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.1 •"• • • i:;;t:!rii'.;t;

Laboratory Studies iu T-ooloc/y. H. D Reed a'-rl
B. P. Young. 1930. viii i)lus 121 pp. McGraw-Hill
Book Company.

This laboratory manual has grown out of the
elementary course in zoology at Cornell. Approx-
imately half the book is devoted to outlines for
the study of the frog. Keys are given for student
identificat'on of Protozoa and for "the larJT'^r
groups of animals." This adds another to the
distinctly teachable laboratory outlines in ele-
mentary zooloo'v for the inrre'^sing nnml)er of
teachers who dislike to "roU-their-own "

— W. C. Allee.

Reviewed in

"Collecting Net"

July 8, 1931

I CO
i 3-

i "-^
I CD

a

CD

m

CD

Reviewed in the "Collecting Net"
July 8, 1931
by W. C. Allee, and presented
to the Marine Biological I-aboratoijj
Library

i

McGRAW-HILL PUBLICATIONS IX Till:

ZOOLOGICAL SCIENCES

A. FRANKLIN SliriJ.. Consultino Editoh

LABORATORY STUDIES IN ZOOLOGY

McGRAW-HILL PUBLICATIONS IN THE
ZOOLOGICAL SCIENCES

A. Franklin Shull, Consulting Editor

Fernald — Applied Entomology
Graham — Principles of Forest

Entomology
Haupt — Fundamentals of Biology
Haupt — Laboratory Directions for

General Biology
Metcnlf and Flint — Destructive

and Useful Insects
Mitchell — General Physiology
Pearse — Animal Ecology
Reed and Young — Laboratory

Studies in Zoology
Riley and Christenson — Guide to

the Study of Animal Parasites
Rogers — Comparative Physiology

Rogers — Laboratory Outlines in
Comparative Physiology

Shull- — Heredity

ShuU,LaRue and Ruthven — Animal
Biology

Shull, LaRue and Ruthven — Labo-
ratory Directions in Animal
Biology

Snodgrass — Anatomy and Physi-
ology of the Honeybee

Van Cleave — Invertebrate Zoology

Wieman — General Zoology

Wieman — An Introduction to
Vertebrate Embryology

Wieman and Weichert — Laboratory
Manual for Vertebrate Embry-
ology

McGRAW-HILL PUBLICATIONS IN THE
AGRICULTURAL AND BOTANICAL SCIENCES

Edmund W. Sinnott, Consulting Editor

Adams — Farm Management

Babcock and Clausen — Genetics in
Relation to Agriculture

Babcock and Collins — Genetics
Laboratory Manual

Belling — The Use of the Micro-
scope

Boyle — Marketing of Argicultural
Products

Brown — Cotton

Carrier — Beginnings of Agricul-
ture in America

Cruess — Commercial Fruit and
Vegetable Products

Cruess and Christie — Laboratory
Manual of Fruit and Vegetable
Products

Eames and MacDaniels — -Plant
Anatomy

Eckles, Combs and Macy — Milk
and Milk Products

Emerson — Soil Characteristics

Fawcett and Lee — Citrus Diseases

Fitzpatrick — The Lower Fungi

Gardner, Bradford and Hooker —
Fruit Production

Gardner, Bradford and Hooker —
Orcharding

Gdumann and Dodge — Compara-
tive Morphology of Fungi

Hayes and Garber — Breeding Crop
Plants

Heald — Plant Diseases

Horlacher — Sheep Production

Hutcheson and Wolfe — Field Crops

Jones and Rosa — Truck Crop

Plants
Loeb — Regeneration

Lohnin and Fred — Agricultural
Bacteriology

Lutman — Microbiology

Piper and Morse — The Soybean

Pool — Flowers and Flowering
Plants

Rice — The Breeding and Improve-
ment of Farm Animals

Sharp — Cytology

Sinnott — Botany

Sinnott — Laboratory Manual for
Elementary Botany

Sinnott and Dumi — Principles of
Genetics

Swingle — A Textbook of System-
atic Botany

Thatcher — Chemistry of Plant Life

Thompson — Vegetable Crops

Waite — Poultry Science and
Practice

Weaver — Root Development of
Field Crops

Weaver and Bruner — Root Devel-
opment of Vegetable Crops

Weaver and Clements — Plant Ecol-
ogy

J

I

LAIJOIJATOIJV STl'DIES
IN ZOOUHJV

BY
ir. D. REED, B.S., Ph.D.

I'rnfr.ssor of Zoolofjy, Conirll Unircrsily

AND

B. P. YOUNG, B.S., Ph.D.

Assistant Professor of Zoology, Cornell I'niversUi/

First Edition

McGRAW-IIILL BOOK COMPANY, Inc.
NEW YORK: 370 SEVENTH AVENUE

LONDON: 6 & 8 BOUVERIE ST.. K. C. 4
1 0 3 0

Copyright, 1930, by the
McGraw-Hill Book Company, Inc.

PRINTED IN THE UNITED STATES OF AMERICA

All rights reserved. This book, or
parts thereof, may not he reproduced •
in any form ivithout permission of
the publishers.

THE MAPLE PRESS COMPANY, YORK, PA.

PREFACE

The laboratory outlines licrc presented have been fashionefl
out of oxporienco with students in the laboratory, extending over
a considerable period of years. An attempt has been made to
discover the most serious difficulties encountered l)y elementary
students and to outline the procedure accordingly. An attempt
has also been made to incorporate the quality of flexibility as
regards detail of methods. Even though several instructors are
engaged in conducting different laboratory sections in the same
course, better results arc obtained when each instructor is free
to employ his own details of method, to act upon his own initia-
tive, and to give expression to his own personality. Questions
have been almost entirely eliminated, in the belief that (jues-
tions formulated by the instructor would be more effective in
stimulating the student to see and Ihink.

The order in which the several studies are arranged need not
necessarily be followed. The authors have found, however, that
a beginning student when studying a series of animals, in what-
ever order they may be arranged, fails to grasp the significance
of his studies as constituting a connected whole. A beginning
study of a higher animal type obviates difficulties of this sort.
The introductory study of the frog, it should be emphasized, is
not outlined for the purpose of learning about the frog as such.
It affords a means of inculcating the principles of bodily organiza-
tion, the services rendered by bodily components, the nature of
protoplasm, and the nature and importance of the cell as a vital
unit ; and finally it affords a means of building up a concept of the
organism as a totahty and superior entity. Incidentally, a
knowledge of all of the fundamental biological principles which a
beginning student can master may be gained in such a study.
Following this a study of the animal types may be made more
significant.

Should it appear that too many types and too many details
are included, the aims of the teacher may be taken as the best
guide in omitting parts or even whole studies. Added interest
may be aroused by the display of living animals, demonstrations,

V

vi PREFACE

and models, according to the facilities of the laboratory and the
ideas of the instructor.

It is assumed that the instructor has a much broader and more
detailed knowledge of the subject than is represented in these
outlines.

The authors wish to acknowledge their indebtedness to Dr.
Mary J. Fisher, Dr. A. Grace Mekeel, and the Misses Eleanor C.
McMullen and Lillian A. Phelps, who have used these outlines
during the building period and have offered valuable suggestions
and criticisms. Grateful acknowledgment is also made of the
efforts and success of Miss Mary Mekeel in producing the
illustrations.

H. D. R.
B. P. Y.

Ithaca, N. Y.
July, 1930.

CONTENTS

I'a<ie

Pkeface. . '^'

Introduction . 1

SippLiEs, Textbooks, and Instkuments 1

Laboratory Regulations 1

Drawings and Observations -

Labelling and Lettering 3

I'sE of Plates Accompanying the Text 4

The Study of an Animal Type, the Frog -^

Moaning of Intrinsic Toponomy 5

Definitions of Toponymic Terms 5

Surface of the Frog's Body and the Organs of the Special Senses 6

The Several Internal Systems of Organs 10

The Skeleton 1"

.\xial Skeleton 10

Appendicular Skeleton 11

Synopsis of Skeletal Parts 13

The Muscular System 14

A Study of an Individual Muscle, the (lastrocnemius 15

Grouping of Muscles According to Their Action 16

The Oral Cavity 18

The Viscera .19

Heart 19

Abdominal Viscera 20

The Blood System .23

General Observations ... 23

The .\xteries ... 24

Tlie Veins 27

The Portal Systems 28

The Nervous System .31

The Dorsal Aspect of the Brain . 31

The Spinal Cord 32

The Cranial Nerves 33

The Spinal Nerves 34

Synoptic Summary 3o

The Compound Microscope 36

The Fine Structure of the Frog . 39

Protoplasm and Cells 39

Epithelial Tissue -^

Connective and Supporting Tissue -^O

Muscular Tissue * 1

Nervous Tissue "1-

vii

37f^o

viii CONTENTS

Page

Mitosis 44

A Study of the Basic Reproductive and Hekedity Phenomena. . 47

Maturation and Fertilization 47

A Study in Development 48

Segmentation and Gastrulation of the Starfish's Egg 49

Segmentation and Gastrulation of the Frog's Egg 50

Larval Development of the Frog 54

An Introduction to the Study of Inheritance 56

A Study op Representatives of the Various Phyla 60

Introduction 60

Phylum Protozoa 61

Amoeba 61

Paramoecium 63

A Study of Mixed Protozoan Cultures 67

Introduction 67

Key for the Identification of Protozoa 68

Phylum Coelenterata 74

Hydra 74

Obelia 77

Gonionemus 80

Phylum Platyhelminthes 82

Planaria 82

Phylum AnneUda 85

Nereis 85

An Earthworm 87

Phylum MoUusca 94

Phylum Arthropoda 97

A Crayfish (or a Lobster) 97

A Grasshopper 102

Phylum Chordata 106

Subphylum Cephalochorda, Branchiostoma (Amphioxus) .... 106

Subphylum Vertebrata HO

A Shark, the Spiny Dogfi,sh 110

A Bony Fish, the Yellow Perch HI

A Review of the Phyla, Subphyla, and Classes op Animals . . .118

'^Introduction 118

A Key for the Identification of the Larger Groups of Animals . . . 118

2D

LAliOlJATORV SllDIKS
IN Z()()i.()(iV

INTRODUCTION

GENERAL DIRECTIONS

Supplies, Textbooks, and Instruments. Students in the oourso
shoultl pruviile tlicniselvcs with tlu' following:

1. A copy of the textbook chosen for the course.

2. Laboratory manual for elementary zoology.

3. A heavy grade of drawing paper, 8 by 10} 2 inches.

4. Large Manila envelopes for laboratory records.

5. Note paper and covers 8 by 10' 2 inches.

6. Hard drawing pencil, 5H or 6H.

7. Eraser with beveled edge.

8. A pad of emery paper for sharpening pencils.

9. A set of dissecting instruments which shouUl include as a
minimum the following articles:

2 pairs of fine forceps, milled tips, o inch.
1 pair of fine scissors.

1 scalpel.

2 teasing needles.
1 millimeter rule.

1 leatheret instrument case is desirable.
All other equipment and materials will be supplied by the
laboratory.

LABORATORY REGULATIONS

Laboratory work begins promjjtly at tiie hour designated.
It is essential that each person should recognize responsibility
for the equipment furnished by the lal)()rat()ry and the neatness
of the place occupied. Kixch article of the equipment bears a
number corresponding to the table assigned. After use it should
be returned in good condition to its proper place. At the begin-

1

2 LABOR ArORY STUDIES IN ZOOLOGY

niiitz; of the laboratory period report should be made to the
instructor concerning any part of the laboratory equipment
which is missing or out of repair.

Whether the laboratory is a clean, quiet, and comfortable
place to work depends upon each member of the class.

All laboratory drawings and notes must be handed in at the
close of each laboratory period. They will be corrected and
returned at the next session. No credit will be given for such
reports after they have been taken from the laboratory. Labora-
tory reports are judged with regard to completeness, correctness,
and neatness. Technique and general attitude toward work and
laboratory associates reveal the character of the worker.

In the upper right-hand corner each sheet of drawings or notes
must bear the name of the student, the section, and laboratory
number. Each sheet should also bear at the top and center the
name of the study upon which it is a report.

RECORD OF OBSERVATIONS

Drawings. — Some record of studies made in the laboratory is
always necessary either as a report upon the work accomplished
or as information to be used in later study. When time permits
there is nothing quite so satisfactory as an original drawing, for,
as an eminent biologist long ago expressed it, "the best eye for a
naturaUst is the point of a lead pencil." But one need not be
an artist in order to produce satisfactory outline drawings
delineating laboratory observations. Indeed, most students
who find their way into biological courses have had no previous
training in drawing. The first attempt at drawing may be
poor but it is likely that the fault Ues in poor observation and
thmking rather than in a lack of abihty to produce simple dia-
grams. Improvement in observation is accompanied by a
corresponding improvement in drawing. No attempt at drawing
should be made until the object of study is understood. An
attempt to draw will lead to closer observation.

Beginners often err in making drawings too small and attempt-
ing to represent too much detail. In the outUnes which follow
appropriate dimensions are suggested in connection with the
drawings required. Each drawing should be so located upon the
page and in its relation to other drawings which may be planned
for the same sheet that a balanced appearance of the plate may
be the result. Adequate space for all labels should be provided.

ISTRODUCTION 3

Perhaps the most common mistake made by beginners is a
faihiro to give sufficient time to the study of proportions. No
amount of care in representing details will compensate a poorly
proportioned outline. The first outline sketch should there-
fore be made lightly to admit of erasures and additions as the
study progresses. The appearance of drawings improves rapidly
as one's sense of proportions becomes more dependable. The
instructor may be asked to pass upon general proportions before
details are represented. When the proportions of the outline
seem satisfactory retrace the corrected outline with an unbroken
clear line. Details of structure may now be located with constant
comparisons of the drawing and the object. Use light lines at
first, following with heavier ones later.

Keep in mind the fact that drawing is only a means to an end,
not the object of laboratory work. Drawings better than words
reveal to the instructor the student's progress and the difficulties
he encounters.

The appearance of a good drawing may be spoiled by labeling
in a careless manner. Good results may be obtained by con-
sidering the following suggestions:

1. Printed or written names of parts should be connected by
guide lines with the parts they represent.

2. A broken line is preferable as a guide line.

3. Never allow guide lines to cross. As far as possible guide
lines should be parallel. There is no substitute for a ruler in
drawing these.

MOPQRSTUVWXYZ

nopa rs t u \/ w x u z
/2J4 5678 ^O

4 LABORATORY STUDIES IN ZOOUXIY

4. Use as short a guide line as possible. Labeling on each side
of a drawing is permissible, when necessary.

5. It is always desirable to print labels. As an aid for those
who have not yet learned to print the accompanying sample of
lettering is included.

Plates. — While the value of original drawings is recognized,
it has become apparent that more than a minimum expenditure
of time consumed in this way is utilized at the expense of a care-
ful study of laboratory materials. With this in mind there has
been prepared a series of plates with diagrams to be labeled or
completed and labeled. What is lost in drawing is more than
compensated by additional time for original study and for an
individual demonstration-quiz. Before the close of every labora-
tory period each student should demonstrate to the instructor
the results of his study and respond to questions. The plates
when labeled may be used as a means of recording information
for later use.

THE STUDY OF AN ANIMAL TYPE

In the study here outlined it is assumeti that the objective is
that of gaining a better understanding of the biological nature
of the high(>r animals and man. At the outset of such a study it
is necessary that one should acquire a clear conception of what
is signified by the term "living individual" or "organism" as a
center about which to organize zoological kncjwlcdge. An
organism is something more than a mere spatial association of
structural components, however orderly they may be arranged.
What constitutes the body of the animal? How are the struc-
tural components of the body related? What are the services
of the various parts and why are these services necessary? How
are these diverse structures and their activities maintained and
combined to form a unit and what is that unit? Studies along
the lines suggested by such questions provide the basis for a
comprehension of what is meant by the term "organism." These
deliberations are, therefore, begun with the study of an animal
type which will furnish the foundation upon which to place a
conception of an organism. The frog is chosen as a convenient
form, since it is a familiar animal exhibiting a moderately complex
structure and in all fundamental respects of structure and phys-
iology may be compared directly with man. The structural
similarity is easily recognized by standing the frog upon its
hind legs and making the comparison part for part.

In the frog and other complex animals it is possible to dis-
tinguish general regions of the body and directions within the
body without reference to the movements of the animal or to any
part of the environment. When such a state prevails the
method of naming part? and directions is known as iiitrinsic
io-ponomy. The following is a list of terms which will bo employed
according to this method of naming parts:

Dorsum, or back, that side of a orawlinR or (luadrupodal animal norinally
away from the sulistratum (support) upon which it rests.
Dorsad, toward the l)a<'k or in that direct i<m.
Dorsal, |)ertaiiiinK to the hack.

Venter, or heily, that side of the animal normally ti»ward tlu' substratum.
Ventrad, toward the venter or in a ventral direction.

6 LABORATORY STUDIES IN ZOOLOGY

Ventral, i)crtaining to the venter.

Cephalon, head, or that end which is foremost in locomotion.

Cephalic, pertaining to the liead or foremost end.

Cephalad, toward the head or foremost end.

Caudal, pertainhig to the tail or hindermost end.

Caudad, toward the tail or hindermost end.

Meson, the imaginary plane in the exact middle of the hodj- dividing it
into a right and left half.

Mesal, pertaining to the middle or mesal plane of the body,

Mesad, toward or in the direction of the meson.

Lateral, on either side of the meson.

Laterad, extending from the meson toward either side.

Ectal, i)ertaining to the surface of the body.

Ectad, from the inner mass of the body toward or in the direction of the
surface.

Ental, pertaining to the interior of the body.

Entad, toward or extending toward the inner mass.

Proximad, toward the proximal or fixed end of an organ {e.g., the shoulder
is at tlie proximal end of the arm).

Distal, pertaining to the free end of an organ; {e.g., the hand is at the
distal end of the arm).

Distad, toward the free end.

Memorizing these terms as a set task is not advised. It is
better to refer to the table when necessary to know the meaning
of a term, thus learning it and its application at the same time.

It is to be emphasized that the frog is studied as a representa-
tive animal to illustrate the fundamentals of organization upon
which our conception of an organism is based and the general
principles of biology in their application to animal study. It is
also studied to reveal the nature and architectural plan of a higher
animal.

The study of the frog is enhanced by observations upon living
specimens, several of which should be available in the laboratory.

Animals are noticeably different from plants in respect to the
necessity of voluntarily approaching the food which they appro-
priate from the world about them.

Animals are rarely passively supplied with food. It is neces-
sary for them to forage, hence the need of organs of locomotion.
It is also necessary that the animal be in possession of some special
means of gathering information concerning objects and forces
about it in order that it may harmoniously adjust itself to these
environmental conditions. The manner in which these and other
similar problems have been solved in the animal body may be taken
as an expression of the object in studying the exterior of the frog.

THE STinV or A.\ AMMAL TYI'E 7

The l)()(ly (■(•inpriscs two regions, htail and Innih. Tlio arms
and legs are regarded as appendage.s of the latter. Note the
color pattern, the distribution and intensity f>f color, and any
striking markings upon the i)ody.

When the frog once confronts its food it is still in need of pro-
visions for getting the food into its digestive organs. Reflect
upon the usefulness of hands and jaws in this service, bearing
in mind the non-grasping nature of the hands.

In the forelimb or arm, beginning at the body, identify upper
arm or brachium; the shoulder joint and its freedom of movement ;
forearm or antebrachium; elbow joint and its movements; wrist;
hand or manus with digits (fingers). Why is your own hand
efficient as a prehensile (grasping) organ? What is lacking in the
frog's hand? What is suggested by the structure, form, attitude,
and flexibility of the arm in its service to the frog?

In the hind limb identify thigh, shank, ankle, foot or pes with
digits (toes). Locate and compare the hip, knee, and ankle
joints with the corresponding joints of the arm. How many
digits in the foot? Are the digits of the hand and foot similar
in arrangement and in length according to numerical position?
Compare the palm of the hand and sole of the foot; the heel
with the corresponding part of the hand. Do these peculiarities
of hands and feet suggest any sort of advantages to the animal?

If not already familiar with both the terrestrial and aquatic
modes of locomotion of the frog make such observations upon
living specimens. Attempt a correlation of these observations
with the position of the limbs when at rest, the movements and
service of parts in active locomotion, determining, if possible,
a general locomotor function which may be assigned to each
pair of limbs, taking into consideration the need of buffers,
propellers, steering devices, leverage, rigidity, and flexibility.
If the limbs meet such needs, explain how it is done.

Organs of Special Sense. — The awareness of the frog to sur-
rounding conditions can l^e readily determined by observation
and simple experiments performed upon the living animal.
The means of gathering information from the surroundings are
sense organs (receptors) either located within restricted areas
as the organs of vision, smell, taste, and hearing or scattered as
the organs of touch and other senses. Some of these organs
cannot be observed by macroscopic study. Touch corpuscles
and fine nerve endings in the skin render the frog sensitive to

8 LABORATORY STUDIES IN ZOOLOGY

contact, changes in temperature and moisture, the chemical
nature of surroundings, and even hght.

A substance which stinmlates the sense of taste must be in
solution. It penetrates the surface membrane of the mouth
and stimulates special taste organs. In the frog these organs
occur apparently on the floor and roof of the mouth and particu-
larly on the flattened surfaces of special mushroom-shaped
elevations, fungiform papilloB, on the tongue. The organs of
taste, like the organs of touch, cannot be made out in a macro-
scopic study but they belong to the surface of the body, since
the mouth lining and the skin form a continuous sheet of material
identical in origin.

Locate the two nostrils or external nares on the upper surface
of the snout. Pass a beaded bristle through one and observe
that it comes out of a round opening in the roof of the mouth
cavity. This is the internal nostril or naris. The canal between
the external and internal nares serves for the passage of air on
its way to and from the mouth cavity. This short canal is
enlarged during its course to form the olfactory sac the lining
of which is thickened and otherwise modified to form the recep-
tive organ of smell, olfactory sense organ. Gases given off from
odorous bodies are detected by these organs. The olfactory
sense organs constitute the doorway through which the animal
communicates with the outside world as regards the nature of
gases (odors) which surround it. The advantage of an organ
of smell located in the walls of the breathing passages is obvious.

Posterior to the external nares are the large prominent eyes,
doorways for communication by means of light waves. In each
may be distinguished the iris, surrounding a central opening,
the pupil. By the proper manipulation with forceps eyelids
may be discovered. Determine their locations and relative
size and importance in covering and protecting the eye. The
nictitating membrane is a thin, transparent "third eyelid" which
is really an outgrowth of the lower lid. This may be observed
in a living animal. In most animals, the nictitating membrane
when present is distinct from the true lower lid. It reaches a
high degree of development in birds, where it may be stretched
over the whole front of the eye. In man it is represented by a
vestigial fold at the inner angle of the eye. What advantage
may reside in the presence and transparency of the nictitating
membrane? Compare the position of the eyes in frog and man.

THE STUDY OF AN AMMAL TYI'K 0

Can both eyes focus together upon the same object (binocular
vision) or each eye separately (monocular vision) ? Why? Ask
the instructor for a method of detcrinininp; your own angle
of vision. Represent by a simple (iiagrain. Looking clown
upon the top of the frog's head determine the angle of vision
of each eye. Represent by a diagram. What do you judge to
he the relative merits of the two kinds of vision?

On the side of the head caudad of the eye is a flat disk, the tym-
panum or eardrum, which responds to vibrations impinging
upon it. By careful manipulation determine tlie nature and
attachments of this membrane. Near the center on the inner
surface of this membrane there is attached a small rod, the
columella, which transmits the vibrations of the tympanic mem-
brane to the inner ear or receptive organ of the sense of hearing.
Carefully remove the cephalic third of the membrane as an aid
in discovering its inner relation.s. If difficulties are encountered
ask the instructor for assistance.

In the mesal line of the head, slightly cephalad of the level of
the eyes, there is a small light-colored spot termed the brown
spot. Its significance will be mentioned later. For the present
locate it only.

The anus (the caudal opening of the intestine) appears to be
located on the dorsal side rather than at the exact caudal end or
on the ventral side.

A survey of the sense organs (receptors) reveals them as organs
located at the surface or in direct communication with the sur-
face. Bearing in mind the general service of the sense organs
what is the fitness of their location?

Letting a horizontal line represent the frog's body, locate, by
means of numbers or symbols, the organs of the five special
senses (vision, smell, hearing, taste, and touch). What is the
result? Of what obvious advantage to the animal?

Identify the dermal plica: or thickened folds of skin extending
caudad from the posterior angle of the eyes. Those folds lodge
important skin glands.

Make a drawing of the dorsal aspect of the frog, life size fif
the frog 1)0 of modium size), representing the features mentioned
in this study.

THE FROG'S SKELETON

For this study prepared skeletons are provided. They arc
fragile and therefore must be handled with care. The value
of each is such that a charge must be made for any breakage
which is the fault of the user.

The need of a firm and, at the same time, flexible support for
the body is apparent in considering such functions as locomotion
in which rigid support and precision of movement are paramount.
Such functions, as well as many others, reside in the skeletal
framework of the body. The skeleton as a whole comprises two
main divisions: (o) the axial skeleton and (6) the appendicular
skeleton.

Axial Skeleton. — Extending along the middle line or main
axis of the body there are found the skull and vertebral column
constituting the axial skeleton.

The Skull. — Recalling the shape of the frog's head examine the
skull and determine the various aspects (i.e., dorsal, ventral,
cephalic, caudal, lateral). The most conspicuous feature of the
skull is the presence of a relatively enormous and somewhat
rectangular space on either side of the middle port on. These
spaces mark the location of the eyes and are known as the orbits.
Through two smaller spaces immediately cephalad of the orbits
the nostrils open.

The skull placed at the cephalic end of the axial skeleton
comprises (a) the cranium which encloses the small brain and
occupies the mesal region between the orbits. Associated with
the cranium are combinations of bones and cartilages forming
protecting encasements for certain sense organs. These are
called "sense capsules." They occur in pairs: the olfactory
capsules surrounding the olfactory organs at the cephalic end of
the cranium and the auditory capsules on either side at the caudal
end. (6) the visceral skeleton includes the framework of the jaws
and hyoid apparatus (tongue support). In the caudal end of
the cranium is an opening, the foramen magnum, through which
the spinal cord extends from the brain. Note the lines (sutures)
formed by the meeting of bones. Determine the location of
teeth. Identify the slender bone, columella, connecting the

10

Till': Fli(K:s SKKI.h'TOX 11

ciital siirliuT (»l the tynipaimin and miicr car. 'I'liis is tin; hone
already seen wlicii studying tlir tyinpamiiii. It transmits
vibrations from the tympanum to the auditory sense organ
encased within the auditory capsule.

The margin of the upper jaw is formed in front hy the prc-
maxilldrics, one on either side, each of which sends a process in a
dorsal direction, and on the side by the majUhinj. Both pre-
nuixillary and maxillary bones bear teeth.

The lower jaw is formed chiefly by the long dentariea, one on
each side.

Vertebral Column. — The vertebral column is composed of a
series of irregular V)ones including nine elements called vertebriT
and a caudal elongate bone, the urostijle. The first vertebra,
or atlas, is slightly modified because of its articulation with the
skull. Determine its peculiarities in this respect. The last
vertebra possesses a lateral projection (transverse process)
which is somewhat enlarged and serves as the attachment for
the skeleton of the hind limb. This vertebra is termed the
sacral vertebra.

Select the fourth vertebra as a typical one for study and
identify the following parts:

a. Centrum, the solid cylindrical portion of the vertebra. This
part is always ventral to the other parts.

b. A'eural canal, the enclosed space or cavity dorsad of the
centrum and lodging the spinal cord.

c. Neural arch, the bony portion forming the sides and roof
of the neural canal.

d. Neural spine, the dorsal projection from the middle of the
neural arch.

e. Transverse processes, lateral projections from the junction
of neural arch and centrum.

/. Zygapophyses, cephalic and caudal projections from the base
of the neural arch. They serve to yoke the vertebne together.

The Appendicular Skeleton. — This division of the skeleton
comprises (a) the bones of the free limbs, or those portions which
may be seen projecting beyond the general surface of the body,
and {b) the girdles which are embeddeil within the body walls
and with which the skeleton of the free limb is articulated.

The pectoral girdle (shoulder girdle) completely encircles the
l)ody at the level of the arms. Mach half consists of two portions,
dorsal and ventral, which meet at the socket of articulation of

12 LABORATORY STUDIES IN ZOOLOGY

the arm bones. This socket or articuhiting excavation in the
girdle is known as the glenoid fossa. In the middle line of the ven-
tral portion the caudally projecting bony element is the sternum.

The skeleton of the arm consists of the humerus in the upper
arm. In the forearm there are two bones side by side, the radius
on the thumb side and the uhia on the other side, as in man.
In the frog the radius and ulna are fused into one solid bone, the
radio-ulna. Distad of (beyond) the lower arm is the wrist or
carpus, containing six small bones known collectively as carpals,
arranged in two rows. The proximal row, situated at the end
of the radio-ulna, includes two elements; the distal row, three.
The sixth element is located on the inner side of the wrist. The
hand comprises five metacarpal bones, which support the palm
and at their ends articulate with the fingers. The first digit
(thumb) is absent. Its metacarpal is small.

The humerus is a good example of a long bone serving as a
lever. The enlarged ends formed of cartilages are known as the
epiphyses, the shaft being the narrower portion between. The
proximal end of the humerus rests in the glenoid cavity, forming a
ball-and-socket joint, and is held in position by muscles and liga-
ments. The strong ridge on the proximal portion of the shaft is the
deltoid ridge and serves for the attachment of muscles.

The distal end of the radio-ulna displays very obvious traces of
its double origin. The proximal end is hollowed out for articula-
tion with the humerus, and the ulnar part is produced proximally
to form a projection, the olecranan, which fits over the rounded
end of the humerus at the elbow.

The pelvic girdle is shaped like a V with the open part directed
cephalad. On each side the arm of the V is a distinct bone, the
ilium. The ilium of each side articulates with the transverse
process of the ninth vertebra. The ilia fuse with one another
at the caudal end where there is formed a circular platelike por-
tion excavated at its center. The cephalic half of this plate is
formed by the fused ilia. The caudal margin is formed by the
ischia (singular ischium) one on each side, which have joined at
the middle line. The ventral margin of the plate is occupied
by the puhes (singular, pubis) which like the ischia have joined
at the middle line to form a triangular mass of cartilage. In old
frogs this element becomes calcified. The ilium, ischium, and
pubis all take part in the formation of the acetabulum, the excava-
tion in which the leg skeleton articulates with the girdle.

THE FROG'H SKELETON

\:\

The skeleton of the leg consists of (1) a thigh bone or fctnur,
(2) a lower leg bone, the tibio-fitula, formed by the united tibia
(great toe side) and fibula (outer side), {'.i) an ankle region
including the tarsal bones, two long proximal elements, and three
imperfectly ossified elements forming a distal row, (4) five
metatarsal bones, and (5) five toes, or digits the segments of which
are called phalanges. Note the rudimentary sixth digit, the pre-
hallnx, on the inner side of the first toe.

After demonstrating to the instructor all the parts of the skele-
ton mentioned in the preceding paragraphs, label the same parts
on the proper plates.

Syxoi'si.s of Skeletal Divisions

[ Brain case
Cranium { Olfactory capsules
Auditory capsules

Skeleton

Axial

Skull

Visceral
skeleton

Upper jaw
Ix)\vor jaw
Ilvoid and larviix

Apj)endicular

Vertebral column (including ribs wlion jircscnt)

Scapula and suprascapula
and a number of elements
not elsewhere mentioneil
in these outlines; viz.,
coracoid, procoracoid,
epicoracoid, clavicle,
opisternum, omosternum,
sternum, xiphisternuni

Girdle

Slioulder

Free limb

Hip

Arm

Leg

Ilium

Iscliium

Pubis

Humerus

Kadio-ulna

Carpals

Metacarpals

Phalanpcs

Kemur

Til)io-(ii>ula

Tarsals

Metatarsals

Phalanges

THE MUSCULAR SYSTEM

All movements of an animal are the results of muscular activ-
ity. The skeletal muscles constituting a great portion of the body
mass are, in most cases, attached to some part of the skeleton.
These are the muscles to which reference is made when the term
"muscular system" is used. The skeletal muscles, because of a
pecuHar banded appearance of their component fibers, are also
termed striated muscles. There is another type of muscle asso-
ciated with internal organs such as the walls of blood vessels
and the intestine. Since these muscles are so arranged that they
extend in a circular fashion about cavities they are known as
hollow muscles. Their fibers are not crossed by bandlike stria-
tions, and thus they present a smooth appearance. They are
therefore termed non-striated or smooth muscles. The skeletal
muscles for the most part can be controlled by the organism and
are therefore often termed voluntary muscles in contrast to the
hollow or involuntary muscles which are not so controlled.

The middle portion of a muscle which shortens and increases
in diameter during contraction is called the belly. From this
part tendons extend to the bones for attachment. The two ends
of the muscles are attached to different bones. Otherwise the
contraction would come to naught as far as moving parts of
the body are concerned. The bones serve as levers and fulcra, the
muscles as the power. A thin, transparent, glistening membrane,
fascia, adheres closely to the muscle. The less movable or fixed
attachment of a muscle is called its origin; the movable end, the
insertion.

The primary reason for the study of a muscle is that of deter-
mining its action, its name and attachments serving as a means to
this end. After the attachments are known it is not ordinarily
a difficult matter to determine the action.

Muscles exhibit force or perform work during contraction only.
When a body part has been moved in one direction by a given
muscle or group of muscles acting in unison there will be found
another muscle or group of muscles for the movement of the body
part in the opposite direction. This is called the antagonistic

14

TIIK Ml'SCf'LAR sysTE.\f 15

luiioii of muscles and siieli ;i inusclc or muscle gr()U{) is known as
the aritagonid of its opponent. The application of this principle
facilitates the study of muscles to a considerable decree. The
contraction of a nuiscle is in the direction of the lonjj; axes of its
fibers which serves as an index to the particular work which a
^iven muscle or group of nuiscles may perform in producing
movement in any part of the body.

Remove the skin from l)oth the body and its appendages. In
doing so it will be noted that over the greater part of the body the
skin is not attached to underlying parts but that along certain
narrow lines there are firm attachments which must be cut in
order to free the skin. This forms underneath the skin great
spaces circumscribed by the lines of attachment. These spaces
in the living frog are filled with lymph and from their location
and contents are termed subdermal lymph spaces.

The removal of the skin exposes the superficial muscles of the
body. The muscle masses may be improved for study by rinsing
in a current of water and at the same time brushing the surface
with a wad of absorbent cotton. During the progress of the
study keep the muscles moist.

A study of the muscles is not difficult but requires careful
observation and thought. It is necessary to see what you look
at and think about what you see.

Manipulate the body of a live frog or one recently killed and
determine those places where there is the greatest amount of move-
ment or flexibility. A list of such places will be found convenient
for later use. Observing the dorsal surface of the frog one notes
that in certain places the muscles are massed while in others they
are almost absent. Considering the dorsum of the body and the
arm and leg of one side only, excluding hand and foot, there are
six of these masses. Identify and give each a name which will
indicate its location and so label the proper figure of the plate
representing the superficial (surface) muscles. Determine and
express the relation of these nmscle masses to points of flexibility.

Repeat these observations upon the ventral side. Express
results.

Study these nmscle masses in the light of what has been said
above concerning muscle antagonism. Results?

The Study of an Individual Muscle. For studying the fibers
and attachments of indiviilual nuiscles the dissecting microscope
may be found useful. The gastrocnemius muscle which forms

16 LABORATORY STUDIES IN ZOOLOGY

the calf of the leg is selected for study. Its name means stomach
plus leg, which is a reference to the enlarged belly of this muscle.
Lay out the frog with its dorsal side upward. Pull the right
foot caudad so as to straighten the leg. The gastrocnemius will
be found to occupy the whole inner border of the shank between
knee and heel. With an orange stick or blunt instrument sepa-
rate it from the adjacent muscles. The origin of the gastro-
cnemius is by two tendinous heads, one, a short clearly visible
tendon extending to a broad sheetlike tendon spreading over the
distal end of the femur and knee joint. This is the equivalent
mechanically to an attachment upon the end of the femur itself.
The other head is atta.ched by a short tendon exposed by
rotating the shank slightly and exposing the "hollow " of the knee.
Here the tendon of this head joins other tendons which are
attached to the end of the femur. Thus the two heads of the
gastrocnemius are seen to have their origin virtually upon the
femur. This muscle tapers toward the heel where a strong
tendon extends over the ankle joint to become inserted upon the
sole of the foot.

In the origin, extent, and insertion of the gastrocnemius muscle
one sees provision made for its action which is that of flexing the
leg at the knee and extending the foot. In addition to its double
function one sees that it extends over two joints (knee and ankle)
instead of one. Muscles which extend over two joints and possess
a double function act in conjunction with other muscles, all of
which increases their mechanical advantage. This is to be cor-
related with providing the power for leaping.

Label this muscle and its parts upon the plate showing the
muscles of the dorsum. Upon the plate point out the reasons
for regarding the gastrocnemius as a two -joint muscle with a
complex action. Label all parts to which reference is made.

The action of a muscle is the movement or movements in the
body resulting from its contraction; that is, what the muscle
does is spoken of as its action. When a part of the body bends,
as, for example, the leg bends at the knee, it is said to be flexed
and the muscle or muscles concerned with the flexing are called
flexors. When a part of the body is straightened it is said to be
extended and the muscle or muscles participating in such move-
ments are called e.rtensors. With the proper attachments a
given muscle may serve as a flexor for one part and at the
same time as an extensor for another. Muscles may, there-

THE AfirsCULAR SYSTE.U 17

fore, be classified aeconlin^; (o their act ions as in I lie folUtwiii^
categories:

Flexors, lieiul a part.

Extensors, straighten a i)art.

Adductors, move one part toward aiiotlier or toward tlic iiiosal j)lane of tlie
liody.

Abductors, move one part away from another or away from the rnesal
phuie.

Rotators, rotate a part upon its axis.

Depressors, lower or depress a part.

Levators, elevate or lift a part.

The action of individual muscles or muscle masses can be
demonstrated by stimulation with a galvanic current upon a
fresh specimen. The experiments will be performed by the
instructor, the class making the observations and formulating
explanations and answers to questions.

By either experiment or judgment of the action of muscles
formed through observing the direction of fibers and attachments
select indivitlual muscles exemplifying each category mentioned
above and label accordingly the proper muscles on the plate.

If time permits, other muscles may be studied under the direc-
tion of the instructor.

THE ORAL CAVITY

An etherized frog is best adapted to this study. Note that the
jaws fit together very tightly. Open the mouth to its full
extent and note the wide mouth (oral) cavity the posterior por-
tion of which, the pharynx, is continued caudad into the eso-
phagus. In the roof of the mouth identify the structures men-
tioned in the paragraphs which follow.

There are two groups of teeth found in this animal. The
maxillary teeth form a row about the edge of the upper jaw
where they are borne by the maxillary and premaxillary bones.
The vomerine teeth form two small patches in the cephalic part
of the roof of the mouth and near the middle line. They are
attached to the vomers (vomerine bones).

Locate again the posterior nares lying laterad of the two groups
of vomerine teeth. The eustachian tubes open into the oral cavity
through large apertures at the sides of the posterior part of the
mouth cavity. Each tube enters a shghtly dilated chamber,
the tympanic cavity (or middle ear), which lodges the columella
and is closed externally by the tympanic membrane already
seen in the study of the surface of the head. Pass a beaded
bristle through the opening of one of the eustachian tubes and
determine the results. If necessary make a slit in the tympanum.

Two rounded prominences on the sides of the roof of the mouth
are caused by the eyeballs. Press down upon one of the eyes with
the finger and note results.

The floor of the mouth cavity presents several features to be
noted. The lower jaw, which lacks teeth, forms a bony margin
for the floor of the mouth. The greater extent of the floor
is soft and supported by a cartilaginous plate, the body of
the hyoid. The tongue is attached to the cephalic portion of
the floor and has its free bilobed end turned caudad toward the
esophagus. If this organ is drawn cephalad the structures
about to be described may be seen more readily.

The glottis, or aperture leading into the lungs, is a longitudinal
slit upon the apex of a prominence, just cephalad of the eso-
phagus. It is supported laterally by the arytenoid cartilages

18

77//-; (>ir\L c.\ 1 /'/■]■ 19

which in the t'roj^ represents the v(»ice box of hijfher animals.
These cartilages cannot he seen without dissection. .Inst beneath
the corners of the mouth are the openings of the vocal sdcs in the
male.

Upon the plate showing the roof and floor of the mouth in
outline represent and label all the oral structures mentioned
above.

THE VISCERA

Lay the frog on its back under water. Hy passing pins through
the Hmbs fasten it to the wax bottoin of a tray. Cut through
the skin, along the middle line, the whole length of the ventral
surface. Separate the skin from tiie underlying parts The
muscles of the ventral body wall and the pectoral girdle should
now be exposed. Note a dark blue streak running along the
mesal longitudinal line just beneath the muscular walls. This
line represents the location of the ventral ahdominal vein. With
forceps pinch up the muscular body wall and with scissors cut
through it into the celom (body cavity) a little to the left of the
median line. Continue this cut caudad to the end of the body
and cephalad to the jaws, cutting through the pectoral girdle
with strong scissors, taking care not to injure the parts beneath.
If incisions taking a lateral course be made through the body wall
and skin in the region of the pelvic girdle the two resulting flaps
of body wall may be lifted and pinned so as to expose the abdom-
inal viscera (organs). It may also be necessary to clip oflF the
mesal portions of the two halves of the pectoral girdle in order
more clearly to reveal the relations of organs in the cephalic
part of the body cavity. In this study locate and identify all
structures mentioned, whether directed to do so or not.

Note that the body cavity is lined by a smooth glistening mem-
brane, the 'peritoneum. The various organs are suspended from
the florsal walls by membranes called mesenteries. These are
double folds of peritoneum.

The Heart. — With great care free the pectoral girdle from the
underlying muscles and blood ve.s.sels. Note the pericardial
cavity and examine the heart with a view to the identification of
the following parts:

1. The thin-w.-dled auricles form the ceijhalic and dorsal divi-
sions of the heart. They are nameil according to their location
upon the right or left side. Blood returning from the several

20 LABORATORY STUDIES IN ZOOLOGY

systems of the body is received by the right auricle and passed
on to the ventricle. The left auricle receives blood coming
from the lungs and passes it on to the ventricle.

2. The thick-walled ventricle is caudad of the auricles; it is
conical in form, with the apex pointing caudad.

3. The truncus arteriosus is a tube arising from the right
cephalic border of the ventricle and extending obliquely cephalad
across the auricles. This trunk is the only course followed by the
blood upon leaving the heart for the several regions of the body.

4. Lift up the ventricle and turn its apex cephalad. Do this
very gently and do not allow too much strain to come upon the
parts disturbed. Note three large vessels (veins) converging
in their course toward the dorsal side of the heart. The thin-
walled compartment which all three veins enter is the si7ms
ve7iosus or receiving station for the blood coursing back to the
heart from the body where it has performed its work. The sinus
venosus communicates with the right auricle which is the final
division receiving blood from the various systems of organs.

On the plate showing the diagram of the heart label the parts.

The Abdominal Viscera. — The liver is a large reddish-brown
organ behind and at the sides of the heart. It is either trilobed
or bilobed with the much larger left lobe further subdivided into
two parts. The lungs are two thin-walled but elastic sacs at
the sides of the heart; they He dorsad of the Uver and are often
concealed by it when viewed from the ventral side. The glottis,
noted in the study of the floor of the mouth, is the opening from
the mouth cavity into the larynx communicating with the lungs.

Study the location and relations of the reproductive organs.
If your specimen is a female the ovaries will be seen as two large
bodies of irregular shape, each comprising a mass of spherical
black and white eggs, appearing like small shot. When fully
developed the eggs break through the walls of the ovaries into
the body cavity and find their way in a cephalic direction to the
openings of the paired oviducts. These are two long very much
convoluted tubes with thick white walls, lying at the sides of the
body cavity. After the relations of ovaries and oviducts have
been noted those of the left side may be removed.

Turn the liver forward and note the stomach concealed by the
left lobe. Pass the handle of a needle through the mouth and
down the esophagus into the stomach which is an enlarged
portion of the alimentary canal between the esophagus and

rilK ORAL CWITY 21

intestine. Tlie stomach is n;uT()\v(>r at its caudal ciui and is
demarcated from the intestine by the distinct circuhir pylorus
or pyloric valve. Beyond the pylorus is the small intestine,
consisting of the duodenum, that part of the intestine lying
parallel to the stomach, and the ileum, which is the slender con-
voluted portion of the small intestine continuous at its distal
end with the large intestine. This passes without noticeable
change of size into the cloaca which is the most caudal division
of the alimentary canal. Locate the urinary bladder which is
a thin-walled, bilobcd sac opening through the ventral walls
of the cloaca.

The gall bladder is a small spherical green sac lying between
the right and left lobes of the liver. The pancreas is a pinkish
irregular mass Ij^ing in the loop between the stomach and the
duodenum and best seen by turning the whole loop toward the
head. The pancreatic ducts are numerous but too small to be
observed readily. They open into the slender bile duct which
passes through the pancreas on its way from the liver and gall
bladder to the duodenum. Bile secreted by the liver passes down
the hepatic ducts into the common bile duct and is stored in
the gall bladder until it is discharged into the intestine. Bring
gentle pressure to bear upon the gall bladder. This will force
bile into the common bile duct which may then be located. It is
about the size of a large thread and enters the duodenum at a
point about one-half inch beyond the pylorus and on the inner
or concave side of the loop formed by the stomach and duodenum.

The spleen is a small, dark-red, ovoid body lying in the mesen-
tery, opposite the beginning of the large intestine. It is not a
part of the digestive system.

After the above-mentioned organs of the digestive system
have been located, turn the alimentary canal and its appendages
over to the left side of the body cavity so that the structures
of the excretory and reproductive systems may be studied on the
right side.

The kidneys are a pair of elongate, reddish-brown organs
attached to the dorsal bodj' wall, close to the middle line, one on
each side of the vertebral column. They lie in the large lymph
space dorsad of (outside) the peritoneum The vreter, or duct
of each kidney, is a light-colored tube appearing to arise from the
outer caudal margin. It extends caudad to open through the
dorsal wall of the cloaca. On the ventral surface and partly

22 LABORATORY STUDIES IN ZOOLOGY

buried in the substance of the kidney is a narrow yellowish band,
the adrenal gland, where there is produced a secretion of impor-
tance to the life of the organism. Usually closely associated
with the anterior ends of the kidneys is a pair of bright yellow
finger-like tufts of flattened processes, the fat bodies. These
vary much in size at different seasons of the year.

The reproductive system consists of the sex organs, or gonads,
in which the sex elements are lodged, and ducts extending to the
cloaca.

In the male frog the gonads are termed the testes (singular,
testis). They may be seen as small, yellow, bean-shaped organs
located at the ventral surface of the kidneys. A number of
slender ducts, the vasa efferentia, may be made out in the mesen-
tery between each testis and the inner border of the corresponding
kidney. Spermatozoa (the male reproductive elements) pass
through these ducts into the tubules of the kidneys and thence
to the cloaca by way of the ureters. A tube conducting the
spermatozoa from the testis toward the exterior is called a vas
deferens. It will be seen that in the frog the ureter serves both
as ureter and vas deferens. In many species, and especially is
this true of the leopard frog {Rana pipiens), the male possesses a
vestigial oviduct which appears as a wavy white tube on each
side, laterad of the ureters.

It will be noted by those who have female frogs that the ovaries
lie in the same relative position as do the testes of the male but
vary considerably in size and shape according to the season of
the year. The most conspicuous organs in the celom of a mature
female in the spring are the ovaries, bearing great numbers of
ova. The ovaries bear no such relation to the kidneys as do the
testes in the male but, as already mentioned, shed their eggs
into the body cavity whence they make their way to the openings
of the oviducts, which they follow to the exterior. The funnel-
shaped mouth of an oviduct may be visible close to the outer
side of the root of the lung of the same side. The opening of the
oviduct through the dorsal wall of the cloaca should be identified.
Unhke the male, the female possesses genital ducts independent
of those of the urinary organs.

After locating and studying all organs and structures described
above, label those shown on the plate and add any which may
not be represented. The reproductive system on the right side
only need be shown.

THE BLOOD SYSTEM

The circulatory system is a closed scries of vessels filled with
blood and ramifying through all parts of the body. Its main
parts are (1) the heart, which by its muscular activity propels
the blood through the vessels, (2) the arteries, which are the
vessels conducting the blood from the heart to all parts of the
body, (3) the veins, which return the blood from the various
parts back to the heart, and (4) the capillaries, a system of very
small vessels forming the transition from arteries to veins. It
is during the course of the blood through capillaries that it
performs its main service in the body.

'J'he order in which blood vessels are studied will depend upon
the way in which the study specimens have been prepared. If
one specimen is to serve for this whole study the veins, whether
injected or not, should be studied before the arteries. The
following directions are based upon the use of two specimens.
For the study of the arteries the vessels are filled with a yellow
starch mass injected through the ventricle which abnormally
distends this compartment of the heart.

Place the frog on its back in a wax-bottomed tray and extend
the slit, made in injecting the animal, cephalad to the tip of the
lower jaw and caudad to the pelvic girdle, cutting through both
the skin and body wall. Note the ventral abdominal vein, which
may be seen as a streak along the mid ventral line. Carefully
separate this vessel from the body wall by gently tearing its
attachments. Next, make transverse slits through the skin and
body wall to the right and left of the midventral incision about a
quarter of an inch cephalad of the caudal end of the body cavity.
Turn back the flaps, thus formed. At this point students dis-
secting a female frog should remove the ovary and oviduct of the
animal's left side. Care must be used in separating the blood
vessels from the body wall, since they will break if placed under
too much strain. Use judgment with regard to the mechanics
of dissecting. If more convenient for the worker the frog may
be removed from the lifjuid and held in the hand.

23

24

LABORATORY STUDIES IN ZOOLOGY

The Arteries. — While the numerous blood vessels of the body
may be confusinji; at first, there is no need for viewing their study
as an impossible or even a difficult task. There are certain
observations which, if kept in mind, will facilitate this study:

1. The heart is the central organ of the whole blood system.

2. Arteries convey currents away from the heart.

3. Veins convey currents toward the heart.

4. The organs of every region of the body must be supplied
with blood from the heart.

5. The organs of every region must be drained of blood toward
the heart.

Fig. 1.

Based upon the distribution of arteries to the various organs
the body may be divided into three main regions: (1) the head,
(2) the lungs and skin, (3) the trunk, arms, and legs. Each
of these regions is supplied on each side by its own main trunk
leaving the heart. Figure 1 is a schematic representation of the
three regions and the arteries which supply them and as well the
main vessels of the whole body. It should be kept in mind that
this figure is schematic and not intended to show actual details.
By a careful study of this schema aptitude will be acquired for
the dissection and study of the vessels themselves.

THE ni.OOI) SYSTEM

Arisiiij; from the ventricle of the heart and passinn ohh<ni(ly
across the auricles is the large vessel, trunrus arteriosus, referred
to above. Note the divisions of the truncus arteriosiis into right

Fig. 1 — DiAGUAM of thk Bloou Vessels of the Kroo.
This diaRrain is schematic and not intended to show details.
The capillary networks of various regions are represented as follows:

A. C, arm; C. H. head; C. S., skin, L. C, leg.

ARTERIES (unshaded)

Main Vessels: —

I. Carotid arch .supplying the head region.
II. Aortic arch supplying the arm-trunk-leg region.
III. Pulmo-cutaneous arch supplying the lung-skin region.

Sul)ordinate Vessels: —

.v. M., anterior mesenteric artery G., gastric artery

B. A., subclavian artery Ge., genital artery

C. \., cutaneous artery He., hepatic artery

C. I., common iliac artery J., junction of aortic arches of
Coe., coeliac artery either side to form the dorsal

C. M., coeliaco-mesenteric artery aorta

D. A., dorsal aorta P. A., pulmonary artery

¥. S., femoral and sciatic arteries P. M., posterior mesenteric art^-ry
T. A., tnmcus arteriosus Re., renal arteries

VEINS (solid black)

Main Vessels: —

Po. C, post cava vein draining the trunk-leg region.

Pr. C., precava vein draining the hcad-arm-skin region.

P. Ve., pulmonary vein draining the lung.

S. v., sinus venosus receiving blood from whole body except the lungs.

Subordinate Vessels: —

Br. V, brachial vein M C, musculo-cutaneous vein

F.. femoral vein P. V., pelvic vein

He. v.. hepatic vein Re. p., renal portal vein

HeP., hepatic portal vein Sc, Sciatic vein

V. Ab., Ventral abdominal vein

HEART
L. A., left auricle; R. A.; right auricle; V., ventricle
Reed and Young "Laboratory Studies in Zoology."

cutaneous artery may tlicn ])e seen, (h) The pulmonary artrrij,
following a somewhat wavy course along the outer side of the

24 LABORATORY STUDIES IN ZOOLOGY

The Arteries. While the numerous blood vessels of the body
may be confusing at first, there is no need for viewing their study
as an impossible or even a difficult task. There are certain

J3y a caretul study ot tms scnema aptituae wiu oe acquired lor
the dissection and study of the vessels themselves.

THE BLOOD SYSTEM 25

Arising from the vcntricU' of tho heart and passing oblicjuely
aeross the aiirieles is the hir^e vessel, tnincus (irteriosus, referred
to above. Note the divisions of the truncus arteriosus into riglit
and left branches, each of which again divides into three arches.
l']ach of these arches supplies one of the regions mentioned above.
In order to gain a clear view of these three arches and the various
arteries arising from them, it will be necessary very carefully to
remove the veins and other structures which overlie them.
Xcvcr take hold of a blood vesacl itself with forceps. Handle it
by seizing the supporting or associated tissues. Begin at the trun-
cus arteriosus and trace out the arches and arteries of the left
side of the animal only, since the two sides are alike, reserving
the right side for the study of the veins.

The branches of the main arches and their subdivisions are
as follows:

1. The carotid arch (Fig. 1, I) is the most anterior of the three.
It extends dorsad around the side of the esophagus and soon
divides into two branches. A small, vascular swelling, the
carotid gland, surrounds the base of these branches and often
prevents the injecting mass from filling the vessels. The two
branches are:

a. The external carotid artery, a small vessel supplying the
tongue and floor of the mouth;

b. The internal carotid artery extending around the (psophagus
to its dorsal side, then cephalad into the roof of the mouth along
the base of the skull. Ix)cate its origin from the carotid arch.
Cut the lower jaw at the angle of the mouth. Peel the lining
from the roof of the mouth and note its distribution in this
region.

Which general region of the body is supplied by the carotid
arch?

2. The pulmo-cutaneous arch (Fig. 1, III) is the third and most
caudal of the three arches. It will be described and dissected
at this point, since its branches are likely to be destroyed in the
dissection of the middle arch. The pulmo-cutaneous arch divides
at about the level of the carotid gland into (a) the cutaneous
artery supplying the skin. Its course can be readily traced. Slit
the skin along the middorsal line and turn it back until the
shoulder region is visible. The course ami distribution of the
cutaneous artery may then be seen, (b) The pulmonary artery,
following a somewhat wavy course along the outer side of the

26 LABORATORY STUDIES IN ZOOLOGY

whole length of the lung, gives off branches to its walls. When
labeling this arch on any of the drawings state the region which
it supplies.

3. The aortic arch (Fig. 1, II), the middle of the three main
divisions, extends somewhat obliquely around the esophagus
to its dorsal side and unites with its fellow of the opposite side
at about the level of the cephalic end of the kidney to form a
single vessel, the dorsal aorta. In order to expose the dorsal
aorta pierce the peritoneum about the left kidney and gently
pull the kidney away from the body wall so as to expose the large
lymph space in which this vessel runs. The aortic arch and its
branches in the region of the pectoral girdle can best be studied
from the side.

Before the union of the two arches to form the dorsal aorta
there are at least four branches given off, but attention is drawn
to one only, the large subclavian artery which arises at about the
level of the shoulder and extends laterad to supply the arm.

Branches given off after the union of the two arches to form the
dorsal aorta are:

a. The cceliaco-mesenteric artery, a large median vessel arising
near the union of the two arches, or sometimes from the left
arch just before the union, and supplying the stomach and
intestines. This vessel in its turn gives rise to two important
branches: (1) the common coeliac artery, whose branches supply the
stomach, liver, and gall bladder; and (2) the mesenteric artery,
whose branches supply the intestine and spleen.

b. The urogenital arteries, four to six in number. These are
small vessels which arise from the ventral surface of the dorsal
aorta between the kidneys. They supply the kidneys, the
reproductive organs and their ducts, and the fat bodies. There
are other small arteries leaving the dorsal aorta, but the study of
these may be omitted.

c. The common iliac arteries are large vessels formed by the
division of the dorsal aorta near the level of the caudal end of
the kidneys and are distributed to the legs. Cut the muscle
mass on either side of and along the urostyle, which can then be
elevated and removed along with the attached muscles. Trace
the artery in its course down the leg.

A recently etherized frog is necessary for the study of the veins.
If the veins are injected the venous system should be studied
first.

77//!,' lif.OOl) SYSTEM 27

The Veins. — Alllmimh (lie iiijcctccl inlcrit's of (lie fr(»n .studied
lire decidedly larger than uiiinj<'('l.ed veins, the hitter in their
normal state are larger than arti-ries. As a rule, the veins lie
nearer the surface than do tlie arteries.

Keep in mind the fact that tlie ventricle is the compartment of
the heart which forces blood out through the arterial system to
all parts of the body. It receives blood from the auricles only.
Four veins return blood to the heart; three open into the sinus
venosus and thence into the right auricle; while one, the pul-
monary vein, opens directly into the left auricle.

As in the case of arteries in their relations to general regions
which they supply, one finds similar relations of the larger veins
antl regions which they drain back toward the heart. The vein
regions differ slightly in the combination of parts from the artery
regions. There are three, as follows: (1) the head, arms, and
skin, (2) the lungs, (3) the trunk and legs. Two of these regions
may be subdivided. The head-arm-skin region according to the
relations of the main vessels draining them is divisible into (a)
head and (6) skin-arm divisions. The trunk-leg region similarly
comprises (a) dorsal-trunk and (6) ventral-trunk divisions.

Throughout the study of the veins make comparisons of the
dissections with Fig. 1 in order to discover for yourself the struc-
tural plan of body regions and the vessels draining them and the
general course and interrelations of the vessels themselves.

Veins Entering the Si7ius Venosus. — The right precava is a large
vessel opening into the right side of the sinus venosus. Its
branches return blood from the right side of the head, the right
forelimb, and the skin of the right side of the back. Gently
take hold of the tip of the ventricle with the forceps, raise the
heart, turn it to the frog's left, and observe the short precava
lying close to the auricle. Follow this short vessel latero-cepha-
lad from the heart to a point just outside the peritoneal membrane
where it is formed by three tributaries:

a. The external jugular is the inner of these three divisions
and drains the floor of the mouth and the tongue. Close to the
ventral surface of each external jugular vein is a small, round,
highly vascular body, the thyroid gland.

h. The middle of the three tributaries of the precava is the
innominate vein, coming from a lateral direction and earlier from
abruptly dorsad, receiving as it turns a small vein from the back
of the arm and shoulder. The main vein iufore the entrance of

28 LABORATORY STUDIES IN ZOOLOGY

tliis branch is (he internal jtujidar, returning blood from tlic
interior of the skull, which it leaves by an aperture at the posterior
border of the orbit.

c. The third and outer tributary of the precava is the subclavian
vein. It is the largest of the three and comes from the body wall
to the base of the arm where it receives the brachial vein from
that appendage. Before this point it is found as the large
miisculo-ciUaneous vein which returns blood from the skin and
muscles of the side and back of the body and from the head.

The left precava in its course and tributaries corresponds to
the right precava. It may be located.

In synoptic fashion (or otherwise), show: (a) the region drained
by the precava, (6) the principal tributaries of the precava and
the areas drained by each.

The postcava is the only vein returning blood from the posterior
part of the body. It drains the kidneys and liver and through
them the remaining organs. Expose both kidneys ventrally by
removing the peritoneum and pushing back the other structures
which obscure them. Note how the postcava is formed between
the kidneys by the renal veins and follow it cephalad to the liver.
Dissect away enough of the substance on the dorsal side of the
left lobe of the liver to show that the postcava passes through this
organ without breaking up into capillaries. As it emerges from
the liver under the apex of the heart it receives the right and left
hepatic veins and passes directly into the sinus venosus. Harmo-
nize this dissection with the structural principle shown in Fig. 1
and relevant statements already made.

Veins Entering the Left Auricle. — The pulmonary vein is formed
by the union of the right and left pulmonary veins and returns
blood to the heart from the lungs. Each pulmonary vein extends
along the inner side of the lung and may be located by dissecting
away, little by little, the membrane between the heart and the
lungs.

The Portal Systems. — The liver is one of the organs in the
frog's body in which veins en route to the heart break up into
capillaries and then reunite to form veins before leaving the organ.
Because of this peculiarity of structure this portion of the venous
system is known as the hepatic portal system. There is another
portal system in the frog which is located in the kidneys and
called the renal portal system. The veins which carry blood to

77//'; lii.ooi) sysTK.\r 2\)

those organs are called portal veins and are distinguished by pro-
fixing the name of the organ.

The Renal Porlal System. — Hcmovc the skin from the dorsal
surface of the left thigh, separate the nmscles by tearing the
connective tissue between them. Between the two larger muscles
will be found a smaller one which may be transected at its middle,
rnderneath this small muscle can be seen the femoral vein
which drains the hind limb. Remove such muscles and portions
of the skin and body wall as are necessary to trace this vein to a
point on the posterior wall of the body cavity where it forks giving
off a dorsal branch, the re7ial portal vein, and a ventral branch,
the pelvic vein. Tear the peritoneum along the outer margin of
the kidney so as to expose this organ. Now trace the left renal
portal vein along the outer margin of the kidney and note that it
breaks up into capillaries within this organ. Through what
vessels does the blood emerge from the kidneys, and by what
main trunk does it reach the heart? The inght renal portal
corresponds in its course and branches to the left one. Uncover
this vessel and also the right.

The Hepatic Portal System. — The union of the two pelvic
veins, one from each side of the body, forms the ventral abdominal
or the vein which was eariier dissected from the ventral body
wall. The hepatic portal system is formed partly by the ventral
abdominal vein, which brings to the liver blood from the hind
limbs; and partly by veins returning blood from the alimentary
canal and its appendages. Trace the ventral abdominal vein
cephalad to the liver and note that it divides into right and left
branches, which enter the right and left lobes of the liver, respec-
tively. The hepatic portal vein is a large vein which runs in the
mesentery and joins the ventral abdominal vein at its point of
division into right and left branches, giving off, before doing so, a
branch to the left lobe of the Hver. It carries to the liver the
blood from the walls of the ahmentary canal and is formed by the
union of the (1) gastric veins, from the stomach, the (2) intestinal
veins, from the whole length of the intestine both smalkmd largo,
and (3) the splenic vein, from the spleen. This usually joins one
of the intestinal veins.

Reduce this dissection to the simple principle of "region
drainage" illustrated in Fig. 1.

On the plate showing outlines of some of the visceral organs,
indicate the course of one of the precaval veins and its tributaries

30 LABORATORY STUDIES IN ZOOLOGY

and label. Do the same for the pulmonary veins. Represent
the postcava and its tributaries, the renal portal system of the
left side, and the hepatic portal system. Label parts of each.
Review the blood system by comparing the schematic represen-
tation of Fig. 1 and the labeled plates.

THE NERVOUS SYSTEM

In an earlier study it has Ix'en dcinonstrated that the con-
traction of muscles when properly attached to skeletal elements
may cause parts to move. Before a muscle contracts it receives a
nervous stimulus from a controlling; center, and before compli-
cated and beneficial movements take place these muscular
contractions must be coordinated. If an animal is to acquire
any degree of intelligence it must be able to accumulate experi-
ences. These may be taken as the general services provided by
the nervous system.

This communicating, coordinating, and controlling system
in animals like the frog and man comprises two divisions: (1)
the central nervous system, formed by the brain and spinal cord;
(2) the peripheral nervous system, comprising the nerves which
extend between the central system and the periphery of the body
(or outlying organs). Specimens for this study have been pre-
pared so as to soften the bones which maybe cut with instruments.

If the skin has not already been removed from the animal
clip off that of the dorsum. Remove a narrow strip of muscle
from the middorsal region beginning at the cranium and extend-
ing to the sacral vertebra. Expose the brain and spinal cord
by carefully snipping away the roof of the skull and vertebral
column with the aid of scalpel, forceps, and scissors. Begin
by cutting through the cartilage just caudad of the external
nares from this point work caudad slicing off the dorsal portion
of the cranium and vertebral column until the outlines of the
brain and spinal cord are exposed to view. Care must be used
to avoid cutting or injuring the soft nervous tissues while remov-
ing the roof of the skull and vertebral column and to avoid injury
to the nerves leaving any part of the central system. Do not
cut away too much of the neural arches of the vertebra). In
removing pieces of .skeletal material from the sides of the central
nervous system always cut away from the middorsal line. When
the central nervous system is clearly exposed identify the parts
to be seen from the dorsal aspect.

Dorsal Aspect of the Brain.— Observe the pigmented membrane
closely applied to the nervous tissue. This membrane is called

31

32 LABORATORY STUDIES IN ZOOLOGY

the pia. In all probability the outer menix (covering or enve-
lope), the (J lira, has been more or less torn in removing the bone,
since in the frog it appears more as a lining of the cranial cavity
than as an envelope of the brain. The pigmented state of the
pia is especially noticeable in the caudal portion of the brain,
where it is rich in blood vessels and roofs over a triangular cavity.
With the forceps or needles remove the pia.

For descriptive purposes the brain will be regarded as compris-
ing divisions and parts as follows:

1. The forehrain exhibiting two divisions. The more cephalic
portion consists of a pair of rounded olfactory lohes, which are
separated by a faint mesal groove and are continued cephalad
as the "olfactory nerves" which extend to the organs of smell
located in the nasal canal. The caudal boundary of the olfac-
tory lobes is marked by a slight transverse depression, behind
which is to be seen the other portion of the forebrain, namely,
a pair of long oval bodies, the forebrain hemispheres.

2. Just caudad of the hemispheres is a constricted region, the
twixt brain or interhrain, bearing in the midline and near the cau-
dal end of this region a short stalk, the pineal body. In the
undisturbed state this is found to extend to the bony roof of the
cranium where it ends in a knoblike enlargement. In the tadpole
(young frog) this outgrowth appears to be connected with that
area already identified on the dorsum of the head as the brown
spot which is looked upon as marking the location of a former
sense organ (or organs). The pineal stalk of the brain represents
its former nervous connections.

3. Caudad of the interbrain is the midbrain of which the optic
lobes are the prominent features of the dorsal aspect.

4. Just behind the optic lobes is a narrow, transverse ridge,
the cerebellum. This division in many other animals is larger
and an important center of equilibrium. In the frog it is not
extensively developed.

5. The division caudad of the cerebellum is the oblongata or
medulla oblongata. Its dorsal wall is a thin, vascular membrane
consisting of pia and endyma (the lining of the cavity of the
brain) . In the roof of this division nervous substance disappears.
The vascular membrane thus formed is known as the posterior
choroid plexus.

The Spinal Cord. — The spinal cord is continuous with the
oblongata and occupies a space within the vertebral column

THE NERVOUS SYSTEAf 33

known :is tlic luiiidl rtiiutl foriiu'd liy tin- n('ur:il arclics cxtciKiinn
tlorsally from the cciilra <»f the vertcltia'. In the mcsal liin' is a
longitudinal ^;roov(', the dorsal Jissurc. ()l)S('rv(' tiic cephalic
or hrdcludl and tlu' caudal or lumbar cidarncnicnts of the cord.
( 'audad of t he lunil)ar enlargements the cord is reduced to a men;
filament, tlie Jiliim Icnninale, which extends into the cavity of
the urostyle and may be seen by dissecting away the dorsal
portion of this part of the skeleton.

The Cranial Nerves. — Ten pairs of nerves arise from the brain
within the cranial cavity, hence their name. Some are sensory,
others motor, and some are both sensory and motor in nature.
The roots of some of these may be seen if care is used in making
the dissections necessary to expose the sides of the brain. A
brief description of these nerves is given as an aid to the identifi-
cation of those which may be found without the expenditure of
too much time. // time is limited proceed directly to the study of
the brain canties. The cranial nerves are in pairs, one leaving
the brain on each side. The first is the olfactory and has already
been seen, arising from the olfactory lobe. The second, or optic
nerve, leaves the ventral surface of the interbrain and extends
directly to the eye. The third, the oculomotor, is small and
arises caudad of the optic nerve and is distributed to muscles of
the eye. The fourth, the trochlearis, is very small and leaves
the brain from the dorsal side between the optic lobe and the
cerebellum. Both the third and fourth nerves arc motor and are
distributed to certain muscles of the eyeball. The fifth, the
trigeminal, is one of the largest of the cranial nerves. It leaves
the ventral side at the cephalic end of the oblongata. It is
distributed to the side of the head and lower jaw. The sixth,
the nbducens, arises from the ventral side of the oblongata and
supplies certain eye muscles. The seventh, the facial, ari.ses
from the oblongata caudad of the fifth and is a mixed nerve to
the side of the head and lower jaw. The eighth, the auditory,
arises from the dorso-latcral wall of the oblongata and supplies
the inner ear. The ninth and tenth, the glossopharyngeal and
vagus, respectively, arise together from the sides of the ol)longata
a short distance caudad of the eighth. Both contain sensory and
motor fibers.

Both brain and spinal cord are hollow, the cavities of the two
being continuous. Carefully slice away the dorsal surface of
the brain in order to expose its cavities called ventricles, and il

34 LABORATORY STUDIES IN ZOOLOGY

lime peiinits proceed to identify the cavities mentioned in tlie
following lines. The cavities of the forebrain hemispheres are
called lateral ventricles. The cavity of the interbrain is the third
ventricle, that of the oblongata region the fourth ventricle. The
narrow canal between the third and fourth ventricles is called
the aqueduct of sylvius.

The Spinal Nerves. — In order to study these nerves, make a
midventral incision through the body wall from the pelvic girdle
to the cephalic margin of the pectoral girdle and lateral incisions
through the body wall just cephalad of the pelvic girdle.
Remove all of the viscera in a mass by cutting across the organs
at the cloaca and loosening them from the vertebral column with
a scalpel, lifting them as the necessary cuts are made. When
they are completely freed from the vertebral column, sever the
mass in the region of the oesophagus. The spinal nerves will
now be seen as white threads lying on the dorsal body wall.

Note in the arm and leg regions the grouping of the spinal
nerves into plexuses. The brachial plexus is formed by the
mingling of the fibers of the second and third nerves. It gives
rise on either side to the brachial nerve, which is the important
supply to the arm. The sciatic plexus is similarly formed from
the seventh, eighth, and ninth nerves and gives rise on each side
to the sciatic nerve, the main nerve of the leg. The first spinal
nerve is small and arises just cephalad of the brachial plexus to
supply the muscles of the back and shoulder.

The fourth, fifth, and sixth nerves are also small and supply the
muscles and skin of the body wall. The small tenth nerve issues
from the urostyle and sends out branches to the bladder and
cloacal region.

Select one of the large nerves making up the sciatic plexus and
trace it to the point where it leaves the vertebral column, care-
fully cutting away the vertebrse on the dorsal side. Each of the
ten pairs of spinal nerves arises from the cord and leaves the
neural canal by way of openings between the vertebrse. Each
spinal nerve has two roots, a dorsal and a ventral. The dorsal
root is known as a sensory root, since it is composed of sensory
fibers and conducts impulses toward the cord (afferent impulses).
The ventral root is termed the motor root, because it is composed
of motor fibers which transmit nerve impulses away from the
cord (efferent impulses). The two roots unite to form a common
trunk outside the neural canal. Trace the roots further toward

THE .\ Kinoes sysTi':.\[

35

the colli ami note that the dorsal root is attached to the dorso-
lateral and the ventral root to the ventro-latcral region of the
cord. A small ganglion (enlargement) lyinp; in the intervertebral
foramen (space between two adjoining vertebrip) and surrounded
by the white pcrignnglionir gland (the calcareous l)ody) is found
on the dorsal root near its union with the ventral root, but
in the frog as a rule the spinal ganglion is continued beyond the
point of union so that the two roots appear to meet in the gang-
lion itself. Examine the periganglionic gland and then remove
it so as to reveal the small brown i^pinal ganglion.

Label the described parts on the outline of the dorsal aspect
of the brain and spinal cord,

SyNOPTU- SlMMAHY OK THK DIVISIONS OK THE NeRVOUS SySTEM

Olfactory lobes

Brain

Nervous
svstein

f Central
system

Peripheral
svstein

Forebrain hemi-
spheres
Lateral ventricles
Pineal body
Pituitary body
Infundibuhim

Third ventricle
Optic lobes
Aqueduct of
I sylviu.s

I CerebeUum
Hindbrain { Oblongata

I Fourth ventricle

Forebrain

Interbraia <

Midbrain

Spinal cord

I. Olfactory
II. Optic
III. Oculomotor
j IV'. Trochlearis
f Cranial nerves \'. TrlRcminiis

\'I. .Vbducens
VII. Facial
VIII. Auditory
IX. Glos.sopharynntal
X. VaRUs
Spinal nerves 1 to U)
Sympathetic system. Not included in tiiis study

THE COMPOUND MICROSCOPE AND ITS USE

In order that one may be able to make the best and safest use
of so complex, deUcate, and expensive an instrument as a com-
pound microscope a limited amount of time is set aside for the
study of its construction, care, and use.

Possibly all will profit somewhat by a careful examination of
the instrument which is to be used during the course. The
following instructions are primarily for beginners, but all are

Ocular

Draw fube

Body -fube

Coarse
adjusimenf

Nosepiece

Objectives

Stage
Iris diaphragm
Condenser
Mirror

Fig.

asked to read them and perform the various manipulations which
are mentioned. As those who have never used a microscope will
require extra time for the study of its parts and especially for
the practice which is necessary to the effective use of the instru-

36

THE COMl'orSI) MKUOSCOFE AM) ITS ISK :\7

iiicnt, those who ;ii(' proficient in its use iii.iy turn iiiniiediately
to the study of the celluliir structure of the fro^. iV» om' should
aUeiupt to .study with the microscope before beiiiK able first to focUH
on an object with the h)\v-power objective and then change to the
high power and find the object without allowing; the high objec-
tive to come in contact with the cover sUp on the shde. Touch
only vietal parts. Consult Fig. 2 of a compound microscope and
identify the base, piUar, stage, handle arm, body tube, coarse
and fine adjustments, nosepiece, objectives, oculars, iris dia-
phrji^m, and mirror.

In using the instrument, light is reflected from the movable
mirror through the aperture of the diaphragm in the stage, upon
which is placed the object to be examined. The observer looks
through the body tube to which the ocular and objectives are
attached. The revolving nosepiece at the lower end of the tube
holds the objectives of different powers and facilitates the change
from one to the other by turning upon its axis. It is, therefore,
unnecessary to remove an objective from its attachment to the
nosepieces.

Always work with the low-power objective and ocular first.
These will soon be learned by the size and number. Place a
prepared slide of a wing of the house fly upon the stage, center
the light with the mirror, and by means of the coarse adjustment
bring the low-pow-er objective one-fourth inch above the slide.
Then, looking into the ocular, focus the microscope by gradually
raising the lens, using the coarse adjustment, and turning counter-
clockwise with the right hand until the object is brought into
view. The focus may then be sharpened by the use of the fine
adjustment. Compare the orientation of object and image.

Note carefully the brightness of the field of vision and the
appearance of the object; it is illuminated by transmitted light,
i.e., light which is reflected from the mirror and passes through
the object. Tilt or cover the mirror and observe the change
in the intensity and character of the light. The object is now
viewed by reflected light, i.e., light which is reflected from the
surface of the object. Reflected light must be employed for all
opaque objects.

In order to use the high-power objective, first place the slide
so that the object appears exactly in the center of the field as
viewed with the low-power objective; tiien increase the light and
change to the high-power objective by revolving the nosepiece

38 LABORATORY STUDIES IN ZOOUKIY

until the objective is in line with the tube. Its exact position
is indicated by the "click" of a friction stop. The object can
then be seen dimly. To sharpen its outlines employ the fine
adjustment turning only slightly to the right or left. It is always
safest to focus up slightly before changing the objective, thus
avoiding the danger of the high objective coming in contact
with the object. Use great care in changing from low to high
power.

Thoughtful practice in the use of the compound microscope
soon results in effectiveness on the operator's part. Always
observe the following rules in using a compound microscope :

1. Do not touch the glass of the objectives and oculars with
the fingers or any object. If the surfaces become soiled ask the
instructor's aid in cleaning them with lens paper.

2. It is dangerous to both lens and object to focus downward
with the eye on ocular.

3. Never permit the objective to touch the cover glass.

4. Do not use high powers when low ones will do.

5. Always carry your instrument by the handle arm. Other-
wise the adjustments may be injured.

6. Do not leave mirrors or lenses exposed to direct sunlight.

7. In case of trouble consult your instructor. When the
microscope does not appear to behave properly, it is safe to assume
that the trouble resides in the operator rather than in the
instrument.

THE FINE STRUCTURE OF THE FROG

In the previous laboratory studies of the frog the gross struc-
ture only has been emphasized. The body was found to be
composed of organs associated as systems of organs each with a
particular service to perform. When a small portion of any
organ is examined microscopically it is found to bo composed of
great numbers of units called celh. Kach cell is a minute mass
of protoplasm. When more extensive microscopic studies of the
body are made two configurations are readily recognized:

1. The protoplasm of the body rather than existing as a mass
is everywhere divisioned as cells. The body is therefore to be
regarded as formed of cells and is said to be niiilti<clli(1or in its
structural nature.

2. The cells are not all alike. Different groups of cells while
agreeing among themselves differ from those of other groups and
each different group is concerned with different categories of
functions. Each of these groups constitutes a tissue which may
be defined as an association of cells differentiated in relation to a
particular category of functions. There are four primary tissues
as enumerated below.

a. P^pithelium or the covering, protecting and secreting tissue.
Normally nowhere in the body is any other kind of tissue exposed.
Not only the external surface but also the lining of every cavity
is composed of this kind of tissue. I'^pithelial tissues constitute
the active elements of glands.

b. Connective tissue, as the name suggests, functions as the
connecting and supporting substance of the body. It fills spaces
in the body, unites the various parts of the body, and binds
organs together.

c. Muscular tissue is the tissue of movement.

d. Nervous tissue comprises elements adapted to the conduc-
tion of impulses and serving as the communicating lines in the
body.

When a cell is studied microscopically it is fouml to ho com-
posed fiot of a homogeneous substance but of organized
protoplasm.

39

40 LABORATORY STUDIES IN ZOOLOdV

A STUDY OF THE PRIMARY TISSUES

Epithelium. — One of the most important functions of epi-
thelium is protection or the covering of other tissues. An exam-
ple of such an association of cells is the pavement-like layer of
flattened cells which constitute the outermost layer of the skin.
Examine a mounted preparation of such a layer which may be
prepared from the sloughed skin of the frog. This shows the
skin as it actually appears in surface view. Note that the cells
are all similar in appearance and so associated with one another
as to protract a sheet of cells which is the tissue. In studying
tissues it is always best to use a minimum of light. Tilt the
mirror of the microscope or reduce the opening in the diaphragm
in order to reduce the amount of light passing through the
preparation.

Study a single cell and determine the parts which are common
to all cells, as follows: (a) cell membrane, the thin but dense mar-
gin of the cell; (b) Jiucleus, composed of dense protoplasm and
located near the center of the cell; (c) all the protoplasm excluding
the nucleus is termed the cytoplasm. Each of these parts and
many others not mentioned is an area of protoplasm differently
organized for particular services in the cell.

Make an enlarged drawing of several cells showing their
relations and parts. Drawings of single cells should not be less
than three-quarters of an inch in diameter.

Many adaptations to various functions are illustrated by epi-
thelial tissues and in each case the tissue takes a name descrip-
tive of its form, structure, or function. For instance, in some
regions, as in the lining of the mouth and oesophagus of the frog,
the exposed surface of the epithelial cells is provided with deli-
cate, vibratile extensions of protoplasm called cilia and it is
accordingly known as a ciliated epithelium. Examine a strip of
the lining from the roof of the frog's mouth stretched and mois-
tened with normal salt solution to demonstrate the transportation
of solid particles such as fine charcoal over the surface of the
epithelium by the effective stroke of the cilia. Examine a piece
of teased epithelium as a demonstration of ciliary action.

Connective tissue performs varied functions and is corre-
spondingly modified in its nature. White fibrous connective
tissue, yellow elastic fibers, adipose tissue, cartilage, and bone
are here considered as forms of connective tissue. While in
some tissues the intercellular substance is relatively small in

77/f; /•7.\A' STHrCTlUE OF Till': iu<h: \\

amount, in connective tissue it is usually abundant. Connective
tissue is composed of scattered cells, to^f'ther with the inter-
cellular substances. The intercellular substances vary according
to the service performed by the tissue.

As an illustration of the binding and connectinR function of
this primary tissue study preparations made from materials
taken from between the larger nuiscles of the frog. The cells
themselves are widely separated by the fibrous intercellular
substance which they secrete. These fibers arc of two kinds:
(o) fine ones arranged in wavy bundles known as white fibers anil
(6) elastic fibers, which are larger, single, and approximately
straight in their course.

Make a drawing of a restricted area to show the characteris-
tics of this type of tissue. Label the parts and point out the
correlation of intercellular substance and the connecting function.

Cartilage serves as an example of connective tissue in which
the intercellular substance is firm, adapting it for the purpose
of meeting the needs of stress, strain, and impact. Examine a
prepared section of the cartilaginous portion of the sternum
of the frog. Note that it is composed of a non-cellular homo-
geneous matrix within which the cells are scattered in rounded
spaces or laciuuv. Each cell secretes about it the intercellular
substance or matrix. Around the border of the cartilage may be
seen a connective tissue layer containing cells, which, as the
cartilage increases in mass, become transformed into functioning
cartilage cells and surrounded by matrix. Keep in mind that
the functional part of cartilage is the matrix.

Make an enlarged drawing of a small area of cartilage and
label the parts.

Muscular tissue is composed of elongate, contractile cells
hound together by connective tissue. Muscle cell and muscle
fiber are synonymous terms. The structure of two types of
muscles, striated and non-striated, will be studied.

Striated Muscle. — Other names for this type of muscle may
be recalled from the directions on the muscular system, llxatnine
a prepared slide of muscle fibers. First locate the nuiterial with
the low-power objective and then study it under the high power.
The long and relatively narrow elements are portions of muscle
cells or fibers, their large size obviating the possibility of securing
.sections of a complete cell. The entls therefore appear broken.
Every skeletal muscle is composed of a large number of fil)ers or

42 LABORATORY STUDIES IN ZOOLOGY

cells. Identify the delicate membrane or sarcolernma which
covers each fiber. This thin covering is best seen in places
where the fibers are crushed or broken apart. Each fiber shows
both a longitudinal and a cross striation. The longitudinal
st rial ion is due to minute strands, the fihrillce, which extend the
length of the fiber and are bound together in the same sarcolemma
sheath. The transverse striations are due to alternately dark
and light bands in the fibrils. Each muscle cell also contains a
number of spindle-shaped nuclei scattered among the fibrils.
The young muscle cell possesses but a single nucleus which during
growth divides repeatedly, resulting in the multinucleate
condition.

Make a drawing which will show all the structures listed
above.

Non-striated Muscle. — Study a stained preparation. Non-
striated muscle tissue is composed of long, slender, spindle-shaped
cells arranged parallel to each other. Each long fiber or cell
possesses an oval nucleus near its center.

Make a drawing of a single fiber, showing parts described.

Nervous Tissue. — A nerve cell, or neuron, consists of a central
portion, called the cell body, which contains a large nucleus, and
of slender processes which extend out from this cell body often
to great distances. Portions of nervous tissue which consist
predominantly of cell bodies are spoken of as gray matter, while
those which consist of the processes constitute the white matter.
The processes of a nerve cell are of two kinds: those which convey
the impulses toward the cell body, called dendrites, usually very
numerous and much branched, and those which convey the
impulse away from the cell body, usually single and unbranched
or slightly branched, called the neurite or axone. What one
refers to as nerves are bundles of these processes. Histologically,
nervous tissue consists of (1) the nervous matter proper, i.e., nerve
fibers or neurones, and (2) delicate supporting and connective
cells called neuroglia cells, in which the nerve cells are embedded.

Study a cross-section of the spinal cord of the frog. Under
low power identify the narrow dorsal fissure and the broader
ventral fissure. Notice that the cord differs in appearance in
different parts. There are two general regions, a central, slightly
darker region, the gray matter, trapezoidal in shape and contain-
ing numerous darkly stained cell bodies; and an outer, lighter
region, the white matter, with only a few small cell bodies. The

77//'.' iiSK srurcrriiE of riiK I'R(h; v.\

curiuTS ol (he liapc/iiitl of ^ray matter cxtciid tlursad and vni-
trad, forming the so-called dorsul and vt nlral Imrns of gray matter
The larger cell bodies seen in the ventral horns are those of the
inolor cells whose axones extend out to the voluntary muscles or
other effectors of the body following ii course through the ventral
root of a spinal nerve. I'^xamine one of these under high jjower.
The structure of the cell l)ody is well shown hut only the begin-
nings of the processes are present, as these have been cut across in
preparing the thin sections. Note the relatively large iiurleus
of the cell body containing a conspicuous round body, the
nucleolus. Often a more deeply staining group of cells may be
seen in the center of the cross-section, the epithelial cells lining
the cavity of the cord.

The general structure of nervous tissue may be determined
by the study of j^repared slides of teased and stained tissue.

Sketch a cross-section of the cord as it appears under low
power (about two and one-half inches in diameter), stippling the
grey matter more heavily than the white matter. Do not attempt
to show cellular structure in the cross-section but draw a single
motor cell body separately as seen under high power.

MITOSIS

As the cellular nature of the fundamental tissues found in the
bodies of higher animals becomes apparent there naturally arises
the question of how these tissues increase in amount or bulk to
account for the increase in the size of the animal during growth.
Since the cells of any given tissue do not increase in size beyond a
certain maximum it seems reasonable to accept the explanation
that increase in the size of an animal is due to an increase in
the number of component cells. The manner of cell increase
is that of cell division. A given cell at the proper time divides
into two daughter cells which grow to the normal size and in
their turn divide. In most tissues the method is that known as
indirect cell division or mitosis.

Growing tissues of almost any organism might be used to illus-
trate indirect cell division, but for several reasons the developing
eggs of Ascaris megalocephala, a parasitic roundworm, are
recommended.

In the female Ascaris the reproductive organs are so modified
as to comprise various specialized parts one of which is the uterus
or part retaining the eggs during development. Sections through
the appropriate portion of the uterus show the eggs (cells) in
various stages of mitosis. Such sections should be mounted
in rows lengthwise of the microscopic slide. A well-established
method is that of arranging sections showing maturation, ferti-
lization, and mitosis in five rows across the sHde, the fifth or
bottom row containing cells in a state of active mitosis. What-
ever the arrangement it should be explained by the instructor
by way of saving time for actual study.

If Ascaris material is used, examine the section of the fifth
row on the slide with the low power of the compound miscroscope
and identify the thin walls of the uterus composed of large epithe-
lial cells and its wide cavity completely filled with circular
objects, each of which is a section of an egg or true cell. Examine
one of the eggs under high power and get a clear idea of its struc-
ture. Identify the thick shell or capsule inclosing a cavity
occupied by the egg cell which is considerably smaller than the

44

Ml'lOS/S Jf)

cavity itself. The cytoplasm of the cnj^ appears vacuolated,
that is, appears to contain empty spaces. Dark-staining bodies,
the chromosomes, will be seen in the nucleus. Search the cells
for typical examples of the stages in n»itotic cell division as
called for below.

It may not prove an easy task to find just the stage desired,
but only as a last resort should assistance be recjuested ()f the
instructor. The difficulty lies in the fact that the sections are
very thin anil therefore a complete picture of what is desired may
not be found in a given section unless it passes through the proper
plane of the cell. Avoid the study and drawing of such partial
figures and represent egg cells at least an inch and a half in
diameter.

In the following paragraphs the stages or phases of mitosis
are arranged in the order in which they occur. Although phases
are referred to for descriptive purposes it is to be kept in mind
that mitosis is a continuous process and that the stages here
described overlap in varying degrees. The term phase or sfngr
is employed as a name for the completion of certain events regard-
less of whether these events are completed before or after another
begins.

Early Prophase Stage. — As cell tli vision begins, the chromatin
substance of the nucleus appears to form a long, coiled thread.
Consider that in sections only pieces of such a coiled thread could
appear and then note in the demonstration of this stage the
deeply stained, elongate pieces of chromatin to be seen in the
nucleus.

Late Prophase. — The thread is resolved into a number of
distinct slender bodies, each of which is called a chromosonw.
In Ascaris there are four of these. The small number of chromo-
somes is one of the advantages of Ascaris material for this stutly
rather than cells from the frog where 24 chromosomes appear.
In well-prepared material there will be ob.served in the cytoplasm
close to the nucleus two dense areas of granules called the a.s7<;-.<?.
Ivich aster contains a dark center, the centrosome, a.ssociated with
radiating fibrils, the astral rays, reaching out into the surround-
ing cytoplasm. Between the centrosomes, which come to be
located at opposite poles of the cell, there extend similar delicate
fibrils which collectively are called the spindle. The spindle
together with two asters constitutes what is known as the
achromatic figure, or amphiaster. Sometime during the processes

40 LABORATORY STUDIES IN ZOOLOGY

just described, a splitting of the chromatin threads has occurred.
These split threads or chromosomes appear to shorten and
thicken. The nuclear membrane disappears leaving the chromo-
somes free in the cytoplasm. The chromosomes now appear
in pairs, due to splitting, and become arranged upon the spindle
in a plane midway between the two centrosomes. This plane is
referred to as the equatorial plane. The series of events culminat-
ing in this manner is said to constitute a stage in mitosis known
as the prophase or the preparation stage for actual division.

Metaphase. — Following late prophase there appears to be a
short period during which the chromosomes are arranged in
the equatorial plane. It is a state of balance. If the chromo-
somes have not already split they do so at this time.

Find a cell cut across the middle of the spindle (in an equatorial
plane) and showing the four split chromosomes free in the
cytoplasm. Centrosomes and astral rays will not show in such
a section. Draw.

Locate a cell which is cut through the axis of the spindle (in a
meridional plane). This should show centrosomes, astral ray,
and spindle with the band of chromosomes across the middle of
the mitotic figure. Draw.

Anaphase. — One of each pair of the split chromosomes moves
toward its respective centrosome or aster. In this migration
the ends of the chromosomes always point toward the axis of the
spindle, so that the cell contains two groups of chromosomes,
each group looking somewhat like an open umbrella with the
delicate threads of the spindle stretching between them. Draw.

Telophase. — The chromosomes approach the asters, where
each group condenses into a mass in which the identity of the
chromosomes is lost. A constriction in the cytoplasm gradually
deepens and divides the cell in two. Draw. The chromatin
mass of each daughter cell reorganizes a nucleus with a nuclear
membrane. Two daughter cells, believed to be exactly like the
original mother cell and like one another, have thus been
produced.

A STUDY OF THE BASIC REPRODUCTIVE AND
HEREDITY PHENOMENA

Maturation and Fertilization. — For this study tlio cuf^s of
Ascaris are doscrihed, but taken from another part of the uterus
than that supplying the cells for the study of mitosis. Sections
of such eggs may be mounted as the first four rows upon a slide
with sections arranged according to the method mentioned
above.

It will be profitable to recall from lecture and textbook studies
what is meant by the terms somatic cells, germ cells, gametes,
tnicrogamete, macrogamete, ovum, spermatazoon, and zygote
It is also important to keep in mind that a new individual comes
into existence through the fertilization and development of an
egg, which means that: An egg (ovum or macrogamete) fuses
with a zoosperm (microgamete) which constitutes the beginning
of a new individual. That is, two independent cells fuse to form
a single cell (fertilized egg or zygote), which is a new individual.

The cells in the body of each species possess a definite and con-
stant number of chromosomes. Since two cells fuse in the
creation of a new individual it ordinarily would follow that with
each fertilization the chromosomes would double in number in
each new generation. This does not occur, as is known from
observation. It follows, then, that as reganls the gametes some
provision is made whereby the normal number of chromosomes
is maintained. The object of the present study is that of demon-
strating the way in wliich this comes about. The process is
known as the maturation of the germ cells or their preparation
for the fertilizing process.

In this species of Ascaris maturation of the egg follows the
entrance of the sperm. The sperm meets and enters the cytoplasm
of the egg which is still naked. Soon after, the walls of the uterus
secrete an albuminous covering about the egg and two maturation
divisions of the egg nucleus take place before it is ready to fuse
with the sperm nucleus, thus completing the formation of the
zygote.

Entrance ofthe Spermatozo on into the Egg. l"]xamine enough
eggs of row 1 to get an idea ofthe form ofthe spermatazoon and its

47

48 LABORATORY STUDIES IN ZOOLOGY

position in the cytoplasm of the egg. Note the head containing
the round nucleus and the more pointed portion termed the
refractive body. Also the lack of an enclosing capsule about the
egg. In some of the eggs the refractive body of the sperm is
probably being absorbed. Draw.

First Maturation Division of the Egg (Row 2). — This is] known
as reductional division, as the number of chromosomes of the egg
are reduced by one-half so that the number of chromosomes
peculiar to the body cells of the species remain constant after
un'on with the sperm nucleus (pronucleus) which has undergone
reductional division of its chromosomes before entering the egg.
Find an egg showing a spindle upon which are two sets of chromo-
somes. One set will be separated off and thrown out of the
cytoplasm of the egg as a small discarded cell known as the first
polar body, the other set will be retained as those of the egg
nucleus. The sperm pronucleus ought to be at rest somewhere
within the cytoplasm. Draw.

Second Maturation Division of the Egg (Row 3). — This is
known as equational division, as the number of chromosomes of the
egg nucleus remains the same thereafter and is a true mitotic
division resulting in a second polar body which is cast off and,
like the first, comes to naught. In a typical example of this
stage the first polar body ought to be seen clinging to the inside
of the egg capsule, the chromosomes of the second polar body on a
spindle with those of the egg mucleus, and the sperm pronucleus
at rest somewhere in the cytoplasm of the egg. Note that the
cytoplasm of the egg has withdrawn from the egg capsule leaving
a space between the two. The cell remaining after the separa-
tion of the two polar bodies becomes the functional egg. Draw.

Stage Preceding the Union of Male and Female Pronuclei
(Row 4). — This might be compared with the resting stage during
mitotic division of somatic cells, since mitotic division follows
the union of the male and female pronuclei. Look for a cell
which shows : (a) two nuclei, one the male, the other the female,
but indistinguishable from one another; (6) the first polar body
within the egg capsule, and the second polar body clinging to the
outer margin of the cytoplasm of the egg. Draw.

A STUDY IN DEVELOPMENT

The object of this study is that of illustrating the manner in
which a multicellular animal is derived from a single cell. All

HAS/C liEPRODnriVK AM) IIEh-KhlTY I'll ESuM HS A 10

mult ici'llular aiiiiiials which n-prixhu'c acct)i(hiin to the ^!;aiiiic
iiH't hod (sexually) begin their existence as a single cell, the zyKotc.
After fertilization (synganiy) or the union of the two gametes
the resulting zygote (^singh^ cell) undergoes mitotic division. In
the division of the zygote this is referretl to as the cleavage or
segmentation of the egg. The resulting cells remain associated
in a cluster, and thus the multicellular state of the new individual
is attained.

These cleavage or segmentation stages, which are preliminary
to the building up of the tissues and organs of the new individu:il,
can better be studied in such an egg as that of the starfish, in
which segmentation is ecjual and complete, than in the egg of
the frog, in which segmentation is complete but unecjual. Thf
principle, however, is the same in both.

Development of the Starfish (Asterias). — Slides should be
furnisiied which contain at least seven stages in the ontogeny
(development of the individual) of this animal. Use low -power
only and locate the unfertilized egg wiiich can be recognized by
its large clear nucleus, containing a black spot, the 7iucleolus.
As it is often difficult to find such small eggs on a slide, it is
suggested that one focus with the low power on the edge of the
cover .slip. Then when the slide is moved so as to bring an
egg under the objective it will be seen. Having found this
initial stage in the development move the shde and with the aid
of the following descriptions identify and study each of the
stages :

1. The unfertilized egg represents a single cell. The cytoplasm
antl nucleus with its small nucleolus should show distinctly;
also the egg membrane (or vitelline membrane). The colors
are due to the dyes used in staining the material in preparation
for study.

2. After fertihzation the egg divides by mitosis. The first
division, the plane of which is meridional in direction, gives rise
to the two-celled stage, the two daughter cells remaining in con-
tact with each other, and \hc fcrtilizahOii nicmhraiic may be .^een
enveloping both cells.

3. The second division occurs at right angles to the first l)Ut
also meridional in direction, resulting in the four-celled stage.

4. The third cleavage plane appears at right angles to the
first two and may be spoken of as e(iuatorial in position. l-]ight
equal cells result.

50 LABORATORY STUDIES IN ZOOLOGY

5. The process of segmentation continues until a large number
of cells is produced. Some slides may show the 16- or 32-cell
stages. Meanwhile a central cavityj^^thc segmentation cavity,
forms, about which as a wall the cells are arranged.

6. A continuation of the process of cleavage results in the
formation of the coarse morula stage, and ultimately there is
reached the fine morula or hlastula stage in which the single
layer of cells surrounding the segmentation cavity persists.
These stages are in the form of a hollow sphere but may be deceiv-
ing in some preparations, as the walls often collapse. Carefully
focus on one of these balls until the appearance is the same as
if a section had actually been made through the center of the
blastula. The blastula then appears as a hollow hemisphere of
cells, the layer being one cell thick, surrounding the large cavity.
Such a view is termed an optical section.

7. Cell division continues but the cells begin to show their
differentiation and shift in position. The cells in one half of
the hollow sphere come by invagination to lie within those of
the other half. It is analagous to pushing in one side of a hollow
rubber ball. Thus an embryo is formed with a body wall of
two layers of cells. Study as in optical section. The outer
layer of cells is called the ectoderm; the inner layer, which has
invaginated, the entoderm; the space resulting from invagination
is the archenteron or primitive intestine; and the opening of the
archenteron to the outside is the blastopore. This stage is called
the gastrula since the alimentary canal is here first formed. The
next stage in development is the formation of a third layer of
cells, the mesoderm, between the other two. These three layers
are called germ layers and from them all of the tissues and organs
of the body are derived.

On the plate showing some of the early stages in the develop-
ment of the starfish, first give a proper heading to the plate,
then supply the appropriate title for each figure and label all
structures discussed in the outline.

Development of the Frog. — The common leopard frog lays its
eggs during April and May in the shallow water of ponds
and the margins of lakes. All the eggs are laid at one time
in a single complement, each egg being surrounded by a
gelatinous envelope.

After fertihzation by the spermatozoa of the male, which are
cast over the eggs as they are extruded by the female, cleavage

BASIC REPRODUCTIVE AM) HEREDITY I'lIESOMENA '> 1

follows and the developmental stages already noted in the study
of the starfish are completed in reg;ular order, n>sulting in a
multicellular body with all the necessary organs. When the
eggs hatch, the young animals arc not in the form nordothry
possess the habits of the adult. They enter upon u true larval
stngr which may be viewed as one occurring between the egg aiul
adult stages for the completion of developiiient. During the
larval period the structure and functions of the body arc such as
conform to its afiuatic life, necessitating many organs such as
gills aiul a swimming tail not present in the adult which leads a
terrestrial life. At the end of the larval period the larval struc-
tures are lost and those of the adult are assumed.

Due to the presence of a large quantity of yolk in the frog's
egg and for other reasons, the details of development vary from
those found to obtain in the starfish. When properly viewed,
however, they are found to be fundamentally alike.

Stages illustrating the early development of the frog may l)e
studied from preserved material.

B}'- pouring the liquid containing this material into a watch
glass or other container the several stages may be studied with a
hand lens or, better, with a dissecting microscope. Small
camcl's-hair brushes are convenient for moving the material
in the liquid. Care must be used not to destroy the eggs and
embryos. Report any mishap or lost stages, that these may be
replaced immediately. Along with the prepared material it will
facilitate study to employ enlarged models of the same stages.

1. One-celled Stage. — The greater part of the frog's egg is
composctl of yolk, which is used for the nutrition of the develop-
ing embryo. That portion of the egg in which the yolk is more
abundant, the vegetal hemisphere, or pole, is marked externally
by its white color, while the opposite, in which there is relatively
less yolk, the animal pole, is colored with black pigment. Due
to the large amount of yolk which it contains the egg of the frog
is relatively nuich larger than that of the starfish but because of
pigment granules the nucleus, which lies in the dark pole cannot
be seen.

2. Two-celled Stage.— Cleavage begins at the animal pole
as yolk retards this process. The depression gradually extends
in the form of a groove until it finally surrounds the egg. This
groove marks the outer boundary of a cleavage plane which
extends through the egg, dividing it into approximately two e(iual

52 LABORATORY STUDIES IN ZOOLOGY

cells. This first cleavage plane may be spoken of as extending
in a vortical or meridional direction.

3. Four-celled Stage. — The next cleavage plane also extends
in a meridional direction but is at right angles to the first, result-
ing in four more or less equal cells.

4. Eight-celled Stage. — The third cleavage plane is said to be
equatorial, although appearing nearer the animal pole. It is at
right angles to the other two. The result is four smaller cells
in the animal hemisphere and four larger ones in the vegetal
hemisphere. This inequality in the size of the blastomeres
(cells) in the two hemispheres is the result of a relatively small
amount of cytoplasm and large amount of inert yolk material
in the vegetal hemisphere as compared with the same components
of the animal hemisphere.

5. Sixteen-celled Stage. — At this stage in the development of
the egg two vertical grooves at right angles to one another appear
simultaneously, thus indicating the directions of the next cleavage
planes. These grooves first cut the 4 cells of the animal pole
into approximately equal halves, forming a 12-celled state, and
then continue through the cells of the vegetal hemisphere to
complete the 16-celled stage. Either the 12- or the 16-celled
state may be found in the material.

6. Crescentic Groove Stage. — From this stage on, the inequal-
ity in the size of the cells of the two hemispheres coupled with
other tendencies results in irregularities in the number and shape
of the cells. These later stages are marked by the appearance of
the segmentation cavity within. The hlastida differs from that
of the starfish in the presence of much thicker walls on the vegetal
side. The thicker walls of the vegetal side comprise large yolk-
laden cells. As a result, the process of gastrulation is very much
modified in the frog from that exemplified by the starfish. The
large accumulation of yolk at the vegetal side of the blastula
prevents the invagination of this region from taking place so
that the gastrula is formed partly by a process of ingrowth and
partly by the growth of the animal pole over the vegetal pole.
The ingrowth and overgrowth take place more on one side of
the egg than on the other and are indicated externally by the
appearance of a crescentic groove. This groove marks the
advancing edge of the down-growing cells of the animal pole.
The crescent represents the beginning of the blastopore and with
its appearance the development passes into the gastrula stage.

HASIC liEI'RoDrcriVI': .\M> llEUEhlTV I'llESoMKS.X .'ili

7. Yolk-plug stage. Tlu* cresccntic j^roovc is (h-cpcbt at the
center and thins out toward the edges, whicli gradually ext<'nd
around the vegetal pole of the egg. In this way the crescent
becomes a circle and as the white-cell area is gradually over-
grown a stage is reached when only a small circle of white yolk
appears in the midst of the black covering. This is known as
the yolk plug, socalled since the yolk cells appear as a plug in the
blastopore. The white cells which have been enclosed by the
dark and other cells which have been overgrown or invaginatcd
now become the entoderm.

By the time the yolk-plug stage is reached the formation of
the mesoderm or middle germ layer is well underway. It develops
from the cells around the blastopore which proliferate and push
their way in between the ectoderm and entoderm with the result
that the embryo comes into the possession of three layers of
cells. These are the primary germ layers, furnishing the cells
out of which the completed body is formed. The method
followed is that which may be expressed as infoldings, outfold-
ings, and thickenings of the layers and special changes in the
component cells.

8. Neural-fold Stage. — This stage is recognized in its early
phases by the elongation of the embryo and by the appearance
of a fold on each side of a median groove extending lengthwise
along the future back of the individual. The edges of these
folds, the neural folds, later meet and fuse along the median dorsal
Hne, thus forming a longitudinal tube which sinks beneath the
ectoderm from which it is separated and forms the central nervous
system. The yolk plug has finally disappeared by further
overgrowth, leaving only a minute pit to indicate the former
position of the blastopore. This pit may be covered over by
the neural folds in this region but a short distance behind this
point the anus begins as an invagination of the ectoderm which
later meets and fuses with the archenteron to establish an open-
ing, the anus, between the latter and the exterior.

The beginning of the mouth may be seen as a hollow depression
of the ectoderm, but it does not comnumicate with the archenteron
until after hatching.

Dorso-caudad of the ventral suckers there develops an eleva-
tion in which two vertical grooves appear. These grooves
represent the first two gill slits. Later two more grooves appear,
one cephalad and one caudad of the first pair. At the time of

54 LABORATORY STUDJES IN ZOOLOGY

hatching all four meet corresponding cvaginations of the ento-
derm of this region thus forming the functional gill slits. The
nostrils appear as a pair of external depressions or pits a little
above the rudiment of the mouth. It is difficult to make out
the beginning of the eyes which are indicated on each side by an
ectodermal thickening, above the nasal pits. Soon after this
stage, life in the jelly of the egg mass is abandoned. This marks
the end of embryonic existence and the beginning of larval life
as a free-swimming organism.

9. Young Larva (Two to Four Days after Hatching).— The
features adapting the larva to an aquatic life are easily recognized.
Note the vertically flattened tail useful in swimming. The sides
of the tail show the zigzag muscle segments. Identify the eyes
on the sides of the head, the ventrally located mouth, the two
nasal openings cephalad of the mouth, and the external gills which
appear as long, branching tufts extending from the side of the
"neck region". The gill slits show beneath. This stage in
the larval life is of a few days' duration only. The disappearance
of the external gills is accompanied by the caudal growth of a
flap of skin, the operculum (meaning "cover") beginning in front
of the first external gill. This cover fuses along its edges with
the integument of the head, thus conceaUng the region of the
gill slits along with the surface of the "shoulder region" from
which the arms are formed. The edges of the caudally growing
opercular flap, throughout its extent, fuses with the surface of
the body excepting at one place on the left side where it remains
open as the spiracle. The external gills are thus covered over
and disappear. Internal gills formed within the margins of the
gill shts become the functional respiratory organs. With the loss
of the external gills and the completion of the tail crest the early
larva enters the tadpole stage. The true tadpole stage endures
until development is completed in which state the larva is said
to be mature. During the tadpole stage the legs may be seen
growing from the base of the tail. The arms, however, are not
to be found upon the exposed surface. If a slit were made
through the spiracle and thence cephalad across the opercular
flap the relations of the spiracle and gill slits and the location
of the arms would be revealed. In the leopard frog larval
maturity is reached from 60 to 80 days after the eggs are laid.
At this time the larva passes into its third stage, namely, metamor-
phosis. That is, there ensues a relatively short period during

HAsic HKi'iionrcrn K wn iiEiiKDiry riiKXoMENA ')')

wliicli it loses its ('(luipiufiil tdr stiiclly .•HHiatic life (ljirv;il
clKirac'tcristics) and assuiiu's the form, struct urc, and liahits of
the adult. There can he ohserved tluring the metamorphosing
period the resorption of the tail, the extension of the mouth
cleft, the elevation of the eyes, the perforation of the integument
of shoulder region by the arms, and many other transformations.
If time permits, study preserved specimens or models of the three
larval periods of the frog.

Arrange the material provided for study (i.e., segmenting eggs,
embryos, and larvae) in order ranging from the earliest to the
latest stages and demonstrate to the instructor, pointing out
not only the stages themselves but also characteristic features
of each.

AN INTRODUCTION TO THE STUDY OF INHERITANCE

In preceding studies attention has been called to the behavior
of the chromosomes in two kinds of mitosis. In one, somatic
mitosis, the chromosomes spUt equally as regards the quality
and quantity of materials which they comprise. Thus, two
daughter nuclei are formed exactly like each other and the result-
ing daughter cells are provided with the normal number of
chromosomes. In the other, reduction mitosis, the number of
chromosomes in the daughter nuclei through synapsis is reduced
by half. Such nuclei become those of the gametes. Thatjs, a
mature ovum and a mature spermatazoon each possesses*one-
half the number of chromosomes normal to the species. A
zygote (new individual) formed by the fusion of two such gametes
is not only provided with the normal number of chromosomes
but also half comes from each of the two parents. While the
offspring of a given pair of parents differ from one another in
certain details they nevertheless resemble each other more than
they resemble the individuals of any other group. This means
that there have been transmitted to the offspring the character-
potential of the parents which may become expressed and recog-
nized. In other words, the offspring biologically inherit from
two parents (biparental inheritance), each of which have inherited
from two parents, and so on back. It is, therefore, readily
understood that each individual harbors in its chromosomes a
great complex of heritable traits which may become expressed
according to chance combinations, thus accounting for both
similarities and differences which may be encountered among
the offspring.

If heredity be interpreted as meaning "organic resemblance
based upon descent," no one can question its importance in the
study of the rise and perfection of animals. As one of the prin-
ciple methods of attack upon the problems of heredity is experi-
mental breeding, it has seemed advisable to introduce a study of a
simple Mendehan ratio. This study presupposes general famili-
arity with the subject gained from the textbook, assigned read-
ings, or lectures.

56

THE STUDY OF IMIKUITANCE 57

The small fruit fly, Diosophila melanogaster, jifTords excellent
material for the study of Mcnddian phenomena. It lays its
eggs on fermenting fruit the yeast in which forms the food of
both the larva and the adult. The complete reproductive
cycle from egg to breeding adult is very short, seldom exceeding
two weeks. The Hies cxhil)it a number of different eye colors,
body colors, and wing characters the inheritance of which may
be studied in the laboratory. They are easily grown in bottles
containing fermenting bananas.

It will be impossible for the student to carry on the actual
i)reeding during the time allowed for laboratory work but the
steps necessary for the preparation of the material are here given
that the process and aims may be better understood.

Each group of four students should be supplied with a culture
of Fi flies produced by crosses involving a single Mendelian fac-
tor, such as vestigial wing or sepia or scarlet eye, also samples of
the Pi and Fi ancestors as well as larvic and pupaj, the object
being that of studying the structural peculiarities of larvae,
pupae, and adults and to observe the inheritance of these factors
through two generations and compare the actual count of individ-
uals in the F2 generation with the expected Mendelian 3:1
ratio. These cultures were produced in the manner set forth in
the paragraphs which follow.

Securing the Fi Generation. — Mrgin females for mating were
obtained by isolating pupte in individual half-pint milk bottles
containing a banana agar-agar preparation for food. Females
cannot be taken from the general stock, as they have almost
certainly been fertilized by the males in the culture. In order
to secure a pair for the first mating (the P, generation) a single
pupa was taken from each of the two cultures to be crossed, one
from the wild type (red eyed) and one from the sepia-eyed type.
Since sex cannot be recognized in the pupal state there are four
chances as regards the results, namely, (1) getting a female wild
and a male sepia, (2) a male wild and a female sepia, (3) two
females, (4) two males. The first two are sati.sfactory for si^cur-
ing the Fi generation; if each of the two females resulting from
the third possibility is given a male from the original culture
these will form two more combinations from which to secure the
desired crosses; the two males wliich may result from the fourth
chance is the only combination which is not usable for the purpose
of this study. After a pair lias been together in the breeding

58 LABORATORY STUDIES IN ZOOLOGY

bottle for about a week they will have mated and eggs will have
been deposited resulting in the presence of many larvse, some of
which will have proceeded as far as the pupal stage. As soon as
pupae have formed, the parents must be removed so as not to
become mixed with their offspring. These Fi offspring may be
collected from such a culture not to exceed ten days after the
first flies appear.

Securing the Fo Generation. — About 15 Fi adults of each sex
are then transferred to breeding bottles in order to insure the
production of a large F2 generation. The expected Mendelian
ratio of 3:1 in the F2 generation resulting from crossing flies in
which there is a single Mendelian character involved can be
approximated only by having a comparatively large number on
which to base a count. As soon as the pupae have formed, the
Fi adults must be removed so as not to mix with the F2 flies soon
to emerge. Only those flies should be counted which emerge
within ten days after the appearance of the first F2 flies in the
culture.

In all holometabolous insects, or those which undergo a complete
metamorphosis, four stages in the life cycle are to be expected,
namely, the eggs, larval, pupal, and adult. The eggs of the
fruit fly will be disregarded because their small size render it
difficult to find sufficient numbers for class use. Examine the
larva and pupse of this fly under a dissecting lens and make
sketches of each upon the proper plates. Look at a pupa case
from which the adult has emerged and note the nature of the
exit.

Each table should be supplied with (1) a milk bottle of flies
(F2 generation) living upon a banana culture; (2) a glass vial
which will fit over the mouth of the milk bottle and into which
the flies are to be driven before etherizing; (3) a black cloth
which when wrapped about the milk bottle will facilitate trans-
ferring the flies to the glass vial on account of their positive
reaction to light; (4) a small bottle of ether and a cotton plug
to be used in etherizing; (5) a petri dish into which the etherized
flies may be poured for examination, segregation, and counting;
(6) a camel's-hair brush for moving the flies.

First, saturate the cotton plug with ether and have it close
at hand in order to stop up the mouth of the vial as soon as the
flies are transferred to it from the milk bottle. The next step
requires much care if all the flies are transferred from one bottle

77/A' sriDY or IMIKh'ir.WCH .'><)

(() tllO other. 'I'lic milk lyotllc shoiiUI iml !»<• Ilinird upside (l(»wii
and shaken violently as the haiiaiia ciillure will become loosened
and fail with the flies, thus incorporat in^ the Hies within its owr>
mass and destroyiiif^ the results of the experiment. In order to
move the flies from one container to another, place a hhick cloth
al)out the milk bottle and hold the shell vial in the direction of
the winilow or .some source of light. The flies hein^; positively
phototropic will crawl or fly into the vial where after a few
minutes most of them will have assend)led. Lift the l>lack cloth
from time to time, making sure that none remains in the milk
bottle before removing the vial so as to place the ether plug of
cotton into its mouth. A quick transfer is necessary if no Jlies
are to be lost. Leave the flies in the etherizing vial for about two
minutes or until all the flies have dropped to the bottom and
then pour them into the petri dish. The work of separating the
sepia-eyed fiies from the wild flies follows, using the dissecting
microscope if necessary, after which the count can be made.
If flies become active place a small piece of etherized cotton in
the petri dish and cover until movements cease. After the count
is made the flies should be returned to the milk bottle and //
7iot over etherized may be used again. Avoid loosing flies, there-
fore, during transfer, and do not leave them in the etherizing
bottle too long.

Before returning flies to the milk bottle compare these Fo
flies with the Fx and the Pi generations, which will l)e supplied
by the instructors. Write a description of the male parent used
in the Pi cross (i.e., a statement of the combination of cliaiaeters
which it po.s.ses.'^es). Do the same for the female used in the
Pi cross. Also a statement of the characters in which the Fi
generation differs from its parents. Then list the number of
individuals of each type of Fo progeny. How does this compare
with the expected ratio?

Two plates are provided upon which a summary of this study
may be recorded.

A STUDY OF REPRESENTATIVES OF THE VARIOUS
ANIMAL PHYLA

INTRODUCTION

The preceding laboratory periods have been devoted to a study
of the organization of a moderately complex animal, the frog.
The grosser features of external structure were considered by
way of illustrating the importance of the surface of the animal,
especially as a means of providing a communicating and buffer
systems between the organism and its surroundings. The vari-
ous internal organs were studied with a view to ascertaining, first,
the services which they render and the manner in which it is
done and, second, the determination of the interrelationships
and interdependence of organs. It became apparent that the
body of the animal is an orderly association of components
organized according to a plan of differentiation resulting in
division of labor among the parts. This organization involves
all parts from the cells to the completed body. Each structural
component, whatever its rank, contributes a service in the organ-
ism as a whole but not independently. Each component in
contributing its service is assisted by other components. This
requires harmony of action or the coordination and control of
the various parts. Such coordination rests largely with the
nervous and hormonic forces. For example, respiration cannot
be considered as a function of any particular organ. There
are involved not only the services of the respiratory organs as
such but also the circulation, muscles, the surrounding medium,
nervous and hormonic activities, the internal environment, and
changes taking place in the protoplasm of the body. Respiration
is rather a function of the organism. And so it is with digestion,
excretion, etc. Thus it appears that the organism is a complex
of interactions taking place in relation with the protoplasm of the
component parts of the body and between it and the internal
and external environments. When life ceases the components
remain in the same state of organization as before death but what
is left is a corpse rather than an organism. That is, the inter-

60

liEPHESENTATl\ ES OF AS I MM. I'llYLA til

actions constitute the organism and as such it is to be regarded :is
superior to its structural components which it builds for itself.

The laboratory studies throughout the ronuiiiider of the course
will be concerned with representative types of each of the animal
phyla. This is an attempt to decipher through the study of
living animals those features of organization which have endowed
animals with such advantages as have enal)led them to advance
beyond a given rank. It is also a means of plotting the probable
pathway in the descent of animal groups.

The animals thus studied will l)e arranged in a series in which
the succession is from the lower to the higher.

Review the various grades of groups by means of which ani-
mals are classified.

PHYLUM PROTOZOA

Class Sarcodina {Amoeba proteus). — The amccba is an organism
which affords an opportunity for studying living protoplasm in a
relatively simple state, since it exists as a small naked mass of
this living substance.

Place a few drops of the culture containing anui'bir on a slide,
cover with a thin cover slip, and allow it to stand for a few
minutes until some of the animals have emerged from the
detritus of the preparation. Cut down the light and look for
specimens using the loiv-power objective of the compound micro-
scope. When an irregularly shaped, granular, slow-moving
object has been located ask the instructor if the desired animal has
been found. These animals appear iron-gray in contrast with the
yellowish-brown color of the plant tissues in the culture. Select
an active specimen in a clear field and study to determine the
mode of locomotion.

Observe that the outhne of the animal is irregular and variable
due to the extension of projections, called pseudopodia, which
are constantly changing in position, numl)er, size, and form. By
flowing into these projections the animal moves with the type
of movement known as amahoid. The pseudopodia are termed
"organs of locomotion," since it is through these that movement
from place to place is efTected. Notice the outer, thin, dear,
firmer layer of protoplasm, called ectoplasm, free from granules,
and an inner granular, more \'n\uU\ mass, the ciidoplasm. Do
form and locomotion indicate that there are anterior and posterior
ends in the animal?

62 LABORATORY STUDIES IN ZOOLOGY

Study the formation of a pseudo podium. The first indication
of its appearance is a bulging of the ectoplasm. This is followed
by a current of endoplasm into the extended ectoplasm. Because
these extensions form only a temporary means of locomotion
they have been given the name "pseudopodia." These tempo-
rary organs appear capable of extending from any part of the
surface.

Make a number (five or six) of one and one -half inch outline
drawings of the amoeba at intervals of a minute or more, to show
successive changes of shape. By arrows indicate the direction
in which the protoplasm is flowing in different parts of the animal,
at the time the figures are drawn.

Study the structure of a favorable specimen (one whose proto-
plasm is not too granular) and look for the following features,
using the high power.

1. Bear in mind that this is a unicellular organism. It is
composed of cytoplasm as the main mass, within which one or
more granular nuclei can often be seen in the living specimen.
If the nucleus is not visible in the active specimen study stained
preparations. Before considering the structure of an amoeba
it will be of advantage to have in mind one of the chief differences
between this single-celled animal and a single tissue cell or a
fertilized egg (zygote) from which all multicellular animals arise.
The single-celled amoeba is independent of all other cells, while
a tissue cell is dependent upon others in the association, and a
fertilized egg cannot exist indefinitely without dividing into a
number of cells, thus forming an interdependent and interacting
association of cells.

2. Search the non-moving part of the endoplasm for a spherical
clear spot. At intervals it contracts and disappears to reappear
later and does so with more or less rhythm. Because of its
nature and behavior it is called the contractile vacuole. Observe
several pulsations and estimate the frequency. The contractile
vacuole is a space so fashioned and functioning as to eliminate
liquids from the interior of the cell.

3. The endoplasm also contains particles of ingested food
the larger of which are surrounded by a fluid and hence are
called food vacuoles. Other cell inclusions may be found such as
oil droplets, crystals, and perhaps foreign particles.

If possible find a specimen which is taking in food and watch
the procedure. Observe the method of passing an object with

HRPKESESTATI\ ES ()F AM MM. flDI.A iVA

vvliich it has conu' in contact. Slioukl a sju'cinicn be fcjund in
the act of dividing; by simple jis.sion watch tho process closely.

One sees only a rolativoly sli^lit amount of visible difTcrcntia-
tion exhibited within the protoplasm of the anueba yet all of
the essential processes of li/e are in progress as effectively, appar-
ently, as in the frog. The amceba takes food and oxygen, dis-
tributes them to various parts of its unicellular body, providing
the materials for energy liberation and the building of new proto-
plasm; it excretes waste, it can move from plac(> to place, respond
to stinuili, and reproduce its kind. Physiologically the highest
multicellular organism can do no more. Such forms as the
anurba, therefore, arc of the greatest interest and value to the
student of life.

Make an enlarged drawing (four inches in diameter) of an
amoeba and show those details of structure which you have
been able to identify. Indicate the granular appearance by
stippling.

Class Infusoria {Paramcccium. cnudnium). — Becau.se of its
relatively large size and the ease with which unlimited supplies
of specimens may be secured this animal lends itself to the study
of the structure and normal activities of a more complex type of
protozoan. Members of the class Infusoria possess both per-
manent form and organs of locomotion. These latter are in the
form of cilia which are similar in appearance and action to those
found upon the surface of the cells lining the roof of the frog's
mouth. These permanent locomotor organs of Paramecium
afford a striking contrast to the transitory pseudopodia of the
amoeba which are formed "when needed" by a local bulging of
the protoplasm of the cell. The permanent form is due to the
condensation of the ectoplasm, which necessitates a number of
permanent organs some of which arc described below. Cilia
are responsible for the rapid movements characteristic of this
organism.

With a pipette place a drop of the infusion containing jiaraino-
cia on a slide, cover, and examine under low power. Among the
various organisms in the preparation, relatively large, slipper-
shaped forms will be noted. These are paramecia. ()bs(>rve
them carefully to determine from observation whether the body
possesses permanence of form. Are there differences in the form
of the two ends of the body? What is the relation of the ends
to the direction of locomotion?

G4 LABORATORY STUDIES IN ZOOLOGY

The most striking structural feature to be noted in the swim-
ming Paramecium is the depression or broad curved groove which
interrupts the even surface of the foremost end. This concavity,
the oral groove, extends diagonally from the tip of the foremost
end to a point beyond the middle of the body, where it terminates
in the "mouth." Study the relative widths of this groove and
the body at different places, compare the length of the organism
with its width, and determine the angle of slant of the oral groove
when the oral surface (that in which the mouth is located) is
toward the observer.

Make an outline drawing about five inches long of that aspect
of the animal in which the oral surface is toward the observer.
Only the general form of the body and the oral groove need be
shown, but as details of structure will be added later special
care should be used in representing proportions.

Various methods have been employed to decrease the rapidity
of movement of both animal and its cilia, thereby facilitating
the study of details. Before trying any of these, however, look
for animals near a piece of scum or other foreign materials which
are usually abundant in the cultures. Paramecia usually remain
relatively quiet around such material and are studied most
satisfactorily when in a normal state. Failing in this ask your
instructor for suggestions as to methods of slowing down the
activities of these animals.

Compare the degree of differentiation of structures to be found
in Paramecium, when studied under high power, with that
observed in amoeba, as suggested in the outlines which follow.

The cytoplasm of Paramecium comprises two regions, ecto-
plasm and endoplasm. The stratified ectoplasm is rather
highly differentiated. The outer layer, or cuticle, is a firm mem-
brane to which the animal owes its permanent shape. Study a
demonstration preparation of an animal in which the trichocysts
have been discharged following stimulation with weak picric
acid. Long threads of the discharged contents of the tricho-
cysts can be seen surrounding the animal. How does their
length compare with that of the cilia? These structures are
supposed to be both offensive and defensive in nature. The
innermost or cortical layer of the ectoplasm contains the main
portion of the trichocysts as well as the two pulsating contractile
vacuoles. These, aside from eliminating water, possibly aid the
animals in maintaining their balance. The two vacuoles appear

liKPRESEXTATn HS O/-' l.V/U.l/. I'IIYI.\ (>.')

one near ci) licr cud »»f t lie aiiiiiial as circular clear spots int«» w hi(;li
from seven to ten slarlikc radiations convey li(|iiids from oiitlyinn
regions of the protoplasm. These rndiatiiKj ciukiIs may be seen
at the times the vacuoles contract and are hesf seen in prepara-
tions which are beginning to dry.

The central mass of protoplasm in the animal, tin; endoplasm.
appears devoid of particular structures when examined without
special treatment. It is much more fluid than the ectoplasm and
appears granular. It generally contains a number of fond
vacuoles, with food in various stages of digestion. The two
nuclei, a large macronucleus and a small micromicleus, are
embedded therein. It is usually very difficult to make out either
in normal animals. Study a stained slide for an idea of these
structures. The macronucleus is a large lobed mass near the
center, and the micronucleus is a small spherical body lying in a
concavity of the macronucleus. The micronucleus plays an
important role in reproduction.

The food of this animal is mainly bacteria, decaN'ing organic
matter, and minute protozoa. The mouth is located at the
base of the oral groove and opens into a funnel-like, S-shaped
pharynx or guUet which leads oblic]Ucly toward the hindermost
end into the endoplasm. The arrangement of cilia about the
oral groove is such that a steady current bearing food particles
is directed toward the mouth. If possible, observe an animal
feeding. Food particles are wafted down the pharynx by its
ciha which are fused into a so-called undulating membrane. The
particles collect into gastric vacuoles at the end of the pharynx.
These food vacuoles are then carried through the protoplasm in a
more or less definite course during the process of digestion and
absorption and the undigested portion is voided through a small
permanent anal spot in the surface of the body just behind the
pharynx. The firm cuticle, giving definiteness of form, has
necessitated the presence of oral groove, moutli. pharynx, and
anal spot as permanent organs.

Reproduction takes place by transverse division (binary fission)
of the animal into two daughter individuals. A.ssoeiated with
binary fission are the phenomena of conjugation iluring which
the oral surfaces of two animals are connected by a protoplasmic
bridge. Across this bridge there is an exchange of micronuclear
material. Illustrations of fissicm and conjugation may be ft>und
in the culture, but, if not, demonstration mounts of stained

66 LABORATORY STUDIES IN ZOOLOdY

specimens should be studied. Conjugation may be looked upon
as a simple form of syngamy.

To the outline drawing already made, add all the details of
structure which have been observed. Such structures as ecto-
plasm, endoplasm, cilia, contractile vacuoles (showing radiating
canals in connection with one), macronucleus, micronucleus, and
gastric vacuoles should be indicated. If the trichocyst threads
were seen, add only a few to one side of figure to show their
relative length. In the lower left- and right-hand corners of
the drawing sheet make sketches of binary fission and
conjugation.

A STUDY OF MIXED PROTOZOAN CULTURES

A study of mixed protozoan cultures is introduced for the
purpose of illustrutinji; the great variety of forms and modes of
life of these minute organisms and that of providing an oppor-
tunity to gather first-hand information concerning them. A
further object in this study is that of furnishing an introduction
to the identification (classification) of animals through the use
of so-called "tables" or "keys." Such keys make use of the
important structural features wherein animals resemble or
differ from one another. The statements of characteristic
features are so contrasted that the problem becomes one of
deciding with which of two contrasting statements a given animal
agrees.

Place a drop of the culture in the center of a glass slide. After
placing a cover glass upon the drop, study the culture with the
low power of the compound microscope. Note differences in
form, size, and -behavior of the individuals coming within the
field of the microscope. ]\Iove the slide so as to bring different
regions of the culture into the field. Such observations should
give one a general idea of the different kinds of protozoans pres-
ent, their means of locomotion, and noticeable peculiarities.

After a short period the organisms will become less active,
enabling one to focus the microscope upon a single individual
for a detailed study which will reveal those peculiarities whereby
it may be distinguished from other kinds. Look for those charac-
teristics mentioned in the first statement of the key designated
by A. The contrasting (opposite) characteristics will be found
under AA in the same vertical column. When the characteris-
tics given either under A or AA fit those of the organism proceed
to the statement immediately following, and so proceed until
a name appears at the end of the statement. If the observations
are correct this name will be that of the group to which the
organism belongs. Reading both of the contrasting statements
will aid one in determining which is descriptive of the organism
in (juestion.

Assistance in tiie identification of these organisms may l»e
gained through comparisons made with the accompanying figures.

67

68 LABORATORY STUDIES IN ZOOLOGY

The matching of organisms with figures is not to be recommended
as a general method, but in an introductory study of micro-
organisms it facihtates the gaining of famiHarity with the different
types.

If needed, further explanation in the use of the key will be
given by the instructor.

Key for the Identification of Protozoans Most Commonly Found
IN Fresh-water Cultures

Should forms be found which do not appear to be included in
this key, they need not be identified.

A. Locomotor organs not cilia.

B. Flagella as organs of locomotion Class Madigophora

C. Solitary (not colonial).

D. With test formed in plates; one anterior horn and one to three

posterior horns; groove encircling body Ceratium

DD. Without test.

E. Colorless; i.e., without green, yellow, or brown chromato-
phores.
V. Body truncate or concave at anterior end, slightly flattened;

two flagella Chilomonas

FF. Body not truncate at anterior end.

G. Body elongate, wider at posterior end; two flagella, one

long and heavy, one short and fine Astasia

GG. Body oval, flattened, not wider at posterior end, and very
flexible, gullet present with rodlike organ back of mouth ;

one flagellum Peranema

EE. With green chromatophores.
F. Body not spindle shaped.

G. Body spherical, or eliptical in form with one largo cup-
shaped chromatophore and stigma (eyespot); two

flagella Chlamydomonas

GG. Body round or pear shaped, not symmetrical, with

caudal process; one flagellum Phacus

FF. Body spindle shaped; gullet present; single flagellum;

stigma present Euglena

CC. Indi^^duals associated in colonies.

D. With yellowish brown chromatophores.
E. Colon}' spheroidal.

F. Individuals embedded on surface of a gelatinous mass; two

yellow chromatophores Uroglena

FF. Individuals not embedded in gelatinous mass and loosely

joined; two flagella Symira

EE. Colony arboroid; each individual resting in a cellulose cup;
one long, one short flagellum; the cup of each individual
attached within the cup preceding it Dinobryon

.4 STUD) OF \U\ED PROTOZOA \ CULTURES 00

1)1). With Rnt'ii (•lin)iiiaU)|)l»»n;s.

K. (xjloiiy fhit (cells in one plants of 4 t<> li> iiniivulualN; llaKullu

(lirccteil fn)in one .surface dimium

EE. Colony spluMoidal.

F. Indivitlual.s ('(lual in size.

G. IndiNaduaLs crowded, inner ends pointed and reaching
center of mass; colony enclosed within definite mem-
brane; two long flagella Pandorina

GG. Individuals scattered in jelly mass (not crowded); two

fiagella Eudorina

FF. Individuals not all of .same size (.smaller ones vegetative,
larger ones germinal).
G. No protoplasmic connections between celLs; larger germ
cells at posterior pole of colony (i.e., poles of colony

difTerentiated) Pleodorina

GG. Protoplasmic connections between cells distinct; poles

of colony not differentiated Volvox

HM. locomotor organs in form of pseudopodia which may be changeable,

blunt, fine, or raylike and rigid Class Sarcodina

(". Pseudopodia fine and raylike; no outer envelope or .shell, body
rounded.
D. Ectoplasm not distinctly differentiated, axial filaments of

pseudopodia extending to nucleus Adiiwphrys

DD. Ectoplasm distinct, axial filaments extending to ect«plasn>

.4 clinosphaeri u m
CC. Pseudopodia not raylike but changeable and flowing; body form
irregular.

D. Body naked (without test) -i "'<^ba

DD. iJody with test.

E. Test chitinous, smooth, hemispherical in form, pro\nded on
its flat surface with circular opening through which pseudo-
podia extend Arcella

EE. Test covered with minute foreign bodies and therefore

appears uneven Difflugui

A A. Ciha present as locomotor organs Class Infusona

B. Mouth surrounded by a spiral zone of large ciiia.
C. Free-living, membranelle winding to left.
D. Entire surface of cell covered with cilia.

E. Adoral zone (fringe of fused cilia near mouth) nearly at right
angles to body axis; cell trumpet shaped; free swimming
(or may become attaciied temporarily but without special

stalk) Stenlor

EE. Adoral zone paralleling body axis.

F. Adoral zone funnel shaped, sunken in the body; cell oblique

in front Bursaria

FF. Adoral zone narrow, elongate, reaching middle of body,

which is elongate in appearance Spirostomum

DD. Ventral surface with cirri (long cilia fused together to form
bristle-like appendages, which are sometimes used as legs);
dorsal surface with only fine cilia or none.

70 LABORATORY STUDIES IN ZOOIAHIY

E. With both ciha and cirri.
F. Body not very flexible.

G. Three caudal or posterior cirri Stylonychia

GG. No caudal cirri Histrio

FF. Body quite flexible; caudal cirri undeveloped. . . .Oxylricha
EE. With cirri only.

F. With four caudal cirri Euplules

FF. With seven to nine caudal cirri Uronychia

CC Sessile, enlarged oral cilia winding to right, usually forming an
almost complete circle.
D. Solitary, attached by a retractile stalk; body bell shaped; circle
of strong ciha about elevated disc of free (broad) end. Vorhcella
DD. Individuals forming arboroid colony; bodies bell shaped.
E. Stalks retractile.

F. Individuals contracting independently Carchesium

FF. Individuals all contracting together Zouthamium

EE. Stalks not retractile Epixtylis

BB. Mouth not surrounded by a spiral zone of large cilia.

C. With a sculptured shell about a barrel-shaped l)ody Colcps

CC. Without such a shell.

D. Cilia not uniform over body.

E. Prominent cilia confined to one or two bands.

F. With two circles or crowns of long cilia, one near the
anterior end, the other in the region of the equator of the
ovoid body; nipple-like elevation bearing mouth and
arising from the center of a flattened anterior end

Didinium
FF. Two zones of strong cilia about body; cell somewhat
cylindrical, with a constriction slightly behind the mid-
dle; a prominent tuft of fused cilia at the posterior end

Urocejitrum
EE. Cilia only on ventral surface; cirri not present.

F. With a long neck; body oval, ending in a short tail. Lionotus
FF. With the anterior end hooklike; body inflexible, ventral sur-
face flattened and showing ciliated ribs; mouth on the left
anterior edge, at the bottom of a slitlike peris tone Loxodes

DD. Cilia uniform over body.

E. Mouth terminal or nearly so; no proboscis.

F. With no evident gullet; body elongate, anterior end nar-
rowed and flattened into a neck which is obliquely trun-
cate Spathidiuni

FF. With more or less evident gullet.

G. Form flask shaped; with a short or long, highly con-
tractile neck, and a rounded posterior end. .Lacrymaria
GG. Form spherical to ovate; without a neck; cytopharynx

long Prorodon

EE. Mouth somewhat posterior to anterior end; sometimes with a
proboscis.
F. With proboscis in front of mouth.

.t STCDV or MIXED I'lxOTo'/j ).\ \ cri/ICh'ES 71

(1. liotly cluiiKiilc; inoiitli .-il luisc uf a hirin, very flcxihli-

|>n)lK)sc'i.s Dileplug

CI(!. Kody fliittcncd, Icafliko; prolmsriH only slightly

(Icvi'lojH'd l.iixnphyUuvi

VV. W'itliout proboscis.

G. Mouth anterior to niidcilo.

H. Form ellipsoidal; mouth not fur from anterior ctid;
genus includes some of tlie largest holotrichs

Frontoiiin
II II. Body somewhat kidney shaped; mouth about one-
third of the distance hack of tlie anterior end; species
small as compared with those of Frontonia . .Colpwla
GO. Mouth near middle; gullet short; peristome oblique

Parnmecium

72

LABORATORY STUDIES IN ZOOLOGY

\ \\ \ \ \ 'I ' / // / /

Actinosphaerium eichornii

Arcella vulgaris

Uvellavirescens

Prorodonsp

Dileptus anser

Fig. 3.

A STUDY 1)1' MIXED I'lioToZo.W ClLTriiES 7:i

Euplotes patella

Fig. 4.

PHYLUM CCELENTERATA

In the phylum Coclenterata there is laid down the fundamentals
of body organization which are adhered to in all higher types of
animals. In contrast to the sponges the representatives of this
phylum fall in the direct line of animal descent. Only two cell
layers are found in the body wall. The cells of both layers
are differentiated in relation to definite functions. All of the
coelenterates are aquatic, mostly marine, and chiefly sessile in
the adult state.

Class Hydrozoa (Hydra). — Specimens of Hydra may usually
be found in quiet ponds or streams where they are attached by
one end to aquatic vegetation.

Examine a living individual in a watch glass with a hand lens,
or with the low power of the compound microscope.

Jar the watch glass and note any response to such a mechanical
stimulus. With the point of a needle very gently touch one of
the tentacles of an extended animal. Is there any evidence
that the stimulus is transmitted from one tentacle to another or
to any other part of the body? Compare the form of the body
when extended and contracted. If a hydra should be found
moving along the object to which it is attached note the type of
locomotion employed. Reflecting upon the hydra's behavior,
what deductions might be made with regard to some details of
organization?

General Structure. — The body of the animal in a moderately
extended state is tubelike in form increasing slightly in diameter
toward the free end so that under certain conditions it is vaselike.
At the fixed end the body expands into a hasal disc for attachment.
A circle of slender tentacles arises from the free end. These may
vary in number. In the arrangement of bodily parts Hydra is
radially symmetrical, that is, similar parts are repeated about
an axis as a center.

The region encircled by the bases of the tentacles projects
as a conical elevation termed the hypostome. At its apex is
located the mouth, which leads into the digestive cavity. The
mouth is usually closed and difficult to distinguish.

74

I' II y I.I'M rn-JLEXTERATA />

( )l)S('rvo the irregular aj)pc!inincc of tlic surface of the tentacles
and body wall. These small elevations indicate the location of
hatterics of stinging cells which are found <»n all parts of the body
except the basal disc but are most numerous on the tentacles.
The high power of the microscope reveals each battery as a com-
pact uroup of specialized cells called niidublasts within each of
which is the stinging nux-hanism or nenidtocyst in the form of a
pear-shaped capsule. Prepared slides should be provided for
this observation.

Determine the extent of the digestive or gadrovaandar cavity.
By focusing carefully on such a partially transparent organism
.some of the details of internal structure can be determined by
bringing into focus different levels of the body. By thus mani-
pulating the microscope the two body layers may be recognized.
The hollow central cavity of the animal appears Ughter than
t he tlenser edges. Ingested food is forced down into the digestive
cavity where the greater part is apparently engulfed by pseudo-
podia of the cells lining the cavity and digested within these
cells in the the protozoan manner. Although digestion is mainly
intracellular there is also a limited amount of extracellular diges-
tion in Hydra similar to that obtaining in the frog and higher
animals. Certain cells among those lining the digestive cavity
secrete juices containing enzymes which are discharged upon
their surfaces where small amounts of food materials are split
into simpler compounds. Undigested food is ejected through
the mouth.

Both agamic and gamic reproduction occur in Hydra. The
common agamic mode is that of budding, according to which a
new individual is formed as a bud growing from the side walls
of the parent. The buds may be found in varying stages of
development. When mature the new individuals separate from
the parent, leading an independent though sessile life. Trans-
verse and longitudinal fission of the whole animal have been
reported.

In its gamic reproduction Hydra is hermaphroditic and without
permanent gonads. During the period of gamic reproduction
the gonads appear as elevations of the surface. The spennaries
form conical elevations in the ectoderm somewhat nearer the
tentacles than the base of the animal, while the ovaries form low,
broad elevations near the base. Both sperm and egg mother
cells ari.se from interstitial cells and are borne by the same

76 LABORATORY STUDIES IN ZOOLOGY

iiulivicliuil. Altliough hcrnuiphroditic it is rather excepticjiial
to find specimens bearing both ovaries and spermaries at the
same time.

Make an outline drawing, at least five inches in length, of an
expanded Hydra as seen from the side. To the same scale
draw the animal in a contracted state.

Details of Cellular Structure. — Examine a stained cross-section
of the animal using the low power for the preliminary study.
Hydra clearly presents the fundamental plan of structure in
the coelenterates. Observe that the cells of the body wall are
arranged in two definite laj^ers, an outer ectoderm and an inner
entoderm, the latter forming the lining of the gastrovascular
cavity. These two layers are sharply marked off from each other
by a very thin non-cellular layer of supporting substance, the
mesoglea.

Study the cross-sections under the high power. The ectoderm
is composed of three principal kinds of cells. By far the common-
est type is the epithelio-museular cell to be distinguished by its
large nucleus and deeply staining nucleolus. The bases of these
are expanded and contain long contractile fibers which form a
thin longitudinal muscular layer accounting for the remarkable
capacity for contraction which Hydra possesses. These con-
tractile bases cannot be made out in thin cross-sections.

A second type of ectodermal cell is called the interstitial cell.
These are small, spherical, somewhat granular cells occurring in
groups between the epithelio-muscular cells. They appear to
be undifferentiated cells held in reserve to take up any one of
several functions when necessary. It may be that they give
rise to cnidoblasts more frequently than to other kinds of cells.

The cnidoblasts are the cells enclosing capsules or nematocysts
containing the stinging threads. Each cnidoblast contains a
nucleus and gives rise to a spinelike projection, the cnidocil,
at its outer end. Nematocysts show an affinity for eosin and
therefore appear stained a pinkish color when treated with this
dye. Threads shot out from these cells penetrate the body of
small animals and inject into them a fluid which has a paralyzing
effect.

At least two types of cells can be distinguished in the entoderm.
The more common type is the large, elongate, vacuolated diges-
tive cells. They are dumb-bell-like in shape, the larger end
extending into the gastrovascular cavity. Their nuclei and

rHVLlM (:(ELENTEliAT.\ 11

nucleoli rcsciiiblc tliose of the epitlielio-iiiuscuhir cells. At
their free ends are two flagelhi which arc not visible in ordinary
preparations. The basal ends of these cells are provided witli
I'xtensions containing contractile fibers.

Between the digestive cells another type of cell may often be
seen. These appear as triangidar cells with the broader end
exposed to the digestive cavity. They are kiiown as ghiinl
cells, since they secrete the enzymes used in the small amount of
extracellular digestion.

The non-cellular mesoglea secreted by cells of the ecto-
derm and entoderm is composed of a gelatinous non-cellular
material.

If possible the details of cellular structure should be reviewed
by a study of mascerated, teased, and stained cells of the body
walls. "When such preparations are successful one should be
able not only to recognize the cell components of the body walls
but also to determine the form and general relations of the
cells. Sensory and nerve cells are difficult to find and study in
transections and are therefore not included in these outlines.

In a four-inch circle representing a diagram of a cross-section
of Hydra show the relative width of ectoderm, mesoglea,
entoderm, and gastrovascular cavity. In a small sector of this
diagram show in detail the structure of the various types of cells
composing the two layers of the body wall.

Class Hydrozoa (Obelia). — In addition to Hydra and a few
other fresh-water representatives, the class Hydrozoa includes a
large number of marine species of diverse form and appearance.
These are, however, all reducible to the fundamental plan of
structure typified by Hydra. Great numbers of these species
are colonial in habit. As an example of a colonial hydroid, Obclia
is chosen for study. It is a common marine form found on docks,
submerged or floating wood, stones, seaweeds, etc. Obelia
commonly occurs in shallow water just below the ebb-tide lev(>l.
It may be found at greater depths.

In Obelia the striking feature is the division of labor which
obtains among the several kinds of indiviriiials comprising the
colony, each of which is specially modified in connection with
the performance of definite functions for the colony as a whole.
There are three kinds of polyps {i.e., three kinds of individuals
or "Obelia persons"): (1) the nutritive polyp, whose service to
the colony is food getting; (2) the reproductive polyp, whose serv-

78 LABORATORY STUDIES /A' ZOOLOGY

ice is the production of medusje which arise as buds; and (3)
the medusoE, whose function is gamic reproduction and the
dissemination of the species. A colony consisting of three or
more different kinds of speciaHzed individuals is said to be
polymorphic.

The Structure of a Colony. — Certain general features of the
colony must be clearly in mind before a detailed study of any
part is begun. Under the dissecting microscope examine a
prepared specimen of a single stem of an Obelia colony. Note
that the main stem is zigzag in form although sometimes in
preserved material this is not pronounced. A demonstration
preparation of a stem exhibiting its natural state should also be
examined. The attached end of the stem, in root fashion, creeps
along the surface to which the colony is attached. This portion
of a stem may be called the "foot."

The main stem gives off alternating side branches each of which
terminates in an individual of the colony. At the extremities
of these side branches observe the nutritive polyps, characterized
by the presence of numerous tentacles. The polyp nearest the
foot is termed the founder polyp, since it founded the colony.

Less numerous are the reproductive polyps, which are usually
borne in the angles where the stems of the nutritive individuals
arise from the main stem. They may be distinguished from
undeveloped feeding polyps by their position on the stem as
well as by their swollen appearance.

All the soft parts of the colony are protected by a translucent
sheath, the perisarc, which becomes expanded and variously
modified in the regions of the nutritive and reproductive polyps.

Make a six-inch diagram showing the growth habit of an
Obelia colony. Use schematic figures to represent the several
kinds of individuals. Label structures described in the preceding
paragraphs.

Details of Structures. — Under the low (or, if necessary, high)
power of the compound microscope study in detail a portion
of the stem and branches containing all types of polyps.

The living tissues of the individuals and stems are called the
cosnosarc, the reference being to the living flesh in contrast to the
perisarc which is composed of inert materials secreted by the cells
of the coenosarc.

The coenosarc of the main stem will be readily recognized
by its granular nature and deeper staining qualities. Note that

PHYLUM CCKLESTERATA 7'.l

the cci'iiosarc (both stem and Ixxly) <»f each ( )l»clia iiidiviilual in a
colony is continuous with that of tlic main stern and therefore
with every other indiviihial in the colony; also that there is a
cavity within the iivinjii; stems which is connected with the dig^'s-
tive cavity of each individual. Of what advantaRe is this
condition to the animal? Some di^iestion takes place in the
cavity of the stems as well as in the f^astrovascular cavity of the
feeding polyps but the predominating type of digestion in ( )l)elia,
as in Hydra, is intracellular.

The perisarc, throughout, stains more lightly than the c(rnosarc
and is of a homogeneous, nature. Is it uniform in thickness on
both sides of the stem? Is this thickening the same in successive
segments? Note the nature of the perisarc surrounding the
stems leading to the polyps.

A nutritive individual of an Obelia colony is similar in fimda-
mental respects to a Hydra; the body wall consists of two cellular
layers, the ectoderm and the entoderm, and the thin, ncm-
cellular mesoglea. Hj/postomc, mouth, and tentacles are in the
same relative positions and are readily recognized. Compare the
tentacles of Hydra and Obelia and determine the most funda-
mental differences. The perisarc, surrounding the nutritive
polyp, is expanded into a goblet-shaped structure, which, since
it harbors a polyp, is called a hydrotheca (meaning hydra case).
Look for variations in the thickness of the hydrotheca. Note the
centrally extending ledge at the base of the hydrotheca supporting
the body of the polyp.

The reproductive polyps are elongate in form, ending in a
broad, flat disk with neither mouth nor tentacles. Tiie walls of
these individuals produce by budding, the third kind of indi-
viduals in the colony, the medu.sae bud.s. Observe carefully the
structure of one of these. The perisarc is vase-shaped around the
reproductive polyps and is known as the gonotheca.

The medusa' buds, when mature, separate from the core oi the
reproductive polyp or l)lastostyle, pass out through an opening
in the end of the gonotheca, and lead a free life. They are to be
regarded, nevertheless, as sister individuals to the feeding and
reproductive |)olyps, which remain attaciied to the colony.

Upon the plate of Obelia label details to which attention has
been directed in the preceding paragraphs.

The Study of a Medusa. .\s .stated al)ov«', the medusa' buds
when fully grown break away from the blastostyle and lead a

80 LABORATORY STUDIES IN ZOOLOGY

free life. Gamic reproduction prevails in this type of individual
and the sexes are distinct.

The medusae of Obelia are small. The medusa of another
hydrozoan, Gonionenms murbachii, has been chosen for the study
of a typical medusa because of its fair size. It is found in con-
siderable numbers through the summer in the vicinity of Woods
Hole, Mass.

Structure. — Study a specimen in a watch glass with a dissecting
microscope. Use great care in turning the animal over for
different views. Never use forceps. A camel 's-hair brush serves
the purpose much better.

Notice the umbrella-shaped body with tentacles hanging free
from the margin and the hypostome hanging down within the
space formed by the concave surface of the umbrella. The
hypostome is the same structure already observed in Hydra and
Obelia. The convex surface of the umbrella is called the
exumhrella (or aboral surface), while the concave portion is
termed the suhumbrella (or oral surface),

A circular muscular shelf, the velum, extends inward from the
edge of the umbrella. By gentle contractions of the umbrella
(or bell) and of the velum, water is driven out of the subumbrella
cavity, thus effecting locomotion.

To understand the relation of parts comprising the food-
distributing system place the animal with aboral side uppermost.
Note the quadrangular area visible through the transparent
tissues; this area marks the location of a relatively large saclike
structure at the base of the manubrium, the stomach, from the
angles of which four delicate, equidistantly spaced radial canals
lead to the edge of the umbrella where they open into the circum-
ferential canal following a circular course about the margin of the
bell. These canals serve as a food-distributing system and
together with the stomach represent, as far as spaces are con-
cerned, the gastrovascular cavity of the nutritive polyps.

On the subumbrella side of the radial canals note the corrugated
reproductive organs or gonads which may be either spermaries or
ovaries.

Observe the mode of distribution of nematocysts on the
tentacles and compare in this respect with tentacles of Hydra
and Obelia. An abrupt bend near the distal end of the tentacles
of Gonionemus indicates the location of a cuplike adhesive

rnyuwr c(EJ.EsrKu.\T.\ 81

(line by niciins of which ihu animal c:ui aLlach ilsclf Icmporaiily
to vegetation or other objects in the water.

Turn a spooinicn witli the vchiiii side toward tht; observer and
stud}' the edge of tlie body for the two kinds of sense organs.
The low objective may be necessary to render these distinguish-
able. At the base of each tentacle and coniniuiiicating with the
circumferential canal is a noticeable round body which is made up
of strongly pigmented cells. These are considered as light-
perceiving organs. Other smaller transparent outgrowths between
the bases of the tentacles are the datocysi'i which serve as
balancing (static) organs. The jelly-like consistency of the
medusie is duo to the enormous dcvclopiiioTit of the mesoglea.

Upon the plate of Gonionemus label all the parts to which
attention is called in the outlines.

PHYLUM PLATYHELMINTHES

There is a double purpose in the study of this phykim. One
is found in the parasitic life which great numbers of these animals
lead and the resulting maladies produced in higher animals which
serve as hosts. The other purpose is found in their body organi-
zation which serves as an index to their relative success as
organisms and their elevation to a higher rank than that attained
by the forms previously studied. Among other advances there
may be noted: (a) the mode of progression, being that of an
elongate animal moving with the same end of the body foremost,
(b) the regional differentiation of the body as a whole which
accompanies this type of locomotion, namely, a true anterior
and posterior end, bilateral symmetry (with right and left
sides), dorsal and ventral surfaces, and (c) triploblastic body walls
which have provided the structural means for these advances in
organization.

Class Turbellaria. Planaria or Procotyla (Dendroccelum). —
Either of these genera of flatworms is found commonly in fresh-
water ponds throughout the United States. The species of
Procotyla are white and somewhat translucent, a condition
which greatly facilitates the study of the digestive and other
internal organs. These free-living {i.e., non-parasitic) flatworms
or turbellarians are found under stones, leaves, or other sub-
merged objects.

Behavior and External Structure. — Make observations upon
a living specimen in a watch glass, using a hand lens or dissecting
microscope. Study the behavior, form, and surface structure
of the animal, making use of the following as a guide: (1) form
of body, making specific references to the relative length of the
three axes (longitudinal, vertical, transverse); (2) relation of
body to the substratum (surface over which the animal crawls) ;

(3) relations of the ends of the body to direction of locomotion;

(4) movements which involve muscular activity and the normal
glidiiig form of locomotion due to the action of cilia covering the
body; (5) muscular movements as a means of crawling, determin-
ing the nature and progress of the waves of contraction; (6)

82

I'll YUM I'LATYUKLMISmES 83

c«iin]);iiis()M of luiisciilar movements of the flatworm and fhosp
of Hydra; (7) observations and description of the behavior of
tlio tentack's and the anterior end of the animal (hiring locomo-
tion, with conclusions; (S) determination of results of stimuliitinn
various parts of the animal with a camers-hair brush, especially
rejiional difTerence in sensiti\it y.

At the conclusion of the laboratory period hand in a written
report embodying the results of observations upon the structure
and behavior of the f^atworm.

Make a five-inch drawing of the animal from the dorsal side.
Show and label eyespots, tentacles, and any other structures
observed.

In a well-fed animal of the white species the digestive canal
may be seen clearly outlined in brown. If such an animal is
being studied note the oval clear region, the pharyngeal chamber
in the center of the body, in which is located an elongate muscular
tube, the pharynx. The pharynx can be extended as a proboscis
through the mouth opening located on the caudal part of the
midventral side. At its cephalic end the pharynx opens into
an intestine comprising three main trunks, a median branch
extending to the cephalic region, and two lateral branches, one
extending caudad on either side of the pharyngeal chamber
toward the posterior end of the body. Each of these branches
further gives off a large number of irregular lateral extensions.
In all probability, the majority of the worms available for
study will be of th? dark species (Planaria). Often these may
be induced to eat blood or liver if such materials be added to the
water in the watch crystal. If a dark-colored worm is being
studied, try such a feeding experiment. When the animal begins
to eat, a better idea of the structure of the pharynx or proboscis
may be gained upon close observation. A little patience while
inducing an animal to feed is often rewarded. The general shape
of the gastrovascular system of Planaria is similar to that of
Procotyla described above. Study a specimen of Planaria pre-
pared to show the digestive system. Locate th(> three main
divisions and determine the ramifications of each.

Represent the digestive system in the drawing already made.
Flatwornis have well-differentiated nervous, excretory, and
reproductive systems, i)ut these are so obscun* that their study is
imi)ossible in a living animal.

84 LABORATORY STUDIES IN ZOOLOGY

Regeneration. — Flatworms show remarkable powers of regen-
erating lost parts. In each section the instructor will cut a
specimen in two while it is gliding across the bottom of a watch
glass and place the two halves in a bottle of water to examine
later. Each student should make a rough sketch of this worm
showing the approximate location of the cut in order to aid his
memory when examining the specimen later for evidences of
regeneration.

PHYLUM ANNELIDA

The phylum Annelida comprises the so-called "true worms''
in contrast to the flat worms, liotii phyla are important in
tracing advances in organization.

In the flat-worms bilateral symmetry and progression with
the same end foremost are associated with noticeable though
moderate regional diff"crentiation, as for example, an anterior
end which may be regarded as an incipient head. In the annelids
the anterior end has become further differentiated. Aside from
this advance in their perfection the annelids are organized upon
the structural plan of metamerism accompanied bj' the presence
of a true body cavity or coelom which is not to be regarded as
the least of important annelid innovations.

Class Chaetopoda (Nereis, a sandwor7n). — Nereis may be
taken as a typical annelid. It lives in burrows in the coarse
sand and mud of the seashore at tide level.

External Structure. — Study an animal in a wax-bottomed
dissecting pan. Make observations upon the surface structure
with a view to determining the kind of symmetry. The most
striking structural character is the ringed appearance of the
body. Each of these rings is a unit in the organization plan of
the body and is called a metamere (or somite or segment). Each
metamere bears a pair of very thin lateral prolongations of the
body wall, known as parapodia, whose double function will be
considered later.

Head. — Two segments in the anterior region are so modified
as to be able to test the nature of the surroundings as the body
advances. Other functions in these segments are lost to a great
extent. The first somite, or prostomium (meaning "in front of
the mouth"), is a dorsal rectangular projection which does not
extend to the ventral side. The second, or peristomium, is a
complete ringlike segment bearing the mouth.

The sense organs of the head have reached a relatively high
state of perfection. Projecting from the middle of the cephalic
edge of the prostomium there are two short prostomial tentacles.
On either side of these is a thick, jointed palp whose service is

S5

86 LABORATORY STUDIES IN ZOOLOGY

probably that of providing a sense subserving as taste. On tlie
dorsal surface of the prostomium arc four indistinct grey spots,
each marking the location of a light-perceiving organ. The
peristomium bears four pairs of lateral peristomial tentacles
or cirri.

Make a four-inch drawing of the dor so -lateral aspect of the
left side of the head and first segment of the body. Label the
parts described above.

Body and Tail Metameres. — The large number of segments
caudad of those already mentioned as constituting the head may
be regarded as the body metameres, excepting the last which is
called the tail segment. Note the similarity between the body
segments. Internally, parts will be found repeated in successive
segments.

The posterior or tail segment differs from the others in the
modification of the parapodia into a pair of tactile processes or
cirri. In this segment the anus is located.

Parapodium. — Compare the parapodia at different parts of
the body for similarities or differences. Study a parapodium
which has been removed and mounted in balsam, or cut off one
with the scissors, mount in water, and cover with a glass slip.
Employ a dissecting lens or the low power of the compound
microscope. Compare the parapodium studied in this way with
those still attached to the animal and determine which is its
dorsal and which its ventral edge.

These lateral outgrowths of the body wall serve both as respira-
tory and locomotor organs. A parapodium can be divided into
two distinct portions, a dorsal called the notopodium and a ven-
tral called the neuropodimn, each of which is stiffened by an
internal chitinous supporting rod, called the aciculum or bristle.
Find the two acicula. The large dorsal lobe of the notopodium
is a respiratory organ, that is, a gill, containing a network of
blood vessels which can easily be seen in life. Attached to its
dorsal edge is a slender vibratile sense organ, the dorsal cirrus.
The ventral portion of the notopodium comprises two lobes the
smaller of which bears fine bristles or seta. The neuropodium
likewise comprises two lobes, the notched one of which is setas
bearing. Beneath these lobes on the ventral margin of the neuro-
podium is a ventral cirrus.

Make a three-inch outline drawing of a parapodium, labeHng
the structures described above.

ruYi.rM A.wi'ji./DA 87

A STUDY OF THE EARTHWORM

The above study of Nereis presented information concerning
what may he regarded as the typical external structure of marine
worms. Tlu're is another great group of worms typified hy the
earthworm. The worms of this group are terrestrial, though
some are aquatic and a few are equally at home in either kind of
environment. These animals feed mostly at night by crawling
entirely or partially from their burrows to the surface of the
ground. Their subterranean habits are associated with the
absence of certain structures which are possessed by the marine
worms.

The structural features to which attention is called in the
following paragraphs apply to the large species, Lumbrirus
terrestris. If other species are studied, allowance must be made
for variations in structural details such as number of metameres,
the location of apertures, and the relations of internal organs
to segments, etc.

External Characters. — Study a preserved specimen in a dissect-
ing pan containing a little water. For the finest structures
employ either a dissecting microscope or the lowest-power
objective of a compound microscope. Distinguish anterior
and posterior ends, dorsal and ventral surfaces. Is the "head"
as well differentiated as in the case of Nereis? The head of
Nereis is to be regarded as more nearly a typical annelid head,
while that of the eartiiworm is simplified or better fitted to the
needs^of subterranean life. Do any obvious vestiges of the
parapodia persist in the earthworm?

As in Nereis, the mouth is surrounded by the first complete
segment or penstomium and is overarched by a small lobe, the
prostomium. C'audad of the peristomium the similarity of the
body segments is quite noticeable, each being readily determined
externally by the grooves extending around the body. Deter-
mine the total number of metameres exclusive of the prostomium.
In the cephalic third of the body of mature worms certain seg-
ments are swollen forming about the body a thick band or girdle
called the cliteUum. This is a glandular region which secretes
the cocoon in which the eggs of the earthworms are deposited.
Counting from the anterior end and omitting the prostomium
determine the metameres occupied by the clitellum.

Pass the fingers in both directions along the ventral part of
the sides of the body. The sensation produced is due to rows

88 LABORATORY STUDIES IN ZOOLOGY

of bristles or 6c(w which aid (he woini in crawUng. These struc-
tures render the removal of these animals from their burrows very
difficult. Determine the relations of the setae to each other,
to the metameres, and to the symmetry of the body.

The body of the earthworm is covered by a delicate trans-
parent cuticle secreted by the cells which lie immediately below it.

Are there any eyespots to be found? While unable to hear,
these animals are very sensitive to vibrations conveyed to the
body through the ground and also to various forms of chemical
stimuli and light.

In addition to the mouth at the anterior end and the anus in
the last segment numerous other external openings are found on
the ventral side of the body. The nephridio'pores, openings
of the excretory organs, should be located previous to dissection of
the specimen. With the exception of a few somites in the
cephalic end and the last somite, a pair of these openings occurs
in every segment. They are usually situated somewhat diago-
nally in front of the outermost setse of the ventral (inner) double
row. If these openings cannot be located examine a specimen
under the demonstration microscope.

Carefully examine the ventral surfaces' of segments 14 and 15
for the genital apertures which are larger than those of the
nephridial tubes and differently located. The openings of the
vasa deferentia are upon rounded elevations one on each side of
the ventral surface of segment 15. The oviducts open in a
similar location upon segment 14 but are not borne upon
elevations.

The food of the earthworm consists of organic matter contained
in the soil which is drawn into the mouth by the bulblike pharynx.
This is controlled by small muscles radiating from its walls to
the body wall.

In order to study the digestive system the animal should be
dissected under water. By means of pins through the two ends
fasten a preserved specimen in water, dorsal side up. Because
the alimentary canal lies close to the dorsal body wall great care
should he used in performing the following dissection. With
forceps hold up the body wall at a point about one inch behind
the clitellum and with the points of the scissors make an incision
a little to the left of the median line. Carefully continue this
cut forward to the prostomium. In order to make it possible to
pin out the body wall on each side and thus expose the internal

I

I'll y LI M AWEIJDA 89

organs it will be necessary to snip with the scissors or cut with a
scalpel the septa which hold the body wall close to the alimentary
canal. Separate the edges of the cut, spread open the walls of
the body, aiul fasten by means of pins inserted diagonrdly near
the periphery in segments V, X, and XV.

At the point where the first incision was made note that the
body wall is separated from the intestine by a distinct space, the
ca>lom. Do you find any indications of metamerism internally?
What is the relation of the scpla to the external rings? Note
the glistening, iridescent lining of the body wall. What is the
relation of this Hning to the coclom?

The large cream-colored structures .somewhat obscuring the
alimentary canal in segments 10, 11, and 12 are the three pairs of
seminal vesicles which are parts of the reproductive system.
Laterad of the anterior pair of vesicles in segments 9 and 10 are
small white spherical objects, the seminal receptax'les (sperma-
thecie), which are also parts of the reproductive system.

Along the dorsal surface of the intestine can be seen a brown
or yellow streak which marks the location of the longitudinal
ridge, the typhlosole, which encroaches upon the enteric cavity.
Its color is due to the yellow chlorogogen cells of which it is mainly
composed. The typhlosole can be more readily distinguished
later when a section of the intestine is removed. Note also the
dorsal blood vessel visible along this streak. Arising from it are
transverse vessels in each segment, best seen in the region of the
intestine. One pair of these in each of the seventh to the eleventh
segments, inclusive, on either side of the a'sophagus, is specialized
as the hearts, which due to their pulsations assist in maintaining
a blood current.

The Digestive Tract. — Identify the following regions in the
digestive tract: the mouth or buccal cavity in the first three seg-
ments; the longer, thick-walled pharynx extending through about
four segments and attached to the body wall by radiating muscle
fibers; the narrower asophagus (partly concealed by the five i)airs
of hearts and by reproductive structures) extending to segment
13 or 14; the large, thin-walled crop or storage reservoir for
food, extending through three or four segments; and the white,
thick-walled gizzard in which the food is ground into small
particles. From the gizzard the intestine stretches to the anus
as a long unspecialized tvibe. It is in the intestine that digestion
is completed and absorption takes place.

90 LABORATORY STUDIES IN ZOOIJKiY

On the plate of the anterior end of the earthworm designate
the parts of the head ; then label the parts of the blood system
and digestive tract. On the small drawing in the lower right-
hand corner label the space representing coelom and the location
of the setae. Write the names on the left of this diagram.

The Excretory Organs. — The excretory system of the earth-
worm consists of a series of paired coiled tubes, the nephridia, one
pair of which is present in every segment except the first three
and the last. Remove a portion of the alimentary canal caudad
of the gizzard by carefully cutting the septa surrounding it and
severing it in two places. Then with the aid of a hand lens study
the pair of coiled tubular nephridia on the floor of each metamere.
The main part of each nephridium consists . of a coiled tube
comprising three loops lodged in the coelom of each segment
through the ventro-lateral walls of which it opens to the exterior.
The aperture is the nephridiopore previously noted in the study
of external characters. The coelomic opening of the nephridium
is situated in the segment cephalad of the one in which the main
structure is located; the tube penetrates the septum and opens
into the coelom of the preceding segment by a funnel, called the
nephrostome. Seize a septum with the fine forceps and gently
move it caudad and cephalad. It will then be possible to
recognize on either side of the midventral line the two minute
nephrostomes as the septum changes position.

During life the coelomic cavity is filled with a fluid. The cilia
on the nephrostome and in the beginning of the tubule create a
current by means of which waste material floating in the coelomic
fluid is drawn into the nephridium and in this way eventually
conducted to the exterior. The middle portion of each tubule is
much thicker and has glandular walls. It functions by removing
waste matter in solution from the blood which reaches the walls
in a network of capillaries. The portion of each tubule near the
excretory pore is dilated and probably subserves the purpose of a
bladder.

On the plate above mentioned label the parts of the excretory
system. Write these names on the right of the small drawing
at the lower right-hand corner.

The Nervous System. — In the place where the alimentary
canal has been removed identify the vcnlral nerve cord and trace
it along the floor of the body wall in the midline. This cord
extends throughout the length of the animal. Study its character

rilYUM .I.V.\A7.//M 91

ill tlu' rcninii t'lttiii which the :ihm('iil;irv (•;iii:il h:i> liccii rclimvctl,
iiotinji; in each nu'laiiicrc an (•nlarnciiiciit , nr (jdnglion, and
Ihnr fxiirs of inriphcidl lurirs, two pairs leaving; tlic ^an^lion
directly, and a third appealing to h-avc the cord itself cej)hahid
of the ganglion. In the third or fourth seiiiiient note that the
two halves of the cord diverge to j)ass around the alimentary
canal as the cirrumphdniuqcnl rituj which unites dorsally with the
cerebral ganglion. Observe the pair of small peripheral iierves
given off from the IiiIoIxmI cerel)ral ganglion; these nerves divide
into very fine branches as they extend forward into the highly
sensitive prostomial region. Other peripheral nerves which
supply the ventral side of the cephahc end of the body are given
off from ihv circumpharj-ngeal ring.

Label the parts of the nervous system on both the large and
small drawings of the plate.

The Reproductive System. — A complete set of l)otli male and
female genital organs occur in the same individual. That is, the
earthworm is hermaphroditic.

By careful dissection remove the intestine from about the sixth
metamere to the twentieth. Avoid cutting any organs which lie
below or to the side of the alimentary canal in the region between
the ninth and fifteenth mctamercs.

Clear away the nephridia of the thirteenth segment and look
for the pair of ovaries, minute white bodies lying against the
septum at the cephalic end, near the nerve cord. By gently
waving the septum between the twelfth and thirteenth segments
the ovaries which look like tiny pears fixed at their broad ends
may be identified. When mature the ova drop from the ovary
into the ca'lom of the thirteenth segment and are pa.ssed out
of the body through a pair of nephridia which have become
modified into oviducts. The internal funnel-shaped openings of
the oviducts lie in segment 13, while the ducts penetrate the
.septum entering the c(elom of the fourteenth segment, where they
lead ol)li(iuely outward, opening to the exterior in this segment.
In the wall of each oviduct is an enlargement, the egg receptacle,
for the storage of eggs.

Associated with the female genital organs are two pairs of small
white spherical bodies, the seminal receptacles, for the temporary
storage of spermatazoa received from the worm with which
reciprocal mating occurs. The.se are located in the ninth and
tenth .somites and open to the outside by two pairs of spi rmathecal

92 LABORArORY STUDIES IN ZOOLOGY '

jxurs situated Ijctwccn segments 9 and 10 and 10 and 11,
respectively.

The most conspicuous structures of the male reproductive
organs are three pairs of seminal vesicles located in segments
9, 11, and 12, respectively, connected with two central reserviors
lying in the midventral portions of somites 10 and 11. These
sperm sacs are associated with the testes of the male which lie
encased within the central reservoirs. By carefully peeling away
the tops of the reservoirs on the right side of the animal the glove-
shaped testes of that side may be exposed, one each at the anterior
ends of the tenth and eleventh segments near the midventral
line. Behind each testis is the enlarged ciliated funnel which
forms the opening of the sperm duct or vas deferens. Trace a vas
deferens back through the septum, noticing the several convolu-
tions, and then the straight caudal extension along the floor of the
body cavity to its opening, through the sperfniducal pore, in
the fifteenth segment. Note that the two vasa deferentia on each
side unite in the twelfth somite.

If any difficulties were experienced in dissecting this system
on the right side of the body repeat the dissection upon the left.

Label the parts of the Reproductive system on the plate of the
anterior end of the earthworm.

A Cross-section of an Earthworm. — Study the cross-section
first under a dissecting microscope for the plan of structure of a
coelomate animal, that is, one which possesses a coelom. Note
the relative thickness of the body wall at different levels and
compare the contour of its outer and inner surfaces. Recall
structures previously studied which may account for the division
of the body wall into definite, well-marked areas. How many of
these areas are there?

If the section studied happens to be in the proper plane the
slender, curved, rodlike setoi already noted upon the surface may
be seen. They are of the same composition as the cuticle and
like it secreted by the epidermis. They may be seen projecting
through the body wall. Between the body wall and the intestine
is the coelom within which fragmentary portions of nephridia
may be made out. Why do the sections not show complete
nephridia? Note the intestine with its dorsally invaginated
typhlosole. Identify the dorsal Mood vessel lying above the
typhlosole and embedded in its large cells, the ventral blood
vessel below the intestine, and the ventral nerve cord just below
the ventral blood vessel.

I'llYhUM A.WKLIDA •••^i

Make a diagram, four inches in diameter, of a cross-section
showing the features described above. Do not represent the
cell structure.

Having ubliiined a j^t'ncral idea of tlu' cross-section, study it
with the low power or if necessary the high power for detailed
structure. Note the following features of the body wall from
without inward: (1) ii very thin nitirlc or non-ccUular covering;

(2) the epidermis, consisting of a single layer of cells, among
which numerous glattd cells may be distinguished by their oval
shape and swollen appearance; (3) the inuscular layers, consisting
of a thinner layer of very long, slender, circular muscle cells
embedded in connective tissue and attached to the septa, the
longitudinal layer of muscle cells which when seen in cross-section
appear feather-Uke; (4) the peritoneum, a thin layer of flat cells
lining the body cavity and attached to the inner surface of the
longitudinal muscle layer.

The intestinal wall shows the parts arranged in layers. Some
of these layers, notably the longitudinal muscle and vascular
layers, are inconspicuous and made out with difficulty, hence may
be omitted from an elementary study. The evident layers are :
(1) the peritoneum on the outer surface, comprising large yellow
cells called the chlorogogen cells; (2) the circular muscles, a thin
but continuous layer of circularly arranged muscle cells; and

(3) the lining epithelium, or the innermost single layer of elongated
ciliated cells.

In a sector of the diagram previously drawn show the details of
cellular structure of the body and intestinal walls.

Nerve Cord.~The nerve cord is somewliat oval in outUne and
is covered externally by a sheath, consisting of peritoneum,
connective tissue, mu.scles, and blood vessels. The subneural
blood vessel on the midvcntral side and the paired lateral neural
blood vessels, one on each side of the subneural vessel, can be
distinguished under high power. In the dorsal portion of the
cord are three large, clear areas, the giant fibers, which extend for
long distances in the worm. I^ach is surrounded by a thick
sheath. If the section happened to pass through a ganghon of
the cord a number of large nerve celis may be present. The rest
of the cord is made up of numerous small nerve fibers forming a
network.

Make a drawing, one and one-fourth inches in diameter, of a
cross-section of a nerve cord. Show in detail the structures
described above.

PHYLUM MOLLUSCA

Many peculiarities of organization set off the animals of the
phylum Mollusca from those previously studied. Molluscs
possess bilateral symmetry, but a pronounced regional differ-
entiation is lacking.

Class Pelecypoda Unio or Anodonia (or Any of the Bivalves
Commoyihj Used). — Animals of these genera wander along the
muddy bottoms of creeks, ponds, and rivers, with the anterior
end buried in the mud. The food consists of minute plants and
animals gathered from the respiratory current.

Exterior of Shell. — The shell comprises right and left halves
(right and left valves) which retain their continuity along the
dorsal side in the elastic hornlike hinge. At other points the
two halves touch upon one another only. Note the concentric
lines on the shell indicating stages in its growth. The knob
on each shell near the hinge about which the growth lines are
concentrically arranged is the beaPc or umbo. Its apex is directed
toward the anterior end of the animal. Taking the position
of the hinge and umbo as a basis, determine the toponomy of the
clam body.

Structure of the Shell. — The shell is composed of three layers:
the thin outer dark-colored layer of conchiolin (hornlike in
appearance) ; the middle or limestone layer of perpendicularly
arranged prisms; and the inner or mother-of-pearl layer formed
of limestone arranged in sheets. Break a fragment from the edge
of one valve and examine these layers.

Inner Surface of the Shell. — Lay back the left half of the shell
and study the internal surface. This can be done by first
opening the shell slightly. Insert a scalpel at each end of the
hinge and cut the muscles which draw the halves together. The
left valve must also be carefully freed from the soft parts within
before the two halves are widely separated.

In Unio the valves articulate with each other by means of
conical and ridged projections called hinge teeth. These dove-
tailing teeth hold the valves in their proper relations when moving
upon one another. Hinge teeth are almost entirely wanting in

94

I'llVIJ.M MoLLI'SCA '.••'>

Anoilonla. The elasticity of the liiiine opens tlie shell. ( "lusiiin
the shell is effected by the action of muscles.

Notice the line on the inner surface of the shell about a half
inch from the free edge of the left valve running more or less
parallel with it. This is the mantle line to which the mantle wa.s
attached. The mantle is the thin sheet of tissue enveloping the
body and lining the shell.

The Body (Soft Parts). — Submerge the right valve, which still
contains the body of the animal, in a dissecting tray of water.
Note the position of the two largest muscles, the ankrior (nhhirtor,
in the cephalic and the posterior adductor in the caudal end of the
l)ody. Follow these muscles to their attachments in slight
depressions on the shell, termed muscle scars. The.se muscles
close the shell working against the elasticity of the hinge which
opens it. Manipulate the valves so as to demonstrate the
elasticity of the hinge.

The body is enveloped or concealed within the inanllc which
consists of two lobes, the right and left, the posterior margins of
which arc thickened and somewhat modified to form the siphons
through which water enters into and pas.ses out of the nuintlc
cavity (the space between the mantle folds).

To facilitate further study, remove the left mantle lobe by
carefully cutting it away with scissors, leaving about an inch of
the lobe in front of the siphons undisturbed, taking great care
neither to remove nor to destroy the labial palps, which adhere
closely to the mantle at its cephalic margin. This exposes the
mantle cavity within which is suspended the nuiscular foot. The
dorsal part of the foot and the mass toward the hinge line lodges
the viscera and is termed the visceral mass.

On either side of the visceral mass, extending into the mantle
space, is a pair of thin, striated gills. Kai.>^e the foot gently and
observe the corresponding pair of gills on the right side.

In the posterior part of the body the thickened margins of the
mantle lobes form by contact the ventral or inhalant siphon,
dorsad of which is the smaller exhalant siphon. With these facts
in mind, determine by dissection the course followed by the
respiratory current.

The 7nouth is situated at the cephalic entl of the body between
the foot and the anterior adductor nuiscle. Identify the labial
palps, which are somewhat n)lled and twisted Haps associated
with the mouth.

96 LABORATORY STUDIES IN ZOOLOdV

Carefully separate the mantle lobes just caudad of the posterior
adductor muscle and trace the caudal course of the intestine
which lies exposed along the caudal border of the muscle. It
terminates in the anus, which opens into the cloacal or exhalant
siphon at a level with the ventral margin of the posterior adductor
muscle.

Make an outline drawing, each valve four and a half inches
long, of the united halves of the shell with the left valve at the
top of the page. In the left valve represent the inner surface
of the shell and also show any external structures which may be
visible from this aspect. In the right valve show as many
details as possible of the soft parts discussed above. Indicate
the course of the respiratory current by means of arrows.

PHYLUM ARTHROPODA

The pliyluu Artliiopoda is iUv largest of all phyhi, coniprisinj?
about four-fifths of all the known animal species. The funda-
mental plan of organization has enabled these animals to compete
successfully both with other animals and with the forces encoun-
tered in their environment.

Class Crustacea Crayfish (or the Lobster May Be Used). —
With few exceptions the animals of the class Crustacea arc
aquatic. Respiration is either by means of gills or directly
through the surface of the body.

The common crayfish is an inhabitant of fresh-water streams
and lakes.

External Structure.— Study a specimen in a dissecting pan.
The hard external covering, the exoskeleton, is secreted by the
ectoderm and corresponds to the cuticle of the earthworm. It is
composed of chitin and serves for proiediou, support, and the
attaehment of muscles. As this covering cannot expand with the
growth of the animal, it must be molted (shed) periodically.

Regional differentiation is pronounced as attested by the
presence of head, thorax, and abdomen in each of which the
component segments resemble each other more than they do
those of other regions. In the crayfish and others of its kind
the head and thorax are outwardly united. The line of demar-
cation is a groove over the sides and dorsum of the shell and
known as the rermcal or ncek groove. When head and thorax are
thus united it constitutes a eephaloihorax. The single piece of
exoskeleton covering this portion of the body dorsally and
laterally is known as the carapace.

The head terminates in the anterior pointed extension of the
carapace called the rostrum. This division of the botly is pro-
vided with a number of sense organs more complex than those
found in forms previously considered. Notice the pair of large
compound eyes. These are stalked and movable and are con-
sidered by some to be appendages. In front of the eyes are the
smaller first sensory appendages or antennules. Just below are
the long, flexible, many-jointed pair, the antmiia'. Both pairs

97

98 LABORATORY STUDIES IN ZOOLOGY

of sensory appendages render services which are tactile and
chemical in nature. Note the openings of the nephridia (green
glands) on the middle of the ventral surface of the basal segment
of the antenna?.

The cervical groove, already referred to, crosses the dorsum
of the carapace at about the middle of its extent and is thence
continued forward on either side as a groove, which ends just
laterad of the antennae. The cervical groove marks the boundary
between head and thorax. The ventro-lateral edge of the
carapace is not attached, the free plate on each side being known
as the gill cover, since underneath are found the gills by means of
which these animals obtain oxygen.

When the animal is viewed from the dorsum, those appendages
constituting the mouth parts (serving as jaws and conveyors of
food to the mouth) may be seen projecting slightly beyond the
cephalic margin of the carapace. These appendages named in
order from the first or cephalic pairs are: mandibles, one pair;
maxillae, two pairs; maxillipeds, three pairs. Caudad of these
and borne by the thorax are five pairs of walking legs the anterior
pair of which is modified into large pincers termed chela.
The basal piece of the third pair of walking legs bears the genital
opening in the female. The fifth pair of walking legs in a
corresponding location bears the opening of the male genital
organs. The appendages will be studied in more detail later.

The abdomen comprises seven segments six of which bear
appendages. These appendages are called swimmerets. In the
female they serve as attachments for the eggs which are thus
carried during the developmental period. The first pair of
abdominal appendages in the female are reduced. In the male
they are fused to form an organ for the transfer of sperm to the
female. In the sixth pair of swimmerets, called the uropods
(meaning "tail-foot"), the parts are greatly enlarged and form
with the telson (last segment bearing the anus) an efficient swim-
ming organ, termed the caudal fin.

y On the appropriate plate label all the above-described struc-
tures, which are visible from the dorsal side.

The Gills. — Remove the carapace of the left side and note the
pinnate (feather-like) gills underneath. Study those above
the second or third walkingjeg. The gill exposed at the base
of the appendage is the podohranch (foot gill). In the lobster
the delicate lamina uniting with its base and forming the division

I'll YUM MrrilL'ol'itnA <M)

line Ix'twccn the ^ills of successive scuniriils is kiKtwii as tlic
epipod. This is very much reduced in the cruyfish. Tiiru
tlie epipods so as to expose the two ar(hri)branrhi(r (joint fjill)
which are fixed to the flexible interarticular nienihrane connectinjr
the liasal joint of the leg to the thorax. In the lobster sHghtly
dorsad of the arthrobranchia' may be found the plfumbrnnrhin
(thoracic wall u;ills) which fz;row out from the sides of the thoracic
walls.

Ivxamine the region where th(> gill cover was cut away and ii«iii-
that this extension of the carapace over the branchial chamber
is not the true sides of the thorax but rather an outward and
downward growth from the carapace. The gills conceal the true
l)()dy wall.

Slice off a portion from the tip end of the eye stalk, including
only the outer pigmented covering. Remove the pigment from
the under surface and mount the transparent piece (cornea) in
water on a slide.

Make a sketch of several corneal facets on the plate of the
dorsal aspect of the animal.

The balancing organs or statocysts are located in the dorsal
portion of the basal segment of the antennules. They consist
of a pocket or invagination of the surface, which is lined with
sense hairs, among which solid particles are lodged.

Remove the right antennule and cut off the ventral wall of the
basal segment. Investigate the saclike statocyst, determining
its relations, contents, and the nature of its lining.

IVIany fine hairlike processes of chitin on the body and append-
ages are of a tactile nature, while others on the antennules,
antennip, and mouth appendages provide a gustatory service.

The Appendages. — The 19 pairs of appendages exhibit con-
siderable diversity of structure in difTerent segn»ents of the body:
yet all possess the same structural plan and in early stages of
development are quite similar. Among these appendages there
is a close correlation between structure and function, a fact
which bears witness to their value as good material for the study
of serial homology.

Typical Segment and Pair of Appendages.— As the abdominal
segments are most distinct and less modified than tho.se of other
regions, the third or fuinih, with its appemlages, may be studied
as a typical somite. Although the regions of the exoskeleton
constitute a continuous whole, it is convenient to speak of the

100 LABORATORY STUDIES IN ZOOLOGY

convex dorsal portion as the tergum (meaning the "back"),
the lateral lobes as the pleura (singular, pleuron, meaning the
"side"), and the slender ventral bar as a sternum (" breastbone").

By removing the right appendage the following parts may be
made out: Its union with the segment is through a division
called the protopod. This consists of two portions, a very small
basal part, the coxopod, and a long distal part, the basipod.
From the basipod arise two flattened, many-jointed plates. The
outer of these is the exopod; the inner one near the median line,
the endopod.

This type of appendage found on the abdominal segments is
called the forked or hiramous type of appendage. It is regarded
as the most primitive arthropod appendage, all other kinds having
been derived from such an appendage through modifications.

The Remaining Abdominal Appendages. — Remove the remain-
ing appendages from the left side of the abdomen and arrange
them in the order of the segments to which they belong, beginning
at the cephalic end. The appendages of the second to fifth
somites, inclusive, in both sexes are quite similar to those of the
typical segment described above. There are the usual two
joints of the protopod comprising a short coxopod and a long
cylindrical hasipod. Both the endopod and exopod are present
as many jointed filaments, the former slightly longer than the
latter. The uropod comprises a very broad and thick single-
jointed protopod and two terminal oval plates which represent the
endopod and exopod. The latter is divided by a transverse
suture into two pieces. Noticeable differences exist between
the appendages of the first abdominal segment of the male and
female. In the male these appendages are stiffened and otherwise
modified so as to form an organ for transferring sperm to the
proper receptacle in the female. The first abdominal appendage
of the female is flexible and much reduced.

Although wide variations in the appendages of the thorax and
head exist, they are nevertheless reducible to the same funda-
mental plan of structure as the abdominal appendages.

The Appendages of the Thorax. — Beginning with the last
pair of walking legs, remove eight appendages from the left
side. Be sure to cut these close to the body wall so as not to
destroy their podohranchioe. The thoracic appendages include five
pairs of walking legs and three pairs of smaller appendages, the
maxilUpeds. Arrange these appendages in serial order for study.

rilYIAM AUTIIh'orohA 101

The /////■(/ tiHi.rilli/Kd is one of I lie most coiiiijIcIc of ihrsi'
:il)IH'ii(l;i^('S and will he used as an approach to the study (»f the
whole series. Compare with a swimmeret. Identify the parts,
note differences, and determine the type. Express the results
in writing and submit as a part of the laboratory report. These
comparisons may be expressed in the form of a tal)le.

The second maxilliped possesses essentially the same com-
ponents as the third, l)Ut the exopod is relatively larger, the
cndopod smaller.

In the first maxilliped the coxopod and the basipod are broad,
thin plates, while the cndopod is short and only two-jointed.
The undivided portion of the exopod is very long. In place of
the podobranchia is a broad membranous plate.

Examine the left third ic(dking leg and compare with the third
maxilliped. This walking leg has a coxopod with an epipod and
a gill, a basipod and an endopod of five joints. The exopod is
lacking, and therefore this more specialized unforked type is
known as a uniramous appendage. Note the pinccr formed l)y
the prolongation of one angle of the distal end of the penultimate
joint, thus forming a fixed jaw for the last joint to work against.
Examine the other walking legs. Do all have pincers, epipods,
and gills? The first pair is greatly enlarged, with a powerful
pinccr for offensive and defensive use.

Draw the left third maxilliped and left third walking leg in the
same relative positions.

The Appendages of the Head.— Remove the remaining
appendages of the left side and arrange in a series for study and
comparison.

The coxopod and basipod of the second maxilla are still thinner
and more lamellate than is the case of these parts in the first
maxilliped and are subdivided by deep fissures which extend
from their inner edges. The endopod is very small and undivided,
while the .so-called bailer is probably formed by a fusion of the
exopod with the epipod. The bailer moves in such a manner as
to draw water through the branchial chamber over the gills
from the caudal end.

In the first maxilla the exopod and epipod have disappeared,
and the endopod is insignificant and unjointed. Its two inner
thin plates are the protopod. The small process in front of this
appendage in the head is not considered as an appendage i)Ut as
a part of the lower lip.

102 LABORATORY STUDIES IN ZOOLOGY

The coxopod (jf the maiulihle is greatly elongated transversely
to form a strong functional jaAv. The hasipod possesses a much
reduced two-jointed endopod which forms the palp. The exopod
is lost. In front of the mouth opening is the upper lip or labrum.

The protopod of the antenna is two-jointed, the coxopod being
small and bearing the aperture of the duct of the renal gland,
while the basipod is larger. The long many-jointed filament
connected with the basipod by two stout basal segments is the
endopod. The thin, sharp projection near the base of the filament
is the exopod.

Draw the left antenna enlarged about three times.

The antenmde possesses a three-jointed protopod, from which
arise two, short, many-jointed filaments. These may or may
not represent the endopod and exopod. It is perhaps doubtful
whether this appendage is strictly comparable with the others.

This study shows that there are at least 5 pairs of appendages
borne upon the head, 8 upon the thorax, and 6 upon the abdomen,
making a total of 19. If the eye stalks are construed as belonging
to the same category of appendages as the others and, therefore,
representing a segment, and the telson accorded the rank of a
segment, then there are represented in the body of the crayfish
21 segments.

Class Insecta : The Lubber Grasshopper , Schistocerca americanum
(or an Allied Species). — One of the Southern species of grass-
hopper is chosen for study because of its large size. Most of our
grasshoppers, so common in the summer and autumn, show the
same fundamental plan of structure but are difficult of study
because of their small size.

External Structure. — Study a specimen in a dissecting pan.
A chitinous exoskeleton, lacking the lime deposits of the crayfish,
is present and is secreted by the ectoderm lying beneath. The
hard surfaces of the exoskeleton are known as sclerites, which are
joined by sutures less densely chitinized.

Regional Differentiation. — Note that the bilaterally sym-
metrical body is divided into three distinct regions; the movable
head, the thorax bearing legs and wings, and the conspicuously
segmented abdomen.

The Head and Its Appendages. — The head exhibits no clear
evidence of segmentation. The six segments (at least) which it
comprises are suggested by comparative structural studies.
The larger part of the head is enclosed in a single sclerite, the

I'll YUM .\irriiii'(>i'(>n.\ \{):\

epicraniinn, in which thc^ dorsinn is spoken of as the rrih.r, the
sides as the gena, and the front as the Jranx. The frons extencis
ventrad to a distinct transverse suture, below which is a very
broad sclerite known as the clypeus. Attache(i to the ventral
l)order of the clypeus is a broad, freely moving flap, the upper
lip, or Idbruni. This is not a true appendage but a part of one
of the segments which enters into the composition of the head
skeleton.

The head bears eyes, antenna?, and three pairs of mouth parts.
Note the two large, brown, oval areas on the dorso-lateral
portions of the head. These are the compound eyes. Remove a
portion of the cornea, clean out the pigment, and mount in water
on a slide. Are the facets of this cornea similar in shape to those
of the cornea taken from the eye of the crayfish? The gra.ss-
iiopper also has three simple eyes, or ocelli, one in the depression
of the middle of the frons, the other two cephalad of the dorsal
portion of the two compound eyes. The antennce are many-
jointed appendages springing from the space between the com-
pound eyes. Raise the upper lip and note a pair of heavy, black
mandibles. Determine the direction of their movements. Ju.st
caudad of the mandibles is the first pair of maxillce with feelers
or palps at the sides, and lying back under the head, bearing
palps on either side, is the second pair of maxillce which have
fused with one another to form the labium or lower lip. The
antenme and mouth parts of the grasshopper represent modifica-
tions of typical arthropod appendages.

The Thorax and Its Appendages.— The thorax comprises three
segments, called the prothorax, mesothorax, and metathorax, when
named in order from the cephalic end. These divisions are
easily recognized by the appendages which they bear. One
pair of legs is attached to the ventro-lateral margin of each thor-
acic segment. In addition, the mesothorax and metathorax each
bears a pair of wings articulated with the dorso-lateral margin.

Remove the wings from the left side and compare them. What
are your deductions? The wings arise as saclike evaginations of
the body wall. During development the two walls of the sac
become pressed together, forming a thin membrane. The veins
of the wings are respiratory tubes or trachea', filled with air, each
surrounded by a tubular blood sinus. After^the insect attains
its full size, blood ceases to flow in the wings and they become
the dry, hard, and lifeless structures of the adult.

104 LAHOUATORY STUDIES IK ZOOLOCY

All Www p;iirs of legs of the grasshopper are used iu walking,
but the third pair are primarily jumping legs and show structural
modifications for such a use. Remove a walking leg from the
right side of the body and study. It has five parts. The short
joint next to the body is the coxa. The second segment or
trochanter is smaller than the coxa, its ventral aspect being longer
than the dorsal. This segment is succeeded by the long femur.
Distad of this is placed the slender, spiny tibia, while the tarsus
includes all that part of the leg distad of the tibia. It consists
of three segments. The last segment of the tarsus bears a pair
of claws and a single cushion or pulvillus. In addition there are
four pairs of pulvilli under the other segments of the tarsus.
Compare the jumping leg with the other walking legs as to
relative proportions of parts and direction of the convexities
of the articulations.

In the membrane along the sides of the thorax, just cephalad
of the mesothorax, is a small opening. This is the mesothoracic
spiracle, one of the openings of the respiratory system. Notice
also on the pleural suture which separates the mesothorax from
the metathorax a similar opening, the metathoracic spiracle.
Both openings are guarded by lips.

The Abdomen and Its Appendages. — Each complete segment
of the abdomen consists of an inverted U-shaped tergum bearing
on its ventral border a slight indentation, the abdominal spiracle.
This arched plate is probably a fused tergum and pleuron. There
is a convex ventral plate, the sternum. The rest of the pleuron
is represented by the membranous fold where tergum and
sternum articulate.

The sternum and tergum of the first abdominal segment are
separated from each other by the depression for the insertion of
the third pair of legs. The tergum of this segment bears upon
either side a kidney-shaped opening, covered by a thin, semi-
transparent membrane. This is the chordotonal organ, erroneously
called an ear. On the anterior border of the chordotonal organ
is the first abdominal spiracle. How many spiracles are present
on the body of the grasshopper?

The next seven segments are alike in both sexes but the remain-
der of the abdomen is different in form and structure in the
male and female. In both sexes the ninth and tenth terga are
narrow and partially fused on their lateral margins. The
eleventh tergum or suranal plate extends caudad forming the roof

I'll VIA' M Ain Uli'ol'nDA 105

of the aiKil opcninji. On cacli side, projecting from hcncatli llir
caudal l)()rdor of tlio tenth torguin, is a pointed appendant'
termed the nrnis (phjral, cerri). These are generally re^sarded
as the modified appenda^jes of the tenth segment. I'^ach cercus
partially covers a much larger, triangular sclerite which ext^'nds
from the lateral border of the tenth tergum caudad. These are
the podical plates.

In the male the hroad ninth sternum is followed hy a houd-
shaped tenth which forms the caudal end of the body and
terminates dorsad in two points. This is commonly called the
subgenital plate as it forms a hood about the genital apparatus.

The most prominent portion of the caudal part of the abdomen
of the female is the ovipositor, composed of two pairs of rigid and
pointed pieces and employed in forming a hole in the ground
within which the eggs are deposited. Between the ventral pair
is the opening of the oviduct. From the median caudal margin
of the eighth sternum a pointed projection, the egg guide, extends
caudally l)etween the ventral pieces of the ovipositor and aids in
placing the eggs.

On the plate of the left lateral aspect of the female indicate
by means of brackets and labels the three divisions of the body.
These should be placed above the drawing. Label the various
external structures described for each region. The abdominal
segments may be numbered serially. The abdominal terga
and sterna may be designated by symbols, as, for example, /j
referring to the tergum of abdominal segment 2, and .^o referring
to the sternum of abdominal segment 2.

Secure an animal of the other sex, study and label the struc-
tural modifications of the caudal end.

It will he profitable to devote .some time to a comparison of the
figures of the crayfish and grasshopper with regard to body
regions and appendages including types, distribution, modifica-
tions, and functions. Such a study might be summarized in the
form of a table.

PHYLUM CHORDATA

'I'ho phylum Chordata, which is the last in tho scries, comprises
animals which are diverse in form and structure. All are alike,
however, in the possession of certain fundamental characteristics
of organization which are not found combined in any other
animals. The phylum is divisible into four subphyla, a represent-
ative of one of which will be studies by way of gathering first-
hand information regarding the general plan of organization
which prevails throughout the phylum.

Subphylum Cephalochorda Branchiostoma (Amphioxus). —
This subphylum comprises about a dozen species of small marine
animals called "lancelets." They possess in a typical state the
fundamentals of organization common to all chordates. These
animals are found near the shore, where they burrow in the sand
which may be entered either head or tail foremost. The body,
with the exception of the anterior end, is usually concealed by
day, but the animals may leave their burrows at night and dart
through the water. While rapid and powerful swimmers, they
topple over upon their sides when forward progression ceases.

External Structure. — Study a stained and mounted specimen
of a young animal under the dissecting microscope or low power
of the compound microscope and note the spindle-shaped body
and the lack of a well-defined head. Along the middorsal line
note the low, nearly transparent fold extending the entire length
of the body. This fold is the dorsal fin which becomes broader
in the tail region and is continued around the end of the tail
to the ventral side where it narrows in its cephalic extent. This
broader portion of the fin fold about the end of the tail is known
as the caudal fin, while the narrower ventral part extending
cephalad from the caudal is the anal fm. Two ventro-lateral
folds, the metapleural folds, border the flattened ventral surface
of the anterior two-thirds of the body and give this portion a
triangular shape when viewed in cross-section. These may be
seen in preserved specimens.

The sides of the body are marked by a series of V-shaped lines,
formed by niyo.septa of connective tissue which divide the great

106

rilYUM CIKth'DATA 10/

hnigitiulinal iimsclr in.iss into scumcnls cullcil myolotnts or
myotnei'cs.

Lociito the opt'iwnn of llic oral hood, which is a larnc <»v:il
aperture on the ventral surface of the cephahc end of the Ixxiy.
It is fringed on each side with about 12 ciHated tentacles or cirri,
known as the oral cirri. The <uiiis is on the left side of the anal
fin just at the base of the caudal fin. The atrinporc is a inediatj
aperture on the ventral surface between the cephalic end of the
anal fin and the converg(>nce of the metapleural folds. The
respiratory current entering the mouth leaves the body through
this pore.

Internal Structure. The Digestive and Res pi rotary Orfians. —
The alimentary canal is essentially a straight tube. The oral
hood and cirri have been mentioned above. The walls of the
oral hood delimit a space called the oral cavity. The anterior
part of the enteron is the pharynx, the word here being used to
mean not merely a throat but a division of the enteron which
serves the double purpose of conveying both the respiratory
medium and the food. It is a compressed tube, occupying ai)out
one-half the total length of the aUmentary canal. It is surrounded
by a space, the atrial cavity, which will be seen in its proper
relations in the study of a transection of this region. The
pharyngeal walls are perforated by numerous sUtlike apertures,
the gill slits, running obUquely ventrad and caudad. Water
taken in at the mouth passes through the gill slits into the atrial
cavity from which it escapes through the atriopore. The
epithelium lining the gill slits constitutes the respiratory tissue.

Between the cavity of the oral hood and the beginning of the
pharynx there is a circular sheet of tissue which appears as a
straight line when viewed from the side of the animal. This
membrane is called the velum. It is perforated by the mouth
opening.

Caudad of the last gill slit the alimentary canal narrows and
continues as the intestine which, a short distance caudad of the
pharynx, gives off from the ventral side a blind pouch. This
evagination is the liver the blind end of which extends cephalad
on the right side of the pharynx.

The Skeleton.— The skeleton is of the endoskeletal type and
extreme in its simplicity. It consi.sts of a flexii)le, rodlike
structure above the alimentary canal and extending throughout
the entire length of the body. This is the notochord which serves

108 LAHOHATORY STUDIES IN ZnOJjOGY

as an axial skolcloii. Other skeletal parts are found supporlinj;
the oral cirri, gill slits, and mesal fin fold.

I* The Central Nervous System. — The brain and spinal cord lie
immediately above the notochord. Determine the extent and
relations of the central nervous organs.

Upon the plate of the left lateral aspect of Branchiostoma add
features of external and internal structure which have been
observed in the above study.

Study of Transverse Sections. — The relations of internal
organs are more readily understood through a study of transverse
sections. For this purpose prepared slides through the region
of the pharynx and liver are most instructive.

Use a low-power microscope to determine the shape and general
location and relations of internal structures. A higher magnifica-
tion may be used for the study of details. An explanation of the
stains used in preparing the slides will be given by the instructors.

The section chosen for description here is one passing through
the body at the level of the liver. In section the body is tri-
angular in shape. In the midvertical portion may be seen the
compressed pharynx on the right of which is the liver. The
gonads on either side appear as elevations from the walls of
the body encroaching upon the atrial cavity.

The epidermis consists of a single layer of cells supported by an
underlying thin layer of connective tissue, the dermis.

Identify and locate pharyn.x, notochord, and spinal cord.
Determine the following: (1) the nature of the notochordal cells,
notochordal sheath, and the gill slits; (2) the nature of the spinal
cord ; (3) the nature and relations of muscle segments (myomeres) ;
(4) the nature and relations of muscle partitions (myotomes) ; (5)
the dorsal groove of the pharynx {epipharyngeal groove) and the
ventral groove (endostyle). These grooves serve to entangle the
minute particles of food and transport them toward the intestine.

The coelom is much reduced, having been encroached upon
by the extensive atrial cavity. The remnants of the coelom
consist of paired cavities at the sides of the epipharyngeal groove,
a single space ventrad of the endostyle, a space between the walls
of the liver and the atrial epithelium, and the space surrounding
the gonads.

The larger blood vessels can often be recognized by the
coagulated blood which they contain. The dorsal aortce comprise
a pair of vessels lying one on each side of the epibranchial groove.

whili! the rtiilnil nortn (or heart) is a iii('(li:iii vessel lyiiin in the
cndostyhir ccelomic canal. Alon^ the dorsal surface of the
liver in the Cd'loniic space between the liver an<l the atrial
membrane may be seen three or four hcpntir veins lyinn side by
side, and in the ctrlomic cavity surroundin^i each j^onad a iiion;
or less prominent blood vessel is located.

The reproductive oryana occupy similar positions in the two
sexes. The sections show them extending; toward the atrial
cavity from the re^;ion of the atrial folds. If availal)le, examine
demonstration section through ovaries containing ripe eggs.

The liver is located at the right of the pharynx and appears to
lie free within the atrial cavity between the pharynx and the
gonad. Its walls are thick.

Upon the outline drawing of the transection represent the
structures which are missing. Certain structures should be
represented in colors as follows:

Nervous organs, green.

Notochord, brown.

Celom, yellow.

Connective tissue, blue.

Blood vessels, red.

Muscle, stippled with black.

Gonads, purple.

SUBPHYLUM VERTEBRATA

This subphylum includes all chordates which possess: (1) a
segmented vertebral column, (2) a heart with at least two
compartments, and (3) a cranium.

Since an extended study of a vertebrate, the frog, has already
been made, the object of the present study is that of affording
some direct contact with the lower or fish-like vertebrates.

Class Elasmobranchii. The Spiny Dogfish, Squalus acanthiaa
(or Any Shark). — Sharks and rays constitute this class of fishlike
vertebrates. In a general way they resemble the true fishes but
differ from them so widely in structure that they are to be
regarded as constituting a separate class.

This species is common along the Atlantic Coast of New
England. Preserved specimens retain their natural coloration
and body form to a remarkable degree. The adults are about
three feet long. Study a preserved specimen on a dissecting
tray. It should be thoroughly rinsed and kept moist during the
progress of study.

Exterior. — The body form is typical of aquatic vertebrates,
being spindle shaped, with the deepest part between the first and
second thirds of the total length. This so-called "stream-line"
form is the most advantageous for progress in a liquid medium.

The body is divided into head, trunk, and a portion caudad
of the cloacal aperture termed the tail. Such a morphological
tail is not found outside the chordate phylum. The skin is beset
with minute placoid scales each of which bears a tiny spine. The
resistance encountered in passing the finger from the tail toward
the head is due to the caudally projecting spines of these scales.
Embedded in the dermis is a bony plate from which the pointed
spine of dentine projects through the skin. The spine is covered
with enamel. View the surface of the skin with a lens.

A light-colored line, the lateral line, extends along the sides of
the body from the head to the tail. Its location along the side
of the body suggested its name. In structure the lateral line is a
canal embedded in the epidermis. It communicates with the
exterior through pores. Within the lining of the canal there are

110

sinrini.iM \ Kin'Knii.viw 111

sense (irp;ans wliose I'uiictioii is the detoction of disturhaiices iti (lie
water. The hiteral-hiie canals are continuous with similar canals
upon the head. Together these constitute the lateral-line
systeni of sense organs.

Study the surface of the animal with special reference to tlie
following features: (1) shape of head; (2) mouth, jaws, and teeth;
(3) nostrils; (4) eyes and the state of lids; (5) external e\ndence of
ears; (0) pores of endoUimphatic ducts, one on either side of the
middle line of the head just caudad of the eyes, communicating
with the inner ears; (7) gill slits, their numbers, relations, and
the location of the functional respiratory tissue; (8) spiracles,
caudad of the eyes, and their relations; (9) the mesal or unpaired
fins comprising a first and second dorsal and a cniidnl or tail fin
the relation of which to the end of the body should be determined,
this relation being known as that constituting the heteroccrcal
toil; (10) the paired fins, those of the shoulder region called the
pectoral fins, those of the hip region, the pelvic fins. In male
dogfishes, the mesal side of each pelvic fin is modified into a stout
process called the clasper which is used by the males as an intro-
mittent organ while transferring the seminal fluid to the females.
All the fins possess flexible supports called the dermal fin rays,
embedded in the skin of the fins.

Draw the left lateral aspect, labeling all the parts mentioned
above as far as they may be seen from the exterior.

If time permits, a further study of the shark may be made
independently.

Class Pisces. — The class Pisces includes aquatic vertebrates
which in numerous ways are readily distinguished from elasmo-
branchs (sharks and rays). In this connection reference might
be made to the presence in fishes of an operculum or gill cover
concealing the gills and gill slits. Within the class one may
recognize four subdivisions. The most numerous and widely
spread of the piscine types constitute the subdivision called the
Teleostei or bony fishes, since the skeleton is formed almost
entirely of bone.

Although the directions which follow refer specifically to tiio
yellow perch (Perca fiavescens), they may be used in the study
of almost any bony fish. Most of the observations can be made
on preserved material, but it is desirable that observations be
made also upon living specimens tluring the progress of the
laboratorv studv.

112 LAliORATOIiV ST ir DIES IN ZOOLOGY

External Features. — Observe carefully the form of the body
with a view to expressing verbally not only its nature but also its
adaptation to a darting mode of locomotion through a liquid
medium. Hold the fish on a level with the eyes, the tail pointing
straight away from the observer's face. What is the nature of the
visible surface? The body may be recognized as possessing
head, trunk, and tail regions. The scales are flat and imbricated
and are arranged in diagonal rows.

The mouth is terminal in location. On the dorsal surface of the
head immediately in front of the eyes is a pair of small openings
on each side. These are the nostrils. The two openings of the
same side lead into a common nasal cavity. Water enters by one
aperture and leaves by the other. Look for the eyelids. Only
that part of the ear mechanism corresponding to the frog's inner
ear is present in fishes. Accordingly, there is no external indica-
tion of the presence of this organ, which is located just caudad of
the dorsal portion of the eyes.

On the sides of the head note the gill cover or operculum com-
posed of fiat bones overlaid by a thin layer of soft tissues.
By elevating the operculum the gills and gill slits may be seen.
Attached to the ventral margin of each operculum is a membrane,
the hranchiostegal membrane, supported by skeletal elements
called hranchiostegal rays. To see these the membrane must be
spread.

In order to study the respiratory structures to a better advan-
tage remove the operculum of the left side. Expose the mouth
cavity and pharynx by cutting through the angle of the jaws and
extending the cut across each of the supporting arches of the
gills. Divaricate the parts thus severed.

The supports of the gills are known as gill arches. They,
together with the jaws and the tongue support (hyoid arch),
constitute the visceral skeleton. Between the gill arches are the
gill slits. The pharynx or posterior portion of the exposed cavity
can be distinguished from the oral or mouth cavity by the
presence of the gill arches and gill slits in its walls.

Of the five gill arches only the first four actually bear gills.
The dorsal ends of the arches of each side are attached to the
undersurface of the brain case, while the ventral ends articulate
with a series of bones in the midventral line. This connecting
series of bones constitutes what are known as the hasibranchials.
The inner surface of each of the first four gill arches bears spine-

SrnrUYlA M \ Kin'EHRATA I 1 :{

like processes known as (jill rakir.^. These appear in two rows
and serve to prevent food from passing throu^li tlie ^ill slits.
On the outer surface of each arch are numerous (jitl Jilnnuiits
supported by gill rays. The double row of filaments form the
respiratory part of the gill. Remove a portion of the first gill-
bearing arch and examine it in water witlj a microscope.

If live fishes are available, study the successive respiratory
movements.

There are many areas in the mouth and pharyngeal cavities
bearing teeth. On the upper jaw teeth are borne by the prc-
maxillary bones. In the center of the anterior portion of the
roof of the mouth are the vomerine teeth. The palatine t<'eth
extend obliquely caudad from the vomerine group. Further
caudad in the roof of the pharynx are two areas, the upper
pharyngeal teeth, supported by the dorsal portion of the gill
arches. In the lower jaw there are teeth on the dentary bones
which form the greater portion of the margin of this jaw.

Three structural features of the oral and pharyngeal cavi-
ties of land vertebrates are lacking in fishes, namely, the
internal nares, the eustachian tube, and the glottis. Account for
their abscence.

I'Jxtending along each side of the body and parallel with the
contour of the back is a line nearer the dorsal than the ventral
side. This is the lateral line. It consists of a row of sense organs
which seive to detect disturbances in the water. These sense
organs lie embedded in the lining of a canal found underneath
the line which shows at the surface and is connected with the
exterior by minute pores which penetrate the scales covering the
lateral-line canal. Remove a scale from the lateral line and
examine it with the microscope for a view of such a pore.

The fins are of two types, median and paired. Of the former
there are two dorsals along the midline of the back, one caudal
(tail fin) at the caudal end of the body, and an anal fin at the
base of the tail on the ventral side. The paired fins correspond
with the fore and hind limbs of terrestrial vertebrates. The more
cephalic pair is known as the pectoral fins, located one on each side
immediately behind the operculum. The pelvic fins appear on
the ventral surface at a level just caudad of the pectoral fins. .Ml
the fins are supported l)y bony structures termed fin rays. These
are usually soft and flexible but may be spinelike as in the first
dorsal fin.

114 LABORATORY STUDIES IN ZOOLOGY

Hold the fish again on a level with the eyes as before mentioned.
What is the relation of dorsal and pectoral fins with regard to
their surfaces which are presented to the water? With a similar
object in view, observe the eyes, mouth, and other parts.

If time permits and living specimens of any species are avail-
able, observe the movements of the fish in order to determine the
important organ of locomotion. Describe the method. By
means of rubber bands slipped over the body, bind the pectoral
fins close to the sides. Describe results. Perform the same
experiment with the pelvic fins. Bind both pairs close to the
body at the same time. Results?

Look on the midventral line just cephalad of the anal fin for the
anus or opening of the intestine to the exterior. Behind this is a
depression in which the urogenital papilla is located. This
papilla bears the small openings of the urinary and genital
organs.

Study more carefully the scaly armor of the fish. Note the
relation of one scale to another and the difference in their size in
different parts of the body. Scales are formed by and set into
pockets of the dermis of the skin, the epidermis being reduced to a
thin film covering the free part of each scale. With forceps
remove a scale and note the scalloped margin which was set in the
dermal pocket. Examine a scale mounted in water on a slide,
using the low power of the compound microscope. Observe the
concentric markings or lines of growth. Knowing that those
lines formed during the winter season are closer together than
those formed during the summer period, determine the approxi-
mate age of the specimen. Note the rows of minute denticles and
the film of epidermis upon the exposed portion of the scale.
Owing to the toothed border this type is known as a ctenoid
scale.

The external fin rays, also called dermal rays, are formed by
the dermis of the skin. Mount one of these in water on a slide
and examine under the microscope. Note that the rays are com-
posed of numerous small joints and that they branch toward the
free end. Are the spiny fin rays jointed or branched?

On the plate illustrating the structural features of the perch
label the nostrils, the branchiostegal membrane, a gill arch,
indicating its numerical position, a gill slit, raker, and gill.
Also the lateral line, fins, the dermal fin rays, the anus, and the
urogenital depression.

SIHI'IIYIAM \ KliTEHI{.\T.\ 1 I o

Oil I lie s;mu> phitr tlraw and lalx'l a scale showing lines of
growth. Also a scale removed from the lateral line showing the
pore to the lateral-line ennal.

Internal Anatomy. Musculature. Keniovc enough of the
skin at the base of the tail to expose the thick layer of muscles
within. This layer is divided into ziRzag i)ands of muscle tissue.
I'iach band is called a muscle segment or myotome. Each myotome
extends from middorsal to midventral line and is separated from
the adjacent myotomes by connective tissue partitions, calletl
mi/osepta. Immcdiatelj' below the lateral line is a longitudinal
partition separating the myotomes into dorsal and ventral
portions.

This arrangement of muscles reminds one of tlie state in .\mphi-
oxus and is the primitive vertebrate plan from which the muscular
system of all land vertebrates is derived. It consists essentially
of a longitudinal scries of muscle segments. It is evidence of the
segmental plan of structure of the vertebrate body.

Skeleton. — It will be recalled that in Amphioxus the skeleton
consists chiefly of an elastic rod, the notochord; in the shark
a more extensive endoskeleton is present and formed entirely of
cartilage. In the teleostean fishes cartilage has, for the most part,
been replaced by bone. This is the reason for referring to them
as the "bony fishes. " During development the vertebral column
replaces the notochord, although vestiges of the latter persist.

Kcfcrcnce to a mounted skeleton reveals the same general
divisions that occur in the skeleton of a land vertebrate. These
arc an axial skeletoji comprising the skull, vertebral column, and
the supports of the unpaired fins and an appendicular skeleton
comprising the supports of the paired fiyis.

Looking further into this internal framework we find the skull
divided into three main divisions, the cranium, the sense capsules,
and the visceral skeleton. These parts which are separate during
development become united in a rather compact whole in the
adult.

The cranium is that portion of the skull which houses the
brain. The sensory capsules are skeletal parts which cnchK-^e or
support the three pairs of sense organs of the head, the nasal
sacs, the eyes, and the internal ears. The visceral skeleton has
already been described and studied.

Note how the bones which support the ilorsal and anal fins
alternate with the neural and luemal spines. Note especially the

116 LABORATORY STUDIES IN ZOOLOGY

vertebral relations of the supporting structures of the caudal
fin.

The dorsal ends of the pectoral girdle are attached to the caudal
end of the cranium. The arch is suspended ventrally to support
the pectoral fins. The pelvic girdle of the perch is composed of
two flat plates of bone on the midventral line free from other
skeletal parts.

Abdominal Viscera,— Make an incision through the body wall
along the midventral line from a point immediately in front of the
anus to the region of the lower jaw. Care should be used that the
internal organs be not injured by too deep a cut. Make a dorsal
incision at the point of origin of the midventral slit. Remove
a portion of the body wall of the left side so as to expose the
abdominal cavity.

Note the glistening membrane, the peritoneum, which lines the
cavity and suspends the various visceral organs from the dorsal
body walls. A transverse septum forms the anterior wall of the
abdominal cavity. In front of this septum is the pericardial
cavity, lined with a thin membrane, the pericardium. It contains
the heart.

From the pharynx the alimentary canal continues caudad into
the oesophagus. The oesophagus merges into stomach the con-
stricted caudal limit of which is the pylorus. Beyond this point the
canal is continued as the intestine. In the region of the pylorus
there are three finger-like blind pouches arising from the
intestine and called pyloric coeca. Note the liver attached by the
coronary ligament to the transverse septum. The gall bladder lies
on the posterior surface of the liver. The spleen appears as a
small dark body between the coils of the intestine. Because
of its diffuse nature the pancreas is difficult to find. A descrip-
tion of this organ is therefore omitted. In order to view the
other viscera to the best advantage it will be necessary to strip
off the layers of fat in which they are embedded.

The reproductive system consists of a pair of gonads. There is
no connection between the testes and the kidneys as is the case in
the males of most vertebrates, but the testes as well as the
ovaries merely taper down to a tube leading to the urogenital
opening.

Along the dorsal wall of the abdominal cavity extends a large
gas-filled sac, the swiyn bladder or air bladder. By slitting the
wall of the bladder the extent of this sac can be determined.

sriil'IIVIJ-^f \ EUTKHIiMW 117

In some fishes the swim bludder still ni.iiiis cuiiiicctiitii with [\\v
l)h;irvn\', from which it arises, hut this comicctiuti is ctitirt'ly
lost in the perch. It is a hydrostatic organ ('(jualizinn the weight
of the animal and the water it (hsplaces. In life the swim
hhulder is tilled with gases. By reducing the volume of gas the
fish is able to descend to greater depths; hy increasing the volume
it is able to rise easily in the water.

Immediately dorsad of the swim bladder and just below the
vertebral column are two dark-ct)lored, irregular masses extending
cephalad as far as the (esophagus. These are the kidneys. The
ureters extend the whole length of the kidneys and pass along the
posterior wall of the abdominal cavity to the urogenital papilla.
Before reaching the papilla, the two ducts unite and then enlarge
to form a urinary bladder located immediately above the caudal
end of the gonads. Jvxtend the mid ventral slit caudad on one
side of the anus. This will facilitate the study of the caudal
portions of the urogenital organs.

The Circulatory System, — The heart of bony fishes consists of
but a single auricle and ventricle. The ventricle is readily
identified as the pale, thick-walled ventral chamber, with the
thin-walled, dark-colored auricle overlying its anterior portion.
Posterior to the auricle is the sinus venosus. From the ventricle
the blood passes cephalad into an enlarged vessel, the bulbits
aurtic, and thence into the ventral aorta which divides to form four
pairs of afferent branchial arteries. Each of these follows the
course along a gill arch to break up into the capillaries of the
gill filaments where an exchange of gases takes place. These
capillaries unite into efferent branhcial arteries which come
together on the middorsal line to form the principal artery of the
body, the dorsal aorta. This is the single type of circulation.

>

A REVIEW OF THE PHYLA, SUBPHYLA, AND CLASSES OF

ANIMALS

The following study is outlined as a review of the animal
groups through the use of a key for their identification. The key
is designed to include the forms which are ordinarily used in
laboratory studies or which one might ordinarily encounter in
general studies.

Unlabeled representatives of the major animal groups should be
provided in numbered jars. Specimens preserved in alcohol
should be dipped in water and kept moist while used for study.
After each specimen is identified, write upon a record sheet the
name of the group or groups to which the animal is judged to
belong. Make these records according to the number borne by
the specimen.

Key for the Identification of the Larger Groups of Animals
A. The body of the organism comprising a single independent cell or many
similar and independently functioning cells associated in a colony with
little or no differentiation {i.e., without forming tissues); or comprising
masses of multinucleate protoplasm; mostly microscopic

Phylum Protozoa
A A. The body of the organism comprising many cells of different kinds (i.e.,
forming tissues).

B. Body usually forming irregular masses without apparent symmetry
but the masses sometimes cylindrical, goblet shaped, or vase shaped,
or definitely arboroid; walls rough, bristly, and pierced by numerous
pores, one (or more) of which is large and conspicuous

Phylum Porifera
BB. Body regular in form, walls not pierced by pores and with evidence
of a definite symmetry.
C. Anus lacking, mouth capable of opening and closing.

D. Symmetry radial or biradial, radii not five or multiples thereof.

E. Body without rows of ciliated swimming plates; tentacles

with batteries of nematocysts (uneven of surface); mouth

surrounded by bases of tentacles Phylum Ccelenterata

F. Bod}^ vase shaped (tapering toward basal end) with hypo-
stome, with stalk or stem for attachment, and usually
colonial; or body umbrella shaped, not colonial.
G. Body vase shaped; or umbrella shaped with velum about

margin of umbrella Class Uydrozoa

GG. Body umbrella shaped without velum and with oral

arms; margin of umbrella notched Class Sajphozon

118

.1 REVIKW OF Tin-: ASIMAL CROVI'S Il'J

FF, Body cyliiidrioiil, without hypostoino, with stomodeum and
mesenteries subdividing the Ra-strovascuhir cavity; scsflilc

without stalk; single or colonial Class Anlhozoa

EE. Body jelly-like in consistency, with eight n)W8 of ciliated
swimming plates, tentacles present or absent but without

nemaU)cysts Phylum Ctcn^iphora

UD. Symmetry bilateral, body depressed ..Phylum I'latyhiiminihcs
E. Moutli and digestive system present.

F. Without sucking di.scs about moutli or upon other i)arts of

the body Class TurbcUaria

FF. Sucking discs present Class Trematoda

EE. Mouth and digestive system absent, body elongate and
divisioned into flat units (Roman girdle-like), one end of
body undivisioncd, narrow with terminal enlargement

liearing hooks or adhesive cups or both Class Cistoda

CC. Anus presejit, mouth provided with accessory parts such as lobes;
palps; hooks, special areas or crowns of cilia; chitinous, calcareous,
or bony jaws; teeth, etc.
D. Skeleton absent or external in location.

E. Sj'mmetry radial. Radii usually five or multiple thereof.
Surface of body with hard plates and spines or leathery with

small calcareous plates Phylum Echinodirmata

EE. Symmetry bilateral, sometimes curved or arrangdd in a spiral.
F. True metamerism lacking or if the body appears metamcric
(annulated) it will bear cilia upon the anterior end.
G. Calcareous or horny sliolls ab.sent, or if present they arc
tubular or of two valves placed dorsally and ventrally,
the ventral valve curved dorsally at narrow end.
H. Body wormlike without crown of tentacles on anterior
end.
I. With eversil)le proboscis which when not everted
rests in a sheath above alimentary canal. Proboscis
with one or more stylets at end but without hooks

Pliylum Nemrrlinea
IF. Without evcrsible proboscis. When such a structure
is present it is permanently extended and its surface
is beset with hooks. Body slender and covered with
glistening cuticle. Expanded lips with teeth some-
times present Phylum N emathelminthes

HII. Body usually not wormlike but if so the anterior end
will l)car tentacles.
I. With one or more crowns or girdles of cilia borne
upon the discoidal or lobed anterior end. Micro-
.scopic in size, not colonial . .Phylum Trochrhninthta
II. With an oval or horseshoe-shaped lophoi)hore, bear-
ing tentacles. Calcareous or horny shells may be
pre.sent as tubular ca.ses or as valves dorsal and
ventral in position. Those without shells are
colonial, the individuals resting in cases, tubes, or

120 LABORATORY STUDIES IN ZOOLOGY

upon the surface of gelatinous masses

Phylum Molluscoida
GG. Calcareous shells present which may be spiral or of two
valves lateral in position or segmented and placed on
back. If sliell appears to be absent the body is elongate
with a "saddle-blanket" patch on the back or the head
bears a pair of eyes and long tentacles al)out the mouth
each tipped with cuplike adhesive organs

Phylum Mollusca
FF. True metamerism obvious.

G. Without jointed locomotor appendages

Phylum Annelida
H. Segments bearing parapodia or lateral bristles or both

Class Choetopoda
HH. Without either parapodia or bristles.

I. Tentacles present Class Archianellida

II. Adhesive organ at either end of body, tentacles

absent Class Hirudinea

GG. Jointed locomotor appendages present

Phylum Arthropoda
H. Antenna; present.

I. Antenna; two pairs; gills present. . . .Class Crustacea
II. Antenna; one pair.

J. Most body segments bearing similar jointed leg-
like appendages. Abdomen not differentiated

Class Myriapoda

JJ. Abdomen differentiated and without locomotor

appendages. Thorax with three pairs of walking

legs. Usuall}^ two (sometimes one) pairs of wings

present Class Insecta

HH. Antenna^ absent or apparently so; head and thorax
combined, equipped for aerial respiration

Class Arachnida
DD. Skeleton internal, metamerism obvious in some, subdued in
others. Axial skeleton in form of notochord or vertebral
column of cartilage or bone or both. Pharynx with gill slits

Phylum Chordata
E. Locomotor appendages absent.

F. Body wormlike with proboscis, collar, and evident gill slits
or (in some exotic forms) polyp-like with tentacles at free
end. Notochord confined to proboscis

Subphylum Hemichorda
FF. Body sachke; inhalant and exhalant apertures; with or
without peduncle (stalk), single or colonial in habit

Sybphyluni Urochorda

EE. Locomotor appendages present in form of mesal or paired fins

or both, or as legs.

F. Notochord serving as axial skeleton, continuous mesal

finfold present Subphylum Cephalochorda

.1 REVIEW OF TffE AM MM. (HiOVrS 121

\'V. \'(Mt('l)r:il ruliiimi !iii<l <riiriium jin'soiit

Subpliyliitn \'rrlibru(a

G. No paired a|)|M'M(laKos ("Ihmm CycloHtomala

GG. Paired nppeiidaKcs present.
H. Paired appeiidaKPs as fins.

I. Oporoiiluin (gill cover) ahaeni .Cluss El(itimobrnru:/iit

II. Opcreuluin jireseiit Cla.s.s Pisces

HH. Paired apjieiidages jientadactyle (with (iiRits)

I. Skin naked, no claws f>n digits ('Ia.s.s Amphibia

II. Digits witii claws, nails, «»r hoof.s.

.1. Horny scales or plates or denticles a.s body

covoring Class Rcplilia

JJ. General body covering not in form of scule.s.

K. Feathers present (Jlass Avea

KK. Hair present Class Mammalia