LABORATORY DIRECTIONS

IN

GENERAL ZOOLOGY

By

WINTERTON C. CurTIS

PROFESSOR OF ZOOLOGY, UNIVERSITY OF MISSOURI

SEPTEMBER, 1913

For SALE BY THE UNIVERSITY CO-OPERATIVE STORE
COLUMBIA, MIssouRI

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PREFACE

These notes are the outcome of one mimeographed and two
printed editions, which have been written for the introductory
course in zoology at the University of Missouri. The effort
has been made with each revision to better adapt them to the
needs of our students and to make corrections where the plan
of work or the phraseology had proved unsatisfactory. As
will be evident to any one with experience in work of this
character, they are unusually full and this will doubtless be
a matter of criticism by those who believe that the student
should receive as little help as possible in the simpler parts of
his laboratory study. The author agrees entirely with this
contention and it is the very thing he has attempted in the
writing of these laboratory directions and in the whole organi-
zation of his work in the teaching of general zoology. With
this end in view, the work of the course is so planned that some
laboratory work shall precede any text-book or lecture study
upon a given form. Where the student begins his study of
each animal with laboratory observation, it will be found that
too brief directions result in his being constantly in need of
help from the instructor. In such a plan of work he needs
notes which will offer adequate direction and at the same time
present a carefully studied attempt to make him determine for
himself all the points which éxperience shows are made out by —
the better students. If, in addition, the instructors in a labo-
ratory will try never to answer any question the student can
be fairly expected to answer for himself, confining their atten-
tion to setting him right when he is on the wrong track with
his material or has misunderstood the directions, and will, on
‘the other hand, spend most of their time in explaining the
_ broader aspects of the facts the student sees and in responding
quickly to the kind of questions he asks when doing under-.
standingly the work called for, the author believes that the

III

maximum of efficiency in laboratory instruction will be obtained,
and these notes have gradually developed in conformity with
this method of instruction. ‘This procedure should, of course,
not be pushed to the extreme of having all the laboratory work
come first, because the student should have another chance at
the material after his lecture and text-book study have given
him a broader appreciation of what he can see in the labora-
tory, the ideal plan being to have the latter part of the labo-
ratory study follow the main portion of the lecture and text-
book assignments. When this plan is adopted, it has been
our experience at the University of Missouri that students can
be trained to work independently with the directions here
given, while the advantage for lecture and text-book work lies
in the fact that the student understands much more readily
what he reads or hears after he has seen something of it at
first hand. Thus a good deal of time may be saved, particu-
larly in lectures, which, when they precede any first hand
knowledge, often labor to explain what could be much better
seen and mastered by the student without any preliminaries.
Most of the work has been written de novo for this course
although the author has made no attempt at originality in
many of the minor points, which have been accumulated from
many different sources and sifted out until they represent the
result of his teaching experience. In the original mimeo-
graphed edition, the notes on a number of forms were largely
a modification of the Laboratory Directions in General Zoology
by Professor E. A. Andrews of the Johns Hopkins University,
to whom more than to any other one man the author feels
indebted for his present habits of thought as a laboratory
teacher. Very little now remains which would connect what
is here given with the notes by Professor Andrews. In the
section on the Earthworm, however, there are a number of
paragraphs which have survived and perhaps a sentence here
and there in the notes on the Frog, the Unicellular Forms and
the Hydra. For permission to use these as they stand in the
present edition, which is copyrighted and placed on general sale,
I am indebted to Professor Andrews. The greater part of the
notes were, however, first written and have since been revised
IV

directly from the material and may be regarded as an outcome
of the laboratory teaching of General Zoology at the University
of Missouri during the past ten years. I have to thank my
colleagues, George Lefevre, G. W. Tannreuther, and G. S.
Dodds, and our assistants who, from year to year, have helped
with each revision to eliminate the most obvious defects in
phraseology and method.
WINTERTON C. CURTIS.
January 1, 1912.

PREFACE TO THE PRESENT EDITION

The present edition has been revised in the light of further
experience at the University of Missouri and of suggestions
from other institutions in which the directions have been
used. Some additions have been made with a view to making
the work more adaptable, particularly in courses where the
plan for introductory work in zoology includes a somewhat
wider range of forms. In this connection, the scope of the
lecture and text-book work in General Zoology as given at
the University of Missouri may well be stated. The course is
one for five hours credit during one semester. The schedule
calls for two lecture periods of one hour and three laboratory
periods of two hours each, with reasonable latitude for the
individual instructor in the substitution of quiz or lecture work
for some of the laboratory periods. The plan of the laboratory
work in relation to the entire course of study will be under- ©
stood by the following outline:

I. Representative Forms of Animal Life.

(Studied with reference to their structure, physiolo-
gical processes and life-cycles and as living animals
rather than as representatives of a particular phylum).
(a) The Frog, as a familiar form.
(b) Unicellular Forms, to illustrate the basic phe-
nomena of living things. |
‘(c) The Hydra, as a simple metazoon.
V

(d) The Earthworm, Crayfish or Mussel, as a
complex metazoon of distinctly different or-
ganization from the more familiar vertebrates.
Only one of these is usually studied in full as
outlined. —

II. The Ontogenetic Development of Animals.

(a) Cell Division, Maturation, etc.

(b) Cleavage and Formation of the Germ-layers.

(c) Life-cycle of Amphibia.

(d) Embryology of Frog and Chick.

III. Ecology, Behavior, Intelligence, etc.

(a) The Insects.

(b) The Parasitic Worms.

IV. The Classification of Animals and their Phylogenetic

Development.

(a) Brief Examination of the Principal Phyla.

V. Organic Evolution, lectures and demonstrations only.

These five main topics, of course, receive emphasis through-
out the work, but they are more extensively developed in con-
nection with the laboratory matter above indicated. The
course, therefore, deals with a rather limited list of animals,
and while the student is given an opportunity to form some
conception of the more important phyla there is no intention
of taking him from end to end of the animal kingdom as is
sometimes done in courses entitled General Zoology. The aim
is rather to present the fundamental phenomena of living mat-
ter as illustrated by representative forms of animal life.

At the request of Professor W. M. Smallwood of Syracuse
University, notes are added upon the bony fish and the snail.
These have been placed in an appendix as they do not logically
belong at any place in the scheme of the course as here out-
lined. For these notes and for the outline of work upon the
arteries of the frog, I have to thank Professor Smallwood and
the staff at Syracuse University.

WINTERTON C. CURTIS.
University of Missouri,
September 1, 1913.

VI

CONTENTS
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INTRODUCTORY NOTE FOR THE STUDENT

Since the proper understanding of any topic studied in the
laboratory often involves an exact knowledge of the facts
previously ascertained in lectures, laboratory and text-book,
the student should make his laboratory work a matter of
thoughtful study and should attempt to correlate each new
fact with what he already knows rather than allow this work
to degenerate into an unthinking manipulation of hands and
instruments. Drawings are used solely as a means of enforc-
ing exact observation and recording the results of the same.
They are without value for zoology save as they show evidence
of an understanding of the subject matter. While the ideal
scientific drawing is not without artistic merit, this is a sub-
ordinate matter when compared with accuracy of detail. A
figure by an unskilled draftsman often shows more real under-
standing of the structures involved than one by a person who is
merely clever with his hands. Neatness is an important item
because, it tends to enforce the habits of careful work which are
conducive to the best observation and representation.

In beginning laboratory work, the student should be guided
by the following suggestions: Bring to your seat at the begin-
ning of the period all the instruments and other articles likely
to be used, thus avoiding unnecessary moving about the room.
Follow the laboratory directions explicitly, asking for informa-
tion only when you do not understand or do not find the
material. Return promptly all slides or specimens not intended
for your exclusive use. Handle museum and demonstration
specimens with great care and do not take from the demonstra-
tion table, without permission, material intended for gen-
eral use.

Your co-operation is asked in the attempt to make the lab-
oratory a quiet and pleasant place of work and in so handling
its equipment that every one may derive the maximum bene-
fit therefrom.

VIII

THE LEOPARD FROG (RANA PIPIENS)

PHYLUM, CHORDATA. SUB-PHYLUM, VERTEBRATA.
CLASS, AMPHIBIA.

ESP RNAL FRATURES

(a) Examine a freshly killed specimen in a dissecting pan
and note the general shape and coloration of the body, the soft
slimy skin, mouth, anus, nostrils and eyes. What is the
relative development of the eye-lids and of the nictitating
membrane, a thin fold which can be drawn over the eye?
Is there an iris and pupil as in your own eye? How does the
ear-drum or tympanic membrane differ in position from the
structure of the same name in your own body?

(b)’ Watch live frogs in the laboratory, or better in a pond,
noting the modes of locomotion on land and water and any
characteristic behavior. In a live frog under a bell-jar watch
the respiratory movements of nostrils, throat and body and
try to explain how air is forced in and out of the lungs. How
is the squatting posture adapted for a quick escape from dan-
ger? If possible watch frogs in the awkward sprawled out
position assumed when floating near the surface of the water
and determine whether this is also a good position for a quick
escape. Note the hump in the back and, by reference to a
skeleton, the bones which cause this. Study skeletons of frog
and man and compare, particularly the skull, vertebrae,
sternum, clavicles, scapulas, pelvis, and bones of the limbs.
Understand the terms, dorsal, ventral, anterior and posterior,
cephalic and caudal.

Exercise I. Place the animal in the pan dorsal side up,
pinning out the fore and hind limbs with digits spread apart.
Show the specimen thus prepared to one of the instructors to
make sure it is properly arranged, or compare with the one thus

(9)

10 THE FROG

pinned out at the centre-table. Have pencils carefully sharp-
ened. Rule a faint line lengthwise in the middle of a sheet of
drawing paper and, using this to represent the median plane of
the animal, show the strict bilateral symmetry which the out-
side exhibits. Draw ona scale of 1 as thus seen from the dorsal
aspect. Measure all the distances accurately with ruler or
compasses and show all the parts to which your attention has
been called in the foregoing section so far as they appear in this
view. Finish the drawing in simple outlines, without shading,
as in the figures posted to illustrate this method of drawing.
Label thoroughly, making index lines with a ruler and arrang-
ing the lines and the names to which they lead neatly.

It. (THE MOU: Canin

(a) Open the mouth and feel the bones in the upper and
lower jaws. How are the teeth distributed? Fine the vo-
merine teeth near the internal nostrils. Explore the nasal
passages with a guarded bristle. How do they differ from
those of man? Posteriorly the mouth narrows down and passes
into the oesophagus, the diameter of which may be deter-
mined by probing with the handle of a needle. Press down
the eyes from without and observe what happens. The frogs
thus “‘pull in their eyes’’ when hiding beneath stones or other
objects on the bottom. What is the shape and attachment of
the tongue? On the mid-line of the floor and well back toward
the oesophagus is an oval area with a slit in the middle, the
glottis, above and on each side a large pit, the Eustachian
recess or tube. Compare these features with what you know
of the human body. Ina male frog there are two small holes
near the angles of the jaws leading into right and left cavities
known as the buccal sacs. These may be demonstrated by
inflation with a blow-pipe.

Exercise 2. Understand these features thoroughly and be
prepared to show the relative position of the several parts by
drawing a sagittal section of the head, or making surface views
of the roof and floor of the mouth cavity.

THE FRoa. 11

ME CORLO@MIC,GAVITY

(a) Place the specimen in a pan ventral side up and fas-
ten with pins through the limbs. Pick up the skin along the
ventral mid-line with forceps and cut through the skin only,
leaving intact the heavier layer of muscles which is separated
from the skin by an open space. Continue the cut as a median
longitudinal incision extending from the jaw to the cleft between
the hind legs. Cut out at right angles to this in the region of
the fore limbs and again at the posterior termination of the
cleft. Reflect the flaps thus formed and pin out in this posi-
tion. The extensive space between skin and muscles is called
a lymph sinus. Examine the thighs and fore limbs, making
small cuts through the skin only and exploring with abristle
the cavities thus disclosed. Can you find how these lymph |
cavities are separated from one another? Note fine branches
of blood vessels extending over the skin and large right
and left vessels which lie along the partition separating the
ventral abdominal lymph sinus from those on the dorso-lateral
surfaces. These are the great cutaneous veins. The cutane-
ous arteries may be found close to them but are not so readily
distinguishable since they are no longer distended with blood.
What fact regarding the distribution of veins and arteries do
you discover upon studying the finer branchings under a hand
lens? Along the mid-line, in the layer of the muscles, is another
blood vessel, the anterior abdominal vein.

(b) With forceps, lift up the muscle layer in the region
of this median vein and cut into the body-cavity or coelome,
being careful not to injure the underlying viscera. Cut along
the mid-line as far forward as the sternum and then have one
of the instructors help you remove a portion of this bone.
Expose the organs dorsal to the sternum by stretching out and
pinning the fore limbs. Cut out at right angles posteriorly and
reflect the flaps as in the case of the skin.

(c) If the specimen has not been dead too long, the heart
will be still beating. Without injuring the heart, open the
sac-like pericardium in which it lies and note the ventricle

12 THE FROG.

which is single and the auricles of which there are two. Lead-
ing out anteriorly from the ventricle is a large vessel, the
truncus arteriosus which divides right and left. On lifting up.
the posterior end of the ventricle the sinus venosus may be
seen leading into the right auricle.

Exercise 3. As in the case of the mouth cavity, be pre-
pared to represent these points by a simple diagram.

(d) As the organs lie in place, one can at once recognize
the liver with its lobes and the coils of the intestine. On the
observer’s right, the stomach comes out from beneath the liver
and passes into the intestine as it bends sharply forward.
Between the liver lobes is the gall-bladder. Lift up the liver
and find the pancreas, lying in the angle made by the stomach
and the beginning of the intestine. Find the dark red spleen
among the coils of intestine and beneath the posterior end of
the stomach. Also find where the small intestine enlarges into
the large intestine and the anterior end of the stomach where
it communicates with the oesophagus. Locate the lungs and
inflate them through the glottis with a blow-pipe. On the
dorsal face of the body wall, find the dark red kidneys with
finger-shaped fat bodies at one end. In a male, the testes
are a pair of bean-shaped organs attached to the ventral face
of the kidney. In the female, the ovaries are attached in a
similar manner, but are larger particularly in the fall and
winter when the eggs are maturing for the spring breeding
season. The oviducts are greatly convoluted tubes lateral to
the kidneys. Rudimentary oviducts are often found in young
males.

(e) With the direction of an instructor, remove the diges-
tive organs from the body by severing the tract across the
oesophagus and large intestine. Note in so doing the mesen-
teries and how the blood vessels run through them. The shiny
membrane which covers these organs and lines the abdominal
and pericardial cavities is the peritoneum. Understand from
the lectures and text-book the meaning of the terms visceral
and somatic layers of peritoneum, and how the mesenteries are
related to the same.

THE FROG. 13

(f) To study the removed digestive tract, begin at the
posterior end and unravel the intestine by cutting the mesen-
teries which hold the various coils in place. Stop this process
before the region of the pancreas is reached and begin to pin
out in the dissecting dish under water, reflecting the liver lobes
as in the specimen placed on the center-table. Find the bile-
duct which enters the intestine about opposite the middle of
the pancreas, through which it passes on its course from the
liver and gall-bladder. The term duodenum is applied to the
region of the intestine where the bile-duct enters.

Exercise 4. Draw, on a scale of 3, showing the various
parts of the tract and its appended glands (pancreas and liver).
Finish as a simple line drawing and label thoroughly with index
lines, etc., as in Exercise 1.

(g) With a sharp scalpel, cut the stomach in two trans-
versely. Examine the cut surfaces and make out the layers
as follows: peritoneum, muscle layers, sub-mucosa and,
lining the tract, the mucous membrane. | ;

(h) Slit the tract lengthwise from rectum to stomach, wash
out thoroughly and examine under water, noting the character
of the lining in different regions. Look for the opening of the
bile duct into the duodenum.

(i) Cut thin slices of the liver lobes and examine the cut
surface under water.

Exercise 5. Make diagrams on a scale of 2 or 3 to illustrate
these points (g), (h) and (i).

IV. THE URINO-GENITAL SYSTEM

(a) The Female Organs. If the specimen is a female you
have already identified the paired oviducts and ovaries.
Examine the latter and note how each ovary is swung to the
back of the body cavity by a membrane, similar to the mesen-
tery of the gut, but called the mesovarium. Notice the
spherical eggs of which the organ is composed. Remove both
the ovaries by cutting along the mesovaria, being careful not
to destroy the kidneys and fat-bodies. Follow one oviduct

14 THE FRrRoa.

to its anterior end and find where it opens into the body-cavity.
Leaving the left oviduct intact, cut away the peritoneum which
holds its coils in place and without breaking the duct itself get
an idea of its total length. Identify the urinary bladder and
the stump of the large intestine and, leaving these intact, find
the place at its posterior end where each oviduct dilates into a
thin-walled sac. Notice how this dilatation passes back dorsal
to the rectum. The eggs become detached from the ovary
during the breeding season and pass into the openings at the
anterior ends of the oviducts. In their passage through the
oviducts they receive their jelly-like membranes. Finally,
they accumulate in the dilatations at the posterior ends of the
oviducts in preparation for the act of laying.

(b) Examine now a skeieton and understand how the large
intestine is placed with reference to the bones of the pelvis.
With the aid of an instructor, cut through the pelvis along the
mid-line, in doing which you must exercise great care not to:
injure the underlying parts. Spread the cleft apart and, within
the region thus exposed, cut away the peritoneum at either lobe
of the bladder, and by breaking away the connective tissue free
the neck of the same down to its entrance into the cloaca or
terminal region of the alimentary canal. Leave the bladder
intact and picking up the stump of the large intestine distin-
guish clearly between this and the two dilatations of the ovi-
ducts. Dissect the dilatations away from the rectum down to
their openings into the cloaca and, lifting each dilatation, find
the underlying ureters or ducts from the kidneys. Follow
these last to their union with the cloaca. Notice that the urine,
feces and reproductive products are all passed into the terminal
portion of the alimentary canal, which is therefore called the
cloaca. Pass a bristle into the anus and by moving it about
determine the diameter of this cloacal region.

(c) Note again the fat-bodies at the head of the kidneys,
their shape and mode of attachment and the yellow stripe along
either kidney which is the ad-renal body.

Exercise 6. Draw this system from a ventral view on a
scale of 2 or 3, showing the above points and be prepared to:
make diagrammatic figures of dorsal and lateral aspects.

THE FRoG. 15

(d) Examine the organs of the other sex, as dissected in
neighboring specimens, and compare with your dissection.

(e) The Male Organs. If the specimen is a male, note the
light colored testes and the mesentery-like membrane, the
mesorchium, which holds each in place against the kidneys.
Look in the mesorchium for fine ducts, vasa efferentia, which
convey the sperm from the testes to the kidneys. Note the
fat-bodies and the adrenal bodies which appear as a yellow
stripe on either kidney. Cut away the peritoneum which
holds either lobe of the urinary bladder and, without destroying
the bladder or large intestine, find the whitish ureters leading
back from either kidney. Free the bladder from its attachment
in the median posterior region, leaving its union with the cloaca
intact.

({) Examine a skeleton and understand how the large intes-
tine is placed with reference to the bones of the pelvis. With
the aid of an instructor, cut through the pelvis along the mid-
line, in doing which care must be exercised not to injure the
underlying parts. Spread the cleft apart and dissect away the
connective tissue until you can see the neck by which the blad-
der opens into the cloaca or terminal region of the digestive
tract. Lift up the large intestine and follow out in the same
way the ureters or the ducts from the kidneys. Notice that
the urine, feces and reproductive products are all passed into
the terminal portion of the alimentary canal which is therefore
called the cloaca. Pass a bristle into the anus and by moving
it about determine the diameter of this cloacal region. In the
frog the seminal fluid passes from the testes into tubules of
the kidneys and along these until it reaches the ureters and so
the cloaca and anus. In immature specimens, rudimentary
structures comparable to the oviducts are often highly devel-
oped. Later, these degenerate and become the seminal
vesicles in which the ripe spermatozoa are stored. These
should be examined in chart figures if not seen in dissection.

Exercise 7. Draw the dissection, on a scale of 3, showing
the bladder reflected to one side and the rectum to the other.

(¢g) Examine the organs of the other sex, as dissected in
neighboring specimens, and compare with your dissection.

16 THE FROG.

V.° THE: DORSAL REGION OF THE BODY \CAvaiy

(a) The Kidneys and Their Blood Vessels. Before begin-
ning this dissection, remove the heart and lungs in the following
manner. With strong scissors make a transverse cut through the
floor of the mouth about midway between the heart and the
anterior end of the jaws. Lift up the posterior edge of this
incision and cut backwards on either side dividing the oesopha-
gus into dorsal and ventral halves. Taking care not to injure
the lungs, you will thus remove a rectangular piece from the
floor of the mouth and oesophagus with the heart and lungs
attached and uninjured. Put this away for future study.

(b) With forceps, take hold of the peritoneum on the mid-
line near the head of the kidneys and by gently raising it see
the extent of the sub-vertebral lymph sinus. If not already
opened by the removal of the oviducts, the cavity of the sinus
should be further exposed by cutting the peritoneum along the
lateral border. Lifting the kidney of one side, make out the
large renal portal vein which runs along the outer margin of
the kidneys, sending off branches, also the dorsal aorta, a large
artery which lies behind the kidneys and is formed anteriorly
by the union of two large systemic arteries. Note how and
where the dorsal aorta gives off smaller arteries. One of these,
larger than the rest, is located at the junction of the two
systemics and is the coeliaco-mesenteric which supplies the
greater part of the digestive tract.

(c) In following the directions given in this paragraph
remove the kidneys and their veins, but not the dorsal aorta.
Cut any of the small branches of the dorsal aorta which pre-
vent the removal of the kidneys, leaving their stumps long
enough to be recognizable. Cut the peritoneum where it
remains attached around the anterior and lateral margins of
the sinus and cut across the ureters and renal portals behind.
' This will entirely free the kidneys and leave the dorsal aorta
and the two systemics uninjured and in place. Upon exami-
nation of the kidneys under water you can now see the single
out-going vein, post cava, which lies between them on the ven-

THE FROG. 17

tral side and the two incoming renal portal veins passing along
the outer margin of either kidney also fine branches from the
dorsal aorta.

Exercise 8. Draw the kidney and its blood vessels on a
scale of 3, showing by arrows the direction of blood flow.

(d) Continuing with the parts not yet removed, examine
the dorsal aorta posteriorly and determine the origin and dis-
tribution of the two iliac arteries. Lift the portion of the
oesophagus remaining in the specimen and look for blood
vessels which leave the systemics. What becomes of the
systemics when followed anteriorly? Remove the roof of the
oesophagus and mouth far enough forward to see two carotid
arteries which pass on either side into a foramen of the skull.
Do these come from the systemics?

(e) The Spinal Nerves. Note the segmented back-bone
covered by a shiny connective-tissue. Examine a skeleton
and see how the back-bone terminates in a peculiar bone the
urostyle. Note three pairs of large white nerves on either side
of the dorsal aorta. Close against the body wall and in front
of these nerves are three smaller pairs which pass diagonally
backwards. Working on one side only, lift up and trim away
the muscles and connective tissue until you find one large and
two small nerves anterior to those just mentioned. In this
connection, notice the large subclavian arteries which originate
from the systemics and pass out along the largest of the nerves.
What part of the body do they supply? The foregoing nine
pairs of spinal nerves are numbered I to IX from in front
backwards. ‘There is in addition a very small X nerve which
will be seen presently. There are connections between nerves
II and III, which constitute the brachial plexus, and the more
complicated unions of nerves VII, VIII and IX which form
the sciatic plexus.

({) The Sympathetic System is not difficult to understand,
although considerable care is necessary in demonstrating to
one’s own satisfaction the various points. To study it success-
fully the dorsal aorta and the two systemics must still remain
intact. Begin by taking the dorsal aorta between your forceps

2

18 THE FROG.

just where the two systemic arteries unite, lift gently and look
for two delicate nerve cords running with a wavy outline in the
connective-tissue a little to the side of either systemic artery.
These are the two main trunks of the sympathetic system.
Each consists of a series of connected ganglia and forms an
unbroken nerve extending along ventral to the pairs of spinal
nerves and parallel to the long axis of the body. Taking care
not to pull too hard on the dorsal aorta, look carefully at the
sympathetic nerve of one side and note that there are short
transverse nerves, the rami communicantes (singular, ramus
communicans), connecting it with the successive spinal nerves.
These rami are most easily recognized in the case of the IV,
V and VI nerves. In the anterior region, they are represented
by the fusion of the sympathetic trunk with the ventral face
of nerves I, II and III. Demonstrate this fusion to your
satisfaction. Follow the sympathetic system posteriorly and,
by careful lifting, make out the number of rami going to the
nerves of the sciatic plexus. In this posterior region there
will be noted some yellowish swellings of the cord. These are
the ganglia of the system. How many can you find and how
are they placed with reference to the rami communicantes
Examine now the sympathetic cords in the region of spinal
nerves I, II and III. The ganglia are here represented by
swellings of the cords where they cross the spinal nerves.

(g) The ganglia which are opposite nerves IV, V and VI
are too small for very satisfactory demonstration in gross dis-
section, but their position is readily ascertained since they lie
at the points on the cord where the three conspicuous rami take
their departure. We have therefore discovered a sympathetic
ganglion and a ramus communicans for each spinal nerve thus
far examined. A tenth and last ganglion is usually found con-
nected with the X spinal nerve, but it is very difficult of demon-
stration and the number of ganglia in the posterior ends of the
cords is often subject to considerable variation. When the
aorta is carefully lifted, the stumps of fine nerves will perhaps
be found here and there passing from the sympathetic trunks in
a ventral direction, one that is largest and most conspicuous

THE FROG. 19

passes along side of the coeliaco-mesenteric artery. This is
the nerve which runs to the solar plexus. For the distribution
of these branches of the sympathetic system see description
in your text-book.

(h) Cut through one of the systemic arteries just above the
union with its fellow and, reflecting it outward, examine the
periganglionic glands, large whitish masses which surround the
exit of the spinal nerves from the vertebral column. Is there
one for each spinal nerve? Note just where each spinal nerve
takes its origin. Find the X pair of spinal nerves and com-
pare the same in your own and other specimens.

Exercise 9. Construct a diagrammatic drawing to show the
spinal and sympathetic systems, on a scale of 3 or 4, as seen
from the ventral or lateral aspect. The back-bone may be
shown, but the dorsal aorta is better omitted.

VI. JOINTS AND MUSCLES

(a) Examine a skeleton to see how the ‘‘head”’ of the femur
fits into a depression, the acetabulum, of the pelvis; the whole
forming a “ball and socket”’ joint. There is a less perfect one
where the humerus articulates with the pectoral girdle. At the
elbows and knees examine the nature of the articulating sur-
faces of “‘hinge-joints.’’ Your specimen will probably have one
of the hip joints still intact and this should be examined by
removing the muscles until the strong capsular ligament, which
encloses the head of the femur, is found. How is this ligament
attached to the femur and to the pelvis? Slit open the liga-
ment and expose the cavity of the synovial capsule. In what
directions can such a joint work?

(b) Strip off the skin of one hind limb and find the gastro-
cnemius, a large muscle constituting most of the “‘calf’’ of the
leg. To what bones are the tendons of its proximal end
attached? Distally it is continued into the tendo Achillis.
Where is this in the human body? What movements do the
contractions of the gastrocnemius produce? This may be
determined by cutting the muscle in two at its middle and

20 THE FROG.

pulling on the stumps. Other muscles, which produce move-
ments of the knee and ankle joints, may be examined to under-
stand further how motion is produced at a hing-joint.

(c) If the nerves of the sciatic plexus are followed outwards
in the hind limb, their distribution to the muscles will be
observed, particularly one which innervates the gastrocnemius.
This muscle and nerve are often used for experimental purposes.

VII. THE CENTRAL NERVOUS SYSTEM

(a) Pin the specimen down dorsal side up and remove the
skin from anus to nostrils. Note in so doing the extensive
lymph sinuses and the rich blood supply of the skin. Anteri-
orly between the eyes the roof of the skull will be seen. Exam-
ine a skeleton and see what bones you must cut through to
expose the brain and spinal cord. It may now be found more
convenient to cut off both hind limbs close to the trunk and to
hold the specimen in the palm of the left hand as you remove the
flesh. Use your scalpel to pare off the muscles until the spinal
column is exposed, then scrape away the muscles on either side
of this until you reach the transverse processes of the vertebrae.
With the vertebral column thus exposed, pare down the tops
of the vertebrae until the spinal cord is reached. Being very
careful not to cut into the cord and brain, continue this paring
process until you can see the entire cord and brain and by
chipping away on the sides expose the full width of both. In
doing this you will probably injure more or less the two mem-
branes which surround the brain and cord. They are, the
outer and thicker dura mater, and the inner and more delicate
pia mater. The former lines the vertebral and cranial cavities,
the latter is the pigmented membrane which closely invests
the surface of the brain and cord and is in places distended with
blood vessels. From this point on the dissection should be
made under water.

(b) Beginning at the anterior end of the brain find the two
large olfactory nerves passing forward to the nasal region. The
olfactory lobes, from which these nerves originate, are not very

(aus EROG: 21

distinctly marked off from the cerebral hemispheres which .
constitute the greater bulk of this anterior region of the brain.
Next is a narrowed portion, the thalamencephalon, followed by
the paired optic-lobes and behind these, if it has not been
destroyed, a dark area formed by a mass of blood vessels in
the choroid plexus. Pull the choroid plexus free along one side
and reflect it to show the cerebellum, a transverse ridge, and the
fourth ventricle, a triangular cavity in the anterior end of the
spinal cord. This anterior end of the cord, which increases in
diameter before it merges into the brain, is the medula oblon-
gata. If not pulled off with the pia mater, a delicate pro-
tuberance, the pineal body, may be seen on the mid-line at the
anterior end of the thalamencephalon. By gently pressing the
brain aside in the region of the thalamencephalon, find the
optic nerve which leads from the ventral side of the brain to
either eye. Another pair of large nerves, the fifth cranial, will
be found coming off from the brain in the region beneath the
optic lobes. There are a number of other cranial nerves but
their dissection is very difficult and you are therefore referred
to figures in your text-book where their position is shown.

(c) The ten pairs of spinal nerves, seen on the dorsal sur-
face of the body cavity, arise from the spinal cord. The
largest of them can now be made out leaving the cord by dorsal
and ventral roots.

Exercise 10. Draw the brain and cord from a dorsal view
on a scale of 3 showing the parts above made out. Indicate
by an outline the position of the head, fore-limbs and eyes.
If the exact outline of the cord is not clear, it may be deter-
mined after removal as in paragraph (d) below.

(d) Remove the cord and brain by lifting gently and cut-
ting the nerves. Place in.water and study the lateral and ven-
tral aspects. Draw if time allows, comparing with figures or
models of other vertebrate brains.

22 THE FROG.

VIII. THE LUNGS AND LARYNX

(a) Examine these organs from the specimen cut out and
laid aside earlier in the work. Note again the character of the
glottis. Find the hyoid cartilage in the floor of mouth. Locate
the larynx and carefully clean off its ventral surface to see
where the lungs connect with it. Is there a wind-pipe or
trachea as in the human body? Separate the dissection into
right and left halves, by a cut passing exactly along the mid-
line and through the glottis. This is best done by a careful use
of the scissors. The laryngo-tracheal chamber into which the
glottis opens is now exposed. Find the vocal cords and the
opening into either lung.

Exercise 11. Make a large outline of a frog’s head and
anterior part of body from a side view. Add to this an outline
of the mouth cavity, the beginning of the oesophagus and the
larynx and lung as they appear when cut as above. Specimens
of whole frogs cut in this way may be examined at the centre-
table.

IX. PHYSIOLOGICAL EXPERIMENTS

(a) Gastric Digestion. Clean thoroughly three test-tubes
and fill each one-half full of distilled water. Put into the first
3 or 4 drops of hydrochloric acid and a little pepsin, into the
second the pepsin, but no acid, and leave the third with only
the water. Put a small amount of some suitable proteid
material into each test tube and watch the changes during the
first few hours. Look up text-book and lecture notes on
gastric digestion. Record the changes taking place in each
tube.

(b) Dialysis Experiments. Make a simple dialyser by
tying a piece of some animal membrane over the end of a wide
piece of glass tubing. Fill about half full with a solution con-
taining sugar in distilled water and place in a somewhat larger
cylindrical vessel. Pour distilled water into the larger vessel
until the liquid stands at the same level in the two. Set aside

THE FROG. 23

and after an hour or two taste the water of the outer tube.
Record the results.

(c) In place of the salt or sugar solution put some white of
egg dissolved in water into the inner tube. After it has stood
for about the same time as the other test the outside water for
albumen. This may be done by pouring a little into a test
tube and heating. Note results and then test in same way
the fluid of the inner tube to which the solution of albumen
was added.

(d) Central Nervous System. Follow the demonstrations
with frogs in which (1) the cerebral hemispheres, (2) the entire
brain and (3) the spinal cord have been successively destroyed
and write out your conclusions regarding the functions of the
various parts of the nervous system, also the importance of
“intelligent’’ acts in the frog’s daily existence.

(e) Muscular Action. Follow the demonstrations of the
gastrocnemius muscle and its nerve and write out your con-
clusions regarding the nature of nervous control over muscle
and the stimuli which affect muscle and nerve. After observ-
ing the action of the heart of a frog or turtle some time removed
from the body, write out a statement of the meaning of death
in the light of these facts.

Sia HEARD AND) BLOOD) VESSELS

(a) The course of arteries and veins is more readily traced
after these vessels have been injected with some colored mass.
- Specimens so prepared may be dissected for the blood vessels
and at the same time as a review of the organs and systems
already studied.

(b) Heart. In a specimen freshly anaesthetized, examine
the uninjured pericardium and consider what important func-
tions this may possess. Determine again the main divisions
of the heart as in (c) on p. 11, and the exact order of their
contraction. Refer to diagrams of the internal mechanism of
valves, etc.

24 THE FROG.

(c) Arteries. Leading away from the ventricle is the
truncus arteriosus which divides right and left over the ante-
rior margin of the auricles into two parts. Each of these
again subdivides into three aortic arches. Of these three,
the most anterior is the carotid, the middle the systemic and
the most posterior the pulmo-cutaneous arch. The aortic
arches subdivide as follows: The carotid arch soon divides
into the lingual or external carotid and the internal carotid,
the carotid gland occurring at the point of division. The
pulmo-cutaneous arch divides almost immediately into the
pulmonary and the cutaneous. The systemic arch passes
dorsally and posteriorly, uniting with its fellow to form the
dorsal aorta, as seen in the earlier dissection. Each systemic
gives off an oesophageal, an occipito-vertebral and a sub-
clavian, the last being known as the brachial after it reaches the
arm and dividing at the elbow into the radial and ulnar. The
dorsal aorta gives rise to: (1) the coeliaco-mesenteric which
branches into the coeliac, to stomach and liver, and the mes-
enteric, to small intestine; (2) the uwurino-genital arteries;
(3) the lumbars; (4) the posterior mesenterics. Posteriorly,
the dorsal aorta divides to become the common iliacs, from
which arise the epigastrics and recto-vesicles. In the thigh,
the common iliac is known as the sciatic and gives off the
femoral. At the knee the sciatic divides into the peroneal
and tibial.

(d) Capillaries. The branches of the three aortic arches
thus distribute the blood from the-heart to all parts of the body
and end in the network of capillaries. Examine a demonstra-
tion of the capillary circulation in the web of a frog’s foot and
determine the following points: Where does the pulse die out?
What is the diameter of these smallest blood vessels as com-
pared with the diameter of the corpuscles? How would you
distinguish between arteries and veins? What is the struc-
tural basis for the interchange of material between the blood
and the tissues?

(e) Veins. The dissection of the veins in the frog is of
greater interest from the standpoint of comparative anatomy
than along the general lines of physiology desirable in the

THE MICROSCOPE 25

present study and may, therefore, be dispensed with in a course
of this nature. Particularly as a considerable number of the
larger veins have already been examined by dissection. These
isolated portions should now be reviewed and put together by
the examination of the present specimen and of text-book or
chart diagrams. In this connection, consider the blood supplies
of the kidneys and the liver and the meaning of the term
“portal system.’’ Also the phenomenon of cutaneous respi-
ration and how the oxygenated and unoxygenated blood occur
in the veins and arteries. Again, can we speak of “pure’’ and
‘“impure”’ blood without a further definition of terms?

THE USE OF THE MICROSCOPE

Py PARTS OF Die (NSERUMENT

(a) If you have previously used a microscope and are
thoroughly familiar with its working, examine carefully the
instrument assigned to you, noting the peculiarities, and then
read over this section as a review. Special work will be
assigned if you are ready to proceed before other members of
the class who are using the instrument for the first time.

(b) . Examine the parts of the instrument and find out their
uses and names by the following description: The light from
the window can be reflected up from a moveable mirror through
a small hole or diaphragm in the flat plate or stage, upon which
is to be placed the object to be examined. The observer looks
through a tube to which the lenses are attached. The cylin-
drical eye-pieces slide into the top of the tube near the eye.
The more complex objectives are to be taken from their brass
boxes and screwed into the lower end of the tube near the
object. At this lower end there is attached a swinging nose-
piece to carry both objectives and make the changing from one
to the other more convenient. The hole in the stage may be

26 THE MICROSCOPE.

made smaller by diaphragms which slip in, or by an iris dia-
phragm in the more elaborate instruments.

(c) As the microscopes used in any course may be from
different makers, you should consult tables posted in the
laboratory and giving the magnifications with the different
combinations of lenses in the instrument you are using. Learn
to recognize, by their numbers and the size of the lenses, the
“high power’’ and “low power’’ eye-pieces and objectives.
Examine a chart showing the parts of a microscope and how the
light passes through the lenses.

(d) Clean thoroughly a glass slide and one of the thin
cover-glasses by washing in weak alcohol and rubbing dry with
a piece of cheese-cloth. With a pipette, put a small drop of
water on the slide and with needles and forceps unravel a few
hairs of woolen cloth in the drop. Handling the cleaned cover-
glass with forceps, lower it carefully upon this drop. Place
the slide thus prepared upon the stage of the microscope and
direct the light through it. Screw the low power objective into
the nose-piece and insert an eye-piece in the top of tube. To
see the object clearly “focus’’ the lenses by moving the tube
with its coarse adjustment until the fibres are clearly seen.
More delicate focusing is obtained by the fine adjustment, a
horizontal milled screw which is turned to the left (counter
clockwise) to raise the tube; to the right (clockwise) to lower
it. Compare the two sides of the mirror and in subsequent
work see what results are obtained by the use of each side.

(e) After a few days’ work with the instrument, a brief
practical examination may be expected upon the following
points: (1) Finding light with mirror, which is most easily
done by removing the eye-piece and looking down into the tube
through the low objective. (2) Finding the focal plane of an
object and determination by focusing of the vertical spacial
relations of its parts. (3) Adjustment of the diaphragm to
different powers and objects. (4) Mechanism of the fine
adjustment.

HISTOLOGY. Di

Me RULES POR Use OF THE MICROSCOPE

1. Do not touch the glass of lenses; if they become dirty ask
the assistant’s aid in cleaning them with lens-paper.

2. Never unscrew the parts of the eye-pieces or objectives.

3. Use a low power first—a high power afterwards and only
when necessary.

4. Do not use the high objective without a cover-glass over
the object you have placed on the slide.

5. Use the high power eye-piece, only after the low one
has been tried.

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

7. With high powers, use a smaller hole in the diaphragm.

8. Learn to keep both eyes open when you are looking
through the microscope.

9. Put the microscope into its case carefully, using care not
to jam the mirror and nose-piece against the back of the box.

HISTOLOGY OF THE FROG

Ltt BLOOD

(a) Bring a clean slide, a cover-slip and forceps to the
centre-table where the instructor will give you a drop of the
frog’s blood. Place the slip upon this at once, lowering it
with the forceps and examine with the low power of micro-
scope. The numerous corpuscles will be seen floating in a
clear fluid, the plasma.

(b) Examine with the high objective and determine the
shape of the red corpuscles. As the blood stands look for the
white corpuscles or leucocytes which are likely to attach them-
selves to the underside of the cover or the surface of the slide.
Get a clear idea of the shape of these, then with a piece of oil-
clay make a model of each kind of corpuscle. Demonstrate the
model to one of the instructors.

28 HISTOLOGY.

(c) Stain with aceto-carmine or methyl-green in the follow-
ing way: Using a slide having a fresh drop of blood covered
with a slip, place a small drop of the stain on the slide near one
side of the cover so it will be drawn under. This may be aided
by touching the opposite edge of the cover with a bit of filter
paper. After a moment or so draw off the stain with filter
paper, using a drop of salt solution to help rinse away any
excess. Look for the nucleus in each kind of corpuscle.

Exercise 1. Make a drawing of each kind of corpuscle.
Size, about 2 inches in diameter.

(d) Examine a demonstration of the circulation in the web
of a frog’s foot, observing the flow of the corpuscles in the
capillaries. Can you tell arteries from veins? Can you see
the pulse in all the vessels? If the material is available, indi-
vidual specimens of small fish or tadpoles, anaesthetized with
chloretone, will be given out for individual study of the cir-
culation in fins or gills. A drawing should be made, if such
a preparation is examined.

Il. PAVEMENT PRIA ELUM

(a) Get from the centre-table a bit of the outer layer of the
skin which frequently sloughs off from formalin specimens.
Spread out flatin a drop of water on a slide, cover with a slip
and look for the polygonal cells and their nuclei.

Exercise 2. Draw a portion of the skin showing a number
of these cells. Size, about 1 inch across the cell.

(b) Understand that this pavement of flattened cells com-
prises only the outermost layer of the skin which is much
thicker than this and made up of a variety of epithelial, gland,
muscle and connective-tissue cells.

Itt. CIrLliAreD EPITHELIUM

(a) Get from the centre-table a bit of mucous membrane
from the mouth of a recently killed frog. Place onaslideina
drop of salt solution and tease into small bits with your needles.

HISTOLOGY. 29

Put on a cover and examine with low and then with high power.
Look for motion among the smaller particles and find out what
is causing this. Find an individual cell which is separated out
and on which you can see the cilia. Look also for the nucleus.
If it cannot be seen in the fresh cells run in a little methyl-
green or aceto-carmine.

Exercise 3. Draw a single cell or better a small group show-
ing the above. Size, about 1 inch across.

(b) Observe in the demonstration at the centre-table how
the cilia act upon small objects placed upon the surface of the
mouth cavity. —

IV. COLUMNAR EPITHELIUM

(a) Get from the centre-table a bit of a frog’s intestine which
has been macerated by soaking in 35 per cent alcohol, or some
other macerating fluid. Place on a slide in a drop of the fluid,
and holding the piece with your forceps scrape off some of the
mucous membrane. Discard the muscular portion of the wall
and tease the bit of mucous membrane into very small particles.
Put on a cover and examine with the low and then with the
high power. Find the elongated cells each containing a
nucleus. Look carefully for any structures in the nucleus.
Some of them, goblet-cells, have a clear oval mass at one end
or a space in the cell from which such a mass has been dis-
charged. This oval mass is a drop of mucus, which was about
to be secreted into the intestine.

(b) The nucleus can perhaps be made clearer by staining
with magenta.

Exercise 4. Draw several of these cells, including if possible
a good specimen of a goblet cell. Size, about 2 inches in length.

Ve Sr RIPE De MUSCLE

(a) Cut from any of the body muscles of a freshly killed
frog, a very small bit of the muscle substance. Put this in a
watch-glass half full of salt solution and tease out with needles

30 HISTOLOGY.

until you can see with your eye the fibres of which it is com-
posed. The fibres will be readily seen and the teasing process
must be stopped as soon as they come apart. Care must also
be taken not to crush the individual fibres: Put on a slide
under a cover slip and examine with the low power. The long
cylindrical fibres are bound together by connective tissue and
each fibre shows a distinct transverse striation. There is a
longitudinal striation which is less distinct. Examine a single
fibre under the high power and make out the sarcolemma or
membrane surrounding the fibre, and the numerous nuclei.
Stain with methyl-green or aceto-carmine if the nuclei are not
easily seen.

Exercise 5. Draw a portion of a single fibre showing these
points. Size, about 1 inch in diameter.

Viv UNSTRIPED MUSCEE

(a) This may be obtained from the urinary bladder or from
the muscular layers of the digestive tract. Get from the
centre-table a piece of this material which has been properly
macerated. Tease out thoroughly and put on a cover slip.
Find the spindle shaped cells. Stain with magenta if the
nucleus is not readily made out.

Exercise 6. Draw a typical cell of this sort. Size, about 2
inches in length.

VII. (CARTILAGE

(a) Get with the aid of the assistant a thin bit of cartilage
from the end of the sternum, or cut with a razor a thin section
from the head of the femur of a freshly killed frog. Put ona
slide in salt solution, cover with a slip and find the transparent
homogeneous matrix containing numerous cell-spaces, or
lacunae, in each of which is a nucleated cell. Observe here
and there the groups of cells formed by binary fission. Stain
with methyl-green or aceto-carmine.

Exercise 7. Draw asmall area, showing several cells and the
other points above noted. Size of cells, about one-half inch
in diameter.

HISTOLOGY. 31

Vi CONNECTIVE. TISSUE

(a) Carefully separate two of the muscles of the leg of a
fresh frog and note the delicate web of connective tissue between
them. Or, note the fine strands of connective tissue between
the skin and the muscles of the body wall. With fine forceps
lift up a small shred of this, snip it off with scissors, and. place
it on a dry slide. Then, with two needles, spread it out into a
thin layer, breathing on it to prevent drying. Place a cover-
glass upon the preparation and then let a very small drop of
salt solution creep under the cover and moisten the tissue. The
reason for this procedure is that if connective tissue is placed
in fluid it contracts into a lump, too opaque for examination,
and cannot be again spread out.

(b) Examine first with the high and then with the low
power and note two kinds of fibres, broad crinkly ones the
white fibres, and narrow branched ones the elastic fibres.
Scattered among these are nuclei. Stain with methyl green.

Exercise 8. Draw, showing the above.

1X. BONE

(a) Pieces of dried bone, ground to thin sections, will be
used. In these only the inorganic substance of the bone
remains, but the extent and distribution of the bone cells is
shown by the cavities which the cells once occupied. These
cavities all appear black, because in the grinding of the section
they become filled with air and dirt. Examination with low
and high power will show elongated black areas, the lacunae,
or spaces once occupied by cells, and radiating out from these
fine black lines the canaliculi, which in life are occupied, in part
at least, by delicate processes of the bone cells. Compare the
structure here observed with that seen in cartilage.

(b) In some bones, the cells are grouped about canals in
which run blood vessels. These are termed the Haversian
canals, each of which with its surrounding cells is an Haver-
sian system.

Exercise 9. Draw several lacunae and their canaliculi.
Size, about 1 inch for the length of a lacuna.

32 HISTOLOGY.

Xo WALE OF DIGESTIVE TRACT

(a) The cells comprising the wall of the digestive tract may
be studied in place by preserving a small section of the tract
and cutting this into very thin sections. As the process by
which such objects are made ready for cutting is somewhat
elaborate, material will be provided already embedded in
paraffin and will be cut for each student by one of the instruc-
tors. Or, permanent slides may be used, in which case great
care should be exercised not to break covers or even to press
upon them with fingers or objectives.

(b) If the material is to be cut for each student, clean a
slide very thoroughly, as this is to be a permanent mount,
smear on one side toward the middle of the slide, and over an
area about the size of your cover-slip, a small amount of
albumen fixative. Allow a drop of distilled water to spread
evenly over the smeared area. Place the ‘“‘ribbon”’ of sections
on this water and draw off the excess of water with filter paper.
See that the ribbon is in such a position as to give a neat appear-
ance and paste a gummed label on one end of the slide. The
preparation should now be set aside until the water has all
evaporated, 24 to 48 hours being sufficient if the slide is kept
in a warm place.

(c) When all the water has evaporated, place the slide in
a jar of xylol for several minutes, to dissolve the paraffin, during
which time a cover-glass may be carefully cleaned. As quickly
as possible after this, place the slide right side up on a clean
piece of filter paper. Add a drop of balsam before there is
time for the xylol to evaporate and then lower the cover glass
into place with forceps, being careful not to include air bubbles.
If the cover glass does not have its sides parallel with those
of the slide, move it into this position so that when the slide
is permanently dry it will present a neat appearance. Wipe
off any xylol remaining on either side of the slide and the
preparation may be studied at once, if care is exercised not to
press down on the cover with the objectives or otherwise, before
the balsam has set hard. Even when hard, a similar precau-

HISTOLOGY. 33

tion should always be exercised in handling this or other slides,
as such preparations represent many hours of work and are
easily ruined through careless handling. Another precaution
is the keeping of the slides in a horizontal position as long as
the balsam is thin enough to flow. This may be for a period
of several weeks. You should therefore always keep such
preparations in the regular slide boxes provided for the pur-
pose and the box on end.

(d) Examine with low power identifying the layers of
peritoneum, longitudinal muscle, circular muscle, sub-mucosa,
and mucosa, comparing them with the figure made from a
transverse section cut with a scalpel. Studying further with
low and high objectives, note the peritoneum, which is a pave-
ment epithelium, here seen edgewise; the layer of longitudinal
muscles, here with its cells cut transversely; and the circular
muscles, here cut lengthwise. Recall text-book or lecture
notes upon the cells of smooth muscle. The sub-mucosa is
composed of connective tissue, blood vessels, etc. The mu-
cosa shows typical columnar epithelial cells, some of which
may be goblet-cells with their drops of mucous. If the stomach
is being studied the gastric glands will be seen.

Exercise 10. Make a figure, about 2 by 5 inches, which
will show a small part of the circumference and all the layers.
‘This figure should show not merely the several layers, but also
the details of their cells as they appear in the section studied
and should accurately represent what appears in your par-
ticular preparation.

xy SECTIONS (OF SKIN

(a) Sections cut at right angles to the surface of the skin
may be prepared in the same way as the sections of the digestive
tract. Examine such a section with low power making out the
two layers, epidermis and dermis. The dermal portion has
conspicuous glands. With the high objective, find the layers
of cells composing the epidermis. Where is the pavement
epithelium of your previous study? Find how the cavities

3

2 ERT EES OO Saree me meee

34 UNICELLULAR FORMS

of the glands open to the outside. Are the cells lining the
glands derivatives of the dermis or the epidermis? What is
the direction of the connective tissue fibers in the dermis?
Do you see anything like blood vessels? Note the position of
any connective tissue nuclei and pigment cells in the dermis.
Exercise 11. Draw a section of the skin showing the above
points. The figure should be made at least 3 by 4 inchesto
enable you to show the cells properly and should be drawn
accurately for the details of your particular section.

UNICELLULAR FORMS
PHYLUM, PROTOZOA

I; (THE “PROTEUS, ANIMALCULES
(AMOEBA PROTEUS)

Amoeba is frequently found in fresh water and is often
obtained for laboratory study by placing pond plants in a dish
and allowing them tostand. After such a culture has remained
undisturbed for several days, the scum which forms on the sur-
face of the water or against the sides of the dish should be
examined for amoeba. For this laboratory work, slides of
such material freshly mounted and known to contain amoeba
will be given out. | ;

(a) Use a very small aperture in the diaphragm and look
with the low power objective for transparent objects having
much the appearance of extended white blood corpuscles, but
considerably larger. After finding such an object examine
under high power and if it is an amoeba you will recognize the
flowing movements seen in the white corpuscles.

(b) Watch the changes in shape. Does the animal accom-
plish a definite locomotion by this means? The processes
which flow out from the amoeba are called pseudopodia, i. e..,.
“false feet.”’

UNICELLULAR FORMS. a5

Exercise 1. Make four drawings showing the outlines
assumed by a single amoeba at intervals of one minute.

Exercise 2. Begin a large drawing of an amoeba by making
an outline 3 to 4 inches across and add to this the items noted
in the following sections as you come to them.

(c) Examine the structure of the substance composing the
amoeba. There is an outer region of clear ectosarc and an
inner mass of granular endosarc. Recall the condition in the
white corpuscles of frog. Some of the larger masses in the
endosarc will be found surrounded by a vacuole. Sometimes
the contents of such vacuoles can be recognized as green plant
cells similar to the ones found living in the water outside; or
if specimens can be successfully fed on carmine the red particles
will be found in many of the vacuoles. These spaces are
vacuoles of digestion or temporary stomachs in which food
particles are being digested. Examine the various granules
of the endosare with a view to determining their size, shape
and nature. What is the nature of the boundary between
ectosarc and endosarc?

(d) Asingle larger vacuole may be identified as the contrac-
tile vacuole if it is seen to contract and reappear.

(e) The nucleus is best made out by looking carefully
among the vacuoles of a large specimen for an oval mass with
finely granular transparent contents and about the size of the
contractile vacuole when expanded. Examine demonstrations
of stained amoebas. Does the nucleus of the living amoeba
change its shape?

(f) If specimens are carefully watched, it is sometimes
possible to observe the manner in which the food is ingested
and the fecal matter egested.

Exercise 3. Complete the large drawing by putting in all
these details and labeling thoroughly.

Exercise 4. Study the contractile vacuole as it appears and
disappears and represent this by diagrams.

Exercise 5. Study the movements of the cytoplasm by
which single pseudopodia are formed and withdrawn and repre-
sent by drawings.

36 UNICELLULAR FORMS.

Exercise 6. Examine amoebas in a drop of water on a slide,
but without the cover glass and under the highest magnifica-
tion obtainable with the low objective. What can you make
of the third dimension? Correct any errors in your previous
figures and make a clay model to show the superficial features
of the amoeba.

(g) Understand from lectures and text-book what is known
regarding the life history of the amoeba.

Il. EUGLENA VIRIDIS

This is another form which frequently occurs in fresh water,
being some times present in such numbers as to cause the
green or reddish color in the ooze at the bottom or in the scum
floating on the surface of ponds and sluggish streams.

(a) Clean a slide and cover and get a drop of the material
containing the eugiena. With the low power, look for elon-
gated green bodies which may be at rest or slowly moving about.
Put one under the high power and observe the form and move-
ments. Can you distinguish an anterior and a posterior end?
Look carefully for the structure which causes the locomotion.
Find specimens which are expanded and others which are con-
tracted; or better, observe how a single specimen may expand
and contract.

Exercise 1. Make a clay model to show the external fea-
tures.

Exercise 2. Draw on a large scale, 3 to 4 inches long, the
outlines of a contracted and of an expanded specimen and as
you make them out add the following details to the latter draw-
ing.

(b) Continue, examining a favorable specimen. Do you
find anything like a nucleus? Anything like a contractile
vacuole? What other structures can you find inside or on the
outer surface? At the anterior end a spot of red pigment will
be observed. Look at this end for a small notch in the outline
of the body. This marks the position of the gullet.

(c) Crush the specimen by pressing on the cover with handle
of scalpel or needle while you watch with the low power, or you

UNICELLULAR FORMS. 37

can place your slide on the table, lay a piece of filter paper over
the cover and press down with finger. Examine a specimen
thus crushed and see what you can find out regarding the sub-
stance of which the euglena is composed, i. e., whether fluid or
solid, granular or homogeneous, etc.

(d) Prepare another slide and stain with strong iodine or
methyl-violet. Look for the flagellum at the anterior end and
add this to the diagram if not already made out.

Exercise 3. See that your drawing of the expanded speci-
men contains all the points made out and is thoroughly labeled.

Exercise 4. Study and draw encysted euglenas if such
material is available.

Ill. THE “SLIPPER ANIMALCULE,” (PARAMOE-
CIUM CAUDATUM)

When hay or some vegetable debris is soaked in pond water
for a time a scum collects on the surface and after some days
numerous moving white specks may appear around the edge
and at the surface of the dish, often these will be found to be
paramoecia; or the animals may be found in abundance in
small stagnant ponds where the water has a foul odor.

(a) Place a small drop from such a culture on a clean slide.
Examine first with the low power and without a cover and note
the rapid movements, characteristic shape and colorless body.

(b) Put a very small amount of absorbent cotton fibres
upon the drop of water and then a cover-slip. The animals
will thus be caught in little pens formed by the meshes of the
cotton and may be kept within a limited space. Find a speci-
men which is thus enclosed, but not in any way crushed and
study with low and high powers. Study the locomotor activ-
ities. Does the paramoecium act as though it might have
volition? What determines its movements?

(c). What is the shape? How does the anterior end differ
from the posterior? As the animal becomes quieter make
out the cilia which cover the surface of the body and cause
the locomotion, on one side the buccal groove leading into the

38 UNICELLULAR FORMS.

substance of the body, the contractile-vacuoles, two clear
vesicles which appear and disappear, food-vacuoles scattered
through the body and having variously appearing contents.

Exercise 1. Make a model of the animal to show its exter-
nal features.

Exercise 2. Make a drawing, 3 to 4 inches long, showing
only the outer surface of the body and the cilia.

Exercise 3. Begin a large sketch, 3 to 4 inches long, showing
the animal in optical section. Put in all you have thus far
observed and add other points as you find them.

(d) Make a fresh mount without cotton and stain with
methyl-green or aceto-carmine. Look for a nucleus. Does
the nucleus react differently from the cytoplasm when the stain
is applied? What do you think the staining indicates regarding
the chemical or physical composition of nucleus and cytoplasm?
A smaller micro-nucleus can be demonstrated by more accu-
rate staining methods. It is embedded in a depression at one
side of the larger micro-nucleus, which is the one you see, and
is not likely to be seen by the staining methods here used.

(e) Look in this preparation for specimens in which many
stiff processes much longer than the cilia have been extruded
from the body as a result of contact with the stain. If you do
not find them try another slide, adding a drop of stain to the
water on the slide before putting on the cover. These are the
trichocysts which are used for defensive purposes.

Exercise 4. Draw, on a large scale, an optical section of a
small portion of the body margin, showing trichocysts and cilia.

({) Take a very small drop of water containing some of the
animalcules and add an equal amount of water containing finely
powdered carmine, or India ink. Watch carefully for some
time and see whether any carmine or ink gets into the body,
where and how. Study also the action of the locomotor cilia
as they drive the particles of carmine about. Examine any
carmine which has entered the body and understand how the
food vacuoles originate.

(g) Mount some specimens in a very small drop of water
and hold in place by the weight of the cover-glass. Study the

UNICELLULAR FORMS. 39

formation and collapse of the contractile vacuole and time the
contractions.

Exercise 5. Write an accurate description, accompanied
by three drawings, showing stages in the process.

(h) Put a small drop of water containing paramoecia upon
a slide and cover with a slip. Draw off the water with filter
paper until the animals are brought under pressure, but not
crushed. Examine a specimen with the high power and look
along the margin of the body for rod-like bodies, the trichocysts
before discharge. The firm line outside these is the cuticle.
The trichocysts lie in the region known as the cortex. Draw off
the water until the animal is crushed and the semi-fluid medul-
lary region of the protoplasm flows out. Examine this mass —
with your highest power and see what you can make of it.

Exercise 6. Complete the drawing of an optical section,
adding as many details as possible.

Exercise 7. Study and draw stages in binary fission and in
conjugation if these can be found in any of the cultures.

IV. PARASITIC PROTOZOA (GREGARINA AND
MONOCYSTIS)

Many protozoa live as parasites in the bodies of other ani.
mals. Notable among these, are the gregarines, which occur
in the digestive tracts of many arthropods. Material for this
study is readily obtained from the larvae or adults of the
meal beetle, Tenebrio.

(a) Take one of the living larvae of the beetle upon a slide
and cut off the tips of the body, not quite severing the head, so
that it may be pulled away and the entire digestive tract of
the animal drawn out. Examine with microscope the contents
of the tract through its transparent wall without a cover-slip
and look for individuals which are heavily infected. When
found, the tract may be chopped or teased to pieces and the
material distributed on several slides. Or, if the parasites are
not abundant, each tract may be at once teased and covered
with a slip. Avoid getting much of the fat-body of the insect

40 UNICELLULAR FORMS.

mixed with the bits of the digestive tract and do not use salt
solution unless necessary as the gregarines live longer when in
the fluid of the gut cavity.

(b) Look for organisms with sharp outlines and definitely
divided into two parts, protomerite and deutomerite. Where
is the nucleus? Is there a cell wall? What is the nature of
the protoplasmic structure? Do the organisms move and how?
Do you find more than one type? Are any specimens attached
in any way?

Exercise 1. Draw figures of good size representing the
above.

(c) Understand the complete life-cycle of such a form, par-
ticularly the stages of spore formation and conjugation. See
demonstrations of these stages in Monocystis a parasite from
the seminal vesicles of the earthworm, and draw if time allows.

Vo YEAST AND BACTEREN

(a) Clean three test-tubes. Fill the first test-tube two-
thirds full with distilled water; the second and third two -thirds
full with Pasteur’s solution. To each tube add a little yeast
culture. Boil the second tube after plugging with cotton.
Set all three tubes aside in a jar.

Exercise 1. Observe and record any changes visible to the
unaided eye in the course of several days.

(b) Take some of the solution from each test-tube, place on
a slide covered by a slip and study with microscope. Do you
find the “‘yeast plants” in each test-tube? Why?

(c) Get material from the yeast culture at the centre-
table. Study and make out the general shape of cells, granu-
lar content, vacuoles, cell wall, methods of growth and repro-
duction. Can you find the nucleus?

Exercise 2. Draw a single cell, size about 1% inch in dia-
meter showing detailed structure and a colony or group of
cells in outline only.

(d) Take potatoes that have been in steam sterilizer for one
hour. Cut in halves with a knife, that has been heated in a

UNICELLULAR FORMS. 4t

flame. Lay halves directly upon the surface of a sterilized glass
plate, with cut surface upward. Be sure that nothing except
heated knife touches cut surface. Leave potatoes exposed to
air of laboratory for one hour, at end of this time cover the
potato with a sterilized finger bowl. Paste label on glass plate
and finger bowl with your name and Lab. Section. The
potato will remain on your table for several days. Each time
you come into laboratory examine the surface for any changes
that are visible to the eye. When growths appear scrape off
a little of the material, dilute with sterile water and examine
under the microscope.

Exercise 3. Record the changes from day to day as seen
with the eye and under microscope.

(e) Get a small drop of water containing carmine or india
ink particles and examine under high power; note the motion
of the smallest specks. This is called ‘Brownian movement.”
Is it a translation or a vibration?

({) Examine a drop of hay or other turbid “infusion’’ and
find the cause of the turbidity. Remove the most of the water
from under the cover and study the objects with a good light
and high power. Is there any Brownian movement? Is there
any active translation from place to place? Focus carefully
and see that each minute body appears light or dark according
to focus.

(g) Study a fresh slide and make out what you can as to
the form and proportions of the different objects. Can you
make out any nucleus or other internal structure. These
small objects are Bacteria. What grounds can you give for
supposing them to be cells?

Exercise 4. Draw outlines, on a very large scale, showing
the shapes of as many distinct types as you can make out.

(h) Examine the various cultures and infusions which are
on the centre-table and get an idea of the kind of material in
which bacteria in the active state may be very abundant.
Do you think they are more widely distributed in their active
or their resting condition?

(i) If time allows try to find good cases of ‘‘spore forma-
tion’’ and of “zooglea.”’ Draw.

A2 THE HyYpDRA.

THE HYDRA. (HYDRA VIRIDIS, OR H. FUSCA.)

PHYLUM, COELENTERATA. CLASS, HYDROZOA.

i HABITAT AND AGMViITtEsS

The hydra occurs in quiet pools containing leaves and other
decaying vegetable matter. When such material is brought
into the laboratory and allowed to stand in a glass jar many of
the animals will crawl out and attach themselves to the leaves
and water plants. There occur commonly about Columbia
two species; Hydra viridis, which is green in color and quite
small, and H. fusca which is larger and of a brownish tinge.

(a) Examine jars containing specimens of hydra and note
whether they tend to collect on the lighter side of the vessel.
In size they will be found to vary from very short ones up to
those about one-fourth inch in length. Examine several
specimens in the jar and see how the free end differs from the
attached. Are they found in colonies or as individuals? Do
any have side branches? If such cases of ‘“‘budding”’ are not
found among the living specimens ask for a slide showing this
condition. The buds are only temporarily attached to the
parent, each becoming eventually set free and beginning an
independent life.

(b) With the aid of the assistant, transfer several with a
pipette to a clean watch glass containing water from the jar.
How firmly are they attached? Examine with the eye and
with a hand lens against the dark background of the table.
Touch with a needle and note the result. Do any of the
hydras attach themselves to the glass?

(c) The process of feeding may be studied next, or it may
be deferred until the completion of section II below. Take
an extremely small bit of fresh meat, which you can get by
teasing out on a slide in a drop of water some lean beef or a
piece of some fresh-water animal, and with a needle push it
into contact with the free end of a hydra. If it adheres to

THE HyYpRA. 43

the tentacles, examine the specimen under the low power of the
microscope. If you are unsuccessful with the first after sev-
eral attempts try other specimens, until you find one that will
take food. Watch the process carefully.

Exercise 1. Make several drawings of good size, 2 to 3
inches long, to show the feeding.

Il. GENERAL EXTERNAL CHARACTERS

(a) Examine with low power of the compound microscope
-.and notice the cylindrical body, which varies much in length
and is attached at one end. At the opposite end is a conical
projection, the hypostome, around which are several tentacles.
How many? The tentacles are covered with knob-like swell-
ings at intervals varying with the state of contraction. Short
developing tentacles will sometimes be found.

(b) The mouth, at the tip end of the hypostome, is round
when widely open. What shape has it when closed? The
base of attachment is the thick end by which the animal
adheres to a support. Sections show that the cells of the base
are glandular and secrete a sticky substance, by which the
hydra attaches itself.

(c) Compare the structure of a bud with that of the parent
animal.

(d) Examine now the body of the animal; it is made up of
a transparent outer portion, the ectoderm, and an inner col-
ored portion, the entoderm.

Exercise 2. Make a detailed drawing, 2 to 3 inches long,
of an expanded specimen to show the above points and an
outline of a contracted one.

Pi UN GE RINAL Se RUCTURE

(a) Using a pipette, transfer a specimen to a slide. Put
on a cover, supported at one side only, by a very small piece
of clean filter paper which should first be dipped into water.
Examine with the low and, for the finer points, with the high

44. THE HYDRA.

power. Be careful not to crush. Make out the following
points, which can be done most successfully if the specimen
is well expanded. The transparent ectoderm will be found
to surround the colored entoderm and the latter to surround
a central cavity. Look for particles in this cavity. This is.
the enteron or digestive cavity. Is there anything to indi-
cate that the tentacles are also hollow? If so, are their cavi-
ties in free communication with the main enteron?

(b) Certain clear oval bodies, the nematocysts, are present
in the ectoderm. In what regions of the body are they found
and where are they most abundant?

(c) Projecting into the water near the nematocysts are
fine hair-like processes, so delicate and transparent they are
easily overlooked. They are called the cnidocils.

(d) Remove the bit of filter paper and press gently on the
cover with a needle until the hydra is crushed, and look for
large nematocysts with threads projecting from them. Com-
pare these with some that have not been discharged. Look
for nematocysts embedded in their cnidoblast cells, and for
the different types of nematocysts.

Exercise 3. Draw on a large scale the large barbed type of
nematocyst, as it appears before and after discharge. Size,
about 1 inch for diameter of bulb.

(e) Mount a fresh specimen under a cover and supported
with filter paper as before and observe the tentacles under
a low power as aqueous Safranin is run under the cover glass.
See if filaments are discharged and how they look when com-
pared with the ones seen above. Remove the filter paper
and with the high power make out the origin of these filaments.
Understand from your lectures and the text-book the use of
these organs. Recall the trichocysts of paramoecium.

Exercise 4. Draw one of the smaller types of nematocyst
before and after discharge. Size, proportionate to Exercise 3.

({) Prepare a fresh slide, supporting the cover with filter
paper as above, and see if you can discover cell outlines in
the ectoderm or endoderm of any part of the body. Review
with this specimen any other points you have in doubt.

THE HyYpDRA. 45

(g) Study prepared cross-sections of hydra. Note the large
central digestive cavity or enteron, also the body wall com-
posed of ectoderm and endoderm and between them a distinct
line marking the supporting lamella.

Exercise 5. Make a diagram of the entire section in out-
line only to show these facts. Size, 4 to 5 inches.

(h) Study under the high power and make out nuclei,
nematocysts, vacuoles, the lines of division between the cells
and any other details which may be found.

Exercise 6. Add these details of ectoderm and endoderm
to a small part of the section shown in Exercise 5.

(i) The shape of the individual cells will be much better
understood after studying the macerated specimens. To do
this, place a hydra on a slide with a very little water, and add
a drop of Bella-Haller’s fluid. After one or two minutes draw
off the fluid with filter paper and add a drop of strong aqueous
methyl-violet, which should stand about the same length of
time. Draw off the stain with filter paper, add a drop of
water, break up the specimen by a little teasing and put on
cover glass. Find the several types of cells. If necessary
separate the masses of cells still further by tapping very gently
on the cover glass with a needle. The large endoderm, the
large ectoderm, the interstitial, the gland cells of the endoderm
and the cnidoblast cells can be made out in the best prepara-
tions. Understand the position of the interstitial cells and their
relation to the cnidoblast cells.

Exercise 7. Draw a typical cell of each kind made out.

IV. SEXUAL REPRODUCTION

If specimens are available, study live individuals having
male and female organs and make drawings, also sections
showing eggs or young embryos in the ovaries and the testes
containing spermatozoa.

46 HyYDROID COLONIES.

V. GENERAL POINTS

Keep hydras for some days in a tumbler, or bottle, near a
window and with water fleas or other forms upon which they
may feed. Watch the process of catching and eating the
living prey. Watch hydras that are budding and see if the
buds separate and form new individuals. Get some way of
marking on the outside of the dish the place of the hydra’s
attachment and see whether it changes from day to day. Cut
several hydras into pieces and see if there is ‘‘regeneration.”’
In making this last experiment use a watch-glass which has
been thoroughly cleaned and cover with another, or a larger
glass dish.

HYDROID COLONIES
(OBELIA GENICULATA AND PENNARIA TIARELLA)

Hydroids are marine animals closely resembling hydra in
their plan of structure. Budding occurs extensively and the
buds instead of dropping off remain connected with the parent
stem, forming a colony. In many hydroid colonies there is
a “physiological division of labor’? between the units of the
colony so that some become nutritive and others reproductive
individuals. For the study outlined below specimens pre-
served in formalin will be used. |

(a) Examine museum specimens of Obelia geniculata to
determine the extent, attachment and mode of vertical and
horizontal growth of the colony. Examine several of the
vertical portions in a watch-glass of water with lens or low power
and note general resemblance to a budded hydra.

Exercise 1. Draw, ona scale of 2 or 3, a single one of these
vertical parts, showing how it arises from a horizontal stem.
So small a figure cannot, of course, show the details and is
to show only the main parts of the colony and manner of
branching.

HyYDROID COLONIES. 47

(b) Mount one or more of these vertical parts on a slide
in a drop of water, selecting with aid of an instructor one
which has formed its reproductive units. See that the speci-
men is properly expanded before putting on the cover, and
support the cover at one side with a bit of filter paper. Notice
under low power the mode of branching and the individuals
of the colony, polyps, at the ends of the branches. Do you
find developing polyps or buds? Compare a single polyp
with a single hydra, noting mouth, hypostome, tentacles, ecto-
derm, endoderm and enteron. Each polyp is surrounded by a cup
formed from an extension of the transparent perisare which cov-
ers the stem of the colony. Are there any modifications of the
perisarc which would make it more flexible? The core of living
material within the perisarc is called the coenosarc. Can you
find any indication of ectoderm, endoderm and enteron in the
coenosarc of the stem? With what part of a hydra is the stem
comparable? How does food pass to a growing bud, or to the
horizontal extensions of the colony? The type of individual
most numerous in the colony and found toward the free ends
is the vegetative or feeding unit and known as a hydranth.

Exercise 2. Draw, on a large scale, a single hydranth show-
ing its connection with the main stem.

(c) Near the bases of the vertical stems are the reproduc-
tive polyps, the blastostyles and medusae. The former have
large cups of perisarc with a small opening at the free end,
and their core is a continuation of the coenosarc. They are
comparable to polyps without mouths and tentacles. They
produce, by budding, the peculiar polyps known as the me-
dusae. These medusae become detached, much as do the
buds of a hydra, as soon as they are fully formed and, pass-
ing through the small opening at the end of the cup, swim away
in the water. Examine a demonstration of these medusae of .
obelia. There are therefore three kinds of units in this col-
ony, all formed by budding: (1) Feeding polyps or hydranths,
(2) blastostyles and (3) medusae.

Exercise 3. Draw a single blastostyle showing its connec-
tion with the main stem, as in Exercise 2, and medusae in
different stages.

48 A Hyproip MEDUSA.

(d) Examine museum specimens of other hydroid colonies,
noting general shape and appearance, as determined by size
of the hydranths and nature of the perisarc. For detailed
comparative study, the hydroid Pennaria tiarella may be used.
Examine a branch of the colony in a watch glass with lens and
low power of microscope. How and where does budding
occur? How do the hydranths differ from those of obelia?
What is the relation of the ectoderm and endoderm in the
tentacles? Where are the medusae buds? How many kinds
of units are present in the pennaria colony when compared
with the obelia as explained in paragraph (c)? Compare these
two hydroids point by point and determine the relative amount
of specialization which the parts exhibit. On the whole, which
species would you consider the more highly organized?

A HYDROID MEDUSA (GONIONEMUS MURBACHI)

Since the medusae of obelia are very small we shall examine
a larger form, Gonionemus murbachii, which originates from
a hydroid colony* in a similar manner.

(a) Examine a specimen in a watch-glass under water.
Notice the numerous tentacles, the shape like a flat bell with
a clapper, the hypostome, and a shelf, the velum, projecting in
from the margin. The mouth is at the end of the hypostome.
We speak of oral and aboral sides, not of ventral and dorsal.
Protruding upon the concave oral surface are four convoluted
ridges, the reproductive organs, from which the eggs and
sperm are shed directly into the water. On the oral surface
above each reproductive organ is a radial canal, extending
from the central stomach to a circumferential canal at the
bases of the tentacles. These canals are a modification of the
simple enteron of an early stage in the medusa’s development.
Each tentacle has a core of endoderm arising from the circum-

*The life-cycle of gonionemus is not completely known, but a period of
budding comparable to the hydroid phase of obelia seems to occur.

THE EARTHWORM. 49

ferential canal and is covered with ectoderm, as is the entire
outer surface of the animal. At the base of each tentacle is
a colored eye spot. Examine the specimen in the watch-glass
from the aboral side under low power, looking along the cir-
cumferential canal for clear vesicles, the lithocysts or organs
of equilibration, and for small developing tentacles.

Exercise 1. Draw the medusa from an oral view. Size
about 3 to 4 inches across bell.

Exercise 2. Draw a vertical section in the plane of the
radial canals. Size the same as in Exercise 1.

(b) Much of the above can be understood completely only
in connection with the explanations in lectures and text-book.
Understand from these the structure of the medusa as com-
pared with the hydranth, and the “‘alternation of generations”
by which the medusa produces the hydroid colony and the
colony the medusa.

THE EARTHWORM (LUMBRICUS HERCULES)

PHYLUM, ANNULATA. CLASS, OLIGOCHAETA

Ey Gh EIVING CANINMAL

(a) Place a vigorous, active worm upon wet filter paper
in a dissecting pan and carefully observe the mode of locomo-
tion. How does it elongate and contract? Can you see stiff
spines projecting from the sides? Can they be drawn in? Is
there a rhythm in these changes? Draw the worm through
the fingers and feel the spines, or setae. How many are there
on one ring? Place the worm on its back. Does it right itself?
Will it crawl backwards? Compare the anterior and posterior
ends, the dorsal and ventral, the right and left sides. Which
are alike? Touch various parts of the worm to see which
seem the most sensitive. Note the movements of the soft lobe
above the mouth, the prostomium. On the mid-dorsal line

4

50 THE EARTHWORM.

look for the blood vessel which shows through the skin. Does
it pulsate? Which way does the blood move? Hold up the
worm to the light and see the dark central axis which is the
digestive tract with its contents. On the ventral side may be
seen light colored swollen areas, the skin glands. Those on
some segments may be associated with a smooth swollen band
passing around the animal, the clitellum. On the 15th seg-
ment, swellings mark out transverse slits on each side, the
openings of the vasa deferentia or ducts for the discharge of
sperm. On the 14th segment in a similar position are the two
very small openings of the oviducts. Count the entire number
of segments or somites and record result, comparing with
counts in neighboring specimens.

Exercise 1. Draw the anterior end, as far back as a point
just behind the clitellum, on a scale of 2 or 3 and from a ven-
tral or a side view. 3

Exercise 2. Draw the posterior end on same scale, showing
about 10 or 12 segments and from a ventral view.

Il. GENERAL INTERNAL STRUCTURE

(a) For this, study a freshly killed or a preserved worm.
Fasten down in a dissecting pan, dorsal side up, by pinning
through the first somite and again toward the posterior end.
Make an incision about one and one-half inches long, just
back of the clitellum and on the mid-dorsal line, but do not
cut too deep. Using fine scissors cut toward the head end
with great care not to cut deeper than the wall of body and to
keep on the dorsal mid-line. Spread out the edges of the cut
body wall and pin them apart after breaking the transverse
partitions, septa, which connect the inner face of the wall and
the outer surface of the gut. Slant the pins outward to give
room for fingers and instruments in working.

(b) You will now be able to see the brownish intestine and
on its upper surface the large dorsal blood vessel. ‘Toward
the head, the gut becomes differentiated and is partly hidden
by other organs which will be indicated presently. The skin

THE EARTHWORM. 51

is made of two layers, the outer, colored part is the real skin,
the white inner part is the muscle; both together form the
body wall. Between the body wall and the digestive tract is
a space, the body cavity or coelom. Thin lines pass from the
digestive tract to the body wall across the body cavity. With
a hand lens and a needle one may see and feel that these are
the partitions, or septa, dividing the body cavity into cham-
bers one behind the other. What is the relative position of
septa and external rings?

(c) Continue the cut forward through the second anterior
ring. Carefully separate the edges of the cut and see the dif-
ferent regions of the digestive tract. Identify the following:
pharynx, oesophagus, crop, gizzard, and stomach-intestine.
In the sexually ripe animal there are large yellowish-white
lobes on certain rings; these are the three pairs of seminal
vesicles. They more or less hide the oesophageal region of
the digestive tract. There are five pairs of large lateral blood
vessels, the hearts, which in the living animal may be seen to
pulsate. On top of the digestive tract in segment 3 is a small
white body, the brain. Spread out the body wall right and
left and pin it to the wax, slanting the pins obliquely outward
as before. In doing this break or cut some of the septa with
a needle or scissors. How do the anterior septa differ from
the others? Have they any different use? In all but a few
of the anterior chambers of the body cavity there are paired
fluffy masses on each side.’ These are the nephridia or excre-
tory organs. With a lens look for fine blood vessels on these
organs. Turning a part of the intestine to one side you may
see these fine vessels connected with a median ventral vessel.
Beneath the median ventral vessel is a large band, the nerve-
cord. Cut the specimen open for its entire length and care-
fully separate the various organs to see them more clearly.
Which segments are differentiated? Which ones merely
repetitions of similar organs?

Exercise 3.. Make a full page diagram of the region from
prostomium to beginning of stomach-intestine to show all the
organs thus far made out. The length of the segments may

52 THE EARTHWORM.

be exaggerated and the organs drawn as if separated by dis-
section.

(d) Lift up the oesophagus with forceps, carefully cutting
its attachment to the septa. Cut it across near the pharynx
and pull it gently back, while cutting off the septa. How are
the seminal vesicles placed with reference to the gut? Be
careful not to remove the seminal vesicles from the worm while
continuing to pull back the digestive tract and to cut the
septa. Continue this as far back as the beginning of the stom-
ach-intestine and so lift up and remove from the worm the
oesophagus, crop, gizzard and part of the intestine in one piece.
Examine this removed portion of the tract under water and
correct any errors in your previous drawing. Find the cal-
ciferous glands, three pairs of lateral pouches on the oesopha-
gus in the region hidden by the seminal vesicles. Cut open
lengthwise, wash out and note the character of the lining and
contents in each region of the tract. If a preserved specimen
has been used, set aside the undissected portion for the sub-
sequent work.

Iii. COELOME AND NEPHRIDIA

(a) Cleana slide and cover and, with the aid of an instructor,
draw out a drop of the coelomic fluid by means of a capillary
pipette. Place immediately upon the slide, adding salt solution
if necessary, and examine under high power. Find the white
corpuscles. What are their characteristic activities? What
organism do they resemble? Have they nuclei?

Exrcise 4. Draw, showing characteristic shapes. Size,
1 to 2e inches across cell.

(b) Using the preserved specimen dissected under Section
II, cut out with fine scissors part of a septum with nephridium
attached and examine under low and high power. The ne-
phridium is a convoluted tube with interlacing blood vessels.
In the larger muscular part there may be parasitic worms.
Look for the ciliated funnel, or nephrostome. Understand
the function and manner of action of the nephridium. With

THE EARTHWORM. 53

the aid of an instructor, obtain a bit of a living nephridium,
or better, one that is complete. Look for the peculiar flick-
ering movement of the cilia within the tubule and study this
with the high power.

Exercise 5. Draw the nephridium in whole or in part as
observed.

bys THE REPRODUCTIVE ORGANS

(a) Using the specimen dissected in Section II, wash off
the region of the reproductive organs by gentle currents from
a pipette and examine the posterior face of the septum between
segments 12 and 13. Under a hand lens the two ovaries may
be seen lying one on either side and near the nerve-cord. Im-
mediately behind each ovary is an oviduct, seen as a whitish
area on the front face of the septum between segments 13 and
14, and in segment 14 as a fine cord which is very short and
passes diagonally outward to its place of exit on the ventral
body wall. Locate these parts without much pulling away of
the remains of septa and nephridia and then make them more
clear by gently pulling or cutting any tissue which renders
them obscure. Examine a model and understand how the
eggs pass from ovary to oviducts.

(b) Examination of the seminal vesicles, which should
still be uninjured, will show that the three lobes which extend
up on either side of the oesophagus are united by a common
median region which lies below the gut and against the ven-
tral body wall. A little picking away of this middle region
will disclose four large bodies, rather indistinct in outline,
but different in texture from the vesicles and resembling
crumpled bits of paper. These are really greatly modified
funnels which lie at the beginning of the male ducts, or vasa
deferentia. Looking on the ventral body wall and outside
the seminal vesicles, it is possible to find a fine duct running
out laterally from the region of each funnel. The two on a
side unite and pass straight back to the opening of the vas
deferens on segment 15. By means of these funnels and ducts

54 THE EARTHWORM.

the sperms pass out of the seminal vesicles. The sperm fun-
nels really open within the closed cavity of the seminal ves-
icles. The sperms originate from bodies somewhat similar
to the ovaries and in the same relative position in segments
10 and 11. Although these bodies, which are the true testes,
are immediately in front of the sperm funnels, the sperms
upon dropping from the testes do not at once enter the fun-
nels, but pass up into the lobes of the seminal vesicles where
they develop to mature spermatozoa, which are then ready
to enter the funnels and vasa deferentia and so pass to the
outside. The four testes and the four funnels have there-
fore a relation to the coelome similar to the ovaries and their
oviducts, while the seminal vesicles by enclosing both testes
and funnels in a common cavity prevent the spermatozoa from
entering the coelome and furnish a place for their later develop-
ment.

(c) The seminal receptacles, which should not be con-
fused with the seminal vesicles, are small whitish bodies at-
tached to the ventral body wall on either side in the region
of segments 9, 10 and 11. They open to the outside only
and their function is to retain the spermatozoa derived during
copulation from another worm and which fertilize the eggs
of this individual.

Exercise 6. Consult a model, or reference figures of the
entire system, and then construct a semi-diagrammatic figure
which will show all these parts. Review their relationships
by tracing the course of the ova and spermatozoa from their
origin to the external openings of oviducts and vasa defer-
entia.

(d) Carefully cut out one of the ovaries and transfer to
a slide. Add a drop of glycerine, put on a cover and study
under the low power. The ova will be seen in various stages
of development. Where are they most advanced? The
largest ones show clearly a nucleus and nucleolus.

Exercise 7. Make a drawing 2 or 3 inches in length show-
ing the entire ovary.

(e) Understand from lectures and text-book the function-
ing of the various parts in copulation and egg laying. Exam-

THE EARTHWORM. 55

ine again in a whole worm the clitellum, the markings which
extend forward from this to the openings of the vasa defer-
entia and the external openings of the oviducts.

Ve NERVOUS SYSTEM

(a) Lift the pharynx with forceps and cut off the muscles
that connect it to the body wall. Trace the connections
between the brain and the ventral nerve-cord and look for
nerves from the brain and from the collar-like connectives
around the oesophagus. Determine the number and place of
exit of the nerves arising from the ventral cord in the region
just back of the “‘collar’’ and in the body at posterior end.
Cut across the nerve-cord in the mid-body region and remove
a bit by tearing out with a quick pull of the forceps. This
piece may help you determine the number of nerves per seg-
ment. —

Exercise 8. Make a diagram of the nervous system from
a dorsal or a lateral view. Scale of 3 or 4.

Win DRANSVERSE, SECTIONS

(a) Cut transverse sections of an alcoholic specimen about
one segment in thickness, using a sharp pair of scissors. Study
under water with the hand lens and make out the position of
gut, coelome, nephridia, septa, nerve-cord, blood vessels, etc.
Can you distinguish the different layers of the body and gut
walls? Notice the typhlosole, a fold of the dorsal wall of the
gut. How may it be of importance in digestion and absorp-
tion?

Exercise 9. Make a drawing, about three inches across,
which will show the relative position and thickness of the
various parts. |

(b) Study the permanently mounted sections of this same
region. Examine first with the hand lens and then with the
low power to make out the appearance of the parts in such a

56 THE EARTHWORM.

section. Then study the cellular structure of each part with
the high power.

(c) Inthe body wall there are four cellular layers. 1. The
epidermis, composed of short columnar epithelial cells, some
of which are gland cells, in various stages of activity. Cov-
ering the outer surface of all these cells is a continuous mem-
brane, the cuticle, of non-cellular nature and produced as a
secretion from the epidermis. 2. A layer of circular muscles,
here cut lengthwise. Are there nuclei and blood vessels
among these? 3. The thickest layer is a series of longitudi-
nal muscles, cut transversely, and so arranged as to have a
feather-like appearance when the groups of fibres are seen in
this plane. 4. The innermost layer is the lining of the body
cavity, or peritoneum, which may show cell outlines and nuclei
in favorable sections.

(d) In the intestine there are three chief layers. 1. The
innermost of elongated, very narrow cells, the mucous mem-
brane. 2. The outermost, a granular mass that may be
resolved into a layer of large cells, the chlorogogue cells.
3. The middle, a narrow band of muscle fibres, both longi-
tudinal and circular. Are there any blood vessels? Any
cilia? The typhlosole will again be recognized. What is the
condition of these three layers in this region of the gut? Blood
vessels, nephridia and septa cut at various angles may require
some careful study in your particular section. Try to under-
stand these parts and why they appear as they do in any one
section.

(e) Examine the structures which appear in the coelome and
interpret them in terms of the organs seen in this region during
your dissection.

Exercise 10. Draw on a large scale a narrow section of the
body wall to show a small portion of each of the foregoing
and on the same page a similar portion of the intestine to be
located in the right position relative to the body wall. Add
anything made out in the coelom.

(f) Study the nerve cord in the above section and note
the outer layer containing muscle fibres, the three large clear

THE CRAYFISH. oi

dorsal areas or “‘giant fibres,” the fibres of the main mass, and
the position and structure of the ganglion cells. Understand
from lectures or text-book the nature of the connections
between the cells of the nervous system.

Exercise 11. Make a drawing of the nerve-cord in section,
about 2 by 3 inches.

THE CRAYFISH.

PHYLUM, ARTHROPODA. CLASS, CRUSTACEA

Pe EOCAL, SEECIES

Two species of the genus Cambarus are commonly found in
this vicinity. C. virilis is the more abundant and is the form
seen in such numbers in the streams and ponds about Colum-
bia throughout the open months. C. gracilis, one of the bur-
rowing crayfish, is seldom found in the open water except dur-
ing February and March, when the females come from their
burrows along the banks of creeks and ponds and may be seen in
in the water with their young. By the latter part of March
these have returned to their burrows, but the young may still
be found in the open water until the end of May. The pres-
ence of C. gracilis during the remainder of the year is however
much in evidence from the “chimneys”? which the animal
builds around the air holes of its burrows. These openings
are very common in moist ground and are often found at a
surprising distance away from any body of water.

i) tee LIVING CRAYFISH

(a) Watch live crayfish in shallow pans or aquaria and
study their manner of swimming and walking. How sensitive
are they to touch? By passing your hand across a short
distance above the specimen, see if it shows any sign of an

58 THE CRAYFISH.

acute sense of sight. Try this again with a specimen out of
water. Place a specimen on its back in the water or on a
table and determine the acuteness of its sense of equilibrium.

(b) Put some carmine in the water and see if you can
detect any currents flowing in a definite direction in the vicin-
ity of an animal when it remains quiet for a short time.
Selecting a small individual, or one having a very clean shell,
look on the outside of the body just above the great claw and
and in line with the eye and see if you can detect a flickering
motion, as though something were moving. beneath the semi-
transparent shell. Recall this observation later when you
come to study the gill chamber. Keep a specimen out of water
for a few minutes and note the bubbles which come from the
front part of the body when it is again placed in the water.
Do they come from a definite place on the body? You should
be able to give an intelligent explanation of the facts noted in
this paragraph after you have studied the gill chambers of
the animal as outlined in section IV of these notes.

(c) Observe crayfish as they remain undisturbed in aquaria
containing stones or other objects. Can you tell what deter-
mines the particular places which the animals occupy. Drop
small pieces of fresh meat into these jars and watch the result.
In some of the jars several small fish may be placed and the
result watched at this and the next laboratory period. Observe
crayfish in the large tanks or in nature and note any habits of
concealment and also their mode of swimming.

li GENERAL EXTERNALLY PBA URES

(a) For this study a good sized specimen may be killed with
some anaesthetic or a preserved specimen may be used. Com-
pare the anterior and posterior ends, the dorsal and ventral
and right and left sides. Is there any departure from a strict
bilateral symmetry? Examine the pairs of limbs from the
posterior to the anterior end. Is the whole animal covered
by a dense shell? What parts are moveable? How many
divisions in the posterior part, so-called abdomen?

THE CRAYFISH. 59

Exercise 1. After looking carefully at the proportions of the
‘body, draw on a scale of 1 the outline of an ideal cross section
through the abdomen to show the shape of the dorsal and ven-
tral parts of the shell and the shape and attachment of the
paired limbs. Do not actually cut across the specimen, but
make the figure as it would appear if cut across.

(b) Find the mouth and anus. Note the round openings
on the bases of the longest feelers (second antennae), they are
the openings of the kidney-like green glands. Find on the
‘dorsal face of the small first antennae the clear flat areas which
mark the position of the lithocysts or organs of equilibration.
Examine the bases of the walking legs for openings; they are
found on the last pair in the male and on the second from the
last pair in the female. In the male of C. virilis the two first
pairs of abdominal appendages are modified to form, when
pressed together, a copulatory organ along which the sperms
pass after leaving the male openings. What is the condition
of the corresponding appendages of the female? Place a male
and a female side by side and note the difference when they are
viewed from the dorsal side. The body of the crayfish consists
of three regions, head, thorax and abdomen. Can you find
anything on the dorsal side which might indicate the line of
division between the head and thorax?

IN rte EleUuS AND GILEL-CHAMBERS

(a) Note how the shell, carapace, extends from the back
down over the bases of the walking legs. Lift up the free
ventral edge and see the spongy mass formed by the gills or
branchiae. Taking care not to injure the gills and using your
strong scissors, remove the overhanging shell from the left
side, thus exposing the full extent of the gill cavity, but do not
cut too far dorsally and injure the organs on that side of the
body. Cut off the walking legs and large claw, chela, of this
side a short distance from their insertion. Place the specimen
under water in a dissecting dish and by floating up and care-
fully parting the mass of the gills get an idea of what a single

60 THE CRAYFISH.

gill is like and where it is attached to the body. Move the
stumps of the legs and see how the outer gills are related to
them. How many of these outer gills are there? To what
appendages are they attached? What effect do you think the
animal’s walking would have upon respiration? What struc-
ture do you find at the place where you saw the flickering move-
ment under the shell of the live specimen? Back of this
‘““bailer’”’ is another, more delicate, blade which you will identify
later as the epipodite of the first maxilliped.

(b) Put together all you know about the gill cavity and its
contents, the water currents you have seen in the vicinity of a
quiet animal and explain how the gills are always bathed with
a constantly changing supply of water.

(c) These outer gills are called podobranchs. Note the
significance of the name. Keeping the specimen entirely
under water and lifting the podobranchs one at a time to be
sure you do not destroy any of the smaller gills which lie close
beneath, remove all of the podobranchs by cutting them off
close to their attachment. Cut one across the middle with
scissors and examine the section under water with a hand lens.
You should see the incurrent and excurrent blood vessels cut
across where they run close together.

(d) The inner layer of gills is now exposed. Are they
attached to the feet? There are five pairs and a single one in
front. Opposite which of the appendages are these gills
located? They are called the arthrobranchs (joint gills.)
Note again the significance of the name.

(e) In the lobster there is another layer of four gills lying
beneath the arthrobranchs. Because they are attached higher
up and on the sides of the body these last are termed the
pleurobranchs (side gills). The common European crayfish
from which the descriptions in most text-books are taken
possesses a single pleurobranch, but in the adult of our C.
virilis even this has disappeared. Examine museum specimens
of the lobster dissected to show the three kinds of gills.

Exercise 2. Make an outline of the cephalothorax in a side
view, on a scale of 2. Show the stumps of the appendages and

THE CRAYFISH. 61

the places from which podobranchs have been removed. Putin
all the arthrobranchs and show also the “‘bailer’’ and the epi-
podite above noted. Indicate the course of the water current
by arrows.

(f) Examine specimens macerated in caustic potash and
notice the delicate chitinous covering of the gills which has
survived the maceration. Are the gills inside or outside the
body? In answering this question imagine how they would
look in a cross section of the animal in the thoracic region of
the body.

VO INGERNAL ANATOMY

(a) Using a freshly killed specimen, cut with large scissors
along the dorso-lateral surface on either side of the cephalo-
thorax, taking care not to injure any of the organs lying imme-
diately beneath the skeleton. Remove this dorsal part of the
skeleton from the posterior margin of the thorax to a point
just back of the eyes. Place the specimen in a dissecting dish
and having it entirely covered with water identify the follow-
ing: The tops of the gills, which are exposed where you have
cut into the gill cavity, are seen on either side. The heart
which may be still beating lies between these on the mid-line
in a cavity known as the pericardium. It is soft and spongy
in its consistency and you should be able to distinguish the
paired openings, ostia, which lie upon its dorsal surface. How
many are there? The gastric mill or gizzard lies well to the
front and is roughly triangular. Note its thin and delicate
walls and the two transverse bars of harder material, by which
its walls are strengthened. When the specimen is intact
muscles pass from each of these bars, or sclerites, to the inner
face of the dorsal skeleton. Find the remains of these muscles
still attached to the shell which you removed, and also to the
posterior sclerites. If the carapace has not been removed too
far forward you should be able to see the muscles arising from
the anterior sclerite and attached to the inner face of the shell
just behind and between the eyes. These muscles form a part

62 THE CRAYFISH.

of the complex system by which the grinding of the gastric
mill is brought about. Passing through the pericardium are
large muscles which diverge as they pass forward. If these pull
on their forward ends as the fixed point, what movement will
they bring about in the abdomen? You can answer this if you
understand how the segments of the abdomen are articulated
to one another. For this see specimens macerated in caustic
potash. The appearance of the region between the heart and
gizzard differs with the sex and sexual maturity of the speci-
men. In a female, with well developed ovaries, these latter
organs are seen as a bi-lobed mass in front and a median mass
behind the heart. In a male the testes are less conspicuous,
but have the same general ‘‘Y’’ shape. In specimens which
are immature or which have recently shed their eggs or sperms
the organs are quite inconspicuous and need not be noted for
the present. The digestive gland which is of a yellowish green
color in a freshly killed specimen will be easily made out, but
in specimens with large ovaries it may be crowded almost
out of sight and only found by pressing aside the latter organs.

(b) Cut off the tops of the gills, sever the extensor muscles
of the abdomen at the level of the heart, cut back along either
side of the abdomen as far as the telson and remove the dorsal
skeleton of this region. The abdominal extensors will be found
as two thin bands of muscle lying close under the skeleton.
They may be taken off with the skeleton, though you should
be careful not to tear away anything else. The intestine will
now be seen in the abdominal region along the mid-line. Be-
neath and to the sides of the intestine are masses of muscle,
which by their combined action flex the abdomen. Compare
the bulk of these flexors with that of the extensors. Why
should there be such a difference in the size and hence the
power of these muscles? Lying on top of the intestine you will
perhaps make out a very small transparent thread, the dorsal
abdominal blood vessel. At the anterior end of the abdomen
the median portion of the reproductive organs may be found
or, if these are immature, the posterior ends of the digestive
glands.

THE CRAYFISH. 63

Exercise 3. Make an outline on a scale of 2 or 3, of the
cephalothorax and abodmen. Put into this the organs asthey
now lie in place.

(c) Remove the heart and look for ostia on its ventral sur-
face. Note the “Y” shape of the reproductive organs and find
their ducts leading to the external openings before noted.
Remove the reproductive organs, being careful not to injure
the digestive gland or the intestine. Trim off more of the gills
and pull away the portions of the abdominal extensors which
remain in the thorax. Make out the connection of the gizzard
with the intestine and the antero-posterior extent of the
digestive glands. Cut in from one side and find the oesopha-
gus; it is very short and can be best located by noting again the
position of the mouth. Trace the intestine to its posterior end,
cut off close to the anus and carefully free it up to its union
with the gizzard, also free the digestive glands. Cut across
the oesophagus and remove the entire digestive tract and its
appended glands in one piece. Float out in water, and cut off
the left digestive gland close to the tract. Note the region
between the gastric mill and the intestine. Open the gizzard
along the ventral mid-line, find the teeth, work them together
and see how they grind.

Exercises 4. Draw a side view from the left, showing the
tract and the right gland in position and the place where the
left one opens into the tract.

(d) To study the Nervous System, carefully remove all
the muscles and viscera from the abdomen and the ventral
nerve cord will then be seen lying on the mid-ventral line.
Notice the ganglia. How many do you count? Notice the
lateral nerves. How many of these? In the cephalothorax
the nerve cord is concealed beneath transverse ridges of the
ventral wall of the shell. Cut these with heavy scissors and’
expose the nerve cord, beginning at the hinder end of the
cephalothorax and working forward. How many thoracic
ganglia do you find? Just back of the oesophagus is the large
sub-oesophageal ganglion, which is connected with the brain
by two connectives passing around the oesophagus. The

os

64 THE CRAYFISH.

brain or supra-oesophageal ganglion is just behind the eyes.
Find the nerves passing from the brain to the eyes and to the
two pairs of antennae.

Exercise 5. Draw a figure of the nervous system thus ex-
posed, showing accurately the number of ganglia made out,
the segments in which they lie and the number of lateral nerves.

(e) At the anterior end of the body, near their external
openings already noted, find the excretory organs or “green
glands.”” Show the position and shape of these by a dotted
outline added to Exercise 3. The thin bladder and underlying
glandular portion of the organ can be readily distinguished.
Refer to text book for further details.

VI. THE APPENDAGES

(a) For this work use either a fresh or a preserved specimen.
In drawing take the appendages one at a time from the right
side of the animal and arrange each in such a way that when
completed all your figures will have the same orientation.
This is very important for your correct understanding of the
homologies between the various appendages. It is also impor-
tant that the parts of each appendage drawn be completely
labeled and that smaller ones be drawn on a scale of 2 or 3.

(b) There are all told 19 pairs of appendages. Beginning
with the abdomen, count the number of pairs in this region
of the body and compare them with the number of segments.
The last pair of these is called the uropods, “‘tail-feet’’, the
others the pleopods or swimmerets. Remove the right appen-
dage of the fourth abdominal somite by cutting close to the
body. A basal piece, the protopodite, bears two terminal
pieces, an inner endopodite and an outer expodite. However
markedly any of the other appendages may seem to differ from
this plan of structure, all can be shown to be derived from this
fundamental plan. The only exception is found in the case of
the first antennae.

Exercise 6. Draw the appendage on a scale of 3 placing it
with the end of attachment upward, the exopod to the right

THE CRAYFISH. 65

and the endopod to the left. Use this same orientation in all
your other drawings of appendages.

Exercise 7. Remove and draw on a scale of 3 the uropod
of the right side. Label its parts and orient as in the last.

(c) Note again the difference in the two anterior pairs of
abdominal appendages in the two sexes. A study of the em-
bryology shows that they are all formed by the modification of
the type above explained.

(d) The thorax has eight pairs of appendages as follows:
Four pairs of walking legs or pereiopods, the great claws or
chelae and three pairs farther forward which will be examined
presently. Remove the right fourth pereiopod and the right
chela being sure to get all of the seven and the six parts of which
they respectively consist. In the pereiopod the two proximal
parts represent a divided protopod while the remaining five
are divisions of the endopod. In the embryo an exopod is
present. The great claws are like the two anterior pairs of
pereiopods save for the union of two of the divisions. Can you
find where this has occurred? Note the simple modification by
which the nipper is formed on the chela.

Exercise 8. Draw this pereiopod in the same orientation as
your previous figures and show by a dotted outline the position
the exopod would have if present.

(e) In front of the great claws are three pairs of appendages,
known as the maxillipeds (jaw feet). The most posterior pair,
or third maxillipeds, are large and easily recognizable. Before
removal, the right hand member of this pair should be com-
pared part by part with the walking leg just examined. It has
the same parts except that an exopod is present and at one
point two of the segments have fused to form a single one as
inthe chela. This third maxilliped is a very important append-
age from the fact that it still has the fundamental plan and so
can be compared with the simpler abdominal appendages, while
the structure of its endopod shows how we may interpret the
adult structure of the walking leg.

Exercise 9. Draw this appendage oriented in the same way
as the others, on a scale of 3.

5

66 THE CRAYFISH.

(f) Examine, without removing, the second maxillipeds
which lie in front of the third. They will be found to have
parts similar to the latter. They should be removed with
care not to destroy the first maxillipeds which lie close in front
of them. Identify, as before without removing, the parts of
these first maxillipeds. There is a large epipodite which lies
in the gill chamber just behind the bailer. Protruding toward
the mid-line are two thin flaps which are an outgrowth from
the protopod, and at about right angles to these are two other
projections which are the exopod and endopod. Which is
which?

Exercise 10. Remove the right one and draw on a large
scale, orienting it properly. :

(¢g) In front of the first maxillipeds are two pairs of maxillae,
the parts of which should all be identified before the attempt
is made to remove either one. The posterior or second max-
illae, have a four cleft protopodite, a delicate endopod and an
exopod which is fused with the epipodite so that it looks like
a forward continuation of the latter. What is the function of
the fused exopod and epipodite? Before this appendage is
removed the parts of the first maxilla should be identified.
This smallest of all the appendages consists of three parts, the
endopod and a bi-lobed protopod. Which is which?

Exercise 11. Remove the right second maxilla and draw
properly oriented and on a large scale.

Exercise 12. Remove and make a similar figure of the right
first maxilla.

(h) The mandibles will now be exposed. Against their
posterior surfaces are a pair of lobes which are not true append-
ages. Each mandible consists of a heavy basal portion on
the median side of which is located the cutting edge which is
shown by the embryology to be a development of the protopod —
and which is comparable to the more delicate median out-
growths on the first and second maxillae. The three-jointed
palp which protrudes from the heavy basal piece has its proxi-
mal joint formed from the protopod and the other two from
the endopod. The exopod is wanting in the adult. Where
would it be if it were present?

THE MUSSEL. 67

Exercise 13. Remove and draw the mandible of the right
side properly oriented and on a scale of 3.

(i) The second antennae will show, when examined in place
on the specimen, the typical exopod, endopod and protopod
and the opening of the green glands.

Exercise 14. Remove the right one of this pair, orient, and
draw on a scale of 3 to show these points.

(j) The first antennae, or antennules as they are sometimes
called, are the only ones which do not show a real division into
the three fundamental parts, although their two terminal
portions would at once suggest the endo- and exopod. Remove
one and examine more carefully the region of the lithocyst or
organ of equilibration.

THE FRESH-WATER MUSSEL

PHyLum, Mo.iusca. Crass, LAMELLiBRANCHIATA

i HAbIPALT, ACTIVITIES AND EXTERNAL
RE AVE URES

(a) The fresh-water mussels or clams are represented in the
Mississippi Valley by many genera and by species which are
numbered in the hundreds. They occur most abundantly
in running water, but some species are more common in ponds
and sloughs. For the most part, the species resemble one
another to such an extent in their general structure that the
following notes may be used for any one of a number of forms
likely to be used for laboratory work. If specimens are avail-
able, examine the shells of several representatives of a single
genus and compare them with one another and with the species
in another genus. Try by doing this to get a more concrete
idea of what is meant by a genus and a species. Of late years
the shells of these mussels have assumed a considerable com-

68 THE MUSSEL.

mercial importance in the manufacture of fresh-water pearl
buttons and, as a by-product, of the lime grits used for chickens.
There have thus come into existence common names for all
the easily recognizable species a few of which are given below.

Quadrula ebena, the nigger head.

Q. pustulosa, the warty back.

Q. metanevra, the maple leaf.

Lampsilis ligamentinus, the mucket.

L. anodontoides, the yellow back.

L. rectus, the black sand shell.

Symphynota complanata, the hatchet back.

(b) _ Before adding the title to any of your figures, the spe-
cies you have been dissecting should be identified, either by
consulting a collection of named shells, or with the aid of an
instructor.

(c) The points which can be observed by study of the liv-
ing animals are better appreciated after one becomes familiar
with a pair of shells. Examine such a pair. They are right
and left. The hinge is dorsal, the gape the ventral side of the
animal. ‘“‘Lines of growth’? mark the outer surface. These
indicate periods of active, alternating with slower growth.
What is the oldest part of the shell judging by these lines?
This part is called the umbo. A line drawn through the umbo
and at right angles to the long axis of the shell will divide it
into distinctly unequal parts. In all species the smaller of
these is anterior. Some species show bands of different color
radiating from the umbos, others have protuberances or ridges
of various sorts on the shell. Why are shells very commonly
eroded at the umbos?

(d) Having thus oriented the shell, note other more detailed
points. Has the hinge more than one layer? Examine the
edge of a piece of broken shell showing three layers, the peri-
ostracum on the outside, the prismatic layer, and the mother
of pearl. What is their relative thickness? Can you find any
lines of growth which will give a clue as to how the shell grows
in thickness? A demonstration of the prismatic layer will be
found at the centre-table.

THE MUSSEL. 69

(e) Inside are teeth which lock tightly when the shells
are together. What function may these have? Good sized
markings indicate the places of insertion for the anterior and
posterior adductor muscles which pull the valves together.
Since there are no muscles which can pull the shells apart how
might this be accomplished. Shells specially prepared to
demonstrate this will be at the centre-table.

(f) There are other muscle scars considerably smaller, but
easily recognizable. They mark the insertion of muscles which
move the foot as will be seen later. They are the posterior
retractor scar, above the posterior adductor; the anterior
retractor, which is posterior to the anterior adductor; and the
protractor, which is a short distance below the anterior retractor.
Extending from one adductor to the other and parallel to the
margin of the shell is a marking known as the mantle line.
This is the so-called ‘water line,’’ often seen in fresh water
pearl buttons of the larger sizes. What can you make out at
the edge of the shell regarding the three shell layers?

Exercise 1. Draw, on a scale of 1, the outer surface of the
right valve with its dorsal margin toward top of page. Below
this the inner surface of the left valve should be represented
in the same orientation. In beginning the figure, put the right
valve down on the paper and trace the two outlines about it.
Show all the points of the foregoing section which can be repre-
sented. Care is necessary in properly representing the exter-
nal lines of growth. |

(g) Test for yourself, or by examining the results of a dem-
onstration at the centre-table, determine the effect of acid
upon the substance composing the shell and also the effect of a
strong alkali like caustic potash. Of what is the shell com-
posed? What reason is there for the fact that heavy shelled
mussels are abundant only in regions of limestone rock?

(h) Living mussels should now be studied in large aquaria,
or in individual dishes with enough sand on the bottom to
allow the clams to bury themselves readily. Lampsilis sub-
rostratus, a small pond form, is admirable for this purpose and
may be examined in a finger bowl. Place the mussel on its

70 THE MUSSEL.

side and watch it begin burrowing. The fleshy organ which
can be protruded from between the antero-ventral margins of
the shells is the foot. How does the animal make its way
down into the sand or move about? The fleshy membrane
exposed between the slightly gaping valves is the mantle.
In a specimen which lies undisturbed on its side or one which
is embedded in the sand, can you see openings between the
right and left sides of the mantle at the posterior end of the
animal? Are there papillae along these openings or elsewhere
along the mantle margin? Touch parts of this region very
gently with a needle and determine its sensitiveness. Can you
distinguish any difference in the degree of sensitiveness between
the region of these two openings, or siphons, and the part of
the mantle near the foot? In a quiet specimen, with the
siphons well open, watch for currents of water in and out of
the clam by way of the siphons. The existence of currents
may be demonstrated by dropping powdered carmine into the
water near the siphons with a clean pipette, or there may be
enough silt in the water to show the same thing. There is a
constant, though gentle, current in one siphon and out the.
other. Which is the inhalent and which the exhalent siphon?
When the mantle edge is strongly stimulated with the needle
note how the shells quickly close driving water out through
both siphons. By examining a number of mussels*which have
been left undisturbed for some days in an aquarium with sand,
determine the normal positions of the animals in their life on
the bottom. The water currents are of great importance to
the animal since in addition to the supply of water for respira-
tion they bring the entire food supply which consists of the
micro-organisms living on and near the bottom. How the
animal acts like a sieve which strains out the water and holds
the organisms will be explained when the internal organs are
examined.

(i) If the dish can be placed in sunlight, test the sensitive-
ness of the siphonal regions to light by casting a strong shadow
over this end of a well expanded specimen.

THE MUSSEL. Ta

Exercise 2. Such points in the foregoing as can be well
described in writing should be properly incorporated in your
laboratory book.

Il; EXTERNAL STRUCTURE*

(a) A specimen preserved in formalin, or one just killed
should be used for this. As the removal of the shell is not
easy for a beginner, you should have the aid of an instructor
for this preliminary step. Remove the right valve and study
the mussel from this right side as it lies in the other valve. You
will then have your specimen in the same orientation as the
drawings of the shell. When the shell has been removed, note
how the mantle everywhere conforms to its inner surface.
There will be no breaks in the mantle unless it has been muti-
lated in the removal of the shell. Find the ends of the follow-
ing muscles the scars of which you have already seen upon the
shell, anterior and posterior adductors, anterior and posterior
retractors and the protractor. Find the line on the mantle
which corresponds to the mantle line on the shell. The follow-
ing internal organs can be more or less definitely recognized
according to the species or the method by which the specimen
has been prepared: digestive gland, kidney, Keber’s organ,
and pericardium containing the heart. By consulting a chart
or blackboard diagram, understand their position even if you
are not able to locate them at this time in your own specimen.

Exercise 3. Make a figure of the mussel, as it thus lies in
the left valve of its shell and seen from the right. The removed
valve may be wiped dry and the first outline of the drawing
laid down by tracing around it.

(b) The space enclosed between the right and left halves
of the mantle and in which the foot lies, is the mantle cavity.
Without tearing or cutting, find how the incurrent siphon com-
municates with this and by lifting up the mantle edge get an
idea of the foot and the four plate-like gills, which extend from

*The features of the mantle surface and the organs in the mantle cav-
ity are really a part of the external surface of the animal.

42 Tue MUSSEL.

the sides and top of the foot to the region of the siphons. Look
carefully and see the line along which the outer surface of the
outer gill and the inner surface of the mantle meet. Find the
palps, a pair of organs on either side of the foot posterior to the
anterior adductor muscles and note their attachment to the
inner surface of the mantle. Remove now the right half of the
mantle by cutting from the middle of the incurrent siphon
along a line about one-fourth inch below and parallel to the
place where the gills and inner face of the mantle meet. At
the region of the palps care should be taken to leave these
organs intact. Continue the cut just below the anterior
adductor muscle and thus expose the organs of the mantle
cavity. Trim off to a neat outline the cut edge of the mantle,
without injuring gills or palps.

Exercise 4. Beginning with an outline made by tracing with
the right valve, construct a figure to show all of the above
organs, omitting for the present the structure of the region
above the cut edge of the mantle and the outline of the cut
edge itself.

(c) The structure and function of the organs concerned in
the water currents should now be studied. By looking into the
uninjured ex-current siphon the intestine ending in the anus
will be seen on the posterior face of the adductor muscle.
Extending beneath this adductor anteriorly, is a cavity into
which a bristle may be thrust for a considerable distance.
Being careful not to cut too deep, make an incision at the top
of the outer gill near the middle of its length and expose a
cavity running along the top of this gill. By gently probing
with the bristle, explore this cavity forward and back. How
does it end in either direction? With the bristle thrust in as
a guide, cut in either direction and expose this supra-branchial
cavity from the anterior end of the gill to its opening into the
cloaca, as the region just within the excurrent siphon is called.
Trim away the tissue on each side of the cut so that the whole
diameter of this supra-branchial cavity is readily seen. The
upper line of the cut edge should be made to pass along the
lower margin of the posterior adductor and end above the anus,

THe MUSSEL. 73

the lower cut edge should pass out to where the two siphonal
openings meet. The floor of this cavity is cut by a series of
transverse partitions inter-lamellar junctions separating cavi-
ties, the water-tubes of the gills. If the gill is not too much
shrunken you can pass a bristle down any of these water-tubes
to the ventral edge of the gill where it ends blindly. Making
a clean cut with the scissors at right angles to the water-tubes,
remove a piece of the gill and examine the cut edge under water
with a hand lens. The water-tubes and inter-lamellar junc-
tions will be seen cut transversely. It is in these water-tubes
that the young of the clam begin their development and you
may find the gill distended with embryos. By looking forward
from beneath the posterior adductor and gently exploring with
a bristle, you can see that the inner gill of this side and the two
gills on the other have each a supra-branchial cavity and water-
tubes as in the gill just examined. How would the four supra-
branchial cavities be connected with the cloaca if looked at
from the dorsal side? Sketch a diagram of this system of cavi-
ties as it would appear if viewed dorsally.

(d) You should now be able to understand how the water
current, from which the clam gets its food and oxygen and by
which its carbon dioxide and other wastes are carried out,
flows through the gills. Coming in by way of the incurrent
siphon the water freely bathes the organs of the mantle cavity.
From here it passes through microscopic openings, the ostia,
which lead from both inner and outer surfaces of all the gills
into the water-tubes. Passing upwards in the water-tubes,
it emerges in the supra-branchial cavities and passing backward
in these it reaches the outside through the cloaca and exhalent
siphon. The water which passes out has been strained of its
micro-organisms which are too large to pass through the ostia
‘of the gills. These organisms upon coming in contact with the
slimy surfaces of the gills, foot or mantle are entangled in the
mucus and carried by cilia along definite lines which finally
bring them between the palps and to the mouth which will be
found anteriorly below the adductor and between the continua-
tions of the inner and outer palps.

74 THE MUSSEL.

(e) Examine under the microscope a bit of tissue cut from
the gill of a living clam and one from the mantle and make
out the cilia on these surfaces. The ostia will be demonstrated
in stained sections of the gill taken in the same plane as the
rough sections previously made with scissors. Place carmine
or pieces of cork upon the gills or upon various parts of the
mantle surface of a living specimen and note the result.

Exercise 4 (continued). Add to your previous drawing
these details of the supra-branchial and cloacal cavities, taking
care to show the cut edges where they occur. Put in arrows
to show the course of the water currents.

(f) Why are we justified in speaking of the mantle cavity
as a part of the external surface of the animal?

Il. INTERNAL STRUCTURE

(a) The mantle, supra-branchial and cloacal cavities are
really portions of the outer surface of the mussel and only in
what follows are we dealing with organs which are internal in
the same sense as the viscera of a frog or other familiar animal.

(b) In the region above the gills and in front of the posterior
adductor is the pericardium. Make a small incision in its
wall and lifting with forceps cut the wall away exposing the
heart, consisting of a single median ventricle wrapped about
the intestine which traverses the pericardium, and of delicate
right and left auricles which lead from the sides of the peri-
cardial cavity. These last can probably be better seen if they
are floated out under water. The dark colored kidney will
be seen underlying the pericardium.

Exercise 4 (concluded.) Add to your figure the pericar-
dium as thus exposed and its contained organs. Show clearly
the cut edge of its wall.

(c) Lift up the outer gill and remove by cutting away the
inner wall of its supra-branchial cavity. Locate the supra-
branchial cavity of the inner gill and cut into this to expose
its full length. The dark color of the kidney will probably
show through the wall of this latter cavity, and well toward

THE MUSSEL. 75

the anterior end there will be found against this dark area two
small openings. They are not as easy to find in some species
as in others but can usually be located. The dorsal one of
these openings is the external opening of the kidney of this
side, the ventral is the opening of the reproductive gland or
genital pore. On the other side of the foot are similar openings
for the left side of the body. Note that the opening of the
kidney is thus into a cavity from which the water flows imme-
diately to the outside. The eggs upon leaving the genital pore
are fertilized by sperm which have been shed to the outside
water from an individual of the opposite sex and entered the
supra-branchial cavity of the female. After being fertilized
the eggs fall into the water tubes and there slat as far as
the larval stage, known as the glochidium.

(d) Begin at the anal end and dissect the intestine entirely
free from its union with the upper surface of the posterior
adductor muscles. Turn the specimen up on the ventral edge
of its shell so you can look into the pericardium from above and
by taking hold of the intestine and turning it over anteriorly
expose the extreme anterior end of the pericardium. Careful
probing with a fine headed bristle should reveal the opening
from the pericardium into the kidney. Push the bristle as far
back as it will go and thrust another finely tipped bristle through
the external opening of the kidney pushing it back also. Cut-
ting into the substance of the kidney will now reveal the fact
that one bristle lies in an upper and thin-walled, the other in a
dark colored and thick-walled cavity. Near the posterior
adductor these upper and lower limbs of the kidney unite.

(e) With the handle of a scalpel scrape the tissue of the
kidney away from the top of the foot and note the two posterior
retractors, the ends of which have been previously observed.
Still using the scalpel handle, free these from the adductor
muscle and the left one where it attaches to the shell. Can
you see why they are called retractors of the foot?

(f) Leaving the intestine intact and attached to the foot
and visceral mass (the term applied to the part of the body
which lies above the foot and is softer and less muscular than

76 THE MUSSEL.

that organ), continue with the handle of the scalpel and break
away the attachment of the visceral mass to the shell in the
region of the teeth, being careful not to injure the mouth.
Remove this part of the body from. the shell leaving the anterior
adductor behind.

(g) Before discarding the left valve with the posterior
adductor attached, look on the ventral surface of this muscle
for a yellowish body which is the fused right and left visceral
ganglia of the nervous system. Look for nerves extending
out from this. The pair of cerebral ganglia will probably also
be seen upon the ventro-posterior face of the anterior adductor
mussel. Indicate the position of these ganglia upon your
general drawing.

(h) Locate the anterior retractors and the protractors of the
foot and see why they are so called. Remove the palps and
any remains of mantle or gills from each side of the visceral
mass and then with a sharp scalpel split this mass and the foot
as nearly into right and left halves as possible, leaving the free
end of the intestine attached to the left half. Examine the
cut surface of the left half under water and pinned down in a
pan. The visceral mass will be seen to be composed of a pasty
mass, made up largely of the reproductive gland, in which the
coils of the digestive tract are embedded. Follow any of these
canals which are cut by the section. The flattened oesophagus
leads upwards to an enlargement of the stomach into which
the right and left halves of the digestive gland open. The
following out accurately of the digestive tract in any species
is a difficult piece of dissection for which a second specimen will
be supplied if you have additional time. The course of the
tract should be examined in text-book or chart figures.

(i) In the soft tissue just above the upper margin of the
foot and a little distance below the mouth, you will find by
gentle scraping, if they are not already exposed, the pair of
pedal ganglia. They are yellowish in color and of firmer
texture than the tissue in which they are embedded. Nerves
will be found running out from them. Show in your general
drawing the position of these within the substance of the vis-

THE MUSSEL. TL

ceral mass. Understand from lectures, text-book or charts,
how the three pairs of ganglia, you have noted, are united by
paired connectives and what parts of the body their nerves
supply. If you have time, a specimen will be supplied for a
special dissection of the ganglia and their connectives.

IV. THE EMBRYOLOGY AND PARASITISM OF
Pirie MUSSEL

(a) At certain periods of the year the gills of the mussel
are found distended with the glochidia which have been pre-
viously referred to. Examine in a watch glass of water some
of these glochidia just removed from a freshly opened mussel.
Note the two halves of the shell, the adductor muscle between
them and certain fine projections, the sensory hairs on the
inner surface. Are there hooks at any point on the shell?
Beyond the valves of the shell none of the organs of the adult
are visible. These embryos are shed from the mussel, by way
of the out-going water current, and scattered upon the bottom
where they must come in contact with the fins or gills of a fish
and fasten themselves there in order to continue their develop-
ment. After leaving the fish they have developed all the organs
of. the adult in miniature and can begin life on the bottom.
Watch the glochidia for any movements and record nature
of same. :

Exercise 5. Draw the glochidium on a large scale, as it
appears gaping open and also from a lateral view when closed.
The closure of all the specimens can be easily effected by adding
a few drops of waste alcohol or of methyl-green.

(b) Take now a considerable number of living glochidia
in a finger bowl of clean water and put into this one or two small
fish. Watch how and where the glochidia attach. If the
fish do not keep the water sufficiently agitated to prevent the
glochidia settling to the bottom it must be stirred gently.
After five or ten minutes take out the fish and put one into an
aquarium. Kill the other without pressing upon the gills or
fins and pin it ventral side up in a pan of water. Remove gills,

78 THE MUSSEL.

fins and tail and examine with microscope in a watch glass.
How and where are the glochidia attached?

Exercise 6. Draw one or more glochidia attached to the
gill or fin, and on such a scale as to make the larvae about one--
half inch in diameter.

(c) Make an estimate of how many glochidia there are on
this one fish, of how many were produced by the single mussel.

(d) The fish which were set aside after infection should
be examined at the next laboratory period and the condition.
of the glochidia with reference to the tissue of the fish deter-.
mined; or fish infected 24 to 48 hours previously may be pro--
vided for examination on the same day as the foregoing.
Record the condition of these glochidia and if you have time
make figures.

V. TRANSVERSE SECTIONS

(a) For a review of many points brought out by the fore-
going study the examination of sections, cut through a speci-
men from which the shell has been removed, is valuable. In
sections from the region of the heart, which are perhaps more
instructive than any others, the following structures should be
made out and compared with the conceptions and figures
already obtained; mantle, foot, gills, supra-branchial, mantle
and pericardial cavities, kidney, Keber’s organ, ventricle,
auricles and intestine. How is the shell related to the whole?
How does the water pass from the mantle cavity to the supra-
branchial cavities? Where are the water-tubes?

Exercise 7. Draw such a section on a large scale labeling
all the parts and showing the course of the water by arrows.

MIC) SEECTAL DISSECTIONS

(a) A second specimen may be used for a review of the
structures previously dissected and the more complete demon-
straction of the nervous and digestive systems. Remove the
shell and mantle of such a specimen, examining again any

CYTOLOGY. 79

points not previously made clear. Locate the cerebral and
visceral ganglia without cutting anything but the mantle. By
careful dissection, follow one of the two nerves, which may be
seen leading anteriorly from the visceral ganglia, to its union
with the cerebral ganglia. From these latter, three pairs of .
nerves arise; the pair of cerebro-visceral connectives just dis-
sected, a pair of mantle nerves, and the cerebro-pedal connec-
tives. Follow one of the last to its union with the pedal
ganglia and determine the number of nerves arising from the
latter. a

Exercise 8. Make a figure of the entire nervous system.

(b) This same specimen may be used for a dissection of the
digestive tract. To do this remove the entire animal (includ-
ing the two adductors) from its shell and pin out under water.
Begin at the mouth and dissect out the tract to show, oesopha-
gus, stomach, openings of digestive glands and coils of the
intestine. These latter must be exposed by removing the side
of the visceral mass which is uppermost and following with
care each part of the intestine as it is found.

Exercise 9. Make a figure of the entire digestive tract.

CYTOLOGY

Cy MITOSIS

The finer details of cell division must, of course, be studied
with the very highest magnifications. The more general
features may be examined with the high powers ordinarily
used in a course of this nature. Mitotic or indirect cell divi-
sion appears to be the common method by which cells divide.
The amitotic or direct mode of division seems to be of less
importance and its significance is still a matter of doubt. For
the study outlined below, sections of growing onion root tips
or the epithelium of salamander larvae may be used.

80 CYTOLOGY.

(a) Examine the sections with low power to understand the
relation of the parts, then with highest powers look for cells in
different stages of division showing the chromatic material in
the form of chromosomes. Examine chart or text-book
diagrams of mitosis and determine which phase of the process
is represented by each cell found in division. Determine, if
possible, the number of chromosomes in each cell.

Exercise 1. Construct six cell outlines for figures showing
consecutive stages. Then put in the nucleus as you find good
examples of the several steps in the process. Have the series
in order when completed, but do not try to find them in this
order. Rather, take representative cells as found insearching
over the slide and draw into their proper place in the series.

(b) The following terms have come into use for designating
the stages in cell division:

Prophase. The division and migration of the centrosome
and formation of the spindle, the assumption by the chro-
matin of thread-like aggregates which segment into chromo-
somes and the arrangement of the chromosomes into an
equatorial plate.

Metaphase. The lengthwise splitting of the chromosomes.

Anaphase. The divergence of the chromosomes into the two
daughter groups, and the division of the cytoplasm.

Telophase. The appearance of a nuclear membrane in each
daughter cell and the reconstruction of the nucleus to its typical
resting condition.

(c) See that all the structures indicated above are properly
labeled. Test your understanding. of the spacial relations.
of parts by seeing whether you can readily interpret sections
cut at irregular angles.

Il. MATURATION

(a) Demonstrations may be examined showing: (1) polar
bodies in superficial view and (2) the reduction divisions of —
the oocytes and spermatocytes in sections. Understand the
relation of this process and of fertilization to the number of
chromosomes and its universal occurrence.

ECHINODERM CLEAVAGE. 81

(b) Demonstrations of the accessory or ‘x’? chromosome
may also be shown. What relation has this chromosome to
sex? What happens to this chromosome in the reduction
division? In fertilization? Do you think we can properly
speak of this as a sex determiner?

Ill. FERTILIZATION

(a) Examine demonstrations showing the entrance of the
sperm and the conjugation of the male and female pronuclei
to form the cleavage nucleus.

CLEAVAGE AND GASTRULATION OF ECHINODERMS

THE EGG OF ASTERIAS OR ARBACIA.

The eggs and spermatozoa of many marine animals are laid
directly into the water where they meet in fertilization. Such
eggs are usually small, having but little yolk. They develop
rapidly into feeding larvae, which swim for a time, and then
take up the life of the parent upon the bottom. Because of |
the ease with which they can be provided with their normal
environment, these eggs are particularly favorable for experi-
mental studies and have become classic examples in the study
of fertilization, artificial parthenogenesis, cleavage, and the
like.

(a) Examine stained material permanently mounted or in
the clearing fluid, showing cleavage, blastula and gastrula
stages in the egg of the starfish or sea-urchin. Note the egg
membrane, sometimes showing the heads of many spermatozoa
which failed to enter. The two-, four-, eight-cell and later
cleavage stages on to the blastula or hollow sphere stage will
be recognized. Find stages of the blastula showing the ingres-
sion of mesenchyme cells at one pole. Is the wall of the

6

82 ONTOGENY OF AMPHIBIA.

blastula of uniform thickness? Can you tell from the first
the region that will invaginate to form the next stage, the
gastrula, in which the primitive gut cavity or archenteron
is formed. Its opening is the blastopore. The invagination
is termed gastrulation. The germ-layers, ectoderm and
endoderm have now been formed. The mesenchyme cells
noted above and other cells which arise from the blind end
of the archenteron constitute the mesoderm.

Exercise 1. Make a series of outline figures illustrating the
foregoing.

(b) The type of cleavage here represented is designated as
“total’’ or holoblastic and alecithal (without yolk). Compare
later with condition in frog and chick. The blastopore be-
comes the anus of the larva. The mouth is formed by an
invagination, the stomodaeum, which unites with the blind
end of the archenteron. Examine demonstrations. A larva
which is strikingly bilateral results and from this, by a curious
metamorphosis, the radially symmetrical adult is formed.
The existence of such a larva constitutes the main evidence for
the belief that the present radially symmetrical echinoderms
have descended from bilaterally symmetrical ancestors. Com-
pare with the inferences drawn from the existence of fish-like
stages in frog and chick.

ONTOGENY OF THE AMPHIBIA

lL BREEDING HABITS, Pre:

(a) If possible go out to collect frogs’ eggs, examine the
places where frogs and salamanders lay and make out what
you can regarding their activities during the breeding season.
Several of the species common about Columbia may deposit
the eggs in February, or early in March, others at some time
later in the spring, or even in early summer.

ONTOGENY OF AMPHIBIA. 83

(b) Take home a mass of eggs you have yourself collected
or have obtained from the laboratory. Placeina shallow dish
or basin and keep in a light place, not exposed to direct sunlight
for much of the day. Record the stage of the eggs when
obtained and note their progress from day to day. Preserve
your notes in the form of a written report to be handed in later.
The influence of temperature upon the rate of development can
be tested by placing part of the eggs out of doors on the cool
north side of a building and comparing them each day with
those having sun and the warmth of indoors. With proper
care they may be kept until the tadpoles have completed their
metamorphosis. At no time should the water in the dish be
allowed to become too low from evaporation or to become foul
from the growth of bacteria. Green water plants will be
beneficial unless growing in too dense masses. When the
tadpoles are fully formed, small bits of bread may be crumbed
up and put in the dish. Too much of this will, however, foul
the water and hence care must be used.

(c) Examine the living frogs and salamanders on exhibition
in the laboratory and find out the species to which the eggs you
are studying belong.

i THE UNFERTILIZED EGG, OR OVUM

(a) Examine in a watch glass of water a small mass of eggs
from the ovary of a frog preserved in formalin. Look for
small eggs among the larger ones of the present season. Some
of these will show, when examined under the low power, the
nucleus with its nucleolus and a small body of cytoplasm.
Further study with proper material would show that the com-
paratively large eggs are single cells in which a great deal of
nutrient yolk has been accumulated in the cytoplasm. The
egg in these stages before fertilization is termed the ovum.

Exercise 1. Draw one of these small ova to show its parts
as a cell.

(b) Permanently mounted sections of the ovary of a young
frog may also be used to demonstrate the cellular structure of

84 ONTOGENY OF AMPHIBIA.

the ovum. These will. show ova of various sizes surrounded
by the nuclei of smaller cells and the nucleus, nucleolus and
cytoplasm.

(c) Remove a living egg from the ovary of a female frog
and crush under a cover slip. What can you make of the
structure when examined with the compound microscope?

lil. THE SPERMATOZOON

(a) Cutinto a piece of testis and examine the milky contents
in normal salt solution. Under the high power look for motile
bodies, the spermatozoa. Each has a very long tail, not at
first observed. Various nucleated cells may be found in the
testes. Some of these can be recognized as stages in the for-
mation of the sperms. During the breeding season, ripe
sperm may be found in the seminal vesicles. As in the case of
the ovum, the spermatozoon is a single cell.

Exercise 2. Draw a ripe spermatozoon and any other cells
which are clearly younger stages of the same.

IV. THE EGG-LAYING, FERTILIZATION AND
COPULATION

(a) Recall the exact structure of the male and female
reproductive organs. The jelly, which is so conspicuous a
feature of the masses of eggs seen in ponds, is a product of the
oviducts. Fertilization occurs in the water as the eggs leave
the cloaca of the female and while the animals are joined in
copulation, or before the swelling of the jelly during the first
few hours exposure to the water. Take several eggs in which
fertilization is in progress and which have the jelly well swollen.
Note the individual envelopes in which the eggs are embedded.
What is the characteristic difference between the jelly of the
frog and that of the salamander eggs? Note the distribution
of the color on the surface of the egg. How does it compare
with the general distribution of light and dark color on adult
frogs, fishes, birds, etc., with which you are familiar? Which

ONTOGENY OF AMPHIBIA. 85

is the heavier side of the egg? The centre of the pigmented
area is called the animal pole, the opposite point on the sphere
the vegetative pole of the egg. If specimens showing the polar
bodies are available, examine these and show in your next
drawing.

Exercise 3. Draw, (a) several eggs, on a scale of 2 or 3,
showing their envelopes and the general mass of jelly, and (b)
a single one from a side view 1 inch or more across to show
distribution of pigment and the jelly envelopes. Label the
poles.

i oe DEVELOPMENT OF THE FERTILIZED EGG

(a) Where the stages noted in the ensuing account are
followed in preserved material, it will, of course, be impossible
to observe the actual progress of the development here de-
scribed. Careful reading will, however, make clear what
points may be observed in preserved material and the method
of description will enable the student to follow more vividly
the changes which the preserved stages represent. When it
is desirable to remove the jelly from any of these stages in
preserved material, it may be easily done by rolling the egg
along on a piece of filter paper.

CLEAVAGE STAGES

(b) If the living eggs are available, begin with the zygote or
one-cell stage and watch closely for the first cleavage furrow,
a dark groove which appears first on the animal pole and, as
it grows deeper, spreads over the vegetative portion until it
encircles the sphere. Observe its exact position with refer-
ence to the polar axis. Record the time occupied in the above
process by which the two-cell stage is produced.

Exercise 4. Draw side and top views to show the furrow
in process of formation and as it appears when completed.
The most satisfactory size will be a figure 11 to 2 inches in
diameter, a scale which should be continued in the subsequent
drawings.

86 ONTOGENY OF AMPHIBIA.

(c) A short period now ensues during which no external
changes occur, but internally the nuclei are preparing for the
next cell division. |

(d) Watch now for the second cleavage furrow. Record
the time of its first appearance and of its completion.

Exercise 5. Draw a top view of this furrow just appearing
and a view from the vegetative pole when it is complete.

(e) Careful watching is necessary lest the third cleavage
furrow, which is horizontal and just above the equator of the
sphere, come in unobserved. Record time of its appearance
as in foregoing. With the completion of the third furrow we
have the eight-cell stage which has four smaller, deeply pig-
mented cells above and four larger, lighter colored cells below.

Exercise 6. Draw a side, or top view of this stage number-
ing the furrows.

(f) Understand that with each division of any one cell the
nucleus also divides, so that in the two, four, eight and later
cell stages and so on to the many celled adult organism, each
cell possesses a nucleus descended through a longer or shorter
series of divisions from the original nucleus of the one celled
stage or zygote which was itself formed by the fusion of nuclear
material from egg and spermatozoon. Hence, we reach the
generalization that every cell of the adult animal may contain
a nucleus descended one-half from the male and one-half from
the female parent.

(g) The next cleavage consists of two vertical furrows which
appear simultaneously at right angles to one another and cut
each of the eight cells approximately in halves. The four
upper cells often complete this division before the furrows have
appeared in the lower hemisphere, thus making, with the eight
smaller above and the four larger cells below, a twelve-cell
stage.

Exercise 7. If this is observed, draw from a top or side view,
to show the twelve-cell stage.

(h) With the division of the four lower cells, the sixteen-cell
stage is produced.

ONTOGENY OF AMPHIBIA. 87

Exercise 8. Draw this from a side view.

(i) By very careful observation, it can be determined that
there next appears an approximately horizontal furrow parallel
to the plane of the third cleavage. This divides the eight
upper cells. A corresponding cleavage plane divides the
eight lower cells, thus making a total of thirty-two. A thirty
two-cell stage is, however, a theoretical rather than an actual
occurrence, because of the fact previously noted that the cells
about the upper pole divide faster than the corresponding yolk
laden cells below. Again, very careful observation shows that
there next follow two more approximately horizontal planes
of division, one above and one below those last mentioned,
making a forty eight-cell stage, but here as in the thirty two-,
this exact number of cells is probably never present because
of the way in which the lower cells lag behind the smaller
upper ones. From the eight-cell stage on, the cleavage is
not carried out with geometrical regularity as will readily
appear in the study of (g) and (h) above.

(j) The term mulberry stage is often applied to these stages.
More definitely, we will speak of it as an early blastula stage,
the complete blastula being reached only by the continued sub-
division of the constituent cells.

Exercise 9. Draw the early blastula stage from a side view.

BLASTULA AND GASTRULA

(a) A characteristic feature of the blastula is the existence
of an internal cleavage or blastula cavity. In the amphibian,
this cavity appears at about the twelve to sixteen-cell stage
and persists until it is obliterated by the gastrulation process.
Take a preserved specimen in the early blastula stage and after
removing the jelly by rolling on filter paper, hold gently
between forceps, without crushing, and divide in halves by a
vertical cut with a sharp scalpel. Examine with hand lens and
note the cleavage cavity and cell outlines.

Exercise 10. Draw the cut surface to show such an early
blastula in vertical section.

88 ONTOGENY OF AMPHIBIA.

(b) If the eggs are followed hour by hour it will be seen
that during the second day, at room temperature, the dark
cells of the animal pole begin to encroach upon the surface
area of the lower light colored ones. The exposed surface of
the lower cells thus becomes diminished around its entire
margin by downward over-growth of the dark upper cells.
By turning the egg upside down there will be seen along part
of the circumference of the diminishing area of exposed yolk-
cells a crescentic depression which is the blastopore. Under-
stand from your lectures the internal changes which are now -
taking place. The stage now reached is called the gastrula.

It can be turned upside down for observation by placing on a
slide a pin bent to an acute angle putting the specimen in the
desired position in the angle and adding a little water and a
cover glass. Find the blastopore with a hand lens and with
low power of microscope. Look for cell outlines in the dark
and in the light areas and indicate in the following figure.

Exercise 11. Draw the gastrula stage as seen from beneath.

(c) At a later stage of the gastrula when the dark cells
have still farther encroached upon the exposed area of the yolk
we have the yolk-plug stage. This may be examined in the
same way as the last or cut in halves as in (a) above and exam-
ined in section.

Exercise 12. Draw this yolk-plug stage. Understand from
your lectures and the text-book the internal structure of the
gastrula, i. e., its ectoderm, endoderm, mesoderm and archen-
teron. The yolk-plug finally disappears within the embryo,
but the blastopore can still be distinguished as a minute pit
which is to be shown in your next drawing.

NEURAL FOLD STAGE*

(a) The first sign of this stage appears about the time that
the yolk-plug is lost to view. The ectoderm thickens along

*The directions as far as this point have been designed either for
the eggs of a frog or asalamander, In the sections which follow
the notes have been written with special reference to the salamander
Amblystoma tigrinum, but will serve almost equally well for the frog.

ONTOGENY OF AMPHIBIA. 89

a certain area and as a result of this a ridge appears upon the
upper portion of the still spherical embryo. This ridge may
be regarded as a continuous structure having something the
shape of an hour glass, but it is customary to speak of the right
and left portions as the two neural folds. Find the blastopore
which now lies at one end of the area enclosed by these folds.
With the appearance of the neural folds, the bilateral symmetry
which characterizes the outside of the adult becomes obvious
externally. Although this stage is not greatly changed from
the spherical condition immediately preceding it, we can now
clearly recognize the axes of the adult body as follows: The
region between the neural folds is on the dorsal mid-line. The
opposite surface is of course the ventral. The end where the
folds are most widely separated represents the anterior, the
end where the blastopore is located the posterior region of the
future adult.

Exercise 13. Draw a neural fold stage from a top view as it
normally lies within the jelly. Make outline of the jelly still
surrounding. Label to show all the above points and the regions
of the future adult.

(b) The neural folds become higher and approach one
another along the dorsal mid-line where they finally fuse.
Examine a slightly later stage in which the embryo has become
flattened and more elongated and rests on one side. Where
do the folds come together last? Where is the blastopore?

Exercise 14. Draw this stage from a side view with ventral
surface below and label thoroughly as in last.

(c) Understand from lectures and text-book what develops
from that part of the ectoderm which is folded in when the
neural folds meet and fuse, also the origin of the neurenteric
canal which for some time connects the neural tube and the
archenteron, also the structures which would appear in sagittal
and transverse sections of such a stage.

BEGINNING OF THE TADPOLE STAGE

(a) After the foregoing stage the embryo becomes more
elongated and assumes the shape of a crescent. Study such a

00 ONTOGENY OF AMPHIBIA.

stage to identify the dorsal mid-line where the neural tube
has disappeared beneath the surface and the anterior end
where there is more suggestion of differentiation than at the
posterior extremity. The larva can be propped up against a
bent pin or some slightly flattened shot and the proctodaeum
found as a minute pit in the posterior region of the ventral
side. Along on each side and just below the dorsal mid-line
are some transverse markings which show the lines of division
between the mesoblastic somites, or first muscle segments.
Identify head, neck and body regions. As not all the larvae
given out will be in exactly the same stage, go over this last
with one of the instructors to make sure you understand what
can be recognized in the particular specimen you have.

Exercise 15. Draw a side view showing all these points and
having the orientation the same as in your last figure of the
neural fold stage, i. e., ventral surface below and head pointing
in same direction.

(b) Get several specimens showing the transition from the
above to the next stage. Note how the crescent straightens
out and the elongated larva gradually shows more definite
rudiments of the adult organs. In the stage to be drawn,
examine from the side, then prop up against a bent pin and
study the ventral surface. The eyes are swellings right and
left on the head, just below them are two smaller dark areas,
the nasal pits, or future nostrils. A depression on the ventral
side and posterior to the nasal pits is the stomodaeum. Rudi-
ments of the suckers and three external gills appear laterally
in the neck region, behind them is a protuberance, the begin-
ning of the fore-limb. Note the tail and the proctodaeum and
the general changes in shape. Go over with an instructor to
make sure of each point before drawing.

Exercise 16. Draw from a side view, labeling thoroughly
and oriented as other side views. |

(c) Study next a larva about ready to hatch. Identify
all the features noted in the last and see to what extent they
have changed. If the living specimen is too active, add a few
drops of ether or kill with five per cent formalin. In aspecimen

ONTOGENY OF AMPHIBIA. 901

‘still alive you will be able to see the heart beating within the
‘pericardium, which lies in the ventral region of the neck.
The stomodaeum becomes about this time connected with the
front of the archenteron and so forms the mouth. The same
thing happens to the proctodaeum which then becomes the
anus. Note the very dark pigment celis scattered everywhere
and look for the beginning of a collar like ridge on the ventral
surface and extending up laterally along where the external °
gills are attached. This is the operculum and if not yet recog-
nizable will be seen in the next stage.

Exercise 17. Draw from side view with orientation same as
previous figure and label all the structures which can be shown
in this view.

TADPOLE STAGES

(a) Examine larvae, or tadpoles, which have been some-
time hatched. Watch them alive, notice their active move-
ments and how the suckers are used. In a specimen anaesthe-
tized with a few drops of ether, examine the gills with low
power of your microscope. Watch the flow of blood in the
capillaries. Note corpuscles and the pulse. -

Exercise 18. Draw the outline of a single gill and its vessels
and show course of blood flow with arrows.

(b) With the microscope or hand lens note the heart beat-
dng in the pericardium. In some specimens, portions of the
digestive tract will be seen showing through the ventral part
of the body wall. Note again the operculum and recall later
when examining the similar structure in the tadpole of a large
bull frog. Note the size and outline of the mouth when seen
‘from below.

Exercise 19. Draw this larva from a ventral view.

(c) Examine Museum or living specimens of the genera
Amblystoma, Diemyctylus and Necturus. Notice the external
gills which persist throughout life in the last. Examine also
specimens dissected to show the viscera in place. These forms
are Amphibia of the class Urodela and are characterized by the

92 ONTOGENY OF AMPHIBIA.

persistence of the tail in the adult. How do they differ from
the class Anura?

Vio THE TADPOLE OF A LARGE PROG

(a) The tadpoles or ‘‘pollywogs”’ of the frogs and toads.
(Anura or tailless Amphibia) have slightly different outlines
from the Urodele tadpole just studied. In the case of our
smaller frogs and of the toads, the tadpole undergoes the
metamorphosis into the miniature adult the same season that
the egg is laid, but in the case of the large ‘‘bull-frog”’ the eggs
are not laid until late in the spring and the embryo remains
in the tadpole condition over the next winter, finally under-
going metamorphosis when about one year old, or in some
cases remaining a tadpole through a second year. Such speci-
mens approaching metamorphosis are abundant in the early
spring and in fact may be obtained at any time during the
open months.

(b) Watch the living specimens in an aquarium or large pan
of water; notice how they come up to breathe and how the
most advanced specimens are beginning to use their legs.

(c) Study a preserved or a freshly killed specimen in a
dissecting pan and covered with water. Make out nostrils,
mouth with horny teeth, hind limbs, anal opening and on one
side of the neck region an opening which leads into the gill
chamber, probe gently into this with a guarded bristle and
find the extent of the cavity into which it opens.

Exercise 20. Draw from a side view orienting same as
drawings of the Urodele tadpole.

(d) Pin the specimen out under water ventral side up.
Remove the outer covering from the cavity just explored with
the bristle. Find the internal gills and between them the gill-
slits. Discover relation of these slits to mouth cavity.

(e) Take a small fish and pin it out beside the tadpole.
Note the flap or operculum which covers the gills on either
side. Cut off these opercula and find out the relation which
the gills and gill-slits of the fish have to its mouth cavity.

ONTOGENY OF AMPHIBIA. 93

Compare this with what you see in the tadpole. Understand
how the membrane covering the tadpole’s gills is homologous
to the fish’s operculum. See models showing development of
operculum. Understand difference between external and in-
ternal gills.

(f) Find the heart on mid-line between gills in both tadpole
and fish. What parts can you recognize in each?

(g) Remove the ventral body wall of the tadpole from the
region between heart and anus with care not to injure the
viscera. Identify, by pressing aside without cutting or tear-
ing, the stomach, the tri-lobed liver, the gall bladder, pan-
creas, fat-bodies, the much coiled intestine and the posterior
end of kidneys. Compare with same in adult frog, as previ-
ously studied.

(h) Cut open the abdominal cavity of the fish and examine
its viscera briefly for comparison.

Exercise 21. Draw the organs of the tadpole as they appear
from ventral view and lying in place. Scale of 3. Make out-
line of body around them.

(i) In the tadpole find the lungs and the oesophagus where
it enters the abdominal cavity. Cut this last off and without
injuring the lungs, kidneys, and fat-bodies, remove the diges-
tive tract severing it again at the rectum. Unravel the intes-
tine, spread out and measure using the distance from mouth
to anus as a unit. Record and compare with your record of
same in the adult frog. Examine now the organs which remain
in the body cavity, lungs, kidneys, spleen, rudiments of
ovaries or testes and the fat-bodies.

Exercise 22. Draw on same scale as last to show these
organs in place.

(j) With a sharp scalpel, cut through the body transversely,
just back of eyes and again a little farther back. Study such
a section under water, noting position and development of
portions of central nervous system thus exposed and whether
any of the bony skeleton is present.

Exercise 23. Draw such a section.

94 EMBRYOLOGY OF CHICK.

VII. TADPOLES IN METAMORPHOSIS

(a) The miniature bull-frogs in which the tail is still present:
and which are just completing the metamorphosis, are not as
readily obtainable in large numbers as the similar stage in the
smaller frogs which metamorphose during their first summer.
Examine museum or living specimens of the larger form and.
then study in a watch glass covered with water a similar stage
of one of the smaller species. Note whether the shape of head.
and mouth have changed and if the tympanum has yet appeared;
also the development of the limbs and tail, which last, from this:
stage on, rapidly dwindles away.

Exercise 24. Draw ona scale of 2 or 3 from a dorsal view.

EMBRYOLOGY OF THE CHICK

(a) Examine the reproductive organs of a male and those
of a laying female to see the testes and their vasa deferentia,
the oviduct with its funnel, its albumen and shell-secreting
parts and its relation to the cloaca and rectum. Notice in the
ovary the eggs in various stages and the places where eggs have
been recently discharged, also the stigmata or non-vascular
areas which rupture when an egg is set free.

(b) Examine under the microscope a small amount of the
yolk obtained from one of these ovarian eggs. Recall the
similar structures in the frog’s egg.

(c) Examine demonstration sections showing the cellular
nature of the ovary.

(d) Take an unincubated hen’s egg and, using scissors, cut
open on one side a space about one inch across, being careful
that the scissors points do not cut too deep and injure the yolk.
The opening may be further enlarged, if necessary, the egg rest-
ing upon a bed of cotton wool in a finger bowl. Find the chal-
azae or twisted cords of albumen at either end. What relation
have they to the yolk and to the shell? Find the two mem-

EMBRYOLOGY OF CHICK. 95

branes which line the shell. These can always be seen at the
large end where there is a space between them. At one place
upon the surface of the yolk is a small whitish area, the blasto-
derm, the central part of which is known as the area pellucida |
and the peripheral part as the area opaqua. Does this always
appear at the top, however the egg is turned? Compare with
the rotation of the frog’s egg in its capsule. Understand the
comparison between such an egg as this and that of the frog
and the starfish and the condition of the blastoderm at this
stage.

Exercise 1. Draw the egg thus dissected, on a scale of 1.

(e) Open an egg which has been under incubation for
twenty-four hours and placing it on the cotton beside the one
just drawn compare the two. Record’or make a simple sketch
to show the changes which have taken place in the blastoderm
during this first day of incubation. Before discarding this.
specimen, the existence of a delicate yolk membrane should be
demonstrated by puncturing.

({) Permanently mounted specimens of the blastoderm and
the developing embryo will be issued for the study of approxi-
mately the 24, 32, and 45 hour stages, in their finer details.
These should be handled with great care lest they be crushed
by wiping or by the microscope objectives. These slides are
secured by removing the blastoderms, which are then fixed,
stained and mounted in balsam. The first to be studied is the
24 hour stage, in which the following parts are to be made out
with the low power of the compound microscope; neural folds,
head folds, mesoblastic somites, primitive streak, area pel-
lucida, the vascular area and the vitelline area. Focus care-
fully to determine the vertical dimension of the parts and com-
pare your results with what is shown by models.

Exercise 2. Draw this stage as a full page figure, including
a small margin from the vitelline area.

(g) Open a 36 hour egg, just from the incubator and notice
the further changes. With the aid of an instructor, inject
some India ink into the cavity beneath the blastoderm and
harden the embryo by dropping strong alcohol upon the out-

06 EMBRYOLOGY OF CHICK.

side. Compare part by part with a permanently mounted
specimen of the same stage, placing the latter across the top
of a watch glass and against a white background. Study with
lens to locate the parts observed in the twenty-four hour stage.
After identifying these with the hand lens in both the fresh
and the preserved specimens, study the mounted specimen
further under the compound microscope and make out, in
addition to the features seen in the last, the beginning of the
brain vesicles, the amnion, heart, notochord and any changes
in the size and proportions of parts. Here again careful
focusing and the comparison of what you see with the models
is necessary for the proper understanding of the third dimen-
sion.

Exercise 3. Draw this stage in a figure similar to the last.

(h) Examine next a freshly opened embryo of 45 to 48 hours
incubation, comparing it with the last. Note the blood ves-
sels, the pulsations of the heart (which should be counted for the
number per minute) and the extent to which the vitelline area
has extended over the egg and then treat with India ink and
alcohol as before. Study together the specimen thus freshly
prepared and a stained and a mounted specimen of the same
stage. Find all the structures observed in the thirty-two hour
stage and in addition note the cranial flexure and the torsion
of the cephalic end of the embryo, the fore, mid, and hind-
brain vesicles, the optic vesicles and the lens of the eye, the
auditory vesicles, the tubular heart, now bent into an “S”’
shape, the vitelline arteries and veins and the sinus termi-
nalis, the gill bars and slits and the extent to which the
amnion has developed.

Exercise 4. Draw this stage, in a figure similar to the last.

(i) Understand from demonstrations of the later stages
of chick and mammal and from the lectures, charts and text-
books, how the embryo is related in its several stages to the
yolk mass and the significance of the amnion, allantois and
yolk-sac in both mammals and birds.

INSECTS. 907

THE INSECTS

PHYLUM, ARTHROPODA. CLass, INSECTA OR HEXAPODA

ia NIORTHORTEROUS) INSECT

(a) The grasshoppers and locusts are the most common
representatives of this order Orthoptera, and any large speci-
men of several species, which are common locally, may be
used. Living individuals should be observed: in glass jars, con-
taining grass and covered with a screen. Exactly how are the
legs used in walking and jumping? The spiracles, or respira-
tory openings will be seen along the sides of the abdomen.
Observe and time the intervals between the respiratory move-
ments. Note the nature and the distribution of color upon the
animal. Can you suggest any value which this may have for
the animal in nature? Offer bits of green vegetation to the
specimens in the jars and see what you can make out regarding
their mode of feeding. Touch the “feelers,’’ antennae, of the
head with a long piece of glass tubing having a plug of absorbent
cotton in the end and observe how sensitive to touch are these
organs as compared with other parts of the body. Moisten
the absorbent cotton with some strong smelling fluid and bring
it near the antennae without touching them. Can the animal
smell with these organs or with any other part of the body?
Remove a specimen from the jar and holding gently examine
the parts at closer range. Look at the compound eyes, the
antennae, etc., with the lens. Note the “molasses” which is
regurgitated from the mouth. This is a digestive fluid mingled
with food. If a good sized drop can be collected from one or
more specimens and placed upon a slide, put a bit of fresh green
vegetation in this and note result before the fluid evaporates.
What may be the significance of this habit of regurgitating the
contents of the digestive tract? If you have time, devise
experiments to determine whether temperature, or sensations

7

98 INSECTS.

akin to fear in the higher animals influence the rate of the
respiratory movements.

Exercise 1. Write out in the form of carefully worded notes
such facts of the above study as can be thus recorded.

(b) A preserved or a freshly killed specimen may now be
used for a study of the structure. Compare the segmentation
with what you know of the crayfish and earthworm. The main
divisions of the body are head, thorax and abdomen. The
thorax has three segments, prothorax, mesothorax and meta-
thorax and has the three pairs of legs. How many segments in
the abdomen? Are there signs of segmentation in the head?
The antennae and compound eyes have already been located,
examine again with the lens. Find the simple eyes, or ocelli,
three small dots between the antennae. About the mouth are
the following parts: the upper lip or labrum, next a pair of
mandibles and, by pressing these last aside, the pair of maxillae
and the labium, which last functions as a lower lip and is really
a second pair of maxillae united. Note the labial and maxil-
lary palps, or ‘feelers.’ The forward, upper and lateral parts
of the head are covered by a simple plate of the skeleton, the
epicranium, with which the mouth parts just mentioned are
articulated. Like the exoskeleton of the crayfish, the covering:
of the grasshopper’s body is a continuous membrane which
thins out at the joints and is of different thickness in different
parts of the body. For convenience we speak of the plates
or sclerites, of the skeleton though neighboring plates are
continuous by the thinner skeleton over the joints.

(c) Examine the thoracic region and determine accurately
the number and position of the plates in each segment, the place
of attachment of the wings proper and of the wing-covers.
Each of the thoracic legs consists of five main divisions: the
coxa by which the leg articulates with the body, a short seg-
ment the trochanter, a long segment the femur, then the tibia
and last the three jointed tarsus terminating in a pair of hooks
and a little pad. Notice how the trochanter of the metatho-
racic leg has fused with the femur and how this limb is a special
adaptation of the same plan which the others present. The

INSECTS. 99

abdominal segments are divided into upper and lower parts
by a horizontal band along which are the spiracles. How
many of these are there and on which segments do they occur?
On the first abdominal segment near the spiracles there are
oval areas covered by a thin membrane. These are the
auditory organs. The tip of the abdomen differs in the two
sexes. Each sex has the following parts in common: a single
terminal dorsal plate; right and left below this the paired
podical plates, between which lies the anus and on the outer
face of which are two small projections, the cerci. Below the
podical plates of the male there is a single large sub-genital
plate which is replaced in a female by the conspicuous plates
of the ovipositors. Understand how the latter are opened for
the extrusion of the egg after digging the cavity in which it is
laid.

Exercise 2. Draw a full page figure showing the grasshopper
as seen from the right side. Spread out dorsally the wing
and wing-cover of this side and arrange the legs so that the
body will show to advantage.

(d) Holding the specimen in one hand cut open the body
along the mid-line a little to one side of the mid-dorsal region.
Use fine scissors and be very careful not to cut deep and injure
the soft parts underlying the skeleton. After opening for the
entire length of the body, pin out under water in a dissecting
pan by slanting two pins across the union of the head and pro-
thorax. Fasten the free end of the abdomen with a single
pin passed through the end of the cut and then spread out and
pin apart the edges of the cut, using great care not to injure
the internal organs. If the heart has not been destroyed in
opening the specimen, it will be found either adhering to the
inner face of the skeleton, along the dorsal mid-line of the
abdomen, or in this position upon the surface of the internal
organs. A lace-like mass of yellow tissue is the fat-body which
should be removed carefully to expose the alimentary canal a
large tube running straight through the body. In exposing
this more fully, the muscles of the thoracic region must be
removed. On top of the tract in the abdominal region are the

100 INSECTS.

reproductive organs which have right and left parts coming
up from either side and meeting dorsally. Their ducts pass
backward from the ventral side and unite in a single duct which
opens ventral to the anus, on the upper face of the sub-genital
plate in males, between the halves of the ovipositors in females.
Among the organs are certain structures which are conspicuous
in the fresh specimen by their silvery color. These are the
tracheal or air-tubes and the air-sacs through which the air
taken in by the spiracles is carried to all parts of the body.
Remove the parts of the fat-body that may conceal the diges-
tive tract. Beginning anteriorly, this is composed of a crop,
which is thin walled; a stomach, encircled by eight elongated
pouches, the gastric caeca; a region called the intestine and a
terminal portion, the rectum. Where the stomach passes into
the intestine there will be found a mass of threads which have
an excretory function and are known as the Malpighian tubules.

Exercise 3. Draw the digestive tract on a scale of 3 or 4,
as it lies in place and seen from the dorsal side, making around
this a simple outline of the body as cut open.

(e) Remove the digestive tract by severing the rectum
near its posterior end and pulling gently forward. The short
oesophagus, by which the crop connects with the mouth, will
now be seen. Before this is severed find the brain just back of
the eyes and dorsal to the tract, and the circum-oesophageal
connectives which pass on either side of the oesophagus and
connect the brain with the sub-oesophageal ganglion (to be
seen later). Cut the oesophagus, without injuring any of
these parts, and examine the gut under water, to get a better
view of its parts; particularly the gastric caeca and Malpighian
tubules. Look on the sides of the crop near its posterior end
for the gastric ganglia, white spots from which fine nerves
radiate. Look on either side of the body in the region from
which the crop has been removed for the salivary glands.
These communicate by fine ducts with the region just inside
the mouth, a point which is difficult to ascertain without a
special dissection. |

(f) Look at the air sacs as now exposed and make out any
regularity in their arrangement. Remove a small bit of the

INSECTS. 101

muscle or fat-body and examine on slide under a cover with
microscope. Find the tracheae lined with their spiral threads.
Draw if you have time. Continue to remove the fat-body and
muscles of the ventral side, in the region of the thorax, until
the nerve cord is exposed. If the reproductive organs have not
been destroyed the union of their right and left parts may be
observed below the gut before their removal. How many
ganglia are there and how many nerves does each give off?
How does the position of the entire nervous system in the body
compare with the same in a frog, a crayfish and an earthworm?
From the brain there are nerves to the compound eyes, the
ocelli and the antennae. The circum-oesophageal connectives
have already been located.

Exercise 4. Draw as much of the nervous system as you
have made out upon the same scale as the drawing of digestive
tract.

II. A COLEOPTEROUS INSECT

(a) Any large beetle will do for this study, provided it is
not too highly modified. By examining the animal from the
ventral side locate the head, thorax and abdomen and the num-
ber of segments visible in each. Look for antennae, compound
eyes, ocelli, mandibles and other mouth parts, the anus and
the thoracic legs, and compare with what you have found in
the grasshopper. Where are the wing covers and the wings?
When the latter are found see how they fold up beneath their
covers. Fasten down, dorsal side up, by pinning through
the prothoracic segment, spread one wing cover out at right
angles and unfold the corresponding wing which can be spread
in the angle between the wing cover and abdomen. Raise the
head, if it bends too far ventrally, and spread out the thoracic
legs on the side where wing and cover are closed.

Exercise 1. Draw the specimen from this view and on such
a scale as to make the figure three or four inches long. Show
the plates of the skeleton with care and number the segments
of thorax and abdomen.

102 INSECTS.

(b) In the larva of a beetle find the main divisions of the
body, head, thorax and abdomen, mouth with its jaws and the
anus. Count the number of segments comparing with adult
of the same species.

Exercise 2. Draw such a larva from a lateral view showing
these parts on a scale of 3 or 4.

(c) Examine, as directed by instructor, such living speci-
mens of beetles and their larvae as are available for individual
study or demonstration.

1 A AY MENOPTEROUSMINsE Gh

(a) Wasps of the genus Polistes are very common and are
easily collected when they enter unscreened buildings with the
approach of cooler weather in the fall. Head, thorax and
abdomen will again be recognized as in the case of the other
insects. How many segments in each? Look for antennae,
compound eyes, ocelli, mouth parts and anus. At the pos-
terior end of the female is the sting. The spiracles are a row
of minute dots on each side of the abdomen. Compare the
divisions of the thorax and of each thoracic leg with the cor-
responding parts of the grasshopper. To which segments are
the wings attached?

Exercise 1. Draw a side view with wings spread dorsally,
on a scale of 3 or 4.

(b) Examine the ‘‘paper’’ nests of this wasp and others if
available. Also artificial ants’ nests and the eggs and larvae
recently taken from an ant colony. The most remarkable
facts regarding the hymenoptera are those connected with
their social life in such colonies, a matter which will be dis-
cussed in lectures or text-book.

IV. A LEPIDOPTEROUS INSECT

(a) Examine a good sized butterfly, or moth, going over
the features noted for other forms (the three main divisions of
the body, eyes, antennae, mouth parts, legs and wings).

INSECTS. 103

Mount some of the dust from the wing surface and examine
under a microscope. What is the significance of the term
“‘lepidoptera’’?

Exercise 1. Draw a dorsal view with wings spread, making
the figure three or four inches across. Omit color pattern.

(b) If available the eggs of butterflies or moths will be
shown as a demonstration. Understand to what species such
eggs belong and where they are laid. ;

(c) Examine now a larva which is large and favorable for
study. Where are the head, thorax and abdomen? Do you
find thoracic legs? There are other pairs of appendages some-
what like them and known as prolegs. How many are there
and what is their structure as compared with the thoracic
legs? Are there eyes, ocelli, antennae and mouth parts as in
other forms? Do you find spiracles?

Exercise 2. Draw a side view on a large scale.

(d) Ifit is the proper season the larvae of various forms will
be placed in the laboratory for individual study or demonstra-
tion. Observe the way of: moving and their voracious habits
in feeding. How does the structure and use of the mouth
parts differ in larva and adult? At the proper season, cater-
pillars will often spin their cocoons in the cages where they are
kept, or such cocoons may be collected and given out for study.
Cut one open and find the resting stage, “‘pupa,’’ within.
Notice the silk of which the cocoon is composed. Such cocoons
if uninjured may be kept in cages and the emergence of the
adult insect observed at some subsequent time.

(e) Understand the complete life history in each of the
groups thus far studied and be able to explain the difference
between direct development as in the grasshopper and the
metamorphosis of butterflies, beetles, etc.

Vo OFT R ORDERS

(a) Of the remaining orders of the Insecta, three are more
commonly known and recognized by popular names. These
are the Hemiptera, or true bugs; the Diptera or two-winged

104. A PLANARIAN.

flies, of which the house fly is our most common representative,
and the Odonata or dragon flies. Representatives of these and
of their larvae will be placed in the laboratory for demonstra-
tion and supplied to individuals if called for.

(b) The life history and habits of insects presents much
which is even more profitable for study than the points hereto-.
fore covered, but such work is difficult to handle properly with
large classes and at fixed periods. Suggestions and assign-
ments will, however, be made upon request to the instructor
in charge and facilities for carrying on such work either at home
or in the laboratory will be provided.

PARASITISM AND OTHER FORMS OF ASSOCIATION
AMONG ANIMALS

I. A PLANARIAN WORM

PHYLUM, PLATODA. CLASS, TURBELLARIA

Planarian worms are common in fresh-water where they are
most easily discovered on the under sides of leaves, stones and
small objects upon the bottom. For this study, the species
Planaria maculata or any other representative form of these
turbellaria may be used.

(a) Examine in a watch-glass of water. How does the
animal move? What changes in shape may the body undergo
n “righting’’? In meeting obstacles? In response-to other
stimuli? What is the shape and distinctive feature of the
two ends? Are there sense organs? Can you find the mouth
and, in sexually mature animals, the genital aperture on the
ventral side? Transparent specimens will show the dendritic
branches of the digestive system, the plan of which should be
understood from chart or text-book figures. Place a small
specimen upon a slide under a cover-slip and look for cilia.

A FLUKEWORM. 105

Can you see the justification for applying the name _ turbel-
laria to these forms? Study also the coloration under micro-
scope and hand lens.

Exercise 1. Draw the animal from a dorsal view, scale of
8 to 10, showing the above features.

(b) Specimens will sometimes feed if crushed snails or bits
of meat are placed in the dish. The muscular pharynx may
then be seen. In this connection, their actions may be watched
for evidence of a sense of smell. Interesting observations may
also be made upon regeneration and upon their behavior with
respect to light. Carry out such observations and experiments
if you have time.

(c) These worms are studied here with a view to empha-
sizing their free-living condition. In nature, they move about
actively, often capturing living prey, and reproduce either
vegetatively by fission or by means of germ-cells. They are
hermaphroditic. The eggs are laid in small stalked capsules
attached to the under sides of the stones and other objects
upon which the animals are living. From each of these cap-
sules or egg-shells a number of young emerge as miniature
adults able at once to take up the life of the parent upon the
bottom. The life-cycle is thus in marked contrast with that
of the parasitic representatives of this phylum.

Il. A FLUKE-WORM

PHYLUM, PLATODA. CLaAss, TREMATODA

To the trematoda belong the external and internal parasites
known as the fluke-worms. For this study, any one of the
genera somewhat resembling Distomum may be used. Haema-
toloechus variegatus, from the lungs of the frog, and another
genus often found free in the body cavity of the frog are excel-
lent material.

(a) Examine living or preserved specimens and locate the
mouth and suckers. How does the shape and behavior, if
specimens are observed alive, compare with the same in the

106 A TAPEWORM.

planarian? Locate the digestive tract and compare with the
planarian. The reproductive organs are complex and varied
in appearance and, if studied, special directions will be given.
The animals are hermaphroditic and produce fertilized eggs
which accumulate before being laid in a terminal portion of
the female organs, the uterus, developing later when they are
laid. The life-cycle is greatly complicated by the parasitism
as described in lectures or text-book. Both in the structure
and conditions of the life-cycle, contrasts should be drawn
between the trematode and the planarian.

Ill. A TAPE-WORM

PHYLUM, PLATODA. CLASS, CESTODA

The cestoda or tape-worms are parasitic forms, even more
highly modified in correlation with their parasitic habits than
are the fluke-worms. The adults occur as parasites within
the digestive tract of another animal, the larval stages mostly
within the tissues of a secondary host upon which the pri-
mary host is likely to feed. Species of the genus Taenia occur
in many common mammals and are excellent for the study of
the external features. They may be examined alive in water
or after preservation in alcohol or formalin.

(a) Examine an adult cestode in a pan of water. The
smaller end has a head, scolex, the posterior end ripe joints
or proglottids. What structures adapted for holding fast are
found upon the scolex? Count the proglottids, compare with
numbers in neighboring specimens and record. Can you see
indications of the developing reproductive organs and of the
genital apertures with copulatory organs, at one side? How
and where do the proglottids seem to originate? Each pro-
glottid contains a complete hermaphroditic reproductive sys-
tem and the chain of proglottids may be regarded as a redupli-
cation many times over of the reproductive machinery. If
living worms are available, test the firmness of their attach-
ment by the scolex to the mucus membrane of the host. Com-

A TAPEWORM. 107

pare the external features with those of other tape worms shown
as museum specimens. Moniezia expansa from the sheep and
Crossobothrium laciniatum from the sand-shark are good for
this purpose.

Exercise 1. Draw a good sized figure of the adult, indicat-
ing the parts as above and with the proglottids accurately
shown. To avoid repetition, the figure may show several
representative regions of the worm connected by dotted out-
lines.

(b) The “ripe”’ proglottids at the posterior end often show
the outlines of the distended uterus, a cavity in which the
development is begun. Here, the egg develops as far as the
six-hooked embryo, a stage which may be obtained from either
living proglottids or formalin material. Cut the proglottid
into bits in a watch-glass and examine some of the material
under high power of the microscope. Embryos surrounded by
a tough shell and other membranes will be found. Can you
find the six hooks? Is there any remnant of the yolk material?
If alive, crush by pressing on the cover and watch movements.
Do they seem effective as ‘boring movements?’’ Can you make
any estimate of the number of six-hooked embryos produced
by a single cestode?

Exercise 2. Draw the embryo and its surrounding parts.

(c) The ripe proglottids, with their six-hooked embryos,
break off and pass out with the feces of the host. The six-
hooked embryos are discharged by the rupture or disinte-
gration of the proglottid and find their way to the secondary
host by the chances of nature, entering with the food or drink.
After its membranes are digested in the stomach of this host,
the six-hooked embryo bores out into the tissue and develops
to a stage known as the bladder-worm. Examine living or
preserved material and make out the scolex and neck and their
peculiar position. Can you see anything adaptive in this
development within the bladder? Understand what hap-
pens when the bladder-worm is eaten by the primary host.

Exercise 3. Draw the bladder-worm, making a good sized
figure.

108 ForMsS OF. ASSOCIATION.

(d) If the internal structure of the proglottid is to be
studied, excellent results may be obtained from the motile
proglottids of Crossobothrium laciniatum stained with alum
cochineal. Further explanations will be given in the labora-
tory.

(e) Other important features in the internal structure of the
cestode, which may be noted in chart or text-book figures or a
further laboratory study, are, the brain and nerve cords,
excretory system, absence of a gut, the granules of CaCQs,
and the cuticular membrane which covers the body. Are
any of these features to be correlated with the parasitism?
How may cestodes and trematodes be homologized?

(f) All tapeworms, so far as known, have two hosts. Inthe
following cases of known life-cycles which would be the pri-
mary and which the secondary host? Man,—pig; dog,—
rabbit; mouse,—cat; house-fly,—hen; fish,—bird; louse,—
dog; man,—fish. Consider where and how each of the three
stages would occur in each case.

IV. OTHER FORMS OF ASSOCIATION
AMONG ANIMALS

The platoda offer an excellent example of closely related
animals existing as free living and as parasitic organisms.
From what you know regarding these and any other parasitic
forms, write out a statement of the kind of modifications in
structure and life history likely to occur in animals which have
assumed parasitic habits. Consider cases of communal para-
sitism in insects as explained elsewhere and the striking cases
of association occurring among marine animals such as crabs,
worms and mollusca, and the whole in relation to lecture, text-
book and field-work bearing upon the inter-relations among
different species and the struggle for life.

CLASSIFICATION. 109

THE CLASSIFICATION OF ANIMALS

ino the PHYLA OF THE ANIMAL KINGDOM

A sufficient number of forms have now been studied in detail
to enable you to form some picture of the types of structure
- which existing animals present. These may be reviewed and
your knowledge extended in certain places with a view to giving
you concrete ideas of other types not yet examined. The
term Phylum is applied to certain larger groupings of ani-
mals though, as we shall see at the conclusion of this survey,
the phyla may again be grouped into larger subdivisions. An
examination of the several phyla by means of museum or other
specimens may be accomplished as outlined below.

Phylum, Protozoa.

The forms studied, Amoeba, Paramoecium, Englena, and
Gregarina, together with figures and démonstrations of other
forms, sufficiently illustrate this phylum. Emphasis is cen-
tered upon the unicellar state, though simple colonies fre-
quently occur.

Phylum, Porifera.

This phylum comprises the sponges. Examine simple
sponges like grantia and leucosolenia, and notice the osculum,
an excurrent opening, and, in grantia, the many small pores
by which the water passes in. The larger sponges like the
bath-sponge, and others which may be upon exhibition, are
regarded as derivatives of the simpler types modified along
the line of extensive budding and vegetative growth. Char-
acteristics of the sponges are: Absence of a stomach or gut
cavity comparable to that of other many-celled forms; attach-
ment except during the earliest stages of development; absence
of what may be properly termed organs, although there are
different kinds of cells; a skeleton of fibres asin the bathsponges

110 CLASSIFICATION.

or spicules as in grantia or the “glass sponges.’’ The sponges
are clearly the simplest of the many celled animals now living.

Phylum, Coelenterata.

Hydra and the hydroids with their jelly fish are the examples.
studied. Examine other and larger jelly fish, a sea anemone,
corals showing the soft parts and theskeletons, sea-pens, fans,
etc., and chart figures of ctenophores. Distinctive features
are: absence of an anal opening; radial symmetry; two layered
or diploblastic structure, 1. e., ectoderm and endoderm as in
hydra; tentacles surrounding mouth and in most cases
attachment during a part of the life-cycle.

Phylum, Platoda.

Planarians and similar forms, fluke-worms and tape-worms.
as studied. Characterized in the forms not degenerate through
parasitism by: bilateral symmetry; absence of an anal open-
ing; absence of a coelomic cavity, though there is a middle germ
layer (mesoderm) and the animal is therefore triploblastic.

Phylum, Annulata.

The earthworm is a representative form, though the group
as a whole is characterized by appendages on the segments
and organs of special sense in the head region which the earth-
worm has presumably lost in the course of its evolution.

Nereis is in this respect a better example. Small species,
related to the earthworms, are common in fresh-water and may
have been observed. There are many tube-building forms
among the marine worms, museum or chart figures of which
may be examined. The leeches of fresh-water are greatly
modified annulates. The annulata are characterized by:
bilateral symmetry; an obvious metamerism; three germ-
layers; a well developed coelome; nephridia; dorsal brain and
ventral nerve cord as in earthworm.

Phylum, Mollusca.
Represented by the clams, mussels, snails, slugs, etc.
Examine specimens of bivalve shells, comparing with the fresh-

CLASSIFICATION. 104

water mussel, also the shells of marine snails showing lines of
growth and peculiar shapes. Watch living pond snails, if
not already studied, and notice the symmetrical head and
creeping foot. Examine museum specimens of the limpets,
marine forms belonging with the snails and adapted for cling-
ing tightly to the rocks with the foot. Also another type of
mollusc the chiton, with its segmented shell. Examine another
type represented by the squids, devil-fishes and cuttle fish,
active, free, swimming forms with an internal shell. As a
phylum, the mollusca are characterized by: bilateral symmetry;
a ventral foot; a dorsal one-pieced shell; a mantle, enclosing a
mantle cavity in which lie gills; absence of metamerism;
presence of a coelome with nephridia; three germ-layers.
Most of these characters may be recognized in the specimens
placed upon exhibition.

Phylum, Echinodermata.

Examine specimens of starfish and sea-urchins, noting the
five-rayed symmetry. Can you find mouth and anus? Organs
known as the tube-feet are used for locomotion. See mace-
rated specimens showing plates of skeleton. Examine sea-
cucumbers and compare, noting the difference in the relation
between body axis in relation to normal position. Can you
see the five rays? Tube feet? How would you homologize
the outer surface of a sea-cucumber and a sea_ urchin?
The sea cucumber and a starfish? The’ echinoderms
are a very aberrant group. For a long time class-
ed with the coelenterata because of their radial structure,
they have since been clearly shown to be forms with far greater
complexity of organization and are clearly animals which have
been modified from bilaterally symmetrical ancestors possessing
three germ-layers and a coelome. See demonstrations of the
bilateral larval forms. Distinctive characters of the phylum
are: a radial symmetry, masking a more fundamental bilateral
symmetry, which appears in the larva; an extensive coelome;
a water vascular system used for locomotion and unique in the
animal kingdom; a skeleton consisting of isolated plates em-

112 CLASSIFICATION.

bedded in the mesoderm; a simple type of nervous system and
sense organs.

Phylum, Arthropoda.

To this phylum belong the familiar crayfish, crabs, insects,
Spiders, scorpions, etc. Examine museum specimens of cray-
fish and lobsters, if not already dissected, and compare with a
crab, noting, mouth and anus, eyes, antennae, jointed appen-
dages, external evidences of metamerism. In all these forms
the relation of the nervous system to the gut is similar to that
in the earthworm or crayfish. Examine water-fleas, as they
swim in an aquarium and in a watch-glass after anaesthetizing
with ether. In what respects do they agree with the larger
forms in structure? Characteristic features of the phylum
are: a continuous cuticular skeleton, thinner at the joints;
bilateral symmetry; metamerism; a pair of jointed appendages
on each segment; a pair of compound eyes; three germ layers.
A well developed coelome is not present but it seems probable
that such was the case in the ancestors of this group.

Phylum, Chordata.

The vertebrates constitute by far the most conspicuous
members of this phylum and are sufficiently familiar without
further examination in this connection. Other less known
forms are the amphioxus and the tunicates or sea squirts.
Examine specimens. The amphioxus with its elongated
metameric body, mouth and anal openings and fins bears a
remote resemblance to a fish. It can, at least, be imagined
when viewed from the outside to have some resemblance to
the simpler vertebrates. Internally there are gill-slits, a
notochord, a dorsaltubular nervous system and other vertebrate
characteristics. The sea-squirt, on the other hand, would
never suggest such a relationship. It is adapted for a sessile
life and possesses an inhalent and exhalent siphon much like
those of a clam. Indeed these animals were for a long time
classed with the mollusca. Later, it was shown that the
embryo possessed the notochord, dorsal tubular nervous sys-

CLASSIFICATION. 113

tem and other features found in no other group but the verte-
brates. Accordingly the tunicates were placed in a group
with the _ vertebrates. Distinctive features of the
chordata are: a dorsal tubular nervous system, formed by
infolding as in the frog embryo; a notochord, present in embryo
only (frog) or throughout life (amphioxus); metamerism more
or less conspicuous; three germ layers; coelome; bilateral sym-
metry, etc.

Il. PHYLOGENY OF THE ANIMAL KINGDOM

(a) After this review of representative types we may next
consider the grouping of the phyla into larger divisions. Here
we must consider only a few very fundamental points of struc-
ture such as, the many celled or single celled condition; with a
gut cavity or without a gut cavity; diploblastic or triploblastic;
with a coelome or without a coelome; with metamerism or
without metamerism.

Exercise 1. Construct a table showing how the phyla will
group themselves when classified along broad lines.

(b) Looked at in another way, this table will represent a
family tree of the animal kingdom for it probably gives us
the broad lines along which evolution has proceeded. Do you
understand now the meaning of a natural classification or one
based upon blood relationship and the meaning of structural
resemblance among animals?

114 APPENDIX.

APPENDIX

A BONY FISH

Any of the common bony fish will serve for this study. The
marine Ctenolabrus, fresh-water perch, or any of the minnows.
They should be collected during the summer and preserved
in formalin. Interest in the work is greatly increased by hav-
ing a few live fish to study action of fins and manner of respi-
ration.

(a) External Characters. What is the shape of the body
as a whole? How is it adapted for motion through the water?
How do you distinguish anterior and posterior ends? Dorsal
and ventral surface? Note the head, trunk and tail regions.
Is there a neck? Are these regions sharply marked? What is
the nature of the coverings of the body? ‘1. Head: Its
shape? Mouth, nostrils, eyes, gill-openings, operculum, which
consists of several parts. Beneath the operculum is the
branchiostigal membrane, supported by bony rays. The
branchiostigal region is connected with the trunk by the nar-
row isthmus. Its shape? Relation to gill openings?

(b) Trunk. Its general shape? How does this region
compare as to length, height and thickness? Describe the
color of your specimen? Compare several specimens, and
male and female. Describe the variations noted. Note the
lateral line on each side of the body. Can you trace it onthe
head? Determine what causes the line.

(c) Fins. How many? How many in pairs? Single?
What ones are in the median line of the body? How are they
supported? The fin on the back is the dorsal. Are there one
or two? Compare as to size and supporting rays. The ter-
minal fin is the caudal, and the one just behind the vent is the
anal. Compare each with the dorsal. Do the paired fins
have supports? What is their position on the trunk? The

A Bony FIsH. 105

anterior pair are the pectorals, the posterior the pelvic. Com-
pare several kinds of fish and determine the variation in posi-
tion of these fins. If practicable, the living fish should be
studied in aquaria to determine the use of each fin.

(d) Integument. Describe the distribution and arrange-
ment of the scales. Is it regular? Do they extend into the
head? Is there skin over the scales? Is the pigment in the
scales? Pull one out. The rounded marginal scales are
cycloid, the toothed or spiny marginal are the ctenoid. Sketch.

(e) External Apertures. Determine the position, size and
shape of the following: (a) mouth, (b) vent, (c) urino-geni-
tal, (d) nostrils, (e) gill openings.

(f) Mouth Cavity. Its general shape? Are there lips?
The bony framework consists of the upper jaw, a pre-maxillary
in front and a maxillary behind. Shape and size of each?
The lower jaw is the dentary. Which ones bear teeth? Are
there other bones that have teeth? Where? How many rows
of teeth in jaw bones? Their shape and size? 1. Tongue:
Shape? Attachment? Size? 2. Oesophagus: Position?
3. Gills: Lift operculum and examine the gills. Each is
composed of a bony arch and numerous gill filaments. On
the inner edge of the bony arch are a number of short processes,
the gill-rakers. How many gill-slits? Their relation to the
pharynx? Are all the gills alike? Compare first and second
and the last two. What use can you suggest for the gill-
rakers?

Exercise 1. Draw as seen from one side, showing the mouth
and gill region dissected.

116 A SNAIL.

A POND SNAIL

For the following study the French snail Helix will be found
very satisfactory, but the common pond snails Physa, Plan-
orbis or Limnea may be used to advantage.

(a) The Shell. Is there any division into valves? What
is its general form? How many turns does the shell make?
How do they vary in size? Compare several specimens of the
same species as well as several different species. Do the coils
turn to the right, dextral, or to the left, sinistral? Is the coil-
ing loose or close, flat or conical? The apex of the shell is
the oldest part and corresponds to the umbo in the clam.
The wide opening is the mouth or peristome (of the shell not
the animal). What is its shape? Is the margin smooth or
toothed? Explain. One side of the peristome is in some
species drawn out into a spout-like process. What is its use?
Do you find in any of the species an oval plate closing the
opening? In some snails there is such a structure which is
called the operculum. To what is it attached? Can you
explain its use? The whorls make a line where they come in
contact; this is the suture. Is the suture a simple or an
irregular line? Explain the lines that run parallel to the edge
of the peristome as lines of growth. Is there any variation?
Explain. The whorls coil around a central axis, the columnella.
Describe it in a demonstration specimen of some large shell,
making a sketch to show its parts.

(b) The Living Animal. How does the snail move? What
is the shape of its foot? Its relation to the rest of the body?
To the shell? The anterior region of the foot is termed the
propodium; the posterior the metapodium; and between these
two is the mesopodium. Are these regions sharply marked off?
To which part is the operculum attached when present?

(c) The Head Region. Dorsal to the foot find the mouth.
Shape? On each side are fleshy tentacles. Their size and
shape? Touch with needle. What happens? Are there one

A SNAIL. stays

or two pairs? Do you find small glistening spots, the eyes,
on the tentacles? Their position? Locate the anal opening on
the right side of the head. In the air breathing snails find the
respiratory opening near the anal opening.

Exercise 1. Draw from a side view, showing foot, head and
shell as they appear when fully expanded.

(d) The snail belongs to one of the sub-divisions of the
Mollusca known as the Gastropoda. Explain the application
of this term. From your study of the clam and snail, write
a definition of the group Mollusca and the sub-group Gas-
tropoda.

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