Charles Wesley Hargitt.

Outlines of general biology ; an introductory laboratory manual online

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borne? Note their size, color, and texture. What is their
relative position in repose? In flight? Spread the wings
and study the arrangement of the veins.

Make drawings of the first and third legs, and of both pairs
of wings.

5. Abdomen. Of how many somites is it composed?
Compare the male and female specimens carefully in shape,
size, number and relations of the somites. In what partic-
ulars do they differ? Compare the first somite with those
following and note any differences. In this somite there
is a membranous tympanum or ear drum.

Study the structure of a somite and observe a dorsal
portion, the tergum and a ventral sternum. Are these parts
well marked? Are they present in each somite? Are the
terga and sterna capable of movement?

In the side walls of the somites are small openings or
pores called spiracles. These are the external openings of



118 GENERAL BIOLOGY

the respiratory system, which is made up of a series of
branching tubes inside the body for carrying air to the
various organs and tissues. There are eight pah's of spiracles
in the abdomen, and two in the thorax; determine the
exact location of these.

At the end of the abdomen the somites are considerably
modified, to form spines, plates and the like. The hard
spines in the female comprise the ovipositor, or egg-laying
organ. Determine the number of spines and the relation
of these to the somites adjoining. In the male there are
smaller spines which function as genital organs during mating.
In both males and females the anal opening is dorsal,
beneath a chitinous plate, and the reproductive opening
is toward the ventral side.

Make a drawing of the entire animal from the side.



II. Internal Anatomy.

Remove the wings and cut along each side of the median
dorsal line. Remove the entire dorsal part of the body
wall and expose the internal organs.

1. Respiratory System. Tracheae or air-tubes will be seen
as fine white tubes, much branched and extending to all
organs and tissues of the body. The tracheae open to the
outside through the spiracles. Demonstrate this connection.

2. Digestive System. Distinguish the following parts:
(a) esophagus, leading from the mouth to the crop; (6)
crop, a large organ located in the prothorax; (c) gastric
caeca, a series of pouches surrounding the posterior end of
the crop; how many are there? Do they connect with
the cavity of the crop? (d) The stomach is an enlarged
part behind the cseca; (e) intestine the posterior portion



THE GRASSHOPPER 119

of the digestive tube ending at the anus. The intestine is
made up of three parts.

3. Excretory System. This comprises a number of deli-
cate capillary tubes, the Malpighian tubules, which are
twisted together and may partly fill the body cavity. They
connect with the digestive canal at the point where the
stomach and intestine join.

4. Reproductive System. The reproductive organs, testes
or ovaries, are present in the abdomen, dorsal to the digestive
tube. These organs are made up of tubules closely packed
together. They open to the exterior through the sperm
ducts or oviducts, whose openings are ventral to the anal
opening. The ovary in mature animals may be a mass of
eggs completely filling the body cavity.

Make a large drawing to show all the organs and systems
worked out.

5. Nervous System. Remove the alimentary canal and
the reproductive organs. The nerve cord should now appear
along the median ventral line, covered over with a thin
sheet of fat tissue. Are ganglia present? How many
in the abdomen? In the thorax? Is there a ganglion to
each somite? Where are the ganglia largest? Trace the
general direction of the nerves which leave the ganglia.
In the head is a ventral inf ra-esophageal ganglion, and a dorsal
supra-esophageal ganglion or brain. These two large ganglia
are connected by circum-esophageal commissures. From the
brain nerves go to the ocelli, compound eyes, and antennae.

Make a large drawing showing the nervous system.

Compare the crayfish, the grasshopper and the earth-
worm in regard to: (a) The plan upon which the body is
constructed; (6) the organization of somites into well
defined regions; (c) the arrangement and structure of the
appendages; (d) the number, position and structure of



120 GENERAL BIOLOGY

the sense organs; (e) the structure of the circulatory,
digestive and nervous systems. Which of these animals is
the more highly specialized? Is one better adapted to its
modes of life than the others? Give reasons for your con-
clusions.

m. Physiology.

From a study in the field and in the laboratory work out
the following activities of the grasshopper.

1. Movements. Describe the kinds and methods of
locomotion. What structural features of the legs are
adaptations for leaping? How many times the length of
the body may the grasshopper leap? What is the purpose
of the hooks on the legs? Are both pairs of wings used for
flight?

2. Sensitiveness. With a bristle touch various parts of
the body, including the antennae . Which is the most sensitive
part? Does the grasshopper see? What evidence is there
of this? Is there any evidence that it hears?

3. Protection. Has the grasshopper any means of de-
fense? Is it protected by color? How does it escape its
enemies?

4. Respiration. Observe the respiratory movements of
the abdomen. Knowing the structure of the respiratory
system, which is characteristic of all insects, explain why
non-poisonous powders may often kill insects.

5. Nutrition. Place animals in a cage with leaves of grass
and other plants. If possible observe the method of using
the different mouth parts. By using different kinds of
plants it may be possible to determine whether there is any
choice of food.



HONEY BEE.

APIS MELLIFICA.

THE honey bee belongs to the class Insecta and, there-
fore, has certain characteristics in common with the grass-
hopper and other insects. For example, there is the same
division into head, thorax and abdomen; a subdivision of
thorax and abdomen into segments; and a similar number
and disposition of antennae, eyes, legs and wings. The
grasshopper, however, is a relatively simple insect, w T hile
the bee is one of the most complex. The bee is of interest
from its habit of community or social life, with different
castes or classes in the community. It is also of interest
in its highly specialized and adapted organs, as compared
with the more simple ones of the grasshopper.

External Anatomy.

1. General Characters. Notice the division of the body
into regions, and compare with the grasshopper. Especially
note the covering of hairs over the body, is this present in
all parts or is it limited in distribution? Remove some
of the hairs, place on a slide and examine with the com-
pound microscope. The longer hairs of the body differ
in what way from the shorter hairs of the appendages?

2. Head. Is the head freely movable? Is it more or
less so than in the grasshopper? The compound eyes are
quite similar to those of the grasshopper, but observe the
short spine-like hairs on their surface. Compare the com-



122 GENERAL BIOLOGY

pound eyes of a worker and of a drone bee; in what respects
do they differ? What explanation can you give for this
difference? The eyes of the queen are like those of the
workers. Three ocelli are present as in the grasshopper.
Observe the position and the structure of the antennae.

3. Mouth Parts. The mouth parts of the bee are the same
in number as those of the grasshopper, but greatly modified
and adapted to different functions.

(a) Labrum. This is a flap of skin forming an upper lip.
(6) Mandible. There is a pair of mandibles or jaws be-
hind the labrum. Both the mandible and the labrum
are quite similar to those of the grasshopper, but
somewhat reduced in size. The mandibles of the
worker differ slightly from those of the queen and the
drone.

The remaining mouth parts, the maxillae and labium,
are much modified and together form a proboscis for
sucking liquid food.

(c) Maxilla. The palp of the maxilla is reduced in size to

a mere rudiment. The remainder of the appendage
forms the hollow outer portion of the proboscis.

(d) Labium. Of this appendage there are three chief

parts, the base, the labial palps, and the glossa or
" tongue. " The glossa forms the center of the pro-
boscis, is covered with long hairs, and ends in a spoon-
like lobe called the labellum.

To study the mouth parts straighten them out,
away from the head, cut off the entire tip of the head
and mount this on a slide in glycerin. It may be
necessary to separate these parts somewhat with
needles.
Make a drawing of the mouth parts.



HONEY BEE 123

4. Thoracic Appendages. (a) Wings. Remove the wings
from the body and mount on a slide. Study the
arrangement of the veins in each wing. With the
compound microscope observe the hooks on the an-
terior border of the hind wings which attach this to
the fore wing. What is there on the fore wing to hold
these hooks?
Make a drawing of the wings.

(6) Legs. The legs are composed of five segments as
those of the grasshopper, but the basal joint of the
tarsus or foot is much enlarged and is sometimes
called the metatarsus. The legs of the bee serve not
only for locomotion, but also as tools for other com-
plex functions.

1. Prothoracic Leg. Between the tibia and the first
tarsal segment is the antenna cleaner; on the outer
end of the tibia is a pollen brush, composed of stiff
hairs.

2. Mesothoracic Leg. At the end of the tibia is a long
spine, the pollen spur.

3. Metathoracic Leg. How do the tibia and first tarsal
joint compare in size with similar parts of the other
legs? The outer surface of the tibia is hollowed
out to form the pollen basket; the inner surface of
the first tarsal joint is covered with rows of stiff
spines, the pollen combs. Between the tibia and
the first tarsal joint are the so-called wax shears,
which, however, are used in gathering pollen and
have nothing to do with wax manipulation.

Compare these adaptive specializations of the legs of the
worker with the legs of the drone, and note what differences
occur. Is it possible to explain these differences?

Remove each of the legs from the body, study with a



124 GENERAL BIOLOGY

lens or low power, and make drawings to show the points
observed.

5. The Sting. The sting is located in a cavity in the end
of the abdomen, which is formed by an infolding of some
of the posterior abdominal segments. The sting is homol-
ogous with the ovipositor of other insects.

Remove the dorsal wall of the end of the abdomen and
dissect out the sting apparatus. Mount this on a slide in
glycerin and study with low power. There is a shaft com-
posed of a dorsal sheath and two barbed lancets or darts.
The sheath and lancets form a hollow tube through which
the poison flows. At the sides is a pair of sting palps, soft
whitish projections, which serve as sense organs by which
the bee can tell when she is in contact with the object which
is to be stung. When the sting apparatus is removed one
or both of the poison glands will usually be present. Other
parts of the complicated apparatus will also be found.
Determine the character of the sting proper and the palps,
and make a drawing to show the structures observed.

As a portion of this study the different classes of the com-
munity, drones (males), queens (females), and workers
(neuters or imperfect females), should be compared. Es-
pecially should this comparison be made to determine the
differences in structure which are correlated with the speciali-
zations of parts for particular functions.

Field studies should be made, if possible, to observe the
habits of the bees, especially that of gathering nectar and
pollen. An interesting study of the activities within the
hive can be made if an observation hive of glass is available.



THE CLAM.

UNIO SP.

THE common fresh-water mussels or clams, of almost any
genus, are excellent for study. Those of some size are best.
The marine clam (Venus) while not so large nor so satis-
factory, is quite similar in most of its structural features.
Clams live partly buried in the sand or mud, w r ith the pos-
terior end of the body protruding. They may be collected
by digging. It is possible to keep them alive for some time
if placed in tanks of running water.

I. External Anatomy.

1. Shell. Note the general form and relations of the shell.
Are the valves (the two parts of the shell) similar in size and
form? The dense horny hinge is the dorsal part, and the
knob or elevation on the shell (umbo) is nearer the anterior
end. Has the animal a right and a left side? Observe the
parallel, concentric lines extending from the umboes to the
margins of the valves; they indicate lines of growth, though
their number gives no evidence of the age of the clam.
Each line w r as at one time the edge of the shell. Study
the action of the ligament or hinge in a recently opened shell ;
what function does it serve? The ligament is an uncal-
cified portion of the shell.

Make a drawing of the shell from the side, and one from
the anterior aspect.



126 GENERAL BIOLOGY

2. Interior Surface of the Shell. Wedge the shell open
and then cut the muscles which are attached to the valves.
When this is done what happens to the valves? What
causes this? What is the function of the muscles? (If the
animal is preserved and the valves are already open, cut
the muscles and determine the functions of muscle and
ligament.) Cut the ligament and remove the left valve,
being careful not to remove any of the body within the
shell; a fold of skin which sticks to the shell must be care-
fully separated.

Compare the color and markings of the interior of the
shell with those on the outside. Are lines of growth present?
Are there any scars on the inside of the shell? What has
been the cause of these? Find the marks made by the
adductor, retractor, and protractor muscles. (In Venus there
is no protractor muscle.) How many of these muscles are
there? What is their function? When the clam was
smaller than it is now where were the muscles attached?
How do you know? Is there any evidence of growth over
any part of the muscle scars that now show? At the dorsal
side of the valve notice several teeth (not present in all
clams), the hinge teeth. WTiat is their function?

Draw the interior of the shell.

3. Structure of the Shell. Break the valve that has been
removed and examine the broken surface. Notice the
thickness of the shell in different regions. Look for layers
in the shell, an outer very thin layer, the periostracum,
greenish or brownish in color. (This layer is not always
seen since it may have been worn off.) Next comes the
prismatic layer, and inside the nacreous or mother-of-pearl
layer. The periostracum and the prismatic layers are
formed by the thickened edge of the mantle. Once formed
they cannot be added to except at the edge of the shell.



THE CLAM 127

The nacreous layer is secreted by the surfaces of the body
and of the mantle in contact with the shell. It may con-
tinue to form throughout life. Is there any proof that this
has happened?

4. Body. While working on the following external features
of the body remember that while the shell is properly a
part of the body, an exoskeleton, yet the fleshy part exposed
by the removal of the shell is still the external portion of
the body of the animal.

(a) Mantle. This is the thin membrane lining the shell
and covering the rest of the body. How many lobes are
there? Are they attached to the shell? If so, where, and
to what extent? Are they joined to each other at any point?
In the posterior part of the body observe that the margins
of the mantle are hollowed out to form two oval openings,
a ventral incurrent, and a dorsal excurrent opening or siphon
(in Venus the mantle is fused to form two tubes). Deter-
mine the cavities into which the openings lead. All the
water that comes into the shell enters through the incurrent
and all leaves by the excurrent opening. The cavity be-
tween the mantle lobes is the mantle cavity and in it are
several organs.

(6) Gills. Remove or turn back the mantle from one
side and expose the gills, which are thin membranes hang-
ing freely in the mantle cavity. How many on each side
of the body? Are they of similar size and form? How
and where are they attached to the body? In the female
the gill acts as a brood pouch during the breeding season
and is then greatly distended by the contained embryos.
A study of sections of the gill may be made to show the
layers of which the gill is composed, the water tubes, and
the bloodvessels.



128 GENERAL BIOLOGY

(c) Foot. This is the large dense median part of the body;
it forms a muscular wedge or keel by means of which the
animal moves. Above the foot is the softer visceral mass
of the body.

(a) Muscles. The adductor muscles, already noted, close
and hold the shell shut. There are protractor muscles for
pulling the foot and body ventrally, and extending it from
the shell. The retractor muscles draw these same parts back
into the shell. Note their position and the manner in which
they work. (In Venus there is no protractor muscle.)

(e) Labial Palps. Small, thin, leaf-like organs behind
the anterior adductor muscle. They aid in passing the
food to the mouth.

(/) Mouth. Between the palps and below the anterior
adductor muscle.

(</) Anus. Opens into the excurrent or cloacal chamber
it will be found against the posterior border of the posterior
adductor muscle.

Make a drawing with the mantle removed.



II. Internal Anatomy.

1. Circulatory System. The heart lies dorsally between the
ligament and the bases of the gills in an oval sac, the pericardial
cavity. Dissect the pericardium from the dorsal side and
expose the cavity and the heart. The latter is made up
of a central muscular portion, the ventricle, and two tri-
angular lateral portions, the auricles. Compare the auricles
and ventricles in thickness of walls. If a live clam is at
hand observe the pulsations of the heart. The ventricle
surrounds the posterior portion of the intestine. There are
two arteries leaving the ventricle, the anterior aorta and



THE CLAM 129

the posterior aorta, which carry blood to different regions.
Veins return the blood to kidneys, gills, and auricles.

2. Excretory System. The kidney is a dark greenish
gland on either side of, and ventral to, the pericardial sac.
Each kidney is a wide thin-walled tube, doubled on itself
so that the two ends are close to each other. These ends
are anterior and about opposite, and ventral to, the anterior
end of the pericardium, while the loop is posterior and lies
against the posterior adductor muscle. One end of the
kidney opens into the pericardium, the other into the cavity
of the inner gill.

3. Nervous System. This system is composed of three
pairs of ganglia connected by nerves. First locate the
visceral ganglion just under the posterior adductor muscle.
It will appear as a yellowish mass under the skin which
covers the muscle. How many nerves arise from this center?
To what regions or organs do they go? A small nerve on
either side extends forward from this mass to the brain.
The brain or cerebral ganglia will be found just under the
palps above the mouth, one on either side. From this nerves
extend to the adductor muscle, mantle and palps. Also
a nerve, the cerebral connective, connects the two ganglia.

The pedal ganglia are a fused pair in the foot and are
joined to the cerebral ganglia by connectives. These ganglia
will be found while working on the digestive system.

4. Digestive System. With a razor split the foot and the
visceral mass vertically in the median line. Identify the
following parts: The mouth is immediately behind the
anterior adductor muscle. From this a short esophagus
leads to the stomach, which is in the dorsal part of the body.
Note the greenish digestive gland, or liver, surrounding the
stomach. The intestine extends from the ventral side of
the stomach to the ventral part of the foot, then poste-



130 GENERAL BIOLOGY

riorly through the foot. Here it turns on itself and extends
anteriorly again, then dorsally, passes through the ventricle
of the heart, goes dorsal to the posterior adductor muscle,
and ends at the anus in the cloacal chamber.

5. The Reproductive Organs. The ovaries, or testes, are
present in the visceral mass .of the body. They are usually
light brown in color and entirely fill the spaces between the
folds of the intestine. The ducts empty near those of the
kidney in the supra-branchial chamber.

Make a large drawing to show all the organs studied.
6. Sections of the Body. In order to show the relations
of the various organs of the body in a manner as clear as
possible a study of sections of the body is desirable. These
are sections across the entire body at different regions.
Make drawings of the sections and show the position and
arrangement of the organs that are in the section. Show the
plan of the organs by making the drawings rather diagram-
matic.

(a) Section through the stomach, shows the stomach,
mantle, palps, liver, reproductive organs, anterior aorta, foot.

(6) Section through the heart. Mantle folds, gills, supra-
branchial chamber, intestine (cut across several times),
pericardial cavity, ventricle, auricles, vena cava (a large vein
in the center of the body below the pericardial cavity),
kidney, ureters, reproductive organs.

(c) Section through the posterior adductor muscle. Ad-
ductor muscle, intestine, gills, supra-branchial cavities, mantle,

visceral ganglia of the nervous system.



m. Physiology.

1. Sensitiveness. Place a clam in a dish of water and
allow it to remain until the shell opens and the foot and



THE CLAM 131

edges of the mantle are extended. Use a bristle or a delicate
glass rod to test the sensitiveness of the various parts ex-
posed. Determine whether foot or mantle, and which
portions of the mantle, are most sensitive; test especially
the edges of the siphons. What response is made to delicate
tactile stimuli? To stronger stimuli?

Sensitiveness to chemical substances may be tested by
directing gentle currents from a pipette against 'various
portions of the body.

Place a specimen in a very dim light, and when the shell
opens direct a beam of light against the body. Is there a
response to this stimulus? Place the animal in sunlight
or bright light from some artificial source, and interpose a
screen between the light and the animal, thus casting a
shadow upon the body. Note the character of such re-
sponses as occur.

2. Circulation of Water. Introduce a few drops of a
colored fluid into the water near the posterior end of a clam
whose shell is open. If the water is drawn into the shell
observe the place where it enters. Does the colored fluid
pass out of the shell again? Where is the point of exit?
What service to the clam would there be in such incurrent
and excurrent movements of the water? Further light on
this advantage will be gained by observing a clam partly
buried in the sand in the normal manner.

3. Feeding. Carefully insert a knife between the valves
of a living clam and cut the two adductor muscles where
they are attached to the shell. Loosen the mantle and
remove one valve entirely, thus exposing the body. Lay
back the mantle, or cut it loose, to expose gills and palps.
Drop some powdered carmine, chalk, or other small solid
particles upon the surface of the gills and note any movement
of these particles. In what direction is the movement?



132 GENERAL BIOLOGY

Are any of the particles carried far enough forward to reach
the mouth? In the clam it is by ciliary movements that
small organic particles are carried to the mouth, and the
entire food is composed of these particles.

4. Heart Beat. In a specimen with one shell removed
observe carefully the region of the body dorsal to the gills
and in front of the posterior adductor muscle. This is the
position of the heart and its pulsations may be seen through
the delicate walls of the mantle. If care is used one may
remove the mantle and pericardial walls and expose the
heart itself. When the heart is exposed the pulsations of
auricle and ventricle may be easily observed.



SNAIL.

HELIX POMATIA.

FOR this study the French snail is suggested, but the
common pond snails, Physa, Planorbis, Limnsea can be
used.

1. The Living Animal. How does the snail move? What
is the shape of the foot? What is the relation of the foot
to the rest of the body? What is its relation to the shell?
The anterior part of the foot is called the propodium, the


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Online LibraryCharles Wesley HargittOutlines of general biology ; an introductory laboratory manual → online text (page 7 of 10)