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| archive.org/details/courseininvertebOOpratuoft
ae of
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
Tis ~ AAD er oe 2 a
a 3
| ‘ALL RIGHTS RESERVED
, | 815.7 cei
| aa: 13 1964
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
lv 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 Vv
Professors A. S. 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. 8. 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. 8. 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 WaAspP.
A BEETLE .
A Fiy
A GRASSHOPPER .
A CATERPILLAR .
A CENTIPED
A SPIDER ee
A CRAYFISH OR A LOBSTER.
A Cras.
A Sow-Bue
An AMPHIPOD
CAPRELLA . :
LARVAL DECAPODs .
A Coprpop
DAPHNIA a!
A Naupuius Larva
CHAPTER II
ANNELIDA
NEREIS . ;
An EARTHWORM .
CHAPTER III
PLATHELMINTHES
A PLANARIAN Worm .
A TAPEWORM .
vii
> GL
67
76
80
Vill
Ectoprocta
Pelecypoda
Gastropoda
Cephalopoda
Ascidiacea
Asteroidea
Echinoidea
Holothurioidea
Hydrozoa
Anthozoa
CONTENTS
CHAPTER IV
BRYOZOA (POLYZOA)
BuGuLA
CHAPTER V
MOLLUSCA
A FRESHWATER MusSEL
AN OYSTER ;
A Harp-SHELL CLAM
A LAND SNAIL .
A Squib
CHAPTER VI
TUNICATA
A SIMPLE ASCIDIAN .
CHAPTER VII
ECHINODERMATA
A STARFISH .
A SEA URCHIN .
A HoLoTrHuRIAN
CHAPTER VIII
CNIDARIA
HypRa . Pe RY a tek
A TUBULARIAN HyDROMEDUSAN.
A CAMPANULARIAN HyDROMEDUSAN
GONIONEMUS .
A.SrEA ANEMONE
PAGE
85
89
99
103
112
123
135
141
149
155
159
163
169
175
178
CONTENTS 1X
CHAPTER IX
SPONGIARIA
PAGE
Calcarea IEEE Waraet tp eee a ger ere a EBL
CHAPTER X
PROTOZOA
Infusoria Peewee MMONI See fe. Gib ay ee os wt yes a LOE
ee eats Totnes tree oe ie lide ee | LOS
Mastigophora EvetENA . . » ~~ ee se + + + we ee 192
Sarcodina RE re Nee guia set te gs lg a we OE
APPENDIX
A SYNOPSIS OF THE CLASSIFICATION OF ANIMALS... .. . 197
eee on erie de Sk ee cokes oe o. QOF
SRR ee gn Pa gms es Spe a) a cre Soe ie eee
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.e., 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
9 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
t
7
r
ee a a a a ee
i [eee ee
ss a a iti ee eae
¥ 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 ?
Exercise 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 antennz, the position of the compound eyes and
ocelli and the upper lip, and label them all.
4 INVERTEBRATE ZOOLOGY
Exercise 3. Remove a metathoracic leg and draw an outline
of it on a scale of 5. Its different segments, beginning
with the proximal one, 7.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.
SS | EEE
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-
ligent 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 sur-
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 antenne, 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 alarge 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.
Exercise 3. Draw, on a large scale, a side view of the head with
the proboscis extended. Note carefully the form of the
antenne 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.
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 antennz 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 maxilla, the median hypo-
pharynx, and the paired under lip or labium. The paired mouth- —
parts are the second, third, and fourth pairs of appendages, the __
antenne 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.
Exercise 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 maxillz
and the labium, also, do not differ materially from those of
the beetle or the grasshopper. The labium les between
the two maxillz, 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 30% 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-cayvity. 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 ductsof 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. (a) Make a semidiagrammatic drawing represent-
ing all the parts of the female reproductive tract.
I i a
a ee ee oe
- h )
~- pete Wee “mv eu
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. (b) 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
tracheee. 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
trachee.
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 valyu-
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
praesophageal ganglion or brain. The brain is the largest
ganglionic mass in the body and is situated in the top of the
hes d 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
an tenn, while near them in the median line is the median
if
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
j
:
:
:
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
Cd
:
i
ioe
A CATERPILLAR 91
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 trache 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 trachez 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 trachez 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 ra
of maxilla, 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
7 ‘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
R 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 maxillze 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
ealled a lung-book, in which the blood circulates. The trachez
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 silk 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;
t.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
ie
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
f 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
ot 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
S oo provided with special sense-organs. Most important to it
are the two pairs of feelers or antenne, which are characteristic
Bot 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 antenne, 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
ee ee een
2 ns
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 antenna, 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 maxilla,
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
ure 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
she 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
jhe eggs from the time they are laid until the young are
natched. The last pair in both sexes is large and broad
ind with the end-segment forms the swimming fin. The end-
segment is called the telson; it bears no appendages; the anal
pening is in its ventral side.
The natural color of the animal is usually a greenish black,
gut hot water or alcohol turns it red.
ixercise 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
sare not to injure the gills beneath. Push aside the gills and
10tice the thin integument which forms the lateral wall of the
sephalothorax. Observe the method of attachment of the gills. -
They are feathery, thin-walled expansions of the body-wall and
ire attached either to it or to the basal portions of the legs..
Chey present a very large surface to the surrounding water, and
he blood circulating through them is thus oxygenated. Notice
the epipodites, the skinny flaps which project from the basal
oints of many of the legs and separate the gills of a segment
rom 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
Exercise 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. ‘he 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. ‘I'he 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 (¢.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.
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, t
cerebro-pedal connective, which goes to the pedal ganglia, an
the pallial nerve, which passes to the mantle. Find them. |
The pedal ganglia form a nervous mass buried in the fo
near its base. Make a shallow longitudinal incision in the bi
‘tom of the foot and gently pull the flaps apart; the pinki
mass and the nerves radiating from it will be seen. In conta
with it is a sense-organ called the otocyst. 4
Exercise 10. Draw a diagram representing the nervous sys fem.
Make several transverse sections with a razor through { h
region of the heart of a mussel which has been previou
hardened. Identify all the organs which appear.
Exercise 11. Draw a diagram representing a cross section; cai
fully label all the organs. 7
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 exten
from the umbo to the ventral and posterior sides of the sh 7
When the anterior, the right, and the left sides of the shell a
known, the ventral and posterior sides can be easily determin
Exercise 1. Make an outline drawing of the right valve, indica
ing the anterior, posterior, dorsal, and ventral aspects an
showing the.lines of growth.
Remove the right valve in the following way: Break off t
edge of the shell with a hammer, insert the blade of a scalps
and cut the large adductor muscle, which is not far from the
edge but nearer the dorsal than the ventral margin. 164
important to keep the blade close to the right valve so as m
to mutilate the internal organs. ‘Force off the right valve ant
examine its inner surface.
Exercise 2. Draw the inner surface of the shell, showing t
muscle scar with its lines of growth and the hinge lig
ment, and label the dorsal, ventral, anterior, and posteri
sides of it.
Study the animal as it lies in the left valve. Note the soi
shiny mantle, which covers the inner surface of the shell an
has secreted it. The mantle is a double fold of the integumen
which extends ventrally from the dorsal side and covers the ty
lateral sides of the body. Its lower edge is bordered by a frin
of short, pigmented tentacles which are the principal sense orga
of the animal; it is also provided with muscle fibers whie
enable it to be slightly extended beyond the edge of the shell.
The most conspicuous organ in the body will be seen to”
the large adductor muscle. Lying between it and the hinge lig
ment is the visceral mass, containing most of the viscera. Alo
the ventral side are the four gills. 4
Put the oyster into a pan of water and with fine scissors @
forceps remove the right mantle. Just in front of the addue
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; 2.e., a palp on the
right side joins one on the left and forms the Eber lip, and the
other two palps join to form the under lip.
_ 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. -
Exercise 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 esophagus, the
‘stomach and the dark-colored liver which surrounds it, and the
Tong intestine. The mouth opens directly into the wsophagus,
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
“3 AF
‘ v
al
*
102 _ INVERTEBRATE ZOOLOGY
and ventral sides of it, and thus back again to the dorsal side o
the muscle, where it ends with the anus. ‘ Most of it is surroundec
by the yellow reproductive gland. Lay bare the intestine. Thi
can be done best after the oyster has been hardened for a fe
days in a 5 per cent. solution of formalin. 4
Exercise 4. Make a drawing of the digestive tract in an outli
of the animal’s body. 3
The remaining systems of organs of the visceral mass will r
be studied in this dissection. § |
The American oyster is a unisexual animal; the comme
European oyster is hermaphroditic. The reproductive gland
the ovaries or testes, are a pair of yellowish or whitish organs
irregular form which occupy the larger part of the visceral ma
and surround the digestive tract and other organs. The kidne
are also a pair of organs of irregular form which, together w
a portion of the intestine, occupy the lower and hinder part 0
the visceral mass, between the muscle and the gills. The nerve
' system has been much modified by the sessile habit of life of 1
oyster. The cerebral ganglia are represented by a nerve ri
containing ganglia, which surrounds the mouth; it is called ¢
circumpallial nerve. Fibers from this ring go to the pigm ont
sense papille at the margin of the mantle. The visceral gang
lie along the antero-ventral side of the muscle and are joine
with the cerebral ring by longitudinal connectives. ‘The pe
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. Y
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.
Kall 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.t
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 t xu
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, #.c., it secretes
it. The lower edge of the mantle is provided with muscle
fibers and can be extended beyond the. edge of the shell;
also possesses sensory functions; in some pelecypods ey
are situated in the mantle’s edge.
Observe the large, soft visceral mass hanging between the
lobes of the mantle; it contains most of the viscera of
animal. On the lower side of the visceral mass, 7.e., towart
the gape of the shell, is the muscular wedge-shaped foot, whicl
can be extended beneath the edge of the shell and is the orga:
of locomotion. Do you see the two leaf-like gills on each sid
of the visceral mass and foot? Observe the two large adduct
muscles, one in front of and the other behind the visceral mass
which pass from one valve to the other and serve to clo:
them. a
Pass a knife between the mantle and the left shell and sepé
rate them from each other. Cut the two muscles close to t
shell; cut the hinge ligament and remove the left shell.
Study the inner surface of the shell. Note the two lar
scars marking the surfaces of attachment of the adductor mu
cles; just above the anterior sear is that of a much sm: ll
1 The shell may also be opened by inserting some sharp, wedge-shaped inst
ment between the valves. The valves are thus pressed apart far enough
admit the blade of a scalpel, by means of which the adductor muscles should
cut close to the left valve of the shell. The hinge ligament should then be
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 th
branchial or incurrent siphon; through it the water streams into
the branchial chamber bearing food and air for respiration. Th
dorsal siphon is called the excurrent or cloacal siphon and throug!
it water passes outward from the cloacal chamber charged wit
carbon dioxide of respiration and with fecal matter from #
alimentary tract. Probe the cloacal chamber.
Carefully remove the left mantle lobe after cutting it ¥
fine scissors at its line of attachment, beginning at the forsill
end. Cut off the siphonal muscle, leaving the siphon in posi
tion. Place the animal in water and study the arrangement ol
the organs. Observe the position of the gills; note in front of
them two triangular flaps, the oral palps; in the median ling
between the two pairs of oral palps is the mouth; find i
Along the base of the gills note an elongated passage leadin
posteriorly to the cloacal chamber, the suprabranchial passage ¢
the outer gill. Blow into this passage at its hinder end in th
cloacal chamber with a blow-pipe, or probe it. .
Observe again: the siphonal region. Note the short septur
which separates the branchial from the cloacal chamber, and th
opening between it and the visceral mass; probe this openin,
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-
-ceardium and the heart and above the posterior adductor muscle
to the cloaca will be seen the rectum. !t 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, Ste pmaerae 3 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 lamellee 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 lamellae. 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, 1
of cross-ridges, the interfilamentary connections, which run betwe on
and connect the vertical filaments. The apertures in the lattice
work place the water-tubes in communication with the water o
the branchial chamber. The gill-filaments are provided with
cilia, as may easily be seen if the gill be alive, the action ¢
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 passage :
Show the direction of the flow of the respiratory water by
means of arrows.
Exercise 7. Draw a diagram showing the structure of a lamel B
The circulatory system. With fine scissors carefully cut ope?
the pericardium by a slit along its dorsal border and expose ‘h
heart. Note the heart with the rectum passing through it. The
heart consists of three chambers —a median, thick-walled ventric
and two lateral auricles. These latter are delicate, thin-walle
organs, triangular in shape, the base of the triangle lying alon;
the dorsal border of the gills and the apex communicating wit
the ventricle. If the left auricle. has been injured in th
dissection, the right one is easily seen by looking across th
pericardial space. From the ventricle an anterior and a 00s
terior artery pass to either end of the body. The posteric
artery expands, near the posterior end of the pericardium,
form a large thick-walled sac, the arterial bulb. These
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. |
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. Their external openings are a pair
of minute pores, one on each side of the visceral mass just —
A HARD-SHELL CLAM be oi
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 wh
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, hi
any large Helix may be used instead. The large slug (
maxima) is very similar to Helix in structure and may also be
used, but as it has no coiled shell that feature of the dissectio
would be omitted. E
‘ The snail is a terrestrial animal and feeds principally up 0 |
leaves. It hibernates in the winter under stones and logs a:
having first closed the mouth of its shell with a thin disal
calcified slime called the epiphragma. If it is still in winte
quarters, when obtained, the epiphragma should be remove
and the animal placed among fresh leaves in a warm roo!
when it will soon come out of its shell and begin to fee
Snails are best killed for dissection by drowning. They shoul
be placed in a large covered jar of water, when they will di
expanded in from one to two. days. If the air be first boile
out of the water the process will be accelerated, but the anima
should not be placed in water which is still hot. =
Study the external characters of the animal. Its body 3
unsegmented and is covered with a shell, but unlike the shel
of the pelecypod that of the snail is a univalye. As il
other mollusks, the shell is the cuticula of the animal charg 7
with calcareous salts, and forms an exoskeleton. In shape #l I
shell is an elongated cone which has been twisted to the righ
forming a closely coiled spiral. The tip of the spiral is al |
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, 7.¢., 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 extremit y-
The mouth of the animal is between and a little below th
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 anima
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. a
Note the asymmetry of the animal. Its spiral twist has been
the cause of the loss of the primitive bilateral symmetry of th
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 r ot
a median posterior position, as must have been the case in .
primitive ancestor of the animal, but have suffered displace
ment to the right side. Other instances of asymmetry will
noticed as the dissection proceeds.
Exercise 1. Draw a side view of the animal seen from the rig
side as it appears when it is moving and when the head
and foot are out of the shell, and label the parts oho
mentioned.
Exercise 2. Draw a similar sketch of a front view of the ani nal.
Remove the dead animal from its shell in the following w y
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. ‘l'ake 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 th
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 wh orl.
The mantle can now be laid back and its cavity with the organs
exposed. The broad rectum will be seen running along ‘h
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 mantl
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, ih
network of blood vessels in the inner surface of the mantle, and
the large pulmonary vein, which runs along the kidney to i”
heart. Slit open the pericardium. The two chambers of tl -
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 respire (OT)
pore; this is accomplished by the alternate enlarging and co oF
tracting of the cavity by means of the muscular body-wall wh
constitutes its floor. Notice the longitudinal and the s-
verse muscles in this floor. The blood circulating in the 4
is oxygenated and passes into the heart through the pulmons
vein as arterial blood. It is forced by the heart through th
aorta, and thence through arteries to all parts of the k =
whence it returns through blood lacune to the lung.
The excretory system. The large kidney has already been s
It is a sac, the glandular projections of the walls of whi :
almost fill its lumen. As is the case with pelecypods,
kidney communicates with the pericardial space through a -
canal and also with the mantle cavity by means of a ur ;
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 and 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 3, 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 csophagus is encircled by the
118 INVERTEBRATE ZOOLOGY
white nerve collar, the dorsal portion of which is the brain. 1]
however, the animal died in a retracted condition the pharyn
_ may have slipped back through the nerve collar, which wou.
then encircle the forward end of that organ. Note the ty
white, leaf-like salivary glands which lie-close against the wi
of the stomach, and trace their ducts forward to the phar a: m
Lying above and across the cesophagus is the white cylind:
penis, which will be seen to extend from the genital poi re
the right of the mouth and to bend sharply on itself. “
bend of the penis is connected by a long retractor muscle
the dorsal body-wall. Find it; cut it and pin the penis on
animal’s right. Note the broad, glistening retractor mu
connecting the pharynx with the ventral, posterior body-wall.
Notice its shape; with strong forceps pull it loose from th
pharynx and entirely remove it. Also beneath it, note the st
larger retractor muscle running from the forward end of th
head back to the same locality. What is the function of tl
different retractors? The dark-colored sheaths and the ret a
muscles of the tentacles will also be seen; trace these muse
to their origin. Find the nerve which passes from tig bi
into each tentacle. 4
Separating the delicate filaments connecting the stom 1
the surrounding organs, and pushing it and the csophagui
the animal’s left, find the large nervous mass which forms
ventral portion of the nerve collar, and the nerves radia
from it. It is an agglomeration of ganglia, being a
principally of the pedal and the visceral ganglia. Press the re
ductive organs to the animal’s right and pin them down,
receptaculum seminis, a small spherical body the size of a §
the end of a long tube, will be found in a bend of the inte est
from which it must be separated. ;
We turn now to the other end of the intestine. aC
rectum from the anus to the point where it is surro ndet
the liver and carefully dissect away the integument which ¢01
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 Ps 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. Obse ve
the thick muscular tongue, the organ by means of which t 2
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. | a .
iy)
Exercise 6. Make a drawing of several of the teeth. |
The reproductive system. The snail is hermaphroditic, but i s
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 hermaphroditi
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 mou ih.
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 glandula
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 th
oviduct, the glandular walls of which, together with the ¢ bu
minous gland, secrete the albumen which surrounds them whe
they are extruded. Near their forward end these two canals
separate. The oviduct loses its glandular walls, becomes cylir
drical in shape, and expands to form the vagina. This is a thie i
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 joim
with the vagina by means of a long tube which lies along thi
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 cesophagus. 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
supracesophageal 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. t
pharynx, where they meet a pair of small pharyngeal ganglia.
The supracesophageal ganglia are connected by broad connect stiv
with the subcesophageal ganglia. Remove the pharynx from tl
body. By slightly scraping the subesophageal ganglia w
small scalpel, it will be seen to consist of two principal
glionic masses. The forward mass is a pair of gwglio #
pedal ganglia; the hinder mass consists of the large visceral g
at the side of which is the pair of small pleural ganglia. Ok one
the nerves radiating from the subcsophageal ganglia, ¢
determine so far as possible to what organs they go. .
Exercise 9. Make a semidiagrammatic drawing of the nerve
system. 4
Organs of special sense. The eyes of the snail at the end of 1]
posterior tentacles have already been noted. They are easi
seen in a large animal which has its tentacles extended.
snail is also provided with a pair of auditory organs. The
consist of two small sacs imbedded in the pedal ganglia. .
order to see them cut off the subcsophageal ganglion, mow
it in glycerine and examine it under a compound micros “a
The auditory nerves are very delicate and come from the s
Beeplaces: ganglia.
“al
A SQUID 123
CEPHALOPODA
A DIBRANCHIATE CEPHALOPOD. A SQUID (Lo/igo 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. Each 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’
head and foot can be withdrawn into its shell. The siphon o1
funnel, a large funnel-shaped organ at the base of the head, als
projects from it and can be similarly withdrawn. Gently prob
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 whic
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 a
unpaired one as in the snail. The squid has no foot, as ha
the clam or the snail, but morphological equivalents of ‘he
foot are present in the arms and the siphon. A
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 a:
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 enc
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 ond —
of the squid is called the forward end, and the fin-bearing
end, the hinder. The side bearing the fins is likewise calle
the upper side or back, and the opposite side, on which is
the siphon, the under or lower side. These terms, althougl
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; ina 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 fu 7 e
shaped tube communicating between the mantle cavity and tl
outside. Slit it open and observe the flap-like valve at the fo
ward end. Notice the lateral pockets on each side of the sipl a
which open toward the mantle cavity and occupy the sm
between the siphon and the median line of the back. 1
are separated from the siphon by the lateral cartilaginous rx
above mentioned. It will be seen that while water can ail
pass into the mantle cavity from the outside all around th
neck, a contraction of the muscular wall of the mantle woul
force the water out through the siphon only, as that which i
forced into the lateral pockets would at once swell them ou
and close the spaces at the sides of the siphon. It is, in fact, b
thus shooting the water in the mantle cavity forcibly throug
the siphon that the animal swims. . .
Note the two large retractor muscles of the siphon and bene:
them the two larger retractor muscles of the head. a
Observe again the visceral mass; it is covered by 3 a thin
transparent membrane, the body-wall, the extreme thinness «
which is correlated with the thickness of the mantle whi }
covers it. If the animal be a female that fact may be know
by the presence of two very large, transversely striated be _
called the nidamental glands, which lie near the center ae th
body, and are a part of the reproductive system. Ca
remove these in order to expose the organs beneath. ‘Itt
animal be a male (and the student should obtain a male if pe )
sible), it can be recognized by the absence of nidamental glant
and also by the presence of the testis, a large white .
organ which lies near the median line toward the hinder end |
the animal. In the female the ovary, which occupies a s
position, is often very full of the granular ova. a
oe
ai
ha
IL
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 i
through these arteries that the mantle is supplied with ble od.
On each side between the base of the gill and the ctu }
and extending parallel with the latter organ, notice agai
delicate kidney ; each of the pair of kidneys extends backw:
to a point a short distance back of the branchial heart, a
forward to a point back of the base of the ink-bag, where:
communicates with the mantle cavity through a small opening,
Find the two openings by lifting up the body-wall with fo oe] .
and blowing on it with a blow-pipe, when they will appear.
Running back from the branchial heart on each side is a wic
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 an
can be seen with difficulty. Near the base of each gill noi
also a vessel which runs forward and laterally into the mantle
this is the mantle vein. Just back of this vein is a musel
which connects the gill with the mantle; it is the b
retractor muscle. |
Note the two large stellate ganglia in the forward part of th
inner surface of the mantle, and the radiating nerves whic
each ganglion sends into the mantle. J
In the hinder portion of the visceral mass in the male animé
observe on the animal’s left (the observer’s right), just behir 1
the branchial heart, a coiled tube, the vas deferens, and in th
female the thick-walled oviduct. Extending farther back am
near the median line is the large white testis in the male
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 lel
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 agait
the mantle veins, which bring blood from the mantle to +
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 branchis
arteries which pass along the upper side of the gills; it the
traverses the delicate transverse filaments of the gills a:
becomes oxygenated, when it collects again in the branchii
veins on the opposite side of the gills; through these it passé
to the systemic heart, whence it is sent through the anteric
and posterior aortas to the different parts of the body.
Exercise 3. Make a diagrammatic drawing of the circulatory an
the respiratory systems. |
The digestive system. Remove the kidneys and precaval vein
Beneath them will be seen a large glandular bilobed organ ©
somewhat doubtful function, called the pancreas. At its forward
end a pair of cylindrical organs, the liver ducts, will be seen ent
ing it from the liver. The pancreas is made up of anastomosi
glandular projections of the walls of these ducts. Remowei 5
gills, branchial hearts, systemic heart, and hinder arteries.
"delicate body-wall should be completely removed from the enti
visceral mass, and great care be taken not to injure the ste nat
pouch beneath. ‘This latter organ is a large bag with tk i
transparent walls which extends to the extreme hinder om
of the body; beneath it will be seen the large testis or ovar
according to the sex of the animal. This pouch is not really
part of the stomach, notwithstanding its name, but is a rest
voir for the secretions of the liver, which communicates with i
through the liver ducts. Carefully loosen the stomach poue
without separating it from the body and let it float in the wate
of the dissecting pan. It communicates with the thick-walle
stomach, which lies just in front of it, but food substances u
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 csophagus, 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 csophagus
is easily found by turning the stomach over. A small ganglion
with radiating nerves will be seen by the side of the cesophagus
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 cesophagus,
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 f int
where the cesophagus enters it; the rectum, which is joined by
the ink-bag and passes to the anus. s
’
-
Exercise 4. Take the alimentary tract out of the body, pin i
down, and make a drawing of it; label all its divisions. a
Slit open the stomach and examine its ridges. Slit open the
pharynx on the upper side; note the large chitinous jaws anc
the radula. The latter organ, like the radula of snails, is used
in chewing the food; examine its surface under a mic oscope
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 witl
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 th
viscera. Take the entire system out of the body, put it i
water, loosen and straighten out, so far as possible, the con-
volutions of the vas deferens. Beginning with its hinder en
we find first a narrow, convoluted tube, then follows a thicke
tubular portion, the vesicula seminalis; near the forward en
of this portion is a glandular body, the prostate gland, and a
membranous sac; a long, straight, narrow portion comes nex
which widens to form the spermatophoric sac, within whicl
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. en Make a drawing of the male genital tract.
Exercise 7. (}) 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 csophagus; broad commissures
134 INVERTEBRATE ZOOLOGY
join it with the subesophageal mass, which is composed of the
visceral, pedal, and in front of the latter, the brachial gang a
Connected with the sides of the cerebral mass are the two o
nerves, which widen out to form the large optic ganglia, and m
ning forward from it are two small nerves which conten 7
with the suprapharyngeal ganglia, a small mass above the hinde
end of the pharynx. From these ganglia small nerves pass
around the c@sophagus to the pair of subpharyngeal ganglia
From the forward surface of the subcesophageal mass, 7.¢., TO]
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 viscer:
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 bae
of the animal and remove the pen; it will be seen to lie quil
loosely in its sac. 4
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
135
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.
stream of water is drawn into the incurrent opening, bes ‘
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 reproductiy 4
products. .
Exercise 1. Make a sketch of the animal on a scale of 2 or 3;
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 structur
through which the internal organs appear. Observe the white
muscle bands in the mantle, especially the transverse and longitudinal
muscles in the 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 orgs :
are the cream-colored genital glands near the center of the bod
and the alimentary canal. The latter lies on the left side ¢
the body, where it appears as an S-shaped structure wh .
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 youl
left) will be seen to have more prominent tentacles than thi
excurrent opening. From the base of the incurrent siphor
the large pharynx, the most voluminous organ of the body an¢
the principal organ of respiration, will be seen extending to the
lower side of the body. Note the six longitudinal ridges whiel
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-
yentral wall of the pharynx; it extends the length of that
structure and ends posteriorly near the opening of the pharynx
into the esophagus. Find this point. The esophagus 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. 3
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. 4
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 o!
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 ve
ular organ which is the single, unpaired kidney; it is ducdlll 3S.
Beneath the ganglion above mentioned is a small glandulai
organ called the subneural gland; it has a duct which communi-
cates with the pharynx. The function of this gland is proball ' i
excretory ; it is supposed to be is Pa isi to the hypophysi
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 whi ch
appear in that aspect. Label the dorsal and the ventra
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.
Exercise 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 phary nx
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 h
consists of minute organisms and particles of organic matter. —
The endostyle is a glandular and ciliated groove; the g wi
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 “|
peripharyngeal ridges which takes them around the pharyngeal al
wall to the dorsal lamina, along which they are driven po
riorly to the opening of the cesophagus. q
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. 7
Exercise 6. Make a large diagram of Molgula and show the ola.
tive positions of the different organs; label all. 7
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 forbsit, 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 starfishe
often lose one or more of their rays by accident; the missi ng
member is soon replaced by a new ray, but while it is growing 7
out it will be shorter than the others. The spaces betwa : b
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 fp
(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 o:
the low power of a compound microscope and notice its porou:
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 _ :
entire aboral surface. Each one is a part of a small calcareot
plate buried beneath the integument. The entire body-wall. 0 0:
the animal is made up largely of these plates, which give
it its stiffness. The plates are not, however, connected ae
one another except by muscles and connective tissue, and th
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 pedicellarice
these are minute pincer-like organs of somewhat uncertain fune-—
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 betwe
their bases are called the bivium; the remaining three,
|
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 pedicellari#, 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 si des
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. 4
:
Exercise 4. Make a sketch of the cut edge of the arm onas ile
of 3, 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 th
ambulacral groove. Note the two rows of slender transversi
plates which form the sides of the groove, and on each side
between every two plates, the minute ambulacral pore.
Exercise 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 s dy
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-
tate. 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 extendin
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 ¢
they may extend almost to the tip of the ray. The testis of t
male and the ovary of the female animal do not differ from e: ach
other in general appearance. In the mature female, hovel ver,
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 animé u |
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. 9
The ambulacral system. This is the most characteristic system
of organs in the Echinodermata. In the starfish it consists 0
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 car
and also project through the ambulacral pores into the body-
cavity, where they expand to form small sacs called ampulla;
sinuous canal, called the stone canal, which connects the ri
canal with the madreporic plate; the madreporic plate, a poroui
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
ameeboid 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. ;
main nerves of the starfish do not lie within the body-cavity, bu
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 th
radial nerves in the median line of the ambulacral grooves; th
ring nerve can also be seen as a slight ridge just beneath
the ring canal. si
Bxercise 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 ea:
be seen in a dissection, except an organ usually called the hear
or axial sinus. ‘This is a tubular sac which will be found besi
the stone canal; within it is an elongated glandular orga
called the axial organ or ovoid gland. 4
Exercise 10. Draw a diagram representing a vertical section ¢
the animal passing through the madreporic plate and th
anterior ray (.e., the middle trivial ray),
; | er
earner orsteattdieerediieees oe anes ee
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 slende
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 pedicellariz, 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
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 é
short time. Great care should be taken, however, not to leaye
it in the solution too long or it will fall to pieces. Study the
aboral side of the shell. Observe the rows of tubercles o
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. i
The center of the aboral surface is free from spines and i ;
made up of several small plates. It is called the periproct an
| ee 2?
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 mou ch;
also the retractor muscles which pass from the lower part of it t¢
the tall inner projections of the shell.
Exercise 5. Draw a diagram showing the dentary apparatus ir
the body and its muscular attachment to the shell. |
The esophagus, after leaving the dentary apparatus, passes
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 wi ids
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 o |
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 se:
are separate and the sexual glands of the male and female ¢ a
alike in appearance. They consist of five radial, granulai
masses, which lie in the upper part of the body-cayity, eacl
mass communicating with the outside through one of the genita
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 ant
the reproductive systems and label all their parts.
Remove the dentary apparatus from the body and examine i
carefully. It is made up principally of five triangular plates
called alveoli, the lower ends of which bear the teeth. he
alveoli are bound together by short muscles. The base of th
dentary apparatus is made up of a complicated system 0
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. |
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 w ater
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 -
of the hydranth. ‘The internal cavity of the hydranth and of
the stem is called the gastro-vascular space, and is the commol 1
digestive and circulatory cavity of the animal. The proboscis-
like portion of the hydranth between the base of the tentae 28
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 expande 1
hydranth on a large scale and label all of its parts.
Exercise 3. Make a sketch of a contracted hydranth.
A CAMPANULARIAN HYDROMEDUSAN Pet
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 actio
of the flagella in a live specimen.
Exercise 6. Make a drawing showing the cellular structure «
the wall of the hydranth and of the stem.
Study a blastostyle. We note that it is a cylindrical obje
enclosed within its transparent gonotheca. Budding out on th
sides are the young disc-like meduse, those towards the free end
being the largest and the oldest. The blastostyle has ne
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 o ani
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 spe 0 ce
The colony lives upon small swimming animals, which th
feeding polyps kill or stun with their nematocysts, and her
swallow into the gastro-vascular space. Digestion goes o1
within the feeding polyps; the products of digestion mingl
with the water present in the gastro-vascular space and ciret
late throughout the colony. The entire colony is thus nour
ished, and if conditions are favorable it will grow rapidly an
produce a large number of medusz. The polyps are a i
destroyed by frost or the beating of waves or by fishes, but n
ones quickly grow in their places.
The medusoid stage. The medusoids of campanularian nv 4
medusans are either sessile sporosacs or free-swimming medus@.
The meduse are minute disc-shaped jelly-fishes, about one
eighth of an inch in diameter, which may be found swimming it
the surface waters of the ocean. Place several in a watch-glas
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 medusz; 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 meduse 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 poly
and just as the latter is attached to the stem at its base, so t
medusa is attached to the blastostyle by its exumbrella. a
digestive, excretory, respiratory, and circulatory functions ‘
carried on in the medusa as they are in the hydranth.
medusa being a free-swimming animal, however, its muscul
and nervous systems are much more highly developed the
the same systems in the hydranth.
In the latter form the only muscles present are de
fibers, elongated projections of the inner ends of ectoder
cells, which cause movement in the tentacles and the be ly ‘a ,
the hydranth, while the nervous system is represented only I
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 contractic
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 th
disc and from which delicate fibers pass to the velum an
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 slight]
into the subumbrella space are the four reproductive organs, which
are also brown in color and present a corrugated appeare 1¢
The sexes are separate, but the animals are not dimorphic.
Observe the number and arrangement of .the tentacles, of whic
an adult medusa possesses from sixty to eighty. Note the spir
arrangement of the nettle cells on each tentacle, and also #
adhesive pad near its outer end. It is by means of the nettle
cells in these pads that the animal anchors itself to seaweed
and other objects when at rest. Note the exact point aboy
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 cana
Between the tentacles are the lithocysts — minute projections
from the margin of the bell which are probably equilibria
function. ,
Observe the velum — the membrane which extends around the
inner margin of the bell towards the manubrium. It is
principal organ of locomotion and contains bands of ectoderma
muscle fibers by the contractions of which the motion of th
bell is produced which propels the animal through the w
Similar bands of muscle fibers are also present in both th
subumbrella and the exumbrella. '
Exercise 1. Draw a semidiagrammatic view of the exumbrel.
on a scale of from 5 to 10, showing the tentacles extende
and all the organs which have been observed. {
, q
Exercise 2. Draw an oblique side view of the animal on th
same scale, showing the velum, the manubrium, and all th
other organs observed.
Exercise 3. Draw a semidiagrammatic view of the subumk ell
on a scale of 5 to 10, showing the velum, the manubriur
and the other organs observed.. F
+
GONIONEMUS 177
_ The hydroid generation of Gonionemus is a minute solitary
jolyp which lives attached to the bottom in shallow water;
t will not be studied here. The polyp is only about one milli-
neter in height and has four tentacles which can be extended
wo millimeters. It is thus very much smaller than the medusa,
hich has a height of about nine millimeters and a diameter of
bout twenty. The polyp forms new polyps by budding, but
as never been observed forming the medusz, so that it is not
mown. how these originate.
178 INVERTEBRATE ZOOLOGY
ANTHOZOA
A SEA ANEMONE (Metridium)
This animal, which is the largest sea anemone along the Nor
Atlantic coast, is often plentiful on rocks, shells, and docks i
shallow water. Place an expanded individual in a deep dish ¢ of
water and observe its shape, color, and method of attachm on |
The upper end of the columnar body is called the disc, and in i
center is the elongate, slit-like mouth, surrounded by the nu ner
ous tentacles. The lower end of the animal is called the foot.
is often expanded and is not permanently attached to the sub
stratum; the animal has some locomotory powers and can slowl
move from place to place. a
Study the form of the mouth. Note the thickened lips ¢
each angle of the mouth; these form a ciliated groove, cé ig
the siphonoglyph, through which the genital products reach t
outside. In some individuals only one siphonoglyph is pre
Study the surface of the disc and the tentacles. The for a
is frequently expanded and thrown into folds and lobes. The
tentacles are elongated diverticula of the disc and are holl OW.
They are charged with nettle cells and are the principal org ;
of defense and offense. They are also useful in feeding; afte
the nettle cells have stung the small animals which constitut
the food of the sea anemone, the tentacles place them in its
mouth. The tentacles are not all the same size, those neare
the mouth being the larger and the older. ”
Note the character of the columnar body. It is po b
small pores through which long, white, glandular threads, arme
with nettle cells and called acontia, may be thrust oie F
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 disc
‘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 divided 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.
TAS ai INVERTEBRATE ZOOLOGY
Make a cross section through the gullet and study the a
ment of the mesenteries, the relation of the primary mes
to the gullet, and the longitudinal muscles.
Exercise 3. Draw a diagram of the cross section, showing t
features. =
a”
Make a cross section through the body beneath the gulle
Exercise 4. Draw a diagram of the cross section, show ng
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
shorter and less regular incurrent canals, which lie between th e
radial canals and open to the outside through external inew ren
pores. There are thus two systems of canals in the body-wall,
(a) the radial canals, which are a part of the central cavity, am
(6) the incurrent canals, which open to the outside. ‘These
systems of canals communicate with each other by means of
minute openings, so that water which enters the incurren
canals from the outside through the external incurrent pore
passes freely into the radial canals, and thence into the central
cavity. From here it passes out through the osculum. E
Exercise 2. Make a semidiagrammatic drawing of the ir ne
surface of the body-wall and the cut edge of the animal,
showing the features above described. 4
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. u
the three different kinds of spicules — the long straight ones whic.
guard the osculum, the short straight ones which guard ch
external incurrent pores, and the triradiate ones which are withi:
the body-wall and give it rigidity and firmness; some of th
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
scale.
Make thin sections of a sponge by placing it between tw:
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 ant
study them under the microscope. ie
Study a cross section in which the canals have been cut lor
gitudinally. Observe the radial and the incurrent canals an
\
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 ¢ f
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 decayir
vegetable matter. It is easily obtained by permitting vegetal
matter to stand in water for a week or two. In shape it is :
elongated ellipsoid with a wide, slightly twisted, longitudina
groove, called the oral groove, on one side; the surface which cot D-
tains the groove may be called the ventral surface, and the oppc
site surface, the dorsal. The animal is colorless and transparen
except when it contains within its body colored food vetlel
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 b
seen swimming rapidly about, but will gradually collect abou
the decaying matter. If they do not become quiet in a fey
minutes, it is because there is too much water under the cover-
glass, and some of it should be withdrawn with a piece ©:
blotting paper. Care should be taken that the water does
all evaporate. ot
Observe the unsymmetrical shape of the animal, and t
difference between the anterior and the posterior ends. Not
the rolling over of the animal as it swims through the wate
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 entosarc.
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
B
as it goes. At its inner end the groove becomes a closed
tube, which extends into the entosare and ends with the mouth.
Notice the trichocysts — slender, radially arranged bodies which
fill the ectosare. They are organs of defense, which remine
one of the nematocysts of the Cnidaria; when the aie
irritated they discharge long, delicate bristles, which proje
beyond the cilia or may leave the body.
Observe the granular nature of the entosare, and the spheri-
cal food vacuoles within it. These are particles of food, usuall
composed of vegetable substances surrounded by water, wh aa
circulate within the semifluid entosare. Watch the entc a
closely, and observe the currents in it. Determine the dire
tion of the currents and whether the direction is ever change
The food vacuoles form at the inner end of the oral groove
where the particles of which they are composed have been swe ¥:
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 tk
surrounding water. ‘They do not appear simultaneously, but
alternate with each other. When a yacuole has disappearec L
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 entosare
_ through the mouth. Here they circulate for some time, while
j the water forming the vacuole is absorbed and the food parti-
cles that it contains are digested. The indigestible matters are
7 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 ¢ ad.
bears the mouth at its inner end. a
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 Zoéthamnium are
colonial and differ from each other in that in the former each
individual animal contracts independently, while in the la
the entire colony always contracts as a unit; in both, the colo-
nies are large and easily visible, appearing often like whi a )
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 animaleule 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 oré
groove and note that the current in the water tends to sw
small objects into it.
al;
ee :
es
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 on a
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, i.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 structu 7
and is easily seen; near it is 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. Th :
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 Vorticellidew both of the individ-
uals produced by the process of division remain on the sté
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;
the latter end is a deep depression, from the bottom of which |
springs a long, thread-like, vibratile flagellum. The body is coy- —
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. | 4
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 mo tion
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. — |
Exercise 1. Draw a number of simple outlines of the bodys |
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.
In 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 microsco De
to detect. 4
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.
one
Exercise 1. Draw several outlines of the animal, showing it:
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. he
ectosare is of firmer consistency than the entosare and secret
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
AMOEBA 195
_ the animal flows in that direction. When this happens the
- ectosare of the hinder portion of the body will be seen to
wrinkle as the entosare flows away from it.
4
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
-yacuoles. 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,
_Yeproduction in Amoeba is largely dependent upon nutrition.
If the nutritive conditions surrounding them are unfavorable
the animals gradually lose their vitality and reproductive powers
a Oe an, es we tC
Fa eS * ee
< ae ee - 2 a
ys : ,
196 INVERTEBRATE ZOOLOGY
and in the course of time will die. Conjugation also occu 8 :
in other Protozoa. The processes of division and conjuge
apparently do not take place frequently, as they have not
often observed. ;
About a dozen species of the genus Amoeba are kno ;
The commonest are probably A. proteus, a large, often <
form with long pseudopodia, A. verrucosa, a large, log
with very short pseudopodia, A. lima, a small form hase
along without definite pseudopodia, and A. radiosa, a_
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 peozaeile 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 nane 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 ccelom.
SuppHytum 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 simp
structure. Ex. Grantia. |
Class 2. Hexactinellida. Glass sponges with six-rayed siliciou
spicules. Ex. Euplectella. q
Class 3. Demospongie. Massive sponges with either silicious spi
ules or spongin fibers or both. Ex. Spongilla.
SuppHyitum II. Cnidaria. Coelenterates provided with nett
cells. |
Class 1. Hydrozoa (Hydromeduse). Hydroid polyps and jell
fish, the former without mesenterial ridges and the latter with |
velum. |
Order 1. Hydrarie. Freshwater hydroids of simple structure.
Ex. Hydra. Z
Order 2. Hydrocoralline. Coral-like marine hydrozoans.
Millepora. :
Order 3. Tubularie. Hydroids without hydrotheca; medus:
with gonads on the manubrium. Ex. Pennaria.
Order 4. Campanularie. Hydroids with hydrotheca; medus%
with gonads on the subumbrella. Ex. Obelia.
Order 5. Trachomeduse. Hydroids (when present) minute ¢
of simple structure; medusz usually large with gonads on the § ub
umbrella. Ex. Gontonsantle | i
Order 6. Narcomeduse. Hydroids wanting; medusz with lobe
rim. Ex. Cunina.
Order 7. Siphonophora. Free-swimming colonial hydrozoans.
Physalia.
Class 2. Scyphozoa (Scyphomeduse). Hydroids and jellyfish
former with mesenterial ridges and the latter without a velum ¢
often of large size. Ex. Aurelia. ;
Class 3. Anthozoa. Sea anemones and corals; solitary or colon
polypoid cnidarians without medusoid generation.
Order 1. Aleyonaria. Anthozoans with eight mesenterial
and eight pinnate tentacles. Ex. Corallium.
Order 2. Zoantharia. Anthozoans with numerous mesen ria
ridges and numerous simple tentacles, Ex. Metridium.
SuppHyium III. Ctenophora. Coelenterates with eight banda
ciliated ridges on outer surface. Ex. Mnemiopsis.
7)
APPENDIX 199
PHYLUM III. VERMES
_ The lower worms. Animals of primitive structure and without
paired locomotory appendages or distinct head.
SusppHyitum 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 Satcciin with mostly
a branched digestive tract and an anterior mouth. Ex. Fasciola.
Class 3. Cestodes. Tapeworms. Elongated, usually segmented para-
sitie 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.
_ Suspnyium II. Nemathelminthes. Round or thread worms; mostly
_ parasitic. Ex. Ascaris.
_ SuspHytum III. Trochelminthes (Rotifera). Minute, aquatic worms
_ with mouth surrounded by cilia. Ex. Rotifer.
_ Svuppuytum IV. Bryozoa. Minute, sessile, colonial animals with
a ridge bearing ciliated tentacles around the mouth. Ex. Bugula.
SuppHyium V. Brachiopoda. Sessile, marine, mollusk-like animals
with a dorsal and a ventral shell. Ex. Terebratulina.
Suppuyium VI. Phoronidea. Sessile, marine worms living in tubes
and with a tentacular ridge around the mouth. Ex. Phoronis.
Susprpnytum 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.
_ Suspuyium 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 sete. Ex. Polygordius.
200 INVERTEBRATE ZOOLOGY
Class 2. Chaetopoda. With sete, segmentally arranged.
Order 1. Polychaeta. Mostly marine chaetopods with para
on which are numerous sete. Ex. Nereis. 4
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 setze. Ex. Hirudo. 4
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. k
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. b
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 antennze 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, hermaphroditic 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-
v ering the head and all or some of the thorax, and with stalked eyes.
Order1. 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. Pseudoseorpionida. 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. t
Order 7. Aranez. Spiders. Arachnids with a constriction betwelal
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. a
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 coon |
segmented body and appendages.
Order 1. Progoneata. Body mostly cylindrical and with two pairs -
of legs to a segment. Ex. Julus. 4
Order 2. Chilopoda. Centipeds. Flattened myriapods with one
pair of legs to a segment. Ex. Lithobius. a
Division 3. Insecta. Insects. Tracheates with body divided into
head, thorax, and abdomen ; with three pairs of legs and usually a
pairs of wings. z
Order 1. Thysanura. Minute, wingless insects without metamor-
phosis. Ex. Lepisma.
Order 2. Pseudoneuroptera. Insects with two pairs of — a
wings, biting mouth-parts, and incomplete mene 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. g
Order 4. Neuroptera. Insects with two pairs of net-veined wings, E
biting mouth-parts, and complete metamorphosis. Ex. Ant lion. q
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. a
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. 7 3
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 splcul in
the body-wall.
Class 1. Crinoidea. Sea lilies. Echinoderms which are sessil 2
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.
SusppHytum I. Enteropneusta. Worm-like chordates with a large
proboscis in front of the mouth. Ex. Balanoglossus.
SuppHuytvum 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. 3
Class 2. Thaliacea. Free-swimming, trae tunicates. Ex.
Salpa.
Class 3. Ascidiacea. Sessile, saccular tunicates, either simple or
colonial. Ex. Molgula.
SuppHyivum III. Leptocardia. Elongated, fish-like chordates, com-—
pressed laterally and attenuated at both ends. Ex. Amphioxus. |
SuppHytum 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. Perea.
APPENDIX . 205
Biss 2. Amphibia. Amphibians. Vertebrates with gills during a
or all of their life, and usually with lungs; scales mostly absent.
x. Rana.
“Class 8. Reptilia. Reptiles. Vertebrates with body covered with
horny scales or plates and without gills. Ex. Coluber.
Bilas 4, Aves. Birds. Feathered vertebrates whose anterior ap-
Bendacés are wings. Ex. Gallus.
a ; Class 5. Mammalia. Mammals. Hair-covered vertebrates which
suckle their young. Ex. Felis. |
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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-pug, 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.
_ Alge: 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, 143, 149, 157.
Ambulacral groove: the elongated groove on the oral side of the rays of
the starfish, 145.
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, 43; sow-bug, 46; amphipod, 48; copepod,
53; 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; C:
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. 4
Arthrobranch: a gill attached to the joint bichon 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 q
in Bryozoa, 87.
Axial organ: a glandular organ in the axial sinus in the starfish, 148; in
the sea urchin, 154. q
Axial sinus: an elongated sac alongside the stone canal in the starfish, i e
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.
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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, 135; 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 poOeSe
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. .
Cecum: 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. | q
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. 3
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; Pare
cium, 185; Vorticella, 189; Euglena, 192.
Cyst: a capsule containing an animal usually in a state of suspended an
mation; tapeworm, 83; Euglena, 193.
Cysticercus: a cyst containing a tapeworm scolex, 84.
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, 139.
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, 82; 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,
31; crab, 43.
Exopodite: the outermost of the two terminal branches of the typical
crustacean foot; crayfish or lobster, 832; 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. ,
yA INVERTEBRATE ZOOLOGY
Fertilization: the union of the spermatozoén and the ovum. a
Flagellum: a vibratory thread-like projection of certain cells; hydroidsy
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. 7
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 paras
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,
_ 187; 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 Hydromedusez, 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.
Tleum : 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. . Oe ad
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, 837; copepod, 55; planarian, 77; Bug
86; mussel, 96; oyster, 101; clam, 110; snail, 118; squid, 131;
gula, 137; starfish, 145; sea urchin, 152; sea cucumber, 156.
Kidney: an excretory organ; spider, 27; crayfish or lobster, 40; Nereis,
65 ; eeigiiiidan. 73; mussel, 95; clam, 109; snail, 116; squad! 12%
Molgula, 138.
Labium: the under lip of insects; fly, 8; grasshopper, 12; beetle, 14; —
wasp, 14; caterpillar, 20; spider, 25. q
Labrum: the upper lip of insects and of some crustaceans ; grasshoppaag
12; beetle, 14; wasp, 14; caterpillar, 20; crayfish, 30.
Lamella: a leaf-like or platotiks 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 ahreinel sense-organ in certain medusez, 173, 176.
Liver: a digestive gland; crayfish or lobster, 39; crab, 44; Daphnia, 57;
mussel, 96; oyster, 101; clam, 107; snail, 119; squid, 131; starfish, 145. ;
Lophophore: a circular or horseshoe-shaped ridge bearing tentacles in
Bryozoa, 86.
~ Lumen: the cavity within a tubular organ.
Macronucleus: the ae 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 arthropomag a
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, 173, 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.
2 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,
375...
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. _ ~ iz
Moult ; to shed the cuticula or the outer portion of it.
Oral: the side of the body containing the mouth in a radiate animal; star-
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, 45.
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 enido-
blast; Hydra, 161; tubularian, 165; campanularian, 171. qy
Nephridium: a urinary tubule in annelids; Nereis, 65; earthworm, 73.
Nephrostome: the ciliated opening of a nephridium into the bot ae
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 See ganglia not of ie! 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. —
Nidamental glands: the large glands which secrete the egg-capsules in
the squid, 133. q
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. a
Ocular plate: the plate at the aboral end of a ray of the sea urchin, 151.
sophagus: the gullet, the division of the digestive canal leading from the
pharynx to the stomach; grasshopper, 15; caterpillar, 21; crayfish or
lobster, 39; 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.
fish, 142; sea urchin, 149; sea cucumber, 155; medusa, 167, 178, 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,
133; starfish, 146; Hydra, 161.
Oviduct : the tube leading from the ovary towards the outside ; grasshopper,
: 16; spider, 27; crayfish or lobster, 39; 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 end the axial organ in the starfish, 148 ; in tie: 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.
Papulz: the delicate projections of the body-wall in the starfish, 142.
_ Paragnatha: delicate lamellae 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 pe gs 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; cla n,
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, 131; 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, 43. j
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.
a a
eT ee i i
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 inkeob 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,
173, 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, 89; 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 diay 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.
22.0 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. a
Segment: one of a number of serial divisions of an animal’s body or of —
an organ. 4
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.
Spermatozoén: 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.
— ee ree
GLOSSARY 291
Sternum : the ventral surface of the thorax in arthropods; wasp, 8; grass-
hopper, 10; spider, 25.
Stigmata: the respiratory openings in the pharyngeal wall in Molgula,
139.
Stipes: a division of the maxilla in insects, 13.
Stomach: a division of the digestive tract in which digestion goes on;
erayfish or lobster, 36; Bugula, 86; mussel, 96; clam,110; snail, 117;
squid, 130; Molgula, 187; 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, 131.
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, 13.
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, 135: 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;
Oe INVERTEBRATE ZOOLOGY
planarian, 77; tapeworm, 83; mussel, 97; oyster, 102; clam, 110; ;
squid, 182; starfish, 146; Hydra, 161. 4
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 dequions of an insect’s leg between the femur and the tarsus; .
wasp, 4; grasshopper, 12; spider, 25. ;
Piedemann'é vesicles : cainute 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, 148, 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 ,o 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, 83.
Zoéa: a larval form of the crab and of certain other crustaceans, 51.
Zoecium: the outer cuticular covering of a bryozoan, 85.
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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 zowcium, 85; polypide,
85; internal organs, 86; avicularia,
87; occia, 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.
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, 137; 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, 53;
ternal anatomy, 54.
Crab: external parts, 42; gills, 43;
internal parts, 44; zoéa of, 51;
megalopa of, 51.
Crayfish or lobster: external parts, 28 ;
appendages, 32; gills, 35; internal
organs, 36; 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;
crab, 42; sow-bug, 46; typical am-
phipod, 48; Caprella, 50; larval
decapods, 51; copepod, 53; Daph-
nia, 56; nauplius larva, 59.
Cyclops, 53.
in-
225
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, 1380; 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; @ cross
siodton: 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, 1388; _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; st :
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 mibnce 110;
nervous system, 111. ees!
Helix pomatia, 112. BASE 2
Holothurian, 155.
Hydra: general form, 159; TeprOnie
tion, 161.
Hydromedusan, 163, 169. 1%
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; cascrgilions 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,
f
2
ee
INDEX
117; reproductive system, 120; nerv-
ous system, 121.
Limax maxima, 112.
Lithobius, 22.
Lobster, see Crayfish.
Loligo pealii, 123,
Macruran decapod, 28.
Metridium, 178.
Molgula: external parts, 185; digest-
ive system, 136; reproductive sys-
tem, 137; circulatory system, 137;
nervous system, 138; excretory sys-
tem, 138; peribranchial chamber,
138 ; 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, 178; 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, 132; 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, 168; 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.
Zodthamnium, 188.
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