Charles Wesley Hargitt.

Outlines of general biology ; an introductory laboratory manual online

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polyp or hydranth, which by budding produces a new
hydroid colony.

The life cycle of this animal is, therefore, somewhat com-
plicated and involves an alternation of generations. A
hydroid, we have seen, by asexual budding produces a
medusa, and this through sex cells gives rise to a hydroid
colony. There is, therefore, an alternation of the asexual
and the sexual methods of reproduction.



HYDROID.

OBELIA OR CAMPANULARIA.

THIS hydroid has about the same mode of life and lives
in the same places as Pennaria.

With a lens examine a colony making out the stem, branches
hydrorhiza, and hydranths. Compare with Pennaria on
these points. Make a drawing of the colony showing its
habit of growth.

With the compound microscope examine the colony more
carefully and discover whether there is a perisarc as in
Pennaria. Does it differ from that in the other hydroid?
In these hydroids the perisarc at the end of each branch
widens out to form a funnel-shaped enlargement (the hy-
drotheca) which may entirely enclose the hydranth. Why
are some hydranths entirely enclosed within hydrothecse,
while others extend beyond this? The perisarc around the
stem, and around the hydranth as well, is of a horny con-
sistency and has been secreted by the ectoderm cells of the
coenosarc. When this was taking place the ectoderm was
in contact with the perisarc. Examine the colony closely
and find different stages in the formation of a hydro theca.

Compare the hydranth with that of Pennaria in size,
shape and structure. How many tentacles are there? How
are they arranged? Are they alike? Note the mouth,
which is at the end of an enlargement, the proboscis or
hypostome. How is the hydranth supported in the hy-
drotheca?



84 GENERAL BIOLOGY

Make an enlarged drawing of an expanded and another
of a contracted hydranth.

Examine a tentacle with the high power and find the
ectoderm and the entoderra layers, and the outlines of the
cells of these layers. How does the tentacle differ from
that of hydra, and from that of Pennaria? Are nematocysts
present? Where are they located? Make a drawing of
the basal portion of a tentacle showing the cell outlines.

Look for branches which have an elongate, rather club-
shaped, enlargement of the perisarc. The ccenosarc within
will show no tentacles and no mouth. This is the gonangium,
or receptacle containing reproductive buds. The ccenosarc
forms a central core the blastostyle, which is a modified
hydranth body; from the sides of this are budded off small
medusae. . These medusae become free, escape from the
gonangium and swim away. Unlike Pennaria the medusae
of Obelia are not sexually mature at the time of escape, but
the eggs or spermatozoa are formed only after several weeks
of active life. The eggs -develop into new hydroids as in
Pennaria, the same alternation of generations being shown.

Draw a gonangium.

Campanularia differs from Obelia chiefly in its repro-
ductive process. In Campanularia no medusae are formed,
but within the gonangium eggs or sperms are produced.
Fertilization occurs within the gonangium and the egg
develops into a free swimming larva (planula) which escapes
from the gonangium. The planula fixes itself and trans-
forms directly into a polyp, which buds and produces a
colony.



THE MEDUSA.

GONIONEMUS MURBACHII.

THE medusae formed by the hydroids studied, Pennaria
and Obelia, are so small that their structure can be made
out only with some difficulty. Therefore, a larger medusa is
taken as a type for study. Although Gonionemus does not
belong to the same order as the hydroids described, and the
hydroid stage -is greatly reduced, it has about the same
structure as the medusae which are formed from these hy-
droids.

Place specimens in a watch glass with water and examine
with a lens. The umbrella or bell shape is rather character-
istic of all medusae. The external convex part is called the
exumbrella or aboral, and the concave part is the subumbrella
or oral side. The under part of the medusa is partly closed
by a membrane called the velum, or veil. Where are the
tentacles? Are they alike. How many are there? Are
they regularly arranged? Are nematocysts present? If
so note their arrangement. Near the tip of the tentacle is
an adhesive or muscular pad used by the medusa for hold-
ing against some object.

Within the subumbrellar space note the central hanging
sac, the manubrium or stomach. Is a mouth present? A
gastric cavity? How does the mouth differ from that of
the hydroids? Note the radial canals, delicate tubes which
extend outward from the center of the bell. How many
canals are there? Is the number the same in all specimens?



86 GENERAL BIOLOGY

Are they symmetrically arranged? Do they join the gastric
cavity? The canals extend to the periphery of the bell and
open into a marginal canal which extends completely around
the medusa and communicates with the hollow tentacles.
Why is there such a system of canals in the medusa and not
in the polyp?

Hanging from the under surface of the canals are large,
convoluted, ribbon-like organs, brownish in color. These
are the reproductive organs. The medusae are males or
females, but the reproductive organs look alike.

Draw the entire medusa from the side; also from the
oral aspect. Draw a portion of a tentacle showing the
arrangement of the nematocysts, and the adhesive organ.



EARTHWORM.

LUMBRICUS SP.

PLACE the worm in the dissecting pan with enough-
water to cover it. What is the form of the body? Does
it vary in any part? What is the color? Does it vary?
Has the body any protective covering? Are there append-
ages such as legs? Are there gills or other respiratory struc-
tures? Are there organs of hearing or sight?

I. External Anatomy.

1. General Features. Notice the regular segmentation
of the body into a series of rings, somites or metameres.
How many? Compare with the number found on other
specimens and indicate whether it is constant. Are the
somites of the same size and form throughout? Notice
the prostomium projecting from the first somite, and the
clitellum or girdle about one-third of the way back from the
anterior end. Which segments make up the clitellum?
In what way does this part of the body differ from the rest?
The clitellum is composed of glands in the skin which secrete
a substance to form the cocoon or case in which the eggs
are deposited.

2. Regions of the Body. Distinguish an anterior or head
end, and a posterior or tail end. Is there a definite head?
How are the dorsal and ventral sides differentiated? Are



88 GENERAL BIOLOGY

these distinctions equally marked in all parts of the body?
Are the two sides of the animal alike? If so, it is said to
be bilaterally symmetrical.

3. Setae are short, horny spines embedded in the body
wall but projecting a little. They aid in locomotion. They
may be felt by rubbing the finger over the ventral surface
of the body. If this region is examined with a lens the
seta? will be seen as tiny brown spots. How many are there
on each somite ? How are they arranged ?

4. Openings of the Body. The mouth will be found on
the ventral side of the body at the first somite. What is
the position of the mouth relative to the prostomium? At
the end of the last segment of the body is the anus, the
posterior end of the digestive tube. On the ventral side
of the fifteenth somite are the openings of the testes, called
the sperm ducts, one on either side surrounded by swollen
lips. The ovaries open through the oviducts on the ventral
side of the fourteenth somite, but they are not surrounded
by swollen lips. The openings to the sperm receptacles,
of which there are two pairs, are situated in the grooves
between the ninth and tenth and the tenth and eleventh
somites, and are on the sides of the animal in the same line
as the lateral rows of setae.

The openings of the excretory organs are found in each
segment on the ventral surface a little anterior to the outer
seta of the ventral row. They are not very plain, but with
a lens will usually show well on some somites. The dorsal
pores, which communicate with the ccelomie cavity, are in
the middorsal line and open in the grooves between the
somites.

Draw the anterior and the posterior parts of the body
to show all that you have observed.



EARTHWORM 89

II. Internal Anatomy.

With the scissors cut through the body wall in the mid-
dorsal line from about the middle of the body to the third
somite, taking care not to cut the viscera lying beneath.
Carefully cut the membranous partitions, the septa, at the
points where they join the body wall and pin back the flaps
of the latter. Notice that the body wall forms a tube in
whose cavity, the body cavity or coelom, lies another tube,
the alimentary or digestive tube: also that the septa divide
the body cavity into smaller chambers. What relation is
there between the septa and the external segmentation?
Observe first the alimentary canal which extends through
the animal; also several pairs of conspicuous white bodies
near the anterior end. The latter are the sperm sacs.

1. Circulatory System. This system is a series of closed
tubes consisting of several longitudinal vessels and many
circular vessels connecting them. The largest of the longitu-
dinal vessels, the dorsal vessel, is in the middorsal line
against the alimentary canal. Beneath the intestine is
the ventral vessel which will be seen later when the alimentary
canal is removed, and ventral to the nerve cord is a third
longitudinal vessel, the subneural vessel. The circular
vessels extend between the dorsal and the ventral vessels
and occur in pairs. Five pairs of these circular vessels in
the anterior region (somites seven to eleven) are very large,
and being contractile are called hearts; the dorsal vessel is
also contractile. Carefully dissect away the septa and
expose the hearts.

2. Reproductive System. The earthworm is a hermaph-
rodite animal containing both the male and the female
organs in a single individual.



90 GENERAL BIOLOGY

(a) The Male Organs. The sperm sacs, or seminal vesicles,
lying in somites ten to fourteen are large white organs, com-
posed of several lobes. In these the spermatozoa under-
go a portion of their development. There are two pairs of
spermaries or testes enclosed within the seminal vesicles,
but they are so minute as to render their dissection very
difficult.

(6) The Female Organs. The sperm receptacles are two
pairs of spherical, whitish or yellowish sacs beneath the
sperm sacs, in the ninth and tenth somites. In these re-
ceptacles the spermatozoa received from another worm are
stored, and from them the sperms are passed into the egg
case in which the eggs are laid. The ovaries (one pair),
are small organs near the median line, attached to the
anterior septum of the thirteenth somite. They will be
rather hard to find. Posterior to them are funnel-shaped
openings which lead into the oviducts, and these in turn
open to the exterior at the fourteenth somite.

Earthworms meet and pair at night in May and June,
and the sperm receptacles of each are filled w r ith spermatozoa
from the other worm. They separate and later the girdle
secretes a fluid which hardens and forms a tough cylindrical
membrane or cocoon about the body. The cocoon is moved
forward and as it passes the fourteenth somite eggs pass
into it, and at somites ten and eleven spermatozoa enter
and the fertilization of the eggs takes place. The cocoon
passes over the anterior end of the animal and drops to the
ground, the ends close and within this free capsule the develop-
ment of the young worms takes place.

3. Digestive System. Carefully remove the sperm sacs
and the septa in the anterior portion of the body, exposing
the tube-like esophagus. Find the following parts : pharynx
(somites tw y o to five), esophagus (six to thirteen), crop (four-



EARTHWORM 91

teen to sixteen), gizzard (seventeen to ninteen), stomach-
intestine extending to the posterior end of the body. In
the walls of the esophagus in somites ten to twelve are
three pairs of small sacs or pouches, the calciferous glands,
which open into the esophagus.

Compare the several organs in size, color, thickness of
walls, the lining of each. In the stomach-intestine note
the dorsal infolding, the typhlosole. Note also the delicate
muscle fibers w y hich extend from the body wall to the pharynx.
What possible function might these serve?

4. Excretory System. This consists of paired segmental
organs, the kidneys or nephridia, which are made up of coiled
tubes held closely together and suspended close to the
ventral and lateral body wall. Remove one of the nephridia,
place on a slide, and examine with the compound micro-
scope.

Make a large drawing and in it show all the internal
structures that you have observed.

5. Nervous System. Dissect and remove the anterior
end of the alimentary canal except the pharynx. This will
expose the white nerve cord, lying in the median ventral side
of the body cavity. Immediately over this is the ventral
bloodvessel, one of the main longitudinal trunks of the
circulatory system.

Examine with the lens and notice that there are small
swellings, the ganglia. How many in each somite? Are
there nerves coming out from the cord? How many in
each somite? Do they come from the ganglia, or from be-
tween the ganglia? Carefully expose the cord anteriorly,
pushing the pharynx to one side, and on the dorsal side of
the pharynx will be found the cerebral ganglia or brain.
How is this connected with the ventral cord? Make a
large drawing of the brain and several of the ganglia and
their nerves.



92 GENERAL ' BIOLOG Y

HI. Microscopic Anatomy. (Histology.)

On the slides furnished are sections across the body in the
region of the stomach-intestine, and these are stained in
drder that the various tissues may be more plainly seen.

1. Study the entire section and identify the following
structures: (a) body wall and its layers; (6) ccelom; (c)
intestine; (d) dorsal and ventral bloodvessels; (e) nerve
cord. Other organs likely to be found are setse, excretory
organs, septa.

Make a drawing of the entire section showing all the
parts mentioned, but not attempting to indicate the cells
which make up the tissues.

2. Body Wall. With the high power study the body wall
and make out the cuticle, epidermis, circular muscles, longi-
tudinal muscles, and a delicate layer of cells lining the ccelomic
cavity, the peritoneum. Make out the cellular character
of the various layers and make a drawing of a small segment
of the body wall showing the layers and the cells which
compose them.

3. Intestine. Are the walls of the same thickness through-
out? The dorsal infolding of the intestinal wall is called
the typhlosole. How much of the cavity of the intestine
does it occupy? Make a careful study of the tissues and
cells of the intestinal wall; from without inward these are
as follows: Chlorogogue, pear-shaped cells rather loosely
arranged; between the bases of the chlorogogue cells are
small scattered fibers, the longitudinal muscle; a definite
and clearly marked circular muscle layer; inside of this there
may be spaces, the bloodvessels of the intestine; lining the
intestine is a thick layer of ciliated, columnar epithelium.

Draw a portion of the wall as seen with the high power,
showing the cells of each layer.



EARTHWORM 93

4. Nerve Cord. What is the shape of the cord as seen in
section? If nerves are present notice the place and the
manner in which they emerge from the cord. The cord is
enclosed within a connective tissue sheath, scattered through
which are many muscle fibers. Are these circular or longi-
tudinal muscles? Also within this sheath are located three
longitudinal bloodvessels, ventrally the subneural, at the
sides the lateral-neural vessels. The pear-shaped cells in
the cord are the nerve cells, and the delicate fibers that seem
to be prolongations of the cells are the nerves. Are nuclei
present in the nerve cells? Are the nerve cells abundant?
Where are they located? At the dorsal side of the cord are
three areas that are called giant fibers. Filling up the bulk
of the cord are connective tissue fibers.

Draw an enlarged section of the entire cord, showing the
points observed.

IV. Physiology.

Make the following study of the living worm.

1. Movements. Place the worm on a damp, rough sur-
face, as filter paper, and observe the kinds of movements
and the way they are produced. By what means does the
worm move from place to place? Can it climb over ob-
structions? Place the worm on a moist, perfectly clean
glass. Explain the behavior observed.

2. Sensitiveness. With a bristle or a blunt instrument,
touch the worm in different places. What regions are the
most sensitive? How is this indicated? Try the effect
of stimuli such as warmth of the breath, sunlight, vapor of
ammonia or chloroform, dilute acetic acid. Record the
results obtained.

3. Circulation. If the body wall is not too thick, nor too
heavily pigmented, the pulsations of the dorsal bloodvessel



94 GENERAL BIOLOGY

may be seen through the wall. In what direction is the
blood flowing? Further observations on circulation may
be made upon a worm, anesthetized with chloroform, which
has been opened to expose the bloodvessels. Observe the
contraction of the dorsal vessel and the hearts, also note
the delicate bloodvessels upon the various organs.



SAND WORM.

NEREIS VIRENS.

THESE animals are found on the seashore in burrows of
sand and mud near low water mark.

I. External Anatomy.

1. General Features. Is there a differentiation into dorsal
and ventral? Anterior and posterior? How are these
regions distinguished? Compare w r ith the earthworm.
How many somites? Is the number as variable as in the
earthworm? Are the somites alike in size and form? Is
the body divided into regions?

2. Head. In the head there are the following parts:
A triangular prostomium which bears on its anterior margin
a pair of short tentacles. On each side there is a fleshy
palp. The four eyes are on the dorsal surface of the pros-
tomium, and are sometimes hard to find. The peristomium
is the ring around the mouth. Compare it with the first
body somite. It bears four lateral or peristomial tentacles
on either side. Note the large jaws which may be partly
extended from the pharynx.

Make a drawing showing the head and several of the
body somites.

3. Appendages. On each side of most of the somites
there is an appendage called a parapodium. In each para-
podium there are the following parts: A dorsal blade, the
gill, which bears a short cirrus; and a ventral blade consist-



96 GENERAL BIOLOGY

ing of two fleshy lobes. There is also a ventral cirrus. From
each blade a number of setae arise in bundles. In each
blade there is embedded a short -stiff rod, the aciculum,
which serves to support the appendage. Examine the last
body somite and note any differences from the other somites.
Make an enlarged drawing of a single parapodium.

n. Internal Anatomy.

Open the worm in the same manner as the earthworm.
Note the body wall, the ccelom, the septa, and observe any
differences from the conditions present in the other worm.

The digestive system has a large muscular pharynx, in
which are the large jaws noted above, and also some small
teeth covering the walls. Can you account for the differences
in the pharynx of this worm and the earthworm? The
pharynx opens into a large crop, into which also empty
digestive glands. Was there anything corresponding to
the digestive glands in the earthworm? The rest of the
digestive tube is composed of the straight stomach-intestine.

The pharynx is protrusible and there are protractor and
retractor muscles to operate the proboscis and the jaws.

The circulatory and excretory systems are much like
those of the earthworm, though they are not so large nor
so easily worked out.

In the sand worm the sexes are separate and the repro-
ductive organs are present only at the breeding season.
A portion of the tissue lining the ccelom produces sperms
or eggs at this time. When the reproductive products are
ripe the body wall is ruptured and the germ cells escape
into the water where the fertilization takes place.. Unless
the worms were obtained during the breeding season the
reproductive organs will not be found.



SAND WORM 97

The digestive tube should be removed to expose the nerve
cord, which is present on the ventral body wall as in the
earthworm. Compare the cord with that of the earth-
worm. Are ganglia present? Describe the arrangement
and distribution of ganglia and nerves. Is there a com-
missure about the pharynx and a brain or cerebral ganglia
on the dorsal side?

On account of the numerous sense organs on the head
the brain is larger and there are more nerves coming from
it than in the earthworm. The brain lies very close to the
surface and is difficult to expose without injury.

Make drawings to represent the various internal systems.



THE FERN.

PTEBIS AQUTLINA.

THE common brake is widely distributed, growing in
nearly all damp, shady places. If the structure of the
entire plant is to be studied, they should be collected and
used fresh or else preserved in formalin. Early summer
is the best time for the collection, though the plants will be
in fairly good condition in the early fall. For the histological
study the rhizome must be sectioned in the usual way.
The sections may be stained, but some of the tissues will
show well without stain.

This organism is composed of organs which are partly
underground and partly above ground, the former com-
posed of the underground stem, or rhizome, and roots which
serve to absorb water and salts from the soil. From the
rhizome leaves, or fronds, extend into the air as the chlorophyll
bearing parts, with supporting and nutritive organs.

The leaf consists of a main stem or stalk divided into
leaflets, or pinnae and pinnules. It is in the leaf that the
food is elaborated from simple compounds and elements
.through the activity of the chlorophyll bodies, or chloro-
plasts, which are but modified masses of protoplasm. Here
are also found organs of reproduction.

The main object in the study here outlined is an insight
into the fundamental structure of a plant, its parts, their
relations and functions. A further aim is, by rough com-
parison, to discover any similarities of structure and organi-



THE FERN 99

zation, between plants and animals, as well as to demon-
strate the contrasts of structure and their relations to the
markedly different functions to be performed.

I. Leaf or Frond.

1. The stalk or stipe bears the expanded, foliaceous part
with its numerous lobes, pinnae, which are further subdivided
into ultimate leaflets, pinnules. Note whether there are,
on any part of the frond, hair-like elements, trichomes.

2. Midrib and veins are special structures forming a sort
of framework of the leaf. Are midrib and veins derived
from the stalk and connected with it? Do they sustain
any relation to the lobings of the leaf? Not only do these
form a structural framework, they are also paths for the
movements of liquids.

3. Histology of the Leaf. From portions of the leaf re-
move bits of the epidermis and examine with both low and
high power and study the structure. Are cells present?
Observe the shape, structure, contents. Compare the
epidermis from both sides of a leaflet and note likenesses and
differences. Look for minute pores, stomata, and note upon
which side of the leaflet they occur. They are the so-
called breathing pores, and relate to the functions of trans-
piration and respiration. Sketch cells of the epidermis.

II. Rhizome.

Study sections of the rhizome and note the varied aspects
of different regions, which indicate the several tissues, or
tissue systems, of the rhizome. On the outside is the cortex,
made of an outer layer of epidermis, lifeless and protective,
and beneath this a subepidermis whose cell walls are hard
and woody, but which contain living protoplasm.



100 GENERAL BIOLOGY

Make a careful drawing of some of the cells of this region.

Within the cortex, and making up the greater part of
the rhizome, is the living tissue, called parenchyma or pith.
What is the shape of the cells? How are they joined to-
gether? Is there protoplasm within these cells? Are there
any bodies within the protoplasm which might be dead
substances as food? If fresh sections are available treat
with iodine solution and determine whether starch is present.

Make drawings of the parenchyma cells.


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Online LibraryCharles Wesley HargittOutlines of general biology ; an introductory laboratory manual → online text (page 5 of 10)