BEGINNERS’ ZOOLOGY
BY
WALTER M. COLEMAN
[Illustration: [Logo]]
_AUTHORIZED BY THE MINISTER OF EDUCATION FOR ONTARIO_
TORONTO
THE MACMILLAN CO. OF CANADA, LIMITED
1921
Copyright, Canada, 1921
BY THE MACMILLAN COMPANY
OF CANADA, LIMITED
CONTENTS
CHAPTER PAGE
I. INTRODUCTION 1
II. PROTOZOANS 10
III. SPONGES 17
IV. POLYPS 22
V. ECHINODERMS 34
VI. WORMS 42
VII. CRUSTACEANS 51
VIII. INSECTS 63
IX. MOLLUSCS 97
X. FISHES 109
XI. BATRACHIANS 126
XII. REPTILES 139
XIII. BIRDS 150
XIV. MAMMALS 184
BEGINNERS’ ZOOLOGY
CHAPTER I
THE PRINCIPLES OF BIOLOGY
Biology (Greek, _bios_, life; _logos_, discourse) means the science of
life. It treats of animals and plants. That branch of biology which
treats of animals is called _zoology_ (Gr. _zoon_, animal; _logos_,
discourse). The biological science of _botany_ (Gr. _botane_, plant or
herb) treats of plants.
Living things are distinguished from the not living by a series of
processes, or changes (feeding, growth, development, multiplication,
etc.), which together constitute what is called life. These processes
are called _functions_. Both plants and animals have certain parts
called _organs_ which have each a definite work, or function; hence
animals and plants are said to be organized. For example, men and most
other animals have a certain organ (the mouth) for taking in
nourishment; another (the food tube), for its digestion.
Because of its _organization_, each animal or plant is said to be an
_organism_. Living things constitute the _organic kingdom_. Things
without life and not formed by life constitute the _inorganic_, or
_mineral_, _kingdom_. Mark I for inorganic and O for organic after the
proper words in this list: granite, sugar, lumber, gold, shellac, sand,
coal, paper, glass, starch, copper, gelatine, cloth, air, potatoes,
alcohol, oil, clay. Which of these things are used for food by animals?
Conclusion?
=Energy in the Organic World.=—We see animals exerting energy; that is,
we see them moving about and doing work. Plants are never seen acting
that way; yet they need energy in order to form their tissues, grow, and
raise themselves in the air.
=Source of Plant Energy.=—We notice that green plants thrive only in the
light, while animal growth is largely independent of light. In fact, in
the salt mines of Poland there are churches and villages below the
ground, and children are born, become adults, and live all their lives
below ground, without seeing the sun. (That these people are not very
strong is doubtless due more to want of fresh air and other causes than
to want of sunlight.)
[Illustration:
FIG. 1.—SURFACES OF A LEAF, magnified.
]
[Illustration:
FIG. 2.—A LEAF STORING ENERGY IN SUNLIGHT.
]
_The need of plants for sunlight shows that they must obtain something
from the sun._ This has been found to be _energy_. This enables them to
_lift_ their _stems_ in growth, and _form_ the various structures called
_tissues_ which make up their stems and leaves. It is noticed that they
take in food and water from the soil through their roots. Experiments
also show that green plants take in through pores (Fig. 1), on the
surface of their leaves, a gas composed of carbon and oxygen, and called
_carbon dioxide_. The _energy in the sunlight_ enables the plant _to
separate out the carbon, of the carbon dioxide_ and to build mineral and
water and carbon into organic substances. The oxygen of the carbon
dioxide is set free and returns to the air (Fig. 2). Starch, sugar, oil,
and woody fibre are examples of substances thus formed. Can you think of
any fuel not due to plants?
=How Animals obtain Energy.=—You have noticed that starch, oil, etc.,
will _burn_, or _oxidize_, that is, _unite with the oxygen of the air_;
thus the sun’s energy, stored in these substances, is changed back to
heat and motion. The oxidation of oil or sugar may occur in a furnace;
it may also occur in the living substance of the active animal.
[Illustration:
FIG. 3.—COLOURLESS plants, as A GREEN LEAF, even after it is cut,
MUSHROOMS, give off no oxygen. gives off oxygen (O) if kept in the
sun.
]
Fortunately for the animals, the plants oxidize very little of the
substances built up by them, since they do not move about nor need to
keep themselves warm. We notice that animals are constantly using plant
substances for food, and constantly drawing the air into their bodies.
If the sunlight had not enabled the green plant to store up these
substances and to set free the oxygen (Fig. 3), animals would have no
food to eat nor air to breathe; hence we may say that the sunlight is
indirectly the source of the life and energy of animals. Mushrooms and
other plants without green matter cannot set oxygen free (Fig. 3).
=Experiment to show the Cause of Burning, or Oxidation.=—Obtain a large
glass bottle (a pickle jar), a short candle, and some matches. Light the
candle and put it on a table near the edge, and cover it with the glass
jar. The flame slowly smothers and goes out. Why is this? Is the air now
in the jar different from that which was in it before the candle was
lighted? Some change must have taken place or the candle would continue
to burn. To try whether the candle will burn again under the jar without
changing the air, slide the jar to the edge of the table and let the
candle drop out. Light the candle and slip it up into the jar again, the
jar being held with its mouth a little over the edge of the table to
receive the candle (Fig. 5). The flame goes out at once. Evidently the
air in the jar is not the same as the air outside. Take up the jar and
wave it to and fro a few times, so as to remove the old air and admit
fresh air. The candle now burns in it with as bright a flame as at
first. So we conclude that the candle will not continue to burn unless
there is a constant supply of fresh air. The gas formed by the burning
is carbon dioxide. It is the gas from which plants extract carbon.
(Beginners’ Botany, Chap. XIII.) One test for the presence of this gas
is that it forms a white, chalky cloud in lime water; another is that it
smothers a fire.
=Experiment to show that Animals give off Carbon Dioxide.=—Place a
cardboard over the mouth of a bottle containing pure air. Take a long
straw, the hollow stem of a weed, a glass tube, or a sheet of stiff
paper rolled into a tube, and pass the tube into the bottle through a
hole in the cardboard. Without drawing in a deep breath, send one long
breath into the bottle through the tube, emptying the lungs by the
breath as nearly as possible (Fig. 4). Next, invert the bottle on the
table as in the former experiment, afterward withdrawing the cardboard.
Move the bottle to the edge of the table and pass the lighted candle up
into it (Fig. 5). Does the flame go out as quickly as in the former
experiment?
If you breathe through a tube into clear lime water, the water turns
milky. The effect of the breath on the candle and on the lime water
shows that carbon dioxide is continually leaving our bodies in the
breath.
[Illustration:
FIG. 4.—Breathing into a bottle.
]
[Illustration:
FIG. 5.—Testing the air in the bottle.
]
=Oxidation and Deoxidation.=—The union of oxygen with carbon and other
substances, which occurs in fires and in the bodies of animals, is
called _oxidation_. The separation of the oxygen from carbon such as
occurs in the leaves of plants is called _deoxidation_. _The first
process sets energy free, the other process stores it up._ Animals give
off carbon dioxide from their lungs or gills, and plants give off oxygen
from their leaves. But plants need some energy in growing, so oxidation
also occurs in plants, but to a far less extent than in animals. At
night, because of the absence of sunlight, no deoxidation is taking
place in the plant, but oxidation and growth continue; _so at night the
plant actually breathes out some carbon dioxide_. The deepest part of
the lungs contains the most carbon dioxide. Why was it necessary to
empty the lungs as nearly as possible in the experiment with the candle?
Why would first drawing a deep breath interfere with the experiment? Why
does closing the draught of a stove, thus shutting off part of the air,
lessen the burning? Why does a “firefly” shine brighter at each breath?
Why is the pulse and breathing faster in a fever? Very slow in a trance?
=The key for understanding any animal= is to find _how it gets food and
oxygen_, and how it uses the energy thus obtained to grow, move, avoid
its enemies, and get more food. Because it moves, it needs senses to
guide it.
=The key for understanding a plant= is to find _how it gets food and
sunlight_ for its growth. It makes little provision against enemies; its
food is in reach, so it needs no senses to guide it. The plant is built
on the plan of having the nutritive activities _near the surface_
(_e.g._ absorption by roots; gas exchange in leaves). The animal is
built on the plan of having its nutritive activities _on the inside_
(_e.g._ digestion; breathing).
=Cell and Protoplasm.=—Both plants and animals are composed of small
parts called _cells_. Cells are usually microscopic in size. They have
various shapes, as spherical, flat, cylindrical, fibre-like,
star-shaped. The living substance of cells is called _protoplasm_. It is
a stiff, gluey fluid, _albuminous_ in its nature. Every cell has a
denser spot or kernel called a _nucleus_, and in the nucleus is a still
smaller speck called a _nucleolus_. Most cells are denser and tougher on
the outside, and are said to have a _cell wall_, but many cells are
naked, or without a wall. Hence the indispensable part of a cell is not
the wall but the nucleus, and a _cell may be defined as a bit of
protoplasm containing a nucleus_. This definition includes naked cells
as well as cells with walls.
=One-celled Animals.=—There are countless millions of animals and plants
the existence of which was not suspected until the invention of the
microscope several centuries ago. They are one-celled, and hence
microscopic in size. It is believed that the large animals and plants
are descended from one-celled animals and plants. In fact, each
individual plant or animal begins life as a single cell, called an egg
cell, and forms its organs by the subdivision of the egg cell into many
cells. An egg cell is shown in Fig. 6, and the first stages in the
development of an egg cell are shown in Fig. 7.
[Illustration:
FIG. 6.—Egg cell of mammal with yolk.
]
[Illustration:
FIG. 7.—Egg cell subdivides into many cells forming a sphere (morula)
containing a liquid. A dimple forms and deepens to form the next
stage (gastrula).
]
The animals to be studied in the first chapter are _one-celled animals_.
To understand them we must learn how they eat, breathe, feel, and move.
They are called _Protozoans_ (Greek _protos_, first, and _zoon_). All
other animals are composed of many cells and are called _Metazoans_
(Greek _meta_, beyond or after). The cells composing the mucous membrane
in man are shown in Fig. 8. The cellular structure of the leaf of a
many-celled plant is illustrated in Fig. 1.
=Method of Classifying Animals.=—The various animals display differences
more or less marked. The question arises, are not some of them more
closely related than others? We conclude that they are, since the
difference between some animals is very slight, while the difference
between others is quite marked.
[Illustration:
FIG. 8.—MUCOUS MEMBRANE formed of one layer of cells. A few cells
secrete mucus.
]
To show _the different steps in classifying_ an animal, we will take an
example,—the cow. Even little children learn to recognize a cow,
although individual cows differ somewhat in form, size, colour, etc. The
varieties of cows, such as short-horn, Jersey, etc., all form one
_species_ of animals, having the scientific name _taurus_. Let us
include in a larger group the animals closest akin to a cow. We see a
cat, a bison, and a dog; rejecting the cat and the dog, we see that the
bison has horns, hoofs, and other similarities. We include it with the
cow in a _genus_ called _Bos_, calling the cow Bos taurus, and the
bison, Bos bison. The sacred cow of India (Bos indicus) is so like the
cow and the buffalo as also to belong to the genus Bos. Why is not the
camel, which, like Bos bison, has a hump, placed in the genus Bos?
The Old World buffaloes,—most abundant in Africa and India,—the
antelopes, sheep, goats, and several other genera are placed with the
genus Bos in a _family_ called the _hollow-horned animals_.
This family, because of its even number of toes and the habit of chewing
the cud, resembles the camel family, the deer family, and several other
families. These are all placed together in the next higher systematic
unit called an _order_, in this case, the order of _ruminants_.
The ruminants, because they are covered with hair and nourish the young
with milk, are in every essential respect related to the one-toed
horses, the beasts of prey, the apes, etc. Hence they are all placed in
a more inclusive division of animals, the _class_ called _mammals_.
All mammals have the skeleton, or support of the body, on the inside,
the axis of which is called the vertebral column. This feature also
belongs to the classes of reptiles, amphibians, and fishes. It is
therefore consistent to unite these classes by a general idea or
conception into a great _branch_ of animals called the _vertebrates_.
Returning from the general to the particular by successive steps, state
the branch, class, order, family, genus, and species to which the cow
belongs.
=The Eight Branches or Sub-kingdoms.=—The simplest classification
divides the whole animal kingdom into eight branches, named and
characterized as follows, beginning with the lowest: I. PROTOZOANS.
One-celled. II. SPONGES. Many openings. III. POLYPS. Circular; cuplike;
having only one opening which is both mouth and vent. IV. ECHINODERMS.
Circular; rough-skinned; two openings. V. MOLLUSCS. No skeleton; usually
with external shell. VI. VERMES. Elongate body, no jointed legs. VII.
ARTHROPODS. External jointed skeleton; jointed legs. VIII. VERTEBRATES.
Internal jointed skeleton with axis or backbone.[1]
Footnote 1:
This is the briefest classification. Animals have also been divided
into twelve branches. The naming of animals is somewhat chaotic at
present, but an attempt to come to an agreement is now being made by
zoologists of all nations.