with the first two somites of the metasoma or
trunk, and the segment thus formed is called the peristomium.
It bears the mouth and four pairs of long, flexible sense-organs
called the peristomial cirri. Carefully observe, with the aid of
a hand lens, their exact position. These cirri are morpholog-
ically not cephalic organs, as are the palps and the tentacles,
but are remnants of appendages of the first two somites.

Exercise 1. Make an outline of the dorsal aspect of the head
and the first five or six somites on a scale of 5. Number
the somites. Carefully label all the parts.

Exercise 2. Draw a side view of the head on a scale of 5. Take
special care to represent accurately the position of the
peristomial cirri.

Exercise 3. Find a specimen, if possible, with the proboscis
thrust out and draw a dorsal view of its head.

Note the tapering of the body at the hinder end. The worm
grows in length at this end. The posterior somites are the
youngest and hence the smallest.

Exercise 4. Make a sketch of the hinder end of the animal.
The long sense-organs at the extreme end are called caudal
cirri. In which direction do they project?

NEREIS 63

The appendages in annelids are called parapodia. Carefully
examine the parapodia at different parts of the body and see if
they are all alike.

Remove a parapodium from the middle of the body; mount
it on a slide in glycerine or water and study it with the aid of a
hand lens or a microscope. Compare it with the parapodia still
on the animal and determine which is its dorsal and which its
ventral side. It can be divided into two distinct portions, the
dorsal and the ventral portions, called the notopodium and the
neuropodium, respectively, each of which is stiffened by an inter-
nal chitinous supporting rod, called the aciculum. Find the two
acicula. The large dorsal lobe of the notopodium is a respira-
tory organ, a gill. It contains branching blood vessels which
can be easily seen. Attached to its dorsal edge is a slender,
vibratile sense-organ, the dorsal cirrus. Beneath the gill are two
lobes, one bearing bristles or sete. The neuropodium is made
up of two lobes, one of them setz-bearing, beneath which is a
ventral cirrus.

Exercise 5. Draw a parapodium on a scale of 6 and label the
parts. :

Remove a parapodium from the hinder end of the animal,
mount it, and study it. Has it the same parts, and if not,
which are missing?

Exercise 6. Draw it on a scale of 6.

Internal anatomy. Make an incision with fine, sharp scissors
in the mid-dorsal line of the integument of the anterior third of
the animal, taking great care not to injure the viscera which lie
beneath. The body will be seen to be divided into compart-
ments corresponding to the somites, by transverse partitions
which are called septa. Holding the cut edge of the integument
with forceps, cut the septa where they join it, and then spread
out and pin down the body-wall, using many pins on each side.

64 INVERTEBRATE ZOOLOGY

The digestive organs. The mouth leads into the large pharynx,
which is composed of an anterior and a posterior portion. With
sharp scissors cut open the pharynx along the mid-dorsal line
and note the number and arrangement of the chitinous teeth
imbedded in its inner surface. Notice the delicate muscles
passing from it to the body-wall by means of which the pharynx
can be thrust out of the mouth and drawn back again. They
are the protractors and the retractors. A pharynx which is thus
protrusile is called a proboscis. Just back of it is the narrow
cesophagus with which a pair of small tubular glands communi-
cates. Back of the cesophagus is the stomach-intestine, which
extends to the anus. Observe the mesenteries. These are longi-
tudinal partitions, in structure like the septa, one of which
attaches the stomach-intestine to the dorsal and the other to
the ventral body-wall. Press the intestine aside and see the
ventral mesentery.

The circulatory system. Nereis has two distinct circulatory
fluids, the colorless or ccelomic and the red blood fluid. The
first consists of a plasma in which float amveboid blood cells; it
circulates freely in the body-cavity or ccelom, being forced by
the movements of the body from one segment to another through
small openings in the septa. The red blood consists of a red
plasma, in which float colorless blood cells, and circulates in
closed tubes. The most important of these blood vessels are
two longitudinal tubes, the dorsal and the ventral arteries,
which lie in the median line, one above and the other below
the alimentary canal. The former, the dorsal artery, pulsates
and drives the blood towards the forward end of the body and
distributes it to lateral segmental arteries. Observe these and
determine how many there are in each segment; also note the
capillary network into which the dorsal artery breaks up at its
anterior end. The dorsal portions of the lateral arteries carry
the blood to the gills and other organs, whence it collects again
in the ventral portions of these arteries and is conducted to the

NEREIS 65

ventral artery. In this vessel the blood flows toward the hinder
end of the body.

Exercise 7. Draw a view of the opened animal on a scale of 5,
showing the organs above described. Label all the organs
carefully.

Sever the alimentary tract at the csophagus and remove the
stomach-intestine from the body. Observe the muscle bands in
the body-wall; note the difference in direction and size of the
different bands. Observe the muscles at the base of the acicula.

The excretory system. ‘The kidneys of the animal consist of a
pair of glandular organs called nephridia, which lie in the body-
cavity against the ventral body-wall in each somite except
the last two or three. Each nephridium opens through the
body-wall to the exterior in a minute pore on the ventral sur-
face of each somite near the base of the parapodium. The
anterior end of the nephridium passes through the septum
which forms the anterior wall of the somite in which that organ
lies, and opens into the body-cavity. The opening, which is
ciliated, is called the nephrostome; it lies, as will be seen, against
the anterior surface of aseptum. Study the nephridia carefully
in several parts of the body under a dissecting microscope;
some of them may have been torn in removing the intestine.
Examine a portion of the worm in which that organ is still
in the body and note the relation of the nephridia to it and
to the septa.

Exercise 8. Draw a diagram representing the opened body-
cavity in a number of somites and the position of the
nephridia and the muscles.

The nervous system. Observe in the mid-ventral line of the
body-cavity the nerve cord. Trace it forward to the brain.
Note the connectives which encircle the pharynx and connect
it with the brain. Remove the forward end of the nervous

66 INVERTEBRATE ZOOLOGY

system from the body, mount it in glycerine, and study it
under a microscope. Note the ganglionic enlargements and the
double nature of the nerve cord. Study the branches which
pass off from the nerve cord and from the brain.

Exercise 9. Draw the nervous system on a scale of 10, showing
all the features above mentioned.

The reproductive system. There is no complicated reproductive
system in Nereis. The sexes are separate. The reproductive
glands make their appearance only during the periods of sexual
activity and then as swellings of the peritoneal lining of the
body-cavity. The eggs or spermatozoa, as the case may be,
fall into the body-cavity and find their way to the outside
through the nephridia or through temporary openings in the
body-wall.

Exercise 10. Draw a diagram representing an ideal cross section
in the region of the stomach-intestine ; show the stomach-
intestine with its mesenteries, the blood vessels, the nerves,
and the muscles.

AN EARTHWORM 67

ANNELIDA

AN OLIGOCHAETOUS ANNELID. AN EARTHWORM

The earthworm is, to most people, the most familiar annelid.
It is distributed over the entire earth, the United States contain-
ing many species. The animal is nocturnal in its habits. It lives
in long burrows in the ground, in which it lies during the day and
the inclement seasons of the year. Its food consists of leaves
and other vegetable substances and also of the organic matter
contained in the soil which passes through its alimentary canal.

Study the animal first alive, but have one also at hand which
has been killed in weak alcohol. Notice its color, or rather
lack of color. How is this correlated with its underground
life? Note its cylindrical, elongated body, the very small head,
and the absence of appendages. Note also the absence of a
hard shell, the external integumentary covering being the glis-
tening cuticula which has not been stiffened by the presence of
calcareous salts. As the animal lacks appendages, locomotion is
accomplished by means of body-movements. Study its method
of locomotion. The animal will be observed successively to
elongate and to shorten its body, which, of course, would be
impossible if it were covered by a hard shell. Notice that along
the ventral and the lateral surfaces are several rows of minute
bristles, the sete; they aid in locomotion and are under the
control of muscles. Determine, by passing the animal through
the fingers and with the aid of a hand lens, how many rows there
are and their relation to the segments. Determine also whether
the set at the forward end of the body project in the same
direction as those at the hinder end. Observe carefully the
importance of the setz in locomotion.

68 INVERTEBRATE ZOOLOGY

The animal is segmented externally, i.e., it is made up of
a number of somites or metameres, like the crustacean body.
Count the somites, beginning with the segment just back of
the mouth, which is the first somite. Notice the equivalence
of the somites; they are apparently all very nearly alike. This
lack of specialization is always a primitive character in a seg-
mented animal and is in sharp contrast to the condition of the
somites in most arthropods. Among the arthropods studied,
which most nearly resemble the earthworm in this particular?

Notice the moist, slimy surface. Moisture is necessary to
the animal’s existence; this accounts largely for its nocturnal
habits. Notice also the red blood vessels through the semi-
transparent body-wall. What movement of the blood can you
detect? What are the differences between the dorsal and the
ventral surfaces? Notice the difference between the anterior and
the posterior ends. The forward end is the older; the animal
grows in length by adding new somites to the hinder end, but
the number of somites is practically complete when the young
worm emerges from the cocoon. Notice the ventral position of
the mouth and the terminal position of the anus; note also the
thickened ring around the body not far from the forward end.
This is the clitellum; its function will be explained in speaking
of the reproductive organs. The animal is without organs of
special sense ; numerous minute tactile sense organs which are
sensitive to light and other stimuli are, however, present. These
are distributed along the body but are especially abundant
toward its anterior end.

Exercise 1. Make a sketch on a scale of 3 of the ventral aspect
of the forward end of the animal back to the posterior border
of the clitellum. Indicate the somites and number them.

The body of the animal may be divided into two portions, the
prosoma or the primitive head, and the metasoma or the primitive
segmented trunk. The prosoma is further subdivided into the

AN EARTHWORM 69

prostomium, the median dorsal projection overhanging the mouth,
and the indistinct metastomium, which contains the mouth, and
is marked off from the prostomium by fine transverse lines.
What somites are included in the clitellum? On the fifteenth
somite a pair of prominent transverse slits will be seen. They
are the external openings of the vasa deferentia or sperm-ducts.
On the fourteenth somite look with the hand lens for the two
minute openings of the oviducts. They are difficult or impos-
sible to see, except during the reproductive period of the animal.
Between the ninth and the tenth and the tenth and the eleventh
somites are the two pairs of minute openings of the sperma-
thece, which are also visible only during the pairing season.
In each somite, except the first three or four and the last one,
is a pair of kidney tubules, called nephridia, which open through
the body-wall to the exterior by minute pores on either the
ventral or the lateral side near the anterior border of the somite.
The ventral integument of a number of somites between the
seventh and nineteenth is often swollen by the presence of the
so-called capsulogenous glands. Carefully label in your sketch all
of these organs which you have observed.

Exercise 2. Make a similar sketch of the ventral view of the
last four somites on a scale of 3.

Internal anatomy. Pin a large worm, that has been killed,
firmly to the wax of the dissecting pan by a strong pin at each
end; then make an incision with fine, sharp scissors through
the integument in the mid-dorsal line from the forward end of
the animal to a point back of the clitellum, taking great care
not to cut the viscera lying beneath. It will be noticed that the
body-cavity is divided into compartments, corresponding to the
somites, by transverse partitions, which are called septa. Hold-
ing the cut edge of the body-wall with the forceps, cut the septa
where they join it, and then spread out and pin down the body-
wall, using many pins on each side.

70 INVERTEBRATE ZOOLOGY

Observe first the large alimentary canal which passes straight
through the animal; also several pairs of conspicuous white
bodies a short distance from the anterior end, which are the
sperm-sacs. If the specimen has been freshly killed, the red
blood vessels will also be seen. Study and identify in detail
the following systems of organs:

The circulatory system. The earthworm has two circulatory
fluids, a red one and a colorless one. The latter consists of
a plasma in which float ameboid blood cells. It is present
only in the body-cavity and circulates throughout the body,
being driven by the movements of the animal from one somite
to another through small openings in the septa; it will, of
course, not be visible in a dissection. The red blood consists
of a red plasma in which float colorless blood cells and it circu-
lates in a system of closed blood-tubes. The most important
of these blood vessels are five longitudinal and numerous
circular vessels. Observe the dorsal longitudinal vessel in the
median line, above the alimentary canal. It is contractile
and propels the blood towards the head. Push aside the
intestine and observe just beneath it the ventral vessel, which
runs parallel to the dorsal one. Notice that these vessels
break into small branches at their anterior ends. The other
three longitudinal vessels are very small and not easily seen
except in microscopic sections. They lie one beneath and the
other two to the right and left of the nerve cord in the
mid-ventral line.

The circular or commissural blood vessels connect the dorsal and
the ventral vessels and have a paired and segmental arrange-
ment. They are not all of equal size. Observe several large
pairs near the forward end of the animal which pass directly
between the dorsal and the ventral vessels. They are, like the
dorsal vessel, contractile and are sometimes called the hearts.
In which somites are they? Find the commissural vessels poste-
rior to them. These are much smaller and do not, in most

AN EARTHWORM 71

cases, pass directly between the longitudinal vessels, but break
into capillaries between them.

The digestive system. The pharynx is an oval, muscular pouch
occupying somites 2 to 6; radiating muscle fibers join it with
the body-wall. The esophagus is a slender tube occupying
somites 7 to 14 and running between the conspicuous sperm-
sacs. Press aside these sacs and notice beneath them three pairs
of white glands; these are lateral diverticula of the esophagus
and contain calcareous crystals. The crop is a thin-walled dila-
tion of the esophagus which lies in somites 15 and 16. The
gizzard is a muscular, thick-walled chamber of the same size as the
crop and lying in soniites 17 to 19. The stomach-intestine is a
large tube with lateral segmental pouches, which passes to the
hinder-end of the body; covering the surface of the stomach-
intestine is a loose mass of yellowish brown cells, the chloragogue
cells, whose function is probably excretory.

Exercise 3. Make a drawing of the opened animal on a scale of
3, showing the segmentation and representing the organs
above described in their proper somites; label all care-
fully.

Seyer the alimentary tract just back of the pharynx and
remove it from the body.

The reproductive system. The earthworm is hermaphroditic
and possesses the following genital organs:

The male organs. 1. The sperm-sacs have already been noticed.
They are large, white, irregularly lobed sacs occupying somites
9 to 13; they vary in size with the sexual condition of the
animal, being largest during periods of sexual activity. 2. The
testes. Two pairs of these organs are present, which lie beneath
the sperm-sacs in the tenth and eleventh somites ; they are very
minute objects and will be seen with difficulty, if at all. Push
aside the sperm-sacs and look for them with the aid of a hand
lens. 3. The sperm-ducts. These are slender tubes which begin

72 INVERTEBRATE ZOOLOGY

with two pairs of funnel-shaped openings just posterior to the two
pairs of testes and in the same somites with them. At the hinder
margin of the twelfth somite the two tubes on each side unite
to form a single one, and the pair of tubes thus formed run back
to the fifteenth somite, where they open through the conspicu-
ous transverse slits already noticed, to the exterior. Look first
for the posterior portion of these tubes and trace them forward.
The spermatozoa pass from the testes, where they but partially
develop, into the sperm-sacs in which their development is com-
pleted and where they are grouped together in balls. From here
they pass, during pairing, into the sperm-ducts, and out of the
animal through the slit-like openings in the fifteenth somite.

The female organs. 1. The spermathece. These are two pairs
of spherical, white sacs beneath the sperm-sacs in the ninth and
tenth somites; they are easily seen. 2. The ovaries. These are
a pair of extremely small organs lying near the median line and
attached to the anterior septum of the thirteenth somite near
the ventral body-wall; they will hardly be seen. 8. The ovi-
ducts. These are two minute, funnel-shaped tubes which extend
from immediately behind the ovaries through the septum to the
external opening in the next somite ; they will also hardly be
seen.

Earthworms meet and pair in the night time during the
months of May and June. Two animals place themselves
alongside of each other in such a way that the spermathece of
each come opposite the openings of the sperm-ducts of the other.
The spermathece of each are then filled with spermatozoa from
the other animal. The worms then separate. Sometime later
the clitellum secretes a viscid fluid which hardens and forms a
tough cylindrical membrane around the body. The worm then
squirms backward, causing this membrane to pass forward toward
its head. As the membrane passes the fourteenth somite, eggs
are poured from the oviducts into the viscous mass which is held
between it and the body, and at the tenth and eleventh somites

AN EARTHWORM 73

spermatozoa pass in from the spermathece which at once fertilize
the eggs. The cylindrical membrane then passes completely off
the worm and its two ends close together. It forms thus a yel-
lowish, spindle-shaped capsule about as large as a small pea, and
is called the cocoon. In it the young animals are born.

Excretory organs. ‘These are the kidneys of the animal. They
consist of a pair of coiled tubules, called nephridia, which lie
near the lateral and ventral wall of the body-cavity in each
somite, except the first three or four and the last one. Each
nephridium has two openings, a funnel-shaped, ciliated opening
into the body-cavity, called the nephrostome, and one through the
body-wall to the outside. The former in each case is attached
to the anterior side of a septum. The tube passes backwards
through the septum to the next somite, in which the greater
portion of it lies, and through the wall of which it communi-
cates with the outside. The distal, middle, and proximal por-
tions of the tube differ from one another. The distal portion
(that next to the nephrostome) is very slender, the middle por-
tion is much thicker and has glandular walls, and the proximal
portion is a dilated tube which probably acts as a urinary bladder.

Notice the four slight projections in the body-cavity on the
ventral side of each somite. These are the setigerous glands;
they secrete the sete.

Exercise 4. Make a sketch of somites 8 to 20, representing dia-
grammatically the reproductive organs and two or three
pairs of nephridia lying in their proper somites, and
label all.

Crush the sperm-sacs of a fresh worm, that has not been in
alcohol, mount some of the milky fluid in it, and examine it
under a compound microscope. Notice the sperm-spheres and
spermatozoa.

Exercise 5. Draw a sperm-sphere and a spermatozoan.

74 INVERTEBRATE ZOOLOGY

With a sharp knife or curved scissors carefully remove a
nephridium from the animal’s body. Mount it on a slide and
examine it under a microscope.

Exercise 6. Draw it and label its three divisions.

The nervous system is essentially similar to that in arthropods.
Remove the sperm-sacs and observe the nerve cord as it lies in
the mid-ventral line. Note the slight swellings, which are the
segmental ganglia. Trace the nerve cord forward to the region of
the mouth, where it encircles the forward end of the pharynx
and joins the small brain. Observe the two ganglia of which
the brain is composed. Remove the forward portion of the
nervous system, together with the brain, from the body. Mount
it on a slide and examine it under a microscope. Note the
double nature of the nerve cord and of the ganglia. What does
this signify as to the primitive condition of the system in
the ancestors of the earthworm? Note accurately the lateral
branches that leave the cord; also the shape and branches of
the brain.

Exercise 7. Draw the nervous system on a large scale, accurately
representing all the details.

Study of a cross section. This is instructive because it shows
the relations of the organs to one another in their natural
positions and also illustrates their finer structure. A properly
stained and mounted cross section of any portion of the body
will serve for this study.

Observe first the integument; it is made up of the cuticula on
the outside and the cellular hypodermis beneath it. The latter is
composed, in most parts of the body, of a single layer of cells
and it secretes the cuticula. Note the numerous single-celled
glands in the hypodermis. If the section passes through a seta,
notice its method of attachment and its muscles. Beneath the
integument are the body-muscles. Of these there are two

AN EARTHWORM 75

systems, the circular and the longitudinal muscles. The former
are a narrow band just beneath the hypodermis. The latter are
much more extensive and project into the body-cavity; they are
arranged in groups and will be seen of course in cross section.
Near the center of the body-cavity note the large alimentary canal.
If the section be in the region of the stomach-intestine, note the
longitudinal fold in the dorsal intestinal wall which very largely
increases its surface. Observe the structure of the alimentary
canal ; its cavity or lumen is bounded by a thick mucous mem-
brane consisting of a single layer of very long, slender cells,
around which are two muscle layers, an inner circular and an
outer, very thin, longitudinal layer. Surrounding the muscle
layers and also forming a thick fold over the dorsal and lateral
intestinal surfaces are the pear-shaped chloragogue cells. Observe
the dorsal and the ventral blood vessels, and also the commissural
blood vessels, if any are in the section. Study carefully the
nervous system. Note the muscular sheath which surrounds the
nerve cord, and imbedded in it the subneural and the two latero-
neural blood vessels. Note the double nature of the nerve. Note
the large pear-shaped nerve cells, and the nerve fibers, also the
three large bodies in the dorsal portion of the ganglion. These
latter are called the giant fibers. Do lateral nerves join the
ganglion? If so, trace their fibers into it. Also trace their
fibers away from the ganglion and see where they go. Exam-
ine carefully the peritoneum. This is a layer of cells which lines
the body-cavity and bounds all the organs in it.

Exercise 8. Draw the cross section and carefully label all the
organs.

CHAPTER III
PLATHELMINTHES

TURBELLARIA
A PLANARIAN WORM

Planarian worms are very common animals in freshwater
streams and ponds as well as in the sea; they may be found on
the underside of stones or on aquatic vegetation. They are
flat, elongated, very soft and contractile animals, brownish or
yellowish in color, and usually half an inch or less in length;
at the forward, broader end, on the dorsal surface, are two
black eyes; the hinder end is pointed. <A variety of forms is
found, some of which are very minute and are without an intes-
tine or have a straight, tubular intestine, while others are much
larger and have a branched intestine. The latter include most
of the commoner turbellarians and those for which these direc-
tions have been prepared.

Study the live animal under a dissecting microscope. Note
the gliding motion with which it moves. This is accom-
plished partly by the action of the cilia which cover its sur-
face and partly by muscular contraction. In the middle of
the ventral surface are the mouth and the protrusile proboscis.
Mount the animal on a slide in water beneath a thick cover-
glass and observe the action of the cilia under a compound
microscope.

Exercise 1. Draw an outline of the animal on a large scale,
with the eyes and proboscis, and indicate its anterior and

posterior ends.
76

A PLANARIAN WORM 77

Study an animal which is under the pressure of a large
cover-glass, and make out as many of the following organs as
possible, using often reflected instead of direct light:

The digestive system. The digestive canal is usually easily
seen. The mouth is a circular opening near the center of the
ventral surface; it leads into the pharynx, a cylindrical organ
with thick, muscular walls, which can be thrust out of the
mouth as a proboscis. At the base of the pharynx the intestine
divides into three trunks, one of which passes forward, and the
other two backward to the extremities of the animal’s body.
Each of these trunks gives off lateral branches which are them-
selves often branched. There is no anus.

Exercise 2. Draw an outline of the animal and place in it the
digestive system in detail.

The reproductive system. Planarians are hermaphroditic; the
sexual organs are complicated in structure and arrangement
and difficult to observe in a live specimen. Near the lateral
edges of the body will be seen, among the ends of the lateral
intestinal branches, two sets of lobed organs. Of these the
larger are the yolk glands, which connect with the oviducts; the
smaller and less apparent ones are the rounded testes. Just
back of the mouth is the uterus, which is often to be recognized
by the spherical eggs it may contain ; it passes back to a sac
called the genital cloaca. The ovaries are a pair of spherical
bodies in the anterior part of the body, and from them a pair of
oviducts extends to the hinder part of the body, receiving the
lateral yolk glands on their course. Leading from the testes are
the vasa efferentia, very delicate tubes, which pass to the con-
spicuous vasa deferentia. There is a pair of the latter organs, one
on each side of the mouth and pharynx, and they extend to
the hinder part of the animal, where they unite to form the
muscular cirrus, which opens into the genital cloaca. The two
oviducts aleo fuse at their hinder ends, and the median duct thus

78 INVERTEBRATE ZOOLOGY

formed opens into the genital cloaca. This structure, which thus
receives all the ducts from the genital glands, communicates
with the outside through the genital pore, a median, ventral
opening in the hinder part of the body.

Exercise 3. Draw a large outline of the animal and place in it as
much of the reproductive system as you have observed.

The nervous system. Beneath the eye-spots will be seen the
opaque brain, a large nervous mass consisting of a pair of minor
masses united by a broad commissure. From its anterior and
lateral sides numerous sensory nerves pass to the anterior body-
surface, which render this extremity a highly sensitive tactile
organ. From its posterior side a ‘pair of large longitudinal nerve
cords passes to the hinder end of the body, being united at
intervals by transverse nerves.

The excretory system. ‘This consists of a system of minute
tubes which extend throughout the body and collect the excrete
matters from the tissues. There are two main longitudinal tubes
extending the length of the body, which open to the outside
through minute pores on the dorsal surface of the animal.
These tubes are not straight but coiled and give off numerous
branches, at the termination of each of which is a peculiar cell
with a vibratory process at its base called a flame cell; they are
joined by a transverse tube at the anterior end of the animal.
Portions of the excretory system can often be seen in the com-
pressed animal, where they appear as fine lines.

Exercise 4. Draw an outline of the animal and place in it as
much of the nervous and the excretory system as you
have observed.

No special respiratory system is present in the Turbellaria,
the ciliated outer surface of the body performing this function.
A circulatory system and a blood fluid are also wanting. The
branching of the digestive and excretory systems is correlated

A PLANARIAN WORM 79

with this feature. Can you explain how? As in other flat
worms, the turbellarians possess no body-cavity, the primitive
body-cavity being filled secondarily by a peculiar vesicular
connective tissue called parenchyma. The muscular system con-
sists of a layer of strong circular and longitudinal muscles just
beneath the surface of the body and of oblique muscles passing
through the parenchyma.

80 INVERTEBRATE ZOOLOGY

CESTODA

A TAPEWORM

Tapeworms are common parasites in the intestines of ver-
tebrate animals. The human tapeworm, Taenia saginata, may
often be obtained from physicians. If it be alive when
obtained it should be placed in a normal salt solution (a 0.75%
solution), in which it will keep alive for several hours, and
may then be studied. If it be dead it should be preserved in
alcohol or formalin. Taenia serrata, a tapeworm of the dog,
and Taenia erassicollis, which lives in the cat, are both common
animals and are convenient forms for study. The intestines
of adult cats or dogs should be slit open and the worms taken
out and placed alive in a normal salt solution. They are
white, band-like objects, six inches or more in length, which are
attached by one end to the wall of the intestine. Care should
be taken in separating them from the intestinal wall not to tear
them.

Study the movements and general form of the animals as
they lie in the salt solution. The worm will be seen to be made
up of a large number of segments, and to bear at the smaller
end a small rounded knob. The segments are called proglot-
tids, and the rounded knob, the scolex. The body of the ani-
mal is not made up of body-divisions which we can call head
and trunk. The scolex, however, may be held to represent
its anterior end, the proglottids having arisen from it by a
process of terminal growth. The scolex is thus the oldest
part of the animal’s body; it, in fact, constitutes the entire
parasite when it first arrives in the intestine of the host (as
the animal is called in which a parasite lives), the proglottids

A TAPEWORM 81

only then beginning to grow. The youngest proglottids are
those nearest the scolex; those at the opposite end of the
body are the oldest and hence the largest. Count the proglot-
tids. The animal attaches itself to the wall of the intestine
by means of its scolex, which is provided for this purpose with
four suckers and usually two rows of chitinous hooks; the scolex
of Tuenia saginata lacks the hooks. Thus attached, it lies
immersed in the digestive fluids of its host and absorbs through
the outer surface of its body the nutriment it needs. It is with-
out a digestive system.

Bxercise 1. Draw an outline of the animal on a scale of 4 or 5,
taking care to represent the number of proglottids accu-
rately.

The scolex. Cut off the scolex, mount it on a slide in glycer-
ine or water, and examine it under the microscope. Notice the
fine excretory canals which occur in every part of it. Can you
determine their arrangement? Note the numerous minute
calcareous bodies.

Exercise 2. Draw the scolex on a scale of 10. Represent accu-
rately the suckers and the number and position of the
hooks, if these are present.

Bxercise 3. Draw a single hook highly magnified.

The proglottids. Each proglottid is composed mainly of repro-
ductive organs and circular, longitudinal, and oblique muscle
fibers imbedded in a spongy tissue called parenchyma. The
parenchyma fills the entire primitive body-cavity, which is thus
absent in this animal. Each proglottid contains a complete set
of both male and female genital organs. ‘These are immature in
the youngest and smallest proglottids; in those at about a
third of the distance from the anterior end of the body they
are mature; in the largest proglottids, those at the posterior

82 INVERTEBRATE ZOOLOGY

end of the body, the uterus is so distended with eggs that most
of the other genital organs are obliterated and do not appear.
A pair of longitudinal excretory canals passes from one end of the
worm to the other, running near to and parallel with each lateral
edge; in each proglottid, also, are one or two transverse canals.
One or more pairs of longitudinal nerves run parallel with and
very near the excretory canals, which are also joined in each
proglottid by a ring commissure.

Cut off two or three proglottids from the forward end of the
body, two or three from about a third of the distance from the
anterior end, and two or three from the posterior end, and soak
them all first for a short time in a solution of caustic potash and
then in one of equal parts of glycerine and water.

Place the proglottids from the hinder end of the body in
dilute glycerine between two glass slides, press them gently so
as to squeeze them as thin as possible without crushing them,
and study them under the microscope. In the middle of
one of the lateral edges of the proglottid notice a slight pro-
jection containing a depression. This is the genital papilla, and
the depression is the genital cloaca. Two canals will be seen
running from the genital cloaca toward the center of the pro-
glottid. These are the vas deferens and the vagina, the former
being the larger of the two. The greater part of the proglottid
will be seen to be occupied by a much-branched organ filled
with a granular substance. This is the uterus, and the granules
are eggs. Near each lateral edge of the proglottid will be seen
a straight band. These two bands are the dorsal excretory canals ;
find the transverse canal near the hinder end of the proglottid.
Between each canal and the edge of the proglottid will be seen
a delicate line running parallel with the canal. These are the
main nerves; they are joined by transverse nerves.

Exercise 4. Draw the proglottid, showing accurately all of these
features that you have observed.

A TAPEWORM 83

Study in the same way the mature proglottids. Find the
uterus. It is here a straight, narrow tube in the middle of
the proglottid, and is not yet distended with eggs. Near the
center and toward the posterior end of the proglottid will be
seen an irregular mass of organs. These are the paired ovaries,
two large, round bodies, one on each side of the uterus; the
median yolk gland, which is below the end of the uterus, near
the posterior margin of the proglottid; the shell gland, between
the yolk gland and the uterus. From the shell gland the vagina
and vas deferens proceed to the genital cloaca, the former being
the smaller and more posterior of the two. Scattered through-
out the proglottid are numerous small round bodies, the testes,
which are joined with the vas deferens by numerous minute
vasa efferentia. Find the excretory canals and the longitudinal nerves.

Exercise 5. Draw the proglottid, showing all of these features
you have observed; carefully label all.

Study in the same way the immature proglottids from the
forward end of the body. Find as many of the organs men-
tioned as are present.

Bxercise 6. Draw the immature proglottid.

The tapeworm may fertilize itself or be fertilized by another
individual, and where self-fertilization takes place one proglottid
of the animal may fertilize another, or a single proglottid may
fertilize itself. The ova from the ovaries, on being fertilized, pass
at once into the uterus. The ripe proglottids, which are filled
with eggs in which the embryo has already begun to develop,
break off from the hinder end of the worm and pass out of the
body of the host. They then break open or are crushed, and
their eggs are scattered on all sides.

The encysted tapeworm. The adult worm alone is found in the
intestine. The eggs, in order to develop, must pass out of the
host and fall upon something which will afterward be eaten by

84 INVERTEBRATE ZOOLOGY

another animal, called the intermediate host, which is itself preyed
upon by the host. After being thus transferred to the stomach
of the intermediate host there hatches from each egg a minute
spherical embryo, called the six-hooked embryo, which is provided
with three pairs of hook-like organs of locomotion. This
embryo works its way through the wall of the intestine of the
animal and migrates finally to some one of the internal organs,
where it lodges and grows into a cyst-like larval form, called
the cysticercus. Within the cysticercus is a fully developed
scolex, but turned wrong side out. If, now, the intermediate
host be eaten by the host, the scolex turns right side out, passes
into the intestine of the latter, attaches itself to the intestinal
wall, and grows into an adult tapeworm.

The intermediate host of Taenia saginata is the beef, in the
muscles of which the cysticercus will be found, if present.
That of Taenia serrata is the rabbit and that of Taenia crassi-
collis is the mouse; in the former animal the cysticerci are
imbedded in the peritoneum or the liver, and in the latter, in
the liver. Open the body-cavity of either of these latter ani-
mals by a median ventral incision and look for cysticerci. They
are large, whitish bodies and are easily detected if present.
When a cysticercus is found, it should be carefully dissected
out, its outer wall slit and the scolex exposed to view. Mount
it on a slide in dilute glycerine and study it.

Exercise 7. Draw a view of the scolex in its cyst,

CHAPTER IV
BRYOZOA (POLYZOA)

ECTOPROCTA
AN ECTOPROCT BRYOZOAN (Bugula turrita)

Bugula turrita is a marine colonial bryozoan which is very
common in the shallow waters along our coast. The colonies
are sessile and are attached to rocks, seaweed, and other objects.
The animals are very small and must be studied with the aid of
a microscope.

Study a large piece of a colony (alive if possible) and notice
the spiral arrangement of the branches. A branch is made up
of a double row of elongated partitions or chambers, each of
which is called a zowcium. Each zocecium represents a separate
individual of the colony ; within its walls are the soft parts of
the animal which are called collectively the polypide. The indi-
vidual bryozoan is thus made up of two distinct parts, the
zocecium and the polypide, the former constituting the chitinous
outer wall of the animal, the latter comprising its viscera and
the tentacles. At its upper or distal end the zocecium has a
large opening through which the forward end of the polypide
can be protruded and into which it withdraws itself when
alarmed. The cuticula which forms the zocecium is rendered
hard by the presence of carbonate of lime; it is thus much
more enduring than the remainder of the animal, and after
death the empty zoccium may persist long after all the
softer parts have disappeared. Look for empty zoccia in

your specimen.
85

86 INVERTEBRATE ZOOLOGY

The different individuals of a colony have arisen by a process
of budding from the individuals below them in the colony.
The oldest individuals are thus those nearest the base of the
colony, the basal one being the progenitor of the entire colony.
This is also the only individual which has not come into exist-
ence by a process of budding; it began its life as a free-
swimming larva which was hatched from an egg.

The zoecium. Mount a small portion of the colony containing
two or three branches on a slide under a cover-glass.

Exercise 1. Draw a large and accurate outline of the zoccia,
leaving out the polypides. Observe very carefully the
boundaries of the zocwcia and their relations to one
another.

The polypide. Study a number of polypides, both retracted
and extended. The forward end of the polypide consists of a
circular ridge, called the lophophore, which bears a row of long
ciliated tentacles. In the midst of the circle is the mouth. The
tentacles are very vibratile and serve as respiratory as well as
prehensile organs. It will be seen that the lophophore can be
entirely withdrawn within the zocecium.

The digestive system. The mouth opens into the pharynx,
which leads into the esophagus. This opens into a large sac-
like stomach, the lower portion of which is lengthened into a
long pouch. From the upper end of the stomach, near the base
of the cesophagus, the short intestine leaves it and passes to the
thick-walled rectum. This leads to the anus, which is situated
just outside the lophophore near the mouth. The digestive tract
has thus the shape of the letter V, the point of which is formed
by the stomach pouch. Passing from the stomach pouch to the
lower end of the body is a broad mesenteric strand called the
funiculus. In order to study the digestive tract satisfactorily,
a polypide should be found in which both arms of the V come
into view.

A BRYOZOAN 87

The muscular system. The retractor muscles, whose function
it is to draw in the lophophore, may, in favorable specimens, be
seen as delicate strands which pass from the wall of the zow-
cium to the pharynx.

The nervous system has not yet been observed in Bugula, but
in nearly allied Bryozoa it consists of a single ganglion between
the mouth and the anus. From it nerves radiate to the ten-
tacles and other organs. ‘There are no organs of special
sense.

The reproductive organs. The animals are hermaphroditic. Ova
develop from the peritoneal lining of the spacious body-cavity
and will be seen, when present, lying near the stomach pouch.
Spermatozoa develop from the funiculus and, when present,
form a mass about that organ.

There are two methods of reproduction, the sexual, in which
the new individual develops from the fertilized egg, and the
asexual, in which the new individual arises by budding. As
already stated, the entire colony, with the exception of its
oldest member, has developed in the latter way.

Exercise 2. Draw an extended individual in which the entire
digestive tract can be seen and label all the organs observed.

There are no special respiratory or excretory organs; the
entire outer surface of the body performs these functions. The
circulatory system is represented by the colorless blood fluid
alone. There are no circulatory vessels, the blood being
contained in the body-cavity.

Avicularia and owecia. These are peculiar structures, found in
connection with the zocecia, which are morphologically equiva-
lent to distinct individuals. An avicularium is a small structure,
like a bird’s head in shape (hence the name), which may be
found attached to the wall of some of the zocecia near the open-
ing. It has a movable lower jaw which can be opened and shut
by two sets of muscles. Its function is to seize and hold small

88 INVERTEBRATE ZOOLOGY

animals. These soon die in its grasp, and their disintegrated
remains are swept into the mouth by the ciliated tentacles. An
oecium is a disc-like structure which, in some parts of the
colony, lies in front of a zocecium. It serves as an egg-capsule
in which the embryo develops. A single embryo will be found
in each.

Ezercise 3. Find a zoccium with an avicularium attached and
draw them.

Exercise 4. Find a zocecium with an ocecium attached and draw
them.

CHAPTER V
MOLLUSCA

PELECYPODA

A FRESHWATER MUSSEL (Anodonta or Unio)

These animals are common in most parts of the country;
they inhabit the sandy bottoms of freshwater streams and
lakes.

Study first the live animal, if possible. Its body is unseg-
mented and entirely enclosed in a bilateral, bivalve shell,
which is the cuticula of the animal richly charged with cal-
careous salts. The two valves of the shell cover the right and
left sides of the animal and are joined together on its dorsal
side by the dark-colored hinge ligament, while their ventral
edges are open; the animal is thus very much compressed
laterally. The anterior end of the animal is more rounded and
less elongated than the posterior end. Which is the right-hand
valve? The elevation on each valve near the hinge towards
the forward end is called the umbo. It is the oldest portion of
the shell; from it as a beginning point the shell has grown in
size by additions to its ventral edge. Note the parallel lines of
growth. The ventral edges of the shell are thus the youngest
portions of them.

Exercise 1. Make a drawing of the right-hand valve, indicating
the anterior, posterior, dorsal, and ventral aspects, and
showing the lines of growth.

Exercise 2. Make a drawing of the dorsal aspect of the animal.
89

90 INVERTEBRATE ZOOLOGY

Kill the animal by immersing it for a few minutes in hot
water (70° C.). As the shell is kept closed by the contraction of
the two muscles which pass between its valves, it will gape open
as soon as the animal is dead and the muscles are relaxed. It is
the elasticity of the hinge ligament which causes it to open.’

Examine the animal as it lies in the shell. It will be
seen that the inner surface of each valve is covered with a
soft, slimy membrane, the lower edge of which is parallel to
the edge of the shell. This is the mantle; it is a double
fold of the dorsal integument of the body, one side of the
body being covered by either fold. The mantle is the matrix
of the shell, z.e., it secretes the shell. Its lower edge is pro-
vided with muscle fibers and can be extended beyond the edge
of the shell; it also possesses sensory functions; in some
pelecypods eyes are situated along the mantle’s edge.

Observe the large, soft visceral mass hanging between the two
lobes of the mantle; it contains the viscera of the animal. On
the lower side of the visceral mass, 7.e., toward the gape of the
shell, is the muscular foot, which can be extended below the edge
of the shell and is the organ of locomotion. Observe the
two leaf-like gills on each side of the visceral mass and foot;
also the two large adductor muscles, one in front of and the other
behind the visceral mass, which pass from one valve of the
shell to the other and serve to close them.

Pass a knife between the mantle and the left shell and sepa-
rate them from each other. Cut the two muscles close to the
shell; cut the elastic hinge ligament and remove the left shell.

Study the inner surface of the shell. Note the two large scars
marking the surfaces of attachment of the adductor muscles;

1The shell may also be opened by inserting some sharp, wedge-shaped
instrument between its valves. The valves are thus pressed apart far enough
to admit the blade of a scalpel, by means of which the adductor muscles should
be cut close to the left valve of the shell. The hinge ligament should then be
cut and the left valve be removed.

A FRESHWATER MUSSEL 91

just above each is the scar of a much smaller muscle, the
retractor of the foot, and just posterior to the anterior adductor
muscle is the scar of the protractor muscle of the foot. Note
the broad line which joins the scars, running parallel with the
edge of the shell. This is the pallial line; it is formed by the
insertion in the shell of the delicate muscle fibers at the edge
of the mantle. Do you find hinge teeth in the shell just beneath
the hinge ligament? Unio has such teeth; Anodonta is without
them and is also characterized by the thinness of its shell.

Bxercise 3. Draw a view of the inner surface of the shell.

Break the shell and examine the broken edge with'a hand
lens. Study the structure of the shell. It is composed of
three layers——the inner mother-of-pearl layer, which is secreted
by the entire surface of the mantle, the prismatic layer, and
the organic layer or periostracum on the outside. The two latter
layers are secreted by the edge of the mantle; the periostracum
is very thin and gives the color to the shell. Place a piece of
the shell in a solution of hydrochloric acid; note the efferves-
cence which results; also that an organic remnant, even of the
two inner layers, is left.

Exercise 4. Draw a view of the broken edge of the shell on a
scale of 5. Show the prisms of the prismatic layer.

Place the animal in water and study it as it lies in the right
shell.1 The two halves of the mantle will be seen to envelop
entirely the visceral mass and the foot. Over the entire dorsal
portion of the visceral mass the mantle is fused with it and
cannot be separated, but the lateral and ventral portions of the
mantle lobes hang free, enclosing an extensive space, which is
called the mantle cavity. In it, on each side of the visceral mass,

1¥For the study of the soft parts of the mussel it is well to have at hand
also a specimen which has been deprived of both valves of the shell.

92 INVERTEBRATE ZOOLOGY

lie the two leaf-like gills. In front of the gills are two pairs of
triangular flaps, the oral palps, between which, in the median
line and just back of the anterior adductor muscle, lies the
mouth. Find it.

Trace the irregular line of attachment of the mantle with the
visceral mass ; it follows the base of the gills and of the oral palps
and passes beneath both adductor muscles. Observe the edges
of the mantle and note that at the hinder end of the animal they
are darkly pigmented, and the middle point of the pigmented
line is joined with the base of the gills by a short septum. This
septum divides the posterior portion of the mantle cavity into
a dorsal and a ventral chamber. The latter is the very large
branchial chamber which contains the gills; the former is the very
small cloacal chamber. The pigmented edges of the mantle are
at this place modified to form, when the edges of the two sides
of the mantle are applied to each other, two short tubular
openings, which place these two chambers in communication
with the outside water and are called the siphons. The ven-
tral siphon is called the branchial or incurrent siphon; through it
water streams into the branchial chamber bearing food and
air for respiration. The dorsal siphon is called the excurrent or
cloacal siphon, and through it water passes outward charged with
feecal matter from the alimentary tract and carbon dioxide of
respiration. Note the sense tentacles on the branchial siphon.

Probe the dorsal siphon. Carefully remove the left lobe of
the mantle after cutting it with fine scissors along its line of
attachment with the visceral mass.

Through the transparent body-wall observe the organs in the
dorsal portion of the visceral mass. Just back of the anterior
adductor muscle is the liver, which can often be recognized by
its greenish color, and back of which is the dark-colored Keber’s
organ. Between the hinge ligament and the base of the gills lies
the heart in its transparent pericardium, and beneath it is the dark-
colored kidney. The rectum may be seen passing through the

A FRESHWATER MUSSEL 93

pericardium and the heart, then extending above the posterior
adductor muscle to the cloaca, where it ends with the anus. Cut
open the cloacal chamber by a slit in the side of its siphon.
Find the hinder end of the rectum and the anus. Note just
beneath the muscle a canal which accompanies the base of the
gill forward. This is the suprabranchial passage of the outer gill;
it runs posteriorly to the cloacal chamber. Blow into it with a
blow-pipe, also probe it from behind.

Exercise 5. Draw a semidiagrammatic view of the animal lying
in the right-hand valve of the shell, representing the organs
above mentioned. Carefully label all.

The respiratory system. The gills have already been noticed.
The two gills on each side of the visceral mass are, by way of
origin, but a single organ, which is called the ctenidium. The
mussel is thus provided with a single pair of ctenidia, which are
homologous to those of the squid and of snails. Each gill con-
sists of a pair of plates or lamelle united at their lower edges
and open above, and further joined by vertical or dorso-ventral
cross-partitions, the interlamellar partitions. The space between
the lamelle is thus divided into parallel, vertical chambers, the
water-tubes, which run from the bottom to the top of the gill
and open above into the suprabranchial passage. One of these
passages runs along the base of each gill, as a wide canal, to
the cloacal chamber. We have already observed the supra-
branchial passage of the outer gill. In order to observe that of
the inner gill, lift up both gills; the inner lamella of the inner
gill will, in most species of mussels, be seen not to be united
with the wall of the visceral mass along the hinder portion of
the foot, but to have a free edge. The long slit-like opening
thus presented leads into the inner suprabranchial passage.
Probe it backward to the cloacal chamber. Probe it also from
the hinder end forward and notice that back of the visceral
mass the two inner suprabranchial passages, 7.e., those belonging

94 INVERTEBRATE ZOOLOGY

to the inner gills of the right and left sides, coalesce, forming a
single passage.

Study the finer structure of the gills. Place a gill on a glass
slide in a little water and with forceps and a knife carefully
separate the lamelle. Mount a piece of a lamella in water and
study it under a compound microscope. Note the vertical inter-
lamellar partitions. Observe that the lamella is a delicate lattice
work made up of ridges, the gill-filaments, running vertically and
thus parallel with the interlamellar partitions, and of cross-
ridges, the interfilamentary connections, which run between and
connect the vertical filaments. The apertures in the lattice
work place the water-tubes in communication with the water in
the branchial chamber. The gill-filaments are provided with
cilia, as may be easily seen if the gill be alive, the action of
which causes streams of water to pass into the water-tubes.
The course of the respiratory water is from the branchial
chamber into the water-tubes, through which it passes into
the suprabranchial passages and through these into the cloacal
chamber.

Exercise 6. Draw a diagram of the respiratory system showing
the gills and their relation to the suprabranchial passages.
Show the direction of the flow of the respiratory water by
means of arrows.

Exercise 7. Draw a diagram showing the minute structure of a
lamella.

The circulatory system. With fine scissors and great care cut
open the pericardium by a slit along its dorsal border. Note the
heart with the rectum passing through it. The heart consists
of three chambers —a median, thick-walled ventricle and two
lateral auricles. These latter are delicate, thin-walled organs,
triangular in shape, the base of the triangle lying along the
dorsal border of the gills and the apex communicating with

A FRESHWATER MUSSEL 95

the ventricle. If the left auricle has been injured in the
dissection, the right one is easily seen by looking across the
pericardial space. From the ventricle an anterior and a poste-
rior artery pass to either end of the body. These arteries lie
alongside the rectum, to which the anterior one is dorsal and
the posterior one is ventral; they are difficult to distinguish
from it, except in specimens in which the heart has been
injected.

The course of the blood is the following: by the contraction
of the heart the blood is sent to all parts of the body; on its
return course it is first conveyed, through a system of lacuna,
to the kidneys, and thence to the gills; here it circulates in
vessels which run through the interlamellar partitions, the gill-
filaments, and the interfilamentary connections, and is oxy-
genated; it then passes into the auricles.

The excretory system consists of a pair of kidneys, which are dark-
colored organs lying just beneath the pericardium and in front
of the posterior adductor muscle. Each kidney consists of two
parts, the kidney proper and the ureter. The former is a dark,
thick-walled gland which lies beneath the ureter and communi-
cates with it at its hinder end. The ureter is a thin-walled
vessel lying above the kidney proper, with a small external
opening on the side of the visceral mass beneath the anterior
end of the kidney and near the base of the inner gill. With
fine scissors cut off the gills and look for the opening; it may
be recognized by its white lips. The kidney also possesses at
its anterior end a duct leading into the pericardial cavity. Slit
open the ureter and kidney proper in clean water and observe
their inner structure.

Exercise 8. Draw a diagram representing the pericardial cavity
and the kidney, showing the relation of the two structures
to each other. Draw the heart in the pericardial cavity,
showing the relation of the auricle to the gills.

96 INVERTEBRATE ZOOLOGY |

The digestive system. Find the mouth between the two pairs
of palps and place a bristle in it;.note the upper and the lower
lips, which connect the upper and the lower pairs of palps,
respectively. The mouth is seen to the greatest advantage in a
specimen which has been deprived of both valves of the shell.
Trace the rectum from the anus to the place of its entrance into
the visceral mass. Carefully remove with forceps and knife
the tough, white integument which covers the left side of the
visceral mass, taking care not to disturb the organs beneath.
The soft cream-colored mass just above the foot is the reproduc-
tive gland; the light greenish mass lying just above this is the
liver. Imbedded in these masses lies the alimentary tract, a
narrow delicate tube, which will be injured in the dissection
unless the greatest care is taken. Beginning with the mouth,
gently scrape away the soft mass which surrounds the alimentary
tract, laying it entirely bare. The water in the dissecting pan
must be frequently renewed to keep it clear, and great care
must be taken not to break the tract. The mouth opens into
the short esophagus, after which the canal dilates to form the
stomach. ‘The liver communicates with the stomach by several
ducts. Back of the stomach is the intestine, a narrow tube
which runs backward and downward to the hinder end of the
visceral mass; it then turns upward and runs forward to a
point above the stomach, where it turns downward to the lower
side of the visceral mass; it then bends dorsally again and
runs to the point where it leaves the visceral mass. Here
the rectum begins and passes through the heart and above
the posterior adductor muscle to the anus in the cloacal
chamber.

Mussels feed upon minute organisms and organic particles
contained in the water. Some of the water in the mantle
cavity is drawn by the ciliated oral palps into the mouth and
passes through the alimentary tract, where organic substances
contained in it are digested and absorbed. The mussel usually

A FRESHWATER MUSSEL 97

lies with its forward end buried in the sand and its hinder end
with the siphons projecting into the water.

Exercise 9. Draw a diagrammatic view of the digestive system.

The reproductive system. The sexes are separate. The repro-
ductive glands (testis or ovary) are very similar to each other and
consist of a pair of cream-colored masses which fill a greater
part of the visceral mass. They communicate with the outside
through a pair of small openings, one on each side of the
visceral mass just below and in front of the opening of the
ureter. The openings can often be located by pressing out
from them eggs or sperm. The eggs, as soon as laid, pass into
the interlamellar space of the outer gills of the mother, where
they hatch. The young larve are very immature and are
called glochidia; they leave the mother and attach themselves
to the sides of fishes by means of a pair of sharp projections on
the ventral edges of the valves of the shell, where they lead a
parasitic life. While here they undergo a metamorphosis and
finally attain the adult structure, when they detach themselves
and drop to the bottom. Look for glochidia in your specimen.

The nervous system consists of three pairs of ganglia — the
cerebral ganglia or brain, the pedal ganglia, and the visceral ganglia,
and the nerves proceeding from them; each of the last two pairs
is joined with the brain by a pair of nerve-connectives.

First find the visceral ganglia. They are a small grayish or
pinkish mass on the ventral surface of the posterior adductor
muscle with nerves radiating in all directions. Two of these
nerves, the cerebro-visceral connectives, will be seen passing forward,
one on each side of the visceral mass.

Find next the brain. It consists of a pair of ganglia situated
above the mouth, just behind the anterior adductor muscle. The
two ganglia are not so close together as those of the visceral
pair; they lie on either side of the muscle and are united by a
commissure. Each ganglion sends out three large nerves — the

98 INVERTEBRATE ZOOLOGY

cerebro-visceral connective, which goes to the visceral ganglia, the
cerebro-pedal connective, which goes to the pedal ganglia, and
the pallial nerve, which passes to the mantle. Find them.

The pedal ganglia form a nervous mass buried in the foot
near its base. Make a shallow longitudinal incision in the bot-
tom of the foot and gently pull the flaps apart; the pinkish
mass and the nerves radiating from it will be seen. In contact
with it is a sense-organ called the otocyst.

Exercise 10. Draw a diagram representing the nervous system.

Make several transverse sections with a razor through the
region of the heart of a mussel which has been previously
hardened. Identify all the organs which appear.

Exercise 11. Draw a diagram representing a cross section; care-
fully label all the organs.

AN OYSTER 99

PELECYPODA
AN OYSTER

Select a large live oyster in the shell, and if it is dirty wash it
thoroughly. ‘The shell is sometimes covered with mud, hydroids,
sponges, tube-forming annelids, and other marine animals. The
small, round holes made by the yellow boring sponge are often
conspicuous.

The two valves of the shell will be seen to be different in
shape, one being more or less flattened and the other much
deeper and more convex. These two valves cover the right and
left sides of the animal’s body, the convex valve being on the
left and the flattened one on the right side. The oyster is a
sessile animal, after it has passed through its youthful migratory
period, and is fastened to a rock or shell or other stationary
object by its left shell. It thus lies on its left side, while the
flat right shell acts as a cover which can be raised to allow
the animal to draw in water containing food and air, and
closed when danger threatens. The very young oyster is a
symmetrical animal which swims about actively in the water.
While it is still very small —so small, in fact, that it is barely
visible to the naked eye —.it settles down and fastens itself
to some stationary object and in its subsequent growth accommo-
dates itself more or less to the irregularities of this substratum.
This is the reason why the shell is so often rough and irregular
in shape.

The smaller end of the shell is the anterior end. The hinge
ligament is situated here, the elasticity of which keeps the shell
open except when it is closed by the contraction of the large
adductor muscle. At this end is also the umbo, the oldest part

100 INVERTEBRATE ZOOLOGY

of the shell. Note the parallel lines of growth which extend
from the umbo to the ventral and posterior sides of the shell.
When the anterior, the right, and the left sides of the shell are
known, the ventral and posterior sides can be easily determined.

Exercise 1. Make an outline drawing of the right valve, indicat-
ing the anterior, posterior, dorsal, and ventral aspects and
showing the lines of growth.

Remove the right valve in the following way: Break off the
edge of the shell with a hammer, insert the blade of a scalpel
and cut the large adductor muscle, which is not far from the
edge but nearer the dorsal than the ventral margin. It is
important to keep the blade close to the right valve so as not
to mutilate the internal organs. Force off the right valve and
examine its inner surface.

Exercise 2. Draw the inner surface of the shell, showing the
muscle scar with its lines of growth and the hinge liga-
ment, and label the dorsal, ventral, anterior, and posterior
sides of it.

Study the animal as it lies in the left valve. Note the soft,
shiny mantle, which covers the inner surface of the shell and
has secreted it. The mantle is a double fold of the integument
which extends ventrally from the dorsal side and covers the two
lateral sides of the body. Its lower edge is bordered by a fringe
of short, pigmented tentacles which are the principal sense organs
of the animal; it is also provided with muscle fibers which
enable it to be slightly extended beyond the edge of the shell.

The most conspicuous organ in the body will be seen to be
the large adductor muscle. Lying between it and the hinge liga-
ment is the visceral mass, containing most of the viscera. Along
the ventral side are the four gills.

Put the oyster into a pan of water and with fine scissors and
forceps remove the right mantle. Just in front of the adductor

AN OYSTER 101

muscle observe the pericardium. Carefully cut it away and see
the heart, which lies in the pericardial cavity ; it will be beating
if the animal is still alive. The ventricle is dorsal in position and
the auricle is ventral, lying next to the gills, from which it re-
ceives the purified blood. The four gills lie close together, no
foot being present to separate the two right-hand from the two
left-hand gills. Just in front of the gills, at the front end of the
body, are the two pairs of large oral palps. The mouth is between
these palps, two being on each side of it. Find the mouth and
note that it lies between an upper and an under lip, each of which
is formed by the union of a pair of palps; ze., a palp on the
right side joins one on the left and forms the upper lip, and the
other two palps join to form the under lp.

Oysters feed on minute organisms contained in the water.
These are caught in the slime which exudes from the surface of
the gills and moved forward by the action of the cilia of the
gills and the palps to the mouth.

The anus and the rectum will be seen on the dorsal side of the
adductor muscle.

Bxercise 3. Make a drawing of the oyster as it lies in the left
shell, representing all the organs above mentioned. Care-
fully label all.

The digestive tract. This consists of the short csophagus, the
stomach and the dark-colored liver which surrounds it, and the
long intestine. The mouth opens directly into the esophagus,
which leads to the stomach. The position of this organ can
easily be determined, because it is imbedded in the dark-brown
liver. Carefully scrape or cut away the side of the visceral
mass and expose the liver; continue the process until the
stomach is seen. The intestine extends straight back from the
stomach to a position ventral to the adductor muscle and between
it and the gills. It then turns on itself and passes straight
forward to the dorsal side of the stomach, around the forward

102 INVERTEBRATE ZOOLOGY

and ventral sides of it, and thus back again to the dorsal side of
the muscle, where it ends with the anus. Most of it is surrounded
by the yellow reproductive gland. Lay bare the intestine. This
can be done best after the oyster has been hardened for a few
days in a 5 per cent. solution of formalin.

Bxercise 4. Make a drawing of the digestive tract in an outline
of the animal’s body.

The remaining systems of organs of the visceral mass will not
be studied in this dissection.

The American oyster is a unisexual animal; the common
European oyster is hermaphroditic. The reproductive glands,
the ovaries or testes, are a pair of yellowish or whitish organs of
irregular form which occupy the larger part of the visceral mass
and surround the digestive tract and other organs. The kidneys
are also a pair of organs of irregular form which, together with
a portion of the intestine, occupy the lower and hinder part of
the visceral mass, between the muscle and the gills. The nervous
system has been much modified by the sessile habit of life of the
oyster. The cerebral ganglia are represented by a nerve ring,
containing ganglia, which surrounds the mouth; it is called the
circumpallial nerve. Fibers from this ring go to the pigmented
sense papille at the margin of the mantle. The visceral ganglia
lie along the antero-ventral side of the muscle and are joined
with the cerebral ring by longitudinal connectives. The pedal
ganglia are wanting.

A HARD-SHELL CLAM 103

PELECYPODA
A HARD-SHELL CLAM (Venus mercenaria)

This is a very common marine mollusk which inhabits the
sandy bottoms of the ocean along our shores. The soft-shell
clam (Mya arenaria), which lives in mud flats between tides,
resembles it very much in structure and may be used for this
dissection.

Study first the live animal, if possible. Its body is unseg-
mented and is entirely enclosed in a bilateral, bivalve shell,
which is the cuticula of the animal richly charged with cal-
careous salts. The two valves of the shell cover the right and
left sides of the animal and are joined together on its dorsal
side by the dark-colored hinge ligament, while their ventral edges
are open; the animal is thus very much compressed laterally.
The anterior end of the animal is truncated; the posterior end
is elongated. Which is the right-hand valve? The elevation
on each valve near the hinge ligament is called the umbo. It is
the oldest portion of the shell; from it as a beginning point
the shell has grown in size to its present proportions by addi-
tion to its ventral edge. Note the parallel lines of growth.
The ventral edges of the shell are thus the youngest portions
of them.

Exercise 1. Make a drawing of the right-hand valve, indicating
the anterior, posterior, dorsal, and ventral aspects, and
showing the lines of growth.

Exercise 2. Make a drawing of the dorsal aspect of the animal.

Kill the animal by immersing it for a few minutes in hot
water (70° C.). As the shell is kept closed by the contraction of

104 INVERTEBRATE ZOOLOGY

the two muscles which pass between the valves, it will gape open
as soon as the animal is dead and the muscles are relaxed. Itis
the elasticity of the hinge ligament which causes it to open.

Examine the animal as it lies in the shell. It will be
seen that the inner surface of each valve is covered with a
soft, slimy membrane, whose lower edge is parallel with the
edge of the shell. This is the mantle; it is a double fold of the
dorsal integument of the body, one side of which is covered by
either fold. The mantle is the matrix of the shell, z.e., it secretes
it. The lower edge of the mantle is provided with muscle
fibers and can be extended beyond the edge of the shell; it
also possesses sensory functions; in some pelecypods eyes
are situated in the mantle’s edge.

Observe the large, soft visceral mass hanging between the two
lobes of the mantle; it contains most of the viscera of the
animal. On the lower side of the visceral mass, 2.e., towards
the gape of the shell, is the muscular wedge-shaped foot, which
can be extended beneath the edge of the shell and is the organ
of locomotion. Do you see the two leaf-like gills on each side
of the visceral mass and foot? Observe the two large adductor
muscles, one in front of and the other behind the visceral mass,
which pass from one valve to the other and serve to close
them.

Pass a knife between the mantle and the left shell and sepa-
rate them from each other. Cut the two muscles close to the
shell; cut the hinge ligament and remove the left shell.

Study the inner surface of the shell. Note the two large
scars marking the surfaces of attachment of the adductor mus-
cles; just above the anterior scar is that of a much smaller

1 The shell may also be opened by inserting some sharp, wedge-shaped instru-
meut between the valves. The valves are thus pressed apart far enough to
admit the blade of a scalpel, by means of which the adductor muscles should be
cut close to the left valve of the shell. The hinge ligament should then be cut
and the left valve be removed.

A HARD-SHELL CLAM 105

muscle, the anterior retractor of the foot. Note the broad line
which joins the scars and runs parallel with the edge of the
shell except near the posterior muscle scar, where it bends for-
ward, forming a triangular indentation. This is the pallial line;
it is formed by the insertion in the shell of the delicate muscle
fibers near the edge of the mantle. The indentation is the
pallial sinus. Note the hinge teeth just beneath the umbo.

Exercise 3. Draw a view of the inner surface of the shell.

Break the shell and examine the broken edge with a hand
lens. Study the structure of the shell. It is composed of
three layers——the inner mother-of-pearl layer, which is secreted
by the entire surface of the mantle, the prismatic layer, and the
organic layer or periostracum on the outside. The two latter
layers are secreted by the edge of the mantle; the periostracum
is very thin and gives the color to the shell. Place a piece of
the shell in a solution of hydrochloric acid; note the efferves-
cence which results; note also that an inorganic remnant, even
of the two inner layers, is left.

Exercise 4. Draw a view of the broken edge of the shell on a
scale of 5. Show the prisms of the prismatic layer.

Place the animal in water and study it as it lies in the right
shell! The two halves of the mantle will be seen to envelop
entirely the visceral mass of the foot. Over the dorsal portion
of the visceral mass the mantle is fused with it and cannot
be separated, but the lateral and the ventral portions of the
mantle lobes hang free, enclosing an extensive space, which is
called the mantle cavity. In this cavity, on each side of the
visceral mass, lie the two leaf-like gills. Observe the edges of
the mantle. They are fused forward of the anterior adductor

1 For the study of the soft parts of the clam it is well to have also at hand a
specimen which has been deprived of both valves of the shell.

106 INVERTEBRATE ZOOLOGY

muscle; the entire ventral edges are free and permit the foot to
protrude between them; their posterior edges are richly pig-
mented, and are also fused and modified to form the two
siphons. These are protrusile tubes, through which water is
taken into and expelled from the mantle cavity. Probe them.
Note on each side below the posterior adductor muscle the
triangular muscle which connects the siphons with the shell.
It is the siphonal retractor muscle. Between the two siphons in the
mantle cavity note the short transverse septum which divides the
posterior portion of the mantle cavity into two chambers, a dorsal
and a ventral one. The latter is the very large branchial chamber,
which contains the visceral mass and the gills, the former,
the very small cloacal chamber. ‘The ventral siphon is called the
branchial or incurrent siphon; through it the water streams into
the branchial chamber bearing food and air for respiration. The
dorsal siphon is called the excurrent or cloacal siphon and through
it water passes outward from the cloacal chamber charged with
carbon dioxide of respiration and with fecal matter from the
alimentary tract. Probe the cloacal chamber.

Carefully remove the left mantle lobe after cutting it with
fine scissors at its line of attachment, beginning at the forward
end. Cut off the siphonal muscle, leaving the siphon in posi-
tion. Place the animal in water and study the arrangement of
the organs. Observe the position of the gills; note in front of
them two triangular flaps, the oral palps; in the median line
between the two pairs of oral palps is the mouth; find it.
Along the base of the gills note an elongated passage leading
posteriorly to the cloacal chamber, the suprabranchial passage of
the outer gill. Blow into this passage at its hinder end in the
cloacal chamber with a blow-pipe, or probe it.

Observe again the siphonal region. Note the short septum
which separates the branchial from the cloacal chamber, and the
opening between it and the visceral mass: probe this opening.
Just beneath the umbo will be seen through the semi-transparent

A HARD-SHELL CLAM 107

body-wall a dark-colored mass, the liver, back of which are
the yellowish reproductive gland and the dark-colored organ of
Keber. Back of the latter is the pericardium, within which is the
heart. Beneath the heart and in front of the posterior adductor
muscle is the dark-colored kidney. Passing through the peri-
cardium and the heart and above the posterior adductor muscle
to the cloaca will be seen the rectum. It ends with the anus near
the hinder surface of the muscle. Open the cloacal chamber
by a slit in the side of its siphon and find the anus.

Exercise 5. Draw a semidiagrammatic view of the animal lying
in the right-hand valve of the shell, representing the organs
above mentioned. Carefully label all.

The respiratory system. The gills have already been noticed.
The two gills on each side are, by way of origin, but a single
organ, which is called the ctenidium. The clam is thus provided
with a single pair of ctenidia, which are homologous to those of
the squid and of snails. Each gill consists of a pair of plates
or lamelle united at their lower edges and open above, and fur-
ther joined by vertical or dorso-ventral cross-partitions, the inter-
lamellar partitions. The space between the lamelle is thus divided
into parallel, vertical chambers, the water-tubes, which run from
the bottom to the top of the gill and open above into the supra-
branchial passage. This is a wide canal running along the base
of each gill to the cloacal chamber. The course of the supra-
branchial passage of the outer gill has already been noted. In
order to observe that of the inner gill, lift up both gills; the
inner suprabranchial passage will be seen at the base of the
inner gill. Probe from the cloacal chamber into it. Notice
that back of the visceral mass the two inner suprabranchial
passages coalesce and form a single passage.

Study the finer structure of the gills. Place a gill on a
glass slide in a little water and with forceps and knife carefully
separate the lamella. Mount a piece of a lamella in water and

108 INVERTEBRATE ZOOLOGY

study it under a compound microscope. Note the vertical
interlamellar partitions. Observe that the lamella is a delicate
lattice work made up of ridges, the gill-filaments, which run
vertically and thus parallel with the interlamellar partitions, and
of cross-ridges, the interfilamentary connections, which run between
and connect the vertical filaments. The apertures in the lattice
work place the water-tubes in communication with the water of
the branchial chamber. The gill-filaments are provided with
cilia, as may easily be seen if the gill be alive, the action of
which causes streams of water to pass into the water-tubes.
The course of the respiratory water is from the branchial cham-
ber into the water-tubes, through which it passes to the supra-
branchial passages, and through these into the cloacal chamber,
whence it is ejected through the cloacal siphon.

Exercise 6. Draw a diagram of the respiratory system showing
the gills and their relation to the suprabranchial passages.
Show the direction of the flow of the respiratory water by
means of arrows.

Exercise 7. Draw a diagram showing the structure of a lamella.

The circulatory system. With fine scissors carefully cut open
the pericardium by a slit along its dorsal border and expose the
heart. Note the heart with the rectum passing through it. The
heart consists of three chambers —a median, thick-walled ventricle
and two lateral auricles. These latter are delicate, thin-walled
organs, triangular in shape, the base of the triangle lying along
the dorsal border of the gills and the apex communicating with
the ventricle. If the left auricle has been injured in the
dissection, the right one is easily seen by looking across the
pericardial space. From the ventricle an anterior and a pos-
terior artery pass to either end of the body. The posterior
artery expands, near the posterior end of the pericardium, to
form a large thick-walled sac, the arterial bulb. These two

A HARD-SHELL CLAM 109

arteries lie alongside the rectum, to which the anterior one is
dorsal and the posterior one is ventral; they are difficult to
distinguish from it, except in specimens in which the heart has
been injected.

The course of the blood is the following: by the contraction
of the heart the blood is sent to all parts of the body, whence it
is conveyed through lacune to the kidneys and thence to the
gills; here it circulates in vessels which run through the inter-
lamellar partitions, the gill-filaments, and the interfilamentary
connections, and is purified; it then passes into the auricles.

The excretory system consists of a pair of kidneys which lie just
beneath the pericardium and in front of the posterior adductor
muscle. Each kidney consists of two parts, the kidney proper
and the ureter. The former is a dark, thick-walled gland which
lies beneath the ureter and communicates with it at its hinder
end. The ureter is a thin-walled vessel lying above the kidney
proper, with a small external opening in the side of the visceral
mass near the base of the inner gill. Cut off the gills and look
for the external opening; it may be recognized by its white
lips. The kidney also possesses at its anterior end a duct lead-
ing into the pericardial cavity. Slit open the ureter and
kidney proper and observe their inner structure.

Exercise 8. Draw a diagram representing the pericardial cavity
and the kidney, showing the relation of the two structures
to each other. Draw the heart in the pericardial cavity,
showing the relation of the auricle to the gills.

The digestive system. Find the mouth between its two pairs of
palps and place a bristle in it; note the upper and the lower lips,
which connect the upper and the lower pair of palps, respectively.
The mouth is seen to the greatest advantage in a specimen
which has been taken out of both shells. Trace the rectum
from the anus through the heart to the point where it meets

110 INVERTEBRATE ZOOLOGY

the visceral mass. With forceps and knife carefully remove
the tough white integument which covers the left side of the
visceral mass. The soft cream-colored mass filling the greater
part of it is the reproductive gland, the greenish mass above is
the liver. Imbedded in these masses lies the alimentary tract, a
narrow, delicate tube, which will be injured in the dissection
unless the greatest care be taken. Beginning with the mouth
gently scrape away the soft mass which surrounds the alimen-
tary tract, laying it entirely bare. The water in the dissecting
pan must be frequently renewed to keep it clear, and great care
taken not to break the canal. The mouth opens into the short
cesophagus, after which the canal dilates to form the stomach.
The liver surrounds the stomach and is connected with it by
several ducts. Back of the stomach is the intestine, which first
runs backward and downward to the posterior part of the
visceral mass, after several turnings in the lower part of which
it bends upward and runs forward parallel with the posterior -
margin of the visceral mass to its dorsal border, where it leaves
it. Here the rectum begins and passes through the heart and
above the posterior adductor muscle to the anus. A small
transparent rod is often present in the intestine; its function
is unknown.

Clams feed upon minute organisms and organic particles
contained in the water. Some of the water in the mantle
cavity is drawn into the mouth by the ciliated oral palps and
passes through the alimentary tract, where the organic sub-
stances are digested and absorbed.

Bxercis? 9. Draw a diagrammatic view of the digestive system.

The reproductive system. The sexes are separate. The repro-
ductive glands (testis or ovary) are very similar to each other and
consist of a pair of cream-colored masses which fill a greater
part of the visceral mass. Their external openings are a pair
of minute pores, one on each side of the visceral mass just

A HARD-SHELL CLAM 111

below and in front of the opening of the ureter. They can
often be located by pressing out from them eggs or sperm.

The nervous system consists of three pairs of ganglia — the
cerebral ganglia or brain, the pedal ganglia, and the visceral ganglia,
and the nerves proceeding from them; each of the last two pairs
is joined with the brain by a pair of nerve-connectives.

First find the visceral ganglia. They are a small pinkish
mass on the ventral surface of the posterior adductor muscle,
with nerves radiating in all directions. Two of these nerves,
the cerebro-visceral connectives, will be seen passing forward, one on
each side of the visceral mass.

Find next the brain. It consists of a pair of pinkish ganglia
situated above the mouth, just behind the anterior adductor
muscle. The two ganglia are not so close together as are
those of the visceral pair; they lie on each side of the muscle
and are united by a commissure. Each ganglion sends out
three large nerves — the cerebro-visceral connective, which goes to
the visceral ganglia, the cerebro-pedal connective, which goes to the
pedal ganglia, and the pallial nerve, which passes to the mantle.
Find these nerves.

The pedal ganglia form a nervous mass buried in the foot
near its base. They must be sought by cutting into the foot
near its base and may be recognized by their pink color. In
contact with them is a sense-organ called the otocyst.

Exercise 10. Draw a diagram representing the nervous system.
Make several transverse sections with a razor through the

region of the heart of a clam which has been previously hardened.
Identify all the organs which appear.

Exercise 11. Draw a diagram representing a cross section; care-
fully label all the organs.

112 INVERTEBRATE ZOOLOGY

GASTROPODA

A PULMONATE GASTROPOD. A LAND SNAIL (Helix pomatia)

This snail is very common in Europe, in many parts of which
it is used for food. It is imported into this country for the
same purpose and may be obtained at small cost in New York
and Philadelphia. It is especially adapted for dissection, but
any large Helix may be used instead. The large slug (Limax
maxima) is very similar to Helix in structure and may also be
used, but as it has no coiled shell that feature of the dissection
would be omitted.

The snail is a terrestrial animal and feeds principally upon
leaves. It hibernates in the winter under stones and logs after
having first closed the mouth of its shell with a thin disc of
calcified slime called the epiphragma. If it is still in winter
quarters, when obtained, the epiphragma should be removed
and the animal placed among fresh leaves in a warm room,
when it will soon come out of its shell and begin to feed.
Snails are best killed for dissection by drowning. They should
be placed in a large covered jar of water, when they will die
expanded in from one to two days. If the air be first boiled
out of the water the process will be accelerated, but the animal
should not be placed in water which is still hot.

Study the external characters of the animal. Its body is
unsegmented and is covered with a shell, but unlike the shell
of the pelecypod that of the snail is a univalve. As in
other mollusks, the shell is the cuticula of the animal charged
with calcareous salts, and forms an exoskeleton. In shape the
shell is an elongated cone which has been twisted to the right,
forming a closely coiled spiral. The tip of the spiral is called

A LAND SNAIL 113

the apex, the opening is called the mouth, and its axis, the
columella. How many turns does the spiral make? The apex
corresponds to the umbo of the lamellibranch; it is the oldest
part of the shell, the point from which its growth has proceeded.
Note the parallel lines of growth. The ventral edge or mouth
of the shell is thus its youngest part. The animal can with-
draw its entire body within the shell, but when it is walking
or feeding it protrudes its head and foot. The visceral mass, how-
ever, containing all of its viscera, is always covered by the shell
and has thus its exact shape, i.c., it is an elongated cone which
has suffered a dextral twisting so as to form a closely coiled
spiral. As a matter of fact, however, it is the visceral mass
which has been primarily twisted; the shell is twisted because
it covers the visceral mass. If the spiral were to be imagined
uncoiled and extending straight up above the foot, the apex
would be the uppermost and the foot the lowermost portion of
the body; the apex is thus, morphologically, the dorsal and the
foot is the ventral aspect of the animal.

As in the pelecypod, the. visceral mass is enclosed in a
mantle, which is a fold of the dorsal integument, but unlike the
pelecypod it is a single fold and not a double one. This
fold falls about and covers the visceral mass on all sides, as
does a thimble the finger it is on, and secretes the shell on its
outer surface. The ventral edge of the mantle is provided
with muscles, so that it can be protruded beyond the mouth of
the shell or retracted within it. This edge is called the collar.
Find it in your specimen. On the right side of the animal note
the deep notch and the round hole in the collar. This is the
respiratory pore, which opens into the respiratory chamber. This
chamber is the mantle cavity. Probe it gently and determine
its extent. The animal being terrestrial has no gills, but
respires by means of a lung, which is a highly vascularized
portion of the wall of the mantle cavity. In a live animal note
its power to open and close the respiratory opening.

114 INVERTEBRATE ZOOLOGY

The foot of the animal forms a broad creeping disc, adapted
for locomotion on flat surfaces. Its wave-like undulations may
be observed by causing the animal to walk over a glass plate.
The head, which is wanting in the pelecypods, forms the ante-
rior end of the animal and bears two pairs of hollow, retractile

‘ tentacles, the posterior pair carrying each an eye at its extremity.
The mouth of the animal is between and a little below the
base of the anterior pair of tentacles. Probe it and note the
paired lobed lips. Just beneath the mouth is the broad opening
of the pedal slime gland. Probe it and note the extent of the
gland. On the right side of the head is a straight groove which
extends to a depression just behind the base of the anterior
tentacle. This depression is the common genital pore, the animal
being hermaphroditic. The anus is a small opening just beneath
the respiratory pore at the end of a deep groove. It is not
easily observed from the outside.

Note the asymmetry of the animal. Its spiral twist has been
the cause of the loss of the primitive bilateral symmetry of the
visceral mass and shell. They are not borne squarely above
the foot, but obliquely and to the left. The respiratory pore
(i.e., the opening of the mantle cavity) and the anus have not
a median posterior position, as must have been the case in the
primitive ancestor of the animal, but have suffered displace-
ment to the right side. Other instances of asymmetry will be
noticed as the dissection proceeds.

Exercise 1. Draw a side view of the animal seen from the right
side as it appears when it is moving and when the head
and foot are out of the shell, and label the parts above
mentioned.

Exercise 2. Draw a similar sketch of a front view of the animal.

Remove the dead animal from its shell in the following way:
place it for five minutes in strong alcohol, or for half a minute

A LAND SNAIL 115

in very hot (not boiling) water, in order to loosen the shell;
twist it then out of the shell; this must be done very gently,
otherwise the animal will be torn.

Exercise 3. Draw the shell showing its opening on the right.

Break off a portion of the edge of the shell and examine the
broken edge with the aid of a hand lens. Note the three layers
which compose the shell—the inner pearly layer, which has been
secreted by the entire surface of the mantle; the thick middle
layer and the thin outer layer or periostracum, which have been
secreted by the collar. The periostracum is a horny, uncalci-
fied layer, which gives the color to the shell.

The internal organs. ‘Take the snail, deprived of its shell, in
the hand, and, remembering that the outer side of each whorl
of the spiral is on the left side of the animal and that the inner
side of the whorl is on the right, observe the extent of the
mantle cavity. Put the blow-pipe through the respiratory pore
and blow into the mantle cavity. It will be seen to extend
from the collar to the posterior side of the first whorl. Exam-
ine the mantle wall with a hand lens and against the light.
The network of blood vessels will be seen, which constitutes
the lung. On the hinder border of the mantle cavity note the
kidney, an elongated, light-colored, triangular organ; just in
front of it and beneath it, z.e., between it and the mantle cavity,
is the heart within the pericardium; note the two chambers of the
heart, the dorsal auricle and the more ventrally placed and
larger ventricle. Back of the kidney is the dark-colored liver,
which, with the intestine and the light-colored reproductive tract,
occupies the remainder of the coils of the spiral. Note the
rectum, a broad tube on the inner (right) border of the mantle
cavity going to the anus. Cut a small hole in it, and through
this pass a probe to the anus.

The mantle cavity. Lay this open in the following way: with
fine scissors cut through the collar at the respiratory pore ;

116 INVERTEBRATE ZOOLOGY

then make an incision in the mantle wall from this opening
following the collar round the outer side of the whorl to the
heart; continue the incision across the artery leading out of
the heart, and through the delicate membrane between the liver
and the kidney to the rectum, at the inner border of the whorl.
The mantle can now be laid back and its cavity with the organs
exposed. The broad rectum will be seen running along the
entire inner border of the mantle cavity. Make, now, an addi-
tional incision from the respiratory pore along the inner (lower)
border of the rectum as far as the kidney. Lay back the mantle
and pin it down as flat as possible under water. Identify the
heart within the pericardium, the kidney, and the rectum.

The respiratory and circulatory systems. Observe the lung, the
network of blood vessels in the inner surface of the mantle, and
the large pulmonary vein, which runs along the kidney to the
heart. Slit open the pericardium. The two chambers of the
heart will be more distinctly seen, the thin-walled auricle into
which the vein runs and the larger ventricle. Back of the latter
the aorta passes into the viscera; its cut end will be seen.

The process of respiration and circulation is the following:
the air is drawn into the mantle cavity through the respiratory
pore; this is accomplished by the alternate enlarging and con-
tracting of the cavity by means of the muscular body-wall which
constitutes its floor. Notice the longitudinal and the trans-
verse muscles in this floor. The blood circulating in the lung
is oxygenated and passes into the heart through the pulmonary
vein as arterial blood. It is forced by the heart through the
aorta, and thence through arteries to all parts of the body,
whence it returns through blood lacune to the lung.

The excretory system. The large kidney has already been seen.
It is a sac, the glandular projections of the walls of which
almost fill its lumen. As is the case with pelecypods, the
kidney communicates with the pericardial space through a fine
canal and also with the mantle cavity by means of a ureter.

A LAND SNAIL 117

The pericardial canal is opposite the ventricle and cannot be
seen easily. The ureter may be easily traced. It is a wide
canal which leaves the kidney at its forward end near the place
where the pulmonary vein approaches the kidney; it first runs
along the inner side of the kidney to its hinder end; here it
doubles on itself and passes forward to the inner edge of the
mantle, where it runs beside the rectum to a point near the
respiratory pore dnd opens into the mantle cavity.

It will be noticed that the heart and the kidneys are
both asymmetrical organs. The heart has but one auricle; it
will be remembered that in the pelecypod the auricles
are paired organs ; one of the pair must thus be wanting in
the snail. There is also only one kidney and one ureter,
instead of a pair of each, as in the pelecypod. It is the left
member of the pair in each case which is wanting.

Exercise 4. Draw a view of the inner surface of the mantle on a
scale of 38, showing the organs mentioned above; label all.

The digestive system. Pass a bristle through the anus into the
rectum in order to mark it. With two strong pins firmly fasten
the extreme forward end of the animal’s foot and also its hinder
end to the wax of the dissecting pan. With sharp, fine scissors
cut through the floor of the mantle cavity and the collar in the
median line ; carry the incision forward in the median line along
the head between the base of the tentacles to the mouth. Care
should be taken in making this incision not to cut the organs
beneath. Spread the flaps as widely as possible to the right
and left and pin them down, exposing thus the organs in the
forward part of the body.

The white organs on the right side of the body belong to the
reproductive system. The large dark organ in the center, or
on the animal’s left, is the stomach. Find the slender curved
esophagus which leads forward from it to the dorsal side of the
large muscular pharynx. The cesophagus is encircled by the

118 INVERTEBRATE ZOOLOGY

white nerve collar, the dorsal portion of which is the brain. If,
however, the animal died in a retracted condition the pharynx
may have slipped back through the nerve collar, which would
then encircle the forward end of that organ. Note the two
white, leaf-like salivary glands which lie close against the wall
of the stomach, and trace their ducts forward to the pharynx.
Lying above and across the cesophagus is the white cylindrical
penis, which will be seen to extend from the genital pore at
the right of the mouth and to bend sharply on itself. The
bend of the penis is connected by a long retractor muscle to
the dorsal body-wall. Find it; cut it and pin the penis on the
animal’s right. Note the broad, glistening retractor muscle
connecting the pharynx with the ventral, posterior body-wall.
Notice its shape; with strong forceps pull it loose from the
pharynx and entirely remove it. Also beneath it, note the still
larger retractor muscle running from the forward end of the
head back to the same locality. What is the function of these
different retractors? The dark-colored sheaths and the retractor
muscles of the tentacles will also be seen; trace these muscles
to their origin. Find the nerve which passes from the brain
into each tentacle.

Separating the delicate filaments connecting the stomach with
the surrounding organs, and pushing it and the cesophagus to
the animal’s left, find the large nervous mass which forms the
ventral portion of the nerve collar, and the nerves radiating
from it. It is an agglomeration of ganglia, being made up
principally of the pedal and the visceral ganglia. Press the repro-
ductive organs to the animal’s right and pin them down. The
receptaculum seminis, a small spherical body the size of a shot, at
the end of a long tube, will be found in a bend of the intestine,
from which it must be separated.

We turn now to the other end of the intestine. Trace the
rectum from the anus to the point where it is surrounded by
the liver and carefully dissect away the integument which covers

A LAND SNAIL 119

the inner surface of the whorl. The light-colored hermaphroditic
gland will be exposed. Remove, then, the delicate integument
which covers the outer surface of the whorl, and the dark-brown
liver will be exposed. Press the liver away from the intestine
and completely free it, without, however, breaking either liver
or intestine. Great care should also be taken not to injure the
hermaphroditic gland, which is the yellowish mass on the inner
side of the last whorl, or the hermaphroditic duct leading away
from it. Note that the liver is composed of two masses, the
smaller of which is of spiral form and occupies the apex of the
shell; the larger is subdivided into three lobes. Note also
the two main bile ducts which join the liver with the intestine.
The visceral artery will be seen lying upon the liver, sending
branches off on both sides, and must not be confused with
the bile ducts, which it resembles in appearance. It carries
blood from the aorta to the top of the spiral, supplying all the
organs of the visceral mass. At the point where the bile
ducts communicate with the intestine that organ makes a
sharp turn.

Spread out the digestive tract to the animal’s left and pin it
down, without, however, removing or breaking the hermaph-
roditic gland or duct. The stomach will be seen to extend
nearly to the liver. It is succeeded by the intestine, which
soon makes the sharp turn above mentioned, receives the bile
ducts, and passes into the rectum at the right side of the
mantle cavity.

Exercise 5. Draw an outline of the alimentary tract from the
mouth to the anus on a scale of 2 and label all its
parts.

Study the structure of the pharynx. Pass a probe into the
mouth and notice the extent of the pharyngeal cavity. Notice
the transverse horny jaw in the roof of the mouth. With a
sharp knife split the dorsal pharyngeal wall, taking care not to

120 INVERTEBRATE ZOOLOGY

injure the nerve collar or reproductive organs. Notice that the
connection of the cesophagus and the salivary ducts with the
pharynx is near the dorsal wall of the latter organ. Observe
the thick muscular tongue, the organ by means of which the
animal grinds its food. Its surface is covered with a ribbon
set with small teeth, called the radula. This can be easily
pulled off with forceps. Mount it on a slide in water or
glycerine and study its surface under a high power of the
microscope.

Exercise 6. Make a drawing of several of the teeth.

The reproductive system. The snail is hermaphroditic, but is
not self-fertilizing. The hermaphroditic gland, which at different
times produces both spermatozoa and ova, is situated on the
inner side of the smaller lobe of the liver. The hermaphroditic
duct is a delicate, white, convoluted tube, which goes from the
hermaphroditic gland to the albuminous gland, a large white body
lying near the liver. From this organ the oviduct and vas
deferens pass forward to the genital opening near the mouth.
These canals are side by side and connected with each other for
the first part of their course, but may be distinguished by the
character of their walls, the oviduct having folded glandular
walls, while the vas deferens is a narrow tube with thin walls.
It is through the latter canal that spermatozoa pass out from
the hermaphroditic duct, while the ova pass out through the
oviduct, the glandular walls of which, together with the albu-
minous gland, secrete the albumen which surrounds them when
they are extruded. Near their forward end these two canals
separate. The oviduct loses its glandular walls, becomes cylin-
drical in shape, and expands to form the vagina. This is a thick-
walled vessel with which are connected the following accessory
genital organs: the receptaculum seminis, a small spherical organ,
already mentioned, lying in the bend of the intestine and joined
with the vagina by means of a long tube which lies along the

A LAND SNAIL 121

oviduct; the mucous glands, two bunches of tubular glands; and
the dart-sac, a thick-walled sac which contains a calcareous spicule.
Identify these organs.

The vas deferens, after separating from the oviduct, passes
under the retractor muscles of the tentacle to the distal end of
the penis. This organ has already been noted; it is tubular in
shape and lies in a bent position across the wsophagus. A
retractor muscle inserted at the bend connects it with the dorsal
body-wall. At the point where the vas deferens meets it is the
flagellum, a long, tubular sac into which spermatozoa pass from
the vas deferens and where they are massed together to form
spermatophores. Both penis and vagina communicate, side by
side, with the genital cloaca, which opens to the exterior through
the common genital pore.

When two animals pair each receives a spermatophore from
the other. This passes into the receptaculum seminis, which
is thus filled with the spermatozoa of the other animal, and
these finally fertilize the eggs as they pass into the vagina from
the oviduct.

Exercise 7. Make a semidiagrammatic drawing of the reproduc-
tive organs on a scale of 2.

Split the dart-sac and take out the dart; mount it on a
slide in water or glycerine and examine it under a compound
microscope.

Exercise 8. Draw the dart.

The nervous system. Sever the cesophagus and remove the
reproductive and digestive systems, leaving the pharynx in
the body and taking care not to injure any of the nerves. The
principal ganglia are contained in the nerve collar. The two
supraesophageal ganglia, which constitute the brain, will be seen
joined by a broad transverse commissure. From their anterior
surface nerves run to the tentacles, and from their inner

122 INVERTEBRATE ZOOLOGY

surface a pair of nerves runs to the posterior end of the
pharynx, where they meet a pair of small pharyngeal ganglia.
The supracesophageal ganglia are connected by broad connectives
with the subcsophageal ganglia. Remove the pharynx from the
body. By slightly scraping the subcesophageal ganglia with a
small scalpel, it will be seen to consist of two principal gan-
glionic masses. The forward mass is a pair of ganglia, the
pedal ganglia; the hinder mass consists of the large visceral ganglia,
at the side of which is the pair of small pleural ganglia. Observe
the nerves radiating from the subcsophageal ganglia, and
determine so far as possible to what organs they go.

Hxercise 9. Make a semidiagrammatic drawing of the nervous
system.

Organs of special sense. The eyes of the snail at the end of the
posterior tentacles have already been noted. They are easily
seen in a large animal which has its tentacles extended. The
snail is also provided with a pair of auditory organs. They
consist of two small sacs imbedded in the pedal ganglia. In
order to see them cut off the subcesophageal ganglion, mount
it in glycerine and examine it under a compound microscope.
The auditory nerves are very delicate and come from the supra-
cesophageal ganglia.

A SQUID 123

CEPHALOPODA
A DIBRANCHIATE CEPHALOPOD. A SQUID (Loligo pealii)

The squid is a very common marine animal. It is social
in its habits and swims about in large schools in search
of its food, which consists of crustaceans, small fishes, etc.
When alarmed by the presence of its natural enemies, which
are many kinds of fishes, it clouds and darkens the water
by ejecting into it an ink-like fluid. The fresh animals are
studied with greater profit than those which have been pre-
served in alcohol, as this changes the nature and appearance
of many of the organs; if they must be preserved, formalin
should be used.

External anatomy. Observe the cylindrical, bilaterally sym-
metrical body; at one end is a pair of broad fins, and at the
other, the movable head bearing ten arms, two of which are
much longer than the others. The mouth is at the base of and
surrounded by the arms, and the brown horny beak may usually
be seen protruding partly from it. The large eyes are on the
sides of the head at the base of the arms. Lach is covered by
a cornea, which is pierced by a small hole between the eye and
the base of the arms, so that sea water is admitted freely
into the space between the cornea and the pupil, and may
take the place of the aqueous humor of the vertebrate eye.
A transverse fold on the side of the head between the eye
and the body is the olfactory organ. Observe the pigment
spots or chromatophores which are distributed over the body;
they are constantly changing in shape and size during life,
causing corresponding changes in the color and appearance of
the animal.

124 INVERTEBRATE ZOOLOGY

The head and neck project from the large mantle cavity, into
which they can be partially withdrawn by means of powerful
retractor muscles, in very much the same way that a snail’s
head and foot can be withdrawn into its shell. The siphon or
funnel, a large funnel-shaped organ at the base of the head, also
projects from it and can be similarly withdrawn. Gently probe
the mantle cavity and determine its extent. The mantle con-
stitutes the outer surface of the body. It will be seen to be a
cylindrical structure with thick, muscular walls, within which
lie all the viscera of the animal; its free edge is called the
collar, as in the snail. It is also necessary to observe that the
mantle is not a paired organ, as it is in the clam, but an
unpaired one as in the snail. The squid has no foot, as has
the clam or the snail, but morphological equivalents of the
foot are present in the arms and the siphon.

Since in all mollusks the foot or its equivalent occupies a
ventral position, and the visceral mass a dorsal position, the
arms of the squid, together with the head, must be on its
ventral side, and the opposite end with the broad fins must
be dorsal; the animal is thus enormously extended dorso-
ventrally. It will be readily seen also that the mantle falls as
a cylindrical fold from the dorsal end about the entire body,
exactly as it does in the case of the snail. In fact, if the
coils of the snail’s visceral mass could be straightened out,
the mantle would fall as a cylindrical fold from its dorsal end
and terminate in the collar below, in the same way as in the
squid. The morphologically posterior side of the animal is
that on which the siphon is situated, the anterior side is the
opposite one. In common parlance, however, the head end
of the squid is called the forward end, and the fin-bearing
end, the hinder. The side bearing the fins is likewise called
the upper side or back, and the opposite side, on which is
the siphon, the under or lower side. These terms, although
incorrect in a strictly morphological sense, are much more

A SQUID 125

convenient for general use and will be employed hereafter in
these directions.

The mantle of the squid does not secrete an external shell as
does that of the snail and the clam; in a long pocket on the
upper side, however, is an elongate, horny structure, called the
pen, which is secreted by the mantle and is the equivalent of
the shell of other mollusks.

Make a short shallow incision in the upper surface of the
mantle, beginning with the collar. Turn the flaps aside and
note the brown, horny pen lying beneath. Do not remove it at
present, as the dissection of the parts beneath might be dis-
turbed by its removal.

Exercise 1. Make a drawing of the underside of the animal.

Note that the arms may be divided into a right and a left
group, each containing five arms. Observe a single arm; how
many rows of suckers has it? Observe the structure of a
sucker. Note the difference between the two long arms and
the others in the place of origin and the arrangement of the
suckers.

The mantle cavity. Open the mantle cavity by a longitudinal
incision through the thick mantle wall of the under side of the
body to one side of the median line, running from the collar to
the apex of the animal, taking care not to injure the delicate
organs within. Notice, in the first place, that the collar is
not attached to the head at any point of its circumference;
and also that on the inner surface of the mantle, on the upper
side of the body in the median line and also on each lateral
surface, there is an elongate, cartilaginous structure which
fits into a corresponding cartilage on the body, an arrange-
ment which enables the collar to be applied very closely to
the head.

Place the animal in water with the head away from you and
pin down the flaps of the mantle. Observe the soft visceral

126 INVERTEBRATE ZOOLOGY

mass Within it, and notice that it is fused with the mantle only
in the median line of the back; also that the pen, which is
imbedded in the mantle, protects the viscera on that side.
Observe the siphon and probe it. It will be seen to be a funnel-
shaped tube communicating between the mantle cavity and the
outside. Slit it open and observe the flap-like valve at the for-
ward end. Notice the lateral pockets on each side of the siphon
which open toward the mantle cavity and occupy the space
between the siphon and the median line of the back. They
are separated from the siphon by the lateral cartilaginous rods
above mentioned. It will be seen that while water can easily
pass into the mantle cavity from the outside all around the
neck, a contraction of the muscular wall of the mantle would
force the water out through the siphon only, as that which is
forced into the lateral pockets would at once swell them out
and close the spaces at the sides of the siphon. It is, in fact, by
thus shooting the water in the mantle cavity forcibly through
the siphon that the animal swims.

Note the two large retractor muscles of the siphon and beneath
them the two larger retractor muscles of the head.

Observe again the visceral mass; it is covered by a thin,
transparent membrane, the body-wall, the extreme thinness of
which is correlated with the thickness of the mantle which
covers it. If the animal be a female that fact may be known
by the presence of two very large, transversely striated bodies,
called the nidamental glands, which lie near the center of the
body, and are a part of the reproductive system. Carefully
remove these in order to expose the organs beneath. If the
animal be a male (and the student should obtain a male if pos-
sible), it can be recognized by the absence of nidamental glands
and also by the presence of the testis, a large white tubular
organ which lies near the median line toward the hinder end of
the animal. In the female the ovary, which occupies a similar
position, is often very full of the granular ova.

A SQUID 127

Notice in the mantle cavity the pair of plumose gills to
the right and the left of the visceral mass, each attached to the
inner surface of the mantle by a mesentery. Between the
retractor muscles of the siphon and extending from the base
of the gills forward to the siphon is the rectum, which terminates
in the anus, with its two projecting valves. Find the valves.
Beneath the rectum is the ink-bag, and both are attached to the
organs beneath them by a mesentery. The ink-bag communi-
cates with the rectum by means of a duct which joins it near
the anus; this duct may be found by slitting the rectum for a
short distance back of the anus, when the small opening may
be made to appear by squeezing the ink-bag and forcing the
ink into the rectum. Together with the fecal matter from
the intestine and other waste products, the ink is voided into
the sea water through the siphon; its function is to cloud the
water and thus hide the animal from its enemies. In the male
animal notice the long, tubular penis to the right of the rectum
(the animal’s left); if the animal is a female, the thick-walled
oviduct will be seen in a corresponding position.

At the base of each gill note a round disc-like body; this is
a branchial heart, from which blood is sent into the gills; near
each branchial heart, toward the median line and running for-
ward alongside the rectum is an elongate, transparent structure,
the kidney. The position of the kidneys may be determined by
the two conspicuous white veins — the precaval veins — which
pass through them longitudinally from one end to the other.
These veins are wide spongy-walled structures which run to
the branchial hearts and will be seen toward the median line
from those organs. Just beneath the base of the two kidneys
and between the branchial hearts is the median or systemic heart,
into which blood pours from the gills. Note a median artery,
the posterior aorta, which leads back from the systemic heart; it
branches into three large mantle arteries, two of which pass to the
right and left, respectively, and enter the mantle at the side,

128 INVERTEBRATE ZOOLOGY

while the other passes into the mantle in the median line; it is
through these arteries that the mantle is supplied with blood.

On each side between the base of the gill and the rectum
and extending parallel with the latter organ, notice again the
delicate kidney; each of the pair of kidneys extends backward
to a point a short distance back of the branchial heart, and
forward to a point back of the base of the ink-bag, where it
communicates with the mantle cavity through a small opening.
Find the two openings by lifting up the body-wall with forceps
and blowing on it with a blow-pipe, when they will appear.

Running back from the branchial heart on each side is a wide
vessel, the postcaval vein; the forward end of this vein has thick,
spongy walls like those of the precavals and is easily seen;
the greater part of it, however, has extremely thin walls and
can be seen with difficulty. Near the base of each gill note
also a vessel which runs forward and laterally into the mantle;
this is the mantle vein. Just back of this vein is a muscle
which connects the gill with the mantle; it is the branchial
retractor muscle.

Note the two large stellate ganglia in the forward part of the
inner surface of the mantle, and the radiating nerves which
each ganglion sends into the mantle.

In the hinder portion of the visceral mass in the male animal
observe on the animal’s left (the observer’s right), just behind
the branchial heart, a coiled tube, the vas deferens, and in the
female the thick-walled oviduct. Extending farther back and
near the median line is the large white testis in the male and
the large ovary in the female.

Exercise 2. Make a large sketch of the mantle cavity of the
animal showing these organs, and label all.

With fine scissors and forceps carefully dissect away the deli-
cate transparent body-wall and expose the organs beneath,
taking care not to injure them.

A SQUID 129

The excretory system. The kidneys and their external openings
have already been observed. As in other mollusks, the kidneys
also communicate with the pericardial space.

The circulatory and respiratory systems. Pushing aside the
organs which partly conceal it, observe again the systemic heart ;
note its shape and slightly asymmetrical position. Extending
from its forward end is the anterior aorta, which takes blood to
the forward part of the body; its course cannot be followed at
present. The hinder part of the body is supplied with blood by
the posterior aorta. This vessel, as we have already seen, leaves
the hinder end of the systemic heart; it sends off two pairs
of small arteries to the stomach and to other viscera, and then
branches into the three mantle arteries already mentioned. Find
them all and trace them as far as possible. Observe again the
two branchial hearts. Note the branchial artery, by which blood
passes from the branchial heart to the gill; also the branchial
vein, through which it passes into the systemic heart.

Observe again the veins which bring the blood to the bran-
chial hearts. The precavals bring blood from the forward part
of the body. Trace them forward. They enter the kidneys
near the forward end of those organs and traverse their glan-
dular walls back to the branchial heart. Press aside the rectum
and the forward end of the kidneys, and observe where the
two precavals come from beneath and enter the kidneys. With
fine scissors cut the connective tissue which binds the veins,
and also the mesentery which holds down the rectum and the
ink-bag, and turn these organs back. ‘Trace the two precavals
forward; they will be seen to come from a delicate median
vein which may be followed into the head. Observe again
the postcaval veins, which bring blood from the hinder part of
the body and join the branchial hearts near the same place
as the precavals. Their forward ends also traverse the glan-
dular walls of the kidneys and are here conspicuous; back of
these they are much wider, but are very thin-walled and not

130 INVERTEBRATE ZOOLOGY

easily seen. Trace them as far as possible. Observe again
the mantle veins, which bring blood from the mantle to the
branchial hearts.

The course of the blood is the following: it enters the bran-
chial hearts through the postcaval, precaval, and mantle veins;
the contraction of these hearts sends it into the branchial
arteries which pass along the upper side of the gills; it then
traverses the delicate transverse filaments of the gills and
becomes oxygenated, when it collects again in the branchial
veins on the opposite side of the gills; through these it passes
to the systemic heart, whence it is sent through the anterior
and posterior aortas to the different parts of the body.

Exercise 3. Make a diagrammatic drawing of the circulatory and
the respiratory systems.

The digestive system. Remove the kidneys and precaval veins.
Beneath them will be seen a large glandular bilobed organ of
somewhat doubtful function, called the pancreas. At its forward
end a pair of cylindrical organs, the liver ducts, will be seen enter-
ing it from the liver. The pancreas is made up of anastomosing
glandular projections of the walls of these ducts. Remove the
gills, branchial hearts, systemic heart, and hinder arteries. The
delicate body-wall should be completely removed from the entire
visceral mass, and great care be taken not to injure the stomach
pouch beneath. This latter organ is a large bag with thin
transparent walls which extends to the extreme hinder end
of the body; beneath it will be seen the large testis or ovary,
according to the sex of the animal. This pouch is not really a
part of the stomach, notwithstanding its name, but is a reser-
voir for the secretions of the liver, which communicates with it
through the liver ducts. Carefully loosen the stomach pouch
without separating it from the body and let it float in the water
of the dissecting pan. It communicates with the thick-walled
stomach, which lies just in front of it, but food substances are

A SQUID 131

prevented from passing into it from the stomach by valves.
Loosen the stomach, noticing that it is bound to the ovary or
testis by an artery, the genital artery. At the forward end of
the stomach are the intestine and the esophagus, side by side;
the former passes between the two halves of the pancreas and
ends with the rectum; the cesophagus goes forward side by side
with the anterior aorta to the middle of the large liver and
passes through it in company with the aorta. The cesophagus
is easily found by turning the stomach over. A small ganglion
with radiating nerves will be seen by the side of the esophagus
near its junction with the stomach.

The liver is an elongated body lying between the retractor
muscles of the head and of the siphon; two ducts emerge
from it and pass through the pancreas to the stomach pouch.
Loosen and remove the connective tissue around the liver and
raise it up; the cesophagus and the aorta will be seen to pass
through it towards the back of the animal and then forward to
the head.

Remove the siphon and split the wall of the head; trace the
esophagus to its forward end. It will be seen to pass through the
ganglionic mass which constitutes the central nervous system,
and which is surrounded by a hard cartilaginous capsule. For-
ward of this it meets and ends in the bulbular pharynx. Near
the forward end of the liver, and resting upon the esophagus,
will be seen the median salivary gland, the duct of which may be
traced to the pharynx; near the hinder end of the pharynx is
a pair of smaller salivary glands, which also communicate with it.
Trace their ducts to the end. The alimentary canal will thus be
seen to consist of the following organs: the muscular pharynx,
with which a pair of small salivary glands and a single large
salivary gland communicate; the narrow esophagus; the thick-
walled stomach; the stomach pouch, which communicates with the
stomach by a valved opening; the elongated liver, which com-
municates with the stomach pouch by two long ducts; the bilobed

132 INVERTEBRATE ZOOLOGY

pancreas; the intestine, which leaves the stomach near the point
where the cesophagus enters it; the rectum, which is joined by
the ink-bag and passes to the anus.

Exercise 4. Take the alimentary tract out of the body, pin it
down, and make a drawing of it; label all its divisions.

Slit open the stomach and examine its ridges. Slit open the
pharynx on the upper side; note the large chitinous jaws and
the radula. The latter organ, like the radula of snails, is used
in chewing the food; examine its surface under a microscope
and note the calcareous teeth.

Exercise 5. Make a drawing of the jaws.

Exercise 6. Draw several of the teeth of the radula.

The reproductive system; the male. The principal genital organs
have already been observed. The single median testis is a large,
flat organ, dorsal to the stomach pouch, in the hinder portion of
the visceral mass; the genital artery joins it with the surface
of the stomach. The testis has no direct connection with
the vas deferens, but is surrounded by a thin transparent mem-
brane within which it lies as in a capsule, and into which the
spermatozoa escape. The vas deferens, which is also unpaired,
communicates with this capsule. It is a long and much-twisted
tube with several wide glandular regions, and lies, bound by
connective tissue into a compact mass, on the left side of the
viscera. Take the entire system out of the body, put it in
water, loosen and straighten out, so far as possible, the con-
volutions of the vas deferens. Beginning with its hinder end
we find first a narrow, convoluted tube, then follows a thicker
tubular portion, the vesicula seminalis; near the forward end
of this portion is a glandular body, the prostate gland, and a
membranous sac; a long, straight, narrow portion comes next,
which widens to form the spermatophoric sac, within which

A SQUID 133

the spermatophores are formed; then follows the tubular penis,
which forms the forward end of the tract and has already been
observed lying in the mantle cavity to the left of the rectum.

Exercise 7. (2) Make a drawing of the male genital tract.

Exercise 7. (1) Open the spermatophoric sac and look for
spermatophores ; they are slender, white objects about half
an inch long. Mount several on a slide and make a draw-
ing of one.

The female. The single ovary, like the testis, is a large
elongated gland occupying the hinder end of the visceral mass
and surrounded by a capsule. The oviduct communicates with
this capsule; it passes forward along the left side of the visceral
mass, its walls becoming thickened in its course to form the
oviducal gland, and opens into the mantle cavity by means of a
large thick-lipped aperture to the left of the rectum.

Two pairs of prominent accessory glands are present in
the female, the large, white, finely striated nidamental glands,
which cover up most of the other organs of the visceral mass,
and beneath them the much smaller accessory nidamental glands,
which are pink-colored in life and lie to the right and left
of the rectum; both pairs of glands open at their forward ends
into the mantle cavity. These glands secrete the egg-capsules
which protect the eggs after they are laid, and while develop-
ment is going on within them.

Exercise 7. (c) Make a drawing of the female organs.

The nervous system. In the position of the principal ganglia
the squid resembles the snail, but these ganglia are difficult to
observe in a dissection because they are compactly massed
together and are protected by a cartilaginous capsule which
forms a sort of skull. The cerebral or supracesophageal ganglia
form a large mass above the cesophagus ; broad commissures

134 INVERTEBRATE ZOOLOGY

join it with the subcesophageal mass, which is composed of the
visceral, pedal, and in front of the latter, the brachial ganglia.
Connected with the sides of the cerebral mass are the two optic
nerves, which widen out to form the large optic ganglia, and run-
ning forward from it are two small nerves which connect it
with the suprapharyngeal ganglia, a small mass above the hinder
end of the pharynx. From these ganglia small nerves pass
around the csophagus to the pair of subpharyngeal ganglia.
From the forward surface of the subcesophageal mass, é.e., from
the brachial ganglia, ten nerves pass off to the arms. These
may be seen on the inner surface of the head after the removal
of the pharynx. From the hinder surface of the visceral
ganglia pleural nerves run to the stellate ganglia in the mantle.
Trace these nerves from the stellate ganglia to their source.

The pen. Make a longitudinal slit in the mantle on the back
of the animal and remove the pen; it will be seen to lie quite
loosely in its sac.

Exercise 8. Draw the pen.

CHAPTER VI
TUNICATA

ASCIDIACEA
A SIMPLE ASCIDIAN (Mo/gu/a)

Ascidians are sessile, marine animals which live attached
to rocks, seaweed, and other objects in the waters along our
shores. Many ascidians are colonial animals; the young indi-
viduals, which arise by a process of budding, remaining attached
to the parents. Ina colony which is thus formed certain organs
are often possessed in common, and a very intimate relation is
established between its individual members. Molgula is non-
colonial; it is usually found in clusters attached to rocks below
low tide.

Molgula is a small saccular animal, an inch or less in length.
Its outer covering is a thick, tough tunic or test, which is charac-
terized by being partly composed of cellulose, a substance rarely
met with in animals. The surface of the tunic is covered with
numerous minute projections, among which sand and dirt lodge
and cause the dirty appearance which characterizes it, except
where it is in contact with that of other individuals.

The animal has: two external body-openings, the incurrent
opening or the mouth and the excurrent opening, each of which is
at the end of a projection of the body-wall called a siphon and is
fringed by short tentacles. The tentacles may, however, have
been drawn into the openings and thus not be apparent. The
incurrent siphon is at the anterior end of the body, the excur-

rent siphon represents the morphologically posterior end; the
185

136 INVERTEBRATE ZOOLOGY

portion of the body lying immediately between the two is the -
dorsal side; the opposite side, which is very much longer and
includes the surface of attachment, is the ventral side. A
stream of water is drawn into the incurrent opening, bearing
the minute organisms which constitute the animal’s food and
the air needed for respiration; through the excurrent opening
the water is ejected, charged with feecal matter and reproductive
products.

Exercise 1. Make a sketch of the animal on a scale of 2 or 8;
label the dorsal and ventral aspects and the siphons.

Beneath the tunic and in contact with it is the mantle, which
is the remainder of the body-wall, the tunic being a highly modified
cuticula protecting its outer surface. Remove the entire tunic.
This may be easily done by snipping it with scissors and then
pulling it off with forceps; it is not tightly joined with the
mantle. The mantle will be seen to be a transparent structure
through which the internal organs appear. Observe the white
muscle bands in the mantle, especially the transverse and longitudinal
muscles inthe siphons by means of which they are extended
and contracted. Note also the short tentacles at the incurrent
and excurrent openings. Count those at each opening.

The digestive system. The most conspicuous internal organs
are the cream-colored genital glands near the center of the body
and the alimentary canal. The latter lies on the left side of
the body, where it appears as an S-shaped structure which
encloses the former. Place the body in water with the left side
uppermost and the siphons away from you, and study the
arrangement of the organs. The incurrent opening (at your
left) will be seen to have more prominent tentacles than the
excurrent opening. From the base of the incurrent siphon
the large pharynx, the most voluminous organ of the body and
the principal organ of respiration, will be seen extending to the
lower side of the body. Note the six longitudinal ridges which

MOLGULA 137

appear as light-colored bands in the pharyngeal wall. Find
and trace a white or cream-colored line extending in the mid-
ventral line from the base of the incurrent siphon to the opposite
side of the body. This is the endostyle; it is a ciliated and
glandular groove which lies between two folds in the mid-
ventral wall of the pharynx; it extends the length of that
structure and ends posteriorly near the opening of the pharynx
into the @sophagus. Find this point. The cesophagus is short
and communicates with the stomach, and these two divisions
form the lower and thicker limb of the S-shaped digestive
tract. The upper limb is formed by the intestine, which passes
to the base of the excurrent siphon, where it ends with the
anus. Find these organs.

The reproductive system. Molgula is hermaphroditic. The
sexual organs consist of a pair of large hermaphroditic glands, one
of which is seen on each of the lateral sides of the body.
A short duct runs from each gland to the base of the excurrent
siphon. On the left side the duct will be seen alongside the
posterior end of the intestine; find it.

The circulatory system. On the right side of the body beneath
the hermaphroditic gland will be seen the heart in its pericardium.
It is a muscular sac from each end of which proceeds a large
blood vessel. The vessel leaving the ventral end (at the
observer’s right) is called the cardio-branchial vessel; it passes
along the mid-ventral side of the pharynx, beneath (external to)
the endostyle, and gives off branches which run transversely
along the pharyngeal wall. The vessel leaving the dorsal end of
the heart is called the cardio-visceral ; it breaks up into numerous
branches, which ramify among the viscera and other parts of
the body. From the viscera the blood is collected again in
a vessel called the viscero-branchial, which passes along the mid-
dorsal pharyngeal wall and gives off transverse branches.

The heart of tunicates is peculiar in that its pulsations
change the direction of the flow of the blood alternately from

138 INVERTEBRATE ZOOLOGY

the cardio-branchial to the cardio-visceral vessels, and back
again. The contraction of the heart is of a peristaltic nature;
it passes from one end to the other of it for a short time; then
after a short pause the contraction is renewed, the peristaltic
motion beginning at the opposite end and driving the blood
in the opposite direction.

The nervous system. About halfway between the two siphons,
imbedded in the mantle beneath the dorsal surface of the animal,
lies a small ganglion from which nerves radiate. No organs of
special sense are present, except the tentacles and minute eye-
spots at the incurrent and excurrent openings.

The excretory system. Beneath the heart is an elongated vesic-
ular organ which is the single, unpaired kidney; it is ductless.
Beneath the ganglion above mentioned is a small glandular
organ called the subneural gland; it has a duct which communi-
cates with the pharynx. The function of this gland is probably
excretory ; it is supposed to be homologous to the hypophysis
of vertebrates.

Exercise 2. Make a drawing of the left side of the animal on a
scale of from 4 to 6, showing all the internal organs which
appear in that aspect. Label the dorsal and the ventral
sides of the body and all the organs.

Exercise 3. Make a drawing of the right side of the animal
showing all the organs which appear in that aspect.

Bxercise 4. Make a drawing of the dorsal side showing the
organs observed there.

The peribranchial chamber. Cut off the excurrent siphon at its
base and with a needle or bristle probe the opening. The probe
will pass into the large space between the mantle and the
pharynx. This is the peribranchial chamber; it surrounds the
pharynx on all sides, except in the mid-ventral line, and commu-
nicates with the outside water through the excurrent siphon.

MOLGULA 139

It is not a part of the body-cavity, but has been formed by an
infolding of the outer surface of the body. Into it, near the
base of the excurrent siphon, the digestive and genital tracts
discharge their products for removal with the current of
respiratory water which streams out of that siphon.

The respiratory system. The principal respiratory organ is the
pharynx, which communicates with the incurrent siphon by
an opening fringed with a circular row of branched tentacles.
Its walls are pierced by numerous slit-like, ciliated openings,
called stigmata, through which the respiratory water streams
from it into the peribranchial chamber. A current of water is
thus maintained, which passes through the incurrent siphon
into the pharynx, and thence through the stigmata into the
peribranchial chamber, and out again at the excurrent siphon.
The stigmata are vertical in position and are arranged in trans-
verse rows, which extend across the pharyngeal wall, and are
separated from one another by delicate vertical bars; the trans-
verse rows have between them large transverse bars, and running
longitudinally along the pharyngeal wall on each side are six
large longitudinal bars or ridges, which are easily seen and have
already been mentioned. Through all of these bars the blood
circulates, being brought to them either by the cardio-branchial
or the viscero-branchial blood vessels, and respiration is thus
carried on.

Lay the animal with the left side uppermost. Slit open the
incurrent siphon and the pharynx by inserting the point of fine
scissors into the siphon and, after cutting its wall to its base,
carrying the cut through the wall of the pharynx along the side
of and parallel with the mid-ventral line to the posterior end of
that organ. Lay the pharynx open. The twelve large longi-
tudinal bars will be seen projecting into the pharyngeal lumen.
Trace them throughout their entire extent. Find with the aid
of a dissecting microscope or a hand lens the row of branched
tentacles at the base of the incurrent siphon and count them.

140 INVERTEBRATE ZOOLOGY

In the mid-ventral line note the endostyle; notice also that it
is a groove. Trace the endostyle forward to the base of the
siphon. At its anterior end the endostyle is continuous with a
ciliated ridge which encircles the anterior end of the pharynx
and is called the peripharyngeal ridge. This ridge is itself
continuous, on the dorsal side of the animal, 7.e., on the side
opposite to the endostyle, with a ciliated longitudinal ridge called
the dorsal lamina, which passes along the mid-dorsal line to the
opening of the cesophagus at the posterior end of the pharynx.
Trace the peripharyngeal ridge and the dorsal lamina.

These organs aid in the ingestion of the animal’s food, which
consists of minute organisms and particles of organic matter.
The endostyle is a glandular and ciliated groove; the gland-
cells secrete a viscid substance which catches the food particles ;
the cilia create a current which drives them towards the ante-
rior end. Here they meet a current created by the cilia of the
peripharyngeal ridges which takes them around the pharyngeal
wall to the dorsal lamina, along which they are driven poste-
riorly to the opening of the cesophagus.

Between the two siphons note the ganglion and, beneath it, the
subneural gland.

Exercise 5. Make a semidiagrammatic drawing showing the
structures which appear in connection with the pharyn-
geal wall.

Bxercise 6. Make a large diagram of Molgula and show the rela-
tive positions of the different organs; label all.

CHAPTER VII
ECHINODERMATA

ASTEROIDEA
A STARFISH

Several species of starfishes are common along our coasts,
the most familiar being Asterias vulgaris, the common New
England form, which is found along the entire Atlantic coast,
and Asterias forbsii, which is found south of Cape Cod.
They are remarkably sluggish creatures which live on the sea
bottom, moving slowly, often in large numbers, from place to
place and feeding on the various mollusks which come in
their way.

Two specimens will be needed for this dissection, a dried one
for the study of the hard parts, and one that is fresh or has
been preserved in formalin or alcohol for the study of the inter-
nal and other soft parts. To prepare a dried starfish the live
animal should be placed in fresh water for half an hour. It
should then be placed in alcohol for an hour, and then dried
thoroughly. If only preserved material be at hand the animals
may be simply dried. The fresh water and alcohol expand the
body-wall of the animals and prevent it from collapsing after
death.

Study the external characters of a fresh or a preserved speci-
men. Observe the color and the flattened radiate body-form.
The body is composed of a central disc from which radiate five
arms or rays. All of these rays are normally of equal length.

Specimens are often found, however, in which the length of
141

142 INVERTEBRATE ZOOLOGY

the rays is unequal. This is due to the fact that starfishes
often lose one or more of their rays by accident; the missing
member is soon replaced by a new ray, but while it is growing
out it will be shorter than the others. The spaces between
the rays are called interrays. In the center of the under surface
of the disc is the mouth; hence this surface of the animal is
called the oral surface. Its upper surface is called the aboral
surface.

In the aboral surface of the disc notice the red madreporic plate
(in preserved specimens it may have lost its color and be white).
Examine it on the dried specimen with the aid of a hand lens or
the low power of a compound microscope and notice its porous
structure. In the aboral surface is also the anus; it is a very
small opening and will be difficult or impossible to see in the
specimens at hand. Note the short fixed spines covering the
entire aboral surface. Each one is a part of a small calcareous
plate buried beneath the integument. The entire body-wall of
the animal is made up largely of these plates, which give
it its stiffness. The plates are not, however, connected with
one another except by muscles and connective tissue, and the
animal’s arms are, consequently, flexible and freely movable.
Demonstrate this fact with your specimen. In the dried animal
this flexibility no longer appears, as the entire body-wall has been
rendered rigid by the drying. In the soft places between the
plates note the delicate tubular projections of the integument ;
they are the contractile papule, and are organs of respiration and
excretion and possibly also of sensation. With the aid of a
hand lens find, around the base of each spine, the pedicellarie ;
these are minute pincer-like organs of somewhat uncertain func-
tion, but which probably aid in keeping the surface of the
animal free from particles of dirt and from minute organisms
which might be harmful.

The two arms which enclose the madreporic plate between
their bases are called the bivium; the remaining three, the

A STARFISH 143

trivium. How can a plane be passed through the body so as to
divide it into two symmetrical halves ?

Exercise 1. Make a life-size drawing of the aboral aspect of the.
animal and label all the features observed.

On the oral surface observe the deep groove which extends
from the mouth along each arm to its tip. This is the ambulacral
groove. Observe the two rows of movable spines which fringe
each side of the groove; also the five pairs of movable spines
which surround the mouth. Separate these spines and observe
the mouth surrounded by a circular membrane, the peristome.

From the sides of each ambulacral groove two zigzag rows
of soft tentacles project. These are the ambulacral feet; they
are muscular tubes with sucker discs at their ends and are
the organs of locomotion. Scrape the feet from a portion of
the groove and examine its sides; note the slender, transverse,
calcareous plates which form it, and the round openings between
them, called the ambulacral pores, through which branches from
the feet project into the body-cavity. Note the zigzag nature
of each of the two rows of these pores. Notice also the delicate
cord which extends along the median line of the groove; it is
the main nerve of the arm; it proceeds from a nerve ring in the
central disc to the tip of the arm. Follow it to the tip and note
the red pigment spot with which it ends. This is the eye. In
preserved specimens the pigment may have lost its color.

Exercise 2. Make a life-size drawing of the oral aspect of the
animal and label all of these features.

Scrape off several pedicellarize, mount them on a slide, and
examine them under a compound microscope. By pressing on
the cover-glass with a needle, the jaws can be made to open and
shut; try it.

Exercise 3. Draw a pedicellaria on a large scale.

144 INVERTEBRATE ZOOLOGY

Cut off an arm of the dried specimen, and also a bivial arm
of the fresh one, and examine the cut surface of each. The
edge of the calcareous plates will be seen, as well as the spaces
between them. Notice the slender plates which form the sides
of the ambulacral groove ; also just beneath the median ridge, in
the upper part of the apex of the groove, a minute opening.
This opening is the radial canal, which extends the length of the
arm; its function will be explained when the ambulacral system
is described. If a portion of the arm be soaked for a short time
in a strong solution of warm caustic potash, the soft parts will
be destroyed and the plates will be seen more distinctly. Care
should be taken not to allow the potash to act too long or the
arm will fall to pieces.

Exercise 4. Make a sketch of the cut edge of the arm on a scale
of 8, showing the edges of the plates and the radial canal.

Cut off the aboral wall of the severed arm of the dried
specimen and scrape away the remains of the internal organs
and the ambulacral feet. Study the inner surface of the
ambulacral groove. Note the two rows of slender transverse
plates which form the sides of the groove, and on each side
between every two plates, the minute ambulacral pore.

Bxercise 5. Make a drawing on a scale of 3 of the inner surface
of the ambulacral groove, showing the plates and the pores.

Cut off the aboral wall of the central disc of the dried speci-
men, scrape away the remains of the internal organs, and study
the arrangement of the plates in the inner surface of the oral
body-wall. Note the circular mouth protected by converging
spines, also the membranous peristome. Observe the con-
vergence of the five arms about the peristome; also the inter-
radial partitions which separate the base of the arms.

Exercise 6. Make a life-size drawing showing these features.

A STARFISH 145

Internal anatomy. Remove the entire aboral body-wall from
the trivium and the central disc of the fresh or preserved
specimen, with the exception of the madreporic plate which
must not be removed, being very careful not to injure the
organs beneath. Study the internal organs and observe the
following systems:

The digestive system. Observe the large sac-like stomach,
which almost fills the central disc. Its walls are much folded,
and five short, bag-like pouches extend from it into the five
arms. When the animal feeds the stomach is everted and
thrust out through the mouth and about its prey. It is drawn
in again by means of five pairs of retractor muscles, which con-
nect the stomach pouches with the inner surface of the ambu-
lacral grooves. Find the pair of retractors belonging to each
stomach pouch. Communicating with the aboral portion of
the stomach are five large radial digestive glands, which
are usually called livers. Each gland almost fills an arm; it
is made up of two main trunks, from which project numerous
side branches; the two ducts leading from the two trunks in
each arm unite to form a single duct which passes to the
stomach. Each trunk is suspended from the aboral wall of
the arm by two mesenteries. Find the mesenteries in one of
the bivial arms. Study the structure of the livers. The
stomach is connected with the mouth by a short esophagus, and
from its upper surface a short slender intestine passes to the
anus. Connected with the intestine is a small branched diver-
ticulum, the intestinal cecum. The intestine, together with its
cecum, may have been removed when the aboral body-wall was
taken off. If this be the case look for them on the portion of
the aboral wall which was taken off and notice also the position
of the anus.

The reproductive system. The sexes of the starfishes are sepa-
rate. The sexual organs are branched glandular organs, ten in
number, which lie in the proximal portion of the rays and open

146 INVERTEBRATE ZOOLOGY

to the outside through minute pores in the aboral walls of the
interrays. Two glands will be found in each ray extending
from the base of the ray toward its tip. The actual size of
these organs depends entirely upon the sexual condition of the
animal. In young or immature animals they may be no more
than half an inch long or less, while in reproducing animals
they may extend almost to the tip of the ray. The testis of the
male and the ovary of the female animal do not differ from each
other in general appearance. In the mature female, however,
the ovaries have a light-yellow color, while in the mature male
the testes are white and are less voluminous than the ovaries.

Exercise 7. Make a semidiagrammatic drawing of the animal
showing the details of the digestive and reproductive
systems; label all.

Remove the stomach and the reproductive organs from the
body, taking care not to injure the sinuous stone canal which is
at one side of the former.

The ambulacral system. This is the most characteristic system
of organs in the Echinodermata. In the starfish it consists of
the following organs: a circular canal, called the _ring canal,
surrounding the mouth; connected with this canal are nine
minute lobated sacs called the racemose or Tiedemann’s vesicles,
two being located in each interray except the one in which is
the stone canal, where but one is present; five radial canals,
which pass from the ring canal along the median line of the
ambulacral grooves to the tips of the arms; the ambulacral feet,
which are connected with the radial canals by short branch canals,
and also project through the ambulacral pores into the body-
cavity, where they expand to form small sacs called ampulle; a
sinuous canal, called the stone canal, which connects the ring
canal with the madreporic plate; the madreporic plate, a porous
plate by means of which the entire system is placed in commu-
nication with the outside sea water.

A STARFISH 147

In studying this system find first the madreporic plate and
the stone canal, and trace the latter from the madreporic plate
to the ring canal. Remove the spines which project over the
peristome and find the ring canal. It is a delicate tube, of
about the diameter of a needle, which surrounds the mouth,
running around the base of the arms at the point where the
peristome joins them; it is thus, like the radial canals, outside
the body-cavity. Remove some of the ambulacral feet from a
ray, and find again the delicate radial canal which lies along
the middle of the ambulacral groove. Trace it to the ring
canal. Cut the aboral body-wall from one of the bivial rays,
remove the liver, and observe the ampulle. Press them and
notice that the feet are thereby extended.

The ambulacral system will be seen to be a system of tubes
extending throughout the body and in communication with the
sea water. They are filled with a fluid which is not, however,
pure sea water, but is rather a watery serum in which float
amceboid cells. This fluid is driven into the tube-like ambu-
lacral feet, which thereby acquire rigidity and are extended.
The system is the locomotory system of the animal. It moves
by extending the feet, attaching the sucker discs at their ends
to some stationary object, and then drawing them in. The
animal is thus able to pull itself slowly along. The ambu-
lacral system possibly also exercises excretory and respiratory
functions.

Exercise 8. Draw a diagram of the ambulacral system.

There are no special respiratory and excretory organs. These
functions are exercised by the papule and possibly the ambu-
lacral feet.

The nervous system consists of a circumoral nerve ring, which
lies just beneath the ambulacral ring canal, and five radial nerves,
which proceed from it along the median line of the ambulacral
grooves to the tips of the arms. Each radial nerve ends with

148 INVERTEBRATE ZOOLOGY

a pigment eye. ‘There are no other organs of special sense. The
main nerves of the starfish do not lie within the body-cavity, but
in the integument, and can thus be seen from the outside. There
are, however, in addition to these nerves, other less impor-
tant ones which are internal. We have already observed the
radial nerves in the median line of the ambulacral grooves; the
ring nerve can also be seen as a slight ridge just beneath
the ring canal.

Exercise 9. Draw a diagram representing the nervous system.

The circulatory system consists of a very complicated system of
tubes and spaces, filled with a blood fluid, none of which can
be seen in a dissection, except an organ usually called the heart
or axial sinus. This is a tubular sac which will be found beside
the stone canal; within it is an elongated glandular organ
called the axial organ or ovoid gland.

Bzxercise 10. Draw a diagram representing a vertical section of
the animal passing through the madreporic plate and the
anterior ray (t.¢., the middle trivial ray).

A SEA URCHIN 149

ECHINOIDEA
A SEA URCHIN

Several species of sea urchins occur along the Atlantic coast,
the most familiar being Arbacia, the dark-colored urchin, and
Strongylocentrotus, the green urchin, the former having a more
southerly distribution than the latter. The animals live on the
sea bottom or on rocks, usually in companies, and move slowly
about from place to place, using not only the ambulacral feet,
but often the spines as well, as organs of locomotion. They
feed partly upon small animals and partly upon organic sub-
stances present in the sand and mud, which they pass through
the intestine.

Two specimens will be needed for this dissection, a dried one
for the study of the hard parts and a fresh or preserved one for
the study of the internal organs.

Observe the radiate spheroidal body entirely covered with
movable spines. Look among the spines and find the ambulacral
feet. These can be extended in life beyond the spines and are
employed by the animal as organs of locomotion. Note the five
ambulacral areas (those containing the feet), and between them
the five interambulacral areas. The flattened surface is the under
or oral surface, on which the animal moves; the rounded surface
is the aboral. It will be seen that the aboral side of the sea
urchin bears ambulacral feet, whereas in the starfish the oral
side alone bears them.

In the center of the oral surface, observe the mouth and the
five calcareous teeth which project from it. Surrounding the
mouth is a membrane which fills the space between the edges
of the shell and is called the peristome. Notice the ten short

150 INVERTEBRATE ZOOLOGY

ambulacral suckers which surround the mouth, and near them the
five groups of pincer-like pedicellarie. Observe the long slender
stalks of these organs. Near the margin of the peristome are
five groups of ambulacral feet.

Exercise 1. Make a drawing of the oral surface on a scale of 2.

With forceps remove some of the pedicellaria, mount them,
and study them under the microscope. Note the three minute
jaws and the long stalk. Press on the cover-glass and cause
the jaws to open and shut.

Exercise 2. Make a drawing of a pedicellaria.

Study the structure and method of articulation of the spines.
Pull off several and notice their ball and socket joint, also the
delicate muscles by which they are moved. Notice the fluting
of the shaft.

Exercise 3. Make a semidiagrammatic drawing of a spine on a
large scale showing the articulation and the muscles.

Remove the spines from the dried specimen and thoroughly
clean the shell. This is accomplished the most effectually by
placing it in a strong solution of warm caustic potash for a
short time. Great care should be taken, however, not to leave
it in the solution too long or it will fall to pieces. Study the
aboral side of the shell. Observe the rows of tubercles on
which the spines have articulated, also the bands of minute
holes, the ambulacral pores, through which the ambulacral feet
have projected. There are ten of these bands arranged in
pairs, and each pair represents an ambulacral area or a ray.
Between the five rays are the five interambulacral areas or the
interrays, which are somewhat broader than the rays; count
the rays and the interrays.

The center of the aboral surface is free from spines and is
made up of several small plates. It is called the periproct and

A SEA URCHIN 151

contains in its center the minute anus. Surrounding the peri-
proct are ten plates, which also bear no spines. Five of these,
which are larger than the others, are situated at the ends of the
interrays and are pierced each by a small hole. These plates
are called the genital plates, and the holes are the external open-
ings of the genital organs. One of the genital plates is larger
than the others and is porous; it is the madreporic plate. The
five smaller of the ten plates which surround the periproct are
situated at the ends of the rays. They are called the ocular
plates. Hach is pierced by one or two holes, through which
project minute pigmented tentacles. Notice that each ray and
each interray is made up of two rows of plates, so that there
are twenty rows of plates altogether. As in the starfish, the
two rays between which the madreporic plate lies are called the
bivium, the other three, the trivium.

Exercise 4. Make a drawing of the aboral side of the shell, with
the spines removed, on a scale of 2, showing accurately
the boundaries of all the plates. Label the rays, interrays,
and all the other parts observed.

The internal organs. Place a fresh or preserved sea urchin in
a pan of water. Carefully cut away the peristome with scissors
and remove the shell of the oral body-wall on one side of the
peristome without disturbing the organs within. Observe the
following systems of organs:

The digestive system. This is quite different from the same
system in the starfish. The mouth opens into the esophagus,
which passes through the center of the large cone-shaped
dentary apparatus, which is also, because of its shape, called
Aristotle’s lantern. This is a complicated structure consisting of
a number of calcareous plates and muscles which project from
the mouth into the body-cavity. Study its muscular attach-
ment with the shell. Note the protractor muscles which pass
from its upper end to the oral body-wall, by means of which

152 INVERTEBRATE ZOOLOGY

the apparatus can be thrust down and partly out of the mouth;
also the retractor muscles which pass from the lower part of it to
the tall inner projections of the shell.

Exercise 5. Draw a diagram showing the dentary apparatus in
the body and its muscular attachment to the shell.

The cesophagus, after leaving the dentary apparatus, passes to
the elongated stomach ; this lies close to the body-wall, to which
it is attached by means of a mesentery. Carefully follow the
stomach, breaking away the wall if necessary, as it winds
around the inner surface of the shell. From the stomach a
short intestine passes to the anus. In making this dissection,
keep the animal immersed in clear water; remove as little of
the shell as possible, and do not remove any of the organs from
the body.

The genital system is similar to that in the starfish. The sexes
are separate and the sexual glands of the male and female are
alike in appearance. They consist of five radial, granular
masses, which lie in the upper part of the body-cavity, each
mass communicating with the outside through one of the genital
pores. The actual extent of the sexual glands depends upon
the sexual condition of the animal. During the breeding
season, in the summer, they may almost fill the body-cavity.

Exercise 6. Make a diagrammatic drawing of the digestive and
the reproductive systems and label all their parts.

Remove the dentary apparatus from the body and examine it
carefully. It is made up principally of five triangular plates
called alveoli, the lower ends of which bear the teeth. The
alveoli are bound together by short muscles. The base of the
dentary apparatus is made up of a complicated system of
smaller plates.

Exercise 7. Make a drawing of the dentary apparatus.

A SEA URCHIN 153

The ambulacral system is similar to that of the starfish. A ring
canal surrounds the cesophagus just inside the inner end of the
dentary apparatus and is connected with the madreporic plate
by means of the stone canal. This organ is a small tube which
lies in contact with the cesophagus and also, in the neighbor-
hood of the aboral body-wall, with the intestine. From the
ring canal five radial canals pass along the median lines of the
rays to their aboral ends, sending off branches to the ambulacral
feet. The entire system of tubes, except the ambulacral feet,
is within the body-cavity, instead of outside of it, as in the star-
fish. Look on the inner surface of a ray for the radial canal.
On each side of it observe the row of small vesicles, the ampulle,
the reservoirs of the ambulacral feet. Determine the exact
relation of the ampulle to the feet, and of both to the ambu-
lacral pores in the shell. It will be seen that there are two
rows of these latter on each side of the radial canal. Through
one of these rows the branch canals pass from the radial canal
to the ambulacral feet on the outside of the shell; through the
other row projections of the feet pass back into the body-cavity,
where they expand to form the ampulle. There is thus a single
row of feet on each side of the radial canal in each ray.

The ambulacral system will be seen to consist of a system of
tubes extending throughout the body, and communicating with
the sea water through the madreporic plate. It is filled with a
fluid which, as in the starfish, is not pure sea water, but is
rather a watery serum in which float amceboid cells. This fluid
can be driven into the ambulacral feet, which acquire rigidity
and are thereby extended. The animal moves by extending
the feet, attaching the sucker discs at their ends to some sta-
tionary object, and then drawing them in; it is able thus to
pull itself slowly along. Some sea urchins with long spines
also move on the tips of their oral spines as on stilts.

Exercise 8. Draw adiagram representing the ambulacral system.

154 INVERTEBRATE ZOOLOGY

The respiratory and exeretory systems are not represented
by special organs. The ambulacral feet may possibly perform
both functions.

The nervous system cannot be studied in a dissection. It is
essentially like that of the starfish. From the ring nerve
around the cesophagus five radial nerves pass along the median
line of the rays to the ocular plates, where each terminates
in a tentacle. The entire system is within the body-cavity
instead of a portion of it being outside as in the starfish.

The circulatory system cannot be seen in a dissection. As in
the starfish it consists of a complicated system of tubes and
spaces which contain a colorless blood fluid. An organ of
problematical function called the heart or axial sinus is found
attached to the upper end of the stone canal; within it is a
glandular organ called the ovoid gland or axial organ.

SEA CUCUMBER 155

HOLOTHURIOIDEA
A HOLOTHURIAN OR SEA CUCUMBER

Two common species of holothurians which live in the shallow
water of the New England coast are suitable for this dissection
— Thyone briareus and Cucumaria frondosa, the former being com-
mon in Vineyard and Long ‘Island Sounds and the latter on the
Maine coast. The latter is the larger of the two species, being
from 10 to 25 cm. or more long and about half as thick, and
differs from Thyone, among other things, in having ambulacral
feet in the radial areas alone; it possesses thus five broad bands
of these appendages, the interradial areas being smooth. Thyone
is from 8 to about 20 cm. long and 5 cm. thick, and is covered
all over with ambulacral feet, the five broad radial bands meet-
ing in the interradial areas. It will be used as the basis of this
dissection.

Observe the form and color of the body. Note that the upper
and lower sides are distinctly differentiated, the former having
fewer feet than the latter. In the center of the forward end is
the mouth, surrounded by the ten branched tentacles by means of
which the animal collects the minute organisms which constitute’
its food. Above the mouth and between the bases of two ten-
tacles is the genital pore. In the center of the hinder end is the
anus, surrounded by five anal teeth. The main longitudinal axis
of the body (that which joins the mouth and the anus) will thus
be seen to be very long, in sharp contrast to that of the starfish
and sea urchin, in which it is much shorter. In consequence of
this feature the body is elongate and more or less worm-like, and
the animal does not rest on the oral surface but on its side.

Exercise 1. Draw a side view of the animal and label carefully
all of the features observed.

156 INVERTEBRATE ZOOLOGY

With strong scissors cut the body open by a longitudinal slit
along the underside. Place it in a pan of water and with large
pins pin down the two sides of the body wall on the right and
left. Without cutting any of them, study the internal organs.

Note the spacious body cavity and the long, coiled intestine
which partly fills it. At the front end of the body and just be-
hind the tentacles is the conspicuous calcareous ring, 2 more or
less rigid cylinder containing five radial and five interradial plates,
which surrounds the esophagus. Projecting from the hinder
end of the calcareous ring will be seen two large cylindrical sacs,
the Polian vesicles, and inserted in the ring are five prominent
retractor muscles, by means of which the tentacles and the forward
end of the body can be invaginated. Note the position of the
genital gland and its duct. The gland is a thick bunch of slender
filaments, in the forward part of the body cavity, joined with the
body wall by a mesentery, which converge to the hinder end of
the duct. This is a slender tube which passes forward on the
upper side of the body cavity and opens to the outside between
two tentacles on the upper side of the body. The sexes are
separate; they are alike, however, in appearance. Note the respir-
atory trees, the profusely branched organs which extend from the
rectum throughout the entire length of the body cavity.

Study the course of the digestive tract. The esophagus passes
through the calcareous ring to the thick-walled, muscular stomach,
which lies directly behind it. From the hinder end of the
stomach the long, thin-walled intestine passes, with many loops
and turns, to the short, wide rectum at the hinder end of the body.
Trace the intestine carefully, but without cutting it, throughout
its entire course and note the three mesenteries by which it is
attached to the body wall.

Note the thick muscular walls of the rectum and the muscle
strands which join it with the body wall. The two branching
respiratory trees spring from the forward end of the rectum and
extend through the body cavity to its forward end. Observe

SEA CUCUMBER 157

carefully their extent. It is by the periodic dilation and con-
traction of the muscular walls of the rectum that water is alter-
‘nately taken into the rectum and the respiratory trees and
expelled from them, and respiration thus carried on.

Exercise 2. Draw a diagrammatic view of the opened animal on
a large scale, showing the organs observed. Carefully
label all.

Cut the esophagus just back of the calcareous ring and remove
the digestive tract with the respiratory trees and the genital
gland from the body. The five retractor muscles of the calca-
reous ring may be followed to the body wall, where they will
be seen to join five longitudinal muscles which extend along the
inner surface of the body wall the length of the body. These
muscles mark the five radial areas of the body. Note the circular
muscles which also lie on the inner surface of the body wall.

Study the ambulacral system. The ring canal, which is often
difficult to see, surrounds the cesophagus at the hinder end of
the calcareous ring. The Polian vesicles, two elongated sacs which
have already been noted, extend from it into the body cavity.
They secrete and store the lymphatic fluid which fills the ambu-
lacral canals. The stone canal, which also extends from the ring
canal, is a slender tube, and the madreporic plate with which it
ends lies in the body cavity and not at the surface of the body.
It is probably a rudimentary structure. The five radial canals
extend from the ring canal along the radial areas of the body
and beneath the five radial muscle bands to the hinder end of the
body. The ambulacral feet extend from the radial canals through
the body wall and are seen thickly studding the outer surface
of the body. The numerous ampulle extend into the body cavity
and will be seen on the inner surface of the body wall. The
tentacles are also a part of the ambulacral system, the canals
which supply them with the ambulacral fluid springing from
the radial canals.

158 INVERTEBRATE ZOOLOGY

Exercise 3. Draw a diagram of the ambulacral system.

Exercise 4. Draw a diagram representing an ideal cross section
through the middle of the body.

The calcareous spicules and plates which form a part of the body
wall and are so characteristic of the echinoderms as a group are
less conspicuous in holothurians than in any of the other classes
of the phylum, and will not be studied in this dissection. They
are of minute size, although definite in shape in the various
species, and do not form a connected skeleton as in the starfish
and the sea urchin. Pedicellariz are absent.

CHAPTER VIII
CNIDARIA

HYDROZOA
A FRESHWATER POLYP. HYDRA

This small animal is of general although sporadic distribu-
tion throughout the country. It frequents ponds and streams
abounding in plant life, and is best obtained by collecting water
together with water plants, sticks, and other objects from sev-
eral such places, and allowing it to stand in glass jars. The
polyps will, if present, be seen, after an interval of some time,
attached to the stems or leaves of the plants, or to the sides of
the jar. They may be kept indefinitely in aquaria of this sort
and will usually multiply rapidly.

Hydra is a slender, tubular animal from one-eighth to one-
half an inch in length; it attaches itself by one end to some
stationary object and projects pendant in the water; at the
other end is the mouth, surrounded by from four to eleven long
thread-like tentacles. It does not attach itself permanently to
one place, but can crawl about or swim slowly through the
water. Its food consists largely of small crustaceans which it
kills or paralyzes with the peculiar stinging organs called nettle
cells, located principally in the tentacles.

Study the animals first, if possible, without disturbing them
and with the aid of a hand lens. Note the extreme contractility
of the body. Look for individuals with distended bodies.
These have just swallowed prey. Look for budding individ-

uals ; budding is one method of reproduction. Observe the
159

160 INVERTEBRATE ZOOLOGY

color of the animal. Two species of the hydra are common in
this country — the green hydra and the brown hydra, the latter
of which has much longer tentacles than the former.

Detach a polyp by means of a pipette, place it in a watch-
glass of water, and study it under a microscope.

Bxercise 1. Draw several outlines of the animal on a large scale,
showing different shapes and positions it can assume.
Notice the mouth in the midst of the tentacles.

Place a polyp on a slide in water and cover it with a cover-
glass, but support the corners of the latter with wax to avoid
crushing the animal. Study its structure under the microscope.
We see that the type of structure is radial and not bilaterally
symmetrical; that the animal is tubular in shape, and that its
internal cavity opens to the outside through the mouth; that
the mouth is a small opening at the end of the conical, terminal
portion of the body, called the hypostome, at the base of which
are the tentacles. The internal cavity is called the gastro
vascular space and is the common digestive and circulatory cavity
of the animal. The end by which the animal is attached is
called the foot. It is an adhesive disc containing gland-cells
which produce a sticky secretion.

Examine the finer structure under a high power of the
microscope. The body-wall is made up of two layers of cells,
the outer ectoderm and the inner entoderm. The cells of the
latter are much longer and more irregular than those of the
ectoderm; their inner surfaces are amceboid and also often
flagellate. Imbedded in the entoderm cells are the chromato-
phores, the bodies which give color to the animals. In the
green hydra these are chlorophyll bodies; in the brown hydra
they consist of a substance similar to chlorophyll. In both
cases they are probably single-celled alge living symbioti-
cally with the polyp. Between these two cell layers is a
thin non-cellular one called the supporting layer. The tentacle

HYDRA 161

is a hollow projection of the body-wall and has the same
structure.

Among the ectoderm cells of the distal portion of the body,
and especially of the tentacles, notice the oval, highly refractive
stinging organs or nematocysts. Each one consists of a spiral
thread-like tube, with several barbs at its base, which lies coiled
within the cavity of a cell called a cnidoblast. The cavity is
filled with a poisonous fluid; its walls form an ovoid sac, of
which the tube is the very much elongated and invaginated
outer end. A minute spine projects beyond the free surface
of the cnidoblast into the water. When the surface of the
ectoderm is irritated the tube is evaginated and shot violently
out, and the poisonous fluid contained in the cavity of the
nematocyst is injected into any animal that may be struck.

Exercise 2. Make a large semidiagrammatic drawing of the
animal showing the details of its structure; label all
carefully.

Methods of reproduction. Hydra reproduces both sexually and
asexually. Well-fed polyps will soon begin to bud off new
individuals. The bud makes its appearance first as a projec-
tion of the body-wall, and soon becomes a distinct branch.
Tentacles and a mouth make their appearance at the extremity
of the branch, and the young polyp is complete. It remains
attached to the parent for a while, then detaches itself and
begins an independent life.

Besides this asexual method of reproduction, which may go
on as long as the animal is well fed and vigorous, reproduction
by sexual methods also occurs at more or less irregular inter-
vals. Sexual organs appear in the form of projections of the
ectoderm of the body-wall. Two classes of these projections
appear, smaller ones, which are testes, and larger ones, which
are ovaries. The former of these organs, which lie near the
distal end of the animal, produce spermatozoa; the latter are

162 INVERTEBRATE ZOOLOGY

near the proximal end, and each produces a single large ovum.
The green hydra is a hermaphroditic animal, having both testes
and ovary when sexually active, while the brown hydra is
diccious, being either male or female.

Exercise 3. Find a polyp with reproductive organs and make a
drawing of it.

Special respiratory, excretory, digestive, and circulatory
organs are absent in the hydra. Respiration and excretion are
carried on through the surface of the body-wall. Digestion,
circulation, and absorption go on within the gastro-vascular space.
The animal’s prey is caught in the water with the tentacles,
which sting it into insensibility, and then swallowed into the
gastro-vascular space. The entoderm cells, which line this
cavity, extend their very plastic inner ends toward or about
it, and some of them secrete a digestive fluid. The object is
then digested and mingles with the water present in the gastro-
vascular space, while by the vibrations of the flagella currents
are produced which cause this fluid to circulate throughout all
the parts of it.

Distinct muscular and nervous systems are absent in the hydra.
Delicate muscle fibers are present, however, in the form of long
parallel projections of the inner ends of ectoderm cells. Nervous
elements are also present in the form of isolated ganglionic cells
situated in the ectoderm, which send delicate projections to the
muscle fibers and to the nematocysts. Both muscle fibers and
ganglion cells are present throughout the animal’s body but
are most numerous in the tentacles. There are no organs of
special sense.

A TUBULARIAN HYDROMEDUSAN 163

HYDROZOA
A TUBULARIAN HYDROMEDUSAN (Pennaria or Bougainvillea)

These are marine animals, and among the commonest hydro-
medusans along our coast. As is characteristic of the group to
which they belong, they exhibit the phenomenon of alternation
of generations. ‘T'wo generations of individuals, a sexual and
an asexual, alternate with each other. The latter is called
the hydroid generation; the animal in this stage is sessile and
colonial, and produces by budding, i.e., by asexual methods, the
sexual generation. This latter is called the medusoid genera-
tion; in it the animal either remains attached to the hydroid
colony (Pennaria) and is then called a sporosac, or separates
itself (Pennaria, Bougainvillea) and becomes a free-swimming
jelly-fish, which is called a medusa; in either case the medusoid
produces by sexual methods embryos which attach themselves
to fixed objects and develop into the hydroid generation.

The hydroid stage in Pennaria.1 In this stage these animals
form branching colonies of polyps, which are attached to the
rocks in shallow water. The colonies are several inches in
length, and are found in thick clusters which often cover the
rocks over small spaces; their color is a delicate pink.

Place a small portion of a colony in a watch-glass of water
or alcohol, and study it under the microscope. Observe the
main stem of the colony and its branches, also the position
of the polyps on the branches. Note carefully the differences
in size between the different polyps. Which is the largest
polyp? Study the method of branching. Has the colony a

1 Bougainvillea or any other tubularian can also be used, with slight changes
in the directions,

164 INVERTEBRATE ZOOLOGY

main axial stem? If it has, which is the oldest polyp? Which
branch is the oldest? Which is the second oldest polyp? In
Bougainvillea, besides the polyps, the medusoids also grow out
from the stem.

The stem of the colony together with the branches is
called the hydrocaulus; the root-like projections by which it
is attached at its base are the hydrorhiza; the polyps are called
hydranths.

Exercise 1. Draw a diagram representing the method of branch-
ing and showing the arrangement of the polyps on the
stem.

Mount a small branch of the colony on a slide in water or
dilute glycerine, and study a number of hydranths of all sizes.
We note the radial type of structure and the tubular body, the
internal cavity of which opens to the outside through the small
terminal mouth. The stem also and its branches have an internal
cavity which is a continuation of that of the hydranth. The
cavity of the hydranth and the stem is called the gastro-vascular
space, and is the common digestive and circulatory cavity of
the animal. Notice the ringed constrictions in various parts
of the stem, especially near the polyps; they give the stem
strength and flexibility.

Study the two kinds of tentacles, the whorl of larger ones
around the base of the hydranth and the shorter ones on the
body of it. In Bougainvillea the basal tentacles alone are
present. Count the basal tentacles. Count the short tentacles
on a large and then on a small hydranth. The larger hydranth
will be found to have more than the smaller one. Notice the
small hydranth buds on the side of the stem; find one whose
tentacles have not yet developed. Some of the hydranths will
be seen to have large ovoid projections of very variable size on
their sides. These are the medusoid buds, which become either
free-swimming medusz or sessile sporosacs. In Bougainvillea

A TUBULARIAN HYDROMEDUSAN 165

the medusoid buds do not appear on the hydranths but on the
stem; they become free-swimming meduse.

Exercise 2. Make a semidiagrammatic sketch of a large hydranth
and a portion of the stem on a large scale; label the
different parts.

Exercise 3. Make a sketch on a large scale of the smallest
hydranth or hydranth bud you can find.

Mount a hydranth and a part of the stem on a slide in dilute
glycerine, and study their finer structure. First study the
structure of a tentacle. It is not hollow as is the tentacle of
Hydra, but is made up of an axis consisting of a single row
of large entoderm cells around which is a layer of small ectoderm
cells. Between these two cell layers is the delicate non-
cellular supporting layer. Find the highly refractive stinging
organs or nematocysts at the end of the tentacle. These are the
organs with which the animal kills its prey. Each one consists
of a spiral thread-like tube, with several barbs at its base, which
lies coiled within the cavity of a cell called the cnidoblast. The
cavity is filled with a poisonous fluid; its walls form an ovoid sac,
of which the tube is the very much elongated and invaginated
outer end. A minute spine projects beyond the free surface
of the cnidoblast into the water. When the surface of the
ectoderm is irritated the tube is evaginated and shot violently
out, and the poisonous fluid contained in the cavity of the nema-
tocyst is injected into any animal that may be struck. Look
for nematocysts which have discharged their spiral threads.

Exercise 4. Draw the distal portion of a tentacle showing its
cellular structure; show the nematocysts at the end,
including several which have been discharged.

Study the structure of the wall of the hydranth. It is made
up of an outer ectoderm and a much thicker inner entoderm, each

166 INVERTEBRATE ZOOLOGY

composed of a single layer of cells; the inner ends of the ento-
derm cells are amoeboid and often flagellate, the function of the
flagella being to maintain in circulation the fluids in the gastro-
vascular space; between these two layers is the thin non-cellu-
lar supporting layer. Study the structure of the stem. Observe
its central cavity, which is a part of the gastro-vascular space,
and the three layers just mentioned. In live specimens notice
the action of the flagella. Notice the cuticula which covers the
outer surface; it is not found in the hydranth. This cuticula
is called the perisarc. It is a supporting structure and gives
the colony rigidity.
Exercise 5. Make a drawing showing the cellular structure
of the wall of the hydranth and of the stalk; carefully
label all.

Study the structure of the medusoid buds. Notice the differ-
ence between the younger and the older buds. Compare the
young buds with the hydranth buds; compare the oldest
medusoid bud with the structure of the medusa, as described
later on.

Exercise 6. Draw the oldest and the youngest buds identifying
as many of the parts as possible.

Special respiratory, excretory, digestive, and circulatory
organs are not present in the hydroid. Respiration and excretion
are carried on through the surface of the body-wall. Digestion,
circulation, and absorption go on within the gastro-vascular space.
The polyps feed upon small swimming animals, which they kill
or stun with their nematocysts, and then swallow into the
gastro-vascular space. Digestion goes on within this space
and waste matters are ejected from the mouth. The products
of digestion mingle with the water present in the gastro-vas-
cular space and circulate throughout the colony, the internal
cavities of all the individual polyps of a colony being in

A TUBULARIAN HYDROMEDUSAN 167

communication with one another. When a colony is well fed
it grows rapidly, new hydranths bud out from the stalk, and
medusoid buds appear and grow into meduse. The hydranths
are frequently destroyed by frost, or by the beating of waves,
or by fishes, but new ones quickly grow in their places.

The medusoid stage. The medusoids of tubularian hydro-
medusans are either sessile sporosacs or free-swimming meduse.
Pennaria produces both kinds. During a greater part and
in some cases the whole of the year they are sporosacs, but
usually during the middle and last of the summer they detach
themselves from the hydroid and become meduse. Both con-
ditions may be found in the same colony and at the same time.
The medusoids of Bougainvillea are always free-swimming and
with other medusz will be found in the surface waters of the
ocean. They may be easily obtained by placing the live hydroid
colony in a small glass of sea water; the medusz will be found
swimming about in the water.

Place several meduse of Bougainvillea or of any other tubu-
larian hydromedusan in a watch-glass of sea water or, if they
are preserved specimens, in alcohol. If they are alive, observe
the swimming motions. Note the radiate type of structure.
The body is bell-shaped, having an outer convex and an inner
concave side, and on its margin are tentacles (in the medusa of
Pennaria they are rudimentary). The convex side is called the
exumbrella or aboral side, and the concave, the subumbrella or oral
side. In the center of the latter is the proboscis-like projection
called the manubrium, at the distal end of which is the mouth,
surrounded by short oral tentacles. ‘The mouth opens into the
gastro-vascular space, which comprises the space within the manu-
brium and also a system of canals in the bell-shaped body.
These canals consist of four radial tubes, which extend from
the base of the manubrium to the periphery of the body, and
are there united by a circular tube, which runs parallel with the
margin and close to it.

168 INVERTEBRATE ZOOLOGY

Observe the arrangement of the marginal tentacles; also of
the oral tentacles. At the base of the groups of marginal
tentacles are minute sense-organs, the ocelli; they are charac-
terized by the presence of pigment and are sensitive to light.
Note the four swellings on the side of the manubrium; these
are the sexual organs and are specialized portions of the ecto-
derm. The sexes are separate; the sexual glands have the
same appearance in the two sexes. Around the inner margin
of the subumbrella, at the base of the tentacles, is a broad
muscular membrane extending inward called the velum.

Exercise V. Make a diagrammatic sketch of the medusa and
label all of its parts.

The medusa is a more highly specialized form than the polyp,
although they are homologous forms and are essentially alike
in structure. The different vegetative functions are carried on
in the medusa as they are in the hydranth. The medusa being
a free-swimming animal, however, its muscular and nervous
systems are much more highly developed than the same systems
are in the hydranth. In the latter the only muscles present
are delicate fibers, elongated projections of the inner ends of
ectodermal cells, which cause movement in the tentacles and
the body of the hydranth, while the nervous system is repre-
sented only by scattered ganglion cells, which lie among the
ectoderm cells. In the medusa the velum is the principal organ
of locomotion. It contains bands of ectodermal muscle fibers,
by the contraction of which the motion of the umbrella is pro-
duced which propels the animal through the water. The nervous
system consists of a double nerve ring of ganglion cells and fibers
‘running around the margin of the disc, from which delicate
fibers run to the velum and to the sense-organs.

A CAMPANULARIAN HYDROMEDUSAN 169

HYDROZOA

A CAMPANULARIAN HYDROMEDUSAN (Obelia or Campanularia)

These are very common marine animals which live in the
shallow water along our coast. In common with other mem-
bers of the group they exhibit the phenomenon of alternation
of generations. Two generations of individuals, a sexual and an
asexual, alternate with each other. The latter is called the
hydroid generation; the animal in this stage is sessile and colo-
nial and produces by budding, #.e., by asexual methods, the
sexual generation. This latter is called the medusoid generation ;
in it the animal either remains attached to the hydroid colony
(Campanularia) and is then called a sporosac, or separates itself
(Obelia) and becomes a free-swimming jelly-fish, which is called
a medusa; in either case the medusoid produces by sexual
methods embryos which attach themselves to fixed objects and
develop into the hydroid generation.

The hydroid stage. While in this stage these animals form
branching colonies, which are attached to seaweed, rocks, and
other objects. Place a small portion of a colony in a watch-
glass in water or alcohol, and study it under the microscope.
Observe the differences in size between the different polyps, as
well as their position on the stem. Determine the method of
branching. Has the colony a main axial stem? If not, which
is the oldest polyp? Notice the ringed constrictions in various
parts of the stem, especially near the polyp; they give the stem
strength and flexibility.

The stem of the colony together with the branches is called
the hydrocaulus ; its root-like projections by which it is attached
at its’ base are the hydrorhiza. Observe that there are two

170 INVERTEBRATE ZOOLOGY

distinctly different kinds of polyps instead of but one, as in
Pennaria or Bougainvillea: (a) the feeding polyp or hydranth,
which is the more numerous and bears tentacles, and (6) the
reproductive polyp or blastostyle, which is a modified hydranth and
is much the larger and the less numerous and bears no tentacles.
Notice that the perisarc, the transparent cuticular covering of
the stem, does not end at the base of the polyp, as is the case
in the tubularian hydroid, but is continued over the polyp,
enclosing it as inacup. It is thus a protective device and is
called in the case of the hydranth the hydrotheca, and in the
case of the blastostyle the gonotheca. The feeding polyp with-
draws within its hydrotheca for protection when alarmed. The
reproductive polyp never emerges from its gonotheca, which is
a closed structure, but the medusoids or their sexual products
escape into the surrounding water through an opening which
finally appears in the gonotheca’s free end.

Exercise 1. Draw a diagram representing the method of branch-
ing of the colony and the arrangement of the polyps.

Mount a portion of a branch with several hydranths in water
or dilute glycerine. Study an expanded hydranth. We note
the radial type of structure and the tubular body, the internal
cavity of which opens to the outside through the terminal mouth;
also that the stem has a cavity which is continuous with that
of the hydranth. The internal cavity of the hydranth and of
the stem is called the gastro-vascular space, and is the common
digestive and circulatory cavity of the animal. The proboscis-
like portion of the hydranth between the base of the tentacles
and the mouth is called the hypostome. Count the tentacles.
Note the absence of medusoid buds on the hydranth.

Exercise 2. Make a semidiagrammatic sketch of the expanded
hydranth on a large scale and label all of its parts.

Exercise 3. Make a sketch of a contracted hydranth.

A CAMPANULARIAN HYDROMEDUSAN ial

Find a hydranth bud and study its structure.

Exercise 4. Make a semidiagrammatic sketch of it.

Study the finer structure of an expanded hydranth. First
study the structure of a tentacle. It is made up of an axis
consisting of a single row of large entoderm cells, around which
is a layer of small ectoderm cells. Between these two cell layers
is the delicate non-cellular supporting layer. Find the highly
refractive nematocysts at the end of the tentacle. These are the
stinging organs with which the animal kills its prey. Each
one consists of a spiral, thread-like tube, with several barbs
at its base, which lies coiled within the cavity of a cell called
the cnidoblast. The cavity is filled with a poisonous fluid; its
walls form an ovoid sac, of which the tube is the very much
elongated and invaginated outer end. A minute spine pro-
jects beyond the free surface of the cnidoblast into the water.
When the surface of the ectoderm is irritated the tube is
evaginated and violently shot out, and the poisonous fluid con-
tained in the cavity is injected into any animal that may be
struck. Look for nematocysts which have discharged their
spiral threads.

Exercise 5. Draw the distal portion of a tentacle showing its
cellular structure; show the nematocysts at the end,
including several which have been discharged.

Study the finer structure of the wall of the hydranth. It is
made up of an outer ectoderm and a much thicker inner entoderm,
each composed of a single layer of cells; the inner ends of the
entoderm cells are amceboid and often flagellate, the function
of the flagella being to maintain in circulation the fluids in the
gastro-vascular space; between these two layers is the thin
non-cellular supporting layer. The hydrotheca encloses all, but it
is not in contact with the ectoderm. Study the structure of
the stem; it has essentially the same structure as the hydranth;

172 INVERTEBRATE ZOOLOGY

note the outer cuticular covering, the perisarc. Note the action
of the flagella in a live specimen.

Exercise 6. Make a drawing showing the cellular structure of
the wall of the hydranth and of the stem.

Study a blastostyle. We note that it is a cylindrical object
enclosed within its transparent gonotheca. Budding out on the
sides are the young disc-like meduse, those towards the free end
being the largest and the oldest. The blastostyle has no
tentacles and no mouth. It has an internal cavity which is
a part of the gastro-vascular space of the colony, and within
which the nutritive fluids circulate.

Exercise 7. Make a drawing of a blastostyle.

Special respiratory, excretory, digestive, and circulatory organs
are not present in the hydroid. Respiration and excretion are
carried on through the surface of the body-wall. Digestion,
circulation, and absorption go on within the gastro-vascular space.
The colony lives upon small swimming animals, which the
feeding polyps kill or stun with their nematocysts, and then
swallow into the gastro-vascular space. Digestion goes on
within the feeding polyps; the products of digestion mingle
with the water present in the gastro-vascular space and circu-
late throughout the colony. The entire colony is thus nour-
ished, and if conditions are favorable it will grow rapidly and
produce a large number of medusz. The polyps are frequently
destroyed by frost or the beating of waves or by fishes, but new
ones quickly grow in their places.

The medusoid stage. The medusoids of campanularian hydro-
medusans are either sessile sporosacs or free-swimming medusa.
The meduse are minute disc-shaped jelly-fishes, about one-
eighth of an inch in diameter, which may be found swimming in
the surface waters of the ocean. Place several in a watch-glass
of sea water, or, if they are preserved specimens, in alcohol.

A CAMPANULARIAN HYDROMEDUSAN 173

If they are alive, observe the swimming motions. Note the
radiate type of structure. The body resembles an umbrella in
shape, having a convex and a concave side, and is bordered
by a fringe of tentacles. The former is called the exumbrella or
aboral side, the latter, the subumbrella or oral side. In the center
of the latter side is the proboscis-like projection called the
manubrium, at the distal end of which is the mouth. This opens
into the gastro-vascular space, which comprises the space within
the manubrium and also a system of canals in the disc-like
body. These canals consist of four or more radial tubes, which
extend from the base of the manubrium to the periphery of the
disc, and are there united by a circular tube which runs parallel
with the margin of the disc and close to it.

Count the marginal tentacles. At the base of certain of the
tentacles are minute sense-organs, called lithocysts, which are
probably organs of equilibrium. Find them.

Near the middle of each radial tube notice a prominent
swelling on the subumbrella. These are the sexual glands and
are specialized portions of the ectoderm. The sexes are sepa-
rate in meduse; the sexual glands have the same appearance
in the two sexes.

Around the inner margin of the subumbrella, at the base of
the tentacles, is a muscular membrane extending towards the
manubrium called the velum. In campanularian medusz it is
often very narrow and not easily seen ; in tubularian meduse it
is broad and very noticeable.

Exercise 8. Make a diagrammatic sketch of a medusa and label
all of its parts.

The medusa is a more highly specialized form than the polyp,
although they are homologous forms and are essentially alike in
structure. The manubrium of the medusa and the hypostome
of the polyp do not differ essentially from each other; the
tentacles are also homologous structures. The exumbrella of

174 INVERTEBRATE ZOOLOGY

the medusa corresponds, consequently, to the base of the polyp,
and just as the latter is attached to the stem at its base, so the
medusa is attached to the blastostyle by its exumbrella. The
digestive, excretory, respiratory, and circulatory functions are
carried on in the medusa as they are in the hydranth. The
medusa being a free-swimming animal, however, its muscular
and nervous systems are much more highly developed than are
the same systems in the hydranth.

In the latter form the only muscles present are delicate
fibers, elongated projections of the inner ends of ectodermal
cells, which cause movement in the tentacles and the body of
the hydranth, while the nervous system is represented only by
scattered ganglionic cells, which are also of ectodermal origin.
In the medusa the velum is the principal organ of locomotion.
It contains bands of ectodermal muscle fibers, by the contraction
of which the motion of the umbrella is produced which pro-
pels the animal through the water. The nervous system consists
of a double nerve ring which runs around the margin of the
disc and from which delicate fibers pass to the velum and
the sense-organs.

GONIONEMUS 175

HYDROZOA
A TRACHOMEDUSA (Gonionemus)

This animal is a better form to study, on account of its larger
size, than the minute tubularian or campanularian meduse. It
is a very common medusa at Woods Hole, but its range of
distribution is very limited although it has also been found in
Long Island Sound.

Place the medusa in a small dish of water, which should be
set upon a dark background. The water should be deep enough
to permit the jelly-fish to be readily turned over. If it is alive,
study the pulsations of the bell, by means of which it swims.
Note the inverted position of the animal when at rest. With a
simple lens or a compound microscope study its form and color.
Note the radiate type of structure. Unlike the bilaterally sym-
metrical animals, the medusa has no dorsal, ventral, anterior, or
posterior side.

The outer, convex surface of the bell-shaped body is called
the exumbrella or the aboral side, and the concave underside is
called the subumbrella or the oral side. From the center of the
latter extends a large, dark-brown projection called the manubrium,
at the distal end of which is the mouth, surrounded by four re- °
curved lips. At the base of the manubrium is the stomach, a
four-sided sac from the four corners of which the four straight
radial canals extend to the periphery of the body, where they are
united by the ring canal, which runs around the margin of the
bell. The radial and ring canals, together with the stomach and
the cavity of the manubrium, form the gastro-vascular space, the
entodermal lining of which is colored brown.

176 INVERTEBRATE ZOOLOGY

Directly beneath the four radial canals and projecting slightly
into the subumbrella space are the four reproductive organs, which
are also brown in color and present a corrugated appearance.
The sexes are separate, but the animals are not dimorphic.

Observe the number and arrangement of the tentacles, of which
an adult medusa possesses from sixty to eighty. Note the spiral
arrangement of the nettle cells on each tentacle, and also the
adhesive pad near its outer end. It is by means of the nettle
cells in these pads that the animal anchors itself to seaweeds
and other objects when at rest. Note the exact point above
the margin of the bell where the tentacles are inserted. In the
basal portion of each tentacle is a conspicuous pigmented body ;
this is a hollow bulb which is connected with the ring canal.
Between the tentacles are the lithocysts— minute projections
from the margin of the bell which are probably equilibrial in
function.

Observe the velum — the membrane which extends around the
inner margin of the bell towards the manubrium. It is the
principal organ of locomotion and contains bands of ectodermal
muscle fibers by the contractions of which the motion of the
bell is produced which propels the animal through the water.
Similar bands of muscle fibers are also present in both the
subumbrella and the exumbrella.

Exercise 1. Draw a semidiagrammatic view of the exumbrella
on a scale of from 5 to 10, showing the tentacles extended
and all the organs which have been observed.

Exercise 2. Draw an oblique side view of the animal on the
same scale, showing the velum, the manubrium, and all the
other organs observed.

Exercise 3. Draw a semidiagrammatic view of the subumbrella
on a scale of 5 to 10, showing the velum, the manubrium,
and the other organs observed.

GONIONEMUS 177

The hydroid generation of Gonionemus is a minute solitary
polyp: which lives attached to the bottom in shallow water;
it will not be studied here. The polyp is only about one milli-
meter in height and has four tentacles which can be extended
two millimeters. It is thus very much smaller than the medusa,
which has a height of about nine millimeters and a diameter of
about twenty. The polyp forms new polyps by budding, but
has never been observed forming the meduse, so that it is not
known how these originate.

178 INVERTEBRATE ZOOLOGY

ANTHOZOA

A SEA ANEMONE (Metridium)

This animal, which is the largest sea anemone along the North
Atlantic coast, is often plentiful on rocks, shells, and docks in
shallow water. Place an expanded individual in a deep dish of
water and observe its shape, color, and method of attachment.
The upper end of the columnar body is called the disc, and in its
center is the elongate, slit-like mouth, surrounded by the numer-
ous tentacles. The lower end of the animal is called the foot. It
is often expanded and is not permanently attached to the sub-
stratum; the animal has some locomotory powers and can slowly
move from place to place.

Study the form of the mouth. Note the thickened lips at
each angle of the mouth; these form a ciliated groove, called
the siphonoglyph, through which the genital products reach the
outside. In some individuals only one siphonoglyph is present.

Study the surface of the disc and the tentacles. The former
is frequently expanded and thrown into folds and lobes. The
tentacles are elongated Civerticula of the disc and are hollow.
They are charged with nettle cells and are the principal organs
of defense and offense. They are also useful in feeding; after
the nettle cells have stung the small animals which constitute
the food of the sea anemone, the tentacles place them in its
mouth. The tentacles are not all the same size, those nearer
the mouth being the larger and the older.

Note the character of the columnar body. It is pierced by
small pores through which long, white, glandular threads, armed
with nettle cells and called acontia, may be thrust when the
animal is irritated.

METRIDIUM 179

Exercise 1. Draw the expanded animal, showing the column and
the disc, with the mouth and the tentacles.

Internal anatomy. Cut the animal into halves by a longitudinal
incision passing at right angles to the mouth and from the dise
to the foot. The mouth will be seen to open into a flattened
tube with more or less corrugated walls, called the gullet. Note
the formation of the siphonoglyphs. The gullet leads into the
gastro-vascular space, which is the general internal cavity of the
animal.

The most prominent structures in this cavity are the mesenteries,
which are longitudinal partitions extending from the outer wall
of the body inward toward its center. These mesenteries will
be seen to occur in pairs; six of these pairs, called the primary
mesenteries, join the body-wall with the wall of the gullet. The
pair at each angle of the gullet which enclose the siphonoglyphs
between them are called the directives. Between the six pairs of
primary mesenteries are secondary, tertiary, and quarternary pairs.
The gastro-vascular space is thus divid'd into a large number
of partially separated longitudinal chambers.

Note carefully the structure of the free edges of the mesen-
teries below the gullet. The thickened corrugated structure
which forms the edge is the mesenterial filament; it contains
digestive glands. From the base of the mesentery extend the
acontia. The reproductive organs, the ‘testes and ovaries, are
also located in the mesenteries, lying alongside the mesenterial
filaments.

Note carefully the position of the longitudinal muscle bands,
one of which is present on the surface of each mesentery. It is
by means of these muscles that the body is contracted. A circu-
lar muscle in the disc closes the mouth by its contraction and aids
in drawing in the tentacles.

Exercise 2. Draw a semidiagrammatic view of the cut surface of
the animal, showing these features.

180 INVERTEBRATE ZOOLOGY

Make a cross section through the gullet and study the arrange-
ment of the mesenteries, the relation of the primary mesenteries
to the gullet, and the longitudinal muscles.

Exercise 3. Draw a diagram of the cross section, showing these
features.

Make a cross section through the body beneath the gullet.

Exercise 4. Draw a diagram of the cross section, showing the
arrangement of the mesenteries.

CHAPTER IX
SPONGIARIA

CALCAREA
A SYCON SPONGE (Grantia)

Grantia is a non-colonial sponge which is common along the
New England coast. It is a small cylindrical animal, about
half an inch in length, and occurs in small groups attached to
rocks or other objects below low-water mark.

Place several specimens in a watch-glass of alcohol or water,
and study their shape and external characters with the aid of a
hand lens. Observe the cylindrical body and at one end of it a
small opening surrounded by straight, needle-like spicules; the
opposite end is the one by which the animal was attached.
The opening is called the osculum or excurrent opening. Notice
the smaller spicules and the openings of numerous minute »
pores which cover the sides of the body. Growing out from
the base of the larger individuals may often be seen small ones,
which will become, in the course of time, independent animals.
Note the evident radial symmetry of the animal.

Exercise 1. Make a drawing of an animal on a scale of 5.

Split a dried sponge with a sharp knife into two equal halves
and study it under a dissecting microscope. Observe the large
central cavity. Large numbers of openings will be seen in its
wall; they are the mouths of the radial canals, which are. pro-
jections of the central cavity into the body-wall. Examine

carefully the cut edges of the body-wall; observe the radial
181

182 INVERTEBRATE ZOOLOGY

canals, which are cut longitudinally here. Notice also the
shorter and less regular incurrent canals, which lie between the
radial canals and open to the outside through external incurrent
pores. There are thus two systems of canals in the body-wall,
(a) the radial canals, which are a part of the central cavity, and
(6) the incurrent canals, which open to the outside. These two
systems of canals communicate with each other by means of
minute openings, so that water which enters the incurrent
canals from the outside through the external incurrent pores
passes freely into the radial canals, and thence into the central
cavity. From here it passes out through the osculum.

Bxercise 2. Make a semidiagrammatic drawing of the inner
surface of the body-wall and the cut edge of the animal,
showing the features above described.

Isolate the spicules of a sponge by boiling a portion of it ina
caustic potash solution. Mount some of them in water and
examine them under a high power of the microscope. Find
the three different kinds of spicules — the long straight ones which
guard the osculum, the short straight ones which guard the
external incurrent pores, and the triradiate ones which are within
the body-wall and give it rigidity and firmness; some of the
latter project into the central cavity. Determine whether the
spicules are solid or hollow.

Exercise 3. Draw an outline of each sort of spicule on a large
scale.

Make thin sections of a sponge by placing it between two
pieces of elder-pith or of cork, and shaving off the sections with
a sharp razor or scalpel. Obtain in this way cross, longitudinal,
and tangential sections. Mount them in dilute glycerine and
study them under the microscope.

Study a cross section in which the canals have been cut lon-
gitudinally. Observe the radial and the incurrent canals and

GRANTIA 183

their relations to one another. Note the arrangement of the
spicules which guard the incurrent pores, also of those tri-
radiate spicules which project into the central cavity.

Exercise 4. Make a drawing of several canals showing these
features.

Study a tangential section in which the canals appear in cross
section and study the arrangement of the triradiate spicules
around them.

Exercise 5. Make a drawing illustrating it.

Specialized reproductive organs are not present in Grantia.
The sexual elements will be found in the form of large
spherical bodies buried in the wall of the sponge. Fertiliza-
tion takes place here, and development begins, and the young
embryos escape into the sea water through the canals. For
a while the embryo is a free-swimming animal, but it finally
fastens itself to a rock and develops into the adult sponge.
Besides this sexual reproduction, the sponge also reproduces
asexually by budding. Each distinct cluster of individuals
probably represents the gemmated progeny of a single indi-
vidual.

Special respiratory, excretory, digestive, circulatory, nervous,
and locomotory organs are wanting in Grantia. Respiration and
excretion are carried on through the entire surface of the body.
The animal feeds on minute organisms and particles of organic
matter suspended in the water which streams into the canal
system through the incurrent pores. The radial canals are
lined with peculiar entoderm cells called collar cells, each one of
which possesses a flagellum. The action of the flagella pro-
duces the current of water through the canals, from which the
collar cells obtain and ingest food particles. Circulation is
from cell to cell.

CHAPTER X
PROTOZOA

INFUSORIA
A FREE-SWIMMING CILIATE INFUSORIAN (Paramecium)

Paramecium, often called the slipper animalcule, is one of
the commonest of the larger infusorians. It is a minute, single-
celled animal, being just on the limit of vision, and is almost
universally present in standing water which contains decaying
vegetable matter. It is easily obtained by permitting vegetable
matter to stand in water for a week or two. In shape it is an
elongated ellipsoid with a wide, slightly twisted, longitudinal
groove, called the oral groove, on one side; the surface which con-
tains the groove may be called the ventral surface, and the oppo-
site surface, the dorsal. The animal is colorless and transparent,
except when it contains within its body colored food particles.

Mount a drop of water containing Paramecia and some decay-
ing matter on a slide, using a large, thick cover-glass, and study
the animals under a low power of the microscope. They will be
seen swimming rapidly about, but will gradually collect about
the decaying matter. If they do not become quiet in a few
minutes, it is because there is too much water under the cover-
glass, and some of it should be withdrawn with a piece of
blotting paper. Care should be taken that the water does not
all evaporate.

Observe the unsymmetrical shape of the animal, and the
difference between the anterior and the posterior ends. Notice

the rolling over of the animal as it swims through the water;
184

PARAMECIUM 185

the peculiar spiral twist of the body is correlated with this
motion, but does not necessarily cause it, as the animal may at
times revolve in the direction opposite to that of the twist. It is
in consequence of this peculiar revolving motion that the animal
is able to maintain a course through the water which is practi-
cally straight. The great majority of swiftly moving animals
are bilaterally symmetrical, and move in straight lines because of
that feature of their structure, but Paramecium, together with
most free infusorians, has an unsymmetrical form and would
tend to move in circles in consequence, without making progress,
if it were not for the revolution of its body on its long axis.

Exercise 1. Draw several simple outlines of the body showing
its shape as seen in different positions.

Exercise 2. Draw an outline of an ideal cross section through
the middle of the body.

Study the structure of the body, using a high power of the
microscope when necessary. Study the action of the hair-like
vibratile cilia which cover the outer surface of the animal and
by means of which it moves. They are usually difficult to see
in the live animal because of their very rapid motion, but by
varying the light and the focus of the microscope they will be
brought into view, and in the dead animal are plainly visible.
Determine the direction in which the cilia move. Are they all
of the same length? Note the delicate transparent cuticula which
covers the body; it appears as a highly refractive line.

The body has no internal cavity, and the protoplasm of which
it is composed is in two distinct layers, the ectosarc and entosare.
The former is the thick, firm, transparent outer layer which,
with the cuticula, gives permanent shape to the body; it often
appears obliquely striated. The entosarc is a semifluid gran-
ular mass which forms the remainder of the body. From near
the anterior end the oral groove runs obliquely along the ventral
side of the body to a point back of the middle, getting deeper

186 INVERTEBRATE ZOOLOGY

as it goes. At its inner end the groove becomes a closed
tube, which extends into the entosarc and ends with the mouth.
Notice the trichocysts — slender, radially arranged bodies which
fill the ectosarc. They are organs of defense, which remind
one of the nematocysts of the Cnidaria; when the animal is
irritated they discharge long, delicate bristles, which project
beyond the cilia or may leave the body.

Observe the granular nature of the entosarc, and the spheri-
cal food vacuoles within it. These are particles of food, usually
composed of vegetable substances surrounded by water, which
circulate within the semifluid entosare. Watch the entosarc
closely, and observe the currents in it. Determine the direc-
tion of the currents and whether the direction is ever changed.
The food vacuoles form at the inner end of the oral groove,
where the particles of which they are composed have been swept
by the cilia of the groove. Watch the formation of them.

Observe the pulsating vacuoles. These are the excretory organs
of the animal. They are globular drops of clear liquid, two in
number, which appear near the aboral surface of the body, not
far from either end, and break through the ectosare into the
surrounding water. They do not appear simultaneously, but
alternate with each other. When a vacuole has disappeared,
radiating canals of clear fluid gradually form about the spot
where it was located, bringing the fluid which is to form the
next vacuole at that end. ‘Time the formation of the pulsating
vacuoles; how many form in a minute ?

Observe the macronucleus, a large, ovoid structure near the
center of the body. At its side are either one or two minute
micronuclei, according to the species, P. caudatum having one and
P. aurelia two; they may be seen if the animal be killed by
adding a 1 per cent. solution of acetic acid to the water.

Exercise 3. Make a large semidiagrammatic drawing of a Para-
mecium, showing all these details, and label all.

PARAMECIUM 187

Paramecium has no special vegetative organs except the
pulsating vacuoles. Food vacuoles are taken into the entosarc
through the mouth. Here they circulate for some time, while
the water forming the vacuole is absorbed and the food parti-
cles that it contains are digested. The indigestible matters are
collected at a spot just back of the mouth and are there ejected
from the body through a temporary opening in the ectosare,
which forms for that purpose; the water of the food vacuole
is collected in the pulsating vacuoles and ejected. Respiration
is carried on through the external surface of the body. The
organs of locomotion are the cilia, which are distributed evenly
over the surface of the body; they are hair-like projections of
the ectosare through pores in the cuticula. Sensation is exercised
by the entire surface of the body.

Reproduction is asexual, by division. A transverse constric-
tion appears in the surface of the middle of the animal’s body
and deepens until it is divided in two. Each half becomes an
independent animal and grows to full size. Look among a
large number of animals for one which is dividing.

A process which is universal among infusorians is conjugation.
Two individuals place the ventral surfaces of their anterior
ends together. In this position their bodies fuse together and
an interchange of micronuclear matter takes place between them.
The two individuals then separate.

Conjugation was formerly supposed to be a process by which
weak and infertile animals renewed their strength and vitality.
It is now supposed to be rather a preparation for unfavorable
life conditions. The change in the structure of the micronucleus
leads to a change in the essential characters of the animals, and
thus gives them additional powers of environmental adaptation
and a better chance to survive unfavorable conditions.

Exercise 4. Look for dividing and also for conjugating indi-
viduals. Observe them carefully and draw them.

188 INVERTEBRATE ZOOLOGY

INFUSORIA
A SESSILE CILIATE INFUSORIAN (Vortice//a)

This infusorian differs from Paramecium in being a sessile
animal, and in that the cilia are not equally distributed over
all parts of the body but are confined to certain parts of it.
Vorticella and its allies are often called bell animalcules. The
animal consists of a bell-shaped body at the end of a long stalk
which is permanently attached to some object in the water.
Around the upper and wider margin of the body is a row of
large cilia. A deep oral groove, which is also bordered by cilia,
extends from the margin towards the center of the animal and
bears the mouth at its inner end.

A number of genera of bell animalcules are found in both
fresh and salt water. Vorticella is non-colonial and possesses
a contractile spiral stalk ; Carchesium and Zodthamnium are
colonial and differ from each other in that in the former each
individual animal contracts independently, while in the latter
the entire colony always contracts as a unit; in both, the colo-
nies are large and easily visible, appearing often like white
mould on the object of attachment; Epistylis is colonial with
a non-contractile stalk.

Mount a drop of water on a slide, together with some vege-
table or other substance to which Vorticella is attached, and
study it under the microscope. (Any other bell animalcule will
do equally well.) Observe the shape of the animal; tap on the
slide with a pencil and cause it to contract; note the marginal
cilia and the current they set up in the water; find the oral
groove and note that the current in the water tends to sweep
small objects into it,

VORTICELLA 189

Notice the partial radial symmetry of the animal; this body-
form is due to its sessile habit of life. Paramecium, which is a
rapidly moving animal, is not radially symmetrical. Can you
explain why a sessile organism tends to be radial ?

Exercise 1. Draw a careful outline of the expanded animal ona
large scale, and another of the contracted animal, and label
the parts above mentioned.

Study the structure of the body. It consists of a single cell,
as does Paramecium, and is composed of two protoplasmic
layers, the ectosarc, which is the firm external layer, and the
entosarc, the more fluid protoplasm of which the inner portion
of the animal is composed. Covering its outer surface is the
cuticula, which, with the ectosarc, gives the animal its perma-
nent shape. The stalk is a continuation of the ectosare and of
the cuticula. Its inner portion alone, 7.e., the axis, is con-
tractile; its cuticula simply accommodates itself by assuming
a spiral shape. Note the longitudinal striations in the ectosare
at the base of the bell.

Observe the granular nature of the entosare and the spher-
ical food vacuoles within it; note the circulation of the latter in
the granular protoplasm. Each food vacuole is composed of
particles of organic matter in a minute globule of water, which
collect in the oral groove and are then driven into the mouth.
Watch the formation of them; this is done easily by placing
grains of indigo or carmine in the water.

Vorticella has a single pulsating vacuole, which is in the upper
part of the body. It is the organ of excretion of the animal and
consists of a globule of clear liquid which collects near the
surface of the body and is then discharged through the ectosare
into the water. As in Paramecium, the water which is ingested
as a part of the food vacuoles is discharged through the pulsat-
ing vacuole together with renal products. Time the formation
of the pulsating vacuoles; how many form a minute?

190 INVERTEBRATE ZOOLOGY

Observe the macronucleus; it is a narrow elongated structure
and is easily seen; near itis the small spherical micronucleus.

Exercise 2. Make a large semidiagrammatic drawing of a Vor-
ticella, showing these details, and label all.

Vorticella has no special vegetative organs except the pulsat-
ing vacuole. The food particles which are ingested into the
entosare are there digested, and waste matters are egested
through a temporary anus in the upper portion of the body.
Respiration is carried on through the external surface of the
body. Organs of locomotion are present in the cilia, by which
the animal can swim about if it is broken from its stalk. The
axial fiber in the stalk is a delicate striated muscle fiber.
Sensation is exercised through the external surface.

Vorticella reproduces asexually, by a longitudinal division.
The process begins at the upper end of the body and proceeds
to the base, so that finally there are two individuals upon a
single stalk. One of these now separates itself from the stalk,
assumes a cylindrical form, and, having developed a band of
temporary cilia near one end, swims away to find a place for
itself. It soon attaches itself, loses the temporary cilia, and
develops a stalk.

In the case of the colonial Vorticellide both of the individ-
uals produced by the process of division remain on the stalk.
In Zoéthamnium the colony is dimorphic; it contains nutritive
individuals which are similar to Vorticella, and reproductive
individuals which are large and globose and do not feed. The
latter separate themselves from the parents and swim off and
found new colonies. This dimorphism and division of labor
remind one of the Hydromeduse. In Vorticella, as in Parame-
cium, reproduction is largely a matter of sufficient nutrition,
well-nourished animals reproducing faster than poorly nourished
ones. Conjugation also occurs; it is brought on by the same
conditions as in Paramecium and is highly important to the

VORTICELLA 191

well-being of the race. The process is, however, somewhat dif-
ferent from conjugation in Paramecium. An individual divides
into from two to eight parts. These free themselves from the
stalk, acquire each a basal band of cilia, and swim about in
the water until they come in contact with individuals of the
ordinary kind, with which they fuse. A permanent conjugation
is then effected instead of a temporary one as in Paramecium.

Conjugation, it will be noticed, while it is not a sexual
process, is closely allied to such a process, and it is probably
through it that sexuality arose in the organic world. In Para-
mecium and Vorticella we have two important steps in the
development of sexuality. In the former animal the conjugat-
ing individuals are of the same size, or isogamous, and the
fusion of the two individuals is temporary, while in the latter
they are of different sizes, or heterogamous, and the fusion is
permanent. As a result of this differentiation in Vorticella
one of the conjugating individuals is a large, passive form,
while the other is a small, active, motile form, which finds and
fuses with the passive form. A distinct foreshadowing of the
two sexes which characterize the Metazoa is thus present.

Exercise 3. Look among a large number of Vorticellas for con-
jugating and for dividing individuals. Observe them care-
fully and draw outlines of those observed.

192 INVERTEBRATE ZOOLOGY

MASTIGOPHORA
A FLAGELLATE (Euglena)

This single-celled organism, which combines the characters of
animals and plants, is often so plentiful in pools and ditches
that it makes the water green. It is a minute elongated proto-
zoan, one end of which is pointed and the other blunt; in
the latter end is a deep depression, from the bottom of which
springs a long, thread-like, vibratile flagellum. The body is cov-
ered by a very delicate cuticula; an oral groove and a mouth are
not present. The animal is colored green by the presence of
chlorophyll in its body.

Mount a drop of water containing Euglena on a slide and
study it under the microscope. Observe its shape and color;
also its swimming motions and the motions of the flagellum.
The latter organ will be seen to be at the anterior end of the
body; it is always in advance as the animal swims. In some
flagellates the flagellum is at the posterior end. Whether the
flagellum in any species is at the anterior or the posterior end
of the body depends upon the direction the vibratile motion of
the flagellum takes. If the motion begins at the base of the
flagellum and proceeds towards its tip, the animal’s body will be
driven ahead with the flagellum at the rear, while if the motion
begins at the tip of the flagellum, the body will be drawn after
it. Note the extreme plasticity of the body. It can assume
a variety of shapes, and will often be seen swimming by the
alternate contraction and expansion of the body, like a worm.

Bxercise 1. Draw a number of simple outlines of the body
showing its shape at different times.

EUGLENA 193

Study the structure of the body. The protoplasm composing
it is clear, its surface often showing delicate striations. Note
the cuticula. In the middle of the body is a spherical nucleus.
At the anterior end near the depression is a clear space called
the reservoir; find it. It receives the discharges of the pulsating
vacuole. ‘This vacuole is a minute globule of clear liquid, which
represents the excretory wastes of the animal; it collects and
discharges into the reservoir periodically, which thus acts as a
urinary bladder and in turn opens into the anterior depression.
Near the reservoir is a red pigment spot, which is sensitive to
light; it is the most primitive form of an eye.

Exercise 2. Draw Euglena on a large scale with the above-
mentioned organs.

Tn its life processes Euglena partakes of the nature of both a
plant and an animal. Through the agency of the chlorophyll a
starch-like carbohydrate called paramylum is manufactured, which
constitutes a large part of the food of the organism. The pro-
cess goes on only during the daytime and is a characteristic plant
process. But Euglena also ingests solid food after the manner
of animals. Food particles are taken into the depression at the
anterior end and thence sink into the soft protoplasmic body.
Excretion is effected through the pulsating vacuole ; respiration,
through the body-surface.

From time to time Euglena encysts itself. It loses its
flagellum, draws itself together into a spherical form, and
secretes a cyst of cellulose. After a while it either throws off
the cyst and assumes its former shape or reproduces by divid-
ing into from two to eight small Euglenas. Reproduction thus
takes place during the period of encystment; also at times free
individuals reproduce by longitudinal division.

Exercise 3. Among a large number of individuals look for divid-
ing and also for encysted ones. Make large drawings of
several.

194 INVERTEBRATE ZOOLOGY

SARCODINA
A NAKED RHIZOPOD. AMOEBA

The amoeba is a jelly-like, single-celled animal which may be
found in stagnant water attached to submerged objects, or in
bottom sediment; it is also often found in moist, damp places
which are not under water. The animals are very variable in
size, the largest being within the range of the unaided vision,
the smallest species requiring high powers of the microscope
to detect.

Mount on a slide a drop of water with sediment or scrapings
from a submerged leaf or stick containing amoebas, and find
one. Observe its shape and granular appearance. From time
to time the shape of the body changes by the thrusting out
of projections called pseudopodia. Observe the formation of
pseudopodia. ;

Exercise 1. Draw several outlines of the animal, showing its
shape at different times.

Observe the structure of the body. The protoplasm forming
it will be seen to be divisible into two layers, the ectosarc
and the entosarc; the former is the clear, transparent layer
which forms the periphery of the body; the latter is the gran-
ular, translucent mass which forms the remainder of it. The
ectosare is of firmer consistency than the entosarc and secretes
a delicate cuticula on its outer surface. When a pseudo-
podium begins to form, it consists at first of ectosare alone,
but entosare finally enters it as it grows larger. The entire
body will often flow into a single pseudopodium, in which case

AMOEBA 195

the animal flows in that direction. When this happens the
ectosarc of the hinder portion of the body will be seen to
wrinkle as the entosare flows away from it.

Observe the granular nature of the entosare and the flowing
of the granules as they move about with the motion of the
protoplasm. Observe the food vacuoles in the entosarc; they are
particles of food surrounded by water. Observe the pulsating
vacuole, the organ of excretion. It will be seen to be a large
globule of clear liquid which forms near the periphery and then
discharges into the surrounding water. Time its pulsations;
how many form a minute? Add a1 per cent. solution of acetic
acid to the water and find the nucleus.

Exercise 2. Makealargesemidiagrammatic drawing of an amoeba,
showing the features above mentioned, and label all.

Amoeba has no special vegetative organs except the pulsat-
ing vacuole. Solid food consisting of plants and animals and
particles of organic matter is ingested in the form of food
vacuoles. These move about in the entosare with the move-
ments of the animal’s body and the nutritive matters are digested
and absorbed. Waste matters are then egested by being thrust
out of a temporary opening in the ectosarc into the water.
Respiration is carried on through the surface of the body. One
reason for the active throwing out of pseudopodia is the neces-
sity of increasing the relative area of the surface of the body
for respiratory purposes.

Reproduction in Amoeba is carried on by division. The
nucleus first divides; the animal then elongates, and a trans-
verse constriction appears in its middle, which is finally carried
through the body. Two animals are thus formed, each of
which contains half of the nucleus. As in other protozoans,
reproduction in Amoeba is largely dependent upon nutrition.
If the nutritive conditions surrounding them are unfavorable
the animals gradually lose their vitality and reproductive powers

196 INVERTEBRATE ZOOLOGY

and in the course of time will die. Conjugation also occurs, as
in other Protozoa. The processes of division and conjugation
apparently do not take place frequently, as they have not been
often observed.

About a dozen species of the genus Amoeba are known.
The commonest are probably A. proteus, a large, often active
form with long pseudopodia, .A. verrucosa, a large, sluggish form
with very short pseudopodia, A. limaz, a small form which flows
along without definite pseudopodia, and A. radiosa, a small
star-shaped form with slender, radiating pseudopodia.

APPENDIX

A SYNOPSIS OF THE CLASSIFICATION OF ANIMALS

PHYLUM I. PROTOZOA

Single-celled animals, aquatic and microscopic.

Class 1. Sarcodina. Protozoans with more or less protractile pseu-
dopodia.

Order 1. Rhizopoda. Pseudopodia without axial filament and
usually very retractile. Ex. Amoeba.

Order 2. Heliozoa. Freshwater Sarcodina with silicious skeleton
and ray-like pseudopodia, each with an axial filament. Ex. Actino-
spherium.

Order 3. Radiolaria. Marine Sarcodina with silicious skeleton.
Ex. Polycystina.

Class 2. Mastigophora (Flagellata). Protozoans with one or more
vibratile flagella. Ex. Euglena.

Class 3. Sporozoa. Protozoans which are internal parasites and
have no locomotory organs as adults. Ex. Gregarina.

Class 4. Infusoria. Protozoans with cilia or sucking tentacles.

Order 1. Ciliata. Ciliate infusorians. Ex. Paramecium.

Order 2. Suctoria. Infusorians with sucking tentacles. Ex. Acineta.

PHYLUM II. COELENTERATA

Radiate animals with a single, but sometimes branched, internal
cavity and no celom.

Suppuytum I. Spongiaria (Porifera). Sessile, mostly colonial
animals without specialized organs or tissues; body-wall pierced by
numerous pores or canals and usually stiffened by either calcareous

or silicious spicules and either with or without spongin fibers.
. 197

198 INVERTEBRATE ZOOLOGY

Class 1. Calcarea. Sponges with calcareous spicules and of simple
structure. Ex. Grantia.

Class 2. Hexactinellida. Glass sponges with six-rayed silicious
spicules. Ex. Euplectella.

Class 3. Demospongie. Massive sponges with either silicious spic-
ules or spongin fibers or both. Ex. Spongilla.

Suppyytum II. Cnidaria. Coelenterates provided with nettle
cells.

Class 1. Hydrozoa (Hydromeduse). Hydroid polyps and jelly-
fish, the former without mesenterial ridges and the latter with a
velum.

Order 1. Hydrarie. Freshwater hydroids of simple structure.
Ex. Hydra.

Order 2. Hydrocoralline. Coral-like marine hydrozoans. Ex.
Millepora.

Order 3. Tubularia. Hydroids without hydrotheca; meduse
with gonads on the manubrium. Ex. Pennaria.

Order 4. Campanularie. Hydroids with hydrotheca; meduse
with gonads on the subumbrella. Ex. Obelia.

Order 5. Trachomeduse. Hydroids (when present) minute and
of simple structure; medusz usually large with gonads on the sub-
umbrella. Ex. Gonionemus.

Order 6. Narcomeduse. Hydroids wanting; medusze with lobed
rim. Ex. Cunina.

Order 7. Siphonophora. Free-swimming colonial hydrozoans. Ex.
Physalia.

Class 2. Scyphozoa (Scyphomeduse). Hydroids and jelly-fish, the
former with mesenterial ridges and the latter without a velum and
often of large size. Ex. Aurelia.

Class 3. Anthozoa. Sea anemones and corals; solitary or colonial
polypoid cnidarians without medusoid generation.

Order 1. Alcyonaria. Anthozoans with eight mesenterial ridges
and eight pinnate tentacles. Ex. Corallium.

Order 2. Zoantharia. Anthozoans with numerous mesenterial
ridges and numerous simple tentacles. Ex. Metridium.

Suspuyium III. Ctenophora. Coelenterates with eight bands of
ciliated ridges on outer surface. Ex. Mnemiopsis.

APPENDIX 199

PHYLUM III. VERMES

The lower worms. Animals of primitive structure and without
paired locomotory appendages or distinct head.

SuppHyitum I. Plathelminthes. Flatworms; no anus present in
most forms and body-cavity filled with a vesicular connective tissue
called parenchyma.

Class 1. Turbellaria. Mostly free-living flatworms with ciliated
outer surface. Ex. Planaria.

Class 2. Trematodes. Flukes. Small parasitic flatworms with mostly
a branched digestive tract and an anterior mouth. Ex. Fasciola.

Class 3. Cestodes. Tapeworms. Elongated, usually segmented para-
sitic flatworms without digestive tract. Ex. Taenia.

Class 4, Nemertea. Nemertean worms. Elongated, mostly free-
swimming flatworms with a protrusile proboscis and a ciliated outer
surface. Ex. Cerebratulus.

SuppHyium IT. Nemathelminthes. Round or thread worms; mostly
parasitic. Ex. Ascaris.

Suspuyivm III. Trochelminthes (Rotifera). Minute, aquatic worms
with mouth surrounded by cilia. Ex. Rotifer.

Susppnytum IV. Bryozoa. Minute, sessile, colonial animals with
a ridge bearing ciliated tentacles around the mouth. Ex. Bugula.

SuBpHytum V. Brachiopoda. Sessile, marine, mollusk-like animals
with a dorsal and a ventral shell. Ex. Terebratulina.

Suppuyitum VI. Phoronidea. Sessile, marine worms living in tubes
and with a tentacular ridge around the mouth. Ex. Phoronis.

SuppHytum VII. Chaetognatha. Minute, transparent, marine
worms with a slender body, two or three pairs of horizontal fins,
and paired prehensile bristles around the mouth. Ex. Sagitta.

SusppHytum VIII. Sipunculoidea. Elongated, marine worms, the
anterior portion of which can be invaginated and is usually sur-
rounded by tentacles. Ex. Sipunculus.

PHYLUM IV. ANNELIDA

The higher worms. Elongated, segmented worms which have
paired, unsegmented appendages, and a usually distinct head.
Class 1. Archiannelida. No parapodia or setw. Ex. Polygordius.

200 INVERTEBRATE ZOOLOGY

Class 2. Chaetopoda. With sete, segmentally arranged.

Order 1. Polychaeta. Mostly marine chaetopods with parapodia
on which are numerous sete. Ex. Nereis.

Order 2. Oligochaeta. Earthworms. Mostly freshwater or land
chaetopods without parapodia and with few sete. Ex. Lumbricus.

Class 3. Hirudinea. Leeches. Annelids with a sucker at each end
and no appendages or sete. Ex. Hirudo.

Class 4. Myzostomida. Disk-shaped parasites of echinoderms with
five pairs of parapodia. Ex. Myzostoma.

PHYLUM V. ARTHROPODA

Externally segmented animals with segmented appendages.

Class 1. Crustacea. Aquatic, gill-bearing arthropods; two pairs of
antenne present.

Division 1. Hntomostraca. Small, simply constructed crustaceans
with a variable number of body-segments and without abdominal
appendages.

Order 1. Phyllopoda. Entomostracans with flat, leaf-like append-
ages.

Suborder 1. Branchiopoda. Elongated phyllopods with segmented
body. Ex. Branchipus.

Suborder 2. Cladocera. Laterally compressed phyllopods, the body
of which is not distinctly segmented and is enclosed in a bivalve
shell; second pair of antenne are swimming organs and _ project
from the shell. Ex. Daphnia.

Order 2. Copepoda. Elongated entomostracans with distinctly
segmented body and without gills; the female often carries one or
two egg-sacs. Ex. Cyclops.

Order 3. Ostracoda. Minute, laterally compressed entomostracans
with entire body enclosed in a bivalve shell. Ex. Cypris.

Order 4. Cirripedia. Sessile, hermaphroditie entomostracans with
body enclosed in a calcareous shell; barnacles. Ex. Lepas.

Division 2. Malacostraca. Crustaceans with a constant number
(20) of body-segments and nineteen pairs of appendages; abdominal
appendages present.

Subdivision 1. Phyllocarida. Primitive malacostracans with cara-
pace and with leaf-like thoracic feet. Ex. Nebalia.

APPENDIX 201

Subdivision 2. Arthrostraca. Malacostracans with usually seven
free thoracic body-segments, and with sessile eyes.

Order 1. Amphipoda. Laterally compressed arthrostracans with
gills on thorax. Ex. Gammarus.

Order 2. Isopoda. Dorso-ventrally depressed arthrostracans with
gills on the abdomen. Ex. Oniscus.

Subdivision 3. Thoracostraca. Malacostracans with carapace cov-
ering the head and all or some of the thorax, and with stalked eyes.

Order 1. Schizopoda. Small thoracostracans with carapace covering
entire thorax, and with one pair of maxillipeds. Ex. Mysis.

Order 2. Stomatopoda. Thoracostracans with three free thoracic
body-segments and large abdomen. Ex. Squilla.

Order 3. Cumacea. Small thoracostracans with reduced carapace.
Ex. Diastylis.

Order 4. Decapoda. Large thoracostracans with carapace covering
entire thorax, and with three pairs of maxillipeds.

Suborder 1. Macrura. Elongated decapods with large abdomen.
Ex. Homarus.

Suborder 2. Brachyura. Broad decapods with reduced abdomen.
Ex. Cancer.

Class 2. Arachnoidea. Arthropods lacking antenne and with body
usually consisting of cephalothorax and abdomen.

Division 1. Xiphosura. Large marine arachnoideans with a long,
spike-like telson. Ex. Limulus.

Division 2. Arachnida. Usually air-breathing arachnoideans with
six pairs of appendages.

Order 1. Scorpionida. Large arachnids with a long segmented
abdomen ending in a poisonous sting. Ex. Scorpio.

Order 2. Palpigradi. Minute arachnids with a long, segmented
caudal filament. Ex. Koenenia.

Order 3. Pedipalpi. Arachnids with a constriction between the
cephalothorax and the segmented abdomen. Ex. Thelyphonus.

Order 4. Solifuge. Arachnids with a constriction between the
head and thorax. Ex. Galeodes.

Order 5. Pseudoscorpionida. Arachnids without a constriction
between cephalothorax and abdomen; pedipalps chelate and very
long. Ex. Chelifer.

202 INVERTEBRATE ZOOLOGY

Order 6. Phalangida. Arachnids with extremely long, slender
legs and a segmented abdomen. Ex. Phalangium.

Order 7. Aranez. Spiders. Arachnids with a constriction between
the cephalothorax and the unsegmented abdomen. Ex. Agelena.

Order 8. Acarina. Mites. Arachnids with body not divided into
cephalothorax and abdomen, and unsegmented. Ex. Hydrachna.

Order 9. Linguatulida. Parasitic arachnids with ringed, vermi-
form body. Ex. Pentastomum.

Order 10. Tardigradi. Minute, aquatic arachnids. Ex. Macrobiotus.

Order 11. Pycnogonida. Sea spiders. Marine arachnids with very
long legs. Ex. Pallene.

Class 3. Tracheata. Air-breathing arthropods with one pair of
antenne.

Division 1. Onychophora. Worm-like tracheates with indistinctly
segmented body and appendages. Ex. Peripatus.

Division 2. Myriapoda. Worm-like tracheates with distinctly
segmented body and appendages.

Order 1. Progoneata. Body mostly cylindrical and with two pairs
of legs toa segment. Ex. Julus.

Order 2. Chilopoda. Centipeds. Flattened myriapods with one
pair of legs to a segment. Ex. Lithobius.

Division 3. Insecta. Insects. Tracheates with body divided into
head, thorax, and abdomen; with three pairs of legs and usually two
pairs of wings.

Order 1. Thysanura. Minute, wingless insects without metamor-
phosis. Ex. Lepisma.

Order 2. Pseudoneuroptera. Insects with two pairs of net-veined
wings, biting mouth-parts, and incomplete metamorphosis. Ex.
Dragon fly.

Order 3. Orthoptera. Insects with two pairs of wings (the first
pair being usually parchment-like), biting mouth-parts, and incom-
plete metamorphosis. Ex. Grasshopper.

Order 4. Neuroptera. Insects with two pairs of net-veined wings,
biting mouth-parts, and complete metamorphosis. Ex. Ant lion.

Order 5. Coleoptera. Beetles. Insects with two pairs of wings
(of which the first pair are elytra), biting mouth-parts, and complete
metamorphosis. Ex. Potato beetle.

APPENDIX 203

Order 6. Hemiptera. Bugs. Insects with two pairs of wings, or
wingless, with sucking mouth-parts in form of a jointed proboscis,
and incomplete metamorphosis. Ex. Aphis.

Order 7. Lepidoptera. Butterflies and moths. Insects with two
pairs of scale-covered wings, sucking mouth-parts in form of a long,
unjointed proboscis, and complete metamorphosis. Ex. Bombyx.

Order 8. Diptera. Insects with one pair of wings, sucking mouth-
parts, and complete metamorphosis. Ex. House fly.

Order 9. Hymenoptera. Insects with two pairs of wings, biting
and licking mouth-parts, and complete metamorphosis. Ex. Bee.

PHYLUM VI. MOLLUSCA

Animals without paired locomotory appendages, and with a soft,
unsegmented body, which is usually enclosed in a calcareous shell.

Class 1. Amphineura. Symmetrical mollusks without a shell or
with one composed of eight pieces in a longitudinal row. Ex.
Chiton.

Class 2. Scaphopoda. Symmetrical mollusks with a cylindrical
shell. Ex. Dentalium.

Class 3. Gastropoda. Snails. Mollusks with an asymmetrical, spiral
shell and a single mantle cavity.

Order 1. Opisthobranchiata. Marine snails with posterior gills.
Ex. Aeolis.

Order 2. Pulmonata. Freshwater and land snails, without gills
but with lungs. Ex. Helix.

Order 3. Prosobranchiata. Mostly marine snails with anterior
gills. Ex. Fulgur.

Class 4. Pelecypoda. Symmetrical mollusks with a bivalve shell
and paired mantle cavities. Ex. Unio.

Class 5. Cephalopoda. Mollusks with a large head, which bears a
number of long arms, and with a single mantle cavity.

Order 1. Tetrabranchiata. Cephalopods with four gills and a
large convoluted shell. Ex. Nautilus.

Order 2. Dibranchiata. Cephalopods with two gills and either
eight or ten arms; shell, when present, concealed in the mantle.
Ex. Loligo.

204 INVERTEBRATE ZOOLOGY

PHYLUM VII. ECHINODERMATA

Radially symmetrical animals with calcareous plates or spicules in
the body-wall.

Class 1. Crinoidea. Sea lilies. Echinoderms which are sessile
throughout life or only as larve. Ex. Comatula.

Class 2. Asteroidea. Starfish. Flattened, star-shaped echino-
derms with an ambulacral furrow on the under side of each ray.
Ex. Asterias.

Class 3. Ophiuroidea. Brittle stars. Flattened echinoderms with
long, vibratile arms and without ambulacral furrows. Ex. Amphiura.

Class 4. Echinoidea. Sea urchins. Spheroidal or flattened echino-
derms without arms. Ex. Arbacia.

Class 5. Holothurioidea. Sea cucumbers. More or less worm-like
echinoderms with oral tentacles. Ex. Synapta.

PHYLUM VIII. CHORDATA

Animals with a dorsal central nervous system, an internal skeletal
system, consisting in the simplest cases of the notochord, and paired
pharyngeal slits and arches.

Suppyyium I. Enteropneusta. Worm-like chordates with a large
proboscis in front of the mouth. Ex. Balanoglossus.

SuppHyivum II. Tunicata. Chordates in which the body is enclosed
in a tunic; a large pharyngeal chamber and a ventral heart present.

Class 1. Larvacea. Minute, free-swimming tunicates with a long
tail. Ex. Appendicularia.

Class 2. Thaliacea. Free-swimming, transparent tunicates. Ex.
Salpa.

Class 3. Ascidiacea. Sessile, saccular tunicates, either simple or
colonial. Ex. Molgula.

Suspuyium III. Leptocardia. Elongated, fish-like chordates, com-
pressed laterally and attenuated at both ends. Ex. Amphioxus.

SuppyyLtum IV. Vertebrata. Chordates with distinct head, bear-
ing organs of special sense, with red blood, and usually with two
pairs of appendages.

Class 1. Pisces. Fishes. Aquatic vertebrates which breathe by means
of gills, and usually with bony scales and paired fins, Ex, Perca.

APPENDIX 205

Class 2. Amphibia. Amphibians. Vertebrates with gills during a
part or all of their life, and usually with lungs; scales mostly absent.
Ex. Rana.

Class 3. Reptilia. Reptiles. Vertebrates with body covered with
horny scales or plates and without gills. Ex. Coluber. .

Class 4. Aves. Birds. Feathered vertebrates whose anterior ap-
pendages are wings. Ex. Gallus.

Class 5. Mammalia. Mammals. Hair-covered vertebrates which
suckle their young. Ex. Felis.

GLOSSARY

Abdomen: the most posterior of the three body-divisions in arthropods;
wasp, 2; fly, 7; grasshopper, 10; caterpillar, 20; spider, 25; crayfish or
lobster, 31; crab, 42; sow-bug,46; amphipod, 48, 50; larval decapods,
51; copepod, 53; Daphnia, 56.

Aboral: the side of the body opposite the mouth in a radiate animal;
starfish, 142; sea urchin, 149; medusa, 167, 173; Gonionemus, 175.

Aciculum: a chitinous supporting rod in the parapodia of annelids, 63.

Acontia: long threads armed with nettle cells in sea anemones, 178.

Adductor muscle: a muscle which draws an organ towards the axis of the
body; mussel, 90; oyster, 100; clam, 104.

Air-sacs: tracheal enlargements in insects, 17.

Algz: very simple green plants, 160.

Alimentary tract: the digestive canal, the organ which ingests, digests,
and absorbs the food; see Digestive System in Index.

Alternation of generations: the alternate succession of sexual and asexual
generations in hydromedusans, 163, 169.

Alveolus: a pyramidal ossicle which supports one of the five teeth in the
dentary apparatus of the sea urchin, 152.

Ambulacral feet: tubular projections with sucker discs at their ends in
echinoderms, 148, 149, 157.

Ambulacral groove: the elongated groove on the oral side of the rays of
the starfish, 143.

Ambulacral pores: minute openings in the body-wall in the starfish, 143 ;
in the sea urchin, 150.

Ametabolic: larval development without metamorphosis in insects.

Ampulla: a sac-like projection of the ambulacral foot in echinoderms,
146, 153, 157.

Anal feelers: paired posterior projections; centiped, 22; sow-bug, 46.

Analogous: having a similar function.

Antenna: a segmented sensory appendage on the head of arthropods;
wasp, 2; beetle, 5; fly, 7; grasshopper, 9; caterpillar, 20; centiped, 22;
crayfish or lobster, 29; crab, 48; sow-bug, 46; amphipod, 48; copepod,
538; Daphnia, 56; nauplius, 59.

207

208 INVERTEBRATE ZOOLOGY

Anterior: at or towards the front end of the body.

Anus: the posterior opening of the digestive canal.

Aorta: a large artery leading directly from the heart; spider, 26; snail,
116; squid, 129.

Appendage: see Extremity; wasp,1; grasshopper, 12; centiped, 22; spider,
24; crayfish or lobster, 30; crab, 43; sow-bug, 47; amphipod, 49; Ca-
prella, 50; larval decapods, 51; copepod, 54; Daphnia, 56; nauplius,

-59; Nereis, 61, 63: a projection from some part of the body.

Appendix: a short diverticulum of the intestine, 40.

Aristotle’s lantern: the dentary apparatus of the sea urchin, 151.

Artery: a blood vessel carrying blood away from the heart to-the tissues;
crayfish or lobster, 37,38; Nereis, 64; mussel, 94; clam, 108; snail, 116,
squid, 127, 129.

Arthrobranch: a gill attached to the joint between the leg and the body
in crustaceans, 35.

Articulate: composed of a series of homologous segments.

Asexual: reproduction by division or budding and not through the agency
of the sexes; Bugula, 87; Hydra, 161; hydromedusan, 163, 169 ; sponge,
183; Paramecium, 187; Vorticella, 190; Euglena, 193; Amoeba, 195.

Auricle: a chamber of the heart which receives the blood from the veins;
mussel, 94; oyster, 101; clam, 108; snail, 116.

Avicularium : a structure shaped like a bird’s head attached to the zocecium
in Bryozoa, 87.

Axial organ: a glandular organ in the axial sinus in the starfish, 148; in
the sea urchin, 154.

Axial sinus: an elongated sac alongside the stone canal in the starfish, 148;
in the sea urchin, 154.

Balancers: the homologues of the metathoracic wings in Diptera, 8.

Bilateral symmetry : having the right and left sides alike.

Bivalve: a shell composed of two distinct and equivalent parts or valves;
mussel, 89; oyster, 99; clam, 103.

Bivium: the two rays of a starfish or a sea urchin which enclose the
madreporic plate between them, 142, 151; the two rays on the upper
side of the holothurian’s body, 155.

Blastostyle: the reproductive polyp of a campanularian hydroid, 170.

Body-cavity: an internal space in the body in which lie the viscera.

Body-wall: the outer portion of the body, which usually bounds the body-
cavity towards the inside.

Brachial: relating to the arms.

GLOSSARY 209

Branchial: relating to the gills.

Branchial heart: a lateral heart in the squid, 129.

Branchiate: bearing gills.

Branchiostegite: a paired lateral fold of the body-wall in crustaceans, 30.

Brood-sac: a chamber in which the eggs develop in certain crustaceans ;
sow-bug, 47; amphipod, 49; Daphnia, 57.

Bud: an outgrowth of an animal which becomes a new individual; Bugula,
87; Hydra, 161; hydromedusan, 166, 172, 177.

Calcareous: formed of carbonate of lime.

Capsulogenous glands: glands of uncertain function, but which may aid in
the secretion of the cocoon in the earthworm, 69.

Carapace: the shell covering a portion or all of the cephalothorax in
crustaceans; crayfish or lobster, 29; crab, 42; larval decapods, 51.

Cardo: the basal division of the maxilla in insects, 13.

Cellulose: the woody cell-wall of plant cells; Molgula, 185; Euglena, 193.

Cephalothorax: a body-division formed by the fusion of the head and the
thorax in arthropods; spider, 24; crayfish or lobster, 28; crab, 42;
larval decapods, 51; copepod, 53.

Cercus: a paired projection at the posterior end in certain insects, 10.

Cheliped: the large grasping claw in many crustaceans, 30.

Chitin: a hard and very resistant substance present in the cuticula of
arthropods.

Chloragogue cells: glandular cells surrounding the digestive canal of the
earthworm, 71.

Chlorophyll: the green coloring matter of plants, 192.

Chromatophores: pigment bodies; squid, 123; Hydra, 160.

Cilia: the numerous vibratory projections on the outer surface of certain
animals; planarian, 76; Paramecium, 185; Vorticella, 188: and of
certain organs; Bugula, 86; mussel, 94; clam, 108.

Cirrus: a filamentous, sensory appendage of annelids, 62, 63: a protrusile,
copulatory organ of flatworms, 77.

Clitellum: a thickened glandular region on the earthworm which secretes
the cocoon, 68.

Cloaca: a tubular or sac-like space which receives the discharge of various
organs; planarian, 77; tapeworm, 83 ; mussel, 92; clam, 106; snail, 121.

Clypeus: a median sclerite in the face of insects just back of the upper
lip, 12.

Cnidoblast: a stinging cell in Cnidaria which contains the nematocyst:.
Hydra, 161; tubularian, 165; campanularian, 171.

210 INVERTEBRATE ZOOLOGY

Cocoon: a case containing one or more developing animals, 73.

Caecum: a sac-like appendage of the digestive tract; grasshopper, 15,
starfish, 145.

Celom: the body-cavity.

Collar: the ventral edge of the mantle in gastropods, 113 ; in cephalopods,
124.

Collar cells in sponges, 183.

Colon: a division of the intestine in insects, 15.

Columella: the axis of a spiral snail’s shell, 113.

Compound eye: an eye made up of a number of separate elements, or
ommatidia, in arthropods; wasp, 2; grasshopper, 9; crayfish or
lobster, 29.

Conjugation: the fusion of two protozoans and interchange of nuclear
matter; Paramecium, 187; Vorticella, 190; Amoeba, 196.

Connective tissue: a tissue whose principal function is to support and hold
in place other tissues and organs.

Coxa: the proximal segment of an insect’s or a spider’s leg, by which it
articulates with the body, 4, 12, 25.

Crop: a dilated portion of the cesophagus; grasshopper, 15; earthworm, 71.

Ctenidium: a respiratory organ in mollusks; mussel, 93; clam, 107.

Cuticula: the outer layer of the integument of most invertebrates; wasp, 1;
beetle, 5; fly, 7; grasshopper, 10; spider, 24; crayfish or lobster, 28;
Nereis, 61; earthworm, 74; Bugula, 85; mussel, 89; clam, 103; snail,
112; Molgula, 136; tubularian, 166; campanularian, 170; Parame-
cium, 185; Vorticella, 189; Euglena, 192.

Cyst: a capsule containing an animal usually in a state of suspended ani-
mation; tapeworm, 83; Euglena, 193.

Cysticercus: a cyst containing a tapeworm scolex, $4.

Dentary apparatus: the five teeth and their supporting structure in the
sea urchin, 151.

Development: the series of changes in the early life of an animal by which
it passes from the condition of a fertilized egg to that of the adult.
Dimorphism : the condition in which a species exists in two distinct forms,

as, for instance, male and female.
Distal: a position away from the point of attachment — opposed to proximal.
Diverticulum : a sac-like projection of a tubular organ.
Dorsal: on or towards the back.
Dorsal lamina: a ciliated ridge in the mid-dorsal line of the pharynx in
the ascidean, 1389.

GLOSSARY 211

Ductus ejaculatorius: the terminal portion of the male reproductive tract in
insects, 17.

Ectoderm: the outermost layer of cells in the Cnidaria and Spongiaria;
Hydra, 160; tubularians, 165; campanularians, 171.

Ectosarc: the outermost layer of non-granular protoplasm in protozoans;
Paramecium, 185; Vorticella, 189; Amoeba, 194.

Elytra: the hard wing-covers in beetles, 5.

Embryo: a young animal which is passing through its developmental
stages, usually within the egg membranes or in the maternal uterus.

Encyst: the act of an animal in forming a cyst about itself.

Endopodite: the innermost of the two terminal branches of the typical
crustacean foot; crayfish or lobster, 832; sow-bug, 47; Daphnia, 56.

Endoskeleton: an internal supporting structure.

Endostyle: a ciliated and glandular groove in the mid-ventral line of the
pharynx in ascidians, 137.

Entoderm: the innermost layer of cells in the Cnidaria and Spongiaria;
Hydra, 160; tubularian, 165 ; campanularian, 171; sponges, 183.

Entosarc: the inner granular protoplasm in protozoans; Paramecium, 185;
Vorticella, 189; Amoeba, 194.

Epicranium: the sclerite forming the dorsal, median, and lateral walls of
the head in insects, 12.

Epigynum: a cuticular plate covering or accompanying the female genital
pore in many species of spiders, 26.

Epimeral plates: plates which may extend from the latero-ventral sides of
the thorax in amphipods, 48.

Epiphragma: the disc of calcified slime with which a land snail can close
the opening of its shell, 112.

Epipodite : a membranous projection of the protopodite; crayfish or lobster,
81; crab, 43.

Exopodite: the outermost of the two terminal branches of the typical
crustacean foot; crayfish or lobster, 32; sow-bug, 47; Daphnia, 56.

Extensor muscle: a muscle that extends an organ, 33.

Extremity: a paired lateral or ventral appendage of the body of an animal,
used primarily for locomotion, although in many cases having second-
arily some other function, 1.

Exumbrella: the aboral side of a medusa, 167, 173, 175.

Femur: the segment of an insect’s or a spider’s leg between the trochanter
and the tibia, 4, 12, 25.

212 INVERTEBRATE ZOOLOGY

Fertilization: the union of the spermatozoén and the ovum.

Flagellum: a vibratory thread-like projection of certain cells; hydroids,
162, 166; sponges, 183; also of flagellate infusorians, 192.

Flame cell: the terminal cell of an excretory tubule of flatworms, 78.

Flexor muscle: a muscle that bends an organ, 37.

Food vacuole: a globule of water containing food particles; Paramecium,
186; Vorticella, 189; Amoeba, 195.

Front: the anterior median portion of the epicranium, 12.

Funiculus: a mesenteric strand connecting the stomach pouch with the
body-wall in bryozoans, 86.

Funnel: the siphon of a cephalopod, 124.

Ganglion: an aggregation of nerve cells; grasshopper, 18; crayfish or
lobster, 41; crab, 44; Daphnia, 57; Nereis, 66; earthworm, 74; mussel,
97; clam, 111; snail, 121; squid, 183; Molgula, 138.

Gastrolith : a calcareous body sometimes present in the stomach of crusta-
ceans, 40.

.Gastro-vascular space: the central cavity in Cnidaria; Hydra, 160; tubu-

larian, 164; campanularian, 170; Gonionemus, 176; sea anemone, 179.

Gastrula: a stage in the development of the embryo in which two cell

layers only are present, the ectoderm and the entoderm.

Gena: the lateral portion of the epicranium in insects, 12.

Genital plate: a sclerite at the posterior end of the abdomen in the male
grasshopper, 11.

Giant fibers: three large fibers in the dorsal portion of the nerve cord in
the earthworm, 75.

Gill: an organ for the breathing of air contained in the water; crayfish or
lobster, 35; crab, 43 ; sow-bug, 47; amphipod, 49; Caprella, 50; Nereis,
63; mussel, 90; oyster, 100; clam, 104; squid, 127.

Gill-filament : ciliated vertical ridges on the surface of the gills of lamelli-
branchs; mussel, 94; clam, 108.

Gizzard: a portion of the alimentary tract with thickened muscular
walls, 71.

Glochidium : the larval form of Anodonta and Unio, which lives a parasitic
life in the skin of fishes, 97.

Gonotheca: the cuticular outer covering of the blastostyle, 170.

Green gland: the kidney of a malacostracan crustacean, 30.

Hemal: pertaining to the blood system.
Head: the anterior body-division of the higher animals.

GLOSSARY 213

Heart: a muscular tube-like or sac-like organ which propels the blood;
grasshopper, 14; spider, 26; crayfish or lobster, 38; crab, 44; Daphnia,
57; earthworm, 70; mussel, 94 ; oyster, 101; clam, 108; snail, 116;
squid, 129; Molgula, 137; starfish, 148; sea urchin, 154.

Hemimetabolic: larval development with incomplete metamorphosis in
insects.

Hermaphroditic: having the two sexes united in one animal; earthworm,
72; planarian, 77; tapeworm, 81; Bryozoa, 87; snail, 120; Molgula,
137; Hydra, 162.

Hinge ligament: the flexible portion of a bivalve shell which joins the
two valves; mussel, 89; oyster, 99; clam, 103.

Holometabolic: insects having a complete metamorphosis.

Homologous: having had a similar origin.

Host: the animal which harbors a parasite, 80.

Hydranth: a feeding polyp in a hydroid colony, 164, 170.

Hydrocaulus: the stem of a hydroid colony, 164, 169.

Hydroid: the sessile, asexual generation of the Hydromeduse, 163, 169.

Hydrorhiza: the root-like projections of a hydroid colony by which it is
attached, 164, 169.

Hydrotheca: the cuticular outer covering of the hydranth in campanularian
hydroids, 170.

Hypodermis: the cellular layer which forms the inner portion of the integu-
ment of most invertebrates; crayfish or lobster, 36; earthworm, 74.
Hypopharynx: a median projection from the ventral wall of the pharynx

in insects — in many insects an important mouth-part, 13.

Hypophysis: a ventral projection of the brain in vertebrates, 138.

Hypostome: the projection of a hydroid’s body which bears the mouth;
Hydra, 160; campanularian, 170.

Neum: a division of the intestine in insects, 15.

Imago: a holometabolic insect which has completed its metamorphosis ;
an adult insect.

Integument: the outer covering of an animal; in most invertebrates it
consists of an outer cuticula and an inner hypodermis.

Interfilamentary connections: cross-ridges which join the gill-filaments in
lamellibranchs; mussel, 94; clam, 108.

Interlamellar partitions: vertical walls which join the two lamelle of a
lamellibranch’s gill; mussel, 93; clam, 107.

Intermediate host: the animal which harbors the larval form of a para-
site, 84.

214 INVERTEBRATE ZOOLOGY

Interray: one of the divisions of the radiate body of echinoderms; starfish,
142; sea urchin, 150; sea cucumber, 155.

Intestine: the division of the digestive tract in which absorption goes on;
spider, 27; crayfish or lobster, 37; copepod, 55; planarian, 77; Bugula,
86; mussel, 96; oyster, 101; clam, 110; snail, 118; squid, 131; Mol-
gula, 187; starfish, 145; sea urchin, 152; sea cucuinber, 156.

Kidney: an excretory organ;. spider, 27; crayfish or lobster, 40; Nereis,
65; earthworm, 73; mussel, 95; clam, 109; snail, 116; squid, 127;
Molgula, 138.

Labium: the under lip of insects; fly, 8; grasshopper, 12; beetle, 14;
wasp, 14; caterpillar, 20; spider, 25.

Labrum: the upper lip of insects and of some crustaceans; grasshopper,
12; beetle, 14; wasp, 14; caterpillar, 20; crayfish, 30.

Lamella: a leaf-like or plate-like structure, 90, 104.

Larva: a young animal which has left the egg and is leading a free life,
but which has not yet completed its development; decapods, 51; ento-
mostracan, 59; tapeworm, 84; mussel, 97: a holometabolic insect
between the embryonic and the pupal stages, 20.

Lateral: a position to the right or left of the median line.

Ligula: the anterior portion of the labium in insects; grasshopper, 13;
wasp, 14.

Lithocyst : a marginal sense-organ in certain meduse, 173, 176.

Liver: a digestive gland; crayfish or lobster, 39; crab, 44; Daphnia, 57;
mussel, 96; oyster, 101; clam, 107; snail, 119; squid, 181; starfish, 145.

Lophophore: a circular or horseshoe-shaped ridge bearing tentacles in
Bryozoa, 86.

Lumen: the cavity within a tubular organ.

Macronucleus: the large nucleus of an infusorian; Paramecium, 186;
Vorticella, 190.

Madreporic plate: a porous plate through which fluids enter the ambulacral
system ; starfish, 142; sea urchin, 151; sea cucumber, 157.

Malpighian tubules: the kidney of insects and certain other arthropods;
grasshopper, 16; caterpillar, 21; spider, 27.

Mandible: the anterior pair of mouth-parts in arthropods; grasshopper,
13; beetle, 14; wasp, 14; caterpillar, 20; spider, 24; crayfish or
lobster, 30; sow-bug, 47; amphipod, 49; copepod, 54; Daphnia, 56;
nauplius, 59.

GLOSSARY 215

Mantle: the integumental fold in mollusks which secretes the shell; mus-
sel, 90; oyster, 100; clam, 104; snail, 113; squid, 124: the body-wall of
ascidians beneath the tunic, 136.

Manubrium : the projection of a medusa’s body which bears the mouth,
167, 178, 175.

Maxilla: the paired mouth-parts immediately behind the mandibles in
arthropods; grasshopper, 13; beetle, 14; wasp, 14; caterpillar, 20;
spider, 25; crayfish or lobster, 30; sow-bug, 47; amphipod, 49; cope-
pod, 54; Daphnia, 56.

Maxillipeds: the anterior thoracic appendages which assist in mastication
in crustaceans; crayfish or lobster, 30; sow-bug, 47; amphipod, 49;
Caprella, 50.

Medusa: a medusoid which becomes a free-swimming jelly-fish, 163, 169,
175.

Medusoid: the sexual generation of a hydromedusan, 163, 169.

Megalopa: a larval stage of the crab, 51.

Mentum : a division of the labium in insects, 13.

Mesentery: a lamella which supports some one of the viscera; Nereis, 64;
Bugula, 86; squid, 127; starfish, 145; sea urchin, 152; sea cucumber,
156; sea anemone, 179.

Mesosternum : the ventral surface of the mesothorax in insects; wasp, 3;
grasshopper, 10.

Mesothorax: the second thoracic somite in insects; wasp, 2; grass-
hopper, 10.

Metamere: one of the serial, homologous body-segments, together with its
appendages, which form the body of an articulate animal.

Metamorphosis: the quiescent period in the life of a holometabolic insect
during which it changes from a larva to an imago.

Metasoma: the primitive segmented trunk of an articulate animal, 62, 68.

Metasternum: the ventral surface of the metathorax in insects; wasp, 3;
grasshopper, 10.

Metastomium : the posterior portion of the prosoma of an annelid, 62, 69.

Metathorax: the third thoracic somite in insects; wasp, 2; grasshopper, 9.

Metazoa: the division of the animal kingdom comprising the many-celled
animals, 191.

Micronucleus: the smaller of the nuclear bodies in infusorians; Parame-
cium, 186; Vorticella, 190.

Mother-of-pearl: the inner layer of the shell of mollusks; mussel, 91;
clam, 105.

Moult : to shed the cuticula or the outer portion of it.

216 INVERTEBRATE ZOOLOGY

Mouth-parts: the masticatory appendages on the head of arthropods; wasp,
2; grasshopper, 12; beetle, 13; wasp, 13; caterpillar, 20; centiped,
22; crayfish or lobster, 30; crab, 43.

Mysis stage: a larval form of the lobster, 51.

Nauplius: a larval form of crustaceans, 59.

Nematocyst: the stinging organ in the Cnidaria which is within the cnido-
blast; Hydra, 161; tubularian, 165; campanularian, 171.

Nephridium: a urinary tubule in annelids; Nereis, 65; earthworm, 73.

Nephrostome: the ciliated opening of a nephridium into the body-cavity ;
Nereis, 65 ; earthworm, 73.

Nerve commissure: a nerve connecting the two members of a pair of gan-
glia; planarian, 78; tapeworm, 82; mussel, 97; clam, 111; snail, 121.

Nerve connective: a nerve connecting two ganglia not of the same pair;
grasshopper, 18; spider, 27; crayfish or lobster, 41; Nereis, 65; mus-
sel, 97; oyster, 102; clam, 111.

Nettle cell: the stinging organ in the Cnidaria; Hydra, 159; Gonionemus,
176; sea anemone, 178.

Neuropodium : the ventral division of the parapodium of an annelid, 63.

Widamental glands: the large glands which secrete the egg-capsules in
the squid, 133.

Notopodium : the dorsal division of the parapodium of an annelid, 63.

Nucleus: a spheroidal body in a cell, the center of its activities ; Parame-
cium, 186; Vorticella, 190; Euglena, 193; Amoeba, 195,

Ocellus: a minute primitive eye; wasp, 2; fly, 7; grasshopper, 9; cater-
pillar, 20; tubularian medusa, 168.

Ocular plate: the plate at the aboral end of a ray of the sea urchin, 151.

Csophagus: the gullet, the division of the digestive canal leading from the
pharynx to the stomach; grasshopper, 15; caterpillar, 21; crayfish or
lobster, 89; Nereis, 64; earthworm, 71; Bugula, 86; mussel, 96;
clam, 110; snail, 117; squid, 130; Molgula, 137; starfish, 145; sea
urchin, 151; sea cucumber, 156.

Ommatidium : a single element of the compound eye of an arthropod.

Occium: a structure in Bryozoa in which the embryo develops, 88.

Oral: the side of the body containing the mouth in a radiate animal; star-
fish, 142; sea urchin, 149; sea cucumber, 155; medusa, 167, 173, 175.

Oral groove: a groove leading to the mouth in ciliate infusorians, 184, 188.

Organ of Keber: an organ probably excretory in function in lamellibranchs ;
mussel, 92; clam, 107.

GLOSSARY 217

Osculum : the cloacal opening in sponges, 181.

Ossicles: the calcareous plates in the body-wall of echinoderms.

Otocyst : an organ of hearing; mussel, 98; clam, 111.

Ovarioles: the tubules forming the ovary of an insect, 16.

Ovary: the female sexual gland; grasshopper, 16; spider, 27; crayfish or
lobster, 37; crab, 44; copepod, 55; Daphnia, 57; earthworm, 72; pla-
narian, 77; tapeworm, 83; mussel, 97; oyster, 102; clam, 110; squid,
183; starfish, 146; Hydra, 161.

Oviduct : the tube leading from the ovary towards the outside; grasshopper,
16; spider, 27; crayfish or lobster, 89; crab, 44; copepod, 55; Daph-
nia, 57; earthworm, 72; planarian, 77; snail, 120; squid, 133.

Ovipositor: the organ by means of which certain insects deposit their eggs;
fly, 8; grasshopper, 10.

Ovoid gland: the axial organ in the starfish, 148; in the sea urchin, 154.

Ovum: the female sexual cell, the egg. °

Pallial line: the line along which the margin of the mantle is attached to
the shell in lamellibranchs; mussel, 91; clam, 195.

Pallial sinus: the indentation in the pallial line caused by the insertion of
the siphonal retractor muscle, 105.

Palp: a sensory organ near the mouth; wasp, 2; grasshopper, 13; crayfish

or lobster, 34; Nereis, 62; mussel, 92; oyster, 101; clam, 106.

Pancreas; a digestive gland in the squid, 130.

Papule: the delicate projections of the body-wall in the starfish, 142.

Paragnatha: delicate lamelle just behind the mandibles in the crayfish
or lobster, 30.

Paramylum: a granular substance resembling starch in Euglena, 193.

Parapodium: the appendage of annelids, 63.

Parasite: an animal which attaches itself to another and lives upon its
nutritive fluids, 80.

Parenchyma: a vesicular connective tissue which fills the body-cavity of
flatworms and leeches; planarians, 79; tapeworm, 81.

Parthenogenesis : reproduction by means of unfertilized eggs, 58.

Pedicellarie: minute pincer-like organs present on the external surface
of starfishes, 142; sea urchins, 150.

Pedipalps: the second pair of appendages in the Arachnida, 24.

Pen: the shell of the squid, 125.

Pericardium : the membrane surrounding the heart; spider, 26; crayfish
or lobster, 38; mussel, 92; oyster, 101; clam, 107; snail, 115; Molgula,
137.

218 INVERTEBRATE ZOOLOGY

Periopods: the thoracic appendages posterior to the maxillipeds in crus.
taceans, 33.

Periostracum: the outer layer of the molluscan shell; mussel, 91; clam,
105; snail, 115.

Periphery: the outer surface of a body.

Periproct: the region immediately around the anus, 150.

Perisarc: the cuticular outer covering of a hydroid; tubularian, 166; cam-
panularian, 170.

Peristome: a membrane surrounding the mouth in echinoderms; starfish,
143; sea urchin, 149.

Peristomium: the posterior portion of the head in most annelids, consisting
of the metastomium and the anterior somites of the metasoma, 62.

Peritoneum : the membrane lining the body-cavity.

Pharynx: the division of the alimentary tract immediately back of the
mouth; grasshopper, 15; Nereis, 64; earthworm, 71; Bugula, 86;
snail, 117; squid, 1381; Molgula, 136.

Plankton: a collective term referring to all small forms of life in the
surface waters of the sea or of fresh water.

Pleopod: an abdominal appendage in crustaceans, 32.

Pleurobranch: a gill attached to the body-wall in crustaceans; crayfish or
lobster, 35; crab, 438.

Pleurum: the lateral surface of the thorax in insects; wasp, 3; grass-
hopper, 10.

Podical plates: paired sclerites at the posterior end of the abdomen in
certain insects, 11.

Podobranch: a gill attached to the leg in crustaceans, 35.

Polian vesicle: a sac extending from the ring canal in echinoderms,
157.

Polyp: a sessile individual in the Cnidaria; Hydra, 159; tubularian, 163;
campanularian, 169; Gonionemus, 177.

Polypide: the soft parts of a bryozoan, 85.

Posterior: at or towards the hinder end of an animal.

Proboscis: a prehensile organ in certain animals, usually a portion of the
pharynx; Nereis, 64; planarian, 76: the beak-like mouth-parts of
certain insects, 7.

Proglottid : a tapeworm segment, 80.

Prosoma: the primitive head of annelids made up of the prostomium and
the metastomium, 62, 68.

Prostate gland: the gland which secretes the fluid in which the spermatozoa
are suspended ; grasshopper, 17; squid, 132.

GLOSSARY 219

Prosternum: the ventral surface of the prothorax in insects; wasp, 3;
grasshopper, 10.

Prostomium : the anterior portion of the head of annelids, 62.

Prothorax: the first thoracic segment in insects; wasp, 2; grasshopper, 9.

Protopodite: the basal segment of a crustacean’s leg; crayfish or lobster, 32.

Protractor muscle: a muscle which extends the organ to which it is
attached; Nereis, 64; mussel, 91.

Proximal: a position towards the point of attachment — opposed to distal.

Pseudopodium : a retractile process in rhizopods, 194.

Pulsating vacuole: a globule of excretory fluid in many protozoans; Para-
mecium, 186; Vorticella, 189; Euglena, 193; Amoeba, 195.

Pulvillus: an adhesive pad on the foot of insects; fly, 8; grasshopper, 12.

Pupa: the stage in the life of a holometabolic insect when it is undergoing
its metamorphosis.

Racemose vesicles: minute diverticula of the ring canal in starfishes, 146.

Radial symmetry: having the parts or organs arranged symmetrically
about a common center.

Radial tubes: a portion of the gastro-vascular space in the medusa, 167,
178, 175.

Radula: the band of calcareous teeth in the pharynx of gastropods and
cephalopods; snail, 120; squid, 132.

Ray: one of the main divisions of the radiate body of echinoderms, 141,
150, 155.

Receptaculum seminis: a receptacle for sperm in the female animal; grass-
hopper, 16; spider, 27; crab, 44; snail, 118.

Rectal glands: glandular structures in the rectum of certain insects, 15.

Rectum: the posterior division of the digestive tract; grasshopper, 15;
caterpillar, 21; crayfish or lobster, 39; Bugula, 86; mussel, 96; clam,
110; snail, 118; squid, 131; sea cucumber, 156.

Respiratory tree: a branched diverticulum of the rectum in holothurians,
156.

Retractor muscles: muscles which draw in an organ to which they are
attached; Nereis, 64; mussel, 91; clam, 105.

Rostrum : a projection of the carapace in crustaceans, 29:

Salivary glands: digestive glands at the anterior end of the digestive tract;
grasshopper, 15; snail, 118; squid, 131.

Scaphognathite: the elongated epipodite of the second maxilla in certain
crustaceans, 34.

220 INVERTEBRATE ZOOLOGY

Sclerite: a small plate forming a portion of the cuticula of a segment
in insects.

Scolex: the anterior end of a tapeworm, 80.

Scutellum: a small sclerite in the tergum of the thoracic segments in
insects.

Segment: one of a number of serial divisions of an animal’s body or of
an organ.

Septum: a plate forming a division wall between two spaces; Nereis, 63;
earthworm, 69; mussel, 92; clam, 106.

Sessile: fixed to one place, without locomotory powers — of an animal;
Bugula, 85; oyster, 99; Molgula, 135 ; tubularian, 163 ; campanularian,
169; Grantia, 181; Vorticella, 188: not on a stalk or stem — of an
organ, 46.

Seta: a bristle; Nereis, 61; earthworm, 67.

Setigerous glands: glands which secrete sete, 73.

Sexual: reproduction through the agency of the two sexes.

Shell gland: the kidney of entomostracans; copepod, 55; Daphnia, 57.

Siphon: the organ through which water enters or leaves the mantle cavity
in mollusks and ascidians; mussel, 92; clam, 106; squid, 124; Mol-
gula, 135.

Siphonoglyph : a ciliated groove in the angle of the gullet in Anthozoa, 178.

Somite: one of the serial, homologous body-segments which form the
body of an articulate animal.

Spermatheca : a sac for the storing of sperm in the female animal, a semi-
nal receptacle, 72.

Spermatophore: a capsule or mass of spermatozoa; copepod, 55; snail, 121;
squid, 133.

Spermatozoon: the male sexual cell.

Sperm-duct : the vas deferens, 27, 71.

Sperm-sac: a sac for the storing of sperm in the male animal, a seminal
vesicle, 71.

Sperm-sphere : a mass of spermatozoa in the earthworm, 73.

Spicule : a minute calcareous or silicious body in sponges and echinoderms.

Spinnerets: the appendages on a spider from which the silk exudes, 25.

Spiracle: an external opening in the tracheal system; wasp, 3; fly, 8;
grasshopper, 11; caterpillar, 21; spider, 26.

Sporosac: a sessile medusoid, one which remains attached to the parent
hydroid; tubularian, 163; campanularian, 169.

Sternite: the ventral portion of an abdominal segment in insects; wasp, 3;
grasshopper, 10.

GLOSSARY 221

Sternum : the ventral surface of the thorax in arthropods; wasp, 3; grass-
hopper, 10; spider, 25.

Stigmata: the respiratory openings in the pharyngeal wall in Molgula,
189.

Stipes: a division of the maxilla in insects, 13.

Stomach: a division of the digestive tract in which digestion goes on;
crayfish or lobster, 36; Bugula, 86; mussel, 96; clam, 110; snail, 117;
squid, 130; Molgula, 137; starfish, 145; sea urchin, 152; sea cucumber,
156; sea anemone, 175.

Stomach-intestine : a division of the digestive tract in which both digestion
and absorption go on; grasshopper, 15; caterpillar, 21; Nereis, 64;
earthworm, 71.

Stomach pouch: a diverticulum of the stomach; Bugula, 86; squid, 181.

Stone canal: a tube joining the madreporic plate with the ring canal in
echinoderms, 146, 153, 157.

Submentum : the basal segment of the labium in insects, 18.

Subneural gland: a glandular body in ascidians, 138.

Subumbrella: the oral surface of a medusa, 167, 173, 175.

Supporting layer: the non-cellular layer between the ectoderm and ento-
derm in Hydrozoa; Hydra, 160; tubularian, 165; campanularian, 171.

Swimmeret: an abdominal appendage of a crustacean, a pleopod; crayfish
or lobster, 32; crab, 43.

Symbiotic: the living together of two dissimilar organisms, each being

dependent upon the other, 160.
Systemic heart: the median heart of the squid, 129.

Tactile: relating to the sense of touch. :

Tarsus: the foot of an insect or a spider; wasp, 4; grasshopper, 12;
spider, 25.

Telson: the terminal segment of a crustacean, 31.

Tentacle: an elongated tactile organ; Nereis, 62; Bugula, 86; oyster, 100;
snail, 114; Molgula, 135; sea cucumber, 155; Hydra, 159; tubularian,
164; campanularian, 170; Gonionemus, 176; sea anemone, 178.

Tergite: the dorsal surface of an abdominal segment in insects, 3, 10.

Tergum: the dorsal surface of a thoracic segment in insects; wasp, 3;
grasshopper, 10.

Terminal: towards or at the posterior or the distal end.

Test: the tunic of the ascidian, 185: the rigid shell of the sea urchin, 150.

Testis: the male sexual gland; grasshopper, 17; spider, 27; crayfish or
lobster, 87; crab, 44; copepod, 55 ; Daphnia, 58; earthworm, 71;

222 INVERTEBRATE ZOOLOGY

planarian, 77; tapeworm, 83; mussel, 97; oyster, 102; clam, 110;
squid, 1382; starfish, 146; Hydra, 161.

Thorax: the body-division of arthropods following the head; wasp, 2; fly,
7; grasshopper, 9; caterpillar, 20; spider, 24; crayfish or lobster, 28;
sow-bug, 46; amphipod, 48; Caprella, 50; larval decapods, 51; cope-
pod, 53; Daphnia, 56.

Tibia: the segment of an insect’s leg between the femur and the tarsus;
wasp, 4; grasshopper, 12; spider, 25.

Tiedemann’s vesicles: minute diverticula of the ring canal of the star-
fish, 146.

Trachea: a respiratory tube; grasshopper, 17; caterpillar, 21; spider, 27.

Trichocyst: a cyst containing a defensive bristle in the ectosare of Infu-
soria, 186.

Trivium : the three rays of an echinoderm opposite to the bivium, 143, 151.

Trochanter: the segment of an insect’s or a spider’s leg, between the coxa
and the femur; wasp, 4; grasshopper, 12; spider, 25.

Trochophore: a larval form common to polychetous annelids.

Tunic: the outer cuticular covering of tunicates, 135.

Umbo: the protuberance above the hinge on the shell of a lamellibranch;
mussel, 89; oyster, 99; clam, 103.

Ureter: a tube forming the outlet of the kidney; crayfish or lobster, 40;
mussel, 95; clam, 109; snail, 116.

Uropod: the sixth swimmeret of the macruran decapod, that which forms
the swimming tail, 32.

Uterus : a dilated portion of the oviduct in which the egg or the developing
animal is detained; planarian, 77; tapeworm, 83.

Vagina: the terminal division of the female reproductive tract; grass-
hopper, 16; tapeworm, 83; snail, 120.

Vas deferens: a duct leading from the testis towards the external opening ;
grasshopper, 17; crayfish or lobster, 37; crab, 44; copepod, 55; earth-
worm, 69; planarian, 77; tapeworm, 83; snail, 120; squid, 132.

Vas efferens: a duct leading from the testis to the vas deferens; planarian,
77; tapeworm, 83.

Vegetative organs: those organs which have to do with the processes of
nutrition, growth, and the expulsion of wastes.

Vein: a vessel which brings blood towards the heart; crayfish or lobster,
38; snail, 116; squid, 120.

Velum : the circular muscular membrane of a medusa, 168, 174, 176.

GLOSSARY 223

Ventral: on or towards the underside of an animal.

Ventricle : a chamber of the heart from which blood is sent over the body;
mussel, 94; clam, 108; oyster, 101; snail, 115.

Vesicula seminalis: a sperm-sac in the male animal; squid, 132.

Viscera: the organs within the body-cavities.

Visceral mass: the compact group of organs comprising the principal viscera
in mollusks; mussel, 90; oyster, 100; clam, 104; snail, 113; squid, 125.

Wing-covers: the first pair of wings of a beetle, the elytra, 5.
Yolk glands: planarian, 77; tapeworm, 88.

Zoéa: a larval form of the crab and of certain other crustaceans, 51.
Zocecium: the outer cuticular covering of a bryozoan, 85.

_ INDEX

Ambulacral system: starfish, 146; sea
urchin, 153 ; sea cucumber, 157.
Amoeba: general form, 194; repro-

duction, 195; conjugation, 196.
Amphipod, 48, 50.
Annelida: Nereis, 61; earthworm, 67.
Anodonta, 89.
Anthozoa, 178.
Arachnida, 24.
Arbacia, 149.
Armadillidium, 46.
Arthropoda, 1.
Ascidiacea, 135.
Asterias forbsii, 141.
Asterias vulgaris, 141.
Asteroidea, 141.

Beetle: external parts, 5; mouth-
parts, 13.

Bell animalcule, 188.

Bougainvillea, 163.

Brachyuran decapod, 42.

Bryozoa, 85.

Bugula: the zocecium, 85; polypide,
85; internal organs, 86; avicularia,
87; ocecia, 87.

Calcarea, 181.

Campanularia, 169.

Campanularian hydromedusan : alter-
nation of generations, 169; hydroid
stage, 169; medusoid stage, 172.

Caprella, 50.

Carchesium, 188.

Caterpillar: external parts, 20; inter-
nal parts, 20.

Centiped, 22.

225

Cephalopoda, 124.

Cestoda, 80.

Chaetopoda: Nereis, 61; earthworm,
67.

Chilopod, 22.

Ciliate infusorian: Paramecium, 184;
Vorticella, 188.

Circulatory system: grasshopper, 18;
crayfish or lobster, 38; Nereis, 64;
earthworm, 70; Bugula, 87; mussel,
94; clam, 108; snail, 116; squid,
129; Molgula, 187; starfish, 148;
sea urchin, 154.

Cladoceran phyllopod, 56.

Clam, see Hard-shell clam.

Cnidaria: Hydra, 159; tubularian
hydromedusan, 163; campanularian
hydromedusan, 169.

Coleopterous insect, 5.

Copepod : external anatomy, 538
ternal anatomy, 54.

Crab: external parts, 42; gills, 48;
internal parts, 44; zoéa of, 51;
megalopa of, 51.

Crayfish or lobster: external parts, 28;
appendages, 32; gills, 35; internal
organs, 86; circulatory system, 38;
reproductive system, 39; digestive
system, 39; excretory system, 40;
nervous system, 41; mysis stage of
lobster, 51.

Crustacea: crayfish or lobster, 28;
erab, 42; sow-bug, 46; typical am-
phipod, 48; Caprella, 50; larval
decapods, 51; copepod, 53; Daph-
nia, 56; nauplius larva, 59.

Cyclops, 53.

?

in-

226

Daphnia: external parts, 56; internal
anatomy, 57; parthenogenesis of, 58.

Decapod: macruran, 28; brachyu-
ran, 42; larve of, 51.

Dibranchiate cephalopod, 123.

Digestive system: grasshopper, 15;
caterpillar, 21; spider, 27; crayfish
or lobster, 39; copepod, 54; Daphnia,
57; Nereis, 64 ; earthworm, 70 ; pla-
narian, 77; Bugula, 86; mussel, 96;
oyster, 101; clam, 109; snail, 117;
squid, 130; Molgula, 136; starfish,
145; sea urchin, 151.

Diplopoda, 22.

Dipterous insect, 7.

Earthworm: external parts, 67; inter-
nal anatomy, 69; circulatory system,
70; digestive system, 71; reproduc-
tive system, 71; excretory organs,
73; nervous system, 74; a cross
section, 74.

Echinodermata: starfish, 141; sea
urchin, 149; sea cucumber, 155.

Echinoidea, 149.

Ectoproct bryozoan, 85.

Euglena, 192.

Excretory system: grasshopper, 16;
crayfish or lobster, 40; copepod, 55;
Nereis, 65; earthworm, 73; plana-
rian, 78; tapeworm, 82; mussel,
95; clam, 109; snail, 116; squid,
129; Molgula, 138; Paramecium,
186; Vorticella, 189; Euglena, 193;
Amoeba, 195.

Fly, 7.

Free-swimming ciliate, 184.

Freshwater mussel: shell, 89; mantle,
90; visceral mass, 90; mantle cavity,
91; respiratory system, 93 ; circula-
tory system, 94; excretory system,
95; digestive system, 96; reproduc-
tive system, 97; nervous system, 97.

INVERTEBRATE ZOOLOGY

Freshwater polyp, 159.
Freshwater shrimp, 48.

Gammarus, 48.

Gastropod, 112.

Gonionemus, 175.

Grantia: general form, 181; repro-
duction, 183.

Grasshopper: external parts, 9; mouth-
parts, 12; digestive system, 15;
excretory system, 16; reproductive
system, 16; respiratory system, 17;
circulatory system, 18; nervous
system, 18.

Hard-shell clam: shell, 103; mantle,
104; visceral mass, 104; mantle
cavity, 105; respiratory system,
107; circulatory system, 108 ; excre-
tory system, 109; digestive system,
109; reproductive system, 110;
nervous system, 111.

Helix pomatia, 112.

Holothurian, 155.

Hydra: general form, 159; reproduc-
tion, 161.

Hydromedusan, 163, 169.

Hydrozoa: Hydra, 159; tubularian
hydromedusan, 163 ; campanularian
hydromedusan, 169.

Hymenopterous insect, 1.

Infusoria: Paramecium, 184; Vorti-
cella, 188; Euglena, 192.

Insect larva, 20.

Insecta: wasp, 1; beetle, 5; grass-
hopper, 9; caterpillar, 20.

Isopod, 46.

Land snail: shell, 112; visceral mass,
113; mantle, 113; head, 114; mantle
cavity, 115; respiratory system,
116; circulatory system, 116; excre-
tory system, 116; digestive system,

INDEX

117; reproductive system, 120; nery-
ous system, 121.

Limax maxima, 112.

Lithobius, 22.

Lobster, see Crayfish.

Loligo pealii, 123.

Macruran decapod, 28.

Metridium, 178.

Molgula: external parts, 135; digest-
ive system, 136; reproductive sys-
tem, 1387; circulatory system, 137;
nervous system, 138; excretory sys-
tem, 138; peribranchial chamber,
188 ; respiratory system, 139.

Mollusca: freshwater mussel, 89;
hard-shell clam, 103; land snail,
112; squid, 123.

Mussel, see Freshwater mussel.

Mya arenaria, 103.

Myriapoda, 22.

Naked rhizopod, 194.

Nereis: external parts, 61; parapodia,
63; internal anatomy, 63; diges-
tive organs, 64; circulatory system,
64; excretory system, 65; nervous
system, 65; reproductive system,
66.

Nervous system: grasshopper, 18;
crayfish or lobster, 41; crab, 44;
Daphnia, 57; Nereis, 65; earth-
worm, 74; planarian, 78; tapeworm,
82; Bugula, 87; mussel, 97; oyster,
102; hard-shell clam, 111; snail,
121; squid, 133; Molgula, 138; star-
fish, 147; sea urchin, 154; medusa,
168, 174.

Obelia, 169.
Oligochaetous annelid, 67.
Oniscus, 46.

Orthopterous insect, 9.
Oyster, 99.

227

Paramecium: general form, 184; re-
production, 187; conjugation, 187.
Pelecypoda: freshwater mussel, 89;
oyster, 99; hard-shell clam, 103. |

Pennaria, 163.

Phyllopod, 56.

Planarian worm: external parts, 76;
digestive system, 77; reproductive
system, 77; nervous system, 78;
excretory system, 78.

Plathelminthes: planarian worm, 76 ;
tapeworm, 80.

Polychaetous annelid, 61.

Polyzoa, 85.

Porcellio, 46.

Protozoa: Paramecium, 184; Vorti-
cella, 188; Euglena, 192; Amoeba,
194.

Pulmonate gastropod, 112.

Reproductive system: grasshopper,
16; caterpillar, 21; crayfish or lob-
ster, 39; copepod, 55; Daphnia, 57;
Nereis, 66; earthworm, 71; plana-
rian, 77; tapeworm, 83; Bugula,
87; mussel, 97; clam, 110; snail,
120; squid, 182; Molgula, 137; star-
fish, 145; sea urchin, 152; Hydra,
161; tubularian, 168; campanula-
rian, 173; Grantia, 183; Parame-
cium, 187; Vorticella, 190; Euglena,
193 ; Amoeba, 195.

Respiratory system: grasshopper, 17;
spider, 27; crayfish or lobster, 35;
Nereis, 63; mussel, 93; clam, 107;
snail,116; squid, 129; Molgula, 139.

Sand-flea, 48.

Schizopodous crustacean, 52; see Ap-
pendix, under Malacostraca.

Sea anemone, 178.

Sea cucumber, 155.

Sea urchin: external parts, 149; di-
gestive system, 151; genital system,

228

152; ambulacral system, 153 ; nerv-
ous system, 154; circulatory system,
154.

Sessile ciliate, 188.

Shrimp, freshwater: external parts,
48; appendages, 49.

Simple ascidian, 135.

Slipper animalcule, 184.

Snail, see Land snail.

Sow-bug: external parts, 46; append-
ages, 47.

Spider, 24.

Spongiaria, 181.

Squid: external anatomy, 123; mantle
cavity, 125; excretory system, 127;
circulatory system, 129; respiratory
system, 129; digestive system, 130;
reproductive system, 182; nervous
system, 133; pen, 134.

Starfish: external parts, 141; digest-
ive system, 145; reproductive sys-
tem, 145; ambulacral system, 146 ;
nervous system, 147; circulatory
system, 148.

Strongylocentrotus, 149.

Sycon sponge, 181.

INVERTEBRATE ZOOLOGY

Taenia crassicollis, 80.

Taenia saginata, 80.

Taenia serrata, 80.

Talorchestia, 48.

Tapeworm: external form, 80; pro-
glottids, 81; encysted tapeworm,
83.

Trachomedusa, 175.

Tubularian hydromedusan: alterna-
tion of generations, 163; hydroid
stage, 163 ; medusoid stage, 167.

Tunicata, 135.

Turbellaria, 76.

Unio, 89.

Venus mercenaria, 103.

Vorticella: general form, 188; repro-
duction, 190; conjugation, 191.

Vorticellide, 188.

Wasp: external parts, 1; mouth-parts,
13.

Zoothamnium, 188.

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